Veterinary Ophthalmic Surgery

VETERINARY OPHTHALMIC SURGERY

Commissioning Editor: Robert Edwards Development Editor: Veronika Watkins Project Manager: Joannah Duncan Designer: Stewart Larking Illustration Manager: Merlyn Harvey Illustrator: Chartwell

V ETERINARY

OPHTHALMIC SURGERY KIRK N. GELATT

VMD Diplomate, American College of Veterinary Ophthalmologists; Emeritus Distinguished Professor of Comparative Ophthalmology, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, USA and

JANICE PETERSON GELATT

Gainesville, FL USA

MFA

#

2011 Elsevier Ltd. All rights reserved.

No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Details on how to seek permission, further information about the Publisher’s permissions policies and our arrangements with organizations such as the Copyright Clearance Center and the Copyright Licensing Agency, can be found at our website: www.elsevier.com/permissions. This book and the individual contributions contained in it are protected under copyright by the Publisher (other than as may be noted herein). ISBN 978-0-7020-3429-9 British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data A catalog record for this book is available from the Library of Congress Notices Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes in research methods, professional practices, or medical treatment may become necessary. Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods, compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and the safety of others, including parties for whom they have a professional responsibility. With respect to any drug or pharmaceutical products identified, readers are advised to check the most current information provided (i) on procedures featured or (ii) by the manufacturer of each product to be administered, to verify the recommended dose or formula, the method and duration of administration, and contraindications. It is the responsibility of practitioners, relying on their own experience and knowledge of their patients, to make diagnoses, to determine dosages and the best treatment for each individual patient, and to take all appropriate safety precautions. To the fullest extent of the law, neither the Publisher nor the authors, contributors, or editors, assume any liability for any injury and/or damage to persons or property as a matter of products liability, negligence or otherwise, or from any use or operation of any methods, products, instructions, or ideas contained in the material herein.

Printed in China

Contributors

Dennis E. Brooks, DVM PhD Dipl ACVO

Bernhard M. Spiess, DVM Dr Med Vet Dipl ACVO and ECVO

University of Florida College of Veterinary Medicine Department of Small Animal and Large Clinical Sciences Gainesville FL, USA

University of Zurich Veterinary Ophthalmology Zurich Switzerland

Douglas W. Esson, DVM Dipl ACVO

Iowa State University College of Veterinary Medicine Department of Clinical Sciences Ames IA, USA

Eye Care for Animals Tustin CA, USA

Brian C. Gilger, DVM MS Dipl ACVO Department DOCS College of Veterinary Medicine North Carolina State University Raleigh NC, USA

Caryn E. Plummer, DVM Dipl ACVO University of Florida College of Veterinary Medicine Department of Small Animal Clinical Sciences Gainesville FL, USA

R. David Whitley, DVM MS Dipl ACVO

David A. Wilkie, DVM MS Dipl ACVO Ohio State University College of Veterinary Medicine Department of Veterinary Clinical Sciences OSU Veterinary Hospital Columbus OH, USA

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Acknowledgments

We would like to thank the new contributors to this book, including Drs Dennis E. Brooks, Douglas W. Esson, Brian C. Gilger, Caryn E. Plummer, Bernhard M. Spiess, R. David Whitley and David A. Wilkie. We would like to also thank Mr Robert Edwards, Commissioning Editor, and Ms Veronika Watkins, Development Editor, Elsevier Limited, for the opportunity to publish this new edition on

ophthalmic surgery for all animal species. We also would like to acknowledge the comparative ophthalmology faculty members and residents, and Edward O. MacKay, PhD, and Tommy Rinkosky, MS, at the College of Veterinary Medicine, University of Florida, Gainesville, Florida, USA for their assistance and support.

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Preface

When the two volumes (Volume 1: Extraocular procedures, and Volume 2: Corneal and intraocular procedures) of the Handbook of Small Animal Ophthalmic Surgery were published in 1994 and 1995, respectively, they were part of a handbook series published by Pergamon Press, Oxford, UK. Because of their popularity, they were out of print within 4 years. We were then presented with the opportunity to update and consolidate these two handbooks into a single text, Fundamentals of Small Animal Ophthalmic Surgery, which was published in 2001 by Butterworth-Heinemann. Next, we were presented with a third challenge – to develop a comprehensive, all-species ophthalmic surgery text, based on the previous texts, which could be used by veterinary ophthalmologists as well as interested veterinary surgeons and practitioners worldwide. Prior to the two first handbooks, the texts devoted to ophthalmic surgery in animals were limited. The most recent books were the Stereoscopic Atlas of Ophthalmic Surgery of Domestic Animals by Harlan Jensen (CV Mosby, St Louis, MO, USA, 1973), the Atlas of Veterinary Ophthalmic Surgery by Stephen Bistner, Gustavo Aguirre, and George Batik (WB Saunders, Philadelphia, PA, USA, 1977), and Surgical Management of Ocular Disease edited by Mark Nasisse (Veterinary Clinics of North America, WB Saunders, Philadelphia, PA, USA, 1997). Most current information on ophthalmic surgery has been published in comprehensive veterinary ophthalmology texts, and in the crush for space, descriptions are limited to brief summaries of the actual surgical techniques. Since 1994, our Handbook of Small Animal Ophthalmic Surgery (Volumes 1 and 2) and subsequent single text, Small Animal Ophthalmic Surgery, are the only textbooks devoted to eye surgery in animals. Only these ophthalmic surgery textbooks focus on all the dimensions of small animal ophthalmic surgery, stressing the pre-, intra-, and postoperative details. This text, Veterinary Ophthalmic Surgery, consists of all of the different types of extraocular and intraocular surgical procedures that are utilized by veterinarians and veterinary ophthalmologists. The base or model species for all of the surgical procedures is the most popular small animal species presented to veterinarians worldwide – the dog and cat. In addition, in each chapter, special sections are devoted to large animals and special species to describe any modifications of these procedures as well as possible new techniques that have evolved to these species. A considerable amount of this new information is on the equine species. The text is divided into 12 chapters: (1) surgical instrumentation; (2) the operating room; (3) anesthesia for ophthalmic surgery; (4) surgery of the orbit; (5) surgery of

the eyelids; (6) surgery of the nasolacrimal apparatus and tear systems; (7) surgical procedures for the conjunctiva and the nictitating membrane; (8) surgery of the cornea and sclera; (9) surgical procedures of the anterior chamber and anterior uvea; (10) surgical procedures for the glaucomas; (11) surgical procedures of the lens and cataract; and (12) vitreoretinal surgery. Each of the surgery chapters is divided into the relevant surgical anatomy, indications for surgery or other medical therapies, the available surgical procedures, the postoperative management, success rates, and postoperative complications followed by any modifications for large animals and special species. Further reading or selected references are included for each chapter for readers interested in consulting the original publications in all animal species. Each chapter contains information that can benefit the veterinary student and veterinary practitioner interested in ophthalmic surgery and who are attempting to expand and/or improve their surgical skills. This text also contains surgical information for the veterinary ophthalmologist in training or the practicing veterinary ophthalmologist wishing to consult a surgical text for the most recent information. A unique aspect of this text is the availability of a special website (www.Gelattonline.com) of actual eye surgeries performed in clinical patients. These videos will be arranged by eye tissue and will follow the same format described and illustrated in the text. The videos will be periodically augmented, so new videos may be added at any time. Any veterinarian is invited to submit ophthalmic surgery videos (on a CD) directly to me (my address is below). If the video is accepted by the author(s) of the associated chapter and the Publisher, it will be added to the website. This presents a unique opportunity for all readers of this text to become actively involved and part of our effort to expand and improve veterinary ophthalmic surgery for all animal species. A gratis copy of the book will be offered for each successful video.

Kirk N. Gelatt, VMD Diplomate, American College of Veterinary Ophthalmologists, Emeritus Distinguished Professor of Comparative Ophthalmology, P.O. Box 100126 Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Florida, Gainesville, FL 32610-0126, USA and Janice Peterson Gelatt, MFA Gainesville, FL, USA

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CHAPTER

1

Surgical instrumentation Kirk N. Gelatt

Chapter contents Introduction

1

Surgical instruments for ophthalmic surgeries

11

Design of ophthalmic instruments

1

Instrument care, storage, and sterilization

13

Ophthalmic surgical instruments

2

Ophthalmic sutures and needles

14

Adaptations for large animals and special species ophthalmic surgeries

11

Introduction Since the 1960s magnification has had a major influence on advances in ophthalmic surgery and instrumentation. With magnification of the ophthalmic surgical field, incisions previously deemed quite satisfactory were viewed as irregular, and wound apposition as imperfect. The standard ophthalmic surgical instruments, as observed under 10–20 magnification, were too large and impaired the surgeon’s view of the surgical field. Forceps were viewed to compress and occasionally tear tissues. The standard ophthalmic needle holders grasped the smaller needles poorly, often flattening the curved needles. The working distance between the surgical field and the bottom of the operating microscope limited both the number and the size of ophthalmic instruments. As a result, a second type of ophthalmic instrument evolved – smaller instruments for microsurgery. While surgical instrumentation for extraocular procedures partially utilizes general surgical instruments, surgical instruments for conjunctival, corneal, and intraocular surgical procedures require an investment in both standard size and microsurgical ophthalmic instruments. Both the standard and microsurgical ophthalmic instruments are small and delicate in comparison to the general surgical instruments. Long-term use and optimal surgical results with these ophthalmic instruments necessitate prudent care and use. The investment in the standard, microsurgical or a combination of ophthalmic instrumentation varies with their predicted amount of use. The most important instruments are the corneoscleral and conjunctival scissors, and needle holders; these instruments should be the best available. If microsurgical instruments are selected, tying forceps rather

than needle holders are used for the small ophthalmic sutures, and these thumb forceps should be of high quality.

Design of ophthalmic instruments A large assortment of standard and microsurgical instruments is available to the veterinarian contemplating corneal and intraocular surgery. The basic design of these instruments includes several common construction features that facilitate their intended use. The standard ophthalmic instruments are usually about 120–140 mm long; the microsurgical instruments are about 100 mm long (20–30% smaller). These limitations are related to two factors. First, the instruments must be sufficiently large to be comfortably grasped and manipulated. Secondly, the working distance of most operating microscopes varies with the magnification but is usually between 150 and 250 mm. If the instruments are too large, inadvertent contact and the resultant contamination with the bottom of the operating microscope may occur. The diameters of the handles of most of the ophthalmic spatulas and knives are about 6–7 mm. The width of the handles of the larger needle holders, scissors, and thumb forceps is about 10–12 mm. The shape of these instruments also directly influences their use. Instruments with 5–6 mm diameter handles often have rounded or four or six sides to permit convenient rotation or turning of the handle while grasping the instrument. Instruments that are flat or expand in only one direction, like corneoscleral scissors or the different thumb forceps, have handles that are flat or serrated for grasping with the fingers and limited to no rotation. To facilitate grasping and manipulation of these small

1

Surgical instrumentation

instruments without slipping, the handles are usually serrated, knurled or six-sided to accommodate and limit placement of the fingers on these gripping areas. If these irregular surfaces are too small, the grasp of the instrument may be less than secure. If these serrated areas are too large, the large finger placement area may actually limit manipulation and even snag sutures during tying. All ophthalmic instruments are constructed from high-quality stainless steel or now more often from titanium, with dull surfaces to minimize light reflections. Thumb forceps and scissors for corneal and intraocular procedures are usually hinged with different mechanisms to facilitate their opening. The three most common hinges include the X-hinge, the vertical pin hinge, and the bar hinge (Fig. 1.1). The common X-hinge for scissor blades or needle holder tips is usually joined by small screws or pins, and often the handles converge to become spring mechanisms that maintain the instrument in an open position. With vertical pin hinges, as in iris scissors, the hinge pin is deformed as the scissor blade is closed to act as a spring device to open the blades upon release. The bar hinge is typical of most thumb forceps, and consists of the junction of the base of both handles; tension of these handles closes the forceps blades and release results in the forceps tips opening. All of these hinges are very delicate and, if extended too far, can easily bend or break. Most of the standard and microsurgical ophthalmic instruments are designed for a single purpose. Hence, the standard corneal or intraocular surgical instrument pack includes several instruments. Occasionally, these instruments are designed to perform two or more functions. One example is the tying thumb forceps. Its tip usually includes teeth (1  2) which permit grasping of the cornea and/or conjunctiva. Just proximal to its tip is a flat tying platform to grasp sutures during tying and construction of knots. These multiple purpose forceps are usually heavily used during corneal and intraocular surgical procedures and can easily become malaligned. During microsurgery, the tips of the ophthalmic instruments are often the only parts of these instruments that are visible. In addition, many microsurgical instruments possess angled tips to facilitate their use at higher magnifications, and minimize obstruction of the surgical field.

A

B

Ophthalmic surgical instruments are often developed for specific tasks and functions. As a result, a considerable choice of standard and microsurgical ophthalmic instruments is available. A certain number of these instruments are essential and recommended for different small and large animal ophthalmic surgeries. For convenience, instruments for the different ophthalmic surgical procedures are listed later in the chapter. They include:

• • • • •

Table 1.2 – instruments for orbital surgeries Table 1.3 – instruments for eyelid surgeries Table 1.4 – instruments for conjunctival and corneal surgeries Table 1.5 – instruments for intraocular and cataract surgeries Box 1.1 – instruments for vitreoretinal surgeries.

These instruments are presented in further detail.

Eyelid specula Eyelid specula are used to retract the eyelids and enhance exposure of the conjunctiva, cornea, and globe. The ideal eyelid speculum should be strong enough to retract the eyelids to the maximal amount possible, but sufficiently lightweight to prevent direct pressure on the cornea and globe. The most versatile eyelid speculum for small animals is the wire type. For most breeds of dogs and cats, the Barraquer wire speculum is preferred with 14 mm blades and an overall length of 40 mm (Fig. 1.2). The pediatric size Barraquer speculum may be useful in young and smaller animals; its blades are 11 mm and overall length is 34 mm. In large dogs and large animals a heavier eyelid speculum may be necessary. Eyelid specula, such as the Guyton–Park (14 mm blades and overall length of 85 mm), Castroviejo (15 or 16 mm blades and overall length of 75–82 mm), and Williams (10 mm blades and overall length of 90 mm) can provide maximum exposure of the palpebral fissure (Fig. 1.3). Sometimes for the lid speculum to conform to the eyelid and palpebral curvatures of the horse and cow, the arms of the specula are bent slightly. With all eyelid specula, the blades should extend beneath the eyelid margins for several millimeters to adequately retract the eyelids and reduce the possibility of dislodgement. In some species, like the avian species, the palpebral fissures and eyelids are very small, and a single 4-0 to 6-0 silk suture is placed in each eyelid to keep the lids open.

C

Fig. 1.1 The different hinge mechanisms used for ophthalmic instruments: (A) X-type; (B) vertical pin; (C) bar hinge.

2

Ophthalmic surgical instruments

Fig. 1.2 The pediatric and adult size wire eyelid specula by Barraquer. These inexpensive lid specula are the most versatile and durable for small animals.

Ophthalmic surgical instruments

(Table 1.1). In selecting these tissue forceps, one should handle them individually and use those forceps that ‘feel’ the most comfortable.

Eyelid/chalazion forceps

Fig. 1.3 The Williams eyelid speculum is reserved for large breeds of dogs and large animals to retract the eyelids.

Tissue forceps The different types of ocular tissue have resulted in the development of a large selection of tissue forceps with specialized tips. These tissue forceps vary by tips, shaft, handles, springs, and bar hinge (Fig. 1.4). The handles of these forceps are usually flat with serrations or knurling on the handles to facilitate their grasp. Microsurgical forceps usually have angled tips, and are about two-thirds the total length of standard ophthalmic instruments. The arms of these forceps are hinged at the base, and this hinge provides sufficient tension to maintain the tips about 5–10 mm apart. Upon digital compression, the tissue forceps tips should completely and perfectly contact each other. The tips of many forceps are angulated to prevent blockage of the surgeon’s view during surgery. The major difference of the ophthalmic tissue forceps is their tips, which have highly specialized indications

Bar hinge

Springs

Handles

Highly specialized forceps have been developed for entropion and chalazion surgery. The chalazion forceps have an open and a solid plate on the fellow tips (Fig. 1.5). These tips may be either circular or oval; the latter tips are more versatile as they can be inserted in the palpebral fissure with the oval in either the vertical or horizontal axis. With the forceps clamped to the eyelid, a small lid tumor or chalazion can be excised while pressure from the special plates maintains hemostasis and exact positioning of the eyelid margins and mass.

Conjunctival forceps Forceps to manipulate the bulbar and palpebral conjunctiva generally possess teeth. Small splay-tooth or dog-tooth tips with 1  2 teeth are most useful to grasp the conjunctiva during most manipulations. Excessive tension of the conjunctival tissues with the small tips will often create small tears or ‘button-holes’ of the conjunctival mucosa. These small breaks in the conjunctival mucosal surface are not usually important, but may be significant in certain grafting procedures. The tips of the von Graefe tissue forceps possess 10–14 fine teeth and generally accommodate considerable tension of the conjunctival mucosa or the leading edge of the nictitans before tearing is evident (Fig. 1.6). Unfortunately, the von Graefe tips are too large for microsurgical procedures. The conjunctival tissues can also be manipulated with serrated tips, devoid of any teeth; however, slippage of the tips from the mucosa is likely.

Corneal, limbal, and scleral forceps The cornea, sclera, and limbus represent the fibrous tunics of the globe and are remarkably tough tissues to incise, manipulate, and suture. As a result, the tips of the corneal or corneoscleral forceps generally possess some type of teeth. Generally the tips consist of either splay-tooth or dog-tooth designs. These types of tips successfully grasp and hold these tissues. Modifications of these tips, such as the closed-cups (von Mandach forceps) and open-cups (Pierse type), are less traumatic to the cornea, but permit limited lateral slippage.

Suture and tying forceps Shafts

X-hinge Tips

Fig. 1.4 Components of ophthalmic forceps include: tips, shaft, handles, springs and bar/X-hinge.

Special forceps have been developed to facilitate suture manipulation and tying during microsurgery. The tying of small diameter sutures requires suture tying forceps but not the standard or microsurgery needle holder which allows these very small diameter sutures to easily slip within the needle holder jaws. The surgeon’s fingers cannot be used as the sutures are too small and often too short. The standard suture-tying forceps is either the straight or curved model with 1  2 teeth or without teeth. The smooth platforms of both tips have rounded edges to accommodate the sutures and prevent any suture breakage or etching (Fig. 1.7). The platforms

3

1

Surgical instrumentation

Table 1.1 Tips of tissue forceps used for corneal and intraocular surgery

Tip design

Designated tissue(s) or use

Von Graefe

Conjunctiva/nictitans

Appearance

Tip design

Designated tissue(s) or use

Lens capsule Extracapsular

Grasp/tear anterior lens capsule

Splay

Intracapsular

Grasp/hold anterior lens capsule

Dog-toothed

Utrata

Anterior capsulorhexis

1  2 teeth

Appearance

Cornea/conjunctiva

Colibri style tip angulation

Cornea/conjunctiva

Intraocular

Grasp/remove lens capsule and fragments

Serrations

Cornea/conjunctiva

Combination 1  2 teeth tying platform

Cornea/conjunctiva and tying sutures

Tying platforms

Tying small sutures

must meet perfectly flush to permit suture manipulation and grasp during tying. These forceps are designed for the very small size ophthalmic sutures (6-0 to 12-0). The addition of 1  2 teeth to the tip of the Harm-type suture-tying forceps permits these forceps to both grasp corneal or conjunctival

Fig. 1.5 The Francis chalazion (top) and Desmarres entropion (bottom) forceps have specialized tips consisting of an oval to round ring and a solid oval to circular tip. The ring base is used to surround the surgical site, and the solid base is used to protect deeper tissues including the eye.

4

Fig. 1.6 Graefe fixation (top) and cilia (bottom) forceps. The Graefe forceps have wide jaws with multiple fine teeth that can grasp the eyelid and conjunctiva without tearing. The cilia forceps have smooth surface jaws that permit grasping of fine cilia.

Ophthalmic surgical instruments

Fig. 1.7 Tying forceps have shafts with smooth platforms to provide flat surfaces to grasp fine suture material during tying. Some tying forceps have combination shafts with distal 1  2 teeth to grasp tissues, and a more proximal smooth tying platform to grasp sutures. Top: O’Gawa–Castroviejo tying forceps; bottom: Castroviejo suturing forceps.

tissues as well as assist in the tying of sutures, and decreases the time and effort during wound apposition. A unique design, the Colibri style, has been used with many tissue forceps to incorporate a tying platform. Often these Colibri-type forceps, with a characteristic angled shaft, have tips with teeth to assist in the grasping of corneal and conjunctival tissues (Fig. 1.8). The tips with different types of teeth are used to grasp tissues; the knee or angle portion can be used as smooth forceps.

surgery in the dog and cat. Intracapsular lens forceps are used to grasp and hold the anterior lens capsule during removal of the entire lens with its capsules (see Table 1.1). The forceps have slender shafts and tips to enter the anterior chamber and pupil. The shafts are also curved or angled to traverse the pupil and facilitate grasping of the anterior lens capsule. Within the tip is a 2.0–2.5 mm cup to grasp, but not tear, the central anterior lens capsule. The extracapsular forceps are very similar in design, but their tips possess either four or five, or five or six, fine teeth to grasp and tear a central portion of the anterior lens capsule (see Table 1.1). Through the defect in the anterior lens capsule, the remainder of the lens cortex and nucleus are expressed or removed by phacoemulsification. Phacoemulsification has largely replaced the standard extracapsular cataract techniques in most animal species in most countries, and circular tearing of the anterior capsule sufficiently large to accommodate the insertion of an intraocular lens (IOL) has become standard. The most frequently used forceps for continuous anterior capsulectomy or capsulorhexis is the Utrata instrument. The Utrata forceps has variable length tips and very small single teeth pointing down from the two tips to grasp the anterior lens capsule. For additional information on the Utrata forceps, see Chapter 11 on surgery of the lens and cataract.

Iris forceps The animal iris and ciliary body tissues are highly friable and vascular. Excessive traction with tissue forceps on the iris results in frequent tearing and hemorrhage. Iris forceps may be straight or curved; their tips are serrated or possess very small teeth. To facilitate anterior chamber manipulations, the tips and shafts of these forceps are quite slender and delicate.

Anterior lens capsule forceps Special forceps have been developed to grasp and hold or grasp and tear the anterior lens capsule during cataract

Intraocular lens instrumentation With the advent of intraocular lenses (IOLs) in humans and animals, special IOL forceps shaped as either tissue forceps or scissors have been developed. These forceps are used to grasp the IOL or its haptic loop, and facilitate the placement of the IOL within the capsular bag or in the posterior chamber. It is important that these tips do not damage the IOL or its surface during insertion. Both hard (polymethylmethacrylate (PMMA) and acrylic) and foldable (silicone and hydrogel) IOLs have been available for the dog for several years, but only recently for the horse and cat. Several IOL instruments have been developed to position and manipulate IOLs within the anterior chamber, the posterior chamber, and the capsular bag. Most IOLs in the dog are placed in the capsular bag after all cataractous material has been removed. Placement of the IOL usually requires a special forceps; another instrument is used to rotate or dial the IOL into its final position. The IOL hook and lens manipulator possess different tips, with single or forked prongs, that can push the IOL haptics into the final position. With the introduction of the recent soft or foldable IOLs for the dog (which permit a smaller corneal incision), new forceps to fold or roll the IOL during insertion through the corneal incision and into the capsular bag, or an injector or insertor were introduced. Each foldable IOL has a specific instrument to insert that particular type of IOL.

Intraocular forceps Fig. 1.8 The distinctive Colibri forceps have a characteristic angled shaft. Top: Troutman–Barraquer corneal fixation forceps – 0.5 mm 1  2 teeth with a 6 mm tying platform; middle: Troutman–Barraquer corneal fixation forceps – 0.5 mm 1  2 teeth; bottom: Pierse type Colibri forceps (0.03 mm Pierse type tips).

Special intraocular forceps have been developed to grasp and remove tissues or foreign bodies within the anterior chamber, posterior chamber, and within the vitreous (Fig. 1.9). The intraocular forceps have 1.5–2.0 mm jaws and long shafts. The shafts are also small in diameter (20 g needle diameter; 0.89 mm) to accommodate insertion into

5

1

Surgical instrumentation

Fig. 1.9 The intraocular forceps is designed to be inserted through a very small opening. Insert shows the different available tip types.

the different compartments of the globe. The Rappazzo intraocular forceps has smooth, cusp or dusted jaws with a 45 angulation. The Storz intraocular forceps has 1.5 mm cup-shaped oval jaws. Both of these intraocular forceps are used in animals to grasp and remove portions of the anterior lens capsule and portions of the lens cortex and nucleus.

Scissors Because of the different ocular tissues, several specific types of scissors have been developed. No single scissors can perform adequately on the wide range of ocular tissues that one commonly confronts. As a result, specific-use scissors have been designed for the conjunctiva, cornea, corneosclera, iris, and intraocular tissues. Corneal and corneoscleral scissors are available as either standard size or microsurgical scissors. The overall length of the scissors’ ring handles is about 100– 110 mm, and the blades are about 18–20 mm long.

Conjunctival scissors Conjunctival scissors include tenotomy, strabismus, eye, conjunctival, and utility types, and are available with either straight or curved tips (Fig. 1.10). The tips are also varied with both sharp (pointed) and blunt, or a combination of

Fig. 1.10 Selected scissors for conjunctival tissues with either straight or curved blades with sharp or blunt tips. Top: Knapp straight strabismus scissors; middle: Steven’s straight tenotomy scissors; bottom: Steven’s curved tenotomy scissors.

6

both. The handles are ribbon style, ring type, or flat serrated spring-type handles; the latter types are more expensive. My preference is the versatile Steven’s tenotomy scissors with slightly curved, blunt-tipped blades. Conjunctival scissors with blunt tips tend to reduce the likelihood of producing ‘button-holes’ or small full-thickness defects in the bulbar conjunctiva during preparation of conjunctival flaps. These scissors may also be used to cut sutures. As most types of ophthalmic suture are very small, one pair of scissors within each surgical pack just to cut sutures is recommended. The scissors to cut sutures often have pointed and sharp tips, and can be easily distinguished from conjunctival tissue scissors.

Corneal scissors Corneal scissors are available as either standard size or microsurgical types. Because dog and cat corneas are difficult to cut, these scissors should be of high quality to ensure precise incisions and minimal tissue trauma. Periodic sharpening of these scissors may ensure long-term use. A large selection of corneal scissors is available (Fig. 1.11). These scissors can be used as a universal type or as pairs (right and left). The mirror-image pair types of corneal scissors complement each other, and are used to extend corneal incisions in opposite directions. The standard scissors range in total length from about 100 to 120 mm long.

Fig. 1.11 Castroviejo corneal section scissors (right and left) for keratectomy and keratoplasty. These scissors with curved blades are to cut the cornea or limbus; the lower blade is slightly longer to retain the scissors within the anterior chamber during cutting.

Ophthalmic surgical instruments

Microsurgical corneal scissors are about 90 mm long. The tips may be straight, slightly curved, or angled. Both tips may be of equal length, or the bottom tip that is inserted beneath the cornea can be 0.5–1.0 mm longer to maintain the scissor tip within the anterior chamber as multiple cuts are performed. Corneal scissors used for keratoplasty possess tips that are quite curved (5 mm radius) and short as the standard full-thickness corneal graft for humans is usually 6–8 mm diameter. Corneal scissors used at the limbus have longer tips. These scissors may cut either vertically or obliquely. For most corneal incisions, vertical rather than oblique incisions are preferred, unless the incision is close to the limbus. To achieve a vertical cut, the lower blade of the corneal scissors is hinged to contact the inside of the concavity of the upper blade.

Corneoscleral or corneal section cataract scissors Corneoscleral scissors are the larger corneal scissors that are used at the limbus. Corneoscleral scissors, like corneal scissors, are available as either standard or microsurgical types (Fig. 1.12). These scissors are usually self-opening with the flexible handles functioning as springs and loosely connected at their ends. Some of these types of scissors have one rigid handle and the opposite flexible handle to maintain the scissors’ blades in an open position. Still other models look like regular scissors with straight handles. Standard corneoscleral scissors are about 100–120 mm long, and have slightly angled and curved tips. The tips are about 12–20 mm long and often the bottom blade is 0.5–1.5 mm longer to maintain the tip within the anterior chamber during repeated cuts of the limbus. In most corneoscleral or cataract section scissors the lower blade cuts against the convex curve of the upper blade, producing an oblique cut. These scissors are used to cut the cornea, limbus, and sclera, to perform keratoplasty, and often in animals to enter the anterior chamber during cataract surgery. For maximum flexibility, a slightly angled curved right and left pair of corneal section scissors is recommended. As most cataract surgery in animals uses a clear corneal incision for entry into the anterior chamber, these scissors should be of high quality for maximum durability.

Fig. 1.12 Castroviejo corneal section cataract scissors (right and left) for entry into the anterior chamber at the periphery cornea or limbus.

Iris scissors The animal iris is a very friable and vascular tissue, which upon incision will often hemorrhage extensively. As a result, incision of the iris often necessitates cautery before or after cutting to seal these vessels. Iris scissors are small and delicate, and are designed to cut the iris on a flat surface. As these scissors must be very sharp, their use should be limited to cutting only iridal tissues. Iris scissors include types by Vannas, DeWecker, and Barraquer, as well as the traditional ophthalmic scissors with ring or curled handles (Fig. 1.13). Their tips are usually pointed and slightly angled. The specialized Vannas and Barraquer iris scissors are quite small (54 mm long); the DeWecker iris scissors are 114 mm long. They can be easily inserted into the anterior chamber to perform a dorsal iridectomy or sphincterotomy. Because of the increased vascularity of most animal basal irides, incision/ excision of the iris is usually performed with the involved part of the structure extended from the anterior chamber or avoiding the basal iris. Limited electrocautery may be necessary to obtain complete hemostasis after incision of the iris and before repositioning into the anterior chamber.

Intraocular scissors With refinement of intraocular surgical techniques, small scissors were developed to cut intraocular tissues often through small corneal, limbal, or scleral incisions, or the pupil. There are two basic types: 1) standard ophthalmic scissors that can be inserted through a complete corneal or corneoscleral incision with 10–15 mm long and very slender blades; and 2) intraocular scissors constructed like the intraocular forceps with a shaft diameter of about 1.0 mm (the outside diameter of a 20 g hypodermic needle). The intraocular scissors’ handles may be spring type, barrel-squeeze type, or the traditional rigid curled handles (Fig. 1.14). The tips are usually pointed, and close as regular scissors or like a guillotine type. The blades of scissors inserted through 2 or 3 mm corneal or limbal incisions range from 1 to 3 mm long. More recently a subtype of intraocular scissors has been developed to insert through limbal or corneal incisions to cut the anterior lens capsule. These microsurgical capsulotomy scissors possess either straight or slightly angled

Fig. 1.13 Special scissors for cutting the iris. Top: Barraquer iris scissors; bottom: McPherson–Vannas curved iris scissors.

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Surgical instrumentation

Fig. 1.14 Intraocular scissors: Storz intraocular scissors; the straight blades are 3.0 mm long and pointed. Insert: close-up of the cutting blades.

pointed blades of 5–11 mm long. The tips of these scissors must be very sharp and their function limited to anterior capsulotomies or capsulectomies.

Instruments used during phacoemulsification When phacoemulsification was first introduced in the 1970s by Kelman, the phaco surgery involved one larger corneoscleral incision for the phaco handpiece (which provided the ultrasonic energy and aspiration) and a separate smaller incision about 90 to the larger incision to insert the infusion needle (balanced salt solution for the anterior chamber was provided by gravity from a bottle on an intravenous stand). Today’s phaco tips possess all three of these functions: 1) aspiration to remove lens material and aqueous humor; 2) infusion to regulate the amount of irrigating solution delivered to the phaco site; and 3) phaco (ultrasonic) energy to fragment and break down the lens material through a single incision. New instruments (quick chopper, nucleus segmenter, prechopper, etc.) have now been developed to assist phacoemulsification by stabilizing as well as chopping (incise and divide) the hard lens nucleus, and these instruments are generally inserted through a second smaller corneal incision, returning to the bimanual phacoemulsification of the 1970s. They are also inserted into the lens nucleus to lift as well as support lens fragments toward the phaco tip for fragmentation. An example is the Steinert nuclear chopping instrument which possesses an angular tip with a wedge-like end (1.5 mm) sharpened on its inner edge. This creates the chop of the nucleus while maintaining contact of the chopper with the nucleus; deep penetration of the nucleus is avoided, thus preventing posterior capsule penetration. Another intralens instrument is similar to a wire hook. Warren (see Further reading) modified the Nagahara technique used in humans for the dog. This procedure uses the phaco tip to impale and, with high vacuum, hold the lens nucleus while a chopper is hooked at the lens equator and pulled centrally, splitting the nucleus along its natural cleavage planes. By dividing the nucleus into quadrants or smaller parts using the chop technique, and combined with the phacoemulsification ‘divide and conquer’ technique, phaco time and energy are significantly reduced, as is corneal endothelial cell damage. Since the dog’s lens is larger than the human, Warren recommends using the human instrument for small dogs (1–2 mm tip) and has modified the Chang combination

8

chopper for medium and large dogs (4 mm tip). For safety, the chopper’s tip is inserted into the nucleus to only one-half thickness. Some canine cataract cortices and nuclei are too hard to ‘chop’ or possess insufficient room for the instrument to pass between the anterior lens capsule and adjacent cortex, and are not amenable to this technique. Additional information on chop techniques is found in Chapter 11.

Knives The dog and cat cornea, limbus, and sclera are very tough tissues, and will dull most stainless steel knives after only a few incisions. As a result, disposable blades are usually employed to ensure a sharp and atraumatic incision. The Beaver or BD Nos 6400, 6500, and 6700 microsurgical blades (Bectin, Dickinson and Company, Franklin Lakes, NJ) are the most often used (Fig. 1.15). The Beaver No. 6400 blade with the traditional shape is used to incise the cornea, limbus, and sclera. As an alternative, the Beaver No. 6700 blade has a more pointed tip and is used for the same incisions. The Beaver No. 6500 blade is pointed and used to incise the full-thickness of the cornea, limbus, and sclera. The Beaver keratomes are preferred to incise the cornea and the anterior lens capsule during cataract surgeries in small animals. This blade is arrow-shaped, and as it is pushed through the cornea or limbus, both of its sides incise the full-thickness corneal, limbal or scleral tissues. The incisions tend to self-seal, but in animals they are often apposed by sutures. The larger Bard–ParkerTM Nos 11 (pointed) and 15 scalpel blades and handle are not designed as microsurgical instruments. They are reserved for eyelid and orbital surgeries in both small and large animals.

Fig. 1.15 BeaverTM or BD microsurgical blades (Bectin, Dickinson and Company, Franklin Lakes, NJ): Left: top, No. 6400; middle, No. 6500. Right: top, No. 6700; middle, keratome. Bottom: Beaver or BD scalpel handle.

Ophthalmic surgical instruments

Diamond knives were introduced several years ago, as a reusable scalpel blade and handle. This knife is used for corneal, limbal, and scleral incisions. A micrometer has been added to some types of diamond knives to control the length of the blade, and to perform corneal refractive surgery. The diamond blade shape ranges from an angle, to spear-like to rounded, and is 1.0–3.0 mm wide. These high-cost blades are very sharp, and must be carefully used, cleaned, and stored. Although a corneal dissector and restricted depth knife are not scalpel blades per se, these instruments are used to bluntly separate the corneal stromal layers. The corneal separators, like the Martinez and Gill corneal dissector knives, are used to dissect the different layers of the corneal stroma and reduce greatly the risk of progressive deeper separation of the cornea and corneal penetration.

Needle holders Needle holders are very important in ophthalmic surgery, as considerable time is consumed during the apposition of surgical incisions. Needle holders are available as either the standard models or the smaller microsurgical types (Fig. 1.16). Their tips are also divided into delicate, fine, medium, and heavy duty. The standard size needle holders are about 120–130 mm long, and the microsurgical types are about 100 mm long. The most common shape is similar to that of the corneal and corneoscleral scissors with flexible serrated or knurled handles which are joined to provide a spring mechanism that automatically maintains the needle holder tips in the open position. Ophthalmic needle holders are designed to be held as a pencil. For general extraocular surgery, the Castroviejo needle holder with flat serrated handles and a lock is often used. The jaws are about 9 mm long and may be straight or gently curved. For microsurgery involving the cornea, the Storz or Barraquer needle holder with curved jaws and no locks is preferred. All of the ophthalmic needle holders are designed for only the small ophthalmic needles and sutures. Large needles and sutures larger than 4-0 will gradually distort these needle holder’s jaws, rendering the instrument useless; hence, these instruments are not useful for tying the very fine ophthalmic sutures (special tying forceps are used instead). The straight to curved tips are 7–16 mm long, and their surfaces may be smooth or serrated.

Fig. 1.16 Top: Smaller microsurgical needle holder (made of titanium and 109 mm long) with no lock and curved 9 mm fine jaws. Bottom: Standard Castroviejo needle holder (130 mm long) with lock and curved 9 mm jaws.

Spatulas/retractors/loops These instruments are essential for specific functions during intraocular surgery. They include the cyclodialysis spatula, iris and extraocular muscle hooks, and the lens loop. The cyclodialysis spatula is used bluntly to create a space between the sclera and the underlying iris and ciliary body for the treatment of glaucoma (Fig. 1.17). This instrument is about 120–140 mm long with a round to square serrated or knurled handle. Its tip is about 0.5–1.0 mm wide and 10–15 mm long with a blunt, rounded, or sharp end. This same design has also been incorporated into a cannula. This instrument can also be used to manipulate the iris, lens capsules, and vitreous. The iris hook is designed to retract the pupillary aspects of the iris. These hooks are about 120–140 mm long, and are constructed of either stainless steel or a nylon-like material (Delrin). These hook tips have a 1–3 mm curved end that is 1–4 mm wide and dull. Sharp or pointed iris hooks are not recommended as tearing of the dog and cat iris will usually cause hemorrhage. The muscle or strabismus hook is similar to the iris hooks, only the tip is much larger (Fig. 1.18). The instrument tip is angulated at 90 to facilitate placement under the extraocular muscles. These instruments are also used to rotate the globe. The lens loop is another vital instrument for lens and cataract removal in small animals. The lens loop is positioned to slide the cataract and lens material from the corneal or corneoscleral wound. With its handle shaped like the iris and muscle hooks, the lens loop’s tip is designed as a circularto-oval solid spoon or loop (Fig. 1.19). The overall size of these tips ranges from 0.3 to 6 mm wide and 7 to 15 mm long.

Fig. 1.17 Top: Two different cyclodialysis spatulas used for glaucoma and lens surgeries. The flat blade should be about 10 mm long and 1 mm wide, and has different angulations. Bottom: Cyclodialysis spatula combined with a cannula for injection into the anterior chamber.

Fig. 1.18 The strabismus or muscle hook is placed under the extraocular muscle to facilitate identification of the insertions as well as rotate the globe. Top: Von Graefe strabismus hook; bottom: Jameson muscle hook has a 6 mm hook with a 2 mm bulbous tip and a flat serrated handle. The tip may also be used for scleral depression during examination of the peripheral fundus.

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Surgical instrumentation

Fig. 1.19 The lens loop is used to facilitate sliding the lens from the eye. The loop may be different sizes and shapes. Top: New Orleans lens spoon has a 3 mm wide  14 mm long, slightly curved spoon on a 134 mm long flat serrated handle; bottom: Gills–Welsh modified lens loop with a 6  7 mm loop.

Cannulas for intraocular injections Special cannulas are necessary for corneal and intraocular surgery. With a reusable silicone bulb or anterior chamber irrigator and cannula, lactated Ringer’s or saline solution is occasionally sprayed on the corneal and conjunctival surfaces to provide essential moisture (Fig. 1.20). These cannulas range in size from 19 to 27 g. This same system is also used to re-inflate the anterior chamber with air or fluids once the corneal or limbal surgical wound has been apposed (Fig. 1.21). The cannulas may also be shaped as cyclodialysis spatulas, providing for two functions. Special cannulas to inject air or solutions have specially constructed ends, such as olive tips, side ports, and hooks. To inject the more viscid viscoelastic solutions, a slightly larger diameter cannula may be necessary.

Fig. 1.21 Ophthalmic cannulas may vary in diameter, length, shape, and purpose. Top: Air injection cannula (27 g); middle: Castroviejo cyclodialysis cannula (21 g); bottom: Bracken anterior chamber cannula. The latter two cannulas are used to inject solutions; for viscoelastics larger bore (18–19 g) needles are necessary.

Calipers During corneal, transscleral laser cyclophotocoagulation, cyclocryothermy, intraocular surgeries, intravitreal injections, and retinal detachment surgeries, distances between intraocular tissues and the exact size of tissues are very important. Several types of caliper are available that can be sterilized and should be part of the standard surgery instrument pack. These instruments permit measurements up to 20 mm in 1 mm or 0.5 mm increments. The Jameson and Castroviejo calipers are the most frequently used (Fig. 1.22). Fig. 1.22 Calipers for measurements during corneal and ocular surgeries. Top: Castroviejo; bottom: Jameson.

Rings

Fig. 1.20 Silicone bulb and cyclodialysis cannula to irrigate the anterior chamber with lactated Ringer’s solution, balanced salt solution or saline.

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Two types of ring are available for ophthalmic surgery; they include the external Flieringa and modified stainless steel single and double rings, and for intraocular use, the new capsular rings to insert within the capsular bag to expand the equatorial capsule. While the human elliptical cornea is about 7  8 mm in diameter, dog and cat corneas are considerably larger (dog: 16  15 mm; cat: 17  16 mm). Larger Flieringa rings, which are fortunately available, must be used; for dogs and cats the 20–22 mm diameter are recommended. Flieringa rings are attached around the cornea or limbus with four to six non-absorbable simple interrupted sutures to prevent globe and anterior chamber collapse as during keratoplasty. These rings are removed once the corneal wound has been apposed.

Surgical instruments for ophthalmic surgeries

Capsular tension rings have been introduced recently to expand the capsular bag after phacoemulsification and to facilitate insertion of an IOL. U-shaped, capsular tension rings are available in 12.5, 13.5 and 14.5 mm diameters for the dog.

Table 1.2 General surgical instruments for orbital surgeries

Instrument

Purpose

Allis tissue forceps

Hold and position tissues

Bard–Parker handle and blades

Incise the eyelids

Bishop–Harmon forceps, toothed

Grasp the conjunctiva and nictitans

Cannula: 19 g

Irrigation of the external eye

Enucleation scissors, large, curved

Incise the optic nerve

Eyelid speculum, wire

Retract the lids and maintain the palpebral fissure

Wet field or disposable cautery

Hemostasis

Jameson muscle hook

Manipulate the extraocular muscles

Metzenbaum scissors, medium

Incise and separate the orbital tissues

Mosquito forceps (2 curved, 2 straight)

Grasp tissues and for hemostasis

Needle holder, medium

Grasp and manipulate needle

Saline cup, small

Hold saline for moistening of tissues

Silicone bulb for irrigation

Irrigate the external eye

Tenotomy scissors, curved

Incise the conjunctiva and nictitans

Towel clamps (4 large, 4 small)

Maintain the surgical drapes

TM

Adaptations for large animals and special species ophthalmic surgeries As the veterinary ophthalmologist may be confronted with animal species that range in size from an elephant to a parakeet, surgical instrumentation is often determined by the size of the patient’s eye and sometimes available anesthesia. Fortunately, the elephant eye is similar in size to the horse, but for the parakeet even a 25 or 27 g needle is very large. For the larger animal species, the standard soft tissues surgical instruments are used for orbital and eyelid surgeries. For conjunctival grafts, corneal and intraocular surgeries, either the standard ophthalmic or microsurgical instruments are used. If the operating microscope is used, microsurgical ophthalmic instruments are recommended. Needle type and suture selection are identical for all species.

Surgical instruments for ophthalmic surgeries As ophthalmic surgeries are generally confined to certain ocular tissues, the development of specific surgical packs is recommended. Surgical packs are designed to limit the number of instruments anticipated for a surgery, and reduce the number of times an instrument requires cleansing, autoclaving, and non-surgical manipulations. Highly specialized ophthalmic instruments are best individually wrapped and sterilized, and used only when necessary.

Recommended instruments for orbital surgeries Although the majority of extraocular surgical procedures can be performed with general soft tissue instruments, the investment in ophthalmic surgical instruments will not only rapidly repay the surgeon the initial purchase costs, but also provide greater success rates for all patients. General soft tissue surgical instruments are used for most orbital surgical procedures and some of the more extensive eyelid surgeries (Table 1.2). Orbital surgery may also require some orthopedic instruments to transect and reappose the zygomatic arch in many animal species. Small Allis tissue forceps can be used to grasp and retract the orbital and eyelid tissues. The small Halsted mosquito forceps with straight and curved jaws are used for hemostasis by control of point bleeders, especially of the orbit, eyelids, and conjunctivas. The larger Kelly and Crile hemostatic forceps with either straight or curved jaws permit grasping of larger areas of tissue and are especially useful for orbital surgery. The curved Metzenbaum scissors, especially the smaller types, are indicated for most of the delicate orbital and eyelid tissue dissections. The Metzenbaum scissors should not be used to cut sutures. The heavy-duty Mayo dissecting scissors are useful for cutting the dense connective tissues of the orbit in large dogs.

Straight Mayo scissors, usually 6" (152 mm) long, are indicated for cutting sutures, especially sutures larger than 4-0. A good quality Mayo–Hegar needle holder is excellent for needles and suture sizes (4-0 to 2-0) that are used for the majority of orbital and eyelid surgical procedures. The Semkin and Adson tissue forceps may be used for orbital, eyelid, and conjunctival tissues, but the smaller ophthalmic fixation forceps may be less traumatic for these tissues. The Bard–ParkerTM scalpel handle, with the Nos 10 and 15 surgical blades, is used to incise orbital and eyelid tissues in small and large animals. The Beaver knife handle with several types of surgical blade (usually the Nos 6400 and 6500 microsurgical blades) is the most common knife for the ocular tissues of animals. A few general surgical instruments are usually part of any corneal or intraocular surgical instrument pack. At least four small (bulldog) towel clamps, and four larger towel clamps, small thumb forceps, small curved Metzenbaum scissors, and a small needle holder are used initially to improve exposure of the cornea and globe, and to perform the lateral canthotomy. The microsurgical instruments should not be used for the eyelids; these large tissues will eventually bend and disable these delicate instruments.

Recommended instruments for eyelid and conjunctival surgeries Although most eyelid, conjunctival, and nictitans surgeries can be performed with general surgical instrumentation, several instruments have been developed for specific lid surgical manipulations. As a result, a special eyelid surgery pack

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Table 1.3 Surgical instruments for eyelid surgeries

Instrument

Purpose

Towel forceps (4 large, 4 small)

Secure the drapes to the patient

Wire eyelid speculum (Barraquer)

Retract the lids and expose the conjunctiva/nictitans

Small curved Mayo scissors (Mayo/Metzenbaum)

Perform lateral canthotomy

Stainless steel cup

Hold saline/lactated Ringer’s solution for ocular irrigation

Silicone bulb and cannula

Periodically moisten the eye

Entropion/chalazion forceps

With an oval-to-round ring and solid base plate. Designed to clamp and stabilize the lid

Cilia forceps

Instrument

Purpose

Instruments for both surgeries Towel clamps (8)

Secure surgical drapes

Small curved Mayo scissors (Mayo/ Metzenbaum)

Lateral canthotomy

Stainless steel cup

Hold saline/lactated Ringer’s solution

Silicone bulb and cannula

Periodically moisten the eye

Wire lid speculum (adult/pediatric: Barraquer)

Retract eyelid/expose cornea

Small needle holder

Suture lateral canthotomy

With smooth tips designed to epilate the cilia

Tissue forceps: tooth/smooth (Adson)

Grasp conjunctiva/cornea

Bishop–Harmon forceps

Both serrated and 1  2 teeth tips. Good general tissue forceps

BeaverTM scalpel handle (Nos 6400 and 6500 microsurgical blades)

Incise cornea

Lid plate

Plastic or stainless steel. Holds the lids taut and protects the cornea from surgical manipulations

Tenotomy (Steven’s) scissors

Cut conjunctiva/sutures

Castroviejo needle holder

Use with 5-0 to 10-0 sutures

Use Beaver No. 6400 or 6700 microsurgical blade to incise eyelid skin/conjunctiva

For corneal surgeries

BeaverTM scalpel handle

Standard needle holder (Castroviejo/Barraquer)

Tenotomy scissors (Steven’s) curved/straight

Corneal section scissors (right/left pair)

Cut cornea/limbus/sclera

Standard size recommended to accommodate the larger needles and suture sizes. Some prefer holders with a lock device

Martinez or Gill dissector

Bluntly separate corneal stromal layers

Calipers

Operative measurements

Two different sizes recommended. Blunt tips preferred

Cyclodialysis spatula

Manipulate iris, lens, vitreous

Disposable ophthalmic cautery

Hemostasis/cut iris

Corneal trephines (5–9 mm)

For keratoplasty

Microsurgery needle holder

For keratoplasty

may be utilized using the standard size ophthalmic surgical instruments (Table 1.3).

Recommended instruments for corneal surgeries For corneal and intraocular surgery in small animals, a number of instruments are essential. Often, a combination of the standard and microsurgical ophthalmic instruments is included in a standard surgical pack. The corneal instrument pack should have a limited number of instruments. Additional infrequent use but essential ophthalmic instruments are individually packaged and sterilized, and can be used as needed. As the basic pack instruments are repeatedly cleaned and sterilized, these instruments can be subjected to considerable wear. A list of surgical instruments for a typical corneal surgical pack is summarized in Table 1.4. These instruments accommodate all of the surgical procedures, except for partial and full-thickness corneal grafts (keratoplasty), including bulbar and palpebral conjunctival grafts, corneoconjunctival and corneoscleral transpositions, superficial and deeper keratectomies, partial and full-thickness corneal lacerations, removal of partial and full-thickness corneal foreign bodies,

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Table 1.4 Surgical instruments for conjunctival and corneal surgeries

and limbal surgeries. The instrumentation for corneal grafts is not extensive but very specific. Because dog and cat corneas are very tough, corneal scissors and trephines must be very sharp.

Recommended instruments for intraocular surgeries and cataract extractions The instrumentation to perform all iris–ciliary body, glaucoma, cataract, and lens removal surgical procedures is summarized in Table 1.5. More instruments are necessary for lens and cataract surgeries than for glaucoma and anterior uveal surgical procedures. The selection of these instruments should serve only as a guide; individual preferences for specific instruments, based on shape and size, vary.

Instruments for vitreoretinal surgeries Current training of veterinary ophthalmologists is similar to human ophthalmology, and provides broad exposure to animal eye diseases and surgery in all animal species during

Instrument care, storage, and sterilization

Table 1.5 Surgical instruments for intraocular surgery in animals

Box 1.1

Recommended instruments and materials for vitreoretinal surgeries*

Instrument

Purpose

Towel clamps (4 large, 4 small)

Secure surgical drapes

General

Small curved Mayo scissors

Lateral canthotomy

• •

Saline cup

Hold saline/lactated Ringer’s solution

Silicone bulb and cannula (cannula: 19 g/25 g)

Periodically moisten the eye

Eyelid speculum (adult/pediatric)

Retract eyelid/expose cornea

Small needle holder

Suture lateral canthotomy

Tissue forceps: toothed/smooth (Adson)

Grasp conjunctiva/cornea

Tying forceps with teeth

Grasp cornea/sutures

Instruments

Beaver scalpel handles (Nos 6400, 6500, and 6700 microsurgical blades and keratome)

Incise cornea/limbus/sclera

Tenotomy scissors (Steven’s)

Cut conjunctiva

Utility scissors (Steven’s tenotomy)

Cut sutures

Corneoscleral scissors (right/left pair)

Incise cornea/limbus/sclera

Iris scissors

Incise iris

Extracapsular lens forceps

Grasp anterior lens capsule

Capsulectomy forceps (Utrata) (capsulorhexis)

Tear/remove anterior lens capsule

• • • • • • • • • • •

Lens loop

Slide lens from eye

Cyclodialysis spatula

Separate tissues

Muscle hook (Jameson)

Rotate globe/cataract surgery

Needle holder (standard/microsurgery)

Suturing

Other Calipers

Operative measurements

Disposable cautery (sterile)

Hemostasis/cut iris

Intraocular forceps

Grasp/remove lens capsule/ fragments

Intraocular scissors

Cut anterior lens capsule

Vannas capsulotomy scissors

Cut anterior lens capsule

Intraocular lens forceps/hook

Position or dial intraocular lens

a 3-year residency. Further specialization in human ophthalmology (often termed fellowships) occurs following their residencies, and provides physicians with in-depth training in, for instance, cornea, glaucoma, retina, and neuro-ophthalmology. Clinical fellowships have yet not developed in veterinary ophthalmology, but could focus on either specific ocular areas or even species. Vitreoretinal surgeries require additional training for veterinary ophthalmologists, and most performing this type of surgery have been trained in medical schools. With a limited number of veterinary vitreoretinal surgeons available, this type of surgery represents a new and exciting frontier for veterinary ophthalmology. For vitreoretinal surgeries, highly

•

Good quality operating microscope. Viewing system for the posterior segment: Machemer irrigating lens, other sew-on ring sets, or non-contact BIOM system. A more expensive wide-angle system is available. Both systems can be used in dogs. These systems use indirect ophthalmoscope principles (which invert the ocular fundus appearance) and may require an inverter for use. Vitrectomy system with light-illuminating sources, electrocautery, and air infusion. Newer units may also have ultrasonic fragmentation and silicone oil pumps. The vitrectomy unit is usually a guillotine-type cutter on the side of a 20 g blunt tube.

Microvitreoretinal (MVR) blades (20 g) High-viscosity infusion tubes (4 mm cannula) Scleral plugs and plug holder Light pipes Electrocautery sets Vitreous scissors and forceps Silicone-tipped 20 g needles Charles (fluted) needle and handle Laser endocoagulation system PFCLs (perfluorocarbons) Silicone oil (1000–5000 cSt)

*Recommended by Vainisi SJ, Wolfer JC 2004 Veterinary Ophthalmology 7:291–306. For more information, see Chapter 12.

specialized instruments are necessary, and are expensive (Box 1.1). Additional information on these instruments and their use is available in Chapter 12.

Instrument care, storage, and sterilization The investment in a complete and high-quality set of corneal and intraocular instruments can be considerable. These instruments, if carefully used, cleaned and stored, can last a very long time. Special instrument trays are available for both sterilized instruments ready for use or for long-term storage as non-sterile instruments. All of these instruments should be maintained in individual compartments within these trays and not allowed to contact each other. The delicate tips of these instruments should be covered and protected with old rubber or plastic tubing. For cleaning, the ultrasound cleaner provides the safest and most thorough method to remove all blood, tears, and other salt-containing residues. The ophthalmic instruments should be individually placed in and removed from the ultrasound unit to avoid any damage. Jostling these instruments together will potentially cause irreversible damage and bend the tips and dull the cutting edges. After thorough cleaning, the instruments should be air dried. Both steam and ethylene gas are used for ophthalmic instrument sterilization. The flash steam cycle may gradually dull the cutting instruments’ edges.

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Table 1.6 Characteristics of sutures for animal ophthalmic surgery

Suture type

Suture size

Ocular tissues

Nylon (monofilament)

5-0 to 12-0

Eyelid skin, cornea, sclera

Silk (braided)

5-0 to 7-0

Eyelid skin, conjunctiva, cornea, limbus

Polyester

5-0 to 7-0

Eyelid skin, limbus

Polypropylene

5-0 to 10-0

Eyelid skin, cornea

Chromic catgut

2-0 to 4-0

Subcutaneous tissues, subconjunctival tissues, fascial layers

Polyglactin 910 (braided and monofilament)

5-0 to 8-0

Subconjunctival tissues, cornea, sclera, limbus

Polyglycolic acid

5-0 to 7-0

Subcutaneous tissues, subconjunctival tissues, cornea, sclera, limbus

Polydioxanone

5-0 to 7-0

Subcutaneous tissues, subconjunctival tissues, cornea, sclera, limbus

Non-absorbable

Absorbable

Ophthalmic sutures and needles The general rule stating that the strength of the suture should approximate the surrounding tissues also pertains to ophthalmic sutures. For surgery of the orbit, suture size approximates that of general soft tissue surgery, with 2-0 to 5-0 absorbable sutures used for ligation and closure of the deeper orbital fascial tissues. Skin closure is usually with non-absorbable 3-0 to 5-0 nylon, polypropylene, polyester, Dacron, or silk. For surgery of the eyelids, 3-0 to 5-0 sutures are recommended, with the absorbable sutures buried and the skin apposed with non-absorbable 3-0 to 5-0 single interrupted sutures. Most conjunctival and corneal sutures are absorbable (to eliminate the need for suture removal), and 5-0 to 8-0 in size to minimize tissue reaction. The different ophthalmic sutures and their characteristics are listed in Table 1.6. Often the choice of the skin sutures is personal preference and nearly always the non-absorbable type. However, in some exotic small animals, skin suture removal may be impractical because of restraint, and absorbable subcutaneous or skin sutures are employed. Silk skin sutures are usually black, soft and pliable; if suture contact with the eye occurs, significant ocular irritation is unlikely. Unfortunately, silk sutures are braided and bacteria can penetrate the sutures, hence suture removal should be performed 10–14 days postoperatively. When nylon and polypropylene monofilament are employed for skin sutures, surgeon and square knots are usually combined to secure

each knot. As these sutures are fairly stiff, suture contact with the conjunctiva and/or cornea usually induces ocular irritation. This stiffness can be used to advantage during parotid duct transposition when these sutures are inserted with a flamed or blunted end into the duct’s lumen to facilitate detection and handling. The Dacron polyester suture is more pliable than the nylon or polypropylene, but its knots tend to loosen. Buried sutures involving the nictitating membrane may be either absorbable or non-absorbable depending on the procedure. Absorbable sutures are most frequently used for the deeper layers of the eyelids, all layers of the conjunctiva and nictitating membrane, and the cornea. Our preference is polyglactin (VicrylW; Ethicon, Somerville, NJ), a multifilamentous suture, with strength and resorption rates that approximate surgical gut (about 6 weeks). This suture, dyed violet, is non-antigenic and produces minimal tissue reaction. Uncoated polyglactin is associated with excessive tissue drag during suturing; coating greatly reduces this drag but additional ties are indicated for knot security. Polyglactin sutures are stable in septic wounds, and can be used in infected corneas. In general, reverse cutting semicircular needles are recommended for the majority of extraocular surgical procedures. Skin closure generally employs conventional cutting needles; the subcutaneous and deeper orbital fascial layers are apposed using spatula and taper needles. Corneal and scleral tissues require reverse cutting needles, and the G-6 semicircular needle is the most useful.

Further reading Boothe HW: Suture materials, tissue adhesives, staplers, and ligating clips. In Slatter D, editor: Textbook of Small Animal Surgery, ed 3, vol 1, Philadelphia, 2003, WB Saunders, pp 235–243. Gelatt KN, Gelatt JP: Handbook of Small Animal Ophthalmic Surgery. Vol 1: Extraocular Procedures, Oxford, 1994, Pergamon Press, pp 1–10.

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Gelatt KN, Gelatt JP: Handbook of Small Animal Ophthalmic Surgery. Vol 2: Corneal and Intraocular Procedures, Oxford, 1995, Pergamon Press, pp 1–14. Gelatt KN, Gelatt JP: Small Animal Ophthalmic Surgery, Oxford, 2001, ButterworthHeinemann, pp 1–16. Grevan VL: Ophthalmic instrumentation, Vet Clin North Am Small Anim Pract 27:963–986, 1997.

Kohn R: Textbook of Ophthalmic Plastic and Reconstructive Surgery, Philadelphia, 1988, Lea and Febiger, pp 2–55. Merkley DF, Wagner SD: Surgical instruments. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 3–33. Nasisse MP: Principles of microsurgery, Vet Clin North Am Small Anim Pract 27:98–1010, 1997.

Further reading Smeak DD: Selection and use of currently available suture material. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 34–39. Stades FC, Gelatt KN: Diseases and surgery of the canine eyelids. In Gelatt KN, editor:

Veterinary Ophthalmology, ed 4, vol 2, Ames, 2007, Blackwell, pp 563–617. Troutman RC: Microsurgery of the Anterior Segment of the Eye, St Louis, 1974, CV Mosby, pp 96–115.

Warren C: Phaco chop technique for cataract surgery in the dog, Vet Ophthalmol 7:348–351, 2004. Wilkie DA, Colitz CMH: Surgery of the canine lens. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, vol 2, Ames, 2007, Blackwell, pp 888–931.

15

CHAPTER

2

The operating room Kirk N. Gelatt

Chapter contents Introduction

17

Electroepilation

26

Magnification

18

Cryotherapy

26

Illumination

20

Laser therapy

27

Chairs for microsurgery

20

Perioperative drugs

30

Patient preparation

21

Patient recovery/restraint

31

Basic operative approach

22

Subpalpebral medication systems

32

Hemostasis

25

Introduction The operating room for extraocular surgeries is usually the standard operating room with more specialized illumination. Limited magnification, provided by head loupes and spectacle-mounted telescopes, is usually sufficient for surgeries of the orbit, eyelids, nasolacrimal system, nictitating membrane and conjunctiva. However, in the operating room where corneal and intraocular surgeries are routinely performed, in addition to the operating microscope, special instruments often include the phacoemulsification unit, ophthalmic cautery, cryotherapy, laser instrumentation, and retinal detachment surgery instrumentation. Depending on the number and type of ophthalmic surgical procedures performed daily or weekly, the composition of the operating environment will vary. The operating microscope is the largest single investment, but will last for a very long time with proper care. To the full-time veterinary ophthalmologist, the operating microscope is indispensable for corneal and intraocular surgeries in all animal species. A cabinet is maintained within the operating room for ophthalmic surgery, with special sterile instruments, individually wrapped, and ready for use. I prefer limited numbers of ophthalmic instruments arranged as external, minor, and major intraocular surgical packs. Another method divides the eye instrument packs based on intended use. Additional special instruments, individually wrapped and sterile, can be opened when needed; this reduces the wear and tear of cleaning and sterilization on instruments used infrequently but vital for certain eye surgeries. The external

eye surgical pack is used to drape the surgical area, expose the globe, perform the lateral canthotomy, and appose the surgical wound. The external eye instrument pack should contain small towel clamps, a small saline bowl, a silicone irrigator for solutions to keep the cornea and conjunctiva moist, a few small hemostats, ophthalmic tissue forceps, strabismus, utility or tenotomy scissors for ocular tissues and sutures, small serrated and 1  2 teeth thumb forceps, knife handle and blades, and one or more eyelid specula. The minor intraocular surgical pack provides the essential surgical instruments for corneal, glaucoma, and iris– ciliary body surgeries. The instruments in this pack can also be used to perform conjunctival grafts, superficial keratectomies, and primary closure of corneal ulcerations, and to treat partial to full-thickness corneal lacerations with an iris prolapse. This pack contains exclusively ophthalmic instruments, with small serrated, 1  2 teeth and tying forceps, curved and straight ocular scissors, cyclodialysis spatula, standard and micro-ophthalmic needle holder, corneal and anterior chamber irrigator, and portable batterypowered cautery unit. Special ophthalmic instruments, such as a corneal separator and iris scissors individually wrapped, sterile and ready for use, should be available within the operating room. The major intraocular surgical packs provide the instrumentation for cataract and lens removal, and posterior segment diseases (mainly vitreous). The instruments in this pack include corneal section (cataract or corneoscleral) scissors, different types of tissue and tying forceps, the lens loop and spoon, cyclodialysis spatula, cautery unit, two or more

2

The operating room

cannulas, extracapsular lens forceps, forceps for tearing of the anterior lens capsule (capsulorhexis), and one or two different size needle holders. Other instruments, individually wrapped and sterile, should include iris scissors, intraocular scissors, and intraocular forceps. Some backup instruments should be available in case contamination or malfunction of instruments occurs during the surgical procedure. Tables 1.2–1.5 and Box 1.1 list the different instruments for the varying ophthalmic surgeries. For more specialized surgeries, such as retinal detachment surgeries (see Table 1.5), instruments are often wrapped and sterilized separately.

Magnification For nearly 40 years veterinary ophthalmic surgery has been progressively refined, and microsurgical procedures performed under the operating microscope, that started in the early 1980s, are now commonplace for surgery of the cornea and intraocular structures. Microsurgery for human ophthalmology started slowly in the 1950s by Perrit. The first commercial operating microscope was produced by Zeiss and featured coaxial illumination. Important refinements by Barraquer (XY mechanism) and Troutman (motorized zoom) defined the basic components of the modern operating microscope. The development of microsurgical instruments, sutures, and needles also stimulated the concurrent requirement for magnification. Surgical procedures of the extraocular tissues including the orbit, eyelids, nasolacrimal, and tear systems are still traditionally non-microsurgical; however, microsurgery involving the conjunctiva, cornea, and intraocular tissues has become common because of the small ophthalmic needles and sutures, and the need for exact apposition of the involved tissues. Initial use of the operating microscope may be somewhat frustrating and may prolong the surgical procedure. However, with patience and practice, the veterinarian will quickly appreciate the advantages of corneal and intraocular surgeries performed under magnification.

Head-mounted magnifiers The exact requirements for magnification vary and are often influenced by the surgical patient load and the different types of ophthalmic surgical procedure performed. The simplest and least expensive magnification device is the binocular magnifier loupe worn on the head (Fig. 2.1). These head loupes can be used over prescription glasses. The head loupe is available in a number of different magnifications. Generally the lower magnifications are the most versatile because at the higher magnifications the focal length of the loupe is reduced, thereby limiting the working distance between the surgeon and the operating field. For instance, the head loupe with the 1.5 magnification has a focal length of 51 cm; the 1.75 magnification has a focal length of 35.5 cm; the 2 magnification is in focus at 25.5 cm; and the 2.5 magnification has a focal length of 20.5 cm. Individual telescope magnifiers are another low-cost alternative, and are generally recommended. They can be added to head loupes or attached directly to spectacles.

18

Fig. 2.1 Binocular magnifier loupe.

These units permit accommodation for different interpupillary distances, allow use of prescription glasses, and can be elevated when not in use (Fig. 2.2). Although these units are lightweight, use for several hours when attached to spectacles can be very tiring.

Operating microscopes Most veterinarians interested in corneal, intraocular, and vitreoretinal surgeries will eventually invest in an operating microscope. Once proficiency is achieved using the operating microscope, corneal and intraocular surgeries can be performed easily and quickly. The microsurgical ophthalmic instruments and very small 7-0 to 12-0 sutures can be easily manipulated with some magnification. The microscopic details provided during corneal incisions and wound apposition enhance the possibility of successful surgeries. Operating microscopes can be portable and attached to either a table or floor base with casters. Table units are the least expensive, usually provide observation for only the surgeon, and changes in focus require manual adjustments (Fig. 2.3). Stationary ceiling-mounted operating microscopes are used infrequently in veterinary ophthalmology because of the need for portability between operating

Fig. 2.2 Telescope magnifier loupe.

Magnification

Support arm to floor or ceiling mount

Assistant surgeon

Primary surgeon

Observer tube for video or 35 mm camera

Base microscope with built-in light system

Fig. 2.3 Portable table-mounted operating microscope. Unit weighs 9 kg and can be clamped to the surgery table. Working distance is 20 cm.

rooms. Most veterinarians use the floor-based operating microscopes which are very stable but mobile (Fig. 2.4). The operating microscope has several standard parts (Fig. 2.5). The base and mount are usually quite heavy and vary depending on whether the unit is table, floor or ceiling mounted. Various supporting arms permit adjustment of the operating microscope’s main body over the patient’s eye and angulation of the scope to the surgical field. With a large footplate that contains several switches, the surgeon can raise and lower the main body of the operating microscope to permit motorized coarse and fine focus of the surgical field. The scope’s main body consists of the focus and zoom systems, and a beam splitter that permits observation of the surgical field by the surgeon and assistant surgeon, and often a video recorder or 35 mm or digital camera. The fine focus of the surgical field and zoom or magnifying system

Fig. 2.5 Standard components of the operating microscope for ophthalmic microsurgery.

are also controlled by a foot pedal. This allows slight adjustments on magnification and/or focus without interrupting surgery. As with the head-mounted magnifiers, the magnification of the operating field is variable and inversely related to the focal length. The range of working distance between the patient’s eye and the base of most operating microscopes is 125–500 mm, with 200–250 mm the most common distance. The larger microscopes provide for dual observations for the surgeon and an assistant, and often an additional observer or camera (35 mm or digital SLR cameras or video recorder). Adjustments in magnification (zoom) and focal length are usually achieved by foot controls that change the focus up and down, and change the magnification (zoom). Magnifications with these operating microscopes vary, but generally range from 3 to 15 or 20. Most Fig. 2.4 Floor-based operating microscope. Unit provides for viewing by the surgeon, assistant surgeon, video recorder, TV and digital camera.

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The operating room

scopes have built-in zoom systems that permit immediate changes in magnification during surgery. Other models have different fixed steps of magnifications that require manual changes. With the operating microscopes with different fixed magnifications, parfocalization is important to avoid marked variations in focus during changes in magnification. To accommodate changes in both magnification and focus, the center of the surgical field should be in the middle of the microscope’s field, and the surgical area should be relatively level. Hence, the animal eye is carefully positioned so that the entire cornea, anterior chamber and iris surface are at the same levels of focus. Resolution of surgical field is optimal in the center of the scope’s optical system. Changes in the amount of magnification directly influence the size of the surgical field. With the 12.5 eyepiece, the 125 mm objective provides a surgical view of about 20 mm diameter; with the 200 mm objective the surgical view is 33 mm diameter; with the 300 mm objective, the surgical view is 50 mm diameter; and with the 500 mm objective, the surgical view is about 80 mm diameter. The most comfortable magnification and working distance is generally in the 175 range. Although higher magnifications may provide additional details, they reduce the working space as well as the depth of field. The magnification also influences the depth of the surgical field; as magnification increases, the depth of the field decreases. During cataract surgery in the dog or cat, some change in the operating microscope focus should be anticipated. Initially at least one area of focus is the cornea and the incision into the anterior chamber, and later a second area of focus is the anterior lens for tearing and removal of the anterior lens capsule. The magnification may need to be changed further to permit visualization of the posterior lens capsule. I recommend the lower range of magnification for the surgeon initially which accommodates longer working distances between the operating microscope and the patient’s eye, and greater depth of the surgical field for most corneal and intraocular surgeries. This usually permits visualization of the entire eye and the palpebral fissure. With experience, the higher magnification or the zoom feature of the microscope can be used, but generally with the surgical field no smaller than the cornea. Some operating microscopes possess sterile caps for both the objectives (to permit small adjustments in the interpupillary distances and the focus of each objective) and the base of the microscope (however, as a general rule, if the surgical instrument touches anything except the patient’s eye and draped instrument table, it is discarded and a new instrument substituted). Illumination systems are usually of two types: 1) the primary light system is incorporated into the operating microscope permitting direct illumination of the eye that is especially helpful during surgery in the posterior chamber and in the vitreous space; and 2) an ancillary light system mounted next to the operating microscope body that directs light to the eye at a slight angle. These light systems also function as a reserve; if one bulb malfunctions, the surgical field will continue to be illuminated. Both systems should have heat-absorbing filters to shield the eye as much as possible. Often the main and accessory light systems possess rheostats, permitting independent changes in the intensity of illumination. Retinal phototoxicity may occur with

20

prolonged and intense illumination of the ocular fundus. The minimum level of illumination to adequately perform the surgery is the best guide. Because of the magnification, positioning of the eye for surgery is important. With 10 to 20 magnification the depth of field is limited. As a result, the dog or cat is placed in dorsal recumbency, the head is stabilized by a U-shaped vacuum pillow or sandbags, and the operated eye is positioned in the center of the operating microscope’s field, with the cornea, anterior chamber, iris, and lens surfaces within focus. Other species, for instance the horse, are placed in lateral recumbency, and vacuum pillows or sandbags are used to position the head so that the eye is parallel to the operating microscope and the different areas of the cornea are in the same focus. If the eye is not level with the operating microscope, surgery in different places on the cornea or elsewhere will require intermittent changes in focus throughout the entire surgery. To simplify the optics of the operating microscope, maintaining both the scope and the patient in a vertical plane (rather than at an angle) will permit the majority, if not all, of the surgical field to remain in simultaneous focus.

Illumination Adequate illumination is essential for ophthalmic surgery. The dark ocular tissues, especially the anterior uvea, require high intensity focal illumination for visibility. Traditional sources of light for ophthalmic surgery include overhead surgical lamps, primarily for extraocular surgical procedures; portable and ceiling-mounted ’cool lamps’ that filter the majority of infrared light waves that dry the tissues, used for both extraocular and intraocular surgical procedures; and direct and fiberoptic light systems that are routed through the operating microscope during microsurgery. Small focal operating and examining lamps that are head mounted may also be considered; however, because of their weight, they are generally used for only short periods of time. Many different models of each illumination system are available; choice of the surgical lamp is also influenced by the anticipated frequency of use and costs. As a general rule, once the ocular tissues are illuminated during ophthalmic surgery, intermittent irrigation of the corneal and conjunctival surfaces with sterile 0.9% saline or balanced salt solution should be performed to prevent corneal and conjunctival epithelial damage.

Chairs for microsurgery All corneal and intraocular surgical procedures in small animals are performed with the surgeon and assistant surgeon seated on adjustable stools with casters (Fig. 2.6). The height of the stools should be adjustable to accommodate different surgeons as well as the height of the operating table and the patient. The recommended operating room chairs can be adjusted with a hydraulic activated foot pedal, permitting changes during surgery without interrupting surgery. In some stools the back rest can be rotated 180 and moved to the front of the surgeon to provide arm rests during microsurgery. These arm rests can be covered with sterile

Patient preparation

purpose. The contact lens is removed immediately before surgery along with any hair and debris from surgical preparation.

Cleansing and disinfection

Fig. 2.6 Adjustable stool for ophthalmic surgery. Stool height is adjusted by the foot-operated hydraulic control, and the back rest can be rotated for use as an arm support.

stockinet. The operating chairs for the surgeon and assistant surgeon should be comfortable and help to avoid fatigue that can adversely impact surgery.

Patient preparation Preparation of the skin of the eyelids and conjunctiva differs from that of most other general surgical procedures. During cleansing and preparation of the eyelid skin, these agents often contact the cornea and conjunctiva. As a result, solutions such as iodine in alcohol (Lugol’s solution) and isopropyl alcohol routinely used for skin preparation in general surgery are avoided as they are very toxic to the corneal and conjunctival epithelia, and cause immediate epithelial sloughing.

Clipping of hair and eye protection The hair and eyelashes are carefully clipped with small electric hair clippers. The eyelashes may be coated with petroleum jelly or ophthalmic ointment, and carefully clipped by small sharp scissors. While removing the hair of the eyelids and adjacent skin about the orbit, one should avoid creating any nicks and abrasions as these wounds can cause unnecessary irritation and unsightly swellings postoperatively. Several different strategies have evolved to protect the eye during surgical preparation of the eyelids and/or conjunctiva. Liberal amounts of ophthalmic ointment or petroleum jelly can be applied to the cornea just before clipping the eyelid hair. Hairs that fall onto the cornea and conjunctiva become embedded in the petroleum jelly, which is carefully removed later with sterile cotton swabs. A reusable plastic contact lens coated with ointment can also be used for this

The eyelids and adjacent orbital skin are cleaned and prepared for corneal and intraocular surgery. A mild antiseptic solution containing aqueous 0.5% povidone–iodine is the recommended ocular surface disinfectant for all ophthalmic surgical procedures. Chlorhexidine diacetate (0.05% and 0.5%) is toxic to the canine eye and causes chemosis, corneal epithelial edema, and corneal erosions. However, chlorhexidine gluconate (0.05%) with 4% isopropyl alcohol is both a safe and effective antimicrobial disinfectant for the dog’s cornea and conjunctiva. Both povidone–iodine and chlorhexidine are bactericidal. The 0.5% aqueous dilution of povidone–iodine produces rapid broad-spectrum antimicrobial effects against the commonly isolated Staphylococcus aureus, Staphylococcus epidermidis, a-hemolytic Streptococcus sp., and Escherichia coli, as well as many fungi and viruses in the dog. At effective antimicrobial dilutions, such as the 0.5% level, povidone– iodine does not cause corneal epithelial edema, corneal epithelial sloughing, eyelid edema, or conjunctival irritation in the dog. After at least two 1-minute cleansing periods with povidone–iodine, the eyelids, conjunctiva, and cornea are liberally flushed with sterile 0.9% saline or balanced salt solution. Sterile cotton-tipped swabs are used to remove any remaining exudates and hair from the conjunctival fornices and surfaces, and the ophthalmic surgical site is ready for draping. The 5% povidone surgical scrub, which contains 4.5% alcohol, provides an excellent germicidal preparation of the facial skin (as for parotid duct transposition), but cannot safely be used for the eyelids. This preparation is toxic to the corneal epithelium, producing a generalized loss of this layer (essentially a chemical superficial keratectomy). Most corneal and intraocular surgeries are performed with the pre-existing ophthalmic condition requiring medication within the operating room. Accordingly, the eye is often medicated immediately preoperatively, during the operative procedure, and following surgery. Often the preoperative condition or the immediate postoperative inflammation can be substantially reduced as a result of this perioperative medication of the eye and adjacent structures. Recent studies in dogs indicate that bacterial contamination of the anterior chamber occurs in about 30% of dogs undergoing cataract surgery, and topical as well as systemic antibiotics should be administered. Antibiotic therapy for full-thickness corneal perforations and lacerations is often administered during the surgical correction in the solutions used to irrigate the external ocular surfaces, and for re-establishment of the anterior chamber after repair of the corneal defect. Fortunately, bacterial endophthalmitis is very rare in the dog after intraocular surgery.

Head positioning The majority of corneal and intraocular surgical procedures are performed with the small animal patient in dorsal recumbency. If head-mounted magnifiers are worn, the

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The operating room

Irrigation To prevent drying of the conjunctival and corneal surfaces during ophthalmic surgery, small volumes of sterile 0.9% saline, balanced salt solution, lactated Ringer’s solution, or other physiologic solutions are used intermittently to moisten the ocular tissues. Both the pH and tonicity of these solutions should approximate the tear and aqueous humor fluids. Inadequate levels of moisture provided during eye surgery will result in unnecessary corneal epithelial damage and possible limitations on the use of certain classes of medications postoperatively.

Sponges/swabs Fig. 2.7 Vacuum U-shaped pack for ophthalmic surgery.

dog may be positioned in lateral recumbency. Ropes and adhesive tape are used to position the animal’s legs. Although the duration of most ophthalmic surgical procedures is less than 1 h, a circulating water heating pad between the patient and the surgery table reduces the possibility of hypothermia. It is important to place the animal’s head in a secure position to prevent any positional changes during surgery. Towels, water bottles, or several small lowcost sandbags can be used to maintain the head in the desired position. An alternative superior scheme uses a vacuum bead-filled U-shaped pack for stabilizing the head (Fig. 2.7). The patient’s head is positioned on the vacuum pack, and the pack is manipulated to provide the selected head position. Once the proper position is achieved, vacuum is applied temporarily to the pack. Once the air is removed, the pack becomes very rigid, holding the head in a fixed position. Release of the vacuum postoperatively causes the pack to return to a soft and moldable structure.

To assist with hemostasis and removal of material during ophthalmic surgery, small sterile cotton swabs are used routinely for corneal surgeries, and for the extraocular aspects of intraocular surgeries. For use inside the anterior chamber during intraocular procedures and full-thickness corneal surgical procedures, disposable cellulose sponges (often triangular shaped) are recommended. Cotton swabs are avoided during intraocular surgical procedures because some of the small cotton fibers may loosen and enter the anterior chamber, increasing the intensity of postoperative anterior uveitis.

Basic operative approach For corneal and intraocular surgeries, exposure of the entire cornea and anterior segment is preferred. In most small animals under general anesthesia, the globe rotates downward and inward. This may be advantageous for corneal and anterior segment surgeries involving the dorsal and dorsolateral regions, but not when access and visibility of the entire cornea and anterior segment are necessary. With less than adequate surgical exposure, the duration of surgery is prolonged and the procedure may be more difficult to perform.

Draping Once surgical preparation of the eye and associated structures is complete, the area is carefully draped for surgery. Simultaneous use of both paper (barrier) and reusable cloth (to absorb any moisture) drapes is recommended. Plastic drapes with self-adherent backings and rubber dental dam material can also be employed immediately about the surgical site. Cloth drapes are used to absorb the irrigation solutions, but unfortunately allow contamination with the other non-sterile surfaces of both patient and operating table. Paper or barrier drapes repel all moisture and prevent contamination from the other areas, and are most often used. Our standard draping procedure is to position four small surgical towels about the surgical site to absorb the irrigation solutions, and secure them with small bulldog towel clamps. An additional large paper drape with a small hole to provide adequate surgical exposure is placed over these towels and secured with additional towel clamps. As with any surgical procedure, draping is designed to provide adequate exposure of only the operative site and a barrier to the adjacent non-sterile areas.

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Retrobulbar injections in dogs Access to the cornea and anterior globe may present exposure problems in small animals, especially in certain breeds of dog. Fortunately, the lateral and dorsolateral aspects of the dog orbit are incomplete, and accommodate retrobulbar injections. Injections of sterile 0.9% saline can enhance the presentation of the cornea and globe, but only with some risk. The injection is performed with the dog under general anesthesia with the objective of forcing the globe further rostrad or forward in the orbit, or to turn the globe and improve exposure of a selected area of the cornea and/or anterior segment. The amount of sterile saline injected is ascertained as the injection is performed and the response of the globe to the space-occupying solution. The hypodermic needle may be inserted caudal to the junction of the lateral orbital ligament and dorsal aspects of the zygomatic arch (Fig. 2.8). The needle is directed towards the retrobulbar space in a ventromedial direction toward the opposite

Basic operative approach

Fig. 2.8 An 8 cm, 22 g hypodermic needle is inserted dorsal to the zygomatic arch and caudal to the lateral orbital ligament, and directed toward the opposite mandibular joint in the dog. A variable volume of sterile saline can be injected in the animal under general anesthesia to force the globe forward.

mandibular joint. The solution may be injected in the lateral aspects of the extraocular muscle cone, or immediately caudal to the globe and within the retrobulbar muscle mass. Injections external to the retrobulbar muscle cone will rotate the globe laterally; injections immediately behind the globe will push the globe forward. The volume injected should be limited to produce the desired outcome but not result in undue pressure and distortion of the globe. Another injection site is ventral to the anterior zygomatic arch and rostrad to the vertical portion of the ramus of the mandible (see Chapter 3). The hypodermic needle, after passing the ramus of the mandible, is directed toward the orbital fissure. Injections external to the retrobulbar muscle cone in the orbital floor and the medial orbit wall are possible with this method, and can be used to shift the globe dorsally. Retrobulbar injections can also be performed with curved hypodermic needles directed through the conjunctiva or the eyelids to deposit solution beside or caudal to the globe. The volume and position of the injection within the orbit will shift the eye accordingly. With the use of neuromuscular paralyzing drugs, retrobulbar injections are generally not necessary.

Retrobulbar injections in cats Retrobulbar injections in the cat are not recommended because of the limited retrobulbar space and difficulty in proper positioning of the injection.

Retrobulbar injections in horses Retrobulbar local anesthetic injections have been described in the horse by Berge and Lichenstern. The posterior orbit and entry of the critical cranial nerves in the horse is about as deep as in cattle, but the posterior orbit is more conical.

With gas inhalation general anesthesia and often neuromuscular blocking agents and forced ventilation, retrobulbar nerve blocks in the horse are infrequent. In the Berge method, an 8–10 cm, 18 g needle is inserted caudal to the supraorbital process of the frontal bone near the supraorbital foramen. The long needle is directed ventromedial (about 40 from the vertical) and slightly caudal toward the area of the orbital fissure where 15–20 mL of local anesthetic is injected (see Chapter 3). In Lichenstern’s method, an 8–10 cm, 18 g needle is inserted 1.5 cm caudal to the middle of the supraorbital process. The needle is directed toward the opposite last upper premolar tooth. The taut extraocular muscles’ fascial cone may be felt as the needle penetrates it. Approximately 20 mL of local anesthetic is injected near the orbital fissure (see Chapter 3). As a third method, the lateral and medial canthal routes may be used to inject about 10–15 mL of local anesthetic at each site. Of the large animal species, intraocular surgery is performed most often in the horse. As this species has considerable scleral elasticity (low scleral rigidity), sizeable retrobulbar injections can markedly indent the posterior segment and increase the likelihood of vitreous prolapse during cataract surgery.

Retrobulbar injections in cattle Because of inherent problems associated with general anesthesia in cattle, as well as economics, regional nerve blocks are common in this species. In fact, most orbital, eyelid, conjunctival, and corneal surgery is performed with regional injectable anesthesia. Of the three different routes for orbital injections of regional anesthesia in the cow, i.e., Peterson’s, Schreiber’s, and Hare’s, Peterson’s is the most common in America, but somewhat more difficult. A relatively simple method in cattle, the four-point block, uses more local anesthetic than the Peterson method, and delivers retrobulbar anesthetic through the dorsal, medial, lateral, and ventral conjunctival fornices directly into the retrobulbar space (see Chapter 3). In Peterson’s regional nerve block, an 8–10 cm, 18–20 g needle is inserted at the posterior angle of the zygomatic arch and lateral orbital rim, and directed anterior of the coronoid process of the mandible and inferomedially to the pterygopalatine fossa near the foramen orbitorotundum. After aspiration (avoiding the internal maxillary artery), 15–20 mL of local anesthetic is injected. Successful retrobulbar nerve block is shown as mydriasis, lack of globe mobility, and loss of corneal sensation. The palpebral nerve is blocked by placing 5–10 mL of local anesthetic subcutaneously along the dorsal zygomatic arch.

Complications of retrobulbar injections Retrobulbar injections require care, and can induce retrobulbar hemorrhage. The animal orbit contains large veins and venous plexuses, and hemorrhage sufficient to produce additional pressure of the globe, and even enter the subconjunctival spaces, fortunately occurs infrequently. Aspiration immediately prior to the injection of local anesthetic minimizes this complication. If this occurs, surgery should be delayed until the hemorrhage has reabsorbed.

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The operating room

Inadvertent puncture of the globe with the needle is rare, but a serious complication. The retrobulbar saline is usually reabsorbed within 30–60 min. With the use of intravenous neuromuscular blocking drugs, use of retrobulbar injections to manipulate the globe is less common and may be redundant. A few cases of cattle have been reported to suffer respiratory collapse and sudden death after the Peterson retrobulbar block, presumably from accidental anesthetic injection within the optic nerve meninges or the cerebrospinal space.

Stay sutures Silk stay sutures (usually 4-0), placed in the limbus, deep subconjunctival tissues, and dorsal rectus muscle insertion, may be used to turn and/or pull the globe forward prior to corneal and intraocular surgeries. After placement of the sutures in the ocular tissues, the opposite end of the stay suture is attached to the eyelid speculum, surgical drape or towel clamp, or to a hemostat clamped to the surgical drape. Two stay sutures may be superior to a single suture. Dependent on the site of the stay suture, the globe may be rotated to the desired position. As with retrobulbar injections, traction by these stay sutures on the anterior segment may distort the globe because of the lower ocular rigidity in the dog and cat. Possible complications of this method include tearing of the tissues by the stay suture, usually associated with excessive traction, and rarely penetration of a thin sclera. Stay sutures can also be used to retract the nictitating membrane from the surgical field. The suture is placed fullthickness around the nictitans cartilage, just beneath its leading margin, and extended to and secured to a towel clamp or hemostat anchored in the adjacent drape. The tension on the stay suture is adjusted to position the nictitans away from the surgical site but with no distortion of the globe.

Flieringa or Flieringa–LeGrand fixation rings The Flieringa rings consist of a single ring or two different sizes of stainless steel wire rings that are attached to each other (Fig. 2.9). Single ring sizes range from 12 mm to 22 mm in 1 mm increments. The double Flieringa ring is available in two sizes: 1) small (pediatric): 14 mm inner ring and 23 mm outer ring; and 2) large (adult): 17 mm inner ring and 24 mm outer ring. Wire rings in excess of 23 mm diameter are also easy to self-construct.

These wire rings are attached to the limbus or 1–4 mm posterior to the limbus with four or more simple interrupted 4-0 silk sutures to maintain the corneal wound during surgery and apposition, as well as to prevent collapse of the anterior chamber and globe. As the canine and feline corneas measure 16  15 mm and 17  16 mm, respectively, a selection of the larger ring sizes is recommended. These rings are used to maintain the shape and relative size of the anterior portion of the globe. Although these rings can adequately stabilize the anterior globe of the dog and cat, their use has not been common because of the time necessary to position the ring. The large Flieringa rings (12–24 mm) are recommended when full-thickness keratoplasty is performed in small animals to maintain the corneal curvature and the anterior chamber depth.

General anesthesia/neuromuscular blocking agents Most general inhalational anesthetics cause the globe to rotate down and inward, and decrease exposure to the eye. As a result, stay sutures are frequently used to stabilize and rotate the globe outward to improve surgical exposure. However, there are limits to the traction created by these sutures, and sometimes the surgical exposure is less than satisfactory. The administration of neuromuscular blocking agents, once general anesthesia has been stabilized, provides the optimal exposure of the dog’s globe, and has become the standard for most dog and equine corneal and intraocular surgeries. With paralysis and loss of all extraocular muscle tone caused by these drugs, the entire cornea is accessible. The globe also becomes somewhat hypotonic, usually negating the administration of intravenous osmotic agents to lower intraocular pressure. In fact, parenteral osmotics are not recommended when neuromuscular blocking agents are used for cataract surgery in dogs, because the eye may become too soft. The drug-induced paralysis may also reduce the impact or weight of the retrobulbar tissues on the posterior segment, and decrease the tendency for forward vitreous displacement during cataract surgeries in both dogs and horses. Neuromuscular blocking agents cause paralysis, but are not anesthetics. It is imperative that the level of general anesthesia be sufficient and closely monitored during use of these neuromuscular blocking agents. The section on these agents in Chapter 3 provides additional information and dosage.

Lateral canthotomy

Fig. 2.9 The Flieringa rings can be attached by eight silk sutures to the limbus in small animals to stabilize the anterior segment of the globe and prevent collapse of the anterior chamber.

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The lateral canthotomy procedure is probably the most frequently performed ophthalmic surgery in animals and is often used prior to corneal and intraocular surgeries. Incision of the lateral canthotomy temporarily increases the size of the palpebral fissure and facilitates surgical exposure of the globe. In many breeds of dogs with prominent eyes and for most cats, a lateral canthotomy for most ophthalmic surgical procedures is not necessary. However, in many mesocephalic and nearly all dolichocephalic breeds of dogs, the lateral canthotomy is indicated. Lateral canthotomies can cause postoperative swelling of the lateral canthus and limited discomfort. With the recent use of

Hemostasis

A

B

Fig. 2.10 Lateral canthotomy increases exposure of the cornea and globe. (a) After placement of the eyelid speculum to ascertain exposure, the lateral canthus is incised by curved Mayo or Metzenbaum scissors for 5–15 mm. The length depends on the breed and the required amount of exposure. (b) Two-layer closure includes: tarsoconjunctiva with 4-0 to 6-0 simple continuous absorbable sutures and the orbicularis oculi–skin layer with 4-0 to 6-0 simple interrupted non-absorbable sutures. The first suture (simple interrupted; simple mattress) is carefully placed near the eyelid margin.

neuromuscular blocking agents during ophthalmic surgery in small animals and the horse, the indications and need for lateral canthotomy are more limited. After insertion of an eyelid speculum, the palpebral fissure is maximized and the surgical exposure ascertained. If additional exposure is necessary, a lateral canthotomy is performed with curved Mayo or Metzenbaum scissors (Fig. 2.10a). The lateral canthal eyelid is incised for 5–15 mm, but the incision should not extend beyond the lateral orbital ligament. Hemorrhage is usually negligible. Point electrocautery can control any minor bleeding. A straight mosquito forceps may be used to slightly crush the tissues prior to the incision to control hemorrhage but is not usually necessary. At the conclusion of surgery, the lateral canthotomy is apposed by two layers of sutures in most breeds of dogs; in toy breeds, however, a single layer of sutures will suffice. The palpebral conjunctiva, submucosal fascia, and tarsus are apposed with 4-0 to 6-0 simple interrupted absorbable sutures (Fig. 2.10b). The external layer of closure, consisting of the orbicularis oculi muscle and lid skin, is apposed with 4-0 simple interrupted non-absorbable sutures. The first suture is carefully placed at the eyelid margin and has the greatest tension on it. Occasionally this suture is a modified interrupted mattress pattern. The skin sutures are removed at 7–10 days postoperatively. The most frequent postoperative complications after lateral canthotomy include dehiscence of the first one or two sutures, usually within the first week, and malalignment of the area. In eyes with lateral canthotomies, postoperative medications and ophthalmic examinations should be performed with care to prevent undue tension on the healing lateral canthus and sutures. Routine use of the E-collar in small animals also helps in the maintenance of the lateral canthotomy. Animals can quickly traumatize this area and tear the sutures from the lateral canthus. In the event of local dehiscence, the wound edges are refreshened and apposed by additional sutures.

Problems with enophthalmia Intraocular surgeries in large and giant breeds of dogs may be more difficult because of enophthalmia and limited exposure of the globe. As a result, surgery must be performed with the globe recessed in the orbit and certain

manipulations may be limited. With time and exposure, the bulbar and palpebral conjunctiva can become edematous and swollen, limiting further the surgical exposure. Attempts to improve access to the globe with lateral canthotomy, retrobulbar injections, and stay sutures are usually less than satisfactory. Excessive pressure on the globe, associated with suture or instrument traction on the anterior globe, or injections of solutions behind the posterior globe, may collapse and distort the globe, increasing the difficulty and duration of the intraocular surgery.

Hemostasis Maintenance of adequate hemostasis is essential for all ophthalmic surgical procedures. Uncontrolled intraoperative bleeding will diminish the visualization of critical ophthalmic structures. Any volume of blood retained within the surgical wound may retard wound healing, increase scarring, and cause immediate distortion of the postoperative wound. Intraocular hemorrhage is also unacceptable, and may promote the formation of synechiae and pupillary and preiridal inflammatory membranes. Hemostasis for most corneal and intraocular surgical procedures relies on direct pressure on the small bleeders, point electrocautery, and intraocular adrenaline (epinephrine). Temporary clamping of the larger conjunctival or subconjunctival blood vessels with a small hemostat is rarely necessary.

Electrocautery Electrocautery units are employed primarily to coagulate blood vessels for hemostasis in ophthalmic surgery in small animals, but are not used for the cutting of ocular tissues, except occasionally the bleeding iris. Unfortunately, cutting by electrocautery units may penetrate deeper than expected, and therefore constitutes a critical limitation for ophthalmic surgery. Generally, the small electrocautery units are most adequate and safest for ophthalmic surgery. Several battery-powered portable cautery units are available (Fig. 2.11a,b) as well as AC units (Fig. 2.11c) that provide wet-field cautery. The hand-held units are inexpensive, battery powered, and possess small microtips. The batteries are long-lasting, but must be removed during sterilization and replaced immediately before surgery. Wet-field cautery units are effective in the presence of blood, have limited systemic effects, and do not require patient grounding.

Local adrenaline (epinephrine) The addition of 1:100 000 adrenaline (epinephrine) to moistened cotton swabs can be used for hemostasis associated with small bleeders during conjunctival and corneal surgery; however, the concurrent use of halothane as an inhalational anesthetic may preclude its use. If adrenaline (epinephrine) is used for hemostasis in ophthalmic surgery, it is generally reserved for intraocular surgery where other modalities cannot be used, and is used at higher concentrations (1:1000). If adrenaline (epinephrine) is expected to be used for hemostasis, as during the repair of a full-thickness corneal laceration with iris prolapse, isoflurane should be the inhalational anesthetic.

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A

B

C

Fig. 2.11 Examples of portable and battery-powered hand-held ophthalmic cautery units. (a) Hand-held battery-power cautery unit. Unit can be steam sterilized and the batteries placed in the unit just before surgery. (b) Disposable battery-powered cautery. (c) Wet-field coagulator. Unit may be AC or batterypowered.

Electroepilation Electroepilation or electrolysis is used to treat canine distichiasis, trichiatic lashes, and ectopic cilia. The objective is to provide low levels of direct current to the hair follicle and destroy the germinal hair cells. For the most effective electrolysis, accurate placement of the electrolysis needle is paramount. Electrolysis is primarily employed when only a few distichia require treatment. Good magnification, illumination, and stabilization of the eyelid margin are important considerations. All electrolysis units have a very fine needle that can be inserted directly into the hair follicle. After 15–30 s of low milliamperage (2–4 mA) small bubbles will appear at the hair follicle opening. These bubbles are formed by hydrogen released by the electrolysis of the basal hair cells. With removal of the electrolysis needle, the offending distichia will usually be withdrawn. Occasionally small cilia forceps are necessary to epilate the distichia after electrolysis. Inadequate electrolysis can result in recurrence of the distichia. Excessive electrolysis can result in inflammation and fibrosis of the eyelid margin. Electrolysis is also less successful when multiple distichiae emerge from a single orifice, which unfortunately is quite frequent. The insertion of the electrolysis needle into each hair follicle is not usually possible and regrowth is common. Additional information on electroepilation can be found in Chapter 5. Several portable electroepilation units are available, and because of the low levels of current necessary they are usually battery powered. Units that provide 2 or 4 mA are safe and the least likely to produce excessive electrolysis (Fig. 2.12). Larger units that consist of the base and battery, manually controlled rheostat, milliamperage gauge, and the hand-held microstylet provide the most consistent results.

of mainly collagen fibers, are relatively unaffected by cryotherapy. The cryoadhesion developed between a cryoprobe and lens necessitates only direct contact, and with the more powerful units can occur even in the presence of aqueous humor and vitreous. Although cryotherapy has been evaluated for many corneal and intraocular surgical procedures in small animals, the primary indications include the treatment of distichiasis and small eyelid tumors, cryoextraction of subluxated, anteriorly and posteriorly luxated lenses, transscleral cyclocryotherapy for the partial destruction of the ciliary body for treatment of glaucoma, and chorioretinal cryotherapy for treatment of localized retinal tears and detachments. There are several different types of cryo-instruments. Those units that use CO2 (–78 C), nitrous oxide (–89 C), and liquid nitrogen (–195 C) are the most versatile. Some cryounits consist of a gas tank and hose, a base unit (often with tank pressure and probe temperature dials), and a hand-held probe (Fig. 2.13). The Frigitronics and Cabot Medical cryo-instruments, as well as the Brymill portable units (Fig. 2.14), are the more frequently used units in veterinary ophthalmology. For accurate cryotherapy, monitoring of the tissue temperature around the cryoprobe is useful for eyelid procedures.

Cryotherapy Cryotherapy in veterinary ophthalmology offers another therapeutic modality for certain ophthalmic disorders. Cryotherapy offers two unique characteristics: 1) selective destruction of normal and neoplastic tissues; and 2) increased adhesion that develops between the cryoprobe and ocular tissues. Ocular tissues sensitive to cryodestruction include the corneal epithelium and endothelium, all intraocular blood vessels, ciliary body epithelium, uveal pigment cells, and the retina. The corneal stroma and sclera, consisting

26

Fig. 2.12 Small battery-powered epilation unit.

Laser therapy

Fig. 2.13 Liquid nitrogen unit for ophthalmic use. (a) Base unit for the cryotherapy. (b) Cryoprobes. Top: cataract, straight; bottom: glaucoma, curved.

B

A

The tip of the small probe is usually covered with a thermal shield to prevent damage or adhesion to adjacent tissues during the cryotherapy. There are usually several different selections of probes for veterinary ophthalmology: the straight cataract (tip diameter 1–2 mm) and slightly curved glaucoma

probes (tip diameter 3–5 mm) are the most useful. Probe tip temperature during cryotherapy should rapidly achieve and maintain temperatures ranging from 30 C for cryoadhesion to 80 C to 90 C for cryodestruction. For cyclocryotherapy, liquid nitrogen is recommended as the coolant. To achieve epithelial destruction of the ciliary body at 20 C to 30 C, the probe tip temperature must be at least 70 C to 90 C. For treatment of distichiasis and eyelid neoplasms, and cyclocryotherapy for end-stage glaucoma, lower cost handheld portable liquid nitrogen units are useful. These units have a generous assortment of open (spray) and closed cryoprobes for ophthalmic use.

Laser therapy Laser therapy was first introduced in human ophthalmology in the 1960s, and quickly these ophthalmologists recognized the benefits of the laser. The eye is an ideal organ for laser therapy with its tissues and media usually clear, and the target tissues usually heavily pigmented. Laser use was first reported in veterinary ophthalmology in the 1980s, once the laser units became considerably smaller, portable, and less expensive.

Laser basics

Fig. 2.14 A less expensive hand-held portable cryounit with variable open (spray) and closed probes can be used for extraocular use and transscleral cyclocryothermy.

Lasers emit light energy; this energy is transmitted to the target tissues, and absorbed selectively by pigmented tissues. There are several types of commercial laser, and each emits energy of specific wavelengths. Each ocular tissue absorbs a particular range of wavelength. The cornea absorbs short

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ultraviolet wavelengths (200–313 nm) and greater than the longer infrared wavelengths (1400–10 000 nm). The lens absorbs ultraviolet wavelengths (315–400 nm), thus protecting the retina from harmful ultraviolet rays from the sun. The blue, blue–green, yellow, red, and near-infrared spectrum of wavelengths (400–1400 nm) pass through the sclera and clear cornea, aqueous humor, lens, and vitreous to be absorbed by the fundic tissues (melanin and hemoglobin). Three ocular pigments absorb the majority of laser energy delivered to the eye; they include melanin, hemoglobin, and xanthophyll (in the human macula). Melanin within the uveal tract and retinal pigment epithelia absorbs the visible and infrared wavelengths (400–1400 nm), and absorption increases as the laser wavelength decreases. Within the retina there may be different absorptions by the individual retinal tissues: 1) short or blue wavelengths are absorbed better by the inner retinal layers; 2) yellow wavelengths are absorbed better by red subretinal neovascular membranes; 3) longer wavelengths in the infrared red range penetrate the sclera better; and lastly, 4) the longer the wavelength, the greater the tissue transmission.

Laser delivery From the laser source, the energy is delivered to the ocular tissues by different avenues. Laser energy may be delivered using a number of transscleral probes in the contact or non-contact mode, as with the neodymium:yttrium aluminum garnet (Nd:YAG) laser. It may also be delivered by endoprobes within the eye, the indirect ophthalmoscope with laser attachment for transcorneal and transpupillary transmission, the slit-lamp biomicroscope, and as an adapter to the operating microscope.

Laser choice Choice of laser by the veterinary ophthalmologist is dependent on its range of clinical use (target ocular tissues and their wavelength absorption ranges), type of intended tissue damage (thermal photocoagulation, photodisruption, photoablation, and/or photochemical), portability, and cost. Lasers can also be used in the continuous wave

mode or in the pulsed mode, which can change the tissue damage they cause. Using the Nd:YAG laser in the continuous mode causes thermal photocoagulation; the same laser in the pulsed mode (either Q-switching with nanosecond pulses or mode-locking with picosecond pulses) produces a photodisruptive effect.

Current ophthalmic lasers Ophthalmic lasers currently commercially available include the CO2, excimer, argon, tunable dye, Nd:YAG, and diode. Their characteristics and veterinary ophthalmic use are summarized in Table 2.1. Of these instruments, the diode laser is the laser most frequently used by the veterinary ophthalmologist; its tissue damage is caused by photocoagulation (Fig. 2.15). The second most frequently used laser is the Nd:YAG laser used in both the contact and non-contact mode; this unit is also shared with veterinary surgeons (Fig. 2.16). The diode laser has a shorter wavelength (810 nm) than the Nd:YAG laser (1064 nm) which allows improved melanin absorption, but less transscleral transmission than the Nd:YAG laser. Diode transscleral transmission can be increased by use in the contact mode. The diode laser also permits transcorneal, transpupillary, and intravitreal (endoscopic laser) energy delivery.

Laser applications In the specialty practices of veterinary ophthalmology world-wide, the diode laser is the most frequently used instrument. Its advantages include high absorption of its energy by melanin, portability (small and lightweight), and low cost. Less frequently used lasers include the Nd: YAG (delivered by contact probe or by slit-lamp biomicroscope) and CO2; the latter is used for the treatment of adnexal, conjunctival, and episcleral lesions in small animals and the horse. Experimental laser refractive surgery or keratomileusis has been performed in the dog, but it is doubtful that it will become useful clinically. The diode, Nd:YAG, and CO2 lasers have been used to treat limbal or epibulbar melanomas in dogs and cats with high success. These lasers are less invasive, faster, excellent for hemostasis, and less technically difficult. The result is charring and

Table 2.1 Lasers used in veterinary ophthalmology

Laser type

Wavelength (nm)

Tissue damage

Clinical use

Excimer

193

Photoablation

Epithelial and anterior stroma keratopathies, LASIK

Argon

488–514

Photocoagulation

Retinal photocoagulation, iridotomy, iridoplasty, sclerostomy

Diode

810

Photocoagulation

Cyclophotocoagulation, retinal photocoagulation, iridotomy, sclerostomy

Nd:YAG (continuous mode)

1064

Photocoagulation

Cyclophotocoagulation, capsulotomy, cataract surgery

Nd:YAG (Q-switched or mode locked)

1084

Photodisruption

Retinal photocoagulation, iridotomy, sclerostomy, hyaloidotomy

CO2

10 600

Photoablation

Blepharoplasty, conjunctival carcinoma, punctoplasty

Modified from Gilmour MA 2002 Lasers in ophthalmology. In: Bartels KE (ed.) Lasers in Medicine and Surgery. WB Saunders, Veterinary Clinics of North America: Small Animal Practice 32:649–672.

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Laser therapy

A

B

Fig. 2.15 The diode laser system is the most popular system in veterinary ophthalmology. (a) The base unit is small and portable. (b) The diopexy hand probe for retinopexy (left); a separate hand probe is necessary for transscleral cyclophotocoagulation (right). (c) The unit can also be mounted on an indirect ophthalmoscope for transpupillary retinopexy. (Photographs courtesy of Iridex Corporation, Mountain View, CA USA)

C

Fig. 2.16 The Nd:YAG laser is available mounted as part of the slit-lamp biomicroscope as in this illustration or as a base unit with hand probes. The former is used for transpupillary iridotomy, hyaloidotomy, and synechiotomy; the latter is used for transscleral cyclophotocoagulation.

contraction of the pigmented mass, and low levels of recurrence. The diode laser delivery systems include indirect ophthalmoscope with a 20 D lens, operating microscope adapter, and either the glaucoma or transscleral non-contact probe. Laser cyclophotocoagulation is commonly used by veterinary ophthalmologists for treatment of canine, feline, and equine glaucomas. The transscleral and recent endoscopic laser photocoagulation methods attempt to partially destroy the ciliary body processes and reduce aqueous humor formation rates. Exact placement of the laser probe during the transscleral methods is essential for ciliary body ablation, and is addressed in the endoscopic method by directly observing the ciliary processes during lasering. Results of laser therapy for the different glaucomas and species are available in Chapter 10.

Both diode and Nd:YAG lasers have been used for synechiotomy, capsulotomy, iridotomy for pupillary block glaucoma, and hyaloidotomy for malignant glaucoma with variable success. Experimentally, the diode laser delivered by the direct ophthalmoscope system in the normal dog failed to produce patent iridotomies either grossly or microscopically. Laser therapy of canine opacified posterior capsule has been attempted with both diode and Nd:YAG lasers. For additional information, see Chapter 10. Both diode and Nd:YAG lasers have been used to treat large uveal cysts (dogs and horses) and cystic corpora nigra (horses) which have the potential to interfere with vision. These cysts deflate during lasering, and may detach and fall into the ventral anterior chamber. Variable fibrin and slight hemorrhage are possible minor complications. Both diode and Nd:YAG lasers have been used in dogs and a few horses to treat primary intraocular neoplasia. Laser energy can be delivered transsclerally, transcorneally or by a sterile fiber inserted through the opposite pars plana into ciliary body tumors. Use of laser therapy for canine intraocular tumors is influenced directly by the following facts: 1) most canine intraocular tumors involve the anterior uvea; and 2) the metastatic rates for these tumors are very low (perhaps 5%). One study in dogs using the Nd:YAG laser to treat both ciliary body and iridal tumors suggested that success was influenced mainly by the extent or size of the tumor and less by tumor pigmentation. Melanomas in the retriever breeds primary involve the anterior iris surface, and are quite successfully treated by either the Nd:YAG or diode laser. Additional information is available in Chapter 9. Laser therapy is a mainstay for the treatment of vitreoretinal diseases, for which the preferred laser is the diode, with its energy delivery transsclerally, transpupillary, and by endophotocoagulation during pars plana retinal detachment surgery. Diode laser or cryotherapy is used to perform retinopexy, either prophylactically or for the treatment of rhegmatogenous retinal detachment surgery. For additional information, see Chapter 12.

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Laser safety As laser energy is potentially hazardous to veterinary ophthalmologists and their staff, several safety precautions are essential. As each laser emits its own range of wavelength energy, all precautions must be based on the selected laser. Laser safety eyewear must be worn whenever laser use occurs. When lasering an eyelid lesion, the patient’s eye must be protected with a non-reflective stainless steel or lead eye shield. Any window within the laser room should be shuttered and doors locked with dead-bolts when the laser is in use.

Table 2.2 Drugs to support corneal and intraocular surgical procedures*

Agent

Purpose

Antifibrin agents

Heparin (1–2 IU/mL) mixed in all topical and intraocular irrigating solutions (usually lactated Ringer’s). To prevent fibrin formation during surgery Tissue plasminogen activator (intracameral): 25 mg to treat fibrin and blood clots (up to 10– 14 days old)

Perioperative drugs Several drugs should be available in the ophthalmic operating room for corneal and intraocular surgical procedures in animals (Table 2.2). These drugs may be administered topically before and after surgery, and injected in the anterior chamber during surgery. All drugs used intraocularly must be sterile and without preservatives. Drugs delivered topically may be placed on the cornea by an operating technician. Drugs injected into the anterior chamber or elsewhere should be administered by the surgeon. The general classes of drugs that should be immediately available to the veterinary ophthalmic surgeon include antifibrin drugs, antibiotics, anti-inflammatory agents, miotics and mydriatics, irrigating solutions, and viscoelastic substances. These drugs may be administered topically, intracamerally (injected directly into the anterior chamber), or injected subconjunctivally beneath the bulbar conjunctiva. Fibrin is an undesirable sequela of anterior uveitis in small animals, and often occurs after the anterior chamber has been entered. The two most useful antifibrin drugs are heparin and tissue plasminogen activator. Heparin (1–2 IU/mL) may be added to all topical and intracameral irrigating solutions, thus impairing fibrin formation as the surgical procedure is performed. If intraocular hemorrhage occurs, the administration of irrigating solutions with heparin is temporarily stopped to permit clotting. Heparin irrigating solutions can often be resumed later in the surgical procedure. Later the blood clot may be irrigated or gently removed by forceps. In the event that excessive fibrin or clot formation occurs postoperatively, tissue plasminogen activator (tPA) may be injected. tPA is a clot-specific fibrinolytic agent developed by gene cloning; it forms a complex with fibrin, activating plasminogen into plasmin that lyses fibrin, fibrinogen, and other procoagulant proteins into soluble by-products. As a result, the fibrin clot breaks down and is reabsorbed. tPA is maintained frozen in 25 mg doses in individual 1 mL syringes ready for injection into the anterior chamber, usually several days after corneal and intraocular surgeries when excessive fibrin has formed. tPA injections appear effective in dissolving most fibrin clots in the anterior chamber that are less than 7–14 days’ duration and in all species. Antibiotics may be administered perioperatively by the topical route as well as by intracameral injection. Topical antibiotics are the standard ophthalmic solutions and ointments, and are usually instilled on the cornea at the conclusion of corneal and intraocular surgeries. Intracameral antibiotics may be injected into the anterior chamber when

30

Antibiotics (add to the irrigating solution for topical and intracameral use)

Penicillin G (1000–4000 IU/mL) Chloramphenicol (1–2 mg)

Anti-inflammatory agents Corticosteroids:

1.0% prednisolone for topical use Methylprednisolone and/or triamcinolone for subconjunctival injections

Non-steroidal anti-inflammatory agents for topical use: Flurbiprofen and suprofen Control of pupil Miotics:

Topical 1% to 2% pilocarpine Intracameral 1:100 acetylcholine chloride

Mydriatics: Topical 1% tropicamide and 1% atropine Subconjunctival atropine Intracameral 1:1000 adrenaline (epinephrine) Topical and intracameral sterile irrigating solutions

Saline, balanced salt solution, and lactated Ringer’s solution

Intraocular hemostasis

Intracameral 1:1000 adrenaline (epinephrine)

Viscoelastic compounds

1% sodium hyaluronate 2% hydroxypropyl methylcellulose 4% sodium chondroitin sulfate plus 3% sodium hyaluronate

*All intracameral drugs should be sterile, without preservatives, and for single use for injection into the anterior chamber.

infection may be present (with full-thickness corneal lacerations or corneal ulcerations), or added to the irrigating solutions used throughout the entire surgical procedure. The concentrations of intracameral antibiotics must be very low to avoid direct damage to the corneal endothelium, and broad spectrum to provide maximum effectiveness.

Patient recovery/restraint

Preoperative treatment with topical and systemic antibiotics to temporarily sterilize the conjunctival and corneal surfaces is not usually successful. In one study, bacterial contamination of the anterior chamber of the dog during cataract surgery occurred in about 30% of the treated eyes. These bacteria, usually staphylococcal species, undoubtedly contribute to the intensity of postoperative anterior uveitis in small animals after intraocular surgeries. As a result, topical and systemic antibiotics are usually administered for a few days preoperatively and for 5–7 days postoperatively. Additional antibiotics may be used intracamerally and the reader should consult ophthalmic pharmacology texts for recommended doses. Anti-inflammatory drugs are essential to control the postoperative inflammations that occur after the dog or cat anterior chamber has been opened. Topical and systemic corticosteroids are usually administered to treat anterior uveitis that can occur after corneal and intraocular surgeries. Corticosteroids may be injected subconjunctivally to provide an additional route to treat the severe forms of anterior uveitis. Topical and systemic non-steroidal antiinflammatory agents are also administered pre- and perioperatively in small animals for concurrent anterior uveitis. During anterior uveitis and upon surgical entry into the anterior chamber, prostaglandins released from the uveal tissues stimulate a rapid miosis, breakdown of the blood– aqueous barrier, and the formation of fibrin in the aqueous humor. These non-steroidal anti-inflammatory agents in the dog appear very useful in the maintenance of a widely dilated pupil during and after lens removal. In intraocular surgery, control of the pupil may be critical during the surgical procedure and in the postoperative period. Miotics to constrict the pupil may be administered topically (usually 1–2% pilocarpine) or injected intracamerally with 1:100 acetylcholine chloride when an immediate miosis is necessary. Intracameral miotics should be sterile, single use, and free of preservatives. Constriction of the pupil may be an immediate complication during surgical entry of the anterior chamber. Pre- and perioperative topical mydriatics and non-steroidal antiinflammatory agents assist in the maintenance of a widely dilated pupil during surgery. Intracameral adrenaline (epinephrine) (1:1000) may also be injected to induce an immediate mydriasis when the anterior chamber has been opened. As some adrenaline (epinephrine) is absorbed systemically in patients in which pupil control may be difficult, isoflurane is the recommended general anesthetic. Atropine sulfate may also be injected subconjunctivally at the conclusion of intraocular surgery to help achieve mydriasis during the immediate postoperative period when pupil movement is still possible. Sterile isotonic solutions are maintained in the ophthalmic operating room to irrigate corneoconjunctival surfaces, and lavage the anterior chamber during intraocular surgeries. The most frequently used solutions are sterile 0.9% saline for topical use and lactated Ringer’s solution for intracameral use. Sometimes other drugs, such as heparin and antibiotics, are added to these solutions during corneal and intraocular surgeries. Two additional groups of drugs are used commonly in small animal and equine ophthalmic surgery. Viscoelastic agents are very viscid solutions used to maintain the anterior

chamber during corneal and intraocular surgeries. They are available, ready for use during surgery, in 1 mL and 2 mL sterile syringes. These agents are designed to coat and protect the corneal endothelium during phacoemulsification and the insertion of an IOL, fill and maintain the anterior chamber, expand the capsular bag for IOL implantation, and temporarily increase intraocular pressure. They are also useful to maintain the anterior chamber during the repair of full-thickness corneal lacerations. These agents can also be used to manage miosis, intraocular hemorrhage, posterior capsular tears, and vitreous presentation. Viscoelastic agents are divided, based on their physical properties, into: 1) cohesive (high viscosity/molecular weight); and 2) dispersive (low viscosity/molecular weight). Cohesive agents tend to aggregate and remain together. Dispersive agents tend to occupy the available space and spread apart. Cohesive agents are better to create space, expand the capsular bag, dilate pupils, and move tissues. In contrast, the dispersive viscoelastics are better to coat surgical instruments, and corneal endothelium and epithelium, partition trouble areas, and tamponade posterior capsular tears. The supercohesive viscoleastics may contribute more to postoperative ocular hypertension. The dispersive viscoelastics remain longer in the anterior chamber after injection, and offer better protection of the corneal endothelium during phacoemulsification. Selected viscoelastics include: HealonW (Pharmacia–Upjohn), a cohesive viscoelastic; ViscoatW (Alcon Laboratories), a dispersive viscoelastic; Healon GVW (Pharmacia–Upjohn), a supercohesive viscoelastic; and DuoViscW (Alcon Laboratories), a combined cohesive and dispersive viscoelastic. Although not listed in Table 2.2, a new group of drugs has recently been added for use in the ophthalmic operating room. Antifibrotic agents are now being used intraoperatively and postoperatively for the different antiglaucoma filtering and anterior chamber shunt surgeries. Excessive fibrous capsule formation often surrounds and eventually impairs the egress of aqueous humor through these surgical fistulae. Freshly mixed mitomycin C has been used in dogs intraoperatively during different glaucoma surgical procedures to prolong their function. Additional details on mitomycin C can be found in Chapter 11.

Patient recovery/restraint Several methods have been developed by veterinarians to restrain animals in order to prevent self-trauma. The technique most useful after most types of small animal ophthalmic surgery is the application of an Elizabethan collar (Fig. 2.17). These collars effectively prevent the animal from touching the eyelids, adjacent orbital areas, and the eye with either front or back paws, as well as from rubbing the operative site on the floor or other objects. The Elizabethan collar is available commercially manufactured from plastic, nylon or cardboard materials, or can be self-constructed from cardboard, X-ray film, or from plastic buckets or waste baskets. Stronger materials, such as plastic collars, buckets, and waste baskets, are recommended for dogs over 20 kg; cardboard or X-ray film collars may be used for smaller dogs and cats. For a self-constructed Elizabethan collar, the collar diameter is approximately 4–8 cm beyond the patient’s

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In horses, eyelid, conjunctival, and corneal sutures can also cause postoperative discomfort. Unprotected, the horse can rub the surgical wound sufficient to cause wound dehiscence and marked swelling, loss of hair and open skin wounds. There are several methods to prevent or minimize this self-induced trauma; they include a neck cradle, cross-tying the horse, and preferably a face mask with hard eye cups to protect either the right or left, or both eyes. As moisture can collect under these masks, frequent cleaning and drying the area can markedly prolong their use.

Subpalpebral medication systems Fig. 2.17 A self-constructed or commercially available Elizabethan collar is an effective deterrent against self-mutilation after ophthalmic surgery. The collar should extend 4–8 cm beyond the animal’s nose and utilized until the eyelid/lateral canthotomy sutures have been removed.

nose. The collar is secured to the neck with gauze bandage tied loosely. Excellent alternatives are plastic buckets or waste baskets. A circle is cut from the bottom of the container sufficient to slide over the head and fit loosely about the neck. A leather or gauze bandage collar is threaded through four or more holes punched in the base of the container to secure the device to the animal’s neck. The Elizabethan collar, commercial or self-constructed, should fit tight enough to prevent its dislodgement, but loose enough to prevent any breathing and eating problems. Other restraint methods include hobbles for the front paws, and/or covering the front paws with bandages or socks. Small animals can still rub the postoperative eye with these devices. Short-term postoperative sedation and tranquilization may also be used to calm a dog or cat, but their use is usually restricted to only a few days.

A

Subpalpebral medication systems were developed for small animals and horses nearly 40 years ago, and have been employed routinely in horses. These systems consist of tubing with or without a footplate that is placed in the animal’s dorsal, dorsolateral or ventral conjunctival fornix (Fig. 2.18), and continued through the eyelid to terminate on the animal’s forehead or upper neck. The subpalpebral system permits medication with solutions of the small animal’s eye while covered with a complete temporary tarsorrhaphy. This system also provides for a reliable system to deliver medications to the horse eye which is painful and difficult to treat as frequently as necessary. The system can be self-constructed from silicone or polyethylene tubing with footplates (Fig. 2.19), and is available commercially (often referred to as one-hole systems). Simple silicone tubing may also be used and placed into the conjunctival fornix through two holes in the upper eyelid. A third system uses an indwelling catheter in the horse’s nasolacrimal duct via the false nostril. As topical medications may persist in the horse’s nasolacrimal duct, this route may be associated with greater systemic absorption of topical ophthalmic drugs, especially atropine.

B

Fig. 2.18 Placement of a subpalpebral system in the standing horse. (a) The supraorbital nerve block is performed (inject 3–5 mL of local anesthetic into the subcutaneous tissues above the supraorbital foramen) to provide local anesthesia and akinesia of the central upper eyelid. The cornea is anesthetized with a few drops of topical anesthetic. Alternate sites include the lateral canthus and central ventral conjunctival fornix. (b) A 12–14 g hypodermic needle is inserted beneath the central upper lid and into the dorsal conjunctival fornix to exit the entire eyelid.

32

Subpalpebral medication systems

C

C

Fig. 2.18, cont’d (c) The subpalpebral tubing is carefully threaded into and through the needle, leaving the footplate within the upper fornix. (d) The subpalpebral tubing is attached to the patient’s skin with either sutures or hospital tape, and usually terminates in the neck region (where the medications can be injected). As the footplate can migrate towards the limbus from the intermittent eyelid movements, its position within the fornix is checked daily. This scheme allows convenient and reliable delivery of medications to horses at any daily frequency.

Fig. 2.19 Footplate of a polyethylene subpalpebral system placed in the dorsolateral conjunctival fornix in a dog. With the footplate within the conjunctival fornix, direct contact and damage to the cornea is avoided. As contractions by the orbicularis oculi will gradually force the footplate toward the cornea, daily inspection of the footplate is recommended. The subpalpebral system permits topical medication of an eye in any animal species covered by a complete temporary tarsorrhaphy.

In small animals the system is placed while the animal is still under general anesthesia. In the horse, the standing patient is either sedated or the system placed at the conclusion of surgery. When the subpalpebral system is used in small animals, an Elizabethan collar is also recommended to prevent the animal from dislodging the system. In horses, a soft or hard cup with

a face mask is used to prevent dislodgement and rubbing of the system. The medication solutions are placed in a small syringe and injected in the tubing as frequently as necessary. The administration of topical drugs in horse ensures delivery of the drug(s) to the eye and reduces the possibility of injury to the treatment personnel. The powerful orbicularis oculi muscle can gradually move the subpalpebral footplate toward the limbus and peripheral cornea. If the footplate touches the cornea, ulceration can result. As a preventive measure, daily inspection of the footplate position is recommended. Suture tension above the upper eyelid on the subpalpebral system, as well as a silicone disk glued to the tubing external to the lid surface, are also possible. Placement of the subpalpebral system in the lower conjunctival fornix is another strategy. Because knowledge of drug interactions is unknown, ophthalmic medications are mixed only during injections into the system. Battery-powered and micro-osmotic pumps have been used to deliver medications in very low volumes continuously and need further research. Complications in horses with home-made subpalpebral systems, constructed from polyethylene tubing, depend on the experience of the nursing staff, construction of these systems, and the duration of their use. The commercial systems are constructed of silicone tubing, the silicone footplates are larger and glued to the end of the tubing, and the systems are more flexible and resistant to breakage and leaks. These subpalpebral systems are often used to deliver topical medications to an equine patient’s eye for several weeks. As with any catheter system used for several weeks in horses, local wound care and disinfection of the subpalpebral lid site is recommended. One study involving 150 horses reported the advantages and relative safety of subpalpebral medication systems. The key is close daily inspection of the system footplate, and correction of any positional changes as the powerful orbicularis oculi muscle forces it toward the limbus and cornea. It must remain safely within the conjunctival fornix to prevent any direct corneal contact and damage.

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2

The operating room

In the same study, minor complications (34%) included mild lid swelling, tearing of the system, and loss of the injection cap (end of the tubing where topical medications are injected). All of these complications are manageable and may, in part, be associated with self-induced trauma by the patient. More severe complications (24%) included premature tubing removal, focal infection of the eyelid, loss of the footplate, and corneal ulceration (1 eye in 150 horses). In another study involving 101 horses using home-made silicone systems, the duration of the subpalpebral systems

ranged from 1 to 14 weeks. Complications were noted in only 15 patients and included corneal ulceration (4 horses), lid swelling (5 horses), conjunctival irritation (2 horses), leaking tubing (2 horses), catheter loss (1 horse), and lid abscess (1 horse). None of these complications prevents reimplantation of another subpalpebral system if the eye disease requires extensive topical therapy. Intensive topical therapy without a subpalpebral system for in pain and difficult horses is unreliable at best, dangerous for the nursing staff, and generally not possible long term (several weeks).

Further reading Preoperative preparation and general Boes DA, Lindquist TD, Fritsche TR, Kalina RE: Effects of povidone–iodine chemical preparation and saline irrigation on the perilimbal flora, Ophthalmology 99:1569–1574, 1992. Boothe HW: Antiseptics and disinfectants, Vet Clin North Am: Small Anim Pract 28:233–248, 1998. Fowler JD, Schuh JCL: Preoperative chemical preparation of the eye: a comparison of chlorhexidine diacetate, chlorhexidine gluconate, and povidone–iodine, J Am Anim Hosp Assoc 28:451–457, 1992. Gelatt KN, Gelatt JP: Handbook of Small Animal Ophthalmic Surgery, Extraocular procedures, vol 1, Oxford, 1994, Pergamon, pp 11–21. Gelatt KN, Gelatt JP: Handbook of Small Animal Ophthalmic Surgery, Corneal and intraocular procedures, vol 2, Oxford, 1995, Pergamon, pp 15–30. Roberts S, Severin GA, Lavach JD: Antibacterial activity of dilute povidone–iodine solutions used for ocular surface disinfection in dogs, Am J Vet Res 47:1207–1210, 1986.

Electrosurgery/electroepilation Greene JE: Electrosurgery. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 40–41. Halliwell WH: Surgical management of canine distichia, J Am Vet Med Assoc 150:874–879, 1967. Lawson DD: Canine distichiasis, J Small Anim Pract 14:469–478, 1973. Long RD: Treatment of distichiasis by conjunctival resection, J Small Anim Pract 32:146–148, 1991. Stades FC, Gelatt KN: Diseases and surgery of the canine eyelids. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 563–617.

Cryotherapy Chambers ED, Slatter DH: Cryotherapy (N2O) of canine distichiasis and trichiasis: an experimental and clinical report, J Small Anim Pract 25:647–659, 1984.

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Magrane WG: Cryosurgical lens extraction: uses and limitations, J Small Anim Pract 9:71–73, 1968. Merideth RE, Gelatt KN: Cryotherapy in veterinary ophthalmology, Vet Clin North Am: Small Anim Pract 10:837–846, 1980. Roberts SM, Severin GA, Lavach JD: Cyclocryotherapy – Part II. Clinical comparison of liquid nitrogen and nitrous oxide cryotherapy on glaucomatous eyes, J Am Anim Hosp Assoc 20:828–833, 1984. West CS, Barrie KP: The use of cryosurgery in a veterinary ophthalmology practice, Semin Vet Med Surg 3:77–82, 1988. Wheeler CA, Severin GA: Cryosurgical epilation for the treatment of distichiasis in the dog and cat, J Am Anim Hosp Assoc 20:877–884, 1984.

Lasers Bacharach J, Lee DA: Iridotomy, trabeculoplasty and trabecular ablation. In Berlin MS, editor: Lasers in Ophthalmology, Ophthalmology Clinics of North America, vol 6, Philadelphia, 1993, WB Saunders, pp 425–436. Bosniak SL, Ginsberg G: Laser eyelid surgery: evaluating the therapeutic options. In Berlin MS, editor: Lasers in Ophthalmology, Ophthalmology Clinics of North America, vol 6, Philadelphia, 1993, WB Saunders, pp 479–490. Brinkman MC, Nasisse MP, Davidson MG, et al: Neodymium:YAG laser treatment of iris bombe´ and pupillary block glaucoma, Progress in Veterinary and Comparative Ophthalmology 2:13–19, 1992. Cook CS: Surgery for glaucoma, Vet Clin North Am: Small Anim Pract 27:1109–1129, 1997. Cook CS, Wilkie DA: Treatment of presumed iris melanoma in dogs by diode laser photocoagulation: 23 cases, Vet Ophthalmol 2:217–225, 1999. English RV, Nasisse MP, Davidson MG: Carbon dioxide laser ablation for treatment of limbal squamous cell carcinomas in horses, J Am Vet Med Assoc 196:439–442, 1990. Fankhauser F, Fankhauser-Kwasniewska S, England C, van der Zypen E: Laser

cyclophotocoagulation in glaucoma therapy. In Berlin MS, editor: Lasers in Ophthalmology, Ophthalmology Clinics of North America, vol 6, Philadelphia, 1993, WB Saunders, pp 449–472. Gilger BC, Davidson MG, Nadelstein B, et al: Neodymium:yttrium aluminum garnet laser treatment of cystic granula iridica in horses: eight cases (1988–1996), J Am Vet Med Assoc 211:341–343, 1997. Gilmour MA: Lasers in ophthalmology. In Bartels KE, editor: Lasers in Medicine and Surgery, Veterinary Clinics of North America: Small Animal Practice, vol 32, Philadelphia, 2002, WB Saunders, pp 649–672. Lin CP: Laser-tissue interactions: basic principles. In Berlin MS, editor: Lasers in Ophthalmology, Ophthalmology Clinics of North America, vol 6, Philadelphia, 1993, WB Saunders, pp 381–392. Nasisse MP, Davidson MG: Laser surgery in veterinary ophthalmology: perspectives and potential, Semin Vet Med Surg (Small Anim) 3:52–61, 1988. Nadelstein B, Davidson MG, Gilger BC: Pilot study on diode laser iridotomy in dogs, Veterinary and Comparative Ophthalmology 6:230–232, 1996. Nasisse MP, Davidson MG, Olivero DK, et al: Neodymium:YAG laser treatment of primary canine intraocular tumors, Progress in Veterinary and Comparative Ophthalmology 3:152–157, 1993. Rosolen SG, Ganem S, Gross M, et al: Refractive corneal surgery on dogs: preliminary results of keratomileusis using a 193 nanometer excimer laser, Veterinary and Comparative Ophthalmology 5:18–24, 1995. Sapienza JS, Miller TR, Gum GG, et al: Contact transscleral cyclophotocoagulation using a neodymium:yttrium aluminum garnet laser in normal dogs, Progress in Veterinary and Comparative Ophthalmology 2:147–153, 1992. Shieh E, Boldy KL, Garbus J: Excimer laser keratectomy in the treatment of corneal opacities, Progress in Veterinary and Comparative Ophthalmology 2:75–79, 1992. Sullivan TC, Nasisse MP, Davidson MG, et al: Photocoagulation of limbal melanoma in

Further reading dogs and cats: 15 cases (1989–1993), J Am Vet Med Assoc 208:891–894, 1996. Vainisi SJ, Packo KH: Management of giant retinal tears in dogs, J Am Vet Med Assoc 206:491–495, 1995. Whigham HM, Brooks DE, Andrew SA, et al: Treatment of equine glaucoma by transscleral neodymium:yttrium aluminum garnet laser cyclophotocoagulation: a retrospective study of 23 eyes of 16 horses, Vet Ophthalmol 2:243–250, 1999.

Perioperative ophthalmic drugs Gerding P, Essex-Sorlie D, Vasaune S, Yack R: Use of tissue plasminogen activator for intraocular fibrinolysis in dogs, Am J Vet Res 53:894–896, 1992. Gerding PA, McLaughlin SA, Brightman AH, Essex-Sorlie D, Helper LC: Effects of intracameral injection of viscoelastic solutions on intraocular pressure in dogs, Am J Vet Res 50:624–628, 1989. Jampol LM, Jain S, Pudzisz B, Weinreb RN: Nonsteroidal anti-inflammatory drugs and cataract surgery, Arch Ophthalmol 112:891–894, 1994. Johnson RN, Balyeat E, Stern WH: Heparin prophylaxis for intraocular fibrin, Ophthalmology 94:597–601, 1987. Liesegang TJ: Viscoelastic substances in ophthalmology, Surv Ophthalmol 43:268–293, 1990. Martin C, Kaswan R, Gratzek A, Champagne E, Salisbury MA, Ward D: Ocular use of tissue plasminogen activator in companion animals, Progress in Veterinary and Comparative Ophthalmology 3:29–36, 1993. Millichamp NJ, Dziezyc J: Comparison of flunixin meglumine and flurbiprofen for control of ocular irritative response in dogs, Am J Vet Res 52:1452–1455, 1991. Nasisse MP, Cook CS, Harling DE: Response of the canine corneal endothelium to intraocular irrigation with saline solution, balanced salt solution, and balanced salt solution with glutathione, Am J Vet Res 47:2261–2265, 1986. Roze M, Thomas E, Davot JL: Tolfenamic acid in the control of ocular inflammation in the dog: pharmacokinetics and clinical results

obtained in an experimental model, J Small Anim Pract 37:371–375, 1996. Skuta GL: Antifibrotic agents in glaucoma filtering surgery, Int Ophthalmol Clin 33:165–182, 1993. Taylor MM, Kern TJ, Riis RC: Intraocular bacterial contamination in canine cataract surgery, Vet Pathol 29:475, 1992. Ward DA, Ferguson DC, Ward SL, Green K, Kaswan RL: Comparison of the blood– aqueous barrier stabilizing effects of steroidal and nonsteroidal anti-inflammatory agents in the dog, Progress in Veterinary and Comparative Ophthalmology 2:117–124, 1992. Wilkie DA, Willis AM: Viscoelastic materials in veterinary ophthalmology, Vet Ophthalmol 2:147–153, 1999.

Subpalpebral medication Blair MJ, Gionfriddo JR, Polazzi LM, et al: Subconjunctivally implanted microosmotic pumps for continuous ocular treatment in horses, Am J Vet Res 60:1102–1105, 1999. Brooks DE: Use of an indwelling nasolacrimal cannula for the administration of medication to the eye, British Veterinary Journal: Equine Ophthalmology Supplement 2:135–137, 1983. Frauenfelder H, McIlwraith W: Placement of a subpalpebral catheter in a standing horse, Vet Med Small Anim Clin 74:724–728, 1979. Gelatt KN: Postoperative medications in horses and dogs, Vet Med 62:1165–1172, 1967. Gelatt KN: Blepharoplastic procedures in horses, J Am Vet Med Assoc 151:27–44, 1967. Gelatt KN: A modified subpalpebral system for the horse, Journal of Equine Medicine and Surgery 3:141–143, 1979. Gelatt KN, Peterson JE, Myers V, McClure R: Continuous subpalpebral medication in the horse, J Am Anim Hosp Assoc 8:35–37, 1972. Giuliano EA, Maggs DJ, Moore CP, et al: Inferomedial placement of a single-entry subpalpebral lavage tube for treatment of equine eye disease, Vet Ophthalmol 3:153–156, 2000. Martin B, Severin G: Topical medication of the eye using a subpalpebral tube. In Proceedings

of the 14th Annual Meeting of the American Association of Equine Practitioners, 1968, p 324. Myrna KE, Herring IP: Constant rate infusion for topical ocular delivery in horses: a pilot study, Vet Ophthalmol 9:1–6, 2006. Schoster JV: Revisiting ocular lavage systems for the horse. In Proceedings of the 36th Annual Meeting of the American Association of Equine Practitioners, 1990, pp 575–583. Schoster JV: The assembly and placement of ocular lavage systems in horses, Vet Med 87:460–471, 1992. Sweeney CR, Russell GE: Complications associated with use of a one-hole subpalpebral lavage system in horse: 150 cases (1977–1996), J Am Vet Med Assoc 211:1271–1274, 1997. White SL: Construction and placement of a subpalpebral lavage system for medication of the eye. In Proceedings of the 43rd Annual Meeting of the American Association of Equine Practitioners, 1997, pp 160–162. Whitley RD, Lavach JD, Gelatt KN: Subpalpebral lavage system for administering frequent topical medications to the equine eye, Florida Veterinary Journal 8:10–14, 1979.

Restraint Hazra S, De D, Roy B, et al: Use of ketamine, xylazine and diazepam anesthesia with retrobulbar block for phacoemulsification in dogs, Vet Ophthalmol 11:255–260, 2008. Hendrix DVH: Eye examination techniques in horses, Clinical Techniques in Equine Practice 4:2–10, 2005. Lavach DJ, Roberts SM, Severin GA: Current concepts in equine ocular therapeutics, Vet Clin North Am Large Anim Pract 6:435–449, 1984. Rubin LF, Gelatt KN: Analgesia of the eye. In Soma LR, editor: Textbook of Veterinary Anesthesia, Baltimore, 1971, Williams and Wilkins, pp 489–499. Seim HB, Creed JE, Smith KW: Restraint techniques for prevention of self-trauma. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 42–49.

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CHAPTER

3

Anesthesia for ophthalmic surgery Kirk N. Gelatt

Chapter contents Introduction

37

Local or regional eyelid injections/nerve blocks

43

Ophthalmic effects of general anesthetics

37

Retrobulbar injections/nerve blocks in animals

44

Preanesthetic medications

39

Injectable general anesthetics

40

Choice of general anesthetic for selected ophthalmic surgical procedures

47

Inhalational general anesthetics

40

Neuromuscular blocking agents

41

ADAPTATIONS FOR LARGE ANIMALS AND SPECIAL SPECIES

47

Ophthalmic drug and anesthetic drug interactions

42

Horse

47

43

Cattle

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Systemic diseases and general anesthesia

Introduction The advances in veterinary anesthesia have paralleled those in veterinary ophthalmic surgery, and have resulted in less anesthetic risk, and improved patient care and management. Studies in different animal species, including humans, suggest frequent similar ophthalmic responses to tranquilizers, narcotic analgesics, dissociative anesthetics, inhalational general anesthetics, and neuromuscular relaxants; however, species differences can occur. Combinations of critical peri-, intra-, and postoperative topical and systemic drugs are common in veterinary ophthalmic patients, and should be accommodated by the choice of general anesthetic agents and protocols. At the same time, concurrent general anesthesia and ophthalmic needs must avoid drug selections that are contraindicated or incompatible when used simultaneously. A significant number of ophthalmic patients are old and may have other diseases that may influence the choice of general anesthetics. In this chapter the impact on the eye and associated structures of drugs administered as part of general anesthesia will be summarized.

Ophthalmic effects of general anesthetics Intraocular pressure Intraocular pressure (IOP) results from a relative equilibrium between aqueous formation, aqueous humor outflow,

and the resistance of the fibrous tunics, e.g., the cornea and sclera, to pressure. The different drugs administered to tranquilize, sedate, and/or anesthetize animals may affect IOP directly by influencing the aqueous humor dynamics, or indirectly by causing hypercapnia, changes in extraocular muscle tone, hypoxemia, and hypothermia. Most general anesthetics lower IOP through actions on the central nervous, respiratory, and circulatory systems. The reduction in IOP is also related directly to the depth of general anesthesia. Most general anesthetics seem to lower IOP by an increase in the rate of aqueous humor outflow. Drugs that directly cause ocular hypotension can also produce ocular hypertension secondary to respiratory depression and acidosis that sometimes occurs with prolonged general anesthesia. As a general observation, drugs that produce an abrupt increase in arterial blood pressure will result in a moderate increase in IOP. This elevation in IOP is usually transient as the aqueous humor dynamics rapidly readjust and return to normal levels of IOP. The major percentage of the resistance of aqueous humor outflow is determined by the episcleral venous pressure. Drugs that produce marked increases in central venous pressure and episcleral venous pressure can also temporarily elevate IOP. The increased central venous pressure may also expand the anterior and posterior uveal vascular beds, indirectly increasing IOP. Expansion of the uveal vascular channels may produce pressure on the vitreous when the globe has been opened, and force the vitreous, its patellar fossa, and even the lens toward the anterior chamber.

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Anesthesia for ophthalmic surgery

Drug-induced changes in extraocular muscle tone can influence IOP. As most animal species have lower scleral rigidity than humans, relaxation of the extraocular and retrobulbar muscles markedly decreases the pressure of these orbital tissues upon the globe. The ketamineassociated elevation in IOP that occurs in humans is thought to be directly related to the increase in extraocular muscle tone. In lightly anesthetized dogs, intravenous administration of succinylcholine can result in a shortterm elevation in IOP. This 5–10 min elevation in IOP is thought to be related to the unusual sensitivity of the extraocular muscles to succinylcholine, and the initial muscle fasciculations that occur during the onset of the drug’s action. When the insertions of the extraocular muscles are severed in the cat, succinylcholine administration does not change IOP. Animals, in general, possess lower ocular rigidity than humans. As a result, when either the cornea or the sclera is incised and IOP released, the entire globe tends to collapse. The sclera in both the dog and cat possesses elastic fibers, in addition to the major complement of collagen, and as a result the sclera lacks rigidity. When the globe is collapsed, corneal and intraocular surgical procedures are more difficult to perform. The level of IOP in animals with low ocular rigidity also enhances the effects of retrobulbar muscle tone. Once the globe has collapsed, extraocular muscle tone may become of greater concern, tending to distort and displace forward the vitreous, lens, and anterior uvea.

Corneal drying and exposure Corneal abrasions, drying of the cornea, conjunctival irritation, and reduced tear formation have been associated with general anesthetics in humans and animals. Ketamine in cats has been associated with corneal drying, although the individual roles of reduced tear formation rates and loss of the protective blink reflex have not been differentiated. Hence, in cats undergoing ketamine anesthesia the corneas should be protected by copious amounts of ophthalmic petroleum-based bland ointment and/or the eyelids closed temporarily by tape. The same applies in dogs, and petroleum-based bland ointment should be applied to both eyes, depending on the type of ophthalmic surgery. The rate of aqueous tear formation in dogs, as determined by Schirmer’s tear test, after combinations of subcutaneous atropine, intravenous thiamylal sodium, and halothane or methoxyflurane was reduced by about 70% within 10 min and by 97% after 60 min. Another study has indicated that subcutaneous atropine reduces Schirmer’s tear test levels in normal dogs by about 55% at 60 min after drug administration. In dogs and cats with reduced levels of tear formation, the administration of parenteral and/or topical atropine can abruptly lower Schirmer’s tear test levels to zero, and initiate the clinical signs of keratoconjunctivitis sicca. Although the topical effects of general anesthetics have not been reported in large and special species animals, petroleum-based bland ointment is applied liberally to protect the corneoconjunctival surfaces during prolonged general anesthesia.

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Oculorespiratory cardiac reflex The oculocardiac or oculorespiratory cardiac reflex was first described by Aschner and Dagnini in 1908 in two simultaneous but independent reports. The afferent aspect of this reflex is carried in the long and short ciliary nerves, the ciliary ganglion, and the ophthalmic branch of the trigeminal nerve via the gasserian ganglion to the trigeminal sensory nucleus. Short internuncial fibers within the reticular formation connect the trigeminal sensory nucleus to the visceral motor nucleus of the vagus nerve and its descending nerve to complete the efferent limb to the heart. The afferent limb of the ophthalmic division of the trigeminal nerve does not appear to be unique. Intraorbital stimulation of the third, fourth, and sixth cranial nerves will also produce consistent respiratory prolongation, but more variable cardiac responses. There appears to be significant species differences for the oculorespiratory cardiac reflex (documented in dogs, cats, horses, and birds), and whether the cardiac, the respiratory, or a combination of both components occurs. In addition to the induced bradycardia, in some species such as the dog, the concurrent respiratory depression can be more profound. The reflex may be initiated by a number of ophthalmic manipulations, including ocular pressure massage for glaucoma, intraorbital injections of local anesthetics (which are also used to block this reflex), surgical traction of the extraocular muscles, and manipulations of the eyelid muscles. In dogs under general anesthesia, neuromuscular blocking agents, and controlled ventilation, only the cardiac portion of this reflex can be appreciated. There may be some individual animal variations relative to the oculorespiratory cardiac reflex in the dog and cat, with only some animals demonstrating this reflex consistently. The primary effect in the cat seems to be respiratory; in the dog, respiratory depression is the dominant response, but bradycardia can develop. To manage the oculorespiratory cardiac reflex, a number of strategies have been developed. To diminish or completely block the vagal effect on the heart, intravenous atropine is the standard treatment. Unfortunately, atropine administration yields inconsistent results. Consequently, the rationale to administer parenteral atropine preoperatively in dogs differs among veterinary anesthesiologists. One school recommends against the routine administration of parenteral atropine preoperatively. If bradycardia develops during the surgical procedure, surgery is temporarily halted and atropine is administered intravenously. Other veterinary anesthesiologists continue to recommend routine use of preoperative parenteral atropine to prevent the potential oculorespiratory cardiac reflex from developing. Unfortunately, intravenous atropine may not only increase the heart rate in the dog, but also increase the possibility of ventricular dysrhythmias. The intravenous dose of atropine to treat and/or prevent the oculorespiratory cardiac reflex in the dog seems critical. In children, although the prophylactic use of parenteral atropine seems to lower the incidence of the oculocardiac reflex, it has also been associated with severe and prolonged ventricular dysrhythmias. Low levels (0.015 mg/kg IV) of atropine in dogs with an experimentally induced oculorespiratory cardiac reflex may actually enhance respiratory depression. Higher doses of

Preanesthetic medications

atropine (0.023–0.04 mg/kg) may eliminate the bradycardia but prolong the apnea. Of these two complications, clinical management of apnea with controlled ventilation is the most feasible solution. An alternative to atropine in the dog is glycopyrrolate (0.01 mg/kg IV, usually given in two divided doses; often the second dose is not necessary) which appears as effective in preventing the oculorespiratory cardiac reflex but produces tachycardia. Under most circumstances, if the oculorespiratory cardiac reflex develops during ophthalmic surgery, surgery is suspended for several minutes and the depth of general anesthesia is increased. Less aggressive surgery is then slowly resumed while the respiratory and cardiac rates are carefully monitored. Fortunately, the onset of the oculorespiratory cardiac reflex is usually in the early aspects of surgery, and in intraocular surgical procedures before critical manipulations have begun.

Eye position During the induction of general anesthesia most injectable and inhalational anesthetics produce a downward and inward rotation of the eye that limits access to the cornea, anterior chamber, and anterior segment. As the globe is rotated ventromedially, the nictitating membrane simultaneously protracts to nearly cover the cornea. Some degree of enophthalmia also develops, decreasing further the exposure of the cornea and globe for surgery. In the large and giant breeds of dogs, access to the eye is already limited, and these drug effects can severely compromise surgical exposure of the eye. This poor positioning of the globe can handicap the surgeon by impairing observation of the entire cornea and anterior segment, increasing the difficulties of surgical manipulations, and unnecessarily prolonging the surgery. Several strategies have been developed to correct the rotation of the globe and exposure difficulties associated with general anesthetics. Unfortunately, most of these remedies to improve exposure may also result in some additional operative risks. Sutures may be placed in the anterior sclera or the rectus muscle insertions, and anchored to the eyelid specula or drapes. Scleral clips may be used similarly. Retrobulbar injections with saline positioned directly into the extraocular muscle cone to push the eye forward, or external to the extraocular muscle cone to turn the globe, may also produce noticeable inward compression of the posterior segment and additional pressure on the vitreous body. The animal cornea and sclera unfortunately lack rigidity, unlike humans and primates in general, and with traction or compression these tunics may become distorted. For certain types of conjunctival and corneal surgery, the distortion of the globe associated with these procedures may be inconsequential. However, when intraocular surgical procedures are planned, any preventable pressure on the globe, in whole or in part, should be avoided. Administration of the different neuromuscular blocking agents has replaced the need for extrabulbar injections to manipulate the position of the globe for surgery.

Pupil size Pupil size has been used historically to monitor the depth of general anesthesia. Without local control by topical mydriatics or miotics, pupil size may vary from marked dilatation to pinpoint in the lighter levels of general anesthesia, to

progressive mydriasis with deep general anesthesia. For conjunctival and corneal surgical procedures, pupil size is often adjusted preoperatively depending upon the concurrent ophthalmic disease. Often the pupil is dilated. Druginduced iridocycloplegia helps reduce the pain associated with preoperative anterior uveitis, and pupil dilatation reduces the likelihood of posterior synechiae formation. In the event of corneal and intraocular surgery, control of pupil size may become critical. Maximum mydriasis is essential for cataract extraction; preoperative pupillary dilatation is usually achieved with 0.3% scopolamine combined with 10% phenylephrine, 1% atropine, or a combination of 1% atropine and 10% phenylephrine. Topical non-steroidal anti-inflammatory agents, such as 0.03% sodium flurbiprofen, can also assist in the maintenance of pupillary dilatation. Prostaglandins appear to be released when the anterior chamber is entered surgically and initiate strong miotic activity. Endocapsular phacoemulsification of canine cataracts requires maximal mydriasis. Without the combination of topical mydriatics, topical and parenteral corticosteroids, and non-steroidal anti-inflammatory agents, the microsurgical refinements and higher success rates for canine cataract surgery would not have been possible.

Extraocular muscular tone The extraocular muscles are well developed in the dog and, in addition to the four rectus and two oblique extraocular muscles, include the retractor oculi muscle that inserts onto the sclera under the rectus muscle insertions and behind the globe’s equator. This bulk of extraocular muscles may produce pressure and indent the posterior segment of the globe, even with optimal general anesthesia. The extraocular muscle pressure, combined with the low scleral rigidity of the dog, seems to be more important once the anterior chamber has been entered, as during cataract and lens removal. If general anesthetics also increase central venous pressure, additional orbital pressure on the globe may develop from the extensive venous plexuses within the orbit. In the cat, the effects of the extraocular muscles during general anesthesia seem less important than in the dog. This may be caused by the poorly developed cat extraocular muscles and the limited orbital space. As a result, increased pressure on the posterior segment is less important and does not appear to be a problem clinically. Several strategies have been developed to address the potential extraocular muscle pressure and its adverse effects when the anterior chamber has been entered surgically. Neuromuscular blocking agents have now become routine for canine and equine intraocular surgery; in addition to greatly reducing extraocular muscle tone, these agents result in optimal eye position for microsurgery.

Preanesthetic medications Preanesthetic medications are designed to facilitate a smooth induction of general anesthesia, and help prevent possible drug-related complications. The controversial routine use of parenteral atropine as an anticholinergic agent has already been discussed. Parenteral glycopyrrolate (0.01 mg/kg IM) is preferred because of fewer cardiac effects.

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Anesthesia for ophthalmic surgery

Sedatives and tranquilizers are often employed preoperatively, especially before intraocular surgery. Both sedatives and tranquilizers lower IOP, probably by increasing the outflow of aqueous humor. Among the phenothiazine tranquilizers, acepromazine maleate is the most frequently recommended. Acepromazine maleate (0.03–0.1 mg/kg IM) is frequently utilized, not only because of the resultant tranquilization, but also for its anti-arrhythmogenic effect associated with the stabilization of the myocardium against catecholamine stimulation and arrhythmogenic agents. The phenothiazine tranquilizers also possess an anti-emetic action perioperatively. Both postoperative vomiting and retching in humans can elevate IOP indirectly by abrupt venous pressure increases. The same effect probably occurs in dogs. Xylazine is not recommended perioperatively in ophthalmic patients because it can cause vomiting and severe bradycardia. Acepromazine may slightly prolong the recovery from general anesthesia, hypothermia, and arterial hypotension, but usually provides a smoother, less traumatic recovery. Most narcotics seem to slightly lower IOP in those animal species studied. The two major advantages of narcotics are that: 1) these drugs are potent analgesics; and 2) they can be chemically antagonized if drug reversal is necessary. Unfortunately, most of these agents except for meperidine are also potent vagotonic and respiratory depressants. Use of narcotic derivatives prior to and following ophthalmic surgery has become more frequent. Occasionally, if the postoperative recovery becomes traumatic, parenteral narcotics are quite effective, probably because of the analgesic effects.

Injectable general anesthetics Most barbiturates lower IOP in animals. This ocular hypotension seems to result from depression of the diencephalon, an increased facility of aqueous humor outflow, and relaxation of the extraocular muscles. Ultrashort-acting barbiturates, such as thiopental and thiamylal (8–12 mg/kg IV) are effective induction agents. The reduction in IOP after administration of these drugs seems to be related to relaxation of the extraocular muscles and an increase in aqueous humor outflow rather than from arterial blood pressure changes. As these agents are potent respiratory depressants, endotracheal intubation should follow immediately after barbiturate administration. Intubation should be standard protocol in all ophthalmic surgical patients. Intermittent and often copious lavage of the corneal and conjunctival surfaces during surgery may exit the nasolacrimal system and accumulate in the mouth and pharynx. Ketamine may be an exception to the rule for injectable anesthetics. Elevated IOP has been associated with ketamine, with increased tone of the extraocular muscles in humans. Ketamine, recommended for the cat, has been reported to either not change or increase IOP in the cat by 10%. Ketamine, used alone, is not recommended for the dog because of its tendency to produce seizures. Ketamine, a dissociative anesthetic, may be injected intramuscularly for the induction of general anesthesia in cats. Ketamine is often combined with diazepam in dogs to reduce the possibility of seizures and produce muscular relaxation. An anticholinergic, such as atropine, is also administered to

40

minimize salivation. After general anesthesia is sufficiently deep to permit intubation, general inhalational anesthesia may be initiated for longer duration surgeries. There are other injectable agents that are now used as induction agents for small animals, and experiences with some of these agents, such as propofol, midazolam, and TelazolW, have been excellent. Propofol, as an induction agent, has a recommended intravenous dose in small animals of 6 mg/kg, and then to effect, and has largely replaced the barbiturates. After rapid, smooth and excitement-free onset of general anesthesia, the duration is also relatively short (range 2.5–9 min). Usually administered as a slow bolus injection (to avoid apnea) for the induction of inhalational anesthesia, propofol can be injected repeatedly; however, its short duration of effect requires several injections for relatively short periods of time. Recovery after propofol is usually very rapid, and excitement free. Propofol is thought to lower IOP. Propofol has become the preferred induction agent world-wide in small animals, and the sole general anesthetic for many short-term ophthalmic procedures. Propofol (2,6-diisopropylphenol) is only soluble in water, and is mixed immediately before use. It comes in sterile glass ampoules and without preservatives. It fits a twocompartment open model, with rapid distribution from the plasma into the tissues and rapid metabolic clearance from plasma. It is metabolized by conjugation primarily by the liver and kidney. It is administered as an intravenous bolus at doses that range from 2.5 mg/kg (sedated dog) to 8 mg/kg (unsedated dog) to allow tracheal intubation and the initiation of inhalational anesthesia. Propofol’s anesthesia is quite brief; in unsedated dogs recovery is only 15 min. Propofol can also be used for the maintenance of anesthesia administered by continuous infusion or intermittent bolus. Propofol has minimal analgesic effects, and drugs with analgesic effects, such as opiates, should be administered concurrently. Propofol lowers IOP in humans, and this effect has also been reported in dogs (a decline of 26%). Midazolam is a water-soluble benzodiazepine. It does not induce anesthesia when used alone; hence midazolam is often combined with ketamine, or one of the ultrashortacting thiobarbiturates (thiamylal or thiopental) to induce general anesthesia. TelazolW consists of equal parts of a dissociative agent, tiletamine, and a benzodiazepine, zolazepam. Once in solution, TelazolW has a limited shelf-life of 4 days at room temperature and 14 days at 4 C. The recommended dose for dogs is 6.6–13.2 mg/kg IM or SC, and for cats 9.7– 15.8 mg/kg IM or SC. After deep intramuscular injection of TelazolW, onset of anesthesia is within 2–5 min and the recovery to walking requires 3–5 h. Induction of anesthesia with TelazolW is usually smooth, but recovery can be traumatic.

Inhalational general anesthetics All of the available inhalational general anesthetics lower IOP. The extent of ocular hypotension is directly related to the depth of general anesthesia. The lowering of IOP after inhalational anesthetics seems to result from collective drug actions on the respiratory, circulatory, and central nervous systems. The changes in arterial pressure associated with inhalational anesthetics do not seem to lower the IOP per se, but central venous pressure can be important. Changes

Neuromuscular blocking agents

Neuromuscular blocking agents Neuromuscular blocking agents have recently been added to the general anesthetic protocol for ophthalmic patients to improve exposure of the cornea and eye during intraocular surgery. Administration of neuromuscular blocking agents in dogs produces relaxation of all of the extraocular muscles, and within 30–60 s causes the eye to return to its normal axis from the ventromedial deviation associated with most general anesthetic agents (Fig. 3.1). In cats administered succinylcholine, the globe may assume a superolateral divergent position. Neuromuscular blocking agents have the potential to influence IOP depending on their mechanism of action. In humans, d-tubocurarine lowers IOP by relaxation of the extraocular muscles; however, if the patient hypoventilates,

A

B Fig. 3.1 Position of the canine eye under general anesthesia (a) before and (b) after the administration of neuromuscular blocking agents. Note the improved exposure of the cornea and globe.

leading to hypercarbia and hypoxemia, IOP may increase. In contrast, succinylcholine administered intravenously can elevate IOP in several animal species including the dog and cat (Fig. 3.2). The transient increase in IOP occurs almost immediately after succinylcholine administration, and appears to be directly associated with initial contraction of the extraocular muscles during the depolarization process. In humans, reported sensations after administration of succinylcholine include a feeling of increased orbital pressure, vertigo, and diplopia. The effect on IOP by parenteral succinylcholine is influenced by the level of general anesthesia at the time succinylcholine is administered. In unanesthetized persons, the average elevation of IOP after succinylcholine administration was 15 mm Hg. In light levels of general anesthesia after succinylcholine administration, IOP is usually increased 2–4 min later; during deep general anesthesia IOP is not affected. The period for drugrelated elevation in IOP is usually 5–6 min. 50

Effect of succinylcholine on IOP in the dog

40 IOP (mmHg)

in blood gases and the methods of ventilation may also influence IOP. Some of these agents may also lower IOP by increasing the facility of aqueous humor outflow. Prolonged general anesthesia with changes in blood pH and other complications may actually increase IOP. For instance, experiments in dogs with increased inspired CO2 indicate that IOP may rise after initial depression. Hypoventilation that leads to hypercapnia and hypoxemia can eventually result in elevation of IOP. Although some species differences may be present, the reduction in IOP after inhalational general anesthetics may be substantial. Methoxyflurane in humans can lower IOP by 15–25%. Halothane-induced ocular hypotension in children may be of greater magnitude in glaucomatous eyes than in normal eyes, but with more variability. Methoxyflurane in dogs presented for cataract surgery lowers IOP an average of 11 mm Hg with a range of 5–20 mm Hg. Isoflurane is the most frequently used inhalational general anesthetic for veterinary ophthalmic surgery (dog, cat, and horse most frequently), and has largely replaced halothane during the last decade. Halothane produces rapid induction and recovery associated with dose-related depression of the central nervous system. When combined with preanesthetics, such as acepromazine, the need for halothane is reduced. Halothane produces more depression of cardiac function than methoxyflurane, and causes more cardiac dysrhythmias than isoflurane. Halothane causes higher cardiac sensitivity to catecholamines; lidocaine (2–4 mg/kg IV in dogs and 1–2 mg/kg IV in cats) can be used to treat these arrhythmias. If adrenaline (epinephrine) is planned for hemostasis during ophthalmic surgery, isoflurane should be selected over halothane. Halothane is a poor analgesic, and is usually combined with nitrous oxide. Isoflurane is now preferred to halothane. The drug is nonflammable at anesthetic concentrations, is highly stable, and is not broken down by sunlight. Isoflurane has a faster onset of action and recovery because of its low blood solubility. Like halothane, isoflurane depresses cardiovascular function in a dose-dependent manner, but is less arrhythmogenic than halothane. Isoflurane may be used in patients with hepatic disease because it is minimally metabolized by the liver. At this time, isoflurane is recommended as the general anesthetic of choice for most aged and debilitated small animal patients. Sevoflurane is also becoming popular in many veterinary practices world-wide.

Drug 30 20

Control

10 0

0:00 0:01 0:02 0:03 0:04 0:05 0:06 0:07 0:08 0:09 0:10 Minutes n = 5 eyes

Fig. 3.2 The effect of IV succinylcholine on intraocular pressure (IOP) (mm Hg) in dogs under light general anesthesia.

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Anesthesia for ophthalmic surgery

Studies in normal cats suggest that succinylcholine not only elevates IOP an average of 10–12 mm Hg, but also causes a forward displacement of the lens and iris when the anterior chamber is open. In an extracapsular cataract extraction, any forward displacement of the iris, lens, and presumably the vitreous is a cause for concern. If this effect occurs during the latter part of extracapsular cataract extraction, the thin posterior lens capsule is a weak barrier to increased pressure generated with the vitreous body. While succinylcholine acts as a depolarizing neuromuscular agent, members of the non-depolarizing relaxants, including d-tubocurarine, gallamine triethiodide, and pancuronium bromide, have not been associated with a drug-related elevation in IOP. Newer neuromuscular blocking agents used clinically, such as pancuronium bromide, vecuronium, and atracurium besylate, have shorter dose-related effects (Table 3.1). As inactivation of these neuromuscular blocking agents depends on the patient’s plasma anticholinesterases, concurrent use of potent topical anticholinesterase miotics in glaucomatous patients, such as echothiophate iodide and demecarium bromide, is contraindicated. Drugs available for reversal of these neuromuscular relaxants include edrophonium, neostigmine, and pyridostigmine. The neuromuscular blocking agents include atracurium, pancuronium, alcurium, and vecuronium. Atracurium besylate has minimal cardiovascular effects at recommended doses, has a relatively short duration of action without apparent cumulative effects, and elimination is independent of liver and kidney function. An intravenous bolus of atracurium (0.25 mg/kg), injected over 1 min, usually provides paralysis of the dog for about 30 min. For an additional intravenous bolus of atracurium, the dosage is reduced to 0.15 mg/kg. Atracurium can be antagonized, if necessary, with intravenous edrophonium at a dose of 0.5 mg/kg. Bradycardia has been associated with edrophonium administration. Either atropine administered previously or the very slow injection of edrophonium minimizes this effect. Neostigmine (2.5 mg), combined with atropine (1.2 mg), can also be used intravenously to antagonize the effects of atracurium. The total dose of neostigmine should not exceed 0.1 mg/kg. Pancuronium bromide is another frequently used neuromuscular blocking agent for canine intraocular surgery. An intravenous injection of pancuronium (0.06 mg/kg) causes a maximum neuromuscular blockage of 3–5 min that produces skeletal muscle relaxation and apnea for about 40 min. However, these muscle relaxants are not anesthetics. For their proper use, the patient’s respiration is carefully controlled by mechanical ventilation, neuromuscular and cardiovascular functions are adequately monitored, and the Table 3.1 Doses and length of paralysis with non-depolarizing neuromuscular blocking agents in dogs

42

Drug

IV dose (mg/kg)

Length of effect (min)

Atracurium

0.5

15–80

Alcurium

0.06–0.1

30–40

Pancuronium

0.06–0.1

20–40

Vecuronium

0.06–0.1

15–20

inhalational general anesthetic is administered at sufficient levels to maintain unconsciousness and analgesia. Without adequate ventilation, these agents may cause respiratory acidosis within as short a time as 5 min. Most general anesthetics cause a ventromedial rotation of the globe, and local attempts to improve exposure of the eye have significant limitations and complications. After the administration of neuromuscular relaxants, the globe position returns to normal, permitting optimum surgical exposure, and IOP appears low. With pancuronium (0.06 mg/kg IV), the ocular changes persist for about 20–30 min following drug administration. The relaxation of the extraocular muscles releases the normal pressure on the globe, and the forward displacement of the vitreous, lens, and anterior uvea is minimal. Use of these neuromuscular blocking agents may contribute directly to improved cataract surgery results in dogs. Once the anterior chamber is surgically entered, and the majority of the cataract removed via extracapsular extraction or phacoemulsification, the forward displacement or central protrusion of the posterior lens capsule within the pupil is reduced as much as possible (Fig. 3.3). With reduced vitreous pressure on the posterior lens capsule, posterior lens capsule tears during surgery are kept to a minimum. Neuromuscular blocking agents that provide about 20– 40 min of muscle relaxation are the most useful (see Table 3.1). These agents are usually administered just before the anterior chamber is entered, and should provide extraocular muscle relaxation for the duration that the anterior chamber is open, the lens is delivered, and most if not all of the time for the apposition of the corneal or limbal wound. If an additional dose is necessary, as with bilateral cataract surgeries, the second dose of neuromuscular blocking agent is usually reduced by one-half.

Ophthalmic drug and anesthetic drug interactions Sometimes the ophthalmic medications and drugs associated with general anesthesia have possible conflicts. For instance, the preoperative treatment of the eye may involve a topical cholinergic miotic, but the anesthetic protocol includes the administration of parenteral anticholinergic agents, such as atropine. Fortunately, the effects of topical ophthalmic drugs are usually predominant because of the systemic dilution that occurs with parenteral drugs. For instance, studies indicate that parenteral glycopyrrolate (0.01 mg/kg IM) in normal dogs does not have any effect on IOP and pupil size. Parenteral atropine and glycopyrrolate at the recommended clinical doses in dogs with glaucoma do not elevate IOP. Other ophthalmic drugs may impact the management of the patient about to be anesthetized. Systemic carbonic anhydrase inhibitors are administered to lower IOP, but can produce a temporary metabolic acidosis and considerable diuresis. Anticholinesterase miotics used for the treatment of glaucoma can reduce the levels of plasma and red blood cell cholinesterases, rendering the patient more sensitive to the neuromuscular blocking agents and causing a prolonged effect. Fortunately, use of miotics for the treatment of glaucoma has become infrequent, and generally replaced by the prostaglandins.

Local or regional eyelid injections/nerve blocks

Fig. 3.3 Effects of extraocular muscle tone during general anesthesia on the posterior lens capsule (a) after extracapsular cataract removal. (b) Changes in the posterior lens capsule after the administration of neuromuscular blocking agents.

A

B

Hyperosmotic agents, such as mannitol and glycerol, are used in veterinary ophthalmology for short-term reduction of IOP, and to reduce the size of the vitreous body preoperatively. In patients with cardiac and pulmonary disease, acute increases in vascular volume associated with hyperosmotic agents may be highly significant. Topical sympathomimetic agents, such as 2% adrenaline (epinephrine) and 10% phenylepinephrine, are important to the veterinary ophthalmologist for their effect on IOP and as mydriatics. Adrenaline (epinephrine) may also be injected (1:10 000 to 1:100 000 concentrations) into the anterior chamber for mydriasis, and to control iridal hemorrhage. Use of halothane as the general anesthetic with these adrenergic agents is associated with occasional extrasystoles and arrhythmias, because the myocardium has been sensitized to these catecholamines. Selection of isoflurane as the general anesthetic for these patients is recommended.

Systemic diseases and general anesthesia Many ophthalmic surgical candidates may have certain systemic diseases that potentially can affect the choice of general anesthesia, the duration of general anesthesia, and the administration of other drugs. In cataract surgery in dogs, animals with diabetes mellitus are the second largest group of patients following those with inherited cataracts. In fact, cataract secondary to diabetes mellitus is the most frequent type of metabolic cataract in the dog and the second most frequent cataract surgery in America. Successful clinical management of the diabetic dog with cataract must not only accommodate the daily control of blood glucose levels, but also control the lens-induced uveitis for optimal success rates after cataract removal. One strategy in diabetic dogs is to substitute aspirin for systemic prednisolone. Topical antiprostaglandins can also reduce the dosage for systemic corticosteroids as well as antiprostaglandins, such as carprofen (RimadylW; Pfizer Animal Health, Exton, PA) and flunixin meglumine (BanamineW; Schering-Plough, Kenilworth, NJ). Administration of topical corticosteroids and even systemic prednisolone may be necessary in some diabetic dogs for treatment of lens-induced uveitis after cataract surgery. Some elevation of blood glucose levels may occur with both topical and systemic corticosteroids in postoperative diabetic dogs. Maintenance of preoperative levels of insulin

doses is usually best in these dogs, until the topical and/or systemic levels of corticosteroids can be reduced or eliminated. Oral glycerin to lower IOP and reduce the vitreous space is not recommended in diabetic dogs as the glycerin is converted to blood glucose. Intravenous mannitol does not elevate blood glucose, and is the recommended systemic osmotic agent for the dog and cat. Systemic hypertension occurs mainly in older dogs and cats, and its presence can complicate intraocular surgery as well as potentially contribute to postoperative intraocular hemorrhage and retinal detachments. The development of these sequelae following apparent successful cataract surgery with an intact corneal or corneoscleral incision should necessitate periodic monitoring of blood pressure. Clinical management of these complications must include successful treatment of the systemic hypertension. Dogs with advanced renal, cardiovascular, and hepatic diseases are not usually candidates for elective intraocular surgeries. Unless these diseases are successfully treated and the animals’ life span significantly increased, the risks and costs of general anesthesia and time for surgery generally negate elective intraocular surgeries in these patients.

Local or regional eyelid injections/ nerve blocks Eyelid injections are used more often in large animals than in small animals for eyelid akinesia, but not local anesthesia, and are targeted at the palpebral nerve and its branches as it extends forward to innervate the orbicularis oculi muscle, the powerful sphincter muscle that closes the upper and lower eyelids. In general, as these palpebral nerve blocks are placed closer to the palpebral fissure, the effects are more localized as the main nerve trunk branches into numerous smaller nerves. Often topical anesthetics are instilled along with eyelid nerve blocks to provide surface anesthesia and permit detailed ophthalmic examinations, subconjunctival injections, collection of samples from the cornea and conjunctiva for cytology or culture, applanation tonometry, and other minimally invasive procedures. The exception in the horse is the supraorbital nerve block, in which local anesthetic is injected at the supraorbital foramen, which provides both mid upper lid akinesia and local anesthesia. Local ophthalmic nerve blocks in large animals

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Anesthesia for ophthalmic surgery

are used for ophthalmic examinations, especially in the horse, and as an adjunct for local or general anesthesia as part of eyelid, orbital or ocular surgery.

Eyelid injections/nerve blocks in the dog Eyelid injections are used in the dog both for eye examination in dogs with very painful ophthalmic disorders, as well as for therapy. Spastic entropion in the dog, a relatively rare condition, may also benefit immediately from the palpebral nerve block. For akinesia of the dog eyelid, local anesthetic (1–3 mL) may be injected subcutaneously along the upper zygomatic arch at its most lateral position or approximately 1–2 cm posterior to the lateral canthus (Fig. 3.4). An effective anesthetic block is demonstrated by drooping of the upper eyelid, an inability to close the palpebral fissure with a fixed and relaxed orbicularis oculi muscle, and an everted lower eyelid. The dog continues to have complete sensitization of the cornea, conjunctivae, and lid surfaces, as well as ocular mobility, and topical anesthetics are usually also instilled to permit minimally invasive diagnostic and therapeutic procedures.

Eyelid injections/nerve blocks in the cat Eyelid injections have not been reported in the cat, but the palpebral nerve pathway in this species is similar to that of other carnivores.

Eyelid injections/nerve blocks in the horse Because the horse’s orbicularis oculi muscle is very powerful, eyelid closure can occur during an eye examination as well as during drug administration in spite of manual efforts by the veterinarian or owner to maintain the palpebral fissure open. As a result, eyelid nerve blocks for akinesia, as well as combined akinesia–anesthesia nerve blocks, are available and used very frequently in the horse (Fig. 3.5).

Fig. 3.5 To perform the palpebral nerve block in the horse, local anesthetic is injected subcutaneously at the highest projection of the zygomatic arch (palpebral nerve only – A), in the groove immediately caudal of the zygomatic arch (B – contains the auriculopalpebral nerve, artery, and vein), or in the supraorbital fossa within the supraorbital process of the frontal bone (C). The first two nerve blocks provide only lid akinesia while the supraorbital nerve block provides both akinesia and analgesia of the mid upper eyelid.

Two different palpebral nerve blocks are frequently used in the horse to produce eyelid akinesia. The most popular is injection of about 1–3 mL of local anesthetic subcutaneously at the highest point of the zygomatic arch, midway in the arch. In the second method, 1–3 mL of local anesthetic is injected in the depression or groove of the ventral edge of the temporal portion of the zygomatic arch, just caudal to the posterior ramus of the mandible. Just before injection of local anesthetic, aspiration is used to check the needle position and avoid injection into the rostral auricular artery or vein. As this nerve block is close to the main trunk of the auriculopalpebral nerve, occasionally more extensive facial nerve block effects may occur, including muscle block effects down to the nostril, as well as a drooping and immobile ear. Topical anesthetic is also instilled for surface anesthesia of the cornea and conjunctiva. The combined akinesia and local analgesia (anesthesia) supraorbital nerve block in the horse is used for diseases localized to the mid upper eyelid. Between 2 and 4 mL of local anesthetic is injected about the supraorbital foramen within the supraorbital arch. Topical anesthetic is also instilled for surface anesthesia of the cornea and conjunctiva.

Eyelid injections/nerve blocks in the cow Eyelid injections in cattle are usually combined with retrobulbar nerve blocks which provide orbital and ophthalmic akinesia and analgesia (anesthesia) during orbital and eyelid surgery. Local anesthetic (2–4 mL) is injected just caudal of the lateral canthus to block the terminal branches of the palpebral nerve.

Retrobulbar injections/nerve blocks in animals

Fig. 3.4 For the palpebral nerve block in the dog, the local anesthetic injection is positioned either immediately above the most lateral projection of the zygomatic arch or about 1–2 cm from the lateral canthus.

44

In non-primates the lateral and part of the caudal floor of the bony orbit is usually open and devoid of bony walls. These areas, consisting of fascial tissue (periorbita), muscles, and blood vessels, and covered with either skin or mucosa, represent potential entry sites for access to the orbital tissues and the injection of drugs. In non-human primate species,

Retrobulbar injections/nerve blocks in animals

orbital access is generally limited to the frontal approach around the intact globe.

Retrobulbar injections/nerve blocks in dogs Access to the cornea and anterior globe may present exposure problems in small animals, especially in certain breeds of dogs. Fortunately, the lateral and dorsolateral aspects of the dog orbit are incomplete, and accommodate retrobulbar injections. Injections of sterile 0.9% saline can enhance the presentation of the cornea and globe, but only with some risk. The injection is performed with the dog under general anesthesia with the objective of forcing the globe further rostrad in the orbit, or to turn the globe and improve exposure of a selected area of the cornea and/or anterior segment. Providing retrobulbar anesthesia is another consideration. The amount of sterile saline injected is ascertained as the injection is performed, and the response of the globe to the space-occupying solution is assessed. The hypodermic needle may be inserted caudal to the junction of the lateral orbital ligament and dorsal aspects of the zygomatic arch (Fig. 3.6). The needle is directed towards the retrobulbar space in a ventromedial direction toward the opposite mandibular joint. The solution may be injected in the lateral aspects of the extraocular muscle cone, or immediately caudal to the globe and within the retrobulbar muscle mass. Injections external to the retrobulbar muscle cone will rotate the globe laterally; injections immediately behind the globe will push the globe forward. The volume injected should be limited to produce the desired outcome, but not result in undue pressure and distortion of the globe. Another injection site is ventral to the anterior zygomatic arch and rostrad to the vertical portion of the ramus of the mandible, the Barth’s nerve block (Fig. 3.7). The hypodermic needle, after passing the ramus of the mandible, is directed

Fig. 3.7 Barth’s method for retrobulbar injection in the dog consists of placement of a 5–8 cm, 22 g hypodermic needle inserted beneath the zygomatic arch at the level of the lateral canthus. The needle must pass rostrad to the vertical portion of the ramus of the mandible and directed to the orbital fissure.

toward the orbital fissure. Injections external to the retrobulbar muscle cone in the orbital floor and the medial orbit wall are possible with this method, and can be used to shift the globe dorsally. Retrobulbar injections can also be performed with curved, 5 cm long hypodermic needles directed through the conjunctiva or the eyelids to deposit solution beside or caudal to the globe (Dietz’s method). The volume and position of the injection within the orbit will shift the eye accordingly.

Retrobulbar injections/nerve blocks in cats Retrobulbar injections in the cat are not recommended because of the limited retrobulbar space and difficulty in proper positioning of the injection.

Retrobulbar injections/nerve blocks in horses

Fig. 3.6 Retrobulbar injections can be positioned in the dog with an 8 cm, 22 g hypodermic needle inserted caudal to the lateral orbital ligament and directed toward the opposite mandibular joint. Because the dog lacks ocular rigidity, extraocular injections that are several milliliters can indent the globe. Injections within the extraocular muscle cone may have greater effects than those injected next to the orbital walls.

Retrobulbar local anesthetic injections have been described in the horse by Berge and Lichenstern. The posterior orbit and entry of the critical cranial nerves in the horse are about as deep as in cattle (10–12 cm), but the posterior orbit is more conical. With gas inhalation general anesthesia, and often neuromuscular blocking agents and forced ventilation, retrobulbar nerve blocks in the horse are unnecessary and redundant. In the Berge method, an 8–10 cm, 18 g needle is inserted caudal to the supraorbital process of the frontal bone near the supraorbital foramen. The long needle is directed ventromedial (about 40 from the vertical) and slightly caudal toward the area of the orbital fissure where 15–20 mL of local anesthetic is injected (Fig. 3.8). In a modification of the Berge technique, in the Lichenstern’s method, an 8–10 cm, 18 g needle is inserted 1.5 cm caudal to the middle of the supraorbital process. The needle is directed toward the opposite last upper premolar tooth. The taut extraocular muscles’ fascial cone may be felt as

45

3

Anesthesia for ophthalmic surgery

combined with neuromuscular blocking agents is highly recommended.

Retrobulbar injections/nerve blocks in cattle

Fig. 3.8 In Berge’s retrobulbar nerve block in the horse for injection within the orbital fissure, the needle is inserted behind the supraorbital foramen of the dorsal orbital rim, inclined 40 to the vertical, and directed medioventrally and somewhat caudally.

the needle penetrates it. Approximately 20 mL of local anesthetic is injected near the orbital fissure. As a third method, the lateral and medial canthal routes may be used to inject about 10–15 mL of local anesthetic at each site. Of the large animal species, intraocular surgery is performed most often in the horse. As this species has considerable high scleral elasticity (low scleral rigidity), sizeable volume retrobulbar injections can markedly indent the posterior segment (as viewed by ophthalmoscopy), and increase the likelihood of vitreous prolapse and posterior lens capsule rupture during cataract surgery. Therefore, when intraocular surgery is considered in this species, general gas anesthesia

A

Because of inherent problems associated with general anesthesia in cattle, as well as economics, regional nerve blocks are common in this species. In fact, most orbital, eyelid, conjunctival, and corneal surgery is performed with regional injectable anesthesia. Of the three different routes for orbital injections of regional anesthesia in the cow, i.e., Peterson’s, Schreiber’s, and Hare’s, Peterson’s is the most common in America, but somewhat more difficult. A relatively simple method in cattle, the four-point block, uses more local anesthetic than the Peterson method, and delivers retrobulbar anesthetic through the dorsal, medial, lateral, and ventral conjunctival fornices directly into the retrobulbar space. In Peterson’s regional nerve block, an 8–10 cm, 18–20 g slightly curved hypodermic needle is inserted at the posterior angle of the zygomatic arch and lateral orbital rim, and directed anterior of the coronoid process of the mandible and inferomedially to the pterygopalatine fossa near the foramen orbitorotundum (Fig. 3.9). After aspiration (avoiding the internal maxillary artery), 15–20 mL of local anesthetic is injected. The auriculopalpebral nerve is blocked by placing 3–5 mL of local anesthetic subcutaneously along the dorsal zygomatic arch. Successful nerve blocks result in mydriasis, lack of globe mobility, loss of corneal sensation, and loss of eyelid movement. The globe in some cows can be proptosed moderately, and maintained in position by the eyelids.

Complications of retrobulbar injections/ nerve blocks Retrobulbar injections require care, and can induce retrobulbar hemorrhage. Hence, after needle placement and before injection, aspiration is attempted to minimize injection into the ocular vasculature. The animal orbit contains large veins

B

Fig. 3.9 In the Peterson retrobulbar nerve block in cattle: (a) View from side of orbit: A slightly curved, 10 cm hypodermic needle is inserted in the caudal angle (arrow) of the supraorbital process and zygomatic arch, and manipulated in front of the coronoid process of the mandible. (b) Frontal view: The hypodermic needle is then directed medial and somewhat ventrally to enter the floor of the pterygopalatine fossa and the orbitorotundum foramen (arrow). After aspiration to make certain the maxillary artery has not been entered, approximately 15–20 mL of local anesthetic is injected. As the hypodermic needle is withdrawn, an additional 3–5 mL of local anesthetic is injected subcutaneously for akinesia of the eyelids.

46

Horse

and venous plexuses, but hemorrhage sufficient to produce additional pressure of the globe, and even enter the subconjunctival spaces, fortunately occurs infrequently. If this occurs, surgery should be delayed until the hemorrhage has reabsorbed. Inadvertent puncture of the globe with the needle is rare, but a serious complication. The retrobulbar saline is usually reabsorbed within 30–60 min. With the use of intravenous neuromuscular blocking drugs, use of retrobulbar injections to manipulate the globe is less common and may be redundant. A few cases of cattle have been reported to suffer respiratory collapse and sudden death after the Peterson retrobulbar block, presumably from accidental anesthetic injection within the optic nerve meninges or the cerebrospinal space.

Choice of general anesthetic for selected ophthalmic surgical procedures The ophthalmic surgical procedure may influence the choice of induction agent and general anesthetic based on the expected duration of the surgery, and the level of pain and discomfort expected postoperatively.

Orbital surgery Orbital surgery is expected to result in some blood loss, and excessive globe traction may initiate the oculorespiratory cardiac reflex. In small animals, a combination of injectable and inhalational anesthetics is used to provide general anesthesia for about 60 min. The administration of acepromazine preoperatively will usually assist in promoting a smooth recovery.

Eyelid surgery Surgical procedures of the eyelids usually require induction with injectable anesthetics and continued general anesthesia with inhalational agents. Occasionally multiple administrations of only injectable anesthetics will suffice. In very young puppies with entropion, correction with the ‘tacking procedure’ often uses halothane anesthesia induced via mask.

Nasolacrimal flush and catheterization Only topical anesthesia (occasionally combined with acepromazine tranquilization, or in non-cooperative patients) is necessary for many of the manipulations required for the nasolacrimal system, including flushes, catheterization, and incisions to open the imperforate lacrimal punctum.

Conjunctival and nictitating membrane surgeries To perform nictitating membrane flaps and small eyelid or conjunctival tumor removals in small animals, propofol in dogs and cats, or ketamine in cats, is recommended. For conjunctival grafts, the time taken to perform these procedures is about 30–60 min. As a result, induction with a shortacting intravenous barbiturate, endotracheal intubation, and maintenance with inhalational anesthesia is recommended.

A smooth recovery is necessary, and usually an analgesic, such as butorphanol tartrate, is indicated.

Corneal and intraocular surgeries For corneal and intraocular surgical procedures, tranquilization with acepromazine, propofol for induction, and inhalation agents for maintenance of general anesthesia are recommended. The administration of neuromuscular blocking agents (such as pancuronium 0.06 mg/kg IV) is initiated once general anesthesia is stabilized and a few minutes before entry into the anterior chamber is achieved. Both a smooth onset and recovery from general anesthesia are anticipated. Some degree of analgesia is usually necessary during the immediate postoperative period, and often butorphanol tartrate or a similar drug is administered.

Recovery from general anesthesia During the recovery period after ophthalmic surgery, the patient should slowly and smoothly recover from general anesthesia. Excessive whining, yelping, barking, vomiting, and uncoordinated movement and thrashing are to be avoided. These effects may threaten the integrity of the surgical wounds and can result in trauma and swelling of the eyelids, subconjunctival hemorrhages, hyphema, and anterior uveitis. The optimum clinical management of these complications is to prevent their occurrence by the appropriate selection of perioperative drugs and general anesthetics. Tranquilizers, such as acepromazine, have a reasonably long duration of action, and this effect usually includes the critical postoperative period. The usual dosage for acepromazine is 0.03– 0.1 mg/kg administered intramuscularly or subcutaneously about 15 min before ophthalmic surgery. The lower dosage level is best for older canine patients; the higher dosage level is recommended for young, healthy, and excitable patients. Butorphanol tartrate, an opiate agonist/antagonist analgesic with strong antitussive activity, may also be administered postoperatively (0.5–1.0 mg/kg SC) to promote a smooth recovery from general anesthesia. Restraint devices, such as the Elizabethan collar, hobbles, and bandaging of the front paws, are additional measures that can protect the eye during the recovery phase from general anesthesia.

ADAPTATIONS FOR LARGE ANIMALS AND SPECIAL SPECIES

Horse The introduction of many drugs for sedation, analgesia, and restraint in large animals, especially the horse, has advanced significantly in the past 40 years. In the 1960s, sedation of horses for eye examination or minor invasive procedures involved only acepromazine, and was not very satisfactory. The introduction of xylazine in the 1970s, used singly or best combined with acepromazine, provided much improved sedation and adequate restraint for detailed ophthalmic examinations in horses with considerable

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Anesthesia for ophthalmic surgery

eye-related pain, as well as more invasive procedures (corneal cytology, nasolacrimal system cannulation, etc.). Nowadays, the availability of detomidine combined with butorphanol (introduced in the 1990s) provides deep sedation and the best possible restraint. In ranking available drugs for sedation and restraint in the horse, we would rank (from lowest to highest sedation):

• • • •

acepromazine (0.02–0.05 mg/kg IV; avoid in stallions because of the potential for priapism) xylazine (usual dose: 0.2–0.4 mg/kg IV) xylazine (0.6 mg/kg IV) combined with acepromazine (0.02 mg/kg IV) detomidine (our dose is 0.005–0.012 mg for an ophthalmic examination rather than the recommended 0.01–0.02 mg/kg used for pain or placing a lavage system) combined with butorphanol (0.02–0.03 mg/kg IV).

Probably most, if not all, sedatives lower IOP in horses. Acepromazine and xylazine lower IOP in horses by about 10–20%. Both xylazine and detomidine are a2-agonist sedatives. IOP decline seems secondary to venous pressure, direct pressure on the globe, blood pressure, tone in the extraocular muscles, head position, and the rate, dose, and rapidity of drug administration. Decline in IOP secondary to lower systemic blood pressures is the likely explanation. Intravenous xylazine at dosages of 0.3 mg/kg (23%), 1.0 mg/kg (27%), and 1.1 mg/kg combined with ketamine (2.2 mg/kg), lower IOP. The majority of ophthalmic surgeries performed in horses use general anesthesia, and for corneal surgery often involving penetrating corneal wounds, as well as surgery of the iris, lens, and cataracts, and neuromuscular paralysis for optimal globe positioning and ocular hypotony. However, general anesthesia is not without risk in the horse! Smooth recovery does not always occur in a horse coming out of general anesthesia, and a smooth recovery is hopefully

characterized by a horse which stands on its first attempt, and does not repeatedly struggle to stand and fall! Unsatisfactory and prolonged recoveries risk injury to the eye and limbs and other serious mishaps. Mortality with general anesthesia in the horse has been reported as 1.9%, and excluding those horses with emergency abdominal procedures, the death rate is 0.9%. Although complications with general anesthesia in horses undergoing ophthalmic surgery have not been reported, fatalities after ear, nose, and throat (ENT) procedures have been reported as 0.88%. As the length of time for the ophthalmic surgical procedure and general anesthesia increases, the likelihood of complications also increases. Fortunately, most ophthalmic procedures in the horse take less than 1 h, or perhaps slightly more! Standing ophthalmic procedures, including standing enucleation, have been reported in horses. Most equine standing surgeries are relatively minor; however, some may become too difficult, requiring use of general anesthesia for successful completion.

Cattle Cattle are most often physically restrained using its stanchion (dairy cattle) or a squeeze chute and variable head restraint (beef cattle). Sedation is generally not employed because of the bovine’s very high sensitivity to drugs, such as xylazine, and must be carefully administered. The recommended dose (see Plumb’s Veterinary Drug Handbook) is 0.05–0.15 mg/kg IV or 0.10–0.33 mg/kg IM. Pretreatment with atropine can decrease the bradycardia and hypersalivation. Xylazine should be avoided in pregnant cattle (last trimester) and in animals that are dehydrated, have urinary tract obstructions, or are debilitated.

Further reading General Auer U, Mosing M, Moens YPS: The effect of low dose rocuronium on globe position, muscle relaxation, and ventilation in dogs: a clinical study, Vet Ophthalmol 10:295–298, 2007. Brunson DB: Anesthesia in ophthalmic surgery, Vet Clin North Am Small Anim Pract 10:481–495, 1980. Gelatt KN: Anesthetic agents. In Veterinary Ophthalmic Pharmacology and Therapeutics, ed 2, Bonner Springs, 1978, VM Publishing, pp 23–28. Hall LW, Clarke KW: Veterinary Anaesthesia, ed 9, London, 1991, Baillie`re Tindall, pp 105–133. Kern TJ: Anesthetic considerations of the ophthalmic patient. In Short CE, editor: Principles and Practice of Veterinary Anesthesia, Baltimore, 1987, Williams and Wilkins, pp 173–176. Langley MS, Heel RC: Propofol: a review of its pharmacodynamic and pharmacokinetic properties and use

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as an intravenous anaesthetic, Drugs 35:334–372, 1988. Plumb DC: Plumb’s Veterinary Drug Handbook, ed 5, Ames, 2005, Blackwell, pp 327–329 and 1156–1160. Rubin LF, Gelatt KN: Analgesia of the eye. In Soma LR, editor: Textbook of Veterinary Anesthesia, Baltimore, 1971, Williams and Wilkins, pp 489–499. Wilson RP: Complications associated with local and general anesthesia, Int Ophthalmol Clin 32:1–22, 1993.

Canine Bagley LH, Lavach JD: Comparison of postoperative phacoemulsification results in dogs with and without diabetes mellitus: 153 cases (1991–1992), J Am Vet Med Assoc 205:1165–1169, 1994. Batista CM, Laus JL, Nunes N, PattoDos Santos PS, Costa JL: Evaluation of intraocular pressure and partial CO2 pressures in dogs anesthetized with propofol, Vet Ophthalmol 3:17–19, 2000.

Clutton RE, Boyd C, Richards DLS, Schwink K: Significance of the oculocardiac reflex during ophthalmic surgery in the dog, J Small Anim Pract 29:573–579, 1988. Frischmeyer KJ, Miller PE, Bellay Y, Smedes SL, Brunson DB: Parenteral anticholinergics in dogs with normal and elevated intraocular pressure, Vet Surg 22:230–234, 1993. Gelatt KN, Gwin RM, Peiffer RL, Gum GG: Tonography in the normal and glaucomatous Beagle, Am J Vet Res 38:515–520, 1977. Hazra S, De D, Roy B, et al: Use of ketamine, xylazine and diazepam anesthesia with retrobulbar block for phacoemulsification in dogs, Vet Ophthalmol 11:255–260, 2008. Hofmeister EH, Williams CO, Braun C, Moore PA: Influence of lidocaine and diazepam on peri-induction intraocular pressure in dogs anesthetized with propofol– atracurium, Can J Vet Res 70:251–256, 2006. Hofmeister EH, Williams CO, Braun C, Moore PA: Propofol versus thiopental:

Further reading effects of peri-induction intraocular pressures in dogs, Vet Anaesth Analg 35:275–281, 2008. Joffe WS, Gay AJ: The oculorespiratory cardiac reflex in the dog, Invest Ophthalmol 5:550–554, 1966. Magrane WG: Methoxyflurane (metofane) anesthesia in intraocular surgery, Pract Vet 3:75–76, 1967. Seim HB, Creed JE, Smith KW: Restraint techniques for prevention of self–trauma. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 42–49. Sullivan TC, Hellyer PW, Lee DD, Davidson MG: Respiratory function and extraocular muscle paralysis following administration of pancuronium bromide in dogs, Vet Ophthalmol 1:125–128, 1998. Vestre WA, Brightman AH, Helper LC, Lowery JC: Decreased tear production associated with general anesthesia in the dog, J Am Vet Med Assoc 174:1006–1007, 1979.

Young SS, Barnett KC, Taylor PM: Anaesthetic regimes for cataract removal in the dog, J Small Anim Pract 32:236–240, 1991.

Feline Hahnenberger EW: Influence of various anesthetic drugs on the intraocular pressure of cats, Von Graefes Archiv fu¨r klinische und experimentelle Ophthalmologie 199:179–186, 1976. Mester U, Stein HJ, Pillat-Moog U: Experiences gained with a combination ketamine anaesthesia for eye surgery on cats, Von Graefes Archiv fu¨r klinische und experimentelle Ophthalmologie 201:289–294, 1977.

Horse Brooks DE: Ophthalmology for the Equine Practitioner, 2009, Teton New Media, Jackson, pp 17–29. Hendrix DVH: Eye examination techniques in horses, Clinical Techniques in Equine Practice 4:2–10, 2005.

Miller-Michau T: Equine ocular examination: basic and advanced diagnostic techniques. In Gilger BC, editor: Equine Ophthalmology, St Louis, 2005, Saunders, pp 1–62. Robertson SA: Standing sedation and pain management for ophthalmic patients, Vet Clin North Am Equine Pract 20:485–497, 2004.

Food and fiber-producing animals Donaldson LL, Holland M, Koch SA: Atracurium as an adjunct to halothane– oxygen anesthesia in a llama undergoing intraocular surgery: a case report, Vet Surg 21:76–79, 1992. Pearce SG, Kerr CL, Boure LP, Thompson K, Dobson H: Comparison of the retrobulbar and Peterson nerve block techniques via magnetic resonance imaging in bovine cadavers, J Am Vet Med Assoc 223:852–855, 2003. Skarda RT: Local and regional anesthesia in ruminants and swine, Vet Clin North Am Food Anim Pract 12:579–626, 1996.

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CHAPTER

4

Surgery of the orbit Kirk N. Gelatt1 and R. David Whitley2 1

Small animals; 2Large animals and special species

Chapter contents Surgical management of orbital diseases

51

Orbitotomy in small animals

76

Ancillary diagnostic procedures

52

Total and partial orbitectomy

81

Surgical anatomy of animal orbits

53

Orbitotomy in large animals and special species

81

Surgical pathophysiology

57

Perioperative medications

59

Surgical management of traumatic proptosis in small animals

82

TYPES OF ORBITAL SURGICAL PROCEDURES

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Surgical augmentation of orbital volume in small animals

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Enucleation procedures in small animals

60

POSTOPERATIVE CARE AND MANAGEMENT

84

63

Postoperative complications and treatment in all species

84

Exenteration in small animals

67

Short- and long-term results in all species

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Enucleation procedures in large animals and special species

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Evisceration with intraocular prosthesis in small animals

Surgical management of orbital diseases Orbital diseases of small animals are common in veterinary practice and are often treated with a combination of medical and surgical modalities. Orbital diseases in animals are traditionally classified into those that cause exophthalmia (which is the largest group) and those associated with enophthalmia. Exophthalmia refers to an abnormal prominence or protrusion of the globe, and is associated with space-occupying diseases, including inflammations, cysts and neoplasms. Exophthalmia can be confused with megaloglobus or buphthalmia when prominence of the eye results from an enlarged globe, as in the glaucomas. Enophthalmia, which is less frequently encountered in veterinary ophthalmology practice, occurs when the globe is recessed into the orbit or is less prominent. Enophthalmia is associated with congenital orbital disorders, pain from inflammation, microphthalmia (a smaller than normal globe), phthisis bulbi (atrophy of the eye secondary to ciliary body destruction and limited to absent aqueous humor production), Horner’s syndrome, dehydration, loss of orbital fat, and fibrosis within the orbit.

Defining the margins of orbital disease Orbital diseases, particularly diffuse septic inflammation and expansive neoplasms, usually infiltrate the orbit within its fascial planes and confound determination of the disease margins, thereby limiting the success rate of surgery or radiotherapy. Before entering the orbit surgically, the disease process and its borders should be identified as best as possible, by the different imaging modalities, as thoroughly as possible. The orbit is highly vascular, and visualization of the different structures during surgery is often limited using only one technique. Vital nerves, blood vessels, and extraocular muscles span the orbital space between the different bony foramina and the globe, tear glands, nictitating membrane, conjunctiva, and eyelids. Although imaging procedures such as computed tomography (CT) and magnetic resonance imaging (MRI) are expensive, they often yield the best results. Fortunately, however, the orbit can be evaluated by a number of physical examination procedures, as follows. When exophthalmia is the presenting primary clinical sign, a number of additional more subtle clinical signs

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Surgery of the orbit

may assist in determining whether the space-occupying disease is inflammatory, cystic, or neoplastic. Primary orbital diseases associated with exophthalmia are usually unilateral, and comparisons of the orbital position and size of both eyes can be informative. If the exophthalmia is bilateral, systemic disease should be suspected. The inability of the animal to retropulse the globe or retract the globe upon eyelid or corneal touch often signals a sizeable space-occupying disease. With orbital inflammatory diseases, retraction of the extraocular muscles and globe may also elicit pain. With orbital cysts or neoplasia, the retropulse reflex is impaired but usually elicits no pain. Imaging techniques to evaluate the orbit initially include plain and special contrast radiologic procedures, and ultrasonography. More sophisticated diagnostic procedures such as CT and MRI offer the best imaging of orbital tissues, and fortunately their availability is increasing.

Strabismus and orbital diseases Strabismus refers to deviation of the globe, and is traditionally divided into dorsal (hypertropia), ventral (hypotropia), lateral (exotropia), and medial (esotropia). Primary strabismus without ocular disease is rare in animals. It has been reported in horses and mules, cattle, and dogs, but appears most frequent in cats, especially the Siamese and Himalayan breeds. Uni- or even bilateral strabismus may occur in dogs, secondary to myositis of selected extraocular muscles, and may be complicated by fibrosis of these muscles. Secondary strabismus is frequently present with orbital diseases, and the direction of the deviation of the globe may suggest the location of the space-occupying lesion. When space-occupying orbital disease is directly behind the globe and confined to the retrobulbar muscle cone, the eye is usually displaced directly forward. The pressure on the globe may be sufficient to indent areas of the posterior segment and be detectable ophthalmoscopically. If the space-occupying mass is located within the medial or ventromedial orbital or zygomatic salivary gland in animals, the resultant strabismus is usually lateral (exotropia) and/or dorsal (hypertropia). If the mass involves the rostral aspect of the medial orbit, the eye may be deviated upward, and the nictitating membrane is usually protracted. If the mass is located within the rostral aspect of the dorsal orbit, the eye is usually deviated downward (hypotropia). In spite of the strabismus, tonic eye reflexes and eye movements are usually normal.

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either resection or recession of affected extraocular muscles. The surgery is carried out at their insertions to the anterior globe, and is relatively easy to perform. Occasionally lateral strabismus develops after traumatic proptosis, and signals either nerve and/or muscle injury to the medial rectus muscle. If exotropia results from damage to the oculomotor nerve, spontaneous recovery often occurs. If the muscle or its insertion to the globe has been transected, recovery is unlikely. Attempts to reattach the severed ends of the medial rectus muscle are not usually successful as the deeper (proximal) aspects of the medial rectus cannot be located. Splitting the dorsal rectus muscle longitudinally and repositioning the medial portion to the medial rectus insertion provides satisfactory results. A fairly recent disorder in dogs, extraocular muscle myositis (also called fibrosing strabismus), usually presents with uni- or bilateral restrictive ventromedial strabismus and enophthalmia. Several breeds of dogs appear affected, but the large breeds as well as the Chinese Shar Pei seem most often affected. Involved muscles include the ventral rectus, ventral oblique, and medial rectus. Medical therapy includes immunosuppressive systemic therapy (prednisone and/or azathioprine) and early cases are the most responsive. Surgical correction usually involves resection of the affected muscle(s) or their insertion(s) rather than recessing the opposite muscle to straighten the globe (because of the inflammation and subsequent fibrosis of the affected muscles).

Ancillary diagnostic procedures If surgery on the orbit is anticipated, additional diagnostic procedures that can assist to define the borders of the orbital disease, and perhaps the type of mass, are recommended. Plain and contrast radiography, combined with B-scan ultrasonography, usually provides the most valuable basic information in most veterinary centers. Special radiographic procedures include venography, arteriography, optic nerve thecography, and the direct injection of air (pneumo-orbitography) or contrast material (positive contrast orbitography) into the orbit. Needle biopsy with B-scan ultrasonography may indicate the histologic characteristics of the orbital mass. CT scans and MRI have markedly improved the diagnosis and definition of orbital diseases in animals, but are currently limited to academic veterinary medical hospitals and large clinical centers.

Strabismus (rectus muscle) surgery

Incomplete orbital walls in domestic animals

Strabismus surgery is infrequently performed because the ocular malalignment usually signals ophthalmic disease. Extraocular muscle surgery for strabismus in the Siamese cat with esotropia has not been successful because of the very small rectus muscles in the cat as well as the underlying neuro-ophthalmic tract malformation. The congenital exotropia occasionally seen in brachycephalic breeds of dogs has not been treated with rectus muscle surgery. Strabismus is infrequent in horses and mules, and some affected horses may also exhibit night blindness (e.g., Appaloosa breed). Strabismus in the horse has been successfully treated by

In contrast to humans, most small and large animal orbital walls are incomplete caudoventrally and laterally. In the primate the contents of the entire orbit are bounded by bone, thereby providing maximum protection for the globe. In many avian species orbits are unusually large and often limit access through only the frontal aspects (like human and non-human primates). The incomplete orbital walls in dogs and cats seem associated with the ability to open the jaw as widely as possible. As a result, the coronoid process of the mandible is medial of the zygomatic arch and in the caudolateral orbit. Hence, in orbital diseases, especially

Surgical anatomy of animal orbits

acute inflammations, manipulation of the mouth will usually elicit pain. Where the bony orbital walls are missing in carnivores, the wall is replaced with a variable thickness fascial layer, the endorbita (or periorbita). In the caudal, dorsal, and lateral orbital walls, the temporalis, masseter, and pterygoid muscles are adjacent to the endorbita. The endorbita constitutes a reasonable barrier to inflammation, trauma, and neoplasia, but still does not provide the protection provided by bony walls. As a result, orbital diseases in small animals may extend from the orbit into the mouth via the caudal floor, perforate anteriorly to the conjunctival surfaces, or extend laterally into the subcutaneous tissues of the lateral orbit and face. While these regional soft-tissue orbital walls represent incomplete and weaker barriers, these same areas provide potential entry routes for surgical invasion of the orbital space.

Enophthalmia and surgery Enophthalmia (recession of the globe within the orbit) is a common clinical sign when the orbital contents are less than normal. The palpebral fissure may be reduced in size. The most frequent condition with enophthalmia is microphthalmia, a congenital and sometimes inherited condition, and phthisis bulbi or atrophy of the eye, an acquired disorder. Enophthalmia can also accompany Horner’s syndrome, the loss of fat associated with debility, dehydration, and pain. An emerging clinical problem in large and giant breeds of dogs is the ‘medial canthal pocket syndrome’, which consists of bilateral enophthalmia, persistent and chronic conjunctivitis, and entropion and/or ectropion secondary to the lack of support and contact between the globe and eyelids. This condition, occurring more frequently in male dogs, is associated with very large heads and deeply recessed eyes. It is difficult to treat medically and/or surgically and resolve. Augmentation of the volume of the orbit with a visual eye has been attempted by adding autogenous fat (usually about 70% is lost before its blood supply is restored), sterile glass beads (about 4–5 mm diameter), medical grade silicone, and newer microporous implants that permit vascular ingrowth into the device.

Surgical anatomy of animal orbits The orbit consists of walls that are either bone or muscle combined with fascia that confine and protect the globe. The anatomy of the orbit differs widely among humans and animals, and these differences modify the clinical manifestations of orbital diseases and their surgical approaches. The orbit in humans and animals is roughly conical in shape, with the apex of the cone directed ventroposteriorly and medially, and the base of the cone accommodating the globe and supporting tissues. Through the apex traverse the different nerves to innervate the extraocular muscles, the sensory nerves to the globe and surrounding structures, and the optic nerve linking the retina to the midbrain and higher visual centers. Adjacent areas, such as the frontal and maxillary sinuses, and the teeth roots within the maxillary bone, are frequent sites of infection and neoplasia that may extend into the orbit and produce clinical disease.

Canine orbit The bones that envelop and confine the orbital tissues in the dog consist of the zygomatic process of the frontal bone dorsally; the frontal bone and palatine bones medially; and the zygomatic arch and vertical ramus of the mandible laterally (Fig. 4.1a). The bony orbital floor is comprised of the sphenoid bone. The orbital rim consists of the zygomatic process of the frontal bone dorsally, the lateral orbital ligament, and parts of the zygomatic, maxillary, and lacrimal bones ventrally. Soft tissues that support the orbital walls include the temporalis muscles posteromedially, the temporalis and pterygoid muscles medially, the masseter muscle laterally, and the medial pterygoid muscle ventrally. The zygomatic or orbital salivary gland is located in the dog in the rostrolateral orbit. In brachycephalic breeds of dogs the orbit is very shallow, while in dolichocephalic breeds the orbit is considerably deeper and difficult to access surgically. The major arteries in the dog orbit are located along the ventral and ventromedial floor, and consist of the pterygopalatine portion of the maxillary artery with its various branches, including the external ophthalmic (orbital) artery, the infraorbital artery, the minor palatine artery, and a trunk that gives rise to the major palatine and sphenopalatine arteries. From the external ophthalmic artery are branches that include the external ethmoidal artery and the anastomotic ramus to the internal carotid artery. Branches from the external ethmoidal artery include, in part, the ventral and dorsal muscular branches to the extraocular muscles, the lacrimal and zygomatic branches. With the union of the external and internal ophthalmic arteries emerge two to four long posterior ciliary arteries to supply the globe. The orbital veins tend to follow the respective arteries, and, in addition, form an extensive and highly variable orbital venous plexus. With the origin of the majority of the extraocular rectus muscles in the apex of the orbit, these muscles span the orbit to insert anterior to the globe’s equator. The four bellies of the retractor oculi muscle envelop the optic nerve, and attach to the globe posterior to the rectus muscle insertions. The ventral oblique muscle has its unique origin in the medial orbital wall. Immediately above the dorsal rectus muscle is the levator palpebrae superioris muscle, with its common origin with the other rectus muscles but its insertion in the tarsal layer of the upper eyelid. In addition to an extensive arterial and venous supply, and space-filling adipose tissues, all the orbital tissues are covered with endorbita or the periorbital fascia that eventually merges with the fascia bulbi (or Tenon’s capsule) that surrounds the globe and attaches at the limbus, the periosteum or endorbita lining the orbital walls, and the tarsal layer within the eyelids as the septum orbitale anteriorly. The subTenon’s space between the fascia bulbi and the sclera is an important surgical plane that permits dissection around the globe with minimal hemorrhage. The third (oculomotor), fourth (trochlear), and sixth (abducens) cranial nerves innervate the retrobulbar muscles, and the second (optic), fifth (trigeminal), and branches of the seventh (facial) cranial nerves permit vision, sensation, and lacrimation (Fig. 4.1b). The orbit also contains

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Surgery of the orbit

A

B

Fig. 4.1 The bones of the canine orbit. The dorsolateral wall and caudal floor of the canine orbit consist of soft tissues. Entry into the canine orbit is restricted to these soft tissues avenues, as well as through the palpebral fissure and orbital opening. (a) The canine orbital anatomy varies considerably based on breed and skull type. The bony orbital rim is incomplete, and laterally is formed by the lateral orbital ligament. The bones that comprise the canine orbit include the frontal bone and its zygomatic process (A), palatine bone (B), zygomatic arch (C), and vertical ramus of the mandible (D). The bony orbital floor consists of the sphenoid bone (not visible). The orbital rim consists of the zygomatic process of the frontal bone (see A), and parts of the zygomatic (see C), maxillary (E), and lacrimal (F) bones. The lateral orbital ligament (missing in this specimen) extends from the zygomatic process of the frontal bone to the zygomatic arch (arrows). Surgical access to the canine orbit is generally through the orbital rim or through the lateral orbital wall, with or without the central zygomatic arch removed. (G) indicates the lacrimal fossa which contains the lacrimal sac. (b) The three important foramina in the apex of the canine orbit are: (A) optic foramen, through which the optic nerve and internal ophthalmic artery pass; (B) orbital fissure, through which the third, fourth and sixth cranial nerves, the ophthalmic division of the trigeminal (fifth) nerve, and the orbital vein pass; (C) rotundum foramen, through which the internal maxillary nerve and artery pass.

autonomic fibers, with the sympathetic fibers extending from the superior cervical ganglion, and parasympathetic fibers entering the orbit to synapse in the ciliary ganglion. Parasympathetic fibers from the ciliary ganglion then continue to innervate the iris sphincter and ciliary body muscles. Canine orbit size varies by breed and skull type. In general, skull length, width, and height range from about 156  27  29 mm in mesaticephalics, 79  28  30 mm in brachycephalics and 214  33  29 mm in dolichocephalics. There is an increase in orbital size from the toy to giant breeds, but the increase is not directly proportional. The canine globe size ranges from 19.7 to 25 mm transverse, 18.7 to 25 mm vertical, and 20.0 to 25 mm anteroposterior.

