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Editor-in-Chief: BENJAMIN F. BOYD, M.D., F.A.C.S.
Editors: SUNITA AGARWAL, M.S.;D.O.;F.S.V.H. ATHIYA AGARWAL, M.D.;D.O.;F.R.S.H. AMAR AGARWAL, M.S.;F.R.C.S.;F.R.C.Ophth
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Project Director: Production Manager: Page Design and Typesetting: Art Design: Spanish Translation: Sales Manager: Marketing Manager: Customer Service Manager: International Communications:
Andres Caballero, Ph.D Kayra Mejia Kayra Mejia Laura Duran Eduardo Chandeck Prof. Juan Murube, M.D. Tomas Martinez Eric Pinzon Miroslava Bonilla Joyce Ortega
©Copyright, English Edition, 2002 by HIGHLIGHTS OF OPHTHALMOLOGY All rights reserved and protected by Copyright. No part of this publication may be reproduced, stored in retrieval system or transmitted in any form by any means, photocopying, mechanical, recording or otherwise, nor the illustrations copied, modified or utilized for projection without the prior, written permission of the copyright owner. Due to the fact that this book will reach ophthalmologists from different countries with different training, cultures and backgrounds, the procedures and practices described in this book should be implemented in a manner consistent with the professional standards set for the circumstances that apply in each specific situation. Every effort has been made to confirm the accuracy of the information presented and to correctly relate generally accepted practices. The authors, editors, and publisher cannot accept responsibility for errors or exclusions or for the outcome of the application of the material presented herein. There is no expressed or implied warranty for this book or information imparted by it. Any review or mention of specific companies or products is not intended as an endorsement by the authors or the publisher. Boyd, Benjamin F., M.D.; Agarwal, Sunita, M.S.; Agarwal, Athiya, M.D.; Agarwal, Amar, M.D. "LASIK and Beyond LASIK - Wavefront Analysis and Customized Ablation" ISBN Nº 9962-613-04-3 Published by: Highlights of Ophthalmology Int'l P.O. Box 6-3299, El Dorado City of Knowledge Clayton, Bldg. 207 Panama, Rep. of Panama Tel: (507)-317-0160 FAX: (507)-317-0155 E-mail:
[email protected] Worldwide Web:www.thehighlights.com Printed in Bogota, Colombia. You may contact HIGHLIGHTS OF OPHTHALMOLOGY INC., for additional information about other books in this field or about the availability of our books.
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Contents
EDITOR-IN-CHIEF BENJAMIN F. BOYD, M.D., D.Sc. (Hon), F.A.C.S. Doctor Honoris Causa Immediate Past President, Academia Ophthalmologica Internationalis Honorary Life Member, International Council of Ophthalmology Editor-in-Chief and Author, HIGHLIGHTS OF OPHTHALMOLOGY, 25 Hard Cover Volumes and the 15 million copies of HIGHLIGHTS OF OPHTHALMOLOGY Bi-Monthly Journal. Recipient of the Duke-Elder International Gold Medal Award (International Council of Ophthalmology), the Barraquer Gold Medal (Barcelona), the First Benjamin F. Boyd Humanitarian Award and Gold Medal for the Americas (Pan American), the Leslie Dana Gold Medal and the National Society for Prevention of Blindness Gold Medal (United States), Moacyr Alvaro Gold Medal (Brazil), the Jorge Malbran Gold Medal (Argentina), the Favaloro Gold Medal (Italy). Recipient of The Great Cross Vasco Nuñez de Balboa Panama's Highest National Award.
EDITORS DR. SUNITA AGARWAL, M.S.;D.O.;F.S.V.H. (Germany) Pioneer in the world in the field of Laser Cataract Surgery. She heads Dr.Agarwal’s Eye Hospital at Bangalore, India and Dr.Agarwal’s Eye Clinic at Dubai (UAE). She is an expert in the field of Lasik Laser as she is in the field of cataract surgery under No Anesthesia. She has brought out for the first time in the world the use of the Air Pump as a new method to prevent surge and also found out that the internal tube of the phaco machine can lead to endophthalmitis . She practices at Dr.Agarwal’s Eye Hospital, 15 Eagle Street, Langford town, Bangalore-560 025, India and at Dr.Agarwal’s Eye Clinic,Villa No.2, Roundhouse 3, Al Wasl Road, Dubai Post box 9168, UAE.
DR. ATHIYA AGARWAL, D.O.;F.R.S.H. (London) Excellent surgeon who trains ophthalmologists from all over the world in Lasik and Phaco. She performs No anesthesia cataract surgery, Phakonit and Lasik Laser quite easily. Dr.Athiya is a very good speaker and teaches routinely in various conferences nationally and internationally. She practices at Dr.Agarwal’s Eye Hospital, 19 Cathedral Road, Chennai (Madras) – 600 086, India.
DR. AMAR AGARWAL, M.S.;F.R.C.S.;F.R.C.Ophth (London) Started for the first time in the world "No anesthesia cataract surgery", "Phakonit (cataract removal through a 0.9 mm incision)" and "Favit" a new technique to remove dropped nuclei. He is a very dynamic speaker. He has a double FRCS to his credit. His parents Dr. J. Agarwal and Dr. Mrs.T.Agarwal, Sister Dr.Sunita Agarwal, wife Dr.Athiya Agarwal and Brother-in-law Mr.Pankaj Sondhi help him in his aim to perfection. He practices at Dr.Agarwal’s Eye Hospital, 19 Cathedral Road, Chennai (Madras) – 600 086, India. Dr.Agarwal’s Eye hospital at Chennai is the only eye hospital in the world built in the shape of an eye and has been included in the Ripley’s Believe it or not series. Dr.Agarwal’s Eye Hospital is at Chennai (India), Bangalore (India) and Dubai. The web site of the hospital is: http://www.dragarwal.com
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Contributing Authors
Agarwal, Amar, M.S.,FRCS;FRCOphth Medical Director, Dr. Agarwal's Group of Eye Hospital Chennai, India Agarwal, J., FORCE;DO;FICS Chairman, Dr. Agarwal's Group of Eye Hospital, Chennai, India; Bangalore, India; Dubai (UAE) Agarwal, Sunita, MS;DO;FSVH Medical Director; Dr. Agarwal's Group of Eye Hospital Bangalore, India Agarwal, T.; FORCE;DO;FICS Managing Director, Dr. Agarwal's Group of Eye Hospital, Chennai, India; Bangalore, India; Dubai (UAE) Alio, Jorge L., M.D. Director, Instituto Oftalmologico de Alicante Alicante, Spain Attia, Walid, M.D. Instituto Oftalmologico de Alicante Alicante, Spain
Avalos U., Guillermo, M.D. Chief, Department of Ophthalmology Hospital Sagrado Corazon; Medical Director, Clinica Laser Oftalmico Guadalajara, Mexico Belda, Jose I., M.D. Instituto Oftalmologico de Alicante Alicante, Spain Benelli, Umberto, M.D. Department of Neurosciences Section of Ophthalmology University of Pisa Pisa, Italy Border, Andrea D., O.D. Discover Vision Centers Kansas City, Missouri
Boyd, Benjamin F., M.D., F.A.C.S. Editor-in-Chief, Highlights of Ophthalmology Int., Panama, Rep. of Panama Butler, Jason, M.D. Long Beach Laser Center Long Beach, California Carriazo E., Cesar, M.D. Medical and Scientific Director Carriazo Ophthalmological Center, Colombia
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Carvalho, Luis A., PhD. Institute of Physics University of Sao Paulo, Brazil Castro, Jarbas C., PhD. Professor, Institute of Physics University of Sao Paulo, Brazil Cigales, Melania, M.D. Instituto Oftalmologico de Sabadell Sabadell, Spain Coelho, Etelvino, M.D. Director, Centro de Microcirugia Refrativa & Excimer Laser de Minas Gerais Belo Horizonte, MG Brazil Coret, Andreu, M.D. Medical Director, Instituto Oftalmologico de Barcelona Barcelona, Spain Cummings, Arthur, MB, ChB Mmed (Ophth) FCS(SA), FRCS (Edin) Wellington Ophthalmic Laser Clinic Dublin, Ireland Charles, Steve, M.D. Clinical Professor Department of Ophthalmology University of Tennessee Center of Health Science Memphis, Tennessee
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CONTRIBUTING AUTHORS Chamon, Wallace, PhD. Refractive Surgery Division Escola Paulista de Medicina University of Sao Paulo, Brazil Choudhry, Saurabh, D.O., FERC. Fellow, Dr. Agarwal's Eye Hospital, Chennai, India Choudhry, Reena, M., DO.;FERC. Fellow, Dr. Agarwal's Eye Hospital, Chennai, India Davis, Elizabeth, A., M.D. Associate, Minnesota Eye Consultants, PA; Assistant Clinical Professor University of Minnesota Minneapolis, Minnesota Denning, James A., B.A., B.S. Discover Vision Centers Kansas City, Missouri
Hardten, David R., M.D. Director of Refractive Surgery Minnesota Eye Consultants; Clinical Associate Professor of Ophthalmology University of Minnesota Minneapolis, Minnesota
Lindstrom, Richard, M.D. Medical Director, Phillips Eye Center for Teaching and Research; Clinical Professor, University of Minnesota, Minnesota, Minneapolis
Haw, Weldon, M.D. Cornea & Refractive Surgery, Department of Ophthalmology, Stanford University School of Medicine Stanford, California
Mahmoud M. Ismail, M.D., Ph.D. University of Al-Azhar, Cairo, Egypt
Hoyos, Jairo E., M.D. Medical Director Instituto Oftalmologico de Sabadell Sabadell, Spain Hoyos-Chacon, Jairo, M.D. Instituto Oftalmologico de Sabadell Sabadell, Spain
Doane, John F., M.D. Discover Vision Centers Kansas City, Missouri
Katsanevaki, VJ, M.D. Department of Ophthalmology University of Crete-Medical School Crete, Greece
EuDaly, Lon S., O.D. Discover Vision Centers Kansas City, Missouri
Knorz, Michael C., M.D. Klinikum Mannheim Mannheim, Germany
Feinerman, Gregg, M.D. Medical Director, Feinerman Vision Institute, Long Beach Laser Center, Long Beach, California; Assistant Clinical Professor, University of California, Irvine, California
Koch, Paul S., M.D. Koch Eye Associates Warwick, Rhode Island
Gatell, Jordi, M.D. Instituto Oftalmologico de Barcelona Barcelona, Spain Ginis, HS., BSc Department of Ophthalmology University of Crete-Medical School Crete, Greece Gomez, Javier J., M.D. Instituto Oftalmologico de Alicante Alicante, Spain
Krueger, Ronald, M.D. Medical Director, Department of Refractive Surgery, The Cleveland Clinic Foundation Cole Eye Institute Cleveland, Ohio Lara, Elvira, O.D. Instituto Oftalmologico de Barcelona Barcelona, Spain Lavery, Frank, MCh FRCSI FRCS (Edin) DOMS Wellington Ophthalmic Laser Clinic Dublin, Ireland
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Manche, Edward E., M.D. Assistant Professor of Ophthalmology Stanford University School of Medicine Stanford, California Martiz, Jaime R., M.D. Refractive Surgery Consultant; The Laser Center, Houston, Texas; Course Director & President International Lasik Course Houston, Texas McDonald, Marguerite, M.D. Director, Southern Vision Institute New Orleans, Louisiana Morris, Scot, O.D. Discover Vision Centers Kansas City, Missouri Murube, Juan, M.D. Professor of Ophthalmology, University of Alcala; Chairman, Dept. of Ophthalmology, Hospital Ramon y Cajal Madrid, Spain Narang, Sameer, M.S. Director, Narang Eye Clinic Ahmedabad, Gujarat, India Narang, Priya, M.S. Director, Narang Eye Clinic Ahmedabad, Gujarat, India Narasimhan, Smita, M.B.B.S.,FERC Consultant, Dr. Agarwal's Eye Hospital, Chennai, India
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CONTRIBUTING AUTHORS Nardi, Marco, M.D. Associate Professor Department of Neurosciences Section of Ophthalmology University of Pisa Pisa, Italy Nguyen, Kim, M.D. Long Beach Laser Center Long Beach, California Oliveira, Canrobert, M.D. Director, Hospital de Olhos de Brasilia Brasilia, DF Brazil Pallikaris, Ioannis G., M.D. Department of Ophthalmology University of Crete-Medical School Crete, Greece
Preetha R., M.B.B.S; FERC Fellow, Dr. Agarwal's Eye Hospital, Chennai, India
Simon-Castellvi, Jose Ma., M.D. Clinica Oftalmologica Simon, Barcelona, Spain
Probst, Louis E., M.D. Medical Director, TLC The Windsor Laser Eye Center, Windsor, Ontario, Canada
Simon-Castellvi, Sarabel, M.D. Clinica Oftalmologica Simon, Barcelona, Spain
Sasikanth, RR., MD Dr. Agarwal's Eye Hospital Chennai, India Schor, Paulo, PhD, M.D. Bioengineering Division Escola Paulista de Medicina University of Sao Paulo Sao Paulo, Brazil
Parul, Goel, M.S., F.E.R.C. Consultant, Dr. Agarwal's Eye Hospital, Chennai, India
Shalaby, Ahmad, M., M.D. Instituto Oftalmologico de Alicante Alicante, Spain
Perez-Santoja, Juan J., M.D. Refractive Surgery and Cornea Unit Alicante Institute of Ophthalmology Miguel Hernandez University School of Medicine Alicante, Spain
Simon-Castellvi, Cristina, M.D. Clinica Oftalmologica Simon, Barcelona, Spain
Peters, Tim, M.D. Nationwide Vision Laser & Eye Center, Clinical Lecturer, University of Arizona Phoenix, Arizona
Simon-Castellvi, Guillermo L., M.D. University of Barcelona, Faculty of Medicine, Dept. of Ophthalmology; Chief Anterior Segment Surgeon, Clinica Oftalmologica Simon, Barcelona, Spain
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Slade, Stephen G., M.D. The Laser Center, Houston, Texas Viera de Carvalho, Luis A., PhD. Professor, University of Sao Paulo Brazil Waring, George, M.D. Professor of Ophthalmology Emory University; Co-Founder Emory Vision Correction Center Atlanta, Georgia Werner, Leonardo P., M.D. Department of Ophthalmology, São Geraldo Eye Hospital, Federal University of Minas Gerais and the "Instituto Vizibelli" Belo Horizonte, Minas Gerais, Brazil Wilson, Steven E., M.D. Chair, Department of Ophthalmology, and Professor of Vision Research University of Washington Seattle, Washington
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Contents
SECTION I - LASIK FUNDAMENTAL PRINCIPLES OF DIAGNOSIS, CORNEAL MAPPING, MECHANISM OF ACTION OF EXCIMER LASERS
CHAPTER 1
CHAPTER 3
UNDERSTANDING REFRACTIVE LASERS
EVALUATION OF THE LASIK FLAP BY CONFOCAL MICROSCOPY
Therapeutic Principles of Excimer Lasers Advances in Excimer Laser Technology Scanning Lasers Eye Tracking Systems How the Corneal Tissues are Affected in LASIK vs Incisional Keratotomy
1 2 2 6
Contents
Section 1 Frequent Problems With the Flap What is Confocal Microscopy? Confocal Microscopy Procedure Results The Importance of Confocal Microscopy to the Sands of Sahara’s Syndrome How to Prevent Sands of Sahara Syndrome
6
CHAPTER 2
Section 2
61 61 62 62
Section 3
63 63
Section 5
Section 4
Section 6
FUNDAMENTALS ON CORNEAL TOPOGRAPHY
CHAPTER 4 Section 7
PREDICTIVE FORMULAS FOR LASIK
Introduction: Human Optics and the Normal Cornea 9 Instruments to Measure the Corneal Surface 10 Causes of Artefacts of the Corneal Topography Map 14 Understanding and Reading Corneal Topography 15 Topographic Scales 16 Computer Displays: Presentation of Topographic Information 16 Special Software Applications and Displays 23 ATLAS OF CORNEAL TOPOGRAPHY 31-42 TOPOGRAPHERS NOW AVAILABLE 43
The Predictive Formulas Main Components Developing Individualized Predictive Formulas The Healing Pattern of the Cornea Excimer Laser Ablation Nomograms for: Photorefractive Keratectomy LASIK Predictive Formulas for LASIK with: VISX S2 SmoothScan Chiron Technolas 116 Technolas 217 Excimer Laser
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65 65 65 66 66 67 68 69 70
Subjects Index Help ?
CONTENTS
SECTION II - LASIK HIGHLIGHTS OF SURGICAL INSTRUMENTATION (MICROKERATOMES) AND SURGICAL TECHNIQUES CHAPTER 5
CHAPTER 9
MICROKERATOMES
LIMITATIONS AND CONTRAINDICATIONS OF LASIK
Different Mechanical Components Applanation Lenses Tonometer Guidelines for Microkeratome Use Astigmatism Inductions by Hinge Ablation Free Cap The Main Microkeratomes: Outline Description How to Use Them
78-80 80 80 80 86 87 87-99
Preoperative Evaluation Special Cases LASIK after IOL Implantation Bilateral Simultaneous vs. Sequential Surgery LASIK after RK Alternatives to LASIK PRK Refractive Lensectomy Phakic Intraocular Lens Thermokeratoplasty (LTK)
127 134 134 134 134 135 135 135 136 136
CHAPTER 6 AUTOMATIC CORNEAL SHAPER
Contents
CHAPTER 10 Note from the Editor-in-Chief Different Components & Instrumentation Surgical Technique Step by Step Troubleshooting Care, Handling & Sterilization
101 101-3 104-5 105 107
Section 2 Patient Selection PREOPERATIVE PREPARATION The Patient The Instruments The Laser The Keratome The Surgeon PREPARATION IN OPERATING ROOM Draping Speculum Positioning the Patient THE LASIK PROCEDURE Marking Placement of the Suction Ring The Microkeratome Cut Laser Ablation Replacing the Flap Intraoperative Bleeding in LASIK Postoperative Care Home Care Instructions
CHAPTER 7 DOWN UP LASIK Setting up of the Hansatome Care, Maintenance & Sterilization Troubleshooting Surgical Technique Step by Step Advantages & Disadvantages
109 112 114 114 114
CHAPTER 8 ALL LASER LASIK With the Pulsion FS Laser Preoperative Evaluation Surgical Logistics Surgical Technique Step by Step Postoperative Care
Section 1
LASIK SURGICAL TECHNIQUE
119 120 120-4 125
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139 140 140 140 140 141 142 142 142 142 143 143 143 143 144 145 146 148 150 150
Section 3 Section 4
Section 5
Section 6 Section 7 Subjects Index Help ?
CONTENTS Maintain Consistent Hydration Perform the Appropriate Ablation Prevent and Remove Debris from Beneath the Flap Properly Align the Flap Achieve Good Flap Adhesion Avoid and Treat Loose Epithelium Conclusion
CHAPTER 11 PEARLS IN LASIK TECHNIQUE Patient Counseling Achieving Adequate Exposure Achieve and Confirm Adequate Suction Create a Complete Flap
151 151 152 153
153 154 155 156 157 157 158
SECTION III LASIK IN COMPLEX CASES
Compound Myopic Astigmatism 188 Simple Hyperopic Astigmatism 188 Compound Hyperopic Astigmatism 188 Mixed Astigmatism 189 Negative Cylinder Ablation to Treat Mixed Astigmatism 189 Positive Cylinder Ablation to Treat Mixed Astigmatism 190 Bitoric Ablation to Treat Mixed Astigmatism 190 Results of Lasik in Mixed Astigmatism 192 Conclusion 192
CHAPTER 12 LASIK FOR HYPEROPIA Technique, Safety and Efficacy 161 Hyperopic Correction using the Excimer Laser 162 Patient Selection and Preoperative Considerations163 Technique 164 Clinical Results 164 Secondary Hyperopia 165 Hyperopia with Astigmatism 165
CHAPTER 15
CHAPTER 13
Section 1
RELASIK LASIK FOR IRREGULAR ASTIGMATISM Etiology of Irregular Astigmatism Diagnosis Clinical Classification Corneal Topography Patterns 1. Irregular astigmatism with defined pattern 2. Irregular astigmatism with undefined pattern Preoperative Evaluation Treatment of Irregular Astigmatism Surgical Techniques with Excimer Laser Automated Anterior Lamellar Keratoplasty Intracorneal Ring Segments (INTACS) Other Non-Surgical Procedures Contact Lens Management
Procedure Results Discussion
169 170 170 170 170
CHAPTER 16
171 171 175 175 184 184 184 184
187 187
ix
Section 7 Subjects Index Help ?
LASIK AFTER PENETRATING KERATOPLASTY
LASIK IN MIXED ASTIGMATISM
Section 4
Section 6 201 202 203 204
CHAPTER 17
Eligible Patients Timing of Surgery Surgical Technique Postoperative Treatment Risks and Possible Complications Results Conclusions
Section 3
Section 5
LASIK AFTER RK AND PRK
CHAPTER 14
Classification Simple Myopic Astigmatism
Section 2 195 196 198
Results of LASIK After RK and PRK RK Group PRK Group Discussion
Contents
208 208 209 209 210 210 212
CONTENTS
CHAPTER 18 LASIK AFTER PREVIOUS CORNEAL SURGERY General Considerations After RK Residual Myopia After RK Hyperopia After RK The Cornea After RK LASIK AFTER RK Preoperative Considerations Contraindications lntraoperative Considerations Results (Pilot Study) LASIK AFTER AK The Cornea After AK Performing LASIK After AK Preoperative Considerations lntraoperative Considerations Results (Pilot Study) LASIK AFTER PRK The Cornea After PRK Performing LASIK After PRK Preoperative Considerations Intraoperative Considerations Postoperative Treatment Results (Pilot Study) LASIK AFTER LTK The Cornea After LTK Performing LASIK After LTK Preoperative Considerations
215 215 216 216 216 217 217 217 218 218 219 219 220 220 220 220 220 221 221 221 222 222 223 223 223 223
lntraoperative Considerations Results (Pilot Study) LASIK AFTER PKP Performing Excimer Laser After PKP Preoperative Considerations Indications High Risk Cases & LASIK Contraindications Preoperative Medications When to Operate Intraoperative Considerations Conclusions LASIK AFTER ALK The Cornea After ALK Performing LASIK After ALK Preoperative Considerations Intraoperative Considerations Conclusions LASIK AFTER EPIKERATOPHAKIA
224 224 225 226 226 227 227 227 228 229 229 229 229 229 229 230 230 230
LASIK AFTER CORNEAL TRAUMA
230
FUTURE OF LASIK AFTER OTHER CORNEAL SURGERIES
230
CHAPTER 19 PEDIATRIC LASIK Patient Selection Surgical Technique Ablation Parameters Results
Contents
234 234 234 235
Section 1
Section 2 Section 3 Section 4
SECTION IV
Section 5
LASIK COMPLICATIONS
Section 6 Section 7 Subjects Index
CHAPTER 20
CHAPTER 21
FIRST NON-INVASIVE TREATMENT FOR SUBLAMELLAR EPITHELIAL INGROWTH AFTER LASIK BY LOCAL FREEZING
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
Sequence of Events Management Techniques Presently Available The New Non-Invasive Method Technique Step by Step Results
Incidence - Relation to Multiple Variables Classification Intraoperative Complications Early Postoperative Complications Late Postoperative Complications
243 243 243 244 245
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247 247 247 250 253
Help ?
CONTENTS
CHAPTER 26
CHAPTER 22 FLAP COMPLICATIONS Diminishing Complications with New Microkeratomes Classification of Complications I) Intraoperative II) Early postoperative period III) Late postoperative period Management of Variety of Flap Complications Sands of Sahara Syndrome Dry Eye Syndrome Epithelial Ingrowth The Hansatome (“Down-Up”) Microkeratome Main Advantages and Disadvantages Cleaning of the Instrument PEARLS TO ASSIST WITH THE MAKING OF A GOOD FLAP
INFLAMMATORY AND INFECTIOUS COMPLICATIONS AFTER LASIK 267 267 267 267 267 267-73 272 273 273 274 274 275 275
CHAPTER 23 FOLDS AND STRIAE OF THE DISC POST LASIK Definition Treatment of: Folds Striae Surgical Technique
INFECTIOUS KERATITIS FOLLOWING LASIK Clinical Findings Causative Organisms Diagnosis & Differential Diagnosis Treatment Prognosis Prevention
297 297 299 300 301 302 303
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
277 280
INTRAOPERATIVE COMPLICATIONS Flap Complications Ablation Complications POSTOPERATIVE COMPLICATIONS
280
TREATMENT OF FLAP STRIAE 284 284 284 285 285 286
307 307 309 311
Contents
Section 1
Section 2 Section 3 Section 4
CHAPTER 28
Section 5
VITREORETINAL COMPLICATIONS OF REFRACTIVE SURGERY
Section 6 Section 7 Subjects Index
Preoperative Evaluation Indications for Prophylaxis of Retinal Breaks and Degenerations Theoretical Mechanisms Resulting in Retinal Breaks and Detachment Anterior Chamber Shallowing Vitreoretinal Complications of PRK & LASIK Retinal Detachment After PRK Retinal Detachment After LASIK Macular Hemorrhage Nerve Fiber Layer Damage Endophthalmitis Dislocated Intraocular Lenses
CHAPTER 25 KERATECTASIA INDUCED BY MYOPIC LASIK Corneal Stromal Changes Induced by LASIK Corneal Evaluation Using the Orbscan Topography System How the Orbscan Helps Evaluating High Risk Cases for LASIK and FFK
293 293 294 294 295-96 296 296 297
CHAPTER 27
CHAPTER 24
SURGICAL TREATMENT Massaging the Flap Using: a) A Spatula over a Contact Lens b) Direct Massaging Appearance of the Cornea After Treatment Outcome
DIFFUSE LAMELLAR KERATITIS (DLK) SYNDROME (SANDS OF SAHARA) Causative Agents Clinical Findings DLK Staging Diagnosis &Differential Diagnosis Treatment Prevention Conclusions
287 288
291
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317 Help ?
317 318 318 319 319 319 320 321 321 321
CONTENTS
SECTION V BEYOND CONVENTIONAL LASIK Corneal Custom Ablation Guided by Wavefront Mapping
CHAPTER 29
CHAPTER 32
REFINING CUSTOM ABLATION THROUGH WAVEFRONT MAPPING
WAVEFRONT ANALYSIS AND CUSTOM ABLATION
Wavefront Analysis Mapping a Profile of the Whole Eye Development of Wavefront Technology The Mechanisms of Wavefront Devices Benefits of Wavefront Analysis Linking Diagnostic Information from Wavefront Mapping to Laser Treatment Wavefront Analysis in Conjunction with Corneal Topography Personalized LASIK Nomograms
Promising Achievements Principle of Wavefront Analysis Availability of Technology Custom Intraocular Lens Goal in Mind
325 325 325 328 329 329
CHAPTER 33 331
THE ROLE OF DIFFERENT ABERRATIONS IN WAVEFRONT ANALYSIS
331
What Do We Mean by Wavefront Sensing Analysis? What do we Understand as an Aberration of the Optical System? How Do Different Aberrations Affect Vision in Humans? Do Aberrations Contribute to Sight in Any Positive Way? Principles for the Study and Diagnosis of Aberrations
CHAPTER 30 COMPUTERIZED CORNEAL TOPOGRAPHY AND ITS IMPORTANCE TO WAVEFRONT TECHNOLOGY Corneal Topography and Wavefront Analysis Current Status of Custom Ablation
339 339 340 340 340
333 334
341 341 343 343
Contents
Section 1
Section 2 Section 3
344 Section 4
Section 5
CHAPTER 34
Section 6
REFRACTION EVALUATION SYSTEMS FOR WAVEFRONT ANALYSIS
CHAPTER 31 CUSTOMIZED CORNEAL ABLATION THROUGH WAVEFRONT MAPPING The Quest for Bionic or Super Vision Promising New Technology Attaining Bionic or Super Vision Generating the Wavefront Map Wavefront Analysis & Corneal Topography
What is Wavefront Technology? Current Ocular Refraction Evaluation Systems Phoroptor and Autorefractors Corneal Topography 20/10 Perfect Vision Wavefront System Other Wavefront Sensing Devices How the Visx 20/10 Wavefront System Works How to Read a Wavefront Map The Shortcomings of Shack-Hartmann Wavefront Analysis Clinical Examples
337 337 337 338
xii
347 349 349 349 349 349 351 353 355 357-69
Section 7 Subjects Index Help ?
CONTENTS Technical Development of PALM Technique
CHAPTER 35 ZYOPTIX PERSONALIZED LASER VISION CORRECTION Performing Zyoptix Treatment Orbscan II (Elevation Topography) The Zywave Aberrometer Bausch & Lomb Technolas 217z Excimer Laser Zyoptix Patient Case
CHAPTER 38 CUSTOMIZED ABLATIONS IN LASIK 373 374 374 375
Present Role of Customized Ablations Technique of TopoLink Examples of Uses of TopoLink Results of TopoLink in Repair Procedures The Bausch & Lomb Aberrometer Wavefront-Deviation Guided LASIK
377
CHAPTER 36 ZYOPTIX Preoperative Procedure Zywave Aberrometer Elevation Topography (Orbscan) Zylink Preparing the Laser Treatment Advantages & Disadvantages Clinical Cases
401 402 402 407 409 411
CHAPTER 39 379 380 386 386 389 391 391 391-3
WAVEFRONT MEASUREMENTS OF THE HUMAN EYE WITH HARTMANN-SHACK SENSOR
Principles of Eye Aberration Measurements with the Hartmann-Shack Sensor Present Technologies for Optimizing Visual Acuity through Refractive Surgery
CHAPTER 37 LASIK – PALM The PALM Gel The PALM Procedure
399
A Look into the Future of Refractive Surgery
396 398
413 Contents
417
Section 1 417
Section 2 Section 3 Section 4
SECTION VI
Section 5
LASIK IN PRESBYOPIA
Section 6 Section 7
CHAPTER 41
CHAPTER 40
PRESBYOPIA
PRESBYOPIA
Theories of Accommodation Treatment with Optical Devices Surgical Methods SCLERAL TECHNIQUES Anterior Ciliary Sclerotomy (ACS) (Thornton’s Technique) Scleral Expansion Band - Schachar´s Technique INTRACORNEAL TECHNIQUE Intracorneal Implants INTRAOCULAR TECHNIQUES LASER TECHNOLOGY TECHNIQUES
Surgical Correction - Current Trends Surgery for Management of Presbyopia through MONOVISION The LADARVision Laser for Myopia and Presbyopia Hyperopia and Presbyopia Emmetropia with Presbyopia Description of Operations on the Sclera to Improve Presbyopia
Subjects Index
427 427 427 428 428
xiii
Help ?
436 437 438 439 439 439 441 441 441 444
CONTENTS
SECTION VI I ALTERNATIVES TO LASIK
CHAPTER 42 NO ANESTHESIA CATARACT / CLEAR LENS EXTRACTION NUCLEUS REMOVAL TECHNIQUES Karate Chop Soft Cataracts Agarwal Chopper Step by Step Technique NO ANESTHESIA CLEAR LENS EXTRACTION Step by Step Technique
451 451 452 452 452-57 458 458-62
Three Basic Styles of Phakic IOL'S ANTERIOR CHAMBER PHAKIC IOL'S THE ARTISAN LENS Step by Step Technique THE NU-VITA ANTERIOR CHAMBER LENS Step by Step Technique POSTERIOR CHAMBER PLATE LENSES THE BARRAQUER PRE-CRYSTALLINE LENS Step by Step Technique THE POSTERIOR CHAMBER FOLDABLE PLATE PHAKIC LENS (The Implantable Contact Lens) Step by Step Technique
471 472 472 473-80 481 481-82 485 485 485-91 492 492 492-97
CHAPTER 43 CHAPTER 45
PHAKONIT AND LASER PHAKONIT Phakonit to Correct Refractive Errors TECHNIQUE OF PHAKONIT FOR CATARACTS Surgical Technique Step by Step PHAKONIT IN CLEAR LENS EXTRACTION Surgical Technique Step by Step
LASIK vs PHAKIC LENS IMPLANTATION TO CORRECT MYOPIA
463 454
Section 1
464-66 467 468
CHAPTER 44 PHAKIC IOL's - SURGICAL MANAGEMENT OF HIGH MYOPIA Limitations of LASIK in Very High Myopia The Important Role of Phakic Intraocular Lenses Contributions of Phakic IOL's Advantages Over Corneal Refractive Surgery Limitations of Phakic IOL's
Contents
Surgical Technique: Ophtec Artisan Myopia Implant Surgical Technique: LASIK The Study: Ophtec Artisan Myopia Implant vs. LASIK Results
499 503 507 508
Section 2 Section 3 Section 4
Section 5
Section 6
CHAPTER 46
469
Section 7
INTACS TM REFRACTIVE CORRECTION WITH AN INTRACORNEAL DEVICE
469 469 470
Surgical Procedure Clinical Outcomes Safety Assurance and Further Indications
470
xiv
514 514 519
Subjects Index Help ?
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Help ?
Zyoptics, Personalized Laser Visual Correction UNDERSTANDING REFRACTIVE LASERS
Chapter 1 UNDERSTANDING REFRACTIVE LASERS Benjamin F. Boyd, M.D., F.A.C.S.
Therapeutic Principles of Excimer Lasers The most significant advance in the past three years has been the emergence of the excimer laser and its rapid rise to dominate refractive corneal surgery. The excimer laser is a source of energy that is very difficult to control and apply to the human eye with the assurance of safety.
Harnessing this laser to safely perform corneal surgery has been a major technical achievement. The argon fluoride (ArF) 193 nanometer excimer laser is a pulsed laser that has wide potential because it can create accurate and very precise excisions of corneal tissue to an exact depth with minimal disruption of the remaining tissue. Fig. 1-1 presents the comparative mechanisms of the excimer laser vs various other lasers commonly used in ophthalmology.
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Section 6 Figure 1-1 Comparative Mechanisms of the Various Lasers Used in Ophthalmology
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(1) The argon and krypton lasers em- Subjects Index ploy a thermal mechanism whereby the laser (L) heats the chorioretinal photocoagulated tissue and produces scarring (arrow). Retina (R), choroid (H) and pigment epithelium (E). (2) The YAG laser works by photodisruption of tissues, creating small acoustical explosions that produce openings (arrow) such as we make in posterior capsulotomy (P). A plasma screen Help ? of ions (+ and -) is created. (3) Excimer ultraviolet laser works by photoablation. Small amounts of tissue (T), essentially the stroma in cases of LASIK, are removed from the cornea (C - arrow) with each pulse. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 1-2: Excimer Laser - Effects on the Tissue The high intensity energy of ultraviolet light from an excimer laser during tissue ablation breaks inter and intramolecular bonds, causing the molecules of the area of ablation to explode away from the surface. Please observe that there is minimal disruption of the remaining surrounding tissue. (After Boyd´s "Atlas of Refractive Surgery").
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Ophthalmic excimer lasers use ultraviolet radiation at a wavelength of 193 nanometers. It is a wavelength that practically does not heat the tissue but actually breaks inter- and intra- molecular bonds. The molecules in the area of ablation explode away from the surface (Fig. 1-2). The concept of ablative surgery is that by removing small amounts of tissue from the anterior surface of the cornea (Fig. 1-3) a significant change of refraction can be attained. The effect in myopes is achieved by flattening the anterior dome of the central cornea over a 5 mm disc shaped area.
ADVANCES IN EXCIMER LASER TECHNOLOGY Scanning Lasers As pointed out by Peter McDonnell, M.D., Professor and Chair, Department of Ophthal2
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mology, University of California, Irvine, and Professor of Ophthalmology and Director of Refractive Surgery at the Doheny Eye Institute, University of Southern California at Los Angeles, in most parts of the world broad beam lasers still predominate in the laser market (Fig. 1-3). Recently, however, scanning or flying spot lasers have gained attention. Instead of using an iris diaphragm to control a broad beam, some scanning lasers use a small slit that is scanned across the corneal surface (Fig. 1-4). Flying spot is another type of scanning laser. Instead of a slit that scans the surface , flying spot lasers (Fig. 1-5) have a small circular or elliptical spot perhaps 1 mm to 2 mm in diameter that is moved across the surface of the cornea by computercontrolled galvanometric mirrors. Advantages of Scanning Lasers Scanning lasers (Figs. 1-4 and 1-5) have several potential advantages over broad beam
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Figure 1-4 (below): Concept of the Scanning Type Laser for Refractive Surgery Another type of excimer laser uses a scanning laser beam. The laser beam (L1) strikes a moving mask (M-arrow) which has a slit through which the beam passes (L2) in a predetermined fashion. More ablation occurs centrally (C) and less peripherally (P) to achieve the desired corneal reshaping. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 1-3 (above): Concept of Broad Beam Laser Application for Refractive Surgery
Section 2 The most common type of excimer laser is the broad beam laser (L1). The method of application uses a widening diaphragm or pre-shaped ablatable mask (M) through which the laser beam (L2) passes. To produce more ablation of the cornea in the center (C) than in midperiphery (P), the thinner central portion of the mask allows the laser to ablate the central cornea longer. As the disk is ablated in a peripheral direction (arrows), the cornea is shaped accordingly in a desired gradient fashion.(After Boyd´s "Atlas of Refractive Surgery").
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Figure 1-5 (left): Concept of the "Flying Spot" Scanning Laser Application for Refractive Surgery
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A third type of excimer laser application is known as the "flying spot". A small laser beam (L) moves across the cornea (arrow) in a predetermined, computer driven pattern to ablate more tissue centrally (C) than in the mid-periphery (P). This type of laser application is very flexible with regard to the type of ablation pattern that can be applied. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 1-6: Flexibility of the "Flying Spot" Scanning Laser May Provide Customized Ablation The "Flying Spot" type excimer laser has an advantage over other broad beam and slit scanning lasers by providing increased flexibility in the ablation profile. The profile can be altered to provide aspheric as well as spherical ablations. The mid-peripheral cornea (red shaded area-P) can be treated with the laser (L) to produce a different curvature than that of the central cornea (D - blue line shaded area). This allows the possibility of a customized ablation unique for every cornea. A lamellar corneal flap (B) is retracted. (After Boyd´s "Atlas of Refractive Surgery").
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lasers (Fig. 1-3). The postoperative corneal surface may be smoother, resulting less often in a healing response which can progress to corneal haze or opacity. A higher quality of vision and improved visual acuity may also result from the smoother and more uniform corneal surface when using scanning lasers. McDonnell emphasizes that another possible advantage of scanning technology is increased flexibility in the ablation profile or algorithm. The profile can produce aspheric rather than only spherical ablations (Figs. 1-6 and 1-7). Larger diameters of ablation can be made. The possibility of using topographical maps of the cornea to guide the ablation is a distinct advantage, which will allow for more flexibility in treating astigmatism. Some patients do not have perfect symmetry of the cornea, particularly those with surgically induced astigmatism after penetrating keratoplasty or cataract surgery, or those with keratoconus. Broad beam lasers do not take the asymmetry of irregular astigmatism into account; they treat all corneas the same. The scanning technology allows the possibility of a customized ablation that is unique for every cornea (Fig. 1-7). 4
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(Note from the Editor in Chief: this flexibility of ablating different profiles in the same cornea is being utilized by some surgeons to create or "sculpt" the so-called "multifocal cornea" which is a significant step forward when it works but of increased risk to the patient's quality of vision when even a minor error in the sculpting occurs. This procedure is experimental). It may even be possible to improve upon the naturally occurring corneal surface, with improvement in best corrected visual acuity, bringing patients who are 20/20 with correction preoperatively to 20/15 uncorrected postoperatively. We still need more experience to know more definitively whether scanning lasers can actually fulfill their early promise. Currently Available Scanning Lasers Several companies are now working on developing scanning lasers. Chiron (now a division of Bausch & Lomb) has the Technolas laser. Autonomous Technologies, recently purchased by Summit, the company that manufactured one of the first broad beam lasers, also manufactures a superior quality scanning laser. This indicates
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Section 4 Figure 1-7: Concept of Spherical vs. Aspherical Ablation Profile as Obtained by the "Flying Spot" Type Laser This cross section of the anterior globe compares a spherical ablation profile (S) to an aspherical profile (A). A spherical treatment results in a corneal surface (1) which has the same radius (R1) throughout its curvature. The common center of the spherical curvature is shown at (C1). By comparison an aspherical ablation profile, made possible by the "flying spot" type excimer laser, is defined as one which has varying curvatures across the treatment zone. In the aspherical example (A), the central curvature (2) has longer radius (R2) than the mid-peripheral curvature (3), which has shorter radius (R3). The centers of curvature for the two areas of the cornea are different (C2 and C3). The curvature change between these two areas is gradual. Thus, the central cornea has a "flatter" curvature than the mid-peripheral cornea in this case. The dotted line represents the pre-op corneal curvature. (After Boyd´s "Atlas of Refractive Surgery").
that they believe the future of lasers is in scanning technology. The Japanese company Nidek and the U.S. company LaserSight also manufacture scanning lasers. The Nidek laser involves a slit that can be moved across the surface like the rectangular beam of a slit lamp . The Meditec is similar. The Visx laser has recently been modified ("Smooth Scan") to achieve a scanning effect. Although it is a broad beam laser, the smooth scan modification allows the broad beam to be broken up into individual beams that scan
the surface. It is predicted that the smoother ablation that results will improve results of surgery. McDonnell explicitly adds, however, that improved surface smoothness has yet to be proven in a prospective, randomized trial to translate into improved visual acuities. The Nidek and Autonomous lasers are now commercially available, with recent approval by the U.S. Food and Drug Administration (FDA). Other scanning lasers, such as the Technolas and LaserSight are now approved in USA by FDA. LASIK AND BEYOND LASIK
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Figure 1-8: Concept of Eye Tracking For More Accurate Corneal Ablations During Movements of the Eye New eye tracking technology can trace eye movements by detecting displacement of the pupil. In microseconds the eye tracking computer can move the treatment spot of an Excimer laser beam appropriately to compensate for these eye movements. For example, laser beam (LA) is treating an area of the cornea when the eye is in position (A). Suddenly, during treatment, the eye moves slightly to the left to position (B). The eye tracking computer detects the movement of the pupil to the left (dotted circle) and commands the laser to track left (LB) the same amount, within microseconds. Thus the laser continues treating the same area of the cornea as desired before the eye movement took place. Such technology aims to increase the accuracy of the desired ablation and resulting correction. (After Boyd´s "Atlas of Refractive Surgery").
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Eye Tracking Systems Another advantage of the scanning lasers is that they can be used in combination with eye tracking technology and computer controlled mirrors (Fig. 1-8) to move the spot automatically in microseconds to compensate for eye movements. At least theoretically, such a laser is not dependent on absolute fixation and can thereby improve the quality of the surface. As described by McDonnell, landmarks are identified at the beginning of the procedure. Without eye-tracking systems, if the patient looks slightly away from the fixation target while a broad beam laser is being used, the surgeon must quickly release the foot pedal and stop the ablation. With eye tracking technology, however, the laser immediately registers the movement of the eye and moves the spot accordingly without interrupting the surgery. Technologically, some of these eye tracking devices are quite impres6
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sive. Even if a patient moves considerably, the ablation spot can be placed perfectly. Autonomous Technologies, Nidek, LaserSight and several other companies now manufacture eye tracking systems. Proof that these trackers improve surgical outcomes is still to be established, according to McDonnell. Data have not yet shown that the eye tracker prevents decentration, or results in improved vision compared to results from a broad beam laser without eye tracking capacity.
How the Corneal Tissues are Affected in LASIK vs Incisional Keratotomy With excimer ablation in LASIK (laser in situ keratomileusis) and PRK (Photorefractive Keratectomy) most of the tissue is removed from the central part of the cornea. The ultraviolet light has so much energy that it smashes the inter- and intra-molecular bonds, ejecting the
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Figure 1-9: How Corneal Tissues are Affected with Different Refractive Techniques In this figure, you will clearly observe the differences in corneal tissue invasion comparing incisional keratotomy to laser in situ keratectomy (LASIK). (A) This cross section view of the cornea shows the tissue penetration of the diamond knife in RK with a deep incision of 500 microns reaching down close to Descemet's. The space shown between the arrows demonstrates the thin, untouched and intact corneal area. The corneal tissue strength is significantly weak and unstable because of the radial cuts. (B) This represents the corneal depth reached in LASIK by the excimer laser in a patient with -8.00 (myopic) diopters. The higher the myopia, the larger the ablation but limited by Jose Barraquer's thickness law. In this case the ablation depth reaches 240 microns (160 microns: corneal flap + 80 microns: stromal laser ablation). The rest of the corneal stroma is untouched (between arrows). (After Boyd´s "Atlas of Refractive Surgery").
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molecules at high speed (Fig. 1-2). Tissue ablation in LASIK reaches an average of 250 microns (Fig.1-9 B) from the original surface of the cornea. On the other hand, during incisional keratotomy (radial keratotomy for myopia and astigmatic keratotomy for astigmatism) the depth of incision into the corneal stroma reaches down to 500 microns, close to Descemet's membrane and almost 90% of the corneal thickness (Fig. 1-9-A). This major difference between the two techniques reveals how the stroma is significantly weakened in incisional keratotomy thereby affecting the strength and stability of the globe. LASIK involves no heat damage, no permanent scarring, not even a thermal effect.
In the long run, RK patients carry two swords of Damocles over their heads. One is the threat of a blow to the eye severe enough to cause a rupture. The RK patient is always more susceptible to rupture because the corneal scars will never be as strong as the original cornea. The second threat is that these scars apparently stretch or relax with time, which may give the patient more effect than the original result. An undercorrected patient moves toward a better result, but a properly corrected or overcorrected patient moves into hyperopia, and can become quite farsighted.
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FUNDAMENTALS ON CORNEAL TOPOGRAPHY
Chapter 2 FUNDAMENTALS ON CORNEAL TOPOGRAPHY Guillermo L. Simón.M.D. , Sarabel Simón, M.D., José Mª Simón, M.D., Cristina Simón, M.D.,
Introduction: Human Optics and the Normal Cornea The cornea is the highest diopter of human eye, accounting alone for about 43-44 diopters at corneal apex (about two thirds of the total dioptric power of the eye). It has an average radius of curvature of 7,8 mm. A healthy cornea is not absolutely transparent: it scatters almost 10 % of the incident light, primarily due to the scattering at the stroma. The corneal geography can be divided into four geographical zones from apex to limbus, which can be easily differentiated in colour corneal videokeratoscopy : 1- The central zone (4 central millimeters): it overlies the pupil and is responsible for the high definition vision. The central part is almost spherical and called apex. 2- The paracentral zone: where the cornea begins to flatten 3- The peripheral zone 4- The limbal zone Refractive surgery refers to a surgical or laser procedure performed on the cornea, to alter its refractive power. The major refractive component of the cornea being its front surface, it is not difficult to understand that most refractive techniques have involved this frontal surface (PRK, radial keratotomies, …). Nevertheless, posterior surface of the cornea also accounts, and that is the reason why a “posterior surface corneal topographer” like the Orbscan™ - Bausch & Lomb® was developed by Orbtek®, in the race for a more precise refractive surgery.
The cornea of an eagle is almost as transparent as glass: there is almost no scattering of incident light. That alone explains the resolution of an eagle eye being much better than ours. As we are never satisfied, we are now developing new tools and exContents tremely promising laser surgical techniques that have proven to increase human being visual acuity by re- Section 1 ducing corneal aberrations: we reduce diopters and Section 2 also improve visual acuity. The new dream is “super-vision”. Topographic and aberrometer-linked Section 3 LASIK are on the way to achieve this goal of betterSection 4 than-normal vision. Bausch & Lomb®’s Zywave™ combines topography and wavefront measurements Section 5 to achieve customized computer controlled flying spot excimer laser ablation, which appears to be fun- Section 6 damental in treating irregular astigmatisms or retreatSection 7 ing unsatisfied LASIK patients to regularize the corneal shape. Regularizing the corneal shape has the Subjects Index theoretical advantage of improving the quality of vision by means of reduction of halos, glare and any other optical aberrations. We are on the way to achieve an aberration-free visual system, though the influence of all other dioptric surfaces (vitreous, lens, …) and interfaces still has to be ascertained. In this chapter we will try to introduce the Help ? novice to this interesting new world of instruments recently developed due to the advent of refractive corneal surgery. We have tried to show different maps from different systems, trying to make an interesting basic atlas of corneal topography. Corneal maps of rare cases and complications can be found in the different chapters of this book. Please refer to them for better knowledge. There is no perfect system to assess true corneal surface shape, but we still have to rely on the instruments we have, waiting for new
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instruments and methods being developed for better accuracy. With that goal in mind BioShape AG® has developed the EyeShape™ system, based on a principle called fringe projection. Patterns of parallel lines are first imaged onto a reference and then onto the surface to be measured. Detection of the lines with a digital camera under a tilted angle yields distorted line patterns. The deviation of the detected lines from the original lines together with the tilt make it possible to calculate the absolute height at any point on the surface of the cornea (or not).
Instruments to Measure the Corneal Surface The normal corneal surface is smooth: a healthy tear film neutralizes corneal irregularities. The cornea, acting as a convex “almost transparent” mirror, reflects part of the incident light. Different instruments have been developed to assess and measure this corneal reflex. These non contact instruments use a light target (lamp, mires, Placido disks, …) and a microscope or another optic system to measure corneal reflex of these light targets.
1- Keratometry A keratometer quantitatively measures the radius of curvature of different corneal zones of 3 mm (diameter). The present day keratometer allows the operator to precisely measure the size of the reflected image, converting the image size to corneal radius using a mathematical relation r= 2 a Y/y where r : anterior corneal radius a: distance from mire to cornea (75 mm in keratometer) Y. image size y: mire size (64 mm in keratometer)
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The keratometer can convert from corneal radius r (measured in meters) into refracting power RP (in Diopters) using the relationship: RP = 337,5 / r Modern -automated or not- keratometers also known as ophthalmometers directly convert from radius to diopters and inversely. They are mainly used to calculate the power of intraocular lenses through different formulas (Hoffer, SRK-T, SRK-II, Holladay, Enrique del Rio & S. Simón, …). Although the theory of measuring corneal reflex may appear to be simple, it is not, since eye movement, decentration or any tear film deficiency may difficult the measure creating errors. Modern video methods (topographers) can freeze the reflected cornea image, and perform the measurements once the image is captured on the video or computer screen, allowing greater precision. Notice that most traditional keratometers perform measurements of the central 3 mm, while computerised topographers can cover almost the whole corneal surface.
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2- Keratoscopy or Photokeratoscopy
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It is a method to evaluate qualitatively the Section 6 reflected light on the corneal surface. The projected Section 7 light may be a simple flash lamp or a Placido disc target, which is a series of concentric rings (10 or 12 Subjects Index rings) or a tube (cone) with illuminated rings lining the inside surface. When we look at the keratoscope, an elliptical distortion of mires suggest astigmatism, and small, narrow and closely spaced mires suggest corneas that have high power (steep regions or short radius of curvature). The use of keratoscopes is being abandoned Help ? in favour of computerised modern topographers which allow qualitative and quantitative measurements of the corneal surface, with higher definition and accuracy (more than 20 rings), and more sensitivity in the peripheral cornea.
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Contents Figure 2-1 : The “ring verification display” in modern videokeratoscopes is a static picture of what the explorer viewed at the keratoscope. Looking at the keratoscope, the explorer is able to evaluate qualitatively the corneal surface. In this case, notice the huge distortion of the mires on the temporal side of a right eye of a patient who underwent a keratoplasty for a keratoconus, and is wearing a soft plano-T therapeutic contact lens. The distortion of the mires is due to an irregularity at contact lens surface: air is in between the cornea and the lens.
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Some of the known deficiencies of the Placido method are: • It requires assumptions about the corneal shape • It misses data on the central cornea (not all topographers) • It is only able to acquire limited data points • It measures slope not height Some more subjective complaints include: • It is difficult to focus and align • In most topographers, the patient is exposed to high light Large Placido disk systems work far away from the eye, while small Placido cones get much closer to the eye. While Placido disk systems easily create shadows caused by the nose and brow blocking the light of the rings, small cone systems fit un-
der the brow and beside the nose, avoiding shadows, Section 7 but can get in contact with large noses and make the patient blink and be afraid. Most small cones have a Subjects Index reputation for difficult focusing: some manufacturers -like Optikon 2000®- have worked out worthwhile automatic capture devices for improved accuracy, precision, and repeatability of measurements.
3- Computerized Videokeratoscopy: Modern Corneal Topographers
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Corneal topography has gained wide acceptance as a clinical examination procedure with the advent of modern laser refractive surgery. It has many advantages over traditional keratometers or keratoscopes: they measure a grater area of the cornea with a much higher number of points and produce permanent records that can be used for followup.
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Figure 2-2: The Placido cone consists of a series of concentric dark and light rings in the configuration of a cone of different sizes depending on the number of rings and the manufacturer. Usually, it is better to have a large number of rings, since more corneal radius values can be measured: notice that while describing the technical characteristics of videokeratographers some manufactures count both clear and dark rings, while others only count light ones. The mires of most systems exclude the very central cornea (where the video camera or CCD is located) and the paralimbal area. Picture shows a large cone of the Haag-Streit® Keratograph CTK 922™ with 22 rings (dark and light rings). (Published with permission from Haag-Streit® AG International).
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Basically, a projection corneal topographer consists of a Placido disk or cone (large or small) that illuminates the cornea by sending a mire of concentric rings, a video camera that captures the corneal reflex from the tear layer and a computer and software that perform the analysis of the data trough different computer algorithms. The computer evaluates the distance between a series of concentric rings of light and darkness in a variable number of points. The shorter the distance, the higher the corneal power, and inversely. Final results can be printed in colours or black-and-white. The Placido disk (Figure 2-2) consists of a series of concentric dark and light rings in the configuration of a disk or a cone, of different sizes, depending on the number of rings and the manufacturer. Usually, it is better to have a large number of rings, since more corneal radius values can be measured. The mires of most systems exclude the very central cornea and the paralimbal area. The reproducibility of videokeratography measurements is mainly dependent on the accuracy of manual adjustment in the focal plane. Videokeratoscopes having small Placido cones show a considerable amount of error when the required working distance between cornea and keratoscope is not maintained. The advantages of small cones (optimal illumination and the reduction of anatomi-
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cally caused shadows) are in no proportion to the Section 2 disadvantage—poor depth of focus, resulting in poor reproducibility. Which one should you choose, a Section 3 small Placido cone or large Placido disk ? Not easy to answer: each family of topographers has advan- Section 4 tages and disadvantages. Being no ideal instrument, Section 5 topographer potential buyers will have to decide upon other important factors, like software ability to ex- Section 6 actly reproduce real corneal height, number of rings, Section 7 price, …. There are two main groups of corneal topog- Subjects Index raphers: those which use the principle of reflection (most), and those which use the principle of projection. Let’s notice that the image captured by most topographers is produced by the thin tear layer covering the cornea that almost reproduces the shape or contour of the corneal surface. Most instruHelp ? ments perform indirect measurements of the corneal surface (reflection technique) and extrapolate to know the height of each point of the cornea. Reflection techniques amplify the corneal topographic distortions. Euclid Systems Corporation® ET-800 uses a completely different method of topography called Fourier profilometry using filtered blue light that induces fluorescence of a liquid that has been applied to the tear film before the examination. This
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projection technique visualizes the surface directly while a reflection technique amplifies the corneal topographic distortions.
Table 1: Advantages and Disadvantages of Projection-Based Systems over Reflection -Based Ones. Advantages: Measurement of direct corneal height Ability to measure: irregular corneal surfaces non-reflective surfaces Higher resolution (theoretical) Uniform accuracy across the whole cornea Less operator dependent Do not suffer from spherical bias Disadvantages: Not standard instruments (most are still prototypes): complex to use need clinical experience validation non standard presentation maps (more difficult to learn)
Figure 2-3: There are different methods of following the clinical course of a corneal ulceration or corneal abscess. While daily slit-lamp examination and daily photographs are invaluable, corneal topographic maps, being less “explorer dependant”, can also be very useful in the follow-up.
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Longer examination time: longer image acquisition time longer image analysis
Section 3 Fluorescein instillation needed (in some, like the Euclid Systems Corporation® ET-800™)
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Table 2: Indications and Uses of Corneal Topographers: The use of computerised Corneal Topography is indicated in the following conditions: 1- Preoperative and postoperative assessment of the refractive patient 2- Preoperative and postoperative assessment of penetrating keratoplasty 3- Irregular astigmatism 4- Corneal dystrophies, bullous keratopathy 5- Keratoconus (diagnostic and follow-up) 6- Follow-up of corneal ulceration or abscess (Figure 2-2). 7- Post-traumatic corneal scarring 8- Contact lens fitting 9- Evaluation of tear film quality 10- Reference instrument for IOL-implants to see the corneal difference before and after surgery 11- To study unexplained low visual acuity after any surgical procedure (trabeculectomy, extracapsular lens extraction, …). 12- Preoperative and postoperative assessment of Intacs™ corneal rings (intrastromal corneal rings)
Table 3: Different Methods of Measuring Corneal Surface Used by Modern Corneal Topographers Placido systems (small cone or large disk) are the most popular
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Placido cone with arc-step mapping (Keratron™ from Optikon 2000®) Placido disk with arc-step mapping (Zeiss Humphrey® Atlas™) Slit-lamp topo-pachimetry (Orbscan™ - Bausch & Lomb®) Fourier profilometry (Euclid Systems Corporation® ET-800™)
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Fringe projection or Moiré interference fringes (EyeShape® from BioShape AG™) Triangulation ellipsoid topometry (Technomed™ colour ellipsoid topometer) Laser interferometry (experimental method, it records the interference pattern generated on the corneal surface by the interference of two lasers or coherent wave fronts)
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Figure 2-4: Trichiasic cilia projects a shadow that may interfere with the mapping. This situation should be addressed prior to corneal topography.
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Section 4 Figure 2-5: Ptosis or non-sufficient eye opening because of induced photophobia or patient anxiety limits and distorts the mapping of the cornea. Notice that the map is not round but oval.
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Causes of Artefacts of the Corneal Topography Map: a- shadows on the cornea from large eyelashes or trichiasis (Figure 2-4). b- ptosis or non-sufficient eye opening (Figure 2-5)
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c- irregularities of the tear film layer (dry eye, mucinous film, greasy film) d- too short working distance of the small Placido disk cone e- incomplete or distorted image (corneal pathology) (Figure 2-6)
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Figure 2-6: An advanced corneal herpetic keratopathy produces an irregular completely distorted corneal map in which no regular pattern can be identified. Notice that the low-vision patient is unable fixate the fixation light.
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Understanding and Reading Corneal Topography The meaningful interpretation of topographic maps requires the examiner to have detailed knowledge and clinical experience on the patterns detailed in them. At first, one must understand how to read the colour scales. The untrained eye may find some confusion and sometimes misinterpretation in evaluating corneal maps. Modern topographers
(videokeratographers) use the Louisiana State University Color-Coded Map to display corneal superficial powers. The power values (measured in diopters) are preferred by clinicians over the radius values (measured in millimeters), although all topographers can map the corneas using both values. Projection-based topography systems, adopted a similar colour scale to represent their height maps. High areas are depicted by warm colours, while low areas are depicted by cool colours.
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The Louisiana State University Color-Coded Map Colours correspond to the following:
Cool colours (violets and blues): low powers. They correspond to flat curvatures (low diopter)
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Greens and yellows: colours found in the normal corneas
Warm or hot colours (oranges and reds): higher powers. They correspond to steep curvatures (high diopter).
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Facing a corneal topography, care has to be taken to interpret coloured maps, since scales (and sometimes colour coding) can be modified in most topographers’ software. For patient examination manufacturer sets default values which are operator adjustable (diopter interval, radius interval). When operator adjusts the values to new parameters, colour scales are modified. Rare are the topographers that directly measure the corneal elevation: most act by extrapolation from corneal curvature and power at each measured point. The Optikon 2000® Keratron™ is one of those systems that accurately maps aspheric surfaces by means of its own method of arc-step mapping. The range of powers found in the normal cornea range from 39 D found at peripheral cornea, close to the limbus, to 48 D found at corneal apex. The colours do not always represent an elevation map, they correspond to curvature values. Therefore, the cornea is most curved towards the centre (green) and flattens out towards the periphery (blue). The nasal side becomes blue more quickly, indicating that the nasal cornea is flatter than the temporal. Some advanced instruments like the Optikon2000® Keratron™, are able to directly represent a coloured elevation map. Apart from colour maps, most topographers also display values of simulated keratometry, that should be equivalent to those obtained by a keratometer. Simulated keratometry values are obtained form the radius values at the corneal position (3 central millimeters) where the reflection from the keratometer mires would take place.
Topographic Scales: Two basic scales are commonly used: absolute and relative.
Absolute, Standardized or International Standard Scale: same scale for every map produced. Good for direct comparisons between different maps, for screening and for gross pathologies. It was designed to make only clinically relevant information obvious, by setting the interval between the contours of the power plot (i.e. in practice, the contours of colours) at 1,5 diopters (which means it has low resolution).
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Relative, Normalized or Adaptative Colour Scale: different scale for each map. The computer determines maximum and minimum curvatures for the map and automatically distributes the range of colours. The computer contracts or expands its colour range according to the range of colours present in a given cornea. It is best suited for looking at variations for a particular cornea. It has the advantage of offering great topographic detail since incremental steps are smaller (around 0.8 diopters) giving high resolution, but suffers from some inconveniences: the meanings of colours are lost (explorer and clinician have to carefully check the meaning of the colours, according to the new scale), a normal cornea may look abnormal while abnormal corneas may appear closer to normal. With this scale, subtle features are made apparent, being good for detail.
Computer Displays: Presentation of Topographic Information
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When confronted to a topography display, ei- Section 3 ther a printed report or on screen, one should study it Section 4 in a structured way to avoid mistakes in interpretation, and get the most of it. Section 5 Proceed as follows: • Check the name of the patient, date of exam Section 6 and examined eye. Section 7 • Check the scale: • type of measurement (height in microns, cur- Subjects Index vature in mm, power in diopters) • step interval • Study the map (type of map, form of abnormalities, …) • Evaluate statistical information (cursor box, statistical indices when given …) Help ? • Compare with topography of the other eye (always perform bilateral exams, when possible) • Compare with the previous maps first verifying they are in the same scale) • Apply statistical analysis or other needed software application (contact lens fit, surgical modules, 3-D colour maps, neural networks, …) • Explain the exam’s results to the patient
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Figure 2-7: Absolute Scale Section 1 Section 2
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Figure 2-8: Normalised Scale
Figures 2-7 and 2-8: These two maps may look different but are the same axial diopter map of the left eye of the same patient (keratoconus) measured in different scales, absolute on the left and relative on the right. Notice very high diopter values under corneal vertex, where corneal surface is most elevated.
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To present a corneal topography, each software application (i.e. each instrument) has a large number of computer displays. Most are produced form data of a single application, and are software dependent. Most instruments are able to show: a ring verification, a numerical display, a large number of corneal maps, a simulated keratometry, a meridional plot, and some can display a 3-D reconstruction of the corneal surface. a) Ring Verification (keratoscopic raw image): (Figure 2-1, in this chapter): displays a
keratoscopic image of the Placido rings reflex on the examined cornea. It is a raw image, that allows qualitative evaluation of the image taken (irregularity of tear film layer, lids aperture, …), helping the examiner to either accept or reject the taken image. It is very useful when there is a question regarding the accuracy of the displayed data. b) Numeric Display: of a number of corneal power values along several meridians shown in a radial display. Helpful to make the data amenable to statistical methods.
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Section 3
Section 4 Figures 2-9 and 2-10: The numeric display shows a number of corneal power values along several meridians in a radial display. It is a very helpful presentation to make the data amenable to statistical methods. Notice that picture on the left (Axial Diopter) displays corneal powers in diopters and that on the right (Axial Radius) shows the same values in millimetres (corneal radius). Most topographers allow you to choose the way you want the results to be shown.
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a) Corneal Maps: details of the most common (axial, tangential, 3-D, …) will be discussed later in this chapter. Each topographer offers different maps or ways of presenting the results. Please refer to your topographer’s manual for more details. b) Simulated Keratometry Readings (SimK): obtained form the radius values at the corneal position (3 millimeters central zone) where the reflection from the keratometer mires would take place. The major axis is that is that with the greatest power, and the minor axis is at 90º to it (per-
pendicular axis). The cylinder is the difference between the major and minor axis. The meridian with the lowest mean power can also be displayed. c) Meridional Plot: shows the minimum and the maximum corneal power values, displaying a cross sectional profile of the cornea along the chosen meridian. It is used to show the general shape of the cornea to the patient, and assessing the toricity for contact lens adaptation. The helps identifying the ablation zone limits following LASIK or PRK.
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Figure 2-11: Shows a “multiple exams” of both eyes of the same patient, a 38 year old man who underwent LASIK in both eyes at a time for high myopia. Corneal map is overlaid upon the keratoscope eye image to aid interpretation. The overlay shows the spatial relationship between the pupil, the ablation zone and the cornea. Notice that immediately after surgery (the day after), ablation zones differ from each other: it is due to the fact that a different excimer laser was used for each eye. Schwind® Keratom™ was used on right eye, while left eye was operated using the Bausch & Lomb® -Chiron Technolas 217™. Although ablation zone seems more perfect and regular on right eye (tangential diopter map), this does not mean that visual result is better. The meridional plots shown under tangential diopter maps help the surgeon to evaluate the effectiveness and ablation pattern of the excimer laser he or she uses.
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or the depth of a corneal defect (ulceration, laser ablation zone, keratoconus, …). Some topographers display the spherical height map relative to a reference spherical surface, by comparing to a best fit calculated reference sphere.
Common Corneal Maps 1)
2)
Axial Map: it is the original and most commonly used map. It provides measurements based on the keratometer formula. It is helpful is evaluating the overall characteristics of the cornea and classify the corneal map (normal or abnormal). It can differentiate between spherical, astigmatic or irregular corneas. It is the most stable type of map, but may confuse the explorer when evaluating the peripheral cornea. (see Figure 2-18 in this chapter). Height Map: true height data (in microns) is immediately available from systems using the principle of projection, although a reflection system like the Optikon 2000® Keratron™ does a good job with its own arc-step method of representing corneal height. Very useful in numeric or cross-sectional format to quantify the elevation
3)
Tangential Map (see Figure 2-11 in this chapter): this very useful display provides a measurement of corneal power over a large portion of the cornea, based on a mathematical radius formula. It is more accurate than axial map in the corneal periphery, but is subject to greater variation when comparing several exams that are repeated. It may help detecting mild corneal changes that might not be detected by standard axial map. It is used for locating corneal distances on the map, and to locate a cone or peak position in keratoconus, as well as to locate the ablation diameter and position after laser refractive surgical ablation.
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Figure 2-12: Shows a “multiple exams view” of left eye of the same patient, a 58 year old women who underwent (a couple of years before consultation) complicated phaco-emulsification converted to extracapsular surgery. In the hurry, surgeon sutured the cornea too loose, thus creating a peripheral superior corneal wound defect. High against-the-rule astigmatism is well represented by the axial diopter display (superior right), and well measured by the keratometer display (5.25 D at 87 º). But only tangential diopter map (down-right) accurately represented the corneal wound suture defect: notice the red superior area where the sutures used to be.
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4) Refractive Map: it is a map based on an axial map, using Snell’s law to calculate the refractive power of the cornea. It is mainly used in pre and post corneal surgery. 5) Elliptical Elevation Map: it represents the height of the cornea in microns, at different cor-
neal positions, relative to a reference elliptical surface. It is useful to visualize corneal shape. In contrast to the spherical height map -which uses a simple spherical reference- the elliptical elevation map matches better to the inherently elliptical shape of the healthy cornea.
Figure 2-13: Shows a “multiple exams view” of both eyes of the same patient, a young man referred for refractive surgery who -to our surprise- was never diagnosed astigmatic. Axial diopter maps are displayed, in normalised (right eye) and absolute scales (left eye). Elliptical elevation with keratometer overlay maps help better assess true corneal shape and direction or axis of astigmatism. Radius of the reference ellipse are displayed and can be modified by operator: BaseR refers to central radius value, and BaseR (2.5 mm) refers to the radius value at 2.5 mm.
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6) 3-D reconstruction Map: is used to visualize the overall shape of the cornea in a more realistic way. Understandable for the patient, it can be rotated and tilted as desired. Some instruments like OCULUS® Keratograph and Haag-Streit® Keratograph CTK 922 offer excellent comprehensive kinetic three-dimensional (3-D) analysis of corneal topography for simple explanation to the patient. (see Figures 2-26, 2-27, 2-32b and 2-38 in this chapter).
7) Irregularity Map: It calculates a best sphere/cylinder correction for the cornea, subtracting the correction from either axial or tangential data and presents the remaining irregularities. Used after refractive surgery to detect irregularities that may explain a low visual acuity. It reports an index that measures eccentricity (a measure of asphericity) and the amount of astigmatism that has been subtracted form the original corneal data (Fig. 2-14).
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Contents Figure 2-14: Shows an axial irregularity map in diopters of the right eye of a 55 year old man suffering form a paracentral progressive corneal ectasia (central keratoconus). Notice the Q index with a value of -1,25 (measuring eccentricity) and an astigmatism of 4.5 D, resulting form the subtraction of the original corneal data and the best sphere/cylinder for that cornea. An overlay option adds an irregularity index to the map for increasing circles of 1 mm radius, best visualised thanks to the overlay circular grid option. Normal values would be 0.2 or 0.4, but this exceptional case shows 3.5 and 4.0 zonal indices.
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Section 5 Table 4: Common overlays that can be added to a topography map to help interpretation (See Fig. 2-15) Pupil margin: displays the visually important region. Helps evaluating photopic pupillary size, and the centration or refractive surgery. Grids Square: helps defining size and location of abnormalities. Circular: helps defining size and location of abnormalities. Polar: helps defining axis of abnormalities and the assessment of radial keratotomies. Optical zone: useful in refractive surgery for planning procedures or assessing results. Angular Scale: useful in refractive surgery of astigmatism for planning procedures or assessing results. It is similar in use to polar grid. Eye image: more realistic than a simple map, it eases patient’s interpretation of the map. Keratoconus : a peak or keratoconus overlay can be applied by Dicon’s CT-200. It is called Bull’s Eye target: if one peak area exists with an index of 10 or greater, the system automatically marks it with a target, indicating the location of this elevation to some but not all maps (see Figures 2-12 and 2-15 in this chapter). Keratometer mires: it is a graphic reference showing a 3mm circle with both major and minor meridians, representing the calculated keratometry readings, 90 degrees apart (perpendicular). It also shows a 5 mm with the steepest and flattest meridians. (see Figures 2-13 in this chapter).
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Section 6 Section 7 Subjects Index
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Section 1 Figure 2-15: Different overlays can be added to a topography to help interpretation. The picture shows a quadruple view of an almost normal cornea of a young contact lens user with mild corneal warpage only diagnosed by means of the tangential maps (c and d). Notice that b) is displayed in radius (mm) while the rest of maps are displayed in diopters (see the colour scale). Map a) displays a centre overlay (small red cross) that indicates where the true centre of the cornea is, and a pupil outline overlay that reproduces pupil margin, the visually important region. Map b) shows a “verify rings” overlay, to better asses the quality of the taken image. Red and green concentric rings should alternate and not cross. The red rings should be located on the outer edge of the white rings, and the green rings should be located on the outer edge of the black rings. Map c) shows an angular scale that helps to locate the axis of astigmatism. Map d) shows “eye image” overlay, the image of the patient’s eye is displayed to ease patient’s interpretation of the map. Notice that a paracentral target marks an elevation zone that has to be carefully inspected. Angular scale is also displayed in map d).
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Special Software Applications and Displays Each available instrument is sold with standard software package and most offer optional packages at additional price. The most common are: Multiple Display Option: a customisable multiple display allows simultaneous screen display
for rapid analysis and ease of use. Depending on the software of your topographer, you can simultaneously view either one, two or four maps. Extremely practice in daily use to ease work and interpretation. Surgical Applications: used to predict the results of refractive surgery, and for postoperative evaluation. Some -but not all- allow refractive surgery simulations and topography linked laser refractive surgery with special excimer laser brand names.
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A
B Contents
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Figures 2-16 a and b: Dicon’s CT200™ trend analysis displays a series of exam maps (pre-operative exam, first post-operative exam, most recent exam and a choice of a K-trend graph, a pre/post operative difference map or a post-last difference map.) Shown are trend analysis of both eyes of a patient who underwent myopic LASIK with two different excimer lasers. Shown are axial diopter pre-operative, tangential diopter immediate postoperative and K-trend graph. Notice that immediately after surgery (the day after), ablation zones differ form each other: it is due to the fact that a different excimer laser was used for each eye. Schwind® Keratom™ was used on right eye, while left eye was operated using the Bausch & Lomb® -Chiron Technolas 217™. K-trend graph shows the major (green) and minor (blue) K values for all exams in the series. The Y axis is power in diopters, and the X axis is the exams’ number spaced out over time. The vertical line marks the date of surgery. Trend analysis eases a rapid overview of healing trend over time.
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Contact Lens Fitting Application: they are used for contact lens fitting, and help choosing the best suggested lens for each case, by simulating the fluorescein pattern and contact lens position of rigid contacts. Not all topographers offer this feature: in some cases this software module is sold as an option. For instance, Dicon’s CT200™ (Fig. 2-16 A-B) offers as standard the Mandell Contact Lens Module “Easy-Fit™”, and as an option the Mandell Contact Lens Module “Advanced-Fit”™ for toric, bi-toric, keratoconic fitting and post-surgical fitting with Labtalk™. Contact your dealer for more precise information. The simulated fluorescein feature is intended to reduce fitting time by viewing the effect of changing lens parameters on a personalized basis, depending on the patient’s corneal exam. Let’s notice that
the true “in vivo” result of any computerised fluorescein test may vary due to differences caused by lid action on the lens (aperture and weight). Ask the manufacturer of your topographer for special software applications, and for the possibility to link your topographer and your excimer laser for better results.
Topography Maps of 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 kind of regularity found in the calibration spheres of a topographer: the eye is not moulded glass-made. Normal corneal topography can take on many topographic patterns (see table 5):
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Table 5: normal topographic patterns:
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Spherical (Round) (Figure 17) 20% With-the-rule (Oval) (Figure 18) 20% With-the-rule (Symmetric bow tie) 17% With-the-rule (Asymmetric bow tie) 30% Against-the-rule Displaced apex: Inferiorly Nasally Irregular 7% causes of irregularity: dry eye corneal scar or ulceration trauma corneal degeneration corneal edema pterygium contact lens overuse (corneal warpage) surgery (cataract, keratoplasty, …)
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Contents Figure 2-17: Shows a “multiple exams view” of left both eyes of the same patient, a 38 year old woman prior to LASIK surgery. Corneal topography remains a routine exam for preoperative and postoperative assessment of the refractive patient. This report shows normal, spherical (round), corneas in both eyes (44 D at vertex, and mostly green colour in the map). The colour zones are approximately circular in shape. Notice that lid aperture is not the same in both eyes, thus making it more difficult to map superior corneal periphery in left eye.
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Regular astigmatism (with-the-rule) gives an oval axial corneal map, being the most common deviation from optically perfect spherical (round) cornea. If the bow tie is vertical (the long axis is near the vertical meridian) in an axial map, it represents a cornea having with-the-rule-astigmatism. If the bow tie is horizontal, it represents an “against-the-rule” astigmatism, ninety degrees rotated when compared to a with-the-rule astigmatism. When the bow tie is diagonal, it represents a cornea having an oblique astigmatism. The shape and colours of the bow tie are influenced by the rate of peripheral corneal flattening, and the appearance is influenced by the scale interval chosen by the explorer. The bow tie may be symmetrical or asymmetrical along the perpendicular meridian: one half of the bow tie is significantly larger than the other,
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the corneal apex being located in the direction of the Subjects Index larger bow half, slightly decentered form the visual axis. 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 the temporal. There is a physiological astigmatism of around 0,75 diopter. Help ? Physiologically, the axis may not be the same superiorly than inferiorly. In an axial map, the rate of flattening is greater when the colour scale interval is larger, and there are many colour zones. A focal steepening inferiorly may exist due to the lower tear meniscus. Generally, the two eyes of the same subject are very similar, and present a mirror image of each other (Figures 2-18 and 2-19). This
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Figure 2-18: Axial diopter displays are showed for both right and left eyes. The patient suffered from regular astigmatism (with-the-rule), that gives an oval corneal map, being the most common deviation from optically perfect spherical (round) cornea. The long axis is near the vertical meridian. The shape and colours of the bow tie are influenced by the rate of peripheral corneal flattening: notice the nasal peripheral flattening in left eye (purple colour). This binocular report form Dicon’s CT-200 topographer shows pupil size and simulated keratometry of both eyes. RE size pupil is 4.03 mm, and astigmatism 3.12 D at 8 º. Notice that the two eyes present a mirror image of each other: this phenomenon is called enantiomorphism.
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Figure 2-19: Enantiomorphism is the phenomenon wherein an individual’s topographies are non-superimposable almost mirror images of each-other. The knowledge of this fact is useful to decide whether a cornea is normal or not, by comparing to the map of contralateral eye. Notice that even pachimetry maps reflect this phenomenon (Corneal thickness was mapped with Bausch & Lomb® Orbscan™ topo-pachimeter).
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phenomenon is called enantiomorphism. The knowledge of this fact is useful to decide whether a cornea is normal or not, by comparing to the map of contralateral eye. Small changes in corneal shape do occur throughout life: • in infancy the cornea is fairly spherical, • in childhood and adolescence, probably due to eyelid pressure on a young tissue, cornea becomes slightly astigmatic with-the-rule • in the middle age, cornea tends to recover its sphericity • late in life, against-the-rule astigmatism tends to develop Short-term fluctuation and diurnal variations are not rare, and usually remain unnoticed by individuals with normal corneas. Some conditions like corneal dystrophies, ocular hypotony, radial keratotomies or contact lens use can make them apparent.
Table 7: Uses of Substraction or Difference Maps: validation of various exams taken in a same session ascertain the existence of progressive corneal astigmatism comparison of preoperative and postoperative corneal maps (LASIK and PRK) follow-up of myopic regression (LASIK and PRK) establishing ablation zone centration (LASIK and PRK) assessing resolution of corneal warpage in rigid contact lens users assessing evolution of a corneal ulcer or abscess
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Table 6: Factors that Slightly Affect the Normal Curvature of the Cornea
Section 7 Subjects Index
Lid closure during sleep time Tear film quality Lid pressure on the cornea (weight, exoftalmos) intraocular pressure Menstruation Pregnancy
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Comparing Displays: Maps can be compared directly only on the same scale, when taken with the same instrument, and preferably by the same explorer. It is not a good idea to compare maps taken with different instruments: every instrument uses a different measuring
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algorithm that may confuse you, specially when comparing subtle details. Most software applications allow the comparison of different maps over time, and even subtract values form two different exams (substraction or difference maps) (Figure 2-20). They are invaluable to the refractive surgeon.
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Figure 2-20: A tangential diopter difference map o the left eye of a 21 year-old patient is shown. The subtraction has been performed between two different eye fixations to determine the existence of any irregularity in the ablation zone. The patient underwent a successful bilateral LASIK surgery to correct a high myopic astigmatism in both eyes a year before.
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Figure 2-21: A diopter difference map is useful to assess the validity of the different exams with the same fixation performed in the same session. Low differences due to tear film irregularities, lid aperture and blinking is acceptable. In case of difference between maps taken at the same moment, they need to be repeated, after a few blinks form the patient. If significant difference persists, try instillating a tear substitute in both eyes and wait a few minutes. Should differences persist, repeat the exams in a few days. Image shows a left eye with regular (wit-the-rule) high astigmatism : both axial diopter maps were taken in the same session: differences exist between the exams. Eye fixation is the same (center): differences a attributable to different lid aperture and form blinking. Axial diopter difference (down, with a square grid overlay) shows that differences are almost non significant (around 0.25 - 0.50 diopters), but exist. Such differences are physiological: difference maps allow validation of various exams taken in a same session.
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Section 1 Section 2 Figure 2-22: Difference maps ease the astigmatism progression follow-up . Tangential diopter displays show right eye maps of a 22 year old myopic patient referred for refractive surgery. To our surprise, neither glasses nor contacts had astigmatism. The existence of astigmatism was ascertained with the keratometer, subjective refraction and skiascopy. Corneal topography was performed and helped the demonstration of its existence. Picture shows a difference map between two exams taken with a 3 months delay (see the dates of the exams). Tangential diopter difference is 0 (green), meaning that no changes have occurred in that period of time. The first impression is that the guy never had good refraction, but new topographic exams will be performed 6 months and one year later, before refractive surgery is decided, so as to make sure that no keratoconic formation is on the way.
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BRIEF ATLAS OF CORNEAL TOPOGRAPHY SPECIAL TOPOGRAPHIC CONDITIONS Figures a1 to a20: All maps have been taken with a KERATRON™ Corneal Topographer (Optikon 2000® S.p.A, Italy - Europe). The corneal maps are courtesy of: Istituto Scientifico Ospedale San Raffaele - Milano (Prof. Brancato - Dr. Carones) Ospedale Fatebenefratelli - Roma (Prof. Neuschüller - D.ssa Cantera) Centro Oculistico - Rovigo (Prof. Merlin - Dr. Camellin) Clinica Oculistica Universitaria - Padova (Prof. Bisantis) University of North Carolina - Chapel Hill (Prof. Cohen - D.ssa Tripoli) University of California - Jules Stein Institute - Los Angeles (Dr. Maloney) We want to specially thank them as well as the manufacturer of the Keratron™ videokeratoscope, Opticon 2000® S.p.A., for the permission to reproduce them.
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Figure a1: Map of a normal round cornea There is a wide spectrum of normality. No human cornea demonstrates the kind of regularity found in the calibration spheres of a topographer: the eye is not polished glass-made. Normal corneal topography can take on many topographic patterns: picture shows the axial map of a right eye normal round cornea, with concentric green rings in an absolute scale. Notice that the nasal side of this healthy corneal map becomes blue more quickly than temporal side, indicating that the nasal cornea is flatter than the temporal. In the central 3 mm zone, there is a small amount of astigmatism (1 D displayed), which is within normal limits, and does not mean that the patient needs to be corrected with this astigmatism.
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Figures a2 and a3: Normal cornea with astigmatism according to the rule Help ? Regular astigmatism (with-the-rule) gives an oval axial corneal map, being the most common deviation from optically perfect spherical (round) cornea. Observe that the bow tie is vertical (the long axis is near the vertical meridian) in an axial map, representing a cornea having with-the-rule-astigmatism. Picture displays an axial curvature map of a -3.7 D regular astigmatism in an adjustable scale. Always check the scale in which the map is offered: colour differences do not always mean a difference in dioptric or radial values, but can mean a difference in the scale used by the explorer. Notice that a simulated keratometric overlay is displayed at the centre of the bow tie. Modern topographers run under Windows™ operating system, and are easy to use. Most software enables to enlarge desired areas for better explanation to the patient and to better view the details. Picture shows an enlarged area of a with-the-rule astigmatism with an absolute scale.
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Section 5 Figure a4: Topographic map of astigmatism expressed in heights
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Representation of the topographic map of an astigmatism (-3.75 D at 176º) expressed in height (in microns). The yellow area corresponds to a sphere with a defined radius, while orange-red and green-blue areas correspond to either elevation or flattening of the cornea. Notice that colour scale may confuse the explorer.
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Figures a5 and a6: Keratoconus An important indication of corneal topography is the screening of candidates for refractive surgery. It is very important to identify patients with corneal ectasia, since surgical outcomes are uncertain in most cases. Early detection of a subclinical keratoconus can save the patient of a refractive procedure (incisional or photoablative) that likely will not result in the desired visual outcome, and may result in dangerous corneal thinning. The most frequent ectatic corneal disorder is keratoconus. This condition is characterised by a corneal stromal thinning. It typically presents in early adulthood, is almost always bilateral (although can be very asymmetric), and progresses slowly over the years. Mild keratoconus cannot be detected easily at the slit-lamp, and only corneal topography can help detecting them. Some other conditions, like corneal warpage of RGP contact lenses may mimic mild keratoconus corneal maps. In most cases, the corneal thinning occurs just inferior to the corneal centre. Protrusion of this region gives the cornea an exaggerated prolapsing shape. The point of maximum protrusion is called the apex of the cone. Picture displays a typical map of a moderate keratoconus (- 5.6 D), showing a corneal steepening inferior to corneal vertex (orange-red, in absolute scale, in the shape of a pear fruit). Notice the high corneal central power (around 50 D), the inferior cornea (orange) steeper than superior cornea (green), and the large difference between the power of the corneal apex and that of the periphery. (Cont. in page 35)
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(Cont. from page 34) A topographic classification of keratoconus can been established: Severity
Site of the cone
Shape of the cone
Slit-lamp detectable
Subclinical
Inferior
like a pear fruit
No
Clinical: Mild
Inferior
Typical, oval like a pear fruit
Moderate
Central +/- Inferior
Globus
Sometimes needs a trained explorer Yes
Severe
Superior
Nipple
Yes, visible without slit-lamp
The comparison of representation of dioptric powers, axial (left) and local (right), of the same eye with an inferotemporal keratoconus is surprising: notice the minimal extension of the corneal surface involved in the pathology, and the flattening of the adjacent area.
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Figure a7: Corneal ulcer By quantifying the irregularity of the cornea, topography helps to determine the proportion of the visual loss of a patient suffering from a corneal ulceration or epithelial disruption close to the visual axis. It also helps to follow-up a corneal abscess or ulceration. Picture shows the true curvature map of a corneal inferior ulceration. Notice the local flattening of the corneal surface (in blue), resulting form the localised depression of the ulcer, surrounded by a ring of oedematous elevated tissue (in red).
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Figure a8: Marginal pellucid degeneration Stromal corneal disease include a variety of inflammatory and non-inflammatory disorders, like Terrien’s marginal degeneration, Mooren’s ulceration, pellucid marginal degeneration an others. Picture displays true elevation map (left) and axial map (right) of a pellucid marginal degeneration, a narrow band of corneal thinning located 1-2 mm from the inferior limbus. Observe the flattening of the central cornea (true elevation and axial maps) along the vertical axis. Extensive peripheral guttering leads to irregular against-the-rule astigmatism, such as this arching inferior bow tie visible in the axial map. These topographic findings are characteristic: they help establishing diagnosis even in patients without slit-lamp typical findings.
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Section 3 Figure a9: Contact lens overuse (warpage) Different types of contact lenses have different impact on corneal surface and different indications. We can classify them into three main groups: soft, rigid gas permeable (RGP) and hard (PMMA). The last are no longer considered suitable for making contacts, and are only prescribed in special cases. Rigid gas permeable contact lenses a relatively popular: they offer good visual performance, they can be polished, they tolerate most known cleaning solutions, and custom designs are possible. The bad side also exists, since they require individualised fitting (by means of k readings, topographic maps, …), they are not easily tolerated at first, and induce with relative ease changes of the shape of the cornea: the process of changes is termed warpage. It is thought due to mechanical pressure on the cornea, although other factors like oxygen deficiency have not been excluded. Many topographic patterns may result, like the one in the picture, depending upon the fit (size, curvature, …) and position of the lens. In this case, observe the inferior steepening in the axial map causing meridian asymmetry as a result of superior riding contact lens. The true elevation map shows corneal surface irregularity (orange). Cessation of the lens wear and good ocular lubrication result in return to corneal former shape.
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Contents Figure a10: Curved arcuate keratotomies (astigmatic keratotomies)
Section 1
Most refractive efforts have concentrated on altering the shape of the cornea, which is the main diopter of the eye. Topography is valuable in the preoperative assessment and planning of the surgery. Picture displays both true elevation (left) and axial maps (right) of an astigmatic patient who underwent astigmatic keratotomies. Two paired circumpherential relaxing incisions centered on the steep axis result in focal steepening (orange-red in true elevation map) and central flattening in that meridian (blue). The final result is 0.13D of astigmatism in the 3mm central cornea.
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Figure a11: Keratotomy with a resulting ectasia Every surgical procedure has some risks the patient must be aware of. Any kind of keratotomy (radial, astigmatic or other) may perforate the globe or result in an ectasia like the one shown in the picture. The inferior ectasia simulates an irregular keratoconus, in both true elevation (left map) and axial (on the right) maps.
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Figure a12: Photorefractive keratectomy PRK To correct myopia, the excimer laser removes more tissue from the centre than the periphery of the treatment zone (ablation zone). The ablation profile is different for every model of laser. The map on the left represents the spherical approach (axial curvature) of a patient who suffered myopic photorefractive keratectomy. Only the “true elevation” map (on the right) shows the transition area, where dioptric powers are very high (ring in red).
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Help ? Figure a13: Subtraction map in a PRK The most effective way of displaying the changes in a cornea that undergoes a refractive procedure are difference maps. The change induced by surgery is obtained by subtracting the preoperative map (upper small axial map) from the postoperative map (lower small axial map). The image on the right shows the result (in terms of dioptric variation, axial curvature) of a myopic PRK. In red, the ablation zone. In orange, the transition zone, which is easily delineated in the postoperative axial map which shows that the central cornea has been flattened (lower small axial map on the left).
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Figure a14: True curvature analysis in pre/post PRK
Contents The comparison between preoperative and postoperative true curvature analysis of the same PRK patient shows no variations of the peripheral cornea after surgery.
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Help ? Figure a15: Paracentral island Many are the potential complications of laser refractive surgery. Some may be attributable to the ablative pattern of each model of excimer laser, like central or paracentral islands, although the origin is uncertain. They are defined as any area within the ablation zone surrounded by areas of lesser curvature on more than 50% of its boundaries. They are a topographic pattern in PRK and LASIK patients, not always obvious. Picture displays a paracentral island after myopic PRK: it can be identified down inside the ablation red ring as a yellow-orange spot. Notice that only with the calculation method of local powers (true curvature map on the right), this small abnormality is made visible, remaining invisible in the axial map (on the left).
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Figure a16: Effect of suture removal after keratoplasty Serial topographic exams after a penetrating keratoplasty reveal large configurational changes the first two months, which remain stable until suture removal. Topography is then used to determine the suture to be removed in order to lower suture induced astigmatism and enhance visual recovery. Picture shows a test comparison: left map displays high astigmatism after a penetrating keratoplasty (-6.18 at 173º), right map displays the reduction to 1.33D after suture removal. Notice the asymmetry of power between the two hemi-meridians, that improves after suture removal. Observe the red areas of high power (and elevation) near the wound. Topographer is preferred over keratometer as most changes do occur outside the 3mm area measured by the keratometer.
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Help ? Figure a17: Software adjustment of a decentred axis The Keratron™ Corneal Topographer (Optikon 2000® S.p.A, Italy - Europe) offers some interesting features like the possibility of replacing the optical axis when the patient’s fixation is not as desired or corneal centration is not perfect. The system is able to recalculate the optical power values for the whole cornea. Notice that values at the optical axis differ from the original map with geometric axis calculations (on the left) and the recalculated map with the new visual axis position (map on the right).
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Contents
Section 1 Section 2 Figure a18: Myopic and hyperopic keratomileusis (LASIK)
Section 3
Shown are two “true curvature” maps of both myopic (left) and hyperopic (right) keratomileusis. To correct myopia, excimer laser removes a central disc of corneal stroma, resulting in central flattening (blue) and the presence of a relative peripheral steepening ring (red). Corneal topographic changes similar to those seen after photorefractive keratectomy (PRK) occur after LASIK for myopia. To correct hyperopia, the excimer laser does just the opposite: it removes an annulus or ring of tissue from the mid-periphery (blue) to steepen the central cornea (red).
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Figure a19: Intrastromal segmented graft for the correction of high myopias Picture shows a “true curvature” map of a left eye cornea that received an intrastromal segmented graft for the correction of high myopia. The map is similar to that of a myopic LASIK, but less regular.
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Help ? Figure a20: Fluorescein simulation in RGP contact lens Contact lens fitting applications are used to help choosing the best lens for every case, by simulating the fluorescein film pattern and contact lens position of rigid contact lenses (RGP and PMMA). The simulated fluorescein feature is intended to reduce fitting time by viewing the effect of changing lens parameters on a personalised basis, depending on the patient’s corneal exam. Let’s notice that the true “in vivo” result of any computerised fluorescein test may vary due to differences caused by lid action on the lens (aperture and weight).
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Figure 2-24: Elevation Map Figure 2-23: Zeiss Humphrey Systems® ATLAS™ Corneal Topography System Models 993 and Eclipse 995
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TOPOGRAPHERS CURRENTLY Technomed Color Ellipsoid Topometer AVAILABLE The reproducibility of videokeratography Zeiss Humphrey Systems® ATLAS™ Corneal Topography System Models 993 and Eclipse 995 (Figure 2-23, with permission) Zeiss Humphrey Systems® ATLAS™ Corneal Topography System Models 993 and Eclipse 995 are best sellers in the USA. They measure true elevation data (Figure 2-24, with permission) through an advanced arc-step algorithm (similar to Optikon 2000® Keratron™), by means of 20-22 ring conical Placido disk. The Atlas Eclipse 995 offers ultra-low illumination and increased peripheral coverage (limbus to limbus). They also offer automatic pupil measurement. Software displays are viewed in a 10,4 “ TFT 640x480 pixel resolution in 18 bit colour; they include: photokeratoscope view, axial map, tangential map, numeric view, and profile view. Very interesting optional software packages are available at a price: MasterFit™ contact lens module, corneal elevation map, corneal irregularity map, refractive power map, keratoconus detection map, VisioPro™ ablation planing software and Healing Trend/ STARS™ display.
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measurements is mainly dependent on the accuracy Section 4 of manual adjustment in the focal plane. Videokeratoscopes having small Placido cones show Section 5 a considerable amount of error when the required working distance between cornea and keratoscope Section 6 is not maintained. The advantages of small cones Section 7 (optimal illumination and the reduction of anatomically caused shadows) are in no proportion to the Subjects Index disadvantage, poor depth of focus, resulting in poor reproducibility. The Color Ellipsoid Topometer compensates defocusing errors with software and hardware, by means of a triangulation measurement., enhancing precision and theoretically avoiding measuring Help ? artefacts. It is the only Placido (30 ring) system with colour coded rings (three coloured rings). By means of a laser, it measures 10800 points, providing real height values and has ray tracing software. A new module enables topography-driven laser ablation. This unit is specially useful in diagnosing postoperative problems in a refractive practice, specially in those cases with a loss of vision that cannot be explained. The Color Ellipsoid Topometer can predict the quality of vision based on the shape of the cornea and pupil.
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Figure 2-25: DICON ® CT200
®
DICON CT200 (Figure 2-25, with permission) The reproducibility of videokeratography measurements is mainly dependent on the accuracy of manual adjustment in the focal plane. The
DICON® CT200 is a cheap easy to use instrument with autofocus and autoalignment that eliminate joystick and explorer subjectivity, thus improving repeatability. The big Placido disk cone in managed from the computer by means of the mouse. Final alignment (up and down) and focusing (forwards and backwards) are automatically performed by the motorized instrument head. It can explore the whole cornea (apex and limbus to limbus) thanks to an offset fixation. The patient can fixate different green lights, to allow complete cornea coverage. Offset-fixation mapping allows for more precise mapping of the central 3mm of the cornea. More true data points from the apex and true limbus-to-limbus measurements over a large corneal area provide for better coverage without extrapolation. Nevertheless, we miss a different chin rest to allow faster exams by eliminating the need for patient’s head re-centration from one eye to the other. The system generates maps in seconds and detailed customized reports can be printed in less than a minute with any colour printer running under MS Windows ’95 ™ operating system.
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Section 6 Section 7 Figure 2-26: Dicon’s CT-200™ can explore the whole cornea (apex, and limbus to limbus) thanks to an offset fixation. Patient fixates different green lights: shown is a quadruple view of right eye corneal maps display a nasal fixation, including 3-D reconstruction with a 45º tilt (left and down). Optional software (Multiview™) provides total cornea coverage using the mentioned multiple fixation targets. Limbal measurements aren’t always reliable, being subject to many artefacts.
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Figure 2-27: Picture shows a quadruple display map of the right eye of a 55 year-old man suffering form progressive bilateral corneal central ectasia. Notice the distortion of the mires in the ring verification map (up and left), the enormous “red” central and paracentral elevation in the axial diopter map (up and right). Statistical information is displayed following the peak detection, identifying the location, size, maximum power, peak index and probability statement (“very high suspect peak area detected”). One such high index (index = 9370) always means that we face a keratoconus or another kind of corneal ectasia. The ectasia was clearly visible at the slit-lamp.
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A very interesting feature of this instrument is the Bull’s Eye Targetting™: the system automatically targets the apex position of a cone (keratoconus or other), providing a numerical index for that cone. An auto-alarm is activated so that any suspicious case of keratoconus (or excessive corneal elevation with an index higher than 10) is automatically detected and acoustically signalled as a peak detection warning window appears in the display after the image capture is complete. New users will appreciate this feature: a low index is not uncommon, and does not always mean that we face a pathologic cornea. High indices in a tangential map almost always mean that we face a keratoconus or another kind of corneal ectasia (Figure 2-27).
Peak detection can be triggered by any sus- Section 6 pect peak, including mucous in the tear film, or localized areas of film break-up. In one such case, al- Section 7 ways have the patient close the eyes for a while and Subjects Index blink a few extra times before retaking the picture. In case of doubt, it is advisable to retake the picture again. The determination of the condition producing the corneal elevation needs to be confirmed by other clinical tests, like slit lamp examination or others. The DICON ® CT-200™ software includes an optional refractive module that allows single Help ? analysis, trend analysis of multiple displays and a special package called VISX ® STAR S2™ Ablation Planner (Fig. 2-28).
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Chapter 2 Figure 2-28: The “Single Analysis” menu option of the DICON ® CT200™ displays a single exam with four customisable map views a) axial diopter, b) refractive diopter (shown with a square grid overlay), c) spherical height and d) irregularity (shown without the eye overlay). The irregularity map d) reports an index (Q = - 0.10) that measures eccentricity (a measure of asphericity) and the amount of astigmatism that has been subtracted form the original ideal spherical corneal data (in this case, 1.12 D).
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The VISX STAR S2™ Ablation Planner is offered as an option and is intended to learn the control system for the Visx® laser. It offers a custom display of the CT 200 Elliptical Elevation Map, and access to the VISX® STAR S2™ control panel. It allows a simulated (not real) image of the before/ after laser ablation for better comprehension of the procedure. Developed by Dr. Robert B. Mandell is a simplified contact lens fitting software, with fluorescein simulation. You can design unique lenses for each cornea (personalized designs) and send the data directly to the manufacturer (via modem) or print the order sheet for faxing or mailing.
EYE SYS® 2000 Topographers from Premier Laser Systems, EyeSys Corneal Analysis System 2000 and EyeSys Vista Hand-held corneal topographer, have been the leading topographers in the USA for years but might have been discontinued at the moment you may read this chapter due to Premier Laser Systems’ bankruptcy. We have included them to honour the topographers we learned with, as most topographic texts still refer to them. We hope that new partners in early future or potential buyers help to guarantee the survival of EyeSys topographers in this hard marketplace.
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KERATRON™ Corneal Topographer (Optikon 2000® S.p.A, Italy -Europe) (Figure 2-29, with permission)
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The Keratron™ topographer is one of our preferred systems: it is a must if you are in refractive Section 4 surgery. The Keratron Topographers offer automatic Section 5 image capture. A patented corneal vertex detector system is housed inside a slight protrusion on either Section 6 side of the cone. If you position the Keratron™ too Section 7 close or too far, image capture just will not happen. Only when the system detects the vertex in the exact Subjects Index right position, image is automatically captured, thus obtaining more reproducible maps. Introduced in 1994, the Keratron™ was the first hardware platform designed to get the most of an ARC STEP surface reconstruction, achieving accuracy and sensitivity, without smoothing of data or extrapolating to fill in topographic shadows. The Help ? Keratron’s own method of arc-step mapping accurately maps aspheric surfaces. It uses a small Placido cone of rings. It’s patented infra-red vertex detector sensor determines the exact position of the corneal vertex and begins constructing a web of “Arcs” between the intersections of 26 rings and 256 meridians, from the vertex to the periphery. Defining corneal vertex position and starting measurements from it provide
FUNDAMENTALS ON CORNEAL TOPOGRAPHY
Figure 2-29: KERATRON™ Corneal Topographer (Optikon 2000® S.p.A, Italy -Europe)
this topographer with high accuracy. Curvature and height are simultaneously derived from the length and shape of each arc. Mapping beginning at the corneal vertex, this instrument easily detects up central islands or minor defects. Each data point of the “web” is related to another one, thus eliminating inaccuracies of traditional Placido “concentric rings method” which take measurement of each point independently from one another, resulting in possible errors. While most topographers first create an axial map and then convert the axial data into different maps, every Keratron’s map is calculated separately without conversions, thus decreasing probability of errors. Since the Keratron does not convert data, map error is minimal in all maps. True corneal elevation (height) in microns as well as the traditional curvature maps are created. This system enables to map the image of a patient with bad fixation-through mathematics reconstruction. The system is fast and easy to use, working under MS Windows™ environment. The powerful software is the gem of the system: novice will find some difficulty but once you master it you will not want to get rid of this topographer. You can design unique lenses for each cornea (personalized designs) and send the data directly to the manufacturer (via modem). A recently developed software by Jim Edwards, OD (patents pending) called WAVE uses a unique but logical approach to contact lens design by effectively creating a mir-
ror image of the peripheral cornea in the lens design process. Contact lenses designed with Wave drape the cornea in a manner similar to a soft lens. As the lens periphery matches the peripheral cornea, lens centration should be unsurpassed, even with reverse geometry lenses. Optikon 2000® has made a small portable topographer called Scout Portable Topographer with the same features as the full size device: at the moment these lines are written it suffers from some youth design defects that will be soon addressed by Opticon 2000®. It is available as slit-lamp model, hand-held model, table top model or surgical microscope model.
ET-800 Corneal Topography System Contents
Euclid Systems Corporation® ET-800 CTS is another interesting product in this round-up, since Section 1 it uses a completely different method of topography Section 2 called Fourier profilometry. The technique uses the projection of 2 iden- Section 3 tical sine wave patterns onto the surface of the eye. The projection is done using filtered blue light that Section 4 induces fluorescence of a liquid (fluorescein) that Section 5 has been applied to the tear film before the examination. The resulting image is captured by a CCD cam- Section 6 era. Two dimensional Fourier transform mathematics are used to calculate the phase shift of the pro- Section 7 jected wave pattern. The phase shift is directly re- Subjects Index lated to the height information. This method analyses over 300,000 data points to achieve true elevation co-ordinates, with each point accurate to approximately the thickness of the tear film (about one micron). The problem is that thickness of the tear film varies with daytime, and is not the same for each patient. Help ? The system uses no rings or Placido disk. It is quite fast (processing time : 4 seconds). The focusing mechanism is a live TV camera. It provides full scleral and corneal coverage up to 22 x 17mm (useful to assess pterygium evolution). It is sold as the “only” topographer to measure true corneal elevation. Let’s observe again that most topographers measure corneal elevation by extrapolating from corneal reflex (thus interfered by tear film layer quality). It might well be the most precise method, each
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of the 300,000 data points being accurate to about 1 micron, but unfortunately it is not widespread enough to become a reference system. It still needs clinical validation. This projection technique visualizes the surface directly while a reflection technique amplifies the corneal topographic distortions. It measures with low light level for patient, offering full K analysis, “e” value analysis, cross sections, ellipsoidal difference map, full patient and radiological histories, and a easy to use four click exam wizard.
Oculus® Keratograph™ and HaagStreit® Keratograph CTK 922 OCULUS ® Keratograph (Figure 2-30) and Haag-Streit ® Keratograph CTK 922 (Figure 2-31) are very similar instruments sold under different brand names and different packaging. They are com-
Eye Map EH-290 Alcon ® Corneal Topography System Alcon® EH-290 Eye Map corneal Topography System is a large 23 narrow modified Placido disk system. The modified patented Placido cone design is supposed to be very accurate and sensitive. Easy and intuitive to use (software runs under Windows™), it offers advanced contact lens software, keratoconus detection, corneal statistics information and advanced communication software.
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TOMEY® Autotopographer Tomey® auto-topographer is a cheap, small and portable fully automatic self-topographer that requires no operator alignment. The patient places his or her face on an ergonomically designed face rest and the automated topographer is activated by proximity sensors, automatically taking the measurements. The software, that can be installed in a preowned PC, runs under Windows™ operating system. The software is very complete and comprehensive, and includes a contact lens wizard with interactive fluorescein displays. Optional software packages include : Height and Height Change Maps, Klyce Corneal Statistics, Keratoconus Screening and the Contact Lens Wizard. The low level lights cone is intended to produce minimal glare and disturbance for the patient.
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Section 6 Figure 2-30: OCULUS
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Figure 2-31: Haag-Streit ® Keratograph CTK 922
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pact systems that can fit any refractive unit and include built-in keratometer in connection with the topography system. The software runs under Windows™ operating system and is easy to use, with automatic measurement. The Oculus® can be an integrated computerised system (Keratograph C, in the picture) or an independent system linked to a preowned computer. A non-contact measurement large Placido system with 22 rings in a hemisphere and 22.000 measuring points try to guarantee a high resolution.
The working distance of 80 mm is enough to make the patient feel comfortable. The light system (warm coloured) is intended to produce minimal glare and disturbance for the patient. They have an interesting software that allows contact lens-fitting in three simple steps: automated contact lens recommendation with a database that includes 20.000 lens geometries from all major contact lens manufacturers, and can be easily enlarged, and realistic fluo-image simulation of contact lens adaptation (Figure 2-32). There is a possibility of
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a
b
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Section 6 Section 7 Subjects Index
c
d Figure 2-32 A-E: Haag-Streit® KERATOGRAPH CTK 922™ output modalities include a) Overview image with simulated keratometer (right and down), b) comprehensive kinetic threedimensional (3-D) analysis of corneal topography for simple explanation to the patient, c) zoom-up image of a map d) fluorescein image simulation for contact lens fitting, and e) Fourier expressive analysis (Published with permission from HAAG-STREIT® AG International).
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Figures 2-33 and 2-34: Oculus® Keratograph™ screen shots with elevation (height) map and refractive map that will be included in 2001 software version (latest review). A new algorithm method for increased precision (Published with permission from OCULUS Optikgeraete GmbH).
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measuring the back surface of rigid gas permeable contact lens through optional Lens Check software. There is also an optional statistics software package called Datagraph, intended for refractive surgeons. This systems allows wonderful comprehensive kinetic three-dimensional analysis of corneal topography for simple explanation to the 50
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patient (Figure 2-31). Fourier surface analysis (Figure 2-31) is available and new software is under development for refractive surgery and contact lens fitters. Also optional is the Topolink software, that integrates the corneal topography data and some but not all excimer laser software .
FUNDAMENTALS ON CORNEAL TOPOGRAPHY
Figure 2-35: ORBSCAN IIz™- Bausch & Lomb® Surgical, Inc.
ORBSCAN IIz™ - Bausch & Lomb® Surgical, Inc. (USA) (Figure 2-35, with permission) This is a truly revolutionary instrument for the study of the cornea. It combines a slit scanning system and a Placido disk (with 40 rings) to measure the anterior elevation and curvature of the cornea and the posterior elevation and curvature of the cornea. It offers a full corneal pachimetry map with white to white measurements.
ORBSCAN IIz™ takes a series of slit-beam images of two scanning slitlamps projected beams at 45 degrees, to the right or left of the instrument axis. During the exam, the patient fixates on a blinking red light coaxial with the imaging system. Forty images are taken by the system, 20 with slit beams projected from the right and 20 from the left. The 20 images are acquired in 0.7 seconds each. Simultaneously, a tracking system measures the non voluntary movements of the eye during the exam. Orbscan IIz™ is able to measure anterior chamber depth, angle kappa, pupil diameter, simulated keratometry readings (3 and 5 central mm of the cornea), Contents and the thinnest corneal pachimetry reading. It offers every traditional map apart Section 1 form those of posterior corneal surface. Elevation topography of the anterior cor- Section 2 nea enables clinicians to more accurately Section 3 visualize the shape of abnormal corneas, which should lead to more accurate diag- Section 4 noses and better surgical results. It has proven to be and extraordinary tool for re- Section 5 search and for the refractive surgeon. Section 6 The system is able to acquire over 9000 data points in 1.5 seconds, which is fast, but not enough Section 7 for the patient to feel comfortable. Not every patient can avoid blinking, and in some cases measurements Subjects Index have to be repeated. A faster processing speed would be desirable, although we feel very comfortable with the system. Easy to use and running under Microsoft® Windows™ NT 4.0 operating system, the major disadvantage is the high price, that makes it not affordHelp ? able for most ophthalmologists. Any colour printer running under NT 4.0 can be used. Three dimensional views of the different maps are available (see Figure 2-38 in this chapter).
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Figure 2-36:
MYOPIC LASIK PRE/POST OPERATIVE with ZYOPTICS™ Excimer laser.
Preoperative Orbscan™ Imaging Anterior Float BFS Keratometric
Posterior Float BFS Thickness
Postoperative (Myopic Zyoptics™ Lasik) Orbscan™ Imaging Anterior Float BFS Keratometric
Picture displays different preoperative and postoperative maps of the right eye of a patient who underwent a refractive myopic Zyoptics™ Lasik procedure. Images were taken with ORBSCAN IIz™ - Bausch & Lomb® Surgical, Inc. (USA) topographer. The Anterior Best Fit Sphere (BFS) is calculated to best match the anterior corneal surface. The Elevation BFS map subtracts the calculated best fit sphere size against the eye surface in millimeters (mm). The difference between the sphere and the eye surface is expressed in distance, in a radial way, from the centre of the sphere as shown in the figure (map Anterior Float BFS). The shape of a sphere being easily imagined by the explorer, deviation from that spherical surface in a special case helps to appreciate the true shape of the eye and its deviation from symmetry (asymmetry). The map has 35 default colour steps, the size of each step being measured at the bottom of each colour. (Five microns is the default for the BFS map). The best fit between eye surface and sphere is represented in green. Areas under this spherical ideal surface are represented in blue, while warmer colours (orange-red) identify areas above this ideal sphere.. The box in the middle of the displays shows patient information of interest like patient’s name,
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Posterior Float BFS Thickness
examination date, diameter (mm) and power (D) of Contents the ideal sphere, diagnosis, simulated keratometry readings, white to white distance, pupil diameter, Section 1 thinnest measurement for that cornea, anterior chamber depth (either from epithelium or endothelium), Section 2 angle Kappa, and Kappa intercept. The Posterior Best Fit Sphere (BFS) is cal- Section 3 culated to best match the posterior corneal surface. Section 4 The Keratometric simulates keratometric Section 5 values at special areas. The Thickness Map (Pachymetry map) Section 6 shows the differences in elevation between the anterior and posterior surfaces of the cornea. By moving Section 7 the mouse over the map, explorer can obtain measurements of the thickness at each point. This map Subjects Index can be overlaid by the average measurements that would be taken with a traditional ultrasound pachymeter (encircled values). This map is invaluable for preoperative assessment of the refractive patient, and to determine the true ablated tissue depth in the postoperative period of PRK and refractive Help ? patients. Thickness maps clearly demonstrate that ablation zone (arrow) has decreased in thickness form 544 to 405 microns. Notice that corneal thickness increases as we get closer to the limbus. (Courtesy of Dr. Andreu Coret, Institut Oftalmològic de Barcelona, Barcelona - Spain)
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Figure 2-36:
MYOPIC LASIK PRE/POST OPERATIVE with ZYOPTICS™ Excimer laser.
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Figure 2-37: KERATOCONUS Anterior Float BFS Keratometric
Posterior Float BFS Thickness
Anterior Float BFS Keratometric
Posterior Float BFS Thickness
Picture displays different maps of the left (OS) eye of a patient with a keratoconus. Images were taken with ORBSCAN IIz™ - Bausch &
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Lomb® Surgical, Inc. (USA) topographer. Notice the central elevation in both anterior and posterior surfaces of the cornea ,with reduced corneal thickness (comparing to a normal eye) and high astigmatism. The four inferior maps display different cross section along the 0º180º meridian that demonstrate how the cornea is higher than the best fit sphere centrally (reddish central mountain overlaid on the corneal display) and lower in the mid-periphery (bluish depression at both sides of the mountain). (Courtesy of Dr. Andreu Coret, Institut Oftalmològic de Barcelona, Barcelona - Spain).
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Section 3 Figure 2-38: 3-D imaging of both surfaces of the cornea with ORBSCAN IIz™ software is really meaningful for the patient. Notice that central protrusion is higher in posterior than in anterior surface of the cornea: in between, corneal thickness is reduced. (Courtesy of Dr. Andreu Coret, Institut Oftalmològic de Barcelona, Barcelona - Spain).
Section 4
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Help ? SPECIAL NOTICE FOR TOPOGRAPHER USERS: Always Follow Manufacturer’s Instructions ALWAYS RECALIBRATE THE SYSTEM: AT LEAST ONCE WEEKLY BEFORE ANY DELICATE EXAM AFTER CLEANING THE CONE. VERIFY CALLIBRATION EACH DAY BEFORE PATIENT TESTING
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REFERENCES 1.
Applegate RA, Nunez R, Buettner J, Howland HC. How accurately can videokeratographic systems measure surface elevation? Optom Vis Sci 1995; 72:785-92.
2.
Arffa RC, Warnicki JW, Rehkopf PG. Corneal topography using rasterstereography. Refract Corneal Surg 1989; 5: 414-17.
3.
Belin MW, Litoff FK, Strods SJ, Winn SS, Smith RS. The PAR technology corneal topography system. Refract Corneal Surg 1992;8: 88–96.
4.
Belin MW, Zloty P. Accuracy of the PAR corneal topography system with spatial misalignment. CLAO J 1993; 19: 64-8.
5.
Belin MW, Ratliff CD. Evaluating data acquisition and smoothing functions of currently available videokeratoscopes. J Cataract Refract Surg 1996; 22: 4216.
6.
Borderie VM, Laroche L. Measurement of irregular astigmatism using semimeridian data from video-keratographs. J Refract Surg 1996;12: 595–600.
7.
Brancato R, Carones F. Topografia corneale computerizzata. Milano, Italy: Fogliazza, ed. 1994.
8.
Cantera E, Carones F, Brancato R, Cantera I, Neuschuler R. Evaluation of a new autofocus device for computer-assisted corneal topography. Invest Ophthalmol Vis Sci 1994; 35 (Suppl): 2063.
9.
Cohen KL, Tripoli NK, Holmgren DE, Coggins JM: Assessment of the height of radial aspheres reported by a computer-assisted keratoscope. Invest Ophthalmol and Vis Sci 1993;34 (suppl): 1217.
10. Cohen KL, Tripoli NK, Holmgren DE, Coggins JM. Assessment of the power and height of radial aspheres reported by a computer-assisted keratoscope. Am J Ophthalmol 1995; l l9: 723-32. 11. Corbett MC, O’Brart DPS, Stultiens Bath, Jongsma FHM, Marshall J. Corneal topography using a new moiré image-based system. Eur J Implant Ref Surg 1995;7: 353 – 70. 12. Corbett MC, Rosen ES, O’Brart D.P.S.. Corneal topography: principles and applications. BMJ books, Great Britain, 1999. 13. Chan WK, Carones F, Maloney RK. Corneal topographic maps: a clinical comparison. International Society of Re-
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fractive Keratoplasty 1994 - Abstract book. 14. Dekking HM. Zur Photographie der Hornhautoberfl-Eche. Graefes Arch Ophtalmol 1930; 124:708-30. 15. Dingeldein SA, Klyce SD, Wilson SE. Quantitative descriptors of corneal shape derived from the computer- assisted analysis of photokeratographs. Refract Corneal Surg 1989;5:372–8. 16. Doss JD, Hutson RL, Rowsey JJ, Brown DR. Method for calculation of corneal profile and power distribution. Arch Ophthalmol 1981; 99: 1261-5. 17. Duke Elder S. – System of Ophthalmology, St Louis, Mo : CV Mosby Co, 1970, V, 96-101. 18. Ediger MN, Pettit GH, Weiblinger RP. Noninvasive monitoring of excimer laser ablation by time-resolved reflectometry. Refract Corneal Surg 1993;9: 268–75. 19. el-Hage SG: The computerized corneal topographer EH270. In: Shanzlin DJ, Robin JB, eds. Corneal topography: measuring and modifying the cornea. New York: SpringerVerlag 1991:l 1-24. 20. el-Hage SG: Suggested new methods for photokeratoscopy: a comparison of their validities. I. Am J Optom Arch Am Acad Optom 1971; 48 :897-912.
Contents
Section 1 Section 2
Section 3
Section 4
21. Eghbali F, Yeung KK, Maloney RK. Topographic determination of corneal asphericity and its lack of effect on the outcome of radial keratotomy. Am J Ophtha1mol 1995;119: 275–80.
Section 5
22. Fleming JF. Should refractive surgeons worry about corneal asphericity? Refract Corneal Surg 1990; 6: 455–7.
Section 7
23. Friedman NE, Zadnik K, Mutti DO, Fusaro RE. Quantifying corneal toricity from videokeratography with fourier analysis. J Refract Surg 1996;12: 108–13.
Section 6
Subjects Index
24. Gardner B.P., Klyce S.D., Thompson H.W., et al. Centration of photorefractive keratectomy : topographic assessment. Invest Ophthalmol Vis Sci, 1993, 35, 803. 25. Greivenkamp JE, Mellinger MD, Snyder RW, Schwiegerling JT, Lowman AE, Miller JM. Comparison of three videokeratoscopes in measurement of toric test surfaces. J Refract Surg 1996; 12: 229-39. 26. Grimm BB. Communicating with keratography. J Refract Surg 1996;12: 156–9. 27. Hannush SB, Crawford SL, Waring GO III, Gemmill MC, Lynn MJ, Nizam A. Accuracy and precision of keratometry, photokeratoscopy and corneal modeling on calibrated steel balls. Arch Ophtalmol 1989; 107:1235-9.
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28. Holladay J., Warring G.O. Optics and topography in radial keratotomy. In : Warring GO, ed. Refractive keratectomy for myopia and Astigmatism. Mosby- Year book, Inc. 1992, 37- 144.
42. Le Geais J.M., Ren Q., Simon G., Parel J.M. Computer Assisted corneal topography: accuracy and reproducibility of the topographic modeling system. Refract Corneal Surgery, 1993, 9, 347-357.
29. Holladay JT, Cravy TV, Koch DD. Calculation of surgically induced refractive change following ocular surgery. J Cat Refract Surg 1992;18: 429–43.
43. Leroux Les Jardins., Pasquier N., Bertrand I. Topographie cornéenne computérisée : Résultats apres kératotomie Radiaire et « T-Cuts ». Bull Soc. Opht. France, 1991, 8-9, XCL, 729-734.
30. Holladay JT. Corneal topography using the Holladay diagnostic summary. J Cat Refract Surg 1997; 23: 209–21. 31. Holladay J.T. – The Holladay diagnostic summary. In : Corneal topography : the state of art, James P. Gills editor, Slack Inc., 1995, 309-323. 32. Huber C, Huber A, Gruber H. Three-dimensional representations of corneal deformations from kerato- topographic data. J Cat Refract Surg 1997; 23: 202–8. 33. Johnson DA, Haight DH, Kelly SE et al. Reproducibility of videokeratographic digital subtraction maps after excimer laser photorefractive keratectomy. Ophthalmology 1996;103: 1392–8. 34. Jongsma FHM, Laan FC, Stultiens BATh. A moiré based corneal topographer suitable for discrete Fourier analysis, Proc Ophthal Tech 1994;2126: 185 – 92. 35. Kawara T. Corneal topography using moiré contour fringes. Appl Optics 1979; 18: 3675 – 8. 36. Kelman SE. Introduction of neural networks with applications to ophthalmology. In: Masters BR (ed) Non-invasive diagnostic techniques in ophthalmology. SpringerVerlag, New York, 1990. 37. Klein SA, Mandell RB. Axial and instantaneous power conversion in corneal topography. Invest Ophthalmol Vis Sci 1995; 36: 2155-9.
44. Leroux Les Jardins., Pasquier N., Bertrand I. Modification de la chirurgie de l’astigmatisme en fonction des résultats de la topographie cornéenne computérisée. Bull Soc. Opht. France, 1991, 12, XCLS, 1097-1104. 45. Koch DD, Foulks GN, Moran CT, Wakil JS. The corneal EyeSys System: accuracy analysis and reproducibility of first-generation prototype. J Refract Corneal Surg 1989; 5: 424-9. 46. Lundergan MK, The Orbscan corneal topography system: verification of accuracy. International Society of Refractive Keratoplasty 1994 - Abstract book. 47. Maeda N, Klyce SD, Smolek MK, Thompson HW. Automated keratoconus screening with corneal topography analysis. Invest Ophthalmol Vis Sci 1994; 35: 2749–57. 48. Maeda M, Klyce SD, Smolek MK. Neural network classification of corneal topography. Invest Ophthalmol Vis Sci 1995;36: 1327-35. 49. Maguire LJ, Singer DE, Klyce SD. Graphic presentation of computer analysed keratoscope photographs. Arch Ophthalmol 1987;105: 223 – 30. 50. Maguire LJ, Wilson SE, Camp JJ, Verity S. Evaluating the reproducibility of topography systems on spherical surfaces. Arch Ophthalmol 1993; 111: 259-62.
38. Klein SA. A corneal topography algorithm that produces continuous curvature. Optom Vis Sci 1992; 69: 829-34.
51. Maloney RK, Bogan SJ, Waring GO III. Determination of corneal image- forming properties from corneal topography. Am J Ophthalmol 1993; l l 5: 31-41.
39. Klyce SD. Computer-assisted corneal topography: high resolution graphic presentation and analysis of keratoscopy. Invest Ophthalmol Vis Sci 1984;25: 1426 – 35.
52. Mandell RB, Horner D. Alignment of videokeratoscopes. In: Sanders DR, Koch DD, eds. An Atlas of Corneal Topography. Thorofare NJ: Slack, 1993: pp 197-206.
40. Klyce SD, Wang JY. Considerations in corneal surface reconstruction from keratoscope images. In: Masters BR, ed. Noninvasive diagnostic techniques in ophthalmology. New York: Springer-Verlag, New York, 1990: 76.
53. Mandell RB. Contact lens practice, 4th ed. Springfield, IL: Charles C.Thomas, 1988: pp 107-35.
41. Klyce SD, Dingeldein SA. Corneal topography. In: Masters BR, ed. Noninvasive diagnostic techniques in ophthalmology. New York: Springer-Verlag, 1990: pp 78-91.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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54. Mandell RB. Keratometry and contact lens practice. Optometric Wkly, May 6, 1965: 69-75. 55. Munger R, Priest D, Jackson WB, Casson EJ. Reliability of corneal surface maps using the PAR CTS. Invest Ophthalmol Vis Sci 1996; 37: s562.
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56. Mattioli R, Carones F. How accurately can corneal profiles heights be measured by Placido-based videokeratography? Invest Ophthalmol Vis Sci 1996; 37: s932. 57. Mattioli R, Carones F, Cantera E. New algorithms to improve the reconstruction of corneal geometry on the Keratron™ videokeratographer. Invest Ophthalmol Vis Sci 1995; 36:s302. 58. Mattioli R, Tripoli NA. Corneal geometry reconstruction with the Keratron Videokeratographer. Optom Vis Sci, 1997; 74:881-894 59. Merlin U. I cheratoscopi: caratteristiche e attendibilita. In: Buratto L, Cantera E, Dal Fiume E, Genisi C, Merlin U, eds. Topografia Corneale. Milano Italy: CAMO, 1995: 43-56. 60. Mishima S. Some physiological aspects of the precorneal tearfilm. Arch Ophthalmol 1965;73: 233. 61. Naufal SC, Hess JS, Friedlander MH, Granet NS. Rasterstereography-based classification of normal corneas. J Cat Refract Surg 1997;23: 222–30. 62. O’Bart D.P.S., Corbett M.C., Rosen E.S. The topography of corneal disease. Eur J Implant Ref Surg, 1995, 7, 173183. 63. Olsen T, Dam-Johansen M, Beke T, Hjortdal JO. Evaluating surgically induced astigmatism by Fourier analysis of corneal topography data. J Cat Refract Surg, 1996;22: 318– 23. 64. Parker P.J., KLYCE S. D., Ryan B. L. et al. Central topographic islands following photorefractive keratectomy. Invest Ophthalmol Vis Sci., 1993, 34, 803. 65. Prydal JI, Campbell FW. Study of precorneal tear film thickness and structure by interferometry and confocal microscopy. Invest Ophthalmol Vis Sci 1992;33: 1996–2005. 66. Rabinowitz YS, McDonnell PJ. Computer-assisted corneal topography in keratoconus. Refract Corneal Surg 1989;5:400-8. 67. Rabinowitz YS, Garbus JJ, Garbus c, McDonnell PJ. Contact lens selection for keratoconus using a computer assisted videokeratoscope. CLAO J 1991; 17:88-93. 68. Roberts C. The Accuracy of power maps to display curvature data in corneal topography systems. Invest Ophthalmol Vis Sci 1994; 35: 3524- 3532.
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69. Roberts C. Characterization of the inherent error in a spherically-biased corneal topography system in mapping a radially aspheric surface. J Refract Corneal Surg 1994; 10: 103-116. 70. Rowsey JJ, Reynolds AE, Brown DR. Corneal topography. Corneascope. Arch Ophthalmo1 1981;99: 1093–100. 71. Ruiz-Montenegro J., Mafra C.H., Wilson S.E. et al. Corneal topography alterations in normal contact lens wearers. Ophthalmology. 1993, 100, 128-134. 72. Salabert D., Cochener B,, Mage F., Collin J. Kératocone et anomalies topographiques cornéennes familiales. J. Fr. Ophtalmol., 1994, 17, lI, 646-656. 73. Sanders RD, Gills JP, Martin RG. When keratometric measurements do not accurately reflect corneal topography. J Cat Refract Surg 1993;19 (Suppl): 131–5. 74. Seiler T, Reckmann W, Maloney RK. Effective spherical aberration of the cornea as a quantitative descriptor in corneal topography. J Cat Refract Surg 1993;19 (Suppl): 155 – 65. 75. Takeda M, Ina H, Kobayashi S. Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry. J Optical Soc Am 1982;72: 156–60. 76. Taylor CT, Sutphin JE. Accuracy and precision of the Orbscan topography unit in measuring standardized radially aspheric surfaces. Invest Ophthalmol Vis Sci 1996; 37: s561.
Contents
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Section 3
Section 4
Section 5
Section 6
77. Thall EH, Lange SR. Preliminary results of a new intraSection 7 operative corneal topography technique. J Cat Refract Surg 1993;19 (Suppl): 193-7. Subjects Index 78. Tripoli NK, Cohen KL, Holmgren DE, Coggins JM. Assessment of radial aspheres by the arc-step algorithm as implemented by the Keratron keratoscope. Am J Ophthalmol 1995; 120: 658-64. 79. Tripoli NK, Cohen KL, Obla P, Coggins JM, Holmgren DE. Height measurement of astigmatic test surfaces by a keratoscope that uses plane geometry reconstruction, Am J Ophthalmol 1996; 121; 668-76. 80. Vass C, Menapace R. Computerised statistical analysis of corneal topography for the evaluation of changes in corneal shape after surgery. Am J Ophthalmol 1994;118:177– 84. 81. Vass C, Menapace R, Rainer G, Schulz H. Improved algorithm for statistical batch-by-batch analysis of corneal topographic data. J Cat Refract Surg 1997;23:903–12.
