Reading Pentacam Topography (Step By Step: Basics and Case Study Series)

Step by Step®

Reading Pentacam Topography

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(Basics and Case Study Series)

System requirement: • Windows XP or above • Power DVD player (Software) • Windows media player 10.0 version or above (Software) Accompanying Photo CD ROM is playable only in Computer and not in DVD player. Kindly wait for few seconds for Photo CD to autorun. If it does not autorun then please do the following: • Click on my computer • Click the drive labelled JAYPEE and after opening the drive, kindly double click the file Jaypee

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Notification The information provided via this book is intended for general information purposes. The information provided via this book is published to assist you, but it is not to be relied upon as authoritative. The author accepts no liability whatsoever for any direct or consequential loss arising from any use of the information contained in this book.

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Step by Step®

Reading Pentacam Topography

(Basics and Case Study Series)

MAZEN M SINJAB MD, MS, CABOphth, PhD

Consultant Ophthalmologist Ophthalmology Department Medical School Damascus University Syria

Published by Jitendar P Vij Jaypee Brothers Medical Publishers (P) Ltd Corporate Office 4838/24 Ansari Road, Daryaganj, New Delhi 110 002, India Phone: +91-11-43574357, Fax: +91-11-43574314 Registered Office B-3 EMCA House, 23/23B Ansari Road, Daryaganj, New Delhi 110 002, India Phones: +91-11-23272143, +91-11-23272703, +91-11-23282021, +91-11-23245672, Rel: +91-11-32558559 Fax: +91-11-23276490, +91-11-23245683 e-mail: [email protected], Website: www.jaypeebrothers.com

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North America Office 1745, Pheasant Run Drive, Maryland Heights (Missouri), MO 63043, USA, Ph: 001-636-6279734 e-mail: [email protected], [email protected] Central America Office Jaypee-Highlights Medical Publishers Inc. City of Knowledge, Bld. 237, Clayton Panama City, Panama Ph: 507-317-0160 Step by Step® Reading Pentacam Topography (Basics and Case Study Series) © 2010, Jaypee Brothers Medical Publishers All rights reserved. No part of this publication and Photo CD ROM should be reproduced, stored in a retrieval system, or transmitted in any form or by any means: electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the author and the publisher. This book has been published in good faith that the material provided by author is original. Every effort is made to ensure accuracy of material, but the publisher, printer and author will not be held responsible for any inadvertent error(s). In case of any dispute, all legal matters are to be settled under Delhi jurisdiction only. First Edition: 2010 ISBN 978-81-8448-804-3 Typeset at JPBMP typesetting unit Printed at

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Acknowledgments The author would like to express his deep gratitude to Ruba his wife whose unwavering support was critical for this book. The author would also like to thank all the researchers concerned in the refractive field for their efforts. His special thanks to Theo Seiler, Jack Holladay and Michael W Belin for their pioneering work in the field.

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Preface Taking the right decision in laser refractive surgery depends to a great extent on good reading of corneal topography and its clinical interpretation. This is very important for having the aimed results and avoiding postoperative complications. Data in this book were obtained and gathered from the user manual of the Pentacam, international conferences, refractive journals, personal contacts with many refractive professors and of course self experience. The strategy in compiling this little book is making a quick refreshment of what has been explained in the previous book “Corneal Topography in Clinical Practice” published by Jaypee, and then follows a systematic approach of topographical pictures in chosen cases. This strategy allows the readers to qualify and quantify any case in the future in a way that no data may be lost. There are sure to be some errors, as the ophthalmology editor, I take full responsibility for these and look forward to being further educated. Mazen M Sinjab

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Contents 1. Instruments Measuring the Corneal Surface .... 1 Curvature Based Instruments 2 Elevation Based Topographers 3

2. Quick Review of Pentacam Main Maps ............ 9 Curvature Maps 10 The Sagittal (axial map) 10 The Tangential (local map) 12 Elevation Maps 16 Corneal Thickness Map 18 Main Page Analysis 21

3. Reading Pentacam Topography......................... 29 Introduction 30 Steps of Reading the Topography Scoring the Case 50

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4. Examining the Patient ......................................... 51 Ocular History 52 Family History 56 Medical History 56 Medications and Allergies 58 Prior Corrective Lenses 59

5. Case Study ............................................................. 61 Case 1: Myopic Astigmatism 62 Case 2: Mixed Astigmatism 74

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Step by Step Reading Pentacam Topography

Case 3: Hyperopia 86 Case 4: Anisometropia 97 Case 5: Suspected Case 118 Case 6: Post-Lasik Ectasia 141 Case 7: Keratoconus 167 Case 8: Keratoconus Possible 179 Case 9: Abnormal Cornea 189 Bibliography ............................................................... 203 Index .......................................................................... 207

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Introduction Here is my second book in this field. The Pentacam camera is an attractive camera; by which you can get many data and maps. It is essential in taking the right decision, hence the need to explain all features, maps, tables and diagrams this camera provides us with, this was the purpose of my previous book “Corneal Topography in Clinical Practice” published by Jaypee Brothers 2009. Since many ophthalmologists need a quick and simple reference, I edited this new book but with no repetition. This book delivers—at the beginning—a quick short refreshment of the main concepts of the Pentacam topography, then it describes a step-by-step reading the Pentacam as a checklist included in a table depicting all available data which I find most useful to produce optimal results. To reach this goal, I discussed many clinical cases in order to highlight the subjects of concern. But still we have to refer to the first book for more details about the principles of maps, tables and diagrams, which is essential in understanding my step-by-step approach.

Instruments Measuring the Corneal Surface

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Instruments Measuring the Corneal Surface

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Step by Step Reading Pentacam Topography

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CURVATURE BASED INSTRUMENTS The normal corneal outer surface is smooth; corneal irregularities being neutralized by the tear film layer. The anterior surface acts as an almost transparent convex mirror; it reflects part of the incident light. Many instruments have been developed to assess the anterior surface by measuring the reflected light. These non-contact instruments use light target (in different shapes) and a microscope or other optical systems. The instruments are either quantitative or qualitative, and either reflectionbased or projection-based. These instruments are as follows: 1. The keratometer: it is a quantitative reflection-based instrument. 2. The photokeratoscope: it is a qualitative reflection-based instrument (Fig. 1.1).

Fig. 1.1: The ‘ring verification display’ in videokeratoscope. The explorer is able to evaluate qualitatively the corneal surface. Corneal irregularity appears as irregular rings with differing interspaces.

Instruments Measuring the Corneal Surface

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3. The computerized videokeratoscope: it is a projectionbased topographer consisting of a Placido disk (Fig. 1.2).

Fig. 1.2: The Placido cone. The larger the cone, the more the rings and the wider the area to be estimated. The very central cornea and the paralimbal area are excluded.

ELEVATION BASED TOPOGRAPHERS Placido based (or curvature based systems) rely on the data collected from the anterior surface of the cornea either with reflection-based or projection-based systems. Additionally, without the information about the posterior surface, complete pachymetric evaluation of the cornea is not possible. Of course, ultrasonic pachymetry can give us central and few paracentral measurements, but now we

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need full pachymetric map. Moreover, the posterior surface of the cornea is being more appreciated as a sensitive indicator of corneal ectasia and can often be abnormal in spite of a normal anterior corneal surface. It is now recognized that while the refractive power of the cornea is mostly determined by the anterior surface, the biomechanical behavior of the cornea is at least equally determined by both surfaces. On the other hand, in the curvature based systems the elevation map of the anterior surface is derived from the curvature map, while it is directly calculated in the elevation based systems. For full discussion of the curvature and elevation maps please refer to my book “Corneal Topography in Clinical Practice” published by Jaypee Brothers 2009. Description of the Unit The OCULUS Pentacam/Pentacam HR is a rotating Scheimpflug camera (Figs 1.3 and 1.4). The rotational measuring procedure generates Scheimpflug images in three dimensions, with the dot matrix fine-meshed in the center due to the rotation. It takes a maximum of 2 seconds to generate a complete image of the anterior eye segment. Any eye movement is detected by a second camera and corrected for in the process to some extent. The Pentacam calculates a 3-dimensional model of the anterior eye segment from as many as 25.000 (HR: 138.000) true elevation points. The topography and pachymetry of the entire anterior and posterior surfaces of the cornea from limbus-to-limbus are calculated and depicted. The analysis of the anterior

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Instruments Measuring the Corneal Surface

Fig. 1.3: The Pentacam system. Central slit light with lateral concentric rotating Scheimpflug camera.

Fig. 1.4: Captured section by the rotating camera of the Pentacam.

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eye segment includes a calculation of the chamber angle, chamber volume and chamber height and a manual measuring function at any location in the anterior chamber of the eye. In a moveable virtual eye, images of the anterior and posterior surface of the cornea, the iris and the anterior and posterior surfaces of the lens are generated. The densitometry of the lens is automatically quantified. The Scheimpflug images taken during the examination are digitalized in the main unit and all image data are transferred to the PC. When the examination is finished, the PC calculates a 3D virtual model of the anterior eye segment, from which all additional information is derived.

Fig. 1.5: The image in the ordinary camera. The main disadvantage is limited depth of focus because the picture plane, the objective plane and the film plane are parallel.

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Fig. 1.6: The Scheimpflug camera. Higher depth of focus, sharp image but distorted. The picture plane, the objective plane and the film plane cut each other in one line or one point of intersection.

To understand Scheimpflug principle, see Figs 1.5 and 1.6. Fig. 1.5 illustrates the image in the normal camera; notice that the three planes (The picture plane, the objective plane and the film plane) are parallel. Fig. 1.6 illustrates the Scheimpflug camera. The Scheimpflug law says: To get a higher depth of focus, move the three planes, provided that the picture plane, the objective plane and the film plane have to cut each other in one line or one point of intersection. The advantages of the Scheimpflug Camera are: higher depth of focus and sharp picture, but distorted.

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Quick Review of Pentacam Main Maps

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Quick Review of Pentacam Main Maps

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CURVATURE MAPS The Sagittal (Axial) Curvature Map

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Principle To measure the refractive power at point “a” (Fig. 2.1), we have to draw a tangent on the surface of the cornea at that point, then we take the “normal” of the tangent at that point, which intersects with a reference axis at point “b”; taking into consideration that the reference axis is the anatomical axis of the cornea, i.e. it passes through its apex. Namely, segment “ab” is the curvature radius (r) of the cornea at point “a”. The equation of refractive surfaces is applied to calculate the refractive power of the cornea at

Fig. 2.1: The sagittal (axial method). The curvature power of the measured surface in point “a” is calculated using a tangent line in this point, the normal in this point intersects the reference axis at point b, ab is the radius (r) of point “a”, finally the equation is applied to calculate the power (K) at point a.

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Fig. 2.2: The sagittal (axial) curvature map of the anterior surface of the cornea.

that point, and in the same way, at other points. The computer displays this power as a colored map with the used color scale beside (Fig. 2.2). This is applied on either the front or back surfaces of the cornea. Values of the back corneal surface power are displayed as negative digits (Fig. 2.3A). Although the posterior surface of the cornea is convex, it acts as a concave surface; because the light rays come from a medium of higher refractive index (corneal stroma) to a medium of lower refractive index (aqueous humor), this leads the rays to diverge rather than converge (Fig. 2.3B).

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Fig. 2.3A: The sagittal (axial) curvature map of the posterior surface of the cornea. Notice the negative values.

The Tangential (Local) Curvature Maps Principle This method uses circles tangential to the examined corneal surface at the points to be measured. The radius of the tangential circle is considered as the curvature radius, on which the equation can be applied. Radii of circles differ according to surface changes (Fig. 2.4). Geometrically, the specifications of the tangent circles are more accurate than

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Fig. 2.3B: The light rays come from a medium of higher refractive index (corneal stroma) to a medium of lower refractive index (aqueous humor), this leads the rays to diverge rather than converge, but this divergence is not significant because the difference between the refractive indexes is very small.

Fig. 2.4: The tangential (local method). The principle depends on tangent circles rather than straight lines.

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Fig. 2.5: The tangential curvature map of the anterior surface of the cornea. It is noisy and more detailed than the sagittal map.

those of the tangent lines. Consequently, this method can highlight any irregularity in the cornea whatever small it is (Fig. 2.5). Again, the values of the back surface are displayed as negative digits, since this surface plays the role of a concave refractive surface.

Quick Review of Pentacam Main Maps 15 The Reference Axis

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As mentioned before, the sagittal or axial method depends on an axis used as a reference in measuring the curvature radii. What is the Reference Axis? There are three important axes in the cornea: 1. The visual axis (Fig. 2.6): It virtually connects the scene object with the foveola.

Fig. 2.6: The visual axis. It connects between the scene object and the foveola.

2. The anatomical axis (Fig. 2.7): It is the symmetric rotational axis, which passes through the apex of the cornea, and not necessarily through the foveola, this is the real reference axis. 3. The videokeratoscope normal (VK normal) (Fig. 2.8): Some topographic systems use light rings known as Placido disk to measure the curvature of the cornea according to the shape of reflected rings against the front surface of the cornea. These systems consider the normal of Placido disk center as the symmetric rotational axis of the cornea.

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Fig. 2.7: The anatomical axis. It is the rotational axis of the cornea that passes through its apex.