Feline orbit The orbit of the cat is similar but not identical to the dog. In contrast to the dog, the feline orbit is only slightly larger than the globe, which greatly restricts orbital exploration unless the globe is first removed. The bones that compose the orbital walls include the sphenoid, maxillary, lacrimal, zygomatic, and frontal (Fig. 4.2). The lateral orbital ligament joins the frontal and zygomatic processes. The bony floor of the feline orbit consists of only a small shelf of maxillary bone that holds the last molar teeth. The extraocular muscles are small and ocular mobility is limited. The zygomatic or intraorbital salivary gland is small in the cat and lies close to the maxillary nerve. The cat’s orbital measurements are about 87 mm long, 26 mm wide, and 23 mm high. The feline globe ranges in size from 20 to 22 mm anteroposteriorly, 19 to 20.7 mm vertically and 18 to 21 mm transversely. The larger Siamese breed globes measure 22.5 mm anteroposteriorly and 22.5 mm transversely.

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Horse orbit Both the horse and cow orbits are among the largest that clinically confront the veterinarian. The orbital bones in the horse include the frontal, lacrimal, zygomatic, temporal, sphenoid, palatine and maxillary (Fig. 4.3a). The bones contributing to the equine orbital rim include the lacrimal (ventromedial orbital rim), the frontal and its zygomatic process (dorsal orbital rim), and the zygomatic processes of the temporal and zygomatic bones (incomplete lateral wall and lateral canthus). The zygomatic process of the frontal bone contains the supraorbital foramen, an important landmark for supraorbital nerve blocks to produce upper eyelid regional anesthesia and paralysis. Hence, the entire orbital rim in horses consists of bones and no fascial tissues or ligaments. The lacrimal bone contains both a shallow fossa for the poorly developed lacrimal sac as well as the entry of the nasolacrimal system into the nasal turbinates. The complete medial orbital wall consists of contributions from the frontal and lacrimal bones and the wing of the presphenoid bone. The dorsal wall is formed by the frontal and, to a smaller extent, the lacrimal bones. The incomplete ventral wall is formed by the zygomatic bone and, to a limited extent, the maxillary and palatine bones. The incomplete lateral wall is formed by the zygomatic processes from both the temporal and zygomatic bones, and the periorbita. A significant lateral barrier to the deep orbital structures is the large coronoid process of the mandible. Four important foramina are sited in the apex of the orbit (Fig. 4.3b). They include: 1. the ethmoid foramen – entry for ethmoid blood vessels and nerves 2. the optic foramen – exit of the optic nerve

Surgical anatomy of animal orbits

A

B

Fig. 4.2 The bones of the feline orbit. Entry into the feline orbit is generally limited to the palpebral fissure and orbital opening. View of the feline skull from the side (a) and from the front (b). The bony orbit provides little more than the essential space to accommodate the cat globe. Like the dog, the bony orbital rim is incomplete laterally and this area is formed by the short lateral orbital ligament. The bones that comprise the cat orbit are, from the side (a): frontal (A), lacrimal (B), maxillary (C), and zygomatic (D). The medial orbital wall (E) consists of the frontal bone dorsally and the sphenoid and palatine bones ventrally. The cat orbital floor is incomplete and very thin. As viewed in the apex of the orbit (b), the dorsal optic foremen and ventrolateral orbital fissure (E) permit passage of the essential ophthalmic nerves and vessels. The globe and orbit accommodate fairly short optic nerves, and very small and limited mobility extraocular muscles.

A

B

Fig. 4.3 The bones of the equine orbit. Entry into the equine orbit is generally limited to the palpebral fissure and orbital opening. Although the dorsolateral orbital wall and caudal floor of the orbit consist of soft tissues, these avenues provide very limited access to the caudal orbit as the extraocular muscle cone, vital blood vessels, and cranial nerves are so deep! (a) The bones that comprise the equine orbit, as viewed laterally, consist of the frontal bone with large supraorbital process (A), zygomatic arch (B), the coronoid process of the mandible (C, not part of the orbit but within the orbit), lacrimal bone (D), and zygomatic bone (E). The medial bony orbital wall is formed by the frontal, lacrimal, and wing of the presphenoid bones. The dorsal orbital wall is formed by the frontal and small part of the lacrimal bones. The ventral floor is formed by the zygomatic bone, zygomatic process of the temporal bone and small part of the maxillary bone. The incomplete lateral wall is formed by the zygomatic bones. In contrast to the dog and cat orbital rims, the horse orbital rim is all bone with limited access to the dorsal orbit structures. (b) At the apex of the equine orbit are four important foramina (arrow): most dorsal and medial is the ethmoidal foramen (passage of the ethmoidal artery, vein, and nerve); more ventrad and further caudad is the optic foramen (passage for the optic nerve and internal ophthalmic artery); just ventral is the orbital fissure (carrying the third, sixth and often the fourth or trochlear and ophthalmic division of the trigeminal nerves); and lastly is the furthest ventral foramen, the round foramen (passage of the maxillary nerve). The apex of the orbit is a considerable distance from the globe (longer than the cow), and generally approached immediately caudal of the supraorbital arch.

3. the orbital fissure – transmits the ophthalmic branch of the trigeminal nerve, the oculomotor (third) nerve, the abducens (sixth) nerve, and often the trochlear (fourth) nerve 4. the round foramen – maxillary branch of the trigeminal nerve.

In the placement of successful retrobulbar nerve blocks in the horse, at least 8–10 cm of distance must be traversed by the hypodermic needle to inject local regional anesthetic in the vicinity of these four foramina. The orbital dimensions of the adult horse are estimated to be 62 mm wide, 59 mm high, 98 mm deep, and

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173 mm between the eyes. The adult horse globe measures 43.7 mm on the meridional anterior–posterior axis, 47.6 mm on the equatorial axis vertical, and 48.5 mm on the horizontal axis.

Cow orbit The cow orbit has many similarities to the horse, but also significant differences. For instance, the frontal bone is very large and well developed to accommodate the cow’s horns. The bones which contribute to the bovine orbit include the frontal, lacrimal, zygomatic, palatine, maxillary, and sphenoid. The bovine orbital rim, composed of three bony structures around 360 , consists of: 1) the frontal bone (dorsal rim); 2) the lacrimal bone (medial canthus); and 3) the zygomatic bone and frontal process of the zygomatic bone (entire ventral rim and lateral canthus). The coronoid process of the mandible is well developed and positioned just caudal to the lateral rim to permit hypodermic needle insertion into the deep orbital tissues from behind the lateral orbital rim (Fig. 4.4a). The bony orbital walls consist of: 1) the lacrimal and sphenoid bones medially; 2) the palatine and sphenoid bones ventrally; 3) the frontal bone dorsally, and 4) the temporal and zygomatic bones laterally. Important orbital foramina include: 1) the ethmoidal foramen (ethmoidal blood vessels and nerves); 2) the optic foramen (passage of the optic nerve); and 3) the orbitorotundum (a combination of the orbital fissure and the foramen rotundum) for passage of the oculomotor (third), the trochlear (fourth), the trigeminal (fifth) and the abducens (sixth) nerves, and retinal and maxillary blood vessels (Fig. 4.4b). The orbital dimensions of the adult cow are estimated to be 65 mm wide, 64 mm high, 120 mm deep, and 151 mm between the eyes. The adult cow globe measures 35.3 mm on the meridional anterior–posterior axis, 40.8 mm on

A

the equatorial axis vertical, and 41.9 mm on the horizontal axis. Hence, for a successful retrobulbar injection in cattle, the hypodermic needle, if positioned near the optic and orbitorotundum foramina, must traverse a distance of about 12 cm.

Rabbit orbit The rabbit has become an increasing popular household pet, as it can be house broken and trained to use a litter box. The rabbit has a large orbit as well as a large globe which occupies most of the orbital space, and a large venous sinus within the orbit. Hence, orbital surgery in this species must be limited to the space between the sclera and Tenon’s capsule, and avoid entering the retrobulbar tissues directly. The bones of the rabbit orbit include the maxillary, orbitosphenoid, alisphenoid, lacrimal, palatine, frontal, pterygoid, and zygomatic. The orbital rim consists of the following bones: frontal bone dorsally, lacrimal bone anteriorly, zygomatic processes of the maxilla, and zygomatic bones (ventral orbital rim). The globe’s lateral displacement allows the temporal bone to also contribute to the lateral orbital rim. The orbit is roughly circular, about 25 mm diameter, with the skull being about 108 mm long and 50 mm wide. The rabbit’s globe measures 16–19 mm anteroposteriorly, 17 mm vertically, and 18–20 mm horizontally. A large Harderian gland (19 mm long, 12–15 mm wide, and 4–6 mm thick at its largest point) occupies the lower anterior part of the orbit. It is medial to the lacrimal gland and almost completely surrounded by a large venous sinus. A very small intraorbital gland is beneath the zygomatic arch.

Avian orbit Avian species that are presented to veterinarians for eye disease are generally in the raptor group (owls, falcons, and hawks) and the psittacines (parrots, cockatiels, and

B

Fig. 4.4 The bones of the bovine orbit. Entry into the bovine orbit is generally through the palpebral fissure and orbital opening. (a) The bones that comprise the cow orbit, as viewed laterally, are the frontal bone with zygomatic process (A), lacrimal bone (B); zygomatic bone with frontal process (C); zygomatic process of the temporal bone (D); and coronoid process of the mandible (E). (b) Viewed through the orbital rim and into the orbital base or apex, are three foramina: the ethmoidal foramen (A); optic foramen (B), lateral to which is the pterygoid crest; and lastly the foramen orbitorotundum (C). Like the horse, the cow orbital rim consists totally of bony structures, but the orbit is shallower than the horse. The pterygoid crest presents a sizeable barrier to orbital nerve blocks (shielding all of the important foramina), and generally local anesthetic is injected deep to it (the pterygoid fossa) or just anterior to successfully block all of the nerves supplying the orbit and globe.

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Surgical pathophysiology

parakeets). Trauma in the raptor group is probably the most frequent single cause of eye disease in this group, and the most treatable. Orbital anatomy varies markedly in the avian species, based on the shape of the skull and beak (Fig. 4.5). The avian orbit and globe are unusually large relative to the bird’s head and body. The large globes result in restricted access to the extraocular muscles as well as limited orbital space during surgery. In fact, sometimes it is best to rupture the globe at the beginning of the enucleation procedure to facilitate surgery and globe removal. Since there is considerable variation in skull and orbital osteology, only some generalizations are possible. In most birds the orbit is almost completely enclosed by bones, the floor being the main exception (contains muscles related to jaw movements). Bones contributing, in part, to the avian orbit include: 1) prefrontal or lacrimal bone; 2) frontal bone; 3) ethmoid or ectethmoidale bone (part of the rostral wall of the orbit, separating it from the nasal cavity); 4) laterosphenoidale bone (ventral caudal wall of orbit); and 5) zygomatic bone. Often pneumatization of the skull bones is present; the reduction in weight of these bones is probably an adaptation for flight. Both globes are separated by a thin bony partition, the interorbital septum (ethmoid bone), which can be fractured easily during enucleation if one is not careful. Another interesting adaptation in birds are two muscles, the M. quadratus membranae nictitantis (originates from beneath the origin of the dorsal oblique muscle) and M. pyramidalis membranae nictitantis (originates near the ventral rectus muscle), which combine and rotate round the optic nerve en route to provide motion to the highly mobile nictitating membrane.

A

Surgical pathophysiology The orbit can be characterized as a roughly conical cavity with bony and fibrous periorbital walls that are relatively resistant to expansion. Suspended within the orbit by a continuous covering of endorbita around the blood vessels, nerves, extraocular muscles, and adipose tissues, the globe is provided mobility. The bulbar and fornix conjunctivae are also thin and flexible, and accommodate ocular movements without restriction, while still creating a significant barrier to the environment and potential infections from entering the orbit and eye. As a result, inflammations, cysts, and masses that increase the volume of the orbital tissues will create pressure on these walls and, as the pathway of least resistance, displace the globe forward into the palpebral fissure. Hence, limited increases in orbital tissue volume can lead to exophthalmia; with large amounts of neoplasia or hemorrhage the globe can be proptosed or displaced beyond the palpebral fissure. This infrastructure of fascial tissues, which permit eye mobility and provide the conduit for the blood vessels, nerves, and muscular attachments for the eye to the rest of the head, can also be damaged. Chronic inflammation, surgery of the orbit, and trauma with hemorrhage can cause fibrosis within the orbit sufficient to restrict globe movement and cause enophthalmia. Loss of the orbital adipose tissues, which fill the orbital spaces and act as flexible ‘shock’ absorbers, can develop after significant orbital hemorrhage and elevated intraorbital pressure, and result in enophthalmia. Typically the orbit may be divided into compartments: 1) intraconal (within the extraocular muscle cone); 2) extraconal (within the orbit but outside of the extraocular muscle

B

Fig. 4.5 The bones of the bird orbit. The avian skull varies markedly in size and shape, and is directly influenced by the bird’s beak. Also, the orbits in birds are generally quite large as compared to the associated skull. (a) In general, the avian bony orbit consists of the following bones: (A) frontal bone; (B) lacrimal bone; (C) the interorbital septum (separating both globes), at the caudal border of which is the optic foramen; and (D) nasal bone (forms the basis for the beak). In this Rhea the orbital rim is much smaller than the bony sclerotic ring (E, representing the globe). In general, the avian orbital rim consists of the following bones: sphenoid, lacrimal (or prefrontals) which form the dorsal orbital rim, nasal and frontal. There may also be an ectethmoid bone. (b) In this Macaw parrot skull, the orbit is very large compared to the bird’s skull, and its shape is influenced by its massive beak. The globes are larger than the orbital rim, requiring special surgical procedures for surgical removal (enucleation) of the globe.

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cone); and 3) extraendorbital (beneath the periosteum of the orbital bones). Intraconal diseases typically cause exophthalmos, while the more frequent extraconal diseases produce strabismus. After orbital surgery, the intraorbital pressure secondary to postoperative hemorrhage and edema may produce some exophthalmos, prolapse of the nictitating membrane, and an impaired blink reflex. If eyelid function is impaired, corneal ulceration can develop rapidly. Hence, after most orbitotomies a partial-to-complete temporary tarsorrhaphy is indicated. Drainage tubes can also be used, separate from the primary incision, to reduce intraorbital pressure and promote drainage. These Penrose drains should be removed 24–48 h postoperatively.

Effect of globe development on orbit growth Development of puppy, kitten and foal orbits is partially determined by concurrent growth and expansion in the size of the eye. In animals that lose an eye to trauma and/or inflammation in early life and while still growing, orbital development will markedly slow and result in noticeable orbital asymmetry at adulthood. The earlier in life that the globe is destroyed, the more pronounced the orbital defect. Orbital asymmetry also occurs in puppies, kittens and foals with unilateral microphthalmia: the more severe the microphthalmia, the more extensive the orbital maldevelopment. Hence in young animals, enucleation of the globe and use of an intraorbital implant after surgery usually help to reduce the orbital deformity to a minimum.

Traumatic proptosis/avulsion/luxation of the globe In proptosis or luxation of the globe, the entire globe is displaced forward. In mild cases, secondary pressure from retrobulbar hemorrhage and edema will force the globe forward sufficiently to induce exophthalmia, exposure keratitis, and an impaired blink reflex. Proptosis occurs most frequently in dogs and certain breeds, especially the brachycephalic breeds, and in cats is usually catastrophic. In the horse, traumatic proptosis is usually incomplete and is typically exhibited by intraorbital hemorrhage, exposure keratitis, exophthalmia, and impaired blink reflex. In other species, proptosis appears rare. When trauma is extensive, the globe may be thrust forward with such force and speed that the equator of the globe extends beyond the palpebral fissure. The compensatory eyelid contractions that should retain the globe within the orbit are delayed, and with the globe already forward of the eyelid margins, the orbicularis oculi muscle spasms prevent retraction of the globe into the orbit. At the same time, forward stretching of the orbital tissues results in intraorbital hemorrhage and edema which can displace the globe even further forward. The stretching, direct pressure, and perhaps thrombosis and ischemia can result in optic nerve inflammation and subsequent atrophy. Elevated intraorbital pressure, and nerve and vascular damage to the lacrimal gland, may cause sufficient destruction to result in keratoconjunctivitis malacia. The extraocular muscles are stretched considerably in traumatic proptosis, and the shortest medial rectus muscle may be transected near its insertion. The impaired

58

blink reflex results in acute corneal exposure and rapidly progressing malacia. Unchecked, the corneal integrity can be compromised within hours. Medical and surgical treatment strategies that directly address the primary and secondary events that can occur in traumatic proptosis are the most successful.

Orbital fractures As the orbital shell is composed primarily of bony tissues, the globe is fairly well protected against trauma. However, considerable trauma can cause orbital fractures of the temporal, zygomatic and frontal bones in most domestic species. With the concurrent hemorrhage and swelling, globe displacement, strabismus, impaired mobility, hemorrhage, pain, and orbital asymmetry result. If the adjacent sinuses are involved, orbital and/or subcutaneous emphysema with crepitus occur. In general, orbital fractures with minimal displacement of the fractured bone heal without surgery; however, if displacement is considerable and unstable, reapposition and internal fixation of the fractured fragments is recommended. A vigorous blink reflex must be maintained in spite of the orbital swelling, and the cornea protected by topical tear substitutes. Temporary complete tarsorrhaphy may be indicted to protect the outer eye and prevent secondary corneal ulceration.

Orbital inflammation: acute and chronic The animal orbit is susceptible to bacterial infections (Fig. 4.6). Orbital cellulitis may present as acute or chronic, and is usually associated with bacterial or fungal infections (often entry cannot be ascertained), as well as foreign bodies. Orbital cellulitis occurs most frequently in dogs (especially the hunting breeds), and is rare in cats. In horses, cattle, and certain species of birds orbital cellulitis may be secondary to adjacent sinus infections or as a sequel of dehorning in cattle. Fungal infections are infrequent in the dog, and are usually associated with foreign bodies. Infection may enter the orbit through several routes. Infectious agents can enter from the mouth, conjunctivae, the adjacent sinuses and nasal cavity, the subcutaneous and skin surfaces of the incomplete lateral and dorsolateral orbital walls, and

Fig. 4.6 English Springer Spaniel with acute orbital cellulitis. Note the swelling of the eyelids and dorsal orbital subcutaneous tissues.

Perioperative medications

hematogenously. In a recent report on orbital abscesses in dogs and cats, the most common bacterial genera isolated from dogs were Staphylococcus, Escherichia, Bacteroides, Clostridium, and Pasteurella. The most frequent bacteria isolated from orbital abscesses in cats were Pasteurella and Bacteroides. The highly vascular orbit and the endorbita that covers the orbital tissues usually respond quickly to antibiotic therapy. This orbital compartmentalization can also impede the spread of the infectious nidus, but also foster the development of focal septic areas that impede antibiotic penetration. As a result, surgical excision of chronic orbital abscesses and focal granulomas may be necessary for complete resolution of the condition. For orbital abscesses in dogs and cats, based on in-vitro susceptibility testing of aerobic bacterial isolates, cephalosporins, extended-spectrum penicillins, potentiated penicillins, and carbapenems are recommended for the initial antimicrobial therapy of orbital abscesses in dogs and cats. Antimicrobial culture is recommended for any severe orbital abscess and in-vitro antimicrobial susceptibility determined to assist in antibiotic selection.

Orbital neoplasms Orbital neoplasms are not infrequent in dogs, but are less common in cats. In both horses and cattle, intraorbital lymphomas, lymphosarcomas, and squamous cell carcinomas are the most frequent types. In dogs, orbital neoplasms consist of a large number of different tumor types, while in cats the most frequent orbital neoplasm is squamous cell carcinoma. Primary orbital neoplasms can arise from any tissue (epithelial, vascular, neural, and connective tissues) within the orbit. Secondary orbital neoplasms also occur and invade locally from the nasal, sinus, and cranial cavities, as well as metastasize from distant sites. The clinical signs of orbital neoplasia are usually associated with a slowly enlarging and painless mass within the orbit (Fig. 4.7). Depending on its position, a neoplasm within the orbit can produce strabismus; the direction of the ocular deviation may assist to localize the mass. The majority of information on orbital neoplasia is on dogs. The mean age of affected dogs with orbital neoplasms is 8–9 years old. Females may be at higher risk. There is no

breed predisposition. Younger dogs may demonstrate more rapidly growing orbital masses. Most neoplasms external to the extraocular cone affect the medial orbital space and wall. This area has the most difficult and limited surgical exposure. In dogs, about 60% of orbital neoplasms are primary. As a result, when orbital neoplasia is suspected, a complete and comprehensive general physical examination is required. The remaining 40% of orbital neoplasms usually invade the orbit from the adjacent nasal and oral cavities, and the sinuses. Unfortunately, 90% of canine orbital neoplasms are malignant. The prognosis for orbital neoplasms is poor, because conservative surgery in an attempt to maintain the globe and vision results in unacceptably high rates of tumor recurrence. Patients with orbital osteolysis usually have a poor prognosis. Most clients do not accept the aggressive attempts of orbitectomy with the resultant loss of the globe and vision, and postoperative facial deformities. A recent study reported that surgical intervention and chemotherapy can prolong life; about 40% of the dogs were alive 6 months after diagnosis, and about 19% were still alive 1 year later. Unfortunately, the other 60% of patients, with advanced orbital neoplasia and most with no therapy, were euthanized within 6 months of diagnosis. The treatment of choice is usually exenteration, which involves excision of the entire orbital contents including the globe. Orbital neoplasms affecting the rostral and lateral orbit may be successfully excised while preserving the eye. Unfortunately, masses involving the ventromedial and posterior orbit, which are the most frequent, generally require removal of the eye during attempts at excising the neoplasm. A major difficulty during surgery is the differentiation of normal and cancerous tissues, often resulting in an incomplete excision of the neoplasm. When considering extensive therapy for advanced orbital neoplasia in small animals and horses, careful education of the client is very important as the postoperative results can markedly affect the facial appearance. Orbital neoplasms in cats are usually malignant. The orbital neoplasms reported most frequently include squamous cell carcinomas, followed by lymphosarcoma– leukemia complex, undifferentiated sarcomas, osteogenic sarcomas, and rhabdomyosarcoma. Orbital neoplasia in cats necessitates a guarded to very poor prognosis. Orbital neoplasia is infrequent in horses and cattle, and careful systemic patient evaluation is essential. Conjunctival squamous cell carcinomas may invade the orbit, especially in the medial canthus. Retrobulbar lymphosarcoma occurs in both species, and not infrequently affects both orbits. The appearance after enucleation or exenteration in horses is a greatly shrunken orbit, and an intraorbital prosthesis may prevent most of the shrinkage.

Perioperative medications

Fig. 4.7 Left orbital neoplasm (meningioma) affecting the medial orbital floor in a 15-year-old Beagle. Note the exophthalmos and dorsolateral deviation of the globe.

Orbital surgery may be performed with the patient under various medications for the pre-existing ophthalmic condition. Topical and systemic antibiotics are often indicated prior to orbital surgical procedures when sepsis is present. When entry into the internal orbit or globe through the conjunctival surfaces is planned, complete asepsis is not

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possible. If an intraocular or an intraorbital prosthesis is implanted, topical and systemic antibiotics are recommended perioperatively. If infection occurs postoperatively around the prosthesis, successful resolution of the condition often necessitates removal of the device. For lateral and dorsal orbitotomy procedures, standard skin preparation is recommended. The planned surgical site is clipped, and cleaned with surgical antimicrobial soap. The area is wiped with iodine (0.5% dilution) and alcohol, and carefully draped, leaving the surgical area exposed. For enucleation and other surgical procedures performed through the palpebral fissure, the eyelids, corneal and conjunctival surfaces are prepared for surgery as outlined in Chapter 2.

TYPES OF ORBITAL SURGICAL PROCEDURES Orbital surgical procedures are divided into several major types including: enucleation, evisceration, exenteration, orbitotomy, and orbitectomy. In the enucleation procedure the globe is excised in total. Most, if not all, of the bulbar and palpebral conjunctivae, the eyelid margins, and the nictitating membrane are also removed. The lacrimal gland may or may not be excised depending on the enucleation procedure. An intraorbital prosthesis may be used to fill the space occupied by the eye. In birds, the enucleation procedure is unique because of the large globes and small orbital rims. In the avian enucleation technique, either additional exposure is created or the globe is collapsed before removal. In the evisceration procedure, the intraocular tissues, including the anterior and posterior uvea, lens, vitreous, and retina, are removed. After implantation of an intraocular prosthesis, the scleral or limbal incision is apposed, leaving the corneal and scleral tunics. Eye movement with the intraocular implant is retained. In the exenteration procedure the contents of the entire orbit including the globe are excised. This procedure is generally reserved for orbital neoplasia in all animal species. In orbitotomy procedures, selected areas of the orbit are exposed, usually for tissue biopsy and excision. Surgical approaches to the orbit are limited to the oral, anterior, lateral, and dorsal routes. The anterior orbitotomy procedure has two surgical approaches: the transpalpebral (through the eyelids) and the transconjunctival (through the bulbar conjunctiva) to gain entry into the anterior orbit. The lateral and dorsal approaches provide access to the posterior orbit through the corresponding soft tissue orbital walls. Because of limited exposure with most orbitotomy procedures with the globe in situ, as accurate a localization of the surgical site as possible is helpful before surgical intervention. The selection of a specific orbitotomy procedure depends on the species. In dogs, a number of different surgical entries, with or without zygomatic arch removal, are available because of the large lateral and dorsolateral fibrous orbital wall. In cats, orbitotomies are limited to the frontal approach, due to very limited space, large globe size relative to orbit, and short optic nerves which limit globe manipulation. In fact, optic nerve chiasm and optic nerve damage to the fellow eye (opposite eye) sufficient to produce blindness can follow excessive surgical handling and tension of the feline’s optic nerve.

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In large animals, the deep orbits are generally approached frontally, and removal of the globe usually precedes deep orbital surgery. In birds, the intraorbital space is very limited, and enucleation and other orbital surgeries are difficult. In some species, the globe must be reduced surgically during the enucleation procedure. In an orbitectomy procedure, the entire contents of the orbit, including the globe, are excised. In addition, some to most of the orbital bones are removed. This radical procedure is reserved for orbital neoplasms localized to the orbit and without distant metastases. With the loss of these tissues, variable facial disfigurement occurs. Preliminary results with orbital neoplasms in dogs suggest that more extensive surgical methods yield improved survival results compared to the more conservative lateral orbitotomy or exenteration procedures. Silicone or methyl methacrylate implants can be used to fill some of the postoperative space and decrease the anticipated disfigurement.

Enucleation procedures in small animals In enucleation, the globe and its contents are excised. In animals, the indications for enucleation include: 1) ocular congenital defects, such as microphthalmia, that result in chronic problems such as conjunctivitis and keratitis; 2) intraocular infections that have destroyed the globe, and are potential sources of systemic infection; 3) intraocular tumors not amenable to local excision or laser therapy and still confined to the globe (Fig. 4.8); 4) proptosis of the globe with several of the extraocular muscles and/or the optic nerve severed; 5) intraocular inflammation that has destroyed the intraocular tissues and resulted in blindness; and 6) extensive trauma to the globe with the loss of intraocular tissues and without the possibility of successful repair. Enlarged and blind glaucomatous globes may also be treated by enucleation; however, the evisceration procedure followed by insertion of an intraocular prosthesis has largely replaced the enucleation procedure because of superior cosmetic results. Advanced glaucoma secondary to intraocular

Fig. 4.8 Primary mast cell sarcoma involving multiple areas of the limbus with secondary glaucoma in an American Cocker Spaniel. The recommended treatment is enucleation.

Enucleation procedures in small animals

neoplasms and non-specific panophthalmitis is best managed by enucleation. In the enucleation procedure in small animals, the eye, eyelid margins, nictitating membrane, and lacrimal gland are excised. Surgical approaches for enucleation include the subconjunctival (through the bulbar conjunctiva), transpalpebral (through the eyelids), and lateral (a modified palpebral procedure starting at the lateral canthus and removing the inner (deeper) one-half of the upper and lower eyelids). During enucleation of the eye in cats, minimal traction on the globe during the procedure is recommended. Excessive traction on the feline globe undergoing enucleation may damage the optic chiasm and the opposite optic nerve. All orbital tissues (including the globes) that are excised should be examined histologically. Microscopic examination of these tissues can confirm the clinical diagnosis, as well as provide additional information that could affect the postoperative clinical management and long-term prognosis for the animal.

Subconjunctival enucleation The subconjunctival enucleation technique is the simplest and most rapid of these procedures, and the most frequently performed in small animals. Using this method, the globe is excised from its surrounding Tenon’s capsule with the majority of the surgical dissection limited to the sub-Tenon’s space. As a result, this method usually has less hemorrhage intraoperatively and less serum accumulation postoperatively. This technique does not usually remove the conjunctivae and lacrimal gland; however, the entire nictitating membrane is excised. Exposure of the deeper orbital tissues may be limited with this procedure because of the edematous bulbar conjunctiva, but can be enhanced by a lateral canthotomy. In the subconjunctival procedure for enucleation, entry into the orbit is through the bulbar conjunctiva. After completion of draping around the palpebral fissure, a 5–10 mm lateral canthotomy may be performed to increase exposure (Fig. 4.9a). With blunt-tipped tenotomy, strabismus, or Metzenbaum scissors, the full-thickness lateral canthus is cut. Hemostasis is usually achieved by direct pressure with a surgical sponge, if necessary supplemented by point electrocautery. The bulbar conjunctiva and Tenon’s capsule are incised at the 12 o’clock position by curved Steven’s tenotomy, strabismus, or Metzenbaum scissors with blunt tips for about 3–5 mm posterior to the limbus, and the incision extended for 360 (Fig. 4.9b). Using the scissors’ blunt tips, the dissection plane between the sclera and Tenon’s capsule is extended deeper into the orbit until each extraocular muscle insertion is identified (Fig. 4.9c). After isolation with a muscle hook, the tendinous insertions of all of the extraocular muscles are incised. Transection of the extraocular muscle insertions, rather than through the muscle per se, minimizes hemorrhage. As each of the four major rectus muscle insertions is incised, the globe becomes more mobile. After incision of the retractor muscle and oblique muscle insertions, the globe will displace slightly forward. To sever the optic nerve and the adjacent posterior ciliary arteries, a small curved hemostat or enucleation forceps are carefully positioned posterior to the globe (Fig. 4.9d). With curved Metzenbaum scissors or the specially curved enucleation scissors, the optic nerve and surrounding blood

vessels are transected just anterior to the hemostat. Placement of the scissors is critical to avoid any contact with the posterior sclera and to prevent inadvertent incision of the posterior segment of the eye. The globe is carefully removed from the orbit to permit placement of a ligature deep to the hemostat still clamped to the optic nerve and accompanying blood vessels. The orbit is now carefully examined for any bleeders, and ligatures or point electrocautery applied if needed. If an intraorbital implant is not used, parts of the remaining extraocular muscles and periorbital fascia are apposed with 2-0 to 4-0 simple interrupted absorbable sutures to reduce the dead space within the orbit. The remaining bulbar conjunctiva and anterior Tenon’s capsule are apposed with 2-0 to 4-0 simple interrupted absorbable sutures. With closure of the bulbar conjunctiva, 4–6 mm of the eyelid margins (including the medial and lateral canthi, and nictitating membrane) are excised circumferentially with tenotomy or strabismus scissors. The nictitating membrane is protracted, and two hemostats are overlapped and clamped at its base (Fig. 4.9e). The remaining nictitating membrane, complete with gland, is excised by tenotomy or strabismus scissors. The remaining eyelids (including the septum orbitale) are closed and apposed with 3-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 4.9f,g). If an orbital prosthesis is planned, an 18–22 mm sterile silicone sphere (Jardon Eye Prosthetics Inc., Southfield, MI) or methyl methacrylate sphere (Storz Instrument Company, St Louis, MO) is usually selected (Fig. 4.10). The surface of the silicone sphere is scarified or roughened with several incisions via scalpel blade to roughen its smooth surface and facilitate orbital retention. The sphere is inserted, and the extraocular muscles and endorbita are apposed about the sphere. An alternative method is the placement of mesh implants on the anterior surface of the orbital rim to prevent postoperative eyelid and orbital shrinkage.

Transpalpebral (‘en bloc’) enucleation The transpalpebral enucleation technique differs from the subconjunctival procedure in that the surgical entry starts at the level of the eyelids, and the deeper aspects of the eyelids and the entire palpebral, fornix, and bulbar conjunctivae, and nictitating membrane are excised (‘en bloc’ method). This technique is performed more frequently in the large animal species. Although more tissues are excised in this procedure, the conjunctival and corneal surfaces are avoided, thereby reducing the chance of orbital contamination and postoperative infection. This method is preferred when infections of the globe and conjunctival surfaces are present. Because the entire conjunctiva is excised, exposure and visualization of the deeper orbital tissues are facilitated. After draping, the eyelids are apposed with simple continuous 3-0 to 4-0 sutures, thereby closing the palpebral fissure (Fig. 4.11a). The eyelid skin is incised circumferentially by scalpel blade about 6–8 mm from the eyelid margins to avoid the bases of the meibomian or tarsal glands (Fig. 4.11b). The skin incision is carefully deepened until the submucosa of the palpebral conjunctiva is reached. Then, with blunt dissection with Steven’s tenotomy, strabismus or Metzenbaum scissors, the incision is continued under the conjunctival fornices, and onto the globe and

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A

D

B

C

E

F

Fig. 4.9 Enucleation – subconjunctival approach: In this procedure the globe is removed from Tenon’s capsule through a bulbar conjunctival incision at the limbus. After removal of the nictitating membrane, the eyelid margins are removed and permanently apposed. (a) The palpebral fissure is temporarily enlarged by a lateral canthotomy. The lateral canthus is incised by small tenotomy scissors for 5–10 mm. (b) The bulbar conjunctiva and Tenon’s capsule are incised 360 by curved Steven’s tenotomy or strabismus scissors a few millimeters behind the limbus. About 2–4 mm of bulbar conjunctiva are left attached at the limbus, to permit manipulation of the globe with forceps during the enucleation procedure. (c) By blunt–sharp dissection with curved tenotomy scissors, the extraocular muscle insertions to the globe are excised. The globe is rotated in different directions to provide the optimal exposure during the dissection process. (d) The optic nerve is clamped by curved hemostat and transected by curved enucleation or Metzenbaum scissors. Special care is required to prevent touching the posterior globe with the tips of the scissors during optic nerve incision. Once the optic nerve has been cut, the globe can be rotated forward for incision of any remaining fascial attachments. (e) The nictitating membrane is protracted by thumb forceps and its base clamped with two curved hemostats. The structure is excised by Mayo scissors. The lacrimal gland may be removed at this time from beneath the lateral orbital ligament. (f) The two layers of closure include apposition of the rostral portion of Tenon’s capsule by simple interrupted absorbable sutures. The skin–orbicularis muscle layer is apposed with simple interrupted non-absorbable sutures. (g) Two weeks following enucleation in a young Labrador Retriever and suture removal.

under the bulbar conjunctiva (Fig. 4.11c). The procedure continues using the same steps as the subconjunctival method. Dissection within the sub-Tenon’s space between the sclera and Tenon’s capsule will usually minimize hemorrhage. All of the extraocular muscles are severed at their insertions (Fig. 4.11d). Isolation, clamping by curved hemostat, incision of the optic nerve, and removal of the globe follow (Fig. 4.11e). The VicrylW ligature is carefully positioned deep to the hemostat on the optic nerve stump. Closure of the anterior periorbital fascial tissues with simple interrupted 3-0 to 5-0 absorbable sutures, with or without an orbital prosthesis, helps to reduce the dead space within the orbit. The orbital septum within the eyelids is apposed

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with 3-0 to 4-0 simple interrupted or horizontal mattress absorbable sutures (Fig. 4.11f). The eyelid–subcutaneous layer is apposed using the same type of suture and suture pattern. The eyelid skin is apposed with several 3-0 to 4-0 simple interrupted non-absorbable sutures (Fig. 4.11g).

Lateral enucleation In the lateral approach for enucleation, the transpalpebral technique has been modified by the inclusion of a lateral canthotomy to increase further the access to, and visualization of, the deeper orbit. This technique is useful in the dolichocephalic canine breeds and for deep orbits. The eyelids

Evisceration with intraocular prosthesis in small animals

Fig. 4.10 Placement of a 14–22 mm silicone or methacrylate sphere after enucleation in the dog and cat. Two-layer closure is recommended with apposition of the dorsal and ventral periorbita and Tenon’s capsule with simple interrupted absorbable sutures, and the eyelid skin and orbicularis oculi muscle layer with simple interrupted non-absorbable sutures. In both cats and horses these orbital implants are more apt to extrude than in dogs. (Modified with permission from Nasisse MP, van Ee RT, Munger RJ, Davidson MG 1988 Use of methyl methacrylate orbital prostheses in dogs and cats: 78 cases (1980–1986). Journal of the American Veterinary Medical Association 192:539–542.)

are temporarily closed during the surgery by sutures and/or instruments to prevent contamination of the corneal and conjunctival surfaces with the orbital tissues. If the eyelids are closed by instrumentation, the time to suture the eyelids is omitted, while still preventing contamination of the orbit with the outer ocular surfaces. After draping, an 8–15 mm lateral canthotomy is performed with curved Steven’s tenotomy, strabismus, or Metzenbaum scissors (Fig. 4.12a). Starting at the lateral canthus and using Metzenbaum scissors, the upper eyelids and then the lower eyelids are divided into an outer layer consisting of the skin and orbicularis oculi, and an inner layer composed of the tarsal plate including the septum orbitale, and the palpebral conjunctiva (Fig. 4.12b). The blunt tipped curved Metzenbaum scissors, with a combination of cutting and blunt dissection, facilitates this process with minimal hemorrhage. Dissection is continued to include the medial canthus, thereby incorporating the entire palpebral fissure. A curved hemostat may be inserted into this cleavage plane to gently clamp the skin surface. The eyelid skin about 5–7 mm from the eyelid margins is incised 360 with the Metzenbaum scissors (Fig. 4.12c), and the eyelid margins apposed with two or three Allis forceps to close the palpebral fissure and cover the corneal and conjunctival surfaces. The globe is rotated medially and the lateral canthal ligament attachment to the orbital rim incised to provide additional mobility to the globe (Fig. 4.12d). Surgical dissection with tenotomy or strabismus scissors is continued under the conjunctival fornices and to the subTenon’s space just caudal of the limbus. Removal of the globe from Tenon’s capsule continues using a method similar to that described in the subconjunctival enucleation technique, except that the medial globe attachments are excised last. The insertions of all of the dorsal, lateral, and ventral extraocular muscles are transected by scissors immediately next to the globe to minimize hemorrhage. As the different extraocular muscles are transected, the globe can be progressively rotated, eventually exposing the optic nerve. The optic nerve and adjacent posterior ciliary blood vessels are carefully

clamped by curved hemostat, and transected by curved Metzenbaum or enucleation scissors immediately in front of the hemostat (Fig. 4.12e). With the posterior attachments free from the globe, further medial rotation permits incision of the medial extraocular muscle insertions and periorbital fascia, freeing the globe, lacrimal gland, conjunctivae, and nictitating membrane ‘en mass’ from the orbital wound (Fig. 4.12f). A sterile silicone sphere with its surfaces scarified by several incisions can be inserted at this time. Closure is accomplished in four layers, including the endorbita, septum orbitale, subcutaneous tissues, and skin (Fig. 4.12g). Portions of endorbita can be apposed with 2-0 to 4-0 simple interrupted absorbable sutures to secure the intraorbital prosthesis and reduce the dead space for serum collection. The septum orbitale, located in the deeper aspects of the eyelids, is apposed with 2-0 to 4-0 simple interrupted or horizontal mattress absorbable sutures. The subcutaneous layer is apposed with 2-0 to 4-0 simple interrupted absorbable sutures. The eyelid skin is apposed with 2-0 to 4-0 simple interrupted non-absorbable sutures.

Evisceration with intraocular prosthesis in small animals Evisceration is an attractive alternative to the enucleation procedure. The procedure, like the enucleation technique, treats blind and painful eyes, removes the need for topical and systemic medications, but provides improved cosmesis. In the evisceration procedure, the entire intraocular contents are removed through a scleral or limbal incision, leaving only the fibrous tunics of the cornea and sclera. Into this corneoscleral shell is inserted a sterile silicone sphere, and the scleral or limbal wound apposed. The usual results are a painless and cosmetically acceptable eye that often requires no medical therapy, has movement, and often shows no obvious ophthalmic disease. The primary indication for evisceration is end-stage primary glaucoma, which has become medically non-responsive, with enlarged and painful globes. Globes with secondary glaucoma associated with septic panophthalmitis and intraocular neoplasms are not candidates for evisceration, and should be treated by the enucleation procedure. Severely lacerated globes with loss of intraocular tissues are occasional candidates for evisceration with intraocular prosthesis, assuming infection is not present. Evisceration with intraocular prosthesis should be delayed or not performed in eyes with major corneal diseases, including deep ulceration and low tear production. Weakened corneas may not be able to accommodate the direct posterior contact with the intraocular implant. Some failures following evisceration with intraocular prosthesis have been associated with recurrence of the preoperative ophthalmic disease, especially unsuspected intraocular neoplasia and mycotic infections. Ophthalmic prosthetic devices have been described in the veterinary literature since the latter part of the nineteenth century. Most of the ophthalmic devices attempted in animals were employed after removal of the eye, and were positioned either in the remaining conjunctival space or within the orbit. The shell-type artificial eyes require daily maintenance, and orbital and conjunctival tissue contracture usually eventually extrudes these devices. Simpson reported on

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G Fig. 4.11 Enucleation – transpalpebral approach: In this technique the globe is removed with the eyelids sutured or clamped together. (a) The palpebral fissure is closed by suturing the eyelids together with a continuous non-absorbable suture. Alternatively, the eyelids can be clamped together by Allis or towel forceps. (b) The eyelid skin and orbicularis oculi muscle layers are incised for 360 to the level of the tarsoconjunctiva. The incision is usually about 6–8 mm from the eyelid margins to avoid the bases of the meibomian glands. (c) With the sutured eyelids clamped by Allis forceps, the dissection is continued by small curved Metzenbaum scissors around the conjunctival fornices and onto the globe. (d) Once the sub-Tenon’s space is entered about the globe, the different extraocular muscle insertions are isolated and transected. Hemorrhage is usually minimal as long as the surgical plane remains in the sub-Tenon’s space. (e) Once the posterior orbit is entered, the optic nerve is carefully isolated, clamped by a curved hemostat, and incised by curved scissors posterior to the clamp. (f) The first of two layers of closure consists of apposition of the orbital septum with simple interrupted or simple mattress absorbable sutures. (g) The second and last closure is apposition of the eyelid and orbicularis oculi muscle layer with simple interrupted non-absorbable sutures.

intrascleral implants in dogs in 1956, but unfortunately excised the cornea to permit visualization of the prosthesis. Recurrent conjunctivitis in most of these dogs required intermittent topical antibiotics, and local infections often resulted in eventual prosthesis extrusion. Following encouraging studies on intrascleral prostheses in dogs by Magrane and Helper, the silicone (Jardon Eye Prosthetics Inc., Southfield, MI) and methyl methacrylate (Storz Instrument Company, St Louis, MO) spheres have been found to be non-painful, similar to the normal eye in appearance, non-toxic, non-antigenic, easily implanted, inexpensive, and approximate the intraocular volume. Sphere size  1 mm is determined by caliper measurement of the horizontal corneal diameter. In adult dogs, the sphere diameter size usually ranges from 18 to 22 mm. When globe size has been increased by glaucoma, the fellow normal eye cornea is measured to determine the optimal sphere size.

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After implantation in glaucomatous globes, the elastic sclera and cornea will reduce in size over 1–3 months to conform to the sphere size. Available in different colors, the black sphere is recommended for dogs and the yellow sphere may be used in cats. A vertical pupil can be tattooed on the sphere for the cat. The silicone sphere can be sterilized by steam or gas if properly aerated. Sterilization of the methyl methacrylate spheres is by gas or by boiling. Chemical sterilization of these spheres is not recommended. After draping, an eyelid speculum is inserted between the upper and lower eyelids to increase surgical exposure. A lateral canthotomy may be used for additional exposure (Fig. 4.13a). With tenotomy or strabismus scissors, a 6 mm limbal-based conjunctival flap is constructed for 180 , usually from the 9 to 3 o’clock position. The bulbar conjunctiva is carefully and bluntly separated from the underlying Tenon’s capsule and sclera (Fig. 4.13b). Hemostasis is

Evisceration with intraocular prosthesis in small animals

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G Fig. 4.12 Enucleation – lateral approach: In this procedure the globe is removed from Tenon’s capsule starting at the lateral canthus. (a) A lateral canthotomy is performed by tenotomy scissors. (b) At the lateral canthus and using curved small Metzenbaum scissors, the skin–muscle and the tarsus–conjunctiva layers of the upper and lower eyelids are separated. (c) The eyelid skin–orbicularis oculi layer is incised for 360 by scissors to expose the deeper tarsoconjunctiva. (d) The skin–muscle layer and eyelid margins are clamped by Allis forceps, and the globe is rotated medially to incise the lateral canthal attachments. (e) With deeper retrobulbar dissection and incision of the lateral rectus and retractor oculi muscle insertions, the globe can be rotated medially to expose, clamp, and transect the optic nerve. (f) Continued rotation of the globe exposes and permits incision of the remaining medial extraocular muscle insertions, the medial canthal ligament, and the conjunctiva–nictitating membrane. (g) Closure is accomplished in four layers including parts of the endorbita, septum orbitale and subcutaneous tissue with simple interrupted absorbable sutures, and eyelid skin layer with simple interrupted non-absorbable sutures.

maintained by point electrocautery. The sclera is incised at the 12 o’clock position with a Beaver No. 6400 microsurgical blade, about 4 mm posterior and parallel to the limbus (Fig. 4.13c,d). Scleral tissues will usually hemorrhage and judicious point electrocautery is usually necessary. The scleral incision is extended both medially and laterally with tenotomy scissors to about 180 . The scleral incision must be 1–2 mm larger than the sphere diameter to accommodate the insertion of the device. Alternatively, the anterior chamber may be entered through a limbal incision. The limbal incision is associated with less hemorrhage than the scleral approach, but may be associated with more frequent postoperative corneal complications. The globe is eviscerated using the lens loop posteriorly and cyclodialysis spatula or an iridal spatula anteriorly to bluntly separate the anterior and posterior uveal tract from the limbus and sclera (Fig. 4.13e). The lens loop may be the most successful instrument and cause the least hemorrhage. With slight traction on the iris, the entire anterior and posterior uvea, lens, vitreous, and retina are removed (Fig. 4.13f). The intraocular space is gently flushed with saline or lactated Ringer’s solution to remove

all blood clots and any remaining intraocular tissues (Fig. 4.13g). Excessive flushing is not recommended as damage to the corneal endothelium may result. A sterile premeasured silicone sphere, rinsed in saline, is carefully introduced into the fibrous tunics with the Carter sphere holder and introducer (Fig. 4.13h–k). Once the sphere is in position, an additional flush with saline of the area is performed. The scleral incision is apposed with 5-0 to 6-0 simple interrupted or continuous absorbable sutures (Fig. 4.13l). The bulbar conjunctiva and Tenon’s capsule are apposed with a 5-0 to 6-0 simple continuous absorbable suture. The lateral canthotomy is closed with 4-0 non-absorbable figureof-eight and interrupted mattress sutures. Complete temporary tarsorrhaphies are often used after the evisceration procedure to protect the cornea for 10–14 days postoperatively. Topical and systemic antibiotics are administered immediately after surgery and continued for 5–7 days. If the cornea develops a central ulceration postoperatively, a bulbar conjunctival graft should be performed as corneal healing in these eyes appears slow and impaired. Penetrating corneal ulcers often necessitate enucleation.

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Fig. 4.13 Evisceration with intraocular prosthesis. In this technique all of the intraocular tissues are removed, and a silicone sphere is introduced into the globe consisting of only the cornea and sclera. (a) A 5–10 mm lateral canthotomy is performed by strabismus or Steven’s tenotomy scissors to increase the size of the palpebral fissure and facilitate surgical exposure. (b) After incision of the bulbar conjunctiva and Tenon’s capsule 4–6 mm from the limbus by tenotomy scissors, the sclera is exposed for about 180–200 . (c) The sclera is incised with the Beaver No. 6400 microsurgical blade for approximately 140–180 . (d) Incision of the sclera results in variable amounts of hemorrhage which is controlled by point electrocautery. (e) A lens loop (or blunt spatula) is inserted into the subscleral space, or between the sclera and the anterior and posterior uvea tracts. All of the intraocular tissues are gently separated from the sclera. Hemorrhage is to be expected. (f) With gentle traction, the iris, ciliary body, lens, vitreous, and retina are protracted from the anterior globe. (g) Intraocular hemorrhage is expected as the intraocular tissues are gently retracted from the corneoscleral tunics. The shell, consisting of the cornea and sclera, is gently flushed with sterile saline to remove any remaining intraocular tissues and clots. (h) The Carter sphere holder and inserter. A yellow sphere is held by the instrument’s tips and is usually used for eviscerations in the cat. A black sphere is recommended for the dog. (i) With the Carter sphere holder and inserter, a premeasured sterile sphere (the diameter is usually 1 mm less than the horizontal corneal diameter) is placed into the fibrous tunic shell. (j) Intraoperative appearance of the Carter sphere holder and inserter. During the insertion of the sphere into the globe, the instrument inserts the sphere while retracting the edges of the scleral wound. (k) Intraoperative appearance of the eye after intrascleral yellow prosthesis placement. Some hemorrhage still remains in the anterior chamber. (l) The two layer closure consists of apposition of the scleral and the bulbar conjunctival wounds with simple interrupted absorbable sutures. Often a temporary complete tarsorrhaphy is then performed to protect the cornea.

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Enucleation procedures in large animals and special species

Exenteration in small animals Exenteration is the complete removal of all of the orbital tissues, including the globe, nictitating membrane, conjunctivae, lacrimal gland, zygomatic salivary gland (in the dog), and extraocular muscles. In some patients, some of the orbital periosteum can also be removed. The indications for exenteration include orbital neoplasia, medically non-responsive orbital infections, and extensive intraocular neoplasia that has extended into the orbit. The surgical procedure is very similar to the transpalpebral enucleation procedure except the surgical dissection is along the orbital walls, external to the extraocular muscles. More hemorrhage is associated with this procedure. Apposition of the eyelids after complete removal of the orbital contents is similar to the other enucleation procedures. Systemic antibiotics should be administered postoperatively for 5–7 days.

Enucleation procedures in large animals and special species Orbital surgery in the horse Retrobulbar nerve blocks Retrobulbar or orbital local anesthesia injections are used to reduce globe and nictitating membrane movement, and to block or lower corneal and conjunctival sensation for standing procedures such as eyelid lacerations, nictitating membrane excision, corneal foreign body removal, iris cyst laser ablation, anterior chamber or vitreous injections or aspirations, and enucleations in standing horses and horses under general anesthesia. Retrobulbar nerve blocks are used to decrease the depth of general anesthesia required for orbital, corneal, and intraocular surgery. Two techniques are used in horses (see Fig. 3.8, p. 45–46). The skin of the orbital fossa just caudal to the posterior rim of the orbit is prepared for aseptic surgery, and a 6.25 cm, 22 g spinal needle is inserted just caudal to the posterior aspect of the bony orbital rim. The needle is inserted until it reaches the extraocular muscle cone. This is detected by

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slight dorsal movement of the eyeball. With the needle in position, 10–12 mL of 2% lidocaine is injected. Slight exophthalmos usually occurs. Anesthesia takes effect in about 5–8 min and lasts 1–2 h. The second technique is performed by curving the needle slightly and placing it through the conjunctival fornices using a four-point or a two-point retrobulbar block. With a two-point block, usually 4–8 mL of lidocaine is injected per site. When a four-point block is used, the injection volume of local anesthetic is 2–6 mL per site

Surgical techniques Enucleation Enucleation is the surgical removal of the globe, third eyelid, and conjunctivae. In most cases the eyelid margins and meibomian glands are removed and the skin sutured to cover the open orbit.

Indications Enucleation is indicated for the removal of a blind, painful, deformed or traumatized eye. The subconjunctival approach is used for corneal disease, glaucoma, and phthisis bulbi (Fig. 4.14). Removal of an equine eye is considered major surgery, and is only rarely considered in a standing non-anesthetized animal. When only one general anesthesia episode is feasible or affordable, and the fellow eye is sighted, enucleation may be the treatment of choice for advanced or painful ocular disease. Enucleation should not be considered a failure of ophthalmic care, but rather the appropriate and planned treatment for some ophthalmic disorders. In horses determined to be at high risk for complications from anesthesia or recovery, those not amenable to frequent medications, and for those cases in which additional expenses are not possible, enucleation is a rapid therapy to restore comfort and prevent further sequelae from disease. It is important to ensure that anesthesia and the recovery phase are not a greater risk than the benefit of surgery. Retrobulbar nerve blocks can dramatically reduce the depth of general anesthesia required for enucleation or facilitate enucleation in a heavily sedated standing horse.

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Fig. 4.14 Patient candidates for enucleation in the horse. (a) Septic panophthalmitis with exudative retinal detachment in an adult horse. (b) Advanced medial canthal and orbital squamous cell carcinoma in an adult horse.

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The client should be educated as to the alternatives to enucleation, expected costs associated with therapy and surgery, expected appearance after enucleation, and possible complications of anesthesia and surgery; all these should be well understood before proceeding. Cosmetic options for the horse should be explained before proceeding with enucleation. These will be discussed later in this section. There are two basic approaches to enucleation in the horse: the subconjunctival approach and the transpalpebral approach. The subconjunctival approach requires less time to perform and usually results in much less hemorrhage. It is used for cases of glaucoma, corneal ulcers, corneal neoplasia, irreparable corneal or scleral tears, refractory uveitis, and endophthalmitis. It is also the better cosmetic result of the two approaches. The subconjunctival technique is used when a cosmetic shell is placed to maintain the integrity of the eyelid margin. The transpalpebral approach is recommended in patients with severe corneal infections, large corneal, third eyelid, or conjunctival neoplasia. This technique creates a larger soft-tissue defect of the orbit than the subconjunctival approach. An orbital prosthesis may be placed with either technique, although a larger silicone sphere is needed with the transpalpebral approach.

Subconjunctival enucleation If severe infection or extensive neoplasia is present, a closed transpalpebral approach is the preferred surgical technique. The subconjunctival approach results in less postoperative discomfort because fewer tissue planes are traversed. Subconjunctival enucleation is initiated by placement of an equine eyelid speculum or sutures to hold the eyelids open for the procedure. A minor lateral canthotomy is performed. The lateral canthus is crushed with hemostats for 0.5–1 min, and the skin and conjunctivae are cut with a blade or surgical scissors. The bulbar conjunctiva is infiltrated with 2% lidocaine, incised 5 mm caudal to the limbus with Steven’s tenotomy scissors, and a complete peritomy performed. The extraocular muscles are identified and isolated with a strabismus (muscle) hook. The muscles are incised near or at their attachment to the sclera, permitting free rotation of the globe. The retractor bulbi muscles attach more posteriorly, and are more difficult to visualize. They are incised somewhat blindly. A curved or angled hemostat is used to crush the optic nerve and associated vessels. The globe is removed and submitted for histologic examination. The orbit may be packed with sterile gauze or GelfoamW. Frequently a silicone sphere is cut to form a flattened anterior surface and placed in the orbital space to eliminate dead space after enucleation. The nictitating membrane and any remaining conjunctivae are removed. The orbital lacrimal gland is rarely identified and removed. The remaining orbital contents should be examined to ensure that all diseased tissue has been removed. Capillary hemorrhage is common but should not preclude examination of the orbit. The orbit should be flushed with dilute povidone–iodine. The orbital space may be packed with sterile gauze sponges or surgical GelfoamW. Infusion of antibiotic solution should be considered if the orbit is contaminated during the procedure. A surgical drain (Penrose) through the ventral orbit

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should also be considered in a contaminated surgical site. If the orbit is contaminated during surgery, an orbital prosthesis is usually not placed. After the remaining conjunctivae are excised, the eyelid margin is resected from lateral to medial. Usually 6–8 mm of eyelid is removed so that no meibomian gland material is left. Care is taken at the medial canthus to remove the entire medial canthal skin but not to incise the medial anguli oculi vein and artery deep to the medial canthus. If the upper or lower lacrimal canaliculus is visible, it is ligated with 3-0 to 4-0 polyglycolic acid sutures.

Transpalpebral enucleation The transpalpebral approach is preferred for large malignant neoplasms and for septic globes. The transpalpebral technique allows for complete separation of the globe from the orbit. After the eye and periocular tissue are prepared for aseptic surgery, the eyelids are sutured tightly with 2-0 or 3-0 nylon, in a Ford interlocking or simple continuous pattern, with the suture ends left long (Fig. 4.15a). Large hemostats or Allis tissue forceps are placed on sutures at each end of the eyelid fissure to provide identification and traction during the procedure. A full-thickness skin incision is made 6–8 mm from the eyelid margins. Tissue planes are then bluntly dissected to separate the skin from the tarsal layer. These tissue planes are a natural separation formed by a potential space from embryonic development. The separation is extended to the periorbital margin with caution to prevent perforating the tarsal layer and contaminating the orbit. The medial canthal ligament and lateral canthal attachments are cut with a surgical blade. Additional dissection will separate the globe from the orbital connective tissue (Fig. 4.15b). Extraocular muscles are dissected and excised. The optic nerve or optic cone is clamped with curved forceps or Carmalt forceps. A ligature may be paced around the optic cone and tightened if desired. The optic nerve is resected anterior to the clamp or about 0.5–2 cm from the globe. This technique naturally removes more orbital tissue than the subconjunctival approach. An orbital prosthesis is routinely placed. In addition, large non-absorbable sutures may be placed vertically, connecting the dorsal and ventral orbital rims to construct some support for the anterior orbit and permanent tarsorrhaphy (Fig. 4.15c,d).

Postoperative management Enucleation in the horse has a low incidence of complications, less than 10%. Complications occur when the entire nictitating membrane and gland are not completely removed, when the eyelid margins do not include the entire meibomian glands (meibomian glands extend about 6 mm into the eyelid skin), and when the bulbar and palpebral conjunctivae are not removed. Care must be taken to remove the eyelid margin at the medial canthus. Rarely is the orbital lacrimal gland removed during enucleation, but complications do not seem to occur. When drainage is observed from the suture line at the medial canthus, the differential diagnosis must be either the retained mucocutaneous junction of the eyelid margin at the medial canthus versus an infected orbit after enucleation. If retained eyelid margin in the medial canthus causes a draining tract, correction is to simply remove

Enucleation procedures in large animals and special species

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the eyelid margin and close the wound. If an infected orbit is present or an infected draining tract, it should be explored, debrided, flushed, and closed. The orbit may be flushed with an antibiotic solution and a dependent drain can be created through a stab incision in the ventral-most portion of the orbit. The drain tubing or Penrose drain is left in place for 24 h beyond the last purulent drainage or for 24 h of clear drainage. Some surgeons will use roll gauze soaked in povidone–iodine, placed in the orbit after debridement. The soaked gauze passes through a separate stab incision, and is held in place with a suture through the skin. A section of the gauze is removed daily for 2–5 days, or until the drainage becomes clear. The stab incision is sutured or allowed to heal by second intention.

Implants to improve postoperative appearance after enucleation Several techniques have been used to improve the cosmesis of the face and orbit following enucleation (Fig. 4.16).

Fig. 4.16 Postoperative appearance after subpalpebral enucleation in the horse. Note some concavity of the wound is present.

These range from the popular intraorbital silicone prosthesis to a conformer and corneoscleral shell.

Intraorbital silicone prosthesis An intraorbital silicone prosthesis may be inserted to prevent the sunken appearance of the orbit after removal of the entire globe in the subconjunctival enucleation procedure (see Fig. 4.13). The silicone prosthesis should be washed to remove surface oils and allowed to dry prior to sterilization. Usually steam sterilization is preferred. At surgery the sterile prosthesis is rinsed with sterile saline or dilute povidone–iodine solution prior to insertion into the orbit. The size of the prosthesis is selected to fill the orbit and approximate the size of the contralateral globe. The fellow eye may be measured prior to surgery to give a size estimate for the orbital prosthesis. Usual prosthesis sizes range from 40 to 48 mm diameter silicone sphere in adult horses (Jardon Eye Prosthetics Inc., Southfield, MI). A silicone orbital implant designed to prevent or decrease skin sinking after enucleation is also marketed by Veterinary Ophthalmic Specialties (Moscow, ID). The silicone prosthesis is rinsed or wiped with sterile saline or dilute povidone–iodine to remove any powder or dust. The anterior surface of the prosthesis is cut to flatten the anterior aspect of the prosthesis to reduce the prominent anterior curvature of the silicone sphere. Non-absorbable suture material is used to close the orbital tissue and the sphere incorporated into the suture pattern to prevent rotation and hold the prosthesis in place. Use of intraorbital implants is not recommended in horses enucleated for orbital infections or neoplasia. Following introduction into the orbit, the prosthesis is fixed in a stable position with 2-0 to 4-0 nylon or prolene shallow sutures, and incorporated into a meshwork or in the closure of the extraocular muscles or orbital connective tissue. A layer of tissue is closed between the prosthesis

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and the skin with 3-0 to 4-0 absorbable sutures, usually in a continuous or interrupted mattress suture pattern. Closure is usually accomplished in several layers. If no prosthesis is introduced, the periorbita may be partially approximated with an interlocking mesh of non-absorbable sutures to prevent sinking in of the skin postoperatively (see Fig. 4.15c). Retracting the skin and subcutaneous tissue will aid in placement of this mesh suture. The subcutaneous tissue is closed with 2-0 to 4-0 absorbable sutures in a Ford interlocking or simple continuous pattern. Some surgeons prefer a simple interrupted or cruciate pattern. Skin is closed with an interrupted cruciate or simple interrupted pattern. To avoid suture removal, an intradermal skin closure in a continuous pattern using 4-0 to 5-0 VicrylW has been used. Tetanus prophylaxis should be verified or given at or prior to surgery. Postsurgical swelling is usually minimal but will increase during recovery as the systemic blood pressure increases. Cold compresses followed by warm compresses 24 h later are used if the horse will tolerate them. Pressure bandaging of the face is rarely used.

Intrascleral silicone implants Evisceration of the globe and implantation of an intraocular silicone prosthesis (ISP), also termed an intrascleral silicone prosthesis, is a procedure used in horses for blind, painful eyes, chronic glaucoma, early stages of phthisis bulbi, and for corneal and sclera lacerations that have a poor prognosis for surgical correction. An ISP requires a single surgical episode, and in most cases is more cosmetic than enucleation. It is considered less cosmetic than placement of a scleral shell or an artificial globe, which requires multiple anesthetic and/or surgical procedures. Many clients accept an ISP to be more cosmetic and preferable to removal of the eye or a phthisical globe. Clients should be educated to the fact that corneal disease can occur and diseases of the eyelid margin and nictitating membrane are possibilities that will require therapy. Eyes with pre-existing corneal disease should be regarded as being at higher risk for keratitis and ulceration following ISP. The presence of corneal disease at the time of surgery increases the risk of postoperative complications. However, an intrascleral silicone prosthesis can be implanted successfully in horses with corneal lacerations. A conjunctival advancement or pedicle flap should be considered at the time of surgery, but may diminish the cosmetic appearance. Diseases (including neoplasia) that involve the eyelid margin, nictitating membrane, and conjunctivae can occur following ISP since these structures are not removed.

Evisceration and intrascleral silicone prosthesis Evisceration is the removal of the intraocular contents: aqueous, lens, uveal tract, retina, and vitreous, with preservation of the fibrous tunic, or cornea and sclera. Careful surgical preparation is performed. Eyelashes are trimmed, periocular skin is washed with baby shampoo, and nasolacrimal ducts are flushed with dilute povidone–iodine. The skin is prepared for aseptic surgery, and the conjunctival fornices are flushed with dilute povidone–iodine, swabbed with

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sterile cotton-tipped applicators, and flushed with sterile saline. With the horse under general anesthesia, sensory nerve blocks of the eyelids are performed along with a retrobulbar block. Topical proparacaine and topical 10% phenylephrine are applied at 5-min intervals, beginning about 20 min prior to surgery. A subconjunctival line block of 2% lidocaine is performed from about 3 to 9 o’clock, using approximately 0.5 mL of lidocaine. A self-adhesive drape or dental dam is used to avoid contamination of the surgical site. A conjunctival flap is raised for about 160–180 , 6–8 mm posterior to the limbus. Wet field or disposable ophthalmic cautery is used to cut through Tenon’s capsule; blunt dissection and cautery are used to expose the sclera. The sclera is scored with the cautery unit and incised full thickness to the uveal tissue using a No. 6400 microsurgical blade. Care should be taken to incise the sclera without perforation of the underlying uveal tissue. If it is necessary to improve exposure to remove uveal contents or to insert the silicone sphere, a T-shaped incision is performed by scissors. To remove the ciliary body and iris, a cyclodialysis spatula is inserted anteriorly between the sclera and the uveal tissue to break the attachments of the iris at the iridocorneal angle. A lens loop is used to separate the uveal tissue from the sclera posteriorly, and to separate the choroid and retina from the sclera. Two non-toothed forceps or hemostats are used to grasp and remove the uveal tract. Caution is exercised to prevent damage to the corneal endothelium. The uveal tissue is placed in fixative for histopathologic evaluation. The remaining intraocular contents are removed, the intraocular space is swabbed with moistened cotton-tipped applicators, and the fibrous shell is flushed with sterile saline. Complete removal of the lens should be verified. Efforts are made to remove the entire uveal tract, but retained remnants of uveal tract do not appear detrimental. An intraocular silicone prosthesis is usually selected after measuring the normal cornea with calipers and adding 1–2 mm. In most adult horses the silicone sphere should be 36–40 mm in diameter. The prosthesis is rinsed in sterile saline or residual powder is removed by wiping the prosthesis with saline or dilute povidone–iodine solution. The silicone sphere is introduced with care to avoid touching the eyelids or conjunctiva. The fit is assessed by apposing the edges of the scleral incision. Some surgeons will use light suction to remove blood from the fibrous cavity. The anterior surface of the prosthesis may be cut, trimmed, and flattened to provide a more cosmetic result and to decrease contact with the corneal endothelium. The scleral incision is closed with 4-0 to 5-0 polyglactin 910 in an interrupted or simple continuous pattern. The full extent of the incision should be visualized and both ends closed carefully to prevent dehiscence. The conjunctiva and Tenon’s capsule are closed with a continuous pattern, ensuring that the scleral incision is completely protected. The lateral canthoplasty, if performed, is closed in two layers. A subpalpebral lavage system may be placed to apply topical antibiotics after surgery. A temporary tarsorrhaphy is performed to reduce exposure and to protect the cornea and scleral closure. The globe is lubricated with OptixcareW gel. Postoperative medication includes topical and systemic antibiotics and systemic anti-inflammatory agents,

Enucleation procedures in large animals and special species

usually flunixin meglumine (BanamineW; Schering-Plough, Kenilworth, NJ). The tarsorrhaphy sutures are removed in 3–4 days. Persistence of, or an increase in, ocular discharge indicates the need for ophthalmic evaluation, possible culture and sensitivity testing, and staining the cornea with fluorescein dye. Corneal ulceration is the most common complication. Less frequent complications include: dehiscence of the surgical site; endophthalmitis, either septic or powder induced; or severe periocular swelling if traumatic dissection occurred. Many corneas vascularize and scar within a few weeks after surgery and may not appear very cosmetic. With time, if pigmentation results, the globe is more cosmetic.

the exposed intrascleral implant. Later studies succeeded by using a silicone sphere placed within the ocular or corneoscleral tunics. Gilger and associates reported use of a custom-made hydroxyapatite orbital implant after enucleation of the eye in a horse (Fig. 4.17). The corneoscleral prosthesis was fitted over the orbital implant. The hydroxyapatite orbital implant permits vascular and fibrous tissue growth from the host into and over the implant, thereby decreasing the chance of infection and implant extrusion. The extraocular muscle insertions can be attached to the orbital implant to provide mobility.

Orbital exenteration in the horse Cosmetic corneoscleral conformer, scleral cosmetic shell, and corneoscleral prosthesis Corneoscleral conformers or extrascleral shell implants are made by ocularists from methyl methacrylate, porcelain, or hydroxyapatite to fit to and cover a phthisical globe or a disfigured eye. The surface is painted by the ocularist from a photograph of the fellow eye and the prosthetic shell is fitted into the conjunctival sac. The eyelids and third eyelid help to fix the conformer in the desired location. The relatively high costs and frequent cleaning of the prosthesis are limiting factors in their use. The results are very cosmetic and most owners are quite happy with the outcome. Extrascleral shell conformers are available from Jardon Eye Prosthetics Inc. (Southfield, MI) or can be individually made for horses by Dallas Eye Prosthetics (Dallas, TX). Early artificial eyes or cosmetic globes (often constructed of glass or ceramic material) inserted into the sclera after evisceration of all the intraocular tissues and removal of the entire cornea failed in horses because of infection eventually extending between the sphere and the host’s sclera. This chronic infection ultimately resulted in extrusion of

A

Exenteration in horses is a surgical technique designed to remove large tumors from the orbit that are unresponsive to other forms of therapy such as radiation therapy or chemotherapy. Systemic antibiotics and flunixin meglumine are given before surgery. Tetanus prophylaxis should be verified or administered prior to surgery. With this technique, the entire orbital contents are surgically removed, including the globe and the periorbita. The globe is removed by enucleation and then periosteal elevators are used to remove the periorbital fascia. Care must be exercised to avoid breaking into a paraorbital sinus. The remaining orbital tissue is removed using electrocautery and sharp dissection. Bleeding should be controlled with cautery and ligatures. An orbital prosthesis is usually not placed when a large neoplasm is excised. The remaining eyelid skin is sutured to cover the open socket. If inadequate skin remains, the facial skin is undermined and walking sutures are used to cover the defect. If excessive skin must be removed, a skin flap or graft can be used. In rare cases, if a large amount of eyelid and facial skin must be sacrificed, the socket may be allowed to granulate and epithelialize.

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Fig. 4.17 Intraorbital implants and corneoscleral conformers are used in the horse to reduce wound disfigurement and attempt to compensate for, at least, some of the tissue loss from the enucleation procedure. (a) The hydroxyapatite intraorbital implant and corneoscleral conformer (generally constructed by an ocularist) for the horse. The extraocular muscle insertions may be attached to the implant, thereby providing globe motility. (b) Postoperative appearance in this type of implant in a horse. (Both photographs courtesy of Brian Gilger, North Carolina State University.)

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Postoperative management after exenteration Pressure bandages over the orbit are used to reduce swelling. Systemic antibiotics and flunixin meglumine are continued. If a sinus is damaged or entered during the procedure it may require trephination, drainage, and lavage.

Orbital surgery in the bovine Enucleation of the bovine eye In adult cattle, the most common enucleation technique is the transpalpebral approach. With this technique more of the orbital contents are removed than with a transconjunctival or subconjunctival approach to enucleation. Frequently, removal of the bovine eye is done for economic reasons for neoplasia of the third eyelid (nictitating membrane) or eyelids, when the eye or globe is normal (Fig. 4.18). In many cases it is easier and preferable to remove the eyelid mass by ‘H-plasty’ in cattle, or to remove the third eyelid when it is affected rather than remove the entire globe, or in some cases perform an exenteration when the globe itself is intact and visual. Excision of eyelid squamous cell carcinoma (SCC) in cattle is commonly performed, and is certainly preferable to enucleation or exenteration when there is no involvement of the globe or the bony orbit. Other forms of therapy for eyelid neoplasia should be considered before enucleation of a normal eyeball. These include cryotherapy, hyperthermic therapy, chemotherapy, immunotherapy, and radiation therapy. Chemotherapy might include 5-fluorouracil (5-FU) or intralesional injections of cisplatin in sesame oil injected every 2 weeks for 8 weeks (four treatments). Immunotherapy has also been used for SCC in cattle. A mycobacterium cell wall immunostimulant has been used successfully in cattle with SCC; however, a major drawback was that it converted the animals into tuberculin reactors. A phenol–saline extract of bovine SCC led to regression of lesions following intramuscular injections. Immunotherapy with bacille Calmette–Gue´rin (BCG) may be considered as well as immunomodulation with oral cimetidine for eyelid neoplasia. Investigation of therapeutic results for SCC in cattle is hindered by the suspected relatively high incidence of spontaneous regression of these tumors. In other cases, exenteration of the orbit may be performed for uveitis, septic panophthalmitis, trauma to the globe, and

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severe ocular trauma that are beyond reasonable repair. Enucleation may be inappropriate if the neoplastic process involves the bony orbit or has metastasized to regional lymph nodes. The veterinarian should examine the oral cavity and teeth to determine the animal’s age and perform rectal palpation to determine pregnancy status. Older age and non-pregnancy may alter the feasibility of enucleation from an economic standpoint. The sale value for breeding use seems to decrease after the removal of one eye. An animal should never have both eyes removed, unless used as a pet, and this practice is questionable from a humane standpoint. In some cases, one-eyed cattle may do poorly in a feedlot situation.

Anesthesia and surgical preparation Most enucleations are performed with the animal standing in a head catch or chute. The head is securely restrained with a halter and nose lead, or a head board restraint device. Intravenous sedation and analgesia are commonly administered. The head is pulled to the opposite side of the chute from the eye to be removed, allowing adequate positioning and exposure for the surgeon. Usually the hair is clipped from the surgical site using a No. 40 clipper blade on a small animal electric clipper. If large amounts of necrotic or neoplastic tissue are present in the surgical area, this should be trimmed with scissors prior to scrubbing the site for surgery. Some surgeons now elect to use sterile drapes for the surgical area. The surgeon must be certain that the diseased eye is being removed and not the normal eye. Intravenous mild sedation is used in some cattle. For standing surgeries, xylazine (0.05 mg/kg IV) and butorphanol (0.02 mg/kg IV) are used. The addition of a low dissociative dose of ketamine (0.1 mg/kg IV) has been used to assist with fractious patients. The combination of xylazine, butorphanol, and ketamine has been called the ‘Ket-Stun’ technique. Anti-inflammatory therapy, flunixin meglumine (1 mg/kg IV), immediately before surgery appears adequate for most enucleation procedures. Local anesthesia is used to infiltrate the retrobulbar tissues. A four-point retrobulbar block is commonly performed by injecting through the lower and upper eyelids and at the medial and lateral canthi. A slightly curved, 8–10 cm, 18–20 g needle is directed toward the posterior orbit and 10–20 mL of lidocaine injected. An alternative is

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Fig. 4.18 Bovine candidates for enucleation. (a) Panophthalmitis with corneal rupture in a cow after injury. (b) Intraocular squamous cell carcinoma in a cow. Tumor apparently originated from the lateral limbus. (c) Extensive orbital squamous cell carcinoma is a 10-year-old Holstein cow.

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to mix a 4:1 injection solution of 0.5% bupivacaine and 2% lidocaine containing 1:100 000 adrenaline (epinephrine). When the retrobulbar tissue has been adequately anesthetized the eye will appear exophthalmic, the pupil will be dilated, and corneal sensation will be absent. Some surgeons have favored the Peterson eye block for this procedure, but it has mostly been replaced with the four-point block, due to unpredictable anesthetic traits of the Petersen method.

Surgical technique Immediately following surgical preparation, the surgical site is draped. Covering the entire head with the drape will provide a more sterile field and may aid in restraint. The eyelids are held together with two or three Backhaus towel clamps. This decreases contamination of the surgical field and the towel clamps are used for light traction during dissection. An alternative method is to use nylon suture material to close the eyelids with the ends left long enough to provide traction during the procedure. A transpalpebral incision is made around the eyelid margins, leaving as much normal tissue as possible. If adequate normal eyelid is present, the incision is usually about 1 cm from the eyelid margins. If additional abnormal eyelid tissue must be removed, maintaining enough normal skin to close the wound is imperative; alternatively, periorbital skin should be undermined for closure without tension on the suture line. The ventral skin incision and dissection are performed first to decrease hemorrhage from the upper eyelid obstructing the surgeon’s view of the surgical field. Dissection is continued for 360 using sharp and blunt methods. This is usually completed with a scalpel blade and large Mayo or serrated surgical scissors, or large curved surgical scissors. The dissection is continued posteriorly to the caudal border of the orbit. Dissection is done in a lateral and posterior fashion to avoid cutting through the conjunctiva. The extraocular muscles, orbital fat, lacrimal gland, conjunctiva, globe, nictitating membrane, and eyelid margins are excised. If the enucleation is performed for neoplasia, the surgeon must be certain that all eyelid, conjunctival, and retrobulbar neoplastic tissue has been satisfactorily removed. When enucleation is performed for non-neoplastic and non-endophthalmitic conditions, more of the retrobulbar tissue may be left in place. This will reduce the amount of postoperative dead space, intraoperative hemorrhage, and the sunken appearance of the orbital skin after surgery. Once the optic nerve and vessels of the optic stalk are isolated, traction on the globe should be minimal and twisting of the globe should be avoided. Contralateral blindness is a consideration in most species when enucleation is performed. If excessive traction or twisting of the globe occurs during removal, these traction forces are transmitted to the optic chiasm and can lead to damage of the chiasmal axons, resulting in blindness or visual field loss in the remaining good eye. The optic nerve and associated blood vessels are clamped with a right-angled forceps, enucleation forceps, large hemostat, Carmalt forceps, or a similar instrument. The blood vessels and optic nerve may be ligated or allowed to clot naturally or by pressure. The surgeon should gently palpate the orbit to be certain that all abnormal tissue has been removed. After removal of the globe a large amount of dead space is usually present. The orbit and retrobulbar

space will fill with blood. This clot will organize during the following few weeks, leaving a depression and sunken appearance to the face. An orbital prosthesis can be placed after surgery as is recommended in horses and small animals. A silicone sphere can be used without carving or a surgical blade may be used to flatten the front of the prosthesis in cattle. Another option to decrease the amount of sunken tissue is to ‘weave’ a non-absorbable suture across the orbit beneath the skin. Three-0 to 4-0 nylon or prolene would work well, if cosmesis is a concern. Some veterinary surgeons elect to pack the orbit with sterile gauze (10  10 cm) sponges immediately after the globe and orbital structures have been removed; the number of sponges packed into the orbit should be known to the surgeon. The gauze sponges are removed and counted prior to tying the final skin sutures. All sponges must be removed from the orbit. In some cases roll gauze may be packed into the orbit and removed at the end of surgery. Many surgeons elect to pack the orbit only if hemorrhage is considered excessive or uncontrollable by other means. Often skin closure is the only suture used in cattle enucleations. Frequently the skin is closed with a non-absorbable suture (No. 3 nylon) in a variety of patterns. Suture patterns used for skin closure in enucleation in cattle include the Ford interlocking, cruciate, simple continuous, and simple interrupted patterns. If a continuous pattern is selected, it may be fortuitous to use a single simple interrupted suture in the medial canthus, if by chance dependent drainage is needed, and the single suture can be removed easily. Nylon or prolene may be used for skin closure. In the past polymerized caprolactam (VetafilW) was used for this closure by many food animal veterinarians. The surgical site is re-examined in 10–12 days and the sutures are removed. Some surgeons now prefer to wait 14–21 days before suture removal. If drainage from the suture line or surgical site is present, the clinician may elect to remove the medial canthal suture, leaving the remainder of the skin sutures in place. If drainage, infection, or the need to remove only part of the suture line is predicted at surgery, then a simple interrupted pattern is recommended. Some veterinarians prefer to close the skin with absorbable sutures when suture removal will be problematic, such as in range conditions where it may be cost prohibitive and impractical to round up the animal for a suture removal. In such circumstances, 3-0 medium catgut or VicrylW is recommended, using a medium curved large animal needle and employing an interrupted horizontal mattress suture pattern using double strands of suture. Some veterinarians also choose to insert a sterile suspension or bolus of soluble antibiotic solution into the orbit at the end of surgery. This practice is met with controversy, since it is felt by some bovine surgeons that any material deposited in the orbit may become a nidus for infection, or may lead to inflammation or increased discomfort and drainage postoperatively, due to their chemical or caustic effects.

Postoperative management The degree of hemorrhage may alarm young or inexperienced surgeons. Many agree that the most appropriate hemostasis is a rapid surgery and pressure from the closed

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skin following surgery. Systemic antibiotics are recommended if infection is present at surgery.

Subconjunctival enucleation in the bovine A subconjunctival enucleation with the animal under general anesthesia may be performed in similar fashion to those performed in horses and small animals.

Evisceration of the globe and intraocular silicone prosthesis In some cases evisceration of the globe and implantation of an intrascleral silicone prosthesis is requested by the owner to maintain a more cosmetic face. This is uncommon in cattle, but may be used in valuable animals. This is most commonly performed after trauma to the globe and early phthisis bulbi formation.

Removal of prolapsed retrobulbar fat Prolapse of varying degrees of retrobulbar fat is an uncommon yet dramatic-appearing lesion in any animal. The diagnosis is usually made by visual assessment and digital palpation using a gloved and lubricated finger. In some cases the diagnosis is made by fine needle aspirate and cytologic examination. If surgical correction is elected, the prolapsed fat is removed following an auriculopalpebral nerve block and topical anesthetic with 5–10 drops of 0.5% proparacaine hydrochloride or ophthalmic tetracaine applied to the cornea and conjunctiva. In some cases anesthesia is facilitated by injection of a small amount of 2% lidocaine subconjunctivally at the incision site. Adequate restraint is necessary for ocular surgery in cattle. Most surgeries are performed with the animal standing in a squeeze chute, head catch, or stanchion, with the head restrained with a halter and nose lead, or head board restraint. The eyelids are prepared for aseptic surgery, and the conjunctiva and cornea are irrigated with dilute povidone–iodine solution. The conjunctival fornices are irrigated and swabbed with sterile cotton-tipped applicators. A conjunctival incision is made rostrally to the prolapsed fat with Steven’s tenotomy scissors (standard, curved, with blunt tips) or other small ophthalmic scissors. The fat is excised in toto. The conjunctival incision is closed to imbricate the area with a simple continuous pattern using 5-0 VicrylW. Some surgeons have used simple interrupted or mattress sutures of 3-0 to 4-0 polyglycolic acid. Topical antibiotic ointment is applied immediately following surgery.

Enucleation procedures in birds Removal of the globe in birds requires further modification of the enucleation procedures already presented. Avian globes are very large in relation to the surrounding bony orbit, and the extraocular space for surgery is quite limited. The avian sclera contains 10–18 small overlapping ossicles that form a bony ring and give shape to the avian eye. In owls these ossicles result in a tubular-shaped globe. In most hawks the globe has a globular shape. At least three different enucleation procedures have been developed for birds; selection depends on the globe shape. In owls a transaural enucleation procedure is recommended as these species have an extensive external ear opening. This method

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expands the palpebral fissure to permit removal of the large intact tubular-shaped globe. The second method, which can be used in any avian species, involves collapse of the globe to permit its removal through the palpebral fissure. The third technique is a modified evisceration method involving removal of the cornea and all of the intraocular tissues, but leaving the sclera and bony ossicles behind. A complete permanent tarsorrhaphy is then performed. Enucleation in birds, including owls and hawks, may be necessary after destruction of the eye and loss of vision following extensive trauma, intraocular infection, and noninfectious intraocular inflammation. As the avian eye is unusually large in relation to its face, enucleation involving complete removal of the globe results in considerable disfigurement. Leaving the sclera, as in the last modified evisceration method, results in less postoperative concavity of the eyelids. Birds have a very thin bony interorbital septum medially, and it should not be penetrated during surgery. As in any enucleation procedure, and even if globe is not removed intact, the contents should be examined histologically.

Transaural enucleation method for owls In the transaural enucleation approach for owls, the feathers over the auricular area and orbit are plucked, and the area prepared for aseptic surgery. The eyelids are retracted by two or more 4-0 silk stay sutures anchored in the eyelid margins or an eyelid speculum (Fig. 4.19a). An incision (indicated by a dotted line in Fig. 4.19a) is used to connect the lateral canthus to the anterior auricular margin. Using a No. 6400 microsurgical blade, the skin incision is extended through the lateral canthus and periorbital fascia to the anterior auricular margin to the junction of the tubular globe and the postorbital process (Fig. 4.19b). Hemostasis is achieved by point electrocautery. The lateral canthal and preaural skin are dissected free to expose the posterior aspects of the tubular globe (Fig. 4.19c). The subconjunctival dissection is continued under the periorbital fascia for 360 and extended posteriorly. A 12 o’clock incision of the periorbital fascia can provide additional mobility for the globe. With digital pressure carefully applied to the limbus, the No. 6400 microsurgical blade is used to create a space between the posterior globe and caudal orbit (Fig. 4.19d). Through this space, small tenotomy scissors are used to sever the globe from its extraocular attachments and transect the optic nerve (Fig. 4.19e). Once relieved of its attachments, the tubular globe is removed. Hemostasis is achieved by direct pressure and gauze sponges. After orbital hemostasis, the conjunctiva, nictitating membrane, and 2 mm of the entire eyelid margins are excised. Closure is started by reapposition of the anterior auricular margin with simple interrupted 5-0 to 7-0 absorbable sutures (Fig. 4.19f). The eyelids are then apposed using simple interrupted 5-0 to 7-0 absorbable sutures (Fig. 4.19g).

Globe-collapsing enucleation procedure for birds The globe-collapsing enucleation method can be used for any avian species. After general anesthesia and preparation for aseptic surgery, a small pediatric wire eyelid speculum is positioned to retract the upper eyelid, lower eyelid, and

Enucleation procedures in large animals and special species

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G Fig. 4.19 Enucleation in the bird: This procedure is complicated by both the shape and size of the globe, and the limited anterior orbital opening. In this method the anterior orbital opening is expanded by a lateral canthotomy that extends to the anterior auricular margin. This method is recommended for owls. (a) Two stay 4-0 silk sutures or an eyelid speculum is used to retract the upper and lower eyelids. The incision line (shown as a dotted line) extends from the lateral canthus to the anterior auricular margin. (b) The lateral canthus and skin are incised by No. 6400 microsurgical blade through the anterior auricular margin to the junction of the tubular globe with the postorbital process. The deeper conjunctiva and periorbital fascia are also incised. (c) By small curved tenotomy scissors, the skin is carefully dissected to expose the posterior aspects of the globe. The subconjunctival dissection is continued 360 to free the globe. (d) With digital pressure at the lateral limbus, the posterior globe is manipulated forward with the surgical blade. (e) Steven’s tenotomy scissors are inserted posterior to the globe to sever the optic nerve and any posterior attachments. The globe is delivered through this lateral incision. Hemorrhage is usually controlled by temporarily packing the orbit with sterile gauze pads. (f) After removal of the remaining conjunctiva and nictitating membrane and a 2 mm strip of eyelid margin, 5-0 to 7-0 absorbable simple interrupted sutures are used to appose the anterior auricular margin, the eyelids, and skin. (g) Immediate postoperative appearance. (Reproduced with permission from Murphy CJ, Brooks DE, Kern TJ, Queensberry KE, Riis RC 1983 Enucleation in birds of prey. Journal of the American Veterinary Medical Association 183:1234–1237.)

nictitating membrane. A lateral canthotomy, extending dorsolaterally to the anterior auricular margin, is performed using a No. 6400 microsurgical blade or small tenotomy scissors (Fig. 4.20a). The limbus is incised by scalpel or a combination of a scalpel and corneal scissors for 180 , and

a stay suture positioned in the center of the cornea for its manipulation (Fig. 4.20b). With curved tenotomy or strabismus scissors the bulbar conjunctiva, nictitating membrane, and periorbital fascia are incised 360 . The area deep to the auricular skin is carefully undermined (Fig. 4.20c). Mayo

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Fig. 4.20 Globe-collapsing procedure for enucleation in the bird. This technique can be used in any avian species. (a) After a fine wire eyelid speculum is positioned, a lateral canthotomy is performed by the No. 6400 microsurgical blade, extending dorsolaterally to the anterior auricular margin. (b) The limbus is incised for 180 and a stay suture is positioned in the central cornea. The conjunctiva, nictitating membrane, and periorbital fascia are incised for 360 . (c) The area medial to the auricular skin is also undermined. (d) By Mayo scissors inserted carefully between the subconjunctival and subscleral spaces, the sclera and scleral ossicles are incised. (e) Forceps are used to collapse the globe and permit access to the posterior globe. The optic nerve and posterior attachments are severed by scissors, and the globe is carefully removed. (f) After removal of the nictitating membrane, conjunctiva, and a 2 mm strip of eyelid margin, the eyelids are apposed with 5-0 to 7-0 absorbable simple interrupted sutures. (Reproduced with permission from Murphy CJ, Brooks DE, Kern TJ, Queensberry KE, Riis RC 1983 Enucleation in birds of prey. Journal of the American Veterinary Medical Association 183:1234–1237.)

scissors, carefully positioned between the uveal tract and sclera, are used to sever the sclera and its ossicles (Fig. 4.20d). With the dorsal sclera incised, forceps are used to collapse the globe. The extraocular muscle attachments and the optic nerve are severed by scissors, and the globe is removed from the orbit (Fig. 4.20e). Excessive traction on the globe as it is manipulated forward should be avoided to prevent damage to the optic chiasm. Hemostasis of the deeper orbit is achieved by direct pressure by gauze sponges and point electrocautery. The entire conjunctiva, nictitating membrane, and a 2 mm strip of eyelid margin are excised by tenotomy scissors. Closure of the remaining eyelids is accomplished by several 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 4.20f).

Modified evisceration method for enucleation in birds This third method for enucleation in birds attempts to address the considerable disfigurement that occurs after removal of the entire globe. However, for this technique to be successful, the postoperative field must be sterile. Hence birds with possible panophthalmitis and intraocular neoplasia should not be considered candidates for this procedure.

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After placement of a small wire speculum, the peripheral cornea is incised for 360 , and the intraocular contents (including the uveal tract, lens, vitreous, and retina) are gently removed from the scleral shell by lens loop, spatula, and scissors. Hemostasis is achieved by direct pressure with surgical sponges and, if necessary, point electrocautery. The conjunctiva, nictitating membrane, and a 2 mm strip of the eyelid margins are excised by tenotomy scissors. The eyelids are apposed with 5-0 to 7-0 simple interrupted absorbable sutures.

Orbitotomy in small animals In the orbitotomy procedures, access to the interior of the orbit is gained with the eye in situ. The avenues include the anterior, lateral, dorsal, and oral approaches. The orbit in dogs can be approached from the frontal, dorsolateral, or lateral aspects, but the feline, equine, bovine, and bird orbits are usually entered frontally (through the palpebral fissure) and often with the globe already removed. The anterior approach enters the orbit through the bulbar conjunctiva or the eyelids beneath the conjunctival fornix. Both of these approaches have been

Orbitotomy in small animals

described as the initial part of the subconjunctival and transpalpebral enucleation procedures. The anterior orbitotomy approaches are the most useful for anterior orbital lesions. The lateral orbitotomy approach permits exploration of the canine anterior and posterior orbit, and is recommended for zygomatic gland diseases, zygomatic arch disease, and retrobulbar lesions lateral to or within the extraocular muscle cone. For maximal lateral orbital exposure, the center of the zygomatic arch can be temporarily transected and reattached at the conclusion of surgery. The dorsal orbitotomy approach provides primary exposure of the upper orbit, and is selected for dorsal retrobulbar, zygomatic process of the frontal bone, and parietal bone diseases. The canine and feline orbital floors are incomplete posteriorly, and limited access is available through an oral approach immediately caudal to the last molar tooth. As indicated earlier, a significant number of orbital masses involve the ventromedial orbit and, as a result, the surgical approach and visualization are difficult. Optimal exploration of the medial and ventromedial canine orbit usually requires removal of the globe and converts the orbitotomy procedure into an exenteration. The specific orbital surgical approach should be selected based on the location of the orbital disease. For instance, if the mass is isolated to the anterior medial or lateral orbit, anterior orbitotomy might provide the most useful route. If the primary lesion is confined to the lateral orbit or zygomatic salivary gland, lateral orbitotomy with temporary removal of the zygomatic arch may provide the best exposure. With a lacrimal gland mass, the recommended approach would be anterior transpalpebral orbitotomy. As previously noted, the feline orbit is only slightly larger than the globe, and surgical access to the retrobulbar space with the eye in situ is very limited. Limited lateral exposure can be attempted via an anterior transpalpebral or lateral orbitotomy approach.

Indications for orbitotomy The clinical indications for orbitotomy include the excision of an isolated inflammatory or neoplastic mass, biopsy of orbital tissue while under direct observation, ligation of major orbital vessels, orbital fracture fixation, orbital cytology and culture. The postoperative results after orbitotomies for the treatment of chronic inflammation (usually as focal abscesses or granulomas), benign tumors, masses and cysts of the zygomatic salivary gland, and the limited posterior extensions of neoplasms of the conjunctival and nictitating membrane are usually good. However, as indicated earlier, the majority of orbital neoplasms in the dog are malignant (about 90%) and most are primary (about 60–70%). In cats, over 90% of orbital neoplasms are malignant and most appear secondary. In addition to the limited barrier offered by the bony orbital walls, intraorbital masses tend to expand irregularly and exhibit indistinct borders. In large animals, most orbital neoplasms are malignant, and warrant a guarded prognosis. Before surgical intervention of the orbit is contemplated, one or more of the orbital diagnostic procedures should be performed in an attempt to define the limits and possible borders of the mass. As 4 of every 10 canine orbital neoplasms are secondary, examination of the nasal cavity and sinuses is imperative. A complete physical examination,

including chest and abdominal radiographs, complete blood count, blood chemistries, and urine analysis should be performed. Neoplastic tissues sometime appear grossly similar to adjacent orbital tissues. If the primary objective of an orbitotomy is to obtain tissue biopsies for diagnosis, or debulk a mass for possible treatment with chemotherapy and/or radiation, then an orbitotomy is recommended. The long-term survival rates for canine orbital neoplasms after diagnosis and attempts to remove by orbitotomy procedures are very low, and few dogs live beyond 3 years after diagnosis. If a primary orbital neoplasm is present in the dog, the most prudent surgical approach appears to be the exenteration procedure and removal of the eye. Preliminary results using the orbitectomy procedure in dogs with orbital neoplasms indicate better results and longer survival rates. The orbitectomy procedure involves excision of the globe, the remaining orbital tissues, and most of the orbital bones.

Lateral orbitotomy The lateral orbitotomy approach is usually performed in the area of the zygomatic arch. For optimal exposure, temporary removal of the zygomatic arch is recommended. Two different lateral orbitotomy procedures have been described. Unfortunately, in both approaches, some of the branches of the palpebral nerve that innervates the orbicularis oculi muscle (eyelid closure), the zygomaticofacial or zygomaticotemporal (maxillary division of the trigeminal nerve that provides sensation to the lateral face), and the parasympathetic fibers to the lacrimal gland can be damaged.

Limited lateral orbitotomy The lateral orbitotomy approach by Harvey is the least difficult procedure, and provides reasonably good exposure of the lateral orbit. After draping, the skin incision by scalpel blade extends from the middle of the lower eyelid to the caudal aspects of the zygomatic arch (Fig. 4.21a,b). The underlying subcutaneous tissues are carefully dissected to permit transection of the orbicularis oculi, retractor anguli oculi, and lateral orbital ligament attachment to the dorsal border of the zygomatic arch. With careful dissection the lateral orbital ligament is reflected dorsally to reveal the lacrimal gland (arrow, Fig. 4.21c) which is immediately beneath the lateral orbital ligament. Blunt deeper dissection, both caudally and rostrally on the dorsal aspects of the zygomatic arch, permits observation of the dorsal portion of the zygomatic gland and lateral periorbital fascia (Fig. 4.21d). The zygomatic salivary gland in the dog occupies the ventrorostral position of the orbital floor. For additional exploration of the orbit, a central portion of the zygomatic arch is removed (Fig. 4.21e–h). A dorsal section of zygomatic arch periosteum is reflected by periosteal elevator, and a 1–2 cm section of the arch is removed in small pieces by rongeur. Immediately medial to the zygomatic arch is the zygomatic salivary gland. With additional dissection, most of the zygomatic salivary gland can be localized (Fig. 4.21i). When the zygomatic arch is partially removed, additional areas within the ventral orbit become accessible. By digital exploration the orbital floor can evaluated, including the infraorbital artery and accompanying maxillary or

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Fig. 4.21 Lateral (limited) orbitotomy (Harvey approach): This procedure provides limited access to the lateral orbit; when combined with partial to total resection of the middle portion of the zygomatic arch, access to the entire lateral orbital walls and most of the orbital floor is possible. This procedure (or minor variations thereof) is the most frequent orbitotomy performed in the dog. (a) The skin incision extends 1 cm lateral from the medial canthus, along the dorsal edge of the zygomatic arch, and terminates about 2 cm caudal of the zygomatic crest. (b) Intraoperative appearance showing the skin incision. The exact position and its length vary depending on the target position (dorsal or ventral) within the orbit. (c) With careful dissection of the subcutaneous tissues, the retractor anguli and orbicularis oculi muscles are transected from their attachments to the lateral orbital ligament to reveal the lacrimal gland (arrow). (d) After transection of the ventral attachment of the lateral orbital ligament to the zygomatic arch, the lateral orbital ligament is reflected dorsally to expose the lateral aspects of the orbital tissues including the zygomatic (orbital) salivary gland (arrow). (e) For exploration of the canine ventral orbit, a central portion of the zygomatic arch is isolated. To maximize entry into the retrobulbar space, the zygomatic arch is removed temporarily by transecting its two ends. It is reattached by four wire sutures during wound closure. (f) A variably sized section of the zygomatic arch periosteum is elevated and portions of the bone are removed by rongeur or bone saw, exposing the majority of the zygomatic salivary gland. (g) Digital exploration of most of the rostral orbital floor is possible. Orbital fat can be excised to facilitate exploration. (A) Lacrimal gland; (B) globe; (C) zygomatic salivary gland; (D) retrobulbar fat. (h) Limited exploration of the medial retrobulbar area is possible by instrumentation (usually a small curved hemostat). (i) Intraoperative appearance in a patient with an orbital mucocele. The cyst wall is being retracted during its excision from within the orbit. After cyst removal, the entire zygomatic gland is also excised. (An alternative to surgery is to inject the mucocele with sclerosing agents, such as tetracycline or polidocanol.) (j) Closure consists of reapposition of the zygomatic arch periosteum, reattachment of the ventral portion of the lateral orbital ligament to the zygomatic arch, and closure of the subcutaneous and skin layers. (k) Immediate postoperative appearance after orbitotomy in the patient from Figure 4.21i. (All drawings with permission from Bistner SI, Aguirre G, Batik, G 1977 Atlas of Veterinary Ophthalmic Surgery. WB Saunders, Philadelphia.)

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infraorbital nerve, pterygopalatine ganglion, and palatine nerves. By digital or blunt instrument probing, the extraocular muscle cone can be evaluated dorsally and ventrally. Removal of some orbital adipose tissues can aid in visualization of the retrobulbar area. A linear incision along the long axis of the retrobulbar muscle cone permits inspection of these tissues, including the orbital portion of the optic nerve. Closure of the lateral orbitotomy apposes the tissues in reverse order (Fig. 4.21j). If excision of tissue or an infected area creates a sizeable defect, a soft rubber or silicone Penrose-type tube is positioned to exit through the masseter muscle ventral to the zygomatic arch. The orbital tissues are usually apposed with a few 2-0 to 4-0 simple interrupted absorbable sutures, as is the periosteum of the zygomatic arch, and the lateral orbital ligament is reattached to the zygomatic arch periosteum with similar type sutures. The zygomatic arch bone will regenerate within the periosteal space. If a single portion of the zygomatic arch was removed, it can be repositioned and wired to the adjacent edges of the arch. If necessary, simple interrupted absorbable sutures are indicated to minimize any dead space. The subcutaneous tissues are apposed with 2-0 to 4-0 simple interrupted absorbable sutures; the skin incision is apposed with 3-0 to 4-0 simple interrupted non-absorbable sutures. As the blink reflex is usually impaired postoperatively, a complete temporary tarsorrhaphy is performed to prevent exposure keratitis. After the blink reflex can be elicited postoperatively, the temporary tarsorrhaphy sutures can be removed (Fig. 4.21k).

medial aspect of the zygomatic arch are separated by blunt dissection with a periosteal elevator. The zygomatic arch, along with the lateral orbital ligament, is reflected dorsally and rostrally from the wound. With the zygomatic arch removed from the surgical site, inspection of the dorsolateral orbit from its rostral border to just in front of the caudal bony orbital wall is possible (Fig. 4.22f). Careful blunt medial dissection of the ventral endorbita reveals the maxillary artery, the maxillary branch of the maxillary nerve, pterygoid muscles, and the pterygopalatine ganglion and nerve. The endorbita of the extraocular muscle cone can be incised carefully along the long axis of the optic nerve. Blunt dissection reveals the optic nerve, ciliary ganglion, retractor bulbi muscles, and the posterior aspects of the globe. Closure of the surgical wound begins with replacement of the zygomatic arch with 18 g stainless steel wire sutures through the eight previously drilled holes and reattachment of the masseter muscle to the ventral zygomatic arch. The edges of the temporalis muscle are reapposed to their original position at the external sagittal crest, external zygomatic process, and the dorsal edge of the zygomatic arch with 2-0 to 4-0 simple interrupted absorbable sutures. The subcutaneous tissues are apposed with 2-0 to 4-0 simple interrupted or simple continuous absorbable sutures. The skin is apposed with 2-0 to 4-0 simple interrupted nonabsorbable sutures (Fig. 4.22g). A rubber or silicone Penrosetype drain, positioned in the retrobulbar space and directed beneath the zygomatic arch for surgical drainage, is indicated for a few days postoperatively. A complete temporary tarsorrhaphy finalizes the procedure.

Major lateral orbitotomy This modified lateral and more versatile orbitotomy provides both lateral and dorsal exposure of the posterior orbit (extraconal space), the intraconal space (with the lateral rectus muscle insertions incised), and for those infrequent patients that appear to have both lateral and dorsal retrobulbar (such as zygomatic gland cysts and neoplasms) or intraconal orbital masses. After surgical preparation and draping, the initial skin incision is made by scalpel blade, starting at the posterior aspect of the zygomatic arch and continuing along the dorsal zygomatic arch to the posterior aspects of the lateral orbital ligament (Fig. 4.22a). The skin incision is then continued dorsally following the posterior curve of the zygomatic process of the frontal bone to terminate in the middle of the external sagittal crest (Fig. 4.22b,c). The palpebral nerve lies subcutaneous and dorsal to the zygomatic arch and should not be disturbed. The skin flap is dissected free of its subcutaneous attachments and reflected caudally. The rostral aponeurosis of the temporalis muscle is incised about 4 mm from its rostral and medial edges to permit convenient reapposition. The temporalis muscle is reflected sufficiently caudally to expose the dorsal retrobulbar space (Fig. 4.22d,e), either by separating its attachment to the periosteum of the parietal bone or by a periosteal elevator to remove both the periosteum and temporalis muscle attachment together. After some superficial dissection, the zygomatic arch is isolated and four holes are drilled at each end prior to its resection. These holes will be used to reattach the zygomatic arch during closure. Both ends of the zygomatic arch are incised, and the temporalis and masseter muscles on the

Dorsal orbitotomy This extensive orbitotomy, reported by Slatter and Abdelbaki in the dog, yields reasonable exposure of the dorsomedial orbital wall, anterior frontal bone and zygomatic process, and the dorsal retrobulbar tissues, and is less often performed. This surgical approach can also damage some portions of the palpebral nerve, particularly the branches to the upper eyelid. In this procedure the temporalis muscle attachments to the frontal bone are reflected dorsally and posteriorly to provide access to the dorsal orbit and retrobulbar area. After draping, a curved skin incision is made, starting external to the sagittal crest and continuing along the posterior margin of the lateral orbital ligament. This skin flap is reflected laterally and ventrally. The periosteum of the frontal bone next to the sagittal crest is incised by scalpel and the temporal muscle reflected caudally with a periosteal elevator, and laterally to the lateral orbital ligament. With this flap of temporal muscle reflected laterally, the dorsal orbit and retrobulbar muscles can be visualized. Closure starts with reapposition of the periosteum along the external sagittal crest, and routine closure of the subcutaneous and skin layers.

Anterior orbitotomies The anterior orbitotomy procedure may be used for lesions in the anterior orbit that are cranial to the equator of the globe. Indications for this approach include zygomatic gland cysts and masses, nictitating membrane cysts and tumors, extraocular muscle biopsies, some retinal detachment surgeries, and disorders of the lacrimal gland.

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G Fig. 4.22 The lateral orbitotomy reported by Slatter and Abdelbaki provides for more extensive exposure of the dorsal canine orbit. (a) The initial skin incision extends the entire length of the zygomatic arch. (b) The skin incision is continued dorsal and immediately lateral of the frontal crest: (A) skin flap; (B) lateral orbital ligament; (C) zygomatic arch; (D) frontal crest. (c) Operative appearance of the lateral orbitotomy skin incision. (d) To reflect the temporalis muscle (arrow) caudally, its aponeurosis is incised along the external frontal and sagittal crests, and the dorsal aspects of the zygomatic arch. A major section of the zygomatic arch is transected and eight holes are pre-placed to facilitate its reattachment. (e) Operative appearance of the U-shaped incision of the aponeurosis of the temporalis muscle prior to its elevation and reflection caudally. The zygomatic arch is immediately below the lower temporalis muscle incision. (f) With removal of the central zygomatic arch and caudal reflection of the temporalis muscle from its medial and lateral attachments, a major portion of the posterior orbit can be directly explored. (A) Frontalis muscle; (B) temporalis muscle; (C) lateral rectus muscle; (D) ventral oblique muscle; (E) ventral rectus muscle; (F) optic nerve; (G) resected zygomatic arch and lateral orbital ligament. (g) Immediate postoperative appearance after lateral orbitotomy for the excision of a zygomatic salivary mucocele. Following this procedure, the patient’s blink reflex may be impaired and a temporary tarsorrhaphy is used for 7–10 days to protect the cornea. The tarsorrhaphy sutures are not removed until a ‘brisk’ blink reflex returns. (All drawings with permission from Slatter DH, Abdelbaki Y 1979 Lateral orbitotomy by zygomatic arch resection in the dog. Journal of the American Veterinary Medical Association 175:1179–1183.)

Access to the anterior orbit may be through either the bulbar conjunctiva (transconjunctival) or the eyelids (transpalpebral). These two approaches provide limited exposure to the retrobulbar (intraconal) space and tissues. Often the dorsal or dorsolateral anterior orbit is entered via the transconjunctival approach which avoids damage to the palpebral nerve branches. Entry into the dorsal orbit may be through either limbal or fornix-based conjunctival incisions. The transpalpebral approach is used for lesions in the ventral anterior orbit. The approach is through the lower eyelid and under the ventral conjunctival fornix. Both of these

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approaches are indicated for orbital biopsies, and to excise conjunctival neoplasms that extend caudally into the anterior orbit. The surgical approach through the conjunctiva has a greater chance of sepsis as this area cannot be sterilized preoperatively. With both anterior approaches, the lid and conjunctival incisions are parallel to the orbital rim. The dissection is continued deeper by blunt tenotomy or strabismus scissors. Once the mass is ‘shelled out’, closure is usually by two layers for the transconjunctival approach, apposing the subconjunctiva, endorbita, and conjunctiva with 4-0 simple

Orbitotomy in large animals and special species

interrupted absorbable sutures. For the transpalpebral approach, the endorbita and tarsus are apposed with 4-0 simple interrupted absorbable sutures and the skin with 2-0 to 40 simple interrupted non-absorbable sutures. Sometimes to facilitate orbital exposure, insertions of the rectus muscles are incised, and reattached later with 6-0 absorbable mattress sutures.

Transoral orbitotomy The transoral approach to the caudal orbit is immediately behind the last molar teeth in the dog and cat, and used for fine-needle aspiration of orbital masses, and ventral drainage of orbital cellulitis and abscessation. In the dog, this portion of the orbital floor is composed primarily of the medial pterygoid muscle and periorbital fascia, and the oral submucosa and mucosa (Fig. 4.23). In the cat, the caudal orbital floor is quite thin, consisting of only a small shelf of tuberous maxillary bone and soft tissues. The oral approach, because of its very limited exposure, is used primarily for culture and cytology of the retrobulbar space, and to provide ventral drainage for orbital cellulitis. Because the mouth is a septic environment, entry into the orbit generally requires the perioperative administration of systemic antibiotics. After short-acting general anesthesia, the animal is intubated and a mouth speculum positioned. Povidone–iodine (0.5% solution) is applied to the oral mucosa immediately caudal to the last molar tooth. After a 5–10 mm linear incision, a blunt probe is inserted into the retrobulbar space. Bacterial and fungal cultures and cytology specimens can be collected. The incision is not closed, but allowed to heal by secondary intention.

Total and partial orbitectomy The partial and total orbitectomy procedures are used to treat orbital and periorbital neoplasia, and include removal of the eye, the other orbital tissues, and not infrequently adjacent bony, sinus, nasal, and oral structures. Muscles adjacent to the orbit, such as the temporalis and masseter, and bones, such as portions of the frontal, zygomatic arch,

Fig. 4.23 Oral orbitotomy: Immediately posterior to the last molar tooth (arrow) is the area to enter the orbit from the mouth. This entry site is most useful for orbital culture and cytology, and to provide ventral drainage for septic orbital cellulitis.

maxilla, and others, may be excised. With total orbitectomies, the globe is removed. Although these more radical surgical approaches are definitely more aggressive, there was local recurrence of orbital neoplasia in 37% of the patients. However, 50% of the patients remained tumor free for 12 months postoperatively.

Orbitotomy in large animals and special species An orbitotomy is indicated in the horse for excision or biopsy of orbital or retrobulbar masses, removal of orbital foreign bodies, and drainage of retrobulbar abscesses that are not responsive to systemic therapy. An orbitotomy may be needed to repair orbital fractures in the horse. Orbitotomies are rarely performed in horses due to the complex nature of the anatomy of the equine orbit and the infrequent indications for the procedure. The most frequent indication is to provide exposure to repair orbital fractures. Due to the infrequent use of the procedure, the surgeon should prepare a careful surgical plan preoperatively, review the anatomy of the area, and peruse the surgical literature to plan the surgical episode. Orbitotomy is a challenging procedure and requires advance planning. An equine skull for review and for visualization of threedimensional concepts during surgery is helpful. An equine anatomic atlas is also helpful. A general equine surgical instrument pack and orthopedic instruments are necessary. An oscillating bone saw, orthopedic drill, periosteal elevators, wire ‘tighteners’, and rongeurs are needed. Two orbital surgical procedures have been described for orbital exploration in the horse: 1) a dorsal orbitotomy approach (Basher et al); and 2) osteotomy of the zygomatic, temporal, and frontal bone components of the zygomatic arch (Koch, Goodhead, and Colitz). The dorsal orbitotomy technique is initiated by careful attention to skin preparation for aseptic surgery. A generous, slightly curved skin incision is made over the dorsal orbit, lateral to the external sagittal crest of the frontal and parietal bones, extending posterior to the zygomatic process of the frontal bone. Lateral retraction of the attachments of the frontoscutularis, interscutularis, and temporal muscles to the temporal and frontal bones allows exposure of the extraocular muscle cone. The second technique involves resection of the zygomatic, temporal, and frontal bone components of the zygomatic arch. A large lateral canthotomy is performed to maximize exposure. A curved skin incision is made over the zygomatic process of the frontal bone, care being taken to preserve the sensory nerve fibers from the frontal nerve and the motor fibers to the orbicularis oculi muscle laterally from the palpebral branch of the facial nerve. The periosteum of the cranial rim of the zygomatic process is incised along its length, and the aponeuroses of the frontoscutularis, interscutularis, temporal, and masseter muscles are reflected. Next, 1.5–2 mm holes are predrilled in the zygomatic process of the frontal bone, the zygomatic arch, and the zygomatic process of the temporal bone. Three bone cuts are then made with an oscillating bone saw. The first is through the zygomatic process of the frontal bone, the next through the zygomatic arch, and the last through the zygomatic

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process of the temporal bone. The resulting wedge of bone is removed to expose the dorsolateral orbit, retrobulbar muscle cone, and the orbital lacrimal gland. The bone wedge is placed in a bowl of sterile saline until needed to replace the bony defect. The orbital lesion is addressed by excision, biopsy, or aspiration. Iridium seeds may be implanted or cisplatin injected into a cancerous mass. The procedure is completed by replacing the bone wedge and using 18–22 g stainless steel wire to reattach the bone through the predrilled holes. The periosteum is reattached using 3-0 polyglycolic acid sutures in a simple interrupted pattern. The subcutaneous tissues are closed with 3-0 to 4-0 absorbable sutures. Skin and lateral canthotomy incisions are sutured with 3-0 to 4-0 nylon or prolene sutures.

possible, using walking sutures and vertical mattress sutures, and the remaining defect is allowed to heal as a granulating open wound or by second intention. Early in the healing process the area should be disinfected, kept clean, and bandaged. Parenteral antibiotics are administered until a good granulation bed is present in the orbit. The orbit is flushed with sterile saline until a healthy granulation tissue bed covers the orbit; lavage is then continued with water. Owners should be prepared for a long-term management period, but a good result can be expected in most cases. Reconstructive skin flaps and grafts should also be considered. Consultation with an equine surgeon is of benefit to determine the best therapeutic modality for each case.

Orbital fracture repair An orbital rim fracture is a potential globe- and visionthreatening injury. These fractures may result in bone fragment displacement, impingement of extraocular muscles, laceration of the globe, impairment of the blink reflex, and restriction of ocular movement. The dorsal orbital rim is fractured most frequently. Diagnosis may be made by examination and palpation, by orbital radiographs, and by CT. The zygomatic arch of the frontal bone may be fractured in one piece. Reduction is usually facilitated by intravenous non-steroidal anti-inflammatory agents and warm compresses for 12–24 h. The fracture may be reduced and repositioned without a surgical incision and without fixation devices. Bone chips in comminuted orbital fractures that are too small to be fixed in position are preferably removed to prevent bone sequestration and osteomyelitis. Ventral orbital rim fractures also occur from various injuries. Polo horses may be more prone to ventral orbital rim fractures. Traumatic fractures of the medial orbit may affect the nasolacrimal canaliculus or nasolacrimal duct. Horses that fall over backward may have fractures of the basioccipital bone and basisphenoid bone of the inner orbit resulting in blindness. CT will delineate these fractures clearly, whereas orbital radiographs do not allow optimal visualization.

Surgical management of traumatic proptosis in small animals Although the surgical management of traumatic proptosis involves primarily eyelid and lateral canthal surgery, proptosis is an important acute orbital disease. The prognosis for traumatic proptosis is determined by several factors. The breed of the dog should be considered as traumatic proptosis occurs more frequently in brachycephalic breeds with shallow orbits and large palpebral fissures. The trauma to produce proptosis in brachycephalic breeds is less than in mesocephalic and dolichocephalic breeds. Traumatic proptosis in cats is infrequent, and is associated with considerable trauma; skull and/or mandibular fractures are often concurrent (Fig. 4.24). The duration of the proptosis must be considered: the longer the cornea is exposed, the more extensive the damage to the epithelium and stroma, and the more extensive the retrobulbar hemorrhage and edema. The size of the resting pupil and the light-induced pupillary reflexes can help to assess possible damage to the optic nerve and pupillary pathways. A widely dilated pupil, with

Partial orbital rim resection for large eyelid skin defects/cosmetic skin orbitectomy When large eyelid skin resection is needed to remove neoplastic masses following enucleation or exenteration, an orbital rim resection will assist closure of the skin margins. In this procedure, the globe is removed, and the neoplastic mass is excised with a large margin. If the skin margins are too far apart to be apposed, an osteotome or oscillating bone saw is used to remove a large amount of the dorsal and lateral rim of the zygomatic process, allowing sufficient movement of the skin to achieve more close apposition of the skin edges. Walking sutures may be used to assist in skin movement to cover the defect. A cross mattress suture pattern may be used, with gradual tightening of the sutures to close the defect. Releasing incisions are also beneficial in allowing adequate skin to cover the defect completely. In severe cases, when sufficient skin cannot be mobilized even with zygomatic arch resection, the orbit may remain open and heal. In these cases the skin is closed as much as

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Fig. 4.24 Proptosis in the cat usually requires a more guarded prognosis than in the dog, because the trauma to displace the globe from the orbit is more extensive, and the resultant damage to the eye and orbit is considerable.

Surgical augmentation of orbital volume in small animals

limited or no light-induced pupillary reflex, signals neural damage. Traumatic proptosis is rare in the other species, and in the horse often incomplete, presenting as acute exophthalmia (secondary to intraorbital hemorrhage), impaired and incomplete blink reflex, and progressive corneal ulceration. Careful orbital examination may detect orbital bone fractures with variable displacement. The prognosis for vision must be cautious, as blindness occurs in about 60% of dogs and 100% of cats. Postproptosis strabismus in dogs is frequent, occurring in 36% of the dogs. The medial rectus muscles are most frequently avulsed; the ventral rectus and ventral oblique muscles are less often involved. Traumatic proptosis is one of the few ophthalmic emergencies in all species (Fig. 4.25). As soon as possible, topical solutions should be applied frequently to the exposed cornea to minimize damage. After total patient evaluation and short-acting general anesthesia, the eyelids are prepared quickly for aseptic surgery. After draping, a liberal (10–15 mm) lateral canthotomy is performed with Steven’s tenotomy or strabismus scissors. A lateral canthotomy is Fig. 4.26 Replacement of the globe during lateral canthotomy and complete temporary tarsorrhaphy. As in this patient, hemorrhage within the orbit causes the globe to place considerable pressure on the temporary tarsorrhaphy. Small clear plastic or rubber band stents are placed under the interrupted mattress sutures to maintain the complete temporary tarsorrhaphy for 10–14 days.

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usually necessary to increase the size of the palpebral fissure in order to return the globe to the orbit. To temporarily cover the cornea and provide direct pressure to the globe, so as to decrease orbital hemorrhage and orbital edema, a complete temporary tarsorrhaphy is performed (Fig. 4.26). Four to six 2-0 to 4-0 non-absorbable interrupted horizontal sutures with stents are pre-placed. Stents may consist of old intravenous tubing, buttons, wide rubber bands or silicone strips. Stents are indicated because of eyelid edema and the considerable pressure that occurs on these sutures. Once all of the eyelid sutures are placed, they are tightened and tied with long ends to accommodate either intermittent ophthalmic examinations or to permit adjustments as the eyelid and orbital swelling decreases. The postoperative medical management of traumatic proptosis will be summarized in the subsequent section.

Surgical augmentation of orbital volume in small animals

B Fig. 4.25 Traumatic proptosis in a small mixed-breed dog. (a) The globe is displaced beyond the eyelid margins and subconjunctival hemorrhage is evident. (b) Appearance of the globe after replacement and the sutures are tied.

Enucleation and exenteration surgeries, trauma, and inflammation can significantly reduce orbital volume, such that health and function of the eye may be impaired. When significant amounts of orbital tissue (including the eye) have been lost, surgical implants such as the silicone and methyl methacrylate spheres (flattened on one side) may be positioned and anchored within the orbit. Non-absorbable sutures (nylon or mylar) and surgical mesh may be used to bridge the bone orbital opening before a permanent tarsorrhaphy is performed to reduce the postoperative concavity that follows.

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POSTOPERATIVE CARE AND MANAGEMENT Perioperative antibiotics are indicated in most orbital surgical procedures. Surgical entry into the orbit through the conjunctiva or mouth should always be considered as possibly contaminated, as these surfaces cannot be sterilized. Surgical drains are infrequently placed in small animals except after lateral and dorsal orbitotomies. Topical antibiotics are instilled perioperatively for eviscerations, and after the more difficult orbitotomies. Systemic corticosteroids and NSAIDs are often administered systemically after traumatic proptosis and eviscerations to reduce orbital inflammation and swelling. Diuretics may also assist in the reduction of excessive orbital fluids. Warm and cold compresses can reduce postoperative eyelid and orbital swelling after all of these surgical procedures. Use of the E-collar postoperatively is good preventive therapy against self-trauma. For those patients with considerable orbital swelling and a visual eye, a complete temporary tarsorrhaphy is often indicated to protect the cornea. Postoperative exophthalmia may increase and impair the blink reflex. Partial-to-complete loss of the blink reflex produces a central corneal ulceration that often progress rather rapidly. The tarsorrhaphy should remain until a vigorous blink reflex returns, which may be several weeks. Hence, single sutures from the tarsorrhaphy may be removed over several days to weeks, to maintain corneal health.

Postoperative complications and treatment in all species Enucleation The complications after enucleation are not usually serious. Swelling immediately after surgery is usually associated with orbital hemorrhage; it may be more frequent after the transpalpebral technique than the subconjunctival method. Orbital hemorrhage may be associated with poor hemostasis during surgery, or from blood vessels that did not bleed and were not ligated during surgery because of the low blood pressure. Counterpressure with a temporary facial bandage is a possibility. Ice packs for a few hours postoperatively may reduce the swelling. Some hemorrhage may also be apparent between the sutures in the skin incision. Orbital hemorrhage may also exit the nose and is thought to be related to the passage of orbital blood through the nasolacrimal system. Postoperative infections after enucleation are infrequent in small animals because of the perioperative administration of systemic antibiotics. Infections usually occur within the first week postoperatively. Culture of the orbital contents is recommended for the selection of the most appropriate antibiotic(s) after oral orbitotomy for orbital cellulitis or for postoperative orbital infections. High levels of systemic antibiotics are recommended for 7–10 days. Postoperative orbital infections with an orbital prosthesis usually require removal of the implant to resolve the orbital infection. Intraorbital prostheses may be less successful in cats than in dogs; about 20–40% of the implants extrude in cats. The reasons are not understood, and although fluid

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Fig. 4.27 Postoperative appearance of a young Great Dane 5 weeks after enucleation. With the short-hair coat breeds, postoperative disfigurement and concavity of the orbit occurs.

accumulation around the implant is a common finding in cats, septic infections are not usually present. The most frequent long-term complication after enucleation is the contracture of the orbital space and the concavity of the permanent complete tarsorrhaphy. This sinkage may be quite noticeable in short-haired dogs and cats, but less obvious in long-haired breeds (Fig. 4.27). Implantation of an orbital sphere after enucleation will markedly reduce the postoperative orbital and eyelid deformity to acceptable levels. Swelling of the orbit or space between the conjunctival sacs may develop infrequently weeks to months postoperatively. Retained lacrimal and/or nictitating membrane glandular tissues are the most likely sources if the swelling is liquid. If the swelling becomes troublesome, excision of the respective glands will generally resolve the problem. Orbital emphysema occurs infrequently postoperatively, and appears to be caused by the passage of air from the nose, through the nasolacrimal duct, into an anterior orbital space. Sneezing by the animals can initiate rather acute and marked swelling of the complete permanent tarsorrhaphy. Resolution consists of excision of one or both of the patent lacrimal puncta. Occasionally a small but chronic fistula from retained conjunctiva may develop, resulting in small amounts of brown fluid that stain the eyelids. Treatment consists of freshening the fistula’s edges and apposition by sutures. Occasionally the lacrimal and/or nictitating membrane gland may also need to be excised.

Evisceration The evisceration procedure is nearly always accompanied with an intraocular prosthesis (Fig. 4.28). The surgical success rate of eviscerations in dogs is 90–95%, but is not reported in cats and horses. Postoperative infections are infrequent, but can necessitate prosthesis removal and even enucleation. Perioperative antibiotics seem to prevent most

Postoperative complications and treatment in all species

A

B

Fig. 4.28 (a) Postoperative appearance of bilateral evisceration with an intrascleral silicone prosthesis 12 months after surgery in a 10-year-old Beagle. The presurgical condition was absolute primary glaucoma which was intractable to continued topical medications. (b) Close-up of the right eye. Usually some corneal edema and/or pigmentation occur after this procedure. Topical medications after 2–4 weeks postoperatively are usually not necessary.

postoperative infections. Long-term successful eviscerations require an intact and reasonably healthy cornea. Postoperative corneal diseases, possibly related to the intraocular implant, include corneal erosions and ulcerations (Fig. 4.29). Often the cornea is compromised preoperatively, as in glaucoma. During evisceration surgery, instrument contact with the posterior cornea is avoided, and in spite of the often considerable hemorrhage that accompanies the procedure, excessive flushing of the globe should be avoided. These corneas usually demonstrate edema postoperatively, but often some clearing will occur in 4–8 weeks. Some corneal superficial pigmentation and vascularization may remain permanently, but are not usually objectionable. Other extraocular diseases, such as keratoconjunctivitis sicca, may affect the cornea and indirectly the intraocular prosthesis success rate. Surgical wound dehiscence is minimized when the scleral

rather than the limbal incision is used. With the extensive incision (often 180 ) necessary to insert the near-globe size prosthesis, considerable corneal or scleral nerves may be transected, rendering these postoperative corneas subject to lower sensitivities, less frequent blinking, and increased exposure. Several weeks may be necessary for these corneal nerves to regenerate. In the event that a central corneal ulcer develops after the evisceration procedure, aggressive medical therapy (antibiotics and serum topically) and often a bulbar conjunctival graft is indicated. If the corneal ulcer becomes full thickness, a conjunctival graft is essential. Infection from the corneal ulcer into the globe with the prosthesis generally requires enucleation.

Exenteration The complications after exenteration are similar to those associated with enucleation. The postoperative swelling and the long-term wound contracture are usually greater because of the larger amounts of orbital tissues that have been excised.

Orbitotomy

Fig. 4.29 After evisceration, the most frequent complication with an intrascleral prosthesis is a central corneal ulcer which develops immediately postoperatively. This is usually very slow healing and typically requires a bulbar pedicle conjunctival graft to resolve quickly. Corneal ulceration after the evisceration procedure is best prevented by a temporary tarsorrhaphy for 10–14 days or until normal blink reflex returns.

The immediate postoperative complications after orbitotomies are usually related to exophthalmia secondary to retrobulbar swelling and hemorrhage, especially after the lateral approaches. The lateral orbitotomies usually transect at least some of the palpebral nerve branches that supply the upper eyelid. As a result, a temporary complete tarsorrhaphy is recommended after all orbitotomies until eyelid swelling is reduced, and a reasonable blink response returns (which may be several weeks). Without a blink reflex, neuroparalytic keratitis and corneal ulceration can develop rapidly. If the lacrimal gland innervation is impaired, tear production may also be insufficient. Oral pilocarpine (usual dose for a 15 kg dog is 2 drops of 2% ophthalmic pilocarpine well mixed in the food, twice daily) will successfully stimulate the denervated gland.

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Post-proptosis Complications after the surgical treatment of traumatic proptosis include short-term retrobulbar hemorrhage and swelling, and corneal malacia and ulceration with secondary iridocyclitis. Systemic corticosteroids, NSAIDs, and diuretics can be administered to rapidly reduce the retrobulbar fluids, and reduce the pressure on the globe and intraorbital portion of the optic nerve. Treatment of corneal disease, hyphema, and anterior uveitis usually consists of topical antibiotics and mydriatics administered between the complete temporary tarsorrhaphy sutures or by the subpalpebral system. Long-term sequelae of traumatic proptosis include enophthalmia and limited globe mobility (related to the loss of orbital fat and orbital fibrosis), optic nerve atrophy (related to excessive pressure of the optic nerve and possible ischemia of the optic nerve), pigmentary keratitis, lagophthalmia, papilloedema, and exotropia (most often divergent strabismus related to palsy or transection of the medial rectus muscle; Fig. 4.30). Attempts to correct the exotropia are not always successful. If the innervation to the medial rectus muscle has been impaired, spontaneous partial-to-complete recovery may occur in several months. If the exotropia is secondary to tearing of the medial rectus muscle or its insertion, spontaneous recovery is unlikely. Treatment usually consists of reapposition of the torn medial rectus portions, or splitting the dorsal rectus muscle and reattaching it medially as previously described.

Short- and long-term results in all species Enucleation The short- and long-term results after enucleation are good. The majority of complications can be either medically or surgically managed. The deformity associated with the loss of the eye is greatly reduced by the use of orbital prostheses.

Fig. 4.30 One of the more frequent complications after traumatic proptosis in the dog is lateral strabismus, which results from either rupture of the medial rectus muscle (the shortest of the retrobulbar muscles) or its insertion just posterior to the globe. Damage to this muscle and/or its nerve supply causes lateral strabismus. A shallow ventral corneal ulcer is also present; it resulted from exposure and an inadequate blink reflex.

86

Although the patient numbers are still limited, intraorbital prostheses may be less successful in cats.

Evisceration The evisceration procedure with intraocular prosthesis has largely replaced the enucleation procedure for the treatment of end-stage, blind, painful and enlarged glaucomatous eyes. The postoperative results are a corneoscleral shell with an intrascleral sphere that is cosmetically acceptable, painless, and has normal ocular movements with the fellow eye. Use of the evisceration procedure with intrascleral prostheses for globes with non-specific uveal inflammations and suspected intraocular neoplasms is not recommended. As a quality control, the intraocular tissues after evisceration should always be examined histologically. The success rate in dogs after evisceration with intrascleral prosthesis is 90–95%, with corneal ulceration as the most frequent complication. As corneal ulcerations tend to heal very slowly in postoperative evisceration eyes with intraocular prostheses, early treatment with bulbar conjunctival grafts is recommended.

Exenteration The short- and long-term success after exenteration is less than with enucleation and evisceration, because this procedure is used primarily for the attempted excision of primary orbital neoplasms. In the event that total excision of the primary orbital neoplasm is achieved, the main evidence of exenteration is the complete permanent tarsorrhaphy, and sinkage of the eyelids and orbit associated with the loss of all of the orbital tissues. Use of a silicone or methyl methacrylate sphere within the orbit after exenteration can markedly reduce, but not totally eliminate, the postoperative sinkage.

Orbitotomy The judicious choice of a specific orbitotomy procedure for orbital disease will minimize the possible short- and longterm side effects. Orbitotomy procedures provide excellent results when used for orbital cysts, benign tumors, and focal inflammations. Orbitotomies for orbital neoplasia are less successful, because the incomplete excision of these malignant tumors is often unavoidable. Based on current information available on canine primary orbital neoplasms, exenteration or the orbitectomy procedure may be the preferred surgical procedure. The orbitectomy procedure may have more success with complete excision of malignant orbital neoplasms than the lateral orbitotomy methods, but results in more postoperative disfigurement. A common sequela to surgery, some periorbital fibrosis usually develops, resulting in some enophthalmia and restricted globe mobility. The loss of orbital adipose tissue may also result in enophthalmia. Some long-term ptosis or drooping of the upper eyelid may persist, probably related to partial loss of some branches of the palpebral nerve.

Traumatic proptosis Postoperative complications related to the surgical treatment of traumatic proptosis are primarily associated with the

Further reading

disease. The improper placement of the eyelid sutures can produce direct corneal damage. These sutures must only partially penetrate the eyelid thickness, and emerge through the

middle of the eyelid margin. As the eyelid swelling decreases, these sutures may require multiple readjustments to avoid corneal contact.

Further reading Small animals Bartoe JT, Brightman AH, Davidson HJ: Modified lateral orbitotomy for visionsparing excision of a zygomatic mucocele in a dog, Vet Ophthalmol 10:127–131, 2007. Bedford PGC: Orbital pneumatosis as an unusual complication to enucleation, J Small Anim Pract 20:551–555, 1979. Bellhorn RW: Enucleation technique: a lateral approach, J Am Anim Hosp Assoc 8:59–60, 1972. Blocker T, Hoffman A, Schaeffer DJ, Wallin JA: Corneal sensitivity and aqueous tear production in dogs undergoing evisceration with intraocular prosthesis placement, Vet Ophthalmol 10:147–154, 2007. Brightman AH, Magrane WG, Huff RW, Helper LC: Intraocular prosthesis in the dog, J Am Anim Hosp Assoc 13:481–485, 1977. Gilger BC, McLaughlin SA, Whitley RD, Wright JC: Orbital neoplasms in cats: 21 cases, J Am Vet Med Assoc 201: 1083–1086, 1992. Gilger BC, Whitley RD, McLaughlin SA: Modified lateral orbitotomy for removal of orbital neoplasms in two dogs, Vet Surg 24:53–58, 1994. Gross S, Aguirre GD, Harvey C: Tumors involving the orbit of the dog, Proceedings of the American College of Veterinary Ophthalmologists 8:229–240, 1979. Hamor RE, Roberts SM, Severin GA: Use of orbital implants after enucleation in dogs, horses, and cats: 161 cases (1980–1990), J Am Vet Med Assoc 203:701–706, 1993. Hamor RE, Whitley RD, McLauglin SA, Lindley DM, Albert RA: Intraocular silicone prostheses in dogs: a review of the literature and 50 new cases, J Am Anim Hosp Assoc 30:66–69, 1994. Harvey CE: Exploration of the orbit. In Bistner SI, Aguirre G, Batik G editors: Atlas of Veterinary Ophthalmic Surgery, Philadelphia, 1977, WB Saunders, pp 258–260. Hendrix DVH, Gelatt KN: Diagnosis, treatment and outcome of orbital neoplasia in dogs: a retrospective study of 44 cases, J Small Anim Pract 41:105–108, 2000. Hong YJ, Jang SU, Lee JH: Limited orbitotomy without transection of the orbital ligament for zygomatic mucocele in three brachycephalic dogs. In Proceedings of the 38th Meeting of the American College of Veterinary Ophthalmologists: Abstract 4, 2007. Kennedy RE: The effect of early enucleation on the orbit in animals and humans, Am J Ophthalmol 60:277–306, 1965. Kern TJ: Orbital neoplasia in 23 dogs, J Am Vet Med Assoc 186:489–491, 1985.

Kern TJ: The canine orbit. In Gelatt KN editor: Veterinary Ophthalmology, ed 2, Philadelphia, 1991, Lea and Febiger, pp 239–255. Koch SA: Intraocular prosthesis in the dog and cat: the failures, J Am Vet Med Assoc 179:883–885, 1981. Konrade KA, Clode AB, Michau TM, Roe SC, Trumpatori BJ, Krug WV, Gilger BC: Surgical correction of severe strabismus and enophthalmos secondary to zygomatic arch fracture in a dog, Vet Ophthalmol 12:119–124, 2009. Martin CL: Orbital emphysema: a complication of ocular enucleation in the dog, Vet Med 66:986–989, 1971. McLaughin SA, Ramsey DT, Lindley DM, et al: Intraocular silicone prosthesis implantation in eyes of dogs and a cat with intraocular neoplasia: nine cases (1983–1994), J Am Vet Med Assoc 207:1441–1443, 1995. Mughannam AJ, Reinke JD: Two cosmetic techniques for enucleation using a periorbital flap, J Am Anim Hosp Assoc 30:308–312, 1994. Nasisse MP, van Ee RT, Munger RJ, Davidson MG: Use of methyl methacrylate orbital prostheses in dogs and cats: 78 cases (1980–1986), J Am Vet Med Assoc 192:539–542, 1988. O’Brien MG, Withrow SJ, Straw RC, et al: Total or partial orbitectomy for the treatment of periorbital tumors in 24 dogs and 6 cats: a retrospective study, Vet Surg 25:471–479, 1996. Prince JH, Diesem CD, Eglitis I, Ruskell GL: Anatomy and Histology of the Eye and Orbit in Domestic Animals, Springfield, 1960, CC Thomas, pp 65–181 and 260–297. Ramsey DT, Fox DB: Surgery of the orbit, Vet Clin North Am Small Anim Pract 27:1215–1264, 1997. Riggs C, Whitley RD: Intraocular silicone prosthesis in a dog and a horse with corneal lacerations, J Am Vet Med Assoc 196:617–619, 1990. Simpson HD: Reconstructive surgery of the eye. I. Plastic eye prosthesis, North Am Vet 37:770–777, 1956. Slatter DH, Abdelbaki Y: Lateral orbitotomy by zygomatic arch resection in the dog, J Am Vet Med Assoc 175:1179–1183, 1979. Speakman AJ, Baines SJ, Williams JM, Kelly DF: Zygomatic salivary cyst with mucocele formation in a cat, J Small Anim Pract 38:468–470, 1997. Spiess BM: Diseases and surgery of the canine orbit. In Gelatt KN editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 539–562.

Wang AL, Ledbetter EC, Kern TJ: Orbital abscess bacterial isolates and in vitro antimicrobial susceptibility patterns in dogs and cats, Vet Ophthalmol 12:91–96, 2009. Whitley RD, Shaffer KW, Albert RA: Implantation of intraocular silicone prosthesis in dogs, The Compendium 7:802–811, 1985.

Large animals and special species Basher AW, Severin GA, Chavkin MJ, Frank AA: Orbital neuroendocrine tumors in three horses, J Am Vet Med Assoc 210:668–671, 1997. Baumel JJ, Whitmer LM: Osteologia. In Baumel JJ editor: Handbook of Avian Anatomy: Nomina Anatomica Avium, Cambridge, 1993, Nuttall Ornithological Club, pp 45–132. Beard WL, Wilkie DA: Partial orbital rim resection, mesh skin expansion, and second intention healing combined with enucleation or exenteration for extensive periocular tumors in horses, Vet Ophthalmol 5:23–28, 2002. Blogg JR, Stanley RG, Philip CJ: Skull and orbital blow-out fractures in a horse, Equine Vet J (Suppl 10): Equine Ophthalmology 5–7, 1990. Bradecamp EA, Matter NE: How to perform an enucleation in the standing horse, Proceedings of the American Association of Equine Practitioners 50:237–239, 2004. Brooks DE: Orbit. In Auer JA editor: Equine Surgery, Philadelphia, 1992, WB Saunders/ Harcourt Brace Jovanovich, pp 654–666. Brooks DE: Ocular emergencies and trauma. In Auer JA, Stick JA editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 508–514. Brooks DE: Orbit. In Auer JA, Stick JA editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 502–505. Brooks DE: Ophthalmology for the Equine Practitioner, Jackson, 2002, Teton New Media, pp 36–41. Brooks DE: Orbit. In Auer JA, Stick JA editors: Equine Surgery, ed 3, St Louis, 2006, Saunders, pp 755–766. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274. Caron JP, Barber SM, Bailey JV, Fretz PB, Pharr JN: Periorbital skull fractures in five horses, J Am Vet Med Assoc 188:280–284, 1986. Colitz C, Gilger BC, Davidson MG: Orbital fibroma in a horse, Vet Ophthalmol 3:213–216, 2000.

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Cutler TJ: Diseases and surgery of the globe and orbit. In Gilger BC editor: Equine Ophthalmology, St Louis, 2005, Saunders, pp 63–106. Davis JL, Gilger BC, Spaulding K, et al: Nasal adenocarcinoma with diffuse metastases involving the orbit, cerebrum, and multiple cranial nerves in a horse, J Am Vet Med Assoc 221:1460–1463, 2002. Gelatt KN, Wolf ED, Boyd CL, Titus RS: The special sense organs. In Oehme FW, Prier JE editors: A Textbook of Large Animal Surgery, ed 2, Baltimore, 1988, Williams and Wilkins, pp 623–669. Gilger BC, Davidson MG: How to prepare for ocular surgery in the standing horse, Proceedings of the American Association of Equine Practitioners 48:266–268, 2002. Gilger BC, Pizzirani S, Johnson LC, Urdiales NR: Use of a hydroxyapatite orbital implant in a cosmetic corneoscleral prosthesis after enucleation in a horse, J Am Vet Med Assoc 222:343–345, 2003. Goodhead AD, Vener IJ, Nesbit JW: Retrobulbar extra-adrenal paraganglioma in a horse and its surgical removal by orbitotomy, Veterinary and Comparative Ophthalmology 7:96–100, 1997. Grier R, Kigurardo G, Shaffer C, Pedrosa B, Myers R, Merkley DF, Touvenelle M: Mast cell destruction by deinonized water, Am J Vet Res 51:1116–1120, 1991. Hadick CL, Stoehr A, Rozmiarek H, Przybyla V: Intraocular prosthesis in a cynomolgus monkey, Vet Med Small Anim Clin 78:86–88, 1983. Hamor RE, Roberts SM, Severin GA: Use of orbital implants after enucleation in dogs, horses, and cats: 161 cases (1980–1990), J Am Vet Med Assoc 203:701–706, 1993. Hoffman D, Jennings P, Spradbrow P: Immunotherapy of bovine ocular squamous cell carcinomas with phenol–saline extracts of allogenic carcinomas, Aust Vet J 57:159–162, 1981. Irby NL: Surgical diseases of the eye in farm animals. In Fubini S, Ducharme NG editors: Farm Animal Surgery, St Louis, 2004, Saunders, pp 429–459.

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Ivany JM: Farm animal anesthesia. In Fubini S, Ducharme NG editors: Farm Animal Surgery, St Louis, 2004, Saunders, pp 97–112. Klein WER, Bier J, van Dieten JS, et al: Radical surgery of bovine ocular squamous cell carcinoma (cancer eye): complications and results, Vet Surg 13:236–242, 1984. Kleinschuster S, Rapp H, Green S, Bier J, Kampen K: Efficacy of intratumorally administered mycobacterial cell walls in the treatment of cattle with ocular carcinoma, J Natl Cancer Inst 67:1165–1171, 1981. Koch DB, Leitch M, Beach J: Orbital surgery in two horses, Vet Surg 9:61–63, 1980. Lavach JD: Large Animal Ophthalmology, St Louis, 1990, CV Mosby, pp 225–236, and 289–298. Machado M, dos Santos Schmidt EM, Montiani-Ferreira F: Interspecies variation in orbital bone structure of psittaciform birds (with emphasis on Psittacidae), Vet Ophthalmol 9:191–194, 2006. Martin CL: Ophthalmic Disease in Veterinary Medicine, London, 2005, Manson Publishing, pp 172–178. McLaughlin SA, Gilger BC, Hamilton HL, Whitley RD, Harrison IW, Comer J: Intraocular silicone prosthesis as a cosmetically acceptable alternative to enucleation in horses, Compendium of Continuing Education 17:945–951, 1995. McLelland J: Color Atlas of Avian Anatomy, Philadelphia, 1991, WB Saunders, pp 33–46. Meek LA: Intraocular silicone prosthesis in a horse, J Am Vet Med Assoc 193:343–345, 1988. Michau TM, Gilger BC: Cosmetic globe surgery in the horse, Vet Clin North Am Equine Pract 20:467–484, 2004. Muir WW: Local anesthesia in ruminants and pigs. In Schrefer J editor: Handbook of Veterinary Anesthesia, ed 4, St. Louis, 2005, Mosby, pp 72–99. Mun˜oz E, Leiva M, Naranjo C, Pen˜a T: Retrobulbar dermoid cyst in a horse: a case report, Vet Ophthalmol 10:394–397, 2007. Murphy CJ, Brooks DE, Kern TJ, Queensberry KE, Riis RC: Enucleation in birds of prey, J Am Vet Med Assoc 183:1234–1237, 1983.

Noordsy JL: Food Animal Surgery, ed 3, Trenton, NJ, 1994, Veterinary Learning Systems, pp 82–85. Pizzirani S, Tseng F, Pirie C: Evisceration in three species of owls. In Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 25, 2008. Provost P, Ortenberg AI, Caron JP: Silicone ocular prosthesis in horse: eleven cases 1983–1987, J Am Vet Med Assoc 194:1764–1766, 1989. Ramsey DT, Fox DB: Surgery of the orbit, Vet Clin North Am Small Anim Pract 27:1215–1264, 1997. Riggs C, Whitley RD: Intraocular silicone prosthesis in a dog and a horse with corneal lacerations, J Am Vet Med Assoc 196:617–619, 1990. Rubin LF: Large animal ophthalmic surgery. In Jennings P Jr, editor: The Practice of Large Animal Surgery, vol II, Philadelphia, 1984, Saunders, pp 1151–1201. Schulz K: Field surgery of the eye and paraorbital tissues, Vet Clin North Am Food Anim Pract 24:527–534, 2008. Severin GA: Severin’s Veterinary Ophthalmology Notes, ed 3, Fort Collins, 1996, Colorado State University Press, pp 486–498. Theon AP, Pascoe JR, Carlson GP, Krag DN: Intratumoral chemotherapy with cisplatin in oily emulsion in horses, J Am Vet Med Assoc 202:261–267, 1993. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1275–1335. Turner AS, McIlwrath CW: Techniques in Large Animal Surgery, Philadelphia, 1982, Lea & Febiger, pp 293–296. Turner LM, Whitley RD, Hagar D: Management of ocular trauma in horses. Part 2: orbit, eyelids, uvea, lens, retina, and optic nerve, Mod Vet Pract 67:341–347, 1986.

CHAPTER

5

Surgery of the eyelids Kirk N. Gelatt1 and R. David Whitley2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

89

Entropion in sheep

Anatomy

90

Preoperative examination procedures

93

Entropion and periocular fat pads in the Vietnamese potbellied pig (Sus scrofa)

113

Surgical considerations of the eyelids

94

SURGICAL PROCEDURES FOR ECTROPION

114

Surgical instrumentation

95

Ectropion in the horse

117

Surgical preparations of the eyelids

95

Tarsorrhaphy in small animals

95

Surgical procedures for combined ectropion and entropion

117

Tarsorrhaphy in the horse

97

OTHER SURGICAL PROCEDURES

120

Aftercare for eyelid surgery in the horse

97

Surgical procedures to decrease palpebral fissure size

120

Lateral canthotomy

98

Surgical procedures to increase palpebral fissure size

122

Surgical procedures for eyelid agenesis

98

Nasal fold trichiasis and resection in dogs

123

Surgical treatment of chalazion

123

Surgical repair of eyelid lacerations

123

Surgical procedures for minor eyelid neoplasms in small animals

126

Reconstructive blepharoplasty after removal of eyelid masses in small animals

128

Surgeries for eyelid neoplasia in the horse

132

Blepharoplastic procedures for the horse

133

Bovine eyelid surgery

137

Surgical procedures for distichiasis

100

Surgical procedures for ectopic cilia

103

SURGICAL PROCEDURES FOR ENTROPION IN SMALL ANIMALS

103

Non-surgical treatment of entropion

103

Surgical management of entropion

105

Postoperative management and complications

111

ADAPTATIONS IN LARGE ANIMALS AND SPECIAL SPECIES

112

Entropion in horses

112

Introduction Eyelid diseases are common in dogs and horses, and infrequent in cats and cattle. In contrast to most ophthalmic diseases, the initial clinical management of eyelid disorders is usually surgery. Traditionally, eyelid diseases are divided into congenital and developmental, inflammatory, traumatic, and neoplastic. The clinical management of all of these groups of eyelid diseases, except for the inflammatory types, is surgery. Surgical treatment may also be indicated for the inflammatory eyelid diseases, after resolution with antimicrobial therapy, to restore the eyelid contours and function associated with the excessive postinflammatory scarring and distortion.

113

Diseases of the canine eyelids Congenital and developmental eyelid disorders in dogs, including entropion, ectropion, distichiasis, and trichiasis, may be treated by a number of different surgical procedures. Selection of the surgical technique for a particular condition may be influenced not only by the most effective procedure, but also by the experience of the surgeon and the surgical instrumentation available. In older dogs eyelid neoplasms are common. Although a significant percentage of the canine eyelid neoplasms are malignant histologically, local recurrence after surgical excision is infrequent. The majority of canine eyelid neoplasms can be excised by reasonably simple surgical procedures.

5

Surgery of the eyelids

Diseases of the feline eyelids Eyelid surgery in cats is less frequent, but just as challenging. Eyelid agenesis occurs not infrequently in the cat, usually affecting the lateral aspects of the upper eyelid. Several eyelid surgical procedures have been developed to treat this condition. Eyelid neoplasms in cats are usually malignant histologically and clinically. Surgical intervention is often combined with radiation, cryotherapy, or other types of therapy for best results. Eyelid trauma occurs in the cat, and as one would expect, is most frequent in young animals. The eyelid trauma may be minor or extensive, and fortunately loss of substantial portions of the eyelids is rare. Although traumatized eyelids may exhibit marked swelling and multiple lacerations, the extensive vascularity of the eyelids usually protects against tissue ischemia and necrosis. As a result, excision and liberal trimming of traumatized eyelid tissues prior to repair are unnecessary and discouraged. Reapposition of severely traumatized eyelids usually yields better postoperative results than excision of still attached but lacerated lid tissues and subsequent reconstructive blepharoplastic surgical procedures to repair these defects.

Anatomy The morphology of the eyelids in domestic animals is quite similar, with size being the major variable. The eyelids represent the transition of the integument system and the beginning of the ophthalmic apparatus with the initiation of the palpebral conjunctiva. The eyelids surround the palpebral fissure, through which the eye contacts the environment. The eyelids are divided clinically into the dorsal, superior, or upper eyelid; the ventral, inferior, or lower eyelid; the medial or nasal canthus; and the lateral or temporal canthus (Fig. 5.1). The dorsal eyelid is the largest, most mobile, and 2–5 mm longer than the lower lid. Distinct ligaments, the septum orbitale, and certain muscles attach at both sides of the palpebral fissure, resulting in an oval rather than round eyelid opening. The medial canthal eyelid area is relatively fixed to the subcutaneous tissues and periosteum by the medial palpebral or canthal ligament. Protected immediately behind the medial canthal ligament is the nasolacrimal sac. The lateral canthal region is more mobile, especially in dogs. The lateral canthal ligament is poorly developed in the dog and is replaced by the retractor anguli oculi lateralis muscle. Hence in dogs, defects often affect the lower lid and lateral canthus.

Diseases of the equine eyelids Developmental lid diseases, such as entropion and ectropion, occur rarely in horses; however, trauma and neoplasia occur not infrequently and are often treated by surgery. Like other animal species, eyelid trauma occurs more frequently in young animals, and maintenance of lid function and preservation of the lid margin are most important. Both squamous cell carcinoma and sarcoid neoplasms commonly involve the eyelids in middle-aged to aged horses, and often surgery is combined with other modalities used to treat these neoplasms and achieve higher success rates.

Diseases of the bovine eyelids Of the different lid diseases, only neoplasia warrants not infrequent lid surgery in this species. Squamous cell carcinoma is the most frequent neoplasm in cattle, and occurs in cattle directly related to aging. The average age of the Hereford breed affected with squamous cell carcinoma is about 7–8 years. Lack of lid and conjunctival pigmentation is also associated with this tumor.

Eyelid skin, cilia (eyelashes), and glands The skin of domestic animal eyelids is thinner than other parts of the integument system (Fig. 5.2). Eyelid movements require both thin and pliable skin. Fine short hairs normally cover the eyelid skin. The subcutaneous tissues under the eyelid skin are relatively thin and attach the lid skin to the deeper orbicularis oculi muscle. Cilia or eyelashes occur primarily on the canine upper eyelid, usually in two or four irregular rows. These cilia are usually the same color as the adjacent eyelid hair coat. Long tactile hairs (pili supraorbitales or vibrissae) appear as a tuft along the dorsal medial orbital margin in several animal species. Eyelashes are not present in cats, although the eyelid hair next to the dorsal eyelid margin may be considered a substitute. Two types of gland, the glands of Moll and glands of Zeis, are located about the cilia follicles. The gland of Moll is a modified sweat (apocrine) gland and the gland of Zeis is a modified sebaceous gland. These glands can become inflamed and abscessed in young animals, resulting in the formation A G

Adaptations from eyelid surgeries in humans The early small animal eyelid surgical procedures were adapted from techniques performed in humans. Human eyelids are quite similar to those in domestic animals, with one major difference: in humans the tarsal layer consists of a distinct cartilaginous plate that provides internal support for the eyelids; in domestic animals the tarsal plate has been replaced by a thinner and more flexible fibrous tarsus. As a result, the eyelids of animals have less internal support, and contact with the anterior portion of the globe is more important to maintain their contours and position.

90

C

D F

E

B

Fig. 5.1 The canine eyelids are divided into upper lid (A), lower lid (B), medial canthus (C), and lateral canthus (D). Other important areas include the nictitating membrane (E), caruncle (F), and cilia (G).

Anatomy

Levator anguli oculi medialis Frontalis

A

Orbicularis oculi

D E

B

F Retractor anguli oculi lateralis

C

Pars palpebralis

G

Fig. 5.2 The different layers of the upper eyelid include: skin (A), orbicularis oculi muscle (B), tarsus (C), insertion of the levator palpebrae superioris muscle (D), meibomian glands (E), palpebral conjunctiva (F), and the cilia (G).

of a stye or external hordeolum. The margo-intermarginalis represents the free margin of the eyelids.

Eyelid muscles The second layer of the eyelids is the muscle layer which consists of several muscles that either close or open the palpebral fissure. The orbicularis oculi muscle is the predominant muscle involved in closure of the palpebral fissure in domestic animals. This muscle encircles the entire palpebral fissure and is attached by the septum orbitale to the medial and lateral canthi. It is divided into the inner pars palpebralis and the outer pars orbitalis. Both the origin and insertion of the orbicularis oculi muscle is the medial palpebral ligament. This muscle is immediately beneath the skin layer, and surgical procedures for entropion (inversion of the eyelid margin) and ectropion (eversion of the eyelid margin) directly involve this muscle. In large animal species the orbicularis oculi muscle is very powerful, especially when ophthalmic pain is present. In large animals, local nerve blocks of the palpebral nerve branch of the auriculopalpebral nerve (branch of the facial nerve) is often necessary to relax this muscle to adequately examine and even treat a painful eye. Several muscles are involved in opening the eyelids and increasing the size of the palpebral fissure in the dog and cat. In the canine upper eyelid these muscles consist of (medial to lateral) the levator anguli oculi medialis, levator palpebrae superioris, and the frontalis, and in the lower lid, the pars palpebralis of the sphincter colli profundus (Fig. 5.3). The levator palpebrae superioris muscle has its origin deep within the orbit, along with the rest of the extraocular muscles, and lies immediately above the dorsal rectus muscle that inserts several millimeters from the dorsal limbus of the globe. Fascial attachments between the dorsal rectus and levator palpebrae superioris muscles result in simultaneous upper movements of the globe and retraction

Fig. 5.3 Muscles that control the size of the palpebral fissure in the dog include: orbicularis oculi (close), levator anguli oculi medialis (open), frontalis (open), retractor anguli oculi lateralis (open), and pars palpebralis (open). Mu¨ller’s muscles (open) and levator palpebrae superioris (open) are not shown.

of the upper eyelid. The levator palpebrae superioris muscle seems to be the most important muscle for upper lid retraction as damage to this muscle or its insertions into the tarsal layer results in ptosis (or drooping of the upper eyelid). The levator anguli oculi medialis muscle elevates the medial upper eyelid and erects the long tactile hairs of the eyebrow. In some of the large breeds of dogs, the action of this muscle results in a noticeable notch at the junction of the medial and middle one-thirds of the upper lid. In the dog, Mu¨ller’s smooth muscle fibers, innervated by the sympathetic nerves, attach to the upper tarsus; in the cat, these muscle fibers also attach to the nictitating membrane. With the release of endogenous adrenaline (epinephrine), or during the fightand-flight reflex, these adrenergic innervated smooth muscle fibers can immediately increase the size of the palpebral fissure. In the cat, the major muscle for closing the palpebral fissure is the orbicularis oculi. The corrugator supercilii medialis raises the majority of the upper eyelid, but laterally the frontoauricularis helps to elevate the upper lid. Lateral and as a substitute for the lateral canthal ligament, the corrugator supercilii lateralis elongates the palpebral fissure. The lower eyelid is relatively fixed and only the orbicularis oculi is present to close the palpebral fissure. In the horse, the anatomy of the eyelids follows the other mammalian patterns. The upper lid is considerably larger than the lower lid and contributes most of the lid motility. The lacrimal puncta are about 2 mm in diameter and about 8 mm from the medial canthus. The medial canthus can be prolonged medioventrally and possesses a prominent, occasionally pigmented, caruncle. The upper lid possesses about 40–50 meibomian glands dorsally and 30–35 glands ventrally. In cattle, the eyelids are quite similar to the horse. They are very thick and strong! The orbicularis oculi is often in small bundles and extends to the edge of the lid margin. The orbicularis oculi is attached medially to the strong medial palpebral ligament and lacrimal bone. Although cattle possess a small and weak lateral palpebral ligament, entropion and ectropion occur rarely in cattle. There are

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Corrugator supercilii medialis

Frontoauricularis

Dorsal portion of orbicularis oculi

Ventral portion of orbicularis oculi

Corrugator supercilii lateralis (retractor anguli oculi)

Fig. 5.4 Muscles that control the size of the palpebral fissure in the cat include: orbicularis oculi (close), corrugator supercilii lateralis (open), frontoauricularis (open), and corrugator supercilii medialis (open). Mu¨ller’s muscles (open) are not shown.

about 32–34 meibomian glands in the upper lid and 26–28 in the ventral lid. The upper fornix measures about 36 mm from the upper lid margin, and the lower fornix is 22 mm from the lower lid margin. The lateral palpebral or canthal ligament is poorly developed in dogs and cats, and usually consists of an irregular thickened lateral septum orbitale. In the large breeds of dogs the lack of or a poorly developed lateral canthal ligament contributes directly to lateral canthal lid diseases in these breeds. The major component of the lateral canthal support system has been replaced by the retractor anguli oculi lateralis (dog) or corrugator supercilii lateralis (cat) muscle (Fig. 5.4). This results in a somewhat mobile but unstable lateral canthus in dogs, and contributes to the frequent involvement of the lateral canthus and lateral lower and upper eyelids with entropion and ectropion. The lateral one-half of the lower eyelid in the dog also has the pars palpebralis muscle, a subdivision of the sphincter colli profundus muscle, which can depress the lateral lower lid.

Eyelid tarsal layer and glands The eyelid skin and tightly adherent muscle layers are easily separated surgically from the deeper two layers, the fibrous tarsus containing the tarsal or meibomian glands and the inner palpebral conjunctiva. The fibrous tarsus provides some infrastructure for the eyelids, but not to the extent that the tarsal hyaline plate does in humans. The fibrous tarsus has fascial attachments to the septum orbitale, resulting in a strong connection to the periosteum of the orbital rim, and a significant barrier for trauma, surgery, and external infectious agents to enter the orbit. The fibrous tarsal layer is also in intimate contact with the medial palpebral or canthal ligament, the base of the nictitating membrane, and the lateral canthus. The medial palpebral ligament is more distinct than the lateral ligament in the dog, and consists of a fibrous band originating from the periosteum of the frontal bone that inserts into the upper and lower tarsal layers. The medial palpebral ligament also serves as the origin and insertion for the circular orbicularis oculi muscle, which undoubtedly assists in the medial movement of tears on the cornea and within the conjunctival sacs. In the

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middle section of the upper eyelid the levator palpebrae superioris muscle inserts into the tarsal layer. The superior and inferior tarsal muscles are smooth muscles in the dog within the endorbita that inserts into the tarsus. These muscles are under sympathetic innervation and help maintain the palpebral fissure open. The tarsal or meibomian glands are sebaceous (holocrine) types and produce the important outer lipid or oily fraction of the preocular or precorneal film. The lipid layer of the preocular film prevents evaporation of the thicker aqueous layer and stabilizes the preocular film. The number of tarsal glands in each lid ranges from 20 to 40, with the upper eyelid containing more glands. The orifices of the tarsal or meibomian glands empty onto the center of the eyelid margin. This area is referred to the ‘gray line’ and is an important surgical zone. The tarsal glands are occasionally visible through the palpebral conjunctiva, and extend for 3–5 mm into the lid substance. The tarsal glands seem able to undergo metaplasia and form additional cilia, called distichia. At the medial canthus at the junction of the upper and lower lids, and at the base of the nictitating membrane, is the lacrimal caruncle. Small fine hairs emerge from its surface, which can act as a wick for tears to moisten the medial canthal skin. The lacrimal caruncle also contains small sebaceous glands.

Palpebral conjunctiva Like the skin and muscle layers of the eyelid, the fibrous tarsus and palpebral conjunctiva are in close contact and difficult to separate surgically. The palpebral conjunctiva starts at the eyelid margin, and continues to the conjunctival fornix to join the bulbar conjunctiva. The palpebral conjunctival surface at the eyelid margin consists of non-keratinized stratified epithelium, but approximately one-third the distance from the lid margin to the conjunctival fornix it changes into pseudostratified epithelium. Once the pseudostratified epithelial layer is established, goblet cells that produce mucin begin to appear. The highest concentrations of goblet cells occur in the conjunctival fornices. Like the cornea, the palpebral conjunctiva is also coated with preocular film to facilitate eyelid movement over the cornea, and to minimize trauma between the bulbar and conjunctival epithelial surfaces.

Anatomy of the equine eyelid Muscles that open the equine eyelids include the levator palpebrae superioris, Mu¨ller’s, levator anguli oculi medialis, frontalis, and malaris. The levator palpebrae superioris muscle, along with the levator anguli oculi medialis muscle, raises the upper eyelid. Mu¨ller’s muscle is a smooth muscle that originates from the posterior surface of the levator muscle in the upper eyelid and from the ventral rectus muscle for the lower eyelid. It is innervated by sympathetic fibers that travel with the ophthalmic branch of the fifth cranial nerve. Mu¨ller’s muscle inserts on the tarsus and, along with other muscles, keeps the palpebral fissure open. It is the muscle, when innervation is interrupted in Horner’s syndrome, that results in ptosis of the upper eyelid. The frontalis muscle inserts laterally on the upper eyelid. The malaris muscle inserts on the ventral orbicularis oculi muscle and

Preoperative examination procedures

functions to open the lower eyelid. The upper eyelid is the more mobile and larger section of the eyelids. It provides the majority of the blinking function. Sensory innervation of the eyelids is via the ophthalmic and maxillary branches of the trigeminal (fifth cranial) nerve. The ophthalmic portion branches into the frontal, lacrimal, and nasociliary nerves. The frontal branch passes anteriorly from the orbit through the supraorbital foramen. It then becomes the supraorbital nerve, dividing over the forehead and innervating most of the upper eyelid. The lacrimal nerve innervates the lacrimal gland and the upper eyelid at the lateral canthus. The nasociliary branch gives rise to the infratrochlear nerve, which provides sensory innervation to the medial canthus, caruncle, nictitating membrane, upper and lower conjunctiva, and nasolacrimal puncta and ducts. The remainder of the lower eyelid is innervated by the zygomatic nerve, which is a branch of the maxillary nerve.

temporal artery. Additional blood supply to the lateral canthus and upper eyelid is derived from the lacrimal and dorsal muscular branch arteries, and the lower eyelid by the zygomatic artery, all branches from the external ethmoidal artery. The medial aspects of the canine eyelids are supplied by branches of the malaris artery, a branch of the infraorbital artery, which anastomose with the inferior palpebral and transverse facial arteries, and branches of the external ophthalmic artery. Limited blood supply to the eyelids is also provided from small vessels within the septum orbitale and conjunctival fornices that originate from the deeper orbital blood vessels. The lymphatic drainage from the eyelids converges at the medial and lateral canthal areas. Lymphatic drainage appears to mainly involve the parotid lymph node. However, some of the same areas may drain to the mandibular lymph nodes. As a result, both lymph nodes need to be accessed clinically if regional metastases from eyelid neoplasms are suspected, particularly in horses and cattle.

Eyelid sensation Most of the sensation of the animal eyelids is provided by several branches of the trigeminal nerve. Sensation of the lateral two-thirds of the upper eyelids is provided by the trigeminal nerve through its frontal nerve and its branch, the supraorbital nerve, and the medial canthus by the infratrochlear nerve. The medial canthus and medial aspects of the upper eyelids are also served by the nasociliary nerve, the largest branch of the ophthalmic nerve. The sensation for the entire lower eyelid is provided by the maxillary division of the trigeminal nerve through its zygomaticotemporal branch.

Eyelid innervation The palpebral branch of the facial or seventh cranial nerve innervates the majority of the muscles that control palpebral fissure size, except for the levator palpebrae superioris muscle that, along with most of the extraocular muscles, is innervated by the oculomotor or third cranial nerve. The pars palpebralis muscle of the lateral lower eyelid of the dog is innervated by the dorsal buccal branch of the facial nerve. In horses, the auriculopalpebral nerve and its branches (branch of the facial nerve), as well as the supraorbital nerve (branch of the ophthalmic division of the trigeminal nerve, sometimes referred to as the frontal nerve), are common sites for local nerve blocks in the horse to provide akinesia (auriculopalpebral nerve) and local analgesia (supraorbital nerve) to the upper lid. In most animal species the rostral aspect of the palpebral nerve can be blocked a few centimeters caudal of the lateral canthus. In this forward position, movement of the upper lid may persist.

Eyelid blood supply and lymphatics The blood supply to the eyelids is derived from several sources, but primarily originates from the medial and lateral canthal areas for both eyelids. The lateral aspects of both eyelids in the dog are supplied by the lateral dorsal and lateral ventral palpebral arteries from the superficial

Eyelid function The functions of the eyelids are numerous and include: 1) protection of the eye; 2) entrapment of material before it contacts the conjunctiva and cornea; 3) production of glandular secretions by the tarsal or meibomian glands, a vital component of the preocular film; 4) distribution of the preocular film and tears across the corneal and conjunctival surfaces; 5) medial movements of tears toward the lacrimal puncta for exit via the nasolacrimal drainage apparatus; and 6) provision of the blink reflex to tactile stimuli applied to the cornea, conjunctiva or nictitating membranes, or following a strong light and/or loud noise. When direct stimuli are applied to the eyelids, conjunctival and corneal surfaces, the eyelids blink. This reflex is subcortical, involving the ophthalmic division of the trigeminal nerve (afferent portion) and palpebral division of the facial nerve (efferent portion). A strong light source directed at the eye will not only initiate a light-induced pupillary response (a subcortical reflex), but also a blink response (also a subcortical function).

Preoperative examination procedures In the assessment of the eyelids preoperatively, their structure, function (blink reflex), and relationship to the face, each other, and to both eyes are carefully evaluated. Adequate illumination and some magnification are essential. The head loupe or magnifier and Finoff transilluminator, or portable slit-lamp biomicroscope are the best instruments that combine these two characteristics. The eyelids, eye, and orbit relationships can also be influenced by the presence of pain, inflammation, enophthalmia or exophthalmia, body condition, age, dehydration, and muscle condition. Not infrequently, the eyelids cannot be restored surgically to completely normal appearance and function because of these other variables, especially the position of the globe. These complex relationships of the eyelids, eye, and orbit in the dog also impede genetic studies of the eyelid diseases. The animal eyelids normally rest on the cornea and bulbar conjunctiva. If the globe is recessed into the orbit, eyelid contact may not be possible and instability of the lower

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eyelid results. The usual result is entropion or an inversion of the eyelid margin and substance. This phenomenon occurs commonly in certain breeds of dogs, foals, and in aging animals (probably associated with loss of orbital fat). Secondary blepharospasm is a common component of most painful eyelid conditions. With eyelid swelling, the eyelid margin usually rolls inward. When the outer eyelid margin, normal cilia (eyelashes), and trichiasis (involving the normal eyelid hair) touch the bulbar conjunctiva, cornea or a combination of both surfaces, the animal reacts by developing secondary blepharospasm. The resultant trigeminal– facial nerve reflex usually worsens the eyelid defect even further, and produces additional irritation and pain. This protective eyelid reflex then produces an ever-increasing cycle of pain and blepharospasm. Hence, in many painful eyelid diseases, the initial structural disease is aggravated by a normally protective eyelid closure reflex. Animals often respond to localized ocular pain by rubbing, which can cause additional localized swelling and even loss of skin integrity. Therefore, in the examination of eyelid diseases that are potential candidates for surgical correction, surgery should be directed at only the underlying structural eyelid disorder. To estimate the extent of secondary blepharospasm in a patient, a few drops of topical anesthetic are instilled onto the cornea and conjunctiva after the initial entropion has been estimated. After 3–5 min, the secondary blepharospasm will usually be relieved, and the basic structural eyelid abnormality can be ascertained. Surgical correction should be directed at only this anatomic eyelid abnormality. The defect is usually undercorrected slightly (about 0.5–1 mm) to accommodate postoperative fibrosis. Infrequently, the eyelid defect can become so painful and the eyelid and associated tissues so inflamed that multiple instillations of topical anesthetic will not totally suppress secondary blepharospasm. In these patients, localized regional eyelid block of the palpebral nerve can be administered. In the dog, a few milliliters of local anesthetic are injected subcutaneously along the dorsal aspects of the middle portion of the zygomatic arch to block the palpebral branch of the facial nerve and the primary innervation to the orbicularis oculi muscle that closes the palpebral fissure (Fig. 5.5). Within a few minutes, total loss of eyelid muscle Fig. 5.5 To perform the palpebral nerve block and produce lid akinesia in most animal species, 3–5 mL of local anesthetic are injected subcutaneously on the dorsal aspect of the middle portion of the zygomatic arch or just caudal of the lateral canthus.

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tone will occur, and the extent of the eyelid problem to be corrected surgically can be determined. In the horse, the auriculopalpebral nerve can be blocked at at least two sites (see Fig. 3.5, p. 44). The auriculopalpebral nerve can be blocked by infiltrating local anesthetic in a fan-like manner subfascially in the depression just caudal to the posterior ramus of the mandible at the ventral edge of the temporal portion of the zygomatic arch. The hypodermic needle is directed dorsally just caudal to the highest point of the arch. Before injecting local anesthetic, aspiration is performed to prevent injection into the rostral auricular artery or vein. This procedure may also result in akinesia of the ear muscles as well as gravitate ventrally and affect other branches of the facial nerve. Within a few minutes, total loss of eyelid muscle tone will occur, but lid sensation is still present. The second palpebral nerve block in the horse blocks multiple branches of the palpebral nerve closer to the eye. Local anesthetic is injected subcutaneously at the highest point of the dorsal border of the zygomatic arch. The supraorbital nerve of the horse is often blocked at the supraorbital foramen to provide akinesia to the forward branches of the palpebral nerve, as well as local anesthesia by blocking the supraorbital nerve, a branch of the trigeminal nerve. This procedure is often used prior to ophthalmic examinations, insertion of dorsal subpalpebral medication systems, and excision of upper eyelid masses. In cattle, the palpebral nerve can be blocked by injecting 3–5 mL of local anesthetic about 4–6 cm caudal of the lateral canthus.

Surgical considerations of the eyelids The upper and lower eyelids share most functions, but also have some unique characteristics. The upper eyelid covers the majority of the cornea, and blinks at a normal rate of about 15 times per minute. Only part of these blink reflexes cover the entire cornea. The upper eyelid has the levator palpebrae superioris muscle that originates from the depths of the orbit above the dorsal rectus muscle. The upper eyelid is primarily responsible for the cosmetic appearance, while the lower eyelid margin serves to collect and prevent the

Tarsorrhaphy in small animals

preocular film and tears from overflowing onto the lower canthi and eyelid surfaces. Surgical and traumatic interruption of the palpebral nerve innervation to the eyelids results in exposure keratitis if upper, rather than lower, eyelid function is impaired. The upper eyelids are larger and longer than the lower lids, and are the principal source for tissues for reconstructive surgical procedures of the eyelids. The higher number of tarsal or meibomian glands occurs in the upper eyelid. Only the canine upper eyelid contains cilia (eyelashes). Although the autogenous transplantation of cilia has not been reported in domestic animals, the surgical technique is not difficult. Hence, surgery of the upper eyelids must consider movements, protection of the eye, and appearance, whereas surgery of the lower eyelids must primarily address the collection, retention, and medial movement of tears. After extensive blepharoplasty, the eyelids (especially the upper) may function poorly for several days to weeks because of lid swelling and possible nerve impairment. To protect the cornea and prevent ulceration, a temporary complete tarsorrhaphy is necessary until a normal blink response returns. The conjunctival cul-de-sac or fornix is considerably larger for the dorsal eyelid, probably to accommodate ventral rotation of the globe. The lower conjunctival fornix is more shallow but is the primary receptacle for the tears and, assisted by the intermittent movements of the orbicularis oculi muscles, gradually propels the tears medially toward the lacrimal puncta. As indicated in an earlier section, the surgical anatomy of the eyelids is usually divided into two layers: the skin and muscle layer, and the deeper tarsus and palpebral conjunctiva. The thin elastic eyelid skin has limited subcutaneous tissue and attaches directly to the orbicularis oculi muscle. Surgical separation of the eyelid skin from the deeper muscle layer is tedious and, in small species, often very difficult. Within the eyelid margins are the numerous orifices of the tarsal or meibomian glands. This area is referred to as the ‘gray line’, an area to surgically split or divide the eyelids longitudinally, as well as for the placement of eyelid sutures that will not contact and directly damage the cornea.

Surgical instrumentation The instrumentation for eyelid surgery usually consists of a mixture of general soft tissue instruments, as well as selected ophthalmic instruments. The recommended ophthalmic instruments include small straight and curved strabismus or tenotomy scissors to cut tissues and sutures, both teeth (1  2) and serrated thumb forceps (such as Bishop–Harmon forceps), small scalpel blades (Nos 6400 and 6500 microsurgical), small wire eyelid speculum, and a standard ophthalmic needle holder (often with lock). Special thumb forceps, such as chalazion and entropion forceps, are useful to clamp and stabilize the eyelids during surgery (see Table 1.3, p. 12). Suture selection is variable and often at the surgeon’s discretion. Sutures for the tarsus and palpebral conjunctiva are usually absorbable (polyglycolic or polyglactic acid, and polydioxanone), and the simple continuous pattern is usually used. The knots should be buried beneath the palpebral conjunctiva to avoid direct contact with the cornea. Sutures

involving the eyelid skin and superficial aspects of the orbicularis oculi muscle are usually non-absorbable and the simple interrupted pattern. Many veterinary ophthalmologists prefer 4-0 to 6-0 silk; if corneal contact with the silk suture occurs, no irritation or damage results. Although tissue reactivity with silk can be a problem, and braided silk is a potential wick for bacterial invasion, eyelid suture removal at 7–10 days postoperatively effectively avoids these potential problems. The other frequently used nonabsorbable suture is 4-0 to 6-0 nylon. Choice of atraumatic swaged-on cutting needles is quite variable; however, the one-fourth to three-eighths curved needles are most useful. Hemostasis is usually provided by small curved mosquito hemostats or point cautery. Vessel ligation with absorbable sutures is infrequent as these areas may develop focal postoperative fibrosis that may influence the surgical result. Point cautery is usually preferred, but used judiciously. Sterile cotton-tipped applicators and cotton surgical sponges can effectively maintain most eyelid surgical fields clear of hemorrhage. Moistening with 1:10 000 or other dilutions of adrenaline (epinephrine) may be helpful. Hemostasis is also provided when the eyelids are grasped and held with chalazion and entropion forceps.

Surgical preparations of the eyelids Surgical preparation of the eyelids is usually performed immediately before surgery. Sometimes the patient is on therapy with topical antibiotics or antibiotics/corticosteroids for treatment of the eyelid disorder, and the same therapy is continued immediately after surgery. The high vascularity of the eyelids promotes healing and often topical corticosteroids are administered perioperatively to control the local inflammation and swelling. A bland petroleum ointment may be placed on the corneal and conjunctival surfaces to collect debris and hair during the surgical preparation. The ointment is carefully removed by sterile cotton-tipped applicators immediately before surgery. The eyelid hair is carefully removed by small hair clippers or shaved. The eyelid skin is thin and, if traumatized during hair removal, swelling may result. The surgical preparation of choice is 0.5% povidone– iodine solution as contact with the cornea is not irritating. At least three scrubs are recommended to clean and reduce the local microbial population. After these scrubs, the area is liberally rinsed with 0.9% sterile saline. Alcohol and other traditional surgical preoperative measures are not recommended as contact with the cornea and conjunctiva can be very irritating and damaging to their epithelia. Draping is performed with four small cotton towels positioned around the palpebral fissure and covered with a surgical drape. Small towel clamps or bulldog clamps may be used to secure the drapes, but should be used sparingly.

Tarsorrhaphy in small animals In the tarsorrhaphy procedure the eyelids are apposed either temporarily or permanently, and the lid apposition may include part or all of the upper and lower eyelids. In the permanent tarsorrhaphy procedure part of the eyelid

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margins of the upper and lower eyelids are excised and, after apposition by sutures, the eyelids should remain sealed. Complete permanent tarsorrhaphies are part of the enucleation and exenteration procedures after removal of the eye and the orbital contents. Partial permanent tarsorrhaphies are indicated to treat long-term ocular disorders, such as neuroparalytic keratitis, neurotropic keratitis, lagophthalmia, and chronic exposure keratitis. In the temporary tarsorrhaphy technique the eyelid margins are apposed by sutures for several days to a few weeks to cover the healing cornea and/or conjunctiva. In the complete temporary tarsorrhaphy method the entire palpebral fissure is closed. In the partial technique, only part (medial, central, or lateral) of the palpebral fissure is closed, thereby permitting vision by the patient, daily inspection by the veterinarian, and topical medication of the eye. The complete temporary tarsorrhaphy is indicated clinically, in part, for the treatment of traumatic proptosis, after most orbitotomies, after many extensive eyelid procedures, after nictitating membrane flaps, after extensive conjunctival surgery, to treat premature opening of the eyelids, to help maintain collagen shields and contact lenses in place, and for the treatment of recurrent corneal erosions and other selected superficial corneal disorders. Complete temporary tarsorrhaphies are also indicated when upper eyelid function is impaired and the development of exposure keratitis is anticipated. The partial temporary tarsorrhaphy is used frequently after conjunctival and corneal surgery to reduce eyelid trauma to the surgical site, and to provide some contact and pressure to fresh grafts. Suture ends in temporary tarsorrhaphies may be left long to facilitate occasional adjustment of the suture pressure, as well as occasional loosening to open the tarsorrhaphy and inspect the eye. The support of a weakened cornea by complete temporary tarsorrhaphy may vary by breed but it does not appear to give as much support as that provided by the nictitating membrane flap or a complete conjunctival graft. However, the complete temporary tarsorrhaphy procedure can supplement these methods to provide additional corneal support. Complete temporary tarsorrhaphy constitutes a barrier to topical medication of an eye, but the subpalpebral system can be inserted in the dorsolateral or lateral conjunctival fornix at the conclusion of surgery to ensure delivery of ophthalmic solutions. The apposed eyelids may also retain the topical solutions in contact with the cornea for longer periods of time, thereby increasing their effectiveness. The permanent apposition of the upper and lower eyelid margins at the medial and lateral canthi is discussed in a later section under surgical procedures to reduce the size of the palpebral fissure. Chronic exposure of the cornea, especially in brachycephalic breeds, may be a major contributing factor in the pathogenesis of recurrent central corneal ulceration, and surgical reduction of the size of the palpebral fissure may significantly reduce the possibility of recurrence.

A

Fig. 5.6 For a lateral permanent tarsorrhaphy. (a) The apposing upper and lower eyelid margins are trimmed by Metzenbaum or Mayo scissors at a depth of 4–5 mm. (b) The lids are apposed by two layers of sutures: the tarsoconjunctival layer with 4-0 to 6-0 simple continuous absorbable sutures placed submucosally, and the orbicularis oculi muscle and skin layer with 4-0 to 6-0 simple interrupted non-absorbable sutures.

entire eyelid margins are excised for 360 , with special care to adequately excise the lid margins at the two canthi. For partial permanent tarsorrhaphy any section of the eyelid may be used, but most often the lateral and medial canthal areas are involved. At a depth of 4–5 mm, the bases of the meibomian glands are excised. The eyelids are usually apposed by two layers of sutures in most dogs (Fig. 5.6b); however, in miniature breeds, a single suture layer may suffice. The deeper tarsopalpebral layer is apposed with either 4-0 to 6-0 simple interrupted or a simple continuous absorbable suture placed submucosally to avoid corneal contact. The eyelid skin–orbicularis oculi layer is usually apposed with 4-0 to 6-0 simple interrupted or interrupted mattress non-absorbable sutures.

Temporary tarsorrhaphy In the complete and partial temporary tarsorrhaphy procedures, 4-0 to 6-0 interrupted mattress non-absorbable sutures are carefully placed in the eyelid margin through or just anterior to the ‘gray line’ to appose the upper and lower lids (Fig. 5.7a). Sutures placed near or within the ‘gray line’ can adequately hold the eyelids together without tearing of the lid margins. Sutures placed within the ‘gray line’ do not penetrate the full thickness of the lid, thereby avoiding direct contact and damage to the cornea. The number of eyelid sutures varies (usually 2–4) depending on whether a

A

Permanent tarsorrhaphy In the permanent tarsorrhaphy procedure the upper and lower eyelid margins are trimmed by curved Metzenbaum scissors 3–5 mm from the lid margins (Fig. 5.6a). This area is usually where the eyelid pigmentation stops and the eyelid hair appears. For complete permanent tarsorrhaphy the

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B

B

Fig. 5.7 For the complete temporary tarsorrhaphy. (a) Three to six 4-0 to 6-0 interrupted mattress non-absorbable sutures are pre-placed in the lids. Stents are used to distribute the tension on the sutures and prevent lid necrosis. (b) The sutures are placed through the ‘gray line’ (or the orifices of the tarsal glands) and outer one-half thickness of the eyelids to avoid touching the cornea and still maintain excellent holding capacity. The sutures are left long to permit occasional adjustments postoperatively.

Aftercare for eyelid surgery in the horse

partial or complete temporary apposition of the eyelids is performed. Because of the tension on the eyelid sutures caused by the muscles effecting opening of the palpebral fissure, stents (consisting of rubber bands, old intravenous tubing, or other material) are used to distribute suture tension, and decrease local lid swelling and the likelihood of pressure necrosis (Fig. 5.7b). The temporary tarsorrhaphy is usually effective for 7–21 days (see Figs 4.25 and 4.26).

Postoperative care and complications after tarsorrhaphy The most frequent postoperative complications after permanent tarsorrhaphy are related to excessive tension on the lid sutures short term, and wound failure long term. As indicated in the eyelid anatomy section, several muscles function to open the palpebral fissure. In the long-term partial permanent tarsorrhaphy procedure, this chronic tension results in gradual weakening and atrophy of the surgical apposition site. Dehiscence within the first few weeks postoperatively is usually repaired by debriding the wound edges and apposition with additional sutures. The most frequent complications immediately after temporary tarsorrhaphy are variable swelling of the eyelids and suture contact with the cornea. Patients with temporary tarsorrhaphies should be examined daily or every other day, as eyelid swelling related to sutures and the preoperative ophthalmic condition may necessitate occasional suture adjustments. If the sutures become too tight, local eyelid necrosis and irritation result. If the sutures become too loose, suture contact and damage to the cornea may occur. Leaving the sutures a little long after performing the temporary tarsorrhaphy procedure permits minor adjustments and avoids these potential problems. Routine use of the E-collar postoperatively in small animals and facial masks in horses is important and effectively prevents self-trauma to the surgical site.

Tarsorrhaphy in the horse A tarsorrhaphy is the apposition of the upper and lower eyelid to each other. The procedure can be temporary or permanent, depending on the expected length of time the tarsorrhaphy is needed. A tarsorrhaphy is used for protection of the cornea in patients with the inability to blink normally, such as in facial nerve paralysis or eyelid swelling. Tarsorrhaphy is indicated after corneal surgery to provide support to the globe, and after eyelid surgery to allow the normal eyelid to act as a splint for the operated eyelid to reduce distortion, cicatrix, and suture line dehiscence.

Temporary tarsorrhaphy in the horse A temporary tarsorrhaphy is used after corneal surgery or eyelid surgery, and is performed after surgery while the horse is maintained under general anesthesia. However, it can easily be performed in the standing horse with sedation, local nerve blocks, and topical ophthalmic anesthetic. Preparation of the periocular area for aseptic surgery should be performed. Three to four horizontal mattress sutures are used (see Fig. 5.7). Most commonly the suture material is

4-0 to 5-0 nylon or proline. Sutures are placed partial thickness through the eyelid margin at the tarsal gland openings. Alternatively, sutures may be placed partial thickness in the eyelid in a pattern parallel to the eyelid margin and tied across the eyelid fissure. The use of stents of sterile intravenous tubing, rubber tubing, sterile rubber bands, or buttons helps to prevent the sutures from cutting into the eyelid tissue.

Permanent tarsorrhaphy in the horse When extended closure for weeks or months is anticipated, such as in facial nerve paralysis, a permanent tarsorrhaphy is performed. It is similar to the temporary tarsorrhaphy except that, prior to placing the sutures, the superficial eyelid margin is excised or debrided to allow adhesion as the tissue heals (see Fig. 5.6). Sutures are removed in 10–12 days, leaving the eyelid margins adhered. The tarsorrhaphy is left in place until the eyelids heal or neurologic function returns. When the tarsorrhaphy is no longer needed, the adhered areas of the eyelid margin are carefully incised with tenotomy scissors to restore the palpebral fissure.

Aftercare for eyelid surgery in the horse The general protocol for aftercare for eyelid surgery is similar to those for skin and reconstructive procedures elsewhere on the body. Often after tarsorrhaphies, the primary condition, such as corneal ulceration or facial nerve paralysis, still requires primary therapy. Preoperative and perioperative topical and systemic antibiotics are indicated. The placement of a subpalpebral lavage system will facilitate topical application of solutions to the eye. Postoperative swelling will be reduced by the administration of systemic non-steroidal anti-inflammatory agents (flunixin meglumine 1 mg/kg IV; BanamineW, ScheringPlough, Kenilworth, NJ) immediately before surgery. Postoperative edema will be lessened by the application of ice packs for the first 24 h after surgery. If swelling is present 24 h after surgery, warm compresses may further reduce the swelling and discomfort at the surgical site. Dimethyl sulfoxide has been applied to the periorbital skin to reduce postsurgical swelling and discomfort. Extreme caution must be exercised to avoid inadvertent contact of this product with the cornea and conjunctiva. If rubbing or self-mutilation is a concern, the surgical site or eye must be protected by a protective hood with a plastic or solid eyecup (EyeSaver™, Jorgensen Laboratories, Loveland, CO.). Cross tying or neck cradles have also been used successfully. In an effort to decrease dust and debris from complicating the suture lines in stabled horses, hay is fed on the ground and hay and bedding may be misted with water to minimize dust. If granulating wounds are present, removal of the exudate once or twice daily, with application of petroleum jelly or a povidone–iodine gel ventral to the wound is helpful, and fly control is essential in warmer climates. Fly control around the horse’s face is achieved by wiping fly repellent around the surgical site, by fitting the horse with a fly mask, or by using fly-repellent strips attached to the halter. Skin sutures are usually removed 8–12 days after surgery. In situations when tension on the suture line cannot be avoided, sutures are left in place for 18–24 days.

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Lateral canthotomy

Surgical procedures for eyelid agenesis

The lateral canthotomy procedure is used to temporarily increase the size of the palpebral fissure and facilitates surgical exposure of the globe. In many prominent-eyed breeds of dogs and for most cats, a lateral canthotomy for most ophthalmic surgical procedures is not necessary. However, in many mesocephalic and nearly all dolichocephalic breeds of dogs, lateral canthotomy is indicated for most corneal and intraocular surgeries. After insertion of an eyelid speculum, the palpebral fissure is maximized and the surgical exposure ascertained. If additional exposure is necessary, a lateral canthotomy is performed with heavy-duty straight or curved Mayo scissors (Fig. 5.8a). The lateral canthal eyelid is incised for 5–15 mm, but the incision should not extend beyond the lateral orbital ligament. Hemorrhage is usually negligible. Point cautery can control any minor bleeding. A straight mosquito forceps may be used to slightly crush the tissues prior to the incision to control hemorrhage but is not usually necessary. At the conclusion of surgery, the lateral canthotomy is usually apposed by one or two layers of sutures. The palpebral conjunctiva, submucosal fascia, and tarsus are apposed with 4-0 to 6-0 simple interrupted absorbable sutures (Fig. 5.8b). The external layer of closure, consisting of the orbicularis oculi muscle and lid skin, is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. The first suture is carefully placed at the eyelid margin. Occasionally this first suture is an interrupted mattress or figureof-eight suture. The skin sutures are removed at 7–10 days postoperatively. The most frequent postoperative complications after lateral canthotomy include dehiscence of the first one or two sutures, usually within the first week, and the malalignment of the area. In eyes with lateral canthotomies, postoperative medications and ophthalmic examinations should be performed with care to prevent undue tension on the healing lateral canthus and sutures. Routine use of the E-collar in small animals also assists maintenance of the lateral canthotomy. Animals can quickly traumatize this area and tear the sutures from the lateral canthus. In the event of local dehiscence, the wound edges are refreshened and apposed by additional sutures.

Eyelid agenesis occurs not infrequently in cats, and no breed predisposition has been demonstrated. The condition is rare in dogs and other animal species. In lambs, congenital eye defects generally appear as ‘notches’. In cats, the upper eyelid is most frequently involved. The condition may be uni- or bilateral. The lateral aspects of the upper eyelid are usually affected. In many cats with eyelid agenesis additional ocular anomalies, such as dermoids, iris defects, cataracts, and optic nerve colobomas, may be present. The defect may be inherited, and also associated with factors that influence eyelid and eye development such as infectious feline enteritis or panleukopenia virus. Clinical signs associated with eyelid agenesis include irritation, epiphora, and the absence of the lateral upper eyelid margin and variable amounts of the lid (Fig. 5.9). Often in the area of eyelid agenesis, the remaining lid is inverted, resulting in focal keratitis. Surgical correction of feline eyelid agenesis is recommended if chronic conjunctival irritation and corneal involvement develop. Several surgical techniques may be used to treat eyelid agenesis successfully. The choice of surgical procedure is influenced by the severity of the lid defect and the extent of reconstruction needed to repair the defect. For mild cases, the leading lid tissue that has become inverted can be corrected by the Hotz–Celsus procedure used for entropion. The more severe defects require tissue transposition from distant sites. Several procedures may be performed, including: 1) the skin, orbicularis oculi, and tarsal pedicle graft from the lower to upper lid; 2) the skin, orbicularis oculi, and tarsal pedicle graft combined with conjunctiva grafted from the anterior surface of the nictitating membrane; 3) the Cutler–Beard or bucket handle technique; and 4) the sliding skin graft. All of these surgical techniques are successful but more difficult, and some are two-step procedures. Both pedicle graft procedures will be described in this section. The bucket handle and sliding skin procedures will be presented in a later section on reconstructive blepharoplasty. As the most frequent form of eyelid agenesis involves the margin and limited amounts of the lid per se, pedicle grafts

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Fig. 5.8 Lateral canthotomy increases exposure of the globe. (a) After placement of the wire eyelid speculum to ascertain exposure, the lateral canthus is incised by curved Mayo scissors for 5–15 mm. The length depends on the breed and required amount of exposure. (b) Two-layer closure includes: tarsoconjunctiva with 4-0 to 6-0 simple continuous absorbable suture and the orbicularis oculi–skin layer with 4-0 to 6-0 simple interrupted non-absorbable sutures. The first suture is carefully placed at the lid margin.

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Fig. 5.9 Eyelid agenesis, affecting the lateral one-half of the upper lid, in a cat. Secondary superficial keratitis is also evident.

Surgical procedures for eyelid agenesis

of skin, orbicularis oculi, and tarsus are quite successful. The technique, described by Roberts and Bistner, uses adjacent palpebral conjunctiva to line the deep aspects of the skin– muscle graft. The procedure by Dziezyc and Millichamp lines the inside of the skin, muscle, and tarsal pedicle graft with mucosa from the anterior surface of the nictitating membrane. Both of these techniques may also be used to treat eyelid neoplasms in cats, such as squamous cell carcinomas, that primarily affect the lid margin.

Roberts and Bistner procedure In this method a myocutaneous pedicle of skin, orbicularis oculi muscle, and tarsus are transplanted from the lateral portion of the lower eyelid to the dorsolateral lid defect. With the transposition of the orbicularis oculi muscle, the blink reflex is strengthened and often returned to near normal. After general anesthesia and surgical preparation of both eyelids, the recipient bed of the upper eyelid defect is prepared by dividing the lid skin and tarsus from the palpebral conjunctiva. Dissection of the upper border of the defect should continue toward the conjunctival fornix for 10–15 mm to separate the palpebral conjunctiva sufficiently to line the posterior aspect of the pedicle graft. The eyelid is split into skin–orbicularis oculi muscle, and tarsus– palpebral conjunctiva for a distance of 3 mm into normal eyelid (Fig. 5.10a). A right-angle incision at the nasal end of the defect is prepared by scissors to accommodate the tip of the pedicle graft. The pedicle graft of skin, orbicularis oculi muscle, and tarsus is prepared by scalpel starting

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15 mm lateral of the lateral canthus and 2 mm parallel to the lower eyelid margin (Fig. 5.10b). The second parallel incision should provide a pedicle that is about 0.5–1 mm wider than the height of the upper lid defect. The length of the pedicle varies depending on the length of the upper defect. By scalpel the skin incision is deepened to include the orbicularis oculi muscle and tarsus (Fig. 5.10c,d). The base of the pedicle graft should be wider than its tip to ensure adequate perfusion of the entire pedicle. The pedicle is repositioned to the defect and apposed by two layers of sutures (Fig. 5.10e). The deep layer attaches the recipient and donor tarsus by a 4-0 to 6-0 simple continuous absorbable suture. The skin and orbicularis oculi layers are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. The posterior aspects of the pedicle graft must be covered by palpebral conjunctiva, separated during preparation of the graft bed. The new posterior conjunctival lining should not produce any traction on the pedicle graft. The lower eyelid wound is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. If traction on the graft is apparent at the conclusion of surgery, a complete temporary tarsorrhaphy is performed to provide counterpressure for 14–21 days. An E-collar should be worn until the healing is complete and all sutures have been removed.

Dziezyc and Millichamp procedure This method not only transplants a lower eyelid myocutaneous pedicle graft to the focal area of lid agenesis, but also requires a pedicle graft of palpebral conjunctiva from

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Fig. 5.10 To treat eyelid agenesis. (a) A pedicle graft of skin, orbicularis oculi muscle and tarsus is transplanted to the dorsolateral lid defect. The upper lid defect is prepared by scissors to separate the skin–orbicularis oculi–tarsus from the palpebral conjunctiva. The palpebral conjunctiva must be adequately dissected to the fornix to ensure posterior cover for the graft without any tension. (b) The pedicle is prepared by incision by scalpel about 2 mm below the lower eyelid margin. The length of the pedicle depends on the length of the upper lid defect. (c) Intraoperative photograph showing the myocutaneous graft, separated from its tarsoconjunctival layer, and ready to attach to the edge of the remaining dorsolateral lid. (d) The pedicle is separated by tenotomy scissors from the deeper palpebral conjunctiva. (e) The tarsal layers of the pedicle graft and defect are apposed with 4-0 to 6-0 simple continuous absorbable sutures. The muscle–skin layers of the graft and defect are apposed with 4-0 to 6-0 simple interrupted nonabsorbable sutures. The adjacent palpebral conjunctiva is apposed to the deep aspect of the pedicle graft by 6-0 simple interrupted absorbable sutures.

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Fig. 5.11 Another technique to treat upper eyelid agenesis in the cat. (a) A lower eyelid pedicle is prepared 5–7 mm below the lid margin by scalpel. The pedicle consists of eyelid skin, orbicularis oculi muscle, and tarsus. The upper lid defect is prepared by tenotomy scissors to receive the graft. (b) A pedicle graft of mucosa is prepared by scissors from the anterior surface of the nictitating membrane to line the posterior aspect of the myocutaneous pedicle lid graft. (c) Both grafts are secured in their positions. For the mucosal graft, 6-0 simple interrupted absorbable sutures are placed. For the external skin–muscle–tarsus graft, 4-0 to 6-0 simple interrupted non-absorbable sutures are used. The conjunctival graft base can be transected 3–4 weeks postoperatively.

the anterior surface of the nictitating membrane. The initial lower eyelid pedicle graft is prepared, as in the Roberts and Bistner method, but further (5–7 mm) from the lower eyelid margin (Fig. 5.11a). The graft bed is prepared to receive the lower lid graft. Both the pedicle’s length and width should be at least 1 mm greater than the defect. By scissors the graft of skin, orbicularis oculi muscle, and tarsus are separated from the underlying palpebral conjunctiva. The graft and the defect edges are apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. A pedicle graft of palpebral conjunctiva is prepared by scissors from the anterior surface of the nictitating membrane to line the posterior surface of the skin, muscle, and tarsus graft already in position (Fig. 5.11b). The base of the graft is lateral, and it should be 1–2 mm wider and longer than its bed. Once adequately separated from the anterior surface of the nictitans, the conjunctival graft is rotated 180 and apposed to the posterior surface of the lid graft by 6-0 simple interrupted absorbable sutures (Fig. 5.11c). The donor area on the anterior surface of the nictitans is left to heal by secondary intention.

removal and graft establishment. Warm and cold compresses may be administered daily to reduce swelling and promote local circulation. The most frequent short-term complication after both of these procedures is postoperative swelling (Fig. 5.12). The most frequent long-term complication after these techniques is the development of a mild cicatricial entropion along the leading margin of the new pedicle graft. The technique by Dziezyc and Millichamp attempts to address this potential complication before its development. An adequate conjunctival lining on the posterior surface of the pedicle graft seems to be the main method to prevent this complication. If trichiasis from the pedicle graft occurs, superficial keratitis at this site may develop. Surgical treatment consists of a focal oval excision of the eyelid skin and orbicularis oculi muscle in the affected area, and eversion of the surgical lid margin.

Postoperative management and complications of myocutaneous pedicle grafts

Distichiasis, or the presence of one or more extra cilia or eyelashes, is a common condition in dogs but rare in cats and other animal species. The cilia emerge from near or within the orifices of the meibomian or tarsal glands (Fig. 5.13). Distichiasis in dogs may be inherited in many breeds, but may also result from metaplasia of the tarsal

Topical and systemic antibiotics are administered after these procedures. An E-collar should be used for the entire postoperative period, and maintained on the patient until suture

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Fig. 5.12 Eight week postoperative appearance of the Roberts–Bistner method for bilateral dorsolateral lid agenesis in a cat. (a) Appearance of face and myopedicle grafts. (b) Close-up appearance of the right eye.

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Surgical procedures for distichiasis

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Fig. 5.13 Positions in the upper eyelid of the dog for normal eyelashes or cilia (A), distichia (B), and ectopic cilia (C).

glands in older animals and from chronic inflammation. Breeds commonly affected with distichiasis include the American Cocker Spaniel, English Cocker Spaniel, English Bulldog, Toy and Miniature Poodles, Boxer, St Bernard, Golden Retriever, Long-haired Miniature Dachshund, Alsatian, Bedlington Terrier, Shetland Sheepdog, Yorkshire Terrier, and the Pekingese. Over 90% of American Cocker Spaniels have distichia; however, treatment for distichiaassociated ophthalmic problems is necessary in only 10% or less of affected dogs. The clinical signs related to distichia are those of irritation, including increased lacrimation, epiphora, blepharospasm, eyelid swelling, conjunctival hyperemia, and corneal disease (vascularization, pigmentation, and/or ulceration). The distichia are fine, the same color as the adjacent hair coat, and best detected by adequate illumination and magnification, and with topical fluorescein stain (Fig. 5.14). Treatment for canine distichiasis consists of either temporary removal of the offending distichia by manual epilation, or the permanent destruction of the distichia follicle by

Fig. 5.14 Distichia coated with mucus emerging from the orifices of the glands of Meibom. Adequate illumination and magnification facilitate their detection.

electroepilation, cryoepilation, and various surgical procedures. The Hotz–Celsus entropion procedures may be used to evert the eyelid margin sufficiently to displace the distichia from touching the conjunctiva or cornea, or both. With the advent of the operating microscope, surgical techniques to remove the distichia follicles and conserve as much as possible of the deeper aspects of the eyelid margin have evolved. Manual epilation of distichia can immediately eliminate the clinical signs associated with these irritating aberrant lashes, but regrowth occurs. Epilation may be used to confirm the clinical signs are secondary to certain distichia, but is usually impractical long term and when multiple distichia are involved. In electrolysis, a fine electrode is inserted into the distichia follicle and 3–5 mA current is used to destroy the follicle germinal cells. Several portable and battery-powered units are available commercially, though current exceeding 5 mA should not be used as excessive electrolysis creates scar tissue formation at the eyelid margin (Fig. 5.15). To adequately perform electrolysis for distichia, general anesthesia is indicated. Magnification and good illumination can help observe the distichia as well as assist the electrolysis. Electrolysis may be selected for treatment of a few distichia but should be avoided when most of the eyelid margin is affected. Electrolysis is of limited success when multiple (compound) distichia exit from a single orifice. Once adequate current is applied, hydrogen gas bubbles occur, and the distichia is easily detached from its base. Low milliamperage is recommended (about 2–3 mA) for 15–30 s. Surgical procedures to excise the distichia follicles have been refined from the initial report of eyelid splitting and excision of the inner margin of the palpebral conjunctiva, to partial tarsal plate excision, and more recently conjunctival resection with minimal disturbance of the lid margin. In humans where distichiasis is infrequent, surgical procedures have been developed to excise the distichia and follicles.

Fig. 5.15 A small battery-powered electroepilation unit may be used to treat limited numbers of distichia.

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Fig. 5.16 For limited numbers of distichia. (a) Resection of the deeper aspects of the lid margin with the tarsoconjunctiva and distichia with the Beaver No. 6500 or 6700 microsurgical blade is performed. The lid margin is stabilized by a chalazion clamp, and the resection of the distichia follicles is limited to only focal parts of the entire eyelid length. (b) A block of tarsoconjunctiva with distichia is excised with small tenotomy scissors at a depth of 4–5 mm. The surgical site(s) should not exceed 5–7 mm long, and three sites per eyelid.

These methods usually divide or split the entire eyelid skin and orbicularis oculi muscle from the tarsus and palpebral conjunctiva from the distichia follicle excision site to the conjunctival fornix. The adjacent tarsus and palpebral conjunctiva are then slid to cover the surgical defect at the eyelid margin. Resection of the distichia follicles and adjacent palpebral conjunctiva is recommended for isolated distichia of the upper and lower eyelid, but should not be used for distichia affecting large portions of the lid margin. The affected eyelid is grasped with a medium to large chalazion clamp to stabilize the lid as well as provide hemostasis. With the Beaver No. 6500 microsurgical blade, the distichia follicle is excised to a depth of 4–5 mm from the eyelid margin (Fig. 5.16a). Once this block of tissue is isolated, small tenotomy scissors are used to excise its base (Fig. 5.16b). The wound is allowed to heal by secondary intention. In the partial tarsal plate excision method, the eyelid is stabilized by a chalazion or entropion clamp. The distichia and follicles are excised by a V-shaped incision on the outer and deeper aspects of the extra eyelashes (Fig. 5.17).

Fig. 5.17 To treat a limited number of distichia in the dog, the distichia may be excised with only part of the tarsal plate to reduce the loss of the eyelid margin tissue. The surgery is limited to those distichia causing eye disease and should not involve the entire eyelid margin. The V-shaped incisions are performed 4–5 mm deep, and the block of eyelid with the distichia follicles excised. During this procedure the eyelid should be stabilized by a chalazion or some other type of clamp.

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Fig. 5.18 Conjunctival resection technique for the treatment of generalized canine distichiasis. (a) The affected area of the eyelid is grasped by the chalazion clamp. The tarsus and palpebral conjunctiva are incised 1 mm and 3–4 mm posterior to the eyelid margin. The block of tarsoconjunctiva and distichia follicles is carefully excised by small tenotomy scissors. Like the previous two methods, the surgery is limited to the offending distichia and should not involve the entire eyelid margin. (b) The surgical defect is allowed to heal by secondary intention.

The incision should be 4–5 mm deep to ensure adequate removal of the distichia follicles. The surgical area is not sutured and allowed to heal by secondary intention. In the conjunctival resection technique, the eyelid is stabilized by a chalazion or entropion clamp. The tarsus and palpebral conjunctiva are incised 1 mm below the eyelid margin in the area of the distichia follicles (Fig. 5.18a). After a second parallel incision, 3–4 mm deep to the first incision, the strip of palpebral conjunctiva, tarsus, and the distichia follicles is excised (Fig. 5.18b). The palpebral conjunctival defect is allowed to heal by secondary intention. Although this method is more tedious than the other methods, it avoids the eyelid margin. More recent investigations have demonstrated the improved benefits of non-invasive cryotherapy for the treatment of canine distichiasis with limited complications. The technique avoids surgery, but necessitates a nitrous (N2O) cryounit. A double freeze–thaw cycle sufficient to produce –25 C with N2O can destroy the distichia follicles without the destruction of the adjacent eyelid margin. The eyelid is grasped and held during cryotherapy by a chalazion or entropion clamp. The cryotherapy procedure should not contact the cornea. As the amount to cryotherapy may vary with each unit, a line pressure of 625 mmHg for the cryoprobe provides for a standard cryofreeze. The cryoprobe is placed on the palpebral conjunctiva directly over the distichia follicles, about 2 mm below the eyelid margin (Fig. 5.19). A glaucoma cryoprobe may freeze about a 4 mm diameter of eyelid tissue. The first freeze of 45 s results in an iceball that advances to about 1 mm anterior to the meibomian gland orifices. After a brief thaw, a second freeze of 25 s is performed.

Postoperative management and complications after distichia surgery Topical treatment with antibiotics and corticosteroids postoperatively minimizes eyelid swelling and reduces the scarring of the eyelid margin that may contribute to occasional

Non-surgical treatment of entropion

Fig. 5.19 (a) For effective cryotherapy of canine distichiasis, a double freeze-thaw cycle is used to destroy the distichia follicles. (b) Immediate appearance after the cryoprobe has been withdrawn to inspect the tissue freeze. Extensive postcryotherapy eyelid swelling should be anticipated, and corticosteroids and non-steroidal antiinflammatory agents should be used perioperatively.