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82. Vass C, Menapace R, Amon M, Hirsch U, Yousef A. Batchby-batch analysis of topographic changes induced by sutured and sutureless clear corneal incisions. J Cat Refract Surg 1996; 22: 324–30. 83. Wang J, Rice DA, Klyce SD. A new reconstruction algorithm for improvement of corneal topographical analysis. J Refract Corneal Surg 1989; 5:379-87 84. Warnicki JW, Rehkopf PG, Arrra RC, Stuart JC. Corneal topography using a projected grid. In: Schanzlin DJ, Robin JB (eds) Corneal topography. Measuring and modifying the cornea. Springer-Verlag, New York, 1992. 85. Warnicki JW, Rehkopf PG, Curtin DY, Burns SA, Arffa RC, Stuart JC. Corneal topography using computer analyzed rasterstereographic images. Appl Optics 1988;27: 1135–40. 86. Warning G.O., Hannush S.B., Bogan S.J., Maloney R.K. – Classification of corneal topography with videotopography. In : Shanzlin D.J., Robin J.B., eds. Corneal topography : measuring and modifying the cornea. New York, NY, Springer-Verlag, 1992, 47-73.
Contents
Section 1 Section 2
87. Wilson SE, Klyce SD, Husseini ZM. Standardized colorcoded maps for corneal topography. Ophthalmology 1993;100: 1723-7.
Section 3
Section 4
88. Wilson SE, Wang JY, Klyce SD. Quantification and mathematical analysis of photokeratoscopic images. In: Shanzlin DJ, Robin JB eds. Corneal topography: measuring and modifying the cornea. New York, Springer-Verlag, 1991: 1-81.
Section 5
89. Wilson SE, Klyce SD. Quantitative descriptors of corneal topography. A clinical study. Arch Ophthalmol 1991;109:349-53.
Subjects Index
Section 6 Section 7
90. Wilson SE, Verity SM, Conger DL. Accuracy and precision of the Corneal Analysis System and the Topographic Modeling System. Cornea 1992; 11: 28-35. 91. Young JA, Siegel IM. Isomorphic corneal topography: a clinical approach to 3-D representation of the corneal surface. Refract Corneal Surg 1993;9: 74–8.
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92. Young JA, Siegel IM. Three-dimensional digital subtraction modeling of corneal topography. J Refract Surg 1995; 11: 188–93.
Dr. Guillermo L. SIMÓN University of Barcelona - Faculty of Medicine Dept. of Ophthalmology Chief Anterior Segment Surgeon Simon Eye Clinic, Barcelona (Spain) E-mail:
[email protected]
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EVALUATION OF THE LASIK FLAP BY CONFOCAL MICROSCOPY
Chapter 3 EVALUATION OF THE LASIK FLAP BY CONFOCAL MICROSCOPY Mahmoud M. Ismail, M.D., Ph.D.
Contents
(Note from the Editor in Chief: this chapter is important in describing a new diagnostic technique for detecting flap problems in LASIK and an important and easy method to prevent the Sands of the Sahara Syndrome.)
edema or wrinkling of the flap. In other occasions, fluctuation of the patient’s refraction is commonly seen during the early postoperative period. The evaluation with the slit lamp is not always decisive in such situations.
Frequent Problems With the Flap
What is Confocal Microscopy?
Section 1 Section 2
Section 3
Section 4
Section 5
The LASIK procedure is a continuous challenge towards perfection. In spite of all the recent advances in the technology of excimer lasers and the updated modifications in the microkeratome industry, we still experience some complications. The major problems that can appear with LASIK are always related to the corneal flap architecture (1)(2)(3). Buttonholes flaps, free cuts, intrastromal keratitis, and superficial flaps among others, are considered to be the most important technical complications (3)(4)(5). This might lead to further and even more serious consequences such as loss of one or more lines of preoperative best-corrected visual acuity (BCVA), epithelial ingrowth and the subsequent flap melting. In order to achieve the desired outcome, calibration of the microkeratome and use of the adequate nomogram are essential for obtaining the correct diameter and thickness of the flap and an adequate result. Also, delayed recovery of the BCVA following LASIK can occasionally occur due to
Confocal microscopy is a revolutionary new Section 6 diagnostic technique offering a high magnification view in living cornea. It is able to visualize Section 7 structures posterior to haze, scars, edema or opacities within the cornea. With the incorporation of the Subjects Index scanning mechanism, a complete and panel controlled automated scan to the corneal layers can be done in 2 seconds. This can provide an accurate measurement of each layer of the cornea, as well as total corneal thickness measurement (6)(7). It also provides understanding of clinical findings such as inHelp ? terface debris deposition and inflammation i.e. “Sands of the Sahara’s Syndrome”. Another use of the confocal microscopy is early detection of epithelial ingrowth, a good follow-up and prompt treatment. The Confocal microscopy post LASIK surgery is used to evaluate the following: 1- The whole corneal thickness (in microns). 2- The flap thickness (in microns). 3- Amount of stromal edema.
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Figure 3-1: Tandem Scanning Confocal Microscopy ASL 1000
Figure 3-2: LASIK interface a seen by confocal microscopy with bits of debris and inflammatory cells.
Confocal Microscopy Procedure
interface were imaged with debris and inflammatory cells (Figure 3-2). The measurement in microns is read followed on the monitor screen or from the micrometer. The stromal edema can be evaluated by the appearance of lacunas adjacent to the flap interface.
We use in our studies a Tandem Scanning Confocal Microscopy ASL 1000 (Advanced Scanning, New Orleans). The confocal microscopic examination is done under topical anesthesia (Figure 3-1) 1, 3 and 7 days post LASIK. We applied one drop of methyl cellulose on the tip of the confocal microscope objective and gently approached the cornea to be examined. The corneal thickness and the LASIK flap thickness were measured by focusing the confocal image on the superficial layer of the epithelium and subsequently focusing the scanning system until the endothelium or the stromal LASIK
Contents
Section 1 Section 2
Section 3
Results
Section 4
The measurements from the flap and whole corneal thickness are plotted in (Table 1). The identification of the flap thickness was determined in all eyes at the 1st day, 3rd and 7th day visits. The ultrasonic flap thickness is done intraoperatively. There
Section 5
Section 6 Section 7 Subjects Index
Table 1 Preoperative
1st day
3rd day
7th day
Confocal
545 ± 33µ
___
___
494 ± 45µ
cornea Ultrasonic
534 ± 28µ
___
___
486 ± 65µ
cornea Confocal flap
___
129.85 ±8 µ
120.25 ±3 µ
119.25 ±3µ
thickness Ultrasonic flap
12.6 ±5 µ*
___
___
___
thickness Edema
___
Present
Present
Absent
Mean BCVA
20/25
20/63
20/32
20/25
*Intraoperative measurement
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EVALUATION OF THE LASIK FLAP BY CONFOCAL MICROSCOPY
is no statistically significant difference when comparing ultrasonic pachymetry and confocal measurements.
The Importance of Confocal Microscopy to Sands of the Sahara’s Syndrome Interface debris deposition and subsequent inflammation commonly named Sands of the Sahara’s Syndrome is one sight threatening complication following LASIK . (Important but fortunately infrequent - Note from the Editor in Chief). It typically present 1 to 4 days following LASIK. Patients usually complain of decreased or cloudy vision, foreign body sensation and significant photophobia. Slitlamp examination reveals fine granular infiltrates with very mild ciliary injection. This condition was spontaneously appearing in sporadic cases in various refractive surgery centers. It was not properly identified until the introduction of the confocal microscope in the field of refractive surgery. Interface debris deposition and consequently inflammation was found to be due to accumulation of greasy material from the microkeratome blades. In rabbits, we experimented cleaning the blades with acetone and rinsing them with distilled water a dramatic improvement of such condition was notable Confocal microscopy imaging in cases of SOS revealed, besides abundant polymorph nuclear leukocytes, significant deposition of greasy material from the microkeratome blades (9)(10)(11). We performed a prospective study to verify the effect of blades cleaning by acetone and absolute alcohol in order to reduce debris deposition in LASIK interface. By such means we can eliminate an important predisposing factor for Sands of the Sahara’s Syndrome. We included in this study 40 patients undergoing bilateral LASIK randomly and equally divided into 2 groups (A and B). The patients were operated simultaneously on both eyes using the Nidek 5000 Excimer Laser and the Carriazo Barrraquer microkeratome (Moria). The mean age was 28.1 years (range from 19 to 52) and the mean spherical correction was -5.75 ± 1.63 D (range from -2.25 to 11.5). In the right eye of all patients in both groups, the microkeratome blade was taken directly from its
Figure 3-3: LASIK interface as seen by confocal microscopy with lot of debris and inflammatory cells suggesting SOS.
package without cleaning. However in the left eye, in group A, the same blade was cleaned with absolute alcohol and rinsed with distilled water prior to use. In group B, the same blade used for their right eye was soaked in acetone and rinsed with distilled water prior to use. Meticulous washing of the interface was performed and flap Reposition was done without contact lens. After 5 days of surgery, slitlamp and confocal microscopy examination were used to record any interface debris.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6
How to Prevent Sands of Sahara Syndrome
Section 7 Subjects Index
All patients had uneventful postoperative period with the LASIK flaps well-reposted and mean follow-up of 9.2 months (8 to 15 months). Clinical examination by slit-lamp showed only 4 eyes with significant interface debris deposition scattered all over the flap area (Figure 3-2). Such 4 eyes corresponded all to the right eye of patients with flap cut using uncleaned microkeratome blades i.e. taken directly from its package. In vivo examination by the confocal microscope of the LASIK interface to the right eye of patients revealed microscopic objects of approximately 10 to 20µ in diameter. These objects correspond to bits of debris scattered throughout the flap interface. Associated with the interface debris, numerous inflammatory cells were seen, mainly polymorph nuclear leukocytes (Figure 3-3). LASIK AND BEYOND LASIK
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On the other hand, no debris deposition was seen by slit-lamp examination of the left eye of the same patients (previously cleaned blades). Also, confocal microscopic examination of the LASIK interfaces of such eyes showed very scanty debris deposition. This debris was seen in 3 to 4 focal pockets surrounded by very few clusters of inflammatory cells. The rest of the interface of the LASIK flap created by the cleaned blade showed no debris or inflammatory cells. Comparing between alcohol and acetone for blade cleaning, no significant difference was seen regarding the confocal microscopic examination.
Other Contributions of Confocal Microscopy The confocal microscope offers the ability to examine objects at high magnification and literally can identify the cellular structure of the cornea. This revolutionary new tool permits real-time observation of living cornea in patients at magnifications ranging from 20 x to 500 x. And as a great advantage, it offers the possibility to visualize structures posterior to haze, scars or edema within the cornea. These advantages makes the confocal microscope the most suitable method to examine LASIK interface. Confocal microscopy can be employed in refractive surgery in general, and specifically in LASIK procedures for the following purposes: 1- Evaluation of interface edema 2- Accurate measurement of the flap thickness 3- Evaluation of interface for the diagnosis of the Sands of Sahara’s syndrome 4- Early diagnosis of epithelial ingrowth.
REFERENCES 1- Knorz MC, Wiesinger B, Liermann A, Seiberth V, Liesenhoff H.: Laser in situ keratomileusis for moderate and high myopia and myopic astigmatism. Ophthalmology 1998; 105:932-940. 2- Arbalez MC, Pérez-Santonja JJ, Ismail MM, Alio JL et al.: Automated Lamellar Keratoplasty (ALK) and Laser In Situ Keratomileusis (LASIK). Chapter 9:131-150 in: Refractive Surgery: Current Techniques and Manage-
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ment. Olivia Serdarevic, IGAKU-SHOIN Medical pubishers, New York-Tokyo, October 1996. 3- Gimbel HV, Penno EE, Van Westenbrugge JA, Ferensowicz, Furlong MT.: Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology 1998; 105:1839-1847. 4- Wilson SE.: LASIK: management of common complications. Laser in situ keratomileusis. Cornea 1998; 17:45967. 5- Smith RJ, Maloney RK.: Diffuse lamellar keratitis. A new syndrome in lamellar refractive surgery. Ophthalmology 1998; 105:1721-6. 6- Beuerman RW, Larid JA, Kaufman SC, Kaufman HE.: Quantification of real-time images of the human cornea. J Neurosci Methods 1994; 54:197-203.
Contents
Section 1
7- Ismail MM.: Corneal Imaging Using white-light Confocal microscopy. Bull Ophthalmol Soc Egypt, 1999. Vol 92, 2:1113-1116
Section 2
Section 3
8- Ismail MM, Kaufman S, Alio JL, Beurman R.: Evaluation of the LASIK flap by confocal microscopy. Cornea 2001 , In Press. 9- Kaufman SC, Maitchouk DY, Chiou AG, Beuerman RW.: Interface inflammation after laser insitu keratomileusis Sands of the Sahara syndrome. J cataract Refact Surg, 1998; 21:1589-1593.
Section 4
Section 5
Section 6 Section 7 Subjects Index
10- Kaufman SC, Ismail MM, Beuerman RW, Maitchouk D, Ohta T,Palkama A, Mustonen R, Chiou AGY.: PostLASIK interface debrisand interface inflammation (Sands of the Sahara). ISRS 1998 Pre-American Academy Conference. November 6-7, 1998. New Orleans-USA. 11- Kaufman SC, Ismail MM, Beuerman RW, Ohta T, Palkama A,Mustonen R.: Post-LASIK interface debris and keratitis: Doesforeign material on the microkeratome blade Cause “Sands of theSahara” Syndrome? Abstract Book page 899, 1999 ARVO meetingFlorida-USA. Mahmoud M. Ismail, M.D., Ph.D. University of Al-Azhar, Cairo - Egypt 21-A El Obour Buildings Salah Salem, 11371 Cairo, EGYPT. E-mail:
[email protected]
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PREDICTIVE FORMULAS FOR LASIK
Chapter 4 PREDICTIVE FORMULAS FOR LASIK Louis E. Probst V MD., Jonathan Woolfson MD., Michiel Kritzinger MB
The Predictive Formulas Main Components The predictive formulas for laser in situ keratomileusis (LASIK) have two components, the excimer laser ablation nomogram and the adjustment factors. The excimer laser ablation nomogram controls the relative distribution of the refraction correction into one or more zones. In some of the newer excimer lasers, such as the VISX Star, the excimer ablation nomogram is controlled by the lasers computer, while in other excimer lasers, such as the Chiron Technolas 116, the ablation nomogram is fully programmable by the surgeon. The adjustment factors allow surgeons to refine the treatment protocol to reflect their particular refractive situation. In order for these formulas to be predictive, a high level of consistency must be achieved in the application of both the ablation nomograms and adjustment factors. Other extraneous variables such as the methods of preoperative refraction, the room temperature and humidity, and room air quality and flow, surgical technique and time, and the postoperative medications must be tightly controlled to avoid deviations from the intended correction.
Developing Individualized Predictive Formulas It is crucial to remember that the predictive formulas including both the excimer laser ablation nomogram and the adjustment factors must be individualized for each surgeon. Direct extrapolations
from the experience of one surgeon or one center will likely lead to an unexpected deviation of the surgical results from emmetropia. Since it is impossible to control every aspect of surgery, each surgeon must develop their own predictive formulas once their technique has become standardized and their postoperative results can be analyzed. For the beginning LASIK surgeon, conservative corrections are preferable as enhancements are easy to perform while overcorrections can be much more challenging.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
The Healing Pattern of the Cornea
Section 6
Once the excimer ablation nomogram and the Section 7 adjustment factors have been standardized and indiSubjects Index vidualized for each excimer laser surgeon, the final uncontrolled variable with LASIK is the healing pattern of the cornea. While there is a clear tendency for greater amounts of regression after LASIK for higher levels of myopia, often the degree of regression after LASIK is unpredictable. Younger patients (< 25 years) often demonstrate significant regression Help ? while older patients (> 50 years) may not regress at all. We have often observed regression of 1.0 – 2.0 D in one eye and no regression in the other eye after bilateral simultaneous LASIK in which the excimer nomogram, the adjustment factors, surgical technique, and extraneous variables were all exactly the same for the correction of both eyes. This unpredictable healing pattern of the cornea represents the limitation of corneal refractive surgery. In order to avoid LASIK overcorrections, it is best to plan for a 10 – 20 % enhancement rate for lower myopes and LASIK AND BEYOND LASIK
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even higher rates with high myopes, which will allow retreatment for those patients that have regressed.
Excimer Laser Ablation Nomograms for Photorefractive Keratectomy The excimer laser nomograms for LASIK have been developed from the excimer LASIK experience with photorefractive keratectomy (PRK). The concepts of laser pretreatment to prevent central islands and multizone ablations to decrease ablation depth and smooth the laser contour evolved as the worldwide PRK experience as well as the technological capabilities of the excimer lasers increased.
Pretreatment Protocols Pretreatment protocols have been added to the ablation profiles of the broad beam excimer lasers such as the Visx Star, Summit Omnimed, and Chiron Technolas Keracor 116 to reduce the incidence of postoperative central islands.1 The Visx Star pretreatment is automatically calculated by the central island factor (CIF) 4.01 software and incorporated into the excimer ablation protocol. Approximately 1 micron per diopter of spherical correction plus an additional 2 microns is added to each ablation protocol and is performed at 2.5 mm. The Chiron Technolas Keracor 116 pretreatment is surgeon programmable. Generally, 1 micron per diopter plus 2 - 4 microns is added to each ablation protocol and is performed at 3.0 mm.2 The Summit Omnimed excimer laser has a gaussian beam distribution for which a relatively greater amount of laser energy is produced in the center of the ablation circle, so less pretreatment is required. A pretreatment of 1 - 2 microns per diopter is generally performed using the patient training “A” mode with optical zone of 2.6 to 2.8 mm. The newer scanning excimer laser systems such as the Chiron Technolas 217 excimer laser do not need pretreatment protocols as this phenomena of undertreatment of the central cornea is avoided with these scanning laser systems
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Single and Multizone Ablations Protocols All excimer laser refractive procedures modify the refracting power of the cornea by altering the anterior corneal curvature by the process of photoablation. The correction of myopia involves the relative flattening of the central cornea compared to the peripheral cornea, which reduces the anterior corneal curvature and hence reduces the refractive power of the treated area. Because the maximal corneal stromal tissue will be photoablated from the central cornea, the thickness of the central cornea becomes important when LASIK is performed for high refractive errors with large ablation depths. The excimer ablation techniques have evolved. The initial single zone techniques increased from 4.0 to 6.0 mm,3,4 to improve the quality of the postoperative vision and reduce the incidence of halos and regression. The multipass multizone technique was developed by Mihai Pop, MD for the Visx excimer laser5,6 and the multi-multizone technique was developed by Jeffery J. Machat, MD for the Chiron Technolas excimer laser.1 These multizone techniques divide the myopic treatment into multiple zones, which decreases the ablation depth and creates a smoother ablation surface. This blending and smoothing effect of the multizone protocols has helped to reduce the incidence of post-PRK regression and haze particularly for the treatment of high myopia.6
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Excimer Laser Ablation Nomograms for LASIK The creation of the corneal flap and the routine correction of higher levels of myopia with LASIK introduced new considerations into the excimer nomograms. The depth of the ablation and the size of the ablations zones have become recognized as crucial consideration to achieve a good quality and quantity of correction while maintaining the safety of the procedure and the stability of the cornea. If all of these factors are considered, LASIK has correction limits of 10 to 15 D of myopia depending on which ablation nomogram is used.
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PREDICTIVE FORMULAS FOR LASIK
Basic Tenets of LASIK There are four critical values or dimensions that must be considered when performing LASIK which are the flap thickness, the amount of the residual corneal stroma, the diameter of the excimer ablation, and the depth of the excimer ablation. The flap thickness must be sufficient to prevent irregular astigmatism while not so excessive to remove stroma potentially available for ablation. We generally use a 160 µm flap for thin corneas or large refractive corrections (> 10.0 D), a 180 µm flap for average corneas and moderate corrections (> 6.0 D), and a 200 µm flap for thick corneas and small corrections (< 6.0 D). Sufficient residual posterior stroma must be left after the LASIK procedure to avoid a decrease of the corneal integrity and the subsequent development of corneal ectasia. Since iatrogenic keratoconus has been observed after automated lamellar keratoplasty (ALK) with 200 µm of remaining posterior stromal tissue, we generally elect to leave at least 250 µm of posterior stromal tissue. The diameter of the excimer ablation should be at least 6.0 mm create a functional postoperative optical zone of at least 4.0 mm which will allow for sufficient quality of vision. Finally, the depth of the excimer ablation determines the quantity of myopia the can be safety treated while preserving adequate residual corneal stroma.
Ablation Depth Per Diopter Each excimer laser ablates a different amount of stromal tissue per diopter of refractive correction because of the differences in the ablation zone diameters, amount of pretreatment, and the ablation protocols. The Munnerlyn formula8 (depth of ablation = diopters of correction X ablation diameter2 : 3) indicates that each spherical equivalent (SE) diopter of myopic correction performed at a 6.0 mm single zone will ablate 12 microns of tissue. Pretreatment protocols added to the ablation profile of broad beam excimer lasers such as the VISX Star and the Chiron Technolas Keracor 116 will increase the depth per SE diopter to 17-20 microns for low corrections (1 - 2 diopters) and 15-17 microns for higher corrections (3 or more diopters). The Summit Omnimed will ablate 13.0 to 14.0 microns per SE diopter for all levels of myopia with pretreatment.
The multipass multizone ablation technique used with Visx Star “international cards” has an average stromal ablation 12.5 microns per SE diopter. The full multi-multizone ablation technique with the ablation pattern distributed between 3.6 and 6.2 mm reduces the average stromal ablation to approximately 10 microns per SE diopter.1 While the full multi-multizone protocol significantly reduces ablation depth, it should be only be used for LASIK when necessitated by a thin cornea associated with high myopia because of the compromised quality of postoperative night vision.
Correction Limits for Primary LASIK The average central cornea thickness is approximately 550 + 100 µm.9 Since the flap thickness during the LASIK procedure is generally 160 µm, the average cornea will have 390 µm of posterior stromal bed left after the flap creation. Therefore, the maximal myopic correction that should be performed on a patient with a 550 µm cornea using a full multi-multizone technique is generally less than 14 D while leaving a residual posterior stromal bed of 250 microns. A partial multizone ablation as performed with the Chiron Technolas 116 and the VISX Star would allow a maximal correction of approximately 12.0 D, and a single zone ablation would allow a maximal myopic correction of 10.0 D.10
VISX Star: Predictive Formulas for LASIK
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
The VISX Star utilizes a propriety multizone nomogram developed from the PRK multizone experience with the VISX 20/20 excimer laser. A pretreatment is combined with a multizone ablation that is not surgeon programmable. While this limits the flexibility of the laser for adjusting ablation zone size, which would be beneficial for patients with large pupils, it does reduce the variation in the techniques of surgeons and therefore allows for good comparisons between centers. One number of factors may contribute to the increased effectiveness of the VISX Star excimer laser when used for LASIK. The vacuum nozzle of this machine may decrease stromal hydration, in-
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creasing the effect of the excimer ablation. The slower pulse frequency may allow the corneal to dehydrate. Surgeon factors such as the time taken to perform the procedure and the methods of drying the cornea have also been considered. Once several centers gained more experience with the VISX Star laser, a pattern began to emerge regarding the “adjustment factors”. The nomograms for 15 surgeons that have performed more than 500 LASIK procedures each on the VISX Star laser were compared (Tab. 1). The range of the myopia treated and the enhancement rates were recorded to ensure that most surgeons were achieving a similar level of predictability with their procedures. The temperature room and the humidity range of the procedure rooms did not correlate with the adjustment factors used at each center. Most surgeons did not use drying techniques. The altitude emerged however as a consistent factor that seemed to be related to the adjustment factor. When the two factors were correlated it was found that there was a statistically significant correlation between the altitude of the refractive center and the surgeon spherical adjustment factor.
This variation in the effectiveness of the excimer laser at different altitudes is probably a function of the changes in air density. Increased humidity will actually decrease the air density. However, its effect on the air density is minimal and most refractive centers have humidity control systems installed. Temperature is usually well controlled so it is unlikely that this would introduce significant variation in results. The station pressure is the direct barometer reading. While we currently adjust the spherical component of the VISX Star ablation by a constant value that seems to be related to altitude, perhaps our adjustments in the future will be based on the daily barometric reading and the corresponding calculations of air density.
VISX S2 SmoothScan: Predictive Formulas for LASIK
Contents
Section 1
The adjustment factors utilized for the VISX S2 Smoothscan excimer laser upgrade are very similar to those used for the VISX Star laser. Most surgeons have made only minor adjustments to their
Section 2
Section 3
Section 4
Section 5
Table 1 Nomogram Comparison Table
Section 6 Section 7 Subjects Index
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VISX Star reduction factor. Increasing the frequency of the excimer pulse to 10 Hz reduces the laser time by almost 50% but does not effect the degree of refractive correction. The spherical reduction factor that we currently utilize at TLC Chicago is outlined (Table 2). Table 2 Probst Nomogram for Visx S2 SmoothScan < 25 years
25 – 45 years > 45 years
< 2.0 D myopia
100%
100%
100%
> 2.0 D myopia
90%
86%
84%
For hyperopic corrections, we utilize the 5.0-mm optical zone with a 9.0-mm blend zone for hyperopic LASIK with the Hansatome. For hyperopes, we add between 10 and 20% to the spherical refractive error to account for the greater amount of regression that occurs with the treatment of hyperopia.
Chiron Technolas 116: Predictive Formulas for LASIK With the Chiron Technolas 116, the ideal zone depth for each step of the multizone LASIK ablation was initially felt to be 15-20 µm to create the smoothest blended multizone ablation2 (Tab. 3). This algorithm was similar to those used for PRK and provided a smooth blend of the myopic ablation with zones that extended from 3.6 mm to 6.2 mm for maximum seven zones. This full multizone ablation allowed the treatment of high levels of myopia as the total ablation depth was minimized with the smaller zone size. Unfortunately, the smaller zone sizes resulted in a significant reduction in the effective optical zone observed on corneal topography following LASIK. High myopes treated with the full multizone algorithm demonstrated effective an optical zone that was often less than 4.0 mm. Clinically, this resulted in complaints of visual distortion and halos at night in the same manner the early small zone PRK ablations were associated with these difficulties. Decentrations are poorly tolerated with the small zone ablations as the refracted light for the edge
Table 3 Previous Machat Chiron 116: LASIK nomogram for high myopia Important points • No vertex distance correction. • Pretreatment 1 micron per diopter plus 2 to 4 microns total • Depth at 3mm for Chiron Technolas Keracor 116 to compensate for central island information • All treatment zones of equal depth (not including pretreatment step) • All zones ideally between 15 and 20 microns • Goal is to achieve at least 6-mm effective optical zone • Compressed air is used intraoperatively to control hydration.
Contents
Lasik nomogram for -13 D attempted correction Optical zone
Dioptric distribution
Percentage of treatment
Micron depth
Petreatment (1 µm/D + 3) 27.9 18.9 14.6 11.2 9.5 8.8 8.15
16
Section 1 Section 2
Section 3 3mm
-5.4D
3.6 mm 4.2 mm 4.8 mm 5.4 mm 5.8 mm 6 mm 6.2 mm
-3.63D -.258D -1.90D -1.46D -1.23D -1.14D -1.06D
Section 4
17 17 17 17 17 17 17
Eight zones of equal micron depth. Each zone 0.6 mm larger than the previous zone, with two additional zones within 0.2 mm of 6-mm optical zone to ensure adequate peripheral blend for reduced spherical aberration and night visual disturbances.
Section 5
Section 6 Section 7 Subjects Index
of the ablation could be in close proximity to the visual axis. Machat has found that the size of the ablation zones should be increased so that most of the treatment is performed at a 5.5 mm or larger ablation zone.11 This increases the depth of ablation to 30 - 40 µm per zone in the partial multi-multizone protocol which accounts for the hydration effects of the deeper stroma and the masking effect of the corneal flap. By increasing the size and depth of ablation of each zone to 30 - 40 µm and decreasing the number of zones, the effective postoperative optical
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zone on videokeratography can be increased, and night vision difficulties minimized (Tab. 4). This partial multi-multizone ablation that we now use for LASIK ablations removes 12.5 microns of stroma per SE diopter. While the quality of the night vision is improved with these new algorithms, the depth of ablation per diopter must be increase with the corresponding increase in zone size. This limits the quantity of myopia that can be safely corrected to approximately 15.0 D in an eye with an average corneal thickness.
KRITZINGER NOMOGRAM FOR TECHNOLAS 217 EXCIMER LASER The success of excellent postoperative visual results does not only depend on the nomogram, but also comes into play: • Environmental factors in the operating room; temperature, humidity and drafts in the air. • surgical technique of the surgeon. • preoperative refraction of the patient. • postoperative medication to the patient.
Table 4 TLC the laser center: Chiron 116 nomogram Contents
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Section 6 Section 7 Subjects Index
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•
type and make of the laser in use, broadbeam/ scanning.
• •
A) GENERAL RULES • • • • •
•
•
•
•
Room temperature: 16º - 18º C. Room humidity: 45 - 50%. Exact super-imposition of red and green HeNe beam critical - or under corrections will occur. Use 6 x magnification - not larger, because you can loose your orientation to the visual axis. Correctly align patient prior to lifting the flap, to limit exposure time of stroma before the treatment starts: Thus it will give you more accurate and consistent visual results. Lift flap with a Colibri - do not use BSS cannula as this may introduce moisture to the bed. Do not use a spatula, since foreign material e.g. epithelium may be introduced into the interface. Commence laser treatment, and let the assistant press the “enter” key to give continuous treatment without breaks, so that you make the treatment time and the stromal exposure time as short as possible. Avoid contact with the stromal bed - do not wipe whilst lasering the stroma - this is totally contraindicated, because it will give overcorrections with the 217 laser.
Minimum residual cornea after ablation 250 micron (excluding flap thickness). Ideal treatment zone 4mm - 6mm. It is advisable not to use a smaller zone diameter than 4.0mm (night vision glaze) and a maximum zone diameter of 6mm (unnecessary vertex ablation and over - corrections will results).
B) KRITZINGER NOMOGRAMS 1. Myopia • • • •
For treatment of -1.0 to - 13.0 spherical equivalent diopters. Use subjective spectacle correction for minus spheres. Add 10% to sphere and cylinder. Subtract / or add the calculated cylindrical correction from / to the calculated spherical correction, because:
Contents
Section 1 Section 2
Section 3
- 20% Hyperopic coupling shift with negative cylinders, on the spherical diopters. - 10% Myopic coupling shift with plus cylinders, on the spherical diopters.
Section 4
Section 5
Section 6 Section 7 Subjects Index
Probst Nomograms Chiron Technolas 217 Planoscan version 2.422
Zone
Sphere
Cylinder
Comment
5.5 6.0
add 10% add 10%
add 10% no change
add 20% -cyl to -sph
Myopia (minus cyl)
Kritzinger Probst
Hyperopia (plus cyl)
Argento4.2-5.5 add 50-75% add 25% add +sph >40 yrs Kritzinger 5.5 add 15% add 10% subtract 10% of cyl from sph Probst 6.0 add 20% no change
Mixed (plus cyl)
Kritzinger Probst
5.5 6.0
add 10% no change
add 10% no change
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add 1/3 +cyl to -sph add 1/3 +cyl to -sph
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2. Hyperopia • •
• • •
For treatment of + 1.0 to + 3.0, (rarely up to +4.0 D) spherical equivalent diopters. Selection of treatment program, of the (217) laser (Hyperopia/myopia) is dependent on the sphere, and not the cylinder. Use subjective spectacle correction. Add 15% to sphere and 10% to the cylinder. Subtract / or add the calculated cylindrical correction from / to the calculated spherical correction, because:
correction, unless monovision is planned in the nondominant eye. Older patients (<50 years) are usually best undercorrected by 0.5 D as they tend to have a greater response to the excimer ablation and are less tolerate of overcorrections. Casebeer has described his nomogram for LASIK based on the dry climate of Arizona13 (Tab. 5).
Table 5 The Casebeer LASIK personal calibration nomogram (based on Arizona’s dry climate
- 20% Hyperopic coupling shift with negative cylinders, on the spherical diopters. - 10% Myopic coupling shift with plus cylinders, on the spherical diopters. Contents
3. • •
•
Information
Hyperopic treatment regress more than Myopic treatments. If one has a high plus sphere and any strength minus cylinder, one should do a transposition to a plus cylinder (less tissue ablation, shorter treatment time, less gas consumption). Most plus spheres are treated in the plus cylinder prescription - therefore a transposition is often required.
Adjustment Factors for the Refractive Correction of LASIK Aside from the altitude of the refractive center, patient age is the other commonly considered adjustment factor. Patient age has been used in the past predominantly for the radial keratotomy and astigmatic keratotomy nomograms.12 Age adjustments have been less consistently applied for LASIK. Since a refractive stability is achieved with LASIK by 3-6 months postoperatively, the hyperopic drift that occurred with RK is not a concern with LASIK. Slight overcorrection of 0.5 D is preferable is patients under the age of 25 years, as the vision will be excellent and small buffer is created against a future regression of effect. Middle aged patients between 25 and 50 years are best treated with the full refractive
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Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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PREDICTIVE FORMULAS FOR LASIK
REFERENCES 1.
2.
Machat JJ. PRK complications and their management. In Excimer Laser Refractive Surgery. Machat JJ (ed). Slack Inc., Thorofare, NJ, 1996. Machat JJ. LASIK Procedure. In Excimer Laser Refractive Surgery. Machat JJ (ed). Slack Inc., Thorofare, NJ, 1996.
3.
Gartry DS, Kerr Muir MG, Marshall J. Photorefractive keratectomy with an argon fluoride excimer laser: a clinical study. Refract Corneal Surg 1991;7:420-435.
4.
Talley AR, Hardten DR, Sher NA, et al. Results one year after using the 193-nm excimer laser for photorefractive keratectomy in mild to moderate myopia. Am J Ophthalmol 1994;118:304-311.
5.
6.
7.
Pop M, Aras M. Multizone/Multipass photorefractive keratectomy: six-month results. J Cataract Refract Surg 1995;21:633-643.
12. Committee on Ophthalmic Procedures Assessment, American Academy of Ophthalmology. Radial keratotomy for myopia. Ophthalmology 1993;100(7):1103-1115. 13. Casebeer JC. A systemized approach to LASIK. In Buratto L (ed) LASIK. Principles and techniques, Slack Inc. Thorofare, 1997, pp. 225-228. 14. Salah T, Waring GO III, Maghraby AE, Moadel K, Grimm SB. Excimer laser in situ keratomileusis under the flap for myopia of 2 to 20 diopters. Am J Ophthalmol 1996;121:143-155.
Louis E. Probst, MD Medical Director TLC The Windsor Laser Center 3200 Deziel Drive, Suite 208 Windsor, Ontario N8W 5K8 CANADA E-mail:
[email protected]
Contents
Section 1 Section 2
Section 3
Pop M. The Multipass/Multizone PRK technique to correct myopia and astigmatism. In Excimer Laser Refractive Surgery. Machat JJ (ed). Slack Inc., Thorofare, NJ, 1996.
Section 4
Section 5
Section 6
Alpins NA, Taylor HR, Kent DG, Lu Y, et al. Three Multizone photorefractive keratectomy algorithms for myopia. J Refract Surg 1997;13:535-544.
8.
Munnerlyn CR, Koons SJ, Marshall J. Photorefractive keratectomy: a technique for laser refractive surgery. J Refract Surg 1988;14:46-52.
9.
Emara B, Probst LE, Tingey D, et al. Correlation of intraocular pressure and corneal thickness in normal myopic eyes and following LASIK. J Cataract Refract Surg 1997 (in press).
Section 7 Subjects Index
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10. Probst LE, Machat JJ. The Mathematics of LASIK for high myopia. J Cataract Refract Surg 1997 (in press). 11. Probst LE, Machat JJ. LASIK enhancements techniques and results. In Buratto L (ed) LASIK. Principles and techniques, Slack Inc. Thorofare, 1997, pp. 325-338.
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Section 2 Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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MICROKERATOMES
Chapter 5 MICROKERATOMES Cesar Carriazo E., M.D.,
The idea to modify the normal corneal shape, looking to correct spherical ametropias of corneal origin (axial or aphakic), goes back to 1949 J. I. Barraquer M. (Fig 1)., 1950: A. Poyales and 1951: Sato. In 1949, Professor J.I. Barraquer M., in his preliminary notes under the tittle REFRACTIVE KERATOPLASTY, proposes the Keratoplasty as a new invention to modify the refraction in ametropIc eyes, without compromising the corneal transparency. In 1958, began the age of manual carving of the corneal graft, previously freezing the flap and posteriorly giving to them a new radius of curvature with a lathe. Until 1962, the corneal flap of the patient was obtained manually, then in 1963 Professor Barraquer M. developed The Microkeratome based on the Electrokeratome from Dr. Castroviejo. Later, Dr. John Charamis, proposes the name of “Keratomileusis” from Greek Kerato=Cornea and Smileusis=sculpture. In later years, the “excimer laser” is introduced to this surgical technique that gives a higher predictability in the results and easier technique known as the name of “LASIK” (Laser Intrastromal Keratomileusis). The Microkeratome is a surgical instrument designed by Professor Jose Ignacio Barraquer Moner in 1963 in order to realize corneal sphere lamellar resections with a predetermined diameter and thickness. The name “ Microkeratome” is the abbreviation of micro-electro-keratome; this instrument was based in the “ carpentry smoothing plane” principle,
Contents
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Section 3
Section 4
Section 5
Section 6 Section 7 Fig 5-1. Photograph of Dr. Jose Ignacio Barraquer M.
and in spite of new designs, the majority kept the same initial principles described by its inventor. In 1964. Strampelli described one Electrokeratome in order to make Corneal Resections based in moulding. In 1966, Katzin and Martinez described their keratophakatome in order to cut lenticules based on moulding. In 1969, Elstein and Katzin described a new prototype of Microkeratome. In 1972, Professor Draeger proposed a Lameralotomy with a circular blade for performing corneal resections. In 1975, he presented his rotary keratome for refractive surgery. In 1986, Krumeich and Swinger developed a complete instrumental kit to perform Keratomileusis without freezing.
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In 1991, Ruiz and Lenchig completed a new Microkeratome model, which automatically slides over a ring; also they modified the suction ring with a height adjustment. In 1993, Guimaraes developed a model named Clear microkeratome. In 1994, Hoffman and Seiler developed a Keratome and a suction ring with a Sapphire blade (Schwind Microkeratome). In 1995 Kpepenick introduced a Microkeratome specially designed to realize Keratomileusis “in situ”, with individual applanation lenses, which would be cut and dried in order to obtain the desired adjustment. (Universal Phoenix keratome). In 1995 C. Carriazo and J.I. Barraquer begin preliminary studies about “ Superior Hinge ” in Lasik as a new surgical technique, and in 1996 introduce the Carriazo-Barraquer Microkeratome designed to leave the hinge in any quadrant of the cornea. In 1997, Chiron House also developed a new prototype of Microkeratome for “Superior hinge” with an automatic advance system with an curveshaped track. In the last two years there have appeared new microkeratomes with rings, shapes, heads and blades, which follow the Barraquer principle (Amadeus, Nidek) being bigger than the existing majority. Nowadays there are new technologies different to the mechanical microkeratome, like the microjet (no commercial samples available), and the femtosecond laser, which is under investigation. The last technologies are more complicated in its assembly, they are more expensive and need more maintenance. This year Carriazo will introduce a new microkeratome concept, that uses a PENDULAR system, which avoids contact with any corneal quadrant and will work at low suction pressure.
Generalities The microkeratomes that follow the line of Barraquer prototype (FIG 5-2) are composed of: Head of Microkeratome 1. -Two lateral guides 2. -The applanation plate 3. -Blade holder
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4. -Blade Motor Suction Ring Cables and power Source Applanation Lens Tonometer
Head of Microkeratome
EXCÉNTRIC OF THE MOTOR
MOTOR
RING HANDLE
RING
PLATE
Contents
BLADE BLADE
Section 1 GUIDES
RING
Fig 5-2. Diagram of the Head, Motor and Ring in Barraquer microkeratome.
Section 2
Section 3
Section 4
Section 5
Two lateral guides: These guides present a v- Section 6 shaped groove which join with its homonym placed in the suction ring and have as their function to al- Section 7 low the sliding of Microkeratome over the suction Subjects Index ring, keeping its correct position over it. The applanation Plate: It is located before the blade and its function is to maintain the cornea flap so the blade can perform uniform cuts of parallel faces. The height of it, related to the blade plane will determine the thickness of the flap that it desires to cut. Help ? Blade holder: It is an independent piece that occupies a cavity in the center of the head. The blade fits into its inferior part; and in one of its faces has a slot that allows the coupling with the eccentric axle of the motor. Blade: Initially commercial blades were used (Schick Injector). Nowadays each commercial house fabricates its own blades, with different shapes and dimensions for each Microkeratome model. The ideal angle attack of the blade is between 26-30.
MICROKERATOMES
Fig 5-3. A- Diagram of the blade with 26 degrees of angular attack. B- Blade with 0 degree of angular attack.
Contents
Section 1 Section 2
Degrees (Fig 5-3). The angle attack of the blade in 0 degree doesn’t have good results.
Section 3
Section 4
Motor The motor generates an oscillating movement to the blade in order to make the cut. Initially work was begun with electric motors, which only moved the blade through an eccentrical in its tip, nowadays there have been adapted reductors and gear system that automatically allow it to advance itself while it cuts. There also exist turbines and systems that can generate this oscillating movement to the blade.
Suction Ring (Fig 5-4) It has the shape of a small cylinder with a central hole through which the cornea comes out. Its superior face has a channel that allows the guiding of the Microkeratome. The inferior face is concave and it has an ample groove in which the suction is established in order to fix the ring to the ocular globe. The suction reaches the cavity of the ring through a hole in the handle that is connected to an suction pump by a plastic tube.
Section 5 Fig 5-4. Original Barraquer Suction Ring.
Section 6 Section 7
The suction ring has different functions de- Subjects Index pending on the type of keratome used: a) to settle the globe; b) to give a plane to the displacement of the Microkeratome; c) to regulate and to keep the intraocular tension; d) to control the resection diameter; e) to serve as brake to obtain the hinge; f) to serve as final coupling to the automatic advance Help ? In the initial nomenclature used by Barraquer, the pneumatic ring is labeled with two numbers. The first one is the scleral radius, and the second, the height, which means the distance. (For example: 1254 tenths of millimeters). This ring can be adapted to almost any ocular globe and obtain a corneal flap of 8.5 to 9 millimeters of diameter. There exists an inverse proportion between the corneal radius and the resection diameter, with the same ring; the flatter corneas will produce smaller resection diameters.
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The corneal flap that is obtained through Microkeratome setting of 26 degrees has beveled edges. The cutting blade edge in small diameter resections has an oblique incidence over the cornea, and in bigger diameter the incidence is more oblique, so the bevel changes with the disc size. This feature allows the positive lenticules resection if the resections are planned in 5 millimeters diameter or smaller.
Tonometer (Fig 6 ) It is use to measure the intraocular pressure. It is of plastic, and is based in the Maklakow principle. It has a constant weight, what varies is the applanation area.
Cables, Pedals and Power Source These regulate and control the energy imparted to the motor and to the suction ring. They are different in size in all microkeratomes.
Applanation Lenses
( Fig 5-5)
They are transparent plastic lenses, labeled with different circles with known diameters. The applanation lenses are used to know beforehand the diameter, which will be obtained in the patient’s cornea and avoid unexpected small diameter, it is clear that the differences will be kept in the order of tenths of millimeters, but nowadays a resection of 8.25 millimeters makes a difference if we are expecting 9 millimeters. The use of the applanation lens also helps in the planning of the hinge in general with 500 of curve longitude, allows an adequate manipulation of the flap and ensures an easy reposition of it.
Fig 5-5. Diagram of the applanation lens.
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Contents
Section 1 Section 2 Fig 5-6. Diagram of the Barraquer tonometer.
Section 3
Section 4
General Steps for the Microkeratome Use
Section 5
Section 6
How to assemble the Microkeratome: In- Section 7 cludes mounting the blade, placing the plate that is going to be used, or select it depending on the sys- Subjects Index tem that the instrument uses. To verify the adequate functioning of the Microkeratome: The sound of the instrument is a guide of the function itself. The adequate movement of the blade and the advance system should be seen. It’s very important to check the vacuum with and Help ? without occlusion. Selection of the suction ring that will be used with the patient: Due to the fact that esklerotomes are not used in the refractive surgery equipment, the ring is clinically chosen according to the exposed diameter of the ocular globe. If we are before a clinically big eye, a high radius ring should be used and vice versa. To use the same ring for all eyes is dangerous as there will always be eyes which are too far from average parameters and they will couple inadequately.
MICROKERATOMES
To regulate the microkeratome brake: The brake of the microkeratome is a system that is used to avoid totally cutting the flap, in that way leaving a hinge, which allows guiding the flap to its original position. Some microkeratomes have labeled brakes, others are regulable in the micro and/or in the ring, and others are adjustable from the power unit. In all cases it is very important to verify, to regulate, and to choose it before the surgery in order to avoid a complete section of the flap. Placement of the suction ring over the ocular globe of the patient: Previous to the placement of the suction ring a corneal references mark must be make in order to guide the flap reposition in the eventual case of a total section. The placement of the suction ring over the ocular globe should be always go together with a previous verification of an adequate suction. The ring should be oriented according to each cutting system of the Microkeratome and should be suitably centered to come out of the cornea with the center of the hole. The best way to verify an adequate coupling of the ring over an eye, is pulling upward on it, and watching for its adequate grip . If the ring loosens, another ring of higher or lower radius should be tried according to the case, or the suction system verified. Measuring intraocular pressure: At this moment, the best Tonometer that lets us verify the intraocular pressure is the Barraquer tonometer; it has to be approximately of 65 mmHg. If applanation inside the tonometer circle is not obtained it means we don’t have an adequate pressure and there is the risk of an irregular cut or a perforation of the flap. This can happen when there is not an adequate coupling of the ring with the ocular globe, which makes it primordial to change the suction ring for another one of a more adequate radius, or to look for the cause of the low pressure obtained . Placement of the applanation lens: To place the applanation lens it is ideal to put it over the cornea coming in from the upper side so that the appla-
nation will be uniform to avoid to friction to the epithelium, and for corneal the distribution to be adequate. This lens is transparent and when place over the cornea it allows the observation of the diameter of the flap that is going to be cut before cutting it, and in this way modify the size of the hinge that is going to be leaf, or to change the suction ring if a flap of another size is wanted. Coupling the guiding groove or grooves of the Microkeratome with the guides of the ring: This coupling must be done softly and uniformly without using leverage. When there is a double guide it has to be verified that both are inside their homonyms before activating the motor. Once the Microkeratome is in the advance position, the cornea must be wet in order to reduce the heat that the blade generates to the corneal stroma Contents during the cut, and for a better displacement of the applanation surfaces of the Microkeratome. Section 1 Activate the motor and make the cut: Once, the motor is activated, if the microkeratome is Section 2 manual, a slow and uniform translation movement Section 3 should be applied in order to avoid the irregular surfaces generated by not uniform movements, or the Section 4 shallowness of the cut that can happen if the moveSection 5 ment is too fast. If the Microkeratome is automatic and of ex- Section 6 posed gears, an adequate initial coupling of the advance gear with the first tooth of the track must be Section 7 verified and you must make sure that there are no Subjects Index structures that will interfere with its path. Remove the microkeratome from the ring: Once the cut is made, the microkeratome should be put in the initial position manually or with the back pedal in automatic cases. If the microkeratome gets stuck on the way a maneuver must be done that includes stopping the suction and uncoupling softly the Help ? ring with the microkeratome as if they were a single unit, taking it in the opposite direction of the advance path. This movement allows the cut flap to slide between the plate and the blade and reposition itself on its original bed.
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Release the suction and remove the ring from the ocular globe: the ideal is to uncouple the head of the microkeratome from the ring ,and then release the suction and remove the ring from the ocular globe. Frequent mistakes are inherent to the inadequate use of the microkeratome and /or surgical technique.
Microkeratome Stopping In manual Microkeratomes, the most frequent stop observed is one of transitory type, which is overcome by increasing the forward force given by the surgeon’s hand. This stop is usually caused by a bad distribution in the direction of the force. To impart a not uniform velocity to the cut, will generate scaled irregularities in the surfaces. When the advance of the Microkeratome is too fast, it generates flap of less thickness and it increases the risk making the cut too shallow and to break the flap. The stopping problems of the microkeratomes that advance by gears over a rail track have different causes: ( Fig 5-7) The engaging gear of the microkeratome should fit perfectly in the first tooth of the rail track,
in order to allow the advance of it. If the tooth of the gear doesn’t fit with the rail track, the motor stops from the beginning, therefore it has to perform and an uncoupling and recoupling in order to achieve an adequate engagement.. If there is not an adequate approach of the gears to the rail track at the moment the motor is activated, it will turn in the air and it will not advance. This is solved advancing the microkeratome adequately; in these last cases there isn´t a real complication as the blade has not made the cut. When the Microkeratome it well engaged the advance is uniform and an excellent regularity of the cut is obtained. These gear systems and exposed rail tracks present the following problems: They depend on a perfect state of the teeth of the rail track and of the gear, and the damage of these generate an imminent obstruction of the machine. The motor that imparts the advance has the adequate potency in order to move the system while the system is adjusted. The back weight of the motor added to the leverage, which transmit a unilateral and superior traction to the contact floor, generates an effect of torque that can stop the movement of the instrument producing an incomplete flap. ( Fig 5-8)
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Help ?
Fig 5-7. Diagram of different possibilities of the microkeratomes engagement that uses external gears.
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Fig 5-8. Corneal disc with incomplete cut.
MICROKERATOMES
Fig 5-9. Corneal disc with irregular cut.
Fig 5-10. Corneal disc with button hole.
Contents
Irregular Cuts of the Flap: (Fig
5-9)
This complication is observed when a defective blade is used or there is a transitory or a permanent suction loss. When this complication presents itself you must abort the procedure and replace the flap as anatomically as possible drying its edges. After this complication you must wait three months as a minimum to perform the procedure again.
Flap Perforation:
(Fig 5-10)
The perforation of the corneal flap is more frequent in curved corneas or with high astigmatisms and it is the result of the inadequate use of the ring or of a microkeratome with an inadequate dimension for these cases. The phenomenon that occasionally presents itself at the moment of flattening a cornea that is too curved is a central folding of the cornea and a superficial cut in the center of the flap. Is due to the fact that in the middle of the cut you are in the area of larger diameter of the flap. This types of corneas need a bigger space to expand to the sides; when the internal lateral walls of the microkeratome don’t allow its lateral extension the cornea has no other chance different than to fold downwards (towards
the anterior chamber of the eye) as it is been flattened by the applanation plate. The handling of this complication is the same as that of irregular cut of the flap.
Irregularity in the Interface
Section 1 Section 2
Section 3
Section 4
Section 5
In the cases of manual microkeratomes it preSection 6 sents a not uniform translation movement as a result of an inadequate push and in the cases of automatic Section 7 Microkeratomes it presents a transitory stopping, which can produce a surface of irregular cut. It also Subjects Index can be seen when the cutting edge of the blade is imperfect. In these cases when the flap is not perforated or ripped, the surgical procedure can be performed keeping in mind to make an adequate repositioning of the disc so that the irregular surfaces a replaced in their exact position. Help ?
Transitory and/or Permanent Suction Loss Promoting microkeratomes with only one suction ring is to subtract importance to the morphology of the ocular globe. And generally, the observed complications are because of this ignorance All eyes are not equal and therefore they don’t have equal curvature scleral radius. We cannot gen-
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Fig 5-11. Color diagram of adequate coupling: A- Eye with small scleral curvature radius (11 mm) and ring with the same curvature radius (11 mm) B- Eye with bigger scleral curvature radius (12 mm) and ring with the same curvature radius (12 mm ).
Fig 5-12. Color diagram of inadequate coupling before to activating the suction: A- Eye with big scleral curvature radius (12 mm ) and ring with smaller curvature radius (11 mm) B- Eye with small scleral curvature radius (11 mm) and ring with bigger curvature radius (12 mm ).
Contents
eralize either saying that myopic eyes have high curvature radius or saying that hypermetropics have low curvature radius, as there exist eyes of high axial length and low scleral radius and vice versa. When we have a ring with an adequate curvature radius for an eye with the same curvature radius, the coupling generated in the vacuum chamber is perfect and it translates in an adequate grip of the ocular globe. As the adjustment is made at the level of corneal limbus, which is the site of highest adherence of the conjunctive. ( Fig 5-11) When a suction ring of a higher radius than the scleral radius is used, its grip is achieved at the expense of the conjunctive and therefore you don’t get an adequate intraocular pressure during the cut. In the opposite case when you use a suction ring with a lesser radius than the scleral radius of the eye, the grip is achieved at the expense of diminishing the ocular diameter, increasing the risk of loss of suction during the cut, as it is subject to tension and will tend to get loose. ( Fig 5-12 and 5-13) The explanation given in the numeral “perforation in the flaps” is also valid in the transitory suction loss, because of the point at which the cornea is held with more strength is in the periphery, where the suction is applied , and the most vulnerable is the corneal center. An inadequate tension because of suction loss or by an inadequate adaptation of the
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ring with the globe, leaves the corneal center as the most hypotense point of the entire cornea and its behavior is similar to the mentioned fold.
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Help ?
Fig 5-13. Color diagram of inadequate coupling after to activating the suction: A- Eye with big scleral curvature radius (12 mm) and ring with smaller curvature radius (11 mm) B- Eye with small scleral curvature radius (11 mm) and ring with bigger curvature radius (12 mm).
MICROKERATOMES
Fig 5-14. Nasal hinge Vs. Superior hinge. A-B-C. Surgical technique sequence and adequate post-operative result. D-E-F-G- Mechanical influence of the upper lid in a case of traumatic displacement of the disc.
Contents
Folds, Displacements, and Detachments of the Corneal Flap Within the complications inherent described to the corneal flap you find folds, displacements, and detachment of the corneal flap, being the last one very infrequent. The folds and displacements of the flap are cause by a twist or wrinkle of the corneal flap of direct traumatic origin (inadequate technique, strokes, friction,) or by the effect of the patient’s blinking . There exists another type of fold less perceptible and it is observes after the flap replacement in deep ablations ( in high myopias). This is due to distribution folds of the flap that are generated when you reposition it upon a stromal bed very different to its original. Many times, these findings pass unnoticed and they are observed more frequently as the surgeon has more experience in the technique and perform a better and more detailed post-surgical examination of the flap. The tinting with fluorescein in post surgery easily lets you evaluate if there exists some degree of displacement of the flap. When this presents itself a larger area of tinting is observed in the superior edges of the flap, since when the hinge is nasal by the blinking effect the tendency to displacement
Section 1
is toward the inferior quadrant. This phenomenon also could be because of an inadequate replacement Section 2 of the corneal flap during the surgery. But it is less Section 3 frequent. These displacements are not generally signifi- Section 4 cant in the patient’s visual recovery unless they are Section 5 accompanied by folds in the corneal flap. In 1995 in our research work on rabbits13, we Section 6 find a significant statistical difference in favor of the hinge that is located in the eyelid quadrant that real- Section 7 izes the active movement. Subjects Index The advantages observed with the “ superior hinge ” technique are: (Fig 5-14) It is more physiological since it is located favoring the blinking. Statistically less flap displacement was presented. More comfort for patient since the superior Help ? epithelium stays intact. Less bleeding in patients with corneal pannus by contact lens, in general located superiorly; less contact of the stromal face of the flap with the eye’s circulating liquid. Less ablation signs of the hinge as it stays above and the majority of astigmatisms are carved in the horizontal meridian. In case of superior hinge ablation less optical aberration is produced since it stays partially covered by the superior eyelid.
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Fig 5-15. Color diagram and Topography of a Negative Hinge Syndrome.
Fig 5-16. Color diagram and Topography of a Positive Hinge Syndrome in comparison with the Negative one in Hyperopic Astigmatism Correction.
Contents
86
Astigmatism Inductions by Hinge Ablation
Section 1
When we perform an intrastromal ablation with laser, the ablation diameter must be less than the flap diameter in order for all the ablation to be done in the stromal bed. I recommend to orientate the hinge in a quadrant 90 degrees away from the astigmatism axis to avoid a negative hinge syndrome (presented at the American Academy of Ophthalmology, Atlanta, GA, USA 1995 , by C. Carriazo). This occurs when there is ablation of the base of the hinge that induces an additional ablation effect that appears once the flap is repositioned over the cornea; topographically, it is seen as a peripheral ablated area at the base of the hinge (Fig 5-15) and induces irregular astigmatism that is difficult to resolve. Initially, to solve this complication, we began to cover the base of the hinge with sponges or spatulas until we observed a few cases of induced astigmatism that showed a topographic image of elevation in red at the hinge’s base. We called it a positive hinge syndrome (Fig 5-16). Finally, we recommend orienting the hinge 90 degree apart from the astigmatism axis or to program a wider diameter flap in those nasal hinge’ Microkeratome (Fig 5-17 and 5-18).
Section 3
SECTION II
Section 2
Section 4
Section 5
Section 6 Section 7 Fig 5-17. Color diagram of the mechanism of Hinge Ablation in Myopic Astigmatism.
Subjects Index
Help ?
Fig 5-18. Color diagram of the advantage of Superior Flaps to orient the hinge 90° from the astigmatic axis.
MICROKERATOMES
Fig 5-20. The third Barraquer microkeratome generation.
Fig 5-19. Clasification of microkeratome systems.
Free Cap This is not a true complication since its adequate repositioning does not generate problems. The complete flap section is produced when there is no way to confirm the hinge size and/or when the applanation lenses that show the diameter of the flap that is going to be cut are not used. When a total flap cut is presented it is usually found between the blade and the applanation plate of the Microkeratome and must be taken off slowly always keeping the stromal face and its orientation identified. “ The simplification of surgical techniques has made us forget some very important principles in the use of the Microkeratome. To consider all ocular globes as having the same size is a big mistake as those eyes that deviate from established parameters set as standards, are at great risk in some Microkeratome “ We have classified the different types of Microkeratome according to the movement of the cutting blade and the advance system. (Fig 5-19).
Barraquer Microkeratome
It has different suction rings with an aperture in the center of 11.5 millimeters for the cornea. Its anterior flat surfaces serves as a guide for the Microkeratome and its posterior concave surface has the appropriate size for it to fit in the anterior segment of the sclera. This last surface has a space that acts as a vacuum chamber that fixes itself to the ring over the anterior aspect of the sclera. The ring is designed with a handle to keep it in position, which also serves as vacuum duct. The plates to change the cutting thickness are numbered according to the tenths of millimeters of the cutting thickness that you wish to obtain. It has applanation lenses labeled with the cutting diameter that you wish to obtain. Later the Barraquer Krumeich-Swinger appeared, which followed the same line as the original Barraquer. This Microkeratome used bases of Teflon, in order to support the cornea and for the first time, allowed the performance of keratomileusis without freezing.
Draeger Microkeratome (Fig 5-21)
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
It was the first Automatic Microkeratome and the only one with rotary movement. This is a single
Help ?
(Fig 5-20)
It is a 3-piece unit 10 to 12 centimeter long; it has an oscillatory motion, an inclined blade at 26 degrees, different height plates, a single shaft, and motor over the blade. Fig 5-21. The Draeger microkeratome.
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Fig 5-22. The Automatic Corneal Shaper (A.C.S).
unit 30-cm long. The body of the instrument consists of one motor that runs with a double shaft at 500 rotations per minute and a periphery speed of 3.140 cm per minute using 6 volts d.c. One circular cutting blade located at the end of the instrument that moves mechanically to 00 with a rotary movement in order to cut the tissue at a speed between 0,06 and 0,08 mm/sec. Added to the body of the instrument there is a suction ring with a central opening of 12 mm and an anterior flat surface and a posterior concave surface. In order to obtain the needed application diameter it uses a plastic transparent plate with a small precision lattice labeled with an adjustable height of 0.5mm. The tissue should be irrigated constantly while the cut is made in order to avoid overheating. This instrument has a plastic tube for a constant irrigation.
and that allows the displacement over it, conducted by the same motor that controls the cutting blade. It has two lateral guides designed to slide in the anterior surface to the fitting ring keeping up a constant cutting plane. The Microkeratome head is composed of a main piece that contains the advancing gears and opens to accept the blade holder and blade. Once it is closed and secured by a cylindrical nut around its “neck” the applanation or gauge plate is placed and secured in its frontal aspect. The stopper can be mounted as a separate adjustable piece over the neck’s nut. In the newer models, it is incorporated as a fixed part of the head’s main piece. The importance of adequate cleaning and maintenance of the Microkeratome parts cannot be overstated. This should include periodic polishing to avoid buildup of a layer of debris. Especially on the lower surface of the plate, this buildup leads to shallower cut. The original ACS system included an adjustable pneumatic fixation (suction) ring with a maximum applanation diameter of 7.5 mm cut. Customs ring can be made to allow fee or larger cuts. If this value is not reached, the vacuum pump should be checked for malfunction. However, if a conjunctiva fold (or any other obstruction along the tubing or at the console valve) blocks the vacuum line, pneumatic fixation will be poor in spite of a normal manometer reading.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Carriazo-Barraquer (Fig 5-23) (C-B Moria and Supratome Schwind)
Automatic Corneal Shaper (ACS) (Fig 5-22) It is a 3-piece unit 12 to 15 cm long. It has a blade with oscillatory movement, inclined 26 degrees, and plates of different height. It is powered by an electric motor that provides both forward motion and blade oscillation of 8,000 oscillations/min. The blade travels along a geared track on top of the suction ring, cutting tissue at a rate of 3.7 mm/sec. The body of the instrument has a gear system that engages over a rail track located laterally in the ring
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It was the first Microkeratome designed in order to perform the Superior Hinge Technique, developed by Dr. C. Carriazo and Dr. J.I. Barraquer M. in 1996. Also, it was the first Microkeratome which gave to the surgeons both manual and automatic system. The Microkeratome is composed of an original crown system located inside a tubular guide of the head, which engages on a pivot located on the ring, it avoids the use of external gears and tracks.
Help ?
MICROKERATOMES
Fig 5-23. The Carriazo-Barraquer microkeratome.
The automated advance mode has a double traction: the crown of the head engages on crowns located at the end of the pivot on the ring, different from other automated Microkeratome. The motor gives the traction to the crown and the pivot ensures the guidance of the pivoting movement. By using rings that pivot without a crown, the head can rotate freely around the pivot; this allows the surgeon to manually rotate the Microkeratome during the cut. The head has a superior opening with an interior coil to set the motor. It has a lateral groove that goes through and permits the introduction of the blade with the blade holder. It has a lateral curved guide that permits the sliding of the Microkeratome over the suction ring and maintains its correct position. On the other side, it has a cylindrical vertical guide that has a rotational advance system in its interior. The head has a fixed built-in plate located in front of the blade that applanates the cornea and determines the flap thickness. In the center of the head is the blade housing, which is an opening that goes from side to side of the head at 300. The blade is made of stainless steel and comes sterile with a disposable blade holder.
Heads are available for cuts of 130, 160, and 180 microns flap thick nests. The motor for automated advancement is electrical with two concentric shafts. The inner shaft rotates at 15,000 revolutions per minute (RPM) and activates blade oscillation. The outer shaft rotates at approximately 1000 RPM and, by means of a worm gear, connects to pinions located inside the head, which will transmit the pivot’s advance movement. A nitrogen turbine can also be used. Turbine motors have a much higher torque than electrical motors. The turbine motor has only one shaft for driving the blade oscillation at 17,000 RPM. When the turbine is used, the Microkeratome is manually advanced. The blade is made of stainless steel and comes sterile with a disposable blade holder. This holder Contents has a protrusion that helps engage the blade in its housing without risk of damaging the cutting edge. Section 1 The holder’s special shape has been developed in order to ensure a very accurate guide into its oscilla- Section 2 tions, for an accurate and predictable cut thickness. Section 3 The rings are very small in order to allow access to all types of eyes, including small and deep. Section 4 The Moria Evolution power unit powers the Carriazo-Barraquer Microkeratome. It is a battery- Section 5 powered device. This unit can drive a nitrogen-pow- Section 6 ered turbine motor or an electrical motor. The nitrogen turbine motor can only be used Section 7 for manual translation of the keratome head. The automated mode requires use of the electrical motor. Subjects Index Both the turbine and electrical motor are supplied with the system in order to allow the surgeon a choice of the advancement mode. The power unit provides the vacuum for the suction ring by means of two vacuum pumps. When the vacuum is activated by the corresponding Help ? footswitch, one pump is activated. The second will act as a back up and operates only if the control unit detects vacuum loss. The unit has several safety devices such as alarms in case of vacuum loss, low battery charge, and deficient nitrogen pressure. It also has a low vacuum mode.
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Fig 5-23 A: The Disposable CarriazoBarraquer microkeratome.
Fig 5-23B: The Carriazo-Barraquer 2 microkeratome
Contents
Recently C. Carriazo modified the original Carriazo –Barraquer system for its disposable (Fig 5-23 A) and reusable use without gears in the head. This Carriazo-Barraquer 2 Microkeratome (Fig 5-23 B) overcomes the inconvenient generated by the use of gears. It can be used manually or automatically. In this model the ring handle has a special rotational system that allows different hinge sizes.
Moria ONE
(Fig 5-24)
speed of 15,000 revolutions per minute (RPM) or Section 1 30,000 blade oscillations per minute. Section 2 The power unit has two powerful vacuum pumps. In normal conditions, only one pump is acti- Section 3 vated. In case of vacuum loss, the vacuum monitoring system will instantaneously activate the second Section 4 pump in order to compensate the detected failure. Section 5 The low vacuum mode. This is one of the innovative features of this unit. It permits fixation of Section 6 the eye by means of the ring handle (assisted fixaSection 7 tion) during the laser ablation without compromising retinal vascular flow. It also allows the control Subjects Index
This manual Microkeratome is made mostly of stainless steel and is gearless. Its BI-faceted blade is also composed of stainless steel. Because of its one-piece pre-assembled heads, the LSK-1 eliminates the risk often associated with presurgical assembly of the device, as a result of the manufacturer. Flap depth is dependent on the head selected and three depths are available: 130 µm, 160 µm and 180 µm. It brings a new power unit (Evolution II), and it is designed to work with the Moria Microkeratome and Carriazo-Barraquer. The versatility of this unit is particularly appealing for the surgeon who wants the option of using different types of microkeratomes. Both the reusable and disposable One is powered by a nitrogen turbine giving high torque and
Help ?
Fig 24. The Moria ONE.
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MICROKERATOMES
of peripheral bleeding in patients with peripheral corneal neovascularization. Audible and visual alarms. The surgeon is alerted in case of loss of vacuum, low nitrogen pressure in the tank, or low battery charge. Test mode. The surgeon is able to check the appropriate suction levels before the procedure. . Moria One Disposable (Fig 5-24 A) The disposable one is the newer sibling of the original One. It has the same basic principles. It has a one-piece plastic molded head with one blade inserted, which, as a safety feature, cannot be removed from the head. The heads are available for cuts of 160 or 180 microns and are powered by the same turbine as the reusable one head, with an oscillation off 15,000RPM. The rings are reassembled with the handle and aspiration tubing, and the two arms of the handle are opposite the head translation. This innovative ergonomic design improves sliding of the head and allows stabilization of the eye by opposing a force to the linear translation of the Microkeratome. The location of the stopper just upward the ring allows complete visibility of the head position in relation to the stop during the cut. This avoids false stops due to the speculum or any other obstacle. The surgeon always knows the position of the head and can control the hinge size during the cut.
The ring has two built-in aspiration holes connected to two different aspiration lines for higher vacuum performance and safety. Three rings sizes –1, 0, and H are available; allowing flap sizes up to 10 mm. The hinge position is set directly on the suction ring by rotating an adjustable stop device located on the upper part of the ring, from 7.5 to 9.5 mm. The adjustment is made by means of a key, also included in the disposable pack.
Chiron (Hansatome Microkeratome) (Fig 5-25) This is a 4-piece unit. It has a blade with oscillatory movement inclined toward 260 and fixed plate. It has one motor with speed of 8.000 rpm. Contents The body of the instrument has a gear system engaging over a curve rail track placed laterally in Section 1 the ring and it allows the displacement over it guided by the same motor that handles the cutting blade. It Section 2 brings a lateral curved guide designed to guide and Section 3 to allow the sliding of the Microkeratome on the anterior surface of the fixing ring keeping up a con- Section 4 stant plane of cut. Section 5 The head has 2 independent pieces, the first one is guided depending on whether the eye is right Section 6 or left, and the second possesses a hole that is coupled Section 7 with a rotation shaft located on the ring. It was designed to create a superiority posi- Subjects Index tioned hinge.
Help ?
Fig 5-24A : The Disposable Moria ONE.
Fig 5-25. The Hansatome microkeratome.
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The Hansatome, like the ACS, relies on a gear drive to provide forward motion, but the number of tracks has been reduced to one, and the drive is now nasally located and slightly elevated, with some space between it and the patient’s eyelid and the speculum. This design prevents impeded forward progress or binding, while the single track allows smoother cuts. The system can create flaps of 8.5 mm to 10 mm. It uses a disposable blade with an affixed holder The power supply unit has an internal diagnostic equipment, it verifies if the system is functioning properly before each procedure, and the system will not allow cutting to begin until the appropriate vacuum level is achieved. Cutting automatically stops if vacuum drops below the threshold, and an electronic compensation system delivers constant motor speed. The Hansatome can create flaps of 160 µm and 180 µm in depth. The system involves hardware to adapt it to either left or right eyes. It is designed to create flap diameters of 9.5 mm.
Clear Corneal Molder
(Fig 5-26)
This instrument consists of one single piece of 25 cm that involves one motor of double shaft, one suction ring and one applanation lens. The cutting blade is of thin metal in a plane of 00, has oscillatory movement, it slides between the suction ring and the applanation lens conducted by one electric motor. This feature allows a complete vision of the entire cut. There is only one suction ring, whose height in relation to the blade is adjustable and allows a resection of the flap between 7 and 10 mm. It has a fixed resection thickness. The system can accept both stainless steel and diamond blades. Although diamond blades are not available for the system commercially. This Microkeratome has a 0° blade-angle of attack on the cornea. Blade speed is manually controlled up to 12,000 oscillations/min, and the keratome head advances manually across a single suction ring on gearless tracks. Separate electrical motors, controlled by a foot switch, perform each function.
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Fig 5-26. The Clear Corneal Molder microkeratome.
Contents
Section 1
The standard model has a fixed flap depth of 180 µm, which is adequate for LASIK.
Section 2
SCHWIND Keratome -Herbert Schwind’s Microkeratome (Fig 5-27)
Section 4
Section 3
Section 5
This is a single piece of automatic hand of 130- Section 6 degree weight and with a sapphire blade of 00 with Section 7 oscillatory movement and two motors. The first one is for the advance of the blade, speed of 1.3-mm/sec Subjects Index and reverse speed of 3 mm/sec, and the other that supplies oscillation of 4.050 rpm of the blade.
Help ?
Fig 5-27. The Schwind microkeratome.
MICROKERATOMES
Both motors get placed in the control unit apart from the handle of Microkeratome. It has a dual suction ring in order to take the anterior sclera and the cornea; the sapphire blade slides between them to make one flap of 9mm diameter, with a fixed thickness of 150 microns. The control unit allows checking the pressure and the suction ring. This was the first Microkeratome with the handle independent from the motors. It is the only Microkeratome in this survey that uses a sapphire blade, a cutting mechanism so sharp that it can create 300 or more corneal flaps before it needs to be replaced. The fully automatic Microkeratome System relies on a motor located in its base console unit for both forward motion and blade oscillation. Power is supplied to a stainless steel hand piece through two plastic-coated drive shafts. The system features a fixed depth plate that cuts at a consistent depth of 160 µm. Globe fixation is achieved through a suction ring affixed to the limbs, while a smaller inner suction ring stabilizes the flap. Loss of suction automatically aborts the procedure and returns the blade to the home position. The system also features an emergency shut off knob that immediately stops all operations and shuts off the power supply. Releasing the foot pedal stops blade motion but maintains suction. If suction is not properly achieved prior to a cut, an audible warning sounds. The dual-position pedal can initiate a selftest and calibration prior to treatment, direct the blade to the home position and activate the vacuum pump to build suction prior to surgery.
The SCMD Turbokeratome
Fig 5-28. The S.C.M.D turbokeratome.
posed toward them. The rings are numbered one to four, with the number one ring being the thinnest and the number four the thickest. The number one ring allows the largest diameter of the cornea to be exposed, while the number four ring allow the smaller diameter of cornea to be exposed. The stop ring limits the travel of the LASIK turbokeratome through the vacuum fixation ring to perform a flap and hinge.
Contents
Section 1 Section 2
Section 3
Section 4
Phoenix Universal Keratome
(Fig 5-29)
Section 5
This instrument is designed for corneal resec- Section 6 tion under molding. It consists of a single unit of 26 Section 7 cm long that holds two motors, one suction ring, and aperture for the applanation of the lens needed, the Subjects Index cutting blade is on a plane of 0 degrees and slides between the suction ring and the applanation lens
(Fig 5-28)
This system features high-speed, high-torque nitrogen driven turbine motor that drives a reciprocating surgical blade at the ideal speed of 13,800 revolutions per minute (RPM). It is a manual, gearless Microkeratome. The turbokeratome has an oscillatory movement and includes one inclined blade of 260 and produces a corneal resection of 150 microns thick. It brings four applanator lenses provided with the turbokeratome system: 7.5 mm, 8.25 mm, 8.75 mm and 9.25 mm. Four different vacuum fixation rings control the diameter of the cornea that is ex-
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Fig 5-29. The Phoenix Universal keratome
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guided by an electric motor. The main characteristics of this instrument are that it operates with a sealed unit using applanation lenses inserted under pressure to mold the cornea. These are lenses of high cutting precision in order to determine the section thickness and the diameter. The advance of the cutting blade is programmed in the control unit determining the cutting diameter. It has a single suction ring with adjustable negative pressure. Several physicians have alleged that the UK left microscopic metallic fragments in the stromal bed. The UK allows surgeons to excise optically correct lenticular cuts of the cornea- so-called power cuts for the mechanical correction of myopia and astigmatism. The UK features a mold for tissue to be excised from the corneal stroma. The diameter, thickness and shape of the excision depend upon the profile ground into this special optical insert. The UK uses a fenestrated stainless steel blade that oscillates at 14,000 oscillations/min and advances across the cornea at a rate of 0.75 mm/sec. The UK features optical inserts that create the lamellar flap with fixed depth and diameter. The most common dimensions are 160 µm depth and 8.5 mm diameter for a myopic LASIK procedure, but dimensions can be preset at the factory anywhere from 0 to 500 µm depth and from 3 mm to 10 mm diameter based on physician request. The UK achieves stabilization of the globe with a single suction ring. Incisions are made temporal to nasal, and superior hinge flaps are not possible. The machine also allows surgeons to adjust intraocular pressure.
Fig 5-30. The Nidek microkeratome.
Contents
Its design only allows creating horizontal hinges.
Section 1
The Summit Krumeich-Barraquer Microkeratome (Fig 5-31)
Section 3
Section 2
Section 4
This instrument is electrically powered, gear- Section 5 less, has a one-piece Microkeratome head with a Section 6 Snap-On mount, multiple port suction rings, and permits full visualization of the applanated cornea. It Section 7 also allows the surgeon to perform customized surgery by permitting selection of hinge and suction ring Subjects Index
Nidek Microkeratome (Fig 5-30) Help ?
This is an instrument only designed for nasal hinge with a built-in hinge stopper. The advance mechanism system doesn’t use gears, allowing slide guide around suction ring, Its dual suction ports, provide measurement of suction pressure. This instrument presents an independent mechanism oscillation blade, and an automated drive control. It has the possibility to obtain two flap diameters and three-flap thickness. Fig 5-31. The Summit Krumeich Barraquer microkeratome.
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size, blade traverse distance, and advancement and oscillation speed of the blade by means of front panel settings on the control unit. Based in the original Barraquer head, the major components of the SKBM are the control unit that involves operator controls, a microcomputer, a vacuum pump, and a back-up power supply a Microkeratome handpiece that contains motor for blade oscillation and advancement of Microkeratome head that has an oscillating steel cutting blade, four suction rings handle, and vacuum tube connector. It is very important to know that in the motor shaft are three small pins. The center pin is the eccentric pin, which drives the blade oscillation. Dial the eccentric pin to the 6 or 12 o’clock position to allow the motor shaft to engage correctly with the Microkeratome head. If the Microkeratome head will not engage with the motor shaft press the extended pins on the side of the Microkeratome head and gently advance the head onto the motor shaft until it clicks. Commendable only to realize nasal hinges due to its size and applanation plates. A total of four suction rings are included with the SKBM: two rings with an outside diameter of 19 mm. The rings must be sterilized prior to every patient procedure. The rings are also marked as either # 3 or # 4 to indicate expected flap size. The # 3 size will normally produce the same diameter flap on both the 19 and 21-mm rings, as will the # 4 rings. The numbers used for flap size follow the original Barraquer nomenclature, whereby the lower the number, the larger the expected applanation and, therefore, the larger the flap diameter.
Suction rings marked # 3 have a shallower depth, so that they sit lower on the cornea. When these rings are used during a procedure, larger flaps (9.0 to 9.5 mm) are obtained. It is important to note that the 19-mm rings do not protect the eyelids and drapes to the same extent as the 21-mm rings (because the steel blade oscillates approximately 0.85 mm beyond the wind of the Microkeratome head). The operator should carefully monitor the progress of the steel blade during the cutting phase to prevent possible injury to the eyelid when using the 19-mm ring. Suction rings marked No 4 have a deeper depth, so that they sit higher on the cornea. When these rings are used during a procedure, a smaller diameter of cornea is applanated and smaller flaps (8.5 to 9.0 mm) are obtained. Contents In order to obtain a flap of the desired size, the meniscus of the cornea must correspond with the Section 1 marking observed in the window of the MicrokeraSection 2 tome head. For example, if 8.5 mm of cornea is visibly Section 3 applanated in the window and the panel setting is maintained at 9.0 mm for the cut diameter, the cut Section 4 may be larger than the flap, causing a free cap. Similarly, if 9.5 mm of the cornea is visibly applanated in Section 5 the window and the panel setting is maintained at Section 6 9.0 mm for the cut diameter, the cut will be smaller and the hinge larger than desired. If these do not cor- Section 7 respond, adjust the panel settings. The system’s blade angle of 26° is borrowed Subjects Index from the original Barraquer design, as is the depth plate, which is fixed on standard models at 160 µm.
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Fig 5-32. The Flap Maker Disposable microkeratome.
The Flapmaker Disposable Microkera- Pendular Microkeratome tome (Fig 5-32) It is a single plastic handpiece with a blade to 26 degrees with oscillatory movement and 2 motors, the first one for moving the blade and the other for the Microkeratome advance. Both motors are placed in the unit control away from the hand piece of the Microkeratome. The control unit sets the Microkeratome advance and its hinge. It was the first automatic disposable Microkeratome. It was developed in the traditional Barraquer style (ie, a horizontal approach). The device is transparent and made of polycarbonate. Transparency enables the surgeon to visualize the flap creation process and intervene should conditions dictate. The Flap Maker is an automated Microkeratome and it is gearless. Its advance system involves a flexible axial cable that is inserted into the new microkeratome head for each new procedure. The control console provides power for the axial cable in order to create a hinge. An external, electrical power source drives the Flapmaker’s head at 6.8 mm/sec. The device’s blade oscillates 12,500 cycles/ min on forward motion only. This machine can create 8.5-mm or 10.5mm flaps. The device features fixed depth plates of 160 µm, but specialty depths are available.
Contents Carriazo developed it, and it is totally different to the actual mechanical systems. Section 1 It uses a curved blade with a curved blade holder. It doesn’t use applanation plates but it uses a Section 2 molding system, which allows making the cut of the Section 3 corneal flap at low suction pressure. Its superior coupling and pendular advance Section 4 system over the ring allows it to be guided in any direction since its coupling is superior, in that way Section 5 any orbit quadrant cannot obstruct it. Section 6 It uses a manual and/or automatic pendular advance system, designed in order to be disposable Section 7 or reused. The advance system is independent from the Subjects Index blade oscillator, the last one being high speed.
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Fig 5-33. The Pendular microkeratome.
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(Fig 33)
MICROKERATOMES
Automatic Disposable Microkeratome (A.D.K): (Fig 5-34) The gear drive is in both sides of the keratome and is shielded by plastic skirts, allowing more symmetrical passage of the keratotomy and essentially eliminating the possibility of incarcerating material, such as cilia drapes, etc., into the gear drive. The keratome is installed in the suction ring at the factory to eliminate the awkward maneuver of putting the keratome in the suction ring already on the eye. The blade angle is 250 in keeping with Jose Barraquer’s tediously worked out principals. The suction ring has an aperture diameter of .488 inches and an outside diameter of .772 inches. Because of a reduction transmission into which the motor is inserted, the gear drive runs at 5.5 mm per second and the blade oscillation speed is 7500 RPM. The keratome head is assembled at the factory, involving installation of a high quality, high power inspected blade. The blade is stainless steel. The suction handle serves as the stopper for the keratome. The drive gear mechanism is covered, which should prevent tissue or eyelashes from interfering with the cut. The stainless steel blade oscillates at 10,000 cycles/min and advances at a rate of 4.5 mm/ sec. The device can create flaps from 9.0 to 9.5 mm in diameter. The suction ring of the disposable unit has a narrow profile, which allows its application to virtually any eye, regardless of size or lid shape. The inside applanation diameter allows the creation of large flaps and decreases the chances of creating free caps in patients with extremely flat corneas. The electric power console features reusable or disposable suction tubing and an internal alarm that alerts the surgeon to inadequate suction. The motorized drive mechanism can be attached directly to the keratome or can be situated remotely with an external drive cable. The motorized drive attaches to the keratome with a rapid coupling device.
Fig 5-34. The Automatic Disposable Keratome ( A.D.K ).
Innovatome
(FIG 5-35)
Contents
Section 1
The Innovatome is a stainless steel, remotely driven electrically powered Microkeratome. Gears Section 2 have been replaced by a dovetail system, and a clear sapphire applanation plate allows visualization of the Section 3 incision. Section 4 To decrease weight and mass, the Innovatome drive mechanism and blade oscillation systems are Section 5 located in a 15-pound table-mounted base unit, so Section 6 the head and its integrated single suction ring is the only components actually held by the surgeon. Section 7 A single, flexible, rotating steel cable propels the instrument forward and allows the blade to os- Subjects Index cillate via a unique, cantilevered counterweight, located on the tip of the spinning cable. The 50 µmthick, 1-mm wide blade incises tissue with a stroke
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Fig 35. The Innovatome microkeratome.
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of 0.9 mm and a variable advance rate of 1 to 4 mm/ sec. The oscillation rate is also variable up to 10,000 cycles/min. Flap diameter is variable from 8 mm to 10 mm. The applanation plate is preset to 160 µm and over the plate is a spring-loaded, disposable blade carrier that is supposedly easier to replace than a blade alone.
Other Mechanical Microkeratomes: Amadeus. ( Fig 5- 36 ) Diamond Barraqueratome. MicroPrecision Microlamellar Keratomileusis System. Med-Logics Microkeratome.
Femtosecond Laser Keratome (INTRALASE) (Fig 5-37) A femtosecond laser is similar to a Neodymium YAG laser except that each laser pulse is approximately one hundred thousand times shorter in duration, lasting only about ten to the minus thir-
Fig 5-36. The Amadeus microkeratome.
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Fig 5-37. The Femtosecond Laser Keratome.
Contents teenth seconds. Each pulse creates a micro cavitation a few microns in size. Many pulses are required Section 1 to create a surgical effect and these are delivered with a sophisticated computer controlled scanning system. Section 2 The possible advantages involved: The abilSection 3 ity to make reproducible cuts no matter the shape of the eye. The ability to keep the intraocular pressure Section 4 in the normal range at all times during the procedure. In this kind of system the side cut can be made Section 5 at any angle or shape. Section 6 The accuracy and reproducibility of the femtosecond keratome has been tested Section 7 in animal eyes with good results. Some technical Subjects Index characteristics are: Laser source: Diode pumped pulsed ND-glass oscillator with a diode pumped regenerative amplifier (chirped pulse amplification, CPA), wavelength: 1052 NM. Pulse energy: 50 micro joules, Repetition rate: 7 kHz, (soon 10 kHz). Pulse length: ~600 fs. Treatment: Pulse energy: 4-5 microjoules, spot Help ? separation: 8-10 micrometers, pulse power: ~10 kW. It is estimated that the cost of the laser Microkeratome system will be comparable with that of an excimer laser.
MICROKERATOMES
Microjet
( Fig 5-38 )
It is defined as a coherent, high-speed waterjet beam with a beam diameter of under 50 um. Although many of the properties of the microjet have been described in other literature they are reviewed briefly here. (Figure 5-38) schematically illustrates the elements of microjet beam information. The microjet system operates at a stagnation pressure of about 20 to 25 Kpsi (Kilopounds per square inch ) (1360 to 1700 atmospheres). The highpressure tubing is flexible and thin, yet strong enough to support the high pressure fluid. The shape and size of the stagnation volume geometry plays a key role in producing a coherent beam. The fabrication of the circular orifice, made of ruby, is critical to proper beam formation. The resulting beam diameter is about 87% of the orifice diameter. A typical beam diameter is 33 um have been used. There is a trade-off between stagnation pressure and beam diameter. The smaller the beam diameter, the greater the required stagnation pressure of 25 Kpsi is relatively straightforward. Higher pressures increase the size and cost of the system. The output nozzle plays a role in stabilizing the beam but is not essential. Although the beam travels in a plane, the cut boundary is not in the same plane. Unambiguously, the beam moved tissue separation. Hence, it cut along interfaces between layers rather than across layers until at the last instant the tissue resisted further displacement and then the beam cut across a layer. Clearly, the beam exerts transverse force on the tissue and moves it. The origins of the transverse force are small angle collisions of the high speed water with the tissue at the perimetric boundary is deflected to the trailing edge of the beam and this produces a reactive transverse force on the tissue. A detailed experimental study of beam forces during the cut has been carried out using an elegant experimental technique. As a result of the collisions, the water breaks section of intact lamella layers away from the stroma as demonstrated later. Hence, cutting is usually accompanied by ablation or erosion. Ablation never involves loss of partial thickness lamellar layers or
Fig 5-38. Microjet elements.
keratocytes. The lamellar layers are carried away by the spent water. By virtue of the applanation, internal hoop forces develop in the cornea and tend to push the Contents cornea back to its normal position. Thus, there is a tendency for the cornea to move upward toward the Section 1 microjet beam in the stromal bed beneath the beam, which tends to move away from the beam. Thus the Section 2 stromal bed experiences more erosion than the un- Section 3 derside of the flap. The important conclusion from this model is that the greater the scan speed of the Section 4 microjet beam, the less time there is for erosion to Section 5 occur and the smaller the amount of eroded tissue. Another important conclusion is that the greater the Section 6 amount of applanation, the greater the rate of erosion. These two characteristics allow shaping merely Section 7 by waterjet cutting. Subjects Index The design of scleral chuck for use in a microjet keratome is unexceptional. The goal is to achieve adequate holding and resistance to motion of the globe without increasing the IOP. Hence, one must avoid distortion of the globe. Typical base IOP values are about 25 mm Hg. The increase in IOP during the cut is about 10 mm Hg. An essential eleHelp ? ment of the scleral chuck is the beam block shown schematically. The edge of the beam block intercepts the microjet beam and directs it away from the cornea. Hence, the tissue is the shadow region of the beam block is not cut, leaving a hinge. Note that the geometry guarantees the position of the hinge relative to the boundary of the flap. The hinge is positioned superiorly.
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REFERENCES
12.Cirugía refractiva de la córnea.Prof Jose Ignacio Barraquer. Instituto Barraquer de América.
1.Barraquer JI. Queratomileusis para la correccion de la Miopia. Arch Soc Am Oftalmol Optom. 1964; 5: 27-48.
13. Carriazo C, Barraquer M JI. Superior Hinge in Lasik (New Surgical technique ) Arch Soc Am Oftal Optom 1996; 24 : 358-354.
2.Barraquer JI : Keratomileusis para la corrección de Miopía e Hipermetropía. Ann Instituto Barraquer de 14. Barraquer C. The Microkeratome. In the book Lasik Principles and Techniques edited by Lucio Buratto and América 1964 ;5 :209-229. Stephen F. Brint. 1998 Chapter 12 Pag 167 to 174. Slack 3.Barraquer José Ignacio . Basis of refractive keratoplasty. Incorporated. Arch. Soc. Amer. Oftal. Optom. 1967 : 6-21. 15. Buratto L. Brint S., Ferrari M.; Keratomileusis. In the 4.Draeger J, Hackelbusch R. Experimentelle book Lasik Principles and Techniques edited by Lucio Untersuchungen und klinische Erfahrungen mit neun Ro- Buratto and Stephen F. Brint. 1998 Chapter 2 Pag 9 to 14. tatory-Instrumenten. Ophthalmologica 1972; 164: 273- Slack Incorporated. 283. 16. Lucio Burato, Stephen Brint; LASIK. Surgical Tech5.Draeger J. Ein Haulbautomatisches elektrisches Keratom niques And Complications. Slack Incorporated; 1998. fur die lamellare Keratoplastik. Klin Monatsbl 17. Roberto Albertazzi, Virgilio Centurion; La Moderna Augenheilkd 1975; 167; 353-359. Cirugia Refractiva. Quilmes, Buenos Aires Argentina; 6.Perry S. Binder, MD ; Patti H.Akers ; Refractive Kerato- 1999. plasty. Microkeratome Evaluation. Arch Ophthalmol SUGGESTED READINGS 1982 ; 100 :802-806. 7.Pallikaris IG, Papatzanaki ME, Siganos DS, Tsilimbaris MK. A corneal flap technique for laser in situ keratomileusis. Arch Ophtalmol. 1991;109:1699-1702. 8.Haimovici R, Cubelrtson WW. Optical lamellar keratoplasty using the Barraquer microkeratome. J Refract Corneal Surg. 1991; 7:177-180. 9.Hanna KD, David T, Besson J, pouliquen Y. Lamellar keratoplasty with the Barraquer microkeratome. J Refract Corneal Surg. 1991;7:177-180.
1-Doane J.F , Slade S., Updegraf S. Microkeratomes; In the book LASIK edited by Ioannis Paliikaris and Dimitrios S. Siganos 1998 Chapter 10 Pag 107 - 117. Slack Incorporated.
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Section 1 Section 2
Section 3
Section 4
Section 5
Section 6
Section 7 2- Krueger R. , Parolini B. , Gordon E. , Juhasz T. ; Nonmechanical microkeratomes using Laser Jet and Subjects Index Waterjet technology; In the book LASIK edited by IoanniS Paliikaris and Dimitrios S. Siganos 1998 Chapter 9 Pag 82 - 1106. Slack Incorporated
3-. Carriazo C, Barraquer M JI. Superior Hinge in Lasik 10.American Academy of Ophthalmology : Keratophakia (New Surgical technique ) Arch Soc Am Oftal Optom 1996; and Keratomileusis : Safety and Effectiveness. Ophthal- 24 : 358-354. mology Volume 99, Number 8, August 1992 :1332-1341. 11. Carol J. Hoffman, Christopher J. Rapuano, Elsabeth J. Cohen, Peter R. Laibson. Displacement of Corneal Lenticle After Automated Lamellar Keratoplasty. American Journal of Ophthalmology, July 1994, Vol 118, No 1 : 109-111.
Contents
Cesar Carriazo E., M.D. Medical and Scientific Director Carriazo Ophthalmological Center; Scientific Advisor and Consultant for “Moria Technology” - France and Schwind Laser Company - Germany E-mail:
[email protected]
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AUTOMATIC CORNEAL SHAPER
Chapter 6 AUTOMATIC CORNEAL SHAPER A. Agarwal.,M.D., T. Agarwal.,M.D., R. R. Sasikanth.,M.D.
(Note from the Editor in Chief: Chiron’s Automated Corneal Shaper is still an excellent microkeratome that creates a very fine lamellar cut. Nevertheless, it has certain limitations when compared with newer equipments. Among them stands out its lack of versatility in which area to make the corneal flap hinge. As with many other microkeratomes, the flap is always cut only in the nasal (horizontal) sector. Some surgeons prefer the new models available from Chiron and from Moria that have important advantages in comparison with the Automatic Corneal Shaper. For example, the flap hinge can be located in any meridian, horizontally or vertically. The superior area is the most popular since it allows a more comfortable placement of the flap at the end of the surgery and it also makes it easier for the flap to stay homogeneous and wrinkle free.)
Presurgical Set-Up The Automatic Corneal shaper consists of three basic units1. Power Pack 2. Suction Ring 3. Microkeratome All three have to be set up for the machine to work smoothly and comfortably.
Contents
Section 1 Section 2
Section 3
Power Pack
Section 4
The Power pack (Figure 6-1) provides elec- Section 5 tric current for the suction pump & microkeratome. Section 6 On the front panel you have sockets as seen in Figure 1 to which the cords of the suction ring and Section 7 microkeratome are connected. In the rear panel there is a receptacle for the main power cord. One should Subjects Index
Introduction The Automatic Corneal Shaper (ACS) is an excellent microkeratome manufactured by Chiron Vision (Bausch & Lomb). It allows for cutting of a precise corneal disc of pre-selected thickness & diameter. When Lasik was started it was not that successful. Later on three important techniques improved and changed the success of Lasik. They were an automated microkeratome, the development of a hinged flap technique and the development of the sutureless technique. For all three, the Automatic Corneal shaper was excellent and the results of Lasik improved drastically with this microkeratome.
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Figure 6-1: Power pack for the automatic corneal shaper
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placed on the eye to encircle the cornea and the foot switch of the suction pump pressed the intraocular pressure should be raised to 65 mm of Hg. This is necessary so that the microkeratome can create a nice pass and resect the cornea. The advantages of the suction ring are – to fixate the eye, to increase the intraocular pressure and to have the track for the microkeratome to move.
Microkeratome
Figure 6-2: Suction ring handle. Note the track for the gears in the suction ring
place the ACS Power Pack on a firm, level surface. In the Chiron 217 Excimer laser (Lasik Laser) there is no need of a separate Power Pack. The power pack is inbuilt in the Excimer Laser itself. Also, the tubing of the suction ring and the cords for the microkeratome are protruding out of the Chiron 217.
Suction Ring The Suction pump is connected to the suction ring handle (Figure 6-2) by a disposable tubing. This comes in a sterile package. On opening this package we will find not only the tubing but also a disposable blade for the microkeratome. The Suction ring consists of the suction handle, the ring and the Track on which the gears of the microkeratome move (See Figure 6-2). The suction handle screws onto the suction ring. The handle is hollow and is in turn connected to the power pack via the disposable suction tubing. The handle is hollow so that the suction can be applied once the foot switch of the suction pump is switched on. Once the suction ring is
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Take the corneal shaper head from the instrument tray. Check the by your thumb and see that there is resistance-free movement. If this does not occur then repeat the cleaning process. Place the corneal shaper head with the serial number facing up. Remove the locking ring on the rear of the corneal Contents shaper head. Holding the shaper so that the serial number is facing up, open the hinged cover to ex- Section 1 pose the blade holder. The blade holder should be completely dry. If the blade holder does not move Section 2 smoothly, clean the blade holder and cavity of the Section 3 shaper head again. Remember that the slot should face the rear of the shaper head and the blade shoul- Section 4 der should face up. Take out the blade from the disSection 5 posable tubing package. Open the blade carrier to expose the blade. Section 6 The blade is packaged in the carrier with the square edge of the slot on the left and the round edge Section 7 on the right to correspond with the correct placement Subjects Index of the blade in the shaper head. Pin the unsharpened, back edge of the blade down with your left forefinger so that it will not jump up to the magnet of the blade insertion tool. With the blade insertion tool in your dominant hand, carefully position the tool over the sharp edge of the blade and allow the magnet to grasp the blade. Lift the blade straight up and off the Help ? carrier (Figure 6-3). Position the blade slot over the raised shoulder of the blade holder & press the blade down firmly with the tool. Pin the blade down in the shaper head with your non-dominant hand’s forefinger and lift the tool off and away. Invert the blade tool and use one or both of the front tines to press down on the blade in several places to assure it is properly seated. Be careful not to contact the sharp
AUTOMATIC CORNEAL SHAPER
Figure 6-4: Assembeled microkeratome
Figure 6-3: Corneal shaper head exposing the blade holder. The blade is adjacent to it. Note the magnet holding the balde so that one does not damage the sharp edge of the blade
Contents
Section 1
edge of the blade. Gently close the shaper head and replace the locking nut with the knurled portion facing out. The head should close flush without force. Test the movement of the blade by placing the test shaft into the rear of the shaper head. Rotate the test shaft to feel the oscillation of the blade, which should be absolutely smooth & free of resistance. While rotating the test shaft, visually confirm that the blade is moving side to side to verify that the blade holder has been installed properly. If the blade movement is restricted, carefully remove the blade and confirm that all surfaces of the shaper head and blade holder are clean and perfectly dry. Replace the blade and check again. If resistance is still detected, install another blade and repeat the testing process until you feel absolutely no resistance. Do not proceed with a blade with restricted movement, as this could cause the unit to jam or create a less than optimal cut. Remove the desired thickness plate from the tray by placing the locking wrench onto the hex nut of the plate and tilting back. Place your forefinger on the plate to keep it from falling off the wrench and lift out of the tray. The thickness plates can be of 130 microns or 160 microns. This means if we use the 130 microns thickness plate the flap will be of 130 microns. If we use the 160-micron thickness plate
the flap created will be of 160-micron thickness. Section 2 Always confirm the engraved number on the plate with your surgical plan. If the corneal pachymetry Section 3 is not much or the refractive error to correct is a lot Section 4 one might use the 130-micron thickness plate so that we get an extra 30 microns to ablate. But by and Section 5 large in our hospital, we prefer to use the 160-micron thickness plate, as the flap created by this is Section 6 better. By using the 130-micron thickness plate we Section 7 found the flap a bit thin and so we shifted to the 160Subjects Index micron thickness plate. The plate has a nut and washer, which must be slightly loosened to allow the plate to be installed into the shaper head. Stabilize the plate with your forefinger on the front and slide the plate completely into the notch on the front of the shaper head. You should feel and hear the plate snap into place so that Help ? it is perfectly flush to the front of the shaper head. Secure the plate by rotating the nut clockwise with the wrench. The plate must be perfectly flush to the shaper head and locked firmly in place so that it will not come loose during a surgical procedure. If the thickness plate is not fixed properly or if we forget to fix the thickness plate we will create a perforation in the anterior chamber. Once the microkeratome is fully installed (Figure 6-4) it has to be fixed to the motor cord which
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Figure 6-5: Automatic corneal shaper head with permanent stopper for use with fixed suction ring
Figure 6-6: Instruments in the set of acs
in turn is fixed to the power pack. Insert the motor cord into the keyed receptacle at the back of the motor. A click will indicate a positive lock has been achieved. With the motor foot switch, run the motor in each direction and listen for any irregular sounds from the operation of the motor. Place the shaper head on the motor shaft and carefully rotate the shaper head until it is firmly attached.
Surgical Technique
Check All Details Before starting the procedure on the patient, check if everything is working. Check the gears, check the movement of the blades etc. Most important, install the microkeratome (shaper head) onto the suction ring (Figure 6-5). Engage the dovetail side first then rotate the shaper flat against the ring. The dovetail of the head should be kept parallel to the track. Gently advance the shaper until the gears are engaged. Press the forward switch of the motor with your foot. Promptly release the foot switch when the permanent stopper abuts the suction ring and stops the forward progress of the shaper. Press the reverse foot switch to retract the shaper head and remove it from the suction ring. The forward and reverse travel of the shaper head across the suction ring must be completely smooth. If binding or resistance is encountered, do not attempt the surgical procedure. Repeat the cleaning process and once again the functional test. If everything has been checked and found right the ACS is ready for use in a surgical procedure. 104
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Contents
The ACS consists of state–of–the-art instru- Section 1 mentation designed for performing lamellar corneal resections. Figure 6-6 shows the instruments of the Section 2 ACS. Once the ACS is ready for use, one can start Section 3 the Lasik procedure. The Excimer Laser is set up for the required refractive power correction and calibra- Section 4 tion done. (The authors have a Chiron 217 Excimer in their Chennai-Madras hospital and a PDI- Photon Section 5 Data Incorporated Excimer in their Bangalore hos- Section 6 pital in India). Once the surgical drape is applied, care be- Section 7 ing taken that the lashes do not come in the surgical Subjects Index field, the procedure is started. A reference mark is made and the suction ring fixed onto the eye. The pre-surgical tonometer (Figure 6-7) is used to check if the intraocular pressure is sufficient. Then the microkeratome (corneal shaper head) is adjusted onto the suction ring till the gears are in place. Then the forward foot switch is pressed and the microkeraHelp ? tome moves forward. It stops at the permanent stopper to prevent a free cap from occurring. Then the reverse foot switch is pressed and the microkeratome moves back. The corneal shaper head is removed. The authors do not remove the suction ring as yet. This helps to stabilize the eye and move it so that the excimer beam is perpendicular to the ablation zone. Dr. Mrs. T. Agarwal started this technique and the authors noticed that even with the IOP high for the duration of ablation no complications
AUTOMATIC CORNEAL SHAPER
call the patient next after a month. This is advantageous so that if regression has occurred then the flap is again lifted and reablation done. It is quite easy to lift the flap within a month of the laser. The patient if alright is called after 6 months.
Problems During Surgery
Figure 6-7: Pre-surgical tonometer
occurred. On the other hand it solved problems of patients being uncooperative and getting decentered ablations. Once the cornea is flapped and the ablations completed, the stroma and the flap are cleaned with the BSS fluid. Then a wet Merocel sponge is taken and the flap cleaned with both sides of the Merocel sponge. This helps to prevent epithelial ingrowths. Then the cannula attached to a syringe with BSS fluid is taken and placed under the flap. It is moved to the junction of the flap and the cornea and gradually the flap lifted with it so that the flap falls back into its original position over the cornea. This method appears to be an excellent method to reposit back the corneal flap. When the flap is in position one should check if the corneal reference markers are in apposition. Check if any foreign body is present in the interface. Wait for a couple of minutes and check if the flap has stuck or not. Then carefully take out the speculum. Both eyes are done simultaneously by the authors. The patient is then seen on the slit lamp after about half an hour and sent home without any pad or shield. The patient is put on topical steroids and artificial tears for 2-3 weeks. The patient is seen the next day. On the first postoperative visit one should generally see only subconjunctival hemorrhages due to the suction ring and nothing on the cornea. The cornea should look like a normal cornea on the slit lamp. Check the vision, which should generally be 6/6 (20/20) without glasses. The authors
Certain problems can occur while performing the keratectomy. Most important is to remember to put the thickness plates on the corneal shaper head otherwise there will be a perforation into the anterior chamber. Check the IOP carefully because if the pressure is not high enough the flap will be very thin. Before starting the keratectomy apply a little bit of fluid on the cornea to make it wet so that the keratectomy is smooth. Do not apply too much of fluid for Contents otherwise the gears can get stuck with too much of fluid. Check that the lids will not get stuck in the Section 1 movement of the microkeratome. Sometimes, temporally the lid gets stuck in the microkeratome and Section 2 this stops the microkeratome in the middle of the Section 3 procedure. Always ablate in the pupillary area so that you do not get a decentered ablation. The ablation Section 4 should always be perpendicular to the cornea and Section 5 not oblique. When the flap is being cleaned and reposited one should be careful that the flap does not Section 6 tear. Wait for a couple of minutes before taking off the speculum otherwise the flap might shift. If after Section 7 half an hour the flap has moved as seen on the slit Subjects Index lamp then take the patient back to the theatre and correct the flap displacement.
TROUBLESHOOTING A. Corneal Shaper Head/Blade Holder
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1. Rough Gear Movement If the gears of the shaper head are completely bound up or moving roughly as you run your thumb over them, it is most likely due to a residue of cleaning solution or BSS left inside the gear cavity. First, try immersing the shaper head in sterile water and
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running your thumb over the gears to purge the residue. If this does not help loosen up the gears, repeat the cleaning process with the toothbrush and cleaning solution, rinse completely with distilled water and dry before sterilizing again.
2. Blade Holder not Moving Freely The blade holder may be restricted within the cavity of the shaper head because of a residue of cleaning solution, BSS or Cidex. Remove the blade holder and thoroughly clean it and the cavity of the shaper head with a toothbrush in the cleaning solution. Make sure to completely rinse the components with distilled water and dry before sterilizing again.
5. Thickness Plate will not Fit into the Shaper Head When you have difficulty inserting or seating a plate, it is probably because the hex nut of the plate is fully tightened. By rotating the locking wrench counterclockwise between your fingers, you will back the hex nut off enough to allow the plate to be installed. If the plate still will not fit flush into the head, check for debris or blockage in the recess of the head or on the post of the thickness plate and clean as necessary.
B. Suction Ring
1. Shaper Head Feels Rough When Pased 3. Restricted Balde Movement With Shaft Through Ring If the blade holder moved freely when tested by itself, but feels restricted with a blade installed and the shaper head closed, remove the thickness plate and open the shaper head to confirm that the blade is properly seated on the blade holder and that all surfaces are perfectly clean and dry. One may use a fiber-free surgical sponge to absorb any moisture in the cavity. Close the shaper head and test the blade again. If the movement still feels restricted, the blade may have been crimpled in the installation process. Replace the blade with another and check with the test shaft again. Proceed only if the blade movement is absolutely smooth and resistance- free.
4. No Blade Movement with Shaft or Motor If the blade does not move at all, remove the test shaft or motor from the shaper head. Look into the back of the shaper head to see if the blade holder is inserted properly. If you do not see the groove, open the shaper head and remove the blade. Take the blade holder out and insert properly, then replace the blade, close the shaper head and re-test.
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If the manual movement of the shaper head through the guide ring feels less than perfectly smooth, inspect the dovetail and gear track of the guide ring as well as the dovetail tracks on the shaper head for residue or debris. Clean both the shaper head and guide ring as necessary. Rinse the components in distilled water only. Tap water may leave deposits.
2. Not Enough Suction
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7
If the suction is insufficient, check the tubing. The tubing might be cracked. So change the tubing. Subjects Index There also could be some blockage in the suction system.
C. Corneal Shape Motor 1. Motor Shaft will Not Rotate When Not Attached to the Shaper Head If the motor shaft does not rotate when the foot switch is depressed, check to see that the unit is turned on. Also confirm that the foot switch and power cord are properly connected.
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AUTOMATIC CORNEAL SHAPER
If the motor will not attach to the shaper head, check to see that the locking nut is installed with the knurled portion out and the smooth portion in. Correct as necessary. Also, confirm that the blade holder is properly installed with the notch facing out towards the back of the shaper head. If not, disassemble the shaper head and remove the blade so that the blade holder may be removed and properly installed.
lutely smooth & resistance-free. The ACS device must be cleaned thoroughly after each use. One should clean with a cleaning solution consisting of 2 parts green Palmolive dishwashing liquid to 100 parts warm water. The type of soap present in Palmolive helps provide lubrication for the device. All parts must be thoroughly rinsed with distilled water after cleaning with the solution. It is best not to perform any cleaning steps in or over a sink, as many of the components are small and could be lost in the drain. Use small plastic bowls or basins instead.
Care & Handling
Sterilization
Problems can be avoided by keeping the ACS as clean as possible. Oscillation of the blade and the passage of the shaper head must be abso-
Sterilization of the ACS is extremely important. In Table 1 the various sterilization techniques are shown.
2. Motor Will Not Attach to the Shaper Head
Contents
Section 1 Section 2
Section 3
TABLE 1 STERILIZATION OF ACS & ITS COMPONENTS
Section 4
Section 5 ACS COMPONENT
AUTOCLAVE
ETO
CIDEX
ALCOHOL
INSTRUMENT TRAY & CONTENTS
YES
YES
NO
NO
APPLANATION LENS
NO
YES
YES
NO
TONOMETER
NO
YES
YES
NO
ACS MOTOR
NO
NO
NO
WIPE ONLY
MOTOR CABLE
NO
YES
NO
WIPE ONLY
Section 6 Section 7 Subjects Index
•
Part of text and some of the figures of this Chapter are presented with permission from Agarwal et al textbook on REFRACTIVE SURGERY published by Jaypee, India , 1999.
•
The authors are grateful to Bausch and Lomb for supplying some of the photos and materials for this Chapter.
LASIK AND BEYOND LASIK
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DOWN UP LASIK
Chapter 7 DOWN UP LASIK T . Agarwal , M.D., S. Agarwal, M.D.
Introduction The Hansatome(1,2) is the latest microkeratome from Chiron Vision (Bausch & Lomb) which performs the Down Up Lasik technique. Instead of creating a nasal hinge this creates a superior hinge. The basic advantage of the hinge being superior is that the eyelid when it moves downward presses on the flap in that direction thus creating less chances of displacement of the flap.
Contents
Section 1 Section 2
Section 3
Section 4
Setting up of the Hansatome
Section 5 Figure 7-1: Power supply unit
Section 6
Power Supply Unit
Section 7
The Hansatome has a power supply unit (Figure 7-1), a suction ring and a motor head. First of all place the power supply unit on a firm surface. The authors place the Hansatome power supply on the Chiron 217 excimer laser machine. This is also called sometimes as the Lasik Laser. Attach the power cords to the power supply unit. Also attach the foot switch cords to the unit.
Subjects Index
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Suction Ring Take the suction tubing and connect it to the appropriate receptacle in the front panel of the power supply unit. Insert the tubing connector until a positive latch is obtained. If the tubing connector is not fully latched, the vacuum panel connector will remain occluded and no suction will be available through the tubing to the patient. Take the suction ring and the suction handle (Figure 7-2) from the
Figure 7-2: Suction ring and handle
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instrument tray. Screw the handle onto the suction port of the suction ring until it is snug, and place the suction tubing firmly over the end of the suction handle. The tracks on the suction ring are temporally so that one can have a down up Lasik done. There is an arch-shaped protrusion which block’s the microkeratome’s cutting action. This is called the Stop.
Microkeratome Head Figure 7-3: Blade cover opened. This way one does not damage the blade
Figure 7-4: Blade being inserted into the groove of the microkeratome’s head
Figure 7-5: Hansatome head showing l for left eye
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The most important step is to assemble the microkeratome head. The first step is to take the blade. Chiron supplies the blade known as the AccuGlide single-use blade. This comes in a sterile package. It is made of steel and is mounted on a bladeholder. The blade holder is made in such a way that Contents it can be inserted in one position only. This will prevent any assembly errors. The blade is first fixed onto Section 1 the supporting instrument. Once that is done the blade cover is opened (Figure 7-3) and the blade inserted Section 2 in the groove in the head of the microkeratome Section 3 (Figure 7-4). Once the blade has been successfully inserted into the Hansatome head. One should in- Section 4 sure that it is centered within the cavity. Section 5 The next step is to take the left/right eye adapter. Place the left/right eye adapter over the motor Section 6 port on top of the head to correspond with the eye that is to be operated on. When preparing the device Section 7 for a right eye surgery, the eye adapter will effecSubjects Index tively cover the “L” for left that is stamped on the head, leaving the “R” for right in full view and indicating that the device is configured for a right eye surgery (Figure 7-5). When preparing the device for a left eye surgery, the eye adapter will effectively cover the “R” for right that is stamped on the head, leaving the “L” for left in full view and indicating Help ? that the device is configured for a left eye surgery.
DOWN UP LASIK
Figure 7-6: Hansatome head showing the 180 & 160 micron thickness marks
Figure 7-7: Head fixed on the adapter.
The head can be 180 or 160 microns (Figure 7-6). This means that if we use the 180-micron head the microkeratome will create a flap of 180 microns and if we use the 160-micron head the flap thickness will be 160 microns. Once the head & the adapter are fixed (Figure 7-7) the motor of the keratome is taken and screwed onto the head of the microkeratome (Figures 7-8 and 7-9). The cord is connected to the motor, which in turn is connected to the power supply. Once the motor has been screwed into place, the blade will swing from right to left with a slow regular
movement. This indicates that the instrument has been assembled correctly.
Contents
Section 1
Test the Microkeratome Place the assembled Hansatome head onto the suction ring by guiding the left/right eye adapter over the pivot pin of the suction ring. Align the head over the approximate starting position appropriate to the selected eye, left or right. This will allow the head/adapter assembly to drop down all the way on the pivot pin. Move the rolling gear up to the first
Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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Figure 7-8: Motor of the microkeratome being screwed onto the head. Figure 7-9: Microkeratome head fixed on the suction ring.
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Figure 7-10: Head moving on the tracks of the suction ring.
gear tooth of the rack. While lightly supporting the motor, press the forward pedal (labeled F) of the motor foot switch to start the head across the ring (Figure 7-10). In normal operation, the head will automatically stop, with two audible beeps. This will happen when the head reaches the mechanical stop and the motor current will drop to zero. Once this happens, depress the reverse pedal (labeled R) of the motor foot switch to reverse the head back off the ring. If everything is alright then only should one proceed with using the Hansatome on the patient.
Care & Maintenance The mechanical components of the Hansatome should be cleaned immediately and thoroughly after each use. Delayed cleaning can leave residual debris such as stromal cells, epithelial cells and strands from surgical sponges. If the components are autoclaved, this debris may become firmly baked onto the com-
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ponents. To remove debris allow the components to soak in very hot distilled water for a minimum of 15 minutes, then employ the cleaning regimen outlined below and repeat until all debris has been removed. Debris allowed to build up on the Hansatome Microkeratome components may affect the performance of the device and result in malfunction of the device and possible patient injury. Chiron Vision recommends use of a cleaning solution consisting of 2 parts green Palmolive dishwashing liquid (unconcentrated product) to 100 parts warm tap water. Do not substitute. The cleaning solution used must not leave any residue. All the components must be thoroughly rinsed with distilled or sterile water after cleaning in the solution. Once this is done one should dry with a lint-free surgical wipe or blow dry with microfiltered forced air. Since Contents most of the components are small and could possible be lost in a sink or drain, it is best to perform Section 1 the cleaning procedure by using small bowls or basins. The bowls or basins should be made of plastic Section 2 and not metal to avoid potential damage to the Chiron Section 3 Vision Hansatome microkeratome mechanical components. Section 4 For cleaning the Hansatome motor, wipe the outside of the motor housing with a cloth dampened Section 5 with isopropyl alcohol and clean the motor shaft with Section 6 a dry toothbrush. Do not immerse it in any fluid. Do not use ethylene oxide sterilization for the motor as Section 7 this can congeal the internal grease and cause potenSubjects Index tial malfunctions. For cleaning the cord, one should wipe it with a cloth dampened with isopropyl alcohol. Do not immerse it in any fluid or autoclave it. Autoclaving will cause convolution of the initially round cable and will cause cumulative damage to the cable and electrical connectors, eventually leading to possible Help ? malfunction.
DOWN UP LASIK
Sterilization The various methods of sterilization for the Hansatome parts are shown in Table 1.
TABLE 1- STERILIZATION OF THE HANSATOME
AUTOCLAVE STERILIZATION5 Component
250o F/121oC for 30 minutes
Flash Cycle At 250oF/ 121oC for 10 minutes
Prevacuum Cycle at 250oF/121oC for 3 minutes
EO STERILIZATION
ALCOHOL SANITIZATION
12/88/EO cycle of 100 minutes at 125oF/52oC at EO conc. of 600 mg/L Level
N/A Contents
Instruments Tray and Contents – Hansatome Head
Section 1 Section 2
Section 3
Yes
Yes
Yes
Yes
No Section 4
Left/Right Eye Adapter
Section 5
Section 6
Suction Ring
Section 7
Suction Handle Subjects Index
Reference Marker Blade Handling Pin Applanation Tonometer Hansatome Motor4 Motor Cord
No
No
No
Yes
No
No
No
No
No
Yes
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Power
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Troubleshooting Head will not Advance Across the Suction Ring The head may be jammed on the first tooth of the gear track. Press the reverse pedal of the motor foot switch to release, then place the head in position and try again.
Head will not Fit Properly Onto the Suction Ring Confirm that the left/right eye adapter has been oriented correctly onto the head for the eye to be operated on. Confirm that the head has been oriented near the correct starting point for the cut, at which point the adapter should drop down onto the pivot pin. Check for any obstructions or debris that may be impeding the loading of the head onto the suction ring. Clean the head, adapter and suction ring and try again.
Figure 7-11: Reference marker making a mark on the cornea.
Contents
Section 1 Section 2
Section 3
Section 4
No Suction Occurring
Section 5
Check if the tubing is all right or if the attachment of the tubing to the power supply is correctly done.
Section 6 Section 7 Subjects Index
SURGICAL TECHNIQUE The surgical technique of Down Up Lasik starts from draping of the patient. When one drapes the patient one should be careful that the eyelashes do not come into the microkeratome. The authors use a cellotape to tape the eyelashes so that they are away from the field of the microkeratome. Then the eyelid speculum is inserted. The eyelid speculum should be a good one, which retracts the eyelids well. Once the eyelid speculum is inserted, one should check the working of the microkeratome. The microkeratome head should be fixed on the suction ring and the movement of the microkeratome checked. One should check that the microkeratome moves smoothly on the tracks of the suction ring. Using the reference marker (Figure 7-11) a mark is made on the cornea. Then the suction ring is 114
SECTION II
Figure 7-12: Suction ring of the Hansatome fixed.
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taken and placed properly on the eye (Figure 7-12). Once the suction ring is fixed in the proper position the foot switch of the vacuum is pressed so that the suction comes on. The tracks of the suction ring should be placed nasally. Once the suction is on one should check the intraocular pressure of the eye using the Barraquer´s pre-surgical tonometer. This creates a black ring in the center. The black ring should be smaller than the white ring seen in the Barraquer’s
DOWN UP LASIK
Figure 7-13: Flap being lifted with a spatula
Figure 7-14: Superior flap made.
Contents
tonometer. If this happens, then the intraocular pressure is greater than 65 mm of Hg and the case can be proceeded with. If it is larger than the white ring then something is wrong with the suction. So release the suction and start the process once again. Once everything is alright swab the area so that excess fluid is not present. When the suction ring is fixed in position, the microkeratome head is now fixed onto the pin of the suction ring. There are notches on the pin of the suction ring, which coincide with the head so that the head gets properly fixed. Then the forward foot switch is depressed and the microkeratome moves on the tracks of the suction ring. This will automatically stop when the head hits the stop mechanism. When this happens two beeps will be heard. Then press the reverse foot switch and the head will move in the reverse direction. Once it has come back fully release the suction and take off both the suction ring and the microkeratome head. Use a fine spatula or repositor and lift the flap from the inferior area (Figure 7-13). Lift the flap so that the hinge is superior and the flap lies superiorly (Figure 7-14). Before the whole Lasik procedure was started one should have calibrated the excimer laser machine and the required refractive power entered. The authors use a Chiron 217 excimer laser machine and overcorrect by 10%. The ablation is then started
(Figure 7-15). One can use an eye tracking system Section 1 or alternatively fixate the eye with a forceps and start the ablation. One should be careful that decentered Section 2 ablation does not occur. See to it that the excimer Section 3 laser hits perpendicular to the cornea and not obliquely. The laser should hit the pupillary area. In Section 4 cases of astigmatism one should be careful that the eye is not rotated otherwise the axis of the astigma- Section 5 tism will become different. Section 6 When the ablation of the excimer is completed, one should wash the stroma with the irrigating fluid Section 7 (BSS). Wash the flap well. See to it that there is no foreign body lying on the stroma. Take a wet Merocel Subjects Index sponge (Figure 7-16) and clean the flap with both ends of the sponge. This will prevent epithelial ingrowths. Then take the syringe with BSS and pass the cannula under the flap. While irrigating lift the flap and the flap will fall back into its original position onto the stroma. One can use a spatula also to Help ? reposit the flap (Figure 7-17). Once the flap has been repositioned check that the reference marks coincide (Figure 7-18). Then wait for a couple of minutes so that the flap is stuck. Carefully take out the speculum without disturbing the flap. The authors see the patient on the slit lamp after half an hour and if everything is all right the patient goes home without a patch. Both eyes are done simultaneously. The patient is put on artificial
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Figure 7-15: Excimer ablations started
Figure 7-16: Flap cleaned with a merocel sponge. This helps prevent epithelial ingrowths.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index Figure 7-17: Superior flap reposited with a spatula. One can use an irrigating cannula to do the same thing
Figure 7-18: Flap back in position. Note the cut edges of the flap. The reference markers should coincide
Help ?
tears; antibiotic and steroid drops for 2-3 weeks only. The patient is seen again the next day. When seen on the slit lamp it should be as if no treatment was done, except for slight subconjunctival hemorrhages due to the suction ring being present. The patient is seen again after a month and if necessary relasik is done by lifting the flap. This is done if regression has occurred. In such cases one need not again make the cut, but lift the same flap back.
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FACTORS RESPONSIBLE FOR SECURING THE FLAP There are basically four factors (3) responsible for securing the flap in position. 1. The natural capillary attraction of the tissues and mucoproteins. This occurs rapidly within seconds to minutes 1. The endothelial pump action. This occurs within minutes to hours.
DOWN UP LASIK
3. Epithelial covering along the margin starts from 12-24 hours and 4. Scarring along the cut edge of Bowman’s layer occurs weeks to months later.
lasers are perpendicular to the cornea thus preventing decentered ablations. This is not possible with the Hansatome.
REFERENCES
ADVANTAGES The main advantage of the Down Up Lasik technique is that as the eyelid moves downwards it presses on the flap which has a superior hinge and thus does not displace the flap. The same does not apply to a flap, which has a hinge nasally. Gravitational forces also help in positioning the flap properly. The compression effect of the eyelid also helps to smoothen the flap. Another advantage of the Down Up Lasik technique is that it creates a large flap. The ablation pattern of the excimer requires a large flap preferably in cases of hyperopia treatment. Further chances of the flap getting shot with the excimer do not occur with the Down Up Lasik. Free caps do not occur with the Hansatome.
DISADVANTAGES There are disadvantages of the Down Up Lasik technique also. One problem is the large flap. If the patient is wearing contact lenses they can have peripheral vascularization of the cornea. On cutting the cornea, as the flap is large these blood vessels bleed and it takes some time for the bleeding to stop. Another problem with the Hansatome is that the palpebral fissure should be large. If the fissure is small then the suction ring of the Hansatome does not fir in the eye and one would have to resort to a canthotomy. In such cases, the authors prefer to use the Automatic corneal shaper. Yet another problem with the Hansatome is that when the cut has been completed the suction ring and the keratome head are removed so that when the laser is being applied there is nothing to stabilize the eye. One can use the eye tracking system to get accurate ablation. The advantage of the Automatic Corneal Shaper in contrast is that once the keratome cuts the cornea the suction ring is not removed and this can stabilize the eye well. The suction is not stopped till the entire ablation is completed. One can move the eye is such a way as the suction is still on so that the excimer
1. Chiron Vision Hansatome Microkeratome operator’s manual 2. Lucio Buratto: Down Up Lasik with the new Chiron Microkeratome; Milano, Italy 1997 3. Jeffery J Machat: Excimer Laser Refractive Surgery: Slack Incorporated 1996.
Contents
Section 1 Section 2 T. Agarwal Dr. Agarwal’s Eye Hospital Chennai, India; Bangalore, India; Dubai
Section 3
Section 4
Section 5
Section 6 Section 7 •
Part of the text and some of the figures of this Chapter are Subjects Index presented with permission from Agarwal et al textbook on REFRACTIVE SURGERY published by Jaypee, India, 1999.
•
The authors are grateful to Bausch and Lomb for supplying some of the photos and materials for this Chapter. Help ?
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ALL LASER LASIK WITH THE PULSION FS LASER
Chapter 8 ALL LASER LASIK WITH THE PULSION FS LASER Jaime R. Martiz, M.D., Stephen G. Slade, M.D.
Introduction This chapter will describe the basic steps in a LASIK procedure using the Pulsion FS Laser to create the corneal flap and the Bausch & Lomb Technolas 217 excimer laser (Figure 8-1). Today, more than a million refractive surgery procedures are performed in United States and LASIK has clearly become the number one choice. The quick visual recovery produced by LASIK makes the surgery very attractive; in addition it is currently the most sophisticated procedure to correct refractive errors. The majority of complication in LASIK are related to the mechanical microkeratome; which use a metal blade to cut the cornea and create a flap. Even in the most expert surgeons hands complications occurs. It is very important that the corneal flap be the optimal diameter, thickness and quality to reproduce excellent short and long-term results. When using microkeratomes, the laser treatment cannot continue if a partial resection has been made, and the procedure must be postponed for usually 3 months. Should an interruption occur during the Pulsion FS laser procedure, we would ask the patient to wait for 45 minutes and then repeat the procedure to create flap. The corneal flap is created under very low vacuum, delivering the laser energy directly to the middle layer of the cornea through a disposable glass lens. There is no trauma to the epithelial surface of the cornea, and the surgery is painless.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index Figure 8-1: Pulsion FS Laser
stable refraction for at least 12 months and healthy corneas. Contraindications should include patients with keratoconus; and autoimmune diseases, but not patients with poor epithelium since there is no trauma to this layer. Patients should undergo an informed consent with their surgeon.
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Preoperative Preparation Patient Selection Selection criteria for flap creation with the Pulsion FS Laser are the same that we use of traditional LASIK procedures. Patients should have a
In most cases, a patient’s preoperative preparation is the same as LASIK patients and includes an oral sedative such as Valium (5 to 10 mg). Immediately before prepping, one drop of a topical anes-
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lizing a fraction of the energy of an Excimer laser, the femtosecond laser technology provides the surgeon with control of the following surgical parameters (Figure 8-2): Hinge angle Hinge position (temporal, nasal, superior) Flap diameter (mm) 8.0, 8.5, 9.0, 9.5 Flap position (superior, inferior, nasal or temporal) Flap Thickness (um) 150,160, 170, 180
Figure 8-2: The Pulsion FS Laser provides the surgeon with control of surgical parameters like Hinge angle, Hinge position, Flap diameter, and Flap position, Flap Thickness.
thetic (Proparacaine) should be instilled and then one more drop before the keratectomy. No preoperative miotic is used. The patient eye is prepared by irrigating the conjunctival fornices with an irrigating solution (Sterile Eye Wash Optopics) to clear the area of any secretions or debris. Swab the skin of the eyelids with a povidine-iodine swab stick and gently dry.
Surgical Logistics The Pulsion FS Laser is an intrastromal scanning laser with a 3 micron spot size that can create a corneal flap with optimal accuracy and precision. Uti-
The laser pulses are placed very closely together in a spiral pattern, and an uncut section of tissue is pre-programmed to create the hinge for the flap (Figures 8-3, 8-4, 8-5 and 8-6) The laser flap procedure offers a very safe and predictable alternative to the traditional microkeratome approach. The Pulsion FS laser is an extremely clean and efficient solid-state laser, which means it does not rely upon a mixture of gases to generate a homogeneous beam, as does the excimer laser.
Contents
Section 1 Section 2
Section 3
Draping and Speculum
Section 4
-Proparacaine drops to lubricate. Place drape Section 5 over the eyelashes. -Continue with the lid speculum and open the Section 6 lids to a comfortable position -Confirm laser is in its Home position and align Section 7 patient comfortably underneath. Subjects Index -Lock patient bed in place.