ELEVATION MAPS Principle The surface of the cornea is mostly similar to the surface of the globe, in terms of elevations and depressions (Fig. 2.8). These elevations and depressions should be measured and expressed to have a realistic topography of the cornea. The main difference between the globe and the cornea is that the former has a reference surface, namely the sea level, to which all elevations and depressions are related. Because the cornea has no similar natural reference surface, it is imperative to create an artificial one depending on the mean central radii of the examined surface. Reference Body The computer of the camera proposes a reference body for each cornea being captured (Fig. 2.9). The reference

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Fig. 2.8: Similarity between surface of the globe and surface of the cornea. Earth has a natural reference surface to measure the altitudes; it is the sea level, while the surface of the cornea does not have a natural reference surface.

Fig. 2.9: The reference body. It is the best body that fits the measured corneal surface according to its elevations and depressions.

body of the front surface may differ from that of the back surface, although both are of the same cornea. The computer adjusts the reference surface with the measured surface. The computer considers all points above the reference surface as elevations, being displayed as

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18 Step by Step Reading Pentacam Topography positive values, and considers all points below the reference surface as depressions, being displayed as negative values, where all values are in microns. The coincidence points between the reference surface and the measured surface are displayed as zeros, i.e. exactly like the sea level (Figs 2.10 to 2.12). The elevation maps are more accurate than curvature maps in evaluating both surfaces of the cornea. They are less affected by tear film disturbance and use of contact lenses.

CORNEAL THICKNESS MAP The computer measures the thickness of the cornea at all points depending on the elevation maps, because the difference between the front and back surface elevations indicates corneal thickness.

Fig. 2.10: The relationship between the reference body and the cornea. Corneal surface (yellow) has steep center and flat periphery in accordance to this particular reference body.

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Fig. 2.11: The relationship between the reference body and the cornea. The steep center appears in hot colors.

Fig. 2.12: The relationship between the reference body and the cornea. The flat midperiphery appears in cold colors.

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Fig. 2.13: Main elements in corneal thickness map: the pupil center location, the pachy apex and the thinnest location. There are two important concepts: the difference in thickness between the pachy apex and the thinnest location, and the coordinates of the thinnest location.

The main points in the map are three locations that appear on the main page (Fig. 2.13): the thinnest location, the corneal apex and the pupil center. The main page displays the coordinates of each location, where the corneal apex is the origin point (zero point). The direction of axis X is from the patient’s right to his left, when the patient is seated opposite to the physician. The direction of axis Y is from the bottom up (Fig. 2.14). Example: a point “e” in the

Fig. 2.14: The origin of the coordinates is the pachy apex.

Quick Review of Pentacam Main Maps 21 left cornea is located at “+0.3,-0.5” position, i.e. this point is located 0.3 mm temporal to and 0.5 mm inferior to corneal apex. The relationship between the coordinates of the three main elements is of great importance.

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MAIN PAGE ANALYSIS This page should be displayed with the four main refractive maps: anterior sagittal curvature map, anterior and posterior elevation maps and thickness map (Fig. 2.15). We should not, by any means, accept a page of one map (Fig. 2.16), especially if it does not include any information, because it is useless.

Fig. 2.15: The main four maps. The sagittal front, elevation front, elevation back and corneal thickness maps. The surgeon should always study these maps to take the right decision.

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Fig. 2.16: The useless map. This map should not be relied upon when taking the decision because there are neither values nor the other important maps to be compared with. The colors are not sufficient to decide because they can be changed according to the chosen scale.

Let us start defining the abbreviations of the page and their interpretations: Cornea Front Surface (Fig. 2.17) K1: Horizontal curvature power of the cornea in the central 3 mm circle expressed in diopters.

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Fig. 2.17: Cornea front and cornea back surfaces in the main page of the Pentacam.

K2: Vertical curvature power of the cornea in the central 3 mm expressed in diopters. Km: Mean curvature power of the cornea in the central 3 mm expressed in diopters. Rh: Horizontal curvature radius of the central 3 mm expressed in mm. Rv: Vertical curvature radius of the central 3 mm expressed in mm. Rm: Mean curvature radius of the central 3 mm expressed in mm. Qs: “Quality specification”. It specifies the quality of the topographic capture and should be displayed “OK”. Otherwise, there is missed information which was virtually

24 Step by Step Reading Pentacam Topography produced by the computer and the capture should preferably be repeated.

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Q-val (6 mm): Value of Q in the central 6 mm as shown between two brackets. Any other central circle can be chosen through the program settings. Astig: Amount of corneal astigmatism on the front cornea surface, i.e. the amount of differentiation between the two curvature radii of the central 3 mm. Axis: The axis of corneal astigmatism in the central 3 mm. Rmin: Minimum radius of curvature expressed in mm. It is shown as a symbol (Fig. 2.18) not necessarily central. Rper: Radius of corneal curvature in the peripheral 9 mm of the cornea expressed in mm. Cornea Back Surface As mentioned before, the cornea back surface plays the role of a concave lens; therefore, the curvature power is displayed on the back surface as negative values (see Figs 2.3A and B). Coordinates of the Corneal Thickness (see Fig. 2.14) Pachy apex: Corneal thickness at the apex. The computer considers the apex as the origin of the coordinates, X for the horizontal and Y for the vertical. Therefore, zero is displayed in both squares of pachy apex coordinates. Pupil center: Corneal thickness in the pupil center. The Xand Y-coordinates show the position of the pupil center from the apex. The two coordinates differ according to pupil medriasis or miosis, because the pupil center is often

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Fig. 2.18: Minimal radius of curvature, a very important item to consider when treating hypermetropia.

shifted superotemporally when dilated. This is very important in the process of decentration, or what is known as offset pupil. Thinnest location: Thinnest point in the cornea. It is the most important in the decision procedure. The X- and Ycoordinates indicate the position of the thinnest location from the apex.

26 Step by Step Reading Pentacam Topography Miscellaneous (Fig. 2.19)

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Cornea volume: Some studies are carried out to realize the relationship between cornea volume and ectatic changes, in order to conclude a new indicator for keratoconus. Chamber volume: Volume less than 100 mm3 should alert us to check the patient for angle closure glaucoma. AC depth (Int.): Central anterior chamber depth, measured from the inner surface of corneal endothelium to the iris

Fig. 2.19: Other functions in the main page. Cornea volume, chamber volume, anterior chamber depth measured from the internal surface of corneal endothelium (Int) or from corneal epithelium (Ext), the IOP modification according to corneal thickness, average of Keratometric power deviation (KPD), anterior chamber angle, pupil diameter and lens thickness, which can be measured only when the pupil is dilated.

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plane. It is important for phakic IOLs. It should not be less than 2.8 mm to keep the corneal endothelium intact. By entering the settings, we can choose (Ext.) instead of (Int.) to have the depth with the corneal thickness added. IOP: Click the icon and input the IOP to have the modified IOP according to corneal thickness. For the same purpose, the nearby square displays the amount that should be added algebraically to IOP to be modified. KPD: The average value of keratometric power deviation of corneal points located within a circle of a diameter between 0.8 mm and 1.6 mm and centered on the corneal apex. The normal value is less than +0.75. When the value is more than +1.5, it is abnormal indicating an abnormal cornea, such as: post-lasik, post-PRK, keratoconus or after a corneal graft. Angle: The average value of anterior chamber angle. An angle less than 25° should alert us to check the patient for angle closure glaucoma. Pupil diameter: It is important to measure the pupil diameter neither in high illumination (photopic pupil) nor in the dark (scotopic pupil) but in medium illumination (mesopic pupil). Lens thickness: Central thickness of the lens. If the pupil is not dilated enough, the slit light of the camera may not reach the posterior surface of the lens, so the computer cannot measure its thickness.

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Reading Pentacam Topography

30 Step by Step Reading Pentacam Topography

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INTRODUCTION Reading corneal topography is a very important step in taking the right decision before performing the refractive surgery. The decision is changed sometimes completely into other modality of treatment (such as switching into phakic IOLs instead of Lasik because of thin cornea), or we may need changing some parameters within the same modality (such as reducing the treatment zone in 0.1 mm steps to gain some more correction when corneal thickness is critical). On the other hand, reading corneal topography should be regularized and arranged in a logical manner to rule out all possible risk factors, such as critical K-readings, corneal thickness, Q-value and keratoconus indices. I am trying in the following paragraph to simplify the procedure, but still we have to refer to my book “Corneal Topography in Clinical Practice” published by Jaypee Brothers 2009, for more details; because this book is concerned in clinical examples to clarify and explain the ideas.

STEPS OF READING THE TOPOGRAPHY Displaying the Four Refractive Maps This option consist of 4 main maps: the anterior sagittal map, the anterior and posterior elevation maps and the corneal thickness map. These maps give us a thorough overview of the case, but we should then display each map separately as will be discussed later. Performing Main Page Analysis We have to look at cornea front and cornea back parameters, then we have to follow the following rules:

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Reading Pentacam Topography 31 • Quality specification (QS): This icon specifies the quality of the topographic capture and should be displayed “OK”. Otherwise, there is missed information which was virtually produced by the computer and the capture should preferably be repeated. • K-readings: We have to consider the flattest K (usually K1) when treating myopia. Each -1 dpt correction flattens the Ks for 0.75 dpt in average. We should not end up with less than 34 dpt after treating myopia in order to have good quality of vision. Ending with less than 34 dpt means that the anterior surface of the cornea became very flat (oblate) and the patient is suffering from positive spherical aberrations (Fig. 3.1). On the other hand, we have to consider the steepest Ks (usually K2) when treating hyperopia. Each +1 dpt steepens the Ks for 1 dpt in average. We should not end up with more than 48 dpt after treating hyperopia in order to have good quality of vision. Ending with more than 48

Fig. 3.1: Positive spherical aberration. This occurs when the peripheral part of the refracting surface has higher power of refraction than its central part (oblate cornea).

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Fig. 3.2: Negative spherical aberration. This occurs when the peripheral part of the refracting surface has lower power of refraction than its central part (prolate cornea).

dpt means that the anterior surface of the cornea became very steep (prolate) and the patient is suffering from negative spherical aberrations (Fig. 3.2). Fig. 3.3 shows the quality of vision in positive and negative spherical aberrations. • Corneal astigmatism: We have to calculate algebraic sum of astigmatism of the anterior and posterior corneal surfaces, then we should compare with the manifest refraction to exclude causes of incongruence, such as lenticular astigmatism, subtle posterior subcapsular cataract, tear film disturbance,…etc. • Q-value: This value describes the slope of the cornea. It is an average value, we should refer to the topometric map to estimate this value with its many clinical interpretations and applications, some examples will be discussed later in the case studies.

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Fig. 3.3: Quality of vision in spherical aberrations.

• Thinnest location: This category gives us an idea about corneal thickness, but we should refer to the thickness map to have full picture about the case. It is very important to study the relationship between the thinnest location and the pachy apex according to the thickness and according to the location. • Pupil center location: It is important when doing decentration of the ablation profile especially when treating hyperopia. Studying the Maps The Anterior Sagittal Curvature Map The normal cornea: When considering the topography of a normal cornea, we feel the need to remember that there is a wide spectrum of normality. No human cornea demonstrates the kinds of regularity found in the calibration spheres of the topographer: the eye is not molded glassmade. Normal corneal topography can take one of the following:

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34 Step by Step Reading Pentacam Topography Regular astigmatism: Every human being has a certain amount of astigmatism, though minimal. The rule is that the vertical meridian of the cornea is slightly steeper than the horizontal. This is known as “with-the-rule astigmatism”. Fig. 3.4 shows the symmetry between segments “a” and “b”. They are also equal in size. That is the normal pattern, it is known as “Symmetric Bow Tie (SB)”(Fig. 3.5). If the symmetrical bowtie is horizontal, it represents an against-the-rule astigmatism, ninety degrees rotated when compared with “with-the-rule astigmatism” (Fig. 3.6).

Fig. 3.4: Symmetric bow tie. This is the normal corneal pattern of the anterior surface curvature, so called: with-the-rule astigmatism.

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Reading Pentacam Topography 35

Fig. 3.5: Topographic shape patterns which characterize irregularity.

Fig. 3.6: Symmetric bow tie with against-the-rule astigmatism, which is normal but less common.

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36 Step by Step Reading Pentacam Topography

Fig. 3.7: Symmetric bow tie with oblique astigmatism, still normal but less common.

When the bow tie is diagonal, it represents a cornea having an oblique astigmatism (Fig. 3.7). In the normal eye, nasal cornea is flatter than temporal. The nasal side of a healthy corneal map becomes blue more quickly, indicating that the nasal cornea is flatter than temporal. Generally, the two eyes of the same normal subject are very similar, and present a mirror image of each other (Fig. 3.8). This phenomenon is called enantiomorphism. The

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Reading Pentacam Topography 37

Fig. 3.8: Enantiomorphism. The anterior sagittal curvature map of the right eye is a mirror to that of the left eye.

knowledge of this fact is useful to decide whether a cornea is normal or not, by comparing with the map of contralateral eye. P.S. When studying the pattern of corneal curvature, it is important to study the single enlarged map choosing the option of projected circles and the two major axes of curvature, in order to easily compare values in the same eye and between both eyes (Fig. 3.9).