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entropion. After all of the distichia techniques, distichia regrowth (about 10–30%) from inadequate excision of the distichia follicles, eyelid margin fibrosis, focal depigmentation of the postoperative eyelid margin (especially after cryotherapy), and entropion are occasional complications. Surgical procedures for post-distichia treatment entropion may be used to evert the eyelid margin to a relatively normal position. Complications after cryotherapy for distichia include immediate and sometimes excessive eyelid and conjunctival swelling that lasts about 48 h, depigmentation of the eyelid and lid margin within 72 h that usually completely re-pigments within 6 months, and occasional distichia regrowth. Properly performed, eyelid margin scarring and distortion are unlikely after cryotherapy with temperatures that do not fall below –25 C. Eyelid temperatures lower than –30 C have been associated with lid scarring, necrosis, and permanent pigment loss, but not increased efficacy. Topical antibiotics/corticosteroids are necessary perioperatively to decrease the not infrequent marked eyelid swelling and chemosis as rapidly as possible. Preoperative flunixin meglumine (0.1–0.5 mg/kg IV) helps reduce the immediate lid swelling and may need to be continued for the next 48–72 h.

Surgical procedures for ectopic cilia Ectopic cilia primarily affect the upper eyelid of dogs, and are associated with intense blepharospasm, ptosis, epiphora, and a dorsal paracentral or peripheral corneal ulcer (Fig. 5.20). The onset of clinical signs is usually acute. Any breed can be affected, and most animals are young. There is also a direct association of ectopic cilia and distichia in the dog. Upon eversion of the upper eyelid, a single or, more often, multiple cilia emerge from the central palpebral conjunctiva about 4–6 mm from the eyelid margin. The ectopic cilia appear to arise from the base of the tarsal or meibomian glands, or from the base of hair follicles from the overlying eyelid skin. After eversion of the affected eyelid by a chalazion or entropion clamp, the follicle of the ectopic cilia is excised ‘en bloc’ with a scalpel blade, skin biopsy punch, or destroyed by electrocautery or cryotherapy.

Fig. 5.20 Ectopic cilia of the central palpebral conjunctiva. The ectopic cilia follicle is excised ‘en bloc’ or destroyed by cryotherapy or electrocautery. (Photograph courtesy of the late Paul A Dice, Seattle, WA.)

SURGICAL PROCEDURES FOR ENTROPION IN SMALL ANIMALS Entropion or the inversion of the eyelid margin can be divided into three categories: congenital/developmental, spastic, and cicatricial. Developmental entropion is a common condition in purebred dogs and not infrequent in cats. Predisposition occurs in the Chow Chow, Norwegian Elkhound, Chinese Shar Pei, St Bernard, English Springer Spaniel, English and American Cocker Spaniels, English Bulldog, Toy and Miniature Poodles, Great Dane, Rottweiler, and the Bull Mastiff (Fig. 5.21). Often each breed has specific affected areas of the eyelids that are commonly involved. Adjacent areas, such as the nasal folds and redundant facial folds of skin, can compound entropion in certain breeds. Spastic entropion is infrequent in dogs, but the pain associated with the trichiasis from developmental entropion often worsens the basic lid defect.

Non-surgical treatment of entropion Several non-surgical methods to treat entropion in small animals have been used. Subcutaneous injections of antibiotics, paraffin, and mineral oil have been used to provide

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Fig. 5.21 Bilateral upper and lower eyelid entropion in a young English Bulldog. With the associated trichiasis, blepharospasm has developed.

temporary eyelid margin eversion, and relief from the trichiasis and blepharospasm, but generally have been replaced by the different lid surgeries: the larger the volume of injection, the greater the extent of eversion of the eyelid margin. Electrocautery of the skin and superficial aspects of the orbicularis oculi muscle may be used to stimulate the formation of scar tissue and correction of the entropion. The predictability of postcautery fibrosis is low. As a result, several surgical procedures have been developed that provide reasonably consistent and beneficial results. Because of economics and the frequency of congenital entropion in sheep, injections to reverse lower lid entropion are not infrequent.

Fig. 5.22 Entropion in an 8-week-old Chinese Shar Pei puppy. The entropion affects about 300 of the eyelids and the lateral canthus, and resulted in bilateral corneal ulceration.

Temporary eversion – ‘tacking’ Entropion generally requires surgical correction. However, in certain breeds, the eyelid defect may be minor, but becomes extensive with secondary blepharospasm. In the Chinese Shar Pei puppy with entropion, secondary blepharospasm can markedly increase the extent of the original entropion (Fig. 5.22). The redundant facial folds can also contribute to the entropion when blepharospasm is present. Early treatment of the Chinese Shar Pei puppy with entropion, often at the age of 2–4 weeks, with temporary sutures to maintain the eyelid margin in a relatively normal position for 10–20 days, may effectively resolve the condition. Overcorrection with the tacking procedure generally provides better results than undercorrection. Usually two tacking sutures are placed at 45 in the upper eyelid, and, if necessary, in the lower eyelid. Sutures (Lembert type) or skin staples can be inserted to temporarily evert the eyelid margins. Two to three 3-0 to 5-0 non-absorbable interrupted vertical mattress sutures are placed in the upper and infrequently the lower eyelids, about 2–3 mm from the margin, and the second 10–20 mm from the margin (Fig. 5.23) near the orbital rim. The ‘bites’ are fairly large, about 4–5 mm long, to ensure that adequate tension and tissue-holding occur. As the sutures are tightened, the inversion of the eyelid margins is corrected. Often the sutures are left long to permit multiple adjustments. Most Chinese Shar Pei puppies respond to the tacking method. Those puppies that are not improved by the

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Fig. 5.23 Temporary eversion of entropion in very young Chinese Shar Pei puppies may avoid surgical correction later. At least two interrupted vertical mattress sutures are placed in each lid near the eyelid margin and 10–20 mm from the eyelid margins to temporarily correct the lid defects. These sutures are maintained for 10–20 days.

temporary tacking methods develop corneal disease and require entropion surgery. These tacking procedures have also been used in adult dogs to treat spastic entropion, which does not respond to medical and other surgical therapies. By preventing the secondary pain caused by the trichiasis touching the conjunctival and corneal surfaces, the tacking procedure may successfully stop the persistent blepharospasm. These same techniques are useful in lambs.

Quickert–Rathbun procedure Williams recently modified the Quickert–Rathbun technique for young and older dogs with lower lid entropion. In this procedure traction is placed from the lower conjunctival fornix by sutures extending from the fornix to the

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Fig. 5.24 In the Quikert–Rathbun procedure, the distal lower eyelid and margin are rotated outward, using a suture based in the deep conjunctival fornix. (a) A double-ended absorbable suture is carefully positioned in the deep conjunctival fornix. (b) These two sutures are inserted in the skin 1–2 mm from the lid margin and carefully tightened to evert the lid margin.

external skin of the eyelid margin. A double-ended 4-0 absorbable suture is positioned from the deep conjunctival fornix to exit on the lid skin 1–2 mm from the lid margin, which immediately everts the lid margin and corrects the entropion (Fig. 5.24). Tension on the sutures as well as their exit position on the lid surface can be varied to effect entropion correction.

Surgical management of entropion The surgical procedures for the treatment of entropion in animals evolved partially from those techniques reported in humans. In the Celsus procedure (cited by Zeis E 1839 Handbuch der plastischen Chirurgie. G. Reimer, Berlin, p 12) a crescentic area of eyelid skin and orbicularis oculi muscle is removed. In the Celsus–Hotz technique (Hotz CC 1879 Operation for entropion. Archives of Ophthalmology 3:249) the apposition of the surgical wound involved placement of the sutures through the tarsus and orbicularis oculi muscles. Adaptation of the Celsus–Hotz technique has resulted in a most useful procedure that can be varied markedly for a number of different forms of entropion in the canine and feline patient. In Veterinary and Comparative Ophthalmology by Eugene Nicolas and translated by Henry Gray (H. and W. Brown, London, 1914), at least three different surgical procedures were described for entropion in animals. Excision of an oval portion of skin involving the lateral lower eyelid and lateral canthus for the treatment of entropion was referred to as the Berlin–Me´gnin method. A simple method to repair entropion in the dog was reported by Veenendaal (1936). Excision of an arrowhead-shaped section of lateral canthal skin for the treatment of entropion has been referred to as the Schleich method. Fro¨hner’s method consisted of the excision of a somewhat circular section of skin to effect correction of entropion.

Hotz–Celsus procedure for entropion The Hotz–Celsus or Celsus–Hotz procedure and its modifications are the basic surgical techniques for the treatment of congenital, developmental, cicatricial, and senile entropion in domestic animals. The key to its success is the need for the procedure to be performed as close as possible to the

eyelid margin, and the positioning of the maximum aspects of the surgical wound to the area of the most extensive entropion. Because animals lack the tarsal plate, the eyelids lack rigidity and require contact with the globe. The presence of enophthalmia complicates the successful repair of entropion because of the lack of lower lid contact with the globe. The lack of a well-developed lateral canthal ligament in many animal species may also account for the frequent involvement of entropion in this area. Entropion sufficient to produce other ophthalmic diseases, including conjunctivitis, keratitis, and epiphora with dermatitis, should be corrected by surgery. The Hotz–Celsus procedure with its different modifications and several other related techniques effectively treats the majority of the different types of entropion in small animals. The Hotz–Celsus technique can be used to correct entropion of the entire lower lid, the upper eyelid, and, with modification, the lateral canthus. For central lower entropion defects, the following procedure is illustrated. A section of lid skin and orbicularis oculi muscle is excised in this procedure. The length and shape of the skin–orbicularis oculi incisions vary, depending on the amount and area of entropion correction. The initial skin incision is parallel to the eyelid margin, usually 1–2 mm from the lid margin and where the pigmentation of the skin ceases and the eyelid hair begins (Fig. 5.25a). The lid may be held by an entropion clamp or held taut and the eye protected by a Jaeger eyelid plate. The depth of the skin incision can include variable amounts of the orbicularis oculi muscle, and is deeper especially in the large and giant breeds of dogs. The primary goal of the procedure is to evert the eyelid margin and stop secondary blepharospasm. The amount of surgical correction should allow for 0.5–1.0 mm of additional eversion of the eyelid margins that occurs during postoperative healing. The ends of the initial skin–orbicularis oculi incision are joined with a ventral elliptical incision, the width determined by the amount of tissue that needs to be excised to evert the eyelid margin into a normal position (Fig. 5.25b). If the lower entropion involves the medial and lateral one-third of the lid, but not the central section, two separate procedures are performed. To stabilize the eyelid during these incisions, a thumb forceps may also be inserted at the lateral canthus to provide tension on the lids. The area of skin may also be outlined and slightly crushed by curved mosquito forceps. This technique is more traumatic, but provides some hemostasis. Hemorrhage is usually minor and occurs from the lateral and medial ends of the incisions. Temporary clamping of the larger blood vessels by hemostats or digital pressure is usually sufficient. Ligature of these bleeders is not usually necessary, and the buried suture material may cause local fibrosis of the lid. The incised area of eyelid skin and orbicularis oculi muscle is elevated by thumb forceps and excised by small curved Steven’s tenotomy scissors. The surgical wound is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures placed about 2–3 mm apart (Fig. 5.25c). Placement of the sutures must accommodate the shorter eyelid margin wound and the longer distal incision (Fig. 5.25d). Suture placement starting from the central defect and working in each direction, as well as wound apposition starting from one end, may be used.

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Fig. 5.25 Modified Hotz–Celsus technique for central lower lid entropion. (a) The skin and orbicularis oculi muscle layers are incised by scalpel. The incision along the eyelid margin should be 1–2 mm from the margin. The lower incision is determined by the length and shape of the entropion. (b) The strip of eyelid skin and orbicularis oculi muscle are carefully dissected and excised by small tenotomy scissors. (c) The surgical wound is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. The sutures should be angled somewhat to accommodate the two different lengths of the wound edges. (d) At the conclusion of surgery because of the eyelid swelling, slight overcorrection may be present. (e) Preoperative appearance of a cat with bilateral lower lid medial entropion (right eye shown). (f) Same cat immediately after bilateral Hotz–Celsus procedure (left eye shown).

Modification of Hotz–Celsus technique for medial entropion The Hotz–Celsus procedure may be modified for medial entropion and epiphora in miniature breeds of dogs. The objective of this technique is to evert the medial lower eyelid margin sufficient to assist the lower lacrimal punctum to conduct tears to its orifice (Fig. 5.26). The extent of the lower eyelid skin–orbicularis oculi muscle to be excised is determined preoperatively by estimating the number of millimeters of correction necessary to evert the medial lower eyelid. The incision should not be deeper than the orbicularis oculi muscle to avoid damage to the lower lacrimal punctum and canaliculus.

Bigelbach modification for medial entropion Bigelbach has modified the medial entropion procedure by the excision of a 2–3 mm strip of the upper and lower eyelids at the medial canthus, after the identification of both lacrimal punta. In addition, the caruncle is excised, resulting in an ‘anchor-shaped’ defect. The areas are not apposed by sutures and allowed to heal by secondary intention. The resultant healing effectively treats the medial upper and lower entropion.

Modification of the Hotz–Celsus method for lateral canthal entropion The Hotz–Celsus procedure may be adapted for entropion of the lateral one-third of the upper and lower eyelids, and the lateral canthus. This modification is recommended when the palpebral fissure size is normal, and an additional enlargement of the palpebral fissure is not necessary. If the lateral canthal entropion is associated with a micropalpebral fissure (or the eyelids are shorter than normal), the arrowhead and other surgical procedures are indicated. The procedure is similar to the methods described previously, but adapted to provide eversion of the outer one-third of both the upper and lower eyelids (Fig. 5.27).

‘Y’ to ‘V’ plasty for entropion

Fig. 5.26 The Hotz–Celsus technique may be modified to treat medial entropion and secondary epiphora in miniature breeds of dogs. The tip of the triangle of the wound is opposite the lower lacrimal punctum and designed to improve lower punctum function.

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The ‘Y’ to ‘V’ plasty for entropion successfully corrects mild central entropion of the upper and lower eyelids. This procedure can also be reversed: ‘V’ to ‘Y’ or the Wharton–Jones blepharoplasty for the correction of mild central cicatricial ectropion. The initial Y incision, starting about 1 mm from the eyelid margin, is sufficiently deep to include the eyelid

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Fig. 5.27 The Hotz–Celsus method can be modified for lateral entropion of the upper and lower eyelids. The correction does not affect the size of the palpebral fissure.

skin and orbicularis oculi layers (Fig. 5.28a). The length of the basal part of the Y incision is designed to provide the appropriate amount of correction for the entropion. The triangular flap of skin is elevated, and its base separated from the underlying tarsus by blunt–sharp dissection with small tenotomy scissors (Fig. 5.28b). The tip of the skin–muscle flap is apposed to the bottom and sides of the skin–muscle layers with 4-0 to 6-0 simple interrupted non-absorbable sutures, resulting in a V-shaped closure (Fig. 5.28c).

Central tarsal pedicle for entropion (Wyman) The central tarsal pedicle has been combined with the Hotz– Celsus procedure to treat central lower entropion. The technique involves construction of a pedicle of tarsus to evert the eyelid margin. This pedicle is secured in the subcutaneous tissues. The procedure has been used for congenital and developmental entropion in the Chow Chow, Chinese Shar Pei, English Bulldog, and Rottweiler. It has also been employed for recurrent entropion in dogs and cats treated previously by surgery. This procedure is recommended for severe and recurrent entropion in small animals. The traditional Hotz–Celsus technique is performed first, but the surgical procedure does not extend as deep as the orbicularis oculi muscle (Fig. 5.29a). The distal elliptical skin incision is performed after the tarsal pedicle has been completed. Two parallel incisions are made through the orbicularis oculi muscle and tarsus immediately below the

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area of the most extensive entropion. The tarsal pedicle is constructed by scalpel dissection with its base at the eyelid margin (Fig. 5.29b). It is then freed from the deeper palpebral conjunctiva and more superficial skin. A subcutaneous tunnel, that is as wide as the pedicle, is prepared by tenotomy scissors in the lower incision to correct the entropion: the more severe the entropion, the longer the subcutaneous tunnel. With a double-armed 5-0 non-absorbable suture, a cruciate stitch is placed in the tarsal pedicle and extended through the subcutaneous tunnel to be tied at the level of the skin with a stent (Fig. 5.29c). As the suture is tightened and tied, the entropion area should be corrected. The distal elliptical section of skin is now excised by tenotomy scissors (Fig. 5.29d). Apposition of the skin wound is by 4-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 5.29e). Multiple tarsal pedicles can be used when more than one area of the eyelid is affected. The tarsal pedicle technique is often combined with a permanent lateral tarsorrhaphy.

Combined entropion–distichiasis procedure The surgical procedures for entropion and distichiasis may be combined in the dog. The distichia follicles are excised using the tarsoconjunctival resection methods described in an earlier section. The Hotz–Celsus procedure is then performed to correct the entropion. Wound apposition is by 4-0 simple interrupted silk sutures. Each skin suture includes a deep bite of tarsus to assist with eyelid margin eversion.

Stades combined entropion–trichiasis procedure The entropion and trichiasis procedures are combined for breeds of dogs with upper eyelid entropion and large areas of redundant skin on the forehead (Fig. 5.30). Performance of only the entropion procedure, usually the Hotz–Celsus method, may not completely correct the defect as the excess skin above both eyes results in recurrent upper entropion. This procedure and modifications of this method are used in selected breeds including the English Cocker Spaniel, Chow Chow, Chinese Shar Pei, and Bloodhound. At least two different surgical methods have been used to treat the unusual entropion complicated by redundant forehead folds of skin. In the combined upper eyelid

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Fig. 5.28 The ‘Y’ to ‘V’ plasty for entropion may be used for mild entropion of the central portion of the lower lid. (a) The initial ‘Y’ incision of the lid skin and orbicularis oculi muscles layers by Beaver No. 6700 microsurgical blade starts about 1 mm from the eyelid margin. The lower part of the incision will determine the extent of the lid eversion. (b) A triangular section of skin and orbicularis oculi muscle, based at the eyelid margin, is dissected from the underlying tarsus by tenotomy scissors. (c) The tip of the skin–muscle flap is apposed in a ‘V’ shape to effect eversion of the eyelid margin with 4-0 to 60 simple interrupted non-absorbable sutures.

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Fig. 5.29 Central tarsal pedicle for entropion. (a) A tarsal pedicle anchored at the eyelid margin is combined with the Hotz–Celsus procedure. The initial skin incision is performed by the Beaver No. 6700 microsurgical blade about 1–2 mm from the eyelid margin. (b) A tarsal pedicle is constructed by scalpel with its base at the eyelid margin of the most extensive entropion. (c) Through a subcutaneous tunnel made by scissors, a 5-0 non-absorbable cruciate suture attached to the tarsal pedicle is secured with a stent below the surgical wound. (d) The second skin incision of the Hotz–Celsus method is performed, and the section of skin is excised by tenotomy scissors. The width of the surgical wound varies with the extent of the entropion. (e) The skin wound, to correct the remainder of the entropion, is apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

Fig. 5.30 The Chinese Shar Pei can benefit from either the Stades procedure or the Hotz–Celsus procedure, combined with resection of variable amounts of forehead skin. These combinations assist greatly when the upper eyelids also have entropion.

trichiasis and entropion procedure, reported by Stades, a section of upper eyelid skin is excised extending vertically 0.5–1.0 mm from the upper eyelid margin to 15–25 mm above the palpebral fissure, and horizontally 2–4 mm medial from the nasal canthus to 5–10 mm external to the lateral canthus (Fig. 5.31a–d). The upper eyelid wound is partially closed by the apposition of the upper eyelid skin to the subcutaneous eyelid layer 5–6 mm from the eyelid

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margin with 4-0 to 5-0 simple interrupted or a combination of simple interrupted and continuous non-absorbable sutures (Fig. 5.31e–g). The exposed area immediately above the upper eyelid margin heals by secondary intention. The resultant fibrosis everts the upper eyelid margin. This area may become pigmented. The animal still retains its facial folds of skin and its overall appearance is not markedly altered. The second procedure consists of two parts: the excision of a large section or facelift of the redundant forehead skin (Fig. 5.32), and the Hotz–Celsus technique (or some modification thereof) to evert the upper eyelid margin and, if indicated, the lateral canthus. The redundant skin in the forehead is excised to an extent that these folds of skin do not affect the eyelids. Two curvilinear skin incisions are performed for the forehead skin resection. The skin is resected by Metzenbaum scissors, and the edges are apposed with 3-0 to 4-0 simple interrupted non-absorbable sutures. The upper entropion, or upper lid and lateral canthal entropion, is corrected by the Hotz–Celsus procedure or modifications.

Modified Hotz–Celsus procedure for entropion and ectropion The Quickert technique for humans has been modified for the dog with a combination of lower entropion and ectropion. After the Hotz–Celsus procedure has been performed, a wedge of eyelid margin is excised from the center of the Hotz–Celsus procedure. The eyelid margin is apposed with a figure-of-eight suture, and the Hotz–Celsus wound apposed with simple interrupted non-absorbable sutures.

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Fig. 5.31 Stades procedure for entropion and redundant forehead folds of skin. (a) A large section of upper eyelid skin will be resected. The skin incisions extend from 0.5–1.0 mm from the eyelid margin to 15–20 mm dorsally. (b) Intraoperative appearance in an English Bulldog. The large skin incision approaches but does not include the upper lid margin. (c) The skin section is excised carefully by tenotomy scissors. The size of the eyelid flap assists correction of the upper eyelid entropion, and compensates for the redundant forehead skinfolds. (d) Intraoperative photograph, showing the extent of the skin removal. (e) Apposition of the surgical wound with 4-0 to 5-0 simple interrupted non-absorbable sutures is incomplete, leaving 5–6 mm of subcutaneous tissue of the upper eyelid to heal by secondary intention and rotate the lid margin outward. (f) Immediate postoperative appearance of the left eye. Note the exposed subcutaneous tissues immediately behind the lid margin. (g) Immediate postoperative appearance of the face after bilateral lid surgeries.

Face lift/skinfold excision and rhytidectomy For many breeds of dogs the excision of periocular (orbital and forehead) skinfolds may be combined with other entropion surgeries, such as the Hotz–Celsus or Stades procedures, to effectively treat upper and lateral canthal entropion. In breeds such as the Chinese Shar Pei, Bloodhound, and some of the spaniel breeds, the skin above the eye and on the forehead may be grasped in the awake patient, and ‘gathered’ until the upper entropion is corrected. Rather large amounts of forehead skin can be safely excised in this method as semicircular areas. The surgical skin defects are apposed with 3-0 to 4-0 simple interrupted sutures.

Surgical procedures for lateral canthal entropion The lateral canthal region of the dog lacks stability because of the absence of a strong and rigid lateral canthal ligament. The lateral retractor anguli oculi muscle partially replaces the function of the lateral palpebral ligament, but the area remains unstable and is a frequent location for entropion. Lateral canthal surgical procedures usually extend variable lengths into the upper and lower eyelids, and not necessarily equally. As a result, each surgical procedure should be modified for the individual lateral canthal defect. At least three surgical procedures concentrate on entropion of the lateral

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Fig. 5.34 The arrowhead procedure for correction of lateral canthal entropion is a further modification of the Hotz–Celsus procedure. The procedure will also slightly increase the size of the palpebral fissure. Fig. 5.32 In certain breeds, like the Chow Chow or the Chinese Shar Pei, treatment of entropion can also include the resection of a large section of forehead skin and the Hotz–Celsus procedure, as shown in this immediate postoperative photograph.

Fig. 5.33 The large and giant breeds of dogs with lateral canthal entropion have lateral canthal instability and often a ‘diamond’-shaped palpebral fissure.

canthus. Two of the three procedures increase the stability of the area by constructing additional lateral canthal support (Fig. 5.33). These three surgical procedures include the arrowhead procedure, lateral canthoplasty by the Wyman technique, and modifications of the Wyman procedure.

Arrowhead procedure for lateral canthal entropion The arrowhead procedure may be used to correct lateral canthal entropion, but does not substantially increase the size of the palpebral fissure. The extent of correction of lower and upper entropion may vary depending on the degree of lid inversion of each eyelid margin. The arrowhead procedure is indicated for lateral canthal entropion with normal-sized palpebral fissures and normal length upper and lower eyelids. A subcutaneous lateral canthal suture may be added to this procedure to anchor and stabilize the lateral canthus, and positioned just before the lid skin is apposed.

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The lateral canthal region is stabilized with a thumb forceps placed in the lateral conjunctival fornix or with the lateral canthus grasped with the Lordan triangular chalazion and/or Desmarres forceps. These forceps also assist with local hemostasis. The technique is similar to the Hotz–Celsus procedure, except for its shape (Fig. 5.34). The skin and orbicularis oculi layers are incised with the Bard–Parker No. 15 blade or Beaver No. 6700 microsurgical blade 1–1.5 mm from the eyelid margin. The width of the surgical site is determined by the size of the original lid defect. The skin and orbicularis oculi layers are carefully excised by tenotomy scissors. If the lateral canthus tension suture is used, it is positioned now. A 4-0 monofilament non-absorbable simple interrupted or horizontal mattress suture is placed at the lateral canthus in the muscle–tarsal layers and then in the fascia overlying the orbital ligament. The suture is gradually tightened to tense the lateral canthus into the desired position. The surgical wound is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures, with the first suture placed at the lateral canthus.

Lateral canthoplasty by Wyman The lateral canthoplasty procedure, as developed by Wyman, attempts to address the lack of lateral canthal stability and the associated lateral canthal entropion of large and giant breeds of dogs. The breeds of dogs that may benefit from this procedure include the St Bernard, Newfoundland, Chow Chow, Golden Retriever, Bull Mastiff, Rottweiler, and English Bulldog. These large breeds often have some enophthalmia, and the lack of globe support for the lower eyelid may also predispose to entropion. These same breeds may also have a round-, diamond- or pergola-shaped palpebral fissure, and a combination of lateral entropion and central ectropion of both eyelids. With correction of the lateral canthal entropion, a significant portion of the central lower ectropion (or central eversion of the eyelid margin) will also resolve. After draping, an elliptical skin incision is made by scalpel (Fig. 5.35a). The incision should be 1–1.5 mm from the lateral eyelid margins. The width between the two elliptical skin incisions is the amount of correction for the lateral canthal entropion. The orbicularis oculi muscle is exposed with blunt–sharp dissection with small tenotomy scissors. Upper and lower pedicles of orbicularis oculi muscle are constructed by scalpel with their base at the lateral canthus (Fig. 5.35b). The lateral canthus is dissected further to

Postoperative management and complications

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Fig. 5.35 The lateral canthoplasty and construction of a lateral canthal ligament by Wyman has proven useful for large and giant breeds with central ectropion and lateral entropion of both eyelids and the lateral canthus. (a) Two elliptical skin incisions are performed. The width of the surgical wound (6–10 mm) should approximate the amount necessary to effect correction of the entropion. (b) Two myotomies are performed with their base at the lateral canthus. These strips of muscle will form the new lateral canthal ligament. (c) After subcutaneous dissection by tenotomy scissors, the pedicle of orbicularis oculi is secured by a cruciate suture to the periosteum of the zygomatic arch by a 4-0 to 5-0 simple interrupted non-absorbable suture. (d) The skin layers are apposed by 4-0 to 5-0 simple interrupted non-absorbable sutures.

expose the lateral orbital rim and/or zygomatic arch. The two muscle pedicles are united with a 4-0 to 5-0 nonabsorbable cruciate suture, and secured to the periosteum of the zygomatic arch (Fig. 5.35c). The skin layer is apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 5.35d). Because of the additional dissection involved with this method, more postoperative swelling of the lateral canthus usually occurs.

Lateral canthoplasty with suture This surgical procedure is a modification of the Wyman lateral canthoplasty and, instead of the orbicularis oculi muscle pedicle, a non-absorbable suture is used to secure the lateral canthus. This adaptation reduces the time for surgery, and with less tissue dissection the postoperative eyelid and lateral canthal swelling are reduced. An alternative method that we have used replaces the non-absorbable suture with a section of frozen scleral homograft. The eyelid skin and part of the orbicularis oculi muscle are excised to correct the lateral canthal entropion. The exact shape and size of the upper and lower aspects of the elliptical incisions vary, depending on the extent of entropion of the upper and lower lids. Once the skin layer is excised, the dissection is continued laterally by small tenotomy scissors to isolate an area to secure the lateral canthus. A single 2-0 non-absorbable suture (or occasionally two sutures) is secured in the lateral canthus and the periosteum of the zygomatic arch (Fig. 5.36). The tension on the suture can be adjusted to provide a reasonably normal sized and shaped palpebral fissure. The skin layer is apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

Robertson’s lateral canthal tendonectomy Robertson has described a procedure to treat lateral canthal entropion that releases the tension in large and giant breeds of dogs by transection of the lateral canthal tendon.

Fig. 5.36 As an alternative to the pedicle of orbicularis oculi muscles in the lateral canthoplasty procedure, one or preferably two sutures or a section of frozen scleral homograft can be used to attach the lateral canthus and the periosteum of the zygomatic arch, and stabilize the lateral canthus.

The lateral canthus is everted by forceps to expose the palpebral conjunctiva. With curved Steven’s or tenotomy scissors, the palpebral conjunctiva is separated from the deeper tarsus in a 9 mm arc. The fibrous band is located by blunt dissection that extends from the lateral canthus to the orbital ligaments and zygomatic arch, and a wedge of the tendon excised near its base. An alternative technique is to sever the tendon (tendonotomy) by scissors midway between its origin and insertion. The conjunctival wound is not apposed by sutures. Other entropion techniques may be combined with this method.

Postoperative management and complications Topical antibiotics/corticosteroids are usually administered after entropion surgery. If corneal ulceration, secondary to the entropion, is present, topical antibiotics and mydriatics are indicated. Systemic antibiotics are infrequently indicated except for the lateral canthoplasty techniques when tissue dissection and surgical time are greater. The E-collar should be used after all of these procedures to prevent self-trauma

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and wound dehiscence. The skin sutures are usually removed at 7–10 days, especially if silk is used. Sutures left too long may cause excessive irritation. Complications after these entropion procedures are usually associated with under- and overcorrection of the defect. Occasionally, another surgical procedure may be necessary to secure a reasonable repair, especially if the surgery is performed in young and growing puppies and kittens. The purpose of these procedures is a cosmetically acceptable and functional eyelid. Completely normal eyelid contour may not always be achieved. If the skin–orbicularis oculi muscle incision is too close to the eyelid margin, the sutures are very difficult to place, and there is a greater possibility of the sutures touching the cornea. If the linear incision along the eyelid margin is too far from the margin, the extent of eversion of the entropion is less. Suture failures are unlikely. Use of the E-collar provides excellent protection against the patient rubbing the surgical site that can result in local lid swelling and premature suture loss. With suture loss and wound dehiscence, there is additional postoperative fibrosis and often overcorrection. If overcorrection of the entropion occurs, the blepharospasm may have been overestimated or excessive tissue was excised. If undercorrection results, usually insufficient tissue was removed. The large and giant breeds of dogs with entropion and enophthalmia present additional challenges because the globe–lower eyelid contact is limited and entropion repair is less predictable. The breeds with excessive forehead skinfolds and heavy ears complicate entropion surgery. They often require concurrent excision of large amounts of forehead skin which will affect the dog’s appearance.

ADAPTATIONS IN LARGE ANIMALS AND SPECIAL SPECIES

Entropion in horses Entropion is an inward rolling of the eyelid, allowing eyelid hair to contact the cornea and conjunctiva. Rubbing and irritation from the hair position result in blepharospasm and increased tearing. Corneal ulcers and keratitis commonly occur. Entropion occurs in young foals and is considered to be hereditary in some cases. However, many episodes of entropion in young foals occur in dehydrated, premature, or septicemic animals, and in such cases acquired entropion seems more likely. Permanent surgical correction, therefore, is not indicated in all cases. Non-surgical management may be corrective in most cases. In acute entropion in foals, lubrication of the cornea and conjunctiva with ophthalmic lubricating ointment (artificial tears, ophthalmic ointment petrolatum, or OptixcareW gel) with manual repositioning may be all that is necessary for a good result and avoidance of surgical correction. The injection of different materials into the lower eyelid will also result in temporary correction of the entropion. The injection of 0.5–1 mL of procaine penicillin G into the eyelid at the base of the entropion and massaged toward the eyelid margin may correct the inrolling for a short period of time.

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The injection of liquid paraffin has been reported, but is not recommended due to the risk of inflammatory reaction. If manual repositioning does not correct the problem in young foals, the use of everting sutures is considered. Sutures are placed in a vertical mattress pattern. To ensure ideal eversion of the eyelid margin and haired skin, the sutures should be placed near the eyelid margin (approximately 2–3 mm from the margin). The suture bite should not be so large as to overcorrect the entropion. If overcorrection occurs, the resulting ectropion may interfere with eyelid closure, and ocular irritation may develop from exposure of tissues. Increased tension on the sutures may cause the sutures to cut through the thin eyelid skin. This will lead to failure of the procedure and increased scar tissue formation. Non-absorbable suture material of 3-0 to 5-0 size is preferred. Sutures are commonly left in place for 7–14 days. Skin staples have been used with variable results. The use of staples may be less stressful on these compromised sick foals. They are readily available and rapid to place in the foal with systemic conditions. Everting the eyelids with sutures or staples will frequently be adequate to achieve correction of the entropion, especially if the cause of the entropion can be corrected.

Permanent correction of entropion in the horse Entropion in older horses is commonly associated with cicatrix formation and requires surgical correction. Entropion associated with localized eyelid disease such as scar formation is corrected using a ‘Y’ to ‘V’ procedure (see Fig. 5.28). Initially a Y incision is made, with the arms of the Y extending slightly (1–2 mm) beyond the lateral and medial extent of the lesion. A flat instrument (e.g., Jaeger eyelid plate, sterile wooden tongue depressor, handle of a surgical scalpel) is inserted behind the eyelid into the conjunctival fornix to stabilize the skin and facilitate the skin incision. Ophthalmic cautery and a No. 15 blade are used. The length of the stem of the Y is determined by the amount of eyelid eversion needed. The skin is dissected from the subcutaneous tissues and undermined, and the existing scar tissue excised. The incision is positioned and sutured in a V-shaped closure, creating eversion of the eyelid margin. The skin is closed in a single layer using 4-0 to 5-0 simple interrupted non-absorbable sutures. In the horse, more generalized and non-cicatricial entropion is corrected using a modified Hotz–Celsus procedure. In this technique, a crescent-shaped or elliptical area of skin and orbicularis oculi muscle is excised (Fig. 5.37). The first incision is made parallel to and near (2–3 mm) the eyelid margin. The amount of skin and orbicularis oculi muscle to be removed is determined in the awake horse by ocular examination. The eyelid is examined, then a blink response or palpebral reflex is induced and the eyelid re-examined. After the examiner is satisfied with this assessment, topical anesthetic (0.5% proparacaine) is applied to the cornea and the eyelid re-examined without the blepharospastic component. The horse is then anesthetized and the surgical site prepared for aseptic surgery. The eyelid skin may be stabilized with a Jaeger eyelid plate, the handle of a surgical scalpel, or a sterile wooden tongue depressor inserted behind the eyelid into the conjunctival fornix. The skin is

Entropion and periocular fat pads in the Vietnamese potbellied pig (Sus scrofa)

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Fig. 5.37 (a) Preoperative appearance of lower lid entropion in a young horse. (b) Postoperative appearance after correction using the Hotz–Celsus surgical procedure.

incised, and the skin and a portion of the orbicularis oculi muscle excised with small surgical scissors (see Fig. 5.25). In many cases about half as much muscle as skin is excised, which leads to good repair for the entropion and a cosmetic result. The skin is closed in a single layer using 4-0 to 5-0 non-absorbable (monofilament nylon) sutures. Sutures are removed in 10–12 days. When entropion is associated with a small eyelid scar, a ‘Y’ to ‘V’ procedure is often the best therapeutic option. The arms of the Y should extend only slightly beyond the extent of the entropion (see Fig. 5.28). The stem and height of the Y are determined by the amount of eyelid eversion needed. The adjacent skin is undermined and the scar tissue excised from normal tissue. The skin is apposed with 4-0 to 5-0 non-absorbable (monofilament nylon) sutures in a simple interrupted pattern. Sutures are removed in 10–12 days.

Aftercare following entropion surgery in the horse Preoperative topical and systemic antibiotics are indicated. The placement of a subpalpebral lavage system will facilitate topical application of solutions to the eye. Postoperative swelling can be reduced by the administration of systemic non-steroidal anti-inflammatory agents (flunixin meglumine 1 mg/kg IV) immediately before surgery. Postoperative edema will be lessened by the application of ice packs for the first 24 h after surgery. If swelling

is present 24 h after surgery, warm compresses may further reduce the swelling and discomfort at the surgical site. As rubbing or self-mutilation is often a concern in the horse, the surgical site or eye must be protected by a protective hood with a plastic or solid eyecup (EyeSaver™, Jorgensen Laboratories, Loveland, CO.). Skin sutures are usually removed 8–12 days after surgery. In situations when tension on the suture line cannot be avoided, sutures are left in place for 18–24 days.

Entropion in sheep Entropion or inversion of the eyelid margins may be fairly common in newborn lambs in some flocks (Fig. 5.38). Financial constraints and the need to treat several lambs in the same flock have led to some interesting forms of therapy. The Hotz–Celsus entropion procedure is also successful in lambs but often cost-prohibitive. Entropion may be corrected by subcutaneous injections in the eyelid skin using procaine penicillin, mineral oil, water, air, and warm beeswax. The amount varies, but 1–2 mL is usually adequate. As the agent is injected, the lid is rotated outward and away from the eye. Another rapid form of correction is office staples and surgical staples to evert the lid margin. Excision of lid skin and muscle followed by a single absorbable suture has also been reported.

Entropion and periocular fat pads in the Vietnamese potbellied pig (Sus scrofa)

Fig. 5.38 Lower lid entropion in a lamb with secondary corneal disease. There are several surgical and non-surgical avenues for repair.

Vietnamese potbellied pigs are predisposed to entropion, relative enophthalmia, large periocular fat pads, predisposition to obesity, and heavy forehead brows and upper eyelids. The upper entropion may induce corneal ulceration, but more often corneal vascularization and scarring. Often with increased age, these interrelated factors eventually decrease vision and produce behavioral changes (apprehension, aggression, poor socialization, and fear biting). Surgery for entropion in this species includes: 1) resection of the fat pads beneath the eyelids; 2) the Hotz–Celsus procedure for entropion, often with overcorrection; 3) resection of part of the large (and heavy) forehead; and 4) postoperative control of diet to reduce the obesity long term. This surgical procedure is similar to that in the large breeds of dogs

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C D Fig. 5.39 Bilateral entropion in a Vietnamese pot-bellied pig. Surgical considerations include correction of the entropion (often 360 ), removal of fat pads within the affected eyelids, and removal of the excessive forehead brows. (a) Preoperative appearance of an affected pig. Note the generalized obesity. (b) Intraoperative photograph. Often over-correction of the entropion is performed to compensate for the obesity. (c) Examples of the large sections of forehead brows removed to reduce pressure on the upper eyelids. (d) Postoperative appearance at surgery. Long-term diet management is essential to prevent return of the entropion.

for forehead resections and entropion procedures, but is complicated by the need to also resect the large and often extensive subcutaneous fatty tissues (Fig. 5.39). The surgery is performed under general anesthesia; premedication includes midazolam (0.3 mg/kg IM) and butorphanol (0.3 mg/kg IM). Isoflurane anesthesia is induced by mask, then the animal intubated and maintained on isoflurane and oxygen. The entire face and forehead are prepared for surgery by clipping the hair and disinfection of the skin by dilute povidone–iodine (0.5%) solution. Correction of the upper entropion may be combined with resection of a large forehead section of skin. When combined with forehead skin resection and upper entropion correction, the skin incision starts just ventral and rostral of the tragus of one ear and continues rostromedially along the ventral aspect of the fat pad to the lateral canthus, and then to within 2–3 mm from the upper lid margin; the skin incision is then continued on the opposite side of the face. Both forehead and upper eyelid skin and fat pads are excised. Any facial muscle is spared, but fatty tissues are excised by sharp dissection, and the large forehead section and upper eyelids excised. After absorbable 2-0 subdermal sutures to close potential dead space, the leading edge of the remaining forehead skin is carefully apposed to the surrounding skin and upper eyelids with simple interrupted non-absorbable sutures. For lower lid entropion, the Hotz–Celsus procedure is used (usually an overcorrection), and the excessive fatty tissues also removed.

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Postoperative medications for several days may include: 1) ceftiofur (3 mg/kg PO or IM) for antibiosis; 2) flunixin meglumine (0.7 mg/kg PO or IM) for postoperative swelling; and 3) butorphanol (0.1–0.17 mg/kg IM q8h) for pain.

SURGICAL PROCEDURES FOR ECTROPION Ectropion or the eversion of the eyelid is less dangerous to the eye, but can produce chronic keratitis, conjunctivitis, keratoconjunctivitis, epiphora, and tear staining of the eyelids (Fig. 5.40). Of the animal species with ectropion, dogs (particularly the large breeds) are most frequently affected. Ectropion may be associated with developmental, cicatricial, traumatic, neurologic, and postoperative causes. The breeds of dogs frequently affected with lower lid ectropion include the Bloodhound, St Bernard, Great Dane, Newfoundland, Mastiff, and many spaniel breeds. In some breeds both the eyelids and palpebral fissure are excessive in size and length. In some large and giant breeds of dogs the laxity of the lower eyelid may vary with the fitness and the age of the animal. Central ectropion may also be associated with lateral canthal entropion. Part of the ophthalmic pathology secondary to ectropion is associated with impaired blink reflex, preocular film defects, and impaired tear movement to the medial conjunctival sac. Surgical correction of ectropion is recommended when secondary ophthalmic disease results and requires

Surgical procedures for ectropion

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Fig. 5.41 Lateral eyelid wedge excision procedure. (a) A full-thickness triangular section of lower lid is excised by scissors. A thumb forceps is inserted at the lateral canthus to provide tension on the lower lid. (b) The surgical defect is apposed by two layers of sutures. The tarsoconjunctival layers are apposed with a 3-0 to 5-0 simple continuous absorbable suture. The skin–muscle layers are apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures. Fig. 5.40 Ectropion can produce chronic ocular irritation, such as conjunctivitis. Ectropion surgical procedures generally shorten the length of the eyelid.

long-term topical medications to control the local inflammation and irritation. Surgery should attempt to provide a relatively normal length lower eyelid. Overcorrection should be avoided as entropion may result and can cause potentially more damage to the cornea and conjunctiva. The different ectropion surgical procedures for the lower eyelid primarily shorten and strengthen the lid. As the medial canthus is relatively fixed and more complicated by the presence of the nasolacrimal apparatus and the nictitating membrane, most ectropion surgical procedures involve the lateral one-half of the lower eyelid and the lateral canthus. Procedures for the correction of ectropion include simple triangle excision at the lateral canthus, ‘V to Y’ plasty for cicatricial ectropion, the Kuhnt–Szymanowski procedure, the Kuhnt–Helmbold procedure, and the Munger and Carter modification of the Kuhnt–Helmbold technique.

Lateral eyelid wedge excision In this procedure, the lower eyelid is shortened by the excision of a full-thickness wedge or triangular section of lid. The lid excision is performed at the lateral canthus to avoid the development of an unsightly postoperative eyelid margin notch that may occur when this surgery is performed elsewhere. The size of the wedge of lower lid to be

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removed should be slightly smaller than the extent of eyelid shortening and correction anticipated. As with entropion procedures, postoperative fibrosis generally provides an additional 0.5–1 mm correction. The surgery is performed immediately next to the lateral canthus. A triangular full-thickness section of lower eyelid is excised by strabismus scissors or small Metzenbaum scissors (Fig. 5.41a). The eyelid may be stabilized by a chalazion or entropion forceps, or the entire lower eyelids may be tensed by a thumb forceps positioned in the lateral canthus. The surgical wound is apposed by two layers of sutures (Fig. 5.41b). In the deep layer, a 3-0 to 5-0 simple continuous absorbable suture is positioned in the submucosa of the palpebral conjunctiva and tarsus. The knots are buried to prevent contact with the cornea. Starting at the eyelid margin, the superficial layer of eyelid skin and orbicularis oculi muscle is apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

‘V’ to Y’ plasty (Wharton–Jones procedure) The ‘V’ to ‘Y’ plasty is the reverse of the surgical procedure used for cicatricial entropion. Unless a section of the eyelid margin is excised, the ‘V’ to ‘Y’ plasty tightens but not substantially shortens a lower eyelid with ectropion. Starting about 1 mm from the lower eyelid margin, two converging skin incisions are performed on each side of the scarred area (Fig. 5.42a). The V-shaped skin flap is retracted upward, and the scar tissue in the subcutaneous layer and, if present, in the tarsal layer is excised by

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Fig. 5.42 The ‘V’ to ‘Y’ plasty may be used to treat mild cicatricial ectropion. (a) Converging skin incisions are performed by the Beaver No. 6700 microsurgical blade starting 1 mm from the eyelid margin. (b) The ‘V’ shaped skin flap is separated from the subcutaneous tissues, and the scar tissue excised. (c) The skin flap is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures as a ‘Y’ shaped closure.

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Fig. 5.43 The Kuhnt–Szymanowski procedure is used to correct ectropion and shorten the length of the lower lid. (a) The lower eyelid is split at the ‘gray line’ of the eyelid margin at a depth of 10–15 mm and the incision is extended beyond the lateral canthus. (b) The skin–muscle flap is separated by blunt dissection using tenotomy scissors. (c) Wedges of equal size of tarsoconjunctiva, orbicularis oculi muscle and skin are excised by tenotomy scissors. (d) The tarsoconjunctival defect is apposed by 4-0 to 6-0 simple interrupted absorbable sutures with the knots buried to avoid corneal contact. The skin wound is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. The eyelid margin is apposed by 5-0 to 6-0 through-and-though interrupted mattress non-absorbable sutures.

tenotomy scissors (Fig. 5.42b). The adjacent subcutaneous tissues are undermined by blunt scissor dissection, and the wound is apposed as a Y-shaped closure with 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.42c).

Kuhnt–Szymanowski procedure The Kuhnt–Szymanowski procedure and the next two surgical techniques are used to correct the more severe forms of ectropion and can substantially shorten the lower eyelid. The Kuhnt–Szymanowski method consists of the excision of a wedge of conjunctiva and tarsus within the area of greatest ectropion, the excision of a wedge of orbicularis oculi muscle and skin at the lateral canthus, and the shortening of the lid with a sliding flap of orbicularis oculi muscle and skin. A major disadvantage of this procedure is that approximately the lateral two-thirds of the lower eyelid margin and eyelid must be split into palpebral conjunctiva–tarsus, and the orbicularis oculi muscle and skin layers. The lower eyelid is split with the No. 6700 microsurgical blade at the eyelid margin and immediately in front of the ‘gray line’ (opening of the meibomian glands), starting medial to the central area of ectropion and extending to the lateral canthus (Fig. 5.43a). The depth of the eyelid splitting should be about 10–15 mm. The skin incision is then continued into the lateral canthus to accommodate the excision of a wedge of skin approximately the same size as the tarsoconjunctival wedge (Fig. 5.43b). By tenotomy scissors a central wedge of tarsoconjunctiva is excised. The

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width of the wedge should be 0.5–1 mm shorter than the length of shortening for the lid (Fig. 5.43c). The tarsoconjunctival wound is apposed by a 4-0 to 6-0 simple continuous absorbable suture with the knots buried to avoid touching the cornea. The skin incision is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. Just below the eyelid margin the split eyelid wound is apposed with 5-0 to 6-0 through-and-through interrupted mattress non-absorbable sutures with the knots on the skin side (Fig. 5.43d).

Kuhnt–Helmbold procedure Like the Kuhnt–Szymanowski technique, the Kuhnt– Helmbold method addresses ectropion by shortening the lower lid, but the surgery concentrates on the central portion of the eyelid. The lower eyelid is split at the ‘gray line’ into tarsus and palpebral conjunctiva, and skin–orbicularis oculi muscle layers with the No. 6500 microsurgical blade to a depth of about 10–15 mm (Fig. 5.44a). The length of the incision should include about 60–70% of the total lid length. Identical sized wedges of tarsoconjunctiva and skin–muscle are excised by small tenotomy scissors at two different locations (Fig. 5.44b). The tarsoconjunctival defect is apposed with 4-0 to 6-0 simple interrupted absorbable sutures. The skin–muscle wedge defect is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. The lid margin wound is apposed with 4-0 to 6-0 through-and-through interrupted mattress non-absorbable sutures (Fig. 5.44c).

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Fig. 5.44 The Kuhnt–Helmbold procedure for ectropion. (a) The lower eyelid is split at the ‘gray line’ into tarsoconjunctival and skin–orbicularis oculi muscle layers to a depth of 10–15 mm. (b) Identical wedges of tarsoconjunctiva and skin–muscle are excised from the lower eyelid. (c) The tarsoconjunctival defect is apposed with 4-0 to 6-0 simple interrupted absorbable sutures. The skin–muscle layer is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures. The lid margin wound is apposed with 4-0 to 6-0 through-and-through interrupted mattress non-absorbable sutures.

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Fig. 5.45 The Munger and Carter modification of the Kuhnt–Szymanowski procedure for ectropion avoids splitting of the eyelid margin. (a) The skin incision is 3 mm below the eyelid margin and extends 10 mm beyond the lateral canthus. The skin–muscle flap is dissected from its deeper tarsal attachments. (b) Equal size wedges of tarsoconjunctiva and skin–muscle are excised by scissors. The tarsoconjunctival wound is apposed by a 4-0 to 6-0 simple continuous absorbable suture. (c) The skin–muscle defect and the remaining skin edges are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

Modified Kuhnt–Szymanowski procedure (Munger and Carter) Both the Kuhnt–Szymanowski and Kuhnt–Helmbold ectropion procedures require a significant portion of the lower eyelid margin to be interrupted and then reapposed. The Munger and Carter modification of the Kuhnt– Szymanowski procedure permits the sliding and shortening of the lower eyelid but avoids splitting of the critical eyelid margin. The initial skin and orbicularis oculi muscle incision is made 3 mm from and parallel to the eyelid margin to approximately 10 mm lateral of the lateral canthus (Fig. 5.45a). A second skin–orbicularis oculi muscle incision is continued ventral for about 15 mm. The skin and muscle flap is undermined by small tenotomy scissors. A wedge of tarsus and palpebral conjunctiva, sufficient to shorten the lid and correct the ectropion, is excised by tenotomy scissors (Fig. 5.45b). The tarsoconjunctival defect is apposed with a 4-0 to 6-0 simple continuous absorbable suture. One additional suture is placed at the eyelid margin to maintain this apposition. A wedge of the skin and muscle flap is excised by tenotomy scissors. The size of this wedge approximates the tarsoconjunctival wedge. The skin–orbicularis oculi muscle flap is pulled dorsolaterally and the wound is apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.45c). If the tension on the skin–muscle flap appears excessive, additional blunt–sharp dissection with tenotomy scissors should be performed. A few simple interrupted absorbable sutures attaching the flap edges to the deeper tarsus may be used to reduce the tension on the flap and skin sutures.

Postoperative management and complications Postoperative treatment after these ectropion procedures includes primarily topical antibiotics/corticosteroids for 10–14 days. Systemic antibiotics may be indicated for the more extensive procedures. The E-collar is used routinely to prevent the patient from rubbing the surgical site, producing local irritation and even suture loss. Partial and complete temporary tarsorrhaphies can provide some countertension for these procedures if necessary. All sutures should be removed at 7–10 days. The main goal of these procedures is to obtain a reasonable length lower lid and normal-appearing palpebral fissure. To avoid overcorrection and the more serious

entropion, the conservative approach is to slightly undercorrect the ectropion. Often the postoperative fibrosis about the surgical site will provide an additional 0.5– 1.0 mm correction. These procedures are frequently used in the large and giant breeds of dogs, and often globe contact with the lower eyelid is minimal or absent. Undercorrection of ectropion is recommended in these breeds to avoid postoperative entropion.

Ectropion in the horse Ectropion is defined as an outward rolling of the eyelid. This abnormality results in increased exposure of the cornea and conjunctiva. The most common cause in horses is contraction of scar tissue everting the eyelid following trauma and surgery. Several surgical techniques have been described for correction of ectropion in humans and in dogs. The most commonly used procedure in horses is the ‘V’ to ‘Y’ technique (see Fig. 5.42). The V portion of the incision is wide enough to extend slightly lateral and medial to the scar. The height of the V should be sufficient to remove the tension creating the ectropion. The skin beneath the V is undermined and the scar tissue is excised with tenotomy scissors. The apex of the V is pushed toward the eyelid margin to allow realignment of the eyelid, and closed to form a Y-shaped suture line with a single layer of simple interrupted sutures. Usually 4-0 to 5-0 non-absorbable suture material is used in the horse eyelid. Sutures are removed in 10–12 days.

Surgical procedures for combined ectropion and entropion Certain breeds of dogs, such as the Bloodhound, St Bernard, and Clumber Spaniel, are selected for ‘diamond’-appearing palpebral fissures that result in persistent conjunctival exposure and inflammation, impaired tear distribution on the ocular surfaces and to the nasolacrimal punta, lower entropion, lateral canthal entropion, and often heavy and excessive facial skinfolds and ears. Eyelid lengths, especially the lower, are excessive and the lateral canthus unstable, resulting in a sagging lower lid and inverted upper and lower lateral canthi. A poorly developed lateral canthal ligament or excessive tension on this area, as well as variable enophthalmia, are other complicating disorders.

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Surgeries to correct combined lower ectropion and lateral canthal entropion must include two concepts: 1) to shorten the lower lid; and 2) to stabilize the lateral canthus and correct the entropion. Available surgeries can effectively address the lower ectropion, but lateral canthal stability can still be a problem. Surgeries for combined ectropion–entropion include the traditional ectropion procedures, i.e., Wyman, the modified Kuhnt–Szymanowski, and the arrowhead entropion technique combined with wedge removal of the outer lower eyelid, and newer methods including those described by Gutbrod and Tietz, Bigelbach (can also be used for the medial canthus), and Bedford. The newer surgeries shorten the lower eyelid, and attempt to stabilize the lateral canthus and correct the entropion. In the Gutbrod–Tietz technique the lower eyelid is shortened and the lateral canthus is removed. In Bigelbach’s procedure a combined tarsorrhaphy–canthoplasty is used for either lateral or medial canthal disorders. Bedford modified the Kuhnt–Szymanowski procedure with additional splitting and resection of the upper eyelid. Combined ectropion–entropion patients are difficult to resolve and additional surgeries such as facial skin lifts or resections may be necessary.

the curve of the lower and upper eyelids, respectively, into the lateral canthus (Fig. 5.46c). A skin incision is used to connect the two incisions, creating a trapezoid shape; the skin-orbicularis oculi section is undermined and excised (Fig. 5.46d). The wound is then closed, resulting in a single vertical wound that is apposed with 4-0 simple interrupted sutures and a figure-of-eight suture at the new lid commissures (Fig. 5.46e,f). As dehiscence occurred in nearly 50% of the patients, a double-layer closure (palpebral conjunctiva–tarsus and orbicularis oculi–skin) is recommended, especially in large and giant breeds of dogs. If this procedure is used for the medial canthus, both the upper and lower lacrimal puncta are identified and avoided. Eyelid shortening in the medial canthal procedure is thereby limited to the distance the puncta are from the medical canthus. After this surgery, approximately 30% of the patients required additional surgeries (Hotz–Celsus, Stades, forehead skin resections) to help resolve the combined ectropion– entropion.

Bigelbach’s lateral tarsorrhaphy–canthoplasty

Bedford recently described a series of dogs treated with a modification of the Kuhnt–Szymanowski procedure in which the lower eyelid margo-intermarginalis is translocated to a new position above the lateral canthus to shorten the lower eyelid and help stabilize the lateral canthus. By two skin incisions by scalpel blade, a triangular skin flap is constructed at the lateral canthus (Fig. 5.47a,b). The 3–6 cm lower skin incision continues the curve of the lower eyelid; the lateral incision is 45 to the original lower skin incision and ends at the point determined to be the correct position for the lateral canthus. The skin flap is excised, leaving beneath the orbicularis oculi muscle. The lower and upper

In Bigelbach’s procedure the lower and upper eyelids can be shortened 20–25% in an attempt to stabilize the lateral or medial canthus. A trapezoid-shaped section of skin and orbicularis oculi muscle is excised from the lateral canthus (Fig. 5.46a). By scalpel blade, two 2 mm incisions are made perpendicular to the eyelid margins; the length of these incisions from the lateral or medial canthus will determine the extent of the eyelid shortening (Fig. 5.46b). Two curved skin incisions twice the length of the lid shortening are then made dorsally and ventrally, following

Bedford’s modification of the Kuhnt– Szymanowski technique

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Fig. 5.46 In the lateral tarsorrhaphy–canthoplasty method by Bigelbach, a trapezoid-shaped section of skin and orbicularis muscle is excised from the lateral canthus. (a) Two 2 mm scalpel incisions (A–B and B–C) are made perpendicular to the upper and lower eyelid margins. They mark the extent of the lid shortening. (b) A curved skin incision is extended from the lateral canthus following the curvature of the lower eyelid. (c) Similarly, a skin incision is performed from the lateral canthus following the curvature of the upper eyelid. (d) Additional skin incisions are used to extend the lid margin incisions and outer aspects of the curved skin incisions. These two wedges of skin are then excised. (e) The resultant surgical defect is trapezoid in shape, and the apposing edges are indicated by connecting arrows. (f) Two-layer closure (subcutaneous or tarsoconjunctival and skin) is recommended.

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Fig. 5.47 In Bedford’s modification of the Kuhnt–Szymanowski procedure, the upper eyelid is also shortened and incorporated into the lower lid and canthus surgery (which shorten the lower lid). (a) Following the curvature of the lower eyelid, a skin incision is constructed with its point at the new lateral canthus. (b) This skin flap is carefully dissected by scissors from its underlying cutaneous tissues. (c) The lower eyelid margin is incised into tarsoconjunctiva and skin–orbicularis oculi muscle layers for a distance that approximates the length of the lid shortening. (d) The two layers of the lid are separated by scissors toward the base of the lids to a depth of several millimeters and laterally to become confluent with the skin flap. (e) The upper eyelid margin is incised similarly, and its two layers (skin–orbicularis oculi and tarsoconjunctiva) separated by blunt scissor dissection. (f) From the upper eyelid, a wedge of outer skin–orbicularis is excised by scissors, with its tip at the new lateral canthus. (g) The base of the original skin flap is excised by scissors following the upper lid curvature. (h) In a similar fashion, the lower eyelid tarsoconjunctival wedge is excised. (i) The eventual edges that appose are indicated after the wedges and skin flap have been excised. (j) The deeper tarsoconjunctival layer is apposed to form the inner new lateral canthus with simple interrupted absorbable sutures (knots buried). (k) The remaining lower skin–orbicularis flap is shifted dorsally and laterally (to complete the shortening of the lids and raise the lateral canthus), and secured with simple interrupted non-absorbable sutures.

eyelid margins are split at the ‘gray line’ (opening of the meibomian glands) to a distance that equals the target shortening (Fig. 5.47c–e). The lower tarsoconjunctival and upper lid skin–orbicularis oculi muscle triangular flaps are excised, leaving overlapping lid sections (Fig. 5.47f–h). With both upper and lower eyelids shortened, the fellow tarsoconjunctival tissues are apposed with 6-0 simple interrupted absorbable sutures (Fig. 5.47i,j). The remaining lower skin–orbicularis oculi muscle flap is advanced dorsally and laterally into the triangular lateral canthal defect, and sutured in place with 3-0 to 4-0 simple interrupted non-absorbable sutures (Fig. 5.47k).

In a series of 22 dogs, including St Bernards (8), Bloodhounds (6), Clumber Spaniels (4), English Cocker Spaniels (2), and Neapolitan Mastiffs (2), surgical shortening of the eyelids was attained, but 5 dogs required additional forehead skin resections for optimum effect.

Grussendorf procedure In the procedure recently reported by Grussendorf, both the upper and lower eyelids are shortened, and the lateral canthus is repositioned and fixed by a traction suture at the lateral canthus in giant breeds of dogs. This procedure

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is a further modification of the Wyman lateral canthoplasty described previously. The excessively long upper and lower lids are shortened, up to one-third of their length, by removing the involved lid margins to permit shifting of the lids laterally, and removal as triangles of skin later. A linear skin incision is extended from the lateral canthus to 2 mm caudal of the lateral orbital ligament, and a new lateral canthus is created with a figure-of-eight non-absorbable suture connecting the lateral canthus and lateral orbital ligament. This suture is tightened to establish a normal-appearing lateral canthus. Any surplus upper and lower lid tissues are removed as skin triangles. The lateral canthal and lid wounds are closed by simple interrupted non-absorbable sutures, appearing as an ‘X’ or cross at closure.

OTHER SURGICAL PROCEDURES

Surgical procedures to decrease palpebral fissure size Surgical procedures to change the size of the palpebral fissure may involve the medial canthus, lateral canthus or, in severe cases, a combination of both areas. Surgical procedures at the medial canthus must first identify the problem area(s), and, often by cannulation with a 2-0 blue or green monofilament nylon suture, locate the lacrimal puncta and canaliculi. The lateral canthus is most accessible, but surgical sites in this area are more apt to atrophy with time. The lack of stability and the increased movements of the lateral canthal region may also complicate these surgical procedures by causing greater short-term stress on the suture line and long-term tension of the apposed eyelid tissues. For both the medial and lateral canthoplasty procedures the usual goal is to reduce the palpebral fissure by one-fourth to one-third. The overall size of the palpebral fissure can significantly influence the health of the conjunctiva and the cornea. Palpebral fissures that are larger than normal (euryblepharon) have eyelids (macroblepharon) that are potentially longer than normal. Enlarged palpebral fissures are often associated with an increased frequency of recurrent conjunctival and corneal diseases (Fig. 5.48). Breeds predisposed to macropalpebral fissures include the Bloodhound, St Bernard, English Cocker Spaniel, American Cocker Spaniel, and English Springer Spaniel. Macropalpebral fissures may be those in excess of 35 mm long, but this limit is relative until additional breed-related information is developed. Surgical reduction of normal sized palpebral fissures may be indicated in the brachycephalic breeds with exophthalmia, such as the Pekingese, Shih Tzu, and Lhasa Apso. These breeds often develop recurrent central corneal ulcerations that have the potential to progress and even perforate. The blink reflex may be weak and incomplete, resulting in a thin preocular film on the center of the cornea and an increased risk of epithelial loss. The retention of topical rose Bengal by the central cornea suggests that this region is at risk for ulceration and confirms the lagophthalmia. Surgical reduction in the size of the palpebral fissure may decrease corneal exposure and hopefully the possibility of recurrent corneal ulceration. Some of these dogs sleep with the central cornea exposed.

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Fig. 5.48 Pekingese with a melting corneal ulcer and lagophthalmos. As part of the clinical management of the corneal ulcer and abscess, surgical reduction in the size of the palpebral fissure is recommended.

Surgical techniques to reduce the size of the palpebral fissure include the lateral canthoplasty (modified Fuch’s), the Jensen/Roberts’ medial and lateral ‘pocket’ canthoplasties, and the lateral canthoplasty method by Wyman and modified by Kaswan. Most of the surgical techniques that address ectropion, as well as the combination of entropion and ectropion, also decrease the size of the palpebral fissure.

Medial canthoplasty The medial canthoplasty procedure reduces the size of the palpebral fissure by creating a permanent union of the medial upper and lower eyelids. As the length of the eyelid union increases, the size of the palpebral fissure decreases, but the correction is more limited with this method. Both upper and lower lacrimal puncta should be identified and, if desired, can be cannulated with short lengths of green or blue non-filament nylon suture. The medial canthal eyelid margin is everted, and the eyelid margin incised to a depth of 3–4 mm by the No. 6400 microsurgical blade, starting 1–2 mm medial of the lower lacrimal punctum and terminating 1–2 mm medial of the upper lacrimal punctum (Fig. 5.49a). Apposition of the surgical wound is by twolayer closure. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable sutures. The eyelid skin and muscle layer are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.49b).

Pocket technique (Roberts and Jensen) The pocket technique, described by Roberts and Jensen, is technically more difficult; however, with the multiple layers of tissue apposition, the attachment of the upper and lower eyelids at the medial canthus is stronger. The technique can also be used to treat medial entropion of this area. Because this method uses a flap of palpebral conjunctiva to secure the lower pocket, the function of the upper lacrimal punctum is lost. This method can also remove the caruncle, and prevent the related medial trichiasis and epiphora. The pocket technique may also be used for the lateral canthus.

Surgical procedures to decrease palpebral fissure size

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Fig. 5.49 The medial canthoplasty procedure reduces the size of the palpebral fissure. (a) After identification of both upper and lower lacrimal puncta, the eyelids margins are incised to a depth of 3–4 mm by tenotomy scissors, starting 1–2 mm medial of the lower lacrimal punctum and terminating 1–2 mm medial of the upper lacrimal punctum. (b) The surgical wound is apposed by two layers of sutures for maximal strength. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin–orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

The upper and lower eyelids are split to a depth of about 10 mm at the ‘gray line’, starting 2–3 mm medial to the lower lacrimal punctum and continuing around the medial canthus, stopping 2–3 mm lateral of the upper lacrimal punctum, using the No. 6400 or No. 6700 microsurgical blade (Fig. 5.50a). Small tenotomy scissors may be used for the deeper aspects of the dissection to develop the ‘pocket’. A small strip of the skin portion of the split eyelid margins is carefully excised by tenotomy scissors (Fig. 5.50b). A triangular flap of palpebral conjunctiva is created by tenotomy scissors by cutting at a right angle at the lateral end of the split upper eyelid which sacrifices the upper lacrimal punctum. A 4-0 non-absorbable suture is inserted through the lower eyelid skin into the lower pocket, and then manipulated dorsally to emerge from the pocket (Fig. 5.50c). The suture is placed in the tip of the upper palpebral conjunctival flap, and then directed into the lower pocket to exit the skin. After the conjunctival flap is secured by suture, the upper and lower eyelid margins are apposed by 4-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 5.50d).

Lateral reduction canthoplasty Lateral canthoplasty can reduce the size of the palpebral fissure by permanently apposing the eyelid margins for several millimeters at the lateral canthus. This procedure is also known as the lateral permanent tarsorrhaphy. Although

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Fig. 5.51 Permanent lateral canthotomy. (a) The upper and lower lid and the lateral canthal margins are excised by tenotomy scissors to a depth of 3– 4 mm: the longer the incision, the greater the reduction in the size of the palpebral fissure. (b) Two layers of sutures are used to appose the eyelid margins. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin–orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

technically easy, the tension on these apposed tissues appears greater than that at the medial canthus, and long-term atrophy of the surgical union may occur. The upper and lower eyelid margins are excised carefully by small tenotomy scissors, to a depth of about 3–4 mm (Fig. 5.51a). At this level both the meibomian glands and the pigmentation of the eyelid margins are excised, resulting in a continuous cover of eyelid hair over the surgical union. The length of the eyelid margins excised directly influences the reduction in the palpebral fissure. The upper and lower eyelid surgical wounds are apposed by a two-layer closure. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The eyelid skin and muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.51b).

Lateral canthoplasty (Fuch’s) The lateral canthoplasty, modified from Fuch, provides a stronger permanent union at the lateral canthus by rotating a section of lower eyelid skin and orbicularis oculi muscle into a lateral upper lid defect. The larger surgical surface area provides a stronger union for the permanent lateral canthoplasty. Both lateral upper and lower eyelids are split by the No. 6400 or 6700 microsurgical blade at the ‘gray line’ into outer skin and muscle, and inner tarsoconjunctival layers. The length of eyelid cleavage will determine the reduction in the size of the palpebral fissure (Fig. 5.52a). The medial

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Fig. 5.50 Medial ‘pocket’ canthoplasty procedure. (a) Both eyelids are split at the ‘gray line’ into tarsoconjunctiva and skin–orbicularis oculi muscle layers 2–3 mm medial of the upper and lower lacrimal puncta. (b) Small tenotomy scissors are used to remove the medial canthal eyelid margins and dissect 10–15 mm into the split lid. (c) A triangular flap of upper tarsoconjunctiva is fashioned by scissors and its leading edge apposed deep within the lower lid ‘pocket’ with a 4-0 simple interrupted non-absorbable suture. (d) After the upper conjunctival flap is secured in the lower ‘pocket’, the skin–orbicularis oculi layers are apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

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Fig. 5.52 The lateral canthoplasty, modified from Fuch, rotates triangular sections of upper and lower lid skin and orbicularis oculi muscle. (a) The lateral portions of the upper and lower lids are split by the No. 6700 microsurgical blade. (b) A triangular section of upper eyelid is excised by tenotomy scissors. The lower eyelid is incised by tenotomy scissors, and its margin is excised. (c) The lower lid section is rotated into the upper lid defect. (d) The tarsoconjunctival layers are apposed with a 4-0 to 6-0 simple continuous absorbable suture. The lid skin and orbicularis oculi muscle layers are apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures.

edge of the lower eyelid is incised by small tenotomy scissors to a depth of about 10–15 mm, and the lower lid margin is trimmed from this area (Fig. 5.52b). Triangular sections of the upper eyelid skin and muscle layer and the lower tarsoconjunctiva are excised by tenotomy scissors. The medial aspects of the upper tarsoconjunctiva and lower lid flap are rotated and apposed to the respective defects by two layers of sutures (Fig. 5.52c). The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The external skin and muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.52d).

Lateral canthoplasty (Wyman and Kaswan) The lateral canthoplasty method by Wyman and modified by Kaswan, like the previous method, strengthens the permanent union of the lateral upper and lower eyelids by creating additional surface areas of the apposed tissues. A full-thickness incision of the upper eyelid is performed by tenotomy scissors at approximately one-fourth of the upper lid length (Fig. 5.53a). The upper eyelid margin and the corresponding length lateral lower eyelid margin are excised by scissors. A triangular section of lower lid skin is incised by the Beaver No. 6400 or 6700 microsurgical blade and excised by tenotomy scissors. A similar triangular section of palpebral conjunctiva from the lateral upper lid is excised by tenotomy scissors (Fig. 5.53b). The upper and lower palpebral conjunctival, tarsal, and subcutaneous layers are apposed by a 4-0 to 6-0 simple continuous absorbable suture (Fig. 5.53c). The apposing eyelid margins are attached by a

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single 4-0 to 6-0 interrupted mattress non-absorbable suture. The remaining skin flap is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.53d).

Surgical procedures to increase palpebral fissure size Smaller than normal palpebral fissures have shorter than normal eyelids, and often lower and/or upper lid entropion and lateral canthal entropion. Breeds predisposed to micropalpebral fissures and the often concurrent entropion include the Chow Chow, Kerry Blue Terrier, Collie, Shetland Sheepdog, and the English Bull Terrier (Fig. 5.54). The surgical techniques to increase the size of the palpebral fissure may also address the entropion that often affects both the upper and lower eyelids. Surgical procedures to increase the size of the palpebral fissure include lateral augmentation canthoplasty and the arrowhead procedure combined with lateral canthotomy.

Lateral augmentation canthotomy Lateral augmentation canthoplasty increases the size of the palpebral fissure by a short incision of the lateral canthus and apposition of the incised eyelid surface. The procedure is quite similar to the lateral canthotomy. The lateral canthus is incised by tenotomy scissors for 5–10 mm (Fig. 5.55a). The length varies with the extent of the palpebral fissure enlargement. The palpebral conjunctiva is undermined in

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Fig. 5.53 Lateral canthoplasty by Wyman and modified by Kaswan. (a) Tenotomy scissors are used to incise the upper eyelid to full thickness (usually at the junction of the middle and lateral one-thirds of the eyelid), and excise the upper and lower eyelid and lateral canthal margins. (b) Corresponding but opposite triangular sections of lower eyelid and upper palpebral conjunctiva are excised by scissors. (c) The palpebral conjunctival wounds are apposed with a 4-0 to 6-0 simple continuous absorbable suture. (d) The skin–muscle layers are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

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Surgical repair of eyelid lacerations

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Fig. 5.54 Micropalpebral fissure in a Chow Chow. (a) Often micropalpebral fissure is combined with entropion of the lateral portions of the upper and lower eyelids and the lateral canthus. (b) Correction of micropalpebral fissure and entropion in the Chow Chow with the arrowhead procedure and lateral canthotomy at 5 days postoperatively.

Nasal fold trichiasis and resection in dogs

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Fig. 5.55 The lateral canthotomy may be modified to increase the size of the palpebral fissure. (a) The lateral canthus is incised by scissors for 5– 10 mm. (b) The palpebral conjunctiva is undermined to the level of the fornix by tenotomy scissors, and apposed to the canthotomy wound by 4-0 to 60 simple interrupted non-absorbable sutures.

the area to the level of the fornix by blunt scissor dissection to line the edges of the new canthus. The palpebral conjunctiva is apposed to the new lateral canthus by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.55b).

Arrowhead procedure for entropion with lateral canthotomy The arrowhead procedure is detailed in a previous section under surgical correction of entropion. The lateral canthus can be incised as part of this procedure to increase the size of the palpebral fissure (Fig. 5.56). The edges of the lateral canthal wound are apposed to the adjacent palpebral conjunctiva.

Several brachycephalic breeds of dogs have large nasal folds whose hair may contact the medial nictitating membrane, conjunctiva, and cornea. The resultant low-grade chronic irritation results in epiphora and conjunctival hyperemia, inflammation, and pigmentation. The corneal sequelae include vascularization, pigmentation, and even ulceration. Medical treatment consists of the application of heavy petrolatum ointment and hair wax to paste the nasal fold hairs away from the eye. Surgical removal of the upper one-half or the entire nasal fold is the permanent method to prevent trichiasis. If medial entropion, exophthalmia, and lagophthalmia are present, reduction in the size of the palpebral fissure with one of the medial canthoplasty procedures should be considered. The base of the nasal fold is carefully inspected and then incised by Mayo scissors (Fig. 5.57a). Hemostasis is obtained by direct pressure with gauze sponges and, if necessary, by vessel ligation. The skin edges are apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures (Fig. 5.57b). Special care is necessary to excise equal portions of both nasal folds to ensure symmetry (Fig. 5.58). Nasal skinfolds should not be removed in show dogs.

Surgical treatment of chalazion A chalazion is a chronic granulomatous inflammation of the tarsal or meibomian glands, and is presented as a swelling immediately beneath the palpebral conjunctiva. The recommended treatment for a chalazion is surgical drainage. After a short-acting injectable general anesthetic, the affected eyelid is grasped with a chalazion clamp (Fig. 5.59). After a short linear incision, the chronic tarsal adenitis and sebaceous secretions are curetted from the area. The wound is left to heal by secondary intention.

Surgical repair of eyelid lacerations

Fig. 5.56 The lateral canthotomy may be added to the arrowhead procedure for entropion to increase the size of the palpebral fissure.

Eyelid lacerations are not infrequent in all animal species, and often require surgical repair. Eyelid lacerations may be divided into partial and full thickness, and marginal and non-marginal. The eyelids are highly vascular and tissue debridement immediately prior to repair should be

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Fig. 5.57 Treatment of nasal fold trichiasis. (a) The nasal folds are carefully excised by curved Mayo scissors. (b) The wound edges are apposed with 4-0 to 5-0 simple interrupted non-absorbable sutures.

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Fig. 5.58 Postoperative appearance of a patient with the nasal folds removed. The left eye has exotropia, healed corneal ulcer, and optic nerve atrophy from a previous traumatic proptosis.

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Injuries at a 90 angle to the eyelid margin have a greater potential to affect eyelid function and cosmesis than injuries parallel to the lid margin (Fig. 5.60). The eyelid margin should be apposed as accurately as possible. Scar tissue at the eyelid margin can cause chronic irritation of the conjunctiva and cornea. Sutures at the eyelid margin should have their knots external to the ‘gray line’ to avoid contact with the cornea. Inflamed and swollen eyelids may develop temporary entropion. Two layers of sutures are recommended: an inner layer of simple continuous absorbable suture for the deeper palpebral conjunctiva and tarsus, and simple interrupted non-absorbable sutures for the external orbicularis oculi muscle and skin layer. A figure-of-eight suture pattern is recommended for lid margin injuries, and may be continued to the upper lid to provide tension on the injury site (Fig. 5.61). After any lid laceration of the medial canthus, the lacrimal puncta and canaliculi should be identified and flushed. In the event of transection, the opposing ends should be isolated and cannulated with 2-0 to 3-0 monofilament nylon. The nylon suture catheter should be left in position for 4–6 weeks or until the healing of the area is complete. After the repair of extensive eyelid injuries, a complete temporary tarsorrhaphy may be indicated to protect the cornea because of the impaired eyelid functions and blink reflex.

Eyelid trauma in the horse

Fig. 5.59 With the eyelid grasped by the chalazion clamp, the palpebral conjunctiva is incised and the contents of the chalazion are removed by curettage.

minimal. There are several guidelines for the surgical correction of eyelid injuries. All lacerations should be apposed by sutures. Lid healing by secondary intention may result in considerable fibrosis and distortion of the eyelids and lid margin that may eventually require surgical correction.

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The horse seems prone to eyelid lacerations from trapping the eyelid margin on metal rings, bucket handles, door latches, waterers, feed racks, lead shank clips, etc. Horses are particularly prone to eyelid lacerations because of the prominence of their eye and their tendency toward very sudden head movements when startled. When eyelid trauma is present or suspected, a thorough ophthalmic examination should be performed to rule out injury to other ocular structures. When hematomas or eyelid edema occur, initial treatment is with the use of ice packs, dimethyl sulfoxide applied to the eyelids, and administration of flunixin meglumine (1 mg/kg IV q24h). If eyelid closure is impaired or if facial nerve damage is present, a temporary tarsorrhaphy or nictitating membrane flap may be used to aid in the protection of the globe. If eyelid abrasions occur, topical antibiotic ointments are used.

Surgical repair of eyelid lacerations

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Fig. 5.60 Example of full-thickness eyelid lacerations in the dog. (a) Preoperative appearance of a recurrent lateral lower lid laceration. No tissue should be trimmed, and the lacerated lid carefully reapposed starting with the lid margin. (b) Appearance of a medial upper lid laceration that was improperly managed, and the lacerated lid excised. The remaining scarred lid is causing direct damage to the underlying cornea. Note the superficial corneal vascularization in the exposed cornea.

Fig. 5.61 The figure-of-eight suture pattern can be used to assist in closure of the tarsoconjunctival layer in vertical lid lacerations. The exact apposition of the eyelid margin helps reduce the likelihood of a postoperative notch.

Lacerations should be managed promptly to avoid distortion from severe swelling, inflammation, infection, scarring, and loss of function (Fig. 5.62). Lacerated tissue should not be excised. Even with the best plastic techniques, it is impossible to reconstruct the mucocutaneous junction of the eyelid margin. If eyelid margin is sacrificed, the occurrence

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of eyelid scar formation and secondary corneal damage is likely. Eyelid lacerations in the horse should be flushed with saline and cleaned to remove all foreign material. Lacerations less than 12 h old are cleaned and repaired as soon as practical. Older lacerations or longstanding infected wounds may be packed with an antibiotic dressing for 24–48 h and then closed. Intravenous flunixin meglumine is administered preoperatively. Eyelid lacerations may be repaired under general anesthesia, or standing with sedation and motor and sensory nerve blocks for the affected area of the eyelid. The wound is prepared with dilute povidone–iodine solution. Debridement should be limited; the wound edges may be scraped with a surgical blade or rubbed with a surgical sponge soaked in dilute povidone–iodine solution. Surgical scrub is not usually used on the wound. However, shampoos that are compatible with mucous membranes (baby shampoo) may be used to cleanse the surgical area. Any necrotic tissue should be excised, but wound debridement is minimal. Every attempt should be made to preserve the entire eyelid margin. Closure is performed in two layers; the tarsoconjunctival layer is closed with 5-0 to 7-0 polyglactin 910 in

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Fig. 5.62 (a) Preoperative appearance of a full-thickness upper eyelid laceration in a young horse. (b) Immediate postoperative appearance after a two-layer repair.

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a simple interrupted or continuous pattern. Suture knots are buried to prevent corneal irritation. The skin is closed beginning at the eyelid margin to prevent scar formation and irritation of the cornea. Usually 4-0 to 6-0 non-absorbable suture material is used in the skin. A figureof-eight suture is used to align the eyelid margin. The remainder of the skin wound is closed in a simple interrupted pattern or an alternating simple interrupted and vertical mattress suture pattern. Usually I leave the ends long on the first figure-of-eight suture and tie the ends into the knot of the interrupted suture adjacent to the eyelid margin suture. If there is significant eyelid swelling or lid closure is impaired, a complete temporary tarsorrhaphy may be indicated. Postoperative care of eyelid lacerations should include standard wound hygiene, application of fly repellent (if necessary), and the prevention of self-trauma. Topical and systemic antibiotics are indicated for 5–7 days. Tetanus prophylaxis should be verified by history or administered at the time of surgical repair. Placement of a subpalpebral lavage system will facilitate topical application of solutions to the eye. Postoperative swelling can be reduced by the administration of systemic non-steroidal anti-inflammatory agents (flunixin meglumine 1 mg/kg IV) immediately before surgery. Postoperative edema will be lessened by the application of ice packs for the first 24 h after surgery. If swelling is present 24 h after surgery, warm compresses may further reduce the swelling and discomfort at the surgical site. Dimethyl sulfoxide has been applied to the periorbital skin to reduce postsurgical swelling and discomfort. Rubbing or self-mutilation is often a concern in the horse, and the surgical site or eye must be protected by a protective hood with a plastic or solid eyecup (EyeSaver™, Jorgensen Laboratories, Loveland, CO.). Skin sutures are usually removed 8–12 days after surgery. In situations when tension on the suture line cannot be avoided, sutures are left in place for 18–24 days. Improper closure of eyelid lacerations may lead to abnormal function and complications, including chronic ulcerative keratitis, cicatricial entropion or ectropion, conjunctivitis, corneal fibrosis, and pigmentary keratitis.

Surgical procedures for minor eyelid neoplasms in small animals Variable size defects of the eyelids result from eyelid agenesis, the excision of congenital, inflammatory, and neoplastic masses, and eyelid loss after injuries. If these defects are less than one-third to one-fourth of the total eyelid length, apposition of the defect may be achieved by sutures. If the lid defect approximates up to one-third of the lid length, a ‘relief’ lateral canthotomy may decrease excessive lid tension. Some canine breeds, like the American and English Cocker Spaniels, have considerable eyelid length and sizeable defects can be accommodated by simple apposition. However, in other breeds, like the Doberman and Collie, surplus eyelid tissue is very limited, and similar size defects may require grafts. In cats, in contrast to dogs, most lid neoplasms are malignant and wider excision is necessary. In cats, the sliding or grafting of adjacent lid and facial tissue is often necessary as ‘surplus’ lid tissue is very limited. Although about 20–30% of canine eyelid neoplasms are malignant histologically, the majority are clinically benign.

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Fig. 5.63 Tarsal adenocarcinoma of the upper eyelid in a 10-year-old dog.

Certain neoplasms, however, such as the melanomas, should be resected and widely excised. The average age of dogs affected with eyelid neoplasia is about 8 years, and the Beagle, Siberian Husky, and English Setter appear to have a higher risk. The tarsal gland or meibomian adenoma and adenocarcinomas are the most frequent group of tumors (about 50%), and are best visualized by everting the lid and inspecting its palpebral surface (Fig. 5.63). Approximately 10% of canine malignant lid tumors are locally invasive and include melanoma, basal cell carcinoma, mast cell sarcoma, squamous cell carcinoma, and hemangiosarcoma. When the recurrence rates of all types of canine eyelid neoplasms were compared after surgical excision or cryotherapy, the mean recurrence rate after surgery was nearly 30 months. After cryotherapy, the mean recurrence rate was about 8 months. In contrast to the dog, eyelid malignancy in cats is high. Squamous cell carcinomas constitute about 60% of eyelid neoplasms, and the average age of affected cats is about 10 years (Fig. 5.64). Other malignant feline lid tumors include fibrosarcoma, adenocarcinoma, basal cell carcinoma, melanoma, and hemangiosarcoma. Feline eyelid neoplasms generally require rather wide excision. For feline squamous cell carcinomas of the eyelids, surgery is often combined with radiation and cryotherapy. The surgical techniques used to

Fig. 5.64 Squamous cell carcinoma of the lower eyelid and palpebral conjunctiva in an aged cat.

Surgical procedures for minor eyelid neoplasms in small animals

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Fig. 5.65 Full-thickness ‘V’ or wedge eyelid excision. (a) A wedge of affected eyelid is excised by tenotomy scissors. (b) The wound is closed by two layers of sutures. The tarsoconjunctival layer is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin–orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures.

excise masses of the eyelids without grafts of adjacent tissues include the partial-thickness excision, the simple ‘V’ technique (full-thickness excision), and the four-sided method. In horses and cattle, the same eyelid surgical techniques can be readily adapted. Like cats, the majority of lid tumors are malignant, and surgery is combined with other modalities, such as local chemotherapy, to produce acceptable ‘cure’ rates in horses and cattle.

healing there is an obvious notch in the eyelid margin where the postoperative tension is greatest. The affected area of the lid may be grasped by a chalazion or entropion clamp. The sides of the eyelid neoplasm are excised by tenotomy scissors or a Beaver No. 6400 or 6700 microsurgical blade (Fig. 5.65a). Hemostasis is usually by direct pressure or point electrocautery. The wound is usually apposed by two layers of sutures. A 4-0 to 6-0 simple continuous absorbable suture is used to appose the tarsoconjunctival layer. The skin and orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.65b). The suture at the external aspect of the eyelid margin is the most critical for lid alignment and to reduce the likelihood of a notch developing postoperatively. In large dogs, an interrupted mattress or figure-of-eight suture is recommended. A relief lateral canthotomy may be necessary if the wedge of lid resection approximates one-third of the lid length. With upper lid surgical defects, a modified lateral canthoplasty may be performed (Fig. 5.66a). The removal of a triangle of skin from the lateral canthus permits the shift of this area to form a new lateral eyelid margin. The two sides of the skin triangle are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.66b).

Partial lid thickness excision of eyelid masses Eyelid neoplasms may affect only the skin and subcutaneous layers, or the tarsal layer as with meibomian gland masses. Many of these masses can be excised conservatively without creating a full-thickness lid defect. Masses on the eyelid skin can be excised by scalpel using a circular or oval-shaped incision. Closure should be vertical or at 90 to the eyelid margin for lower lid defects and parallel to the upper lid margin to reduce the scar tissue effect on lid movement. Other skin flaps, such as the ‘Z’ plasty transpositional, pedicle, advancement, and rhombic types, can be used for partial-thickness lid defects after neoplasm removal. The eyelid may be grasped and everted by a chalazion clamp to expose tarsal or meibomian gland tumors. The tumor is excised by tenotomy scissors, and the palpebral conjunctival defect is left to heal by secondary intention.

‘V’ full-thickness excision The V-shaped full-thickness excision of eyelid neoplasms is frequently used for most types of canine eyelid neoplasms. The ‘V’ method is simple, but not infrequently after

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Four-sided full-thickness excision The four-sided full-thickness excision technique provides improved results compared to the ‘V’ type method. This procedure creates a larger surface area of the eyelid to distribute the tension associated with the apposition of the wound. The eyelid neoplasm is excised by tenotomy scissors to create a four-sided defect (Fig. 5.67a). The wound is apposed by two layers of sutures. The tarsoconjunctiva is apposed by a 4-0 to 6-0 simple continuous absorbable suture, and the skin–muscle layer by 4-0 to 6-0 simple interrupted nonabsorbable sutures (Fig. 5.67b).

Postoperative management and complications The usual postoperative treatment after the excision of small lid masses is topical antibiotics, often combined with topical corticosteroids. The E-collar is useful to prevent the patient from rubbing and possibly interrupting the surgical wound. The most frequent result after these procedures is the development of an obvious V-shaped notch at the eyelid margin. This can usually be avoided by use of the four-sided procedure.

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Fig. 5.66 A relief lateral canthotomy may be indicated when the ‘V’ shaped and four-sided full-thickness lid excision techniques are used. (a) The wedge removed approximates one-third or more of the eyelid length. After a lateral canthotomy is performed by scissors, a triangular skin flap is incised at the lower aspects of the lateral canthus with the Bard–Parker No. 15 scalpel blade. The skin flap is elevated from the subcutaneous tissues and excised by tenotomy scissors. (b) The skin flap edges are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. The new upper lid margin should be covered by palpebral conjunctiva, attached by a few 6-0 simple interrupted absorbable sutures.

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C Fig. 5.67 The four-sided full-thickness eyelid excision technique. (a) The lid mass is removed by tenotomy scissors, creating a four-sided surgical defect. (b) Wound closure is by two layers of sutures. The inner tarsoconjunctiva is apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin– orbicularis oculi muscle layer is apposed by 4-0 to 6-0 simple interrupted nonabsorbable sutures. The eyelid margin suture is carefully positioned on its outer aspects to avoid corneal contact and provide exact apposition of the eyelid margin. (c) Preoperative appearance of a large lid melanoma with its base at the lid margin. The mass was excised using the four-sided fullthickness technique. (d) Postoperative appearance several weeks later.

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Reconstructive blepharoplasty after removal of eyelid masses in small animals There are many different reconstructive blepharoplastic procedures available for small animals to repair defects that are one-third or more the length of the eyelid (Fig. 5.68). Some of these techniques include the sliding skin flap, sliding ‘Z’ skin flap, semicircular skin graft, pedicle skin graft, tarsoconjunctival graft, palpebral conjunctival graft (sliding and free), buccal mucosa grafts, rhomboid grafts, and the ‘bucket handle’ (Cutler–Beard) procedure. These blepharoplastic procedures can be modified for each patient, and are limited in application only by the skill and imagination of the veterinarian. Additional surgical procedures are available in the standard human oculoplastic surgery texts. The presence of the tarsal hyaline plate in humans presents additional opportunities as well as potential complications. The upper eyelid has the unique characteristics for the primary protection of the cornea, the major contributor for the blink reflex, the larger donor source of autogenous full-thickness lid and tarsoconjunctival tissues, the primary effect on the appearance of the eye, and in the dog the only place for cilia. The lower lid is smaller. Its primary function is to capture and hold the tears, and facilitate the medial movements of tears to the lower lacrimal punctum. A reasonable lower conjunctival fornix is essential to hold the tears.

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Eyelid and tarsoconjunctival grafts should be handled with care. Their bases should be wide to assist perfusion of the distal portion of the graft and prevent ischemia. After tissue grafts, 0.5–1.0 mm contraction usually occurs in small animals, and must be accommodated for in the blepharoplastic procedure. Movement of eyelid and tarsoconjunctival grafts should be limited to maximize successful transposition. Partial-to-complete temporary tarsorrhaphies are usually performed after reconstructive blepharoplasty in small animals. The closed eyelids reduce graft movement, prevent lid trauma to the graft edges, and can apply direct pressure to the deeper tarsoconjunctival and buccal mucosa grafts to reduce postoperative swelling. E-collars are essential after blepharoplasty to prevent the small animal patient from traumatizing the surgical site and prematurely removing the sutures.

Sliding skin flap The sliding skin flap or graft represents the most basic reconstructive blepharoplastic technique. It is used when surgical and traumatic eyelid defects are greater than one-third of the lid length. Sliding skin grafts should always be lined with mucosa harvested from adjacent conjunctiva or more remote sites. Sliding skin flaps are appropriate for both upper and lower lid defects. After full-thickness excision of the lid neoplasm by scissors or No. 6700 microsurgical blade, two slightly diverging

Reconstructive blepharoplasty after removal of eyelid masses in small animals

Fig. 5.68 Extensive meibomian adenocarcinoma of the upper eyelid of a dog. Close inspection of the palpebral aspect of this eyelid mass will determine whether conservative excision or reconstructive blepharoplasty is necessary.

skin incisions are performed approximately twice as long as the height of the defect (Fig. 5.69a,b). Two equal-sized triangles of skin (Burow’s triangles) are excised to accommodate shifting the graft into the defect (Fig. 5.69c,d).

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After liberal dissection to adequately separate the skin flap from its subcutaneous attachments, the skin flap is moved into the defect, thereby collapsing the Burow’s triangles (Fig. 5.69e). Before apposition of the skin flap, adjacent palpebral and fornix conjunctivae are mobilized to cover the deeper aspect of the skin flap. Other sources for mucosa to line the skin flap include the tarsopalpebral conjunctiva from the upper lid and a free or island graft of buccal mucosa. This dissection must provide adequate mucosa without any tension to avoid excessive fibrosis and inversion of the leading edge of the skin flap. After placement of the leading edge of the skin flap about 0.5–1.0 mm above the adjacent eyelid margin to compensate for postoperative shrinkage of the graft, the sides of the skin flap are apposed with 4-0 to 6-0 simple interrupted non-absorbable sutures (Fig. 5.69f,g). The conjunctiva is attached to the posterior aspects of the skin flap by 4-0 to 6-0 simple interrupted absorbable sutures with the knots buried or exposed on the eyelid flap skin. If some tension can be demonstrated on the skin flap, a complete temporary tarsorrhaphy is performed and left in place for 4–6 weeks to provide countertension.

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G Fig. 5.69 Sliding skin graft. (a) After full-thickness excision of the eyelid neoplasm, two slightly diverging skin incisions are continued from the base of the wound. These skin incisions should be twice as long as the defect’s height. (b) Intraoperative appearance, and removal of a full-thickness melanoma from the lower eyelid in a dog. (c) Two equal size triangles (Burow’s triangles) of skin are excised to facilitate shifting the graft into the surgical wound. (d) Intraoperative appearance, showing construction of the sliding skin graft. (e) After extensive subcutaneous dissection under the skin graft, the flap is moved into the wound. The leading edge of the skin graft should be 0.5–1.0 mm above the adjacent eyelid margin. (f) The skin graft is secured by 4-0 to 6-0 simple interrupted non-absorbable sutures. The posterior aspects of the skin graft must be lined with mucosa, from adjacent palpebral conjunctiva, buccal mucosa, or an island graft from bulbar conjunctiva of the opposite eye. (g) Immediate postoperative appearance, after completion of the lower sliding skin graft.

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‘Z’ plasty skin flap

Semicircular skin grafts

The ‘Z’ plasty is a modification of the sliding skin flap and is recommended for lateral defects of the upper eyelid. The neoplasm is removed by ‘en bloc’ excision by tenotomy scissors (Fig. 5.70a). After blunt–sharp dissection of the entire subcutaneous lateral canthus by scissors, two equilateral triangles of skin are excised by the Beaver No. 6700 microsurgical blade (Fig. 5.70b). The length of these skin triangles should be about 1 mm larger than the sides of the surgical defect. The skin flap is slid ventrally to fill the upper lid defect and collapse the lower skin triangle defect. The skin flap is apposed to the adjacent skin with 4-0 to 6-0 simple interrupted nonabsorbable sutures (Fig. 5.70c). The posterior aspect of the skin flap is lined by conjunctival mucosa, usually harvested from adjacent areas. The mucosa is apposed with a 4-0 to 6-0 simple continuous absorbable suture (Fig. 5.70d).

Semicircular skin grafts are used in dogs for restoration of surgical defects involving 30–60% of the center of the upper and lower eyelids. Semicircular grafts utilize both rotational and sliding components. Following full-thickness excision of eyelid neoplasms (Fig. 5.71a), the semicircular skin graft is constructed by a curved skin incision starting at the lateral canthus and of a length that approximates the width of the surgical defect (Fig. 5.71b). Excision of a Burow’s triangle of skin at the end of the semicircular graft allows medial movement without focal terminal distortion. In the areas in which the semicircular flap is not covered with conjunctiva, adjacent conjunctiva may be slid from the lateral canthal region and attached with absorbable sutures with the knots buried (Fig. 5.71c,d). In areas in which a new eyelid margin occurs, the potential for trichiasis arises.

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Fig. 5.70 The ‘Z’ plasty procedure is a modified sliding skin graft for the lateral canthal region. (a) The mass is removed full-thickness by tenotomy scissors from the lateral portion of the upper eyelid. (b) After blunt dissection of the subcutaneous tissues in the lateral canthus, two equal size triangles of skin are excised by the Beaver No. 6700 microsurgical blade. (c) The skin flaps are slid into position and secured by 4-0 to 6-0 simple interrupted non-absorbable sutures. The posterior aspect of the upper skin flap must be lined with mucosa from adjacent palpebral conjunctiva, buccal mucosa, or a free island bulbar conjunctival mucosa graft. (d) Three week postoperative appearance of a dog with a ‘Z’ plasty procedure after excision of a large neoplasm of the lateral aspects of the upper eyelid.

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D Fig. 5.71 Semicircular skin grafts may also be used to repair large eyelid defects. (a) The eyelid mass is excised full-thickness using the four-sided method, and a skin incision is extended to the lateral canthus (length approximates the width of the surgical defect). (b) A triangle (Burow’s) of skin is excised from the end of the skin incision, and the semicircular skin flap is dissected carefully from its underlying subcutaneous attachments. (c) The semicircular skin flap is slid medially, and the eyelid defect apposed by sutures, usually in two layers: tarsoconjunctiva (simple continuous absorbable) and muscle–skin (simple interrupted). The remainder of the graft is secured with simple interrupted non-absorbable sutures. The portion of the semicircular graft that forms the new lateral upper lid must be lined with palpebral conjunctiva. (d) Immediate postoperative appearance after an upper semicircular skin graft in a dog.

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Sliding skin flaps combined with tarsoconjunctival grafts For full-thickness eyelid defects that involve more than one-half of the length of the eyelid, a sliding flap adjacent to the surgical defect may be combined with a tarsoconjunctival graft from the opposite eyelid. The combined procedure may be used for either upper or lower lid defects. After removal of the lower lid eyelid mass, an upper tarsoconjunctival graft is constructed. About 2 mm beyond the eyelid margin, a broad pedicle graft of tarsoconjunctiva about 1 mm wider than the surgical defect is prepared by tenotomy scissors (Fig. 5.72a). After adequate preparation, the tarsoconjunctival graft is secured to the tarsoconjunctival layer of the surgical defect by 4-0 to 6-0 simple interrupted absorbable sutures (Fig. 5.72b). The sliding skin flap is then prepared as described in the earlier

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section (Fig. 5.72c). To secure and stabilize both grafts, a complete temporary tarsorrhaphy is performed and maintained for 4–6 weeks. If topical medications are necessary, a subpalpebral medication system is implanted in the upper conjunctival fornix.

Full-thickness lid flaps (‘bucket handle’ or Cutler–Beard method) For eyelid defects greater than one-half the length of the eyelid the full-thickness eyelid graft may be used. Although the upper lid has considerably more mass than the lower lid, full-thickness grafts may be provided by either eyelid. After the lower eyelid neoplasm has been excised, a full-thickness upper lid graft is prepared about 4–5 mm above the lid margin (Fig. 5.73a). The tip of the lid graft should be 0.5–1 mm

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Fig. 5.72 Sliding skin flaps involving one eyelid may be combined with tarsoconjunctival grafts from the opposite eyelid. (a) The lower eyelid neoplasm is excised full-thickness. The upper tarsoconjunctival graft is constructed to be slightly larger than the lower lid defect. About 2 mm from the eyelid margin, the palpebral conjunctiva and tarsus pedicle graft is prepared by tenotomy scissors. (b) The tarsoconjunctival graft is secured in the lower lid defect by 4-0 to 6-0 simple interrupted absorbable sutures. (c) The lower lid sliding skin graft is prepared as described in Figure 5.69. A temporary complete tarsorrhaphy is performed to immobilize the graft sites. The skin sutures are removed in 7–10 days. The tarsorrhaphy sutures are removed in 4–6 weeks and the base of the tarsoconjunctival graft is transected by tenotomy scissors. The upper tarsoconjunctival defect is allowed to heal by secondary intention.

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D Fig. 5.73 For full-thickness eyelid (‘bucket handle’ or Cutler–Beard technique) grafts, either the lower or upper eyelid may be used as the donor. (a) The full-thickness lid graft is constructed about 4–5 mm from the eyelid margin and should be 0.5–1 mm larger that the surgical wound. (b) The upper lid graft is positioned under (deep to) the strip of remaining upper lid margin and secured in the lower lid defect by two layers of sutures. The tarsoconjunctival layers are apposed by a 4-0 to 6-0 simple continuous absorbable suture. The skin–orbicularis oculi layer is apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. (c) A complete temporary tarsorrhaphy is performed to stabilize the graft site. After 3–4 weeks all the skin and tarsorrhaphy sutures are removed, and the base of the full-thickness lid graft transected. The upper lid edges are reapposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. (d) Two week postoperative appearance of a dog with a lower full-thickness eyelid graft to the upper eyelid. Note the remaining strip of upper eyelid and margin. The base of the graft will be transected in 2 weeks and reapposed to the remaining upper eyelid strip.

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larger than the surgical wound. The lid graft is manipulated under the upper lid leading margin and apposed to the lower lid defect by two layers of sutures (Fig. 5.73b). The tarsoconjunctival layers are apposed by 4-0 to 6-0 simple interrupted absorbable sutures. The external skin and muscle layers are apposed by 4-0 to 6-0 simple interrupted non-absorbable sutures. A complete temporary tarsorrhaphy, apposing the remaining upper lid edge and lower lid, is performed to restrict eyelid movements and assist graft establishment (Fig. 5.73c). If topical medication is necessary for the eye, a subpalpebral system is implanted in the dorsolateral conjunctival fornix. After 3–4 weeks to permit establishment of the eyelid graft, all of the skin and tarsorrhaphy sutures are removed (Fig. 5.73d). The eyelid graft is transected 0.5 mm above the adjacent lower eyelid margin to compensate for shrinkage. The remaining upper lid is reattached to the upper lid margin by 4-0 to 6-0 simple interrupted non-absorbable sutures.

Large pedicle skin grafts Large pedicle skin grafts may be used in small animals in the surgical management of very large eyelid defects which result from the excision of locally malignant skin neoplasms. Because of the greater frequency of locally aggressive malignant tumors, the cat is more often treated by these large grafts than the dog. These skin grafts, harvested from nearby sites, must be carefully constructed to ensure a viable skin blood supply, especially at the tip or end of the graft (Fig. 5.74a,b). As the tip is often the eyelid, lower or upper, it must be lined with either nearby conjunctiva or buccal mucosa. As the grafts do not usually contain functional muscle, the blink reflex is usually absent and depends on the now mobile nictitating membrane for corneal protection in the cat. These skin grafts are often two-step procedures.

Postoperative management and complications After all of these rather extensive reconstructive blepharoplastic procedures, topical and systemic antibiotics are administered. If other corneal and conjunctival diseases are present,

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additional medications are administered directly to the eye or by subpalpebral systems (see Chapter 2). An E-collar is used as long as any sutures are present or until the tarsorrhaphy sutures have been removed. Warm and cold compresses may be used to reduce eyelid swelling and promote circulation to the grafts. The primary objective of these procedures is to obtain adequate eyelid function and appearance, and prevent recurrence of the lid neoplasm. Restoration to complete normalcy is not usually obtained. The usual postoperative appearance is an irregular but acceptable eyelid margin. Fibrosis and slight inversion of the new eyelid margin may develop and require minor resection of the outer skin to evert the area and prevent trichiasis. If tension of the skin flap is excessive, some ectropion of the lower lid may develop. Treatment is not usually necessary as long as epiphora and chronic conjunctivitis do not develop.

Surgeries for eyelid neoplasia in the horse Several different eyelid tumors have been reported in the horse. These include squamous cell carcinomas, equine sarcoids, papillomas, melanomas, fibromas, schwannomas, basal cell carcinomas, hemangiosarcoma, lymphosarcomas, mastocytomas, and adenocarcinomas. Approximately 10% of all equine neoplasms are related to the eye. Squamous cell carcinoma is by far the most common ocular tumor in the horse, followed by sarcoids and papillomas. The other reported tumor types are considered rare in occurrence. Biopsy and histopathology or fine needle aspiration for cytologic interpretation is recommended to differentiate the tumor types and to distinguish them from inflammatory lesions before multiple therapies. Papillomas usually occur in young horses; they are commonly self-limiting, and do not require surgical excision. Squamous cell carcinomas affect the eyelids, nictitating membrane, and globe (Fig. 5.75). Lesions may be bilateral but are usually not symmetrical. Draft breeds (especially Belgians), Appaloosas, and horses with decreased eyelid pigmentation appear to be predisposed. The average age of horses presented with squamous cell carcinoma (SCC) is 8–11 years. Males are twice as likely as females to be affected,

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Fig. 5.74 Postoperative appearance after large skin grafts in the cat for large malignant eyelid tumors involving the entire lower or upper eyelid, or canthi. (a) Upper pedicle skin graft 2 weeks after surgery and removal of a large squamous cell carcinoma. (b) Upper and lower pedicle grafts 1 week after surgery and removal of a large squamous cell carcinoma of the lateral canthus, and lateral upper and lower eyelids.

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Blepharoplastic procedures for the horse

Fig. 5.75 Squamous cell carcinoma of the entire lower eyelid in a horse.

and geldings are five times more likely to have SCC than stallions. Coat color, such as white, cremello/palomino, gray, strawberry/white, buckskin and chestnut/sorrel, also predisposes to SCC. Although the tumor is aggressive locally, its metastatic rate is low (6–15%), with the regional submandibular lymph nodes, salivary glands, thorax and orbit, sinus, and calvaria affected. Sarcoid is the second most common tumor of the eyelid and the most common tumor observed in horses. Sarcoids are divided into several clinical groups; they include occult, verrucose, nodular, fibroblastic, and mixed types. Molecular biology techniques have confirmed the presence of bovine papilloma virus DNA in a high number of equine sarcoids. Predisposition is seen in the American Quarter Horse, Arabian, and Appaloosa breeds. Periocular sarcoids are often proliferative, may have nodules, may have a broad base or be pedunculated, may infiltrate into deeper tissues, and may be ulcerative. Sarcoids affect both upper and lower lids (Fig. 5.76). Some sarcoids may undergo spontaneous regression.

Blepharoplastic procedures for the horse Several surgical and blepharoplastic procedures are available for horses affected with either SCC or sarcoid. Choice of the specific surgical procedure as presented below often depends on the size and location of the mass, vision status, intended use of the animal, available equipment, prior experience of the veterinarian, value of the animal, and owner financial constraints. Retrospective studies strongly

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Fig. 5.76 Sarcoid affecting the lateral lower eyelid and lateral canthus.

suggest that surgical excision or debulking, combined with some form of adjunctive therapy, provides better long-term recurrence-free status than surgery alone.

Four-sided excision Masses that can be excised by removing one-third of the eyelid or less can be removed by ‘four-sided’ excision of tissue and direct closure of the wound (Fig. 5.77). The margins of the mass are excised perpendicular to the eyelid margin and connected with two angled incisions. The tarsoconjunctiva is closed with a 6-0 simple continuous absorbable suture, beginning at the distal incision, and the skin–muscle layer apposed with simple interrupted nonabsorbable sutures.

Reconstructive blepharoplasty Blepharoplasty techniques are indicated when more than one-third of the eyelid margin has been removed. These procedures are best performed with the horse under general anesthesia. When considering extensive blepharoplastic techniques in the horse, it should be noted that although the eyelid skin is very mobile, the surrounding facial skin is relatively immobile and may not slide to provide good donor tissue for eyelid defects. The skin is apposed with 5-0 nylon beginning at the eyelid margin. The eyelid margin is closed in a figure-eight suture using 5-0 nylon or silk. The remainder of the incision is closed with non-absorbable sutures in a simple interrupted pattern.

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Fig. 5.77 Four-sided or wedge excision of a very small squamous cell carcinoma of the central lower eyelid in a horse. (a) Preoperative appearance prior to wedge excision and after marking the incision line. (b) The tumor is excised by scalpel and scissors. (c) Appearance of the surgical wound as the tumor is removed. The wound was apposed with three simple interrupted skin sutures.

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Sliding skin graft or ‘H’ plasty One of the easiest forms of blepharoplasty is the sliding skin flap (see Fig. 5.69). The affected lesion is removed and the incisions are extended for twice the amount of skin removed. The incision is slightly diverging to allow for skin contracture after surgery (Fig. 5.78). These divergent incisions are not absolutely necessary in eyelid skin, due to its relative pliability and plasticity. Triangular pieces of skin are excised external to the base of the incisions. These triangular skin excisions allow skin closure without puckering of the skin (‘dog-ears’) and distribute the tension on the skin. The sides of the triangle should approximate the height of the excised triangle. Adjacent skin should be undermined to provide mobility for skin closure. Palpebral conjunctiva adjacent to the wound is undermined and mobilized utilizing Steven’s tenotomy scissors. The eyelid defect is slightly overcorrected to allow for wound contracture. There should never be tension on the conjunctival portion of the skin at closure. The conjunctiva is sutured using 6-0 polyglactin in a continuous pattern. Skin closure begins at the eyelid margin, utilizing an interrupted pattern of 4-0 to 5-0 nonabsorbable material. The skin is anchored to the conjunctiva using 6-0 polyglactin in a mattress or continuous pattern with buried knots to avoid irritation of the cornea. A temporary tarsorrhaphy is performed and left in place for 7–10 days to provide support for the skin flap during the initial healing phase.

Tarsoconjunctival advancement graft When large areas of palpebral conjunctiva are excised, a tarsoconjunctival advancement flap from the opposing eyelid is used to fill the conjunctival defect. This is a twostage procedure. The affected area of eyelid is excised and the sliding skin flap prepared as described above. Instead of using adjacent conjunctiva to line the defect, tarsoconjunctiva from the opposite eyelid is used to line the defect. The donor conjunctiva is incised 4 mm from the eyelid margin. The conjunctiva is dissected from a flap to fill the recipient area using Westcott or Steven’s tenotomy scissors. The tarsoconjunctiva is sutured across the eyelid to fill the defect, and then the skin is advanced to cover the defect. A few anchoring sutures are used in the donor graft to anchor

the conjunctiva. A temporary tarsorrhaphy is necessary to relieve tension on the conjunctiva in this procedure. A second surgical procedure is required to cut the conjunctival flap at the eyelid fissure to restore the eyelid margin. Cutting of the conjunctival flap is usually performed no earlier than 3 weeks after the initial surgery. It may be advantageous to the leave the flap in place for 4–6 weeks, or longer, after the primary surgery.

Full-thickness eyelid graft (Cutler– Beard procedure) A full-thickness eyelid flap is used for neoplasia or traumatic defects involving the lower eyelid where eyelid and facial skin are less mobile. A flap of more mobile and pliable upper eyelid is used. The width of the flap approximates the width of the eyelid defect. The lower eyelid lesion is excised as in the sliding skin flap technique. In more extensive defects, a lateral canthotomy is helpful to release tension at the surgical site. The opposing eyelid is incised about 5–6 mm from the eyelid margin, preserving the tarsal glands. Splitting the flap into skin–muscle and tarsoconjunctiva sections facilitates mobility and reduces the size of the graft required. The tarsoconjunctival portion of the flap is sutured using 6-0 to 7-0 polyglactin 910, with the knots buried away from the cornea to prevent irritation. The skin wound is closed with simple interrupted sutures of 4-0 to 5-0 nylon, prolene or silk. The bridge portion of skin is sutured to the flap using 5-0 nylon. The flap is left in place for several weeks (usually 4–8) until tension has normalized. In a second procedure, the flap is transected in line with the original eyelid margin and sutured to the bridge with 6-0 to 7-0 material. The newly created eyelid margin is sutured to appose the conjunctiva and skin with 6-0 to 7-0 polyglactin 910 (VicrylW). A temporary tarsorrhaphy is placed to prevent tension on the flap. The tarsorrhaphy can be removed in 3–4 weeks or left in place until the flap is incised in the second procedure to form the new eyelid margin.

Rhomboid graft Blanchard et al described a rhomboid graft flap for repairing defects of more than 50% of the eyelid (a rhomboid is an equal-sided parallelogram). One side of the rhomboid is used to recreate the eyelid margin. The replacement flap is made by two incisions: the first is an extension of the diagonal of the rhomboid and equal in length to the sides of the rhomboid; the second incision is made parallel to the rhomboid for an equal length. Palpebral or bulbar conjunctiva is undermined to cover the replacement skin flap. The skin is undermined and rotated to fill the defect. The conjunctiva is sutured to the skin to form an eyelid margin in a simple continuous pattern using 6-0 polyglactin material. The skin is closed in a simple interrupted pattern using 4-0 to 5-0 non-absorbable material.

Sliding ‘Z’ graft

Fig. 5.78 Immediate postoperative appearance after a large ‘H’ plasty for squamous cell carcinoma of the entire lower eyelid in a horse.

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Large defects in the lateral upper eyelid that occur after excision of eyelid tumors can be closed with a sliding ‘Z’ flap. Prior to excision of the lesion, the proposed excision area is marked with a CO2 laser, ophthalmic electrocautery, or

Blepharoplastic procedures for the horse

with surgical marking ink. Two triangles of skin, one above and one below the defect, are also marked. The lesion (mass) is excised. Adjacent skin is undermined with surgical scissors. Conjunctiva is undermined and mobilized to fill the defect, and closed with 6-0 to 7-0 VicrylW. The two triangles, which are equal to the sides of the excised defect, are then excised. Conjunctiva is undermined and mobilized to fill the defect, and sutured to the free skin edge with 6-0 to 7-0 VicrylW. The skin is apposed with 4-0 to 5-0 nylon in a simple interrupted pattern.

Partial orbital rim resection In 2002, Beard and Wilkie described a technique of enucleation or exenteration combined with a partial orbital rim resection and mesh skin expansion to fill the skin defects. Following enucleation or exenteration and radical excision of periocular skin, there may be inadequate tissue to close the wound using more conventional reconstructive and flap techniques. In this procedure, a portion of the dorsal rim of the orbit is resected after globe removal to decrease the wound area and reduce the tension on the skin sutures. Extensive undermining of the adjacent skin is performed and mesh skin expansion is added to allow advancement and closure of the wound.

Aftercare for blepharoplasty in the horse The general protocol for aftercare after blepharoplasty is similar to that for skin and reconstructive procedures elsewhere on the body. Pre- and perioperative topical and systemic antibiotics are indicated. The placement of a subpalpebral lavage system will facilitate topical application of solutions to the eye. Postoperative swelling will be reduced by the administration of systemic non-steroidal anti-inflammatory agents (flunixin meglumine 1 mg/kg IV) immediately before surgery. Postoperative edema will be lessened by the application of ice packs for the first 24 h after surgery. If swelling is present 24 h after surgery, warm compresses may further reduce the swelling and discomfort at the surgical site. As rubbing or self-mutilation is always a concern in horses, the surgical site or eye must be protected by a protective hood with a plastic or solid eyecup (EyeSaver™, Jorgensen Laboratories, Loveland, CO.). Cross tying or neck cradles have also been used successfully. If granulating wounds are present, removal of the exudate once or twice daily, with application of petroleum jelly or a povidone– iodine gel ventral to the wound is helpful, and fly-control is essential in warmer climates. Fly control around the horse’s face is achieved by wiping fly repellent around the surgical site, by fitting the horse with a fly mask, or by using fly-repellent strips attached to the halter. Skin sutures are usually removed 8–12 days after surgery. In situations when tension on the suture line cannot be avoided, sutures are left in place for 18–24 days.

Adjunctive therapeutic modalities which can be combined with surgery for the horse For eyelid squamous cell carcinoma and sarcoid in horses, surgical removal of these tumors generally results in about 50% non-recurrence with a single year follow-up.

Squamous cell carcinoma Of the different sites in the horse for SCC (eyelid, orbit, limbus, and nictitating membrane), the eyelids have the poorest prognosis, with an average of 30–40% recurrence rate. Perhaps one reason for the poorer prognosis with eyelid SCC is the fact that they are often presented as large masses and ‘clean’ surgical margins are not possible. Mean survival time after diagnosis is 47 months. The recommendation of a 2 cm tumor-free margin for surgical excision of the lids is generally impossible. As a result, surgery is often limited to biopsy or debulking of the mass, and then some form of adjunctive therapy. These adjunctive therapies depend on the size and location of the tumor, vision status of the patient, prior experience of the veterinarian, value of the animal, and owner financial constraints. These therapeutic options include cryotherapy, radiofrequency hyperthermia, intralesional (intratumoral) injections of biologic modifiers (usually mycobacterial cell wall fraction or bacille CalmetteGue´rin (BCG)), intralesional chemotherapy using cisplatin, and radiotherapy (using cesium-137, cobalt-60, gold-198, iridium-192, and strontium-90.)

Cryotherapy Cryotherapy is performed using liquid nitrogen as the refrigerant, either as a spray or solid probe delivery system, to freeze tissues to –20 C to –40 C, using either a double or triple freeze–thaw technique. The tissue should be allowed to completely thaw between freeze cycles. Use of a thermocouple to monitor the depth of freezing for larger masses is recommended. A heavy layer of petrolatum or a piece of styrofoam is used to protect the surrounding area from freezing. The iceball should extend at least 3–5 mm beyond the mass’s base. Even with the sloughing of cryonecrotic tissues within 2–4 weeks, the eyelid is usually able to heal and maintain its architecture and function following cryotherapy. Cryotherapy combined with surgery for lid SCC in horses has about 30–100% nonrecurrence rate.

Radiofrequency hyperthermia Radiofrequency employs a device that uses either a surface or a piercing probe to heat the tumor to 50 C (122 F) for 50 s; tumor cells are selectively destroyed over normal cells. Multiple application sites are needed if the mass exceeds 0.5 cm in diameter, and therapy should extend 3–4 mm beyond the mass’s base. Tumors in excess of 5 cm in diameter are not candidates for hyperthermia. Reports suggest about 75% complete regression after one treatment; for two treatments 66% completely regressed.

Immunotherapy Immunotherapy has been used successfully for equine eyelid SCC using BCG cell wall extract. The usual dose for BCG is 1 mL extract/cm3 of tumor injected throughout the mass. Treatments are spaced every 2–4 weeks, and continued until the mass has completely regressed. Both systemic and local anaphylaxis have been reported, and pretreatment with flunixin meglumine, antihistamine or corticosteroids may be necessary. This therapy has a high rate of tumor non-recurrence.

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Fig. 5.79 Intralesional/intratumoral chemotherapy with cisplatin for eyelid squamous cell carcinoma (SCC) in a horse. (a) Appearance of the SCC before cisplatin intratumoral therapy. (b) Appearance of the tumor after the second of four cisplatin injections. After the last cisplatin injection, the region will be assessed for regression and after biopsy has indicated that the area is tumor free.

Intralesional/intratumoral chemotherapy

Carbon dioxide laser

Intratumoral injection of cisplatin has been used successfully for treating lid SCC in horses, and has partly replaced the BCG technique. The usual cisplatin dose is four injections at 2-week intervals with 1 mg cisplatin (3.3 mg/mL; 10 mg cisplatin in 1 mL water and 2 mL of purified medical grade sesame seed oil) which should extend about 1 cm beyond the tumor margin (Fig. 5.79). Complete face protection from any cisplatin spray during the injection technique is required to prevent exposure of administering personnel to the drug especially after the first series of injections. The non-recurrence rate is about 65–90%. 5-Fluorouracil (5-FU) has also been used for intralesional treatments of SCC in the horse: 10 mL 5-FU (50 mg/mL), combined with 3 mL of 1:1000 adrenaline (epinephrine). Intratumoral bleomycin has also been compared to cisplatin, but is more expensive and perhaps not as successful (1 year follow-up: cisplatin 93% non-recurrence; bleomycin 78% non-recurrence).

Carbon dioxide laser has been reported for equine lid SCC, applied after tumor debulking. Laser settings were 3 and 8 W, and the tumor surface was lasered (ablated) until covered with a brown char.

Radiation therapy Radiation therapy with beta radiation (strontium-90) and brachytherapy with cesium-137, gold-198, radon-222, cobalt-60, and iridium-192 have been reported for equine lid SCC. Beta radiation has limited penetration (and is primarily used for corneoconjunctival SCC), but the brachytherapy agents are generally placed directly within the eyelid mass. The iridium-192 isotope, contained in stainless steel rods at 1 cm intervals in a plastic coating or within needles, is placed in the SCC mass in parallel rows about 1 cm apart (Fig. 5.80). The usual dose is 6000–7000 cGy and requires about 7–10 days of implantation. Unfortunately, availability, transportation and material costs, radiation exposure to personnel, isolation of the patient, and state radiation safety guidelines are important limitations. Brachyradiation yields the highest success rate for lid SC in the horse, and has well over 95% non-recurrence. Complications of brachytherapy include hair loss, hair and skin depigmentation, necrosis, fibrosis, keratitis, cataract formation, and corneal ulceration.

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Sarcoid Sarcoids, like SCC, have an unacceptably high rate of recurrence of about 50% after surgery alone. Hence, like SCC, adjunctive therapies are necessary to treat this tumor group successfully. Sarcoids tend to occur in young horses (3–6 years old); in contrast, SCCs occur in older horses (7–10 years old). Sarcoids are locally aggressive and tend to recur.

BCG immunotherapy The same menu of therapeutic choices used to treat SCC is used for sarcoids. Surgery is used to biopsy and debulk sarcoids before commencing these adjunctive therapies. The most common sarcoid therapy is immunotherapy using multiple injections of BCG (1.0 mL/cm2 of tumor surface). These injections, within the mass as well as at its borders, are repeated at 2- to 4-week intervals, and continue until complete regression of the tumor (Fig. 5.81). Both systemic

Fig. 5.80 Brachytherapy of a large upper eyelid squamous cell carcinoma using iridium-192. The stainless steel needles, about 1 cm apart, contain the iridium 192 isotope. Treatment exposure (usually 7–10 days) is dependent on the calculated total radiation dose.

Bovine eyelid surgery

in North America. It occurs in Hereford, Hereford crosses, Simmental and Shorthorn breeds; other breeds are affected infrequently. The economic impact includes carcass condemnations, production costs, treatment costs, and management expenses.

Surgery and surgery combinations for eyelid SCC in cattle

Fig. 5.81 Treatment of sarcoid with intralesional/intratumoral BCG injections. The needles have been pre-placed to ensure adequate coverage of the mass with the BCG injections.

and local anaphylaxis have been reported, and pretreatment with flunixin meglumine, antihistamine or corticosteroids may be necessary. One study reported complete regression of all sarcoids with an average of 3.2 treatments (11.7 mL per treatment) with a range of 14–253 days to resolve. Immunotherapy with BCG seems most effective for the fibroblastic and nodular types of sarcoid.

Intratumoral (intralesional) chemotherapy Intralesional cisplatin is now the most common local chemotherapy method for sarcoids. Multiple injections of the cisplatin oily emulsion (1 mg cisplatin/cm3 tumor tissue) are administered four times at 2-week intervals. In one report, complete regression occurred in 95% of the sarcoids, with 1-year relapse-free non-recurrence of 87%. Another report noted 33% non-recurrence.

Cryotherapy and radiofrequency hyperthermia Both of these therapies are administered as for SCC. Information about effectiveness for sarcoids is unknown.

Brachytherapy

Several treatment modalities are available; choice depends on availability of instrumentation, training of the veterinarian, location and size of the tumor, intended use of the animal, and value of the animal. Therapeutic choices include radiofrequency hyperthermia, immunotherapy, cryotherapy, radiation, CO2 laser ablation, and intralesional chemotherapy using cisplatin. Of these modalities, the lower cost cryotherapy and hyperthermia are used most frequently in cattle, combined with surgical debulking of the mass (see above section on the horse).

Sliding skin graft or ‘H’ plasty One of the frequent forms of blepharoplasty in cattle is the sliding skin graft. The lid mass is excised, and often treated by cryotherapy (Figs 5.82 and 5.83). The skin incisions are then extended for twice the amount of skin removed. The incision diverges slightly to allow for skin contracture after surgery. These divergent incisions are not absolutely necessary in eyelid skin, due to its relative pliability and plasticity. Triangular pieces of skin are excised external to the base of the incisions. These triangular skin excisions allow skin closure without puckering of the skin (‘dog-ears’) and distribute the tension on the skin. The sides of the triangle should approximate the height of the excised triangle. Adjacent skin should be undermined to provide mobility for skin closure. Palpebral conjunctiva adjacent to the wound is undermined and mobilized utilizing Steven’s tenotomy scissors. The width and length of the eyelid defect are slightly overcorrected to allow for wound contracture. There should never be tension on the conjunctival portion of the skin at closure. The conjunctiva is sutured using 6-0 polyglactin in a continuous pattern. Skin closure begins at

Like squamous cell carcinomas in horses, brachytherapy is effective to treat all forms of sarcoid. Several forms of isotope have been used. Iridium-192 has been reported most frequently, and for sarcoids provides a non-recurrence rate as high as 94% at 1 year. The usual radiation dose is 5000–9000 cGy and requires 7–14 days of implantation. High costs and restricted availability are the main limitations.

Bovine eyelid surgery Eyelid SCC, as part of ocular squamous cell carcinoma (OSCC), is the most frequent indication for lid surgery in cattle. Eyelid lacerations occur infrequently in cattle, and are repaired in a similar fashion to horses and small animals. Ocular squamous cell carcinoma in cattle, often termed cancer eye, is the most economically important neoplasia in cattle. It is the most common neoplasm affecting cattle

Fig. 5.82 Intraoperative photograph of ‘H’ plasty in a cow with squamous cell carcinoma of the entire lower lid. The skin graft has been advanced into the surgical wound.

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Fig. 5.83 Three different delivery probes for liquid nitrogen and cryotherapy in cattle. (a) Use of a small direct contact cryoprobe for a limbal squamous cell carcinoma. (b) Intraoperative photograph of a large direct contact cryoprobe used after debulking a large lower eyelid squamous cell carcinoma. (c) Intraoperative photograph using liquid nitrogen spray for squamous cell carcinoma after debulking the mass affecting the lower eyelid. Adjacent normal tissues are protected from the nitrogen spray with a thick coat of petrolatum gel.

the eyelid margin, utilizing an interrupted pattern of 4-0 to 5-0 non-absorbable material. The skin is anchored to the conjunctiva using 6-0 polyglactin in a mattress or continuous pattern with buried knots to avoid irritation of the cornea. A temporary tarsorrhaphy is performed and left in place for 7–10 days to provide support for the skin graft during the initial healing phase.

is necessary to relieve tension on the conjunctiva in this procedure. A second surgical procedure is required to cut the conjunctival flap at the eyelid fissure to restore the eyelid margin. The cutting of the base of the conjunctival graft is usually performed no earlier than 3 weeks after the initial surgery. It may be advantageous to the leave the flap in place for 4–6 weeks after the primary surgery.

Tarsoconjunctival advancement graft

Full-thickness eyelid graft

When large areas of palpebral conjunctiva are excised, a tarsoconjunctival advancement graft from the opposing eyelid is used to fill the conjunctival defect. This is a two-stage procedure, as described in the horse. A temporary tarsorrhaphy

A full-thickness eyelid flap is used for neoplasia or traumatic defects involving the lower eyelid where eyelid and facial skin are less mobile. The procedure is identical to that in the horse.

Further reading Small animals Barrie KP, Gelatt KN, Parshall CP: Eyelid squamous cell carcinoma in four dogs, J Am Anim Hosp Assoc 18:123–127, 1982. Bedford PGC: Eyelashes and adventitious cilia as causes of corneal irritation, J Small Anim Pract 12:11–17, 1971. Bedford PGC: The treatment of canine distichiasis by the method of partial tarsal plate excision, J Am Anim Hosp Assoc 15:59–60, 1979. Bedford PGC: Conditions of the eyelids in the dog, J Small Anim Pract 29:416–428, 1988. Bedford PGC: Surgical correction of facial droop in the English Cocker Spaniel, J Small Anim Pract 31:255–258, 1990. Bedford PGC: Technique of lateral canthoplasty for the correction of macropalpebral fissure in the dog, J Small Anim Pract 39:117–120, 1998. Bedford PGC: Diseases and surgery of the canine eyelid. In Gelatt KN, editor: Veterinary Ophthalmology, ed 3, Baltimore, 1999, Lippincott Williams and Wilkins, pp 535–568. Bellhorn RW: Variation of canine distichiasis, J Am Vet Med Assoc 157:342–343, 1970. Bigelbach A: A combined tarsorrhaphy– canthoplasty technique for repair of entropion and ectropion, Veterinary and Comparative Ophthalmology 6:220–224, 1996.

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Blanchard GL, Keller WF: The rhomboid graftflap for the repair of extensive ocular adnexal defects, J Am Anim Hosp Assoc 12:576–580, 1976. Blaskovies L: Ectropion. In: Fox SA, editor: Ophthalmic Plastic Surgery, ed 4, New York, 1976, Grune and Stratton, pp 278–279. Brightman AH, Helper LC: Full thickness resection of the eyelid, J Am Anim Hosp Assoc 14:483–485, 1978. Carter JD: Combined operation for noncicatricial entropion, J Am Anim Hosp Assoc 8:53–58, 1972. Carter JD: Medial conjunctivoplasty for aberrant dermis of the Lhasa apso, J Am Anim Hosp Assoc 9:242–244, 1973. Chambers ED, Slatter DH: Cryotherapy (N2O) of canine distichiasis and trichiasis: an experimental and clinical report, J Small Anim Pract 25:647–659, 1984. Christmas RE: Common ocular problems of Shih Tzu dogs, Can Vet J 33:390–393, 1992. D’Anna N, Sapienza JP, Guandalini A, Guerriero A: Use of a dermal biopsy punch for removal of ectopic cilia in dogs: 19 cases, Vet Ophthalmol 10:65–67, 2007. Doherty MJ: A bridge-flap blepharorrhaphy method for eyelid reconstruction in a cat, J Am Anim Hosp Assoc 9:238–241, 1973. Dziezyc J, Millichamp NJ: Surgical correction of eyelid agenesis in a cat, J Am Anim Hosp Assoc 25:513–516, 1989.

Esson D: A modification of the Mustarde´ technique for the surgical repair of a large feline eyelid coloboma, Vet Ophthalmol 4:159–160, 2001. Gelatt KN: Resection of cilia-bearing tarsoconjunctiva for correction of canine distichia, J Am Vet Med Assoc 155:892–897, 1969. Gelatt KN, Blogg JR: Blepharoplastic procedures in small animals, J Am Anim Hosp Assoc 5:67–78, 1969. Grier RL, Brewer WG, Theilen GH: Hyperthermic treatment of superficial tumors in cats and dogs, J Am Vet Med Assoc 177:227–233, 1980. Gross SL: Surgery of the eyelids. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, Philadelphia, 1990, Lea and Febiger, pp 68–76. Grussendorf H: Outcome of a surgical technique for dogs suffering from macroblepharon, Munich, 2004, Transactions of the ECVO/ ESVO/DOK Meeting, 41. Gutbrod F, Tietz B: Entropion – operation mit Lidrandverku¨rzung, Vet Spiegel 4:14, 1993. Gwin RM: Selected blepharoplastic procedures of the canine eyelid, The Compendium 2:267–272, 1980. Halliwell WH: Surgical management of canine distichia, Am Vet Med Assoc 150:874–879, 1967.

Further reading Hamilton HL, Whitley RD, McLaughlin SA, Swaim SF: Basic blepharoplasty techniques, Compendium on Continuing Education for the Practicing Veterinarian 21:946–953, 1999. Helper LC, Magrane WG: Ectopic cilia of the canine eyelid, J Small Anim Pract 11:185–189, 1970. Jensen HE: Canthus closure, The Compendium 1:735–741, 1979. Johnson BW, Gerding PA, McLaughlin SA, Helper LC, Szajerski ME, Cormany KA: Nonsurgical correction of entropion in Shar Pei puppies, Vet Med 83:482–483, 1988. Kasa G, Kasa F: Exizionsraffung zur behebung eines entropiums beim chow-chow, Tierarztl Prax 7:341–349, 1979. Kirschner SE: Modified brow sling technique for upper lid entropion, Proceedings of the 25th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 25:68, 1994. Krehbiel JD, Langham RF: Eyelid neoplasms of dogs, Am J Vet Res 36:115–119, 1975. Lawson DD: Canine distichiasis, J Small Anim Pract 14:469–478, 1973. Lenarduzzi RF: Management of eyelid problems in Chinese Shar-Pei puppies, Vet Med 78:548–550, 1983. Long RD: Treatment of distichiasis by conjunctival resection, J Small Anim Pract 32:146–148, 1991. McCallum P, Welser J: Coronal rhytidectomy in conjunction with deep plane walking sutures, modified Hotz–Celsus and lateral canthoplasty procedure in a dog, Vet Ophthalmol 5:376–379, 2004. McLaughlin SA, Whitley RD, Gilger BC, Wright JC, Lindley DM: Eyelid neoplasms in cats: a review of demographic data (1979 to 1989), J Am Anim Hosp Assoc 29:63–67, 1993. Miller WJ, Albert RA: Canine entropion, Compendium on Continuing Education for the Practicing Veterinarian 10:431–438, 1988. Moore CP: Eyelid and adnexal surgery from a practitioner’s perspective, North American Veterinary Conference Proceedings 14:556–559, 2000. Moore CP, Constantinescu GM: Surgery of the adnexa, Vet Clin North Am Small Anim Pract 27:1011–1066, 1997. Munger RJ, Carter JD: A further modification of the Kuhnt–Szymanowski procedure for correction of atonic ectropion in dogs, J Am Anim Hosp Assoc 20:651–656, 1984. Munger RJ, Gourley IM: Cross lid flap for repair of large upper eyelid defects, J Am Vet Med Assoc 178:45–48, 1981. Peiffer RL: Four-sided excision of canine eyelid neoplasms, Canine Practice 6:35–133, 1979. Peiffer RL, Gelatt KN, Gwin RM, Williams LW: Correction of inferior medial entropion as a cause of epiphora, Canine Practice 5:27–31, 1978. Pellicane CP, Meek LA, Brooks DE, Miller TR: Eyelid reconstruction in five dogs by the semicircular flap technique, Veterinary

and Comparative Ophthalmology 4:93–103, 1994. Read RA, Broun HC: Entropion correction in dogs and cats using a combination Hotz– Celsus and lateral eyelid wedge resection: results in 311 eyes, Vet Ophthalmol 10:6–11, 2007. Roberts SM, Severin GA, Lavach JD: Prevalence and treatment of palpebral neoplasms in the dog: 200 cases (1975–1983), J Am Vet Med Assoc 189:1355–1359, 1986. Roberts SR, Bistner SI: Surgical correction of eyelid agenesis in the feline. In Proceedings of the American Society of Veterinary Ophthalmologists, 1968, pp 18–21. Robertson BF, Roberts SM: Lateral canthus entropion in the dog, part 1: comparative anatomic studies, Veterinary and Comparative Ophthalmology 4:151–156, 1995. Robertson BF, Roberts SM: Lateral canthus entropion in the dog, part 2: surgical correction. Results and follow-up from 21 cases (1991–1994), Veterinary and Comparative Ophthalmology 5:162–169, 1995. Schmidt V: Kryochirurgische therapie der distichiasis des hundes Mh, Vet Med 35:711–712, 1980. Stades FC: A new method for surgical correction of upper eyelid trichiasis– entropion: operation method, J Am Anim Hosp Assoc 23:603–606, 1987. Stades FC: Reconstructive eyelid surgery, Tijdschr Diergeneeskd 112(Suppl 1): 585–635, 1987. Stades FC, Boeve MH: Surgical correction of upper eyelid trichiasis–entropion: results and follow-up in 55 eyes, J Am Anim Hosp Assoc 23:607–610, 1987. Stades FC, Gelatt KN: Diseases and surgery of the canine eyelids. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 563–617. Stades FC, Boeve´ MH, van der Woerdt A: Palpebral fissure length in the dog and cat, Progress in Veterinary and Comparative Ophthalmology 2:155–161, 1992. Stuhr CM, Stanz K, Murphy CJ, McAnulty J: Stellate rhytidectomy: superior entropion repair in a dog with excessive facial skin, J Am Anim Hosp Assoc 33:342–345, 1997. Van der Woerdt A: Adnexal surgery in dogs and cats, Vet Ophthalmol 7:284–290, 2004. Wheeler CA, Severin GA: Cryosurgical epilation for the treatment of distichiasis in the dog and cat, J Am Anim Hosp Assoc 20:877–884, 1984. Williams DL: Entropion correction by fornixbased suture placement: use of the Quickert–Rathbun technique in ten dogs, Vet Ophthalmol 7:343–347, 2004. Willis M, Martin C, Stiles J, Kirschner S: Brow suspension for treatment of ptosis and entropion in dogs with redundant facial skin folds, J Am Vet Med Assoc 214:660–662, 1999. Wyman M: Lateral canthoplasty, J Am Anim Hosp Assoc 7:196–201, 1971.

Wyman M: Ophthalmic surgery for the practitioner, Vet Clin North Am Small Anim Pract 9:311–348, 1979. Wyman M, Wilkie DA: New surgical procedure for entropion correction: tarsal pedicle technique, J Am Anim Hosp Assoc 24:345–349, 1988. Wyman M, Donovan EF, Rudy RL: Surgical correction of cicatricial ectropion in the dog, Southwestern Veterinarian 23:229–232, 1970.

Large animals and special species Allbaugh RA, Davidson HJ: Surgical correction of periocular fat pads and entropion in a potbellied pig (Sus scrofa), Vet Ophthalmol 12:115–118, 2009. Andrea CR, George LW: Surgical correction of periocular fad pad hypertrophy in potbellied pigs, Vet Surg 28:311–314, 1999. Baker JR, Leyland A: Histologic survey of tumors of the horse with particular reference to those of the skin, Vet Rec 96:419–422, 1975. Barnett KC: The eye of the newborn foal, J Reprod Fertil Suppl 23:701–703, 1969. Beard WL, Wilkie DA: Partial orbital rim resection, mesh skin expansion, and second intention healing combined with enucleation or exenteration for extensive periocular tumors in horses, Vet Ophthalmol 5:23–28, 2002. Bertone AL, McClure JJ: Therapy for sarcoids, Compendium on Continuing Education for the Practicing Veterinarian 12:262–265, 1990. Blanchard GL, Keller WF: The rhomboid graft flap for the repair of extensive ocular adnexal defects, J Am Anim Hosp Assoc 12:576–580, 1976. Blodi FC, Ramsey FK: Ocular tumors in domestic animals, Am J Ophthalmol 50:109–115, 1967. Brooks DE: Orbit. In Auer JA, Stick JA, editors: Equine Surgery, ed 3, St Louis, 2006, Saunders, pp 755–766. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1165–1274. Cotchin E: A general survey of tumors in the horse, Equine Vet J 9:16–21, 1977. Cutler N, Beard C: A method for partial and total upper lid reconstruction, Am J Ophthalmol 39:1–7, 1955. Diesem C: The organ of vision. In Getty R, editor: Sisson and Grossman’s Anatomy of Domestic Animals, ed 5, Philadelphia, 1975, WB Saunders, pp 226–244. Dugan SJ: Ocular neoplasia, Vet Clin North Am 8:609–626, 1992. Dugan SJ, Curtis CR, Roberts SM, Severin GA: Epidemiologic study of ocular/adnexal squamous cell carcinoma in horses, J Am Vet Med Assoc 198:251–256, 1991. Englis RV, Nassisse MP, Davidson MG: Carbon dioxide laser ablation for treatment of limbal squamous cell carcinoma in horses, J Am Vet Med Assoc 196:439–442, 1990.

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Farris H, Fraunfelder F: Cryosurgical treatment of ocular squamous cell carcinoma of cattle, J Am Vet Med Assoc 168:213–216, 1976. Fox LM, Thurmon JC: Bilateral ankyloblepharon congenital in a newborn foal, Vet Med Small Anim Clin 64:237, 1969. Gelatt KN: Blepharoplastic procedures in horses, J Am Vet Med Assoc 151:27–44, 1967. Gilger BC, Stoppini R: Diseases of the eyelids, conjunctiva, and nasolacrimal system. In Gilger BC, editor: Equine Ophthalmology, St Louis, 2005, Mosby, pp 107–156. Giuliano EA, MacDonald I, McCaw DI, et al: Photodynamic therapy for the treatment of periocular squamous cell carcinoma in horses: a pilot study, Vet Ophthalmol 11:27–34, 2008. Green LE, Berriatua E, Morgan KL: The prevalence and risk factors for congenital entropion in intensively reared lambs in south west England, Prev Vet Med 24:15–21, 1995. Grier RL, Brewer WG, Paul SR, Theilen GH: Treatment of bovine and equine ocular squamous cell carcinoma by radiofrequency hyperthermia, J Am Vet Med Assoc 177:55–61, 1980. Hamilton HL, Whitley RD, McLaughlin SA, Swaim SF: Basic blepharoplasty techniques, Compendium on Continuing Education for the Practicing Veterinarian 21:946–953, 1999. Hendrix DVH: Equine ocular squamous cell carcinoma, Clinical Techniques in Equine Practice 4:87–94, 2005. Kainer R, Stringer J, Lueker D: Hyperthermia for treatment of ocular squamous cell tumors in cattle, J Am Vet Med Assoc 176:356–360, 1980. Knottenbelt DC, Kelly DF: The diagnosis and treatment of periorbital sarcoid in the horse: 445 cases from 1974 to 1999, Vet Ophthalmol 3:169–191, 2000. Komaromy AM, Andrew SE, Brooks DE, Detrisac CJ, Gelatt KN: Periocular sarcoid in a horse, Vet Ophthalmol 7:141–146, 2004. Latimer CA: Diseases of the adnexa and conjunctiva. In Robinson NE, editor: Current Therapy in Equine Medicine, ed 2, Philadelphia, 1987, Saunders, pp 440–445. Lavach JD: The Handbook of Equine Ophthalmology, Fort Collins, Colorado, 1987, Gidding Studio, pp 63–97.

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Lavach JD: Large Animal Ophthalmology, St Louis, 1990, CV Mosby, pp 42–66. Lavach JD, Severin GA: Neoplasia of the equine eye, adnexa, and orbit: a review of 68 cases, J Am Vet Med Assoc 170:202–203, 1977. Lavach JD, Sullins K, Roberts S, Severin GA, et al: BCG treatment of periocular sarcoid, Equine Vet J 17:445–448, 1985. Linton LL, Collins BK: Entropion repair in a Vietnamese pot bellied pig, Journal of Small Exotic Animal Medicine 2:124–127, 1993. Martin CL: Ophthalmic disease in veterinary medicine, London, 2005, Manson, pp 145–182. McLaughlin SA, Whitley RD: Eyelid wounds. In Swaim SF, Henderson RA, editors: Small Animal Wound Management, ed 2, Baltimore, 1997, Williams and Wilkins, pp 403–430. Miller TR: Eyelids. In Auer JA, Stick JA, editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 450–464. Miller TR: Eyelids. In Auer JA, Stick JA, editors: Equine Surgery, ed 3, St Louis, 2006, Saunders, pp 702–715. Moore AS, Beam SL, Rassnick KM, Provost P: Long-term control of mucocutaneous squamous cell carcinoma and metastases in a horse using piroxicam, Equine Vet J 35:715–718, 2003. Moore CP, Whitley RD: Ophthalmic diseases of small domestic ruminants, Vet Clin North Am Large Anim Pract 6:641–665, 1984. Munger RJ, Gourley IM: Cross-lid flap for repair of large upper eyelid defects, J Am Vet Med Assoc 178:45–48, 1981. Peiffer RL, Williams R, Schenk M: Correction of congenital entropion in a foal, Vet Med Small Anim Clin 72:1219–1225, 1977. Plummer CE: Equine eyelid disease, Current Techniques in Equine Practice 4:95–105, 2005. Priester WA: Congenital ocular defects in cattle, horses, cats, and dogs, J Am Vet Med Assoc 160:1504–1511, 1972. Rasmussen RE: Repair of entropion in lambs, Mod Vet Pract 61:943–944, 1980. Riis RC: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology,

Philadelphia, 1981, Lea and Febiger, pp 569–605. Roberts SM: Ocular neoplasia. In Smith BP, editor: Large Animal Internal Medicine, ed 4, St Louis, 2009, Mosby, pp 1299–1305. Schwink K: Factors influencing morbidity and outcome of equine ocular squamous cell carcinoma, Equine Vet J 19:198–200, 1987. Severin GA: Severin’s Veterinary Ophthalmology Notes, ed 3, Fort Collins, 1996, Colorado State University Press, pp 200–207. Sundberg JP, Burnstein T, Page EH, et al: Neoplasms of equidae, J Am Vet Med Assoc 170:150–152, 1977. Theon AP, Pascoe JR: Iridium-192 interstitial brachytherapy for equine periocular tumours: treatment results and prognostic factors in 115 horses, Equine Vet J 27:117–121, 1995. Theon AP, Pascoe JR, Carlson GP, Krag DN: Intratumoral chemotherapy with cisplatin in oily emulsion in horses, J Am Vet Med Assoc 202:261–267, 1993. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1275–1335. Walker M, Adams W, Hoskinson J, et al: Iridium-192 brachytherapy for equine sarcoid, one and two year remission rates, Veterinary Radiology 32:206–208, 1991. Welker B, Modransky PD, Hoffsis GF, Wyman MW, Rings DM, Hull BL: Excision of neoplasms of the bovine lower eyelid by H-blepharoplasty, Vet Surg 20:133–139, 1991. Whitley RD: Neonatal equine ophthalmology. In Koterba AM, Drummond WH, Kosch PC, editors: Equine Clinical Neonatology, Philadelphia, 1990, Lea and Febiger, pp 531–557. Whitley RD, Vygantas KR, Whitley EM: Ocular trauma. In Smith BP, editor: Large Animal Internal Medicine, ed 4, St Louis, 2009, Mosby, pp 1269–1274. Wyman M, Rings M, Tarr M, Alden C: Immunotherapy in equine sarcoid: a report of two cases, J Am Vet Med Assoc 171:449–451, 1997.

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Surgery of nasolacrimal apparatus and tear systems Kirk N. Gelatt

Chapter contents Introduction

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Nasolacrimal apparatus

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Nasolacrimal duct obstructions (extracorneal bullous spectaculopathy) in snakes

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Surgical procedures for the nasolacrimal apparatus

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SURGERY FOR KERATOCONJUNCTIVITIS SICCA

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ADAPTATIONS IN LARGE ANIMALS AND SPECIAL SPECIES

Surgical anatomy

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Introduction Diseases of the nasolacrimal and tear systems occur frequently in small animals and, to a lesser extent, horses. They can be grouped into those affecting the drainage apparatus, and those involving the tear-producing lacrimal gland and the superficial gland of the nictitating membrane. The health of the cornea, conjunctiva, and eyelids depends on continuous secretion of tears and removal by the drainage apparatus. Malfunctions by either or both tear-drainage and tear-producing systems can lead to overt acute-to-chronic diseases of the cornea, conjunctiva, and eyelids. Recent advances in the diagnosis and treatment of diseases of the nasolacrimal drainage and tear-producing systems in all animal species have resulted in markedly improved prognosis and successful clinical management of these patients. For convenience, the surgical procedures of the nasolacrimal and tear systems in this chapter are divided into surgical procedures that improve the drainage of tears, and those that increase or substitute for tear production. Diseases of the nasolacrimal apparatus that require surgical intervention are associated with partial-to-complete obstruction. Diseases of the lacrimal and tear-producing glands that require surgical management are usually associated with reduced levels of aqueous tear formation. With reduced levels of tear formation, disorders of the aqueous portion of the preocular or precorneal film develop, resulting in secondary corneal and conjunctival disease. Excessive lacrimation is usually secondary to pain, or external and internal ophthalmic diseases. Excessive tear secretion can exceed the normal capacity of the tear drainage system, thereby causing clinical signs of epiphora. Similarly,

a drainage system with disease also produces epiphora but tear production is at normal levels. Therapy of tear drainage system diseases is usually a combination of medical and surgical modalities, and re-establishment of patency.

Nasolacrimal apparatus The nasolacrimal drainage apparatus conveys tears and other debris from the external eye to the nasal cavity. This process appears to be only a passive capillary-like activity in animals, and the valve-like structures within the human nasolacrimal apparatus that prevent reverse flow have not been identified in small animals. The orbicularis oculi muscle may affect the lacrimal sac to create a vacuum and/or pressure that may assist in the movement of tears through the system. The anatomic arrangement of the orbicularis oculi muscle in the medial canthus and near the lacrimal sac also supports a more active process which may be involved in the uptake and movement of tears down the nasolacrimal apparatus. Two species possess only one lacrimal punctum: 1) the rabbit has a single ventral lacrimal punctum; and 2) the pig has a single upper lacrimal punctum (the ventral punctum and canaliculus are occluded and non-functional).

Nasolacrimal anatomy in dogs and cats The nasolacrimal apparatus consists of the upper and lower lacrimal puncta, the upper and lower canaliculi, the lacrimal sac, and the long nasolacrimal duct that empties into the rostral nasal cavity (Fig. 6.1). Although there are considerable

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Fig. 6.1 Latex preparations of normal nasolacrimal systems (metric scale shown). (a) Short-haired domestic cat. (b) Brachycephalic dog. (c) Dolichocephalic dog. (Reproduced with permission from Gelatt KN, Cure TH, Guffy MM, Jessen CL 1972 Dacryocystorhinography in the dog and cat. Journal of Small Animal Practice 13:381–397.)

variations in head shape and size in the different breeds of dogs, the predominant anatomic variation of the nasolacrimal apparatus is the variable length and diameter of the nasolacrimal duct. In dogs, the upper and lower lacrimal puncta are located in the palpebral conjunctiva just deep to the mucocutaneous junction, about 5 mm from the medial canthus, and appear as slit-like openings. In cats, the lacrimal puncta are more circular and smaller. From both lacrimal puncta the nasolacrimal system continues as two canaliculi that converge beneath the medial canthal ligament at the level of the lacrimal bone and fossa to form a poorly developed nasolacrimal sac. From the ventral portion of the lacrimal sac emerges the nasolacrimal duct to traverse the small intraosseous canal of the maxillary bone to enter the nasal cavity within the maxilloturbinate to the nasal meatus. This intraosseous portion of the nasolacrimal duct appears to have the smallest diameter, and appears to be the area most apt to become obstructed by inflammation and debris. The variable length of the nasolacrimal duct has a larger diameter, and may also have accessory openings immediately above the root of the upper canine teeth, perhaps just as it enters the nasal cavity. The distal opening of the nasolacrimal duct of both the dog and the cat can be located ventrolateral near the margin of the alar fold. Dilatation of the external nares by speculum assists in locating the distal opening. The distal opening can be cannulated for retrograde lavage of the nasolacrimal system. Because of the difficulty of retrograde nasolacrimal cannulation at the nares in the dog and cat, the convenient and readily accessible upper and lower lacrimal puncta are the usual entry for nasolacrimal flushes and other manipulations.

Nasolacrimal anatomy in large animals The anatomy of the nasolacrimal system of the horse and cow is very similar to that of the dog and cat, but much larger. In horses, the system starts as two lacrimal puncta, about 2 mm in diameter, located about 8 mm from the medial canthus and inside the lid margins. The two canaliculi or lacrimal canals connect the puncta with the lacrimal sac, which is poorly developed in the horse. The long and tortuous nasolacrimal duct, with a prominent dilatation above the first premolar tooth and about 25–30 cm long, extends from the lacrimal sac to the floor of the mucocutaneous junction of the nostril where its diameter is about 3–4 mm. From its beginning of about 6–7 mm diameter,

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it extends from the lacrimal sac through the osseous lacrimal canal of the maxillary bone (about 3–4 mm diameter). In mules, the nasolacrimal canal exits on the lateral part of the floor or lateral wall of the nostril. Accessory openings may also occur further caudad. In general, the primary clinical entry into the equine nasolacrimal system is into its distal orifice, at the beginning of the mucosa on the floor of the nostril. In cattle, the entire length of the nasolacrimal system is about 16–18 cm long. The upper and lower lacrimal puncta are 2–5 mm diameter and connected by the 1–1.5 cm diameter lacrimal canaliculi to the lacrimal sac (about 5–8 mm diameter). The nasolacrimal duct is about 12–15 cm long and straighter than the horse nasolacrimal duct. The distal orifice of cattle, which is not easily accessible clinically, is located near the lateral wall of the nostril on the medial surface of the alar fold of the ventral nasal concha. Hence, for nasolacrimal flushes in cattle, entry is usually through the upper or lower lacrimal punctum.

Clinical diagnostic tests for the nasolacrimal drainage apparatus The two most useful diagnostic tests for the determination of nasolacrimal apparatus functions in all animal species are: 1) the passage of topical fluorescein; and 2) the nasolacrimal flush and cannulation. The fluorescein test measures both the anatomic and physiologic patency of the nasolacrimal system. Aqueous fluorescein instilled onto the eye will normally enter the lacrimal puncta (mainly the lower punctum), traverse the entire nasolacrimal system, and appear at the external nares in 2–5 min. Fluorescein passage time seems directly related to the length of the entire nasolacrimal system. In brachycephalic breeds of dogs and cats, the nasolacrimal duct is considerably shorter and tortuous, and fluorescein may exit the nasolacrimal duct to enter the nasopharynx rather than the external nares. In any breed of dog, if the dog’s head is restrained upward during the test, the dye can also collect in the nasopharynx. With a delayed or negative fluorescein test, the entire nasolacrimal system can be flushed. The nasolacrimal flush tests for the anatomic patency of the nasolacrimal system. Under topical anesthesia and with the head of the dog firmly restrained, either the upper or lower lacrimal punctum is located, cannulated with a lacrimal or 20–22 g blunt stainless steel needle, and flushed with 1–3 mL of sterile saline. The saline should exit out of the external nares,

Surgical procedures for the nasolacrimal apparatus

unless the head is maintained dorsally, in which case the saline will enter the nasopharynx, and the animal may gag or sneeze. In the cat, topical anesthesia, sedation, and some magnification are generally necessary for nasolacrimal flushes. The cat’s lacrimal puncta are round rather than oval, and best cannulated with a 25–26 g blunt hypodermic needle or lacrimal cannula. In horses, the entire nasolacrimal system is flushed from its distal orifice, located on the floor of the nostril at its mucocutaneous junction. An 18 g blunt hypodermic needle connected via tubing and a 10 mL syringe is used to flush the system. Careful observation can usually distinguish the individual patency of the upper and lower lacrimal puncta during the injection of saline or sterile water. In cattle, nasolacrimal flushes are conducted under topical anesthesia and manual restraint of the animal’s head. Either the upper or lower lacrimal punctum is cannulated with an 18 g blunt hypodermic needle and a 10 mL syringe, and either saline or sterile water is used to flush the entire system. Visualization of the nasolacrimal system is possible in all animal species with dacryocystorhinography (Fig. 6.2). Observation of the system may be necessary when there is medically non-responsive or recurrent nasolacrimal sac or duct obstructions, or the possibility of nasal cavity masses. For dacryocystorhinography, general anesthesia of the patient and at least two radiographic views of the nasolacrimal system are necessary. A viscid cardiovascular radio-opaque solution (0.2–0.7 mL) is slowly injected into the upper lacrimal punctum in small animals and about 4–6 mL in foals and adult horses; 10–30 s later at least two radiographic views are taken. Dacryocystorhinography can detect irregularities in both the system’s diameter and course, and is generally most useful prior to consideration of surgeries of the lacrimal sac and nasolacrimal duct.

Nasolacrimal catheterization Nasolacrimal catheterization in the dog, cat, and horse consists of the placement of indwelling sutures or tubing spanning the upper or lower lacrimal punctum to the external nares for several days to a few months to help maintain patency. Nasolacrimal catheterization is indicated in patients with repeated obstructions of the nasolacrimal system (usually the nasolacrimal sac and duct), secondary to nasolacrimal duct atresia in foals, following lacerations of the upper nasolacrimal system (usually the lacrimal puncta

A

B

and canaliculi), and postoperatively after nasolacrimal system surgery. With the dog or cat under short-acting general anesthesia, a blunted (smooth melted end) 2-0 to 3-0 monofilament nylon suture is carefully inserted into the upper lacrimal punctum, upper canaliculus, lacrimal sac, and nasolacrimal duct to emerge from the external nares (Fig. 6.3a). The nylon suture can potentially become halted temporarily at the base of the lacrimal sac and at the accessory opening of the nasolacrimal duct immediately above the root of the upper canine tooth. Gentle turning and twisting of the suture can pass these barriers en route to the external nares. Once the nylon suture has traversed the system, PE 90 polyethylene, fine polyvinyl, or silicone tubing is slid over the entire length of the suture if a larger diameter cannula is preferred. The suture is removed leaving the tubing within the nasolacrimal system; both ends are attached by one or two simple interrupted non-absorbable sutures to the skin of the medial canthus and lateral of the external nares (Fig. 6.3b,c). In foals and adult horses, the entire nasolacrimal system from the upper or lower lacrimal punctum to its distal orifice can be easily traversed by a No. 5 French catheter. In some small animal patients only the nylon suture can be passed through the nasolacrimal system. Perhaps the lumen within the system is too restricted or swollen to permit passage of the larger diameter tubing. In these patients, the presence of the suture can still maintain the patency of the system. If the dog is lightly anesthetized, contact of the catheter in the distal nasolacrimal duct, perhaps at the accessory opening, may initiate sneezing. The system should remain in place for several days to a few weeks. Both topical solutions and systemic medications are usually administered with the nasolacrimal catheter in position. In general, an E-collar is necessary in small animals, or a face mask and stockinet in horses to prevent the animal from dislodging the ends of the nasolacrimal catheter. For sufficient and complete epithelialization of a new tear bypass, it is necessary for the catheter to remain in position for several weeks.

Surgical procedures for the nasolacrimal apparatus Surgical procedures for the nasolacrimal apparatus are divided into minor and major procedures. Minor procedures include surgical treatment of the imperforate punctum,

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Fig. 6.2 (a) Normal dacryocystorhinogram in the dog (lateral position): the canaliculi (A), nasolacrimal sac (B), and nasolacrimal duct (C). A secondary nasolacrimal orifice may be located immediately above the canine tooth (corner or third incisor). (b) Normal dacryocystorhinogram in the cat (lateral position). (c) Abnormal dacryocystorhinogram of a foal with atresia of the distal nasolacrimal duct (arrow). Note this ‘blind’ end of the nasolacrimal duct is considerably enlarged. (Reproduced with permission from Gelatt KN, Guffy MM, Boggess TS 1970 Radiographic contrast techniques for detecting orbital and nasolacrimal tumors in dogs. Journal of the American Veterinary Medical Association 156:741–746.)

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Fig. 6.3 Catheterization of the canine nasolacrimal system has both diagnostic and therapeutic advantages. Catheterization of the canine nasolacrimal system utilizes either a monofilament nylon suture or very small diameter silicone tubing. Both ends are sutured to adjacent skin. The system may remain in position for several weeks in ensure patency of the nasolacrimal system. (a) After deep sedation or short-acting general anesthesia, a 2-0 to 3-0 nylon suture is passed through the nasolacrimal system, starting at the dorsal lacrimal punctum. (b) Once the nylon suture has traversed the nasolacrimal system, 50 to 90 size polyethylene tubing is threaded down the suture. (c) Once completed, both ends of the tubing are transfixed to the adjacent skin by one or two simple interrupted non-absorbable sutures. An E-collar is recommended when the nasolacrimal catheterization is in place to prevent its dislodgement.

displacement of the lower punctum, enlargement of the lower punctum, lacerations of the canaliculi, and dacryocystotomy. The more extensive or major surgical procedures, which construct new avenues for the drainage of tears from the conjunctival fornix, include conjunctivorhinostomy, conjunctivomaxillary sinusotomy, and conjunctivoralostomy (or conjunctivobuccostomy). In the conjunctivorhinostomy technique, a tear drainage bypass is created into the caudal nasal cavity from the medial conjunctival fornix. In the conjunctivobuccostomy procedure, a subcutaneous tear drainage bypass is created from the middle of the ventral conjunctival fornix to terminate in the oral mucosa beneath the upper lip. These surgical procedures are indicated when the nasolacrimal system has been irreversibly damaged by inflammation, trauma, and neoplasia, and restoration of its patency is impossible in all animal species.

Surgery for imperforate lacrimal punctum Imperforate lacrimal punctum occurs in a number of breeds of dogs, but most frequently in the Toy and Miniature Poodles, Sealyham Terrier, American Cocker Spaniel, Golden Retriever, and Bedlington Terrier. Lower punctum obstructions are commonly presented because of epiphora. However, upper punctum obstructions do not generally produce clinical signs and are only detected as part of an ophthalmic examination. The imperforate lacrimal punctum should be distinguished from atresia of the puncta. In the imperforate lacrimal punctum, the opening of the punctum is covered by a thin veil of mucosa. Absence of the punctum indicates that the entire punctum is missing; with punctum absence the corresponding canaliculus is also missing. In my experience, imperforate lacrimal puncta are not infrequent in dogs, but atresia of the lacrimal puncta is rare. With the impaired drainage of tears with lower lacrimal punctum obstruction, excessive moisture and rust-colored staining of the medial canthal skin and hair are usually

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present (Fig. 6.4). Concurrent conjunctivitis is usually absent, but variable amounts of dermatitis of the eyelids and face may be present. Close inspection of the medial lower palpebral conjunctiva detects the absence of the lower lacrimal punctum. The topical fluorescein test is usually delayed or negative. The nasolacrimal flush performed through the upper lacrimal punctum exits from the nasolacrimal duct and external nares, but not through the lower punctum. Observation of the medial lower palpebral conjunctiva during the initial injection of saline may reveal a slightly raised or ballooned area during the initial flush that corresponds to the orifice of the lower punctum (Fig. 6.5a). The mucosa overlying the lower punctum may be excised, leaving an oval to round defect, or a cruciate incision may be performed in the area (Fig. 6.5b). The nasolacrimal flush is again performed to confirm patency. Topical antibiotic/ corticosteroid solutions are instilled six to eight times daily

Fig. 6.4 Young Miniature Poodle with unilateral imperforate lower lacrimal punctum. Note the epiphora and staining of the medial canthal hair.

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administered six to eight times daily to control the healing process and prevent fibrosis.

Displacement of the lower lacrimal punctum

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Fig. 6.5 With an imperforate lower lacrimal punctum, the upper lacrimal punctum is cannulated and flushed with sterile saline. (a) With the initial flush, the mucosa overlying the imperforate lacrimal punctum will bulge or tent, thereby indicating its position and the patency of the lower canaliculus. (b) Treatment of the imperforate lacrimal punctum is by excision of the mucosa over the lacrimal punctum orifice by small tenotomy scissors. Alternatively, the mucosa is incised in a cruciate manner. Topical antibiotics/ corticosteroids are instilled frequently for the next several days to maintain the lacrimal punctum orifice and to prevent the healing process from recovering the opening.

for 10–14 days to maintain patency and prevent the orifice wall from healing together. Intracanalicular gelatin implants may also be used to maintain the punctum’s patency.

Enlargement of the lower punctum Lower lacrimal micropuncta occur occasionally in the dog and result in epiphora. Scarring following conjunctival inflammation and trauma may also reduce the lower lacrimal punctum’s diameter and impair the drainage of tears. The fluorescein test will be delayed or negative. The nasolacrimal flush will indicate patency of the lower lacrimal punctum, but greater resistance to the flush. Treatment consists of surgical enlargement of the lower punctum. Under short-acting general anesthesia, the opening of the micropunctum is incised with the Bard–Parker No. 11 scalpel or Beaver No. 6500 or 6700 microsurgical blade (Fig. 6.6). The knife blade is slid further into the lower canaliculus, and an additional 3–5 mm of canaliculus wall is incised. Alternatively, the mucosa around the lower punctum is incised into three sections and excised. Postoperative treatment consists of topical antibiotics and corticosteroids

The lower punctum is normally situated 3–5 mm from the medial canthus and 1–2 mm bulbar of the eyelid margin in the palpebral conjunctiva. Displacement of the punctum occurs infrequently in the dog; in these patients the lower punctum is usually displaced several millimeters ventral of its normal position. The condition may be primary or secondary to entropion, ectropion, trauma, and scarring. Treatment for a displaced lower punctum is influenced by the extent and severity of epiphora, the associated dermatitis, and tear staining. Mild or intermittent epiphora is usually tolerated, and no surgical treatment is attempted. Patients with extensive medial canthal dermatitis and irritation require treatment. The fluorescein passage test is either delayed or negative. The nasolacrimal flush will indicate if the system is patent, but the lower punctum is failing to convey the normal volume of tears into the lower canaliculus. The recommended initial treatment is to dilate the displaced lower punctum and canaliculus to enhance the uptake of the tears. In the event that this fails, the displaced punctum can be relocated to its normal position or a new exit for tear drainage is constructed to the mouth, maxillary sinus, or nasal cavity. Transposition of the lower punctum, although minor surgery, requires magnification and cannulation of the punctum and canaliculus during surgery and for several weeks postoperatively. After general anesthesia and surgical preparation of the medial canthus, the lower punctum and canaliculus are cannulated with 2-0 to 3-0 monofilament nylon, and PE 90 polyethylene tubing is slid over the suture. The mucosa around the lower punctum is incised with the Beaver No. 6400 microsurgical blade. By dissection with tenotomy scissors, the lower canaliculus is isolated for approximately 5–8 mm. The lower punctum and canaliculus are moved to a small linear incision in the lower palpebral conjunctival mucosa, 1–2 mm deep in the eyelid margin. The monofilament suture or polyethylene tubing catheter is sutured to the medial lower eyelid and the skin caudal to the nostril. If the transplanted lacrimal punctum and canaliculus have some surrounding mucosa, at least three 6-0 simple interrupted absorbable sutures are placed about the punctum to secure it. If limited mucosa is available, sutures may adversely affect the punctum, and the cannula is critical to maintain the transplanted tissues in position. Topical antibiotics and corticosteroids as well as systemic antibiotics are administered for 7–10 days. The nasolacrimal catheter is removed after 3–4 weeks.

Lacerations of the canaliculi Fig. 6.6 Lower lacrimal micropunctum is associated with epiphora, but a patent nasolacrimal flush. The small size of the lower lacrimal punctum prevents the normal volume of tears entering the nasolacrimal system, and hence, the epiphora. Treatment of lower lacrimal micropunctum consists of enlargement of the orifice, beginning at the lower canaliculus with a 3–5 mm linear incision with the Bard–Parker No. 11 or Beaver No. 6500 blade. Alternatively, the periphery of the lower punctum orifice is incised into three sections and partially excised.

Most lacerations of the dog’s eyelids involve the lateral aspects; medial eyelid lacerations are infrequent. If the laceration affects the medial canthus, transection of the canaliculus is likely. Lacerations that involve the canaliculi, generally the lower, are usually in the vertical or somewhat angled plane. The torn eyelid is usually highly edematous; debris and hemorrhage may obscure the extent of the injury.

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Identification of the canaliculus is usually difficult but is enhanced during the injection of air either retrogradely from the nares or from the fellow nasolacrimal punctum. The exit of bubbles from within the lacerated lid can greatly facilitate localization and canalization of the severed canaliculus. Tissue destruction and resultant inflammation can markedly distort the area. After surgical preparation, the upper lacrimal punctum and canaliculus are cannulated with the gold lacrimal or 22–23 g stainless steel needle, and the system is flushed to locate the lower canaliculus. The distal portion of the lacerated lower canaliculus is usually difficult to locate because of tissue trauma and swelling. If both parts of the canaliculus can be identified and cannulated, the edges of the eyelid laceration are carefully apposed, usually in two layers. The nasolacrimal catheter of PE 50 to 90 polyethylene is manipulated over the suture through the system, tied, and sutured to the skin at the medial canthus and lateral to the nostril. Postoperative treatment includes topical and systemic antibiotics and corticosteroids. The nasolacrimal catheter is left in situ for 4–6 weeks. Frequency of topical therapy should be about six times daily. After most of the eyelid swelling has decreased, topical therapy is applied three to four times daily until the nasolacrimal catheter is removed.

Dacryocystotomy Surgical procedures of the canine and feline lacrimal sac are infrequent, as the sac is poorly developed, partially covered by the lacrimal bone, and caudal of the medial aspects of the orbicularis oculi muscle. Dacryocystitis is not infrequent in the dog. Foreign bodies, bacterial infections, and obstruction of the lacrimal sac characterize dacryocystitis. Occasionally a fistula may develop from the lacrimal sac onto the skin of the medial canthus (Fig. 6.7). Dacryocystitis usually responds to a combination of nasolacrimal flushes and antibiotic therapy. For recurrent dacryocystitis, nasolacrimal catheterization is recommended. In those patients that do not respond to these treatments, an exploratory dacryocystotomy for foreign bodies is recommended. The fluorescein passage test is usually negative; if a fistula is present, the dye may exit its distal opening. The nasolacrimal flush, normally through the upper lacrimal punctum,

Fig. 6.7 A dog with chronic dacryocystitis. Note the swelling of the medial lower eyelid and a fistula extending from the nasolacrimal sac onto the skin.

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usually indicates whether the system is plugged; if a fistula is present, the flush may exit this route. When additional pressure is applied during flushing, purulent material will often exit from the lower lacrimal punctum. Once the saline flush emerges freely from the lower lacrimal punctum, digital pressure is applied to the lower lacrimal punctum to redirect the flush through the lacrimal sac and nasolacrimal duct. Additional purulent exudates may emerge from the external nares. Fortunately, most nasolacrimal foreign bodies lodge in the lower canaliculus or nasolacrimal sac, and are expelled by nasolacrimal flushes from the upper lacrimal punctum. Occasionally a small serrated or 1  2 teeth Bishop–Harmon forceps is necessary to extract the foreign body. Post-flushing treatment is directed at combating infection, reducing inflammation, and maintaining patency. Broadspectrum antibiotics are administered topically and parenterally. Choice of antibiotics may also be altered by sensitivity tests. Most bacteria isolated from dacryocystitis in dogs are similar to those recovered from conjunctivitis, and include hemolytic and non-hemolytic Staphylococcus spp., Escherichia coli, Enterobacter spp., and alpha-hemolytic streptococci. Antibiotics in aqueous and non-irritating solutions can also be added to sterile saline during the nasolacrimal flush. Corticosteroids are infrequently used, but if the swelling is severe and the results of sensitivity tests guide the choice of antibiotics, anti-inflammatory agents may be helpful. To maintain nasolacrimal patency, either repeated nasolacrimal flushes or catheterization of the system may be necessary. In dacryocystotomy, the medial canthal and ventromedial lower eyelid regions are prepared for aseptic surgery. A PE 50 to 90 polyethylene catheter is inserted through either the lower or upper lacrimal punctum into the lacrimal sac. This catheter must be maintained in position to locate the lacrimal sac, and preserve the integrity of the cannulated lacrimal punctum and associated canaliculus. The lacrimal sac is located in a fossa in the lacrimal and frontal bones, posterior to the lacrimal crest (Fig. 6.8). A 2–3 cm skin incision is made parallel to the lower eyelid

Fig. 6.8 The nasolacrimal sac is located in a fossa in the lacrimal and frontal bones (arrow), posterior to the lacrimal crest. As the nasolacrimal sac is not well developed in the dog, a polyethylene catheter inserted into the lower lacrimal punctum, lower canaliculus, and into the nasolacrimal sac facilitates its location.

Surgical procedures for the nasolacrimal apparatus

margin along the ventromedial orbital rim. By blunt–sharp dissection, the subcutaneous and periorbital tissues are penetrated to reach the lacrimal bone. The nasolacrimal catheter can be palpated as it enters the lacrimal sac within the lacrimal fossa, about 5 mm ventral of the orbital rim. A 3 mm bone burr is used to drill a hole in the lacrimal bone and into the lacrimal sac. Once the lacrimal sac is entered, flushing from the nasolacrimal catheter will enter the freshly drilled hole. Any foreign body and other material can be removed from the lacrimal sac. Closure consists of 4-0 simple interrupted absorbable sutures of the periosteum of the lacrimal bone, the periorbita, and the subcutaneous layer of the eyelid. Skin apposition is by 4-0 simple interrupted non-absorbable sutures. The nasolacrimal catheter is retained in the system for 14– 21 days to maintain patency as the nasolacrimal sac wall is not apposed by sutures, and to ensure delivery of topical antibiotics to the area. Systemic antibiotics are also recommended because contamination of the surgical site occurs once the lacrimal sac is opened and irrigated.

Conjunctivorhinostomy (caudal nasal cavity) With congenital and acquired loss of the different parts of the nasolacrimal system, an alternative route can be constructed surgically to prevent epiphora and to drain the tears directly into the nose or oral cavity. The continuous presence of tears at the medial canthus and adjacent skin frequently results in medically uncontrollable chronic dermatitis, rust-colored changes in the hair, and pruritus. Alternative routes that can be constructed surgically in small animals for the tears to exit the ventral conjunctival fornix include the caudal nasal cavity, the maxillary sinus, and the mouth (Fig. 6.9). Fortunately, atresia of the distal nasolacrimal duct in young horses is usually within the area of the nostril, and can be reached through the nostril. In conjunctivorhinostomy, a permanent fistula is constructed surgically to extend from the medioventral conjunctival fornix to the nasal cavity or maxillary sinus (often termed conjunctival maxillary sinusotomy). Over time, this

Fig. 6.9 When the nasolacrimal system has been permanently damaged, alternative routes for exit of the tears can be constructed surgically to enter the posterior nasal cavity or maxillary sinus (conjunctivorhinostomy), or the mouth (conjunctivobuccostomy). The approximate sites for entry into the caudal nasal cavity (A) and maxillary sinus (B) are depicted on the canine skull.

surgical fistula is eventually lined with mucous membrane while its patency is maintained by an indwelling catheter. Polyethylene (3 mm outside diameter) or silicone tubing can be constructed to fit in the fistula, and maintain patency during healing. Polyethylene tubing is more rigid and when exposed to heat will flare to form an 8  1.4 mm flange which can be attached by sutures to adjacent tissues. Silicone tubing is more flexible, but sometimes cannot be manipulated into confined areas without buckling. To add a flange to the silicone tubing, special silicone glue is necessary to attach the silicone sheeting fashioned into any shape and size. For this procedure, the stiffer polyethylene tubing is clearly superior. The polyethylene tubing (40 mm long), with the heat-produced flange on its proximal end and a beveled end, protrudes into the nasal cavity. Premature loss of the indwelling catheter and its non-replacement will usually result in closure of the surgical fistula and failure of the surgery. After surgical preparation of the medial canthal region, an incision is made in the area of the caruncle at the base of the nictitating membrane. With blunt dissection of the ventromedial orbital rim periorbita, the periosteum is isolated for approximately 3–4 mm. The periosteum and maxillary bone are incised with either a trephine or progressively larger Steinmann pins to enter the nasal cavity. Entry into the nose usually produces variable amounts of hemorrhage. After the tract has been flushed and cleared of debris, a 40 mm length of polyethylene tubing, positioned about the malleable probe, is manipulated into position. If the tubing tends to protrude after placement, it is probably in contact with the nasal floor or medial septum and should be shortened. At least three non-absorbable sutures are used to anchor the proximal end of the tubing to the conjunctival mucosa and medial canthus. After anchoring of the indwelling catheter, a final flush with sterile saline should indicate its patency and position within the posterior nasal cavity. Postoperative therapy consists of topical and systemic antibiotics and topical corticosteroids for 5–7 days. An E-collar, while annoying, is valuable to maintain the catheter in place for as long as possible. The tubing should remain in situ for at least 2 months to permit epithelialization of the fistula. Topical antibiotics once or twice daily are useful. If the tubing becomes plugged, flushing with 0.9% sterile saline solution is used to re-establish patency. Possible complications after this procedure include tube displacement and loss, closure of the fistula, mucous membrane overgrowth, and increased epiphora. The success rate of this method is 85–90%. Maintenance of the tubing during the time of permanent fistulization is critical; premature loss of the tubing generally requires placement of another as soon as possible and before the fistula heals closed. Conjunctivorhinostomy is less successful in cats as the fistulas tend to close eventually. The indwelling catheter should be left in the cat for as long as possible.

Conjunctival maxillary sinusotomy (into the maxillary sinus) Another method developed for the dog constructs a buccal mucosa tunnel that extends from the medial lower conjunctival fornix through the subcutaneous tissues and the

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maxilla to enter the maxillary sinus. Patency of the buccal tunnel is maintained by 4 cm long indwelling polyethylene tubing (PE 50 to 90) for several weeks. The buccal mucosa tunnel is constructed from a freshly harvested 15  20 mm section of buccal mucosa. A polyethylene tube is threaded through its lumen to maintain its shape and facilitate handling. After surgical preparation of the lower eyelid and area over the maxillary sinus, a skin incision is made 1 cm lateral of the medial canthus for 3 cm to the area over the maxillary sinus. Once over the maxillary sinus, the periosteum is reflected and an 8–10 mm trephine is used to enter the maxillary sinus. The buccal tunnel is positioned between the conjunctival fornix and maxillary sinus, and its ends secured. Simple interrupted absorbable sutures are used to attach the proximal buccal tunnel to the conjunctival mucosa and submucosa, and the distal end of the tunnel to the maxillary sinus mucosa and periosteum. The skin incision is apposed with simple interrupted non-absorbable sutures. Postoperative management after this method is identical to the earlier procedure. Maintenance of the indwelling catheter within the buccal tunnel for several weeks is critical for its success.

Conjunctivobuccostomy An alternative to conjunctivorhinostomy, conjunctivobuccostomy is technically easier because the facial bones are not involved. In this procedure, a subcutaneous tunnel is constructed from the middle part of the lower conjunctival fornix to the upper fornix of the upper lip (Fig. 6.10). A buccal mucosa tunnel can be constructed and positioned between the two fornices. A long-term indwelling catheter of polyethylene tubing must also be constructed and maintained within the subcutaneous buccal tunnel to maintain patency as the surgical bypass epithelializes. An alternative method is to insert a long-term indwelling polyethylene catheter, anchored securely in the conjunctival and buccal fornices, and allow for epithelialization to occur. Postoperative management is identical to the two previous procedures.

ADAPTATIONS IN LARGE ANIMALS AND SPECIAL SPECIES

Nasolacrimal obstructions in large animals Nasolacrimal obstructions are in frequent in horses. In foals and young horses, atresia of the distal nasolacrimal duct and nasal punctum manifests as epiphora, chronic reflex conjunctivitis, and a prominent bulge in the distal nasolacrimal canal, fortunately accessible through the nostril. Other surgically treated diseases are lacrimal punctum atresia, and more generalized nasolacrimal duct agenesis. Dacryocystitis is infrequent in adult horses, and is usually associated with chronic obstruction and bacterial infection of the lacrimal sac and chronic reflux conjunctivitis. Dacryocystorhinography is an excellent diagnostic procedure for nasolacrimal obstruction in horses and cattle.

Distal nasolacrimal duct atresia in foals and young horses This surgery can be performed in the sedated and standing foal, but may involve less time if general anesthesia is used. The bulging area of the distal nasolacrimal duct (basically a blind pouch) is cleaned with surgical soap and rinsed with 0.5% povidone–iodine (Fig. 6.11a). The entire nasolacrimal system is catheterized through the upper lacrimal punctum with silicone tubing, polyethylene tubing, or a No. 40 French catheter so that the catheter tip can be palpated in the ‘blind’ pouch. The top of bulge is incised by scalpel; considerable hemorrhage may result and is controlled by surgical sponges and direct pressure. The wound is left open to heal with the catheter in position to ensure patency. Both ends of the catheter are secured by non-absorbable sutures to the medial canthus and upper nostril respectively (Fig. 6.11b). The entire area is covered by stockinet and a mask with a hard cup to reduce rubbing and protect the indwelling catheter for several weeks. Topical antibiotics/ corticosteroids are administered daily for several days. In absence of the lower nasolacrimal system, canaliculorhinostomy can be performed in the horse.

Nasolacrimal duct obstructions in cattle

A Fig. 6.10 In conjunctivobuccostomy the tears drain from the lower conjunctival fornix through a subcutaneous fistula into the mouth. (a) A subcutaneous tunnel of buccal mucosa is constructed to span the ventral conjunctival fornix to the dorsocaudal buccal area. (b) To maintain patency of this new buccal mucosa tunnel, a custom-constructed polyethylene tubing is left in situ for several weeks as shown in this immediate postoperative appearance after conjunctivorhinostomy in a cat. The silicone tubing has been inserted in the new surgical fistula into the nasal cavity, and must remain in position for several weeks for epithelialization of the fistula.

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Nasolacrimal obstructions are rare in cattle. Dacryocystorhinography should precede any surgery for either the lacrimal sac or nasolacrimal duct in cattle. Conjunctivorhinostomy has been reported in cattle, providing passage for tears from the front of the caruncle through the lacrimal bone and ventral nasal concha into the ventral nasal meatus. A section of polyethylene urinary catheter is positioned within the fistula (ends are secured to the medial canthus and nostril) and maintained for several weeks.

Nasolacrimal duct obstructions (extracorneal bullous spectaculopathy) in snakes In snakes and certain lizards the cornea is protected by a transparent spectacle formed by fusion of the eyelids during embryonic development. The tears, formed by the

Nasolacrimal duct obstructions (extracorneal bullous spectaculopathy) in snakes

Fig. 6.11 Atresia of the nasolacrimal duct in the foal. (a) The blind end of the distal nasolacrimal duct is usually visible and accessible just caudal of the mucocutaneous junction on the floor of the nostril. (b) After a simple incision of the top of this ‘blind end’ of the nasolacrimal duct, silicone or polyethylene tubing is positioned within the entire nasolacrimal system for several weeks to maintain the healing distal orifice patent, and secured by skin sutures at both ends or simply tied together. A stockinet is placed over the face to prevent dislodgement of the catheter until removal.

Harderian gland, enter the subspectacular and precorneal space to drain via the lacrimal duct into the mouth or the duct of Jacobson’s organ within the mouth. Obstruction of the lacrimal duct, usually at the level of the roof of the mouth, results in accumulation of tears with enlargement of the subspectacular space and swelling of the spectacle that mimics enlargement of the eye and glaucoma (pseudobuphthalmos). Development of the lacrimal duct occlusion and distention of the spectacle is usually acute. Occlusion of the lacrimal duct usually results from pressure or scarring from tumors and granulomas, and oral lesions, usually grouped together as ulcerative and/or necrotic stomatitis, and inflammations of Jacobson’s organ (Fig. 6.12). With obstruction of the lacrimal duct and ascending infections from the mouth, a septic process can develop within the subspectacular space. Pseudomonas spp., Proteus spp., and

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Providencia rettgeri, commonly isolated from oral infections, can also be recovered from the subspectacular fluids. Flagellates can also be recovered; their role in the development of subspectacular infection is unknown. With subspectacular infections, the spectacle loses its clarity, and may develop ulcerations and bullae. Fluorescein can be injected carefully into the subspectacular space to demonstrate patency or obstruction of the lacrimal drainage apparatus. Treatment of the condition is essential to prevent infection of the cornea and intraocular tissues, and damage to the spectacle. The subspectacular space can be aspirated and injected with low concentrations of antibiotics. In severe cases, a significant section of the spectacle has been excised, but the exposed cornea must be medicated daily with ophthalmic antibiotic ointments until the next shedding of the skin or ecdysis occurs.

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Fig. 6.12 Nasolacrimal (lacrimal) duct obstructions (a) and ascending oral infections (b) in snakes are characterized by enlargement of the subspectacular space with tears and inflammatory debris and swelling of the spectacle as well as the oral infection. Initial treatment consists of aspiration and culture and cytology of the subspectacular fluids, and treatment of any infections. (c) Sometimes partial removal of the spectacle is also necessary.

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Another effective method is excision of a small 30 wedge of the ventral spectacle that permits sampling of the tears for possible pathogens, and an entry for repeated flushing and treatment of the condition. With the next shedding, the spectacle integrity will be restored. Examination of the mouth and treatment of ulcerative and necrotic stomatitis with parenteral systemic antibiotics are also indicated to prevent recurrence of the lacrimal duct obstruction. Conjunctivoralostomy has also been performed in snakes, using a curved 18 g hypodermic needle to create a fistula between the inferior fornix of the subspectacular space and the roof of the mouth. Patency during healing is maintained by a catheter 0.635 mm in diameter sutured to the roof of the mouth and ventral periocular scales with 5-0 sutures (absorbable in the mouth and silk for the skin). Because of the importance of Pseudomonas species in oral infections and infected subspectacular tissues in snakes, systemic and topical gentamicin are administered postoperatively.

SURGERY FOR KERATOCONJUNCTIVITIS SICCA Diseases of the tear-secreting glands are demonstrated by reduction in tear production, changes in the preocular (precorneal) film, and secondary keratoconjunctivitis. Tears are composite secretions with oily, aqueous, and mucoid portions. The lacrimal gland, the superficial gland of the nictitating membrane, and any accessory lacrimal glands within the conjunctiva produce tears. In the dog, excision of either the lacrimal or the nictitans gland does not result in clinical disease, i.e., keratoconjunctivitis sicca (KCS), or significant changes in the Schirmer tear test 1. However, the Schirmer tear test 2, conducted under topical anesthesia, indicates a lower level of basal tear production. In dogs, the surgical loss of both glands results in keratoconjunctivitis sicca. Surgical studies in the dog suggest that the lacrimal gland provides about 60–75% of the total tears, and the superficial gland of the nictitating membrane 25–40%. Diseases of the nictitating membrane tear gland, such as ‘cherry eye’ or a prolapsed and inflamed gland, can predispose the same eye to keratoconjunctivitis sicca at a later time (even if treated successfully by surgical replacement of the gland). Keratoconjunctivitis sicca occurs most frequently in the dog; it is infrequent in cats, and is rare in horses and cattle.

Surgical anatomy Tear production in animals results primarily from two glands. The lacrimal gland is located in the periorbital fascia dorsolateral to the globe and immediately beneath the lateral orbital ligament and zygomatic arch in the dog and cat. The superficial gland of the nictitating membrane is the smaller tear-producing gland, and surrounds the lower aspects of the base of the cartilage of the third eyelid. While the tears from the lacrimal gland flow ventral and medial to the nasolacrimal drainage apparatus, the tears produced by the superficial gland of the nictitans are probably mixed and distributed across the cornea and conjunctiva by a combination of movements by the nictitating membrane and upper eyelid. Movements of the lower eyelid are limited, and it appears that the lower eyelid and conjunctival fornix mainly

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serve as the collecting ‘pool’ for the tears en route to the ventromedial conjunctival fornix and the lower lacrimal punctum. In humans, accessory tear glands within the conjunctiva, the glands of Krause and Wolfring, have not been identified in animals, and may have been consolidated through evolution into the single gland of the nictitating membrane. Both the lacrimal gland and superficial gland of the nictitating membrane have considerable cholinergic and adrenergic nerve endings. The adrenergic nerve endings are associated with the blood vessels and are probably involved in local regulation of blood flow. The cholinergic nerve endings are mainly around the acini in both glands. Experimental electrical stimulation of the lacrimal nerve in cats results in marked increases in the rate of tear formation. The superficial gland of the nictitating membrane in the dog may be the analog for the accessory lacrimal glands in humans. Studies in the dog suggest that tear production may differ from that of humans in that both tear glands appear to contribute to the basal and reflex portions of tear formation. The lacrimal gland contributes about 60–75% of the total tear volume; the superficial gland of the nictitating membrane contributes 25–40%. As a reasonable substitute for tears, saliva from the parotid gland is well tolerated by the cornea and conjunctival surfaces in humans, dogs, cats, and horses. Parotid secretions are continuous, but of much larger quantities during eating. The parotid gland is located caudal to the mandible with its duct emerging from its base. The origin of the parotid duct consists of several small ducts that converge to form one large duct at the base of the gland and a single duct that passes forward external to the masseter muscle. The parotid duct is closely attached to the external masseter fascia, and separation of the two structures during surgery is sometimes quite tedious. In most breeds of dogs the course of the parotid duct is straight from the base of the parotid salivary gland to its papilla. However, in brachycephalic breeds, the course of the parotid duct is less predictable, and often tends to be quite ventral of its usual straight course. The parotid duct is medial to and between the dorsal and ventral buccal divisions of the facial nerve in the dog (Fig. 6.13). The duct usually appears pink–white, whereas the nerve branches are white. Cannulation of the parotid duct with either green or blue monofilament nylon greatly aids in its identification and prevents confusion with either of the dorsal and ventral buccal nerves during surgery. The parotid duct terminates in a papilla located immediately caudolateral to the carnassial tooth. In this area the buccal nerves and facial vein usually have multiple branches that complicate the final phase of parotid duct dissection. The parotid duct often extends 0.5–1 cm submucosally before it enters the papilla. The papilla of the parotid duct should not be confused with the one or more papillae of the zygomatic salivary gland in the dog. The anatomy of the parotid gland and duct in the cat is very similar to the dog but smaller (Fig. 6.14). The papilla of the parotid duct enters the cat’s mouth immediately adjacent to the last premolar tooth. The parotid duct can be cannulated with 4-0 monofilament nylon in cats. The dorsal and ventral buccal nerves are more distant to the parotid duct, but converge just before the anterior facial vein and before the duct terminates in its papilla.

Surgical anatomy

Surgical treatment of acute keratoconjunctivitis sicca (KCS) The treatment of acute KCS includes medical or surgical management, or a combination of both, and should be considered an ophthalmic emergency. Medical therapy of acute KCS includes topical tear substitutes as well as stimulation of existing tear formation to increase moisture to the external eye. Antibiotics are administered to suppress or eliminate opportunistic bacteria. Surgical procedures for acute KCS include bulbar and palpebral conjunctival grafts as well as nictitating membrane flaps to manage the rapid and often progressive corneal ulceration of acute KCS. These surgical procedures will be presented in Chapter 7.

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Fig. 6.13 The major anatomic landmarks and surgical considerations for parotid duct transposition in the dog from the original drawing by Lavignette (1966). During surgical dissection of the parotid duct (1), the facial vein (2), the dorsal buccal nerve (3), and the ventral buccal nerve (4) should be identified. A skin biopsy punch or corneal trephine is used to incise the parotid duct papilla in the mouth (5). A small hemostat is inserted through the ventrolateral conjunctival fornix and a subcutaneous tunnel to pull the parotid duct into the fornix for apposition. (Reproduced with permission from Lavingnette AN: 1966 Keratoconjunctivitis sicca in a dog treated by transposition of the parotid salivary duct. Journal of the American Veterinary Medical Association 148: 778–786.)

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Fig. 6.14 Surgical anatomy for parotid duct transposition in the cat. As in the dog, the feline parotid duct (A) traverses anteriorly external to the masseter muscle and between the dorsal (B) and ventral (C) buccal nerves. As the distal end of the duct and papilla are approached, several small branches of the facial vein are encountered. (Reproduced with permission from Gwin RM, Gelatt KN, Peiffer RL 1977 Parotid duct transposition in the cat with keratoconjunctivitis sicca. Journal of the American Animal Hospital Association 13:42–45.)

Surgical treatment of medically nonresponsive chronic keratoconjunctivitis sicca by parotid duct transposition in dogs and cats In those patients that have failed to respond to medical treatment for chronic KCS, parotid duct transposition to substitute saliva for tears is recommended (Fig. 6.15). Trial medical therapy with topical cyclosporin A twice daily should span at least 2–3 months with repeated monitoring with the Schirmer tear test to detect any improvement in tear secretion. Topical treatment with antibiotics and corticosteroids is also continued during this time. Surgical or electrocautery ablation of the lower lacrimal punctum or insertion of lower punctal occluders in the dog to conserve existing tears has not been successful because the level of tear production is too low. Reduction in the size of the palpebral fissure with lateral canthoplasty, partial permanent tarsorrhaphy, or other methods to conserve the existing moisture have not been useful in the dog because most KCS patients have little, if any, tear production. The dog and cat must be evaluated for parotid function before surgery. The gland and duct should be palpated for abnormalities. The papilla of the parotid duct immediately adjacent to the caudal aspect of the carnassial tooth should be inspected, and saliva flow should be observed. Parotid gland function can be tested by applying a few drops of 1% atropine ophthalmic solution to the patient’s tongue. Profuse salivation should follow, associated with the bitter taste of atropine.

Fig. 6.15 Chronic keratoconjunctivitis sicca in an American Cocker Spaniel. The eye is characterized by a completely pigmented cornea and copious mucopurulent conjunctival exudates. The condition, not respondent to either long-term topical cyclosporin A or oral pilocarpine, is recommended for parotid duct transposition.

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Parotid secretion has many similarities to tears and is nonirritating to the eye. Canine KCS patients with parotid duct transpositions lasting over 7 years have not exhibited corneal irritation to parotid secretions. Parotid duct transposition was first reported in experimental dogs in 1959 in Japan; the first description of this procedure for the management of canine KCS was in 1966. Since then, several veterinary investigators have reported slight modifications of the original surgical procedure, postoperative results, and complications. Parotid duct transposition can also be performed in cats, using the same surgical procedure and clinical management.

Surgical procedure The parotid duct can be approached by either the oral or lateral route. The lateral approach is preferred because of better exposure, less potential for transection of the duct, and septic contamination of the incision from the mouth is markedly reduced. The oral approach was developed initially in humans to avoid any facial skin incision and resultant scar. After general anesthesia and surgical preparation of the eyelids and lateral face, the papilla of the parotid duct is identified near the base (ventrolateral) of the upper carnassial tooth. Care must be taken not to confuse it with the papillae of the ducts of the zygomatic salivary gland, which open near the gingival border above the last molar tooth. A 2-0 to 3-0 monofilament nylon suture, with the tip flamed to ‘blunt’ it, is passed into the parotid duct papilla. The suture can often be observed and felt moving beneath the skin as it passes caudally in the parotid duct to the gland. Two methods have been used to incise the papilla and rostral parotid duct. The mucosa can be incised and a round to oval portion of mucosa removed with the papilla. With this method, dissection can be difficult and excessive buccal mucosa may be excised. An alternative oral approach using a 6 mm biopsy punch or corneal trephine is recommended (Fig. 6.16a). After the mucosal incision around the parotid duct papilla and placement of the suture cannula, a 0.5% povidone–iodine soaked gauze sponge is positioned in the mouth to provide at least some disinfection in the area. After draping of the area directly over the entire length of the parotid duct and the eye, the position of the nylon suture in the duct is again palpated through the skin. A skin incision is made along the duct through the skin and superficial facial muscles to expose the duct (Fig. 6.16b,c). The parotid duct is very carefully dissected from the superficial fascia of the masseter muscle, and retracted by suture or muscle hook to avoid excessive trauma to the duct (Fig. 6.16d–f). The duct is dissected free posterior to the angle of the mandible or where the duct begins to divide into smaller ductules immediately rostral to the base of the parotid gland to provide adequate length for the duct’s relocation to the lateral conjunctival fornix (Fig. 6.16g). Separation of the parotid duct from the masseter muscle is continued rostrally; one must avoid the facial vein and the anastomotic nerve branch between the dorsal and ventral buccal nerves. Near the buccal mucosa, the parotid duct usually continues for about 0.5–1 cm submucosally before terminating in the papilla adjacent to the carnassial tooth.

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The lip is raised and the gauze sponge removed. The mucosa should not be penetrated beyond the submucosa. The papilla and surrounding 3 mm radius of mucosa are dissected free, and the papilla and parotid duct are retracted back into the initial external incision. The oral incision is apposed with 2-0 to 4-0 simple interrupted absorbable sutures. All instruments used within the mouth are set aside, and the surgeon should reglove. With a small straight hemostat or mosquito forceps, a subcutaneous tunnel is constructed to the lateral conjunctival fornix, superficial to the masseter muscle and the zygomatic arch. Pressure is applied until the instrument’s tips appear subconjunctivally and the overlying conjunctiva is incised. An alternative method is to excise a 2–3 mm diameter conjunctival plug. The mosquito forceps, placed within the subcutaneous tunnel, is used to grasp the edge of the mucosa with the papilla and carefully draw the duct to the conjunctival fornix (Fig. 6.16h). The mucosa about the papilla is trimmed, if excessive, and is sutured to the adjacent conjunctiva with at least three to four 6-0 simple interrupted absorbable sutures (Fig. 6.16i). The facial skin exposure is closed. Interrupted 2-0 to 4-0 absorbable sutures are used to reduce the ‘dead space’ between the subcutaneous tissues and the masseter muscle. The skin is apposed with simple interrupted 3-0 or 4-0 nonabsorbable sutures (Fig. 6.16j,k).

Oral approach for parotid duct transposition in dogs The oral approach for parotid duct transposition is an alterative method and was developed in humans to omit the postoperative skin incision and scarring. In this procedure, the initial step is to remove the oval mucosal plug with the papilla and then, by blunt–sharp dissection, free the duct from its masseter fascial attachments. A tunnel from the conjunctival fornix is formed from the ventrolateral conjunctival fornix with a mosquito forceps, and the mucosa and papilla are transposed to the conjunctival sac. The papilla of the parotid duct is apposed as in the previous method, and the oral incision is closed with 3-0 to 4-0 simple interrupted absorbable sutures.

Postoperative management and results Postoperative care after parotid duct transposition includes topical antibiotics and corticosteroids four to six times daily and systemic antibiotics for 7–10 days. If considerable facial edema occurs postoperatively, diuretics are useful. Gentle massage and occasional warm compresses to the surgical site help reduce the subcutaneous swelling and enhance duct function between meals. The skin sutures are removed in 7–10 days. Parotid duct function should be exhibited on the first postoperative day, with epiphora during snacks or meals. A drop of 1% atropine ophthalmic solution applied to the tongue can be used to check for duct patency, as well as to flush the debris associated with the trauma of surgery and cannulation from the duct or its papilla (or both). Parotid secretions may occasionally be intermittent, perhaps associated with subcutaneous facial edema, minor damage, or irregularities along the path of the duct. When the skin

Surgical anatomy

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Fig. 6.16 For parotid duct transposition in the dog, the parotid duct is cannulated with blue or green 2-0 to 4-0 monofilament nylon inserted into the papilla. (a) The mucosa around the papilla of the parotid duct (immediately adjacent to the carnassial tooth) is incised with a 4 mm skin trephine, and cannulated with a 2-0 monofilament nylon suture to facilitate its identification during the lateral surgical approach. (b) The skin incision is made directly over the cannulated duct, which can often be palpated. (c) The dotted line is the site for the skin incision directly along the parotid duct. (d) After the skin is incised, the parotid duct is carefully dissected from its deeper masseter muscle attachments, and differentiated from the dorsal and ventral buccal nerves. (e) Intraoperative photograph with the cannulated parotid duct (with blue nylon suture) exposed. A branch between the dorsal and ventral buccal nerves is external to the parotid duct and in the center of the surgical field. (f) The parotid duct is carefully separated from the fascial attachments to the masseter muscle from the base of the parotid gland to its distal opening into the mouth. (g) Intraoperative photograph showing the parotid duct papilla retracted into the lateral incision. The duct is routed subcutaneously to the lateral or ventrolateral conjunctival fornix (using a straight hemostat forceps). (h) The dissection is continued rostrally to the parotid duct papilla which may be incised from the surgical site, thereby freeing the entire parotid duct. A small hemostat is directed from the lateral ventral conjunctival fornix into the surgical site to protract the parotid papilla and duct for apposition to the conjunctival mucosa. (i) A lateral canthotomy can assist in the exposure of the lower conjunctival fornix. At least three 6-0 simple interrupted absorbable sutures are used to appose the parotid papilla mucosa to the conjunctival fornix. (j) Closure after parotid duct transposition consists of reduction of the dead space between the masseter muscle and the subcutaneous tissues with simple interrupted absorbable sutures, and apposition of the skin with simple interrupted non-absorbable sutures. The lateral canthotomy is apposed with simple interrupted non-absorbable sutures. (k) Immediate postoperative appearance after apposition of the parotid duct papilla to the conjunctival mucosa with three to five 5-0 to 6-0 simple interrupted absorbable sutures.

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sutures are removed, parotid duct function, as evaluated by the appearance of the eye and increased values of the Schirmer tear test, should be stabilized. Epiphora is usually evident only during eating. If the moisture to the eye is inadequate between meals, oral pilocarpine therapy is again initiated. After chronic KCS and successful parotid duct transposition, benefit to the eye becomes rapidly apparent. Corneal vascularization and pigmentation gradually decrease. Conjunctival exudates gradually decrease; their character changes from mucopurulent to seromucoid (Fig. 6.17). The surgical success rate of parotid duct transposition in the dog is high. Most investigators report 85–95% success rates with case follow-ups for as long as 5 years. Following surgery, patients with parotid duct transposition should be re-examined every 6 months.

Postoperative complications Most of the immediate postoperative surgical complications are related to the parotid duct’s small size. Transection and twisting of the parotid duct are obvious operative failures. Torsion of the duct greater than 180 may be manifested by intermittent, reduced, or absent secretions. Infections of the surgical wound after parotid duct transposition are rare, due to pre- and postoperative treatment with topical and systemic antibiotics. Absence of parotid secretions after a successful uncomplicated surgical technique and preoperative confirmation of parotid gland function for 3 or more days following surgery merits immediate surgical investigation. Postoperative focal stenosis of the parotid duct can occur in 1–8 weeks, associated with fibrosis. Parotid secretion is reduced or absent. To facilitate determination of the site of

Fig. 6.17 Miniature Schnauzer dog with bilateral parotid transposition of 3 years’ duration. Signs of the bilateral keratoconjunctivitis sicca have disappeared, and the dog is visual.

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obstruction, the surgeon may dilate the parotid duct proximal to the area of obstruction. Correction by careful removal of the fibrotic tissues surrounding the duct can be successful. Lack of parotid gland function can usually be detected preoperatively; loss of function postoperatively can be correlated to duct obstruction with subsequent pressure atrophy of the gland. The parotid gland may also undergo atrophy, perhaps associated with a generalized condition affecting all glandular tissues. About 10–20% of dogs with KCS also have xerostomia and are not candidates for parotid duct transplantation. Excessive saliva may be a problem in some dogs, but fortunately this is infrequent. In a few patients, ligation of smail branches of the parotid duct may eventually be necessary. In humans, partial resection of the parotid salivary gland has been performed to remedy this problem; however, it has not been reported in the dog, but seems possible. Expansion of the tear drainage apparatus is another possibility. Inadequate length of the parotid duct is not usually a problem in dogs, in contrast to humans. Elongation of the parotid duct by 1–2 cm can be achieved by construction of a tunnel of mucosa about the parotid duct papilla. Alternatively, dissection about the base of the parotid gland and rostral displacement can provide a marginal length parotid duct with several extra millimeters. White crystal-like precipitates occur infrequently postoperatively, but may occur more often than when parotid duct procedures were first performed in dogs. At the present time, the development of these crystals in dogs is the most frequent and often serious postoperative complication. Scrapings of these precipitates, as viewed by light microscopy, dissolve quickly in 0.5–1.0% EDTA solutions. These precipitates appear to be calcium carbonate, phosphate, oxalate, or a combination thereof. The precipitates occur on the corneal surface, conjunctivae, and nictitating membrane, and even adhere to the eyelid skin and hair, giving a ‘frosted appearance’ (Fig. 6.18).

Fig. 6.18 Occasionally after parotid duct transposition in the dog, precipitates of calcium oxalates, phosphates, and carbonates may form on the corneal and conjunctival surfaces, and even on the eyelid hair, giving a frosted appearance. These precipitates dissolve in 1% or 2% EDTA ointment, but once incorporated into the cornea or beneath the corneal epithelium do not usually respond to EDTA therapy. These precipitates seem associated with high rates of parotid secretion, and medical and/or surgical attempts to reduce the salivation rates may be beneficial.

Adaptations in large animals and special species

It appears that these precipitates are related to a high rate of parotid gland secretion: the higher the rate of parotid saliva formation, the higher the concentrations of these substances, and the greater the likelihood of their formation. If the cornea is ulcerated or has not epithelialized following a superficial keratectomy, deposition of this white material may be extensive. Use of 0.5% EDTA as a solution with a rinse cap, or preferably a 0.5–1.0% ointment, provides partial but not total removal of the precipitates. Frequent use of commercial eye washes with EDTA may also assist. Placement of the dog on a diet low in minerals for 1–2 months before parotid duct surgery, and maintenance thereafter, has been another approach. Surgical approaches to reducing the volume of salivary secretions are also possible and include: 1) a loose ligature using a non-absorbable suture along the middle of the transposed parotid gland’s duct; or, preferably, 2) two or three ligatures of accessory or feeder ducts at the level of the parotid gland. Both methods have successfully reduced the levels of salivary secretion, improved comfort, and reduced the amount of ocular irritation, but still maintained adequate Schirmer tear test levels. In addition, both methods can be repeated to lower further salivary secretion levels, if necessary.

Adaptations in large animals and special species The secretory abilities of the parotid gland vary by species. In ruminant species, parotid gland secretions are of very large quantities (as much as 50 L daily), and are critical to their rumination cycle and gastrointestinal function. Fortunately in the horse, the parotid salivary gland appears more limited in function and volume, rendering it useful for

surgical therapy of medically non-responsive keratoconjunctivitis sicca in horses. The horse parotid gland is still larger than its counterpart in ruminants, but apparently actively secretes only during chewing (the ruminant parotid gland continuously secretes).

Parotid duct transposition in the horse The parotid gland is located at the base of the ear, caudal to the mandible. The parotid duct arises from the combination of several collecting ductules at the base of the gland, and courses rostrad parallel to the facial vein. It continues anteriorly ventromedial to the mandible, and turns dorsally to pass the lateral mandible across the mandibular notch. Within this notch, the combination of the parotid duct, facial artery and vein can be palpated. From this notch, the parotid duct continues between the facial vein and masseter muscle to enter the oral cavity via a small papilla lying opposite the third cheek tooth. The surgical technique is modified from the dog and cat, by starting with a skin incision extending ventrally from the mandibular notch along the ventral aspect of the mandible to the base of the parotid duct. The parotid duct is identified and isolated from the base of the gland to within 4 cm of its oral papilla. Once adequate length is obtained, the duct is transected 4 cm from its papilla, and inserted through a subcutaneous tunnel to enter the lower conjunctival sac. The lumen of the distal duct is incised by scissors for about 3–4 mm, and the ends of the duct attached to the conjunctival mucosa with three simple interrupted absorbable sutures. Postoperative therapy is the same as for small animals. In one study, epiphora occurred during eating, but the previous eye irritation and signs of keratoconjunctivitis disappeared.

Further reading Small animals Baker GJ, Formston C: An evaluation of transplantation of the parotid duct in the treatment of keratoconjunctivitis sicca in the dog, J Small Anim Pract 9:261–268, 1968. Barnett KC: Imperforate and micro-lachrymal puncta in the dog, J Small Anim Pract 20:481–490, 1979. Betts DM: The surgical correction of parotid duct transposition failures, J Am Anim Hosp Assoc 13:695–700, 1977. Covitz D, Hunziker J, Koch SA: Conjunctivorhinostomy: a surgical method for the control of epiphora in the dog and cat, J Am Vet Med Assoc 171:251–255, 1977. Gelatt KN: Treatment of canine keratoconjunctivitis sicca by parotid duct transposition, J Am Anim Hosp Assoc 6:1–12, 1970. Gelatt KN, Guffy MM, Boggess TS: Radiographic contrast techniques for detecting orbital and nasolacrimal tumors in dogs, J Am Vet Med Assoc 156:741–746, 1970.

Gelatt KN, Cure TH, Guffy MM, Jessen CL: Dacryocystorhinography in the dog and cat, J Small Anim Pract 13:381–397, 1972. Giuliano EA, Moore CP: Diseases and surgery of the lacrimal secretory system. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 633–661. Giuliano EA, Pope ER, Champagne ES, et al: Dacryocystomaxillorhinostomy for chronic dacryocystitis in a dog, Vet Ophthalmol 9:89–94, 2006. Glen JB, Lawson DD: A modified technique of parotid duct transposition for the treatment of keratoconjunctivitis sicca in a dog, Vet Res 88:210–213, 1971. Grahn BH, Sandmeyer LS: Diseases and surgery of the canine nasolacrimal system. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 618–632. Guinan J, Willis AM, Cullen CL, Walshaw R: Post-enucleation orbital sialocele in a dog associated with prior parotid duct transposition, Vet Ophthalmol 10:386–389, 2007.