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Figures 8-3 & 8-4: The laser pulses are placed closely together in a spiral pattern, and an uncut section of tissue is pre-programmed to create the hinge for the flap
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ALL LASER LASIK WITH THE PULSION FS LASER
Figure 8-5: An uncut section of tissue is pre-programmed to create the hinge for the flap.
Figure 8-6: Lid speculum is applied to open the lids to a comfortable position.
Marking the Cornea
Application
Contents
Section 1
-Mark the cornea with appropriate alignment markers. -Center the eye between the lids and focus the laser.
Preparation Step 1. Outer Tray. Position tray with Pulsion PI label facing up, firmly grasp lower left corner and peel lid from left to right to reveal inner tray. Discard lid. Step 2. Inner Tray. To preserve sterility, remove inner tray while wearing sterile, powderless surgical gloves and complete steps 2 through 6. Position inner tray with Pulsion PI label facing up, grasp lower right corner and peel lid from right to left to remove.
Step 4. Applanation Lens. Section 2 Grasp applanation lens by the upper rim with the contact lens facing downwards. Slide the appla- Section 3 nation lens into the guides located at the bottom of Section 4 the objective lens assembly on the Pulsion FS Laser. Lock the lens assembly by turning the locking Section 5 mechanism upward. When the applanation lens is properly seated, a slight click should be heard. Section 6 (Figure 8-7) Section 7 Remove protective cap on applanation lens and inspect through the operating microscope for Subjects Index scratches. A scratched applanation lens should not be used.
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Step 3. Inspection. Remove applanation lens and suction ring assembly from tray, and place onto sterile field. Inspect all parts for damage or disconnection. Do not attempt to use any damaged product.
Figure 8-7. Applanation lens is properly seated.
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Chapter 8
Step 5. Suction Ring Assembly. The suction ring assembly serves two functions: 1) Fixating the globe and 2) Rigidly coupling the globe to the applanation lens. The suction ring assembly consists of a limbal suction ring mounted on the bottom of an actuating cylinder assembly. The suction ring attaches to the limbus by means of low suction applied through a syringe and intraocular pressure increase to around 30 mmHg. (Figure 8-8)
Application Fully depress the syringe plunger and place the limbal suction ring onto the cornea, centering over the pupil. Apply a slight downward pressure to the ring, and then release the plunger allowing the suction ring to firmly affix to the eye. (Figure 8-9). Step 6. Applanation Procedure With the eye fixated, the laser’s delivery system must then be properly centered over the suction ring assembly opening (Figure 8-10). This is accomplished by manipulation of the x and y joystick controls located on the laser’s control panel. Once centered over the opening, grasp the two molded levers on the suction ring assembly and gently squeeze to expand the opening in the cylinder wide enough to accommodate the apex of the applanation lens. Slowly lower the delivery device using the z joystick control, gently guiding the applanation lens through the cylinder while holding the suction ring assembly open (Figure 8-11). When the cornea is fully applanated and the lens is well centered in the suction ring assembly, release the molded levers to allow the suction ring assembly to “grip” the applanation lens. The resection may now be initiated. (Figures 8-12, 8-13)
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Figure 8-8. The suction ring attaches to the limbus with low suction applied through a syringe.
Section 7 Subjects Index
Help ?
Figure 8-9. Surgeon applies a slight downward pressure to the ring, and then releases the plunger allowing the suction ring to firmly affix to the eye.
122
SECTION II
Figure 8-10. The laser’s delivery system must be centered over the suction ring assembly opening.
ALL LASER LASIK WITH THE PULSION FS LASER
Figure 8-11. Surgeon slowly lowers the delivery device using the z joystick control and gently guiding the applanation lens through the cylinder while holding the suction ring.
Figure 8-12. Intrastromal resection.
Contents
Section 1 Section 2
Releasing the Cornea
Section 3
When the resection is complete, depress the syringe plunger to release the cornea from suction. Utilize the z joystick on the control panel to raise the delivery device from the eye. Lift the suction ring assembly from the eye, release lens assembly lock and remove the applanation lens by grasping the cone and sliding it away from the objective. Depress the “Home” button on the control panel to raise the delivery device and safely remove the patient from the surgical field. Discard the Pulsion PI components in an appropriate receptacle.
Section 4
Section 5
Section 6 Section 7 Figure 8-13. Cornea is fully applanated and the lens is well Subjects Index centered in the suction ring
Flap elevation and Excimer Laser Ablation
Help ?
The patient may be safely switch to the Excimer Laser for Refractive ablation The corneal flap is lifted superiorly with curved forceps (Figure 8-14); the laser focus is achieved over the pupillary center. At this point, the surgeon can proceed with the ablation of stromal bed (Figures 8-15 and 8-16). Figure 8-14. The corneal flap is lifted with curved forceps.
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Chapter 8
Figure 8-15. The laser focus is achieved over the pupillary center.
Figure 8-16. Surgeon can proceed with the ablation of stromal bed.
Reposition of the Flap
cannula is placed underneath the flap and irrigation is completed to clear any remaining debris from the interface as well as allowing BSS under the flap to facilitate “floating” back into its original position. (Figures 8-19 and 8-20)
When the ablation is complete, the corneal flap is replaced onto the stromal bed using the cannula starting superiorly (Figures 8-17 and 8-18). The
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Figures 8-17 & 8-18. The corneal flap is replaced onto the stromal bed using the cannula.
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Figures 8-19 & 8-20. The cannula is placed underneath the flap and irrigation is completed to clear any remaining debris from the interface.
124
SECTION II
ALL LASER LASIK WITH THE PULSION FS LASER
Figure 8-21. The Merocel sponge is moistened and squeezed dry and then used to “paint the flap” in the direction of the hinge.
Figure 8-22. One day Postoperative.
Contents
The Merocel sponge is moistened and squeezed dry and then used to “paint the flap” in the direction of the hinge (Figure 8-21). The flap is inspected to reassure that there are no wrinkles and for proper position by making sure an identical distance between the gutter and keratectomy edge is present all over the flap circumference. Depressing the peripheral “non flap” cornea with closed blunt 0.12 forceps completes a Slade’s striae test. When striae test is positive around the flap edge appropriate apposition has been achieved. During this phase it is recommended to keep a BSS drop over the central corneal epithelium to keep it wet. There is no specific waiting time with this technique, but we recommend waiting 3-5 minutes before removing the speculum.
The case is completed by carefully removing the speculum. When doing this step, make sure to lift and close the speculum at the same time to avoid displacement of the flap. Patient is then instructed to blink normally, and is observed through the microscope. The flap should remain in the same position and appear adhered to the cornea bed.
Postoperative Care
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7
Immediately postoperatively, several drops of an antibiotic are instilled. The eye is not taped or shielded. The patient is asked to follow the home care instructions (Figure 8-22).
Subjects Index
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125
LIMITATIONS AND CONTRAINDICATIONS OF LASIK
Chapter 9 LIMITATIONS AND CONTRAINDICATIONS OF LASIK Gregg Feinerman, M.D., Tim Peters, M.D., Jason Butler, Kim Nguyen
The belief that any one refractive procedure is best for all ranges of refractive error places patients at risk for a poor outcome. Laser in situ keratomileusis (LASIK), like any surgical procedure, has its limitations. It is essential for the refractive surgeon to understand the limitations of LASIK when performing preoperative exams and counseling patients. During the preoperative assessment the surgeon can identify specific measurements that disqualify patients from LASIK, thus preventing suboptimal postoperative results.
Patient History At our center we offer LASIK to patients who are at least 18 years of age and have two or more years of refractive stability. The range of correction varies depending on the patient’s corneal thickness and pupil size; but we generally correct between – 12.00 to +4.00 diopters of ametropia with LASIK. The ocular history should include details regarding medications, allergies, and any previous ocular surgery or infection (e.g. Herpes Simplex Virus). Ocular Herpes Simplex is a contraindication to LASIK because the surgery may induce reactivation. Questions regarding recurrent corneal erosion should be addressed, as these patients are more likely to have epithelial adherence problems during surgery. Patients with significant glaucoma should avoid LASIK due to the increased intraocular pressure resulting from the microkeratome. Patients with a history of
prior scleral buckling procedures have an increased Contents risk for inability to achieve proper suction and proper elevation of the intraocular pressure with the suc- Section 1 tion ring. Section 2 Additionally, a thorough medical history should include systemic conditions such as diabetes Section 3 mellitus, collagen vascular disorders, or pregnancy, Section 4 as the healing process may be affected. Pregnant or lactating women should postpone LASIK until after Section 5 their first menstrual period postpartum. Diabetics with unstable blood sugars or significant diabetic re- Section 6 tinopathy should be excluded from refractive surgery. Section 7 Additionally, diabetics may be at higher risk for postoperative infection, epithelial adherence problems, Subjects Index and dry eye. Collagen vascular disease may predispose patients to dry eye and corneal melting. Patients with inappropriate expectations should be identified preoperatively to avoid postoperative disappointments. For example, patients with amblyopia should be informed that refractive surHelp ? gery would not improve their best corrected visual acuity. It is also important to address the possibility of nocturnal halos, especially in patients with high correction and/or large pupils.
Exam When first examining the patient, it is wise to note the palpebral fissure size. If the patient has very deep-set eyes or narrow palpebral fissures, they should be informed that they might have some intraLASIK AND BEYOND LASIK
127
Chapter 9
Figure 9-1: Nidek MK 2000 Microkeratome
operative exposure problems. Smaller footprint microkeratomes, such as the Nidek MK 2000 may be helpful in such cases (Fig 9-1). Otherwise, PRK or a possible lateral canthotomy can be discussed in advance so the patient is aware of the possible alternatives. Patients with incomplete eyelid closure are at risk of flap dislocation, and should not undergo refractive surgery. Keratitis Sicca should be diagnosed and treated preoperatively with adequate pre and postoperative artificial tears. Punctal plugs should also be considered preoperatively. Blepharitis should be treated prior to surgery because it may predispose patients to an increased risk for infections or infiltrates. Computerized corneal topography is performed on all of our refractive surgery candidates to screen for keratoconus, pellucid marginal degeneration, and other corneal disorders (Figs 9-2 & 9-3). It is also helpful to obtain ORBSCAN II topographies in high ametropes because it provides measurements of the anterior chamber depth for phakic intraocular lens implantation. (Fig 9-4) After completing corneal topography, manual keratometry is measured. The results are compared to the manifest refraction and topographical simulated keratometry to identify lenticular cylinder. It is also important to calculate the theoretical postoperative keratometry prior to surgery in order to prevent the cornea from becoming excessively flat or steep. In myopic treatments we try to avoid creating postoperative corneal curvatures less than 34 diopt128
SECTION II
Figure 9-2: Keratoconus Note the inferior steepening OS on the keratometric map with a mean central corneal power of 44.78 D. There is also more than 3.00 D of variability in corneal power over the central 3mm zone. Thinning was found on pachymetry inferiorly OS.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Help ? Figure 9-3: Pellucid Marginal Degeneration Note the characteristic loop cylinder pattern on this patient with pellucid marginal degeneration.
ers. For hyperopic treatments we do not steepen the cornea beyond 48 diopters. Iatrogenic keratoconus with apical stromal scarring has occurred after hyperopic LASIK when the postoperative curvature exceeds 48 diopters.1
LIMITATIONS AND CONTRAINDICATIONS OF LASIK
Figure 9-5: Buttonhole following LASIK Retroillumination
Contents
Section 1 Section 2 Figure 9-4: ORBSCAN II Corneal Topographer
When reviewing the preoperative keratometry measurements, it is also important to consider that there is an increased likelihood of a buttonhole when performing LASIK on corneas with a preoperative curvature greater than 46 diopters (Fig 9-5). Additionally, there is an increased likelihood of free caps in large flat corneas (corneal curvature is less than 41 diopters) due to the smaller than usual area of applanation as the microkeratome pass is performed. This may be due to the interaction of the suction ring and microkeratome with the globe.2 . Although this data was predominantly determined with the Chiron ACS, it should be kept in mind regardless of the microkeratome used. Pupil size in dim and room light is carefully measured and recorded. It is helpful to document the nocturnal pupil size with the Colvard Infrared Pupillometer. Patients with large pupils should be counseled regarding pupillary induced optical aberrations such as nocturnal halos, glare, and decreased contrast sensitivity. In our center we pay particular attention to pupil size in myopic patients with greater than 5 mm pupils in room light or 7 mm in dim illumination. This is even more important in those with
Section 3
Section 4
Section 5 Figure 9-6: Toric IOL
Section 6 Section 7
higher myopic refractive errors (greater than 5 diopters). In hyperopic patients we avoid treating pa- Subjects Index tients with greater than 6 mm pupils in dim illumination because the effective optical zone is smaller. On slit lamp exam the surgeon should check for corneal dystrophies. For example, patients with anterior basement membrane dystrophy are likely to have shifted corneal epithelium intraoperatively. They are also more likely to suffer from recurrent Help ? corneal erosions exacerbated postoperatively. The slit lamp exam should also include an assessment of the lens clarity. In our practice any patient over 50 with lenticular changes is counseled about refractive lensectomy. Significant lenticular changes include more than 2+ nuclear sclerosis, any posterior subcapsular cataract, or cortical changes. A toric IOL is considered in patients with greater than 1.5 diopters of astigmatism (Fig 9-6). Astigmatic keratotomy alone can be considered in patients with more than 2 LASIK AND BEYOND LASIK
129
Chapter 9
Table 1-1
•
Contents
Section 1 Section 2
Section 3
diopters of astigmatism with a spherical equivalent of -0.50 to +0.50 diopters. Where permissible, a phakic intraocular lens (phakic IOL) can be considered in patients younger than 50 that are not candidates for LASIK. If LASIK is contraindicated, phakic IOLs can be offered to patients with hyperopia or moderate to high myopia if the anterior chamber depth is sufficient. Iatrogenic keratoectasia following LASIK has been reported.3 Thus, it is important to measure the corneal thickness prior to LASIK to help ensure that there is adequate residual stromal bed thickness postoperatively. We measure corneal thickness with the Mentor Pach-Pen instrument (Bio-Rad, Santa Ana California) or the ORBSCAN II topography unit. It is currently accepted that the residual thickness in the stromal bed after LASIK should be at least 200 µm, preferably 250 µm.4 The residual corneal stromal bed thickness is calculated by first determining the ablation depth with the Munnerlyn formula (Depth of ablation = desired refractive change * optical zone2/3). The calculated ablation depth is added to the thickness of the microkeratome depth plate. Next, the total is subtracted from the patient’s preoperative minimal corneal thickness. This estimate 130
SECTION II
is useful, but the actual depth of ablation depends on Section 4 the laser used and type of treatment performed (Table 1-1). For example, cross cylinder ablations Section 5 (ablations done in plus and minus cylinder) remove Section 6 less corneal tissue.5 If calculations reveal borderline residual stromal bed thickness, then it should be Section 7 discussed with the patient prior to primary LASIK. Additionally, the patient is informed that an enhance- Subjects Index ment may not be possible. The optical zone becomes a limiting factor in higher corrections (Table 1-2). Table 1-3 and Table 1-4 demonstrate a spreadsheet formula created to determine the largest optical zone achievable based on the Munnerlyn Formula, microkeratome depth plate, and a correction/stromal bed Help ? limit of 250µm. Several unique aspects of hyperopic LASIK treatments should be considered preoperatively. Firstly, the hinge location may have an effect on astigmatism. The astigmatic ablation for hyperopia with against the rule astigmatism occurs along the vertical axis (induces steepening along the short axis). For with the rule hyperopia and astigmatism treatments, the astigmatic ablation occurs along the horizontal axis. Thus, the surgeon should consider creating a superior hinge flap when treating hyperopia
LIMITATIONS AND CONTRAINDICATIONS OF LASIK
Table 1-2
Calculation of Ablation Depth Using Munnerlyn Formula Optical Zone Diameter 5.5
Diopters
0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25 4.50 4.75 5.00 5.25 5.50 5.75 6.00 6.25 6.50 6.75 7.00 7.25 7.50 7.75 8.00 8.25 8.50 8.75 9.00 9.25 9.50 9.75 10.00
6.0
6.5
7.0
7.5
5.04
6.00
7.04
8.17
9.38
7.56
9.00
10.56
12.25
14.06
10.08
12.00
14.08
16.33
18.75
12.60
15.00
17.60
20.42
23.44
15.13
18.00
21.13
24.50
28.13
17.65
21.00
24.65
28.58
32.81
20.17
24.00
28.17
32.67
37.50
22.69
27.00
31.69
36.75
42.19
25.21
30.00
35.21
40.83
46.88
27.73
33.00
38.73
44.92
51.56
30.25
36.00
42.25
49.00
56.25
32.77
39.00
45.77
53.08
60.94
35.29
42.00
49.29
57.17
65.63
37.81
45.00
52.81
61.25
70.31
40.33
48.00
56.33
65.33
75.00
42.85
51.00
59.85
69.42
79.69
45.38
54.00
63.38
73.50
84.38
47.90 50.42
57.00 60.00
66.90 70.42
77.58 81.67
89.06 93.75
52.94
63.00
73.94
85.75
98.44
55.46
66.00
77.46
89.83
103.13
57.98
69.00
80.98
93.92
107.81
60.50
72.00
84.50
98.00
112.50
63.02
75.00
88.02
102.08
117.19
65.54
78.00
91.54
106.17
121.88
68.06
81.00
95.06
110.25
126.56
70.58
84.00
98.58
114.33
131.25
73.10
87.00
102.10
118.42
135.94
75.63
90.00
105.63
122.50
140.63
78.15
93.00
109.15
126.58
145.31
80.67
96.00
112.67
130.67
150.00
83.19
99.00
116.19
134.75
154.69
85.71
102.00
119.71
138.83
159.38
88.23
105.00
123.23
142.92
164.06
90.75 93.27
108.00 111.00
126.75 130.27
147.00 151.08
168.75 173.44
95.79
114.00
133.79
155.17
178.13
98.31
117.00
137.31
159.25
182.81
100.83
120.00
140.83
163.33
187.50
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Help ?
Formula: Ablation Depth = (Diopters*((Optical Zone)^2))/3 This chart gives an approximate ablation depth for a given correction and optical zone. Surgeons should consider these calculations a rough estimate of ablation depth. The laser software calculations of ablation depth should also be checked in cases where the calculation results in a residual stromal bed thickness close to 250um.
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131
Chapter 9
Diopters
Section 4
Section 5
Table 1-3
Section 3
Section 6
Section 7
10.95
450
8.66
12.25
460
9.49
10.95
13.42
470
10.25
11.83
14.49
480
8.37
9.17
10.00
7.75
8.49
7.75 7.07 7.25
7.75
7.75
6.71
7.17
6.32 6.12 6.48
6.83
6.55
6.00
6.32
5.48 5.48 5.92
6.18
5.77
5.48
5.72
4.90 5.00 5.48
5.68
5.22
5.07
5.26
4.47 4.63
4.97
5.29 5.12
4.80
4.60
4.90 4.74
4.14
4.20
4.70
4.83
4.47 4.33
4.35
4.47
3.76 3.97
4.47
4.58
4.08
4.14
4.24
3.55 3.78
3.87
4.27
4.37
3.38
3.96
4.05
4.18
3.61
3.87
3.69 3.54
4.02
4.10
3.23 3.16
3.72
3.79
3.87
3.94
3.40
3.59
3.65
3.46
3.27
3.33
3.04 2.93
2.98
3.10
3.30
3.46
3.65
4.00 3.87
4.30
4.67
5.16
5.86
6.93
8.94
15.49 11.62
13.42
16.43
500
10.95 9.49
10.39
4.39
4.47
4.56
4.65
4.74
4.85
4.95
5.07
5.20
5.33
5.48
5.64
6.00 5.81
6.21
6.45
6.71
7.01
7.35
7.75
8.22
8.78
8.94
4.14
4.22
4.30
4.38
4.47
4.57
4.67
4.78
4.90
5.03
5.16
5.31
5.66 5.48
5.86
6.08
6.32
6.61
6.93
7.30
7.75
8.28
9.80
12.65
490
4.63
4.71
4.80
4.90
5.00
5.11
5.22
5.35
5.48
5.62
5.77
5.94
6.32 6.12
6.55
6.79
7.07
7.39
7.75
8.16
8.66
9.26
10.00
10.95
12.25
14.14
17.32
510
4.86
4.94
5.04
5.14
5.24
5.36
5.48
5.61
5.74
5.89
6.06
6.23
6.63 6.42
6.87
7.13
7.42
7.75
8.12
8.56
9.08
9.71
10.49
11.49
12.85
14.83
18.17
520
5.07
5.16
5.26
5.37
5.48
5.60
5.72
5.86
6.00
6.16
6.32
6.51
6.93 6.71
7.17
7.44
7.75
8.09
8.49
8.94
9.49
10.14
10.95
12.00
13.42
15.49
18.97
530
Pachymetry
Calcualation of Maximal Optical Zone (160 um plate)
Section 2
Formula: Optical Zone = SQRT((3*(Pachymetry-410))/Diopters)
1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50 10.00 10.50 11.00 11.50 12.00 12.50 13.00 13.50 14.00
Section 1
19.75
540
14.49
16.73
20.49
550
15.00
17.32
21.21
560
12.25
13.42
13.96
11.83
12.96
10.61
11.34
11.40
10.25
10.95
9.49
10.00
9.87
9.17
8.66
9.05
9.66
8.37
8.74
8.83 8.06
8.02 7.75 7.50
8.32
7.28
7.75 7.48 7.25
8.04
7.03
6.88
7.07
7.46
6.77
7.21 6.98
6.65
6.83
6.55
6.71
6.41
6.32
6.48
6.26
6.40
6.09
6.04
6.12
6.18 5.92
5.88
6.00
5.82 5.70
5.68
5.67
5.77
5.80
5.48
5.58
5.48 5.28
5.37
5.59
5.95
6.24
6.58
7.75
8.42
9.31
10.56
12.49
16.12
Subjects Index
This chart gives an approximate maximal optical zone available for a given correction and pachymetry using a 160 um plate. These calculations assume the preservation of a residual 250um stromal bed.
21.91
570
15.97
18.44
22.58
580
16.43
18.97
23.24
590
16.88
19.49
23.87
600
13.78
15.10
15.49
13.42
14.70
17.89
13.04
14.28
11.94
12.76
12.65
11.62
12.42
13.86
11.29
12.07
10.68
11.25
10.95
10.39
10.95
11.71
10.10
9.75
10.18
10.65
9.49
9.91
9.80
9.22
9.63
10.33
8.94
9.34
9.02
8.72 8.44
9.36
8.19
8.78
8.49 8.22
9.11
7.97
8.54
8.25 7.98
8.86
7.75
7.75
7.96
8.28 8.00 7.75
7.54
7.75
8.59
7.51
7.33
7.53
7.37
7.55
7.11
7.17
7.35
7.30
6.97
7.14
7.04
7.20
6.76
6.85
7.01
6.93
6.66
6.75
6.89
6.81
6.71
6.46
6.52
6.57
6.61 6.32
6.45
6.62
6.26
6.38
6.50
6.39
6.21
6.32
6.08
6.04
6.15
6.20
5.86
5.96
SECTION II
132
Contents
Help ?
2.93
2.54
2.07 3.27
3.33
3.40
3.46
3.54
3.61
3.69
3.78
3.87
3.97
4.08
4.20
4.47 4.33
4.63
4.80
5.00
5.22
5.48
5.77
6.12
6.55
7.07
7.75
8.66
10.00
12.25
3.59
3.65
3.72
3.79
3.87
3.96
4.05
4.14
4.24
4.35
4.47
4.60
4.90 4.74
5.07
5.26
5.48
5.72
6.00
6.32
6.71
7.17
7.75
8.49
9.49
10.95
13.42
490
3.87
3.94
4.02
4.10
4.18
4.27
4.37
4.47
4.58
4.70
4.83
4.97
5.29 5.12
5.48
5.68
5.92
6.18
6.48
6.83
7.25
7.75
8.37
9.17
10.25
11.83
14.49
500
Formula: Optical Zone = SQRT((3*(Pachymetry-430))/Diopters)
3.04 2.98
3.16 3.10
2.74 2.68
2.24
2.19 2.63
3.23
2.80
2.58
3.30
2.86
2.34
2.28
2.15
3.38
2.93
2.39
2.11
3.55 3.46
3.08 3.00
2.51
2.45
3.76 3.65
3.25 3.16
2.66
4.00 3.87
3.46 3.35
2.83 2.74
2.58
4.30 4.14
3.72 3.59
3.04
4.47
3.87
3.16
2.93
4.90
5.16
4.47
3.65 4.67
5.48
4.74
3.87 4.24
5.86
5.07
4.14
4.05
6.32
5.48
4.47
3.46
6.93
6.00
4.90
3.30
8.94 7.75
7.75 6.71
6.32
5.48
10.95
9.49
7.75
480
4.14
4.22
4.30
4.38
4.47
4.57
4.67
4.78
4.90
5.03
5.16
5.31
5.66 5.48
5.86
6.08
6.32
6.61
6.93
7.30
7.75
8.28
8.94
9.80
10.95
12.65
15.49
510
4.39
4.47
4.56
4.65
4.74
4.85
4.95
5.07
5.20
5.33
5.48
5.64
6.00 5.81
6.21
6.45
6.71
7.01
7.35
7.75
8.22
8.78
9.49
10.39
11.62
13.42
16.43
520
8.94
8.56
4.63
4.71
4.80
4.90
5.00
5.11
5.22
5.35
5.48
5.62
5.77
5.94
6.32 6.12
6.55
6.79
7.07
7.39
7.75
8.16
5.26 5.16 5.07
5.04 4.94 4.86
5.48 5.37
5.24 5.14
5.72
5.86
5.61
5.60
6.00
5.74 5.48
6.16
5.89
5.36
6.51 6.32
6.23
6.93 6.71
6.63 6.42 6.06
7.44 7.17
7.13 6.87
7.75
9.49
9.08
7.42
10.14
9.71
9.26
8.49
10.95
10.49
10.00
8.09
12.00
11.49
10.95
8.12
13.42
12.85
12.25
7.75
15.49
14.83
14.14
8.66
550 18.97
540 18.17
17.32
530
Pachymetry 560
5.28
5.37
5.48
5.59
5.70
5.82
5.95
6.09
6.24
6.41
6.58
6.77
7.21 6.98
7.46
7.75
8.06
8.42
8.83
9.31
9.87
10.56
11.40
12.49
13.96
16.12
19.75
This chart gives an approximate maximal optical zone available for a given correction and pachymetry using a 180 um plate. These calculations assume the preservation of a residual 250um stromal bed.
Diopters
1.00 1.50 2.00 2.50 3.00 3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00 7.50 8.00 8.50 9.00 9.50 10.00 10.50 11.00 11.50 12.00 12.50 13.00 13.50 14.00
470
460
450
Calculation of Maximal Optical Zone (180 micron plate)
Table 1-4
570
5.48
5.58
5.68
5.80
5.92
6.04
6.18
6.32
6.48
6.65
6.83
7.03
7.48 7.25
7.75
8.04
8.37
8.74
9.17
9.66
10.25
10.95
11.83
12.96
14.49
16.73
20.49
580
5.67
5.77
5.88
6.00
6.12
6.26
6.40
6.55
6.71
6.88
7.07
7.28
7.75 7.50
8.02
8.32
8.66
9.05
9.49
10.00
10.61
11.34
12.25
13.42
15.00
17.32
21.21
590
5.86
5.96
6.08
6.20
6.32
6.46
6.61
6.76
6.93
7.11
7.30
7.51
8.00 7.75
8.28
8.59
8.94
9.34
9.80
10.33
10.95
11.71
12.65
13.86
15.49
17.89
21.91
600
6.04
6.15
6.26
6.39
6.52
6.66
6.81
6.97
7.14
7.33
7.53
7.75
8.25 7.98
8.54
8.86
9.22
9.63
10.10
10.65
11.29
12.07
13.04
14.28
15.97
18.44
22.58
LIMITATIONS AND CONTRAINDICATIONS OF LASIK
LASIK AND BEYOND LASIK
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6
Section 7
Subjects Index
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and with the rule astigmatism. Conversely, a nasal hinged flap is more advantages when treating hyperopic astigmatism that is against the rule. Secondly, fluid at the hinge should be avoided because it may change the results. Larger diameter flaps have a greater potential for causing bleeding from the corneal pannus. If any blood or other fluid collects at the hinge, the ablation should be paused and continued after the fluid is removed.
Presbyopia Patients in the presbyopic age range should be counseled about the need for reading glasses after surgery. This is especially important for presbyopes that have low myopia, because they are generally used to seeing well at near without glasses. They may be unaware that by having refractive surgery they will be exchanging distance correction for readers. In our experience this is particularly disturbing to women who discover that they can no longer apply eye makeup without a magnifying mirror. Some patients may find that even though they were able to read with their distance glasses preoperatively, they require reading glasses postoperatively. This is because there is an increased accommodative demand (for near work) when a myope’s correction is done at the corneal plane, such as contact lenses or refractive surgery.6 Monovision correction should be discussed and a trial of soft contact lenses or trail frame should be offered in order to simulate it. We generally begin by correcting the dominant eye for distance (unless the patient is successfully wearing monovision contact lenses with the distance correction in the nondominant eye). If the patient does not like monovision with the dominant eye for distance, then a trial using the non-dominant eye for distance is done. In general, we have found that patients involved with visually demanding work or play requirements do not usually like monovision correction. For example, golfers tend to prefer full distance correction in both eyes. Patients should be aware that monovision correction will not completely free them from glasses for all activities. For example, glasses may be needed for improved depth perception when driving at night. Methods for correcting presbyopia, such as scleral 134
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expansion bands, are currently being developed. Undoubtedly, they will someday replace monovision correction; but monovision is currently the best current alternative to reading glasses.
SPECIAL CASES LASIK after IOL Implantation We routinely perform LASIK after refractive lensectomy or cataract surgery in order to correct residual refractive errors. The LASIK procedure should be scheduled at least three months after IOL implantation to allow for the corneal wound to heal. In our experience and others, LASIK is a safe and effective method as an enhancement procedure after IOL implantation.7
Bilateral Simultaneous vs. Sequential Surgery
Contents
Section 1 Section 2
Section 3
In most cases we perform simultaneous bilateral LASIK. It has been demonstrated that simulta- Section 4 neous bilateral LASIK is as safe and effective as se- Section 5 quential surgery.8 However, this is limited to uncomplicated LASIK in the first eye. If a complica- Section 6 tion occurs during surgery in the first eye, then we postpone surgery in the fellow eye until it heals. In Section 7 some instances sequential surgery may initially be Subjects Index preferred, or it may be necessary to modify the approach in the fellow eye. For example, we consider sequential LASIK surgery in patients with complicated refractive errors such as large corrections with mixed astigmatism.
LASIK after RK It is well known that corneal stromal haze may occur when PRK is performed after RK.9 ,10 Additionally, there is increased regression, higher risk of infection, delayed re-epithelization and uncertain refractive effects. Thus, many surgeons perform LASIK after RK. Although technically more challenging, we have performed a large number of LASIK procedures after RK. In the past there was concern that RK incisions would decrease the LASIK
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LIMITATIONS AND CONTRAINDICATIONS OF LASIK
flap integrity, resulting from dehiscence of the RK incisions. However, with careful manipulation of the flap we have avoided this problem. The incisions usually hold together well, although there may be some dehiscence at the flap periphery. If subsequent enhancements are necessary we recommend re-cutting rather than re-lifting the flap, due to possible dehiscence of old RK incisions. The results of LASIK after RK have been very good at our refractive surgery center. Compared to PRK, recovery is quicker with less regression and a higher refractive correction is possible. However, we have found some variability in response to the laser. Also, prolonged refractive instability and hyperopic shifts due to the RK incisions have occurred. Epithelial ingrowth occurs more often in post RK patients. It is seen more commonly when there is gaping of the RK wound seen on preoperative exam.
Alternatives to LASIK PRK Although LASIK is overwhelmingly the most popular procedure performed at our center, PRK remains an excellent option for low to moderate myopia and low to moderate astigmatism.11 It remains a good alternative to LASIK and IntacsTM for this range of refractive error. In some cases PRK may be preferable to LASIK. For example, patients with inadequate corneal thickness for LASIK and low to moderate myopia will usually do well with PRK. Another instance when PRK may be preferable to LASIK is when the preoperative corneal curvature is less than 41 or greater than 46 diopters. Some patients may even prefer PRK because they are concerned about the possibility of flap complications. Counseling patients about the risks, benefits, alternatives and complications of PRK should include a discussion of early postoperative discomfort, corneal haze and infection.
Refractive Lensectomy Refractive lensectomy and IOL implantation offers another alternative in both the presbyopic and high refractive error patients who are not appropri-
ate candidates for corneal refractive surgery. It can be considered in cases with larger pupils, limited pachymetry, high corrections, or when lens opacities are present.12 In our practice any patient over 50 with lenticular changes is counseled about refractive lensectomy. Patients opting for refractive lensectomy should generally be older than 50 years of age because of the loss of accommodation. Significant lenticular changes include more than 2+ nuclear sclerosis, any posterior subcapsular cataract, or cortical changes. Refractive lensectomy may also be considered for near-presbyopes in select cases, for example, extreme hyperopia and myopia. A toric IOL is considered in patients with greater than 1.5 diopters of astigmatism. Advantages of refractive lensectomy are early refractive stability and rapid visual rehabilitation. It Contents maintains the corneal integrity and there is no change in corneal asphericity. Additionally, refractive lensec- Section 1 tomy will give an improved quality of vision in higher refractive corrections when compared to corneal re- Section 2 fractive surgery. There is minimal loss of contrast Section 3 sensitivity and no risk of decentered ablations or phakic IOL placement. Refractive lensectomy avoids Section 4 the future need for cataract surgery in patients with Section 5 lenticular changes. Refractive lensectomy is an intraocular pro- Section 6 cedure, making it relatively more invasive than corneal reshaping surgery. It causes loss of accommo- Section 7 dation and the long-term risks are still unknown. In a recent report by Gimbel, he evaluated the results Subjects Index of 212 hyperopic and 163 myopic lensectomies performed between in 1986-1998.13 The overall rate of retinal detachment in the myopic group was 0% and 0.47% in the hyperopic group. There were no reported cases of endophthalmitis or cystoid macular edema. Eighteen patients required Nd:YAG posteHelp ? rior capsulotomy. Surgeons performing refractive lensectomy should be skilled in modern phacoemulsification and managing its complications. The intraoperative and postoperative complications of standard modern phacoemulsification are comparable to refractive lensectomy. Intraoperative complications should be discussed with the patient including capsular tears, iris prolapse, zonular dialysis, dropped nucleus, and vitreous prolapse. Postoperative complications should be addressed, including iritis, cystoid macuLASIK AND BEYOND LASIK
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lar edema, endophthalmitis, wound leakage, posterior capsule opacification, and IOL decentration. In myopic eyes the risks of retinal detachment must also be carefully considered. Patient expectations after refractive lensectomy should be addressed preoperatively. Patients should be warned that they will need reading glasses postoperatively if the targeted refraction is near plano. Monovision should be discussed. The possibility of an enhancement with PRK, LASIK, or AK should also be discussed. Patients with long or short axial lengths should be warned about the increased difficulty in predicting refractive outcome. In summary, our experience indicates that refractive lensectomy is a safe and effective procedure. It is a good surgical option for patients with high refractive errors, and is most beneficial to patients in the presbyopic age group. Advantages of refractive lensectomy include rapid visual rehabilitation, refractive predictability, and early stability. It maintains the prolate cornea and there is minimal loss of contrast sensitivity. There is no risk of decentered ablation or phakic IOL placement. The disadvantages of refractive lensectomy revolve around the relative risks of any intraocular surgery, and the loss of accommodation. The long term risks of retinal detachment and other late complications need to be evaluated as do any quality of vision concerns.
Phakic Intraocular Lens Although not FDA approved in the U.S., a phakic IOL can be considered internationally in patients younger than 50 years of age who are not good candidates for LASIK. Phakic IOLs may be a good option for patients with high refractive error when the corneal pachymetry is not sufficient to perform LASIK. Phakic IOLs are most beneficial to patients with moderate to high myopia and hyperopia. Patient selection criteria depend on lens type. For the Staar ICL, the anterior chamber depth needs to be greater than 3.0 mm in myopes and greater than 2.75 mm in hyperopes. It should be avoided in patients with large pupils because the optics range from 4.5 to 5.5 mm in diameter, predisposing to nocturnal halos.
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Phakic IOL implantation requires additional preoperative testing. The corneal horizontal whiteto-white, endothelial cell counts, and anterior chamber depth should be measured. Additionally, a YAG iridotomy is required to prevent papillary block in posterior chamber phakic implants. Complications of phakic IOL implantation include iritis, early postoperative elevation of IOP, wound leakage, induced astigmatism, papillary irregularities, and implant decentration, dislocation or rotation. Other postoperative complications include nocturnal halos, pigmentary glaucoma, residual refractive error, corneal edema, endothelial cell loss, retinal detachment, and cataract formation. Although there have been no reports of cataract formation following anterior chamber phakic IOL implantation; posterior chamber phakic IOLs have been reported to cause cataracts.14
Thermokeratoplasty (LTK)
Contents
Section 1 Section 2
Seiler introduced laser thermokeratoplasty Section 3 over a decade ago.15 The Hyperion LTK System is the first laser procedure designed specifically for far- Section 4 sightedness. Hyperion LTK technology represents Section 5 an innovative alternative for a significant segment of this over-forty group, representing millions far- Section 6 sighted Americans. The Hyperion LTK system (Sunrise Technolo- Section 7 gies) uses a non-contact delivery system that emits a Subjects Index 2.13 mm infrared laser radiation wavelength in a pulsed mode with a 0.25 millisecond pulse and repetition rat of 5 Hz. The benefits of LTK are that no corneal flap is necessary and the procedure takes only a few seconds to perform. As a result, the possibility of intraoperative complications, postoperative infections, or healing irregularities is minimized. The Help ? system is easy to learn and operate. In addition, the quickness of the procedure and the absence of cutting or ablation remove the fear factor for patients. The benefits of LTK are that it is a quick “notouch” procedure with a good safety profile. However, some of the effects of LTK are known to regress with time, and it is not currently FDA approved to treat any significant degree of astigmatism. Thus, it is less desirable than LASIK for many patients. However, LTK may be an option for patients with
LIMITATIONS AND CONTRAINDICATIONS OF LASIK
little astigmatism who desire the “no-touch” technique. In the future, LTK may play a more significant role in refractive surgery if it is approved to treat significant degrees of astigmatism. The safety record exhibited during U.S. clinical trials of the Hyperion LTK procedure has been exceptional. Close to 700 eyes were treated in the two-year trial, with patients generally showing improved vision immediately after the procedure and most resuming regular activities the day after treatment. It received FDA approval on June 30, 2000 for the temporary reduction of hyperopia in patients with +0.75 to + 2.50 diopters of MRSE with less than or equal to +/- 0.75 diopters of astigmatism. The FDA recently (December 13, 2000) approved a change to the company’s label reflecting that some of the effects of the sunrise LTKTM procedure can last for ten years and beyond. Patients should be aware of the possibility of regression. Regression appears to be less common in patients over 40 years of age. Poor response to LTK is more common in young patients, high intraocular pressure, and thicker pachymetry. We do not currently offer LTK at our center because of its limitations and the success of other available refractive surgery techniques such as excimer laser and refractive lensectomy.
Summary The limitations of LASIK need to be considered and explained when counseling patients for refractive surgery. Careful attention to details of the preoperative history and exam allows the surgeon to counsel the patient that he or she is at a higher risk for a particular complication. It also allows the surgeon to avoid particular complications and to suggest an alternative surgical procedure, or to recommend the patient not undergo refractive surgery. It is important to educate the patients about other procedures that may be more suitable for their particular situation. Fully informed patients tend to have much more positive experiences because they usually have realistic expectations.
REFERENCES 1
Gimbel (personal communication)
2
Slade SG. LASIK complications and their management. Free cap, thin and perforated corneal flaps. In: Machat JJ, ed. Excimer Laser Refractive Surgery. Practice and Principles. Thorofare, NJ: SLACK Incorporated; 1996. 3
Seiler T, Koufala K, Richter G. Iatrogenic keratectasia after laser in situ keratomileusis. J Refractive Surgery. 1998;14(3):312-317. 4
Wang Z, Chen J, Yan B. Posterior corneal surface topographic changes after laser in situ keratomileusis are related to residual corneal bed thickness. Ophthalmology. 1999;106(2):406-409. 5
Vinciguerra P, Sborgia M, Epstein D, Azzolini M, McCrae S. Photorefractive keratectomy to correct myopic or hyperopic astigmatism with a cross-cylinder ablation. J Refract Surg. 1999; 15 (suppl):S183-S185.
Contents
Section 1 Section 2
6
Hunter, D., West C. Last Minute Optics
7
Stulting RD, Carr JD, Thompson HP, Wiley W, Waring III GO. Laser-in-situikeratomileusis for the correction of myopia after previous ocular surgery. (Abstract #144). In American Society of Cataract and Refractive Surgey. Symposium on Cataract, IOL, and Refractive Surgery, 1998, p.37.
Section 3
Section 4
Section 5
Section 6 Section 7
8
Gimbel HV, van Westenbrugge JA, Penno EA, Subjects Index Ferensowicz M, Feinerman G, Chen R. Simultaneous Bilateral Laser In Situ Keratomileusis: Safety and Efficacy. Ophthalmology 1999;106:1461-1468. 9
Suarez E, Cardenas JJ. Intraoperative Complications of LASIK. In: Buratto L, Brint, S, eds. LASIK: Principles and Techniques. Thorofare, NJ: SLACK Incorporated; 1998:337.
Help ?
10
Seiler T, Jean B. Photorefractive keratectomy to correct residual myopia after radial keratotomy. J Refractive Surg. 1992;8:211-214. 11
American Academy of Ophthalmology. Ophthalmic procedure preliminary assessment. Excimer laser photorefractive keratectomy (PRK) for myopia and astigmatism. Ophthalmology. 1999;106:422-437.
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Chen R, Feinerman G, Penno E, Gimbel H. Refractive Lensectomy. In: Gimbel HV, ed. Refractive Surgery: A Manual of Principles and Practice. Thorofare, NJ: SLACK Incorporated; 2000. 13
Gimbel H. Retinal detachment rate after high myopia lensectomy/IOL. Presented at the Hawaiian Eye Meeting, January 2001. 14
Baikoff G. Phakic myopic intraocular lenses. In; Serdarevic ON, ed. Refractive Surgery: Current Techniques and Management. New York, NY: Igaku-Shoin Medical Publishers Inc; 1887:165-173. 15
Seiler T, Matallana M, Bende T. Laser thermokeratoplasty by means of a pulsed holmium:YAG laser for hyperopic correction. Refract Corneal Surg. 1990;6;335-339. Contents
Section 1
Gregg Allen Feinerman, M.D. Medical Director Feinerman Vision Institute Long Beach Laser Center Long Beach, California Associate Clinical Professor University of California, Irvine, California E-mail:
[email protected]
Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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LASIK SURGICAL TECHNIQUE
Chapter 10 LASIK SURGICAL TECHNIQUE Jaime R. Martiz, M.D., Stephen G. Slade, M.D.
Introduction This chapter will describe the basic steps in a LASIK (laser intrastromal keratomileusis) procedure using the Hansatome microkeratome and Bausch & Lomb Technolas 217 laser (Figures 10-1 and 10-2). LASIK is currently the most refined procedure to correct refractive errors. We base many aspects of the technique, such as not wearing gloves and avoiding handling the cornea as much as possible, on a classical teaching, learned from Barraquer. We leave out several steps, such as marking the cornea and checking pressure that we would not leave out if we were doing our first 300 cases. The common approach is one of simplicity, discipline and concentration. Carefully follow of a protocol in every surgery will prevent complications and more predictable outcome. Appropriate informed consent must be obtained in every patient before surgery. LASIK can become a significant part of your refractive surgical practice, but first you must fully understand the risks as well as the benefits and be intimately familiar with standard and emergency procedures. The surgical team should be carefully trained and well known with every element of the laser center. An appropriate corneal refractive referral source should be available during the learning course period of LASIK.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index Figure 10-1. Bausch & Lomb Technolas 217 laser
Help ?
Patient Selection Candidates for LASIK procedures should have a stable refraction for at least 12 months and healthy corneas. Contraindications for LASIK should include patients with keratoconus, autoimmune diseases or patients with poor epithelium.
Figure 10-2. Hansatome microkeratome parts.
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tient eye is prepared by irrigating the conjunctival fornices with an irrigating solution (Sterile Eye Wash Optopics) to clear the area of any secretions or debris. Swab the skin of the eyelids with a povidineiodine swabstick and gently dry.
The Instruments Some specific surgical instruments we required for the completion of a LASIK procedure (Figure 10-3):
Figure 10-3. Surgical instruments for LASIK procedure.
Patients should undergo an informed consent with their surgeon and be fully knowledgeable of: -Risks -Benefits -Reasonable expectations -Other surgical alternatives They must comprehend that irreversible complications do happen and can result in loss of sight. Patient with more than 6 mm pupil size, high myopia and less than 250 microns residual bed should understand that surgeon might need to either decrease laser ablation diameter or patient treatment. We perform bilateral surgery the same day in all our patients except: >50 years old >-7 diopters sphere or > 3 diopters of cylinder Patient with nystagmus have the option for Laser with an eye tracker system.
PREOPERATIVE PREPARATION The Patient Patient’s preoperative preparation includes an oral sedative such as Valium (5 to 10 mg) prior to the procedure. Immediately before prepping, one drop of a topical anesthetic (Proparacaine) should be instilled and then one more drop before the keratectomy. No preoperative miotic is used. The pa140
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-Looked lid speculum -Smooth-angle forceps -Merocel sponges -Curved Irrigation cannula with BSS -Clear Eye shield -3M Sterile Drape 1020 -Gauze 4 x 4 -Assembled microkeratome -Excimer Laser
Contents
Section 1 Section 2
Section 3
The Laser
Section 4
The proper laser room environment is critical Section 5 for optimal laser performance. The laser is set up per the manufacturer’s recommendations, but we use Section 6 the following nomogram: Section 7 • If Plano result is desired back up –0.25 D on Subjects Index laser set up • Patient 35 to 45 years old back up –0.50 D for non-dominant eye • Patient >45 years old back up –0.75 D or more for non-dominant eye • To determine the dominant eye the patient is asked which is his or her “camera” eye or “shooting Help ? eye”. The laser room environment should be maintained for two endpoints, standard treatment and longevity of laser optics. The best environment for laser optics is in a room that is cool, dry and as low particulate matter count as possible. Ideally the temperature should be maintained between 600 to 700 F (180 to 240 C), and the humidity should be kept at a stable level between 30 to 40%. In addition, several air filtration units should be used continuously in the laser room to keep the atmosphere surgically clean
LASIK SURGICAL TECHNIQUE
Figure 10-5. Ablation depth should leave more than 250 microns residual bed.
Figure 10-4. A sample of color change in the fluence test from white to red.
and to achieve standard laser ablation rates. It is unacceptable for the environment to be turned off for night or weekends. Laser beam calibration, homogeneity and alignment of the beam are achieved by fluence testing. In the case of the Bausch & Lomb Technolas 217 laser appropriate fluence is 65 pulses. The test is perform on polymethacrylate (PMMA) plate on which a subtle silver-plated foil is placed with the interposition of a layer of glue. The total number of spot necessary to obtain a complete exposure of the PMMA foil must be equal to 65 ± 2; in normal conditions, there is a color change from white to red in an interval of five to seven spots. A fine and dispersed white granularity can remain. (Figure 10-4) The surgeon should also verify patient data inserted in the computer is appropriate for surgical operation and that the axis of astigmatism is correct and corresponds with that found topographically and by refraction. The minimum diameter of the ablation should be appropriate to the patient’s pupil diameter and the ablation depth should leave more than 250 microns residual stroma bed (Figure 10-5).
The Keratome After inserting the blade into the microkeratome head, examine it very carefully under the operating microscope at maximum magnification to check the condition of the blade edge (Figure 10-6). All the parts of the keratome should be inspected
Contents
Section 1 Section 2
Section 3 Figure 10-6. Always check the condition of the blade edge.
Section 4
Section 5
Section 6
before proceeding with the cut. Discard a blade with Section 7 notches or stains. Very small irregularities on the Subjects Index blade margin can be also detected by observing the reflection of the microscope’s light on the edge of the blade. By depressing the foot pedal, the head advances along the track for a test run on the suction ring. Although an alarm indicates when the microkeratome has reached the end of its pass, the surgeon should also understand and visually memorize Help ? the end point of the forward pass, so as not to rely solely on hearing the “beep-beep”. If during advancement, the speculum obstructs the microkeratome and interrupts the run, the computer interprets this interruption as the end of the pass. Once the head reaches the end of the pass, push the foot pedal once again to return the microkeratome to its starting point. At this point, rotating the head through half turn in the opposite direction to insertion raises the keratome head along the pin until it detaches from the suction
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Figure 10-7. During advancement, the current on the display should not exceed 80 milliamps. Figure 10-8. Make sure to include the lid margins in the adhesive backing of the drape so they will not be in the way of the microkeratome on course over the suction ring.
Contents
ring. During advancement, the current on the display should not exceed 80 milliamps (Figure 10-7). The instrument is now ready for surgery.
Section 1
The Surgeon
Section 3
Section 2
Section 4
Lasik should be performed in a sterile environment wearing cap, mask and boots. We prefer no-glove technique with a Betadine hand scrub between patients, drying with a lint free cloth.
Section 5
Section 6 Section 7
SURGERY PREPARATION
Subjects Index
Draping Apply a disposable self-adhesive drape (fenestrated is easier to apply). Ask the patient to open both eyes as much as possible. To exclude the eyelashes from the operating field, have your assistant hold the drapes’ opposite corners as you apply the drape at the edge of the superior eyelid first and then do the same with the inferior eyelid. Make sure to include the lid margins in the adhesive backing of the drape so they will not be in the way of the microkeratome on course over the suction ring (Figure 10-8).
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Figure 10-9. Accommodate suction ring within the intrapalpebral opening.
Speculum A locking eyelid speculum is recommended, but either locking or non-locking speculum can be used. The ideal speculum should provide maximal patient comfort when fully opened, allow for temporal and superior approaches, accommodate suction ring within the intrapalpebral opening and maximize exposure to enable clear passage of microkeratome (Figure 10-9).
Help ?
LASIK SURGICAL TECHNIQUE
Figure 10-10. Prior to placing the LASIK suction ring, the head should be positioned so the chin and forehead are in the same frontal plane.
Figure 10-11. The LASIK suction ring is placed slightly decentered 1 mm superiorly.
Contents
Positioning the Patient
Section 1 Section 2
Prior to placing the LASIK suction ring, the head should be positioned so the chin and forehead are in the same frontal plane (Figure 10-10). Make sure the amount of inferior and superior sclera’s are the same therefore the cornea is centered between the lids (Figure 10-9).
Section 3
Section 4
Section 5
Section 6
THE LASIK PROCEDURE Marking
Section 7 Figure 10-12. Confirming that the area of applanated cornea is Subjects Index the same side or smaller than the circular mark on the applanating surface of the tonometer.
The cornea should be marked with a pararadial line that facilitates exact repositioning of the flap in case of a free cap. A minimum amount of gentian violet should be used to avoid epithelial toxicity. Help ?
Placement of the Suction Ring The LASIK suction ring is placed slightly decentered 1 mm superiorly (Figure 10-11). Suction ring should be firmly placed on the globe with one hand and at the same time apply downward pressure on speculum to proptose the eye. The vacuum pump is activated and the intraocular pressure is checked with a Barraquer tonometer lens to assure an intraocular pressure
greater than 65 mm Hg., confirming that the area of applanated cornea is the same side or smaller than the circular mark on the applanating surface of the tonometer (Figure 10-12). The tonometer and corneal surfaces should be dried to avoid a false reading. Many expert surgeons no longer perform tonometry, relying in digital touch, small displacements and observing the slight mydriasis induced by the suction itself. The surgeon should remember that reLASIK AND BEYOND LASIK
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Figure 10-13. Loading the microkeratome.
Figure 10-14. After loading the keratome onto the post of the suction ring press down on the motor to slightly compress the cornea and thereby fully seat the eye adapter before engagement of gear to the rack.
dundant conjunctiva could produce the false sensation that the suction ring has adhered to the globe by obstructing the suction. It is very important to remember to keep the cornea wet at all times, and just dried prior to the tonometer reading, as it could result in a complication.
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When the above is satisfied the surgeon is ready to progress with the keratectomy. After loading the keratome onto the post of the suction ring press down on the motor to slightly compress the cornea and thereby fully seat the eye adapter before engagement of gear to the rack (Figures 10-13 and 10-14). Immediately prior to passage of the microkeratome, one or two drops of glycerin-based anesthetic (Proparacaine) are instilled over the surface of the cornea to allow the microkeratome to advance more smoothly. Make sure to apply the drops directly from the bottle and not through a cannula since the drop size vary and sometimes is not enough fluid to lubricate the cornea. Excess fluid should be removed using a Merocel sponge to prevent it from going into the gears of the microkeratome and then onto the mirrors of the laser consequently disturbing beam quality. Proparacaine is used rather than BSS in order to keep salts away from the microkeratome.
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Figure 10-15. The microkeratome and suction ring can be removed at the same time as a one unit.
The keratome is placed into the suction ring and advanced by depressing the pedal. The microkeratome is reversed and the vacuum is stopped. The microkeratome and suction ring can be removed at the same time as a one unit (Figure 10-15).
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Figure 10-16. The corneal flap is lifted superiorly with curved forceps
Figure 10-17. The corneal flap is lifted superiorly with curved cannula.
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Section 6 Section 7 Figure 10-19. The head is rotated to the right and the body to the left; as a result the ablation will be decentered. Subjects Index Figure 10-18. The laser focus is achieved over the pupillary center
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Laser Ablation The corneal flap is lifted superiorly with curved forceps (Figures 10-16, 10-17), the laser focus is achieved over the pupillary center (Figure 10-18), and patient’s head is again aligned so the chin and forehead are in the same frontal plane; a straight imaginary line passes through the feet, umbilicus and nose (Figures 10-19 and 10-20). At this point, the surgeon can proceed with the ablation of stromal bed.
Figure 10-20. A straight imaginary line passes through the feet, umbilicus and nose
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Figures 10-21 & 10-22. If ablation or astigmatism are being completed the surgeon must protect the hinge from ablation by holding a Merocel sponge over this area.
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Section 6 Section 7 Figure 10-23. Couples of drops of BSS are added onto the stromal bed.
Figure 10-24. The corneal flap is replaced using the cannula starting superiorly. Subjects Index
When the larger zones of ablation or astigmatism are being completed the surgeon must protect the hinge from ablation by holding a Merocel sponge over this area (Figures 10-21 and 10-22). Help ?
Replacing the Flap When the ablation is complete, couple of drops of BSS is added onto the stromal bed and then the corneal flap is replaced using the cannula starting superiorly (Figures 10-23 and 10-24). Make sure the tip of the cannula is outside the flap before flap is positioned back because surgeon can either place a hole on the flap or scratch the stromal bed, especially when using sharp tips cannulas. (Figure 10-25 and 10-26) The cannula is placed underneath the 146
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Figure 10-25. Make sure the tip of the cannula is outside and parallel to the flap before flap is positioned back
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Figure 10-26. Canulla is not parallel; surgeon can accidentally scratch the stromal bed
Figure 10-27. The cannula is placed underneath the flap and irrigation is completed to clear any remaining debris
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Figure 10-28. BSS is use under the flap to facilitate “floating” back into its original position.
Figure 10-29. Merocel sponge is moistened and squeezed dry and then used to “paint the flap” in the direction of the hinge. Help ?
flap and irrigation is completed to clear any remaining debris from the interface as well as allowing BSS under the flap to facilitate “floating” back into its original position. (Figures 10-27 and 10-28)
The Merocel sponge is moistened and squeezed dry and then used to “paint the flap” in the direction of the hinge (Figure 10-29). The flap is inspected to reassure that there are no wrinkles and for proper position by making sure
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Figure 10-30. The flap is inspected to reassure that there are no wrinkles and identical distance between the gutter and keratectomy edge is present.
Figure 10-31. When striae test is positive around the flap edge appropriate apposition has been achieved.
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an identical distance between the gutter and keratectomy edge is present all over the flap circumference (Figure 10-30). Depressing the peripheral “non flap” cornea with closed blunt 0.12 forceps completes a Slade’s striae test (Figure 10-31). When striae test is positive around the flap edge appropriate apposition has been achieved. During this phase it is recommended to keep a BSS drop over the central corneal epithelium to keep it wet. There is no specific waiting time with this technique, but we recommend waiting 3-5 minutes before removing the speculum. The case is completed by carefully removing the speculum. When doing this step, make sure to lift and close the speculum at the same time to avoid displacement of the flap. The patient is then instructed to blink normally, and is observed through the microscope. The flap should remain in the same position and appear adhered to the cornea bed (Figure 10-32).
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Section 6 Section 7 Subjects Index Figure 10-32. The patient is instructed to blink normally, and is observed through the microscope.
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Intraoperative Bleeding in LASIK Bleeding of peripheral corneal vessels usually occur in long-term contact lens wear patients. The occurrence is higher when we use the 9.5 Hansatome suction ring. We prevent this by using an 8.5 suction ring if we notice any limbal pannus in the slit lamp examination. We don’t use any drug to stop intraoperative bleeding, because some of them could
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interfere with the iris, causing irregular dilation of the pupil. We use a Merocel sponge and apply some pressure on the peripheral vessels to stop the bleeding; generally is over by the time we finish the ablation treatment and reposition the flap (Figures 10-33 to 10-36)
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Figure 10-33. The corneal flap is lifted superiorly with curved forceps
Figure 10-34. Merocel sponge is use to clean the corneal stromal bed
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Section 6 Section 7 Figure 10-35. The laser focus is achieved over the pupillary center and the ablation start.
Figure 10-36. Cornea still looks with some blood cell.
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Inferior eyelashes bleeding is usually due a poor technique when loading the keratome; the surgeon is either applying to much pressure onto the suction ring and it end deeper than the speculum or not applying downward pressure on speculum to proptose the eye. (Figure 10-37)
Figure 10-37. The surgeon is applying too much pressure onto the suction ring and it end deeper than the speculum.
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Postoperative Care Immediately postoperatively, several drops of an antibiotic are instilled. The eye is not taped or shielded. The patient is asked to follow the home care instructions.
HOME CARE INSTRUCTIONS -Wear a clear eye shield to sleep for the first five days. -Wear protective sunglasses anytime patient is outside for the first five days. -Use Acular eye drops only on the first day post-op and only for discomfort. -Two hours after surgery start 1 drop of Ocuflox and Lotemax every 3 hours while awake -Patient should wait about one minute between drops. -Make sure to shake the Lotemax before using. -Next four days use Ocuflox and Lotemax four times a day. -Patients may need Lubricating drops for dry eyes. -Do not to rub the eyes for 5 days after the surgery, avoid any trauma to the eyes. -Patient may wash face, but avoid getting anything into the eyes. -Use good hand washing technique and cleanliness. -No eye makeup for 3 days -No swimming for 10 days -Stay out of hot tubs for 4 weeks -Patient may shower; however keep the force of the water away from the eyes -We advice against driving
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PEARLS IN LASIK TECHNIQUE
Chapter 11 PEARLS IN LASIK TECHNIQUE Elizabeth A. Davis, M.D., David R. Hardten, M.D., Richard L. Lindstrom, M.D.
LASIK surgery has become a quick, automated procedure. However, a good outcome still depends largely on the surgeon’s knowledge, skill, and experience. A successful procedure begins with appropriate patient selection and counseling. Intraoperatively, there must be great attention to detail. This chapter will describe surgical techniques designed to achieve the best outcomes and lowest risk of complications in LASIK surgery.
Patient Counseling A successful LASIK surgery depends as much on a technically good operation as it does on an appropriately counseled patient. The patient must not only be informed of the risks and benefits of the procedures, but also its limitations. Thus, the patient must have realistic expectations of what the outcomes could be. In counseling the patient, it is far better to counsel for lesser outcomes and have the patient pleasantly surprised than the converse. The goal of the surgery is functional vision without glasses or contact lenses. There can be no guarantee of 20/20 vision. The vast majority of the time, results will be excellent and the patient will be pleased. Presbyopic patients should understand that reading glasses will still be needed after LASIK. For surgeons who aim for some initial overcorrection, the patient should also be forewarned about some difficulty with their intermediate range of vision as well. Myopic patients need to understand that their faces may be blurry in the mirror postoperatively. Hyperopic patients should be informed that they may be temporarily myopic.
The surgeon should explain that, particularly for the higher levels of correction, visual recovery may take several weeks to months. Although a big improvement in their uncorrected visual acuity will occur in the first 24 hours, continued improvement can occur after this. Additionally, patients should understand that 5-10% will require an enhancement to achieve the desired results. They should be given an estimate of the time at which this might occur, if desired, based upon their preoperative refractive error. We prefer to wait one month per diopter of myopia and three months per diopter of hyperopia prior to performing an enhancement.
Achieve Adequate Exposure
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Achieving adequate exposure is the first and one of the most important steps of the LASIK proce- Subjects Index dure. All of the subsequent maneuvers in the surgery rely on this step. Adequate exposure is critical to visibility, achieving adequate suction, ability to place the microkeratome properly, unobstructed passage of the microkeratome, and a well-exposed stromal bed. There are certain orbital anatomies that Help ? predispose to difficult exposure and these should be noted preoperatively. Deep set orbits, prominent brows, or small palpebral fissures may all interfere with placement of instruments on the globe. In these instances, as well as others, it is often helpful to have the patient maintain a chin-up position for adequate visibility and instrument placement. If the patient has a prominent lower cheek that overhangs the lower blade of the speculum, the surgeon may use his/her 4th and 5th fingers to retract this tissue inferiorly and out of the surgical field. Similarly, a technician can LASIK AND BEYOND LASIK
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Figure 11-1. Isolation of lashes: Tegaderm over upper and lower lids.
Figure 11-2. Placement of suction ring.
assist with this maneuver. Some speculae have been designed to help retract any overhanging skin. The lashes should be isolated from the surgical field. This is not only important for sterility purposes, but to prevent cilia from becoming engaged in the keratome and prematurely stopping the pass. Isolation of the lashes can be done by simply placing tape or steri-strips over the lashes. A Tegaderm adhesive plastic also works well. If cut in half, one half can be used for the upper lid and the other half for the lower lid (Figure 11-1). Another option is to use a surgical drape. Or, one may simply use a closed-bladed speculum. Placement of the suction ring may be facilitated by pressing down on the speculum gently (Figure 11-2). This causes the globe to proptose and results in greater exposure. Additionally, once adequate suction has been achieved, one can carefully and gently lift the eye up and out of the orbit with the suction ring to allow unobstructed passage of the microkeratome. Care must be taken during this maneuver not to break suction. In cases of small palpebral fissures, it is often useful to have several lid specula available. Often, switching from a closed bladed speculum to an openbladed one may provide the few millimeters needed to insert the suction ring. Exposure is sometimes limited by eyelid squeezing. The vast majority of these situations are easily circumvented by proper instruction to the patient and a calm, reassuring demeanor. Also, specula with a screw or locking mechanism counteract squeezing much better than self-retaining specula.
Nevertheless, in a few cases, it may not be possible to get the patient to relax the eyelids. Here, one might consider a facial nerve block. Less frequently, and only with the patient’s consent, one might perform a lateral canthotomy. Rarely, some surgeons have reported doing a retrobulbar injection in order to proptose the globe.
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Achieve and Confirm Adequate Suction
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Adequate suction is necessary to create a proper flap. Loss of suction or inadequate suction Section 6 can have serious consequences such as a short flap, Section 7 a small flap, a free cap, a buttonhole, or an irregular edge. As mentioned above, good exposure is criti- Subjects Index cal. If it is not possible to seat the suction ring on the globe unobstructed, vacuum cannot be obtained. Additionally, a prolonged struggle to fit the instruments onto the eye can lead to conjunctival chemosis and either inability to obtain suction or pseudosuction. Pseudosuction is when the vacuum registers high because the conjunctiva or drapes are Help ? occluding the suction holes. In this case, the intraocular pressure will not be sufficiently elevated to pass the microkeratome. In cases of conjunctival chemosis, a Merocel sponge can be used in an attempt to “milk” the excess fluid away from the limbus. If chemosis has occurred because of some intraoperative manipulations, then waiting 30 to 40 minutes for the edema to subside may result in success. If not, then the procedure should be postponed a day or two to allow reabsorption of the fluid.
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It is important to seat the suction ring properly on the globe and then apply firm, even pressure. Once this is done, suction can be applied. There are several indicators of sufficient suction. No single indicator should be relied upon alone. Rather, the surgeon should be observant for several of them. Firstly, when adequate suction is achieved, the sound of the pump changes. Secondly, the vacuum pressure should register as greater than 25 mm Hg and this should be verbally announced by the assistant. Additionally, the pupil will dilate slightly. If asked, the patient will report that the vision has dimmed or blacked out. The surgeon may use tonometry to confirm that the intraocular pressure has risen. A commonly used device is the Barraquer tonometer. And lastly, one can confirm good suction if the globe can be elevated out of the orbit by lifting up gently on the suction ring. After adequate suction has been achieved and confirmed, it is important not to torque or pull on the suction ring to any great extent. Such maneuvers can result in immediate loss of suction.
Create a Complete Flap Flap complications should occur in less than 0.1% of cases with the newer microkeratomes in experienced hands. In some instances, unusual corneal anatomy may predispose to a flap complication. For example, corneas steeper than 46.00 D may buckle during the keratome pass, leading to buttonholed or centrally thinned flaps. Likewise, corneas flatter than 41.00 D are more prone to developing free caps. Keratometry readings should be noted preoperatively and used to select the appropriate ring size. A smaller deeper flap should be made when corneas are unusually steep and a larger flap should be created for flat corneas. The surgeon should carefully inspect all parts of the microkeratome including the blade, gears, and flap receptacle. The equipment should be meticulously cleaned and assembled. The motor should be tested prior to each pass to insure it runs with minimal resistance. As mentioned above, adequate exposure is necessary to allow unimpeded passage of the microkeratome. Both the surgeon and assistant should
check to make sure that the lids, lashes, and drapes are clear of the surgical field prior to the forward pass of the keratome. If resistance is met during the forward passage of the keratome or the keratome comes to a stop, the surgeon should stop and examine the field. Are the drapes caught in the speculum? Is the patient squeezing or is the speculum in the way? Any obstruction should be gently removed with care taken not to torque the suction ring off the eye. If no obvious obstruction is found, then the surgeon can tap on the forward foot pedal of the microkeratome. Sometimes this allows the motor to overcome some temporary resistance. If this is not successful then the microkeratome should be reversed and removed from the eye even if an incomplete pass has been made. One should never reverse the microkeratome and then Contents go forward. This can result in the blade penetrating to a deeper level than the initial pass. A case of ante- Section 1 rior segment perforation has occurred when the surgeon reversed the microkeratome part way and then Section 2 proceeded forward again. Section 3 In the case of an incomplete pass, if there is not enough room beneath the flap to perform the Section 4 ablation, then the surgeon should reposition the flap and conclude the surgery. Should a buttonholed flap Section 5 occur, ablation should not be performed through the Section 6 remaining epithelium. The flap should be repositioned and smoothed into place. In neither case Section 7 should the surgeon move on to the second eye. A waiting period of 3 to 6 months should ensue prior Subjects Index to attempting to create a new flap. Close observation for epithelial ingrowth is necessary during this time period in the case of a buttonholed flap.
Maintain Consistent Hydration Hydration of the stromal bed needs to be adjusted evenly and consistently in all cases. Too much moisture results in overhydration, less tissue removed per pulse of the laser, and undercorrection. Too little moisture results in an excessively dry bed, more tissue ablation per pulse of laser, and overcorrection. Uneven hydration can lead to central islands and/or irregular astigmatism. After the flap has been created and prior to turning it back, the top of the cap should be wiped off. This prevents any excess fluid LASIK AND BEYOND LASIK
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Figure 11-3. Adjusting hydration by drying bed.
Figure 11-4. Uneven hydration: with and without ring light.
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from getting onto the stromal bed as the flap is lifted. Some surgeons prefer forceps to lift the flap rather than a cannula, which can drip fluid. Some surgeons prefer to treat with the bed moist, while others like it drier (Figure 11-3). Either method is acceptable, but it is critical to be consistent so that a nomogram may be developed that is based on that particular technique. In very humid or dry climates, it may be necessary to intermittently pause during the ablation to adjust the hydration of the stroma if there is excessive moisture or drying as the ablation proceeds. Using the ring light and high magnification will best allow the surgeon to determine the hydration status. Without the ring light it is much more difficult to follow fluid patterns (Figures 11-4 and 11-5). Excess pooling of fluid can often be found on the stromal bed near the hinge after folding back the flap. This should be wicked away with a soft surgical sponge. Likewise, any bleeding from the vessels of a peripheral pannus should be wiped away. If a soft surgical sponge is touched near the edge of the area of bleeding during the treatment, it may be possible to wick away the blood without having to stop the laser periodically. A smaller flap size may also be used to avoid cutting through these vessels. Some surgeons have reported success in using a drop of phenylephrine, iopidine, or brimonidine just prior to the procedure to constrict these vessels. However, this should be done with caution. If too much time 154
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Section 6 Figure 11-5. Even hydration: with and without ring light.
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passes, pupil dilation can occur with phenylephrine. Additionally, some cases of slipped flaps have been reported when iopidine or brimonidine was used. In all situations the surgeon should try to minimize the amount of time between turning the flap and ablating. Focus and centration should be adjusted and treatment numbers checked prior to lifting back the flap. Once the flap is lifted, the stromal hydration adjusted, and patient fixation achieved, the ablation should proceed without delay.
Perform the Appropriate Ablation Performing the correct ablation is the surgeon’s responsibility. The original clinical work-up with refraction and topography should be brought to the operating room. The cylinder orientation should be
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checked against the topography. If the axes are vastly different, particularly if the power of the cylinder is significant, this should be double checked in a second refraction. If it is necessary to transpose the cylinder format before entering the refraction into the laser or to perform a nomogram adjustment, then special care must be made to ensure that the axis is shifted appropriately. Multiple checks by both the surgeon and technician can reduce the incidence of errors. The surgeon and technician should check the numbers prior to entering the laser suite and then again after the nomogram adjustment has been performed. One final check can then be performed by having the technician hold the chart next to the laser screen (Figure 11-6). The technician and surgeon then together check that the numbers entered into the laser are correct. This is done for the first eye before gloving and for the second eye before the flap is created. It is also helpful to read the patient’s name and eye to be treated aloud. In this way, no errors are made by using the wrong chart or switching the treatments for the two eyes.
Contents Figure 11-6. Surgeon and technician check entered refraction against patient’s chart.
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Prevent and Remove Debris from Beneath the Flap Debris can originate from multiple sources. Metal particles from the microkeratome or blade, meibomian oil and makeup from the lids, lint from surgical sponges, and debris from the cannula or irrigating fluid can all accumulate beneath the flap. In order to prevent these particles from gaining access to the surgical field, certain measures can be taken. Firstly, the surgeon should examine the lids preoperatively and treat ocular surface disease aggressively. Warm soaks, a topical antibiotic, or even systemic doxycycline should be considered to treat meibomian gland disease. Patients should be instructed to carefully remove makeup prior to surgery and clean the lids and lashes the night before and morning of surgery. One may consider irrigating the ocular surface prior to surgery, but sometimes this can just stir up more meibomian particles. However, this may useful to wash away other debris. A Chayet sponge may
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Figure 11-7. Irrigation beneath the flap to remove debris.
be placed around the cornea after the flap is created to isolate the stromal bed from the rest of the surgical field. If this is done, it is important to carefully monitor hydration to ensure no pooling of fluid is induced with the presence of a sponge. Once the ablation is performed and the flap replaced, a cannula should be used to irrigate beneath the flap (Figure 11-7). The cannula should be moved back and forth beneath the flap to loosen any particles adherent to the stromal bed or back of the flap. Excess irrigation should be collected with suction, a LASIK AND BEYOND LASIK
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Figure 11-9. Stroking flap into place with Merocel sponge. Figure 11-8. Marking the cornea.
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suction speculum, a Merocel sponge, or a drain. Overly aggressive irrigation should be avoided, however, to prevent cap edema and retraction of the flap edges. Additionally, excess irrigation may lead to the reflux of more meibomian particles from the conjunctival fornices. Using high magnification and side illumination, the surgeon should carefully inspect the flap interface to ensure all debris has been removed. Some surgeons prefer to examine the patient once more at the slit lamp prior to discharging the patient. If any significant debris is noted, the flap can be relifted and irrigated.
Properly Align the Flap Preventing striae begins with proper flap alignment. Striae can be problematic if they are prominent and centrally located. In these cases, striae can result in irregular astigmatism and poor uncorrected visual acuity as well as a loss of best spectacle corrected acuity. Marking the cornea prior to creating the flap can help in aligning the flap after the ablation (Figure 11-8). However, excessive marking should be avoided to prevent epithelial toxicity. Also, the sur156
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geon should be aware that if the epithelium shifts Section 3 during passage of the microkeratome, the marks may Section 4 be misleading. A more important indicator of proper flap alignment is gutter symmetry. Once the flap is Section 5 turned over, care should be taken to make sure it is neatly positioned in the fornix or on the lid specu- Section 6 lum. It should not be folded over on itself or Section 7 wrinkled. If this occurs, a significant crease can develop across the flap that may be difficult to smooth Subjects Index out. Various instruments are available to iron the flap, but simply stroking or painting the flap back into position with a moistened surgical sponge can achieve an excellent result. Initially this is done by stroking the flap from the hinge toward the opposite Help ? direction (Figure 11-9). Once good alignment is achieved and the flap begins to adhere, gentle stroking may be performed in the oblique directions in a radial fashion. More aggressive surgeons may use a drier sponge to perform stretching by placing the sponge on the flap edge and pulling in a radial direction. The ring light is very useful in identifying striae. One can see discontinuities in the reflection rather than a smooth continuous circle of light (Figure 11-10).
PEARLS IN LASIK TECHNIQUE
Figure 11-10. Follow ring light to identify striae. Figure 11-11. Lubrication prior to microkeratome pass.
Lastly, as mentioned above, excessive irrigation should be avoided as this can lead to cap swelling, retraction from the edges of the bed, and gutter asymmetry. These flaps can be difficult to align and are more prone to striae postoperatively.
Achieve Good Flap Adhesion The surgeon should ensure that the flap adheres well to the underlying stromal bed before removing the lid speculum. There are several options available to drying the cornea. The flap may be allowed to simply air dry. This should be done for 3-5 minutes. Alternatively, with some lasers (such as the VISX laser) the surgeon may turn on the aspiration for 30-60 seconds to dehydrate the flap. Or, filtered low-power compressed air may be directed onto the epithelium for 10-20 seconds. Over-drying should be avoided as this can result in cap retraction and striae. Good adhesion can be confirmed with the striae test. Using a dry Merocel sponge or other blunt instrument, gentle pressure is applied downward on the epithelium just beyond the keratectomy. If good adhesion is present, fine folds will radiate into the flap. Lubrication should be applied to the cornea prior to removing the lid speculum. This will reduce friction from the lid postoperatively as the patient blinks and decreases the risk of flap displacement.
Care should be taken in removing the speculum so as not to displace the flap. As the speculum is closed it should be lifted upward off of the globe. The patient should be instructed not to squeeze on speculum removal. Once the speculum is out, the surgeon should have the patient open their eyes once more to inspect the flap position.
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Avoid and Treat Loose Epithelium
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Loose epithelium may be encountered intra- Section 7 operatively after the microkeratome makes its pass. Most commonly this is found near the flap hinge but Subjects Index occasionally it can involve a more diffuse area of the flap surface. Patients may be predisposed to this complication if they have evidence of anterior basement membrane dystrophy and/or recurrent erosions. A careful history depicting any prior episodes of spontaneous eye pain should be sought. A thorough Help ? slit lamp examination should be performed looking for epithelial abnormalities. In severe cases, topography will show irregular astigmatism. Epithelial toxicity should be avoided. The surgeon should minimize the use of preoperative anesthetic drops. No more than two drops per eye should be applied. Additionally, marking of the cornea should be done sparingly since the ink is toxic to the epithelium. A lubricating drop should be placed on the corneal surface just prior to the microkeratome pass (Figure 11-11). LASIK AND BEYOND LASIK
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One method, which appears to decrease the incidence of epithelial defects with the Hansatome microkeratome, is to release suction on the reverse pass. This allows the flap to unroll under no tension. Gentle downward pressure with the suction ring prevents the patient from moving their eye during these few seconds. If loose epithelium is encountered, after the flap is repositioned appropriately, it should be manipulated back into place with a Merocel sponge. If this is not possible, or if loose epithelium is an impediment to stroking the flap, then it should be removed with forceps or a dry Merocel sponge. For central or large epithelial defects, a bandage contact lens should be placed. This is typically left in position for a week until the surface is completely reepithelialized. Patients should be watched carefully for signs of infection or diffuse lamellar keratitis. The latter frequently occurs in association with an epithelial defect and should be treated appropriately with frequent topical steroid eye drops. Longer-term follow-up is necessary to monitor for epithelial ingrowth, which occurs in a greater percentage of these cases than usual.
Conclusion
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Although not exhaustive, the above sections provide some helpful techniques in achieving a good LASIK outcome. Each procedure must be modified as appropriate according to the particular case. Knowledge of potential complications, their risk factors, and methods of prevention are crucial to success.
Elizabeth A. Davis,M.D. Associate, Minnesota Eye Consultants, P.A. Assistant Clinical Professor University of Minnesota E-mail:
[email protected]
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LASIK (Laser In-Situ Keratomileusis) FOR HYPEROPIA
Chapter 12 LASIK (Laser In-Situ Keratomileusis) FOR HYPEROPIA Weldon W. Haw, M.D., Edward E. Manche, M.D.
(Note from the Editor in Chief: This chapter is an excellent presentation of how hyperopic LASIK can be safe, predictable and effective at reducing low to moderate levels of hyperopia in appropriate candidates. It merits that it be read by all ophthalmic surgeons interested in further advancing their expertise in refractive surgery.)
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TECHNIQUE, SAFETY AND EFFICACY Until recently, excimer laser keratorefractive surgery has focused on the treatment of myopia and myopic astigmatism. Recent advances in excimer laser technology have resulted in the expansion of options available to patients with hyperopia. Excimer laser technology can be used to correct hyperopia by creating a doughnut shaped annular photoablation in the peripheryof the cornea. The peripheral ablation results in central steepening of the cornea that corrects hyperopia (Fig. 12-1). Initial attempts at correcting hyperopic refractive error with photorefractive keratectomy (PRK) using this method resulted in unacceptable levels of regression, decentration, and loss of best spectacle corrected visual acuity. (1) The expansion of the optical zone and the development of laser in situ keratomileusis (LASIK) have significantly improved the results of hyperopic keratorefractive surgery. (2-16) This chapter will review issues in technique, safety, and efficacy of LASIK for hyperopia.
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Section 6 Figure 12-1: LASIK in Hyperopia - Steepening Effect on Cornea Leading to Correction of Hyperopia Section 7 The central cornea has become steepened (A) following the mid-peripheral and peripheral ablation performed with the excimer laser (red). The darkened center within the red beam Subjects Index corresponds to the optical zone from which the ablation into the periphery begins. Dotted lines shows previous curvature. (Courtesy of Boyd’s “Atlas of Refractive Surgery” of HIGHLIGHTS OF OPHTHALMOLOGY.)
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Figure 12-2: LASIK for Hyperopia - Ablation of Peripheral and Mid-Peripheral Cornea The corneal flap with superior hinge has a diameter of 9.5 to 10.0 mm, certainly much larger than the flap performed with LASIK for myopia. This is now possible through more sophisticated microkeratomes. The optical zone in the center identified by the red arrow is 6.0 mm in diameter. It always must be 6 mm or larger. The mid-peripheral and peripheral zone identified as "A" is the area of stromal ablation where tissue is removed with the excimer laser. The ablation of the cornea into this area "A" begins where the limiting diameter of the six millimeter optical zone is located (red arrow). (Courtesy of Boyd’s “Atlas of Refractive Surgery” of HIGHLIGHTS OF OPHTHALMOLOGY.)
Figure 12-3: In the hyperopic eye, light rays are focused beyond the retinal plane resulting in a blurred retinal image. This may be due to a flatter than normal cornea or a shorter diameter eye (VISX Inc., Santa Clara, CA, USA)
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Section 6
Hyperopic Correction using the Excimer Laser
Section 7 Subjects Index
In order to correct hyperopia, the excimer laser ablation must be concentrated in an annular ablation zone at the corneal plane (Figs. 12-2 & 12-3). Several excimer laser manufacturers have successfully applied their technology to accommodate the hyperopic ablation profile. VISX (Santa Clara, CA, USA) uses an offset scanning beam to concentrate the excimer laser energy in an annular transition zone 5 to 9 mm in diameter (Figs. 12-4, 12-5). LADARVision (Summit-Autonomous Technology, Orlando, FL) uses a flying spot beam (0.8 to 0.9mm) that scans across the surface of the cornea (Fig. 6). The cumulative ablation is achieved by partial overlap of multiple laser shots. During hyperopic correction, the density of laser ablation is concentrated peripherally. Currently, a 6.0 mm optical zone with a 1.5mm blend zone (9.0 mm total) is currently
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Figure 12-4: VISX uses an offset scanning beam to concentrate the excimer laser energy in an annular transition zone. This steepens the central cornea resulting in the correction of hyperopia. (VISX Inc., Santa Clara, CA, USA)
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Figure 12-5: The annular hyperopic ablation profile. (VISX Inc., Santa Clara, CA, USA)
Figure 12-6: LADARVision uses a flying spot beam to scan an annular ablation zone in order to correct hyperopia. (SummitAutonomous Technology, Orlando, FL, USA)
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Section 1
under clinical investigation. Hyperopic astigmatism may also be corrected by differential application of excimer laser along the annular ablation zone. Summit Technology (Waltham, MA) corrected hyperopia by creating an annular ablation profile by using an erodible disc and axicon quartz lens system.(18) The erodible disc delivery system has the theoretical advantage of transferring any tridimensional shape on to the corneal surface by photoablation. The axicon quartz lens is used to gradually smooth the peripheral blend zone.
Patient Selection and Preoperative Considerations Typically, LASIK has been successfully used to correct low to moderate levels of hyperopia (+1.0 to +5.0 diopters). As with myopic LASIK, patients should be older than 21 years and demonstrate stability in the refractive error for at least 12 months. Absolute contraindications include eyes with active pathology in corneal shape, thickness, or inflammation. Eyes with systemic vasculitis, autoimmune diseases, collagen vascular disorders, unstable diabetes or other states with abnormal healing are also suboptimal candidates.
As in the case of LASIK for myopia,the patient should Section 2 undergo a complete history and examination. This Section 3 includes a manifest refraction, cycloplegic refraction, corneal topography, slit lamp examination, Section 4 pachymetry, and dilated fundus examination. PotenSection 5 tial risk factors for a complicated procedure can be identified with a careful preoperative examination. Section 6 The identification of corneal neovascularization is especially important since a large primary keratec- Section 7 tomy is required to accommodate the large hyperSubjects Index opic annular photoablation. Cycloplegic refraction is also an integral part of the preoperative examination as it may unmask latent hyperopia in patients with vigorous accommodation ability. The mean central keratometry should be carefully evaluated. Eyes with low preoperative mean keratometry readings are more likely to have smaller diameter flaps Help ? which cannot accommodate a large diameter hyperopic ablation profile. Eyes with a postoperative mean central keratometry of >51 to 52 diopters may suffer from poor quality of vision, monocular diplopia and loss of best spectacle corrected visual acuity similar to patients with keratoconus. These eyes may also suffer from chronic apical dryness that may exacerbate the patient’s symptoms during the postoperative course. Thus, keratorefractive surgery should be avoided in eyes with a steep preoperative mean cen-
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tral keratometry and a large hyperopic correction. In these eyes, other alternatives such as a hyperopic phakic intraocular lens may be a more viable option. Patients with secondary hyperopia resulting from previous keratorefractive surgery (RK, PRK, LASIK) require special attention. Since overcorrections may regress significantly, the refractive stability should be evaluated prior to the retreatment procedure. In our experience, this requires a minimum of 6 months. In addition, the location and number of radial keratotomy incisions should be noted. LASIK on eyes with over 8 incisions may result in an unstable flap and wound dehiscence. It is also important to evaluate the RK incisions for epithelial plugging and/or wound gape. In these eyes, a thicker plate (i.e. 180 microns) will result in a thicker, more stable flap. The diameter and centration of the primary keratectomy of eyes that had undergone previous LASIK should be carefully noted. Significantly decentered flaps and small diameter flaps will require a new flap in order to accommodate the large diameter hyperopic ablation. Eyes with hyperopia from unintended overcorrection of myopia may require an adjustment in the hyperopic LASIK nomogram.(4) Since these eyes achieve more effective correction than eyes with primary hyperopia, we typically reduce our attempted correction by 20 to 30 %.
Technique The fundamentals of performing a successful hyperopic LASIK are similar to performing a successful myopic LASIK with a few exceptions. Thus, a surgeon skilled in lamellar surgery should make the transition from myopic LASIK to hyperopic LASIK with little difficulty. After the instillation of a topical anesthetic and topical vasoconstictor, we isolate the eyelashes with a sterile drape and speculum. The corneal marking is performed and the pneumatic suction ring is positioned. A large suction ring >9.5 mm should be used in order to accommodate the large ablation profile of a hyperopic correction. Careful positioning of the pneumatic suction ring is important in hyperopic LASIK. While a slightly decentered primary keratectomy will accommodate even the largest myopic ablation profiles, it
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may not accommodate a 9.5 mm hyperopic ablation profile. Slight decentration of the pneumatic ring towards the hinge is useful in placing the hinge out of the field of the hyperopic ablation. Positioning the pneumatic ring to place the hinge in areas of corneal vascularization will also limit the degree of hemorrhaging that may occur when making a large diameter flap. A moist methylcellulose sponge may be expanded and used to protect the hinge during the photoablation. Centration of the photoablation is mandatory since the relatively small optical zone created by hyperopic LASIK is less forgiving than the larger optical zone of a comparative level of myopic treatment. After the photoablation, the stromal bed is irrigated, the flap is refloated and the epithelial markings are re-aligned. A topical antibiotic, nonsteroidal anti-inflammatory, and steroid is administered. The postoperative medication regimen is identical to that following LASIK for myopia. We administer fluometholone 0.3% and ciprofloxacin 0.3% four times a day for four days.
Clinical Results
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Section 3
Section 4
A general review of the current literature Section 5 demonstrates effective reduction of low to moderate levels of spherical hyperopia, simple hyperopic Section 6 astigmatism and compound hyperopic astigmatism.(4-16) In these studies, approximately 70 to 90% Section 7 of the hyperopia is corrected depending on the level Subjects Index of preoperative hyperopia and duration of follow-up. Predictability is also an important measure of refractive accuracy and is typically recorded as the percentage of eyes within +/- 1.0 diopter of attempted correction. In these studies, 60 to 100% of eyes were within +/- 1.0 diopter of attempted correction for low to moderate hyperopia. For higher levels of correcHelp ? tion, the predictability within +/- 1.0 diopter of attempted correction decreases to approximately 50 to 80%. (5,7,16) Significant regression can occur following LASIK for hyperopia. (4) In our experience, eyes may be initially slightly overcorrected in the early postoperative period. Stability often requires 3 to 6 months before complete stabilization of the refractive error. After 6 months, eyes may be safely retreated.
LASIK (Laser In-Situ Keratomileusis) FOR HYPEROPIA
Uncorrected visual acuity of 20/40 or better was demonstrated in approximately 70 to 95% of eyes depending on the level of preoperative correction. (4-16) In these same studies, loss of best spectacle corrected visual acuity generally ranged from 0 to 7%. However, LASIK for hyperopia greater than +5.0 diopters is not recommended as it may result in a loss of best spectacle corrected visual acuity in a significant number of eyes (13 to 15%). (8) The type and frequency of complications following hyperopic LASIK are similar to myopic LASIK with few exceptions. As noted previously, intraoperative hemorrhages may occur following the microkeratome pass for large diameter flaps. Common avoidable causes of loss of best spectacle corrected visual acuity include decentration and steepening of the central cornea >51 to 52 diopters. The comparatively small optical zone following hyperopic LASIK mandates meticulous attention to centration during the photoablation. There are anecdotal reports of an increased rate of epithelial ingrowth following hyperopic LASIK. This may be related to spill-over ablation outside margin of the primary keratectomy.
Secondary Hyperopia Secondary hyperopia may be safely treated using hyperopic LASIK technology. (4,10) In these limited studies hyperopic LASIK for eyes previously treated with myopic LASIK or RK demonstrated effective reduction of hyperopia. 83% to 93% of these eyes demonstrated an uncorrected visual acuity of 20/40 or better and no eyes lost best spectacle corrected visual acuity. At Stanford University, we prospectively evaluated 19 eyes with secondary hyperopia resulting from PRK, LASIK, or RK. These eyes underwent hyperopic LASIK with theVISX S2 Smoothscan excimer laser for a mean spherical equivalent of +1.64+/-0.80 diopters (range, +1.5 to +2.75 D). In these eyes with secondary hyperopia, we reduced our nomogram by 20 to 30%. The procedure was performed as described in the technique section of this chapter. The Hansatome microkeratome (Bausch & Lomb, Rochester, NY) was used with the 9.5mm pneumatic suction ring in cases that required a new flap.
On the first postoperative day, mean spherical equivalent was –0.16 +/-0.63 D and 82% demonstrated an uncorrected visual acuity of 20/40 or better. At 6 months, mean spherical equivalent was +0.58+/-0.59 D, 78% were within +/-1.0 D of attempted correction, and 78 % of eyes demonstrated an uncorrected visual acuity of 20/40 or better. No eyeslost two or more lines of best spectacle corrected visual acuity and there were no significant decentrations. A hyperopic shift of +0.76 D occurred during the first 6 postoperative months. Stability within +/-0.50 diopters occurred between 3 and 6 months postoperatively.
Hyperopia with Astigmatism Hyperopic astigmatism can be corrected by Contents additional steepening along the flat meridian. Toric correction of hyperopia may result in significantly Section 1 less predictable results and higher loss of BSCVA than comparative levels of spherical treatments. (7-8) As Section 2 in myopic corrections, the lower predictability of toric Section 3 ablations is likely related to axis misalignment. (17) In an ongoing prospective study at Stanford Section 4 University, 119 eyes of 76 patients with compound Section 5 hyperopic astigmatism underwent LASIK with the VISX S2 Smoothscan excimer laser (VISX Inc., Section 6 Santa Clara, CA). Inclusion criteria included eyes with +1.0 to +6.0 diopters of spherical hyperopia and Section 7 +1.0 to +4.0 diopters of hyperopic astigmatism. Mean Subjects Index preoperative sphere was +1.91 +/- 1.50 D (range +1.0 to +6.0), mean preoperative cylinder was +1.58 +/-0.88 D (range, +1.0 to +4.0), and mean spherical equivalent was +2.74+/-1.51 (range, +1.5 to +7.0 D). Patients were prospectively evaluated at 1 day, 1 month, 3 months, 6 months, and 12 months. On the first postoperative day, the mean Help ? spherical equivalent was –0.39 +/- 0.61 diopters (range, -2.75 to +1.0 D). 91% of eyes were within +/ -1.0 diopters of attempted correction. 91% of eyes demonstrated an uncorrected visual acuity of 20/40 or better and 0% of eyes lost 2 or more lines of best spectacle corrected visual acuity. 1.7% of eyes experienced a displaced flap on the first day following surgery. These flaps were repositioned without visual deficits. 0.8% of eyes experienced diffuse lamellar keratitis that resolved uneventfully with topical steroids. LASIK AND BEYOND LASIK
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At 1 year, mean sphere was –0.12+/-0.67 diopters (range, -1.25 to +1.5 D), mean cylinder was +0.44+/-0.43 diopters (range, 0 to +2.0 D), and mean spherical equivalent was +0.13 +/-0.69 diopters (range, -1.0 to +1.75 diopters). 88% of eyes were within +/-1.0 diopter of attempted correction and 97% of eyes demonstrated an uncorrected visual acuity of 20/40 or better. Vector analysis demonstrated a mean magnitude of error of –0.20 D +/-0.67 D. The mean angle of error was 0.37 degrees +/- 18.9 degrees. 92% of eyes had a difference vector within +/-1.0 diopters. There were no intraoperative flap complications, no significant decentrations, and no eyes lost 2 or more lines of best spectacle corrected visual acuity. There was a mean regression in the spherical equivalent of +0.4 diopters between first postoperative day and 6 months. Stability within +/-0.25 diopters occurred between 3 and 6 postoperative months. The average regression between 6 months and 1 year was +0.13 diopters. (Note from the Editor in Chief: For the surgical management of hyperopia, Mahmoud M. Ismail, M.D., Ph.D, a distinguished ophthalmic surgeon from Egypt has reported highly positive results with the use of intracorneal lenses for the correction of hyperopia in albino rabbits. Dr. Ismail used a new hydrogel intracorneal contact lens (PermaVision, Anamed, Inc.), a product developed to address the limitations reported with the current relatively thick hydrogel lens implants. It is comprised of water content more than 70% and a refractive index that is substantially close to the refractive index of the corneal tissue (1.376). It is designed to correct hyperopia up to +6 diopters. All animals were followed up for at least 6 months by confocal microscopy. The PermaVision lens intracorneal implant shows excellent compatibility according to the author. The new generations of soft intracorneal lenses may present a new alternative for the correction of hyperopia in the future. The procedure seems to be reproducible and implant removal is possible. This thin PermaVision lens which allows the passage of nutrients and fluid through the implant to nourish the corneal layers may offer a new scope for the application of intracorneal implants in hyperopia. We will need to see the results in humans in later years.)
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REFERENCES 1.
2.
3.
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9. 10.
11.
12.
13.
14.
15.
16.
Dausch D, Klein R, Schroder E. Excimer laser photorefractive krratectomy for hyperopia. Refract Corneal Surg 1993; 9:20-8. Dausch D, Smecka Z, Klein R, Schroder, Kirchner S. Excimer laser photorefractive keratectomy for hyperopia. J Cataract Refract Surg 1997; 13:504-10. Jackson WB, Mintsioulis G, Agapitos PJ, Casson EJ. Excimer laser photorefractive keratectomy for low hyperopia: safety and efficacy. J Cataract Refract Surg 1997; 23:480-7. Lindstrom RL, Hardten DR, Houtman DM, et. al. Sixmonth results of hyperopic and astigmatic LASIK in eyes with primary and secondary hyperopia. Trans Am Ophthalmol Soc 1999; 97:241-55. Zadok D, Maskaleris G, Montes M. et. al. Hyperopic laser in situ keratomileusis with the Nidek EC-5000 excimer laser. Ophthalmology 2000; 107:1132-7. Contents Esquenazi S, Mendoza A. Two-year follow-up of laSection 1 ser in situ keratomileusis for hyperopia. J Refract Surg 1999; 15:648-52. Section 2 Barraquer C, Gutierrez AM. Results of laser in situ keratomileusis in hyperopic compound astigmatism. Section 3 J Cataract Refract Surg 1999; 25:198-204. Arbelaez MC, Knorz MC. Laser in situ keratomileusis Section 4 for hyperopia and hyperopic astigmatism. J Refract Section 5 Surg 1999; 15:406-14. Rosa DS, Febbraro JL. Laser in situ keratomileusis Section 6 for hyperopia. J Refract Surg 1999; 15:S212-5. Buzard KA, Fundingstand BR. Excimer laser assisted Section 7 in situ keratomileusis for hyperopia. J Cataract Refract Surg 1999; 25:197-204. Subjects Index Goker S, Er H, Kahvecioglu C. Laser in situ keratomileusis to correct hyperopia from+4.25 diopters. J Refract Surg 1998; 14:26-30. Argento CJ, Consentino MJ. Laser in situ keratomileusis for hyperopia. J Cataract Refract Surg 1998; 24:1050-8. Ibrahim O. Laser in situ keratomileusis for hyperopia and hyperopic astigmatism. J Refract Surg 1998; 14 Help ? (2 Suppl): S179-82. Chayet AS, Magallanes R, Montes M, et. al. Laser in situ keratomileusis for myopic, mixed and simple hyperopic astigmatism. J Refract Surg 1998; 14(2Suppl)S175-6. Ditzen K, Huschka H, Pieger S. Laser in situ keratomileusis for hyperopia. J Cataract Refract Surg 1998; 24:42-7. Argento CJ, Consentino MJ, Biondini A. Treatment of hyperopic astigmatism. J Cataract Refract Surg; 1997; 23:1480-90.
LASIK (Laser In-Situ Keratomileusis) FOR HYPEROPIA 17. Snibson GR, Carson CA, Aldred GF, Taylor HR. Oneyear evaluation of excimer alser photorefractive keratectomy for myopia and myopic astigmatism. Melbourne Excimer Laser Group. Arch Ophthalmol 1995; 113:994-1000. 18. Haw W., Manche E. Prospective study of photorefractive keratectomy for hyperopia using an axicon lens and erodible mask. Journal of Refractive Surgery 2000; 16:724-730.
Weldon Haw, M.D. Cornea & Refractive Surgery Department of Ophthalmology Stanford University School of Medicine 300 Pasteur Drive, Suite A157 Stanford, CA 94305 Phone:(650)-723-5517; Fax: (650)-723-7918 E-Mail:
[email protected]
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Section 6 Section 7 Subjects Index
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IRREGULAR ASTIGMATISM: LASIK AS A CORRECTING TOOL
Chapter 13 IRREGULAR ASTIGMATISM: LASIK AS A CORRECTING TOOL Prof. Jorge L Alió, MD, PhD, José I. Belda Sanchis, MD, PhD., Dr. Ahmad MM Shalaby, MD
Introduction Irregular astigmatism represents one of the problems that are very difficult to manage and frustrating in results to refractive surgeons. It is also one of the worst sequelae of corneal injuries. It can also complicate certain corneal diseases as keratoconus. With the recent evolution of refractive surgery techniques and diagnostic tools, new types of irregular astigmatism are being observed 1,2. The astigmatism is defined as irregular if the principal meridians are not 90 degrees apart, usually because of an irregularity of the corneal curvature. It cannot be completely corrected with a sphero-cylindrical lens 3. Duke –Elder defines irregular astigmatism as a refractive state in which the refraction in different meridians conforms to no geometric plan and the refracted rays have no planes of symmetry 4. The alternatives for correction of irregular astigmatism are very scarce and with very limited expectations. Spectacle correction is usually not useful in the correction of corneal irregular astigmatism as it is difficult to define principle meridians. Hard contact lenses represent a good alternative in which the tear fluid layer under the contact lens evens out the irregularity. We should consider that adaptation and stability of contact lenses is limited by irregularity corneal surface and the patient’s comfort. We also must remember that our patients consented to undergo refractive surgery because they did not want to use more the contact lens. Lamelar and full thickness corneal grafting are surgical alternatives. The limited availability of corneal donor as well as the biological and refractive
complications of allografic corneal graft limit the clinical applicability of these procedures. Many surgeons have made great efforts in finding a solution to this problem.5-7 To this date, we believe there should be safe, efficient and predictable methods to resolve this problem. Accordingly, the approach to new surgical methods for the correction of irregular astigmatism is one of the greatest expectations in today’s refractive surgery, especially when the very near future is supposed to bring generalization of corneal refractive surgical techniques.
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Etiology of Irregular Astigmatism a) Primary Idiopathic
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There is a general prevalence of low levels of Subjects Index irregular astigmatism of unknown cause within the population. This might explain the mildly reduced best corrected visual acuity (BCVA) in patients presenting for laser vision correction 1.
b) Secondary 1) Dystrophic In the cornea, keratoconus, which, in optical terms, is primarily an irregularity of the anterior corneal surface, is the best example. Pelucid degeneration and keratoglobus may also be associated with posterior corneal surface irregularity causing irregular astigmatism. In the lens, lenticonus may cause irregular astigmatism; and in the retina, posterior staphyloma 1.
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2) Traumatic Corneal irregularity is caused commonly by corneal wounds (incision or excision) or burns (chemical, thermal or electrical) 1. 3) Postinfective Postherpetic keratitits is the most common form of postkeratitic healing and scarring that may lead to an irregular surface 1. 4) Postsurgical Irregular corneal astigmatism can complicate any if the following refractive surgical procedures: keratoplasty, photorefractive keratectomy (PRK), laser in situ keratomileusis (LASIK), radial keratotomy (RK), arcuate keratotomy (AK), and cataract incisions. Scleral encirclement or external plombage may also contribute 1.
Diagnosis of Irregular Astigmatism Clinically, irregular astigmatism will present with one of those typical retinoscopy patterns, the most common being spinning and scissoring of the red reflex. On attempting keratometry the mires will appear distorted. Corneal topography shows certain patterns for irregular astigmatism that will be discussed in detail later. The most recent and sophisticated technique is the application of wavefront analysis (aberrometers) 8. This emerging method measures the refractive status of the whole internal ocular light path at selected corneal intercepts of incident light pencils. By comparing the wavefront of a pattern of several small beams of coherent light projected through to the retina with the emerging reflected light wavefront, it is possible to measure the refractive path taken by each beam and to infer the specific spatial correction required on each path.
Clinical Classification of Irregular Astigmatism Following Corneal Refractive Surgery In corneal refractive surgery using laser in situ keratomileusis (LASIK) the surgeon uses a microkeratome, whether automated or manual, to fashion a corneal flap and a stromal bed. Once the flap is fashioned and lifted, the excimer laser is used 170
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to ablate tissue from the bed for the planned correction, depending on the capabilities of the laser. In this clinical prespective, irregular astigmatism induced by LASIK can be classified according to its location as: 1. Superficial: due to flap irregularities. 2. Stromal: induced by bed irregularities. 3. Mixed: due to irregularities in both flap and stroma.
Corneal Topography Patterns of Irregular Astigmatism Topographic classification of irregular astigmatism patterns is very important in the following aspects: 1. To unify terms and concepts when we referring corneal topography images. 2. To determine the cause of the subjective symptoms referred by the patient (Halos, glare, monocular diplopia, etc.). 3. Reaching a topographic basis for retreatment. The topographic approach for treatment patients with a previous unsuccessful excimer laser surgery should allow reshaping the cornea in the pattern appropriate for the specific patient.
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Based on the topography, we proposed the following classification for irregular astigmatism 7: Subjects Index • Irregular astigmatism with defined pattern, and • Irregular astigmatism with undefined pattern
1. Irregular astigmatism with defined pattern We define irregular astigmatism with defined pattern when there is a steep or flat area of at least 2 mm of diameter, at any location of the corneal topography, which is the main cause of the irregular astigmatism. It is divided into five groups: A. Decentered Ablation: Shows a corneal topographic pattern with decentered myopic ablation in more than 1.5 mm in relation to the center of the cornea. The flattening area is not centered in the center of the cornea; the
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B.
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optical zone of the cornea has one flat and one steep area (Figure 13-1a). Decentered Steep: Shows a corneal hyperopic treatment decentered in more than 1.5 mm in relation to the center of the cornea (Figure 13-1b). Central island: Shows an image with an increase in the central power of the ablation zone for myopic treatment ablation at least 3.00D and 1.5mm in diameter, surrounded by areas of lesser curvature (Figure 13-1c). Central irregularity: Shows an irregular pattern with more than one area not larger than 1.0 mm and no more than 1.50D in relationship with the flattest radius, located into the area of the myopic ablation treatment (Figure 13-1d). Peripheral Irregularity: It is a corneal topographic pattern, similar to Central Island, extending to the periphery. The myopic ablation is not homogeneous, there is a central zone measuring 1.5 mm in diameter and 3.00 D in relation to the flattest radius, connected with the periphery of the ablation zone in one meridian (Figure 13-1e).
2. Irregular astigmatism with undefined pattern We consider irregular astigmatism with undefined pattern when the image shows a surface with multiples irregularities; big and small steep and flat areas, defined as more than one area measuring more than 3 mm in diameter in the central 6 mm (Figure 13-1f). The differential between flat and steep areas were not possible to calculate in the Profile Map and Dk showed an irregular line or a plane line. Normally, Dk is the difference between the steep k and the flat k, given in diopters at the cross of the profile map. A plane line is produced when the ∆k cannot recognize the difference between the steep k and the flat k in severe corneal surface irregularities.
Evaluation of Irregular Astigmatism In managing irregular astigmatism patients, a meticulous preoperative evaluation is necessary. We perform a complete preoperative ocular examination, including previous medical reports and complete ocular examination: uncorrected and best corrected visual acuity, pinhole visual acuity and cycloplegic refraction, keratometry, contact ultrasonic pachymetry (Ophthasonic Pachymeter Teknar Inc. St. Louis, USA) and computerized corneal topography. We perform the corneal topography with Eye Sys 2000 Corneal Analysis System (Eye Sys Co., Houston, Texas, USA). We also use the Ray Tracing mode of the C-SCAN Color-EllipsoidTopometer (Technomed GmbH, Germany) to deterContents mine the Superficial Corneal Surface Quality (SCSQ) and the Predicted Corneal Visual Acuity (PCVA), in Section 1 addition to the topography. Recently, we have incorporated the elevation topography of the Orbscan Section 2 System (Orbtek, Bausch & Lomb Surgical, Orbscan Section 3 II corneal topography, Salt Lake City, Utah, USA) in Section 4 our evaluation tools. Follow up examinations after surgery were Section 5 performed at 48 hours, and then at one, three and six months. Post-operative follow up included: uncor- Section 6 rected and best-corrected visual acuity, pinhole visual acuity and cycloplegic refraction, biomicros- Section 7 copy with slip-lamp and complete corneal topogra- Subjects Index phy screening with the previously mentioned instrumentation. During the pre-operative and post-operative period the surface quality of the cornea was studied using the Ray Tracing module of the C-SCAN 3.0 (Technomed GmbH, Germany). This device determines the Predicted Corneal Visual Acuity from the Help ? videokeratography map, by simulating the propagation of rays emanating from 2 light dots, which impinge on the best-fit image plane after projection via the maximum of 10,800 previously determined corneal surface power values. Refraction and reflec-
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Topographic Patterns of Irregular Astigmatism With Ray Tracing Study (Figs. 13-1 A-F) Figure 13-1 A (left): Decentered ablation (myopic treatment more than 1.5 mm in relation to the center of the cornea. Note that although the peak distortion is minimal in the rat tracing study, the corneal surface quality outside the 3 mm reference pupil is markedly reduced, meaning that the patient will suffer glare and night vision troubles when this pupil dilates under scotopic conditions)
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Figure 13-1 B (right): Decentered steep (hyperopic treatment decentered in more than 1.5 mm in relation to the center of the cornea. Note the reduction in PCVA in spite of a uniform peak, and the irregular base diameter which correlates with the spherical aberrations this patient would suffer).
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IRREGULAR ASTIGMATISM: LASIK AS A CORRECTING TOOL Figure 13-1 C (left): Central Island (increase in the central power of the ablation zone for myopic treatment ablation at least 3.00D and 1.5 mm in diameter, surrounded by areas of lesser curvature. Note again the reduction in the peripheral SCSQ, i.e. night vision problems).
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Figure 13-1 D (right): Central irregularity (irregular pattern with more than one area not larger than 1.0 mm and no more than 1.50D in relationship with the flattest radius, located into the area of the myopic ablation treatment. Note the distorted base diameter and the marked peak separation, and the irregular reduced SCSQ).
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Chapter 13 Figure 13-1 E: Peripheral irregularity (pattern similar to Central Island, extending to the periphery in which the myopic ablation is not homogeneous. Note an extremely reduced SCSQ and markedly irregular base diameter, once more spherical aberrations).
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Figure 13-1 F: Irregular astigmatism with undefined pattern (surface with multiple irregularities with big and small steep and flat areas. Note the extensive scatter at the base diameter which is extremely irregular, even worse than the previous examples).
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tion of the rays at the optical interfaces, the pupil diameter, and the anterior chamber depth are taken into account according to laws of geometric optics. The Ray Tracing module calculates the pupil size by the captured image of the pupil during videokeratography. This is measured under the luminance of the videokeratography rings (25.5 cd/m2) and is automatically integrated into the Ray Tracing Analysis with the videokeratography map. Hence, the projection of objects onto a detection plane can be determined. The Ray Tracing module calculates the optical function of the eye by means of optical Ray Tracing, using the cornea as the refractive element of the system. It measured and analyzed the interaction between the corneal shape, the functional optical zone, and the pupil diameter, providing valuable additional information by the resulting diagram. The image points on the detection plane are represented by two intensity peaks that must be spatially resolved to discriminate them separately and individually. The peak distance (distance between the functional maxima) and the distortion index (basic diameter of the point cloud in the detection plane) are parameters defined to help understanding when these two peaks are spatially resolved. They help to objectively quantify the individual retinal image in each subject. We found it very useful to evaluate the corneal surface and corneal healing. It is very useful also to explain visual phenomena referred by the patients, and that cannot be explained by older versions of corneal topographers. We don’t consider it a substitution of the Eye Sys 2000 Corneal Analysis System (Houston, Texas, USA), but it showed to be a very useful tool 9. Subjective symptoms from the pre and postoperative periods should be noted in the medical report such as halos, glare, dazzling, corneal and conjunctival dryness, dark-light adaptation and visual satisfaction reported by the patient.
laser is gaining priority with the advent of finely controlled corneal ablation. Before that, limited alteration of corneal topography was possible by, for instance, selective incision placement, placement and removal of sutures, or penetrating and lamellar keratoplasty. Other “treatment” options for irregular corneal astigmatism include optical correction with hard contact lenses in which the tear fluid layer under the contact lens “evens out”’ the irregularity 1, but the patient’s aim to get rid of glasses as well as contact lenses still limits their use. Intracorneal ring segments, originally used for myopia treatment 10, represent another option that is under investigation.
Treatment of Irregular Astigmatism
2. Excimer Laser Assisted by Sodium Hyaluronate (ELASHY). Designed mainly to improve
Treatment options for irregular astigmatism have expanded greatly during recent years. Excimer
Surgical Techniques with Excimer Laser Contents
These represent the main subject of discussion in this chapter. The ultimate goal excimer laser Section 1 treatment is to correct the refractive error while Section 2 reducing corneal astigmatism and topographic disparity but not increasing aberrations within the eye. Section 3 With the advent of the excimer laser, it may be possible to correct directly some forms of corneal Section 4 irregularity. Before considering any treatment op- Section 5 tion, the relationship between the topographical irregularity and the refraction must be considered; a Section 6 therapeutic balance between refractive and corneal Section 7 astigmatism must be reached so that overall visual function is optimal. In other words, an optimal treat- Subjects Index ment should include both topographic and refractive values, rather than excluding one 1. We have used different methods for the surgical correction of irregular astigmatism. At this moment we consider three surgical procedures with excimer laser for correction of the irregular astigmatism: Help ? 1. Selective Zonal Ablation (SELZA). Designed to improve the irregular astigmatism with defined pattern.7
the irregular astigmatism with undefined pattern.11
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3. Topographic Linked excimer laser ablation 1. Selective Zonal Ablation (SELZA) (TOPOLINK). Combines data of the topography and patient refraction in as software to improve the irregular astigmatism with defined pattern and the refractive error, with the same procedure.12 The three surgical procedures were performed under topical anaesthesia of Oxibuprocaine 0.2% (Prescaina 0,2%; Laboratorios Llorens, Barcelona, Spain) drops; no patient required sedation. The postoperative treatment consisted of instillation of topical tobramycin 0.3% and dexamethasone 0,1% drops (Tobradex, Alcon-Cusi, Barcelona, Spain) three times daily for the five days of the follow-up and then discontinued. When the ablation was performed onto the cornea (surface ELASHY, some patients of SELZA), a bandage contact lens (Actifresh 400, power +0.5, diameter 14.3mm, radius of curvature 8.8mm – Hydron Ltd., Hampshire, U.K.) was used during the first three days of the post-operative and the patient was examined daily. It was removed when complete reepithelialization was observed. Then treatment with topical fluorometholone (FML forte, AlconCusi, Barcelona, Spain) was used three times daily for the three months of follow-up and then stopped.13 Non-preserved artificial tears (Sodium Hyaluronate 0.18%, Vislube‚, CHEMEDICA, Ophthalmic line, München, Germany) were used up to three months in every case. Supplementation with oral pain management medications was also used as necessary. Statistical Analysis. Statistical Analysis was performed with the SPSS/Pc+4.0 for Windows (SPSS Inc, Madrid, 1996). Measurements typically are reported as the mean ± 1 standard deviation (using [ n - 1]1/2 in the denominator of the definition for standard deviation, where n is the number of observations for each measurement) and as the range of all measurements at each follow up visit. Patients’ data samples were fitting the normal distribution curves. Statistically significant differences between data sample means were determined by the “Student’s t test” ; P values less than 0.05 were considered significant. Data concerning the standards for reporting the outcome of refractive surgery procedures, as the safety, efficacy and predictability, was analyzed as previously defined.14
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In this study we report the results of a prospective clinically controlled study performed on 31 eyes of 26 patients with irregular astigmatism induced by refractive surgery. All cases were treated with SELZA using an excimer laser of broad circular beam (Visx Twenty/Tweenty, 4.02, Visx, Inc. Sunnyvale, California, USA). The surgical planning was applied using the Munnerlyn formula 15, modified by Buzard 16, to calculate the depth of the ablation depending on the amount of correction desired and the ablation zone. In this formula the resection depth is equal to the dioptric correction, divided by 3, and multiplied by the ablation zone (mm) squared. We used a correction factor of 1.5 times, to avoid undercorrection:
Ablation
(Dioptric correction) x 1.5 depth = x (ablation zone)2 3
Contents
Section 1 Section 2
Section 3
Methods
Section 4
Section 5
In general, we use ablation zone of 2.5 to 3.0 mm, depending on the steep area of the corneal Section 6 topography to be modified. The ablation zone was Section 7 determined by observing the color map. The form of videokeratoscope provides additional information Subjects Index about the irregular zones, and the profile map gave the values for performed ablation. In cases of irregular corneal surface, treatment was performed on the center of irregularity, which was located using the color map of the corneal topography. First we located the center of the cornea, then we located the exact center of irregularity. Here we use the dotted boxes in Help ? the map (each dot represents 1 mm2) to detect the exact center of irregularity in relation to the center of the cornea. The amount of ablation is determined using the cross section of the profile map (vertical line corresponding to diopters and horizontal line corresponding to corneal diameter). When the patient had LASIK previously we lift the flap or we do a new LASIK cut and after we perform excimer laser using PTK mode.
IRREGULAR ASTIGMATISM: LASIK AS A CORRECTING TOOL
The technique is based on subtraction of tissues to eliminate the induced irregular astigmatism and to achieve a uniform corneal surface using excimer laser; we center the effect of laser on zones where the corneal surface is steeper.
Results In patients with Irregular Astigmatism with a Defined Pattern, the visual acuity improved significantly, reaching in many cases near the BCVA before the initial refractive procedure. The difference between the BCVA before the therapeutic procedure was highly statistically significant (P < 0.001). The mean BCVA after 3 months of surgery it was 20/25 ± 20/100 (range 20/50 - 20/20), which was as good as the initial BCVA 20/29 ± 20/100 (range 20/50 - 20/20). The BCVA before selective ablation improved from 20/40 ± 20/100 (range 20/100 - 20/25) to 20/25 ± 20/100 (range 20/50 - 20/20). We did not have any patients with one or more lines lost of BCVA. The Corneal Uniformity Index (CUI) before versus after selective zonal ablation with excimer laser improved from 55.65 ± 15.90 % (range 20 - 80 %) to 87.83 ± 10.43 % (range 70 - 100), a change that was also statistically significant (P < 0.005). The safety index (the ratio of mean postoperative BCVA over mean preoperative BCVA) was equal to 1.55. The efficacy of the procedure in percent UCVA 20/40 was 85%. The predictability (astigmatic correction) using CUI was expressed as a percentage. The various relationships between the preoperative CUI and the surgically induced postoperative CUI provided the information about the magnitude of irregular astigmatism correction and the corneal surface uniformity. Correction index, which is the ratio of mean postoperative CUI (87.83 ± 10.43 %; range, 70-100%) over the mean preoperative CUI (55.65 ± 15.90 %; range, 20-80 %), was equal to 1.58. The results observed in all cases of irregular astigmatism without a defined pattern were poor. Efficaccy in percentage of eyes with UCVA of 20/40 was 6%, and predictability (astigmatic correction) was 0.58. In some cases, visual acuity became worse: the refraction error and corneal topography were considerably modified.
Discussion The results of the selective zonal ablations technique were satisfactory as regards the correction of irregular astigmatism with a defined topographic pattern. Visual Acuity improved in the postoperative period, achieving values near the initial BCVA of the patients (before the initial surgical procedure). The corneal uniformity index was used to evaluate the central 3 mm zone of the cornea. It started to improve in the early postoperative period and stabilized after 3 months, just as the issues of visual acuity (p<0.005). Normally, this refractive procedure requires a stable corneal topography (6 months after the last corneal procedure) and its adequate interpretation 17. However, our results have proven that it is not suitable for correcting all patterns of irregular astigmatism.
2. Excimer Laser Assisted By Sodium Hyaluronate (ELASHY)
Contents
Section 1 Section 2
This can be considered as one of the Section 3 ablatable masking techniques. We report the results Section 4 of a prospective clinically controlled study performed on 32 eyes of 32 patients with irregular Section 5 astigmatism.11 All the patients had been subjected Section 6 previously to one or more of the following procedures: LASIK, Incisional Keratotomy, Section 7 Photorefractive Keratotomy, Phototherapeutic Keratotomy, Laser Thermokeratoplasty, and Corneal Subjects Index Trauma. Irregular astigmatism was induced thereafter. Six months after the last corneal procedure, for the aim of stability, the cases were selected for ELASHY. Help ?
Methods The correction of irregular astigmatism was made with a Plano Scan Technolas 217 C-LASIK Scanning spot Excimer laser (Bausch & Lomb, Chiron Technolas GmbH, Doranch, Germany) in PTK mode, assisted by viscous masking sodium hyaluronate 0.25% solution (LASERVIS CHEMEDICA, Ophthalmic line, Munchen, Germany). The physical characteristics of sodium hyaluronate confer important
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each of the intervals, a new drop of the viscous substance was added at the center of the ablation area and again spread out with the same maneuvers with the 23-G canula. Total treatment was calculated to ablate the prominent areas to the calculated K value at the 4 to 6 mm optical zone or calculated from the tangential map of the Technomed topographer. Assuming a decrease in the ablative effect of the laser due to the use of the viscous agent, we target at a 50% more ablation than the one that corresponds to the real ablation depth necessary for the smoothing procedure. Figure 13-2: Safety of ELASHY procedure (note that most of the eyes fall at or above the reference line of no change in BCVA with 6.3% of eyes losing 2 lines of BCVA, and that the safety index is higher than 1)
rheological properties to the product. The photoablation rate is similar to that of corneal tissue, forming a stable and uniform coating on the surface of the eye, filling depressions on the cornea and effectively masking tissues to be protected against ablation by the laser pulses 18, 19. In cases where the irregular astigmatism was induced by a flap irregularity or superficial corneal scarring, ELASHY ablations were performed onto the corneal surface. The epithelium was removed also using the excimer laser assisted by viscous masking. When the irregularity was inside the stroma, at the previous stromal bed, the previous flap was lifted up whenever possible or a new cut was done. Then ELASHY was performed at the stroma and after the procedure the flap was repositioned. We centered the ablation area at the corneal center and fixed it with the eye-tracking device in the center of the pupillary area. After this, one drop of the viscous masking and fluorescein was scattered on the cornea that should be ablated and spread out with the 23-G canula (Alcon laboratories, U.S.A.) used for the viscous substance instillation. With fluorescein, it was also possible to observe the spot and the effect of laser. Because fluorescent light is emitted during ablation of corneal tissue, cessation of the fluorescence signifies complete removal of the viscous masking solution, i.e. tissue ablation. The laser was prepared for ablation at 15 microns intervals. After
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Results Corneal topography corresponded to our established classification of irregular astigmatism: Pattern Irregular Corneal astigmatism was identified in 23 eyes (71.9%) and irregularly irregular corneal astigmatism was identified in the other 9 eyes (28.1%). The mean preoperative BCVA improved from 20/40 ± 20/80 (range 20/200 to 20/20) to 20/32 ± 20/100 (range 20/200 to 20/20) (p = 0.013, Student T test), six months after surgery. There were only 2 eyes losing 2 lines of BCVA (6.3%) and 3 eyes (9.4%) losing 1 line. The procedure was safe with a safety index equal to 1.1 (Figure 13-2).
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Help ?
Figure 13-3: Evolution of Superficial Corneal Surface Quality (SCSQ) (note the continuous statistically significant improvement of SCSQ over time which correlated with the improvement of patients’ subjective symptoms of glare, halos, etc.)
IRREGULAR ASTIGMATISM: LASIK AS A CORRECTING TOOL
We had 28.1% of eyes at 6 months with postoperative UCVA of 20/40 or better with 3.1% reaching 20/20. The efficacy index of the procedure (the ratio [mean postoperative UCVA] / [mean preoperative BCVA]), was equal to 0.74. As ELASHY is based on the subtraction of tissues to achieve a smoother corneal surface, we expected improvement in the patients’ BCVA and subjective symptoms as glare, halos, etc. rather than changes in the spherical equivalent. The Astigmatic Correction was evaluated in respect to the improvement of the corneal surface, using the data of the SCSQ provided by the Ray-Tracing study (C-SCAN Color-Ellipsoid-Topometer, Technomed GmbH,
Germany). The SCSQ (Figure 13-3) pre vs. post therapeutic procedure, evaluated by the Ray Tracing study, improved from a mean of 69.38% ± 9.48 preoperatively to 73.13% ± 8.87 6 months postoperative (p = 0.002, Student T test). Other parameters of the Ray-Tracing study also improved. The PCVA improved from a mean of 20/40 ± 20/80 (range 20/100 to 20/16) preoperatively to 20/32 ± 20/80 (range 20/125 to 20/16) (p = 0.11, Student T test) postoperatively. Also the image distortion significantly improved from a mean of 14.39 ± 3.78 (range 8 to 23.2) preoperatively to 13.29 ± 3.87 (range 7.2 to 26) at 6 months (p = 0.05, Student T test).
A Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7
B
Subjects Index
Help ?
Figure 13-4: ELASHY: Preoperative (A) and postoperative (B) corneal topography with Raytracing; Note the improvement of the Raytracing. (Note the reduction in the difference between the highest and lowest radii of curvature in the central cornea in the topography image with a less marked improvement in the ray tracing where the peak distance and distortion index are less than preoperative, and the base diameter which correlates with the spherical aberration has become more regular).
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The corneal surface was left smooth. Almost all patients (89.3%) subjectively noted improvement of the visual acuity and disappearance of the visual aberrations that previously impaired their quality of vision. This coincided with the improvement in the peak distortion and the Ray Tracing (Figure 13-4).
Discusion The results of this study could add the excimer laser plano Scan surgery assisted by sodium hyaluronate 0.25% (LASERVIS CHEMEDICA, Ophthalmic line, Munchen, Germany) (ELASHY) to the tools useful for the treatment of irregular astigmatism, both with and without defined pattern. The clinical indications include irregular astigmatism caused by irregularity in flap or irregularity on stromal base induced by laser in situ keratomileusis (LASIK). Excimer laser application in PTK mode may be undertaken to improve various visual symptoms through improving the corneal surface 20, 21. PTK also can help in cases of irregularities and opacities on corneal surface or anterior stroma, induced by LASIK. In 1994, Gibralter and Trokel applied excimer laser in PTK mode to treat a surgically induced irregular astigmatism in two patients. They used the corneal topographic maps to plan focal treatment areas with good results 5. The correction of irregular astigmatism should be considered one of these therapeutic indications. The use of a viscous masking agent should increase the efficiency of the procedure, through protection of the valleys between the irregular corneal peaks, leaving these peaks of pathology exposed to laser treatment. In this study, we used the sodium hyaluronate 0.25% (LASERVIS CHEMEDICA, Ophthalmic line, Munchen, Germany) for this purpose. When the treatment is performed on corneal surface, Bowman’s membrane is removed. However, the new epithelium was able to grow and adhere well to the residual stroma. Interestingly, none of our patients developed significant postoperative haze (grade II – III) – normally seen after PRK -, even those subjected to surface treatment. We suggest this effect could be due to the protective properties of the viscoelastic agent, sodium hyaluronate 0.25% (LASERVIS CHEMEDICA, Ophthalmic line, 180
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Munchen, Germany), against the oxidative free radical tissue damage 22. Many authors have evaluated different masking agents 18,19. Methylcellulose is the most commonly used agent and is available in different concentrations. Some properties of the methylcellulose, such as to turn white during ablation due to its low boiling point, make this substance not ideal for the purpose of this study. We found sodium hyaluronate 0.25% (LASERVIS CHEMEDICA, Ophthalmic line, Munchen, Germany) the most suitable for our purpose. It has a photoablation rate similar to that of the corneal tissue. Its stability on the corneal surface forms a uniform coating that fills the depressions on the cornea, protecting them against ablation by the laser pulses 18. Adding fluorescein to the viscous Contents masking solution is very useful to observe the excimer laser action during corneal ablation at the corneal Section 1 surface. With experience, it is very easy to distinguish between the ablated areas (in dark) and the Section 2 marked areas (in green) while the laser radiation is Section 3 ablating the cornea during the treatment. The actual corneal ablation is equal to 63% Section 4 of the ablation depth programmed in the software of the excimer laser 23. If the corneal surface has a Section 5 masking agent, the initial effect of the laser will be Section 6 ablating the viscous masking. The viscous masking solution functions to Section 7 shield the tissues partially. Multiple applications of viscous masking solution often are required, and a Subjects Index familiarity with the ablation characteristics will be learned with experience. When the laser ablation is performed on corneal surface, we increase the ablation by 50 mm, necessary for the epithelium ablation 24. ELASHY was originally designed for the Help ? correction of those irregular astigmatism cases that did not show a pattern and were not available to SELZA correction, yet it proved to be as effective in cases with pattern irregular astigmatism. Ray Tracing improved considerably, coinciding with the improvement of the visual subjective symptoms. The Superficial Corneal Surface Quality and image distortion were improved, achieving values significantly better than the preoperative values. This demonstrates that a relationship exists between the quality of the corneal surface and the quality of
IRREGULAR ASTIGMATISM: LASIK AS A CORRECTING TOOL
the vision. When the corneal surface is smoothened, the halos, glare and refractive symptoms improve 25. From our results, we can also conclude that the procedure achieves more stability with time, improving from the 3rd to the 6th months. Further follow up of these cases should be carried on to obtain better judgment of the biomechanical response of these special corneas to the procedure and to decide a proper timing for a re-intervention if necessary.
3.Topographic Linked Excimer Laser Ablation (TOPOLINK) About forty percent of human corneas show some irregularities that cannot be taken into account in a standard basis treatment with excimer laser 26. For these patients, and for those suffering an irregular astigmatism after trauma or refractive surgery, a custom-tailored, topography-based ablation, which has been adapted to the corneal irregularity, would be the best approach to improve not only their refractive problem but also to improve their quality of vision. This treatment was the first step in customized ablation depending mainly on the corneal topography as well as the refraction for calculating the treatment. It aimed at obtaining the best corrected visual acuity that can be attained by wearing hard contact lenses. Its requirements were an excimer laser with spot scanning technology, in which a small laser spot delivers a multitude of single shots fired in diverse positions to fashion the desired ablation profile. The laser spot is programmable, thus any profile could be obtained. A videokeratography system that provides an elevation map at high resolution is needed, and specific software is used to create a customized ablation program for the spot scanner laser.