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38 Step by Step Reading Pentacam Topography

Fig. 3.9: Projected circles and the two major axes of curvature on the curvature map. This is very important for quantification of this map.

Topographic Shape Patterns which Characterize Irregularity (Fig. 3.5) Please refer to my book “Corneal Topography in Clinical Practice” published by Jaypee Brothers 2009, to study these patterns carefully. But in general, the most concerning here are the steep K-readings, inferior-superior asymmetry and skewing of the steep axis. Look at the central 4 mm circle: • Calculate I-S Rabinovich ratio, it should be <+2. • Beware of Rowsey’s rule of 2’s. • The curvature power of the lower point in the circle should be no more than 1.5D from the upper point and no more than 2.5D vice versa.

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Reading Pentacam Topography 39 Important figures: • Previously, it was recommended—when taking the decision—that any anterior K readings should not be more than 47D on the front sagittal curvature map. Recently, with the availability of thin flap technology, the power 49D became acceptable. More than 49D is risky regardless of the patient’s refractive error. • Corneal astigmatism on either surface should not be higher than 6D; otherwise it is a risk factor. • Against the rule astigmatism is considered suspicious.

The Elevation Maps We look at the values within the central 4 mm circle using the best fit sphere float reference body (BFS). That is because the following normative data depend on this particular kind of reference bodies: 1. The elevation values on the front surface map should not exceed +12 µ. Values between +13 µ and +15 µ are suspected, and any value > +15 µ is considered a risk factor. 2. The elevation values on the back surface map should not exceed +17 µ. Values between +18 µ and +20 µ are suspected, and any value >+20 µ is considered a risk factor. 3. The difference between the back and front surfaces (back-front) should not exceed +5 µ at the same point. For example: if the back is +12 µ and the front is +4 µ at the same point, it is suspicious although both values are within the normal limits. 4. If there is any isolated island on either front or back surfaces, it would be suspected, even with values within the normal limits (Fig. 3.10).

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40 Step by Step Reading Pentacam Topography

Fig. 3.10: Nearly isolated island on the posterior surface of the cornea. We should pay attention to this sign and quantify it carefully to exclude any risk factor.

P.S. 1: Be careful when any value of the central 4 mm of the elevation maps is more than +15 µ for the anterior surface, and more than +20 µ for the posterior surface. P.S. 2: Be careful when the “back-front” difference is more than +5 µ at the same point. P.S. 3: Be careful when there is an isolated island on either surface. Corneal Thickness Map 1. Look at the shape of the thickness map, it gives an idea about the shape of the cornea (Fig. 3.11).

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Reading Pentacam Topography 41

Fig. 3.11: The thinnest location is severely displaced giving the thickness map the shape of a cone.

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42 Step by Step Reading Pentacam Topography 2. The relation between the apex of the cornea and the center of the pupil: It is important in the issue of “decentration” or “offset pupil”. 3. The relation between the apex of the cornea and the thinnest location: This relationship could be according to thickness or to coordinates. • The relationship according to thickness: Let us look at Fig. 2.13 to compare the thickness at the apex with the thickness at the thinnest location. The difference should be no more than 10 µ and not increasing with follow up. • The relationship according to coordinates (Fig. 3.12): When the value exceeds -500 µ, it is a risk factor, especially when the difference is increasing with follow up at one to two years intervals. When this value exceeds -1000 µ, it is an important sign of an advanced keratoconus (see Fig. 2.13). 4. Look for the thickness on the 4 mm circle: There should be no more than 30 µ difference between the superior and inferior points (we will call this from now as superior-inferior difference).

Fig. 3.12: The relationship between pachy apex and thinnest location coordinates. The ‘y’ coordinate is more important than ‘X’; because the thinnest location is generally displaced vertically in the development of keratoconus or keratoectasia.

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Reading Pentacam Topography 43

Fig. 3.13: The topometric map. Q-value measured and displayed in the four main sectors of the cornea.

5. Compare the thinnest location between the examined cornea and its fellow, the difference should be no more than 30 microns. Topometric Map Fig. 3.13 illustrates Q-value in four sectors of the cornea: nasal, temporal, upper and lower sectors. It also shows the average vertical and horizontal values. Fig. 3.14 shows Q-values in the four sectors of the cornea within circles centered on the apex of the cornea with 6, 7, 8, and 9 mm diameters (or in angles of 20 °, 25°, 30° and 35° respectively). The most important values are the vertical in general and the inferior in particular, as in Fig. 3.15. The normal

Fig. 3.14: Q-values according to different concentric rings and in the four main sectors.

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44 Step by Step Reading Pentacam Topography

Fig. 3.15: The important Q-values in the topometric map. The average vertical in general and the inferior in particular.

value is < -0.5 (as an absolute value). It is border line when it falls between -0.5 and -0.55. If the value is > -0.55 (as an absolute value), we should hesitate a lot before proceeding to the standard Lasik treatment. The most important sector is the 6 mm or 20° sector. Keratoconus Indices Page • Diagram of the relation between corneal thickness and location (Fig. 3.16). • Diagram of the relation between thickness increment and location (Fig. 3.17). It is important for the red curve to be within the normal range and the course of the red curve to be parallel to the normal range. In certain cases the red curve deviates after few millimeters (Fig. 3.18). If the red curve deviates at the 6 mm circle or after, it is normal, otherwise it is a risk factor because the quick downward deviation means that the corneal center is relatively thinned in relation to the periphery, which proved to be risky either with Lasik, or to some extent with PRK, whether the patient is hyperopic or myopic.

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Reading Pentacam Topography 45

Fig. 3.16: Mean corneal thickness values on rings concentrically to the thinnest location. The black dotted lines are the normal range and average in normative data. The red line is for the measured cornea.

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46 Step by Step Reading Pentacam Topography

Fig. 3.17: Progression of corneal thickness. The black dotted lines are the normal range and average in normative data. The red line is for the measured cornea.

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Reading Pentacam Topography 47

Fig. 3.18: The progression of corneal thickness of a keratoconic cornea. The measured red line is out of the normal range, and it deviates before 6 mm indicating a rapidly increasing thickness from the thinnest location towards periphery. Table 3.1: The normal, suspected and abnormal findings in corneal topography Normal value(s)

Suspected value(s)

Abnormal value(s)

Quality specification (QS)

white

yellow

red

K-readings:

look at flat K for myopic treatment, look at steep K for hyperopic treatment

>48

Corneal astigmatism

compare with manifest astigmatism

>6

Average Q-value

0 to -1

0,-1

Topometric map (vertical and inferior Q-values)

-0.5 to -0.55

>-0.55

< 470

Thinnest location Thickness

> 500

470 – 500

Difference in thickness between patchy apex and thinnest location

<5µ

5 – 10 µ

>10 µ

Coordinates

< 500 µ

500 – 1000 µ

>1000 µ

Pupil center coordinates

important for treating hyperopia and >3D astigmatism

Contd...

48 Step by Step Reading Pentacam Topography Contd...

KPD

Normal value(s)

Suspected value(s)

Abnormal value(s)

<+0.75

+0.75 to +1.5

>+1.5

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Anterior curvature map Maximal K

important when treating hyperopia

Pattern

refer to topographical patterns

I-S Rabinovich ratio

>+2

Skewed Steepest Radial Axis Index (SRAX)

>22°

Superior-inferior difference on the 4 mm circle

>1.5D when the inferior is steeper >2.5 when the superior is steeper

Elevation maps (within the 4 mm central circle) Anterior

≤12 µ

13 - 15 µ

>15 µ

Posterior

≤17 µ

18 – 20 µ

>20 µ

Anterior-posterior difference

<5 µ

>5 µ

Isolated island (or tongue like extension)

might be an indicator for FFKC or subclinical keratoconus

Corneal thickness map Shape

cone like

Superior-inferior difference

<30 µ

>30 µ

Thinnest location difference between both eyes

<30 µ

>30 µ

Keratoconus diagram Shape and location of the curve

- out of normative range - deviation before the 6 mm circle

Average

1

1.1 – 1.2

> 1.2

Indices of irregularity

white

yellow

red

451 – 480 µm

> -14.00

MRSE

> -12.00 to -14.00

< 450 µm

CT

240 – 259 µm 18 – 21 yrs

< 240 µm

RSB

Inferior steepening/ skewed radial axis

3

Age

Abnormal topography

4

Points

Topography

Pattern

> -10.00 to -12.00

481 – 510 µm

22 – 25 yrs

260 – 279 µm

2

> -8.00 to -10.00

26 – 29 yrs

280 – 299 µm

Asymmetrical bow tie

1

-8.00 or less

≥ 510 µm

≥ 30 yrs

≥ 300 µm

Normal/ symmetrical bow tie

0

Table 3.2: The ectasia risk score system for identifying eyes at high risk of developing ectasia after Lasik

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Reading Pentacam Topography 49

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Table 3.3: Grading the risk of ectasia according to the scoring system shown in Table 3.2 Total risk score

Relative risk

Recommendations

0-2

Low

Proceed with Lasik or Surface

3

Moderate

Proceed with caution, special informed consent, safety of surface ablation unknown

4

High

Do not perform any

• Progression index: The average (colored with red) should be no more than 1. Table 3.1 summarizes all the above normal, suspected and abnormal findings in the topography

SCORING THE CASE After careful study of the topography, it is very important to score the case in order to exclude the risky cases and to decide correctly which modality of treatment is the best. Scoring each case must depend on the scoring system shown in Tables 3.2 and 3.3. This scoring system depends not only on the topographical pattern, but also on the proposed residual stromal bed (RSB), patient’s age and preoperative corneal thickness (CT) in the thinnest location.

Examining the Patient 51

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chapter

4

Examining the Patient

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52 Step by Step Reading Pentacam Topography In the next chapters the case study will be presented very simply without mentioning all the data of the patient. That is because this book concentrates on the topography readings, but in our practice we should take care of every tiny data we obtain from the patient in order to give the patient his best chance and avoid any undesired complications, which might be due to our ignorance. For this reason, I am presenting in Table 4.1 a suggested evaluation sheet. It must be the basic but not the full for evaluation, i.e. you may add on what you feel is necessary. The sheet includes demographic information, ocular and systemic history and full ocular examination as follows.

OCULAR HISTORY A patient’s ocular history helps to identify any potential postoperative problems that may arise and allows for adjustment, postponement, or cancellation of the procedure in question if necessary. We have to put in mind that when the patient is mono-ocular, he is not a candidate for any refractive surgery. Previous Trauma • Identification of any trauma in the cornea or other component of the visual axis that may alter corneal wound healing or potential visual outcome. • Determination of condition, location, duration, and method of treatment (if possible).

Examining the Patient 53 Table 4.1: The examination sheet Name

Age

Sex

Occupation

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Address Tel

Mob

e-mail Ocular History Dryness

Chronic tearing

Chronic allergy

Recurrent conjunctivitis

Blepharitis

Contact lens use

Previous ocular trauma Previous ocular surgery Any other ocular disease Systemic History Diabetes Blood pressure Known medication allergy Known allergy to food, metals or others Collagen systemic diseases Use of anti-coagulants or steroids

or immunosuppressant

or isotretinoin

or sumatriptan

Pregnancy

Lactation Contd...

54 Step by Step Reading Pentacam Topography Refraction

OD

UCVA

Distance

OS

Near Sph Cyl

Axis BSCVA Sph

Cyl Axis BSCVA

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Old Auto Manifest Cycloplegic Final refraction Contrast sensitivity Examination OD

OS

Photopic Pupillometry

Mesopic Scotopic Lid closure Mebomian

Slit lamp

Cornea

H.S. H.Z. EBMD RCEs

BUT Schirmer Fundus IOP WTW (white to white) ACD (anterior chamber depth) Other Contd...

Examining the Patient 55 Intraoperative data OD

OS

Refractive modality choice* Flap thickness

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Blade If Lasik

Hinge Contact lens Complications**

Remarks Visits*** 1st visit (next day): 2nd visit (5-7 days): 2nd visit (1 month): 3rd visit (3 month): 4th visit (6 month): * Refractive treatment modalities can be coded as follows: (1) Lasik, (2) LASEK, (3) Epi-Lasik, (4) PRK, (5) PTK, (6) Topography guided, (7) Q-guided, (8) Wavefront guided, (9) Phakic IOLs, (10) Rings, (11) Cross-linking **Intraoperative complications of Lasik can be coded as follows: (1) Perforated cornea, (2) Short flap, (3) Thin flap, (4) Irregular flap, (5) Button hole, (6) Free flap ***Post-Lasik complications can be coded as follows: (1) Post-Lasik pain, (2) Epithelial defects, (3) Infection, (4) Lasik Interface Keratitis or Diffuse Lamellar Keratitis (LIK or DLK): (a) Grade I, (b) Grade II, (c) Grade III, (d) Grade IV, (5) Lasik flap striae: (a) Micro, (b) Macro, (6) Dislodged flap, (7) Interface debris, (8) Epithelial ingrowth: (a) Grade I, (b) Grade II, (c) Grade III, (9) Refractive outcome errors, (10) Irregular astigmatism, (11) Central island, (12) Decentered ablation

56 Step by Step Reading Pentacam Topography

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Previous Ocular Surgery The identification and evaluation of a patient’s previous ocular surgery status is critical to the success of subsequent refractive surgery. Several situations must be considered. • Artificial alteration of the refractive index secondary to faulty assumptions or calculations based on the IOL, scleral buckle, or other retinal procedures. • Increased risk of retinal complications after surgical intervention. • Difficulty obtaining proper suction and resultant flap complications.