Gwin RM, Gelatt KN, Peiffer RL: Parotid duct transposition in the cat with keratoconjunctivitis sicca, J Am Anim Hosp Assoc 13:42–45, 1977. Hallstrom M: Transplantation av ductus parotideus som behandlingsmethod vid kerato-conjunctivitis sicca hos hund, Nord Vet Med 23:5–8, 1971. Harvey CE, Koch SA: Surgical complications of parotid duct transposition, J Am Anim Hosp Assoc 7:122–126, 1971. Kamiya S, Horiuchi T, Hatakeyama A, Abe K, Matumura T: Transplantation of the parotid duct into the conjunctival sac for the treatment of xerophthalmia, Jpn J Ophthalmol 3:189–196, 1959. Kaswan RL, Salisbury MA: A new perspective on canine keratoconjunctivitis sicca: treatment with ophthalmic cyclosporine, Vet Clin North Am: Small Anim Pract 20:583–613, 1990. Laing EJ, Spiess B, Binnington AG: Dacryocystotomy: a treatment for chronic dacryocystitis in the dog, J Am Anim Hosp Assoc 24:223–226, 1988.

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Lavignette AN: Keratoconjunctivitis sicca in a dog treated by transposition of the parotid salivary duct, J Am Vet Med Assoc 148:778–786, 1966. Long RD: The relief of epiphora by conjunctivorhinostomy, J Small Anim Pract 16:381–386, 1975. Moore CP: Dry eye syndromes: KCS and other tear deficient diseases, Transactions of the North American Veterinary Conference 14:560–562, 2000. Murphy JM, Severin GA, Lavach JD: Nasolacrimal catheterization for treating chronic dacryocystitis, Vet Med 72:883–887, 1977. Pope ER, Champagne ES, Fox D: Intraosseous approach to the nasolacrimal duct for removal of a foreign body in a dog, J Am Vet Med Assoc 218:541–542, 2001. Salisbury MA, Kaswan RL, Ward DA, et al: Topical application of cyclosporine in the management of keratoconjunctivitis sicca in dogs, J Am Anim Hosp Assoc 26:269–274, 1990. Schilke HK, Sapienza JS: 2008, Partial ligation of the transposed parotid duct at the level of the parotid gland for excessive salivary secretions in the Yorkshire terrier breed. In Proceedings of the 39th Meeting of the

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American College of Veterinary Ophthalmologists: Abstract 11. Schmidt G, Magrane WG, Helper LC: Parotid duct transposition: a follow-up study of 60 eyes, J Am Anim Hosp Assoc 6:235–241, 1970. Severin GA: Nasolacrimal duct catheterization in the dog, J Am Anim Hosp Assoc 8:13–16, 1972. Smythe RH: Veterinary Ophthalmology, ed 2, London, 1958, Baillie`re, Tindall and Cox, pp 206–207. Stanley RG: Failure of parotid duct transposition due to sialolith formation, Veterinary and Comparative Ophthalmology 7:26–127, 1997. Startup FG: Intra-canalicular gelatin implants in lacrimal punctum surgery, J Small Anim Pract 25:635–637, 1984. White RAS, Herrtage ME, Watkins SB: Endoscopic management of a cystic naso-lacrimal obstruction in a dog, J Small Anim Pract 25:729–735, 1984.

Large animals and special species Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274.

Burling K, Murphy CJ, da Silva Curiel J, Koblik P, Bellhorn RW: Anatomy of the rabbit nasolacrimal duct and its clinical implications, Progress in Veterinary and Comparative Ophthalmology 1:33–40, 1991. Maitchouk DY, Beuerman RW, Ohta T, Stern M, Varnell RJ: Tear production after unilateral removal of the main lacrimal gland in squirrel monkeys, Arch Ophthalmol 118:246–252, 2000. Mangan BG, Gionfriddo JR, Powell CC: Bilateral nasolacrimal duct atresia in a cria, Vet Ophthalmol 11:49–54, 2008. McIlnay TR, Miller SM, Dugan SJ: Use of canaliculorhinostomy for repair of nasolacrimal duct obstruction in a horse, J Am Vet Med Assoc 218:1323–1324, 2001. Millichamp NJ, Jacobson ER, Dziezyc J: Conjunctivoralostomy for treatment of an occluded lacrimal duct in a blood python, J Am Vet Med Assoc 189:1136–1138, 1986. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1275–1335. Wilkie DA, Rings DM: Repair of anomalous nasolacrimal duct in a bull by use of conjunctivorhinostomy, J Am Vet Med Assoc 196:1647–1650, 1990.

CHAPTER

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Surgical procedures for the conjunctiva and the nictitating membrane Kirk N. Gelatt1 and Dennis E. Brooks2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

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Adaptations in large animals and special species

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Conjunctival anatomy

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SURGERIES OF THE NICTITANS

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Anatomy of the nictitans

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Surgical treatment of everted nictitans

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Bulbar/palpebral conjunctival biopsy (punch/snip)

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Surgical treatment for hyperplastic lymphoid follicles

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Surgical repair of conjunctival lacerations

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Surgical repair of conjunctival defects

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Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’

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Adaptations in large animals and special species

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Surgical procedures for prominent/protruded nictitans

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Surgical treatment for symblepharon

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Nictitating membrane flaps

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Conjunctival grafts/transplantation

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Partial/complete excision of the nictitans

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Substitute materials for conjunctival grafts

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Adaptations in large animals and special species

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Introduction Conjunctival and nictitating membrane diseases occur frequently in all animals. In the dog, the majority of conjunctival inflammations are secondary, and bacteria isolated from these eyes usually yield a variety of normal residents of the conjunctival surfaces. In the cat, most conjunctival inflammations are primary, infectious, and associated with viruses, chlamydia, and mycoplasma. In horses, primary conjunctivitis is infrequent, but both the conjunctiva and the nictitans are often involved with neoplasia in older horses. In cattle, primary inflammations and neoplasia of the conjunctiva and nictitans are frequent. Surgery for conjunctival diseases in the dog and cat is infrequent except for excision of conjunctival masses, which are often combined with other surgical procedures involving the eyelids. The most frequent conjunctival surgical procedures are the several different types of conjunctival grafts or flaps for treatment of corneal ulcers that threaten the integrity of the globe, and the maintenance of vision. Fortunately, there is ample and mobile conjunctiva for the

construction of these grafts. The success rates for the different conjunctival autografts are very high (>90%), and their value in the overall clinical management of small animal patients is often understated. In horses and cattle, neoplasia is often treated with surgery, sometimes combined with cryotherapy or local chemotherapy. The nictitating membrane has several synonyms including membrana nictitans, palpebra tertia, plica semilunaris, third eyelid, and the haws. The nictitating membrane is a semilunar fold of conjunctiva, which also occurs in redimentary form in humans and non-human primates, that protrudes from the medial canthus and can extend over a significant portion of the cornea. It is more mobile in birds and cats, and in birds it is very thin and semitransparent. Diseases of the nictitating membrane are not infrequent in small animals. In dogs and cats, congenital, inflammatory, traumatic, and neoplastic disorders may be treated surgically. In cats, more frequently than in dogs, disorders of the nictitating membranes may also signal serious systemic diseases. In both horses and cattle, neoplasms are the most frequent surgical indications.

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Surgical procedures for the conjunctiva and the nictitating membrane

Movement of the nictitating membrane somewhat parallels its development in the different species. In dogs, the dorsolateral movement of the nictitating membrane appears passive and associated with movement of the retractor oculi muscle, and the shifting of the endorbita fascia and orbit fat pad. As the globe is retracted into the depths of the orbit, the orbital adipose tissues shift forward to push the base of the nictitating membrane anteriorly and protract the structure across the cornea. Fascial attachments in the canine nictitating membrane attach the base of the hyaline cartilage and the nictitans tear gland to the bulbar fascia, medial canthal ligament, and endorbita or periorbita fascia. In cats, movements of the nictitating membrane result from contraction of smooth muscles, and are associated with its sympathetic nerve supply. Stimulation of the preganglionic cervical sympathetic nerve produces frequencydependent contractions of the nictitating membrane. The feline nictitating membrane contains two thin sheets of muscle, named by Acheson in 1938 as the medial and inferior muscles (also called Mu¨ller’s muscles), that arise deeply within the orbit from the periorbital fascia covering the medial and ventral rectus muscles to insert into the adjacent sides of the T-shaped nictitans cartilage. Alpha1-adrenoceptor antagonists, whether selective or non-selective, produce a dose-dependent depression of the evoked nictitating membrane movements, suggesting that the feline nictitans contains mainly a1-adrenoceptors postsynaptically. In horses and cattle, movements of the nictitans result from contraction of the rectus and retractor oculi muscles which displace the orbital fat rostrally and protract the nictitans across the cornea in a more horizontal direction. In birds, the active movement of the nictitating membrane is highly developed, and is rapidly protracted over the cornea toward the lateral canthus by the pyramidalis muscle. Protraction of the third eyelid is accomplished by contraction of the striated pyramidalis muscle that originates in the posterior sclera and attaches to the nasal edge of the nictitans. The quadratus muscle forms a sleeve dorsal to the optic nerve through which the tendon of the pyramidalis muscle passes, allowing a pulley action of the quadratus muscle to amplify or modify action of the pyramidalis. Innervation of both muscles by the sixth cranial nerve is widely cited. The leading edge is pigmented and forms a marginal plait (plica marginalis). The avian nictitans can be very thin and difficult to appose by sutures after trauma.

tarsus, septum orbitale, and the endorbita. The collective conjunctiva is often referred to as the conjunctival sac. Traditionally the conjunctiva is divided macroscopically into palpebral, fornix, and bulbar components. The palpebral conjunctiva lines the inner aspects of the eyelids. The bulbar conjunctiva mucosa starts at the corneal epithelial layer at the limbus. It covers Tenon’s capsule or bulbar fascia, and extends to join the palpebral conjunctiva at the fornix or the conjunctival cul-de-sac. Tenon’s capsule or bulbar fascia is quite thin in cats, horses, and cattle but variable in dogs, sometimes 5 mm or more thick. Medially a conjunctival apex or fold, the nictitating membrane or third eyelid, divides the ventral conjunctival fornix into two parts: the outer or palpebral portion, and the deeper or bulbar component (Fig. 7.1). As the conjunctival fornices span the globe and eyelids for 360
, the fornices may be divided into dorsal, lateral canthal, ventral, and medial canthal parts. The dorsal conjunctival fornix is deeper than the ventral fornix, and this may be necessary to accommodate downward eye movements. The ventral conjunctival fornix is shallower and its primary function is as a collecting basin for the tears. The medial conjunctival fornix is divided into anterior and posterior fornices of the nictitating membrane. Medial movement of tears toward the upper and, more

C B

A

Conjunctival anatomy Conjunctival anatomy is similar in all mammals. The conjunctiva spans the eyelid margins to the limbus of the globe and is the major barrier to the external environment for the globe and orbit. The conjunctiva, as a mucous membrane, forms the first line of defense against the external elements. Its elastic nature accommodates both globe and eyelid movements. The conjunctiva rests on the endorbita or periorbita fascia; on the globe the conjunctiva is in intimate contact with the bulbar fascia (or Tenon’s capsule) and attaches at the limbus. As a result, the conjunctiva accommodates globe mobility and provides for nearly unrestricted ocular movements. The conjunctiva lining the inner aspects of the eyelids and fornix for 360
is next to the fibrous

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D E F

Fig. 7.1 Cross-section of the medial eyelids and anterior globe to demonstrate the palpebral conjunctiva (A), bulbar conjunctiva (B), and dorsal fornix (C) of the conjunctiva. The nictitating membrane (D) divides the medial lower conjunctival fornix into anterior or palpebral (E), and posterior or bulbar portions (F).

Anatomy of the nictitans

importantly, the lower lacrimal puncta by the eyelid is not understood, but it appears to be an active rather than a passive process. The palpebral conjunctiva originates at the eyelid margin (the margo-intermarginalis) and the orifices of the meibomian glands. The margo-intermarginalis is the last tissue that when contact occurs with the cornea and conjunctiva produces no damage; when the outer leading edge of the eyelid skin touches the cornea, as in entropion, corneal and conjunctival damage start! The palpebral conjunctival surface epithelium at the eyelid margin consists of nonkeratinized stratified epithelium, but changes after several millimeters from the lid margin into pseudostratified columnar epithelium. Immediately beneath the palpebral conjunctiva is the thicker connective tissue, the tarsal layer, which contains the sebum-producing tarsal or meibomian glands. Once the pseudostratified epithelial surface is established, conjunctival goblet cells begin to appear and are most numerous in the fornices. These goblet cells produce mucin, an important deep component of the preocular or precorneal film, and an essential lubricant to prevent eyelid trauma to the conjunctival and the corneal surfaces (Fig. 7.2). Mucin forms the innermost layer of the preocular (precorneal) film and ranges in thickness from 1 mm on the cornea to 2 mm or more on the conjunctival surfaces. Mucin, a hydrated glycoprotein, forms an interface between the larger aqueous portion of the preocular film and the hydrophobic corneal epithelium. A relatively small portion of mucin is water soluble and part of the middle or aqueous fraction of the preocular film. The goblet cell-derived mucin decreases the surface tension of the preocular film, enhances the stability of the preocular film, and aids in the coherence of the aqueous portion of the preocular film to the corneal and conjunctival epithelia. Mucin also coats and reduces the irregularities of the corneal epithelium to produce an optically smooth corneal surface. The palpebral conjunctiva is quite transparent and often allows visualization of impacted or inflamed meibomian (or Meibom) glands on the deep aspects of both eyelids. The bulbar conjunctiva consists of entirely pseudostratified epithelium, and is most firmly attached at the fornices and the limbus. About 3 mm from the corneal periphery,

the bulbar conjunctiva, Tenon’s capsule (orbital fascia), and the limbus become closely united. Because of its surface area and availability, the dorsal bulbar conjunctiva is the principal source of mucous membrane for graft construction and transplantation to the cornea. The bulbar conjunctiva contains few goblet cells. The limbal conjunctival cell may have special significance as a critical stem cell for conjunctival surgical procedures. Transplantation of limbal stem autografts to defects in the corneal epithelium in humans successfully re-establishes the corneal epithelial characteristics and clarity, and offers potential for animals. Normal corneal epithelial cells migrate centripetally from the periphery to the center of the cornea. The limbal cells appear to be the corneal epithelial stem cells and capable of additional cell multiplication and differentiation, and a terminal transparent cell. Epithelial cells from the limbus readily grow as explants; however, peripheral and central corneal explants are progressively less likely to grow as explants. The peripheral and, to a greater extent, the central corneal epithelial cells appear committed to terminal differentiation. As a result, both the limbal and conjunctival epithelia are excellent sources for autografts. Lymphoid follicles are scattered throughout the conjunctiva, but may be more numerous in the fornices. These lymphoid follicles, acting as regional lymph nodes, are the major defense for the conjunctival surfaces, and during inflammation increase both in size and number. Grossly lymphoid follicles appear as clear-to-translucent raised circular areas. The substantia propria of the conjunctiva consists of two layers: a superficial layer that contains lymphatic follicles and glands, and the deeper fibrous layer that attaches the conjunctiva to the orbital and eyelid fascia. The latter layer tends to be quite variable in dogs, and in certain breeds is sometimes quite thick; however, in contrast, it tends to be quite thin in cats, horses, and cows. In the preparation of bulbar conjunctival grafts, the thickness of this layer can contribute to excessive tension of the graft and retraction toward the limbus. The nerves and vessels of the conjunctiva are primarily in the deep layer, and are derived from the anterior ciliary arteries that are branches from the external ophthalmic arteries. Additional arterial branches arise from the superficial temporal, malar, and palpebral arteries. Venous drainage from the conjunctiva occurs to adjacent palpebral and malar veins that eventually join the facial vein, or deep into the orbit with the superficial angularis oculi vein to the orbital plexus and superficial temporal vein. The lymphatics of the conjunctiva are divided into superficial and deep systems. Lymphatic drainage from the medial aspects of the conjunctiva is to the submaxillary lymph nodes and laterally to the parotid lymph nodes.

Anatomy of the nictitans

Fig. 7.2 Photomicrograph of the canine palpebral conjunctiva near the fornix. The goblet cells (stained red), the primary source of mucin for the preocular film, are outlined by periodic acid–Schiff stain. 200.

The gross anatomy of the nictitating membrane is quite similar among mammals. Located in the medial canthus, the nictitating membrane is a roughly triangular-shaped fold of conjunctiva, with the base of the triangle consisting of its free or leading margin (Fig. 7.3). Both anterior (palpebral) and posterior (bulbar) surfaces are confluent with the

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Fig. 7.3 By distortion of the palpebral fissure, the canine globe retracts to partially protrude the nictitating membrane. Note its pigmented margin.

palpebral and bulbar conjunctival mucosa. Its free margin or border is usually pigmented in animals. When nonpigmented, the nictitans appears more prominent. Within the substance of the nictitating membrane is a hyaline T-shaped cartilage plate, which helps provide rigidity to the structure, assists conformation to the corneal curvature, and prevents disfigurement during movement (Fig. 7.4). The ’arms’ of the T-shaped cartilage are immediately under its leading margin, and are relatively thin and slender compared to the thicker stem or base. The superficial gland of the nictitating membrane in both dogs and cats surrounds the base of the nictitans cartilage and produces seromucoid tears. Both dogs and cats possess a single nictitans gland, but in some species such as birds, the third eyelid gland may have two divisions. The deeper avian third eyelid gland is referred to as the Harderian gland. In horses, the nictitans gland is quite large (19 mm anteroposterior  11 mm wide). In cattle, the triangular-shaped nictitans gland (41 mm long  26 mm wide) is in two parts, although it appears as one confluent structure: the anterior seromucoid nictitans gland which surrounds the cartilage shaft (serous-appearing acini, but periodic acid–Schiff positive), and the deeper Harderian gland, which also has two parts, and is also mucoid but periodic acid–Schiff negative.

C

The nictitans gland in small animals is an important accessory tear-producing gland providing about 25–40% of the total tears. Lymphoid follicles are usually present on the posterior or bulbar surface of the nictitans, appearing as raised translucent spots, and especially prominent in the horse. Lymphoid follicles are infrequent on the anterior or palpebral surface of the nictitating membrane and often signal chronic conjunctival irritation. The blood supply to the canine nictitating membrane is derived from a branch of the internal maxillary artery located within the space between the ventral and medial rectus muscles. Smaller branches are often located on both sides of the stem portion of the cartilage and should be avoided during surgery. Sensation is provided by the infratrochlear nerve branch of the ophthalmic nerve, a subdivision of the trigeminal nerve. The primary functions of the nictitating membrane are to assist in the protection of the cornea and provide the second largest portion of tears. Mucin from the third eyelid tears forms an essential part of the preocular film. Nictitating membrane movement may assist in the movement of tears to the medial canthus, and the ’pick-up’ of the tears by the lacrimal puncta. Loss of the nictitans results in a larger medial lacrimal lake or conjunctival sac and often chronic conjunctivitis due to the collection and impaired drainage of tears from this area. The nictitating membrane is an essential component of the conjunctiva as well as the tearproducing system. Total excision of the nictitating membrane should be reserved for extensive neoplastic involvement of this structure.

Bulbar/palpebral conjunctival biopsy (punch/snip) Biopsy of the conjunctiva may be indicated for diagnosis of non-specific diffuse and focal conjunctival inflammations (Fig. 7.5), and for possible neoplasia in all animal species. For biopsies of suspected conjunctival inflammations,

A

B

D

Fig. 7.4 The important surgical anatomy of the nictitating membrane includes the leading margin (A), its base (B), the T-shaped hyaline cartilage (C), and the superficial gland of the nictitans (D).

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Fig. 7.5 Aged mixed-breed dog with episcleritis. Located beneath the dorsal bulbar conjunctiva, the inflammatory mass is raised and bright red. A wide excisional biopsy was performed.

Surgical repair of conjunctival lacerations

selection of the ventral conjunctiva may be more rewarding. Focal swellings, such as conjunctival cysts, parasitic granulomas, nodular granulomatous episclerokeratitis, proliferative keratoconjunctivitis of Collies, and nodular fasciitis, can be biopsied or removed for histologic examination. In contrast to the majority of eyelid neoplasms in the dog, primary conjunctival neoplasms may be invasive locally and should be widely excised. Hemangiomas, hemangiosarcomas, angiokeratomas, viral papillomas, squamous cell carcinomas, and malignant melanomas have been reported in the dog. In the cat, the most frequent conjunctival neoplasm is squamous cell carcinoma. Neoplasms of the conjunctiva affect the dorsal to dorsolateral limbal area most frequently, suggesting solar (ultraviolet) radiation may play an important role in their genesis. If a conjunctival neoplasm penetrates the anterior orbital fascia, intraorbital extension is likely and the clinical appearance of the neoplasm may be deceptive. In the clinical assessment before excision, involvement of the deeper layers of the conjunctiva should be determined by ultrasonography or other imaging procedures. If the mass involves the superficial layers of the conjunctiva, it is usually easily manipulated and moves with the conjunctival mucosa. If the tumor has extended into the deeper submucosa or even infiltrated the periorbital fascia, the tumor usually remains fixed as the surrounding conjunctiva is manipulated. In horses and cattle, solitary masses of the conjunctiva are assumed to be neoplastic until proven different histologically. In both species, squamous cell carcinomas are the most frequent neoplasms, affecting the eyelid margin, nictitans, and limbus. Because of malignancy and infiltration of adjacent tissues, surgery is often combined with other treatment modalities, such as cryotherapy. Sedation or short-acting general anesthesia is usually necessary for conjunctival biopsy. Topical anesthesia, such as 0.5% proparacaine or 0.5% tetracaine, can also be used. The eyelids are not usually clipped or prepared for surgery. The conjunctival surfaces, including the fornices, are cleansed with sterile cotton-tipped applicators and 0.5% povidone– iodine solution. The elastic and accessible conjunctiva can be easily biopsied. Small biopsies less than 1 cm do not require sutures and readily heal by secondary intention. The eyelids are retracted with a small wire speculum, conjunctival area to be biopsied is elevated by small thumb forceps, such as the Bishop–Harmon, and the conjunctiva excised by small tenotomy scissors. If the conjunctival defect is greater than 1 cm, the mucosa edges are apposed with 4-0 to 7-0 simple interrupted or continuous absorbable sutures. Postoperative treatment usually consists of topical antibiotics or antibiotics/corticosteroids administered three or four times daily for several days.

Surgical repair of conjunctival lacerations Conjunctival lacerations are infrequent and usually combined with lacerations of the eyelids, cornea, and sclera. The presence of bulbar conjunctival lacerations signals the need for a complete eye examination. Bulbar conjunctival lacerations may mask more serious and vision-threatening full-thickness scleral lacerations and intraocular damage.

Small conjunctival lacerations less than 1 cm will usually heal by secondary intention. These lacerations should be carefully examined to exclude any intraocular damage, and any foreign material removed manually or irrigated from the tissues. Topical antibiotic solutions are administered several times daily for 5–7 days, or until the conjunctival epithelium has bridged the wound. Larger conjunctival lacerations are usually apposed by sutures. Palpebral conjunctival wounds often involve the full-thickness eyelids. Large bulbar conjunctival lacerations should be approached with caution, as intraocular tissue involvement is likely. If hyphema is present with a bulbar conjunctival laceration, intraocular damage has occurred, and careful examination of the entire globe is warranted. Both direct and indirect trauma can result in intraocular hemorrhage and inflammation. Large conjunctival lacerations (>1 cm) are best treated by apposition with sutures. After short-acting general anesthesia, the conjunctival surfaces are carefully cleaned with cotton-tipped applicators and, if necessary, with serrated thumb forceps. Any foreign material should be removed and, if possible, identified. Vegetative material will often provoke an acute and intense inflammation. Fungal organisms may also be introduced into the tissues. Debridement of conjunctival tissues, like that of the eyelids, should be minimal to preserve as much of the conjunctiva as possible. Small thumb forceps with 1  2 teeth and a small Castroviejo needle holder are used. Simple interrupted absorbable sutures (usually 5-0 to 7-0) are used for apposition. Some chemosis is anticipated postoperatively. Topical antibiotics, often combined with corticosteroids, are instilled four to six times daily for 5–7 days. The ointment form of medication may be more advantageous as drug contact time is prolonged, and the ointment coats the conjunctival and suture surfaces to act as a lubricant. If the conjunctival swelling is excessive, hot and cold packs to the area may promote local circulation and reduce the swelling. Systemic antibiotics and corticosteroids are also added to the topical therapy for more serious conjunctival lacerations. Topical and systemic (oral) non-steroidal anti-inflammatory agents can also be added. Conjunctival healing after lacerations is usually uneventful. Focal scar tissue formation is usually minor and not sufficient to restrict globe mobility or eyelid movements. Palpebral conjunctival lacerations usually signal full-thickness eyelid perforations. In most small animals, full-thickness eyelid lacerations are repaired by two layers of sutures: one layer for the eyelid skin and orbicularis oculi muscle, and the second and deeper layer for the tarsus and palpebral conjunctiva. Both layers may be apposed by 4-0 to 6-0 simple interrupted sutures, absorbable sutures for the deep layer and non-absorbable sutures for the muscle and skin layer. The deep layer of the tarsus and palpebral conjunctiva may also be apposed with a simple continuous suture. The suture apposing the eyelid margin is most important and is often a figure-of-eight stitch that either avoids the eyelid margin with its knot or is temporarily positioned in the opposite eyelid to provide some tension on the healing conjunctiva and eyelid tissues. Postoperative treatment varies with the depth and extent of the palpebral conjunctival and eyelid lacerations. Often topical antibiotics and corticosteroids are supplemented

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with systemic antibiotics and corticosteroids. The eyelids after trauma and laceration apposition may become quite swollen. The swelling may elicit self-trauma by the patient. Accordingly, an E-collar is often used to ensure the patient cannot damage the postoperative area. The skin sutures are removed in 7–14 days, sometimes at two different times.

Surgical repair of conjunctival defects Conjunctival defects may occur after the excision of large conjunctival dermoids (Fig. 7.6) and neoplasms, after loss from severe trauma, and extensive chemical burns. Fortunately, large conjunctival defects are infrequent in animals and may be repaired by a number of techniques. In contrast to the lid tumors in most species, conjunctival neoplasms tend to be more aggressive clinically and merit larger incisional margins during attempted excision. Small conjunctival defects (<1 cm) usually heal by secondary intention and resolve without adverse sequelae. Large palpebral and bulbar conjunctival defects (>1 cm) should be apposed by sutures. For bulbar conjunctival defects of about 2 cm or larger, the adjacent conjunctiva may be undermined and shifted to cover the defect. For larger defects, autografts of bulbar conjunctiva from the opposite fellow eye or the buccal mucosa may be transplanted. The mucosa is usually harvested free-hand, must be thin, and 1–3 mm larger than the defect to compensate for tissue shrinkage. The edges of the transplant are carefully apposed to the wound with 4-0 to 7-0 simple interrupted absorbable sutures. Often an incomplete temporary tarsorrhaphy is performed after conjunctival transplantation to prevent eyelid trauma and apply pressure to the surgical site to retard swelling. Autografts of conjunctiva and buccal mucosa to the conjunctiva in small animals are highly successful. When the conjunctival wound or autograft edges involve the limbal area, the conjunctival margin is apposed to the limbus by sutures to avoid overgrowth or migration onto the cornea.

Carcinoma in situ of the conjunctiva can be excised with sedation, an auriculopalpebral nerve block, and topical anesthetic in a good horse.

Surgical treatment for symblepharon Symblepharon is the adhesion of bulbar to palpebral conjunctiva, the adhesion of the palpebral conjunctiva to the cornea, or the adhesion of the bulbar conjunctiva to the cornea. Symblepharon can also involve the nictitating membrane. Symblepharon is rare in dogs, but more frequent in cats. In horses, symblepharon may follow trauma, and either no surgical correction or improper surgical alignment. In dogs, symblepharon may develop after trauma, surgery, and chemical burns to the cornea and conjunctiva. In cats with ocular herpes (FHV-1), symblepharon may develop usually involving the cornea and the bulbar conjunctiva, the palpebral conjunctiva, or a combination of both conjunctivae (Fig. 7.7). Symblepharon associated with FHV-1 can be corrected successfully in cats, but since these corneal and conjunctival inflammations are often chronic, symblepharon formation may recur. Symblepharon affecting the cornea produces disfigurement and, if extensive, impairment of vision. Adhesions involving the bulbar and palpebral conjunctivae may shallow the conjunctival fornix, impair the drainage of tears, produce chronic conjunctivitis, and retard ocular motility. The objectives for the surgical correction of symblepharon are to excise the fibrous adhesions between the conjunctiva and cornea, and to restore viable epithelial surfaces to the palpebral and bulbar conjunctivae, and to the cornea. Various conformers, symblepharon lenses, and silicone strips are available to physically separate the healing conjunctival surfaces and help establish and maintain the conjunctival fornix. These temporary implants are generally retained in position by complete temporary tarsorrhaphies for a few weeks for the epithelial healing to be completed. If any of

Adaptations in large animals and special species Surgical resection alone of conjunctival squamous cell carcinoma may be adequate if clean margins can be obtained. Small tumors or carcinoma in situ of the conjunctiva or third eyelid may also be effectively treated with simple excision.

Fig. 7.6 Dermoid in a puppy affecting only the palpebral conjunctiva. Treatment is excision of the mass.

162

Fig. 7.7 Symblepharon in a 2-year-old, short-haired, domestic cat. The symblepharon involves the lateral cornea, bulbar and palpebral conjunctiva. The patient has recurrent conjunctivitis and keratitis associated with feline herpes virus (FHV-1).

Conjunctival grafts/transplantation

these corneal or conjunctival structures is not covered with epithelium postoperatively, adhesions will recur. After general anesthesia, clipping of the eyelid hair, and surgical preparation of the eyelids, the area is draped for aseptic surgery. The conjunctiva is thoroughly cleaned with sterile saline and all foreign material removed by cottontipped applicators. After placement of a wire speculum to retract the eyelids, the conjunctiva adhered to the cornea is removed by superficial lamellar keratectomy. The periphery of the corneal lesion is incised by the Beaver No. 6400 microsurgical blade to the level of the superficial stroma (Fig. 7.8a). After lifting the edge of the incision with thumb forceps with 1  2 fine teeth jaws, the adherent conjunctiva is excised from the corneal surface (Fig. 7.8b). If the symblepharon continues into the conjunctiva, the incision is continued and the affected conjunctiva excised (Fig. 7.8c). Once the conjunctiva is freely moveable, its edge is apposed to the limbus with 5-0 to 7-0 simple interrupted absorbable sutures. If a defect remains in the bulbar and/or palpebral conjunctiva, its edges are apposed with 5-0 to 7-0 simple interrupted absorbable sutures. To cover the healing cornea and prevent the development of new adhesions between the cornea and conjunctiva, a plastic methyl methacrylate corneal protector (Crouch corneal protector; Storz, St Louis, MO) may be inserted or amniotic membrane apposed by sutures. A soft corneal contact lens may be used instead of the thicker corneal protector (Fig. 7.8d). If considerable adhesions are present between the bulbar and palpebral conjunctivae, a thin strip of silicone sheeting is fashioned to fill the area and secured in position with 4-0 to 7-0 simple interrupted non-absorbable sutures as well as 5-0 to 7-0 simple mattress sutures placed through the silicone strip and the full-thickness eyelid with the suture knots on the external lid surface

(Fig. 7.8e). To retain the corneal contact lens and reduce eyelid movements, a partial temporary tarsorrhaphy is performed with 4-0 to 6-0 simple mattress sutures positioned at one-half thickness of the eyelids (Fig. 7.8f). For details on how to perform the temporary tarsorrhaphy, see Chapter 5. After recovery from general anesthesia, an E-collar is placed on the animal to prevent self-mutilation of the surgical site. Postoperatively, topical antibiotic solution is instilled on the eye four to six times daily. Systemic antibiotics are also administered. Once corneal epithelialization is complete, as evidenced by the lack of topical fluorescein, topical corticosteroids are added to reduce scar tissue formation. After 2–4 weeks, the tarsorrhaphy sutures are released to remove the corneal contact lens. About 2 weeks later, the fornix silicone strip and sutures are removed. Topical antibiotics/ corticosteroids are continued for another 7–10 days. This procedure provides good results in dogs and cats in which the symblepharon was secondary to trauma or chemical burns, provided the contact lens is retained in position for several weeks to permit complete epithelialization of the apposing conjunctival surfaces. This method is less successful in cats when the symblepharon appears secondary to chronic feline herpes virus infections, because with recurrent or chronic FHV-1 the corneal and conjunctival epithelia may be damaged again and re-adhesion occurs.

Conjunctival grafts/transplantation Conjunctival grafts or flaps were first performed in humans in 1860 (Teale) and 1884 (Bock) for the treatment of symblepharon. Conjunctival autografts for the treatment of corneal ulcerations in humans for the past several decades

A

B

C

D

E

F

Fig. 7.8 Surgical treatment of symblepharon in the cat. (a) The corneal portion of the symblepharon is excised by superficial keratectomy. The periphery of the corneal lesion is incised by Bard–Parker No. 15 or Beaver No. 6400 blade to the level of the superficial stroma. (b) With fine teeth thumb forceps, the edge of the corneal incision is elevated, and the adherent conjunctiva is dissected from the anterior corneal stroma. (c) Excision of the adherent conjunctiva is continued onto the affected bulbar and palpebral conjunctival surfaces. (d) After apposition of the remaining conjunctiva to the limbus with 5-0 to 7-0 simple interrupted absorbable sutures, a corneal protector is positioned on the cornea to cover the corneal stroma and attempt to prevent re-adherence of the conjunctiva. (e) A strip of silicone sheeting is inserted into the lower conjunctival fornix to maintain the separation between the ventral bulbar and palpebral conjunctiva, and secured with 5-0 to 7-0 simple mattress sutures placed full-thickness through the eyelids. (f) A partial temporary tarsorrhaphy is performed to protect the surgical sites, retain the corneal protector during the epithelialization of the corneal wound, and maintain the silicone sheeting in the fornix to separate the healing conjunctival surfaces.

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have been replaced by partial- and full-thickness keratoplasty. The major reason is the high visual acuity in humans and the absolute need for a clear cornea. Nevertheless, conjunctival autografts are still used in humans for fungal keratitis, selected herpes simplex ulcerations, and chemical burns of the cornea. Reports of bulbar and palpebral conjunctival grafts and conjunctival keratoplasty first appeared in the veterinary medical literature more than 50 years ago (Uberreiter 1937, Shuttleworth 1939, Stern 1950, Livingston 1950, Henderson 1951, Dimic 1957, and Berge and Westhues 1956). Most reports described advancement bulbar conjunctival grafts, complete bulbar conjunctival grafts, and palpebral conjunctival grafts. In veterinary ophthalmology the routine use of keratoplasty has not yet occurred, but the development of conjunctival autografts for the surgical management of corneal ulceration has been continuously refined. As a result, more transparent corneas now result. Further improvements may follow in the future using porcine small intestinal submucosa (available commercially) and amniotic membranes (not available commercially), rather than conjunctival grafts. Because the veterinary ophthalmologist is concerned first for the preservation of the globe and second for clinical vision in animals, the cornea need not be perfectly and totally clear. As each animal has ample bulbar and palpebral conjunctivae for temporary or even permanent transplantation to the cornea, availability and host acceptance are not limiting factors. Treatment of deep corneal ulcerations, descemetoceles, and perforated corneal ulcers with conjunctival autografts in small animals usually halts progression and initiates healing of the corneal ulcer, transplants epithelium, fibroblasts and blood vessels to a weakened cornea, and maintains vision.

Conjunctival autografts Conjunctiva to conjunctiva Conjunctival autografts are used infrequently, because canine and feline conjunctival defects usually heal by secondary intention, and transposition to other areas in the same eye or between eyes is seldom indicated. Nevertheless, destruction of large areas of the conjunctiva after trauma, chemical burns, and loss after conjunctival neoplasm excision may require transposition of conjunctival tissues from other conjunctival sites. Thin mucosal grafts can be easily constructed from the dorsal bulbar conjunctiva because this is the most accessible and the largest source. Most grafts are performed free-hand, because the conjunctival defects are usually irregular in shape and size. Transplantation to the ventral bulbar and palpebral conjunctival areas is more difficult, and construction of the ventral fornix requires long-term conformers. Grafts from the dorsal bulbar and palpebral conjunctivae are more convenient. The upper conjunctival fornix provides primarily for ocular mobility, but not for the collection and maintenance of tears. Conjunctival autografts are performed under general anesthesia and routine surgical preparation of the eyelids and conjunctival surfaces. Conjunctival grafts must be thin and devoid of most of the underlying connective tissues. Most conjunctival grafts are either free-hand island or pedicle types. Pedicle grafts are preferred if sufficient adjacent

164

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Fig. 7.9 An autogenous pedicle bulbar conjunctival graft is used to cover significant defects following tumor excision. (a) Preparation of the site in the dorsolateral conjunctiva to receive an autogenous pedicle conjunctival graft. The surgical defect resulted from previous excision of a hemangioma. The adjacent area for the pedicle bulbar conjunctival autograft is outlined. (b) Completion of the pedicle conjunctival graft. The graft edges are apposed with 5-0 to 7-0 simple interrupted absorbable sutures.

conjunctiva is available. Mucous membrane grafts should be free of pigmentation. The conjunctival graft site must be carefully prepared, and any necrotic or potentially infected tissues removed. The adjacent bulbar conjunctiva is incised by small tenotomy scissors to produce a pedicle flap to cover the surgical defect (Fig. 7.9a). The thin conjunctival pedicle should be 1–2 mm larger than the graft site to compensate for graft shrinkage. As the scissors undermine and separate the conjunctival mucosa from Tenon’s capsule, the scissors’ tips should be plainly visible when the graft is sufficiently thin. Once fitted to the graft site, the edges of the graft and conjunctival mucosa are carefully apposed to ensure epithelium to epithelium apposition with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.9b). A partial temporary tarsorrhaphy can be used to decrease eyelid trauma, and provide pressure to facilitate apposition of the graft to the underlying Tenon’s capsule.

Buccal mucosa autografts to conjunctiva The buccal mucosa is a nearly unlimited potential graft source for the conjunctiva. The buccal mucosa is thicker than the conjunctiva and often pigmented. In construction of buccal mucosa grafts, as much as possible of the submucosal tissues should be dissected from the graft to provide a very thin mucosa graft. Like autogenous conjunctival grafts, buccal mucosa grafts are performed free-hand, their shape and size being dependent on the conjunctival defect. After transposition, the buccal mucosa will become white for several days and pink color will gradually return as the graft revascularizes. Partial temporary tarsorrhaphies can assist with graft transposition by providing a protective cover to the graft site, and counterpressure to assist graft establishment and vascularization.

Conjunctival autografts to cornea Conjunctival autografts are frequently used in small animal ophthalmology in clinical management of deep corneal ulcers, descemetoceles, and perforated corneal ulcers (Figs 7.10–7.12). Conjunctival autografts consist of either bulbar or palpebral conjunctival mucosa with epithelium and connective tissue (fibroblasts, blood vessels, and lymphatics). These autografts can be transposed and sutured onto the

Conjunctival grafts/transplantation

Fig. 7.10 Extensive keratomalacia in a young dog. This patient is a candidate for a conjunctival autograft.

Fig. 7.11 Deep central corneal ulcer in a brachycephalic dog. Note the steep sides of the corneal ulcer and the lack of corneal vascularization. A conjunctival autograft is recommended.

Fig. 7.12 Central descemetocele in a brachycephalic dog. The center of the corneal defect is clear and did not retain topical fluorescein. A conjunctival autograft is recommended.

cornea to provide additional support and tissue for a cornea weakened by deep ulceration, descemetocele, or perforation with or without iris prolapse. The transplanted conjunctival autograft provides additional tissues and no risk of host rejection. Conjunctival autografts provide sufficient tissue to strengthen a weakened cornea and prevent staphyloma formation. If additional strength is indicated, a frozen section of sterile cornea or sclera is positioned in the corneal defect before the conjunctival graft is applied. Conjunctival grafts provide new and often highly viable epithelium. When harvested from the limbal area, the transplanted

conjunctival epithelium is also a stem cell capable of additional generation and transition into corneal epithelium. The conjunctival autograft contains blood vessels and lymphatics to offer significant antibacterial, antifungal, antiviral, antiprotease, and anticollagenase effects. With conjunctival transplants, leukocytes, antibodies, serum, and a2-macroglobulin (thought to be the anticollagenase factor) are immediately incorporated into the corneal ulcer bed. Because of the conjunctival blood vessels, systemic antibiotics can enter the ulcer site in higher levels. The fibrovascular or deeper layer of the conjunctival transplant offers immediate fibroblasts and collagen to begin rebuilding the corneal stroma (Fig. 7.13). Conjunctival autografts from either bulbar or palpebral conjunctiva should be thin, and not include Tenon’s capsule or the bulbar fascia. The inclusion of Tenon’s capsule creates a thicker than necessary graft, and may contribute to surgical failure by increasing tissue contraction and tension by the transplanted conjunctiva. The scar will be more prominent with a thick autograft. Transpalpebral conjunctival autografts contain limited portions of the fibrous tarsal layer which may be necessary to maintain the graft base from the deeper aspects of the eyelid to the corneal surface. As a general guide, if the surgeon can visualize the ophthalmic scissors beneath the conjunctival graft as it is being prepared, the graft is sufficiently thin. Conjunctival autografts are more difficult to perform than nictitating membrane flaps, but are easier than corneoconjunctival and corneoscleral transpositions, and the different types of keratoplasty procedures. Conjunctival autografts are indicated for progressive and medically non-responsive corneal ulcers, fungal corneal ulcers, deep stromal corneal ulcers, descemetoceles, ’leaking’ corneal ulcers (positive Seidel test), perforated corneal ulcers, and perforated corneal ulcers with iris prolapse. Some ophthalmic instrumentation is essential to perform these grafts and usually includes: an eyelid speculum, Beaver No. 6400 or 6700 microsurgical blade, Beaver scalpel handle, small tenotomy or Steven’s scissors, both small serrated and 1  2 teeth thumb forceps to handle the conjunctiva, ophthalmic needle holder usually with a lock (to accommodate 5-0 to 7-0 ophthalmic sutures), and suture tying thumb forceps. Some magnification (5–10) for the operative procedure is highly recommended. There are several different types of conjunctival autograft (Table 7.1). The divisions are based on the source of the mucosa (bulbar, tarsopalpebral, or corneoconjunctival) and the type of graft (advancement, bridge, complete, island (free), or pedicle). The dorsal bulbar conjunctiva is the most frequent source of mucosa, because of its accessibility and large surface area. The transpalpebral graft is usually constructed from the upper eyelid and sufficient tissue is available for any size corneal defect. Generally, the more central the corneal defect, the more critical the conjunctival grafting procedure. The different types of conjunctival autograft have different clinical characteristics that influence their clinical use (Table 7.2). The larger the surface area of the cornea covered by the conjunctival graft, the greater the postoperative impairment to patient’s vision, the greater the barrier to postoperative intraocular examination, and, at least theoretically, the greater impediment for the corneal and intraocular

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A

B

Fig. 7.13 (a) Descemetocele in a dog treated by a pedicle conjunctival graft (6 weeks postoperative). (b) Pedicle bulbar conjunctival graft in a cat with a deep stromal corneal ulcer (immediate postoperative).

Table 7.1 Types of conjunctival autograft for corneal defects

Position of corneal defect

Type of conjunctival autograft

Peripheral

Paracentral

Central

Corneoconjunctival, bulbar

Sliding/pedicle

þþþ

þþ

þ

þþþ

þþ

þþ

Complete (360 )

þ

þþ

þþþ

Island

þ

þþþ

þþþ

Pedicle

þþþ

þþþ

þþþ

Island

þ

þþþ

þþþ

Pedicle

þ

þþþ

þþþ

Advancement (hood)


Tarsopalpebral

þþþ most used; þþ occasionally used; þ infrequently used.

Table 7.2 Clinical characteristics of conjunctival grafts

Type of graft Characteristics

Advancement

Bridge

Complete

Island (bulbar/TP)

Pedicle (bulbar/TP)

Barrier to eye exam

Partial

Partial

Total

Partial

Partial

Barrier to eye drugs

Minor

Minor

Major

Minor

Minor

Difficult to perform

Low

Moderate

Moderate

Low

Moderate

Dehiscence potential

Low

Low

Medium

Medium

Medium

Maintenance of viability

High

High

High

Moderate

Moderate

Obstructs vision

No

Little

Total

Little

Little

Surgical trauma

Low

Moderate

High

Little

Moderate

Suture patterns

Simple

Simple

Simple and mattress

Simple

Simple

TP, tarsopalpebral.

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Conjunctival grafts/transplantation

penetration of most ophthalmic drugs. In those types of graft used to cover the central cornea, and for the more serious corneal ulcers, these techniques are often more difficult to perform. Attachment of the conjunctival graft to the progressive central corneal ulceration must be exact. Magnification provided by a head loupe or preferably the operating microscope is necessary for those types of conjunctival autograft that are apposed by sutures directly to the adjacent corneal epithelium and stroma. Preparation for surgery for the different types of conjunctival autograft is similar. Once under general anesthesia, the eyelids are carefully clipped and the eyelid skin prepared for surgery. The conjunctival surfaces are carefully cleaned of any debris with sterile cotton-tipped applicators. Dilute solutions of 0.5% povidone–iodine are used to treat the surfaces of both the conjunctiva and cornea to reduce the overall microbial population, and then rinsed from the eye with sterile saline. A lateral canthotomy may be indicated to increase exposure of the surgical site and facilitate the surgery for most dogs except the brachycephalic breeds.

Complete (360
) bulbar conjunctival autograft (Gundersen type) The complete, 360
, or Gundersen-type conjunctival autograft has been used extensively in veterinary ophthalmology since its first description nearly 50 years ago, but has now been partly replaced by conjunctival grafts that only partially cover the cornea. In this graft nearly all of the bulbar conjunctiva is separated from the underlying Tenon’s capsule to cover the entire cornea. The graft covers the corneal defect but is not apposed directly by sutures. Because the entire cornea is covered, patient vision, examination of the

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eye, and the intraocular penetration of topical drugs through both the vascularized mucosa and the cornea is reduced. With this graft, systemic as well as topical administration of drugs is recommended. Of all of the different types of conjunctival graft, the complete 360
conjunctival graft provides the maximum support for the entire cornea. Corneal defects involving the central and paracentral areas of the cornea are treated with this type of conjunctival graft. For the 360
fornix-based conjunctival graft, the dorsal bulbar conjunctiva is elevated by fine teeth thumb forceps and incised by scissors at the limbus (Fig. 7.14a). The bulbar conjunctiva is separated from the underlying Tenon’s capsule by alternating blunt–sharp dissection by small tenotomy scissors with blunt tips. For a reasonably thin conjunctival graft, the scissors’ tips should be easily observed through the thin mucosa (Fig. 7.14b). To facilitate dissection, saline can be injected subconjunctivally to help separate the bulbar conjunctiva from Tenon’s capsule. Some hemorrhage is expected and depends on the extent of conjunctival hyperemia associated with the corneal ulceration and secondary iridocyclitis. If the surgical dissection plane enters Tenon’s capsule, additional hemorrhage results. The bulbar conjunctiva is dissected for 360
about the limbus. The most difficult area is usually under the nictitating membrane (Fig. 7.14b). As the cornea measures about 15  16 mm in the dog, and 16  17 mm in the cat, in vertical and horizontal diameters, respectively, adequate amounts of bulbar conjunctiva necessitate 8–10 mm of dissection from the limbus for 360
. As the different rectus muscles in the dog and cat insert 6–10 mm from the limbus, preparation of the conjunctival graft requires surgical dissection immediately beneath the bulbar conjunctiva and not on the sclera.

C

D Fig. 7.14 In the 360
, or Gundersen-type, conjunctival graft, (a) The dorsal bulbar conjunctiva is elevated by fine 1  2 thumb forceps and incised by tenotomy scissors. (b) A thin bulbar conjunctival graft is constructed by careful separation from the underlying Tenon’s capsule. The tips of the tenotomy scissors should be visible under the conjunctival mucosa. The bulbar conjunctiva is incised at the limbus for 360
and separated from Tenon’s capsule for approximately 10–12 mm posterior to the limbus. (c) Once the bulbar conjunctival graft has been constructed, its dorsal and ventral edges are apposed with 5-0 to 7-0 absorbable simple interrupted or simple mattress sutures, or a combination of both suture patterns. (d) Once completed, the 360
bulbar conjunctival graft covers the entire cornea.

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Modified complete (360
) bulbar conjunctival graft with two suture lines

Fig. 7.15 A complete bulbar conjunctival graft 4 weeks postoperatively. The entire cornea was covered by bulbar conjunctival mucosa, but this is now retracting and several sutures are missing.

The conjunctival graft must be thin to minimize traction and excessive pressure on the sutures postoperatively. When properly prepared, the loosened edges of the bulbar conjunctival graft should rest on the central cornea and not retract spontaneously to the limbus. The edges of the bulbar conjunctiva are apposed horizontally with 5-0 to 7-0 absorbable simple interrupted or simple mattress sutures (Fig. 7.14c). Usually four to six sutures are necessary to appose the dorsal and ventral conjunctival edges. Simple interrupted mattress sutures are recommended if the graft is thicker than desirable or additional traction on the suture line is anticipated. A pursestring stitch has also be used but is not recommended as this produces additional tension on the graft as all edges are pulled to the center of the cornea. Once completed, the 360
bulbar conjunctival graft covers the entire cornea (Fig. 7.14d). The transposed conjunctival mucosa is not usually sutured directly to the corneal defect, but can be if perforation is likely or the deep corneal ulcer is already leaking aqueous humor (Fig. 7.15). As these grafts completely cover the cornea, vision in the eye is obscured and intraocular inspection is not possible.

A

B

The complete or 360
bulbar conjunctival graft has been modified to include two suture lines instead of a single suture line. The major reason for failure of the complete or 360
bulbar conjunctival graft is the premature retraction of the conjunctiva from the central cornea, and the failure of the sutures to hold the dorsal and ventral conjunctival edges together. In this technique a ‘relief incision’ of the dorsal bulbar conjunctiva is performed to lessen the ‘pressure’ on the sutures apposing the upper and lower edges of the graft. In this technique, a wide 10–15 mm strip of dorsal bulbar conjunctiva is prepared by incisions at the dorsal limbus for 180
, and parallel to the limbus 10–15 mm for 180
(Fig. 7.16a). Beyond the second incision, additional bulbar conjunctival mucosa is separated from Tenon’s capsule to eventually slide ventrally toward the limbus. The conjunctival graft must be thin and the tips of the curved blunt-tipped tenotomy scissors should be clearly visible through the thin graft. The surgical plane is in the subconjunctival fascia above Tenon’s capsule to avoid the deeper dorsal extraocular muscle insertions. Both edges of the wide strip of dorsal bulbar conjunctiva are apposed to the adjacent loosened conjunctiva by 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.16b). The ventral 180
of the bulbar conjunctiva is prepared as described in the previous procedure to separate at least 8–10 mm of thin ventral conjunctival mucosa from Tenon’s capsule (Fig. 7.16c). The presence of a double rather than a single suture line substantially reduces the likelihood of suture failure, but increases the time required to prepare this graft.

Advancement (hood or 180
) bulbar conjunctival graft The advancement (hood or 180
) bulbar conjunctival graft is very similar to the complete 360
technique, except that only the dorsal or lateral bulbar conjunctiva is transposed onto the cornea. This method is most useful for dorsal and lateral paracentral and peripheral corneal defects. Advancement bulbar conjunctival grafts are difficult, but

C

Fig. 7.16 The modified complete bulbar conjunctival graft is a modified very wide bridge graft. (a) In the modified complete bulbar conjunctival graft, a wide strip (10–15 mm) of dorsal bulbar conjunctiva is constructed by tenotomy scissors. The bulbar conjunctival graft should be sufficiently thin to permit visualization of the scissors’ tips through the mucosa while performing the initial 360
peritomy starting at the limbus. (b) The dorsal aspects of the dorsal bulbar conjunctival graft are positioned over the center of the cornea and apposed to the limbus with 5-0 to 7-0 simple interrupted absorbable sutures. The remaining exposed surgical wound thereby provides a relief incision. (c) The ventral edge of the wide strip of dorsal bulbar conjunctiva is apposed with 5-0 to 7-0 simple interrupted absorbable sutures to the edge of the ventral bulbar conjunctiva. Hence, with two lines of sutures instead of a single row to appose the complete bulbar conjunctival graft, and the 10–15 mm from the relief incision, the possibility of general suture failure and dehiscence is reduced.

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Conjunctival grafts/transplantation

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B

C

Fig. 7.17 Most advancement (hood or 180
) bulbar conjunctival grafts are performed in the dorsal or lateral quadrants because of accessibility. (a) The bulbar conjunctiva is incised at the limbus with small tenotomy scissors and separated for 180
from the underlying Tenon’s capsule. (b) The advancement bulbar conjunctival graft is positioned over the paracentral corneal defect, and its edges apposed to the corneal defect and adjacent areas with 5-0 to 7-0 simple interrupted absorbable sutures. (c) Postoperative appearance of an advancement or hood conjunctival graft several weeks after surgery. As this graft does not obscure vision, it can be left permanently in situ.

not impossible, to prepare from the medial bulbar conjunctiva beneath the nictitating membrane or from the ventral bulbar conjunctiva. Advancement grafts permit patient vision and intraocular examinations, and appear to impact minimally on corneal and intraocular drug penetration. If the advancement graft has limited-to-no impact on vision and the central cornea, it may be left permanently in position. The dorsal or lateral bulbar conjunctiva is incised by small curved blunt-tipped tenotomy scissors at the limbus for 180–200
and dissected toward the conjunctival fornix for about 10–12 mm (Fig. 7.17a). The bulbar conjunctiva is separated primarily by blunt dissection from the underlying Tenon’s capsule, and should be sufficiently thin to allow visualization of the scissors’ tips under the mucosa. The graft is manipulated to cover the corneal defect without excessive traction, and apposed to the central edge of the corneal ulcer with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.17b). Additional sutures are positioned along the leading edge of the conjunctival graft to the cornea to provide additional support for the graft and decrease the possibility of suture failure at the corneal ulcer site. One or more additional sutures can be added to attach the conjunctival graft to other areas of the corneal defect, especially at the limbus. Conjunctival graft adhesion will occur only at the corneal ulcer site. Once suture removal occurs, the areas of the conjunctival graft covering the cornea with epithelium will not adhere. Depending on the pre-existing disease, advancement bulbar conjunctival grafts usually do not interfere with vision and can be left permanently in situ (Fig. 7.17c). An example is use of a permanent advancement graft to strengthen the postoperative corneoscleral wound after excision of a limbal or epibulbar melanoma in a dog or cat.

bulbar conjunctival graft is recommended for central, dorsal paracentral, and lateral paracentral corneal defects. The bridge of conjunctiva is usually prepared from the dorsal bulbar conjunctiva because of its accessibility and quantity. Two parallel bulbar conjunctival incisions are performed by small curved blunt-tipped tenotomy scissors at the limbus and about 10–12 mm toward the conjunctival fornix (Fig. 7.18a). The conjunctival graft should be sufficiently thin to permit visualization of the scissors underneath. The bridge of bulbar conjunctiva is manipulated across the cornea and its edges apposed to the underlying corneal defect and adjacent normal cornea with 5-0 to 7-0 simple interrupted absorbable sutures. Additional sutures may be used about the corneal defect to ensure graft adherence to the corneal ulcer edges and base (Fig. 7.18b). Often a temporary partial tarsorrhaphy is also used to prevent excessive lid trauma to the graft and its suture, but still accommodate topical medication and limited vision.

Pedicle bulbar conjunctival graft Pedicle bulbar conjunctival grafts are becoming more popular in small animal ophthalmology because of their minimal effect on vision, intraocular examination, and drug penetration into the anterior segment. Their preparation is not difficult, but adequate corneal bed preparation is critical. All suspect necrotic corneal tissue must be excised by sharp dissection from the corneal ulcer to ensure graft apposition to the ulcer base and edges, and for maintenance of the surrounding sutures. The pedicle graft must be of sufficient size to cover the entire corneal ulcer; it is usually constructed 1–2 mm wider than the diameter of the corneal defect.

Bridge bulbar conjunctival graft The bridge (or bipedicle) bulbar conjunctival graft is a further modification of the complete bulbar conjunctival graft with two suture lines. The approximate width of this bridge of bulbar conjunctiva should be 10 mm or more to ensure its vitality. As the bridge of dorsal bulbar conjunctival mucosa is perfused at both ends, ischemia of the graft is less likely than with pedicle grafts. Sutures may be used to attach the corneal defect to the bridge of conjunctival mucosa. As with the other incomplete conjunctival grafts, the impact on vision, intraocular examination, and corneal and intraocular drug penetration is only partial. The bridge

A

B

Fig. 7.18 Bridge bulbar conjunctival graft. (a) A 10 mm or wider strip of thin dorsal conjunctiva is constructed with small tenotomy scissors. The dotted lines indicate the extent of the bridge of mucosa. (b) After placement on the cornea, the bridge bulbar conjunctival graft is apposed to the corneal defect and other edges of the graft to the cornea by 5-0 to 7-0 simple interrupted absorbable sutures.

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B

D

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Fig. 7.19 Pedicle bulbar conjunctival graft. (a) The corneal ulcer is carefully debrided to remove all suspect necrotic and/or infected tissues. (b) The dorsolateral bulbar conjunctiva is most accessible and the graft’s base is usually lateral or at the 12 o’clock position. The dotted line indicates the outline for the pedicle graft. (c) A pedicle strip of thin bulbar conjunctiva is prepared primarily by small tenotomy scissors. (d) After preparation of the bulbar conjunctival pedicle graft, its end is trimmed by scissors to conform to the ventral edge of the corneal ulcer. The pedicle graft should lie flat on the corneal surface, and be neither stretched nor excessive in length. (e) The entire tip of the pedicle is apposed to the corneal ulcer by 5-0 to 7-0 simple interrupted absorbable sutures. At least one suture is carefully positioned between the dorsal edge of the corneal ulcer and the pedicle; this suture is positioned along the long axis of the graft to minimize its effect on the graft’s blood supply.

Pedicle bulbar conjunctival grafts may be used for central, paracentral, and peripheral corneal defects. The recipient bed for the pedicle graft is prepared in the corneal ulcer. Debridement of the ulcer’s edges and base with the Beaver No. 64 blade should remove all necrotic tissues (Fig. 7.19a). The tissues are usually transparent to opaque and partially liquefied or very soft. The pedicle graft is usually prepared from the dorsal bulbar conjunctiva because of improved exposure. The size and shape of the pedicle are outlined on the dorsolateral bulbar conjunctiva (Fig. 7.19b). The pedicle edges include the dorsolateral limbus and toward the fornix. The pedicle should be approximately 1–2 mm wider than the corneal defect. The pedicle base is constructed to be slightly wider than its tip to ensure adequate perfusion of the pedicle’s tip. The bulbar conjunctiva is incised and separated from the underlying Tenon’s capsule by alternating blunt–sharp dissection by small curved blunt-tipped tenotomy or Steven’s scissors

Fig. 7.20 Three-week postoperative appearance of an established bulbar conjunctival pedicle graft in a dog.

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(Fig. 7.19c). Once prepared, the conjunctival pedicle graft is placed on the cornea and its tip trimmed to match the edge of the ventral corneal defect (Fig. 7.19d). The pedicle graft should not be stretched or excessively slack, and rotated less than 45
from the vertical. A single suture is placed along the long axis of the pedicle graft in the dorsal corneal defect edge to ensure contact between the corneal ulcer base and the graft. The remaining tip of the pedicle graft and then the sides are gradually spread and apposed directly to the corneal defect edges with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.19e). The conjunctival wound created by the construction of the conjunctival pedicle graft is apposed with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.20).

Pedicle tarsopalpebral conjunctival graft Pedicle tarsopalpebral conjunctival grafts from the upper eyelid offer another source, the tarsopalpebral conjunctiva, for an autogenous mucosa transplant for corneal defects. The pedicle of the tarsopalpebral conjunctiva is directly apposed to the central corneal defect. This method may be used when dorsal bulbar conjunctiva is not available or diseased. As movement between the eye and upper eyelid is unavoidable, a partial temporary tarsorrhaphy for 2–4 weeks is recommended after placement of the tarsopalpebral conjunctival graft. The corneal ulcer is carefully debrided to remove all the potentially necrotic tissues and prepare a bed for the conjunctival graft. The upper eyelid is grasped and everted with a chalazion or entropion clamp (Fig. 7.21a). The clamp facilitates graft construction and provides hemostasis. The

Conjunctival grafts/transplantation

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Fig. 7.21 Tarsopalpebral conjunctival graft in the dog or cat. (a) The upper eyelid is clamped and everted with a chalazion forceps. A small transpalpebral conjunctival graft is prepared by incision with the Beaver No. 6400 blade. (b) The tarsopalpebral conjunctival graft is apposed to the central corneal ulcer by at least three 5-0 to 7-0 simple interrupted absorbable sutures. After apposition of the graft to the corneal ulcer, a partial temporary tarsorrhaphy is performed to cover the graft and reduce eyelid movements.

tarsoconjunctiva is incised to prepare a pedicle graft that is about 1 mm larger than the corneal defect. The length of the pedicle graft should be sufficient to span the corneal surface and upper eyelid without traction and restriction of eyelid movements. The tarsopalpebral conjunctiva is elevated from the underlying tarsus and orbicularis oculi muscle layer by sharp dissection with a scalpel or tenotomy scissors. The tarsopalpebral conjunctival graft with the epithelial layer exposed is attached to the corneal defect with at least three 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 7.21b). The sutures should be placed to a depth of one-half to two-thirds thickness of the viable cornea surrounding the graft. A partial temporary tarsorrhaphy may be used to restrict eyelid movement, but still allow topical medication, patient vision, and eye examinations. Excessive manipulation of the eyelids postoperatively should be avoided.

postoperative period as with the other conjunctival grafts. Like the other partial conjunctival grafts, preservation of the patient’s vision, unimpaired drug penetration into the cornea and anterior segment, and postoperative eye examinations are facilitated. However, unlike the other conjunctival grafts, improvement of blood supply of the corneal ulcer area is not rapid, which may be very important in septic corneal ulcers. The surgical technique is quite simple. The corneal ulcer is carefully debrided and all possible necrotic tissues excised. With the upper eyelid everted and clamped with a 9 mm chalazion clamp, a circular section of transpalpebral conjunctiva is harvested by a razor blade held by the Castroviejo blade breaker (Fig. 7.22a). An alternative procedure utilizes dorsal bulbar conjunctiva. Incision with the Beaver No. 6400 microsurgical blade is usually less satisfactory. The graft’s base is undermined at the level of the mid tarsus with Steven’s tenotomy scissors (Fig. 7.22b). The graft should be about 10% larger than the corneal wound to compensate for graft shrinkage. After trimming to conform to the wound shape, the tarsoconjunctival graft is apposed to the corneal wound with either 8-0 to 9-0 nylon or simple interrupted absorbable sutures (Fig. 7.22c). Critical to the success of this type of graft is the meticulously closely placed sutures; often 15–20 sutures are employed for exact apposition between the free graft and the corneal wound edges (Fig. 7.23). The palpebral or bulbar conjunctival wound is allowed to heal by secondary intention. Without a blood supply, island grafts will rapidly blanch and remain white until vascularization from the cornea occurs within 10–14 days. Graft subsistence is apparently derived from the adjacent corneal stroma, aqueous humor, and tears. Central island grafts in corneas with no or very limited vascularization require additional time for the vascular supply to develop to the graft.

Corneoconjunctival autograft Island tarsopalpebral conjunctival graft Island tarsopalpebral conjunctival grafts have been used in dogs and cats. The free or island grafts have been useful for the surgical management of deep corneal ulcers, descemetoceles, and corneal perforations. These grafts with no blood supply are apposed directly to central or paracentral corneal defects. There is no need to trim these grafts in the

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The corneoconjunctival graft is a modified sliding conjunctival graft that transplants adjacent peripheral cornea and the attached bulbar conjunctiva into the central corneal wound. Another modification is corneoscleral transposition in which the adjacent cornea and sclera are shifted into a corneal defect. These methods permit transplantation of autogenous cornea from an adjacent healthy area in the

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Fig. 7.22 Island or free transpalpebral conjunctival graft. (a) An 8–9 mm circular section of tarsopalpebral conjunctiva is incised from the upper eyelid, grasped and clamped by a chalazion forceps. (b) The graft is separated from the deeper layers of the tarsus by scissors. The graft should be 1 mm larger than the corneal defect to compensate for tissue shrinkage. (c) The island tarsopalpebral conjunctival graft is apposed to the edges of the carefully debrided corneal ulcer by 15–20, 8-0 to 9-0 simple interrupted sutures with either non-absorbable or absorbable material. These sutures are meticulously placed to prevent any interruptions between the graft and corneal ulcer surfaces.

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Fig. 7.23 One month postoperative appearance of an island or free transpalpebral conjunctival graft in a dog. Both graft and cornea contain numerous blood vessels.

Fig. 7.24 Corneal sequestrum involving the deeper corneal stroma in a short-haired domestic cat. After excision of the sequestrum, the corneal defect will be filled with a corneoconjunctival transposition.

same eye and usually yield less central corneal scarring. Their use in infected and progressive bacterial corneal ulcers should be delayed until the infectious and melting (protease) process has been resolved. Their use in fungal infected corneas is not recommended. Transposition of a normal healthy cornea into an infected environment will not be successful. Corneoconjunctival transposition has been used successfully for treatment of deep corneal ulceration, descemetocele, and feline corneal sequestration affecting the deeper layers of the cornea (Fig. 7.24). Corneoscleral transposition is indicated for full-thickness defects of the cornea and is presented in Chapter 8. After surgical preparation and placement of a lightweight eyelid speculum, a lateral canthotomy is performed to improve exposure. The corneal ulcer site is carefully

debrided to remove all potentially infected and/or necrotic tissue. Often the corneal bed is enlarged 1 or 2 mm for adequate removal of all suspect tissues. The sliding graft of cornea and conjunctiva is then prepared. Extending from the corneal wound dorsally, two partial-thickness, slightly diverging corneal incisions are created by the Beaver No. 6400 microsurgical blade (Fig. 7.25a). Once the limbus is traversed, the dissection plane is altered to subconjunctiva, and the bulbar conjunctiva is incised by the scalpel blade or small tenotomy scissors. The edge of the corneal transposition is elevated by small thumb forceps, and, by sharp dissection with the Beaver No. 6400 microsurgical blade or a corneal lamellar knife-dissector, the corneal epithelium and about one-half of the thickness of the stroma are

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D Fig. 7.25 Corneoconjunctival transposition. (a) The corneal bed is carefully prepared to remove any diseased tissues. Two slightly diverging corneal stromal incisions with the Beaver No. 6400 blade are extended dorsally to the limbus. (b) The pedicle of anterior corneal stroma and epithelium is carefully separated from the deeper stroma by sharp dissection. (c) The dissection is continued by small tenotomy scissors between the bulbar conjunctiva and Tenon’s capsule for a sufficient length to accommodate ventral sliding into the corneal defect. (d) The end and sides of the corneoconjunctival pedicle are apposed by 5-0 to 7-0 simple interrupted absorbable sutures.

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Conjunctival grafts/transplantation

Fig. 7.26 One-month postoperative appearance of a corneoconjunctival graft. The portion of the graft at the center of the cornea will remain clear.

carefully incised to the limbus (Fig. 7.25b), usually using the base of the corneal defect as a reference. The dissection is continued by scissors into the subconjunctival space, separating the bulbar conjunctiva from the underlying Tenon’s capsule (Fig. 7.25c). When the subconjunctival attachments of the conjunctival mucosa have been separated, the entire graft can be positioned into the corneal defect and trimmed, if necessary, to fill the corneal wound. The transplanted cornea should be 0.5–1 mm wider than the corneal defect to compensate for shrinkage of the grafted corneal tissue. The edges of the entire corneoconjunctival graft are carefully apposed to the corneal wound with 5-0 to 7-0 simple interrupted absorbable sutures (Figs 7.25d and 7.26).

Postoperative patient management, success rates, and potential complications The postoperative management of all of the conjunctival grafts is similar. Often a partial temporary tarsorrhaphy is used at the conclusion of the graft procedure to reduce eyelid trauma to the surgical site, reduce exposure, provide pressure on the graft site, permit topical medication, allow patient vision, and facilitate daily ophthalmic examinations. An E-collar or other restraint device is also recommended to prevent self-trauma to the eye and surgical site by the small animal patient. Although inconvenient, these protective collars should be worn by the patient for approximately 2 weeks or until the conjunctival graft appears well established. Topical medications are directed at the corneal ulcer, tear film proteases, and secondary anterior uveitis. Topical and often systemic antibiotics are administered to either treat corneal sepsis or prevent secondary corneal infection. Topical mydriatics, such as 1% atropine, are instilled a few times to initiate and maintain mydriasis, but prolonged and excessive topical atropine can reduce tear production by 50% or more. Topical antiproteases such as autologous serum and/ or EDTA are used to reduce tear film protease activity to allow for faster healing. Tear film proteases will attack absorbable sutures to cause premature graft retraction. Topical and systemic treatments are usually administered for 5–10 days; thereafter only topical medications are continued until the graft is established. Topical antibiotics/ corticosteroids and/or cyclosporine may be administered about 20–30 days postoperatively to reduce corneal scarring and pigmentation. Suture removal is generally not necessary unless nonabsorbable sutures are employed. The complete,

advancement, and pedicle conjunctival grafts are usually trimmed and the limbal base severed by scissors under topical anesthesia about 4–6 weeks postoperatively. Trimming of the conjunctival graft that is adherent to the corneal wound is not usually necessary unless excessive and protruding mucosa are present. In time, these conjunctival grafts will gradually conform to the corneal curvature, and the majority will become pigmented. The success rates for conjunctival grafts in all animal species are quite high. In one study in which 90% of the conjunctival grafts were pedicle, the overall success rate in dogs as judged by structural integrity of the cornea was 91%. The success rate for the free or island tarsopalpebral conjunctival graft in dogs and cats was 98%. There are several reasons for conjunctival graft failures and most are related to: 1) technique; 2) inadequate corneal wound preparation; and 3) aqueous humor leakage under these grafts (Box 7.1). Adequate corneal wound debridement cannot be overemphasized, as the presence of necrotic and infected tissues within the corneal bed can contribute to graft dehiscence. Bacterial wound infections of the surgical site and suture failures are infrequent. Aqueous humor appears toxic to conjunctival fibroblasts; leakage of aqueous humor under these grafts causes graft thickening and seems to prevent permanent apposition of the graft to the base of the corneal wound. Seidel’s tests should be performed pre- and postoperatively to detect corneal perforations. Circumferential sutures placed at one-half to two-thirds thickness of the cornea seem to offer the best technique to minimize this complication. Sutures within a conjunctival graft should be placed radially and along the long axis of the pedicle graft not only to avoid blood vessel occlusion, but also to provide the optimum apposition of the graft to the corneal wound. In deep or perforated corneal ulceration, failure of a conjunctival graft should not prevent the placement of another conjunctival graft to maintain corneal integrity and hopefully preserve vision.

Permanent conjunctival grafts Conjunctival grafts are usually employed as temporary transplants to strengthen a weakened cornea. Within 4–6 weeks, the base of the conjunctival graft is severed. However, the advancement and pedicle bulbar conjunctival grafts may be left in position permanently with their bases not transected for selected chronic and/or recurrent conditions, such as keratoconjunctivitis sicca and feline corneal sequestration.

Box 7.1

Causes of conjunctival graft failures

1. Incomplete corneal site preparation and debridement of necrotic and/or septic tissues 2. Incomplete covering of the surgical site 3. Aqueous humor leakage from deep or perforated corneal ulcers 4. Graft direction is greater than 45
from the vertical 5. Excessive stretching of the graft 6. Wound infection 7. Suture and/or knot failure 8. Infarction of conjunctival graft vessels

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Depending on the size and position of the conjunctival graft and pupil size, vision may still be present. The persistent corneal edema in phthisis bulbi (results from intraocular pressure below 5 mmHg) and corneal endothelial dystrophy (results from defective corneal endothelia) can be permanently and totally covered by a thin complete bulbar conjunctival graft. These grafts can reduce corneal edema, prevent the formation of painful vesicles, and, if thin enough, can permit limited clinical vision in small animals.

Substitute materials for conjunctival grafts There are patients in which adequate and viable conjunctiva may not be available for grafting to corneal defects. Most of these patients have had previous conjunctiva and/or lid surgeries, and the dorsal conjunctiva is scarred or of inadequate amount to perform the surgery. Pedicle bulbar grafts may be constructed from the ventral conjunctiva, but the surgery is more difficult and the amount of available conjunctiva quite limited. Fortunately, there are both experimental and commercially available alternatives. These include the porcine small intestinal submucosa (SIS) graft which is available commercially, and the amniotic graft, available experimentally. Both grafts have been covered with pedicle conjunctival grafts in some patients while in other patients they are the sole ‘patch’ to cover the corneal defect. Both grafts seem to tolerate placement in uncontrolled septic corneal ulcers; in these patients covering these avascular grafts with a pedicle bulbar conjunctival graft is recommended.

Porcine small intestinal submucosa (SIS) grafts The SIS graft provides a scaffold for corneal healing as well as additional strength to the overlying bulbar conjunctival graft. Rabbit corneal SIS graft studies suggest that the graft collagen sheet is actually incorporated into the healing process. The SIS graft is derived from the porcine jejunum and is composed of three distinct layers: 1) tunica muscularis mucosa; 2) tunica mucosa; and 3) the stratum compactum layer of the tunica mucosa. Following processing and mechanical debridement, a few remaining endothelial cells and fibrocytes are lyzed with a hypotonic wash, leaving a sheet of collagen with a smooth surface (stratum compactum) and a rough surface (tunica muscularis mucosa). The SIS graft is sterilized by ethylene oxide, and supplied commercially as either 7  10 mm sheets, or 10 mm and 15 mm diameter ophthalmic discs. The SIS graft is a biomaterial consisting primarily of proteins and, to a lesser extent, carbohydrates and lipids. Closer analyses of the SIS graft indicate that it has ideal qualities for corneal replacement and healing, and consists of collagen (types I, III, and VI), glycosaminoglycans (hyaluronic acid, chondroitin sulfate A and B, heparin, and heparin sulfate), and other glycoproteins (fibronectin), as well as fibroblastic growth factor (FGF-2) and transforming growth factor b (TGF-b). The SIS graft is acellular, biodegradable, non-immunogenic, and xenogeneic. By providing a scaffold for healing, the results are more like regeneration, rather than replacement and scar formation. In rabbits

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and dogs, after lamellar corneal transplantation with SIS grafts, re-epithelialization occurred after 7 and 14 days, respectively. After debridement of the septic corneal ulcer, the SIS graft is carefully trimmed and ‘fitted’ to cover in excess of 1– 1.5 mm of the entire corneal ulcerative bed. After securing the graft to the ulcer’s edges with several 7-0 to 9-0 simple interrupted absorbable sutures, the entire SIS graft is covered with a bulbar pedicle conjunctival graft. SIS grafts have been reported in dogs, cats, rabbits, and horses. SIS grafts have been reported to fill the limbocorneal defect after limbal melanocytoma excision and covered with bulbar conjunctiva, for full-thickness corneal ulcerative disease in dogs and covered with conjunctival grafts, after corneal ulcers and corneal sequestra in cats and not covered with conjunctival grafts, and after corneal ulceration and corneal stromal abscess formation in horses and covered with conjunctival grafts. These grafts are convenient to use, are commercially available and ready for use, avoid potential virus transmission as is possible with feline-based grafts, and are easy to handle during surgery. If placed in an uncontrolled septic corneal ulcer, covering with a conjunctival graft is highly recommended. If used alone and successful, it appears that the SIS graft-treated corneal defects are more translucent than those treated with pedicle bulbar conjunctival grafts.

Amniotic grafts as conjunctival substitutes Amniotic grafts have been reported to repair deep corneal ulcers in horses and for experimentally induced full-thickness corneal defects dogs. The amniotic grafts for both the horse and dog studies were harvested from normal equine placenta and are not available commercially. In the dog study, after harvest, the amniotic grafts were preserved in 98% sterile glycerol (full-thickness scleral grafts are commonly preserved in glycerol). The equine amniotic graft is obtained aseptically as a 5 mm2 section of amnion after death or cesarean section. After harvest, the tissues are preserved in 98% sterile glycerol; immediately before use the tissue is rehydrated in sterile saline solution.

Other tissues for conjunctival substitutes The equine pericardium has also been used in surgery to correct canine lateral canthal entropion, deep corneal ulcerations in dogs, fill the orbital cavity of dogs after enucleation, and as a scleral graft. Equine renal capsule grafts have also been used to cover large corneal defects in dogs.

Adaptations in large animals and special species Conjunctival grafts or flaps are used frequently in equine ophthalmology for the clinical management of deep, melting, and large corneal ulcers, descemetoceles, and for perforated corneal ulcers with and without iris prolapse. Conjunctival flaps are best mobilized from the bulbar conjunctiva. We do not recommend using the conjunctiva near the nictitans, as nictitans movement postoperatively can put tension on the graft and result in premature graft release. Conjunctival grafts can be

Adaptations in large animals and special species

transposed and sutured onto the cornea to provide sufficient tissue to strengthen most weakened corneas, but are not as strong as corneal grafts (Fig. 7.27). Conjunctival autografts contain limbal stem cells, blood vessels, and lymphatics to offer significant antibacterial, antifungal, antiviral, antiprotease, and anticollagenase effects. With conjunctival grafts, polymorphonuclear leukocytes, antibodies, serum, and a2macroglobulins are immediately placed in the corneal ulcer bed. Systemic antibiotics can enter the ulcer site in higher levels through leakage from the conjunctival graft vasculature. The fibrovascular or deeper layer of the conjunctival transplant offers immediate fibroblasts and collagen to begin rebuilding of the corneal stroma. Conjunctival grafts usually result in various sizes and degrees of corneal scars. Scarring can be minimized by removal of necrotic cornea by keratectomy prior to graft placement. Postoperative topical corticosteroids can reduce this postoperative scar tissue formation to a minimum, but corneal scarring after conjunctival grafts should be anticipated. Conjunctival autografts are more difficult to perform than nictitating membrane flaps, but are simpler than corneoconjunctival and corneoscleral transpositions, and penetrating

keratoplasty surgeries. They are easier to perform in the horse than in other species as the horse has a great deal of very mobile conjunctiva. To perform optimal conjunctival grafts in horses, general anesthesia is recommended. Magnification using a head loupe, head-mounted telescope or the operating microscope is recommended. Ophthalmic instruments and suture sizes are identical to those in small animals. Conjunctival autografts from either bulbar or palpebral conjunctiva should be thin, and should not include Tenon’s capsule or the bulbar fascia. Tenon’s capsule should be stripped or cut from the graft such that the graft lies over the corneal defect prior to suture placement. The inclusion of Tenon’s capsule may contribute to surgical failure by increasing the traction on the transplanted conjunctival graft. Conjunctival flaps should have tension-relieving sutures placed at the limbus to prevent the graft pulling off the ulcer bed prematurely. Conjunctival pedicle grafts utilizing bulbar conjunctiva from the dorsal or temporal quadrants are my preference as the conjunctiva in those areas is surgically available, and the pedicle flaps cover only the ulcer surface to allow postoperative observation of the pupil and anterior chamber as the graft does not

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Fig. 7.27 Examples of bulbar conjunctival grafts in the horse. (a) Acute corneal ulceration with central descemetocele in a young Thoroughbred foal. Note the diffuse corneal edema and peripheral corneal vascularization. (b) Same eye 2 weeks postoperatively after successful treatment with a pedicle bulbar conjunctival graft. The ocular and corneal inflammation have markedly regressed. (c) Postoperative appearance (4 weeks) of a combination of bridge (horizontal) and pedicle (6 o’clock position) bulbar conjunctival grafts in an adult horse with a deep central corneal ulcer. (d) Three day postoperative appearance of a dehisced or failed pedicle bulbar conjunctival graft in a deep corneal ulcer infected with a combination of b-Streptococcus and Pseudomonas spp. in a adult horse. The loose end of the unsuccessful pedicle graft as well as the remaining corneal absorbable sutures are still present.

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cover the entire cornea. If possible, melting ulcers should be stabilized with medical therapy prior to graft placement in order to prevent protease digestion of absorbable sutures holding the conjunctival graft in place. Temporary tarsorrhaphies are performed concurrently with conjunctival grafts to minimize blinking movements to the corneal sutures and allow quick graft adherence to the stroma.

Surgery for aberrant conjunctival overgrowth in rabbits Aberrant conjunctival overgrowth, pseudopterygium or precorneal membranous occlusion is a recently described conjunctival disease which appears unique to this species. The disease is characterized by proliferation of the bulbar and palpebral conjunctiva in a circular manner which eventually nearly totally occludes the corneal surface (Fig. 7.28). This aberrant conjunctiva does not adhere to the cornea. It can affect one or both eyes in young and adult rabbits, and the dwarf breeds may be predisposed. Surgeries used to treat this condition include: 1) simple resection; 2) repositioning of conjunctiva to the limbus; 3) dividing the aberrant conjunctiva into medial and lateral portions, and relocation to the fornix; and 4) centrifugal incisions of the aberrant conjunctiva to the limbus and transpalpebral fixation of the conjunctiva. In the last technique, the conjunctival overgrowth is divided into six more-or-less equal sections and incised to the limbus. With simple mattress non-absorbable sutures placed through the base of the eyelid, the tip of each conjunctival section is retracted into the conjunctival fornix. Postoperative treatment usually consists of topical antibiotics and corticosteroids for several days. Topical cyclosporine may delay or prevent recurrence. The transpalpebral method of fixation of the aberrant conjunctiva to the conjunctival fornix seems the most effective procedure at this time.

SURGERIES OF THE NICTITANS Surgeries of the nictitans are common in small animal practice, and may be used to treat primary nictitans diseases, as well as diseases of the adjacent conjunctiva and cornea. Excision of the entire nictitans is not recommended except for

Fig. 7.28 Rabbit with aberrant conjunctiva. The proliferative conjunctival overgrowth is attached at the limbus but is not adhered to the conjunctiva, and totally surrounds the cornea.

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generalized and advanced third eyelid neoplasia. In the past 10–15 years, several surgical procedures have evolved to treat the prolapsed nictitans gland or ’cherry eye’, and preserve as much as possible tear production in the dog. Surgeries of the nictitans in horses and cattle most often involve neoplasia. Squamous cell carcinomas are the most frequent neoplasms in both species, and with the often considerable involvement the entire nictitans must be removed. In addition, neoplasia of the nictitans of both of these species has a greater tendency to infiltrate the deeper orbital tissues and necessitate exenteration of the entire orbit.

Surgical treatment of everted nictitans Occasional malformations of the nictitating membrane cartilage occur, usually resulting in eversion of its leading margin (Fig. 7.29). Infrequently, the abnormality results in an inversion or an inward scroll-like deformity of the cartilage. The condition usually presents unilaterally, but bilateral involvement may occur eventually. Eversion of the third eyelid cartilage usually affects the large and giant breeds of dogs, including the Great Dane, St Bernard, German Shepherd, Weimaraner, Newfoundland, German Shorthaired Pointer, many retriever breeds, and English Bulldog. Inheritance has been suggested in the German Shorthaired Pointer. Eversion of the nictitating membrane cartilage may also occur after trauma and surgery. Eversion of the nictitans usually occurs in dogs during the first year of life. The condition also occurs in cats. Clinical signs consist of a raised pink deformity of the medial canthus, which upon closer inspection is the curled nictitans with its posterior leading margin exposed. Secondary chronic conjunctivitis and epiphora may be present. The defect affects the upper portion of the stem of the T-shaped cartilage resulting in a U-shaped abnormality that reflects forward from the leading margin of the nictitans (Fig. 7.30). Microscopic examination of affected areas of the cartilage reveals no abnormalities, although this area is probably the weakest part of the cartilage. Suggested cause(s) include prominence of the nictitans, cartilage defect, and adherent conjunctival surfaces.

Fig. 7.29 Eversion of the nictitating membrane in a Great Dane puppy. With eversion of the leading margin, the posterior or bulbar aspect of the nictitans becomes visible.

Surgical treatment for hyperplastic lymphoid follicles

Fig. 7.30 Curled section of the hyaline cartilage excised to treat eversion of the nictitating membrane. Scale in millimeters.

Surgical treatment for eversion of the nictitating membrane cartilage consists of local excision of the affected cartilage without disturbing the pigmented margin (Fig. 7.31a). Surgical trauma to the pigmented margin may result in the loss of pigment to this area. After excision of the ’curled’ cartilage, the leading margin of the nictitating membrane should re-establish in its normal position and conform to the corneal curvature (Fig. 7.31b). After general anesthesia, the corneal and conjunctival surfaces are carefully cleansed with sterile cotton-tipped applicators and the area irrigated with 0.5% povidone–iodine.

The eyelid hair is not usually clipped. After draping, the nictitating membrane is protracted by thumb forceps, being careful to avoid the leading margin. A small linear incision through the bulbar surface of the mucosa is performed with small tenotomy scissors directly over the involved cartilage (Fig. 7.32a). By careful blunt–sharp dissection, the scroll-like section of the nictitating membrane cartilage is removed (Fig. 7.32b). The surgical wound is not usually apposed and is allowed to heal by secondary intention. If apposition by sutures is preferred, a 50 to 7-0 simple continuous suture or simple interrupted absorbable sutures are placed submucosally and the knots buried to avoid suture contact with the cornea. The immediate postoperative appearance is usually a slightly swollen but normal-appearing nictitating membrane (Fig. 7.32c). Postoperative medical treatment consists of topical antibiotics/ corticosteroids several times a day for 5–7 days. Recurrence after surgical correction is most unlikely.

Surgical treatment for hyperplastic lymphoid follicles Limited numbers of lymphoid follicles occur normally on the deep or bulbar surface of the nictitating membrane. In chronic inflammation there may be abundant numbers of lymphoid follicles on both surfaces (Fig. 7.33). Mechanical debridement of excessive lymphoid follicles with dry cotton gauze or a blunt scalpel blade is sometimes indicated if topical antibiotic/corticosteroid therapy has been unsuccessful. Use of silver nitrate or

Fig. 7.31 Results of surgical correction of the everted nictitating membrane in a dog. (a) Preoperative appearance of an everted nictitating membrane in a German Shepherd dog. (b) Immediate postoperative appearance after excision of the affected cartilage portion.

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Fig. 7.32 Technique for surgical correction of the everted nictitating membrane. (a) To correct the everted nictitating membrane, the nictitans is protracted to expose its bulbar (deep) surface. With tenotomy scissors, a small linear incision is made through the mucosa directly over the affected cartilage. (b) By blunt–sharp scissor dissection, the scroll-like section of cartilage is isolated and excised. (c) With the defective area of cartilage removed, the nictitating membrane leading margins will return to normal position.

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Fig. 7.35 Protrusion of the gland of the nictitating membrane in a young Miniature Poodle dog. Note the smooth surface of the prolapsed gland.

Fig. 7.33 Excessive lymphoid follicles on the bulbar (deep) surface of the nictitating membrane.

copper sulfate crystals to chemically destroy these follicles is not recommended because additional conjunctival and/or corneal damage may result if these compounds contact their surface. After topical anesthesia, the nictitating membrane is protracted with thumb forceps to expose the excessive lymphoid follicles on the palpebral and/or bulbar surfaces. With a blunt scalpel blade or a section of dry surgical sponge wrapped around a small curved hemostat, the surface is vigorously rubbed to rupture and remove the follicles (Fig. 7.34). Limited hemorrhage may occur. After scraping of the lymphoid follicles, topical antibiotics/corticosteroids are usually administered three or four times a day for several days.

Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’ Protrusion of the gland of the nictitating membrane is not infrequent in dogs and most affected animals are less than 1 year of age (Fig. 7.35). Although usually presented with a unilateral protrusion of the nictitans gland, the condition may eventually become bilateral. The condition occurs most commonly in the American and English Cocker Spaniel, English Bulldog, Beagle, Pekingese, Boston Terrier, Basset

Fig. 7.34 To remove most of the lymphoid follicles, carefully scrape the area with a dull Beaver No. 6400 microsurgical blade.

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Hound, Lhasa Apso, and Shih Tzu. The condition occurs infrequently in young cats and mainly in the Burmese breed. Although protrusion and prolapse of the nictitating membrane gland is a relatively common condition in the dog, the pathogenesis of the condition has not been determined.

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Is the adenitis primary to the development of the gland enlargement and protrusion or secondary? Are fascial abnormalities present that attach the cartilage and/or gland to the periorbital fascia and predispose to the condition? Are specific pathogens involved in this adenitis? With protrusion and enlargement of the third eyelid gland, are there simultaneous changes occurring in the lacrimal gland?

The occurrence of keratoconjunctivitis sicca in dogs after this condition would certainly suggest that both the lacrimal and the nictitans tear glands are eventually involved. As the pathogenesis of the protrusion of the nictitating membrane gland is revealed, medical and/or surgical treatment strategies may become further refined. Protrusion of the superficial gland of the nictitating membrane results from hypertrophy and hyperplasia of the gland sufficient to extend beyond the leading margin of the nictitans (Fig. 7.36). Secondary epiphora, conjunctivitis, an obvious mass at the medial canthus, and local irritation are the usual presenting clinical signs (Fig. 7.37). Microscopic examination of affected glands usually reveals dacryoadenitis, but detailed studies and isolates for viral and other pathogens have not been reported.

Fig. 7.36 Protrusion of the gland of the nictitating membrane in a Boston Terrier dog as viewed from its posterior surface. Part of the swollen gland extends from the base of the nictitans.

Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’

Box 7.2 •

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Fig. 7.37 Chronic protrusion of the gland of the nictitating membrane in a mixed breed dog. Note the lymphoid follicles on the surface of the swollen gland.

Topical antibiotics or antibiotic/corticosteroid therapy may be used to treat early and mild cases. Reduction in the local inflammation and edema of the conjunctiva may result in the gland returning to its normal size and position. Unfortunately, topical medical treatment is often unsuccessful, and surgical treatment of the prolapsed gland of the nictitans is necessary. The standard procedure for surgical treatment of the prolapsed third eyelid gland prior to about 1980 was conservative excision of the prolapsed portion of the gland to preserve as much as possible of this important tear source. As indicated earlier, the gland of the nictitating membrane in both the dog and cat provides about 25–40% of the total tears. Although protrusion of the nictitating membrane gland and keratoconjunctivitis sicca occur in many breeds of dogs, the interrelationships of these two conditions is poorly understood. One study involving 33 dogs with protrusion of the third eyelid gland for at least 2 years that had had either excision (partial) of the nictitans gland or surgical replacement, suggested that keratoconjunctivitis sicca developed in 48% of the eyes treated by excision of the gland, in 43% of the eyes with prolapsed glands left untreated, and in 14% of the eyes treated with surgical replacement of the gland. In the most frequently affected breeds, i.e., American Cocker Spaniel, Lhasa Apso, and English Bulldog, keratoconjunctivitis sicca developed in 47.3% of all affected eyes: 59% of eyes treated by gland excision, 17% of eyes treated with gland replacement, and 75% of eyes with the nictitans gland left prolapsed. Several procedures have been developed to treat protrusion of the nictitating membrane and still retain this tear gland (Box 7.2). These methods may be arbitrarily divided into those that retract or anchor the prolapsed gland via its cartilage, and those that cover (envelope or imbrication) the prolapsed gland with adjacent mucosa to force it into a normal position. Those methods that attempt to anchor the cartilage and retract the prolapsed gland prevent normal movements and protraction of the nictitating membrane. The surgical procedures that incise the bulbar (or deep aspects) of the nictitating membrane surface and cover the prolapsed gland with adjacent conjunctival mucosa risk

Surgical procedures for replacement of the canine prolapsed gland of the nictitating membrane

Posterior nictitans anchoring or tacking approach – To ventral oblique muscle (Albert, Garrett, Whitley) – To ventral equatorial sclera (Gross) – To ventral periorbital fascia (Blogg) Anterior nictitans anchoring or tacking approach – To ventral periorbital rim (Kaswan and Martin) Intranictitans anchoring of glands (Plummer et al) Imbrication or mucosa envelope: scarification and cover with adjacent conjunctival mucosa (Moore) Envelope or mucosa pocket: cover with adjacent mucosa (Morgan/Moore)

direct damage to the ducts of the third eyelid gland, and have generally been replaced by the anterior approach. The excretory ducts of the nictitans gland exit the gland and emerge in the middle section of the bulbar mucosa surface. Hence, any surgical technique to treat this condition should have three goals: 1) adequately replace the prolapsed gland behind the nictitans leading margin; 2) result in no postoperative limitations on nictitating membrane movements; and 3) produce no damage or loss of glandular tissues including the excretory ducts. One method may not achieve all of these goals equally nor be effective in treating all degrees of third eyelid gland protrusion: those procedures that effect anchoring the nictitans cartilage more deeply may be more successful for the more extensive and chronic gland prolapses; the pocket methods may be more effective in puppies and for mild protrusions of the third eyelid gland. The surgical procedures will be divided based on entry to the prolapsed nictitans gland: 1) from the posterior or bulbar surface of the nictitans to anchor the cartilage base to the ventral epibulbar fascia, ventral equatorial sclera, or ventral oblique muscle; 2) from the anterior or palpebral surface of the nictitans to anchor the nictitans cartilage to the periosteum of the orbital rim; 3) intranictitans anchoring or tacking of the gland; and 4) partial-to-complete covering of the prolapsed gland with adjacent conjunctival mucosa (pocket and imbrication methods). For all of these surgical procedures, surgical preparation is limited. After the onset of general anesthesia, the eyelid hair is not usually clipped, but thoroughly cleansed with surgical soap and irrigated with sterile saline. The conjunctival and corneal surfaces are cleansed with sterile cotton-tipped applicators to remove any exudates and debris, and rinsed with 0.5% povidone–iodine solution. A small wire eyelid speculum is placed to retract the eyelids.

Posterior (bulbar) nictitans anchoring approach For the posterior nictitans anchoring approach, the posterior conjunctival fornix behind the nictitating membrane is incised, an anchor suture is positioned into the deeper fascial or ocular tissues, and the gland is retracted by suture. The anchoring suture retracts the prolapsed gland into position, but prevents normal nictitans movements thereafter.

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Surgical procedures for the conjunctiva and the nictitating membrane

Recent studies indicate that the posterior surface of the nictitans gland contains ductules from the underlying secretary gland; therefore, to maintain tear secretion, the nictitans gland and its posterior surface should not be separated. Also, the posterior methods are more difficult to perform than the anterior approach, and the anchoring suture is more likely to retract from the orbital or globe base. As a result, the anterior methods are more popular. In the anchoring procedures by Blogg, Gross, and others, the nictitating membrane is protracted by thumb forceps to expose its deep or bulbar surface and the prolapsed gland (Fig. 7.38a). By Bard–Parker No. 15 scalpel or Beaver No. 6400 microsurgical blade, an incision is made starting at the limbus and extending to the posterior aspects of the prolapsed gland (Fig. 7.38b). The gland is thoroughly separated from its conjunctival and periorbital fascial attachments by blunt-tipped tenotomy scissors. The globe is then rotated by thumb forceps to expose the bulbar conjunctival fornix. By blunt dissection with tenotomy scissors, the deeper

aspects of the incision are exposed to reveal the ventral sclera close to the equator of the globe, the ventral oblique muscle, or strong periorbital fascia (Fig. 7.38c). A 4-0 monofilament nylon (or other non-absorbable) suture with a cutting needle is placed through the dorsal portion of the gland and then 6–10 mm into the peribulbar area to anchor to the ventromedial equator, periorbital fascia, or the ventral oblique muscle (Fig. 7.38d). The more extensive the nictitans gland protrusion, the deeper the site for the anchoring suture. As the suture is tied, the gland should return to its approximate normal position (Fig. 7.38e). The conjunctival mucosa incision is apposed with a 5-0 to 6-0 simple continuous absorbable suture (Fig. 7.38f,g). A modification of this procedure reduces the possibility of disturbing the gland and its posterior ductules, but is more difficult. The initial incision extends from the ventromedial limbus to the posterior aspects of the gland, and then is continued to encircle the gland’s posterior surface (Fig. 7.39a). Using tenotomy scissors, the gland is isolated

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Fig. 7.38 Posterior nictitans anchoring method for treating gland protrusion. (a) The bulbar surface of the nictitans is exposed to reveal the extent of the gland prolapse. (b) The mucosa is incised by a Beaver No. 6400 microsurgical blade from posterior of the gland to the medioventral conjunctival fornix and then to the limbus. Unfortunately, this may damage the majority of the nictitans gland’s ducts. (c) The basal portion of the gland and the nictitans cartilage are carefully separated from their fascial attachments by scissor dissection. By blunt dissection with tenotomy scissors, the anchor site (the ventral sclera, ventral oblique muscle or periorbital fascia) is isolated. (d) A 4-0 green monofilament nylon suture with a reverse-cutting needle is passed through the prolapsed portion of the gland and the anchor site. (e) As the suture is tightened and tied, the gland should return to its original position. (f) The conjunctival mucosa is apposed with a 5-0 to 6-0 simple continuous suture. The knots are buried to prevent corneal contact. (g) Cross-section of the completed surgery: (A) eyelid; (B) nictitans cartilage; (C) nictitans’ tear gland; (D) orbital bony rim; (E) deep anchor of the green non-absorbable suture.

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Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’

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Fig. 7.39 A modification of the posterior anchoring procedure attempts to retain as much of the prolapsed gland posterior mucosa and secretory ductules as possible. Because of the limited surgical exposure, large prolapses may not be candidates for this procedure. (a) The initial conjunctival incision by a Bard– Parker No. 15 scalpel blade extends from the ventromedial limbus to encircle the prolapsed gland. (b) The fascial attachments beneath the gland that attach to the stem of the nictitans cartilage are carefully transected by blunt scissor dissection. The ventral sclera, periorbital fascia or the ventral oblique muscles are also isolated. (c) A 4-0 green monofilament nylon suture with a cutting needle is used to encircle the gland and its deep orbit anchor. (d) As the suture is tied, the gland should shift to deep within the posterior nictitans fornix. (e) The conjunctival wound is closed with the nictitans gland posterior mucosal surface within its center with several 5-0 to 6-0 simple interrupted absorbable sutures. The knots of these sutures should not touch the cornea.

and the deeper ventral sclera exposed (Fig. 7.39b). A 4-0 monofilament nylon suture with a cutting needle is carefully positioned in the dorsal aspects of the prolapsed gland and then into the ventromedial equator, periorbital fascia, or ventral oblique muscle (Fig. 7.39c). As the knot is tied, the gland is positioned deep in the posterior conjunctival fornix (Fig. 7.39d). The conjunctival wound is apposed with the prolapsed gland and its mucosa in its center with several 5-0 to 6-0 simple interrupted absorbable sutures (Fig. 7.39e). The knots should not touch the corneal surface.

Anterior nictitans anchoring approach The anterior nictitans anchoring technique differs from the posterior anchoring technique by using the conjunctival fornix in front of the nictitans or the medial lower eyelid. The suture is still embedded beneath the conjunctival mucosa over the nictitans gland. If the anchoring point is more anterior of the current nictitans base, as the suture to retract the gland is tightened the nictitans may be displaced more anteriorly. In this approach, the nictitans is protracted by forceps to expose its palpebral surface and the palpebral conjunctival fornix at its base. A ventral linear incision of the anterior mucosa of the nictitans is performed with small tenotomy scissors (Fig. 7.40a). A 3-0 to 4-0 monofilament nylon suture is carefully placed in the periosteum of the ventromedial orbital rim and then directed dorsally to exit the top of the prolapsed nictitans gland (Fig. 7.40b). The suture is reintroduced into its exit hole and directed to the opposite side of the top of the prolapsed gland (Fig. 7.40c). The suture is then redirected into its second exit hole to emerge in the incision (Fig. 7.40d). As the suture is tied, the prolapsed gland should gradually

return to its normal position behind the leading margin (Fig. 7.40e). The conjunctival wound is apposed with a 5-0 to 6-0 simple continuous suture (Fig. 7.40f,g).

Intranictitans tacking procedure This new procedure, developed by the Florida veterinary ophthalmologists, utilizes the suture anchoring technique around the entire nictitans tear glands, but limits the surgery (essentially placement of a single suture) to only the nictitans, thereby permitting nictitans movements postoperatively. Imperative in this procedure is the base of the nictitans cartilage when the single suture enters and exits the nictitans, thereby providing an excellent strong base to anchor to the gland. This suture must pierce and not encircle the shaft of the nictitans cartilage during its insertion and egress to avoid the small blood vessels which parallel the shaft’s sides. This procedure involves no conjunctival mucosal incisions, and does not restrict nictitans movements postoperatively. A 4-0 nylon suture with a three-eighths circle 13 mm reverse P-3 cutting needle is passed from the anterior surface of the third eyelid through the base of the cartilage to the posterior aspect and tunneled circumferentially beneath the conjunctiva over and around the prolapsed nictitans gland. The suture is then passed back through the base of the cartilage shaft to the anterior surface of the nictitans. It is gradually tightened to compress the prolapsed gland into its normal position and tied with a surgeon’s knot (Fig. 7.41).

Conjunctival mucosa envelope procedure The conjunctival mucosa may be used to cover the prolapsed nictitans gland permanently and apply pressure to

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Surgical procedures for the conjunctiva and the nictitating membrane

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Fig. 7.40 Anterior nictitans anchoring (or tacking) technique. (a) The nictitans is protracted by thumb forceps to expose its palpebral (anterior) surface and the conjunctival fornix. A linear incision of the conjunctival mucosa is performed by small tenotomy scissors. (b) A 3-0 to 4-0 green monofilament nylon suture with a reverse-cutting needle is secured first in the periosteum of the ventromedial orbital rim and then directed dorsally to exit at the top of the gland. (c) Through the same suture hole, the needle is reinserted to exit at the opposite side of the gland. (d) The suture is then reinserted again to exit in the incision. (e) As the suture is tightened and tied, the prolapsed gland should return to its original position. (f) The conjunctival mucosal wound is apposed with a 5-0 to 6-0 simple continuous absorbable suture. (g) As viewed in cross-section, the suture is secured in the distal position of the prolapsed nictitating membrane gland and ventral periorbital fascia or the periosteum of the ventral orbital rim. Lower eyelid (A), cartilage of the nictitans (B), prolapsed gland of the nictitating membrane (C), the ventral orbital bony rim (D), and the deep anchor of the nylon suture (E).

maintain the gland protrusion behind the leading margin of the nictitating membrane. The imbrication or envelope method has been reported to be most successful for young puppies (10–12 weeks old) and for acutely prolapsed nictitans glands that are not large. The mucosa over the prolapsed gland is lightly scarified with a Bard–Parker No. 15 scalpel or Beaver No. 6700 microsurgical blade (Fig. 7.42a). The more extensive the scarification, the greater the permanent adhesions that develop postoperatively. With a 6-0 to 7-0 absorbable suture, two 4 mm bites on the ventral aspects of the gland and a larger 6–8 mm bite on the dorsal side of the prolapsed gland is performed (Fig. 7.42b). As the suture is tied, a sterile cotton-tipped applicator is used to depress the gland as the conjunctival mucosa is pulled over the prolapsed gland.

Conjunctival mucosa pocket procedure The conjunctival pocket method is recommended for older dogs and for chronic prolapses of the nictitans gland. Some

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veterinary ophthalmologists use this technique for all nictitans gland prolapses. In this procedure, the adjacent conjunctiva is incised into two 120–140
sections and apposed by sutures over the prolapsed gland. The open ends of the two conjunctival flaps allow the nictitans gland’s tears to continue to exit onto the corneoconjunctival surfaces. The nictitating membrane is protracted by thumb forceps to reveal the bulbar surface and the prolapsed gland (Fig. 7.43a). With the Beaver No. 6400 microsurgical blade, the mucosa above (about 2–3 mm from the leading margin) and below (next to the prolapsed gland and toward the bulbar conjunctival fornix for 6–10 mm) the prolapsed gland is incised for about 1 cm (120–140
). The ends of the two incisions should not connect to each other (Fig. 7.43b). The conjunctival mucosa overlying the prolapsed gland is left undisturbed. After careful dissection of the submucosa layer about both incisions by tenotomy or Steven’s scissors, the conjunctival incisions are apposed with a 5-0 to 6-0 simple continuous absorbable suture (Fig. 7.43c). If the tension

Surgical procedures for protrusion of the gland of the nictitating membrane or ’cherry eye’

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Fig. 7.41 Intranictitans tacking technique for nictitans prolapsed gland. (a) The 4-0 green nylon suture with a three-eighths circle 13 mm reverse P-3 cutting needle is first placed through the base of the cartilage of the third eyelid. (b) The suture is tunneled subconjunctivally around the gland on the posterior face of the nictitans. The needle must exit and re-enter the subconjunctival space at each corner for proper placement of the suture around the gland. (c) With the same suture exit and re-entry sites, no suture is exposed to irritate the corneal surface. (d) With the suture around the gland, the suture is passed back through the nictitans cartilage to its anterior surface. (e) The two ends of the suture are carefully tightened and tied to achieve the desired reduction of the prolapsed gland. (f) Side view of the prolapsed gland with its anchoring suture through the nictitans cartilage. (Reproduced with permission from Plummer CE, Ka¨llberg ME, Gelatt KN et al 2008 Intranictitans tacking for replacement of prolapsed gland of the third eyelid of dogs. Veterinary Ophthalmology 11:228–233.)

on the suture appears extensive because of a large glandular prolapse, 4-0 to 5-0 simple interrupted absorbable sutures are recommended. The knots are carefully buried to avoid corneal contact. Both ends of the incisions are left open to accommodate continued tear production by the nictitans gland (Fig. 7.43d,e).

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Fig. 7.42 The conjunctival mucosa envelope procedure is used to treat prolapsed nictitating membrane glands in young puppies. (a) The mucosa over the gland protrusion is lightly scarified by scraping with the Bard–Parker No. 15 scalpel or Beaver No. 6700 microsurgical blade. (b) With a 6-0 to 70 absorbable suture, two 4 mm bites of mucosa ventral of the gland and a single 6–8 mm bite anterior to the gland are used to appose the mucosa.

Postoperative treatment and complications Postoperative therapy after these procedures to reposition the gland of the nictitating membrane usually consists of topical antibiotics or antibiotics/corticosteroids three to four times daily until the prolapsed gland has reduced to about normal size, and supplemented for several days with an oral non-steroidal anti-inflammatory, such as carprofen (4 mg/kg PO q24h; RimadylW; Pfizer Animal Health, Exton, PA), and an E-collar or other restraint device. The surgical procedures that anchor the prolapsed nictitans gland to the retrobulbar sites are more difficult because of the more limited exposure, and may exhibit more lid or conjunctival swelling. With prolapsed glands that are chronic and large, the swelling within the gland may require several weeks to approximate normalcy. Long-term postoperative problems associated with the anterior and posterior anchor methods include entropion, restriction of movements by the nictitans, and re-prolapse if suture failure occurs or the anchor site is inadequate. Anchoring to the anterior periosteum has been associated with a mild anterior displacement of the nictitans base. Long-term postoperative complications after the envelope and pocket procedures avoid suture and/or wound failure

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Fig. 7.43 Conjunctival mucosa pocket procedure to treat nictitans gland protrusion. (a) The nictitans is protracted by thumb forceps to reveal its bulbar (deep) surface and the affected gland. (b) Two semicircular (140–160
) mucosal incisions are performed with the Bard–Parker No. 15 or Beaver No. 64 blade. (c) After separation from the submucosa, the two edges of the mucosa are pulled over the gland and apposed with a 5-0 to 6-0 simple continuous absorbable suture. (d) With both ends of the conjunctival mucosa open (see arrows), secretions from the nictitans glands can exit. (e) Immediate postoperative view of a patient with conjunctival mucosal pocket procedure. Note the central continuous suture and that both ends of the ‘pocket’ are open.

when the prolapsed glands are very large, there is limited distortion and displacement of the nictitans base, and there are limited-to-no movement restrictions that are associated with the anchoring methods. Recurrence of gland prolapse after either of these two groups of procedures does not preclude an additional technique several weeks later to effect resolution. In the most recent report, using the intranictitans tacking procedure, all prolapsed glands returned to normalcy in 14 of 15 eyes. This technique, once mastered, requires little time as no tissue incisions are required. The basic histopathology of these prolapsed nictitans glands is poorly understood; however, many biopsies indicate acute dacryocystitis, with both intra- and extra-gland inflammation. The condition of the fellow tear gland in the same eye, the lacrimal gland, is unknown at this date. Dogs with prolapse of the nictitans gland and treated by these surgical procedures, only medically, or no therapy, are predisposed to keratoconjunctivitis sicca months to years later. In the study involving 33 dogs of all breeds with protrusion of the third eyelid glands for at least 2 years previously, keratoconjunctivitis sicca developed in 48% of the eyes treated by excision of the gland, in 43% of the eyes with prolapsed glands and no therapy, and in 14% of the eyes treated with these techniques to replace the gland. As a result, continued postoperative clinical monitoring of these dogs with periodic Schirmer tear tests is recommended as the development of keratoconjunctivitis sicca months-toyears after prolapse of the nictitans gland is significantly higher than in the general canine population (5.6% in dogs without gland prolapse).

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Surgical procedures for prominent/ protruded nictitans Prominent and protruding nictitating membranes are infrequent in small animals, and are usually secondary to other orbital, ophthalmic, and systemic diseases. However, occasionally in the large and giant breeds of dogs, bilateral prominent and protruding nictitating membranes occur (Fig. 7.44). In some of these animals, the defect appears more obvious by the absence of pigmentation of the nictitans leading margins. Surgical reduction of the overall size of the nictitans can be performed to not affect tear formation by the nictitans gland, maintain the integrity of the medial conjunctival fornix, and re-establish normalappearing nictitating membranes. Removal of just the leading margins of the nictitans is not recommended as the shape and the appearance of the

Fig. 7.44 Bilateral prominent nictitating membranes in a 2-year-old dog.

Nictitating membrane flaps

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Fig. 7.45 Surgical reduction of protracted nictitating membrane. (a) An enlarged nictitans can be reduced by a full-thickness excision of a section just behind the leading margin. The dotted lines are the nictitans cartilage. (b) After the full-thickness excision, the nictitans posterior and anterior surfaces are apposed with a submucosa 5-0 to 6-0 simple continuous absorbable suture and a mucosa 5-0 to 6-0 simple continuous absorbable suture, respectively.

structures are markedly altered. Total removal of the nictitating membrane will result in medial canthal disfigurement, and the development of a chronic conjunctivitis or keratoconjunctivitis because of the loss of the nictitans tear gland, and an excessively large medial conjunctival fornix. The recommended procedure to reduce the overall size of the nictitating membrane is achieved by full-thickness excision of the nictitans just below the leading margin but above the thicker portion of the cartilage that surrounds the tear gland (Fig. 7.45a). Part of the upper stem of the nictitans cartilage is removed to accommodate the reduction. Wound closure consists of two layers of simple continuous absorbable sutures involving the deeper or bulbar submucosa, and the anterior or palpebral submucosa and mucosa (Fig. 7.45b).

Nictitating membrane flaps The nictitating membrane flap has been popular for the treatment of canine and feline corneal diseases, and is relatively easily performed by most small animal practitioners. The nictitating membrane flap can be quickly performed with a minimum of ophthalmic instrumentation. The nictitating membrane is used as a flap to strengthen a weakened cornea, but generally not to graft submucosa or mucosa to corneal defects. Nictitating membrane flaps are generally indicated for neuroparalytic and neurotropic keratitis, temporary exposure keratitis, corneal erosions (Fig. 7.46), superficial corneal ulcers, after corneal laceration repair (Fig. 7.47), acute keratoconjunctivitis sicca, and for corneal vesicles associated with corneal edema (Fig. 7.48). Conjunctival grafts have largely

Fig. 7.46 The healing of a recurrent corneal erosion can be assisted by a temporary nictitating membrane flap.

Fig. 7.47 In this cat with focal corneal edema, a nictitating membrane flap can provide temporary support.

Fig. 7.48 The painful vesicles that can form with corneal endothelial dystrophy can be treated temporarily with a nictitating membrane flap.

replaced the nictitating membrane flap for the surgical treatment of deep and leaking corneal ulcerations, descemetoceles, and corneal perforations with iris prolapse. The nictitating membrane flap, used to cover the corneal surface, provides a number of benefits. The corneal surface is warmed by the flap and the increased temperature promotes higher cellular metabolic rates. The bulbar nictitans surface is rich with lymphoid follicles; scarification will provide serum, inflammatory cells, fibroblasts, and blood directly to the cornea. The nictitans flap obstructs light entering the eye and promotes mydriasis. The flap reduces the evaporation of tears from the corneal surface. It provides support to a weakened cornea and helps prevent distortion of the central cornea. The flap also protects the healing corneal epithelium from the trauma associated with normal eyelid movements.

Nictitating membrane flap–conjunctival fornix The nictitating membrane flap to cover the cornea is secured to either the dorsolateral conjunctival fornix or the dorsolateral episclera. When secured to the conjunctival fornix, extra long sutures may be used that permit occasional release to examine and treat the protected cornea. The conjunctival fornix method does not accommodate concurrent eye movements as with the episcleral technique. In the episcleral method, the securing sutures must be carefully placed and should not penetrate the sclera which may produce intraocular hemorrhage. For nictitating membrane flaps, surgical preparation is usually minimal. The eyelids are clipped and carefully cleaned with surgical soap and water for the conjunctival fornix procedure. The corneal and conjunctival surfaces are fully cleansed with sterile cotton-tipped applicators to remove all debris and exudates. Both corneal and conjunctival surfaces are rinsed with 0.5% povidone–iodine solution.

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D Fig. 7.49 Securing the nictitating membrane temporarily to the dorsolateral conjunctival fornix. (a) One tip of the thumb forceps is placed above and the other tip below the eyelid margin. The forceps tips, inserted as far as possible, indicate the position of the conjunctival fornix (arrowed) and where the sutures should traverse the eyelid. (b) The first 2-0 to 3-0 non-absorbable suture is placed through the eyelid stent (a rubber band is illustrated), through the eyelid, and into the conjunctival fornix. The needle and suture are then extended to the dorsal surface of the leading edge of the nictitating membrane to penetrate its full thickness. (c) At least two horizontal mattress sutures are pre-placed, and the part of both sutures that penetrates the leading edge of the nictitating membrane should incorporate the upper stem of the nictitans cartilage. (d) After placement of both sutures, they are tightened to secure the nictitans in the dorsolateral conjunctival fornix. Leaving the suture ends long permits occasional adjustments and lowering of the flap for inspection and medication of the eye.

Securing the nictitating membrane to the dorsolateral conjunctival fornix is the most frequent and easiest procedure using two to four interrupted mattress sutures. Old intravenous tubing, buttons, suture foam or holders, or rubber band stents can be used on the eyelid surface to distribute suture tension and prevent eyelid necrosis. All sutures must be pre-placed to ensure proper placement and tied once all are positioned. The nictitating membrane is protracted by thumb forceps and its dorsolateral movement ascertained. The extent of the dorsolateral conjunctival fornix is determined by thumb forceps with one tip above and one tip below the eyelids (Fig. 7.49a). Two to four 2-0 to 3-0 non-absorbable sutures are carefully pre-positioned through the dorsolateral eyelid and the conjunctival fornix and the leading margin of the nictitans (Fig. 7.49b). The sutures must traverse the outer portion of the leading margin to reduce its eversion, and part of at least two sutures are placed through the upper stem of the T-shaped hyaline cartilage for maximal holding ability (Fig. 7.49c). After all sutures are pre-placed, they are carefully tightened and tied (Fig. 7.49d). Often the suture ends are left long to permit occasional release to inspect and medicate the eye.

Nictitating membrane flap – Blogg and Helper modification Similar to a modification of the technique reported in a large number of cattle in the 1970s, Blogg and Helper describe a method that uses a single suture to secure the nictitans to the dorsolateral conjunctival fornix in small animals. A 2-0 double-armed suture is passed through the palpebral (or anterior) surface of the nictitating membrane

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to encircle the upper stem of the T-shaped nictitans hyaline cartilage at a point one-half to one-fourth of the distance between the leading margin and its base (Fig. 7.50a). The nictitans bulbar surface is not penetrated to avoid suture contact with the cornea. Both sutures are then passed through the dorsolateral conjunctival fornix and a rubber band or button stent. The nictitans is protracted until its leading margin is at the limbus or within the conjunctival fornix, but not so tight that compression or distortion occurs (Fig. 7.50b).

Nictitating membrane flap – episcleral fixation The nictitating membrane flap can also be secured to the dorsolateral episclera. This procedure allows simultaneous eye and nictitans movements, but is more difficult to

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Fig. 7.50 Helper–Blogg modification of the nictitating membrane flap. (a) A double-armed, single suture is used to encircle the middle portion of the stem of the T-shaped nictitans cartilage. (b) Both ends of the suture are continued to the dorsolateral conjunctival fornix and upper eyelid. A section of old intravenous tubing or rubber band stent helps distribute the suture pressure over a larger area of the eyelids.

Partial/complete excision of the nictitans

Partial/complete excision of the nictitans

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Fig. 7.51 The nictitating membrane flap can also be secured to the dorsolateral episclera and conjunctiva. (a) Two to four 1-0 to 2-0 interrupted mattress non-absorbable sutures are pre-placed full thickness behind the leading margin of the nictitating membrane and firmly in the dorsolateral episclera and bulbar conjunctiva. (b) After all sutures are positioned, they are tightened and tied.

perform. The ’holding’ power of the episclera and dorsolateral conjunctiva are more limited, and penetration of the sclera during suture placement may cause intraocular hemorrhage. The site of the dorsolateral conjunctiva and episcleral fixation to accommodate the sutures emerging from the nictitans is about 2–4 mm from the limbus. Two to four 1-0 to 2-0 simple mattress non-absorbable sutures are pre-placed through the nictitating membrane and the dorsolateral bulbar conjunctiva and episclera (Fig. 7.51a). At least one suture should be secured to the stem portion of the T-shaped nictitans cartilage. After pre-placement of all sutures, they are tightened and tied (Fig. 7.51b). Adequate suture placement in the dorsolateral bulbar conjunctiva, episclera, and Tenon’s capsule is critical to the flap’s success: sutures placed too superficial will prematurely tear from the area; sutures placed too deep may penetrate the sclera and produce intraocular hemorrhage.

Postoperative management and complications The nictitating membrane flaps are usually left in position for 10–14 days. An E-collar or other restraint device is recommended to prevent the animal damaging the eye and surgical site. Postoperative medications are directed at the underlying corneal disease, and usually include topical antibiotics and mydriatics. The thick and vascular nictitans probably impairs the delivery of many medications to the corneal surface. As a result, systemic medications are often added to those administered topically. Complications associated with nictitating membrane flaps include eyelid necrosis related to the sutures, corneal irritation from suture contact, membrane cartilage deformation, and protrusion for several days after release. Often eyelid swelling is present preoperatively and with the conjunctival fornix technique will occur postoperatively. The correct position of the nictitans flap is critical to its success with all of these techniques. If suture contact occurs with the cornea, the patient will demonstrate considerable pain and blepharospasm. Periodic postoperative examinations are recommended to check the position of the flap daily or every other day. With long sutures, the position of the nictitans flap can be adjusted to accommodate changes in the corneal disease and the eyelids.

Partial-to-complete excision of the nictitating membrane is reserved for advanced and invasive neoplasia in small animals. The most common reported nictitating membrane neoplasm in the dog is the adenocarcinoma (Fig. 7.52). In the cat, the most frequent nictitans neoplasm is the squamous cell carcinoma. Both neoplasms are locally invasive, occur most frequently in older animals, and have postoperative recurrence rates as high as 70%. Nictitating membrane neoplasms often extend both outward and inward through the periorbital fascia to gain entry into the anterior orbit. Orbital radiology and ultrasonography are recommended for nictitating membrane neoplasms to thoroughly evaluate the potential surgical site. The surgical procedure for excision of the nictitating membrane with advanced neoplasia must occasionally be converted during surgery into an exenteration. For complete excision of the nictitating membrane, the eyelid hair is clipped, and cleaned with surgical soap. The conjunctival surfaces, fornices, and the corneal surfaces are cleaned with sterile cotton-tipped applicators, and all debris and exudates removed. The corneal and conjunctival surfaces are irrigated with 0.5% povidone–iodine solution, and then rinsed with sterile saline. After placement of a small wire eyelid speculum, the nictitans is protracted and inspected carefully. Two curved hemostats are carefully placed at the base of the nictitans to slightly overlap to facilitate excision and to provide hemostasis. With Metzenbaum scissors, the nictitans is excised, including the entire cartilage and gland (Fig. 7.53a) The adjacent mucosa on each side of the hemostats is apposed with a 2-0 to 4-0 simple continuous absorbable suture (Fig. 7.53b). When a continuous suture is used, the hemostats are left in place when the suture is being positioned. Once the suture is placed, the hemostats are slowly released and retracted from the incision. The suture is then tightened and its ends tied. An alternative method does not use hemostats, but instead consists of blunt–sharp dissection by small tenotomy scissors; hemostasis is maintained by cautery and vessel ligation. For partial excision of the third eyelid, its outer portion may be excised immediately above the base of the T-shaped

Fig. 7.52 Adenocarcinoma of the nictitating membrane gland in a 10-yearold American Cocker Spaniel. Complete excision of the nictitating membrane at its base is recommended for this type of neoplasm.

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A

B

Fig. 7.53 Removing the entire nictitating membrane. (a) Two curved hemostats or Carmalt forceps are positioned and slightly overlapped at the base of the nictitating membrane, which is then excised with Metzenbaum scissors. (b) The conjunctival mucosa edges are apposed with a 2-0 to 4-0 simple continuous absorbable suture that is pre-placed loosely with the forceps in place. As the forceps is carefully removed, the sutures are tightened.

cartilage and the gland of the nictitans. This method preserves tear formation and the reduced medial lacrimal lake, but results in some disfigurement with the loss of the leading margin. The mucosa edges should be apposed to prevent exposure of the cartilage with a 5-0 to 6-0 simple continuous absorbable suture. Postoperative management after excision of the nictitating membrane consists of topical antibiotics/corticosteroids, and systemic antibiotics administered for 7–10 days. With the loss of the nictitans, tear formation should be carefully monitored and, if signs of keratoconjunctivitis sicca begin to appear, topical cyclosporine (2% solution twice daily) or oral pilocarpine (2% solution, two drops well mixed in the food twice daily for a 15 kg dog; reduce the dose for smaller animals) initiated. Because of an enlarged lacrimal lake in the medial canthus created by the loss of the nictitans, chronic conjunctivitis may develop. Intermittent administration of topical antibiotics/corticosteroids may be necessary indefinitely.

Adaptations in large animals and special species Nictitating membrane flaps provide more support to the diseased cornea than the temporary complete tarsorrhaphy in horses. Nictitating membrane flaps are used to cover and

protect a weakened cornea, but are not usually a source of tissues for the cornea. Nictitating flaps in large animals are recommended for superficial corneal diseases including corneal erosions, neuroparalytic and neurotropic keratitis, temporary exposure keratitis, and superficial corneal ulcers, and to reinforce a bulbar conjunctival graft. In one study, nictitating membrane flaps were used as an alternative to complete temporary tarsorrhaphies for the treatment of advanced infectious keratoconjunctivitis and ulcerative keratitis in 1845 cattle, with 96% success (Anderson et al). This same technique can also be used for small animals as reported by Blogg and Helper (1989; see earlier section for a description of the technique). In range beef cattle, a ‘single catch’ is often a limitation to optimal therapy; as a result, the eye examination, administering topical, subconjunctival or systemic antibiotics, and nictitating flap surgery is performed with the animal restrained in a catch chute. Absorbable sutures are preferred as, once the cow is released, re-examination and suture removal are unlikely. After a subcutaneous ring block of both eyelids and the base of the nictitans, the nictitating flap is performed using a single mattress 0 chromic gut suture (non-absorbable can also be used) with a slightly curved cutting needle. The needle is directed through the dorsolateral upper lid and into the conjunctival fornix. After exiting the lid, the needle is placed through the palpebral surface of the nictitans and under or circumventing the stem of its cartilage, just beneath its extensions. The suture is again positioned through the upper conjunctival fornix and upper eyelid and securely tied, protracting the leading margin of the nictitans onto the dorsolateral bulbar conjunctiva. With an absorbable suture, the nictitans flap will remain in position for 7–14 days. Partial-to-complete excision of the nictitans is performed not infrequently in large animals. Squamous cell carcinomas may occur in both horses and cattle, and can expand into sizeable masses, which can readily invade the deeper medial orbit. Small masses which can be manually elevated above the subcutaneous tissues may be excised; often the surgical wound is not apposed by sutures. Larger masses which invade the nictitans cartilage and gland result in total excision of the nictitans using the same procedure as in small animals.

Further reading Small animals: conjunctiva Barros PSM, Safatle AMV, Malerba TA, Burnier M Jr: The surgical repair of the cornea of the dog using pericardium as a keratoprosthesis, Brazilian Journal of Veterinary Research and Animal Science 32:251–255, 1995. Barros PSM, Garcia JA, Laus JL, Ferreira AL, Gomes TLS: The use of xenologous amniotic membrane to repair canine corneal perforation created by penetrating keratectomy, Vet Ophthalmol 1:119–123, 1998. Blogg JR, Stanley RG, Dutton AG: Use of conjunctival pedicle grafts in the management of feline keratitis nigrum, J Small Anim Pract 30:678–684, 1989.

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Bussieres M, Krohne SG, Stiles J, Townsend WM: The use of porcine small intestinal submucosa for the repair of full-thickness corneal defects in dogs, cats and horses, Vet Ophthalmol 7:352–359, 2004. Carter JD: Medial conjunctivoplasty for aberrant dermis of the Lhasa apso, J Am Anim Hosp Assoc 9:242–244, 1973. Featherstone H, Sansom J, Heinrich C: Intestinal submucosa in two cases of feline ulcerative keratitis, Vet Rec 146:136–138, 2000. Featherstone H, Sansom J, Heinrich C: The use of porcine small intestinal submucosa in ten cases of feline corneal disease, Vet Ophthalmol 4:147–153, 2001.

Gundersen T: Conjunctival flaps in the treatment of corneal diseases with reference to a new technique of application, Arch Ophthalmol 60:880–888, 1958. Hakanson NE, Merideth RE: Conjunctival pedicle grafting in the treatment of corneal ulcers in the dog and cat, J Am Anim Hosp Assoc 23:641–648, 1987. Hakanson N, Lorimer D, Merideth RE: Further comments on conjunctival pedicle grafting in the treatment of corneal ulcers in the dog and cat, J Am Anim Hosp Assoc 24:602–605, 1988. Henderson W: The repair of corneal injuries in the dog by conjunctival keratoplasty, Vet Rec 63:240–241, 1951.

Further reading Hendrix DVH: Canine conjunctiva and nictitating membrane. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 662–689. Mannis MJ: Conjunctival flaps, Int Ophthalmol Clin 28:165–168, 1988. Moore CP: Qualitative tear film disease, Vet Clin North Am Small Anim Pract 20:565–581, 1990. Moore CP: Surgery of the conjunctiva. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 18–56. Moore CP, Constantinescu GM: Surgery of the adnexa, Vet Clin North Am Small Anim Pract 27:1011–1066, 1997. Ollivier FJ, Kallberg ME, Plummer CE, et al: Amniotic membrane transplantation for corneal surface reconstruction after excision of corneolimbal squamous cell carcinomas in nine horses, Vet Ophthalmol 9:404–413, 2006. Parshall CJ: Lamellar corneal–scleral transplantation, J Am Anim Hosp Assoc 9:220–277, 1973. Peiffer RL, Gelatt KN: Complete bulbar conjunctival flap in the dog, Canine Practice 2:15–18, 1975. Peiffer RL, Gelatt KN, Gwin RM: Tarsoconjunctival pedicle grafts for deep corneal ulceration in the dog and cat, J Am Anim Hosp Assoc 13:387–391, 1977. Pirie CG, Dubielzig RR: Feline conjunctival hemangioma and hemangiosarcoma: a retrospective evaluation of eight cases (1993–2004), Vet Ophthalmol 9:227–232, 2006. Pirie CG, Knollinger AM, Thomas CB, Dubielzig RR: Canine conjunctival hemangioma and hemangiosarcoma: a retrospective evaluation of 108 cases (1989– 2004), Vet Ophthalmol 9:215–226, 2006. Roberts SR: The conjunctival flap operation in small animals, J Am Vet Med Assoc 22:86–90, 1953. Scagliotti RH: Tarsoconjunctival island graft for the treatment of deep corneal ulcers, descemetocoeles, and perforations in 35 dogs and 6 cats, Semin Vet Med Surg 3:69–76, 1988. Stern AI: Conjunctival flap operation, J Am Vet Med Assoc 117:44–45, 1950. Tsuzuki K, Yamashita K, Izumisawa Y, Kotani T: Microstructure and glycosaminoglycan ratio of canine cornea after reconstructive transplantation with glycerin-preserved porcine amniotic membranes, Vet Ophthalmol 11:222–227, 2008. Vanore M, Chahory S, Payen G, Clerc B: Surgical repair of deep melting ulcers with porcine small intestinal submucosa (SIS) graft in dogs and cats, Vet Ophthalmol 10:93–99, 2007. Wagner J, Nasisse M, Davidson M: A retrospective study of conjunctival flaps in 67 dogs and 17 horses (1987–1991), Abstract Verterinary Pathology 29:476, 1992. Williams DL: Laboratory animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1336–1369.

Small animals: nictitating membrane Barnett KC: Diseases of the nictitating membrane of the dog, J Small Anim Pract 18:101–108, 1978. Blogg JR: Surgical replacement of a prolapsed gland of the third eyelid (’cherry eye’): a new technique, Aust Vet J 9:75, 1979. Bromberg NM: The nictitating membrane, The Compendium 2:627–632, 1980. Brooks DE: The canine conjunctiva and nictitans. In Gelatt KN, editor: Veterinary Ophthalmology, ed 2, Philadelphia, 1991, Lea and Febiger, pp 290–306. Constantinescu GM, McClure RC: Anatomy of the orbital fasciae and the third eyelids in dogs, Am J Vet Res 51:260–263, 1990. Dugan SJ, Severin GA, Hungerford LL, Whiteley HE, Roberts SM: Clinical and histologic evaluation of the prolapsed third eyelids gland in dogs, J Am Vet Med Assoc 201:1861–1867, 1992. Gelatt KN: Surgical correction of everted nictitating membrane in the dog, Vet Med 67:291–292, 1972. Gross SL: Effectiveness of a modification of the Blogg technique for replacing the prolapsed gland of the canine third eyelid, Transactions of the American College of Veterinary Ophthalmologists 14:38–42, 1983. Helper LC, Blogg R: A modified third eyelid flap procedure, J Am Vet Med Assoc 19:955–956, 1983. Kaswan RL, Martin CL: Surgical correction of third eyelid prolapse in dogs, J Am Vet Med Assoc 186:83, 1985. Moore CP: Imbrication technique for replacement of prolapsed third eyelid gland. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 126–128. Moore CP, Constantinescu GM: Surgery of the adnexa, Vet Clin North Am Small Anim Pract 27:1011–1066, 1997. Moore CP, Frappier BL, Linton LL: Distribution and course of ducts of the canine third eyelid gland: effects of two surgical replacement techniques, Veterinary and Comparative Ophthalmology 6:258–264, 1996. Morgan RV: To excise or not to excise, Progress in Veterinary and Comparative Ophthalmology 3:109–110, 1993. Morgan RV, Duddy JM, McClurg K: Prolapse of the gland of the third eyelid in dogs: a retrospective study of 89 cases (1980–1990), J Am Anim Hosp Assoc 29:56–60, 1993. Ojay E, Milinsky HC: Surgical correction of unpigmented prominent membrana nictitans, J Am Vet Med Assoc 144:857, 1964. Peruccio C: Surgical correction of prominent third eyelid in the dog, Calif Vet 4:24–25, 1981. Petersen-Jones S: Repositioning prolapsed third eyelid glands while preserving secretory function, J Small Anim Pract 13:202–203, 1991.

Plummer CE, Ka¨llberg ME, Gelatt KN, et al: Intranictitans tacking for replacement of prolapsed gland of the third eyelid of dogs, Vet Ophthalmol 11:228–233, 2008. Quinn AJ: Lacrimal apparatus and nictitating membrane. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 82–86. Richards DA: An adjustable suture: a technique for altering the tension of stitches postoperatively, especially in third-lid flaps, Vet Med 68:881–883, 1973. Stanley RG, Kaswan RL: Modification of the orbital rim anchorage method for surgical replacement of the gland of the third eyelid in dogs, J Am Vet Med Assoc 205:1412–1414, 1994. Startup FG: Corneal ulceration in the dog, J Small Anim Pract 25:737–752, 1984. Wilcock B, Peiffer RL: Adenocarcinoma of the gland of the third eyelid in seven dogs, J Am Vet Med Assoc 193:1549–1550, 1988.

Large animals and special species: conjunctiva and nictitans Allgoewer I, Malho P, Schulze H, Schaffer E: Aberrant conjunctival stricture and overgrowth in the rabbit, Vet Ophthalmol 11:18–22, 2008. Anderson JF, Gelatt KN, Farnsworth RJ: A modified membrana nictitans flap technique for the treatment of ulcerative keratitis in cattle, J Am Vet Med Assoc 168:706–709, 1976. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1165–1274. Dugan SJ: Ocular neoplasia, Vet Clin North Am 8:609–626, 1992. Dugan SJ, Curtis CR, Roberts SM, Severin GA: Epidemiologic study of ocular/adnexal squamous cell carcinoma in horses, J Am Vet Med Assoc 198:251–256, 1991. Hendrix DVH: Equine ocular squamous cell carcinoma, Current Techniques in Equine Practice 4:87–94, 2005. Kainer RA, Stringer JM, Lueker DC: Hyperthermia for treatment of ocular squamous cell tumors in cattle, J Am Vet Med Assoc 176:356–360, 1980. King TC, Priehs DR, Gum GG, Miller TR: Therapeutic management of ocular squamous cell carcinoma in the horse: 43 cases (1979– 1989), Equine Vet J 23:449–452, 1991. Lavach JD, Severin GA: Neoplasia of the equine eye, adnexa and orbit, J Am Vet Med Assoc 170:202–203, 1977. McCalla TL, Moore CP, Collier LL: Immunotherapy of periocular squamous cell carcinoma with metastasis in a pony, J Am Vet Med Assoc 200:1678–1681, 1992. Millichamp NJ: Conjunctiva. In Auer JA, Stick JA, editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 465–471.

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Mosunic CB, Moore PA, Carmicheal KP, et al: Effects of treatment with and without adjuvant radiation therapy on recurrence of ocular and adnexal squamous cell carcinoma in horses: 157 cases (1985–2002), J Am Vet Med Assoc 225:1733–1738, 2004. The´on AP, Pascoe JR, Carlson GP, Krag DN: Intratumoral chemotherapy with cisplatin in oily emulsion in horses, J Am Vet Med Assoc 202:261–267, 1993. The´on AP, Pascoe JR, Meagher DM: Perioperative intratumoral administration

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of cisplatin for treatment of cutaneous tumors in equidae, J Am Vet Med Assoc 205:1170–1176, 1994. The´on AP, Pascoe JR, Madigan JE, Carlson G, Metzger L: Comparison of intratumoral administration of cisplatin versus bleomycin for treatment of periocular squamous cell carcinomas in horses, Am J Vet Res 58:431–436, 1997. Townsend WM: Food and fiber–producing animal ophthalmology. In Gelatt KN,

editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1275–1335. Wilkie DA, Burt JK: Combined treatment of ocular squamous cell carcinoma in a horse, using radiofrequency hyperthermia and interstitial 198Au implants, J Am Vet Med Assoc 196:1831–1833, 1990. Witt RP: Treating ocular carcinoma in cattle, Vet Med Small Anim Clin 79:1087–1089, 1984.

CHAPTER

8

Surgery of the cornea and sclera Kirk N. Gelatt1 and Dennis E. Brooks2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

191

Surgery for corneal lacerations

210

Surgical anatomy

192

Surgery for corneal foreign bodies

214

Surgical pathophysiology

193

Corneal adhesives

215

Preoperative treatment considerations

194

Corneal grafts/keratoplasty

216

Surgical instrumentation for corneal and scleral surgeries

195

Thermokeratoplasty

228

Surgical procedures for superficial corneal diseases

196

Surgical treatment of limbal and scleral diseases

229

Surgical procedures for deep corneal ulcerations

201

Adaptations for large animals and special species

232

Introduction Corneal diseases occur frequently in the dog and cat. In the dog, corneal diseases may be primary or secondary to other ophthalmic diseases. Secondary corneal diseases occur frequently in the brachycephalic breeds and with keratoconjunctivitis sicca. In dogs, the common causes of corneal diseases are trauma, inflammations and ulcerations, degenerations, and dystrophies. Congenital abnormalities and neoplasia of the canine cornea are infrequent. In cats, corneal diseases are common, and are usually associated with inflammations, trauma, and sequestration (corneal black spot, corneal mummification). In both cats and dogs, trauma of the cornea occurs most frequently in animals under 1 or 2 years of age. Corneal diseases cause varying degrees of opacification. Invasion of blood vessels, pigment cells, neoplastic cells, lipid material, and leukocytes from the limbus reduce corneal transparency. Edema results from local corneal inflammation or impaired corneal endothelia that can no longer remove fluids from the cornea. With reduction in corneal transparency, vision can be gradually impaired; with total corneal opacification, vision can be lost temporarily or permanently. Treatment of corneal diseases in dogs and cats is quite successful using medical, surgical, and a combination of these therapies. Corneal diseases are often noticed early by the pet’s owner because of the onset of pain, blepharospasm, photophobia, conjunctival hyperemia and chemosis, tearing, and rubbing of the eyelids. As a result, the possibility of successful

treatment is higher. Medical treatment of corneal diseases usually involves the direct instillation of drugs on the affected tissue. Topical drugs include solutions, suspensions, and/or ointments. When corneal diseases are progressing or are unusually severe, the topical route may be supplemented with drugs provided systemically and subconjunctivally. Corneal penetration by most antibiotics is limited by the lipophilic corneal epithelium. Chloramphenicol is still the antibiotic of choice when the epithelium is intact, and therapeutic levels of antibiotic are necessary in the cornea and anterior chamber. With corneal ulceration, the epithelial barrier is markedly reduced, and the administration of broad-spectrum topical antibiotics is recommended. The most frequently used topical antibiotics include gentamicin, chloramphenicol, tobramycin, the fluoroquinolones and the combination of neomycin, polymyxin B, and bacitracin. In corneal diseases with vascularization of the cornea and/or secondary iridocyclitis, systemic antibiotics are often indicated and are highly successful. Surgical treatment of corneal diseases in the dog and cat is often the primary modality. The normal cornea, exposed suddenly to trauma or ulceration, often requires several days to initiate satisfactory inflammatory and healing responses. In the meantime, the infectious agents, proteases, and collagenases (from bacteria and damaged corneal cells) can cause rapid degradation of the cornea, and threaten the integrity of the cornea and maintenance of vision. Surgical treatment can jump-start the healing process and markedly reduce the length of the lag phase for healing, as well as provide vital structural corneal support. Corneal surgery

8

Surgery of the cornea and sclera

includes partial keratectomy (or removal for treatment or biopsy), keratotomies (single or multiple incisions), transposition (movement from one site to another), primary closure for small corneal ulcers and lacerations, and transplantation (autogenous and homologous) or grafting of corneal tissues to replace cornea lost to disease.

Surgical anatomy Dog and cat corneal anatomy Dog and cat corneas are relatively large compared to those of humans, probably to assist in night vision. Animals with large corneas are typically nocturnal, as large corneas allow greater amounts of light to enter the pupil during reduced illumination. Most animal corneas are roughly elliptical in shape with the vertical diameter slightly less than the horizontal diameter. The normal dog cornea measures 12–16 mm vertically and 13–17 mm horizontally, and is 0.45–0.55 mm thick centrally and 0.50–0.65 mm thick peripherally. The normal cat cornea measures 15– 16 mm vertically and 16–17 mm horizontally, and is about 0.58 mm thick centrally and peripherally. Corneal measurements, both diameters and thicknesses, have not been established for different ages and the different breeds in either the dog or cat. The cornea, along with the sclera, forms the fibrous tunic of the globe (Fig. 8.1). The zone where the cornea gradually

Central (axial) cornea Pupil

becomes opaque and changes to sclera is the limbus. The limbus is sufficiently forward of the aqueous humor filtration angle or the iridociliary cleft (or ciliary cleft) to prevent direct visualization of the aqueous outflow pathways. Dog and cat corneas are divided into axial (central) and peripheral, with the central area most important for vision. Often the cornea is divided into quadrants. The central cornea is generally the thinnest and most often affected with ulcerations. Dog and cat corneas have four different microscopic regions. From external to internal, these subdivisions include: 1) epithelia with basal membrane; 2) thick stromal layer; 3) Descemet’s membrane; and 4) the posterior single layer endothelia. A modified anterior region of the corneal stroma, Bowman’s membrane, is absent in the dog and cat, but present in humans and most birds. The epithelial layer is normally about 5–7 cells thick and consists of: 1) outer two to three layers of non-keratinized squamous cells; 2) middle two to three layers of polyhedral or wing cells; and 3) a single layer of basal columnar cells that are positioned on a basement membrane (Fig. 8.2). The apparent turnover of corneal basal epithelia is about 7 days. The basement membrane, produced by the basal corneal epithelia, attaches the basal epithelial cells via hemidesmosomes to the anterior stroma. Defects in the canine basal corneal epithelia and basement membrane are thought to contribute directly to the development of recurrent corneal erosions. The corneal stroma, or substantia propria, accounts for about 90% of the corneal thickness, and consists of parallel

Peripheral (para-axial) cornea

Anterior chamber

Limbus

Anterior chamber angle

Sclera

Posterior chamber Lens Iris Zonules A

Ciliary body (pars plicata)

B

Fig. 8.1 The surgical and microanatomy of the dog and cat cornea. (a) The anatomic relationships of the cornea to the other tissues in the anterior segment of the eye. (b) The microscopic layers of the dog and cat cornea include: (A) epithelium; (B) stroma; (C) Descemet’s membrane; and (D) the endothelium. H & E, 25
.

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Surgical pathophysiology

(mean), respectively. Corneal endothelial count varies by age, and a count of 3216 cells/mm2 has been reported in the horse.

Bovine corneal anatomy The oval cornea of the adult cow is roughly pear-shaped and measures 22–24 mm vertically and 27–32 mm horizontally. Its thickness also varies with the center thicker (range from center and periphery: 0.75 to 0.85 mm). The radius of curvature for the bovine cornea varies from 14.7 mm (vertically) and 16.8 mm (horizontally).

Surgical pathophysiology Fig. 8.2 The epithelial layer is usually five to seven cells thick. The basal epithelia are secured to the anterior stroma by a basement membrane. H & E, 100
.

bundles of collagen fibrils, few fibrocytes (also called keratocytes), and a matrix of glycosaminoglycans. The arrangement of these fibrils and the matrix of glycosaminoglycans become distorted with disease and is the basis of corneal opacification. Corneal sensory nerves, distributed from the mid posterior stroma from the ophthalmic branch of the trigeminal nerve, eventually terminate in subepithelial plexuses to provide free nerve endings in the epithelial wing cell layer. As a result, superficial corneal ulcers are usually more painful in dogs than ulcerations involving the deep corneal stroma. Corneal sensitivity may be reduced in the brachycephalic breeds, possibly predisposing the cornea to damage. Descemet’s membrane is the basement membrane produced by the posterior cells, the endothelia. Descemet’s membrane, a relatively thick basement membrane that increases in thickness with aging, is clear and somewhat elastic. Surgical repair is necessary to prevent imminent corneal rupture when exposed Descemet’s membrane or a descemetocele is clinically visible. The single layer of endothelia forms the posterior layer of the cornea, and consists of hexagonal-shaped cells that interdigitate with each other laterally with different cell junctions, including zonulae occludentes, maculae adherentes, and nexi. These metabolically active cells are the principal site for removal of water from the cornea via an NaþKþ ATPase ‘pump’. Surgical and traumatic damage, as well as aging and decreased numbers of endothelia, alter this state of ‘deturgescence’, and edema of the cornea may result.

Equine corneal anatomy The oval adult equine cornea measures 26–28 mm vertically and 32–38 mm horizontally, with a radius of curvature of about 17 mm. The thickness also varies, with the center measuring as thin as 0.56 mm and the periphery 0.8 mm. Corneal thickness measurements can vary by the in-vivo or in-vitro method used (direct measurement in fixed tissue), ultrasonography or ultrasound pachymetry and specular microscopy. Ultrasonic pachymetry of the central equine cornea reveals 785  2.98 mm to 858 mm (mean). Dorsal and lateral measurements are 932.5 mm (mean) and 879.5 mm

Diseases alter corneal transparency. Invasion of the cornea with blood vessels from the limbus and bulbar conjunctiva; accumulation of extracellular and intracellular fluids and edema; infiltration with the different types of leukocyte; migration of pigment cells from the limbus, conjunctiva, and anterior synechiae; and deposition of lipid, cholesterol, and calcium products all reduce the cornea’s ability to transmit images. Fortunately, dog and cat corneas have considerable capacity for repair and the reestablishment of transparency. Corneal nutrition is from three sources: precorneal/preocular film, limbal vasculature, and the aqueous humor posteriorly. The corneal epithelia respond quickly to damage by undergoing mitosis and sliding of new wing cells into the corneal defect. The entire cornea can be re-epithelialized in 7–10 days, although firm adhesion of the new epithelia by hemidesmosomes requires several weeks. New corneal epithelium is usually semipermeable to topical fluorescein, staining a faint green. During the corneal ulcerative process, proteases, collagenases, and other enzymes are released from degenerating corneal cells, leukocytes, and certain bacteria. These enzymes degrade the collagen fibrils and glycosaminoglycans, potentiating the ulcer’s progression even in the absence of sepsis. Superficial corneal ulcers are often more painful than deeper ulcerations. Both the corneal epithelium and anterior corneal stroma possess pain and pressure receptors that are part of the long ciliary nerves that arise from the ophthalmic branch of the trigeminal (fifth) nerve. Not only does pain occur from stimulation of these nerve endings, but also an axonal reflex that results in a secondary iridocyclitis (reflex miosis, conjunctival and anterior uveal hyperemia), and altered blood–aqueous barrier (aqueous flare). Hence, corneal ulceration commonly causes secondary iridocyclitis, which requires treatment concurrent with the corneal ulcer therapy. As the corneal ulcer is being rapidly covered by healing epithelia, the corneal stroma has a slower and longer repair phase. Often the stroma is invaded by blood vessels from the limbus and bulbar conjunctiva, as well as leukocytes from tears, blood vessels, and limbus. Fibroblasts, converted from keratocytes and histiocytes, slowly produce new collagen fibrils and local glycosaminoglycans matrix. This process takes several weeks to a few months. Following deep keratectomy, complete recovery of corneal stroma to normal thickness may take months, and the stroma may not totally

193

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return to normal thickness. It has been suggested that the limit of three superficial keratectomies for the dog appears related to failure of total stromal regeneration. After superficial keratectomy, the new collagen fibrils may not perfectly realign with adjacent normal corneal lamellae, resulting in variable amounts of scarring. Fortunately, scarring after superficial keratectomies in the dog and cat is limited. In fact, if one ranks the tendency for corneal scarring among animals, it appears that the cat and cow have the least tendency, the dog ranks in the middle, and the horse has the greatest tendency for corneal scarring after disease or surgery. Resolution of the corneal blood vessels after stromal repair requires several weeks, often resulting in ghost vessels that can be observed years later by biomicroscopy. Chronic corneal irritation in animals usually results in invasion of the cornea with melanocytes from limbus and bulbar conjunctiva, epithelial cells, and histiocytes. This intracellular melanin pigment, observed clinically as brown-to-black areas in the cornea, appears histologically in the corneal basal and wing cell layers, and in anterior corneal stroma. Once the canine cornea becomes pigmented, the opacification from this pigmentation is difficult to eliminate medically or excise surgically, but can usually be controlled sufficiently to allow clinical vision. Repair of defects in Descemet’s membrane depend on the formation of new basement membrane by corneal endothelium and requires several weeks. Posterior endothelial regeneration is influenced by animal species and age: in young animals the defect is covered by new corneal endothelia derived primarily by mitosis; in older animals these defects are covered primarily by endothelial cell enlargement by adjacent cells. In older animals, it appears that Descemet’s membrane progressively thickens. Once Descemet’s membrane is cut, the membrane curls and retracts. The exposed posterior stroma is rapidly covered with a fibrin clot. Adjacent endothelial cells, by either mitosis or enlargement, cover the fibrin clot, and over several weeks produce a new Descemet’s membrane. The rabbit corneal endothelia seem to rapidly undergo mitosis and slide to cover areas on Descemet’s membrane or posterior stroma within days. Regeneration of endothelia in the dog and cat is poorly understood. Like children, the puppy and kitten corneal endothelia demonstrate remarkable and rapid regeneration by mitosis. However, the density of corneal endothelia in the dog gradually declines with age, suggesting that regeneration is not occurring. The occurrence of persistent corneal edema and primary endothelial dystrophies in dogs indicate that regeneration of corneal endothelial cells in older animals does not occur. The normal cornea also becomes slightly thicker in older dogs, presumably from less effective corneal dehydration associated with decreased numbers of corneal endothelia. The density of corneal endothelial cells in the dog, critical to maintain a cornea devoid of edema, ranges from 1200 to 1500 cells mm2, with 2500–3000 cells mm2 being normal. In corneal tissue banks for humans, at least 2000 cells mm2 is considerable essential for corneal donor tissue for corneal transplantation. Because of limited numbers of endothelial cells in older dogs, corneal edema is more apt to occur after cataract surgery. Cataract surgery in dogs generally results in the loss of 10–20% of the corneal endothelia. Hence, in very

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old dogs having cataract surgery, damage to the corneal endothelium during phacoemulsification must be considered seriously, and more postoperative corneal edema is expected.

Preoperative treatment considerations The preoperative treatment of corneal diseases in animals depends on the condition. With limbal and corneal neoplasms, dermoids, focal corneal lipidosis, and corneal cysts, treatment of the cornea prior to surgery is not usually necessary. In contrast, corneal inflammations, foreign bodies, ulcerations, and partial and full-thickness lacerations may require adequate preoperative treatment to ensure the success of the surgical procedure, especially if entry into the anterior chamber is likely. With corneal defects, i.e., ulcerations, descemetoceles, corneal ulcerations with iris prolapse, corneal foreign bodies, and partial-to-full-thickness lacerations, topical and systemic antibiotics are indicated to prevent the infectious process from spreading intraocularly.

Dog and cat Topical antibiotics most frequently include chloramphenicol, gentamicin, tobramycin, and the combination of neomycin, polymyxin B, and bacitracin. Most often the bacteria recovered from corneal ulcers by culture are Staphylococcus and Streptococcus spp., which are sensitive to most antibiotics. Systemic antibiotics, such as amoxicillin or cephalexin, are administered when corneal disease is advanced and integrity of the globe threatened. With inflammatory corneal diseases, secondary involvement of the anterior uvea is common. Miosis, flare in the anterior chamber, fibrin formation, lowered intraocular pressure, photophobia, and swelling of the iris and ciliary body usually accompany corneal ulcerations and lacerations. Instillations of iridocycloplegics, such as 1% atropine or 0.3% scopolamine with 10% phenylephrine, are indicated to reduce ocular pain, decrease the likelihood of posterior synechiae and cataract formation, and retract the iris from full-thickness axial corneal wounds. The physical objective of mydriatic treatment is to moderately dilate the pupil, but still permit some iris movement that discourages the formation of posterior synechiae. The strong iridocycloplegics, such as 1–3% atropine, are long acting and can markedly decrease aqueous tear production. An acutely dry cornea does not heal readily! As the pupil size can be ascertained daily through most corneas, the intensity and concentration of mydriatic(s) can be adjusted quickly to maximize therapeutic effects and minimize side effects. Corneal ulcers in the dog occasionally progress even though sepsis is not demonstrable. This expansion of the edges of the corneal ulcer may result from the local release of proteases, collagenases, and other enzymes liberated by dying corneal and inflammatory cells. Specific treatment to combat this effect may be achieved by topical 5.0% acetylcysteine or preferably autogenous serum. Non-steroidal anti-inflammatory drugs (NSAIDs) such as flunixin meglumine (0.5 mg/kg IV; BanamineW, ScheringPlough, Kenilworth, NJ) or carprofen (2 mg/kg PO; RimadylW, Pfizer Animal Health, Exton, PA) are used in the

Surgical instrumentation for corneal and scleral surgeries

dog to reduce postoperative iridocyclitis, pain, and conjunctival and eyelid swelling. These drugs may mimic the effects of steroids on the eye but with few side effects; however, like corticosteroids, they appear to delay corneal vascularization. The dog and cat eyes rotate during gas anesthesia ventromedially, and collapse once the anterior chamber has been opened. The use of non-depolarizing neuromuscular blocking agents such as atracurium (0.2 mg/kg IV; GlaxoWellcome Research, Triangle Park, NC) paralyzes the animal, including the extraocular muscles. As a result, the eye position remains normal and the lack of extraocular muscle tone reduces intraocular tissue displacement once the anterior chamber is entered. Because of the paralysis of all striated musculature, including the muscles associated with breathing, artificial ventilation in these anesthetized patients is essential until the drug-induced paralysis ceases or is reversed (see Chapter 3). With general anesthesia, loss of tear production, and lack of the protective blink reflex, the cornea quickly dries. During surgery, the corneal surface should be intermittently irrigated with lactated Ringer’s solution or balanced saline solution.

Horse Preoperative treatment is not uncommon in horses, and often directed at the primary corneal disease. Although the most common topical antibiotics for the horse include the triple antibiotics (neomycin, bacitracin, and polymyxin) and gentamicin or tobramycin, ciprofloxacin may have the greatest activity and least number of resistant organisms. Topical gentamicin, perhaps because of its high frequency of use as the first-line topical antibiotic for nearly four decades, has been reported to now encounter the highest number of resistant Pseudomonas and Streptococcus organisms. As a result, intensive or progressive corneal ulcers in the horse should be cultured, if possible, to help guide antibiotic therapy. Mydriasis is often indicated for horses with corneal diseases to reduce the ocular pain, dilate the pupil, and stabilize the blood–aqueous barrier. Of the species requiring mydriatics, the horse appears the most sensitive to the systemic effects of atropinization. Hence, mydriatics are administered to effect (a maximally dilated pupil) for a day or two, and then reduced to maintain the dilated pupil to minimum levels. Close daily observation of the horse for intestinal motility and output of feces is important. Any decrease in intestinal motility or apparent abdominal distress should initiate immediate reduction or cessation of topical anticholinergic mydriatic therapy. Antifungal medications are important in the horse because of the not-infrequent fungal involvement in corneal disease in many areas of the world. Natamycin, also known as pimaricin, (5%) is the only commercially available antifungal agent in the United States; its reported activity is for Fusarium and some Aspergillus species. Other antifungals must be individually prepared and include miconazole (1%), fluconazole (0.2%), voriconazole (1%), itraconazole (1%), and amphotericin (0.15%). These topical antifungals are often administered for several weeks. The search for effective systemic antifungals continues! The horse eye is characterized by a profound inflammatory response which often must be medically controlled in

order to treat the infectious agents, but prevent excessive inflammation which can cause anterior and posterior synechiae formation, secondary cataracts, and phthisis bulbi (destruction of the ciliary body with markedly reduced aqueous formation rates, intraocular pressure less than 5 mmHg, cataract formation, and retinal detachment). Topical and systemic corticosteroids must be administered carefully in the horse, as potential adverse effects are not infrequent. Topical and especially systemic non-steroidals, such as flunixin meglumine (1 mg/kg PO, IV, or IM q12h) are effective in controlling secondary uveitis, reducing uveal exudation, and relieving ocular discomfort. For horses with severe corneal disease, the subpalpebral medication system to administer medications to the eye is most useful when the medications are delivered to the eye six to eight times daily for many weeks.

Cattle Generally economics preclude preoperative treatments in cattle. However, for highly valuable cattle, therapy similar to the horse can be used. Systemic antibiotics and other drugs are often different between horses and cattle, and drug residues in milk and meat may be important in cattle.

Surgical instrumentation for corneal and scleral surgeries Small animals The investment in surgical instruments depends on the expertise of the veterinary surgeon and the anticipated patient load with corneal surgical diseases (see Table 1.4, p. 12). Magnification is essential for corneal surgeries. Head loupes can provide magnification at levels of 2.5 to 4
; the operating microscope provides at least 10
and is generally preferred. With considerable corneal surgery and keratoplasty, the operating microscope is recommended. Either standard or microsurgical instruments may be used, or a combination of both sizes. Minimal instruments include the following.

•

•

•

For exposure of the cornea and a possible lateral canthotomy: tenotomy or Steven’s scissors, eyelid speculum, tissue forceps (Bishop–Harmon), and needle holder (standard; with lock: Castroviejo). For additional information on lateral canthotomy, see Chapter 2. For corneal tissues: Colibri and tying forceps (with 1
2 teeth), Beaver scalpel handle and blades (Nos 6400, 6500, and keratome), corneal scissors (right and left handed), iris scissors, disposable electrocautery, Martinez corneal dissector, associated cannulas, needle holder (microsurgical size and without lock), and a set of corneal trephines (at 0.5 mm increments). The diamond knife is very useful for corneal surgery and can provide exact control of the depth of the corneal incision in increments of 0.2, 0.3, 0.4, 0.5, 0.6 and 0.8 mm. For keratoplasty, additional instruments include corneal cutting block (often TeflonW) and punch. At least one or two different sizes of Flieringa rings are useful for corneal transplantation, and are temporarily sutured to the bulbar conjunctiva and episclera to prevent collapse of the globe (see Chapter 1).

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Both absorbable and non-absorbable 6-0 to 10-0 sutures are used for corneal surgeries. The least reactive suture is the non-absorbable nylon, and is essential for keratoplasty, but removal of the sutures is usually necessary. Absorbable sutures, such as polyglactin 910 or polyglyconate, are the usual choices with either reverse cutting or spatula needles. Suture techniques include simple interrupted, simple continuous, double saw-tooth, and others. Ideally a corneal stitch should be 75–90% of the corneal thickness with ‘bites’ about 2 mm of tissue for maximum tissue holding (especially with edematous corneal tissue).

Large animals The ophthalmic surgical instrumentation for performing corneal or corneoscleral surgeries in large animals is identical to that for small animals. For these surgeries using limited magnification, standard size instruments are most useful; if the operating microscope is used as well as general anesthesia, microsurgery ophthalmic instruments are often employed.

Surgical procedures for superficial corneal diseases Superficial corneal diseases are usually confined to corneal epithelia and anterior stroma, and may be treated surgically. For instance, corneal dermoids generally extend into the anterior stroma and may involve adjacent bulbar conjunctiva (Fig. 8.3). Treatment is superficial keratectomy. Corneal lipidosis often affects the anterior corneal stroma, and may be removed by superficial keratectomy. Recurrent corneal erosions in the dog appear related to corneal epithelial dystrophy and defects in the basement membrane which result in defective adhesion during healing of these superficial erosions and frequent recurrences (Fig. 8.4). Several surgical procedures, including superficial keratectomy, have been used to treat this condition. The superficial keratectomy procedure may be used for corneal sequestra in cats limited to the anterior corneal stroma.

Fig. 8.3 Corneal dermoid in a St Bernard puppy. Covered with long coarse hair, that is highly irritating, the congenital mass involves the lateral cornea, limbus, and bulbar conjunctiva. Recommended treatment is superficial keratectomy.

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Fig. 8.4 Recurrent corneal erosion in a 5-year-old Boxer dog. The raised epithelial rim or lip, which stains with rose Bengal, surrounds the erosion (also stains with fluorescein).

In this section, surgical techniques that involve corneal epithelium and anterior aspects of the corneal stroma are presented and include: 1) superficial keratectomy (partial and complete); 2) superficial punctate, grid or linear keratotomy; and 3) corneal biopsy.

Superficial keratectomy (partial and complete) Keratectomy may prove useful in the early stages of ulcerative keratitis when infection is confined to the corneal epithelium and anterior third or half of the cornea stroma, and in later stages of stromal keratitis when the epithelium has healed. Removing necrotic tissue by keratectomy speeds healing, minimizes scarring, and decreases the stimulus for keratitis and iridocyclitis. In superficial keratectomy the corneal epithelia and variable amounts of anterior stroma are excised. The procedure may involve the entire cornea or only part of the cornea. The thickness of stroma removed depends on the corneal disease. When the superficial keratectomy is limited to the outer one-third of the cornea, the postoperative wound is treated medically as a corneal ulcer. However, when the partial superficial keratectomy extends for more than one-half to two-thirds of the corneal stroma, the defect is covered with a conjunctival graft. While regeneration of corneal epithelia appears complete after superficial keratectomy, total recovery of the corneal stromal thickness is questionable. A single cornea subjected to three superficial keratectomies appears to have a stroma of about one-half to two-thirds normal thickness thereafter. Indications for superficial keratectomies include corneal dermoid, chronic superficial keratitis (pannus), pigmentary keratitis, chronic and recurrent corneal erosions, corneal and/or limbal neoplasia, ulcerative keratitis with sequestration in cats (Fig. 8.5), corneal superficial dystrophies (usually lipidosis and calcification), and superficial corneal foreign bodies. In some of these diseases, the cause(s) has not been determined, and although the involved corneal tissue(s) appears completely excised, recurrence may occur. For some of these conditions, such as pigmentary keratitis, the superficial keratectomy may re-establish a clear cornea, but if the predisposing factors, such as lagophthalmia, nasal fold trichiasis, or tear film disorder, are not resolved, the cornea will become pigmented again.

Surgical procedures for superficial corneal diseases

A

B

Fig. 8.5 Corneal sequestration in cats consists of a distinct central brown-to-black area of necrotic stroma. (a) Corneal vascularization and inflammation may surround the lesion. (b) Immediate postoperative appearance after superficial keratectomy. If the keratectomy is limited to less than one-third of the corneal stroma, it is treated as a corneal ulcer. A bulbar conjunctival graft may also be used to cover the surgical defect, and may decrease the possibility for recurrence of sequestrum.

There are several different modifications of the superficial keratectomy procedure. As a rule, only the diseased area within epithelial and anterior stromal layers is excised. While the normal dog and cat corneas are about 0.5–0.6 mm thick, the abnormal cornea may exceed 1.0 mm in thickness. When the entire cornea is diseased, superficial keratectomy may be performed using a limited-depth corneal trephine or diamond knife, or by dividing the cornea into four quadrants (much like cutting a pie or cake) and separating the opaque superficial layers of cornea from the deeper clear corneal stroma. Instruments used to perform the superficial keratectomy include: eyelid speculum, smooth and 1
2 teeth tissue forceps (Bishop–Harmon or Colibri), Beaver scalpel handle and No. 6400 microsurgical blade or diamond knife, strabismus or tenotomy scissors, irrigator bulb, and small cannula. Additional instruments to perform the lateral canthotomy may be necessary when improved exposure of the corneal site is necessary. Other corneal instruments that can assist in the superficial keratectomy are the Martinez dissector, a corneal trephine whose depth can be preset to 0.2–0.3 mm, and the diamond knife with a micrometer (which limits the depth of the corneal incision). This procedure is generally performed under general anesthesia. Superficial keratectomy is usually limited (partial) to the diseased cornea. The periphery of the diseased area is encircled with an incision using the Beaver scalpel handle and No. 6400 microsurgical blade, or the diamond knife with the micrometer set at 0.15 or 0.25 mm, or a preset corneal trephine (0.15–0.25 mm). The incision should be of sufficient depth to remove the base of the diseased cornea, as estimated preoperatively by slit-lamp biomicroscopy (Fig. 8.6a). Often, the cornea is vascularized, and limited hemorrhage occurs during the incision. To prevent hemorrhage from obscuring the incision, a continuous stream of 0.9% sterile saline is directed at the leading aspects of the corneal incision as it is performed. This hemorrhage will usually cease once sufficient time has elapsed to permit clotting. If a conjunctival graft is applied to the keratectomy site, the surgical defect may be constructed as a square lesion. Once the corneal lesion has been outlined, the edge of the superficial keratectomy section is grasped carefully

with 1
2 teeth tissue forceps to permit separation of the diseased cornea from the underlying stroma (Fig. 8.6b). The dissection plane within the stroma should remain in the same parallel lamellae throughout the superficial keratectomy. If the Beaver knife is used, the instrument must be held tangential to the corneal stroma to prevent progressive deeper dissection into the stroma (Fig. 8.6c). Alternately, the Martinez dissector facilitates this dissection to remain within the respective corneal lamellae (Fig. 8.6d). Once the diseased cornea has been completely separated from the stroma, it is lifted from the surgical wound (Fig. 8.6e). If some tags of stroma remain, they are carefully cut with utility or tenotomy scissors. If additional areas of diseased cornea are still present, the procedure may be repeated in these areas. Partial superficial keratectomies are generally limited to the outer one-half of the cornea unless a conjunctival graft, corneoconjunctival graft, or lamellar corneal graft is attached afterwards to the surgical wound. Postoperatively, the superficial keratectomy wound is not usually covered with a nictitating membrane flap or complete temporary tarsorrhaphy. Topical broad-spectrum antibiotics are instilled four to six times daily. Topical 1% atropine is instilled to maintain a moderate to completely dilated pupil (one drop daily or every other day). Topical atropine can reduce aqueous tear formation, as measured by the Schirmer tear test, by 50–75%. A marked decrease in tears can prolong corneal reepithelialization by several days. Every day or every 2 days the re-epithelialization of the superficial keratectomy wound is evaluated with and without topical fluorescein. Re-epithelialization usually starts within 48 h. The entire canine cornea can re-epithelialize within 7–10 days. New epithelia are somewhat translucent, stain faintly with topical fluorescein, and adhere incompletely. Each day the area of fluorescein retention (devoid of corneal epithelia) should become smaller, as reepithelialization occurs 360 . If re-epithelialization is slow or ceases, topical aqueous 0.5% povidone–iodine solution is carefully applied to the wound edges to stimulate epithelial activity.

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A

B

D

E

C

Fig. 8.6 In the superficial keratectomy procedure, a section of corneal epithelium and the superficial stroma are excised. (a) The periphery of the corneal dermoid is incised with the Beaver No. 6400 microsurgical blade to a depth of about 0.2–0.3 mm. (b) The edge of the lesion is grasped and lifted with a 1
2 teeth thumb forceps, and separation of the lesion from the underlying clear stroma is continued by scalpel dissection. (c) During the dissection of the stroma, the microsurgical blade is held tangential to avoid entry into the deeper stromal lamellae. (d) The Martinez corneal dissector or separator may also be used (instead of the microsurgical blade) during this part of the surgery for lamellar dissection. (e) Once the stromal dissection has been completed, the lesion is carefully removed, resulting in a corneal defect.

Corneal healing after superficial keratectomy for the treatment of feline corneal sequestration is often slower than normal and more scarring results. Once re-epithelialization of the superficial keratectomy site is complete, topical antibiotics are continued for few days. Final corneal clarity may require several weeks during which the corneal stroma becomes reorganized. Topical corticosteroids, such as 0.25– 0.5% prednisolone or 2.5% hydrocortisone, may be administered two to four times daily, or cyclosporine administered once daily may be used to minimize corneal scarring, but are not usually necessary. Although some corneal scarring may result after the superficial keratectomy procedure, the opacity is not usually dense in the dog and cat. Postoperative complications after superficial keratectomies are infrequent. Bacterial infection of the surgical wound is rare, provided appropriate topical antibiotics are administered. Postoperative reduction in tear production will delay corneal healing, and increase the possibility of corneal vascularization and more scarring. After superficial keratectomies in brachycephalic breeds, the cornea should be evaluated daily or every other day. Lagophthalmos, infrequent blinking, central corneal exposure, and marginal tear production are often associated with corneal diseases in these breeds, and can prolong corneal re-epithelialization of the superficial keratectomy site excessively. Postoperative corneal scarring may be more in dogs than in cats. Use of only superficial keratectomies to treat pigmentary keratitis in dogs is not successful. The surgical areas often re-pigment within months. For the superficial keratectomy to have reasonable success for canine pigmentary keratitis, additional medical and/or surgical treatments are indicated, such as permanent medial or lateral canthoplasty, removal of nasal fold trichiasis, and medically increasing tear production using topical cyclosporine or oral pilocarpine.

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These treatment modalities address the basic problems that contributed to the development of the original corneal pigmentation. Superficial keratectomy for the clinical management of canine chronic superficial keratitis (pannus) is not curative, but can remove the dense corneal pigmentation in advanced disease and immediately restore vision in these dogs. However, the healing periods after superficial keratectomies for the treatment of this disease are not predictable. Recurrence of pannus and corneal vascularization may occur before or concurrent with the corneal re-epithelialization, and necessitate topical corticosteroids or cyclosporine before re-epithelialization is complete. Beta radiation may be indicated to retard corneal vascularization during immediate postoperative healing in selected patients. Long-term control of pannus still depends on daily instillations of corticosteroids and/or cyclosporine, adjusted for the severity of the disease. Overall results with superficial keratectomies are very good. Recurrence of the original corneal disease may again opacify the cornea, but the procedure provides a temporarily clear cornea. Removal of corneal scar tissue, corneal dermoids, embedded corneal foreign bodies, and other corneal opacities with superficial keratectomies is usually curative.

Adaptations in large animals and special species Keratectomy may be indicated in cases of melting ulcers in horses. Keratectomy is thought to speed healing by removing necrotic and infected tissue, and encouraging vascularization, minimizing scarring, and decreasing the stimulus for anterior uveitis. Necrotic tissues that are often present in case of melting ulcers should be removed and this can be achieved with a cellulose sponge or a fine-toothed

Surgical procedures for superficial corneal diseases

A

B

Fig. 8.7 Treatment of corneal scarring by superficial keratectomy and amnion graft in a horse. (a) A granulomatous scar is present at the surgical site 2 years postoperatively for superficial keratectomy and permanent conjunctival graft for corneal squamous cell carcinoma. (b) A slight scar is present at the surgical site five months postoperatively.

forceps (e.g., 0.12 mm Colibri forceps). Additionally, careful debridement can be done with microsurgical corneal scissors, a microsurgical blade or a corneal dissector. A corneal incision to outline the lesion to be removed can be done with a corneal trephine, a diamond knife or a microsurgical blade (e.g., Beaver No. 6400 microsurgical blade). The depth of the incision in the stroma should be adequate to remove the lesion completely. Once the initial incision is made, the edge of the tissue to be removed is grasped by a forceps (e.g., 0.12 mm Colibri forceps), and a corneal dissector (e.g., Martinez corneal dissector) is introduced and held parallel to the cornea. The dissector is used tangentially to separate the corneal lamella without penetrating deeper than the original cutting plane. The cornea is then separated until the opposite incision line is reached. Depending on the stromal defect, a conjunctival graft may be placed subsequently. Superficial keratectomy is also performed during any grafting procedure to prepare the bed for conjunctival, amniotic membrane or corneal graft. The complications of superficial keratectomy are minimal, but include slow healing, infection, granulation tissue formation, perforation, and excessive scar formation. Superficial keratectomy may also be used in the treatment of superficial corneal scarring, with postoperative treatment of the corneal healing response (Fig. 8.7).

Superficial punctate, grid, and linear keratotomies Superficial punctate, grid, and linear keratotomies are relatively new surgical procedures used to treat chronic corneal erosions and refractory corneal ulcers in dogs and other species (Fig. 8.8). Investigations into corneal recurrent erosions (indolent ulcer or Boxer ulcer) in the dog indicate defective basal corneal epithelia and basement membrane. Defects in the basement membrane, including paucity of hemidesmosomes and multiple layers of basement membrane, appear

Fig. 8.8 Corneal erosions, stained with topical fluorescein, are characterized by slow healing and recurrence. New surgical procedures, such as the superficial punctate and grid keratotomies, attempt to enhance healing and prevent recurrences by expanding the adhesion of the epithelia and basement membrane to the anterior stroma.

to contribute directly to the onset of these highly painful but shallow corneal ulcers, and to their variable but often prolonged healing. Both surgical procedures attempt to improve adhesion of the defective epithelia and basement membrane to the anterior stroma by making multiple shallow grooves in the epithelia and anterior stroma that provide deeper attachment sites. As a result, basal corneal epithelia increase their surface contact and adhesion through these incomplete needle or linear tracks to the anterior stroma. As the entire cornea is involved, these procedures are used for most of the entire cornea including the actual erosion site. Punctate keratotomy leaves smaller scars than grid keratotomy. The keratotomy procedures are usually preceded by debridement using a cotton swab and topical anesthesia of the edges of these chronic erosions for 1 or 2 weeks. If epithelialization has not occurred in 12–14 days, one of these

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keratotomies is performed. Partial-to-complete superficial keratectomy has also been used for this condition. Other surgical procedures for recurrent and slow healing corneal erosions, such as transplantation of small lenticules of new and healthy epithelium (keratoepithelioplasty), microdiathermy of Bowman’s membrane, and neodymium:yttrium aluminum garnet (Nd:YAG) laser photo-induced adhesion of corneal epithelia, have not been reported in the dog.

Superficial punctate keratotomy Superficial punctate keratotomy may be performed in quiet dogs with only topical anesthesia, or with some sedation in less cooperative dogs. The grid procedure may be performed under local anesthesia, but general anesthesia is recommended if most of the cornea is involved. Prior to both procedures, loose corneal epithelia surrounding the chronic erosion are debrided with thumb forceps or sterile cotton swabs. In superficial punctate keratotomy, multiple anterior stromal punctures are performed with a 20–23 g disposable hypodermic needle or a diamond corneal knife with the micrometer set at 0.10–0.2 mm (Fig. 8.9a). The hypodermic needle is grasped directly or clamped with a small hemostat to expose 0.1–0.2 mm of the tip. The needle should enter the cornea at a 45–90 angle. The 23 g hypodermic needle will penetrate deeper into the corneal stroma than the 20 g hypodermic needle. Alternatively, the Nd:YAG laser may be used with multiple impulses set at 2 mJ. About 15–25 punctures are usually made about 1.5 mm apart surrounding the erosion and extending into the adjacent normal cornea (Fig. 8.9b). The cornea is slightly indented when the 0.1–0.2 mm depth is achieved. If inadvertent complete puncture of the cornea results, rapid selfsealing occurs.

A

Superficial grid keratotomy In the superficial grid keratotomy procedure, the corneal epithelia and anterior stroma are incised numerous times in a grid, cross-hatching or linear pattern. The majority of the grid incisions are adjacent to the corneal erosion, but this procedure may cover most of the corneal surface. The linear incisions for superficial grid keratotomy are made with a 20 g disposable hypodermic needle, Beaver No. 6400 microsurgical blade, or a diamond knife with the micrometer set at 0.2–0.3 mm deep (Fig. 8.10a). Incisions at 90 to the first series of incisions complete the grid keratotomy (Fig. 8.10b). Smaller gauge hypodermic needles are not recommended, as their incisions extend too deep. The grids are about 1–1.5 mm apart.

Superficial linear keratotomy The superficial grid keratotomy procedure has been partially replaced by a linear keratotomy which is easier to perform in the clinical patient with only topical corneal anesthesia. In this modification, the corneal epithelia and superficial stroma are incised in vertical linear incisions using a 20–22 g hypodermic needle. The incisions, about 1 mm apart, overlap the corneal erosion by a few millimeters in all directions. As with the superficial punctate and grid keratotomies, smaller gauge hypodermic needles (smaller than 22 g) are avoided because of their tendency to penetrate too deeply. Postoperative management after these three procedures is topical broad-spectrum antibiotics instilled every 8 h for 5–7 days. Healing of the erosions should occur during this period. The success rate of these procedures for the treatment of recurrent corneal erosions in dogs is about 80–90% within 2 weeks.

B

Fig. 8.9 In the superficial punctate keratotomy procedure, multiple partial-thickness hypodermic needle punctures are made in the erosion and adjacent cornea. (a) After thumb forceps removal of the loose epithelia about the erosion, the epithelia and 0.1–0.2 mm of the anterior stroma are repeatedly partially penetrated with a 20 g hypodermic needle grasped with a hemostat to prevent deeper corneal penetration. (b) About 15–25 partial corneal punctures are positioned within the erosion and adjacent area.

A

B

Fig. 8.10 In the superficial grid keratotomy procedure, the corneal epithelia and anterior stroma are incised in a grid or cross-hatching manner within the corneal erosion and adjacent area. (a) The initial corneal incisions, about 0.1–0.25 mm deep, may be performed with the Beaver No. 6400 microsurgical blade, diamond knife or a disposable 20 g hypodermic needle. (b) A second set of crosshatching incisions are placed at 90 to the initial incisions. The grids should be 1.0–1.5 mm apart.

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Surgical procedures for deep corneal ulcerations

Alternative treatments appear to yield lower success rates. Treatment of canine recurrent erosions with only aqueous iodine cautery of the erosion requires an average of 46 days for complete re-epithelialization. Contact lenses for corneal erosions yield 73% success, the major limitation being retention of the lens. If the lens is retained for 7–10 days, the success rate increases to 92%. Other forms of treatment for this disorder include nictitating membrane flaps, temporary tarsorrhaphy, and bulbar conjunctival grafts (see Chapters 5 and 6). The success rates of these treatment methods have focused on short-term management of the healing of the recurrent erosions. The real value of these procedures, yet to be established, is long-term prevention of recurrent corneal erosions. Postoperative complications after superficial punctate and grid keratotomies are infrequent. Inadvertent puncture of the cornea is rare, after the technique has been mastered. Fortunately, these punctures will self-seal immediately, but a small corneal scar results. Both techniques may produce faint anterior stromal scars, appearing as individual spots or a grid. This scar formation is usually negligible when compared to the repeated effects of recurrent corneal erosions of the canine cornea, including influx of vascularization and pigmentation, and the occasional deposition of lipids, cholesterol, and calcium. Recently the clinical use of these different keratotomies in the cat has been questioned because of the development of corneal sequestrum following their use. Perhaps the feline herpes virus (FHV-1) is present in some corneal sequestra, and, following keratotomy, the virus can penetrate deeper into the stroma. As a result, pending further clinical studies, keratotomies in cats must be most cautiously performed.

Corneal biopsy Biopsy of the cornea is usually performed to establish a diagnosis. Diagnosis of specific infectious agents (bacterial/ fungal) and possible neoplasia is provided by corneal biopsy. Corneal biopsies may be limited to the anterior epithelium, anywhere in the stroma, or even full thickness. Under the rubric of corneal biopsies is corneal cytology (obtained by deep scraping), and superficial and deep keratectomies. Deep keratectomies are performed in the same manner as superficial keratectomies, but the surgical wound is usually covered with a bulbar conjunctival graft or corneal graft. Excisional corneal biopsies can combine both diagnosis and initial treatment. When ulcerated or inflamed cornea is biopsied, all necrotic and involved tissues should be excised to enhance the possibility of diagnosis, demonstrate infectious agents, and facilitate attachment and retention of the conjunctival graft. The corneal biopsy procedure is modified by the depth of the corneal disease: 1) superficial keratectomy for diseases of the epithelia and anterior one-half of corneal stroma; 2) deep keratectomy for corneal diseases involving the posterior one-half of the corneal stroma; and 3) full-thickness keratectomy with homologous corneal grafts when the entire depth of the cornea is involved. These surgical procedures are presented in the respective sections in this chapter.

Adaptation for large animals and special species Keratectomy to obtain tissue for culture or histology in melting ulcers is similar to the techniques used in small animals. Large amounts of necrotic cornea can be removed with tenotomy scissors to speed healing of melting ulcers in horses and cows. Stromal biopsies to aid in the diagnosis of stromal abscesses or immune-mediated keratopathies in horses can be obtained in the standing horse. Utilizing sedation and topical anesthesia, a linear incision in the corneal epithelium is made with the Beaver No. 6400 or 6900 microsurgical blade (Fig. 8.11). A Martinez corneal dissector is then used to separate the epithelium from the stroma. A small biopsy punch is utilized to obtain a stromal sample, and the tissue placed on a sponge in a histologic cassette in fixative. The corneal epithelium is sutured with 8-0 sutures in a simple interrupted pattern. Topical antibiotics and NSAIDs can be used post-biopsy.

Surgical procedures for deep corneal ulcerations Corneal ulcerations are frequent in dogs but less common in cats. In the dog, corneal ulcers may be initiated by minor trauma. In certain breeds, particularly brachycephalic dogs, corneal ulceration may be associated with several predisposing factors. In brachycephalic breeds the eye is very prominent, suffers lagophthalmia, and the rate of blinking may be less than normal. Corneal microtrauma may occur from distichia and nasal fold trichiasis. The precorneal film may be thin and abnormal centrally, placing the central corneal epithelia in constant jeopardy. Retention of rose Bengal by the central corneal epithelia in these dogs suggests that these cells are degenerating at a faster rate than normal. These eyes are frequently also victims of marginal or low levels of aqueous tear production. The combinative effect is the development of a central-to-paracentral corneal ulcer that rapidly becomes deeper and larger (Fig. 8.12). Clinical signs associated with pain are often minimal or absent. Initial medical treatment usually includes topical broad-spectrum antibiotics, topical autogenous serum, and mydriatics. If the corneal ulcer continues to progress to involve the deep corneal stroma, becomes a descemetocele, or perforates with iris prolapse, surgical treatment with conjunctival or corneal grafts is recommended. Maintenance of vision and the least corneal scarring are achieved when conjunctival grafts are positioned before development of corneal perforation and iris prolapse. Administration of antibiotic treatment to all potential corneal ulcerations is recommended. Surgical correction of these ulcerations will usually be successful, provided the infectious agents are eliminated. Bacteria, usually Staphylococcus and Streptococcus spp., are frequently isolated from canine corneal ulcers. These organisms seem to originate from the conjunctival surfaces. Staphylococcus spp. are usually susceptible to chloramphenicol, bacitracin, and gentamicin; Streptococcus spp. are usually susceptible to chloramphenicol, erythromycin, carbenicillin, and cephalothin. Infrequently recovered in small animals, Pseudomonas spp. are susceptible to gentamicin, tobramycin, polymyxin B, and amikacin.

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Fig. 8.11 Corneal stromal biopsy in a horse with suspected immune-mediated keratitis. (a) Incision of the corneal epithelium in a sedated standing horse. (b) The corneal dissector is used to expose the corneal stroma. (c) Corneal forceps and scissors are used to remove a section of stroma for histopathology. d) Biopsy site is apposed by sutures.

Primary closure of small deep corneal ulcers Small deep corneal ulcers may be closed by direct suturing. The maximum diameter of corneal ulcers that can be apposed by sutures is about 3 mm or less. Control and hopefully

Fig. 8.12 Deep central corneal ulcer in a Pekingese dog. Primary closure with sutures of small and deep corneal ulcers (<3 mm diameter) may be attempted provided local sepsis is eliminated. 202

elimination of the potential pathogenic bacteria from the ulcer site contributes directly to the success or failure of this method. After general anesthesia and surgical preparation of the eyelids and conjunctiva, the eye is draped and an eyelid speculum positioned. The corneal ulcer is closely examined, and any necrotic or suspect tissue carefully removed by Beaver No. 6400 microsurgical blade (Fig. 8.13a). These tissues should be cultured and evaluated histologically. The edges of the corneal ulcer are carefully treated with aqueous 0.5% povidone–iodine solution applied with sterile cotton swabs to attempt sterilization of the ulcer. The same solution may be applied carefully to the ulcer base, but only if some deep corneal stroma remains. Two or three 5-0 to 6-0 braided polyglactin 910 simple interrupted sutures, or a combination of a central interrupted horizontal mattress suture and two simple interrupted sutures, are used to appose the ulcer’s edges (Fig. 8.13b). Sutures are placed into the deep corneal stroma. Some distortion of the cornea develops as the sutures are tied and ulcer edges apposed (Fig. 8.13c). Fortunately, as corneal healing occurs during the next 7–10 days, the corneal curvature gradually returns to normal. For success with this procedure, sutures must be placed in viable corneal stroma. Placement of the sutures in necrotic

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Fig. 8.13 Primary closure of corneal ulcers may be attempted with deep corneal ulcers <3 mm diameter. (a) To ensure suture stability, any necrotic or potentially infected corneal epithelia and stroma are excised with the Beaver No. 6400 microsurgical blade. These tissues should be cultured for bacteria and examined microscopically. (b) Two or three 5-0 to 6-0 simple interrupted absorbable sutures are pre-placed. If the cornea appears quite friable, interrupted mattress sutures may be used. The corneal bites for these sutures should be about 2 mm and deep in the normal corneal stroma. (c) All sutures are tightened and tied to effect primary ulcer closure. Some temporary corneal distortion is usually evident for several days postoperatively.

and friable stroma usually results in sutures tearing from the stroma in 24–48 h. Braided polyglactin 910 sutures are recommended as this material is not adversely affected by sepsis. After recovery from general anesthesia, medical treatment is continued with topical and occasionally systemic broad-spectrum antibiotics, topical autogenous serum, and mydriatics. Maintenance of the wound beyond 5–7 days usually results in a successful apposition. If premature dehiscence of the wound and sutures occurs, treatment of the ulcer with a bulbar conjunctival graft is recommended.

Conjunctival autografts Conjunctival autografts are frequently used in small animal ophthalmology for the clinical management of deep and large corneal ulcers, descemetoceles, mycotic ulcers, stromal abscesses, after sequestrum removal in cats, keratomalacia, and for perforated corneal ulcers with and without iris prolapse. Conjunctival autografts were presented in Chapter 7. Conjunctival autografts consist of either bulbar or palpebral conjunctival mucosa with epithelium, and connective tissue. These autografts can be transposed and sutured directly to the edges of the corneal ulcer or defect to provide additional support and tissue for a cornea weakened by deep ulceration, descemetocele, or perforation with or without iris prolapse. The transplanted conjunctival autograft provides additional tissues and no risk of host rejection. Conjunctival autografts provide sufficient tissue to strengthen most weakened corneas and prevent staphyloma formation, but are not as strong as corneal grafts. When harvested from the limbus, the transplanted limbal conjunctiva contains stem cells capable of additional generation and transition into corneal epithelium. Conjunctival autografts contain blood vessels and lymphatics to offer significant antibacterial, antifungal, antiviral, antiprotease, and anticollagenase effects. With conjunctival transplants, leukocytes, antibodies, serum, and a2-macroglobulin (thought to be the anticollagenase factor) are immediately incorporated into the corneal ulcer bed. Through the conjunctival blood vessels, systemic antibiotics can enter the ulcer site in higher levels. The fibrovascular or deeper layer of the conjunctival transplant offers immediate fibroblasts and collagen to begin rebuilding the corneal stroma. Conjunctival grafts usually result in corneal scars of various sizes and depths. Postoperative topical corticosteroids and/or cyclosporine can reduce this postoperative scar tissue formation to a minimum, but corneal scarring after conjunctival grafts should be anticipated.

Conjunctival autografts from either bulbar or palpebral conjunctiva should be thin, and not include Tenon’s capsule or the bulbar fascia. The inclusion of Tenon’s capsule may contribute to surgical failure by increasing the traction on the transplanted conjunctival graft. Transpalpebral conjunctival autografts contain limited portions of the fibrous tarsal layer which may be necessary to maintain the graft base from the deeper aspects of the eyelid to the corneal surface. Conjunctival autografts are more difficult to perform than nictitating membrane flaps, but are easier than corneoconjunctival and corneoscleral transpositions, and the different types of keratoplasty. The most frequent type of bulbar conjunctival graft is the pedicle type (Fig. 8.14).

Porcine small intestinal submucosa (SIS) grafts The porcine small intestinal submucosa graft is a biomaterial consisting primarily of proteins and, to a lesser extent, carbohydrates and lipids. SIS grafts have been reported in dogs, cats, rabbits, and horses. The SIS graft, derived from the porcine jejunum, is composed of three distinct layers: 1) tunica muscularis mucosa; 2) tunica mucosa; and 3) the stratum compactum layer of the tunica mucosa. Following processing and mechanical debridement, a few remaining endothelial cells and fibrocytes are lyzed with a hypotonic wash, leaving a sheet of collagen with a smooth surface (stratum compactum) and a rough surface (tunica muscularis mucosa). The SIS graft is sterilized by ethylene oxide,

Fig. 8.14 Bulbar pedicle conjunctival grafts used in the dog to treat a central and deep corneal ulcer. 203

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and is supplied commercially as 7
10 cm sheets, and 10 or 15 mm diameter ophthalmic discs. After debridement of the septic corneal ulcer, the SIS graft is carefully trimmed and ‘fitted’ to cover in excess of 1–1.5 mm of the entire corneal ulcerative bed. After securing the graft to the ulcer’s edges with several 7-0 to 9-0 simple interrupted absorbable sutures, the entire SIS graft is covered with a bulbar pedicle conjunctival graft. The SIS graft provides a scaffold for corneal healing as well as additional strength to the overlying bulbar conjunctival graft. Rabbit corneal SIS graft studies suggest that the graft collagen sheet is actually incorporated into the healing process. SIS grafts have been reported to fill the limbocorneal defect after limbal melanocytoma excision and covered with bulbar conjunctiva, for full-thickness corneal ulcerative disease in dogs and covered with conjunctival grafts, after corneal ulcers and corneal sequestra in cats and not covered with conjunctival grafts, and after corneal ulceration and corneal stromal abscess formation in horses and covered with conjunctival grafts. These grafts are convenient to use, are commercially available and ready for use, avoid potential virus transmission as is possible with feline-based grafts, and are easy to handle during surgery. If placed in an uncontrolled septic corneal ulcer, covering with a conjunctival graft is highly recommended.

Amniotic conjunctival grafts Amniotic grafts have been reported to repair deep corneal ulcers in horses and for experimentally induced fullthickness corneal defects dogs. The amniotic grafts for both the horse and dog studies were harvested from normal equine placenta and are not available commercially. In the dog study, after harvest, the amniotic grafts were preserved in 98% sterile glycerol (full-thickness scleral grafts are commonly preserved in glycerol). The equine amniotic graft is obtained aseptically as a 5 mm2 section of amnion after death or cesarean section. After harvest, the tissues are preserved in 98% sterile glycerol; immediately before use the tissue is rehydrated in sterile saline solution. The equine pericardium has also been used in surgery to correct canine lateral canthal entropion, deep corneal ulcerations in dogs, fill the orbital cavity of dogs after enucleation, and as a scleral graft.

Nictitating membrane flaps Nictitating membrane flaps provide more support to the diseased cornea than temporary complete tarsorrhaphy in small animals. Nictitating membrane flaps are used to cover and protect a weakened cornea, but are not usually a source of tissues for the cornea. Nictitating flaps are recommended for superficial corneal diseases, including corneal erosions, neuroparalytic and neurotropic keratitis, temporary exposure keratitis, superficial corneal ulcers, and acute keratoconjunctivitis sicca, and to reinforce a bulbar conjunctival graft. Surgical procedures for nictitating membrane flaps are presented in Chapter 7.

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Corneoscleral transposition Corneoscleral transposition shifts the peripheral cornea into central corneal defects and moves adjacent sclera into the peripheral cornea. As this procedure is primarily used for the repair of corneal ulcerations it is included in this section; however, corneoscleral and corneoconjunctival transpositions may also be considered as distinct types of autologous sliding lamellar keratoplasty. As a result, axial (central) and visually important cornea remains clear, but the peripheral cornea with the transposed sclera becomes somewhat translucent. A modification of this surgery, the corneoconjunctival autograft, was presented in Chapter 7. Corneoscleral transpositions are used to treat deep corneal ulcerations, descemetoceles, and feline corneal sequestra involving the deeper stroma. The advancement of corneoscleral tissues into central corneal ulcers, suspected as septic or not treated with antibiotics, is not recommended as these grafts may also be destroyed with the progressive melting process. If the tip of the corneoscleral graft is already vascularized, the chance of slough from infectious agents is reduced. Hence, before corneoscleral transpositions are performed, the corneal ulcer’s edges should be scraped and examined microscopically for bacterial and fungal organisms. Alternatively, the corneal ulcer may be treated hourly with topical broad-spectrum antibiotics for several hours to attempt sterilization of the ulcer site. After the onset of general anesthesia, and surgical preparation of the eyelids, conjunctiva, and cornea with aqueous 0.5% povidone–iodine solution, the eye is draped and an eyelid speculum positioned. The corneal ulcer is carefully debrided to remove all potentially necrotic and/or infected tissues (Fig. 8.15a). Once these tissues have been removed, the corneal defect may be 1–2 mm larger. The corneoscleral advancement graft is prepared. Two slightly diverging corneal incisions with the Beaver No. 6400 microsurgical blade are performed, extending from the corneal bed to the limbus (Fig. 8.15b). These incisions are approximately one-half of the stromal thickness. At the limbus, the bulbar conjunctiva and Tenon’s capsule are incised by tenotomy scissors for about 15–20 mm and reflected caudally to expose the sclera (Fig. 8.15c). The ends of the two corneal incisions are extended into the sclera at a distance equal to the height of the corneal ulcer bed (Fig. 8.15d). These incisions should be about 0.2–0.3 mm deep. Hemorrhage during these incisions is anticipated and judicious cautery with the disposable battery-powered electrocautery unit is necessary for hemostasis. The tip of the corneoscleral transposition is elevated with 1
2 teeth thumb forceps and a corneal dissector, and separated from the corneal bed to the end of the scleral incisions (Fig. 8.15e). The corneal separator, in contrast to sharp dissection with a scalpel blade, facilitates dissection within the corneal lamellae without the danger of shifting the plane of tissue separation. Once separation from the underlying corneosclera is complete, the base of the graft is incised with tenotomy scissors (Fig. 8.15f). The length and width of the tip of the corneoscleral graft should be 1–2 mm larger than the corneal ulcer bed. The corneoscleral graft is positioned in the corneal ulcer bed, trimmed if necessary, and apposed with 7-0

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Fig. 8.15 In corneoscleral transposition, cornea and adjacent sclera are slid from the periphery into a central corneal defect. (a) With the Beaver No. 6400 microsurgical blade, all necrotic and suspicious corneal epithelia and stroma are carefully excised. (b) Two slightly diverging corneal incisions are excised from the edge of the corneal ulcer to the limbus with the Beaver No. 6400 microsurgical blade to prepare the corneoscleral graft. (c) At the limbus, the bulbar conjunctiva and epibulbar fascia (Tenon’s capsule) are incised by Steven’s tenotomy scissors to expose the underlying sclera. (d) The ends of both corneal incisions are extended into the superficial (about 0.2–0.3 mm deep) sclera with the Beaver No. 6400 microsurgical blade. Hemorrhage from these scleral incisions is controlled by point electrocautery. (e) The tip of the corneoscleral graft is grasped with 1
2 teeth thumb forceps, and the corneal stromal dissection is started with a corneal dissector or separator. (f) After the corneoscleral graft is completely separated from the deeper corneal and scleral tissues, its base is incised with Steven’s tenotomy scissors. (g) The corneoscleral graft is carefully trimmed to fit the corneal defect, and should be 0.5–1 mm larger than the defect to compensate for tissue shrinkage. It is attached by 7-0 to 9-0 simple interrupted absorbable sutures. (h) After the corneoscleral graft is secured by sutures, the bulbar conjunctiva is apposed to the limbus with a 7-0 to 9-0 simple continuous absorbable suture. (i) The 3-week postoperative appearance of a corneoconjunctival graft in a cat after removal of a corneal sequestrum.

to 9-0 simple interrupted braided polyglactin 910 sutures (Fig. 8.15g). The edge of the bulbar conjunctiva is apposed back to the limbus with a 7-0 to 9-0 simple continuous braided polyglactin 910 suture (Fig. 8.15h). Postoperative treatment after corneoscleral transpositions includes topical and systemic broad-spectrum antibiotics, and topical mydriatics sufficient to maintain a moderately dilated and mobile pupil. After 7–10 days, topical corticosteroids are started to reduce corneal scarring. Clearing of the cornea usually starts 2–6 weeks postoperatively. Success rates with corneoscleral transpositions are 75– 80% (Fig. 8.15i). Complications after this surgery include septic involvement of the tip of the transposition with the ulcer process, suture loss, and abscesses. Iridocyclitis is often intense in these eyes, and vigorous mydriatic therapy indicated. With inadequate control of the iridocyclitis, deposits of iridal tissue on the anterior lens capsule, posterior synechiae, and secondary cataract formation result.

Adaptations for large animals and special species Conjunctival grafts or flaps are frequently used in equine ophthalmology for clinical treatment of deep, melting, and large corneal ulcers, descemetoceles, and perforated corneal ulcers. Melting ulcers should be stabilized with medical therapy, if possible, before the surgical placement of the graft to prevent protease digestion of any absorbable suture that will hold the conjunctival graft in place. The preoperative application of topical antiproteolytic agents before a conjunctival graft slows or stops ulcer progression in many cases and provides a healthier cornea for suturing. All conjunctival flaps consist of thin conjunctival tissue transposed onto the cornea to cover a severe corneal lesion and provide sufficient tissue to strengthen most weakened melting corneas. They are not as strong as corneal grafts. Conjunctival autografts consist of either bulbar or palpebral

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conjunctival mucosa with epithelium, and connective tissue (fibroblasts, blood vessels, and lymphatics), thus offering a new and highly viable epithelium and significant antibacterial, antifungal, antiprotease, and anticollagenase effects. With conjunctival grafts, polymorphonuclear leukocytes, antibodies, serum, and a2-macroglobulin are immediately placed in the corneal ulcer bed. The fibrovascular, or deeper, layer of the conjunctival transplant offers immediate fibroblasts and collagen with which to begin rebuilding the corneal stroma. Conjunctival autografts are more difficult to perform than nictitating membrane flaps but simpler than surgeries such as corneoconjunctival grafts, corneoscleral transpositions, and penetrating keratoplasty (PK). They are also easier to perform in the horse than in other species, because horses have a great deal of very mobile bulbar conjunctiva. There are different types of conjunctival graft based on the source of the mucosa (bulbar or palpebral) and the type of graft (total or 360 , bridge or bipedicle, hood or 180 , pedicle or rotational, and island). Conjunctival grafts are usually harvested from adjacent bulbar conjunctiva; however, the palpebral conjunctiva can also be used. The disadvantage of the palpebral conjunctival flap is that the eyelid is mobile and some tension will be applied to the sutured conjunctival graft, possibly leading to a higher rate of graft dehiscence. However, as the bulbar conjunctival flap moves with the eye, no tension is applied to the flap itself. It is also not recommended to use the conjunctiva near the nictitating membrane if possible because its movements can put tension on the graft, resulting in premature graft release. Conjunctival autografts from either bulbar or palpebral conjunctiva should be thin, and not include Tenon’s capsule or the bulbar fascia. It seems beneficial to administer a drop of 2.5% phenylephrine prior to dissection of the conjunctiva to limit hemorrhage. Tenon’s capsule should be stripped or cut from the graft so that the graft easily covers the corneal defect without any tension, prior to suture placement. The inclusion of Tenon’s capsule may contribute to surgical failure by increasing postoperative traction on the transplanted conjunctival graft. Conjunctival grafts should have tension-relieving sutures placed at the limbus to prevent the graft pulling away from the ulcer bed prematurely. Conjunctival pedicle grafts using the bulbar conjunctiva from the dorsal or temporal quadrants are preferred, because the conjunctiva in those areas is surgically available and the pedicle flap covers only the ulcer surface, allowing postoperative observation of the pupil and anterior chamber. The pedicle graft is a focal transplant and does not cover the entire cornea. With all the flaps, it is important that the corneal graft bed and ulcer be properly and carefully prepared. The recipient bed for the conjunctival graft is prepared by debridement and keratectomy of the corneal ulcer with a Beaver No. 6400 microsurgical blade, thereby removing loose epithelium and necrotic corneal tissues. Great care should be taken to prevent corneal perforation during this debridement. Temporary tarsorrhaphy is performed concurrently with conjunctival grafts to minimize blinking movement, prevent excessive lid trauma to the graft and its sutures, and allow quick graft adherences to the stroma. The most common complication from any type of conjunctival grafting procedure is dehiscence of the graft from

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the corneal lesion (retraction of the graft). This may occur because the corneal lesion is progressing (worsening) and damaging the cornea at the points where the sutures secure the graft. Cytokines released by the tissue may induce infarction of the flap vessels and cause premature release. Excessive tension on the graft, or allowing a significant portion of the fibrous Tenon’s capsule to remain attached to the graft, may result in premature dehiscence of the graft. Proper suture placement in healthy cornea using a thin conjunctival graft concurrent with appropriate medical therapy will greatly decrease the complications following conjunctival graft surgery. Conjunctival grafts usually result in corneal scars of various sizes and degrees. Scarring can be minimized, however, by removal of necrotic cornea with keratectomy before graft placement. Corticosteroids are not recommended but they can be used topically very carefully after surgery to reduce postoperative scar tissue formation to a minimum, but some degree of corneal scarring after conjunctival grafts should be anticipated.

Total or 360 conjunctival graft This type of graft is indicated in eyes with a large melting ulcer that affects most of the cornea. After Castroviejo eyelid speculum placement to expose the eye and conjunctiva, and a drop of 2.5% phenylephrine, the dorsal bulbar conjunctiva is grasped with forceps (0.12 mm Colibri forceps or Bishop–Harmon forceps) and incised with tenotomy scissors (Westcott scissors or Steven’s tenotomy scissors) 2 mm from the limbus (limbus-based 360 conjunctival graft). The incision is then continued 360 around the limbus (i.e., peritomy). The bulbar conjunctiva is then separated from the underlying Tenon’s capsule by alternating blunt– sharp dissection that is continued up to 10 mm behind the limbus. The conjunctival graft should be thin to minimize traction, and the loose edges of the graft should rest on the central cornea without spontaneously retracting. The conjunctiva is then pulled over the cornea and sutured to itself in the center of the cornea in a linear pattern (horizontal mattress) using 7-0 or 8-0 absorbable sutures. A 360 conjunctival graft is easy to perform and effective for large corneal lesions; however, it covers the entire cornea which makes vision impossible, prevents monitoring of lesion progression, and leaves large corneal scars.

Bridge or bipedicle graft The bridge or bipedicle flap is indicated for large melting ulcers in the central, dorsal paracentral, and lateral paracentral corneal regions (Fig. 8.16). This type of graft is also done when the corneal defect is too large for a pedicle graft (>6–8 mm) but too small for a total graft. The first incision is made with the Westcott scissors in the conjunctiva at 1–2 mm from the limbus, and extended parallel to the limbus for approximately 180 . This conjunctival incision should be made in order to obtain a graft that will be perpendicular to the eyelid margins when in place on the cornea so as to minimize eyelid trauma to the corneal sutures and conjunctival graft. This conjunctiva is extensively undermined, and the underlying fibrous tissue removed in order to obtain a conjunctival graft that is almost transparent. You should be able to visualize the

Surgical procedures for deep corneal ulcerations

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Fig. 8.16 Bipedicle or bridge bulbar conjunctival graft in the horse for treatment of a large corneal ulcer. (a) Preoperative appearance of the deep corneal ulcer with a thin center. (b) Two week postoperative appearance of the bipedicle (bridge) bulbar conjunctival graft.

scissors’ tips underneath the tissue. A second conjunctival incision is made 8–10 mm peripheral and parallel to the original conjunctival incision, thus creating a ‘bridge’ of conjunctiva that should be 1–2 mm wider than the corneal ulcer. This bridge is then advanced over the lesion by rotation (the rotation should be less than 45 from the vertical) and sutured using 7-0 or 8-0 simple interrupted absorbable sutures in the cornea around the lesion. The original graft harvesting site may be closed by apposing the remaining conjunctiva with simple interrupted or continuous sutures, but this is not necessary. The advantage of this procedure is that it provides exquisite blood supply to lesions of the cornea.

Hood or 180 conjunctival graft The hood or 180 conjunctival graft is indicated for large peripheral melting corneal ulcers. The conjunctiva is cut from the limbus (2 mm away) and undermined. The conjunctiva is separated from Tenon’s capsule and should be sufficiently thin to allow visualization of the scissors’ tips under the mucosa. The conjunctival graft is then advanced to cover the lesion without tension and sutured in place,

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generally with two or four simple interrupted sutures or a continuous suture pattern using 7-0 or 8-0 absorbable material. Large scars result from this type of graft.

Pedicle or rotational conjunctival graft The pedicle or rotational graft is probably the most useful and versatile conjunctival graft as it generally leaves a smaller scar to have minimal effects on vision, allows for postoperative intraocular examination, and does not inhibit drug penetration into the anterior chamber. The conjunctival graft should be oriented vertically on the cornea so as to minimize eyelid trauma to the corneal sutures and conjunctival graft. The base of the pedicle should be directed at the area of the limbus closest to the lesion (Figs 8.17 and 8.18). Once the location is determined, the conjunctiva is tented with the 0.12 mm Colibri forceps, a small slit is made with the Westcott scissors in the conjunctiva perpendicular to the limbus at 1–2 mm from the limbus, and this initial conjunctival incision continued, parallel to the limbus. The entire conjunctival flap site is then undermined using blunt dissection with Steven’s tenotomy scissors. The underlying fibrous tissue (i.e., Tenon’s capsule) should be

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Fig. 8.17 Treatment of a central deep corneal ulcer with a tectonic corneal transplant and bulbar conjunctival pedicle graft in a horse. (a) A large diameter melting corneal ulcer is surrounded by a strong cellular infiltrate and corneal edema. (b) After filling the corneal defect with frozen (tectonic) corneal tissue, the entire ulcer is covered with a bulbar conjunctival pedicle graft (appearance 5 weeks postoperatively). (c) At 7 weeks postoperatively, the cornea has healed, the pupil is well dilated, but the dorsal corpora nigra has adhered to the posterior corneal wound.

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Fig. 8.18 Treatment of melting corneal ulcer with iris prolapse with penetrating keratoplasty (frozen tectonic graft) and conjunctival and amnion grafts in a horse. (a) Perforated corneal ulcer with iris prolapse in an adult horse. (b) Penetrating keratoplasty has been covered by a conjunctival graft but is beginning to fail. The avascular portion of the failed conjunctival graft has been covered by an amnion graft. (c) The cornea has healed, the amnion graft has sloughed, and the pedicle conjunctival graft at 7 weeks postoperatively is ready to be transected at its base.

freed from the overlying conjunctiva so that the conjunctiva appears nearly transparent and permits the visualization of the scissors’ tips underneath the conjunctiva. The second incision is then made perpendicular to the first incision (and to the limbus) at the tip of the graft. The width of the incision should be 1–2 mm wider than the size of the corneal lesion to be covered. The third and final incision is made parallel to the first, extending to the bulbar attachment of the graft. The strip of conjunctiva thus created is then rotated to cover the corneal lesion. It should cover the corneal defect with no tension or retraction. The flap is then sutured to the cornea with 7-0 to 8-0 simple interrupted absorbable sutures. The cardinal sutures are placed first at the distal corners of the flap, and then 1.0–1.5 mm apart. Two interrupted sutures may be placed at the limbus on either side of the graft to decrease the tension applied to the corneal recipient site. To prevent disruption of the blood supply, sutures are not placed within the pedicle portion of the graft, or at the proximal portion of the lesion. Conjunctival grafts will adhere to the exposed corneal stroma of the lesion but they will not usually adhere to the epithelium surrounding the flap. Between 6 and 8 weeks after the placement of the flap, the blood supply can be interrupted by cutting the base of the flap at the limbus. This procedure can usually be performed with the use of a topical anesthesia and Steven’s tenotomy scissors. Eliminating the blood supply will allow the conjunctival graft to recede and lessen the resulting corneal scar. If the pedicle graft does not impede the horse’s vision, trimming of the pedicle conjunctival graft is not recommended since episodes of uveitis have been reported following this procedure in horses. Whether bridge flaps are more or less successful than pedicle flaps in these types of lesion is not definitively known, but pedicle flaps are easier to perform.