Methods The aim of this study was to fashion a regular corneal surface in 41 eyes of 41 patients with irregular astigmatism induced by LASIK: 27 eyes (51,9%) had irregular astigmatism with a defined pattern; 14 eyes (48,1%) had irregular astigmatism without a defined pattern.
All cases were treated with a Plano Scan Technolas 217 C-LASIK Scanning spot Excimer laser (Bausch & Lomb, Chiron Technolas GmbH, Doranch, Germany) assisted by a C-SCAN ColorEllipsoid-Topometer (Technomed GmbH, Germany). We performed several corneal topographies of same eye; the software of the automated corneal topographer selected the four exactly equal. These corneal maps, the refractive error, the pachymetry value and desired k-readings calculated for each patient were sent to Technolas by modem. The information was analyzed and a special software program for each patient was created, including it in the Technolas 217 C-LASIK excimer laser by system modem. The basis for the topography-assisted procedure was the preoperative topography 12,27. This data was transferred into true height data and the treatment for correcting the refractive values in sphere and astigmatism, taking into account the corneal irregularities, was calculated. After that, a postoperative topography was simulated. With this technique, real customized treatment should become a reality, not only treating the refractive error but also improving the patient’s visual acuity.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Results
Section 6
After 3 months of the surgery: The mean preoperative UCVA improved from 20/80 ±0.25 Section 7 (range 20/400 - 20/60) to 20/40±0.54 (range 20/100 Subjects Index - 20/32); mean preoperative BCVA improved from 20/60±0.20 (range 20/200 - 20/32) to 20/32±0.15 (range 20/60 - 20/25). This proved to be statistically significant (p<0.001). Even though emmetropia was our goal, it was considered more important to achieve a regular corneal surface. The spherical equivalent of the indiHelp ? vidual refraction was taken into account in determining the corneal k-value. Preoperatively, mean sphere was -0.26 ±4.50 D (range –5.75 to +3.70 D) and mean cylinder was –1.71±3.08 D (range –6.00 to +2.56 D). Three months after surgery, the mean sphere was 0.70±1.25 D (range –1.75 to +1.50 D) and the mean cylinder was -0.89±1.00 D (range –1.92 to +1.00).
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Corneal topography improved significantly in those cases that presented an irregular astigmatism with a defined pattern. The mean Corneal Surface Quality improved from 45% (range 35% - 60%) to 76.6% (range 60.06% - 96.43%). The corneal surface is left smooth and the Ray-Tracing improved in the peak distortion, coinciding with the improvement of the visual acuity (Figure 13-5). In 60.29% patients the visual aberrations disappeared. At 3 months of follow up, the safety of the procedure was 74.31%, the efficacy (Figure 13-6) in
%UCVA 20/40 was 63.68% and the predictability for the spherical equivalent within the ± 1D zone was 68.23%.
Discussion Using the corneal topographic map as a guide, excimer laser ablation can be used to create a more regular surface with improved visual acuity. In a program consisting of a combination of phototherapeutic and photorefractive ablation pat-
A
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7
B
Subjects Index
Help ?
Figure 13-5: Topolink: Preoperative (A) and postoperative (B) corneal topography with Raytracing. (Note the improvement in the topography image with reduction in the difference between the highest and lowest radii of curvature in the central cornea. This is reflected in the ray tracing where the peak distance and distortion index are reduced and the base diameter has become more regular).
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Figure 13-6: Efficacy of the Topolink procedure at 3 months. (UCVA improved from 20/80 ±0.25 (range 20/400 - 20/60) to 20/40±0.54 (range 20/100 - 20/32) and 63.68% of patients had an UCVA of 20/40 or better)
terns, the amount of tissue to be removed is calculated on the basis of the diameter and steepness of the irregular areas of the corneal surface. At present, customized ablation based on topography can improve spectacle-corrected visual acuity. Limitations for this technique exist. With this procedure some irregular astigmatisms cannot be corrected. Some patients could not be selected as candidates for Topolink because any of the following criteria were present: 1. Different between steep and flat meridians more than 10D at the 6,0 mm treatment area. 2. Corneal pachymetry was not thick enough (< 400 mm). 3. Diameter of the corneal topography more than 5.0 mm. 4. Corneal topography showing an irregular astigmatism with undefined pattern (irregularly irregular). This preliminary study showed that topographic-assisted LASIK (Topolink) could be a useful tool to treat irregular astigmatism. This technique was, as aforementioned, the early stage of developing customized ablation. The surgeon depends only on the Placido topographic images, their precision
Figure 13-7: Aberromety, Clinical example of a preoperative normal eye showing the patient’s refraction, aberrography in a color-coded scale map with and without the astigmatic component (to segregate high order aberrations), the simulated point spread function of this eye following a standard treatment (high order aberrations are expected to survive) and following an aberrography based treatment (high order aberrations eliminated).
and their reproducibility. To the moment, this cannot provide us with the actual customization and we are still left with some patients waiting for a solution.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
The Future
Section 6
A new view of customization could be Section 7 achieved with more reliable instruments (elevation Subjects Index topography, aberrometer, etc...). As aforementioned, wavefront analysis (aberroemtery, Figure 13-7) can measure the refractive state of the entire internal ocular light path 8. Using this technology, it has been shown that using only the refractive error of the eye to treat the ammetropia can greatly increase optical aberrations within the eye 28. Increases in wavefront Help ? aberrations are evident after both PRK and LASIK 29, and increased spherical aberration has been shown to occur in cases of increased corneal astigmatism 30. This increase in spherical aberration and coma will interfere with visual function, particularly in lowlight conditions where the pupil size increases, increasing the effect of aberrations within the eye, a condition that is diminished in daylight where the pupil constricts 31. We are now conducting the second phase of a study incorporating the data of the wafefront analyLASIK AND BEYOND LASIK
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sis using the ZyWave aberrometer (BAUSCH & LOMB, CHIRON Technolas GmbH, Doranch, Germany) together with the elevation topography of the Orbscan II (Orbtek, Bausch & Lomb Surgical, Orbscan II corneal topography, Salt Lake City, Utah, USA) to correct ametropia. To the moment the system is under trial, and is only applicable to regular virgin corneas. With the proper development of the technique, we think that it would provide us with the real customized ablation necessary not only for our desperate irregular astigmatism patients but also for obtaining a super vision for ametropes who are to be treated for the first time.
Other Surgical Procedures Automated Anterior Lamellar Keratoplasty This technique was originally designed to treat superficial stromal disorders, but it has also been used for the treatment of difficult cases of irregular astigmatism, with very poor results 32. The surgeon performs phototherapeutic keratectomy or a microkeratome lamelar resection to 250-400 mm stromal depth, followed by trasplantation of a donor lamella of the same dimension on to the recipient bed33. We have limited experience with this subject. We think it is a good option for patients with thin corneas, and with the preservation of the Descemet’s membrane, the complications of rejection should be extremely minimized if not eliminated. However, the subject is out of the scope of discussion in this chapter.
tism whether natural as in keratoconous or surgically induced. To the moment we have a little experience with this technique, which is also beyond the scope of this chapter.
Other Non-Surgical Procedures Contact Lens Management Contact lenses are sometimes needed in the postoperative management of refractive surgery. This need arises as it has become evident to the refractive surgeon that an undesirable result has occurred. The decision of contact lens fitting has to be based on the impossibility of performing new surgeries, or the willing of the patient 36. Contents
Summary
Section 1
It is clear from the previous discussions that Section 2 the subject of irregular astigmatism is still under Section 3 investigation. In spite of the availability of various methods attempting to solve this problem, we are left Section 4 with patients who are not satisfied with their vision and are in need for intervention. Penetrating kerato- Section 5 plasty is an ultimate solution that has to be under- Section 6 taken only when the patient has no other alternative. More effort should be done to try to help these Section 7 patients improving their corneal surface quality and Subjects Index BCVA. The evolution of newer techniques and the experience gained by refractive surgeons day after day represent a hope for irregular astigmatism patients.
REFERENCES
Intracorneal Ring Segments (INTACS) 1.
These segments were originally designed to correct low to moderate myopia by inducing flattening of the central cornea through intralamellar insertion of 2 PMMA ring segments in the corneal midperiphery 34. Studies indicated that the range of corneal asphericity before and after surgery, provided good visual acuity and normal contrast sensitivity 10, 35. These segments could be used to modify the corneal surface in patients with irregular astigma-
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2.
3.
Goggin M, Alpins N, Schmid LM. Management of irregular astigmatism. Curr Opin Ophthalmol 2000; 11: 260-266 Alió JL, Artola A, Claramonte PJ, et al. Complications of photorefractive keratectomy for myopia: two year follow-up of 3000 cases. J Cataract Refract Surg 1998, 24: 619-26. Azar DT, Strauss I. Principles of applied optics. In: Albert DM, Jakobiec FA, eds. Principles and Practice of Ophthalmology, Vol 5. Philadelphia, PA, WB Saunders Co, 1994: 3603-3621.
Help ?
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17. 18.
19.
Duke-Elder S (Ed): Pathological refractive errors. In System of Ophthalmology. London: Publisher; 1970: 363. Gibralter R, Trokel SL. Correction of irregular astigmatism with the excimer laser. Ophthalmology 1994; 101: 1310-1315. Alpins NA. Treatment of irregular astigmatism. J Cataract Refract Surg 1998; 24: 634-646. Alió J.L, Artola A, Rodríguez-Mier F.A. Selective Zonal Ablations with excimer laser for correction of irregular astigmatism induced by refractive surgery. Ophthalmology 2000; 107: 662-73. Harris WF: Wavefronts and their propagation in astigmatic optical systems. Optom Vis Sci 1996,73:606– 12 Dick HB, Krummenauer F, Schwenn O, et al. Objective and subjective evaluation of photic phenomena after monofocal and multifocal intraocular lens implantation. Ophthalmology 1999; 106: 1878-86 Holmes-Higgin DK, Burris TE, and The INTACS Study Group. Corneal surface topography and associated visual performance with INTACS for myopia. Phase III clinical trial results. Ophthalmology 2000; 107: 2061-71. Alió JL, Belda JI, Shalaby AMM. Excimer Laser Assisted by Sodium Hyaluronate for correction of irregular astigmatism (ELASHY). Accepted for publication to Ophthalmology, September 2000. Wiesinger-Jendritza B, Knorz M, Hugger P, Liermann A. Laser in situ keratomileusis assisted by corneal topography. J Cataract Surg 1998; 24:166-174 Sher NA, Kreuger RR, Teal P, et al. Role of topical corticoids and nonsteroidal anti-inflammatory drugs in the etiology of stromal infiltrates after photorefractive keratectomy. J Refract Corneal Surg 1994; 10:587-588. Koch DD, Kohnen T, Obstbaum SA, Rosen ES. Format for reporting refractive surgical data. [letter]. J Cataract Refract Surg 1998; 24:285-287. Munnerlyn C, Koons S, Marshall J. Photorefractive Keratectomy: A technique for laser refractive surgery. J Cataract Refract Surg 1988; 14:46-52. Buzard K, Fundingsland B. Treament of irregular astigmatism with a broad beam excimer laser. Journal of refractive. J Refract Surg 1997; 13:624-636. Seitz B, Behrens A, Langenbucher A. Corneal topography. Curr Opin Ophthalmol 1997; 8: 8-24. Kornmehl E.W; Steiner R.F; Puliafito C.A. A comparative study of masking fluids for excimer laser phototherapeutic keratectomy. Arch Ophthalmol 1991;109:860-863. Kornmehl EW, Steinert RF, Puliafito CA, Reidy W.
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Morphology of an irregular corneal surface following 193 nm ArF excimer laser large area ablation with 0.3% hydroxypropyl methylcellulose 2910 and 0.1% dextran 70.1% carboxy-methylcellulose sodium or 0.9% saline (ARVO abstracts). Invest Ophthalmol Vis Sci 1990; 31:245. Trokel S.L, Srinivasan R, Braren B. Excimer laser surgery of the cornea. Am J Ophthalmol 1983; 96:705710. Orndahl M, Fagerholm P, Fitzsimmons T, Tengroth B. Treatment of corneal dystrophies with excimer laser. Acta Ophthalmol 1994; 72: 235-240. Artola A, Alió JL, Bellot JL, Ruiz JM. Protective properties of viscoelastic substances (sodium hyaluronate and 2% hydroxymethyl cellulose) against experimental free radical damage to the corneal endothelium. Cornea 1993; 12: 109-114. Kreuger RR, Trokel SL. Quantification of corneal ablation by ultraviolet light. Arch Ophthalmol 1986; Contents 103:1741-1742. Seiler T, Bendee T, Wollensak J. Ablation rate of Section 1 human corneal epithelium and Bowman’s layer with the excimer laser (193nm). J Refract Corneal Surg. Section 2 1990; 6: 99-102. Section 3 Klyce SD, Smolek MK. Corneal topography of excimer laser photorefractive keratectomy. J CataSection 4 ract Refract Surg 1993;19:122-130. Bogan SJ, Waring GO III, Ibrahim O, et al. ClassifiSection 5 cation of normal corneal topography based on computer-assisted videokeratography. Arch Ophthalmol Section 6 1990; 108: 945-949. Section 7 Dausch D, Schröder E, Dausch S. Topography-controlled excimer laser photorefractive keratectomy. J Subjects Index Refract Surg 2000; 16: 13-22. Mierdel P, Kaemmerer M, Krinke H-E, Seiler T: Effects of photorefractive keratectomy and cataract surgery on ocular optical errors of higher order. Graefe’s Arch Clin Exp Ophthalmol 1999,237:725– 729. Oshika T, Klyce SD, Applegate RA, et al.: Comparison of corneal wavefront aberrations after Help ? photrefractive keratectomy and laser in situ keratomieusis. Am J Ophthalmol 1999,127:1–7. Seiler T, Reckmann W, Maloney RK: Effective spherical aberration of the cornea as a quantitative descriptor in corneal topography. J Cataract Refract Surg 1993,19(Suppl):155–165. Applegate RA, Howard HC: Refractive surgery, optical aberrations and visual performance. J Refract Surg 1997,13:295–299. Sugita J., Kondo J. Deep lamellar keratoplasty with complete removal of pathological stroma for vision improvement. Br J Ophthalmol 1997; 81: 184-8 LASIK AND BEYOND LASIK
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Chapter 13 33. Melles GRJ, Remeijer L, Geerards AJM, Beekhuis WH. The future of lamellar keratoplasty. Curr Opin Ophthalmol 1999; 10: 253-259. 34. Ruckhofer J, Stoiber J, Alzner E, Grabner G. Intrastromal corneal ring segments (ICRS, KeraVision Ring, Intacs): clinical outcome after 2 years. Klin Monatsbl Augenheilkd 2000; 216:133-42 (abstract). 35. Holmes-Higgin DK, Baker PC, Burris TE, Silvestrini TA. Characterization of the aspheric corneal surface with intrastromal corneal ring segments. J Refract Surg 1999; 15: 520-8. 36. Zadnik K. Contact lens management of patients who have had unsuccessful refractive surgery. Curr Opin Ophthalmol 1999; 10: 260-263.
Prof. Jorge L. Alió, M.D. Instituto Oftalmologico de Alicante Avda. de Denia 111, 03015 Alicante – Spain Tel. +34-96-5150025 E-mail:
[email protected]
Contents
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LASIK IN MIXED ASTIGMATISM
Chapter 14 LASIK IN MIXED ASTIGMATISM Melania Cigales, MD. Jairo E. Hoyos, MD. Jairo Hoyos-Chacón, MD.
Corneal astigmatism occurs when the curvatures of the principal meridians of the cornea at right angles to each other are different (one is steep, the other flat). Thus, when a ray of light from a point image crosses an astigmatic cornea, it divides into two focal lines that are projected in front and/or behind the retina. Depending on where these focal lines are projected with respect to the retina, we can classify astigmatism as myopic, hyperopic or mixed. Figure 14-1 shows the typical placido disc topography of a corneal astigmatism of 4.5 diopters (D). The Sim K (simulated keratoscopic reading) indicates that the steepest meridian (dioptric power 45.0 D) is at 90º and the flattest meridian (dioptric power 40.5 D) is at 180º. Using this as an example, we shall classify astigmatism and analyze its treatment with LASIK.
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Section 5 Figure 14-1- Topographic image of corneal astigmatism
Section 6 Section 7 Subjects Index
CLASSIFICATION OF ASTIGMATISM
Simple Myopic Astigmatism In simple myopic astigmatism one of the focal lines is projected in front of the retina and the other is brought to focus on the retina. Following the example described above, figure 14-2 shows a simple myopic astigmatism of refraction: Plano –4.5 x 180º. In this case, the steep meridian (45.0 D x 90º) has a myopic power of –4.5 D and projects an image in front of the retina; and the flat meridian (40.5 D x 180º) is emmetropic and brings an image to focus on the retina. To treat this astigmatism, we need to flatten the steep axis (45.0 x 90º) without modifying the flat
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Figure 14-2- Simple myopic astigmatism
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Figure 14-3- Compound myopic astigmatism
Figure 14-4- Simple hyperopic astigmatism
meridian (40.5 D x 180º). To do this, the ablation is performed with a negative cylinder of –4.5 x 180º. Ablation is performed in the center of the cornea by carving a cylinder that opens onto the steep meridian such that this axis is flattened until it becomes emmetropic.
Contents
Section 1 Section 2
Section 3
Compound Myopic Astigmatism
Section 4
In compound myopic astigmatism, both focal lines are projected in front of the retina. Following the example, figure 14-3 shows a compound myopic astigmatism of refraction -2 –4.5 x 180º. In this case, the steep meridian (45.0 D x 90º) has a myopic power of –6.5 D and projects an image in front of the retina; and the flat meridian (40.5 D x 180º) has a myopic power of –2.0 D and also projects an image in front of the retina. To treat this astigmatism we need to flatten both meridians, but one more than the other. For this we perform the ablation with a negative cylinder (–4.5 x 180º) to flatten the steepest axis (45.0 x 90º) from –6.5 to –2.0 D. Then, on the spherical cornea obtained, we perform a central spherical ablation of –2.0 D that flattens both axes until emmetropy.
Simple Hyperopic Astigmatism In simple hyperopic astigmatism, one focal line is projected behind the retina and the other is brought to focus on the retina. Following the example, figure 14-4 shows a simple hyperopic astigmatism of
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Section 5
Section 6 Figure 14-5- Compound hyperopic astigmatism
Section 7
refraction: Plano +4.5 x 90º (or its transposition +4.5 Subjects Index –4.5 x 180º). In this case, the flat meridian (40.5 D x 180º) has a hyperopic power of +4.5 D and projects behind the retina; and the steep meridian (45.0 D x 90º) acts emmetropically and projects focal lines on the retina. To treat this astigmatism, we need to steepen the flat axis (40.5 D x 180º) without modifying the steep Help ? axis (45.0 x 90º), which is emmetropic. To do this we perform the ablation using a positive cylinder (+4.5 x 90º). Ablation is performed along the periphery of the flattest meridian, steepening it until it becomes emmetropic.
Compound Hyperopic Astigmatism In compound hyperopic astigmatism, both focal lines are projected behind the retina. Following
LASIK IN MIXED ASTIGMATISM
Figure 14-6-A- Mixed astigmatism
Figure 14-6-B- Treatment models for mixed astigmatism
the example, figure 14-5 shows a compound hyperopic astigmatism of refraction: +1.5 +4.5 x 90º (or its transposition +6 –4.5 x 180º). In this case, the steep meridian (45.0 D x 90º) has a hyperopic power of +1.5 D and projects behind the retina; and the flat meridian (40.5 D x 180º) is of hyperopic power +6.0 D and also projects images behind the retina. To treat this type of astigmatism, we need to steepen both meridians, but one more than the other. To do this we perform the ablation using a positive cylinder (+4.5 x 90º) to steepen the flat axis (40.5 x 180º) from +6.0 to +1.5 D and, once the cornea is spherical, we perform a spherical peripheral ablation of +1.5 D, which steepens both axes until they become emmetropic.
(figure 14-6-B): negative cylinder with positive sphere, positive cylinder with negative sphere or bitoric treatment, where positive and negative cylinders are combined. Based on clinical cases, these three treatment models are examined below.
Mixed Astigmatism In mixed astigmatism, one focal line is projected in front of the retina and the other is projected behind the retina. Following the example, figure 14-6-A shows a mixed astigmatism of refraction: +2 –4.5 x 180º. In this case, the steep meridian (45.0 D x 90º) has a myopic power of –2.5 D and projects an image in front of the retina; and the flat meridian (40.5 D x 180º) is hyperopic (+2.0 D) and projects an image behind the retina. To treat this astigmatism, we need to flatten the steep axis (45.0 x 90º), which is myopic, and steepen the flat hyperopic axis (40.5 D x 180º). This may be done according to several treatment models
Contents
Section 1 Section 2
Negative Cylinder Ablation to Treat Mixed Astigmatism
Section 3
Section 4
Figure 14-7-A shows an example of mixed astig- Section 5 matism of refraction: +4 –5 x 170º and a topographic Sim K of 43.5 x 80º / 38.6 x 170º. In this case, the Section 6 steep meridian (43.5 D x 80º) has a myopic power of Section 7 –1.0 D and projects an image in front of the retina; and the flat meridian (38.6 D x 170º) is hyperopic Subjects Index (+4.0 D) and projects images behind the retina. This astigmatism was treated using the negative cylinder
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Figure 14-7-A- Negative cylinder ablation to treat mixed astigmatism
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Figure 14-7-B- Differential map of treatment of mixed astigmatism with negative cylinder ablation
ablation. We programmed the ablation for a negative cylinder of -5 x 170º to flatten the steep axis (43.5 x 80º) from -1 to +4 D. Once the cornea was spherical, we performed a spherical peripheral ablation of +4 D to steepen both axes until emmetropy. The post-operative refractive outcome was +0.5 –1 x 170º. The differential map (figure 14-7-B) shows that this treatment induced a flattening of 0.75 D of the steep axis (43.5 x 80º), which had a myopia of –1 D and a steepening of 3.25 D of the flat axis (38.6 x 170º), which was hyperopic (+4.0 D).
Positive Cylinder Ablation to Treat Mixed Astigmatism Figure 14-8-A shows an example of mixed astigmatism of refraction +2 –4 x 20º (or its transposition –2 +4 x 110º) and a topographic Sim K of 43.1 x 110º / 39.4 x 20º. In this case, the steep meridian (43.1 D x 110º) shows a myopic power of –2.0 D and projects an image in front of the retina; and the flat meridian (39.4 D x 20º) has a hypermetropy of +2.0 D and projects behind the retina. This time, treatment was performed using the positive cylinder program. The excimer laser was programmed for an ablation of a positive cylinder of +4 x 110º. This steepened the flat axis (39.4 x 20º) from +2 to -2 D. Next, we performed a spherical central ablation of 2 D on the now spherical cornea which flattened the axes until they became emmetropic.
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Figure 14-8-A- Positive cylinder ablation to treat mixed astigmatism
Contents
Section 1 Section 2
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Section 4
Section 5 Figure 14-8-B- Differential map of treatment of mixed astigmatism with positive cylinder ablation
Section 6 Section 7 Subjects Index
The differential map (figure 14-8-B) shows that treatment led to a flattening of 2.25 D of the steep axis (43.1 x 110º), which showed a myopia of –2, and a 1.75 D steepening of the flat meridian (39.4 x 20º), which showed a hypermetropy of +2.0 D.
Bitoric Ablation to Treat Mixed Astigmatism Figure 14-9-A shows an example of mixed astigmatism of refraction +2.25 –4 x 90º and a topographic Sim K of 43.2 x 180º / 40.0 x 90º. In this case, the steep meridian (43.2 D x 180º) shows a myopic power of –1.75 D and projects an image in front of the retina, whereas the flat meridian (40.0 D x 90º) is
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LASIK IN MIXED ASTIGMATISM
Figure 14-9-A- Bitoric ablation to treat mixed astigmatism
hyperopic to the extent of +2.25 D and projects behind the retina. In this case, treatment was performed using the positive plus negative cylinder ablation. First, we programmed an ablation of a negative cylinder of –1.75 x 90º which flattened the steep axis (43.2 D x 180º), taking it from –1.75 D to emmetropy, followed by ablating a positive cylinder of +2.25 x 180º which steepens the flat axis (40.0 x 90º) from +2.25 to emmetropy. The postoperative refractive outcome was –0.5 x 40º. The differential map in figure 14-9-B shows that treatment leads to a flattening of 2.25 D of the steep axis (43.2 x 180º), which had a myopia of –1.75 D and a steepening of 2.25 D of the flat axis (40.0 x 90º), which showed a hypermetropy of +2.25 D. Using the three treatment models, the effect induced by ablation was similar: flattening of the steep axis and steepening of the flat axis. Nevertheless, the bitoric ablation method was most direct and resulted in the loss of least stromal tissue. When a bitoric approach is used, it is important to precisely know along which meridian we wish to perform each cylinder ablation and the dioptric power to be treated at each axis. We use the “Cigales-Hoyos bitoric rule” to calculate the two cylinders. The bitoric rule states: 1- Record the negative cylinder refraction. 2- Note the positive cylinder refraction (its transposition). 3- Cross spheres and axes of the formulae (see figure 14-10) to obtain the cylinders to be treated.
Figure 14-9-B- Differential map of bitoric treatment of mixed astigmatism
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Figure 14-10- Cigales-Hoyos bitoric rule
Figure 14-10 shows the application of the bitoric rule to the previous example. We apply this rule by performing the negative cylindrical ablation first. The bitoric ablation method was developed by Chayet to treat mixed and myopic astigmatism. Chayet, however, introduces a correction factor in his bitoric nomogram to compensate for his observation of hypermetropy induced by the negative cylinder along the meridian that is at right angles to it. A further form of treatment using a two cylinder method, is the cross-cylinder program described by Vinciguerra. This treatment was proposed for mixed and myopic compound astigmatism whereby half the amount of the cylinder is ablated along the steepest meridian and the remaining half along the flattest
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meridian. This is followed by central ablation of the spherical equivalent. Both these authors perform positive cylindrical ablation first.
Results of Lasik in Mixed Astigmatism Evaluation was made of the visual and refractive outcomes recorded in a series of 36 eyes of 24 patients with mixed astigmatism undergoing LASIK. Follow-up was at least one year. Three study groups were established according to the ablation method used: -Group 1 (negative cylinder plus positive sphere): 1 eye. -Group 2 (positive cylinder plus negative sphere): 12 eyes. -Group 3 (bitoric treatment): 23 eyes. Keratectomy was performed using the Automated Corneal Shaper microkeratome (Chiron Vision, Claremont, CA) using the 160 micron thickness plate. Ablation was performed with the broad beam Apollo laser (Apollo Vision Inc., California, CA). Negative cylinder ablation was performed for an optical zone of 4.5 mm and a transition zone of 6.5 mm. Positive cylinder ablation was performed for an optical zone of 5.5 mm and transition zone of 8.0 mm. Treatment was performed according to the “Cigales-Hoyos bitoric rule”, with negative cylinder ablation performed first. Refractive outcomes are shown in figure 14-11. The technique yielded predictable results in the treatment of mixed astigmatism using the three ablation models. No significant differences were shown among the methods. By performing the ablation according to the bitoric rule, we recorded no induced hypermetropy of the negative cylinder. Thus, the deviation noted by Chayet probably depends on the laser used and the ablation parameters, which should be tailored to suit each patient. Visual acuity values are provided in figure 14-12. Each group showed improved uncorrected and best-corrected visual acuity. No eye lost lines of vision. No significant difference in visual acuity was
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Figure 14-11- Bitoric treatment of mixed astigmatism: refractive outcomes
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Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Figura 14-12- Bitoric treatment of mixed astigmatism
Section 7 Subjects Index
shown between groups, although in group 3 (bitoric treatment), mean postoperative uncorrected visual acuity was better than best-corrected preoperative visual acuity. Help ?
Conclusion LASIK is an effective method of treating mixed astigmatism according to any of the three ablation models proposed. The bitoric form of treatment is the most physiological and results in the removal of
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least stromal tissue when we need to flatten one of the meridians and steepen the other. The “CigalesHoyos bitoric rule” is useful for calculating the two cylinders when the bitoric procedure is applied.
Suggested Readings - Chayet AS, Magallanes R, Montes M, Chavez S, Robledo N. Laser in situ keratomielusis for simple myopic, mixed, and simple hyperopic astigmatism. J Refract Surg 1998 Apr;14 (2 Suppl):S175-6. - Vinciguerra P, Sborgia M, Epstein D, Azzolini M, MacRae S. Photorefractive keratectomy to correct myopic or hyperopic astigmatism with a cross-cylinder ablation. J Refract Surg 1999 Mar-Apr;15 (2 Suppl):S183-5.
Contents
- Cigales M, Hoyos JE, Hoyos-Chacón J, Pradas J, Rodríguez-Mier F. Bitoric-LASIK for mixed astigmatism. ARVO Annual Meeting (abstract book). Fort Lauderdale (Florida-USA). Abril 30 – Mayo 5 de 2000, S690.
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Section 6 Section 7 Subjects Index
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RELASIK
Chapter 15 RELASIK T. Agarwal, M.D, J. Agarwal, M.D., P. Goel, M.D., S. Choudhry, M.D., Preetha R., M.D., R. Choudhry, M.D, S. Narasimhan, M.D.
Introduction After the introduction of Keratomileusis by Barraquer, there have been great developments in refractive surgery.1 Pallikaris et al started excimer laser in situ keratomileusis (LASIK) after lifting a flap.1 At present LASIK has become the first choice for eye surgeons for the treatment of high myopia. While LASIK surgeons performed corrections over 20 D, it is now limited to much lower levels of myopia to preserve the integrity of the cornea and quality of postoperative vision. While there is a great tendency for greater amounts of residual myopia after LASIK, for higher levels of myopia, often the degree of residual refraction is unpredictable. Surgeons have a responsibility to inform the patients, who want 100 % success from LASIK, that the objective of LASIK is to eliminate their dependency on glasses and contact lenses. The percentage of correction that is obtainable depends on several factors such as diopteric power of the patient, and a combination of different ametropias (myopia and astigmatism, hypermetropia and astigmatism).2 As the myopia increases, the amount of residual myopia and subsequent need for enhancement procedures increase as well.2 It may be necessary and useful to do an enhancement in order to refine the results obtained after the first surgery. As LASIK surgery is performed within the stroma, sparing the epithelium and Bowman’s membrane, it allows the surgeon a better adjustability to do a second ablation to correct any regression. It is a better procedure than RK and PRK over previous LASIK treatment because of its less complications like irregular astigmatism, tissue melting and overcorrection.2
There are two options for performing the reablation, lifting a flap with blunt dissection or performing a second cut usually six months after primary LASIK when the process of healing is almost complete. Contents
Procedure
Section 1
LASIK was performed in 1000 eyes within Section 2 20 months between January1997 and August 1998 Section 3 at our center. 50 eyes (5 %) of 29 patients (17 male and 12 female) had undergone retreatment with sec- Section 4 ondary LASIK. 21 patients had undergone the procedure bilaterally. All the eyes had a residual myo- Section 5 pia more than or equal to –1.0 D spherical equiva- Section 6 lent. The primary LASIK was performed with an Section 7 Automated Corneal Shaper (ACS) microkeratome Subjects Index (Bausch and Lomb) and Chiron Technolas Keracor 217 excimer laser. (Bausch and Lomb) Fluence was 130mJ/cm2, 10 Hz repetition rate, diameter 7.8 to 8.2 mm and multi zone algorithm with optical zone 4-6 mm. Retreatment with LASIK was done after 5.84 ± 3.24 (SD) months. Previous intraocular surgery, any posterior segment pathology, active inflamHelp ? mations and infections, corneal scarring, pachymetry value less than 410 µm, keratoconus, intraocular pressure more than 21 mmHg, narrow palpebral fissure and Schirmer’s test less than 5 mm were the exclusion criteria. Routine preoperative UCVA and BCVA in decimal equivalent of Snellen’s visual acuity chart, cycloplegic refraction, estimation of palpebral fissure, anterior segment evaluation with slitlamp biomicroscope, Schirmer’s test, intraocular pressure with applanation tonometry, corneal topography LASIK AND BEYOND LASIK
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(Tomey, TMS 2.1) pachymetry, corneal diameter and detailed fundus examination by indirect ophthalmoscopy were done. As a safety measure eyes having pachymetry less than 410 µm (250µm of stromal bed and 160µm of corneal flap) were excluded. If the patient came to us before 6 months of the primary LASIK we would lift up the same flap. If the patient came to us after 6 months we would recut the cornea. We found the results of both the techniques good with not much difference between the two groups. The same automated corneal shaper (ACS) microkeratome (Chiron vision) and Chiron Technolas Keracor 217 excimer laser, with the same algorithms was used. All the surgeries were performed under topical anesthesia using 4% lidocaine. Before starting the procedure all the instruments were checked . ACS microkeratome was test run on the base plate before each individual procedure. The eye was cleaned with Betadine‚ 5% solution. A speculum was used to keep the palpebral fissure wide open and eyelashes out of the field. The entrance pupil was marked with gentian violet tip marker. A reference mark was made on the cornea. The suction ring was centered on the corneal marking and activated. The Intraocular pressure was confirmed with the presurgical tonometer to be more than 65 mm Hg. In 10 eyes the primary flap was lifted with a blunt dissection using a spatula. In 40 eyes the second cut was made with the ACS microkeratome. The microkeratome was adjusted on the suction ring. It was moved forward with the forward footswitch untill it stopped at the permanent stopper to prevent a free cap. The microkeratome was then moved back with the reverse footswitch and was removed. Once the ablation was completed, the tissue and both sides of the flap were cleaned with balanced salt solution and with a Merocel sponge. After checking that there were no foreign particles in interface, the flap was reposited back into original position. The corneal reference markers were checked whether they were in apposition. The suction ring was removed. After a couple of minutes the flap was checked whether it had stuck or not. Then the speculum was taken out carefully. The patients were examined on the slit lamp half an hour after surgery and sent home. The patients were put on topical antibiotic tobramycin 3%, 196
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topical steroid dexamethasone 0.1 with a tapered dose and artificial tears for one month. The patients were reviewed on the first postoperative day, after one week, one month, six months and one year after surgery. At each follow up uncorrected and best spectacle corrected visual acuity, cycloplegic refraction, anterior segment evaluation, Intraocular pressure, corneal topography and detailed fundus examination were done.
Results The demographic data are shown in Table 1. All the patients were followed up. The mean postoperative period was 16.58 ± 3.06 (SD) months. Secondary LASIK was performed after a mean period of 5.84 ± 3.24 (SD) months. The mean spherical equivalent before secondary procedure was – 4.3 ± 1.83 D (SD). Mean pachymetry was 462.96 ± 27.05 (SD) µm. After RELASIK, postoperative spherical equivalent was -0.39 ± 0.67D (SD) on the first postoperative day and was -0.45 ± 1.16 D (SD) at the last follow-up. (p < 0.005). Mean pachymetry was
Contents
Section 1 Section 2
Section 3
Section 4
Table 1
Section 5
Section 6 Section 7 Subjects Index
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RELASIK Table 2
Contents
Section 1 Section 2
Table 3 Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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416.96 ± 27.05 (SD) µm. 31 (62%) eyes became emmetropic. 13 (26%) eyes were within ± 1 D of emmetropia. 5 (10 %) eyes were within ± 2 D of emmetropia. One (2 %.) eye had surgery induced irregular astigmatism of –3.5-D cylinders. At the last follow-up uncorrected visual acuity improved from 0.22 ± 0.15 (SD) to 0.56 ± 0.22 (SD) (p<0.05) after
the secondary procedure. 36 (72 %) eyes had UCVA more than 0.5, 12 (24 %) eyes had UCVA between 0.25 to 0.5. (Table –2). BCVA improved from 0.59 ± 0.19 (SD ) to 0.66 ± 0.22 (SD) at last followup. (Table- 3). In 17 eyes BCVA improved by 1 line on Snellen’s visual acuity chart. One eye lost one line of BCVA due to decentered ablation. . Post LASIK AND BEYOND LASIK
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Contents Figure 15-2: Corneal Topography-After Lasik
Section 1 Section 2
Figure 15-1: Relasik Corneal Topography-Before Lasik
Section 3
RELASIK corneal topography showed uniform central ablation in 49 eyes. (Figure 15-1 shows corneal topograph before LASIK. Figure 15-2 shows the corneal topograph after LASIK and Figure 15-3 shows the topograph of the same eye after RELASIK.) Only one eye showed decentered ablation.
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Section 6 Section 7 Subjects Index
Discussion LASIK has become increasingly popular among the eye surgeons to treat refractive errors like high myopias. Residual myopia is common in majority of the refractive procedures. The degree of correction obtained after surgery depends on several factors. Amount of residual power appears to be more common in young patients than adults. 4. Causes of undercorrection, which can be avoided, are improper data entry, poor calibration of laser, discrepancy between manifest and cycloplegic refraction. We tried to avoid them by meticulous cross-checking of data entry, careful preoperative cycloplegic refraction algorithm adjustments as necessary. 13 Several studies show that a higher rate of residual myopic refraction after LASIK for high myopia in comparison to moderate myopia. In one 198
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Figure 15-3: Corneal Topography- After Relasik
RELASIK
study A.M Bas et al divided patients into 4 groups depending on the diopteric power before LASIK . 1) –3.0 To –6.0 D 2) –6.25 to –10 D 3) –10.25 to –15 D 4) –15.25 to –25.5 D . After LASIK group 4 had shown residual myopia > -1.0 D (-1.49 ± 1.54 (SD).5 M.C Knortz et al had shown in eyes with myopia > -12 D, accuracy and patient satisfaction was sufficiently poor. In 28 % eyes residual power was > -1 D. 6,7.Perez et al observed similar results .8 Other possible mechanisms are proliferation of keratocytes in corneal stroma, epithelial hyperplasia and central corneal thickness associated with central corneal steepening. 2,9,12 As LASIK surgery was performed intrastromally, it allows the surgeon to do a second ablation to correct any undercorrection or any defect, which have occurred during the first surgery. One can do RK or PRK as an enhancement procedure after LASIK, but it has several disadvantages like the possibility of overcorrection, irregular astigmatism, tissue melting and limitation in correcting high myopia.2 Postoperative refraction in high myopia is supposed to be settled after six months.2 In 10 eyes where we did RELASIK within 3 months of the primary procedure, we could reopen the corneal flap by blunt dissection using a spatula. In 40 eyes we did the secondary procedure after six months. At this time as the healing was almost complete, we could not reopen the flap by blunt dissection. So we used the second cut for RELASIK using the same algorithms but used the residual myopia as a subjective refraction . We limited our ablation zone between 4-6 mm to prevent night glare problems due to smaller zone and unnecessary vertex ablation and overcorrection due to larger zone ablations. 4 As a safety we excluded the patients having pachymetry less than 410 µm (250µm-stromal bed and 160 µm of corneal flap) from the study. 2,3 The Mean spherical equivalent improved from -4.3 ± 1.83D (SD) to –0.45± 0.68(SD) at the last follow-up. (p< 0.005). The UCVA improved from 0.22 ± 0.15 (SD) to 0.53 ± 0.22 (SD) at the last follow-up. (p<0.05). 17 eyes gained one line of BSCVA. Only one eye lost one line of BSCVA due to decentered ablation .No sight threatening complications had occurred.
We compare our study with the study of Ozdamer et al who did secondary LASIK on six eyes who had mean residual myopia of –6.20 ±1.10 D(SD) After RELASIK, spherical equivalent was –0.18 ± 0.77 D (SD) .10 J.J. Perez et al did RELASIK on 59 eyes. Spherical equivalent improved from –2.92 ± 1.22D (SD) to –0.44 ± 0.88 D (SD) at 6 months and -0.61 ± 0.82D (SD) at 12 months.11 In summary we find RELASIK is a safe, effective and stable procedure for the treatment of residual myopia after primary procedure. But proper selection of the patients is necessary before LASIK for better results.
REFERENCES Contents 1) Ionnis Pallikaris,T.G.Papadaki; From Keratomileusis in situ to LASIK .The evaluation of lamellar corneal Section 1 procedures, Refractive Surgery ,Jaypee ,20,211-215 2) Gullermo Avalos ; RELASIK, Refractive Surgery, Section 2 Jaypee, 36,364-381 Section 3 3) Amar Agarwal, T. Agarwal, R.R. Sashikanth; Automatic Corneal Shaper, Refractive Surgery, Jaypee, 23, Section 4 238- 246. 4) L.E. Frost, J.Woolfson, M Kritzinger; Predictive forSection 5 mulas for LASIK, Refractive Surgery, Jaypee, 21,218- 228 Section 6 5) Arturo.M.Bas, R.Onnis ; Results of laser in situ keratomileusis in different degrees of myopia, OphSection 7 thalmology, April 1998 6) M.C.Knorz,B.Weisinger , A.Leirman and V.Seiberth Subjects Index et al ; Laser in situ keratomileusis for moderate and high myopia and myopic astigmatism., Ophthalmology, May 1998 7) M.C.Knorz, Jendritza B, and Liermann A et l; LASIK for myopia correction ,2 year follow-up, Ophthalmology, July 1998, 95:,7,494-8 8) Perez Santonja J.J., Bellot J, ClarmonateP and Ismail Help ? et al; Laser in situ keratomileusis to correct high myopia, J.C. and Reefer Surg, 1997, Apr. 23: 3,37285. 9) A.C. Chayet ,K.K. Assil ,M.Montes and M.E. Lagana et al ; Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia, Ophthalmology, July 1998 10) A .Ozdamar, C Aras, H. Bahcecioglu, B.Sener; Secondary laser in situ keratomileusis , 1 year after primary LASIK for high myopia, J.C. Ref.Surg, vol25, March 1999.
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Chapter 15 11) J.J. Perez&ndash, Santonja, M.S. Ayala and H.F. Sakla et al; Retreatment after laser in situ keratomileusis, Ophthalmology, January 1999. 12) Lohman C.P, Guell JL; Regression after LASIK for treatment of Myopia, Role of corneal epithelium, Semin Ophthalmology, 1998 June 13: 2. 79-82 13) Howard Gimbel ,E.E. Permo; LASIK the Technique, Refractive Surgery, Jaypee,25, 254-265. 14) Guell J.L, Lohman C.P, Melecaze FA and Junger J et al; Intraepithelial Photorefractive Keratectomy for regression after LASER in situ Keratomileusis, J.C. Ref Surg, 1999 May 25: 5, 670-4.
T. Agarwal, M.D. Dr. Agarwal’s Eye Hospital, 19 Cathedral Road, Chennai (Madras)- 600 086, India
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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LASIK AFTER RK AND PRK
Chapter 16 LASIK AFTER RK AND PRK S. Agarwal, M.S., N. Mathur, M.D., T. R. Indumathy, M.D., A. Bagmar, M.D.
Introduction Over the years great attempts have been made to permanently correct refractive errors like high myopia. Surgical procedures that have been used in attempt to correct high myopia include radial keratotomy (RK), keratomileusis, keratophakia, freeze myopic keratomileusis, Excimer laser keratectomy (PRK) and Laser in situ keratomileusis (LASIK)1,2.Among these, radial keratotomy (RK) has been the most popular5. In this procedure, radial incisions flex the peripheral cornea, leading to a compensatory flattening of central cornea. The amount of central flattening that can be achieved with RK, however, is limited5. Although various algorithms were used, radial keratotomy was found to be associated with frequent failures in achieving emmetropia, with surgical results often shifting towards hyperopia2. Because of this possible shift, surgeons tend to undercorrect myopia. Patients therefore frequently need correction with spectacles or contact lenses. Residual myopia after RK, whether intentional or unexpected, may result when RK surgery did not entirely correct a patient’s myopia because of a large optical zone, few incisions, or shallow incisions. If necessary, a later redeepening procedure, which extends existing RK incisions and places additional incisions, may be required to correct the residual error5,15. Although excimer laser PRK is effective, predictable, and safe in treating myopia, undercorrections persist in some highly myopic eyes even after one or more repeated procedures due to the limitations of available techniques or the unique tissue response of each eye. As LASIK surgery is
performed within the stroma, sparing the epithelium and Bowman’s membrane, it allows the surgeon better adjustability to do ablation to correct any regression. We conducted a retrospective analysis of 20 eyes treated with LASIK for residual myopia. Ten eyes had formerly been treated with RK, and ten had been treated with PRK. The five post RK patients were all male; there were three males and two females in the post PRK group.
Lasik After RK and PRK
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Ten post RK eyes of five patients (all male) Section 6 and ten post PRK eyes of five patients (three males and two females), which were subjected to LASIK Section 7 procedure to correct residual myopia, were retrospectively analyzed. The average age (in years) of the Subjects Index patients among the post RK group was 25.6 ± 6.88 SD, and among the post PRK group it was 33.67 ± 5.77 SD. The mean interval between the primary procedure and LASIK was 24.30 ± 0.75 (SD), with a range of 14 to 36 months. The mean interval in the post RK group was 22 ± 1.07 (SD), with a range of Help ? 20 to 24 months in the post PRK group. Patients were treated with the LASIK procedure only if there was a stable residual refractive power > - 1.25 D for at least 1 year, if they did not want to wear spectacles, and if did not tolerate contact lenses. A full informed consent was obtained from all the patients before the procedure. Exclusion criteria included any active corneal pathology or inflammation, corneal scars, monocular patients, keratoconus and thin corneas, raised Intraocular pressure (more than 21 mm Hg), the presLASIK AND BEYOND LASIK
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ence of active collagen vascular disease, pachymetry less than 420 mm, narrow palpebral fissure, or Schirmer ‘s test less than 5mm. Routine preoperative tests included UCVA and BCVA according to Snellen’s visual acuity chart, cycloplegic refraction, and slit-lamp biomicroscopic anterior segment examination that assessed the palpebral aperture. Measures were also taken of the corneal diameter, pupil diameter, corneal sensitivity, Schirmer’s test, and intraocular pressure. Corneal topography (Tomey TMS 2.1) and pachymetry were also done. A complete retinal evaluation ruled out any retinal tears or pathology. Patients were instructed to remove soft contact lenses at least 2 weeks before and hard and semi-soft contact lenses at least 4 weeks before evaluation. LASIK was performed using the Chiron Technolas Keracor 217 Excimer laser (Bausch & Lomb) with the Automated Corneal Shaper microkeratome (Bausch & Lomb). Fluency was 130 j/cm2, with a 10 Hz repetition rate, diameter of 7.8mm to 8.2mm, and multi-zone algorithm with optical zone from 4mm-6mm. All the surgeries were performed under topical anesthesia using 4 % lidocaine. Fluence was checked before every procedure by verifying the homogeneity and symmetry of the pulses according to optimal values of 65 ± 1 shots. Before the procedure was begun, all the instruments were checked. The ACS microkeratome was test-run on the base plate before each individual procedure. The autotracking mechanism was used .A speculum was inserted to keep the palpebral fissure wide open and eyelashes out of field. The entrance pupil was marked with a Gentian violet tip marker. A reference mark was made on the cornea. The suction ring was centered on the corneal marking and activated. The intraocular pressure was confirmed with the presurgical tonometer to be more than 65 mm Hg. The microkeratome was adjusted on the suction ring and moved forward with the forward footswitch till it stopped at the permanent stopper to prevent a free cap. The microkeratome was moved back with a reverse footswitch and removed.The lamellar corneal flap was fashioned with a nasal hinge and carefully lifted with a blunt instrument and reflected on its hinge. The surgeon carefully performed the laser ablation to ensure accurate centration. Once the ablation was completed, tissue and both the sides of 202
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the flap were cleaned with balanced salt solution and a Merocel sponge. After determining that no foreign particles remained in the interface, the surgeon repositioned the flap in the original position. The corneal surface markers were checked to ensure that they were in opposition. Care was taken to ensure there were no striae in the flap. The suction ring was then gently removed. After a few minutes the adhesion of the flap was checked. Then the speculum was removed carefully. Patients were examined with the slit lamp 1 hour after surgery and sent home. The following medications were prescribed: topical antibiotic ciprofloxacin 0.1%, topical steroid Dexamethasone 0.1% with a tapered dose, and artificial tears for 1 month. Patients were examined on the first postoperative day, after 1 week, 1 month, 6 months, 1 year after surgery, and afterwards if necessary. At each follow-up, the surgeon monitored UCVA and BCVA, cycloplegic refraction, anterior segment evaluation, intraocular pressure, corneal topography, and a detailed fundus examination.
Results of Lasik After RK and PRK
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Demographic data are provided in Table 1. All the patients were followed. The mean postop- Section 6 erative follow-up period was 14.23 ± 2.23 (SD) months in the RK group, and 16.43 ± 1.54 (SD) Section 7 months in the PRK group. LASIK was performed Subjects Index after a mean period of 24.3 ± 0.75 (SD) months in the RK group and 22 ± 1.07 (SD) months in the PRK group after the primary procedure.
RK Group At the last follow-up, the mean spherical equivalent was –1.19 ± 0.71 (SD), compared to 6.05 ± 1.98 (SD) (P<0.05) before LASIK. Four eyes (40%) became emmetropic, four eyes (40%) were within ± 1 D of emmetropia, and two eyes (20 %) were within ± 2 D of emmetropia. The mean UCVA improved from 0.07 ± 0.05 (SD), to 0.63 ± 0.19 (SD)(P<0.05). UCVA was ≥ 0.5 in eight eyes (80 %). (Table 2). The mean BCVA improved from 0.88 ± 0.19 (SD) to 0.9 ± 0.22 (SD)(P<0.5). In two eyes the BCVA improved by 1 line on Snellen’s vi-
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LASIK AFTER RK AND PRK Table 1
Table 2
Contents
Section 1 Section 2
Section 3
sual acuity chart. One eye lost a single line of BCVA. The mean pachymetry changed from 556 ± 30 (SD) to 426 ± 20 (SD) after LASIK. Postoperative corneal topography showed centered ablation in all the eyes. (Fig. 16-1 shows a corneal topograph after RK. Fig. 16-2 is a corneal topograph of the same eye after LASIK).
PRK Group At the last follow-up the mean spherical equivalent was –0.4 ± 0.5 (SD), compared to -3.38 ± 1.3(SD) (P<0.005) before LASIK. Five eyes (50 %) became emmetropic, five eyes (50%) were within ± 1 D of emmetropia, and one eye(10%) was within ± 2 D of emmetropia. The mean UCVA improved from 0.25 ± 0.12 (SD), to 0.87 ± 0.22 (SD)(P<0.05). The UCVA was ≥ 0.5 in eight eyes (80 %) (Table 2). The mean BCVA improved from 0.88 ± 0.19(SD), to 0.9 ± 0.16 (SD)(P<0.5). In three eyes the BCVA improved by 1 line on Snellen’s visual acuity chart. No eye lost a line of BCVA. The mean pachymetry changed from 552 ± 36 (SD), to 452 ± 27 (SD) after LASIK. Postoperative corneal topography showed
Section 4
Section 5
Section 6 Section 7 Figure 16-1: Preoperative topograph of a case in which RK was Done Previously
Subjects Index
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Figure 16-2: Postoperative topograph of the same case in which Lasik was done after RK.
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Chapter 16
Contents
Section 1 Figure 16-4: Postoperative topograph of the same case in which Lasik was done after PRK
Section 2
Section 3 Figure 16-3: Preoperative topograph of a case in which PRK (photorefractive keratectomy) was done.
centered ablation in all the eyes. (Figure 16-3 shows a corneal topograph after PRK. Figure 16-4 is a corneal topograph of the same eye after LASIK). No complications that jeopardize sight like free flap, corneal ectasia, or any retinal complication occurred. Two eyes in the RK group required repositioning of the flap within a few hours after surgery due to wrinkles and irregular opposition of the flap to the stromal bed. There was no statistically significant difference in corneal haze before and after LASIK.
Discussion of Lasik After RK and PRK The main adverse effects of laser surgery are the loss of BCVA and regression. With LASIK the corneal epithelium as well as Bowman’s membrane are preserved. Therefore, the distinct wound healing that occurs after PRK is not present with this procedure. For this reason, there is less regression after LASIK than after PRK, and the potential for corneal haze or scar formation should be of less concern. 204
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We did LASIK using the same algorithms Section 4 but considered residual myopia as a subjective refraction. We limited our ablation zone between 4mm- Section 5 6mm to prevent night glare that can result from Section 6 unnecessary vertex ablation and overcorrections due to a large zone ablation4. As a safety measure Section 7 we excluded patients having pachymetry less than 410µm (250µm stromal bed and 160mm stromal Subjects Index flap). In our study there was significant reduction in mean spherical equivalent from –6.05 ±1.98 (SD) to –1.19 ± 0.71(SD) in the RK group, and from –3.38 ±1.3 (SD) to –0.4 ± 0.5 (SD) D in the PRK group. We compared our study with the study conducted by Ozdamar et al., who did LASIK after PRK Help ? for residual myopia ranging from 1.5 to 12.5 D. The mean spherical equivalent was changed from –5.96 ± 3.06D (SD) to 1.19± 0.77 D (SD). Better statistical results were obtained in the PRK group than the RK group, which may be due to the higher residual myopia in the RK group. The percentage of patients achieving a UCVA of 20/40 (0.5) or more was similar in both the groups after LASIK. No significant complications were reported. At the last follow-up, the mean spherical equivalent reduced from -6.05 ± 1.98 (SD) to
LASIK AFTER RK AND PRK
–1.19 ± 0.71 (SD) (P<0.05) in the RK group, and from –3.38 ± 1.3 (SD) to –0.4 ± 0.5 (SD) (P<0.005) in the PRK group. Uncorrected visual acuity was improved from 0.07 ± 0.05 (SD) to 0.63 ± 0 .19 (SD) (P<0.05) in the RK patients, and from 0.25 ± 012(SD) to 0.87 ± 0.22 (SD) (P<0.05) in the PRK group. Two eyes in the RK group and three eyes in the PRK group gained one line of BCVA. Two eyes in the RK group lost one line of BCVA. No complications that jeopardize sight, like free flap, corneal ectasia, or any retinal complication occurred. There was no statistically significant difference in corneal haze before and after LASIK. Two eyes in the RK group required quick repositioning of the flap due to irregular opposition to the stromal bed. Although the number of eyes studied is limited, LASIK treatment for residual myopia after RK or PRK appears safe, effective, and stable.
REFERENCES 1)Ionniis G Pallikaris, T.G Papadaski, From Keratomileusis to LASIK – Evaluation of lamellar corneal procedures , Refractive Surgery, ,Jaypee, 210-215 2)Steven C, Shallorn, P.J. Mcdonnell, Refractive SurgeryPast ,present and future, Cornea, Mosby, 1997-2006 3)Howard Gimbel,E.E.A. Penno, LASIK the technique , Refractive Surgery, Jaypee 254-265 4)L.E.Probst ,T Woolfson ,M.Knitzinger , Predictive formulas for LASIK , Refractive Surgery,Jaypee, 218-228 5)Dimitri T. Azar, M.D. Suhas Tuli, M.D., Robert Alan Benson, et al. Photorefractive Keratectomy for residual myopia after radial keratotomy. J Cat Refract Surg- vol 24,MARCH 1998, 303 –311. 6)William J Jory , Predictability of radial keratotomy after excimer laser photorefractive keratectomy, J Cat Refract Surg ,vol. 24, March 1998, 312-314 7)Marwin l Kwitko, S Jovker, Hua Yan , M. Atas, Radial keratotomy for residual myopia after photorefractive keratectomy, J Cat Refract Surg ,vol. 24, March 1998, 315319
8)Mihai Pop, Prompt retreatment after photorefractive keratectomy, J Cat Refract Surg ,vol. 24, March 1998,320330 9)Anita Panda, Gopal Das, M Vasanthi, Abhisan kumar, Corneal infection after radial keratotomy; J Cataract Refract Surg vol. 24, March 1998, 331-334. 10)Garthy D S,Larki DF, Hill AR and Ficker LA et al, Retreatment for significant regression after excimer laser photorefractive keratectomy , prospective ,randomized, masked trial, Ophthalmology, 1998, Jan, 105:1, 131-41 11)Rozsival P, Feyurmannova A, Retreatment after photorefractive keratectomy for low myopia, Ophthalmology, 1998, Jul,105:7, 1189-92 12)Ghaith AA, Daniel J, Stulting RD, and Thompson KP et al, Contrast sensitivity and glare disability after radial keratotomy and photorefractive keratectomy, Arch Ophthalmol, 1998 Jan,116:1, 12-8 13)Ozdamar A, Sener B, Aras C, Aktunc R, Laser in situ keratomileusis for myopic regression, J Cat Refract Surg, 1998 Sep, 24:9 ,1208-11 14)Kolahdouz Isfahani AH, WuFM, Salz JJ, Refractive keratotomy after photorefractive keratectomy, J Refract Surg 1999 Jan,15:1 ,53-7
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 15)Probst LE, Machat JJ , Conservative photorefractive keratectomy for residual myopia after radial keratotomy, Can J Ophthalmol, 1998 Feb, 33 :1 ,20-7
Section 7 Subjects Index
16)Allo Jl, Artola a, Claramonte PJ, Ayala MJ, Snachez SP, Complications of photorefractive keratectomy for myopia :two year follow-up of 3000 cases 17)Hersh PS , S. F Brint, R.K Mololeyand D.D Durrie et al; Photorefractive keratectomy versus laser in situ keratomileusis for moderate to high myopia; Ophthalmology, 1998 Aug, 105:8,1512-22
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18)Jorge Alio, A Artola, P Claramonte and N J Ayala et al, PRK for pediatric myopic anisometropia , J. Cat Refract Surg, vol-24, no-3, March 1998, 327-330 Sunita Agarwal, M.S. Dr. Agarwal’s Eye Hospital, 13 Cathedral Road, Chennai (Madras)- 600 086, India Tel: + 91 44 8113704 -- Fax: + 91 44 8115871 E-mail:
[email protected]
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LASIK AFTER PENETRATING KERATOPLASTY
Chapter 17 LASIK AFTER PENETRATING KERATOPLASTY Umberto Benelli, MD and Marco Nardi, MD
Introduction Visual recovery after penetrating keratoplasty is often adversely affected by residual refractive errors, despite a clear graft. Residual myopia and regular and irregular astigmatism account for most of the decreased visual acuity. A large amount of corneal astigmatism can greatly influence the visual outcome of an otherwise successful corneal transplant. The mean amount of astigmatism reported after penetrating keratoplasty averages 4.00 to 6.00 diopters (D) in different series, but it can range from 0 to 20.00 D or more. Most patients are not able to tolerate more than 3 D of anisometropia because of image size disparity, or astigmatism of greater than 1.5 to 3 D (Olson et al., 2000). To treat these conditions, it should initially consider clinical visual rehabilitation. Some patients can be corrected with spectacles but many others must use contact lenses (Applegate and Howland, 1993). Contact lenses are vital to the rehabilitation of the post-keratoplasty patient. Ten percent to 30% of patients who had penetrating keratoplasty wear contact lenses for visual rehabilitation. The incidence of contact lens wear after penetrating keratoplasty for keratoconus is 25% to 50%. Both soft and gas permeable contact lenses are extremely effective and remain the primary technique of visual rehabilitation for patients who cannot tolerate spectacles. Wearing contact lenses after penetrating keratoplasty could not be ideal, especially when a patient had surgery because of intolerance to contact lenses, as occurs with keratoconus. Even when a patient is successfully fitted with contact
lenses, the lenses may irritate the donor cornea because of peripheral touch and in some instances, peripheral neovascularization occurs with risk of corneal rejection. If the patient is unable to wear specContents tacles or contact lenses, surgical treatment should be considered (Genvert et al., 1985; Lim et al., 2000). Section 1 Additional modalities to correct myopia and astigmatism after penetrating keratoplasty, especially in Section 2 the first period after corneal transplantation (plastic Section 3 phase), may be suture adjustment, selective suture removal or compression sutures (Binder, 1985; Section 4 Mandel et al., 1987; Limberg et al., 1989; McNeill and Wessels, 1989; Karabatsas et al., 1998). The sta- Section 5 bility and predictability of these procedures are not Section 6 ideal and there is a risk of damaging the transplanted cornea. Frequently, if acceptable astigmatism is Section 7 achieved, sutures are left in place for 1 or more years. However, breakage often results, requiring suture Subjects Index removal. Additionally, there may be suture-related complications including inflammation, infection, vascularization, epithelial erosion, and ulceration. Radial keratotomy and transverse keratotomies can be effective in the treatment of astigmatism following penetrating keratoplasty but treatment does not Help ? effectively treat the remaining spherical equivalent ametropia because of the coupling phenomenon (Risko and Antonios, 1993). The use of excimer laser has provided the opportunity to develop new refractive surgical procedures. Although recent reports suggest that photorefractive keratectomy (PRK) is relatively safe and effective in reducing refractive error after penetrating keratoplasty, it still has limits (Campos et al., 1992). PRK for myopia after penetrating keratoplasty is associated with increased incidence LASIK AND BEYOND LASIK 207
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outcome with no significant post-operative complications (Figure 17-1).
Eligible Patients
Figure 17-1. Biomicroscopy examination of cornea before LASIK and 2 hours after.
of irregular astigmatism, corneal scarring, and significant regression. In addition, some cases of transplant rejection after PRK have been described (Hersh et al., 1993; Epstein and Robin, 1994; Bilgihan et al., 2000). In 1991, Pallikaris et al. proposed the corneal flap technique for laser in situ keratomileusis (LASIK) as an alternative to PRK. LASIK has become increasingly popular over the past several years in treating myopia, astigmatism, and, more recently, hyperopia (Salchow et al., 1998; Zadok et al., 2000). Enthusiasm for this procedure has been tempered by the potential for complications, particularly during the preparation of the corneal flap (superficial keratectomy) (Stulting et al., 1999; Holland et al., 2000). There are different authors who use LASIK after penetrating keratoplasty to correct residual visual defects. In the majority of cases the LASIK procedure resulted in an excellent visual
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The use of LASIK after corneal transplantation as an enhancement or secondary operation markedly improves the optical results of corneal transplantation. The disease present before penetrating keratoplasty made no difference in the refractive results. It is important to advocate a conservative approach to treating refractive errors after penetrating keratoplasty. Contact lens remain the standard of care and are to be encouraged whenever feasible. When contact lens use is not possible, it is a good idea to suggest slightly undercorrection. The ideal Contents patient must be all spectacle and contact lenses correction intolerant and the astigmatism must be regu- Section 1 lar. After penetrating keratoplasty, many patients Section 2 will have irregular or high astigmatism that may pre- Section 3 dispose them to flap complications during the keratectomy. This would be especially true in steep post- Section 4 operative corneas where there is a large difference Section 5 between the flat and steep axis. These patients, although not amenable to spectacle correction, can be Section 6 rehabilitated with a gas-permeable contact lens. It is important to discourage these patients from having Section 7 LASIK if they are at all tolerant of contact lenses Subjects Index (Parisi et al., 1997).
Time of Surgery There are several alterations of normal LASIK technique when treating myopia or astigmatism or both after penetrating keratoplasty. An accurate assessment of the patient’s true refraction depends on the donor cornea returning to its normal shape after suture removal. With gas-permeable contact lens wear, most LASIK surgeons recommend a minimum of 1 month to allow resolution of corneal warpage, and with long-term gas-permeable contact lens wear, the corneal warpage may take several months to abate (Lam et al., 1998). In our opinion minimum time for LASIK after suture removal is 12 months and minimum time
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LASIK AFTER PENETRATING KERATOPLASTY
for LASIK after penetrating keratoplasty is 1 year. Although there are reports of LASIK being performed as early as 12 months following penetrating keratoplasty without complications, the minimum or ideal time interval between the initial penetrating keratoplasty to LASIK treatment is not yet established. It seems very important to evaluate the strength of the scar at the graft-host junction and the stability of refraction after keratoplasty and/or suture removal (Lam et al., 1998). Other less quantifiable factors, such as initial corneal pathology and the duration of topical corticosteroid application, may also affect graft-host junction strength. Younger patients may heal faster and might be eligible for earlier treatment with LASIK.
Surgical Technique The LASIK procedure used by the majority of the surgeons is the standard technique. There are small differences between different authors due to different microkeratome models and/or different LASIK personal techniques. Some authors suggested that the LASIK flap must be cut first and then laid back down to allow the eye to settle and the residual refractive error and astigmatism to adjust. Once the eye is stable, after several days to a week, the refractive error is reassessed and then the corrective LASIK ablation is performed (Vajpayee and Dada, 2000). It has been observed that the lamellar cut of the microkeratome and the creation of a 160/180 micron depth flap, leads to a modification of the axis and the magnitude of the cylinder, which may be significant, especially in eyes with a high astigmatic error. The cylindrical error after a corneal grafting procedure may be caused by irregular contractile forces emanating from the host-graft junction and inducing a toric contracture of the cornea. The large lamellar cut performed by the microkeratome may lead to a release of these contractile forces and subsequent realignment of the corneal tissues. Therefore, the creation of a lamellar corneal flap may be associated with a significant change in the magnitude and the axis of the astigmatism. For this reason performing laser ablation on the basis of the preop-
erative refractive error may not be a good option, because the original cylinder may have undergone significant modification after the creation of a lamellar corneal flap. In addition, in some patients there may be a continued shift in the keratometry, up to a period of 8 to 12 weeks after cutting the flap. For this reason some authors think that LASIK after penetrating keratoplasty should be done as a two-stage procedure. The first stage involves the use of the microkeratome to perform the lamellar corneal cut, without any laser ablation. The change in the corneal topography, keratometry, and the refraction should be noted on the subsequent day and monitored on a weekly basis. The flap can then be relifted after an interval of 4 to 6 weeks or after the refraction is stable over a 2-week period. The excimer laser ablation is performed at this stage on the basis of Contents the current refractive status. This two-stage procedure yields better visual results and is recommended Section 1 in all eyes that undergo LASIK for the correction of significant residual astigmatism after penetrating Section 2 keratoplasty (Vajpayee and Dada, 2000). Although this technique may improve re- Section 3 sults, it also requires two procedures each with po- Section 4 tential complications including graft rejection. The lamellar flap heals more aggressively over the cor- Section 5 neal graft/host interface, which can result in diffiSection 6 culty elevating flap during enhancements. The edge of the lamellar flap may not oppose the stromal bed Section 7 perfectly in LASIK after penetrating keratoplasty: this increase the possibility of epithelial ingrowth, Subjects Index which is known to occur more commonly after all enhancement procedures. In addition any surgical manipulation of the eye results in an increased incidence of allograft rejection.
Post-Surgical Treatment
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It is important to be more liberal with the use of postoperative corticosteroids than in normal LASIK patients. Usually, after conventional LASIK surgery, patients are treated with fluorometholone 0.1% four times daily for 5-7 days. In LASIK after penetrating keratoplasty, it is better to use prednisolone acetate 1% four times daily for 10 days and then prednisolone acetate 1% once daily for 2-4 weeks. This additional use of corticosteroids is indicated because of the potential risk of graft rejection after LASIK AND BEYOND LASIK 209
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any surgical procedure on a penetrating keratoplasty (Donnefeld et al., 1999).
Risks and Possible Complications Endothelial alterations after LASIK have been studied. Pallikaris and Siganos (1994) believe that the presence of endothelial loss of up to 4.11%, related to the quantity of the desired correction, is probably caused by the shock waves produced by the excimer laser photoablation and corneal manipulation during keratomileusis. Other studies, however, have demonstrated no significant endothelial alterations after LASIK following penetrating keratoplasty (Holland et al., 2000). Another major concern in performing LASIK after penetrating keratoplasty is the risk of damage to the corneal transplant or the graft-hostwound interface, or both. Wound dehiscence after penetrating keratoplasty is a well-described case of extrusion of the intraocular contents. During LASIK surgery after keratoplasty, it is important to minimize the suction time. In LASIK, intraocular pressure is elevated to more than 65 mm Hg and there is a risk of wound dehiscence with the possibility event that could potentially reduce best spectacle-corrected visual acuity, regardless of whether vision actually was lost because of this event. The substantial decrease of corneal thickness after surgery is similar to that obtained in studies of LASIK for the correction of myopia and myopic astigmatism with no prior surgery. The more frequent problems are undercorrection and decentered ablation. Difficulties in accurately measuring refractive cylinder due to irregular astigmatism and decreased best spectaclecorrected visual acuity as well as the long-term instability of penetrating keratoplasty wounds, continue to be major obstacles to improve results.
Results LASIK treatment after keratoplasty is a recent method to correct residual myopia and astigmatism. (Figures 17-2, 17-3 and 17-4) show the modification of computerized corneal maps after
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Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Figure 17-2 (a-b). Computerized corneal map before (a) and 10 days after LASIK to correct astigmatism and high myopia.
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post-keratoplasty LASIK. In literature there are few reports that show the results obtained by different authors. Rashad (2000) performed LASIK on 19 eyes with high astigmatism after penetrating keratoplasty, using the Chiron Automated Corneal Shaper and the Chiron-Technolas Keracor 116 excimer laser. The amount of preoperative refractive astigmatism ranged from 6.50 to 14.50 D (mean, 9.21 ± 1.95 D) and the spherical component of manifest refraction ranged
LASIK AFTER PENETRATING KERATOPLASTY
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Figure 17-3 (a-b). Computerized corneal map before (a) and 14 days after LASIK to correct regular astigmatism. Residual astigmatism is still detectable.
Figure 17-4 (a-b). Computerized corneal map before (a) and 12 days after LASIK to treat irregular astigmatism.
from -7.00 to +1.25 D (mean, -2.14 ± 2.11 D). At 1 year after 91SECTION 1Chapter 10LASIK, the amount of refractive astigmatism was reduced to a mean of 1.09 ± 0.33 D (range, 0.50 to 1.75 D), with 57.9% of the eyes within ±1.00 D of refractive astigmatism. The mean percent reduction of astigmatism was 87.9 ± 3.7%. The postoperative spherical component of manifest refraction ranged from -1.00 to +1.75 D with a mean of +0.43 ± 0.82 D. There were no intraoperative complications. Spectacle-corrected
visual acuity was not reduced in any eye, and improved by 2 or more lines in 42.1% of eyes after LASIK. Forseto et al. (1999) reported the results of LASIK after penetrating keratoplasty in 22 eyes. They used the VISX Twenty-Twenty excimer laser, which utilizes a constricting slit to achieve an elliptical ablation profile. Mean preoperative astigmatism was 4.24 ± 2.28 D (range, 0 to 9.00 D), and mean postoperative astigmatism was 1.79 ± 1.12 D (range,
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LASIK AND BEYOND LASIK 211
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0 to 5.50 D). The mean percent reduction of astigmatism was 57.7% and the mean percent correction of astigmatism was 54.0%. Arenas and Maglione (1997) showed the results of LASIK in 4 eyes with myopia and astigmatism after penetrating keratoplasty using the Keracor 116 excimer laser. They reported that LASIK was effective in reducing myopia but astigmatism changed from a mean -2.87 D preoperatively (range, -1.00 to -5.00 D) to a mean -3.50 D after LASIK (range, -1.00 to -5.00 D). The ablation zone used in their study for the correction of astigmatism was probably too small (only 3.5 mm), which accounts for the limited change in amount of astigmatism after LASIK. An ablation zone of 5.0-5.5 mm for astigmatic correction seems to be better, yielding better results in terms of astigmatism correction. Donnenfeld et al. (1999) reported 3-month results of LASIK in 22 eyes with myopia and astigmatism after penetrating keratoplasty using the VISX Star excimer laser. Mean refractive cylinder before surgery was 3.64 ± 1.72 D. One eye had 8.50 D of astigmatism and 21 eyes had less than 6.00 D of astigmatism. The amount of astigmatism was reduced to a mean of 1.64 ± 1.14 D at 3 months after LASIK. There was undercorrection of astigmatism in many eyes. Nine eyes (40.9%) had refractive astigmatism of less than 1.00 D and 18 eyes (81.8%) had refractive astigmatism of less than 2.00 D. LASIK retreatment was performed on 2 eyes for correction of residual astigmatism at 3 months after the primary LASIK procedure, Koay et al. (2000) performed LASIK on 8 eyes after a mean 71 months following the initial penetrating keratoplasty. No eyes lost any Snellen lines of best spectacle-corrected visual acuity at the latest follow-up (12 months). Mean reduction in spherical equivalent refraction was 91% from -6.79 ± 4.17 D to -0.64 ± 1.92 D and mean reduction of cylinder was 72% from -6.79 ± 3.28 D to -1.93 ± 1.17 D. Nassaralla and Nassaralla (2000) treated 8 eyes with the Chiron Technolas 217 excimer laser and the Automated Corneal Shaper microkeratome. Mean spherical equivalent refraction decreased from -4.50 D (range, -3.00 to -7.25 D) to -0.75 D (range, 1.50 to +0.50 D) and the mean pre-operative astigmatism decreased from 3.50 D (range, 1.50 to 5.00
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D) to 1.25 D (range, 0.75 to 2.00 D). Uncorrected visual acuity improved by at least two Snellen lines in all eyes. Best spectacle-corrected visual acuity did not change in four eyes (50%) and improved in three eyes (37.5%). Webber et al. (1999) reported the results of a series of 26 eyes treated with LASIK to correct post penetrating keratoplasty ametropia; 14 eyes also received arcuate cuts in the stromal bed at the time of surgery. The mean preoperative spherical equivalent was -5.20 D and the mean preoperative astigmatism was 8.67 D. The final follow up results for these eyes were -1.91 D and 2.92 D for spherical equivalent and astigmatism. The patients undergoing arcuate cuts were less myopic but had greater astigmatism than those not. One eye suffered a surgical complication. No eyes lost more than one line of BSCVA and all eyes gained between 0 and 6 lines UCVA. Changes in refractive astigmatism in the majority of the studies showed stability of refraction at 3 months after LASIK or LASIK retreatment. Changes in refractive astigmatism between 6 and 12 months were minimal and statistically insignificant. No change was at this moment observed on transparency of the grafts after LASIK. Haze was not observed in any patient. No corneal graft rejection episode was noted.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7
Conclusions The primary goal of LASIK after penetrating keratoplasty is to reduce the refractive error to allow spectacle correction. The uncorrected visual acuity remains a secondary goal with LASIK after penetrating keratoplasty, whereas uncorrected visual acuity is clearly the primary objective of cosmetic LASIK. For this reason, return to binocularity and optimized best corrected visual acuity with spectacles is the true endpoint for success with LASIK after penetrating keratoplasty. A potential advantage of LASIK over surface excimer laser photoablation is that there is better corneal sensation after LASIK than after PRK. In LASIK, the 2 to 3 clock-hours of hinge nasally allows the passage of corneal nerves into the central cornea. This has been shown to provide improved sensation. One of the main predictors of graft sur-
Subjects Index
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LASIK AFTER PENETRATING KERATOPLASTY
vivability is corneal sensation. There is always a diminution of corneal sensation after penetrating keratoplasty due to trephination of the corneal nerves. LASIK offers an additional advantage over PRK in that there is less loss of corneal sensation (Donnenfeld et al., 1999). Because of the results obtained by different surgeons, it results that LASIK is a good alternative to treat high amounts of myopia and/or astigmatism after penetrating keratoplasty. LASIK is predictable and produces rapid recovery of visual acuity not possible with any previously described method. Based on studies of corneal wound healing after penetrating keratoplasty, this type of surgery should be delayed at least 12 months after keratoplasty because of the risk of corneal dehiscence from the high pressure (60 mm Hg) applied to place the suction ring of the microkeratome. The topographic results in the majority of the patients show some changes in the postoperative patterns, with good tendency to correct astigmatism and myopia. LASIK preserves the donor Bowman’s membrane, facilitates good wound healing, and excellent visual recovery. After penetrating keratoplasty, many patients will have irregular astigmatism, which, although not amenable to spectacle correction, can be rehabilitated with a gas-permeable contact lens. These patients must be discouraged if they are at all contact lenstolerant from having LASIK performed, as the excimer laser currently is not successful in treating irregular astigmatism. Although laser technology is excellent for regular astigmatism and myopia, it cannot currently treat irregular astigmatism. The development of flying spot excimer lasers guided by corneal topography will successfully treat some forms of irregular astigmatism in the next several years (Tamayo Fernandez and Serrano, 2000). This will allow even more accurate treatment of post-penetrating keratoplasty refractive errors.
References Applegate RA, Howland HC. Magnification and visual acuity in refractive surgery. Arch Ophthalmol 1993; 111: 1335-1342. Arenas A, Maglione A. Laser in situ keratomileusis for astigmatism and myopia after penetrating keratoplasty. J Refract Surg 1997; 13: 27-32. Bilgihan K, Ozdek SC, Akata F, Hasanreisoglu B. Photorefractive keratectomy for post-penetrating keratoplasty myopia and astigmatism. J Cataract Refract Surg 2000; 26: 1590-1595. Binder PS. Selective suture removal can reduce post-keratoplasty astigmatism. Ophthalmology 1985; 92: 1412-1416. Contents
Campos M, Hertzog L, Garbus J, Lee M, McDonnell PJ. Photorefractive keratectomy for severe post-keratoplasty astigmatism. Am J Ophthalmol 1992; 114: 429-436. Donnenfeld ED, Kornstein HS, Amin A, Speaker MD, Seedor JA, Sforza PD, Landrio LM, Perry HD. Laser in situ keratomileusis for correction of myopia and astigmatism after penetrating keratoplasty. Ophthalmology 1999; 106: 1966-1975.
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6
Epstein RJ, Robin JB. Corneal graft rejection epiSection 7 sode after excimer laser phototherapeutic keratectomy. Arch Ophthalmol 1994; 112: 157. Subjects Index Forseto AS, Francesconi CM, Nose RA, Nose W. Laser in situ keratomileusis to correct refractive errors after keratoplasty. J Cataract Refract Surg 1999; 25: 479-485. Genvert GL, Cohen EJ, Arentsen JJ, Laibson PR. Fitting gas-permeable contact lenses after penetrating keratoplasty. Am J Ophthalmol 1985; 99: 511-514.
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Hersh PS, Jordan AJ, Mayers M. Corneal graft rejection episode after excimer laser phototherapeutic keratectomy. Arch Ophthalmol 1993; 111: 735-736. Holland SP, Srivannaboon S, Reinstein DZ. Avoiding serious corneal complications of laser assisted in situ keratomileusis and photorefractive keratectomy. Ophthalmology 2000; 107: 640-652.
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Karabatsas CH, Cook SD, Figueiredo FC, Diamond JP, Easty DL. Surgical control of late post-keratoplasty astigmatism with or without the use of computerized videokeratography. Ophthalmology 1998; 105: 19992006. Koay PYP, McGhee CNJ, Weed KH, Craig JP. Laser in situ keratomileusis for ametropia after penetrating keratoplasty J Refract Surg 2000; 16 :140-147. Lam DS, Leung AT, Wu JT, Tham CC, Fan DS. How long should one wait to perform LASIK after PKP. J Cataract Refract Surg 1998; 24: 6-7. Lim L, Pesudovs K, Coster DJ. Penetrating keratoplasty for keratoconus: visual outcome and success. Ophthalmology 2000; 107: 1125-1131. Limberg MB, Dingeldein SA, Green MT, Klyce SD, Insler MS, Kaufman HE. Corneal compression sutures for the reduction of astigmatism after penetrating keratoplasty. Am J Ophthalmol 1989; 108: 36-42. Mandel MR, Shapiro MB, Krachmer JH. Relaxing incisions with augmentation sutures for the correction of post-keratoplasty astigmatism. Am J Ophthalmol 1987; 103: 441-447. McNeill JI, Wessels JF. Adjustment of single continuous suture to control astigmatism after penetrating keratoplasty. J Refract Corneal Surg 1989; 5: 216-223. Nassaralla BRA, Nassaralla JJ. Laser in situ keratomileusis after penetrating keratoplasty. J Refract Surg 2000; 16: 431-437. Olson RJ, Pingree M, Ridges R, Lundergan ML, Alldredge C Jr, Clinch TE. Penetrating keratoplasty for keratoconus: a long-term review of results and complications. J Cataract Refract Surg 2000; 26: 987-991. Pallikaris IG, Papatzanaki ME, Siganos DS, Tsilimbaris MK. A corneal flap technique for laser in situ keratomileusis. Human studies. Arch Ophthalmol 1991; 109: 1699-1702. Pallikaris IG, Siganos DS. Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia. J Refract Corneal Surg 1994; 10: 498-510.
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Parisi A, Salchow DJ, Zirm ME, Stieldorf C. Laser in situ keratomileusis after automated lamellar keratoplasty and penetrating keratoplasty. J Cataract Refract Surg 1997; 23: 1114-1118. Rashad KM. Laser in situ keratomileusis retreatment for residual myopia and astigmatism. J Refract Surg 2000; 16: 170-176. Rashad KM. Laser in situ keratomileusis for correction of high astigmatism after penetrating keratoplasty. J Refract Surg 2000; 16: 701-710. Risco JM, Antonios SR. Arcuate keratotomy with compression sutures for correction of high post-keratoplasty astigmatism. Middle East J Ophthalmol 1993; 1: 17-18. Salchow DJ, Zirm ME, Stieldorf C, Parisi A. Laser in situ keratomileusis for myopia and myopic astigmatism. J Cataract Refract Surg 1998; 24: 175-182. Stulting RD, Carr JD, Thompson KP, Waring III GO, Wiley WM, Walker JD. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology 1999; 106: 13-20. Tamayo Fernandez GE, Serrano MG. Early clinical experience using custom excimer laser ablations to treat irregular astigmatism. J Cataract Refract Surg 2000; 26: 1442-1450.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6
Section 7 Vajpayee RB, Dada T. Lasik after penetrating keratoplasty (Letter). Ophthalmology 2000; 107: 1801- Subjects Index 1802.
Zadok D, Maskaleris G, Montes M, Shah S, Garcia V, Chayet A. Hyperopic laser in situ keratomileusis with the Nidek EC-5000 excimer laser. Ophthalmology 2000; 107: 1132-1137. Webber SK, Lawless MA, Sutton GL, Rogers CM. LASIK for post penetrating keratoplasty astigmatism and myopia. Br J Ophthalmol 1999; 83: 1013-1018.
Umberto Benelli, MD Department of Neurosciences Section of Ophthalmology University of Pisa Via Roma, 67 56126 Pisa - Italy E-Mail:
[email protected]
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LASIK AFTER PREVIOUS CORNEAL SURGERY
Chapter 18 LASIK AFTER PREVIOUS CORNEAL SURGERY Jorge L. Alió, MD, PhD, Walid H. Attia MD, Javier Gómez, MD
Contents
Laser-assisted in situ keratomileusis (LASIK) is gaining acceptance as a versatile refractive surgical procedure. LASIK is gaining popularity due to quick visual rehabilitation, minimal postoperative discomfort, and the ability to correct variable forms and high degrees of refractive errors with minimal postoperative complications. LASIK efficacy has been reported in several studies for the correction of primary refractive errors such as myopia, hyperopia, and astigmatism. However, there have been very few studies reporting the use of LASIK in treating patients with residual refractive errors following other corneal or nonrefractive refractive procedures. LASIK is an evolving surgical technique with both therapeutic and refractive indications, especially in cases where refractive defects or irregular astigmatism have been induced by previous refractive surgery, trauma, or penetrating keratoplasty. This chapter is dedicated to study the use of LASIK in treating the following residual refractive problems after different corneal surgical procedures: 1. Radial keratotomy (RK) 2. Astigmatic keratotomy (AK) 3. Photorefractive keratectomy (PRK) 4. Laser thermokeratoplasty (LTK) 5. Penetrating keratoplasty (PKP) 6. Automated lamellar keratoplasty (ALK) 7. Epikeratophakia 8. Corneal trauma
General Considerations After RK
Section 1 Section 2
RK was a widely used surgical technique to correct myopia. lt flattens the central cornea indi- Section 3 rectly through peripheral radial incisions, however Section 4 the amount of central flattening that can be achieved is limited. 1,2 The most common side effect of this Section 5 procedure is overcorrection or undercorrection. WarSection 6 ing et al in 1994 reported the result of a multicenter prospective evaluation of an RK study in which 43% Section 7 of patients had a hyperopic shift of 1 diopter (D) or more by 10 years after treatment.3 Treatment of hy- Subjects Index peropia after RK has heen a complicated problem. To avoid this problem, most radial keratotomy surgeons prefer to perform conservative initial surgery as a safeguard against the development of hyperopic shift, with intentionally undercorrected postoperative results, thus increasing the incidence of patients Help ? with significant undercorrection. Eventually, this group will need additional treatment. Myopic regression is a common finding following RK and is more evident in young patients; again this group of patients will need additional treatment.
Residual Myopia After RK Unexpected or intentional residual myopia after RK may be due to a large optical zone, few incisions, or shallow incisions. Each patient’s corLASIK AND BEYOND LASIK
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neal reaction to the procedure differs.4 A number of patients with residual myopia after RK exist and need additional treatment. Correcting residual myopia can be done by spectacles, contact lenses, or reoperations either by redeepening, or extending the RK incisions, or performing additional RK incisions. However, although there are many nomograms for performing radial keratotomy,5,6 nomograms for enhancing refractive procedures do not exist. Reoperations cannot be based on the same calculations used in the initial surgery because the predictable effect of adding incisions and reducing optical zones is lower than in primary nomograms.7 An increase in the incidence of microperforations is observed with RK enhancement procedures.8 Overcorrection is another serious complication that has been reported in several studies using RK as an enhancement procedure.5,9 While young patients may be able to accommodate to compensate for an overcorrection now, in time the patient will be complaining of severe and early presbyopia. Photorefractive keratectomy is another form of treatment, but today there is a major concern about using it after RK. Several complications have been reported, including different degrees of haze and regression due to keratocyte activation, dehiscence of the RK incisions during scraping of the epithelium, and signifícant decrease in best spectacle corrected visual acuity (BSCVA) due to surface irregularity and subepithelial scarring.10,11 Azar, et al in 1998 advised against using PRK to correct residual myopia after RK in patients with high amounts of pre-RK and residual post-RK myopia.4 LASIK is more likely to provide an accurate result with early and long-term stability without the risk of haze (figura 18-1).
Hyperopia After RK Progressive hyperopia is a common complication following RK. It may result from lack of preoperative cycloplegic refraction, extending the radial incisions to the limbus, multiple RK enhancement procedures, redeepening procedures, extended contact lens wearing after RK, and possibly postoperative ocular rubbing.12 Treatment of hyperopia after RK is a complicated problem.13 Hexagonal keratotomy was used,
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Figure 18-1: LASIK over RK.
but the results were not predictable. Grene lasso sutures are more predictable but still not highly efficient. Thermal keratoplasty shows variable degrees of regression; thus, it is not reliable in treating hyperopic shift after RK. Hyperopic PRK has a high incidence of postoperative haze and disappointing results. Hyperopic LASIK is a promising technique in the management of these cases, especially with new reliable software for treating hyperopia.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6
The Cornea After RK
Section 7
RK incisions can be seen for a long time af- Subjects Index ter surgery. These incisions never completely heal. Epithelial ingrowth may be found in the RK incisions. Patients wearing contact lenses may have deep vascularization especially in deep incisions. Flat corneas are more common in patients with overcorrections. Help ?
LASIK AFTER RK LASIK seems to be an attractive alternative to correct residual myopia and hyperopic shift after RK. However, due to the fact that the cornea underwent previous RK surgery, it requires special handling both preoperatively and postoperatively to get the best results, to avoid any refractive surprise, and to decrease the possibility of developing haze.
LASIK AFTER PREVIOUS CORNEAL SURGERY
Preoperative Considerations LASIK should only be attempted after 1 year post-RK, with a stable refraction for at least the last 6 months, and a corneal topographic pattern stable for two consecutive examinations in a 1 month interval. Timing is very important especially with patients showing regression after RK. Overactive healing is responsible for this regression, and its effect may continue after LASIK if it is performed too early. Patients wearing contact lenses should discontinue use for at least 15 days before evaluation. Soft contact lenses should be discontinued for 15 days before LASIK, and both hard and gas-permeable contact lenses should be discontinued for at least 1 month before LASIK. In patients with blood vessels in the incisions, more time is needed to allow for blood vessel regression. If the patient has irregular astigmatism, or if the astigmatic value is larger than the spherical value, topographic linked excimer laser ablation (topolink) is preferred. A classic LASIK procedure will produce unpredictable results.
Contraindications Post-RK corneas are unstable corneas that may cause unpredictable results, thus great care is needed while dealing with these corneas. LASIK should not be performed if one or more of the following items exist. • Epithelial ingrowth: epithelial inclusions in the RK incisions is a serious problem and LASIK should be avoided in these cases, as the epithelium may pass under the flap, causing flap melting. • Macroperforation: LASIK should not be attempted in any case with prior macroperforations. • Deep vascularization: may he found in the deep incisions and is more common in patients who wear contact lenses. • Flat cornea: LASIK on flat corneas may cause a free cap, which will make it difficult to achieve good
results, as the diameter of the cut will not be large enough to perform hyperopic ablation. • Unstable refraction: this should be excluded before any attempt to perform LASIK; the patient may end up with an unpredictable and untreatable refractive condition.
lntraoperative Considerations In post-RK corneas, we are cutting across RK incisions, and it is well-documented that these incisions never completely heal. Our main concern is to prevent opening of the incisions while creating the flap. As long as the RK incisions are well-healed without epithelial ingrowth at the time of surgery, a safe regular cut can be performed with a 160 µm blade; however, it is better to use a thicker depth Contents blade. A 180 µm or 200 µm blade is safer, but the corneal thickness and amount of ablation determine Section 1 this. lt is important to always keep the corneal epithelium wet during the cut, this will serve as a lubri- Section 2 cant and facilitate the pass of the microkeratome. Lifting the flap should he done very care- Section 3 fully with a wide spatula, while avoiding forceps to Section 4 grab the edge of the flap. This will protect the incisions from splitting apart. Perfect fixation is needed. Section 5 lf it is not maintained, eccentric correction and unSection 6 predictable astigmatism could result. When replacing the flap, good apposition is mandatory; this will Section 7 prevent migration of the epithelium, especially if an incision in the flap is opened. During the procedure, Subjects Index avoid traumatizing the epithelium to avoid any epithelial scraping, which may cause keratocyte activation and increase in corneal haze. Applying a contact lens after surgery is not necessary unless there is opening in one or more of the RK incisions in the flap. Help ? If we are treating hyperopic shift, we attempt to obtain a large flap at least 9.5 mm, by using a large suction ring to avoid hinge syndrome. Fixation is usually more difficult with these patients. For better results, we give the patient extra training in fixation.
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Figure 18-2: Pilot study on patients with LASIK over RK, depending on they were undercorrected or hipercorrected. BSCVA and UCVA before and after LASIK
Contents
Results (Pilot Study) Ten myopic patients had previous RK. After 1 year, six patients had significant undercorrection, and the other four patients developed overcorrection. LASIK was done to correct the residual refractive defects in the 10 patients. Patients with undercorrection showed the following results 3 months after LASIK: the mean spherical equivalent changed from -2.50 D ± 2.47 (-6.25 to -0.50) to 0.12 D ± 0.26 (-0.25 to +0.50). Mean BSCVA improved from 0.75 ± 0.24 (0.5 to 1.0) to 0.83 ± 0.25 (0.5 to 1.0), and mean uncorrected visual acuity (UCVA) significantly improved from 0.33 ± 0.22 (0.1 to 1.0) to 0.80 ± 0.24 (0.5 to 1.0). Patients with overcorrection showed the following results 3 months after LASIK: the mean spherical equivalent changed from 1.87 D ± 0.66 (1.00 to 2.50) to -0.25 D ± 0.50 (-0.50 to 0.50). Mean BSCVA improved from 0.72 (0.6 to 0.8) to 0.80 (0.7 to 0.9), and mean UCVA improved from 0.52 (0.4 to 0.6) to 0.70 (0.6 to 0.8). Treating both undercorrection and overcorrection with LASIK following RK is almost equally safe, effective, and highly predictable. There were no major intraoperative or postoperative complications (Figure 18-2).
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Conclusions Although LASIK for the correction of residual refractive errors after RK seems to be a promising and safe procedure, great care should be taken with the flap during the entire procedure to avoid possible complications.
LASIK AFTER AK
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6
As the treatment of spherical refractive er- Section 7 rors, myopia, and hyperopia evolved, treatment of Subjects Index astigmatism has lagged behind. The incidence of clinically significant astigmatism varies between 7.5% to 75%.14 However, an astigmatic refractive error of more than 2.0 D is less common, between 3% and 15%. 15 Astigmatism corrected by spectacles may cause distortion due to the meridional magnification.16 Contact lenses may alleviate this problem, Help ? but not all patients can tolerate them. Here, the discussion is limited to the surgical correction of naturally occurring mixed astigmatism more than 3.0 D. The general goal of incisional or ablative astigmatic surgery is to reduce the magnitude of astig-
LASIK AFTER PREVIOUS CORNEAL SURGERY
matism by flattening the cornea at its steepest meridian, steepening the cornea at its flattest meridian, or a combination. Any corneal incision flattens the comea adjacent to it and at the meridian perpendicular to the cut. AK is a common method to correct astigmatism and is a very powerful tool in reducing astigmatism. It flattens the steep cylinder axis and, at the same time, steepens the flat axis, a process known as coupling.17 The coupling ratio (flattening/ steepening ratio) depends on the location, length, and depth of the incision. In patients with large amounts of astigmatism, AK can be used to significantly lessen the astigmatism however it is important to consider the patient’s refractive error and how astigmatismreducing surgery will affect the spherical equivalent. The benefits of AK are greater in patients with myopic astigmatism. Transverse incisions in the cornea cause flattening in the meridian of the incision and steepening of the meridian 90° away. Arcuate or curvilinear incisions have heen reported as more effective than straight transverse incisions.18,19 The distance between the AK and the center of the pupil is an important factor as well. The smaller the distance, the smaller the optical zone, with a higher incidence of irregular astigmatism near the pupil result in poor visual quality, especially in low-light conditions. McDonnell and colleagues were the first to report the success of toric sculpting of the cornea with an excimer laser to correct regular corneal astigmatism.20 This initial success encouraged refractive surgeons to use the same principle to correct astigmatism. The current approach to correct astigmatism by excimer laser, involves a nonradially symmetrical ablation of the corneal tissue, with greater ablation in the steep axis and minimal or no ablation in the flat axis.21 Recently, the Technolas, LaserSight, Autonomous, and Nidek lasers have been used to correct astigmatic errors in which the scanning beam moves along the axis of astigmatism and differentially ablates the cornea.
The Cornea After AK Following uncomplicated AK, the anatomical structure of the cornea does not show significant alteration, both in the superficial layers and the deep
stroma. Scars from the previous arcuate keratotomy are usually seen at a 7.0 mm optic zone. There is no need to avoid cutting through them with the microkeratome. A LASIK procedure can be carried out without special intraoperative precautions (Figure 18-3).
Contents
Section 1 Figure 18-3: LASIK over AK
Section 2
Section 3
Section 4
Performing LASIK After AK
Section 5
Section 6
The predictability of AK is of great concern for refractive surgeons, undercorrection, overcorrec- Section 7 tion, and change in the axis are complications that must be dealt with and corrected. Undercorrection is Subjects Index more common and better tolerated than overcorrection. In spite of several medical and surgical options used to manage these conditions, results are not predictable, but with LASIK we are getting more predictable and stable results. Coupling effect and hyperopic shift in the Help ? spherical equivalent are commonly seen after AK. For small amounts of myopia in association with astigmatism, the astigmatic surgery may be all the patient needs. However, astigmatism associated with high myopic or hyperopic spherical error will need a second approach in an attempt to achieve emmetropia. Radial keratotomy, photorefractive keratotomy, or LASIK can treat coupling and residual refractive defects. LASIK has proved itself as the most predictable and reliable procedure in dealing with most refractive errors. LASIK AND BEYOND LASIK
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Preoperative Considerations Allowing the refraction to stabilize is just as important in astigmatic surgery as in any other form of refractive surgery. We wait about 3 months after AK to perform LASIK; this period suffices in achieving a stable refraction. Usually in astigmatic correction with or without spherical error, treatment is based on the manifest refraction for axis correction; however, if the refractive axis differs from the topographic axis by more than 10°, we prefer to use the topographic axis. Patients who wear contact lenses should stop use of soft for 3 days and hard contact lenses for 2 weeks before getting manifest refraction results. Patients with binocular spectacle-corrected astigmatism are showing adaptation to the meridional magnification induced by their spectacles. Surgical correction of their astigmatism may result in torsional diplopia, and readaptation may take months. We discuss this problem with astigmatic patients before any surgery to correct astigmatic errors is attempted. With irregular astigmatism, normal LASIK treatment is contraindicated. It may worsen the condition, and it is advisable to treat these cases with the topography-assisted lasers.
lntraoperative Considerations In cases of previous AK, LASIK can be carried out as normal. The procedure has proven to he very safe following AK. All LASIK steps can be carried out as usual, as long as the procedure does not take place before 3 months following AK. Centration should be very precise and accurate to avoid decentration, which is usually more common with astigmatic treatment. Corneal topography should be our guide to achieve the best possible centration.
Results (Pilot Study) Ten patients with mixed astigmatism underwent AK. The mean spherical equivalent after AK was +0.57 D ± 2.8 (-1.5 to +6.0). The mean astigmatic value after AK was -1.50 D ± 0.60 (-0.5 to -2.5). Mean BSCVA was 0.76 ± 0. 15 (0.4 to 0.9), and mean UCVA was 0. 51 ± 0.16 (0.3 to 0.8). All patients underwent LASIK surgery in an attempt to
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correct the residual refractive error. In all cases, the procedure was carried out at least 3 months after AK. One month after LASIK, mean spherical equivalent was +0.87 D ± 0.5 (0.0 to +2), mean BSCVA was 0.76 ± 0.16 (0.4 to 1.0), and mean UCVA significantly improved to 0.73 ± 0.14 (0.4 to 0.9). Three months after LASIK, mean spherical equivalent became +0.60 D ± 0.31 (0.25 to 1.25), mean BSCVA improved to 0.79 ± 0.17 (0.4 to 1.0), and mean UCVA was 0.74 ± 0.18 (0.4 to 1.0). The cylinder’s vectorcorrected change was 1.61 D ± 0.71. LASIK after AK proved to he safe, highly efficient, and predictable. There were no adverse events during LASIK and no major complications were reported during or after the procedure.
Conclusions Patients with a residual refractive defect after AK can benefit from LASIK. For the best results, LASIK should he done 3 months after AK. There were no problems with the cut, and with handling the flap. Surgeons are advised to treat the cornea as a virgin one (Figure 18-3 and 18-4).
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
LASIK AFTER PRK
Section 6
Since the introduction of excimer laser Section 7 PRK,22 there has heen a steady increase in the number of PRK procedures performed worldwide.23 The Subjects Index most frequent complications after PRK are regression, haze, central islands, decentered ablations, as well as other less frequently seen complications.24 An estimated 10% to 20% of patients require a repeat PRK procedure for significant regression. Regression is caused by the corneal wound healing response, which may differ from one patient to another Help ? and results in various refractive outcomes and incidence of complications.
The Cornea After PRK It is now well documented that the cornea demonstrates specific acute and delayed responses to excimer laser ablation. Epithelial wounds usually heal over a period of months following PRK. The epithelium first slides to cover the defect initially it
LASIK AFTER PREVIOUS CORNEAL SURGERY
is thinner than normal, but later hyperplasia takes place, and the number of cells becomes greater than normal. Epithelial hyperplasia may be responsible for postoperative regression. The basement membrane, which is removed during PRK, usually regenerates with focal discontinuities and duplication. Normal epithelial attachment completes are regenerated within weeks to months after surgery.25 Stromal changes continue for months or even years after PRK. After closure of the epithelial defect, keratocytes begin transformation into activated fibroblasts and migrate into the treated region, so that the subepithelial 10 to 15 microns become hypercellular. These activated keratocytes synthesize new collagen and extracellular matrix, which may contribute to corneal haze that is observed postoperatively. The new collagen lacks the organized lamellar arrangement characteristics of corneal stromal collagen fibers. 26 Proteoglycans, including keratan sulfate and hyaluronic acid, are produced in response to the injury. The produced hyaluronic acid may change the water balance and thus create disruptions in the lamellar arrangement.26 Depending on the depth of ablation, Bowman’s layer may be partially or completely excised during the procedure.25
Performing LASIK After PRK PRK retreatment for significant regression will significantly reduce residual myopia. However, the risk of further regression, haze and loss of visual acuity exists.27 In addition, treating residual myopia by PRK is less successful than primary PRK.30 LASIK has been used primarily to treat moderate to high myopia because of its superiority over PRK for this range of refractive error.28 Many surgeons are now advocating the use of LASIK rather than PRK for lower levels of myopia, because LASIK preserves Bowman’s layer, decreases the amount of disruption of keratocytes and anterior stromal collagen, and avoids the large epithelial defect seen with surface PRK.29 Because LASIK causes less regression and haze, we studied the results of LASIK in treating residual rnyopia after primary PRK.
Preoperative Considerations It is clear that regression and haze are the most common complications after PRK. These complications will determine, to a great extent, the outcome of treating these patients with LASIK. • Regression: the amount of regression after PRK is related to the amount of myopic correction attempted. The deeper the ablation, the more frequently regression occurs. Regression may continue over months, thus a stable refraction is important to prevent further regression after LASIK. An interval of 1 year is usually enough to achieve a stable refraction. This should be documented by repeated refraction and corneal topography at least twice within 1 month before any attempt to perform LASIK. Contents • Haze: the grade of haze present after PRK can affect the outcome of LASIK. The incidence of Section 1 regression after LASIK is higher in corneas with grade 2 haze or more. In patients with grade 2 or Section 2 more corneal haze, our target should be over- Section 3 correction to compensate for expected postoperative regression. In patients with minimal to Section 4 no corneal haze, our target is emmetropia, as re- Section 5 gression is less likely to occur. For example, in a patient with manifest refraction of -4.0 D with Section 6 corneal haze grade 2, the LASIK surgical plan should be -5.0 D. The immediate postoperative Section 7 overcorrection will be compensated by the ex- Subjects Index pected regression.
Intraoperative Considerations The cut is a critical step in performing LASIK after PRK. The flap should be as thick as possible —not less than 160 µm— the thicker the better. With a thin flap, we may encounter two problems: • First, the microkeratome blade will pass through a peripherally normal clear cornea, and then through a more tough area due to the previous PRK treatment. This will affect the smoothness of the cut in the corneal stroma, resulting in an irregular surface. With a thicker blade, we can avoid this problem by passing beneath the previous PRK treatment area.
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Second, after PRK, Bowman’s membrane may be partially or completely removed, thus the flap will be more liable to wrinkles due to lack of Bowman’s membrane support. This can be compensated by creating a thicker flap. Patients with a keratometric value less than 40 D are more likely to have a free cap and require care in creating the flap.
Postoperative Treatment Patients who undergo LASIK after PRK should be managed with the same regimen used after PRK, using extensive steroids for a long period. Although after a regular LASIK procedure prolonged steroid therapy is not necessary, we found it very effective in decreasing the amount and incidence of haze in LASIK after PRK (Figures 18-3 and 18-4).
Results after LASIK Mean UCVA significantly improved to 0.4 ± 0.29 (0.2 to 0.8) at 1 month, 0.6 ± 0.26 (0.2 to 0.9) at 3 months, and 0.6 ± 0.18 (0.2 to 1.0) at 6 months. One month after LASIK, BSCVA was 0.5 ± 0.31 (0.2 to 0.9); at 3 months, BSCVA was 0.7 ± 0.22 (0.2 to 1.0); and at 6 months, BSCVA was 0.7 ± 0.17 (0.4 to 0. 1). In 78% and 85% of eyes, UCVA was better than 0.5 at 3 and 6 months respectively. Only one eye lost more than two lines of BSCVA after LASIK; this was related to severe haze that developed following an intraoperative flap complication in which the flap was cut into two halves. At the end of follow-up, 98% of the patients where within ± 1.0 D of intended refraction and 77% were within ± 0.5 D.
Conclusions
Contents
Section 1
LASIK seems to be a good alternative to correct post-PRK regression; the procedure is safe, Section 2 effective, and highly predictable. The curve of viSection 3 sual improvement after LASIK seems to follow that of PRK (decrease in immediate postoperative visual Section 4 acuity, followed by an improvement after the first month). This could be related to the significant Section 5 amount of haze observed in this group of patients Section 6 immediately after LASIK, therefore aggressive and prolonged use of topical corticosteroids is necessary Section 7 (Figure 18-5). The microkeratome cut is more difficult after PRK than with virgin corneas. The flap has Subjects Index to be as thick as possible to avoid the increased risk of developing wrinkles and an irregular surface. Figure 18-4: Corneal haze over RK, PRK and LASIK.
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Results (Pilot Study) Thirty patients with regression after PRK were treated by LASIK. The procedure was performed at least 12 months after PRK. The mean preLASIK spherical equivalent was -3.65 ± 1.9 (-1.75 to -6.0), mean pre-LASIK BSCVA was 0.7 ± 0.23 (0.4 to 1.0), and rnean UCVA was 0.24 ± 0.41 (0.1 to 0.6). 222
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Figure 18-5: Haze in LASIK over PRK
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LASIK AFTER LTK When hyperopic errors are corrected by corneal refractive surgery, the goal is to steepen the central cornea in an amount proporcional to the hyperopic error to be corrected. With recent advances in laser technology, LTK was studied for the correction of hyperopia. Erbium, C02, and holmiurn (Ho): YAG lasers were investigated as potencial candidates for this procedure. The C0 2 (10.6 mm) LTK was studied by Peyman, et al, and resulted in superficial retraction of the corneal collagen, as well as early regression of the refractive effect.31 Yr-erbium- glass laser spots (1.54 mm) resulted in extensive penetration and tissue necrosis.32 Ho: YAG laser (2.06 microns) LTK was then used for the correction of hyperopia. Ho: YAG LTK changes the anterior corneal curvature by using the infrared laser energy heat generated in the cornea to change the anterior corneal curvature.33 The corneal collagen shrinks by 30% to 45% of its original length at temperatures ranging from 58ºC to 60ºC. Higher temperatures cause tissue necrosis and relaxation.34 Stromal haze at the treatment site extends from 50% to 70% of the corneal thickness.35 LTK flattens the periphery and thus steepens the central area. The results from Koch3,5 indicate that this could be a promising technology to correct low to moderate hyperopic refractive error. Alió, et al37 recommend that algorithms to improve final results should include an initial calculated overcorrection adjusted to variables that influence regression, such as age and corneal thickness. However, in spite of all these refinements, regression of effect has been a major limitation to the potential refractive outcome of LTK. Regression is variable and may even be total. It was found to be mainly a biophysical mechanism,38 which proved difficult or impossible in most cases to be solved with LTK retreatment.
over time, it is usually present for a long period after LTK. The density and depth of haze are related to the pulse energy. Up to 1 year after LTK, the mean central corneal thickness was slightly thinner than the preoperative value. However, after 2 years, the mean central corneal thickness was almost identical to the preoperative value. From our observations, it seems that the cornea remains unstable for a long time after LTK treatment, especially with unsuccessful treatment. The corneas in these patients tend to return to their original preoperative topographic status, with a multifocal irregular corneal surface.
Performing LASIK After LTK Many patients previously treated with LTK Contents are seeking an altemative surgical treatment for the correction of their residual refractive error. LASIK Section 1 may offer a good alternative for these corrections. With LASIK, it is possible to ablate the corneal pe- Section 2 riphery by stromal photorefractive ablation and pre- Section 3 vent strong epithelial regression with the overlying flap.39 With virgin hyperopic corneas, LASIK proved Section 4 to be very efficient, safe, and predictable. However, Section 5 laser energy is expected to have its own effect at the level of the previous LTK spots, and this may sig- Section 6 nificantly influence its effect on the correction achieved, stability of the refractive results, and cor- Section 7 neal wound healing. Thus, performing LASIK on Subjects Index corneas with previous LTK treatment requires special care in both preoperative evaluation and intraoperative precautions to achieve the best possible results. The only contraindication for this procedure is the presence of a dense corneal opacity that interferes with vision; but even in cases developing irHelp ? regular astigmatism, topography-linked excimer laser ablation can be used.
Preoperative Considerations
The Cornea After LTK After LTK, the opacities in each treatment spot (average diameter is 0.7 mm) decrease with time. After 2 months, they can be observed only under the slit lamp. Although the degree of opacity decreases
As, regression is the main complication after LTK and may continue over a variable duration, LASIK should be postponed until regression has stopped. This might take up to 1 year or even more. Factors affecting regression are:
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Figure 18-6: LASIK over LTK.
Figure 18-7: LASIK over LTK
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more accurate and easier if corneal topography is used to assess centration. The LASIK cut should be performed away from the LTK corneal spots, otherwise the cornea will show dense ring-shaped haze.40 Although this does not influence the immediate visual result, the long term stability of the achieved refractive results are still unknown. A large flap is always preferable to allow perfect peripheral corneal ablation; the flap should be 8.5 mm or more.
•
Age. Greater regression is seen in young adults with relatively elastic stromal tissue and Bowman’s membrane, thus complete refractive stability is essential before LASIK. High pre-LTK hyperopia invites greater and prolonged regression. We need to have at least three consecutive stable corneal topographies over 3 months before performing LASIK.
It is important to distinguish between undercorrection and regression; undercorrection is present in the immediate postoperative period, while regression occurs during the course of healing. However, a longer interval between the two operations allows us to perfonn more accurate surgery and avoid future complications. With our patients, we wait at least 1 year after LTK to perform LASIK. Patients with pre-LTK high degrees of hyperopia should wait up to 18 to 24 months, as they usually show more regression. In general, no LASIK attempt should be considered unless we have a stable refraction and corneal topography for 2 consecutive months. Corneal topography is important to assess the size and shape of the optic zone and to plan the new surgery. Biomicroscopic examination is important in assessing the sites, degree, and extension of stromal scars, usually seen at the LTK treatment sites, to plan the LASIK cut (Figures 18-6 & 18-7).
lntraoperative Considerations Centration is always essential. Decentration is more common in hyperopic patients and will be 224
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Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6
Results (Pilot Study)
Section 7
Twenty-three eyes with significant regres- Subjects Index sion following noncontact LTK treatment underwent LASIK in an attempt to correct their refractive error. LASIK was performed at least 18 months after the LTK treatment. The pre-LASIK mean spherical equivalent changed from +3.14 D ± 1.82 (+0.50 to +6.50) to +0.52 D ± 1.71 (-2.75 to +3.75) 6 months Help ? after LASIK. There was a significant change in refraction between the preoperative and postoperative spherical equivalent values at 1, 3, and 6 months (p < 0.05). There was a minor insignificant change between the pre-LASIK mean BSCVA (0.74 ± 0.15, range: 0.4 to 1.0) and the post-LASIK mean BSCVA at 6 months (0.74 ± 0.18, range: 0.4 to 1.0). Three patients lost one line of BSCVA, and two patients lost more than one line of BSCVA. Six months after LASIK, UCVA significantly improved from a mean value of 0.36 + 0.16 (0.1 to 0.7) to 0.61 ± 0.25 (0.2
LASIK AFTER PREVIOUS CORNEAL SURGERY
to 1.0). Although the procedure seems to be safe, it was not as effective. Six patients (26%) showed no change in preoperative BSCVA from the postoperative UCVA. Three patients (13%) gained one or more Snellen lines, five patients (21%) lost one Snellen line, and nine patients (39%) lost two or more Snellen lines. Seventeen patients (73 %) were within ± 1 D of intended hyperopic correction. Four patients (27%) had regression during the period of 6 months alter LASIK. Regression ranged from 0.75 D to 3.75 D; we believe this regression was a continuation of the regression taking place after LTK.
Conclusions Hyperopic LASIK is a good alternative for the correction of residual refractive errors after holmium LTK. Efficacy and predictability are inferior to that of virgin hyperopic corneas that undergo LASIK, but the procedure seems to be equally safe. We should keep in mind that these corneas are unstable, and a completely stable corneal topographic map is very important to decrease the incidence of further regression after LASIK. To avoid the development of severe haze after LASIK, we perform the LASIK cut away from the previous LTK spots.
LASIK AFTER PKP PKP is a procedure frequently performed worldwide, with more than 34,000 yearly in the United States.40 Most of these cases are left with refractive errors both spherically and cylindrically that may cause variable degrees of anisometropia. Irregular astigmatism is frequently found after PKP, leading to significant limitation in visual performance. The visual result after PKP is influenced by biological and refractive factors. The biological quality of the donor tissue and episodes of graft rejection affect the transparency of the graft. Despite the corneal graft being optically clear, a high astigmatism average of 4 to 6 D,42 and irregular astigmatism associated with the spherical error explains why these patients are unable to reach BCVA with spectacles or contact lenses.
In summary, the main aspects involved in the optical and refractive outcome of this surgical procedure include the following: Biological factors: • Quality of the donor cornea • Difference in thickness between the donor and recipient corneas • Wound healing • Underlying corneal disease Surgical factors: • Graft-recipient disparity • Wound dehiscence • Wound configuration • Eccentric trephination of donor or host cornea • Previous astigmatism of donor cornea • Previous anterior segment surgery (PKP, phacoemulsification, RK) • Time of suture removal and suturing technique are the most important of all. The double-running 10-0 nylon sutures or the combined interrupted and continuous sutures can minimize irregular post-keratoplasty astigmatism when compared with interrupted sutures.43,44 In addition to the wound healing process, there are different responses according to the age of the patient. The younger the patient, the stronger and faster the wound healing. Wound integrity is determined by the amount of whitening and scarring at the PKP wound, especially if associated with vascular invasion.45
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Corneal Refractive Surgery Several techniques are available to correct refractive errors after PKP: • Incisional surgery: effective but unpredictable due to the different quality of the donor cornea, wound healing, and tensional forces of the cornea generated by the wound healing structure. • PRK: produces problems due to laser interaction with wound healing, increasing the risk of haze. Moreover, this can lead to a major risk of graft rejection due to the removal of the epithelium and Bowman’s membrane.
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Figure 18-9: LASIK over PKP. Figure 18-8: LASIK over PKP.
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LASIK: may he the best alternative treatment, especially with the help of topography-linked excimer laser ablation (topolink). With LASIK, we are able to offer an improvement in visual acuity with fast visual recovery and less pain (Figure 18-8 & 18-9). Haze can also appear after LASIK in the donor’s corneal buttom (Figure 18-10).
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Performing Excimer Laser After PKP Surgical correction of the refractive error following PKP depends on corneal regularity. For spherical defects associated with regular astigmatism, we perform: • Standard LASIK treatment with or without previous AK. In cases of astigmatism more than 4 D, we usually perform AK followed by LASIK. For irregular astigmatism, we perfonn: • Topolink • Excimer laser ablation assisted by sodium hyaluronate (ELASHY) • Selective excimer laser zonal ablation (SELZA)
Preoperative Considerations Preoperative ophthalmologic evaluation: • Medical history: it is essential to investigate the causes that led to PKP, with special attention to herpetic keratitis, previous graft rejection, and in keratoconus, which may induce severe astig-
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Figure 18-10: Corneal haze in a patiene thah underwent LASIK over PKP.
Section 6 Section 7 Subjects Index
matic effect, especially after suture removal. Systemic diseases affecting the healing process, as collagen vascular diseases, must be excluded. This might affect the outcome of LASIK. • UCVA and BCVA (with spectacles and rigid/gaspermeable contact lenses). • Refraction should be stable for the last two months before LASIK treatment. • Pinhole visual acuity is a rapid method to diagnose the presence of irregular astigmatism. Details concerning the graft: • Date of surgery, date of suture removal, diameter of corneal button, signs of wound integrity, healing, site and depth of neovascularization.
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•
•
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Corneal topography: we must have a series of two stable consecutive corneal topographies with a 2-month interval to assure a low activity of wound healing and corneal remodeling.45 Recently, the Orbscan elevation maps, the corneal uniformity index (EyeSys), and potential corneal visual acuity (Technomed) give quantitative estimation of corneal regularity not only at the anterior surface but also at the posterior surface of the cornea. Slit lamp biomicroscopy: to plan the cut, it is important to study the presence and extension of corneal neovascularization, the amount of wound scarring, the presence of ectatic areas at the level of previous stitches or dehiscence that could limit or render the LASIK procedure more dangerous. Endothelial microscopy: although LASIK is not dangerous to the corneal endothelium,46 it is always advisable to ascertain the endothelial condition before surgery, considering that the cornea after PKP has continuous cell loss.47 A LASIK procedure should not be considered if the corneal endothelium is severely decreased or at high risk of decompensation. Peripheral and central corneal pachymetry: it is important to measure 8 to 16 corneal points, using the topographic map as a guide, especially at the wound level and at the sites where the cornea seems thinner upon slit lamp examination to avoid perforation of undetected ectasia.
LASIK Indications •
•
Significant spherical and/or astigmatic errors induced by PKP, especially if not correctable with spectacles or contact lenses. Anisokonia due to postoperative refractive defect.
High Risk Cases Contraindications •
and
LASIK
Herpetic keratitis represents a well-known contraindication to excimer laser treatment.48,49 in corneas with post-herpetic PKP, we must consider the possibility not only of keratitis recur-
• • •
•
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rence, but also the risk of allograft rejection due to the reactivation of latent herpes simplex virus present in the corneal nerve and in the keratocytes under the effect of the excimer laser and mechanical trauma. Diffuse corneal neovascularization could represent a considerable problem during surgery. Corneal inflammation is a contraindication —it increases the risk of rejection. High residual astigmatism can render LASIK unuseful even with topolink. Alternative procedures should be considered to treat irregular astigmatism. The presence of sutures is a relative contraindication. In fact, an average of 8.8 D of astigmatism has heen reported after suture removal,43 so it is mandatory to postpone the operation. Bad optical quality of the donor button. Corneal ectasia.
Preoperative Medications
Contents
Section 1 Section 2
We can divide post-PKP patients into four Section 3 main groups suitable for prophylactic therapy before Section 4 undergoing LASIK: 1. Patients with no history of graft rejection Section 5 or herpetic keratitis. To prevent an eventual rejecSection 6 tion we should use topical steroids, dexamethasone 0.1%, or prednisolone 1%, one drop four times a day Section 7 for 15 days before surgery and for 1 month after surSubjects Index gery. 2. Patients with previous rejection episodes. Topical treatment includes dexamethasone 0.1 % or prednisolone 1%, one drop four times a day for 15 days hefore surgery and 1 month after surgery. Systemic treatment: 1 mg/kg per day of prednisolone, 5 days before and after surgery, and then tapered. Help ? 3. Patients with previous herpetic keratitis. In order to avoid recurrence and/or rejection: systemic acyclovir 800 mg per day for 15 days before surgery and 1 month after surgery. 4. Patients with history of herpetic keratitis and rejection. Systemic acyclovir 800 mg per day for 15 days before surgery and 1 month after surgery. Systemic low grade steroids: 15 mg per day for 15 days before surgery and 1 month after surgery.
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When to Operate An interval of 18 to 24 months after PKP is enough for the graft to form a stable union with the host’s peripheral cornea.45,51 The corneal topography should be stable for 2 months after removing the stitches. There are particular circumstances in which it is recommended to perform LASIK treatment earlier, as in young patients intolerant to contact lenses who require fast recovery of their binocular vision.45
Kritzinger performs laser ablation 2 weeks after the microkeratome cut, allowing the cornea to achieve its new refractive configuration after releasing the tensional forces of the fibrotic wound.52 We prefer to do the microkeratome cut and wait one month to assess the change of the astigmatic value. In a considerable number of patients we observed a reduction in the power of the previous astigmatism after the microkeratome cut (Figures 18-11 and 18-12). Patients should be informed of the possibility of undergoing more than one procedure to reach the best refractive results.
Contents
Section 1 Section 2
Section 3 Figure 18-11: Corneal topography in a patient with penetrating keratoplasty with high astigmatism left. We plan to perform LASIK in two stages, first the microkeratome cut and then laser ablation one month later.
Section 4
Section 5
Section 6 Section 7 Subjects Index
Figure 18-12: The same patient two months after laser ablation.
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Intraoperative Considerations Flap diameter: should be as small as possible to avoid bleeding from the injured corneal neovascularization, which could affect the quality of ablation, clarity of the interface, and increase the risk of rejection. If this happens, the surgeon has to clean the interface. If bleeding is severe, we apply to the peripheral limbus a sponge soaked with phenylephrine to induce vasoconstriction in the feeder vessels before ablation. Hinge position: To avoid hinge syndrome, we do not perform the cut opposite the astigmatic axis by using lateral, oblique, or down-up position. The thickness of the flap should not he less than 160 µm.
Conclusions There are few published reports concerning LASIK after PKP45,51,52 and the long-term refractive stability after suture removal.43 It is very difficult to achieve predictable refractive results after LASIK performed on eyes with previous PKP surgery. If we can not guarantee emmetropia to these patients, at least we can offer them benefits by reducing the astigmatism of this «unstable biological tissue» (Figure 18-10). In summary the main aspects involved and to be remembered in LASIK after PKP are: • Corneal stability • Corneal regularity • First reduce the astigmatism with AK if necessary • Size of the flap • Hinge position • Prophylactic therapy against rejection and herpetic keratitis
LASIK AFTER ALK ALK is a lamellar refractive surgery technique used to change the anterior surface of the cornea by removing a portion of the corneal stroma. In ALK, a three-piece suction ring is used to create the flap. The suction ring also enables us to determine
and perform the second refractive cut. Myopic treatment depends on removing a portion of the central corneal stroma. Hyperopic treatment uses a transverse circular cut of corneal lamellae at 70% depth of the corneal thickness and 6.0 mm diameter. Predictability is the main problem we faced in the past with this type of surgery, resulting in a high incidence of over or undercorrection. Now, these patients are requiring a second surgery to correct residual refractive error. Here we report the outcome of LASIK in treating these patients.
The Cornea After ALK The following features may be found in the cornea after ALK: nonadherent or lost cap, epithelial growth in the interface, and regular or irregular astigmatism. Concerning visual outcome, it is true that this technique is relatively efficient in the correction of myopia. However, it is also true that any minimal decentration between the two corneal cuts could produce distortion of the central optical zone, leading to irregular astigmatism and subjective visual alterations such as glare, diplopia and decrease in the contrast sensitivity. In myopic treatment, ALK will produce a small central depression corresponding with the central corneal cut. In hyperopic treatment, we may find induced keratoconus due to central corneal ectasia.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Performing LASIK After ALK LASIK may be an efficient tool in treating residual refractive error after ALK, but as it uses a lamellar cut, additional technical and intraoperative problems may arise, which might render this technique very difficult and unsafe in some cases. Thus, careful patient selection is mandatory to improve the outcome of this procedure.
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Preoperative Considerations After ALK, time is the most important factor to assure good corneal healing. Albino Parisi re-
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ported a case of an involuntarily dissected and elevated ALK flap during a LASIK attempt 6 months after ALK.11 A period of 2 years is essential to achieve a stable corneal condition and to decrease the possibility of such a major complication. The refractive state of the cornea should be stable to improve the predictability of the treatment. We carefully study the corneal topography of these patients to exclude the possibility of induced keratoconus (central corneal ectasia) after hyperopic ALK treatment, which is a contraindication for LASIK.
Intraoperative Considerations The LASIK cut is the most critical step, it should be performed superficial to the previous cut, which is difficult to judge. The cut may pass parallel to or intersect with the previous ALK cut, inducing irregular astigmatism or increasing the already present astigmatism. In cases of undiagnosed induced keratoconus, the LASIK cut will be too deep, the cornea will be thinner and more ectasia will develop, inducing major complications and a significant decrease in the visual acuity. lt is advisable to abort the procedure as soon as any difficulty is encountered in performing the cut to avoid further complications. We experienced some problems with the LASIK cut as it intersected with the previous ALK keratectomy, producing an irregular surface.
Conclusions LASIK is not a highly predictable procedure in treating a residual refractive defect after ALK. Careful patient selection and a 2-year interval between surgeries should be enough to improve the efficacy and predictability of the procedure. Other techniques to treat irregular astigmatism should be considered in treating these patients.
LASIK AFTER EPIKERATOPHAKIA Epikeratophakia was used to treat adult aphakia, pediatric aphakia, and severe myopia. This tech-
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nique is obsolete due to the high incidence of complications, including lack of predictability, poor optical results, almost constant irregular astigmatism, chronic epithelial defects with scarring, tissue melting, long period of time to recover BSCVA due to lack of corneal transparency, undercorrection, overcorrection, glare, diplopia, and reduced contrast sensitivity. Also, the procedure is not totally reversible, as it was previously thought to be. Before LASIK treatment, it is important to assess corneal transparency and measure the button diameter. During LASIK, the cut should be done within the lamellar button by creating the smallest possible flap to avoid peripheral lamellar dissection. We have limited experience with these cases and further studies are needed to evaluate the long-term refractive outcome. Contents
LASIK AFTER CORNEAL TRAUMA
Section 1
Several types of trauma, such as penetrating Section 2 corneal wounds, chemical burns, and radiant energy, Section 3 could affect the cornea. It is very important before performing a LASIK treatment to check the pres- Section 4 ence of corneal opacity, neovascularization, and irSection 5 regular astigmatism. In the presence of a corneal scar, we avoid cutting through it, especially if it is close Section 6 to the limbus, to avoid bleeding from the new vessels. The possibility of cutting through corneal ecta- Section 7 sia should be excluded by evaluating the pachymetric Subjects Index value of the suspected zone. The quality of laser ablation and its rate differ according to the density of the corneal scar, thus the patient should be advised that he or she might need more than one procedure to correct the refractive defect. Topography linked excimer laser ablation (topolink) should be useful in most cases. Help ?
FUTURE OF LASIK AFTER OTHER CORNEAL SURGERIES Regression, undercorrection, and overcorrection are possible complications following various refractive surgical procedures. LASIK has proved to be a safe method in treating these refractive defects in most cases. However, these corneas are usually
LASIK AFTER PREVIOUS CORNEAL SURGERY
unstable. With careful patient selection, preoperative evaluation and intraoperative management, we can usually improve the efficacy and predictability of this procedure.