FAMILY HISTORY A thorough family history may elucidate potential contraindications or concerns with refractive surgery and long-term visual prognosis. A positive history of any of the following warrants further careful ocular evaluation prior to surgical intervention: • Glaucoma • Past history of high intraocular pressure after topical steroid application • Corneal dystrophy or degeneration • Untreated retinal pathology (e.g. retinal holes, tears, or detachment).

MEDICAL HISTORY The preoperative systemic history should include questions related to several diseases and conditions, including pregnancy and lactation that may affect a surgical candidate’s suitability for surgery. The medical history should also include the followings:

Examining the Patient 57

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Ocular Diseases Pre-surgical assessment of refractive surgery candidates may reveal a history of several ocular diseases that precludes surgery or poses increased risk of intraoperative or postoperative complications such as: • Corneal dystrophy • Cataracts • Keratoconus • Iritis (must rule out preoperatively if visually symptomatic) • Herpetic infection • Corneal bacterial infection • Retinal disease • Significant lagophthalmos. Vascular Diseases Any vascular disease that compromises a person’s ocular performance or health is a contraindication for refractive surgery. Some are listed here: • Malignant hypertension • The controlled diabetes mellitus is a relative contraindication, otherwise it is contraindicated. • Clotting or other blood disorders Collagen Vascular Diseases The severity of collagen vascular disease determines whether it needs to be evaluated before refractive surgery. Most patients with collagen vascular disease have very mild symptoms and use very little medication. If a patient rheumatoid-factor is positive and has severe collagen

58 Step by Step Reading Pentacam Topography

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vascular disease, refractive procedures are contraindicated. Examples of collagen vascular disease are listed here: • Systemic lupus erythematous • Rheumatoid arthritis • Scleroderma • Fibromyalgia. Inflammatory Disorders Inflammatory disorders, such as those listed below, should be controlled and stable prior to refractive surgery: • Multiple sclerosis • Hyperthyroidism • Crohn’s disease. Infectious Diseases An active infectious disease is generally a contraindication for refractive surgery: • Viral • Bacterial • Fungal.

MEDICATIONS AND ALLERGIES Certain drug therapies may be contraindicated or alter postoperative outcome in patients undergoing refractive surgery. Allergies must also be considered. We should pay attention to such drugs: • Isotretinoin (Accutane; Hoffmann-La Roche Inc., Nutley, N]) [contraindicated in potential photorefractive keratectomy (PRK) patients because of increased risk of PRK haze]

Examining the Patient 59

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• Sumatriptin (increased risk for epithelial defects after refractive surgery) • Antimetabolites and antirheumatic drugs (prolong or retard wound healing after refractive surgery) • Topical or systemic allergies to metals, latex, or laser gases.

PRIOR CORRECTIVE LENSES The patient’s refractive history provides data that enables the surgeon to utilize the surgical correction that will provide the best vision over the patient’s lifetime. • Frequency of previous visual exams • Refractive stability over the last few years • Frequency of and reason for changes in spectacle or contact lens prescription • Acceptance and adaptability of various near-correction options • Problems wearing eyeglasses or contact lenses (e.g. discomfort and intolerance) • Frequency and duration of contact lens wear (typical schedule) • Contact lens type (e.g. rigid gas permeable, hydrogel, polymethyl methacrylate) • Acceptance of monovision or bifocal contact lens correction. Table 4.1 summarizes the above data, but again you may add and you may refer to those books concerned in ocular examination for more details.

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Case Study 61

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chapter

5

Case Study

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62 Step by Step Reading Pentacam Topography In this chapter, we will apply all the previously mentioned data on many clinical cases. Each case will be studied according to the following strategy: 1. The Qualifying step: in this step, we have to look for abnormal findings and risk factors if any. 2. The Quantifying step: in this step, patient’s data will be studied according to the topographical features. 3. The Scoring step: apply the “Ectasia Scoring System” to score the case for degree of risk, which helps taking the right decision.

CASE 1: MYOPIC ASTIGMATISM A 21-year-old male came with stable refractive error. His manifest refraction (MR) was: Eye

SPH

CYL

AXIS

OD OS

- 8.00 - 7.50

- 1.75 - 2.00

180 175

Fig. 5.1A shows his right eye corneal topography (4 refractive maps). The Qualifying Step 1. In a general look, the sagittal curvature map has a symmetrical bow tie pattern oriented as with-the-rule astigmatism. The elevation maps seem to be symmetric with no isolated islands. 2. Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (43.3, 45.6) and corneal astigmatism (the algebraic sum of the anterior and posterior astigmatism)

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Case Study 63 is also normal (-1.6 <-6). Q-value of the cornea front is normal at the 6 mm circle (-0.20). Corneal thickness at the thinnest location is normal (535) and has normal coordinates with the pachy apex. There is also no difference in thickness between pachy apex and thinnest location. 3. Studying each map: • Corneal thickness map (Fig. 5.1B): The shape of this map is the normal shape, i.e. no displacement of the thinnest location (please compare with Fig. 5.1C to understand this point: the white arrow points to the thinnest location). The difference between the lower and upper points of the central 4 mm circle is <30 µ (Fig. 5.1B red circles). • The sagittal curvature front (Fig. 5.1D): Symmetrical bow tie, no skew or angulation between the lower and upper axes of the pattern, the difference between the upper and lower points of the 4 mm circle is less than 1.5 dpt (white arrows). • The elevation front map—Based on the BFS as a reference body—presents regular shape with no isolated island or tongue-like extension, normal values within the central 4 mm circle (Fig. 5.1E). • The elevation back map—Based on the BFS as a reference body- presents regular shape with no isolated island or tongue-like extension, normal values within the central 4 mm circle, but there are some points where the difference between anterior and posterior values is >+5 µ (Fig. 5.1F). • The Topometric map (Fig. 5.1G red arrows): Both the average vertical value and the lower value are normal (<-0.55).

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Fig. 5.1A: Main page in Pentacam display. It consists of numeric values on the left side, and the four refractive maps on the right side. These four maps are the main important maps for qualifying and quantifying any case. This case is an ordinary case for Lasik treatment.

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Case Study 65

Fig. 5.1B: The corneal thickness map. There are three important things to look at: the general shape of the map, the position of the thinnest location (white arrow) and the inferior and superior values on the 4 mm circle (red circles). This map is within normal limits.

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Fig. 5.1C: The corneal thickness map in an abnormal cornea. Notice the big displacement of the thinnest location (white arrow) and the coniclike shape of the map.

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Case Study 67

Fig. 5.1D: The sagittal (axial) curvature map of the anterior corneal surface. This map should be studied with projecting circles and major astigmatic axes. This is important for qualifying and quantifying any case.

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Fig. 5.1E: The elevation map of the anterior corneal surface. There are two important things to look at: regularity and values within the central 4 mm. In this case the shape is regular and symmetric and the values are within normal limits.

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Case Study 69

Fig. 5.1F: The elevation map of the posterior corneal surface. There are two important things to look at: regularity and values within the central 4 mm. In this case the shape is regular and symmetric but there are some abnormal values (white arrow). Although these values are abnormal, they are still accepted with Sphere Float Best Fit Body because of the regular and symmetric shape of the map.

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Fig. 5.1G: The Topometric map. It represents corneal slope as Q-value. This value represents the Asphericity of each corneal surface at multiple zones, and as vertical and horizontal averages, and in the four meridians. It is important to look at two main values: the average vertical value and the inferior value in particular (red arrows). In this case these values are within normal limits. We should also notice whether there is more than 0.3 between the vertical and the horizontal averages, which is important in topography guided treatment.

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Case Study 71

Fig. 5.1H: The keratoconus indices page. The red curves are within normal ranges with no rapid deviation. The average is 0.8, which is normal.

72 Step by Step Reading Pentacam Topography

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• The keratoconus indices page (Fig. 5.1H): the curve lines are within the normal range, no deviation before the 6 mm circle. The average is normal (0.8<1.1). The indices of irregularity are displayed with white, which is normal. The Quantifying Step If we want to correct the refractive error of the right eye of the patient in the given example, we have to look at three important figures: the K-readings, the thickness at the thinnest location and the Q-value. 1. K-readings: Because the patient is myopic, we have to consider the flattest K, here is 43.3 dpt. The spherical refractive error is -8.00 dpt, this means that after correction, the flat K will be reduced roughly by: -8.00 × 0.75 = -6 dpt, therefore, the post flat K will be = 43.3 – 6 = 37.3 dpt, which is normal (> 34D). 2. Thickness: Correcting each -1 dpt causes ablation of 12-16 µ depending on the diameter of the Optical Zone (OZ), for example 13.4 µ for 6.0 mm OZ and 15.7 µ for 6.5mm OZ. This means ablation of 7(not 8) × 15.7 µ = 110 µ (this is according to Wellington Clinic Nomogram used with Allegretto) to correct the -8 dpt. We have to follow 2 rules in this field: the first rule, we must not ablate more than 20% of the original corneal thickness, the second rule is, we must keep at least 55% of the original corneal thickness as a residual stromal bed (RSB), putting in mind that the RSB still is >250 µ. So, in our case, we must not ablate more than 20% × 535 = 107 µ, and must keep 55% × 535 = 294 µ. If you add the thickness of the thin flap (100 µ), you will have the

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Case Study 73 allowed ablation depth according to the second rule 294 + 100 = 394, 535 – 394 = 141 µ. We always take the smaller calculated value to be on the safe side, so we should consider the 107 µ. In this case we can correct all the refractive errors. 3. Q-value: correcting ≥ -6 dpt leads to positive Q-value, which means oblate cornea. In such cases, it is recommended to use the Q-guided profile in order to conserve the normal Q-value of the patient, otherwise we will end up with spherical aberrations. The Scoring Step Scoring the right eye: 1. Corneal topography is normal with symmetrical bow tie pattern, giving the score 0. 2. RSB: This depends in our case on the thickness of the flap. If we chose the 100 µ flap, the RSB will be 535-107100 = 328 µ, giving the score 0. 3. Age: The patient is 21-year old, giving the score 3. 4. CT is 535 giving the score 0. 5. MRSE is about -9, giving the score 1. The final scoring is 1, therefore, the relative risk is low and we can proceed with Lasik.

74 Step by Step Reading Pentacam Topography

CASE 2: MIXED ASTIGMATISM

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A 21-year-old female came with stable refractive error. Her MR was: Eye OD

SPH +0.5

CYL -2.5

AXIS 180

OS

+0.5

-2

180

Fig. 5-2A shows her right eye corneal topography (4 refractive maps). The Qualifying Step 1. In a general look, the sagittal curvature map has a symmetrical bow tie pattern oriented as with-the-rule astigmatism. The elevation maps—by BFS reference body—seem to be symmetric with no isolated islands. 2. Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (45.5, 47.9) and corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-1.6 <-6). Q-value at the 6 mm circle of the cornea front is normal (-0.34). Corneal thickness at the thinnest location is normal (524) and has normal coordinates with pachy apex. There is also no significant difference in thickness between pachy apex and thinnest location (<5 µ). 3. Studying each map: • Corneal thickness map (Fig. 5.2B): the shape of this map is normal shape, i.e. no significant displacement of the thinnest location (< -500 µ on ‘y’ axis). But the

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Case Study 75 difference between the lower and upper points of the central 4 mm circle is >30 µ (36 µ, which is not significant) (Fig. 5.2B red circles). • The sagittal curvature front map (Fig. 5.2C): Symmetrical bow tie, no skew or angulation between the lower and upper axes of the pattern, the difference between the upper and lower points of the 4 mm circle is less than 1.5 dpt. • The elevation BFS front map (Fig. 5.2D): Regular shape with no isolated island or tongue-like extension, normal values within the central 4 mm circle. • The elevation BFS back map (Fig. 5.2E): Regular shape with no isolated island or tongue-like extension. There are some suspected values within the central 4 mm circle (arrows) and there are some points where the difference between anterior and posterior values is >+5 µ. • The Topometric map (Fig. 5.2F red arrows): Both the average vertical value and the lower value are normal (<-0.55). • The keratoconus indices page (Fig. 5.2G): The curve lines are within the normal range, no deviation before the 6 mm circle. The average is normal (1). All irregularity indices are displayed in white except one, which is the corneal aberration coefficient factor (ABR), and there is no risk in treating the cornea with ABR less than 2.5. The mentioned abnormal findings are not significant since all other parameters are normal.

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76 Step by Step Reading Pentacam Topography

Fig. 5.2A: The four refractive maps. Quality of the capture (QS) is OK. Symmetric bow tie pattern oriented as with-the-rule astigmatism. The elevation maps seem to be symmetric with no isolated islands. All other features are normal, e.g. K readings, corneal astigmatism, Q-value,...etc.

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Case Study 77

Fig. 5.2B: The corneal thickness map. Normal shape with no significant displacement of the thinnest location (white arrows), but the difference between the upper and lower values on the 4 mm circle is >30 µ (red circles).