Island conjunctival graft A conjunctival, free island graft is a modified conjunctival graft in which the blood supply is severed from the outset. It is simply a transplant of conjunctival tissue to the cornea, and its use has been described in deep, central, and paracentral corneal lesions. The donor site can be the tarsal

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(palpebral) or the bulbar conjunctiva. The conjunctiva is undermined and excised from the donor site using Colibri forceps and Westcott tenotomy scissors, and then transposed to cover the corneal lesion, with the epithelial site external to allow proper attachment of the graft to the lesion. Simple interrupted or continuous sutures can be used to secure the graft to the cornea using 7-0 to 8-0 absorbable material. The lack of blood supply to the island graft reduces graft viability and increases susceptibility to infection. For these reasons, the island conjunctival graft is not recommended in equine corneal disease.

Amniotic membrane grafts The use of equine amniotic membrane grafts for eye problems in horses, and particularly to surgically treat melting corneal ulcers, has been reported. Amniotic membrane (AM) consists of an epithelium, a thick basement membrane, and an avascular stroma. High concentrations of basic fibroblast growth factor and basement membrane components such as collagen are present. It provides a good cell–basement membrane structure that is critical for epithelial proliferation and differentiation. Reports have shown interest in the AM as a graft for reconstruction of various ocular surfaces, as it is a strong biomaterial that contains anti-angiogenic, anti-inflammatory, antifibrotic, and growth factors. A recent investigation revealed that AM contains several protease inhibitors such as a2-macroglobulin, a1-chymotrypsin inhibitor, inter-a1-trypsin inhibitor, a1-trypsin inhibitor, and a2plasmin inhibitor. The therapeutic effect of AM on severely damaged melting ulcers may be due to the inhibitory effect of AM on corneal protease activity that would otherwise induce severe and irreversible stromal destruction. It has also been suggested that the AM can decrease the protease activity directed against the corneal stroma by providing exogenous collagen as a deviant substrate for tear film proteases. For the cases we initially treated at the University of Florida Veterinary Medical Teaching Hospital, an equine placenta was harvested during an elective cesarean section for term pregnancy on a 12-year-old mare. We have since successfully used amnion obtained at term deliveries. The allantoamnion is separated from the allantochorion and

Surgical procedures for deep corneal ulcerations

Fig. 8.19 Treatment of a large corneal ulcer with amnion graft in a horse. (a) Preoperative appearance of the corneal ulcer with edema, keratomalacia, and hypopyon. (b) Preoperative appearance of the large corneal ulcer after staining with topical fluorescein. (c) An amnion graft that has covered the corneal ulcer has nearly sloughed off at two weeks postoperatively. (d) The corneal ulcer is healing nicely surrounded with superficial vascularization and granuloma formation.

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the amnion (epithelium, stroma, and basement membrane), then separated by blunt dissection from the allantois. The AM is then placed on a nitrocellulose paper and stored frozen at – 80 C for years in Dulbecco’s modified Eagle medium also containing glycerol, antibiotics, and antifungals (penicillin, streptomycin, neomycin, and amphotericin B). After storage in the freezer, the AM epithelium is almost non-existent, and therefore the AM graft material consists of a stroma and a basement membrane. Prior to corneal surgery, the AM is naturally thawed, and then rinsed with sterile saline over 30 min to wash off the glycerol. During the wash, the AM is kept on the nitrocellulose paper with the allantoic (stromal) side against the paper. The AM is then prepared and cut according to the size of the corneal defect to be covered. To reduce premature graft retraction, AM grafts should simply cover the corneal defect with little tension present before the suture placement. As with conjunctival grafts, it is important that the corneal graft site and the ulcer be properly prepared. The recipient bed for the AM graft is prepared by removing loose epithelium and necrotic corneal tissues with a Beaver No. 6400 microsurgical blade. Great care should be taken to prevent corneal perforation during this debridement. The purpose and the evolution of the AM graft depends on how the AM is placed on the cornea: if the allantoic (stromal) side of the AM faces the cornea, the AM graft will adhere to the corneal stroma and the AM is expected to be incorporated into the corneal stroma; on the other hand, if the basement membrane of the AM faces the cornea, the corneal epithelial cells will migrate along the membrane and therefore the AM is used as a bandage. It is expected to slough off in 7–10 days. The AM is then sutured to the cornea with 7-0 to 8-0 simple interrupted absorbable sutures (Fig. 8.19). Several layers of AM can be used and piled up to fill the corneal defect if necessary. The AM may be placed limbus to limbus to cover the complete cornea as a bandage. A temporary tarsorrhaphy is then placed to minimize blinking movement,

prevent excessive lid trauma to the graft and its sutures, and allow quick graft adherence to the stroma.

Other biomaterials with potential use in corneal surgery in horses Other biomaterials have been used in corneal surgeries in other species (human, dogs, cats, rabbits): equine pericardium, peritoneum, equine renal capsule, porcine small intestinal submucosa (SIS), and porcine bladder submucosa (ACell, Columbia, MD) with some interesting results (Fig. 8.20). With the exception of the porcine bladder submucosa that has been used in a few equine cases, including at the University of Florida, College of Veterinary Medicine, to our knowledge the use of these biomaterials has not been reported in horses. Further studies need to be performed in order to assess their potential use for corneal surgery in horses with melting corneal ulcers.

Fig. 8.20 Treatment of a leaking corneal suture with tissue glue and BIOSIS graft in a horse. Tissue glue and a BIOSIS graft were used to successfully stop a leaking corneal suture in this horse.

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Nictitating membrane or third eyelid flap Nictitating membrane flaps provide more support to a diseased cornea than a temporary complete tarsorrhaphy. They are used to cover and protect a weakened cornea, but are not a source of nutrients or collagen to replace corneal tissue loss. Nictitating membrane flaps are recommended for superficial corneal diseases, as well as to reinforce a bulbar conjunctival graft. Third eyelid flaps are contraindicated for most corneal ulcers in horses, especially the melting ulcers that progress rapidly because they do not provide a blood supply or fibrovascular tissues to the ulcer. In addition, it is impossible to visually observe the progression of the disease and cover the normal cornea. Furthermore, third eyelid flaps might impede the penetration of topical medication and retain inflammatory exudates adjacent to the lesion. To place a third eyelid flap, one tip of the forceps (Bishop– Harmon forceps) is placed above and the other tip below the lateral aspect of the upper eyelid margin. The forceps tips are inserted as far as possible into the conjunctival fornix where the sutures should traverse the eyelid. The first suture (4-0 non-absorbable suture) with a pre-placed stent (intravenous tubing, buttons, polystyrene foam strip, rubber bands) is passed through the eyelid skin and into the conjunctival fornix. The suture is then passed through the palpebral (anterior) side of the nictitating membrane to encircle the upper stem of the T-shaped nictitating hyaline cartilage. The suture is then finally passed through the dorsolateral conjunctival fornix, the upper eyelid, and the stent again. The nictitating membrane is then protracted until its leading margin is at the limbus or within the conjunctival fornix.

Temporary tarsorrhaphy A temporary tarsorrhaphy minimizes eyelid movement over the corneal sutures, conjunctival grafts, and corneal grafts, thus reducing any microtrauma to the surgical site and promoting graft adherence. A tarsorrhaphy is recommended after most equine corneal surgical procedures, particularly conjunctival, amniotic membrane, and corneal grafts. The sutures may be left in place for a few days to a week. If not placed properly, the tarsorrhaphy suture can cause a corneal ulcer. Mild pressure necrosis of the eyelid skin can result from a temporary tarsorrhaphy suture left in place for more than several days. Using 4-0 non-absorbable material, a horizontal mattress suture is placed across the palpebral fissure. To achieve accurate apposition of the lids, the needle should exit and enter the lid margin at the level of the meibomian glands. Intravenous tubing, buttons, polystyrene foam strip, or rubber bands should be used as stents to minimize the pressure applied to the eyelids. The tarsorrhaphy should be oriented along the eyelid to allow for evaluation of the surgical site. The number of eyelid sutures varies (usually two or three) depending on whether a complete or partial temporary apposition of the eyelids is performed. Alternatively, the knot may be tied first with a surgeon’s throw and then finished in a bow-tie to allow for loosening of the tarsorrhaphy suture to facilitate corneal evaluation. This technique requires some patience, however, and a protective eyecup is required. Additionally, thorough sedation is necessary to untie and retie the bow.

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Surgery for corneal lacerations Corneal lacerations in small animals are frequent, and occur mainly in young animals (Fig. 8.21). Corneal lacerations are divided clinically into partial thickness and full thickness (or complete). Full-thickness lacerations are subdivided into: 1) with and without iris prolapse; 2) with and without lens involvement; and 3) with loss of intraocular contents. The prognosis for successful treatment of corneal lacerations in small animals is determined by: dog or cat; age of the patient; cause of the laceration; duration of the laceration; depth, position, and size of the laceration; and the involvement of other ocular tissues. Dogs tend to have a more intense anterior uveal inflammation than cats following corneal lacerations and repair. The age of the patient is important as young animals (less than 1 year old) have a greater chance of developing phthisis bulbi than older animals. Although most corneal lacerations are caused by trauma with metal objects, corneal lacerations secondary to cat scratches and wood splinters, with possible embedment of organic material, produce a more intense postoperative anterior uveitis and carry a guarded prognosis. Lacerations with iris prolapse in excess of 24 h have a poor prognosis as the exposed iris must be excised (rather than replaced in the anterior chamber) and a more intense anterior uveitis results. Intraocular hemorrhage is also possible. Axial or central corneal lacerations have a greater adverse effect on restoration of vision and a greater chance of lens involvement. Additional ocular tissue involvement with full-thickness corneal lacerations, such as iris prolapse, laceration of the anterior lens capsule, loss of lens and vitreous, intraocular hemorrhage, and lacerations of the sclera decrease the prognosis markedly for restoration of vision. Eyes with large corneal lacerations, loss of intraocular contents, and no realistic possibility for vision are best treated by enucleation or evisceration with an intrascleral prosthesis.

Fig. 8.21 Corneal lacerations in the dog often occur in young animals and are usually penetrating with iris prolapse. Immediate postoperative appearance of a corneal laceration after repair, with apposition of its edges with several 7-0 simple interrupted absorbable sutures. Some hemorrhage still remains in the anterior chamber. Mydriasis will be induced with 1% atropine instillation, and if the hemorrhage persists, intracameral 25 mg tissue plasminogen activator may be injected after about 7 days.

Surgery for corneal lacerations

Preoperative medical treatment Corneal lacerations are one of the few ophthalmic emergencies. Surgical correction for corneal lacerations should be performed as soon as possible. In the interim, medical therapy is immediately initiated. Not infrequently, these patients are young animals, and the pain from the injury often results in a patient that is difficult to handle and examine. Once the diagnosis is established, patient restraint should be minimal. Initial medical treatment includes topical (gentamicin or chloramphenicol) and systemic antibiotics (amoxicillin or cephalexin). Topical mydriatics, such as atropine, are usually delayed until surgery or later, since, with a full-thickness corneal laceration, iris prolapse may be important in maintaining the anterior chamber and providing at least some intraocular pressure.

Partial-thickness corneal lacerations Partial-thickness corneal lacerations usually bear a guarded but favorable prognosis. Once under general anesthesia, the eyelids and corneoconjunctival surfaces are prepared for aseptic surgery, the area draped, and an eyelid speculum inserted. The partial-thickness corneal laceration and, if present, the resultant corneal flap, are carefully cleansed with aqueous 0.5% povidone–iodine solution and sterile cotton swabs, and the rest of the cornea and globe are closely inspected for additional injuries (Fig. 8.22a). Like other ophthalmic tissues, excision of the injured corneal tissue is avoided. The corneal flap is carefully apposed with 5-0 to 7-0 simple interrupted absorbable sutures (Fig. 8.22b). The traumatized cornea will appear edematous and thicker than normal. The pupil is usually miotic with some aqueous humor flare present. Topical mydriatics, such as 1% atropine, are instilled during surgery to treat the secondary anterior uveitis. Postoperatively, topical and systemic antibiotics, mydriatics, and NSAIDs (systemic and occasionally topical) are administered daily. As healing progresses and the anterior uveitis resolves, the frequency of the medications is gradually reduced: systemic medications are usually stopped in 7–14 days; topical medications may continue for 4–6 weeks depending on resolution of the anterior uveitis. Topical corticosteroids may be initiated after 10–14 days to minimize corneal scarring. Overall results with partial corneal lacerations are usually good, with an acceptable corneal scar resulting.

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Fig. 8.22 Partial corneal lacerations may involve a large gash in the cornea with loss of these tissues or a resultant pedicle of traumatized corneal epithelia and stroma. This pedicle should, if possible, be apposed to the underlying corneal defect. (a) The corneal pedicle is carefully inspected and cleansed with 0.5% povidone–iodine solution. (b) The corneal flap is apposed to the underlying corneal stroma with 5-0 to 7-0 simple interrupted absorbable sutures.

Penetrating corneal laceration with/without iris prolapse Full-thickness corneal lacerations with iris prolapse are unfortunately the more frequent type of corneal injury. The iris becomes incarcerated in the corneal laceration. The amount of iridal protrusion varies with the size, shape, and duration of the corneal tear. Surgical repair should be attempted as soon as possible. Medical therapy with topical and systemic antibiotics is initiated immediately. After general anesthesia and preparation of the eyelids and external eye, the area is carefully draped. An eyelid speculum is inserted to retract the eyelids. The iris prolapse and underlying corneal tear are carefully cleaned with sterile lactated Ringer’s solution with penicillin G (1:2000 IU/mL) added (Fig. 8.23a). The remainder of the globe is carefully inspected for tears and hemorrhages. The pupil and anterior lens capsule should also be carefully inspected. The decision to amputate the prolapsed iris or replace it in the anterior chamber is based on the length of time that the iris has been exposed and the overall size of the iris prolapse. There is little relationship between the size of the iris prolapse and the size of the corneal laceration. Once the iris becomes plugged in the cornea, venous congestion, iridal swelling, and seepage of fibrin rapidly enlarge the initial iris prolapse. Fortunately, most corneal lacerations are quite small under fairly large iris prolapses. With an iris prolapse more than 12 h old, the exposed iris is protracted to fresh iris and amputated close to the corneal surface with sharp iris scissors (DeWecker, Vannas or Westcott) (Fig. 8.23b). Several minutes are permitted to elapse for clotting and sealing of the iris blood vessels with the fresh iris still incarcerated within the corneal wound, before repositioning of the remaining iris within the anterior chamber. If iridal hemorrhage persists, point electrocautery is performed with a disposable unit (Fig. 8.23c). The iris is carefully freed of its attachments to the adjacent cornea and carefully replaced into the anterior chamber with a cyclodialysis spatula (Fig. 8.23d,e) or viscoelastic material. Through the corneal laceration, the anterior chamber is flushed with sterile lactated Ringer’s or balanced salt solution containing penicillin G (Fig. 8.23f). All fibrin and any blood clots are carefully irrigated from the anterior chamber. Excessive lavage of the anterior chamber should be avoided. The anterior chamber is then reformed with a viscoelastic agent (1% sodium hyaluronate or 2% hydroxypropyl methylcellulose) to facilitate corneal wound apposition and maintain the iris away from the posterior corneal surface. The corneal wound is apposed with 7-0 to 9-0 simple interrupted absorbable (braided polyglactin 910) sutures placed about 1–1.5 mm apart (Fig. 8.23g). Other suture techniques are the simple continuous and the double sawtoothed continuous patterns. These sutures should be placed into the deeper corneal stroma to ensure apposition of the endothelia and Descemet’s membrane as well as the anterior corneal stroma and epithelia. Two mm bites of the corneal stroma on each side of the suture line are recommended as these tissues are edematous and friable. Just before placement of the last corneal suture, the viscoelastic agent is flushed from the anterior chamber with balanced salt or lactated Ringer’s solution.

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Fig. 8.23 Full-thickness or penetrating corneal lacerations are usually complicated by an iris prolapse. (a) The full-thickness corneal laceration affects the axial cornea and the thumb forceps is touching the iris prolapse. The corneal tear is carefully cleaned and irrigated with lactated Ringer’s solution containing penicillin G (1:2000 IU/mL). (b) An iris prolapse that has been exposed more than 12 h is carefully protracted into the defect and amputated with sharp iris scissors (DeWecker). (c) Iridal hemorrhage usually results and hemostasis is secured by judicious electrocautery using a disposable cautery unit. (d) Once iridal hemostasis is achieved, a cyclodialysis spatula is inserted through the corneal laceration to separate any iridocorneal adhesions. (e) The cyclodialysis spatula should not touch the posterior corneal surface to reposition the iris into the anterior chamber. (f) The anterior chamber is lavaged with sterile lactated Ringer’s solution with penicillin G (1:2000 IU/mL) to remove any remaining blood and fibrin, and then reformed with a viscoelastic agent to maintain its shape and prevent the iris from contacting the posterior cornea during closure of the corneal laceration. (g) The corneal wound is apposed with 7-0 to 9-0 simple interrupted absorbable sutures placed deeply in the corneal stroma. Before placement of the last corneal suture, the viscoelastic agent is flushed from the anterior chamber with the lactated Ringer’s solution–penicillin G combination. (h) After completion of the corneal wound closure, a small gauge hypodermic needle is carefully inserted between two corneal sutures and the lactated Ringer’s solution–penicillin G combination injected to increase the intraocular pressure to about 10 mmHg and to check the integrity of the wound closure.

If the corneal edges in the wound are quite friable, or the wound closure marginal, a bulbar pedicle conjunctival graft may be performed. The entire corneal wound minus its epithelium is covered with the tip of the conjunctival graft. The addition of the graft will increase the postoperative corneal scar, but can reduce the likelihood of the breakdown of the corneal wound postoperatively and loss of the eye. Once the corneal wound is closed, the integrity of the apposition should be tested. Lactated Ringer’s solution is injected between two corneal sutures with a very small diameter cannula (25 g), or at the limbus with a 25 g hypodermic needle (Fig. 8.23h). Topical fluorescein can be applied directly to the wound apposition to detect any leaks in the wound closure. Postoperative management of full-thickness corneal lacerations with iridal involvement anticipates variable corneal edema and severe anterior uveitis. Topical and systemic antibiotics, topical mydriatics, and, cautiously, systemic NSAIDs or systemic corticosteroids are administered to

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effect. Because of the corneal wound, topical corticosteroids are avoided. However, once the healing of the corneal wound is advanced, at 3–6 weeks postoperatively, topical corticosteroids may be added. The pupil, with the surgical iris defect, should be maintained in a moderately dilated position. Some iridal movement is preferred to minimize formation of posterior synechiae. Fortunately, bacterial contamination of the anterior chamber and postoperative endophthalmitis in the dog and cat are rare. However, the intensity of the anterior uveitis may be considerable. Medication frequency is dependent on daily assessments of the eye, the corneal wound, level of intraocular pressure, pupil size, and appearance of the iris. About 5–7 days postoperatively, 25–50 mg tissue plasminogen activator (tPA) may be injected into the anterior chamber to degrade excessive clots of fibrin. Once corneal wound integrity has been firmly established in 10–14 days, topical corticosteroids may be initiated, but only when daily evaluations are possible.

Surgery for corneal lacerations

Postoperative complications after full-thickness corneal lacerations with iris prolapse include dense corneal scar formation, anterior and posterior synechiae, iris tissue deposits on the anterior lens capsule, cataract formation, secondary glaucoma, and phthisis bulbi. Because of the full-thickness injury to the cornea, a corneal scar of variable size and opacity results. The size of the scar and its position in the cornea directly influence its effect on vision. Small corneal scars or corneal scars in the peripheral rather than the central cornea minimally impact vision. Dense, large, and central corneal scars probably impair vision; however, with a dilated pupil, reasonable clinical vision may result. With an intense postoperative anterior uveitis, the possibility of posterior synechiae and secondary cataract formation is likely. These complications are minimized by adequate control of the iridocyclitis during the postoperative period. Phthisis bulbi usually results secondary to intense anterior uveitis and occurs more frequently in young animals. The overall results after repair of full-thickness corneal lacerations with iris prolapse are usually favorable, but guarded. The final outcome depends on successful treatment of the resultant anterior uveitis.

Penetrating corneal lacerations and anterior lens capsule tears with or without iris prolapse Penetrating corneal lacerations and tears of the anterior lens capsule with or without an iris prolapse occur primarily in small animals. Puppies and young dogs are most likely to experience self-sealing corneal lacerations, usually secondary to a cat claw or a dog fight. In some animals the cat claw can bridge the anterior chamber and tear the anterior lens capsule. Anterior lens capsule tears larger than 1.5 mm, treated only medically, are associated with severe and progressive anterior uveitis and cataract formation that often result in phthisis bulbi, enucleation, or evisceration. With large anterior lens capsule tears, the anterior cortical material quickly becomes cataractous and is gradually released into the anterior chamber. This lens material is antigenic and incites a progressively more intense lens-induced anterior uveitis. The resultant anterior uveal inflammation, stimulated by exposure to progressively more amounts of lens material, can eventually destroy the eye. Successful treatment of patients with traumatic tears of the anterior lens capsule requires early recognition and lens removal. Anterior lens capsular tears usually present as focal deposits of fibrinous and inflammatory material on the anterior lens capsule or as focal progressing anterior subcapsular and anterior cortical cataracts. The majority of these patients have a small corneal laceration that eventually self-seals. Infrequently, the patient will require both surgical correction of the full-thickness corneal laceration and extracapsular cataract removal. Late surgical intervention in these patients is less successful, because the anterior uveitis has become advanced and difficult to control medically. Correction of the full-thickness corneal penetration, if not sealed, is performed as described in the previous section. If the corneal puncture has self-sealed but is greater than 2 mm, the corneal wound should be reinforced with additional 7-0 to 9-0 simple interrupted absorbable sutures. Sometimes these wounds do not leak until the intraocular pressure begins to return to normal levels. Removal of part

of the anterior lens capsule and the remainder of the lens nucleus and cortex, as an extracapsular lens extraction or by phacoemulsification, is presented in Chapter 9.

Adaptation for large animals and special species Corneal lacerations Corneal lacerations in the horse are always accompanied by varying degrees of iridocyclitis. Medical therapy should be sufficient for superficial, non-perforating lacerations. Topically applied broad-spectrum antibiotics, mydriatics/cycloplegics, and serum are recommended. Topically applied serum reduces enzymatic collagen breakdown of the cornea. Systemic NSAIDs are also strongly indicated. Deep or irregular corneal lacerations require surgical support of the cornea and more aggressive therapy for iridocyclitis. Direct corneal suturing and conjunctival flaps are indicated to more rapidly restore corneal integrity. Topically applied antibiotics and mydriatics/cycloplegics, as well as systemically administered NSAIDs, are used until healing is complete. Full-thickness corneal perforations are usually associated with iris prolapse, shallow anterior chamber, and hyphema. If the corneal lesion extends to the limbus, the sclera should also be carefully checked for perforation as it can be obscured by conjunctival chemosis and hemorrhage. Failure to detect such a scleral tear results in chronic hypotony and globe atrophy (phthisis bulbi). Both small and large corneal perforations should be surgically repaired. Complications include infection, iris prolapse, anterior synechiae, cataract formation, and persistent iridocyclitis. Both small and large corneal or scleral fullthickness defects can result in phthisis bulbi if left untreated. Successful surgical repair of the iris prolapse and corneal perforation requires good illumination, magnification, and proper instrumentation. The prognosis of a full-thickness corneal perforation depends on the duration and size, the amount of iris and lens involvement, and the presence of infection and hemorrhage. A horse with a traumatic corneal perforation that defies repair, extensive extrusion of intraocular contents, severe intraocular hemorrhage, or evidence of bacterial infection should have the affected globe enucleated. The eye of the horse does not tolerate much damage to its vasculature. Severe intraocular hemorrhage usually results in phthisis bulbi. Septic intrusion into the globe results in painful endophthalmitis. Such infection can spread to surrounding soft tissues and necessitates enucleation.

Iris prolapse Perforating corneal lacerations with iris prolapse confined to the cornea and measuring 15 mm or less in length tend to have a favorable visual outcome after surgical repair. Iridectomy does not generally exacerbate postoperative uveitis or adversely affect visual outcome, and may facilitate postoperative mydriasis and prevent septic endophthalmitis. Conversely, perforating corneal lacerations longer than 15 mm, extending to, along or beyond the limbus, are inclined to poor visual outcome and enucleation. Chances of retaining vision may also be substantially reduced in perforating

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corneal wounds accompanied by hyphema, even when comprising only 10–50% of the anterior chamber. Primary enucleation should therefore be more seriously considered in cases with these clinical and surgical findings. Finally, eyes with perforating corneal ulcers due to ulcerative keratitis of more than 2 weeks’ duration, and melting ulcers and/ or ulcers with concomitant fungal and bacterial infections, tend to have a poor visual outcome or result in enucleation due to endophthalmitis in a majority of such cases. All horses with iris prolapse in the immediate preoperative period should be treated with a systemic NSAID, including either flunixin meglumine (1 mg/kg IV q12h) or phenylbutazone (2 mg/kg PO q12h). All horses should be started on a systemic antibiotic. Antibiotics used include potassium penicillin G (22 000 IU/kg IV q8h), gentamicin sulphate (2.2 mg/kg IV q8h), procaine penicillin (22 000 IU/kg IM q8h), and trimethoprim–sulfamethoxazole (15 mg/kg PO q12h). Tetanus antitoxoid is administered to most horses. A subpalpebral lavage system aids topical therapy. Initial topical lavage therapy in all horses includes a topical antibiotic, with gentamicin, tobramycin, and chloramphenicol, or neomycin, polymyxin B, and gramicidin. All horses are also started on topical 1% atropine. Miconazole (1%), natamycin or other antifungal therapy is instituted in horses with cytologic, histologic or culture-positive evidence of fungi. Autologous serum or acetylcysteine (10%) therapy is instituted for their anticollagenase effects. Topical NSAID therapy, either suprofen or diclofenac sodium, can be used in horses to reduce severe uveitis. Under general (inhalation) anesthesia, each perforation site is explored to determine both length and extent of corneal or corneoscleral involvement. Prolapsed iridal tissue that appears desiccated, necrotic or contaminated, or has been prolapsed for more than 24 h, is generally best excised. Iridal bleeding can be controlled with pressure and electrocautery following iridectomy. Corneal defect margins may require debridement or keratectomy. Direct corneal closure can be used in small or linear lesions. Conjunctival pedicle, hood or island grafts can be used to provide additional physical support when the corneal closure is tenuous or when keratomalacia is prominent. Corneoconjunctival transposition may be used if corneal tissue is missing. A donor corneal graft is used for larger perforations and ulcers, and then covered with a conjunctival flap or amniotic membrane. Systemic antibiotics are continued for a minimum of 5 days following surgical repair of iris prolapse. Following surgical repair, all horses are also maintained on systemic NSAIDs at presurgical doses for several days, and the dose then decreased as the severity of the anterior uveitis diminishes. Topical antimicrobial therapy is initiated immediately following surgery and modified, if appropriate, based on corneal cytology and culture findings. In general, tapering doses of topical atropine, antimicrobials, and oral NSAIDs are continued for a minimum of 4–6 weeks after surgery until clinical signs of anterior uveitis have resolved.

Affected animals present with acute ocular pain, tearing, blepharospasm, conjunctival swelling, variable amounts of corneal edema, and anterior uveitis. Corneal foreign bodies occur less frequently in the cat, and the ocular inflammatory response is considerably less than in the dog. Surgery for corneal foreign bodies depends on their composition (organic vs metallic), size and shape, duration, integrity of the corneal defect, and involvement of other ocular tissues. Organic foreign bodies are more irritating than metallic objects. Superficial corneal foreign bodies can often be removed under topical anesthesia with a strong stream of balanced salt solution, by sterile cotton-tipped swab, sterile 20–23 g hypodermic needle, or corneal foreign body spatula (Fig. 8.24). Post-removal topical treatment usually consists of topical antibiotics. If secondary anterior uveitis is present, topical mydriatics are indicated. Intracorneal foreign bodies may be divided into those embedded in the corneal stroma and those partially in the cornea and protruding into the anterior chamber (Fig. 8.25). These foreign objects are usually thorns, wood splinters, and other plant material. Immediate surgical removal of corneal foreign bodies provides the best results before corneal transparency decreases and secondary iridocyclitis intensifies. After the onset of general anesthesia, surgical preparation of the eyelids, conjunctiva, and cornea, and draping, the eyelids are retracted by a wire speculum. The area about the corneal foreign body is carefully inspected, and cleaned with aqueous 0.5% povidone–iodine solution. If complete corneal penetration is suspected, topical fluorescein is applied to determine if any aqueous humor leakage (positive Seidel’s test) can be demonstrated. With 1
2 teeth tissue forceps, the corneal foreign body is gently extracted from the stroma. If the foreign body cannot be loosened by forceps from the stroma, it is carefully dissected with the Beaver scalpel handle and No. 6400 microsurgical blade. As most foreign bodies are of plant origin, the entire object must be excised. The area is not usually apposed by sutures if the foreign body did not penetrate into the anterior chamber, but allowed to heal and treated as a potentially infected corneal ulcer. When the corneal foreign body penetrates the cornea, and partially protrudes into the anterior chamber, removal is more complicated. Depending on the size and shape of

Surgery for corneal foreign bodies Corneal foreign bodies occur infrequently in small animals. In dogs, foreign bodies occur primarily in hunting and working breeds. Corneal foreign bodies are usually highly irritating.

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Fig. 8.24 Intraoperative appearance of a penetrating corneal foreign body (cat claw or nail) in a dog. Surgical removal requires a deep keratotomy to remove the foreign body. Organic (i.e., plant material) corneal foreign bodies are generally best removed as infection (bacteria/fungal) often results.

Corneal adhesives

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Fig. 8.25 Examples of deep corneal foreign bodies in the dog. (a) Intracorneal foreign body (wood sliver) in a 5-year-old Labrador retriever dog. The foreign body was removed by superficial keratectomy. (b) Foreign body consisting of a cactus spine partially protruding into the anterior chamber and anterior lens in a young cat.

the corneal foreign body, surgical removal is approached from either the anterior cornea or the posterior cornea from the anterior chamber, which is more difficult. If the largest part of the corneal foreign body is anterior to Descemet’s membrane, removal from the anterior corneal approach is usually recommended. However, if the largest part of the corneal foreign body is already in the anterior chamber, entry through a limbal or peripheral corneal incision is necessary and the least traumatic. Once the penetrating corneal foreign body is removed, apposition of the corneal wound is usually necessary. Simple interrupted 6-0 to 7-0 absorbable sutures placed at depth of 70–80% of the corneal depth and at least 1.5– 2 mm ‘bites’ or penetrations into the adjacent healthy cornea is recommended. Once the corneal wound is apposed, lactated Ringer’s or balanced salt solution is carefully injected into the anterior chamber between the sutures or through the limbal cornea. Intraocular pressure after closure should approximate at least 10 mmHg. Postoperative management after corneal foreign bodies is to prevent sepsis, control the secondary corneal and anterior uveal inflammation, and minimize corneal scarring. Topical and systemic broad-spectrum antibiotics are administered. Topical chloramphenicol is useful because of its ability to penetrate the intact cornea. Because of the anterior uveitis, most systemic antibiotics probably enter the aqueous humor in therapeutic levels. Mydriatics, usually starting with topical 1% atropine, are instilled hourly until moderate pupillary dilatation is achieved. Once mydriasis is obtained, the frequency of the 1% atropine instillations is reduced to two to four times daily. NSAIDs are administered systemically. Corticosteroids are added if the anterior uveitis becomes uncontrollable. Once corneal healing is advanced, based on re-epithelialization and complete vascularization of the foreign body site, topical corticosteroids are slowly initiated to resolve the keratitis and reduce to a minimum the density and size of the corneal scar. In many cases with limited keratitis, topical corticosteroids are not necessary. Postoperative complications after non-penetrating corneal foreign bodies in dogs are fortunately few. Infection of the corneal site is rare and some scarring is expected. Corneal penetrations, secondary to cat scratches, should be considered infected, and usually demonstrate more intense corneal

and anterior uveal inflammations. Sequelae of the anterior uveitis, i.e., posterior and anterior synechiae and secondary cataract formation, are infrequent. When the corneal foreign body penetrates the cornea and necessitates extraction from the anterior chamber, the possibility of complications increases. Bacterial infection of the corneal site and the anterior segment is fortunately rare. More often, sequelae of the anterior uveitis, i.e., iris pigment deposits on the anterior lens capsule, posterior synechiae, and secondary cataract formation, develop. A dense corneal scar is expected when all layers are damaged. Final results after most penetrating corneal foreign bodies are directly related to successful control of post-removal intraocular inflammation and resultant corneal scarring. Culturing of the foreign body may also aid in the selection of antibiotics. This section has been limited to corneal foreign bodies, primarily of plant origin. Penetration of the cornea, lens, vitreous, and posterior segment with metal objects, such as bullets and buckshot, are more difficult to manage clinically. Corneal wounds after buckshot or birdshot are usually self-sealing. Penetration of the lens necessitates immediate lens removal. Intraocular lead pellets within the anterior chamber and vitreous are usually relatively inert. However, the newer ferrous or tin pellets are toxic to the retina and must be removed as soon as the intraocular inflammation, secondary to the trauma, is controlled medically. Penetration of the vitreous and posterior segment will be discussed in Chapter 12.

Adaptations for large animals and special species Management of corneal foreign bodies in large animals is similar to that in small animals. Superficial foreign bodies can generally be removed with topical anesthesia (Fig. 8.26). Deeper foreign bodies may require microsurgical removal.

Corneal adhesives Corneal adhesives may be used to treat small partial corneal lacerations, pinpoint descemetoceles, small diameter deep stromal corneal ulcers, and recurrent corneal erosions in

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Fig. 8.26 Removal of chronic superficial corneal foreign body with granuloma formation in a horse. (a) A small vegetative foreign body has embedded itself in the cornea, resulting in a focal granuloma formation. (b) The foreign body is carefully removed with a hypodermic needle.

small animals. Corneal adhesives are also used to support sutures or as an alternate to sutures for selected corneal diseases. The initial cyanoacrylate studies in ophthalmic tissues were of limited success because of the slow polymerization time and local toxicity associated with the glue. The polymer n-butyl cyanoacrylate (NexabandW, CRX Medical, Raleigh, NC) has been used in both human and veterinary ophthalmology. It has low local tissue toxicity, exerts an antibacterial effect (bacteriostatic), and inhibits corneal stroma melting. The glue will slough from the cornea about 2–4 weeks after application depending on the size and depth of the corneal wound treated. Several steps are important for success with the cyanoacrylate adhesive. The patient must be sedated or anesthetized so that eyelid and eye movements are absent. The site for gluing must be carefully debrided to remove all necrotic and/or friable corneal tissues. The corneal site is carefully and completely dried with sterile cotton-tipped swabs or cellulose sponges and a warm air stream (hair dryer) as water and adhesive contact result in immediate polymerization. A very thin layer of glue is applied with a 30 g hypodermic needle; the glue will rapidly polymerize and cannot be disturbed thereafter. The area is permitted to dry completely before blinking, or other tissues and instruments touch the site. The resultant ‘glued’ area becomes very hard. The surface of the glued area should be as smooth as possible to prevent irritation of the conjunctiva and/or eyelid margin. The glue, after 2–6 weeks, is surrounded by corneal inflammation, and is extruded en masse or in fragments. Corneal epithelium migrates under the glued site. Failure of the glue to seal the corneal defect usually results from excessive applications of cyanoacrylate. Treatment after adhesive application is directed at the primary corneal defect and the secondary iridocyclitis.

glued to cover a leaking perforation (Fig. 8.27). Fibrin glue provides faster healing and induces significantly less corneal vascularization; however, it requires a significantly longer time for adhesive plug formation.

Corneal grafts/keratoplasty Introduction More than 80 years ago, the first successful penetrating corneal graft was reported in humans by Zirm. However, the first corneal graft in an animal was by Bigger in 1837, who published a report describing a successful homograft in a pet gazelle. With technical and biological advances, penetrating keratoplasties have become one of the most successful and frequent homograft surgeries in humans. The advent of microsurgery, fine instruments, new suture materials, and more effective anti-inflammatory and immunosuppressive drugs have collectively contributed to the current status of keratoplasty in human ophthalmology.

Adaptations for large animals and special species Fibrin glue and cyanoacrylate tissue adhesive are both effective in the closure of small corneal perforations in horses. Amnion or small intestinal submucosa membranes can be

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Fig. 8.27 Treatment of a very small descemetocele in a horse with tissue glue.

Corneal grafts/keratoplasty

Keratoplasties, both lamellar (partial thickness) and penetrating (full thickness), have not become ‘mainstream’ surgeries in veterinary ophthalmology. Part of the reason is costs, and the effectiveness and versatility achieved with conjunctival flaps/autografts. In contrast to humans, most animals demonstrate reasonable clinical vision with a less than clear cornea. Nevertheless, all of the advances that have contributed to the highly successful keratoplasty procedures can be used for our patients in veterinary ophthalmology.

History There have been several studies in lamellar (anterior stroma and epithelium) and penetrating (full-thickness) keratoplasties in dogs and, to a lesser extent, in cats.

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In 1957, Holt described a corneal homograft in a Pekingese blind from pigmentary keratitis. The opposite eye was blind and affected with microphthalmia. Also in 1957, Singleton reported on keratoplasty in a Welsh Corgi with bilateral pigmentary keratitis. In 1961, Cella reported corneal homografts in 19 dogs with corneal diseases. In 1962, lamellar keratoplasty was evaluated in 21 dogs with corneal diseases by Lavignette. The success rate with the lamellar corneal grafts was 70% (16/23 eyes). In 1963, Jensen reported on both partial- and fullthickness corneal grafts in 37 experimental dogs. In 1968, McEntyre reported a success rate of 78% in experimental dogs with penetrating corneal homografts and microsurgery. In 1969, Mueller and Formston described anterior lamellar grafts in experimental dogs (11 of 21 grafts were successful), full-thickness grafts (3 of 27 were successful), and posterior lamellar grafts (15 of 16 were successful). In 1973, Dice, Severin, and Lumb described autogenous and homologous corneal grafts in eight experimental dogs. Silk sutures were used and found to be very reactive with corneal grafts. In 1982, Bahn and co-workers evaluated penetrating keratoplasties in cats. Both homografts and rotating autografts were performed. Penetrating keratoplasties in cats resulted in the loss of about 30% of the endothelial cells, about the same percentage established in humans. Lastly, in 1989, Brightman and co-workers reported autogenous lamellar corneal grafts in nine experimental dogs and seven dogs with corneal diseases. In the clinical patients, six of the seven grafts were considered successful.

These past reports record the evolution of keratoplasties in small animals. For optimal results, keratoplasty in small animals requires microsurgical instruments, an operating microscope, 8-0 to 10-0 nylon sutures, vigorous perioperative treatment, and long-term postoperative treatment and clinical management. Using these advances, lamellar and penetrating keratoplasties can achieve higher success rates in the dog and cat than reported in the past literature. Indications for corneal grafts in small animals include corneal endothelial dystrophy and degeneration, opaque central (or axial) corneal scars and blindness, deep corneal ulcers, corneal sequestra in cats, and descemetoceles. While penetrating keratoplasties are clearly indicated for the first

two conditions, the latter conditions may be treated quite successfully with conjunctival grafts. Keratoplasty is traditionally divided by the source of the donor cornea and the depth of the graft. Sources of corneal grafts are divided into: 1) heterologous grafts/heteroplastic/ xenograft/heterografts (from other species); 2) homologous graft/allogeneic/homoplastic/homografts (donor is same species); and 3) autologous/autograft/autoplastic/autogenous grafts (same patient, usually a rotating or sliding graft). The types of keratoplasty include: 1) anterior lamellar (corneal epithelium and anterior stroma; 2) full-thickness or penetrating; and 3) posterior lamellar (posterior stroma). Keratoplasties also vary by diameter. Most corneal trephines, designed for use in humans, range from 2 to 9 mm in diameter. As corneas in the dog and cat are about twice as large as in humans, the largest corneal graft in small animals is about 9 mm. With corneal trephines now available up to 17 mm diameter, keratoplasty in small animals can become more useful clinically.

Preparation of donor corneas Potential donor cornea, sclera, and whole eyes may be obtained from dogs and cats free of infectious diseases (dogs – distemper and rabies; cats – feline leukemia virus and feline immunodeficiency virus). Successful transplantation of corneal tissues starts with careful harvest and storage of donor corneas before either lamellar or penetrating keratoplasty. Donor material is obtained from complete globes, freshly enucleated, or from corneas with a scleral rim maintained in tissue cell media (Optisol-GSW, Bausch and Lomb Surgical, Irvine, CA) for several days to 2 weeks. Removal of the globe for donor corneal tissue is performed aseptically with several drops of neomycin, bacitracin, and polymyxin B placed on the cornea as the subconjunctival enucleation is performed. The enucleated eye, placed in a sterile moist chamber with the cornea upward and maintained in a standard refrigerator, should be transplanted within 7 days. An alternative procedure is to remove aseptically only the cornea with a 2 mm scleral rim. The cornea is very carefully lifted from the globe to prevent detachment of Descemet’s membrane and endothelia. The corneoscleral tissue is placed in a tissue culture bottle and maintained in a refrigerator for a maximum of 2–3 weeks with MK or K-sol media. Donor corneas for tectonic grafts are maintained frozen, and ready for use. Since viability of the corneal cells is not important, corneas may be obtained from any age patient. The corneas are excised from the donors’ eyes with a 1–2 mm scleral rim, placed in an ophthalmic neomycin, bacitracin, and polymyxin B solution and stored in a small sterile bottle. The bottle and cornea are maintained in a standard freezer (–20 C) ready for use. A maximum of 18 months of frozen storage has been recommended. Prior to use, the bottle and donor cornea are thawed at room temperature or in a warm water bath. The trimmed tissue is a source of preserved corneal and scleral collagen lamellae, but has no viable cells. Prior to use, the epithelia and endothelia with Descemet’s membrane surfaces are vigorously scraped with a scalpel blade, leaving just the corneal stromal collagenous lamellae. Tectonic grafts should be covered with a conjunctival graft or nictitans flap to ensure graft survival and reduce the likelihood of graft infection, collagenolysis, and dehiscence.

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Cryopreservation of potential corneal grafts has not been reported in small animals. If this technology is successful, corneal graft materials with viable cells could be stored for several months or more.

Instrumentation for keratoplasties Instruments to perform lamellar and full-thickness corneal grafts are a combination of standard size and microsurgical instruments. These instruments include: eyelid speculum (usually the Barraquer wire speculum), Flieringa rings (to stabilize and maintain the peripheral cornea, anterior sclera, and anterior segment), tissue fixation forceps (1
2 teeth and tying), tenotomy or utility scissors, right- and lefthanded corneal transplantation scissors, standard and microsurgical needle holders, corneal trephines (Castroviejo set 8– 12 mm diameter in 0.5 mm increments), and Teflon corneal graft block. Corneal transplantation scissors differ from the corneal section scissors used for cataract surgery by having a greater curvature, and the lower blade inside the upper blade to create a more perpendicular or less beveled incision. Recommended sutures include: 1) 4-0 to 6-0 braided silk sutures to temporarily attach the Flieringa ring to the limbus or sclera; 2) 7-0 to 9-0 nylon for graft stabilization (usually 8–16 simple interrupted sutures); and 3) 8-0 to 10-0 nylon (a simple or saw-toothed continuous suture to supplement the simple interrupted sutures).

Indications for keratoplasty Keratoplasties in small animals may be divided into: 1) autogenous sliding lamellar grafts (sliding transparent corneal tissues into an axial defect created by excision of an opacity of the anterior corneal stroma); 2) homologous lamellar grafts (homografts of corneal stroma); 3) rotating autogenous full-thickness grafts (rotation of a central opaque scar to the peripheral cornea); and 4) homologous full-thickness corneal grafts. For successful keratoplasties in small animals, selection of patients is very important. Blindness associated with deep corneal stromal, Descemet’s membrane, deep corneal sequestra in cats, and endothelial diseases are the best candidates (Fig. 8.28). The axial or central areas of the cornea are the most

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important for vision in small animals, and penetrating keratoplasties should be confined to this area. Concurrent diseases, such as chronic keratoconjunctivitis sicca, acute-to-chronic iridocyclitis, and glaucoma, usually preclude keratoplasties. The primary corneal endothelial dystrophies observed in certain breeds of dogs and in older dogs and cats are the best candidates. Active and progressive corneal ulceration constitutes a primary indication for penetrating corneal keratoplasty in humans, but in small animals keratoplasty has not been thoroughly evaluated because of the highly successful conjunctival grafts. A major concern of keratoplasties in small animals is graft rejection, usually demonstrated as postoperative vascularization, edema, inflammation, and eventual opacification of the transplanted corneal tissue. However, this concern may be overstated. Alternative surgical procedures to keratoplasties in small animals are the bulbar and tarsopalpebral conjunctival grafts which always produce a variable size corneal opacity. Keratoplasties, when unsuccessful, yield an opaque area. However, if successful, the resultant clear cornea permits vision. Long-term topical corticosteroids (1% prednisolone and 0.1% dexamethasone) and/or cyclosporin A are instilled for graft rejection eyes.

Preoperative treatment Medical treatments preoperatively for lamellar and penetrating keratoplasties are different. As penetrating keratoplasties involve entry into the anterior chamber, preoperative treatments for full-thickness grafts also include suppressing the formation of fibrin in the aqueous humor and the anterior uveitis that develop intra- and postoperatively. For both lamellar and full-thickness corneal grafts, the preexisting corneal disease is stabilized, and topical and systemic antibiotics are usually indicated. For topical antibiotics, the triple antibiotic combination (neomycin, bacitracin, and polymyxin B) or chloramphenicol is recommended. The pupil is dilated with 1% atropine pre-, intra-, and postoperatively. Frequency of atropine instillations varies, depending on maintenance of a moderate mydriasis with limited iris movements to reduce the likelihood of posterior synechiae and secondary cataract formation. For full-thickness corneal grafts, several drugs are administered to treat the resultant iridocyclitis once the anterior

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Fig. 8.28 Bilateral corneal dystrophy in a Boston Terrier and treatment with full-thickness keratoplasty. (a) Bilateral corneal endothelial dystrophy in a 6-year-old female Boston terrier. (b) Often the accumulation of corneal edema results in marked visual impairment and the development of painful bullae. Therapeutic options are thermokeratoplasty or penetrating (full-thickness) keratoplasty.

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chamber has been entered. Fibrin and inflammatory cells within the aqueous humor can adversely affect the full-thickness corneal graft success rate. These inflammatory products coat the posterior aspects of the graft and form retrocorneal membranes that impair the transplanted cornea’s transparency. Topical and systemic corticosteroids and non-steroidal non-inflammatory agents are administered preoperatively. Systemic antihistamines (for the dog, chlorpheniramine 0.5 mg/kg IM, 45 min before surgery) and heparin (1000 IU in 0.1–0.2 mL instilled directly through the corneal wound into the anterior chamber) are recommended to reduce the possibility of plasmid aqueous humor and overt fibrin formation in the anterior chamber intra- and postoperatively.

Preparation of corneal donor graft The best source for corneal grafts is young dogs and cats. Corneal endothelial cell counts are directly associated to age and, as animals age, the density of corneal endothelia decreases. Corneal endothelia are also lost during penetrating keratoplasty. In humans and the cat, about 20–30% of the endothelial cells are lost after keratoplasty. The donor corneal graft is prepared immediately before surgery from a freshly enucleated eye or a cornea with a scleral rim. If a fresh intact globe is used, the entire cornea with 1–2 mm of sclera is carefully excised using sharp scissors under aseptic conditions. The cornea, with attached sclera, is placed on the TeflonW block with the corneal epithelial surface down (Fig. 8.29a). With a corneal trephine 0.5 mm larger than the surgical wound, the cornea is trephined carefully, ensuring a perpendicular cut (Fig. 8.29b). The corneal graft is moistened with lactated Ringer’s solution or cell culture media to ensure viability. The corneal graft is transferred to the surgical site, still maintaining the corneal epithelia down. The posterior aspect of the corneal graft, lined with the single layer of endothelial cells, is most susceptible to damage, and this side should not touch any surface or instruments. For anterior lamellar corneal grafts, the donor material is now divided. Dependent upon the relative thickness of the

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Fig. 8.29 Preparation of corneal donor material. (a) The full globe is incised immediately posterior to the limbus in front of the iris or just caudal to the iris, and positioned with the corneal epithelium down onto a TeflonW keratoplasty block for cutting. (b) The full-thickness donor corneal graft is cut perpendicularly with a corneal trephine that is 0.5 mm larger in diameter than the recipient’s bed. Either the full-thickness or the anterior stroma and epithelia are available for keratoplasty.

desired graft, the stroma is incised and graft is split into two parts: the endothelium and posterior one-third of the stroma, which is discarded, and the anterior two-thirds of the stroma and epithelium which is transferred to the corneal defect with the epithelial surface upright. If a full-thickness or penetrating corneal graft is performed, the graft is constructed 0.5 mm larger than the recipient’s defect. The corneal graft is rotated with the posterior endothelial surface facing the anterior chamber and placed on the recipient’s bed ready to be apposed.

Autogenous sliding lamellar grafts Autogenous lamellar keratoplasty represents the simplest corneal graft. Corneal epithelial and stromal tissues are slid from a clear and healthy area to cover a central corneal defect, and graft rejection does not occur. With relocation of the central anterior stromal opacity with peripheral clear cornea, vision is enhanced. After the onset of general anesthesia, surgical preparation of the eyelids and conjunctiva, and draping, the eyelids are retracted by a wire speculum. With a corneal trephine about 0.5 mm larger in diameter than the diseased area of the cornea to be excised, the corneal epithelia and stroma are incised to a depth sufficient to remove the opacity. A corneal trephine that can be preset to depths of 0.25–0.35 mm works well for this procedure (Fig. 8.30a, b). The edge of the trephined cornea is grasped by 1
2 teeth tissue forceps and the underlying stroma is dissected at approximately one-half depth with the Beaver scalpel handle and No. 6400 microsurgical blade or the Martinez corneal dissector, and excised (Fig. 8.30c). This surgical defect represents the recipient bed. The excised tissue should be evaluated histologically. Two slightly diverging corneal stromal incisions with the Beaver scalpel handle and No. 6400 microsurgical blade are performed, extending from the corneal defect to the limbus (Fig. 8.30d). Grasping the end of this graft, the stroma is carefully separated at approximately one-half depth from the central wound to the limbus (Fig. 8.30e). Once the corneal stromal dissection is complete, the corneal stromal graft is excised at the limbus by corneal scissors or the Beaver No. 6400 microsurgical blade (Fig. 8.30f). The corneal graft is ‘fitted’ into the corneal wound, and should be 0.5 mm larger in length and width to compensate for graft shrinkage (Fig. 8.30g). The transplanted cornea is attached to the surrounding wound edge with 7-0 to 9-0 nylon or braided polyglactin 910 simple interrupted sutures (Fig. 8.30h). Postoperative treatments include topical and systemic antibiotics, and topical mydriatics (usually 1% atropine). Once fluorescein retention is absent in the transplant, topical corticosteroids are instilled (0.25–0.5% prednisolone q12h to q6h) to minimize corneal scarring.

Homologous lamellar corneal grafts For homologous lamellar keratoplasty, a fresh corneal graft must be available. These grafts are used in small animals for deep central corneal ulcers and descemetoceles. If possible, the surgical site should be treated intensively for several hours with broad-spectrum antibiotics to reduce the possibility of infection of the transplanted cornea.

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Fig. 8.30 In autogenous sliding lamellar corneal keratoplasty, a superficial portion of clear peripheral cornea is slid into an axial or central superficial corneal defect, thereby ensuring the central cornea is clear for vision. (a) By corneal trephine, the central superficial cornea is incised, usually to a depth of 0.25–0.35 mm. (b) The corneal incision should be perpendicular to the cornea to ensure exact apposition and minimal scarring. (c) The edge of the corneal lesion to be excised is grasped with 1
2 teeth thumb forceps and separated from the underlying clear corneal stroma with the Martinez corneal dissector. (d) From the central corneal wound, two slightly diverging superficial corneal incisions are performed with the Beaver No. 6400 microsurgical blade to about the limbus. (e) The tip of this pedicle of cornea is grasped with 1
2 teeth thumb forceps and separated from the deeper stroma with the Martinez corneal dissector. (f) Once this pedicle of cornea has been completely separated from the stroma, its base is incised by corneal or keratoplasty scissors. (g) The corneal pedicle is positioned in the corneal bed and trimmed to provide a corneal graft about 0.5 mm larger than the bed. (h) The corneal sliding graft is apposed to the graft bed edges with simple interrupted 7-0 to 9-0 nylon or absorbable sutures. The donor area is allowed to heal and treated as a sterile corneal ulcer.

After the onset of general anesthesia, surgical preparation of the eyelids, conjunctival and corneal surfaces with aqueous 0.5% povidone–iodine solution, and draping, the eyelids are retracted by a wire speculum. With a corneal trephine about 1–2 mm larger than the area of cornea to be excised, the cornea is excised to a depth of 0.25–0.35 mm (Fig. 8.31a,b). This circular area should include all of the ulcer’s edge and any necrotic or suspicious tissues. The edge of the central trephined area to be removed is grasped by 1
2 teeth tissue forceps and elevated to permit dissection of the stroma with the Beaver No. 6400 microsurgical blade or the Martinez corneal dissector (Fig. 8.31c). The corneal lamellar graft is 0.5 mm larger than the corneal defect to compensate for tissue shrinkage. The corneal lamellar graft is apposed with 8-0 to 10-0 simple continuous or simple interrupted nylon sutures (Fig. 8.31d). Postoperative treatment includes topical and systemic broad-spectrum antibiotics, cyclosporine, NSAIDs, and topical mydriatics. Topical corticosteroids are initiated 7–14 days postoperatively to minimize corneal scarring and maximize the chance of a successful lamellar transplant.

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Topical treatment should continue for 2–3 months before the final surgical result can be ascertained. Sutures should be removed once the wound has adequately healed, which occurs at 2–3 weeks postoperatively.

Autogenous rotating full-thickness corneal grafts This keratoplasty procedure is used for patients with deep and dense central corneal scars that markedly impair vision. In this technique, the patient’s full-thickness cornea is trephined, the dense corneal scar is rotated to the periphery, and clear cornea is positioned in the axial cornea. There is no possibility of graft rejection. If the opacity is isolated to the anterior stroma, a rotating lamellar corneal graft is indicated. An alternative non-surgical route is long-term treatment with mydriatics to permit the patient to see around the deep axial corneal opacity regardless of the illumination. After the onset of general anesthesia, preparation of the eyelids, cornea, and conjunctiva with aqueous 0.5%

Corneal grafts/keratoplasty

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D Fig. 8.31 In homologous lamellar corneal keratoplasties, fresh grafts are transplanted into defects of the outer one-third to one-half of the corneal epithelia and stroma. (a) Homologous corneal grafts are usually performed for large but superficial central corneal lesions. (b) With a corneal trephine, pre-set to 0.25–0.35 mm deep, the central corneal lesion is incised. (c) The edge of the central corneal lesion is lifted with 1
2 teeth thumb forceps and the lesion is carefully separated and removed from the underlying clear stroma with the Beaver No. 6400 microsurgical blade or the Martinez corneal dissector. (d) A fresh homologous lamellar graft, 0.5 mm larger in diameter, is placed in the graft bed and apposed with 8-0 to 10-0 simple interrupted nylon sutures.

povidone–iodine solution, and draping, the eyelids are retracted by a wire speculum. As the anterior chamber will be entered, a Flieringa ring is attached to the limbus with 8–10 simple interrupted 4-0 to 6-0 silk sutures (Fig. 8.32a). As the globe, cornea, and anterior chamber of the dog and cat partially collapse once the anterior chamber has been entered and intraocular pressure lost, the Flieringa ring helps to prevent collapse and maintains the relative shape of the anterior segment and cornea. Once the surgical site is ascertained, a corneal trephine is used to incise the cornea nearly full thickness (Fig. 8.32b). The trephine is held perpendicular to the cornea, and cutting is achieved with a downward pressure and an alternate twisting clockwise and counterclockwise motion. Once at least 80% of the stroma has been cut with the corneal trephine, the anterior chamber is entered with a stab incision with the Beaver No. 6500 microsurgical blade (Fig. 8.32c). Complete corneal penetration by the trephine is avoided to prevent any focal detachment of Descemet’s membrane and endothelia. Once the incision has been enlarged to about 5 mm long, corneal section or keratoplasty scissors are used to complete the incision 360 (Fig. 8.32d). The corneal scissors must be carefully inserted into the anterior chamber to cut the remaining corneal incision perpendicular to the surface. The anterior chamber is filled with a viscoelastic agent to maintain the anterior chamber and the posterior aspect of the corneal graft. The viscoelastic agent is flushed from the anterior chamber just before the last suture for the corneal graft is finished and replaced with lactated Ringer’s or balanced salt solution (Fig. 8.32e). With the corneal incision completed, the corneal ‘button’ is rotated about 180 to move the opacity peripherally and clear peripheral cornea to the axial or central cornea (Fig. 8.32f). The corneal graft is secured in each quadrant with four 8-0 simple interrupted nylon sutures (Fig. 8.32g). These sutures

should not penetrate the full thickness of the cornea but should reach the deeper two-thirds of the stroma. Once the corneal graft is stabilized, an additional four to eight simple interrupted sutures are added. One mm bites of the donor graft and 2 mm bites of the recipient’s bed are recommended to prevent suture loss postoperatively. A simple continuous or saw-toothed continuous 8-0 to 10-0 nylon suture is used to reinforce the simple interrupted sutures around the entire graft’s periphery (Fig. 8.32h). These sutures should also be placed deep in the corneal stroma. If a single continuous suture and a single knot are not preferred for the entire circumference, it can be divided into two to four simple continuous sutures and knots. Postoperative treatment includes topical and systemic broad-spectrum antibiotics, cyclosporine, NSAIDs, and topical mydriatics (instilled to maintain a moderate dilatation). Systemic corticosteroids are administered only if the postoperative iridocyclitis requires additional suppression. The nylon sutures are removed in two steps: 1) most of the single interrupted sutures are removed at 2 weeks; and 2) the remaining sutures are removed by 3–4 weeks. Clarity of the rotated full-thickness corneal autograft should be ascertained by 3 months postoperatively.

Homologous full-thickness/penetrating corneal grafts The homologous full-thickness or penetrating keratoplasty is the type performed most frequently in humans. The full-thickness corneal graft is used to replace opaque and weakened infected corneas that do not permit vision. If these grafts are used for descemetocele or perforated corneal ulcer, several hours of intensive topical and systemic broad-spectrum antibiotics are recommended to try to eliminate all bacteria from the ulcer site before keratoplasty. For

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Fig. 8.32 In autogenous rotating full-thickness keratoplasty, a full-thickness axial (central) corneal lesion is rotated to the corneal periphery and replaced with clear peripheral cornea. As the graft is autogenous, there is no possibility of graft rejection. (a) A Flieringa ring is attached to the limbus with 8–10 simple interrupted 4-0 to 6-0 silk sutures. This ring helps maintain the anterior segment and prevents collapse of the globe during keratoplasty. (b) The corneal trephine, held perpendicular to the corneal surface and twisted clockwise and counterclockwise, is used to incise the cornea to nearly full-thickness. (c) Once about 80% of the corneal stroma has been cut with the trephine, the anterior chamber is entered with a stab incision with the Beaver No. 6500 microsurgical blade. (d) With keratoplasty scissors the remaining full-thickness corneal incision is completed. (e) Viscoelastic agent is injected to fill the anterior chamber and to help maintain its shape during apposition of the corneal graft. It is flushed from the anterior chamber just before the last corneal suture is placed. (f) The corneal button is rotated 180 to reposition the opaque cornea at the limbus. (g) The graft is secured with 8-0 simple interrupted nylon sutures in each quadrant. These sutures should be two-thirds of the stromal thickness. (h) Additional 8-0 simple interrupted nylon sutures are placed around the graft. An 8-0 to 10-0 simple continuous nylon suture is placed on top of these simple interrupted sutures to provide additional wound security.

successful penetrating keratoplasty in small animals, several factors appear important (Box 8.1). After the onset of general anesthesia, preparation of the eyelids, conjunctival and corneal surfaces with aqueous 0.5% povidone–iodine solution, and draping, the eyelids are retracted by a wire speculum. For optimal positioning of the eye, neuromuscular blocking agents are administered. A Flieringa ring is attached to the limbus with 8–10 simple interrupted 4-0 to 6-0 braided silk sutures (Fig. 8.33a). The corneal region to be excised is centered within the minimum size corneal trephine. The corneal trephine is held perpendicular to the corneal surface, and is twisted clockwise and counterclockwise until about 80% of the stroma has been incised (Fig. 8.33b). With the Beaver No. 6500 microsurgical blade, a 5 mm incision is made in the trephine incision into the anterior chamber (Fig. 8.33c). Complete penetration of the cornea with the trephine is not recommended as focal detachment of Descemet’s membrane and endothelia may occur.

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With escape of aqueous humor, the anterior chamber is re-established with a viscoelastic agent to maintain the anterior chamber during apposition of the corneal graft (Fig. 8.33d). With right-and left-handed corneal transplantation scissors, the lower blade of the scissors is carefully inserted into the anterior chamber to avoid direct contact with the endothelia (Fig. 8.33e). The incision is completed by scissors and the diseased corneal section removed (Fig. 8.33f). The corneal graft is carefully positioned in the recipient’s bed (Fig. 8.33g). Donor tissue must be 0.5 mm larger to compensate for tissue shrinkage. Four stabilizing (or cardinal) 8-0 simple interrupted nylon sutures are placed at the corner of each quadrant to hold the transplant (Fig. 8.33h). Each suture is placed relatively deep within the corneal stroma, but penetration of Descemet’s membrane and the endothelia is avoided. One mm bites of the donor graft and 2 mm bites of the recipient’s bed are recommended to prevent suture loss postoperatively.

Corneal grafts/keratoplasty

Box 8.1 • • • • • •

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Determinants for successful penetrating keratoplasty

Optimal positioning of globe: use neuromuscular blocking agents. Stabilize anterior segment: suture Flieringa rings to limbus to prevent anterior chamber collapse. Prevent aqueous fibrin: preoperative treatment with corticosteroids and non-steroidal anti-inflammatory agents. Intraoperative intracameral heparin. Size of donor corneal graft: 0.5 mm larger than recipient bed. Sutures: 8-0 to 10-0 nylon (must be non-reactive): – Use 8–16 overlapping simple interrupted sutures and simple continuous suture. – Bites: 1 mm donor side and 2 mm recipient side. Suture removal: 2 and 4 weeks. Best to remove part of the sutures at two different times. Corticosteroids: start topical steroids 7–10 days postoperatively; add subconjunctival steroids if there is excessive corneal vascularization. Cyclosporin A: can be used concurrently with topical corticosteroids or long term.

Once the corneal transplant is secured with the four sutures, an additional 10–12 simple interrupted sutures are placed to secure the graft, provide even tension over the graft’s edges, and limit postoperative optical aberrations. These sutures are reinforced with an 8-0 to 10-0 simple or saw-toothed continuous nylon suture (Fig. 8.33i). If a single continuous suture is not preferred, the apposition may be divided into two to four simple continuous sutures. Before the last suture is placed, the viscoelastic agent is flushed from the anterior chamber and replaced with lactated Ringer’s solution. With placement of the last suture, the integrity of the apposition may be checked with topical fluorescein or by carefully injecting lactated Ringer’s solution with a very small cannula between two sutures into the anterior chamber. Postoperative treatment after penetrating keratoplasty consists of topical and systemic broad-spectrum antibiotics, topical mydriatics (usually 1% atropine to obtain a moderately dilated but moving pupil), and systemic NSAIDs. Topical and systemic corticosteroids are not usually indicated until 2–3 weeks postoperatively, once healing of the corneal wound has advanced. It is important to minimize corneal vascularization as this clinical sign appears directly related to the graft rejection process. Topical corticosteroids (1% prednisolone or 0.1% dexamethasone) and/or 1–2% topical cyclosporin A are initiated 2–4 weeks postoperatively and are continued for 3–6 months, depending on the appearance of the cornea. The corneal sutures are removed in two phases, usually at 2 and 4 weeks. Since the nylon sutures are relatively non-reactive, these sutures should not be removed until healing of the corneal incision is nearly complete (Fig. 8.33j). The overall results of penetrating keratoplasty in both dogs and cats are favorable. Success rates in small numbers of clinical canine patients suggest that 70–80% of the surgeries result in clear grafts 3–6 months postoperatively. In cats, the success rate is higher than in dogs, because of the reduced intensity of corneal and anterior uveal inflammations. Successful keratoplasty requires an operating microscope, microsurgical surgical instruments, and inert fine sutures such as 8-0 to 10-0 nylon.

Complications include surgical failures (usually associated with learning this procedure and with existing corneal sepsis), corneal ulcerations, sequelae of anterior uveitis (excessive fibrin and flare in the anterior chamber, retrocorneal membranes, anterior and posterior synechiae, and secondary cataract formation), and long-term graft vascularization, pigmentation, and opacification (graft rejection). Retrocorneal membrane formation causes most of the opaque grafts in dogs, and is associated with intraoperative damage to the corneal endothelial cells and poor posterior corneal wound apposition. Most of these complications can be prevented by careful selection of patients, adequate pre-, peri-, and postoperative treatments, and surgical experience. The diameter of the donor corneas must be 0.5 mm larger than the corneal defect to compensate for shrinkage of the transplanted corneal tissue. It also avoids tension on the anterior segment which, in humans, is associated with ocular hypertension (elevated intraocular pressure) postoperatively. Corneal graft rejections are characterized by the presence of subepithelial infiltrates, occurrence of keratic precipitates on the endothelial surface, and development of a rejection line within the corneal endothelia. Early graft rejection may be reversed by intensive topical corticosteroid therapy (1% prednisolone hourly for 24–48 h). In humans, rejection rates appear related to age (older patients produce a limited graft rejection), size of graft (grafts 8 mm in diameter and close to the limbus are more likely to have rejection), gender (females are less likely to have rejection), and pre-existing corneal vascularization, especially the deep blood vessels (can double the chance of rejection). Topical cyclosporin A (1–2%) may be initiated once to twice daily immediately postoperatively and may also supplement the topical steroid treatments. Topical steroids are initiated 2–3 weeks postoperatively once corneal wound healing is advanced. Subconjunctival corticosteroid injections are used to supplement or reduce the frequency of topical therapy. Topical immunosuppressant therapy is administered for 4–6 months or more and after corneal vascularization and inflammation have resolved. If the homograft clears with topical steroid therapy, the process is termed an ‘allograft reaction’. If the graft becomes opaque or translucent, the diagnosis is ‘allograft rejection’. In experimental studies, the frequency of penetrating homograft rejections in dogs is 20% and in cats 15% without intensive postoperative steroid and/or cyclosporine therapy.

Frozen (tectonic) corneal grafts Preparation of tectonic corneal grafts was discussed in an earlier section in this chapter. Tectonic corneal grafts offer the convenience of frozen storage, but are sources of only collagen. Although there are no viable cells in these grafts, endothelial cells, keratocytes (fibroblasts), and epithelial cells can migrate from the host into this graft and become established. As a result, tectonic grafts often result in translucent grafts. The objective is to provide a homograft of collagen to support and/or replace severely damaged corneas. Indications for tectonic corneal grafts are similar to those for lamellar and full-thickness keratoplasties, and include deep corneal ulcers, descemetoceles, and impending or

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J Fig. 8.33 In homologous penetrating keratoplasty, a full-thickness corneal graft is transplanted. Essential for successful full-thickness corneal grafts, are viable endothelia on the graft’s posterior surface. (a) The Flieringa ring is secured to the limbus with 8–10 simple interrupted 4-0 to 6-0 silk sutures to maintain the shape of the anterior segment. (b) By corneal trephine, about 80% of the corneal stroma is incised. (c) With the Beaver No. 6500 microsurgical blade, a stab incision into the anterior chamber is performed within the trephine incision. (d) Viscoelastic agent is injected to reform and maintain the anterior chamber during the rest of the keratoplasty. (e) With keratoplasty scissors (either universal or right and left handed), the remainder of the full-thickness trephine incision is completed. (f) Once the full-thickness incision has been completed by the keratoplasty scissors, the diseased corneal button is removed for histology. (g) The corneal graft, 0.5 mm larger in diameter than the corneal bed, is carefully positioned with the endothelia toward the anterior chamber. (h) The four quadrants of the graft are secured to the host with 8-0 simple interrupted nylon stabilizing sutures. (i) After placement of 10–12 simple interrupted 8-0 to 9-0 nylon sutures, the entire incision is encircled with an 8-0 to 10-0 simple continuous nylon suture for additional security. All corneal sutures are at least two-thirds corneal thickness and extend 2 mm from the wound edge. (j) Twelve months postoperative appearance of full-thickness corneal graft. Anterior capsule–cortex cataract formation is present within the pupil.

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existing corneal perforations. For corneal lesions, the surgical procedure is identical to that described in the full-thickness keratoplasty section. Free-hand tectonic grafts are also performed for peripheral corneal diseases, such as limbal (epibulbar) melanomas in dogs. These transplants range in shape from round, to square, to rectangular. The postoperative management and complications for tectonic corneal grafts are similar to those for the penetrating keratoplasties. Success rates for both dogs and cats with tectonic corneal grafts have been reported as 84%.

Heterologous corneal grafts in small animals Based on availability of corneal tissues, medical and financial limitations, heterologous or heterogenous (graft of one species to a different species) corneal transplants in both dogs and cats have been reported. In cats, use of homologous (homogenous; same species to same species) corneal transplants is limited as feline corneas can be infected with the feline herpes virus (FHV-1) and the feline immunodeficiency virus (FIV). Presumably all animal corneas can also be infected with the rabies virus. Equine and porcine tissues have been successfully transplanted to the canine cornea; dog and porcine corneal tissues have been transplanted successfully to the feline cornea.

Adaptations for large animals and special species Corneal transplantation Corneal transplantation has been performed successfully in horses at the University of Florida since 1995. Most corneal transplants performed in horses are for therapeutic and tectonic reasons. Two basic corneal transplantation surgical procedures have been described for the horse: penetrating keratoplasty (PK) for full-thickness stromal abscesses or ulcers/iris prolapses, and a split-thickness form of PK, the posterior lamellar keratoplasty (PLK) for deep stromal

corneal abscesses (DSA) with a clear overlying anterior stroma. A third type of split-thickness PK procedure, the deep lamellar endothelial keratoplasty (DLEK), has recently been used for DSA in the horse where the superficial cornea may be vascularized but is otherwise normal. A fourth type of corneal transplant surgery, the deep anterior lamellar keratoplasty (DALK), can be used for corneal lesions in which the posterior cornea and Descemet’s membrane are normal and the anterior cornea diseased. When indicated, these techniques result in a shorter duration of therapy and faster recovery than medical treatment of these conditions alone. These four surgical methods of corneal transplantation in horses can have good visual outcomes, although partial graft rejection and scar formation have been unavoidable with all of these procedures.

Penetrating keratoplasty Penetrating keratoplasty (PK) involves full-thickness removal and replacement of a portion of the cornea. Corneal sutures are necessarily utilized to heal a vertical stromal incision with associated disruption of the corneal surface and topography. Medical therapy is similar to that for iris prolapse surgeries. The surgical approach for PK in horses is as follows (Fig. 8.34). 1. Donor corneal material is harvested preferentially from fresh or frozen equine cadaver eyes (i.e., within 24 h of death). The size of the lesion is determined with calipers. A full-thickness button of cornea that is 1 mm larger than the recipient bed is trephined from the endothelial to the epithelial side of the donor cornea. The ideal graft size in horses is 6–8 mm diameter, but larger grafts are possible. The donor button is grasped with fine-toothed forceps while paying particular attention to the orientation of the epithelium/endothelium, placed on a gauze swab, and kept moistened with lactated Ringer’s solution. The epithelium is not removed from the corneal donor button. Fig. 8.34 Treatment of deep corneal stromal abscess with penetrating keratoplasty and conjunctival pedicle graft in a horse. (a) A deep corneal stromal abscess, corneal edema, and peripheral corneal vascularization are present. (b) A trephine is used to remove the stromal abscess. (c) The donor tissue is the same diameter as the lesion. (d) Three months postoperatively the corneal has healed and is covered with the conjunctival pedicle graft.

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2. The recipient globe is stabilized with scleral fixation sutures of 5-0 nylon. A corneal trephine of appropriate size (i.e., 6–8 mm or greater) is centered over the diseased area and then rotated with minimal downward pressure to obtain a clear-cut, round incision with vertical sides. The incision with the trephine approaches to just near Descemet’s membrane. 3. The remaining intact deep stromal tissue is incised vertically with a Beaver No. 6500 microsurgical blade to enter the anterior chamber, being careful to avoid the iris, corpora nigra, and lens. The button of diseased host tissue is then removed with corneal section scissors. The keratectomy button is processed for culture and sensitivity, cytology, and histopathology. 4. Bulging of the iris and the corpora nigra into the incision site may occur. Adhesions or synechiae between the abscess and iris may be present. Fibrin membranes may be present on the posterior cornea and anterior iris face. The pupil can be occluded by these membranes. The anterior chamber is reformed by injecting viscoelastic solution (hyaluronate sodium, 10 mg/mL; Hylartin VW, Pfizer Animal Health, New York, NY) into the anterior chamber. The viscoelastic solution will also move the iris posteriorly, and break down any adhesions between the abscess and the iris. Iris membranes should be removed with caution due to the risk of hemorrhage. Direct contact with the lens capsule is also avoided by reforming the anterior chamber with the viscoelastics. 5. The donor cornea is removed from the moistened gauze swab and placed in the recipient bed, and four cardinal sutures of 8-0 VicrylW (Ethicon, Somerville, NJ) or 90 nylon (EthilonW; Ethicon) placed at the 12-, 6-, 9-, and 3-o’clock positions. Simple interrupted sutures are placed to fill in the remaining sectors in each quadrant, or, alternatively, a simple continuous suture pattern can be placed to hold the graft. Once the donor cornea is sutured into place, viscoelastic solution may again be injected via a limbal incision to reform the anterior chamber. 6. A conjunctival pedicle graft or amnion transplant may then be sutured over the keratectomy/graft site in those eyes with evidence of infection or vascularization to achieve more rapid assimilation into the cornea. A temporary lateral tarsorrhaphy is performed to minimize eyelid trauma to the PK. Among PK cases in which conjunctival grafts are used, the function of the corneal graft is tectonic (i.e., it maintains corneal integrity). Fresh, clear corneal grafts are preferred, but such grafts are not always available. In these cases, frozen tissue with dead endothelium can be used. Donor corneal grafts in most equine cases perform their tectonic role superbly, but I have seen a few frozen horse grafts become completely clear postoperatively. This may be due to migration of recipient endothelial cells into the donor graft. Vascularization of the grafts, indicating rejection, begins at 5–10 days postoperatively. Postoperative medications are maintained for an average of nearly 50 days until healing is complete. The visual outcome is greater than 75% for the PK horse eyes. Pupil occlusion is a major problem.

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Split-thickness penetrating keratoplasty The superficial cornea may be vascularized, but is otherwise normal in deep stromal abscesses. For horses with DSA and anterior chamber fungal invasion that persist, or even progress, with severe pain and vision-threatening uveitis in the face of aggressive medical therapy, surgical removal of the posterior stroma and endothelium containing the abscess by corneal transplantation is warranted. The inherent philosophy of split-thickness or lamellar surgery is to replace only the diseased portion of the cornea, leaving the normal tissue intact. In other words, do the least amount of resection for the greatest amount of benefit. Both the PLK and DLEK surgical methods are forms of split-thickness PK as they avoid removal of superficial normal tissue but do surgically enter the anterior chamber. These surgical methods are important in resolving deep stromal abscesses with anterior chamber invasion in horses. The DALK method maintains globe integrity by utilizing the intact Descemet’s membrane.

Posterior lamellar keratoplasty Posterior lamellar keratoplasty (PLK) is recommended for deep stromal abscesses in the central cornea that are 8 mm or less, and have a clear overlying anterior stroma. Medical therapy is similar to that for iris prolapse surgeries. The surgical approach for PLK in horses is as follows (Fig. 8.35). 1. A rectangular, anterior lamellar corneal flap, hinged on one side, is constructed by hand dissection to two-thirds stromal thickness over the stromal abscess. 2. A Martinez corneal dissector is used to undermine and elevate the superficial corneal layers to expose the abscess. 3. The flap is gently raised, and a trephine, Beaver No. 6500 blade and corneal transplant scissors used to remove the posterior stromal abscess, Descemet’s membrane, and endothelium. A retrocorneal posterior collagenous layer may be present. The anterior chamber is reformed with viscoelastic solution. 4. A circular graft of posterior stroma, Descemet’s membrane, and endothelium 1 mm larger than the defect is cut from donor tissue using a trephine. 5. The graft is placed in the corneal defect, and sutured every 2 mm using 8-0 absorbable suture material in a simple interrupted pattern. 6. The three-sided superficial flap is then sutured in place using 8-0 absorbable suture material. 7. Partial temporary tarsorrhaphies are placed in all eyes to protect the graft during recovery. Medical therapy postoperatively includes topical atropine, cyclosporin A, autogenous serum, antifungals and antibiotics, and systemic antibiotics and NSAIDs. PLK is associated with a shorter surgery and treatment time than PK. Complications of PLK include superficial suture abscesses, suture incision leaks, flap ulcers, and flap edema. The donor graft remains transparent for up to 7 days and then opacifies. Median time to end of treatment is 24 days. Partial graft rejection and scar formation have been unavoidable for both the PLK and PK procedures. The resulting scar, which is typically vascularized and eventually

Corneal grafts/keratoplasty

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Fig. 8.35 Surgical treatment of deep corneal stromal abscess and hypopyon with posterior lamellar keratoplasty (PLK). (a) Deep corneal stromal abscess and hypopyon are present in this horse eye. (b) A posterior lamellar keratoplasty is used to remove the abscess. (c) At 1 month postoperatively, scarring of the PLK graft is present.

opaque, is similar between PLK and PK. The retrocorneal and iris membranes can resolve in many cases. Pupil occlusion is a major problem. The visual outcome is greater than 90% for eyes that had the PLK procedure.

Deep lamellar endothelial keratoplasty Deep lamellar endothelial keratoplasty (DLEK) is recommended for deep stromal abscesses in the peripheral cornea that are 6 mm or less, and have a clear overlying anterior stroma. It avoids superficial incisions and suturing of the central cornea. The DLEK transfers healthy endothelium while preserving corneal surface integrity. A fully intact epithelium with no corneal sutures is present postoperatively. Medical therapy is similar to that for iris prolapse surgeries. The surgical approach for DLEK in horses is as follows. 1. A two-thirds depth, limbal incision up to 23 mm in length is made with a Beaver No. 64 blade. 2. A stromal pocket is formed over the DSA with a Martinez corneal dissector. Bleeding from the vascularized cornea is controlled with electrocautery. 3. The superficial corneal flap is gently retracted and the abscess removed with a trephine, Beaver No. 65 blade, and corneal scissors. The anterior chamber is reformed with viscoelastic solution. 4. The anterior two-thirds of the donor cornea is removed by hand dissection, and a trephine 1 mm larger in diameter than the recipient site used to obtain the circular donor graft from the remaining split-thickness cornea. 5. The superficial corneal flap is partially sutured with 8-0 VicrylW. The donor graft is inserted into place with Utrata forceps, and the limbal incision closed. The graft self-adheres to the recipient stroma by action of the endothelial pump, but may need to be positioned in place by a needle inserted between the flap sutures, or at the limbus. The graft is supported by the viscoelastic solution in the anterior chamber. The viscoelastic solution can be safely left in the anterior chamber. 6. Partial temporary tarsorrhaphies are placed in all eyes to protect the surgical site during recovery. DLEK is associated with a shorter surgery and treatment time than PK. Complications include suture abscesses, suture incision leaks, incision edema, and graft misalignment. The donor graft remains transparent for up to 7 days and

then vascularizes and opacifies. Median time to end of treatment is 22 days. The resulting scar, which is typically vascularized and eventually opaque, is similar between PLK and DLEK. The visual outcome is greater than 90% for eyes that had the DLEK procedure. Pupil occlusion is a major problem.

Deep anterior lamellar keratoplasty Deep anterior lamellar keratoplasty (DALK) is a partialthickness graft that preserves the innermost layers of the cornea: Descemet’s membrane and the endothelium. The goal of the procedure is to retain the endothelial layer of the host. This layer keeps the cornea clear by removing fluid from the bulk of the cornea. Retaining this layer avoids the risk of potentially blinding graft rejection that can occur with PK. If the endothelial layer and Descemet’s membrane are normal, then they are worth preserving. Medical therapy is similar to that for iris prolapse surgeries. The procedure is technically skilled and involves dissecting the cornea to almost 95% thickness, and removing the superficial layers. A donor corneal button is prepared by removing Descemet’s membrane and donor endothelium. The donor graft is then sutured to the host. The cornea takes a little longer to clear but visual results can be similar to those of PK.

Corneal transplant discussion for horses Penetrating keratoplasty suffers from the inherent problem of creating a vertical stromal wound that requires surface corneal sutures. The incised stroma never develops the structural integrity and strength of normal stroma. The PK graft epithelium often sloughs, leaving the graft open to infection and melting. PK wounds and suture tracts can leak. The sutures loosen as stromal edema resolves and the tissue contracts, allowing aqueous leakage. Vertical incisions are more prone to leak at low intraocular pressure levels. The location and size of the transplant sites in the cornea may influence corneal rejection. Graft sites closer to the limbus, presumably because of their proximity to limbal blood vessels, and keratoplasties greater than 8.0 mm in diameter are associated with increased rejection rates in humans. Paradoxically, vascularization provides tectonic support to

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the horse corneal transplant graft, and a donor graft is not considered healed until it vascularizes. Grafts closer to the limbus are considered more desirable for transplant in horses with DSA due to their proximity to limbal blood vessels, yet this proximity to the limbus undoubtedly increases the rejection rate. The existence of a maximal size for donor cornea in the horse should also be appreciated (i.e., use the minimal graft size necessary to achieve the therapeutic goal desired). Corneal transplants have been performed in horses using both fresh and frozen grafts. Fresh grafts maximize endothelial cell preservation, thereby minimizing postoperative corneal opacity. The endothelium of frozen cornea is damaged by changes in pH, osmolality, solute concentration, and by ice crystal formation. Because fresh cornea is not often available, most corneal transplants in horses are still done quite satisfactorily with frozen grafts. The frozen grafts in horses display transparency initially but become opaque within 10 days of surgery. Corneal grafts performed for non-inflammatory dystrophic conditions are the most successful clinical transplants in humans, with those done for acquired corneal degenerative diseases having a high risk of rejection. Corneal inflammation, infection, and vascularization contribute significantly to the failure or rejection of corneal grafts. All eyes in horses that have corneal transplants would be considered high risk for failure or rejection based on the human criteria as the grafts are placed in inflamed, infected, and vascularized cornea. Graft rejection is manifested by a loss of transparency. Partial graft rejection and scar formation have been unavoidable with PK, PLK, and DLEK procedures despite the use of cyclosporin A. Vascularization abolishes the immune privilege of the cornea by allowing antigens to leave the graft via blood vessels and lymphatics, and also by allowing host antigen-presenting cells into the graft. Smaller grafts in humans are associated with lower rejection rates, and high volume surgeons have better success, presumably due to better postoperative management decisions. In one study of corneal transplantation in humans, the 1-year graft survival rate was 88%, the 5-year survival rate was 74%, and at 10 years the survival rate was 62%. Corneal transplants are associated with high success rates, good visual outcomes (75–90%), and shorter treatment times than without surgery, although all corneal transplants in horses vascularize and have some degree of opacity, and are thus considered partially rejected. These procedures are still evolving in the horse. Automated microkeratomes, artificial anterior chambers, and specialized corneal forceps and scissors could technically improve the PLK and DLEK procedures.

Thermokeratoplasty In thermokeratoplasty or corneal diathermy multiple focal points of superficial thermal cautery are applied to the cornea. Sources of cautery range from the disposable batterypowered cautery unit to the excimer laser. This procedure has been reported recently as effective in the treatment of bullous keratopathy. In certain breeds of dogs, such as Boston Terriers, and in older animals, impaired corneal endothelial function may eventually result in severe corneal

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Fig. 8.36 Thermokeratoplasty (Salaras procedure) in the dog is one method to treat corneal edema associated with endothelial dystrophy. Appearance of corneal endothelial dystrophy immediately after treatment with thermokeratoplasty

edema. With prolonged corneal edema, the intermittent formation of painful bullae is common (Fig. 8.36). The intracorneal fluids tend to accumulate immediately beneath the corneal epithelia, resulting in variable size corneal epithelial vesicles. There are several methods of therapy for this condition. Full-thickness keratoplasty may be used to provide a new source of corneal endothelial cells. A permanent very thin bulbar conjunctival graft may be used to reduce the corneal edema, prevent the formation of painful vesicles, and, if thin enough, can permit clinical vision in small animals. Thermal cautery to create superficial scarring of the corneal stroma is another method. The anterior stromal collagen fibers contract after thermal cautery, resulting in a flatter cornea. The resultant scar tissue forms a barrier to corneal edema. After the onset of general anesthesia, surgical preparation of the eyelids, cornea, and conjunctiva with aqueous 0.5% povidone–iodine solution and sterile cotton swabs, the eyelids are retracted by speculum. The central corneal epithelia is debrided using a dull Beaver No. 64 or 67 scalpel blade (Fig. 8.37a), and a cellulose sponge containing absolute alcohol (Fig. 8.37b). All corneal epithelia is removed to about 2–4 mm from the limbus. With a disposable hand-held cautery unit with a very fine tip, a grid of superficial burns is performed (Fig. 8.37c). Post-thermokeratoplasty, the eyes are treated with topical broad-spectrum antibiotics and mydriatics (1% atropine). After corneal re-epithelialization is complete, topical corticosteroids are instilled to minimize corneal scarring. The anticipated result is a slightly scarred cornea, free of recurrent bullae, erosions, and pain, and often sufficiently translucent to permit clinical vision.

Adaptations for large animals and special species Thermokeratoplasty can easily be done in the standing, sedated horse for persistent corneal edema from uveitis and glaucoma. Burns are made with a portable cautery device every 2 mm in the edematous cornea. Ulcers are present postoperatively and require antibiotic and antiprotease therapy.

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Fig. 8.37 In thermokeratoplasty focal superficial cautery is applied to stimulate scar tissue formation. Thermokeratoplasty has been used to treat endothelial dystrophy and prevent recurrent and painful epithelial bullae. This procedure uses a portable ophthalmic cautery unit and induces an anterior stromal fibrotic barrier to the corneal hydration, thereby decreasing the development of corneal bullae and ulcers. (a) Nearly all of the corneal epithelia are carefully removed by scraping with the Beaver No. 64 scalpel blade. (b) Additional epithelia are removed with a cotton swab soaked with absolute alcohol. (c) With a disposable cautery unit, a grid of superficial cornea burns is created.

Surgical treatment of limbal and scleral diseases The limbus or transition from sclera to cornea and the sclera share many similarities with the cornea. Surgical treatments of limbal and scleral diseases are usually directed toward removal of neoplastic and inflammatory masses. The most common limbal tumor in the dog and cat is the epibulbar melanoma (Fig. 8.38). These tumors are usually heavily pigmented, enlarge slowly, invade slowly the anterior sclera, limbus, and cornea, and usually remain superficial. As a result, most epibulbar masses are amenable to surgical excision or laser treatment. The German Shepherd breed appears most frequently affected. These tumors have also been reported in cats and may be more malignant. While epibulbar melanomas tend to expand externally, these masses can invade the deeper sclera and enter the anterior chamber. As primary anterior uveal melanomas in the dog and cat are more destructive, gonioscopy and ultrasonography are indicated to distinguish between the relatively benign epibulbar melanomas and the more serious primary anterior uveal masses. Other neoplasms affect the limbus in small animals, but are rare. Squamous cell carcinomas and adenocarcinomas have been reported in small animals. These tumors can involve the deeper aspects of the limbus, sclera, and cornea,

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Local excision with partial-thickness scleral excision Partial-thickness excision of the limbus and sclera may not require reinforcement of the remaining defect. However, if the excision involves in excess of two-thirds to three-fourths of the limbal or scleral thickness, free-cut fresh or frozen scleral homografts are recommended for reinforcement. A scleral graft is positioned within the scleral defect and apposed with 6-0 to 7-0 simple interrupted absorbable sutures. Use of the nictitans cartilage has been recommended as a replacement for sclera. Most scleral homografts in small animals have been limited to the peripheral cornea, limbus, and anterior sclera. These scleral grafts are usually free-cut to fit the various sizes and shapes of the partialto full-thickness scleral defects. Scleral homografts may

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Fig. 8.38 Epibulbar or limbal melanomas often affect the dorsolateral limbus and the German Shepherd breed. (a) Preoperative appearance. (b) One month postoperatively after local excision with homologous scleral graft.

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Fig. 8.39 Proliferative keratoconjunctivitis in a 3-year-old Collie dog. If there is no response to topical and intralesional corticosteroids, the mass is removed usually with partial-thickness excision of the underlying sclera.

also be used to correct traumatic or postoperative anterior staphylomas, usually by reinforcing the existing bulging sclera.

Preparation of scleral donor material Scleral homografts are relatively easy to prepare and maintain. These grafts are convenient ‘patches’ of primarily collagen. Scleral homografts are stored in the standard freezer (–20 to –30 C), or ultra freezer (–80 C), as well as non-refrigerated in 95% alcohol or 100% glycerol solutions. A supply of frozen scleral homografts for the dog and cat should be maintained for these surgical procedures as well as for emergency corneal grafts. Scleral grafts are obtained aseptically. The globe is enucleated and placed on a sterile surgical drape. The globe is opened 360 at the limbus and all intraocular contents (anterior and posterior uvea, lens, vitreous, and retina) are eviscerated. The sclera is vigorously scraped with the Beaver No. 64 or 67 scalpel blade to remove as much as possible of the uveal tissues. The sclera is then cut into a variety of sizes and shapes for potential grafts. These tissues are carefully transferred into individual small sterile glass bottles and frozen until use. Anterior full-thickness scleral grafts are used after surgical removal of a limbal (epibulbar) melanoma or as part of the excision of an iridal or iridociliary neoplasm. The fresh or frozen scleral homograft is trimmed to exceed the surgical defect by about 0.5–1.0 mm to compensate for graft shrinkage.

Excision of limbal melanoma with fullthickness scleral homograft The preoperative examination of a limbal melanoma in a dog suggests that local excision and a full-thickness scleral homograft may be curative (Fig. 8.40). After onset of general anesthesia, preparation of the eyelids, conjunctiva, and cornea with aqueous 0.5% povidone–iodine solution and sterile cotton swabs, the area is draped and the eyelids are retracted by a wire speculum (Fig. 8.41a).The bulbar conjunctiva and episclera above the mass are incised by tenotomy scissors and retracted toward the conjunctival fornix (Fig. 8.41b). The edges of the scleral incision are defined, and the sclera is incised slowly with the Beaver No. 64 or 67 scalpel blade (Fig. 8.41c).

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Fig. 8.40 Large epibulbar melanoma in a 5-year-old German Shepherd dog. Treatment is by local excision with a full-thickness scleral graft.

The incision is performed slowly in multiple depths. The scleral hemorrhage is controlled by judicious cautery with a disposable battery-powered unit. Once the black anterior uveal pigmentation appears, the deeper incisions of the sclera are made very carefully to avoid incision and penetration of the iris and/or ciliary body (Fig. 8.41d). After the four sides of the scleral incision are completed, the attachments of the underlying iris and ciliary body to the sclera are carefully and bluntly separated with a cyclodialysis spatula (Fig. 8.41e). The spatula must be manipulated in the potential subscleral space (Fig. 8.41f). If the spatula is inserted into the uveal tissue per se, considerable intraocular hemorrhage occurs. There should be very limited or no hemorrhage associated with this part of the surgery. Once anterior uveal separation from the sclera is complete, the section of sclera and limbal melanoma are removed (Fig. 8.41g). Any remaining tissue attachments are carefully cut by tenotomy or utility scissors. If the anterior chamber is collapsed excessively, it can be re-established with 0.5–0.7 mL of a viscoelastic agent (Fig. 8.41h). The scleral transplant is compared to the recipient’s bed and carefully trimmed by tenotomy scissors until about 0.5–1.0 mm larger than the defect (Fig. 8.41i). The scleral homograft is apposed to the recipient’s bed by simple interrupted 5-0 to 7-0 braided polyglactin 910 sutures (Fig. 8.41j). When apposition is nearly complete, the viscoelastic agent is lavaged from the anterior chamber and replaced with lactated Ringer’s solution. Any fibrin or blood should also be irrigated from the anterior chamber. After the last suture is placed, the wound apposition is evaluated by the injection of additional lactated Ringer’s solution sufficient to provide about 10–15 mmHg intraocular pressure. The scleral homograft is covered with the adjacent bulbar conjunctiva and apposed to the limbus by simple interrupted 4-0 to 6-0 braided polyglactin 910 sutures (Fig. 8.41k).

Postoperative management and results Postoperative management after these procedures includes topical antibiotics and mydriatics, and systemic broadspectrum antibiotics, corticosteroids, and NSAIDs. Mydriasis should be sufficient to provide a moderately dilated but moving pupil. Corneal edema adjacent to the opaque scleral homograft is expected. After 5–7 days, the intensity of

Surgical treatment of limbal and scleral diseases

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Fig. 8.41 Excision of a limbal mass with a full-thickness homologous scleral graft. (a) The epibulbar or limbal melanoma involves the dorsolateral limbus and sclera. (b) The bulbar conjunctiva and Tenon’s capsule are incised by Steven’s tenotomy scissors and retracted toward the conjunctival fornix to expose the mass. (c) The extent of the scleral excision is determined and the scleral edges are incised with a Beaver No. 64 scalpel blade. Scleral hemorrhage is controlled with point electrocautery. (d) The full-thickness limbus or peripheral cornea is incised similarly with a Beaver No. 64 scalpel blade, permitting entry into the anterior chamber. (e,f) With a cyclodialysis spatula inserted through the limbal or corneal incision, the spatula tip is used to separate the overlying scleral block from the adjacent iris and ciliary body. (g) By Steven’s tenotomy scissors, any remaining tissues are incised and the scleral block with the pigmented mass excised. (h) About 0.7 mL viscoelastic agent is injected into the anterior chamber to reform the anterior segment of the globe and facilitate apposition of the scleral graft. (i) The homologous scleral graft, which should be about 0.5 mm larger than the defect, is carefully fitted to the scleral wound. (j) The scleral graft is apposed with 5-0 to 7-0 simple interrupted absorbable sutures. Just before the last limbal suture is placed, the viscoelastic agent is flushed from the anterior chamber and replaced with lactated Ringer’s solution. (k) The bulbar conjunctiva is apposed to the limbus and anterior edge of the scleral graft with 4-0 to 6-0 simple interrupted absorbable sutures.

the topical and systemic treatments can be reduced. Postoperative complications after this procedure include hyphema, corneal scarring adjacent to the graft, and if the anterior uveitis is poorly controlled, iris deposits on the anterior lens capsule, posterior synechiae, and secondary cataract formation. Glaucoma is unlikely to occur as only a small percentage of the iridocorneal angle has been excised. Success of this type of surgical procedure and the preservation of vision is high (85–95%).

Laser treatment of limbal melanomas Both Nd:YAG and diode lasers have been used to treat limbal melanomas in the dog. In an Nd:YAG laser study, the total energy applied was 7.5–572.0 J. The non-contact probe was positioned 1–3 mm from the surface of the mass and the beam was directed away from the interior of the eye. Both charring and contraction of the mass occurred during lasering. Of

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the 15 dogs and cats studied, limbal melanomas recurred in three patients within 12 months. The advantages of laser treatment are that it is noninvasive, avoids the intraocular complications of surgery, requires only a short duration of general anesthesia, and does not require donor graft tissues. Its main limitation is the higher recurrence rate.

Adaptations for large animals and special species Surgeries for squamous cell carcinoma in the horse Squamous cell carcinoma (SCC) is a commonly occurring neoplasm of the equine cornea and adnexa. Even though many treatments are available, too many lesions are not treated until they are large and ulcerated. Early treatment should be easier and more accessible to the practitioner with the availability of topical and intralesional chemotherapeutic drugs. Early diagnosis and treatment result in decreased morbidity and mortality. Surgical resection alone of SCC may be adequate if clean margins can be obtained. Small tumors or carcinoma in situ of the conjunctiva or third eyelid may be treated effectively with simple excision. Carcinoma in situ of the conjunctiva can be excised with sedation, an auriculopalpebral nerve block, and topical anesthetic in a good horse. Unfortunately, many eyelid tumors are not diagnosed until it is difficult to obtain clean surgical margins without compromising lid function. Therefore, it is recommended that eyelid SCC be treated with radiation therapy, cryotherapy, radiofrequency hyperthermia, or intralesional chemotherapy without or in combination with excision (Fig. 8.42). Occasionally, a tumor will be so extensive that enucleation is necessary because lid function cannot be maintained with therapy. Excision of extensive periocular SCC can be difficult because of the possibility of an insufficient amount of skin to close the orbit. Partial orbital rim resection with mesh skin expansion has been shown to be an effective treatment in these cases. A traditional transpalpebral enucleation or exenteration is performed. When tumor is present on the eyelids, an incision is made to allow a 5–10 mm margin around the visible tumor. After exenteration of the orbit, the protuberant caudal portion of the dorsal orbital rim is excised with an osteome. This facilitates closure of the orbit as less skin is required

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for closure. Mesh expansion of the skin can also be used. Multiple rows or parallel stab incisions in the skin allow it to stretch over the orbit.

Cryotherapy Cryotherapy with liquid nitrogen or nitrous oxide can be effective, with optimal cryonecrosis of malignant cells being achieved between –20 and –40 C using a double freeze–thaw technique. Either a closed probe or spray can be used. The closed probe gives better application accuracy while the spray is faster; however, collateral tissue damage or runoff distant to the site is a potential complication. Cryosurgery is affordable and easily attainable. It can be used for eyelid, nictitans, conjunctival, and corneal tumors. Use of a thermocouple is helpful in thick eyelid tumors to ensure an adequate freeze and prevent overfreezing. Cryotherapy is especially useful when treatment of a limbal tumor cannot be done with a strontium probe due to lack of availability or when the time required to treat a very large tumor is prohibitive due to exposure and anesthetic time. The skin and cornea that is not to be frozen can be protected using a heavy layer of petrolatum. A rounded piece of polystyrene foam, as from a cup, covered in petrolatum works well to protect the cornea when freezing the eyelids. Small superficial tumors should be frozen until the iceball extends 3–5 mm beyond the visible tumor margin. Keratectomy sites that have been frozen seem to heal exceptionally slowly. The ulcers are treated with a broad-spectrum ophthalmic antibiotic and atropine as needed postoperatively. Post-cryotherapy, eyelids are extremely erythemic and edematous for several days.

Radiation therapy Radiation therapy with beta irradiation (i.e., strontium-90) or brachytherapy is effective in the treatment of SCC. Beta radiation is most beneficial in superficial SCC of the cornea and limbus after keratectomy. Eighty to 90% of horses with corneal SCC that undergo keratectomy and beta irradiation are cured after one treatment. As strontium has limited penetration into soft tissue, it is very safe for corneal lesions as the lens is not damaged, but it cannot penetrate lesions of the eyelid. Strontium irradiation is delivered via a probe. Healing of resultant ulcers is delayed compared to ulcers that have not been irradiated. In addition, it is not unusual for granulation tissue to develop at the site that can be

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Fig. 8.42 Treatment of equine corneoconjunctival squamous cell carcinoma in situ with superficial keratectomy, beta irradiation, and amnion graft in a horse. (a) Generalized carcinoma in situ is present. (b) Keratectomy, beta irradiation, and amnion graft cover the corneal ulcer wound for 3 weeks postoperatively. (c) Seven weeks postoperatively the cornea has healed with minimal vascularization and scarring.

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indistinguishable from tumor recurrence without biopsy. Recurrent tumors are often cured with a second treatment. Bacterial keratitis is not an unusual complication following strontium; therefore, conjunctival grafts are commonly placed over the ulcer bed. Interstitial radiation therapy or brachytherapy provides the advantage of continuous tumor exposure to high levels of radiation over a period of time. Treatments with cesium137, radon-222, gold-198, cobalt-60, and iridium-192 have all been described. Brachytherapy involves the placement of tubes containing radioactive beads within neoplastic tissue. One-year local control rates with brachytherapy alone are 74%. The 2- and 4-year progression-free survival rates are about 70%. Advantages of brachytherapy include preservation of eyelid anatomy and function even with extensive SCC and the high cure rate. Disadvantages of brachytherapy include cost, required expertise, radiation exposure of personnel, and necessity of isolation of the horse. Local toxicoses and acute reactions include swelling, localized infection, and dry and moist desquamation; generally these respond to therapy or are self-limiting. Chronic radiation reactions include hair loss, hair and skin depigmentation, necrosis, fibrosis, cataract, keratitis, and corneal ulceration. Generally the placement, number of beads, and time of exposure are calculated using a computer program. The implants can be placed within an eyelid tumor or within debulked eyelid tissue. The benefit of debulking a large tumor is that less radiation is necessary, decreasing the amount of tissue necrosis. If the tumor is debulked, interstitial therapy can be instituted intra- or postoperatively. We prefer to debulk the tumor mass if necessary, close the incision normally, and place the tubes at closure. If the horse is cooperative, the beads can be placed in the standing horse 5 days postoperatively, avoiding another anesthesia. This allows healing of the incision prior to irradiating the tissue. Generally the horses are in isolation for 5–7 days. If any health problems arise, the treatment is terminated by removing the beads as radiation exposure is too high to work on a horse with radioactive beads. Possible complications are loss of the beads. In one case, the horse ingested the beads and had to remain in isolation until the beads were passed in the manure.

Hyperthermia Hyperthermia of small, superficial SCC has been described. Malignant cells appear to be more sensitive to temperatures between 41 C and 45 C than normal cells. Conjunctival and eyelid swelling is minimal after this procedure. Tumors are held at a temperature of 50 C for 30 s. Eyelid tumors should be treated for 3–4 mm beyond the tumor margin. One must be careful to not overlap applications from opposite directions. Hyperthermia should not be used in large tumors of 4–5 cm diameter that penetrate deeply into the eyelid or conjunctiva.

Carbon dioxide laser Carbon dioxide laser ablation of superficial limbal SCC can be effective. The advantages are ease and speed, minimal pain and inflammation, and precision. The disadvantages are the cost of the instrumentation, lack of specificity for

neoplastic cell destruction, and the slow healing rate of the resultant corneal ulcers. The technique involves using a CO2 laser with an articulated arm. The laser is operated in the continuous mode with a power setting of 3–6 on the low scale, which corresponds to an average output of 3–8 W. A defocused beam is used to provide ablation rather than cutting. Depending on the size of the tumor, a keratectomy may be done prior to laser ablation. The tumors are vaporized in situ until all visible tumor is gone. The bed is then lasered until it is covered with a brown char extending 5 mm into normal tissue. Topical broad-spectrum antibiotics are used until the cornea is fluorescein negative.

Immunotherapy Immunotherapy with bacille Calmette-Gue´rin (BCG) cell wall extract has been used successfully for large SCC in the horse. The tumors are injected with 1 mL vaccine/cm2. Multiple injections are required approximately 1 week apart. Flunixin meglumine (1 mg/kg) should be administered concurrently to help prevent anaphylaxis. Complications include severe inflammation and risk of anaphylaxis. The benefit of BCG is that the eyelid architecture is preserved. Other newer, safer chemotherapeutic drugs that can be used intralesionally have largely replaced BCG therapy.

Intralesional chemotherapy Intralesional chemotherapy with cisplatin or 5-fluorouracil (5-FU) is an effective therapy for eyelid SCC. Like brachytherapy, intralesional chemotherapy results in very little eyelid distortion or functional alterations. Chemotherapy with intralesional, slow-release cisplatin can give very effective results, with or without surgical debulking, in large eyelid SCC. Cisplatin, 3.3 mg/mL (10 mg of cisplatin in 1 mL of water and 2 mL of purified, medical-grade sesame oil), is used. The solutions must be mixed for 1 min to create an emulsion. The emulsion is injected using a 20 or 22 g needle inserted into the tissue. The emulsion is injected while withdrawing the needle. Multiple injections are made to cover the treatment field and include 1 cm of normal margin tissue. Multiple planes of injections are needed for large tumors. Treatments are generally done under sedation. Four sessions at 2-week intervals with 1 mg/cm3 for tumors 10–20 cm3 in size are necessary. The 1-year relapse-free rates for SCC treated with cisplatin approach 90%. Similar metastasis rates in studies using cisplatin indicate that damage to the blood vessels and lymphatics by the injections does not increase the rate of metastasis. Topical therapy with 1% 5-FU can be used for corneal, limbal, conjunctival, and superficial eyelid SCC. Topical 5-FU, 1% solution, applied three to four times daily can be effective for corneal and conjunctival intraepithelial carcinoma. Superficial eyelid tumors can be treated with 5-FU cream; however, this treatment occasionally causes severe necrosis. 5-FU, 50 mg/mL with 3 mL of 1:1000 adrenaline (epinephrine) per 10 mL of 5-FU, can be injected into eyelid SCC. Most horses will tolerate intralesional treatments very nicely although alopecia may result. Often the ocular discharge increases, necessitating the use of a fly mask. Generally the response is positive, and a relatively normal eyelid with normal function is the result.

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Piroxicam, an NSAID, has been shown to have antitumor effects. It is thought to exert its effects by inhibiting cyclooxygenase-2 which is overexpressed in epithelial cancers. Although there are no publications describing the use of piroxicam in the treatment of ocular SCC in horses, it has been used successfully in a horse with mucocutaneous carcinoma and metastasis. Piroxicam is administered at 150 mg per day for several months.

Surgeries for infectious keratoconjunctivitis and squamous cell carcinoma in cattle Infectious bovine keratoconjunctivitis (IBK) and bovine squamous cell carcinoma (BSCC) are the predominant diseases for corneoscleral surgeries in the bovine species. The bovine cornea has a remarkable ability to heal rapidly, and develops less corneal scarring than occurs in the horse. The corneal ulceration associated with IBK and Moraxella bovis is sensitive to most topical antibiotics, and infrequently is surgery necessary (usually a nictitating membrane flap sutured to the upper eyelid) to strengthen those corneas with deep and perforated ulcerations (see Chapter 7). BSCC is one of the most frequent neoplasms in this species. About two-thirds of BSCCs affect the corneolimbus region, usually the lateral and/or dorsolateral limbus, and less frequently the medial limbus. The Hereford,

occasionally Simmental, and infrequently the Holstein breeds (white or non-pigmented eyelids) most often develop BSCC, at an average age of about 7–9 years. Other sites affected with BSCC include the medial corneolimbus, eyelids and palpebral conjunctiva, lacrimal caruncle, and nictitating membrane. Client education is important for the management of BSCC, as in the Hereford breed there are heritable factors, and therapy of small masses is far more successful and less costly than for those masses with intraorbital invasion and metastases to the regional palpebral lymph nodes and other tissues. All of the therapies used in the horse for the treatment of SCC are available for cattle, but financial constraints generally limit those techniques to initial surgery and tumor excision, cryotherapy, and hyperthermia. Anesthesia is usually retrobulbar and local eyelid blocks. Enucleation surgeries for BSCC yield about 37% recurrences. Salvage procedures may be used for advanced BSCC. For palpebral conjunctival BSCC, the ‘H’ blepharoplasty procedure is used most often. For corneolimbal BSCC, superficial-to-deep keratectomy covered with a permanent advancement (hood or 180 ) bulbar conjunctival graft is preferred. Cryotherapy may be applied to the keratectomy site before the conjunctival graft is applied. Surgical reduction of the BSCC mass can also reduce the amount of cryotherapy. Hyperthermia is another option, and is often reserved for small masses (avoid in masses over 3–4 cm).

Further reading Small animals: general Dubielzig RR, Schobert CS, Dreyfus J: Corneal squamous cell carcinoma in dogs with a history of chronic keratitis, Proceedings of the 39th Meeting of the American College of Veterinary Ophthalmologists: Abstract 112, 2008. Gelatt KN, Gelatt JP: Surgical procedures of the cornea and sclera. In Handbook of Small Animal Ophthalmic Surgery, vol 2, Oxford, 1995, Corneal and Intraocular Procedures. Pergamon Press, pp 43–84. Gilger BC, Bentley E, Ollivier FJ: Diseases and surgery of the canine cornea and sclera. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 690–752. Giuliano EA, Ota J, Tucker SA: Photodynamic therapy: basic principles and potential uses for the veterinary ophthalmologist, Vet Ophthalmol 10:337–343, 2007. Hirst LW, Rice TA: Surgery for ocular injuries. In Rice TA, Michels RG, Stark WJ, editors: Ophthalmic Surgery, ed 4, St Louis, 1984, Mosby, pp 399–428. Rampazzo A, Eule C, Speier S, Grest P, Spiess B: Scleral rupture in dogs, cats and horses, Vet Ophthalmol 9:149–156, 2006. Stark WJ, Bruner WE, Maumenee AE: Surgery of the cornea. In Rice TA, Michels RG, Stark WJ, editors: Ophthalmic Surgery, ed 4, St Louis, 1984, Mosby, pp 115–137. Wilkie DA, Whittaker C: Surgery of the cornea, Vet Clin North Am Small Anim Pract 27:1067–1107, 1997.

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Small animals: keratectomies Champagne ES, Munger RJ: Multiple punctate keratotomy for the treatment of recurrent epithelial erosions in dogs, J Am Anim Hosp Assoc 28:213–216, 1992. Peiffer RL, Gelatt KN: Superficial keratectomy for the treatment of chronic ulcerative keratitis and sequestrum in the domestic cat, Feline Practice 6:37–40, 1976. Thoft RA: Keratoepithelioplasty, Am J Ophthalmol 97:1–6, 1984. Vestre WA: Surgery of the cornea. In Bojrab MJ, Birchard SJ, Tomlinson JL, editors: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 94–98. Whitley RD: The canine cornea. In Gelatt KN, editor: Veterinary Ophthalmology, ed 2, Philadelphia, 1991, Lea and Febiger, pp 307–356.

Small animals: corneal repair of lacerations/ulcerations Barnett KC: The corneal ulcer–VI. Surgical treatment, J Small Anim Pract 7:275–277, 1966. Barros PSM, Safatle AMV, Malerba TA, Burnier M Jr: The surgical repair of the cornea of the dog using pericardium as a keratoprosthesis, Brazilian Journal of Veterinary Research and Animal Science 32:251–255, 1995.

Barros PSM, Garcia JA, Laus JL, Ferreira AL, Gomes TLS: The use of xenologous amniotic membrane to repair canine corneal perforation created by penetrating keratectomy, Vet Ophthalmol 1:119–123, 1998. Blogg JR, Dutton AG, Stanley RG: Use of third eyelid grafts to repair full-thickness defects in the cornea and sclera, J Am Anim Hosp Assoc 25:505–512, 1989. Bussieres M, Krohne SG, Stiles J, Townsend WM: The use of porcine small intestinal submucosa for the repair of full-thickness corneal defects in dogs, cats and horses, Vet Ophthalmol 7:352–359, 2004. Crispin S: Corneal foreign bodies in cats and dogs: is the damage comparable? Vet Med 82:800–801, 1987. Davidson MG, Nasisse MP, Jamieson VE, English RV, Olivero DK: Traumatic anterior lens capsule disruption, J Am Anim Hosp Assoc 27:410–414, 1991. Dice PF, Colley PL: Use of contact lenses to treat corneal diseases in small animals, Semin Vet Med Surg 3:46–51, 1988. Featherstone HJ, Sansom J: Intestinal submucosa repair in two cases of feline ulcerative keratitis, Vet Rec 145:136–138, 2000. Featherstone HJ, Sansom J, Heinrich CL: The use of porcine small intestinal submucosa in ten cases of feline corneal disease, Vet Ophthalmol 4:147–153, 2001. Gerding PA, McLaughlin SA, Troop MW: Pathogenic bacteria and fungi associated

Adaptations for large animals and special species with external ocular diseases in dogs: 131 cases (1981–1986), J Am Vet Med Assoc 192:242–244, 1988. Kern TJ: Ulcerative keratitis, Vet Clin North Am 20:643–666, 1990. Kuhns EL, Keller WF, Blanchard GL: The treatment of pannus in dogs by use of a corneal–scleral graft, J Am Vet Med Assoc 162:950–952, 1973. Morgan RV, Bachrach A, Ogilvie GK: An evaluation of soft contact lens usage in the dog and cat, J Am Anim Hosp Assoc 20:885–888, 1984. Parshall CJ: Lamellar corneal–scleral transposition, J Am Anim Hosp Assoc 9:270–277, 1973. Schmidt GM, Blanchard GL, Keller WF: The use of hydrophilic contact lenses in corneal diseases of the dog and cat: a preliminary report, J Small Anim Pract 18:773–777, 1977. Stanley RG: Results of grid keratotomy, superficial keratectomy, and debridement for the management of persistent corneal erosions in 92 dogs, Vet Ophthalmol 1:233–238, 1998. Williams MM, Spiess BM, Pascoe PJ, O’Grady M: Systemic effects of topical and subconjunctival ophthalmic atropine in the horse, Vet Ophthalmol 3:193–199, 2000.

Small animals: corneal adhesives Boruchoff SA, Refojo M, Slansky HH, et al: Clinical applications of adhesives in corneal surgery, Trans Am Acad Ophthalmol Otolaryngol 73:499–505, 1969. Eiferman RA, Synder JW: Antibacterial effect of cyanoacrylate glue, Arch Ophthalmol 101:953–960, 1983. Laus JL, Barbosa VT, Ribeiro AP: Effect of the ethyl-cyanoacrylate or the octhylcyanoacrylate in experimental corneal lesions in rabbits, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 23, 2007. Refojo MF, Dohlma CH, Ahmad B, et al: Evaluation of adhesives for corneal surgery, Arch Ophthalmol 80:645–656, 1968. Refojo MF, Dohlman CH, Koliopoulos J: Adhesives in ophthalmology: a review, Surveys in Ophthalmology 15:217–236, 1971. Watte´ CM, Elks R, Moore DL, McLellan GJ: Clinical experience with butyl-2cyanoacrylate adhesive in the management of canine and feline corneal disease, Vet Ophthalmol 7:319–327, 2004.

Small animals: corneal grafts/ keratoplasty Andrade AL, Laus JL, Figueiredo F, Batista CM: The use of preserved equine renal capsule to repair lamellar corneal lesions in normal dogs, Vet Ophthalmol 2:79–82, 1999. Andrew SE, Samuelson DA, Lewis PA, Kubilis PS: Comparison of Optisol-GS and neomycin–polymyxin B–gramicidin ophthalmic solution for corneal storage in the dog, Vet Ophthalmol 2:155–161, 1999.

Bahn CF, Meyer RF, MacCallum DK, et al: Penetrating keratoplasty in the cat, Ophthalmology 89:687–699, 1982. Brightman AH, McLaughlin SA, Brogdon JD: Autogenous lamellar corneal grafting in dogs, J Am Vet Med Assoc 195:469–475, 1989. Cella F: Corneal graft in the dog, Ad. in Small Animal Practice 3:101–103, 1961. Dice PF, Severin GA, Limb WV: Experimental autogenous and homologous corneal transplantation in the dog, J Am Anim Hosp Assoc 9:245–251, 1973. Gimrnez MTP, Farin˜a IM: Lamellar keratoplasty for the treatment of feline corneal sequestrum, Vet Ophthalmol 1:163–166, 1998. Hacker DV: Frozen corneal grafts in dogs and cats: a report on 19 cases, J Am Anim Hosp Assoc 27:387–398, 1991. Holt JR: Corneal graft in a dog, Vet Res 69:454, 1957. Jensen EC: Experimental corneal transplantation in the dog, J Am Vet Med Assoc 142:11–22, 1963. Lavignette AM: Lamellar keratoplasty in the dog, Small Animal Clinician 2:183–197, 1962. Mannis MJ, Krachmer JH: Keratoplasty: a historical perspective, Surveys in Ophthalmology 25:333–338, 1981. McEntyre JM: Experimental penetrating keratoplasty in the dog, Arch Ophthalmol 80:372–376, 1968. Mueller FO, Formston C: Keratoplasty in the dog, Res Vet Sci 19:168–175, 1969. Stechschulte SU, Azar DT: Complications after penetrating keratoplasty, Int Ophthalmol Clin 40:27–43, 2000. Townsend WM, Rankin AJ, Stiles J, Krohne SG: Heterologous penetrating keratoplasty for treatment of a corneal sequestrum in a cat, Vet Ophthalmol 11:273–278, 2008.

Small animals: limbal surgery Donaldson D, Sansom J, Adams V: Canine limbal melanomas: 30 cases (1992–2004). Part 2. Treatment with lamellar resection and adjunctive strontium-90 beta plesiotherapy: efficacy and morbidity, Vet Ophthalmol 9:179–186, 2006. Featherstone HJ, Renwick P, Heinrich CL, Manning S: Efficacy of cryotherapy for the treatment of canine limbal melanoma, Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 93, 2008. Harling DE, Peiffer RL, Cook CS, Belkin PV: Feline limbal melanoma: four cases, J Am Anim Hosp Assoc 22:795–802, 1986. Hirst LW: Epibulbar tumors, pterygia, enucleation and evisceration. In Rice TA, Michels RG, Stark WJ, editors: Ophthalmic Surgery, ed 4, St Louis, 1984, Mosby, pp 63–84. Kanai K, Kanemaki N, Matsuo S, et al: Excision of a feline limbal melanoma and use of nictitans cartilage to repair the resulting

corneoscleral defect, Vet Ophthalmol 9:255–258, 2006. Lewin GA: Repair of a full thickness corneoscleral defect in a German Shepherd dog using porcine small intestinal submucosa, J Small Anim Pract 40:340–342, 1999. Norman JC, Urbanz JL, Calvares ST: Penetrating keratoscleroplasty and bimodal grafting for treatment of limbal melanocytoma, Vet Ophthalmol 11:340–345, 2008. Plummer CE, Ka¨llberg ME, Ollivier FJ, et al: Use of a biosynthetic material to repair the surgical defect following excision of an epibulbar melanoma in a cat, Vet Ophthalmol 11:254, 2008. Schepens CL, Acosta F: Scleral implants: an historical perspective, Surveys in Ophthalmology 35:447–453, 1991. Sullivan TC, Nasisse MP, Davidson MG, Glover TL: Photocoagulation of limbal melanomas in dogs and cats: 15 cases (1989–1993), J Am Vet Med Assoc 208:891–894, 1996. Wilkie DA, Wolf ED: Treatment of epibulbar melanocytoma in a dog, using full-thickness eyewall resection and synthetic graft, J Am Vet Med Assoc 198:1019–1022, 1991.

Small animals: other Bentley E, Murphy CJ: Thermal cautery of the cornea for the treatment of spontaneous chronic corneal epithelial defects in dogs and horses, J Am Vet Med Assoc 224:250–253, 2004. Michau TM, Gilger BC, Maggio F, Davidson MG: Use of thermokeratoplasty for treatment of ulcerative keratitis and bullous keratopathy secondary to corneal endothelial disease in dogs: 13 cases (1994– 2001), J Am Vet Med Assoc 222:607–612, 2003. Murphy CJ, Burling T, Hollingsworth S: Thermokeratoplasty for the treatment of chronic bullous keratopathy in the dog, Transactions of the 24th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 21, 1993. Shieh E, Boldy KL, Garbus J, McDonnell PJ: Excimer laser keratectomy in the treatment of canine corneal opacities, Progress in Veterinary and Comparative Ophthalmology 2:75–79, 1992.

Large animals: equine Alexander GR, Chester Z: Use of free conjunctival grafts in horses: ten cases, Aust Vet J 82:206–210, 2004. Anderson JF, Gelatt KN, Farnsworth RJ: A modified membrane nictitans flap technique for the treatment of ulcerative keratitis in cattle, J Am Vet Med Assoc 168:706–708, 1976. Andrew SE, Willis AM: Disease of the cornea and sclera. In Gilger BC, editor: Equine Ophthalmology, St Louis, 2005, Saunders, pp 157–251.

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Andrew SE, Brooks DE, Smith PJ, Gelatt KN, Chmielewski NT, Whittaker C: Equine ulcerative keratomycosis: visual outcome and ocular survival in 39 cases (1987–1996), Equine Vet J 30:109–116, 1998. Andrew SE, Brooks DE, Biros DJ, Denis HM, Cutler TJ, Gelatt KN: Posterior lamellar keratoplasty for treatment of deep stromal abscesses in nine horses, Vet Ophthalmol 3:99–103, 2000. Baker A, Brooks DE, Plummer CE, et al: Penetrating lamellar keratoplasty for corneal stromal abscess in the horse: a retrospective study of 21 clinical cases, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 68, 2007. Bentley E, Murphy CJ: Thermal cautery of the cornea for the treatment of spontaneous chronic corneal epithelial defects in dogs and horses, J Am Vet Med Assoc 224:250–253, 2004. Blackwood SE, Brooks DE, Plummer CE, et al: Penetrating keratoplasty in the horse: visual outcome and ocular survival, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 69, 2007. Bosch G, Klein WR: Superficial keratectomy and cryosurgery as therapy for limbal neoplasms in 13 horses, Vet Ophthalmol 8:241–246, 2005. Brooks DE: Equine stromal and endothelial keratopathies: medical management of stromal abscesses, eosinophilic keratitis, calcific band keratopathy, striate band opacities, and endotheliitis in the horse, Current Techniques in Equine Practice 4:21–28, 2005. Brooks DE: Penetrating keratoplasty, deep lamellar endothelial keratoplasty, and posterior lamellar keratoplasty in the horse, Current Techniques in Equine Practice 4:37–49, 2005. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274. Brooks DE, Andrew SE, Biros DJ, Denis HM, Cutler TJ, Strubbe DT, Gelatt KN: Ulcerative keratitis caused by beta hemolytic Streptococcus equi in 11 horses, Vet Ophthalmol 3:121–126, 2000. Brooks DE, Plummer CE, Ka¨llberg ME, et al: Corneal transplantation for inflammatory keratopathies in the horse: visual outcome in 206 cases (1993–2007), Vet Ophthalmol 11:123–130, 2008. Bru¨nott A, Boeve´ MH, Velden MA: Grid keratotomy as a treatment for superficial nonhealing corneal ulcers in 10 horses, Vet Ophthalmol 10:162–167, 2007. Bussieres M, Krohne SG, Stiles J, Townsend WM: The use of porcine small intestinal submucosa for the repair of fullthickness corneal defects in dogs, cats and horses, Vet Ophthalmol 7:352–359, 2004.

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Chmielewski NT, Brooks DE, Smith PJ, et al: Visual outcome and ocular survival following iris prolapse in the horse: a review of 32 cases, Equine Vet J 29:31–39, 1997. Cooley PL, Wyman M: Indolent-like corneal ulcers in 3 horses, J Am Vet Med Assoc 188:295–297, 1986. Denis HM: Equine corneal surgery and transplantation, Vet Clin North Am Equine Pract 20:361–380, 2004. English RV, Nasisse MP, Davidson MG: Carbon dioxide laser ablation for treatment of limbal squamous cell carcinoma in horses, J Am Vet Med Assoc 196:439–442, 1990. Grahn B, Wolfer J, Keller C, Wilcock B: Equine keratomycosis: clinical and laboratory findings in 23 cases, Progress in Veterinary and Comparative Ophthalmology 3:2–7, 1993. Hendrix DVH, Brooks DE, Smith PJ, et al: Corneal stromal abscesses in the horse: a review of 24 cases, Equine Vet J 27:440–447, 1995. Lassaline ME, Brooks DE, Ollivier FJ: Equine amniotic membrane transplantation for corneal laceration and keratomalacia in three horses, Vet Ophthalmol 8:311–317, 2005. Lavach JD, Severin GA, Roberts SM: Lacerations of the equine eye: a review of 48 cases, J Am Vet Med Assoc 184:1243–1248, 1984. Michau TM, Schwabenton B, Davidson MG, Gilger BC: Superficial, nonhealing corneal ulcers in horses: 23 cases (1989–2003), Vet Ophthalmol 6:291–297, 2003. McMullen RJ, Clode AB, Pandiri AKR, et al: Epibulbar melanoma in a foal, Vet Ophthalmol 11:44–50, 2008. Nasisse MP, Jamieson VE: Cornea and sclera. In Auer JA, Stick JA, editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 480–491. Ollivier FJ, Ka¨llberg ME, Plummer CE, et al: Amniotic membrane transplantation for corneal surface reconstruction after excision of corneolimbal squamous cell carcinomas in nine horses, Vet Ophthalmol 9:404–413, 2006. Plummer CE, Brooks DE, Ka¨llberg ME, et al: Deep lamellar endothelial keratoplasty for equine corneal stromal abscesses: 57 cases (2003–2007), Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 70, 2007. Plummer CE, Smith S, Andrew SE, et al: Combined keratectomy, strontium-90 irradiation and permanent bulbar conjunctival grafts for corneolimbal squamous cell carcinomas in horses (1990–2002): 38 horses, Vet Ophthalmol 10:37–42, 2007. Plummer CE, Ka¨llberg ME, Ollivier FJ, et al: Deep lamellar endothelial keratoplasty in 10 horses, Vet Ophthalmol 11:35–43, 2008. Rampazzo A, Eule C, Speier S, Grest P, Spiess B: Scleral rupture in dogs, cats and horses, Vet Ophthalmol 9:149–156, 2006.

Rebhun WC: Treatment of advanced squamous cell carcinomas involving the equine cornea, Vet Surg 19:297–302, 1990. Sansom J, Featherstone H, Barnett KC: Keratomycosis in six horses in the United Kingdom, Vet Rec 6:13–17, 2005. Schoster JV: Using combined excision and cryotherapy to treat limbal squamous cell carcinoma, Vet Med 87:357–365, 1992. Townsend WM: Food and fiber-producing ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1275–1335. Whitley RD, Turner LM: Management of ocular trauma in horses. Part 1: cornea and sclera, Mod Vet Pract 67:233–238, 1986. Whittaker CJG, Smith PJ, Brooks DE, et al: Therapeutic penetrating keratoplasty for deep corneal stromal abscesses in eight horses, Veterinary and Comparative Ophthalmology 7:19–28, 1997.

Large animals: bovine English RV, Nasisse MP, Davidson MG: Carbon dioxide laser ablation for treatment of limbal squamous cell carcinoma in horses, J Am Vet Med Assoc 196:439–442, 1990. Farris HE: Cryosurgical treatment of bovine ocular squamous cell carcinoma, Vet Clin North Am Large Anim Pract 104:861–867, 1980. Farris HE, Fraunfelder FT: Cryosurgical treatment of ocular squamous cell carcinoma of cattle, J Am Vet Med Assoc 168:213–216, 1976. Grier RL, Brewer WG, Paul SR, et al: Treatment of bovine and equine ocular squamous cell carcinoma by radiofrequency hyperthermia, J Am Vet Med Assoc 177:55–61, 1980. Kainer RA: Current concepts in the treatment of bovine ocular squamous cell tumors, Vet Clin North Am Large Anim Pract 6:609–622, 1984. Klein WR, Brier J, van Dieten JS, et al: Radical surgery of bovine ocular squamous cell carcinoma (cancer eye). Complications and results, Vet Surg 13:236–242, 1984. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2007, Blackwell, pp 1275–1335.

Other species Gionfriddo JR, Powell CC: Primary closure of the corneas of two Great Horned owls after resection of nonhealing ulcers, Vet Ophthalmol 9:251–254, 2006. Lin X-C, Hui Y-N, Wand Y-S, et al: Lamellar keratoplasty with a graft of lyophilized acellular porcine corneal stroma in a rabbit, Vet Ophthalmol 11:61–66, 2008. Lynch GL, Scagliotti RH, Hoffman A, Dubielzig RR: Penetrating keratoplasty in a California Brown Pelican, Vet Ophthalmol 10:254–261, 2007.

CHAPTER

9

Surgical procedures of the anterior chamber and anterior uvea Kirk N. Gelatt1 and David A. Wilkie2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

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Surgical procedures of the anterior uvea

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Surgical anatomy

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Pathophysiology

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Laser treatment of anterior uveal cysts in the dog and cat

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Perioperative considerations

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Laser treatment of anterior uveal neoplasms in the dog

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Adaptations for large animals and special species

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Introduction Diseases of the anterior chamber and anterior uvea (iris and ciliary body) are frequent in small and large animals. Causes of these diseases include trauma, congenital anomalies, inflammations, neoplasms, immune diseases, and degenerations. Aqueous humor within the posterior chamber, pupil, and anterior chamber delivers nutrients and removes wastes from the lens and posterior cornea, and contains cells, proteins, and other substances that may be useful for diagnostic and therapeutic techniques. Trauma affecting the anterior chamber and anterior uvea is common in small animals and horses, often resulting in hemorrhage within the anterior chamber (hyphema). Ocular trauma also includes foreign bodies that may be embedded within the cornea, those partially extending into the anterior chamber, or those that penetrate the globe and lodge in the orbit or posterior orbit. Inflammations involving the anterior chamber and anterior uvea are common in older small animals, and may be isolated to one eye or affect both eyes with systemic diseases. Immune-mediate inflammation, termed equine recurrent uveitis (ERU), is the most common cause of blindness in the horse. An example of immune-mediated panuveitis in dogs is uveodermatologic or Vogt–Koyanagi–Harada syndrome. Both of these chronic uveitides are apt to cause secondary cataracts with posterior synechiae, secondary glaucoma, retinal degeneration, and optic nerve atrophy. Leukocytic infiltration of the anterior uvea also affects the anterior chamber, causing the aqueous humor to become

cloudy (‘aqueous flare’ – Tyndall effect), with gravitation of cells in the ventral anterior chamber producing hypopyon and the adherence of inflammatory cells on the posterior cornea (keratic precipitates). Anterior uveal inflammations in cats are usually associated with systemic diseases, and frequently require additional diagnostic procedures to establish the diagnosis (Fig. 9.1). Anterior chamber paracentesis (keratocentesis) with cytologic and protein (globulin, albumin, antibodies, etc.) analysis may assist in establishing the diagnosis. Congenital anomalies of the anterior uvea are less frequent in small animals, but occur in purebred dogs with some frequency. Microphthalmia results in microcornea and micro-anterior chamber. Anterior uveal anomalies, such as persistent pupillary membranes, are not usually candidates for surgery, but may be associated with secondary hemorrhage that requires therapy. Congenital abnormalities of the anterior segment have also been described in the horse; specifically, anterior segment dysgenesis, megaloglobus, and other ocular abnormalities seen in the Rocky Mountain and similar breed horses. Anterior uveal neoplasms are frequent in small animals, but less frequent in horses. Clinical differences in the malignancy of these tumors in the dog and cat necessitate different strategies for their clinical management. Anterior uveal neoplasms in the dog are primarily malignant melanomas and, less frequently, ciliary body adenomas and adenocarcinomas (Fig. 9.2). These neoplasms, affecting the iris, ciliary body or both structures, usually enlarge slowly and metastasize late and infrequently (about 5%). The clinical history of

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Surgical procedures of the anterior chamber and anterior uvea

Fig. 9.1 Anterior uveitis and hypopyon in a cat. Note the presence of clotted blood distributed throughout the hypopyon. As this condition is bilateral, cytologic examination of these cells may help establish the cause of the iridocyclitis.

these neoplasms usually includes local irritation, ocular inflammation, and enlargement of the globe. Space-occupying masses are commonly associated with secondary glaucoma and retinal detachments. Hyphema or hemorrhage in the anterior chamber may result from the rapidly growing tumor, secondary glaucoma and lens luxation, and retinal detachments. Types of neoplasm affecting the anterior uvea of large animals are similar, with melanoma the most common primary tumor. Small isolated iridal neoplasms in dogs and horses may be treated by iridectomy or iridocyclectomy combined with excision of the adjacent sclera, and more recently by diode laser photocoagulation (Fig. 9.3a,b). Diffuse iridal melanomas in cats are managed differently, because the potential for local infiltration and metastasis is greater. Cats with diffuse iridal melanomas are usually presented with a progressive brown to black pigmentation of the iris (Fig. 9.3c). The iridal mass increases in thickness late in the disease.

A

Pupillary changes, secondary glaucoma, hyphema, and retinal detachments indicate that the iridal neoplasm is advanced, and an enucleation should be performed. Controversy exists among veterinary ophthalmologists and veterinary pathologists as to early clinical management of these neoplasms when the only clinical sign is the iridal pigmentation, which is progressing slowly. Diffuse iridal melanomas in cats usually involve the majority of the iris and are not amenable to sectional iridectomy or iridocyclectomy. Cysts of the iris and ciliary body are not infrequent in older dogs, cats, and horses (including those of the granula iridica). Iris cysts arise from the posterior iridal epithelium, and appear as densely pigmented, single or multiple spherical bodies. In dogs, they may be free-floating within the anterior chamber, in the pupil, or still attached to the posterior iridal surface (Fig. 9.4). In cats, most iridal cysts remain attached to the pupillary margin. In dogs presented with iridal cysts in the anterior chamber, the drug-induced mydriasis associated with the ophthalmic examination may liberate additional cysts into the anterior chamber that were trapped behind the pupil in the posterior chamber. The free-floating cysts gravitate to the most ventral portion of the anterior chamber. Manipulation of the animal’s head and ocular movements will often cause these bodies to move within the anterior chamber. Sometimes these iridal cysts become trapped in the anterior chamber angle, and may simulate a basal iridal melanoma. These small round black iridal cysts transilluminate, distinguishing them from anterior uveal melanomas. B-scan ultrasonography will also reveal hollow centers. Treatment includes temporization, laser-induced rupture or deflation, and paracentesis or lavage from the anterior chamber. Unfortunately, not all anterior uveal cysts appear innocuous. Anterior uveal cysts have been associated with glaucoma in the Golden Retriever and Great Dane breeds. In the Golden Retriever, nearly one-half of the dogs develop glaucoma and most of these animals lose their vision. The clinical significance of iridal and ciliary body cysts is not known; histologically, the ciliary body cysts contain periodic acid– Schiff (PAS)-positive material which may be deleterious to

B

Fig. 9.2 Primary anterior uveal masses in the dog. (a) Sometimes the animal is presented because the owner notices a mass or something within the eye or pupil. (b) Other frequent presenting clinical signs include hyphema, anterior uveitis, and secondary glaucoma.

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Surgical anatomy

A

B

C

Fig. 9.3 Iridal melanomas may present in different ways in the dog and cat. (a) The single ventrolateral pigmented mass in this dog was noted by the owner because of the contrast to the surrounding light brown iridal tissues. (b) In contrast, this owner noted multiple pigmented masses in their dog’s iris. Multiple masses complicate the therapy options. (c) In this cat, the entire iris has become densely pigmented and the pupil irregular.

A

B

Fig. 9.4 Pigmented iris (usually black) or ciliary (usually red or clear) cysts in the dog may have different clinical significance. (a) This single iris pigmented cyst in a 12-year-old Golden Retriever can be deflated by laser therapy or aspiration. The cyst readily transilluminates and the prognosis is good. (b) In contrast, these ciliary cysts (clear cysts behind the pupil) and two pigmented iridal cysts (one dorsal and one in the ventral anterior chamber) in a 3-year-old Golden Retriever often progress to uveitis, pigment deposition on the anterior lens capsule, secondary cataract and glaucoma formation, and warrant a much more guarded prognosis.

aqueous outflow pathways. The high number of these cysts within the posterior chamber may also displace the basal iris forward and compress the opening of the sclerociliary cleft. Laser deflation of these cysts seems not to delay the onset of the glaucoma, but more study is indicated.

Surgical anatomy Limbus Surgical entry into the anterior chamber usually occurs through the peripheral cornea, limbus, and at the limbal– scleral junction (Fig. 9.5). Most approaches for anterior uvea and glaucoma surgeries enter the anterior chamber at the limbus (‘blue zone’), but may be accompanied by limited hemorrhage. Peripheral corneal incisions are usually used for cataract and lens removals, are performed faster, and preferred by most veterinary ophthalmologists. The limbus–

scleral incision is not usually performed because of the resultant hemorrhage but offers the possibility of the least postoperative corneal astigmatism. The limbus (‘blue zone’) is the 0.5–1.0 mm junction of the clear cornea and opaque white anterior sclera (Fig. 9.6). The limbus may contain some pigmentation (especially laterally), and a few small blood vessels. On its anterior surface the non-keratinized squamous epithelium of the cornea begins to transform to keratinized squamous epithelium of the bulbar conjunctiva. The limbus prevents direct observation of the anterior chamber angle and the aqueous humor outflow passages into the ciliary or sclerociliary cleft. In this zone regular corneal stroma lamellae begin to form the irregular dense connective tissues of the sclera. Blood vessels, absent in the normal cornea, are present in the anterior scleral tissues next to the limbus. The outer anterior boundary of the limbus is the transition of the corneal epithelia into conjunctival epithelia, and the inner posterior boundary is the termination of

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Pupillary margin, iris Basal (peripheral) iris Pectinate ligaments Sclerociliary cleft

Cornea Anterior chamber Posterior chamber

Zonules Pars plicata ciliaris Pars plana ciliaris Ora ciliaris retinae Fig. 9.5 Relationships of the iris and ciliary body to the other structures of the eye.

Fig. 9.6 The surgical limbus is the area between the external transition of the corneal to conjunctival epithelium (A) and the internal termination of Descemet’s membrane, anterior insertions of the pectinate ligaments, and anterior border of the corneoscleral trabeculae (B). H & E, 25.

Descemet’s membrane, insertion of the primary pectinate ligaments, and the corneoscleral trabecular meshwork. Hence, limbal incision and entry of the anterior chamber is just caudal of the termination of Descemet’s membrane and anterior to the insertion of the pectinate ligaments and the anterior chamber angle.

portion of the anterior lens capsule. The central iris is often most pigmented and subject to marked changes in thickness. Iridal color changes occur in these species in response to chronic inflammations and intraocular neoplasms with progressive pigmentation. The animal iris is comprised of highly vascular, friable, and spongy tissues and, in contrast to humans, will usually hemorrhage when incised by a sharp scalpel or scissors. Dorsal and ventral branches from the medial and lateral long posterior ciliary arteries and veins enter the basal iris or anterior ciliary body to form an incomplete vascular circle providing the majority of the blood supply to the anterior uvea (Fig. 9.7). In dogs, this incomplete vascular annular circle occupies the basal iris in about 50% of animals; in the remaining animals the vascular circle is positioned in the anterior portion of the ciliary body. As a result, hemorrhage occurs about one-half of the time when the basal iris is incised. Radial arteriolar branches from this circle terminate in capillary beds in the animal pupil. The minor arteriolar circle of the iris, observed in humans, is lacking or incomplete in many animal species. Incision of the basal iris of animals is expected to hemorrhage and may require cautery for hemostasis, which, if possible, should be performed with the peripheral iris protracted from the anterior chamber. The inflamed animal iris can markedly thicken; this increased thickness is a significant deterrent to surgicaland laser-produced iridotomies, and unfortunately these small holes will usually seal and close within a few days. The animal iris is remarkably similar microscopically among the mammalian animal species, with often the main difference being the size and shape of the pupil. The iris separates the anterior and posterior chamber, with the former considerably larger. Aqueous humor, produced primarily by ciliary body processes, flows from the posterior chamber, through the pupil to enter the anterior chamber, and eventually exits the conventional and uveoscleral outflow passages. The different layers of the iris (from anterior to posterior) include: 1) the anterior border; 2) stroma and iridal sphincter musculature; and 3) the posterior epithelial layers including the iridal dilator muscles (Fig. 9.8). The anterior border of the iris, consisting of fibroblasts and melanocytes, has direct contact with the aqueous humor,

Iris The most striking gross difference between the cat and dog irides, and the horse and cow irides, is the shape of the pupil. The round pupil of the dog, when the anterior uveal tissues are severely inflamed, becomes very small and subject to temporary or permanent occlusion. In contrast, the vertical slit pupil of the domestic cat, and the horizontal oval pupil of the horse and cow with its considerable pupillary margin length, are less likely to occlude secondary to iridocyclitis. Nevertheless, iris bombe´ glaucoma from pupillary occlusion may occur in these three species, but are less common. Iridal coloration also varies between species, and among the different breeds of these species. The central portion of the iris with a normal size pupil usually touches the axial

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Fig. 9.7 The base of the iris in both dogs and cats often contains large blood vessels that restrict the benefits of basal iridectomies, and can hemorrhage profusely when transected. H & E, 100.

Surgical anatomy

Ciliary body

Fig. 9.8 The iridal sphincter muscle is located at the pupillary margin and is the dominant muscle affecting pupil size in mammals. H & E, 100.

and forms a more-or-less continuous cellular surface. The iris stroma consists of fine collagenous fibers, fibroblasts and melanocytes, and numerous blood vessels. The considerable extracellular spaces accommodate the physical changes in iris size secondary to the variations in pupil size. The iridal sphincter, a non-striated muscle in the dog, cat, horse, and cow, and a striated muscle in birds, is located in the stroma near the pupil margin. In mammals, the iridal sphincter muscle is innervated by ciliary parasympathetic fibers from the ciliary ganglion within the orbit, but sympathetic innervation has also been demonstrated. The posterior layer of the iris is formed by the dilator muscles and the posterior iridal pigmented epithelium. The iridal dilator muscles, arranged like the spokes of a wheel, are highly developed pigmented myoepithelial cells, innervated primarily by the sympathetic fibers from the cranial cervical ganglion in mammals. The single layer posterior iridal epithelium is heavily pigmented and has direct contact with the posterior chamber and anterior surface of the lens. In the avian species, pupil size and motility are under voluntary control, and light-induced testing of pupil reflexes of very limited value. If one undertakes entry into the anterior chamber and even cataract surgery in the avian species, the commercially available mydriatics have no effect. Often systemic ketamine is part of the avian general anesthesia protocol and can maintain a dilated pupil during anterior chamber, iris, and lens surgeries. Alternatively, intracameral use of non-depolarizing neuromuscular blocking agents has been described for mydriasis during cataract surgery in birds. The corpora nigra (also known as granula iridica) are numerous black nodules or masses on the upper pupillary border and fewer small nodules on the ventral pupillary border of the iris in the horse and cow, and are especially well developed in South American camelids or cria (llamas, alpaca, etc.). Their function seems to assist the horizontal oval pupil in limiting light entry through the lens and vitreous, and to the retina. Fortunately, the corpora nigra are relatively avascular. They may become cystic, avulse secondary to trauma or undergo atrophy, or form synechiae to either the anterior lens capsule or posterior cornea secondary to chronic inflammation.

The ciliary body is the second component of the anterior uvea, and continues posteriorly with the choroid. The ciliary body has contact with both anterior and posterior chambers, the sclera externally, the lens and vitreous internally, and the retina and choroid posteriorly (Fig. 9.9). The ciliary body is the principal source of aqueous humor, controls accommodation, and is important in the control of intraocular pressure (IOP). Aqueous humor is produced by active secretion by the non-pigmented ciliary body epithelium and by ultrafiltration from the capillaries in the ciliary body processes. Aqueous humor provides nutrients and removes waste products for the lens, anterior vitreous, iris, and posterior cornea. Aqueous humor, once leaving the ciliary body processes, enters the posterior chamber, traverses the pupil, and exits the anterior chamber through the iridocorneal angle and trabecular meshwork including the cilioscleral cleft or sinus within the anterior aspect of the ciliary body, or posteriorly through the uveoscleral route. Hence, the aqueous humor dynamics of the ciliary body are directly related to maintenance of IOP, essential for most of the intraocular tissues’ health and functions. The ciliary body, through its musculature, changes the tension on the zonulary attachments to the lens equator, and effects accommodation. Accommodation, or changes in the anterior–posterior length of the lens, appears minor in most mammals, and is seen mainly in young animals. Accommodation and the ciliary body musculature in non-human primates, some avian species, and humans are highly developed. The ciliary body is divided grossly into: 1) anterior pars plicata (corona ciliaris or ciliary processes), and 2) posterior pars plana ciliaris. The anterior pars plicata consists of about 70 major and minor ciliary processes, the primary source for aqueous humor formation and the attachment of the zonules. The posterior flat pars plana ciliaris extends from the ciliary processes to the periphery of the retina, and serves as the termination for some of the lenticular zonules. Each quadrant of the pars plana ciliaris varies markedly in thickness by fractions of millimeters, and these differences are critical when entry into the vitreous

Fig. 9.9 The anterior uvea consists of the iris and ciliary body. Base of the iris (A), iridal pupillary margins (B), and ciliary body: pars plicata ciliaris (C) and pars plana ciliaris (D). SEM, 25. (Courtesy of Dr Don Samuelson, University of Florida.)

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is attempted as during retinal detachment surgery in the dog, cat, and horse. The pars plana ciliaris varies in width, with the ventral and medial aspects the shortest in the dog and cat. In dogs, the posterior boundary of the pars plana ciliaris is 8 mm from the limbus dorsally and laterally, but only 4 mm behind the limbus ventrally and medially. Hence, entry into the anterior vitreous space through the pars plana ciliaris is usually through the larger dorsal and lateral quadrants. In horses, the width of the ciliary body and, in particular, the pars plana ciliaris also varies by quadrant. These pars plana ciliaris widths range from 2.92 mm dorsally, 3 mm temporally or laterally, 0.33 mm nasally or medially, and 2.33 mm ventrally in fresh enucleated globes. Measurements by Fru¨hauf et al for 12 o’clock vitrectomy suggest that the width of the dorsal equine pars plana ciliaris ranges from 7 to 12.06 mm posterior to the limbus, with an average of 5.06  0.58 mm. Fortunately, both exposure of the eye and the dorsal quadrant of the pars plana ciliaris (about 3 mm wide) accommodate the single port vitrectomy in the horse. These measurements may also be increased when the equine eye is enlarged from glaucoma. Microscopically the ciliary processes consist of a core of stroma rich in blood vessels, and two layers of epithelium (Fig. 9.10). The inner non-pigmented ciliary epithelium’s primary function is the formation of aqueous humor. It continues posteriorly as the inner neurosensory retina. The non-pigmented ciliary epithelia are linked to each other with tight gap junctions that represent ultrastructurally the blood–aqueous barrier. The deeper pigmented ciliary epithelium provides the majority of the pigmentation of the ciliary processes. The core of connective tissue and blood vessels within the ciliary process supply the energy needs of the two layers of epithelia, and the ultrafiltration portion of the aqueous humor. The more external aspect of the ciliary body consists of smooth muscles. With limited accommodation, the primary ciliary body musculature in the cat and dog is meridionally arranged and extends to the iridocorneal angle, forming the collagen beams for the trabecular meshwork. These ciliary muscles are richly innervated with

Fig. 9.10 The ciliary body’s main function in dogs and cats involves the formation of aqueous humor. The ciliary body process consists of a layer of non-pigmented and pigmented epithelia, and a central core rich in blood vessels. H & E, 100.

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parasympathetic nerve endings. Ciliary blood vessels are surrounded with numerous sympathetic nerve endings.

Iridocorneal angle The anatomy of the iridocorneal angle is presented in Chapter 10. The pathogenesis of most animal primary and secondary glaucomas appears to result from diseases of the outflow pathways, with the subsequent increase in resistance to aqueous humor outflow, and increase in IOP.

Pathophysiology Surgical entry of the anterior chamber elicits an acute inflammatory response by the anterior uvea (iris and ciliary body) which is mediated by the release of prostaglandins. Similarly, the surgical approach to the iris and ciliary body usually involves entry into the anterior chamber. The highly vascular sclera presents a significant barrier for entry to the iris, ciliary body, and posterior segment (including the vitreous space and retina). Cautery of the sclera is often necessary to control hemorrhage. Because penetration of the retina may result in retinal detachment, access for vitreous and retinal surgeries is limited to the pupillary approach, or through incisions in the pars plana ciliaris. The pathophysiology of the anterior uvea during intraocular surgery includes several significant considerations. Both the iris and ciliary body are highly vascular. Tearing with forceps or incisions with scissors or scalpel result in variable hemorrhage. Control of the iridal and ciliary body hemorrhage requires strategies that can be effective in the presence of aqueous humor and blood. Judicious wet-field cautery, diode laser, intracameral adrenaline (epinephrine) injections, and viscotamponade are the usual methods to control anterior uveal hemorrhage. For large bleeders of the iris, wet-field cautery units are superior. Direct surgical trauma or entry into the anterior chamber in the dog and cat results in variable miosis. In some breeds, such as the Miniature Schnauzer, the miosis may result in a pupil of only 1–2 mm (sometimes referred to as atropineor mydriatic-resistant miosis). Pupillary constriction may limit the visualization of the lens or posterior segment, and impede, delay or preclude the surgery. This miosis, previously thought to be associated with the release of histamine or other substances, is now believed to be secondary to the release of uveal endogenous prostaglandins. The prostaglandins elicit an immediate contraction by the iridal sphincter muscles, breakdown of the blood–aqueous barrier at the level of the ciliary body epithelium with the resultant plasmoid or secondary aqueous humor, an acute elevation in IOP with subsequent decrease in IOP (ocular hypotony), and hyperemia of the anterior uveal and bulbar conjunctival blood vessels. Ocular hypotony from anterior uveal inflammation and release of prostaglandins is associated with an increase in the unconventional or uveoscleral aqueous humor outflow through the posterior ciliary body. Administration of non-steroidal anti-inflammatory drugs (NSAIDs) prior to intraocular surgery, and prevention of the release of prostaglandins during anterior chamber entry, may directly affect the eventual success or failure of the surgery. Pre-, peri-, and postoperative administrations of

Surgery of the anterior chamber

topical antiprostaglandins and indometacin, as well as systemic carprofen (RimadylW Pfizer Animal Health, Exton, PA) and flunixin meglumine (BanamineW Schering-Plough, Kenilworth, NJ), are used to suppress the release of intraocular endogenous prostaglandins. As a result, intra- and postoperative control of the pupil in animals with topical mydriatics has become more successful. Simple entry into the anterior chamber to aspirate aqueous humor (anterior chamber paracentesis or keratocentesis), with the resultant decrease in IOP, immediately disrupts the blood–aqueous barrier. The secondary aqueous humor quickly restores the normal volume of the posterior and anterior chambers but contains high levels of albumin and globulins. These proteins result in increased turbidity of the aqueous humor and formation of frank fibrin clots within the anterior chamber. The fibrin clots may serve as scaffolds for attachments of the iris to the lens, posterior lens capsule, posterior cornea, and peripheral cornea. The fibrin clots can also be gradually replaced with fibroblasts, collagen, and pigment cells. The resultant opaque fibrous bands can permanently link the iris to the lens or its capsules, the posterior cornea or the edges of the pupillary margins, resulting in small and irregular pupils that impair vision. Pre- and postoperative treatment with topical and systemic corticosteroids and NSAIDs, and intracameral heparin during surgery help to reduce the formation of intraocular fibrin. Introduction of tissue plasminogen activator (tPA), injected directly into the anterior chamber, can dissolve any existing aqueous humor fibrin and clotted blood within 1–2 weeks post-formation. Intracameral tPA cannot, however, prevent the formation of future aqueous humor fibrin. With any postoperative iridocyclitis, the iris becomes inflamed and thicker than normal. From its inflammatory products the iridal surface becomes sticky and readily adheres to any intraocular tissues it contacts. As a result, temporary to permanent attachments may develop involving the iris and lens (posterior synechiae), the iridocorneal angle (peripheral anterior synechiae), the posterior cornea (anterior synechiae), or its pupillary margins (pupillary synechiae). Permanent iridal contact with the anterior lens capsule results in anterior capsular and anterior cortical cataract formation. Permanent iridal contact with the posterior cornea results in edema and dense corneal scars. Formation of peripheral anterior synechiae within the iridocorneal angle predisposes the eye to angle-closure glaucoma by filling and closing the opening of the sclerociliary cleft. Adherence of the pupillary margins creates an irregular pupil and may completely occlude the pupil, resulting in an immediate iris bombe´ and loss of vision. Treatment strategies to prevent the formation of synechiae are summarized in Box 9.1.

Perioperative considerations As iris and ciliary body inflammation always occurs following anterior chamber penetration and the resulting abrupt decrease in IOP, medical treatments should be implemented pre-, peri-, and postoperatively. If treatment is limited to the postoperative period, less than optimal results should be anticipated. The intensity of postoperative iridocyclitis is variable, and should be assessed daily. With these changes in the intensity of postoperative iridocyclitis, the types and

Box 9.1 •

•

• • • •

Benefits of iridocycloplegia during iridocyclitis

Administration of a mydriatic or combination of mydriatics to constantly change the pupil size, produce iridal movement, and discourage iridal attachments to the lens or posterior cornea. Dilatation of the pupil to position the majority of the iris near the peripheral lens and away from the closer central and visually important axis. Dilatation of the pupil to prevent obstruction with inflammatory materials or formation of annular (360 ) posterior synechiae. Suppress iridociliary inflammation and tissue swelling. Paralyze the iridal sphincter and ciliary body musculature to minimize the pain from iridocyclitis. Restore the blood–aqueous barrier to decrease as much as possible the cellular and protein (fibrin) content of the secondary or plasmoid aqueous humor, and reduce the possibility of formation of fibropupillary membranes.

frequencies of the topical and systemic medications should be adjusted accordingly. The peak in the anterior uveal inflammation after intraocular surgery usually occurs 3–5 days postoperatively. An indirect method of assessing the intensity of the iridocyclitis is to measure IOP daily by applanation tonometry. After the initial elevation in IOP associated with iridocyclitis (which is often missed clinically because it lasts for only a few hours), daily tonometry, performed about the same time each day, can monitor the extent and duration of the ocular hypotony. As the iridocyclitis gradually resolves, IOP will return to normal levels. As a clinical guide, medical treatments should be administered until normal IOP returns. Normal IOP with intense iridocyclitis often signals the onset of secondary glaucoma and the obstruction of the aqueous filtration angle with inflammatory debris and the formation of peripheral anterior synechiae. Preoperative treatment before entry into the anterior chamber or surgery of the iris and ciliary body involves: 1) dilatation of the pupil with a mydriatic (usually 1% atropine or 1% tropicamide) or a combination of mydriatics (1% atropine or 1% tropicamide plus 10% phenylephrine); 2) topical (usually 1% prednisolone or 0.1% dexamethasone) and systemic corticosteroids (e.g., prednisolone 0.5–1.0 mg/kg PO once or twice daily) to suppress preoperative or anticipated postoperative iridocyclitis; 3) topical and systemic NSAIDs and antiprostaglandins to reduce anterior uveal inflammation and assist in maintenance of the dilated pupil during surgery; and 4) topical and systemic antibiotics to prevent bacterial infection if contamination of the anterior chamber occurs during surgery.

Surgery of the anterior chamber Entry into the anterior chamber is usually through the periphery of the cornea or surgical limbus, or by a limbal– scleral incision. As the last approach usually causes hemorrhage from the posterior limbal and anterior scleral blood vessels, the clear corneal and limbal approaches are usually performed. Entry into the anterior chamber may be gained

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by a hypodermic needle, or scalpel blade (Beaver No. 6500 microsurgical blade or 55M (keratome)).

Keratocentesis/anterior chamber paracentesis In keratocentesis a small gauge (25–30) hypodermic needle is inserted into the peripheral clear cornea or limbus to enter the anterior chamber and aspirate a small amount (0.1–0.2 mL) of aqueous humor. Alternatively, this technique may also be used for intracameral injection of materials such as tPA, adrenaline (epinephrine) or antibiotics. The indications for keratocentesis are summarized in Box 9.2. The aqueous humor sample has a limited volume, usually 0.1–0.3 mL. The value of each diagnostic procedure (cytology, culture, protein analyses, antibody titers) may require prioritization and only the most important tests performed (Fig. 9.11). For keratocentesis, short-acting general anesthesia or deep sedation is used to provide restraint. In the horse, general anesthesia or use of a retrobulbar nerve block in conjunction with sedation is required. Topical anesthetic is instilled on the cornea and the eyelids retracted by speculum. Exudates, if present, are removed by sterile cotton swabs and the corneoconjunctival surfaces are flushed liberally with 0.5% povidone–iodine solution. For keratocentesis, a 25–30 g hypodermic needle and 1 mL syringe are used (Fig. 9.12a). A thumb forceps is used to grasp the bulbar conjunctiva and stabilize the eye. The hypodermic needle is directed through the peripheral cornea into the anterior chamber at an angle that avoids contact with the posterior cornea and the anterior iris (Fig. 9.12b). A small volume (0.1–0.3 mL) of aqueous humor is withdrawn. The needle bevel may be positioned down (or toward the iris) to avoiding snagging the iris and to provide a self-sealing needle puncture. The hypodermic needle is carefully retracted. The needle track should be self-sealing; if a small amount of aqueous humor escapes, the needle hole is covered briefly with a sterile cotton swab. Depending on the amount of aqueous humor aspirated, IOP will be decreased proportionally. As a variation of the clear corneal method, the hypodermic needle is inserted in the bulbar conjunctiva 2–4 mm posterior to the limbus (Fig. 9.13a). It is then carefully moved forward subconjunctivally to the limbus, and then inserted through the limbus at an angle between the posterior cornea and anterior iris (Fig. 9.13b). After aqueous humor sampling, the hypodermic needle is carefully and slowly retracted. If some aqueous humor leaks from the limbal penetration, it remains trapped in the bulbar subconjunctival space.

Box 9.2 • • • • •

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Indications for keratocentesis in animals

Aqueous humor cytology may assist in the diagnosis of the anterior uveal inflammation. Aqueous humor culture may determine the infectious organism. Aqueous humor titers to selected diseases. Aspiration of small iris/ciliary body cysts. To abruptly decrease intraocular pressure in patients with medically non-responsive glaucoma.

Fig. 9.11 Anterior uveitis and hypopyon in a shorthair cat with infectious peritonitis. Note the hypopyon also contains limited hemorrhage. The anterior uveitis affects both eyes.

A

B

Fig. 9.12 Keratocentesis through the peripheral cornea. (a) The von Graefe thumb forceps is used to stabilize the eye and the hypodermic needle is inserted through the peripheral cornea. (b) The angle of the needle pathway must avoid the anterior iris and posterior cornea.

A

B

Fig. 9.13 Keratocentesis through the limbus and under the bulbar conjunctiva. (a) With the von Graefe thumb forceps holding the bulbar conjunctiva and globe, the hypodermic needle is inserted in the bulbar conjunctiva about 2–4 mm posterior of the limbus. The needle is advanced subconjunctivally to traverse the limbus. (b) The hypodermic needle angle is between the anterior iris and posterior cornea.

An alternative keratocentesis technique uses two 1 mL syringes connected by a two-way stopcock, and a single 25–30 g hypodermic needle. One syringe is used to aspirate 0.1–0.3 mL of aqueous humor; the other is filled with 0.5 mL sterile lactated Ringer’s or balanced salt solution (BSS), and is used to refill the anterior chamber with a volume equal to the aqueous humor removed (Fig. 9.14). This technique immediately replaces the lost aqueous humor, reduces the influx of the plasmoid or secondary aqueous humor, avoids any ocular hypotony, and requires only a single needle penetration into the anterior chamber.

Surgery of the anterior chamber

shifting of the lens and vitreous, and retinal and/or choroidal detachments. While keratocentesis temporarily lowers IOP in glaucomatous eyes, the resultant release of anterior uveal prostaglandins may elevate the IOP further within a few hours. Hence, keratocentesis is recommended to lower IOP only after intensive antiglaucoma medical therapy, including intravenous mannitol, has failed to lower IOP to safe levels, or immediately before an appropriate glaucoma surgery is performed. When used for acute glaucoma, a 30 g needle should be used without a syringe, allowing the needle hub to passively fill and the IOP to be gradually reduced. This will help to minimize complications such as an expulsive choroidal hemorrhage.

Fig. 9.14 Use of two syringes, stopcock, and a single hypodermic needle permits keratocentesis and restoration of the lost aqueous humor as a single procedure.

Corneal/limbal incisions

When injecting materials intracamerally, a tuberculin syringe and 30 g needle are used. The volume to be administered is generally about 0.1 mL in small animals and up to 0.3 mL in large animals, and usually requires removal of an equal volume of aqueous humor before injection of the agent. The total volume to be administered should be the total volume in the syringe. The anterior chamber is entered in the same manner as for keratocentesis, the material injected, and the syringe removed as for keratocentesis. Leakage of a small volume of aqueous humor is acceptable as this will help maintain a more normal IOP since the anterior chamber has been volume-expanded. Post-keratocentesis treatment includes topical mydriatics, antibiotics, and corticosteroids to control the resultant mild iridocyclitis. As any pre-existing iridocyclitis is usually intensified by keratocentesis, the benefits and risks of keratocentesis should be ascertained. Complications after keratocentesis are infrequent. Keratocentesis is used experimentally to break down the blood– aqueous barrier, and markedly elevate serum proteins in the resultant (secondary or plasmoid) aqueous humor. These effects seem directly related to the release of prostaglandins from the anterior uvea. After keratocentesis, the anterior chamber is quickly reformed with new (secondary) aqueous humor rich in proteins (plasmoid aqueous). This secondary aqueous humor frequently contains fibrin clots. In glaucomatous eyes, keratocentesis acutely decreases IOP, but may worsen iridocorneal angle closure. A misdirected hypodermic needle can penetrate the posterior cornea, creating a temporary corneal opacity secondary to penetration of Descemet’s membrane. If the hypodermic needle touches the iris, limited hemorrhage may result. If iridal hemorrhage occurs, the secondary aqueous humor contains additional levels of serum proteins. The use of anterior chamber paracentesis in glaucomatous eyes has a potential benefit of lowering medically nonresponsive elevated IOP to reduce damage to the optic nerve and retina versus the risks of causing further anterior chamber angle closure, intraocular hemorrhage, forward

Surgical entry into the anterior chamber is the fundamental step in most intraocular procedures. For surgery involving the iris, ciliary body, certain glaucoma procedures, phacoemulsification, extracapsular and intracapsular lens extraction, proficiency in performing clear corneal or limbal incisions into the anterior chamber is essential. In the 1950s and 1960s, entry into the dog and cat anterior chamber was through the limbus under a limbal- or fornix-based bulbar conjunctival flap. Since the 1980s, the clear corneal incision has become popular in all animal species. Clear corneal incisions can be performed rapidly, avoid limbal blood vessels and any hemorrhage, and are easier to appose with simple interrupted or continuous sutures. However, without protective cover by the bulbar conjunctiva, exact apposition of the corneal incision is essential to maintain the integrity of the wound and IOP postoperatively. The peripheral cornea and limbus may be incised perpendicular to the corneal surface, as a beveled incision to the corneal surface, or an incision that combines both perpendicular and beveled characteristics (Fig. 9.15). Those entries that include a beveled or angled entry into the anterior chamber are self-sealing. Entry into the anterior chamber that involves incisions that are perpendicular to the corneal surface are not self-sealing, but result in the least corneal scar formation. Limbal incisions are usually performed under a limbal- or fornix- based bulbar conjunctival flap. If a limbal-based conjunctival flap is used, the flap is usually only 3–5 mm wide to minimize its adverse effect on observation of the anterior chamber during iris and lens surgeries. Sutures for closure of the limbal wound may be buried under the limbal- or fornix- based conjunctival flap, or the knots may be exposed at the external limbus. Suturing of the limbal wound under a limbal-based conjunctival flap is more tedious as braided sutures often snag on the flap. Selection of ophthalmic scissors determines the type of corneal incision. Corneal scissors provide corneal incisions perpendicular to the corneal surface. Corneal section or corneoscleral scissors provide corneal incisions at an oblique angle. Corneal scissors are used to completely incise the cornea; the resultant wound edges are perpendicular to each

A

B

C

Fig. 9.15 The different types of corneal and limbal incisions. (a) Perpendicular to the corneal surface. (b) Beveled incision. (c) Combination perpendicular–beveled, most popular.

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other. Corneal cataract section or corneoscleral scissors provide beveled or angled incisions of the cornea or limbus. They may be for full-thickness incisions, creating a completely beveled limbal incision. This type of incision provides a larger wound surface area, is self-sealing, and apposition with sutures is less exacting. However, the wound edges can slide during suture apposition, resulting in greater corneal scarring. The most useful variation for a longer clear corneal or limbal incision is to combine an outer perpendicular incision using the Beaver No. 6400 microsurgical blade, and an inner beveled incision performed with the corneal section or corneoscleral scissors. The resultant incision is self-sealing, has a large surface area for healing and apposition, and the edges do not slip. The initial outer scalpel incision also provides a track for the deeper incision with the corneoscleral scissors. The length of the clear corneal or limbal incision varies with the surgical procedure. For entry into the anterior chamber to permit insertion of small thumb forceps to retrieve iris/ciliary body cysts, penetrating foreign bodies, or immature heartworms (Dirofilaria immitis), the incision is usually 4–6 mm long (or at least 140 ). The incision should be of sufficient length that the ends are not damaged or torn during intraocular manipulations with the ophthalmic instruments. For most surgical procedures of the iris, ciliary body, glaucoma, and lens using extra- and intracapsular lens extractions, the clear corneal incision approximates 150–180 . The incision must be sufficiently long to accommodate the essential intraocular instrument manipulations within the anterior chamber but without contact with the posterior cornea. In the different stages of cataract formation, the overall lens size varies. Accurate estimation of cataract size allows a minimal length corneal or limbal incision, but of sufficient length to permit cataract extraction without causing additional difficulty and damage to the corneal endothelium. For phacoemulsification, the length of the clear corneal incision depends on the diameter of the phaco probe (usually 3–4 mm) and the diameter of the intraocular lens (if one is inserted). Apposition of all three types of clear corneal and limbal incisions is by simple interrupted or one to two simple continuous absorbable 6-0 to 8-0 sutures. One author (KNG) prefers simple interrupted sutures using polyglactin 910 braided material, especially when the corneal incision is longer than 3 mm. These sutures, which are stable in infected tissues, reabsorb within 6–8 weeks. When first attempting these procedures, simple interrupted sutures are recommended. With additional experience, the incision apposition is divided into two or a single simple continuous 6-0 to 7-0 absorbable suture pattern. The other author (DAW) prefers a double continuous pattern using 9-0

Fig. 9.16 Depth for corneal and limbal sutures for optimal apposition. (a) Recommended depth is about two-thirds thickness of the stroma. (b) Sutures too superficial result in incomplete posterior apposition and additional edema and scarring. (c) Sutures that penetrate the entire cornea permit aqueous humor (arrows) to enter the cornea, and may allow the corneal epithelia to enter the anterior chamber along the suture track.

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A

monofilament polyglactin 910 or, if a larger suture is preferred, 8-0 braided polyglactin 910 in a simple continuous pattern. Successful clear corneal or limbal sutures must be placed in two-thirds thickness of the stroma (Fig. 9.16a). Sutures placed in the anterior one-third of the corneal stroma do not provide adequate wound apposition, as the posterior stroma, Descemet’s membrane, and the endothelium are not adequately apposed (Fig. 9.16b). Sutures that penetrate all layers of the cornea, including Descemet’s membrane, permit exposure of the stroma to aqueous humor, are generally associated with more corneal edema, and are a potential pathway for the corneal epithelium (corneal epithelialization) or bacteria to migrate into the anterior chamber (Fig. 9.16c).

Surgical treatment of hypopyon, hyphema, and anterior chamber foreign body or parasites Surgery for hypopyon The presence of pus (hypopyon) or blood (hyphema) in the anterior chamber occasionally necessitates surgical removal. Removal of this debris from the anterior chamber is usually for diagnosis but occasionally it is a therapeutic procedure. Generally the preferred treatment for hypopyon is to medically reduce the intensity of the underlying iridocyclitis and reduce the rate of its formation. Hypopyon is a collection of cells, fibrin, and proteins. Cells can include the different types of leukocytes, erythrocytes, macrophages, and even neoplastic cells. Aqueous proteins include albumin, globulins, antibodies, and fibrin. The latter tends to hold cells together, and gravitates to the ventral anterior chamber. Hypopyon, usually the result of iridocyclitis, and primary or secondary intraocular neoplasms, is rarely associated with elevated IOP. Hypopyon may be aspirated in an attempt to determine the cause of the anterior uveal inflammation or the type of intraocular neoplasia (Fig. 9.17).

Surgical removal/aspiration Most often, a hypodermic needle is inserted through the peripheral cornea or the limbus under 2–3 mm of bulbar conjunctiva. Because of the cellular and protein consistency, a 20–22 g hypodermic needle may be indicated, as small diameter needles tend to plug. Entry into the anterior chamber with the hypodermic needle or scalpel blade requires deep sedation or preferably a short-acting general anesthesia (propofol).

B

C

Surgery of the anterior chamber

Fig. 9.18 Hyphema or hemorrhage in the anterior chamber may result from trauma, inflammation, intraocular neoplasms, retinal detachments, and blood clotting disorders. This clotted hemorrhage in the anterior chamber is the result of trauma. Fig. 9.17 Anterior uveitis and hypopyon in a cat. Note the presence of small foci of fresh blood clots within the hypopyon. As this condition is bilateral, cytologic examination of these cells may help establish the cause of the iridocyclitis.

Surgery for hyphema Hyphema or blood in the anterior chamber may be secondary to trauma, congenital ocular anomalies (such as retinal detachments), anterior uveal inflammations, primary and secondary intraocular neoplasms, certain systemic diseases (such as ehrlichiosis (Ehrlichia canis) and Rocky Mountain spotted fever (Rickettsia rickettsii)), several vascular diseases (such as immune-mediated thrombocytopenia), and systemic hypertension. The appearance of hyphema may suggest its cause. Clotted blood in the anterior chamber may indicate trauma or the cessation of the source of bleeding (Fig. 9.18). Clotted hyphema suggests that fibrin is present, as well as intraocular inflammation. Multiple layers of blood in the anterior chamber, in which the dorsal aspect is bright red and the ventral portion is deep purple, suggest recurrent episodes of bleeding. In older dogs and cats, hyphema, combined with glaucoma or iridocyclitis, is often secondary to primary and secondary intraocular neoplasia. Hyphema that results from intravitreal hemorrhage (often associated with retinal detachments) often contains little fibrin and tends to gravitate in the anterior chamber and level dorsal surface. In older dogs with advanced renal disease, with and without hypothyroidism, systemic hypertension may be the cause. Hyphema in older cats is often secondary to retinal and choroidal hemorrhages, retinal detachments, and systemic hypertension. Once the hyphema is sufficiently reabsorbed, the deeper intravitreal hemorrhage can be directly visualized. Hyphema that prevents complete examination of the lens and posterior segment is an indication for ocular ultrasonography. This is especially true in the case of ocular trauma as is often seen in the horse. Ultrasound is performed transcorneal or transpalpebral, depending on the health of the cornea, using a 7.5–20 mHz probe. The eye is evaluated for abnormalities of the lens with respect to position and

integrity, presence of blood in the vitreous, retinal detachment, foreign body, and the integrity of the posterior eyewall. Aspiration of hyphema is usually reserved for diagnostic purposes, to clear the anterior chamber to permit examination of the iris, lens, and posterior segment, and rarely if elevated IOP appears secondary to the hyphema. Hyphema is highly cellular and a 20–22 g hypodermic needle is recommended to aspirate the anterior chamber. Even the larger hypodermic needles run the risk of becoming plugged. This technique is not without significant risk and is a procedure of last resort. Hence, removal of part or all of a large hyphema may be expanded to include: 1) a peripheral clear corneal incision 3–4 mm long, and 2) lavage of the anterior chamber with balanced salt or lactated Ringer’s solution to flush liquefied blood and/or blood clots from the anterior chamber. Large blood clots may be carefully removed by fine thumb forceps with serrated tips; however, if the blood clots have adhered firmly to the anterior iridal surface, secondary hemorrhage may result. Any blood clot removed from the anterior chamber should be examined microscopically for possible neoplasia.

Enzymatic therapy for hyphema Injection of various enzymes into the anterior chamber may be used to dissolve blood clots. In the rabbit, reabsorption of blood clots in the anterior chamber involves digestion of the fibrin matrix and egress of intact erythrocytes from the iridocorneal angle. Fibrin tends to hold the erythrocytes and impede the exit of these cells. Erythrocytes that hemolyze are eventually phagocytosed by macrophages, usually a very slow process. Although several enzymes have been evaluated, only two, i.e., urokinase and tPA, have been effective, and the latter most beneficial. Intracameral injections of urokinase have had variable success in resolving hyphema. Within the past few years, intracameral (25–50 mg) tPA has offered improved success rates in dogs, cats, and horses, provided the hyphema and

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fibrin are less than 10–14 days old. However, excessive levels of tPA can be toxic to the retina; doses of tPA exceeding 50 mg in cats have produced retinal damage. Ideally, intracameral tPA is injected several days after hyphema (to allow clotting/sealing of the bleeding vessels and avoid re-bleeding), but before 10–14 days while the enzyme is still effective.

Anterior chamber foreign body and parasites Parasites, such as Dirofilaria immitis in dogs, Cuterebra larvae in cats, and Setaria digitata in horses, occasionally enter the anterior chamber, cause clinical signs of anterior uveitis and variable corneal edema, and can be removed (Fig. 9.19). These parasites are visible and mobile within the anterior chamber, can occasionally traverse the pupil, and infrequently enter the vitreous. Hence, in their manual removal through a 3–4 mm clear corneal incision, a small serrated thumb forceps is inserted to grasp the mobile parasite and carefully remove it in its entirety. Anterior chamber or penetrating foreign bodies (FB) are infrequent in dogs, cats, and horses. FBs consisting of vegetative material are apt to also carry bacteria or fungal organisms into the anterior chamber and should be carefully removed. Shotgun pellets generally seal their corneal wounds and appear as slightly tan areas, and do not require surgical removal. If the lens is penetrated by the pellet, lens removal by phacoemulsification should be considered, as the gradual release of lens material through the lens wound causes a progressive and eventually medically refractory anterior uveitis.

Postoperative management and complications Entry into the anterior chamber to recover part of a hypopyon usually intensifies the existing iridocyclitis. In fact, therapy of selected cases of chronic iridocyclitis may include keratocentesis to stimulate and hopefully resolve the inflammation. Keratocentesis for hyphema results infrequently in

secondary or recurrent hemorrhage. The abrupt decrease in IOP during keratocentesis apparently causes the damaged blood vessels to again hemorrhage. Use of the two-syringe technique to restore the anterior chamber volume and IOP immediately after keratocentesis is recommended for eyes with hyphema. Medical treatment after keratocentesis is directed at the underlying disease. Often topical mydriatics, antibiotics, and corticosteroids are administered. Keratocentesis is not usually injurious to the clinical management of most ophthalmic diseases, often aids diagnosis of the disease process, and occasionally assists in focusing therapy for anterior uveal diseases.

Surgical procedures of the anterior uvea Both iris and ciliary body are friable and highly vascular tissues that tear and hemorrhage readily. Both tissues are highly pigmented and require additional illumination during surgery for observation. These pigmented tissues are also excellent targets for laser therapy. The surgical approach to the iris and ciliary body is generally through a peripheral corneal or limbal incision (addressed in a previous section in this chapter). Anterior chamber entry and surgical manipulations of the iris, ciliary body, or a combination of both, elicit a variable but often intense inflammation. As a result, topical and systemic corticosteroids and NSAIDs are used to temper and control the anterior uveal inflammation. Failure to adequately control the postoperative iridocyclitis can markedly decrease the possibility of a successful outcome. In addition, intracameral adrenaline (epinephrine) for vasoconstriction will minimize vascular leakage of fibrin, and help to avoid and manage hemorrhage. Finally, use of viscoelastic agents to maintain space, project, and manipulate tissues, and as a means of viscotamponade, will also greatly improve outcome. Medical treatment of these patients following surgery usually spans several weeks. In this section, the common surgeries of the iris and ciliary body are presented. These procedures include: 1) iridotomy (creating a small hole or incision of the iris by scalpel blade, scissors, or laser); 2) sphincterotomy (one or more incisions of the iridal sphincter muscle to enlarge the pupil or impede miosis); 3) coreoplasty (creation of a larger pupil by the excision of iridal tissue and/or inflammatory pupillary membranes to improve vision and aqueous humor flow through an existing small and/or paracentral pupil); 4) iridectomy (removal or biopsy of a sector or small region of the iris); 5) surgical treatment of iris bombe´; and 6) iridocyclectomy or sclerouvectomy (excision of a section of iris and ciliary body with or without a scleral homograft). The treatment and clinical management of iris prolapse have been addressed in Chapter 8 under corneal ulceration and full-thickness corneal lacerations.

Iridotomy Fig. 9.19 Iridocyclitis and corneal edema, secondary to the parasite, Dirofilaria immitis, in the anterior chamber in a dog. Treatment is removal of the parasite through a limbal or corneal incision. Often some corneal edema remains long term.

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In the iridotomy procedure, the full-thickness iris is incised by iris scissors or scalpel blade, or photocoagulated by laser. Neodymium:yttrium aluminum garnet (Nd:YAG) laser photocoagulation has been used to create full-thickness holes in the canine iris; however, these holes are usually temporary,

Surgical procedures of the anterior uvea

healing closed in a few weeks. There are considerable differences between normal dog and cat irides, and irides affected with inflammation and neoplasia. The cat and dog inflamed iris can be two to four times thicker than normal; hence, production of surgical or laser-produced full-thickness holes is difficult. Chronic iritis in both dogs and cats may result in the formation of pre-iridal fibrovascular membranes which include capillaries; presumably these vessels are also sources of hemorrhage and fibrin. These irides hemorrhage more readily after contact with iris forceps and incision by iris scissors or cautery, and release more fibrin postoperatively. Hence, the results of iris surgery in normal dogs and cats cannot be directly transferred to clinical patients, and usually yield superior results compared to the clinical patients. Iridotomies may be used to construct alternative pathways for the flow of aqueous humor from the posterior chamber to the anterior chamber when aqueous passage through the pupil is impossible. Often iridal holes constructed during iridotomies will heal closed in several weeks, unless very large. Laser-induced iridotomy, at sites approximately twothirds the distance from the pupil to the base of the iris, employing the diode laser using short duration (200– 500 ms) and lower power (200–500 mW), produced a focal burn with hyperpigmentation, dyscoria, and pigment dispersion into the anterior chamber, but no evidence of a visible patent iridotomy in normal dogs. Histologically, there was focal coagulation necrosis and thinning of the iris stroma, and some loss of the iridal pigmented epithelium, but no definitive iridotomy or communication between the anterior and posterior chambers. In the iridotomy surgical procedure, the middle one-third of the dorsal iris is incised by iris scissors to avoid the iridal sphincter muscle at the pupil and the base of the iris which contains the major arteriolar circle which occurs in at least 50% of dogs. If the iris is greatly thickened, cautery may substitute for iris scissors to incise as well as cauterize for hemostasis. For iridal cautery, retraction of the iris above the remaining aqueous humor within the anterior chamber is recommended. After general anesthesia, clipping of the eyelid hair, and preparation of the eyelids, corneal and conjunctival surfaces with 0.5% povidone–iodine solution, an eyelid speculum is inserted to retract the eyelids. The limbal or clear corneal incision should be directly adjacent to the iridotomy site. Entry into the anterior chamber may be through a clear corneal incision, or under a limbal- or fornix-based conjunctival flap and through the limbus. In this example, the iridotomy is performed through the limbus and under a fornix-based conjunctival flap (Fig. 9.20a). The initial partial-thickness incision, perpendicular to the limbus and within clear cornea, is by the Beaver No. 6400 microsurgical blade (Fig. 9.20b). Entry into the anterior chamber, in the center of the limbus, is by Beaver No. 6500 microsurgical blade or keratome (Fig. 9.20c). After the stab incision into the anterior chamber and release of aqueous humor, the limbal incision is lengthened to 10–15 mm (90–140 ) with right- and lefthanded corneoscleral scissors to permit access to the iris (Fig. 9.20d). Intracameral 1:10 000 adrenaline (epinephrine) and a viscoelastic agent are used for pupil dilatation and vasoconstriction, and to reform the anterior chamber. For iridotomy of the mid iris, the surface of the iris is carefully protracted by thumb forceps (Fig. 9.20e) and carefully

excised by DeWecker iris scissors (Fig. 9.20f). Hemorrhage may be controlled by point electrocautery. Alternatively, both iridotomy and hemorrhage can be performed by electrocautery. When iridal hemorrhage is excessive, several procedures may be employed for hemostasis, including: 1) re-inflate the anterior chamber using a viscoelastic material, allow time for clotting, and then gently irrigate the clotted blood from the anterior chamber; 2) irrigate the anterior chamber with 1:1000 adrenaline (epinephrine) (when using adrenaline the patient should not be under halothane inhalational anesthesia, and isoflurane should be selected instead); 3) limited and judicious wet-field cautery of the incised edges of the iris may attempted, but contact with the posterior cornea and anterior lens must be avoided; or 4) about 4–7 days postoperatively (after sufficient time for the iridal blood vessels to seal) inject 25–50 mg tPA into the anterior chamber to facilitate clot dissolution. The limbal incision is apposed by 8-0 to 9-0 simple interrupted absorbable sutures about 1–1.5 mm apart (Fig. 9.20g). Before placement of the last one or two sutures, the viscoelastic agent is irrigated from the anterior chamber with lactated Ringer’s solution, preferably using an automated irrigation/aspiration system, and any additional blood clots removed. After the limbal incision is completely apposed, a small gauge hypodermic needle is carefully inserted between two sutures to reform the anterior chamber and check the integrity of the closure. Intraocular pressure at this time should approximate 10–15 mmHg. The fornix-based conjunctival flap is apposed with a 7-0 to 8-0 simple continuous absorbable suture. Postoperative management after iridotomy includes topical and systemic antibiotics, corticosteroids, and NSAIDs. Pupil dilatation and movement is achieved by changing the daily frequency of the mydriatics, 1% atropine or 1% tropicamide, and, if necessary, 10% phenylephrine. Extreme mydriasis risks closure of the iridotomy site, but the miosis that occurs with postoperative iridocyclitis can result in posterior synechiae formation, and pupil movements can minimize formation of posterior synechiae. Postoperative complications after iridotomy are infrequent. With iridotomies, surgically induced small iridal holes may heal closed within several weeks. Formation of excess fibrin and failure to eliminate its presence in the anterior chamber provide the scaffolding for fibropupillary formation with attachments in the pupil or the iridal incision. Elevated IOP is a concern, as the preoperative pupil may be very small, and from the pre-existing iridocyclitis, peripheral anterior synechiae, and aqueous humor outflow may be compromised. Hence, daily applanation tonometry is recommended to monitor IOP. If elevations in IOP occur, gonioscopy to observe the iridocorneal angle is indicated. Overall results after iridotomy in dogs and cats are good; however, smaller iridal defects may seal within 1–2 months. Hence, beneficial effects from iridotomy are often temporary.

Sphincterotomy A variation of the iridotomy procedure that is useful in dogs and cats is the sphincterotomy procedure in which one or more 1–2 mm long incisions of the iridal sphincter muscle result in a more dilated and irregular pupil. The

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G Fig. 9.20 Iridotomy (full-thickness incision of the iris) provides an alternative communication between the anterior and posterior chambers of the flow of aqueous humor. (a) A fornix-based conjunctival flap is prepared with Steven’s tenotomy scissors. (b) The initial half-thickness limbal incision by Beaver No. 6400 microsurgical blade is perpendicular to the limbal surface. (c) In the center of the incision, the anterior chamber is entered with a stab incision with the Beaver No. 6500 microsurgical blade. (d) The limbal incision is lengthened by right- and left-handed corneoscleral scissors to about 140 . The anterior chamber is reformed with viscoelastic solution. (e) For an iridotomy involving the mid section, the iris is grasped by thumb forceps and protracted into the limbal incision. (f) An oval section is incised with the DeWecker iris scissors. If hemostasis is necessary, point electrocautery is used. Alternatively, both iris incision and hemostasis may be performed by electrocautery. (g) Closure of the limbal incision is by 8-0 to 9-0 simple interrupted absorbable sutures. Before placement of the last suture, the anterior chamber is flushed to remove any remaining viscoelastic solution and re-inflated with lactated Ringer’s solution. After all limbal sutures have been completed, a 22 g hypodermic needle is inserted between two sutures, and sufficient solution is injected to provide an intraocular pressure of about 10 mmHg. The conjunctival wound is apposed with a 7-0 to 8-0 simple continuous absorbable suture.

larger pupil is less likely to become obstructed and enhances vision. Sphincterotomies may also be performed by cryotherapy. Temperatures below –25 C destroy the iridal sphincter musculature, and cause focal depigmentation of the area. Sphincterotomies are also indicated to enlarge a small (1–2 mm) pupil, fixed by posterior synechiae after cataract surgery, which can impair vision in most dogs. Entry into the anterior chamber may be through a clear corneal incision, or under a limbal- or fornix-based conjunctival flap and through the limbus. In this example, the iridotomy is performed through the limbus and under a fornix-based conjunctival flap. After general anesthesia, clipping of the eyelid hair, and preparation of the eyelids, corneal and conjunctival surfaces with 0.5% povidone– iodine solution, an eyelid speculum is inserted to retract the eyelids. For sphincterotomies, entry is closest to the pupil (which is sometimes off center). Entry into the anterior chamber is by fornix-based limbal incision under a

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fornix-based bulbar conjunctival flap constructed by tenotomy scissors (Fig. 9.21a–d). Intracameral 1:10 000 adrenaline (epinephrine) and a viscoelastic agent are used for pupil dilatation and vasoconstriction, and to reform the anterior chamber. For sphincterotomies, the pupillary margin of the iris is incised by sharp iris scissors for 2–3 mm, in two to four positions (usually by quadrants). An immediate enlargement of an irregular pupil results (Fig. 9.21e,f). Thumb forceps are not usually necessary to grasp the pupillary margins of the iris during the scissor incisions. As with any incision of the iris, limited hemorrhage is anticipated and fibrin will form soon after. Alternatively, a non-invasive sphincterotomy can be performed using the diode endolaser to cauterize and retract the pupil margin and sphincter prior to incising with scissors. If collapse of the anterior chamber interferes with the iridotomy or sphincterotomy, the anterior chamber is reformed

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Fig. 9.21 The sphincterotomy procedure involves multiple incisions of the iridal sphincter area to enlarge the existing pupil diameter. These limited incisions (2–3 mm long) are performed with special and very sharp iridal scissors. (a) A fornix-based conjunctival flap is prepared with Steven’s tenotomy scissors. (b) The initial half-thickness limbal incision by Beaver No. 6400 microsurgical blade is perpendicular to the limbal surface. (c) In the center of the incision, the anterior chamber is entered with a stab incision with the Beaver No. 6500 microsurgical blade. (d) The limbal incision is lengthened by right- and left-handed corneoscleral scissors to about 140 , and the anterior chamber is reformed with viscoelastic solution. (e) For two to four sphincterotomies, the pupillary margin is incised for 2–3 mm by iris scissors, sufficient to incise the sphincter musculature, but avoid the more vascular basal iris. (f) Three or four sphincterotomies are usually performed, resulting in an irregular pupil. (g) Closure of the limbal incision is by 8-0 to 9-0 simple interrupted absorbable sutures. Before placement of the last suture, the anterior chamber is flushed for the last time with lactated Ringer’s solution. After all limbal sutures have been completed, a 22 g hypodermic needle is inserted between two sutures, and sufficient solution is injected to provide an intraocular pressure of about 10 mmHg. (h) The conjunctival wound is apposed with a 7-0 to 8-0 simple continuous absorbable suture.

with a viscoelastic agent. The highly viscous solution maintains the anterior chamber in the presence of the limbal incision. Iridal hemorrhage is infrequent with this procedure provided the sphincterotomies are not greater than 2–3 mm deep and tearing of the iris does not occur. If excessive, the several procedures described in the iridectomy section can be employed. If significant hyphema is still present 7–10 days postoperatively (after sufficient time for the iridal blood vessels to seal) 25–50 mg tPA can be injected into the anterior chamber to facilitate blood clot and any fibrin dissolution. The limbal incision is apposed by 8-0 to 9-0 simple interrupted absorbable sutures about 1–1.5 mm apart (Fig. 9.21g). Before placement of the last one or two sutures, the viscoelastic agent is irrigated from the anterior chamber with lactated Ringer’s solution, preferably using an automated irrigation/aspiration system, and any additional blood clots

removed. After the wound is completely apposed, a small gauge hypodermic needle is carefully inserted between two sutures to reform the anterior chamber and check the integrity of the closure. Intraocular pressure at this time should approximate 10–15 mmHg. The limbal-based conjunctival flap is apposed with a 7-0 to 8-0 simple continuous absorbable suture (Fig. 9.21h). Postoperative management after sphincterotomy includes topical and systemic antibiotics, corticosteroids, and NSAIDs. Pupil dilatation and movement are achieved by changing the daily frequency of the mydriatics, 1% atropine or 1% tropicamide, and, if necessary, 10% phenylephrine. The constant pupil movements can minimize formation of posterior synechiae; miosis from the postoperative iridocyclitis is counteracted by the drug-induced mydriasis and helps to reduce the possibility of posterior synechiae formation.

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Postoperative complications with sphincterotomy are infrequent, provided the procedure did not result in hemorrhage. This is usually associated with iris incisions greater than 3–4 mm. The success of sphincterotomies is higher than iridotomies, but the resultant enlargement of the pupil by one or more incisions may be less than anticipated because of variable and restricting posterior synechiae (usually to the remaining anterior and/or posterior lens capsules). Nevertheless, temporary blindness in a postoperative cataract eye with a 1 mm pupil can be successfully treated by pupillary enlargement to 4–6 mm diameter.

Coreoplasty In the coreoplasty or pupilloplasty procedure, focal iridectomy is usually combined with posterior synechiolysis and pupillary membranectomy because the small pupil results from adhesions that involve not only the pupillary borders but also larger areas of the posterior iris surface. Entry into the anterior chamber may be through a clear corneal incision, or under a limbal- or fornix-based conjunctival flap and through the limbus. In this example, the iridotomy is performed through the limbus and under a fornix-based conjunctival flap. Before the coreoplasty is performed, the eye is treated preoperatively for the existing disease and in anticipation that the surgery will elicit an intense iridocyclitis. Hence, topical and systemic antibiotics, corticosteroids, and NSAIDs are administered for 3–5 days preoperatively. Mydriatics are not usually instilled preoperatively unless the coreoplasty procedure is performed or an iridocyclitis is present. IOP should be monitored preoperatively to provide a reference for the postoperative period. After general anesthesia with inhalational isoflurane, clipping of the eyelid hair, and preparation of the eyelids, corneal and conjunctival surfaces with 0.5% povidone– iodine solution, the eyelids are retracted by speculum to expose the globe. If exposure to and observation of the entire anterior chamber is not possible, a lateral canthotomy is performed to increase exposure. Entry into the anterior chamber is by a peripheral clear corneal incision. The initial one-half thickness of the corneal incision, perpendicular to the corneal surface, is performed with the Beaver No. 6400 microsurgical blade and completed with corneoscleral scissors (Fig. 9.22a–c). The corneal incision is directly adjacent to the iridectomy site. For the coreoplasty procedure (creation of a new or enlargement of an existing small pupil), a central iridectomy is performed. Not infrequently a small pupil is complicated by multiple posterior synechiae, a fibropupillary membrane, and variable incorporation of opacified anterior and posterior lens capsules. Disruption of posterior synechiae usually produces variable amounts of hemorrhage. The fibropupillary membrane, often consisting of tough fibrous tissue, can be excised only by sharp iris, vitreous, or intraocular scissors. These membranes cannot be torn by thumb forceps without considerable damage to the iris and hemorrhage. The anterior chamber is maintained with a viscoelastic agent (Fig. 9.22d). The margins of the pupil are carefully separated from the anterior lens capsule and/or posterior lens capsule with a cyclodialysis spatula (Fig. 9.22e). Hemorrhage is

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anticipated; tearing of the iris should be avoided. For hemostasis, 1:10 000 adrenaline (epinephrine) is intermittently lavaged into the surgical site. Once sufficient pupil margin has been freed, the pupillary iris and fibropupillary membrane are carefully excised by sharp iris, vitreous, or intraocular scissors (Fig. 9.22f). The resultant irregular pupil should approximate 5–6 mm in diameter, and be clear of any tissues (Fig. 9.22g). If portions of the anterior and posterior lens capsules and vitreous are incarnated in the pupil, they must be excised by intraocular scissors or a guillotine-type vitrector. The clear corneal incision is apposed with 8-0 to 9-0 simple interrupted absorbable sutures placed 1–1.5 mm apart. Before placement of the last two corneal sutures, the anterior chamber is once more irrigated with 1:10 000 adrenaline (epinephrine) and balanced salt solution to remove any remaining viscoelastic agent, hemorrhage, and plasmoid aqueous humor. After the last corneal suture, a 27–30 g cannula is carefully inserted between two sutures, and the anterior chamber reformed to about 10–15 mmHg IOP (Fig. 9.22h).

Sectoral iridectomy In the iridectomy procedure a full-thickness section of iris is excised. This procedure is used to excise iridal cysts, remove focal pigmented iridal neoplasms, and biopsy inflamed irides to establish an etiology. The iridectomy procedures may be further divided into the different parts of the iris: pupillary, peripheral, sectoral, stenopeic (slit shape), and basal. Before the iridectomy is performed, the eye is treated preoperatively for the existing disease and in anticipation that the iridectomy procedure will elicit an intense iridocyclitis. Hence, topical and systemic antibiotics, corticosteroids, and NSAIDs are administered for 3–5 days preoperatively. Mydriatics are not usually instilled preoperatively, unless an iridocyclitis is present. IOP should be monitored preoperatively to provide a reference for the postoperative period. After general anesthesia with inhalational isoflurane, clipping of the eyelid hair, and preparation of the eyelids, corneal and conjunctival surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum to expose the globe. If exposure to and observation of the entire anterior chamber is not possible, a lateral canthotomy may be performed to increase exposure. Entry into the anterior chamber may be through a clear corneal incision, or under a limbal- or fornix-based conjunctival flap and through the limbus. In this example, the iridotomy is performed by entry into the anterior chamber via a peripheral clear corneal incision. The initial one-half thickness of the corneal incision, perpendicular to the corneal surface, is performed with the Beaver No. 6400 microsurgical blade (Fig. 9.23a). The corneal incision is directly adjacent to the iridectomy site. A stab incision into the anterior chamber with the Beaver No. 6500 microsurgical blade or keratome is performed through the center of this partial corneal incision (Fig. 9.23b). Aqueous humor will leak through this stab incision. The deeper portion of the corneal incision is completed using the rightand left-handed corneoscleral scissors (Fig. 9.23c). The incision is usually about 140–180 . The anterior chamber is then filled with 1:10 000 adrenaline (epinephrine) and a viscoelastic

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Fig. 9.22 Coreoplasty is the surgical creation of a new or larger pupil. The preoperative pupil which requires coreoplasty is generally very small, off-center, and often obscured by inflammatory and capsular opacities from previous cataract surgery. (a) The peripheral cornea is initially incised about half-thickness for about 120–180 with the Beaver No. 6400 microsurgical blade. (b) With the Beaver No. 6500 microsurgical blade or keratome, the anterior chamber is entered by a stab incision. (c) The deeper corneal incision is lengthened by right- and left-handed corneoscleral scissors. (d) For the coreoplasty procedure, the small pupil is usually adhered to the lens (with phakia) or to the posterior lens capsule and anterior vitreous (with aphakia). To maintain a deep anterior chamber, a viscoelastic solution is injected. (e) With a cyclodialysis spatula, adhesions between the iris and other tissues are gently separated, resulting in some enlargement of the pupil. (f) With sharp intraocular scissors, all other remaining adhesions and pupillary membranes are excised, increasing the pupil size further. (g) The resultant pupil should be enlarged, but usually irregular. (h) Closure of the corneal incision is by 8-0 to 9-0 simple interrupted absorbable sutures placed about 1.5 mm apart. Before the last corneal suture is placed, any remaining viscoelastic solution is flushed from the anterior chamber and replaced with balanced salt solution or lactated Ringer’s solution.

agent. For a complete sectoral iridectomy, as for removal of an isolated pigmented iridal tumor, the iris is retracted by a blunt iris hook or serrated thumb forceps away from the anterior lens surface and partially into the incision (Fig. 9.23d). Care must be taken to avoid tearing of the iris. The iris, on both sides of the mass, is slowly incised radially towards its base by iris scissors or by cautery (Fig. 9.23e,f). The base is incised by the same method. There should be limited or no hemorrhage during the radial incisions. Because the major arteriolar circle occurs in the basal iris in about 50% of dog and horse eyes, some hemorrhage is expected during the basal incision. The resultant complete iridectomy results in a keyhole-shaped pupil (Fig. 9.23g). The clear corneal incision is apposed with 8-0 to 9-0 simple interrupted absorbable sutures placed 1–1.5 mm apart (Fig. 9.23h). Before placement of the last two corneal sutures, the anterior chamber is once more irrigated with 1:10 000 adrenaline (epinephrine) and balanced salt

solution to remove any remaining viscoelastic agent, hemorrhage, and plasmoid aqueous humor. After the last corneal suture, a 27–30 g cannula is carefully inserted between two sutures, and the anterior chamber reformed to about 10–15 mmHg IOP (Fig. 9.23i). Postoperative management after complete or sectoral iridectomy procedures is quite similar to that for all iridal surgeries. Topical and systemic antibiotics, corticosteroids, and NSAIDs are administered to treat the anticipated postoperative iridocyclitis. The intensity of these treatments is adjusted daily to control the iridocyclitis. Postoperative pupil size should be as large as possible by varying the frequency of topical instillations of 1% atropine, 1% tropicamide, 10% phenylephrine, or some combinations. If excessive fibrin occurs, 25–50 mg tPA may be injected intracamerally about 7–10 days postoperatively. The enzyme should not be injected at the conclusion of surgery or for a few days postoperatively, as adequate time must be provided

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Fig. 9.23 Sectoral iridectomy is the full-thickness excision of a section of iris and may involve the base (peripheral iridectomy) or other areas. As the iridal arterial circle is within the iridal base about 50% of the time, excessive hemorrhage occurs about in about one-half of the eyes. (a) The peripheral cornea is initially incised about half-thickness for about 120–180 with the Beaver No. 6400 microsurgical blade. (b) With the Beaver No. 6500 microsurgical blade or keratome, the anterior chamber is entered by a stab incision. (c) The deeper corneal incision is lengthened by right- and left-handed corneoscleral scissors, and the anterior chamber is reformed with viscoelastic solution. (d) For iridectomy, the involved iris is protracted with a thumb forceps into the corneal incision. (e, f) Once partially externalized from the anterior chamber, the involved iris is both cauterized and excised. (g) The resultant pupil after a complete iridectomy is the shape of a keyhole. (h) Closure of the corneal incision is by 8-0 to 9-0 simple interrupted absorbable sutures placed about 1.5 mm apart. (i) Immediate postoperative appearance of dorsal sectoral iridectomy for removal of an iridal melanomas. Some hemorrhage remains within the animal chamber and a dorsal bulbar conjunctival advancement (hood) has been used to cover the sclera immediately dorsal of the excised tumor site.

for sealing of the iridal blood vessels to avoid secondary or recurrent hemorrhage. IOP is monitored daily, although glaucoma is unlikely as long as the pupil remains unobstructed. The intensity of the medical treatment is gradually tapered, based on the clinical appearance of the iris and pupil, and the gradual return of IOP toward normalcy. Medical treatment is usually continued for 3–6 months or until IOP has returned to normal levels and all clinical signs of anterior uveitis have resolved. Postoperative complications include an intense iridocyclitis that may be difficult to control medically, with a plasmoid aqueous humor and large amounts of fibrin. This fibrin can form adhesions within the pupil, on the iridal

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surface, or adhere to the anterior or posterior lens capsule. If the lens is present, as in eyes with an iris tumor, posterior synechiae and secondary cataract formation may result. The possibility of secondary glaucoma resulting from pupillary or iridocorneal angle obstruction is low. Phthisis bulbi or atrophy of the globe is infrequent postoperatively unless the iridocyclitis is intense and/or prolonged. Critical for successful iridectomy procedures is the medical control of the resultant iridocyclitis and maintenance of the largest and mobile pupil possible. The sectoral iridectomy techniques can be successful in the removal of isolated iridal tumors; however, if the tumor invades the sclera or ciliary body success is limited. Intracameral injections of tPA during the first 7–10 days

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postoperatively after these procedures can markedly reduce the fibrin and hemorrhage in these eyes and improve the success rates.

Iris bombe´ Iris bombe´ is a forward ballooning of the iris caused by total occlusion of the pupil. Iris bombe´ is usually associated with 360 or annular posterior synechiae (Fig. 9.24). These iridolenticular adhesions usually involve the pupillary area of the iris and may be temporary or permanent. Without transpupillary flow of aqueous humor, the fluid and pressure gradually increase within the posterior chamber, pushing the basal iris forward into the anterior chamber and closing the iridocorneal angle. Iris bombe´ may also be limited to a section of the iris, as evidenced by a focal raised area traversing the iris from its base to the pupil margin. Pupil size with iris bombe´ is usually very miotic. The pupillary aspects of the iris normally rest on the axial anterior lens capsule in a phakic eye, or on the anterior and posterior capsules and vitreous in an aphakic eye. With iridal inflammation, the pupil becomes miotic, and contact with the anterior lens capsule results in temporary to permanent iridolenticular adhesions. Often underestimated is the concurrent compression of the opening of the sclerociliary cleft and rapid formation of peripheral anterior synechiae. Clinical management of iris bombe´ is influenced by the presence (phakia) or absence (aphakia) of the lens. Iris bombe´ in phakic eyes occurs with severe iridocyclitis and a miotic pupil. In aphakic eyes, iris bombe´ usually involves a small pupil, and occlusion of the pupil with the anterior lens capsule, posterior lens capsule, vitreous, fibropupillary membranes, or a combination of these tissues. Clinical management of iris bombe´ is also influenced by its duration and the possibility of vision. With ballooning of the basal iris in iris bombe´, closure of the iridocorneal angle and the formation of peripheral anterior synechiae rapidly result. After 48–72 h these iridocorneal angle changes are difficult to reverse medically, and even after surgical resolution of iris bombe´, treatment of angle-closure glaucoma may be necessary. Regardless of whether the lens is present or absent, successful treatment of iris bombe´ in small animals

Fig. 9.24 Iris bombe´ in the dog usually results from iridocyclitis, annular (360 ) posterior synechiae, and obstruction of the pupil.

requires re-establishment of aqueous humor flow through the pupil as soon as possible. The administration of mannitol (1 g/kg IV) or oral and topical carbonic anhydrase inhibitors immediately before surgery may reduce the size of the iris bombe´ and retract the vitreous body. Prognosis for iris bombe´ should always be guarded as the response to medical, surgical, or a combination of both therapies is not always predictable. The treatment of iris bombe´ in phakic eyes is usually medical initially. Intense therapy with topical and systemic corticosteroids and NSAIDs is indicated to suppress the anterior uveal inflammation. Topical mydriatics, such as 1% atropine and 10% phenylephrine, or 0.3% scopolamine and 10% phenylephrine, are instilled hourly to effect pupillary dilatation and break down the annular posterior synechiae. If this treatment fails to resolve the iris bombe´, surgical intervention is recommended. Surgical entry into the anterior chamber in eyes with iris bombe´ is difficult, because the iris is very close to the posterior cornea. Iris bombe´ in aphakic eyes usually occurs within the first postoperative month after lens removal. A small pupil after cataract surgery is more prone to iris bombe´. Incarceration of the posterior lens capsule, with or without vitreous, and inflammatory-based fibropupillary membranes often clog the pupil. If the iris bombe´ occurs postoperatively in an aphakic eye within the first week, intensive mydriatic therapy (such as 0.3% scopolamine and 10% phenylephrine hourly) may dilate the pupil and re-establish aqueous humor passage. However, if iris bombe´ occurs two or more weeks after cataract surgery, dilatation of the pupil with intensive mydriatic therapy is unlikely to be successful because of the formation of posterior synechiae. Persistence of iris bombe´ after 1–2 days with the appropriate intensive medical therapy requires surgical intervention. Treatment of iris bombe´ secondary to iridocyclitis consists of: 1) hypodermic needle or laser-induced multiple fullthickness holes in the middle one-third of the iris to reduce ballooning of the iris and allow aqueous humor to flow into the anterior chamber; 2) continuation of intensive topical mydriatic treatments for a few days; and 3) surgical entry of the anterior chamber if pupillary dilatation is not achieved, and freeing of the pupillary margins of the iris from the anterior lens capsule. Hemorrhage is anticipated. If vitreous is associated with the iris bombe´ post-cataract surgery, then an anterior vitrectomy may be indicated. If iridocorneal angle closure is suspected or can be confirmed by gonioscopy, an iridencleisis should be performed (see Chapter 10). Viscoelastic agents should be injected during surgery of the iris and pupil to expand the depth of the anterior chamber and attempt opening of the sclerociliary cleft. Nd:YAG laser treatment of iris bombe´ and pupillary block glaucoma, primarily following cataract surgery, has been evaluated in the dog. Laser surgery was 91% successful in immediately relieving the iris bombe´ and re-establishing the anterior chamber. However, these iridotomies did not remain functional long term, and after the reformation to a normal or near normal anterior chamber depth, surgical procedures such as hyaloidotomy and synechiotomy were necessary to maintain a patent and larger pupil. As most of these dogs had had cataract extractions, it is not surprising that laser iridotomies were unsuccessful. Often the pupillary

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occlusion in these patients includes inflammatory fibropupillary membranes, anterior and posterior capsular fibrosis and adhesions, and miotic pupils, and requires coreoplasty (creation of a new pupil) with synechiotomy, capsulotomy (or capsulectomy), and hyaloidotomy (or anterior hyaloidectomy). Laser iridotomy for iris bombe´ glaucoma offers the surgeon the advantage of immediately re-establishing a near normal depth anterior chamber before surgical entry into the anterior chamber to enlarge and re-establish a patent pupil. Entering the anterior chamber with iris bombe´ glaucoma is difficult because the anterior chamber volume is so compressed, and manipulation of instruments between the forwardly displaced iris and the posterior corneal endothelium is difficult and sometimes impossible. In one study, the mean amount of diode laser energy delivered was 1098 mJ (range 30–5900 mJ), and the mean number of bursts was 25.2 (range 1–118) or an average of 126 pulses. Corneal transparency is critical in these laser therapies, and the earlier iris bombe´ glaucoma is diagnosed and treated, the higher the success rate for resolving the glaucoma and maintaining vision. Medically non-responsive iris bombe´ with aphakia is most apt to develop 5–10 days postoperatively (usually after cataract surgery or intracapsular lensectomy for lens luxations). It is usually complicated by pupillary obstruction with lens capsules, vitreous, inflammatory membranes, or a combination of these tissues. Surgical treatment includes entry into the anterior chamber at the limbus, breakdown of the pupillary blockage with sharp iris scissors, and removal of all materials in the pupil. An anterior vitrectomy may also be performed (see Chapter 12). Postoperative management after iris bombe´ consists of topical and systemic antibiotics, corticosteroids, and NSAIDs, and vigorous topical mydriatic therapy. The pupil after iris bombe´ must be dilated to at least 5–8 mm in dogs and cats, and some daily change in pupil diameter is recommended to reduce the likelihood of posterior synechiae formation. Hyphema and excessive fibrin in the aqueous humor are common postoperatively, and should be treated by intracameral 25 mg tPA for 3–7 days. Postoperative IOP must be closely monitored; if an increase occurs, topical timolol or other beta antagonist, or carbonic anhydrase inhibitors (either topically or systemically), should be initiated. The most serious complications are the persistence of the glaucoma, usually from the formation of peripheral anterior synechiae, and the development of phthisis bulbi (failure of the ciliary body and ocular hypotony – IOP <5 mmHg). Only the former can be treated, usually by iridencleisis or other glaucoma surgeries (see Chapter 10).

adenomas and adenocarcinomas) when the borders of these masses can be reasonably determined pre- and intraoperatively (Fig. 9.25). Large limbal (epibulbar) melanomas may extend into the sclera and necessitate an iridocyclosclerectomy with scleral graft. Assessment of the iridocorneal angle by gonioscopy, and determination of the posterior borders by indirect ophthalmoscopy (use sedation or general anesthesia, and scleral depression), slit-lamp biomicroscopy, ocular ultrasonography or ultrasound biomicroscopy are necessary. If the borders of the mass cannot be defined, enucleation may be indicated. Permission from the pet owner should be secured prior to surgery that, if complete tumor excision is not possible, enucleation can be performed. After general anesthesia, clipping of the eyelid hair, and preparation of the eyelids, corneal and conjunctival surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. A lateral canthotomy may be performed to increase exposure (Fig. 9.26a). In this example, the nonpigmented ciliary body adenoma is visible in the dorsal pupil. A limbal-based conjunctival flap is performed by tenotomy scissors immediately above the iridocyclosclerectomy site (Fig. 9.26b). The limbus is incised with the Beaver No. 6500 microsurgical blade or keratome (Fig. 9.26c), and enlarged with corneoscleral scissors to the appropriate length (Fig. 9.26d). The block of sclera to be excised is outlined and slowly incised with the Beaver No. 6400 microsurgical blade (Fig. 9.26e). Scleral hemorrhage will occur and judicious cautery must be applied to maintain hemostasis. As the scleral incisions are deepened and approach the iris and ciliary body, uveal pigmentation will become evident. The scleral incision is cauterized more deeply to help provide hemostasis during excision of the iris and ciliary body (Fig. 9.26f). The iris is incised on both sides, from the pupillary margin to its base, by sharp iris scissors (Fig. 9.26g). The incision by the scissors is continued around the sclera to complete the ciliary body incisions (Fig. 9.26h,i). Any zonules attached to the ciliary body are carefully torn or cut by iris scissors. The underlying lens should not be touched. Any hemorrhage is carefully irrigated from the surgical site with balanced salt solution. If uveal hemorrhage persists, additional cautery is applied, or the area is lavaged

Iridocyclectomy In the iridocyclectomy procedure, a portion of iris and adjacent ciliary body is excised. Iridocyclectomy can also include removal of the adjacent sclera, and replacement with a frozen or fresh scleral homograft (see Chapter 8). The surgery should be limited to less than one quadrant (90 ) or smaller to minimize the occurrence of phthisis bulbi postoperatively, secondary to ciliary body inadequacy. Iridocyclectomies are indicated for isolated iris and/or ciliary body masses (such as iridal melanomas, ciliary body

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Fig. 9.25 Ciliary body adenoma is evidenced as a non-pigmented mass posterior to the pupil. Other frequent concurrent clinical signs may include iridocyclitis, glaucoma, hyphema, and cataract formation. The eye is a candidate for iridocyclectomy.