REFERENCES 1. Villaseñor RA, Cox KO. Radial keratotomy: reoperations. Journal of Refractive Surgery. 1985; 1:34-37. 2. Saiz JJ. Radial keratotomy. In: Thornpson FB, ed. Myopia Surgery: Anterior and Posterior Segments. New York, NY: Macmillan; 1990. 3. Waring GO III, Lynn MJ, MeDonnel PJ. PERK study group. Results of the prospective evaluation of radial keratotomy (PERK) study 10 years after surgery. Arch Ophthalmol. 1994; 112:1298-1308. 4. Azar DT, Benson RA, Hardten DR. The PRK after RK study group. Photorefractive keratectomy for residual myopia after radial keratotomy. J Cataract Refract Surg. 1998;24:303-311. 5. Salz JJ, Salz JM, Salz M, Jones D. Ten years experience with a conservative approach to radial keratotomy. J Refract Corneal Surg. 1991;7:12-22. 6. Werblin TP, Stafford GM. The Casebeer system for predictable keratorefractive surgery: 1-year evaluation of 205 consecutive eyes. Ophthalmology. 1993; 100: 1095-1102. 7. Sawelson H, Marks RG. Two-year results of reoperations for radial keratotomy. Arch Ophtalmol. 1988;106:497-501. 8 . Gayton JL, Van Der Karr M, Sanders V. Radial keratotomy enhancements for residual myopia. Journal of Refractive Surgery. 1997;13:374-381. 9. Werblin TP, Stafford GM. Radial keratotomy predictability (letter). Ophthalmology. 1994;101:416. 10. Hahn TW, Kim JH, Lee YC. Excimer laser photorefractive keratotomy to correct residual myopia after radial keratotomy. J Refract Corneal Surg. 1993;9(suppl):S25-S29. 11. Durrie DS, Schumer DJ, Cavanaugh TB. Photorefractive keratectorny for residual myopia after previous refractive keratotomy. J Refract Corneal Surg. 1994;10:S235-5238. 12. Salz JJ, Assil KK, Colin J. Radial keratotomy. In: Serdarevic 0, ed. Refractive Surgery: Current Techniques and Management. New York: Igaku-Shoin Medical Publishers. 1997;27-36. 13. Deitz MR, Sanders DR. Progressive hyperopia with longterm follow-up of a radial keratotomy. Arch Ophthalmol. 1985;103:782-784. 14. Duke-Elder SS, Abrams D. Ophthalmic optics and refraction. In: System of Ophthalmology. Vol 5. St.Louis, Mo: CV Mosby; 1970. 15. Buzard K, Shearing S, Relyea R. Incidence of astigmatisrn in a cataract practice. Journal of Refractive Surgery. 1988;4:173. 16. Guyton DL. Prescribing cylinders: the problem of distortion. Surv Ophthalmol 1977;22:177-188. 17. Thompson V. Astigmatic keratotomy. In: Serdarevic 0, ed. Refractive Surgery: Current Techniques and Management. New York: Igaku-Shoin Medical Publishers. 1997.
18. Duffey RJ, Jain VN, Tachah H, et al. Paired arcuate keratotomy. A surgical approach to mixed and myopie astigmatism. Arch Ophthalmol. 1988; 106:1130-1135. 19. Merlin U. Curved keratotomy procedures for congenital astigmatism. Journal of Refractive Surgery. 1987;3:92-97. 20. MeDonnell PJ, Moreira H, Terrance N, et al. Photoreractive keratectomy for astigmatism-initial clinical results. Arch Ophthalmol. 1991; 109:1370-1373. 21. Vajpayee RB, Taylor HR. Photorefractive keratectomy for astigmatism. In: Serdarevic 0, ed. Refractive Surgery: Current Techniques and Management. New York: Igaku-Shoin Medical Publishers. 1997; 207-216. 22. Munnerlyn CR, Koons SJ, Marshall J. Photorefractive keratectomy: a technique for laser refractive surgery. J Cataract Refract Surg. 1988; 14:46-52. 23. Seiler T, McDonnell PJ. Excimer laser photorefractive keratectomy. Surv Ophthalmol. 1995;40:89-118. 24. Kim JH, Sah WJ, Kim MS, et al. Three-year results of photorefractive keratectomy for myopia. Journal of Refractive Surgery. 1995;11(3suppl):418-20. 25. Wu WCS, Stark WJ, Green WR. Corneal wound healing after Contents 193-nm excimer laser keratectomy. Arch Ophthalmol. 1991;109:1426-1432. Section 1 26. Tuft SJ, Zabel RW, Marshall J. Corneal repair following keratectomy: a comparison between convencional surgery and Section 2 laser photoablation. Invest Ophthalmol Vis Sci. 1989;30:17691777. Section 3 27. Chayet AS, Assil KK, Montes M, Espinosa-Lagana M, Castellanos A, Tsioulias G. Regression and its mechanisms after laser Section 4 in situ keratomileusis in moderate and high myopia. Ophthalmology. 1998;105:1194-1199. Section 5 28. Pallikaris IG, Papatzanaki ME, Stathi E. Laser in situ keratomileusis. Lasers Surg Med. 1990; 10:463-468. Section 6 29. Fiander DC, Tayfour F. Excimer laser in situ keratomileusis in 124 myopic eyes. Journal of Refractive Surgery. 1995; Section 7 11(3suppl):S234-8. 30. Sutton G, Kalski RS, Lawless MA, Rogers C. Excimer Subjects Index retreatment for scarring and regression after photorefractive keratectomy for myopia. Br J Ophthalmol. 1995;79:756- 759. 31. Andrews AH. Modification of rabbit corneal curvature with the use of carbon dioxide laser burns. Ophthalmic Surg. 1980;11:325-329. 32. Kanoda AN, Sorokin AS. Corneal curvature change using energy of laser radiation. In: Fydorov SN, ed. Microsurgery of the Eye. Moscow: Mir Publishers; 1987:147-154. Help ? 33. Koch DD, Berry MJ, Vassiliadias AJ, et al. Noncontact holmium: Yag laser thermal keratoplasty. In: Salz JJ, ed. Corneal Laser Surgery. St. Louis, Mo: Moshy-Year Book, Inc; 1995. 34. Moreira H, Campos M, Sawush MR, et al. Holmium laser thermokeratoplasty. Ophthalmology. 1993;100:752-761. 35. Koch DD, Abarca A, Villarreal R, et al. Hyperopia correction by noncontact holmium: yag laser thermal keratoplasty: clinical study with 2-year follow-up. Ophthalmology. 1996;103:731-740. 36. Koch D, Abarca A. Laser thermal keratoplasty. Ophthalmology. 1996;103:1525-1536. 37. Alió JL, Ismail M, Sanchez-Pego JL. Correction of hyperopia with noncontact Ho: yag laser thermal keratoplasty. Journal of Refractive Surgery. 1997; 113:17-22.
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38. lsmail MM, Perez Santonja JJ, Alió JL. Correction of hyperopia and hyperopic astigmatism by laser. In: Serdarevic 0, ed. Refractive Surgery: Current Techniques and Management. New York: Igaku-Shoin Medical Publishers. 1997. 39. Ditzin K, Huschka H, Pieger S. Laser in situ keratomilcusis for hyperopia. J Cataract Refract Surg. 1998;24:42-47. 40. Attia WH, Alió JL, Perez Santonja JJ. LASIK following LTK regression in hyperopic patients. Journal of Refractive Surgery. Submitted for publication April 1999. 41. Eye Bank Association of America. 1996 Eye Banking Statistical Repori. Eye Bank Association of America, Washington, DC; 1996. 42. Vail A, Gore SM, Bradley BA, et al. Corneal graft survival and visual outcome. A multicenter study. Ophthalmology. 1994; 10 1: 120-7. 43. Hoppenreijs VP, Van Rij G, et al. Causes of astigmatisrn after penetrating keratoplasty. Doc Ophthalmol. 1993;85:21-34. 44. Busin M, Monk T, Al Nawaiseh I. Different suturing techniques variously affect the regularity of postkeratoplasty astigmatism. Ophthalmology. 1998;105:1200-1205. 45. Lam DS, Leung AT,Wu JT, Tham CC, Fan DS. How long should one wait to perfonn LASIK after PKP? J Cataraci Refract Surg. 1998;24:6-7. 46. Perez-Santonja JJ, Sakla HF, Alió JA. Evaluation of endothelial cell changes 1 year after excimer laser in situ keratomileusis. Arch Ophthalmol 1997; 115:841-846. 47. Bourne WM, Hodge DO, Nelson LR. Corneal endothelium 5 years after transplantation. Am J Ophthalmol. 1994; 1 18:185196. 48. Pepose JS, Laycock KA, Miller JK, et al. Reactivation of latent herpes virus by excimer laser photokeratectomy. Am J Ophthalmol 1992; 144:45-50. 49. Vrabec MP, Durrie DS, Chase DS. Recurrence of herpes simplex after excimer laser keratectomy. Am J Ophthalmol. 1992; 1 16:101-102. 50. Xie LX, Dong XG, Kaufman HE. Investigation of herpes simplex virus type-1 latency in corneas. Chin Med J Engl. 1993;106(4):288-91.
51. Parisi A, Salchow DL, et al. Laser in situ keratomileusis after automated lamellar keratoplasty and penetrating keratoplasty. J Cataract Refract Surg. 1997;23:1114-1 1 1 S. 52. Kritzinger MS. Corneal transplant patients far better with LASIK than PRK. Ocular Surgery News. 1998,16:34. 53. Artola A, Ayala MJ, Pérez-Santonja JJ, Salem TF, Muñoz G, Alió JL. Haze after LASIK in eyes with previous PRK. J Cataract Refract Surg (acepted for publication). 54. Alió JL, Artola A, Attia WH, Pérez-Santonja JJ, Ayala MJ, Claramonte P, Ruiz-Moreno JM. Lasik for the treatment of residual myopia. American Journal of Ophthalmology (acepted for publication).
Jorge L. Alió, M.D., PhD. Instituto Oftalmológico de Alicante Fundación Jorge Alió Avda. de Denia, 111 03015 Alicante, España E-mail:
[email protected]
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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PEDIATRIC LASIK
Chapter 19 PEDIATRIC
LASIK
T. Agarwal,M.D., S. Narang, M.D, P. Narang, M.D., S. Choudhry, M.D., R. M. Choudhry, M.D.
Introduction The cornea contributes 2/3 rd of the refracting power of the eye. As most of light reflection occurs at the air / tear film interface, Barraquer attempted to alter the tear film / anterior cornea interface radius of curvature by adding or removing corneal tissue1. The term Keratomileusis is derived from the Greek roots Keras (horn-like = cornea) and smileusis(carving), was introduced to describe lamellar techniques2. LASIK was introduced, designed and developed at the university of Crete and the Vardinoyannion Eye institute of Crete (VEIC) in 19883. The procedure involves raising a corneal cap and removing the tissue by photoablation from the residual stromal bed.
LASIK Lasik is usually performed in patients more than 18 years of age after refraction stability has been achieved. Exception is made for those anisometropic patients that have difficulty in maintaining contact lenses4. A variety of options are available for correcting pediatric refractive errors; but spectacle and contact lenses form the most common mode. Spectacles are affordable and allow frequent correction of changing refractive error. But they have their own disadvantages in the sense that they are not suitable in cases of uniocular high refractive errors, are prone for scratches, cosmetically not acceptable and provide an image of suboptimal quality. Contact lenses
have the advantage of a bigger field and better quality of vision, especially in eyes with higher refracContents tive errors. In contrast sensitivity testing, the visual performance of highly myopic patients is better with Section 1 contact lenses than with spectacles5. In cases of unio- Section 2 cular high refractive errors with a refractive error difference of more than 3.0 diopters that is uncor- Section 3 rected, it has been shown that the eyes develop aniSection 4 sometropic amblyopia, which prevents the development of binocular single vision. Treating anisome- Section 5 tropic amblyopia at 4 years of age seems to be efficacious in most cases, although it has been shown Section 6 that the response is better if treatment is done at 2 Section 7 years of age6. The critical factors in a successful outcome Subjects Index are the amount of anisometropia, visual acuity at the start of treatment, and patient compliance7, which is often poor in children. Children usually develop diplopia and intolerance if corrected with glasses. In such cases, contact lenses are the preferred mode of correction. Contact lenses are used for the therapeuHelp ? tic treatment of aphakia, anisometropia, myopia, hyperopia, esotropia, irregular astigmatism, and nystagmus8, but contact lenses are difficult to maintain in children. Radial keratotomy (RK) reduces the refractive error in highly myopic patients9, but its safety in children is yet not proven. Photorefractive keratectomy(PRK) has shown promising results in selected patients. The results of myopic PRK in pediatric eyes with amblyopia resulting from anisometropia are good10,11 .The question which arises
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is that could LASIK do a good job for correction of pediatric myopic anisometropia. LASIK is a viable method for correcting high myopia with few complications. It preserves the Bowman’s layer in addition to the excimer laser precision like PRK12.
Patient Selection 25 pediatric eyes with uniocular high myopia underwent LASIK surgery and were retrospectively analyzed. Patients underwent Lasik only if the refractive error difference between their eyes was more than 4.0 diopters. All patients were less than 11 years of age. Exclusion criteria - were previous intraocular surgery, any associated posterior segment pathology, active inflammation, infection, corneal scarring, pachymetry value less than 500 microns, keratoconus, intraocular pressure(IOP) more than 19 mm Hg, a narrow palpebral fissure, associated astigmatism, and a Schirmer test of less than 5.0 mm. The following pre-operative evaluations were done: best corrected visual acuity (BCVA), cycloplegic refraction, estimation of the palpebral aperture, anterior segment evaluation, measurement of the corneal diameter, Schirmer test, corneal topography, pachymetry, IOP evaluation by noncontact tonometry, and a detailed fundus evaluation by indirect ophthalmoscopy.
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shielded from the laser by a cellulose strip. After the ablation, the flap was repositioned and the interface thoroughly washed to remove particulate and cellular debris. Care was taken to ensure there were no striae in the flap. The suction ring was gently removed and the flap was allowed to settle for at least 3 minutes, and then a patch was applied to the eye for 6 hours. The eyes were patched in case the children did not co-operate in keeping the flap in place and so the flap was not disturbed during recovery from anesthesia. Two patients had a free cap during the procedure. The caps were replaced using the alignment marks and sutured with 4 interrupted 10/0 polyester fiber(Mersiline) sutures that were removed at the 6th month visit. Tobramycin 0.3% with dexamethasone eye drops were applied 4 times a day for 1 month.
Follow-up The patients were reviewed at 1 day, 1 week, and 1,6, and 12 months post-operatively. The follow-up examinations included uncorrected visual acuity (UCVA), BCVA, refraction(noting induced astigmatism, if present), detailed anterior segment evaluation, grading of haze based on a 5-point scale(with 0 as no haze and 4 as maximal haze), IOP, corneal topography, and a detailed fundus evaluation.
Surgical Technique
Ablation Parameters
All surgeries were performed at Agarwal’s Eye hospital, Chennai. Fully informed consent was taken from the parents before the procedure. The patients were sedated with intravenous Ketamine (2-3 mg/kg) under a qualified anesthetist supervision. The Automatic corneal shaper- ACS (Bausch and Lomb) equipped with a mechanical stop and a modified suction ring was used to cut a 160 micron lamellar corneal flap with 9 mm diameter and a nasal hinge. The flap was carefully lifted with a blunt instrument and reflected on its hinge. The laser was carefully centered and the ablation performed. The flap was
Ablation was performed using Chiron Technolas Keracor 217 excimer laser(Bausch and Lomb). Laser fluence was checked before each procedure by verifying the homogeneity and symmetry of pulses according to optimal values of 65 shots +/- 1(SD). The fluence was 130 mJ and an autotracking mechanism with scanning laser technology and a 2 mm beam spot size was used. The ablation diameter was generally 6.0 mm, but in some cases it was reduced to 4.0 mm based on pre-operative refraction.
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Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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PEDIATRIC LASIK
TABLE-1. Patient Demographics CHARACTERISTICS No. of eyes Mean age ± SD (yrs)
RESULTS 25
Results
8.04 ± 2.13
Male:Female
11:14
OD:OS
12:13
Followup period
Excess of airborne debris in the operating room was controlled by ultrafiltration of air, and ultraviolet exposure of the laser device was done 24 hours before the day of surgery.
12 months
Mean preop spherical eq.
14.57 ± 3.15
Mean postop spherical eq.
1.36 ± 1.075
Mean preop BCVA
0.53 ± 0.27
Mean postop BCVA
0.55 ± 0.26
All 25 eyes were followed for 12 months. Statistical analysis showed the refractive power was reduced significantly after LASIK. The results followed a normal distribution. The demographic data are shown in Table 1 & Table 2. Student’s t-test was used for statistical analysis. The mean pre-operative BCVA in decimal equivalent was 0.53 ± 0.27 SD (range 0.17 to 1) and the mean postoperative BCVA Contents
Section 1 Section 2
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TABLE-2 Results of Pediatric Lasik
Section 4
Section 5
Section 6 Section 7 Subjects Index
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Figure 19-1- Shift in decimal equivalent
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Section 3
Section 4
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Section 6 Section 7 Subjects Index
Figure 19-2- Best-corrected visual acuity (BCVA)
in decimal equivalent at the 12th month was 0.55 ± 0.26 SD (range 0.17 to 1) [p = 0.34](Figure 19-1). The mean uncorrected UCVA at the 12th month was 0.33 ± 0.27 SD (range 0.1 to 1). The safety index (Mean postoperative BCVA / Mean preoperative BCVA ) was 1.04 and the efficacy index (Mean postoperative UCVA / Mean preoperative BCVA) was 0.6. The mean preoperative spherical equivalent was -14.57±3.15 SD (range -9D to -23D). The mean postoperative spherical equivalent was 1.36 ± 1.07 SD (range 0D to -2.5D) [p<0.05] (Figure s 19-2 & 19-3).
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The details of the results are shown in Table 2. None of our patients had an induced astigmatism of more than 0.5 diopters. 2 patients had an induced astigmatism of 0.5 D evident on corneal topography but did not significantly contribute to the refractive correction. Figure 19-4 shows the preoperative topography of a patient and Figure 19-5 shows the post operative topograph of the same patient. Two patients had a free flap during the procedure; in 1, the BCVA decreased by one line due to persistent grade 2 haze. Three eyes that had a preoperative spherical equivalent of more than -17 diopt-
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Figure 19-3- Power residue
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Section 1 Section 2
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Section 6 Section 7 Subjects Index
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Figure 19-4- Pre-Operative Topograph
Figure 19-5- Post-Operative Topograph
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ers developed grade 2 haze, one of which spontaneously resolved by the visit at the sixth month. The other two, (including one eye which had a free cap), had persistent haze even upto the 12th month follow-up and subsequently had a drop in their BCVA by one line. None of the patients developed corneal haze more than grade 2. 19 eyes regained their preoperative BCVA after the procedure and 4 eyes improved by one line. None of the eyes developed rise in IOP or any retinal complication. The reason for the haze is not known. The haze was diffuse and present in the interface. It would seem that children have more tendencies than adults for this phenomenon and it could be due to the cornea being younger in children. It was not a very dense haze to cause extreme loss of vision. The postoperative spherical equivalent was -1D or less in 11 of the 25 eyes (44%), between -1 and -2 D in 10 eyes(40%), -2.5 D in 2 eyes(8%) , -3 D in I eye(4%) and -4 D in one eye(4%). No child with a low pachymetry reading was included in the study. The minimum pachymetry reading was 570 microns and the range was from 570 microns to 630 microns.
SUMMARY Myopia is a common refractive error in children. Spectacle correction and contact lenses are the popular modes of correction. In cases of uniocular high myopia, if the refractive error is more than 3.0 D, a high incidence of intolerance because of dissimilar image size and optical aberrations has been found with spectacles. These cases develop anisometropic amblyopia if left uncorrected. This is because of the minifying effect of concave lenses and vertex distance factor. Conventional amblyopia therapy includes occlusion, to which all children are not compliant. Contact lenses do not minify images, do not have optical aberration, and do not have anisometropia problems. But some children become contact lens intolerant and have problems maintaining them. Studies show that LASIK in adults is accurate and predictable13. LASIK is not usually done in children because myopia does not stabilize until early adulthood. However, treatment resistant anisometropic amblyopia is a strong medical indication for
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LASIK treatment. Our goal in this study was to equalize the refractive power and thereby retard the stimulus and, if possible, reverse amblyopia. The children were sedated for obvious reasons. But the children could not fixate on the light, and the microkeratome footplate was used to aid in fixation. The eyes were patched so that the flap was not disturbed in the immediate postoperative period. Two patients had a free cap, which was sutured in place. The retrospective keratometry value was 39.0 D. One of the eyes lost 1 line of BCVA because of flap striae and persistent grade 2 haze. In 4 eyes BCVA improved, probably amblyopia reversal or better quality of vision after the refractive correction. We do not recommend including cases with keratometry readings below 40.0 D. Our one year results show that LASIK is a safe alternative to correct pediatric myopic anisometropia. We think that LASIK can be performed in children if done with care. One should first try contact lenses. If this is not possible or successful, LASIK can be performed. The problem we saw in our pediatric patients that is not generally seen in adults was haze in the interface. We think this could be due to the age of the cornea since it seems to appear more in children than in adults. At present, we think LASIK is a good alternative in the treatment of anisometropic amblyopia. The study of LASIK in pediatric hyperopic patients is yet to be conducted and its results to be scrutinised.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
REFERENCES 1. 2.
3. 4.
5.
Barraquer JI: Keratoplastic refractive. Estudies Inform 10: 2-21, 1949. Bores L: Lamellar refractive surgery. In Bores L (Ed): Refractive eye surgery. Blackwell scientific publications: Boston 324-92, 1993. Pallikaris I, Papatzanaki M, Stathi EZ et al: Laser in situ keratomileusis. Laser surg Med 10: 463-68, 1990. Luiz Antonio Pereira Santini : LASIK: How to achieve a better outcome. Refractive surgery, Jaypee brothers publications : New Delhi,2000, 29; 306-310. Collins JW; Carney LG. Visual performance in high myopia. Curr Eye Res 1990; 9:217-23.
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6.
7.
8. 9.
10.
11.
12.
13.
Lithander J; Sjostrand J. Anisometropia and strabismic amblyopia in the age group 2 years and above: a prospective study of the results of treatment. Br.J.Ophthal 1991;75:111-6. Beardsell R; Clarke S; Hill M. Outcome of occlusion treatment for amblyopia. J Pediatric ophthalmol strabismus 1999;36: 19-24. Jurkus JM. Contact lenses for children. Optom clin 1996; 5: 91-104. Pak KH; Kim JH. Radial keratotomy for the purpose of reducing glasses power in high myopia. Korean J Ophthal 1992; 6: 83-90. Hugo D Nano, Jr, MD,Sergio Muzzin, MD, L. Fernandez Irigaray, MD. Excimer laser photorefractive keratectomy in pediatric patients. J cataract refractive surg 1997; 23: 736-739. Jorge L. Alio, MD, Ph.D, Alberto Artola, PhD, Pascual Claramonte, MD, Maria J. Ayala, PhD, Enrique Chipont, PhD. Photorefractive keratectomy for pediatric myopic anisometropia. J Cataract Refract Surg 1998; 24: 327-330. Marinho A; Pinto MC; Pinto R; Vaz F; Neves MC. LASIK for high myopia: one year experience. Ophthalmic surg Lasers, 1996; 27: Suppl, S517-20. Condon PI; Mulhem M; Fulcher T; Foley Nolan A; Okeefe M. Laser intrastromal keratomileusis for high myopia and myopic astigmatism. Br J Ophthalmol, 1997; 81: 199-206.
Contents
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Section 3
Section 4
Section 5
Section 6 Section 7
T. Agarwal, M.D. Dr. Agarwal’s Eye Hospital, 19 Cathedral Road, Chennai (Madras)- 600 086, India
Subjects Index
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• Part of the text and some of the figures of this Chapter are presented with permission from Agarwal et al textbook on REFRACTIVE SURGERY published by Jaypee, India , 1999.
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Section 4 Section 5
Section 6 Section 7 Subjects Index
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LOCAL FREEZING FOR EPITHELIAL INGROWTH AFTER LASIK
Chapter 20 FIRST NON-INVASIVE TREATMENT FOR SUBLAMELLAR EPITHELIAL INGROWTH AFTER LASIK BY LOCAL FREEZING Juan Murube, MD., PhD.
Sequence of Events Epithelial ingrowth under the corneal flap of LASIK is a frequent complication, affecting between 2 and 10% of the operated eyes (1,2,3,8). The epithelial invasion is usually initiated from a fistulous tract at the edge of the flap. This complication does not occur as a consequence of a free implantation of epithelial cells in the interface during surgery. It forms a continuous sheet with scattered hyperplasic dots, forming geographical figures like an archipelagus. When the epithelial ingrowth is limited to the peripheral part of the flap, it can give rise to a foreign body sensation, photophobia, necrosis of the suprajacent stroma, and pain. Occasionally it may act as an entry point for interlamellar infection. When the epithelial ingrowth advances centrally and invades the optical zone it provokes irregular astigmatism, haze, dazzling, low visual acuity and low contrast sensitivity (2,4).
Contents
flap in order to avoid folds and striae when reattaching it. After lifting the corneal flap, the invading Section 1 epithelium is removed with a surgical knife, drill, PTK, Nd:YAG laser, or irrigation associated with Section 2 scraping with the point of a cannula (2, 5, 6, 8). Some Section 3 authors introduce alcohol or cocaine in the interface Section 4 to facilitate the scraping. But invasive methods may give rise to many Section 5 problems: laceration of the flap edge –especially when six months have elapsed, or when there is Section 6 keratolysis-, (accidental ablation of corneal stroma), Section 7 or creation of folds when replacing the flap. The epithelial pearls are easy to detect under the slit lamp Subjects Index or the surgical microscope when the corneal layers are all in place, but when the flap is lifted or detached to remove the pearls, they are undetectable and any remaining epithelium goes unnoticed. Therefore, new methods must be found to avoid use of the currently existing invasive techniques. Help ?
The New Non-Invasive Method Management Techniques Presently Available All the methods previously published for elimination of post-LASIK epithelial ingrowth are invasive, and involve lifting of the corneal flap. Some authors detach only the flap sector occupied by the epithelial pearls, while others prefer to lift the whole
To the best of our knowledge, this is the first non-invasive method reported in the literature. It consists in the destruction of the sublamellar epithelial ingrowth by brief freezing of the invaded sector. This is achieved by application of a surgical cryoprobe over the affected corneal surface, specifically where the epithelium has invaded the interface. The cryoprobe begins to be applied at the LASIK AND BEYOND LASIK
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Section 4
Section 5 Figure 20-1: Murube’s Non-Invasive Cryo Application Method to Destroy Invading Epithelial Cells at the Edge of the LASIK Flap Following LASIK, the epithelial ingrowth invading the edge of the cornea (E) is a complication affecting between 2 – 10% of operated eyes. In this illustration you may observe Murube’s non-invasive method to eliminate the epithelial cells growth. This is accomplished by application of a surgical cryoprobe (C) over the affected corneal surface and freezing of the invaded sector. This is effectively accomplished without having to lift the flap. (Courtesy of Highlights of Ophthalmology)
edge of the flap, which is where the epithelial pearls are first located. It is important to apply the cryo before too extensive epithelial invasion is present.
Technique Step by Step Topical anesthesia is applied to the patient lying flat on a stretcher. A lid speculum is inserted in, and the cornea observed under surgical microscope. The area of intralamellar invasion is marked on the epithelium with a dermographic
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gentian violet pencil. The epithelial pearls are more visible with mydriasis. A cryoprobe for retinopexy (Model Erbokryo AE, Erbe, Germany or equivalent), is applied over the edge of the flap in the sector of epithelial invasion, and applied for 3-4 seconds, reaching a temperature of -70/-80ºC (Fig. 20-1). Each application is performed twice (Fig. 20-1). When the ice ball has disappeared and the cryoprobe can be removed from the cornea, a drop of dexamethasone is instilled and the eye is covered for 24 hours. The drops are applied q.i.d for one week.
Section 6 Section 7 Subjects Index
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LOCAL FREEZING FOR EPITHELIAL INGROWTH AFTER LASIK
Results On the first postoperative day the epithelial ingrowth looks very similar to the one seen in the preoperative stages. It is not possible to determine whether the cells are still alive or not. There is a small edema localized where the cornea was frozen. The epithelium stains diffusely with fluorescein. The patient may feel discomfort, and sometimes moderate pain for several hours which diminishes with sedatives and disappears with anesthetic drops. One week after cryoapplication, the invasive epithelial sheet and most of the pearls have disappeared, and the remaining ones present diffuse, not round, regular edges. The epithelium does not stain. Pachymetry and endothelial count are as they were preoperatively. We do not know if this is because the cells did not die or because they are replaced by the surrounding cells. One month after cryoapplication, there is no evidence of epithelial sublamellar ingrowth. Occasionaly a diffuse interface opacity may persist. Corneal pachymetry, endothelial cell count and refractometry do not change.
6. Kapadia MS, Wilson SE. Transepithelial photorefractive keratectomy for treatment of thin flaps or caps after complicated laser in situ keratosmileusis. Am J Ophthalmol 1998;126:827-829. 7. Murube J, Murube E, Gómez Carrasquel R, ChenZhuo L, Duran P. Nuevo tratamiento mediante crioterapia de la invasión sublamelar epitelial tras lasik. Arch Soc Canar Oftalmol 2000;11:117-120. 8. Boyd, B.F.,: Postoperative flap complications after LASIK. Atlas of Refractive Surgery, Highlights of Ophthalmology, 2000; 4:94-99.
Prof. Juan Murube, M.D. Clinica Murube San Modesto, 44-1º Madrid E-28034, Spain E-mail:
[email protected]
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
REFERENCES
Section 6 Section 7
1. Lin RT, Maloney RK. Flap complications associated with lamellar refractive surgery. Am J Ophthalmol 1999; 127:202-204. 2. Marotta H. Treatment of epithelial ingrowth. In: Buratto L et al. Lasik surgical techniquess and complications. 2000, Slack Inc. Thorofare, NJ, pp. 547-553. 3. Pérez Santonja JJ, Ayala M, Sakla H, Ruiz Moreno J, Alió JL. Retreatment after LASIK. Ophthalmology 1999; 106:21-28. 4. Castillo A, Díaz VD, Gutiérrez A, Tolendo N, Romero F. Peripheral melt of flap after LASIK. J Refract Surg 1998; 14:61-63. 5. Lim JS, Kim EK, Lee JB, Lee JH. A simple method for the removal of epithelium grown beneath the hinge after LASIK. Yonsei Med J. 1998; 39:236-239.
Subjects Index
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PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
Chapter 21 PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS Weldon W. Haw, M.D., Edward E. Manche, M.D.
(Note from the Editor in Chief: the following is one of the very best presentations on this subject available today. It is complete, well written, allencompassing, balanced, clear and well organized. I encourage all ophthalmic surgeons interested in refractive surgery to read the entire chapter.)
INCIDENCE – RELATION TO MULTIPLE VARIABLES New advances in lamellar refractive surgery have resulted in an expansion of indications for laser in situ keratomileusis (LASIK). However, the increased popularity of LASIK has also resulted in the recognition of new complications. These complications occur in less than 1 to 5% of cases and include free caps, button-holes flaps, thin, incomplete, and irregular flaps. (1-10) The most severe complication, corneal perforation has also been reported. (11-12) The incidence of complications depends on multiple variables. Surgeon variables, microkeratome variables, laser variables, and patient variables must all be evaluated when attempting to assess the cause of a complication. Surgeon variables include appropriate training, experience, and meticulous attention to details. In view of the steep surgical learning curve, it is not suprising that the complication rate is much higher in surgeons with limited experience. Microkeratome variables include the type of microkeratome, proper maintenance, blade quality, and proper assembly. The excimer laser should be routinely calibrated and evaluated with regards to its energy fluence and beam homogenicity. Patient variables include cooperation with intraoperative/postoperative instructions and the individual’s wound healing response during the postoperative
period. Often, there is no identifiable cause for a complication. Although optimizing known variables will not guarantee a complication-free procedure, they will dramatically increase the likelihood of a successful outcome. This chapter will discuss the prevention and management of the primary complications following LASIK.
Contents
Section 1
CLASSIFICATION OF COMPLICATIONS
Section 2
Section 3
LASIK complications can be classified as occurring during the intraoperative period, early postoperative period (days to weeks), or late postoperative period (weeks to months). This classification system is artificial, as there may be considerable overlap among many of these complications.
Section 4
Section 5
Section 6 Section 7
Intraoperative LASIK Complications
Subjects Index
The most severe intraoperative LASIK complications typically occur during the creation of the lamellar keratectomy. These complications should be recognized immediately. In many cases, a meticulous preoperative examination by an experienced surgeon will identify eyes at risk for these complications. Although many preoperative and intraoperative maneuvers by experienced surgeons can minimize these risks, they cannot be completely eliminated.
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Subconjunctival Hemorrhages Incidental trauma to subconjunctival vessels during vacuum application of the microkeratome can result in a subconjunctival hemorrhage. An inflamed LASIK AND BEYOND LASIK
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or injected conjunctiva increases the risk of hemorrhaging and can occur immediately following the administration of any topical medication. This is most commonly seen following the administration of a topical anesthetic immediately preoperatively. We routinely use a topical vasoconstrictor to blanch these vessels immediately prior to surgery. Chilled balanced salt solution can also be used for this purpose. Recently, the use of Alphagan for this purpose has resulted in empirical reports of increased flap displacement during the immediate postoperative period. In any case, the significance of subconjunctival hemorrhages is only cosmetic and does not affect the visual outcome. Thus, “treatment” is limited to educating the patient on the natural course of the “bruised eye” and reassurance that it will not affect the visual outcome.
Chemosis Chemosis during surgery may result from rapid fluid shifts that may occur from a reaction to the instillation of topical medication immediately preoperatively or by repeated attempts/manipulation of the conjunctiva during pneumatic suction ring placement. Chemosis may interfere with obtaining appropriate suction. With severe chemosis, a dry firm methylcellulose sponge should be used to massage the subconjunctival fluid posteriorly. In advanced cases of chemosis, a 30-gauge needle may be used to drain the excess subconjunctival fluid. After these maneuvers, it is best to check that the pneumatic suction ring achieves “true” suction by applanation tonometry (>65mm Hg) or by slightly lifting the globe with the suction ring. If the intraocular pressure is artificially low or the globe does not lift with the pneumatic suction ring, “pseudo” suction (only conjunctiva occluded in the suction ring) has been achieved and the case should be aborted. When in doubt, delaying the surgery is also a viable alternative to risking a poor quality lamellar keratectomy resulting from“pseudo” suction or no suction.
Deep Set Orbits/Small Palpebral Fissure Adequate exposure during LASIK is an important step that facilitates the entire procedure including placement of the microkeratome. Deep set 248
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eyes with small palpebral fissures limit exposure and should be avoided by inexperienced surgeons. Exposure can be improved by placing downward pressure on the speculum to prolapse the globe anteriorly or by using an adjustable speculum. Occasionally it may be necessary to remove the speculum altogether in order to appropriately position the pneumatic suction ring. A retrobulbar injection or lateral canthotomy are alternative measures that may be required. However, these methods are associated with independent risks and should be carefully considered before implementing.
Limbal Neovascularization/Pannus Since many refractive surgery patients have a long history of soft contact lens wear, it is not uncommon to be faced with significant superior limbal Contents vascularization. This should be identified preoperatively and appropriate measures should be planned Section 1 to avoid hemorrhaging during the microkeratome Section 2 pass. Topical vasoconstrictors may be applied locally by using a methylcellulose sponge soaked in Section 3 the vasoconstricting agent. Also, purposefully positioning the flap to avoid the vascularization (i.e. su- Section 4 perior hinge) or using a smaller keratectomy flap are Section 5 also useful in limiting intraoperative limbal hemorrhage. Slight inferior decentration of a superior- Section 6 hinged flap to avoid superior neovasculariztion will also not effect the outcome of the LASIK procedure. Section 7 Fortunately, limbal hemorrhage can be controlled Subjects Index with application of a methylcellulose sponge to adsorb and place pressure on the origin of hemorrhage during photoablation. Additionally, maintaining the pneumatic suction ring on low vacuum will also limit hemorrhaging during the photoablation. After photoablation careful irrigation with balance salt solution will remove most of the hemorrhage from the Help ? interface prior to repositioning of the flap. It is important not to overhydrate the flap or bed as this may result in poor interface adhesion, flap displacement, and microstriae. Following repositioning of the flap, limbal hemorrhage may continue to bleed at the limbus gutter but not within the interface. Residual hemorrhage within the interface can be left alone. Some surgeons may elect to administer stronger topical steroids (prednisolone acetate 1%) postoperatively to patients with residual interface hemorrhage to prevent diffuse lamellar keratitis.
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
Decentered Flap Slight flap decentration does not affect the visual outcome. In fact, slightly decentering the flap towards the hinge will ensure that the hinge will be out of the field during laser photoablation. Significant flap decentration occurs because of inadequate placement of the pneumatic suction ring. This may occur in patients with poor exposure or when the suction ring is not firmly applanated 360 degrees to the globe when the vacuum is initiated. (eye will rotate) This is also commonly seen in patients with large corneas >13 mm in diameter as the suction ring tends to rotate until it applanates conjunctiva/sclera. In either case, the pass with the microkeratome should not be made when the pneumatic suction ring is significantly decentered (i.e. >1mm). The vacuum should be immediately discontinued. Further attempts at repositioning the pneumatic suction ring may prove difficult, as repeat attempts tend to fall within the scleral ridge created by the previous decentered attempt. Thus, delaying a repeat attempt in a few hours (or the next day) may be necessary. It is best to abort the LASIK procedure if the flap is significantly decentered. This is especially significant in hyperopic LASIK procedures and large zone myopic treatments.
Incomplete Flap During a microkeratome pass, the microkeratome may occasionally stop creating a partial or incomplete flap. This can occur despite appropriate maintenance of the microkeratome. Causes of this complication include debris in the gears, obstruction of the microkeratome by the eyelid or speculum, or the surgeon prematurely discontinuing the pass. If the flap is good quality and has sufficient diameter to safely apply the photoablation, then the LASIK procedure can be completed. Usually, however, the incomplete keratectomy is of insufficient diameter to accommodate the photoablation. In this case, it is best to abort the LASIK procedure, reposition the flap, apply a bandage contact lens, apply a topical nonsteroidal agent and begin a course of topical antibiotics and steroids. The procedure can be
repeated in 3-6 months using a deeper microkeratome head. Although the microkeratome almost never cuts the cornea at exactly the same plane, it is safer to use a deeper microkeratome head to minimize this risk following an incomplete flap. Gentle manipulation of the flap during the repeat procedure will also help avoid “slivers” of tissue.
Free Cap Free caps were performed intentionally in the early days of lamellar surgery. Free caps occur when the microkeratome head amputates the hinge resulting in a “free cap” of lamellar tissue. Eyes at risk for this complication include eyes with a small corneal diameter <10.5mm and a flat cornea with a mean keratometry <40-42 D. Free caps can also occur from insufficient intraoperative intraocular pressure <65 Contents mm Hg during the microkeratome pass or inappropriate assembly (head stop screw not set) of the Section 1 Bausch & Lomb Automated Corneal Shaper Section 2 microkeratome. Most surgeons will experience a free-cap at some point in time. When it does occur, Section 3 the cap should be carefully removed from the microkeratome head to avoid tearing the flap. This Section 4 typically involves disassembly of the microkeratome Section 5 head. When the cap is removed, it should be placed epithelial side down on a drop of balanced saline salt Section 6 solution in an antidessication chamber. It is imporSection 7 tant to avoid hydration of the stromal side of the cap as a small amount of fluid will result in significant Subjects Index flap swelling. In addition, preservation of the epithelium and the alignment marks will assist the surgeon in identification of the epithelial side of the cap and will insure appropriate re-alignment of the flap. If the lamellar keratectomy is of good quality, the photoablation can be performed. A drop of balanced salt solution should only be applied immediately prior Help ? to flap placement since overhydration of the stromal bed is also to be avoided. The cap is placed epithelial side up and realigned according to the epithelial markings. Sufficient time should be allowed to insure adequate flap adhesion to the bed. Suturing the flap is typically not required. However, a bandage contact lens should be applied overnight and the patient should be instructed to keep the eyes closed.
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Thin, Irregular Flap (“button-hole”) This complication typically occurs in the setting of a poorly functioning blade, inadequate intraocular pressure or malfunction of the microkeratome. Nicks in the blade during microkeratome head assembly or problems with quality control during blade manufacturing are rare but can occur. Thus, each blade should be evaluated under the laser microscope under high magnification prior to use. Since these blades are manufactured for “disposable” use, repeated use of blades is not advisable. With multiple uses, the blade quality may deteriorate becoming increasingly dull which affects the quality and the depth of the lamellar resection. Use of the same blade in a bilateral case of the same patient is reasonable unless a thin or suboptimal flap is made on the first eye. Following recognition of a central “buttonhole”, the LASIK procedure should be aborted and treatment of the other eye should be delayed. Immediate management includes repositioning of the flap. Depending on the complexity and irregularity of the flap, proper re-alignment may prove challenging. Once the flap is repositioned, adequate time (5 minutes) should be allowed for flap adhesion to the stromal bed. A bandage contact lens should be placed until healing of the corneal epithelium is complete, usually in 1-2 days. The patient should be monitored for the development of epithelial ingrowth under the “button hole”. A minimum of 3 to 6 months should be allowed for stabilization of the refractive error and an assessment of the best spectacle corrected visual acuity. In cases of intact best spectacle corrected visual acuity, repeat LASIK with a deeper microkeratome head can be considered. Unfortunately, best spectacle corrected visual acuity may be severely compromised from irregular astigmatism and corneal opacification at the “button hole”. A rigid gas permeable contact lens is the most conservative approach and may dramatically improve the vision by masking the irregular astigmatism. When there is loss of best spectacle corrected visual acuity from corneal opacification, PRK with a transepithelial approach may be required. Difficult cases may require removal of the flap completely and topographically guided or customized ablations to remove topographic irregulari-
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ties. If complete removal of the flap is necessary it must be remembered that an irregular flap may or may not have a neutral refractive error. In any event, smoothing of the hinge edge following flap removal will facilitate re-epithelialization. Aggressive topical steroids should be administered similar to a PRK regimen to prevent the development of stromal haze. PRK may also be performed within the stromal bed following complete flap removal for residual refractive error. A preoperative regular topography and intact best spectacle corrected visual acuity will optimize results.
Corneal Perforation Corneal perforation with anterior chamber entry is the most severe intraoperative complication Contents during LASIK. This can occur with inappropriate assembly of the microkeratome (failure of the depth Section 1 plate) and can be recognized by an outflow of aqueous during the microkeratome pass. When this oc- Section 2 curs, immediate recognition is imperative. The suc- Section 3 tion should be immediately discontinued and a detailed assessment of the extent of the injury should Section 4 be completed. The immediate goal is closure of the Section 5 rupture site which usually requires sutures. Reformation of the anterior chamber may be required. Section 6 Repair of ancillary damage such as cataract removal may be performed in a sterile operating room set- Section 7 ting. The postoperative course should include anti- Subjects Index biotic prophylaxis with attention to developing signs of endophthalmitis. After corneal healing, it is not uncommon for the patient to have irregular astigmatism. In such cases, a rigid gas permeable contact lensis the most conservative approach to visual rehabilitation. A repeat refractive procedure may result in satisfactory visual function without the need for Help ? corrective lenses. Again, patients without a preoperative loss of best spectacle corrected visual acuity and regular topography will optimize results of a subsequent refractive procedure.
Early Postoperative LASIK Complications Early postoperative LASIK complications occur within the first days-weeks following the
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
LASIK procedure. For most of these complications familiarity, immediate recognition, and appropriate management are important in optimizing the patient’s visual recovery.
Interface Debris Interface debris may result from glove powder/talc, oil or metallic microkeratome deposits or filaments from methylcellulose sponges. Usually, interface debris is not problematic. Occasionally, it may serve as a focus for interface inflammation. In such cases, management should include aggressive use of potent topical steroids (i.e. prednisolone acetate) and topical antibiotic prophylaxis. Rarely, inflammation will become severe enough to warrant lifting of the flap and irrigation of the interface. Exposed filaments at the edge of the flap should be removed with a forceps to prevent microbial tracking.
Displaced Flap Acute onset of pain, foreign body sensation, and decreased vision may herald the onset of a displaced flap. This typically occurs within the first 24 hours following the surgery. Occasionally, patients may have limited symptoms if the displacement is small. On examination, the flap may be completely dislodged (macro-slip) or may be identified only by parallel folds radiating through the flap (microslip). Eyes at risk for this complication include dry eyes and eyes with small/tight palpebral fissures. An overhydrated cap/stromal bed and eyes with large refractive errors (stromal bed does not “fit” the cap following a large ablation) are also at risk. Identification of the risk factors and prevention are the goals in limiting this complication. Avoid overhydration of the flap or stromal bed. Allow sufficient time for “drying” following re-alignment of the flap (>3-5 minutes). A flap striae test may be performed by gentle pressure on the limbus which should create temporary striae through the flap. Alternatively, monitoring the flap while having the patient blink following the procedure will also achieve the same goal. Supplemental oxygen and carefully drying the gutter with a methylcellulose sponge may also help flap adherence. Finally a bandage contact
lens should be placed over the flap for the first day in all eyes at risk. The patient should be instructed to keep the eyes closed and vigorous preservative free lubrication should be administered. Punctal plugs placed preoperatively or at the time of surgery in patients with significant dry eyes is also recommended. Management of a displaced flap includes lifting and re-alignment of the entire flap. Gently stroking the flap perpendicular to the folds towards the gutter will remove the folds. The methylcellulose sponge should be firm (not overhydrated) and used to “iron” out the folds. It is most important to remove folds in the visual axis. Caution should be exercised as too vigorous stroking may result in dislodgment of the flap. After performing the maneuvers discussed above to insure adequate adherence of the flap, a bandage contact lens and eye shield should be left in place. Again, the patient should be reminded to keep the eyes closed with the exception of vigorous preservative free lubrication. During the postoperative period, the patient should be monitored for the development of infectious consequences and epithelial ingrowth.
Contents
Section 1 Section 2
Section 3
Section 4
Epithelial Defects
Section 5
Epithelial defects usually occur during the Section 6 passage of the microkeratome head over the cornea in patients with unrecognized anterior basement Section 7 membrane dystrophy or following the aggressive use Subjects Index of preoperative topical medications (epithelial toxicity). A disturbance in the epithelium may also occur following the application of gentian violent during corneal marking and corneal dehydration of the second eye during bilateral surgery. Preventative measures include judicious use of gentian violet and taping the second eye closed during the LASIK proceHelp ? dure on the first eye of a bilateral surgery. Patients with loose epithelium may be identified preoperatively by applying a methylcellulose sponge to the epithelium at the slit lamp under topical anesthesia. Patients with anterior basement dystrophy and poorly adherent epithelium are not ideal candidates for LASIK. In such cases PRK should be considered as an alternative. Intraoperative epithelial defects require the use of a bandage contact lens. A topical nonsteroidal
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agent such as diclofenac sodium 0.1% and ketorolac tromomethamine 0.5% may be required for pain control. These agents should not be used longer than 72 hours as they may delay re-epithelialization. Broad spectrum topical antibiotics are necessary for microbial prophylaxis. Topical steroids are also useful to limit the frequency and severity of diffuse lamellar keratitis (DLK) which can occur following an epithelial disturbance in a post-LASIK patient. The patient should be monitored regularly for the development of infectious or sterile (DLK) infiltrates until the epithelium is completely healed. The bandage contact lens and the topical antibiotic may be discontinued when the epithelial surface is healed. The topical steroid may also be tapered off over the next 5 to 7 days. The patient should be carefully monitored the first postoperative month for the development of epithelial ingrowth.
Diffuse Lamellar Keratitis (DLK) Sterile inflammation following LASIK may occur in 1.8 to 4% of cases. (10,13) The presentation of diffuse lamellar keratitis was originally described as a sterile interface inflammation that occurred 2-6 days following LASIK with symptoms of pain, photophobia, redness, or tearing. (13) On slit lamp examination the infiltrates are multifocal, granular, peripheral, confined to the interface, and have a characteristic waves of shifting “sands of Sahara” appearance. Postulated causes of flap inflammation include talc from latex gloves, meibomian gland secretions, povidone-iodine used to sterilize lids, endotoxins in sterilizer reservoirs, distortions in the epithelium, residual disinfectants on sterilized equipment, and microkeratome related debris. (13-18) We have described multiple cases of late onset DLK 2 to 12 months following an uncomplicated LASIK procedure. (51) All cases occurred following relatively mild injury to the epithelium in the absence of flap manipulation. In our series, common causes of epithelial injury included trauma, dry eyes, and recurrent erosion syndrome. All cases resolved uneventfully with the use of a topical antibiotic (until the epithelium had healed) and a tapered regimen of topical prednisolone acetate. Untreated severe diffuse lamellar keratitis may result in sterile necrosis, melting of the flap, interface haze, irregular astigmatism, and a hyperopic 252
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refractive shift. It is therefore important to recognize this complication and treat it aggressively with potent topical steroids (prednisolone acetate 1%). In atypical cases, it is important to exclude a microbial etiology with appropriate cultures and to treat with antibiotic prophylaxis. This is particularly important in aggressive, monofocal infiltrates that extend into the flap or stromal bed. In moderately aggressive forms of DLK, we have successfully used a short pulse of oral steroids (prednisone 60-80 mg every day) for 5 to 7 days in conjunction with topical steroids. In severe forms of DLK, it is appropriate to lift the flap and irrigate the inflammatory mediators from the flap interface. This should be done before confluent DLK results in irreversible stromal necrosis.
Infectious Keratitis
Contents
Section 1
Infectious keratitis following lamellar surgery such as LASIK is rare. Unlike PRK, the epithe- Section 2 lium is only minimally disturbed and the underlying Section 3 stroma is exposed for only a small duration during LASIK. Appropriate technique and precautions will Section 4 limit but not extinguish the risk of infection. These precautions include treating patients with blepharitis Section 5 preoperatively, discontinuing contact lenses for an ap- Section 6 propriate amount of time preoperatively, isolating the eyelashes from the surgical field with a sterile drape, Section 7 proper sterilization technique between cases, and Subjects Index antibiotic prophylaxis. Obviously, patients with a complicated procedure, epithelial defects, and flap displacement are at a higher risk for the development of infectious consequences. Sterile marginal keratitis resulting from staphylococcus species antigens may also occur and should be distinguished from infectious keratitis. (14) Infectious keratitis following Help ? LASIK should be cultured and treated aggressively with topical antibiotics. Occasionally, complete removal of a nonviable flap will be necessary to increase antibiotic delivery to the site of infection.
Flap Micro/Macrostriae Wrinkles in the flap occur when the flap is not perfectly re-approximated. Thin flaps, higher refractive corrections, and grossly overhydrated flaps are at risk for the development of flap striae. Atten-
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
tion should be directed at preventing wrinkles during the primary LASIK procedure. Avoid overhydration of the flap during repositioning of the flap. Careful alignment of the epithelial markings and proper technique during flap smoothing are integral components in avoiding flap striae. A bandage contact lens applied for the first postoperative night may also stabilize the flap. The location of the striae in the flap is an important factor in determining the need for a second procedure. Peripheral, visually insignificant striae (not associated with flap displacement) are cosmetic and need not be removed. Central, visually symptomatic striae associated with loss of best spectacle corrected visual acuity should be addressed earlier in the postoperative course. Flap striae become more difficult to remove beyond the first postoperative month. When the decision is made to attempt striae removal, the flap may be lifted, refloated, and smoothed using the “ironing” technique described in the displaced flap section. Careful stroking perpendicular to the flap striae and the application of a bandage contact lens usually result in a dramatic improvement in the striae. Persistent folds may require repeat lifting and hydration of the flap with sterile water before repositioning. Heat has also been proposed as an adjunct to removal of recalcitrant striae. One additional technique that we have found useful for the removal of persistent long-term striae includes removing the entire epithelium from the flap and surrounding cornea. This allows complete visualization of the striae. The flap is then lifted and stretched back into place with direct visualization of the primary keratectomy flap and gutter. A bandage contact lens is placed until the epithelium is healed. If this technique fails, then tightly suturing the flap is also an effective method of striae management. However, these advanced techniques should be performed only by refractive surgeons experienced in lamellar surgery.
plaints in post-LASIK patients. Approximately 80 to 90 % of eyes are within +/- 1.0 diopter of attempted correction after stabilization of the refractive error. (18-21) In higher levels of corrections, the predictability decreases to 60 to 80% within +/- 1.0 diopter of attempted correction. (22-24) An enhancement procedure may be required in approximately 5 to 15% of eyes depending on the surgical algorithm and the level of attempted correction. Patients with unsatisfactory uncorrected visual acuity should be given a prescription for temporary spectacles and/or disposable contact lenses. Contact lenses may be safely used 1-2 weeks following the LASIK procedure. It should be emphasized to the patient that these are temporary measures until an enhancement procedure can be performed after 3+ postoperative months. It may require 3 to 6 months before complete stabilizaContents tion of the refractive error following high magnitude myopic or hyperopic corrections. Section 1 Patients that present with large unexpected undercorrections with or without loss of best spec- Section 2 tacle corrected visual acuity following photoablation with a broad beam excimer laser may also have steep Section 3 central topographic islands. If not carefully exam- Section 4 ined, the inexperienced refractive surgeon may misdiagnosis this topographic finding. Topographic steep Section 5 central islands are discussed in more details below. Constant review of the surgeon’s results with Section 6 continuous adjustments in the surgical nomogram will Section 7 improve the predictability of the procedure for each individual surgeon. When adjusting the nomogram, Subjects Index it should be remembered that it is easier to correct undercorrections than overcorrections. It should also be remembered that younger patients might accommodate through small residual hyperopia while borderline presbyopic patients may react poorly to the loss of near vision in the case of residual hyperopia/ consecutive hyperopia. Help ?
Late Postoperative LASIK Complications
Our previous experience with LASIK has demonstrated that higher level corrections regress more than low level corrections and hyperopic corrections regress more than myopic corrections. Most of the regression occurs within the first 0 to 3 months following LASIK. Potential causes for the regression of refractive effect include epithelial hyperpla-
Undercorrection/Overcorrection Although this is not a true “complication” it is probably responsible for the most common com-
Regression of Refractive Effect
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sia and stromal remodeling. Unfortunately unlike PRK, pharmocologic manipulation of regression following LASIK is unproven. Regression of refractive effect is managed similar to the guidelines explained in the undercorrection/overcorrection section. However, one special consideration is noteworthy before proceeding with treatment of regression. Large regression of refractive effect in eyes with high myopia and/or thin corneas deserves special attention. Careful examination before enhancement should be performed to exclude the development of corneal ectasia. Iatrogenic corneal ectasia is discussed below.
Glare/Halos Glare and halos typically develop during dim light situations when the pupil dilation is larger than the effective optical zone. Studies have confirmed an alteration in the distribution and magnitude of coma and spherical aberrations following pupil dilation in eyes after excimer laser refractive surgery. (25-26) Fortunately, in our experience these symptoms typically subside over the course of 3 to 12 months. Occasionally these symptoms are permanent and visually disabling. Eyes at risk for the development of these symptoms include patients with large pupils, higher levels of attempted correction, and higher levels of astigmatism. Innovations in excimer laser technology have resulted in the development of larger ablation zones, aspheric ablation profiles, and multizone techniques. These techniques can be considered in patients “at risk” for developing glare and halos following LASIK. Unlike multizone techniques, a larger ablation zone results in an increase in tissue removal that can be predicted according to the Munnerlyn equation. (27) Thus, large zone ablations are limited by the preoperative corneal thickness. Additionally, large zone ablations with broad beam excimer lasers may result in a higher incidence of topographic steep central islands. (Haw W., Manche E., publication pending) The first step in the management of a patient with glare and halos is to determine the cause of the symptoms. The most common etiology is residual refractive error. If the symptoms of glare and halos resolve with a trial of spectacles, enhancement sur-
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gery may be all that is necessary. If there is no residual refractive error, then topographic evaluation is critical. This will assist in the diagnosis of conditions such as steep central islands, irregular ablations, and decentered ablations which may be responsible for the symptoms. Depending on the topographic appearance, the eye may be effectively treated. It is also important to assess the degree of functional disability caused by these symptoms. For patients with minimalfunctional disability, reassurance and observation are all that is required as these symptoms may resolve over time. For patients with disabling symptoms, a trial of dilute pilocarpine (<1%) or a rigid gas permeable contact lens may be warranted. Pilocarpine induces pupillary constriction and can be administered by the patient as needed before night driving or under conditions when the symptoms are severe. Dilute pilocarpine is recommended to prevent dose dependent adverse effects such as induced myopia, brow ache, and retinal detachment. A rigid gas permeable contact lens may be useful in treating topographic irregularities and/ or residual refractive error. Lightly tinted polarized spectacles may also be useful in some patients with night vision difficulties.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Decreased Contrast Sensitivity
Section 6
Early in the postoperative period, many pa- Section 7 tients may complain of poor quality of vision despite Subjects Index an uncorrected visual acuity of 20/20 on the Snellen eye chart. In these cases, it should be remembered that the Snellen eye chart is a high contrast eye chart that is used under artificial environmental circumstances. Thus, it may not adequately reflect the functional visual capacity in the “real-world”. These patients may complain that they“don’t have enough light Help ? to see well.” Fortunately, most patients experience full recovery of their contrast threshold. (21) Recovery of the contrast threshold usually returns to normal by 3 to 6 months. (28-29) However, it may require up to 1 year for some patients with higher levels of correction. Thus, management consists of excluding other causes of poor vision (topographic irregularities, striae, etc…) and reassurance. Occasionally, a temporary prescription for residual refractive error (to be used on a “as needed” basis) may be required.
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
The cause of a decrease in contrast sensitivity are related to changes in the optical quality of the cornea in addition to the aspheric cornea becoming oblate.(30)
Epithelial Ingrowth Epithelial ingrowth is a well-recognized complication following lamellar surgery. Most studies report a variable incidence of epithelial growth within the interface following LASIK as being between 0.3% and 15%. (5-6,23,21-36) Following retreatment, the incidence of epithelial ingrowth may be as higher. (37) The primary risk factors for the development of epithelial ingrowth include peripheral epithelial defects involving the edge of the keratectomy incision, poor flap adhesion, spill-over ablation, flap displacement, or perforation of the corneal flap. Following any of these complicated cases, preventative measures should be taken. These include careful repositioning of the epithelium at the edge of the primary keratectomy and the use of a bandage contact lens. Patients should be followed carefully within the first few weeks for the development of epithelial ingrowth. The natural history of epithelial ingrowth following LASIK is self-limited. Thus, nonprogressive peripheral epithelial ingrowth of <1 mm does not require removal. However, careful follow-up over the first 0 to 3 months is recommended to monitor its status. Follow-up is variable and depends upon the appearance of the ingrowth and surgeon preference. A typical follow-up period may be 1 day, 2 weeks, 1 month, 2 months, and 3 months. Epithelial ingrowth is occasionally progressive and extends > 2mm centrally, extends over the visual axis, melts the stroma, or causes irregular astigmatism and loss of best spectacle corrected visual acuity. (37-38) In these cases, standard management includes marking the flap, lifting the flap, mechanically removing the epithelial ingrowth, gentle irrigation to remove epithelial cells, repositioning the flap, and a bandage contact lens. Removal of the epithelial cells may be done using a dry methylcellulose sponge or PRK spatula. Both the underside of the flap and the stromal bed should be scraped to remove all residual epithelial cells. A clean sponge should be used on each pass to avoid re-implantation of the
epithelium. The epithelium can usually be removed as an entire sheet. Usually, this technique is sufficient to remove all epithelial cells and no further intervention is required. Epithelial ingrowth meeting the criteria for removal should not be delayed. However, aggressive epithelial ingrowth, longstanding or unrecognized epithelial ingrowth, and recurrent epithelial ingrowth may be refractory to standard removal techniques. In these cases, the management becomes more difficult. Suturing the flap edge down with tension can be used to close the fistulous track created by recurrent or longstanding epithelial ingrowth. Sutures may then be removed after the first two weeks. However, suturing is invasive, creates flap microperforations from the needle, requires suture removal, induces microstriae, and may result in poor uncorrected and best spectacle corrected visual acuity from the induction of irregular astigmatism. In cases of epithelial ingrowth refractory to standard measures, we have successfully used dilute ethanol 50% as an adjunctive agent immediately following mechanical removal of the epithelial ingrowth. Phototherapeautic keratectomy of the bed and the underside of the flap has also been used to remove residual epithelial nests. However the use of adjunctive medical agents and phototherapeautic keratectomy is controversial and is not advisable for inexperienced refractive surgeons.
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Irregular Astigmatism It is not uncommon for eyes to have some degree of irregular astigmatism in the early postoperative period. These patients may complain of “hazy” vision. Generally, with healing and epithelial hyperplasia, the topography tends to regularize over the course of two to four weeks. Thus, the visual quality tends to improve over this time period. However, irregular astigmatism may result in a permanent loss of best spectacle corrected visual acuity in <1-2% of cases. In these cases, common causes for clinically significant irregular astigmatism includes flap striae, decentered ablations, irregular ablations, steep central islands, button-holes, and inadvertent ablation of the flap hinge. These causes can be identified by careful examination at the slit lamp and of the computerized corneal videokeratography.
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The most conservative approach to managing irregular astigmatism includes the use of arigid gas permeable contact lens. A rigid gas permeable contact lens affords the best quality of vision. However, it does not treat the underlying cause of the irregular astigmatism. Flap striae management has already been addressed. Decentered ablations > 1mm may be clinically significant resulting in poor uncorrected visual acuity, loss of contrast sensitivity, symptoms of glare, and loss of best spectacle corrected visual acuity. Decentrations of this magnitude may occur in up to 5% of eyes following PRK and LASIK. (39) Several evolving technologies are emerging as viable options in the treatment of decentered ablations. The primary treatment strategy includes customized topographically guided excimer laser photoablations which may successfully improve the corneal regularity, quality of vision, and best spectacle corrected visual acuity. (40-41) Topographic steep central islands result from spatial variance of tissue removal with relative central undercorrection. Although the development of steep central islands is likely to be multifactorial, the most prevalent theories include the differential hydration/acoustic shockwave theory and the vortex plume theory. (42) Steep central islands occur with the use of broad beam excimer laser systems. The reported incidence is 0 to 4.7% of eyes up to 12 months following LASIK. (43-44) Symptomatic topographic steep central islands include complaints of poor quality of vision and monocular diplopia or “ghosting”. Slit lamp examination is unremarkable but uncorrected visual acuity may be poor. Refraction may demonstrate significant undercorrection with loss of best spectacle corrected visual acuity. Computerized corneal videokeratography is used to confirm the clinical diagnosis. The topography reveals a central elevated area shown as a red or yellow (warm colors) surrounded by a flat area shown as a sea of blue (cool color). Iatrogenic keraectasia may also present in a similar fashion and needs to be distinguished from a steep central island. Since many islands will spontaneously resolve over time, a symptomatic steep central island should be observed a minimum of 3 to 6 months. A rigid gas permeable contact lens will afford reasonable vision in the interim. 256
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If the island does not resolve and the patient is symptomatic, treatment of a steep central island includes the use of PRK or PTK over the island. (45-46,52) The diameter of the ablation zone is calculated from the diameter of the island on videokeratography while the depth of the ablation can be calculated using the Munnerlyn equation. (27) Topographic guided custom ablations are expected to further improve results not only for steep central islands but also for decentered/irregular ablations.
Corneal Ectasia Eyes with high myopia or thin corneas are at risk for developing iatrogenic corneal ectasia following LASIK. (47) Corneal ectasia may also follow uncomplicated LASIK in patients with keratoconus and/ Contents or lower levels of myopia (less than –4.0 to –7.0 di(48) opters). This rare complication typically presents Section 1 as an unexpectedly large regression of refractive effect with or without loss of best spectacle corrected Section 2 visual acuity following LASIK for high myopia in Section 3 an eye with marginal corneal thickness. Significant degrees of ectasia may be diagnosed by progression Section 4 of the ectasia on serial computerized corneal videokeratography. More subtle degrees of ectasia Section 5 must be diagnosed with posterior surface elevation Section 6 maps using scanning slit technology such as the Orbscan topography system (Orbtek Inc., Salt Lake Section 7 City, UT). In order to minimize the risk of ectasia, a minimum of 250 microns should remain in the stro- Subjects Index mal bed to preserve the long-term corneal integrity. (49) In addition, LASIK should be deferred in eyes with keratoconus and other ectactic corneal disorders. Once postoperative corneal ectasia has been diagnosed, further photoablation of the central cornea is to be avoided as this has the potential to exacerbate Help ? the ectasia. A rigid gas permeable contact lens may provide satisfactory vision indefinitely. For progressive ectasia with loss of best spectacle corrected visual acuity, a penetrating keratoplasty may be required.
Vitreoretinal Complications Eyes with high myopia are at risk for the development of peripheral retinal degeneration, retinal breaks, lacquer cracks, rhegmatogenous retinal de-
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
tachment, and choroidal neovascularization. It is controversial whether acute changes in the intraocular pressure during LASIK affects the natural history of these vitreoretinal complications in eyes with high myopia. The largest published series demonstrated an overall incidence of 0.06% within 2 years of the LASIK procedure (11). In this retrospective case series of 29,916 cases, 14 eyes had rhegmatogeneous retinal detachments, 2 eyes had corneal-scleral perforations, 4 eyes had retinal tears without retinal detachments, and 1 eye had a choroidal neovascular
membrane. Bilateral macular hemorrhages have also been reported to occur following LASIK. (50) While most experienced refractive surgeons believe that LASIK does not increase the risk of vitreoretinal complications beyond the natural history of high myopia, all patients should undergo a thorough preoperative examination including dilated fundus examination to evaluate the posterior pole for pathology. Patients with significant pathology should be referred to a retinal specialist for examination before undergoing LASIK.
(At the request of the author, all illustrations are presented at the end of this chapter).
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Figure 21-1 and 21-2. Late Onset Diffuse Lamellar Keratitis. Six months following uncomplicated LASIK, the patient presented with complaints of photophobia and redness. Examination demonstrated an epithelial defect associated with inflammation to the interface. The late onset DLK was treated with agressive topical steroids with complete resolution of the DLK without loss of best spectacle corrected visual acuity.
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Figure 21-3 and 21-4. Bilateral Decentered Ablations. This patient was referred to Stanford University for complaints of glare, halos, and loss of best spectacle acuity in both eyes following bilateral LASIK. Corneal topographies demonstrated bilateral inferior decentered ablations and irregular astigmatism. The patient was succesfully managed with a rigid gas permeable contact lens.
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Figure 21-5, 21-6 and 21-7. Inadvertent Entry into the Anterior Chamber. This patient was referred to Stanford University following corneal perforation during the primary keratectomy pass with the Automated Corneal Shaper. (Figure 21-5). This was due to incorrect assembly of the microkeratome. Figure 21-6 demonstrates the well-healed scar 6 months following the perforation. The asymmetric perforation functioned as an arcuate keratotomy with the induction of high magnitude, irregular with-the-rule astigmatism. Figure 21-7 - Visual accuity was 20/25 with a rigid gas permeable contact lens.
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Figure 21-8 and 21-9. Steep Central Topographic Island. Figure 21-8 demonstrates the corneal topography of a visually significant 7.5 D steep central island following LASIK for -10.0 diopters with a broad beam excimer laser. Figure 21-9 demonstrates significant improvement in the topographic steep central island 3 months following lifting of the flap and treatment of the island with phototherapeutic keratectomy. Best spectacle corrected visual acuity improved from 20/40 to 20/20.
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Figure 21-10. Flap Striae following LASIK. This patient was referred to the Stanford University for visually significant flap macro-striae 6 months following LASIK. The patient was succesfuly managed with lifting and smoothing of the flap.
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Figure 21-11. Nonprogressive Epithelial Ingrowth. Figure 2111 demonstrates nonprogressive epithelial nests confined to the border of the interface 1 month following LASIK. There was no evidence of stromal melting. The patient did not require removal of epithelial ingrowth.
Figure 21-12. Progressive Epithelial Ingrowth. Figure 21-12 demonstrates progressive epithelial ingrowth associated with loss of 40% of the superior flap stroma despite flap sutures for recurrent epithelial ingrowth.
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Section 6 Section 7 Figure 21-13 and 21-14: Successful Suturing of the Primary Keratectomy Flap for Recurrent Epithelial Ingrowth. This patient was Subjects Index referred to Stanford University for progressive epithelial ingrowth and flap necrosis following LASIK. The epithelial ingrowth was successfully managed with lifting the flap, manual ingrowth removal, ethanol debridement, and suturing of the flap.
Figure 21-15. Multiple Keratectomy Flaps with “Pizza Pie” involvement of the incisions. This patient had an incomplete pass with the microkeratome. Six weeks later, the primary surgeon performed multiple passes of the microkeratome transecting into the cornea into several fragments. The patient developed epithelial ingrowth and corneal scarring. Following epithelial ingrowth removal, best spectacle corrected visual acuity was 20/ 200 due to persistent corneal scarring. The patient was intolerant of a rigid gas permeable contact lens and is scheduled for penetrating keratoplasty.
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Figure 21-16 and 21-17. Mycobacterium Corneal Ulcer. This patient was referred to Stanford University for interface infiltrates that did not resolve with topical steroids 6 weeks following LASIK. Examination revealed a centrally dense-interface infiltrate extending into the anterior and posterior stroma associated with stromal necrosis. (Figure 21-16) Flap lifting and culture demonstrated Mycobacterium Chelonae. The patient required removal of the necrotic flap and aggressive antibiotic management. Figure 21-17 demonstrates the resulting dense corneal scar.
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Section 1 Section 2 Figure 21-18. Iatrogenic Section 3 Corneal Ectasia. The corneal topography demonSection 4 strates central steepening 9 Section 5 months following LASIK for -10.00 D. There was a Section 6 progressive myopic shift from -3.0 D to -9.0 D from Section 7 3 to 9 months post-LASIK. Total corneal thickness was 350 microns. The patient Subjects Index was managed with a rigid gas permeable contact lens.
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Figure 21-19. Corneal Mycrocysts. Central corneal mycrocysts resulted in irregular astigmatism and loss of best spectacle corrected visual acuity following LASIK in an eye with subclinical Anterior Basement Membrane Corneal Dystrophy. The eye was successfully treated with phototherapeutic keratectomy.
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Figure 21-20 and 21-21. Active Diffuse Lamellar Keratitis. The patient presented with redness, pain, and photophobia 3 days following uncomplicated LASIK. Examination demonstrated diffuse inflammation confined to the flap interface consistent with grade II DLK. There was complete resolution of the inflammation with aggressive topical steroids.
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Section 1 Figure 21-22. Central Buttonhole. Figure 21-22 demonstrates a central buttonhole 3 months following an aborted LASIK procedure. There was no loss of best spectacle corrected visual acuity. A repeat LASIK procedure 6 months following the buttonhole was performed without complications.
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REFERENCES 1.
Walker MB, Wilson SE. Lower intraoperative flap complication rate with the Hansatome microkeratome compared to the Automated Corneal Shaper. J Refract Surg 2000; 16:79-82.
2.
Tham VM, Maloney RK. Microkeratome complications of laser in situ keratomileusis. Ophthalmology 2000; 107:920-4.
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Manche EE, Carr JD, Haw WW., Hersh PS. Excimer laser refractive surgery. West J Med 1998; 169:30-8.
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Holland SP, Srivannaboon S, Reinstein DZ. Avoiding serious corneal complications of laser assisted in situ keratomileusis and photorefractive keratectomy. Ophthalmology 2000; 107:640-52.
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Stulting RD, Carr JD, Thompson KP, et. al. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology 1999; 106:13-20.
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Gimbel HV, Penno EE, Van Westenbrugge JA, et. al. Incidence and management of intraoperative and early postoperative complications in 1000 consecutive laser in situ keratomileusis cases. Ophthalmology 1998; 105:1839-47.
7.
Davidorf JM, Zaldivar R, Oscherow S. Results and complications of laser in situ keratomileusis by experienced surgeons. J Refract Surg 1998; 14: 114-22.
8.
Carpel EF, Carlson KH, Shannon S. Folds and striae in laser in situ keratomileusis flaps. J Refract Surg 1999; 15:687-90.
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Lam DS, Leung AT, Wu JT, et. al. Management of severe flap wrinkling or dislodgment after laser in situ keratomileusis. J Cataract Refract Surg 1999; 25:1441-7.
20. Zaldivar R, Davidorf JM, Sjultz MC, Oscherow S. Laser in situ keratomileusis for low myopia and astigmatism with a scanning spot excimer laser. J Refract Surg 1997; 13:614-9.
10. Lin RT, Maloney RK. Flap complications associated with lamellar refractive surgery. Am J Ophthalmol 1999. 127:129-36.
21. Wang Z, ChenJ, Yang B. Comparison of laser in situ keratomileusis and photorefractive keratectomy to correct myopia from –1.25 to –6.00 diopters. J Refract Surg 1997; 13:528-534.
11. Arevalo JF, Ramirez E, Suarez E, et. al. Incidence of vitreoretinal pathologic conditions within 24 months after laser in situ keratomileusis. Ophthalmology 2000; 107:258-62.
22. Pesando PM, Ghiringhello MP, Tagliavacche P. Excimer laser in situ keratomileusis for myopia. J Refract Surg 1997; 13:521-7.
12. Pallikaris IG, Siganos DS. Laser in situ keratomileusis to treat myopia: early experience. J Cataract Refract Surg 1997; 23:39-49.
23. Perez-Santonja JJ, Bellot J, Claramonte P, Ismail MM, Alio JL. Laser in situ keratomileusis to correct high myopia. J Cataract Refract Surg 1997; 23:372-85.
13. Smith RJ, Maloney RK. Diffuse lamellar keratitis. A new syndrome in refractive surgery. Ophthalmology 1998; 105:1721-6
24. Knorz MC, Liermann A, Seiberth V, Steiner H, Wiesinger B. Laser in situ keratomileusis to correct myopia of –6.0 to –29.0 diopters. J Refract Surg 1996; 12:575-84.
14. Haw WW, Manche EE. Sterile peripheral keratitis following laser in situ keratomileusis. J Refract Surg 1999; 15:61-3. 15. Lyle WA, George JC. Interface fluid associated with diffuse lamellar keratitis and epithelial ingrowth after laser in situ keratomileusis. J Cataract Refract Surg 1999; 25:1009-12. 16. Steinert RF, McColgin AZ, White A, Horsburgh GM. Diffuse Interface Keratitis After Laser In Situ Keratomileusis (LASIK): A Nonspecific Syndrome. Am J Ophthalmology 2000; 129:380-1.
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25. Martinez CE, Applegate RA, Klyce SD, et al. Effect of pupillary dilation on corneal optical aberrations after photorefractive keratectomy. Arch Ophthalmol 1998; 116:1053-62. 26. Oshika T, Klyce SD, Applegate RA, et al. Comparison of corneal wavefront aberratios after photorefractive keratectomy and laser in situ keratomileusis. Am J Ophthalmol 1999; 127:1-7.
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Section 6 Section 7
27. Munnerlyn CR, Koons SJ, Marshall J. Photorefractive Subjects Index keratectomy: a technique for laser refractive surgery. J Cataract Refract Surg 1988; 14:46-52.
17. Holland SP, Mathias RG, Morck DW, Chiu J, Slade SG. Diffuse Lamellar Keratitis Related to Endotoxins Released from Sterilizer Reservoir Biofilms. Ophthalmology 2000; 107:1227-33.
28. Perez-Santonja JJ, Sakla HF, Alio JL. Contrast sensitivity after laser in situ keratomileusis. J Cataract Refract Surg 1998; 24:183-9.
18. Maloney RK, Binder PS, Machat JJ, et. al. Sterile interface inflammation after laser in situ keratomileusis: experience and opinions. J Refract Surg 1998; 14:6616.
29. Sano Y, Carr JD, Takei K, Thompson KP, Stulting RD,Waring GO 3rd. Videokeratography after excimer alser in situ keratomieleusis for myopia. Ophthalmology 2000; 107:674-84.
19. Lindstrom RL, Hardten DR, Chu YR. Laser in situ keratomileusis (LASIK) for the multicenter phase I treatment of low, moderate, and high myopia. Trans Am Ophthalmol Soc 1997; 95:285-96.
30. Holladay JT, Dudeja DR, Chang J. Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography. J Cataract Refract Surg 1999; 25: 663-9.
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PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS 31. Walker MB, Wilson SE. Incidence and prevention of epithelial growth within the interface after laser in situ keratomileusis. Cornea 2000; 19:170-3.
43. Salchow DJ, Zirm ME, Stieldorf C, Parisi A. Laser in situ keratomileusis for myopia and myopic astigmatism. J Cataract Refract Surg 1998; 24:175-82.
32. Farah SG, Azar DT, Gurdal C, Wong J. Laser in situ keratomileusis: literature review of a developing technique. J Cataract Refract Surg 1998; 24:989-1006.
44. Knorz MC, Liermann A, Wiesinger B, Seiberth V, Liesenhoff H. Laser in situ keratomileusis (LASIK) for correction of myopia. Ophthalmologe 1998; 95:142-7.
33. Knorz MC, Jendritza B, Hugger P, Liermann A. Complications of laser in situ keratomileusis. Ophthalmologe 1999; 96:503-8. 34. Guell JL, Muller A. Laser in situ keratomileusis (LASIK) for myopia from –7 to –18 diopters.. J Refract Surg 1996; 12:222-8. 35. Marinho A, Pinto MC, Pinto R, Vaz F, Neves MC. LASIK for high myopia: one year experience. Ophthalmic Surg Lasers 1996; 27:S517-20. 36. Lindstrom RL, Hardten DR, Houtman DM, Witte B, Preschel N, Chu Y, Samuleson TW, Linebarger EJ. Six-month results of hyperopic and astigmatic LASIK in eyes with primary and secondary hyperopia. Trans Am Ophthalmol Soc 1999; 241-55. 37. Perez-Santonja JJ, Ayala MJ, Sakia HF, Ruiz-Moreno JM, Alio JL. Retreatment after laser in situ keratomileusis. Ophthalmology 1999; 106:21-8. 38. Castillo A, Diaz-Valle D, Gutierrez AR, Toledano N, Romero F. Peripheral melt of flap after laser in situ keratomileusis. J Refract Surg 1998; 14:61-3. 39. Lee JB, Jung JJ, Chu YK, et al. Analysis of the factors affecting decentration in photorefractive keratectomy and laser in situ keratomileusis.Yonsei Med J 1999; 40:221-5. 40. Alio JL, Artola A, Rodriquez-Mier FA. Selective Zonal ablation with the excimer laser for correction of irregular astigmatism induced by refractive surgery. Ophthalmology 2000; 107:662-73. 41. Knorz MC, Jendritz B. Topographically-guided laser in situ keratomileusis to treat corneal irregularities. Ophthalmology 2000; 107:1138-43.) 42. Krueger R, Saedy NF, McDonnell PJ. Clnical analysis of steep central islands after excimer laser photorefractive keratectomy. Arch Ophthalmol 1996; 114:377-81.
45. Manche EE, Maloney RK, Smith RJ. Treatment of topographic central islands following refractive surgery. J Cataract Refract Surg 1998; 24:464-70. 46. Castillo A, Romero F, Martin-Valverde JA, et al. Management and treatment of steep islands after excimer laser photorefractive keratectomy. J Refract Surg 1996; 12:715-20. 47. Seiler T, Koufala K, Richter G. Iatrogenic keraectasia after laser in situ keratomileusis. J Refract Surg 1998; 14:312-7.
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48. Amoils SP, Deist MB, Gous P, et. al. Iatrogenic keratectasia after laser in situ keratomileusis for less than –4.0 to –7.0 diopters of myopia. J Cataract Refract Surg 2000; 26(7):967-77.
Section 2
49. Probst LE, Machat JJ. Mathematics of laser in situ keratomileusis for high myopia. J Cataract Refract Surg 1998; 24: 190-5.
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Section 7 50. Luna JD, Reviglio VE, Juarez CP. Bilateral macular hemorrhage after laser in situ keratomileusis. Graefes Subjects Index Arch Clin Exp Ophthalmol 1999; 237:611-3.
51. Haw WW, Manche EE. Late onset diffuse lamellar keratits associated with an epithelial defect. Journal Refract Surg 2000; 16:744-8. 52. Haw W, Manche E. Management of Steep Central Islands. In: S MacRae, R Krueger,and RA Applegate, eds. Customized Corneal Ablation: The Quest for SuperVision. 1st edition. Thorofare, NJ: Slack Inc., 2000.
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Weldon Haw, M.D. Cornea & Refractive Surgery Department of Ophthalmology Stanford University School of Medicine 300 Pasteur Drive, Suite A157 Stanford, CA 94305 Phone:(650)-723-5517; Fax: (650)-723-7918 E-Mail:
[email protected] LASIK AND BEYOND LASIK
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FLAP COMPLICATIONS
Chapter 22 FLAP COMPLICATIONS Arthur Cummings, M.D., Frank Lavery, M.D.
Diminishing Complications with New Microkeratomes Complications with the creation of the flap have diminished with the use of the newer microkeratomes. Some of the complications discussed here would not be rare if it were not because of the technological advancements associated with the new microkeratomes. In our experience, the visual results are not different using the Hansatome or any other microkeratome that has created a good flap. The refractive results are also completely comparable. Nevertheless, the ease of use of the Hansatome and the fact that excellent flaps are created all of the time in our experience thus far, have taken a load off our shoulders. The experience of doing LASIK has changed from a bit of a “hope and see” attitude to one where the result is basically guaranteed.
COMPLICATIONS These can be divided into intraoperative, early postoperative and late postoperative stages.
I) Intraoperative Complete cut: Free flap Decentered flap Superficial/too thin/ irregular flap Perforated cap Incomplete cut: Under half Over 3/4
II) Early postoperative period (within the first hours to days) Dislocated / Moved flap Foreign bodies “Sands of the Sahara” Keratitis Microstriae
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III) Late postoperative period (from 2 days to first few weeks)
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Infection Keratitis Dry eye syndrome Epithelial ingrowth
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MANAGEMENT OF COMPLICATIONS
Section 7 Subjects Index
The Complete Free Flap This complication would most probably be the most serious and devastating complication for both the surgeon and the patient. It occurs very infrequently and is usually as a result of inadequate suction on the suction ring, a very flat cornea or an adjustable microkeratome that has been set incorrectly. The instant recognition of the problem as well as the appropriate management is of paramount importance. Once the flap has been located and stored safely in a sterile container, the bed needs to be inspected. If the bed is suitable for laser, the treatment can be applied. The flap is then replaced onto the cornea and any of the following procedures can be followed : the flap can be managed in the usual fashion and
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then once the surgeon is satisfied that it has re-attached, the patient can be monitored at regular intervals in the ensuing 6 hours to make sure that the flap remains on the cornea. Bandage contact lenses (soft disposable contact lenses) can be applied to further secure the free flap. Not all surgeons agree that the contact lens enhances the chances of the flap remaining in position however, and there are some who believe it places the flap at additional risk of displacing and getting lost. Free flaps have also been secured in position by placing 2 or more 10-0 Nylon sutures through the flap into the adjacent superficial cornea. This prevents loss of the cap better than any other procedure, but almost always will cause striae in the flap. Fortunately very few microkeratome cuts have ended up with free flaps so that there is not much data around on the best method to manage this problem. It is also true that most free flap cases do end up with a satisfactory result. It is very important to note that if enhancement surgery is to be performed, then a new flap needs to be fashioned with the microkeratome. The initial cause of the free flap must be borne in mind and all possible precautions taken to prevent it from occurring again. Figures 22-1 through 22-5 shows a patient who had a free cap and how he was managed. Some surgeons state that the corneal reference markings are unnecessary. These are essential if one needs to reposition the flap in the correct orientation after a free flap has been made. They are also very useful to correctly align the flap in any case where the surgery has gone perfectly well too. Fig.22-1 illustrates the value of these markings following a case where a free flap occurred. In those rare cases where a free flap eventually loses permanently, the management varies according to the final visual and refractive result. Most postoperative lost cap refractions will be hyperopic in nature. Once the refraction is stable and the cornea clear, laser correction can be done for the manifest refractive error if it is within the range successfully treated with hyperopic PRK. A lamellar keratoplasty can also be performed with the donor button being fashioned with a microkeratome off the donor eye. This is placed onto the recipient corneal bed and sutured into position. Once the healing process is complete and the refraction stable, LASIK or PRK can be performed for the residual refractive error. It is very worthwhile re268
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membering that contact lenses can be very useful in some of these patients and that they might be the preferred method of visual rehabilitation where cap problems might be expected again.
The Decentered Flap This complication occurs infrequently because the fact that the suction ring is decentered is usually observed before the microkeratome is activated and the flap cut. If it is noticed that the suction ring is not well centered, the suction is broken by switching off the vacuum and the ring is re-applied. If there is a deep scleral groove all the way round the limbus, it would be better to wait for 30 minutes or until the groove has disappeared and then reapply the suction ring. Decentration can occur after the suction Contents ring has been engaged and accepted to be adequately centered. Once the flap has been cut and the suction Section 1 ring removed, the decentered flap is noticed then sometimes. In these cases, only one of two options Section 2 can be followed. Either the decentration is so mini- Section 3 mal that the planned ablation zone can still be delivered under the flap, in which case the operation sim- Section 4 ply proceeds as usual, or, the flap is so decentered Section 5 that the ablation zone will not be under the flap in its entirety. Then the decision needs to be made to abort Section 6 the procedure, wait 6 to 12 weeks for the flap to reattach firmly, and then start from anew. The use of a Section 7 caliper set to the optical zone to be treated, is of great Subjects Index benefit in assessing whether the area to be lasered lies beneath the area of the flap. The best way to eliminate decentered flaps would be to apply the suction ring to the eye and applanate it manually, quite firmly, and in your mind’s eye, stretching the underlying bulbar conjunctiva posteriorly so that the suction ring is sucking down onto Help ? a flat, stretched out surface rather than a rolled up surface with excess tissue. Once this manual applanation is deemed to be adequate, the vacuum pump is activated and the suction ring is officially applied.
Thin Flap Occasionally flaps are created that are thinner than intended. This would occur where the suction on the eye was not adequate and an insufficient protrusion of cornea through the suction ring is achieved.
FLAP COMPLICATIONS
Figure 22-1: The preoperative corneal topography of both the left and right eyes. The preoperative refraction was -2.25 sph on the right and -2.50/ -0.50 axis 76 on the left.
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Section 6 Section 7 Subjects Index
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Figure 22-2: The postoperative corneal topography of the right eye. The right eye looks just as expected on day 1 with 6/6 unaided vision.
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Section 1 Section 2
Section 3 Figure 22-3: The day 1 postoperative topography of the left eye with very unusual appearance of steepening nasally and flattening temporally. This is due to a free cap created the day before with LASIK, having been placed incorrectley on the eye due to poor reference marks. The flap appeared hazy and the best corrected visual acuity (BCVA) was 6/7.5 with +3.00/-6.00 axis 160.
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Section 6 Section 7 Subjects Index
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Figure 22-4: 3 weeks later the flap was removed and rotated through 180 degrees. The corneal topography looks very similar to the previous one and the refraction is also very similar, namely +4.00 /-6.00 155. Best corrected vision now 6/12.
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FLAP COMPLICATIONS
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Section 1 Section 2 Figure 22-5: 3 weeks later the flap was again completely removed and the corneal bed was debrided of any epithelium. The flap was replaced and repositioned again to give the most appropriate fit. This topography shows the day 1 appearance after this procedure. The unaided visual acuity was now 6/15- and with a correction of +1.00/-1.25 axis 110 the visual acuity was 6/9+. One week later the refraction was +1.75/-1.25 axis 115 and the visual acuity 6/7.5+2. Four months later the refraction is +0.50/-0.75 axis 5 and the vision is 6/5. Unaided visual acuity is 6/9-. The refraction has remained stable at this level for the past 2 years. This case demonstrates the importance of aligning the flap correctly postoperatively and the importance of reference marks especially in the case of a free flap.
In almost all instances, the laser treatment can still be applied. The thin flap often results in sub-epithelial corneal scarring. If the flap is less than 100 microns thick, do not proceed. Replace the flap and wait for 6 to 12 weeks before recutting. If one was to proceed, you would notice severe sub-epithelial haze especially if the correction to be lasered is over 3 diopter spherical equivalent.
Perforated Flap This rare complication arises when suction is inadequate and when the corneal curvature is very flat. A doughnut shaped flap is fashioned with the central area remaining uncut. Obviously it is impossible to laser in this situation and the flap must simply be replaced and there should be a waiting period of at least 3 months before this is attempted again. Scarring can occur along the margin of the perforation and this can be reduced with the use of cortisone drops.
Section 3
Section 4
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Section 6
(Note from Editor-in-Chief: The steroidal Section 7 drops must be tapered approximately in a period of 3 to 4 months to reduce the amount of fibrous tissue Subjects Index observed in the borders of the perforated corneal flap.)
Incomplete Flaps (Note from Editor-in-Chief: It is important to maintain the microkeratome path free of obstacles at the time of the keratectomy to avoid this type of complication. Sometimes this occurs from electrical failure, incorrect use of the automated microkeratome or gear obstruction by eyelids, lashes, speculum or drape.)
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Half-Cut The flap is replaced and allowed 3 months to heal at which time, the procedure is approached as any new procedure would be with new refraction, etc. LASIK AND BEYOND LASIK
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Cut This flap can sometimes still facilitate treatment especially where a cylinder is involved. If the area to be treated can fit onto the exposed area, laser treatment can continue. If the area to be treated cannot fit onto the exposed area, the flap is replaced into position and a 3 months waiting period is entered into again before recutting the flap. Never try to enlarge the flap by manual dissection.
Dislocated or Moved Flap This occurs approximately 0.5% of the times. More than 90% will displace or move within the first hour after surgery and for this reason, patients should be examined 1 hour postoperatively before being dismissed to ensure that the flap has not moved. The displacement is usually very minimal and the management required is to immediately return to the operating room, lift the flap, stretch it out, make sure that any epithelial tissue is removed from the corneal bed and then the flap is replaced and managed further in the usual way. 1 hour later the eye is reexamined to ensure that the flap is in position. Flaps can also move if the eye is rubbed or the patient blinks forcefully after the first hour. This has only happened twice in more than 4500 patients so it is a very rare finding. It is usually observed on the first postoperative day or earlier if the patient complains about any unusual or unexpected symptom afterwards and calls the office before the first day postoperative visit. The treatment is the same as with the earlier dislocation. It should just be noted that epithelial ingrowth or coverage of the exposed corneal bed can be substantial overnight and that the corneal bed and undersurface of the flap must be scrupulously cleaned from epithelial cells so as to minimize the chances of epithelial ingrowth occurring. A small PTK may be done over the area of ingrowth to destroy microscopic nests of epithelial cells.
Foreign Bodies Often foreign bodies like particles of eye make up, debris from linen sterile drapes, oil globules from the lid margin, etc. can land up beneath the corneal
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flap. The majority of these are removed when the flap is being replaced after doing the laser treatment, but sometimes tiny particles might still remain. In clinics where there is a 1 hour postoperative examination, these particles are detected very early, and if it is deemed necessary due to the nature, size or position of the particle, they can be removed immediately by returning to the theatre, lifting the flap and rinsing away the particle. Where patients are seen the next day for the first time postoperatively, only more serious particles would justify going back to the theatre to remove them. Centrally located particles or any particles that might cause visual disturbances or increase the risk of infection, should be removed.
“Sands of the Sahara”
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This term is used for a condition of sterile Section 1 nonspecific interlamellar keratitis. It reflects a situation of considerable confusion as to the etiology. It Section 2 is non-infectious as in no cases thus far has any cul- Section 3 ture been positive. There are many possible causes including toxic effects, side-effects of medications, Section 4 sterile inflammations and more non-specific causes. Section 5 It is our feeling that it occurs most likely due to the use of non-steroidal anti-inflammatory drops intra Section 6 and postoperatively. We have had little experience of this condition, but since abandoning the use of Section 7 NSAID’s, have not yet seen another case. The treat- Subjects Index ment is the early detection of the condition and the liberal use of topical steroids used hourly initially and tapered over the next 2 to 3 weeks. It seems appropriate to recommend that if you have not yet encountered this condition, don’t change anything in your intra and postoperative regimen. If you do encounter the phenomenon on a regular bases, change Help ? one variable at a time to try and establish the cause in your specific setting. This condition may have a variable number of criteria to meet before manifesting. The final outcome is usually good and very few cases proceed to corneal melt or loss of the flap.
Keratitis Keratitis (non-infective) can occur as a result of reactions to the chemicals used to clean the equip-
FLAP COMPLICATIONS
ment, the antiseptics used to clean the area around the eye as well as the eye and it may result from the use of eyedrops to which the patient is sensitive. It often blurs the vision and causes discomfort. Cylinders are also often induced by asymmetrical or paracentral areas of keratitis. The typical appearance is that of punctate superficial keratitis. It responds to topical lubrication with natural tears (preservativefree preferably) and low dosage cortisone preparations and may sometimes take 6 weeks or even longer to clear up. The condition usually clears up within 2 to 3 weeks however.
Microstriae These are very fine vertical, horizontal or obliquely orientated folds or lines within the corneal cap. If they involve the central visual axis and are detracting from the visual acuity, it is advisable to lift the flap and reposition it again. The earlier the folds are detected, the greater the probability that they are resolved by lifting and repositioning the flap. If the folds are only detected during the later visits at the 3 month period, no visual benefit will be detected by lifting the cap and relifting it. It is also interesting to note that some fine microstriae present on day 1 have resolved by the 2nd week. It appears that microstriae are less of a problem with the downup keratomes (e.g. Hansatome, Chiron) that create a horizontal hinge than with the conventional microkeratomes that create a nasal vertical hinge.
Infection Not much can be said about infection except that it would be a very unwanted complication. This is a problem that is extremely rare. The most likely place for the infection to manifest itself would be under the corneal cap. In the event that such an infection did occur, the most appropriate management would include the lifting of the corneal flap, the rinsing the washing away of the infected material (after taking a pus swab for culture) and then replacing the flap. Antibiotic drops would have been used from directly after the procedure anyhow, and these will simply continue and possibly other antibiotics added according to the culture and sensitivity profile of the
pus swab. Infection would rarely cause a serious loss of vision. (Note from the Editor-in-Chief: On the area affected by the infection, either the stromal bed or the corneal flap, a corneal ulcer may develop with important limitations to the final visual acuity.)
Dry Eye Syndrome The comforting and lubricating effect of tears on the eyes is well known. Tears are produced by the tear glands and are removed by evaporation with the remainder of tears being directed through the nasolacrimal duct to the nose. Contact lens wearers as well as people that wear glasses permanently have a much reduced evaporation rate of the tear film. Consequently, less tears are produced to maintain the apContents propriate wetting level of the eyes. Once the glasses or contact lenses are not being worn due to success- Section 1 ful refractive surgery, the evaporation element of tear removal increases again. This results in a rela- Section 2 tive shortfall of tear production for a while until such Section 3 a time that the production rate increases and the tear system is in equilibrium again. This usually takes Section 4 about 6 months and can be lengthened by the use of Section 5 certain medications e.g. hormones, antihypertensives, anti-cholesterol, anti-acne and others. Section 6 The second consideration is that the shape of the cornea changes after surgery with flattening of Section 7 the central area being the most common change. This Subjects Index could result in poorer applanation between the lids and the cornea than previously. The result of this would be a cornea that is wet less satisfactorily. The use of natural tears for 3 to 6 months usually alleviates the symptoms.
Epithelial Ingrowth
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This complication occurs at different rates for different surgeons. Some might almost never encounter it while other surgeons see it a number of times per year. It tends to occur in situations where the flap might have been displaced on day 1 and was then repositioned. If the corneal bed was not cleaned up properly, some epithelial tissue might now find itself beneath the edge of the flap. These cells can continue to proliferate and grow in under the flap
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and eventually involve central vision. Most often however, the cells will grow for a short while and then suddenly start regressing. It is thought that growth factors and stimulants for epithelial growth are not found under the flap and that growth eventually ceases. In cases where the ingrowth continues, it makes sense to surgically remove the epithelial ingrowth by lifting the flap and cleaning both the bed and the undersurface of the flap properly and removing all epithelial cells. This condition also occurs more readily in patients where it was noted intraoperatively that the epithelium has poor adherence to the corneal basement membrane. Ingrowth occurs more easily now as the affinity of the epithelium for the basement membrane is reduced for whatever reason, and the epithelial front of growing cells simply follows the path of least resistance. This phenomenon occurs less in those microkeratomes that have a high angle of attack such as the Hansatome (Chiron).
THE HANSATOME (“DOWN-UP”) MICROKERATOME The Hansatome microkeratome came on to the refractive surgery market at a time when many surgeons worldwide had already operated a great number of LASIK’s using other microkeratomes and having had to go through the learning curve procedure. Obviously while learning a new technique, more complications are experienced as compared to an experienced surgeon doing the same procedure. The Hansatome has however taken a load off the shoulders of experienced surgeons and even more so, of surgeons learning to do LASIK.
Main Advantages 1. The primary advantage of this microkeratome is the fact that the hinge is now horizontal and situated beneath the upper eye lid. With each and every blink action of the lids, the flap is smoothed out into position in the direct postoperative period.
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2. The quality of the flap created by the Hansatome is the best flap that either of us have seen. The flap is of uniform thickness with a very precise margin all the way round. The alignment of the flap postoperatively is also easier than most thanks to the quality of the flap and the tendency to want to “spring” back into position. Thus far using the Hansatome, we have had no thin flaps and no partially cut flaps. 3. The suction or vacuum generated by the vacuum unit is also superior to any other unit that we have used. The suction is so good that thin flaps have simply not occurred to date. Approximately 25% of patients to however have subconjunctival hemorrhages postoperatively due to the suction ring, but we feel that this is a small price to pay for the superior flap that the microkeratome produces time after time. 4. The suction ring is elevated and surrounding tissue (lids, conjunctiva, lashes, etc.) tend to post less of a problem than with conventional keratomes. 5. The Hansatome has another built in safety feature that if the pressure or vacuum should drop causing the suction ring to applanate poorly or even come off the eye, the microkeratome stops its forward progression and in this way ensures that no free pieces of flap can be created.
Disadvantages 1. The suction ring is bigger than most others and sometimes poses a problem with getting it to fit into the interpalpebral fissure and to applanate well onto the eye. We normally use the nasal speculum made by Rumex (14-041) and when we experience difficulty with the applanation of the suction ring, try a different speculum. Different speculums give different amounts of exposure to the eye on a varying basis – one must try different ones until a suitable one, giving adequate exposure, is found. Cases do arise where no speculum can be found to give adequate exposure and in these cases one can simply go ahead without the use of a speculum. The vacuum on the Hansatome is so good that once it has been
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Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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applied and the pressure risen to the desired amount, it is safe to go ahead and make the pass with the microkeratome in the absence of a speculum. 2. The Hansatome is relatively expensive but to date none of the disposable microkeratomes can give the quality of corneal flap on the consistent and predictable basis that the Hansatome does. As with any piece of equipment, it is very important to know the equipment well and to check it before use. We recommend you test the Hansatome motor before connecting it to the microkeratome and ensure that the resistance (read out from the display on the unit console) is below 50mA. (Although mA is a unit of electrical current, it is indirectly reflecting the resistance that the motor is experiencing. The higher the resistance, the higher the current necessary to drive the motor and vice versa)). Once the head piece is fitted, test it again. Now the resistance should be lower than 100 mA. Also, test the microkeratome by making a run with it and checking the resistance once again on the console as well as listening to the sound it makes and observing the way it progresses. Having made these checks preoperatively and having found the machine to be in good working order, it is extremely unlikely that the microkeratome is going to malfunction on the eye.
Cleaning of the Instrument
verse for 15 seconds. The tip is then wiped with a Merocel spear sponge. The motor is stored with the drive tip down. This prevents liquids from migrating down into the motor and gear box and will keep the motor clean and running smoothly. If the motor becomes jammed, the distal 2 to 3 mm of the motor tip is soaked in 99% alcohol for up to one hour and is then cleaned as above. The microkeratome is cleaned by soaking it in alcohol and by washing the gears with Palmolive soap. This keeps them well lubricated and prevents excessive wear and tare on the gears and motor. Blades are supposed to be for single use only but are often used for 2 eyes of the same patient. Once a blade has been used, it may still be fit to make another safe cut. By inspecting it under the microscope and having considered it fit for further use, it can be sterilized again by soaking it for a minimum of 10 hours in Cidex long life solution. In poorer countries where new blades are at a premium, recleaned and re-sterilized blades can be used once more if they are found to still be in good condition following microscopic examination.
PEARLS TO ASSIST WITH THE MAKING OF A GOOD FLAP
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Section 3
Section 4
Section 5
Section 6 Section 7
During use, only sterile distilled water is used with the microkeratome. Only once the flap has been created and the microkeratome removed, do we start using BSS again. It is thought that the corrosive qualities of the salt in the BSS add to wear and tare of the microkeratome. Following each patient, the microkeratome is cleaned with Palmolive concentrated liquid diluted with sterile water. Each part is gently cleaned using a soft toothbrush and is then placed in a dish of sterile water, where again all the parts are gently brushed to ensure that the liquid Palmolive is removed prior to sterilization. At the end of each session, prior to storage, the distal 2 to 3 mm of the motor is dipped in 99% alcohol and is electrically driven forward and in re-
First apply the suction ring to the eye and applanate it well before the suction is applied. It helps Subjects Index to stretch out the bulbar conjunctiva posteriorly as the suction ring is applied to ensure a good applanation and final suction. Check the intraocular pressure with the tonometer before proceeding and we always enquire about the vision at this stage. In most cases, it has already darkened in front of the eyes and even blacked out completely. This confirms that Help ? the suction ring is adequately applied and ready for the microkeratome pass. Some surgeons reckon that it is better to have visual feedback on exactly what the microkeratome is doing and to look at the flap being created. Our feeling is that if your faith in the microkeratome is very good and that your complication record suggests that you are experienced with creating flaps,
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that there is absolutely no advantage in being able to see the flap being fashioned. The possibility exists that the procedure can be unduly interrupted by a surgeon watching the flap being created and thinking that there is a problem, terminating the pass of the microkeratome. This could occur in spite of everything going ahead well.
Arthur Cummings, MB., ChB Mmed (Ophth) FCS(SA) FRCS(Edin) Wellington Ophthalmic Laser Clinic 2a Wellington Road, Ballsbridge Dublin 4, Ireland
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Section 6 Section 7 Subjects Index
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FOLDS AND STRIAE OF THE DISC POST LASIK
Chapter 23 FOLDS AND STRIAE OF THE DISC POST LASIK Canrobert Oliveira, M.D., Etelvino Coelho,M.D.
Because it is a very recent technique, some LASIK complications are still unsolved. We have seen recently on the last meeting of the American Academy, many presentations about “ Sands of Sahara Syndrome” which the etiology still unknown, could not show us a definite treatment. We have the same impressions about the folds and striae . The revision of the literature about the subject showed us how uniformed the authors are, relating to the definitions gave to the folds, striae and it’s respective treatments. In this chapter, we propose, after the definition of each entity and indications for the specific treatment and a logical name.
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Section 3
Section 4
Section 5
Figure 23-1: Folds
Section 6
Definition Folds are the thick waves of the disc, caused by accidental slipping of the disc over the stromal bed, generally traumatic. It is a emergency situation with tears and pain, associated to a low visual acuity, when affecting a optical zone. This frequently occurs during the first hours, although, it could result on late trauma (we have a case after six months of a surgery) (Figure 23-1). Anatomically, the folds are constituted by the three layers which, compose the disc: the epithelium, Bowman membrane and the stroma. It is caused by the adherence of the stromal side of the disc itself on the waves (Figure 23-2). That is why, it can not be dissolute with a simple massage with the finger or with a steel spatula. Striaes are microscopic wrinklings which affect just the Bowman membrane, secondary to the misalignment of the disc with the stromal bed
Section 7 Subjects Index
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Figure 23-2: The three layers of the folds
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Figure 23-3: Striaes Figure 23-4: The sign of the growing moon
(“the tent effect” secondary to the brake of the relationship between the content and the continent – the disc and the corneal stroma, after the stromal ablation by the excimer laser). We have noticed a pattern of striae similar to a broken glass (see figure 23-9) which does not keep any relation with the myopia grade and which appears immediately after a surgery, in which the cause is still obscure. The striae are not an emergency situation, and are always easy to identify in the immediate post op of Lasik. It never occurs later on. Although a decrease on the visual acuity is not so emphasized as in the folds, enabling the patients to read 20/25 or 20/30, the main complaint refers to a loss on the a vision quality (Figure 23-3).
Folds Treatment The folds should be treated even if it is not affecting the central area of the cornea. The treatment is completely successful, because more than fixing the biomicroscopic esthetics on the slit lamp, it recovers the visual acuity. Surgical technique: We look forward to identify on the slit lamp, the region in the which the border of the disc is far off the stromal bed border. This space has the aspect of a growing moon, that’s why we denominate it as “the sign of the growing moon”. Depending on time of the accident occurred, the epitelization has already completely (Figure 23-4).
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The first step to the surgery will be the reContents motion of the epithelium on the area of the “growing moon”, after a great irrigation, to avoid that the loosen Section 1 epithelial cells remain in the surround surgical area Section 2 of the stromal bed. The second step will be the detachment of the disc, through the introduction of a Section 3 cannula over the epitelized disc, and after, with an Section 4 BSS injection, we promote it’s hydrodissection. We prefer this method to the detachment with steel Section 5 spatula, because it is less traumatic, though the corneal stroma is composed by 78% of water. During Section 6 the third step, after reverting the disc, we rehydrate Section 7 abundantly it’s stroma, till the edema of the lamellas promote a liberation of the stroma faces adhered. Subjects Index We know that the folds are undone when, we relocate the disc with a soft brush ( Martha Brush, for example), noticing the space in shape of a “growing moon” disappearing, signalizing that the board of the disc found the margin of the stromal bed (Figures 23-5, 23-6, 23-7). Help ? If the folds are old, even though the border of the disc has found the margin stromal bed, we will still observe on the surgical microscope epithelial signs on the original place of the folds, which disappear in a few days. Finally, we put a disposable contact lens and prescribe the habitual drops of the LASIK post op routine prescriptions. We have a successful case folds unmade, after six months of a LASIK surgery.
FOLDS AND STRIAE OF THE DISC POST LASIK
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Section 4
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Section 6 Section 7 Subjects Index
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Figures 23-5, 23-6 and 23-7: Rehidratation of the stromae
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Figure 23-8: Striae
Figure 23-9: “Broken glass image”
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Striae
Section 1
The striae should be treated just when it cross the optical zone, affecting the visual acuity. On a striking way, we will be able to notice striae on the optical zone with no complaints. On the other hand striae out of the optical zone can not be perceived.
Section 2
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Section 5
Surgical Technique The only way to remove the striae of the Bowman membrane, is to take out the epithelium of the disc (Figures 23-8, 23-9). Therefore, it’s total desepithelization is the first step to the surgery. After, we wash the hole surface in order to eliminate the loosen epithelial cells. During the second step, we do the hydrodissection described over (Figure 23-10). The third step is similar to the folds technique. We revert and rehydrate abundantly the stroma of the disc. On the forth step, we relocate the disc and brush the surface of the Bowman membrane with movements from the center to he disc periphery, in all directions, till all the striae has disappeared (Figures 23-11, 23-12).
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Section 6 Section 7 Subjects Index
Figure 23-10: Hidrodissection of the disc.
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FOLDS AND STRIAE OF THE DISC POST LASIK
Figure 23-11: Using a brush in Bowman’s mebrane
Figure 23-12: Rehidratation of the stroma of the disc.
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Finally, we put the contact lenses in place and prescribed the routine medications for LASIK post op. In four or five days, the epithelization occurs, but an improvement on the visual acuity could take a few weeks to succeed.
We have a successful case in which the striae were unmade in three weeks after the LASIK post op.
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Section 6 Section 7
Canrobert Oliveira, M.D., Director of the Hospital de Olhos de Brasilia – Brasilia DF Brazil Av. L2 Sul Q 607 Modulo G Brasilia DFCEP 70.200-670 Phone 55 61 242 4000 Fax 55 61 244 49 10 www.hobr.com.br
[email protected]
Subjects Index
Etelvino Coelho,M.D. Director of the “Centro de Microcirurgia Refrativa & Excimer Laser de Minas Gerais” Rua Guajajaras 40 suite 1103 Belo Horizonte MG Brazil CEP 30.180.910 Phone 55 31 3 224 52 00 / 0 800 31 20 20 Fax 55 31 3 226 92 92 www.excimer.com.br
[email protected]
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TREATMENT OF FLAP STRIAE
Chapter 24 TREATMENT OF FLAP STRIAE Jairo E. Hoyos, MD. Melania Cigales, MD. Jairo Hoyos-Chacón, MD.
One of the complications of LASIK is the formation of folds or striae in the corneal flap, which cause irregular astigmatism and loss of visual acuity. Striae may form during surgery due to the incorrect repositioning of the flap over the stromal bed, or in the early postoperative period if the disc is slightly displaced by blinking. In the early days of LASIK, flaps created with large hinges were easily correctly repositioned. Nowadays, however, to perform ablations with large optical zones and peripheral ablations to correct hyperopia, we try to create a flap of minimum hinge. In these cases, it is important to make epithelial reference marks and correctly align these when we reposition the flap over its bed. If the reference marks are misaligned, this means that the flap is wrinkled or slightly displaced leading to the formation of folds and striae. It is important to check for correct alignment using the slit-lamp, and if this complication is noted, to immediately lift the flap, hydrate it and reposition it by careful alignment. It was thought in the past that the nasal flap was a cause of striae formation, since it favored displacement during blinking in the early postoperative course. Displacement is less common with a superior flap but striae still appear. We generally observe horizontal striae in nasal flaps and vertical striae in superior flaps. Striae formation is also more common in the case of a thin corneal disc. Thus, good prophylactic practice is to plan for a corneal disc of 160 µm in thickness. The LASIK surgeon should be aware of the complication and try to avoid it. If detected, folds and striae need to be rapidly treated. We present a new technique for the treatment of flap striae.
Case Report We report the clinical case of a patient undergoing LASIK in both eyes. Preoperative refraction was –2.75 -0.50 x 180° in the right eye (RE) Contents and -3.0 -0.75 x 180° in the left eye (LE). Corrected visual acuity was 20/20 in each eye. A superior Section 1 160 µm flap was created using a Hansatome Section 2 microkeratome and ablation performed using an Chiron 217 C Technolas excimer laser. Section 3 One day after LASIK, visual acuity was 20/ 40 in the RE and 20/20 in the LE. The patient pre- Section 4 sented flap striae in the RE. An attempt to resolve Section 5 this complication by lifting the flap and profusely hydrating it did not prove effective. A week later the Section 6 flap was once again lifted and the entire epithelium Section 7 was removed to eliminate persisting striae, but the complication did not improve. A month later, RE Subjects Index visual acuity was 20/60 and did not improve with correction. Irregular astigmatism was shown on topography. Figure 24-1 shows the appearance of
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Figure 24-1: Flap striae one month post-LASIK.
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the eye showing folds and striae of the flap. We subsequently decided to perform a new treatment protocol described below.
SURGICAL TREATMENT Lifting of the Flap Using a Spatula (figure 24-2). Using the slit-lamp, the flap edge is identified and lifted slightly using the tip of an insulin needle and the lifting procedure completed under the surgical microscope. In such cases, we avoid making epithelial reference marks, since the disc is incorrectly positioned and we would induce the same error when repositioning it over the stromal bed.
Figure 24-3: Treatment: checking the stromal bed.
Hydrating and Repositioning the Flap Over the Stromal Bed (figure 24-4). The flap is profusely hydrated with Ringer’s lactate with simultaneous aspiration. As part of the same irrigation-aspiration maneuver, the disc is repositioned over its bed.
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Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Figure 24-2: Treatment: lifting the flap with a spatula.
Checking the Stromal Bed (figure 24-3).
Help ? Figure 24-4: Treatment: repositioning the flap.
Once the flap is lifted, we check the stromal bed for any irregularity which could lead to the formation of striae. In the present case, the bed was perfectly uniform and even. The technique applied was aimed at smoothing out the wrinkled corneal disc. First, we scrape the edges of the corneal epithelium to avoid peripheral epithelialization, since at the end of treatment the disc will be stretched and will therefore be larger than the exposed bed. 284
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Massaging the Flap Using a Spatula Over a Contact Lens (figure 24-5). A soft contact lens is placed on the cornea and using a flat spatula the flap is massaged over the contact lens. The contact lens allows us to perform an intense massage without damaging the corneal
TREATMENT OF FLAP STRIAE
Figure 24-5: Treatment: massaging over a contact lens.
Figure 24-6: Treatment: direct massaging of the cornea.
disc and evenly distributes tension preventing the formation of further striae. When folds are considerable, the epithelium covering a stria may rupture. Other times, the epithelium readapts to the underlying flattened disc without breaking. We commence the massage over the pupillary area (where it is most important to achieve an even flap) performing circular movements. When we observe a highly marked fold, we place the spatula parallel to the fold and massage in a perpendicular direction. While we perform these maneuvers it is important to keep irrigating the flap on its stromal side to prevent adhering to the bed. If the disc adheres, massage is ineffective. Similarly, we frequently hydrate the epithelial side of the disc to prevent it sticking to the contact lens and damaging the epithelium. The massaging procedure is the most important step of treatment and should be performed for as long as considered necessary. We generally massage for about an hour.
thelium with the spatula and to perform this direct massage until the flap has completely adhered to the bed.
Appearance of the Cornea After Treatment (figure 24-7).
Section 1 Section 2
Section 3
Section 4
Despite the fact that folds appear to persist, the stromal interface is seen to be perfectly even on Section 5 slit-lamp examination. What we are really seeing at Section 6 first, are the imprint of past folds on the epithelium. After treatment, mydriatic and antibiotic drops are Section 7 instilled. We also recommend the use of a non-oppressive dressing for 12-24 hours to avoid displace- Subjects Index
Direct Massaging of the Flap (figure 24-6). After massaging, the contact lens is removed, the stromal bed is rehydrated, and with the spatula directly on the cornea, we undertake a smoothing out maneuver from the hinge towards the opposite edge of the flap. This direct massaging of the flap over the cornea favors the adhesion of the flap over the stromal bed. It is important to wet the epithelial side of the corneal disc to avoid damaging the epi-
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Figure 24-7: Final image after treatment.
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ment due to blinking and favor the adequate epitheliazation of the cornea.
SUGGESTED READINGS 1.
Carpel EF, Carlson KH, Shannon S. Folds and Stria in Laser in situ Keratomileusis Flaps. J Refract Surg 1999;15: 687-690.
2.
Gimbel HV, Peters NT, Iskander NG, Penno EA. Laser in situ Keratomileusis Flap Complications and Management. J Refract Surg 2000;16: s223-225.
3.
Gutierrez AM. Treatment of flap folds and striae following lasik. In: Buratto L, Brint SF, eds. LASIK: Surgical Techniques and Complications. Thorofare, NJ: SLACK Incorporated; 1999; 557-562.
Outcome After 12 hours, we removed the dressing and confirmed the disappearance of the striae (figure 248). The cornea was reepithelialized and uncorrected visual acuity was 20/25. A week later, corrected visual acuity was 20/20 and an even cornea was shown on topography.
Jairo E. Hoyos, M.D. Director Médico Instituto Oftalmológico de Sabadell Rambla, 62, 1a. Sabadell (08201), España E-mail:
[email protected]
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Figure 24-8: Outcome one day after treatment.
Section 7 Subjects Index
Conclusion Any stria or fold affecting the pupillary area
should receive early treatment during the first 24-48 hours following LASIK. Unlike other methods of treatment, massaging the flap with a spatula over a contact lens is an effective method of removing flap striae as late as one month after surgery.
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KERATECTASIA INDUCED BY MYOPIC LASIK
Chapter 25 KERATECTASIA INDUCED BY MYOPIC LASIK Leonardo P. Werner, M.D., Henrique Vizibelli Chaves, M.D.
Introduction Laser in situ keratomileusis (LASIK) for the surgical correction of myopia is gaining acceptance as a versatile refractive surgical procedure. Quick visual rehabilitation, minimal postoperative discomfort, and the ability to correct high degrees of myopia with little postoperative corneal haze are some reasons for LASIK’s popularity over other surgical vision correction options.1-4 However, postoperatively detected corneal ectasia is a possible complication of the procedure, even with temporary improvement in vision.5-7 Because the maximal corneal stromal tissue will be photoablated from the central cornea, the thickness of that area becomes important when LASIK is performed for high refractive errors with large ablation depths.7 In viewing the risk of creating iatrogenic keratectasia by removing excessive stromal tissue during LASIK, we have found that the mechanism have not yet been completely clarified and some analysis has been attempted in other to provide a more accurate understanding of keratectasia after LASIK.
Corneal Stromal Changes Induced by LASIK All excimer laser refractive procedures modify the refracting power of the cornea by altering the anterior corneal curvature using photoablation. The procedure substantially weakens the mechanical strength of the cornea because the biomechanically effective thickness of the cornea is reduced by the thickness of the lamella plus the keratectomy
depth.7,8 Biomechanical weakening may only become manifest months after a surgical procedure and some surgeons have recommended that at least 250 to 300 mm of residual posterior stroma be left untouched to ensure adequate biomechanical corneal strength Contents to minimize the risk of keratectasia.9-11 Performing LASIK in patients with high myopia and a thin cor- Section 1 nea should result in posterior stromal bed thickness less than 250 mm.12 The keratectasia is probably due Section 2 to the action of intraocular pressure (IOP) on that Section 3 weakened cornea, producing a corneal steepening revealed on corneal topography. This steepening ap- Section 4 pears to be greater in older patients and provides furSection 5 ther evidence of the ability of IOP to produce ectasia in a thinned cornea.10 The correction of myopia in- Section 6 volves the relative flattening of the central rather than the peripheral cornea, which reduces the anterior cor- Section 7 neal curvature and thus the refractive power of the Subjects Index treated area. This becomes a particularly contentious issue when, in the absence of classic clinical evidence of keratoconus, inferior steepening of the cornea seen on corneal topographic scan after LASIK suggests the possibility of subclinical keratoconus.11,12 Keratoconus usually starts during puberty and, in most cases, it takes more than 5 years to manifest cliniHelp ? cally. At any stage, the cornea may return to its original tensile strength or at least increase its stiffness, leading to an abortive form of keratoconus, forme fruste keratoconus (FFK).7 The diagnosis of FFK is not always easy. In some cases clinical signs such as the Fleischer ring are present without any progression of myopia and astigmatism over years. Also, corneal topography may look keratoconus-like, with a temporal inferior steepened area. In other cases, however, no clinical diagnostic signs can be detected
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at the slit lamp; an asymmetric bow-tie pattern on corneal topography may be the only diagnostic hint to explain the slightly tilted Javal mires described and classified by Amsler.8-12 Asymmetric bow-tie patterns, however, appear to be more frequent than symmetric patterns in a population of normal eyes. To substantiate the relationship between FFK and iatrogenic keratectasia after LASIK, the populations of large prospective studies currently underway should be investigated for FFK cases.13 Until a clinical relationship between FFK and complications after LASIK has been established or refuted, we should consider FFK a contraindication for LASIK.
Corneal Evaluation Using the Orbscan Topography System Computer-assisted videokeratoscopes are now used in clinical practice, and videokeratography has enhanced our ability to detect early keratoconus in a quantifiable and reproducible manner. Evaluation of the cornea in refractive surgery routinely includes some form of 2-dimensional corneal surface mapping. However, axial power maps commonly produced by most videokeratography systems do not correlate well with refractive changes. Most computerized videokeratoscopes used in clinical practice are Placido-disk-based systems. In this system, a Placidodisk pattern is projected onto the cornea, video-image captured, and analyzed by computer. Axial power calculated from Placido-based systems represents only local or refractive power of the cornea within the paraxial region (approximately the central 2.5 mm zone of the cornea). The limitations of these systems have been discussed and the Placido skew ray error, information reflected from only tear film, and sensitivity to focus and alignment. Furthermore, Placidobased systems cannot distinguish convex from concave shape changes on corneal surface. Therefore zheight calculations from Placido-based data have severe accuracy limitations.13-16 The Orbscan Topography System (Orbtek, Inc.) is a 3-dimensional (3-D) slit-scan topography system designed for analysis of the cornea and anterior chamber surfaces. It uses a calibrated video and scanning slit-beam system to independently measure the x, y, and z locations of several thousand points
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on each surface of the cornea and anterior chamber. The instrument therefore measures elevation, from which shape and power calculations are derived. From the slit images, the anterior and posterior corneal surfaces can be reconstructed mathematically based on ray tracing and triangulation between the light emitter, the corneal surfaces, and the sensor video capture.17 We used the Orbscan Topography System to evaluate a series of postoperative patients submitted by LASIK (Figures 25-1 through 25-4). Using the reconstructed anterior and posterior corneal surfaces, it is possible to apply ray-tracing models to calculate the cornea’s total effective lens power. Thus, the Orbscan produces total optical power maps that describe the Snellen refractive power of the cornea as a 3-dimensional structure, mapped locally onto the front surface using a false color scale. Contents The power calculation is based on tracing parallel rays traveling through the anterior surface and, subSection 1 sequently, posterior corneal surface.18 Therefore, the results should correlate more closely with the mani- Section 2 fest change in refractive power than paraxially calSection 3 culated maps of the anterior surface alone. Analysis of the Orbscan color maps can be Section 4 focused on quantitative topographic parameters at 3 points: the central point of the cornea; the apex, the Section 5 point with maximum reading on the anterior elevaSection 6 tion best-fit sphere map (anterior elevation BFS); and the thinnest point, the spot with minimum value on Section 7 the pachymetry map. Analysis of these parameters Subjects Index include the following: 1. Location – radius (the distance from the central point of the cornea) and semimeridiam (designated from 0 to 360 degrees, proceeding counterclock-wise from 3 o’clock in both right and left eyes). Help ?
2. Elevation – compared to a best-fit sphere. The anterior BFS is calculated to best match the anterior surface. This match is determined using a least squares method. The displayed map data represent the sphere subtracted from the eye surface in millimeters. The difference between the sphere and the eye surface is expressed as the distance radially from the center of the sphere rather than perpendicular to a plane.
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1
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2
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Help ? Figures 25-1 through 25-4: Examples of cornea topography maps created with the Orbscan system showing keratectasia induced by myopic LASIK. Changes in the elevation map (in relation to a best fit sphere), posterior float, mean power keratometric map and pachymetry map of the corneas can be seen in all cases.
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4
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Section 6 Section 7 Subjects Index
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KERATECTASIA INDUCED BY MYOPIC LASIK
of keratoconus is on the posterior surface, not on the anterior topographic readings. Therefore, if LASIK is done using ultrasonic pachymetry and surface topographic analysis, one may miss corneas that are at risk for ectasia.
3. Pachymetry – the elevation difference between anterior and posterior corneal surfaces. 4. Tangential curvature – also called instantaneous curvature, calculated from single plane and multiple axes. The plane runs from a central point radially to the periphery, as in the sagittal map, but the curvature is calculated by the tangent circle at each point along the plane. 5. Mean curvature, composite curvature – calculated from 3-D surface data. Composite curvature maps display curvature from all directions. Each map point is the mean of its curvatures in all directions.
How the Orbscan Helps Evaluating High Risk Cases for LASIK and FFK. 1. Pachymetry – The Orbscan gives a full corneal readout and in the preoperatory eye is probably more accurate than ultrasonic pachymetry. This especially true when you realize that the thinnest part of the cornea is often not central. Full corneal readouts are also important because the difference from the periphery to the thinnest area is also important. If there is a difference from the thickest to the thinnest of 200 microns, and a suspicious anterior surface (over 3D of asymmetrical astigmatism etc.) then one may be dealing with a high risk case. 2. Posterior Float – This measures the forward bulge on the posterior corneal surface. It is felt that this measurement can be used to evaluate risk factors for LASIK. The location of the steepest posterior float is also important, those that are paracentral can be more threatening than those that are central. Preoperatory values more than 50-65 microns are suspicious risks for ectasia. The posterior float almost always increases after surgery. In thin corneas when there is some question as to whether there is enough cornea to perform a LASIK the posterior float often is the deciding factor. Many people feel that the first sign
REFERENCES 1.
Heitzmann J, Binder PS, Kassar BS, Nordan LT. The correction of high myopia using the excimer laser. Arch Ophthalmol 1993;111:1627-1634.
2.
Güell JL, Muller A. Laser in situ keratomileusis (LASIK) for myopia from –7 to –18 diopters. J Refract Surg 1996;12:222-228.
3.
Helmy SA, Salah A, Badawy TT, Sidky AN. Photorefractive keratectomy and laser in situ keratomileusis for myopia betwee 6.00 and 10.00 diopters. J Refract Surg 1996;2:417-421.
Contents
Section 1 Section 2
4.
5.
6.
Chayet AS, Assil KK, Montes M, Espinosa-Lagana M, Castellanos A, Tsioulias G. Regression and its mechanisms after laser in situ keratomileusis in moderate and high myopia. Ophthalmology 1998;105:1194-1199.
Section 3
Section 4
Section 5
Section 6 Seiler T, Koufala K, Richter G. Iatrogenic keratectasia after laser in situ keratomileusis. J Refract Surg Section 7 1998;14:312-317. Seiler T, Quurke AW. Iatrogenic keratectasia after Subjects Index LASIK in a case of forme fruste keratoconus. J Cataract Refract Surg 1998;24:1007-1009.
7.
Speicher L, Göttinger W. Progressive keratektasie nach Laser-in-situ-keratomileusis (LASIK). Klin Monatsbl Augenheilkd 1998;213:247-251; errata p 372.
8.
Rao SK, Padmanabhan P. Posterior keratoconus; an expanded classification scheme based on corneal topography. Ophthalmology 1998;105:1206-1212.
9.
Geggel HS, Talley AR. Delayed onset keratectasia following laser in situ keratomileusis. J Cataract Refract Surg 1999;25:582-586.
Help ?
10. Leung ATS, Lam DSC. Delayed onset keratectasia after LASIK. J Cataract Refract Surg 1999;25:10361040.
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11. Seiler T. Iatrogenic keratectasia: academic anxiety or serious risk? J Cataract Refract Surg 1999;25:13071308.
18. Auffarth GU, Wang Li, Völcker HE. Keratoconus evaluation using the Orbscan Topography System. J Cataract Refract Surg 2000;26:222-228.
12. Joo CK, Kim TG. Corneal ectasia detected after laser in situ keratomileusis for correction of less than –12 diopters of myopia. J Cataract Refract Surg 2000;26:292-295. 13. Vesaluoma M, Pérez-Santonja J, Petroll WM, Linna T, Alio J, Tervo T. Corneal stromal changes induced by LASIK. Invest Ophthalmol Vis Sci 2000;41:369376. 14. Maguire LJ, Bourne WM. Corneal topography of early keratoconus. Am J Ophthalmol 1989;108:107-112. 15. Maguire LJ, Lowry JC. Identifying progression of subclinical keratoconus by serial topography analysis. Am J Ophthalmol 1991;112:41-45.
Leonardo P. Werner, M.D. Department of Ophthalmology, São Geraldo Eye Hospital, Federal University of Minas Gerais, and the “Instituto Vizibelli”, Belo Horizonte, Minas Gerais, Brazil. Contents
Section 1
16. Maeda N, Klyce SD, Smolek MK. Comparison of methods for detecting keratoconus using videokeratography. Arch Ophthalmol 1995;113:870874. 17. Srivannaboon S, Reinstein DZ, Sutton HFS, Holland SP. Accuracy of Orbscan total optical power maps in detecting refractive change after myopic laser in situ keratomileusis. J Cataract Refract Surg 1999;25:15961599.
Section 2
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Section 6 Section 7 Subjects Index
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INFLAMMATORY AND INFECTIOUS COMPLICATIONS AFTER LASIK
Chapter 26 INFLAMMATORY AND INFECTIOUS COMPLICATIONS AFTER LASIK Juan J. Pérez-Santonja, MD; Jorge L. Alió, MD.