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78 Step by Step Reading Pentacam Topography

Fig. 5.2C: The sagittal curvature front map. Symmetric bow tie oriented as with the rule astigmatism. Normal superior-inferior values on the 4 mm circle.

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Case Study 79

Fig. 5.2D: The elevation front map. Regular shape with normal central values.

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80 Step by Step Reading Pentacam Topography

Fig. 5.2E: The elevation back map. Regular shape with some suspicious values (arrows).

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Case Study 81

Fig. 5.2F: The Topometric map. Normal values (arrows).

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82 Step by Step Reading Pentacam Topography

Fig. 5.2G: The keratoconus indices page. The curve lines are within the normal range. The average is normal (1). All irregularity indices are displayed in white except one indicating almost regular cornea.

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Case Study 83

Fig. 5.2H: The ablation profile. It is peripheral and on axis 180° to steepen this axis and to correct the +2.5 dpt astigmatism in this case.

84 Step by Step Reading Pentacam Topography

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The Quantifying Step To correct the refractive error of the right eye, we have to look at four important figures: the K-readings, the thickness at the thinnest location, Q-value and pupil center coordinates because there is a plus component, i.e. mixed astigmatism. 1. K-readings: The patient has mixed astigmatism. In laser treatment profile, the treatment is designed to be +2.5 cylindrical diopters and -2 spherical diopters. The periphery of the cornea is ablated on axis 180° in order to steepen this axis and correct the +2.5 dpt (Fig. 5.2H). This increases the flat K-readings on axis 180° by 2.5 × 1 = 2.5 dpt, therefore, the flat K will be increased up to 48 dpt. As we see, the cylindrical correction eliminates the difference between the two major axes of corneal astigmatism. Correcting the -2 dpt sphere will reduce the overall K-readings in the OZ by 2 × 0.75 = 1.5 dpt to become finally 48 – 1.5 = 46.5, which is still within the accepted range. 2. Thickness: Correcting plus astigmatism ablates the periphery, while correcting minus sphere ablates the center of the cornea. In our case, the central ablation depth is almost 2 × 15.7 = 31.4 µ. Considering the two rules of thickness limits, we are still on the safe side even when creating thick flap (160 µ) as follows: 524 – 160 – 31.4 = 332.6 µ, which is the residual stromal bed (RSB) thickness. 3. Q-value and pupil center coordinates: There are two reasons for choosing the topography-guided treatment modality in general: first, a difference of >0.3 between vertical and horizontal Q-values, second, large angle

Case Study 85

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kappa. If we look at Fig. 5.2F, we find that there is no significant difference between vertical and horizontal Q-values. Also, the pupil center coordinates (and therefore angle kappa) are not significant. In this case we can use the standard treatment. The Scoring Step 1. Corneal topography is normal with symmetrical bow tie pattern, giving the score 0. 2. RSB: in our case, even if we choose the thick flap (160 µ) the RSB will be >300 µ, giving the score 0. 3. Age: The patient is 21-year old, giving the score 3. 4. CT is 524 giving the score 0. 5. MRSE is less than -8, giving the score 0. The final score is almost 0 to 1, therefore, the relative risk is low and we can proceed with Lasik.

86 Step by Step Reading Pentacam Topography

CASE 3: HYPEROPIA

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A 50-year-old female came with stable refractive error. Her MR was: Eye OD

SPH +5.5

CYL 0

AXIS 0

OS

+5.5

0

0

Fig. 5.3A shows her right eye corneal topography (4 refractive maps). The Qualifying Step 1. In a general look, the sagittal curvature map has a slightly irregular pattern. There is an obvious tonguelike pattern on both elevation BFS maps (white arrows). The thickness map shows very clear pattern of thinnest location displacement (red arrows). 2. Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (45.1, 45.4) and corneal astigmatism is almost insignificant. Q-value at the 6 mm circle of the cornea front is normal (-0.31). Corneal thickness at the thinnest location is below 500 µ (496 µ), and has abnormal coordinates with pachy apex especially on “y” axis (>-1000 µ). There is no difference in thickness between pachy apex and thinnest location. 3. Studying each map: • Corneal thickness map (Fig. 5.3B): The shape of this map is abnormal; there is a significant displacement of the thinnest location, which gives the map the

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Case Study 87 shape of a cone. The difference between the lower and upper points of the central 4 mm circle is 31 µ (red circles). • The sagittal curvature front (Fig. 5.3C): Although this map is slightly irregular, the two major axes of cornea front astigmatism are perpendicular and show no skew or angulation between the lower and upper axes of the pattern. The difference between the upper and lower points (the superior-inferior difference) of the 4 mm circle is less than 1.5 dpt (white arrows). • The elevation front map (Fig. 5.3D): There is an irregular shape with tongue-like extension, but still the values are normal within the central 4 mm circle. • The elevation back map (Fig. 5.3E): It is more irregular with tongue-like extension. The central 4 mm circle values are abnormal giving the impression of cone like shape (white arrow). There are also some points where the difference between anterior and posterior values is >+5 µ. P.S. In case of any irregularity or suspicious values on elevation maps with the BFS, it is recommended to see the elevation maps with Toric Ellipsoid float reference body; when the irregularities are due to corneal astigmatism, they will vanish, otherwise they stay when they are due to real corneal surface irregularity. The toric ellipsoid option eliminates the effect of corneal astigmatic slope on the elevation maps. This is important especially for the back surface where the subclinical keratoconus begins.

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88 Step by Step Reading Pentacam Topography

Fig. 5.3A: The four refractive maps. Slightly irregular anterior sagittal curvature map. Tongue-like pattern on both elevation maps (white arrows). Significant displacement of the thinnest location on the corneal thickness map (red arrows). Corneal thickness at the thinnest location is below 500 µ (496 µ), and has abnormal coordinates with pachy apex especially on “y” axis (>-1000 µ).

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Case Study 89

Fig. 5.3B: The corneal thickness map. Abnormal shape because of the significant thinnest location displacement. No important superiorinferior difference (red circles).

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90 Step by Step Reading Pentacam Topography

Fig. 5.3C: The sagittal curvature front map. No skew of major axes. Normal superior-inferior values.

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Case Study 91

Fig. 5.3D: The elevation front map. Irregular shape with tongue-like extension, but with normal values.

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92 Step by Step Reading Pentacam Topography

Fig. 5.3E: The elevation back map. Irregular shape with tongue-like extension and abnormal values giving the impression of cone-like shape (arrow).

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Case Study 93

Fig. 5.3F: The Topometric map. Normal values (arrows).

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94 Step by Step Reading Pentacam Topography

Fig. 5.3G: The keratoconus indices page. The curve lines are within the normal range, but they deviate before the 6 mm circle (red arrows). The average is abnormal (1.2) and the ABR is also abnormal.

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Case Study 95 • The Topometric map (Fig. 5.3F red arrows): Both the average vertical value and the lower value are normal (<-0.55). • The keratoconus indices page (Fig. 5.3G): Although the curve lines are within the normal range, they deviate before the 6 mm circle (red arrows). The average is abnormal (1.2). One of the irregularity indices is displayed in red because of the slight irregularity of the anterior corneal surface. It is the corneal aberration coefficient factor (ABR), but there is no risk in treating the cornea with ABR less than 2.5. The Quantifying Step In the given example, to correct the refractive error of the right eye, we have to look at four important figures: the Kreadings, the thickness at the thinnest location, Q-value and pupil center coordinates. 1. K-readings: Because the patient is hyperopic, we have to consider the steepest K, here is 45.4 dpt. The spherical refractive error is +5.5 dpt, this means after correction the steep K will increase by: +5.5 × 1 = 5.5 dpt, therefore the postoperative steep K will be = 45.4 + 5.5 = 50.9 dpt, which is very abnormal. We have to remember always when treating hyperopia that the steep K must not end up with more than 48 dpt. So, we can correct in this case only about +2.5 dpt (in case of good corneal characteristics). 2. Thickness: The hyperopic laser profile ablates the periphery of the cornea in order to steepen the central part depending on corneal biomechanics. Therefore, the peripheral thickness is the concerned part here.

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96 Step by Step Reading Pentacam Topography 3. Q-value and pupil center coordinates: Correcting the +6 dpt leads to very negative Q-value, which means very prolate cornea. On the other hand, we have to consider angle kappa when treating hyperopia (this fully explained in my previous book). For these two important reasons, we should use the customized topography-guided ablation profile to conserve a normal Q-value and to compensate for angle kappa. The Scoring Step and Discussion Although our case here falls within score 2, which means low relative risk, I would not proceed with the operation. There are some reasons for that: 1. The K readings allow for +2.5 dpt correction only, which is not accepted by the patient. 2. The thickness map shows cone-like appearance and more than 30 µ difference between the two concerning points. 3. The thinnest location coordinates show abnormal displacement. 4. The posterior elevation map shows very high elevations. 5. The average of the progression index is 1.2, which is usually abnormal. 6. The shape of the red curves is suspicious. All these findings are –at least in my opinion—sufficient to postpone the operation; because of the very high risk of cone-like formation postoperatively. We can think about other treatment modalities such as phakic IOLs.

Case Study 97

CASE 4: ANISOMETROPIA

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A 34-year-old female came with stable refractive error. Her MR was: Eye OD

SPH -6.00

CYL -1.75

AXIS 45

OS

-2.00

-0.50

150

We will study the left eye first for educational purposes. Fig. 5.4A shows her left eye corneal topography (4 refractive maps). The Qualifying Step 1. In a general look, the sagittal curvature front map has a slightly irregular pattern oriented as with-the-rule astigmatism. The elevation maps show irregular shapes more obvious on the posterior map. There is nothing suspicious in the thickness map in general. 2. Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (42.1, 42.9) and the corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-0.5 <-6). Q-value at the 6 mm circle of the cornea front is normal (-0.31). Corneal thickness at the thinnest location is normal (568) and has normal coordinates with pachy apex. There is also no significant difference in thickness between pachy apex and thinnest location. 3. Studying each map: • Corneal thickness map (Fig. 5.4B): The shape of this map is normal with slight displacement of the

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98 Step by Step Reading Pentacam Topography thinnest location. The difference between the lower and upper points of the central 4 mm circle (superiorinferior difference) is 34 µ (red circles), which is slightly abnormal but not suspicious. • The sagittal curvature front map (Fig. 5.4C): Asymmetrical bow tie/inferior steep (AB/IS). There is skew (angulation) between the lower and upper axes of the pattern, but this skew is about 10°, which is within normal limits. The difference between the upper and lower points of the 4 mm circle is less than 1.5 dpt (Fig. 5.4D red circles). • The elevation front map (Fig. 5.4E): Irregular shape with tongue like extension, but the values within the central 4 mm circle are still within the normal range. • The elevation back map (Fig. 5.4F): Irregular shape with abnormal values within the central 4 mm circle. There are also some points where the difference between anterior and posterior values is >+5 µ. P.S. In case of any irregularity or suspicious values on elevation maps with the BFS, it is recommended to see the elevation maps with Toric Ellipsoid float reference body; when the irregularities are due to corneal astigmatism, they will vanish, otherwise they stay when they are due to real corneal surface irregularity. The toric ellipsoid option eliminates the effect of corneal astigmatic slope on the elevation maps. This is important especially for the back surface where the subclinical keratoconus begins. • The Topometric map (Fig. 5.4G): The average vertical value is normal but the lower value is not (red circle).

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Case Study 99 • The keratoconus indices page (Fig. 5.4H): The curve lines are within the normal range, no deviation before the 6 mm circle. The average is normal (0.9). One of the irregularity indices is displayed in red because of the slight irregularity of the anterior corneal surface. It is the corneal aberration coefficient factor (ABR), but there is no risk in treating the cornea with ABR less than 2.5. Now before moving to the Quantifying step, we should ask ourselves the following questions: 1. What is the reason behind anisometropia that the patient has? 2. What about the other eye? Let us look at the right eye topography (Fig. 5.4I). The Qualifying Step 1. In a general look, the sagittal curvature map has a clear asymmetrical pattern oriented as with-the-rule astigmatism. The posterior elevation map shows suspicious numbers. There is nothing suspicious in the thickness map in general. 2. Main page analysis reveals that the quality of the capture (QS) is not OK and on repeating the capture the same QS appears, which means a problem in the cornea itself. The K-readings in the central 3 mm are normal (43.6, 45.7) and the corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-1.75 <-6). Q-value at the 6mm circle of the cornea front is slightly high (-0.62). Corneal thickness at the thinnest location is normal (542) and has normal

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100 Step by Step Reading Pentacam Topography coordinates with pachy apex. There is also no significant difference in thickness between pachy apex and thinnest location. 3. Studying each map: • Corneal thickness map (Fig. 5.4J): The shape of this map is normal. The difference between the lower and upper points of the central 4 mm circle is <30 µ (red circles). • The sagittal curvature front map (Fig. 5.4K): Asymmetrical bow tie/inferior steep with angulation (AB/SRAX): as you see in this picture, the pattern is inferior steep and the difference between the upper and lower points of the 4 mm circle is 4.5, which is more than 1.5 dpt (see also Fig. 5.5L white circles), and the angle between axes of the segments according to SRAX low is more than 22°. • The elevation front map (Fig. 5.4M): Shows irregular shape with tongue-like extension, but the values within the central 4 mm circle are still within the normal range. • The elevation back map (Fig. 5.4N): Shows irregular shape with abnormal values within the central 4 mm circle. There are also some points where the difference between anterior and posterior values is >+5 µ. • The Topometric map (Fig. 5.4O red circles): As you see, both the average vertical value and the inferior value are abnormal (the average vertical at 7 mm is -0.66 and the inferior value is -0.95 with very big difference between the inferior and superior values on the vertical meridian).