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Fig. 9.26 Iridocyclectomy with or without homologous scleral graft. (a) A section of iris and ciliary body is excised usually for a focal neoplasm. (b) A limbalbased bulbar conjunctival flap is performed by Steven’s tenotomy scissors immediately above the iridociliary mass. (c) The limbus is incised one-half thickness with the Beaver No. 6500 microsurgical blade. (d) The limbal incision is enlarged to about 120–180 with right- and left-handed corneoscleral scissors, and the anterior chamber is reformed with a viscoelastic agent. (e) A block of sclera is incised full-thickness immediately over the iridocyclectomy area with the Beaver No. 6400 microsurgical blade. (f) Scleral hemorrhage will occur throughout the incision and is controlled by point electrocautery. (g) Both sides of the iris are incised by DeWecker or similar small iris scissors. (h) From the basal incisions of the iris, the ciliary body is incised with iris scissors. (i) The block of iris and ciliary body, attached to the adjacent sclera, is carefully separated from any remaining tissues and removed. (j) A homologous graft of sclera, about 0.5 mm larger than the surgical wound, is carefully fitted into the defect, and all four sides of the scleral graft are apposed with 7-0 to 8-0 simple interrupted absorbable sutures. (k) After placement of all but the last of the limbal 7-0 to 8-0 simple interrupted absorbable sutures, the anterior chamber is flushed with lactated Ringer’s solution and reformed so intraocular pressure is adjusted to about 10–15 mmHg. (l) The limbal-based conjunctival flap is apposed with a 7-0 to 80 simple continuous absorbable suture.

with 1:1000 rather than the 1:10 000 adrenaline (epinephrine) solution. A scleral homograft, constructed by tenotomy scissors and about 0.5 mm larger than the scleral defect, is apposed to the scleral defect and limbus with 7-0 to 8-0 simple interrupted absorbable sutures (Fig. 9.26j). The limbal incision is apposed with several simple interrupted 7-0 to

8-0 absorbable sutures (Fig. 9.26k). Once the scleral graft has been secured, balanced salt solution is injected into the anterior chamber to test the integrity of the wound apposition, and re-establish about 10–15 mmHg IOP (Fig. 9.26k). The limbal-based bulbar conjunctival flap is apposed with a 7-0 to 8-0 simple continuous absorbable suture (Fig. 9.26l).

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Postoperative treatment consists of topical and systemic antibiotics, corticosteroids, and NSAIDs to control and resolve the iridocyclitis. Intraocular pressure is monitored daily. As the iridocyclitis resolves, the IOP gradually returns to normal. Topical cyclosporine is started a few days postoperatively to reduce the host response to the scleral graft. Postoperative complications after iridocyclosclerectomy are usually associated with the iridocyclitis, any remaining intraocular hemorrhage, fibropupillary membrane, a raised area from the scleral graft, and secondary cataract formation. Tumor recurrence after this type of surgery is infrequent. Intracameral 25 mg tPA may be injected 3–7 days postoperatively to help dissolve any intraocular fibrin bands and hemorrhage. Failure to successfully control postoperative iridocyclitis may result in either phthisis bulbi or angle-closure secondary glaucoma.

Laser treatment of anterior uveal cysts in the dog and cat Pigmented iridal cysts in dogs may be free-floating within the anterior chamber, trapped in the iridocorneal angle, or wedged within the posterior chamber, and originate from the posterior iridal pigmented epithelium. More often than not, they are detached from the posterior iris in dogs. Sometimes in an eye presented for a pigmented cyst, druginduced mydriasis will release additional cysts trapped within the posterior chamber. Ciliary body cysts usually arise from the anterior pars plicata or corona ciliaris (ciliary body processes), and rarely the posterior pars plana ciliaris (pars plana of the ciliary body). In contrast, ciliary body cysts may appear as brown, red or clear bubbles, and are usually still attached to their ciliary body. Most iridal and ciliary body cysts are innocuous in the dog; however, in the Great Dane and Golden Retriever breeds, these anterior uveal cysts have been associated with serious eye disease, including defoliation of iridal pigmentation onto the anterior lens capsule, cataract formation, and the development of a refractory secondary glaucoma. In cats, pigmented iridal cysts are the more common type of anterior uveal cyst, and when presented are pigmented hollow cysts, sometimes relatively large, still attached to the posterior pigmented iris. As these large pigmented cysts in cats can mimic anterior uveal melanomas, ultrasonography is very important to distinguish these cysts from solid pigmented masses (melanomas and ciliary body pigmented epithelial tumors). Most cats with iridal cysts present with focal shallowing of the anterior chamber and dyscoric

pupils. Cats are also more often affected bilaterally and with multiple cysts. IOP may increase in cats with iridial cysts upon drug-induced mydriasis. Laser therapy of anterior uveal cysts in the dog and cat represents non-invasive therapy, in contrast to surgical entry into the anterior chamber and either grasping and manual removal of the cysts, or puncture of the cyst wall by a small hypodermic needle and cyst removal. Laser therapy causes less postoperative anterior uveitis, and reduces the need for post-cyst deflation therapy with topical mydriatic, steroidal, and non-steroidal therapy. Both the Nd:YAG and diode lasers are effective; however, the more versatile diode laser is the most common laser type in veterinary ophthalmology, and usually used for these surgeries. The diode laser’s mechanism of action on the cyst wall is by photocoagulation (rather than photodisruption). Hence, it is most commonly used for anterior uveal cysts in all species (Fig. 9.27). As deflation of the anterior cyst depends on its size and number of cysts, laser therapy is to effect (the cysts deflate once the cyst wall has been penetrated). In general, in the dog, the average power setting of the diode laser is about 1000 mW, the average duration ranges from 500 to 1500 ms, and the average number of spots per cyst is about 15. In cats with iridal cysts, when the diode laser was applied in pulse, the average power setting was 700 mW, the average duration was 1000 ms, and the average number of spots to achieve rupture and coagulation of the cysts was 97 per eye. As expected, with more laser energy used in cats, the greater the intensity of post-laser anterior uveitis.

Laser treatment of anterior uveal neoplasms in the dog Therapies are evolving to eliminate intraocular melanoma in the dog while still preserving the eye and vision using laser photocoagulation. In the past, focal primarily iridal melanomas have been removed by sectional iridectomy with limited involvement of the ciliary body, or by sectional iridocyclectomy, often with a scleral graft. Anterior uveal melanomas in the dog, in contrast to the cat, seem to metastasize late and with limited frequency (about 5%). These melanomas, if allowed to expand within the eye, may result in persistent iridocyclitis, hyphema, cataract formation, angle-closure glaucoma, and retinal detachment. As a result, at least two clinical studies have been reported evaluating laser photocoagulation for melanomas of the canine iris

Fig. 9.27 Treatment of a large pigmented iris cyst in a cat with diode laser therapy. Ultrasonography has indicated this cyst is hollow; histopathology confirms the diagnosis. (a) Preoperative appearance. (b) Post-laser therapy. Note the cyst has deflated.

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and ciliary body. The most effective laser results seem to be with the more superficial iridal melanomas, rather than those tumors which are deeper within the ciliary body. Transscleral and transcorneal Nd:YAG laser photocoagulation was reported for the treatment of four iris tumors and 11 ciliary body tumors in the dog (Fig. 9.28). Although no histopathology was performed, six of the 11 ciliary body tumors were presumed epithelial in origin; the remaining five tumors were pigmented and presumed melanomas. The total energy used was 10–400 joules per treatment. The iridal tumors responded more favorably, with all four of the masses regressing. Of the ciliary body masses, complete or partial shrinkage occurred in five of the seven tumors that appeared confined to the ciliary body, but only an incomplete response in three of the four ciliary body tumors with iridal and scleral extension. Multiple treatments were often used. After Nd:YAG photocoagulation, the eyes developed conjunctival hyperemia, mild to moderate aqueous flare, variable hyphema, and vitreal hemorrhage. Focal cataract formation occurred in those eyes in which the tumor was in close proximity to the lens. Although this report demonstrated potential effectiveness of laser photocoagulation of these tumors, the clinical results were not impressive. Unfortunately, several cases were lost to follow-up during the study and the remission rates of those patients in the study were considerable. In the second report, the diode laser was used to treat presumed iridal melanomas in 23 dogs. The iridal masses ranged in size from 2  3 mm to 4  12 mm, appeared as focal raised iridal hyperpigmentation, and occurred mainly in one breed. The diode laser system was attached to either an operating microscope adaptor or used as a laser indirect ophthalmoscope. Laser treatments consisted of 80–1000 mW and cumulative durations up to 14.3 min, and experience suggested that emphasis on a hyperthermic response (lower W/mm2 with longer durations) yielded better results. Five of the 23 cases required multiple treatments. There was immediate shrinkage of the mass after laser photocoagulation; long-term complications included dyscoria, iridal hyperpigmentation, pigment on the anterior lens capsule, iris atrophy, and corneal edema. Glaucoma and cataract formation were not observed, and follow-up ranged from 6 months to 4.5 years. Twenty of the cases had follow-ups of 1 year or longer. Twelve of the 23 dogs were Labrador Retrievers, and 12 dogs were 3 years of age or less. Laser treatments were given to effect and discontinued after no further shrinkage was observed, surface disruption ceased, and release of pigment cells into the aqueous humor

stopped. Immediately after diode laser photocoagulation, mild blepharospasm, conjunctival hyperemia, and aqueous flare were observed. Postoperative therapy consisted of subconjunctival and topical corticosteroids. The newer endoscopic diode laser may prove to be even more beneficial in the treatment of anterior uveal neoplasms. This technique uses a 20 g endoprobe that provides light, video, and diode laser. This technique permits access to the posterior iris and ciliary body, and allows for precise visualization and delivery of laser energy to the target tissue while maintaining the anterior chamber and avoiding collapse of the eye.

Adaptations for large animals and special species In general terms, the anterior chamber and uvea of large animal species are similar in anatomy and physiology to those of the dog and cat. The equine eye is the most common large animal eye in veterinary ophthalmology for which anterior segment surgery is performed. Anatomic differences include the presence of dorsal and ventral corpora nigra, a horizontal pupil, and a relatively shallow anterior chamber at the iridocorneal angle. The dorsal corpora nigra are the largest, consisting of three to four pigmented, irregular structures at the dorsal pupil margin of the iris. Corpora nigra may undergo atrophy or adhere to the cornea or anterior lens as a result of inflammatory disease. They may undergo cystic changes that can be associated with visual and behavioral changes. They may also present a mechanical problem in surgery of the anterior segment by impeding access to structures such as the lens during cataract surgery. As a result of corneal curvature, the anterior chamber is relatively shallow at the equine iridocorneal angle, making access to the anterior chamber more difficult than in the dog or cat. In general, a two-step, clear corneal or corneoscleral incision is used to enter the equine anterior chamber and a high viscosity, cohesive viscoelastic agent is required to maintain the anterior chamber during anterior segment surgery. Surgery of the anterior uvea may be indicated for treatment of iris prolapse, uveal neoplasia, uveal cysts, cataract, glaucoma, and equine recurrent uveitis (ERU). For discussion of techniques for the treatment of iris prolapse (Chapter 8), cataract (Chapter 11), glaucoma (Chapter 10), and ERU (Chapter 12), the reader is directed to the specific chapters regarding these equine surgeries. Anterior uveal cysts are relatively common in the equine eye; they most frequently involve the dorsal corpora nigra or, less frequently, the ventral corpora nigra or pupillary margin. Fig. 9.28 Treatment of a focal iridal melanoma in a dog with diode laser therapy. (a) Preoperative appearance. (b) Postoperative appearance after iris biopsy and diode laser photocoagulation of an iridal melanoma in a dog 5 months previously. The mass recurred and was treated again with diode laser coagulation. (Photographs courtesy of D.E. Brooks, University of Florida.)

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Affected horses are generally middle-aged or older. Uveal cysts are an acquired lesion, and do not appear to be associated with intraocular inflammation or other abnormalities. Corpora nigra cysts appear as pigmented, smooth, round structures projecting over the pupil. They may be uni- or bilateral, and vary in number and size (Fig. 9.29). The differential diagnosis would be an anterior uveal melanoma. In most instances, clinical examination alone is sufficient for a diagnosis, but ocular ultrasound can be used to confirm the diagnosis. A cyst will appear hollow while a melanoma is solid. Depending on the ultrasound probe, an offset may be required to image the anterior segment. If they are large enough, corpora nigra cysts may result in visual disturbance and behavioral abnormalities (Fig. 9.30). To assess the area of the visual field affected, the cyst should be evaluated with the pupil in an undilated state. If vision is compromised, surgical intervention is indicated. Corpora nigra cysts can be managed in a non-invasive manner using focused laser energy to cauterize and disrupt the cyst wall. The goal should not be to simply rupture the cyst as it will reform; rather the goal is to cauterize the entire cyst wall to prevent continued fluid secretion (Fig. 9.31a,b).

Fig. 9.29 Two dorsal corpora nigra or granula iridica cysts of moderate size are present in a horse.

Fig. 9.30 Several large dorsal corpora nigra or granula iridica cysts are present in a horse. The pupil is shown in a non-dilated state. Significant visual impairment results from these cysts.

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Techniques using the Nd:YAG laser or an 810 nm diode laser and an indirect ophthalmoscope for cyst ablation have been described. This is performed in the standing horse using only sedation and an auriculopalpebral nerve block (Fig. 9.31c). The pupil should be undilated and the horse premedicated with a systemic NSAID. Care is taken when ablating those areas of the cyst in proximity to the cornea or the lens as heat may be transferred, resulting in collateral damage. If possible, treat the areas of the cyst distant to the cornea and lens, shrinking the overall size of the cyst and increasing the distance from the cornea and lens. When ablating the cyst, the clinician should attempt to focus the laser energy in as small and round an area as possible to ensure maximal energy delivery. The goal is photocoagulation rather than photodisruption. Following ablation, a single administration of a mydriatic and 24–48 h of a systemic NSAID are all that is usually required for postoperative care. With the availability of non-invasive laser ablation, more invasive techniques such as centesis of the cyst are rarely indicated. If a centesis is required, it should be performed under general anesthesia and is most indicated for a freefloating cyst. A 27 or 30 g needle on a tuberculin syringe is introduced into the anterior chamber at the limbus. The cyst is then carefully aspirated and removed. Postoperative miosis and aqueous flare are typical following centesis, and are managed using topical mydriatics and systemic NSAIDs. Primary neoplasia of the equine anterior uvea includes melanoma, adenoma, adenocarcinoma, and medulloepithelioma. Of the secondary neoplasms, lymphoma is the most common. In general, anterior uveal neoplasia is rare in the horse. Of the primary neoplasms, melanoma is the most common. Equine ocular melanoma is generally a solitary mass without association with cutaneous melanoma. Based on the literature, intraocular melanomas are reported more commonly in gray horses, with the most commonly affected horses being between 5 and 10 years of age. Equine intraocular melanoma most commonly originates from the iris and ciliary body. Although intraocular melanoma can demonstrate rapid growth, distant metastasis is extremely rare, and histologic diagnosis is generally benign. Clinical signs are variable, and may include a pigmented mass, corneal edema, dyscoria, cataract, and glaucoma (Fig. 9.32). Additional clinical signs vary depending on the size and location of the mass. Ultrasonography may be indicated to confirm the mass as solid rather than cystic, and to evaluate the extent of the mass and its effect on adjacent structures. Treatment for anterior uveal melanoma may include monitoring, sector iridectomy/iridocyclectomy, laser ablation or enucleation. Treatment selection is based on use of the horse, cost, location and size of the melanoma, availability of treatment modalities, and surgical abilities. Laser ablation may be performed using either the Nd:YAG or diode laser in a non-invasive manner transcorneally or transsclerally. In addition, diode endolaser ablation may also be indicated with either an anterior limbal or a posterior pars plana approach. Laser ablation would be most indicated for small melanomas typically involving less than 1–2 clock hours of the anterior uvea. Iridectomy/iridocyclectomy is a more invasive procedure and again is typically indicated for melanomas affecting less than 25% of the anterior uvea. One of the authors (DAW) has successfully excised 50% of the equine iris affected by melanoma, but secondary

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Fig. 9.31 (a) A ventral anterior uveal cyst is shown prior to diode laser ablation. (b) The same eye immediately following diode laser ablation of the ventral anterior uveal cyst. (c) Performing photoablation of the cyst using an indirect ophthalmoscope, condensing lens and a diode laser.

Fig. 9.32 A large anterior uveal melanoma affecting 50% of the iris, extending into the anterior chamber and resulting in secondary corneal edema and vascularization.

Fig. 9.33 A teratoid medulloepithelioma originating from the ciliary body and extending into the posterior segment and resulting in a leukocoria.

cataract is a common sequela. The techniques for iridectomy/iridocycletomy in the horse are similar to those described for the dog. For an iridectomy, a limbal approach is preferred, incising adjacent to the affected iris base. For an iridocyclectomy, a limbus-based scleral flap provides the best exposure. For both procedures, magnification, viscoelastic material, wet-field cautery, and intracameral adrenaline (epinephrine) are required. Intraoperative hemorrhage, retinal detachment, vitreous prolapse, phthisis bulbi, and cataract are all potential intra- and postoperative complications of iridectomy/iridocyclectomy. Medulloepithelioma of the anterior uvea originates from the undifferentiated neurectodermal cells lining the

embryonic optic cup. Histologically, medulloepitheliomas contain non-pigmented neuroepithelial cells in tubules and rosettes. They are further classified into teratoid and non-teratoid, based on whether they also contain non-ocular tissue such as bone, cartilage, and brain. They are most commonly diagnosed in young horses, appearing as a white-to-pink mass in the pupil or anterior chamber (Fig. 9.33). On ultrasound they are solid in appearance. The age of the horse and the clinical appearance are usually sufficient to make the diagnosis. Equine ocular medulloepitheliomas are slow growing and rarely metastasize, and enucleation/exenteration is the treatment of choice.

Further reading Small animals: anterior chamber Bedford PGC: The anterior uveal cyst as an unusual cause of corneal pigmentation in the dog, J Small Anim Pract 21:97–101, 1980. Callahan A, Zubero J: Hyphema surgery, Am J Ophthalmol 53:522–523, 1962.

Carastro SM, Dugan SJ, Paul AJ: Intraocular dirofilariasis in dogs, Compendium on Continuing Education 14:209–217, 1992. Carter JD, Mausolf F: Clinical and histologic features of pigmented ocular cysts, J Am Anim Hosp Assoc 6:194–200, 1970. Gerding PA, Essex-Sorlie D, Yack R, Vasaune S: Effects of intracameral injection of tissue

plasminogen activator on corneal endothelium and intraocular pressure in dogs, Am J Vet Res 53:890–896, 1992. Gerding P, Essex-Sorlie D, Vasaune S, Yack R: Use of tissue plasminogen activator for intraocular fibrinolysis in dogs, Am J Vet Res 53:894–896, 1992.

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Hill K: Cryoextraction of total hyphema, Arch Ophthalmol 80:368–370, 1968. Howard DR: Canine anterior chamber paracentesis, Southwestern Veterinarian 21:299–301, 1968. Johnson BW, Helper LC, Szajerski ME: Intraocular Cuterebra in a cat, J Am Vet Med Assoc 193:829–830, 1988. Komaromy AM, Brooks DE, Kallberg ME, Andrew SE, Ramsey DT, Ramsey CC: Hyphema. Part I, pathophysiologic considerations, Compendium of Continuing Education 21:1064–1091, 1999. Komaromy AM, Brooks DE, Kallberg ME, Andrew SE, Ramsey DT, Ramsey CC: Hyphema. Part II, diagnosis and treatment, Compendium of Continuing Education 22:74–79, 2000. Laver DW, Spratt DM, Thomas C: Dirofilaria immitis from the eye of a dog, Aust Vet J 45:284–286, 1969. Lim JI, Maguire AM, John G, Mohler MA, Fiscella RG: Intraocular tissue plasminogen activator concentrations after subconjunctival delivery, Ophthalmology 100:373–376, 1993. Martin C, Kaswan R, Gratzek A, Champagne E, Salisbury MA, Ward D: Ocular use of tissue plasminogen activator in companion animals, Progress in Veterinary and Comparative Ophthalmology 3:29–36, 1993. Miller W, Cooper RB: Identifying and treating intraocular Dirofilaria immitis in dogs, Vet Med 82:381–385, 1987. Moon J, Chung S, Myong Y, Chung S, Park C, Baek N, Rhee S: Treatment of post-cataract fibrinous membranes with tissue plasminogen activator, Ophthalmology 99:1256–1259, 1992. Nelms SR, Nasisse MP, Davidson MG, Kirschner SE: Hyphema associated with retinal disease in dogs: 17 cases (1986–1991), J Am Vet Med Assoc 202:1289–1292, 1993. Stiles J, Rankin A: Ophthalmomyiasis interna anterior in a cat: surgical resolution, Vet Ophthalmol 9:165–168, 2006.

Brinkmann MC, Nasisse MP, Davidson MG, English RV, Olivero DK: Neodymium:YAG laser treatment of iris bombe´ and pupillary block glaucoma, Progress in Veterinary and Comparative Ophthalmology 2:13–19, 1992. Cook CS, Wilkie DA: Treatment of presumed iris melanoma in dogs by diode laser photocoagulation: 23 cases, Vet Ophthalmol 2:217–225, 1999. Clerc B: Surgery and chemotherapy for the treatment of adenocarcinoma of the iris and ciliary body in five dogs, Veterinary and Comparative Ophthalmology 6:265–270, 1996. Gelatt KN, Henry JD, Strafuss AC: Excision of an adenocarcinoma of the iris and ciliary body in a dog, J Am Anim Hosp Assoc 6:59–70, 1970. Gelatt KN, Johnson KA, Peiffer RL: Primary pigmented masses in three dogs, J Am Anim Hosp Assoc 15:339–344, 1979. Gemensky-Metzler AJ, Wilkie DA, Cook CS: The use of semiconductor diode laser for deflation and coagulation of anterior uveal cysts in dogs, cats, and horses, Vet Ophthalmol 7:360–367, 2004. Hendrix DVM: Canine anterior uvea. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 812–858. Koster HR, Kenyon KR: Complications of surgery associated with ocular trauma, Int Ophthalmol Clin 32:157–178, 1992. Nadelstein B, Davidson MG, Gilger BC: Pilot study on diode laser iridotomy in dogs, Veterinary and Comparative Ophthalmology 6:230–232, 1996. Nasisse MP, Davidson MG, Olivero DK, Brinkmann M, Nelms S: Neodymium:YAG laser treatment of primary canine intraocular tumors, Progress in Veterinary and Comparative Ophthalmology 3:152–157, 1993. Peiffer RL: Surgery of the iris and ciliary body. In Bojrab MJ, Birchard SJ, Tomlinson JL, editors: Current Techniques in Small Animal Surgery, Philadelphia, 1990, Lea and Febiger, pp 112–117.

Small animals: anterior uvea

Large animals and special species: general

Beckman H, Barraco R, Sugar HS, Gaynes E, Gaynes E: Laser iridectomies, Am J Ophthalmol 72:393–402, 1971. Bellhorn RW, Vainisi SJ: Successful removal of ciliary body adenoma, Mod Vet Pract 50:47–49, 1969.

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Barnett K: Iris and ciliary body. In Barnett KC, Crispin SM, Lavach JD, Matthews AG, editors: Equine Ophthalmology, ed 2, Edinburgh, 2004, Saunders, pp 183–200.

Berger JM, Bell SA, Holmberg BJ, Madigan JE: Successful treatment of head shaking by use of infrared diode laser deflation and coagulation of corpora nigra cysts and behavioral modification in a horse, J Am Vet Med Assoc 233:1610–1612, 2008. Brooks DE, Matthews AG: Anterior chamber, aqueous and glaucoma. In Barnett KC, Crispin SM, Lavach JD, Matthews AG, editors: Equine Ophthalmology, ed 2, Edinburgh, 2004, Saunders, pp 149–164. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274. Canton DD, Murphy CJ, Buyukmihci NC, Schulz T: Pupilloplasty in a great horned owl with pupillary occlusion and cataracts, J Am Vet Med Assoc 201:1087–1090, 1992. Fru¨hauf B, Ohnesorge B, Deegen E, Boeve´ M: Surgical management of equine recurrent uveitis with single port pars plana vitrectomy, Vet Ophthalmol 1:137–151, 1998. Gemensky-Metzler AJ, Wilkie DA, Cook CS: The use of semiconductor diode laser for deflation and coagulation of anterior uveal cysts in dogs, cats, and horses, Vet Ophthalmol 7:360–367, 2004. Gilger BC, Davidson MG, Nadelstein B, Nasisse M: Nd:YAG laser treatment of cystic granula iridica in horses: eight cases (1988–1996), J Am Vet Med Assoc 211:341–343, 1997. Hollingsworth SR: Diseases of the anterior uvea. In Gilger BC, editor: Ophthalmology Equine, St Louis, 2005, Saunders, pp 253–268. Latimer CA, Wyman M: Sector iridectomy in the management of iris melanoma in a horse, Equine Vet J Suppl 2:101–104, 1983. Miller TL, Willis AM, Wilkie DA, HoshawWoodard S, Stanley JRL: Description of ciliary body anatomy and identification of sites for transscleral cyclophotocoagulation in the equine eye, Vet Ophthalmol 4:183–190, 2001. Scotty N, Barrie KP, Brooks DE, Taylor D: Surgical management of a progressive melanocytoma in a Mustang, Vet Ophthalmol 11:75–80, 2008. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1275–1335.

CHAPTER

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Surgical procedures for the glaucomas Kirk N. Gelatt1, Douglas W. Esson1 and Caryn E. Plummer2 1

Small animals; 2Large animals and special species

Chapter contents Anterior chamber shunts/gonioimplants

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Pharmacologic ablation of the ciliary body

299

Surgical anatomy

269

Neuroprotection

300

Preoperative treatment

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273

Introduction Diagnostic and monitoring techniques for glaucoma patients

263

Introduction The glaucomas in animals consist of a group of diseases that share the common feature of elevated intraocular pressure (IOP) and subsequent retinal ganglion cell (RGC) loss and optic nerve atrophy. In humans, an additional form of glaucoma, normal tension glaucoma, consists of progressive optic disk cupping and vision loss in the presence of normal levels of IOP. Normal tension glaucoma has not been reported in animals, although canine patients with progressive optic disk atrophy and gradual loss of vision, in the face of an apparent normal range of IOP, have been identified clinically. Traditionally, the veterinary glaucomas are divided into: 1) breed-related or primary (either ‘open’ or ‘closed’ angle); 2) secondary, in which an underlying cause for the elevated IOP can be determined; and 3) congenital, in which embryonic developmental iridocorneal angle anomalies result in dramatically elevated IOP in very young animals.

The canine glaucomas Glaucomas occur in 1.8% of the canine population in North America. The frequency of bilateral breed-predisposed glaucomas in purebred dogs is the highest of any animal species, except humans. Primary glaucomas are of both open and closed iridocorneal angle types that affect primarily purebred dogs and are thought to be inherited in many breeds. The modes of inheritance have been reported for primary open-angle glaucoma in Beagles (autosomal recessive), and in the Great Dane and Welsh Springer Spaniel (autosomal

dominant). Whereas primary open-angle glaucoma occurs as a chronic disease spanning several years, the angle-closure glaucomas typically manifest as acute clinical situations, followed by a chronic cycle of secondary degeneration. Glaucomas in small animals may be divided by gonioscopy (examination of the iridocorneal anterior chamber angle) and etiology into primary, secondary, and congenital (Box 10.1). Primary glaucomas affect both eyes, although one eye may demonstrate clinical signs of glaucoma several months to years before the opposite eye. Traditionally, the symptoms of primary glaucomas are divided into acute and chronic. However, clinical experience suggests that many of the primary breed-related glaucomas are chronic in their development, with acute elevations in IOP toward the end of the disease that produce overt clinical signs which prompt presentation to the veterinarian. This suggests that treatment for most primary glaucomas in dogs is started with the disease in an already quite advanced state. The clinical signs of acute and often marked elevated levels of IOP, associated with primary closed-angle glaucoma, are a dilated, fixed, or sluggish pupil, bulbar conjunctival and episcleral venous congestion, and corneal edema, as well as patient discomfort and visual disturbances (Fig. 10.1). With prolonged elevations of IOP, secondary enlargement of the globe, lens displacement, breaks in Descemet’s membrane of the cornea, and eventual buphthalmos (enlargement of the globe due to stretching) result (Fig. 10.2). Pain is usually manifested by behavioral changes and sometimes periorbital pain rather than blepharospasm, or not at all. Treatment of the secondary glaucomas, which are often unilateral, is determined based on the underlying disease.

10

Surgical procedures for the glaucomas

Box 10.1 The different types of glaucoma in animals

Primary: • •

Open iridocorneal angle – dog, cat, and horse Narrow/closed angle – dog, cat and horse

Secondary: open/narrow/closed angle – all species •

•

• • • • • • • •

Anterior uveitis – Peripheral anterior synechiae – Pupillary obstruction – Iris bombe´ Lens-induced – Cataract – Displacement: anterior luxation, subluxation, posterior luxation Intraocular neoplasms Hyphema Pigmentary (dog only) Traumatic Aphakic (angle/pupil obstruction) Silicone oil Rhegmatogenous retinal detachment Malignant

Fig. 10.2 Glaucoma and subluxated lens in a dog.

Congenital iridocorneal anomalies •

Open/narrow/closed angle: – Pectinate ligament dysplasia – dog – Goniodysgenesis – dog, cat, foal, and rabbit

Fig. 10.1 Early glaucoma in the dog is often associated with moderate mydriasis, conjunctival congestion, and corneal edema. Repeated tonometry may be necessary to detect the brief bouts of elevated intraocular pressure.

The most frequent cause of secondary glaucoma in the dog is lens displacement, manifested as subluxation, anterior luxation, or posterior luxation (Fig. 10.3). However, with megaloglobus and subtle but gradual increases in IOP, secondary lens subluxation is also common in the primary glaucomas as tension of the lens zonules eventually results in their tearing, usually just below their attachment to the lens equator. In addition, lens-induced uveitis (LIU) is common in the dog, secondary to leakage of lens proteins from cataracts. Occasionally the iridocorneal angles of globes affected by LIU become plugged with lens proteins and inflammatory cells; peripheral anterior synechiae then form,

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Fig. 10.3 Acute anterior lens luxation in a Smooth Fox Terrier. The periphery of the lens is easily visible because corneal edema has not developed.

sufficient to elevate IOP. In both of these mechanisms of secondary glaucoma in dogs, lens or cataract removal may be important in the treatment of elevated IOP. Secondary changes, such as peripheral anterior synechiation due to iridocyclitis, preiridal membrane formation, and filtration angle and cleft closure may necessitate additional medical and/or surgical treatments. Primary and secondary intraocular neoplasms commonly produce secondary glaucoma in dogs and cats. Enucleation is usually the preferred treatment for glaucoma resulting from advanced primary intraocular neoplasms. Secondary pigmentary glaucoma occurs in the Cairn Terrier, manifested by a progressive and relentless infiltration of the anterior uvea and drainage structures by large,

Introduction

round, pigment-laden cells. The optimal treatment for pigmentary glaucoma has not been established, and the visual prognosis for these animals remains poor. A syndrome of iridociliary cystic and pigment-dispersive glaucoma is also recognized with increased frequency in the Golden Retriever. This disease is typically chronic in its development, manifested by the development of thinwalled iridociliary cysts, cataract formation, proteinaceous exudation, pigmentary dispersion, and ultimately glaucoma associated with trabecular meshwork remodeling and cleft collapse. These animals do not typically display iridocorneal abnormalities gonioscopically, and the disease (although often asymmetrical in presentation) is typically bilateral in nature. With the increased frequency of extracapsular and phacoemulsification cataract surgery in dogs, aphakic glaucoma is not infrequent postoperatively. True postsurgical glaucoma should be differentiated from ‘postoperative hypertension’ (POH), which represents an increase in postoperative IOP following phacoemulsification and which occurs 6–12 h postoperatively and typically resolves (with or without adjunctive treatment). This secondary glaucoma results from closure of the iridocorneal angle and subsequent cleft collapse due to peripheral anterior synechiation, or occlusion of the pupil, secondary to annular posterior synechiation. Aphakic glaucoma, with pupillary blockage, requires surgery within 24–48 h after onset. New glaucomas, observed in dogs, are those occurring secondary to silicone oil in the anterior chamber, and those secondary to rhegmatogenous retinal detachments. Silicone oil is used in the repair of retinal detachments in dogs (see Chapter 12). Leakage of this oil into the anterior chamber results in epithelial toxicity, impaired aqueous outflow, and increased IOP, and the oil must be removed from the anterior chamber. Subconjunctival silicone oil appears relatively inert. Retinal detachments in dogs are usually associated with ocular hypotony (low IOP), presumably from increased uveoscleral aqueous humor outflow. However, rhegmatogenous detachments in dogs, especially in those patients with giant retinal tears (90 or more), may release outer rod and cone fragments into the subretinal fluids and vitreous that eventually enter the anterior chamber. This cellular debris in the aqueous humor outflow pathways elevates IOP.

The feline glaucomas Glaucomas in cats occur predominately secondary to anterior uveitis and neoplasia; however, primary open-angle glaucoma also occurs at a very low frequency. In one report, based on 131 enucleated eyes, feline glaucomas were associated with chronic lymphocytic–plasmacytic anterior uveitis (53 eyes), diffuse iridal melanoma/melanocytoma (38 eyes), other neoplasms (14 eyes), lens rupture (4 eyes), anterior lens luxation (4 eyes), primary glaucoma (3 eyes), and other causes (15 eyes). In clinical reports, the most frequent form of glaucoma in cats occurs secondary to anterior uveitis, and neoplasia (Fig. 10.4). In cats with inflammatory-related secondary glaucomas, topical and systemic corticosteroids frequently reduce the anterior uveitis sufficiently to lower IOP. Cats, usually older than 10 years, may also develop lens luxation in the absence of iridocyclitis (Fig. 10.5). Some

Fig. 10.4 Glaucoma secondary to iridocyclitis in the cat. Note the numerous posterior synechiae.

Fig. 10.5 Anterior lens luxation, cataract formation, and secondary glaucoma in an aged cat.

feline eyes have normal levels of IOP; in others the IOP is elevated. The globe is usually slightly enlarged, but the eye often remains visual. Gonioscopy of affected cats (which, unlike dogs, may be performed without the aid of a refracting goniolens) usually reveals open iridocorneal angles; in fact, some iridocorneal angles appear recessed posteriorly in enlarged globes and are wider than normal. Lens removal in normotensive eyes may resolve the problem. If glaucoma is already present, lens removal alone may not sufficiently address the elevated IOP because of permanent outflow abnormalities. An apparently unique feline manifestation of glaucoma is represented by the syndrome of aqueous misdirection. In this poorly understood condition, expansion of the vitreous body (potentially resulting from an inappropriate ‘misdirected’ shunting of aqueous into this space) results in marked

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anterior chamber shallowing, and iridocorneal angle and ciliary cleft compromise. Glaucoma which results from aqueous misdirection is typically chronic in development, and many cats appear to tolerate elevated IOPs surprisingly well. Medical management of this situation is, however, generally less successful with progression. Lenticular phacoemulsification and limited vitrectomy likely represent the most effective surgical course of action when faced with progressively escalating IOP.

The equine glaucomas Glaucomas in horses have been classified into congenital, primary, and secondary to anterior uveitis, lens luxation, and intraocular neoplasia. Aging, persistent anterior uveitis, and breed (Appaloosa is most often affected) are predisposing factors. The signs of elevated IOP in the horse are more subtle, and include enlargement of the globe, variable corneal edema, and corneal striae or deep linear band opacities. Intraocular pressure tends to fluctuate more than in small animals, and higher levels (30–40 mmHg) tend to occur more frequently. Topical medications should be attempted before diode laser cyclophotocoagulation to reduce any existing anterior uveitis and lower IOP. Topical medications which may be used for treatment of glaucoma in the horse include beta adrenergic agents (i.e. 0.5% timolol) and carbonic anhydrase inhibitors (2% dorzolamide). Topical prostaglandins, i.e. latanoprost, may lower IOP only slightly, and their use is tempered by side effects including miosis and ocular irritation.

Congenital glaucoma in rabbits Glaucoma in this species may be encountered by the small animal veterinarian, as pet rabbits become more popular, as well as by the laboratory animal veterinarian. Congenital glaucoma in rabbits, occurring most frequently in New Zealand whites, is inherited as an autosomal recessive trait. Affected rabbits may grow less than normal littermates, and a 25% mortality of affected rabbits occurs. This same form of glaucoma occurs in all breeds of pet and pigmented rabbits. Congenital glaucoma results from iridocorneal angle anomalies, including disorganization and lack

A

of development of the trabecular meshwork, and posterior displacement of the aqueous plexus within the sclera. In affected rabbits, impaired aqueous humor outflow occurs by 3 months, and IOP elevates by 6 months. Corneal and globe enlargement are detectable in animals as young as 4–6 months old. Pet rabbits are typically presented with, at least, one buphthalmic eye (Fig. 10.6). Corneal edema, pupillary dilatation, and elevated IOP are present. Medical treatment of pet rabbits is generally limited to topical agents; however, miotics and beta adrenergics are less effective and of shorter duration than in dogs and cats. Glaucoma surgical procedures, including iridencleisis, can provide normal IOP for several months. Anterior chamber shunts in congenital glaucomatous rabbits have been successful for periods greater than 3 years; however, rabbits generally exhibit an even more aggressive healing and subsequent scarring response at the site of surgical intervention than dogs and cats.

The bovine glaucomas Glaucomas occur rarely in cattle. Primary glaucoma occurs in the Holstein breed and is concurrent with cataract formation, lens luxation, and globe enlargement. Secondary glaucoma from anterior uveitis and perforated corneal ulcers with iris prolapse occurs more frequently, but is not usually treated. In some of these inflammatory glaucomas, once the anterior uveitis decreases, IOP may return to normal.

Diagnostic and monitoring techniques for glaucoma patients Several basic diagnostic procedures are essential to manage the glaucomas pre- and postoperatively in animals. They include: tonometry, ophthalmoscopy (direct/indirect), and gonioscopy (visualization of the iridocorneal angle). These procedures should be used each time the patient is examined. Newer techniques, such as pattern electroretinograms and visual evoked potentials, that estimate damage to the retinal ganglion cells and their axons, detect the changes that precede overt clinical signs of glaucoma by many months to a few years in small animals. Confocal scanning

B

Fig. 10.6 Inherited and congenital glaucoma in rabbits. (a) This disease is a bilateral inherited disease. Note the enlarged globes. (b) It manifests as mydriasis, corneal edema, and enlargement of the globe in animals 3–6 months old.

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Diagnostic and monitoring techniques for glaucoma patients

A

B

Fig. 10.7 Instrumental tonometry is an essential diagnostic and monitoring procedure for glaucomatous small animal patients. (a) The TonoPen™ XL applanation tonometer. (b) Applanation tonometry in a dog with the TonoPen™ tonometer.

microscopy (Heidelberg retinal tomography (HRT), optical coherence tomography (OCT), and nerve fiber analyzers) which is more commonly used in the monitoring of human glaucoma and select research situations, has not found wide usage in veterinary medicine based on cost prohibition as well as logistical challenges associated with patient restraint and poor operator reproducibility. Only applanation tonometers are used in all of the different animal species to estimate IOP, and fortunately are fairly accurate (in spite of varying corneal diameters) within the normal range of IOP, though they tend to underestimate when pressure exceeds about 40 mmHg (Fig. 10.7). Rebound tonometry is increasingly used to estimate IOP based on its ease and excellent patient compliance. Ophthalmoscopy, especially the direct method, permits detection of IOP-related damage to the retina and optic disk. Gonioscopy, or the direct observation of the iridocorneal angle through a special contact goniolens, is the basis for classification of all glaucomas, monitors iridocorneal angle and cleft changes as the glaucoma progresses, and assists selection of the different medical and surgical treatments (Figs 10.8 and 10.9). In most primary open-angle and narrow-angle glaucomas in animals, the iridocorneal angle, as viewed by gonioscopy, progressively narrows and eventually closes with the secondary formation of peripheral anterior synechiae. As the outflow pathways become involved in the glaucomatous process, medical control of IOP becomes progressively more difficult and eventually fails.

Fig. 10.8 Evaluation of the iridocorneal angle is important for classification of the glaucoma and to assist in selection of treatment methods. Beagle with gonioscopic lens on the cornea and examination with the portable slit-lamp biomicroscope.

Glaucoma classification as a guide to therapy Classification of the etiology of glaucoma, based on ophthalmic, gonioscopic, and ultrasonographic examinations, assists in the optimal planning of clinical management and the preservation of vision (Box 10.2). With progressive iridocorneal angle closure that occurs in most canine glaucomas, the choice of medical, surgical or, most frequently a combination of both modalities, must be tailored. In the case of acute goniodysgenic/angle-closure glaucoma in dogs, surgical treatment is the first choice, with medical treatment usually providing only a few weeks to months of effective IOP control. Unfortunately, surgical treatments for the primary canine glaucomas and the maintenance of effective long-term IOP

Fig. 10.9 Appearance of the normal canine iridocorneal angle: (A) iris; (B) cross-section of cornea; (C) corneoscleral trabeculae; and (D) pectinate ligaments. SEM, 29. (Courtesy of Dr Don Samuelson.)

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Box 10.2 Recommended medical and surgical treatment modalities for the different glaucomas in animals

Primary open angle glaucoma Short and long term •

•

•

•

•

•

Prostaglandins (not useful in horses and cats) – Bimatoprost (0.03%) q12–24h – Latanoprost (0.005%) q12–24h – Travoprost (0.004%) q12–24h – Unoprostone isopropyl (12% and 0.15%) q12–24h Miotics (limited use in horses) – Pilocarpine (1–2%) q6–12h – Carbachol (0.75–3%) q8–12h – Demecarium (0.125–0.25%) q12–24h – Echothiophate (0.125–0.25%) q12–24h Carbonic anhydrase inhibitors (CAI) (all species) – Systemic CAI ○ Acetazolamide, 10–25 mg/kg PO q12h ○ Dichlorphenamide, 10–15 mg/kg PO, q8–12h ○ Ethoxyzolamide, 2–8 mg/kg PO q12h ○ Methazolamide, 2.5–10 mg/kg PO q12h – Topical CAI ○ Dorzolamide (2%) q8–12h ○ Brinzolamide (1%) q8–12h Adrenergics (all species) – Adrenaline (epinephrine) (1–2%) q8–12h – Dipivefrin (0.1%) q8–12h Osmotics (all species) – Mannitol, 1–2 g/kg IV – Glycerol, 1–2 mL/kg PO Beta-blocking adrenergics (all species; caution in very small patients)

control have been notoriously challenging. However, diode laser cyclophotocoagulation and anterior chamber shunts appear to offer longer periods of successful control of IOP at this time. In horses, laser cyclophotocoagulation appears more successful than in dogs, although use of anterior chamber shunts is still under study. Surgical procedures for the treatment of the canine glaucomas have traditionally provided only short-term resolution because the filtering fistulae eventually close and fail in the face of inflammation and subsequent tissue remodeling and scarring. Newer anterior chamber shunts, with and without valves, offer improved results. Antifibrotic drugs, such as mitomycin C and 5-fluorouracil (5-FU), may delay or prevent scarring of the alternative aqueous outflow channels and prolong their function. Although intraoperative mitomycin C application has yielded less promising results in animals than those displayed by human patients, the postoperative use of 5-FU has significantly improved the survivability of filtration blebs. Indeed, systemic anti-inflammatory therapy, as well as careful postoperative ‘bleb’ management, appears key to maintaining the functionality of filtering surgeries for as long as possible. Hopefully, during the next decade, advances in surgical treatments of the primary glaucomas in the dog will be similar to those that occurred during the past two decades in cataract surgery in small animals.

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•

– Betaxolol (0.25%) q12–24h – Levobunolol (0.25% and 0.5%) q12–24h – Timolol (0.25% and 0.5%) q12–24h Corticosteroids and non-steroidal anti-inflammatory agents (all species)

Narrow/closed angle Initial control • • • • • •

Osmotics Prostaglandins or miotics Carbonic anhydrase inhibitors Adrenergics Beta-blocking adrenergics Corticosteroids and non-steroidal anti-inflammatory agents

Short and long term • • •

Surgery: filtering procedures, anterior chamber shunts Cyclocryotherapy Laser transscleral or endoscopic cyclophotocoagulation

Secondary glaucomas • •

Address primary underlying condition Antihypertensive medications as necessary

End-stage glaucoma with buphthalmia and blindness (all species) • • •

Surgery: intrascleral prosthesis, enucleation Cyclocryothermy Intravitreal gentamicin (10–25 mg)

Recurrent studies in the canine primary glaucomas suggest that the aqueous humor contains high levels of myocilin, CD44, matrix metalloproteinases (MMPs), and other large proteins; these substances probably adversely affect aqueous outflow after the traditional glaucoma surgeries as well as laser cyclophotocoagulation. High concentrations of these substances are found not only within the trabecular meshwork, but also within the non-pigmented ciliary body epithelium. The inflammatory cascade induced by aqueous humor at the site of filtering surgeries has been characterized in several animal models, and an increased understanding of the major mediators of this process will underlie more effective postoperative treatment strategies. The relatively recent introduction of endoscopic diode cyclophotocoagulation has permitted the direct observation of ciliary body processes as they are sequentially treated, significantly improving the efficacy of this treatment modality.

Medical and/or surgical treatment The decision to employ medical and/or surgical therapy for the veterinary glaucomas is determined by the stage of the disease and the appearance of the iridocorneal angle as judged by gonioscopy, as well as the perceived viability of the visual structures and optic nerve. The dilemma that

Surgical anatomy

confronts the veterinarian is that both medical and those traditional filtering surgical procedures adopted from human ophthalmology do not usually provide long-term relief. As these patients are usually only of middle age, more successful surgical treatments need to be developed. Anterior chamber shunts and newer laser cyclophotocoagulation techniques offer this potential. In general, horses, because of their size, are more difficult to manage medically long term, as the owners must medicate these patients themselves. Medical treatments for the glaucomas either decrease the rate of aqueous humor formation or increase its outflow. A few drugs, such as 1% and 2% adrenaline (epinephrine), affect both aqueous humor outflow and formation. Medical therapy is most effective with open iridocorneal angles. Unfortunately, most forms of primary glaucomas in dogs exhibit narrow iridocorneal angles and outflow tracts, and result in eventual angle and cleft closure; thus medical therapy will be successful only short term or when combined with surgery. In some breeds, angle closure seems secondary and directly associated with enlargement of the globe (megaloglobus or buphthalmia). With narrow angles and closure, medical therapy that primarily affects aqueous humor outflow is ineffective for significant periods of time. Drugs that decrease aqueous humor formation rates are most useful whether the iridocorneal angle is open, narrow or closed. Intravenous osmotic agents are employed to rapidly lower IOP when the possibility for the return of vision is ascertained to be good and/or immediately before surgery. These drugs are typically effective at rapidly lowering IOP in the presence of an intact blood–aqueous barrier; however, their effect is short lived. The use of miotics after glaucoma surgery is recommended infrequently because these drugs may cause mild iridocyclitis and aqueous flare, which may contribute to the failure of filtering surgical procedures. Topical prostaglandins, introduced in the 1990s, can lower significantly IOP in dogs, but are not useful in cats or horses. Traditional surgical treatments of the canine primary glaucomas have enjoyed only limited success rates. These surgeries, including iridencleisis, cyclodialysis, and a combination of both procedures, are not difficult to perform, but these new surgical fistulae for the escape of aqueous humor usually seal and fibrose closed within 6–12 months. With the relatively recent introduction of antifibrotic agents, these techniques may be more successful. Although both contact and non-contact laser-induced partial destruction of the ciliary body (transscleral and endoscopic cyclophotocoagulation) have shown promise, at least 40% of the treated eyes develop cataracts within 6 months of the transscleral technique. Recently, anterior chamber shunts consisting of silicone tubing introduced into the anterior chamber, a pressuresensitive valve, and a biocompatible extrascleral base have shown promise in dogs. These drainage devices are not trouble free, as fibrosis around the episcleral bases can develop rapidly. Patients with successful postoperative control of IOP in excess of 3 years are, however, now common, especially when operated on early in the course of the disease. Blind end-stage glaucomatous globes do represent suitable candidates for these complex surgeries, and are more ideally managed via ‘procedures of comfort’, including enucleation, gentamicin-induced ciliary body destruction, cyclocryoablation or intrascleral prosthesis placement in all animal species.

Surgical anatomy Procedures for the surgical management of glaucoma require accurate knowledge of the anterior orbit, globe, and intraocular tissues, including the iridocorneal angle, lens, iris, and ciliary body (Fig. 10.10). The anatomy of the last three structures (the iris and ciliary body, and the lens) is presented in Chapters 9 and 11, respectively. However, some additional comments regarding the anatomy of this area are important for the effective performance of the different glaucoma surgical procedures. When cyclodialysis, posterior sclerotomy, and anterior chamber shunts are performed in small animals, the surgeon should be familiar with the anterior orbit and, in particular, the extraocular muscular insertions to the globe (Table 10.1). The dog orbit has considerably more room for instrument manipulations and glaucoma surgeries than the cat. Entry through the sclera (posterior sclerotomy for cyclodialysis) is usually performed at the 12 o’clock position because of improved surgical exposure. Like cataract patients, use of neuromuscular blocking drugs during surgery enhances maximal exposure of the globe, reduces intraorbital pressure on the globe, and facilitates anterior chamber surgeries. Placement of the episcleral portion of the anterior chamber shunts is usually performed between the dorsal rectus muscle and medial or lateral rectus muscle insertions. If the anterior chamber shunt is wider than the space between these muscles, portions of it may be manipulated under these muscles. If the implant is long, it may extend posteriorly beyond the equator of the globe and upon the insertions of the retractor oculi muscles. Subsequent implants (if deemed clinically necessary) may be placed in the dorsonasal, ventrolateral, and ventronasal quadrants in that order of preference. At the insertions of the major rectus muscles, both arterial and venous connections with the anterior globe occur. Incision of these rectus muscle insertions should be avoided since any hemorrhage in the wound field will further disseminate and stimulate those growth factors which mediate subsequent bleb fibrosis and failure. Meticulous wet-field cautery facilitates a blood-free surgical site. With most gonioimplants, placement at least 10–14 mm behind the limbus is recommended in dogs. Pupillary margin of iris Basal iris Pectinate ligaments

Cornea

Bulbar conjunctiva Limbus

Pars plicata ciliaris Pars plana ciliaris Ora ciliaris retinae

Sclerociliary cleft

Zonules

Fig. 10.10 Diagram of anterior segment anatomy for surgeries for the glaucomas.

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Table 10.1 Anatomy of the rectus muscles in dogs and cats

Mean distance of the extraocular insertions of the dorsal (DR), medial (MR), lateral (LR), and ventral (VR) rectus

Species

DR

MR

LR

VR

Muscles from the limbus (mm) Canine

7.5

5.5

8.7

5.7

Feline

7.5

7.0

9–10

6–9

Width of the rectus muscle insertions (mm) Canine

8.5

10

9.9

8.0

Feline

5.5

6.2

5.5

5.3

Distance between the extraocular rectus muscles (mm) Canine

17.9

17.4

18.2

18.1

Feline

16.3

16.0

16.4

16.1

Most glaucoma surgeries are performed in the dorsal or dorsolateral one-half of the globe because of limited surgical exposure medially and ventrally in small animals. The 9 and 3 o’clock positions of the sclera are avoided because of the medial and lateral long posterior ciliary arteries. These two vessels provide the majority of the blood supply to the anterior uvea, and should not be disturbed surgically or during laser or cryothermy destruction of the ciliary body. If a scleral incision is being performed (such as in the case of sclerotomy, cyclodialysis or iridencleisis), the proper distance of the scleral incision from the limbus is critical. This distance is also important in judging the site of probe application when applying transscleral laser photocoagulation. Ideally, the scleral incision is positioned directly over the pars plana ciliaris or posterior portion of the ciliary body. Anterior penetration increases the risk of intraocular hemorrhage because of damage to the ciliary body processes. Scleral incisions that are too far posterior, overlying the ora serrata or peripheral retina, have an increased risk of producing a retinal hole and secondary retinal detachment. With globe enlargement that is frequent with small animal glaucoma, selection of the site over the pars plana is more difficult. Dorsal sclerotomy is performed at the 12 o’clock position, and its anterior and posterior borders are about 4–5 and 7 mm, respectively, from the limbus. The length of the pars plana ciliaris varies in dogs by quadrant, with the medial aspect the shortest. For laser and cryothermy destruction of the ciliary processes, measurements from the limbus to the ciliary body processes (pars plicata (corona) ciliaris) are critical for placement of the probe. These measurements change in the glaucomas when dog and cat globes are enlarged, and the sclera stretches. For measurement of the exact distance from the limbus, calipers are recommended. In the dog, laser cyclophotocoagulation is applied 5 mm behind the dorsal limbus. Application of laser transscleral cyclophotocoagulation or cyclocryothermy at the incorrect position attenuates the anticipated results. The iris is a highly vascular and spongy tissue. Tearing of the iris of the dog usually results in variable hemorrhage which can be controlled only by electrocautery. The

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large major iridal arteriolar circle is located about 50% of the time in either the base of the iris or the anterior ciliary body of dogs. Hence, incision of the basal iris (as with a peripheral iridectomy) may cause excessive hemorrhage in about 50% of dogs. Iridectomies in dogs usually require wet-field cautery for hemostasis, applied simultaneously with the electrocautery for excision of the iris or following sharp incision by iris scissors. An embryologic cleavage line is present between the sclera and the underlying iris and ciliary body. This area can be traversed, without significant hemorrhage, by a cyclodialysis spatula inserted through the sclera about 5–7 mm posterior to the limbus, and extending into the anterior chamber. If the spatula is malpositioned within the outer aspects of the iris and ciliary body, copious hemorrhage results. While the macroscopic anatomy of the iridocorneal or anterior chamber angle of the dog and cat differs somewhat from the radial canal of Schlemm in humans and nonhuman primates, the ultrastructure of the trabecular meshwork and the aqueous humor dynamics are remarkably similar (Fig. 10.11). In dogs and humans the percentage of aqueous humor that exits the trabecular meshwork is about 85–90% (conventional outflow), and about 10–15% leaves by the uveoscleral route. The rates of aqueous humor turnover in dogs, cats, and humans appear quite similar (about 5.0–6.0 mL/min), although cats have been thought to have a much higher rate (about 15 mL/min). In horses, the best studies to date suggest that the majority of aqueous humor leaves through the uveoscleral outflow pathway. Hence, aqueous humor gradually flows posteriorly through the base of the iris and ciliary body to enter the subscleral space between the choroid and sclera. Aqueous humor outflow pathways have the following boundaries: 1) the limbus and anterior chamber; 2) inwardly the pectinate ligaments, base of the iris, and inner aspects of the ciliary or sclerociliary cleft or sinus; 3) posteriorly the deeper aspects of the ciliary cleft or sinus; and 4) outwardly the sclera anteriorly and the outer aspects of the ciliary or sclerociliary cleft posteriorly (Fig. 10.12). Canine and feline aqueous outflow pathways differ slightly from those of humans by a cleavage of the anterior ciliary body which contains most of the trabeculae, and the iris base that directly communicates with the peripheral anterior chamber. Pectinate ligaments of various sizes and shapes connect

Fig. 10.11 The anterior segment of the dog eye: (A) cornea; (B) iris; (C) ciliary body (pars plicata ciliaris); (D) iridocorneal angle; (E) ciliary cleft; and (F) pectinate ligaments. SEM, 20. (Courtesy of Dr Don Samuelson.)

Surgical anatomy

Pupil Anterior chamber

Corneoscleral trabeculae

Posterior chamber

Sclerociliary cleft

Ciliary body process Uveoscleral pathways

Fig. 10.12 The flow (arrows) of aqueous humor in the dog and cat. Formation by the ciliary body process, into the posterior chamber, through the pupil, into the anterior chamber, and exit through the corneoscleral trabeculae and uveoscleral pathways.

the inner posterior limbus and termination of Descemet’s membrane to the anterior base of the iris. Although these pectinate ligaments appear to play no direct role in aqueous humor outflow unless significantly malformed/imperforate, they do provide stability for the iris. These iridocorneal angle anatomic differences between humans, non-human primates, and other animal species are thought to be associated with lens accommodation rather any differences in aqueous humor outflow physiology. In horses, very stout pectinate ligaments span the opening of the sclerociliary cleft and are often visible without a gonioscopic lens at the nasal and temporal quadrants. The uveal trabecular meshwork (UTM; 74%), corneoscleral trabecular meshwork (CSTM; 22%), and angular aqueous plexus (AAP; 4%) have been quantified in horses; conventional trabecular aqueous humor outflow, as measured by pneumatonography, is 0.90 mL/min (about four times greater than in humans, dogs, and cats). The intertrabecular spaces of the uveal trabecular meshwork are very wide compared to the corneoscleral meshwork; this suggests that a significant resistance to aqueous humor outflow occurs in the latter trabeculae. Using microsphere perfusion studies it also appears that the majority of aqueous humor exiting the equine outflow pathways moves more posteriorly to enter mainly the vortex venous system. The anatomic differences in the outflow pathways in many species of animals appear related primarily to the needs of accommodation rather than physiologic and morphologic differences in aqueous humor dynamics. The musculature of the ciliary body in dogs and cats is less developed than in humans, as accommodation, i.e. changes in the lens shape, is limited. The limited ciliary musculature and very large lenses in horses and cows suggest very limited accommodation. Aqueous humor leaves most of the non-human primate species through the corneal or corneoscleral trabecular meshwork (conventional or pressure-sensitive outflow) to enter eventually the episcleral plexus anteriorly, or uveal meshwork, and to pass through the ciliary body posteriorly (unconventional/uveoscleral or pressure-insensitive outflow). In humans, microsurgical techniques have been developed that include suture cannulation of Schlemm’s canal and excision of segments of the corneoscleral trabecular meshwork

(external trabeculectomy). Other procedures, such as goniosynechiolysis (restoring areas of the iridocorneal angle closed by peripheral anterior synechiae) and goniotomy (incision of congenital tissues obstructing aqueous humor flow into Schlemm’s canal), have not been reported in small animals. These microsurgical procedures represent the current refinement of human glaucoma surgical techniques, and suggest future possibilities for small animals. However, most primary glaucomas in the dog, when first presented to the veterinarian, already exhibit narrow-to-closed iridocorneal angles and clefts. The above techniques are more applicable to open iridocorneal angles. Nevertheless, experimental procedures such as goniotomy, trabecular meshwork transplantation, and gene transfer to the trabecular cells are future techniques worthy of investigation. The pathophysiology of glaucoma surgery is influenced by the type and stage of glaucoma, the presence of secondary changes, and the type of glaucoma surgery performed, as well as changes resulting from either cryo- or cyclociliary destruction. For the majority of the primary glaucomas in dogs, the anatomic and biochemical status of the aqueous outflow pathways during the genesis of elevation of IOP have not been determined. Progressive narrowing and eventual closure of the iridocorneal angle occurs with all primary glaucomas in dogs, but these changes may be secondary to gradual enlargement of the lens and/or globe, iridal irritation, lenticular subluxation and instability, iridocorneal angle and trabecular meshwork remodeling in the face of chronic inflammation and/or cellular infiltration, and secondary instability of the ciliary cleft. These changes, whether primary or secondary, further complicate the medical and surgical treatment of primary canine glaucoma. The initial presentation of canine glaucoma is typified by narrow-to-closed anterior chambers and iridocorneal angles. The distances between the basal iris and posterior limbus, as well as the anterior opening of the ciliary cleft, are reduced or closed as viewed by gonioscopy. Hence, surgical entry into the anterior chamber through a limbal incision in the glaucomatous eye must compensate for these changes. The term ‘goniodysgenesis’ has unfortunately been applied inappropriately to many of the primary glaucomas in dogs. Goniodysgenesis refers to a diverse group of congenital iridocorneal anomalies in children that result in glaucoma in early life and infancy. Congenital glaucomas in puppies and kittens resulting from goniodysgenesis are rare. The term goniodysgenesis was first applied to the presence of large areas of consolidated pectinate ligaments (mesodermal bands) in primary glaucoma in the Basset hound. Primary glaucoma in the Basset hound, like most breeds of dogs with breed-predisposed glaucoma, occurs in adulthood, and is not considered a congenital glaucoma. For these areas of consolidated pectinate ligaments to significantly impair the outflow of aqueous humor, essentially the entire iridocorneal angle would need to be affected. Often ‘flow holes’ are present in these consolidated pectinate ligaments (pectinate ligament dysplasia), permitting aqueous humor to traverse the entire filtration angle. The physiologic status of the trabecular meshwork environment, as well as stability of the ciliary cleft in the primary glaucomas with pectinate ligament dysplasia, remain a mystery, and may be the key to the treatment of these glaucomas.

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The persistence of large, poorly differentiated sheets of pectinate ligaments in dogs should be classified as dysplasia of the pectinate ligaments. It appears that, in the dog, the formation of primary and secondary pectinate ligaments is often imperfect, and the range and relative size of the persistent areas of dysplastic ligaments in normal dogs and selected breeds need to be established, with a significant variation in the ‘normal’ population likely being present. The presence of dysplastic pectinate ligaments in dogs correlates to, but does not parallel, the genesis of the primary glaucomas. Significant diseases of the adjacent trabecular meshwork, not yet defined, may underlie the mechanisms of glaucoma. Surgery of the pectinate ligaments, as it relates to the outflow of aqueous humor, has not been reported in dogs, but these broad sheets of pectinate ligaments may be of increased relevance in those glaucoma surgeries that invade the iridocorneal angle. Pre-iridal fibrovascular membranes (PIFMs) are common in advanced glaucomas in dogs. These membranes are potential sources of fibrin and other proteins, as well as erythrocytes and inflammatory cells that are released when the anterior chamber is opened and IOP lowered abruptly to 0 mmHg (Fig. 10.13). These same membranes may bridge the anterior iridocorneal angle, contributing to the formation of peripheral anterior synechiae (PAS), and even extend across the pupil and anterior lens capsule, and into the posterior chamber. Both PIFMs and PAS interfere with surgical entry into the anterior chamber by scalpel blade or hypodermic needle, and may contribute to early failures of many of the traditional filtering procedures in dogs. Experience suggests that glaucoma filtering procedures in the primary glaucomas in dogs are more successful when performed in the early phases of the disease. This opportunity usually occurs in the fellow asymptomatic eye as opposed to the opposite symptomatic eye which often exhibits end-stage glaucoma and blindness at the initial presentation. The status of the ciliary body and its ability to form aqueous humor are important considerations when planning glaucoma surgery. Extensive damage to the ciliary body may occur in cases of advanced glaucoma, and is influenced, in part, by the severity and chronicity of IOP elevation, as well as the presence of inflammation. Marked elevations in IOP in the dog are often followed by brief (usually a

Fig. 10.13 Pre-iridal membrane (arrows) on the anterior surface of the iris in a Chow Chow with advanced glaucoma. These vascular membranes may impair aqueous humor outflow through the iridocorneal angle and interfere with glaucoma filtering surgical procedures in small animals. H & E, 100.

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few days) ocular hypotony; this is presumably the result of reduced rates of aqueous humor formation due to pressure-associated pathology at the ciliary body (sometimes termed ‘ciliary body shock’). If this damage is extensive and irreversible, phthisis bulbi results when normal aqueous humor outflow cannot be re-established. The rate of aqueous humor formation, as measured by fluorophotometry, has not been performed clinically in glaucomatous dogs, and therefore the status of the ciliary body and its ability to produce normal levels of aqueous humor are determined by clinical history and evaluation, tonography, and daily monitoring of IOP prior to surgical intervention. The position of the lens can markedly influence the success or failure of glaucoma surgeries in all animal species. The lens may intermittently occlude the pupil, causing the basal iris to contact the inner posterior limbus and stimulate formation of peripheral anterior synechiae. These abrupt and temporary increases in IOP may hasten progressive damage to all ocular tissues, including the retina and optic disk. Lenticular instability (as well as increased lens/iris contact and microabrasion) may also stimulate chronic, low-intensity inflammation and pigment dispersion. Free melanin pigment dispersion has been demonstrated with the trabecular meshwork of advanced glaucomatous globes (including those affected by primary structural or dysplastic changes). Inflammatory cells may contribute to trabecular meshwork atrophy and subsequent ciliary cleft collapse which typifies end-stage glaucomatous globes. The exact relationship between these factors during the genesis of the canine glaucomas, however, remains poorly understood. An anteriorly luxated lens, stuck in the anterior chamber, often has vitreous still affixed at its hyaloideocapsular (Wieger’s ligament) attachments that can completely occlude the pupil and cause marked elevations in IOP posterior to the pupil. Subluxation or luxation of the lens posteriorly into the vitreous can displace vitreous into the pupil and anterior chamber. In most types of glaucoma the vitreous frequently undergoes partial liquefaction (syneresis). Hence, during many surgical procedures for glaucoma when the anterior hyaloid membrane has been already torn, presentation of the vitreous may occur within the anterior chamber. To minimize vitreous disturbances, osmotic agents are essential not only to reduce IOP, but also to dehydrate the vitreous, reducing its size. In advanced glaucoma eyes, syneresis of the vitreous is often complete. Preoperative administration of an osmotic agent provides the additional benefit of minimizing the dangers presented by rapid decompression of a hypertensive globe. Potentially the most significant complication associated with the glaucoma surgeries is the pronounced inflammatory response which occurs at the surgical site in which aqueous humor is redirected into the episcleral space and surrounding tissues. This response results in considerable fibrosis about the area, and ultimately contributes to the failure of filtration blebs or drainage setons. Of interest, the normal passage of aqueous humor through the uveoscleral pathway all the way posterior to the optic nerve head does not incite this inflammatory response! Although not fully understood, the mechanism of this response appears to follow the general parameters of the wound-healing cascade, with growth factors mediating fibroblastic recruitment

Surgical procedures for the glaucomas

and transformation. Connective tissue growth factor (CTGF) and transforming growth factor beta 2 (TGF-b2) have been shown to mediate these initial events in multiple animal models (Tables 10.2a and 10.2b). Subsequent tissue fibrosis and cicatricial remodeling is at least partially matrix metalloproteinase mediated. Successfully controlling this postoperative fibrotic response is crucial to improving the long-term success rates of all glaucoma surgeries. Ultimately, this may require a ‘chemotherapeutic’ approach involving multiple targeted intraoperative and postoperative medications (applied topically as well as systemically). Achieving this goal represents the single greatest challenge in the successful long-term surgical treatment of this disease complex!

Preoperative treatment Preoperative considerations in the treatment of glaucoma include: 1) preoperative control of IOP to levels consistent with normal RGC physiologic function (<25–33 mmHg); 2) suppression of concurrent anterior segment inflammation; and 3) vitreous body dehydration and shrinkage with osmotic agents. IOP must be reduced to the low normal range in patients prior to glaucoma surgery if at all possible. Fortunately, combinations of miotics, osmotic agents, adrenergic agents, and carbonic anhydrase inhibitors can usually lower IOP to 10–15 mmHg, albeit temporarily. Surgical entry into the anterior chamber when IOP is 25 mmHg or higher can be hazardous to the eye and surgical outcome. If necessary, additional vigorous massage and hypotensive medical treatment should be initiated (such as an additional intravenous dose of osmotic agents) before the eye is entered. Glaucoma procedures in a globe with elevated IOP exhibit higher risk and lower surgical success rates. A glaucomatous eye without satisfactory ocular hypotension upon entry may exhibit choroidal hemorrhage, choroidal edema, vitreous protrusion through the pupil, and

Table 10.2a Matrix metalloproteinases (MMPs) important in ocular wound healing

MMP common name

Designation

Substrates and actions

Fibroblast collagenase

(MMP-1)

Cleaves single bond in native types I, II and III collagens

72 kDa Gelatinase

(MMP-2)

Degrades types IV, V, and VII collagens, gelatin, fibronectin; synthesized by fibroblasts and macrophages

92 kDa Gelatinase

(MMP-9)

Degrades types IV and V collagen, gelatin; synthesized by epithelial cells, macrophages, polymorphonuclear leukocytes

Stromelysin

(MMP-3)

Degrades proteoglycans, fibronectin, laminin, gelatin and types III, IV, and V collagen

Neutrophil collagenase

(MMP-8)

Similar to MMP-1, degrades type I, II, and III collagen

forward displacement of the iris. Intraocular hemorrhage is also more apt to occur in these globes. Cautious anterior chamber paracentesis may be performed in a glaucomatous eye that has not responded to vigorous medical treatment. Keratocentesis is usually performed under general anesthesia or deep sedation, and aqueous humor is removed slowly from the anterior chamber after first decompressing the syringe plunger (see Chapter 9). Many types of canine glaucoma exhibit concurrent aqueous humor flare, altered blood–aqueous barrier, and mild to chronic iridocyclitis. The iridocyclitis may also be a primary or secondary factor in the genesis of the glaucoma. Topical and systemic corticosteroids and non-steroidal anti-inflammatory drugs (NSAIDs) are indicated to suppress inflammation and reduce inflammatory cells and proteins in the aqueous humor. The iridocyclitis and aqueous exudates can compromise short- and long-term existing aqueous humor outflow pathways as well as the new surgical site. Aggressive systemic anti-inflammatory therapy may additionally contribute to arresting the destructive and selfperpetuating milieu of RGC death. Control of the pupil immediately before surgery often contributes to the overall success rate of intraocular procedures. For most types of glaucoma surgery, the desired pupil size at the time of surgery is either normal or miotic. The pupil is usually constricted for surgical procedures, including iridencleisis, cyclodialysis, iridencleisis–cyclodialysis, corneoscleral trephination, and cyclocryothermy. Pupil size when luxated lenses are removed depends on the position of the lens. For anterior luxated lenses, the pupil is constricted immediately before surgery to maintain the lens within the anterior chamber. Prior to surgery, 10% phenylephrine may assist in re-establishing pupillary flow and lower IOP in the posterior segment; sometimes a combination of 2% pilocarpine and 10% phenylephrine is alternated to provide a constantly moving and moderatesized pupil. A miotic pupil may aggravate the glaucomatous process by creating an acute pupillary blockage related to the lens or adherent vitreous, or both. Before removal of subluxated and posterior luxated lenses, the pupil is dilated with several instillations of 1% tropicamide, 1% atropine or 10% phenylephrine, or some combination of these agents. At the time of mydriasis, IOP should be within normal limits. Following the intact removal of a luxated or subluxated lens, degenerate vitreous within the pupillary opening or anterior chamber should be carefully removed by the judicious use of automated vitrectomy where possible.

Surgical procedures for the glaucomas Surgical procedures for the treatment of the glaucomas may be divided into two types: 1) those that increase outflow of aqueous humor via alternative pathways of drainage; and 2) those that decrease the rate of formation of aqueous humor by destroying part of the pars plicata or corona ciliaris (Table 10.3). Procedures to increase the outflow of aqueous humor include iridencleisis, corneoscleral trephination, cyclodialysis, combined iridencleisis and cyclodialysis, posterior sclerectomy, and anterior chamber shunts (gonioimplants). Additional procedures to increase the outflow of aqueous humor include goniopuncture, iridosclerectomy,

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Table 10.2b Growth factors and cytokines important in ocular wound healing

Abbreviation

Description

Epidermal growth factor

EGF

Synthesized by corneal epithelial cells, lacrimal gland; mitogen and chemotactic factor for all three types of corneal cell

Transforming growth factor alpha

TGF-a

Structurally and functionally similar to EGF; synthesized by corneal epithelial cells, lacrimal gland

Transforming growth factor beta

TGF-b

Three isoforms: TGF-b1, TGF-b2, TGF-b3; promotes formation of extracellular matrix; TGF-b2 present in aqueous humor; synthesized by multiple types of cell

Basic fibroblast growth factor

bFGF

Detected in basement membranes; synthesized by endothelial cells; mitogen for fibroblasts and endothelial cells; angiogenic

Acidic fibroblast growth factor

aFGF

Detected in basal layer of corneal epithelial cells and basement membranes; synthesized by endothelial cells; mitogen for fibroblasts and endothelial cells; angiogenic

Keratinocyte growth factor

KGF

Synthesized by keratocytes; stimulates corneal epidermal cell proliferation and migration

Hepatocyte growth factor

HGF

Synthesized by corneal epithelial cells; stimulates corneal epidermal cell proliferation and migration

Platelet-derived growth factor

PDGF

Synthesized by corneal epithelial cells; stimulates proliferation of stromal fibroblasts

Insulin-like growth factor I

IGF-I

Part of the IGF axis (comprising surface receptors, ligands, binding proteins and proteases). Involved in early healing and promotes cellular proliferation.

Connective tissue growth factor

CTGF

Stimulates fibrosis and mediates the actions of TGF-b on matrix formation

Tumor necrosis factor alpha

TNF-a

Proinflammatory cytokine with multiple effects including chemotaxis of leukocytes, increased production of MMPs, and induction of apoptosis; soluble TNF-a is released by TACE cleavage of transmembrane pro-TNF-a

Interleukin-1 beta

IL-1b

Proinflammatory cytokine synthesized by corneal epithelial cells; stimulates MMP production by keratocytes

Growth factor

Cytokines

TACE, tumor necrosis factor-a converting enzyme.

Table 10.3 Mechanisms of surgical treatments for the glaucomas

Mechanism

Type of surgery

Filtration

Iridencleisis

Filtration/decrease formation*

Cyclodialysis

Pupil bypass

Iridectomy

Filtration/decrease formation*

Iridencleisis/cyclodialysis

Iridocorneal angle bypass

Corneoscleral trephination

Filtration/decrease formation

Cyclodialysis/iridocyclectomy

Iridocorneal angle bypass

Anterior chamber shunts/ gonioimplants

Decrease aqueous formation

Cyclocryotherapy

Decrease aqueous formation

Transscleral or endoscopic cyclophotocoagulation (diode laser)

Destroy ciliary body epithelia

Intravitreal gentamicin

*Short term only.

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goniotomy, trabeculectomy, and sinusotomy, but these surgical procedures have not been described in dogs. Techniques used to reduce the rate of aqueous humor formation by partial destruction of the ciliary body include cyclocryothermy, cyclodiathermy, and diode laser transscleral or endoscopic cyclophotocoagulation. The popularity, staging, and combining of these different glaucoma surgical techniques are constantly evolving. However, as new antifibrosis drugs are developed, some of these older traditional selected filtration procedures may again be more useful. Additionally, minimizing the egress of blood into the surgical wound field during all forms of glaucoma surgery will help minimize the subsequent healing and scarring response which is mediated by red blood cell-delivered growth factors. Removal of the lens, although not commonly considered a surgical procedure for treatment of lens-induced glaucoma, may be necessary in the management of many canine glaucomas. Lens removal may be indicated for secondary glaucomas associated with lens-induced uveitis and cataract resorption, intumescent cataracts, anterior and posterior lens luxations, and subluxations. When the lens is displaced from its patellar fossa in a primary glaucomatous eye, maintenance of IOP within normal limits by surgical or medical treatment, or a combination of both modalities, may be impossible without first removing the luxated lens.

Surgical procedures for the glaucomas

The canine lens may additionally need to be removed in the face of aggressive endoscopic cyclophotocoagulation in order to facilitate adequate exposure and reduce the necessity for subsequent cataract removal. Furthermore, the absence of the lens in the face of developing/outright glaucoma may contribute via decreasing lens/iridal contact and pigment shedding, anterior chamber crowding, and iridocorneal angle and/or ciliary cleft collapse.

Iridencleisis In the iridencleisis procedure, a radial section of iris is permanently positioned through a limbal incision into the subconjunctival spaces beneath the bulbar conjunctiva (Fig. 10.14). Reduction in IOP following iridencleisis is primarily related to the escape of aqueous humor through this area. Aqueous may also filter through the space between the two pillars of the iris, as well as through the iridal stroma itself. Iridencleisis may be used successfully in the management of narrow- and closed-angle glaucoma, acute iris bombe´ associated with annular posterior synechiae, and glaucoma associated with peripheral anterior synechiae. When the iris is thin, atrophied, or adhered to the lens with focal posterior synechiae, iridencleisis is not recommended. After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of corneal and conjunctival surfaces with 0.5% povidone–iodine solution with swabs, the eyelids are retracted by speculum. The iridencleisis procedure is performed at the dorsal one-half of the limbus, usually at the 12 o’clock position. An alternative surgical site may be selected if other surgical procedures have been previously performed in the preferred site. With curved blunt-tipped tenotomy scissors, a limbalbased 10 mm bulbar conjunctival flap is constructed. The flap is usually 12–18 mm long. Tenon’s capsule is identified and, if extensive, excised from the overlying bulbar conjunctiva and sclera in the area of the limbal incision (Fig. 10.15a).

Fig. 10.14 Iridencleisis 1 year postoperatively in a dog. A large posterior synechia is present as well as some pigment migration on the anterior lens capsule. Early cortical cataract formation is also present.

The anterior chamber is entered through the limbus with the Beaver No. 6500 microsurgical (Fig. 10.15b). The limbal incision is usually 8–10 mm long. A 1–2 mm section of sclera in the caudal aspect of the limbal incision is carefully excised (anterior sclerectomy). Hemostasis and limited tissue destruction are achieved by cautious electrocautery (Fig. 10.15c). The wet-field coagulator is superior in this region because of the frequent presence of aqueous humor. Limited application of electrocautery on the scleral aspect of the incision seems to facilitate maintenance of an open fistula and reduces the possibility of closure by fibrosis. During the limbal incision and subsequent anterior sclerectomy, the iris may protrude into the incision. A blunt iris hook or serrated iris forceps is carefully manipulated into the anterior chamber to grasp the dorsal pupillary margin and protract the iris into the limbal incision (Fig. 10.15d). Using the iris hook and serrated forceps, the iris is carefully pulled from the anterior chamber into the limbal incision (Fig. 10.15e). With both iris forceps pulling in opposite directions, the iris is slowly torn radially to its base. Each pillar of the iris, with its pigmented epithelium exposed, is manipulated into the respective end of the limbal incision (Fig. 10.15f). To minimize the possibility of the iris pillar retracting back into the anterior chamber, each tag of the iris is attached to the sclera with a 6-0 simple interrupted absorbable suture (Fig. 10.15g). The anterior chamber is carefully irrigated with balanced salt solution to remove all fibrin and blood. With successful manipulation of the iris and judicious use of electrocautery, hemorrhage and fibrin in the anterior chamber at the conclusion of surgery are generally avoided. In the event that fibrin remains, or continues to be formed in the anterior chamber, tissue plasminogen activator (tPA; 25–50 mg) is injected between the two iris pillars into the anterior chamber (Fig. 10.15h). The limbal wound is not apposed with sutures. The bulbar conjunctival flap is apposed with a 6-0 to 7-0 simple continuous absorbable suture (Fig. 10.15i). Postoperative treatment after iridencleisis consists of: 1) maintenance of a pupil of normal size (neither dilated nor constricted); 2) maintenance of a normal range of IOP; and 3) suppression of postoperative iridocyclitis with topical and systemic corticosteroids, NSAIDs, or a combination of these agents. Topical and systemic antibiotics are administered to prevent postoperative infections. Phenylephrine (10%) and pilocarpine (2%) are alternately instilled to facilitate movement of the pupil and minimize the possibility of focal posterior synechiae. The ratio of these two drugs is varied depending on pupil size. In the event that a relatively normal-sized pupil cannot be obtained because of postoperative inflammation, 1% tropicamide is administered until a moderately dilated pupil is achieved. Topical and systemic carbonic anhydrase inhibitors are administered postoperatively if IOP exceeds 25 mmHg. They are not necessary if the IOP is normal and can be monitored daily. Potential complications that may occur following iridencleisis include excessive/uncontrolled iridocyclitis, hyphema, posterior synechiation, iridal pigment shedding onto the anterior lens capsule, and cataract formation. Blebs usually occur following iridencleisis in the area of the limbal incision. These blebs may eventually flatten, but may still function. The bulbar conjunctiva in the area of the limbal incision usually demonstrates increased vascularity.

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Surgical procedures for the glaucomas

A

B

C

D

E

F

G

H

l

Fig. 10.15 In the iridencleisis procedure, two pillars of iris are externalized into the subconjunctival tissues through a limbal incision. Filtration of aqueous humor occurs through the space between the iris pillars as well as within the pillars themselves. (a) A 10 mm wide limbal-based conjunctival flap is constructed with Steven’s tenotomy scissors. (b) The anterior chamber is entered at the limbus with a stab incision with the Beaver No. 6500 microsurgical blade. The limbal incision is lengthened with the scalpel blade or corneoscleral scissors to about 8–10 mm. (c) In the central of the limbal incision, a 1–2 mm section of sclera (anterior sclerectomy) is excised by scissors. Some cautery may be necessary for scleral hemostasis. (d) A blunt iris hook is carefully inserted into the anterior chamber to the pupillary margin to retract the iris into the limbal incision. (e) The iris is protracted further by thumb forceps. (f) The iris is then grasped with an additional thumb forceps and gradually torn to its base. (g) Each pillar of iris is anchored to the sclera with a 6-0 simple interrupted absorbable suture. (h) Any hemorrhage and/or fibrin is irrigated from the anterior chamber with lactated Ringer’s solution. (i) The conjunctival flap is apposed with a 6-0 to 7-0 simple continuous absorbable suture.

Failure of the iridencleisis procedure to satisfactorily control IOP is usually related to the short-term closure of the limbal incision with inflammatory products, secondary to postoperative iridocyclitis, or long-term loss of filtration secondary to fibrosis several months later. Gentle massage of the eye postoperatively for several months is recommended. Long-term administration of topical 1% prednisolone for 6 months or indefinitely may increase the success rate of the iridencleisis procedure.

Cyclodialysis In the cyclodialysis procedure, an artificial fistula is created from the anterior chamber within the subscleral space beneath the iris and ciliary body to a posterior opening in the sclera and the subconjunctival space. Cyclodialysis appears to lower IOP by: 1) rerouting part of the outflow of aqueous humor from the anterior chamber into the subconjunctival space; 2) increasing the outflow of aqueous humor into the

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suprachoroidal space (the non-conventional or uveoscleral route); and 3) temporarily reducing the rate of aqueous humor formation probably secondary to separation of the ciliary body from the sclera and some of its vascular supply. The cyclodialysis procedure may be performed posteriorly through the scleral incision or anteriorly from the anterior chamber, usually in conjunction with removal of the lens. The cyclodialysis technique may have application in the treatment of narrow-angle glaucoma, glaucoma associated with extensive peripheral anterior synechiae, goniodysgenesis-associated glaucoma (congenital glaucoma), and glaucoma associated with iris atrophy. After the onset of general anesthesia, clipping the eyelid hair and cleansing of corneal and conjunctival surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. The operation is usually performed in the dorsal one-half of the globe at the 12 o’clock position. With blunt-tipped, slightly curved, tenotomy eye scissors, a fornix-based bulbar conjunctival flap, measuring 10 mm deep by 10 mm wide, is

Surgical procedures for the glaucomas

fashioned (Fig. 10.16a). Excessive Tenon’s capsule, when present between the bulbar conjunctiva and the sclera, is excised from the surgical site. As an intact bulbar conjunctiva covers the filtering area, inadvertent incisions in the conjunctiva (‘buttonholes’) should be studiously avoided. A linear scleral incision is made 4–5 mm from and parallel to the limbus for approximately 8–10 mm using the Beaver No. 6400 microsurgical blade (Fig. 10.16b). Hemorrhage from the sclera, which may be extensive, is controlled using wet-field coagulation (or less ideally with hand electrocautery). After completion of the scleral incision parallel to the limbus, a rectangular section of sclera, measuring 2  6–8 mm, is incised. The depth of the scleral incision should be carefully controlled so that the underlying ciliary body is not penetrated (Fig. 10.16c). When the pigmented ciliary body becomes evident, the scleral block is carefully excised by tenotomy scissors (Fig. 10.16d). The sides of the scleral defect are lightly coagulated to reduce the possibility of the defect healing closed.

A cyclodialysis spatula is carefully inserted in the anterior part of the scleral incision between the sclera and ciliary body, and manipulated forward into the anterior chamber (Fig. 10.16e). When the anterior chamber is entered, aqueous humor escapes along the sides of the spatula. Choice of cyclodialysis spatula is important in dogs. A flat, blunt-tipped 10 mm cyclodialysis spatula is recommended rather than a slightly round-tipped cyclodialysis spatula that does not penetrate this area easily in dogs and often contributes to excessive hemorrhage. The spatula is moved medially and laterally about 8–10 mm to enlarge the artificial fistula to the full extent of the sclerotomy (Fig. 10.16f). A cyclodialysis hypodermic needle may be used instead of the spatula; its advantage is that, at the conclusion of the sweep, the anterior chamber may be gently irrigated with balanced salt solution, removing any hemorrhage or fibrin. The scleral incision is left open. If any fibrin or hemorrhage remains in the anterior chamber, 25–50 mg tPA is injected into the anterior chamber. The bulbar conjunctival

A

B

C

D

E

F

G Fig. 10.16 In the cyclodialysis procedure, a surgical fistula is created from the anterior chamber, between the iris and ciliary body and sclera, to exit through a scleral window into the subconjunctival spaces. (a) A fornix-based conjunctival flap is prepared with Steven’s tenotomy scissors. (b) The sclera is incised 8–10 mm with the Beaver No. 6400 microsurgical blade about 4–5 mm posterior to the limbus. (c) A 2  8 mm block of sclera is incised with the Beaver No. 6400 microsurgical blade. Cautery is usually necessary for scleral hemostasis. (d) The scleral block is carefully separated from the underlying ciliary body and excised with Steven’s tenotomy scissors. (e) A cyclodialysis spatula is carefully introduced through the scleral wound, immediately below the sclera, and directed into the anterior chamber. (f) The cyclodialysis spatula is moved to each side of the scleral wound to create a large fistula beneath the sclera into the anterior chamber. (g) Closure consists of apposition of the fornix-based conjunctival flap with 6-0 to 7-0 simple interrupted absorbable sutures. The posterior flow of aqueous humor will produce a noticeable bleb in the conjunctiva.

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flap is apposed with 6-0 to 7-0 simple interrupted absorbable sutures (Fig. 10.16g). Postoperative treatment after cyclodialysis consists of: 1) control of the iridocyclitis using topical and systemic corticosteroids and NSAIDs; 2) prevention of sepsis with topical and systemic antibiotics; 3) maintenance of normal IOP, if necessary, using topical or systemic carbonic anhydrase inhibitors; and 4) maintenance of a normalsized pupil (neither constricted nor dilated). Pupil size is controlled by varying the instillation frequency of a mydriatic (1% tropicamide or 10% phenylephrine); the postoperative iridocyclitis will cause miosis. Drugs that may alter the blood–aqueous barrier are avoided to prevent excessive fibrin formation within the aqueous humor. The intensity of postoperative medication depends on IOP and the degree of postoperative iridocyclitis. All drugs, except for topical corticosteroids (usually 1% prednisolone), are gradually tapered over several weeks. The topical steroids are continued for several months or indefinitely. Possible complications after cyclodialysis include hyphema, excessive/uncontrolled iridocyclitis, corneal endothelial damage as a result of inadvertent contact with the spatula, and recurrent/recalcitrant glaucoma. Hyphema is minimized by accurate surgical techniques, and proper use of the cyclodialysis spatula. If excessive fibrin or hemorrhage occurs within the anterior chamber during the immediate postoperative period, 25–50 mg tPA is injected into the anterior chamber to dissolve this material. Corneal damage is minimized by using a cyclodialysis spatula that does not exceed 10 mm in length. The scleral defect may close soon after surgery as a result of the incorporation of inflammatory debris from the iridocyclitis, or months later as a result of fibrosis and closure of the surgical pathway secondary to the wound-healing response. Massaging the globe two or three times daily in a careful fashion may promote patency of the cyclodialysis fistula.

Iridectomy In the iridectomy procedure a radial (complete) or basal (peripheral) section of iris is excised. This procedure has proven highly successful for treatment of narrow-angle glaucoma in humans. Unfortunately, in the dog, narrow- and closed-angle glaucomas are frequently complicated by extensive peripheral anterior synechiae and collapse of the sclerociliary cleft. As a result, complete and peripheral iridectomies have not been effective in the more advanced narrow- to closed-angle glaucoma. Complete iridectomy may, however, have application in the treatment of acute canine glaucoma associated with iris bombe´ and annular posterior synechiae. In the event that this type of glaucoma has been present for more than 48–72 h in the dog, the iridencleisis procedure rather than complete iridectomy is recommended, anticipating that angle closure and peripheral anterior synechiae have already occurred. The presence of the major basal arteriolar circle in at least 50% of the dogs has also discouraged the peripheral or basal iridectomy; excision of a basal section of iris without electrocautery will sometimes produce copious hemorrhage. After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of corneal and conjunctival surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. A limbus-based bulbar conjunctival flap is created

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approximately 5 mm from the limbus with blunt, slightly curved, tenotomy scissors. The length of the bulbar conjunctival incision is approximately 10–12 mm (Fig. 10.17a). The anterior chamber is entered by incision of the limbus with the Beaver No. 6500 microsurgical blade. If iris bombe´ is present, entry into the shallow anterior chamber with the bulging iris must be performed slowly and carefully (Fig. 10.17b,c). The 7–10 mm long limbal incision is then enlarged with rightand left-handed corneoscleral scissors (Fig. 10.17d). The iris is gently grasped with serrated forceps and protracted into the limbal incision. During this procedure aqueous humor escapes as patency of the pupil is restored by separation of the iris from the temporary adhesions to the anterior lens capsule (Fig. 10.17e). A cyclodialysis spatula may be used to carefully separate the remaining posterior synechiae. In postoperative aphakic or pseudophakic eyes, the lens capsule and inflammatory membranes may also be involved in the pupillary blockage (Fig. 10.17f). The pupillary margin of the iris is grasped with serrated iris forceps and the iris is protracted into the limbal wound (Fig. 10.17g). Two radial incisions of the iris are performed using sharp iris scissors, supplemented with careful wet-field coagulation for hemostasis (Fig. 10.17h,i). The limbal incision is closed with 6-0 simple interrupted absorbable sutures (Fig. 10.17j). The anterior chamber is reformed with balanced salt solution and a small air bubble. If fibrin or hemorrhage remains in the anterior chamber, 25–50 mg tPA is injected through the surgical incision (Fig. 10.17k). The bulbar conjunctival flap is apposed with a 6-0 simple continuous absorbable suture (Fig. 10.17l). Postoperative care after complete iridectomy in the dog depends, in part, on the preceding ocular condition. Topical and systemic corticosteroids, NSAIDs, and antimicrobials are administered to control postoperative iridocyclitis. IOP is monitored daily by applanation tonometry. If necessary, topical or systemic carbonic anhydrase inhibitors may be administered to help maintain IOP within normal limits. Complications associated with complete and peripheral iridectomies are usually related to postoperative iridocyclitis. Variable amounts of hyphema and fibrin may occur postoperatively associated with the iridal incision as well as postoperative inflammation. Complete iridectomy in the absence of other ocular disease should be regarded as a safe intraocular procedure in small animals. However, when complicated by iris bombe´ or other factors, postoperative inflammation may be intense. Aqueous levels of fibrin are high, and focal posterior synechiae may form. Additionally, the iridectomy itself may occlude with fibrinous or hemorrhagic debris. Secondary cataracts may develop, related to either the intraocular surgery or postoperative inflammation.

Combined iridencleisis and cyclodialysis The iridencleisis–cyclodialysis procedure combines the previous two methods for the treatment of more advanced canine angle-closure glaucomas. A portion of the iris is positioned through the surgical scleral defect beneath the ciliary body into the subconjunctival space. Iridencleisis– cyclodialysis may be employed in the treatment of advanced narrow-angle glaucoma, closed-angle glaucoma, and glaucomas associated with iridocyclitis and iris bombe´.

Surgical procedures for the glaucomas

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Fig. 10.17 In the iridectomy procedure, a full-thickness section of iris is excised to provide a bypass to the pupillary flow of aqueous humor. As incision of the basal iris in the dog is usually associated with hemorrhage, the surgical site extends 2–3 mm from the iridal base to the pupillary margin. The resultant pupil will be keyhole shaped. (a) A limbal-based conjunctival flap is prepared with Steven’s tenotomy scissors. (b) The anterior chamber is entered at the limbus incision with a stab incision with the Beaver No. 6500 microsurgical blade. (c) If iris bombe´ is present, the stab incision into the anterior chamber is more difficult because of the bulging iris. (d) After the limbal stab incision, the incision is enlarged with right- and left-handed corneoscleral scissors. (e) If iris bombe´ is present, the iris is gently grasped with thumb forceps and retracted slightly to re-establish aqueous humor flow through the pupil and deepen the anterior chamber. (f) If posterior synechiae are present, a cyclodialysis spatula is inserted into the pupil to break these adhesions. Intraocular scissors may be necessary to excise fibrous pupillary membranes in the aphakic eyes. (g) The freed pupillary margin is grasped with thumb forceps and protracted to the limbal incision. (h) A section of iris is excised using a combination of sharp iris scissors and cautery for hemostasis. (i) With incision of the base of the iris, the involved iris is removed, creating a keyhole-shaped pupil. (j) The limbal incision is apposed with 6-0 simple interrupted absorbable sutures. (k) The anterior chamber is reformed with lactated Ringer’s solution introduced via a 22 g hypodermic needle inserted between two limbal sutures. (l) The conjunctival flap is apposed with a 6-0 simple continuous absorbable suture.

After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of corneal and conjunctival surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. A fornix-based conjunctival flap is prepared with slightly curved tenotomy scissors. The conjunctival flap is started about 8 mm from the limbus and continued for about

10 mm (Fig. 10.18a). In dogs where Tenon’s capsule appears excessive, it is carefully excised from the overlying bulbar conjunctiva. Care is exercised to prevent ‘buttonholing’ of the bulbar conjunctival flap. The sclera is first incised parallel to and 3–4 mm posterior to the limbus with the Beaver No. 6400 microsurgical blade in a linear fashion (Fig. 10.18b).

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Fig. 10.18 In the combined iridencleisis–cyclodialysis procedure, a section of iris is protracted through the subscleral space into a scleral window (anterior sclerectomy) and into the subconjunctival spaces. Aqueous humor traverses this fistula as well as filters through the iridal tissues. (a) A fornix-based conjunctival flap is prepared with Steven’s tenotomy scissors. (b) The sclera is incised 5–8 mm with the Beaver No. 6400 microsurgical blade 3–4 mm parallel to the limbus. (c) A 2  6 mm section of full-thickness sclera is excised with the Beaver No. 6400 microsurgical blade. (d) For scleral hemostasis, point electrocautery is necessary. (e) With Steven’s tenotomy scissors, the deep attachments of the scleral block to the iris and ciliary body are incised. (f) Through the anterior sclerectomy, a cyclodialysis spatula is carefully inserted subsclerally and directed into the anterior chamber. Once in the anterior chamber, the spatula is moved from side to side to enlarge the fistula. (g) A blunt iris hook is inserted through the subscleral fistula to the dorsal pupillary margin to protract the iris into the anterior sclerectomy window. (h) The iris is grasped by thumb forceps and manipulated into the sclerectomy window. (i,j) With two thumb forceps and a disposable cautery unit, the iris is radially cauterized and torn to its base. (k) The two iris pillars are anchored to the sclera with 6-0 simple interrupted absorbable sutures. (l) The resultant iris pillars traverse the surgical fistula from the anterior chamber, through the anterior sclerectomy, and into the subconjunctival spaces. (m) The anterior chamber is flushed with lactated Ringer’s solution to remove any remaining fibrin and blood. (n) The conjunctival wound is apposed with several 6-0 simple interrupted absorbable sutures. 280

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A scleral section, approximately 2  6 mm in size, is excised without penetration of the underlying iris and ciliary body (Fig. 10.18c). Scleral hemorrhage is controlled by wetfield coagulation or, less ideally, with point electrocautery with a disposable unit (Fig. 10.18d). As the scleral incision approaches the underlying ciliary body, the pigment of the ciliary body is observed. The full-thickness scleral block is separated from the underlying ciliary body by careful sharp dissection using a microvitreoretinal (MVR) blade and excised (Fig. 10.18e). A 10 mm cyclodialysis spatula is carefully manipulated forward between the ciliary body and sclera into the anterior chamber. Upon entry in the anterior chamber, aqueous humor begins to flow into the incision. The cyclodialysis spatula is manipulated side to side to enlarge the subscleral fistula (Fig. 10.18f). A blunt iris hook is carefully inserted through the newly created fistula into the anterior chamber, and manipulated to the pupillary margin of the dorsal iris (Fig. 10.18g). The iris is carefully protracted by iris hook to the scleral wound and grasped by thumb forceps (Fig. 10.18h). The iris is grasped with two pairs of serrated iris forceps at the pupillary margin. Cautery is applied slowly between the forceps at the pupillary margin of the iris and continued to its base, using either an electroscalpel or the wet-field coagulator. Iris hemorrhage is usually minimal (Fig. 10.18i). The iris is gradually separated, starting at the pupil margin and continuing to its base, creating two separate pillars (Fig. 10.18j). These pillars are attached at each end of the scleral defect with 6-0 simple interrupted absorbable sutures (Fig. 10.18k,l). The anterior chamber is reformed with balanced salt solution, using a cyclodialysis hypodermic needle. Hemorrhage and fibrin are carefully irrigated from the anterior chamber. The anterior chamber is reformed again, and an air bubble approximating one-fourth of the volume of the anterior chamber is injected (Fig. 10.18m). The scleral wound is not apposed by sutures. The bulbar conjunctival incision is apposed with several 6-0 simple interrupted absorbable sutures (Fig. 10.18n). If any fibrin or hemorrhage persists in the anterior chamber, 25–50 mg tPA is injected into the anterior chamber. Postoperative treatment after iridencleisis–cyclodialysis is similar to that described for both individual procedures. Postoperative complications are also similar to those of iridencleisis and cyclodialysis individually. The success rate for this procedure appears to be similar to that of scleral trephination (the Scheie procedure), approximating 50% with 6- to 12-month follow-up.

Corneoscleral trephination Corneoscleral trephination is the creation of a surgical fistula at the limbus to permit the escape of aqueous humor from the anterior chamber, directly into the subconjunctival spaces. Corneoscleral trephination in dogs is usually combined with peripheral iridectomy. The iridectomy prevents occlusion of the corneoscleral fistula by basal iris tissue. The peripheral or basal iridectomy also permits an additional communication, besides the pupil, between the posterior and anterior chambers. The peripheral iridectomy must be of sufficient size so that the iridal surgical defect will not readily heal closed.

After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of corneal and conjunctival surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. A limbal-based conjunctival flap, approximately 5 mm wide and 6 mm deep, is constructed with blunttipped, slightly curved, tenotomy scissors. Excess Tenon’s capsule beneath the bulbar conjunctiva is carefully excised so as not to ‘buttonhole’ the mucous membrane (Fig. 10.19a). With the trephine method, entry into the anterior chamber is completed with the Beaver No. 6400 microsurgical blade, and right- and left-handed corneoscleral scissors (Fig. 10.19b–d). This method permits convenient removal of the corneoscleral disk by special trephine scissors, and prevents it from falling back into the anterior chamber; however, the limbal incision is larger. Alternatively, the limbus may be incised with a Beaver No. 6500 microsurgical blade for approximately 5–7 mm, and a corneoscleral punch may be positioned to excise a 2–3 mm diameter section in the center of the posterior limbal incision. After exposure of the limbus and rostral reflection of the limbus-based conjunctival flap, a small anterior sclerectomy, about 2 mm in diameter, is made with a trephine or special scleral trephine scissors at the 12 o’clock position. The anterior edge of the 2 mm trephine hole is placed next to the scleral aspect of the limbus to prevent any damage to the superficial corneal tissues and overlying conjunctival flap (Fig. 10.19e). Often the posterior edge of the trephine is lightly cauterized to delay healing and facilitate the flow of aqueous humor through this new fistula. For peripheral or basal iridectomy, the basal iris is grasped with fine serrated iris forceps and protracted slightly to permit excision with either sharp iris scissors, supplemented with electrocautery, or by electrocautery (Fig. 10.19f,g). Because the basal iridal arterial circle occurs about 50% of the time in the base of the iris and the remainder of the time in the ciliary body, copious hemorrhage occurs with this procedure in about 50% of the dogs. Once iridal hemostasis has been achieved, the iris is permitted to retract within the eye, or it may be repositioned with a cyclodialysis spatula. The anterior chamber is irrigated with balanced salt solution to remove any hemorrhage and fibrin. The limbal incision is apposed with 5-0 to 6-0 simple interrupted absorbable sutures (Fig. 10.19h). After injection of additional balanced salt solution and a small air bubble to reform the anterior chamber (Fig. 10.19i), the bulbar conjunctival flap is apposed with several 6-0 simple interrupted absorbable sutures (Fig. 10.19j). If any fibrin or hemorrhage persists in the anterior chamber, 25–50 mg tPA is injected into the anterior chamber. Postoperative treatment after corneoscleral trephination and peripheral iridectomy is similar to that of other glaucoma procedures. Pupil size is maintained in mid-position; extreme miosis and mydriasis are avoided. IOP is maintained within normal limits, if necessary with carbonic anhydrase inhibitors. Postoperative iridocyclitis is controlled by topical and systemic corticosteroids, and NSAIDs. Topical and systemic antibiotics are administered to prevent sepsis. Daily careful gentle massage of the eye may also be useful postoperatively during the first month to maximize maintenance of patency of the corneoscleral fistula. Topical corticosteroids, such as 1% prednisolone, are instilled daily for several months to help maintain patency of the trephined fistula.

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The success rate with corneoscleral trephination and peripheral iridectomy is approximately 40–50% with 1-year follow-up. Complications associated with this procedure are similar to those of iridencleisis, cyclodialysis, and the combination of these procedures.

Cyclodialysis–iridocyclectomy In the cyclodialysis–iridocyclectomy procedure, a portion of the iris and ciliary body are excised immediately anterior to

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the standard cyclodialysis site. Iridocyclectomy is performed in order to reduce the possibility of obstruction of the cyclodialysis fistula by incorporation of the anterior uveal tissue. This procedure is used for advanced narrow- and closed-angle glaucoma in dogs. After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of corneal and conjunctival surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. A limbal-based conjunctival flap is prepared using blunt-tipped, slightly curved,

Surgical procedures for the glaucomas

tenotomy scissors, approximately 8 mm from the limbus. The conjunctival flap and Tenon’s capsule are reflected rostrally to expose a large area of sclera. Excess Tenon’s capsule is carefully excised from the overlying bulbar conjunctiva (Fig. 10.20a). A rectangular block of full-thickness sclera, measuring between 2  7 mm and 3  9 mm, is excised approximately 4 mm posterior to the limbus with the Beaver No. 6400 microsurgical blade (Fig. 10.20b). Hemostasis is maintained by point electrocautery or wetfield cautery. The rectangular block of sclera is carefully lifted to expose the underlying pigmented ciliary body and excised by Steven’s tenotomy scissors (Fig. 10.20c). A 10 mm cyclodialysis spatula is manipulated forward into the anterior chamber through the subscleral space. The spatula is moved from side to side for approximately 90 to enlarge the fistula (Fig. 10.20d). An iris hook is manipulated through the subscleral space into the anterior chamber to grasp the peripheral iris and protract it into the scleral incision (Fig. 10.20e). Peripheral iris and ciliary body are retracted into the scleral window and excised using

electrocautery. The cautery unit should be at sufficiently high temperature to cut the iris and ciliary body cleanly but with minimal coagulation (Fig. 10.20f,g). With a cyclodialysis hypodermic needle positioned in the anterior chamber, fibrin and hemorrhage are irrigated from the anterior chamber. The anterior chamber is restored with balanced salt solution and a small air bubble (Fig. 10.20h). The scleral window is allowed to remain open. The conjunctival flap is apposed with a 6-0 simple continuous absorbable suture. If fibrin or hemorrhage remain in the anterior chamber, 25–50 mg tPA is injected into the anterior chamber (Fig. 10.20i). Postoperative treatment after cyclodialysis–iridocyclectomy is similar to the treatment for these operations individually. This procedure, like others, has a success rate of approximately 50% with 6- to 12-month follow-up in the dog. Wet-field or electrocautery is essential for this procedure to excise the section of iris and ciliary body with minimal hemorrhage. Complications of this procedure are similar to those of the two operations individually.

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Fig. 10.20 In the cyclodialysis–iridocyclectomy procedure, a surgical fistula is created from the anterior chamber, through a scleral window (anterior sclerectomy) to the subconjunctival spaces. The adjacent iris and ciliary body are excised to reduce the likelihood of obstructing this fistula. (a) A limbal-based conjunctival flap is prepared with Steven’s tenotomy scissors. (b) A 2–3  7–9 mm full-thickness block of sclera (anterior sclerectomy) 4 mm posterior to the limbus is prepared with the Beaver No. 6400 microsurgical blade. Scleral hemostasis is provided by point electrocautery. (c) The scleral block is separated from the deeper iris and ciliary body attachments with Steven’s tenotomy scissors and excised. (d) A cyclodialysis spatula is carefully inserted subsclerally into the anterior chamber and moved from side to side to enlarge the surgical fistula. (e) A blunt iris hook is inserted through the surgical fistula into the anterior chamber to protract the iris into the anterior sclerectomy window. (f) The section of iris and anterior ciliary body is protracted further with thumb forceps and excised using a point cautery unit. Cautery is necessary to maintain hemostasis. (g) The resultant surgical fistula permits aqueous humor to escape from the anterior chamber, through the anterior sclerectomy, and into the subconjunctival spaces. (h) Any fibrin and hemorrhage are flushed from the anterior chamber with lactated Ringer’s solution. (i) Closure consists of apposition of the conjunctival wound a 6-0 simple continuous absorbable suture.

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Anterior chamber shunts/gonioimplants Clinical management of the primary canine glaucomas has traditionally followed the basic algorithm of medically controlling IOP at levels that maintain vision for as long as possible, and only treating the condition surgically when medical therapy is no longer successful at maintaining vision, or if adverse ocular or systemic effects result. This strategy was based on the low initial success rates achieved by the traditional filtering glaucoma surgical procedures. However, two new treatment modalities – laser transscleral cyclophotocoagulation and anterior chamber surgical shunts (gonioimplants) – have shown promise in the clinical management of canine primary glaucomas. Hence, a newer treatment strategy for the management of canine primary glaucomas is evolving, and now typically involves initial surgical implantation of an anterior chamber shunt (gonioimplant), often in combination with diode laser cyclophotocoagulation, supplemented, if necessary, with postoperative medical therapy. Clinical experience suggests that the early timing of surgical intervention contributes to increased long-term success.

Progression of implant design The design of glaucoma drainage implants has evolved from the initial use of a horse hair for this purpose by Rollett in 1907. This progression has included the introduction of the Molteno implant in 1969, the Krupin implant in 1979, the

Baerveldt implant in 1992, and the Ahmed implant in 1993. The original Krupin–Denver valved gonioimplant was evaluated in normal Beagles and Beagles with inherited glaucoma. A modified Joseph implant was subsequently evaluated in 15 dogs (21 eyes) with primary glaucoma with encouraging results. The range of observation postoperatively was from 9 to 15 months, and a success rate of 80% was reported, although some dogs required concurrent medications, usually at reduced doses. Additional reports have evaluated Ahmed, Baerveldt, and other anterior chamber shunts for the treatment of primary glaucomas in dogs. These reports indicate encouraging results, but the postoperative management after anterior chamber shunt implantation is critical for their long-term success.

Valved versus non-valved systems Perhaps the most significant difference in gonioimplant design is the presence or absence of an internal valve mechanism. Gonioimplants with unidirectional (valved) systems are designed to permit aqueous humor passage at about 10–11 mmHg. Bidirectional (non-valved) systems have no pressure regulatory devices, except for the limited resistance within the shunt (Fig. 10.21). Valved (or unidirectional) systems maintain a minimal IOP, preventing ocular hypotony and collapse of the anterior chamber, as well as minimizing hypotony-related uveitic changes to the aqueous, immediately after surgery. The non-valved (or bidirectional) flow systems may result in

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Fig. 10.21 Commercial and self-constructed anterior shunts. (a) Ahmed (small, large, and attached to a 10  30 mm silicone band). (b) Molteno (single and double plate). (c) Self-constructed ‘T’ shunt (with and without a valve). (d) Joseph.

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ocular hypotony, a shallow anterior chamber, disruption of the blood–aqueous barrier in the immediate postoperative period, and even retinal detachment. IOP increases as resistance increases, as a result of the fibrous capsule that forms around all extrascleral implants several weeks postoperatively. The immediate postoperative medical management of valved and non-valved systems is also different because of the ocular hypotony associated with non-valved systems. To limit postoperative hypotony and shallowing of the anterior chamber when placing non-valved devices, the implant drainage tubing may be temporarily occluded intraoperatively with a non-absorbable suture inside the tubing, a ligature (either absorbable or non-absorbable suture) around the tube, or other techniques. The valved systems in early glaucoma eyes in dogs are more effective in avoiding early ocular hypotony. The bidirectional non-valved systems in dogs with advanced or refractory glaucoma are not usually associated with postoperative ocular hypotony, perhaps because aqueous humor flow is so compromised through the usual aqueous humor outflow pathways. Without effective antifibrotic therapy at this time, increased IOP about 3–6 weeks postoperatively results from the fibrous capsule that forms around the extrascleral implant. The presence or absence of a valve mechanism in the anterior chamber shunt influences immediate postoperative management, as IOP below 5 mmHg is injurious to the eye and the long-term function of the implant.

The different types of anterior chamber shunt used in the surgical treatment of primary canine glaucoma are summarized in Table 10.4. Several new implants are being evaluated in dogs, and specific devices may be more successful than others in the treatment of the different types of primary glaucoma; however, anterior chamber shunts for dogs and cats share similar characteristics.

Size of the implant The total size of the implant directly determines the overall surface area of the host’s resultant fibrous capsule, and indirectly long-term clinical success or failure. The resultant permeability of the surrounding capsules is another important variable. The optimal range of implant surface area for the dog has not been determined, and may range from 300 to 600 mm2. Implants that are very small seem to function for brief periods of time in the dog. However, the overall orbital space also provides a limit to maximal implant size in the different animal species (especially the cat). There is a considerable variation in size of the commercially available implants, ranging from about 200 to 500 mm2. Because of the retrobulbar position of these shunts, a postoperative bleb is often not visible. Without effective antifibrosing agents, the size of the implant is balanced between the smallest size that can accommodate adequate aqueous reabsorption and the largest surfaces that prolong function and do not interfere with other ocular

Table 10.4 Available anterior chamber (AC) shunts in small animals

Implant*

AC tubing

Scleral explant

Implant

Silicone ID 0.3 mm OD 0.6 mm

Oval-to-half circle base Radiopaque Three sizes: 400, 700, and 1000 mm2

Ahmed

Silicone ID 0.3 mm OD 0.63 mm No valve

Polypropylene base Single/double plates: 320 mm2 single plate; 640 mm2 double plates

Modified by Gelatt

Silastic ID 0.3 mm OD 0.64 mm No valve

No. 20 silicone band; 360 Variable – 900 mm2

‘T’-implant

Silicone ID 0.3 mm OD 0.6 mm No valve

Silicone – 7  30 mm 420 mm2

White

Silicone ID 0.3 mm OD 0.64 mm Unidirectional No valve

Silicone compressible reservoir and base with tubing (1.04 mm ID and 1.42 mm)

Non-valved Baerveldt

Schocket et al

Scleral explant

Silicone ID 0.3 mm OD 0.6 mm; Valve opens at 8–10 mmHg

Five-sided polypropylene body Three different sizes

Valved

No valve Molteno et al

AC tubing

Silicone strap (12  30 mm) added

Hitchings

Silicone ID 0.3 mm OD 0.64 mm Valve, slit (side): opens at 4–20 mmHg

1  9 mm silicone strap 180–360

Joseph

Silicone ID 0.3 mm OD 0.64 mm Valve, slit (side): opens at 4–20 mmHg

Silicone strap 1  9 mm 8.5 cm long <1600 mm2 Bedford – used as non-valve in dogs

Krupin et al

Silastic ID 0.3 mm OD 0.64 mm Valve, slit: opens at 11 mmHg; closes at 9 mmHg

Later No. 220 episcleral explant, 180–360 in length

ID, inner diameter; OD, outer diameter. *Implant dimensions are calculated for the entire surface areas of each implant.

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functions. Among the different breeds of small dog, there is a variably sized orbit that can accommodate different sizes of implant; however, in the cat, the space for gonioimplants is very restricted. Placement of valved gonioimplants may be especially challenging in particularly small eyes and, in such cases, the (Ahmed) valve mechanism (and tubing) itself may have its surrounding silicone plate carefully removed and be implanted alone. Large implants in humans have been associated with diplopia and impaired ocular mobility.

conjunctiva. The optimum diameter of the anterior chamber tubing for the dog has yet to be determined, and larger diameter tubing can accommodate greater flow rates with less resistance. Anterior chamber silicone tubing of 0.40– 0.45 mm ID and 0.6–0.8 mm OD may be a reasonable range for dogs. The tubing diameter should be small enough to allow its insertion into the anterior chamber through a 20–22 g hypodermic needle track. Implants with larger anterior tubing diameters may be indicated for those dog and cat glaucomas complicated by iridocyclitis.

Shape of the implant

Biocompatibility of implant material

The overall size of the implant appears to be more important than its shape. Current anterior chamber shunts range in shape from round, oval, shell-shaped or C-shaped to long slender silicone straps. Large implants, because of limited space between the rectus muscles, can be shaped to extend conveniently under two or more extraocular muscles, or more posteriorly into the retrobulbar spaces. If the nonabsorbable sutures attaching the implant to the sclera break or fail to secure the implant, these larger types of implant are less likely to be displaced anteriorly and subsequently extrude through the bulbar conjunctiva.

Both silicone tubing within the anterior chamber and implant bases constructed of silicone or intraocular lens plastics seem to be well tolerated in the dog. Softer materials appear more biocompatible, and are less likely to be associated with postoperative patient discomfort and selftrauma, abrasion of overlying tissues, and the potential complication of implant extrusion. A fibrous capsule forms around the implant’s episcleral base. The capsule’s thickness and permeability eventually determine the final success of the device’s ability to maintain IOP within a safe range. Several antifibrotic drugs may be employed in order to delay and/or prevent excessive fibrous capsule formation, and are under study. If effective antifibrosis drugs/strategies are eventually developed, most implants will require some form of valve or pressure maintenance system. Development of the capsule around these shunts may suggest a limited problem with biocompatibility and/or local stimulatory effects of aqueous humor when exposed to non-endothelial covered surfaces. Capsule thickness is somewhat related to its permeability, but the matrix, such as the glycosaminoglycans, surrounding these collagen fibers and vascular angiogenesis may also have a marked influence on the passage of aqueous humor.

Size of the anterior chamber tubing All commercially available anterior chamber shunts utilize silicone tubing with 0.3 mm inner diameter (ID) and 0.6 mm outer diameter (OD) (Fig. 10.22). The total 3–6 mL of aqueous humor outflow per minute in dogs and cats can easily be accommodated by this diameter tubing. This same size of tubing can accommodate in-vitro flow of 20 mL/min without significant resistance as may be necessary in the horse. In the dog, occlusion of the small diameter tubes may be more likely because of the higher levels of aqueous proteins, inflammatory cells, and fibrin from a more fragile blood–aqueous barrier. There are, however, upper limits for tubing diameter, as too large a diameter of silicone tubing may result in increased rigidity and corneal endothelial contact after placement. The bend which occurs when tubing is inserted into the anterior chamber at the limbus is also a concern, and may cause pressure and tension on the overlying bulbar

Position of the implant’s episcleral base Implants placed close to the limbus in the subconjunctival spaces are more easily occluded by the host’s fibrous capsule, and must be relatively small. Consequently, newer implants are more ideally positioned 10–14 mm behind the limbus (approximately at the site of rectus muscle insertions) at the equator of the globe, to extend an additional 10–15 mm into the retrobulbar space (Fig. 10.23). As a result, these implants may be larger and provide for the formation of a larger fibrous capsule. Implants placed forward near the limbus are more likely to erode through the thin, overlying bulbar conjunctiva.

Wound healing following glaucoma filtration surgery

Fig. 10.22 The standard size of shunt tubing (0.6 mm OD and 0.3 mm ID) within the anterior chamber in a dog with primary glaucoma.

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Wound healing following glaucoma filtration surgery (GFS) occurs along similar general principles to that following other ocular surgeries, and may be divided into three phases: inflammation, proliferation, and remodeling. Inflammation is initiated by the presence of blood in the wound field. Inflammatory cells are attracted within hours, and release growth factors and inflammatory cytokines. In response to these stimuli, fibroblasts are recruited and activated to form extracellular matrix and vascular tufts. This tissue is

Anterior chamber shunts/gonioimplants

Shunts to other areas

Fig. 10.23 Position of the episcleral base (arrows) of the anterior chamber shunt in a rabbit. H & E, 20.

subsequently remodeled through collagen deposition and wound contracture over months to years under the influence of matrix metalloproteinases The major cause of failure following GFS is the formation of scar tissue, which decreases the filtration of aqueous humor into the sub-Tenon’s space. Currently, the general, non-specific modulation of wound healing following GFS involves the use of antimetabolites which broadly disrupt cell migration, proliferation, and extracellular matrix production. Mitomycin C (MMC) is an alkylating agent that acts by disrupting RNA and protein synthesis, and by generating reactive oxygen species. Its intraoperative application to the site of GFS in veterinary patients has been disappointing, and it is frequently associated with the formation of thin-walled, avascular filtration blebs and an aggressive subsequent fibrosing reaction as a result of capsular tension. 5-Fluorouracil (5-FU) exhibits several cytotoxic effects, including inhibiting DNA synthesis by inhibiting thymidylate synthetase, reducing protein synthesis by interfering with RNA synthesis, indirectly disrupting actin cytoskeleton stability, and promoting fibroblast apoptosis. The beneficial properties of 5-FU may be employed in veterinary patients through its repeated postoperative administration directly into the filtration bleb site, where its effects increase bleb survivability and functionality. During the last few years, significant progress has been made in our understanding of the mechanisms of wound healing following GFS. Human, rabbit, and murine gene microarrays have allowed the mapping of gene expression across this process, and identified its major mediators. These include cytokines and growth factors, specifically the two growth factors thought to play dominant roles in promoting scarring (transforming growth factor beta and connective tissue growth factor), extracellular matrix protein genes (types I, II, III, V, and XVIII collagens, fibronectin, vitronectin, and proteoglycans), proteases involved in cell migration and extracellular matrix remodeling (MMP-2, -9, -11), and the tissue inhibitors of metalloproteinases (TIMPs 1, 2, 3). This information allows us to identify newer potential therapeutic targets (see Tables 10.2a and 10.2b).

Because of the fibrosis that develops around intraorbital implants and causes them to gradually fail (in response to growth- and fibroblast-stimulating substances within the aqueous humor), other sites for termination of these anterior chamber shunts have been attempted in dogs. As newer antifibrotic drugs and protocols are developed, medical control of the host’s fibrotic response to the implant and aqueous humor may be possible. In the meantime, other potential drainage sites are being investigated; to date they include the frontal shunt, subcutaneous tissues, jugular vein, and parotid duct. As these implants do not stimulate the development of a fibrous capsule, which serves as the eventual resistance to maintain IOP at 10–15 mmHg, these shunts should have a resistance that approximates low normal IOP (10–12 mmHg) related to either the length and diameter of the tubing or a valve mechanism. At this stage these surgeries should be considered experimental. However, they signal a continued search for improved surgical procedures for small animal and equine glaucomas, they are presented here.

Surgical procedures for anterior chamber shunts The different surgical procedures for anterior shunts continue to progress in the dog, and in this section, the different sites will be presented separately. The first procedure, the intraorbital/subconjunctival implantation, is the most established technique. For those techniques that position the exit for aqueous humor in non-orbital sites, the main difference in the surgical procedure is the latter stage. Careful patient selection and intervention prior to the development of significant ocular inflammation will help maximize long-term surgical success. Preoperative medical management similar to that recommended prior to cataract phacoemulsification will help reduce the postoperative inflammatory cascade, and may comprise topical and/or systemic anti-inflammatory and/or antimicrobial therapy at the surgeon’s discretion.

Intraorbital/subconjunctival implantation After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of corneal and conjunctival surfaces with 0.5% povidone–iodine solution and swabs, the eyelids are retracted by speculum. Surgery to position the different anterior chamber shunts is similar, with the primary difference related to the additional dissection beneath the rectus muscles to accommodate the larger size implants. Generally, the patient is positioned in spinal recumbency, and the use of a neuromuscular blocking agent such as atracurium (facilitated by assisted ventilation) may be employed in order to permit maximal globe rotation and surgical exposure. The superotemporal quadrant generally represents the ideal site for initial implant placement based on ease of exposure. The second choice is the superonasal quadrant, third the inferotemporal quadrant, and fourth the inferonasal quadrant. This order of selection is also applicable if a site is being selected for repeat surgical intervention.

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Evidence suggests that gonioimplants should not be replaced at the site of original (or ‘primary’) intervention if this step becomes necessary during the course of surgical IOP management. If necessary, the globe may be held in position using two traction sutures or fine mosquito forceps located at the limbal junction. A deep fornix-based incision is made approximately 10 mm behind the limbus using a combination of blunt–sharp dissection with blunt-tipped, slightly curved, tenotomy scissors. The incision should be approximately 8–10 mm in width, such that the insertion of the gonioimplant is just possible. This will minimize the danger of subsequent implant extrusion. Throughout the dissection, conjunctival and Tenon’s tissues are grasped extremely gently in order to minimize tissue trauma (Fig. 10.24a). The dissection plane, using mainly tenotomy scissors and alternating sharp and blunt dissection, is continued posteriorly between Tenon’s capsule and the sclera, and between the dorsal and lateral, or dorsal and medial, rectus muscle insertions. Excessive Tenon’s capsule may be carefully excised. Meticulous hemostasis (ideally using wet-field cautery) during the dissection is vital in order to minimize the delivery of those growth factors that will subsequently mediate wound healing and fibrosis (Fig. 10.24b). The implant is usually positioned at or just posterior to the equator, its rostral end about 10–12 mm from the limbus. Hence, postoperatively, the episcleral portion of the device cannot usually be visualized through the bulbar conjunctiva, except for the tubing that extends into the anterior chamber. Devices placed too close to the limbus are more prone to erode the adjacent bulbar conjunctiva. The insertion of the dorsal rectus muscle may be used as a guide (Fig. 10.24c). The anterior border of the implant should be posterior of this landmark. The episcleral or main portion of the anterior chamber shunt is placed between the dorsal rectus and medial rectus muscles, or, as a second choice, the space between the dorsal rectus and the lateral rectus muscle. These muscle insertions may be individually identified and manipulated by muscle hooks (Fig. 10.24d). Dissection is limited to immediately above the sclera, and below the bulbar fascia (Tenon’s capsule) to minimize hemorrhage. Muscle bellies in particular should be carefully avoided since their inadvertent incision or transection will result in copious hemorrhage. The intraoperative application of MMC at the surgical site has been advocated by some surgeons to impede fibrosis; however, long-term evidence that it is beneficial in dogs is lacking. If elected, the surgical site is treated with a sterile surgical cellulose spear soaked with MMC for 5 min (0.25–0.5 mg/mL; Fig. 10.24e). The optimal dose (drug concentration and duration of exposure) of MMC for the dog has not been determined. After exposure, the area is flushed with 20–30 mL of balanced salt solution. Mitomycin C should not make contact with the wound edges or the anterior chamber. All anterior chamber shunts are checked for function and patency at this time. A 25–27 g hypodermic needle is cannulated into the end of the anterior chamber tubing and lactated Ringer’s or sterile balanced salt solution is injected. The use of tPA as a priming agent has been advocated by some surgeons in an effort to reduce the likelihood of fibrinous occlusion postoperatively. With the shunt system

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filled with fluid, it is now ‘primed’ and ready for implantation (Fig. 10.24f). If the system is not primed with lactated Ringer’s solution, air within the device will impede the transit of aqueous humor through the system. In the case of the Ahmed valved implant, an audible ‘pop’ may be heard as the pretensioned membranes within the valve are separated by fluids. The device is carefully positioned into the sub-Tenon’s capsule space, ensuring that the implant borders are in direct contact with the sclera (Fig. 10.24g). Once the device is properly positioned, it is secured to the sclera and Tenon’s capsule by two to four 7-0 to 9-0 nonabsorbable nylon sutures, usually placed at the anterior border and near the extraocular muscle insertions (Fig. 10.24h). In many glaucomatous patients the sclera in this area may be very thin, rendering suturing difficult. Small needle sizes will help minimize the danger of deep scleral penetration and hemorrhage. Sutures may be passed directly through soft implant material or into preformed suture holes if these are present within the device. The overall length of the anterior chamber tubing is carefully estimated prior to trimming by laying the tubing directly onto the cornea. If cut too long, tubing may contact the endothelial surface of the cornea, partially occlude the pupil, and produce focal edema. However, if cut too short, the tubing lumen can become obstructed by the base of the iris or pre-iridal inflammatory membrane formation. If megaloglobus develops after placement of an anterior chamber shunt, stretching of the sclera can retract too-short anterior chamber tubing completely from the anterior chamber. Ideally, once in the anterior chamber, the tubing should not touch either the iris or the cornea, and avoid crossing the center of the pupillary axis extending 3–4 mm into the anterior chamber. The tip of the tubing is usually cut with a wide, upward-facing bevel using Westcott scissors to facilitate insertion into the anterior chamber. The beveled opening of the tubing may also be less subject to plugging with fibrin postoperatively (Fig. 10.24i). If additional intraocular surgery is being performed as part of a combined procedure (such as cataractous or noncataractous lenticular phacoemulsification or endoscopic cytophotocoagulation), it is performed at this time. Implant plate placement and suturing prior to intraocular surgery avoids the potential complications associated with placement within a soft/hypotonous globe. The limbal area through which the implant tubing will pass is carefully prepared. The bulbar conjunctival flap is elevated and the limbus exposed. The surgeon should studiously avoid any ‘buttonholing’ of the thin overlying conjunctiva. A 2–3  3–4 mm partial-thickness scleral flap may be created at the site of tube entry into the anterior chamber if deemed necessary. Entry is achieved by creating a scleral track, using a 22 g needle attached to a syringe. Entry into the canine anterior chamber is usually performed at about the 12 o’clock position. The hypodermic needle is carefully removed using a twisting motion, and the beveled silicone tubing inserted in a single smooth exchange. A surgical assistant may facilitate this procedure (Fig. 10.24j). During anterior chamber entry and tube exchange, maintenance of IOP is preferred in order to minimize the formation of excessive fibrin in the aqueous humor. Grasping and manipulation of the tubing with specialized silicone tubing forceps with specifically designed

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Fig. 10.24 The surgical procedures for all of the anterior chamber shunts are quite similar. The larger devices require additional retrobulbar and extraocular muscle dissection. All of the shunts are positioned 10–12 mm posterior to the limbus. (a) A 120–140 fornix-based conjunctival flap is prepared with Steven’s tenotomy scissors. (b) The scissor dissection continues to the sclera, beneath Tenon’s capsule (bulbar fascia), to between the dorsal and medial rectus muscle insertions. (c) The surgical dissection continues between the dorsal and medial rectus muscle insertions. The base of the anterior chamber shunt will be posterior (caudal) to the dorsal rectus muscle insertion. (d) The dorsal and medial rectus muscles are identified with a muscle hook, and space between and beneath these muscle is established for the implant. (e) A few drops of mitomycin C (0.25–0.5 mg/mL) may be placed on a surgical cellulose spear and positioned in the surgical site for 5 min. This intraoperative drug will hopefully delay fibrosis about the implant. (f) The implant is primed with lactated Ringer’s solution to ensure patency of the implant’s tubing and valve function. (g) The base of the anterior chamber shunt is fitted into the space between the medial and dorsal rectus muscles. (h) The anterior chamber shunt is secured to the sclera and/or rectus muscle insertions with two to four 7-0 to 9-0 non-absorbable sutures. (i) The length of the anterior chamber tubing is determined and its end cut with scissors to create a beveled opening. (j) The tunnel for insertion of the anterior chamber tubing is created with a 22 g hypodermic needle carefully inserted through the limbus into the anterior chamber. (k) With a special gonioimplant tubing thumb forceps, the tubing is carefully positioned through the limbal tunnel into the anterior chamber. (l) A small (4  6 mm) homologous scleral graft is positioned over the anterior chamber tubing immediately posterior to the limbus, and attached to the sclera with four 6-0 to 70 simple interrupted absorbable sutures. The scleral graft stabilizes the tubing and protects the bulbar conjunctiva from direct contact and pressure with the tubing. (m) The conjunctival wound is apposed with several 6-0 to 7-0 interrupted absorbable sutures. (n) With proper positioning of the anterior chamber shunt’s base, filtering blebs are retrobulbar and not usually visible through the upper conjunctiva. 289

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Surgical procedures for the glaucomas

tips is recommended, to prevent damage to the soft silicone tubing. Slightly turning/rotating the beveled end of the tubing may assist insertion into the needle puncture site (Fig. 10.24k). An additional proposed benefit of creating a partialthickness scleral flap at the site of anterior chamber entry is reduction in the risk of conjunctival erosion above the silicone tubing. In cases where this risk is deemed significant, such as those dogs with thin/friable overlying tissues, this may also be achieved by covering the anterior 5–7 mm of silicone tubing with a thin (2 mm) scleral homograft, maintained frozen until required (Fig. 10.24l). The four corners of the scleral homograft are apposed to the underlying host sclera with four 6-0 to 7-0 simple interrupted absorbable sutures. Care must be taken, however, not to occlude the tubing with excessively tight sutures. Aqueous humor will generally be noted flowing through the device. Provided little aqueous humor has escaped through the anterior chamber needle track, IOP should stabilize at about 10 mmHg. To dissolve any fibrin in the aqueous humor, 25 mg tPA is usually injected into the anterior chamber from the limbus at this stage. Two layers of wound closure are preferred. The endorbita or Tenon’s capsule wound is closed with several 6-0 to 7-0 simple interrupted sutures or a continuous suture covering the gonioimplant. The bulbar conjunctival flap wound is apposed using several 6-0 to 7-0 simple interrupted sutures or a continuous absorbable suture (Fig. 10.24m,n).

Anterior chamber shunt to subcutaneous tissues and the facial and jugular veins This pilot study by Ha˚kanson involved four glaucomatous Norwegian elkhounds and non-valved gonioimplants, consisting of tubing of 0.5 mm ID and 1.0 mm OD, that were implanted extending from the anterior chamber to either a subcutaneous site or via the facial vein to the jugular vein ending at the thoracic inlet. The surgical placement of the anterior chamber portion of the shunt was similar to all implants. The tubing was anchored by silicone glue to a 0.5  4  10 mm piece of silicone that was sutured to the sclera with 9-0 nylon sutures, and served to anchor the tubing to the eye. The tubing was inserted into the anterior chamber under a 2  4 mm partial-thickness scleral flap hinged at the limbus. The tubing was inserted through a 0.9 mm hypodermic needle track into the anterior chamber and the scleral flap closed with sutures. For the subcutaneous shunt, about 100 mm of 0.5  1.0 mm diameter tubing was extended to a 90 mm section of silicone tubing, 6.6 mm ID and 9.0 mm OD, with tapering ends. Through a second skin incision, along the anterior portion of the zygomatic arch, a subcutaneous pocket was constructed to accommodate the large aqueous distribution device of the larger diameter tubing, which was secured by sutures. The tubing from the anterior chamber was positioned into the larger diameter tubing. In two patients in which the shunt was positioned into the jugular vein, the tubing was extended into the facial vein and the jugular vein for about 300–310 mm to terminate in the anterior thoracic inlet. The facial vein was entered along the face, ventral to the lateral nasal vein, and severed and

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ligated; the tubing was advanced into the severed facial vein which was then secured with a suture. This experimental study illustrates the problems associated with non-valved systems immediately postoperatively because of the lack of resistance. The non-valved systems implanted in the orbital tissues cause ocular hypotony (IOP <5 mmHg) until the host’s fibrous capsule develops about the implant’s base. In dogs, this fibrosis occurs in 2–4 weeks. With ocular hypotony, aqueous flare, aqueous fibrin formation, and hyphema can occur from the anterior uvea, and even retinal detachments develop. These exudates can repeatedly plug the drainage system, and compromise the surgical bypass. The result is alternating periods of ocular hypotony (the system is patent) and elevated IOP (the system is plugged). With the intravenous system, both hyphema and the formation of blood clots at the end of the tubing within the jugular vein can develop; similar results occur when this type of shunt is used for the treatment of hydrocephalus in dogs and the cerebrospinal flow rate is considerably more. With the subcutaneous system, ocular hypotony and intraocular fibrin formation occurred, but not hyphema. At 4 months postoperatively in one dog, the subcutaneous device became non-functional because of the fibrous capsule around the device.

Anterior chamber shunt to the frontal sinus Shunts from the anterior chamber to the frontal sinus have been reported in normal and glaucomatous dogs by Grahn and Cullen. The frontal sinus was selected because of its proximity to the orbit; although the frontal sinus is potentially a source of infection, no infections developed in either the normal or glaucomatous dogs. The pilot study was conducted in four normal dogs. Using Bernoulli’s equation, a tube size of 0.76 mm ID and 1.65 mm OD and 45 mm long was selected; there was no valve device, only the resistance created by the tubing’s length and diameter. Through a 1.5 cm skin incision dorsomedial of the orbit, the rostromedial compartment of the frontal sinus was entered with a 3/32" Steinman pin and Jacob’s chuck. The tubing, along with its footplate, was attached to the periosteum with 5-0 simple interrupted nylon sutures. The surgery about the eye was similar to other anterior chamber shunts. From an incision in the dorsobulbar conjunctiva and Tenon’s capsule, the tubing from the frontal sinus was pulled through a subcutaneous tunnel. After cutting the tubing to the appropriate length and at a bevel, and priming the tubing with balanced saline solution, the tube was inserted into the anterior chamber through a 2.5 mm keratome limbal incision under a conjunctival flap. Another silicone footplate was secured to the tubing, and both were secured to the sclera with 7-0 simple interrupted absorbable sutures. The conjunctival wound was apposed with 5-0 simple interrupted monofilament nylon sutures. Postoperative treatments consisted of topical 1% prednisolone, 0.03% flurbiprofen, 1% atropine, and 0.3% ciprofloxacin, and all treatments ceased within 1 month. The results were encouraging after some experience with refining the surgical technique. Self-trauma occurred in three of the four dogs that partially or completely dislodged the implant

Anterior chamber shunts/gonioimplants

site at the frontal sinus. Ocular complications included iridal attachment to the implant, mild iridocyclitis, anterior subcapsular cataracts, and focal corneal and scleral scarring. Postoperative pneumatonography indicates that aqueous humor outflow is usually doubled, and the mean IOP is about 10 mmHg. No retrograde infection from the frontal sinus to the eye occurred. The same surgical procedure was evaluated in seven glaucomatous dogs that were followed for a minimum of 6 months. The surgery was successful in four dogs, resulting in IOPs of 8–23 mmHg and maintenance of vision. The three failures included: anterior chamber tube extrusion at 1 week; one dog lost to follow-up; and the last dog with fibrosis and plugging of the anterior chamber tubing.

Anterior chamber shunt to parotid duct In another experimental study, anterior chamber shunts to the parotid duct were evaluated in glaucomatous Beagles, involving two different designs of valved implants by Gelatt and MacKay. The parotid duct site was selected as no fibrosis should develop with the aqueous humor entering a hollow, mucous membrane-lined duct. Also, the parotid duct lumen appears to be sterile. Unfortunately, retrograde flow of the aqueous humor within the parotid duct occurred over several months and eventually reached the main episcleral implant, necessitating its removal. Perhaps the flow of aqueous humor within the parotid duct (with the parotid gland ligated) was inadequate to prevent the infection, and needed combination with continued parotid gland salivary flow. The gonioimplant evolved in a series of nine surgeries, and became progressively more refined and smaller. The gonioimplant consisted of a modified small Ahmed valve, encased in an 8 mm diameter thin silicone envelope, with 0.3 mm ID and 0.6 mm OD tubing, extending from both ends to connect the anterior chamber to the parotid duct through a unidirectional valve with an opening pressure of about 10–12 mmHg. The main body of the implant was initially positioned close to the parotid duct below the zygomatic arch, but was eventually changed to directly posterior of the orbit on the surface of the temporal muscle. The surgery is divided into four parts: 1) placement of the implant on the temporal muscle caudal of the orbit; 2) isolation and transection of the parotid duct, and placement of the exit tubing into the duct’s lumen; 3) placement of a silicone tube stabilizing strip in the subconjunctival and sub-Tenon’s space; and 4) the insertion of the intake tube into the anterior chamber (Fig. 10.25).

Postoperative management following gonioimplantation The postoperative management of gonioimplants is divided into those without valves and those with valves. In general, for valved implants, iridocyclitis is intensively treated with topical and/or systemic corticosteroids and NSAIDs, and no aqueous humor flare is tolerated that may potentially plug the tubing and/or valve mechanism. In contrast, mild iridocyclitis is tolerated initially following the placement of non-valved systems as immediate postoperative ocular hypotony is a constant concern. A few

Fig. 10.25 Experimental anterior chamber shunt to the parotid duct. The approximate pathway for this type of valved shunt in the dog. This experimental surgery failed after development of ascending infections from the mouth into the parotid duct and explant, suggesting that the parotid duct allowed bidirectional flow and the volume of flow of aqueous humor was inadequate to prevent retrograde infections.

days of profound ocular hypotony in the dog can result in complete retinal detachment; fortunately, once the glaucoma device plugs with fibrin or is ligated temporarily, IOP rises and retinal reattachment is achievable. Aqueous fibrin may temporarily plug the gonioimplant and maintain IOP at 15–20 mmHg. Higher levels may require intracameral 0.25–0.5 mg tPA to dissolve clots of no longer than 10–14 days’ duration. Fibrin which accumulates within the anterior chamber portion of the implant tubing may be particularly challenging to manage, and, if necessary, may be gently ‘teased’ using a fine hypodermic needle and tPA injected directly into the bore of the anterior chamber tubing itself. In these patients, digital massage may also assist resolution of blockage and restore IOP. Miotics are generally avoided because of their potential to cause aqueous humor flare and perhaps stimulate fibroblast proliferation. Mydriatics are indicated for the treatment of iridocyclitis, but usually only weaker agents, such as 1% tropicamide, to promote a constantly moving pupil. It is important postoperatively to carefully monitor IOP, and any spikes over 20 mmHg or so should receive treatment to minimize any further damage to the optic nerve head and retina. Ocular hypotensives that may be safely used with gonioimplants include the topical and systemic carbonic anhydrase inhibitors, beta adrenergics, and rarely intravenous mannitol. The role of digital massage has not been explored, but might have some benefit. Successful valved anterior chamber shunts provide IOP of 8–12 mmHg immediately after surgery. With development of the fibrous capsule about the base of both valved and non-valved shunts, IOP will gradually increase to 12–20 mmHg several weeks postoperatively. As antifibrotic drugs are employed at therapeutic levels in small animals, the postoperative IOP will be lower. Topical corticosteroids, such as 1% prednisolone, and oral systemic NSAIDs may be administered postoperatively for several months to resolve the iridocyclitis and impede capsule formation about the anterior chamber shunt base. As antifibrotic drugs and protocols evolve, changes in these intraoperative and postoperative therapies will occur.

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The long-term functionality of the filtration bleb which surrounds the implant base may be maximized by the repeated local administration of antimetabolites such as 5-FU. Protocols vary among surgeons, but 1 month postoperatively, 3 months thereafter, and then every 6–12 months as a maintenance regimen has been proposed. Approximately 0.1–0.2 mL (50 mg/mL) 5-FU is injected directly into the bleb site, usually facilitated by sedation or anesthesia depending on patient temperament. It is crucial that this solution does not contact exposed cornea, either during administration or by leakage in the immediate postinjection period, otherwise severe and recalcitrant corneal ulceration may result. Corneal protection using a protective ointment prior to injection, diligent injection technique, local pressure following injection, and topical antimicrobial cover will help avoid this complication.

Complications of anterior chamber shunts and results Failures of anterior chamber shunts may be grouped into: 1) short term – related to surgical technique, postoperative iridocyclitis, and glaucomatous progression; and 2) long term – related to shunt failure from capsule formation and recurrent glaucoma (Table 10.5). Experience with anterior

Table 10.5 Potential postoperative complications with anterior chamber (AC) shunts

Complication Short term Glaucoma-related

Lens displacement Additional globe enlargement Additional iridocorneal angle closure Pre-iridal and inflammatory membranes Vitreous plug of AC tubing

Surgical technique

Iridocyclitis with aqueous fibrin Hyphema Ocular hypotony/flat anterior chamber AC tubing too long/too short Suture failure – tubing and implant dislodgement Bulbar conjunctival erosion below AC tubing AC tubing touching posterior cornea Suture blockage of AC tubing

Implant-related

Valve failure AC tubing, small diameter Implant base, small

chamber shunt placement will avoid the difficulties associated with the surgical procedure. Often iridocyclitis is present preoperatively in the dog and cat, and every attempt should be made to control this inflammation before surgical entry into the anterior chamber since any fibrin or blood in the anterior chamber may occlude the anterior chamber tubing, either temporarily or permanently (Fig. 10.26). If fibrin is detected in the tip of the tubing, injection of 25 mg tPA will digest the clot, but higher levels of topical and systemic corticosteroids and NSAIDs are indicated to resolve the iridocyclitis. Long-term failure of anterior chamber shunts is usually associated with development of a fibrotic capsule around the episcleral base of the device, and a resultant decrease in its ability to filter and resorb aqueous humor. As these shunts do not stop the progression of the original cause of the primary glaucoma, the outflow of aqueous humor through the iridocorneal angle continues to decline. Aqueous humor is proinflammatory and may stimulate continued capsular thickening. With time, the capsule becomes thicker and/or less permeable, and IOP gradually increases over weeks or several months. Topical corticosteroids may impede, but not prevent, the development of these capsules. Surgical removal of the capsule overlying the implant or needling the capsule’s walls will immediately restore normal levels of IOP, assuming the system has not become plugged. As the capsule is stripped from the implant during surgery, aqueous humor will immediately flow into the incision and IOP will decrease. Recurrent capsule formation may, however, result in more rapid and aggressive fibrosis following surgical ‘deroofing’. More effective antifibrotic drugs are needed to markedly impede or totally prevent capsule formation around these implant extrascleral bases. These drugs may be injected or inserted, as timed-release medications into the retrobulbar space intraoperatively, or 1–2 months postoperatively after some capsule has formed around the implant and healing is complete. A complete strategy for the placement and postoperative management of anterior chamber shunts in dogs is still evolving, but some guidelines are emerging. A single implant

Long term

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Glaucoma-related

Continued iridocorneal closure Additional peripheral anterior synechiae Implant and AC tubing invasion by inflammatory membranes Cataract progression

Implant-related

Inadequate size of base and size of capsule Capsule begins to fail/insufficient aqueous absorption Implant extrusion

Fig. 10.26 A temporary fibrin plug (arrow) lodged in the end of the anterior chamber tubing in a dog 3 days postoperatively. Fibrinolysis can be achieved with an intracameral injection of 25 mg tissue plasminogen activator.

Anterior chamber shunts/gonioimplants

design may not be effective for all types of canine glaucoma, and the primary glaucomas in dogs may benefit from more than one type of implant. Surgical intervention early in the course of glaucoma when limited aqueous humor outflow remains, may respond better to gonioimplantation than the advanced glaucomas with no normal residual aqueous humor outflow. A different shunt with a larger diameter anterior chamber tubing may be optimal for glaucomas associated with iridocyclitis. A different and thinner implant may perform better in the cat. Optimal canine candidates for gonioimplants are visual patients with early glaucoma, devoid of iridocyclitis and lens subluxation, and normal-appearing optic disks. An implant with a valve mechanism may be optimal for these patients. Patients with vision and IOP that is increasing despite maximum levels of medical therapy are also good candidates for these gonioimplants. Anterior chamber shunts for canine patients with advanced glaucoma, not under adequate medical control, may be less promising candidates and require different strategies. Anterior chamber shunts without valve systems, and perhaps with a fairly large diameter anterior chamber tubing and episcleral implant, may be better choices for these patients. Anterior chamber shunts have been less successful in glaucomatous eyes with uncontrolled IOP as the rapid lowering of IOP at surgery often causes formation of excessive aqueous fibrin and intraocular hemorrhage. Vitreous within the anterior chamber, associated with luxated lenses and rupture of the anterior vitreous, may additionally plug these shunts. If vitreous plugs the tip of the anterior chamber tubing, hyaluronidase (25–100 IU) may be injected into the anterior chamber to attempt enzymatic degradation of the vitreous; alternatively, surgical vitrectomy may be employed. At this time, the success of anterior chamber shunts is both improving and encouraging (Fig. 10.27). In a large series involving 83 eyes of 65 dogs that evaluated both the non-valved and Ahmed gonioimplants, maintenance of IOP of 20 mmHg or less ranged from 4 to 10 months depending on the implant. Fifteen of the 22 eyes with IOP 20 mmHg or below were visual 1 year postoperatively. A smaller series of 18 dogs combined the Ahmed implant with either cyclocryotherapy or laser cyclophotocoagulation. One year postoperatively 11 of the 19 eyes had vision and 14 of the 19 eyes had IOP of less than 25 mmHg. Sapienza and van der Woerdt reported using the combined transscleral cyclophotocoagulation and Ahmed valved

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implant in 48 dogs and 51 eyes. Good IOP control was achieved in 76% of the eyes, nearly 50% of the eyes maintained vision for 6 months, and 41% were still visual at 12 months. Their results, like the previous report, suggest that these combined procedures are more successful. With further refinement in these devices, the refinement of antifibrotic drugs and protocols, and the adjunctive use of cyclodestructive procedures, anterior chamber shunts may become our most useful surgical procedures for management of small animal glaucoma.

Adaptations in large animals and special species Methods of surgical aqueous diversion such as placement of gonioimplants or shunts have been only sparingly utilized for the treatment of equine glaucoma. There have been sporadic reports of the use of gonioshunts in the experimental setting and the occasional clinical patient, but no efficacy data are available for review. Placement of a gonioimplant to increase aqueous outflow has only been described for valved shunts that divert aqueous humor into the subconjunctival space in the horse. The surgical procedure is identical to that in the dog with the exception that the tubing must be longer to accommodate the large size of the eye and the greater distance between the tubing tip in the anterior chamber and the body of the shunt placed at the equator of the globe beneath the rectus musculature. The procedure requires that the horse be placed under general anesthesia in lateral recumbency. Neuromuscular paralysis will facilitate placement since the globe must be retracted ventrally in order to expose a dorsal placement site. A conjunctival pocket is created and the body of the shunt is sutured to the sclera with 6-0 or 7-0 nylon at the level of and beneath the dorsal rectus muscle. The tubing is then primed with tPA, its tip is cut on the bevel so that its length will allow it to extend 5–8 mm into the anterior chamber, and then placed into the anterior chamber through a scleral tunnel that has been created with a 22 g needle. The conjunctiva is then apposed atop the implant. Treatment of the surgical site prior to the completion of surgery with an antifibrosing agent such as MMC may extend the filtering capacity of the bleb by decreasing the scarring around the shunt. Data regarding the long-term efficacy of this step are lacking, but given the horse’s propensity for fibrosis and scar formation, it is reasonable to assume that this may extend the usefulness of the implant.

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Fig. 10.27 Postoperative appearance after gonioimplants in the dog. (a) Six months postoperatively with an Ahmed gonioimplant in a 7-year-old American Cocker Spaniel with primary angle-closure glaucoma. (b) Twelve months postoperatively with an Ahmed gonioimplant in a Beagle with inherited open-angle glaucoma. (c) Slit-lamp biomicroscopic appearance of the anterior chamber tubing in a glaucomatous eye 2 years postoperatively.

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Commercially available shunts are relatively small compared to the large size of the equine globe, and their tubing is necessarily narrow to combat structural rigidity. Although the tubing in most can accommodate in-vitro flow rates of 20 mL/min, which should in theory be sufficient to facilitate shunted aqueous outflow in the horse, when inflammatory products or pressure from the tissues surrounding its tunnel into the anterior chamber obstruct the diameter of the lumen, increased resistance to flow and decreased flow result, potentially diminishing the efficacy of the implant. The use of more than one gonioimplant has been suggested to avoid this potential problem in the horse. Gonioimplants may be most useful as an adjunctive modality combined with a cyclodestructive procedure and medical therapy. Postoperative care consists of topical antibiotics and corticosteroids, and systemic administration of an NSAID such as flunixin meglumine. Intracameral tPA is often necessary in the immediate postoperative period to lyze accumulations of fibrin that may obstruct the shunt tubing. If possible, careful direct injection into the tubing lumen will have the greatest effect in clearing any fibrin clots within it. This is often not possible if the injection is administered while the animal is sedated yet standing. A short-acting general anesthetic will permit easier access to the shunt tubing.

Cyclodestructive procedures Several procedures have been developed to treat the different primary glaucomas in small animals by decreasing the rate of aqueous humor formation by partial destruction of the ciliary body processes. Use of these techniques was stimulated by the limited initial success of the filtering glaucoma procedures, even though the genesis of the primary glaucomas has not been demonstrated to involve the ciliary body and excessive rates of aqueous humor production. Using excessive heat, as in diathermy or lasers, or extreme cold, as in cryotherapy, these energies are directed through the overlying sclera to the ciliary body processes. Additionally, drugs, such as intraocular gentamicin, injected into the vitreous space, are extremely toxic to the ciliary body epithelium and retina. Cyclodestructive therapies have the advantages of multiple non-invasive applications and can be performed in animals under only deep sedation. Application of the cryo- and laser probes is critical and must be directly over the ciliary body processes. Laser techniques create more limited and focal lesions than cryocyclothermy, and with less collateral tissue damage and complications. In dogs, the treatment target area is 5 mm behind the limbus in the dorsal aspects of the globe. With globe enlargement, the ciliary processes (pars plicata ciliaris) may shift an additional 0.5–1 mm posteriorly. The ciliary body epithelia and ciliary processes possess remarkable regenerative capabilities, and complete recovery from laser and cryotherapy may result. Excessive applications of these energies result in phthisis bulbi, with irreversible destruction of the ciliary body and permanent ocular hypotony (IOP <5 mmHg). With the ciliary body cellular destruction in these procedures, large amounts of pigment, erythrocytes, fibrin, and cellular membranes will be released into the posterior chamber, and eventually into the already compromised

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aqueous humor outflow pathways. As a result, an elevation in IOP immediately following laser or cryotherapy application is anticipated. If the IOP elevation is significant and lasts for more than a few hours, additional damage to the retina, optic nerve, and thus vision may result. Consequently, these treatment modalities tend to be applied to medically non-responsive glaucomatous eyes, although attempted ‘prophylactic’ treatment of eyes considered to be at risk for the development of disease has been proposed. As the effects of laser cyclodestruction are more controllable, treatment of visual eyes has become commonplace, and is now additionally offered by endolaser cyclophotocoagulation systems. Unfortunately, these laser instruments are expensive and these costs are reflected to the clients. As all these therapies induce an intense iridocyclitis, preoperative treatment of the eye must include: 1) the appropriate glaucoma therapy to maintain IOP as low as possible; and 2) anti-inflammatory agents to suppress the anticipated iridocyclitis in the form of topical and systemic corticosteroids and NSAIDs.

Cyclocryothermy Cyclocryothermy is the application of intense cold directly through the bulbar conjunctiva and sclera to partially damage the ciliary body and reduce the rate of aqueous humor formation. Cyclocryothermy can be applied repeatedly because the bulbar conjunctiva and sclera are not adversely affected. The extensive scleral and conjunctival inflammation and damage observed after application of diathermy does not occur in small animals. Cyclocryothermy is employed primarily in advanced glaucomatous eyes to reduce IOP in the presence of persistent pain or to induce phthisis bulbi, which is more cosmetically acceptable than the buphthalmic eye. This technique is also used for the treatment of glaucomatous eyes that are nonresponsive to intensive medical treatments and the possibly for restoration of vision is low. Cyclocryothermy is used less frequently in visual eyes with less-advanced canine glaucoma. For effective cyclocryothermy, part of the ciliary body processes are frozen and the ciliary body epithelium destroyed by the freeze–thaw cycle. Immediately after freezing, rupture of the ciliary epithelia and pigmented cells in the ciliary body stroma occurs. Ciliary body blood vessels are damaged and leak erythrocytes and plasma. The aqueous humor will be filled with these products which will eventually be reabsorbed, primarily through the compromised aqueous humor outflow pathways. After the induction of deep sedation or short-acting general anesthesia, topical anesthetic is instilled onto the eye and the eyelids are retracted by speculum. The globe may be manipulated with thumb forceps by grasping the bulbar conjunctiva. The sites for cyclocryothermy application are determined by calipers, measuring 5 mm posterior to the limbus (Fig. 10.28a). Repeatable and accurate freezing temperatures are achieved using nitrous oxide. A 2.0–3.0 mm cryoprobe is applied 5 mm from the limbus directly onto the dorsal bulbar conjunctiva (Fig. 10.28b,c). Four to eight sites in the dorsal one-half of the eye are frozen for 120 s, each with the temperature of the cryoprobe reaching –60 to –80 C (reflecting a ‘killing’ temperature

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Fig. 10.28 Cyclocryothermy attempts to partially destroy the ciliary body and reduce the rate of aqueous humor formation and intraocular pressure. (a) The sites, 4–5 mm posterior to the limbus, for cyclocryothermy are determined by calipers. (b) The cyclocryothermy probe is applied to four to eight sites. Each site is frozen for 120 s. (c) Cyclocryotherapy using the nitrogen cryoprobe for absolute angle-closure glaucoma in a dog.

of –25 to –30 C at the ciliary body). The 3 and 9 o’clock positions are avoided to prevent direct damage to the long posterior ciliary blood vessels. During and after the application of cryotherapy, chemosis and hyperemia of the bulbar conjunctiva develop. Repository subconjunctival anti-inflammatories may be used to minimize swelling and patient discomfort.

Transscleral laser cyclophotocoagulation Transscleral laser cyclophotocoagulation (TSCPC) uses energy developed by different types of laser (usually Nd: YAG and diode lasers in veterinary ophthalmology) to destroy ciliary body tissue, and reduce aqueous humor formation through coagulative necrosis. The non-contact and contact Nd:YAG and now, most frequently, diode lasers have been used in different animal species, and although costly, they offer considerable promise in the treatment of glaucoma in animals. As with other procedures that attempt to destroy the ciliary body, considerable post-treatment anterior uveitis is an anticipated sequela, and may be minimized with the judicious use of preoperative anti-inflammatory therapy. Varying success rates have been reported for eyes with less uveal pigmentation; however, recent investigation has confirmed that although pigment in blue-eyed dogs is more sparsely distributed within the iridal stroma and musculature, the amount of pigment within the ciliary epithelium is no different when compared to that of brown-eyed dogs. TSCPC may also be combined with anterior chamber shunts in sighted glaucomatous dogs. This combination seems to offer improved success rates for maintenance of vision long term. In a recent report of 46 glaucomatous canine eyes treated with transscleral Nd:YAG cyclophotocoagulation, the number of laser ‘spots’ averaged 35, with a total energy delivered to each eye of 228 joules (mean energy per burst was 7 joules). Both the dorsal and ventral scleral areas were treated using a contact ‘G’-probe; the 3 and 9 o’clock positions were avoided to prevent contact with the long posterior ciliary vessels (Fig. 10.29). Audible ‘pops’ are the concussive result of tissue micro-explosions and indicate excessive energy application. Although excessive ‘pops’ should be avoided, the occasional pop reassures the surgeon that close to the ideal amount of laser energy is being applied at each site, resulting in effective photocoagulation.

Fig. 10.29 Appearance of a glaucomatous eye after contact laser cyclophotocoagulation. Note the individual laser applications in the sclera.

In 44 glaucomatous eyes in dogs, laser cyclodestruction reduced IOP to less than 25 mmHg in 83% of the eyes for 12–24 weeks. In another study, 184 eyes of dogs with primary glaucomas were treated with diode laser at 35 sites, 3 mm posterior to the limbus with a power of 1500 mW for a duration of 1500 ms (2.25 joules/site). IOP less than 30 mmHg was achieved in 71% of the eyes. Of 39 eyes assessed to have potential for preservation of vision, only 17 eyes (44%) retained vision 8 weeks post-laser therapy.

Diode endoscopic cyclophotocoagulation Endoscopic cyclophotocoagulation facilitates direct observation of the ciliary tissues as laser energy is delivered to each process. Although the amount of energy used varies based on pigment distribution, tissue proximity, and the presence of cystic uveal structures, the average amount of laser energy delivered to each site approximates 250 mW (range 200–350 mW) at a continuous duration. The average extent of each ciliary body ablation is 272.5  41.4 (range 185–300 ). In the first study by Bras et al, nine dogs and one cat with medically resistant glaucoma were treated by diode endoscopic cyclophotocoagulation, either through a limbal incision in combination with lenticular phacoemulsification, or posteriorly via a pars plana approach. The average laser setting was 0.4 mW (range 0.25–0.5 mW) with continuous duration; the average treated area was 158 (range 90–180 ) in either the ventronasal or ventrotemporal quadrants. With follow-up

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times ranging from 1 week to 7 months, IOP was less than 20 mmHg in 90% of the patients. All patients were visual at last examination; 9 of the 10 animals required less medication to maintain IOP than before laser therapy. In a second report by Lutz and Sapienza, 10 pseudophakic and aphakic dogs were treated by diode endoscopic cyclophotocoagulation for secondary glaucoma through a limbal approach. The average laser energy delivered to each site was 250 mW (range 200–350 mW) at a continuous duration. The average extent of ciliary process ablation was 272.5  41.4 (range 185–300 ). IOP was maintained within the normal range in 8 of the 10 dogs (average follow-up 5.7  1.7 months), and 5 dogs remained visual. Current experience would suggest that an anterior approach (via either one- or two-port limbal entry) is most appropriate for veterinary patients that do not require posterior segment surgery. Concurrent lenticular phacoemulsification facilitates maximal ciliary sulcus exposure, as well as obviating subsequent cataract formation as a potential complication (secondary to diode laser energy or direct surgical contact and manipulation). Removal of the lens may itself have beneficial effects in cases of anterior chamber crowding secondary to intumescences. Adequate ciliary sulcus inflation is necessary in order to fully visualize the ciliary processes. This is accomplished using a sodium hyaluronatebased viscoelastic material, which permits the transmission of laser energy. With four to six ciliary processes in view, the laser targeting beam should be situated over the ciliary processes to be treated, and energy applied in an upward ‘painting’ motion. Effectively treated ciliary processes will be noted to shrink and turn white. Copious proteinaceous debris may be released during the coagulation process and may need to be irrigated periodically in order to maintain optimal visualization. Residual viscoelastic material is completely aspirated following surgery, and the incision closed using a single cruciate suture of 6-0 to 9-0 absorbable material. The immediate postoperative use of an intracameral antiinflammatory agent (0.1–0.2 mL dexamethasone 4 mg/mL) as well as tPA has been advocated by some surgeons.

Postoperative management and results Conjunctival hyperemia and chemosis follow cyclocryothermy and may be intense. Topical and systemic corticosteroids and antiprostaglandins reduce cryogenic inflammation and tissue destruction. IOP is maintained within normal limits with topical and/or systemic carbonic anhydrase inhibitors. After approximately 4–6 weeks, the eventual result of cyclocryothermy can be ascertained. In the event that IOP is still elevated in the absence of other medications, cyclocryothermy can be repeated. Complications following cyclocryotherapy include chemosis, conjunctivitis, corneal granulation, iris depigmentation, retinal detachments, transiently increased IOP, iridocyclitis, and phthisis bulbi. Cryotherapy may be more likely to produce retinal detachments than laser cyclodestruction. In a series in 1990 involving 56 eyes of 37 dogs with glaucoma, short-term treatment success after laser cyclodestruction, as determined by maintenance of IOP less than 25 mmHg for 12–24 weeks, was 83%. Three of the four treatment failures were in eyes devoid of uveal pigmentation.

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Hyphema occurred as a short-term complication in 16% of treated eyes, but in one-fourth of these eyes the hyphema was complete and did not resolve. Cataract formation seems the most visually damaging complication and occurred in 37% of the eyes as a long-term complication. Phthisis bulbi also developed. In a larger series involving 176 eyes of 144 dogs, diode laser transscleral cyclophotocoagulation, a contact probe with a spot size of 600 microns, was applied in 30–40 sites 3–4 mm posterior to the limbus with a power of 1250– 2000 mW and a duration of 1500 ms for an average of 85 joules per eye. Often an immediate increase in IOP occurred, requiring anterior chamber paracentesis, and during the first week IOP fluctuations were common and required systemic carbonic anhydrase inhibitor treatment. With follow-ups of 6 months or longer on 106 eyes, 65% (69 eyes) had IOP less than 30 mmHg. Of the 45 eyes assessed to have the potential for vision, 53% (10 of 19 eyes) had vision. Failures were associated with persistent or recurrent increases in IOP, cataract formation, intraocular hemorrhage, corneal ulceration due to lagophthalmos, and retinal detachment. This clinical study was applied to primary glaucoma cases at different stages of the disease, and many eyes had no potential for vision. For a future study, careful selection of patients prior to laser cyclophotocoagulation may yield improved results. In the study by Lutz and Sapienza of 10 dogs treated by laser endoscopic cyclophotocoagulation, vision was preserved in 6 of 10 patients, and the amount of glaucoma medications to maintain IOP below 25 mmHg was markedly reduced. Complications included superficial corneal ulceration (1/10) and recurrence of glaucoma (2/10).

Adaptations in large animals and special species Cyclodestructive procedures such as cyclocryothermy and transscleral cyclophotocoagulation are the most common surgical approaches to the treatment of equine glaucomas (Figs 10.30 and 10.31). This is due to the non-invasive nature of these procedures compared to placement of an anterior chamber shunt, and the ability to perform either procedure in the standing animal under adequate sedation with local anesthesia. General anesthesia may be necessary with certain individuals whose temperament does not permit a standing procedure, and may ease the administration of the chosen treatment modality. Recently technology has evolved for endoscopic cyclophotocoagulation which permits direct visualization of the target ciliary processes during the application of laser energy and therefore a more precise treatment. This procedure, however, must be performed under general anesthesia.

Cyclocryothermy Cyclocryothermy employs intense cold applied directly to the globe to partially destroy the ciliary epithelium that is the site of aqueous humor formation. After intravenous sedation or short-acting general anesthesia, topical anesthesia is applied to the globe to facilitate anesthesia and analgesia. A 3 mm cryoprobe with a nitrous oxide source is placed

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Fig. 10.30 (a) Glaucoma in an Appaloosa. Note the buphthalmos, corneal edema, and mydriasis of the right eye. (b) Intraoperative photograph of transscleral cyclophotocoagulation with the diode laser in a horse with glaucoma.

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Fig. 10.31 (a) This horse has clinical signs of glaucoma, including mydriasis and corneal edema. (b) The same eye 6 months later after laser transscleral cyclophotocoagulation. The corneal edema has cleared but keratitis is present.

on the conjunctiva pressed to the sclera 6 mm posterior to the limbus for a double fast-freeze, slow-thaw session at six sites on the globe. The cryoprobe is applied to each site for 1 min. Care must be taken to avoid the 3 and 9 o’clock positions on the globe to prevent damage to the long posterior ciliary arteries. Cyclocryodestruction is often reserved for buphthalmic globes that are blind or have questionable vision since this procedure is usually associated with significant postoperative uveitis. In visual eyes, this uveitis can be severe enough to damage any remaining visual capacity the eye may have. Chemosis is a common, although transient, sequela. Postoperative treatment consists of supportive topical corticosteroids and systemic NSAIDs. Topical

lubricant or antibiotic ointments may be necessary to support the external ocular structures if chemosis is profound. The hypotensive effect of this procedure may be short lived as recurrence of elevated IOP has been reported as early as 6 weeks postoperatively. This is most likely the result of regeneration of the ciliary epithelium.

Laser cyclophotocoagulation Cyclophotocoagulation has fewer intraocular side effects than cyclocryothermy and is therefore the surgical treatment of choice. Contact TSCPC has been performed with both the Nd:YAG and the semiconductor diode lasers with

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similar results. Since the equine ciliary body varies in anteroposterior length by the quadrant of the globe, the surgeon should be familiar with the anatomy of this target tissue. The contact probe of the laser should be placed on the globe 4–6 mm posterior to the limbus, avoiding the nasal quadrant and the 3 and 9 o’clock positions. Treatment in the nasal quadrant is more likely to be associated with cataract formation and retinal detachment. Prior to TSCPC, an affected eye should be treated medically to control any active anterior uveitis. Laser surgery performed on an already inflamed eye is more likely to result in profound postoperative uveitis and lesser control of the elevated IOP. Topical corticosteroids should be instituted at least 24 h before surgery and dosed four times daily. Systemic NSAIDs should also be given the day prior to surgery and continued as necessary into the postoperative period. A single dose of atropine should be administered prior to surgery and may be necessary postoperatively as well. After the animal has been sedated heavily or placed under general anesthesia, an eyelid speculum is placed and topical anesthetic agents applied to the globe. Using a diode laser setting of 1200–2000 mW, 40–60 sites are treated for a duration of 1500–5000 ms. The settings are then adjusted so that an audible ‘pop’ is heard in approximately one-third of the sites treated. In general, a good initial power setting is 1500 mW for a duration of 1500 ms, which will deliver 2.25 joules/ site. This has been determined to be the ideal energy to achieve the desired effects without causing significant unwanted collateral damage to normal tissue. When using the Nd:YAG laser, a power setting of 11 W for a duration of 0.4 s at 60 sites will deliver a total energy dose of 264 joules. Immediately after the laser procedure has been performed, the IOP should be determined. Ocular hypertension is common following laser ablative procedures and should be treated via aqueous paracentesis with a 30 g needle and an attached 1 cc syringe inserted into the anterior chamber at the corneoscleral limbus. Aqueous humor is removed to restore IOP to between 10 and 15 mmHg. After surgery, topical and systemic anti-inflammatory

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medications are continued and tapered as the postoperative inflammation improves over the next few weeks. Topical antiglaucoma medications should also be continued, and may remain necessary in the extended postoperative period to maintain the target IOP. The IOP should be evaluated 24 h after surgery since it may rise again following paracentesis, and this procedure may need to be repeated. The IOP lowering effect from the destruction of the ciliary body epithelium occurs 2–4 weeks after the laser procedure. Cyclophotocoagulation may need to be repeated at some point due to ciliary epithelial regeneration. Diligent long-term monitoring of IOP will be necessary for the life of the patient. If concurrent equine recurrent uveitis (ERU) is present, topical and systemic anti-inflammatories may be necessary long term, and the addition of a slow-release suprachoroidal cyclosporine implant may be indicated. A recent retrospective evaluation of diode laser TSCPC in 27 horses revealed that, in 90% of horses, adjunctive medical therapy was required to keep the IOP within the target range (Figs 10.32 and 10.33). Vision was maintained in 64% of these patients over a mean follow-up period of 33 months. A recent study using the Nd:YAG laser in 23 eyes of 16 horses revealed that IOP was maintained in the target range in 70% of cases more than 20 weeks after surgery. Sixty percent of these animals remained visual after the procedure, which was the same percentage of animals visual before the procedure. Complications of TSCPC included chemosis and conjunctival hyperemia, transient scleral fistulas, corneal ulcerations, hyphema, cataract, retinal detachment, phthisis bulbi, and failure to control IOP. Serious complications are rare, however. The most common complications noted were corneal ulcerations that healed quickly and uneventfully. These may occur due to corneal desensitization from the TSCPC or from exposure during the procedure. There are no published reports of diode endoscopic cyclophotocoagulation in horses to date, but research is ongoing. Preliminary results indicate that this may be an effective procedure for the control of IOP in glaucomatous horse eyes. The disadvantage of this procedure is that it must

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Fig. 10.32 (a) Intraoperative photograph of transscleral cyclophotocoagulation with Nd:YAG in a horse. (b) The same eye 5 days after transscleral diode cyclophotocoagulation. The intraocular pressure is still elevated but expected to decrease.

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Pharmacologic ablation of the ciliary body

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Fig. 10.33 (a) Burns are apparent on the surface of the sclera of a horse after transscleral cyclophotocoagulation. (b) Intraoperative photograph of burns of the ciliary body processes made with endoscopic cyclophotocoagulation.

be performed under general anesthesia; however, that may provide the opportunity for combined procedures. An equine patient under general anesthesia for endoscopic cyclophotocoagulation may also benefit from the placement of a gonioshunt or, if ERU is a concurrent problem, a slowrelease suprachoroidal cyclosporine implant. The procedure is similar to that in small animals with exceptions made for the comparatively large size of the equine eye. A longer probe has been developed by the manufacturer to accommodate the large diameter of the globe. There are two possible approaches for this procedure. The limbal approach is begun with a 2–3 mm corneal incision. Viscoelastic materials are injected through this incision to fill the anterior chamber and the ciliary sulcus between the iris and the lens. The endoscopic probe is then inserted into the eye and the laser energy is applied to the visible ciliary processes. Once the treatment is complete, the viscoelastic material is removed and the incision is closed routinely. Intracameral tPA injected at the completion of surgery may aid in the dissolution of fibrin that forms as a result of tissue trauma. To date, the limbal approach has only been employed in aphakic or pseudophakic animals. In an experimental protocol using cadaver eyes, the limbal approach resulted in excessive contact with the normal lens which is likely to result in postoperative cataract formation. The alternative or posterior approach through the para plana requires a scleral incision 10 mm posterior to the limbus; although this appears to be potentially less traumatic to the normal lens, it is likely to be associated with higher rates of complications for the posterior segment, including hemorrhage and retinal detachment. The large size of the horse eye may necessitate the use of multiple incisions to access sufficient ciliary tissue to effect the desired result. Sufficient data are not available to recommend the ideal amount of tissue

to treat, but it is likely that between 180 and 270 will be a reasonable starting point.

Pharmacologic ablation of the ciliary body Unfortunately, with less than optimal success rates of traditional glaucoma filtration surgical procedures and the often late initial presentation of glaucomatous eyes in small animals, salvage procedures to prevent ocular pain, reduce to near normal size the enlarged globe, and still provide a cosmetically acceptable eye may be necessary. These procedures include: 1) pharmacologic destruction of the ciliary body with intravitreal injection of gentamicin; 2) intrascleral (or intraocular) silicone prosthesis within an eviscerated globe; and 3) enucleation (surgical removal of the entire globe). For the latter two surgical procedures, see Chapter 4. Pharmacologic destruction of the ciliary body with intraocular injections of gentamicin is a salvage procedure reserved for advanced and blind primary glaucomatous eyes in small animals. This method is an economic alternative to enucleation and intraocular prosthesis surgical procedures. An intravitreal injection of gentamicin at the cytotoxic dose of 25 mg can destroy the ciliary body and reduce aqueous humor formation. The procedure is restricted to blind chronic primary glaucomatous eyes that are buphthalmic and painful in the dog and horse. This procedure is not recommended for cats, as some cats have been reported to develop intraocular sarcomas after intravitreal gentamicin administration. Glaucomatous eyes with concurrent intraocular inflammation or neoplasia are not candidates for this procedure. The technique is performed under short-acting general anesthesia or tranquilization combined with topical

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Fig. 10.34 In pharmacologic ablation of the ciliary body, a cytotoxic dose of gentamicin is injected into the vitreous space. (a) A 2.5 cm (1") 20 g hypodermic needle is inserted 6–8 mm posterior to the limbus into the vitreous body. (b) After aspiration of an equal volume of liquefied vitreous, 25 mg gentamicin and 1 mg dexamethasone are injected.

anesthesia. The eyelids are retracted by speculum, and the corneal and conjunctival surfaces are cleansed with 0.5% povidone–iodine solution. To inject 25 mg of gentamicin combined with 1 mg dexamethasone (to moderate the post-injection inflammation), a 2.5 cm (1") 20 g hypodermic needle is inserted 6–8 mm posterior to the dorsal limbus and directed about 10–15 mm into the center of the vitreous space (Fig. 10.34a). After the aspiration of 0.5–0.6 mL of liquid vitreous, gentamicin (0.25 mL of a 100 mg/mL solution) and dexamethasone (0.25 mL of a 4 mg/mL solution) are injected (Fig. 10.34b). Post-injection management after pharmacologic ablation of the ciliary body includes primarily topical antibiotics and corticosteroids. If IOP elevations develop, short-term medical therapy is used. Pharmacologic ablation of the eye is successful in about 65% of dog eyes in markedly lowering IOP. Eyes with marked elevations in IOP are less likely to respond to intraocular gentamicin injections. Eyes that fail to respond to the initial intravitreal injection of gentamicin have only a 50% success rate to the second injection. Marked reduction in the size of the normal globe (phthisis bulbi) occurs in about 10–50% of the eyes. Reduction in the size of advanced and enlarged glaucomatous eyes in dogs is common, occurring in about 80% of the eyes. Frequent complications of intravitreal gentamicin include intraocular hemorrhage, corneal opacification, cataract formation, and phthisis bulbi.

Adaptations in large animals and special species Pharmacologic ablation of the ciliary body in horses should be reserved for permanently blind eyes that have persistently elevated IOP and buphthalmia. It is a particularly useful treatment option for an animal in which the risks of general anesthesia for enucleation or placement of an intraocular prosthesis are great, such as in older animals and very large individuals. The procedure is similar to that in dogs, but when performed in the standing animal will require adequate sedation, an auriculopalpebral motor block, and the instillation of both topical anesthetic and phenylephrine (2.5% to blanch or vasoconstrict the conjunctival vasculature). The reported doses of gentamicin used vary from a total dose of 25 to 100 mg, but generally 25 mg is sufficient to decrease aqueous humor production enough to lower IOP and induce mild shrinkage of the globe. Higher doses

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are associated with a higher incidence of severe phthisis bulbi. Dexamethasone (1 mg) may be combined with the gentamicin to minimize the inflammation and discomfort that result from the injection. Once the patient has been adequately sedated and locally anesthetized, the eye and the conjunctival fornices should be cleaned with a dilute povidone–iodine solution. An eyelid speculum may facilitate exposure of the injection site. A 20 or 22 g needle attached to a 6 mL syringe is positioned dorsolaterally, approximately 7 mm posterior to the limbus and directed at a 45 angle away from the lens and toward the optic nerve. Before the gentamicin or gentamicin–dexamethasone combination is injected, an equal or greater volume of vitreous should be removed. If vitreous cannot be aspirated, aqueocentesis should be performed to decrease the ocular volume and temporarily lower IOP. Aqueocentesis is performed with a small gauge needle, usually 27 or 30 g, inserted at the limbus into the anterior chamber. Care should be taken to ensure that the needle stays parallel to the plane of the iris while it is inside to eye to avoid damage to the iris and lens, which could result in intraocular hemorrhage and inflammation. This procedure, a form of cyclodestruction, is effective at lowering IOP, but does not address any other disease processes that may be ongoing within the eye. If uveitis is the initiator of glaucoma, this procedure will not treat the persistent inflammatory response. Uveitic eyes with controlled ocular hypertension may still require antiinflammatory therapy to keep the animal comfortable. This procedure should be used with caution in eyes with diseased corneas. Animals with blind, glaucomatous eyes and complicated corneal ulcers may be best served by enucleation.

Neuroprotection The pathophysiology of the glaucomas is marked by neurodegeneration. This degeneration is mediated through cellular apoptosis and shares many similarities with other neurodegenerative diseases, including Alzheimer’s, Parkinson’s and AIDS-related dementia. The exact mechanisms of this process are complex and incompletely understood, but a decreased supply of vital neurotrophic substances to RGC bodies, as well as alterations in vascular delivery and autoregulation, have been postulated to result in altered mitochondrial function and permeability and a local milieu of glutamate-related toxicity, leading to the calcium influx which marks the apoptotic process. Additionally, this process has been shown to be self-perpetuating, such that neuronal death may continue in spite of control of the initiating stimulus, in this case elevated IOP. Hence, a complete strategy for the successful long-term management of glaucoma should encompass not only IOP control (through the various medical and surgical techniques discussed above) but also an attempt to limit the ensuing cycle of neurodegeneration. The translation of this ‘neuroprotective’ approach into a meaningful clinical strategy is challenging, and is compounded by the difficulties associated with objectively assessing the potential benefits of such therapies. Proposed neuroprotective therapies are summarized in Table 10.6.

Neuroprotection

Table 10.6 Possible neuroprotectants for the animal glaucomas

Class

Name

Description

NMDA antagonists

Memantine, flupirtine

Excitotoxicity results from excessive activation (excitation) of NMDA receptors and is thought to mediate Ca-dependent neurotoxicity associated with neurologic injury, through alterations in the receptor’s ion channel NMDA antagonists remain potentially promising compounds, in spite of early disappointing human trial results Memantine is an open channel blocker giving rise to the property of ‘use dependence’ (higher concentrations of glutamate open a greater proportion of channels, which results in greater access for memantine) Second-generation amantadine derivatives are currently in development

Calcium channel blockers

Flunarazine, lomerazine, betaxolol, nifedipine

Calcium channel blockers reduce Ca influx into stressed cells and may also slow the influx of cytosol free Ca into mitochondria; they may also prevent ET1-mediated nitric oxide hypoperfusion Betaxolol, a beta-blocker used to reduce IOP, has Ca channel-blocking properties and has also demonstrated potentially neuroprotective effects

Adrenergic agents

Nipradilol, brimonidine

The beta-blocker nipradilol and the a2-agonist brimonidine promote the survival and function of RGCs and may act as anti-apototics; they may also directly modulate NMDA-receptor function and stabilize ion pores

Prostaglandin analogs

Unoprostone

Unoprostone may inhibit glutamate stimulation and open potassium channels under conditions of high intracellular Ca, thereby closing voltage-gated Ca channels and limiting neuronal damage

Immunomodulators

Cyclosporine

The inner mitochondrial membrane permeability transition pore complex (PTPC) is cyclosporine inhibited, thus raising its potential for therapeutic use

NOS inhibitors/ROS scavengers

N-nitro-l-arginine, aminoguanidine, SC-51, L-N (6)-(1-iminoethyl)lysine 5-tetrazole amide, vitamin E

Inhibitors of nitric oxide synthase (NOS) have been shown to experimentally reduce levels of nitric oxide and consequently exhibit neuroprotective properties

IOP, intraocular pressure; NMDA, N-methyl-D-aspartic acid; RCG, retinal ganglion cell; ROS, reactive oxygen species.

Further reading General and conventional filtration procedures Abraham LM, Selva D, Casson R, Leibovitch I: Mitomycin: clinical applications in ophthalmic practice, Drugs 66:321–340, 2006. Atreides SP, Skuta GL, Reynolds AC: Wound healing modulation in glaucoma filtering surgery, Int Ophthalmol Clin 44:61–106, 2004. Barton K, Heuer DK: Modern aqueous shunt implantation: future challenges, Prog Brain Res 173:263–276, 2008. Bedford PGC: The surgical treatment of canine glaucoma, J Small Anim Pract 18:713–730, 1977. Bedford PGC: The treatment of canine glaucoma, Vet Rec 107:101–104, 1980. Ching-Costa A, Chen TC: Malignant glaucoma, Int Ophthalmol Clin 40:117–125, 2000. Cook C: Surgery for glaucoma, Vet Clin North Am Small Anim Pract 27:1109–1129, 1997. Czederpiltz JM, La Croix NC, van der Woerdt A, et al: Putative aqueous humor misdirection syndrome as a cause of glaucoma in cats:

32 cases (1997–2003), J Am Vet Med Assoc 227(9):1434–1441, 2005. Gelatt KN: Canine glaucoma. In Gelatt KN, editor: Veterinary Ophthalmology, ed 2, Philadelphia, 1991, Lea and Febiger, pp 396–428. Gelatt KN, Brooks DE: The glaucomas. In Gelatt KN, editor: Veterinary Ophthalmology, ed 3, Baltimore, 1999, Lippincott, Williams and Wilkins, pp 701–754. Khaw PT, Sherwood MB, Doyle JW, Smith MF, Grierson I, McGorray S, Schultz GS: Intraoperative and postoperative treatment with 5-fluorouracil and mitomycin-c: long term effects in vivo on subconjunctival and scleral fibroblasts, Int Ophthalmol 16(4–5):381–385, 1992. Khaw PT, Occleston NL, Schultz G, Grierson I, Sherwood MB, Larkin G: Activation and suppression of fibroblast function [review], Eye 8(Pt 2):188–195, 1994. Keller SJ: Glaukom bein Pferd-2, Pferdeheikunde 10:261–266, 1994. Osborne NN: Pathogenesis of ganglion ’cell death’ in glaucoma and neuroprotection:

focus on ganglion cell axonal mitochondria, Prog Brain Res 173:339–352, 2008. Peiffer RL, Gwin RM, Gelatt KN, Schenk M: Combined posterior sclerectomy, cyclodialysis, and trans-scleral iridencleisis in the management of primary glaucoma, Canine Practice 4:54–61, 1977. Stack WF: Posterior sclerotomy – a surgical procedure for treatment of glaucoma, J Am Vet Med Assoc 136:453–455, 1960. Vierheller RC: Surgery for glaucoma: an analysis of technics, Mod Vet Pract 49:46–68, 1968. Weinstein WL, Dietrich UM, Sapienza JS, Carmichael KP, Moore PA, Krunkosky T: Identification of ocular matrix metalloproteinases (MMPs) within the aqueous humor of normal canine eyes and canine eyes with glaucoma, Proceedings of the 36th Meeting of the American College of Veterinary Ophthalmologists: Abstract 66, 2005. Whitley RD: Surgical management of glaucoma. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 104–112.

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Anterior chamber shunts/gonioimplants Bedford PGC: A clinical evaluation of a onepiece drainage system in the treatment of canine glaucoma, J Small Anim Pract 30:68–75, 1989. Bentley E, Nasisse MP, Glover T, Nelms S: Implantation of filtering devices in dogs with glaucoma: preliminary results in 13 eyes, Progress in Veterinary and Comparative Ophthalmology 6:243–246, 1996. Bentley E, Miller PE, Murphy CJ, Schoster JV: Combined cycloablation and gonioimplantation for treatment of glaucoma in dogs: 18 cases (1992–1998), J Am Vet Med Assoc 215:1469–1472, 1999. Cullen CL, Allen AL, Grahn BH: Anterior chamber to frontal sinus shunt for the diversion of aqueous humor: a pilot study in four normal dogs, Vet Ophthalmol 1:31–39, 1998. Garcia GA, Brooks DE, Gelatt KN, et al: Clinical evaluation of a nonvalved ’T’-shaped gonioimplant in acutely glaucomatous dogs at the University of Mexico, Proceedings of the American College of Veterinary Ophthalmologists 24:124, 1993. Garcia-Sanchez GA, Brooks DE, Gelatt KN, Kubilis PS, Gil F, Whitley RD: Evaluation of valved and nonvalved gonioimplants in 83 eyes of 65 dogs with glaucoma, Animal Eye Research 17:9–16, 1998. Gelatt KN: Evaluation of the Krupin–Denver valve implant in normotensive and glaucomatous Beagles, J Am Vet Med Assoc 191:1404–1409, 1987. Gelatt KN, Mackay EO: Pilot study of a valved anterior shunt to the parotid duct in glaucomatous dogs [abstract], Proceedings of the American College of Veterinary Ophthalmologists 31:250, 2000. Gelatt KN, Brooks DE, Miller TR, Smith PJ, Sapienza JS, Pellicane CP: Issues in ophthalmic surgery: the development of anterior chamber shunts for the clinical management of the canine glaucomas, Progress in Veterinary and Comparative Ophthalmology 2:59–64, 1992. Grahn BH, Cullen CL: Frontal sinus shunting of aqueous humor in dogs with primary glaucoma [abstract], Proceedings of the American College of Veterinary Ophthalmologists 30:28, 1999. Guerrero AH, Latina MA: Complications of glaucoma drainage implant surgery, Int Ophthalmol Clin 40:149–163, 2000. Ha˚kanson NW: Extraorbital diversion of aqueous humor in the treatment of glaucoma in the dog: a pilot study including two recipient sites, Veterinary and Comparative Ophthalmology 6:82–90, 1996. Pellicane CP, Gelatt KN, Brooks DE, Smith PM, McCalla T, Dice P: A clinical comparison of five gonioimplant types in the dog, Proceedings of the American College of Veterinary Ophthalmologists 24:123, 1993. Sapienza JS, van der Woerdt A: Combined transscleral diode laser

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cyclophotocoagulation and Ahmed gonioimplantation in dogs with primary glaucoma: 51 cases, Vet Ophthalmol 8: 121–127, 2005. Sapienza JS, Simo´ FJ, Prades-Sapienza A: Golden Retriever uveitis: 75 cases (1994–1999), Vet Ophthalmol 3 (4):241–246, 2000. Sherwood MB: Complications of silicone tube drainage devices. In Sherwood MB, Spaeth GL, editors: Complications in Glaucoma Surgery, Thorofare, NJ, 1990, Slack, pp 307–326. Strubbe DT, Gelatt KN, Mackay MO: In vitro flow characteristics of the Ahmed and selfconstructed anterior chamber shunts, Am J Vet Res 58:1332–1337, 1997. Tinsley DM, Betts DM: Clinical experience with a glaucoma drainage device in dogs, Veterinary and Comparative Ophthalmology 4:77–84, 1994. Tinsley DM, Niyo Y, Tinsley LM, Betts DM: In vitro evaluation of the effects of 5fluorouracil and mitomycin-c on canine subconjunctival and subtenon’s fibroblasts, Veterinary and Comparative Ophthalmology 5:218–230, 1995. Wirostko WJ, Mieler WF, Levin DS, et al: Hypotony and retinal complications after aqueous humor shunt implantation; the 1999 Dohlman lecture, Int Ophthalmol Clin 40:1–12, 2000.

Cyclodestructive procedures Bingaman DP, Lindley DM, Glickman NW, Krohne SG, Bryan GM: Intraocular gentamicin and glaucoma: a retrospective study of 60 dog and cat eyes (1985–1993), Veterinary and Comparative Ophthalmology 4:113–119, 1994. Bras ID, Robbin TE, Wyman M, Rogers AL: Diode endoscopic cyclophotocoagulation in canine and feline glaucoma, Proceedings of the 36th Meeting of the American College of Veterinary Ophthalmologists: Abstract 50, 2005. Brightman AH, Vestre WA, Helper LC, Tomes JE: Cryosurgery for the treatment of canine glaucoma, J Am Anim Hosp Assoc 18:319–322, 1982. Brinkmann MC, Nasisse MP, Davidson MG, English RV, Olivero DK: Neodymium:YAG laser treatment of iris bombe´ and pupillary block glaucoma, Progress in Veterinary and Comparative Ophthalmology 2:13–19, 1992. Cook C, Brinkmann M, Priehs D, Abrams K, Nasisse M, Faya G: Diode laser transscleral cyclophotocoagulation for glaucoma in dogs [abstract], Proceedings of the American College of Veterinary Ophthalmologists 25:76, 1994. Cook C, Davidson M, Brinkmann M, Priehs D, Abrams K, Nasisse M: Diode laser transscleral cyclophotocoagulation for the treatment of glaucoma in dogs: results of six and twelve month follow-up, Veterinary and Comparative Ophthalmology 7:148–154, 1997. Cullen CL: Cullen frontal sinus valved glaucoma shunt: preliminary findings in

dogs with primary glaucoma, Vet Ophthalmol 7:311–318, 2004. Hardman C, Stanley RG: Diode laser transscleral cyclophotocoagulation for the treatment of primary glaucoma in 18 dogs: a retrospective study, Vet Ophthalmol 4:209–216, 2001. Lutz EA, Sapienza JS: Diode endoscopic cyclophotocoagulation of pseudophakic and aphakic dogs with secondary glaucoma, Proceedings of the 39th Meeting of the American College of Veterinary Ophthalmologists: Abstract 75, 2008. Merideth RE, Gelatt KN: Cryotherapy in veterinary ophthalmology, Vet Clin North Am 10:837–846, 1980. Moller I, Cook CC, Peiffer RL, Nasisse MP, Harling DE: Indications for and complications of pharmacological ablation of the ciliary body for the treatment of chronic glaucoma in the dog, J Am Anim Hosp Assoc 22:319–326, 1986. Nadelstein B, Wilcock B, Cook C, Davidson M: Clinical and histopathologic effects of diode laser transscleral cyclophotocoagulation in the normal canine eye, Veterinary and Comparative Ophthalmology 7:155–162, 1997. Nasisse MP, Davidson MG: Laser therapy in veterinary ophthalmology: perspective and potential, Semin Vet Med Surg 3:52–61, 1988. Nasisse MP, Davidson MG, English RV, Jamieson V, Harling DE, Tate LP: Treatment of glaucoma by use of transscleral neodymium:yttrium aluminum garnet laser cyclophotocoagulation in dogs, J Am Vet Med Assoc 197:350–354, 1990. Newkirk KN, Haines DK, Calvarese ST, Esson DW, Chandler HL: Differences in pigment distribution within the ciliary body of blue-eyed and brown-eyed dogs, Proceedings of the 39th Meeting of the American College of Veterinary Ophthalmologists: Abstract 102:2008. Quinn RF, Parkinson K, Wilcock BP, Tingey DP: The effects of continuous wave Nd:YAG and semiconductor diode laser energy on the canine ciliary body: in vitro thermographic analysis, Veterinary and Comparative Ophthalmology 6:45–50, 1996. Roberts SM, Severin GA, Lavach JD: Cyclocryotherapy – part II. Clinical comparison of liquid nitrogen and nitrous oxide cryotherapy on glaucomatous eyes, J Am Anim Hosp Assoc 20:828–833, 1984. Sapienza JP, Miller TR, Gum GG, Gelatt KN: Contact transscleral cyclophotocoagulation using a neodymium:yttrium aluminum garnet laser in normal dogs, Progress in Veterinary and Comparative Ophthalmology 2:147–153, 1992. Sullivan TC, Davidson MG, Nasisse MP, Glover TL: Canine retinopexy – a determination of surgical landmarks, and a comparison of cryoapplication and diode laser methods, Veterinary and Comparative Ophthalmology 7:89–95, 1997.

Further reading Vestre WA, Brightman AH: Ciliary body temperatures during cyclocryotherapy in clinically normal dogs, Am J Vet Res 44:135–143, 1983. West CS, Barrie K: The use of cryosurgery in a veterinary ophthalmology practice, Semin Vet Med Surg 3:77–82, 1988. Wolfer J, Wyman D, Wilson B: Use of a noncontact neodymium:yttrium aluminum garnet laser in the treatment of canine glaucoma, Proceedings of the American College of Veterinary Ophthalmologists 24:138, 1993.

Antifibrosis drugs Glover TL, Nasisse MP, Davidson MG: The effects of topical mitomycin-c on fibrosis following glaucoma filtration implant surgery in normal dogs, Proceedings of the American College of Veterinary Ophthalmologists 25:75, 1994. Lee DA: Antifibrosis agents and glaucoma surgery, Invest Ophthalmol Vis Sci 35:3789–3791, 1994. Polak MB, Valamanesh F, Felt O, et al: Controlled delivery of 5-chlorouracil using poly(ortho esters) in filtering surgery for glaucoma, Invest Ophthalmol Vis Sci 49:2993–3003, 2008. Skuta GL: Antifibrotic agents in glaucoma filtering surgery, Int Ophthalmol Clin 33:165–182, 1993.

Equine and special species glaucoma Annear MJ, Wilkie DA, Gemensky-Metzler AJ: Diode laser transscleral cyclophotocoagulation for treatment of equine glaucoma: a retrospective study of 42 eyes of 36 horses), Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmology: Abstract 86, 2008.

Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274. Esson DW, Popp MP, Liu L, Schultz GS, Sherwood MB: Microarray analysis of the failure of filtering blebs in a rat model of glaucoma filtering surgery, Invest Ophthalmol Vis Sci 45(12):4450–4462, 2004. Esson DW, Sherwood MB, Sampson EM, Schultz GS, Samuelson DA: Glaucoma drainage implant surgery has a higher survival rate as a primary procedure in a rabbit model, Proceedings of the 36th Meeting of the American College of Veterinary Ophthalmologists: Abstract 5, 2005. Esson DW, Gelatt KN, MacKay E, et al: Development of gene microarray chips for canine and rabbit ocular tissues, Proceedings of the 36th Meeting of the American College of Veterinary Ophthalmologists: Abstract 8, 2005. Esson DW, Sherwood MB, Tuli SS, Sampson EM, Schultz GS, Samuelson DA: A sequential multiple treatment approach to influence wound healing following glaucoma filtration surgery in a rabbit model, Proceedings of the 36th Meeting of the American College of Veterinary Ophthalmologists: Abstract 9, 2005. Frauenfelder HC, Vestre WA: Cryosurgical treatment of glaucoma in a horse, Vet Med Small Anim Clin 76:183–186, 1981. Kellner SJ: Glaukom beim Pferd-2. Teil. [Glaucoma in the horse. Part II.], Pferdeheilkunde 10:261–266, 1994. Lassaline ME, Brooks DE: Equine glaucoma. In Gilger BC, editor: Equine Ophthalmology, St Louis, 2005, Saunders, pp 323–339. Meek LA: Intraocular silicone prosthesis in a horse, J Am Vet Med Assoc 193:343–345, 1988.

Miller TL, Willis AM, Wilkie DA, HoshawWoodard S, Stanley JRL: Description of ciliary body anatomy and identification of sites for transscleral cyclophotocoagulation in the equine eye, Vet Ophthalmol 4:183–190, 2001. Miller TR, Brooks DE, Smith PJ, et al: Equine glaucoma: clinical findings and response to treatment in 14 horses, Veterinary and Comparative Ophthalmology 5:170–182, 1995. Morreale RJ, Wilkie DA, Gemensky-Metzler AJ, et al: Histologic effect of semiconductor diode laser transscleral cyclophotocoagulation on the equine eye, Vet Ophthalmol 11:84–92, 2007. Pickett JP, Ryan J: Equine glaucoma: a retrospective study of 11 cases from 1988 to 1993, Vet Med 88:756–763, 1993. Popp MP, Liu L, Timmers A, Esson DW, et al: Development of a microarray chip for gene expression in rabbit ocular research, Mol Vis 13:164–173, 2007. Townsend WM: Food and fiber-producing animal ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1275–1335. Weber AJ, Harman CD, Viswanathan S: Effects of optic nerve injury, glaucoma, and neuroprotection on the survival, structure, and function of ganglion cells in the mammalian retina, J Physiol 586(Pt 18): 4393–4400, 2008. Whigham HM, Brooks DE, Andrews SE, et al: Treatment of equine glaucoma by transscleral neodymium–yttrium aluminum garnet laser cyclophotocoagulation: a retrospective study of 23 eyes of 16 horses, Vet Ophthalmol 2:243–250, 1999.

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CHAPTER

11

Surgical procedures of the lens and cataract Kirk N. Gelatt1 and David A. Wilkie2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

305

Phacoemulsification in the horse

330

Evolution of cataract surgery in dogs

307

Intraocular lens implantation in small animals

334

Evolution of cataract surgery in horses

308

Development of the intraocular lens for the dog, cat, and horse

Intracapsular cataract or lens extraction in small animals

334

309

Intracapsular cataract or lens extraction in the horse

335

Surgical anatomy

311

Removal of the unstable lens in small animals

335

Surgical pathophysiology

312

Intraocular lens implantation

339

Patient selection for all species

314

Non-surgical treatment of cataracts

316

Postoperative treatment and management in small animals

342

Preoperative preparation

319

Surgical procedures for cataracts and lens removal

320

Postoperative treatment and management in the horse

342

Choice of ophthalmic anesthesia and surgical exposure

321

Postoperative results and complications in small animals

343

Anterior chamber entry for cataract and lens extraction

322

Complications of cataract surgery in dogs

343

Capsulorhexis and anterior capsulectomies

322

Phacoemulsification

324

Phacoemulsification in small animals

327

Introduction The major causes of blindness in small animals are corneal diseases, cataracts, the glaucomas, and retinal degenerations. Of these disorders, the treatment of cataracts is clearly a surgical condition, and has been the surgery that has characterized the specialty of human and veterinary ophthalmology since their beginning. Embryologically, the lens originates from surface ectoderm. Congenital abnormalities of the lens may or may not be associated with other congenital intraocular abnormalities or cataract. Examples of congenital anomalies that may be associated with cataracts include persistent pupillary membranes, persistent hyaloid artery, persistent hyperplastic primary vitreous/tunica vasculosa lentis (PHPV/PHTVL), posterior lenticonus, microphakia, lens coloboma, and microphthalmos.

Postoperative results and complications after lens surgery in the horse The future and challenges of cataract and lens surgery in animals

351 352

Cataracts in dogs parallel those in humans, and considering the large number of recognized breeds of dogs, the number of inherited cataracts in the dog probably exceeds those in humans. Primary and possibly inherited cataracts affect a large number (about 125) of breeds of purebred dogs. In about 20 breeds, the age of onset, mode of inheritance, and site of the lens initially involved in cataract formation have been documented. In other breeds of dogs, cataracts appear at a higher frequency than in the general population, but their characteristics have not yet been defined. Cataracts secondary to traumatic, inflammatory, and metabolic disorders also affect dogs, and are also treated by surgical removal. Cataracts in cats occur less frequently. Primary cataracts occur infrequently in young cats, and most of the inherited cataracts appear in kittens rather than in adults. The most frequent cataracts in cats are secondary types, associated

11

Surgical procedures of the lens and cataract

with anterior uveal inflammations. As many uveal inflammations are secondary to serious systemic diseases, cats presented for evaluation for cataract surgery require a complete physical examination and blood tests for feline viral leukemia, feline immune-deficiency virus, and other infectious diseases. Cats usually have less intense iridocyclitis than dogs after lens and cataract extraction, and higher success rates, although only limited numbers of reports are available. Cataracts are not infrequent in horses, but are infrequent in cattle (and more rarely diagnosed). The majority of cataracts in the horse are secondary to inflammation and trauma, but inherited cataracts occur in the Morgan, Belgian, Quarter Horse, and Rocky Mountain horses. The cataracts in the latter three breeds also have additional concurrent ocular anomalies. Inherited cataracts may occur in other breeds of horses. When presented with a foal with congenital cataracts, a dilated examination of the mare and, if possible, the stallion is advised as they may also have incipient cataracts, supporting the possibility of inheritance. Breeding of foals with congenital cataracts should be discouraged and the mare, if re-bred, should not be bred back to the same stallion. Cataracts in cattle are rarely reported but when herds of cattle are closely examined, the frequency of cataract formation is more common. Inherited cataracts occur in the Holstein–Friesian, Jersey, and Hereford breeds. Cataracts with other ocular anomalies occur in the Hereford, Holstein–Friesian, Jersey, and Shorthorn breeds. Cattle also exhibit a viral-induced congenital cataract, retinal detachment, and microphthalmia in calves secondary to bovine viral diarrhea and developed in the first part of pregnancy (76–150 days post-gestation). Removal of displaced or luxated lenses in dogs, cats, and horses is often utilized either to prevent the onset of secondary glaucoma or to assist in the treatment of these glaucomas. The possible mechanisms by which these displaced lenses contribute to the onset of secondary glaucomas are presented in a later section. Loss of part-to-all of the zonulary attachments results in lens subluxation, posterior (intravitreal) luxation, and anterior chamber luxation. The lens is normally held within the patellar fossa by 120–180 zonules attaching the lens equator to the ciliary body. In dogs, the zonules appear to be of two major types, resulting in a cruciate type of arrangement at the lens equatorial capsule. These zonules may degenerate with age, trauma, inflammation, malformation, and breed-associated and chronic glaucoma. With significant loss of zonules, the lens position changes, with tilting, decentralization, looseness within the patellar fossa (phacodonesis), possible tearing of the hyaloideocapsular ligaments (Wieger’s ligament), and tearing of the anterior hyaloid membrane, resulting in vitreous entering the posterior chamber, pupil, and eventually the anterior chamber. The iris normally touches the middle and central positions of the lens; however, with these lens positional changes, the iris becomes unstable and iridodonesis occurs. As a result, lensectomy or removal of the entire lens with its capsules (intracapsular extraction) is often performed in dogs and less frequently in cats.

306

Cataract classification in animals Cataracts appear in many different forms and, as a result, classification of these lens changes is the basis for qualifying these opacifications. No single classification method accommodates all these variables. As a result, several different cataract classifications have evolved. Classification of cataracts ensures a common system to identify cataracts in all animals and provides a uniform language among veterinarians diagnosing and performing cataract surgery. In small animals, the biochemical changes that initiate cataractogenesis have not been documented, except to some extent in the inherited and congenital cataract in the Miniature Schnauzer and sheep. The lens is highly cellular with no extracapsular spaces. The lens is also predominately proteins (soluble and insoluble) and cellular structures. In cataract formation, regardless of the inciting cause, the lens fibers eventually die, and lens epithelial cells may die or undergo transformation and proliferation. With continued lens fiber death, lens osmolarity is altered, resulting in an osmotic imbalance and the imbibition of water. With hydration of the lens, which occurs late in the genesis of progressive cataracts, the lens becomes translucent and then opaque.

Types of cataract classification The different cataract classifications in animals include: 1) age of onset; 2) position within the lens; 3) degree of opacification; and 4) possible cause (Table 11.1). Hence, for the clinical description of a cataract, all methods are usually combined. For instance, the breed-specific cataract in Golden Retrievers is a juvenile, inherited, axial, posterior cortical and capsular incipient cataract. The early cataract secondary to diabetes mellitus in dogs and cats is an equatorial cortical incipient cataract. Relative to surgery, the classification system that assesses the degree of opacification (or maturity) of cataracts is most useful, as this quantification of lens opacity correlates to clinical vision (Fig. 11.1). Incipient cataracts are the earliest detectable lens opacities. Often appearing as vacuoles and water clefts, these opacities do not significantly impair clinical vision in dogs, cats, or horses. Immature cataracts have noticeable opacification and a tapetal fundic reflection. The animal still has clinical vision, but some visual impairment may be demonstrable, especially during daytime with miosis. With an immature cataract the lens is still normal in size. By indirect ophthalmoscopy, the ocular fundus is visible but some details may be hazy from lens opacification. With mature cataracts, the entire lens is opaque, there is no tapetal fundic reflex, no demonstrable vision with or without mydriasis, and the ocular fundus cannot be observed with indirect ophthalmoscopy. With mydriasis, the lens periphery is opaque, and the peripheral ocular fundus cannot be viewed. In hypermature cataracts, the entire lens is opaque and there is no demonstrable vision. The ocular fundus is not observable with indirect ophthalmoscopy; however, with mydriasis, some of the peripheral ocular fundus may be

Evolution of cataract surgery in dogs

Table 11.1 Different classifications for cataracts in animals

Classification

Description

Age of onset

Congenital Developmental (juvenile or adult) Senile

Position within the lens

Anterior capsular Anterior cortical Nuclear Posterior cortical Posterior capsular Equatorial and axial

Degree of opacification and lens size

Incipient Immature Mature (subdivision intumescent) Hypermature (subdivision Morgagnian) Resorbing

Possible cause

Inherited Associated with other ocular anomalies Secondary to retinal degeneration Secondary to trauma (direct/indirect) Viral Post-inflammatory Metabolic Toxic (infant formulas, radiation, drugs)

observed around the shrunken lens. The dog or cat is blind unless mydriasis is induced, and then visual impairment is present. However, the cataract is reduced in size and beginning to undergo dissolution, probably secondary to the death of the lens fibers and the release of intracellular proteases. As a result, the high molecular weight lens proteins break down into small proteins and even polypeptides that diffuse through the intact anterior lens capsule and perhaps even the posterior lens capsule. A subdivision of the

A

D

B

hypermature cataract in small animals is the Morgagnian cataract, in which the lens cortex becomes liquefied, resulting in a nucleus that moves freely through the internal lens and settles in the dependent and most ventral area of the lens. A hypermature cataract often has associated secondary lens-induced uveitis (LIU). This may result in miosis, iris hyperemia, ectropion uvea, synechia, hypotony, aqueous flare, keratitic precipitates, glaucoma, zonulary and vitreous degeneration, and retinal detachment. An additional subdivision of the hypermature cataract, the resorbing cataract, occurs not infrequently in dogs less than 3 years of age and frequently in dogs younger than 1 year old. In resorbing cataracts the overall size of the lens ranges from slightly smaller than normal to the complete loss of all intralenticular material except for the anterior and posterior lens capsules which now contact each other. As the cataractous material is lost, clinical vision may gradually return.

Evolution of cataract surgery in dogs Variations in the techniques for canine cataract surgery, including discission, couching, and extracapsular extractions, were reported in the latter part of the nineteenth and first part of the twentieth century. During this same time, the different types of cataract surgery were being developed and refined in humans. The first cataract extractions in dogs were performed by Mo¨ller in 1886 and later by Berlin in 1887. Nicolas reported discission, couching, and extracapsular cataract removals in dogs in 1908. Gray, describing the same procedures, was less impressed with the results in dogs. Muller and Glass in 1926 and Ratigan in 1928 reported good results with the discission technique in young animals. Intracapsular cataract extraction in the dog was described in 1936 by Bartholo¨ berreiter published several reports on the mew. In 1937, U different cataract surgeries, including removal of luxated lenses. Several additional veterinarians, such as Condemine

C

Fig. 11.1 The different stages of cataract maturity in the dog. (a) Incipient cataract – the beginning of cataract formation. (b) Immature cataract with more advanced opacification. This is generally the best candidate for phacoemulsification. (c) Mature cataract. These cataracts generally also have concurrent lens-induced uveitis. (d) Hypermature cataract with secondary lens-induced anterior uveitis. Note the dense opacities scattered throughout the anterior cortex.