General Considerations Laser in situ Keratomileusis (LASIK) has become the treatment of choice for the correction of moderate and high myopia1-5. At present, many surgeons use LASIK for lower levels of myopia because LASIK preserves the epithelium and Bowman membrane, and decreases the amount of corneal inflammation and wound healing1,6,7. This procedure involves lifting a corneal flap with a microkeratome, laser ablation of the underlying stromal bed, and flap reposition to its original place1-6. LASIK is more difficult to perform than surface photorefractive keratectomy (PRK) and introduces new additional possible complications due to the creation of a corneal flap or to its reposition, including incomplete flap, thin flap, flap amputation, epithelial bullae, flap dislocation, and flap wrinkling. In addition, the interface between the corneal flap and the stromal bed is a possible new source for complications, such as epithelial ingrowth, flap melting, interface opacities, non-infectious diffuse keratitis, and infectious keratitis7-10. Concerning interface complications, infectious keratitis is one of the most vision-threatening complications after lamellar corneal surgery, and it has been reported following myopic keratomileusis11 and LASIK9,12. Its management involves lifting the flap, scraping the stromal bed, and intensive topical fortified antibiotics. Non-infectious diffuse keratitis or diffuse lamellar keratitis is a diffuse interface inflammatory response after lamellar corneal surgery, which responds to corticosteroids, and most cases resolve with no sequelae10. It is important to distinguish diffuse lamellar keratitis from infectious keratitis to avoid the aggressive management of infectious cases.
DIFFUSE LAMELLAR KERATITIS SYNDROME (Sands of Sahara) Introduction
Contents
Diffuse lamellar keratitis (DLK), nonspecific Section 1 diffuse interface keratitis (NSDIK) or Sands of the Sahara syndrome (SOS) is a diffuse interface inflam- Section 2 mation after lamellar corneal surgery reported anec- Section 3 dotally by many refractive surgeons during the last five years, but described properly as a distinct syn- Section 4 drome by Maddox (ASCRS meeting, April, 1997), Section 5 and Smith and Maloney10. It is very important to distinguish it from infectious keratitis to avoid the ag- Section 6 gressive management and intensive treatment of inSection 7 fectious cases. Diffuse lamellar keratitis following LASIK Subjects Index surgery is not very common, probably on the order of one in 3013 to 400 (authors data) LASIK procedures. In this revision, our goal is to describe the characteristics of DLK and to help practitioners properly identify and treat this condition.
Causative Agents
Help ?
Diffuse lamellar keratitis has been reported after myopic keratomileusis in situ, primary LASIK, LASIK enhancement, and after lifting the flap for interface epithelium removal10,13. The incidence of diffuse lamellar keratitis was higher in eyes treated by LASIK (3.2%) than in eyes that had undergone myopic keratomileusis in situ (0.2%)13. The etiology of DLK is uncertain. The diffuse aspect of the infiltrate, the absence of a single focus,
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and the confinement of the infiltrate to the interface suggest a non-infectious etiology. An allergic or a toxic inflammatory reaction is the most likely cause of DLK, although the inciting agent is uncertain. Talc from gloves has been associated with interface infiltrates, although in many cases of DLK, talc-free gloves were used during the procedure10. Interface inflammation may be related to material that is present on the surface of the LASIK microkeratome blades, as cleaning the microkeratome blade before use can reduce the interface debris and inflammation14, although DLK can occur without the use of a microkeratome. For some surgeons, there is some evidence that oil or other substances coming out from the microkeratome motor during the LASIK procedure are involved as a cause of DLK in specific cases. Recently, Richard Sherin and John Doane, MD, (unpublished data) hypothesized the endotoxin contamination as a cause of SOS. Bacteria can contaminate the instruments after surgery, and subdivide quickly if the instruments are not sterilized promptly. If the instruments are autoclaved several hours later (i.e. one day after surgery), all the accumulated bacteria will release, in their death, lipopolysaccharide (LPS) (endotoxin) from their shells. This LPS is in no way detoxified by the autoclave, and coats the instruments. This LPS is well known to be extremely toxic to the corneal stroma. This theory can explain the cases of DLK following removal of epithelial ingrowth or LASIK enhancement, where neither the laser nor the microkeratome were used. Other possible factors that may be associated with DLK in some cases are substances produced by the laser ablation, meibomian gland secretions, and povidone-iodine. In conclusion, DLK is a nonspecific inflammatory response to one or several possible inciting agents that have not completely been elucidated.
Clinical Findings Diffuse lamellar keratitis presents 1-6 days following LASIK, LASIK enhancement, removal of interface epithelium, keratomileusis in situ or related lamellar procedures with discomfort, mild to moderate pain, foreign body sensation, tearing, or photophobia10. Conversely, some cases are asymptomatic.
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Figure 26-1.- Diffuse lamellar keratitis (DLK) in a 34 year-old woman 3 days after LASIK. An interface intiltrate limited to periphery is present (Stage 1).
The diffuse infiltrate in the lamellar interface in DLK has the following characteristics10: Contents 1.- It is diffuse and scattered through a large area of the interface (Figs. 26-1, 26-2A, and 26-2B). Section 1 The technique of iris retroillumination is particularly Section 2 helpful in visualizing these fine infiltrates. 2.- It is confined to the interface, extending Section 3 neither anteriorly into the flap nor posteriorly into Section 4 the stroma (Fig. 26-2B). 3.- Absence of a dominant focus, although Section 5 multiple faint foci may be present (Fig. 26-2A). 4.- There is little or no anterior chamber reac- Section 6 tion. Section 7 5.- There is no overlying epithelial defect. 6.- The conjuctiva is relatively non-inflamed, Subjects Index and there is little or no ciliary injection. It is important to pay attention to these distinct features of DLK infiltrates for a proper diagnosis.
DLK Staging Diffuse lamellar keratitis (DLK) can be classified into 4 grades to facilitate treatment guidelines and prognosis (Table 1): STAGE 1: Partial interface infiltrate, usually limited to periphery. The central area over the pupil is not involved (Fig 26-1). STAGE 2: Complete mild-to-moderate interface infiltrate (Fig 26-2).
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A
B Figures 26-2 A & B: A) DLK in a 36 year-old man 2 days after LASIK. Mild-to-moderate interface infiltrates affecting all the interface, including the central area over the pupil. B) The slit beam shows that the infiltrate is confined to the interface (Stage 2). (Courtesy of José Alfonso, MD, Instituto Oftalmológico Fernández-Vega, Oviedo, Spain).
Contents
Table 1 Stages of Diffuse Lamellar Keratitis Following LASIK Stage
Description
Stage 1
Partial interface infiltrate, usually limited to periphery. The central area over the pupil is not involved
Stage 2
Complete, mild-to-moderate interface infiltrate
Stage 3
Complete, dense interface infiltrate with aggregates or clumps of cells
Stage 4
Complete, very dense interface infiltrates with aggregates of cells and extracorneal involvement (i.e., anterior chamber reaction, ciliary injection, lid edema, poor vision)
STAGE 3: Complete dense interface infil- Section 1 trate with aggregates or clumps of cells. Section 2 STAGE 4: Complete very dense interface infiltrates with aggregates of cells and extra-corneal Section 3 involvement (i.e. anterior chamber reaction, ciliary Section 4 injection, lid edema, poor vision). Stage 1 and 2 are self-limiting, and gradually Section 5 resolve over the following weeks. Conversely, Stage 3 and 4 have the potential to melt the corneal stroma Section 6 resulting in a permanent loss of vision. Section 7 A Stage 1 DLK can progress to a Stage 2 on the second or third day, while a Stage 2 can progress Subjects Index to a Stage 3 needing a completely different treatment. For this reason, all patients should be monitored daily to detect any progression, particularly during the first 3-4 days.
Diagnosis Help ?
The diagnosis of diffuse lamellar keratitis after corneal lamellar surgery is made based on the history (previous lamellar surgery), symptoms, and a detailed slit-lamp examination. When an interface infiltrate is suspected of being diffuse lamellar keratitis, immediate therapy is mandatory to avoid progression of the infiltrate. We believe that a daily monitoring of the interface infiltrate is the key for a proper treatment and for a good result in DLK following corneal lamellar surgery. LASIK AND BEYOND LASIK
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Differential Diagnosis The differential diagnosis for interface infiltrates in the early postoperative period includes DLK, infectious keratitis, epithelial cells, and interface opacities. All these interface disorders, that can be confusing for the ophthalmologist, should be ruled out before a suspected clinical diagnosis of diffuse lamellar keratitis is made. In contrast to DLK, acute infectious kerati9,12,15-19 presents with decreased visual acuity, pain tis and inflammation (redness). Infectious keratitis is characterized by a single or dominant focus with extension anteriorly into the flap and posteriorly into the stroma. Infectious keratitis does not respect the boundaries of the flap interface. There is also conjunctival/ciliary injection, epithelial defects over the infiltrate, and inflammatory cells in the anterior chamber. DLK can be distinguished from infectious infiltrates by clinical presentation and close followup. Patients with this syndrome should be spared the more invasive treatment of infectious keratitis. Epithelial cells in the interface may be present in the early postoperative period, and they appear as a few scattered fine translucent cells in the interface without inflammation. The cells are more transparent, and there are fewer cells than would be present in diffuse lamellar keratitis. In addition, a small area is affected. Non-infectious interface opacities are common within the first postoperative weeks, and are related to tear film debris, or foreign particles from the microkeratome, blade or sponge. Interface debris can also be caused by the powder of the gloves, or blood from cut pannus7,20. Usually, it is not difficult to recognize these interface opacities after lamellar refractive surgery. The foreign bodies are usually well tolerated but may be a nidus for infection or inflammation. If inflammation is present, then flap repositioning and foreign body removal could be considered.
Treatment Once the diagnosis of DLK syndrome is made, and other causes of interface infiltrates are ruled out, a therapeutic plan is developed to most effectively manage the problem. The goals of therapy include
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to decrease the acute polymorphonuclear inflammatory reaction, to prevent degranulation of the polymorphonucleocytes enzymes, and, sometimes, removal of the proteolytic enzymes along with the inciting agent. Many of these goals are best achieved by prompt initiation of steroid therapy8,10. For patients with Stage 1 and 2 DLK, a therapy with prednisolone acetate 1% one drop every 1 to 2 hours is recommended. Most cases resolve with no sequelae over the course of the first postoperative month during which time the patient is weaned off corticosteroids. These patients should be followed closely because of the condition could worsen, and the high-dose topical steroid therapy could accelerate infectious keratitis. If the infiltrate worsens, or for patients with Stage 3 and 4 DLK, the flap is lifted, the infiltrates are cultured and removed, the flap is replaced to its original position, and the interface is irrigated copiously with balanced salt solution. Approximately 4-6 hours after washout, an intensive therapy with prednisolone acetate 1% one drop every 1 to 2 hours should be established. Washing the interface is to washout the deposited proteolytic enzymes from neutrophilic cells, thus limiting tissue destruction, and also the inciting agent. The intensive steroid therapy is for preventing enzymatic release from the infiltrating cells, and for decreasing the number of polymorphonuclear cells (Table 2).
Prevention Several possible inciting agents may contribute to diffuse lamellar keratitis following LASIK. Prevention of DLK following LASIK can be achieved by avoiding all involved agents, at least, until a definitive agent is identified. The eyelids should be draped to cover completely the meibomian glands orifices as well as the eyelashes. Powder-free surgical gloves are recommended. The ocular surface should be irrigated copiously prior to keratomileusis in order to remove all debris. The microkeratome head and blades should be cleaned before use using distilled water, and the motor tip should be checked for oil contamination. Immediately after surgery, all instruments should be cleaned and sterilized. Never leave instruments stand-
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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Table 2 Suggested schedule for the initial treatment of Diffuse Lamellar Keratitis (Sands of Sahara) after LASIK
Stage 1 and 2
Prednisolone acetate 1% one drop every 1 to 2 hours, and slowly taper off this medication based on clinical improvement.
Stage 3 and 4
Lift the flap (second or third day), remove and culture the infiltrates, replace the flap, and irrigate the interface with balanced salt solution. Approximately 4-6 h. after washout, prednisolone acetate 1% one drop every 1 to 2 hours, then reduction in therapy if clinical improvement. Consider addition of a topical antibiotic if infectious keratitis is suspected.
ing wet and unsterilized for an extended period of time. In this way, the count of dead bacteria is kept low and the production of clinically significant amounts of endotoxin is prevented. The interface should be irrigated under the flap with balanced salt solution, once the flap is replaced to its original position. In this way, all particles, debris, and inciting agents in the interface are removed, and, at the same time, the tear film debris are prevented to reach the interface. After surgery, topical corticosteroids should be used routinely four times per day for 5 to 7 days to prevent DLK, beginning 12-24 hours after the procedure.
Conclusions Diffuse lamellar keratitis is a distinct syndrome of noninfectious inflammation of the lamellar interface following LASIK and related lamellar surgery. The inflammation can be identified on careful slitlamp examination and can be differentiated from other causes of interface infiltrates. DLK responds to corticosteroids, however if the inflammation does not respond as expected, if the inflammation is severe, or if there is a suspicion of infection, the flap should be lifted, the infiltrates cultured and removed, and intensive corticosteroids and/or antibiotics should be considered.
INFECTIOUS KERATITIS FOLLOWING LASIK
Contents
Section 1
Introduction
Section 2
Infectious keratitis is one of the most serious Section 3 vision-threatening complications after corneal refractive surgery. Bacterial keratitis has been reported after Section 4 radial keratotomy21,22,23, photorefractive keratecSection 5 tomy 24,25, and myopic keratomileusis 11 . PérezSantonja and associates9 reported the first case of Section 6 infectious keratitis after LASIK. Since then, several reports of corneal infections after LASIK have ap- Section 7 peared in the literature. Subjects Index Infectious keratitis following LASIK surgery is rare. The rate of infection following LASIK is 8 around one in 5,000 (0.02%) LASIK procedures . In this review, we have analyzed our experience and cases reported in the literature of infection following LASIK. The findings may help to formulate an approach for the prevention and management of inHelp ? fectious keratitis after LASIK.
Clinical Findings A total of 16 infectious keratitis cases have been described in 13 patients, 11 patients were im-
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Table 3 Clinical Signs of Infection in 16 Cases Following LASIK 9,12,15-19,26-28 Sign Redness Stromal infiltrates Epithelial defect Hypopyon Edema of corneal flap Corneal flap melt Single corneal infiltrate Multiple corneal infiltrate
No.
(%)
13 16 8 3 4 3 5 9
(81) (100) (50) (19) (25) (19) (31) (56)
A
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munocompetent individuals and 2 were HIV positive9, 12,15-19,26,27,28. The infection was unilateral in 10 patients and bilateral in 312,27,28. The HIV positive individuals developed bilateral staphylococcal keratitis27,28 . Patients ranged from 18 to 55 years of age, with a mean of 38.7 ± 11 years; 6 patients were females and 7 were males. Eight of the 16 infections were in the right eye and 8 in the left. Twelve patients developed infection within 3 weeks of LASIK, and 9 within the first week. The mean time of early onset keratitis was 5.3 ± 6 days (range, 1 to 21 days). Only 1 case had a late onset infection that developed infection 28 days after LASIK. The symptoms of infectious keratitis after LASIK are similar in most patients, but may differ depending on the severity of the infection. The most common symptoms include decreased visual acuity, pain, photophobia, and redness. Other commonly encountered symptoms include discharge, foreign-body sensation, tearing, and eyelid edema9,12,15-19,26-28. The most common signs of infectious keratitis after LASIK include9,15-19,26 ciliary and conjunctival hyperemia, and whitish stromal infiltrates in the interface (Table 3). Other signs include anteriorchamber reaction, hypopyon, stromal/flap edema, and flap melting. Stromal infiltrates may be single or multiple and begin anywhere in the stromal interface as a dense, gray-white abscess. The edges of the stromal infiltrate are usually indistinct and often
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Section 1 Section 2
Section 3
B
Section 4
Section 5 Figures 26-3 A-B: A) Slit-lamp photograph shows two welldefined whitish nodules in the corneal interface surrounded by stromal infiltrate 6 days after LASIK retreatment (Nocardia asteroides). B) Central mild corneal opacity 6 months after successful treatment.
extend into the surrounding stroma. Cellular infiltration and edema may occur subjacent or adjacent to the abscess. The corneal flap and epithelium may be involved, causing an overlying cellular infiltration and epithelial defect (very common) that stains with fluorescein. Sometimes, the corneal flap shows evidence of melting and complete disintegration. (Figs 26-3 A & B and 26-4). During the initial clinical examination of the patient, a detailed drawing should be made of the corneal infiltrate. This drawing should include accurate measurements of the size and shape of the epithelial defect and stromal infiltration using the slitlamp ruler. In addition, it is important a careful as-
Section 6 Section 7 Subjects Index
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INFLAMMATORY AND INFECTIOUS COMPLICATIONS AFTER LASIK
were isolated from late-onset infection cases (three weeks after surgery). Gram-positive cocci included Staphylococcus aureus in 5 (38%) patients, Streptococcus viridans in 2 (15.4%), and Streptococcus pneumoniae in 1 (7.7%). Gram-positive filamentous bacillus was Nocardia asteroides in 1 (7.7%) patient. The acidfast bacilli infection was caused by Mycobacterium chelonei. Three cultures were sterile. (Table 4).
Table 4 Microorganisms Causing LASIK Infections Figure 26-4.- Slit-lamp photograph showing a round interface abscess surrounded by stromal infiltration and satellite lesions 3 days after primary LASIK. An overlying epithelial defect that stains with fuorescein is present. (The culture was negative).
sessment of the depth of the stromal infiltration, appearance of the infiltrate borders, and anterior chamber reaction. Slit-lamp photography can be extremely helpful as a baseline and for documenting changes in the appearance of the corneal infiltrate29. This would help in assessing improvement after initiation of antibiotic therapy.
No. of Patients (N=13) Bacterial Gram-positive cocci Staphylococcus aureus 5 Streptococcus viridans 2 Streptococcus pneumoniae 1
(%) Contents
Section 1
(38.4) (15.4) (7.7)
Section 2
Section 3
Section 4
Gram-positive bacilli Nocardia asteroides
1
(7.7)
Acid-fast bacilli Mycobacterium chelonei
1
(7.7)
Section 5
Section 6 Section 7
Causative Organisms In the cases reported, the diagnosis was confirmed by cultures which were obtained either by scraping the corneal ulcer or by scraping the stromal interface after lifting the flap. Microorganisms were isolated from 10 (77%) of the 13 cultures. Three cultures were negative, but a bacterial infection was presumed, based on the clinical presentation and the response to therapy15,28. All 10 patients with positive cultures had bacterial isolates and no fungi were found. Gram-positive cocci were isolated in 8 (61.5%) of the 13 cultures, gram-positive filamentous bacilli in 1 (7.7%) culture, and acid-fast bacilli in 1 (7.7%). Three cultures were negative. No gram-negative bacilli were isolated. All gram-positive bacterial cultures were isolated from infections occurring within the first 3 weeks of surgery. Only acid-fast bacilli
No growth
3
(23)
Laboratory Diagnosis
Subjects Index
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The patient history and clinical examination are insufficient for making a definitive diagnosis of infectious keratitis. In patients with suspected infectious keratitis, obtaining corneal scrapings of the infiltrates is mandatory to confirm the diagnosis, to isolate the organism, and to determine the sensitivity to antibiotics. Broad spectrum antibiotic therapy may be initiated after obtaining corneal scraping specimens for culture and staining. LASIK AND BEYOND LASIK
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The initial step should be obtaining culture material from the conjunctiva. The use of anesthesia in this procedure should be avoided because preservatives may decrease the yield of live isolates. Calcium alginate swabs or cotton swabs are used for this purpose. The swab should be moistened and the entire lower cul-de-sac should be wiped. The material obtained is placed directly onto culture plates. All conjunctival specimens should be plated directly onto blood agar, chocolate agar, MacConkey agar, Sabouraud’s agar, and thioglycolate broth. Growth from the conjunctival cultures is helpful only when the corneal cultures are all negative, especially when the one ipsilateral to the keratitis grows a pathogen not found in the other eye. Then, following topical anesthetic eyedrops such as proparacaine hydrochloride (0.5%), the patient is aligned under the surgical microscope and a lid speculum is inserted. The corneal flap is marked with a marker at the cut edge. The corneal flap is lifted using a spatula or forceps, and the interface is exposed. A sterilized spatula is used for scraping the corneal stromal bed of the interface. Multiple scrapings are required, and each of them may be inoculated onto the surface of different culture media. Direct corneal scraping, without lifting the flap is not recommended because the corneal flap can be sloughed off in the process26. After corneal cultures are taken, the interface is irrigated with antibiotics or 5% povidone iodine12,15,19. Then, the flap is replaced and aligned to its original position, and the flap circular edge is dried with a microsponge12,15. The exudate and material obtained from the interface is placed on a microscope slide for Gram and Giemsa staining, and also directly onto blood agar, chocolate agar, MacConkey agar, thioglycolate broth, and Sabouraud’s medium9,29. Gram and Giemsa staining results can be useful to guide the initial antibiotic therapy. The bacteria of most keratitis begin to grow on some media within 24 to 48 hours. Then, antibiotic sensitivity testing is begun even before the final species identification is made. This may allow rational adjustments in therapy when correlated with the clinical response29.
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Diagnosis The diagnosis of infectious keratitis after LASIK is made based on the symptoms, slit-lamp examination, and laboratory results. When a lesion is suspected of being infectious keratitis, lifting the corneal flap and scraping the stromal bed is mandatory to obtain abundant material for microbiologic processing and microbial identification to initiate proper treatment. We believe that immediate management by lifting the flap and scraping the stromal bed is the key for a good result in keratitis after LASIK9,15,17,19. Documenting the size, depth, and location of the corneal infiltrate, and the assessment of the anterior-chamber reaction at the initial examination, is important for providing a baseline for documentation of improvement following specific antibiotic therapy.
Differential Diagnosis
Contents
Section 1 Section 2
Section 3
Infectious keratitis is one of the most visionSection 4 threatening complications after LASIK. Early diagnosis and prompt management are essential. Certain Section 5 interface disorders have to be ruled out before a suspected clinical diagnosis of infectious keratitis is Section 6 made. Section 7 Non-infectious interface opacities are common within the first postoperative weeks, and are related Subjects Index to epithelial implantation, tear film or mucus debris, or foreign particles. Interface debris can also be caused by powder, metal fragments from the microkeratome blade lint, or blood from severed blood vessels in a pannus7,20. Usually, it is not difficult to recognize these interface opacities after lamellar reHelp ? fractive surgery. Diffuse lamellar keratitis (DLK) is a recently described syndrome that follows LASIK and related lamellar corneal surgery10. Patients with diffuse keratitis present 1 to 6 days after surgery reporting pain, photophobia, redness or tearing. The infiltrate in DLK is confined to the interface, extending neither anteriorly into the flap nor posteriorly into the
INFLAMMATORY AND INFECTIOUS COMPLICATIONS AFTER LASIK
stroma; it is diffuse and scattered through a large area; there are multiple faint foci; there is little or no anterior chamber reaction, no overlying epithelial defect, and little or no ciliary flush10. DLK can be distinguished from infectious infiltrates by clinical presentation and close follow-up. Patients with this syndrome may show spontaneous slow and progressive resolution over the next two to three weeks.
Treatment After the clinical and microbiologic work-up has been completed, a therapeutic plan is developed to most effectively manage the infected cornea. The goals of therapy include the eradication of viable bacteria and rapid suppression of the inflammatory response elicited by the microorganisms. These goals are best achieved by prompt initiation of specific antimicrobial therapy29. In cases of corneal infections, not only after LASIK, it is advocated to initiate broad spectrum antibiotics, with modifications of this therapy based on the clinical impression and culture results. Broadspectrum antibiotics should be used until organisms are identified on culture. Based on data that fortified antibiotic eyedrops are as effective as subconjunctival injections, the standard route of administration of antibiotics for the treatment of corneal infections is topical30. Subconjunctival administration of the drug is appropriate when compliance is in question, there is a delay or inability to administer topical medications, or in very severe cases of infectious keratitis29. Numerous reports have shown that systemic administration of antibiotics is ineffective in treating bacterial keratitis31,32. This route of administration is reserved for perforated corneal ulcers. Double therapy with fortified cefazolin (50 mg/ml) plus fortified tobramycin (15 mg/ml) or ciprofloxacin (3 mg/ml) plus fortified cefazolin (50 mg/ml), are first choice regimens to which the most common bacteria responsible for bacterial keratitis are sensitive30. An alternative therapy in patients allergic to cephalosporins is vancomycin (25-50 mg/ml) 30. Initial therapy regimens should be
modified after isolation of the organism and if there is evidence of deterioration. Change in therapy should also be made if the corneal infection continues to worsen and the laboratory reports a pathogen resistant to the initial combination of antibiotics. One large multi-center study33 concluded that fluoroquinolone monotherapy (ciprofloxacin) was equivalent to fortified cefazolin-tobramycin in treating bacterial keratitis. However, this monotherapy regimen is not recommended in view of the rapid emergence of resistant strains to the fluoroquinolones34. Cefazolin, a first generation cephalosporin, has an excellent coverage for streptococcus and penicillinase-producing organisms. Cefazolin is usually active against gram-positive cocci, including betalactamase producing Staphylococcus aureus and Contents S. Epidermidis, group A beta-hemolytic streptococci (S. Pyogenes), group B streptococci, and Streptococ- Section 1 cus pneumoniae. It has limited activity against gram-negative bacteria, and is not effective for the Section 2 treatment of methicillin-resistant staphylococci. Section 3 Tobramycin, an aminoglycoside antibiotic, is usually effective against most gram-negative organ- Section 4 isms (e.g., Pseudomonas, Proteus, Klebsiella, E. Coli, H. Influenzae, Serratia) and some gram-posi- Section 5 tive organisms (S. Aureus and S. Epidermidis, includ- Section 6 ing beta-lactamase-producing strains). Tobramycin is ineffective against Streptococcus. Ciprofloxacin, Section 7 the most active fluoroquinolone, is highly effective against a broad spectrum of gram-positive (Staphy- Subjects Index lococcus and methicillin-resistant Staphylococcus), gram-negative (Haemophylus, Pseudomonas, Proteus, E. Coli, Serratia, Klebsiella, Moraxella), mycobacteria (including Mycobacterium chelonei), and chlamydial organisms 29,30. The recommended therapy for the initial treatment of bacterial keratitis Help ? after LASIK includes irrigation of the interface with two fortified antibiotics after lifting the flap and obtaining specimens for microbiologic work-up. Topical fortified antibiotic should be given every hour alternating with another topical fortified antibiotic every hour (on the half hour) for 48 hours. If clinical improvement occurs after 48 hours, the antibiotic therapy can be reduced to two topical fortified anti-
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biotics every 2 hours, 5 minutes apart. After 72 hours topical fortified antibiotics frequency may be reduced to every 3-4 hours, and one fortified antibiotic can be discontinued. After 5 days, regular strength antibiotic drops may be used (if available), and this medication is slowly tapered off based on clinical improvement. This suggested schedule is similar to that recommended for regular bacterial keratitis29. (Table 5).
Table 5 Suggested Schedule for the Initial Treatment of Bacterial Keratitis after LASIK Time Intraoperatively
Initial treatment
48 hours
302
Treatment Irrigation of interface with two antibiotics after lifting the flap and scraping of the stroma Topical fortified antibiotic A every hour on the hour along with topical fortified antibiotic B every hour on the half hour Reduction in therapy if clinical improvement: Topical fortified antibiotic A every 2 hours along with Topical fortified antibiotic B every 2 hours, 5 minutes after antibiotic A
72 hours
Topical fortified antibiotic A every 3 hours. Topical fortified antibiotic B discontinued
120 hours (5 days)
Change to regular strength antibiotic drops and slowly taper off based on clinical improvement. Consider addition of a topical steroid if the organism has been identified and treated with an antibiotic to which the organism is sensitive and if the epithelium has healed
SECTION IV
The patient needs daily evaluation with repeat photography of the cornea and measurements of the size of the infiltrate and epithelial ulcer. The most important criteria in evaluating the response to treatment include the degree of eye pain, the size and depth of the infiltrate, the size of the epithelial defect over the infiltrate, and the anterior-chamber reaction. If the corneal infiltrate worsens, the antibiotic regimen is adjusted according to the culture and sensitivity results. If the original cultures are negative and the corneal infection does not seem to be responding to the current antibiotic regimen, new cultures should be taken and subjected to special culture media and stains. A corneal biopsy may have to be performed if the condition is worsening and the cultures are negative. The successful management of bacterial keratitis includes the use of adjunctive therapy to prevent or ameliorate possible complications. Cycloplegics drugs should be used in all cases to prevent the formation of posterior synechia and to relieve the ciliary spasm. Topical 1% cyclopentolate, or 1% atropine used twice daily is generally adequate. The use of corticosteroids in the management of bacterial keratitis is controversial. In cases with corneal infiltrates involving the visual axis, it is suggested that topical corticosteroids should be used after a 96-hour period of treatment with fortified topical antibiotics and after the organism is identified.
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Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Prognosis In 15 of 16 eyes with infectious keratitis after LASIK, the best-corrected visual acuity (BCVA) after complete medical or surgical treatment was 20/40 or better. Five eyes did not lose any line of BCVA, 1 eye lost 3 lines, 1 eye lost 4 lines, and 2 eyes lost 5 lines9,12,15-19,16. In 7 eyes BCVA loss is not available27,28. The most common late complication of infectious keratitis after LASIK was mild or moderate stromal scarring in the affected area (13 eyes or 81%), and irregular astigmatism. Three (18.7%) eyes required penetrating keratoplasty, which resulted in a BCVA of 20/25 or better after surgery, at least, in two eyes16,27,28.
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INFLAMMATORY AND INFECTIOUS COMPLICATIONS AFTER LASIK
In conclusion, infectious keratitis is a serious complication after LASIK. However, if treated promptly and appropriately, it is possible to achieve a good visual outcome.
Prevention of Infectious Keratitis Following LASIK Laser in-situ keratomileusis is an invasive surgical procedure which creates a flap in the cornea. Several factors may contribute to infectious keratitis following LASIK, and certain preoperative, intraoperative and postoperative measures can be taken for prevention (Table 6). Table 6 Preoperative, Intraoperative and Postoperative Measures for Prevention of Infection following LASIK Preoperative 1. Treatment of eyelid, conjunctival or adnexal infection prior to LASIK 2. Proper sterilization of the instruments 3. Proper intraoperative sterile techniques 4. Wearing of powderless sterile gloves 5. Disinfection of the skin of the eyelids and lid margin with Betadine 6. Applying a sterile drape over the lid margin Intraoperative 1. Irrigation with BSS without recycling of the fluid from the ocular surface to under the flap 2. Use of a fresh, sterile bottle of BSS 3. Use of a sterile cannula 4. Avoiding touching the eyelashes Postoperative 1. Proper instruction to patient not to rub the eye 2. Use of postoperative prophylactic antibiotics for 3 to 5 days
In the preoperative care, patient should be examined properly to rule out a nasolacrimal duct obstruction, a sub-clinical dacryocystitis or chronic conjunctivitis35. Patients with lid margin disease such as Staphylococcal blepharitis should be treated properly prior to LASIK. Culture from the lids is obtained and appropriate topical antibiotics are used to eradicate the infection from the lid margin. Patients with chronic meibomianitis may have to be given systemic antibiotics before LASIK. Ocular and periocular infections are considered contraindications to LASIK. In these cases, appropriate antibiotic therapy should be given prior to any surgical intervention. During the preoperative stage of LASIK, all instruments should be properly sterilized. In the preoperative preparation, the surgeon should be dressed with an operating room attire and sterile coat Contents and gloves should be worn. The preoperative preparations should include scrubbing of the eyelids and Section 1 lid margins with Betadine. The lid margins and the eyelashes should be Section 2 covered with a sterile drape. A lid speculum can be Section 3 placed in such a way so that the drape can be turned over the lid margin covering the lid margin. The blade Section 4 should be used once only. Irrigation of the flap should be brief without allowing pooling of the Balanced Section 5 Salt Solution (BSS) over the eye and back under the Section 6 flap. Irrigation should be one way from the cannula to under the flap and to the outside without allowing Section 7 the recycling of the BSS under the flap. BSS should not be stored, and a fresh bottle of BSS (BSS 15 ml, Subjects Index Alcon) should be used for each case. The corneal flap should be well approximated at the end of the procedure and allowed to dry in place. A broad-spectrum antibiotic may be instilled at the end of the procedure, such as ofloxacin 0.3% eyedrops or lomefloxacin 0.3% eyedrops. Help ? Following surgery, the patient may be placed on topical broad-spectrum antibiotics every 2 hours for the first 12 hours and then four times daily for a period of 3 to 5 days. Steroids are not indicated in the early postoperative period and may be started 12 to 24 hours after the procedure. Furthermore, bilateral simultaneous LASIK should be avoided in patients who are HIV positive or who are immunologically compromised27,28.
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LASIK is an elective procedure and should be performed under optimal conditions. Any patient with evidence of ocular surface or adnexal infection should be cancelled and rescheduled after the infection has been eradicated.
Conclusion LASIK is an elective procedure and should not be performed unless optimal ocular surface conditions are present. Ocular surface or adnexal infections are considered to be contraindications to LASIK. Prevention of infection is much better than managing the cure of infection that may follow the surgical procedure. Early recognition and prompt therapy of infections following LASIK may lead to full visual recovery and rehabilitation. Although laboratory testing has been the basis for identifying many types of infections, the clinician is often the first to recognize a very early infection following LASIK.
REFERENCES 1.- Pallikaris IG, Siganos DS. Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia. J Refract Corneal Surg. 1994; 10:498-510. 2.- Knorz MC, Liermann A, Seiberth V, Steiner H, Wiesinger B. Laser in situ keratomileusis to correct myopia of –6.00 to –29.00 diopters. J Refract Surg. 1996; 12:575-584. 3.- Fiander DC, Tayfour F. Excimer laser in situ keratomileusis in 124 myopic eyes. J Refract Surg. 1995; 11(suppl):S234-S238. 4.- Kremer FB, Dufek M. Excimer laser in situ keratomileusis. J Refract Surg. 1995; 11(suppl):S244S247. 5.- Güell JL, Muller A. Laser in situ keratomileusis (LASIK) for myopia from -7 to -18 diopters. J Refract Surg. 1996; 12:222-228. 6.- Pérez-Santonja JJ, Linna TU, Tervo KM, Sakla HF, Alió JL, Tervo TM. Corneal wound healing after laser in situ keratomileusis in rabbits. J Refract Surg. 1998; 14:602-609. 7.- Pérez-Santonja JJ, Bellot J, Claramonte P, Ismail MM, Alió JL. Laser in situ keratomileusis to correct high myopia. J Cataract Refract Surg. 1997; 23:372-385.
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8.- Gimbel HV, Anderson-Penno EE. Early postoperative complications: 24 to 48 hours. In: Gimbel HV, AndersonPenno EE, eds. LASIK complications, prevention and management. Thorofare, NJ: Slack Inc.; 1999; 81-91. 9.- Pérez-Santonja JJ, Sakla HF, Abad JL, Zorraquino A, Esteban J, Alió JL. Nocardial keratitis after laser in situ keratomileusis. J Refract Surg. 1997; 13:314-317. 10.- Smith RJ, Maloney RK. Diffuse lamellar keratitis. A new syndrome in lamellar refractive surgery. Ophthalmology. 1998; 105:1721-1726. 11.- Nascimento EG, Carvalho MJ, de Freitas D. Campos M. Nocardial keratitis following myopic keratomileusis. J Refract Surg. 1995; 11: 210-211. 12.- Watanabe H, Sato S, Maeda N, Inoue Y, Shimomura Y, Tano Y. Bilateral corneal infection as a complication of laser in situ keratomileusis. Arch Ophthalmol. 1997; 115: 1593-1594. 13.- Lin RT, Maloney RK. Flap complications associated with lamellar refractive surgery. Am J Ophthalmol. 1999; Contents 127:129-136. 14.- Kaufman SC, Maitchouk DY, Chiou AGY, Beuerman Section 1 RW. Interface inflammation after laser in situ keratomileusis. Sands of the Sahara syndrome. J Cataract Section 2 Refract Surg. 1998; 24:1589-1593. Section 3 15.- Aras C, Ozdamar A, Bahçecioglu H, Sener B. Corneal interface abscess after excimer laser in situ Section 4 keratomileusis. J Refract Surg. 1998; 14:156-157. 16.- Reviglio V, Rodriguez ML, Picotti GS, Paradello M, Section 5 Luna JD, Juárez CP. Mycobacterium chelonae keratitis following laser in situ keratomileusis. J Refract Surg. Section 6 1998; 14:357-360. Section 7 17.- Kim HM, Song JS, Han HS, Jung HR. Streptococcal keratitis after myopic laser in situ keratomileusis. Korean Subjects Index J Ophthalmol. 1998; 12:108-111. 18.- Al-Reefy M. Bacterial keratitis following laser in situ keratomileusis for hyperopia. J Refract Surg. 1999; 15(suppl):S216-S217. 19.- Webber SK, Lawless MA, Sutton GL, Rogers CM. Staphylococcal infection under a LASIK flap. Cornea. 1999; 18:361-365. 20.- Condon PI, Mulhern M, Fulcher T, Foley-Nolan A, Help ? O’Keefe M. Laser intrastromal keratomileusis for high myopia and myopic astigmatism. Br J Ophthalmol. 1997; 81:199-206. 21.- Gussler JR, Miller D, Jaffe M, Alfonso EC. Infection after radial keratotomy. Am J Ophthalmol. 1995; 119:798799. 22.- Grimmett MR, Holland EJ, Krachmer JH. Therapeutic keratoplasty after radial keratotomy. Am J Ophthalmol. 1994; 118:108-109.
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23.- Hoffer KJ, Darin JJ, Pettit TH, Hofbauer JD, Elander R, Levenson JE. Three year experience with radial keratotomy: the UCLA study. Ophthalmology. 1983; 90:627636. 24.- Amayem A, Tawfik Ali A, Waring III GO, Ibrahim O. Bacterial keratitits after photorefractive keratectomy. J Refract Surg. 1996; 12:642-644. 25.- Sampath R, Ridgway AEA, Leatherbarrow B. Bacterial keratitis following excimer laser photorefractive keratectomy: a case report. Eye. 1994; 8:481-482. 26.- Mulhern MG, Condon PI, O’Keefe M. Endophthalmitis after astigmatic myopic laser in situ keratomileusis. J Cataract Refract Surg. 1997; 23:948-950. 27.- Hovanesian JA, Faktorovich EG, Hoffbauer JD, Shah SS, Maloney RK. Bilateral bacterial keratitis after Laser in-situ keratomileusis in a patient with human immunodeficiency virus infection. Arch Ophthalmol. 1999;117:968-970. 28.- Quiros PA, Chuck RS, Smith RE, Irvine JA, McDonnell PJ, Chao LC, McDonell PJ. Infectious Ulcerative keratitis after laser in situ keratomileusis. Arch Ophthalmol. 1999; 117:1423-1427. 29.- Abbott RL, Zegans M, Kremer PA. Bacterial corneal ulcers. In: Tasman W, Jaeger EA, eds. Duane’s Clinical Ophthalmology. 1998 edition. Philadelphia, Pennsylvania: Lippincott Williams and Wilkins; 1998; Vol 4: chap 18. 30.- Baum JL. Antibiotic use in ophthalmology. In: Tasman W, Jaeger EA, eds. Duane’s Clinical Ophthalmology. 1998 edition. Philadelphia, Pennsylvania: Lippincott Williams and Wilkins; 1998; Vol 4: chap 26. 31.- Woo FL, Johnson AP, Insler MS, George WJ, LaCorte WS. Gentamicin, tobramycin, amikacin and netilmicin levels in tears following intravenous administration. Arch Ophthalmol. 1985; 103: 216-218. 32.- Davis SD, Sarff LD, Hyndiuk RA. Comparison of therapeutic routes in experimental pseudomonas keratitis. Am J Ophthalmol. 1979; 87:710-716. 33.- Hyndiuk RA, Eiferman RA, Caldwell DR, Rosenwasser GO, Santos CI, Katz HR, Badrinath SS, Reddy MK, Adenis JP, Klauss V. Comparison of ciprofloxacin ophthalmic solution 0.3% to fortified tobramycin-cefazolin in treating bacterial corneal ulcers. Ophthalmology. 1996; 103:1854-1862.
34.- Goldstein MH, Kowalski RP, Gordon YJ. Emerging fluoroquinolone resistance in bacterial keratitis. A 5-year review. Ophthalmology. 1999; 106:1313-1318. 35.- Tabbara KF. Prevention of ocular infections. In: Tabbara KF, Hyndiuk RA, eds. Infections of the Eye, 2nd ed. Boston: Little, Brown and Company, 1996:7-12.
Juan J. Pérez-Santonja, M.D. Refractive Surgery and Cornea Unit Alicate Institute of Ophthalmology Miguel Hernandez University School of Medicine Alicante, Spain
Contents
Section 1 Section 2 • Part of the text and some of the figures of this Chapter are presented with permission from Agarwal et al textbook on REFRACTIVE SURGERY published by Jaypee, India , 1999.
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
Chapter 27 PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS Elizabeth A. Davis, M.D., David R. Hardten, M.D., Richard L. Lindstrom, M.D.
LASIK surgery is a highly successful surgery. However, like all surgical procedures, complications can occur. Knowledge of their causes and careful attention to details can prevent the vast majority of complications. Furthermore when complications do occur, if appropriate management is employed, good outcomes are still achievable.
INTRAOPERATIVE COMPLICATIONS Flap Complications Thin Flap and Buttonholes Thin flaps and buttonholes may result from one of several causes. These include inadequate suction, a damaged blade, or an excessively steep cornea. Intraocular pressure must exceed 65 mm Hg for an optimal cut to be made by the microkeratome. Confirmation of adequate pressure can be confirmed by intraoperative Barraquer tonometry. Other signs supportive of adequate suction include ability to elevate the globe with the suction ring, pupil dilation, and the patient’s report that his/her vision has dimmed or blacked out. The keratome blade should be carefully inspected under the microscope for nicks or poor finishes. Steep corneas (curvature > 45 or 46 D) may buckle during the microkeratome pass, resulting in a buttonhole or thin flap. In these cases, a smaller ring size should be chosen. Thin flaps can also occur in cases of steep corneas. A thin flap is more difficult to reposition and is more likely to wrinkle. (1) If the flap is com-
plete enough to allow repositioning, then the case can proceed. When possible, a deeper of depth plate of 180 mm rather than 160 mm should be chosen for patients with keratometry readings > 46 D. If buttonholing or a break in Bowman’s layer occurs within the optical zone, then the flap must be repositioned as well as possible and the procedure postponed for 3 to 6 months.
Contents
Section 1 Section 2
Free Cap
Section 3
Free caps can occur in cases of equipment Section 4 malfunction or excessively flat corneas. When usSection 5 ing the Chiron Automated Corneal Shaper, improper setting of the stopper can lead to this complication. Section 6 The more frequent cause of this complication, however, is a very flat cornea. With corneas flatter than Section 7 41 D, less tissue protrudes through the suction ring, Subjects Index thereby presenting a smaller cap diameter to the microkeratome blade. Hence, a free cap may result. It is still possible to complete a successful LASIK procedure in certain cases of free caps. As long as the stromal bed beneath the cap is centered and of adequate size for the ablation, then surgery can proceed. During the ablation the cap can be stored Help ? in an antidesiccation chamber or on the conjunctiva with the epithelial side down. After the completion of the laser treatment, the bed is irrigated with sterile balanced salt solution. The cap is then repositioned into the same orientation as before the surgery. The use of orientation marks can be helpful in realigning the cap. Five to 10 minutes of drying time allows the cap to adhere without sutures. Some surgeons tape the lid shut overnight.
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Incomplete Flap If the microkeratome prematurely stops in its pass across the cornea, then an incomplete flap is created. Advancement of the microkeratome may be halted by its obstruction with various objects such as the lids, speculum, or drape. Debris or crystals from incompletely removed balanced salt solution can block the proper advancement of the microkeratome gears. Good exposure is crucial to LASIK surgery. In cases of blepharospasm, deep-set orbits, or small lids, one should consider a lid block, retrobulbar block (to proptose the globe), or a lateral canthotomy. It is necessary to keep the microkeratome clean and check that it runs without resistance in both the forward and reverse pass. With an incomplete pass occurs, the surgeon must decide whether the ablation can be completed. If the hinge is near the edge of the planned ablation, then laser treatment can proceed while the flap is protected with a moist Merocel sponge. If the hinge is close to or crosses the pupil, the flap should be repositioned and allowed to heal for 3-6 months before creating a new flap.
Anterior Segment Perforation Although rare, one of the most feared intraoperative complications is entry into the anterior chamber during creation of the flap (2). This can occur with the Chiron ACS if the depth plate is not inserted or if it is improperly seated. If the plate is left out, then the cut will be well over 1 mm thickness, resulting in a full-thickness cut (3). This can result in significant injury to the cornea, lens, or iris and require anterior segment reconstructive procedures (Figure 27-1). Fortunately, the newer microkeratomes with a fixed plate have reduced the possibility of entry into the anterior chamber.
Intraoperative Bleeding Intraoperative bleeding is usually more of a nuisance than a serious problem. Patients may have bleeding from a peripheral corneal pannus that has resulted from long-term contact lens wear. Microkeratomes, such as the Hansatome or Moria, that make larger diameter flaps may be more likely to cut across these vessels. A Merocel sponge or Chayet sponge should be used to swab or wick the blood away from the ablation zone. It may be necessary to intermittently pause during the ablation to clear the field of any blood. Prior to replacing the flap, the stromal bed should be irrigated of any remaining cells or debris.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Epithelial Defects
Figure 27-1. Suture repair of a full-thickness cut of the lamellar flap.
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Epithelial defects are one of the most common intraoperative complications of LASIK. Typically these occur in the periphery of the flap near the hinge (Figure 27-2). Occasionally they can occur as a central defect and impact the early visual outcome. Epithelial defects result from the frictional force as the microkeratome passes over the cornea under high pressure. An epithelial defect may lead to greater cap edema with poorer adherence in the area of the defect, increasing the risk of epithelial ingrowth. Oftentimes, they are associated with a localized area of interface inflammation. Typically this is responsive to frequent topical steroid medication.
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PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
Figure 27-2. Epithelial defect near flap hinge.
As with any corneal abrasion, an epithelial defect can heal with excess anterior basement membrane material and irregular astigmatism. Treatment depends on the size and location of the defect. For small defects, the loose epithelium may be simply removed or repositioned and copious lubrication administered postoperatively. For larger defects, placement of a bandage contact lens should also be done. In some cases, phototherapeutic keratectomy might be considered to remove excess anterior basement membrane material and allow good adhesion of the
epithelium to the underlying Bowman’s layer. If this is required, then careful monitoring for haze must be performed because the cornea is more likely to develop haze in patients having excimer laser treatment after lamellar surgery. Prevention of epithelial defects starts with adequate lubrication of the cornea before the microkeratome pass. Also, toxic anesthetics should be minimized. Screening for anterior basement membrane dystrophy also can reduce intraoperative surprises. In high myopes with mild anterior basement dystrophy that is visually significant, LASIK may still be preferred over PRK because of the reduced incidence of haze with LASIK. In patients with visually significant irregular astigmatism associated with anterior basement dystrophy, PRK may be preferred over LASIK. In some patients, superficial keratectomy or phototherapeutic keratectomy 3 to 4 months before LASIK may be helpful in preventing an erosion associated with anterior basement membrane dystrophy in higher myopes.
Ablation Complications
Contents
Section 1 Section 2
Section 3
Section 4
Central Islands Central islands are small central elevations in the corneal topography (Figure 27-3), which may
Section 5
Section 6 Section 7 Subjects Index
Figure 27-3. Corneal topography of central island showing small area of elevation. Help ?
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Figure 27-4. Corneal topography of treatment decentered nasally in the left eye.
Contents
Section 1
occur for a variety of reasons.(4, 5) Beam profile abnormalities, increased hydration of the central corneal stroma, or particulate material falling onto the cornea may block subsequent laser pulses. A flat ablation beam may direct stromal fluid into the central area of ablation, and the hydrated tissue is ablated at a slower rate. This is more common with broad-beam lasers and rare with scanning-beam lasers. (6) The presence of more hydrated central stromal tissue can result in less effective ablation in the central 1 to 3 mm of the cornea. Laser software can add extra pulses in the central cornea to compensate for this, yet careful monitoring of the hydration of the central cornea is important. If excessive hydration is noted, the procedure should be paused and excess fluid removed from the center of the cornea. Typically these islands resolve with time as epithelial remodeling fills in the surrounding area. These resolve more slowly after LASIK than after PRK. If resolution has not occurred by 3 months, then the flap can be lifted and the island retreated to reduce irregular astigmatism. Elevation topography should be used to measure the diameter and height of the island. Typically these islands are 2 to 3 mm in diameter and 7 to 15 mm in height.
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Decentration
Section 2
Decentration of the refractive excimer laser Section 3 ablation (Figure 27-4) can result in irregular astig- Section 4 matism causing glare, halos, diplopia, and a decrease in best corrected visual acuity (7). Controversy exists Section 5 as to whether refractive procedures should be cenSection 6 tered on the pupil or the corneal light reflex (8). The patient should be continuously coached throughout Section 7 the ablation to look at the fixation target. Minimizing sedation will also help the patient to remain alert Subjects Index and cooperative. If the patient is unable to maintain fixation despite these measures, then the suction ring or a Fine-Thornton fixation ring may be used to stabilize the globe. Some lasers now have pupil trackers available to adjust for small eye movements. Typically if the excimer ablation is Help ? decentered by more than 1 mm, adverse visual consequences can result. Greater impairment occurs with smaller total ablation areas than larger ones. The management of this complication requires a retreatment with ablation applied asymmetrically to the previously undertreated area, to enlarge and smooth the optical zone (9). This can be accomplished by masking the previously treated area or by purposely decentering the excimer beam. Acceptable result have been reported after PRK but are certainly quite challenging (10).
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
POSTOPERATIVE COMPLICATIONS
Flap Displacement
Interface Debris
Displaced flaps most commonly occur in the first 24 hours postoperatively (Figure 27-6). This may occur from trauma, poor flap adhesion, or as a result of the lids adhering to the flap due to a dry surface. The epithelium at the flap edge grows remarkably fast to cover the exposed stromal bed. The patient typically experiences discomfort and blurred vision. With such cases the flap should be lifted and repositioned (11). Care must be taken to clean the bed and back of the flap of debris and epithelial cells. Stroking the cap slightly with a moist Merocel sponge (Solan Ophthalmic Products, Jacksonville, FL) can minimize persistent folds and properly align the flap. A dry Merocel can then be used to stretch the cap into position. Realignment is confirmed by carefully observing the gutter to ensure it is symmetric and minimal. A drying period of 4-5 minutes should then be allowed. The eye should then be taped shut and a pressure patch applied. Careful follow-up is necessary to monitor for subsequent epithelial ingrowth.
Metal filings, sponge fibers, or meibomian secretions can become trapped in the interface of the flap and stromal bed (Figure 27-5). This may occur even with appropriate irrigation, use of a wick, or aspiration. In some instances, overly aggressive irrigation may carry debris from the conjunctival fornices onto the stromal bed. These particles rarely incite inflammation or affect vision. However, in cases of large amounts of debris, the flap can be relifted and the debris irrigated. Operating in a lintfree environment, the use of nonfragmenting sponges, draping of the lashes, and careful irrigation can limit this complication.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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Figure 27-6. Displacement of a nasally hinged flap. Figure 27-5. Debris in the flap interface.
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Figure 27-7. Diffuse lamellar keratitis extending over the pupil.
Figure 27-8. Infectious keratitis after LASIK.
Punctate Epithelial Keratopathy
Contents lowing LASIK. Patients are asymptomatic and often have no visual impairment, particularly in the Section 1 early stages. The eye remains white and quiet. A fine granular appearing infiltrate that looks like dust Section 2 or sand typically presents initially in the interface Section 3 periphery. The inflammation, if left untreated, can progress through several stages. The cells can spread Section 4 centrally to cover the pupil (Figure 27-7). Next, they Section 5 may clump and, with the release of inflammatory mediators, can result in a stromal melt. The cause of Section 6 DLK is likely multifactorial but its exact etiology is uncertain. Bacterial toxins or antigens, debris on the Section 7 instruments, eyelid secretions, or other unknown facSubjects Index tors may play a role. Treatment involves frequent topical steroids. In rare cases where inflammation continues to progress, the flap must be lifted and the interface irrigated.
Punctate epithelial keratopathy is not uncommon after LASIK. Mild cases are usually asymptomatic, but more severe cases can cause poor uncorrected and best corrected vision. Preexisting dry eye or blepharitis may be contributory. In fact, many patients choose to have refractive surgery because of contact lens intolerance resulting from dry eyes. The corneal nerves are severed at the time of LASIK and this may increase the susceptibility to keratopathy. Corneal sensation returns more quickly, however, after LASIK than PRK(12). Treatment involves frequent lubrication of the ocular surface with artificial tears. Nonpreserved tears may be required in more advanced cases. Management of any lid disease with lid hygiene, antibiotic ointment, or oral tetracyclines may also be of benefit. In refractory cases, punctal occlusion with silicone plugs, argon laser, or thermal cautery may be required. When ocular surface disease is recognized preoperatively, some of these measures may be started prior to surgery as a preventative measure.
Diffuse Lamellar Keratitis (Sands of Sahara) Diffuse lamellar keratitis (DLK), also known as Sands of Sahara, is an interface inflammatory process that occurs in the early postoperative period fol-
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Infectious Keratitis Help ?
Infectious keratitis is extremely rare after LASIK with a reported incidence of 1 in 5,000 (13) (Figure 27-8). The presence of an epithelial defect in the early postoperative period may increase the risk. Presumed microbial keratitis after LASIK should be cultured and treated with frequent broad spectrum topical drops. A fluoroquinolone, such as ofloxacin, or a combination of fortified antibiotics, such as vancomycin 33 mg/ml and tobramycin 15 mg/ml, should be used. Hourly drops around-the-
PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
clock are necessary. In certain cases, this may require hospitalization to ensure compliance. If the keratitis is resistant to treatment, the flap should be lifted, debrided, and irrigated with antibiotic solution. Oral and subconjunctival antibiotics are of no value. Careful intraoperative and postoperative sterility is important. Patients should be instructed to wash their hands before touching their lids. Swimming in lakes or Jacuzzis should be avoided in the first month.
Overcorrection and Undercorrection Overcorrection or undercorrection may result from an inaccurate refraction, improper surgical ablation, decentration, beam inhomogeneity, abnormal corneal hydration status, or an excessive or inadequate healing response. Consistent and uniform stromal hydration during the ablation is crucial. If desiccation of the corneal tissue occurs, it will be relatively more compact, and more tissue will be removed per pulse of the laser. This result will be an overcorrection. If the stroma is overly hydrated, then less tissue per pulse will be ablated, resulting in undercorrection. Each surgeon should attempt to standardize the time between anesthetic administration, lid speculum insertion, flap creation, and laser application to reduce the variability of the hydration status. Attempted versus achieved results should continuously be analyzed to modify personal nomograms and improve predictability. Such nomograms are dependent on laser type, individual surgical technique, humidity, temperature, and geographic location. Patient age may also be a factor (14). An enhancement may be performed once refractive stability is achieved. However, a visually significant undercorrection may be treated earlier, particularly if the patient had a low to moderate amount of myopia preoperatively.
Epithelial Ingrowth Epithelium can grow in the interface between the cap and the stromal bed. This appears as small cysts or pearls of epithelial cells at the flap edge (Figure 27-9). Most often, the epithelial cells remain confined to the periphery and do not progress. Rarely,
Figure 27-9. Small pearls of epithelial cells in interface of flap periphery.
Contents
Section 1 Section 2
Section 3
however, growth may progress toward the central Section 4 visual axis causing irregular astigmatism and loss of best corrected acuity. In some cases, the epithelial Section 5 cells in the interface will block nutritional support Section 6 for the overlying stroma and lead to a flap melt. Epithelial ingrowth occurs in 2 to 3% of myo- Section 7 pic LASIK surgeries, most commonly after enhancements (15). In relifting the flap, epithelial cells may Subjects Index gain access to the interface because of irregularities that may result from dissection of the flap edge. Because of this, epithelial tags at the edge of the flap bed should be pushed back with a sponge prior to repositioning the flap. The risk of epithelial ingrowth is even higher after hyperopic LASIK, possibly beHelp ? cause the ablation strikes the epithelium at edge of the flap cut and stimulates cellular proliferation. Prevention of this complication is not always possible. Even with careful irrigation of the interface, epithelial ingrowth may still occur. An epithelial defect at the time of surgery can lead to stromal edema with poor adherence of cap to the underlying stromal bed. This allows an avenue for epithelial cells to transit under the flap. Epithelial ingrowth should be treated when it extends more than 2 mm from the flap edge, when
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Figure 27-11. Nonsignificant peripheral haze where Bowman’s membrane was cut in creating the flap.
there is documented progression in size, or when it threatens the visual axis. Other indications for removal include an altered residual refractive error, induced astigmatism, reduced uncorrected or best corrected visual acuity, or a stromal melt. Treatment involves relifting the flap. The location of the ingrowth should be noted preoperatively. The edge of the flap should be marked with a sterile fine 27 or 30 gauge needle at the slit lamp. Under the microscope, the flap should then be lifted. Using a PRK spatula or a surgical spear, both the stromal bed and the undersurface of the flap should be debrided. Typically the cells come off in a single sheet. Spears should be discarded with each pass to avoid re-implantation of cells. The peripheral stromal bed should then be cleared of epithelial tags and the flap replaced. Irrigation beneath the flap should then be performed and the flap allowed to dry adequately. A bandage contact lens may be placed if the epithelium is disrupted. In aggressive or recurrent cases of epithelial ingrowth, some surgeons advocate using 70 or 100% alcohol.
with retroillumination. Most cases of microstriae are visually insignificant, especially when the folds lie Section 3 outside of the visual axis (Figure 27-10). Epithelial hyperplasia occurs over these irregularities, smooth- Section 4 ing out the refractive surface. Nevertheless, when Section 5 microstriae occur over the pupil or when macrostria exist, irregular astigmatism with visual aberrations Section 6 and monocular diplopia may result. In such cases, Section 7 the flap should be relifted, hydrated, and stretched back into position as described above in ‘Flap Dis- Subjects Index placement.’
Flap Striae Microstriae are not uncommonly seen after LASIK, particularly if the flap is carefully examined
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Figure 27-10. Peripheral microstriae that were not visually significant.
SECTION IV
Section 1 Section 2
Haze Haze under the flap is extremely uncommon after LASIK. There is consistently a circular haze in the region where the microkeratome cut Bowman’s layer (16) (Figure 27-11). Haze can occur if the detergent used to sterilize the instruments and equipment is not completely removed. Frequent topical steroids reduce the inflammatory response and minimize the long-lasting effects of this complication.
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PREVENTION AND MANAGEMENT OF LASIK COMPLICATIONS
REFERENCES
Ectasia The general consensus among refractive surgeons is that 200 to 250 mm should remain in the stromal bed at the completion of the ablation in order to avoid problems with ectasia. The Munnerlyn formula calculates the ablation depth based on the magnitude of the refractive error and size of the optical zone. In patients with higher refractive errors, the surgeon may reduce the size of the optical zone in order to limit the amount of tissue removed. However, this increases the likelihood of visual side effects such as glare and halos. In such cases, other refractive surgical options, such as phakic intraocular lenses or natural lens extraction, should be considered.
1.
Burato L, Ferrari M, Genisi C. Myopic keratomileusis with the excimer laser: One year follow-up. Refract Corneal Surg 9: 1219, 1993.
2.
Brint SF, Ostrick M, Fisher C, et al. 6 month results of the multi-center phase I study of excimer laser myopia keratomileusis. J Cataract Refract Surg 20: 610-615, 1994.
3.
Pallikaris IG, Siganos DS. Excimer laser in situ keratomileusis and photorefractive keratectomy for correction of high myopia. J Refract Corneal Surg 10: 498-510, 1994.
4.
Trokel SL, Srinivasan R, Branen R. Excimer laser surgery of the cornea. Am J Ophthalmol 96: 710-715, 1983.
Visual Aberrations
Contents
Section 1
Visual aberrations can occur because of irregular astigmatism after LASIK. Small optical zones or a large pupil can result in halos from refraction of light off the transition zone. Monocular diplopia can result from a wrinkled flap, decentered ablation, or a central island. Visual aberrations are more common in higher corrections, although these patients are more likely to experience visual aberrations with other forms of correction, such as spectacles and contact lenses. Large pupils can lead to reduced contrast at night as well as glare and halos.
5.
6.
Slade SG. Abnormal induced topography. Central islands. In: Machat JJ, ed. Excimer Laser Refractive Surgery. Practice and Principles. Thorofare, NJ: Slack, Inc; 1996: 399.
7.
Burato L, Ferrari M, Rama P. Excimer laser intrastromal keratomileusis. Am J Ophthalmol 113: 291-295, 1992.
8.
Seiler T, Kahle G, Kriegerowski M. Excimer laser (193 nm) myopic keratomileusis in sighted and blind human eyes. Refract Corneal Surg 6: 165-173, 1990.
Conclusion Complications are much less likely to lead to visual loss if handled promptly and properly. Proper knowledge and careful use and maintenance of the microkeratome can reduce the incidence of complications. Overall, LASIK is a relatively safe operation in experienced hands.
Burato L, Ferrari M. Photorefractive keratectomy or keratomileusis with excimer laser in surgical correction of severe myopia: Which technique is better? Eur J Implant Refr Surg 5: 183-186, 1993.
9.
Pallikaris IG, Patzanaki ME, Stathi Ez, et al. Laser in-situ keratomileusis. Lasers Surg Med 10: 463-468, 1990.
10.
Burato L. Excimer laser intrastromal keratomileusis: Case reports. J Cataract Refract Surg 18: 37-41, 1992.
LASIK AND BEYOND LASIK
Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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11.
Martines E, John ME. The Martines enhancement technique for correcting residual myopia following laser assisted in situ keratomileusis. Ophthalmic Surgery & Lasers 27: S512-516, 1996 (suppl 5).
12.
Lin DT, Sutton HF, Berman M. Corneal topography following excimer photorefractive keratectomy for myopia. J Cataract Refract Surg 19: 149–154, 1993 (suppl).
13.
Slade SG. LASIK complications and their management. In: Machat JJ, ed. Excimer Laser Refractive Surgery. Practice and Principles. Thorofare, NJ: SLACK Inc.; 1996: 359.
14.
Spivack LD. Results of LASIK using a New Nomogram. (Abstract #10). In American Society of Cataract and Refractive Surgery, Symposium on Cataract, IOL, and Refractive Surgery, 1998, p. 37.
Contents
Section 1 Section 2
15.
16.
Maloney RK. Epithelial ingrowth after lamellar refractive surgery. Ophthalmic Surg Lasers. 116; 27 (5 pl): S535. Campos M, Wang XW, Herzog J, et al. Ablation rates and surface ultrastructure of 193 nm excimer laser keratotomies. Invest Ophthalmol Vis Sci 34: 2493, 1993.
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Elizabeth A. Davis, M.D., Minnesota Eye Consultants, P.A. 710 East 24th St. Suite 105 Minneapolis, MN 55404 Fax: 612-813-3601 Help ?
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VITREORETINAL COMPLICATIONS OF REFRACTIVE SURGERY
Chapter 28 VITREORETINAL COMPLICATIONS OF REFRACTIVE SURGERY Steve Charles, M.D.
PREOPERATIVE EXAMINATION It is unknown what examination methods are sufficient when a refractive surgery candidate is referred to a retinal consultant before refractive surgery. Options include: indirect ophthalmoscopy with or without 360-degree scleral depression and/ or 3-mirror contact lens examination. In view of the common notion of “clearing” patients for refractive surgery, it is essential that the retinal consultant perform a very careful examination while explaining to the patient that “clearing” or a “guarantee” against retinal detachment is not possible.
INDICATIONS FOR PROPHYLAXIS OF RETINAL BREAKS AND DEGENERATIONS The efficacy of laser or cryopexy prophylaxis in preventing detachment by treating retinal breaks prior to refractive procedures is assumed, but has not been proven. The majority of retinal breaks in retinal detachment failure cases are located immediately posterior to areas of cryopexy leading to the conclusion that only definite holes/tears/breaks, not “peripheral changes” should be treated. Pattern, scatter, barrage, PRP, and “new ora” concepts are unwarranted by today’s standards. Which retinal breaks should be treated is not known. Some retinal consultants stress that only symptomatic breaks should be treated 1-3. The author has seen several asymptomatic patients with significant retinal detachments discovered during preLASIK screening. It is probable that all surgeons would recommend treatment of these retinal
detachments even though the patients had no symptoms. Patients vary widely in their reporting of symptoms caused by PVD, retinal breaks and detachment. It is clear that symptoms are highly dependent on attitudes, level of activity, denial, coContents morbidity, and other societal and psychological factors. Relaying solely on symptoms is insufficient Section 1 to address the real issue of safety. Most surgeons recommend treating all breaks Section 2 outside lattice but not those within the lattice. It is Section 3 unknown whether upcoming clear lens extraction, phakic IOL implantation, PRK, or LASIK should Section 4 change these treatment indications. Similarly, no Section 5 recognized expert recommends treatment of lattice without retinal breaks. It is again unknown if Section 6 refractive surgery means that this concept should change although most experts have recommended no Section 7 change in treatment indications when refractive Subjects Index surgery is planned. There is no evidence that degenerations other than lattice should be treated with laser. White without pressure is a generic term that is used to describe peripheral microcystoid (a degenerative retinoschsis precursor), the normal vitreous which is often visible in highly pigmented patients and a variety of other Help ? “changes”, none of which need retinopexy. The term “atrophic” break is often used but unfortunately is ill-defined. To some ophthalmologists, “atrophic” implies that prophylactic retinopexy is not indicated, but this has not been proven. Although superior retinal breaks are probably more likely to result in clinical retinal detachment, location is seldom cited as a criterion for retinopexy. All surgeons treat horseshoe tears, any break/hole/ tear with apparent traction, and symptomatic tears.
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Most surgeons are more likely to treat borderline pathology in patients with a family history of retinal detachment or a history of detachment in the other eye. Personal history of retinal detachment in the same or eye is a relative contraindication for refractive surgery. If a decision is made to perform refractive surgery on such patients, careful peripheral retinal examination and prophylactic treatment of breaks/holes/tears is mandatory. There is significant controversy about whether extensive peripheral retinopexy (PRP, scatter, barrage) is effective in preventing retinal detachment in giant break “other eyes”, proliferative vitreoretinopathy (PVR), and clear-lens extraction patients.
THEORETICAL MECHANISMS RESULTING IN RETINAL BREAKS AND DETACHMENT Anterior Chamber Shallowing Anterior movement of lens and anterior vitreous causes “traction” forces on peripheral retina and traction induced retinal breaks. Microperforation is a significant cause of anterior chamber shallowing during radial keratotomy, astigmatic keratotomy, and occasionally the microkeratome step in LASIK or the
placement of intrastromal rings (Figure 28-1). Improved pachymetry, depth adjustments on diamond knives, microkeratomes and other precautions have reduced, but not eliminated, microperforation. Clear-lens extraction causes intraoperative anterior chamber shallowing with secondary anterior movement of the lens and vitreous in all cases (Figure 28-2). Many point out that a low or negative power IOL may prevent anterior displacement of the vitreous, but this is true only in the postoperative period. Retinal detachment is more frequent after clear-lens extraction than in standard cataract surgery because the patient population is myopic. Some experts feel that clear lens extraction is never indicated. Clear-lens extraction is probably contraindicated in eyes with high retinal detachment risk factors. Phakic IOL’s for high myopia are assumed by many surgeons to have no risk of retinal detachment but again this is untrue because of the obligatory intraoperative shallowing of the anterior chamber. The author was referred a case of bilateral inoperable retinal detachment from Russia occurring soon after phakic IOL implantation in a young male. Both eyes had inoperable retinal detachments and went on to become phthisical. There are very few articles on this subject, but it is likely that the incidence of detachment is less than in clear-lens extraction cases.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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Figure 28-1. Microperforation of the cornea can lead to anterior chamber shallowing. This allows anterior movement of the vitreous, with resulting retinal breaks at areas of high vitreoretinal adherence.
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Figure 28-2. Lens displacement during clear-lens extraction causes movement of the vitreous and subsequent traction on peripheral retina.
VITREORETINAL COMPLICATIONS OF REFRACTIVE SURGERY
Vitreoretinal Complications of PRK & LASIK Laser-tissue interaction creates acoustic pressure waves, which propagate through the vitreous and theoretically could cause retinal breaks. The concave surface of the ocular interior will focus the acoustic energy, significantly increasing local acoustic power density. Photorefractive keratectomy (PRK) and laser-in-situ-keratomileusis (LASIK) produce high-energy acoustic waves, which have the potential of producing significant forces on the vitreous and retina. The author has seen a patient that developed a macular hole instantaneously during a YAG (yttrium-aluminum-garnet) laser capsulotomy. A careful and experienced surgeon used normal power settings and a low number of pulses and the patient had a excellent vision and glare complaints preoperatively. It is probable that an acoustic pressure wave jerked on the posterior vitreous cortex attached to the macula. There are few articles on vitreoretinal complications of LASIK and PRK. Many anecdotal case reports have been obtained from refractive surgeons and retinal consultants. The incidence of vitreoretinal complication appears to be quite low in the few series published. A low incidence could theoretically be explained by observer bias, short follow-up intervals, lack of a control group, and poor study design but it is probable that the incidence of vitreoretinal complications is low.
Retinal Detachment After PRK Ruiz-Moreno JM, Artola A, and Alio JL reported on retinal detachment in myopic eyes after photorefractive keratectomy. They analyzed the incidence and characteristics of retinal detachment (RD) in myopic patients who had photorefractive keratectomy (PRK). The incidence of RD in 5936 consecutive eyes that had PRK to correct myopia was studied. Mean follow-up was 38.5 months +/17.4 (SD). They found that retinal detachment occurred in 5 eyes (0.08%); 2 in women and 3 in men. The mean interval between PRK and RD was 21.00 +/- 15.89 months (range 9 to 48 months). The
mean best-corrected visual acuity (BCVA) after PRK and before RD development was 20/81 (range 20/ 200 to 20/25). After RD repair, the mean BCVA was 20/460 (range 20/2000 to 20/29). In 4 of the 5 eyes, BCVA after RD was within 1 line of the preoperative value; in 1 eye, it decreased from 20/40 to 20/2000. The mean spherical equivalent (SE) before RD treatment was -1.35 +/- 1.08 diopters (D) (range 0 to -3.00 D) and after RD treatment, -2.95 +/- 0.83 D (range -2.00 to -4.00 D). Differences between SE before and after RD treatment were statistically significant (P =. 01, paired Student t test). They concluded that the incidence of RD after PRK to correct myopia was 0.08%. In 4 of 5 eyes, there was little or no visual loss; but in the group as a whole, there was a significant increase in myopic SE.
Retinal Detachment After LASIK
Contents
Section 1
Ruiz-Moreno JM, Perez-Santonja JJ, and Alio JL reported in a study of retrospective study of Section 2 retinal detachments observed in 1,554 consecutive Section 3 eyes (878 patients) undergoing laser-in-situ keratomileusis for the correction of myopia (follow- Section 4 up, 30.34+/-10.27 months; range, 16 to 54). Mean Section 5 patient age was 33.09+/-8.6 years (range, 20 to 60). Before treatment with laser-in-situ keratomileusis, all Section 6 patients had a comprehensive examination, and detected lesions predisposing to retinal detachment Section 7 were treated before performing the laser-in-situ Subjects Index keratomileusis procedure. They found that retinal detachment occurred in four (0.25%) of 1,554 eyes of four (0.45%) of 878 patients. All four patients who developed retinal detachment in one eye were women. Degree of preoperative myopia was -13.52+/-3.38 diopters (range, -8.00 to -27.50). The time interval between refractive surgery and retinal detachment Help ? was 11.25+/-8.53 months (range, 2 to 19 months). In all cases retinal detachment was spontaneous. In all eyes the retina was reattached successfully at the first retinal detachment surgery. Mean best-corrected visual acuity after laser-assisted in situ keratomileusis and before retinal detachment development was 20/43 (range, 20/50 to 20/30). After retinal detachment repair, best-corrected visual acuity was 20/45 (range, 20/50 to 20/32). Differences between
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best-corrected visual acuity before and after reattachment were not statistically significant (P = .21, paired Student t test). A myopic shift was induced in three eyes that had retinal detachment repaired by scleral buckling, from -0.58+/-0.72 diopter (range, +0.25 to -1.00) before retinal detachment and -2.25+/-1.14 diopters (range, -1.00 to -3.25) after retinal detachment surgery (P = .03, paired Student t test). They concluded that laser-insitu keratomileusis for correction of myopia is followed by a low incidence of retinal detachment. Conventional scleral buckling surgery was successful in most cases and did not cause significant changes in the final best-corrected visual acuity. A significant increase in the myopic spherical equivalent was observed after scleral buckling in these patients. Several reports have appeared concerning retinal detachment after LASIK 4-12. Arevalo et al state in a discussion of an article Ruiz-Moreno and associates 11 that ”The authors are to be commended for reporting the results of a retrospective study to analyze the incidence and characteristics of retinal detachment in myopic patients treated by laserassisted in situ keratomileusis. Dr Ruiz-Moreno and associates conclude: ‘’Our study reported a large number of eyes consecutively corrected by laserassisted in situ keratomileusis for the correction of myopia (1,554 eyes of 878 patients), with a follow up of 30.34 ± 10.27 months and with a 0.25% incidence of retinal detachment.’’ We agree that retinal detachment after laser in situ keratomileusis is infrequent and recently studied the incidence and characteristics of rhegmatogenous retinal detachment after laser-in-situ keratomileusis (Arevalo JF, unpublished data, 1999). We found 20 eyes (17 patients) with rhegmatogenous retinal detachment after laser-in-situ keratomileusis, for an incidence of 0.06% (20/31,739 eyes). Patients were followed for a mean of 36 months (range, 3 to 48 months), and rhegmatogenous retinal detachment occurred between 1 and 36 months (mean, 13.9 months) after laser-insitu keratomileusis. Eyes that developed a detachment had from -1.50 to -16.00 diopters of myopia (mean, 7.35 diopters) before laser in situ keratomileusis. Retinal detachment characteristics in our study showed that most rhegmatogenous retinal detachments and retinal breaks occurred in the temporal quadrants (71.4%). This is a very interesting 320
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finding; because the surgical microkeratome used to create the corneal flap in laser in situ keratomileusis has a temporal handle that may be responsible for extra pressure on that side of the eye. Rhegmatogenous retinal detachment (RRD) following laser-in-situ keratomileusis (LASIK) is uncommon(8) according to a recent report. Arevalo studied 24,890 myopic eyes that underwent the surgical procedure. The clinical files of five refractive surgeons from four institutions were reviewed for instances of RRD. All eyes in the study underwent LASIK for correction of myopia ranging from –0.75 to –29.00 diopters (D) (mean, -6.19 D). RRD occurred in 13 eyes from 12 patients between one and 36 months (mean, 12.6 months) after LASIK. The incidence of RRD was .05 percent at a mean of 24 months after surgery. Vitrectomy, cryopexy, scleral Contents buckling, argon laser retinopexy or pneumatic retinopexy techniques were used to manage RRD. Section 1 Myopia before surgery ranged from –1.50 to –16.00 D (mean, -6.96 D) in eyes that later developed RRD. Section 2 Although the study did not reveal a cause-effect Section 3 relationship between the corrective procedure and retinal detachment, the researchers recommended that Section 4 “patients scheduled for refractive surgery undergo a thorough dilated indirect fundus examination with Section 5 scleral depression and treatment of any retinal lesions Section 6 predisposing them to the development of retinal detachment before LASIK surgery is performed.” Section 7 The incidence of retinal detachment after PRK appears to be very low although there is little data 13. Subjects Index
Macular Hemorrhage Secondary to Choroidal Neovascularization After LASIK and PRK Macular hemorrhage secondary to choroidal neovascular membranes occurs in many myopic patients that have not undergone refractive surgery. It has been reported 14 that age-related macular degeneration (AMD) patients have an increased incidence of submacular hemorrhage immediately after cataract surgery. It is thought that preexisting neovascular membranes are caused to bleed by the obligatory lowering of IOP that occurs during cataract removal and IOL placement. This mechanism is similar to the pathogenesis of suprachoroidal
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VITREORETINAL COMPLICATIONS OF REFRACTIVE SURGERY
hemorrhage during or within days after cataract or filtering surgery. It is probable that the same mechanism could occur in any refractive procedure that transiently lowers the IOP. It is possible that any membrane that bled would have done so without surgery but this has not been proven. Many choroidal neovascular membranes have a self-limited course in myopic patients and never hemorrhage. It should be assumed that some patients will develop a submacular hemorrhage as a result of refractive surgery that otherwise would have stabilized without bleeding. These patients would have a worse visual outcome than a patient without bleeding. It is probable that the incidence of this complication is very low 15. A careful history and Amsler’s grid assessment should be performed preoperatively to determine if the patient has subjective evidence of choroidal neovascular membrane. Any suspicious changes indicate the need for fluoroscein angiography. Any active, untreatable membranes should probably be treated with PDT if subfoveal, PDT or laser if subfoveal is juxta-foveal or observed until inactive before any refractive procedure is performed. Ruiz-Moreno and colleagues 15 reported on Choroidal neovascularization in myopic eyes after photorefractive keratectomy. They evaluated the incidence, characteristics, and results of treatment of choroidal neovascularization (CNV) in 5936 consecutive eyes that had PRK for the correction of myopia myopic eyes corrected by photorefractive keratectomy (PRK). Mean follow-up was 38.5 months +/- 17.4 (SD). This study had one patient that developed CNV. Extrafoveal CNV developed in the right eye of a 44-year-old woman 26 months after PRK for the correction of -12.00 diopters (D) of myopia. The follow-up after PRK was 38 months. Best corrected visual acuity (BCVA) before PRK was 20/40 (spherical equivalent [SE] -12.00 D). After PRK, BCVA was 20/32 SE -1.75 D). The CNV was treated by direct argon-green laser photocoagulation and did not recur in the subsequent 12 months). After CNV treatment, BCVA was 20/32 (SE -2.25 D). The incidence of CNV after PRK for myopia was low. Choroidal neovascularization is a possible complication in myopic eyes, and the risk exists
before PRK. After PRK, the risk of CNV in myopic patients did not increase .
Nerve Fiber Layer Damage Nerve fiber layer damage can be caused by increased IOP during suction cup usage before LASIK. A recent paper demonstrates reduction of this effect by the use of Brimonidine in a randomized, controlled clinical trial.
Endophthalmitis Endophthalmitis can occur anytime an incision is made into the eye. There are few reports of endophthalmitis after refractive surgery, but the results can be devastating in at least 50 percent of the patients. Few patients are informed about this potential complication before surgery is performed. One case has been reported after phakic IOL implantation 16.
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Dislocated Intraocular Lenses
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Posterior dislocation of a plate haptic IOL into the vitreous cavity immediately after LASIK has been observed. Acoustic effects or suction cup application most likely cause this complication.
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Retinal Detachment After Phakic IOL Implantation
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Moreno et al 17 studied retinal detachments in 166 consecutive eyes (98 patients) that underwent implantation of angle-supported phakic anterior chamber intraocular lenses (models ZB5M and ZB5MF; Domilens; Lyon, France) for the correction of severe myopia (follow-up ± SD, 45.26 ± 14.65 months; range, 20 to 84 months). Their results were as follows: Retinal detachment occurred in eight eyes (4.8%); four eyes belonged to men and four to women. The time between implanting surgery and retinal detachment was 17.43 ± 16.4 months (range, 1 to 44 months).
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REFERENCES 1. Byer N. Natural history of posterior vitreous detachment with early management as the premier line of defense against retinal detachment. Ophthalmology. 1994;101:1503-1513 2. Byer N. What happens to untreated asymptomatic retinal breaks, and are they affected by posterior vitreous detachment? Ophthalmology. 1998;105:1045-1049 3. Davis M. Natural history of retinal breaks without detachment. Arch Ophthalmol. 1974;2:183-194 4. Alio JL R-MJ, Artola A. Retinal detachment as a potential hazard in surgical correction of severe myopia with phakic anterior chamber lenses. Am J Ophthalmol. 1993;15:145-148 5. Aras C OA, Karacorlu M, Sener B, Bahcecioglu H. Retinal detachment following laser in situ keratomileusis. Ophthalmic Surg Lasers. 2000;31:121-125
12. Stulting RD CJ, Thompson KP, Waring GO 3rd, Wiley WM, Walker JG. Complications of laser in situ keratomileusis for the correction of myopia. Ophthalmology. 1999;106:13-20 13. Ruiz-Moreno JM AA, Alio JL. Retinal detachment in myopic eyes after photorefractive keratectomy. J Cataract Refract Surg. 2000;26:340-344 14. Blair CJ, Ferguson J, Jr. Exacerbation of senile macular degeneration following cataract extraction. Am J Ophthalmol. 1979;87:77-83 15. Ruiz-Moreno JM AA, Ayala MJ, Claramonte P, Alio JL. Choroidal neovascularization in myopic eyes after photorefractive keratectomy. J Cataract Refract Surg. 2000;26:1492-1495 16. Perez-Santonja JJ, Ruiz-Moreno JM, de la Hoz F, Giner-Gorriti C, Alio JL. Endophthalmitis after phakic intraocular lens implantation to correct high myopia. J Cataract Refract Surg. 1999;25:1295-1298
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6. Arevalo JF A-AO. Retinal detachment in myopic eyes after laser in situ keratomileusis. Am J Ophthalmol. 2000;129:825-826 7. Arevalo JF RE, Suarez E, Antzoulatos G, Torres F, Cortez R, Morales-Stopello J, Ramirez G. Rhegmatogenous retinal detachment after laser-assisted in situ keratomileusis (LASIK) for the correction of myopia. Retina. 2000;20:338-341 8. Farah ME, Hofling-Lima AL, Nascimento E. Early rhegmatogenous retinal detachment following laser in situ keratomileusis for high myopia [In Process Citation]. J Refract Surg. 2000;16:739-743 9. Han HS SJ, Kim HM. Long-term results of laser in situ keratomileusis for high myopia. Korean J Ophthalmol. 2000;14:1-6. 10. Mazur DO HR, Gee W. Related Articles. Retinal detachment in myopic eyes after laser in situ keratomileusis. Am J Ophthalmol. 2000;129:823-824 11. Ruiz-Moreno JM P-SJ, Alio JL. Retinal detachment in myopic eyes after laser in situ keratomileusis. Am J Ophthalmol. 1999;128:588-594
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17. Ruiz-Moreno JM AJ, Perez-Santonja JJ, de la Hoz F. Retinal detachment in phakic eyes with anterior chamber intraocular lenses to correct severe myopia. Am J Ophthalmol. 1999;127:270-275
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Note from the Editor-in-Chief Providing our patients a corneal ablation customized for each person is the new laser treatment of utmost interest in refractive surgery. This is being accomplished by mapping the profile of refraction of the whole eye through wavefront sensing devices. This very sophisticated method identifies aberrations in the entire optical system and not only the corneal surface. The latter is all we could get from corneal topography. The specific aberrations found can be used to obtain valuable diagnostic information of the whole eye. The present challenge is how to correct these aberrations by providing a distinctive laser treatment plan for each eye, like “matching a finger print” to create a perfect optical surface rather than rely upon the basic laser algorithms or mathematical formulas. Although we are identifying aberrations in the whole eye, since the cornea is the major refracting surface of the eye, about 80% of the aberrations can be corrected by operating on the cornea itself, whether they are defocused errors of sphere and cylinder or higher order aberrations. We give so much attention to the cornea because all of the light that goes in and out of the eye has to go through the cornea. So a distortion that is present on the lens or possibly even at the retinal level can be corrected by correcting the shape of the cornea.
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In the following chapters, very prestigious refractive surgeons present their concepts and experiences on how to link diagnostic information obtained from wavefront analysis and corneal topography to the excimer laser treatment. They also identify the sophisticated equipment being made available for this purpose and discuss the usefulness of the information being provided by these methods. In the end, we seem to be closer to the goal of attaining “bionic vision” or “super vision”.
BENJAMIN F. BOYD, M.D., F.A.C.S.
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Chapter 29 REFINING CUSTOM ABLATION THROUGH WAVEFRONT MAPPING Ronald Krueger, M.D.
Custom ablation is a very broad term. It can refer to treatment of the cornea that does not depend on recent technological advances: surgeon-oriented customization occurs, for instance, if the surgeon decides to treat a small zone for a central island that has developed following laser vision correction. The usual meaning of custom ablation today does involve recent advances. Custom ablation can be guided by topography, and more recently by wavefront mapping. Wavefront guided customization will be the most successful method of corneal ablation in the future. Most companies in industry related to ophthalmology are focusing their resources on this technology because it promises to yield all the information needed for doing customized laser treatment.
WAVEFRONT ANALYSIS Mapping a Profile of the Whole Eye The wavefront sensing device provides a new and objective way of mapping the profile of refraction and of higher order defects in the eye such as coma and spherical aberrations. Whereas corneal topography allows us to map a profile of the corneal surface, wavefront mapping makes it possible to map a profile of the whole eye.
Wave-front analysis is a more sophisticated method of defining aberrations that the surgeon is trying to correct through refractive surgery (Figs. 29-1, 29-2, 29-3). Until the present time the basis for diagnosis has essentially been corneal topography.
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Development of Wavefront Technology Different Methods Available
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Wavefront technology originated from two main sources more than 100 years ago. A physicist Section 6 named Hartmann developed principles of subjec- Section 7 tively measuring optical aberrations in a reproducible way. This system was later developed into what Subjects Index is called the Hartmann-Shack wavefront analyzing device, which is used by most manufacturers today (Fig. 29-3). Tscherning, an ophthalmologist working in the late 1800s, devised another method of doing wavefront mapping. Tscherning’s method was further developed by Howland and Howland in the Help ? 1970’s. Recently, Dr. Theo Seiler became involved with this method, which is the method some of the German manufacturers use. A third method of wavefront analysis, which Nidek is using, operates more by retinoscopic principles (Figs. 29-4, 29-5). Still another method is used by the group at Emory University in Atlanta, Georgia. Their method involves a spatially resolved re-
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Figure 29-1 - Inability to Correct Aberrations with Broad Beam Laser Treatment - Pre-op This conceptual view shows a cornea where Lasik for myopia is indicated, which also has a local aberration. Most of the light passing through the cornea is focused in front (green arrow) of the macula (M), a myopic refraction. Light passing through one extra steep area of the cornea (white arrow) causes light to focus even further forward in the eye (yellow arrow). Minute aberrations as such can also exist within the eye through any tissue or medium between the cornea and macula.(Courtesy of Highlights of Ophthalmology).
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Figure 29-2 - Inability to Correct Aberrations with Broad Beam Laser Treatment - Application The broad beam Excimer laser (L) treats a large area of the cornea without regard to the special requirements for custom treatment to a local aberration (white arrow). For this reason, the aberration is not eliminated, giving a refractive result which is theoretically less than optimal. Reflected corneal flap of the Lasik procedure (F). (Courtesy of Highlights of Ophthalmology).
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Figure 29-3 - Aberrometry Type 1 - Wavefront Sensing - Concept of "Outgoing" Reflective Aberrometry (Shack-Hartmann Device) Rather than an average refraction taken across the cornea, wavefront analysis measures refraction at each area of the cornea. This is accomplished by analyzing and recording light that is reflected off the macula and refracts out of the eye through each part of the cornea and lens. First, a small low energy laser beam (1-red) is directed into the eye. The light is then reflected (2-green) off the macula (M), with some directed back out the pupil and out through the cornea as a wavefront. This light reflected off the macula is analyzed for how it refractively emanates through each part of the cornea. In the simplified example shown, a local aberration in the cornea (3) causes this outward reflected light to deviate (yellow rays) in comparison to the light emanating through the rest of the cornea. The light then passes through a series of small lenses (lenslet array - 4) which defines the deviation of focused spots from their ideal position. The wavefront pattern, with denoted deviations from aberrations, is recorded (5 ˆ note area of aberration). This information can be used to treat local areas of the cornea with a small spot laser to give an optimal overall refractive correction. (Courtesy of Highlights of Ophthalmology).
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Section 6 Section 7 Subjects Index Figure 29-4 - Aberrometry Type 2 - Wavefront Sensing - Concept of "Ingoing" Adjustable Aberrometry (Spatially Resolved Refractometer) Ingoing Adjustable Aberrometry involves recording the ingoing rays of light which are manually steered by the patient to define the wavefront needed to cancel ocular aberrations. In the simplified example shown, the patient steers points of light (A) presented at various locations across the cornea toward their macula (M). In an area of aberration (white arrow), the patient subjectively redirects the point source of light (B), compensating for the aberration, so that the light strikes the macula. Recording these deviations presents a wavefront pattern at the level of the cornea to custom treat each part of the cornea for a more optimal overall result. (Courtesy of Highlights of Ophthalmology).
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Section 4 Figure 29-5 - Aberrometry Type 3 - Wavefront Sensing - Concept of "Ingoing" Retinal Imaging Aberrometry (Tscherning Device) With Retinal Imaging Wavefront sensing, laser light (L) as a grid (B) passes through an aberroscope lens (A) and the laser pattern is projected on the retina (G). Any deviation from ideal computes the aberration profile by ray tracing. In the simplified example shown, an aberration in the cornea (white arrow) causes misdirection of the refraction of laser light onto the retina. The resulting deviation in the grid pattern can be seen (C), and is recorded. This information can be used to treat local areas of the cornea with small spot laser to give a more optimal overall refractive correction.(Courtesy of Highlights of Ophthalmology).
fractometer which evaluates the wavefront profile by soliciting the patient’s subjective response to a series of light rays entering the eye (Fig. 29-5).
The Mechanisms of Wavefront Devices Light passing in and out of the eye has to go through multiple structures like the lens and the back surface of the cornea, ultimately passing through the vitreous. Aberrations inside the eye can affect the passage of the light. Ultimately, seeing where the light is emitted from the eye in relation to the cornea allows the ophthalmologist to predict the change in corneal shape needed to give the patient perfect focus (Fig. 29-3).
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Wavefront devices can be categorized into three groups. With “outgoing” wavefront analysis, the wavefront is defined by the foveal reflection of the laser with light going out of the eye. The Hartmann-Shack devices represented by Alcon, Visx, Bausch & Lomb, and Meditec are all based on this form of wavefront analysis (Fig. 29-3). The Tscherning device, named after a prominent ophthalmologist from the late 1800s, is based on “retinal imaging” wavefront analysis (Figs. 29-4, 29-5). The Tscherning device involves a grid of laser energy shone into the eye. The way the grid deviates as it enters the eye and is imagined on the retina defines the wavefront pattern. This device uses the retina to obtain the wavefront pattern. It has been popularized
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through Dr. Theo Seiler, who introduced the technology to two German companies, Wavelight, and Schwind. The last method is an ingoing adjustable way of determining the wavefront pattern (Figs. 29-4, 29-5). It measures the light rays coming in, sometimes individually, sometimes in a retinoscopic fashion. The measured deviation can be either manually adjusted by patients depending upon what they see, or recorded by retinoscopic principles. Nidek OPD and the Spatially Resolved Refractometer use this mechanism (Figs. 29-4, 29-5).
whole profile of the shape of the cornea, giving us much more information for diagnosis. Approaching patients with spherocylindrical refraction, we base the laser treatment on the refractive error with sphere, cylinder and axis. But those are only three numbers, just as keratometry is defined with only a few numbers. Our goal is to get the whole profile of refraction, with an equivalent value at every point within the pupillary aperture. Once this information is obtained, the ophthalmologist can use the laser to create the perfect optical surface.
Benefits of Wavefront Analysis
Linking Diagnostic Information from Wavefront Mapping to Laser Treatment
Probably the best analogy to the development of wavefront technology relates to the early days of radial keratometry in refractive surgery. At that point, before the age of corneal topography, the surgeon needed to know the keratometry value and certain other numbers about the shape of the cornea. The advent of corneal topography allowed us to map a
It is already possible to link diagnostic information obtained from wavefront analysis to the excimer laser treatment (Figs. 29-6, 29-7, 29-8). Several companies are actively doing this form of cus-
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Section 6 Section 7 Figure 29-6 - Custom Laser Treatment of the Cornea Using Small Spot Laser Coupled with Wavefront Analysis Using any of the wavefront analysis techniques described, a small spot laser can custom treat each part of the cornea to optimize the overall refractive result. If each part of the cornea is optimally refracting light to strike the macula, the overall refractive result is maximized. In the simplified example shown here, the small spot laser is providing extra treatment (L) to a localized steep portion of the cornea (white arrow) corresponding to the local aberration. Reflected corneal flap of the Lasik procedure (F).(Courtesy of Highlights of Ophthalmology).
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Figure 29-7 - Final Refractive Outcome of non-Custom Lasik Treatment with Broad Beam Laser This conceptual illustration shows the refractive outcome following broad beam laser treatment without custom treatment to local aberrations of the cornea. Postoperatively, most of the cornea properly refracts light to become focused on the macula (green arrow). However, an area of corneal aberration (white arrow) still causes a deviation in the refraction which is not optimally focused on the macula (yellow rays and yellow arrow). Overall refraction is not optimized. (Courtesy of Highlights of Ophthalmology).
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Figure 29-8 - Final Refractive Outcome of Custom Lasik Treatment Using Small Spot Laser Coupled with Wavefront Analysis This conceptual illustration shows the refractive outcome following small spot laser application, with custom treatment to local aberrations of the cornea. With this approach optimized, each part of the cornea properly refracts light to become focused on the macula (green arrow). This includes an area of the cornea which preoperatively had an area of aberration (yellow rays) that was treated locally with the laser beam of small spot size. (Courtesy of Highlights of Ophthalmology).
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tomized treatment in studies performed in non-US countries. Alcon-Summit-Autonomous is using the technology as part of the clinical trials in cooperation with the U.S. Food and Drug Administration (FDA). Autonomous, which had a very effective scanning spot laser, was purchased by Summit, which owns many patents in the U.S. Now Summit has been acquired by Alcon. Alcon is now refining their LADARVision excimer laser to be used with the custom cornea wavefront device. The specific aberrations can be used to obtain diagnostic information. Then, with the laser, that diagnostic information can be directly applied to the treatment. All the companies that have excimer lasers are developing their own unique wavefront devices. Alcon-Summit-Autonomous, has their Custom Cornea Wavefront System. Visx has the WaveScan device, Bausch & Lomb has the Zioptics device and Meditec has their WOSCA program. Each of these are modified Hartman-Shack devices, using “outgoing optics” to define the wavefront pattern. Wavelight and Schwind have their own wavefront devices based on Tscherning’s design of “retinal imaging” optics. Nidek has the OPD Scan, which is a special device based on slit Skioloscopy, using a modification of retinoscopic principles. Because there is variation among all these types, it would not be wise to obtain a device from Alcon and a laser from Nidek, because the two may not correspond to allow for custom ablation. At this point in the development of the technology no one really knows which is the best device, and comparative studies are yet to be done. The best approach is to examine the technology, consider the manufacturers behind the various devices, and try to predict which are likely to be successful.
Wavefront Analysis in Conjunction with Corneal Topography
ture. Although it is uncertain whether corneal topography will continue to be used a decade from now as technology continues to advance, there is definitely a place for it. The wavefront device provides a more detailed information about what the patient is likely to see because it measures the light passage into the eye focusing on the retina. Whereas the shape of the cornea is important, it is more important to ensure that the focus on the retina is perfectly sharp.
Personalized LASIK Nomograms At present there is considerable interest in developing a commercial database system for nomograms. A number of researchers and companies are working on programs tailor-made for collecting data and determining individual nomograms. There may be several ways to achieve this goal. You can obtain your own Excel file. Using this file you can compare the attempted correction to what is achieved, and then assess the difference. Through regression analysis and adjusting according to different variables, a nomogram can be derived. In the future wavefront mapping may be used to refine some of these measures. When wavefront guided treatment is available, it may rely on very complex nomograms determined by computer that will guide the treatment with even more precision.
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Ronald Krueger, M.D. Medical Director, Department of Refractive Surgery The Cleveland Clinic Foundation Cole Eye Institute 9500 Euclid Avenue /32 Cleveland, Ohio 44195
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Ophthalmologists have learned to depend on corneal topography devices to help screen for disease before surgery and to monitor patients after surgery. More and more we will use the wavefront device for diagnostic testing before and after surgery. Wavefront mapping in conjunction with corneal topography will provide the most complete pic-
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COMPUTERIZED CORNEAL TOPOGRAPHY AND ITS IMPORTANCE TO WAVEFRONT TECHNOLOGY
Chapter 30 COMPUTERIZED CORNEAL TOPOGRAPHY AND ITS IMPORTANCE TO WAVEFRONT TECHNOLOGY Steven E. Wilson, M.D.
CORNEAL TOPOGRAPHY AND both technologies (corneal topography and wavefront analysis) can be integrated to provide WAVEFRONT ANALYSIS
a fuller picture of the refraction and higher-order aberrations that can occur in normal eyes, How Useful Is the Information and that certainly occur in eyes with poor outThey Provide? comes after refractive surgery. Corneal topograBoth corneal topography and wave front phy by itelf cannot provide a complete assessanalysis provide useful information about the ment of severe higher order aberrations. anterior corneal surface. Some manufacturers of Is Wavefront Technology by Itself the many topography instruments available claim their instruments also provide information about Sufficient to Perform Custom Ablation? the posterior corneal surface as well. From a comSome ophthalmologists predict that we will bination of anterior and posterior measurements, ophthalmologists could then deduce the nature be able to use wave front technology excluof the intervening tissues. In my experience, the sively to perform custom ablation (See Figs. anterior surface information provided by corneal 29-6, 29-7, 29-8, Chapter 29). This may be true topography is excellent, but posterior measure- in treating normal eyes because general assumpments are not as reliable. Still, specific changes tions can be made about the shape of the normal on the anterior surface cannot be measured as cornea. With patients who have some kind of precisely as we would desire for performing cus- corneal abnormality, we will not be able to make tom ablation. Both corneal topography and wave these assumptions. We will not know the relafront technology need to be improved over time. tion between higher order aberrations and corWavefront analysis is a technology that can neal shape, or how to change the shape of the provide detailed information about the overall cornea to eliminate these aberrations. To aprefractive status of the eye, including the cor- proach these challenges, both corneal topogranea, but also the lens, the shape of the eye and phy and wave front technology are needed. changes that occur with pupil dilation (See Figs. Eventually, the instrumentation for both tech29-1, 29-2, 29-3, 29-4, 29-5, Chapter 29). It pro- nologies will be integrated into the same system; vides information about all the aberrations that some manufacturers are already exploring these exist within the eye. Information gained through possibilities. LASIK AND BEYOND LASIK
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Variability of Wave Front Mapping Many factors contribute to the complexity of interpreting wave front maps. The wave front map is affected by changes in the eye like the development of cataracts or even by pupil dilation. The analysis will differ at different stages of pupil dilation from very bright light to fainter light. On which reading should the surgeon base the refractive ablation? The answer to that question may depend on what the patient does most of the time. If the patient drives and works at night, perhaps the more dilated pupil wave front information should be used. On the other hand, perhaps the small pupil reading should be used if the patient works primarily outside during the day. All these considerations need to be better understood in order to make optimal corrections for patients.
Current Status of Custom Ablation Custom ablation ideally means that the dimensions of the ablation will change precisely according to the particular aberrations of an individual eye in order to give that optimal function under particular conditions. Excimer laser surgeons currently perform minimal customizations by providing some variation in the diameter of the ablation. For instance, it is now very common to use a 6.5mm diameter ablation in a lower correction patient with larger pupils. Subtle variations in corneal shape cause the same diagnostic label to reflect different conditions in different eyes. Yet current customization is really a one-size-fits-all approach. For instance, all patients who need a –9 diopter ablation get the same ablation, even if one has 1/2 diopter of assymetric bow-tie astigmatism. With true custom ablation, the corneal surface and wave front mapping will be integrated to determine a very
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precise ablation for the individual eye and the conditions of the patient’s two eyes. Two patients with the same refraction may be treated with different ablation because of differences in the patients’ corneal shape, lenses, and pupils. Probably ten groups today are directly applying wave front and corneal topography. They are attempting to take the diagnostic information yielded by corneal topography and wave front analysis and translating that into precise treatment through corneal ablation. People closely associated with the development of the technology say that part of its difficulty involves knowing how to interpret the massive amount of information from the aberrometer and corneal topography. Wilson thinks we do not yet have enough information to determine which of the several types of wave front analysis systems provide optimal information. As interpretive capacity evolves, Wilson believes we will understand precisely what the reading from each instrument indicates in terms of desirable changes to the cornea to correct the aberrations. Although we are not quite there yet, this area evolves from month to month.
Controlling Wound Healing
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Its Relation to Achieving the Ultimate Potential Custom Ablation Even after we clearly understand how the cornea needs to change in order to correct the pattern, ophthalmologists must still keep in mind that the cornea is not a piece of plastic. If we are to achieve the ultimate potential custom ablation, we must also learn how to control wound healing and understand corneal biomechanics. There is no doubt that the cornea will confound our very small corrections. The changes involved in ablation are very tiny; they are measured by one, two, or three microns. A subtle change in the epithelial thickness or in the way the stroma heals
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may reverse these small changes. Many companies are now pouring considerable resources into the actual analysis of the wave front and the application in the ablation, but almost nothing into what happens afterwards. Unless they realize that we must look at how to maintain correction, we will end up with great analysis software and applications but an unpredictable result when the technology is applied. Only 6 years ago, we discovered at our laboratory the concept of keratocyte apoptosis. Since that time, much more knowledge is available about the proliferation of keratocytes, the migration of inflammatory cells and their evolution into different cell types that manufacture collagen. Progress is being made toward understanding how all these contributions are associated with wound healing, and how the wound healing process can be controlled. During the next 5 years we predict that pharmacological manipulation of the corneal wound healing response will become a standard part of refractive surgery. The familiar objective of blocking wound healing reflects a misguided approach. We encourage ophthalmologists to focus on normalizing the wound healing process. The greatest challenge to understanding and manipulating wound healing is the variability in the wound healing process: one patient may have a much lower healing response than another along a continuum of possible responses. Our goal should be to make the healing process consistent—not to prevent healing, because these wounds must be healed, but to prevent an aggressive healing response that tends to produce regression, haze and other complications like irregular astigmatism. A very low response, resulting in a large overcorrection, is also an undesirable outcome. Somehow we need to ensure that patients will heal in the middle
range. This will require detecting ahead of time the necessary regimen, perhaps pharmacological, to ensure the stroma and the epithelium stay within a certain level of wound healing. This pharmacological regimen must begin before surgery. The instant the corneal epithelium is touched in some way, the wound healing response begins. It is so rapid in animal models that before surgery is even complete, early changes in keratocyte apoptosis in the anterior stoma can be seen. Unless the pharmacological agent is delivered before surgery starts, the beginning of surgery will lead to a cascade of events that cannot be controlled. It has been discovered that the apoptosis process itself is a very complex pathway with many enzymes and proteins involved. It is necessary to intervene right at the beginning of the pathway to modulate it. There is currently no agent that can be administered by drop and that acts early enough in the apoptosis cascade to block the apoptosis process without causing cell necrosis, which would not be beneficial at all. Therefore, at the University of Washington in Seattle are exploring other methods of administration besides applying a drop, methods involving gene delivery. It may be possible to use safe viral vectors just before surgery deliver a gene temporarily to the cornea that will prevent apoptosis from occurring in the cornea until 3 or 4 days after surgery. By that time the eye should have healed, and therefore the effect does not have to be long-term.
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Steven E. Wilson, M.D. Chair, Department of Ophthalmology and Professor of Vision Research University of Washington Seattle, Washington (USA)
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CUSTOMIZED CORNEAL ABLATION THROUGH WAVEFRONT MAPPING
Chapter 31 CUSTOMIZED CORNEAL ABLATION THROUGH WAVEFRONT MAPPING The Quest for Bionic or Super Vision Marguerite McDonald, M.D.
PROMISING NEW TECHNOLOGY: WAVEFRONT ANALYSIS Attaining Bionic or Super Vision Recent technological advances now allow us to measure and treat lower-order aberrations of the eye, problems of the sphere and the cylinder. Experts in neural biology now tell us that in the future human vision will be pushed to the limits of the spacing of the retinal photoreceptors, which is 20/8 or 20/5. Some people call this bionic vision or super vision. For purposes of comparison, the visual acuity of hawks is about 20/6 and of eagles is 20/4. Humans will be able to see not quite as well as eagles but as well as hawks if higher-order aberrations can be corrected. The technology that will make it possible to correct these higher-order aberrations is wavefront analysis. The wavefront is a like a wrinkled sheet of light that emerges from the eye (See Figs. 29-1, 29-2, 29-3, 29-4, 29-5, Chapter 29). Some people find this image confusing, as they imagine light traveling in rays like arrows. The wavefront is perpendicular to the ray—indeed, the two images are two different ways of describing how light travels. The first surgeon in the world to perform excimer laser surgery based entirely on wavefront mapping or analysis instead of phoropter refraction was Dr. Teo Seiler in March 1999. Our team in New Orleans under my direction was the first to perform this surgery in the U.S (See Figs. 29-6, 29-7, 29-8, Chapter 29). We accomplished this wavefront-based
laser surgery in October 1999, 7 months after Dr. Seiler’s first procedure. There are patients in different regions of the world who see 20/8 after wavefront surgery. The expanding number of patients treated by research teams around the globe who see 20/8 after wavefront surgery make it clear that we will be able to improve on Mother Nature.
Generating the Wavefront Map
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This is how the technology works (See Section 5 Fig.29-3, Chapter 29). When the eye is dilated, a probe beam of light is focused in the eye, and a 905 Section 6 wavelength diode laser is sent in. It hits the retina and bounces back out of the dilated pupil. As it bounces Section 7 back, it picks up the optical characteristics of the eye. Subjects Index When it emerges from the cornea, it hits a lens slit array or slit groupings comprised of many dozens of small lenses. Then the point image of each lens slit is captured by a CCD camera. A color-coded wavefront map is generated from the point image of each lens slit. A mathematical equation called the Zernecki polynomials is applied to these raw data. Help ? The information obtained from wave front analysis is actually integrated into the excimer laser, making it possible to utilize the diagnostic information in the therapeutic mode. The map is then used to generate the shot pattern. This information is written on a floppy disk placed inside the laser to drive the ablation. The wave front sensing device is a separate machine located close to the laser, but not attached to the laser. It is a diagnostic device that is easy to use and painless for the patient.
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Wavefront Analysis and Corneal Topography Wavefront maps are in color and look somewhat like corneal topography. Although they are sometimes used in conjunction with corneal topography, they are actually quite different. Corneal topography will never be supplanted by wavefront analysis, as it is important to know the shape of the cornea. Although one manufacturer, Nidek, uses both a colored wavefront and a colored topography map together to generate the treatment pattern, the two maps are separate.
Marguerite McDonald, M.D. Director Southern Vision Institute New Orleans, Louisiana (USA)
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WAVEFRONT ANALYSIS AND CUSTOM ABLATION
Chapter 32 WAVEFRONT ANALYSIS AND CUSTOM ABLATION George Waring, M.D.
Promising Achievements Refractive surgery has always dealt with the correction of spectacle refractive error, or problems with the sphere and the cylinder. Now, when performing a standard LASIK technique with the majority of laser systems the surgeon can achieve correction within half a diopter of the desired refraction for about 75% to 80% of patients with myopia of 10 diopters or less. But what about the other 20% of patients? Our goal is to correct 90% of patients who wear glasses or contact lenses to 20/10 by the year 2010. The technology that promises to achieve even better refractive correction is called wavefront analysis. Whereas correcting the sphere and the cylinder takes care of 80% to 90% of the visual problems both of patients with myopia and hyperopia, wavefront analysis and wave front correction will take care of the additional 10% to 20%.
Principle of Wavefront Analysis The basic principle behind wavefront analysis is different from the principle behind an ordinary refraction. An ordinary refraction results in an average correction over the entrance of the pupil of the eye. Wavefront analysis, on the other hand, assesses the correction at each point measured over the pupil (See Figs. 29-1, 29-2, 29-3, 29-4, 29-5, Chapter 29). The refraction over the pupil is not uniform—it may be –3 diopters in the center but –4 diopters at the edge of the pupil. Wavefront analysis makes it possible to detect the refractive error at each point (See
Figs. 29-6, 29-7, 29-8, Chapter 29). The resulting spatially resolved fraction serves as the basis for using a 1-mm flying spot excimer laser to refine the refraction by making a different correction at each Contents spot over the pupil. In addition to eliminating the sphere and the cylinder of the average correction, Section 1 wave front analysis also eliminates the finer points Section 2 such as the spherical aberration and coma aberration. With these precise corrections the patient’s vision can Section 3 go from 20/20 down to 20/10. Section 4 This technology has been used for many years in the field of astronomy. Stars at a distance look Section 5 blurry through a telescope because of the aberrations in the telescope. Special optical techniques have been Section 6 shown to decrease the aberrations in the telescope, Section 7 allowing astronomers to see an individual star very clearly. This technology is now being transferred Subjects Index from astronomy and optical science to clinical ophthalmology to help patients see not blurry stars, as it were, but very fine and discrete stars. Wavefront guided optical correction of the eye will have broad application across many aspects of refractive surgery. It will decrease the problem of Help ? aberrations that result from surgery. LASIK treatment to induce a standard myopic or hyperopic correction actually increases the amount of spherical aberration and coma aberration. High resolution central acuity is improved, but night vision becomes worse. Wavefront analysis and wave front guided treatments make it possible to reduce spherical and coma aberration and the other finer distortions that occur in vision. Clinical trials have compared treatment with the standard excimer laser sphere and cylinder correction to wave front guided correction. Wavefront
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guided correction is proving superior in small increments in a stepwise process of clinical refinement of this technology. The ultimate goal, optimal vision for each patient, means that each excimer laser treatment of the cornea will be unique. Each eye truly has a unique refractive error and a unique visual system. The goal of wavefront guided surgery is to create an individual correction appropriate for the individual eye.
Availability of Technology A more practical question concerns the availability of the technology for clinical use. In the year 2001 it is at the experimental level. Approximately six laser systems have coupled with them a wavefront analysis unit and the software to convert the results of the analysis into customized laser treatment of the eye. (Consult Chapter 29 for more specific information on the equipment being made available).
George Waring, M.D. Professor of Ophthalmology Emory University; Co-Founder Emory Vision Correction Center Atlanta, Georgia (USA)
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Custom Intraocular Lens
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But the story does not stop there. Besides the excimer laser, the other major force in refractive surgery today is the phakic intraocular lens. This lens offers the potential of using wave front guided optics to create a custom intraocular lens. The patient’s eye would be analyzed. The manufacturer would make a custom intraocular lens. The implanted custom lens would correct not only the sphere and the cylinder, as today’s lenses do, but would also correct the higher order aberrations, giving the patient 20/10 vision. Cataract surgery today is truly refractive surgery. Removing the opaque lens is now standard procedure and fairly easy for a competent ophthalmologist. The current challenge is to enable the cataract patient to see 20/10 uncorrected if the condition of the macula makes this possible.
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Goal in Mind With this new goal in mind, ophthalmologists will be performing more and more combined procedures. The cataract will be removed. An aphakic intraocular lens will be placed in the eye. LASIK will then be done with wave front guidance to create
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20/10 vision.Similarly, when phakic intraocular lenses are implanted, the majority of correction will be done with the phakic intraocular lens, possibly even with a custom lens. A refinement will then be done in the cornea to fine-tune the refraction in order to attain the best possible vision for the patient.
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Chapter 33 THE ROLE OF DIFFERENT ABERRATIONS IN WAVEFRONT ANALYSIS Prof. Juan Murube, M.D., Ph.D.
General Considerations The correction of the conventional refractive errors present in the eye by modifying the curvature of the anterior surface of the cornea using the excimer laser is already an accomplished technological fact. The next step is to significantly improve this technology and have it perform closer to perfection in the following manner: 1) Correct the optical aberrations that naturally exist in all eyes and which people are born with, some more, some less. 2) Prevent the optical aberrations that may be induced by LASIK surgery such as when we treat myopia, astigmatism and hypermetropia with LASIK. If, on the contrary, we create surface irregularities or opacities of the cornea, these will increase the quantity and the quality of already existing aberrations and consequently reduce the benefits that we are trying to attain through emmetropia. In order to accomplish this, we need to be able to measure these aberrations during our diagnostic analysis, a procedure that we call "aberrometry". The second step following diagnosis and identification of the existing aberrations is to correct those aberrations, a procedure that we might call "aberrocorrection", even though this term does not yet exist.
What Do We Mean by Wavefront Sensing Analysis? Contents
When you throw a stone into a peaceful pond, a series of waves are formed in the water. They Section 1 are concentric around the area where the stone fell into the pond. These concentric waves begin to get Section 2 farther away from the area of impact in successive Section 3 circles or half circles that we call “wavefronts”. The more these concentric waves become farther away Section 4 from where the stone entered the water, the smaller Section 5 the radius of curvature will be and consequently the wavefront. Since the wavefronts are difficult to Section 6 represent graphically, specially where we try to convey the refractive changes associated with them, it is Section 7 more practical to show them as rays of light perpen- Subjects Index dicular to the wavefront (Figure 33-1).
What do we Understand as an Aberration of the Optical System? Aberration is derived from the Latin term "ab-erratio", that means “going out of the way or deviate”. It refers to the difference that exists between the image that we expect to see when the wavefronts are refracted according to Snell's law and what really occurs. According to Snell's law, a
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Section 3 Figure 33-1: Wavefront Analysis Effects: Normal Eye Figure above shows the multiple small deviations that a ray of light undergoes when it "travels" through irregularities or aberrations in the optical system of the normal eye. Ray of light coming from infinity (I) (yellow arrow) passes through the cornea (A) and is deflected by aberrations in the anterior and posterior surfaces of the cornea, the crystalline lens, the vitreous body (B) and focus on different areas of the retina (R) (yellow arrows). The light rays also undergo deviations upon encountering aberrations on their way out (see path of the green arrows). These phenomena supposedly result in being unable to see 20/10 instead of 20/20. (Courtesy of Highlights of Ophthalmology).
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ray of light that is refracted over a perfect spherical surface follows a direct and straight path. But at the eye level, this does not happen because the corneal surface is not perfect since it generally presents aberrations. This results in that the light rays will follow these small variations transforming themselves into rays of light that are not straight but irregular (Figure 33-1). Among the different aberrations, the most important ones are six geometrical aberrations (prismatic, astigmatic, coma, spherical, field curvature and distortion) and two chromatic aberrations (axial and lateral). In the human eye these optical aberrations occur mainly in the anterior and posterior
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surfaces of the cornea and the crystalline lens, although they also occur within the irregularities existing in the refractive media (cornea, crystalline lens, vitreous body and the retinal tissues). This is why a wavefront that will enter through the anterior surface of the cornea, will not constitute during its path or form one perfect focal point in an exact spot. This is because of the aberrations existing in the "perfect" spherical optical lenses that we have described. Among the irregularities of shape or form, the more significant aberrations are those of the anterior surface of the cornea. For example, the cornea is more curved in the center than in the periphery. It also has multiple astigmatic deforma-
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THE ROLE OF DIFFERENT ABERRATIONS IN WAVEFRONT ANALYSIS
tions or irregularities. The superficial corneal surface is not smooth as we all have been accustomed to think but is more like the skin of an orange, which has multiple irregularities. In the eye the irregularities of the anterior surface of the cornea are diminished upon being covered by the lacrimal film, which has a very smooth anterior surface. The phenomena of aberrations are repeated in all the optical surfaces of the eye that constitute the media such as the posterior surface of the cornea, the anterior and the posterior surface of the crystalline lens and the anterior surface of the retina. To these surface irregularities, we must add those related to the imperfect position of the optical surfaces of the eye. Neither the cornea nor the crystalline lens are centered over the visual axis so the wavefronts cannot have an oblique direction or tilting over them. We also must take into consideration the irregularities in the transparency and the index of refraction of the ocular media (Figure 1). They exist in the cornea, in the crystalline lens, and in the vitreous body and they are greater as the patient gets older. These different irregularities or aberrations occur as characteristics of each particular individual but many of them are increased when the patient undergoes refractive surgery.
How Do Different Aberrations Affect Vision in Humans? The two main types of aberrations: the "perfect" spheric lenses and the "imperfect" spheric lenses do affect vision in humans. A ray of light that is following a path parallel to the eye's optical axis and is refracted on the anterior surface of the cornea theoretically should converge and be focused at one single point located in the photoreceptors of the retina. This does not occur because the personal characteristics of each person vary in relation to the form, position and transparency of the ocular refractive elements. The latter will deviate the different components of the wavefront toward different focal points in the retina (Figure 33-1). This results in defocusing of the images that are manifested as a
lowering of visual acuity if we compare it with the same person with the same shape of the eye if he / she would not have such aberrations. These deviations or aberrations that the rays of light undergo can be partially predetermined with the present methods of diagnosis available. Identifying each one of these aberrations enter into the category of “aberrometry” or specific diagnosis of aberrations.
Do Aberrations Contribute to Sight in Any Positive Way? Aberrations in a normal human eye, yes, they do. The anomalous aberrations produced by refractive surgery, for instance, do not provide any Contents positive contribution to sight. Aberrations in the normal eye produce a Section 1 luminous focus that the visual system in the retina and the brain analyze and provide the patient with Section 2 extensive information including depth perception, Section 3 pupillary aperture, luminosity, color proportions and continuity of the visual field even though the retinal Section 4 images may continuously change position, due to the fluctuations of the palpebral curvature upon blink- Section 5 ing, as well as fluctuations of the crystalline lens Section 6 upon accommodating on fluctuations on the position of the retina when the choroid becomes engorged in Section 7 blood by changes in the position of the body. For Subjects Index these reasons, the person whose eye does not have the aberrations in perfect spherical lenses that we are describing would see worse than one who does have these aberrations. On the other hand, a different situation is present with large aberrations caused by irregularities in the shape, position and transparency of an Help ? abnormal eye, that may have been produced by congenital malformations such as in keratoconus or corneal dystrophies, or in patients with trauma or who have undergone refractive surgery. These aberrations in abnormal eyes diminish the visual acuity and contrast sensitivity. We should correct them when they already exist or avoid inducing them as much as we possibly can.
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Principles for the Study and Diagnosis of Aberrations The present methods of diagnosis to determine the different types of aberrations function according to the following principles: a. b.
Outgoing reflective aberrometry (Figure 29-3) Ingoing adjustable aberrometry (Figures 29-4 and 29-5)
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Ingoing retinal imaging aberrometry (Figures 29-4 and 29-5)
Aberrometers are an important conceptual development in the investigation of Physiological Optics. Nevertheless, at present they are of medium practical interest to the clinician that performs surgery on ametropias because the instruments available are still somewhat “crude,” not 100% exact for the precision required for the determination of an aberration (Figure 33-2). With the equipment now
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Figure 33-2: Principles of Wavefront Sensing Analysis The study of existing aberrations is done not only in normal eyes but also in previously operated corneas and those with decentrations and with irregular astigmatism (See Chapters 13 and 18). This study is made by using a laser (L) and a computerized optical system through a dilated pupil (inset) that identify the geographical areas and the size of the aberrations found in the in and out pathways of light in the human eye (G - and yellow and red arrows). Once these aberrations are identified, they are interpreted by means of a tridimensional topograph and the corneal areas to be treated with the excimer laser are determined.(Courtesy of Highlights of Ophthalmology).
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Section 1 Figure 33-3: Customized Corneal Ablation The presently existing highly sophisticated lasers have a light beam 1 mm in diameter. This is very effective for the methods of corneal ablation we use now. In order to take advantage of the technology being developed for diagnosis through wavefront analysis, we will need lasers with a much smaller light beam that can proceed to correct very small corneal ablations (E) and obtain a customized corneal ablation for each individual patient. (Courtesy of Highlights of Ophthalmology).
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available we cannot yet measure the aberrations in the entire corneal diameter, but only in a limited number of small areas distributed throughout the cornea. The other aberrations present are not determined by the study. The limitation for future correction of the aberrations is that it will have to limit itself to correct these areas. Even so, it is not an important limitation because the diameter of the flying spots of excimer lasers that we have available are still larger than the diameter of the corneal aberrations existing. (Figure 33-3). Because of this, the possibilities at present of correcting aberrations based on outgoing or ingoing aberrometry are only slightly superior to those in which the information obtained is through corneal topography that measures only the geometry of the anterior surface of the cornea. Because the present devices to detect and measure aberrations are still very limited, their clinical application to refractive surgery reflects
these limitations. Therefore, we must continue the Section 7 development of more exact devices if we aim to Subjects Index correct as many aberrations as possible and obtain the perfect vision we are all aiming for.
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Prof. Juan Murube, M.D. Clinica Murube San Modesto, 44-1º Madrid E-28034, Spain E-mail:
[email protected]
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Chapter 34 WAVEFRONT ANALYSIS Doane, John F., M.D., Morris, Scot, O.D., Border, Andrea D., O.D., EuDaly Lon S., O.D., Denning James A., B.A., B.S., Probst Louis E., M.D.
What is Wavefront Technology? Just as you may or may not have become accustomed to understanding corneal topography maps the next evolution of refractive ocular imaging in the form of “Wave Front Analysis” has come on to the visual science scene. This technology is rooted in the astrophysics domain where astronomers hoped
to perfect the images impinging on their telescopes. To do this astrophysicists had to be able to measure, let alone, correct the imperfect higher-order aberrations or wavefront distortions that entered their telescopic lens system from the galaxy. Using a process called “ adaptive optics “ deformable mirrors were used to reform the distorted wavefront to allow clear visualization of celestial objects ( See Figures 34-1 AB and 34-2).
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Figure 34-1 A & B: (A, left, upper) Image taken without adaptive optics reveals what appears to be a single star. (B, right, upper) Applying adaptive optics technique and resolving wavefront distortions two separate stars are actually revealed.
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Figure 34-2. Sensing Mirrors and Adaptive Optic Deformable Mirror. Lower right of slide reveals a chip detector microlens array for obtaining the wavefront and the upper right of slide reveals a deformable chip mirror to perfect the imperfect wavefront.
Figure 34-3. Patient being examined by technician. Note desktop CPU, monitor, keyboard and acquisition device.
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Josef Bille, Ph.D., professor and physicist at the University of Heidelberg, Germany, is considered by many to be the “father” of wavefront technology.1 Dr. Bille who is the Director of the Institute of Applied Physics at the University of Heidelberg first began work in this field while developing this specific technology for astronomy applications in the mid-1970’s. He issued and received the first German patents in 1982 and 1986, respectively. In 1997 he co-founded 20/10 Perfect Vision. Since that time he and his co-workers have designed and brought to market a stand-alone desktop-sized testing device which includes: image acquisition device, monitor, computer processing unit and keyboard (See Figure 34-3 ).
Definition of Important Terms 2,3 Spherical Aberration - Spherical lenses do not bring all rays to a perfect point focus. For a plus spherical lens there is increasing converging power as the lateral distance from the central ray is increased. Thus, spherical aberration causes rays at the edge of the lens to be focused anterior to the focus of the central ray. Instead of all of the rays of light coming to a concise point of focus, they are distributed over a small region of the image and there is no single sharp point of focus for all of the light rays passing
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through the pupil. Spherical aberration in humans is due to the anterior surface of the cornea and the ante- Section 2 rior and posterior surfaces of the crystalline lens. Spherical aberration increases as the fourth power Section 3 of the pupil size. At night, pupil dilation increases Section 4 spherical aberration, which causes a slight (0.5 to 1.0 diopter) increase in myopia, due to the shift in image Section 5 location which defines the condition of night myoSection 6 pia. Chromatic Aberration - The ocular me- Section 7 dia have a different refractive index for each wavelength of light. Hence, blue light which has a short Subjects Index wavelength is brought to a focus in front of longer wavelength red light resulting in an imperfect point of focus. In the human eye chromatic aberration is the result of this differential refraction by the cornea and crystalline lens. As with spherical aberration, chromatic aberration increases as the size of the puHelp ? pil increases and both are accentuated the further one moves from the optical center of the cornea or crystalline lens. In consideration of spherical and chromatic aberration, the sharpest retinal image is produced when the pupil is 2-3 millimeters in diameter. A smaller pupil will degrade the sharpness of the retinal image by diffraction effects about the edge of the papillary aperture. Coma and off-axis astigmatism cause rays to be distributed over a small area of the image rather
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than to converge to a single point. Coma derives its name from the fact that the rays are distributed in a pattern reminiscent of a comet. Coma and off-axis astigmatism increase as the object moves away from or lateral to the optical axis. Point-spread-function is explained by directing a normal emmetropic eye toward a tiny single point source of light such as a star. The resulting image on the retina will not be a point but a small circle of finite size. This effect is called point-spreadfunction and results from diffraction effects about the margin of the pupil. Modular transfer function is an optical bench measurement used by engineers to evaluate the performance of a lens, or lens systems. The MTF is a method to describe the contrast sensitivity of a lens. Modulation transfer is the ability of a lens system to transfer an object’s contrast to its image. Modulation is therefore a ratio of image contrast to object contrast. Ideally, it would be one, or 100%. Modulation transfer plots describe the modulation of a lens system as the object increases in complexity. The Y-axis is modulation and the X-axis is spatial frequency, measured in line pairs per millimeter. As the spatial frequency increases, the modulation of any lens system decreases. ( Definition courtesy of Warren Hill, M.D., Mesa, Arizona )
CURRENT OCULAR REFRACTION EVALUATION SYSTEMS Phoroptor and Autorefractors Manual refraction with the time-tested phoropter incorporates both objective retinoscopy by trained examiner and subjective refinement with patient input. Autorefraction obtains objective measurement followed by subjective input from the patient. With either of these formats, only sphere, cylinder and axis of cylinder are quantifiable. Irregular astigmatism and other higher order aberrations are not measurable. Minimal measurement is 0.12 diopters.
Corneal Topography Placido-disc or slit-light systems supply corneal curvature and elevation data with an accuracy
of 0.25 diopters or 2-3 microns. The excimer laser can remove tissue at 0.25 microns per pulse of ablation. The actual depth depends on tissue hydration at the time of photoablation.4
20/10 Perfect Vision Wavefront System This system describes the refraction of the eye within 0.05 microns. This is five times more accurate than the excimer laser beam and approximately 25-50 times more accurate than phoropter, autorefractor and topography based systems. It is important to understand that the Wavefront System is not a “ newer “ version of corneal topography but a visual acuity measuring device that takes all elements of the optical train into consideration which includes: tear film, anterior corneal surface, corneal stroma, posterior corneal surface, anterior crystalline lens surface, crystalline lens substance, posterior crystalline lens surface, vitreous and retina.
Other Wavefront Sensing Devices 5
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A. Autonomous Technologies Custom Cornea / LadarVision Wavefront Measurement De- Section 5 vice. This is a Shack-Hartmann style device. All Shack-Hartmann devices are outgoing testing devices Section 6 in that they evaluate the light being bounced back Section 7 out through optical system. B. Dresden Wavefront Analyzer. Theo Subjects Index Seiler, M.D. and his colleagues from University Eye Clinic, Dresden, Germany have developed this system. It is to be distributed by Technomed GmbH of Baesweiler, Germany. The system will work in conjunction with the Wavelight ( Erlangen, Germany ) Allegretto scanning spot laser and the soon to be inHelp ? troduced scanning spot laser from Schwind Eye-TechSolutions GmbH ( Kleinostheim, Germany ). This system is based upon the Tschernig aberroscope, first described in 1894. A bundle of equidistant light rays are projected onto the cornea and, due to optical imaging, become focused on the retina. In an aberration free eye, the retinal image pattern consists of equidistant light spots. The spot pattern of a normal eye is distorted due to ocular aberration. The deviation of all spots from the ideal pattern is measured by an indirect ophthalmoscope and directed to a low-
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light charge couple device (CCD) linked to a computer, and these patterns are used to compute wavefront aberrations in the form of Zernike polynomials. When compared to and integrated with preoperative corneal topography, an ablation profile is computed and used to feed the excimer laser to correct for all of the eye’s aberrations. The device uses a frequency-doubled Nd:YAG laser at 532 nM and mask system to create 168 equidistant and parallel light rays for projection onto the cornea. The overall exposure time is 40 ms. The precision of the device allows for an objective measurement of spherical and cylindrical refractive error with an accuracy of better than +/- 0.25 diopters. By definition this is an ingoing testing device in that the image formed on the retina is observed and evaluated. No information on outgoing light is necessary. Contents Figure A: The CustomCornea System to be used with the LADARVision excimer laser
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Figure B. The Zyoptics Custom LASIK screen with the preoperative keratometric and aberrometer maps along with the preoperative pachymetry obtained from the Orbscan.