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Case Study 101

Fig. 5.4A: The four refractive maps of the left eye. Slightly irregular anterior curvature map and suspicious posterior elevation map.

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102 Step by Step Reading Pentacam Topography

Fig. 5.4B: The corneal thickness map: nothing significant.

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Case Study 103

Fig. 5.4C: The sagittal curvature front map. Asymmetric bow tie/inferior steep (AB/IS). There is an angulation of about 10° between inferior and superior axes, but still within normal limits.

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104 Step by Step Reading Pentacam Topography

Fig. 5.4D: The sagittal curvature front map. Asymmetric bow tie/ inferior steep (AB/IS) with normal superior-inferior values.

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Case Study 105

Fig. 5.4E: The elevation front map. Irregular shape with tongue-like extension.

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106 Step by Step Reading Pentacam Topography

Fig. 5.4F: The elevation back map. Irregular shape with abnormal values within the central 4 mm circle.

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Case Study 107

Fig. 5.4G: The Topometric map. The inferior value is abnormal.

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108 Step by Step Reading Pentacam Topography

Fig. 5.4H: The keratoconus indices page. Nothing significant.

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Case Study 109

Fig. 5.4I: The four refractive maps of the right eye. Asymmetric anterior sagittal curvature map, suspicious numbers on the posterior elevation map.

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110 Step by Step Reading Pentacam Topography

Fig. 5.4J: Normal corneal thickness map.

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Case Study 111

Fig. 5.4K: The sagittal curvature front map. Asymmetric bow tie/inferior steep with angulation (AB/SRAX): the superior-inferior difference is abnormal.

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112 Step by Step Reading Pentacam Topography

Fig. 5.4L: The sagittal curvature front map. Asymmetric bow tie/inferior steep with angulation (AB/SRAX): there is about 25° of angulation between the two axes, which is abnormal.

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Case Study 113

Fig. 5.4M: The elevation front map. Irregular shape with tongue-like extension.

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114 Step by Step Reading Pentacam Topography

Fig. 5.4N: The elevation back map. Irregular shape with abnormal values within the central 4 mm circle.

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Case Study 115

Fig. 5.4O: The Topometric map. Both the average vertical value and the inferior value are abnormal.

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116 Step by Step Reading Pentacam Topography

Fig. 5.4P: The keratoconus indices page. The average is abnormal (1.2), the diagnosis box displays KK1 (keratoconus level 1), most irregularity indices are abnormal.

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Case Study 117 • The keratoconus indices page (Fig. 5.4P): Although the curve lines are within the normal range and there is no deviation before the 6 mm circle, the average is abnormal (1.2). The diagnosis box displays KK1, which means keratoconus level one according to Amsler classification. Most irregularity indices are also abnormal. P.S. Amsler classification is based on clinical signs and anterior curvature map (not elevation based) topography. As we see, we should always study both eyes together, and wherever we find one eye is normal and the other eye is abnormal, this means both eyes are abnormal. In our case, the left eye seems to be an early stage of keratoconus; this is obvious when we look at the elevation back map. On the other hand, whenever we see abnormal findings in the topography of any patient, it is better to do topography to his/her father, mother, brothers or sisters. That is because there may be some relatives with keratoconus in early stages with no complaints or vice versa, as we are going to see in the next case study.

118 Step by Step Reading Pentacam Topography

CASE 5: SUSPECTED CASE

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A 20-year-old male came with stable refractive error. His MR was: Eye OD

SPH -3.00

CYL -1.75

AXIS 45

OS

-3.00

-2.25

150

Although as a sequence we should begin with the right eye topography, we are going to see the left eye topography first for educational purpose. Fig. 5.5A shows his left eye corneal topography (4 refractive maps). The Qualifying Step 1. In a general look, the sagittal curvature map has a slightly irregular pattern oriented as oblique astigmatism. The anterior elevation map shows regular shape while the posterior map is slightly irregular. There is nothing suspicious in the thickness map in general. 2. Main page analysis reveals that the quality of the capture (QS) is not OK, but on repeating the capture the same quality remains, which indicates that the problem might be in the cornea itself. The K-readings in the central 3 mm are normal (44.8, 47.1) and the corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-1.7 <-6). Q-value at the 6 mm circle of the cornea front is normal (-0.46). Corneal thickness at the thinnest location is normal (528) and has normal coordinates with pachy apex. There is also no significant difference in thickness between pachy apex and thinnest location.

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Case Study 119 3. Studying each map: • Corneal thickness map (Fig. 5.5B): The shape of this map is normal with a slight displacement of the thinnest location. The difference between the lower and upper points of the central 4 mm circle is 23 µ (red circles), which is normal. • The sagittal curvature front (Fig. 5.5C): Shows a symmetrical bow tie, there is no skew (angulation) between the lower and upper axes of the pattern. The difference between the upper and lower points of the 4 mm circle is less than 1.5 dpt (Fig. 5.5C white circles). • The elevation front map (Fig. 5.5D): Regular shape with normal values within the central 4 mm circle. • The elevation back map (Fig. 5.5E): Slightly irregular shape with normal values within the central 4 mm circle. There are also some points where the difference between anterior and posterior values is >+5 µ. P.S. In case of any irregularity or suspicious values on elevation maps with the BFS, it is recommended to see the elevation maps with Toric Ellipsoid float reference body; when the irregularities are due to corneal astigmatism, they will vanish, otherwise they stay when they are due to real corneal surface irregularity. The toric ellipsoid option eliminates the effect of corneal astigmatic slope on the elevation maps. This is important especially for the back surface where the subclinical keratoconus begins. • The Keratometric power deviation map (KPD): Let us mention the importance of this map in this case. This map is calculated by excluding the effect of the

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120 Step by Step Reading Pentacam Topography anterior curvature power map from the true net power map, i.e. it represents the effect of the back surface of the cornea on the true net power map in every corneal point (Figure 5.5F). The normal value at any point in this map should be <+0.75. Any value falling between +0.75 and +1.5 is doubtful and borderline, but it is not considered significant unless there is a corresponding posterior elevation. Any value more than +1.5 is abnormal, especially if it is in the inferior half of the map, or if there is a corresponding elevation at the back elevation map. To understand the meaning of this map, let us imagine the back surface of a cornea with its elevations and depressions. The depressions are protrusions towards the anterior chamber, and the elevations are protrusions towards the front surface of the cornea, i.e. concavities which appear on this map with values more positive than other areas. So, when we look at the illustration in Fig. 5.5G, we can see the concave marked area, which holds either the risk of posterior keratoconus, or the possibility of postoperative out bulging of the posterior corneal surface. The significance of this map becomes more obvious when compared with the posterior tangential curvature map, which displays the irregularity more clearly, and with the posterior elevation map, which displays corresponding elevations. As we see in our case (Fig. 5.5F), there are many points on this map with abnormal values. This is an indicator of irregular posterior surface, which brings to our mind the fear of very early keratoconus. • The Topometric map (Fig. 5.5H red circle): Both the average vertical value and inferior value are abnormal.

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Case Study 121 • The keratoconus indices page (Fig. 5.5I): the curve lines are within the normal range with no deviation before the 6 mm circle. The average is abnormal (1.4). One of the irregularity indices is displayed in red because of the slight irregularity of the cornea. It is the corneal aberration coefficient factor (ABR), but there is no risk in treating the cornea with ABR less than 2.5. Let us look at the right eye topography (Fig. 5.5J). The Qualifying Step 1. In a general look, the sagittal curvature map has a clear irregular pattern oriented as with-the-rule astigmatism. The posterior elevation map shows abnormal numbers. There is nothing suspicious in the thickness map in general but it seems a little bit irregular. 2. Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (43.6, 45.7) and the corneal astigmatism (the algebraic sum of the anterior and posterior astigmatism) is also normal (-1.75 <-6). Q-value at the 6 mm circle of the cornea front is slightly high (-0.62). Corneal thickness at the thinnest location is normal (542) and has normal coordinates with pachy apex. There is also no significant difference in thickness between pachy apex and thinnest location. 3. Studying each map: • Corneal thickness map (Fig. 5.5K): The shape of this map is slightly irregular with a horizontal displacement of the thinnest location (-0.72 µ red arrow). The

122 Step by Step Reading Pentacam Topography

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•

•

•

•

•

difference between the lower and upper points of the central 4 mm circle is <30 µ (red circles). The sagittal curvature front map (Fig. 5.5L): Asymmetrical bow tie/superior steep (AB/SS): as you see in this picture, the pattern is superior steep and the difference between the upper and lower points at the 4 mm circle is 5.2, which is more than 2.5 dpt. On the other hand, this is a superior hot spot with high Kreadings (51.7), which is absolutely abnormal. The elevation front map (Fig. 5.5M): Shows irregular shape with tongue-like extension, but the values within the central 4 mm circle are still within the normal range. The elevation back (Fig. 5.5N): Shows irregular shape with abnormal values within the central 4 mm circle. There are also some points where the difference between anterior and posterior values is >+5 µ. The Keratometric power deviation map (Fig. 5.5O): It is highly irregular with abnormal values in the center (+2.5), which indicates abnormal posterior corneal surface. The Topometric map (Fig. 5.5P): Let’s look first at the Asphericity table, if you compare between the mean values at 6, 7 and 8 mm (red arrows), you will see that these values increase towards the periphery, which means that the irregularity is increasing towards the periphery of the cornea, this will be clear when you notice that there is a high difference between horizontal and vertical values in general, and between the four meridians (temp. nasal, etc. yellow arrows).

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Case Study 123

Fig. 5.5A: The four refractive maps of the left eye. Slightly irregular anterior curvature map and posterior elevation map. The quality of the capture (QS) is not OK, but on repeating the capture the same quality remains, which indicates that the problem might be in the cornea itself.

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124 Step by Step Reading Pentacam Topography

Fig. 5.5B: Corneal thickness map. No abnormal findings.

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Case Study 125

Fig. 5.5C: The sagittal curvature front map. No abnormal findings.

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126 Step by Step Reading Pentacam Topography

Fig. 5.5D: The elevation front map. No abnormal findings.

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Case Study 127

Fig. 5.5E: The elevation back map. Slightly irregular shape with normal values within the central 4 mm circle. There are also some points where the difference between anterior and posterior values is >+5 µ.

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128 Step by Step Reading Pentacam Topography

Fig. 5.5F: The Keratometric power deviation map (KPD). Many points with abnormal values. This is an indicator of irregular posterior surface, which brings to our mind the fear of very early keratoconus.

Fig. 5.5G: An excavation on the posterior corneal surface.

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Case Study 129

Fig. 5.5H: The Topometric map. The vertical average is border line, but the inferior value is abnormal (red circles).

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130 Step by Step Reading Pentacam Topography

Fig. 5.5I: The keratoconus indices page. The average is abnormal (1.4), one of the irregularity indices is displayed in red because of the slight irregularity of the cornea.

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Case Study 131

Fig. 5.5J: The four refractive maps of the right eye. The sagittal curvature map has a clear irregular pattern oriented as with-the-rule astigmatism. The posterior elevation map shows abnormal numbers. There is nothing suspicious in the thickness map in general but seems a little bit irregular. The quality of the capture (QS) is OK.

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132 Step by Step Reading Pentacam Topography

Fig. 5.5K: Corneal thickness map. The shape of this map is slightly irregular with a horizontal displacement of the thinnest location.

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Case Study 133

Fig. 5.5L: The sagittal curvature front map. Asymmetric bow tie/superior steep (AB/SS), which means a superior hot spot. The superior-inferior difference is abnormal. High K-readings in the hot spot.

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134 Step by Step Reading Pentacam Topography

Fig. 5.5M: The elevation front map. Irregular shape with tongue-like extension.

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Case Study 135

Fig. 5.5N: The elevation back map. Irregular shape with abnormal values within the central 4 mm circle, the difference between anterior and posterior values is >+5 µ in some points.

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136 Step by Step Reading Pentacam Topography

Fig. 5.5O: The Keratometric power deviation map. It is highly irregular with abnormal values in the center.

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Case Study 137

Fig. 5.5P: The Topometric map: there is high difference between horizontal and vertical values in general, and between the four meridians (yellow arrows). This indicates corneal irregularity, which increases towards the periphery (red arrows).

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138 Step by Step Reading Pentacam Topography

Fig. 5.5Q: The keratoconus indices page: the average is abnormal, the diagnosis box displays KK Possible, and most irregularity indices are also abnormal.

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Case Study 139

Fig. 5.5R: Corneal topography of the right eye of the above patient’s sister: she has keratoconus.