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(1939), Love (1940), Perry (1941), Means (1942), O’Connor (1942), Brumley (1943), Greaud (1950), and Morgan (1952) recommended specific types of cataract extraction, and debated the advisability of cataract surgery in small animals. In 1952, Formston cautioned that cataract surgery is ’fraught with difficulties and is speculative’. Nevertheless, the evolution of cataract surgery continued in small animals. In 1953, Magrane described aspiration of canine cataracts, and the following year defended the rationale for canine cataract surgery using extracapsular extraction. Knight, in 1957, reported fair results (29%) in 106 cases of cataract extraction in dogs, primarily using the intracapsular technique. Three years later, Knight reported a 34% success rate in 233 cases of cataract removal, primarily using the intracapsular technique. Throughout the 1960s the debate among veterinarians performing cataract surgeries in small animals no longer focused on the justification for the surgery, but on whether the extracapsular or the intracapsular technique was superior. At this same time, in humans, the intracapsular cataract extraction method with enzymatic zonulolysis (alpha chymotrypsin) was yielding the highest success rates. In this decade (1960s) it gradually became apparent that the highest success rates for cataract surgery in dogs resulted from extracapsular lens removal, because of adherence of the vitreous to the posterior lens capsule, and the inability of alpha chymotrypsin to produce zonulolysis within a few minutes. In 1961, from a series of 104 cataract extractions in the dog, Magrane reported a 76% success rate in dogs undergoing operations for juvenile cataracts and a 37% success rate in dogs with senile cataracts. The difference between these two groups was believed to be associated with undetected accompanying degenerative changes, exaggerated intraocular inflammation, and postoperative complications. A larger series of cataract extractions by Magrane (429 cases) in 1969 revealed an 80% success rate. The higher success rate was believed to be associated with an improved extracapsular extraction procedure, and pre- and postoperative administration of corticosteroids. The more years of cataract surgery experience the veterinary ophthalmologist had, the higher the rate of surgical success. If the dog’s fellow eye underwent a subsequent operation, the success rate was 20% less than for the entire group. This lower success rate for second operated eyes appears related to the sensitization of both eyes during the first cataract surgery to the cataractous material, and the more intense uveitis that resulted in these second eyes postoperatively. The success rate was 15% higher for cataract extractions for congenital and juvenile cataracts than for diabetic and senile cataract extractions. The success rate for lensectomy decreased 18% when combined with iridectomy, which in the dog is often associated with intraocular hemorrhage and a more severe iridocyclitis. In the late 1960s, Startup published several articles on cataract surgery, including cryoextraction, in dogs. In a more recent series of 113 unilateral and 77 bilateral extracapsular cataract extractions in dogs, restoration or improvement of functional vision was achieved in 79.6% of the eyes with unilateral extractions and 85.7% of the eyes with bilateral extractions at 4–6 weeks postoperatively. Success at 3–9 months postoperatively was 68.9% (unilateral

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extractions) and 69.4% (bilateral extractions not performed at the same time). In dogs with bilateral cataract extractions, 93.5% exhibited restoration or improvement of vision with successful surgery in one or both eyes. In the late 1970s and early 1980s the new technique of phacoemulsification of cataracts was developed, with postoperative aphakia being treated intraoperatively with implantation of intraocular lenses (IOLs). With about the same postoperative results, shorter hospitalization, smaller corneal incision and astigmatism, and same-day surgery, phacoemulsification of cataracts became the preferred cataract surgery in humans in the 1980s and to date. With the same surgical instrumentation, phacoemulsification of cataracts evolved for small animals. As a result, phacoemulsification has largely replaced the extracapsular cataract method in many veterinary ophthalmology clinics worldwide. Although limited in patient numbers, Miller and co-workers reported on the success of phacofragmentation and aspiration. In 82 cataracts removed by this method, vision was present immediately after surgery in 95% of the dogs. At 2 years after surgery, vision was still present in 85% of these patients. The reasons for this gradual decline were primarily related to postoperative anterior uveitis and capsular fibrosis. In a later series by Nasisse and Davidson that included 158 dogs, phacoemulsification with and without IOL implantation resulted in good-to-excellent postoperative visual results in 90.3% of the eyes. Phacoemulsification time of the cataractous lens increased with patient age but hypermature cataracts required less fragmentation time (average times for immature, mature, and hypermature cataract were 180 s, 174 s, and 137 s, respectively). The endocapsular (’in the capsular bag’) fragmentation technique was used and the main intraoperative complication was posterior lens capsular tears (19%). Today, the majority of veterinary ophthalmologists in the US and other countries regard phacoemulsification, a refinement of the extracapsular technique, as the cataract surgery method of choice in dogs, cats, and horses. Extracapsular lens extraction is also used routinely by ophthalmologists with limited numbers of cataract surgeries, but with favorable results. The intracapsular lens technique is used primarily for subluxated lens, and anterior and posterior (intravitreal) lens luxations.

Evolution of cataract surgery in horses While there was keen interest in cataract surgery in horses, most of the early reports concentrated on the dog. With very low success rates for canine surgery in the 1940s and 1950s, there has been considerable discussion and debate as to whether cataract surgery in dogs could be recommended. Fortunately, with considerable progress in cataract surgery in both humans and dogs in the 1970s and 1980s, cataract surgery was finally advocated for other species, especially the horse. In the veterinary literature, cataract surgery in horses is infrequently mentioned. Lack of adequate general anesthesia was often reported as a major impediment to equine cataract surgery; general anesthesia at this time consisted of a combination of chloroform, morphine, and local or

Development of the intraocular lens for the dog, cat, and horse

¨ berreiter, in his chapter in Advances in regional anesthesia. U Veterinary Science (1959), reported on the current progress in canine surgery, but barely mentioned the horse. He noted that Daviel (1753) reported cataract surgery in the horse, ¨ berreiter noted that attempting catabut gave no details. U ract surgery in horses with recurrent uveitis invariably ended in atrophy of the globe (presumably from recurrence of the disease). Cataract surgeries were divided into: 1) discission; 2) linear extraction (similar to aspiration); 3) reclination (or couching); and 4) flap extraction (the traditional extracapsular and intracapsular methods). Other pioneers in veterinary ophthalmology, including Lanzillotti-Buonsanti, Ro¨der and Bayer, reported no success in the horse using the discission method. In America, cataract surgery was reported in adult horses using the intracapsular method by Van Krunigen in 1964. He demonstrated that these surgical techniques were possible, although the majority (18/19) of the operated horses had normal lenses. During this time, inhalational anesthesia with halothane become available, but positive-pressure ventilation and neuromuscular paralysis, as well as the delivery of topical medications via the subpalpebral system, were not introduced until later. Gelatt reported discission and aspiration of congenital and soft cataracts in a foal in 1969, and in a larger series with Meyer and McClure in 1972 and 1974 (28 horses). Higher success rates were reported in foals less than 6 months old (77% with vision) versus older horses (60% visual). Riis first reported phacofragmentation in the horse in 1981 in the first edition of Veterinary Ophthalmology (Lea and Febiger). Whitley, Moore, and Sloan (1983) reviewed the state of cataract surgery in the horse, and described aspiration surgery in eight foals with success in nine of the 16 eyes. In a subsequent report by Whitley and co-workers in 1990, both aspiration and phacofragmentation were described in six horses. Five of the six animals were less than 6 months old; a single 4-year-old stallion was operated. They noted the problem of postoperative enteritis in the horse, and its profound adverse effect on the success of surgery. In the last 20 years or so, additional and more comprehensive reports of cataract surgery in the horse were published by Dziezyc and co-workers (1991, 1992, 1999), Brooks et al (1999, 2005, 2006), and Fife et al (2006). These studies used the current general anesthesia and neuromuscular paralysis methodologies, and provide the best results to date for the horse. Again, the higher success rates occurred in young foals (less than 6 months old). Success rates in older horses were lower, in part related to the possibility of recurrent uveitis, previous trauma, and lens displacement. Phacoemulsification was preferred, although the current human ultrasonic tips of the phaco handpiece are a little short to access the ventral capsular bag in the adult horse. This has been corrected with the introduction of a longer phaco needle specifically designed for use in the equine eye (Acrivet, Hennigsdorf, Germany). In the last reported series of 39 horses with 55 cataracts removed by phacoemulsification (Fife et al 2006), similar results were obtained. The majority of patients were foals (25/39 animals); there were 14 adults with either traumatic cataracts (9/39) or cataracts secondary to uveitis (5/39).

Success rates varied by age group and duration of followup (46/47 sighted immediately after surgery; 23/29 eyes sighted at 4 weeks postoperatively). At last examination, 38/47 eyes (81%) were sighted; 2/47 eyes (4%) had poor vision, and 7/47 eyes (15% were blind). The success rate for congenital cataracts was 85% at 4 weeks, for the traumatic cataracts 100% at 6 weeks and 1 year (three horses lost to follow-up), and for cataracts secondary to anterior uveitis, 20% (five horses; one eye sighted at 1.5 years postoperatively).

Development of the intraocular lens for the dog, cat, and horse The implantation of the modern IOL in humans was first reported by Ridley in 1951 in England. The plastic IOL was positioned between the iris and the anterior lens capsule. Hundreds of studies followed, with general consensus to place the IOL within the capsular bag, after phacoemulsification.

IOL in the dog The first report of IOLs in dogs was by Simpson in 1956 in America. His study evaluated two different IOLs: 1) an 11 mm diameter IOL for intracapsular placement after an extracapsular lens extraction; and 2) a 14 mm diameter plastic IOL positioned in front of the posterior lens capsule and presumably the ciliary sulcus after extracapsular lens extraction through either a peripheral iridotomy or the pupil. In 1980 Olson and co-workers evaluated the Shearing IOL in the dog, because the canine ciliary body sulcus diameter is approximately equal to that of humans. With improved success rates of extracapsular extractions and phacoemulsification in dogs in the early 1980s, and the common use of IOLs in humans following phacoemulsification, the routine implantation of IOLs was evaluated in dogs by many veterinary investigators, including Campbell, Davidson, Gaiddon, Nasisse, Peiffer, and co-workers. It quickly became apparent that the initial IOLs developed for humans (15–20 dioptric power) were not of sufficient strength for dogs. The IOLs used now in dogs have dioptric powers of 40–42 D. The materials from which IOLs are constructed may influence the development of postoperative capsular opacification (PCO) in dogs. Both the hard polymethylmethacrylate (PMMA) and soft foldable (acrylic hydrophil) IOLs are now available for the dog, cat, and horse. Although the PMMA IOL, supported by two haptics, has been the most common IOL for the dog (Fig. 11.2), the foldable IOLs have recently also become popular. The 6–7 mm biconvex optical center of the IOL, or the optic, produces the refractive power of the IOL. The þ41 diopter (D) canine IOL requires a fairly large optic (compared to humans); larger optics tolerate slight decentralization without significant optical aberrations. Currently, foldable acrylic IOLs are the most commonly implanted IOLs in dogs, cats, and horses. These allow for implantation through a smaller incision, resulting in less astigmatism, shortened surgical time, and possibly less PCO.

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A

B

Fig. 11.2 An intraocular lens can restore the post-cataract eye to preoperative optics. (a) An example of a polymethylmethacrylate (PMMA) intraocular lens (IOL) implanted in a dog after phacoemulsification. (b) Foldable or soft IOLs (generally hydrophilic acrylic) are also available for the dog. (Photograph courtesy of l-MED Animal Health, a division of l-MED Pharma Inc., Dollard des Ormeaux, Qc, Canada.)

The haptics are the arms of the IOL and serve to center the optic within the capsular bag. In the one-piece IOL the haptics are part of the IOL; in the three-piece IOL the haptics are usually polypropylene (prolene) and much more flexible. The stiffer haptics and one-piece IOL are recommended for the dog, and range from about 13.5 to 17 mm in diameter. The IOL design angles or vaults the haptics about 3–10 posteriorly to reduce chaffing and increase contact between the optic and the posterior lens capsule. The direct contact between the optic and the posterior lens capsule is thought to reduce the development of posterior capsular opacities. Dialing holes (one or two) are often part of the canine IOL. Rotation of the IOL into the capsular bag or once within the capsular bag may also use IOL forceps grasping the junction (or base) of the haptic to the optic. Forceps contact with the optic is avoided as scratches may result. The placement of IOLs in humans has been variable. IOLs have been implanted in the anterior chamber, pupil supported, posterior chamber, and within the lens capsular bag. The anterior chamber IOLs are conveniently inserted, and do not require an intact posterior lens capsule, but are associated with damage to the iridocorneal angle and corneal endothelia. The pupil-supported IOLs have fewer complications than the anterior chamber IOLs, but unacceptable rates of corneal edema. Direct contact of posterior chamber IOLs, placed in front of the anterior lens capsule, causes iridal problems. Currently, the most frequent IOLs in humans are those placed in the posterior chamber, usually in the capsular bag. Different placements of IOLs have not been compared experimentally in small animals, as the early results on IOL placement in humans were accepted; however, almost all IOLs used clinically in dogs, cats, and horses are implanted in the capsular bag. When capsular bag integrity is compromised, the IOL may be placed in the ciliary sulcus using various suture techniques. The foldable IOL, made of hydrophilic acrylate and ultraviolet blocking material, has also become available for the dog, and allows a shorter corneal incision through which to introduce the IOL into the anterior chamber. Many veterinary ophthalmologists now prefer these IOLs. These

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foldable IOLs require a holding/folder forceps or cartridge injector to introduce the IOL through the corneal incision and into the capsular bag. Current research in canine IOLs is investigating the role of the IOL in the genesis of PCO. Early studies suggest that some IOLs can significantly reduce these opacities, which adversely affect vision in the dog and reduce the success of cataract surgery long term. Also, lens instability and use of IOLs in these eyes has attracted attention. As glaucoma and retinal detachments are the most frequent complications after the removal of lens luxations in the dog, it is hoped that earlier surgical intervention and implantation of an IOL will improve vision postoperatively and significantly reduce these complications.

IOL in the cat Studies have recently been reported on IOLs in the cat. The mean lens thickness is 7.77  0.23 mm. IOL studies in vitro and in vivo in normal cat eyes suggest that the IOL power should be 53–55 D, with the cornea curvature, as measured by keratotomy, to be 38.93  0.73 D. Experimental implantation of IOLs ranging in power from 48 to 60 D suggested that a 52–53 D IOL would be most appropriate. The apparent difference between the cat and the dog is related to the anterior chamber depth (cat, 5.0 mm; dog, 3.5 mm) and lens axial length (cat, 7.9 mm; dog, 7.6 mm). Cat IOLs are commercially available.

IOL in the horse Experimental IOLs placed in the horse eye range in size from þ14 D (resulted in 6 and 12 D postoperative refractive error of þ2.5 D) to þ30 D (resulted in overcorrection in equine cadaver eyes of þ2.96 D), and þ25 D IOLs in clinical patients resulted in þ3.94 D at 30 days post-surgery. The current equine IOL is made of a foldable acrylic material (Acrivet 90W). There are three different equine IOLs commercially available. The optic size ranges from 12 to 13 mm and the haptic to haptic length from 21 to 24 mm.

Surgical anatomy

The diopter power of the current equine IOLs is either 14 D or 21 D, and there remains some discussion regarding the optimum IOL power to achieve emmetropia in the horse. One of the difficulties in determining the optimal IOL power for the horse is the limited number of IOLs that are implanted clinically and the even smaller number of horses that are refracted once the IOL is in place. While calculations of IOL power based on globe measurements are valuable, the final position of the IOL in the eye with respect to the retina has a significant effect on final refraction. It would appear that the current one-piece, plate haptic acrylic equine IOLs, once implanted in the equine eye, tend to sit more anteriorly in the lens capsule than expected. As a result, recent reports suggest an 18 D IOL may be required to achieve emmetropia (McMullen R, personal communication). An 18 D IOL is currently in production (13 mm optic, 24 mm haptic to haptic) and should be available at the time of publication (Acrivet). Currently, no data are available on this IOL in vivo. Equine IOLs are commercially available.

Surgical anatomy To perform cataract surgery in animals, the anatomy of the peripheral cornea and limbus, iris and ciliary body, lens, and anterior vitreous is important (Fig. 11.3). Cataract surgeries gain access to the anterior chamber, pupil, and anterior lens capsule through corneal or limbal incisions. Sclerotomies and removal of cataracts through the pars plana ciliaris and equatorial or posterior lens capsule are technically difficult and not used. The corneal incision is performed in the most peripheral cornea, consisting of a combination of beveled and perpendicular incisions, or only a perpendicular incision. The combination method provides a larger tissue surface for closure of the cornea and is less likely to leak aqueous humor postoperatively. The limbal incision is performed in the ’blue zone’ just before the bulbar conjunctiva attaches to the cornea. The incision can also combine corneal and limbal incisions, starting with a beveled partial (about 50–75%) thickness in the limbus beneath the beginning of the bulbar conjunctiva, and once in the clear peripheral cornea, entering the anterior chamber through a perpendicular incision. Whether

Anterior capsule

Cornea (axial) Anterior chamber

Anterior cortex

Pupillary iris Basal (peripheral) iris Limbus

Nucleus

Ciliary sulcus Posterior chamber Pars plicata ciliaris Pars plana ciliaris

Posterior cortex

Ora ciliaris retinae Posterior capsule (axial)

Anterior vitreous

Anterior hyaloid membrane

Fig. 11.3 Surgical anatomy for lens and cataract removal in the dog.

peripheral corneal or limbal incisions are used, entry into the anterior chamber should be in front of the insertions of the pectinate ligaments, and at or near the termination of Descemet’s membrane. Access to the anterior lens capsule and entire lens requires a maximally dilated pupil. Small and irregular pupils limit access to the lens and physically impair delivery of the lens. The dog iris is friable and highly vascular. Contact with the iris and ciliary body with instrumentation should be avoided as it may stimulate miosis (probably from the release of prostaglandins from the iris). The first ’valley’ between the peripheral posterior iris and the anterior boundary of the ciliary body is termed the ciliary sulcus. This area was the initial site for securing posterior chamber IOLs and is currently used for sutured IOLs. However, posterior chamber IOLs were eventually replaced with IOLs fixed within the capsular bag because of several complications including decentration, pupil capture, chronic iridocyclitis, and the formation of posterior synechiae. Placement of sulcus-fixated IOLs is reserved for cases of lens luxation and lens capsule insufficiency.

Normal lens anatomy in the dog and cat The lens volume in dogs and cats is about 0.5 mL. The feline lens is slightly larger than that of the dog. The diameter of the canine lens at its equators is 10–11 mm; its anteroposterior length is 7–7.7 mm. The lens is surrounded by two capsules, usually identified as the anterior lens capsule (ALC) and the posterior lens capsule (PLC). These lens capsules are the basement membrane for the lens. The ALC and PLC are highly elastic and stain deeply with periodic acid– Schiff stain. The thickness of the ALC in the dog and cat appears to vary with age, with older animals possessing thicker capsules. The ALC is decidedly thicker (50–70 mm) than the PLC (2–4 mm), and their equatorial junction is about 8–12 mm. The ALC also varies in thickness by region. It is thickest in its axial portion and becomes noticeably thinner approximately 2 mm from the equator. For capsulotomies and capsulectomies performed by tearing the ALC with special forceps, the irregular and thick ALC can present problems. Radial tears of the ALC can readily enter the thinner equatorial lens capsule and PLC, and result in IOL instability. The surface of the PLC totally contacts the anterior vitreous. The concave front of the vitreous is referred to as the patellar fossa. The PLC is nearly inseparable from the anterior hyaloid membrane, and often the two structures appear as one, held together by the lenticulohyaloid or hyaloideocapsular (Wieger’s) ligament. Tears or holes in the PLC invariably result in defects in the anterior hyaloid membrane. The ALC encloses the lens cortex and the central nucleus. Beneath the ALC is a single layer of epithelia that, at the equator, turns inward (’the lens bow’) to form lens fibers throughout life. These elongated cells span 180 of the lens. The ends of these lens fibers contact each other in the anterior and posterior cortices, forming the anterior and posterior lens sutures. The outer cortex consists of the youngest lens fibers; these cells become more compact as they travel centrally, forming the central adult lens nucleus. As these central fibers compact, first noticeable in dogs and

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Surgical procedures of the lens and cataract

cats at about 3 years of age, the nucleus becomes a noticeable blue or gray in small animals over about 6 years of age. This is termed lenticular or nuclear sclerosis. Lenticular sclerosis is bilateral and symmetrical, affecting the central nuclear portion of the lens. It must be differentiated from a cataract and is a normal aging change. As the lens nucleus ages, it becomes progressively dense and more resistant to fragmentation by instruments and phacoemulsification. The lens anatomy in cats is poorly defined. Slightly larger than that of the dog, the feline lens has a steeper anterior curvature, a 12–13 mm diameter, and a thickness of 8 mm anteroposteriorly. The large cornea of the cat, in spite of the more rounded anterior lens shape, accommodates a fairly deep anterior chamber. The anterior lens capsule measures 40–50 microns thick, with the equatorial capsule about 10 microns and the posterior lens capsule about 3–7 microns. Experimental IOLs for the cat are currently available at 53 D while the average IOL for the dog is 41 D. Cataract surgery is less common in the cat as cataracts are often secondary to anterior uveitis and systemic disease.

Normal lens anatomy in the horse The normal equine lens measures 20 mm in diameter, and has an axial length of 11–13.5 mm. Its volume is about 2.5–3.2 mL, and its optical power is about 14.88 D. The thickness of the lens capsule is similar to other species, with the anterior lens capsule the thickest (91 mm), the posterior capsule the thinnest (14 mm), and the equatorial capsule in the middle range (20 mm thick). Like other animal species, the thickness of the anterior lens capsule increases with age. Cataracts in horses are described as being congenital or juvenile-onset, inherited, post-traumatic, and postinflammatory, with the last being the most common cause of cataract in the horse.

Surgical pathophysiology The pathophysiology of cataract surgery includes the formation of cataracts, the effects of surgical entry into the eye, the development of lens-induced iridocyclitis (immunemediated) secondary to lens and cataractous lens material, and lens-induced iridocyclitis (physical effects) secondary to lens displacement and instability. Cataract formation in animals is incompletely understood. In congenital and inherited cataracts in the Miniature Schnauzer, the cataractogenesis has been partially defined, including early development, biochemical, and electron microscopic studies. In cataract formation, the lens fibers die probably secondary to abnormalities involving specific intracellular enzymes or structural defects of the lens membranes. Once lens fibers begin to die, clinical ’vacuoles’ develop that eventually coalesce into ’water clefts’. Once significant numbers of lens fibers die, the intracellular debris probably causes further lens fiber loss. As the lens functions as an osmometer, the breakdown of the large molecular weight proteins results in increased lens osmolarity, and water is imbibed into the lens causing translucency and eventually opacification. This process can occur rather quickly, and explains why some cataracts seem to progress slowly by slit-lamp biomicroscopy only to become opaque in a few weeks.

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Surgical entry into the anterior chamber is usually through the peripheral cornea or the limbus under a limbal- or fornix-based conjunctival flap. The most frequent entry for cataract surgery in small animals throughout the early 1980s was the limbal approach. However, the peripheral corneal entry has gradually increased in popularity so that now it is the most common approach for cataract surgery in small animals. Once the anterior chamber is entered, IOP rapidly decreases. This causes release of endogenous prostaglandins from the iris and perhaps other substances (primarily from the anterior uveal tissues) that may result in miosis, breakdown in the blood–aqueous barrier (BAB), increased levels of proteins and fibrin in the aqueous humor, and once the surgical wound has been apposed by sutures, a transient increase in IOP. In the 1960s and early 1970s, this cascade of events after surgical entry of the anterior chamber was thought to be associated with release of histamines; however, pretreatment with antihistamines did not prevent the miosis and other effects. Fortunately, topical and systemic non-steroidal anti-inflammatory drugs (NSAIDs) inhibit the release of anterior uveal prostaglandins, delaying or decreasing these tissue events, and limit the miosis. Miosis during cataract surgery can markedly impair and even prevent cataract or lens extraction. The small pupil prevents instrument and lens manipulations, limits the size of lens material delivered through the pupil, prevents visualization of the majority of the cataract, and increases the likelihood of direct surgical trauma to the iris, ciliary body, and even the anterior vitreous. As a result, the intensity of postoperative iridocyclitis is greater, control of the pupil is more difficult, and the overall surgical success rate is decreased. Use of preoperative mydriatics and NSAIDs, as well as intraoperative use of adrenaline (epinephrine), lidocaine, and viscoelastic agents, has resulted in miosis becoming a rare intraoperative complication. Perhaps the most important single event that affects the intraoperative and long-term postoperative cataract surgery success rates in small animals is iridocyclitis. Lens-induced uveitis (LIU) is the most frequent type of anterior uveitis in the dog, and has been associated with all stages of cataract formation by fluorophotometer measurements of the blood–aqueous barrier. Hypermature cataracts in dogs are the most frequent type of cataract extracted. Unfortunately, the release of lens materials during this phase of cataract development and maturity results in a variable and sometimes intense pre- and postoperative LIU. In the prenatal development of the lens, the embryonic lens is already well developed and is surrounded with anterior and posterior lens capsules before the embryo’s immune system becomes organized. Consequently, release of lens material (e.g., following a traumatic or surgical tear in the anterior lens capsule, or a spontaneous lens capsule rupture, most common in diabetes mellitus) or a hypermature cataract results in iridocyclitis. In cataractous canine eyes, the presence of cataractous lens material in the posterior and anterior chambers incites a progressively intense iridocyclitis. This disparity in the intensity of lens-induced iridocyclitis between a normal lens and cataractous material may be associated with the gradual loss of cataractous material, rather than acute exposure to normal lens material, the progressive sensitization of the uveal tissues to the

Surgical pathophysiology

cataractous material, and/or the greater antigenicity of cataractous versus normal lens proteins. A recent study using fluorophotometry in cataractous dogs indicated that the blood–aqueous barrier is changed in all types of cataract maturity, suggesting that LIU occurs very early in the development of lens opacification. From the 1950s through the late 1970s, cataract surgery was recommended once the dog became blind from bilateral cataracts becoming mature and opaque. The rationale, with the prevailing 70–80% success rates for cataract surgery, was that the dog was blind from cataracts, and if the surgery was unsuccessful, the dog would still be blind. Unfortunately, in these same patients, the most advanced cataract had usually become hypermature, sensitizing the uveal tracts of both eyes to lens materials. Some of this lens material may remain even after the best cataract surgery. Unfortunately, dogs with hypermature cataracts, as well as the second eye cataract surgeries, have lower success rates than dogs selected with immature cataracts that still have some vision, a low likelihood of LIU preoperatively, and less intense iridocyclitis postoperatively. As a result, selection of dogs for cataract surgery continues to change, choosing dogs with immature cataracts and a higher possibility of successful restoration of vision. Monitoring of IOP by periodic tonometry in cataractous dogs appears to be a convenient diagnostic procedure to detect early LIU. Tonometry in dogs with LIU usually reveals an IOP of less than 10 or 12 mmHg. Some conjunctival hyperemia may also be associated with iridocyclitis. Intravenous fluorescein will indicate that the blood–aqueous barrier is impaired, as the dye rapidly diffuses into the pupil from the ciliary body and into the anterior chamber from the anterior surface of the iris. These pupils often dilate slowly and incompletely to 1% tropicamide. Preoperative treatment with topical corticosteroids and NSAIDs, and, if the anterior uveitis is intense, supplemented with these drugs systemically, usually controls the inflammation and results in a gradual increase in IOP to normal levels. Topical mydriatics, 1% tropicamide or 1% atropine, are instilled concurrently to dilate the pupil and prevent the formation of posterior synechiae. With stimulation or reactivation of an existing iridocyclitis by cataract surgery, the plasmoid or secondary aqueous humor contains high levels of globulin, albumin, and fibrin. These proteins coat the posterior surface of the cornea, anterior and posterior surfaces of the iris, and aqueous humor outflow pathways. As a result, temporary or permanent iridal adhesions to the lens (posterior synechiae) and peripheral posterior cornea (peripheral anterior synechiae) are common in postoperative iridocyclitis in dogs and cats. The fibrin can also attach to remnants of the anterior lens capsule, posterior lens capsule, and anterior vitreous membrane, and form the scaffolding for other lens epithelia, fibrocytes, and iridal pigment cells to migrate on and establish permanent fibropupillary and capsular opacities. These inflammatory membranes can also crisscross the pupil, resulting in small and irregular pupils that limit vision. The other important effect of postoperative iridocyclitis is miosis, secondary in part to the release of endogenous prostaglandins. Miosis starts during lens and cataract surgery, and continues thereafter until the anterior uveal inflammation from the entry of the anterior chamber and

any remaining lens material has been resorbed or isolated. Mydriatics to achieve a moderately dilated and continuously moving pupil are started preoperatively and continued postoperatively. Control and establishment of a moderately dilated pupil are usually obtained within 4–7 days postoperatively. After about 2 weeks, pupil changes (usually dilatation) are more difficult to obtain because of the formation of posterior synechiae. Frequency of daily instillations of a single or a combination of mydriatics is determined after periodic inspection of the eye and pupil size for the first 5–10 days postoperatively. Failure to control and obtain a reasonably sized pupil after cataract surgery usually contributes directly to most surgical failures. Topical atropine can reduce the rate of tear production to levels which result in acute keratoconjunctivitis sicca, and may affect both eyes. If corneal lesions develop soon after topical atropine instillations and low Schirmer tear test values are measured, cataract surgery should be delayed for several days. For an alternative mydriatic, 1% tropicamide may be used with apparently less effect on tear production. The period of postoperative iridocyclitis after cataract surgery varies, but apparently spans several months. Continuing clinical investigations suggest that postoperative cataract patients should be treated topically (and occasionally systemically) with mydriatics, NSAIDs, and corticosteroids for 6 months or longer. Premature cessation of these cataract treatments contributes to smaller pupils, progressive fibropupillary membrane formation, and capsular fibrosis that cause a decline in the long-term success rates in small animals. The relationship between the stability of the lens and its direct contact with the posterior surface of the iris and anterior hyaloid membrane is poorly understood. With the loss of 90–180 of the zonulary attachments to the lens, instability results. This lack of lens stability may be determined by close examination of the iris and its base during ocular movements to detect partial movement of the lens and the basal iris. Alternatively, after mydriasis, the periphery of the lens can be examined by slit-lamp biomicroscopy, and any instability ascertained. With the loss of additional zonules, more lens instability results. The role of the hyaloideocapsular (Wieger’s) ligament between the posterior lens capsule and the anterior hyaloid membrane in stabilizing the lens is unknown, but may be important in younger dogs and cats. With instability of the lens, microtrauma of the iris results in iridocyclitis. Increased aqueous humor levels of fibrin, proteins, and inflammatory cells occur. The inflamed iris may adhere with formation of posterior synechiae to the unstable lens. Aqueous humor dynamics can also be impacted by lens instability, temporarily impairing pupillary passage of aqueous humor, and balloon the peripheral iris to embarrass the iridocorneal angle outflow pathways and contribute to the development of peripheral anterior synechiae. With the loss of all zonulary attachments, the hyaloideocapsular attachments may tear, resulting in presentation of anterior vitreous through the rent, often partially adhering to the posterior lens capsule. The loose lens can remain in the patellar fossa, luxate into the anterior chamber or, through the torn anterior vitreal face, displace posteriorly into the vitreous.

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With displacement of the lens from the patellar fossa and tearing of the anterior hyaloid membrane, vitreous can complicate these cascading events. Vitreous adhering to the posterior lens capsule with an anterior lens luxation may occlude the pupil, preventing pupillary flow of aqueous humor, and displace the base of the iris forward to cause iridocorneal angle and sclerociliary cleft closure. The complete effect on aqueous humor flow of this type of iris bombe´ is often missed as the peripheral lens masks the basal iris changes. With posterior or vitreal luxation of the lens, the torn anterior vitreal membrane allows both liquid and formed (gel) vitreous access into the pupil and anterior chamber. Formed vitreous may cause pupillary blockage and secondary glaucoma. It can also adhere to the posterior cornea and iridocorneal angle. Blockage of the iridocorneal angle with formed vitreous sufficient to increase IOP is infrequent, and pupillary blockage is more common. Vitreous loss also seems associated with the development of retinal detachment; a major difference between extracapsular and intracapsular cataract extractions is the higher postoperative frequency of retinal detachment after the intracapsular procedure.

Patient selection for all species Patient selection for cataract surgery is an important factor in determining the eventual success or failure of this elective surgery. Cataract surgery is a rapid but expensive procedure requiring approximately 1 h of general anesthesia. However, postoperative treatment requires considerable time and effort, and directly determines the overall success rate and restoration of vision. The owner must be involved with their pet, be able to administer topical and systemic medications, and be committed to provide postoperative medications in a tapering fashion for at least 3–6 months. Not all cataract surgeries are successful, and the owner must be informed that, as with any surgery, failures may occur.

Age Age is not a major determining factor in patient selection assuming the dog, cat or horse is in good general physical condition. Physical examination, complete blood count, serum chemistries, and urine analyses are important screening clinical laboratory tests. In dogs and cats older than 10–12 years of age, the lens capsules are often thicker, more difficult to tear with capsular forceps, and may contain opaque areas of fibrosis and calcification. The vitreous may become liquefied with increased age, so that tears in the posterior lens capsule and anterior hyaloid membrane result in presentation of mostly liquefied vitreous.

Temperament The general behavior of the patient is important. Animals that are fractious, aggressive or highly excitable should be excluded from cataract surgery, unless there is some compelling factor. Small animals difficult to control and treat postoperatively are prone to more complications, including hyphema, surgical wound dehiscence, and more intense iridocyclitis, and may be dangerous to the hospital personnel. If cataract surgery is performed in these animals, the owners

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must be actively involved in their postoperative care, administer all systemic and topical medications, and present the animals frequently for eye examinations and, if necessary, accommodate adjustments to the medication dosing schedules. In horses, the patient should be halter trained and also accustomed to topical medication. Foals should be halter trained and broke to lead prior to surgery. All horses can be acclimatized to topical medication by applying topical artificial tear ointment twice daily for a few weeks prior to surgery. Regardless, the overall surgical success rate in fractious patients is usually lower and less predictable.

Concurrent eye disease Pre-existing eye diseases can also affect patient selection and either delay or prevent cataract surgeries. Congenital abnormalities such as persistent pupillary membranes, persistent hyaloid artery, persistent hyperplastic primary vitreous/tunica vasculosa lentis (PHPV/PHTVL), posterior lenticonus, microphakia, lens coloboma, and microphthalmos may affect cataract surgery technique, outcome, and IOL selection. Keratoconjunctivitis sicca (KCS) is a common disease in dogs that can either delay or prevent cataract extraction. Cataractous dogs with KCS with Schirmer tear test levels of 10–15 mm/min may be reasonable candidates for cataract surgeries, but topical 1–2% cyclosporine should be instilled once to twice daily along with the other postoperative medications. Cataract surgery should be delayed until tear production rates can be enhanced further by topical cyclosporine or tacrolimus, and 1% tropicamide should be substituted for 1% atropine as the mydriatic of choice. Postoperatively, topical tear replacement therapy using viscous materials may be indicated for the first few weeks following surgery. The major risk with KCS patients is the anticipated decline in tear values postoperatively. A cornea, marginally dry and under the influence of topical and systemic corticosteroids, is prone to develop central progressive corneal ulcerations. These corneal ulcers are slow to heal, sometimes require conjunctival grafts to prevent corneal perforation, and usually necessitate cessation of topical corticosteroids and NSAIDs until the ulcer has epithelialized. Sometimes systemic corticosteroids can be administered cautiously in these patients to attempt control of the postoperative iridocyclitis. Other corneal diseases, such as pigmentary keratitis, are not deterrents to cataract surgery, but prior treatment and control are imperative. Glaucoma is another important consideration. If the cataract is ascertained important in the genesis of the secondary glaucoma, cataract surgery should not be delayed. Concurrent diode endolaser cyclophotocoagulation may be considered in eyes with cataract and elevated IOP. However, cataract extraction in a glaucomatous and blind eye is not recommended. The brachycephalic breeds must be carefully managed postoperatively after cataract surgeries. The less frequent blinking rate, thinner than normal central precorneal tear films, and the compromised and exposed corneas predispose these patients to potential postoperative corneal problems that impact the postoperative treatment of these eyes. If cataract surgery is performed in brachycephalic breeds, the patient should be examined daily as long as intense mydriatic and corticosteroid therapy is maintained.

Patient selection for all species

Some surgeons advise a partial temporary tarsorrhaphy in these patients to decrease corneal exposure. An Elizabethan collar or other head restraint device, and exercise restriction should be maintained in all small animal cataract patients until all sutures have been removed or dissolved, and the intensity of topical and systemic medications reduced to twice daily or less frequent intervals. The presence of uveitis and cataract is common in the horse. Typically, the uveitis is immune mediated, and is the primary disease occurring as equine recurrent uveitis (ERU). Chronic ERU may result in secondary changes such as cataract, glaucoma, and retinal detachment. If cataract surgery is to be performed in these patients, the ERU must first be well controlled. The eye must be evaluated using electroretinography and ultrasound to ensure that the posterior segment is functional. Finally, implantation of a sustained-release suprachoroidal cyclosporine device should be considered concurrent with the cataract surgery and IOL implantation. (See Chapter 12 for a more complete discussion of the surgical management of ERU.)

Maturity of cataract The stage of cataractogenesis and maturity are important factors in selecting small animal patients for cataract extraction. The cataract stages usually operated are the immature, mature, and hypermature (see Fig. 11.1). Clinical experience suggests that selection of dogs with immature cataracts and no evidence of LIU yields the highest success rates possible. The recent association of retinal detachment and vitreous abnormalities with hypermature cataracts in dogs provides additional credence to operate on cataracts while immature or at the latest in early maturity.

Diabetes mellitus Cataracts develop in 50–70% of diabetic dogs within the first several months of the disease, and not infrequently these patients are presented for cataract surgery (Fig. 11.4). In fact, dogs with cataracts secondary to diabetes mellitus are the secondary largest group of patients having cataract surgery. Assuming the diabetes is under reasonable

control, these patients are usually excellent candidates for cataract extraction. As the diabetic cataract develops rapidly, it becomes quite intumescent or swollen, and cases of spontaneous lens capsule rupture and the release of lens material have occurred. Hence, cataract surgery for diabetic cataracts should be performed early and not be delayed unduly. As general anesthesia, cataract surgery, and topical and systemic corticosteroids may elevate blood glucose levels, close daily monitoring of urine and/or blood glucose postoperatively is essential. The pre-existing daily insulin dose levels are continued postoperatively, and some glycosuria is acceptable. One-half of the daily insulin dose is usually administered on the day of surgery. It is not unusual for these dogs to also have systemic hyperlipemia, urinary tract infections, and other systemic diseases. These should be assessed and, when indicated, treated. In a recent study by Bagley and Lavach, the success of cataract surgeries in diabetic dogs after phacoemulsification was similar to non-diabetic dogs.

Unilateral cataracts Cataract surgery for small animal patients with unilateral cataracts is more frequent with the availability of IOL implantation and restoration of emmetropia. These animals, especially if young, benefit from an IOL postoperatively as theoretically the retinal image of both eyes would be reasonably comparable. In addition, waiting to see if the contralateral eye develops a cataract may allow progression of the cataract in the initially affected eye. Progression to hypermaturity may lead to secondary complications and result in the initial eye no longer being a candidate for vision restoration. Unilateral cataract surgery is common in the horse and may be of more benefit given the limited binocular vision in the horse and the availability of an equine IOL.

Bilateral cataract surgery Cataract surgery is usually performed for both eyes at the same time in small animals. With the development of phacoemulsification, the time of cataract surgeries has become compressed, and more often than not, both cataracts are removed within a short period of time. Similar to the reports on extracapsular cataract extractions in the second eye by Magrane in 1969, the phacoemulsification study by Davidson, Nasisse and co-workers revealed a success rate from unilateral cataract extractions in dogs of 79.6%, and 85.7% in eyes with bilateral cataract removals. If the restoration of vision in these bilateral cataract extractions was based on return of vision in at least one eye, the surgical success rate was 98.7%. With general anesthesia, systemic medications, and hospitalization costs about the same for either uni- or bilateral cataract surgeries, bilateral cataract removals have now become commonplace.

Intraocular pressure

Fig. 11.4 Intumescent and mature diabetic cataract in a dog.

Intraocular pressure (IOP) is an important determinant for small animal candidates for cataract surgeries. Many of the canine breeds with inherited cataracts are also the same breeds with inherited primary glaucomas. IOP less than 10–12 mmHg usually signals low-grade or chronic lens-induced iridocyclitis. These cataractous eyes usually

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respond to topical and systemic corticosteroids. Once IOP returns to about 15–18 mmHg, cataract surgery can be performed. IOP in excess of 25 mmHg should be carefully monitored for several days or a few weeks for evidence of an early or low-tension glaucoma. Once IOP is within the normal range of 15–20 mmHg, cataract surgery may be considered.

Preoperative electroretinography and ultrasonography In referral and institutional veterinary ophthalmology clinics, cataract patients are also evaluated immediately before surgery with electroretinography (ERG) and ultrasonography (US). Most potential cataract patients are presented for surgical evaluation when both cataracts are mature or hypermature, and visualization of the ocular fundi is not possible. The visual history should be reviewed with the owner, especially night vision. The flash ERG test is an excellent diagnostic procedure to detect progressive retinal degeneration (PRD) in small animals, and most often cataracts in dogs develop late in retinal degeneration. The flash ERG test should be standardized (time for dark adaptation, intensity and color of light stimulus, presence of mydriasis, grounding, etc.). The flash ERG test in most cataract patients with PRD is usually negative or the b-wave is barely detectable. Dogs with cataracts and electroretinograms with low amplitudes present problems. Some of these dogs have early retinal degeneration that within 1–2 years will cause blindness. Cataract surgeries in these patients may be performed, but with the client understanding that postoperative vision may gradually decline in the following 12–24 months. In the horse, preoperative ERG is especially indicated in eyes with cataract secondary to ERU or in breeds such as the Appaloosa or Paso Fino that are known to be predisposed to congenital stationary night blindness (CSNB). Recently Wilkie and co-workers reported on the preoperative value of ultrasound in evaluating cataractous eyes that prevent inspection of the ocular fundi. Preoperative ultrasonography in dogs detected retinal detachments in 11% of all cataractous eyes. The frequency of retinal detachments was also related to the stage of cataract maturity, occurring in 4% of immature cataract eyes, 6.5% of mature cataract eyes, and 19% of the eyes with hypermature cataracts. The high incidence of retinal detachment in the eyes with hypermature cataracts is an additional reason to operate on cataracts in dogs before they progress to hypermaturity. The cause–effect relationships between hypermature cataracts, LIU, and the development of retinal detachment have not been established, although the majority of postoperative retinal detachments and tears observed ophthalmoscopically involve the peripheral retina. Perhaps the overall shrinkage of the lens and its capsules postoperatively creates tension on the zonules, ciliary body processes, and peripheral retina. As retinal detachments that develop postoperatively after cataract surgeries often result in blindness and surgical failure, the elimination of these patients before cataract extraction maximizes success rates and prevents unnecessary surgeries. In the horse, preoperative ultrasonography is indicated in all eyes with cataract whether congenital, posttraumatic or secondary to ERU.

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Risk of retinal detachment in certain breeds Experience has shown that certain breeds with cataract formation and vitreous degeneration are predisposed to retinal detachment. These breeds include the Bichon Frise, Havanese, Maltese, and American Cocker Spaniel, and vitreous degeneration in the Shih Tzu. In these breeds prophylactic transscleral retinopexy or transpupillary retinopexy after IOL implantation should be considered. In the Bichon Frise breed, retinal detachments may be related to LIU and cataract resorption, as these detachments occur with and without cataract surgery. Use of prophylactic transscleral retinopexy, using either cryotherapy or the diode laser photocoagulation procedure, can reduce the frequency of retinal detachments in the Bichon Frise breed after cataract surgery from 55% to 12%. Retinal detachment may also occur more commonly in certain breeds of horse such as the Rocky Mountain horse, and success of cataract surgery has been reported to be lower in this breed.

Non-surgical treatment of cataracts Not all cataracts in animals are amenable to surgical extraction, nor are all owners prepared to elect cataract surgery for their pet. Because of the animal’s general health, possible cataract resorption, presence of other ocular diseases, or lack of owner finances, some animals with cataracts are not candidates for cataract surgery.

Medical treatment of cataracts For several centuries, many substances have been administered topically and systemically to either delay the formation of cataracts or cause their dissolution. Controlled investigations of these compounds have indicated no efficacy to date. Medications used in the past in small animals included selenium–tocopherol injections, doses of sulfadiazine, injections of an equine serum extract after sensitization of the horse to injections of Actinomyces bovis, topical zinc citrate ascorbate, and aldose-reductase inhibitors. In humans, the role of long-term ultraviolet radiation B and the release of intralenticular oxidants may be important in the pathogenesis of cataracts. It is doubtful that these conditions are as important in small animals, and heredity and other issues may be major contributing factors.

Spontaneous cataract resorption in young dogs Spontaneous cataract resorption can occur in young dogs, especially in animals less than 1 or 2 years of age. Apparently in the maturation of the cataract and death of lens fibers, sufficient levels of intracellular proteases are liberated, breaking down the high molecular weight lens proteins in young dogs. Changes in the permeability of the lens capsule have not been demonstrated, but may also occur. With progressive loss of the lenticular proteins, the cataract gradually shrinks, and aphakic vision returns (Fig. 11.5). There is no breed predisposition to cataract resorption in dogs, but those breeds with inherited and congenital cataracts that progress to maturity early in life are most likely affected.

Non-surgical treatment of cataracts

A

B

C

D

Fig. 11.5 Examples of advanced spontaneous cataract resorption in generally young dogs. Hence, cataract resorption tends to occur most frequently in those breeds which develop cataracts in early life. (a) The majority of cortical cataractous material has resorbed, leaving some organized posterior cortex and tiny foci of proliferating lens cells (Elschnig’s pearls). (b) The majority of the cortical cataractous material has resorbed with some lingering cortex at 12 o’clock. Elschnig’s pearls or proliferating lens cells are scattered throughout. (c) Most of the cortical cataract has resorbed, leaving scattered foci of proliferating lens cells (Elschnig’s pearls). (d) Lens material has settled within the ventral capsular bag, and is mobile with eye movements.

The history is usually acute loss of vision and rapidly developing cataracts. Ophthalmic examination usually reveals mature to hypermature cataracts with lens-induced iridocyclitis. IOP is usually low, and the pupils are resistant to dilatation with 1% tropicamide. Aqueous flare and bulbar conjunctival hyperemia (’ciliary flush’) may be evident. The cataracts usually appear as immature, mature, or hypermature, but signs of lens-induced iridocyclitis are present. In some young dogs, progression of immature to hypermature cataract seems to skip the mature phase. With resorption, the hypermature cataract gradually decreases in size. The anterior lens capsule and surface become irregular and wrinkled. Eventually, as resorption of the cortices and nucleus advance, the anterior lens

surface becomes plano and even concave. The cataractous lens assumes a homogenous appearance with loss of all lens detail. Minute white reflective bodies suspended in the lens may signal areas of resorption. The nucleus of the cataract is the most resistant to spontaneous resorption, and only in very young dogs will it nearly or totally resorb. In young dogs, these patients present two options: 1) immediate cataract surgery before the lens-induced iridocyclitis becomes long term and sensitization to lens proteins is firmly established; or 2) if conditions are not favorable for bilateral lens extraction, the patient is examined frequently and the lens-induced iridocyclitis controlled with topical mydriatics and topical corticosteroids (usually 1%

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prednisolone or 0.1% dexamethasone), sometimes supplemented with systemic prednisolone. Topical and systemic NSAIDs may be substituted for, or supplemented by, corticosteroids if the lens-induced iridocyclitis becomes intense. The pupil size should be changed continuously with mydriatics to prevent formation of posterior synechiae. The possibility of cataract resorption appears related primarily to the age of the dog. In dogs less than 1 year old with mature cataracts, lens resorption sufficient to restore at least some vision occurs in about 50–70% of the eyes. If the dog is over 3 years old, resorption of the cortices does not always result in the dissolution of the nucleus. Proliferation of the lens epithelia (Elschnig’s or crystalline pearls) and the lens fibers that produce wrinkling of the lens capsules are usually limited. In dogs less than 1 year old, uncomplicated bilateral cataract resorption may result in clear lens capsules, and the disappearance of the lens cortices and nucleus. In older dogs, some residual cataractous lens nucleus can remain; however, with long-term drug-induced mydriasis, the animal can have reasonable vision.

Axial non-progressive cataracts and long-term mydriasis Dogs with non-progressive axial cataracts that are visually impaired or blind but with normal sized pupils can regain reasonable clinical vision after instillations of mydriatics. These cataracts include anterior capsular and cortical cataracts secondary to persistent pupillary membranes, congenital nuclear cataracts with clear cortices, posterior cortical cataracts in the Golden Retriever and Labrador Retriever dogs, and posterior capsular and cortical cataracts associated with persistent hyaloid blood vessels (Fig. 11.6).

Fig. 11.6 Posterior capsular and cortical cataract, secondary to persistent hyperplastic primary vitreous, in a 6-month-old Vizsla. The red patent blood vessels are visible within the cataract.

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Long-term mydriatics, such as 1% atropine once daily or once every 2 days, are instilled to fully dilate the pupils and allow the patient to see around the non-progressive cataract. Cataract surgeries in small animals with large persistent pupillary membranes adherent to the anterior lens capsule may hemorrhage. If cataract extraction is considered because the cataract still interferes with vision with mydriasis, the pupillary membranes may be transected with laser. Then several weeks later, once the laser-induced iridocyclitis has resolved, an extracapsular or phacoemulsification cataract extraction is performed. If posterior capsular and posterior cortical cataracts are present, secondary to persistent hyaloid vasculature (persistent hyperplastic primary vitreous), and complete mydriasis does not permit vision, cataract surgery may be performed but with a poorer prognosis. These posterior cataracts usually have weak and thin posterior capsules that may rupture during extracapsular or phacoemulsification surgeries, allowing the anterior vitreous to displace forward. A planned posterior capsulorhexis may be required to restore a clear visual axis. The hyaloid blood vessels may hemorrhage. Adrenaline (epinephrine; 1:1000 or 1:10 000) irrigated directly into the cataract surgical site usually provides the most effective but sometimes incomplete hemostasis. An anterior vitrectomy may be necessary to excise the formed vitreous behind the patellar fossa, but may be hindered by hemorrhage from the hyaloid blood vessels. Use of a dispersive viscoelastic agent to keep the vitreous from prolapsing is indicated.

Secondary cataracts and iridocyclitis Secondary cataracts complicated with iridocyclitis are not usually good candidates for cataract surgery. Most cataracts in cats are secondary to iridocyclitis, usually associated with serious systemic diseases. Recurrent iridocyclitis is less frequent in dogs (Fig. 11.7), but these patients are usually not good candidates for cataract surgery unless the iridocyclitis can be resolved. Cataract surgeries in eyes with chronic or recurrent iridocyclitis also have additional risks with recurrence of the anterior uveal inflammation postoperatively, and a greater possibility of phthisis bulbi and secondary

Fig. 11.7 Cataract secondary to chronic iridocyclitis in a 7-year-old mixed breed dog. Numerous posterior synechiae are present.

Preoperative preparation

glaucoma with peripheral anterior synechiae. In the horse with ERU, lifelong management of the iridocyclitis is required and may be addressed surgically with a sustained release cyclosporine implant placed at the time of the cataract surgery.

Blind animals As with any surgical procedure, there is a group of cataractous patients in which removal of the opaque lenses is neither beneficial nor feasible. Cats may adapt to blindness more readily than dogs. Older animals seem to adapt to blindness better than young and active animals. Small animals that have the chance to adapt slowly to the onset of blindness over several months appear to tolerate blindness better than those animals that become acutely and permanently blind. Often blind animals sleep excessively, maintain hearty appetites, exercise little, and gain weight. Excitable animals may adapt poorly, and loud noises may induce vocalization and aggressive responses. Most blind animals are able to maneuver about the home without colliding excessively with furniture and walls. Behavioral changes in blind animals can be complicated by other aging and mental changes as well as pain. If other ophthalmic disorders are concurrent with cataracts, such as glaucoma or lens-induced iridocyclitis, periodic examinations and medical or surgical control of these conditions are recommended. Horses with cataracts must be considered visually unsound and may pose a risk to themselves and the owner/rider depending on their use.

Continued monitoring of non-surgical cataractous patients For those patients that do not have cataract surgery, continued long-term monitoring and examinations are usually indicated. Lens-induced uveitis occurs with all stages of cataract maturity, and may require medications to suppress the uveitis, such as topical and systemic corticosteroids and NSAIDs. Signs of early and mild LIU include aqueous flare, miosis, decreased IOP, conjunctival hyperemia, iris hyperpigmentation, ectropion uvea, and delayed-to-incomplete mydriasis to 1% tropicamide. Signs of more severe LIU may include: fibrin formation to hypopyon, very low IOP, keratitic precipitates, conjunctival hyperemia and ciliary flush, and a pupil refractory to 1% tropicamide. Instillation of mydriatics, such as 1% tropicamide and 1% atropine, can induce pupillary movements and discourage the formation of posterior synechiae. Advanced hypermature cataracts are also associated with vitreal degeneration, retinal detachments, and secondary glaucoma.

Preoperative preparation As cataract surgeries are almost always elective, careful medical preparation of the patient and education of the owner are recommended for optimal results. The patient is carefully examined and selected. The patient owner is informed of the principles of cataract surgery, postoperative care, the need for several examinations postoperatively to ensure the highest possibility of successful restoration of vision, correct methods to instill medications (solutions and/or

ointments) onto the operated eye, and clinical signs that may signal potential problems. Owner compliance and cooperation are as vital to the outcome as the skill of the surgeon and the effectiveness of the medications! In horses, the patient should be halter trained and also accustomed to topical medication. Foals should be halter trained and broke to lead prior to surgery. All horses can be acclimatized to topical medication by applying topical artificial tear ointment twice daily for a few weeks prior to surgery. This will ensure that both the patient and owner are comfortable with the application of topical ophthalmic medication.

Perioperative medications The objectives of the perioperative medications include: 1) mydriasis or dilatation of the pupil to facilitate visualization of the cataract during surgery and prevent miosis; 2) control of the lens-induced and surgical-related iridocyclitis; and 3) antibiosis. Intensive therapy and control of the iridocyclitis may be required several weeks preoperatively, and is adjusted based on the ophthalmic findings. Each veterinary ophthalmologist has a personal ’menu’ for preoperative medications before cataract surgery (Tables 11.2a and 11.2b). Initiation of preoperative medication will vary according to the presence or absence of LIU. If LIU is present, medication should be initiated several days prior to surgery and the clinical signs of LIU controlled. Starting 24–48 h prior to surgery, topical broad-spectrum antibiotics and corticosteroids are administered every 6 h. On the day of surgery the pupil is dilated using a parasympatholytic such as 1% atropine or 1% tropicamide. Topical corticosteroids and NSAIDs are administered every 30 min starting 1–2 h prior to surgery. A systemic NSAID and systemic broad-spectrum antibiotic are administered immediately prior to surgery. Postoperatively, topical antibiotics and corticosteroids are continued. Surgeons vary as to the use of postoperative mydriatics, systemic antibiotics, and NSAIDs. In the horse, an intravenous catheter is placed prior to surgery for the administration of antibiotics and NSAIDs. This catheter is left in place for 2–3 days to continue systemic antibiotics and NSAID therapy. In addition, many surgeons will place a subpalpebral lavage catheter at the conclusion of surgery to ensure administration of topical medication postoperatively.

Table 11.2a Recommended drugs and drug schedules for canine cataractous patients without lens-induced uveitis prior to cataract surgery

Schedule

Drug

24 h preoperatively

Topical 1% atropine or 1% tropicamide q6h Topical 1% prednisolone acetate q6h Topical broad spectrum antibiotics q6h Systemic prednisolone, 1 mg/kg q12h Systemic amoxicillin, 10–20 mg/kg q12h

90 min preoperatively

Topical antiprostaglandin (suprofen) every 30 min

Perioperatively

Flunixin meglumine, 0.2 mg/kg IV at surgery and once 24 h later, or Carprofen, 1–2 mg/kg q12h (do not use in cats)

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Table 11.2b Recommended drugs and drug schedules for horses 24 h before cataract surgery

Medication

Frequency

Topical

consisting of sodium hyaluronate, chondroitin sulfate, hydroxypropyl methylcellulose, polyacrylamide, or some combinations of these compounds, are critical to maintain the shape and size of the anterior chamber and to protect the corneal endothelium once the corneal incision is made. They also are injected into the capsular bag to expand or separate the anterior and posterior lens capsules prior to the insertion of the IOL. They can also be used to manipulate intraocular tissues, such as in hemorrhage or tamponade due to the vitreous protruding through a posterior lens capsule tear or around the lens equator. (For additional information on viscoelastic agents, see Chapter 2.)

1% Prednisolone or 0.1% dexamethasone

Every 6 h

Repeat steroids

1.5 h preoperatively

Triple antibiotic

Every 6 h

NSAIDs (OcufenW, Allergan; or VoltarenW, Novartis)

Every 30 min for 1.5 h preoperatively

1% Atropine

Once 2–3 h preoperatively

Surgical procedures for cataracts and lens removal

Gentamicin (6.6 mg/kg) combined with potassium penicillin (20 000 IU/kg IV) or ampicillin (10 mg/kg IV)

Prior to induction

Lens surgical procedure choices in animals

Flunixin meglumine (1–1.5 mg/kg IV)

At induction

Systemic

From: Fife TM, Gemensky-Metzler AJ, Wilkie DA, Colitz CMH, Bras ID, Klages DC 2006 Clinical features and outcomes of phacoemulsification in 39 horses: a retrospective study (1993–2003). Veterinary Ophthalmology 9:361–368.

IOP is monitored closely. Cataract surgery is recommended when IOP is about 15–20 mmHg. Different levels of IOP usually parallel the intensity of the LIU. Low IOP usually indicates that more time and medications are necessary to control the iridocyclitis preoperatively. As fibrin in the aqueous humor is undesirable, heparin (1–2 IU/mL) is added to the infusion solutions, such as lactated Ringer’s or balanced salt solution, that are used to moisten the eye, flush the anterior chamber, and restore the anterior chamber. Heparin at this level seems to satisfactorily prevent the formation of fibrin but not promote hemorrhage within the anterior chamber. Viscoelastic agents are very important in cataract surgery and in protecting the corneal endothelium. These agents,

There are many different surgical procedures to remove lenses and cataracts in veterinary ophthalmology (Table 11.3). There are criteria for each surgical technique, but personal experience and expertise also help determine the preferred surgical technique. Justification for the removal of subluxated and posterior lens luxations is still not resolved. In this section, the different procedures to remove cataracts in animals, based on frequency, include: 1) phacoemulsification within the lens capsules (endocapsular or intercapsular) or capsular bag; 2) extracapsular extraction; and 3) discission and aspiration. The intracapsular extraction technique is rarely used for cataract removal because of its hazards and vitreal loss, but is used for lens luxations. Phacoemulsification cataract surgery is the most frequent type of cataract surgery performed in all species of animals. The phacoemulsification modification uses a small corneal incision, and fragmentation and aspiration of the cataractous lens through an anterior capsulectomy. The posterior lens capsule should not be disturbed. Implantation of IOLs to treat the surgical aphakia is also presented, and is commonly combined with the phacoemulsification and extracapsular cataract removals.

Table 11.3 Different methods for cataract and lens extractions in animals

Method

Description

Indications

Discission

Multiple incisions of lens capsule and substance

Congenital/soft cataracts

Aspiration

Suction of lens material

Soft/pieces of cataract

Phacoemulsification

Leaves part ALC and all PLC

Immature/mature/hypermature cataracts

Extracapsular

Leaves part ALC and all PLC

Immature/mature/hypermature cataracts

Intracapsular

Removal of entire lens with ALC and PLC

Not recommended

For cataracts

For displaced lenses Phacoemulsification

Removal of lens but not always ALC and PLC

For unstable lenses; can use lens fixation

Intracapsular

Removal of entire lens with ALC and PLC

For anterior and posterior luxations, and subluxated/partially displaced lenses

ALC, anterior lens capsule; PLC, posterior lens capsule.

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Choice of ophthalmic anesthesia and surgical exposure

The extracapsular procedure, used in the dog in the 1960s through the early 1980s, has been largely replaced by phacoemulsification. It requires a larger corneal or limbal incision (about 140–160 ). The axial or central portion of the anterior lens capsule is excised, and the cataractous cortices and nucleus removed or slid through the larger incision. The posterior lens capsule remains. The extracapsular technique is still the fundamental procedure, and is used by veterinary ophthalmologists when phacoemulsification is not available. The discission–aspiration method was traditionally used for congenital and soft cataracts in young animals before phacoemulsification was developed. In this technique the cataractous lens is incised into small pieces (discission) and aspirated from within the lens capsular bag. This method is rarely used and has been largely replaced with the phacoemulsification procedure that performs these same functions more efficiently and rapidly. The soft cataract in young horses and some birds still can benefit from this technique if phacoemulsification is not available. The intracapsular technique for cataract extraction in animals is presented under the lensectomy section. The intracapsular method for cataract removal has more risks and yields the lowest success rates. However, removal of subluxated lenses, anterior luxated lenses, and posterior luxated (intravitreal) lenses uses the intracapsular technique. With partially-to-totally displaced lenses, the zonular attachments extending from the equatorial capsule to the ciliary body have been transected by age, trauma, malformation, or inflammation. Without the zonulary attachments, the entire lens is delivered intracapsularly with the lens nucleus and cortices inside its capsule.

Choice of ophthalmic anesthesia and surgical exposure In general, a similar surgical preparation is used for all of the different types of cataract surgery and lensectomies regardless of species. The small animal patient is usually positioned in dorsal recumbency and the head stabilized with a vacuum pillow for bilateral cataract surgery. If unilateral cataract extraction is performed, the animal’s head is placed in either dorsal or lateral recumbency. Horses may be positioned in lateral or dorsal recumbency with the head rotated to have the eyelids parallel to the floor and the surgical eye looking up. The latter technique is best when bilateral surgery is planned so the horse does not need to be turned over during the surgery. To facilitate positioning and protect the down eye, a partially inflated inner tube may be used under the horse’s head to elevate the head and the down eye off the operating table. The optimal position for the primary surgeon is above the animal’s head and eye. For both large and small animals a surgical table that can be elevated or lowered and an adjustable surgeon’s chair with armrests is advised. The surgeon should be seated and the chair and table height adjusted so that the surgeon is comfortable, with a straight back and the arms resting on the armrests and bent 90 at the elbow. This is the optimal working distance. In addition, foot pedals for control of both phacoemulsification and the operating microscope must be positioned so that the

surgeon can operate these comfortably and use both the right and left feet. Cataract surgery should be performed using an operating microscope for magnification and illumination. The 5 to 20 magnification is preferred, with the lower magnification used during the initial approach, and increased magnification used for capsulorhexis and delivery of the cataract, and for suture apposition of the corneal or limbal wound. Once the surgical preparation is complete, the patient’s head is carefully positioned with a vacuum pillow and fixed beneath the microscope so that the eye is looking up into the microscope. The eye is centered in the scope’s field and the instrument’s focus adjusted. Additional adjustments in both the operating microscope’s magnification (by changing the zoom) and focus are made at the beginning of surgery. The eyelid hair is carefully removed with small hair clippers or by shaving. Whichever method is used, all hair from the eyelids and approximate surgical site are removed with no nicks and abrasions of the skin. The eyelids and the corneal and conjunctival surfaces are cleansed with 0.5% povidone–iodine solution and sterile cotton or Dacron swabs. The corneal and conjunctival surfaces are carefully flushed with sterile saline, and any debris removed by sterile Dacron swabs. The area is carefully draped to expose only the palpebral fissure.

General anesthesia and neuromuscular blocking agents General anesthesia with isoflurane is recommended for all cataract patients. With general anesthesia, the globe rotates ventral and medial, and complete visualization of the anterior segment may be impossible. Lateral canthotomy in some dogs can improve exposure (see Chapter 2). For optimal exposure of the anterior segment and position of the eye, neuromuscular blocking agents such as atracurium (0.2 mg/kg IV in dogs and 0.05 mg/kg in horses) are recommended. The atracurium-induced paralysis also results in reducing the extraocular muscle tone and the vitreous pressure. As the breathing muscles are also paralyzed, assisted ventilation is required. To reverse atracurium’s effects, edrophonium (2 mg/kg IV) may be used (for additional information, see Chapter 3). Neuromuscular blocking agents in both the dog and horse, assisted by intermittent positive pressure ventilation, result in optimal eye exposure for microsurgery, as well as relaxation of the extraocular muscles and reduced pressure on the globe and posterior lens capsule (when the eye is open). The intravenous administration of mannitol (1–2 g/kg) to decrease IOP should be avoided when neuromuscular blocking agents are used. In fact, if both mannitol and neuromuscular blocking agents are combined, the eye may be too hypotensive for cataract surgery.

Lateral canthotomy Surgical exposure to the globe may be enhanced with the lateral canthotomy. However, with neuromuscular blocking agents, the need for the lateral canthotomy is also lessened. As a result, once general anesthesia is stabilized and the neuromuscular blocking agent is administered, the eyelids are

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retracted by wire speculum. If exposure is ascertained to be insufficient, a lateral canthotomy is performed. For additional information on lateral canthotomy, see Chapter 2.

Anterior chamber entry for cataract and lens extraction The surgical approach for removal of cataracts or displaced lenses is identical. Entry into the anterior chamber may be through the peripheral cornea or the limbus under a limbalor fornix-based bulbar conjunctival flap. Scleral incisions into the anterior chamber in small animals are associated with hemorrhage from the scleral vasculature, and hemostasis usually requires point electrocautery. As a result, the corneal or limbal approach is preferred by most veterinary ophthalmologists. Entry through the limbus under a limbal- or fornix-based conjunctival flap requires more time than the corneal incision, and may produce limited hemorrhage. The resultant hemorrhage is not usually extensive and is controlled by point electrocautery or DacronW swabs soaked with 1:10 000 adrenaline (epinephrine). It is imperative that hemorrhage during the limbal and conjunctival phases of the approach is completely eliminated so that no blood enters the anterior chamber. Large limbal-based conjunctival flaps interfere with manipulation of the cornea, visibility of the anterior chamber, iris, and pupil, and surgical apposition of the limbal incision. Hence, limbal-based conjunctival flaps are usually small and limited to 3–5 mm from the limbus. Apposition of the limbal incision requires that sutures are placed under the limbal-based conjunctival flap, such as the McLean interrupted mattress sutures or simple interrupted sutures with the knots buried or exposed. Both apposition methods require additional time to manipulate around the conjunctival flap, but provide two layers of closure for the incision. For fornix-based conjunctival flaps, the bulbar conjunctiva is incised at the limbus and reflected posteriorly for only 3–5 mm. The approach for and apposition of the limbal incision are not interfered with by the conjunctival flap, and the suture knots for the limbal apposition are usually buried under the fornix-based conjunctival flap. The peripheral cornea, limbus, or a combination limbus– cornea entry into the anterior chamber incision may be perpendicular to the cornea or limbus, beveled, or a combination outer one-half perpendicular and inner one-half beveled. The advantages and limitations of each anterior chamber entry were presented in Chapter 9. The combination perpendicular–beveled incision is preferred. The outer one-half thickness perpendicular incision is performed with the Beaver No. 6400 microsurgical blade, and the inner onehalf thickness beveled incision is performed with cataract or corneoscleral scissors. The resultant incision has a large surface area for apposition, tends to be self-sealing, and is conveniently apposed with sutures.

Peripheral iridectomies Small peripheral iridectomies are not usually performed in small animal cataract surgeries because of the possibility of hemorrhage. Excision of the basal or peripheral iris

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in small animals usually requires a combination of sharp iris scissors and cautery for hemorrhage, or simultaneous excision–cautery by electrocautery. If intraoperative mydriasis is incomplete, or the anticipated postoperative mydriasis is to be a problem, two to four sphincterotomies may be performed, incising the pupillary aspects of the iris about 2–3 mm in each quadrant. The resultant pupil is irregular and slightly dilated.

Capsulorhexis and anterior capsulectomies With the evolution of phacoemulsification surgery and the introduction of the IOL, refinements in the entry through the anterior lens capsule were necessary. No longer was grasping and tearing the anterior lens capsule by the extracapsular forceps acceptable; the anterior lens capsulotomy and capsulectomy needed to be of an exact diameter not only to accommodate phacoemulsification, but also to permit implantation of the IOL and retain the IOL indefinitely. In traditional terms, capsulotomy implies cutting or tearing the lens capsule, and capsulectomy refers to its excision. Capsulorhexis indicates tearing or rupture of the lens capsule and is generally used to describe the entire process. The completion of an acceptable capsulorhexis for cataract surgery is an important step for an uncomplicated cataract surgery. Unfortunately, the response of the anterior lens capsule of the dog to shearing, tearing, and cutting is the least predictable aspect of cataract surgery, and sometimes the most frustrating portion. In capsulorhexis, an opening is created in the anterior lens capsule that is sufficiently large to accommodate the implantation of an IOL but small enough to maintain IOL stability long term. In the continuous curvilinear capsulorhexis (CCC) procedure, the circular tear of the anterior lens capsule contains no irregularities that could result in radial tears toward the lens equator. If an IOL is to be inserted into the remaining capsular bag, the diameter of the anterior capsulectomy should be slightly smaller (1 mm) than the diameter of the IOL optic. During anterior capsulectomy, the anterior chamber can be reformed with either lactated Ringer’s or balanced salt solution, or preferably with a viscoelastic agent. The highly viscous viscoelastic solution should not escape from the anterior chamber when the corneal incision is open during anterior capsulectomy or capsulorhexis. The surgical defect in the anterior capsule should be of sufficient size to accommodate the extraction of the cataract, but small enough to retain the IOL. Capsulorhexis is performed prior to delivery of the cataract. The most frequent difficulty in performing the capsulectomy is observation of the anterior lens capsule and its incised or torn edges. Often increased magnification using the operating microscope is necessary. Sometimes the capsulectomy may require some additional attention once the cataract is delivered, and retroillumination from the ocular fundus aids its identification. Trypan blue and indocyanine green are also available to stain the anterior capsule faintly and either is injected immediately before the capsulorhexis. The staining of the anterior lens capsule and its edges greatly facilitates its recognition. There are two important principles for continuous curvilinear capsulorhexis: shearing and ripping. Shearing is

Capsulorhexis and anterior capsulectomies

recommended over ripping because less force is necessary and the force is distributed over a smaller area. In shearing force the lens capsule is rolled onto itself with Utrata capsular forceps, and the pulling force is concentrated in the direction of the tear. The tear is more directed and less likely to result in radial tears toward the lens equator where the capsule becomes much thinner. In ripping the lens capsule, the pulling force is greater and distributed over a larger area. The pulling force is perpendicular to the desired direction of the tear. Irregularities in lens capsule thickness and consistency, such as fibrosis or plaques, result in ripping forces being less predictable and more apt to extend radially toward the lens equator. There are two primary types of anterior capsulectomy: 1) the continuous tear capsulectomy (CTC) or capsulorhexis method; and 2) the ’can-opener’ technique. Both of these methods can be modified and combined. The objective of capsulectomy or capsulorhexis is to produce a round anterior lens capsule defect, without radial tears extending toward the lens equator. In young dogs, the anterior lens capsule is thinner than in old dogs and more easily torn with the can-opener method. The direction of the continuous capsulorhexis is more difficult to control in young

animals, and more likely to tear radially toward the equator. The anterior lens capsule in dogs 6–8 years or older is thicker and more easily torn with the continuous tear or capsulorhexis procedure. However, the presence of focal lens capsule opacities (fibrosis or calcification) often encountered with hypermature cataracts makes tears difficult with forceps, and incision with intraocular scissors is recommended. Current techniques utilize tearing or multiple needle punctures; however, if the anterior capsulectomy begins to change direction, corrective incisions of the anterior capsule with intraocular scissors are necessary.

Continuous curvilinear capsulorhexis The continuous tear anterior capsulectomy or capsulorhexis procedure is initiated with a curved incision of the anterior lens capsule with a 22–25 g hypodermic needle, cystotome or Vannas scissors to reduce tension on the anterior lens capsule (Fig. 11.8a). This incision is somewhat internal to the desired CCC. A second hypodermic needle incision or releasing incision is usually made at 90 to the initial stab incision of the anterior lens capsule performed during the initial corneal or limbal entry into the anterior chamber.

A

B

C

D

E

F

G

H

Fig. 11.8 The continuous anterior capsulectomy or capsulorhexis method removes a central circular portion of the anterior lens capsule sufficiently large to permit extracapsular or phacoemulsification methods to remove the cataract, but of limited diameter (usually 1 mm less than the intraocular lens optic diameter). The anterior chamber is usually maintained by the infusion of viscoelastic agent. (a) A short radial relief incision of the anterior lens capsule is performed with a 22–25 g hypodermic needle. (b) From this relief incision, with Utrata capsule forceps, a continuous circular tear of the central anterior lens capsule is performed. (c) For fibrotic and/or thicker areas of the anterior lens capsule, intraocular scissors may be necessary to incise the anterior lens capsule in the intended direction. (d) Any remaining portions of the anterior capsulectomy are carefully removed by Utrata capsule forceps, avoiding radial tears that may extend to the equatorial lens capsule. (e,f) A recent modification uses the Vannas capsulotomy and Utrata forceps. The Vannas capsulotomy scissors are carefully inserted and used to make two opposing semicircular incisions of the anterior lens capsule. (g,h) Shearing of the anterior lens capsule between the ends of these two incisions using the Utrata forceps completes the circular capsulectomy.

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The edge of the incised flap of anterior capsule is then grasped with Utrata forceps, and gradually rolled to tear the anterior capsule to create a 5–7 mm diameter defect in the anterior lens capsule (Fig. 11.8b). Every 2 or 3 mm of tear, the anterior capsule is regrasped with forceps to continue shearing the circular tear. Shearing forces are preferred during the CCC; however, at the 6 o’clock position or directly opposite from the corneal incision, some tearing of the anterior capsule may occur, making radial tears more frequent in this position. If the initial CCC is too small, this is repeated in the same fashion. Occasionally the anterior capsule or portions of it appear thickened, fibrotic, and/or opaque, and resist forceps tearing. Intraocular scissors are necessary to incise these areas of the anterior lens capsule (Fig. 11.8c). The intraocular scissors are carefully inserted with the blades closed. At the capsulectomy site, the scissors are rotated 90 and the lower blade inserted into the intact capsule or beneath the edge of the torn capsule; the capsule is then incised, usually circumlinearly. Once a central portion of the anterior lens capsule of about 7 mm diameter is achieved, the incised portion of capsule is carefully removed by forceps (Fig. 11.8d). A recent modification of the CCC procedure for the dog anticipates anterior lens irregularities (areas of thickening, fibrosis, and calcification), and combines the cutting of the Vannas capsulotomy scissors with the shearing technique using the Utrata forceps and connecting these two incisions (Fig. 11.8e,f). The Vannas capsulotomy scissors are carefully introduced into the anterior chamber and used to incise two opposing curved incisions of the anterior lens capsule. The Utrata forceps is then used to grasp and shear the anterior lens capsule between the two scissor incisions, thus completing a circular capsulectomy (Fig. 11.8g,h).

Can-opener method In the can-opener method, the anterior lens capsule is repeatedly incised or lacerated (about 40–50 punctures) circumferentially with a 22 or 25 g bent hypodermic needle (Fig. 11.9a). With puncture of the anterior lens capsule and central movement of the hypodermic needle, another connecting needle laceration is performed. This type of capsulectomy requires more time than the CCC method. Radial tears may develop from the individual needle lacerations. Once the central portion of the anterior lens capsule has been ringed with needle lacerations, the central capsule is carefully removed by Utrata capsule forceps (Fig. 11.9b). In humans this technique is less popular as it has been associated with an increased frequency of radial anterior capsular tears. Fig. 11.9 In the can-opener method for anterior capsulectomies in small animals, 40–50 needle penetrations are made in a circular pattern about 7–8 mm in diameter. The tip of the hypodermic needle is bent 90 or a lens cystotome may be used. (a) The bent hypodermic needle is used to perform 40–50 punctures of the anterior lens capsule in a 7 mm diameter circle. (b) Once the area is completely surrounded by needle punctures, Utrata capsule forceps are used to remove the central portion of the anterior lens capsule.

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A

Modifications The can-opener and CCC methods may be combined to various extents. The dorsal anterior lens capsule may be lacerated with the 22–25 g hypodermic needle between the 10 and 2 o’clock positions and the remaining capsule torn circumferentially with Utrata capsule forceps. Another modification is to perform the hypodermic needle lacerations of the anterior lens capsule at the 11–12, 3–4, 6–7, and 9–10 o’clock positions, and connect the lacerated areas by tearing with the Utrata capsule forceps. There are also other methods for anterior capsulectomies, such as the envelope procedure, in which a single linear incision is performed in the upper anterior capsule; phacoemulsification (endocapsular or intercapsular) and IOL implantation are performed through this single tear. Theoretically, this method of phacoemulsification has the least effect on the corneal endothelium, but can result in additional tears to the anterior lens capsule during the surgery. Once phacoemulsification has been completed, the anterior lens capsule is visualized by both direct and retroillumination, and the CCC performed. If an IOL is implanted, the diameter of the anterior capsulectomy should be about 1 mm less than the diameter of the IOL optic. If an IOL is not planned, the anterior capsulectomy may be larger and performed with extracapsular forceps. If anterior capsulectomy with Utrata forceps is not acceptable, the procedure may be completed using intraocular scissors. Anterior capsulectomies are less predictable in older dogs and with hypermature cataracts.

Phacoemulsification Phacoemulsification was first introduced by Kelman in 1967. The procedure involves ultrasonic fragmentation and aspiration of the cataractous lens through a small incision. The technique was designed to permit removal of a cataract through a small incision, eliminate some of the complications associated with large incision cataract surgeries, and shorten the recovery period. Phacoemulsification is a further refinement of the extracapsular cataract extraction. Because of the high cost of the Kelman phacoemulsification instrument, many veterinarians first performed this technique in small animals using small phacofragmentation units in the mid 1970s. Phacoemulsification is technically more difficult than traditional extracapsular extraction techniques, and the instrumentation is considerably more expensive. At this time, phacoemulsification yields the highest success rates, and is the technique of choice for cataract extraction in dogs, cats, and horses.

B

Phacoemulsification

Fundamentals of phacoemulsification Phacoemulsification instruments possess two major integrated functions: 1) fluidic systems consisting of irrigation, aspiration, and cooling; and 2) an ultrasonic system to fragment the lens. Additional components of the newer and larger phacoemulsification systems may include cautery and vitrectomy units. The fluidic system involves the active flow of fluids into and from the anterior chamber of the eye. During phacoemulsification the fluidics are designed to maintain a stable anterior chamber which is particularly important in animals in which the low scleral rigidity collapses the anterior segment once aqueous humor is removed. The delivery and egress of lactated Ringer’s or balanced salt solution is controlled by the ophthalmic surgeon via a foot control to maintain a balance of irrigation and aspiration to provide sufficient inflation of the anterior segment, facilitate removal of lens fragments, and cool the ultrasonic tip. The flow rate for irrigation, the amount of vacuum for aspiration, and the amplitude of vibration (power settings) are controlled by foot pedal. During phacoemulsification, the foot pedal has three positions: the first level activates only the irrigation system; the second level activates the irrigation and aspiration systems; and with the foot pedal fully depressed (third level), the irrigation, aspiration, and fragmentation systems are activated.

Irrigation and delivery of fluids to the anterior chamber The irrigation and aspiration of fluid to and from the anterior chamber involves an infusion system with a bottle of lactated Ringer’s or balanced salt solution (often with 1–2 IU/mL heparin added) and a pump (either peristaltic, Venturi, or diaphragm). Heparin is added to reduce the formation of fibrin during surgery. With the early systems, the height of the fluid bottle may be raised and lowered to change the rate of flow of the irrigation fluid and assist the phacoemulsification pump. Current phacoemulsification units control the irrigation of fluids during surgery by a foot-activated pump.

Aspiration and vacuum levels Three different pumps have been developed for phacoemulsification, and each has certain advantages and limitations. The peristaltic pump is the oldest type and consists of a roller system that forces the fluid forward, utilizing a series of roller heads that collapse and push the fluid through the tubing. The pressure created by this pump results in a negative pressure differential or vacuum. This vacuum is dependent on its speed; when the system is moving slowly the vacuum is very limited. However, at faster rates with this type of pump the vacuum level is greater. The ’rise time’ or time for the vacuum pressure to build up is low, which makes this a less responsive but safer system, especially for surgeons in training. The Venturi and diaphragm pumps are more advanced systems, and both provide fast flow rates and rapid vacuum rise times. The Venturi pump uses a mechanism of compressed gas that is passed through a tube that has a small opening over a pressure or drip chamber. This pressure

differential generates a vacuum which also helps to aspirate fluids and fragmented lens material from the anterior chamber. With increased rates of compressed gas and pump activity, the vacuum levels are also simultaneously increased. The diaphragm pump consists of a motor that rotates causing a diaphragm to be elevated and depressed that forms a compartment to connect to the two lower compartments and one-way valves. Since these three pumps operate with different principles, they provide different rates of fluid flow, vacuum levels, and rise times. Although the Venturi and diaphragm pumps are more responsive to pressure changes, the surgeon must appreciate that these changes can occur within fractions of a second. The peristaltic pump provides a slower response time and the vacuum pressure is influenced by the rate of infusion; that is, the higher rates of irrigation create higher levels of vacuum. Regardless of the choice of aspiration pump, adequate levels of fluids must be delivered to the anterior chamber to maintain the anterior chamber and some degree of IOP, remove lens fragments, and cool the phaco needle during phacoemulsification. The aspiration component of a phacoemulsification unit removes lens fragments and fluids from the anterior chamber. Aspiration occurs through the bore of the ultrasonic probe needle, and is connected by tubing to a collection reservoir. The vacuum is produced by the negative pressure of the different pumps, i.e., peristaltic, Venturi, and diaphragm. In aspiration, two other principles are important: venting and aspiration reversal. In venting, the vacuum is relieved by the foot pedal and ceases before irrigation is stopped. Venting allows the surgeon to release lens fragments, lens capsule, or vitreous that plug the ultrasonic needle. Aspiration reversal refers to the reversal of the pump mechanism so that lens fragments, lens capsule, or vitreous that temporarily plug the phaco ultrasonic needle are actively pumped from the aspiration system within the ultrasonic needle.

Ultrasonic or ’cutting’ system The phacoemulsification handpiece generates ultrasonic energy that fragments the lens material into small pieces that can be aspirated from the capsular bag and anterior chamber. The piezoelectric ultrasonic system is light, durable, and requires less power, and has an extremely high speed frequency (27 000–60 000 cycles/s or kilohertz (KHz)). The power of the ultrasonic handpiece is determined by several factors including: frequency of vibration, amplitude or stroke length (back and forth movement of the ultrasonic needle), shape and sharpness of the needle tip, aspiration, and resonance (maintenance of frequency during phacoemulsification). Power settings (percentage of the maximum power) are available on the instrument console, and change the stroke length of the ultrasonic needle. Both fixed and linear modes are also available: in the fixed mode the power is constant as the foot pedal activates the ultrasonic handpiece; in the linear mode (as the ultrasonic foot pedal is depressed by the surgeon) additional ultrasonic power is provided. The linear power setting is preferred by many surgeons as power can be varied (higher during sculpting and lower when in the area of the posterior lens capsule). The handpiece, with the vibrating needle enclosed within a blue plastic protective sleeve, accommodates aspiration and irrigation (Fig. 11.10).

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15° Bevel tips

30°

45° 60°

Ultrasonic needle Infusion Ultrasonic fragmentation and aspiration Fig. 11.10 Diagram of the tip of the phacoemulsification handpiece. The tip, inserted into the anterior chamber, accommodates ultrasonic fragmentation, aspiration, and infusion of the irrigating solution.

Ultrasonic needles The ultrasonic needle is threaded onto the phaco handpiece to permit the transfer of the ultrasonic energy. The ultrasound needle is available with a number of different (0 (blunt), 15 , 30 , and 45 ) bevels. The degree of needle bevel is influenced by several factors including: 1) the experience of the surgeon; 2) the phacoemulsification technique (either sculpting procedure or the port occlusion method); and 3) the relative softness of the cataract. With limited phaco experience the 15 needle bevel is recommended as it accommodates slow sculpting and is therefore the safest; it is, however, more easily occluded with lens fragments, and more difficult to introduce into the anterior chamber through the corneal incision. The 45 bevel needle is recommended for harder cataracts, and the 30 bevel needle for softer cataracts. The 45 bevel needle provides not only the most rapid sculpting, but can also penetrate the posterior capsule the easiest. In addition, bent or Kelman tips and flare tips are available to improve fragmentation and tip occlusion.

Irrigation/aspiration (I/A) handpiece The I/A handpiece does not generate ultrasonic energy; therefore it is used, after nearly all of the cataractous material has been removed by the phaco ultrasonic handpiece, to remove all residual lens cortex with minimal trauma to the lens capsules. Its tip is smoothly rounded, and aspiration occurs on the side ports. Irrigation occurs at 90 from the aspiration ports to facilitate movement of the lens fragments into the aspiration ports. The I/A tip may be straight or angled 45 or 90 . A 0.5–0.7 mm aspiration port is usually required for cortical aspiration as a smaller lumen will frequently become occluded with canine and equine lens cortex.

Corneal damage during phacoemulsification Corneal damage of two types, i.e., physical and thermal damage to the entry wound into the anterior chamber and corneal endothelial loss, has been associated with phacoemulsification. With refinement in the phacoemulsification instrumentation and the use of viscoelastic agents, both

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types of corneal injury have been markedly reduced. In phacoemulsification, the corneal incision (usually 3.0–3.2 mm) must be sufficiently large to accommodate repeated insertion of the phaco ultrasonic needle and sleeve. Incisions too small result in direct damage to the corneal tissues and increased postoperative edema. However, a larger than necessary corneal wound causes excessive leakage of the irrigating fluids, difficulty in maintaining inflation of the anterior chamber, and the additional fluids cause unnecessary corneal endothelial cell loss. The phacoemulsification ultrasonic needle generates heat, and thermal damage may result. Newer designs contain an additional sleeve that decreases the friction between the needle, cornea, and sleeve, and permits the irrigation fluids to flow about the needle and dissipate the heat. Phacoemulsification, to maximally protect the corneal endothelium, should be performed within the capsular bag (endocapsular phacoemulsification). Phacoemulsification of lens fragments within the anterior chamber and close to the corneal endothelium should be avoided if possible. The addition of viscoelastic agents just before phacoemulsification, as well as before the insertion of the IOL, provides excellent protection for the corneal endothelium. Cavitation bubbles occur during phacoemulsification, and consist of high pressures and temperatures, and free radicals that can damage the corneal endothelium. They appear to be formed on the backstroke of the phacoemulsification needle vibrations. Higher phaco power (greater than 60% of maximum power) and larger tip surface areas cause more cavitation bubbles. Cavitation bubbles can also arise at the junction of the ultrasonic needle and needle piece, especially in those abrupt or square threading devices. These cavitation bubbles at the phaco tip also decrease contact between the ultrasonic needle and the lens tissues, reduce the cutting ability of the needle, and interfere with visualization of the anterior chamber and cataract. To reduce cavitation bubbles several strategies have evolved. Phacoemulsification should be performed at lower power (30–40%) with small needles and limited bevels. New needles have tapered junctions to the thread (stealth or bubbleless needles), and can be used with a 2.7 mm corneal incision.

Fundamental phacoemulsification procedures Two phaco procedures form the fundamental methods of providing contact of the lens tissues to the tip of the ultrasonic needle: 1) sculpting or movement of the ultrasonic needle tip, gradually allowing the ultrasound to fragment the lens material within a relatively fixed cataractous lens; and 2) port occlusion or the obstruction of the ultrasonic needle with loose lens fragments using aspiration (and vacuum pressure) while performing phacoemulsification. Vacuum surges may occur with the latter technique. To reduce the magnitude of these surges, vacuum levels, irrigation, and aspiration rates are reduced, and areas close to the posterior capsule are avoided.

One- and two-handed phacoemulsification Phacoemulsification in small animals has the potential to provide the highest success rates, shorter surgery times, smaller corneal or limbal incision, and less intense

Phacoemulsification in small animals

postoperative iridocyclitis. Both one-handed and twohanded phacoemulsification procedures are used in small and large animals. The one-handed coaxial technique is easier to master, but the two-handed technique may result in shorter phacoemulsification times, lower energy levels, and the ability to manage hard and unstable or subluxated lenses. In the two-handed phaco procedure, the dominant hand is used to hold the phaco handpiece, and the opposite hand can maneuver other ophthalmic instruments, such as the nuclear manipulator to shift and rotate lens fragments, or the chopper to divide the lens into smaller pieces, during phacoemulsification. Because both instruments are in the eye and lens simultaneously, two-handed phacoemulsification is more difficult to master. Phacoemulsification is performed through a widely dilated pupil within the capsular bag (intercapsular/endocapsular technique). Phacoemulsification of lens fragments within the anterior chamber should be avoided. All lenses and cataracts can be potentially fragmented by phacoemulsification, but old animals (over 8–10 years of age) possess a harder nucleus that can prolong the phacoemulsification time. There are many phacoemulsification units available to veterinarians. Experience, purchase, and operating costs generally dictate the instrument obtained.

Once the clear corneal incision is completed, the anterior chamber volume is restored with an injection of viscoelastic agent (Fig. 11.11c), and the anterior capsulorhexis– capsulectomy performed.

Hydrodissection In hydrodissection, lactated Ringer’s or a balanced salt solution is carefully injected between the anterior lens capsule and the cortex to ’hydrodissect’ or loosen the outer cortex from the lens capsule. Hydrodissection is useful when a two-handed technique is planned. It is less desirable for one-handed coaxial phacoemulsification. A 27 g cannula with a 3 mL syringe is carefully inserted between the anterior lens capsule and cortex a few millimeters from the capsulotomy edge toward the lens equator. Fluid is carefully injected; the initial injection requires more pressure. Eventually the injected fluid will surface from the opposite side of the capsulotomy. Hydrodelineation has been reported in humans to remove as many lens cells and fibers as possible, and reduce the extent of the lens capsular opacification. Unfortunately, this technique is difficult in the dog (perhaps related to hypermaturity of most cataracts). In this technique, a cannula is used to inject fluid to separate the nucleus from the epinucleus.

Phacoemulsification of the cataract Phacoemulsification in small animals For phacoemulsification, a peripheral corneal incision is performed about 1 mm anterior to the limbus. It should approximate 3.0–3.2 mm in length and be sufficient to accommodate the phaco tip’s diameter and, if indicated, the diameter of the IOL (Fig. 11.11a). The two-step corneal incision involves a partial incision with the Beaver No. 6400 microsurgical blade (50–70% corneal thickness), and the deeper aspect into the anterior chamber with the keratome. The first half-thickness corneal incision is initially performed with the Beaver No. 6400 microsurgical blade perpendicular to the corneal surface; its length is determined by whether only phacoemulsification or phacoemulsification plus an IOL is planned. If a PMMA IOL implantation is anticipated, the eventual corneal incision will be about 8–10 mm long, and will be enlarged after phacoemulsification has been completed. With a foldable acrylic IOL, the entire procedure may be performed through a 3–4 mm incision. Once the outer cornea is partially incised for about 3.5–4.0 mm, a 3.0 or 3.2 mm keratome is inserted through the center of the corneal incision and into the anterior chamber. The length of the initial corneal incision is important, as it should be long enough to accommodate the tip of the phaco handpiece, but not as excessively long as would permit loss of irrigating fluids, resulting in excessive volumes of fluid escaping from the anterior chamber. Often during the deeper aspects of the corneal incision, the keratome or scalpel blade may also be advanced into the anterior lens capsule to perform the initial incision for the anterior capsulectomy (Fig. 11.11b). If two-handed phacoemulsification is planned, a second 1 mm corneal incision is made about 80–90 from the first incision. Through this second port, instruments such as the nuclear manipulator and viscoelastic agents can be injected.

With the anterior capsulectomy complete, the ultrasonic handpiece is carefully inserted through the corneal incision and into the anterior capsulectomy site (Fig. 11.11d). The ultrasonic handpiece may be held as a pencil or screwdriver, whichever is more comfortable, but accommodates fine movements. The bevel of the phaco needle is positioned down or toward the eye to avoid catching on the iris and stripping Descemet’s membrane, and the irrigation system is activated during entrance. The bevel of the phaco needle within the cataract may be either up or down, depending on the surgeon’s preference and the position within the lens. When the bevel is down, observation of the phaco site is more difficult, but damage to and penetration of the posterior lens capsule is less likely. When the phaco needle bevel is up or toward the surgeon, the phaco site is fully visible, but penetration of the posterior lens capsule is more likely. Hence, my preference (KNG) for beginners is bevel up during the initial phacoemulsification of the anterior cortex and lens nucleus, and bevel down when in the posterior cortex and near the posterior lens capsule. Phacoemulsification of the lens may be performed using many techniques. With one-handed phacoemulsification, the three principles for lens removal include central sculpting, nuclear rotation, and removal of the residual central and deep nucleus. These techniques are divided into: ’chip and flip’, ’crater divide and conquer’, ’trough divide and conquer’, and various modifications. All of these techniques are based on the observation that the central and hard nucleus is the most difficult and requires the most energy for phacoemulsification, and the softer cortex provides some protection during this ‘high energy’ phase of phacoemulsification. Once the nucleus is fragmented and aspirated, the remaining cataractous cortical material is easily removed. Reducing the cataractous lens into small pieces can markedly reduce the time and energy for phacoemulsification in the dog.

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Fig. 11.11 Phacoemulsification is a modification of the extraction technique in which the cataractous material is removed by ultrasonic fragmentation and aspiration through a small corneal incision. (a) A 4–5 mm corneal incision is performed with a keratome, sufficient to permit insertion of the phaco needle but small enough to prevent excessive loss of the irrigation fluids. The length of the corneal incision is related initially to the diameter of the phaco tip. Depending on the diameter of the optic of the intraocular lens, the corneal incision may be enlarged later in the surgery. (b) During the corneal incision, the anterior lens capsule may also be incised with the keratome. (c) The anterior chamber is filled with viscoelastic agent to maintain the anterior chamber during phacoemulsification. (d) The Utrata capsule forceps are used to tear a continuous anterior capsulectomy (about 6–8 mm diameter). If an intraocular lens (IOL) is implanted, the diameter of the anterior capsulectomy should be 1 mm less than the diameter of the IOL optic. (e) The phaco ultrasonic tip is carefully inserted (bevel up) through the corneal incision, then through the anterior capsulectomy (bevel up) into the anterior lens cortex. (f) Phacoemulsification is started in the anterior lens cortex and nucleus. (g) If a chopper is used to divide the lens nucleus into halves, it is inserted through a separate corneal incision. It is carefully manipulated across the pupil and beneath the anterior capsule. Using the phaco tip and aspiration to stabilize the nucleus, the tip of the chopper is advanced to divide the nucleus into halves. The tip of the instrument should not extend below the posterior lens nucleus. (h) The sculpting is initially limited to the nucleus, fragmenting it into four pieces, and then removing it. (i) The remaining nucleus and cortices are fragmented by parallel sculpting. (j) With most of the cataractous lens material fragmented and aspirated, any remaining material is carefully removed, avoiding tearing of the posterior lens capsule. An irrigation–aspirating handpiece is useful during this final phase for removing any remaining cataractous material from the equator and surface of the posterior lens capsule (polishing). (k) The short corneal incision is apposed with two or three 8-0 to 9-0 simple interrupted absorbable sutures, and the anterior chamber is reformed with lactated Ringer’s solution. 328

Phacoemulsification in small animals

The concept of ‘nucleofractis’ is about 60 years old and developed along with phacofragmentation/phacoemulsification. Nucleofractis is the fracturing or cracking of the lens nucleus as this area of the lens is the oldest and most resistant to phacoemulsification. The nucleus is also the largest part of the lens and requires most of the phacoemulsification process. By subdividing the lens nucleus into smaller pieces, less time, less phaco energy, and less potential damage to the eye results. Dividing the nucleus, when it is relatively large, generally requires two instruments: one is the phaco tip and its aspiration, and the other, an instrument to divide, rotate, and manipulate the nucleus while still within the cortices – hence, the re-emergence of two-handed techniques in phacoemulsification. However, these techniques can also be performed using the single phaco incision. The nucleofractis concept involves deep sculpting of the lens nucleus so a division or fracture can occur; fracture of the lens nuclear rim and posterior nucleus; dividing or fracturing the remaining nucleus into smaller wedge-shaped fragments; and rotation of the lens nucleus (to expose its posterior aspects for fragmentation).

Divide and conquer technique The divide and conquer techniques are generally divided into: 1) trench (for softer to medium hard lens nuclei); and 2) crater (for hard to very hard and dense nuclei). The latter method creates a very large and deep crater and peripheral lens nucleus rim to fracture into multiple sections. Two instruments (and incisions) are used to manipulate the lens, fracture the nucleus, and rotate the lens. However, for the one-handed technique and using only the phaco tip, the phacoemulsification process creates the nucleus fractures and rotation using its fragmentation, aspiration, and irrigation capabilities. The divide and conquer method was popularized in Gimbel (1991). In this method the dense nucleus is fragmented to a deep central groove or deep trough (about 70–90% of the depth of the nucleus or twice the width of the phaco tip), and the nucleus is fractured using the phaco tip and a lens manipulator. The manipulator, initially a cyclodialysis spatula and now a lens manipulator, helps steady the nucleus during fracturing, and rotation requires a separate, small (1 mm) corneal incision at about 90 to the phaco incision. The nucleus is then rotated 90 and a second groove is made perpendicular to the first fracture. The cortices are then sculpted into four to six more-or-less equal pieces, and these pie-shaped pieces are then individually fragmented. This method or its modifications is the most popular in the dog. An alternative trough ‘divide and conquer’ procedure divides the lens with a softer nucleus with a single central sculpted trough, the nucleus fractured by opposing actions of the phaco tip and cyclodialysis spatula, and then the remainder of the cortices into several wedge-shaped sections for individual fragmentation.

Chip and flip technique The chip and flip technique was first published by Fine (1991). In this technique, both hydrodissection and hydrodelineation are performed so that the central and often hard

nucleus and epinucleus can be removed separately. It begins with sculpting a central bowl which is rotated and the entire nucleus rim is removed. With a second handpiece the inner (deeper) nucleus is lifted and removed. A nuclear rotator is used to ‘flip’ the anterior (outer) nuclear bowl, allowing fragmentation. Hence, in this technique phacofragmentation is always performed on the outer surface of the cataract, and the posterior lens is flipped for fragmentation to minimize the possibility of posterior lens capsule damage. This method has been modified for the dense canine nucleus. In this procedure, hydrodissection and hydrodelineation are not necessary. A large bowl is sculpted with a central groove in the central nucleus and epinucleus. The nucleus is then fractured using the phacoemulsification tip and a nucleus rotator, and divided into five or six pie-shaped pieces for fragmentation.

Phaco chop technique The phaco chop was introduced by Nagahara (2002) and utilized the natural cleavage planes of the lens. It utilizes a chop to divide the nucleus; the human lens instrument is too short for the canine nucleus (1–2 mm tip for humans; 4 mm for dogs). Warren modified the Nagahara technique from humans for the dog. This procedure uses the phaco tip to impale and high vacuum to hold the lens nucleus while a chopper is hooked at the lens equator and pulled centrally, splitting the nucleus along its natural planes. By dividing the nucleus into quadrants or smaller parts using the chop technique, and combined with the phacoemulsification ‘divide and conquer’ technique, phaco time and energy are significantly reduced, as is corneal endothelial cell damage. Because the lens in the dog is larger than in the human, Warren recommends using the human instrument for small dogs (1–2 mm tip) and has modified the Chang combination chopper for medium and large dogs (a longer 4 mm tip). For safety, the chopper’s tip is inserted into the nucleus to only one-half thickness. Some canine cataract cortices and nuclei are too hard to ‘chop’ or possess insufficient room for the instrument to pass between the anterior lens capsule and adjacent cortex, and are not amenable to this technique.

Sculpting and lens rotation For phacoemulsification surgery, sculpting and lens rotation are important concepts. For sculpting, either the 30 or the 45 bevel of the tip of the phaco ultrasonic needle is recommended. The 30 bevel is preferred by many surgeons because of its safety near the posterior lens capsule, but it is slower and more easily occluded with lens fragments. The 45 bevel needle provides more cutting power for sculpting of the harder cataracts, but is associated with a higher incidence of posterior lens capsule tears. These tears can be prevented, for the most part, by constant visualization of the phaco’s tip, and changing its bevel when sculpting deep in the posterior cortex and near the posterior lens capsule. Generally in small animals the phaco technique first removes the anterior cortex just below the anterior capsulectomy site, and then attacks the lens nucleus (Fig. 11.11e,f).

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The most effective sculpting is from the corneal incision to the opposite side of the cataract, and the development of a large V-shaped groove. This groove also accommodates the sleeve of the phaco tip which increases the diameter of the entire ultrasonic needle. As the lens nucleus is the hardest and most resistant to phacoemulsification, it should be addressed early in the phaco procedure. Often when the nucleus is sculpted, resulting in a wide and deep V-shaped groove, it may collapse on itself. Pulling rather than pushing forces are recommended to rotate or move large lens fragments. Either the nuclear rotator (with two-handed phacoemulsification) or the phaco needle using aspiration can be used to manipulate lens fragments. Eventually the lens is divided into four or more pieces that are addressed individually by phacoemulsification (Fig. 11.11g,h). With the collapse of the nucleus, the cataract may loosen slightly from the equatorial capsules. Recent modifications during the phacoemulsification of the lens utilize special instruments to either manipulate (rotate) or divide (phaco chop) the lens into smaller sections and reduce the time and possible trauma of phacoemulsification. Generally these instruments require two entries into the anterior chamber: one for the phaco tip and the other, which is smaller, for the insertion of these special instruments. If two-handed phacoemulsification is used, a second instrument can be inserted to manipulate, stabilize, chop, divide or rotate the lens. A nuclear manipulator (i.e., Bechert nucleus rotator) or other instruments can be inserted through the second port, and used to rotate the lens fragments and facilitate and reduce the time and energy for phacoemulsification. The instruments, i.e., quick chopper, nucleus segmenter, prechopper, etc., attempt to assist phacoemulsification by stabilization as well as to chop (incise and divide) the hard lens nucleus (Fig. 11.11g). They are also inserted into the lens nucleus to lift as well as support lens fragments toward the phaco tip for fragmentation. The Steinert nuclear chopping instrument which possesses an angular tip with a wedge-like end (1.5 mm) is sharpened on its inner edge. This creates the chop of the nucleus while maintaining contact of the chopper with the nucleus; deep penetration of the nucleus is avoided to prevent posterior capsule penetration. After the majority of the lens nucleus is fragmented, the sculpting of the remaining lens fragments consists of linear movements extending from the corneal incision (Fig. 11.11i,j). The equatorial and posterior cortices are fragmented last, as visibility during this phase should be optimal. Port occlusion, using aspiration from the phaco’s tip to hold lens fragments, is used for the smaller lens fragments and to maintain them within the capsular bag. Equatorial cortices opposite and immediately below the corneal incision are often the most difficult to access. The pupil needs to be widely dilated for observation and optimal fragmentation of equatorial areas. During this part of phacoemulsification, the posterior lens capsule can be damaged and torn, usually by direct penetration with the phaco needle, or an abrupt change in aspiration flow with the posterior lens capsule suddenly pulled into the phaco needle. With the phaco needle bevel down and caution, the possibility of posterior lens capsule tears is reduced. Toward the end of phacoemulsification, irrigation and aspiration are used primarily with the ultrasonic tip, rather

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than the fragmentation cycle, to polish or remove any remaining lens material from the equatorial and posterior lens capsules. The aspiration (vacuum) levels during this step should be reduced to decrease the risk of posterior lens capsule tears. If lens fragments exit the capsular bag and enter the anterior chamber, they are removed primarily with irrigation and aspiration. Fragmentation in the anterior chamber is apt to produce direct corneal endothelial damage. If lens fragments penetrate the posterior lens capsule, their retrieval depends on their size and position within the vitreous, the size of the posterior lens capsule tear, potential damage to the anterior vitreous during fragment removal, and the need for an anterior vitrectomy. Most phaco units have a separate small irrigation/aspiration (I/A) handpiece that may be used at this stage to remove the softer and any remaining cortex still attached to the lens capsule. The I/A tip is preferred during the latter stages of phacoemulsification because of the low likelihood of damage to the lens capsule and posterior lens tears. The linear mode is recommended for I/A as it allows the cortex to be removed in large sheets and perhaps increases the possibility of the removal of as much lens material as possible with the least trauma. The I/A handpiece consists of only aspiration and irrigation, and its tip is rounded, providing the least trauma to the lens capsule. To remove any remaining sheets of lens material within the equatorial regions, the lens material is engaged with the I/A tip and then gradually stripped from the capsule, moving the I/A tip to the center of the lens. Vacuum levels should be low so as not to wrinkle or penetrate the lens capsules. Engagement of the lens capsule with the I/A tip is corrected by reflux (not additional traction) and dislodging the capsule. The most difficult remaining cortex to remove is that directly beneath the corneal incision. Angled I/A tips (either 45 or 90 ) are available for this region. The I/A tip is reintroduced and the remaining lens material removed. Polishing the posterior lens capsule with the I/A handpiece has been proposed to reduce posterior capsular opacities postoperatively. The I/A tip is carefully manipulated to remove any remaining lens material. Unfortunately, there appears to be no benefit from this technique. Once phacoemulsification is complete, and no IOL is planned, the corneal incision is apposed with two or three 8-0 to 9-0 simple interrupted absorbable sutures (Fig. 11.11k). The anterior chamber is re-filled with lactated Ringer’s or balanced salt solution injected with a 27–30 g irrigation cannula carefully inserted between two sutures. The immediate postoperative IOP should be about 10–15 mmHg (Fig. 11.12).

Phacoemulsification in the horse There are several differences in cataract surgery of the equine eye as compared to small animals. The size of the patient makes anesthesia, patient positioning, and pre- and postoperative care more difficult. The size of the eye and the lens may require modifications of technique and instrumentation. The decision on implantation of an IOL, which IOL to implant, and the technique and instrumentation required to implant an equine-specific IOL must be considered.

Phacoemulsification in the horse

Fig. 11.12 Intraoperative appearance of phacoemulsification after nearly all of the cataractous material has been removed in a dog.

Finally, the purpose of the animal and the risk associated with visual impairment to both the animal and owner/rider must be addressed. The technique of choice for equine cataract surgery is phacoemulsification. Typically, equine cataracts fall into one of several etiologic categories: congenital or juvenile-onset, traumatic, postinflammatory, and senile (Fig. 11.13). While the most common cause for cataracts in the horse is uveitis, the most common cataract surgical patient is a foal with congenital or juvenile-onset cataract. In one study, 25/39 horses undergoing phacoemulsification surgery were foals, 9/39 had traumatic cataracts and only 5/39 had uveitisassociated cataract (Fife et al 2006). Prior to cataract surgery, a complete ophthalmic examination, including an ultrasound and electroretinogram, is performed as indicated. This can generally be performed in the standing horse using sedation and nerve blocks. With congenital cataracts in young foals, the eye should be examined for other congenital abnormalities such as anterior segment dysgenesis or microphthalmos. When other congenital ocular abnormalities are present, a decrease in successful outcome of cataract surgery is reported. In addition, when possible, the mare and stallion should have a complete dilated ophthalmic examination to look for abnormalities that would support a hereditary basis for the foal’s cataract. Breeds considered to have a predisposition for cataracts include the Morgan, Quarter Horse, Belgian, Arabian, and Thoroughbred. Regardless, a recommendation not to use an affected foal for breeding should be made. Cataracts secondary to ERU are the most common type of cataract

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seen in the horse. Horses with cataracts secondary to ERU may have additional intraocular abnormalities such as glaucoma, synechia, phthisis bulbi, and retinal detachment/ degeneration. Preoperative medication for equine cataract patients is similar to that in small animals. In horses, the patient should be halter trained and also accustomed to topical medication prior to surgery. Foals should be halter trained and broke to lead prior to surgery. All horses can be acclimatized to topical medication by applying topical artificial tear ointment twice daily for a few weeks prior to surgery. The author’s (DAW) preference is to administer topical 1% prednisolone acetate and broad-spectrum topical antibiotics every 6 h, starting 48 h prior to surgery. In horses with ERU, all intraocular inflammation must be controlled prior to considering surgery. Topical prednisolone and a topical NSAID are administered every 30 min, starting 2 h prior to surgery. Topical 1% atropine is administered the morning of surgery. At induction of anesthesia intravenous flunixin meglumine (1.0 mg/kg; BanamineW; Schering-Plough, Kenilworth, NJ) and systemic antibiotics are administered. General inhalational anesthesia with neuromuscular blocking agents such as atracurium (0.05 mg/kg) is preferred. The horse must be assisted using intermittent positive pressure ventilation following administration of a neuromuscular blocking agent. A hydraulic table that can be raised and lowered is preferred. For unilateral surgery the horse is placed in lateral recumbency with the surgical eye up. For bilateral surgery, the horse can be placed in dorsal recumbency and the head turned to have the operated eye facing up; the head is then repositioned for the second eye. The author (DAW) prefers to use a moderately inflated inner tube under the head to help with positioning and to keep the down eye off the table. The operating microscope, surgical chair, and phacoemulsification equipment are then positioned around the head. The eye is routinely clipped and prepped similar to that described for small animals. An equine eyelid speculum is placed and, if required, a lateral canthotomy performed. A stay suture(s) is placed at the discretion of the surgeon. The surgeon should be positioned at the dorsal eyelid. With the horizontal pupil and large dorsal corpora nigra, the easiest approach will be from the lateral or nasal aspect of the equine pupil, giving the surgeon the most direct and unimpeded access to the lens. A two-plane limbal incision is performed. A 3.2 mm, 75% depth groove is made at the limbus and the anterior chamber entered using a 3.2 mm keratome. The anterior chamber

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Fig. 11.13 Examples of cataracts in the horse. (a) A hypermature juvenile-onset cataract in a 7-month-old American Paint Horse filly. (b) A post-traumatic cataract secondary to a penetrating trauma 1 year previously. There is a focal corneal scar, anterior and posterior synechiae, and corpora nigra avulsion. (c) A hypermature cataract, posterior synechiae, and corpora nigra atrophy secondary to chronic equine recurrent uveitis.

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depth of the horse at the iridocorneal angle is shallow compared to the dog, and the surgeon must be careful to make the entry in one continuous motion without traumatizing the iris. Following entry, the anterior chamber is re-inflated using 1:10 000 adrenaline (epinephrine) for pupil dilatation and vasoconstriction, followed by a high-viscosity viscoelastic agent placed intracamerally. The technique used to complete the anterior capsulorhexis will depend on whether the surgeon plans to implant an IOL. If no IOL is planned, a large anterior capsulorhexis is usually performed. This can be done using Vannas scissors or the can-opener technique with a bent needle or cystotome, followed by intraocular forceps to complete the capsulorhexis. The typical Utrata forceps used for capsulorhexis in small animals is too short to reach the distal aspect of the equine anterior capsule. Longer Utrata forceps or modified equine Utrata-type capsulorhexis forceps are available (Acrivet). If implantation of an IOL is planned, then a controlled circular anterior capsulorhexis must be performed similar to the small animal patient. The optic of the equine IOL is 12–13 mm so the anterior capsulorhexis should be 10–11 mm in diameter. In the author’s (DAW) opinion the easiest and most precise method for performing a circular anterior capsulorhexis in the horse is using the bipolar capsulotomy device that is available with the Alexos anterior segment surgical system (Fig. 11.14). This bipolar capsulotomy probe has been further modified by elongating it for the equine eye (Acrivet). This will allow a precise and perfect axial anterior capsulorhexis to be performed (Fig. 11.15a,b). The anterior capsule, once cut using the bipolar tip, can be removed using modified Utrata-type forceps (Fig. 11.15c). If a bipolar capsulotomy tip is not available, then intraocular scissors and forceps are used to perform a controlled tear circular anterior capsulorhexis. In young foals, the cataractous lens is soft and a onehanded coaxial phacoemulsification is routinely performed. A 30 or 45 phaco tip is used, and the majority of the lens is removed using irrigation/aspiration with only minimal phaco energy required. The author (DAW) prefers to use the pulse setting and short controlled bursts of energy to emulsify the harder nucleus. The standard length phaco tips will not reach the distal aspect of the equine lens (Fig. 11.15d). A longer equine phaco tip is available (Acrivet) and will facilitate access to the far cortex (Fig. 11.15e). If this longer needle is not available, the surgeon should rely on careful aspiration to grasp the cortex that can be reached and to gently pull the associated distal cortex closer until it too may be grasped. The posterior lens capsule in the foal

Fig. 11.14 The standard and the longer equine bipolar capsulotomy tip for anterior capsulorhexis.

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is very thin and the large area of the capsule renders it prone to wave and undulate in the I/A fluid currents. This makes it much easier to inadvertently contact, aspirate, and tear the posterior capsule. To avoid this, the surgeon should perform phacoemulsification in the mid-pupil at the level of the anterior lens capsule with the bevel up as much as possible. Once the majority of the lens has been removed, the handpiece is changed for a curved 0.5 mm I/A handpiece. Again, a longer I/A tip is available (Acrivet) specifically for the equine eye (Fig. 11.15f). If no IOL is to be implanted, a planned posterior capsulorhexis may be advised in foals as posterior capsule opacification is a frequent postoperative sequela. A high-viscosity viscoelastic is used to displace the posterior capsule, and the bipolar capsulotomy probe or intraocular scissors and forceps are used to complete a controlled continuous tear circular posterior capsulorhexis. The corneal incision is then closed using 8-0 absorbable suture in a cruciate or other continuous pattern. The current equine IOL is made of a foldable acrylic material (Acrivet 90VW). There are three different equine IOLs commercially available. The optic size ranges from 12 to 13 mm and the haptic to haptic length from 21 to 24 mm. The diopter power of the current equine IOLs is either 14 D or 21 D, and there remains some discussion regarding the optimum IOL power to achieve emmetropia in the horse. One of the difficulties in determining the optimal IOL power for the horse is the limited number of IOLs that are implanted clinically and the even smaller number of horses that are refracted once the IOL is in place. While calculations of IOL power based on globe measurements are valuable, the final position of the IOL in the eye with respect to the retina has a significant effect on final refraction. It would appear that the current one-piece, plate haptic acrylic equine IOLs, once implanted in the equine eye, tend to sit more anteriorly in the lens capsule than expected. As a result, recent reports suggest an 18 D IOL may be required to achieve emmetropia (McMullen R, personal communication). An 18 D IOL is currently in production (13 mm optic, 24 mm haptic to haptic; Acrivet) and should be available at the time of publication. Currently, no data are available on this IOL in vivo. If an IOL is to be implanted, viscoelastic material is used to expand the capsular bag and vault the anterior chamber. The corneal incision is enlarged to a length of 7–8 mm using corneal section scissors. The IOL is grasped in lens-holding forceps and folded using IOL implantation forceps, both of which are specifically designed for the equine IOL (Acrivet) (Fig. 11.15g). The folded IOL is gently placed through the corneal incision and into the anterior chamber, and the distal haptic is directed through the anterior capsulorhexis and into the lens capsule (Fig. 11.15h). The IOL is rotated 90 and the IOL implantation forceps are slowly opened, allowing the IOL to expand downwards below the forceps and into the lens capsule. An IOL manipulator is used to push the optic away from the corneal incision and direct the proximal haptic into the lens capsule (Fig. 11.15i,j). The corneal incision is closed using an 8-0 absorbable suture in a double continuous pattern. The author prefers to leave the viscoelastic agent in the equine eye to maintain the anterior chamber and keep the IOL and vitreous face from moving anteriorly in the immediate postoperative period.

Phacoemulsification in the horse

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J Fig. 11.15 Phacoemulsification in the horse. (a) Anterior capsulotomy is performed using the modified equine Alexos bipolar capsulotomy tip. (b) The area of anterior capsule to be removed can be visualized as the capsulotomy is completed. (c) The anterior capsulorhexis is completed using curved 17 mm capsulorhexis gripper forceps (Acrivet). (d) The standard length phacoemulsification needle is too short to reach the distal aspect of the equine lens. (e) A longer, modified equine phaco needle is available (Acrivet) and permits easy access to the distal lens nucleus and cortex. (f) A longer, modified equine I/A cannula (Acrivet) is used to grasp and remove the lens cortex. (g) The intraocular lens (IOL) is grasped in equine lens-holding forceps and gently folded using equine lens-implantation forceps (Acrivet). (h) The IOL is rotated and introduced through the corneal incision into the anterior chamber. The distal haptic is placed into the lens bag through the anterior capsulorhexis. (i) An IOL manipulator is used to position the IOL in the capsular bag. (j) Photograph immediately postoperatively following implantation of an Acrivet 90V 14D 13 mm optic, 22 mm haptic IOL. (Photographs 11.15a–c, e and f, courtesy of Dr Brian Gilger.)

For older horses and those whose cataract is secondary to ERU the surgeon should expect the lens to be harder and more difficult to fragment. In these instances, a twohanded approach is preferred. Once the anterior capsulorhexis has been performed and the phaco needle inserted, the irrigation is used to vault the anterior chamber. A 1 mm keratome is then used to make a second limbal entry at the opposite side of the pupil and dorsal corpora nigra to the

first incision. This incision is used to place a nucleus rotator, chopper or manipulator into the anterior chamber (Fig. 11.16). The surgeon now has two instruments in the eye, one temporal and one nasal to the dorsal corpora nigra. The standard two-handed techniques described for small animal phacoemulsification may be used. Use of the second instrument will decrease the surgical time and ultrasonic energy required to remove the cataract. This will also

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Surgical procedures of the lens and cataract

Fig. 11.16 A two-handed technique is used to manipulate and fragment the lens in an older horse. A 45 phaco needle tip enters the eye to the right and a lens rotator to the left of the dorsal corpora nigra.

facilitate access to the large lens, allowing fragments to be stabilized and moved to the phaco tip. Prior to closure, any vitreous strands that have presented into the anterior chamber, especially those that extend into the corneal incision, must be removed or displaced posteriorly using viscoelastic material. Vitreous that is incarcerated into the corneal wound is a risk for tracking of bacteria and secondary endophthalmitis. If the cataract is secondary to ERU, the surgeon should consider the implantation of a sustained-release cyclosporine delivery device at the conclusion of the cataract procedure (see Chapter 12). If fibrin formation is observed at the conclusion of surgery, 75 mg of intracameral tissue plasminogen activator (tPA) may be administered using a 27–30 g irrigation cannula inserted between the sutures. Prior to recovery, a subpalpebral lavage catheter (Mila International, Florence, KY) is placed to facilitate postoperative medication delivery. The horse is recovered in as atraumatic a fashion as possible. Foals are recovered by hand, often in a bedded stall, and older horses are generally recovered using head and tail ropes in a padded recovery room. Protective headgear may be used at the surgeon’s discretion. Postoperative medication includes systemic antibiotics for 3–5 days, systemic flunixin meglumine every 12 h for a week and then used in a tapering dose fashion as required. Topical broad-spectrum antibiotics and prednisolone acetate or dexamethasone are administered every 6 h, and atropine is used as needed to maintain a dilated to mid-dilated pupil. Exercise is restricted for a few weeks. Once the horse can be treated topically using ointments the lavage catheter may be removed. The topical antibiotics are discontinued after 14 days, and the topical and systemic NSAIDs are tapered as indicted by the postoperative uveitis and comfort over the next weeks to months.

bag. After the phacoemulsification procedure, the corneal incision is enlarged to 8–10 mm by corneoscleral scissors, sufficient to accommodate the 8–9 mm diameter optic of the PMMA IOL. If a foldable acrylic IOL is used, the incision length does not usually need to be enlarged. The anterior chamber and capsular bag are reformed with viscoelastic agent to assist with IOL placement into the capsular bag, as well as protect the posterior surface of the cornea. The procedure for IOL placement is presented in a subsequent section. Foldable or soft IOLs can be inserted through the 3–4 mm corneal incision directly into the capsular bag and do not require changes in the original phaco corneal incision length. Once the IOL is properly positioned, the viscoelastic agent is removed from the anterior chamber using the automated I/A handpiece, and the corneal incision apposed with 7-0 to 9-0 simple interrupted or continuous absorbable sutures. IOP of about 10–15 mmHg is restored with the same irrigation solution carefully injected between the corneal sutures.

Intracapsular cataract or lens extraction in small animals In intracapsular lens removal, the entire lens and its capsule are extracted. The firm attachments by the hyaloideocapsular ligaments between the posterior lens capsule and anterior vitreous membrane that occur in dogs, but not in humans, render the intracapsular method more hazardous and decidedly less successful in dogs. As a result, the extracapsular technique and modification with phacoemulsification are the only recommended surgical techniques for the removal of cataracts in dogs and cats. However, the intracapsular method is used in dogs and cats when the lens is displaced partially or completely from its patellar fossa. Often these lenses are completely clear and not cataractous. Lens luxations or displacements are divided into three types, although gradients occur. In subluxated lens, some zonulary attachments are still present (Fig. 11.17). The lens is usually within the patellar fossa, but may be tilted. It does not provide stability to the iris, creating variable amounts of iridodonesis. With loss of all

Intraocular lens implantation in small animals If IOL implantation is planned after phacoemulsification or extracapsular extraction, the IOL is inserted once all of the possible lens material has been removed from the capsular

334

Fig. 11.17 Subluxated and cataractous lens in a dog. Note the medial aphakic crescent.

Removal of the unstable lens in small animals

zonulary attachments, the lens can slide from its patellar fossa into the anterior chamber, usually with its posterior capsule adhered to the anterior hyaloid membrane. The anterior luxated lens may contact the posterior surface of the cornea causing loss of the endothelial cells and variable corneal edema (Fig. 11.18). The displaced lens can also cause iridocyclitis. The adherent formed vitreous can occlude the pupil and prevent aqueous humor from flowing through the pupil into the anterior chamber. As a result, IOP becomes elevated in the posterior segment of the eye, ballooning the basal iris and closing the anterior chamber outflow pathways with formation of temporary-to-permanent peripheral anterior synechiae. The high posterior segment pressure damages the retina and optic disk, probably by impairing regional blood flow and mechanically distorting the scleral lamina cribrosa. IOP measured at the level of the cornea in these eyes is misleading and erroneously low. In some eyes, loss of zonulary attachments to the lens results in the lens displacing or luxating posteriorly into the vitreous. For posterior lens luxations, the anterior vitreous membrane is torn, allowing the lens this posterior route; however, the liquid and/or formed vitreous are displaced into the pupil and anterior chamber. If the displaced vitreous is liquefied, it appears mixed with aqueous humor and is eventually lost; however, if the displaced vitreous is formed and occludes the pupil, it can produce acute elevations in IOP. If the formed vitreous contacts the posterior surface of the cornea, focal edema results. There may also be significant differences in the pathophysiology, clinical findings, and surgical results in dogs with clear lenses and displacements, versus those dogs with hypermature cataracts, lens instability, and LIU. The former patients are primarily at risk for secondary glaucoma and retinal detachments; the latter patients are at higher risk for chronic uveitis, glaucoma, and retinal detachments.

Intracapsular cataract or lens extraction in the horse

Fig. 11.18 Anterior lens luxation in a Smooth Hair Terrier. The entire periphery of the lens is detectable.

Fig. 11.19 Congenital microphakia and anterior lens luxation in a Thoroughbred foal. The condition was bilateral.

Lens subluxation and anterior or posterior luxation is uncommon in the horse and is typically secondary to chronic ERU, glaucoma or trauma. In addition, congenital microphakia and lens luxation occur in the horse (Fig. 11.19). Intracapsular lens extraction has been reported in the horse, but the numbers of cases are few and the outcomes poor. The size of the incision required and the concurrent intraocular diseases make this a high-risk procedure. Eyes with a lens luxation that are comfortable may be monitored and medically managed. Enucleation or an intrascleral prosthesis may be considered in a blind or painful eye with a lens luxation.

Removal of the unstable lens in small animals There is no unanimous agreement among veterinary ophthalmologists for surgical and medical treatment of lens luxations in animals. The primary objective for intracapsular lens removal is to either prevent or treat the not-infrequent secondary glaucoma in these patients. Not surprisingly, the lack of adequate clinical studies fosters these disagreements. One recent report suggests that glaucoma occurs in 73% of eyes with anterior lens luxations, in 43% of eyes with subluxations, and in 38% of eyes with posterior lens luxations. However, the duration of the lens luxation, the condition of the aqueous outflow pathways (as judged by repeated tonometry, tonography, and gonioscopy), and the age and breed of the dogs are important interrelated variables. The absence of medical and/or surgical treatment of eyes with displaced lenses eventually results in secondary glaucoma. Early removal of unstable or displaced lenses, particularly in the terrier breeds, has the highest possibly of success for retention of vision and prevention of secondary glaucoma. Hopefully, additional information can be developed to assist in the clinical management of these patients. As indicated in an earlier section, many displaced lenses in dogs are clear, and detection of the lens within the vitreal space can be difficult. The displaced lens may shift from one compartment to another. For instance, in the surgical

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11

Surgical procedures of the lens and cataract

removal of an anterior lens luxation, after the onset of general anesthesia or surgical entry into the anterior chamber, the lens may gravitate into the vitreous body. A clear posterior lens luxation is difficult to detect in the formed vitreous. Hence, intracapsular lens extractions or lensectomies in dogs and cats are used in the treatment of displaced lenses, whether clear or cataractous, to prevent or treat secondary glaucoma. Vitreous problems during surgery are common, and successful lens removal with intracapsular methods depends on surgical treatment of the concurrent vitreous disorder. General anesthesia combined with neuromuscular blocking agents is recommended for intracapsular lens removal in the dog. Because vitreous presentations are anticipated during or after delivery of the lens, the lack of scleral rigidity in the dog, and the need for optimal exposure of the globe, the neuromuscular blocking agents are most important. As more intraoperative complications are likely to occur with the intracapsular lens extraction procedure with unstable lenses, we prefer to remove these lenses, if possible, by phacoemulsification as this appears to be less traumatic and time-consuming. If necessary, the unstable lenses can be positioned in front of fixation hypodermic needles or other devices inserted at the limbus or through the pars plana.

Operative procedure For intracapsular lens removal, either the peripheral corneal or the limbal approach into the anterior chamber is used. The limbal approach offers the security of two layers of wound apposition and may be advantageous if secondary glaucoma is already present, or if an additional glaucoma surgery procedure is anticipated. The incision is identical to that described in the earlier section on the anterior chamber approach (see Fig. 11.11a–c). It is not unusual that during entry into the anterior chamber, formed vitreous protrudes into the incision. A single pre-placed suture is recommended in the event that extensive vitreous prolapse into the anterior chamber occurs. The pupil size intraoperatively depends on the position of the luxated lens. With anterior luxated lens, 2% pilocarpine is instilled about 1 h preoperatively to try to induce a small pupil during surgery to retain the lens in the anterior chamber. Miotics are not recommended preoperatively to treat an anterior luxated lens, as the miotic pupil is more prone to obstruction with the vitreous, and are administered only Fig. 11.20 Intracapsular lens extraction involves the removal of the entire lens and its capsules, and is generally the procedure for removal of displaced lenses in small animals. Because of the lens–vitreous attachments, vitreal presentation during lens removal usually occurs. (a) The anterior luxated lens may be removed by several techniques, anticipating that formed vitreous will be adherent to the posterior lens capsule. In the first procedure, the anteriorly displaced lens is removed by retracting the limbal incision with thumb forceps, and scooping the anteriorly luxated lens from the anterior chamber with a lens loop. (b) The loop also partially separates the formed vitreous from the posterior lens capsule.

336

A

immediately before lensectomy. Even with the pupil under the influence of 2% pilocarpine, the pupil may dilate during general anesthesia and surgery, allowing the lens to settle in the vitreous. Another fixation technique is to place one or two long 22–25 g hypodermic needles posterior to the anterior luxated lens to attempt to trap the lens within the anterior chamber. Extraction of the anterior luxated lens may use a lens loop, viscoelevation, cryothermy, or an intracapsular forceps. Each method has advantages and limitations. In the lens loop method, the lens loop is carefully manipulated behind the posterior lens surface, and the lens is carefully lifted from the anterior chamber and removed (Fig. 11.20a). The adherent vitreous may be separated from the posterior surface of the lens with the lens loop while simultaneously preventing the lens from migrating into the vitreous. If vitreous is adherent to the posterior lens, it is carefully separated with a cyclodialysis spatula (Fig. 11.20b). Alternatively, viscoelastic material may be placed posterior to the lens and used to elevate the lens and float it out of the corneal incision. If cryotherapy is used, a cryoprobe should use either carbon dioxide or nitrous oxide to provide a temperature of about –25 C at the tip for firm attachment to the lens periphery in the presence of aqueous humor or formed vitreous (Fig. 11.21a). Once adhered to the tip of the cryoprobe, the anterior luxated lens is carefully slid from the anterior chamber. Any vitreous adherent to the posterior surface of the lens is carefully separated with a cyclodialysis spatula (Fig. 11.21b). Care must be taken to avoid contact of the cryoprobe with the cornea or iris. With the intracapsular forceps, the anterior lens capsule is firmly grasped. However, with luxated lenses, the unstable lens may be difficult to grasp, and will shift in an opposite direction. If the first attempt with intracapsular forceps is unsuccessful, either the lens should be stabilized by another forceps for another attempt, or the lens loop or cryotherapy method should be used. After removal of the anterior luxated lens, any formed vitreous within the anterior chamber and pupil is carefully excised using cellulose spears and scissors, or a vitrector (Fig. 11.21c). An air bubble may be injected into the anterior chamber to check for the presence of formed vitreous. Excessive irrigation of the anterior chamber with possible formed vitreous may aggravate the problem, as fluids may also enter the vitreous space and displace additional gel vitreous into the anterior chamber.

B

Removal of the unstable lens in small animals

A

B

C

Fig. 11.21 Another technique for removal of the anterior lens luxation is cryosurgery, with the limbal incision retracted by thumb forceps. (a) The cryoprobe is positioned at the lens equator and after freezing attaches the probe to the lens, the lens is carefully slid from the anterior chamber. Cryoprobe contact with the iris or limbal incision is avoided. (b) The cyclodialysis spatula is used to carefully separate the formed vitreous attachment to the posterior lens capsule during the cryoextraction. (c) Formed vitreous is removed from the anterior chamber using cellulose spears to lift the vitreous for excision with sharp iris scissors parallel to the surface of the iris. No formed vitreous should remain in the anterior chamber and pupil.

For subluxated lenses with loss of all or nearly all zonulary attachments, the pupil is maximally dilated as in cataract surgery (Fig. 11.22a). The lens is removed using any of the three intracapsular methods used for removal of anterior lens luxations. However, if the remaining zonules are still holding the lens within the patellar fossa during entry into the anterior chamber, an extracapsular lens or phacoemulsification removal is preferable. Because of the hyaloideocapsular attachments, vitreous presentation is common, especially through the larger aphakic crescents (Fig. 11.22b). Once the lens is removed, any formed vitreous within the pupil and anterior chamber is carefully removed by cellulose spears and scissors, or preferably a vitrector. An air bubble, injected into the anterior chamber, is the simplest method to detect formed vitreous. Hence, an anterior vitrectomy is often performed after the intracapsular procedure. Removal of the posterior luxated or intravitreal lens requires the cryoprobe or the lens loop to extract the lens from the formed vitreous. These instruments should not contact the retina. Clear lenses are most difficult to differentiate from

A

B

formed vitreous, but are usually located in the most ventral quadrant of the vitreal space. Ultraviolet illumination may assist in their detection. A translucent or opaque lens luxated posteriorly is easily located in the formed vitreous. For removal of intravitreal lenses, cryosurgery with a carbon dioxide or nitrous probe can rapidly freeze in the presence of formed vitreous and firmly adhere to the lens (Fig. 11.23). The lens is carefully maneuvered through the pupil and out the surgical incision. Formed vitreous presentation in the pupil, anterior chamber, and even in the corneal or limbal incision is frequent. All formed vitreous within the anterior chamber, pupil, and anterior vitreal space is carefully removed using cellulose spears and scissors, or preferably a portable vitrector. An air bubble is used to detect any remaining formed vitreous within the anterior chamber. The corneal or limbal incision is apposed with 8-0 to 9-0 simple interrupted absorbable sutures placed 1–1.5 mm apart. These sutures should be placed at two-thirds thickness of the cornea to ensure apposition of all layers of the cornea.

C

Fig. 11.22 For subluxated lenses with some zonulary attachments, the extracapsular and phacoemulsification methods are recommended. Cryoextraction is preferred for the intracapsular removal of the subluxated lens without any significant zonulary attachments. (a) Through a dilated pupil, the cryoprobe is touched to the dorsal anterior lens surface. Once a firm adherence is established, the lens is carefully slid from the patellar fossa and through the limbal incision. (b) The lens–vitreous attachment usually results in formed vitreous presentation behind the subluxated lens. This attachment is carefully separated by the cyclodialysis spatula. No formed vitreous should remain in the anterior chamber and pupil. Removal is by cellulose spears and sharp iris scissors, or a vitrector. (c) Intraoperative photograph showing cryoextraction of a subluxated lens through a clear corneal incision.

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11

Surgical procedures of the lens and cataract

Fig. 11.23 In the removal of the posterior or intravitreal luxated lens, identification of a clear lens in the vitreous space is very difficult. A carbon dioxide or nitrous cryoprobe is touched to the lens periphery (usually in the presence of formed vitreous). Once the freezing and attachment occur, the lens is carefully removed from the vitreal space. At the conclusion of the lens extraction, no formed vitreous is permitted within the pupil or anterior chamber.

Once the last suture has been placed, a small 22–25 g hypodermic needle is carefully placed between two of these sutures, and the anterior chamber is restored with lactated Ringer’s or balanced salt solution until about 10–15 mmHg IOP is achieved. This level of IOP permits integrity of the wound apposition to be ascertained and any leaks detected. If leaks occur, additional 8-0 to 9-0 simple interrupted absorbable sutures are placed in the area. If a limbal- or fornix-based conjunctival flap was used, the conjunctival flap is apposed with a 8-0 to 9-0 simple continuous absorbable suture.

Ciliary sulcus intraocular lens fixation or placement In the early development of IOLs, these devices were placed in several positions within the anterior chamber, pupil, ciliary sulcus, and capsular bag. Eventually, the routine and optimal position for the IOL was established as within the capsular bag; all of the other sites were determined as less satisfactory. Ciliary sulcus placement of IOLs in humans was associated with iridal rubbing, iris irritation, and pigment loss from the posterior iris surface. However, with lens instability, lens luxation, large posterior capsular tears, and large capsular tears in the dog, placement of the IOL within the capsular bag may be impossible and new strategies have evolved to treat these problems. Placement of the IOL by either ab externo or ab interno methods secures the IOL within the ciliary sulcus with non-absorbable nylon sutures, hopefully improves vision (from aphakia), and reduces the frequency of the serious postoperative complications of glaucoma and retinal detachments in the dog. If possible, phacoemulsification is used for these unstable lenses, which permits a smaller incision (and less surgical trauma and time, as well as less postoperative inflammation) and allows the placement of these ciliary sulcus IOLs through a small corneal incision.

338

Lens instability may provide excessive movement of the vitreous base with associated peripheral retinal traction, tears, and eventual detachment. The mechanisms for the genesis of glaucoma in eyes with unstable lenses is more complex; however, the low-grade anterior segment inflammation, collapse of the sclerociliary cleft, and displacement of part to all of the basal iris circumference contribute to reduced aqueous humor outflow and the increase in IOP. In some clinical terrier breed patients with early lens subluxation and limited, if any, displacement, pneumatonography often indicates that impaired conventional aqueous outflow is already present and glaucoma is likely to occur. Hence, when presented with an unstable lens, the extent of the zonulary loss should be determined intraoperatively. If the zonulary loss is less than 180 , the unstable lens can be treated by a capsular ring and an IOL implanted into the capsular bag. If the zonulary loss is in excess of 180 or is too unstable to receive an IOL within the capsular bag, the IOL can be placed in the ciliary sulcus using either the ab externo or the ab interno approach. The ab interno approach requires IOL placement through the anterior chamber, posterior to the iris and in the ciliary sulcus in a blind fashion using a 160 or ‘open sky’ corneal incision. This technique is more difficult than the ab externo approach and has significant postoperative complications. Generally, two rather than three sutures are used to fix the IOL in place and, as a result, accurate IOL positioning is more difficult. Ab externo fixation of IOLs in the ciliary sulcus has been recommended by Wilkie and co-workers (2008) immediately following phacoemulsification of unstable lenses with a small corneal incision and viscoelastic agents already present. Prior to entry into the eye, a ciliary sulcus-designed PMMA (K9400; Ocularvision, Inc., Solvang, CA) or foldable acrylic IOL (Acritec 10V-17W; Acri.Tec, Hennigsdorf, Germany) is prepared by attaching 9-0 nylon sutures (with needles removed) to the haptic eyelets for either a two- or threepoint fixation. The three-point fixation results in less chance of decentralization and IOL tilt postoperatively but is more difficult. If the lens capsules are to remain in situ, an axial posterior capsulorhexis is performed. Viscoelastic is injected from the corneal incision to behind the iris to expand the ciliary sulcus, pushing the iris forward and the anterior vitreous posteriorly. A 2 cm 30 g (0.3 mm) needle is inserted 1.5 mm posterior of the limbus from outside the globe and anterior of the anterior vitreous, to emerge from the corneal incision. For optimal dorsal and ventral fixation suture placement about 180 apart, the ventral needle is placed about 120 from the corneal incision and the dorsal needle is positioned about 60 from the same incision. The IOL with sutures attached to each haptic is carefully passed into the lumen of the ventral needle first, followed by the dorsal suture and needle, respectively. With a 4 mm corneal incision a foldable IOL can be used; for a PMMA or hard IOL the corneal incision must be about 8 mm long. If a PMMA IOL is used, the IOL is carefully slid into the pupil and sulcus; if a foldable acrylic IOL is used, the IOL is introduced into the pupil with the special forceps or injector. The corneal incision is apposed by sutures, the viscoelastic agent removed, and the anterior chamber is reformed. Using the sutures attached to the IOL haptics, the IOL is carefully centered and the ends of both haptic sutures

Intraocular lens implantation

secured to the sclera with a separate 9-0 nylon suture and then covered by small individual conjunctival flaps. In a limited number of patients, the ab externo approach was well tolerated with good centralization of the ciliary sulcus-fixed IOL. Mild anterior vitreal hemorrhage occurred in about 50% of the patients, but resolved within 2 weeks. This technique, combined with phacoemulsification of unstable lenses and foldable IOLs, seems promising for the dog. Additional patients and long-term follow-ups are necessary to determine if the serious postoperative complications of glaucoma and retinal detachments are significantly reduced. Clearly with both the ab externo and ab interno techniques, and the sutures placed through the vascularized posterior iris and in the ciliary sulcus, intraocular hemorrhage is almost certain! Can these fixation sutures be avoided by specially designed IOLs with larger haptics for the aphakic dog without an acceptable and stable capsular bag? Time will tell!

Intraocular lens implantation The technique for IOL implantation in the different animal species is very similar, allowing for the differences in size of the IOL. In general, the most universal IOL for the dog is þ41 D, and for the cat þ53 D; however, the ideal IOL for the horse is still unresolved (IOLs ranged from þ14, þ25 to þ30 D). Most dogs are within 1 D of emmetropia. The majority of the different breeds, as evaluated by retinoscopy, are slightly hyperopic, and astigmatism is infrequent. Accommodation is also limited in dogs; 2–3 D has been proposed. A þ41 D IOL after lensectomy in dogs can re-establish emmetropia in most dogs. The formula to calculate the refractive power of an IOL requires axial length of the globe (by a-scan ultrasonography), corneal curvature (by keratometry), and an equation (such as the Binkhorst formula). As most dogs are within 1 D of emmetropia, a standardized þ41 D IOL is used. After cataract surgery, aphakic dogs are approximately 14 D hypermetropic, although some veterinary ophthalmologists have observed that refractive changes in dogs over several months do not remain static.

A

An IOL may be implanted in the remaining capsular bag after the cataract has been removed by phacoemulsification or by the extracapsular method (Fig. 11.24). Phacoemulsification is preferred for IOL implantation because of the limited size of the anterior capsulectomy (usually 1 mm less than the diameter of the IOL optic). Delivery of the cataractous lens nucleus and cortices in the extracapsular extraction method through an anterior lens capsulectomy of about 7 mm diameter may be difficult or impossible. Forcing the cataractous material through this size of anterior capsulectomy may produce additional tears of the anterior lens capsule, often radiating toward the thinner capsule at the equator. There are many commercially available IOLs for animals (Table 11.4). The preferred dioptric power (D) for the canine IOL is about 41 D. Canine IOLs are designed for insertion through small incision phacoemulsification procedures, but can also be used with extracapsular methods. IOLs with a continuous haptic (ring or disk type) usually require a larger corneal or limbal wound and larger anterior capsulectomy. One-piece IOLs are preferred by most veterinary ophthalmologists. The IOL may be either hydrophilic (preferred) or hydrophobic. The recent introduction of foldable IOLs for dogs using hydrophilic acrylic represents another advancement for cataract surgery (Fig. 11.25). These ‘soft’ IOLs are grasped by either holding and folding forceps, or within an injector, and placed through a small corneal incision (2.7–4.0 mm) into the capsular bag. The technique for placement of the hard IOL in the capsular bag is about the same for the different canine IOLs. The anterior chamber is filled with viscoelastic agent to protect the corneal endothelia and prevent their adherence to the IOL should accidental contact occur. Additional viscoelastic agent may be injected to expand the capsular bag. The corneal incision for extracapsular cataract extraction is more than long enough. The corneal incision used for phacoemulsification is lengthened by corneoscleral scissors to 8 mm to accommodate the 7 mm diameter optic of these IOLs. If foldable or soft IOLs are eventually used in dogs, the same small phaco incision is used. These IOLs are inserted folded through the corneal incision and, once inserted in the capsular bag, are allowed to regain their original shape.

B

Fig. 11.24 Examples of intraocular lens (IOL) implants in the dog. (a) Six-month postoperative appearance of PMMA IOL in the dog. There is minimal posterior capsular opacity. (b) Three-month postoperative appearance of the foldable IOL in an aged dog.

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Table 11.4 Types of intraocular lenses (IOLs) and capsular rings for animals*

IOL dioptric power (D)

IOL overall diameter (mm)

IOL optic diameter (mm)

IOL construction

IOL haptic type and material

IOL manufacturer

41

12, 13, 14

7

1 piece

Foldable; acrylic

Acrivet

41

15

7

3 piece

Foldable; acrylic Nylon

Acrivet

41

12, 14

7

1 piece

Foldable; acrylic

Cara

26, 30

17

7

3 piece

J/C; PMMA

Cutting Edge

40

11,12

6-7

1 piece

Foldable; acrylic

Dioptrix

41

14, 15, 16

6

1 piece

J; PMMA

Domilens

41

15

7

1 piece

C; PMMA

Eye Care

41

14–17

6–7

1 piece

J; PMMA

I-MED Pharma

41

13

6.5

1 piece

Foldable; acrylic

I-MED Pharma

41

12, 14

6

1 piece

Foldable; acrylic

I-MED Pharma

29

10.5

6.5

1 piece

Disk; PMMA

Morcher GmbH

45

13

6.5

1 piece

Disk; PMMA

Morcher GmbH

40, 41

14–17

6–7

1 and 3 piece

J/C/Disk; PMMA

Ocularvision

40

13, 16.5

7

1 piece

PMMA; Sulcus

Ocularvision

41

16–18

6–7

1 piece

Foldable; acrylic

Ocularvision

38, 41, 43

15, 16, 17

7

1 piece

C; PMMA

Storz

42

16

7

3 piece

C (blue); PMMA

Surgidev

30, 36

15

8

1 piece

C; PMMA

Thackray

53.5

12, 13, 14

7

1 piece

Foldable; acrylic

Acrivet

53

16, 18

7, 6–7

1 piece

J; PMMA

Ocularvision

14, 21

12, 13

1 piece

Foldable; acrylic

Acrivet

Dog

Cat

Horse 14, 21

Capsular rings for dogs

Size (mm)

Manufacturer

12.5, 13.5, 15.5

Acrivet

14–16

I-MED Pharma

*IOLs, capsular rings, and manufacturer may vary by country. C and J, haptic shapes; PMMA, polymethylmethacrylate.

With special IOL forceps, the IOL is grasped and the ventral haptic is inserted through the anterior capsulectomy into the ventral capsular bag (Fig. 11.26a). For three-piece IOLs with flexible suture-like haptics, the opposite or dorsal haptic is grasped with a tying forceps, flexed over the optic, and placed into the capsular bag. Once the three-piece IOL is totally in the capsular bag, the IOL is released and the haptics permitted to expand to the limits of the capsular bag.

340

For one-piece IOLs, a lens positioning instrument is used to dial the opposite haptic into the capsular bag by rotating the IOL clockwise. Alternatively, the upper haptic is grasped by forceps and carefully positioned into the dorsal capsular bag. With the entire IOL in the capsular bag, the IOL is rotated clockwise until the haptics are directed medially and laterally (Fig. 11.26b). With the more recent foldable or ‘soft’ IOLs, the original corneal incision, used during phacoemulsification, is not enlarged

Intraocular lens implantation

Fig. 11.25 Foldable or soft intraocular lenses (IOLs) are becoming increasing popular worldwide, and may eventually replace the PMMA type as the most popular IOL for the dog. (a) One type of foldable or soft acrylic IOL for the dog. Foldable IOLs are also available for the cat and horse. (b) For most foldable IOLs, a companion inserter or injector is essential to implant the IOL. (Photographs courtesy of I-MED Animals Health, a division of I-MED Pharma Inc., Dollard des Ormeaux, QC, Canada.)

A

B

as these IOLs can be folded and inserted through the smaller corneal incision and into the capsular bag. Once in the capsular bag, the IOL is allowed to ‘unfold’ and is rotated within the bag for proper positioning and centralization.

Intraoperative complications with IOLs Several intraoperative problems may occur with insertion of IOLs. The most frequent problems include: onset of miosis, limited diameter anterior capsulectomy, irregular margins of the anterior capsulectomy, inadequate separation of the anterior and posterior capsules, vitreous protrusion through a posterior capsular tear, and the expanding vitreous syndrome. Miosis is usually associated with prolonged or traumatic surgery, or perhaps in certain breeds, such as the Miniature Schnauzer. The pupil can usually be enlarged with 1:1000 to 1:10 000 adrenaline (epinephrine) and viscoelastic agent injected into the anterior chamber. If the opening of the anterior capsulectomy is too small, further enlargement with the continuous curvilinear capsulorhexis method is recommended. Intraocular scissors

A

B

Fig. 11.26 Placement of an intraocular lens (IOL) is through the large extracapsular corneal or limbus incision, or through an enlarged (usually to 8–9 mm long) corneal incision after phacoemulsification. The anterior capsulectomy diameter should be 1 mm less than the IOL optic diameter. (a) After the anterior chamber is filled with viscoelastic agent, the lower haptic of the IOL is carefully slid into the capsular bag. (b) The upper haptic of the IOL is positioned into the capsular bag by dialing the IOL (one-piece IOL) clockwise or actually placing the three-piece IOP haptic directly into the capsular bag. Once the IOL is completely in the capsular bag, it is rotated clockwise until the haptics are situated at the 3 and 9 o’clock positions.

can be used to enlarge the diameter of the anterior capsulectomy or provide a regular edge to the existing anterior capsulectomy. Forcing the IOL through a small capsulectomy may result in the development of one or more radial tears. The opening should be about 5–6 mm wide to accommodate the 7 mm diameter optic of most canine IOLs. Viscoelastic agents (sodium chondroitin sulfate–sodium hyaluronate preferred) can be injected into the capsular bag to separate the anterior and posterior lens capsules for IOL insertion. The expanding vitreous syndrome occurs with an intact posterior lens capsule, most often in the brachycephalic breeds. The intravitreal pressure seems to displace the posterior lens capsule forward, occasionally entering the anterior capsulectomy and pupil. Prevention of the expanding vitreous syndrome includes deep general anesthesia, neuromuscular blocking agents, liberal lateral canthotomy, and no direct pressure on the globe (eyelid speculum and stay sutures). The expanding vitreous syndrome may be treated by tamponade with viscoelastic agents, or by temporarily closing the corneal or limbal incision and increasing IOP for 10–15 min to reduce the size of the vitreous. One or multiple radial capsular tears may preclude the implantation of an IOL. These tears may result in displacement or decentralization of the IOL. Sometimes these radial tears can be corrected by incorporation into the capsulectomy. Sometimes an IOL can be implanted perpendicular to the direction of the radial tear or a posterior chamber IOL is sutured into the ciliary sulcus. Often in these cases implantation of the IOL is possible. Posterior capsular tears can occur, especially as the ophthalmologist masters phacoemulsification. Sculpting too deeply or rapidly, as well as higher vacuum levels when phacoemulsification is performed near the posterior lens capsule, are the usually causes. If the vitreous presentation in the posterior capsule tear is minimal, an IOL may still be implanted. If limited vitreous is protruding through a posterior capsular tear, it should be removed by vitrector before IOL placement. Alternatively, a posterior chamber IOL may be sutured in the ciliary sulcus. Posterior capsular opacities are occasionally encountered at the conclusion of surgery that are large enough and within the pupillary axis to cause significant visual impairment after phacoemulsification (and after extracapsular cataract extractions). The opacities are usually fibrotic plaques and

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involve the polar posterior capsule. Some may represent residues of the prenatal hyaloid system. Using intraocular scissors or the continuous curvilinear capsulorhexis method, these polar posterior capsular opacities are carefully removed after all of the cataractous material has been removed. While a slight bulge of vitreous is tolerated, a significant presentation of vitreous is removed carefully by intraocular scissors or vitrector.

Postoperative treatment and management in small animals The major objective of postoperative treatment in small animals is to control and resolve the iridocyclitis. Failure to adequately control the iridocyclitis markedly reduces the success rate for the different types of cataract extractions and lensectomies. Medical treatments for postoperative iridocyclitis are summarized in Box 11.1. With phacoemulsification in the dog the intensity of the postoperative iridocyclitis is considerably less than after the routine extracapsular lens removal techniques. The cat has less intraocular inflammation post-cataract surgery than the dog. The postoperative pupil should be moderately dilated (about 6–8 mm). Changes in the postoperative pupil size are best achieved during the first 7 days. Eventually, posterior synechiae and fibropupillary membranes may fix the pupil size and movements, and hopefully can be avoided. Excessive fibrin usually signals an intense postoperative iridocyclitis. The frequency of topical and systemic corticosteroids and NSAIDs can be temporarily increased. If necessary, within 7–10 postoperative days, 25 mg tPA can be injected into the anterior chamber to dissolve most fibrin clots.

Box 11.1 Recommended postoperative treatments for dogs after cataract extraction and lensectomy (the choice and intensity of medications is based on the individual patient)

Mydriatics: To effect and maintain a moderately dilated and ’moving’ pupil •

Topical 1% tropicamide, 1% atropine or, if necessary, 0.3% scopolamine–10% phenylephrine q6h or adjust to patient

Anti-inflammatory agents: To reduce the iridocyclitis and stabilize the blood–aqueous barrier • • •

Topical 1% prednisolone q6h (can increase to q4h) Topical antiprostaglandin q6h (may also assist with pupil size) Systemic prednisolone 1 mg/kg q12h, gradually taper for 2 weeks. Maintenance dose for 4–6 months. Can substitute with topical or systemic non-steroidal in dogs

Antibiosis • •

Topical antibiotics Systemic amoxicillin: 10–120 mg/kg q12h; continue for 7–10 days

If complications • •

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With elevated IOP: systemic and/or topical carbonic anhydrase inhibitors; topical 0.5% timolol If excessive aqueous humor fibrin: 25 mg tissue plasminogen activator (tPA) injected into the anterior chamber

After lensectomies for displaced lenses, IOP is carefully monitored, as the possibility of postoperative glaucoma is 40–70% within the first 3 months. Medical treatment of elevated IOP in these patients is initially topical 0.5% timolol, and topical and/or systemic carbonic anhydrase inhibitors. Elizabethan collars or other restraint devices are recommended to prevent self-trauma during the first 4–8 weeks. Small animals tend to try to rub these eyes during the first 7–10 days, and immediately after instillations of the ophthalmic solutions. Direct damage may be induced to the lateral canthotomy site, necessitating reapposition with sutures. These eyes should be examined postoperatively daily for the first 5–7 days, then weekly for 2–4 weeks, and then every 2 months until 6 months after surgery. Based on the results of these eye examinations, medications and dosing schedules can be changed. If possible, cataract surgical patients should be examined every 3 or 6 months thereafter.

Postoperative treatment and management in the horse Postoperative medication includes systemic antibiotics for 3–5 days, systemic flunixin meglumine every 12 h for 1 week and then used in a tapering dose fashion as required (Table 11.5). Topical broad-spectrum antibiotics and prednisolone acetate or dexamethasone are administered every 6 h, and atropine is used as needed to maintain a dilated to mid-dilated pupil. Foals undergoing cataract surgery should be monitored for and protected against gastric ulceration. Exercise is restricted for a few weeks. Once the horse can be treated topically using ointments the lavage catheter may be removed. The topical antibiotics are discontinued after 14 days, and the topical and systemic NSAIDs are tapered as indicted by the postoperative uveitis and comfort over the next weeks to months. Unlike small animal patients, most horse owners/trainers will often discontinue topical and systemic medications within a few months Table 11.5 Recommended postoperative treatments for horses after cataract extraction and lensectomy

Medication

Frequency

Topical 1% prednisolone acetate

Every 6 h

Chloramphenicol or triple antibiotics

Every 6 h

1% atropine

Every 6 h

NSAID (such as diclofenac)

Every 6 h

Systemic Omeprazole (to prevent gastric ulcer and erosions)

4 mg/kg PO q24h for 28 days

Flunixin meglumine (NSAID with analgesic, anti-inflammatory and antipyretic effects)

1 mg/kg IV, IM, or PO q12h

Trimethoprim–sulfamethoxazole (TMP–SMS)

15 mg/kg PO q12h

Modified from Brooks DE 2005 Phacoemulsification cataract surgery in the horse. Clinical Techniques in Equine Practice 4:11–20.

Complications of cataract surgery in dogs

following cataract surgery in the horse, and many horses are lost to long-term follow-up.

Postoperative results and complications in small animals The success rates after cataract surgery in dogs have steadily improved during the past 30 years. Current success rates in dogs with extracapsular cataract extractions range from 70% to 90%. The success rates for phacoemulsification for cataracts in dogs are 80–90%. When bilateral cataract extractions are performed by phacoemulsification in dogs, the short-term success rates with restoration of vision in at least one eye are 95–98% As these success rates are projected for 3–5 years, the overall success rates for cataract extractions in dogs decrease about 10–20% because of the development of PCO within the pupil. After phacoemulsification and IOL implantation in humans, the possibility of PCO is 50% within the first postoperative year. Laser treatment of PCO in humans is highly effective. Unfortunately, as discussed in a later section, postoperative PCO is more complex in dogs, as well as thicker and tougher than in humans. Fortunately, with some degree of PCO, dogs still maintain clinical vision. At least two ingredients may improve canine success rates further, both short and long term. First, selection of candidates for cataract surgery should concentrate on dogs with immature cataracts before development to hypermature cataracts and lens-induced iridocyclitis. Secondly, postoperative medical treatments with low levels of topical and systemic corticosteroids or systemic NSAIDs should be continued for 6–12 months or perhaps for the remainder of their lives to impede development and opacification of the posterior capsules. The short-term and long-term postoperative complications and approximate frequencies after extracapsular, phacoemulsification and intracapsular cataract surgeries in dogs are summarized in Boxes 11.2 and 11.3.

Complications of cataract surgery in dogs In this discussion the complications associated with cataract surgery in dogs are divided into: 1) intraoperative; 2) short-term postoperative; and 3) long-term postoperative complications. Box 11.2 Summary of short- and long-term complications after phacoemulsification and extracapsular extraction in dogs •

•

• • • • •

Anterior uveitis: 100% – with posterior synechiae, 40% – with iris bombe´, 1% Corneal edema: – focal, 10% – generalized, 1–2% Transient ocular hypertension: 50% Aphakic glaucoma: 10–15% Hyphema: 2% Posterior capsular opacification: 90–95% Retinal detachments: 5%

Box 11.3 Summary of short- and long-term complications after intracapsular extraction in dogs

Intraoperative • • •

Fibrin accumulation Ciliary body origin hemorrhage Vitreous expansion and prolapse (all vitreous must be removed from the anterior chamber)

Postoperative • • • •

Some refractive error (even with ciliary sulcus intraocular lenses) Greater possibility of wound dehiscence Secondary glaucoma (occurs in 12–16% of dogs) Retinal detachment (second most common complication in dogs; unknown frequency). Consider prophylactic transscleral laser or cryotherapy retinopexy

Intraoperative complications Intraoperative complications during cataract and lens surgery generally require immediate resolution. Some intraoperative complications represent less than adequate patient selection, less than complete medical preparation preoperatively, or unexpected events during surgery. As with any surgical complications, prevention is the most effective treatment. Long-term success of cataract surgery depends, in part, on successful resolution of significant intraoperative complications. Experience with hundreds of cataract surgeries in small animals eventually encompasses most complications.

Inadequate exposure Access to the eye varies among different breeds of dogs, but is more consistent in various breeds of cats. An enophthalmic eye turned ventromedially, with the nictitating membrane protruding, increases the difficulty and the duration of surgery. Differences in prominence of the eye vary among the various breeds of dogs, and the surgeon must take account of these differences. Cataract surgeries in an American Cocker Spaniel and an enophthalmic Akita are different. An enophthalmic globe requires additional patience and time for cataract extraction. Sutures to pull the globe forward and retract the nictitans from the cornea have both benefits and limitations. General inhalational anesthesia supplemented with neuromuscular blocking agents provides the best exposure to the anterior segment and cataract. The lateral canthotomy provides, as much as possible, an improved exposure of the globe without any limitations. The surgical exposure also includes the corneal and limbal incisions. The limbal approach, as it is closer to the center of the globe, can be longer with fewer degrees. The corneal incision for the extra- and intracapsular cataract and lens removals usually extends 140–180 , sufficient to accommodate the largest lens fragment without damage to the corneal endothelia. The fornix-based conjunctival flap offers the benefits of two layers of closure, but without the limitation of decreased observation through the cornea and the inconvenience of limbal apposition, suturing on both sides of the limbal-based conjunctival flap. For phacoemulsification, the optimum peripheral corneal or limbal incision is between

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3 and 4 mm: shorter incisions result in thermal burns and direct damage to the cornea from the phaco needle; longer incisions result in excessive volumes of fluid during the phacoemulsification procedure from leakage around the phaco needle.

Miotic pupil The pupil should be fully dilated for all types of cataract extraction and lensectomies for subluxated and intravitreal lenses. The presence of a small pupil immediately before the onset of general anesthesia should delay surgery for a few days until vigorous mydriatic treatment can produce maximal pupillary dilatation. Dogs less than 1 year old, eyes with hypermature cataracts, and the Miniature Schnauzer breed are more apt to respond incompletely to topical 1% atropine every 6 h preoperatively, and the combination 0.3% scopolamine–10% phenylephrine ophthalmic solutions are recommended for these patients. Intraoperative miosis may occur to various extents, but a 1 mm pupil can stop cataract surgery. Intraoperative miosis is best prevented by intensive preoperative treatment with mydriatics, often for several days. Production of mydriasis in a patient for only 24 h preoperatively may result in a less than well dilated pupil during cataract surgery. Dogs with LIU and hypermature cataracts require mydriatics and topical and sometimes systemic corticosteroids for several weeks before cataract surgery. Preoperative treatment with topical and systemic NSAIDs seems most important in dogs to prevent the release of endogenous prostaglandins that cause an immediate miosis. With even the best preoperative treatments, intraoperative miosis may result. There may be several explanations, including: 1) the corneal or limbal incision required extra time and manipulations; 2) the iris was repeatedly touched with surgical instruments; 3) excessive volumes of irrigation fluids were used during the phacoemulsification procedure; 4) the irrigating solutions for the anterior chamber were cold; and 5) the time for cataract extraction was unduly long. When intraoperative miosis begins, the injection of 1:1000 adrenaline (epinephrine) (the adrenaline (epinephrine) solution should contain no preservatives) can halt and reverse the pupillary constriction sufficiently to permit cataract extraction. An alternative method is to perform four iridal sphincterotomies, incising the pupillary margins of the iris about 2 mm with sharp iris scissors at the 12, 3, 6, and 9 o’clock positions.

Excessive fibrin within the aqueous humor Fibrin may form during cataract surgery, resulting in increased aqueous humor turbidity or formation of fibrinous clots. There may be many reasons for increased aqueous fibrin levels intraoperatively. The increased aqueous humor fibrin may be related to the pre-existing lens-induced iridocyclitis, often in older dogs with hypermature cataracts. The extracapsular cataract surgery may have been excessively long, with the anterior chamber open and IOP at 0 mmHg, resulting in marked breakdown of the blood–aqueous barrier. Hemorrhage may have occurred during the limbal incision, or from the iris or ciliary body during lens removal, resulting in excessive fibrin even after removal of overt blood clots.

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The best treatment for increased levels of fibrin intraoperatively is its prevention with adequate preoperative treatment with topical and systemic corticosteroids and NSAIDs. Monitoring of IOP by tonometry may also aid in reducing this intraoperative complication. Cataract surgeries in dogs with decreased IOP should be delayed until sufficient time and treatment with topical and systemic corticosteroids and NSAIDs permits IOP to return to normal levels preoperatively. All topical and anterior chamber irrigation solutions should have heparin added (1–2 IU/mL) to help discourage intraoperative formation of aqueous humor fibrin. These levels of heparin do not significantly impair hemostasis. Heparin (1000 IU/mL) may also be injected directly into the anterior chamber (0.1–0.2 mL), but should not be used if iridal or ciliary body hemorrhage occurred intraoperatively. Large fibrin clots may be addressed immediately after surgery or within the first week postoperatively by injection of 25 mg tPA into the anterior chamber at the conclusion of surgery, after the corneal or limbal incision has been closed, or within 7 days postoperatively. This method markedly assists in dissolution of excessive aqueous humor fibrin. Fibrin clots in excess of 7–10 days old appear not to respond to tPA treatments.

Intraoperative bacterial contamination Cataract surgery in small animals is performed under aseptic conditions. Nevertheless, bacterial contamination, as recently reported by Taylor et al and Ledbetter et al, occurs in at least 25% of dog eyes, as analyzed by culture of the aqueous humor after cataract extraction. Eyes undergoing phacoemulsification were less often contaminated than eyes undergoing large incision extracapsular extractions. Bacteria recovered from the aqueous humor were unrelated to those recovered from the conjunctival and eyelid surfaces. Contaminated eyes with large incision extracapsular cataract extractions had a greater likelihood of developing postoperative glaucoma. In spite of bacterial contamination of the aqueous humor, these eyes did not develop bacterial endophthalmitis or panophthalmitis. The authors present a convincing argument for use of preoperative and postoperative topical and systemic broad-spectrum antibiotics in small animals.

Aberrant and radial anterior capsule tears Anterior capsulectomies are one of the least predictable steps of cataract surgery in small animals. During the roughly circular capsulectomy for extracapsular or phacoemulsification extraction, the needle-produced can-opener or continuous capsulorhexis may go awry and begins to extend toward the thinner equator capsule or even into the posterior lens capsule, with the resultant presentation of a small portion of formed vitreous. The anterior lens capsule appears thicker in older dogs and those with hypermature cataracts. Focal areas of fibrosis and calcification can affect these anterior lens capsules. As a result, anterior capsulectomies under these circumstances can be less predictable. In these animals, the anterior capsulectomy can be performed initially by incising the majority of the circular capsulotomy with intraocular scissors. The Utrata forceps are then used to carefully grasp and remove the incised portion of the anterior lens capsule.

Complications of cataract surgery in dogs

If radial tears develop during an anterior capsulectomy being performed with extracapsular forceps, needle, or Utrata forceps, the anterior capsulectomy should be stopped and completed with sharp intraocular scissors. Once radial tears start, there is no means available to seal the tear. Radial tears can also develop with small diameter anterior capsulectomies during the extracapsular and phacoemulsification extractions. This is usually associated with a too small anterior capsulectomy or excessive manipulations during the subsequent cataract extraction. Intraocular scissors may be used to enlarge the anterior capsulectomy.

Anterior and posterior capsular opacities The anterior lens capsule may change during cataract formation in dogs, and focal areas of capsular thickening, fibrosis, calcification, and plaque formation may occur. Fortunately, the posterior lens capsule is usually clear in small animals, and not involved in the opacification process except in hypermature, posterior cortical, and capsular cataracts. If the posterior lens capsule appears translucent, or contains a few small opacities, a prudent intraoperative decision is to wait. However, if the axial posterior lens capsule is opaque and quite large, this section of the posterior capsule is excised with intraocular scissors after the cataract removal has been completed. As excision of the central posterior lens capsule results in presentation of formed vitreous of varying amounts, the corneal or limbal incision can be partially closed. The anterior chamber and patellar fossa are filled with viscoelastic agent to maintain the anterior chamber and eventually tamponade the vitreous presentation. With a 22 g hypodermic needle, a hole is made in the posterior lens capsule. With intraocular scissors the opaque posterior lens capsule is carefully excised, and the opaque portion is removed by forceps. Formed vitreous that protrudes is gently excised using cellulose spears and sharp iris scissors, or preferably by vitrector with a guillotine-type cutter. No formed vitreous should remain in front of the posterior capsulectomy. An air bubble can be used to detect any formed vitreous. Once the anterior vitrectomy is complete, the corneal or limbal incision is apposed by sutures, and the anterior chamber reformed with lactated Ringer’s or balanced salt solution and a small air bubble (less than 25% of the anterior chamber). IOLs may be implanted in eyes with posterior lens capsule defects, usually less than 4–5 mm, and without formed vitreous protruding.

Posterior capsular tears The posterior lens capsule in dogs and cats is very thin (about 2–4 mm), and about 4–6% of the thickness of the anterior lens capsule. Tears in the posterior lens capsule are not uncommon in dogs and usually occur during the delivery of the lens during the extracapsular technique, or late in the phacoemulsification technique. There are several contributing events that may be addressed pre- and intraoperatively to prevent development of these tears. Once the eye is opened, the levels of general anesthesia should not change. Lighter general anesthesia increases the tone and effect of the extraocular and orbicularis oculi muscles on the globe. Incorporation of neuromuscular blocking agents into the general anesthesia

protocol for cataract surgery in dogs appears to reduce the possibility of posterior capsule tears intraoperatively. It appears that the loss of extraocular muscle tone decreases pressure on the posterior segment. As a result, with the eye open during extracapsular or phacoemulsification extraction, the posterior lens capsule remains relatively unchanged and does not protrude forward, becoming less concave. Consequently, accidental contact with instrumentation, including the tip of the phaco handpiece, is lessened. Many posterior lens capsule tears occur late in the phacoemulsification procedure secondary to abrupt changes in aspiration, with phaco needles with 30 or 45 bevels, deep manipulations with the phaco tip, and when excessive levels of aspiration are employed. Use of the pulse cycle (intermittent fragmentation), reducing the levels (vacuum) of aspiration, increased magnification, and use of the I/A handpiece (rather than the phaco handpiece) for clearing and polishing the posterior lens capsule are important considerations. IOLs can still be inserted in eyes after posterior lens capsule tears and anterior vitrectomy.

Anterior vitreous presentation Formed vitreous may be presented in the pupil and anterior chamber when zonulary attachments are torn during anterior capsulectomies, when some zonulary attachments have degenerated causing a small subluxation, when the posterior lens capsule is torn during phacoemulsification, during clearing and polishing of the posterior lens capsule, and after posterior capsulectomies for large opaque and axial opacities. Potential vitreous problems may be addressed preoperatively by use of deep general anesthesia and neuromuscular blocking agents to minimize extraocular muscle tone on the posterior segment, mannitol (1–2 g/kg IV) at the onset of general anesthesia for maximum reduction in the size of the vitreous body in 60–90 min, and careful intraocular manipulations. At the conclusion of cataract extraction, any formed vitreous anterior to the posterior lens capsule should be removed by vitrector.

Short- and long-term complications Iridocyclitis and sequelae Comparing the dog, cat, and horse for the relative intensity of postoperative iridocyclitis after phacoemulsification, the dog generally has the most intense inflammation, and cats and horses relatively mild inflammation. Fortunately, topical and occasionally systemic corticosteroids and NSAIDS can effectively control nearly all of these postoperative iridocyclitides. Well over one-half of the postoperative complications may be directly related to the iridocyclitis that is present in many dogs preoperatively. Control of the iridocyclitis is primarily achieved with topical and systemic corticosteroids and NSAIDs. As the inflamed iris adheres to any tissues it contacts, posterior synechiae form between the iris and remaining anterior and posterior lens capsules, and perhaps the anterior vitreous face (Fig. 11.27). A moderately dilated and moving pupil helps control the iridocyclitis, reduces the pain, facilitates vision, and reduces the possibility of posterior synechiae formation. A

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A

B

C

D

Fig. 11.27 Complications after cataract surgery, secondary to iridocyclitis. (a) Iridocyclitis with ventral hypopyon in a dog 4 days after phacoemulsification. (b) Iridocyclitis with excessive fibrin in a dog which developed a gastrointestinal disease postoperatively. The anterior chamber fibrin was successfully treated by intracameral injection of 22 mg tPA. (c) Iridocyclitis with a large posterior synechia at the 12 o’clock position 7 days after extracapsular cataract extraction. Intensive mydriatic therapy may break this posterior synechia if the pupil can be fully dilated. (d) The immediate iridocyclitis after phacoemulsification appears less intense than after the traditional extracapsular extraction methods. Phacoemulsification was performed 9 days earlier in this dog, and the intensity of topical and systemic medications are being reduced.

moderately dilated pupil is also less apt to adhere to itself or become obstructed, reducing the possibility of aphakic glaucoma and iris bombe´.

dogs should be as atraumatic and as short a duration as possible.

Transient IOP hypertension Corneal edema Focal corneal edema is more frequent with corneal incisions. Additional trauma and thermal effects during phacoemulsification may also contribute to the local edema. Generalized corneal edema occurs infrequently, and may be associated with excessive intraocular manipulations and volumes of irrigating fluids during cataract surgery. Corneal edema also occurs more frequently in old dogs, where the number of corneal endothelial cells is marginal. In a report by Gwin and co-workers, routine extracapsular cataract extraction reduced the central and peripheral corneal endothelial cell densities by 34% and 31%, respectively, and the phacoemulsification procedure reduced the central and peripheral corneal endothelial counts by 22% and 13%, respectively. Cataract extractions in old

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Monitoring IOP immediately after cataract extraction by extracapsular or phacoemulsification techniques indicates that 40–50% of the dogs develop elevated IOP that persists for 12–72 h. In the majority of patients no clinical signs develop. In other patients with higher IOPs (30–40 mmHg), the cornea develops generalized edema and mydriasis occurs. Treatment is recommended if IOP exceeds 30 mmHg, and consists of mannitol (1–2 g/kg IV), topical 0.5% timolol, and systemic carbonic anhydrase inhibitors. The intensity of the topical and systemic NSAIDs is increased. Treatment usually spans 2–4 days. The transient rise in IOP appears associated with a temporary decrease in the outflow of aqueous humor rather than pupillary obstructions. Contributing factors appear to be iridocorneal angle debris from cataract surgery, remaining

Complications of cataract surgery in dogs

viscoelastic agent, excessive volumes of irrigation fluids, and, perhaps the most important, the release of endogenous prostaglandins intra- and postoperatively.

Corneal ulcerations Corneal ulcerations, usually central, may develop in some postoperative patients (Fig. 11.28). Contributing factors are as follows: 1) the intensive mydriatic therapy can significantly reduce tear formation rates; 2) self-trauma may occur, especially in dogs without Elizabethan collars; 3) in brachycephalic breeds the impaired and infrequent blinking, and a thin central precorneal tear film may render the central corneal epithelia to damage; and 4) intensive corticosteroid therapy may delay healing of small abrasions that progress to large and central ulcerations. With development of corneal ulceration in postoperative patients, topical and perhaps even systemic corticosteroid therapy is markedly reduced. If tear production is reduced, the intensity of mydriatic therapy is decreased to encourage corneal healing. Tropicamide instillations may be substituted for the 1% atropine drops. Unfortunately, during the time that the intensity of these medications must be decreased, the postoperative iridocyclitis is progressing. The pupil size gradually decreases. These corneal ulcers are often either progressive or slow to heal, and conjunctival grafts may be necessary to treat the ulcer as well as allow the medications for the iridocyclitis to be resumed. Often the iridocyclitis has significantly worsened, and the success rates for these eyes are decreased.

Surgical wound leakage and flat anterior chamber Fortunately, leakage of the corneal or limbal incision is rare. In postoperative cataractous eyes with a narrow to flat anterior chamber and/or hyphema, leakage of the corneal or limbal wound should be suspected. These leaks may occur only when IOP exceeds certain levels or even after repeated barking (and assumed marked elevations in IOP). These

A

leaks can also self-seal, only to recur a few days later. Treatment consists of an additional suture or application of glue in the leaking area.

Hyphema Hyphema or blood in the anterior chamber may be an early or late complication of cataract extractions and lensectomies. Hyphema ranges from small focal blood clots in the ventral anterior chamber to an anterior chamber completely filled with blood. Intraoperative hyphema results from hemorrhage from the scleral aspects of the limbal incision, the iris, and the ciliary body. Incision of the iris results in variable hemorrhage, with large amounts with incisions of its base. Accidental instrument contact with the canine iris may cause limited hemorrhage. Tension on the zonules during anterior capsulectomies may provoke limited hemorrhage from the ciliary body. Contact of the iris and ciliary body with the phaco needle may also produce limited hemorrhage. Most intraoperative hemorrhages are limited and removed at the conclusion of cataract extractions and lensectomies. Hyphema may also occur postoperatively, usually during the first few weeks or later. A leaking corneal or limbal wound produces a narrow-to-flat anterior chamber and ocular hypotony. The low IOP may cause hemorrhage, usually originating from the ciliary body. Sealing the leaking incision with an additional suture or glue results in an immediate rise in IOP, cessation of hemorrhage, and gradual resorption of the blood, usually within 5–7 days. Hyphema that occurs in postoperative cataract extractions and lensectomies several months after surgery is usually secondary to retinal detachments with tearing of retinal blood vessels. IOP in these eyes is usually normal or slightly elevated. If the hyphema obstructs a view of the ocular fundus by ophthalmoscopy, ultrasonography can usually detect the retinal detachment. Surgical treatment of retinal detachments is presented in Chapter 12.

B

Fig. 11.28 Corneal ulcerations are infrequent after cataract surgery in the dog, but if they develop, they must be treated aggressively. Corneal ulceration can also restrict the use of topical and systemic corticosteroids post-cataract surgery. (a) Large but shallow corneal ulceration 2 days after cataract surgery. Cause was apparently a weak and inadequate blink reflex. (b) Suture line infection and leak 3 days after cataract surgery. Topical fluorescein has been applied. Note the anterior chamber is very shallow.

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Postoperative glaucoma or aphakic glaucoma Secondary glaucoma is one of the more common complications of cataract surgery, and is usually related to severe and/ or chronic anterior uveitis (Fig. 11.29). In the largest study to date, 16.8% of the dogs (58 of 346 eyes) developed glaucoma after cataract surgery. Mixed breeds of dogs were at low risk compared to the purebreds. Eyes with IOLs had lower risks, and eyes with hypermature cataracts were at increased risk. The aphakic glaucomas may be divided clinically into two types based on pupil size. With a small pupil, posterior synechiae and inflammatory membrane formation, and any bulging of the vitreous face, an obstruction of the pupil may result. With aqueous humor trapped behind the pupil and in the posterior chamber, iris bombe´ results. This type of acute aphakic glaucoma occurs more often within the first month postoperatively. Over a period of only a few days and with persistence of the iris bombe´, additional changes begin to occur in the anterior chamber. With iris bombe´ and collapse of the anterior chamber, the iridocorneal angle and ciliary cleft close, peripheral anterior synechiae form, and angle-closure glaucoma develops. For aphakic glaucoma with pupillary obstructions, iridotomies are not usually curable in small animals. Because of the concurrent iridocorneal angle closure, the re-establishment of only patency of the pupil is not sufficient therapy. Iridencleisis and anterior vitrectomy are recommended. The second type of aphakic glaucoma occurs with a moderately to fully dilated pupil and occlusion of the outflow channels with inflammatory cells short term, and extensive peripheral anterior synechiae and angle closure long term. Initial medical treatment includes beta adrenergics, carbonic anhydrase inhibitors, and high levels of corticosteroids for the concurrent iridocyclitis. If medical therapy fails to control IOP, an anterior chamber shunt or other filtering glaucoma surgery, or laser cyclophotoablation is recommended.

Fibropupillary and inflammatory membranes/ anterior, intralenticular, and posterior capsular fibrosis Opacities may develop in the pupil after cataract extraction due to fibropupillary membranes, and opacification of the anterior and posterior lens capsules and IOL surfaces.

Fig. 11.29 Postoperative aphakic glaucoma in a dog 4 weeks after extracapsular cataract extraction. The miotic pupil (arrow) eventually became obstructed with the fibropupillary membrane.

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Fibropupillary membranes, associated with postoperative iridocyclitis, may occur following all types of cataract and lens surgery. Development of pupillary opacities may occur soon after lens removal, as with the fibropupillary membranes, or later with opacification of the posterior lens capsule with lens epithelial proliferation and metaplasia. Removal of large central sections of the anterior lens capsule during extracapsular lens extraction or phacoemulsification may reduce these post-surgery opacities. The decline in success rates of cataract surgery in dogs, as measured by restoration of sight, appears directly related to the development and progression of these fibropupillary and posterior lens capsule opacities (Fig. 11.30). Fibropupillary membrane formation starts with postoperative iridocyclitis and the fibrin-rich secondary aqueous humor. Accumulation of inflammatory cells and fibrin within the pupil and on the anterior surface of the iris during the first several days postoperatively forms the scaffolding for the migration of iris pigment cells, lens epithelium, fibrous cells, and even neovascularization. Fortunately, most inflammatory membranes gradually resorb, but some may remain on the surface of the iris and the anterior and/or posterior lens capsules, to distort the pupil shape, form posterior synechiae, and impair vision. The fibropupillary membrane may fuse eventually with the anterior and/or posterior lens capsules to form a combined fibropupillary and lens capsule membrane. Opacification of the anterior and posterior lens capsules follows the different types of cataract extraction, involving parts of the anterior capsule and all of the posterior capsule. In intracapsular lens extractions, where the entire lens and its capsules are removed, pupillary opacification results from development and organization of fibropupillary membranes on the surface of the anterior hyaloid membrane or the secondary vitreous. Postoperative anterior and posterior capsular opacification is also associated with proliferation of the remaining anterior lens epithelium to form Elschnig or crystalline pearls (sometimes called secondary or after cataract), and fibrous and myofibroblastic differentiation by the lens fiber cells. The myofibroblastic cells produce collagen deposits, and contract, producing numerous wrinkles in the posterior lens capsule. Studies in cats also indicate a concurrent development of a pigment-containing membrane arising from the iris root and ciliary body that eventually extends onto the lens capsules. Presence of posterior synechiae and a fixed immobile pupil assist in the migration of the pigment cells onto the lens capsules. Postoperative pupil size in eyes with these opacities can either lessen or worsen effects and assist in the choice of medical and/or surgical corrections. If the pupil is small, these pupil obstructions and opacities may eventually nearly close the pupil and produce blindness. If the pupil is moderately to widely dilated, these opacities are less likely to physically obstruct the pupil and prevent vision. Treatment of fibropupillary membranes and opacification of the lens capsules consists of laser treatment for recently developed cases (Fig. 11.31), and surgical treatment for longterm opacifications. Nd:YAG laser may be used to noninvasively photocoagulate these opacities within several weeks postoperatively. These tough thick fibrous membranes are difficult to incise, excise or treat by laser unless recently

Complications of cataract surgery in dogs

A

B

C

D

E

F

G Fig. 11.30 Fibropupillary membrane and posterior capsule opacifications currently affect almost all dogs after cataract surgery with long-term checkups. (a) An axial posterior capsulectomy was performed for posterior capsular opacification during phacoemulsification 9 months previously. The capsular fibrosis is limited to the remaining anterior and posterior lens capsules. (b) Close-up of posterior capsular opacities (PCO) showing lens cell proliferation as well as pigment immigration, from the posterior iris and possible posterior synechia. (c) Postoperative appearance of PCO in the dog after phacoemulsification and IOL at 6 months. Control of postoperative capsular fibrosis is important for long-term successful cataract surgery and maintenance of vision. (d) Postoperative appearance of PCO in the dog after phacoemulsification and IOL at 1 week. (e) Postoperative appearance of PCO in the dog after phacoemulsification and IOL at 1 month. (f) Postoperative appearance of PCO in the dog after phacoemulsification and IOL at 1 year. (g) Postoperative appearance of PCO in a Siberian Husky after phacoemulsification and IOL at 3 years.

A

B

Fig. 11.31 Laser therapy for PCO in the dog using either the Nd:YAG or the diode laser. (a) Positioning of the dog with the Nd:YAG laser. (b) Immediate appearance after Nd:YAG laser treatment with subsequent enlargement of the pupil and deepening of the anterior chamber. Pupil has increased in diameter by 4.

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formed. The surgeries may include capsulotomy or capsulectomy by a vertical, linear, or oval dissection by intraocular scissors, small needle knife or a hypodermic needle with its bevel partially bent to form a hook and, if indicated, enlargement of the pupil (coreoplasty), often combined with anterior vitrectomy (see Chapter 9). The prevention of capsular fibrosis, rather than its treatment, requires additional attention as the therapy results in the dog are not promising. Since this complication is difficult to treat, prevention may be the key to its resolution. Improved IOL design, as well as coating IOLs with certain drugs, will hopefully significantly reduce the frequency and severity of capsular opacities in the dog in the near future. As reported by Gift et al, the three most important surgical factors contributing to PCO in humans are: 1) cortical cleaving hydrodissection (removal of all possible lens cells, especially within the equator); 2) complete capsular fixation (good contact between the IOL and posterior lens capsule); and 3) a continuous curvilinear capsulorhexis (0.5 mm diameter smaller than the IOL optic). The three most important IOL factors related to PCO in humans are: 1) a biocompatible IOL; 2) maximum IOL optic posterior capsule contact; and 3) IOL geometry (the edge of the IOL presents a physical barrier to cell migration between the IOL optic and the posterior lens capsule). Attention to these facts in humans has led to significant improvements in phacoemulsification surgical techniques and IOL design, and has reduced the frequency of PCO in humans from about 50% to <10%. Their study in the dog concluded that the square-edged foldable acrylic IOLs showed a predisposition toward having less PCO than the round-edged PMMA IOLs in the early postoperative period, but the acrylic IOLs (two different types were studied) had greater persistent hyperopia than the PMMA IOLs. Hopefully more studies in the dog can compare phacoemulsification techniques and additional IOLs, and gradually reduce the frequency and severity of PCO in the dog.

IOL complications Short- and long-term complications of IOLs in small animals are similar to those observed in humans. Frequencies of IOL complications from large clinical studies in dogs are not unlimited. It appears that pseudophakes improve

A

the immediate postoperative vision in dogs, but the aphakic dogs eventually regain their vision, perhaps compensating for objects closer than 1–3 meters. However, IOL implantation is not always successful, and a tilted or decentralized IOL may impair vision in dogs. IOLs cause additional surgery and anesthesia time, and client expense for cataract extractions, although that has not been a significant limitation. Some clients can afford the basic cataract surgeries, but not the additional IOL costs. The implantation of IOLs requires patience and practice. Dogs undergoing cataract surgeries that consume considerable time and where there is difficulty during extraction of the cataract may not be candidates for IOLs. The additional time and manipulations for IOL implantation may result in an intense postoperative iridocyclitis with uncontrollable miosis. For most veterinary surgeons, large posterior capsule tears negate IOL implantation. Dogs with small posterior capsule tears without vitreous presentation may be candidates for IOLs. In humans, certain types of IOL complications have been associated with the different IOL designs and their site of implantation. In dogs, most clinical reports involve IOLs within the capsular bag (Fig. 11.32). Decentralization is probably the most frequent complication in dogs, usually resulting from haptic failure and displacement, excessive fibropupillary membrane, and posterior capsule opacification. If the anterior capsulectomy is large, the IOL may displace forward and cause partial-to-complete pupillary rupture. Many veterinary surgeons prefer the stiffer haptics of the one-piece IOLs for maintenance of the IOL within the capsular bag rather than the three-piece IOLs with prolene haptics. The role of IOLs in the postoperative development of inflammatory fibropupillary membranes and opacification of the posterior lens capsule has not been determined. Surgical removal of pupillary opacities that also include IOLs can be quite difficult.

Retinal detachment Retinal detachments may present at variable times, but usually occur several months following cataract extractions and lensectomies. The majority of these cases appear associated with alterations within the vitreous body that allow the retina to detach and to also be more common in certain breeds of dogs such as the Bichon Frise (Fig. 11.33). Fibrous

B

Fig. 11.32 Complications following IOL placement after cataract surgery. (a) There is anterior displacement of a PMMA IOL from the capsular bag. The upper haptic can be seen protruding from the anterior capsulectomy at the 12 o’clock position into the anterior chamber. (b) A PMMA IOL has become decentered in the dog but is still within the capsular bag. 350

Postoperative results and complications after lens surgery in the horse

Fig. 11.33 Hyphema and vitreal hemorrhage secondary to early retinal detachment following intracapsular lensectomy for lens luxation in a dog.

membranes may develop within the pupil and anterior vitreous, then contract and place traction on the anterior retina. Surgical intervention may be indicated in selected cases to break down the vitreal membranes and to reattach the retina (see Chapter 12). However, the prognosis for restoration of vision in these cases is usually poor (20–30%).

and IOL implantation are relatively recent in the horse, further refinements are predicated. One study by Millichamp and Dziezyc (2000) evaluated outcomes of phacoemulsification in horses and found that corneal edema (56%) and corneal ulcerations (45%) were the most frequently seen complications. Other reported complications were intraoperative posterior capsule tears (28%), intraocular fibrin formation (16%), postoperative ocular hypertension (10%), and endophthalmitis (8%). A more recent retrospective study by Fife et al (2006) looked at visual outcome for cataracts in 55 eyes of 39 horses (Figs 11.34 and 11.35). Of the 55 cataractous eyes, 47 underwent phacoemulsification. At the time of last follow-up (range 1 day to 9 years, median 4 weeks), 38/47 eyes (81%) were sighted, 2/47 eyes (4%) were reported to have poor vision, and 7/47 eyes in six horses (15%) were blind. The most common complications observed were corneal edema (19/47), fibrin (11/47), postoperative hypertension (9/47), dyscoria (9/47), hyphema (7/47), corneal ulceration (5/ 47), retinal detachment (3/47), phthisis bulbi (2/47), and

Postoperative results and complications after lens surgery in the horse Unlike the small animal patient, most horse patients are lost to follow-up shortly after surgery. This, combined with the smaller numbers of equine cataract surgeries performed and the very recent introduction of IOL implantation in the equine eye, makes discussion of long-term success rates and complications more difficult and less accurate in this group. In one study, 38% of eyes were lost to follow-up by 4 weeks following surgery. Complications after lens removal in the horse are similar to those in the dog, but there are also significant differences (Box 11.4). As cataract surgery Box 11.4 Summary of short- and long-term complications after cataract removal and phacoemulsification in horses

Fig. 11.34 The foal seen in Figure 11.13a 2 weeks post-phacoemulsification. There is a large, almost complete anterior and a partial posterior capsulorhexis. The pupil has been pharmacologically dilated and focal corneal edema is observed at the phaco entry wound. The eye is aphakic.

Gelatt (1974) Intraoperative complications included rupture of posterior lens capsule (5.%) and loss of vitreous (2%). Postoperative complications included excessive fibrin in anterior chamber (63%), iridocyclitis (100%), corneal incision edema (80%), posterior synechiae (100%), fixed pupil (75%), opacity of posterior lens capsule (21%), endophthalmitis (7%), and phthisis bulbi (16%). Total horses: 28.

Dziezyc and Millichamp (1990–91) Corneal edema (56%) and corneal ulcerations (45%) were the most frequently seen complications. Other reported complications were intraoperative posterior capsule tears (28%), intraocular fibrin formation (16%), postoperative ocular hypertension (10%), and endophthalmitis (8%). Total horses: 12.

Fife et al (2006) Complications included corneal edema (40%), fibrin (23%), postoperative hypertension (19%), dyscoria (19%), hyphema (15%), corneal ulceration (11%), retinal detachment (6%), phthisis bulbi (4%), and enucleation (4%). Total horses: 39.

Fig. 11.35 An adult horse 2 years after phacoemulsification. A complete anterior and a partial posterior capsulorhexis were performed. There is a focal corneal scar and a few bands of fibrosis in the area of the posterior lens capsule. The eye is aphakic. 351

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Fig. 11.36 A foal 1 year following phacoemulsification. There is significant posterior capsule opacification. A posterior capsulorhexis was not performed in this eye at the time of surgery.

enucleation (2/47). Of the eyes with follow-up of greater than 1 year, 2/13 had posterior capsule opacification (Fig. 11.36). When visual outcome was assessed, 98% of the eyes were sighted immediately postoperatively. The overall long-term visual outcome was 76% (13/17 eyes) at 1 year. When examined by etiology of cataract, the long-term visual outcome with juvenile-onset cataracts was 88% (7/8), traumatic 100% (4/4), and uveitis 100% (2/2) at 1 year following surgery. The success of the juvenile cataracts was reduced to 64% (7/11) at 1 year when eyes with concurrent anterior segment dysgenesis (ASD) were included. This would suggest that foals with cataracts and ASD are poor candidates for cataract surgery and long-term vision (Fig. 11.37). None of the eyes in either of these studies received an IOL. A final point to consider when discussing visual outcome in the equine cataract patient is related to visual soundness. Just because a horse has a menace response and refracts to emmetropia, does not guarantee the horse to be visually sound. The specific use of the horse and safety of both the horse and the owner/rider must be considered. Unlike a dog or cat which often returns to a safe and restricted environment, the horse may be expected to perform activities such as jumping or trail riding in an unfamiliar environment. This may be further complicated by a rider, whose safety must be considered. With current techniques and IOLs it is still wise to consider that a horse following a successful cataract surgery is visually unsound for the purpose of visually challenging activities. In addition, foals with congenital or juvenile cataracts are best considered unsound for the purpose of breeding.

Fig. 11.37 A foal with congenital cataract, microphthalmos, ectropion uvea, and anterior segment dysgenesis.

The future and challenges of cataract and lens surgery in animals Cataract surgery in both human and animal ophthalmology continues to be identified with the specialty, and undoubtedly is the most important intraocular surgery performed in the dog. When one observes and analyzes the advances in cataract surgery in the dog from the 1960s to the present, one cannot be but most impressed! Nevertheless, there are still many opportunities to further increase the chance of the restoration of vision in our cataract patients. The role of LIU and its control is still a considerable challenge. Preexisting LIU in dogs increases the likelihood of postoperative glaucoma and retinal detachment. If these significant postoperative complications develop, the cataract surgery success rate falls accordingly. Capsular opacities, developing on the anterior and posterior lens capsule and within the pupil, gradually restrict vision and adversely affect long-term success rates after cataract surgery. Improvements in patient selection (LIU; operate on patients at an earlier stage of cataract formation), improved medical and surgical procedures to remove all lens material from the capsular bag, and improved IOL designs and coating with certain drugs are, at least, some possibilities to enhance our long-term success rates for canine surgery. Further studies will decide the correct IOL power for the equine eye. In addition, as more IOLs are implanted in the horse, evaluation of the long-term outcome with the equine IOL in both foals and adult horses will be published.

Further reading Small animals: displaced lenses Breaux CB, Dugan SJ, Siegel AM, Schreiner T: Retrospective study of intracapsular extraction in the dog, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 29, 2007. Curtis R, Barnett KC, Lewis SJ: Clinical and pathological observations concerning the

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aetiology of primary lens luxation in the dog, Vet Rec 112:238–246, 1983. Glover TL, Davidson MG, Nasisse MP, Olivero DK: The intracapsular extraction of displaced lenses in dogs: a retrospective study of 57 cases (1984–1990), J Am Anim Hosp Assoc 31:77–81, 1995. Gwin RM, Samuelson DA, Powell NG, Gelatt KN, Wolf ED, Merideth R: Primary

lens luxation in the dog associated with lenticular zonule degeneration and its relationship to glaucoma, J Am Anim Hosp Assoc 18:485–491, 1982. Knight GC: The extraction of the dislocated and the cataractous crystalline lens of the dog with the object of preserving some useful vision, Vet Rec 69:318–321, 1957.

Further reading

Stuhr CM, Forte C: Intracapsular lensectomy with sulcus intraocular lens implantation in dogs with primary lens luxation or subluxation, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 77, 2007. Wilkie DA, Stone SG, Gemensky-Metzler AJ, Basham CR, Norris KN: Canine lens instability surgical option – part 2: a modified ab externo approach for suture fixation of an intraocular lens implant in the dog [abstract], Vet Ophthalmol 10:409, 2007. Wilkie DA, Gemensky-Metzler AJ, Stone SG, et al: A modified ab externo approach for suture fixation of an intraocular lens implant in the dog, Vet Ophthalmol 11:43–48, 2008.

Small animals: cataract surgery Allgoewer I, Heinrich CL, Renwick PW, et al: Spontaneous posterior lens rupture associated with rapidly progressive cataracts in non-diabetic dogs, Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 96, 2008. Bagley LH, Lavach JD: Comparison of postoperative phacoemulsification results in dogs with and without diabetes mellitus: 153 cases (1991–1992), J Am Vet Med Assoc 205:1165–1169, 1994. Biros DJ, Gelatt KN, Brooks DE, Kubilis PS, Andrew SE, Strubbe DT, Whigham HM: Development of glaucoma after cataract surgery in dogs: 220 cases (1987–1998), J Am Vet Med Assoc 216:1780–1786, 2000. Blody KL: Current status of canine cataract surgery, Seminars in Veterinary Medicine and Surgery 3:62–68, 1988. Colitz CMH, Malarkey D, Dykstra MJ, McGahan MC, Davidson MG: Histologic and immunohistochemical characterization of lens capsule plaques in dogs with cataracts, Am J Vet Res 61:139–143, 2000. Davidson MG, Nasisse MP, Rusnak IM, Corbett WT, English RV: Success rates of unilateral vs bilateral cataract extraction in dogs, Vet Surg 19:232–236, 1990. Davidson MG, Nasisse MP, Jamieson VE, English RV, Olivero DK: Phacoemulsification and intraocular lens implantation: a study of surgical results in 182 dogs, Progress in Veterinary and Comparative Ophthalmology 1:233–238, 1991. Dziezyc J: Cataract surgery: current approaches, Vet Clin North Am 20:737–754, 1990. Gaiddon JA, Lallement PE, Peiffer RL: Implantation of a foldable intraocular lens in dogs, J Am Vet Med Assoc 216:875–877, 2000. Gerardi JG, Colitz CMH, Dubielzig RR, Davidson MG: Immunohistochemical analysis of lens epithelial-derived membranes following cataract extraction in the dog, Vet Ophthalmol 2:163–168, 1999.

Gilger BC: Phacoemulsification: technology and fundamentals, Vet Clin North Am 27:1131–1141, 1997. Gilger BC, Davidson MG, Colitz CMH: Experimental implantation of posterior chamber prototype intraocular lenses for the feline eye, Am J Vet Res 59:1339–1343, 1998. Glover TD, Constantinescu GM: Surgery for cataracts, Vet Clin North Am 27:1143–1173, 1997. Glover TL, Davidson MG, Nasisse MP, Olivero DK: The intracapsular extraction of displaced lenses in dogs: a retrospective study of 57 cases (1984–1990), J Am Anim Hosp Assoc 31:77–81, 1995. Hendrix DV, Nasisse MP, Cowen P, Davidson MG: Clinical signs, concurrent diseases, and risk factors associated with retinal detachments in dogs, Progress in Veterinary and Comparative Ophthalmology 3:87–91, 1993. Isard PF, Rosolen S, Le Gargasson JF: A new foldable injectable intraocular lens designed for the canine eye: the pfi/c 2000. Preliminary results of surgical technique, Invest Ophthalmol Vis Sci Abstract 41:S487, 2000. Lane SS, Lindstrom RL: Viscoelastic agents: formulation, clinical applications, and complications, Semin Ophthalmol 7:253–260, 1992. Ledbetter EC, Millichamp NJ, Dziezyc J: Microbial contamination of the anterior chamber during cataract phacoemulsification and intraocular lens implantation in dogs, Vet Ophthalmol 7:327–334, 2004. Liesegang TJ: Viscoelastics, Int Ophthalmol Clin 33:127–147, 1993. Linebarger EJ, Hardten DR, Shah GK, Lindstrom RL: Phacoemulsification and modern cataract surgery, Surveys in Ophthalmology 44:123–147, 1999. Lynch GL, Esson D, Evans P: Phacoemulsification surgery for juvenileonset feline cataracts, Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 97, 2008. Maggio F, Pirie CG, Pizzirani S: ‘Stop and chop’ phacoemulsification technique for canine cataracts using a single incision and Akahoshi phaco prechopper, Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 94, 2008. Magrane WG: Cryosurgical lens extraction: uses and limitations, J Small Anim Pract 9:71–73, 1968. Magrane WG: Cataract extraction: a follow-up study of 104 cases, J Small Anim Pract 1:163–170, 1969. Magrane WG: Cataract extraction; A follow-up study (429 cases), J Small Anim Pract 10:545–553, 1969. Miller PE, Lannek EB: Glaucoma following phacoemulsification cataract surgery in dogs: a case-controlled retrospective study [abstract], Proceedings of the American

College of Veterinary Ophthalmologists 30:57, 1999. Miller PE, Stanz KM, Dubielzig RR, Murphy CR: Mechanisms of acute intraocular pressure increases after phacoemulsification lens extraction in dogs, Am J Vet Res 58:1159–1165, 1997. Miller TR, Whitley RD, Meek LA, Garcia GA, Wilson MC, Rawls BH: Phacofragmentation and aspiration for cataract extraction in dogs: 56 cases (1980–1984), J Am Vet Med Assoc 190:1577–1580, 1987. Nasisse MP, Glover TL: Surgery for lens instability, Vet Clin North Am 27: 1175–1192, 1997. Nasisse MP, Davidson MG, English RV, Roberts SM, Newman HC: Neodymium: YAG laser treatment of lens extractioninduced pupillary opacification in dogs, J Am Anim Hosp Assoc 26:275–281, 1990. Nasisse MP, Davidson MG, Jamieson VE, English RV, Olivero DK: Phacoemulsification and intraocular lens implantation: a study of technique in 182 dogs, Progress in Veterinary and Comparative Ophthalmology 1:225–244, 1991. Nelms SR, Davidson MG, Nasisse MP, Glover TL: Comparison of corneal and scleral surgical approaches for cataract extraction by phacoemulsification and intraocular lens implantation in normal dogs, Veterinary and Comparative Ophthalmology 4:53–60, 1994. Rooks RL, Brightman AH, Musselman EE, Helper LC, Magrane WG: Extracapsular cataract extraction: an analysis of 240 operations in dogs, J Am Vet Med Assoc 187:1013–1015, 1985. Rubin LF, Gelatt KN: Spontaneous resorption of the cataractous lens in dogs, J Am Vet Med Assoc 152:139–153, 1968. Schellini SA, Creppe MC, Grego´rio EA, Padovani CR: Lidocaine effects on corneal endothelial cells ultrastructure, Vet Ophthalmol 10:239–244, 2007. Sigle KJ, Nasisse MP: Long-term complications after phacoemulsification for cataract removal in dogs: 172 cases (1995–2002), J Am Vet Med Assoc 228:74–79, 2006. Stone SG, Wilkie DA, Gemensky-Metzler AJ: Canine lens instability options – part 1: capsular tension ring use for phacoemulsification and intraocular lens placement [abstract], Vet Ophthalmol 10:407, 2007. Stone SG, Wilkie DA, Gemensky-Metzler AJ: Canine capsular tension ring safety and complication rates in eyes with stable and unstable lenses [abstract], Vet Ophthalmol 11:426, 2008. Spiess BM, Bolliger J, Ru¨hli MB: Radiofrequency anterior capsulotomy to facilitate phacoemulsification and intraocular lens implantation, Veterinary and Comparative Ophthalmology 6:233–236, 1996. Spreull JSA, Chawla HB, Crispin SM: Routine lens extraction for the treatment of cataract

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in the dog, J Small Anim Pract 21:535–553, 1980. Startup FG: Cataract surgery in the dog – I. history and review of the literature, J Small Anim Pract 8:667–670, 1967. Startup FG: Cataract surgery in the dog – II. published results, J Small Anim Pract 8:671–674, 1967. Startup FG: Cataract surgery in the dog – III. factors responsible for failure, J Small Anim Pract 8:675–679, 1967. Startup FG: Cataract surgery in the dog – VII. cryoextraction, J Small Anim Pract 8:693–701, 1967. Startup FG: Cataract surgery in the dog, J Small Anim Pract 10:457–460, 1969. Stiles J, Didier E, Ritchie B, Greenacre C, Willis M, Martin C: Encephalitozoon cuniculi in the lens of a rabbit with phacoclastic uveitis: confirmation and treatment, Veterinary and Comparative Ophthalmology 7:233–238, 1997. Taylor MM, Kern TJ, Riis RC, McDonough PL, Erb HN: Intraocular bacterial contamination during cataract surgery, J Am Vet Med Assoc 206:1716–1720, 1995. van der Woerdt A, Wilkie DA, Myer CW: Ultrasonographic abnormalities in the eyes of dogs with cataracts: 147 cases (1986–1992), J Am Vet Med Assoc 203(6):838–841, 1993. Warren C: Phaco chop technique for cataract surgery in the dog, Vet Ophthalmol 7: 348–351, 2004. Wilkie DA, Colitz C: Surgery of the canine lens. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 888–931. Wilkie DA, Wolf ED: Cataract surgery. In Bojrab MJ, editor: Current Techniques in Small Animal Surgery, ed 3, Philadelphia, 1990, Lea and Febiger, pp 98–104. Wilkie DA, Gemensky-Metzler AJ, Colitz CMH, et al: Canine cataracts, diabetes mellitus and spontaneous lens capsule rupture: a retrospective study of 18 dogs, Vet Ophthalmol 9:328–334, 2006. Williams DL, Heath MF: Prevalence of feline cataract: results of a cross-sectional study of 2000 normal, 50 cats with diabetes and 100 cats following dehydrational crises, Vet Ophthalmol 9:341–349, 2006.

Horse and special species: cataract surgery Beech J, Irby I: Inherited nuclear cataracts in the Morgan horse, J Hered 76:371–372, 1985. Beech J, Aguirre G, Gross S: Congenital nuclear cataracts in the Morgan horse, J Am Vet Med Assoc 184:1363–1365, 1984. Brooks DE: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 3, Philadelphia, 1999, Lippincott, Williams and Wilkins, pp 1053–1116. Brooks DE: Phacoemulsification surgery in the horse, Current Techniques in Equine Practice 4:11–20, 2005. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor:

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Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274. Cooley PL: Phacoemulsification in a clouded leopard (Neofelis nebulosa), Vet Ophthalmol 4:113–118, 2001. Cutler TJ, Brooks DE, Andrew SA, et al: Visual outcome in young horses undergoing phacoemulsification [abstract], Vet Ophthalmol 4:291, 2002. Dziezyc J: Intraocular surgery. In Auer JA, editor: Equine Surgery, Philadelphia, 1992, WB Saunders, pp 648–654. Dziezyc J: Intraocular surgery. In Auer JA, Stick JA, editors: Equine Surgery, ed 2, Philadelphia, 1999, WB Saunders, pp 492–496. Dziezyc J, Millichamp NJ, Keller C: Use of phacofragmentation for cataract removal in horses: 12 cases (1985–1989), J Am Vet Med Assoc 198:1774–1778, 1991. Farrall H, Handscombe MC: Follow-up report of a case of surgical aphakia with an analysis of equine visual function, Equine Vet J 10 (Suppl 2):91–93, 1990. Fife TM, Gemensky-Metzler AJ, Wilkie DA, et al: Clinical features and outcomes of phacoemulsification in 39 horses: a retrospective study (1993–2003), Vet Ophthalmol 9:361–368, 2006. Frazer AC: An operation for the treatment of congenital bilateral total cataracts in a Thoroughbred colt, Vet Rec 73:587–591, 1961. Gelatt KN: The eye. In Equine Medicine and Surgery, ed 2, Wheaton, IL, 1972, American Veterinary Publications, pp 399–432. Gelatt KN: The special sense organs – eye and eyelid. In Oehme FW, Prier JE, editors: Textbook of Large Animal Surgery, Baltimore, 1974, Williams and Wilkins, pp 546–574. Gelatt KN, Kraft WE: A technique for aspiration of cataracts in young horses, Vet Med 64:415–421, 1969. Gelatt KN, Myers VS, McClure JR: Aspiration of congenital and soft cataracts in foals and young horses, J Am Vet Med Assoc 165:613–616, 1974. Grahn BH, Cullen CL: Equine phacoclastic uveitis: the clinical manifestations, light microscopic findings, and therapy of 7 cases, Can Vet J 41:376–382, 2000. Hardman C, McIlnay TR, Dugan SJ: Phacofragmentation for morgagnian cataract in a horse, Vet Ophthalmol 4:221–225, 2001. Matthews AG: The lens and cataracts, Vet Clin North Am Equine Pract 20:393–415, 2004. Matthews AG, Barnett K: Lens. In Barnett KC, Crispin SM, Lavach JD, Matthews AG, editors: Equine Ophthalmology, ed 2, Edinburgh, 2004, Saunders, pp 165–182. McLaughlin SA, Whitley RB, Gilger BC: Diagnosis and treatment of lens diseases, Vet Clin North Am 8:575–585, 1992. Millichamp NJ, Dziezyc J: Cataract surgery in horses [abstract], Invest Ophthalmol Vis Sci 37:S763, 1996.

Millichamp NJ, Dziezyc J: Cataract phacofragmentation in horses, Vet Ophthalmol 3:157–164, 2000. Ramsey DT, Ewart SL, Render JA, Cook CS, Latimer CA: Congenital ocular abnormalities of Rocky Mountain horses, Vet Ophthalmol 2:47–59, 1999. Riis RC: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, Philadelphia, 1981, Lea and Febiger, pp 569–605. Scotty NC, Cutler TJ, Brooks DE, Ferrell E: Diagnostic ultrasonography of equine lens and posterior segment abnormalities, Vet Ophthalmol 7:127–139, 2004. Van Kruiningen HJ: Intracapsular cataract extraction in the horse, J Am Vet Med Assoc 145:773–777, 1964. Whitley RD: Diseases and surgery of the lens. In Gilger BC, editor: Equine Ophthalmology, St Louis, 2005, Saunders, pp 269–284. Whitley RD, Moore CP, Slone DE: Cataract surgery in the horse: a review, Equine Vet J 2 (Suppl 2):127–134, 1983. Whitley RD, Meek LA, Millichamp NJ, et al: Cataract surgery in the horse: 6 cases, Equine Vet J 13(Suppl 3):85–90, 1990.