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C. Bausch & Lomb Surgical (Claremont, CA) Aberrometer/Wavefront Analyzer (designed by Technolas GmbH of Munich, Germany) which is to be incorporated into the Bausch & Lomb Orbtek (Salt Lake City, Utah) Orbscan topography device. This system appears to be a Shack-Hartmann type system operating in a similar fashion to Visx 20/10 Perfect Vision and Autonomous systems. D. Tracy Technologies ( Bellaire, TX ) Electro-optical Ray-Tracing Analyzer. Unlike the Shack-Hartmann-type devices the Tracy ray-tracing device uses the fundamental thin-beam principle of optical ray tracing to measure the refractive power of the eye on a point-by-point basis. The device measures one point in the entrance pupil at a time rather than measuring the entire entrance pupil at once, like the aberroscopes and Shack-Hartmann devices which supposedly have the possibility of data points criss crossing with a highly aberrated eye leading to erroneous information and subsequent conclusions. The ray tracer is designed to fire a rapid series of parallel light beams into the eye one at a time, passing through the entrance pupil in an infinite selection of software-selectable patterns. With this technique, the Tracy system can probe particular areas of the aperture of the eye. By design, the Tracey system can register where each “ bullet “ of light strikes the retina as the fovea is represented by the conjugate focal point of the system from the patient’s fixation. Semiconductor photodetectors are able to detect the location of where each light ray strikes the retina and provide raw data measuring the error distance from the ideal conjugate focus point, giving
direct measurement of refractive error for that point in the entrance pupil. 64 points of light within a 6 mm pupil can be measured five times each in just over 10 ms. This device like the Dresden system is an ingoing measuring device. When measuring a physiological system, such as the eye, with its range of refractive errors, this system in essence measures the point-spread function that can easily provide for full calculation of wavefront deformation and modulation transfer function of the eye. One major hurdle for this system is that it currently does not have adaptive optics possibilities ( see below ) which would seem to be imperative to assess preoperatively that the correct wavefront-augmented treatment will be performed. E. Spatially Resolved Refractometer of Emory University ( Atlanta, GA ). This device is being designed, built and tested by the Emory Vision Correction Center. It takes a relatively lengthy 3-4 minutes to complete the test but does have direct patient involvement in the testing which adds important subjective value. 6
How the Visx 20/10 Wavefront System Works
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With the Visx 20/10 System a 785 nM nomi- Section 6 nal wavelength light is projected into the eye onto the macula ( Figure 34-4 ). This light is not a laser, Section 7 so there is a considerable spread about the center Subjects Index wavelength. The light is projected as flat sheets or “ wavefronts “. The wavefronts are projected through the entire optical system and reflected back and col-
Figure 34-4. Schematic diagram of a SH type aberrometer. The key component is the ShackHartmann wavefront sensor shown in the gray box. Dashed rays show the conjugacy relationship between the eye’s entrance pupil and the lenslet array. Solid lines show the conjugacy relationship between the retina and the CCD video sensor. F is the fixation target. For calibration purposes the light trap T is replaced by a mirror that reflects the collimated laser beam into the Shack-Hartmann wavefront sensor. ( Figure courtesy American Academy of Optometry - Thibos LN, Hong X. Clinical applications of the Shack-Hartmann Aberrometer. Optom Vis Sci 1999;76:817-825. ) 7
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lected by a CCD video camera within the acquisition module. If the optical system is without aberration, the wavefront exits the eye as parallel flat sheets
just as they entered (Figures 34-5 A, 34-6A). If the optical system has aberrations the flat sheets entering will exit as irregular curved sheets ( Figures 345 B, 34-6 B ).
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Figure 34-5B. Light emerging from an eye with significant aberration. The emerging wavefronts are not straight but are curved.
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Figure 34-6A. Incident plane wave resulting in a square grid of spots.
The returning wavefront after being captured by the CCD video camera is converted to a color coded Acuity Map for points over the pupil area. Some prefer the term “Phase Map” or “Spatially Resolved Refractometer Map”. Nevertheless, the map is a translation of 100,000 data point numbers for a 6 mm pupil. Measurements are taken every 20 microns over a 6 mm pupil area and thus describe the refractive properties of the eye from tear film to retina. The technique of adaptive optics can then be employed on the irregular wavefront to correct for all aberrations above sphere and regular astigmatism. What physicians call irregular astigmatism (any re352
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Figure 34-6B. Distorted wavefront causes lateral displacement of spots.
fractive error which can not be corrected by spherocylinder lens combinations) physicists call higher order aberrations (comma, spherical aberration, chromatic aberration). Wavefront data can determine abnormalities within the ocular system, as depicted on the wavefront map, but it can not tell the clinician at what level the abnormality is located, i.e. cornea, lens, vitreous, or retina. Therefore, complete ocular examination (retinoscopy, slit lamp examination, fundus biomicroscopy, and ophthalmoscopy) in combination with data from keratometry and corneal topography will define the locale of pathology.
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How to Read a Wavefront Map Visx 20/10 has called their maps “ Acuity Maps“. Acuity maps are color coded and separated into 20 shades of color which are autoformated in micron scale for the given eye. The total interval of measurement of the individual map is determined by the actual microns of difference in the most advanced (maximum) and most latent or trailing (minimum) of the wavefronts for the individual eye. Figure 34-7 A (above right) Visx 20/10 Perfect Vision Acuity Map of an unoperated “ normal “ eye. Upper left gives patient name, presumed refraction and eye of regard. Upper right provides CCD picture of cornea and pupil (In future formats, the raw Shack-Hartmann data image will be placed here). Lower Right provides the measured refraction via the wavefront reading for first order – sphere and second order – regular astigmatism and axis. The lower left provides the acuity map with sphere, astigmatism and higher order aberrations on the left and the acuity map with sphere and regular astigmatism removed. The second map only describes the higher order aberrations. Note the left map is scaled from –1.5 microns to +1.5 microns with most values from 0 (baseline reference plane) to +1.5 microns and the second map is scaled from –0.5 microns to + 0.5 microns. In this example there are essentially no higher order aberrations. These maps should be looked upon as contour maps. After taking the scale range in microns into account, if there are widely spaced contours this would indicate an eye relatively free of optical aberrations whereas if the contours are tightly spaced there is a greater degree of aberration. Figure 34-7B (below right) Humphrey corneal topography provided at right for comparison.
The acuity map is purely an objective reading of the wavefront. The “ loop “ per se for an individual eye is “closed “ by enlisting the patient to provide subjective feedback when the adaptive optics technology of deformable mirrors which correct the aberrations and project a Snellen-like acuity chart onto the patient’s fovea. The patient is asked to read as far down on the “chart” as possible and this will be the best acuity the treating physician could hope to achieve after surgical intervention. In theory, this
Visx 20/10 Perfect Vision Acuity Map (Figs. 34-7 A-B)
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should create the optimal ablation with laser vision correction for each eye and correctly treat the irregular corneal optic. According to Dr. Bille, in the population undergoing surgery 99.9% have retinas capable of seeing 20/10 but their corneal shape does not permit this to happen and programming the laser to reshape the cornea to compensate for these imperfections and allow the patient to realize their best possible acuity. A very helpful image for the clinician to evaluate with each visual acuity map, phase map or spatial map, as used by Thibon and Hong 7 ,(color coded map in the lower left of figure 34-7) is the ShackHartmann data map. The SH data map is the raw light image impinging on the CCD camera. It appears as a grid of light dots as seen in Figure 34-8A.
If the eye is without aberration the pattern will be extremely uniform with the dots perfectly aligned horizontally and vertically. In addition the image of each dot will be very precise without blurring of the edges or “trailing” of the edges in “comet like “ fashion. (Figure 34-8A). If the eye has significant aberration the image will show a distorted pattern with individual qualitative abnormalities of the dots and overall irregularity of the group pattern. (Figure 34-8B ) Data from the wavefront map is explained mathematically in three dimensions with polynomial functions. It turns out that most investigators have chosen the Zernike method for this analysis although Taylor series can be used. 8 The ray points described by Zernike Polynomials are used to obtain a best-fit toric to compensate for the refractive error of Contents the eye. The points are described in the x and y coordinates and the third dimension, height, Section 1 is described in the z-axis. The first order polynomial describes the spherical error or power Section 2 of the eye. The second order polynomial deSection 3 scribes the regular astigmatic component and its orientation or axis of the standard refrac- Section 4 tion clinicians are accustomed to obtaining. Third order aberrations are considered to be Section 5 coma and fourth order aberrations are consid- Section 6 ered to be spherical aberration. Zernike polynomial descriptions for wavefront analysis Section 7 typically go up to the tenth order of expression. A normal straight curve would have Subjects Index two orders, first and second, to describe its morphology. As one adds more local maximum and minimum points more or higher orders of the polynomial series are required to describe the surface. The power of wavefront analysis is the fact that it can deHelp ? scribe these other aberrations within the optical system that to date have only been explained as “ irregular astigmatism “ and treated with a rigid contact lens.
Figures 34-8 A-B. Note in figure A ( left ) that the central dots are relatively regular in size and alignment in the horizontal and vertical axis. In figure B ( right ) note the loss of dots centrally “ moth-eaten “ and the overall irregularity of horizontal and vertical alignment of the spots of this eye with significant aberration.
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Contents Figure 34-9. Optical effects of tear film disruption. The upper row of images was captured immediately after a blink; the bottom row of images was obtained after the subject had held his lids open for about 40 seconds. Left column contains images obtained by retroillumination of the pupil; middle column shows the data images captured by the SH aberrometer; right column shows contour maps of the aberrated wavefront emerging from the eye computed from the SH data image. Contour intervals in the reconstructed wavefront are 1 micron and the wavefront phase at pupil center has been set to zero. Pupil coordinates are in millimeters. (Figure courtesy of the American Academy of Optometry - Thibos LN, Hong X. Clinical applications of the ShackHartmann Aberrometer. Optom Vis Sci 1999;76:817-825.) 7
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What are the Shortcomings of ShackHartmann Wavefront Analysis? Tear film abnormalities can significantly affect the quality of wavefront analysis. This can be to such a degree that Thibon and Hong have suggested that wavefront analysis via the Shack-Hartmann method may be useful in future investigations of the tear film and the dry eye syndrome. 7 So, even though the cornea proper and all optical elements behind it in the optical pathway are normal, an irregular tear film will provide data suggesting significant wavefront aberration. See Figure 34-9. Opaque opacities are also poorly defined by the current Shack-Hartmann like devices. This is
likely do to complete light scatter and the inability of Subjects Index the source testing light to reach the retina and reflect back let alone get back to the CCD video camera. Eyes with marked aberrations may be virtually impossible to obtain a measurement such as scars or keratoconus. In addition, eyes with relatively miotic pupils may be very hard to measure and require Help ? pharmaceutical dilation (See Figures 34-10 & 34-11). While current devices appear to work extremely well with normal eyes and eyes with mild to marked aberrations, there is room for improvement in measuring eyes with marked aberrations. In addition, Thibon and Hong have recommend that light scatter needs to be incorporated into our optical model of the eye to fully account for the optical imperfections of specific eyes such as keratoconics. 7
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Reproducibility and Effect of Pupil Size
Figure 34-10. The above three contour maps show that wavefront measurements can demonstrate consistent results through time. It is important to understand that the tear film is an ever changing structure and the contour maps will thus change accordingly.
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Figure 34-11. The observed map and data can also vary depending on the size of the pupil in which the study is carried out. In the accompanying figure the same examination at varying pupil sizes demonstrates the contour changes within the defined three and seven millimeter apertures.
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There appear to be at least three junctures where the best realization for exquisite unaided acu- Section 6 ities may possibly be constrained: visual cortex, retina proper and the spectacle, corneal, or implant Section 7 level. Will clinical or subclinical amblyopia dilute Subjects Index our results? Will all maculas be able to support 20/10 vision? Do all maculae have the optimal orientation of cone receptors or Stiles-Crawford profile or even sufficient cone density to support “super vision “. Can we as clinicians create the “ perfectly adapted optic “ be it spectacle or corneal or implant surgical technique to neutralize the pre-existing abHelp ? normal wavefront? It is also very important to remember that as we currently understand and work with wavefront sensing technology it may not in most cases define the exact locale of the pathology causing the aberration: hence, clinical examination and other refractive tools, such as corneal topographic mapping, along with sound clinical judgment will be required for proper understanding of the eye and its individual refractive status.
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Clinical Examples Case 1. Keratoconus Visual acuity map of a 45 year-old keratoconic patient without RGP in place (left slide) and with RGP in place (right slide). Left Acuity Map: Note 46 micron scaling range of the left map. The higher order aberration map does show the area of cone (red, lower right quadrant). The numerous contour lines in this locale describe the intensity of the aberration. Areas of red depict areas where the light travel along the optical pathway is ahead of the reference plane (traveling through thinner areas of tissue or shorter distance) and blue areas depict Contents
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areas where light travel along the optical pathway is behind or latent from the reference plane (traveling through thicker areas of tissue or longer distance). This patients measured acuity via wavefront is –5.4 - 1.8 x 000. Manual refraction was –4.75 – 1.25 x 170 for 20/40- best spectacle corrected acuity. Autorefraction was –5.5 – 2.75 x 175. Manual keratometry was 43.5 @ 175 / 44.75 @ 085 with 1 + mire distortion. Autokeratometry was 43.75 @ 007 / 46.00 @ 097.
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Note that on the right slide most of the higher order aberrations appear to disappear. In some keratoconics a measurement can not be made unless an RGP is placed over the eye as described by Thibon and Hong. 7 In this situation, it is hopeful that future versions of the wavefront device will be able to image even the most irregular surface contours. For comparison sake a Humphrey Atlas Topography has been included (lower figure).
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Case 2. Status of Post Radial Keratotomy Left eye of 50 year-old female who was 6 years s/p four cut radial keratotomy. She has residual wavefront defined refractive error of –0.3 – 0.7 x 011. Her autorefractometer and autokeratometer readings were –0.75 – 0.5 x 015 and 42.75 @ 136 / 43.25 @ 046, respectively. Manifest refraction revealed –0.25 – 0.75 x 007. Manual keratometry revealed 42.5 @ 178 / 43.12 @ 088
with no distortion. Note her higher order map displays numerous contour changes centrally describing higher order aberration but the scaling of this map is 3 microns with the bulk of the map from 0 to +1.5 microns centrally. Compare the Humphrey Irregularity / Wavefront Map ( Upper Map, Right Image ) to the Visx 20/10 Map. She had no subjective visual complaints.
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Case 3. Posterior Subcapsular Cataract and Anterior Cortical Cataract Sixty –seven year-old female with night glare symptoms from cataract. Best spectacle corrected vision is 20/25 O.S. and Potential Acuity Measures 20/20. Uncorrected distance vision is 20/40. Manifest refraction is +1.25 – 0.5 x 149. Wavefront refraction was + 4.3 –1.6 x 020. Autokeratometry measurements were 44.00 @ 031 / 44.25 @ 121. The SH data image clearly outlines the morphology of the posterior subcapsular cataract in the central region. Significant higher order aberrations are noted on the lower right quadrant of
the higher order aberration map (slide right) consistent with anterior subcapsular / cortical changes. If one looks back at the SH data image there are no light points for these corresponding areas. This incongruity amplifies the importance of comparing the raw data image to the color coded map and making a clinical correlate with direct visualization of the anatomical structure, in this case the posterior crystalline lens (PSC) and anterior crystalline (anterior cortical spoking).
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Case 4. Unoperated “ Normal “ Eyes Thirty year-old male with no prior ocular history or surgery. Uncorrected acuities were 20/20- O. D and 20/20 O.S. Autorefraction was +0.50 - 0.25 x 006 O.D. and +1.0 - 0.25 x 141 O.S. Autokeratometry was 43.50 @ 164 / 43.75 @ 074 O.D. and 43.25 @ 145 / 44.00 @ 055 O.S. Wavefront refraction was +1.2 – 0.2 x 132 O.D. and +1.3 –0.3 x 131 O.S. Manifest refraction was +1.0 sphere for 20/20- best spectacle correction O.D. and + 1.75 - 0.5 x 136 for 20/20 best spectacle
correction O.S. The Visual Acuity Maps show some higher order aberrations inferiorly in both eyes but observe that the scaling range is 2 microns. Corneal topographies are given below for comparison. Note comparison of the upper right irregularity map from Humphrey Topography with wavefront scaling with the Visx 20/10 Perfect Vision Acuity Map for each eye. (See two additional maps of this case in next page).
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Case 4. Unoperated “ Normal “ Eyes (Cont.)
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Case 5. Status of Post Penetrating Keratoplasty for Keratoconus Forty-five year-old male who was 19 months s/p PKP for keratoconus. Sutures were removed at 12 months. Wavefront refraction was – 7.5 – 0.4 x 125. Autorefraction and autokeratometry were –8.75 – 0.75 x 127 and 46.00 @ 126 / 46.75 @ 036, respectively. Manifest refraction was – 7.50 –1.00 x 070 with best spectacle corrected vision of
20/20. Manual keratometry was 45.75 @ 100 / 46.5 @ 010 with 1+ mire distortion. Higher order aberrations appear to be present on the right higher order acuity map but the scaling range is 1 micron. With trial frame lenses he stated excellent subjective quality of vision.
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Case 6. Irregular Lasik Ablation Twenty-six year-old man who complains of blurred vision after myopic lasik of his left eye. It is the surgeon’s (JFD) opinion that fluid masked the ablation in the supero-temporal quadrant. The fluid accumulated unbeknownst to the surgeon at the time of the case and retrospectively is the most likely source of this patient’s irregular pattern. Un-
corrected vision was 20/15 O.D. and 20/30+ O.S. Autorefraction O.S. was + 0.75 – 0.25 x 054. Manifest refraction O.S. was + 3.25 - 1.50 x 031 for 20/15 best spectacle corrected vision. Wavefront refraction O.S. was –0.7 sphere. Autokeratometry O.S. was 37.25 @ 097 / 38.00 @ 007.
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Case 7. Normal Examination / No Refractive Error Thirty year-old female with no subjective complaints and no ocular or surgical history. Uncorrected acuity was 20/15 in each eye. Manifest refraction was plano sphere O.D. for 20/15 best spectacle corrected acuity and + 0.25 – 0.25 x 180 for 20/15 best spectacle corrected acuity. Wavefront refraction was –0.2 – 0.6 x 092 O.D.
and + 0.1 – 0.4 x 058. Autokeratometry was 43.25 @ 099 / 43.5 @ 009 O.D. and 43.5 @ 046 / 43.75 @ 136 O. S. and manual keratometry was 43.25 @ 177 / 43.5 @ 187 O.D. and 43.37 @ 177 / 43.75 @ 187 O.S. Humphrey topography provided for comparison (See two additional topographies of this case in next page).
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Case 7. Normal Examination / No Refractive Error (Cont.)
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Case 8. Status Post Hyperopic Lasik This forty year-old female underwent uneventful lasik for + 4.75 – 0.75 x 090 which was followed by enhancement for a residual refractive error of + 2.75 – 1.25 x 065. Her best spectacle corrected vision preoperatively was 20/20-0. Manifest refraction at time of wavefront analysis was +0.75 – 0.5 x 105 for 20/30+1 best spectacle corrected vision. Autorefraction was + 3.0 – 0.5 x 100. Wavefront refraction was + 2.7 – 0.3 x 104.
Autokeratometry was 46.0 @ 154 / 48.0 @ 064. The patient felt her vision in the left eye was not as “ crisp “ as she would desire. Note the eccentricity of the left contour image and its significant large scaling range of 19 microns and the aberration on the higher order map with a scaling range of 5 microns. There is significant higher order aberration for this eye. The Humphrey Atlas topography map is displayed for comparison.
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Case 9. Status Post Myopic Lasik Fifty-one year-old male optometrist who underwent bilateral myopic astigmatic lasik. He has no unwanted subjective visual symptoms and is very happy with his postoperative status monocularly and binocularly. Preoperative refraction of the left eye was – 4.0 – 2.0 x 176 for 20/15 best spectacle corrected vision. Target refraction was –1.87 – 0.25 x 176 for monovision. Uncorrected distance vision in the left eye was 20/80 and near vision was J-1+. Manifest refraction was – 1.63 – 0.5 x 160 for 20/15 best spectacle corrected
acuity. Autorefraction was –2.25 – 1.0 x 177 and wavefront refraction was –1.7 – 1.1 x 011. Manual keratometry was 38.25 @ 005 / 39.12 @ 095 and autokeratometry was 38.25 @ 174 / 39.75 @ 084. The left visual acuity map has a scaling range of 28 microns and the higher order map has a scaling range of 3 microns. Note on the left acuity map what appears to be with-the-rule astigmatism. Thibos and Hong 7 have shown an increase in higher order aberrations specifically spherical aberration after myopic lasik. The following comparison below nicely displays this finding.(Cont. in next page)
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Case 9. Status Post Myopic Lasik (Cont.) Normal eye the day before and the day after myopic lasik. Upper row shows pupil phase maps (contour maps analogous to Visx 20/10 Perfect Vision Acuity Maps), lower row shows the distribution of wavefront error by Zernike order. To emphasize the change in higher order aberrations, the residual spherocylindrical refractive er-
rors were omitted from the analysis. Note the significant increase of 3rd, 4th orders along with increase in 5th –10th orders. (Figure courtesy American Academy of Optometry - Thibos LN, Hong X. Clinical applications of the Shack-Hartmann Aberrometer. Optom Vis Sci 1999;76:817-825.)7
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Case 10. Normal Examination - Minimal Refractive Error Thirty-one year-old female with no subjective complaints and no ocular or surgical history. She has no contact lens history. Uncorrected acuities were 20/20- O.D. and 20/20 O.S. Manifest refraction was +0.25 – 1.25 x 105 O.D. for 20/15 best spectacle corrected vision and – 1.0 sphere for 20/20+ best spectacle corrected vision O.S. Wavefront refraction was + 0.7 – 1.8 x 101 O.D. and –0.7 sphere O.S. Manual keratometry
was 41.37 @ 000 / 42.12 @ 090 O.D. and 41.37 @ 000 / 41.50 @ 090 O.S. and autokeratometry was 41.25 @ 090 / 41.37 @ 180 O.D. and 41.00 @ 022 / 41.50 @ 112 O.S. The acuity map of the right eye shows the against- the- rule astigmatism pattern nicely corresponding with the plus cylinder manifest steep axis of 015. This can be appreciated by knowing the red color scheme peripherally at 015 (Cont. in next page)
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Case 10. Normal Examination / Minimal Refractive Error (Cont.) and 195 meridia reflects the wavefront being ahead of the reference plane and the 105 and 285 meridia wavefront shaded in blue lagging behind the reference plane. This accurately describes the wavefront emerging sooner from the steep or recessed horizontal axis peripherally and emerging latter from the flat or protruding vertical axis peripherally. The acuity map of the left eye reveals a relatively spheri-
cal eye. The higher order map has a relatively narrow scaling of 3 microns with the contour changes noted between 0 and – 1.5 microns inferiorly. No clinical correlate could be made to this except for the outside possibility of tear film abnormality at the time of the test. No SH data image was available for assessment. Humphrey topographies provided for comparison.
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REFERENCES 1. Liang J, Grimm B, Goelz S, Bille JF. Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor. J Opt Soc Am A 1994;11:1949-57. 2. Optics, Refraction, and Contact Lenses, Basic and Clinical Science Course, American Academy of Ophthalmology, 1993-4, p.p. 94-7. 3. Records RE, Brown JL. Visual Acuity, Contour Resolution, and Temporal Charachteristics of the Visual System. In Biomedical Foundation of Ophthalmology, Vol. 2, Chapter 17.
Wave Front Analysis - Clinical Primer John F. Doane, M.D.1 Scot Morris, O.D.1 Andrea D. Border, O.D. 1 Lon S. EuDaly, O.D.1 James A. Denning, B.A., B.S.1 Louis E. Probst MD2 1
Discover Vision Centers Kansas City, Missouri, U.S.A. 2
Medical Director TLC The Laser Eye Centers, USA
4. Dougherty PJ, Wellish KL, Maloney RK. Excimer laser ablation rate and corneal hydration. Am J Ophthalmol. 1994;118:169-76.
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5. Customized Ablations: The Future is Close. Medical Laser Report 2000; January;3-6.
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6. Webb R, Penny CM, Thompson K. Measurement of ocular local wavefront distortion with a spatially resolved refractometer. Appl Opt 1992;31:3678-86.
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Section 5 7. Thibos LN, Hong X. Clinical applications of the Shack Hartmann Aberrometer. Optom Vis Sci 1999; 76:817-825.
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8. Oshika T, Klyce SD, Applegate RA, Howland HC, El Danasoury MA. Comparison of Corneal Wavefront Aberrations after Photorefractive Keratectomy and Laser in situ Keratomileusis. Am J Ophthalmol 1999; 127:1-7.
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The authors would like to thank Greg Halstead, Thomas McKay and Kevin Tausend of Visx, Inc., Santa Clara, California, for their technical support and encouragement in this manuscript.
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ZYOPTIX - PERSONALIZED LASER VISION CORRECTION
Chapter 35 ZYOPTIX PERSONALIZED LASER VISION CORRECTION Jaime R. Martiz, M.D., Stephen G. Slade, M.D.
To date, LASIK surgery is accomplished through a set of algorithms or mathematic formulas that are pre-programmed into the laser’s computer. These formulas are based on the standard refractive errors usually originate in patients undergoing LASIK surgery. They have been provided in a non-customized approach. Laser surgery using these standard formulas produce remarkable results in a large number of patients. Pre-operative diagnostics, including topography, are routinely performed, but an analysis of the eye’s entire optical system was not available. The Bausch & Lomb Zyoptix system for the Technolas 217 laser can customize LASIK for each patient. Like matching a fingerprint, it provides a distinctive laser treatment plan for each eye to potentially reach better visual results than before in a safer process. Zywave is a distinct approach of looking at the eye. The information collect by this system is shared with that of corneal mapping system Orbscan II. With this entire information of the eye’s optical system, surgeons could plan personalized treatments for their patients rather than rely upon the basic laser algorithms or mathematic formulas.
PERFORMING ZYOPTIX TREATMENT For Zyoptix treatment to be performed, there are several hardware and software requirements (Table 1). A- Orbscan II multidimensional diagnostic system that collect 9000 data points in 1.5 seconds and bring corneal mapping technologies (Figure 35-1). B- Zywave diagnostic device designed to identify abnormalities throughout the entire optical system with the use of wavefront technology (Figure 35-2). C- Zylink is use to generate an optimal treatment (Figure 35-3).
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TABLE 1. REQUIREMENT FOR ZYOPTIX
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TREATMENT Orbscan IIz Zywave aberrometer Zylink Technolas 217z
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The Zywave Aberrometer The Zywave is a Bausch & Lomb’s diagnostic device designed to identify abnormalities throughout the entire optical system with the use of wavefront technology. The Zywave directs a beam of light into the eye that is then reflected off the retina to identify abnormalities. In eyes where there is an abnormality, the measurement of the variations between the actual direction of the beams of the outgoing beam of light, and their optimal positions, will determine the overall aberration of the eye.
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Section 3 Figure 35-1: Orbscan II multidimensional diagnostic system. Figure 35-2: Zywave diagnostic device.
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D- Bausch & Lomb Technolas 217z laser with an active eye tracking system utilizes a 2-mm and 1-mm flying spot beam. The Soft spot system allow the surgeon to eliminate most of the tissue with 2 mm laser beam, and then use the 1 mm beam to treat higher-order aberration and “polish up” the ablation (Figure 35-4).
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Orbscan II The Orbscan II is a multi-dimensional diagnostic system that enables eye surgeons to map both the anterior and posterior surface of the cornea. By mapping the entire corneal surface, the surgeon can detect any corneal imperfections in elevation or curvature that might impact the expected surgical results.
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Section 4 Figure 35-3: Zylink feasibility study to generate an optimal treatment.
Section 5 Figure 35-4: Bausch & Lomb Technolas 217z laser.
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Bausch & Lomb Technolas 217z Excimer Laser
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Using a scanning and flying spot technology, the Technolas 217z, allows surgeons to treat to treat up to -12.00 diopters of nearsightedness, up to +6.00 diopters of farsightedness and up to 5.00 diopters of astigmatism. Technolas 217z combines the advantages of common beam shapes, the flap top and the Gaussian beam to produce a Truncate Gaussian Beam Shape (Figure 35-5).
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Flat top Advantage: the energy level is constant across the whole surface and superior to the threshold value for cold ablation
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Gaussian Beam Advantage: provides a smooth surface. Disadvantage: creation of thermal effect due to a reduction in the energy level below the threshold value required for cold ablation. The Truncated Gaussian Beam Shape maximizes the smoothness and minimizes the thermal ef-
fect of cornea, resulting in reduction of ablation depth and enhancement rate. Also, this system increases visual acuity, treat larger optical zones to reduce “Halos”, and produce smother corneal surface to reduce “Glare”.
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Section 1 Figure 35-5: Technolas 217z combines the advantages of common beam shapes, the flap top and the Gaussian beam to produce a Truncate Gaussian Beam Shape.
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TABLE 2. TECHNOLAS 217z SPECIFICATIONS Homogenization Pulse Rate Beam Shaping Beam Size Zyoptix Energy/Pulse Energy/Pulse at laser head output Acoustic Shock Ablation Zone Transition Zone Fluence Adjustable Transition Zone Tracking System Eye Fixation Hyperopic & Cylinder Tx Limits to Tracker Card Gases Required Gas Fill Quantity Cooling System
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Optical integrator 50 Hz Quartz for 2mm +1 mm Truncated Gaussian 2 mm = 1 mm Truncated Gaussian Combine wavefront & multi 3D mapping 200-400 mJ 3.7 mJ Moderate 15 mm x 15 mm 2.6 mm – 7.2 mm 120 mJ/cm2 Optimized Active and Passive Constant Yes 120 Hz Card Positioning Robot 3 cylinder ArF pre-mix 2-3 days/20 liters Internal H2O Cooled
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Conclusions Zyoptix system is designed to enable surgeons to correct or reduce refractive errors with the possibility to improve the visual performance of the eye, reduce the potential for glare and halo by using wider optical zones. Also reduce invasive treatment depths and the number of re-treatments by possibly helping patients achieves their desired outcome with primary treatments. Excimer laser custom ablation technology is not just another passing fashion; the technology could improve LASIK results, allowing for improved postoperative visual acuity and superior vision under low light environment. A lot of the inconsistency in outcome is caused by refraction measurement errors,
Fig. 35-6
which wavefront sensors eliminate. This system could obtain 0.1 D of the intended refraction rather than within the standard 0.5 D. Therefore, the wavefront technology will progressively move the “bar up” for what is considered successful LASIK surgery.
Zyoptix Patient Case Figures 35-6 and 35-7 show preoperative wavefront including all aberrations. The patient had a refraction of –6.75 –0.25 x 150o and a BCVA of 0.8. Figures 35-8 and 35-9 show preoperative wavefront including only High order aberrations on the same patient. Contents
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Figures 35-6 and 35-7: preoperative wavefront including all aberrations.
Fig. 35-8
Fig. 35-9
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Figures 35-8 and 35-9: preoperative wavefront including only High order aberrations on the same patient.
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Figures 35-10 and 35-11 shows a change in the high order aberrations by Zyoptix. Patient Postoperative refraction was 0.00 –0.25 x 150o, UCVA improve to 1.2 and BCVA was 1.4. Figures 35-12 and 35-13 show preoperative versus postoperative wavefront deformation.
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Chapter 36 ZYOPTIX Andreu Coret, M.D., Jordi Gatell, M.D., Elvira Lara, M.D.
Introduction Zyoptix is the new generation of excimer lasers used for the treatment of refractive disorders. Nowadays, we are treating the refractive disorders with standard treatments, only having in mind the subjective refraction. However with such a technique, it is not always possible to achieve the previous best corrected visual acuity. Zyoptix’s technique takes into account the patient’s subjective refraction, ocular optical aberrations and corneal topography, with the latter not only for the diagnosis, but also for the therapeutic
treatment, in order to design a personalized treatment based on the total structure of the eye. (Figures 36-1a and 36-1b)
PREOPERATIVE PROCEDURE
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There are several differences between a Zyoptix and a LASIK procedure. Although the laser step is more or less the same, what is more complicated, delicate and long-lasting is gathering all the data we need to manage when deciding the best treatment before performing a Zyoptix session. The step by step the procedure is as follows:
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Figure 36-1a: Zyoptix procedure
Figure 36-1b: The approach to Zyoptix
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Refractive Exam First of all we have to get the patient’s visual acuity, uncorrected and corrected, as well as his subjective refraction, undilated and with cycloplejic.
Zywave Aberrometer Optical Aberrations All through the study of the human eye, optical aberrations have been attracting a continuous interest. In the beginning, some systems based on subjective ray tracing were developed, like the Foucault test and modified aberroscopes.(1-4) Further on, an objective wavefront sensor was developed: the Hartmann-Shack wavefront sensor.(5) Zywave is an advanced wave-front sensor based on the Hartmann-Shack principle that provide us with a precise and fast test of the aberrations of the eye. To understand how the Zywave works, we should know something about the optical aberrations of the eye and its influence on retinal image quality. Optical aberrations can be divided into chromatic aberrations and monochromatic aberrations.(6)
Chromatic Aberration: Lenses bring different colors of light to a focus at different points. Monochromatic Aberrations Spherical aberration: A spherical lens does not focus paralel rays to a point, but along a line. In this way, off-axis rays are brought to a focus closer to the lens than are on-axis rays. This is also applicable to spherical mirrors. Astigmatism: A lens has different focal lenghts for rays of different orientations, resulting in a distortion of the image. Rays of light from the different meridians in a plane of the object are not focused to the same plane on the edges of the image.
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Coma: Off-axis rays do not quite converge at the focal plane. Coma is positive when off-axis rays focus furthest from the axis, and negative when they are closest. Distortion: The transverse magnification may be a function of the off-axis image distance. It can be positive (pin-cushion), or negative (barrel). Field curvature (Petzval field curvature): It is caused because the focal plane is actually not planar, but spherical. To know how these different aberrations have an effect on the eye one must have in mind two important terms: the Zernike polynomials and the Point Spread Function. The Zernike polynomials are a widely used method in optics to describe wavefront aberrations.(7) The aberration function ___n__m __is expanded as follows :
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c
___n,m)= __ ___abcA Z (_nm,_nm) a,b?0,c a-/c/even
ac
b
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where __abc refers to the maximal optical path differ- Section 5 ence of the lens mesured in units of wavelenght, while Section 6 the factor Aac is determined by the object location (rocos _o, ro sin _o) and the orientation of the inci- Section 7 dent wavevector is given by the polar coordinates Subjects Index (_nm , _nm). We can descompose eye’s aberrations into Zernike polynomials up to tenth order.(7,8) The firstorder Zernike modes are the linear terms (corresponding to tilt). The second-order modes correspondes to the familiar aberrations, defocus and astigmatism. The third-order modes represents coma aberrations. Help ? The fourth-order contains spherical aberrations and other modes. The fifth to tenth-orders are the higherorder, irregular aberrations (they include trifoil, tetrafoil,...) (Fig. 36-2). It has been proved that aberrations corresponding to fifth to tenth orders do not play a significant role in image quality, mainly for small pupils.(8)
ZYOPTIX
But, how can the retinal image quality be represented? How can we know the degree of degradation? Human eyes are not perfect optical systems. As a result when visual stimuli are passed through the optic elements of the eye, they suffer a certain degree of degradation.(8) If we have a very small dot of light and project it through a lens, the image of this point will be not the same as the original: the lens introduces a small amount of blur. The Point Spread Function (PSF) is the squared amplitude of the Fourier transform of the Generalized Pupil Function of the displayed wave aberration function. The ratio of the values of PSF is called Strehl ratio, and it
is a tool that can provide information about “image quality”.
Basis and Usefulness As we explained before, Zywave is based on a Hartmann-Shack wavefront sensor. It is composed by a laser beam, and a junction of lenses and some elements (collimators, diaphragms, lights) that focus the light on the retina. On the emerging path, it has an array of spherical lenslets and a CCD camera (Figure 36-3).
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Fig. 36-2: Zernike description of eye’s aberrations.(8) It describes the different types of aberrations in the human eye.
Fig. 36-3. Schematic diagram of an experimental setup. It shows the light pathway from the laser source to the CCD camera.(5)
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Zywave projects the laser beam into the eye and use the diffuse reflection from the retina (Figure 36-4). The reflected light passes through the eye and then passes through the array of spherical lenslets that divides the tested wavefront into a number of subapertures. The light through each subaperture is brought to a focus in the focal plane of the lens array. If we do the test of an ideal plane wave it will result in a regular array of focus spots (Figure 36-5). Then, we use this pattern of a plane wave as a reference pattern. If a deformed wavefront is measured, the image spot at each subaperture shifts with respect to the corresponding point in the reference pattern.(5) The tested wavefront can be detected by measuring the shift of the focus spots.
When we measure the wavefront emerging from the eye we find a distorted wavefront, (Figures 36-6a and 36-6b) that is due to the ocular aberrations. The image of the wavefront is captured by the CCD camera (Figure 36-7a). The shift with respect to the reference pattern is analysed by the Zernike polynomials. Then Zywave shows in the computer screen the image spots, as well as diferent aberration maps. Ocular aberrations are represented in 2 maps, one of them shows us the astigmatic aberration and the other one the high-order aberrations. To allow an easier interpretation, the PSF is also showed. Therefore, you can know how much optical aberrations affect this eye. The program also makes a comparison between predicted PSF if we treat this eye with refractive surgery with a standard laser or if we do it with the Zyoptix laser. (Figure 36-8b) Contents
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Section 6 Section 7 Subjects Index Figure 36-4: Zywave projects the laser beam into the eye and use the diffuse reflection from the retina.
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Figure 36-5: Plane wavefront will result in a regular array of focus spots reflecting from the retina.
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Figure 36-6a: Distorted wavefront when measuring the wavefront emerging from the eye.
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Section 6 Figure 36-6b: Distorted wavefront emerging from the eye due to the ocular aberrations.
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Figure 36-7a: Image of the wavefront captured by a CCD camera.
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Is important to know that for the same eye (as well as for any optical system), the mesured wavefront will change with the size of the pupil. The bigger the pupil is, the more distorted the
wavefront.(5,7,8) It is due to an increase of the aberrations in the peripheral zones of the optical systems. (Figure 36-7b).
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Section 5 Figure 36-7b: Calculated wavefront deformation measuring the aspheric wavefront aberrations.
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Zywave Procedure Phoropter Predicted Refraction (PPR) This is the refraction given by the aberrometer. It is important to know that this refraction is not the one to be corrected, but just a tool to correlate subjective refraction got by the phoropter and the aberrometric refraction (obtained by the wave front) which is going to be used by the Zylink in order to calculate the more suitable treatment for each patient. What we have to do is to seat the patient in front of the aberrometer (Figure 36-8a) and switch off any source of light in order to get a more trust-
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able aberrations acquisition. So, we have to take three samples undilated, then three samples dilated just with fenilefrin drops in order to avoid any aberration induced by cycloplegic effect. Afterwards we take three samples with cycloplegic just to compare the results obtained by the three methods. After this, we choose one of the measures obtained just with fenilefrin drops. If they are not similar we calculate the spherical equivalent choosing the more similar to the spherical equivalent of the phoropter refraction. We do not use the cycloplegic PPR refraction because these drops can induce some new aberrations when dilating that would be taken into account in the treatment although they do not really exist.
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Figure 36-8a: Aberrometer system. The patient is seated in a dark room in front of the beam aperture.
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Figure 36-8b: The softwave program makes a comparison between a standard laser. The point spread function for the image quality.
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Elevation Topography (Orbscan) (Figure 36-9) What we should focus on in the orbscan is: -Anterior corneal shape (to leave aside keratoconus and other pathology) -Posterior corneal shape (to leave aside frustre keratoconus ) -Paquimetry -Kappa angle. This can suggest us to decentre a little bit the eyetracker when performing the laser session. -Others: -Thinnest point. - Keratometric map. - Pupillometry
Figure 36-10: Integral refractive workstation
Other Exams we Perform Rutinely are: -Curvature topography. -Ultrasonic paquimetry. -Pupilar scotopic diameter (colvard) -Biomicroscopy -Intraocular pressure -Complete retinal exam
Figure 36-9: Elevation map performed by the Orbscan topography unit.
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Zylink (Figure 36-11)
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Once we have collected all the data we need, Section 4 we introduce them in an special software called Zylink which is used to calculate the final treatment Section 5 we will order the laser to execute. Zylink requires the PPR and the orbscan Section 6 data, and then it automatically, after mixing both, Section 7 gives you the exact refraction to perform. There are two parameters you can vary ac- Subjects Index cording to the patient characteristics which are the optical zone and the ablation. The Zylink recommends an optical zone and a depth of ablation, but you can enlarge the optical zone as much as you want according to the scotopic pupil diameter so as to reduce to the maximum the risk of halos and glare post Help ? lasik.
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Figure 36-11: Zylink software used to calculate the final treatment.
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The bigger the optical zone, the higher ablation it will do, so we must take care of the paquimetry, not to leave a residual stroma thinner than 225 microns, if so the risk of ectasias is so high (Figure 36-12). Another interesting and useful aspect of the Zylink is that it shows you the Point Spread Function (PSF). This is in a few words the image projected on the retina of a single remote point (e.g. a star in the sky). The perfect PSF would be a single and sharp point. What Zylink shows you is the actual PSF without correction in the right of the screen,
the predicted PSF if we use a Planoscan laser in the middle, and the predicted PSF if performing a Zyoptix (refer to figure 36-8b). This way you can compare the predicted results, and it helps you decide whether Zyoptix would really be useful for the selected patient or not. If there is a large difference between the PSF with Planoscan and the PSF with Zyoptics in favour of it (smaller PSF), we can conclude that the latter is worth doing. The other way round we may choose the technique we feel more comfortable. (Figure 36-13).
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Figure 36-12: Zywave features displaying integral parameters during laser ablation.
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Section 5 Figure 36-13: High order aberrations with astigmatic component. Comparison between Zyoptix and standard laser treatment.
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PREPARING THE LASER The next step is transferring the final refraction given by the Zylink to the laser (Keracor 217 Z). We do so by a diskette of 3.5”. After saving all the data from the Zylink in it, we introduce it to the laser. (Figure 36-10).
Another aspect that makes Zyoptics different is the need of a special card to be introduced inside the laser for any eye we treat. Without this card you cannot perform the laser because the laser beam has to pass through it to be effective. Every card has three holes, two of them are of 2 mm diameter, one for the truncated gaussian beam which is used to do the treatment, and the other one is for the flat top beam which is used for the fluence test. The third
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hole is 1 mm diameter and it is also for a truncated gaussian beam, not to treat, but to smooth the surface (Figure 36-14). The problem of the flat top beam is that ablates more than necessary and that cannot make uniform and smooth ablations. Otherwise, the gaussian beam defect is that the periphery of the beam has just a thermal effect due to its low energy level.
Its ablation does not have any refractive effect, so it is unnecessary. (Figures 36-15 and 36-16) What we have achieved with the truncated gaussian beam is to ablate just what has a real refractive effect, with no thermal effect, and succeed in having a smooth and uniform ablation with an ideal transition area.
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Section 1 Figure 36-15: Maximized smoothness and minimized thermal effect.
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Figure 36-16: Advantages of the Gaussian Beam Shape.
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TREATMENT The surgical technique is absolutely the same as a standard LASIK, the only difference is the way the laser ablates the cornea. First of all, a truncated gaussian beam of 2 mm diameter is used to do the most part of the treatment. Afterwards it automatically changes into the spot of 1 mm, also with a truncated gaussian beam, in orther to smooth the cornea and make irregularities disappear. After this the treatment is finished.
ADVANTAGES 1-Personalized ablation: It does not ablate in an standard pattern, but specifically in every area just to correct the aberrations beyond the cornea. So, some areas will be more ablated than others, and this way it helps to preserve corneal tissue. With today’s lasers we are ablating homogeneously, taking out more tissue than necessary in some areas, and without correcting the existing aberrations, leading to a not as good quality of vision. 2-Less ablation: It is possible because of the specific ablation, just ablating the necessary tissue in each area, not ablating tissue if it is not going to produce a refractive effect. It enables us to include patients in our Zyoptic sessions that could not have been operated by a conventional LASIK. It ablates 15% - 20% less of corneal tissue.
3-Larger optical zones: You can do an optical zone as big as you want according to the pachimetry and pupillometry. 4-Smoother corneal surface: Reducing glare 5-In the next future it will be possible to achieve a visual acuity better than 20/20 if we can correct the most important aberrations of the eye.
DISADVANTAGES There are no real disadvantages compared with a common LASIK,but there are some questions that should be solved. One to be commented is that the aberrometer calculates the eye aberrations as a whole. This can be a problem when there is an aberration change in just one part of the eye, as it will happen when this young people who are now being treated with Zyoptix get older, develop a cataract and will be phacoemulsificated and endowed with an intraocular lens. The lens aberrations will disappear, but their correction in the cornea will remain. What is going to happen? We still do not know the answer. Maybe we will have to do an ablation topographically guided, another Zyoptix or even a simple LASIK to correct the possible residual ametropy. Unfortunately we are still far from the answer to these questions.
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CLINICAL CASES
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Examples of clinical cases are shown in: (Figures 36-17a, 36-17b, 36-17c, 36-17d)
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Section 4 Figure 36-17a: Preoperative comparative topography in a myopic patient.
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Figure 36-17b: Postoperative topography 1 day after laser ablation.
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Section 3 Figure 36-17c: Postoperative topography 1 week after laser ablation.
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Figure 36-17d: Comparative results in the same patient between PlanoScan and Zyoptix.
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REFERENCES 1. W.M. Rosenblum and J.L. Christensen, “Objective and subjective spherical aberration mesurement of the human eye”, in Progress in Optics, E.Wolf, ed.(NorthHolland, Amsterdam, 1976), Vol. 13, pp. 69-91. 2. M.Campbell,E.Harrison,and P. Simonet”, Psychophysical measurement of blur on the retina due to optical aberrations of the eye”, Vision Res. 30, 1587-1602 (1990). 3. H. Howland and B.Howland “A subjective method for the measurement of monochromatic aberrations of the eye” J. Opt. Soc. Am 67, 1508-1518 (1977) 4. G. Walsh, W. M. Charman, and H. Howland “Objective technology for the determonation of monochromatic aberrations of the human eye” J. Opt. Soc. Am A1, 987-992 (1984) 5. J.Liang, B.Grimm,S.Goelz,and J.F. Bille “ Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor” J. Opt. Soc. Am 11, 1949 - 1957 (1994). 6. E. Hecht, A. Zajac, ”Optics” ed. Addison-Wesley Iberoamericana, (1986). 7. J. Y. Wang and D.E. Silva, “Wave-front Interpretation with Zernike polynomials. Applied Opt., vol.19, No 9 (1980). 8. J.Liang and D.R. Williams “ Aberrations and retinal image quality of the normal human eye” J. Opt. Soc. Am. vol 14, No 11, 2873-2883 (1997).
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Andreu Coret, M.D. Medical Director Instituto Oftalmológico de Barcelona Barcelona, Spain Help ?
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Chapter 37 LASIK – PALM IG Pallikaris MD, HS Ginis BSc, VJ Katsanevaki MD.
Introduction The PALM Technique is a method developed in the University of Crete for the correction of corneal surface irregularities. The PALM technique refers to corneal excimer laser phototherapeutic keratectomy through a gel used as masking agent. PALM technique can be either applied on the surface of the cornea or under a corneal flap. The basic principles of the PALM procedure as well as the special considerations related to application under a corneal flap are presented.
General Considerations Irregularities of the corneal surface can deteriorate vision quality by introducing refractive
variations across the optical zone. Such ocular optics are not effective in focusing light in a confined and symmetric retinal spot. Elevation differences within the cornea can be eliminated or reduced by selectively ablating the relatively elevated areas while preserving the depressed areas of the cornea. Smoothing agents, either molded in situ or self-shaped by surface tension, tend to form thinner films at the elevated parts of the cornea. During ablation, as modulator film is ablated, elevated areas are exposed to laser ablation before the depressed ones (figure 37-1AB). Laser ablation at the presence of a smoothing agent will smooth the cornea to some extent, depending on smoothing agent film properties. Ideally, the free surface of smoothing agent layer should have the desired shape of the cornea, which shape should be geometrically stable during ablation.
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Figure 37-1 AB: A) Schematic illustration of smoothing agent effect on a corneal surface having irregularities. B) Testing PALM gel ablation rate: Pig eyes received 60-microns of ablation at the presence of a stainless steel mesh in order to produce a periodic grid-like pattern on the corneal surface. A PALM lenticule was formed over this irregularity and half of the cornea was irradiated until gel was totally ablated.
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Smoothing agent material should have ablation rate equal to that of the treated cornea. Smoothing of the corneal surface with phototherapeutic keratectomy through a masking agent or a protective shield has been reported for the treatment of various types of corneal dystrophies, for recentering of prior eccentric ablations or as adjunct to photorefractive keratectomy[1-4].
The PALM Gel PALM gel consists of a mixture of porcine skin and vegetable gelatin. A small quantity of Sodium fluorescence is added to the gelatin solution in order to produce a colored gel. PALM gel biocompatibility was examined on rabbit corneas in a three-month follow-up
study carried out in the University of Crete. Light and transmission electron microscopy did not reveal differences of corneal ultra-structure between experimental (through PALM gel) and control specimens. PALM gel is fully thermoreversible. Being gel at room temperature, it transforms to a high viscosity liquid solution when heated. In this form it is applied onto the cornea. For gel temperature control a custom syringe heater is utilized (Figure 37-2). When still in liquid state, a customized rigid contact lens (Figure 37-3) is used to mold the lenticule’s upper surface. The total diameter of these lenses is of 7.4 mm having an optical zone of 6.8 mm and a transition zone of 0.3 mm. A carved mark on the lenses’ geometrical center ensures lens centration during the molding process. The radii of curvature available of the customized lenses used for the PALM technique vary from 7.0 mm to 10mm in steps of 0.1mm.
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Figure 37-2: Customized heater unit used in the PALM technique. The syringe heater contains ten heating elements (resistors) evenly distributed circumferentially around the syringe. A thermocouple tip is located about 1 mm from the syringe tip. Thermocouple output provides feedback for the temperature stabilizing circuit.
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Figure 37-3: PALM molding lenses are made of optical grade glass (BK7), which ensures geometrical stability over a wide temperature range as well as adequate heat conductivity to allow gel cooling in a reasonably short time interval. Flat edge permits use under a LASIK flap.
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The molding surface of each lens prior to use is covered with a thin PVC membrane. Membrane thickness is 10 ±1 microns. This membrane facilitates lens removal from the gel surface without exerting any deforming forces on the mold.
The selection of the lens to be used as mold for each case is based on the principle of best-fitted sphere of the operative cornea and is calculated by videokeratography based software program (Figure 37-4).
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Figure 37-4: Computer program that simulates the gel thickness distribution. Red areas correspond to thin parts of the lenticule while violet areas represent areas with maximal gel thickness. The color scale on the left of the topographic image shows the thickness values corresponding to the color-coded map. The small picture box on the right of the program window simulates the positioning of the lens in respect to the topography axis. Supports automatic selection of the best-fitted lens.
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The PALM Procedure The PALM technique can be applied either on deepithelized cornea or under a flap. LASIK advantages over PRK, favors the method for optimal results of the PALM technique concerning the management of prior eccentric ablations. Lifting of an initial flap, if possible would minimize the risk of using the keratome on a flat cornea. Superficial corneal irregularities such as corneal scars, can be treated after corneal deepithelization. After the exposure of the treated surface, the surgeon marks the optical axis asking the patient to fixate at the microscope light. One drop of preheated gel solution is applied on the stromal bed and the pre-selected lens is applied on the surface of the gel in a three-point alignment process. Proper positioning of the lens requires alignment of the central lens mark over the corneal mark, and the microscope light reflection from the anterior surface of the lens (Figure 37-5).
The lens as well as the PVC protecting membrane is carefully removed 4 minutes after application (when the gel has solidified) to expose a stable lenticule. An ArF Excimer laser system operating in phototherapeutic keratectomy (PTK) mode is utilized to ablate the lenticule. The colored gel is visually distinguishable from the cornea so as the ablation process is terminated when the modulator is thoroughly removed. The pattern of the removal of the lenticule during ablation should ideally apply to the preoperative elevation map of the cornea. Cornea is irrigated and any gel remnants are removed before flap is repositioned in place. A therapeutic contact lens is applied onto the operative eye in cases of reoperating under existing flaps. The PALM technique is currently under clinical trial in the University of Crete. Although initially developed for the management of eccentric ablations, the PALM technique is applied in selected cases according to a partial sighted eyes protocol for the correction of corneal surface irregularities as described above. Inclusion criteria of the protocol
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Figure 37-5: The three-point alignment process for the proper positioning of the lens onto the liquid gel.
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require irregular videokeratography pattern of the operative eye, spectacle corrected visual acuity 20/40 or worse, hard contact lens intolerance, free medical history with no known allergies to ophthalmic administered steroids or antibiotics and age over 18 years. [5]
Technical Development of PALM Technique. Theoretically, as already mentioned, the shape of the lenticule’s free surface will be reproduced onto the stromal bed after the lenticule’s photoablation. This hypothesis holds true not only for molding surface curvature but also for molding surface orientation (tilt) and position. A tilted or eccentrically positioned molding lens will produce a wedge – shaped lenticule. When ablated such a lenticule will not only induce astigmatism but also create a respectively wedged - like ablation profile with gross elevation differences across the diameter of decentration or tilt. This will result in unwanted and unnecessary- overablation of the corneal area under the thinnest part of the lenticule. Therefore it
is essential to carefully align and center the molding lens as described above (figure 37-5). Clinical practice has shown that the gel -being thermoreversible- quickly sets upon contact with the relatively cold corneal surface and molding lens. In consequence, the time interval provided to the surgeon to center the molding lens proves to be between 5 and 10 seconds. This short time interval is a limiting factor to the accuracy of the molding lens –and molded lenticule- centration. Moreover lenticule mean thickness is related to the pressure that the surgeon applies during the first few seconds of the application and therefore is unpredictable. Additional risk to the effectiveness of PALM technique corresponds to possibility of altering the lenticule’s free surface by exerting stresses during molding lens removal. Although use of the PVC membrane seems to facilitate safe molding lens removal, it is desirable to have a lenticule as stiff as possible during lens removal. In order to address these technical problems and to achieve more persistent lenticule preparation, new devices are under development and evaluation at the University of Crete (Figure 37-6).
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Figure 37-6: Modified PALM molding lens featuring a cavity through which water of controlled temperature is circulated. Lens temperature can be varied from 8 to 70 Co. The precise quantity of PALM gel required to produce a lenticule is pre applied on the molding surface of the lens (Bottom right). Gel is preheated and liquefied by means of 80o water circulating through its cavity. After gel liquefaction the lens is automatically brought to 45oC and preserved at this temperature until application. A protective cup (top) preserves PALM’s humidity during the heating cycle.
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These devices consist of molding lenses and dedicated control units that allow temperature control of the gel after application, ensuring that gel does not solidify before proper alignment is performed. These devices are expected to create thinner lenticules and complete the procedure faster as they will drastically decrease the gel cooling time. Preliminary experiments using the prototypes revealed that when the molding lens (and the lenticule in contact with it) is cooled to a temperature of about 10o C the risk of deforming the lenticule during lens removal is substantially reduced. This can be explained on the basis of increased mechanical stiffness of PALM gel at these temperatures. The PALM technique seems to surpass the ablation surface quality problems without requiring highly sophisticated laser systems, thus remaining within the grasp of any refractive surgeon. Future multicentered prospective studies will appoint its position in the armamentarium of the refractive surgeon.
5. Pallikaris IG, Katsanevaki VJ, Ginis HS. PALM technique as an alternative to customized ablations. Seminars in Ophthalmology 2000 (15): 160-169.
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REFERENCES 1. Kornmehl EW, Steinert RF, Puliafito CA. A comparative study of masking fluids for excimer laser phototherapeutic keratectomy. Arch Ophthalmol 1991;109:860-863. 2. Englanoff JS, Kolandouz-Isfahani AH, Moreira H, Cheung DT, Trokel SL, Mc Donnel PJ. In situ collagen mold as an aid in excimer laser superficial keratectomy. Ophthalmology 1992;99:1201-1208. 3. Fasano PA, Moreira H, Mc Donnel PJ, Sinbawy A. Excimer laser smoothing with model of anterior corneal surface irregularity. Ophthalmology 1991;98:1782-1785 4. De Vore DP, Scott JB, Nordquist RE, Hoffman RS, Nguyen H, Eifferman RA. Rapidly polymerized collagen gel as a smoothing agent in excimer laser photoablation. J Refract Surg, 1995;11:1, 50-55
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Pallikaris I, Panagopoulou S, Katsanevaki V. The PALM technique: photoablated lenticular modulator. In: Pallikaris I, Siganos D (eds). LASIK. Thorofare, NJ: Slack, Inc; 1997:277-278. Kapadia MS, Wilson SE. Transepithelial photorefractive keratectomy for treatment of thin flaps or caps after complicated laser in situ keratomileusis. Am J Ophthalmol 1998;126:6, 827-829) Maloney RK, Friedman M, Harmon T, Hayward M, Hagen K, Gailitis RP, Waring GO. A prototype errodible mask delivery system for the excimer laser. Ophthalmology 1993;100:542Contents 549. Egging CA, De Boo TM, Lemmens WA, Section 1 Deutman AF. Photorefractive keratectomy with Section 2 an ablatable mask for myopic astigmatism. J Refract Surg 1999; 15: 550-555. Section 3 Vinciguerra P, Nizzola GD, Airaghi P, Ascari A, Nizzola F, Azzolini M. A new technique for the Section 4 excimer laser correction of decentration after PRK and LASIK. In: Pallikaris I, Siganos D Section 5 (eds). LASIK. Thorofare, NJ: Slack, Inc; Section 6 1997:281. Margaritis AG, Pallikaris IG, Siganos DS. PropSection 7 erties of a new two component gel material as an aid in PRK corneal remodeling Inv Subjects Index Ophthalmol Vis Sci 35(4):3553,1994 Stevens SX, Bowyer BL, Sanchez-Thorin JC, Rocha G, Young DA, Rowsy JJ. The BioMask for treatment of corneal surface irregularities with excimer Laser phototherapeutic keratectomy. Cornea 1999;18(2):155-63. Help ?
Ioannis G. Pallikaris, M.D. Department of Ophthalmology University of Crete-Medical School P. O. Box 1352, Crete
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Chapter 38 CUSTOMIZED ABLATIONS IN LASIK Michael C. Knorz, M.D.
Present Role of Customized Ablations The techniques for customized ablations have matured and are already being introduced in our daily routine. There are many ways to “customize” treatment. Some of these ways can be considered “art,” as they strongly depend on the surgeon performing them. Others can be called “science,” as they rely on more reproducible ways to achieve the desired result. The introduction of ablation profiles calculated based on corneal topography was the first step towards a more standardized approach. The final step towards the ultimate goal of perfect customization seems to be the introduction of wavefront-deviation guided ablations. This technology objectively measures the refractive error of the whole eye, plus all the higher-order optical aberrations such as coma. Eliminating the optical aberrations of the eye could mean an increase of visual acuity well above the preoperative level. Statistically, it will also mean a much higher percentage of patients seeing 20/20 or better without correction after LASIK and a much smaller percentage complaining about problems of quality of vision in dim light or at night. Customized ablations have finally arrived, and they are here to stay as an integral part of refractive surgery. I had the opportunity to become involved with customized ablations quite early. When we started, we felt that corneal topography was the ideal data source on which to base a customized ablation. Corneal topography, which is readily available, pro-
vides considerable data on the most important part of the eye’s optical system, the cornea. Our initial study therefore used corneal topography data to calContents culate a customized ablation. We used several systems, including the C-Scan (Technomed Co., Section 1 Baesweiler, Germany) and the Orbscan II corneal toSection 2 mography system (Bausch & Lomb Surgical, Claremont, CA). We initially treated eyes that had Section 3 previously undergone refractive surgery (“repair procedures”). Later, we included so-called normal eyes Section 4 in patients who had undergone a routine LASIK pro- Section 5 cedure. During the last year, we have expanded our repertoire by adding an aberrometer, which is used Section 6 to measure the wavefront-deviation of the whole eye. The measured wavefront-deviation reflects both the Section 7 refractive error of the eye and higher-order optical Subjects Index aberrations such as coma. Any treatment based on wavefront-deviation will in theory, therefore, not only treat the refractive error but also optimize the optics of the eye by removing the higher-order optical aberrations. In this chapter, I will describe the technique of using corneal topography for this purpose and present the first results obtained with wavefrontHelp ? deviation guided ablations. The work presented here is not based on the efforts of one individual, but on the support of many of my colleagues and friends all over the world. Those who contributed significantly include Dr. Maria Clara Arbelaez, Dr. Jorge Alio, Dr. Stephen G. Slade, Dr Michiel Kritzinger, and Dr. Thomas Neuhann. All of us were supported by a dedicated team from Bausch & Lomb Technolas.
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Technique of TopoLink Spot-scanning or flying-spot excimer lasers provide the technological platform to perform ablations of any shape (1). Corneal topography enables us to measure the shape of the individual cornea with great precision, and elevation-based systems like the Orbscan II (Bausch & Lomb Surgical) provide an even better basis for the calculation of the required ablation. The question that challenged us a few years ago was whether we could combine corneal topography and scanning lasers to create customized ablations (2). The surgical technique of TopoLink involves the use of the Hansatome microkeratome (Bausch & Lomb Surgical, St. Louis, MO) and the Keracor 217 excimer laser with an active eye tracker. The laser ablation was based on the preoperative corneal topographic map obtained with the Orbscan II corneal analysis system (Bausch & Lomb Surgical, Irvine, CA). Three different maps were obtained, and the one featuring the least eye movements was used. The maximum movements considered acceptable were 200 µm. Patients who did not comply with the requirement to have three maps taken were excluded. Once the topography was taken, data were copied, and a technician from Bausch & Lomb Surgical Technolas in Munich calculated the ablation profile on site using special software called TopoLink (Version 2.9992TL) Input values were manifest sphere in minus cylinder format and corneal thickness as measured by the Orbscan II. The software determined the target K-value by subtracting the manifest sphere from the K-value in the steep corneal meridian. The target K-value and a preset shape factor of -0.25 defined the target asphere which we aimed to achieve after LASIK. The TopoLink software basically compares the shape of the target asphere to the corneal shape actually measured. The target shape is fitted from beneath to the actual cornea for a given planned optical zone size. The difference between the target and actual shapes is then ablated. As tissue cannot be added but only ablated, any overlap between the target and actual shape must be outside the planned
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optical zone. The TopoLink software represents a new approach to customized ablation that is not based on Munnerlyn´s formula. Instead, it calculates a certain “lenticle” of corneal tissue to be removed, and the scanning laser removes this tissue even if its shape is asymmetrical or irregular. The diameter of the planned optical zone was 6 to 7 mm, except in cases in which the ablation required to achieve these optical zones would have left a residual corneal stromal bed of less than 250 µm. In these cases, the diameter of the planned optical zone was decreased. Based on these data, TopoLink calculated a session file, which basically contained information about which ablation pattern the scanning laser should perform. The session file was transferred via disc and loaded into the Keracor 217 excimer laser (Bausch & Lomb) just prior to treatment.This laser uses a 2-mm beam scanned across the cornea at a shot frequency of 50 Hz. It was modified by including an aperture that allows the use of both a 1-mm beam and a 2-mm beam.
Examples of Uses of TopoLink
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Patient 1. Irregular astigmatism after penetrating injury
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This 6-year-old patient had suffered a pen- Section 6 etrating injury in her left eye when a light bulb ex- Section 7 ploded, and glass fragments penetrated her eye, causing corneal lacerations extending from 10 to 12 Subjects Index o’clock peripherally. One year after the initial repair, scar formation caused significant irregular astigmatism. Uncorrected visual acuity was 20/200. With a correction of +0.5 sphere -5.0 cyl axis 170°, an acuity of 20/100 was achieved. Contact lenses were tried but not tolerated by the patient. Corneal topography Help ? showed marked irregular astigmatism. We therefore discussed treatment options with the parents of this child. As contact lenses were not tolerated, surgery seemed to be the only option to prevent amblyopia. We considered t-cuts, corneal grafts, and TopoLink LASIK. LASIK was selected as the least invasive and most predictable option.
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Surgery was performed with the patient under general anesthesia. Figure 38-1 shows the topographic workplace on which the ablation is planned. The preoperative topographic map (scale in diopters) is on the upper left, and the ablation profile suggested by the TopoLink LASIK software (scale in µm) is on the upper right. On the lower left, the surgeon can add individual fudge factors to allow for a margin of error, and the expected result is
displayed on the lower right side. Comparing maps, we can see that the flat area at the lower right (blue) of the preoperative topography map is steepened by the ablation (red) at the lower right of the ablation map. Superimposing the two maps in the upper row, the resulting map, which is displayed at the lower right, should be a perfect sphere, at least theoretically.
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Figure 38-1: Topographic workplace used to design the ablation of patient 1. The preoperative topographic map (scale in diopters) is on the upper left, and the ablation profile suggested by the TopoLink LASIK software (scale in µm) on the upper right. On the lower left, the surgeon can add individual fudge factors, and the expected result is displayed on the lower right hand side.
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The preoperative topographic map and the topographic map 1day after surgery are shown in Figure 38-2. The color scale is the same in both maps, allowing them to be easily compared. The clearly visible steep area on the upper left is considerably flatter, and visual acuity without correction improved to 20/60 on Day 1. Figure 38-2 also shows the differential map. The change map, which visualizes the ablation, closely resembles the planned ablation (see Figure 1, upper right, for comparison). One year after surgery, visual acuity without correction was 20/80, and with correction of -2 cyl axis 140°, acu-
ity was 20/60. To prevent amblyopia, the right eye was occluded 4 hours a day. Corneal topography at 1 year shows considerable regression of effect. The cornea was still more regular than it had been preoperatively, but most of the effect had regressed. We considered a retreatment and calculated an ablation of 50µ. Preoperatively, corneal thickness was 587µ. Flap thickness was 160µ, and ablation depth during the first TA-LASIK procedure was 86µ. Central corneal thickness after the first procedure was 430µ. We therefore decided against a retreatment to avoid possible late keratectasia due to corneal thinning.
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Figure 38-2: Pre- and postoperative topographic maps and differential map of patient 1 (penetrating injury with irregular astigmatism).
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Patient 2. Irregular astigmatism after external margins of the graft were well aligned with the host cornea. PKP and RK. This patient had a penetrating corneal graft because of recurrent stromal herpetic keratitis in 1992. He was first referred in 1993. Manifest refraction was +0.25 sphere -6 cyl axis 135°. Corneal astigmatism was -8 D axis 135° and slightly asymmetric. Initially, astigmatic keratotomy (AK) was performed in 1994. After AK, manifest refraction was -2.5 sphere -4 cyl axis 165°. UCVA was 20/400, and BCVA was 20/60. Corneal topography showed marked irregularity and axis shift (Figure 3, upper left). We therefore decided to perform TopoLink LASIK. The average refractive power of the cornea overlaying the entrance pupil was estimated to be 45 D. The spherical equivalent of manifest refraction was -4.5 D. We therefore selected a target K-value of 40.5 D. A 5.4 mm optical zone was used, and ablation depth was 150 µ. Corneal thickness was 610 µ centrally, and both the internal and
It is very important to check alignment prior to the lamellar cut. In poor alignment or localized ectasia at the edge, corneal thickness might be reduced, and the keratome cut may cause further weakening of the cornea, inducing more ectasia, or even a penetration of the anterior chamber. In this patient, alignment was perfect, and the LASIK procedure performed in July 1997 was uneventful. A 160µ flap was used. One day after TopoLink LASIK, UCVA had improved to 20/30, and BCVA was 20/25 (correction: +0.75 sphere). After 4 months, UCVA was 20/30 and BCVA 20/25, but manifest refraction had changed slightly to +1 sphere -2.0 cyl axis 10°. Corneal topography 4 months after TopoLink LASIK showed marked improvement of the irregularity (Figure 3). Some residual WTR astigmatism was present, but the irregular astigmatism present preoperatively had virtually disappeared, as shown by the differential map (Figure 38-3).
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Figure 38-3: Pre- and postoperative topographic maps and differential map of patient 2 (irregular astigmatism after PKP and RK).
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Patient 3: Decentered ablation This 36-year-old woman had LASIK in both eyes in 1998 and was referred to me because of a decentered ablation. The right eye was perfect, but she complained bitterly about permanent monocular diplopia and distorted halos in her left eye. A TopoLink LASIK was planned. The corneal topography taken prior to the TopoLink LASIK is shown in Figure 38-4, lower left, and Figure 38-5, lower right. A decentered myopic ablation is visible. The
ablation is decentered about 1.5 mm downwards and 1 mm temporally. We calculated a customized ablation based on the Orbscan II topographic map just described. The planned ablation pattern is shown in Figure 4, upper right. The scale is in µm. The predicted outcome of corneal topography is shown in Figure 4, lower right (scale in diopters). I used the Hansatome to create a new flap with a thickness of 160 µm and a diameter of 8.5mm (8.5mm suction ring). The surgery was uneventful. The ablation was
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Figure 38-4: Treatment plan in TopoLink LASIK. This plan is shown on the screen of the Keracor 217 excimer laser when the treatment is loaded. It features patient data, upper left, preoperative topography, lower left, the simulated ablation pattern, upper right, and the expected postoperative topography, lower right.
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Section 3 Figure 38-5: Orbscan II differential map after treatment. The preoperative map, lower right, shows a decentered ablation, the postoperative map, upper right, shows improved centration. The differential map is shown on the left.
centered on the center of the entrance pupil, and the eye tracker was used. Figure 38-5 shows the pre- and postoperative maps as well as the differential map, taken 1 day after surgery. The postoperative map, upper right, shows significantly improved centration and no residual astigmatism. The differential map, left, shows the asymmetric ablation pattern, customized to this individual eye. Visual acuity improved to 20/25 uncorrected, and even more important, monocular double vision and halos were no longer visible. This case indicates that TopoLink LASIK is a valuable tool in the treatment of decentered ablations.
Results of TopoLink in Repair Procedures In our initial prospective study, we evaluated 29 eyes of 27 patients treated between July 1996 and July 1997. Inclusion criteria were irregular corneal astigmatism due to trauma or previous corneal
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surgery. We considered TopoLink LASIK as patients’ last option prior to corneal graft. Eyes were divided Section 7 into four groups: Group 1 (post-keratoplasty group) consisted of six eyes (five patients) with irregular Subjects Index corneal astigmatism after penetrating keratoplasty. All grafts were performed more than 2 years previously. Group 2 (post-trauma group) consisted of six eyes (six patients) with irregular corneal astigmatism after corneal trauma. The trauma had occurred more than 2 years in the past in all eyes. Group 3 Help ? (decentered/small optical zones group) consisted of 11 eyes (10 patients) with irregular corneal astigmatism after PRK (one eye) or LASIK (10 eyes) due to decentered or small optical zones. All patients in this subgroup complained about halos and image distortion even during the day. Group 4 (central islands group) consisted of six eyes (six patients) with irregular astigmatism after PRK (two eyes) or LASIK (four eyes) due to central islands or keyhole patterns. All patients in Group 4 complained about blurred vision or image distortion even during the day. LASIK AND BEYOND LASIK
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In the post-keratoplasty group and in the post-trauma group, corrective cylinder was significantly reduced.The topographic success rate was defined as either the planned correction fully achieved or the attempted correction partially achieved (decrease of irregularity of more than 1 D on the differential map and / or increase of optical zone size by at least 1 mm). Success rate was highest (91%) in the decentered/small optical zones group, followed by the post-trauma group, which had a success rate of 83%. The lowest success rate was observed in the central island group, at 50%. Overall, 14 of the 29 eyes were reoperated (48%) due to regression of effect or undercorrection. The rate of reoperations was lowest in the decentered/small op-
tical zones group, at 36%, as compared to 50% in all other groups (Table 1). These results demonstrate that TopoLink LASIK definitely works to significantly reduce irregularities in extremely irregular corneas. Results also showed that most eyes were undercorrected, which led us to adjust the algorithm. Finally, the problem of targeting the right spot on the cornea must be addressed. The results of group 4 (central islands) were poor, which suggests that we may not have hit the right target in these eyes with small and circumscribed irregularities. Ideally, the laser should be locked on a topographic map of the cornea prior to treatment, and that is what we are currently working on to improve results in these rare cases. Contents
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Refraction, visual acuity, and corneal topography 12 months after TopoLink LASIK (UCVA: uncorrected visual acuity; SCVA: spectacle-corrected visual acuity; *: p = 0.01; **: p = 0.001)
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Results of TopoLink in Normal Eyes In a prospective, non-comparative case series, we operated on 203 eyes of 203 patients between January 1999 and July 1999. Inclusion criteria were myopia of -1.00 to -12.00 D with or without astigmatism of up to -4.00 D. Patients were divided into two groups: Group 1 (low myopia) consisted of 114 patients with myopia of -1.00 to -6.00 D (mean, -3.83 +/-1.67 D), and astigmatism of 0 to -4.00 D (mean, -1.32 +/-1.06 D). Group 2 (high myopia) consisted of 89 patients with myopia of -6.10 to -12.00 D (mean, -7.83 +/-1.38 D) and astigmatism of 0 to -3.50 D (mean, -1.06 +/-0.92 D). No reoperations were performed in these series, and no complications occurred. Three months after surgery, 51 patients in the low myopia group and 40 patients in the high myopia group were available for follow-up. A total of 96.1% of patients in the low myopia group and 75% in the high myopia group were within +/-0.50 D of emmetropia. Uncorrected visual acuity was 20/20 or better in 82.4% of patients in the low myopia group and in 62.5% in the high myopia group; 20/25 or better in 98.0% in the low myopia group and in 70.0% of the high myopia group; and 20/40 or better in 100% of the low myopia group and 95.0% of the high myopia group. In low myopia, spectacle-corrected acuity at the higher levels improved as compared to preoperative values, and 13.7% (n=7) had a spectacle-corrected visual acuity of 20/12.5 or better. A total of 47.1% (n=24) saw 20/15 or better after TopoLink LASIK, as compared to the preoperative values of 5.9% (n=3) and 37.3% (n=19), respectively. Differences were statistically significant (p<0.01). However, when mean values (log scale) of spectacle-corrected visual acuity were compared, differences were not statistically significant (p=0.2).
The larger percentage of patients seeing 20/12.5 or 20/15 3 months postoperatively than preoperatively in the low myopia group may indicate an improvement of spectacle-corrected visual acuity due to the customized LASIK. In the high myopia group, no improvement was observed, even though a one-line improve-
ment should be expected due to higher magnification (3). The lack of improvement in the high myopia group is most likely because corneal refractive surgery in high myopia causes a significant decrease in optical quality of the eye and, consequently in quality of vision because of the relationship of optical zone size, reversed asphericity, and pupil size (4,5). We were able to demonstrate that the new approach, customized ablation based on corneal topography, works clinically at least as well as a standard ablation in normal eyes. This is a significant finding as our approach is based on a totally different calculation of the ablation: Instead of ablations based on Munnerlyn´s formula, we defined a target asphere and ablated the difference between this target and the actual cornea.
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The Bausch & Lomb Aberrometer The Bausch & Lomb aberrometer (Figure 38-6) uses a low-intensity HeNe-laser that is shone into the eye. The pupil is dilated prior to examination to allow for a measured optical zone of at least 6 mm and to prevent accommodation. The reflected light from the fundus is focused by a number of small
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Figure 38-6: Beta-version of the Bausch & Lomb Surgical Aberrometer. The chin- and headrest are visible on the right.
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lenses, a so-called lenslet-array, and the resulting picture is captured by a CCD-camera (Figure 38-7). Ideally, each of the bright white spots focused by each of the small lenses should have the same intensity and pattern. This would equal a plane wavefront, which means a perfect optical system. As most eyes are not perfect optical systems, the white spots will have different intensities and / or patterns, indicating deviations of the wavefront from plano. The deviations from plano are calculated based on the image captured by the CCD-camera, and the actual wavefront deviation is depicted graphically in color-
coded maps. Figure 8 shows an example of astigmatism. The spherical error was not included. The 3D graph shows the typical “potato chip” pattern of astigmatism. The wavefront deviation is expressed in µm above or below the ideal plane wavefront. The measured deviation, simply multiplied by a constant, can be used to perform the laser ablation. As such, wavefront-deviation guided ablations seem a very logical choice. As always, actually performing the procedure is not as easy as it looks, and my description of aberrometer technology is considerably simplified.
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Figure 38-7: Schematic illustration of the Bausch & Lomb Aberrometer. A low-intensity laser light is shone into the eye, the reflected light is focused by a number of small lenses (lenslet-array), and pictured by a CCD-camera. The captured image is shown on the left.
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Section 1 Section 2 Figure 38-8: Calculated wavefront-deformation of an eye with astigmatism (Bausch & Lomb Aberrometer). X- and Y-axis are in mm and represent the diameter of the optical zone measured. Z-axis is in µm and shows the deviation of the wavefront from plano (“residual aspheric wavefront aberration”). The “potato chips” pattern visible is typical in astigmatism.
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Wavefront-Deviation Guided LASIK The first clinical work using wavefront guided ablations was done by Dr. Marguerite McDonald in New Orleans and Dr. Seiler in Dresden, Germany. Some patients showed improvement of best-correctable visual acuity; others did not. We began these treatments in January 2000 in Mannheim, Germany, with our first treatments using the Bausch & Lomb aberrometer. Patients were enrolled as part
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of a prospective study comparing eyes intraindividually. One eye of each patient received a Subjects Index standard LASIK, the fellow eye a LASIK using wavefront-deviation guided ablations. Of our first ten patients treated, three improved by 2 lines over preoperative spectacle-corrected visual acuity, and seven reached the same visual acuity they had preoperatively. The first number of patients treated is still far too small for any conclusions to be drawn. Help ?
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REFERENCES 1.
2.
3.
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Knorz MC. Broad-beam versus scanning-beam lasers for refractive surgery. Ophthalmic Practice 1997;15:142-145 Wiesinger-Jendritza B, Knorz MC, Hugger P, et al. Laser in situ keratomileusis assisted by corneal topography. J Cataract Refract Surg 1998;24:166-174 Applegate RA, Howland HC. Magnification and visual acuity in refractive surgery. Arch Ophthalmol 1993;111:1335-1342 Holladay JT, Dudeja DR, Chang J. Functional vision and corneal changes after laser in situ keratomileusis determined by contrast sensitivity, glare testing, and corneal topography. J Cataract Refract Surg 1999;25:663-669 Pallikaris IG. Quality of vision in refractive surgery. J Refract Surg 1998;14:551-558 Contents
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Michael C. Knorz, M.D. Klinikum Mannheim Theodor Kutzer Ufer 1-3, Mannheim, Germany
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Chapter 39 WAVEFRONT MEASUREMENTS OF THE HUMAN EYE WITH HARTMANN-SHACK SENSOR CURRENT STATE OF THE ART TECHNOLOGY FOR EXCIMER LASER REFRACTIVE SURGERY L. A. Carvalho, M.D., J. C. Castro, M.D., W. Chamon, M.D. P. Schor, M.D., L. A. V. Carvalho, M.D.,
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Introduction The technological advances in refractive surgery techniques in the past decade have been overwhelming. For the first time ever there is a plausible chance of using corneal topography and eye aberration data to develop algorithms for optimized excimer laser ablations. The main objective is to obtain the best possible visual acuity. The first excimer (from the word excited dimer) lasers for refractive surgery started to operate at mid 1980’s and could only correct simple cases of myopia. With the evolution of these lasers we can talk today about point by point corneal ablations with “flying spot” lasers and correction of many other corneal abnormalities, such as irregular astigmatism. The next obvious question that came to mind at the end of this decade is: if we have a precise method for measuring the front surface of the cornea and a laser that can “mold” it into whatever shape desired, what’s missing? Why are we not quite there yet? The answer is that there are still lots of aspects to be considered before refractive surgery gets close to perfection. One of these aspects comes from the current auto-refractors. It’s necessary to know how weak or strong is the optical system of the whole eye, including the lens. Corneal topography by it self doesn’t measure myopia and hyperopia, and in terms
of astigmatism, it can determine only the corneal contribution. Axial and Tangential maps are good Section 2 only for measuring differences in corneal refractive Section 3 power, but not for determining total eye refraction. Data obtained with actual auto-refractors are incom- Section 4 plete because they determine only the best sphero- Section 5 cylindrical lens, usually by measuring power in three [11, 12, 13] different meridians . But this is crude infor- Section 6 mation compared to the non-symmetrical aberrations that occur in the eye, and also compared to the preci- Section 7 sion with which lasers can ablate the cornea and to- Subjects Index pographers can measure it. These two equipments can act on much more complicated surfaces than simple torics. The conclusion is evident: the actual auto-refractors do not have the required precision; therefore it is necessary to search and develop techniques that can measure refractive error for all points. Help ?
Principles of Eye Aberration Measurements with the HartmannShack Sensor In this section we’ll describe in more details the optical and mathematical principals of eye aberration measurements with the use of the HartmannShack (HS) sensor. In the year of 1971 Shack[15] proposed the use of micro-lens arrays instead of regular
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Hartmann screens. Remember that the subject had to tell whether the light points were joined or not, because the examiner had no idea of what the light rays did after they entered the eye. Now imagine an opposite direction of propagation of the light rays. Imagine that we could shine a single light beam onto the fovea and, instead of asking the patient what he or she was seeing, in some way we could detect how the light rays came out of the eye. If we take a look at Figure 39-1 we might understand better the point that we want to make here. We may notice that a point of light scattered at the retina of a normal eye generates at the exit
pupil what we call in physics a plane wave front. Although we have mentioned this term in the previous section, this is a good opportunity do define what it means. As we all know, light may be described as rays, such as in geometrical optics, or as waves, in physical optics. When describing light as wave phenomena, it has, as any other wave in physics, a wavelength, a velocity, amplitude and a phase (see these parameters in figure 39-2).
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Section 5 Figure 39-2: Parameters of a wave.
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Figure 39-1: A dot of light reflecting at the fovea and leaving the eyes of three subjects with myopia, hyperopia and a normal eye (emetropic).
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The phase of a wave is determined by the position of the wave crest. The wave front of a bundle of rays is determined by the connection of crests of neighboring waves. In figure 39-3 we may see two kinds of wave-fronts, one that is said to be “in phase” and other that is said to be “out of phase”, that is, with aberrations. The most interesting aspect about the HS sensor is that, by comparing the dot pattern of a distorted wave-front with those of a plane wave front, one may precisely determine the exact shape of the distorted wave-front. This is so because the amount of displacement of each dot is directly proportional to the distortion of the wave front (see figure 39-4) Liang at. Al. used the optical diagram depicted in figure 39-5 to measure optical aberrations of two subjects [14].
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Figure 39-3: Waves in phase and out of phase
Figure 39-4. A plane wave front focuses light at a point that lies over the optical axis of the lens, but a distorted wave front focuses light at a displaced point. The amount of displacement determines the wave front distortion.
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Figure 39-5. Schematic diagram of optical setup used by Liang to measure aberrations of the eye. A He-Ne laser beam (1) is focused at the back of the eye. In this first optical path the objective is to generate a small spot of light at the retina, by adjusting position of lens (16). The accommodation system consists of a light bulb (5) that shines a picture (5), which is viewed by the eye. Lens (3) is shifted until the far point of the eye is found. The diffused light reflected at the retina return passing by all eye components (vitreous humor, crystalline, aqueous humor, cornea), goes through lens (16), reflects on the beam splitter (7) and continuous through lenses (8), (9) and (11), going through the stop (10). The stop eliminates reflections from the accommodation system, from the cornea and lens (16). Finally the wave-front hits at the HS sensor (12) and is focused at the CCD array (13). The CCD image is digitized in a “frame grabber” (14) and processed at an IBM PC, which displays the graphical information at the colored monitor (15).
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In figure 39-6 we may see an example of the type of images that are obtained with the optical setup in figure 39-5. The center of “mass” of each spot is detected using image-processing algorithms [28]. The and coordinates of each spot are then compared with coordinates of corresponding spots of a calibration image. The calibration image is obtained from an aberration free eye (emetropic), or more often from an artificial eye. In figure 39-7 we present an eye wave-front measured with the HS sensor. Figure 39-6. Example of image formed at the CCD plane using the optical diagram of figure X.
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Section 3 Figure 39-7. Typical output of wavefront measurement device. This is the eye of one of the authors (Luis Carvalho), which was done in October 2000 at the American Academy of Ophthalmology at the ZeissHumprhey booth. Notice the different plots: (upper left) HS image; (upper right) eye image; (lower left) color coded map of total aberrations; (lower right) color coded map of high order aberrations.
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Present Technologies for Optimizing Visual Acuity through Refractive Surgery In this section we’ll describe the current state of the art technologies for refractive surgery that are being tested and that will probably be available in the very near future.
Corneal Topography and Elevation Maps In the 1980’s, computer algorithms could do all measuring processes. The photographic camera was substituted by CCD cameras (from the words “Charge Coupling Device”), and cards called “frame grabbers”, which grab images from the CCD into the computer memory. The manual and tiresome Placido image measurements could now be accomplished by image processing algorithms[28] and so the whole process would take only a few minutes. As computers grew more powerful, this process became faster and faster and with the popularity of colored monitors, the first high resolution corneal topography maps were plotted, originally suggested by Klyce[32]. These instruments are quite popular nowadays and became generally known as VKS (Videokeratoscopes) or Corneal Topographers. Since the beginning of the computerized VKS, many authors have proposed different mathematical algorithms to calculate corneal features. It is important to notice that there are lots of parameters that may be calculated and that each of them have a different meaning. To make our point clear let’s look at the diagrams in figure 39-8:
Flying Spot Lasers and Eye Tracking Recent excimer lasers, like the Nidek EC-5000[36], have a scanning slit delivery system that can treat over 7.5 mm of the cornea in myopia and up to 10 mm in hyperopic, using a 10 to 40 Hz frequency. A larger area ablation can be combined with a small area (1.0 mm) over a 10 mm diameter of the cornea.
Figura 39-8. Different descriptors for corneal surface, each one with it’s own advantages and disadvantages for corneal diagnosis. The curvature maps (A and B) and the refractive map (C) are particularly useful for pre and post-surgical evaluation, because they are proportional to corneal power. Descriptors D, E and F are all elevation maps. They measure the “true” topography of the cornea, relative to a plain (D), to a small sphere (E) and to a big sphere (F). A detailed analysis of advantages and disadvantages of each descriptor may be found in the works of Salmon[33] and Klein[34].
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Authors like Ronald Krueger (Summit-Autonomous Custom Cornea) argue that effective wavefront based customized ablations require small scanning spot gaussian beams[37]. In essence, Krueger states that small gaussian beams allow for very smooth ablation profiles, which directly affect post surgical visual acuity. The other aspect to consider is the size of the spot. If we have high-resolution corneal topographers and wave-front devices, the size of the laser beam has to be proportional to that resolution. Unpublished mathematical calculations[37] show that to correct up to fourth order aberrations a spot size of less than 1 mm is necessary and therefore lasers with greater beam profiles would fail to
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correct common high order aberrations, like coma and spherical aberration. Studies with a 2 mm profile beam have shown poor performance[38]. Because of the involuntary constant movements of the eye (called saccadic movements) there is a need to correct eye position in order to place beam with precision. There are basically two types of eye tracking systems in the market: the CCD based systems and radar systems. The CCD based systems work with image processing algorithms to find eye position and input feedback to mirror micro-motors; they have tracking frequencies that are limited by the CCD frequency and range from 30 to 300 Hz. Radar based systems work with retro-reflected diode laser light and may obtain even higher frequencies[37].
A Look into the Future of Refractive Surgery In this section we’ll make brief comments with references about certain aspects that, in our point of view, have yet to be considered in order to maximize refractive surgery efficiency.
Physiological Limitations to Visual Acuity Although most people in the refractive surgery community show excitement with supernormal vision possibilities, we must consider the physiological limitations of the eye. No matter how well we can measure and correct low and high order aberrations, there is a clear limitation imposed by the human photoreceptor configuration and dimensions. The region of the retina where images are formed is the foveola, an approximately 0.35mm disk. In the foveola the cones are very packed and have a mean diameter of 2 µm. Just like the number and size of photo sensitive cells in a CCD camera imposes limitation to the camera’s resolution, so does the number and size of cones in our eyes. Seeing with higher acuity essentially means seeing more detail at longer distances. It is easy to understand by simple image
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formation principles from geometric optics, that smaller objects in the outer world will form smaller images at the retina. The question is: how small can an image formed at the retina still be interpreted? If it gets too small it will unavoidably be interpreted as a single point. A simple calculation may be done to show that visual acuity is limited in the retina to about 20/08. But there are certainly many other aspects that have to be considered in an individual basis, such as receptor sampling[46].
Considering Cyclotocion Another interesting question that we think worthwhile is the consideration of cyclotorcion factors in refractive surgery procedures. Most pre and post surgery eye examinations are done in the vertiContents cal position of the head. But surgery takes place in the horizontal position. Our question is: how impor- Section 1 tant is the cyclotorcion movements of the eye and head misalignment in cases of refractive surgery for Section 2 cases of medium to high astigmatisms? Section 3 To answer this question we’ll make some theoretical calculations. Suppose a patient with 4 Section 4 degrees of astigmatism with the rule (40D (8.43 mm of radius) at the horizontal meridian and 44D Section 5 (7.67mm of radius) at the vertical meridian) under- Section 6 goes refractive surgery and an accumulated meridian angle error of 5 degrees is caused by cyclototion Section 7 and more 5 degrees because of head misalignment. Subjects Index Let’s suppose that the simple refractive procedure would be to ablate the cornea in such a way as to flatten the steeper meridian, that is, the vertical meridian. So we know that the correct radius of curvature at the vertical meridian would be 8.43 mm. Simple geometrical calculations show that, for a radial distance of 1.0 mm from the apex of the cornea Help ? (which means 2 mm central region of the cornea) up to 0.2D errors may occur. Although theoretical, these simple calculations show that the head alignment and cyclotorcion are important aspects in customized ablations, since the precision of all instruments involved are much higher than 0.2D.
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Effectiveness of the Hartmann-Shack Sensor It is important to consider optical design optimizations when using HS sensors to measure optical aberrations of the eye. Because the HS sensor was originally conceived for application in astronomy
and aberrations in this field differ from those of human eyes, we believe some studies have to be made in this sense. We have developed simulations of HS patterns for real and artificial corneal topography data of eyes with astigmatism, keratocone, and uniform curvature corneas. The basic principle of HS simulation using ray tracing may be seen in figure 39-9.
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Figure 39-9. Ray-tracing diagram for generating the HS image pattern. We start by sampling pixels at the CCD array (480x640) and back-word ray trace from CCD plane towards the cornea. V1, V2 and V3 represent vectors at each refraction stage. Rays refract at micro-lens array then at cornea and finally hits the retina. If it falls inside the fovea (a 10µm disk) it is said to be a “good ray”, otherwise it is a “bad ray”.
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Illustration of simulated HS patterns obtained for three interesting cases are shown in figure 39-10. In general we notice that for eyes with little corneal irregularities (“smooth” corneas) the spots have a quite well behaved distribution; on the
other hand for eyes with high astigmatism, keratocone or other severe corneal irregularities (such as post RK), there is a superposition of the HS spots. Our HS patterns are in agreement with the corneal elevation data and for most cases of regular
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Figure 39-10. Examples of HS simulations for a regular (top) and astigmatic (bottom) corneas. (Top-Left) Hartmann Shack pattern simulation for regular cornea; notice uniform distribution of spots; (top-middle) semi-meridian cut of regular cornea elevation; notice that curve is smooth and there is no local irregularities; (bottom-left) HS pattern for astigmatic eye; notice that spots are closer where corneal curvature is more intense and are further away for less curved region; (bottom-middle) Blue curve represents flatter meridian and red curve represents meridian with higher curvature; (bottom-right) curvature map of astigmatic eye, showing the “hour glass” shape in agreement with HS pattern and meridian cuts.
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(“smooth”) corneas, small and medium astigmatisms, there was no spot overlap (see figure 39-11). But for cases of severe keratocone (simulated), we observed overlapping (see figure 39-11). Other types of irregularities should be investigated, such as post-cataract, post-RK, and post-Keratoplasty. We believe there will be overlapping for these types of irregular corneas. On figure 39-11 we may see examples of HS patterns obtained for artificial corneas generated using ellipsoids and spheres of different sizes and pa-
rameters. It is important to notice how the HS pattern varies with small changes in parameters such as radius of curvature, entrance pupil, HS image plane distance, number and size of micro-lenses, CCD resolution and scaling, and so on. Our objective here is to show a qualitative view of how these parameters affect the HS patterns. Further work should be done in order to quantify these factors, and possibly suggest HS sensor setups that will generate less superposition in cases of highly distorted corneas.
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Figure 39-11. HS patterns generated for simulated corneas. (a) Sphere of radius 8.0 mm, (c) Discentered Keratocone (to the left) with 5 mm local radius over a highly astigmatic ellipsoid (a:=7 mm, b:=5 mm, c:=8 mm), showing the superposition (to the left) case when the surface is off axis; (c) Highly astigmatic ellipsoid (a:=8 mm, b:=5 mm, c:=7.5 mm), showing high distortion of HS patterns.
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REFERENCES 1. Placido, A., Novo Instrumento de Exploração da Cornea, Periodico d’Oftalmológica Practica, Lisboa, 1880;5:27-30. 2. Mammone, R. J., Gersten, M., Gormley,D. J., Koplin ,R. S., Lubkin,V. L., 3D Corneal Modeling System, IEEE Trans. Biomedical Eng, 1990;37:66-73. 3. Mandell, R. B.,St Helen R., Mathematical Model of the Corneal Contour, Brit. J. Physiol. Optics., 1971;26:183-197. 4. Doss, James D., Hutson, Richard L., Rowsey, J., Brown, R., Method for Calculation of Corneal Profile and Power Distribution, Arch Ofthalmol, 1981;99:1261-1265. 5. Wang, J., Rice, D.A., Klyce, S.D., A New Reconstruction Algorithm for Improvement of Corneal Topographical Analysis, Refract. Corneal Surg.1989;5:379-387. 6. van Saarlos, Paul P., Constable, Ian J., Improved Method for Calculation of Corneal Topography for Any Photokeratoscope Geometry, American Academy of Optometry, 1991;68:960-965.
16. Hartmann J, Bemerkungen uber den bau und Die Justirung von Spektrographen, Z Instrumentenkd, 1900;20:47. 17. Thibos LN, Principles of Hartmann-Shack Aberrometry, Journal of Refractive Surgery, Vol. 16, September/October 2000, 540-545. 18. Tscherning M, Die monochromatischen aberrationen des menschlichen auges, Z Psychol Physol Sinne 1894;6: 456471. 19. Howland B, Use of crossed cylinder lens in photographic lens evaluation, Appl Optics 1960;7:1587-1588. 20. Howland HC, Howland B, A subjective method for measurement of chromatic aberrations of the eye, J Opt Soc Am 1977; 67:1508-1518. 21. Born, M., Principles of Optics, Pergamon Press,1975: 464466.
7. Mandell, Robert B., The Enigma of the Corneal Contour, CLAO J, 1992;18:267-273.
22. Noll R, Zernike polynomials and atmosferic turbulence, J Opt Soc Am 1976; 66, 3, 207-211.
8. Halstead, Mark A.,Barsky, Brian A. , Klein, Stanley A., Mandell, R. B.,Geometric Modeling of the Cornea Using Videokeratography, Mathematical Methods for Curves and Surfaces,1995;213-223.
23. Walsh G, Charman WN, Howland HC, Objective techique for the determination of monochromatic aberrations of the human eye, J Opt Soc Am A1984;1:987-992.
9. Halstead, Mark A.,Barsky, Brian A. , Klein, Stanley A., Mandell, R. B. “A Spline Surface Algorithm for Reconstruction of Corneal Topography from a Videokeratographic Reflection Pattern”. Optometry and Vision Science. 1995;72:821-827. 10. KLEIN, S. A., (1997). Corneal topography algorithm that avoids the skew ray ambiguity and the skew ray error, Optometry and Vision Science, vol. 74, 11: 945-962. 11. Campbell FW, Robson JG, High speed infrared optometer, J. Opt. Soc. Am., 1959;49:268-272.
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15. Shack RV, Platt BC, Production and use of a lenticular Hartmann screen, Optical Sciences Center, University of Arizona, Tucson, Spring Meeting, Optical Society of America, 1971: 656.
24. Babcock HW, The possibility of compensating astronomical seeing, Publ Astron Soc Pac, 65, 229, 1953.
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25. Malbet F, Shao M, Yu J, Active optics and coronography Subjects Index with the Hubble Space Telescope, SPIE Symposium in Astronomical Telescopes &Instrumentation for the 21st Century, 1994, 13-18. 26. Liang J, Willliams DR, (1997b), Aberrations and retinal image quality of the normal human eye. J. Opt. Soc. Am., Vol. 14, No. 11/ November, 2873-2883.
12. Charman WN, A pioneering instrument: the Collin’s electronic refractionometer, Opthalmol. Opt., 1976;16:345.
27. Liang J, Williams DR, Miller DT, Supernormal vision and high-resolution retinal imaging through adaptive optics, J. Opt. Soc. Am., (1997a)Vol. 14, No. 11/ November, 28842892.
13. Cornsweet TN, Crane HD, Servo-controlled infrared optometer, J. Opt. Soc. Am., 1976;60:1-35.
28. Gonzales RC, Woods RE, Digital Image Processing, Addison-Wesley,1992.
14. Liang J, Grimm B, Goelz S, Bille JF, Objective measurement of wave aberrations of the human eye with the use of a Hartmann-Shack wave-front sensor. J. Opt. Soc. Am., Vol. 14, No. 11/ July, 1994: 1949-1957.
29. DeVries PL, A first course in computational physics, John Willey & Sons, Inc., 1994.
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30. Press WH, Flannery BP, Teukolsky SA, Vetterling WT, Numerical recipes in pascal – the art of scientific computing, Cambridge University Press, 1989.
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WAVEFRONT MEASUREMENTS OF THE HUMAN EYE WITH HARTMANN-SHACK SENSOR 31. Le Grand Y, El Hage SG, Physiological Optics, Springer Series in Optical Sciences, Vol. 13, 1980. 32. Klyce, S.D., Computer-Assisted Corneal Topography, High Resolution Graphics Presentation and Analyses of Keratoscopy, Invest. Ofthalmol.Vis. Sci.,1984;25:426-435. 33. Salmon, T.O., Horner, DG, Comparison of Elevation, Curvature, and Power Descriptors for Corneal Topographic Mapping, Optometry and Vision Science, 1995; 72: 800808.
40. Klein SA, Optimal corneal ablations for eye with arbitrary Hartmann-Shack aberrations, J Opt Soc A, 1998, Vol 15,9:2580-2588. 41. Schwiegerling J, Snyder RW, Custom photorefractive keratectomy ablations for the correction of spherical and cylindrical refractive error and higher-order aberration, J. Opt. Soc. Am. A/ Vol. 15, No. 9, September 1998, 2572-2579. 42. Tyson RK, Principles of adaptive optics, Academic Press, 1998.
34. Klein SA, Mandell RB, Shape and refractive powers in corneal topography, Invest Ophthalmol Vis Sci 1995;36:2096-2109.
43. Bille JF, Preoperative simulations of outcomes using adaptive optics, Journal of Refract. Surg., 2000,Vol 16, 5: 602607.
35. Hermann Von Helmholtz, Ed. by James P.C. Southall, Helmholtz’s Treatise on Physiological Optics, July 2000.
44. Williams D, Yoon GY, Porter J, Guirao A, Visual benefits of correcting higher order aberrations of the eye, Journal of Refract. Surg., 2000,Vol 16, 5: 554-559. 45. Roberts C, Future challenges to aberration free ablative procedures, Journal of Refract. Surg., 2000,Vol 16, 5: 623-629.
36. MacRae S, Fujieda M, Slit skiascopic-guided ablation using the Nidek laser, Journal of Refract. Surg., 2000,Vol 16, 5:576-579. 37. Krueger R, Technology requirements for Summit-Autonomous CustomCornea, Journal of Refract. Surg., 2000,Vol 16, 5: 592-601. 38. Campin JA, Pettit GH, Gray GP, Required laser beam resolution and PRK system configuration for custom high fidelity corneal shaping, Invest Ophthalmol Vis Sci 1999; 38(suppl): S538.
46. Applegate RA, Limits to vision: can we do better than nature?, Journal of Refract. Surg., 2000,Vol 16, 5: 547-551. 47. Carvalho LAV, Castro JC, Schor P, Chamon W, A software simmulation of Hartmann-Schack patterns for real corneas, International Symposium: Adaptive Optics: from telescopes to the human eye, Murcia, Spain, November 13-14, 2000.
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Section 6 Section 7 Subjects Index The authors have no financial interest in the products or brands presented in this chapter. Information about the authors: Luis Alberto Carvalho, PhD graduated in Physics from the University of São Paulo – Brazil where he also received his PhD. He also conducted research as a visiting scholar at the University of California – Berkeley - USA. Jarbas Caiado Castro, PhD, graduated in Physics from the University of São Paulo – Brazil, did his PhD at MIT-USA and is full professor at the Institute of Physcis of the University of São Paulo - Brazil.
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Wallace Chamon, PhD, MD, graduated in Ophthalmology from the University of São Paulo – Brazil, conducted his PhD at the Escola Paulista de Medicina, and today is responsible for the Refractive Surgery Devision at that school. He has been fellowship and visiting scientist at the The Johns Hopkins University – USA and is Associate Editor of the Journal of Refractive Surgery. Paulo Schor, PhD, MD, graduated in Ophthalmology from the University of São Paulo – Brazil, conducted his PhD at the Escola Paulista de Medicina, and today is responsible for Bioengineering Division of that school. He has been fellowship and visiting scientist at MIT and Harvard - USA. Luiz Antonio Vieira de Carvalho, PhD, graduated in mathematics from University Júlio Mesquita Filho – Brazil, conducted his PhD at Brown University – USA in applied mathematics, and is full professor at University of São Paulo – Brazil.
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PRESBYOPIA
Chapter 40 PRESBYOPIA Surgical Correction - Current Trends Prof. Benjamin F. Boyd, M.D., FACS With the Collaboration of: Ronald Krueger, M.D.
Prof. Juan Murube, M.D.
Marguerite McDonald, M.D.
Steven Wilson, M.D. Contents
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Surgery for Management of Presbyopia through MONOVISION Patients with a combination of mild hyperopia as well as presbyopia generally do not have a good visual adjustment unless they wear spectacles or contact lenses all the time. Before treating patients over 40, Ronald Krueger, M.D. discusses with them the concept of monovision. Monovision involves identifying the dominant eye and treating it in such a way that the patient can see as sharply as possible at distance. Then the non-dominant eye is treated but left a little myopic so the patient can still read, see at intermediate distance and at close range. Krueger estimates that 80-90% of his patients over the age of 40 report satisfaction with monovision surgery.
The LADARVision Laser for Myopia and Presbyopia (Monovision Method) With a patient who is nearsighted, Krueger performs LASIK and uses the Autonomous LADARVision laser, by Alcon. For presbyopic patients, he corrects one eye for distance and leaves
the other eye slightly undercorrected, depending upon the patient’s age. For instance, Krueger may Section 2 treat a patient in his early 40's to a target of -1.0D in Section 3 the non dominant eye. At -1.0D, they should see everything at 1 meter away and maybe somewhat Section 4 closer because they still have some accommodation. Section 5 He often targets patients in their late 40’s or early 50’s so they end up with -1.25D, and patients Section 6 in their mid-50’s or older at about -1.5D. This allows patients to have maximum flexibility with mid-range Section 7 and near vision in one eye. The other eye, as long as Subjects Index it is very sharply focused at distance, will give them the clear vision without glasses that they want.
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In patients with hyperopia, Krueger treats the dominant eye for the hyperopia prescription so they can see well at distance. Then he overcorrects the non-dominant eye to bring patients from hyperopia, beyond emmetropia to mild myopia. This is still a monovision treatment. Often patients require slightly less myopia in the non-dominant eye as the hyperopic correction gives them a certain amount of negative asphericity (steeper in center) which favors better near vision when the pupil constricts.
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Wavefront technology will help us better understand these subtle benefits of asphericity in the future as well. Krueger's experience with the FDA approved Alcon-Summit Autonomous LADARVision Laser is that up to 6 diopters of hyperopia can be treated with up to 6 diopters of hyperopic astigmatism as well as mixed astigmatism. In the past a small plus refraction with a higher minus cylinder mixed astigmatism could not be treated with the laser. Now the entire continuum from farsightedness to farsighted astigmatism to mixed astigmatism to myopic astigmatism to myopia can be treated using the laser. Krueger advocates LASIK, but not in combination with thermokeratoplasty. He is somewhat skeptical of the possibility that significant regression may occur over time. If patients are not expecting a temporary procedure with a change in their refraction with time, they might tend to be dissatisfied and have unrealistic expectations. Again, in presbyopia complicated by moderate hyperopia, Steven E. Wilson, M.D. advises patients with up to 4 diopters of hyperopia that LASIK can do a beautiful job of correcting their problem. Patients who are 1 to 4 diopters farsighted, which amplifies the presbyopic problem, can have their near vision dramatically improved just by the correction of their hyperopia, depending on the age of the patient. Wilson has even observed that in patients in their 60s or 70s with 2 to 4 diopters of hyperopia, the hyperopia excimer laser correction can result in 20/20 or 20/25 vision at distance and provide the ability to read. This cannot be promised to the patient, but is likely to occur due to the multifocality of the ablation for hyperopia when using the Visx 52 Star laser. Wilson never promises his patients these results because the results are not uniform. The specific way the hyperopic correction is produced with LASIK probably causes some patients to get enough multifocal effect on the cornea to see both distance and near. Wilson once performed this procedure on both members of a couple. The husband was so thrilled after his surgery that he recommended it to his wife, who was also farsighted. She underwent it 1 month later. Wilson was very careful to warn her she might not have the same surgical result. In fact, she still needs glasses to read. But her glasses no longer need to be so thick. 428
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Marguerite McDonald, M.D., always suggests monovision to her refractive patients who have presbyopia, with one eye for distance (dominant eye) and one eye for near. Otherwise, she feels they will have traded one pair of glasses for another. In hyperopia and presbyopia, in a patient who is +2.00 diopters in both eyes, Dr. McDonald performs a LASIK procedure and corrects the dominant eye for distance using a full +2.00 diopters correction. Patients aged 40 to 43 will be treated in the non-dominant eye to end up with a +1.00 addition to the +2.00 hyperopic correction. That is, they will have +3.00 diopters correction to induce myopia in the reading eye (non-dominant eye). In slightly older patients, those between 44 and 46, she induces a correction of +3.50 (+2.00 of hyperopia and +1.50 addition). In patients above 46 years, she induces a +3.75 correction (+2.00 of hyperopia and +1.75 diopters addition to induce myopia for reading). The strongest addition Dr. McDonald gives patients is +1.75. Otherwise, distance vision becomes so uncomfortable in the reading eye that patients have much difficulty fusing the images.
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Emmetropia with Presbyopia (Monovision Method)
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Krueger has treated several emmetropic Section 7 patients who complain about their inability to read. He makes them slightly myopic in the non-dominant Subjects Index eye, using LASIK. Only the non-dominant eye is treated. This monovision treatment give patients the ability to read, and yet not lose the distance vision in their other eye. In their patients also, Krueger uses the FDA approved Alcon Summit Autonomous Help ? LADARVision Laser.
Description of Operations on the Sclera to Improve Presbyopia In order to understand the current trends in surgical improvement of presbyopia through operations on the sclera, it is important that we keep in mind the two theories of accommodation that have
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been under intense discussion during the past 4 years. They are: Helmholtz's Theory: this has been and continues to be the generally accepted theory of accommodation since it was postulated in 1855. Helmholtz formally stated that accommodation occurs through a change in the shape of the lens. He postulated that the ciliary muscle is relaxed when the eye is focused for distance. The relaxed ciliary muscle maintains the zonule under tension to flatten the crystalline lens for distance viewing. When the eye focuses on a near object, the ciliary muscle contracts and releases tension on the zonule. The release of zonular tension results in increased curvature of both the anterior and posterior surfaces of the crystalline lens. This in turn allows the crystalline lens to become more curved due to elastic forces in the lens. Schachar's Theory: Ronald Schachar, M.D., from Texas has challenged the Helmholtz's theory and presented his own theory in 1995,
which has created a great deal of controversy. Dr. Schachar's theorizes that presbyopia occurs because normal lens growth, as a result of age, increases its equatorial diameter and, as a result, the lens equator moves closer to the ciliary muscle, rendering the contracting muscles less capable of steepening the crystalline lens curvature.
OPERATIONS FOR SCLERAL EXPANSION Two different operations performed on the sclera are currently used to surgically treat presbyopia without resorting to the monovision method. These operations are generally known as scleral expansion procedures. They are very different from one another. These operations are: 1) the anterior ciliary sclerotomy (ACS) (Figs. 40-1 and 40-2) and Schachar's procedure, or scleral expansion buckles
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Section 6 Section 7 Subjects Index Figure 40-1: Concept of Scleral Incisions (Slits) Technique for Correction of Presbyopia (ACS Procedure) This procedure involves the use of a 3 to 4 small radial sclerotomy incisions (slits S) over the area of the ciliary body (C) to induce a shift of the ciliary body out (red arrows). Each incision is 600 microns in depth. The mode of action of this operation theoretically is to change the distance between the ciliary body (C) and lens (L), possibly increasing the ability of zonular fibers to exert traction (white arrows) on the lens capsule and consequently change the shape of the lens. These incisions cause expansion of the sclera in the region of the ciliary muscle thereby changing the biomechanical forces and restore accommodation to some degree (pseudoaccommodation. Notice the change in shape (blue arrow) of the sclera in the area of the slits (S). (After Boyd´s "Atlas of Refractive Surgery").
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Section 4 Figure 40-2: External Configuration of Scleral Slits Technique for Correction of Presbyopia (ACS Procedure) This external view of the eye shows the location, size and number of radial sclerotomy incisions or slits (S) placed in the area between the extraocular muscles (M), for the treatment of presbyopia. The limitation of this procedure is that the scleral incisions close with time leading to regression. H. Fukasaku, M.D., in Japan has attempted to "integrate" this operation with the surgical principles of the Schachar 's procedure (Figs. 40-3 to 40-8) by inserting silicone expansion plugs or rods within the radial sclerotomy incisions to delay their closure, increase the effect of ACS and overcome regression to a limited extent. (After Boyd´s "Atlas of Refractive Surgery").
(Figs. 40-3 - 40-5). Krueger finds both of these methods problematic because the principles on which they are based go against the mainstream theories of Helmholtz. These methods are based on an opposing theory for loss of accommodation, and they intend to stretch the sclera overlying the ciliary musculature to make more space in the posterior chamber, allowing the lens more room to expand equatorially during accommodation. A number of vision scientists in the U.S., however, have made rather conclusive observations that confirm the accuracy of the Helmholtz theory which allows the lens to relax equatorially during accommodation. This leads us to wonder what scleral incisions (Figs. 40-1 and 40-2) and bands (Figs. 40-3 40-5) actually do. Krueger points out that in some 430
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cases these procedures seem to work; in others, they are unsuccessful. Murube believes that although Schachar's theory of accommodation may be incorrect, the surgical procedures based on his theory do work, although they result in small amounts of correction. One proposed explanation when they work is that these patients develop pseudo accommodation. Scleral implants and scleral incisions (slits) probably work according to the same mechanism. Krueger feels that something in the re-adjustment of the sclera is allowing the lens or the cornea to behave a little differently so that the patients perceive an improvement. It is very curious that when only one eye is treated with the scleral bands (Figs. 40-3 40-5) , patients often report that both the treated and untreated eyes can now see up close when nothing
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Figure 40-3: Schachar's Procedure External Configuration of Scleral Implants for Correction of Presbyopia This external view of the eye shows the location and size of the four scleral PMMA implants buried in the area between the extraocular muscles (M). One implant (I) is shown just before implantation into the scleral tunnel (T). Although the implant shown here looks like a straight rod, its real shape is curved, the center has a concave shape so that, when buried, as shown in this figure, it will exert pressure on the sclera inward over the ciliary body to lift it away from the lens, thereby altering the relative positions of the ciliary muscle and the lens. (After Boyd´s "Atlas of Refractive Surgery").
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Section 6 Section 7 Subjects Index Figure 40-4: Scleral Implant Surgical Technique for Correction of Presbyopia The conjunctiva has been reflected in the four quadrants. Two small parallel vertical slits have been made with a short diamond knife at 2 mm posterior to the limbus, pre-marked with dye. A long diamond knife (F) is used to create a scleral tunnel (arrow) between the two vertical slits. (After Boyd´s "Atlas of Refractive Surgery").
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Section 5 Figure 40-5: Scleral Implant Surgical Technique for Correction of Presbyopia The tubular implant (I) has been inserted into the scleral tunnel with forceps. This magnified view of one quadrant shows the final position of the scleral implant (I) within the scleral tunnel (T). At the two end points (entry and exit) the sclera has been pushed away over the ciliary body to lift the ciliary body away from the lens. As a consequence, the zonules become tense which in turn facilitates accommodation. In real life, the ends of the implant (I) do not protrude nearly as much as shown here for didactic purposes. (After Boyd´s "Atlas of Refractive Surgery").
was done to the other eye. Why should that happen? It is very important that we learn exactly what is the mechanism of action so we can understand what we are doing and ensure that we are not surgically harming the eye. A large database of scleral incision patients (ACS) is being collected by Spencer Thornton, M.D., and others in the U.S. They have not published their results, probably because they are waiting for long term follow-up. Steven Wilson, M.D., Professor and Chairman, Department of Ophthalmology, University of Washington Medical Center in Seattle, Washington
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believes that of the primary theories currently advanced to explain presbyopia, the Helmholtz theory is closer to the truth based on fairly conclusive data presented recently. There are occasional anecdotal reports form physicians who believe that successful treatment of individual patients can be based on scleral expansion theories (Figs. 40-1 - 40-5). Wilson points out that Robert Maloney. M.D. from Los Angeles, California, is a careful investigator who reports that some patients get increased accommodation using the Schachar's procedure. According to Wilson, even if the Shachar's hypothesis is
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incorrect, something involved in scleral expansion treatment corrects at least part of the problem. Wilson does not perform scleral expansion surgery because he does not believe it has enough efficacy to be warranted.
Changing the Anatomy of the Anterior Segment These surgical procedures are based on the theory that loss of accommodation is a problem of geometry rather than of muscle atrophy or hardening of the lens with age. The two operations that have been proposed and that we here describe change the anatomy of the anterior segment, altering the relative positions of the ciliary muscle and the lens. An operation on the sclera may possibly change the biomechanical dynamics in the anterior segment to restore accommodation (Figs. 40-1 to 40-5).
THE SCHACHAR PROCEDURE Another approach in the scleral expansion procedures has been spearheaded by Ronald Shachar, M.D., Ph.D from Texas. It is an ingenious procedure that involves placing four small implants partially buried in the sclera like small scleral buckles over the ciliary body to lift the ciliary body away from the lens (Figs. 40-3 to 40-5). These small buckles consist of small segments of polymethylmethacrylate (PMMA) in each quadrant. Although this surgery has been reported to restore accommodation and reading vision in some patients, data are still incomplete, and no published peer reviewed scientific studies have taken place. There is positive experience by prestigious surgeons that the operation seems to work, providing a small presbyopic correction perhaps through pseudo accommodation that enables some patients to read without glasses.
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ANTERIOR CILIARY SCLEROTOMY (ACS)
MODIFYING THE CRYSTALLINE LENS
This approach involves creating radial sclerotomy incisions in the sclera over the ciliary muscle (Figs. 40-1 and 40-2). These incisions cause expansion of the sclera in the region of the ciliary muscle, which changes the biomechanical forces and restores accommodation to some degree or more likely, a pseudo-accommodation. Dr. Spencer Thornton, who was a pioneer of this approach has found that it helps restore reading vision in some patients. The problem with this procedure is that the scleral incisions close with time and regression takes place in about 10 months. Hideharu Fukasaku, M.D., of Yokohama, Japan, has modified the original ACS procedure in order to avoid or significantly delay regressions. He performs eight 3-mm incisions divided equally in the four quadrants (Fig. 40-2). Each incision is 600 micron deep using a diamond keratotomy blade. He is inserting silicone - expansion plugs in each incision to delay closure of the incisions, increase the effect of ACS and overcome regression. His results seem to be encouraging although they don't last long enough. There is a significant reduction of presbyopia but again, does not last.
The next frontier in presbyopia correction will probably involve modifying the crystalline lens, Section 5 to restore its elastic properties or perhaps to change Section 6 its shape in some way. Then we could actually restore accommodation, rather than creating pseudo Section 7 accommodation or a multifocal corneal ablation. Krueger estimates that we are still years away Subjects Index from restoring real accommodation to the presbyopic lens. He is now working on using very short pulse lasers inside the lens to see if the properties of the lens can be changed. But no concrete data are yet available to show if this will work on the in vivo human lens. Application of laser shots to the crystalHelp ? line lens is at the stage of experimentation with animal models, and with explanted human cadaver lenses. Krueger has not seen long-term cataracts develop, although critics of these experiments predict this procedure will never work because of probable development of cataracts. The future of this technology is still uncertain but it is likely that wavefront technology will help us in the process of understanding this further.
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Chapter 41 PRESBYOPIA Guillermo Avalos-Urzua, M.D., Ariadna Silva-Lepe, M.D.
Introduction
Definition
Presbyopia is the age-related normal process where accommodation is lost and the eye is no longer capable to comfortably sustain the accommodation necessary for clear near vision. It is a fact that the range of accommodative amplitude decreases with increasing age, such that the nearest point that can be focused gradually recedes, leading (in humans, at least) to the need for optical prostheses for close work such as reading and, eventually, even for focus in the middle distance. It is the most frequent eye problem in the world, since 40% of the population is presbyopic. In Latin America there are 115 millions of presbyopic, and every year this number increases up to 3 millions; it is said that in 2010 there are going to be almost 145 millions. Even thought it is not a legal blindness cause, the cost from this problem in productivity loss is high in USA.
In presbyopia the nearest point that can be focused gradually recedes, leading to the need for optical prostheses for close work such as reading and, eventually, even for focus in the middle distance. For emmetropic persons, presbyopia seems to appear practically overnight when they reach their mid 40s. However, the loss of near focus is actually progressive over a person’s lifetime, whether he or she is emmetropic, myopic, or hyperopic, and the age at which a person requires assistance for near focus will depend in large part on his or her refractive error (Fig. 41-1).
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Help ? Figure 41-1. Clear visual zones in an emmetropic eye (a), neutralizing (b) and with add correction (c).
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Theories of Accommodation Helmholtz’s book on Physiological Optics is a careful combination of experimental observations and closely reasoned progressions of logic to demonstrate that accommodation occurs through a change in the shape of the lens, attributing the origin of this hypothesis to Descartes and mentioning an earlier version of this hypothesis, from Leeuwenhoek, which assumed that the lens material was itself contractile like muscle. He observed that the accommodative process is associated with, in addition to pupillary contraction and an anterior movement of the iris, an increased curvature of both the anterior and posterior surfaces of the crystalline lens. The anterior surface of the lens changes curvature with greater amplitude than the posterior surface, and these changes in lens shape result in (1) a thicker lens along the symmetry axis, (2) a thinner lens along the equatorial axis, (3) a shallowing of the anterior chamber as the anterior lens surface is moved forward, and (4) essentially no change in the distance from the cornea to the posterior lens surface along the symmetry axis. Thus, when the human eye is focused on infinity, the lens is under maximum stress and at its thinnest and least sharply curved. As accommodation to a closer focal point proceeds (Fig. 41-2), the contraction of the ciliary muscle is coupled with a controlled elastic recovery or relaxation that allows the lens to “round up” and make a greater refractive contribution to overall globe power through its more sharply curved shape and decreased anterior distance from the cornea. The zonular geometry described by Farnsworth and Burke is more complex, since some of the zonules from the anterior of the lens pass through the ciliary processes to attach quite posteriorly to the lens, near the ora serrata, while others can attach more anteriorly. The zonules from the posterior of the lens also attach in a posterior location, and the equatorial zonules attach perpendicular to the lens equator. During the contraction of the ciliary muscle, both the anterior and posterior zonular attachments to the ciliary body would be moved forward and inward, and the resultant change in shape of the lens would be a function of the relative degrees of relaxation of the variously oriented fibers.
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Figure 41-2: Schematic representation of retinal image for a near object.
The classical Helmholtz theory of accommodation has, over the years, not gone unchallenged and most recently has been opposed by Schachar et al. who suggest that increased zonular tension increases rather than decreases the power of the lens. This view is supported by a numerical analysis of the lens based on a linear form of the governing equations. Burd et al proposed an alternative numerical model in which the geometric non-linear behavior of the lens is explicitly included. Their results differ from those of Schachar and are consistent with the classical Helmholtz mechanism.
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Age-Related Changes of Accommodation Accommodative amplitude (the difference between the nearest and farthest point of comfortable focus) decreases with increasing age. The far point is essentially unaffected, while the near point gradually recedes (Fig. 41-3), resulting in an accommodative amplitude of only about 2 diopters by age 50 years, much of which comes from the pinhole effect of a constricted iris and the intrinsic depth of field of the crystalline lens itself. As the lens grows and thickens in the polar and equatorial directions, the location of internal regions relative to the cornea changes. Cortical growth, which along the optical axis is the same for the anterior and posterior regions, shifts the location of the lens nucleus in the anterior direction. The central
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Figure 41-3: Ranges of accommodation for an emmetropic (a), myopic (b) and hypermetropic (c) eye.
sulcus, too, is shifted toward the anterior. Thus as the mass of the lens increases, its center of mass is shifted toward the cornea, as are three of the four major refractive surfaces of the lens (the lens-aqueous boundary and the anterior and posterior cortex nucleus boundaries). These age-dependent changes, all other factors being unchanged, should result in a greater overall refractive contribution by the lens and concomitant degradation of far vision.
Signs and Symptoms As we already defined, presbyopia is the agerelated loss of the ability to comfortably sustain the accommodation necessary for clear vision. This loss of accommodation is not to be considered as abnormal, and it proceeds gradually throughout the whole life without any sudden alterations. At first no inconvenience is experienced, but eventually a time comes when the near point has receded beyond the distance to which the individual is accustomed to read or to
work or beyond the distances to which his arm allows him o her to hold the printage page, and then, being unable to see clearly. At early age the amplitude of accommodation (AA) is about 14D, and the near point is situated at 7 cm distance. At age of 36 it has reached 14 cm, and the AA is now 7 D; by the age of 45 it has reached 25 cm, and the AA is only 4D, at the age of 60 being only about 1D. This has been studied by Blystone who reported that in 23 years of practice recorded from his patients the age and the add power needed to correct presbyopia. He found in nearly 3,600 refractions a nearly parabolic relationship between age and addition from approximately the age of 40 to 75 years. The failure of accommodation becomes evident gradually, and as a rule becomes apparent Contents first in reading. Small prints becomes indistinct, and in order to get within the limits of the receding near Section 1 point, the patients tends to hold his head back and the book well forward until a distance is reached when Section 2 clear vision in any circumstances is difficult. Trouble is experienced at first in the evening, when the light is Section 3 dim and the pupils are dilated, permitting large Section 4 diffusion circles; at this time, too, after the work of the day, fatigue comes on easily. For this reason, in more Section 5 advanced years when the pupils become smaller, and Section 6 old person with no accommodation may see near objects with a fair degree of detail. Section 7 Complaint is usually made of visual failure rather than visual fatigue. Sooner or later, however, Subjects Index symptoms of eyestrain appear. The ciliary apparatus working near its limit becomes fatigued, and the accommodative effort, strained in excess of the convergence, gives rise to distress. Headaches may occur, and the eyes feel tired and ache, sometimes tend to assume a chronically suffused appearance. Help ?
Treatment The treatment of presbyopia is to provide the patient the best near vision doing so by the reinforcement of the accommodation, bringing the near point within a useful working distance or both. The correction of presbyopia requires knowledge of refraction, accommodative status and working point of the patient.
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Optical Devices
Bifocals
Beginning with the refraction for distance, an estimated add is chosen by subtracting half the amplitude of accommodation from the number of diopters needed for the desired working distance. With the estimated add in place, the resulting range of accommodation is measured and add adjusted so that the patient’s near tasks are brought within the zone of clarity and comfort. Usually the patient is best served by placing most of the range of clarity farther away than the chosen working distance, choosing a lesser add (it is better to undercorrect than overcorrect). This avoids blurring of the middle distance and gives a larger range of accommodation. For adds less than +1.25 D, separate reading glasses may be preferable to bifocals, as the patient is likely to want the add only for prolonged reading. Eyes with unequal visual acuities, but equal AA, should be given equal adds. On the other hand, when the amplitudes of accommodation are unequal, adds are prescribed so that each eye is using half of its respective amplitude of accommodation for clarity at the desired reading distance. The presumption here is that this amount of accommodation will be produced by equal accommodative innervation of the two eyes.
Translating designs use temporally spaced images through two distinct contact lens zones: one for distance and one for near. The retina is expected to receive only one focused image at a time. Translating lenses have either a segment or an annular-concentric design. Segment bifocal contact lenses resemble their spectacle counterparts in having superiorly located distance and inferiorly located reading powers. The translation of the lens that occurs with a change in gaze is accompanied by the shift of the visual axis into the appropriate zone as the eye rotates under the lens. Proper orientation of segment bifocal designs is achieved by prism ballasting, lens truncation, and periballasting. Lens wearing comfort may be Contents compromised by the tendency of these lenses to position low. Patients having hyperopic refractive Section 1 errors tend to be more successful with these lens Section 2 designs. Concentric translating bifocal contact lenses Section 3 incorporate the reading power circumferentially and therefore do not require a specific rotational Section 4 orientation. The transition from the center distance power to the peripheral reading add is abrupt. Since Section 5 translating bifocal designs are gaze-dependent, near Section 6 acuity is achieved only in the traditional reading posture. Patients requiring near acuity in primary Section 7 gaze are poor candidates for this design. Since Subjects Index predictable translation is required, translating soft lenses are less effective than translating rigid lenses.