140 Step by Step Reading Pentacam Topography

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• The keratoconus indices page (Fig. 5.5Q): Although the curve lines are within the normal range, the average is abnormal (1.6). The diagnosis box displays KK Possible, which means probable keratoconus according to Amsler classification. Most irregularity indices are also abnormal. P.S. Amsler classification is based on clinical signs and anterior curvature map (not elevation based) topography. As there is abnormality in the right eye corneal topography with Amsler diagnosis of KK Possible, it is highly recommended to capture the patient’s relatives. Fig. 5.5R shows corneal topography of the right eye of the patient’s sister. It is very clear that the cornea is keratoconic.

Case Study 141

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CASE 6: POST-LASIK ECTASIA A 28-year-old female came to my office complaining of progressive reduction in her visual acuity (more severe in the left eye) since 3 years. Her history revealed Lasik treatment for myopia in 2003 (6 years ago) for both eyes. Her exam was as follows: Eye SPH CYL

AXIS UCVA BSCVA BSCVA+PH

OD -0.50 -2.25 60 OS 0 -4.5 95

0.7 0.05

1.0 0.1

1.0 0.6

According to her complaint and history, one can think about post-Lasik ectasia (keratoectasia), and when looking at her refraction, there is low uncorrected and best corrected visual acuity in the left eye with an astigmatic refractive error that does not explain this reduction. Fig. 5.6A shows corneal topography of the right eye. The Qualifying Step 1. In a general look, the sagittal curvature map has a highly irregular pattern. The anterior and posterior elevation maps show irregular shape with abnormal values. The thickness map shows a horizontally displaced thinnest location giving the shape of a conic pattern. 2. Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are normal (40.4, 42.4) and the corneal astigmatism (the algebraic sum of anterior and posterior astigmatism) is also normal (-1.3 <-6). Q-value at the 6 mm circle of the cornea front is abnormal (+0.39). Corneal thickness at the thinnest location is normal (489) and has abnormal

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142 Step by Step Reading Pentacam Topography horizontal coordinate with pachy apex. There is a significant difference in thickness between pachy apex and thinnest location (12 µ). 3. Studying each map: • Corneal thickness map (Fig. 5.6B): The shape of this map is abnormal with a horizontal displacement of the thinnest location (red arrow). The difference between the lower and upper points of the central 4 mm circle is 2 µ (red circles), which is normal. • The sagittal curvature front map (Fig. 5.6C): Shows the smiling face pattern, which is very abnormal pattern. When projecting the major axes on this map, you can see clearly the vortex pattern also (Fig. 5.6D). The difference between the upper and lower points at the 4 mm circle is much more than 1.5 dpt (Fig. 5.6D white arrows). So as you see, the K-readings of the central 3 mm are not enough to qualify the case, they are sometimes misleading and we should look at every single map. • The elevation front map (Fig. 5.6E): There are an obvious cone and abnormal values (white arrow). • The elevation back map (Fig. 5.6F): There are an obvious cone and abnormal values (white arrow). P.S. There is no need of course in this case to see the toric ellipsoid; the diagnosis is clearly keratoconus. • The Keratometric power deviation map (KPD): It is irregular and displays abnormal values (Fig. 5.6G). • The Topometric map (Fig. 5.6H): All values in all meridians and on all circles are positive and abnormal indicating an oblate cornea, this is normal after Lasik treatment of myopia.

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Case Study 143 • The keratoconus indices page (Fig. 5.6I): Look at the upper diagram; although the red curve begins within the normal range, it deviates rapidly. On the other hand, the lower diagram shows that the progression percentage is below normal. These findings are consistent with the diagnosis shown “Post Corneal Surgery?”. The average is high (1.7) and most of irregularity indices are abnormal, indicating irregular cornea. • Fig. 5.6J is one of the Scheimpflug image sectors, it is difficult here to assess the ectatic part of the cornea even on other sectors, and this is opposite to what we are going to see in the left eye topography. Fig. 5.6K shows corneal topography of the left eye. The Qualifying Step 1. In a general look, the sagittal curvature map and the anterior and posterior elevation maps show the pattern of just like keratoconus. The thickness map shows abnormal values within the central part. 2. Main page analysis reveals that the quality of the capture (QS) is OK. The K-readings in the central 3 mm are abnormal (53.1, 52.9) with very little amount of astigmatism, which indicates that the cone is not central but peripheral. Q-value at the 6 mm circle of the cornea front is abnormal (-1.36). Corneal thickness at the thinnest location is abnormal (423). There is a significant difference in thickness between pachy apex and thinnest location (17 µ).

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144 Step by Step Reading Pentacam Topography

Fig. 5.6A: The four refractive maps of the right eye. This topography is abnormal: the anterior sagittal curvature map is irregular with an inferior hot spot, there are high elevations on the anterior and posterior elevation maps.

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Case Study 145

Fig. 5.6B: Corneal thickness map. Abnormal shape with horizontal displacement of the thinnest location (red arrow), normal superior – inferior difference (red circles).

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146 Step by Step Reading Pentacam Topography

Fig. 5.6C: The sagittal curvature front map. This map shows the smiling face pattern, which is highly abnormal.

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Case Study 147

Fig. 5.6D: The sagittal curvature front map. We can see here the vortex pattern after projecting the circles and the major axes. We can see also that there is no significant superior-inferior difference on the 4 mm circle although the pattern is abnormal (white arrows).

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148 Step by Step Reading Pentacam Topography

Fig. 5.6E: The elevation front map. There are an obvious cone and abnormal values (white arrow).

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Case Study 149

Fig. 5.6F: The elevation back map. There are an obvious cone and abnormal values (white arrow).

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150 Step by Step Reading Pentacam Topography

Fig. 5.6G: The Keratometric power deviation map (KPD). It is irregular and displays abnormal values.

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Case Study 151

Fig. 5.6H: The Topometric map. All values in all meridians and on all circles are positive and abnormal indicating an oblate cornea.

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152 Step by Step Reading Pentacam Topography

Fig. 5.6I: The keratoconus indices page. The red curve in the upper diagram begins within the normal range, and then it deviates rapidly. The progression percentage red curve is below normal in the lower diagram. This is consistent with the diagnosis shown “Post Corneal Surgery?” The average is high (1.7) and most of irregularity indices are abnormal, indicating irregular cornea.

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Case Study 153

Fig. 5.6J: Scheimpflug image. It is difficult here to assess the ectatic part of the cornea.

3. Studying each map: • Corneal thickness map (Fig. 5.6L): The shape of this map is abnormal and irregular. The periphery is very thick and the central part is relatively thin, this is reflected on the thickness curves as will be shown in Fig. 5.6U. We cannot say here that the difference between the lower and upper points of the central 4 mm circle is normal, but we have to remember one of the important figures of Rowsey’s rule of 2’s: the peripheral thickness should not be >20 µ more than the central thickness, which is obviously absent in this case. • The sagittal curvature front map (Fig. 5.6M): Shows a huge cone. But, to see the size of the central part of the cone, we have to adjust the color settings and we will have a better detailed picture (Fig. 5.6N). When projecting the major axes on this map, you can see clearly the abnormal distribution of the axes (Fig. 5.6O). • The elevation front map (Fig. 5.6P): There are a large cone and abnormal values.

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154 Step by Step Reading Pentacam Topography

Fig. 5.6K: The four refractive maps of the left eye. Keratoconus like topography with thin central cornea. The K-readings in the central 3 mm are abnormal with very small amount of astigmatism, which indicates that the cone is not central but peripheral. Q-value at the 6 mm circle of the cornea front is abnormal. Corneal thickness at the thinnest location is abnormal.

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Case Study 155

Fig. 5.6L: Corneal thickness map. Thin central cornea with more than 20 µ difference between the periphery and the center, this is abnormal according to Rowsey’s rule of 2’s.

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156 Step by Step Reading Pentacam Topography

Fig. 5.6M: The sagittal curvature front map. There is a clear cone.

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Case Study 157

Fig. 5.6N: The sagittal curvature front map. The real cone can be better displayed after adjusting the color settings.

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158 Step by Step Reading Pentacam Topography

Fig. 5.6O: The sagittal curvature front map. Abnormal distribution of the axes.

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Case Study 159

Fig. 5.6P: The elevation front map. Very high elevations giving the shape of a cone.

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160 Step by Step Reading Pentacam Topography

Fig. 5.6Q: The elevation back map. Very high elevations giving the shape of a cone. Notice that the elevations on the back surface map are higher than those on the front surface map, which is consistent with clinical keratoconus where the ectasia is severer on the posterior surface than on the anterior surface.

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Case Study 161

Fig. 5.6R: The elevation back map. Very high elevations giving the shape of a cone, these elevations became more obvious when manually adjusting the diameter of the BFS into 8 mm (red circle).

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162 Step by Step Reading Pentacam Topography

Fig. 5.6S: The Keratometric power deviation map (KPD) .It is irregular and displays abnormal values. This means that the problem is bigger on the posterior surface than on the anterior surface, which is consistent with clinical keratoconus.

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Case Study 163

Fig. 5.6T: The Topometric map. All values are negative and most of them are highly abnormal (>-1). There is also big differences between meridians and between the vertical and horizontal averages (>0.3 difference).

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164 Step by Step Reading Pentacam Topography

Fig. 5.6U: The keratoconus indices page. The red curves give an idea about the rapid progression of corneal thickness towards periphery. The average is very high. Almost all irregularity indices are highly abnormal. These findings give the reason for the diagnosis displayed in the diagnosis box “KK 3-4”.

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Case Study 165

Fig. 5.6V: Scheimpflug image. It is very clear that there is an inferior-temporal corneal thinning (white arrow).

• The elevation back map (Fig. 5.6Q): There are a large cone and abnormal values, which become more obvious when adjusting the diameter of the BFS manually on 8 mm (Fig. 5.6R red circle). Notice that the posterior elevations are much higher than the anterior, which is consistent with clinical keratoconus. • The Keratometric power deviation map (KPD): It is irregular and displays abnormal values (Fig. 5.6S). • The Topometric map (Fig. 5.6T): Let’s go back first to the same map of the right eye (Fig. 5.6H) where all values in all meridians and on all circles are positive and abnormal indicating an oblate cornea, which is normal after Lasik treatment of myopia as we said before. So, we expect to see the same thing in the left eye map, but the truth is the opposite. As you see here, all values are negative and most of them are high, indicating a very prolate cornea, which is consistent with keratoconus and advanced keratoectasia. So we can say that in the very early stage of

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166 Step by Step Reading Pentacam Topography keratoectasia after myopic treatment, the cornea may still have the oblate shape, then it gets the prolate shape when the case progresses. • The keratoconus indices page (Fig. 5.6U): Both diagrams indicate a very rapid increase in thickness and progression percentage towards the periphery; this is consistent with the very thick periphery and the relatively thin center of the cornea (see Fig. 5.6L). The average is very high (4.1) and most of the irregularity indices are abnormal. The diagnosis box displays keratoconus level 3 to 4. • Figure 5.6V is one of the Scheimpflug image sectors, the ectatic part is very clear (white arrow). Discussion The right eye of the patient is slightly ectatic; there is small amount of astigmatism with very good UCVA and BSCVA. In my opinion the best management in this case is to crosslink this cornea because of the progressive deterioration of vision as the patient describes. Or at least, we have to observe the topography in 3 months periodicals. The left eye is highly ectatic. The visual acuity is very low. Here we have to judge, is it better to do DALK, or to put rings and then do cross linking? In my opinion, taking the second decision will improve the irregularity of the cornea and will raise the cone towards the center of the cornea causing iatrogenic myopia and hence the need for more procedures such as phakic IOL. I am prone to choose the first choice (DALK) bearing the risk of PKP probability and hence graft rejection possibility. Such cases will be discussed in my forthcoming book on Keratoconus, which will be published also by Jaypee Brothers.

Case Study 167

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CASE 7: KERATOCONUS This is a keratoconus case. In this case I will present the topography and you will try yourself to read each map, writing notes and discussing the case depending on the skills you have learned, then you can read the discussion. 1. The four refractive maps (Fig. 5.7A). 2. The corneal thickness map (Fig. 5.7B). 3. The sagittal curvature front map (Fig. 5.7C). 4. The sagittal curvature front map after adjusting the color scale (Fig. 5.7D). 5. The sagittal curvature front map with the major axes projected (Fig. 5.7E). 6. The elevation front map (Fig. 5.7F). 7. The elevation back map (Fig. 5.7G). 8. The Keratometric power deviation map (Fig. 5.7H). 9. The Topometric map (Fig. 5.7I). 10. The keratoconus indices page (Fig. 5.7J).

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168 Step by Step Reading Pentacam Topography

Fig. 5.7A: The four refractive maps.

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Case Study 169

Fig. 5.7B: The corneal thickness map.

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170 Step by Step Reading Pentacam Topography

Fig. 5.7C: The sagittal curvature front map.

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Case Study 171

Fig. 5.7D: The sagittal curvature front map after adjusting the color scale.

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172 Step by Step Reading Pentacam Topography

Fig. 5.7E: The sagittal curvature front map with the major axes projected.

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Case Study 173

Fig. 5.7F: The elevation front map.

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174 Step by Step Reading Pentacam Topography

Fig. 5.7G: The elevation back map.

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Case Study 175

Fig. 5.7H: The Keratometric power deviation map.

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176 Step by Step Reading Pentacam Topography

Fig. 5.7I: The Topometric map.