Intraocular lenses and phacoemulsification instruments Carlson AN, Stewart WC, Tso PC: Intraocular lens complications requiring removal or exchange, Surveys in Ophthalmology 42:417–440, 1998. Davidson MG, Murphy CJ, Nasisse MP, et al: Refractive state of aphakic and pseudophakic eyes of dogs, Am J Vet Res 54:174–177, 1993. Fine H: The chip and flip phacoemulsification technique, J Cataract Refract Surg 17:366–371, 1991. Gaiddon J, Rosolen SG, Steru L, Cook CS, Peiffer RL: Use of biometry and keratometry for determining optimal power for intraocular lens implants in dogs, Am J Vet Res 52:781–783, 1991. Gilger BC, Whitley RD, McLaughlin SA, Wright JC, Boosinger TR: Clinicopathologic findings after experimental implantation of synthetic intraocular lenses in dogs, Am J Vet Res 54:616–621, 1993. Gilger BC, Whitley RD, McLaughlin SA, Wright JC, Boosinger TR: Scanning electron microscopy of intraocular lenses that had been implanted in dogs, Am J Vet Res 54:1183–1187, 1993. Gilger BC, Davidson MG, Colitz CMH: Experimental implantation of posterior chamber prototype intraocular lenses for the feline eye, Am J Vet Res 59:1339–1341, 1998. Gimbel HV: Divide and conquer nucleofractis phacoemulsification: development and variations, J Cataract Refract Surg 17:281–291, 1991. McMullen RJ, Gilger BC: Keratometry, biometry and prediction of intraocular lens power in

Further reading the equine eye, Vet Ophthalmol 9:357–360, 2006. McMullen RJ, Salmon JH, Davidson MG, Gilger BC: In vitro and in vivo evaluation of an equine intraocular lens, Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 62, 2008. Mello MO, Scott IU, Smiddy WE, Flynn HW, Feuer W: Surgical management and outcomes of dislocated intraocular lenses, Ophthalmology 107:62–67, 2000. Nagahara KP: Phaco chop. In Fishkind WJ, editor: Complications in Phacoemulsification: Avoidance, Recognition and Management, New York, 2002, Thieme, pp 94–99. Nasisse MP, Glover TL, Davidson MG, Nelms S, Sullivan T: Technique for suture fixation of intraocular lenses in dogs, Veterinary and Comparative Ophthalmology 5:146–150, 1995. Olivero DK, Davidson MG, Nasisse MP, Dykstra MJ: Canine intraocular lens quality control: light and scanning electron microscopic evaluation, Progress in Veterinary and Comparative Ophthalmology 3:98–105, 1993. Olson RJ, Morgan KS, Kolodner H: The Shearing intraocular lens, Ophthalmology 87:668–672, 1980. Peiffer RL, Gaiddon J: Posterior chamber intraocular lens implantation in the dog: results of 65 implants in 61 patients, J Am Anim Hosp Assoc 27:453–462, 1991. Simpson HD: Intra-ocular plastic lens implantation in canine cataract surgery, North Am Vet 37:573–581, 1956.

Townsend WM, Jacobi S, Peterson-Jones SM, Bartoe JT: Phacoemulsification and implantation of a þ14 diopter foldable intraocular lens in an adult horse, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 79, 2007. von Plettenberg DG, Do¨rner M, Hoffs B: Nachstarfreie kataraktextraktion mit geplanter virektomie und implantation einer transkeral sulkusfixierten hinterkammerlinse bein hund, Kleinterpraxis 36:29–36, 1991. Watson JL, Bras ID, Webb TR, et al: A quantitative comparison of posterior capsular opacification in canine patients following intraocular implantation with polymethylmethacrylate and foldable acrylic lense, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 78, 2007. Wilkie DA, Gemensky-Metzler AJ, Stone SG, et al: A modified ab externo approach for suture fixation of an intraocular lens implant in the dog, Vet Ophthalmol 11:43–48, 2008.

Postoperative complications: all species Apple DJ, Solomon KD, Tetz MR, et al: Posterior capsule opacification, Surveys in Ophthalmology 37:73–116, 1992. Bras ID, Colitz CMH, Saville WJA, et al: Posterior capsular opacification in diabetic and nondiabetic canine patients following cataract surgery, Vet Ophthalmol 9:317–327, 2006.

Champion R, McDonnell PJ, Green WR: Intraocular lenses. Histopathologic characteristics of a large series of autopsy eyes, Surveys in Ophthalmology 30:1–32, 1985. Cobo LM, Ohsawa E, Chandler D, Arguello R, George G: Pathogenesis of capsular opacification after extracapsular cataract extraction: an animal model, Ophthalmology 91:857–863, 1984. Gift BW, English RV, Nadelstein B, Weigt AK, Gilger BC: Comparison of capsular opacification and refractive status after placement of three different intraocular lens implants following phacoemulsification and aspiration of cataracts in dogs, Vet Ophthalmol 12:13–21, 2008. Gwin RM, Warren JK, Samuelson DA, Gum GG: Effects of phacoemulsification and extracapsular lens removal on corneal thickness and endothelial cell density in the dog, Invest Ophthalmol Vis Sci 24:227–236, 1983. Lynch GL, Brinkis JL: The effect of elective phacofragmentation on central corneal thickness in the dog, Vet Ophthalmol 9:303–310, 2006. Nasisse MP, Davidson MG: Surgery of the lens. In Gelatt KN, editor: Veterinary Ophthalmology, ed 3, Baltimore, 1999, Lippincott, Williams and Wilkins, pp 827–856. Nasisse MP, Davidson MG, English RV, Roberts SM, Newman HC: Neodymium: YAG laser treatment of lens extractioninduced pupillary opacification in dogs, J Am Anim Hosp Assoc 26:275–281, 1990.

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CHAPTER

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Vitreoretinal surgery Kirk N. Gelatt1, Bernhard M. Spiess2 and Brian C. Gilger2 1

Small animals; 2Large animals and special species

Chapter contents Introduction

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Surgical anatomy

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Surgical pathophysiology

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Types of retinal detachment

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Types of vitreoretinal surgery

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Clinical evaluation of retinal detachments

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Instrumentation for vitreoretinal surgeries

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Introduction Diseases of the posterior segment, including those affecting the vitreous, retina, choroid, and optic disk, are common in small animals. These diseases may be of congenital, traumatic, inflammatory, degenerative, and neoplastic origin. Diseases of the vitreous affect both cats and dogs, but are more frequent in dogs. Vitreal conditions include persistence of the primary hyaloid vasculature (persistent hyperplastic primary vitreous (PHPV)), vitreal syneresis (liquefaction of the vitreous), asteroid hyalosis (presence of numerous white spherical opacities suspended in the vitreous), vitreal hemorrhage, and vitreal herniation through the pupil. Presentation of vitreous in the pupil and anterior chamber is usually associated with lens displacement and lensectomy, and cataract removal with rupture of the posterior lens capsule and anterior vitreous membrane. Neoplasms, pigment, parasites, foreign bodies, and cysts also affect the vitreous. For these vitreal diseases, surgery may be indicated for diagnosis, or treatment of the vitreal pupillary herniation into the anterior chamber. The removal of diseased vitreous and traction bands in the repair of retinal detachments will be presented in the section on retinal surgeries. Congenital and degenerative retinopathies are among the more frequently diagnosed clinical disorders in dogs, and the majority of these retinopathies appear inherited. Inflammations of the retina and choroid in dogs are frequent, and often associated with systemic infections. In cats, congenital

Preoperative considerations for vitreal aspiration and removal

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Preoperative considerations for retinal detachments

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TYPES OF VITREORETINAL SURGERY

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Surgery of the vitreous

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Adaptations for large animals and special species

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Surgery of the retina

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and degenerative retinopathies are less frequent, but inflammations of the ocular fundus and hypertensive retinopathies are common. Surgeries of the retina and choroid in small animals include retinal or chorioretinal biopsies, and the correction of retinal detachments. The development of the different types of vitreoretinal surgery in small animals is still early, but these surgeries have been reported since the 1970s. The expensive instrumentation and time-consuming training have delayed application of vitreoretinal surgical procedures in veterinary ophthalmology. Nevertheless, several referral veterinary ophthalmology centers offer this highly specialized service. The inclusion of vitreoretinal surgery in this text will hopefully stimulate its continued development in small animals. In horses, anterior vitrectomy has been recommended in the treatment of recurrent uveitis, and is used widely in Europe.

Surgical anatomy The surgical anatomy of the canine vitreoretinal surgeries includes the extraocular space, insertions of the rectus muscles, and the different landmarks of the external sclera (Fig. 12.1). The surgical approach to the anterior vitreous is usually through the pupil, posterior lens capsule (after extracapsular cataract surgery), and anterior vitreal membrane

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Cross-section dorsal oblique muscle, tendon and insertion Dorsal rectus muscle

Anterior ciliary artery Limbus

Vortex vein

Anterior chamber

Retractor oculi muscle

Cornea

Optic nerve Pupil Long posterior ciliary artery

Short posterior ciliary arteries Vortex vein Cross-section ventral oblique muscle

Insertion medial rectus muscle

Ventral rectus muscle

Fig. 12.1 Lateral view of the canine globe with important landmarks for vitreoretinal surgeries.

(after intracapsular cataract and lens removal). Vitreoretinal surgeries involve entry into the vitreal space through multiple small sclerotomies or surgical ports in the pars plana ciliaris. Incisions of the retina are avoided as the resultant hole may produce a rhegmatogenous retinal detachment. Full-thickness retinal holes, whether surgical or spontaneous, require laser, diathermy or cryotherapy to seal the area and stimulate formation of a strong chorioretinal scar. This scar prevents aqueous or vitreous from entering the subretinal space through the retinal break and causing a retinal detachment. To perform vitreous paracentesis (hyalocentesis), the extent of the pars plana ciliaris or the flat posterior portion of the ciliary body is determined based on measurements posterior to the limbus (Fig. 12.2). The exact anterior and posterior borders of the pars plana ciliaris have been determined in the dog but not in the cat. The width of this tissue varies by quadrant, with the pars plana ciliaris in the lateral quadrant the longest. Hypodermic needle penetration of the ciliary body processes (pars plicata ciliaris) may result in considerable intraocular hemorrhage. Hypodermic needle penetration posterior of the pars plana ciliaris will produce retinal holes. Hence, access to the vitreal space without Pars plicata ciliaris Pars plana ciliaris Limbus

Pars ciliaris retinae Sclera Vitreous body

Cornea Tapetal fundus Anterior chamber

Optic disc

Posterior chamber Non-tapetal fundus Iridocorneal angle Fig. 12.2 Cross-section of the globe of the dog. Critical anatomic areas for vitreoretinal surgeries are the pars plana ciliaris and the posterior segment.

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these serious complications necessitates the external penetration of the sclera and pars plana ciliaris, or the insertion of a hypodermic needle through the pupil after entry into the anterior chamber through a corneal or limbal incision into the anterior chamber. In order to access the vitreous space during retinal detachment surgery through small scleral incisions (sclerotomies or ports), and for vitreous samples, the critical entry areas are between the end of the anterior pars plicata (ciliary body processes) and the ora ciliaris retinae (beginning of the retina). In a study by Smith and co-workers, the following sites (as determined by calipers posterior to the canine limbus) are recommended for the dog: 1) superotemporal, 6 mm; 2) inferotemporal, 9 mm; 3) superonasal, 5 mm; and 4) inferonasal, 7 mm. Eye size and head size are correlated, and in larger dogs the anterior and middle portions of the pars plana are more posterior. In another study by Sullivan and co-workers, the distances from the limbus to the ora ciliaris retinae were: 1) dorsal quadrant, 9.25
0.81 mm; 2) lateral quadrant, 9.41
0.79 mm; 3) ventral quadrant, 7.18
0.89 mm; and 4) medial quadrant, 5.30
0.77 mm. Another important site to avoid in the canine is the intrascleral plexus, which drains aqueous humor and is located in the anterior sclera. The intrascleral plexus is located 4–5 mm posterior to the limbus, and may be 4–5 mm wide. Sclerotomies that penetrate the intrascleral plexus often hemorrhage, and judicious cautery is necessary when these sclerotomies are being performed. Under most circumstances, the sclerotomies are posterior to the intrascleral plexus. The anatomy of the vitreous is critical to vitreoretinal surgeries, as part of the surgical procedure will nearly always be within the vitreous space (Fig. 12.3). The vitreous humor is normally a clear gel that adjoins the entire retina, and this interface is termed the posterior vitreal membrane. This attachment to the retina appears relatively weak, except at the periphery of the retina (pars plana retinae) and the optic disk. The vitreous border continues anteriorly onto the pars plana ciliaris and, just before the origins and insertions of the zonules or suspensory ligaments between the ciliary body and lens equator, forms the posterior border of the posterior chamber.

Surgical pathophysiology

Pars ciliaris retinae

Ciliary body

Pars plana Pars plicata

Mittendorf’s dot

Hyaloideocapsular ligament (Weiger’s ligament)

Berger’s space

Patellar fossa or fossa hyaloiden

Zonules (tertiary vitreous)

Hyaloid canal, canalis hydoideus, primary vitreous, or Cloquet’s canal Secondary vitreous Anterior hyaloid membrane (membrana vitrea)

Fig. 12.3 The different components of the vitreous body. The strongest attachments for the vitreous body are the pars plana retinae and the optic disk.

The anterior aspect of the vitreous is immediately posterior to the posterior lens capsule, and has been termed the hyaloideocapsular ligament or Weiger’s ligament. The potential space between the posterior lens capsule and hyaloideocapsular ligaments is termed Berger’s space. This separation between the dog’s posterior lens capsule and the hyaloideocapsular ligament appears more potential than real, as tears or penetration of one structure also affects the other. The principal attachment or base of the vitreous appears to be the pars ciliaris retinae or the anterior border of the peripheral retina. The vitreous body is divided into primary (that vitreous formed and heavily vascularized prenatally) and secondary (that vitreous formed postnatally as the eye grows to normal adult size). The central primary vitreous in adulthood, usually termed Cloquet’s canal, is a clear zone that extends from the optic disk to the central or axial posterior lens capsule. The prenatal blood vessels that traverse this space may persist as remnants at the axial posterior lens capsule (Mittendorf’s dot) or at the optic disk (Bergmeister’s papilla). The majority of retinal surgeries address repair of retinal detachments. Retinal detachments are microscopic separations of the inner nine layers of the neurosensory retina from the retinal pigment epithelium. Because of retinal development, a potential space exists between the inner nine layers of the retina and the retinal epithelium. With hemorrhage, inflammatory exudates, edema, or the influx of vitreous through a retinal hole, these fluids can separate these retinal layers, and produce the ophthalmoscopic findings of the retinal detachment. Hence, in the repair of retinal detachments, contact must be re-established between the inner nine retinal layers and outer retinal pigment epithelium. Aspiration of subretinal fluids involves the removal of fluids from this space. Repair of retinal detachments usually includes the placement of a silicone strap (buckle) around the entire globe about the equator, pars plana vitrectomy, retinopexy with laser photocoagulation or cryothermy, tamponade with intravitreal gas or silicone oil, or a combination procedure

such as the vitrectomy and a scleral buckle. Hence, knowledge of the insertions of the rectus and oblique extraocular muscles in dogs is important, as these muscles are identified during surgical dissection to place this silicone strap. The bulbar conjunctiva is usually incised 360 posterior to the limbus for exposure of the entire globe. The sclera constitutes the fibrous tunic for the entire posterior segment. There are several channels or emissaria where the full-thickness sclera is penetrated, and during vitreoretinal surgeries, these regions are avoided (see Fig. 12.1). These channels also represent weak areas of the sclera, and during glaucoma, focal enlargements or staphylomas may develop. At least four vortex veins exit the posterior segment, usually by quadrant and at the equator. These large veins provide the majority of venous drainage from the anterior and posterior segments of the eye and should be avoided. At the 3 and 9 o’clock positions within the external sclera are the long posterior ciliary arteries and veins that are branches of the external ophthalmic artery and vein. These vessels are avoided as they provide the majority of the blood supply to the anterior segment of the eye. Numerous anterior ciliary arteries and veins penetrate the anterior sclera at the insertions of the different rectus muscles. These blood vessels eventually anastomose with other intraocular vessels. Hence, transection of the rectus muscle insertions can decrease the blood supply to the anterior segment of the eye.

Surgical pathophysiology The pathophysiology of the vitreous and retina are closely related; however, for purposes of discussion, each is presented separately. The vitreous is a clear and fairly firm gel in the young cat and dog, but with aging, the vitreous gradually undergoes liquefaction or syneresis. Intraocular diseases, such as iridocyclitis, the glaucomas, cataract formation, retinal degenerations, and retinochoroiditis accelerate the rate and extent of liquefaction of the vitreous. Hence, if the posterior lens capsule is penetrated during cataract surgery in a young dog, the vitreous is usually a well-formed gel. However, with posterior lens capsule tears in older dogs, the vitreous presentation usually involves a more liquefied vitreous. Vitreous syneresis is also enhanced by cataract and vitreoretinal surgeries.

The role of the vitreous The appearance of vitreous within the pupil, as after lens displacement or cataract surgery, signals many potential problems. Vitreocorneal contact results in temporary corneal edema. Separation of the vitreous from the cornea may detach the corneal endothelium, resulting in permanent corneal edema. Vitreous can obstruct the pupil and iridocorneal angle resulting in elevations in intraocular pressure (IOP). A miotic pupil can be more easily ‘plugged’ with formed vitreous than a dilated pupil. With vitreous herniated in the anterior chamber and pupil, removal of the vitreous (anterior vitrectomy) is indicated. The vitreous provides variable support to the entire retina in the dog and cat. However, absence of part to all of the vitreous does not automatically result in retinal detachment. Formation of inflammatory

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traction bands involving the iris, ciliary body, lens capsules, and the vitreous, and the development of holes in the peripheral retina in dogs after cataract and vitreoretinal surgeries, seem more influential in the genesis of retinal detachments than the lack of the vitreous per se. Hence, abnormalities in both the vitreous and retina are key factors in the pathogenesis of rhegmatogenous retinal detachments. Certain breeds of dogs, i.e., Shih Tzu, Boston Terrier, and Toy and Miniature Poodles, develop excessive vitreous degeneration. This degeneration results in considerable syneresis; if the dog is a violent head shaker with toys, rhegmatogenous retinal detachments (RRDs) may result.

Cataract surgery In dogs, the most common cause of RRD is cataract surgery. Complications associated with cataract surgery in the dog, such as large tears in the posterior capsule, vitreous loss, intraocular hemorrhage, or retained lens fragments, appear to contribute directly to RRD.

Inherited cataracts and lens-induced uveitis In breeds with inherited cataracts, i.e., American Cocker Spaniel, Siberian Husky, Bichon Frise, and others which occur in young ages, cataract resorption and lens-induced uveitis are common. This uveitis seems to be associated with a significant number of RRDs, including vitreous retraction, vitreous degeneration or liquefaction, obliteration of retinal vessels and secondary peripheral retinal thinning, formation of retinal cysts, and transient glaucoma attacks with intermittent stretching of the globe, all of which add further insult to the peripheral retina.

Inherited retinal dysplasia Certain breeds of dogs have inherited retinal dysplasia, i.e., Labrador Retrievers and English Springer Spaniels. These dysplastic retinas are prone to RRD, especially when the retina is thin or develops holes, and has liquefied vitreous.

Predisposed breeds Certain breeds of dogs, i.e., Bichon Frise and Havanese, appear predisposed to RRD when affected with inherited and early onset cataract formation, cataract resorption, lens-induced uveitis, and prior to or after cataract surgery. As a result, laser or cryoretinopexy is often performed in these two breeds prior to or immediately before cataract surgery.

Other factors Ocular trauma, luxated lens, and retinal cysts can also predispose to the development of RRD. Systemic hypertension and choroiditis are associated with intraocular hemorrhage and serous to exudative non-rhegmatogenous retinal detachments. Immune-mediated diseases, as well as fungal, bacterial and rickettsial chorioretinitis, can also result in exudative non-rhegmatogenous retinal detachments. Generally, non-rhegmatogenous retinal detachments are treated medically. 360

Types of retinal detachment Retinal detachments in small animals are classified using several different schemes. They are divided into partial and complete. They are also classified into rhegmatogenous (having retinal holes or tears) or non-rhegmatogenous (no defects in the neurosensory retina). They are also divided by cause: 1) bullous, when the retinal layers are separated by fluids (serous), cells from inflammations (exudative), neoplasms, and hemorrhages; 2) traction, when inflammatory or other types of bands pull the inner retinal layers away from the retinal pigment epithelium, usually resulting in a retinal hole(s); and 3) congenital, in which the retinal detachments are associated with retinal dysplasia or optic disk pits.

Types of vitreoretinal surgery Vitreoretinal surgeries, presented in subsequent sections, concentrate on vitreous aspiration for diagnosis or injections; vitrectomy (anterior and posterior) for removal of formed or gel vitreous in the pupil and/or anterior chamber, or in treatment of rhegmatogenous retinal detachments; chorioretinal biopsies for tissue analyses; and the surgical management of retinal detachments. Vitreoretinal surgeries are indicated for the rhegmatogenous retinal detachments associated with retinal holes and inflammatory and/or vitreal traction bands. Non-rhegmatogenous retinal detachments are usually treated medically. If possible, the inciting cause is identified and treated. For instance, if systemic hypertension has resulted in the retinal detachment, systemic antihypertensive therapy is administered (Fig. 12.4). If the retinal detachment has resulted from a chorioretinitis, the appropriate therapy is administered. Retinal detachments are also treated symptomatically. Systemic drugs, such as corticosteroids and diuretics, may hasten the reabsorption of the subretinal fluids, and reapposition of the neurosensory retinal layers and the retinal pigment epithelium.

Clinical evaluation of retinal detachments The broad objective for this type of retinal detachment surgery is the identification of the retinal breaks and sealing these breaks. Detection of retinal breaks in small animals requires meticulous examination of the retina by ophthalmoscopy (usually the indirect method). Mydriasis is necessary to observe as much as possible of the peripheral retina. Often the dog requires sedation to accommodate the time for this examination and the scleral depression. Postoperative capsular and pupillary opacities after cataract surgeries may limit fundic observations. Scleral depression can be achieved under topical anesthesia with a scleral depressor instrument, Jameson muscle hook or a moist cotton swab. The scleral depressor is used to indent the globe a few millimeters posterior to the limbus while simultaneously performing indirect ophthalmoscopy. Most retinal breaks (holes and tears) occur in the peripheral retina. Once the fundoscopic examination has been performed and any retinal breaks identified and localized, retinal surgery may be indicated. The general principles for the surgical

Instrumentation for vitreoretinal surgeries

A

B

Fig. 12.4 Retinal detachment in a cat associated with systemic hypertension. (a) The retinal detachment occurs in front of both sides of the optic disk. (b) Reattachment of the retinal detachment in this cat’s eye after successful treatment of the systemic hypertension, but some retinal pigment epithelium proliferation is present (suggesting some retinal damage).

treatment of rhegmatogenous retinal detachments are summarized in Box 12.1, part A. Once the retinal traction is removed and the retinal breaks are sealed, normal physiologic function of the retina may resume with the pigmented epithelium to evacuate the subretinal fluids, and eliminate any space between the neurosensory retina and the retinal pigment epithelial layers. Additional invaluable diagnostic procedures for small animals are electroretinography and ultrasonography. Electroretinography may provide information as to the viability of the retina, and for detecting retinal detachments. Ultrasonography is used particularly to evaluate the posterior segment in which visualization is incomplete because of a small pupil, or lens or vitreal opacities (Fig. 12.5).

Instrumentation for vitreoretinal surgeries For optimal results in vitreoretinal surgeries, a considerable investment in training and instrumentation is necessary.

Surgical instruments Basic ophthalmic instruments are necessary to perform the surgical approach for retinal detachments. These instruments are necessary to perform the conjunctival (peritomy) and periocular surgery to isolate and sometimes transect the extraocular muscle insertions. The sclerotomies or small 20 g incisions through the sclera and pars plana of the ciliary body require a basic set of 20 g diameter instrumentation

Box 12.1 General principles for the treatment of rhegmatogenous retinal detachments

Part A. Principles 1. Closure of retinal break: By diathermy, cryotherapy, or laser. 2. Collapse of the space between the separated retinal layers: – Drainage of subretinal fluids, and with an externally applied silicone buckle. 3. Excision of vitreal and/or inflammatory traction bands that appear to pull on the retina. 4. Occasional temporary intravitreal injections of silicone oil and/or perfluorocarbon gases to push and flatten (tamponade) the area of retinal detachment. 5. Development of focal chorioretinitis that eventually resolves to form scar tissue that adheres to the retinal layers within the detached area and, most importantly, around the retinal break.

Part B. Specialized instruments for pars plana retinal detachment surgery 20 g microvitreoretinal (MVR) blades 20 g end gripping microforceps 20 g DeJuan intraocular forceps 20 g horizontal and vertical forceps 20 g membrane scratcher 20g retinal pick 20 g scleral plugs 20 g scleral plug forceps (pair)

Other Accessory aspiration tubing Intraocular pressure control line with filter Two stopcocks 20 g high viscosity infusion cannula Grizzard cannula 0.2 filter for perfluorocarbon gas and air 28 D lens

Modified from Smith PJ 1999 Surgery of the canine posterior segment. In: Gelatt KN (ed.) Veterinary Ophthalmology, 3rd edn. Lippincott, Williams and Wilkins, Baltimore, p 935–980.

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Vitreoretinal surgery Fig. 12.5 Ultrasonography can be useful to detect retinal detachments in eyes with dense cataracts or other opaque media. (a) Retinal detachment in a horse, appearing as a ‘V’ or ‘seagull’ with its attachments at the optic nerve and ora ciliaris retinae. Note also the opacities within the vitreous. (b) Retinal detachment in a dog, with lens luxation and cataract formation.

B

A

(Box 12.1, part B). These 20 g instruments can be inserted and withdrawn from these ports without causing damage. In addition, several of the instruments are essential. Posterior vitreous cutter, light source, IOP control, and wet-field cautery are necessary. The Machemer lens rests on the cornea and provides irrigation to the cornea, and a wide field of vision and magnification. To inject silicone oil, either a large bore high viscosity cannula with a Luer-lock syringe for manual injection or a special syringe pump and high-viscosity injection, are necessary. A nitrous oxide cryounit with a retinal probe and/or a diode laser with endolaser and indirect delivery modes are essential for retinopexy.

Perfluorocarbon gases The perfluorocarbon gases are used to manipulate and flatten retinal detachments during pars plana retinal detachment surgeries. They are biologically inert, clear optically, immiscible with water, and have a higher specific gravity than saline. Of the perfluorocarbon gases in use, perfluorooctane, perfluorotributylamine, perfluorodecalin, and perfluoroperhydrophenanthrene, only the first two gases have been used in the dog. Approximately twice as heavy as water, these gases can very effectively tamponade and flatten the retina intraoperatively, and displace subretinal fluid anteriorly from peripheral retinal breaks into the vitreous. They are removed after retinopexy because of potential retinal toxicity, and replaced with silicone oil which will remain in the eye postoperatively for several months.

Silicone oil (SiO) The silicone oils are different molecular weights of polydimethylsiloxane. Of those available, the medical grade 5000 centistoke SiO is the most frequently used in the dog. With a specific gravity of 0.971, which is less than water, SiO forms a buoyant bubble in the vitreous space that provides long-term tamponade to the dorsal retina. In aphakic and pseudophakic dogs after SiO injection into the vitreal space, the oil may enter the anterior chamber,

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causing corneal edema and, if in significant quantity, angleobstruction glaucoma. In phakic dogs, cataract formation has been associated with intravitreal SiO. Silicone oil is routinely left within the vitreous after retinal detachment surgery in dogs, and is not removed (unless it escapes into the anterior chamber). In dogs, intravitreal silicone oil appears to be a reasonable vitreous substitute; in humans, silicone oil is usually removed 3–6 months post-surgery, and not left long term.

Preoperative considerations for vitreal aspiration and removal Small animal patients, presented for possible vitreous aspiration, usually have exudative retinal detachments, intense chorioretinitis with vitreal infiltration, and endophthalmitis. Often the ophthalmic disease is part of a systemic infectious disease, and the vitreal aspirate may assist in identification of the infectious agent. Systemic aspergillosis, blastomycosis, and cryptococcosis can often be diagnosed by vitreous aspiration and the demonstration of organisms within the aspirate. During vitreal aspirations, the hypodermic needle can often be directed under direct observation through a dilated pupil to the inflammatory material suspended within the vitreous. Hence, the diagnostic value of vitreal aspirates with a fairly clear anterior segment and lens is quite high. When the cornea, pupil or lens prevents direct observation of the hypodermic needle within the vitreous, the accuracy of the technique declines. Concurrent ultrasonography during vitreous aspiration in eyes with complete opacities can ensure that the hypodermic needle is positioned as accurately as possible within the vitreal body. Small animal patients with vitreal diseases that may require partial-to-complete surgical excision are usually presented with lens displacement, with or without concurrent secondary and aqueous misdirection (or malignant) glaucoma, or postoperatively after cataract surgery. Formed or gel vitreous, partially herniated in the pupil and anterior chamber, appears as a formed, slightly translucent bulge with occasional fine white fibril strands. Corneal contact will cause focal edema. The pupil margin can be distorted by formed

Preoperative considerations for retinal detachments

vitreous, and vitreous strands may extend from the pupil into the previous corneal or limbal incision. If the pupil is miotic or miotics are inadvertently instilled, pupillary occlusion with the formed or gel vitreal herniation may result, necessitating additional therapy for the secondary glaucoma. Medical therapy is usually first attempted for vitreal herniations without corneal contact. Topical corticosteroids and mydriatics are used to suppress the iridocyclitis. The resultant pupillary dilatation decreases the possibility of pupillary occlusion with the herniated vitreous and secondary glaucoma. Mannitol (1–2 g/kg IV) may be administered once or even twice to dehydrate and shrink the formed vitreous and lower IOP. Ideally, the herniated vitreous will retract behind the dilated pupil and remain. The effects of mannitol in a highly inflamed eye are usually less than optimal because the blood–aqueous barrier is reduced, and the osmotic imbalance caused by the intravascular mannitol is diminished. After 24–72 h of less than successful medical treatment, an anterior vitrectomy is indicated to remove the vitreous from the anterior chamber and pupil.

Preoperative considerations for retinal detachments Surgical treatment of retinal detachment has been reported in dogs with serous retinal detachments secondary to optic disk pits or idiopathic (Fig. 12.6), and for rhegmatogenous retinal detachments associated with retinal holes or tears that developed after cataract surgery. As indicated in an earlier section, exudative retinal detachments associated with posterior segment inflammations, systemic hypertension, and other causes are treated by therapy for the specific systemic disorder, and systemic corticosteroids and diuretics to attempt to remove the subretinal fluids before the retinal degeneration becomes advanced. Unfortunately, most retinal detachments are presented late in small animals, and often entire retinas are detached in both eyes. Retinal detachments that develop after lens and cataract removal are often detected earlier during the periodic postoperative examinations (Fig. 12.7).

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Fig. 12.7 A large retinal detachment with a giant ventral retinal tear in an eye 6 months after successful cataract removal.

TYPES OF VITREORETINAL SURGERY In this section, the fundamentals of vitreoretinal surgery are presented. As these types of surgical procedure are still evolving in the dog, and to a limited extent in cats, textbooks devoted to retinal detachment surgery in humans should be consulted for additional details. For vitreal surgery, the procedures for vitreal paracentesis (hyalocentesis) and anterior vitrectomy are presented. For retinal detachment surgery, the basic approach is presented for both the extraand intraocular procedures. Procedures such as the intraocular excision of pupillary and traction bands, posterior vitrectomy, aspiration of subretinal fluids, and the injection of intravitreal perfluorocarbon gases and silicone oil will also be discussed.

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Fig. 12.6 Dorsal serous non-rhegmatogenous retinal detachment in a dog of unknown cause. (a) The retinal detachment is immediately above the disk. (b) Several spots of laser photocoagulation were positioned immediately adjacent to the retinal detachment.

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Surgery of the vitreous Surgery of the vitreous includes vitreal paracentesis (hyalocentesis), anterior vitrectomy performed through the pupil, and complete vitrectomy performed through the pars plana ciliaris. Vitreal paracentesis is used to obtain liquid vitreous for cytology and culture. Vitreous samples may also be analyzed for drug levels, antibodies, and different substances. In the anterior vitrectomy procedure, often performed at the conclusion of lens removal, vitreous is excised that has entered the anterior chamber or pupil. In the complete vitrectomy procedure, the majority of the vitreous is removed, usually through one or more sclerotomies at the level of the pars plana of the ciliary body. Modern vitreous surgery techniques have been developed in humans since about 1965. With the demonstration that the excision of vitreous in humans did not result in the detachment of the retina and loss of vision, specialized instrumentation and techniques have been developed in humans to perform vitreoretinal surgeries through small incisions in the pars plana of the ciliary body. Anterior vitrectomy involves the excision of vitreous herniated or protruding through the pupil, as well as pupillary opacities that develop postoperatively after cataract surgeries in small animals. These pupillary opacities usually consist of anterior and posterior lens capsules, organized anterior vitreous and inflammatory fibropupillary membranes. In the former case, the herniated organized anterior vitreous is excised using cellulose sponges or forceps, and vitreous scissors utilizing an anterior vitrector (either portable or attached to a cataract surgical unit). For the postoperative pupillary opacities that develop in dogs and, to a lesser extent, in cats, the anterior vitreous and tough fibrotic membranes require excision by sharp scissors and forceps (anterior vitrectomy and pupillary membranectomy). Depending on its composition, the anterior vitreous may be excised (formed vitreous) or aspirated (liquid vitreous). Sometimes the irregular and often miotic pupil requires coreoplasty (see Chapter 9) to not only excise the opacities within the pupil but also enlarge the pupil to enhance vision. The instrumentation to perform anterior vitrectomy through a corneal or limbal incision varies, but the basic procedure in small animals may be performed with sharp vitreous scissors, cellulose sponges, cyclodialysis spatula, intraocular forceps, and intraocular scissors. For pars plana vitreoretinal surgeries, a considerable investment in specialized instrumentation is necessary, and only a few veterinary ophthalmology clinical centers have acquired these resources and mastered the surgical techniques. Vitreoretinal surgery, as presented in this chapter, represents one of the surgical frontiers for veterinary ophthalmology where significant advances will undoubtedly occur during the next decade. Anterior vitrectomy procedures are indicated for excision of persistent hyperplastic vitreous, opacified vitreous, herniation of the vitreous through the pupil, partial excision of the vitreous within the pupil in malignant glaucoma, removal of anterior vitreal foreign bodies, and for excision of vitreous incarcerated within a corneal or limbal wound. Pars plana vitrectomy is indicated for deeper vitreal opacities, including hemorrhages, treatment of malignant glaucoma, treatment for vitreous prolapsed into the anterior

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chamber, vitreous removal in endophthalmitis, removal of deep vitreal foreign bodies, excision or transection of vitreous traction and inflammatory bands, and in the management of rhegmatogenous retinal detachments, especially with giant tears.

Hyalocentesis/vitreous paracentesis In vitreal paracentesis or hyalocentesis a small quantity of liquid vitreous is aspirated for analysis, usually cytology and bacterial/fungal culture. The formed gel vitreous cannot be aspirated; however, vitreous syneresis or liquefaction occurs with aging, cataract formation, intraocular inflammation, and glaucoma in small animals. As a result, some portion of the vitreous is liquefied, unless the cat or dog is less than 1 year old. Vitreal paracentesis is a most useful diagnostic technique for dogs and cats presented with bilateral exudative retinal detachments or endophthalmitis associated with Blastomyces dermatitidis, Histoplasma capsulatum, Cryptococcus neoformans, Coccidioides immitis, Geotrichum candidum, and Prototheca organisms (Fig. 12.8). Hyalocentesis may also be used to diagnose posterior segment neoplasia; however, this technique is not recommended for this purpose. Direct hypodermic needle contact of the neoplasm is usually associated with hemorrhage. However, if cellular material is present in the vitreous adjacent to the chorioretinal mass, aspiration of the vitreous in this area is reasonably safe.

Vitreous aspiration procedure Hyalocentesis is performed after the onset of general anesthesia, clipping of the eyelid hair, and cleansing of the eyelid skin, conjunctival and corneal surfaces with 0.5%

Fig. 12.8 Chorioretinitis in a cat secondary to systemic cryptococcosis. Note the chorioretinal granulomas and surrounding focal exudative retinal detachments.

Surgery of the vitreous

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Fig. 12.9 Aspiration of liquid vitreous through the pars plana ciliaris. (a) Approach is usually via the dorsal or dorsolateral pars plana ciliaris because of greater accessibility. By Jameson calipers, the needle puncture site is localized 8 mm posterior to the limbus. (b) The hypodermic needle is inserted through the dorsal conjunctiva, sclera, and pars plana ciliaris. (c) The needle is directed toward the optic disk or floaters within the vitreous. About 0.1–0.25 mL of liquid vitreous may be removed.

20 1 30 40

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povidone–iodine solution. The pupil is dilated before the onset of general anesthesia. For convenience, the eyelids are retracted by speculum. The pupil and anterior vitreous are usually visible. The bulbar conjunctiva is grasped by thumb forceps with teeth several millimeters posterior to the dorsal limbus (Fig. 12.9a). By calipers the site to penetrate the bulbar conjunctiva is determined as 6–9 mm (dorsal) to 8–9 mm (lateral) posterior to the limbus. At this position, the 22–23 g hypodermic needle, aimed at the optic disk, should penetrate the sclera and pars plana ciliaris to enter the anterior vitreous (Fig. 12.9b). Often once the hypodermic needle is in the anterior vitreous, it can be directly observed. If vitreal opacities or floaters are present, the hypodermic needle is carefully directed to these opacities (Fig. 12.9c). Aspiration of vitreous depends on it being liquefied. Formed vitreous or large opacities may plug the needle and require flushing to relieve the obstruction. The quantity of liquid vitreous aspirated is limited to 0.1–0.25 mL. If larger volumes are removed, an equal volume of saline or lactated Ringer’s solution is injected to immediately restore the lost vitreous volume and IOP. Hyalocentesis is an excellent diagnostic procedure that can retrieve vitreal opacities for analyses. Identification of the infectious organism, obtained by hyalocentesis, frequently aids in the treatment and prognosis for small animal patients. Treatment after hyalocentesis is usually directed at the pre-existing posterior segment inflammation. Effective treatment of diseases of the anterior vitreous includes the administration of both topical and systemic antibiotics, and/or antifungals. Mydriatics are indicated for the iridocyclitis and are administered at levels sufficient to maintain a reasonably dilated pupil.

Potential complications after hyalocentesis Post-hyalocentesis complications are negligible, provided the procedure is properly performed. Obstruction of the hypodermic needle by gel vitreous or organized inflammatory exudates during hyalocentesis is infrequent, and is remedied by alternate flushing with sterile saline and aspiration, or repositioning the needle tip to another area. If the needle puncture site is anterior to the pars plana ciliaris, penetration of the ciliary body processes results in secondary intraocular hemorrhage. If the hypodermic needle is inserted more perpendicular, the lens may be touched by the needle. Penetration posterior to the pars plana ciliaris may result in chorioretinitis and full-thickness retinal holes, which may lead to retinal detachments.

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Intravitreal injections The same technique used for hyalocentesis can be used to deliver drugs directly into the vitreous space. As described in Chapter 10, intravitreal injections of gentamicin (10–25 mg), with and without 1 mg dexamethasone, have been used to destroy the ciliary body epithelia, and induce phthisis bulbi and ocular hypotony in advanced end-stage primary glaucomatous eyes. Antibiotics and antifungal agents can be injected intravitreally for bacterial and fungal chorioretinitis, and endophthalmitis. Both volume and concentration of drugs injected intravitreally are limited. The retina and lens appear quite sensitive to drugs, and excess drug concentrations result in cataract formation and retinal degeneration. The doses of selected antibiotics and antifungal agents, based on those for humans, are summarized in Table 12.1.

Transpupillary vitreal aspirations Aspiration of liquefied vitreous from the vitreous space may be performed through the pupil during lens and cataract surgery, when formed or gel vitreous herniates through the pupil. Aspiration of some vitreous can be performed in most older dogs during cataract and lens removal surgery, as a portion of the vitreous is usually liquefied. In dogs less than 1 year of age with congenital cataracts, there may be limited-to-no liquefied vitreous, and vitreal aspiration is not possible. Vitreous herniation may follow development of a tear in the posterior lens capsule, or after intracapsular lens and cataract removal. As the posterior lens capsule and anterior vitreal face are in close approximation, damage usually affects both structures. Table 12.1 Doses for intravitreal antibiotics in the dog

Antibiotic

Dose

Amikacin

0.4 mg

Ampicillin

5.0 mg

Cefazolin

2.25 mg

Cephaloridine

0.25 mg

Chloramphenicol

2.0 mg

Gentamicin

0.4 mg

Tobramycin

0.4 mg

Vancomycin

1.0 mg

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Appearance of formed vitreous within the pupil may also necessitate excision of any organized vitreous within the anterior chamber with vitreous scissors or the anterior vitrector. Aspiration of liquid vitreous from within the vitreal space is one method to assist in the retraction of formed vitreous behind the pupil. Part of the pathogenesis of vitreal presentation within the pupil includes not only a tear in the posterior lens capsule and anterior hyaloid face, but also pressure on the vitreal space because of decreased scleral rigidity in dogs and cats under general anesthesia. The possibility of herniation of formed vitreous is reduced by avoidance of tears of the posterior lens capsule during cataract surgery, no instrument pressure on the globe, and the use of neuromuscular blocking agents during general anesthesia in the dog to reduce the extraocular muscle tone on the posterior globe. Aspiration of liquefied vitreous is usually performed at the completion of phacoemulsification, or extracapsular and intracapsular lens removal. Entry into the anterior chamber has already been established through the small incision used in phacoemulsification, or through the larger corneal or limbal incisions used for extracapsular and intracapsular lens extractions. The cornea is retracted by thumb forceps to expose the anterior chamber and pupil. The anterior chamber is maintained with viscoelastic agents. The formed vitreous may be indistinguishable from the aqueous humor or liquefied vitreous, unless some vitreal floaters (cells, fibrils, opacities) are present (Fig. 12.10a). A blunt 18–20 g hypodermic needle, attached to a 1–3 mL syringe, is carefully inserted through the pupil and the remaining posterior lens capsule and/or anterior hyaloid face about 5 mm into the most dorsal vitreal space. Insertion of the hypodermic needle through the external sclera and pars plana ciliaris, as used for hyalocentesis, is not recommended as it may collapse the globe and cause additional formed vitreous to appear in the pupil (Fig. 12.10b). Liquid vitreous is always above the formed or gel portion, and shifts to remain dorsal during the different positions of the eye. As a result, the hypodermic needle to aspirate liquid vitreous must be placed in the upper vitreal body. Liquefied vitreous is slowly aspirated, usually 0.1–0.5 mL. Often with removal of the liquid vitreous, the formed vitreous within the pupil and anterior chamber will partially or completely shift behind the pupil. Availability of a vitrector has replaced the hypodermic needle approach. During vitrectomy, contact with the iris

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is avoided, and the tip of the instrument should always be visible. Contact with the iris and ciliary body may result in significant hemorrhage. The iridal diaphragm may appear somewhat concave after successful vitreous aspiration, and restoration of all formed vitreous to behind the pupil (Fig. 12.10c). As the gel vitreous and solutions used to lavage the anterior chamber are indistinguishable, a small air bubble may be injected into the anterior chamber to assist in detection of any residual gel vitreous (Fig. 12.10d). The air bubble should be freely maneuverable through the entire anterior chamber when all gel vitreous has been removed or retracted through the pupil. If some gel vitreous remains within the anterior chamber, the air bubble movement is restricted and may outline the formed vitreous. No formed or gel vitreous should remain in the anterior chamber at the conclusion of this technique. Vitreous aspiration is one of several methods to treat presentation of gel or formed vitreous in the pupil during cataract or lens surgery. Success of this procedure is dependent on some portion of vitreous being liquefied, and is generally unsuccessful in cats and dogs less than 1 year old. This technique may be performed through a tear in the posterior lens capsule and anterior vitreous face. Placement through the pupil must be performed carefully, and a blunt 18–20 g hypodermic needle should be inserted only 5–7 mm posterior to the pupil. Inadvertent needle contact with the retina may produce a retinal hole and predispose to retinal detachment. Nevertheless, this procedure, performed properly, is a useful method to treat vitreal herniation and presentation through the pupil and into the anterior chamber. Medical treatment after vitreal aspiration is directed at the underlying disease, usually postoperative iridocyclitis. The anterior chamber and pupil should be examined daily by slit-lamp biomicroscopy to observe the size and patency of the pupil. Any irregular shape in the pupil may indicate some vitreal contact.

Anterior/partial vitrectomy in small animals Anterior vitrectomy is divided into two procedures: it may be performed at the conclusion of lens and cataract surgery in the dog and cat, and may also be performed weeks to months after cataract surgery to excise pupillary opacities that also include the lens capsules and anterior vitreous. In the first procedure, which is more common in the dog, anterior vitrectomy is performed when formed vitreous is presented within the pupil, anterior chamber, or the corneal or limbal incision. This complication occurs when the posterior lens capsule and anterior vitreous face are torn or

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Fig. 12.10 Aspiration of liquefied vitreous through the pupil. (a) Entry to the anterior chamber is through a limbal or corneal incision. (b) A blunt 18–20 g hypodermic needle with a 3 mL syringe is carefully inserted about 5 mm through the pupil into the most dorsal vitreous space. (c) With aspiration of the dorsal liquefied vitreous, the formed vitreous will often retract from the anterior chamber into the vitreous space, causing the iris diaphragm to become concave. (d) An air bubble is injected into the anterior chamber to aid in detecting formed vitreous.

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Surgery of the vitreous

interrupted during phacoemulsification, extracapsular and intracapsular cataract and lens surgeries. Occasionally in intracapsular lens extractions, i.e., anterior lens luxation, formed vitreous may be present in the anterior chamber or even emerge within the corneal or limbal incision as it is performed. For satisfactory conclusion of cataract and lens removal surgery with vitreal presentation, all formed vitreous must be excised and/or replaced behind the pupil before complete apposition of the corneal or limbal surgical wound. Vitreous touching the posterior cornea is associated with persistent edema. Vitreous spanning the pupil and incarcerated in the corneal or limbal surgical wound can distort the pupil and serve as the scaffolding for pupillary inflammatory membrane formation. Traction bands from this area may extend into the anterior vitreous and peripheral retina, eventually resulting in retinal detachment. Vitreous within the pupil may also potentially occlude aqueous humor flow, especially when the pupil becomes small. The anterior vitrectomy procedure is also used for postcataract pupillary opacification after cataract surgeries in the dog and cat. This procedure may also be combined with coreoplasty (creation of a larger pupil), synechiolysis (cutting or tearing posterior synechia), and removal of extensive fibrotic lens capsules (capsulectomy). These opaque pupillary membranes consist of one or more components including: 1) inflammatory membranes from the postoperative iridocyclitis, when fibrin from the secondary aqueous humor forms the scaffolding for fibroblast proliferation and production of dense collagen fibers; 2) proliferation of remaining lens epithelial cells (Elschnig’s pearls); 3) migration of anterior uveal pigment cells on these membranes from the iris and posterior synechiae; and 4) proliferation of lens fibers as myofibroblasts that contract and distort the posterior lens capsule. These posterior capsular changes account for the gradual decline in the success rates of cataract surgery in the dog, from 90–95þ% at 4–6 weeks postoperatively to about 80% at 2–3 years after surgery. For comparison, posterior lens opacification that requires laser therapy after phacoemulsification cataract surgery in humans occurs in about 50% of the patients within the first postoperative year. Laser intervention in humans is highly successful for restoring visual acuity. In the dog, these capsular changes may also contract the remaining posterior lens capsule, and indirectly (through the zonulary fibers) or directly (by inflammatory traction bands) contribute to the genesis of peripheral retinal holes, tears, and detachments. Part of the rationale for long-term

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postoperative medical therapy, including topical corticosteroids and systemic non-steroidal anti-inflammatory drugs (NSAIDs), after cataract surgery in the dog is to either retard or prevent formation of these pupillary membranes. The cat, in contrast to the dog, shows a less intense iridocyclitis after cataract surgery, and a lower tendency to develop these pupillary membranes. When the anterior vitrectomy is performed immediately after lens or cataract removal, the majority of the procedure is performed within the anterior chamber. The formed vitreous may be clear or contain suspended cells, fibrin, vitreous opacities (such as with hyalosis), and blood. In the anterior vitrectomy procedure for anterior chamber vitreal presentation, small cellulose surgical sponges are touched to the formed vitreous (Fig. 12.11a).The adherent gel vitreous is slowly retracted and carefully cut with sharp iris or vitreous scissors. The scissors are held parallel to the surface of the iris to minimize traction on the deeper vitreous and indirectly on the retina (Fig. 12.11b). All gel vitreous within the anterior chamber may be removed by this procedure. The iris surface should be slightly concave afterwards because of the loss of formed vitreous immediately posterior to it (Fig. 12.11c). Many phacoemulsification units also offer vitrectomy capacity that can be used to cut and aspirate the formed vitreous from the anterior chamber. Liquid vitreous, located in the most dorsal vitreal space, may be aspirated with a blunt 18–20 g hypodermic needle carefully inserted through the pupil 5–8 mm into the vitreous body. Aspiration of the liquid vitreous often results in retraction of the formed gel vitreous within the pupil (Fig. 12.11d). When the anterior vitrectomy procedure is performed several weeks to months after cataract surgery in dogs, and to a lesser extent in cats, the surgical entry into the anterior chamber is usually thorough the original corneal incision or in a different area with improved access to the pupil. Anterior vitrectomy may be combined with other techniques to excise fibropupillary membranes (membranectomy) and posterior synechiae (synechiolysis), and enlarge the pupil (coreoplasty) to enhance vision. In contrast to humans, the fibropupillary membranes in the dog often cannot be treated successfully with laser photocoagulation because of their extent and thickness. These membranes are also more difficult to incise and excise than in humans, and are often complicated by a small fixed pupil with numerous posterior synechiae. Incision and tearing of the iris invariably result in hemorrhage that necessitates intracameral adrenaline (epinephrine; 1:1000 to 1:10 000) and/or cautery of the

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Fig. 12.11 Anterior vitrectomy in small animals using surgical cellulose spears. (a) Through a corneal incision, a small cellulose surgical spear is inserted into the anterior chamber to touch the formed vitreous. (b) The surgical spear is retracted with the formed vitreous adhered and carefully excised by sharp iris or vitreous scissors held parallel to the anterior surface of the iris. (c) Once the formed vitreous is removed from the anterior chamber, the iris appears concave. (d) Aspiration of additional liquefied vitreous may help maintain the remaining gel vitreous within the vitreous space.

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edges of the iris. Wet-field cautery of the iris is advantageous as aqueous humor is usually in the cautery site. Sharp iris, intraocular or vitreous scissors are essential to excise the fibropupillary membranes in the dog.

Surgical procedure After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of the eyelid skin, corneal and conjunctival surfaces with 0.5% povidone–iodine solution and sterile cotton swabs, the eyelids are retracted by speculum. To enhance exposure, a lateral canthotomy may be performed. Neuromuscular blocking agents may be injected intravenously (see Chapter 3) to provide optimal positioning of the globe and reduce extraocular muscle tone on the posterior segment of the eye. Entry into the anterior chamber may be through the original corneal incision or in another site that is closer to the pupil for the anterior vitrectomy, occasionally combined with synechiolysis and/or membranectomy. The cornea is partially incised with the Beaver No. 6400 microsurgical blade (Fig. 12.12a). The deeper aspects of the corneal incision are completed with right- and left-handed corneoscleral scissors (Fig. 12.12b). Once the corneal incision is complete, the anterior chamber is filled with 0.5–0.7 mL viscoelastic agent to maintain the chamber during the intraocular manipulations. Instrument contact with the posterior cornea is avoided (Fig. 12.12c). With a cyclodialysis spatula, Fig. 12.12 Anterior vitrectomy through a corneal incision and through the pupil. Often anterior vitrectomy is combined with other procedures including coreoplasty, membranectomy, and synechiolysis. (a) The peripheral cornea is incised to one-half thickness with the Beaver No. 6400 microsurgical blade. (b) After a stab incision with a Beaver No. 6500 microsurgical blade and entry into the anterior chamber, the corneal incision is completed with right- and lefthanded corneoscleral scissors. (c) The anterior chamber is filled with a viscoelastic agent to maintain the anterior chamber. (d) All posterior synechiae are carefully separated from the remaining lens capsules and anterior vitreous. (e) With intraocular forceps and scissors, all opacified fibropupillary material is excised. This material includes remaining anterior and posterior lens capsules, post-inflammatory membranes, and anterior vitreous. (f) A vitrector unit may be used to complete the removal of the anterior vitreous. (g) An air bubble is injected into the anterior chamber to check for any remaining gel vitreous. (h) After the removal of all pupillary debris and the anterior vitreous, the corneal incision is apposed with 6-0 to 7-0 simple interrupted absorbable sutures. A 22 g hypodermic needle is inserted between two sutures and the anterior chamber is restored with lactated Ringer’s solution until about 10 mmHg is achieved.

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the free borders of the pupil are identified, and posterior synechiae are carefully torn between the posterior iris and the fibropupillary membrane. Limited iridal hemorrhage is anticipated. If observation of the surgical site is impaired, adrenaline (epinephrine; 1:1000 to 1:10 000) is injected to secure iridal hemostasis, and perhaps some mydriasis. The iris is often two to four times thicker than normal (Fig. 12.12d). With 1  2 teeth fine thumb forceps or an intraocular forceps, the center of the fibropupillary membrane is grasped and carefully excised by sharp iris, vitreous or intraocular scissors (Fig. 12.12e). These membranes may contain fine blood vessels and limited hemorrhage may result. With the excision and removal of the fibropupillary membranes, the opacified portions of the anterior and posterior lens capsules and anterior vitreous are removed similarly. Traction and tearing of these opaque pupillary membranes are avoided, as iridal and ciliary body hemorrhage result. A portion of the anterior vitreous is removed with the vitrector (Fig. 12.12f). The pupil is carefully inspected for any remaining portions of the fibropupillary membrane which are grasped and excised by sharp scissors. Any anterior vitreous that remains in the pupil or anterior chamber is excised by sharp scissors or the vitrector unit. An air bubble, injected immediately in front of the pupil and under the viscoelastic agent that fills the entire anterior chamber, can be used to detect presence of any residual gel or formed vitreous within or immediately caudal to the pupil (Fig. 12.12g). The clear

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Suprachoroidal cyclosporine implants for the treatment of equine recurrent uveitis

corneal incision is apposed with several 6-0 to 7-0 simple interrupted absorbable sutures (Fig. 12.12h). Before placement of the last two sutures, the viscoelastic agent is flushed from the anterior chamber and replaced with lactated Ringer’s or balanced salt solution. After placement of all corneal sutures, the integrity of the wound apposition is checked with an additional injection of lactated Ringer’s or balanced salt solution. The resultant IOP should approximate preoperative levels.

Postoperative management Postoperative management after anterior vitrectomy for fibropupillary membrane formation in the dog is similar to the medical treatments after cataract removal. The eye should be closely monitored during the first 2 weeks postoperatively, and, if necessary, changes in the medication schedule made, depending upon the intensity of the iridocyclitis and the size of the pupil. Topical and systemic antibiotics are administered to prevent intraocular infection if intraoperative contamination occurred. Topical and systemic corticosteroids and NSAIDs are administered to control the postoperative iridocyclitis. Mydriatics are administered to effect; a moderately dilated pupil is preferred. Atropine (1%) combined with 10% phenylephrine, or 0.3% scopolamine combined with 10% phenylephrine, is instilled once to several times daily. Postoperative movements and the eventual size of the pupil are dependent on a moderately dilated pupil established soon after surgery. A miotic pupil postoperatively unfortunately often negates the benefits of this surgical procedure. If excessive fibrin and any blood clots are present 5–7 days postoperatively, 25 mg of tissue plasminogen activator (tPA) is injected into the anterior chamber through a corneal or limbal site under short-acting general anesthesia. Ideally at 1 week postoperatively, very little fibrin or blood is present within the anterior chamber and pupil. IOP is monitored daily and can serve as an indicator of the intensity of the iridocyclitis. As IOP gradually increases toward normal levels of about 15–18 mmHg, the intensity of the postoperative medications is gradually decreased. Topical 1% prednisolone is often instilled for several months postoperatively to impede development of another fibropupillary membrane. The success of this procedure is related directly to the ease or difficulty in removing the fibropupillary membrane and anterior vitreous, amount of intraoperative hemorrhage, successful control of the postoperative iridocyclitis, and resultant size of the pupil. As a guide, the success rate with this procedure ranges from 50% to 80%. Angle-closure glaucoma and phthisis bulbi are infrequent complications.

Pars plana posterior vitrectomy In pars plana vitrectomy, portions of the anterior vitreous, posterior vitreous, or most of the vitreous are excised. The surgery is performed using special instrumentation, inserted through small (20 g needle) incisions (ports or sclerotomies) in the sclera and pars plana ciliaris. This procedure is usually part of the vitreoretinal procedure used for the intraocular portion in the treatment of retinal detachments complicated by retinal holes, giant tears (retinal tears that are 90 or more in circumference), and/or traction bands. This procedure has become quite popular in humans, and

has also demonstrated success in dogs. It will be presented in the subsequent section on retinal detachment surgery.

Adaptations for large animals and special species Suprachoroidal cyclosporine implants for the treatment of equine recurrent uveitis Brian C. Gilger Horses with equine recurrent uveitis (ERU) have episodes of ocular inflammation that characteristically recur and cause blindness in more than half of horses over a 2-year period. Treatment of ERU is generally symptomatic, consisting of topical and systemic anti-inflammatory therapy. Cyclosporin A (CsA) blocks interleukin 2 (IL-2) transcription and impairs proliferation of activated T-helper and T-cytotoxic cells. Therefore, CsA may be an ideal drug to prevent reactivation of ocular inflammation in ERU, which is an immunemediated disease. Because of the difficulty of treatment and the long-term health concerns of some anti-inflammatory medications in horses, sustained delivery of CsA to the eye via implantable drug devices without reliance on the horse owner’s compliance with treatment would greatly facilitate the ability to control ERU. Previous studies have demonstrated that intravitreal sustained-release CsA devices are well tolerated in the equine eye, with and without ERU; however, late-onset traction retinal detachments occurred. Placing sustained release implants in the deep sclera and suprachoroidal space prevents the need to enter the eye, which would eliminate the chance of injuring the lens, minimize the chance of developing endophthalmitis, and decrease rates of retinal detachment, all complications of intraocular surgery. In 2006 we reported on the long-term results of horses that received a suprachoroidal CsA implant for ERU (see further reading, Gilger et al 2006). Horses entered into this study had severe ERU despite topical and systemic antiinflammatory therapy. Sixty-seven horses with 80 eyes treated had a mean of 5.5
2.1 (SD) uveitis flare-ups, or approximately one every 2 months, occurring in the year prior to surgical implantation. Aggressive control of clinically active ocular inflammation with traditional antiinflammatory medications, such as topical and oral steroidal and non-steroidal anti-inflammatory medications, was performed before placement of the deep scleral lamellar CsA device, so that the uveitis was not active at the time of surgery. Presence of vision was required and animals with significant cataract formation (i.e., more than 20% of the anterior cortical surface) were excluded from the study. In-vitro analysis of the CsA implant suggested a projected duration of release of CsA from the implant of 3.18 years. For the suprachoroidal implantation of the CsA device, general anesthesia of the horses is required. After sterile ocular preparation, a conjunctival incision is made followed by a 7 mm partial-thickness scleral flap (90–95% depth centrally) 8 mm posterior to the limbus superotemporally, immediately temporal to the dorsal rectus

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Fig. 12.13 A 7 mm partial-thickness scleral flap (90–95% depth) is made 8 mm posterior to the limbus superotemporally. Exposure of the external choroid (dark central spot) and suprachoroidal space is made in the central area of the scleral dissection.

muscles (Fig. 12.13). Exposure of the external choroid and suprachoroidal space is made in the central area of the scleral dissection. The CsA implant is placed under the flap (Fig. 12.14), and the flap is closed with a 6-0 polyglactin 910 suture (VicrylW; Ethicon, Somerville, NJ). Horses are typically evaluated at 1, 3, and 6 months, and then every 6 months after implantation. In the 2006 study, the 67 horses had exhibited signs of ERU, on average, 16.4
16.0 months (SD; median 12; range 3–120) before receiving the implant. Mean follow-up time was 14.2
9.9 months (range, 3–36; median, 11.5). The number of uveitis flare-ups was significantly decreased after surgery (p ¼ 0.0001), with a mean of 0.544 flare-ups per month before surgery and 0.096 per month (approximately one flare-up per 12 months) after surgery. The only significant correlation between preoperative clinical features and outcome was the presence of preoperative glaucoma, even if medically controlled, and an increase in postoperative uveitis flare-ups (p ¼ 0.0016). No complications were associated with the surgical procedure. Twelve of the 80 eyes became blind (15%) in the 2 years after implantation. Blindness was attributed to uncontrolled uveitis (n ¼ 4), glaucoma

(n ¼ 4), complete cataract (n ¼ 2), retinal detachment (n ¼ 1), and fungal keratitis (n ¼ 1). There was no significant correlation between signalment of the animal, location of surgery, and preoperative ocular clinical signs (e.g., presence of aqueous flare, synechiae, vitreous opacity, cataract, or glaucoma) to postoperative development of blindness. Duration of clinical signs before surgery was significantly longer in eyes that became blind (mean, 31.0
9.1 months) compared with eyes that retained vision (mean, 13.7
10.1 months; p ¼ 0.0003), suggesting that earlier implantation in the course of the disease would result in a better outcome. Overall, the percentage of eyes with vision at 6 months after surgery was 98% (68/69), after 12 months was 93% (43/46), after 18 months was 90% (28/31), and after 24 months was 96% (22/23). Overall, 85% (68/80) of eyes had vision after surgery. Since the publication of this paper, over 500 horses have been implanted worldwide. Success, defined as eliminating flare-ups and maintaining vision, is approximately 85%. The duration of effect is unknown, but if the flare-ups are controlled, most horses have a duration of effect of the implant greater than 5 years. We have reimplanted only two horses in which flare-ups recurred. In two other horses where a single implant did not decrease flare-ups after surgery, a second implant placed in the same eye completely eliminated flare-ups of inflammation. Despite the favorable response of most horses to the use of the suprachoroidal CsA implant, there are several negative aspects of its use. First, the CsA implant is not commercially available, although regulatory approval for marketing the devices is being considered. Implants are available through several universities until the device is commercially available. Second, accurate diagnosis of ERU is required for the device to be effective; the implant may not be effective in infectious or other primary uveitis cases. Third, horses with significant posterior uveitis and associated vitreal opacity should be considered as candidates for vitrectomy to remove the cloudy vitreous (and clear the visual axis) and obtain diagnostic material. Use of vitrectomy and a CsA implant together is a possibility, but further study is needed to determine clinical effectiveness.

Pars plana (anterior) vitrectomy Bernhard M. Spiess

Fig. 12.14 The cyclosporine implant is placed under the sclera flap, adjacent to the exposed suprachoroidal space. The flap is closed over the implant with a 6-0 polyglactin 910 suture. 370

For more than 25 years, pars plana vitrectomy (PPV) has been used in the management of chronic endogenous uveitis (CEU) in people. The main goal was to improve vision by clearing the media or removing membranes. However, it turned out that PPV in eyes with CEU also altered or diminished the severity as well as the frequency of attacks. There is evidence that PPV has a beneficial effect on the clinical course of chronic endogenous posterior uveitis, possibly by physically removing any resident inflammatory cells with the vitreous. Despite the reported complications (i.e., vitreal hemorrhage, cataract formation, retinal detachment) following PPV, an overwhelming majority of the patients were able to switch from rigorous systemic preoperative medication to simple eye drops or no treatment at all. Vitrectomy has been studied in experimental, proteininduced uveitis in rabbits, but it was not until 1991 that

Pars plana (anterior) vitrectomy

PPV was described in the management of ERU. PPV has since been increasingly employed in the treatment of ERU in Europe. Similar to the human counterpart, the most common complications reported in horses are transient hypopyon, vitreal and/or retinal hemorrhage, retinal detachment, and cataract formation. In the majority of reported cases in Europe, Leptospira sp. has been identified in serum and diluted vitreous samples. This indicates that ERU is probably often a sequela of systemic Leptospira infection. The presence of intact Leptospira and specific antibodies in eyes affected with ERU indicates a local antibody production to Leptospira organisms and/or their antigens.

Patient selection Because of the possible serious complications of PPV, patient selection is of great importance. All patients are examined by slit-lamp biomicroscopy, indirect and direct ophthalmoscopy, and applanation tonometry. Ultrasonography is performed in cases with opaque media. The diagnosis of ERU is based on the typical signs of acute or chronic uveitis and a documented history of recurrent episodes of acute uveitis. Recent clinical evidence suggests that horses with aqueous humor samples testing positive for Leptospira sp. should be considered suitable candidates for PPV, while those testing negative should receive alternative therapies. Horses ideally are operated in the quiescent stage of the disease. Because of the transpupillary visualization of the vitrectomy probe during the procedure, the optical media (i.e., cornea, anterior chamber, lens) should be as transparent as possible. The pupil should dilate maximally with no or few

posterior synechiae. Pre-existing focal cataracts are likely to progress following PPV. This should be taken into consideration. In patients with secondary glaucoma, phthisis bulbi, or pre-existing retinal detachment, PPV should not be recommended. Owners should be carefully informed on the surgery, as well as the possible intra- and postoperative complications.

Pre- and postoperative medication Topical 0.1% dexamethasone drops in combination with neomycin and polymyxin B are administered once daily beginning 1 week prior to surgery. Systemic NSAIDs (i.e., vedaprofen, flunixin meglumine) are administered beginning 3 days preoperatively. The pupil is dilated with 1% atropine drops on the day of surgery. Postoperatively, topical dexamethasone/neomycin/polymyxin B eye drops are continued three times a day for 2 weeks, and then tapered over another 4 weeks. Systemic NSAIDs are continued for 1 week.

Surgical technique A standard two-port PPV is performed in lateral recumbency under general inhalational anesthesia. The eye is prepared for intraocular surgery. After draping, an eyelid speculum is inserted. A lateral canthotomy may improve exposure of the globe; however, this is usually not necessary. A limbal stay suture in the 12 o’clock position is placed for globe manipulation (Fig. 12.15a). A limbal-based conjunctival flap is prepared and the sclera exposed medially and

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Fig. 12.15 Pars plana (anterior) vitrectomy in the horse. (a) The eye is prepared for intraocular surgery. A bridle suture has been placed in the 12 o’clock position. (b) After preparing a conjunctival flap, the first sclerotomy is performed in the 11 o’clock position using a CO2 laser. (c) A small amount of vitreous is protruding through the sclerotomy. (d) The irrigation port is introduced into the sclerotomy and anchored to the sclera using 4-0 VicrylW. (e) The vitrectomy probe is introduced in the 1 o’clock position through a second laser sclerotomy. The tip of the probe can be seen behind the lens. (f) The deeper parts of the vitreous are visualized with the 20 D lens and an indirect ophthalmoscope. 371

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laterally to the dorsal rectus muscle. Using a CO2 laser, a first sclerotomy is performed 10 mm posterior to the limbus (Fig. 12.15b,c). A right-handed surgeon will place this first entry to the left of the rectus muscle. A double-ended lacrimal dilator may be used to enlarge the sclerotomy if necessary. The irrigation port is inserted and its footplate secured to the sclera with two 4-0 polyglactin 910 sutures (Fig. 12.15d). With the vitrectomy unit in continuous irrigation mode and the fluid-containing bottle positioned 85 cm higher than the surgical site, the IOP will be around 40 mmHg. Balanced salt solution (BSS) with 40 mg of gentamicin added per 500 mL is used as irrigation fluid. A second laser sclerotomy is performed, again 10 mm posterior to the limbus and to the right of the rectus muscle. The vitrectomy probe is carefully inserted and advanced in the direction of the center of the vitreous. Again, the sclerotomy may be enlarged with a lacrimal dilator if necessary. Both sclerotomies should be tight enough to prevent leakage of irrigation fluid, which would make maintenance of IOP difficult. The vitrectomy probe should be held at an approximately 70 angle and passed toward the optic nerve, taking care to avoid touching the lens when inserting the probe. The probe tip should be held with the aspiration port facing the surgeon. In this position the port can be visualized through the pupil using the light of an indirect binocular ophthalmoscope (Fig. 12.15e). The central and anterior parts of the vitreous can be removed by direct visualization through the dilated pupil. Indirect ophthalmoscopy using a 20 D lens is used to visualize posterior and peripheral parts of the vitreous (Fig. 12.15f). Aspiration of vitreous can easily be observed, especially if there are inflammatory materials. Again, care is taken to avoid the lens. Estimating the distance between the probe and its shadow cast onto the retina will help the surgeon to avoid touching the retina. Throughout the entire procedure, the IOP should be maintained at approximately 40 mmHg. Slight wrinkling of the retina, seen with the aid of the ophthalmoscope, indicates that the IOP may be too low. Vitrectomy should be interrupted until a normal IOP is restored. The procedure is continued until all turbid vitreal material has been removed. Under continuous irrigation, the vitrectomy probe is removed and the sclerotomy closed with one or two single interrupted sutures using 4-0 polyglactin 910. Subsequently the irrigation port is removed. Remaining peripheral vitreous will usually prevent fluid from escaping through this sclerotomy, which is closed with 4-0 polyglactin 910. The conjunctiva is closed with polyglactin 910 in a continuous pattern. A canthotomy is closed with a figure-of-eight suture using 4-0 non-absorbable suture materials. At the end of surgery 20 mg of methylprednisolone is injected subconjunctivally in the inferior bulbar conjunctiva. Some differences performing this procedure in the horse have been established. To avoid uveal hemorrhage, both sclerotomies are performed using a CO2 laser in continuous mode at 50 W. Commercially available vitrectomy probes are too short for use in horses. A custom-made 55 mm oscillating vitrectomy with a guillotine-like chopping blade probe is used at 12.0 Hz, an aspiration vacuum of 400 mmHg, and a flow rate of 15 mL/min. High oscillation frequency, moderate suction, and low flow is used to minimize vitreoretinal traction and decrease the incidence of iatrogenic retinal breaks.

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Complications Intraoperative complications include vitreal/retinal hemorrhage and retinal detachment. Maintaining IOP at around 40 mmHg and using a CO2 laser for the sclerotomies instead of surgical blades or cannulas can avoid hemorrhage. Touching the retina should also be avoided as it results in immediate hemorrhage and subsequent detachment. Early postoperative complications (less than 3 months) include cataract formation and retinal detachment. Late complications occurring after 3 months include cataract formation as well as recurrence of active uveitis.

Long-term results Seventy-three percent of horses that underwent pars plana vitrectomy showed no further recurrence of uveitis; 22% continued to suffer from recurrent episodes of uveitis. The remaining horses were reported to have experienced only one more episode of uveitis, which was easily controlled with topical anti-inflammatory therapy. Vitreous samples of every horse were submitted and 78% were positive for Leptospira sp. The most common serovars were L. grippotyphosa, L. copenhageni, L. bratislava, L. canicola, L. pyogenes, and L. pomona. Of the Leptospira-positive horses, 81% showed no further recurrences after vitrectomy, while of the Leptospira-negative patients, 83% had further recurrences. It appears that pars plana vitrectomy represents a successful surgical therapy for horses suffering from Leptospira-related ERU, while patients testing negative for Leptospira sp. are poorer candidates for this surgery. They may, however, be more suitable candidates for the implantation of cyclosporinereleasing devices. Clinical experience would suggest that aqueous humor and/or vitreous samples of horses suffering from ERU should be tested for Leptospira sp., and that the decision to perform pars plana vitrectomy should be based on these results. In another study of 38 cases, five eyes showed recurrence of uveitis between 10 days and 3 years postoperatively. Thirty-three eyes showed no recurrence during a follow-up period of up to 5 years. Vision remained stable in 28 eyes and improved in one eye. The remaining eyes showed marked vision loss as a result of cataracts (3), phthisis bulbi (22), or unknown cause (22). Of the five eyes with recurrent uveitis, two demonstrated marked loss of vision, while three maintained preoperative vision. In an earlier study of 43 eyes post PPV, 42 remained free of recurrent uveitis during a follow-up period of 67 months, with 70% of these eyes retaining some vision. The most common complication was cataract formation in 19/43 eyes, followed by phthisis bulbi in six eyes, and retinal detachment in four eyes. Most veterinary ophthalmologists agree that the longterm prognosis for ERU with medical therapy alone is poor. Even aggressive therapy is often insufficient to prevent recurrent painful inflammatory episodes. Cumulative intraocular damage often leads to phthisis bulbi, glaucoma, or loss of vision as a result of cataract formation or retinal detachment. In selected patients with consenting owners, PPV offers a promising alternative to conventional therapy. With few exceptions, eyes show no recurrence of uveitis after PPV.

Surgery of the retina

However, a significant number of postoperative complications cause visual impairment or blindness. The most common long-term postoperative complication appears to be cataract formation. It is unclear whether pre-existing lenticular opacities progress despite PPV or if the progression is caused by the procedure. Touching the posterior lens capsule during PPV invariably leads to focal cataracts, which very often progress. Retinal and vitreal hemorrhage is the most common intraoperative complication. Maintaining a high normal IOP, careful manipulation of the vitrectomy probe, and avoidance of touching the retina usually prevents such complications. Choroidal hemorrhage can be avoided with the use of a CO2 laser instead of a surgical blade. Pars plana vitrectomy appears to be a promising method for long-term control of equine recurrent uveitis.

Surgery of the retina Different types of surgical procedure In this section the different surgical procedures for the dog and cat retina and retinochoroid are described. They include: 1) subretinal fluid aspiration; 2) chorioretinal biopsy; 3) retinopexy; and 4) retinal detachment surgery. The aspiration of subretinal fluids is often part of retinal detachment surgeries but will be presented separately. Chorioretinal biopsies have been performed in dogs experimentally for the analysis of retinal tissues. This technique permits multiple evaluations of retinal tissues in a single eye in a dog to document tissue changes as the retinal disease progresses. Retinal detachment surgeries represent an under-utilized opportunity for veterinary ophthalmology. The surgical advances in these same surgical techniques used in humans are being applied to the dog. Retinal detachments in small animals are unfortunately presented much later than in humans. However, periodic fundus examinations of highrisk patients such as dogs with congenital posterior segment diseases, such as the Collie, Shetland sheepdog and Australian shepherd breeds, and all dogs that have undergone cataract surgeries, can detect retinal detachments amenable to repair, and before blindness and irreversible retinal degeneration have occurred. Some retinal detachment surgical procedures have become routine in major veterinary ophthalmology referral centers. Vitreoretinal surgeries performed through small incisions in the pars plana ciliaris require special and expensive instrumentation, which has delayed implementation in small animal patients. A recent study by Grahan and associates of 17 canine patients with chronic complete retinal detachments found that, for those eyes not treated or treated only medically, the majority had to be enucleated within 12 months because of intractable uveitis, cataract formation, pre-iridal membrane formation, and secondary glaucoma. In contrast, those eyes (4/6 eyes) with vitrectomy and perfluorocarbon gas retained some vision at 3 years. Although limited in patient numbers, this report suggests that surgical treatment of complete detachments should be attempted in dogs; if not, most affected eyes must be removed within 12 months for painful and intractable eye diseases.

Subretinal fluid aspiration Subretinal fluids may be aspirated in the treatment of serous retinal detachments as well as to obtain subretinal fluids for analyses for cytology and culture for bacterial and fungal organisms. For aspiration of subretinal fluids, the location and extent of the retinal detachment must be accurately determined by direct and indirect ophthalmoscopy, and ultrasonography. The technique is performed after the onset of general anesthesia, clipping of the eyelid hair, cleansing of the eyelid skin, corneal and conjunctival surfaces with 0.5% povidone–iodine solution and sterile cotton swabs, and retraction of eyelids by speculum. Depending on the position of the serous or exudative retinal detachment, a fornix-based bulbar conjunctival flap is incised by Steven’s tenotomy scissors about 5 mm posterior to the limbus (Fig. 12.16a). The dissection is continued posteriorly beneath the epibulbar fascia or Tenon’s capsule. This tissue plane allows blunt–sharp tissue dissection without significant hemorrhage. If the posterior dissection strays into Tenon’s capsule, hemorrhage results and impedes the surgical procedure (Fig. 12.16b). At about 10–12 mm posterior to the limbus, the insertions of the rectus muscles are identified (Fig. 12.16c). If one of these muscles is directly over the subretinal aspiration site, it may be transected immediately posterior to its insertion into the sclera. A single 4-0 nylon suture is placed in both of the incised ends of the rectus muscle, for eventual reattachment to its insertion after completion of the subretinal fluid aspiration. To double-check the position for the subretinal fluid aspiration, indirect ophthalmoscopy is performed using a sterile 20 diopter lens and a headset placed temporarily on the surgeon’s head. Aspiration of subretinal fluids is performed with a 28–30 g hypodermic needle attached to a 1 mL sterile syringe inserted through the adjacent sclera and choroid. As hemorrhage from both sclera and choroid may occur, a 30 g diathermy needle is inserted to provide both a needle pathway and hemostasis (Fig. 12.16d). The aspirating needle is carefully inserted through the diathermy site and a quantity of subretinal fluid aspirated (Fig. 12.16e). The volume is usually about 0.1–0.2 mL. The fundus is re-checked and the retinal detachment is usually reduced from loss of subretinal fluids. An alternative and safer method consists of a small linear scleral incision parallel to the underlying choroidal blood vessels. Through this small scleral incision, a 30 g diathermy tip is inserted into the subretinal space. Subretinal fluids are drained by rolling a cotton swab on the external sclera toward the diathermy hole. Closure includes: 1) reapposition of the rectus muscle insertion with two or three 4-0 to 6-0 simple interrupted non-absorbable sutures if the rectus muscle insertion was transected; and 2) apposition of the limbal-based bulbar conjunctival flap with a 6-0 to 7-0 simple continuous absorbable suture (Fig. 12.16f). Complications after the aspiration of subretinal fluids are infrequent, provided the procedure is properly performed. Subretinal hemorrhage is the most common sequela. If hypodermic needle penetration of the retina occurs, cryotherapy is immediately applied to the site.

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Fig. 12.16 Aspiration of subretinal fluids is used in the treatment of retinal detachments and to assist in the diagnosis of chorioretinitis. (a) A fornix-based conjunctival flap is performed with Steven’s tenotomy scissors. (b) By blunt–sharp dissection beneath the bulbar fascia (Tenon’s capsule), the retrobulbar space is entered. (c) Depending on the position of the subretinal fluids, the adjacent rectus muscles are identified. (d) After checking the ocular fundus and site for subretinal fluids by indirect ophthalmoscopy, a 30 g diathermy needle is applied for hemostasis to the sclera and choroid for the site of the needle puncture. (e) After entry of the subretinal space with a 25 g hypodermic needle, a small volume (0.1–0.2 mL) of subretinal fluid is withdrawn. Indirect ophthalmoscopy is repeated and with loss of the subretinal fluids, the serous or exudative retinal detachment is usually flatter. (f) Closure consists of apposition of the conjunctival wound with a 6-0 to 7-0 simple continuous absorbable suture.

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Chorioretinal biopsy Chorioretinal biopsies permit histologic and biochemical analyses of small sections of choroid and retina. Chorioretinal biopsies have been performed in both normal dogs and in dogs with progressive retinal degenerations to investigate the different stages of the disease. This technique could also be used for potential chorioretinal neoplasia to establish the diagnosis. The principal concern of any surgical procedure that incises the full-thickness retina is immediate vitreous loss and secondary retinal detachment. Both techniques reported in the dog have avoided these serious complications. Both procedures use a similar surgical approach, and will be presented together. Preoperative treatments with topical and systemic antibiotics and corticosteroids are recommended. The pupil is dilated with 1% atropine to accommodate intraoperative indirect ophthalmoscopy. After the onset of general inhalational anesthesia, clipping of the eyelid hair, and cleansing of the eyelid skin, corneal and conjunctival surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. A lateral canthotomy may be performed to enhance surgical exposure. Neuromuscular blocking agents (see Chapter 3) are administered intravenously for optimal positioning of the globe and relaxation of all extraocular muscles. Mannitol (2 gm/kg IV) is administered at the start of surgery to shrink the vitreous body. Immediately prior to the scleral incision and chorioretinal biopsy, the mean arterial (aortic) blood pressure is slowly reduced over 10 min from about 120 to 50 mmHg with the use of 3–4% halothane and intermittent positive pressure ventilation (20 cycles/min). Both methods reduce IOP, minimize choroidal bulging, and constrict the choroidal and retinal blood vessels. The surgical approach is performed in the dorsal fundus, where access is the most convenient. A fornix-based conjunctival flap is performed with small thumb forceps and tenotomy scissors (Fig. 12.17a). Dissection is continued posteriorly beneath Tenon’s capsule (bulbar

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fascia) to minimize hemorrhage. The insertions of the dorsal and lateral (or the dorsal and medial) rectus muscles are identified and isolated (Fig. 12.17b). The biopsy site is usually posterior to the equator and the exit of the vortex veins. A full-thickness scleral flap about 3–4 mm in diameter is carefully constructed using the Beaver No. 6400 microsurgical blade. The incision for the scleral flap is about 270 with its hinge at the caudal aspects (Fig. 12.17c). The scleral flap is carefully elevated and blunt dissection with tenotomy scissors is used to separate the deep aspects of the scleral flap from the choroid (Fig. 12.17d). Three sutures of 9-0 nylon are pre-placed through both edges of the scleral incision and the scleral flap prior to biopsy to, if necessary, effect immediate wound closure (Fig. 12.17e,f). The center of the choroid is grasped and elevated with serrated thumb forceps. With curved Vannas scissors, a full-thickness incision of the choroid and retina is made to excise a 1–3 mm circular section (Fig. 12.17g). The scleral flap is apposed with the three pre-placed sutures. Two or three additional simple interrupted 9-0 nylon sutures are positioned between the pre-placed sutures for complete apposition of the scleral flap (Fig. 12.17h). The conjunctival flap is apposed with a 6-0 simple continuous absorbable suture (Fig. 12.17i).

Postoperative management Postoperative management includes topical and systemic antibiotics and corticosteroids. Mydriatics, such as 1% atropine, are instilled to maintain moderate pupillary dilatation. If possible, the surgical site should be monitored daily for 1–2 weeks, and then weekly until healing occurs, as evidenced by a depressed pigmented circular retinal defect. Potential complications include occasional intraoperative vitreous loss, and excessive hemorrhage from the retinal and/or choroidal blood vessels. Postoperative retinal detachments secondary to the full-thickness retinal defect are possible, but did not result in the experimental studies.

Surgery of the retina

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Fig. 12.17 Chorioretinal biopsy in the dog is used to obtain small (1–3 mm) samples of generalized disorder of the choroid and retina for diagnosis. (a) A dorsal fornix-based conjunctival flap is performed with Steven’s tenotomy scissors. (b) Blunt–sharp dissection is continued posteriorly by Steven’s tenotomy scissors, usually between the dorsal and lateral rectus muscle insertions. (c) Posterior to the equator, a full-thickness scleral flap is performed with the Beaver No. 64 scalpel blade. The hinge for the scleral flap is caudal of the surgical approach. (d) By blunt dissection the scleral flap is raised, and with Steven’s tenotomy scissors the underlying choroid is separated for the sclera. (e) Three pre-placed 9-0 nylon sutures are positioned on both sides and at the end of the scleral flap. (f) An enlarged view of the scleral flap for entry to the choroid and retina. Note the three pre-placed sutures are about one-half to two-thirds the thickness of the sclera. (g) With sharp Vannas scissors a section (1–3 mm diameter) of choroid and retina is excised. (h) The scleral flap is secured with the three pre-placed sutures as well as additional 9-0 simple interrupted nylon sutures. (i) Closure consists of apposition of the conjunctival wound with a 6-0 simple continuous absorbable suture.

The different types of retinopexy Pneumatic retinopexy Pneumatic retinopexy has been described for the dog, but unfortunately has several limitations. In this procedure expansile gases are used to tamponade the retina against the underlying retinal pigment epithelium and close a retinal tear or break. Laser or cryotherapy is used to seal the retinal break and produce a focal chorioretinal adhesion. Sulfur hexafluoride (SF6) or perfluoropropane (C3F8) gases have also been used. These gases can persist in the vitreous space for different periods and expand differently. SF6 gas expands 2.5 within 48 h and usually persists for 10–14 days. In contrast, C3F8 gas expands 4 within 72 h and persists for 4–6 weeks. As these are gases, they are mobile in the vitreous; to be effective, the gas bubble needs to be positioned directly over the retinal break. In humans, the patient’s head is immobilized for long periods for small dorsal retinal detachments (less than 1 clock hour in size); unfortunately in dogs this is not possible, thereby limiting this technique in dogs. An excessive amount of gas within the vitreous can increase IOP and

escape subconjunctivally. Most retinal detachments and retinal tears in dogs are too large (greater than 3 clock hour in size; giant tears) and are not amenable to pneumatic retinopexy.

Therapeutic retinopexy Therapeutic retinopexy, or the sealing of retinal holes or breaks with no or limited flat retinal detachments, is performed with laser photocoagulation, cryotherapy or cryopexy, and scleral buckling. Laser photocoagulation is usually used for those retinal breaks located more posterior and near the optic disk, as may occur in Collie eye anomaly (Fig. 12.18). The laser therapy is delivered through the pupil and directly about the retinal break. For more anterior retinal breaks, cryopexy is recommended and may be delivered transconjunctivally (without incision) or directly on the sclera through a fornix-based conjunctival approach. During these retinopexies, the break should be directly visualized by indirect ophthalmoscopy, and the therapy directed to surround the retinal break with one or more layers of retinopexy. Retinopexy is less satisfactory for these retinal breaks and small retinal detachments but with vitreal traction.

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Fig. 12.18 Collie eye anomaly (CEA) and possible indications for retinopexy. (a) A young Collie with a peripapillary coloboma next to the optic nerve head. These lesions may predispose this eye to retinal detachment. (b) Another young Collie with retinal hemorrhage and retinal detachment. (c) A young Collie with retinal detachment treated with diode laser retinopexy. Note the large preretinal hemorrhage which was caused by the laser retinopexy.

In a comparative study by Sullivan and co-workers, cryoretinopexy and diode laser transscleral retinopexy were compared in the dog. Nitrous oxide cryoretinopexy caused retinal edema and transfocal serous retinal detachments and, in general, produced larger and more severe retinal degeneration. The cryotherapy procedure used a retinopexy cryoprobe that produced an expanding iceball around the retinal tissue in 10–15 s. In contrast, diode laser retinopexy produced more obvious retinal vasculature damage. In 30 days, both techniques caused mild perivascular scleritis, choroidal thinning, retinal degeneration, and retinal pigment migration. The diode laser was used to produce two rows of retinal burns immediately posterior to the ora ciliaris retinae with 0.8 s and 400 mW settings. The laser induced an immediate white to light gray spot.

Demarcation and barrier retinopexy Retinopexy has been used successfully to treat early retinal detachments in collie eye anomaly. These serous retinal detachments were associated with optic disk pits and successfully treated with xenon arc photocoagulation applied along the edges of the detachment. In one report, 25 of 28 eyes with focal retinal detachments responded to a single treatment of photocoagulation. Two additional eyes responded after the administration of a second xenon arc photocoagulation. Only one eye failed to respond and eventually the retina totally detached. The duration of the xenon arc photocoagulation for each site was 1 s with a power setting of 8 mV. Treatment consisted of a single row of contiguous photocoagulation applications placed immediately adjacent to the edge of the retinal detachment along the edge of the optic disk. The individual spots of the xenon arc photocoagulation appeared orange in the tapetal fundus and white on the non-tapetal fundus. Retinal reattachment occurred in most dogs within 2–4 weeks after photocoagulation. The area of retinal detachment invariably resulted in focal retinal degeneration. In another report, rhegmatogenous (retinal breaks, holes, or tears) retinal detachments in three of four dogs that developed postoperatively after cataract surgery were successful treated by scleral buckling and cryotherapy of the retinal hole. This fundamental retinal detachment surgical procedure, performed primarily extraocularly, will be presented.

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Prophylactic retinopexy Prophylactic retinopexy is being used more frequently by veterinary ophthalmologists in dogs of certain breeds (Bichon Frise, American Cocker Spaniel, Siberian Husky, Havanese) that may develop retinal breaks and peripheral retinal detachments after cataract surgery, and in fellow or opposite eyes of phakic dogs with unilateral retinal detachment. Eyes at risk for retinal detachment in dogs appear to be those with hypermature cataracts, as well as those breeds with lens luxations and intracapsular lensectomies. Prophylactic retinopexy is usually delivered by cryotherapy directed to the dorsal peripheral retina, either before or immediately following cataract surgery or intracapsular lensectomy. This therapy should be performed with the dorsal peripheral retina under direct observation. The goal of this therapy is to stimulate the development of dorsal chorioretinal scarring and adhesions to the region of the retina most apt to develop retinal breaks and detachment. In a recurrent study by Schmidt and Vainisi in the Bichon Frise breed with cataract formation, the effectiveness of prophylactic transscleral retinopexy was investigated. The control group had no retinopexy and cataract resorption (20 eyes); 12 (60%) of the eyes developed rhegmatogenous retinal detachments (RRD). The second group consisted of dogs that had phacoemulsification of cataracts (18 eyes); 10 eyes (55%) developed RRD. The third group consisted of dogs that had prophylactic transscleral retinopexy and cataract resorption (19 eyes); 2 eyes (10%) developed RRD. In the fourth and last group, 39 eyes had both prophylactic transscleral retinopexy and phacoemulsification of cataracts. In this last group, RRD developed in 5 eyes (12%). This study is the largest to date, and clearly demonstrates the value of prophylactic transscleral retinopexy in the Bichon Frise breed with inherited cataracts. In the Schmidt and Vainisi study, prophylactic transscleral retinopexy was delivered by either cryopexy or laser retinopexy. For the cryopexy, a nitrous oxide curved retinal probe was placed 10 mm posterior to the limbus with five to six freezes per site for 10–12 contiguous sites, 360 around the globe. For laser retinopexy, a diode transscleral probe was used with 800 mV and 1000 ms settings. The laser probe was positioned 10 mm posterior to the limbus; five to six burns were directed toward the optic nerve and continued

Surgery of the retina

clockwise around the globe. Recommended laser burns were changed from 25–40 to 65–75 laser burns per eye. Retinopexy can also be performed by either cryotherapy or laser combined with the indirect ophthalmoscope in a transpupillary fashion when direct observation of the peripheral retina is possible. Excessive treatment is avoided, as vitreous contraction and giant retinal tear may occur. For cryopexy of the peripheral retina, the cryoprobe must be placed 10 mm posterior to the limbus except inferiorly and nasally, where it can be 2 and 4 mm closer, respectively. Schmidt and Vainisi recommend 10–12 contiguous freezes around the globe. The freeze is stopped once the cryoprobe touches the sclera (6–7 s) or when a white spot develops as viewed by indirect ophthalmoscopy. For chorioretinal adhesions to develop, 10–12 days are required. For laser retinopexy delivered through the pupil by indirect ophthalmoscopy, the ocular media must be sufficiently clear to permit focus on the target retina. Two rows of contiguous burns of the peripheral retina for 360 are performed. Laser settings vary based on tissue pigmentation, laser, clarity of the ocular media, and angle of incidence of the laser beam; one recommendation with the diode laser is 250 mW of power at 1000 ms. With both methods of performing retinopexy in the dog, a minimum of 2 weeks is recommended before attempting cataract surgery to ensure good chorioretinal adhesion.

performed both extra- and intraocularly using a pars plana approach. The former more basic technique has been described in the veterinary medical literature, and has been employed by several veterinary ophthalmologists. The pars plana approach is used for the more extensive retinal detachments complicated by retinal breaks and tears, requires special instrumentation and training, and is the preferred procedure by most vitreoretinal surgeons today. This technique is the most frequently performed procedure in humans and is most useful for rhematogenous retinal detachments. Retinal detachments and secondary glaucomas are the most serious complications after cataract surgery in the dog. Both of these conditions can also develop in dogs with only cataract formation, lens-induced uveitis, and the result of resorbing cataracts. Both of these complications, if diagnosed early, can be effectively treated and vision prolonged. Retinal detachments have been reported in occur in 4.2–10.3% of dogs after cataract surgery. As these retinal detachments usually develop unilaterally, only repeated postoperative examination can detect early and limited size detachments. Hence, the recommendation after cataract surgery is for repeated, often quarterly, re-examinations indefinitely. Retinal detachments should be assumed rhematogenous until proven otherwise, and considerable time and patience may be necessary during indirect ophthalmoscopy, often with scleral depression, to detect the retinal break(s).

Patient selection

Retinal detachment surgery Retinal detachment surgery in small animals is still in its infancy; however, there are several reports of successful surgical treatment of retinal detachments in dogs. For simplicity, retinal detachment surgery may be divided into: 1) that performed primarily extraocularly; and 2) that

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Fig. 12.19 Examples of retinal detachments and giant tears. (a) External appearance of a Lhasa Apso dog presented with vitreal syneresis, hemorrhages, retinal detachment, and a giant retinal tear. (b) Ophthalmoscopic view of the same eye showing the retinal detachment and a giant retinal tear. (c) An American Cocker Spaniel with retinal detachment and a giant retinal tear. (d) Another American Cocker Spaniel with retinal detachment and a giant retinal tear.

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of 20/20 visual acuity is possible if the retina is reattached with 7–9 days post-detachment. In dogs, reattachment of the retina within 4 weeks after retinal detachment provides a reasonable chance for some functional clinical vision. Pupillary light reflexes are helpful to assess retinal function; flash electroretinography has been less reliable. Eyes with RD and almost extinguished electroretinograms can recover vision; within 1 week after reattachment the ERG begins to return to normal. Corneal opacities as well as post-cataract opacities can also interfere with RD surgery, and may need to be treated either before or during surgery. As secondary glaucoma is not uncommon after RD surgery, preoperative gonioscopy is also recommended. The general health of the patient must also be determined, as most retinal detachment surgeries are 2–3 h long.

Preoperative medication As retinal detachment surgeries often span 2–3 h, topical and systemic antibiotics are administered beginning 2 or 3 days preoperatively. Topical and systemic corticosteroids are also administered to combat the anticipated postoperative intraocular inflammation. Systemic and topical NSAIDs are also usually administered. Mydriasis is critical intraoperatively to observe the retinal detachment and the operative changes. Atropine (1%) combined with 10% phenylephrine, or 0.3% scopolamine combined with 10% phenylephrine, is instilled starting the day before surgery. Control of IOP may become important postoperatively, especially if a scleral buckle or silicone oil is used. Hence, a few tonometries at different times of the day should be performed preoperatively to establish the range of IOP each patient should approximate postoperatively. If higher levels occur postoperatively, drugs to lower and maintain safe levels of IOP are important to prevent pressure-induced retinal degeneration.

Basic retinal detachment surgery with a retinal hole or small tear After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of the eyelid skin, conjunctival and corneal surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. A lateral canthotomy is used to increase exposure. A 180–360 fornix-based conjunctival flap is performed with small thumb forceps and tenotomy scissors (Fig. 12.20a). This peritomy is performed 1–2 mm from the limbus. Dissection is continued posteriorly beneath Tenon’s capsule to the insertions of all of the rectus muscles (Fig. 12.20b,c). If surgical exposure about the rectus muscles and the equator is adequate, transection of each rectus muscle insertion is avoided. Because of the usual dorsal approach, the lateral and medial rectus muscles are secured by sutures, and with traction, can proptose the globe forward. However, if surgical exposure is poor, each rectus muscle insertion is identified, tagged with nylon or silk sutures, and transected. With loss of the rectus muscles, the globe can usually be manipulated forward for improved exposure. Indirect ophthalmoscopy is performed with a sterile 20 diopter condensing lens to locate the retinal tear. A cotton-tipped applicator or sterilized scleral depressor is

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used to indent the sclera to locate the break (Fig. 12.20d). The sclera overlying the retinal hole may be marked with a disposable cautery unit (diathermy) or a nylon suture (Fig. 12.20e). Interrupted horizontal mattress 5-0 braided polyester sutures are pre-placed partial thickness in the sclera in each quadrant to secure later a 4–5 mm encircling retinal silicone buckle or some other type of scleral buckle around the equator. If additional focal depression on the sclera is anticipated in the area of the retinal break, four additional interrupted mattress sutures are pre-placed (Fig. 12.20f). The retinal break may be sealed by nitrous oxide cryopexy or transscleral diode laser photocoagulation while being directly visualized by indirect ophthalmoscopy (see previous retinopexy section). Cryotherapy is applied until the first signs of retinal freezing (whitening of the edges of the torn retina) are detected. Multiple sites are frozen until the retinal tear has been surrounded by these freezes (Fig. 12.20g,h). To help appose the retinal detachment and the retinal pigment epithelium, scleral buckling is necessary. Scleral buckles range from round or encircling hard silicone straps to small soft silicone sponges. These buckles must extend at least 2 mm beyond the retinal break and are applied externally to the sclera in a radial, circumferential, or encircling fashion, or some combination thereof. Ideally the buckle should also extend forward of the break and near the vitreous base. The small radial buckle is placed perpendicular to the limbus and is effective for small retinal breaks and more posterior breaks. The circumferential buckles are used for multiple retinal breaks, wide and anterior breaks. The encircling retinal buckle is used to surround the entire globe with extensive retinal detachments and when the retinal break (because of hazy media) cannot be localized. These encircling buckles can be augmented with focal sponges to apply additional pressure and indentation in the area of the retinal break. A 4–5 mm wide retinal detachment silicone band (buckle), presoaked in gentamicin (50 mg/mL) for 30 min, is applied under the four rectus muscles to encircle the entire globe and positioned over the retinal break. The retinal detachment band or buckle is secured to the globe with the four pre-placed interrupted mattress sutures. The ends of the band are secured by a clove hitch (Fig. 12.20i–l). Any subretinal fluids may be aspirated. After a small deep scleral incision parallel to the underlying large choroidal blood vessels, a puncture into the subretinal space is performed with a 30 g diathermy needle. Subretinal fluids are drained by rolling a sterile cotton swab in several directions toward the diathermy hole. The silicone band is tightened to indent the globe to effect or about 2 mm, thereby shortening the globe circumference by about 15%. Indirect ophthalmoscopy is used again, to check that the buckle is properly positioned and that the retina is against the underlying retinal pigment epithelium (Fig. 12.20m). Closure includes apposition of the fornix-based conjunctival flap with several 6-0 simple interrupted absorbable sutures or two interrupted mattress sutures at the 9 and 3 o’clock positions (Fig. 12.20n).

Surgery of the retina

Postoperative management Postoperative care includes topical and systemic antibiotics for 5–7 days. Topical and systemic corticosteroids are administered to effect, depending on the intensity of the postoperative iridocyclitis. Since the eye is not entered surgically, the postoperative posterior segment inflammation is focal and controllable. Mydriatics, such as 1% atropine, are instilled daily, to maintain a dilated pupil that accommodates periodic indirect ophthalmoscopy and inspections of the retinal break and retinal detachment. Successful repair results in a gradual flattening of the retinal detachment, and development of pigmented and non-pigmented retinal scars within the retinal break, secondary to cryotherapy. IOP must be monitored daily postoperatively for the first week. If IOP is increased, topical adrenergics, and systemic or topical carbonic anhydrase inhibitors are administered. In the event that IOP is still elevated, anterior chamber paracentesis may be necessary. Postoperative complications after retinal detachment surgery in dogs appear infrequent, but too few cases have been reported to date. Potential serious complications include: 1) angle-closure glaucoma secondary to an excessively tight scleral encircling buckle or excessive cryopexy; 2) necrosis of the anterior segment from damage to the long posterior ciliary blood vessels, tenotomy of the insertions of all of the rectus muscles, or an excessively tight encircling band; 3) 25–50% cataract formation in phakic animals; 4) orbital hemorrhage with some exophthalmia and impaired ocular motility; 5) posterior uveitis with re-detachment; and 6) corneal ulceration (from the prolonged surgery and perhaps impaired blink postoperatively).

Pars plana retinal detachment surgery The second retinal detachment surgical procedure, using both extraocular and intraocular manipulations, is performed in the phakic and aphakic dog for more serious retinal breaks, including giant retinal tears. Giant retinal detachments and retinal tear or breaks (greater than 3 clock hours in size) are the most common RD in dogs, and this surgical procedure is the most frequently performed in the dog. This procedure is considerably more difficult, time consuming, and requires additional training and an investment in special instrumentation for intraocular irrigation, aspiration, and cutting, but it may provide the best anatomic and visual postoperative results. Newer techniques, such as intravitreal injections of silicone oil and perfluorocarbon gases (short term, sulfur hexafluoride (SF6); long term, perfluoropropane (C3F8)), have been demonstrated effective in dogs with retinal detachments associated with large or giant retinal tears. The perfluorocarbon gas initially and later intravitreal silicone oil are used intraoperatively to tamponade and roll the retina against the retinal pigment epithelium, and postoperatively silicone oil is left in the vitreous space to continue the tamponade of the retinal break, independent of eye position. However, silicone oil can migrate to the anterior chamber of aphakic dogs and has been associated with elevated IOP, corneal decompensation, and edema. The perfluorocarbon gases have similar benefits to silicone oil, but eye positioning is critical for the gas to be in direct contact with the retinal break. This is impossible to achieve

in the dog unless the retinal hole or tear is present in the dorsal ocular fundus. Retinal tacks (3 mm diameter stainless steel) have been reported by Vainisi and Packo in dogs to treat giant retinal tears. In all dogs, the retinal tears were 360 . In three of the 16 dogs, retinal detachments developed after cataract surgery; the remaining 13 retinal detachments were idiopathic. The tacks, loaded in a special holder and inserted through the pars plana ’ports’, were used to impale or tack the retina, choroid, and sclera approximately 1–2 mm posterior to the edge of the retinal tear. After tacking of the edge of the torn retina, endophotocoagulation or cryoretinopexy (applied external to the globe) is used for additional chorioretinal adhesions. The former technique, endophotocoagulation, was preferred when the retinal tacks were used. Use of these tacks with the newer silicone oil methods to hold the retina in position has been reduced. Traction bands connecting the posterior iris, pupil, posterior lens capsule, ciliary body, and peripheral retina frequently develop during postoperative iridocyclitis after cataract surgery in the dog. These traction bands may be important in the pathogenesis of retinal detachments that occur pre- and postoperatively in about 5–10% of dogs undergoing cataract surgery. Retinal detachments usually develop within the first few months postoperatively. Treatment of retinal detachments in these patients, in which inflammatory membranes and bands appear important, requires anterior vitrectomy to remove all pupillary debris (inflammatory membranes, capsular fibrosis, and posterior synechiae) as well as the specific treatment for retinal detachment. The pars plana vitreoretinal approach accommodates all of these procedures. At this time the surgical results (anatomic correction and restoration of vision) of these postoperative retinal detachments are poorer than in the phakic dogs without pre-existing lens-associated uveitis. If cataract or lens capsular opacities and an IOL prevent an adequate view of the posterior segment, they are removed either by routine phacoemulsification or during pars plana retinal detachment surgery with the phacofragmatome.

Vitreoretinal instruments The recommended indications for, and vitreoretinal instruments to perform, pars plana retinal detachment surgery are listed in Box 1.1 (Vainisi and Wolfer), and Box 12.1A and 12.1B (Smith). Several of these instruments are sterilized in individual units as they are not always used, but should be available. A good operating microscope with coaxial illumination and X–Y functions is essential. Several lens-viewing systems are satisfactory for the dog; the Machemer irrigating lens can be used. Wide-angle (between 90 and 130 ) non-contact lenses such as BIOMW (Insights Instruments, Inc., Sanford, FL) or Eibos 200W (Mo¨ller-Wedel GmbH, Wedel, Germany) are also used in the dog; these lenses are based on indirect ophthalmoscope principles, and require an inverter mounted on the operating microscope. Vitrectomy units are available and often have light illumination systems, electrocautery, air infusion capabilities, and even ultrasonic fragmentation and silicone oil pumps. Vitrectomy probes are disposable and small; they have a guillotine-type cutter on the side of a 2 g blunt needle. Most cutters operate at 500–1500 cuts/min, but higher speed

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Surgery of the retina

Fig. 12.20—cont’d Retinal detachment surgery for rhegmatogenous retinal detachments. Basic approach. (a) The bulbar conjunctiva 1–2 mm from the limbus is incised 360 (peritomy) by Steven’s tenotomy scissors. (b) Intraoperative appearance of the eye, with a strabismus hook around the insertion of the dorsal rectus muscle. (c) The dissection is continued posteriorly between Tenon’s capsule (bulbar fascia) by Steven’s tenotomy scissors to expose the dorsal and lateral aspects of the globe. Access to the globe is optimal in this area. (d) By indirect ophthalmoscopy and with a sterile cotton swab to depress the sclera, the exact site of the retinal break is identified. (e) The sclera immediately above the retinal break site is marked by diathermy or a nylon suture. (f) Four 5-0 interrupted mattress sutures are pre-placed at each quadrant of the equator to secure a retinal silicone buckle later. (g) Cryothermy is applied around the retinal break. Cryothermy is applied at each site until the retina begins to turn white, as viewed by indirect ophthalmoscopy. (h) If necessary, subretinal fluids are aspirated through a scleral hole made with a 30 g diathermy needle; the retinal detachment should noticeably flatten during this procedure. (i) A 4–5 mm silicone retinal buckle is carefully placed around the globe at the equator and through the pre-placed interrupted mattress sutures in each quadrant. (j) Intraoperative photograph: the scleral buckle has been placed just posterior to the equator and is being manipulated beneath the medial rectus muscle. (k) Intraoperative photograph: the scleral buckle has been manipulated around the entire globe. (l) Intraoperative photograph: the scleral buckle has been positioned around the entire equator of the globe, over the retinal break (arrow), and is ready to be tied. (m) As viewed by indirect ophthalmoscopy, the retinal detachment should be flattened and the globe indented with the tightened silicone buckle. (n) Closure consists of apposition of the conjunctival flap with several simple interrupted absorbable sutures at the limbus.

cutters (2500 cuts/min) are available. The faster cutters operate at less vacuum and have less tendency to draw the retina into the tip (causing an iatrogenic retina tear).

Surgical procedure After the onset of general anesthesia, clipping of the eyelid hair, and cleansing of the eyelid skin, conjunctival and corneal surfaces with 0.5% povidone–iodine solution, the eyelids are retracted by speculum. A lateral canthotomy is performed to provide maximum exposure. As sufficient exposure of the globe is often not possible for three-port vitrectomy, the globe is usually proptosed. A 360 peritomy is prepared with thumb forceps and tenotomy scissors incising the bulbar conjunctiva near the limbus (Fig. 12.21a). The dissection is continued posteriorly to expose 6–8 mm of the sclera behind the limbus in the dorsomedial quadrant and the entire lateral one-half of the globe (Fig. 12.21b). For the pars plana approach, three 20 g sclerotomies (’ports’) are made through the pars plana ciliaris: 1) two scleral incisions 5–6 mm posterior to the limbus at the 10 and 2 o’clock positions are used for the insertion of the intravitreal instrumentation; and 2) one incision 7–8 mm posterior to the limbus at the 4 o’clock position for intraocular fluids (inferotemporal, Fig. 12.21c). Vainisi and coworkers now place all three ports in the dorsal portion of the eye. The sclerotomies are performed with the 20 g microvitreoretinal (MVR) blades. Through these three sclerotomies, one will be used for infusion to maintain IOP and volume, the second will be the port to insert the illuminator, and the third will be the entry site for the vitrector and endolaser instruments. In the Siberian Husky breed, the nasal pars plana is very narrow (1 mm); hence in this breed the third port is placed temporally. Because the intrascleral venous plexus in the dog is in or near the site for the sclerotomies, a modification may be used. This intrascleral plexus or circle of Hovius is 3–4 mm from the limbus and 4–5 mm wide. A 20 g diathermy tip is used to make the sclerotomies. This essential cautery procedure usually avoids intraocular hemorrhage from the intrascleral venous plexus. A 20 g infusion cannula is sutured to the 4 o’clock sclerotomy site with a 7-0 absorbable suture. The infusion cannula delivers balanced salt solution into the vitreous cavity throughout surgery. The

rate of infusion and the level of IOP during vitreoretinal surgery are controlled by changes in the level of the infusion reservoir. In the pars plana method, IOP must always be maintained during the surgery to prevent further retinal detachment and intraocular (retinal and choroidal) hemorrhages (Fig. 12.21d). With special intraocular scissors and aspirations, the vitreous and any material around the retinal detachment and break, and within the pupil, are excised. The vitreous is removed in small pieces and low vacuum pressure (<150 mmHg). If hemorrhages results, adrenaline (epinephrine; 1:1000 to 1:10 000) may be infused. Any formed vitreous and potential inflammatory bands near the retinal break are also excised (Fig. 12.21e). Once the vitreous has been sufficiently removed, the retina can be gently manipulated using the tip of the light pipe and the vitrectomy probe. Once the retina falls back into place, careful inspection often reveals additional retinal tears or breaks. Endolaser can be initiated. However, since 75% of canine retinal detachments have tears over 270 , perfluoro-n-octane (PFO), which is heavier than water, is needed to flatten the retina. Perfluorocarbon (sulfur hexafluoride (SF6) or perfluoropropane (C3F8)) gas (or air for small retinal breaks) is carefully and slowly injected into the vitreous space, using a soft-tipped silicone needle over the optic nerve head, to unfold and flatten the retinal detachment. The gas is injected very slowly and a single large bubble is maintained, if possible. As the retina begins to unfold or flatten, folds may persist; they can be gently flattened using the silicone-tipped needle. If additional membranes are detected, they are removed and the PFO injection completed. Once the gas bubble has manipulated the retina into place, either laser using the transpupillary or endovitreal route, or cryotherapy is applied externally, and is directed at any retinal break (Fig. 12.21f). Often multiple rows of laser retinopexy are applied. Two or three rows of contiguous burns near the ora serrata are applied for 360 . The retina insults (burns or freezes) will appear as small white spots. In subalbinotic animals, transscleral cryotherapy may be substituted for endolaser photocoagulation. After the laser or cryoretinopexy procedure has been completed, silicone oil (medical grade 5000 centistoke SiO) or air is exchanged with the perfluorocarbon gas. For large retinal tears in the dog, silicone oil is preferred to air. The silicone oil is injected deep within the vitreous space 381

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Fig. 12.21 Retinal detachment surgery for rhegmatogenous retinal detachments. The pars plana approach is more difficult and requires special instrumentation, but is highly recommended for large retinal breaks and tears in dogs. (a) The bulbar conjunctiva is incised 360 (peritomy) by Steven’s tenotomy scissors. (b) The retrobulbar dissection is continued between the sclera and Tenon’s capsule to completely expose the entire lateral and dorsomedial globe. (c) Three 20 g sclerotomies (’ports’) are made by diathermy at the 10 and 2 o’clock positions for the insertion of instruments (scissors, forceps, diathermy, light probe, and other intravitreal instruments), and at the 4 o’clock position (inferotemporal). (d) The upper sclerotomies are performed 6–7 mm posterior to the limbus. The ventrolateral sclerotomy is 7–8 mm posterior to the limbus to avoid the intrascleral venous plexus but penetrate the pars plana ciliaris. (e) As viewed in cross section, a special contact lens (arrow) permits fundus examination during surgery without ophthalmoscopy. Special intravitreal scissors are used to incise a vitreal traction band. (f) Retinopexy via nitrous oxide cryothermy is applied to effect in the area of the retinal break. (g) A 4–5 mm silicone retinal buckle is manipulated under the four rectus muscles and the four pre-placed interrupted mattress sutures. Once complete, the buckle is tightened and tied, sufficient to indent the globe. In many patients, the buckle is not necessary. (h) Closure consists of a 7-0 simple absorbable suture at each sclerotomy site, and apposition of the conjunctival flap to the limbus with two interrupted mattress 7-0 absorbable sutures.

(usually 2–3 mm in front of the optic disk) to produce a large and single bubble. During the silicone oil and perfluorocarbon exchange, ocular hypotony must be avoided; choroidal and retinal hemorrhages can rapidly result if IOP falls. If the retinal break does not remain in apposition to the underlying retinal pigment epithelium, the silicone oil is allowed to remain in the vitreal space. The silicone oil may be removed 3–6 months later, or left in situ indefinitely. The external retinal strap or buckle, if needed, is inserted and apposed as described in the previous procedure. Fortunately with this procedure, placement of the scleral buckle is not usually necessary. A silicone sponge can also be used to apply additional external pressure to the retinal break area. The retinal buckle must be tightened sufficient to indent the globe to effect, usually about 2 mm (Fig. 12.21g).

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For closure: 1) single three-throw pattern 7-0 absorbable sutures are placed in each pars plana port; and 2) the fornix-based conjunctival flap is apposed to the limbus with buried interrupted mattress 7-0 absorbable sutures at the 3 and 9 o’clock positions (Fig. 12.21h) or a continuous pattern. The globe is carefully repositioned. If a lateral canthotomy was used, it is apposed with non-absorbable sutures. In addition, a temporary tarsorrhaphy with at least two nonabsorbable mattress sutures is completed to protect the cornea for at least 7–10 days.

Postoperative management Postoperative management of these patients includes several avenues. Postoperative iridocyclitis and control of the IOP

Surgery of the retina

are most important. Systemic and topical antibiotics are administered for 5–7 days. Topical and systemic corticosteroids and NSAIDs are administered for several weeks. Corneal erosions are not uncommon due to exposure as well as occasional corneal decompensation. Mydriatics are instilled at a frequency to ensure moderate pupillary dilatation for the iridocyclitis, and to permit periodic fundus examination of the retinal break and detachment. If intravitreal gas, silicone oil, and retinal buckle were used, IOP is closely monitored, and if ocular hypertension occurs, topical beta-blocking agents and systemic carbonic anhydrase inhibitors are administered. The gas or silicone oil may require removal if complications related to either develop. As glaucoma also occurs in breeds with RRDs, long-term IOP monitoring is essential!

Postoperative complications Complications after this surgery appear the same as for basic retinal detachment surgery, and include the formation of new retinal tears, extension of existing retinal tears, glaucoma, cataract formation, endophthalmitis, and proliferative vitreoretinopathy (PVR). Remaining perfluorocarbon gas can cause considerable inflammation; small amounts are usually tolerated, but larger amounts (50% of the vitreous) can result in intractable endophthalmitis. Silicone oil in the anterior chamber can cause corneal decompensation (direct contact of the silicone oil with the corneal endothelium) as well as glaucoma. Intravitreal silicone oil is apparently well tolerated by the dog, and can be left in the vitreous for the dog’s life.

Postoperative glaucoma or late-onset glaucoma Glaucoma is one of the more frequent complications; factors which contribute to its genesis include breed predisposition as many of the breeds presented for RRD also have inherited glaucoma (American Cocker Spaniel, and Toy and Miniature Poodles) as well as cataract formation and lens-induced uveitis (Fig. 12.22). Hence, gonioscopy is recommended in these patients preoperatively to ascertain the status of the ciliary cleft and iridocorneal angle. The glaucomas occur in the immediate postoperative period (probably related to uveitis or operative factors),

Fig. 12.22 Glaucoma following retinal detachment surgery. Note the episcleral congestion, diffuse corneal edema, and few perfluorocarbon gas bubbles within the anterior chamber.

or later (persistent uveitis and gradual iridocorneal angle closure). As these eyes have experienced considerable intraocular surgery and uveitis, clinical management of the glaucomas is medical. Topical (dorzolamide or brinzolamide) and systemic (methazolamide) carbonic anhydrase inhibitors, as well as topical beta antagonists (timolol or betaxolol), are administered, and IOP monitored long term. Irreversible glaucoma, as well as persistent uveitis, can result in phthisis bulbi.

Corneal exposure and ulceration RRD repair usually involves surgery of at least 1–2 hours’ duration. The cornea is in continuous jeopardy as the globe is partially proptosed, exposed to continuous drying, and the consistent lavage of irrigating fluids. Proper selection of the irrigating contact lens for retinal detachment surgery is critical to try to prevent corneal damage intraoperatively. In the brachycephalic breeds, corneal exposure is a frequent problem after RRD surgery. As a result, topical methylcellulose can be substituted for balanced salt solution for irrigation during surgery and a partial temporary tarsorrhaphy for 5–10 days postoperatively are important preventive measures. In fact, partial temporary tarsorrhaphies (the medial one-half of the palpebral fissure is closed) are recommended for all dogs after RRD surgery; the amount of the palpebral fissure which remains open should be sufficient to inspect the entire cornea and intraocular tissues postoperatively. These corneal ulcers appear as shallow central erosions and usually respond to frequent topical antibiotics and serum administrations (Fig. 12.23). Partial temporary tarsorrhaphy is an important preventive as well as therapeutic procedure for these ulcers. The presence of these postoperative erosions is best prevented as they can limit the use and frequency of topical medications for the postoperative uveitis.

Cataract formation Cataract formation in phakic dogs is generally limited to those breeds which develop RRDs secondary to vitreous degeneration. Fortunately, the frequency of these canine patients is less than those breeds which develop RRD after cataract surgery. Many of these dogs will already have lens opacities prior to presentation with RRD. Cataract progression is likely after RRD surgery; however, the rapidity of cataract progression is less predictable.

Fig. 12.23 Central and shallow corneal ulceration after retinal surgery.

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Scleral buckle-related complications It appears that tolerance for the silicone scleral buckle in dogs is less than in humans. Scleral buckle-related complications include buckle migration and extrusion, strabismus and impaired ocular motility (related to buckle size and orbital limits), and retrobulbar hemorrhage. The dog sclera in its equator is very thin, and sutures about the buckle in this area can easily penetrate the thin sclera. As a result, the intraocular method of pars plana retinal detachment repair without the scleral buckle has become more popular in the dog.

Retinal complications Retinal complications may occur intraoperatively as well as postoperatively. They include new or extensions of existing retinal tears, difficulties with the intravitreal gas (sulfur hexafluoride, SF6, and perfluoropropane, C3F8) and silicone oil, and other factors. As glaucoma also occurs in many breeds with RRDs, long-term IOP monitoring is essential! Fortunately, proliferative vitreoretinopathy is uncommon in the dog, and early surgery, as well as closure of all retinal holes and tears, seems to markedly decrease the chance of this complication.

anterior chamber, especially in aphakes or pseudophakes (Fig. 12.25). Thus, all possible PFO gas should be removed before the conclusion of RRD surgery!

Silicone oil complications Silicone oil is an excellent adjunct for canine RRD surgery and seems well tolerated in the dog. In fact, intravitreal silicone oil in the dog seems tolerated better than in humans, and has been left in situ for months to years. Hence, in the dog, intravitreal silicone oil can be used as a permanent tamponade after vitreoretinal surgeries (Fig. 12.26). Because of its toxicity to the lens in humans, intravitreal silicone oil is usually removed within 3 months postoperatively.

Subretinal gas (sulfur hexafluoride (SF6) and perfluoropropane (C3F8)) migration These gases are valuable to manipulate the retinal detachment intraoperatively, but unfortunately can migrate subretinally. This seems to occur more frequently when multiple bubbles are present. Fortunately, a thump to the globe during surgery can usually coalesce these bubbles into a single bubble! Airplane travel for the canine patient after RRD surgery should be avoided as any remaining intravitreal gas may expand at the higher altitudes. As a result, non-expansile concentrations of SF6 and C3F8 are used. Retention of these gases after surgery in the dog can cause subretinal inflammation, even endophthalmitis; they may also migrate subretinally and prevent retinal reattachment. A small bubble of PFO gas in the vitreous is usually tolerated, but a large bubble should be removed intraoperatively (Fig. 12.24). PFO gas can also migrate into the ventral

Fig. 12.24 Multiple bubbles of perfluorocarbon gas within the dorsal anterior chamber after retinal detachment surgery in an aphakic dog following cataract surgery.

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Fig. 12.25 In pneumatic retinopexy, perfluorocarbon gas is injected to assist the intraoperative repositioning of the detached retina to directly contact the retinal pigment epithelium. In this patient a large volume of the gas has entered the anterior chamber postoperatively.

Fig. 12.26 Silicone oil within the vitreous can be a permanent tamponade after retinal detachment surgery as in this aphakic dog. The ocular fundus is clearly visible.

Surgery of the retina

However, in aphakes, pseudophakes, and rarely phakes, silicone oil migration may occur into the anterior chamber, obstruct the outflow channels, and cause glaucoma. Small amounts of intracameral silicone oil can contact the posterior cornea and cause localized edema. A large silicone bubble in contact with the corneal endothelium can cause corneal decompensation. Silicone oil can also migrate into the subconjunctival tissues through improperly closed scleral ports. As a result, small amounts of floating silicone oil in the anterior chamber are usually not treated, but larger amounts are removed. Removal from the anterior chamber is usually delayed 2–4 weeks after RRD surgery to allow sufficient time for the retinal scars to develop and securely reattach the retina.

Other complications Postoperative endophthalmitis is rare after RRD surgery in the dog, in spite of the long surgery duration. Perioperative topical and systemic antibiotics are usually administered in the dog. Vitreal and silicone oil may be incarcerated in improperly closed scleral ports.

Postoperative results Postoperative results are divided into anatomic repair of the retinal detachment, and restoration of vision. It appears

that treatment of RRDs in phakic eyes that have not had intraocular surgery yields higher successful anatomic corrections in about 90% of the patients, and restores clinical vision in about 80% of the dogs. In dogs that developed RRDs after cataract surgery, the success rates are much lower, with anatomic correction in 90% of the patients and clinical vision in 30% of the dogs. In operated dogs with retinal detachments secondary to vitreous degeneration, about 90–95% of the surgeries are anatomically successful and about 85% of the patients recover clinical vision. With additional patients and surgical experience, these postoperative results are expected to improve. Significant problems in postoperative cataract dogs are lens-induced uveitis and the inflammatory and capsular changes that develop postoperatively. Nevertheless, major advances in the surgical repair of retinal detachments in dogs have occurred and improved results are predicated. In general, about 90% of canine retinas are reattached after pars plana retinal detachment surgery, and 76% of the patients recover clinical vision. Onset of vision after surgery may occur as early as 24 h or up to several weeks postoperatively. Most patients recover vision in 10–14 days post-surgery. The sooner the surgery for retinal detachment, the greater the chance of vision! The recently introduced 25 g transconjunctival sutureless vitrectomy procedure has been used in humans and may offer advantages in dogs. This procedure offers less surgical trauma and inflammation, and may become an important pars plana vitrectomy technique for the dog.

Further reading Small animals Archambeau PL, Henderson JW: Transscleral freezing of the retina: an experimental study, Invest Ophthalmol 4:885–892, 1965. Blair NP, Dodge JT, Schmidt GM: Rhegmatogenous retinal detachment in Labrador retrievers. I. Development of retinal tears and detachment, Arch Opthalmol 103:842–847, 1985. Blair NP, Dodge JT, Schmidt GM: Rhegmatogenous retinal detachment in Labrador retrievers. II. Proliferative vitreoretinopathy, Arch Ophthalmol 103:848–854, 1985. Boeve´ MH, Stades FC: Diseases and surgery of the canine vitreous. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 932–943. Constable IJ, Slatter DH, Horine R: Chorioretinal biopsy in dogs, Invest Ophthalmol Vis Sci 19:603–609, 1980. Dziezyc J, Wolf ED, Barrie KP: Surgical repair of rhegmatogenous retinal detachments in dogs, J Am Vet Med Assoc 188:902–904, 1986. Grahan BH, Barnes LD, Breaux CB, Sandmeyer LS: Chronic complete retinal detachments in dogs: outcome comparison of no treatment, medical therapy and retinal reattachment after vitrectomy, Proceedings of the 37th Annual Meeting of

the American College of Veterinary Ophthalmologists: Abstract 30, 2006. Hendrix DV, Nasisse MP, Cowen C, Davidson MG: Clinical signs, concurrent diseases, and risk factors associated with retinal detachments in dogs, Progress in Veterinary and Comparative Ophthalmology 3:87–91, 1993. Klassen H, Schwartz PH, Ziaeian B, et al: Neural precursors isolated from the developing cat brain show retinal integration following transplantation to the retina of the dystrophic cat, Vet Ophthalmol 10:245–253, 2007. Leon AL: Diseases of the vitreous in the dog and cat, J Small Anim Pract 29:448–461, 1988. Millichamp N: Investigations of inherited retinal disease in the dog, PhD Thesis, 1985, University of London. Narfstro¨m K, Petersen-Jones S: Diseases of the canine ocular fundus. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 944–1025. Okun E, Rubin LF, Collins EM: Retinal breaks in the senile dog eye, Arch Ophthalmol 66:702–707, 1961. Ollivier FJ, Barrie KP, Mames RN: Pars plana vitrectomy for the treatment of ophthalmomyiasis interna posterior in a dog, Vet Ophthalmol 9:259–264, 2006.

Peiffer RL, Weintraub BA: Clinical and histopathologic effects of lensectomy and anterior vitrectomy in the canine eye, J Am Anim Hosp Assoc 14:421–432, 1979. Rubin LF: Correction of retinal detachment in a dog, J Am Vet Med Assoc 157:461–466, 1970. Schmidt GM, Vainisi SJ: Retrospective study of prophylactic random transscleral retinopexy in the Bichon Frise with cataract, Vet Ophthalmol 7:307–310, 2004. Smith PJ: Surgery of the canine posterior segment. In Gelatt KN, editor: Veterinary Ophthalmology, ed 3, Baltimore, 1999, Lippincott, Williams and Wilkins, pp 935–980. Smith PJ, Mames RN, Samuelson DA, Lewis PA, Brooks DE: Photoreceptor outer segments in aqueous humor from dogs with rhegmatogenous retinal detachments, J Am Vet Med Assoc 211:1254–1256, 1997. Smith PJ, Pennea L, Mackay EO, Mames RN: Identification of sclerotomy sites for posterior segment surgery in the dog, Veterinary and Comparative Ophthalmology 7:180–189, 1997. Sullivan TC: Surgery for retinal detachment, Vet Clin North Am Small Anim Pract 27:1193–1214, 1997. Sullivan TC, Davidson MG, Nasisse MP, Glover TL: Canine retinopexy – a

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determination of surgical landmarks, and a comparison of cryoapplication and diode laser methods, Veterinary and Comparative Ophthalmology 7:89–95, 1997. Tolentino FI, Donovan RH, Freeman HM: Biomicroscopy of the vitreous in collie dogs with fundus abnormalities, Arch Ophthalmol 73:700–706, 1965. Vainisi SJ, Packo KH: Management of giant retinal tears in dogs, J Am Vet Med Assoc 206:491–495, 1995. Vainisi SJ, Wolfer JC: Canine retinal surgery, Vet Ophthalmol 7:291–306, 2004. Vainisi SJ, Peyman GA, Wolf ED, West CS: Treatment of serous retinal detachments associated with optic disk pits in dogs, J Am Vet Med Assoc 195:1233–1236, 1989. Vainisi SJ, Packo K, Schmidt GM: Retinal detachments in the Shih Tzu, Transactions of the American College of Veterinary Ophthalmologists 25:115, 1990. Vainisi SJ, Wolfer JC, Smith PJ: Surgery of the canine posterior segment. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1026–1058. Webb TR, Bras ID, Griffiths C: Retrospective evaluation of diode endolaser usage for retinopexy in canine patients: 16 patients, Proceedings of the 39th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 99, 2008.

Horses Brem S, Gerhards B, Wollanke P, et al: Intraokularer Leptospirennachweis bei 4 pferden mit rezidivierender uveitis (ERU), Berlinder und Munchener Tierarztliche Wochenschrift 111:415–417, 1998. Brem S, Gerhards B, Wollanke P, et al: 35 Leptospirenisolationen aus glaskorpern von 32 pferden mit rezidivierender uveitis (ERU), Berlinder und Munchener Tierarztliche Wochenschrift 112:390–393, 1999. Brooks DE, Matthews AG: Equine ophthalmology. In Gelatt KN, editor: Veterinary Ophthalmology, ed 4, Ames, 2006, Blackwell, pp 1165–1274. Deeg CA, Kaspers B, Gerhards H, Thurau SR, Wollanke B, Wildner G: Immune responses to retinal autoantigens and peptides in equine recurrent uveitis, Invest Ophthalmol Vis Sci 42:393–398, 2001. Dwyer AE: Visual prognosis in horses with uveitis, American Society of Veterinary Ophthalmology Annual Meeting. Chicago, 1998. Dwyer A, Gilger BC: Equine recurrent uveitis. In Gilger BC, editor: Equine Ophthalmology, St Louis, 2005, Saunders, pp 285–322. Fru¨hauf B, Ohnesorg B, Deegen E, Boeve´ M: Surgical management of equine recurrent uveitis with single port pars plana vitrectomy, Vet Ophthalmol 1:137–151, 1998. Gesell S, Brem S, Gerhards H, Wollanke B: Examination of normal equine eyes for the

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presence of leptospires, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 98, 2007. Gilger BC, Michau TM: Equine recurrent uveitis: new methods of management, Vet Clin North Am Equine Pract 20:417–427, 2004. Gilger BC, Spiess BM: Surgical management of equine uveitis. In Stick JA, editor: Equine Surgery, Philadelphia, 2006, WB Saunders, pp 749–755. Gilger BC, Malok E, Cutter KV, Stewart T, Horohov DW, Allen JB: Characterization of T-lymphocytes in the anterior uvea of eyes with chronic equine recurrent uveitis, Vet Immunol Immunopathol 71:17–28, 1999. Gilger BC, Malok E, Stewart T, Ashton P, Smith T, Jaffe GJ, Allen JB: Long-term effect on the equine eye of an intravitreal device used for sustained release of cyclosporin A, Vet Ophthalmol 3:105–110, 2000. Gilger BC, Malok E, Stewart T, et al: Effect of an intravitreal cyclosporine implant on experimental uveitis in horses, Vet Immunol Immunopathol 76:239–255, 2000. Gilger BC, Wilkie DA, Davidson MG, Allen JB: Use of an intravitreal sustained-release cyclosporine delivery device for treatment of equine recurrent uveitis, Am J Vet Res 62:1892–1896, 2001. Gilger BC, Salmon JH, Wilkie DA, et al: A novel bioerodible deep scleral lamellar cyclosporine implant for uveitis, Invest Ophthalmol Vis Sci 47:2596–2605, 2006. Hesselink DA, Baarsma GS, Kuijpers RW, van Hagen PM: Experience with cyclosporine in endogenous uveitis posterior, Transplant Proceedings 36 (Suppl 2):372S–377S, 2004. Kay JE: Inhibitory effects of cyclosporin A on lymphocyte activation. In Thomson AW, editor: Cyclosporine: Mode of Action and Clinical Application, Dordrecht, 1989, Kluwer, pp 1–23. Kermani-Arab V, Salehmoghaddam S, Danovitch G, Hirji K, Rezai A: Mediation of the antiproliferative effect of cyclosporine on human lymphocytes by blockade of interleukin 2 biosynthesis, Transplantation 39:439–442, 1985. Ma¨tz-Rensing K, Drommer W, Kaup FJ, Gerhards H: Retinal detachment in horses, Equine Vet J 28:111–116, 1996. Storey ES, Gerhards H, Wollanke B: Transscleral vitrectomy for the diagnosis of Leptospira and treatment of equine recurrent uveitis in a horse in the United States, Proceedings of the 38th Annual Meeting of the American College of Veterinary Ophthalmologists: Abstract 99:2007. Strobel BW, Wilkie DA, Gilger BC: Retinal detachment in horses: 40 cases (1998– 2005), Vet Ophthalmol 10:380–385, 2007. To¨mo¨rdy E: Verlaufsstudie der vitrektomie bei equiner rezidivierender uveitis, Zurich, 2009, Vetsuisse Faculty.

Werry H, Gerhards H: Mo¨glichkeiten der und indikationen zur chirurgischen behandlung der equinen rezidivierenden uveitis (ERU), Pferdeheilkunde 7:321–331, 1991. Werry H, Gerhards H: Zur operation therapie der equinen rezidivierenden uveitis (ERU), Tiera¨rzliche Praxis 20:178–186, 1992. Winterberg A, Gerhards H: Langzeitergebnisse der pars-plana vitrektomie bei equiner rezidivierender uveitis, Pferdeheilkunde 13:377–383, 1997. Wollanke B, Gerhards H, Brem S, Meyer P, Kopp H: Etiology of equine recurrent uveitis (ERU): autoimmune disease or intraocular leptospiral infection, Pferdeheilkunde 20:327–340, 2004. Wollanke B, Rohrbach BW, Gerhards H: Serum and vitreous humor antibody titers in and isolation of Leptospira interrogans from horses with recurrent uveitis, J Am Vet Med Assoc 219:795–800, 2001.

Humans Allen AW: Giant retinal tears, Ophthalmol Clin North Am 7:31–37, 1994. Ambati J, Arroyo JG: Postoperative complications of scleral buckling surgery, Int Ophthalmol Clin 40:175–185, 2000. Becker MD, Harsch N, Zierhut M, Davis JL, Holz FG: Therapeutische Vitrektomie bei Uveitis. Aktueller Stand und Empfehlungen, Ophthalmologe 100(10):787–795, 2003. Berrocal MH, Chang S: Perfluorocarbon liquids in vitreous surgery, Ophthalmol Clin North Am 7:67–76, 1994. Binder S, Freyler H: Vitrektomie bei entzundlichen Erkrankungen des hinteren Augenabschnittes, Klin Monatsbl Augenheilkd 183(2):86–89, 1983. Brinton DA, Hilton GF: Pneumatic retinopexy, Ophthalmol Clin North Am 7:1–12, 1994. Chang S: Perfluorocarbon liquids in vitreoretinal surgery, Int Ophthalmol Clin 32:153–163, 1992. Diamond JG, Kaplan HJ: Lensectomy and vitrectomy for complicated cataract secondary to uveitis, Arch Ophthalmol 96 (10):1798–1804, 1978. Diamond JG, Kaplan HJ: Uveitis: effect of vitrectomy combined with lensectomy, Ophthalmology 86:1320–1329, 1979. Gardner RC: Anterior vitrectomy, Ann Ophthalmol 7:723–726, 1975. Glaser BM, Carter JB, Kuppermann BD, Michels RG: Perfluorooctane in the treatment of giant retinal tears with proliferative vitreoretinopathy, Int Ophthalmol Clin 32:1–14, 1992. Hutton WL, Fuller DG: Silicone oil in treatment of retinal disease, Ophthalmol Clin North Am 7:89–99, 1994. Kaufman HE: Vitrectomy from the anterior approach, Ophthalmic Surg 6:58–65, 1975. Kim RY, D’Amico DJ: Postoperative complications of pneumatic retinopexy, Int Ophthalmol Clin 40:165–173, 2000.

Surgery of the retina Kloti R: Pars-plana Vitrektomie bei chronischer Uveitis, Klin Monatsbl Augenheilkd 192 (5):425–429, 1988. Krzystolik MG, D’Amico DJ: Complications of intraocular tamponade: silicone oil versus intraocular gas, Int Ophthalmol Clin 40:187–200, 2000. Leaver PK: Use of intravitreal liquid silicone, Int Ophthalmol Clin 32:81–93, 1992.

McDonald HR, Schatz H, Johnson RN: Treatment of retinal detachment associated with optic pits, Int Ophthalmol Clin 32:35–42, 1992. Scott RA, Haynes RJ, Orr: Vitreous surgery in the management of chronic endogenous posterior uveitis, Eye 17(2):221–227, 2003. Tornambe PE: Pneumatic retinopexy: current status and future directions, Int Ophthalmol Clin 32:61–80, 1992.

Verbracken H: Therapeutic pars plana vitrectomy for chronic uveitis: a retrospective study of the long-term results, Graefes Arch Clin Exp Ophthalmol 234:288–293, 1996. Werry H, Honegger H: Pars-plana vitrektomie bei chronischer uveitis, Klin Monatsbl Augenheilkd 191:2–7, 1987.

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Index

Note: page numbers in italics refer to tables, page numbers in bold refer to figures, page numbers followed by a ‘b’ refer to boxes.

A Abdelbaki orbitotomy 79, 80 Abscesses deep stromal corneal 225, 225, 226, 227, 228 orbital 59 Acepromazine 18, 40, 47 Adenocarcinoma nictitating membrane 187, 187 tarsal 126, 129 Adenoma, ciliary body 256 Adhesives, corneal 215–16 Adrenaline (epinephrine) anesthetic drugs and 43 for intraoperative hemostasis 25, 30 mydriasis with 31, 43 Adrenergic agents, neuroprotectant 301 Advancement (hood, 180 ) conjunctival grafts 166, 168–9, 169, 207 Alcurium 42 Amniotic membrane grafts 174, 204, 208–9, 209 Anesthesia 37–48 for cataract surgery 321 general 24 choice of 47 inhalational 39, 40–1 injectable 39, 40 in large animals 47–8 neuromuscular blocking agents and 24, 41–2, 195, 321 ophthalmic drug interactions with 42–3 ophthalmic effects of 37–9, 195 preanesthetic medications with 39–40 recovery from 47, 48 systemic diseases and 43 local/regional eyelid injections/nerve blocks 43–4, 94 retrobulbar injections/nerve blocks 23, 24, 37, 44–7, 67, 72–3 Anterior capsule forceps 4, 5, 6 Anterior capsule opacities 345, 348, 349 Anterior capsule scissors 7–8 Anterior capsule tears 213, 344–5 Anterior capsulectomies 322–4, 344–5 Anterior chamber anatomy 239–40, 269 cataract surgery entry through 322 surgical pathophysiology 312 diseases of 237

Anterior chamber (Continued) gonioimplants see Anterior chamber shunts (gonioimplants) perioperative considerations 243, 248, 273 surgery of 243–8 corneal incisions 245–6, 311 cyclodialysis 276–81, 277, 280, 282–3, 283 foreign bodies 248 for hyphema 247–8, 247 for hypopyon 246, 247 keratocentesis 244–5, 248 in large animals 259–61 limbal incisions 245–6, 311, 322 parasites 248, 248 postoperative care 248 surgical pathophysiology 242–3 Anterior chamber shunts (gonioimplants) 269, 284–94, 289 complications of 292–3, 292, 292–3 implant design 284–6, 284, 286, 287 in large animals 293–4 postoperative management 291–2 shunt types 285 surgical procedures for 287 facial vein shunt 290 frontal sinus shunt 290–1 intraorbital/subconjunctival implant 287–90, 289 jugular vein shunt 290 parotid duct shunt 291, 291 subcutaneous shunt 290 Anterior nictitans anchoring technique 181, 182, 183 Anterior orbitotomy 79–81 Anterior uveal surgery anatomy 239–42, 269, 270 corneal incisions for 246 diseases managed by 237–8, 239 iridocorneal angle see Iridocorneal angle laser treatment of cysts 29, 258, 260, 261 laser treatment of neoplasms 258–9 perioperative considerations 243 procedures 248–58 coreoplasty 248, 252, 253 iridocyclectomy 248, 256–8, 257 iridotomy 248–9, 250 iris bombe´ 248, 255–6, 255 iris prolapse 210, 211–13, 212, 213–14 in large animals 259–61 sectoral iridectomy 248, 252–4, 253, 270

Anterior uveal surgery (Continued) sphincterotomy 249–52, 251 see also Iris; glaucoma surgery surgical pathophysiology 242–3 see also Ciliary body; Iris Anterior vitrectomy 363, 364, 366–9, 370–3 Antibiotics after enucleation 84 for conjunctival lacerations 161 for corneal diseases 191, 201 for dacryocystitis 146 intravitreal 365, 365 for orbital abscesses 59 perioperative use of 30–1 for cataract surgery 344 for corneal surgery 194, 195, 215 for iris prolapse in horses 214 for orbital surgery 59–60, 81, 84 Antifibrin drugs for hyphema 247 perioperative use of 30, 243, 344 Antifibrotic agents 31, 268, 287, 292 Antifungal medications 195, 365 Anti-inflammatory agents anterior chamber pathophysiology and 242–3 for iris prolapse in horses 214 perioperative use of 30, 31, 194–5 Antiseptic solutions 21 Aphakic glaucomas 348, 348 Applanation tonometry 267, 267 Aqueous humor 237, 243 anatomy 240, 241, 270–1 flow pathways 270–1, 271 glaucoma surgery pathophysiology 272–3 glaucoma surgery procedures 273–4 anterior chamber shunts (gonioimplants) 284–94 corneoscleral trephination 281–2, 282 cyclodestructive 270, 294–9, 295, 297–9 cyclodialysis 276 iridencleisis 275 glaucoma treatment options 268, 269 intraoperative fibrin in 344 keratocentesis 244–5 Aqueous misdirection syndrome 265–6 Argon lasers 28 Arrowhead procedure for lateral canthal entropion 110, 110, 123, 123 Artificial eyes 71

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Index Aspiration cataract 309, 320, 321 subretinal fluid 373, 374 vitreal 362–3, 365–6 Atracurium 42, 195, 321 Atropine mydriasis with 31, 194, 318 oculorespiratory cardiac reflex and 38–9 as preanesthetic medication 38–9 Avian species see Birds Avulsion of the globe 58

B Barbiturates 40 Bard–Parker blades 8, 11 Barraquer eyelid speculum 2 Barraquer forceps 5 Barraquer iris scissors 7, 7 Barraquer needle holder 9 Barrier retinopexy 376 Barth nerve block 45, 45 Basher orbitotomy 81 BCG immunotherapy for sarcoid 136–7, 137 for squamous cell carcinoma 135, 233 BD microsurgical blades 8 Beaver blades 8, 11 Bedford modifed Kuhnt–Szymanowski procedure 118–19, 119 Berge retrobulbar nerve block 23, 45, 46 Beta-blockers 301 Bigelbach technique for entropion 106 with ectropion 118, 118 Biopsies chorioretinal 374, 375 conjunctival 160–1 corneal 201, 202 Bipedicle (bridge) conjunctival grafts 166, 168, 168, 169, 169, 206–7, 207 Birds iris anatomy 241 nictitating membrane surgery 158, 160 orbital surgery in enucleation 60, 74–6, 75–6 orbital anatomy 56–7, 57 orbital inflammation and 58 orbitotomy 76 surgical instrumentation for 2, 11 Bleeding see Hemorrhage Blepharoplasty, reconstructive in cattle 137–8 in the horse 133–5, 134 for small animals 128–32, 129–32 Blepharospasm, secondary 94, 104 Blind animals 319 Blink reflex, eyelid function 93 Blogg–Helper nictitating membrane flap 186, 186 Blood clots, intracameral see Hyphema Bovine species see Cattle Bovine squamous cell carcinoma (BSCC) 72, 72, 90, 137–8, 138, 234 Brachytherapy for sarcoid 137 for squamous cell carcinoma 136, 136, 232–3

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Bridge (bipedicle) conjunctival grafts 166, 168, 168, 169, 169, 206–7, 207 Buccal mucosa grafts 164 Bucket handle (Cutler–Beard) eyelid grafts 131–2, 131, 134 Bulbar conjunctiva 158, 159 biopsy 160–1 defect repair 162 grafts 164, 165, 166, 166, 167–70, 167–70, 175–6, 175, 203, 203, 205–6 lacerations 161 symblepharon 162–3, 162 Bullous spectaculopathy 148–50 Burow triangles 129 Butorphanol 48, 72

C Calcium channel blockers 301 Calipers 10 Canaliculi (lacrimal canals) anatomy 141–2 lacerations of 145–6 Cancer eye see Bovine squamous cell carcinoma Canine species see Dog(s) Cannulas 10 Can-opener capsulectomy 323, 324, 324 Canthus 92 see also Lateral canthus; Medial canthus Capsulorhexis 322–4 Carbon dioxide laser therapy 28–9 for squamous cell carcinoma 136, 233 Cardiac reflex, oculorespiratory 38–9 Cardiovascular disease 43 Castroviejo calipers 10, 10 Castroviejo corneal scissors 6, 7 Castroviejo cyclodialysis cannula 10 Castroviejo eyelid speculum 2 Castroviejo forceps 5 Castroviejo needle holder 9, 9 Cataract surgery 305–6 alternatives to 316–19, 317 anesthesia 321 anterior capsulectomies 322–4, 344–5 anterior chamber entry for 322 anterior vitrectomy after 367–8 aspiration 309, 320, 321 capsulorhexis 322–4 cataract classification 306–7, 307, 307 cataract resorption and 316–18 corneal incisions for 246, 311, 322 corneal pathophysiology and 194 discission 320, 321 evolution of in dogs 307–8 evolution of in horses 308–9 extracapsular extraction 307, 308, 320 see also Cataract surgery; phacoemulsification future of 352 instruments for 12, 13 corneoscleral scissors 7 lens loops 9, 10 phacoemulsification 5, 8, 11, 325–6, 330, 332 intracapsular extraction 307, 308, 309, 320, 321, 334–5

Cataract surgery (Continued) intraocular lenses anterior capsulectomies 322, 324 capsulorhexis 322 development of 308, 309–11 equine 332, 333, 340 implantation of 334, 339–41 intraoperative complications 341–2 postoperative complications 350 intraoperative complications 343–5 iris bombe´ following 255–6, 314 mydriasis for 39 neuromuscular blocking agents 24, 42, 321 operating conditions 321 operating microscopes for 20, 321 patient selection 314–16 peripheral iridectomies 322 phacoemulsification 308, 309, 320, 321, 324–34, 351–2, 351–2 instruments for 5, 8, 11, 325–6, 330, 332 phacofragmentation 309 postoperative care 334, 342–3 postoperative complications 343, 345–52 preoperative preparation 313, 316, 319–20 procedure options 320–1, 320 surgical anatomy 311–12, 311 surgical exposure 321–2, 343–4 surgical pathophysiology 312–14 systemic diseases and 43, 315 Cataracts, postoperative 383 Cat(s) anterior chamber surgery corneal incisions for 245 foreign bodies 248 for hyphema 247–8 hypopyon 238, 244, 248 keratocentesis 244 parasites 248 anterior uveal diseases 237, 238 ciliary body anatomy 242, 242 iris anatomy 240, 240, 241 iris cysts 238, 252, 258, 258 neoplasms 237–8, 239, 252, 254–5, 256–8 surgical pathophysiology 242 anterior uveal surgery coreoplasty 252, 253 iridectomy 252–4, 253 iridocyclectomy 256–8, 257 iridotomy 248–9, 250 iris bombe´ 255 sphincterotomy 249–52, 251 blindness 319 cataract surgery 305–6 alternatives to 318–19 anterior vitrectomy after 367–8 cataract classification 306–7 intracapsular extraction 334 intraocular lens implants 310, 340 intraocular pressure during 42 magnification for 20 patient selection 314 phacoemulsification 324 postoperative care 342 surgical anatomy 311–12 systemic hypertension and 43 conjunctival surgery diseases managed by 157

Index Cat(s) (Continued) grafts 157, 164–73, 166, 174, 203, 204–5, 205 neoplasms 161, 162 for symblepharon 162–3, 162, 163 corneal surgery 191–2 corneal anatomy for 192–3, 192 corneal pathophysiology 193–4 for deep ulcerations 164–73, 166, 174, 201, 203–5, 205 for foreign bodies 214–15, 215 keratoplasty (corneal graft) 217–25 lacerations 210–13 preoperative considerations 194–5 superficial keratectomy 196–8, 197 superficial keratotomies 201 entropion in 103–4, 105 eyelid anatomy 90–1, 92, 92, 93 eyelid injections/nerve blocks 44 eyelid surgery diseases managed by 90 for distichiasis 100 for entropion 105–7, 106, 111–12 for eyelid agenesis 98–100, 98–100 lacerations 90, 123–4 lateral canthotomy 24, 98 for neoplasms 90, 126–7, 126, 132, 132 tarsorrhaphy 95–7 general anesthesia for injectable 40 neuromuscular blocking agents and 41, 42, 195 ophthalmic effects of 38, 39 systemic diseases and 43 glaucomas 265–6, 265 diode endoscopic cyclophotocoagulation 295–6 gonioimplants 269 pharmacologic ablation of the ciliary body 299 surgical anatomy 269–71 laser therapy in 28–9, 231–2, 258, 295–6 lens surgery cataracts see Cat(s), cataract surgery lens removal 306 luxated lenses 306, 334–6 limbal neoplasms 229–32 nasolacrimal apparatus and tear systems anatomy 141–2, 142, 150, 151 catheterization 143 conjunctivobuccostomy 148, 148 conjunctivorhinostomy 147 dacryocystotomy 146–7 diagnostic tests 142, 143 keratoconjunctivitis sicca 150, 151–2, 151 nictitating membrane surgery 157, 158 anatomy for 159–60 everted nictitating membrane 176–7 membrane flaps 185–7, 185 for neoplasms 187–8 orbital surgery in enucleation 60–3, 63, 84 evisceration with intraocular prostheses 63–5, 66, 84–5 incomplete orbital walls and 52–3 orbital anatomy 54, 55 orbital growth and 58

Cat(s) (Continued) for orbital inflammation 58, 59 for orbital neoplasms 59, 77 orbitotomy 60, 76–7, 81 postoperative complications 84 strabismus and 52 traumatic proptosis 82–3, 82 perioperative drugs for 31, 194–5 see also Cat(s); general anesthesia for positioning for surgery 20, 24 retrobulbar injections in 23, 45 scleral homografts 229–31 self-induced trauma prevention 31–2 subpalpebral medication systems 33 surgical instrumentation for 195–6 anterior lens capsule forceps 5 eyelid specula 2 knives 8 rings 10, 24 scissors 6 vitreoretinal surgery 357 anterior vitrectomy 366–9 hyalocentesis 364–5 retinal detachments 361 surgical pathophysiology 359–60 types of 363 vitreal aspirations 366 Cattle anesthesia 72–3 eyelid injections/nerve blocks 44, 94 retrobulbar injections/nerve blocks 23, 24, 46, 46, 47, 72–3 cancer eye see Cattle, squamous cell carcinoma cataract surgery 306 conjunctival surgery 157, 161 corneal surgery anatomy for 193 corneal pathophysiology 194 for infectious keratoconjunctivitis 234 preoperative treatment 195 for squamous cell carcinoma 234 eyelid specula for 2 eyelid surgery diseases managed by 90 eyelid anatomy for 91–2 for neoplasms 72, 90 glaucomas 266 iris anatomy 240, 241 nasolacrimal apparatus and tear systems anatomy 142 diagnostic tests 143, 148 keratoconjunctivitis sicca 150 obstructions 148 nictitating membrane surgery 157, 158, 159–60, 188 orbital surgery in enucleation 72–4 evisceration with intraocular prostheses 74 orbital anatomy 56, 56 orbital inflammation and 58 for orbital neoplasms 59 orbitotomy 76 removal of prolapsed retrobulbar fat 74 restraint of 48, 72 sedation 48, 72

Cattle (Continued) squamous cell carcinoma 72, 72, 90, 137–8, 138, 234 strabismus 52 Cautery units for intraoperative hemostasis 25, 26 thermokeratoplasty 228, 229 Cavitation bubbles 326 Cellulitis, orbital 58 Celsus–Hotz procedure for entropion 105, 106, 106, 107, 108, 112–13, 113 Central tarsal pedicle for entropion 107, 108 Chairs, operating room 20–1, 321 Chalazion 123, 124 Chalazion forceps 3, 4 Chemotherapy for sarcoid 137 for squamous cell carcinoma 72, 136, 136, 233–4 Cherry eye (nictitating membrane gland protrusion) 178–84, 178–84 Chlorhexidine 21 Chop technique, phacoemulsification 329 Chorioretinal biopsy 374, 375 Cilia see Eyelashes Ciliary body anatomy 241–2, 241–2, 269, 270, 358, 358 corneal incisions for surgery on 246 cysts 238, 239, 258 glaucoma surgery cyclodestructive 270, 294–300, 295, 297–300 cyclodialysis 276–8, 277 cyclodialysis–iridencleisis 278–81, 280 cyclodialysis–iridocyclectomy 282–3, 283 pharmacologic ablation 299–300, 300 neoplasms 254–5, 256–9, 260, 261 perioperative considerations 243, 248 surgical pathophysiology 242, 272 surgical procedures for 248 iridocyclectomy 248, 256–8, 257 see also Ciliary body; glaucoma surgery vitreoretinal surgery hyalocentesis 358 retinal detachment surgery 379–85, 382–4 vitrectomy 364, 370–3 Ciliary sulcus-fixed IOLs 338–9 Cisplatin 136, 136, 137, 233 Colibri forceps 5 Colitz orbitotomy 81–2 Collars, postoperative use of 31–2 Collie eye anomaly (CEA) 375–6, 376 Complete (360 , Gundersen-type) bulbar conjunctival grafts 166, 167–8, 167–8, 206 Conjunctival maxillary sinusotomy 147–8 Conjunctival mucosa envelope procedure 181–2, 183–4, 183 Conjunctival mucosa pocket procedure 182–4, 184 Conjunctival surgery 157 biopsy 160–1 conjunctival anatomy for 158–9, 158 defect repair 162 diseases managed by 157 general anesthesia for 47

391

Index Conjunctival surgery (Continued) grafts 157, 162, 163–76 buccal mucosa to conjunctiva 164 conjunctiva to conjunctiva 164 conjunctiva to cornea 163–71, 173, 203, 205–9 corneoconjunctival 165, 171–3, 204–5 large animal adaptations 174–6 permanent 173–4 substitute materials for 174, 203–4, 208–9 instrumentation for 11–12, 165 forceps 3, 4, 5 scissors 6 laceration repair 161–2 neoplasms 161, 162, 232, 233 for overgrowth in rabbits 176 patient preparation 21 resection for distichiasis 102 sutures for 14 for symblepharon 162–3 see also Nictitating membrane surgery Conjunctivobuccostomy 148, 148 Conjunctivoralostomy 150 Conjunctivorhinostomy 147, 147, 148 Continuous curvilinear capsulorhexis (CCC) 322–4, 323 Continuous tear capsulectomy (CTC) 323–4, 323 Coreoplasty 248, 252, 253 Corneal diseases 191 after evisceration 85 cataract surgery and 314 conjunctival grafts for 163–73, 174–6, 203, 205–9 nictitating membrane flaps for 185–7, 188, 204, 210 pathophysiology of ulceration 193 symblepharon 162–3 see also Corneal surgery Corneal drying 38 Corneal injury, surgery causing 326, 346, 347, 383, 383 Corneal surgery 191–228 adhesives for 215–16 basic operative approach in 22–5 biopsies 201, 202 corneal anatomy and 192–3 corneal grafts (keratoplasty) 164, 216–28 corneal pathophysiology 193–4 deep keratectomy 201 for deep ulcerations 201–10 conjunctival autografts 163–71, 173, 203, 205–9 corneoscleral transposition 204–5 primary closure of 202–3, 203 substitute graft materials 174, 203–4, 208–9 equine squamous cell carcinoma 232–4 for foreign bodies 214–15 general anesthesia for 47, 48 incisions for anterior chamber entry 245–6, 322 instrumentation for 4, 12, 195–6, 218, 245 forceps 3, 4, 5 knives 8, 9 needles 14 rings 10 scissors 6–7

392

Corneal surgery (Continued) for lacerations 210–14 patient preparation for 21–2, 194–5 perioperative drugs for 30, 194–5 superficial keratectomy 196–9 superficial keratotomies 199–201 sutures for 14, 24, 246 thermokeratoplasty 228, 229 see also Anterior chamber Corneoconjunctival grafts 165, 171–3, 172, 204–5, 205 Corneoscleral prostheses 71 Corneoscleral scissors 7 Corneoscleral transposition 204–5, 205 Corneoscleral trephination 281–2, 282 Corpora nigra 241, 259 cysts 259–60, 260 Corticosteroids anterior chamber pathophysiology 243 diabetic dogs and 43 perioperative use of 30, 31, 195 Cosmetic globes 71 Cosmetic skin orbitectomy 82 Cow(s) see Cattle Cryotherapy 26–7 for distichiasis 26–7, 102, 103, 103 prophylactic retinopexy 377 for sarcoid 137 for squamous cell carcinoma 135, 138, 232 Cutler–Beard (bucket handle) eyelid grafts 131–2, 131, 134 Cyanoacrylate adhesive 216 Cyclocryothermy 294–5, 295, 296–7 Cyclodestructive therapies 270, 294–9, 295, 297–9 cyclocryothermy 294–5, 295, 296–7 diode endoscopic cyclophotocoagulation 295–6, 298–9, 299 in large animals 296–9, 297–9 pharmacologic ablation 299–300, 300 transscleral laser cyclophotocoagulation 295, 295, 296, 297–8, 297–9 Cyclodialysis 276–8, 277 with iridencleisis 278–81, 280 with iridocyclectomy 282–3, 283 Cyclodialysis spatulas 9, 9, 10 Cyclosporine (CsA) implants 369–70 Cysts, anterior uveal 29, 238, 239, 252, 258, 259–60, 260–1 Cytokines 274, 286, 287

D Dacryocystitis 146, 146, 148 Dacryocystorhinography 143, 143, 148 Dacryocystotomy 146–7, 146 Deep anterior lamellar keratoplasty (DALK) 225, 227 Deep lamellar endothelial keratoplasty (DLEK) 225, 227, 228 Deep stromal corneal abscesses (DSA) 225, 225, 226, 227, 228 Demarcation retinopexy 376 Dermoids conjunctival 162, 162 corneal 196, 196

Descemetoceles conjunctival grafts for 165, 166, 175, 203 corneal adhesives for 215–16, 216 keratoplasty for 217, 219–20, 221–2 Descemet’s membrane 192, 192, 193 surgical pathophysiology 194 Detomidine 48 DeWecker iris scissors 7 Diabetes mellitus cataract surgery and 315, 315 general anesthesia and 43 Diamond knives 9 Diode lasers 28–9 diode endoscopic cyclophotocoagulation 295–6, 298–9, 299 iridal melanomas 259 transscleral cyclophotocoagulation 295, 296, 297–8, 297, 298 uveal cysts 258 Discission, cataract surgery 320, 321 Distichiasis 92, 100–3 combined entropion–distichiasis procedure 107 cryotherapy for 26, 27, 102, 103, 103 electroepilation for 26, 101 Divide and conquer phacoemulsification 329 Dog(s) anterior chamber surgery corneal/limbal incisions for 245 foreign bodies 248 for hyphema 247–8 parasites 248, 248 anterior uveal diseases 237 ciliary body anatomy 242, 242 ciliary body cysts 238 iris anatomy 240, 240, 241 iris cysts 238, 239, 252, 258 neoplasms 237–8, 238, 239, 252, 254–5, 256–9 surgical pathophysiology 242 anterior uveal surgery coreoplasty 252, 253 iridectomy 252–4, 253, 270, 278 iridocyclectomy 256–8 iridotomy 248–9, 250 iris bombe´ 255–6, 255 sphincterotomy 249–52, 251 blindness 319 cataract surgery 305 alternatives to 316–18, 317, 318 anterior capsulectomy 323, 344–5 anterior vitrectomy after 367–8 anterior vitreous presentation 345 bacterial contamination 21, 31, 344 capsulorhexis 323, 324 cataract classification 306–7, 307 cataract resorption and 316–18 corneal edema after 346 corneal pathophysiology and 194 corneal ulcerations after 347, 348 evolution of 307–8 exposure 343–4 fibrin in the aqueous humor 344 fibropupillary membranes 348–50, 349, 369 glaucoma after 348 hyphema after 347

Index Dog(s) (Continued) intracapsular extraction 334, 334 intraocular lenses 309–10, 310, 334, 339–42, 339, 340, 350 intraoperative complications 343–5 iridocyclitis 345–6, 346, 348 iris bombe´ following 255–6 lens capsule opacities 345, 348, 349, 350, 367 lens capsule tears 344–5 magnification for 20 miotic pupil 344 neuromuscular blocking agents and 24, 42, 321 patient selection 314–15, 316 perioperative drugs with 31, 39 phacoemulsification 8, 308, 324, 327–30, 328 posterior capsule opacities 345, 348, 349, 350, 367 postoperative care 342 postoperative complications 343, 343, 345–51, 348–51 retinal detachment 316, 350–1, 351, 360, 383 surgical anatomy 311–12 surgical pathophysiology 312–13 systemic diseases and 43, 315 transient IOP hypertension 346–7 wound leakage 347 conjunctival surgery biopsy 160, 161 defect repair 162, 164 diseases managed by 157 grafts 157, 164–73, 174, 203 neoplasms 161, 162 palpebral conjunctiva 159 for symblepharon 162–3 corneal surgery 191–2 corneal anatomy for 192–3, 192 corneal pathophysiology 193–4 for deep ulcerations 164–73, 174, 201, 202, 203–4 for foreign bodies 214–15, 214–15 keratoplasty (corneal graft) 217–25, 218 lacerations 210–13, 210 preoperative considerations 194–5 superficial keratectomy 196–8, 196 superficial keratotomies 199–201, 199–200 thermokeratoplasty 228, 228, 229 diabetes mellitus in 43, 315, 315 Elizabethan collars for 31–2, 32 enophthalmia in 25, 53 entropion in 103–12, 123 extraocular muscle myositis in 52 eyelid injections/nerve blocks 44, 94, 94 eyelid surgery diseases managed by 89 for distichiasis 100–3, 101–2, 107 for ectopic cilia 103 for ectropion 108, 114–20, 115–17, 118–19 for entropion 103, 105–12, 106–11, 117–20, 118–19, 123 for eyelid agenesis 98 eyelid anatomy for 90–1, 91, 92, 93, 101

Dog(s) (Continued) forehead skinfolds and 107–8, 108, 109, 109, 110 for lacerations 123–4, 125 lateral canthotomy 24–5, 98 for nasal fold trichiasis 123, 124 for neoplasms 89, 126, 126, 129, 130, 131, 132 for palpebral fissure size increase 122–3, 123 for palpebral fissure size reduction 120–2, 120–2 preliminary examination for 93–4 secondary blepharospasm and 94, 104 tarsorrhaphy 83, 95–7, 95 for trichiasis 107–8, 108, 109, 123, 124 general anesthesia for injectable 40 neuromuscular blocking agents and 24, 41, 41, 42, 42, 195, 321 ophthalmic effects of 38–9, 40–1 preanesthetic medications with 40 systemic diseases and 43 glaucomas 263–5, 264 anterior chamber shunts 269, 284–93, 289 corneoscleral trephination 281–2, 282 cyclodestructive procedures 294–6, 295 cyclodialysis 276–8, 277 cyclodialysis–iridocyclectomy 282–3, 283 diagnostic procedures 267 gonioimplants 269 iridectomy 278, 281 iridencleisis 275–6, 275–6 iridencleisis–cyclodialysis 278–81, 280 lens removal prior to surgery 274–5 pharmacologic ablation of the ciliary body 299–300, 300 postoperative 348 preoperative treatment 273 surgical anatomy 269–71 surgical pathophysiology 271–3 treatment options 267–8, 269 laser therapy in 28–9, 29, 231–2, 255–6, 258–9 lens surgery cataracts see Dog(s), cataract surgery ciliary sulcus-fixed IOLs 338–9 lens removal 306 luxated lenses 306, 334–9, 342 limbal neoplasms 229–32, 229, 230–1 medial canthal pocket syndrome 53 nasolacrimal apparatus and tear systems anatomy 141–2, 142, 150, 151 catheterization 143, 144 conjunctival maxillary sinusotomy 147–8 conjunctivobuccostomy 148, 148 conjunctivorhinostomy 147 dacryocystotomy 146–7, 146 diagnostic tests 142–3, 143, 150 displaced lower punctum 145 imperforate punctum 144–5, 144 keratoconjunctivitis sicca 150, 151–5, 151, 153–4 lacerations of the canaliculi 145–6 lower micropunctum 145

Dog(s) (Continued) nictitating membrane surgery 157, 158 anatomy for 159–60, 160 cherry eye 178–84, 178–84 everted membrane 176–7, 176–7 membrane flaps 185–7 membrane protrusion 184–5, 184 for neoplasms 187–8, 187 orbital surgery in enopthalmia and 53 enucleation 60–3, 60, 62, 63, 84, 84 evisceration with intraocular prostheses 63–5, 66, 84–5, 85, 86 incomplete orbital walls and 52–3 orbital anatomy 53–4, 54 orbital growth and 58 for orbital inflammation 58, 59 for orbital neoplasms 59, 59, 60, 77, 86 orbitectomy 60, 77, 86 orbitotomy 60, 76–81, 78, 80, 86 postoperative complications 84, 84 strabismus and 52, 86 traumatic proptosis 82–3, 83, 86 perioperative drugs for 31, 39, 194–5 see also Dog(s); general anesthesia for positioning for surgery 20, 22–3, 24, 39, 45, 321 retinal detachment 316, 350–1, 351 see also Dog(s); vitreoretinal surgery retrobulbar injections/nerve blocks 22–3, 23, 39, 45, 45 scleral homografts 229–31, 231 self-induced trauma prevention 31–2 skin preparation for surgery 21 subpalpebral medication systems 33, 33 surgical instrumentation for 195–6 anterior lens capsule forceps 5 eyelid specula 2 intraocular lens instrumentation 5 knives 8 phacoemulsification 8 rings 10, 11, 24 scissors 6, 11 systemic diseases in 43, 315 vitreoretinal surgery 357 anterior vitrectomy 366–9 chorioretinal biopsies 374, 375 demarcation retinopexy 376 hyalocentesis 364–5 intravitreal antibiotics 365 pneumatic retinopexy 375 postoperative complications 383–5 preoperative considerations 363 prophylactic retinopexy 376–7 retinal detachments 360, 362, 362–3, 373, 377–85 surgical anatomy 357–9, 358 surgical pathophysiology 359–60 therapeutic retinopexy 375–6, 376 types of 363 vitreal aspirations 365, 366 Dorsal orbitotomy in the horse 81 in small animals 79 Draping 22 Drugs, perioperative 30–1, 42–3, 47–8 for anterior uveal surgery 243 for cataract surgery 319–20, 344

393

Index Drugs, perioperative (Continued) for corneal surgery 194–5 for glaucoma surgery 273 for orbital surgery 59–60, 81, 84 see also Anesthesia; specific drugs Dziezyc–Millichamp procedure 99–100, 100

E Ectopic cilia 101, 103, 103 Ectropion 114–17, 115 entropion and 108, 117–20 Edrophonium 42 Electrocautery for entropion 104 for intraoperative hemostasis 25, 26 Electroepilation 26, 101 Electroretinography (ERG) 316, 361 Elizabethan collars 31–2 Emphysema, orbital 84 ‘En bloc’ enucleation see Transpalpebral enucleation Endoscopic cyclophotocoagulation 295–6, 298–9, 299 Enophthalmia 25, 51, 53 Entropion 103 non-surgical treatment 103–5, 112, 113 surgical management of ectropion and 108, 117–20 in the horse 112–13 in sheep 113 in small animals 105–12, 117–20, 123 in Vietnamese potbellied pig 113–14 Entropion forceps 3, 4 Enucleation procedure 60 in birds 60, 74–6, 75–6 in cattle 72–4 in the horse 67–70, 71, 71 orbital volume augmentation after 83 postoperative complications 68–9, 84, 86 in small animals 60–3 indications for 60 lateral approach 62–3, 65 postoperative complications 84 subconjunctival approach 61, 62 transpalpebral approach 61–2, 64 Enzymatic therapy, for hyphema 247–8 Epinephrine (adrenaline) anesthetic drugs and 43 for intraoperative hemostasis 25, 30 mydriasis with 31, 43 Episcleral fixation, nictitating membrane flap 186–7, 187 Equine recurrent uveitis (ERU) 315, 331, 333, 334, 369–73 Equine species see Horse(s) Evisceration for enucleation in birds 76 with intraocular prosthesis in cattle 74 in the horse 70–1 in small animals 63–5, 66, 84–5, 85, 86 postoperative complications 84–5, 86 Excimer lasers 28 Exenteration in cattle 72 in the horse 71–2 of orbital neoplasms 59, 71–2, 74

394

Exenteration (Continued) orbital volume augmentation after 83 postoperative complications 85, 86 in small animals 67 Exophthalmia, orbital surgery and 51–2, 58 Expanding vitreous syndrome 341 Extracorneal bullous spectaculopathy 148–50 Extraocular muscle myositis 52 Extraocular muscle tone 39, 41–2, 43, 195 Extrascleral shell implants 71 Eyelashes anatomy 90, 91, 101 distichiasis 26, 27, 92, 100–3, 107 ectopic 101, 103, 103 electroepilation of 26, 101 presurgical clipping of 21 Eyelid agenesis 98–100, 98–100 Eyelid anatomy 90, 90, 95 blood supply 93 eyelashes 90, 101 glands 90–1 gray line 95 innervation 93 lymphatics 93 muscles 91–3, 91, 92 palpebral conjunctiva 92 skin 90, 91 tarsal glands 92, 95 tarsal layer 92 Eyelid diseases 89–90 see also Eyelid neoplasms; Eyelid surgery; diseases managed by; specific diseases Eyelid function 93, 94–5 Eyelid injections/nerve blocks 43–4, 94 Eyelid neoplasms in cattle 72, 90, 127, 137–8 in the horse 90, 127, 132–7, 232, 233 in small animals 89, 90, 126–32 Eyelid skin 90, 91 grafts for eyelid agenesis 98–100, 98–100 orbital rim resection for defects of 82, 135 preparation 21 repair after neoplasm removal in cattle 137–8, 137 in the horse 133–5, 134 in small animals 128–32, 129–32 Eyelid specula 2 Eyelid surgery 89–138 adaptations from human surgery 90 anesthesia for 43–4, 47, 94 cryotherapy in 26, 27, 102, 103 diseases managed by 89–90 agenesis 98–100 chalazion 123 distichiasis 26, 27, 100–3, 107 ectopic cilia 103 ectropion 108, 114–20 entropion 105–14, 117–20, 123 lacerations 123–6 neoplasms 89, 90, 126–38, 232, 233 secondary blepharospasm and 94, 104 trichiasis 107–8, 123 eyelid anatomy for 90–3, 95 eyelid preparation for 95 the gray line 95, 96 instrumentation for 3, 4, 11–12, 95 lateral canthotomy 24–5, 62–3, 83, 98

Eyelid surgery (Continued) for palpebral fissure size alteration 120–3 preoperative examination 93–4 special considerations in 94–5 sutures for 14, 95 tarsorrhaphy 83, 84, 85, 95–7, 118

F Facial vein–anterior chamber shunt 290 Fat, prolapsed retrobulbar 74 Fat pads, in Vietnamese potbellied pig 113–14 Feline species see Cat(s) Fibrin 30, 243 anterior chamber shunts 292, 292 hyphema 247–8 intraoperative excess 344 see also Antifibrin drugs Fibrin glue 216 Fibropupillary membranes 348–50, 349, 369 Fibrosing strabismus 52 Fibrotic response, glaucoma surgeries 272–3, 287, 290, 292 Fistulas, post-enucleation 84 Fixation rings 10, 24 Flieringa rings 10, 24 Flieringa–LeGrand rings 24 Fluorescein test, nasolacrimal system 142 5-Fluorouracil (5-FU) for glaucomas 268, 287, 292 for squamous cell carcinoma 136, 233 Forceps 2, 3–6, 11 Forehead skinfolds 107–8, 108, 109, 109, 110, 113–14 Foreign bodies anterior chamber 248 corneal 214–15, 214–16 Fornices, conjunctival 158–9, 185–6, 186 Four-sided full-thickness eyelid excision 127, 128, 133, 133 Fractures, orbital 58, 81, 82 Free (island) conjunctival grafts 166, 171, 171, 172, 173, 208 Frontal sinus–anterior chamber shunt 290–1 Frozen (tectonic) keratoplasty 217, 223–5, 226 Fuch lateral canthoplasty 121–2, 122 Fungal infections orbital involvement 58–9 perioperative drugs for 195

G General anesthesia see Anesthesia, general Gentamicin, for ciliary body ablation 299–300, 300 Gills–Welsh lens loop 10 Glaucoma filtration surgery (GFS) 286–7 Glaucomas 263–301 aphakic 348, 348 bovine 266 canine 263–5, 264 classification 267–8, 268b diagnostic procedures 266–7 equine 266 feline 265–6, 265

Index Glaucomas (Continued) iris bombe´ 255, 256 keratocentesis and 245 laser therapy for 29, 255–6, 295–9, 295, 297–9 medical treatments 24, 267–9, 268b neuroprotection 300, 301 pharmacologic ablation of the ciliary body 299–300 postoperative 348, 383, 383 preoperative treatment 273 in rabbits 266, 266 surgical anatomy 269–73 surgical instrumentation for 12, 13 cyclodialysis spatulas 9 surgical pathophysiology 271–3 surgical procedures for 267–9, 273–5 anterior chamber shunts/gonioimplants 269, 284–94, 289 corneal incisions for 246 corneoscleral trephination 281–2, 282 cyclodestructive 270, 294–300, 295, 297–300 cyclodialysis 276–8, 277 cyclodialysis–iridocyclectomy 282–3, 283 enucleation 60–1 evisceration with intraocular prostheses 63, 64, 86 iridectomy 278, 279 iridencleisis 275–6, 275–6 iridencleisis–cyclodialysis 278–81, 280 mechanisms of 273–4, 274 ophthalmic–anesthetic drug interactions 42 types of 263, 264b Globe-collapsing enucleation for birds 74–6, 75–6 Goblet cells 159 Goniodysgenesis 271–2 Gonioimplants see Anterior chamber shunts (gonioimplants) Gonioscopy 267, 267 Goodhead orbitotomy 81–2 Graefe forceps 3, 4, 4 Graefe strabismus hook 9 Grafts after eyelid mass removal in cattle 137–8, 137 in the horse 133–5, 134 in small animals 128–32, 129–32 conjunctival 157, 162, 163–76 corneal transplants see Keratoplasty for eyelid agenesis 98–100, 98–100 scleral 229–31, 229, 231 Granula iridica see Corpora nigra Grid keratotomy 199–200, 200, 201 Growth factors 273, 274, 286, 287 Grussendorf procedure 119–20 Gundersen-type (360 ) bulbar conjunctival grafts 166, 167–8, 167–8, 206 Gutbrod–Tietz procedure 118 Guyton–Park eyelid speculum 2

H H plasty in cattle 137–8, 137 in the horse 134, 134

Hair presurgical clipping of 21 trichiasis 107–8, 108, 109, 123, 124 see also Eyelashes Halothane 41, 43 Harvey orbitotomy 77–9, 78 Haws see Nictitating membrane Head positioning 20, 21–2, 321 Head-mounted magnifiers 18 Helper–Blogg nictitating membrane flap 186, 186 Hemorrhage hyphema 247, 247, 347 intraoperative 25, 26, 30, 95 orbital 84 Hemostasis, intraoperative 25, 26, 30, 95 Heparin 30, 243, 344 Hepatic disease 43 Hood (advancement, 180 ) conjunctival grafts 166, 168–9, 169, 207 Horse(s) anesthesia eyelid injections/nerve blocks 43–4, 94 general 46, 48, 67 retrobulbar injections/nerve blocks 23, 45–6, 67 anterior chamber surgery 237, 259–61 foreign bodies 248 for hyphema 247–8 keratocentesis 244 parasites 248 anterior uveal diseases 237 ciliary body anatomy 242 cysts 259–60, 260, 261 iris anatomy 240, 241 neoplasms 260–1, 261 surgery for 259–61 blindness 319 cataract surgery 306 evolution of 308–9 intracapsular 335 intraocular lens implants 310–11, 340 patient selection 314, 315, 316 phacoemulsification 309, 324, 330–4, 331, 333–4, 351–2, 351–2 postoperative care 342–3, 343 postoperative complications 351–2, 351–2 preoperative preparation 319, 320, 331 retinal detachment risk 316 surgical anatomy 312 conjunctival surgery diseases managed by 157 grafts 174–6, 175, 205–9 neoplasms 161, 162, 232, 233 for symblepharon 162 corneal surgery adhesives for 216, 216 anatomy for 193 biopsy 202 corneal pathophysiology 194 corneal transplantation (keratoplasty) 225–8, 225, 227 for foreign bodies 215, 216 grafts 174–6, 175, 203–4, 205–9, 207–9 iris prolapse 213–14 lacerations 213–14 nictitating membrane flaps 210 perioperative drugs 195

Horse(s) (Continued) squamous cell carcinoma 232–4, 232 superficial keratectomy 198–9, 199 temporary tarsorrhaphy 210 thermokeratoplasty 228 eyelid specula for 2 eyelid surgery aftercare 97, 113, 135 diseases managed by 90 for ectropion 117 for entropion 112–13, 113 eyelid anatomy for 91, 92–3 for lacerations 124–6, 125 for neoplasms 90, 127, 132–7, 232, 233 tarsorrhaphy 97 glaucomas 266 anterior chamber shunts 293–4 cyclodestructive therapies 296–9, 297–9 pharmacologic ablation of the ciliary body 299, 300 surgical anatomy 270, 271 laser therapy in 29, 136, 233, 260, 261, 297–9 lens surgery cataracts see Horse(s), cataract surgery luxated lenses 306, 335, 335 nasolacrimal apparatus and tear systems anatomy 142 catheterization 143 diagnostic tests 143, 148 keratoconjunctivitis sicca 150, 155 obstructions 148, 149 parotid duct transposition 155 neuromuscular blocking agents in 24, 321 nictitating membrane surgery 157, 158, 159–60, 188 for neoplasms 188 orbital surgery in enucleation 67–70, 67, 69, 71, 71 evisceration with intraocular prosthesis 70–1 exenteration 71–2 orbital anatomy 54–6, 55 for orbital fractures 82 orbital growth and 58 orbital inflammation and 58 for orbital neoplasms 59, 67, 81, 82 orbitotomy 76, 81–2 traumatic proptosis 83 positioning for surgery 20, 321 recurrent uveitis (ERU) 315, 331, 333, 334, 369–73 retinal detachment 316, 362 sedation of 47–8 self-induced trauma prevention 32, 97 squamous cell carcinoma in 67, 90, 132–3, 134, 135–6, 188, 232–4 strabismus in 52 subpalpebral medication systems 32–4, 32–3, 214 vitreoretinal surgery pars plana vitrectomy 370–3, 371 suprachoroidal cyclosporine implants 369–70 Hotz–Celsus procedure for entropion 105, 106, 106, 107, 108, 112–13, 113

395

Index Hyalocentesis (vitreal paracentesis) 358, 364–5, 365 Hydroxyapatite orbital implants, for the horse 71, 71 Hyperosmotic agents 43, 321, 363 Hypertension ocular see Intraocular pressure systemic 43 Hyperthermia see Radiofrequency hyperthermia Hyphema 247–8, 247, 347 Hypopyon 238, 244, 246, 248

I Illumination systems 20 Immunomodulators cyclosporine implants 369–70 for glaucoma 301 Immunotherapy for sarcoid 136–7, 137 for squamous cell carcinoma 135, 233 Imperforate lacrimal punctum 144–5, 144–5 Implants anterior chamber shunts 269, 284–94, 289 intraocular lenses see Intraocular lenses (IOLs) orbital in cattle 73, 74 in the horse 69–71, 71 in small animals 63–5, 66, 84–5, 85, 86 suprachoroidal cyclosporine 369–70 symblepharon 162–3 Infections postoperative 84 prevention of see Antibiotics, perioperative use of Infectious bovine keratoconjunctivitis (IBK) 234 Inflammatory response cataract surgery 348 glaucoma surgeries 268, 272–3, 273–4, 286–7 Instrumentation see Surgical instrumentation Intracapsular lens extraction 307, 308, 309, 320, 321, 334–9, 342, 343 Intranictitans tacking technique 181, 183, 184 Intraocular injection cannulas 10 Intraocular lenses (IOLs) anterior capsulectomies 322, 324 capsulorhexis 322 ciliary sulcus placement 338–9 development of 308, 309–11 equine 332, 333, 340 implantation of 334, 339–41 intraoperative complications 341–2 postoperative complications 350 surgical instrumentation for 5 types of 340 Intraocular pressure (IOP) cataract surgery and 313, 315–16, 342, 346–7 ciliary body and 241, 242 general anesthetics and 37–8, 40–2, 43 glaucomas 263, 265, 266 anterior chamber shunts 284–5, 291, 292, 293 applanation tonometry 267 classification 267–8

396

Intraocular pressure (IOP) (Continued) cyclodestructive procedures 294, 295, 296, 298, 300 cyclodialysis 276 iridocyclitis 243 pharmacologic ablation of the ciliary body 300 preoperative treatment 273 surgical pathophysiology 272 keratocentesis and 245, 248 sedatives in the horse and 48 Intraocular silicone prostheses see Intrascleral silicone prostheses Intraocular surgery basic operative approach in 22–5 general anesthesia for 47 instrumentation for 12, 13 cannulas 10 forceps 4, 5–6 intraocular lens instrumentation 5 major intraocular surgical packs 17–18 minor intraocular surgical packs 17 scissors 7–8 patient preparation for 21–2 perioperative drugs for 30 see also specific surgeries Intraorbital hydroxyapatite implants, 71, 71 Intraorbital silicone prostheses 69–70 Intrascleral silicone prostheses in cattle 74 for the horse 70–1 postoperative complications 84–5, 85, 86 for small animals 64, 65, 66, 84–5, 85 Intravitreal injections 365 Iridectomy 248, 252–4, 253, 270, 278, 281, 322 Iridencleisis 275–6, 275–6 with cyclodialysis 278–81, 280 Iridocorneal angle anatomy 242, 269, 270 evaluation 267, 267 surgical pathophysiology 271–2 Iridocyclectomy 248, 256–8, 257 with cyclodialysis 282–3, 283 Iridocyclitis cataract surgery and 312–13, 318–19, 318, 342, 345–6, 346, 348 with gonoimplants 291 keratocentesis and 248 parasite-related 248 postoperative 243, 254 Iridotomy 248–9, 250 Iris anatomy 240–1, 241, 269, 270 cataract surgery and 312–13, 318–19, 342, 345–6, 346 corneal incisions for surgery on 246 cysts 238, 239, 252, 258, 259–60 glaucoma surgery cyclodialysis–iridocyclectomy 282–3, 283 iridectomy 278, 279, 281 iridencleisis 275–6, 275–6 iridencleisis–cyclodialysis 278–81, 280 neoplasms 238, 239, 252, 254–5, 254, 256–9, 260–1, 261 perioperative considerations 243, 248

Iris (Continued) peripheral iridectomy with cataract surgery 322 surgical pathophysiology 242, 243, 272, 272 surgical procedures for 248 coreoplasty 248, 252, 253 iridectomy 248, 252–4, 253, 270, 278, 281 iridocyclectomy 248, 256–8, 257, 282–3 iridotomy 248–9, 250 iris bombe´ 248, 255–6, 255 prolapse 210, 211–13, 212, 213–14 sphincterotomy 248, 249–52, 251 see also Iris; glaucoma surgery Iris bombe´ 248, 255–6, 255, 314 Iris forceps 5 Iris hooks 9 Iris scissors 7 Irrigating solutions 30, 31 Irrigation 10, 22 Island (free) conjunctival grafts 166, 171, 171, 172, 173, 208 Isoflurane 41, 43, 321

J Jameson calipers 10, 10 Jameson muscle hook 9 Jugular vein–anterior chamber shunt 290

K Kaswan lateral canthoplasty 122, 122 Keratectomy deep 201 superficial 193–4, 196–9, 196–9 Keratitis 196, 198 Keratocentesis 244–5, 244, 245, 248 Keratoconjunctivitis infectious 234 proliferative 229, 230 Keratoconjunctivitis sicca (KCS) 150 acute 151, 178, 179, 184, 185, 188 cataract surgery and 314 parotid duct transposition for chronic 150, 151–5 Keratomalacia 165 Keratoplasty (corneal graft) 164, 216–28 autogenous rotating full-thickness 220–1, 222 autogenous sliding lamellar 219, 220 donor cornea preparation 217–18, 219, 219, 225 graft rejection 223, 227–8 heterologous 225 history 217 homologous full-thickness (penetrating) 221–3, 224, 225–6, 225 homologous lamellar 219–20, 221 in the horse 225–8, 225, 227 indications for 217, 218, 218 instrumentation for 6, 7, 218 preoperative treatment 218–19 tectonic (frozen) 217, 223–5, 226 Keratotomies 199–201, 199–201 Ketamine for general anesthesia 40 for sedation of cattle 72

Index Knapp straight strabismus scissors 6 Knives 8–9, 11 Koch orbitotomy 81–2 Kuhnt–Helmbold procedure 116, 116 Kuhnt–Szymanowski procedure 116, 116, 117, 118–19

L Lacerations conjunctival 161–2 corneal 210–14 of the eyelid 90, 123–6 of the lacrimal canals 145–6 Lacrimal apparatus see Nasolacrimal apparatus and tear systems Laser therapy 27–30 anterior uveal cysts 29, 258, 260, 261 anterior uveal neoplasms 258–9 for glaucoma 29, 255–6, 295–9, 295, 297–9 of iris bombe´ 255–6 for limbal melanomas 231–2 prophylactic retinopexy 376–7 squamous cell carcinoma 136, 233 therapeutic retinopexy 375–6 Lashes see Eyelashes Lateral canthoplasty 110–11, 111, 118 palpebral fissure size changes 121–3, 121–3 Lateral canthotomy 24–5, 98, 98 cataract surgery and 321–2 enucleation and 62–3 palpebral fissure size augmentation 122–3, 123 traumatic proptosis and 83 with V-shaped excision for eyelid neoplasms 127, 127 Lateral canthus ectropion 115, 116, 116, 117, 118–20 entropion 106, 107, 109–11, 110, 118–20, 123 palpebral fissure size increase 122–3 palpebral fissure size reduction 120, 121–2 tendonectomy 111 Z plasty skin flap for 130, 130 see also Lateral canthoplasty; Lateral canthotomy Lateral enucleation 62–3, 65 Lateral eyelid wedge excision procedure 115, 115 Lateral orbitotomy 77–9, 78, 80, 85 Lateral permanent tarsorrhaphy 121, 121 Lateral tarsorrhaphy–canthoplasty 118, 118 Lens anatomy 306, 311–12, 311 capsule opacities 345, 348, 349, 350, 367 capsule tears 213, 344–5 cataracts see Cataract surgery development of 305 intraocular see Intraocular lenses (IOLs) iris bombe´ and 255, 256, 314 Lens position, glaucoma surgery and 272, 273 Lens removal, glaucoma surgery and 274–5 Lens surgery 306 anterior capsulectomies 322–4

Lens surgery (Continued) capsulorhexis 322–4 cataracts see Cataract surgery corneal incisions for 246, 311, 322 displaced lenses 306, 313–14, 320, 321, 334–9, 342, 343–7 future of 352 instruments for 12, 13 cyclodialysis spatulas 9 forceps 4, 5, 6 intraocular lenses 5 lens loops 9, 10 scissors 7–8 Lens-induced uveitis (LIU) 312–13, 319, 352, 360 Lichenstern retrobulbar injections 23, 45–6 Light systems 20 Limbal anatomy 239–40 Limbal conjunctival cells 159, 165, 203 Limbal surgery 229–32, 233 corneal scissors used at 6, 7 corneoscleral trephination 281–2, 282 forceps 3 incisions for anterior chamber entry 245–6, 322 knives 8, 9 rings 10 see also Anterior chamber; surgery of Linear keratotomy 199–200, 201 Local anesthesia eyelid injections 43–4, 94 retrobulbar injections 23, 24, 45–6, 67, 72–3 Luxated globe 58 Luxated lenses 306, 313–14, 334–9 Lymphoid follicles conjunctival 159 of the nictitating membrane 160, 177–8, 178

M Magnifying instruments 18–20 Mannitol 321, 363 Mast cell sarcoma 60 Matrix metalloproteinases (MMPs) 268, 273, 273, 287 Maxillary sinusotomy 147–8 Mayo scissors 11 McPherson–Vannas iris scissors 7 Medial canthal pocket syndrome 53 Medial canthoplasty 120–1, 121 Medial canthus, palpebral fissure size 120–1, 121 Medulloepithelioma 261, 261 Meibomian glands see Tarsal (meibomian) glands Melanomas anterior uveal 158–9, 237, 238, 239, 254, 256, 260–1, 261 eyelid 126, 128, 129 limbal 229, 229, 230, 230–1, 231–2 Memantine 301 Membrana nictitans see Nictitating membrane Methoxyflurane 41 Methyl methacrylate spheres 64 Metzenbaum scissors 11 Micropalpebral fissures 122–3, 123

Microscopes, operating 18–20, 321 Microsurgery instrumentation for 1 magnification for 18–19 operating room chairs for 20–1 Midazolam 40 Miosis 242 after cataract surgery 313 intraoperative 344 Miotics anesthetic drugs and 42 gonoimplants and 291 perioperative use of 30, 31, 273, 312 Mitomycin C 31, 268, 287 Moll gland 90–1 Mucin 159 Munger–Carter procedure 117, 117 Muscle hooks 9, 9 Mydriatics 30, 39, 43 anterior uveal surgery 243 cataract surgery 344 corneal surgery 194, 195 glaucoma surgery 373 gonoimplants and 291 long-term 318

N Nagahara phacoemulsification 8 Narcotics 40 Nasal fold trichiasis 123, 124 Nasolacrimal apparatus and tear systems 141–55 anatomy 141–2, 150 catheterization 143, 144 diagnostic tests for 47, 142–3, 148, 150 diseases of 141 nictitating membrane function 150, 160 orbitotomy complications 85 surgical procedures for 143–55 conjunctival maxillary sinusotomy 147–8 conjunctivobuccostomy 148 conjunctivorhinostomy 147, 148 dacryocystotomy 146–7 displaced lower punctum 145 imperforate punctum 144–5 keratoconjunctivitis sicca 150–5, 184 lacerations of the canaliculi 145–6 lower micropunctum 145 obstructions in large animals 148 obstructions in snakes 148–50 parotid duct transposition 150, 151–5, 151, 153–4 Nasolacrimal flush tests 47, 142–3 Nd:YAG laser therapy 28–9 anterior uveal disease 29, 256, 258, 259, 260 limbal melanomas 231–2 transscleral laser cyclophotocoagulation 295, 297–8, 298 Needle holders 2, 9 Needles 14 ultrasonic 326 Neoplasms adjunctive therapeutic modalities 72, 135–7, 138

397

Index Neoplasms (Continued) anterior uveal 237–8, 239, 252, 254–5, 256–9, 260–1 conjunctival 157, 161, 162, 233 corneolimbal 229–32, 229, 230, 231, 233, 234 eyelid in large animals 72, 90, 127, 132–8, 232, 233 in small animals 89, 90, 126–32 laser therapy for 29 nictitating membrane 157, 187–8 orbital 59 enucleation 60, 60, 67, 68, 72 exenteration 59, 71–2, 74, 86 orbitectomy 60, 77, 81, 82, 86 orbitotomy 77, 81, 86 Nerve blocks 23, 24, 32, 43–7, 67, 72–3 secondary blepharospasm and 94 Neuromuscular blocking agents 24, 41–2, 195, 321 Neuroprotectants 300–1, 301 New Orleans lens spoon 10 Nictitating membrane 157 anatomy of 158, 159–60, 160 diseases of 157–8, 187–8 function 160 movement of 158 sutures for 14, 24 tear production by 150, 160 Nictitating membrane surgery 176 everted membrane 176–7 general anesthesia for 47 hyperplastic lymphoid follicles 177–8 instrumentation for 11–12 in large animals 188 membrane excision 187–8 membrane flaps 185–7, 188, 204, 210 membrane gland protrusion (cherry eye) 178–84 membrane protrusion 184–5 Nitric oxide synthase (NOS) inhibitors 301 NMDA antagonists 301 Non-steroidal anti-inflammatory agents anterior chamber pathophysiology 242–3 antitumor effects 234 for iris prolapse in horses 214 perioperative use of 30, 31, 194–5

O Oculorespiratory cardiac reflex 38–9 O’Gawa–Castroviejo forceps 5 180 (advancement, hood) conjunctival grafts 166, 168–9, 169, 207 Operating room 17–34 basic operative approaches 22–5 chairs in 20–1, 321 cryotherapy in 26–7 electroepilation in 26 hemostasis in 25, 30 illumination of 20 laser therapy in 27–30 magnifying instruments in 18–20, 321 patient preparation in 21–2 perioperative drugs in 30–1 see also Anesthesia postoperative patient care 31–2, 47

398

Operating room (Continued) subpalpebral medication systems in 32–4 see also specific procedures Ophthalmic instruments see Surgical instrumentation Orbital abscesses 59 Orbital anatomy 53–7 Orbital emphysema 84 Orbital fractures 58, 81, 82 Orbital growth 58 Orbital implants see Implants, orbital Orbital inflammation 58–9 Orbital neoplasms 59 enucleation 60, 60, 67, 68 exenteration 59, 71–2, 74, 86 orbitectomy 60, 77, 81, 82, 86 orbitotomy 77, 81, 86 Orbital rim resection 82, 135 Orbital skin preparation 21, 60 Orbital surgery 51–87 diagnostic procedures prior to 51–3 disease margin definition for 51–2 diseases managed by 51 general anesthesia 47 instrumentation for 11, 14 orbital anatomy for 53–7 orbital pathophysiology and 57–9 perioperative medications 47, 59–60, 81, 84 postoperative care and management 84–7 procedures 60–83 enucleation 60–3, 67–70, 73–6, 84, 86 evisceration 60, 63–5, 66, 70–1, 76, 84–5, 86 exenteration 60, 67, 71–2, 85, 86 for orbital fractures 81, 82 orbital rim resection 82, 135 for orbital volume augmentation 83 orbitectomy 60, 77, 81, 82, 86 orbitotomy 60, 76–82, 85, 86 postoperative complications 68–9, 84–7 in traumatic proptosis 82–3, 86, 87–8 strabismus and 52, 86 sutures for 14 Orbitectomy 60, 77, 81, 82, 86 Orbitotomy indications for 77 in large animals 81–2 postoperative complications 85, 86 in small animals 76–81, 78, 86 Owls, enucleation 74, 75

P Palpebra tertia see Nictitating membrane Palpebral conjunctiva 92, 158, 159, 159 biopsy 160–1 defect repair 162, 162 grafts 164, 165, 166, 170–1, 171, 172, 203, 205–6 lacerations 161–2 symblepharon 162–3, 162 Palpebral fissure lateral canthotomy 24–5, 62–3, 83, 98 muscles controlling 91, 91, 92, 92 surgery to decrease 120–2 surgery to increase 122–3 Palpebral nerve blocks 43, 44, 94

Pancuronium 42 Pannus (chronic superficial keratitis) 196, 198 Paracentesis anterior chamber (keratocentesis) 244–5, 244, 245, 248 vitreal (hyalocentesis) 358, 364–5, 365 Parasites 248, 248 Parotid duct–anterior chamber shunt 291, 291 Parotid duct transposition 150, 151–5, 151, 153–4 Pars plana ciliary body anatomy 358 hyalocentesis 358, 365 retinal detachment surgery 379–85, 382–4 vitrectomy 364, 370–3 Pectinate ligaments 271–2 Pedicle grafts after eyelid neoplasm removal 132, 132 conjunctival 164, 166, 169–71, 175–6, 203, 206, 207–8 for eyelid agenesis 98–100, 98–100 Penetrating keratoplasty (PK) in the horse 225–6, 225, 227, 228 in small animals 221–3, 224 Perfluorocarbon gases 362, 379, 384, 384 Peterson retrobulbar nerve block 23, 24, 46, 46, 47, 72 Phacoemulsification 320, 321, 324–34 chop technique 329 corneal damage during 326 divide and conquer technique 329 history of 308, 309 in the horse 330–4, 331, 333–4, 351–2, 351–2 instruments for 5, 8, 11, 325–6, 330, 332 lens rotation 329–30 sculpting 329–30 in small animals 327–30, 328 Phenothiazine tranquilizers 40, 47 Pigmentary keratitis 196, 198 Piroxicam 234 Plica semilunaris see Nictitating membrane Pneumatic retinopexy 375 Pocket canthoplasty procedure 120–1, 121 Porcine small intestinal submucosa (SIS) grafts 174, 203–4 Posterior capsule opacities (PCOs) 345, 348, 349, 350, 367 Posterior lamellar keratoplasty (PLK) 225, 226–7, 227, 228 Posterior nictitans anchoring technique 179–81, 180–1, 183 Povidone-iodine 21 Preanesthetic medications 39–40 Pre-iridal fibrovascular membranes (PIFMs) 272, 272 Prolapsed retrobulbar fat 74 Prophylactic retinopexy 376–7 Propofol 40 Proptosis, traumatic 58, 82–3, 86, 87–8 Prostaglandin analogs 301 Prostaglandins 242, 243 Prostheses see Implants Punctate keratotomy 199–200, 200, 201

Index Pupil cataract surgery and 313, 342, 344, 348–50, 349 coreoplasty 248, 252, 253 effects of general anesthetics on size of 39 glaucoma surgery and 273 iris anatomy 240, 241 iris bombe´ 255–6, 255 perioperative drugs for 30, 31, 39, 194, 273, 344 surgical pathophysiology 243 vitreoretinal surgery 364, 367 Pupilloplasty (coreoplasty) 248, 252, 253 Pus, hypopyon 238, 244, 246, 248

Q Quickert–Rathbun procedure 104–5, 105

R Rabbit anterior chamber shunts 287 conjunctival overgrowth 176, 176 corneal surgery 174, 194, 203–4 glaucomas 266, 266 hyphema 247 orbital anatomy 56 Radiation therapy for sarcoid 137 for squamous cell carcinoma 136, 136, 232–3 Radiofrequency hyperthermia for sarcoid 137 for squamous cell carcinoma 135, 233 Rappazzo intraocular forceps 6 Reactive oxygen species (ROS) scavengers, 301 Rectus muscle anatomy 269, 270, 359 Rectus muscle surgery 52 traumatic proptosis 86 Regional nerve blocks 23, 24, 43–7, 67, 72–3 secondary blepharospasm and 94 Renal disease 43 Restraint methods for cattle 48, 72 for horses 47–8, 97 postoperative 31–2, 97 Retinal degeneration 316 Retinal detachments cataract surgery and 316, 350–1, 351, 360 classification 360 clinical evaluation of 360–1, 361, 362 demarcation retinopexy 376 medical treatment 360 preoperative considerations 363, 363 prophylactic retinopexy 376–7 subretinal fluid aspiration 373, 374 surgery for 358, 359, 377–85, 377 basic technique 378–9, 380–1 pars plana approach 379–85, 382–4 patient selection 377–8 postoperative complications 383–5, 383–4 postoperative management 379, 382–3 preoperative medication 378 surgical anatomy 358, 359 surgical instrumentation 361–2, 379–81

Retinal detachments (Continued) surgical pathophysiology 359–60 treatment principles 361 Retinal procedures 360, 373 barrier retinopexy 376 chorioretinal biopsy 374, 375 demarcation retinopexy 376 pneumatic retinopexy 375 prophylactic retinopexy 376–7 retinal detachment see Retinal detachments subretinal fluid aspiration 373, 374 therapeutic retinopexy 375–6, 376 Retractors 9 Retrobulbar fat, prolapsed 74 Retrobulbar injections 22–4, 44–7 in cats 23, 45 in cattle 23, 24, 46, 47, 72–3 complications of 23–4, 46–7 in dogs 22–3, 39, 45 in the horse 23, 45–6, 67 Rhomboid graft, eyelid repair 134 Rings 10–11, 24 Ripping principle 322–3 Roberts–Bistner eyelid agenesis procedure 99, 99, 100, 100 Roberts–Jensen palpebral fissure size reduction 120–1, 121 Robertson lateral canthal tendonectomy 111

S Salaras procedure (thermokeratoplasty) 228, 228 Sarcoid 133, 133, 135, 136–7, 137 Schirmer tear test 38, 150 Scissors 2, 6–8, 11 Scleral buckles 378, 381, 382, 384 Scleral incisions 270, 277 Scleral surgery 229–32 corneoscleral transposition 204–5 instrumentation for 195–6 forceps 3 knives 8, 9 needles 14 scissors 7 sutures for 14 Sedatives 40, 47–8, 72 Self-trauma, prevention 31–2, 47, 97 Semicircular skin grafts 130, 130 Shearing principle 322–3 Sheep, entropion in 104, 113, 113 Silicone buckles 378, 381, 382, 384 Silicone oils (SiOs) 362, 379, 384–5, 384 Silicone prostheses for cattle 73, 74 for horses 69–71 for small animals 64, 65, 66 Skin, eyelid 90, 91 Skin grafts in cattle 137–8, 137 for eyelid agenesis 98–100, 98–100 in the horse 133–5, 134 in small animals 128–32, 129–32 Skin preparation 21 Skinfolds entropion and 107–8, 108, 109, 109, 110, 113–14 nasal fold trichiasis 123, 124

Slatter orbitotomy 79, 80 Sliding conjunctival grafts 166, 171–3 Sliding skin grafts in cattle 137–8, 137 in the horse 134–5 in small animals 128–9, 129, 131, 131 Small intestinal submucosa (SIS) grafts 174, 203–4 Snake(s) 148–50, 149 Spatulas 9, 10 Spectaculopathy, bullous 148–50 Sphincterotomy 248, 249–52, 251 Sponges 22 Squamous cell carcinoma (SCC) bovine 72, 72, 90, 137–8, 138, 234 conjunctival 161, 162 corneolimbal 229, 232, 233, 234 equine 67, 90, 132–3, 134, 135–6, 188, 232–4 in the eyelid in cats 126–7, 126 in cattle 72, 72, 90, 137–8, 138 in the horse 90, 132–3, 133, 134, 135–6, 136, 232, 233 in the nictitating membrane 187, 188 Stades combined entropion–trichiasis procedure 107–8, 108, 109 Stay sutures 24 Sterilization of instruments 13 Steven tenotomy scissors 6 Storz intraocular forceps 6 Storz intraocular scissors 8 Storz needle holder 9 Strabismus after traumatic proptosis 86 orbital diseases and 52 Strabismus hooks 9, 9 Strabismus surgery 52, 86 Subconjunctival enucleation 61, 62, 67, 68, 74 Subpalpebral medication systems 32–4, 214 Succinylcholine 41–2 Suprachoroidal cyclosporine (CsA) implants 369–70 Supraorbital nerve blocks 32, 43–4, 94 Surgical instrumentation 1–14, 17–18 calipers 10 cannulas 10 care of 13 for cataract surgery 7, 9, 10, 12, 13 phacoemulsification 5, 8, 11, 325–6, 330, 332 for conjunctival surgery 11–12 for corneal surgery 4, 12, 14 design of 1–2 external surgical packs 17 eyelid specula 2 for eyelid surgery 11–12, 95 forceps 2, 3–6, 11 importance of microsurgical 1 for intraocular surgery 4, 5–6, 7–8, 10, 12, 13, 17–18 investment in 1 iris hooks 9 knives 8–9, 11 for large animals 2, 11 lens loops 9 needle holders 2, 9

399

Index Surgical instrumentation (Continued) needles 14 for orbital surgery 11, 14 retractors 9 rings 10–11 scissors 2, 6–8, 11 spatulas 9, 10 for special species 2, 11 sterilization of 13 storage of 13 sutures 2, 3–5, 6, 14, 24 for vitreoretinal surgery 12–13, 361–2, 364, 379–81 see also specific procedures Sutures 14 corneal 246, 246 for eyelid surgery 14, 95 following enucleation in cattle 73 lateral canthoplasty with 111, 111 for lateral canthotomy 25 limbal 246, 246 postoperative protection of 32, 97 scissors for cutting 6 stay 24 tacking procedures 104, 104, 112, 181, 183, 184 in traumatic proptosis surgery 83, 86–7 tying forceps for 2, 3–5 Swabs 22 Symblepharon 162–3, 162, 163

T Tacking procedure for entropion 104, 104, 112 intranictitans 181, 183, 184 Tarsal (meibomian) glands 92, 95 distichiasis see Distichiasis neoplasms 126, 126, 129 Tarsal pedicle for entropion 107, 108 Tarsal plate excision for distichiasis 102 Tarsoconjunctival grafts in cattle 138 in the horse 134 in small animals 128, 131, 131 Tarsopalpebral conjunctival grafts 165, 166, 170–1, 171, 172, 173 Tarsorrhaphy after orbital surgery 83, 84, 85 in the horse 97, 210 in small animals 83, 95–7 Tear systems see Nasolacrimal apparatus and tear systems Tectonic (frozen) keratoplasty 217, 223–5, 226 TelazolW 40 Telescope magnifiers 18 Tenotomy scissors 6 Therapeutic retinopexy 375–6, 376 Thermokeratoplasty 228, 228, 229 Third eyelid see Nictitating membrane

400

360 (complete, Gundersen-type) bulbar conjunctival grafts 166, 167–8, 167–8, 206 Tissue plasminogen activator (tPA) 30, 243, 247–8, 344 Total (360 ) conjunctival grafts 166, 167–8, 167–8, 206 Tranquilizers 40, 47 Transaural enucleation 74 Transoral orbitotomy 81, 81 Transpalpebral enucleation in cattle 72, 73 in the horse 68, 69 in small animals 61–2, 64 Transpupillary vitreal aspirations 365–6 Transscleral laser cyclophotocoagulation (TSCPC) 295, 295, 296, 297–8, 297–9 Traumatic proptosis 58, 82–3, 86, 87–8 Trichiasis combined entropion procedure 107–8, 108, 109 nasal fold 123, 124 Troutman–Barraquer forceps 5 Tumors see Neoplasms Tying forceps 2, 3–5

Ultrasonographic equipment, phacoemulsification 325–6, 326 Ultrasonography (US) 316, 361, 362 Urokinase 247 Utrata forceps 5, 323, 324 Uvea, anterior see Anterior uvea

Vitreoretinal surgery (Continued) retinal procedures 360, 373 barrier retinopexy 376 chorioretinal biopsy 374, 375 demarcation retinopexy 376 pneumatic retinopexy 375 prophylactic retinopexy 376–7 retinal detachment see Vitreoretinal surgery, retinal detachments subretinal fluid aspiration 373, 374 therapeutic retinopexy 375–6, 376 surgical anatomy 357–9, 358–9 vitreal procedures 360, 364 anterior vitrectomy 363, 364, 366–9, 370–3 equine recurrent uveitis 369–73 hyalocentesis 358, 364–5 intravitreal injections 365 pars plana vitrectomy 364, 369, 370–3 preoperative considerations 362–3 suprachoroidal cyclosporine implants 369–70 surgical pathophysiology 359–60 vitreal aspiration 362–3, 365–6 Vitreous humor anatomy of 358–9 anterior chamber shunts 293 cataract surgery and 345 expanding vitreous syndrome 341 glaucoma surgery pathophysiology 272 surgical pathophysiology 359–60 see also Vitreoretinal surgery Von Graefe forceps 3, 4, 4 Von Graefe strabismus hook 9

V

W

V-shaped (wedge) excision 127, 127 V to Y plasty (Wharton–Jones procedure) 106, 115–16, 115 Vannas scissors 7, 7, 323, 324 Vecuronium 42 Venturi pumps 325 Vietnamese potbellied pig, entropion 113–14, 114 Viscoelastic agents 30, 31, 320 Vitreoretinal diseases 357 laser therapy for 29 surgery for see Vitreoretinal surgery Vitreoretinal surgery 357–85 instrumentation for 12–13, 361–2, 364, 379–81 retinal detachments cataract surgery and 316, 350–1, 351, 360 classification 360 demarcation retinopexy 376 evaluation 360–1, 361 preoperative considerations 363 surgery for 358, 359, 377–85, 380–4 surgical anatomy 358, 359 surgical pathophysiology 359–60

Warren phacoemulsification 8 Wedge excision, eyelid neoplasms 127, 127 Wharton–Jones procedure for ectropion 106, 115–16, 115 Williams eyelid speculum 2, 3 Wound healing 268, 272–3, 273–4, 286–7 Wyman lateral canthoplasty 110–11, 111, 122, 122

U

X Xylazine 40, 47–8, 72

Y Y to V plasty for entropion 106–7, 107, 112

Z Z plasty skin flaps 130, 130, 134–5 Zeiss gland 90–1