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Case Study 177

Fig. 5.7J: The keratoconus indices page.

178 Step by Step Reading Pentacam Topography

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Discussion This is a keratoconus case. The patient is 21-year-old male complaining of progressive reduction of visual acuity in both eyes. His eye examination and family history raised the suspicion of keratoconus. On doing corneal topography, the diagnosis was established. In the four refractive maps, you can notice the abnormal cornea. The corneal thickness map has a cone-like appearance because of the thinnest location displacement; there is also a very big superior-inferior difference (77 µ). The sagittal curvature front map has AB/IS pattern, but there is no skew in axes. There is a big cone on both elevation maps, more obvious on the posterior map, which is consistent with the abnormal KPD map. The cornea is very prolate as shown on the topometric map with more than 0.3 difference between vertical and horizontal averages. The keratoconus indices page establishes the diagnosis, all parameters are abnormal (the curve lines, the average and the indices). This case is keratoconus level three according to Amsler classification.

Case Study 179

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CASE 8: KERATOCONUS POSSIBLE This is a keratoconus possible case. As in the previous case, I will present the topography and you will try yourself to read each map, writing notes and discussing the case depending on the skills you have learned, then you can read the discussion. 1. The four refractive maps of the right eye (Fig. 5.8A). 2. The sagittal curvature front map of the right eye (Fig. 5.8B). 3. The sagittal curvature front map of the right eye with the major axes projected (Fig. 5.8C). 4. The elevation front map of the right eye (Fig. 5.8D). 5. The elevation back map of the right eye (Fig. 5.8E). 6. The Topometric map of the right eye (Fig. 5.8F). 7. The keratoconus indices page of the right eye (Fig. 5.8G). 8. The four refractive maps of the left eye (Fig. 5.8H).

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180 Step by Step Reading Pentacam Topography

Fig. 5.8A: The four refractive maps of the right eye.

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Case Study 181

Fig. 5.8B: The sagittal curvature front map of the right eye.

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182 Step by Step Reading Pentacam Topography

Fig. 5.8C: The sagittal curvature front map of the right eye with the major axes projected.

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Case Study 183

Fig. 5.8D: The elevation front map of the right eye.

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184 Step by Step Reading Pentacam Topography

Fig. 5.8E: The elevation back map of the right eye.

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Case Study 185

Fig. 5.8F: The Topometric map of the right eye.

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186 Step by Step Reading Pentacam Topography

Fig. 5.8G: The keratoconus indices page of the right eye.

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Case Study 187

Fig. 5.8H: The four refractive maps of the left eye.

188 Step by Step Reading Pentacam Topography

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Discussion According to Amsler classification, this is a keratoconus possible case. The possibility came from: the pattern of the sagittal curvature front map. As you see, other parameters are within the accepted range. The sagittal curvature front map has two patterns: AB/ IS and the vortex pattern, although there is no skew in the very central major axes. The posterior elevation map is irregular in spite of its normal values. There are two indices in the keratoconus indices page with abnormal values, the ABR and the IHD. The ABR stands for Aberration Coefficient. The IHD stands for Index of Height Decentration; it indicates the degree of decentration of the elevations in vertical direction, elevated in keratoconus. That was for the right cornea, but looking to the left corneal topography reveals the diagnosis of left eye keratoconus, hence, the need to see the topography of both eyes.

Case Study 189

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CASE 9: ABNORMAL CORNEA This case is very strange, the right cornea is normal while the left cornea is abnormal, but still the diagnosis is neither keratoconus nor keratoconus possible. As in the previous cases, I will present the topography of the case and you will try yourself reading each map, writing notes and discussing the case depending on the skills you have learned, then you can read the discussion. 1. The four refractive maps of the right eye (Fig. 5.9A). 2. The four refractive maps of the left eye (Fig. 5.9B). 3. The corneal thickness map of the left eye (Fig. 5.9C). 4. The sagittal curvature front map of the left eye (Fig. 5.9D). 5. The elevation front map of the left eye (Fig. 5.9E). 6. The elevation back map of the left eye (Fig. 5.9F). 7. The Keratometric power deviation map of the left eye (Fig. 5.9G). 8. The Topometric map of the left eye (Fig. 5.9H). 9. The keratoconus indices page of the left eye (Fig. 5.9I). 10. Two difference thickness maps (Fig. 5.9J). 11. Two difference Topometric maps (Fig. 5.9K). 12. Two difference keratoconus indices pages (Fig. 5.9L).

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190 Step by Step Reading Pentacam Topography

Fig. 5.9A: The four refractive maps of the right eye.

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Case Study 191

Fig. 5.9B: The four refractive maps of the left eye.

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192 Step by Step Reading Pentacam Topography

Fig. 5.9C: The corneal thickness map of the left eye.

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Case Study 193

Fig. 5.9D: The sagittal curvature front map of the left eye.

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194 Step by Step Reading Pentacam Topography

Fig. 5.9E: The elevation front map of the left eye.

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Case Study 195

Fig. 5.9F: The elevation back map of the left eye.

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196 Step by Step Reading Pentacam Topography

Fig. 5.9G: The Keratometric power deviation map of the left eye.

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Case Study 197

Fig. 5.9H: The Topometric map of the left eye.

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198 Step by Step Reading Pentacam Topography

Fig. 5.9I: The keratoconus indices page of the left eye.

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Case Study 199

Fig. 5.9J: Two difference thickness maps.

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200 Step by Step Reading Pentacam Topography

Fig. 5.9K: Two difference Topometric maps.

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Case Study 201

Fig. 5.9L: Two difference keratoconus indices pages.

202 Step by Step Reading Pentacam Topography

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Discussion This case presents a patient with aberrant normal right corneal topography and very abnormal topography of the left cornea. This patient is a chronic user of contact lenses (CL), but even after she stopped using the CL for more than one month, the topography did not change. If you compare the two topographies, you will notice three important things: very steep symmetric bow tie on the sagittal curvature map, conic thickness map and much displaced thinnest location. The elevation maps seem to be normal. The KPD map is also normal. I presented in this case three comparison maps. The first map compares thickness; the difference in thickness is 42 µ, which is abnormal. The second map compares topometry; the vertical values are abnormal in the left eye. The third map compares keratoconus indices pages, see the abnormal curves and average. The diagnosis is abnormal cornea according to Amsler classification. I think the computer did not consider this case as keratoconus or at least keratoconus possible because of the symmetrical bow tie because—as previously mentioned—Amsler is based on curvature front map. However, this case is not a candidate neither for Lasik nor for PRK because of the abnormal and strange topography and because of the possibility of unpredictable post-Lasik results. P.S. Because the Amsler classification is based on curvature front map and clinical signs, it is coded as TKC among the irregularity indices in the new version of Pentacam software; as it takes part of the decision and not to be completely dependable.

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Bibliography 1. Agarwal Sunita, et al. Dr Agarwals’ Textbook on Corneal Topography. Section I: introduction to corneal topography. Chapter 1: Fundamentals on corneal topography. Eds. Guillermo L. Simón and others. Jaypee Brothers 2006; 4-8. 2. Alan N Carlson. The Oculus Pentacam: Steering clear of bad decisions. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007. 3. Azar T Dimitri, et al. LASEK, PRK, and Excimer Laser Stromal Surface Ablation. Marcel Dekker 2003; 25-26. 4. Belin W Michael, Khachikian S Stephen. Elevation based topography: Screening for refractive surgery. Chapter 3: Understanding elevation based topography. Highlights of Ophthalmology International 2008; 40. 5. Benjamin F Boyd, et al. Wavefront analysis, aberrometers and corneal topography: section I: chapter 1: the refractive media of the human eye. Eds. Vidushi Sharma and others. Section II: chapter 3: Fundamentals on corneal topography. Eds. Guillermo L. Simón and others. Section III: chapter 8: corneal topography in irregular astigmatism: diagnostic tool in the evaluation of the quality of vision. Eds. Jorge L. Alió and others. Chapter 9: topographic and pachymetric changes induced by contact lenses. Eds. Jairo E. Hoyos and others. Chapter 10: corneal topography in cataract surgery. Eds. Samuel Boyd and Virgilio Centurion. Highlights of Ophthalmology International 2003;3-7;25;146;160-164;173176. 6. David D Bogorad. Getting started with the Pentacam. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007.

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204 Step by Step Reading Pentacam Topography 7. David R Hardten. Innovative uses of the Pentacam in a complex anterior segment practice. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007. 8. J James Rowsey. Keratoconus topography and indices. AAO New Orleans Nov. 2007. 9. J Trevor Woodhams. Pentacam: The new standard beyond Placido topography. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007. 10. Jason E Stahl. Why the Pentacam is essential in my refractive & cataract practice. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007 . 11. Marc A Michelson. Understanding the role of the Pentacam in refractive surgery. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007. 12. Mazen M. Sinjab. Corneal Topography in Clinical Practice (Pentacam System): Basics and Clinical Interpretation. Jaypee Brothers Medical Publishers 2009. 13. Michael W Belin. A new enhanced keratoconus detection program for refractive surgery screening. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007. 14. Pentacam user manual. Oculus 2007, 2008. 15. Perez-straziota E Claudia, Randleman J Bradley. Ectasia risk-scoring system improves identification of high-risk patients. Cataract & Refractive Surgery Today Europe. September 2008; 43,44. 16. Perry S Binder. Analysis of ectasia after laser in situ keraomileusis: Risk factors. J Cataract Refract Surg 2007; 33: 1530-38. 17. Probst E Louis, Doane F John. Refractive Surgery: A Color Synopsis. Chapter 4: Preoperative Assessment. Thieme Medical Publishers. 2001;32-33. 18. Renato Ambrósio, et al. Corneal-thickness spatial profile and corneal-volume distribution: Tomographic indices to

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Bibliography 205 detect keratoconus. J Cataract Refract Surg 2006; 32: 185159. 19. Stephen E Pascucci. Surgical screening & planning using the Oculus Pentacam. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007. 20. Steven C Schalhorn. The added value of the Pentacam in a refractive practice. Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007. 21. Steven J Dell. Why do I need a Pentacam? Oculus: The Pentacam: the next wave in comprehensive eye scanner technology. ESCRS Sweden 2007.

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Index A Aberration coefficient 188 Abnormal cornea 189 Abnormal findings in corneal topography 47 Amsler classification 117, 140, 178, 188, 202 Anisometropia 97 qualifying step 97, 99 Aqueous humor 11 tangential 12 principle 12

C Collagen vascular diseases 57 Conic thickness map 202 Corneal astigmatism 39, 87,98, 119, 141 Corneal ectasia 4 Corneal stroma 11 Corneal thickness map 18, 97 Curvature based instruments 2 keratometer 2 photokeratoscope 2 Curvature maps 10 sagittal 10 principle 10

D DALK 166 Diabetes mellitus 57

E Ectasia risk score system 49 Elevation back map 165 Elevation based topographers 3 Elevation maps 16 principle 16 reference body 16 Examining the patient 51 family history 56 medical history 56 ocular history 52 previous ocular surgery 56 previous trauma 52

H Hypermetropia 25 Hyperopia 86 qualifying step 86 quantifying step 95 scoring step 96

208 Step by Step Reading Pentacam Topography

I Index of height decentration 188 Infectious diseases 58 Inflammatory disorders 58

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K Keratoconus 139, 142, 167, 178 Keratoconus indices pages 44, 202 Keratoconus possible case 179, 188 Keratoectasia 165 Keratometric power deviation map 162, 165, 175

L Lasik treatment of myopia 165

M Main page analysis 21 coordinates of the corneal thickness 24 pachy apex 24 pupil center 24 thinnest location 25 cornea back surface 24 cornea front surface 22 miscellaneous 26 AC depth (Int.) 26 angle 27 chamber volume 26 IOP 27 KPD 27 lens thickness 27 pupil diameter 27

Medications and allergies 58 Mixed astigmatism 74, 84 qualifying step 74 quantifying step 84 scoring step 85 Myopic astigmatism 62 qualifying step 62 quantifying step 72 scoring step 73

O Oblate cornea 142, 151 Oblique astigmatism 118 Ocular diseases 57

P Placido disk 15 Post-Lasik ectasia 141 qualifying step 141 Prior corrective lenses 59

Q Qualifying step 62 Quantifying step 62 Quick review of pentacam main maps 9

R Radii of circles 12 Reading corneal topography 30 important maps 38 corneal thickness map 41 elevation maps 39 topometric map 43

basmala blog (always original)

Index 209 steps 30 displaying four refractive maps 30 performing main page analysis 30 studying maps 33 anterior sagittal curvature map 33 topographic shape patterns 36 Reference axis 15 anatomical axis 15 videokeratoscope 15 visual axis 15 Regular astigmatism 34 Ring verification display 2 computerized videokeratoscope 3 Rowsey’s rule 153, 155

Scoring the case 50 Steps of reading the topography 30 Suspected case 118 qualifying step 118, 121

T TKC 202 Topometric map 70 163, 165, 176, 185, 197, 200 Toric ellipsoid float reference body 87, 98, 119 Transparent convex mirror 2

U Ultrasonic pachymetry 3

V S Sagittal curvature 188 Scheimpflug image 6, 153, 166 Scheimpflug law 7

Vascular diseases 57

W With-the-rule astigmatism 131