CONTACT LENSES: MONOVISION, BIFOCALS, MULTIFOCALS Monovision
The monovision approach to contact lens use Multifocals (Simultaneous Vision) utilizes one eye for distance and the other for near vision. Although the dominant eye is usually selected Simultaneous vision lens designs are based for distance correction, this is not mandatory. This on the concurrent presentation of distance and near method of correction provides functional distance images on the retina, and their success is dependent and near visual acuity but may compromise stereopsis, on the patient’s ability to ignore the undesired image. contrast sensitivity, and other aspects of binocular Several designs are available: annular-concentric, visual function. Patients with uncompromising vision aspheric, and diffractive. requirements who need higher add powers (more than 2.00 D) are usually not good candidates for SURGICAL METHODS monovision correction unless the reading add is prescribed in steps over a period of time. For some patients, standard optical correction for presbyopia is not satisfactory. That is why surgeons
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are trying to develop some techniques to reverse this state. Most of them are undergoing the investigative process.
SCLERAL TECHNIQUES Anterior Ciliary Sclerotomy (ACS) (Thornton’s Technique) Anterior ciliary Sclerotomy (ACS) was inadvertently performed by the first radial keratotomy surgeons (RK), who continued their incisions past the limbus into the anterior sclera, reversing its affect and causing less than predicted hyperopic shifts. These incisions produced regression and undercorrection arose as complication. The theory behind an incisional reversal of presbyopia involves placing incisions radially, beginning in the limbus and carried back to, but not over, the pars plana to avoid retinal complications. The ciliary body expands the globe and increases the space for the ciliary body zonular complex. The underlying rationale of ACS is based on the observation that the lens is ectodermic in origin and constantly grows throughout life, gradually “crowding” the posterior chamber and eventually preventing full function of the ciliary body/zonular complex. Rather than a loss of elasticity of the lens with age, it is felt that this “crowded” state is the cause of the reduction of lens power change with attempted accommodation. If ciliary body is impaired in its ability to change the shape of the lens because it is “crowded” by the lens, then making more room for the ciliary body would allow more space for the lenszonule complex. By expanding the globe in the area of the ciliary body, this could be accomplished. The ACS technique involves placing eight or more symmetrical, partial-thickness radial incisions into the sclera over the ciliary body to allow an expansion of the sclera and resulting increase in scleral diameter over the ciliary body. This allows an increased area for ciliary muscle action and consequent increased zonular effectiveness in changing the focal power of the lens.
Under topical anesthesia, four radial incisions (first protocols used eight) through the bulbar conjunctiva and tenons at 12, 3, 6 and 9 o’clock are performed. Blunt dissection under the conjunctiva is made and this opened are pulled to one side and to the other. Four radial scleral incisions are made in each quadrant, beginning 1 mm back from the surgical limbus and carried 2 to 3 mm posteriorly, to cut circumferential ligament. These incisions are 95% sclera depth, calculated by ultrasound microscopy, as reported by Dr. Fusaka . According to Dr. Thornton, surgeons performed procedures on 157 eyes that have more than 6 months follow-up. The age range was from 42 to 66, with an average age of 47. The preoperative accommodative amplitude was from 1.3D to 2.2D, with a mean of 1.7 D. Average reading vision with Contents distance correction was J7. Six months postoperative amplitude ranged Section 1 from 1.9 D to 4.7 D, with a mean of 2.8D reading J1 to J2 with distance correction. The average increase Section 2 of accommodation was 1.2D in both phase 1 and 2 despite the regression noted in phase 1. The average Section 3 regression of effect for all 157 cases was 2.7D. Section 4 The surgery lowered intraocular pressure (IOP) by an average of 2mmHg to 4 mmHg. Transient Section 5 elevation of IOP occurred in only two cases. Limbal Section 6 perforation with an irregular pupil in one case, and perforation into the ciliary body requiring a suture in Section 7 one case. There was no visual loss and no infections in this series, however patients did experience myopic Subjects Index shifts of 0.5D to 1D. Regressions were more common and greater in phase 1 (8 incisions). Conclusions are not definitive because techniques varied an evolved. The measurements of accommodation are largely subjective that’s why the technique needs to be improved and standardized Help ? for consistent and reproducible results. A carefully monitored, multicenter clinical trial is needed before ACS would be recommended for general use.
Scleral Expansion Band - (Schachar´s Technique) Schachar et al recently proposed an alternative accommodative mechanism for the primate eye
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that is similar to a theory originally proposed by Tschering. They believe that the equatorial zonule inserts to the anterior aspect of the ciliary muscle at the root of the iris, and the posterior zonule inserts into the posterior ciliary body. Schachar and Anderson contend that contraction of the ciliary muscle causes a posterior-outward movement of the anterior ciliary muscle toward the sclera at the iris root, increasing tension on the equatorial zonular fibers while releasing tension of the anterior and posterior zonular bundles. They believe that this provides a net outward-directed force at the lens equator through the equatorial zonular fibers. This force, would pull the lens equator toward the sclera during accommodation and, together with the concurrent relaxation of the anterior and posterior zonular bundles, would cause a flattening of the peripheral lens surface while increasing the central anterior and posterior lens surface curvatures. From a theoretical standpoint, pulling on the lens equator could cause an increase in the central lens curvatures, depending on the viscoelastic properties of the lens. This theory, unlike that of Tschering, identifies no role for the vitreous. Schachar believes that the presbyopia is due to the continued growth of the lens throughout life, which results in an increased lens equatorial diameter, a crowding of the posterior chamber, and a reduction in tension of the zonular fibers at the lens equator with increasing age. On the basis of this theory, this would result in a failure of zonular tension to increase sufficiently during contraction of the ciliary muscle (Fig. 41-4). Schachar´s surgical procedure for the reversal of presbyopia, is intended to increase the scleral diameter at the ciliary region, reintroducing zonular tension at the lens equator. He predicts that the lens equator will move toward the sclera and that the lens equator diameter will increase during accommodation. The technique consists of inserting four polimethylmetacrilate implants into an scleral tunnel performed 6mm from the limbus. The sclerotomy is made with a 5 mm diamond knife in a size of 900 µm, the implant is inserted leaving both free extremes outside the sclera. The implant over the ciliary body perform an outward traction, which theorically, would restore accommodation.
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Figure 41-4: Schachar´s force diagram of the circular fibers at equilibrium. Fa- force directed towards the effective attachment point of the equatorial zonules, Fc- force of the circular fibers, Fp-the force directed towards the posterior radial fibers, Rresultant force transmitted by the radial fibers that can be divided in Fa and Fc.
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This technique is experimental, but results Section 4 from some trial centers in Puerto Vallarta and Tijuana Section 5 (Mexico) and Marseille (France), show an average dioptric change of 2.33D. Section 6 There are groups, like Glaser et al, who found no accommodation with SEB. They measured Section 7 accommodation with objective infrared refractometry Subjects Index in three subjects examined by an independent observer. They proposed that this difference can be attributable to the fact that Schachar´s group used only subjective near vision as an assessment of accommodation. They conclude that, on the base of retinoscopy aberrations, that surgical expansion of the sclera may induce lenticular aberrations in a multiHelp ? focal optical system, rather than true accommodation. Mathew refers that there are reasons suggesting that further verification of the efficacy of SEB would be prudent, since Schachar´s results of improving accommodation are based on subjective recordings of near vision, utilizing same near card in the “push-up” testing. Sing et al report as complication of SEB scleral thinning with resultant axial lengthening and
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myopic shift in one case, and Yee reports anterior segment ischemia in some of his patients.
INTRACORNEAL TECHNIQUE Intracorneal Implants The theoretical benefits of synthetic keratophakia over conventional cornea lamellar procedures are the elimination of donor concerns and superior refractive predictability. Additionally, synthetic material can be inspected for optical quality and power, and it can be sterilized. Several materiales have been used, as is the unfenestrated polysulfone intracorneal lens by Horgan’s group, which appears to be associated with color change and varying degree of stromal opacity in eyes evaluated 12 years postoperatively and this cannot be considered clinically acceptable. Permalens hydrogel intracorneal lenses, highly glucose-permeable with an equilibrium water content of 68% (Lidofilcon A), seem to be well tolerated by the corneal stroma and can provide predictable refractive results. Limitations of the procedure are uneven microkeratome resections, loss of best-corrected visual acuity, and irregular astigmatism in some patients, as reported by Steinert. Although their data show good evidence of biocompatibility of the implant material, technical surgical progress is needed to advance this procedure into clinical therapeutic practice. CxGelSix is a novel type VI collagen preparation studied by Leskull et al as a biomaterial in the rabbit cornea stroma. They found this disc does not alter the structure of the corneal epithelium above the implant, suggesting normal transport of nutrients trough the implant. This material is remarkably stable despite its exposure to endogenous enzymes during inflammation and wound healing. They conclude that the result of the study suggest that CxGelsix is potentially useful as a biomaterial. In Colombia, Barraquer and his group implanted in humans intracorneal hydrogel lenses (Permalens) and reported good tolerability and their refractive results were stable. The use of this intracorneal implants for presbyopia is still in an experimental phase.
INTRAOCULAR TECHNIQUES 1. Pseudoaccommodative IOL (A-45) This is a silicon lens that contacts the vitreous and its movement is done by ciliary muscle contraction and the vitreous pressure from behind. For each millimeter of anterior movement, this lens gives 2D of accommodation. The results of 16 patients reached a visual capacity near J4 or better. This technique is also experimental and more trials are needed to start using this in the clinic as reported by Avitable and his group (Fig. 41-5).
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Figure 41-5: Pseudoaccommodative IOL and its changes.
2. Multifocals (IOLsM)
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Conventional IOLs have one focal point, and after implantation, patients have clear vision at one distance only. Bifocal, distance, or reading glasses are required to provide a usable vision at an additional focal distance Multifocal IOLs were recently developed in an effort to treat both surgical aphakia and loss of accommodation. Jacobi et al implanted in 29 patients bilateral multifocal IOL with asymmetrical light
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distribution for far and near focus. Each patient had a distant-dominant multifocal IOL implanted in one eye and a near-dominant multifocal IOL implanted in the fellow eye. They concluded that bilateral implantation of asymmetrical diffractive IOL is an effective alternative for restoring simultaneous distance and near vision with a potential for improved contrast sensitivity compared with conventional multifocal IOLs.
3M Multifocal IOL This lens design is based on diffractive optics, whereby light is partitioned into two focal points, one for distance vision and one for near vision. With diffractive optics, the wave nature of light is manipulated to allow the wave fronts to combine constructively and destructively to place light at different focal points. Forty-one percent of the light entering the eye is focused at the distance focus point, and 41% is focused at the near focus point. The remaining 18% is focused at higher orders of diffraction, not contributing to the image that is perceived. Only one focus point is located directly on the fovea at one time, giving one clear image. The precise placement of light is accomplished by the microscopic diffractive structure (steps) embedded onto the posterior surface of the IOL in a multiple ring pattern. The spacing and height of each ring (20 to 40) determine the power of the near focal point or add power of the lens. One of the primary advantages of this lens is that the entire lens surface contributes to both focal points. As a result, lens performance should function independently of pupil size for both distance and near vision. The results from the clinical evaluation of the Food and Drug Administration (FDA) study for the 3M diffractive multifocal IOL demonstrated that the overall uncorrected distance visual acuity after one year from the surgery showed 57% of patients with 20/40 or better acuity. In this same group, 78% achieved J3 or better. Measurements of contrast sensitivity consistently documented a small loss, which is considered clinically insignificant. This multifocal lens appears to work very well for most patients, and the study showed several considerations that are important for optimizing clinical performance and patient satisfaction: patient
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selection, realistic expectations, accurate biometry, and adequate control of surgical procedures.
AMO-ARRAY Multifocal IOL The goals when using the ARRAY Multifocal IOL are: 1) Maintain distance acuity and function (20/20) distance, 2) Decrease dependence on glasses (J3 or better), 3) Increase range of focus (useful near and intermediate). The optical design of the lens has a progressive multifocal optic; the refractive design has a multifocal power on the anterior surface. Is a distance dominant lens with a 3.5 diopter add. The lens has five concentric zones, each zone repeats entire refractive sequence of variable and continuous power. The available range goes from 6 to 30 D, in 0.5D steps (Fig. 41-6). These lenses shouldn’t be used in patients with unilateral cataracts, with pre-existing pathology, when we expect high residual post-operatory astigmatism, when the patients have professional nighttime jobs, and when nighttime glare is the presenting complaint. Multifocal IOLS produce a 41% of independence for daily life [distance vision (85% vs. 52%) and near vision (38.4% vs. 9.8%)] , in contrast of the 11.7% from monofocal IOLs. Comparing with monofocals they produce halos in 9.3% of cases and halos in 3.3%. Binocularity is present in 82% and
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Figure 41-6: Optical design of multifocal AMO-ARRAY IOL
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Vaquero-Ruano and his group report that with appropriate patient selection, the AMO Array IOL provide distance acuity and contrast sensitivity similar to that of monofocal IOLs, and excellent intermedi-
ate vision. Near vision, without spectacles, with the multifocal IOL was functionally acceptable although short of refractive power for best acuity results (Table 1).
Table 1 Comparative representation between monofocal and multifocal IOL’s
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LASER TECHNOLOGY TECHNIQUES Laser Presbyopia Reversal (Lin´s Technique) J.T. Lin invented laser presbyopia reversal (LPR), the first technique that uses an infrared laser to counteract the effects of ocular aging. The IR-3000 device incorporates an infrared laser, a beam-shaping delivery unit, and a scanning mechanism. This laser is a 3m range, cold laser that has a minimal thermal effect on ocular tissue. In the LPR procedure, the laser produces changes in the zonular activity removing between 500 and 600 µm of tissue from outside the optical zone. This is one of the major advantages of this procedure, so that the patient’s distance vision remains unaffected. Another advantage is that the procedure can be completed in 5 to 0 minutes, as stated by Lin. The first international patients who underwent LPR in South America, have not had a regression on visual acuity after a follow-up of about 7 months. Clinical trials started in Venezuela in June 1999 showed data from 100 patients aged from 42 to 65 who had 1.5 to 3.5D of presbyopia. These data were presented in the fall of 2000. Clinical trials have not yet begun in United States, also this technique has not been approved by FDA.
Excimer Laser Keratectomy
Photorefractive
Using a specially designed mask, Vicinguerra et al developed a procedure for correcting presbyopia with EXCIMER laser photorefractive keratectomy (PRK). A mask consisting of a mobile diaphragm formed by two blunt blades was used to ablate a 10-17 µm deep semilunar-shaped zone immediately below the pupillary center, steepening the corneal curvature in that area (videokeratography controlled), in three patients. After an initial regression of 1 D during the first 6 months, the presbyopic correction remained stable for the duration of one-
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year follow-up period, enabling uncorrected near vision of J3 in al three eyes. Uncorrected distance visual acuity was not altered. Contrast sensitivity was slightly decreased only at the 11% level. This technique is also in the experimental phase and more clinical studies are required before it can be used in the clinical practice.
LASIK TECHNIQUES For some patients, standard optical correction for presbyopia is not satisfactory, that’s why the latest technology has been under experimentation in order to treat this problem. LASIK is an alternative method for correcting presbyopia. Myopia, hypermetropia and astigmatism are nowadays treated with LASIK by modifying the corneal curvature, that is the rationale under the treatment for presbyopia. Up to day, two techniques are under trial for presbyopia: monofocal vision and PARM.
a) Monofocal Treatment
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The main goal of this technique is to make the patient anisommetropic, in this way one eye is Section 5 used for distance vision and the other for near vision. Section 6 This treatment is not indicated in all subjects, since its residual consequences are partial loss of stereop- Section 7 sis, astenopia, headache, aniseiconia and decreased Subjects Index binocularity. It is possible to increase the myopic effect in the eye for near vision with a posterior LASIK treatment, as the presbyopic changes increase, but this will generate more anisometropia with the concomitant astenopia. Monofocal treatment is indicated for people with low demands on distance and near vision, like people who drive only in the city, people who are not used to read and do not perform manual jobs. So this treatment is not recommended for night drivers, accountants, computer users, engineers, etc. Frequently, patients with monocular vision depend on glasses for different activities, either distance or near vision.
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b) Presbyopia - Avalos and Rosakis Method (PARM ) With this LASIK technique the corneal curvature is modified, creating a bilateral bifocal cornea. The preoperatively corneal curvature is the main factor to consider in this type of corrective method. In order to have a high quality of vision, corneal keratometry should not be modified up to 48 D. Corneas
with more than 48 D produce undesired optical alterations like glare, halos, decreased visual acuity and decreased contrast sensitivity. For each hypermetropic diopter corrected, the corneal curvature increases in 0.89 keratometric diopters as an average, that is why it is recommended to treat patients with keratometry in the range between 41 to 43 D to obtain postoperatively curves under 48 D (Fig. 41-7)
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Figure 41-7: Pre-op topography of patient treated with PARM technique.
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The corneal flap performed with the microkeratome must be between 8.5 to 9.5 mm in order to have an available corneal surface for treatment of at least 8 mm, in this way the laser beam does not touch the temporal edge of the flap. Pachymetry is not fundamental for this treatment. PARM has been used to treat patients with 20/20 distance vision and addition of +3.5D; for hypermetropic patients up to +3.5D in order to treat the addition for presbyopia, always taking into account the preoperatively keratometric measurements, as previously explained. If astigmatism is present it is recommended to use as a limit 2.50D and in myopic patients the limit is –5.00D
Because of the corneal shape produced after the surgery , there is an induced astigmatism between 0.50 to 0.75 D, which could decrease one or two lines of visual acuity. The usual LASIK re-treatment average for myopia, astigmatism and hyperopia is 7%, in cases treated for presbyopia it is increased up to 22% as seen in Dr. Avalos and Dr. Rozakis patients in the first two years of trial, after modifying the nomogram this retreatment percentage should diminish under the range of 12% (Fig. 41-8). This group has not seen complications from the surgery, beside those already reported for regular LASIK technique.
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Figure 41-8: Post-op topography of patient treated with PARM technique.
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Conclusion Presbyopia treatment is one of the main goals for refractive surgery. Up to date and with the treatment techniques available one can consider that this is possible. As we have reviewed in this chapter, there are several treatment techniques for presbyopia, the new have been remarkable. This different techniques can be used for different types of patients and all of the surgical ones are in experimental phase, so they need to be improved. In a near future we will be finally say that there is a real solution for a refractive problem that affects to almost all the world population after the fourth decade of life.
REFERENCES
1. 6th. Varilux presbyopia forum. www.presbyopia.org 2. Aguilar M, Mateos Felipe. Óptica Fisiológica Tomo 1. España: Universidad politécnica de Valencia, 1993:191-214 3. Atwood JD. Presbyopic contact lenses. Curr Opin Ophthalmol 2000;1:296-8 4. Avitabile T, Marano F. Multifocal intra-ocular lenses. Curr Opin Ophthalmol 200l;l2:l2-l6 5. Barraquer JI, Gomez ML. Permalens hydrogel intracorneal lenses for spherical ametropia. J Refract Surg 1997;13:342-8 6. Beers AP, Van Der Heijde GL. Age-related changes in the accommodation mechanism. Optom Vis Sci 1996;73:235-42 7. Beers AP, Van der Heijde GL. Presbyopia and velocity of sound in the lens. Optom Vis Sci 1994; 71:2503 8. Blystone PA. Relationship between age and presbyopic addition using a sample of 3,645 examinations from a single private practice. J Am Optom Assoc 1999;70:505-8 9. Boyd BF. Atlas de Cirugía Refractiva. Colombia: Highlights of Ophthalmology, 2000: Capítulo 9 10. Burd HJ, Judge SJ, Flavell MJ. Mechanics of accommodation of the human eye. Vision Res 1999;39:1591-5.
11. Chylack LT Jr: Aging changes in the crystalline, lens and zonules. En: Albert and Jakobiec ed. Principles and Practice of Ophthalmology (Clinical practice). Philadelphia: WB Saunders company, 1994: Chapter 54B. 12. Cuadernos de óptica oftálmica: Lentes de adición progresiva. Essilor Internacional 13. Dimitri TA, Leon Strauss. Principles of applied clinical optics. En: Albert and Jakobiec ed. Principles and Practice of Ophthalmology (Clinical practice). Philadelphia: WB Saunders company, 1994: Chapter 291 14. Gal et al. Image formation by bifocal lenses in a trilobite eye? Vision Research 2000;40:843-53 15. Gilmartin B. The aetiology of presbyopia: a summary of the role of lenticular and extralenticular structures. Ophthalmic Physiol Opt 1995; 15:431-7 16. Glasser A, Campbell MC. Presbyopia and the optical changes in the human crystalline lens with age. Vision Res 1998;38:209-29 17. Glasser A, Kaufman PL. The mechanism of Contents accommodation in primates. Ophthalmology 1999;106:863-872 Section 1 18. Herreman R. Manual de Refractometría clínica. 2ª. ed. España: Salvat Editores, 1994: 52-53 Section 2 19. Hom MM. Monovision and LASIK. J Am Optom Section 3 Assoc 1999;70:117-22 20. Horgan SE et al. Twelve years follow-up of Section 4 unfenestrated polysulfone intracorneal lenses in human sighted eyes. J Cataract Refract Surg 1996;22:1045-51 Section 5 21. Jakobi FK et al. Bilateral implantation of asymmetrical diffractive multifocal intraocular lenses. Arch Section 6 Ophthalmol l999;ll7:l7-23 Section 7 22. Kaufman P, Glasser A. The mechanism of Accommodation in primates. Ophthalmology 1999; Subjects Index 106:863-872. 23. Kaufman P. Acomodación y presbiopía: Aspectos neuromusculares y biofísicos. En: Hart W, ed. Adler Fisiología del ojo. Aplicación clínica. España: Mosby, División de Times Mirror de España,1994: 393-404 24. Kaufman P. Acomodación y presbiopía: Envejecimiento de los mecanismos de acomodación. En: Hart W, ed. Adler Fisiología del ojo (Aplicación clínica). España: Help ? Mosby, División de Times Mirror de España, 1994:404410 25. Key JE, Morris K, Mobley CL. Prospective clinical evaluation of Sunsoft Multifocal contact lens. CLAO J 1996;22:179-84 26. Koretz F. Accommodation and presbyopia. En: Albert and Jakobiec ed. Principles and Practice of Ophthalmology Clinical practice). Philadelphia: WB Saunders company, 1994: Chapter 16
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27. Koretz JF, Cook CA, Kaufman PL. Accommodation and presbyopia in the human eye. Changes in the anterior segment and crystalline lens with focus. Invest Ophthalmol Vis Sci 1997;38:569-78 28. Leskul M et al. CxGELSIX: a novel preparation of type VI collagen with possible use as a biomaterial. Cornea 2000;19:194-203 29. Lindstrom RL. Food and drug administration Study update. One-year results from 67l patients with the 3M multifocal intraocular lens. Ophthalmology l993;l00:9l97 30. Mathews S. Scleral expansion surgery does not restore accommodation in human presbyopia. Ophthalmology 1999; 106:873-877. 31. Michaels DD.: Visual optics and refraction a clinical approach, Saint Louis, 1975, Mosby Company, Chapter 16:268-314 32. Oates DC, Belcher CD. Aging changes in trabecular meshwork, iris and ciliary body. En: Albert and Jakobiec ed. Principles and Practice of Ophthalmology (Clinical practice). Philadelphia: WB Saunders company, 1994: Chapter 53B 33. Rosenthal P, Cotter JM. Contact lenses. En: Albert and Jakobiec ed. Principles and Practice of Ophthalmology (Clinical practice). Philadelphia: WB Saunders company, 1994 : Chapter 292. 34. Salud visual España. www.Essilor.es 35. Schachar RA y col. In vivo increase of the human lens equatorial diameter during accommodation. Am J Physiol 1996; 271:R670-6 36. Schachar RA, Anderson DA. The mechanism of ciliary muscle function. Ann Ophthalmol 1995;27:126132 37. Schachar RA, Huang T, Huang X. Mathematic proof of Schachar´s hypothesis of accommodation. Ann Ophthalmol 1993;25:5-9 38. Schachar Ra. Cause and treatment of presbyopia with a method for increasing the amplitude of accommodation. Ann Ophthalmol 1992;24:445-7 39. Schachar RA. http://www.presbycorp.com 40. Schachar RA. Pathophysiology of accommodation and presbyopia. Understanding the clinical implications. J. Florida M.A 1994;81:4 41. Singh G, Chalfin S. A complication of scleral expansion surgery for treatment of presbyopia. Am J Ophthalmol 2000;130:521-33 42. Steinert RF et al. Hydrogel intracorneal lenses in aphakic eyes. Arch Ophthalmol 1996;114:135-41 43. Strenk SA. Ages-related changes in human ciliary muscle and lens: a magnetic resonance imaging study. Invest Ophthalmol Vis Sci 1999; 40:1162-9
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44. Sunsoft. www.sunsoftlenses.com 45. Thornton SP. Presbyopia: The new frontier. A Report on a procedure to reverse presbyopia: anterior ciliary sclerotomy. http://www.slackinc.com/eye/osn/ 1996a/presby.asp 46. Vaquero-Ruano M et al. AMO Array multifocal versus monofocal intraocular lenses: long-term follow-up. J Cataract Refract Surg l998;24:ll8-23 47. Vicinguerra P et al. EXCIMER laser photorefractive keratectomy for presbyopia: 24-month follow-up in three eyes. J Refract Surg 1998;14:31-37 48. Wahl HW et al. Deteriorating vision in the elderly: double stress?. Ophthalmologe 1998;95:389-99
Guillermo Avalos-Urzua, M.D. Av. Morelos #617 Centro Guadalajara, Jalisco , México E-mail:
[email protected]
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NO ANESTHESIA CATARACT / CLEAR LENS EXTRACTION
Chapter 42 NO ANESTHESIA CATARACT / CLEAR LENS EXTRACTION Athiya Agarwal, M.D., Sunita Agarwal, M.S., Amar Agarwal, M.S.
technique, surgeons throughout the world have been attempting to make this new procedure safer and easier to perform while assuring good visual Contents outcome and patient recovery . The fundamental goal of Phaco is to remove the cataract with minimal Section 1 disturbance to the eye using least number of surgical Introduction manipulations. Each maneuver should be performed Section 2 th On June 13 1998 at Ahmedabad, India the with minimal force and maximal efficiency should Section 3 first No-anesthesia cataract sur gery was done by be obtained. The latest generation Phaco procedures Section 4 the authors (Amar Agarwal) at the Phako & began with .Howard Dr Gimbel’s “divide and Refractive Surgery conference.This was performed conquer” nuclear fracture technique in which he Section 5 as a livegery sur in front of 250 delegates. This has opened up various new concepts in cataract simply split apart the nuclear rim. Since then we Section 6 surgery (1). In this surgery the technique of karate have evolved through the various techniques namely four quadrant cracking, chip and flip, spring Section 7 chop was used. For high refractive errors, clear lens surgery, stop and chop and phaco chop. Clear lens removal by phacoemulsification Subjects Index extraction with phacoemulsification is a very good alternative. In such cases, if necessary one can implant is a very good alternative to manage refractive errors. an IOL or leave the patient aphakic if the myopia is In these cases, as the nucleus is soft one can use only very high & does not warrant an IOL. This technique phacoaspiration to remove the nuclei, rather than is very useful in hypermetropes, as Lasik does not use ultrasound power. Note from the Editor in Chief: Chapters 42 and 43 are presented in this Volume because both are focused toward the use of this technique for purposes of correction of high refractive errors.
give excellent results in such cases. The most commonly done refractive surgery in the world is not PRK or LASIK, it is cataract surgery. This is why this chapter will discuss phacoemsulification techniques for removal of cataract as well as clear lens extraction.
Karate Chop
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Unlike the peripheral chopping of Nagahara or other stop and chop techniques we have developed a safer technique called ”Central Anterior chopping” or “karate chop”. In this method the phaco tip is NUCLEUS REMOVAL embedded by a single burst of power in the central TECHNIQUES safe zone and after lifting the nucleus a little bit (to lessen the pressure on the posterior capsule) the Since the introduction of Phacoemulsification chopper is used to chop the nucleus. In soft nuclei, it as an alternative to standard cataract extraction is very difficult to chop the nucleus. In most cases, LASIK AND BEYOND LASIK
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one can take it out in toto. But if the patient is about 40 years of age then one might have to chop the nucleus. In such cases we embed the phaco probe in the nucleus and then with the left hand cut the nucleus as if we are cutting a piece of cake. This movement should be done three times in the same place. This will chop the nucleus.
If the astigmatism is plus at 90 degrees then the incision is made superiorly. (Read the chapter on corneal topography). First of all, a needle with viscoelastic is injected inside the eye in the area where the second site is made (Figure 42-1). This will distend the eye so that when you make a clear corneal incision, the eye will be tense and one can create a good valve. Now use a straight rod to stabilize the eye Soft Cataracts with the left hand. W ith the right hand make the clear In soft cataracts, the technique is a bit corneal incision (Figure 42-2). When we started making the temporal different. W e embed the phaco tip and then cut the incisions, we positioned ourselves temporally . The nucleus as if we are cutting a piece of cake. This problem by this method is that, every time the should be done 2-3 times in the same area so that the microscope has to be turned which in turn would cataract gets cut. It is very tough to chop a soft affect the cables connected to the video camera. cataract, so this technique helps in splitting the Further the theatre staf f would get disturbed cataract. between right eye and left eye. o T solve this Contents problem, we then decided on a different strategy. W e Section 1 Agarwal Chopper have operating trolleys on wheels. The patient is wheeled inside the operation theatre and for the right Section 2 We have devised our own chopper . The eye the trolley is placed slightly obliquely so that the Section 3 other choppers, which cut from the periphery, are surgeon does not change his or her position. The blunt choppers. Our chopper is a sharp chopper . It surgeon stays at the 12’o’clock position. For the left Section 4 has a sharp cutting edge. It also has a sharp point. eye the trolley with the patient is rotated horizontally Section 5 The advantage of such a chopper is that you canso that the temporal portion of the left eye comes at chop in the center and need not go to the periphery . 12’o’clock. This way the patient is moved and not Section 6 In this method by going directly into the the surgeon. Section 7 center of the nucleus without any sculpting ultra sound energy required is reduced. The chopper Rhexis Subjects Index always remains within the rhexis margin and never goes underneath the anterior capsule. Hence it is Capsulorhexis is then performed through the easy to work with even small pupils or glaucomatous same incision (Figure 42-3). While performing the eyes. Since we don’t have to widen the pupil, there rhexis it is important to note that the rhexis is is little likelihood of tearing the sphincter andstarted from the center and the needle moved to the right and then downward.This is important because allowing prostaglandins to leak out and cause Help ? inflammation or cystoid macular edema. In this today concepts have changed of temporal and nasal. technique we can easily go into even hard nuclei on It is better to remember it as superior, inferior, right or left. If we would start the rhexis from the center the first attempt. and move it to the left then the weakest point of the rhexis is generally where you finish it. In other KARATE CHOP TECHNIQUE words, the point where you tend to lose the rhexis is near its completion. If you have done the rhexis from Incision the center and moved to the left, then you might have an incomplete rhexis on the left-hand side either Ours is a modification of the Nagahara chop. inferiorly or superiorly . Now, the phaco probe is The important feature is that we don’ t chop the always moved down and to the left. So every stroke periphery. A temporal clear corneal section is made. 452
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Section 1 Figure 42-1: Eye with cataract. Needle with viscoelastic entering the eye to inject the viscoelastic. This is the most important step in no anesthesia cataract/clear lens surgery. This gives an entry into the eye through which a straight rod can be passed to Figure 42-3: Rhexis being done with a needle. stabilize the eye. Note no forceps hold the eye.
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of your hand can extend the rhexis posteriorly creating a posterior capsular rupture. Now , if we perform the rhexis from the center and move to the Help ? right and then push the flap inferiorly- then if we have an incomplete rhexis near the end of the rhexis it will be superiorly and to the right. Any incomplete rhexis can extend and create a posterior capsular tear. But in this case, the chances of survival are better. This is because we are moving the phaco probe down and to the left, but the rhexis is incomplete up and to the right. Figure 42-2: Clear corneal incision. Note the straight rod inside If you are a left handed person, start the the eye in the left hand. The right hand is performing the clear corneal incision. This is a temporal incision and the surgeon is rhexis from the center and move to the left and then sitting temporally. down.
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Hydrodissection Hydrodissection is then performed (Figure 42-4). We watch for the fluid wave to see that hydrodissection is complete. We do not perform hydrodilenation or test for rotation of the nucleus. Viscoelastic is then introduced before inserting the phaco probe.
Karate Chop - Two Halves We then insert the Phaco probe through the incision slightly superior to the center of the nucleus (Figure 42-5). At that point apply ultrasound and see that the phaco tip gets embedded in the nucleus (Figure 42-6). The direction of the phaco probe should be obliquely downwards toward the vitreous and not horizontally towards the iris. Then only the nucleus will get embedded. The settings at this Figure 42-4: Hydrodissection
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Figure 42-5: Phaco probe placed at the superior end of the rhexis.
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Figure 42-6: Phaco probe embedded in the nucleus. We started from the superior end of the rhexis and note it has got embedded in the middle of the nucleus. If we had started in the middle then we would have embedded only inferiorly, that is, at the edge of the rhexis and chopping would be difficult.
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Remember, do not go to the periphery for stage are 70% phaco power, 24 ml/minute flow rate and 101 mm of Hg suction. By the time the phaco chopping, but do it at the center. Once you have created a crack, split the tip gets embedded in the nucleus the tip would have . Then rotate the nucleus 180 reached the middle of the nucleus. We do not turn nucleus till the center the bevel of the phaco tip downards when we do this degrees and crack again so that you get two halves step, as the embedding is better the other way. We of the nucleus. In brown cataracts, the nucleus will crack but sometimes in the center the nucleus will prefer a 15-degree tip but any tip can be used. Now stop phaco ultrasound and bring your still be attached. You have to split the nucleus totally foot to position 2 so that only suction is being used. in two halves and you should see the posterior Now lift the nucleus. When we say lift it does notcapsule throughout. mean lift a lot but just a little so that when we apply Karate Chop - Further Chopping pressure on the nucleus with the chopper the direction of the pressure is downwards. If the capsule Now that you have two halves, you have a is a bit thin like in hypermature cataracts you might rupture the posterior capsule and create a nucleus shelf to embed the probe. So, now place the probe drop. So when we lift the nucleus the pressure on the with ultrasound into one half of the nucleus posterior capsule is lessened. Now, with the chopper (Figure 42-8). You can pass the direction of the probe Contents cut the nucleus with a straight downward motion horizontally as now you have a shelf. Embed the (Figure 42-7) and then move the chopper to the left probe, then pull it a little bit.This step is important Section 1 so that you get the extra bit of space for chopping. when you reach the center of the nucleus. In other words, your left hand moves the chopper like a This will prevent you from chopping the rhexis Section 2 margin. Apply the force of the chopper downwards. laterally reversed L. Section 3
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Figure 42-7: Left hand chops the nucleus and splits like a laterally reversed L, that is downwards and to the left.
Figure 42-8: Phaco probe embedded in one half of the nucleus. Go horizontally and not vertically as you have now a shelf of nucleus to embed. Chop and then split the nucleus.
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Then move the chopper to the left so that the nucleus gets split.Again, you should see posterior capsule throughout so that you know the nucleus is totally split. Then release the probe, as the probe will still be embedded into the nucleus. Like this create three quadrants in one half of the nucleus. Then make another three halves with the second half of the nucleus.Thus, you now have 6 quadrants or pieshaped fragments. The settings at this stage are 50% phaco power , 24 ml/minute flow rate and 101 mm of Hg suction. Remember 5 words - Embed, Pull, Chop, Split and Release.
Pulse Phaco Contents
Once all the pieces have been chopped, take out each piece one by one and in pulse phaco mode aspirate the pieces at the level of the iris. Do not Figure 42-9: Cortical aspiration completed. Note the straight rod in the left hand which helps control the movements of the work in the bag unless the cornea is pre-operatively eye. bad or the patient is very elderly . The setting at this stage can be Phaco power 50-30%, flow rate 24 ml and suction 101 mm of Hg. Remember- it is better to have striae keratitis than posterior capsular rupture.
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Cortical Washing and Foldable IOL Implantation
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The next step is to do cortical washing (Figure 42-9). Always try to remove the subincisional cortex first, as that is the most difficult. In Figure 42-10 note the cortical aspiration complete. Note also the rhexis mar gins. Note also that everytime the left hand has the straight rod controlling the movements of the eye. If necessary use a bimanual irrigation aspiration technique. Then inject viscoelastic and implant the foldable IOL. W e use the plate haptic foldable IOL (Figure 42-11) with large fenestration’ s generally as we find them superior. Take out the viscoelastic with the irrigation Figure 42-10: Eye distended with viscoelastic. Note the rhexis aspiration probe (Figure 42-12). margins.
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Stromal Hydration At the end of the procedure, inject the BSS inside the lips of the clear corneal incision (Figure 42-13). This will create a stromal hydration at the wound. This will create a whiteness, which will disappear after 4-5 hours. The advantage of this is that the wound gets sealed better.
No Pad, S/C Injections No subconjunctival injections or pad are put in the eye. The patient walks out of the theatre and goes home. The patient is seen the next day and after a month glasses prescribed. Contents
Section 1 Figure 42-11: Plate haptic foldable IOL with large fenestrations being implanted.
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Figure 42-12: Foldable IOL in capsular bag. Viscoelastic removed with the irrigation aspiration probe.
Figure 42-13: Stromal hydration done and the case completed
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NO ANESTHESIA CLEAR LENS EXTRACTION In cases of clear lens removal’s, the same technique is followed. No anesthesia is used. If one is not good then it is advisable to use a parabulbar anesthesia (pinpoint anesthesia) rather than a peribulbar block. The reason is that in such cases one could perforate the globe with the needle. Once the patient is draped, the syringe with viscoelastic is taken and the viscoelastic injected inside the eye using a 26-gauge needle. Then the temporal clear corneal incision is made. If the astigmatism is + at 90 degrees then a superior incision is made. The rhexis is then done using a needle. This is followed by hydrodissection. The phaco probe is passed into the eye and using phaco aspiration the soft nucleus removed. One does not have to use ultrasound, as the nucleus in such cases is very soft. This is followed by cortical aspiration. Depending on the Biometry a foldable IOL is implanted in the eye. If the patient has high myopia and an IOL is not required then an IOL is not implanted. The authors have realized that chances of retinal detachment do not increase just because the eye is aphakic. The authors prefer to keep one eye emmetropic and the other slightly myopic to about 1 to 1.5 D so that the patient can see without glasses for distance and near with both eyes open. Compared to Lasik this is a very good alternative, as Lasik does not help much in hyperopes and in high myopes (powers above –15 D).
that the vacuum can be raised from 120 to 200 mm of Hg. After embedding the phaco needle with mild linear ultrasound power in foot switch position 3, it is important to raise the pedal back to foot switch position 2, while the vacuum builds up. This is because the purpose of ultrasound was to completely embed the aspiration port into the nucleus to obtain good vacuum seal. In foot switch 3, there is risk of adverse heat build up because the occluded tip prohibits any flow of cooling. Also, when manipulating the nucleus by pulling with the embedded tip, the vacuum seal is likely to be compromised by the vibrating needle if it is in foot switch position 3.
Advantages
The phacoemulsification procedure hasContents been proved to be reasonably safe to the Section 1 endothelium. As compared to the “divide and conquer” technique, this phaco karate chop Section 2 technique eliminates the need for trenching thereby producing significant reduction in phaco time and Section 3 power consumed which in turn decreasesSection 4 endothelial cell damage. Even with increased density of cataract, there is a less pronounced in- Section 5 crease in phaco time. Here we utilize the “Chop” to Section 6 divide the nucleus by mechanical energy. It is safe and effective in nuclear handling during Section 7 phacoemulsification. In conventional chop, the disadvantage isSubjects Index that the chopper is placed underneath the anterior capsule and then pulled towards the center . This can potentially damage the capsule and the zonules. Phacodynamics of the In phaco chop, we don’ t go under the rhexis, the vertical element of the chopper remains within the Phaco Chop Technique rhexis margin and is visible at all stages. Hence very Help ? We should take full advantage of the phaco easy to work with even in small pupils or machines capability thereby decreasing physicalglaucomatous eyes. The stress is taken by the manipulation of the intraocular tissues. In thisimpacted phaco tip and the chopper rather than phaco chop technique, we use a vacuum of 101 mm transmitting it to the fragile capsule. By going directly into the centre of the of Hg, about 70% phaco power and the flow rate is nucleus with the phaco tip and not doing any 24 ml/minute. sculpting, we don’t need as much ultrasound energy In this phaco chop technique, the most important is the vacuum, which needs to be as is usually required. It is safe and easy to perform sufficient to stabilize the nucleus while the chopper and we don’t have to pass as much balanced salt (irrigating fluid) through the eye. is splitting it. If the action of the choppersolution is dislodging the vacuum seal on the phaco tip, it is said 458
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NO ANESTHESIA CATARACT / CLEAR LENS EXTRACTION
is high, which in turn generates heat. This causes pain to the patient. If you follow these rules one This technique demands continuous use of can perform o anesthesia cataract or clear lens the left hand and hence requires practise to extraction surgery. It is not necessary to do this, as there is no harm in instilling some drops of xylocaine master it. in the eye. The point that there is always a discussion which anaesthetic drop to use. It does not matter . Topical Anesthesia Cataract / The technique, which you perform, should not Clear Lens Surgery produce pain to the patient.
Disadvantages
All cases done by the authors were previously Blurhex (Trypan Blue) in done under topical anesthesia. 4% xylocaine drops was instilled in the eye about 3 time’s 10-15 minutes Mature Cataracts before surgery. No intracameral anesthesia was used. Various techniques are present which can It is not advisable to use xylocaine drops while help one perform rhexis in mature cataracts. operating. This can damage the epithelium and create more trouble in visualization. No stitches and Contents no pad are applied. This is called the No Injection, 1. One should use a good operating microscope. If the operating microscope is good one can faintly No Stitch, No Pad Cataract Surgery Technique. Section 1 see the outline of the rhexis. Now the authors have shifted all their cases 100 % to the No anesthesia technique. This is done in both their Section 2 hospitals in India (Chennai & Bangalore) and their 2. Use of an endoilluminator. While one is performing the rhexis with the right hand (dominant Section 3 hospital in Dubai (UAE). hand), in the left hand (non-dominant hand) one can hold an endoilluminator. By adjusting the Section 4 No Anesthesia Cataract / endoilluminator in various positions, one can Section 5 Clear Lens Surgery complete the rhexis as the edge of the rhexis can Section 6 be seen. We had been wondering whether any topical anesthesia is required or not. So we then operated 3. Use of a forceps. A forceps is easier to use than a Section 7 needle especially in mature cataracts. One can Subjects Index patients without any anesthesia. In these patients no xylocaine drops were instilled. The patients did not use a good rhexis forceps to complete the rhexis. have any pain. It is paradoxical because we have been taught from the beginning that we should apply 4. Use of paraxial light. xylocaine. This is possible because we do not touch But with all these techniques, still one is not the conjunctiva or sclera. eWnever use any onetooth forceps to stabilize the eye. Instead what wevery sure of completing a rhexis in all cases. Many use is a straight rod which is passed inside the eye to times if the rhexis is incomplete, one might have to Help ? convert to an Extracapsular cataract extraction to prestabilize it when we are performing rhexis etc. The first step is very important. In this we first enter the vent a posterior capsular rupture or nucleus drop. The solution to this problem is to have a dye, eye with a needle having viscoelastic and inject the which stains the anterior capsule. This dye is viscoelastic inside the eye. This is done in the area of the side port. Now, we have an opening in the eye TRYPAN BLUE. It is marketed as Blurhex made by through which a straight rod can be passed to stabilize Dr.Agarwal’s Pharma. Each ml of Blurhex contains the eye. The anterior chamber should be well 0.6 mg Trypan blue, 1.9 mg of sodium mono-hydromaintained and the amount of ultrasound power gen orthophosphate, 0.3 mg of sodium di-hydrogen used very less. If you tend to use the techniquesorthophosphate, 8.2 mg of sodium chloride, sodium like trenching then the ultrasound power generated hydroxide for adjusting the pH and water for injection.
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One can inject Blurhex directly or first inject air into the anterior chamber. This prevents waterlike dilution of the Trypan blue. Then the Trypan blue is withdrawn from the vial into a syringe. This is then injected by a cannula into the anterior chamber between the air bubble and the lens capsule. It is kept like that for a minute or two for staining of the anterior capsule to occur. Next viscoelastic is injected into the anterior chamber to remove the air bubble and the Trypan blue. Now, rhexis is started with a needle (Figure 42-14). One can use a forceps also. We prefer to use a needle as it gives better control on the size of the rhexis. Note the left hand holding a rod stabilizing
the eye while the rhexis is being performed. The rhexis is continued with the needle. Note the contrast between the capsule, which has been stained, and the cortex, which is not stained. The rhexis is continued and finally completed (Figure 42-15). When the rhexis is complete, we can see the stained anterior capsule lying in the anterior chamber .
Air Pump to Prevent Surge One of the main bugbears of phacoemulsification is Surge1. The problem is that as the nuclear piece gets occluded in the phaco tip and we emulsify
Contents
Section 1 Section 2 Figure 42-14: Blurhex (Trypan Blue) used to stain the anterior capsule. Note the blue staining of the anterior capsule and the needle performing the rhexis.
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
Help ? Figure 42-15: Rhexis completed. Note the white nucleus in the center and the stained anterior capsule in the periphery.
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Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Figure 42-16: Diagrammatic representation of the air pump and infusion bottle. Note two infusion bottles connected to a transurethral resecton tubing (tur set). Also note the air pump connects to one of the infusion bottles.
Section 7 Subjects Index
it, surge occurs. Many people have tried various methods to solve this problem. Some Phaco machines like the Sovereign have been devised with the help of I. Howard Fine, Barry Seibel and William Fishkind to solve this problem. Others have tried to use an anterior chamber maintainer to get more fluid into the eye. The problem with the anterior chamber maintainer is that another port has to be made. In other words now, we have three ports and if you are doing the case under topical or no anesthesia (as we do in our hospital) it becomes quite cumbersome. Another method to solve surge is to use more of phacoaspiration and chop the nuclear pieces with the left hand (non-dominant hand). The problem by this is the surgical time decreases and if the case is of a hard brown cataract, phacoaspiration will not suffice.
Surge occurs when an occluded fragment is held by high vacuum and is then abruptly aspirated with a burst of ultrasound. What happens is that fluid from the anterior chamber rushes into the phaco tip and this leads to a collapse of the anterior chamber. One of us (Sunita Agarwal), then thought of a method to solve surge using an air pump. We got this idea as when we were operating cases with Phakonit (a new technique in which cataract is removed through a 0.9 mm opening); we wanted more fluid entering the eye. Now we, routinely use the air pump to solve the problem of surge.
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The Method 1. First of all (Figure 42-16), we use two BSS bottles and not one. These are put in the IV stand.
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2. Instead of using an IV set for the fluid to move from the Bottle to the phaco hand piece, we use a TUR set. This is a Transurethral Resection (TUR) tubing set, which is used by urologists. The advantage of this is that, the bore of the tubing is quite large and so more fluid passes from the infusion bottle to the phaco hand piece. The TUR set has two tubes, which go into each infusion bottle, and then the TUR set becomes one, which then passes into the phaco handpiece. 3. Now we take an air pump. This air pump is the same air pump, which is used in fish tanks to give oxygen to the fishes. The air pump is plugged on to the electrical connection. 4. An IV set now connects the air pump to the infusion bottle. The tubing passes from the air pump and the end of the tubing is passed into one of the infusion bottles. 5. What happens now is that when the air pump is switched on, it pumps air into the infusion bottle. This air goes to the top of the bottle and because of the pressure, it pumps the fluid down with greater force. With this, the TUR set also is in place and so the fluid now flows from the infusion bottle into the TUR set to reach the phaco handpiece. The amount of fluid now coming out of the hand piece is much more than what would normally come out and with more force. 6. One can use an air filter between the air pump and the infusion bottle so that the air which is being pumped into the bottle is sterile. 7. This extra amount of fluid coming out compensates for the surge which could occur.
Conclusion As in any other field, progress is inevitable in ophthalmology more so in refractive surgery. We have started to look on refractive surgery as a craft and should constantly try to improve our craft and become better every day. By this, we will be able to provide good vision to more people than any one dared dream a few decades ago. It also goes without saying that we are and will be forever grateful to all our patients because without their faith, we would never have had the courage to proceed. Keeping this in mind, we hope and wish that the effectiveness and the advantages of this “No anesthesia Clear lens extraction Technique” be realized and practiced thereby making the technique of phacoemulsification safer and easier Contents providing good visual outcome and patient recovery. Section 1
REFERENCES:
Section 3
1.Sunita Agarwal, Athiya Agarwal, Mahipal S Sachdev, Keiki R Mehta, I Howard Fine, Amar Agarwal: Phacoemulsification, Laser Cataract Surgery & Foldable IOL’s; Jaypee Brothers; 1998, Delhi, India
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Section 6 Section 7
Athiya Agarwal, M.D. Consultant Dr. Agarwal’s Eye Hospital Chennai, India; Bangalore, India; Dubai
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Part of text and some of the figures of this Chapter are presented with permission from Agarwal et al textbook on REFRACTIVE SURGERY published by Jaypee, India , 1999.
Subjects Index
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PHAKONIT AND LASER PHAKONIT- LENS REMOVAL THROUGH A 0.9-mm INCISION
Chapter 43 PHAKONIT AND LASER PHAKONITLENS REMOVAL THROUGH A 0.9-mm INCISION Amar Agarwal, M.S., Sunita Agarwal, M.S., Athiya Agarwal, M.D.
Introduction Since Charles Kelman started phacoemulsification, various new modalities have developed which have made this technique more refined. One problem still persists which is the size of the incision. The normal size of the incision is 3.2 mm. With time and more advances in phaco machines and phaco tips this reduced to 2.8 mm and then to 2.6 mm. Today certain phaco machines like the Alcon’s Legacy and the Staar phaco machine have produced a 1.9-mm phaco probe. In other words cataract surgery has become a sub 2-mm incision. The authors (Sunita Agarwal) worked on Laser cataract surgery and have achieved cataract removal through an incision below 2-mm (1.8-mm) using laser phaco energy coupled with high aspiration. But the problem of the incision still remained and the 1-mm barrier could not be broken. Today, the authors have started a new technique called PHAKONIT in which the size of the incision is below 1 mm. In other words the size of the incision through which the cataract is removed is 0.9 mm. The authors (Amar Agarwal) performed this technique for the first time in the world on August 15th 1998. It was performed without any anesthesia. No anesthetic drops were instilled in the eye nor was any anesthetic given intracamerally. The first live surgery in the world of Phakonit was performed on August 22nd 1998 at Pune, India by the authors (Amar Agarwal) at the Phako & Refractive surgery conference. This was done in front of 350 ophthalmologists. This technique will revolutionize cataract surgery because now the foldable Intraocular lenses which pass into the eye through a size of below 2 mm (1.9 mm) will have to pass through a below
(1)
1 mm incision . They will have to pass through a 0.9-mm incision.
Principle
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The problem in phacoemulsification is that Section 1 we are not able to go below an incision of 1.9 mm. The reason is because of the infusion sleeve. The in- Section 2 fusion sleeve takes up a lot of space. The titanium tip Section 3 of the phaco handpiece has a diameter of 0.9 mm. This is surrounded by the infusion sleeve which al- Section 4 lows fluid to pass into the eye. It also cools the hand(2) Section 5 piece tip so that a corneal burn will not occur . The authors separated the phaco tip from the Section 6 infusion sleeve. In other words, the infusion sleeve was taken out. The tip was passed inside the eye and Section 7 as there was no infusion sleeve present the size of Subjects Index the incision was 0.9 mm. In the left hand an irrigating chopper was held which had fluid passing inside the eye. The left hand was in the same position where the chopper is normally held; i.e.; the side port incision. The assistant injects fluid (BSS) continuously at the site of the incision to cool the phaco tip. Thus the cataract is removed through a 0.9 mm opening. Help ?
Phakonit to Correct Refractive Errors The same technique can be used to remove clear lenses when trying to correct refractive errors. If the patient is a high myope, then instead of Lasik one can perform Phakonit. In these cases, one does not need an irrigating chopper also, because the nucleus is very soft. In such cases an irrigating rod is
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used in the left (nondominant) hand. Once the soft nucleus is removed, bimanual cortical aspiration is done. An IOL is not implanted if the myopia is very high (depending upon the Biometry). Thus the chances of creating astigmatism is very less.
Terminology The name PHAKONIT has been given because it shows phaco (PHAKO) being done with a needle (N) opening via an incision (I) and with the phako tip (T).
Rhexis The rhexis is then performed. This is done with a needle (Figure 43-3). In the left hand a straight rod is held to stabilize the eye. The advantage of this is that the movements of the eye can get controlled as one is working without any anesthesia.
Hydrodissection
TECHNIQUE OF PHAKONIT FOR CATARACTS
Hydrodissection (Figure 43-4) is performed and the fluid wave passing under the nucleus checked. Check for rotation of the nucleus.
Anesthesia
Phakonit
All the cases done by the authors have been done WITHOUT ANY ANESTHESIA. In these cases no anesthetic drops were instilled in the eye nor was any intracameral anesthetic injected inside the eye. The authors have analyzed that there is no difference between topical anesthesia cataract surgery and No anesthesia cataract surgery. They have stopped using anesthetic drops totally in all their hospitals in India (Bangalore and Chennai) and Dubai (UAE).
Incision In the first step a needle with viscoelastic is taken and pierced in the eye in the area where the side port has to be made (Figure 43-1). The viscoelastic is then injected inside the eye. This will distend the eye so that the clear corneal incision can be made. Now a temporal clear corneal incision is made. The problem here is that the diamond knives are all 2.6 mm or larger. Since our aim is to make only a 0.9-mm opening the diamond knives are not sufficient. So a Microvitreoretinal (MVR) blade is used (Figure 43-2). This creates an opening of 0.9 mm. With time when companies start manufacturing diamond knives to create a 0.9-mm opening, one can start using them. When this incision is made it should be done in such a fashion that a clear corneal valve is made. The authors have devised a sapphire knife
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keratome of 0.9 mm which they now use. This keratome creates a good valve.
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The phaco tip without the infusion sleeve is Section 1 kept in the right hand (Figure 43-5) In the left hand Section 2 an irrigating chopper of 18 gauge is taken (Figure 43-6) . The irrigating chopper is then passed through Section 3 the side port into the eye. This is connected to the Section 4 phaco machine. When the foot switch is in position 1 fluid passes into the eye and the eye gets distended. Section 5 Now the phaco tip is passed into the eye. This is passed through the 0.9-mm incision. Remember the Section 6 phaco needle has no infusion sleeve. Section 7 The foot switch is pressed for phacoemulsification. Karate chopping is done with Subjects Index the left hand (Figure 43-7) and the nucleus removed.
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Figure 43-1: Viscoelastic injected inside the eye to distend the eye. This is done with a 26 guage needle.
PHAKONIT AND LASER PHAKONIT- LENS REMOVAL THROUGH A 0.9-mm INCISION
Figure 43-2: Clear corneal incision made with the microvitreoretinal blade (0.9 mm). Note the left hand has a straight rod to stabilize the eye as the case is done without any anesthesia.
Figure 43-3: Rhexis started with a needle.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Figure 43-4: Hydrodissection
Figure 43-5: Phaco probe without an infussion sleeve.
Section 7 Subjects Index
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Figure 43-6: Irrigating probe with a fork, irrigating chopper and irrigating probe. One can use either of these instruments in the left (nondominant hand).
Figure 43-7: Phakonit started. Note the Phako needle in the right hand and an irrigating chopper in the left hand. Phakonit being performed. Note the crack created by Karate Chopping. The assistant continuously irrigates the Phaco probe area from outside to prevent corneal burns.
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The assistant injects fluid over the phaco tip at the area of the clear corneal incision to prevent thermal burns of the eye.
Cortical Washing, Foldable IOL Implantation and Stromal Hydration Cortical washing is done with the bimanual irrigation aspiration technique. Note in Figure 43-8 the nucleus has been removed but there are no corneal burns. Figure 43-9 shows the bimanual irrigation aspiration probes. This is like the irrigating chopper but does not have the chopper in it. The advantage of this is that as the chopper is not present the posterior capsule will not be cut accidentally. If one wants they can also use the aspiration probe of the phaco machine but take out the sleeve of the probe. In cases of small pupil irrigation aspiration is difficult with this set up so the authors devised an irrigating probe with a fork at the tip. The advantage of the fork is that it can push the iris with the left hand and the right hand with the aspirating probe can go under the rhexis and remove the trapped cortex. Figure 43-6 shows all three instruments, which can be, used in the left hand- the irrigating probe with a fork, the irrigating chopper and the blunt irrigating probe. The cortical aspiration is completed with the bimanual irrigation aspiration probes (Figure 43-10). Then the foldable IOL is implanted depending upon the biometry.At present one has to extend
Figure 43-8: Phakonit completed. Noth the nucleus has been removed and there are no corneal burns.
Contents
(Figure 43-11) and then implant the foldable IOL Section 1 (Figure 43-12). If the cases is of a cataract with high Section 2 myopia and an IOL is not necessary then no lens is implanted. At present, the lowest available is the Staar Section 3 sub 2 mm foldable IOL’s so one has to increase the size of the incision from 0.9 mm to 2 mm. With time Section 4 the foldable IOL’S will come to less than 1 mm and Section 5 the size of the incision will not have to be increased. The authors prefer the Staar plate haptic foldable Section 6 IOL’s with large fenestration’s. Finally the viscoelasSection 7 tic is removed with the bimanual irrigation aspiration technique and stromal hydration done. Injecting Subjects Index
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Figure 43-9: Bimanual irrigation aspiration probes.
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Figure 43-10: Bimanual irrigation aspiration. Note the clear corneal wound does not have any corneal burns.
PHAKONIT AND LASER PHAKONIT- LENS REMOVAL THROUGH A 0.9-mm INCISION
Figure 43-11: Incision enlarged to implant the foldable IOL.
Figure 43-12: Foldable IOL being implanted.
Contents
fluid into the sides of the clear corneal incisions does stromal hydration. No subconjunctival injections or pad are applied in the eye. The patient walks out of the operation theatre and is seen the next day. The next follow up is after a month and suitable glasses prescribed if necessary.
PHAKONIT IN CLEAR LENS EXTRACTION If one is performing a clear lens extraction as a refractive procedure, then Phakonit is a good alternative as the incision is only 0.9 mm. If necessary one can implant an IOL depending on the Biometry. If the case is a high myope then one need not implant an IOL. The pre and post topographic pictures are nearly the same of cases who have undergone Phakonit indicating the advantage of having a very small incision of 0.9 mm.
Discussion This technique of Phakonit can change various concepts of cataract surgery. One of the main bugbears of cataract surgery was to break the 1-mm barrier. With Phakonit the barrier is broken. There are various questions , which come to one’s mind on this technique, and these will have to be answered with time as this procedure is so new.
The first is of the left hand. The amount of Section 1 fluid flowing into the eye normally in phaco is about 40 ml / minute. If we have a 20-gauge cannula in our Section 2 left hand enough fluid does not flow inside the eye. Section 3 So one has to use an 18 gauge irrigating chopper, otherwise when doing phakoemulsification the ante- Section 4 rior chamber will collapse as the amount of fluid passing into the eye is very less compared to the suction. Section 5 This problem can be solved with the use of an air Section 6 pump which we always use in our cases. The next problem is of the foldable IOL. At Section 7 present the lowest one can go is to 1.9 mm. Remember phaco came before the foldable IOL’s. So obvi- Subjects Index ously once Phakonit will catch on the companies will have to manufacture foldable IOL’s which pass through an incision less than 1 mm. Another solution to solve the thermal burn could be to paint the tip of the phaco needle to insulate it from heating any structures. Help ? The solution to the problems of Phakonit could be the surgery of a Three-Port Phakectomy in which an anterior chamber maintainer could be like the infusion cannula, an irrigating chopper could be the second port and the phako needle the third port just akin to a three-port vitrectomy. Another modification of Phakonit is the technique of Laser Phakonit. In this the laser probe is passed into the phaco probe so that one can use a two port technique.
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Three Port Phakectomy
Summary
Another technique by which one can perform Phakonit is to use an anterior chamber maintainer. The authors started this technique. They call it ThreePort Phakectomy. Just as a three port vitrectomy, here also we have three ports, hence the name- ThreePort Phakectomy. There are pros and cons in every technique. The problem in three port phakectomy is that it is too cumbersome. Surgeons prefer to have two ports only. Some surgeons prefer three ports as an anterior chamber maintainer is present in the eye and thus the anterior chamber is always formed.
There are various problems, which are encountered, in any new technique and so also with Phakonit. With time these will have to be solved. The important point is that today we have broken the 1 mm barrier for cataract removals. This can be done easily by separating the phaco needle from the infusion sleeve. As the saying goes- We have miles to go before we can sleep.
Laser Phakonit Laser Phakonit uses laser energy (coupled with ultrasound energy in hard nuclei) to remove the nucleus. This technique was started first time in the world by the authors (Sunita Agarwal). The laser machine used is the Paradigm Laser Photon. In these cases, two ports are used. One port has fluid (BSS) flowing through an irrigating chopper of 20 gauge and in the other hand is the phaco probe without a sleeve. In the center of the phaco probe is passed the laser probe. The diameter of the phaco probe is 900 microns. The laser probe reduces the orifice opening to 550 microns. Thus the nucleus can be removed through a very small 0.9 mm opening.
REFERENCES 1. Sunita Agarwal, Athiya Agarwal, Mahipal S Sachdev, Keiki R Mehta, I Howard Fine, Amar Agarwal: Phacoemulsification, Laser Cataract Surgery & Foldable IOL’s; Jaypee Brothers; 1998, Delhi, India 2. Laura J Ronge: Clinical Update; Five Ways to avoid Phaco Burns; February 1999
Contents
Section 1 Section 2
Section 3
Section 4
Amar Agarwal, M.D. Consultant Dr. Agarwal’s Eye Hospital Chennai, India; Bangalore, India; Dubai
Section 5
Section 6 Section 7 Subjects Index
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PHAKIC I OL's SURGICAL MANAGEMENT OF HIGH MYOPIA
Chapter 44 PHAKIC IOL's SURGICAL MANAGEMENT OF HIGH MYOPIA Benjamin F. Boyd, M.D., F.A.C.S.
Contents
Limitations of LASIK in Very High Myopia The general consensus is that although, initially, different prestigious refractive surgeons from various countries performed and recommended LASIK for all degrees of myopia (low, moderate, moderately high and very high) it is now clear that this procedure is not recommended in very high myopias (greater than -10 diopters). This is because of important limitations in night vision, loss of best spectacle-corrected visual acuity, some visual aberrations and diminished quality of vision. The surgeon’s goal is to provide his/her patient not only a satisfactory postoperative visual acuity as measured in the Snellen chart, but also to sustain a very good quality of vision. Some ophthalmologists have seen patients operated with LASIK for myopia larger than 10.50 D who end up with a postoperative vision of 20/25 without spectacles or contact lens correction but, at day’s end, they must rush back home because they cannot drive at night or go about normal activities in surroundings with low illumination.
The Important Role of Phakic Intraocular Lenses We are entering a new age with this procedure. We are moving away from an exclusively extractive concept with the crystalline lens being replaced by a posterior chamber intraocular lens for aphakia, toward a refractive concept of implanting an intraocular lens leaving the crystalline lens intact.
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7
Contributions of Phakic IOL's Subjects Index
In these specific patients (-10-50 D or higher) phakic IOL’s provide the following: 1) excellent refractive accuracy; 2) preservation of corneal sphericity and the patient’s accommodation; 3) reversibility or adjustability; 4) predictable healing and; 5) rapid visual recovery and a stable postoperative refraction. High myopes are usually very satisfied. Their post-op uncorrected visual acuity is generally better than their pre-op best-corrected visual acuity.
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Advantages Over Corneal Refractive Surgery Phakic IOL’s have a major advantage over corneal refractive surgery: they can be removed; the procedure is reversible. It is easy to remove a Baikoff style anterior chamber lens (Nu-Vita lens) by sliding it out of the incision (Fig. 44-14). The Worst’s Artisan lens can be removed by spreading the claws to release the iris (Fig. 44-8). The posterior chamber plate lenses can be easily removed (Fig. 44-27). Waring’s experience with the soft, foldable lens made by Staar is that this very thin lens can be slid back out through the original incision without cutting the IOL into smaller pieces.
Limitations of Phakic IOL's 1) There are concerns about safety. We lack long-term data and strict follow-up with the Nu Vita and the foldable posterior chamber plate lens. The procedure and the lenses are still being improved. The longest experience has been that of Dr. Jan Worst’s anterior chamber Artisan Lens although both design of the lens and the implantation technique have gone through modifications that we feel are positive. Joaquin Barraquer’s hard, PMMA pre-crystalline lens has had the second longest and very thorough follow-up. Because of the safety concerns and limited follow-up with some lenses, it is important that the ophthalmic surgeon use only those phakic lenses which have been tested and for which there is long or medium-term data. Those include the four (4) phakic lenses that we presented in this chapter, as follows: (1) Anterior Chamber Lenses: the Artisan and the Nu Vita lenses. (2) Posterior Chamber Phakic “Plate” Pre-crystalline Lenses: the Barraquer PMMA Lens. The Guimaraes-Zaldivar is made of a hydrogel collamer.
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Experience with other lenses, of various designs and made of different chemical materials have begun to show significant late complications. Brauweiler et al from Bonn, Germany, have reported a 73% incidence of anterior subcapsular cataract after implantation of posterior chamber silicone lenses in phakic eyes followed for a minimum of two years. These Fyodorov style lenses were made of silicone, by Adatomed. So far these anterior subcapsular opacities have not affected visual acuity but they do discourage the implantation of this specific type of phakic lenses. Consequently, surgeons using posterior chamber phakic plate lenses should be extra cautious and inform their patients of this risk. Other posterior chamber phakic lenses presented in this chapter have also shown this complication but they have been minimal. Long term data and using the already tested lenses is essential. 2) The implantation of these lenses demand much surgical skill and great attention to detail. It is much more demanding than phaco and posterior chamber IOL insertion for cataract surgery. Certain parts of the surgery are similar, but there are many new difficult challenges to meet and overcome. For success, it is essential to prevent damage to the corneal endothelium, anterior chamber angle, the iris or the crystalline lens.
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7
Three Basic Styles of Phakic IOL'S They are: 1) The former Baikoff Multiflex style Nu Vita anterior chamber lens with fixation in the angle, made of PMMA (Fig. 44-1A). (2) The Artisan lens designed by Jan Worst with a fixation mechanism to the peripheral iris stroma (Fig. 44-1B); and (3) the posterior chamber plate lenses that fixate in the ciliary sulcus (Fig. 44-1C). Waring prefers to use the latter in the form of a foldable lens that can be inserted through a non-
Subjects Index
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PHAKIC I OL's SURGICAL MANAGEMENT OF HIGH MYOPIA
Contents
Section 1 Section 2
Section 3 Figure 44-1: Three Basic Styles of Phakic Intraocular Lenses
Section 4
The anterior chamber Multiflex NuVita phakic intraocular lens has fixation of the lens haptics (F) within the angle (arrow) of the eye. Note the relationship of the artificial lens (I) anterior to the natural lens (L) and to the iris. (B) The Artisan (iris claw) lens is also placed in the anterior chamber but is clipped to the peripheral iris stroma (arrows) by means of a slot in the haptic. Note the relationship of the Artisan lens (I) anterior to the natural lens (L) and the iris. (C) A third type of phakic IOL is the posterior chamber plate lens group, which are fixated in the ciliary sulcus (arrow). These lenses (I), are anterior to the natural lens (L), but located posterior to the iris (shown in dotted line). (After Boyd´s "Atlas of Refractive Surgery").
sutured 3 mm or 3 1/2 mm clear corneal internal valve self-sealing incision. (Note from the Editor in Chief: this type of lens is also known as the “implantable intraocular contact lens”.) This is the type of incision many phaco surgeons use for cataract surgery. The posterior chamber phakic lenses consist of two important sub-types: a) The Joaquin Barraquer hard, PMMA IOL pre-crystalline plate lens and,
b) The foldable “Implantable Contact Lens” also implanted in the pre-crystalline space between the posterior surface of the iris and the anterior capsule of the crystalline lens. This lens is made of hydrogel/collagen polymer and was jointly pioneered by Ricardo Guimaraes, M.D., (Brazil) and Roberto Zaldivar, M.D., (Argentina). This group of lenses (pre-crystalline) are fixated in the ciliary sulcus.
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Special Precautions During Surgery Because of the minimal space available, it is challenging to insert a phakic IOL without causing complications like corneal endothelial damage and secondary cataract. Waring provides general advice for surgeons about technique: First, when implanting anterior chamber lenses, the surgeon should determine before the surgery that the patient’s anterior chamber is more than 3 mm deep. Second, in all implantations, anterior and posterior chamber, the incision should be very carefully constructed, and a viscoelastic that can be completely removed from the eye at the end of the surgery should be used. (The anterior chamber lenses: Nu-Vita and Artisan, need a corneal valve incision. The Joaquin Barraquer posterior chamber plate lens or pre-crystalline lens requires a 7 mm limbal incision). Anesthesia depends upon the surgeon’s choice. Topical anesthesia is possible, but with a larger incision there is some collapse of the anterior
chamber even when viscoelastic is used. Peribulbar or retrobulbar anesthesia is certainly useful, especially if a large incision is going to be made. When actually inserting the lens, the surgeon must pay meticulous attention to surgical detail so that the lens does not hit the corneal endothelium or the crystalline lens.
Calculating the Power of Phakic Lenses Tables are used for most phakic IOL’s currently to look up the power of the lens needed to correct a given refractive error. No mathematical formulas, yet. This makes it much easier. This includes the Artisan and Nu Vita lenses. For the Artisan lenses, the tables were constructed by Van der Heijde, a world class authority on lens implant power calculation and selection. For the Barraquer pre-crystalline lens, the manufacturer calculates the power based on clinical data provided by the surgeon, and each lens is custom-made.
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ANTERIOR CHAMBER PHAKIC IOL'S THE ARTISAN LENS
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The Artisan (Iris Claw) Lens (Fig. 44-2) requires a more demanding insertion technique than anterior chamber lenses which are angle fixated such as the Nu Vita Multiflex style lens. The method of implanting the Artisan lens usually requires a limbal incision of 5 mm to 6 mm. This lens, designed by Jan Worst from Holland, has the advantage that
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Figure 44-2: Concept of the Artisan Intraocular Lens The Artisan IOL is placed in the anterior chamber and is clipped to the iris (arrows) through slots in the peripheral portion of the haptics. Note the relationship of the Artisan Lens (I) vaulted anterior to the natural lens (L) and iris. (After Boyd´s "Atlas of Refractive Surgery").
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one size fits all eyes and that it has been used with considerable success over the past 12 years in both aphakic and phakic eyes.
How Does Peripheral Iris Support Differ from the Old Iris Clip Lens Implant Design? The so-called iris clip lenses such as the Binkhorst 4-loop and Worst Medallion were really pupil margin and iris supported. The haptics were never «clipped» onto the iris; instead the lens was fixated by the pupil and the haptics cradled the iris in their arms. Iris clip lenses were used only in aphakic eyes. Skillfully inserted they were capable of good long term results, but they had several disadvantages. Pseudophakodonesis (wobbling as the eye moved) could lead to corneal endothelial touch and damage. This was most often seen if the lens (the pupil) was decentered, displacing one of the anterior haptics too near the peripheral cornea. Dislocation occasionally occurred, especially in patients who rubbed their eyes, and was a worrisome possibility if the pupil needed to be dilated. Dislocation could be limited to subluxation by using an iris or trans-iridectomy suture, but these added to the difficulty of the surgery. Even subluxation could lead to major endothelial damage if the IOL fell forward and rested against the cornea. Long term pupil margin erosion by the loops led to glare and more dislocations. These problems were ameliorated if extracapsular surgery (ECCE) was done so that the stability of the posterior capsule was retained. But by the time ECCE was widely adopted, posterior chamber lenses had supplanted other styles.
In 1978 Worst began using lenses of an entirely new design, literally clipped to the peripheral iris. Because the slotted tips of the haptics pinched the iris (Figs. 44-2, 44-8, 44-9), Worst unfortunately named them «Lobster claw,» belying the gentleness of these lenses on the eye post operatively. Happily, the name has been changed to Artisan.
What are the Advantages? No major investments are needed in lasers, keratomes, and disposables. Techniques are those already known well by anterior segment surgeons, and special instrument investment is small. The iris periphery is a stable platform, moving very little even with dilation of the pupil, and providing a privileged area for the fixation of an intraocular lens. The mode of enclavation of the loop tips (Figs. 44-8 - 44-11) produces a pillow of iris over the most peripheral part of the haptics, further guarding against touch of the plastic to endothelium (Fig. 44-3). Most (but not all) studies have shown no late leak on fluorescein iris angiography. Although peripheral iris damage can occur if surgery is difficult or clumsy, long term iris atrophy and/or late subluxation of the lens is rarely seen.
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Help ? Figure 44-3: Positive Features of the Artisan IOL with Regard to the Corneal Endothelium
The Artisan IOL with its mode of enclavation of the loop tips produces a pillow of iris (P) over the most peripheral part of the haptics. This pillow of iris guards against touch of the plastic to endothelium (E) as shown in this eye with corneal depression (arrow). (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-4: Artisan IOL Surgical Implantation Technique - Incisions One or two paracentesis stab incisions (P) are made according to the technique to be used. The anterior chamber is filled with a high molecular weight viscoelastic via a cannula (C) placed through one of the paracentesis. A 5-6 mm incision (I) is then made. A peripheral iridotomy must be made now or at the end of the procedure. (After Boyd´s "Atlas of Refractive Surgery").
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The pupil can be widely dilated and scleral indentation used without worry. The lens does not depend on anterior chamber angle support, thus avoiding ovaling of the pupil, UGH syndrome, and the late corneal decompensation of some anterior chamber lenses. It does not rest on the crystalline lens, avoiding possible late production of cataract, such as the anterior subcapsular cataract now being seen in some patients with phakic pre-crystalline posterior chamber lenses. The theoretical complications of chronic iritis, iris atrophy, IOL dislocation, and corneal decompensation require more prospective study, but so far have been rare, including the results of a European multicenter study and phases 1 and 2 of the US Clinical Trials. There is no iridodonesis in the phakic eye, and therefore minimal pseudophakodonesis. This lens has the advantage that one size fits all eyes. It has been used with considerable success over the past 12 years in both aphakic and phakic eyes. Moreover, it can be centered directly over the pupil (Figs. 44-7, 44-8, 44-11, 44-12), unlike both the anterior chamber angle fixated lens that centers on the angle and the precrystalline posterior chamber plate lens that centers on the ciliary sulcus.
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What are the Disadvantages?
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Like most intraocular lenses, this lens deSection 5 pends on excellent quality control and superb finish for its good results. (Posterior chamber lenses placed Section 6 in the capsular bag may be an exception.) Those lenses used by Worst himself are made by Ophtec. Section 7 Poorly made copies can, of course, give bad results. Surgical technique needs to be smooth and Subjects Index gentle. Patient relaxation and control are paramount. Some surgeons prefer general anesthesia when skilled modern anesthesiology is available. A high density viscoelastic should be used to ensure avoidance of endothelial touch during insertion and manipulation in the shallower phakic anterior chamber (Fig. 44-4). Help ? Until a foldable version becomes available, a 5-6 mm incision is required and must be closed skillfully. A peripheral iridotomy is needed, as with all phakic intraocular lenses (Figs. 44-11, 44-12). Correct clipping of the loops onto the iris is critical and so far has been best accomplished with a two handed approach (Figs. 44-8, 44-10). Newer, simpler instruments should allow this part of the surgery to become easier.
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Figure 44-5: Artisan IOL Surgical Implantation Technique - Insertion - Stage 1
A lens glide (G) is placed through the incision and across the anterior chamber. With viscoelastic filling the anterior chamber, the Artisan lens (L) is grasped with a special forceps (F) and inserted into the wound on the lens glide. A second instrument, an irrigating cannula (C), is placed inside the haptic loop and serves to push the lens (arrow) inside the anterior chamber. (After Boyd´s "Atlas of Refractive Surgery").
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Surgical Technique
Two Handed Enclavation
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How Difficult Is the Technique for Implantation? The technique is shown in figures 44-544-12. Implantation of these lenses makes use of the techniques that anterior segment surgeons know well already. Because the phakic anterior chamber is not as deep as in aphakia, and because the lens is manipulated in front of the iris, extra care must be taken to assure maximum chamber depth throughout the procedure.
The pupil should be kept moderately constricted. One or two stab incisions are made accord- Section 7 ing to the technique to be used (Fig. 44-4), and the Subjects Index anterior chamber filled with high molecular weight viscoelastic (Fig. 44-4). Methylcellulose should not be used. A 5-6 mm incision is made (Fig.44-4). A peripheral iridotomy must be made, now or at the end of the procedure, and the iris reposited completely (Figs. 44-11, 44-12). The lens is gently and slowly nudged into the eye (Figs. 44-5, 44-6), rotated Help ? into the 3 to 9 o’clock axis and centered over the pupil (Fig 44-7). The wound is partially sutured, leaving an opening sufficient to introduce a forceps.
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Figure 44-6: Artisan IOL Surgical Implantation Technique - Insertion - Stage 2 The irrigating enclavation instrument (E) is then used to nudge (arrow) the Artisan lens (L) into position inside the anterior chamber. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-7: Artisan IOL Surgical Implantation Technique - Centration The lens glide is removed. A special lens forceps, the Artisan forceps, (F) grasps the Artisan lens (L) and further rotates it (arrow) into the 3 o’clock - 9 o’clock axis. The lens is centered over the pupil and gently pressed onto the iris with the Artisan forceps. The longer inferior blade (B) of the Artisan forceps is an important feature, ensuring stability of the lens while it is attached to the iris. (After Boyd´s "Atlas of Refractive Surgery").
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Section 3
Section 4 Figure 44-8: Artisan IOL Surgical Implantation Technique - Enclavation The special Operaid irrigating enclavation instrument (E) is introduced through the stab incision (P) or through the main incision under the Artisan loop tip. Using the instrument, a fold of iris is lifted (arrow) through the slot in the tip of the lens haptic. The instrument is withdrawn slowly, being careful that it does not catch the iris. The Artisan forceps (F) stabilizes the lens during this maneuver. (After Boyd´s "Atlas of Refractive Surgery").
The lens is centered over the pupil and gently pressed onto the iris with an Artisan forceps (Fig. 44-7). The longer inferior blade of this forceps is an important feature, ensuring stability of the lens while it is attached to the iris (Figs. 44-7, 44-8). An Operaid Enclavation Instrument is introduced through the stab incision superior to the Artisan loop tip. This instrument comes double armed, in right and left hand configurations, to use depending on which loop of the IOL the iris is being attached. Using the enclavation instrument, a fold of iris is lifted through the slot in the tip of the lens
haptic (Fig. 44-8 and detail in Fig. 44-9). The instrument is withdrawn slowly, being careful that it does not catch the iris. The maneuver is repeated for the other tip of the lens (Fig. 44-10). If a peripheral iridotomy has not already been made, it must be made now (Fig. 44-11). The iridotomy is a vital part of the procedure and must not be omitted. Lens position and fixation is inspected (Fig. 44-12). When perfect, the wound is closed carefully. All viscoelastic is patiently removed while maintaining the depth of the anterior chamber with balanced salt. Steroid and antibiotic drops are placed. If there might
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Figure 44-9: Artisan IOL Surgical Implantation Technique - Enclavation Detail This magnified portion of the lens haptics shows how the enclavation instrument (E) engages a small fold of the iris (I) beneath the distal haptic (H). The iris fold is “snowplowed” forward (white arrow) and gently captured in the slot (S) of the haptics. The IOL and its haptics are pushed posteirorly (black arrows) to assist this enclavation of the iris. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-10: Artisan IOL Surgical Implantation Technique - Enclavation
The enclavation maneuver is repeated for the other tip of the Artisan lens, using the other irrigating hook. It is inserted through a paracentesis on the other side or through the main incision. The Artisan forceps (F) stabilizes the lens during this maneuver. Note the iris properly captured by the right haptic (S). The inset shows a magnified view of the iris (I) captured between the claws of the haptics (H). (After Boyd´s "Atlas of Refractive Surgery").
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be residual viscoelastic, prophylactic Iopidine or Latanoprost may be used to control any rise in pressure.
One Handed Enclavation Instruments Instruments and techniques are being devised to allow easier, one handed attachment of the lens to the iris.
Postoperative Care The normal postoperative course is benign, with rapid gain of vision. As with all intraocular surgery, the patient is cautioned to be seen at once if the eye becomes red or painful, or the vision becomes blurred. Intraocular pressure and cellular reaction in the anterior chamber are watched. Steroid and antibiotic drops are used until all reaction has subsided.
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Figure 44-11: Artisan IOL Surgical Implantation Technique Iridotomy A small iridotomy is placed superiorly using a scissors (S). A check for patency is performed to ensure thorough penetration of the full iris thickness. Note that the iris is properly trapped by both the left and the right haptic slots (A). (After Boyd´s "Atlas of Refractive Surgery").
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Section 3 Figure 44-12: Artisan IOL Surgical Implantation Technique - Final Configuration
Section 4
This illustration shows the properly placed and centered Artisan IOL. The wound is then carefully closed and all viscoelastic is meticulously removed while maintaining the anterior chamber depth. Note the properly trapped iris (A) within the haptic slots. Peripheral iridotomy (I). (After Boyd´s "Atlas of Refractive Surgery").
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Postoperative Complications What if the Implant Needs to be Repositioned, Removed, or Exchanged? Should the lens not be centered, a loop can be detached and reattached with some ease. Detachment only requires that one side of the loop be depressed while the lens is stabilized by forceps. In the rare event that a loop of the IOL is found not to be securely attached to the iris, it can be reattached through stab incisions, repeating the maneuvers illustrated in Figs. 44-4 - 44-10. Should an IOL need to be removed (for power exchange, for example),
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detachment of both tips is done as described above, under high density viscoelastic. Then enlarge the wound, slide the lens out, and replace it. Be gentle with the iris, and do not touch the corneal endothelium.
Availability The lenses may be obtained from Ophtec, Schweitzerlaan 15, 9728 NR Groningen, Holland. They are distributed for the clinical investigation under FDA regulation in the US by Ophtec USA, Inc., 6421 Congress Ave., Suite 112, Boca Raton, FL 33487.
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THE NU-VITA ANTERIOR CHAMBER LENS The Nu Vita phakic anterior chamber IOL (MA-20) is produced by Bausch & Lomb. It is made of PMMA. A new generation lens is made of a foldable hydrogel biocompatible material that is hoped to be safer than PMMA in the anterior chamber. This may be available in the near future also through Bausch & Lomb. The Nu-Vita lens, formerly the Baikoff ACIOL is based on the Kelman Multiflex style. Waring emphasizes that the only style of aphakic anterior chamber lens that has survived during the last 15 years is the Kelman Multiflex style (Fig. 44-13). The published clinical literature documents that this lens is safe for the eye. According to Waring, the advantage of using a Multiflex style phakic anterior chamber lens is that it is the easiest lens to
insert. Therefore, there is a lesser risk of surgical damage or complication than occurs with the other phakic IOL’s. This technology takes advantage of the fact that most surgeons can place an anterior chamber lens more easily than the other styles. In Fig. 44-13, you will find an important comparison of the main features of the Nu Vita Phakic Anterior Chamber IOL with the previous Kelman Multiflex design.
Surgical Technique The step-by-step technique is shown and described in Figs. 44-14 - 14-19. There is little difference from the usual implantation of a Kelman style anterior chamber lens except that greater care must be taken to ensure good anterior chamber depth to avoid damage to the corneal endothelium, iris, and lens.
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Figure 44-13: Comparison of Nu Vita Phakic Anterior Chamber Intraocular Lens With Previous Kelman Multiflex Design (A) An earlier design of the Kelman Multiflex anterior chamber lens had the two haptics (H) originating from the same side of the optic. (B) Shows how the compression (arrows) of the haptics (dotted lines) was transferred to only one side of the lens (E). (C) In an attempt to distribute the forces of the compression of the haptics more evenly, to prevent decentration, the Nu Vita IOL design has the two haptics (H) originating from opposite sides of the optic. (D) Shows how compression (arrows) of the haptics (dotted lines) is now more evenly distributed in a directly opposing fashion. This cancels out lateral movement of the optic from the center on compression. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-14: Insertion Technique of the Nu-Vita Anterior Phakic Chamber Intraocular Lens - Step 1 A temporal 5.5 mm self-sealing corneal incision is made. A forceps (F) grasps the optic of the intraocular lens (L) and inserts it into the anterior chamber as shown. The distal footplate must be snaked through the incision. (After Boyd´s "Atlas of Refractive Surgery").
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Maria Clara Arbelaez, M.D., considers the Nu-Vita lens her technique of choice for the correction of high myopia, from -8.00 D and up, because the results are predictable and safe, and the lens provides good quality of vision with improved contrast sensitivity. She emphasizes that a miotic must be used and a small iridectomy be performed, as needed when implanting all anterior chamber lenses. These are very delicate lenses and the haptics can be easily broken. Their cost is around US$700.00.
Calculation of Size This is a most important measure to take with the use of the Nu Vita lens. Meticulous calculation of
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size is essential so as to avoid inserting a lens that is too small. Dr. Arbelaez measures the limbus from white-to white and adds 1.0 mm. The need for exact size measurement contrasts with the Artisan lens which has the advantage of one-size fits all, although it is more difficult to implant than the Nu Vita lens.
Presence of Large Astigmatism and High Myopia In these patients, Arbelaez inserts the NuVita lens first and later follows with LASIK in a second stage to correct the astigmatism.
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Figure 44-15: Insertion Technique of the Nu-Vita Anterior Phakic Chamber Intraocular Lens - Step 2 The forceps retain a grasp on the optic and the IOL is placed into the anterior chamber (arrow). The forceps (F) are repositioned to grasp the elbow (H) of the proximal haptic and the IOL is continued into the anterior chamber (arrow). This technique avoids the insertion of an instrument into a phakic eye all the way into the pupillary area. The distal footplates are directed toward the angle. The proximal haptic is then placed in the incision, but the proximal footplates remain outside the eye. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-16: Insertion Technique of the Nu-Vita Anterior Phakic Chamber Intraocular Lens - Step 3 A check of the position of the distal footplates is made with a gonio prism. This is done to check that there is no tucking of the iris peripherally. Note that the footplates (H) are indeed in the correct location in the angle with no iris tuck. The proximal fooplates (S) are still outside the incision at this stage. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-17 (above right): Insertion Technique of the Nu-Vita Anterior Phakic Chamber Intraocular Lens - Step 4 A forked or collar-button IOL manipulator (R) is positioned on the curved bridge of the haptic between the two footplates. The entire haptic is then pushed into the eye (arrow) and under the posterior edge of the incision. The footplates are placed into position. This technique avoids insertion of a forceps into the phakic eye and eliminates a second instrument for opening the incision and putting the footplates in place. (After Boyd´s "Atlas of Refractive Surgery").
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Section 1 Figure 44-18 (left): Insertion Technique of the Nu-Vita Anterior Phakic Chamber Intraocular Lens - Step 5
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A gonioscopic mirror is used to check the position of the proximal footplates, and to ensure that there is no iris tuck. The distal footplates are also checked again with the gonio prism to ensure that they have not been displaced during placement of the proximal haptics. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-19 (below right): Insertion Technique of the Nu-Vita Anterior Phakic Chamber Intraocular Lens - Step 6 A Sinskey hook or cystitome (H) is used to retract and reposition any footplates which are not correctly placed. Each of the four footplates can be manipulated individually (arrows) by engaging the haptics in the positions shown. An iridotomy is performed, any viscoelastic irrigated out and the incision closed with 2 or 3 sutures (not shown). (After Boyd´s "Atlas of Refractive Surgery").
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THE POSTERIOR CHAMBER PLATE LENSES THE BARRAQUER PRECRYSTALLINE LENS In the search to correct high myopia above -8.00 and -9.00 D with methods other than excimer laser (LASIK) Professor Joaquin Barraquer, M.D., F.A.C.S., developed in 1995 an ingenious technique for the implantation of an ultra delicate PMMA phakic lens between the posterior surface of the iris and the anterior surface of the patient’s own crystalline lens (Fig. 44-27). This is the pre-crystalline lens to correct high myopia, starting with -8.00 D and higher as advised by Professor Barraquer. The reasons for avoiding LASIK in high myopia have already been outlined: lower quality of vision and contrast sensitivity than with phakic IOL’s, in addition to the other occasional problems inherent to the LASIK technique.
Barraquer has implanted these lenses in 183 eyes since 1995 with the valuable collaboration of Dr. Mercedes Uxo. A thorough and meticulous follow-up and analysis of each case has been performed. Fig. 44-20 shows how this lens fits into the pre-crystalline space and corrects high myopia.
Historical Significance Historically, we must keep in mind that Joaquin Barraquer, Director of the Barraquer Ophthalmological Center in Barcelona, and Professor of Ocular Surgery at the Autonomous University of Barcelona, Spain, after becoming a world recognized leader in the implantation of anterior chamber lenses over 30 years ago, was the first one to report through multiple lectures and world literature the complications that he was observing with these lenses after several years of successful implantation. The fact that after very careful consideration, he has now created a new method for the correction of high
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Section 6 Section 7 Subjects Index Figure 44-20: Optical System of Highly Myopic Patient with PreCrystalline Posterior Chamber IOL Versus Human Lens Only (A) The top figure shows refraction in high myopia with the focal point of the image (F) anterior to the retina. The image is blurred. (B) The lower figure shows the post-op refraction with pre-crystalline lens in place, with the image focusing (F’) on the retina. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-21: The Barraquer PreCrystalline Posterior Chamber Lens The second generation lens is shown at the top. The third generation lens, which is Barraquer’s current choice, is shown below. There is a slight difference between the two lenses. The third generation lens has a 9 mm instead of the 8 mm length of the second generation lens. The design of the third generation lens with two 1.5 mm plates above and below prevents capture of the lens by the pupil. The other characteristics are the same for both lenses: optics are 6 mm in diameter, flexible haptics up to 14 mm in diameter. In both lenses the channels of circulation of aqueous between the posterior surface of the IOL and the anterior surface of the crystalline lens assure good aqueous humor circulation preventing a suction effect on the IOL.
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myopia based on this pre-crystalline posterior chamber IOL implant is important because of his widely respected reputation and credibility.
Description of the Barraquer Lens The lens has evolved through three (3) generation-designs. The third generation lens has successfully overcome initial problems that presented with the first two (2) generations. The majority of the Barraquer series has been performed with the third generation lenses which began in June 1997 (120 eyes from a total of 183.) The lens is manufactured by Corneal W.K. in France. It is fixated in the sulcus (Fig. 44-28). It has an optical diameter of 6 mm. The length of the “body” of the lens is 9 mm. It has flexible haptics up to 14 mm in diameter (Fig. 44-21) to allow adequate sulcus fixation (Figs. 44-26 - 44-27). The “body” of the lens, the 6 mm diameter optic, has two 1.5 mm plates which are necessary to avoid capture of the lens by the iris when the pupil dilates. The iris glides smoothly over the plates and the optic. The periphery of the IOL remains in front of the crystalline lens and behind the iris (Figs. 44-27 - 44-28).
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Two lateral channels ensure communication Section 2 with the posterior chamber and adequate circulation of aqueous in the space between the IOL and the Section 3 anterior surface of the crystalline lens. This avoids a Section 4 suction effect which could produce contact between the posterior concave surface of the myopic IOL and Section 5 the anterior convex surface of the crystalline lens. The anterior surface of the IOL is slightly convex, Section 6 and very smooth. The optical correction is produced Section 7 by the difference in curvatures of the two surfaces of the IOL (Figs. 44-21 - 44-28). This design insures no Subjects Index interference with the normal movement of the iris and adequate separation of the implant from the anterior surface of the crystalline lens.
Advantages of the Barraquer Lens The Barraquer pre-crystalline lens, with its 6 mm optic, prevents the patient from seeing confused images at night when the pupil dilates. Spontaneous widening of the pupil at night is particularly common in young highly myopic patients. The foldable soft lenses utilized for high myopia have a smaller central optical area and some patients seem to have problems seeing at night.
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Figure 44-22: Barraquer’s PreCrystalline Posterior Chamber IOL Implantation Technique - Step 1 A non-penetrating perpendicular incision is performed 1mm behind the limbus with a diamond blade knife (K). The incision is shown here beginning at 2 o’clock while the blade (K) is shown at 10 o’clock. This incision is extended superiorly from 2 to 10 o’clock (arrow) for a length of 8mm. This is the first plane of the two plane incision. Fixation forceps (F). A paracentesis at the limbus is made temporally as shown with a stiletto knife (S). Note: YAG laser peripheral iridotomy (B) is performed 15 days before the operation to facilitate aqueous circulation from the posterior to the anterior chamber and avoid relative pupillary block and possible angle-closure glaucoma. (After Boyd´s "Atlas of Refractive Surgery").
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Section 6 Section 7 Subjects Index Figure 44-23: Barraquer’s Pre-Crystalline Posterior Chamber IOL Implantation Technique - Step 2 A viscoelastic substance is injected through the paracentesis via a cannula (C) to fill the anterior chamber. This will maintain the chamber depth and increase dilation of the pupil. At one end of the nonpenetrating limbal incision, a horizontal beveled incision is made with a disposable keratome knife (D) shown here at 2 o’clock. This will begin the second plane of the two plane incision. Fixation forceps (F). (After Boyd´s "Atlas of Refractive Surgery").
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Section 5 Figure 44-24: Barraquer’s Pre-Crystalline Posterior Chamber IOL Implantation Technique - Step 3 (A) The two plane horizontal beveled incision made with the keratome (D -figure 6) is completed (red arrow) with Jose Barraquer’s scissors (S) in the deep layers of the groove. (B) Viscoelastic is introduced with a cannula behind the iris, in front of the crystalline lens, toward the ciliary sulcus at 6 o’clock (1-blue arrow) and then (2- blue arrow) at 2 o’clock. This will facilitate safer and easier introduction of the flexible haptics into the sulcus. (After Boyd´s "Atlas of Refractive Surgery").
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Surgical Technique Step by Step
Inserting an intraocular foreign body between the posterior surface of the iris and the anterior surface of the crystalline lens certainly requires a highly skilled surgeon to prevent harming these delicate tissues. Perhaps, with time, more experience and a great deal of teaching and training of other surgeons, this technique might prove to be an important positive step in the quest for a method that is certainly much less costly than the present Excimer procedures and would be available to more surgeons and more patients.
1) Two weeks before the lens implantation two YAG laser iridotomies are performed (Fig. 4429A). 2) Deep general anesthesia. This has been Professor Barraquer’s preferred method for many years. 3) Intravenous Mannitol, in order to obtain maximum hypotony. 4) Fornix based conjunctival flap which is provisionally sutured to the sterile drape, covering the lid margin to avoid contact of instruments and the IOL with the eyelashes.
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Figure 44-25: Barraquer’s Pre-Crystalline Posterior Chamber IOL Implantation Technique - Step 4
5) The step by step technique is illustrated in Figs. 44-22 - 44-28 and described in their respective figure legends. 6) The viscoelastic present in the anterior chamber (Figs. 44-23 and 44-24) and behind the iris at 6 o’clock and 2 o’clock serves as a protective and anti-trauma lubricant. 7) When the lens is “in situ” (Fig. 44-28), one (10-0 nylon ) suture is placed in the wound and miosis is obtained with acetylcholine 1%. At this stage, it is always important to carefully “depress” the anterior surface of the IOL with the cannula, in order to help in centering the IOL and obtaining miosis. 8) The incision is closed with 7 or more 10-0 nylon sutures. The knots are buried on the corneal side of the incision 9) The viscoelastic substance is replaced by balanced salt solution. 10) The fornix based conjunctival flap is sutured over the wound.
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Section 3 The pre-crystalline intraocular lens (L) is introduced into the eye, maintaining a plane as parallel as possible to the iris and lens planes to avoid damage to the anterior lens capsule. The intraocular lens is grasped by the peripheral plate (P) of the lens with a forceps (F), and guided with a Sinsky hook (H) placed in the manipulation hole (M) of the plate. The distal haptic is directed into the ciliary sulcus (arrow). (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-26: Barraquer’s Pre-Crystalline Posterior Chamber IOL Implantation Technique - Step 5 Help ?
Once the pre-crystalline lens is inside the eye, the Sinsky hook (H) is placed through the plate manipulation hole and pushes the lens away from the incision (red arrow). At the same time, the blunt-tipped forceps (F) grasps the upper haptic at the special haptic manipulation hole. The haptic is compressed and directed behind the iris and into the ciliary sulcus (blue arrow). The Sinsky hook (H) is used to depress the optic slightly during this maneuver to assist in directing the haptic behind the iris. (After Boyd´s "Atlas of Refractive Surgery").
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How to Order a Custom-Made Lens for Each Patient Barraquer and Uxo send the manufacturer (Corneal WK) the following clinical information to obtain a lens which is custom made for each patient. This is necessary because of the very high power lenses needed. 1) Visual acuity without refractive correction. 2) Visual acuity with spectacle or contact lens correction; 3) Spectacle prescription and vertex distance. 4) Refraction with the autorefractometer. 5) Axial length. 6) Depth of the anterior chamber. 7) Keratometer readings. 8) Corneal topography.
Where Is the Barraquer Lens Available This lens is available through the following company: CORNEAL, oupe W.K*.; Parc d’ Activities Pré Mairie; B.P. 13; F-74371 PRINGY Cedex, France - FAX Nº: 33-04 50 27 26 89.
Contents Figure 44-27: Side View of Implantation Maneuver of Barraquer’s Pre-Crytalline Lens The implantation technique shown in Figs. 44-25 and 44-26 as surgeon’s view is presented here as a side view. It provides a graphic demonstration of how the lens glides into the very narrow space between the postgerior surface of the iris and the anterior surface of the patient’s own crystalline lens. (1) Represents the lens optics, (H) the haptics being inserted to rest in the sulcus (red arrow). (2) Shows the lens finally in place with the two blue arrows pointing toward the lens. (L) is the patient’s own crystalline lens. The green arrow demonstratges how the other haptic is inserted in the sulcus. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-28: Barraquer’s Pre-Crystalline Posterior Chamber IOL Implantation Technique - Final Configuration This oblique cross section view shows the final threedimensional configuration of the pre-crystalline IOL in place. Note that the incision is closed with 9 or 10 interrupted corneoscleral sutures. A section of the IOL is shown in cross section (X) to see its relationship to the anterior capsule (A) of the natural crystalline lens. The IOL does not come into contact with the natural lens except for two small areas near the periphery (arrows). Haptics (14mm) are properly placed in the ciliary sulcus (S). Note YAG laser peripheral iridotomy (B). (After Boyd´s "Atlas of Refractive Surgery").
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Complications Postoperative Lens Opacities Using third generation lenses, subcapsular lens opacities have been observed in 3% of the 120 operated eyes. These opacities have appeared 11 to 18 months postoperatively. The management was to remove the IOL, proceed with an extracapsular extraction of the cataract and implant a posterior chamber aphakic IOL within the bag. This resulted in excellent visual acuity.
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Postoperative Astigmatism By making the incision superiorly, between 10 and 2, and placing adequate tension on the sutures, the wound is hermetically sealed. In the early stages postoperatively a -4.00 diopter with the rule astigmatism or even higher is initially seen (Fig.4429A). This astigmatism is spontaneously reduced to -0.75 or -1.00 D with the rule upon healing of the corneo scleral incision (Fig. 4429B). If the astigmatism persists, the sutures can be cut with the YAG laser 3 months postoperatively. Joaquin Barraquer believes that the low postoperative astigmatism (Fig. 44-29-B) is the result of a well healed incision done in two planes at the surgical limbus (corneo-scleral), very precise suturing and eventually cutting any remaining suture causing traction 3 months postoperatively.
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Section 6 Section 7 Subjects Index Figure 44-29 A-B: Postoperative Quiet Eye with Intact Pupil and Small Astigmatism Following Barraquer’s Technique for Pre-Crystalline IOL Implantation Figure 44-29-A (above) shows a highly myopic right eye in the preoperative stage. The patient is 39 years old, visual acuity is 0.5 (20/40) J1 with a correction of -23.00 -1.00 x 35º. A YAG laser iridotomy at 10 o’clock was performed 15 days preoperatively. Fig. 44-29-A (right) shows the same eye 9 months postoperatively with a visual acuity of 0.9 (20/20-) J1 with good accommodation to read without spectacles. Please observe that there are no keratic precipitates over the surface of the pre-crystalline lens nor the anterior capsule of the crystalline lens of the patient. The anterior chamber is normal. Good pupillary light reaction. Applanation tonometry 11 mm Hg. Figure 44-29-B (below) shows corneal topography of the same eye 40 days postoperatively with astigmatism of -0.66 D with the rule. The postoperative astigmatism 7 days postop, however, was -4.00 D with the rule. (Photos courtesy of Professor Joaquin Barraquer, M.D., F.A.C.S.)
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THE POSTERIOR CHAMBER FOLDABLE PLATE PHAKIC LENS (The Implantable Contact Lens) Figure 44-30: Foldable Posterior Chamber Phakic Lens (ICL) - Insertion Technique - Step 1 A double YAG laser peripheral iridotomy (A) to avoid iris blockage, is performed the week prior to lens implantation in order to avoid iris pigment deposition on the lens. Iridotomies would be very difficult to do intraoperatively because of the widely dilated pupil. First, a 3.0mm temporal clear corneal incision (C) is performed, as well as two side port incisions (S) 90 degrees away from the main incision and 180 degrees away from each other. The chamber is filled with viscoelastic material (not shown). The foldable posterior chamber lens will be placed between the iris and natural lens. The folded lens (L) is inserted into the eye via the special inserter (I) which has been placed through the corneal incision. A plunger (P) inside the inserter pushes the distal haptics of the ICL into the anterior chamber (arrow) while unfolding as shown. The lens haptics will be placed in the posterior chamber later. This illustration is shown from the surgeon’s point of view as he/she is operating. The lens is implanted from the temporal side of the eye. (After Boyd´s "Atlas of Refractive Surgery").
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This is an ingenious development originally known as the “Implantable Contact Lens” ( ICL) or foldable, soft pre-crystalline lens as pioneered by Ricardo Guimãraes, M.D., in Brazil and Roberto Zaldivar, M.D., in Argentina. It is manufactured by the Swiss company, Staar Surgical. The original name of ICL was chosen to differentiate this lens from the posterior chamber intraocular lens (PCIOL). The critical feature of this lens is the new material of which it is made: a mixture of hydrogel and collagen polymer, which is called a collamer. It is very permeable and hydrophilic. The ICL is placed between the iris and the natural crystalline lens. It is soft and very thin - only 100 microns in thickness, as compared to the 1 mm required for a 30 diopter power silicone lens. Although this lens is fitted in the posterior chamber, it does not lie on the surface of the crystalline lens. A space that varies between 100 and 150 microns exists between the capsule of the crystalline lens and the new ICL
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(Fig. 44-31B). This space allows for circulation Section 6 between the two. This new lens is so thin that almost Section 7 no pigment movement occurs in the eye. Many surgeons refer to this lens now as a Subjects Index posterior chamber foldable phakic lens, to avoid confusion by the term “implantable contact lens.”
Indications Guimarães recommends this lens for the young adult patient with myopia higher than -10 diopters as the first option and for every case of hyperopia over +3 D. Zaldivar, who has limited his practice to refractive surgery and has extensive experience with all refractive procedures prefers its use for patients with more than 10 diopters of myopia or more than 4 diopters of hyperopia. With this lens Zaldivar can correct up to 20 diopters of myopia and up to 12 diopters of hyperopia.
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Section 3 Figure 44-31A: Foldable Posterior Chamber Phakic Lens (ICL) - Insertion Technique - Step 2 The lens (L) is shown unfolded further as the plunger pushes (arrow) the lens out of the inserter and into the anterior chamber. This illustration is shown from the surgeon’s point of view as he/she is operating. The lens is implanted from the temporal side of the eye as shown in Figs. 44-31-B and C. (After Boyd´s "Atlas of Refractive Surgery").
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ICL vs LASIK Both Guimarães and Zaldivar consider that patients with myopia less than -9 D diopters are better candidates for laser in situ keratomileusis (LASIK). Patients with more than -10 D myopia suffer from glare and have poor contrast sensitivity after LASIK. They prefer to use ICL rather than LASIK in the group of patients with high ametropias.
Disadvantages of the ICL There are two main disadvantages: 1) it is a somewhat risky procedure and must be done by a very experienced surgeon so as to avoid harming vital surrounding tissues, especially the crystalline
lens (Figs. 44-31B and C; 44-32B, 44-33) and; 2) it has high cost. The lens itself, which is manufactured Subjects Index in Switzerland, costs about $700. The final cost of dispatching and courier not including import tax is about $800. Obtaining the lens from the manufacturer takes about 1 month.
Description of the Lens
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It is identified by Staar Surgical as the IC 2020. It has a flat, very delicate plate (optics) with very thin haptics and a 5 mm meniscus optic (Figs. 44-31 B-C). It is foldable (Figs. 44-31 A-C). It is inserted through a 3 mm wide, temporal clear corneal incision with an internal corneal valve.
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Figure 44-31 B: Insertion Technique of the Foldable Posterior Chamber Phakic Lens (ICL) - Cross Section View Step 2 With a viscoelastic present, a foldable posterior chamber phakic IOL (C) is placed into the anterior chamber via a special injector placed through a small corneal incision. A plunger (P) within the injector pushes the IOL out into the anterior chamber with the distal haptic directed toward the angle (A). Some surgeons add a piece of microsponge to act as a softer pusher. Note the position of the IOL (C), as it unfolds, in relation to the natural lens (L). (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-31 C: Insertion Technique of the Foldable Posterior Chamber Phakic IOL Cross Section View - Step 2 The plunger (P) continues to push (arrow) the IOL (C) out of the injector until the entire unfolded lens rests on the iris in the anterior chamber. The injector is removed from the incision. (After Boyd´s "Atlas of Refractive Surgery").
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Implantation Technique One week previous to the surgery, two peripheral iridectomies are performed using the YAG laser, to avoid pupil blockage (Fig. 44-30). They are done one week before surgery because they are difficult to do intraoperatively when the pupil is dilated. The iridectomies are performed very close to 12 o’clock. Implanting the lens requires a 3 mm temporal clear corneal incision (Fig. 44-30). The lens is so thin that it can be folded and inserted through this very small incision (Fig. 44-31A). The surgical
technique must be very smooth. A temporal corneal tunnel incision is made followed by two paracentesis. Then the chamber is filled with viscoelastic. The pupil must be very dilated. The lens must be folded in a special cartridge and injected very slowly inside the eye (Figs. 44-30, 44-31 A-C). The recently redesigned lens injector has a sponge attached to the plunger that facilitates insertion, prevents air bubbles and allows better lens positioning. Insert the plunger and release the lens. Place the haptics beneath the iris with a spatula without applying any pressure to the optic (Figs. 44-32, 44-33).
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Figure 44-32A: Foldable Posterior Chamber Phakic Lens (ICL) - Insertion Technique - Step 3 The distal haptics of the ICL are placed in behind the iris before the proximal haptics. With a spatula (S), inserted through one of the side ports, the distal extremity of the ICL is gently pushed (arrow) into the posterior chamber, to the ciliary sulcus. The same movement is used to place the proximal haptics into the posterior chamber. This illustration is shown from the surgeon’s point of view as he/she is operating. The lens is implanted from the temporal side of the eye as shown in Fig. 44-32B. (After Boyd´s "Atlas of Refractive Surgery").
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As the lens is injected, it slides on the surface of the crystalline lens because the iris is very dilated. The lens unfolds (Fig. 44-31A). When the lens is floating on the viscoelastic on the surface of the crystalline lens, the surgeon must introduce the four small haptics or footplates behind the iris and in the sulcus (Fig. 44-32 A, B). When the haptics are in place behind the iris (Fig. 44-33), the pupil is constricted, leaving the lens lying in the posterior chamber, and the viscoelastic is removed (Fig. 4434). The pupil is treated with acetylcholine. Zaldivar uses Miochol.
Contents Figure 44-32B: Insertion Technique of the Foldable Posterior Chamber Phakic Lens (ICL) - Cross Section View - Step 3 A special spatula (S) is inserted through one of the prepared side ports and engages the distal footplate of the IOL. The spatula (white arrow) pushes the distal footplates directly behind the iris (green arrow) and into the ciliary sulcus. (After Boyd´s "Atlas of Refractive Surgery").
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Figure 44-33: Insertion Technique of the Foldable Posterior Chamber Phakic Lens (ICL) - Side View - Step 4 The special spatula (S) then engages the proximal footplates of the IOL. The spatula (white arrow) pushes the proximal footplates directly behind the iris (green arrow) and into the ciliary sulcus. (After Boyd´s "Atlas of Refractive Surgery").
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Section 4 Figure 44-34: Conceptual Cross Section of All Stages for Implantation of a Foldable Posterior Chamber Phakic Lens (ICL) This conceptual cross section shows the insertion and unfolding of the (ICL) compared to the final configuration of the ICL in position behind the iris and in front of the crystalline lens. (1) The plunger (P) inside the inserter pushes the distal haptics of the ICL into the anterior chamber (blue arrows) while unfolding as shown. (2) In separate maneuvers, the haptics are then placed (red arrows) into the posterior chamber behind the iris and into the ciliary sulcus. The iris will then be constricted. The inset shows a surgeon’s view of this final configuration. This illustration is a section of the eye taken from 3 to 9 o’clock, as the ICL is inserted through the temporal approach. (After Boyd´s "Atlas of Refractive Surgery").
Complications In a group of 160 human eyes (patients), operated by Guimarães there have been no complications from the ICL. In fact, he has observed that this patient group has been the most satisfied of any group of the refractive surgery patients he has had. He has patients who have an ICL in one eye and have undergone a LASIK procedure in the other. The patients themselves can compare the results. Even though the correction using the ICL was much higher, patients said they had better vision in the eye
with the ICL than the one on which the corneal refractive procedure was performed. Guimarães considers that the ICL is reliable because it is reversible and offers predictability and high quality. Zaldivar began to work with this lens in 1993. After 4 years of follow-up, no patient from the original group has developed cataracts. At first Zaldivar was concerned about the possible development of pigment dispersion glaucoma because of the contact of the iris with the lens, but the first lenses of this type were redesigned and improved. This new lens is so thin that almost no pigment movement in the eye occurs. LASIK AND BEYOND LASIK
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BIBLIOGRAPHY Baikoff, G., "Phakic Anterior Chamber Intraocular Lenses", International Ophthalmology Clinics, Vol. 31:1, Winter, 1991. Barraquer, Joaquin, "Pre-Crystalline Posterior Chamber Phakic Intraocular Lenses for High Myopia", Highlights of Ophthalmology Journal, Nº 2,1998;1624. Guimaraes, R., "The Implantable Contact Lens", Highlights of Ophthalmology Journal, Nº 4,1998;3942. Landerz, M., Worst, JG., Siertsema, JV., Van Riji G., "Correction of High Myopia with the Worst Myopia Claw Intraocular Lens", Journal of Refractive Surgery, 11:1995. Worst, J., "The Artisan IOL for the Correction of Refractive Errors", Highlights of Ophthalmology Journal, Nº 3,1999. Zaldivar, Roberto, "The Implantable Contact Lens", Highlights of Ophthalmology Journal, Nº 4,1998;39-42.
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Benjamin F. Boyd, M.D., F.A.C.S. Editor in Chief Highlights of Ophthalmology Box 6-3299 -El Dorado Panama, Rep. of Panama Fax= (507) 317-0156 E-mail:
[email protected]
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Chapter 45 THE RELATIVE ADVANTAGES OF LASIK AND PHAKIC LENS IMPLANTATION TO CORRECT MYOPIA FROM -8.00 TO -12.00 DIOPTERS Paul S. Koch, M.D.
Among the mysteries still to be resolved about LASIK is what is the upper range of its practical value. There is certainly a point that will vary from patient to patient, but still be consistent among a large population, at which the postoperative optics of LASIK begin to deteriorate and at which the potential complications outweigh the practical benefits when compared to other methods of treating myopia. When LASIK first became practical, there were attempts to correct as much as 25 diopters of myopia. This proved to be quite unsatisfactory, and so the range of attempted LASIK correction has to a large degree moderated. There is general consensus that LASIK up to 8 diopters is quite good and that LASIK much above 12 diopters is not. It remains necessary to attempt to demonstrate whether LASIK in the range in between 8 and 12 diopters is as good as or better than other ways of correcting high myopia. There are only a few alternatives to LASIK in this refractive group. One adequate alternative is implanting a phakic intraocular lens. Another less attractive alternative is lensectomy with lens implantation. Lensectomy is certainly quick and efficient, with very rapid visual recovery, measured usually in minutes or hours. However, the risk to the eye in terms of retinal complications among high myopes may be excessive, considering the elective nature of the full procedure. The major options, then, are either LASIK or phakic intraocular lens. One very good phakic intraocular lens is the Ophtec Artisan™ lens, from Holland. This lens is
available in American clinical trials in powers ranging from –5.00 to –20.00 diopters. Outside the U.S., an extended power range is available. The lens is a rigid polymethylmethacrylate (PMMA) lens, with an optic diameter of 6 mm up to –15.00 diopters, and 5 mm from -16.00 to -20.00 diopters. We can review a series of patients to determine whether the Artisan lens has different outcomes than LASIK for a focused group of patients with preoperative refractions from –8.00 to –12.00 diopters. When the two techniques are compared, it may be possible to determine whether at this level of refractive correction there is a demonstrable advantage of one technique over the other.
Surgical Technique: Ophtec Artisan Myopia Implant The eye is anesthetized using a peribulbar or retrobulbar block. The procedure can be performed under topical anesthesia, but enclavation disturbs the incision and some viscoelastic may escape, especially if the eye moves, thereby permitting optic-endothelial touch. The risk of endothelial touch should be avoided because one of the advantages of this lens is that endothelial cell loss is essentially nil when surgery is performed carefully. Two stab incisions are made in the peripheral cornea, directed parallel to the axis of lens insertion. For example, if the lens is going to be inserted temporally in the right eye at the 9 o’clock position, the stab incision will be directed from the 10 o’clock position to the 2 o’clock position and from 8 o’clock
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Figure 45- 1: The two stab incisions are not radial; they are oriented parallel to the direction of lens insertion. The entry of the stab incision should be pointed directly towards the site on the iris where the enclavation will take place.
to 4 o’clock. The first two stab incisions are designed to permit the enclavation needle to enter the eye directed exactly to the spot where enclavation will take place (Figure 45-1). Once the stab incisions are made, the anterior chamber is irrigated first with Miochol. Then it is filled with a cohesive viscoelastic such as Healon
or Amvisc Plus. A cohesive viscoelastic is very helpful in cases of phakic lens implantation, because it can be irrigated from the eye very easily at the end of the procedure (Figures 45-2,45-3). The primary incision for phakic lens implantation needs to be made in a very specific manner. A simple shelf incision in the peripheral cornea facilitates viscoelastic leakage from the anterior chamber during enclavation and makes the case more difficult than necessary. The best incision has a partialthickness groove and then a shallow tunnel into the cornea of only 1 mm or 2 mm. This gives the eye an adequate corneal incision lip and at the same time limits how much the incision must be distorted in order to use the enclavation instruments (Figures 45-4, 45-5). The intraocular lens is slipped into the anterior chamber and allowed to rest there. Immediately, two or three interrupted 10-0 nylon sutures are used to tightly close the incision in order to be able to control the anterior chamber. Contact between iris and lens is essential for easy enclavation, so a lens manipulation hook is placed in the eye and on top of the implant. It presses the lens gently down against the iris to remove most of the viscoelastic separating the two. Pushing the lens down also increases the distance of the implant from the corneal endothelium.
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Figure 45-2: The miotic is injected into the eye. Notice that the needle is pointed directly towards the anticipated enclavation site.
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Figure 45-3: After the pupil is constricted, a cohesive viscoelastic is injected into the anterior chamber. At the risk of some redundancy, notice again that the direction of the corneal incision is straight to the enclavation site and not radial.
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Figure 45-4: The incision is constructed in two planes. The first plane is a groove of about one-half the corneal thickness.
Figure 45-5: The second plane is a short tunnel of roughly 1 mm to 2 mm. The groove and the tunnel are planned so that the external groove and the internal tunnel are in a line parallel to and slightly above the iris. This minimizes the likelihood of incision distortion and viscoelastic leakage.
The lens hook then rotates the lens perpendicular to the original incision. Using again the example of a 9 o’clock incision, the lens is placed in the eye initially from 9 o’clock to 3 o’clock. It is now rotated from 6 o’clock to 12 o’clock (Figures 45-6, 45-7). The enclavation needle is slipped into the eye through one of the stab incisions before the lens forceps are passed through the primary incision. If these steps are reversed, it is common to see viscoelastic leakage at the primary incision when the enclavation
needle is placed. Therefore, the needle is always put in first. The lens forceps hold the optic of the lens gently downward against the iris while the first enclavation takes place. The enclavation needle pushes down and forward against the iris, gathering a knuckle of iris in front of it. The enclavation needle is then lifted into the claw, scooping iris with it in a single, easy motion. If the amount of iris secured in the claw is insufficient, the enclavation can be re-
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Figure 45-6: The intraocular lens is placed in the anterior chamber and left there until after the incision has been sutured and the anterior chamber controlled.
Figure 45-7: A lens hook is used to rotate the lens perpendicular to the direction of insertion. For example, for a temporal incision in the right eye, the lens was inserted from 9:00 towards 3:00. Now it is rotated from 12:00 to 6:00.
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Figure 45-8: The enclavation is always difficult to capsule for demonstration. The lens is held with the forceps and the enclavation needle gathers the iris. In this view the tip of the needle is pushing down and forward against the iris, gathering a fold in front, in much the way a snowplow pushes snow.
Figure 45-9: In this view a split second later, the needle is lifted into the claw of the lens, still pushing the iris in front of it. The tips of the claw give way as the needle and iris pass between them. When the needle is completely through the claw, the tips close against the iris, capturing it and causing fixation.
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peated until a sufficient amount of iris is captured (Figures 45-8, 45-9). Typically, at this point a little more viscoelastic is placed in the eye to deepen the chamber and again to push the lens against the iris. The last step is repeated, this time using the second stab incision to
make the second enclavation. The position of the lens during enclavation is critical because the lens must be perfectly centered over the pupil when iris fixates it. If it is not centered, the iris should be pushed out of the claw, the lens recentered, and the enclavation repeated.
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Figure 45-10: The iridotomy is made by gathering some iris with the tip of sharp scissors, just like the enclavation needle gathered some iris for the enclavation. The scissors are twisted so that the iris lifts away from the crystalline lens. The scissors are closed, making a snip iridotomy. The tips can be opened within the iridotomy to make it larger if needed.
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Figure 45-11: A close-up of an enclavation showing an adequate amount of iris captured in the claws.
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The final step is to remove the viscoelastic from the eye by irrigating the anterior chamber and simultaneously pressing on the corneal lip. The cohesive viscoelastic can be burped from the eye easily, ensuring a near-total removal. An additional 10-0 nylon suture is placed if necessary. At the conclusion of the operation, the lens is centered over the iris with two adequate enclavations (Figures 45-11,45-12).
Surgical Technique: LASIK
Figure 45-12: The completed case, with the lens centered, adequate enclavations, and an iridotomy.
A small peripheral iridectomy or iridotomy must be performed. The easiest method is to slip very small, very sharp scissors into the anterior chamber and use one tip of the scissor to capture and lift a piece of iris. When the scissors close, they snip a piece of the iris, forming an iridotomy. If necessary, the tips of the scissors can be placed in the small iridotomy and opened to enlarge the opening (Figure 45-10).
The LASIK technique varies depending upon the laser and the fixation method used. When I conducted this study, I used a Summit Apex Plus Laser and a Moria LSK One microkeratome. The LASIK flap was made with a nasal hinge. Immediately after the microkeratome is removed, the vacuum of the Moria unit is turned to the low setting, allowing the surgeon to continue holding on to the eye with the ring while near-normal intraocular pressure is restored to the eye. In this way the eye can be manually fixated and steadily held under the laser while the ablation is performed (Figures 45-13 -- 45-15). I use a lint-free cellulose sponge in two ways: as a sponge to attract moisture and as an instrument to manipulate the flap. Once the flap is cut, I use the sponge to dry most of the moisture on the surface of
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Figure 45-13: The lashes of the lateral upper eyelid are draped because they could interfere with the movement of the microkeratome.
Figure 45-14: The Moria suction ring is placed on the eye, centered, and activated with high vacuum in preparation for making the flap.
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Figure 45-15: The flap is made with the forward pass of the microkeratome while the ring is on high vacuum. When the head reaches its stop, the motor is inactivated and the vacuum is reduced to its low setting before the head is retracted. Retraction under low vacuum reduces epithelial friction and abrasions.
Figure 45-16:The superior, inferior, and temporal areas of the ring’s surface are dried to reduce the moisture to the stromal bed. The nasal area is left moist to prevent flap adhesion to the ring.
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the ring except where the flap will rest when flipped. I used to dry everywhere but once I lost suction and the ring moved. The flap was stuck to the dried ring and ripped off the eye, leaving a free cap (Figure 45-16). The tip of a second sponge is used to lift the flap and flip it over. That same sponge is immedi-
ately used to wipe the moisture from the stromal bed. If moisture appears on the stroma during the ablation, it is wiped away with a sponge, but if the cornea remains adequately dry during the ablation, the laser is fired until the treatment is finished (Figures 45-17 -- 45-21).
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Figure 45-17: Stage one of lifting the flap with the cellulose sponge. A new, dry sponge is used as a pusher, engaging the flap at its temporal edge.
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Figure 45-18: Stage two of lifting the flap with the cellulose sponge. The tip of the sponge pushes the flap and begins to flip it over.
LASIK VS PHAKIC LENS IMPLANTATION TO CORRECT MYOPIA
Figure 45-19: Stage three of lifting the flap with the cellulose sponge. The flap is completely lifted and flipped. The sponge smoothes out the flap to prevent wrinkles.
Figure 45-20: The same sponge is immediately used to dry any moisture that may have settled on the stromal bed.
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After the ablation the corneal bed and the underside of the flap are irrigated vigorously with balanced salt solution and wiped thoroughly with the cellulose sponge. After I am confident that both surfaces are completely clean and free of debris, the same
sponge is used to reposition the flap. The surface of the flap is massaged several times with the lint-free sponge to remove underlying fluid, the gutters are dried, and the flap is allowed to seal in place (Figures 45-22 -- 45-25).
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Figure 45-21: Stage three of lifting the flap with the cellulose sponge. The flap is completely lifted and flipped. The sponge smoothes out the flap to prevent wrinkles.
Figure 45-22: Once the ablation is completed, the assistant irrigates the bed and the underside of the flap vigorously with BSS, while the surgeon scrubs each with the cellulose sponge.
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Figure 45-23: Once all the debris has been cleaned from the bed, the same sponge is used to wipe the flap back into position and to massage it several times to remove much of the underlying fluid.
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Figure 45-24: A new, dry sponge is used to dry the
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Figure 45-25: The edge of the gutter is dried a second time with a gentle flow of compressed air. Only the gutter is dried, not the flap itself. Too much drying will desiccate the flap and displace it.
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LASIK VS PHAKIC LENS IMPLANTATION TO CORRECT MYOPIA
The Study: Ophtec Artisan Myopia Implant vs. LASIK In order to determine whether one technique is demonstrably superior to the other, we conducted a prospective study in which we enrolled patients who required refractive correction of –8.00 to –12.00 diopters. In this evaluation, we included 97 eyes, 79 of which were treated with LASIK, and 18 of which had the Artisan™ myopia implant. We were able to follow both of these groups for a period of time ranging from 6 to 24 months. The two groups were not thoroughly randomized. Some patients had astigmatism greater than the 2 diopters allowed for enrollment in the Artisan lens clinical study. All patients in this subgroup were treated with LASIK. Other patients had corneal curvatures too flat or thicknesses too thin for LASIK and therefore had lens implantation. Other patients
preferred one procedure over another and could therefore not be randomized. The preoperative BCVA was different for the two groups. Patients having LASIK saw better before surgery than the patients who received the Artisan implant. This was not part of the study design, nor does it reflect a bias; it was simply a coincidence of patient distribution. The pre-operative BCVA are summarized in Table 1 and Graph 1 which demonstrate clearly that far more patients in the LASIK group had a potential visual acuity of 20/20 than those eyes in the Artisan implant group. When patients with preexisting astigmatism were assigned to have LASIK, the laser was used to correct the astigmatism as well. Only patients with 2 diopters of astigmatism or less were enrolled in the Artisan implant group. The only attempt to correct the astigmatism in this group was through incision placement and suture tension.
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Results Following surgery, the postoperative uncorrected visual acuities were very similar. 43% of the LASIK patients and 50% of the Artisan patients saw 20/20 or better without correction. A total of 68% of the LASIK patients and 66% of the Artisan patients saw 20/25 or better, and 88% of the LASIK patients and 94% of the Artisan patients saw 20/40 or better. The trend toward improved vision in the Artisan patients had mild statistical significance (p=0.04), but the difference between the two is still very slight (Table 2, Graph 2).
There is, however, a tremendous difference in the postoperative BCVA between the two treatment groups. Sixty-three percent of the LASIK group and 94% of the Artisan implant group were able to see 20/20 or better with correction following surgery. All of the Artisan patients saw at least 20/25 or better. However, only 84% of the LASIK patients saw 20/25, and only 97% of them saw 20/40. This represents a dramatic shift from the BCVA prior to surgery, where the LASIK patients clearly had the advantage. Postoperatively, the advantage shifted to the Artisan lens patients. This is statistically significant to the level of p=0.0001 (Table 3, Graph 3).
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LASIK VS PHAKIC LENS IMPLANTATION TO CORRECT MYOPIA
The average visual acuity in the LASIK group fell slightly, from 20/21 to 20/24, while in the Artisan lens group it improved slightly from 20/24 to 20/18 (Table 4). In the Artisan lens group, there was a dramatic improvement in the number of eyes that gained BCVA. Thirteen percent of the LASIK eyes improved by one or more lines of visual acuity, and only 2% improved by two lines of vision or more. On the other hand, 83% of the Artisan patients improved by one or more lines, and 22% of the eyes improved by two or more lines (Table 5).
Just the reverse was found when we examined loss of BCVA. None of the Artisan implant eyes lost any visual acuity; however, 25% of the LASIK eyes lost one or more lines, and 6% lost two or more lines of BCVA. In many cases, the recorded loss of one line occurred because some patients before surgery were examined while wearing a hard contact lens, whereas they were examined behind the phoropter postoperatively. This variable applied to Artisan lens patients as well. There was no question that the Artisan lens eyes gained more vision and lost no vision, while the LASIK eyes gained only a little vision and lost some as well (Table 6).
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Graph 4
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This distribution can be seen in Graph 4, which clearly demonstrates the variability of changes of vision with the LASIK group, but only stability or improvement in the Artisan implant group. The LASIK group had a series of reoperations: 8 of the 79 eyes (10.1%) required an enhancement procedure. None of the Artisan implant eyes required further surgery. The endothelial cell counts were evaluated for the Artisan lens group. The mean preoperative endothelial cell count was 2,026 cells. After 1 year the mean count was 2,191 cells, showing overall stability of cell counts without significant cell loss (Tables 7,8).
Summary Comparing the results of LASIK and Artisan myopia implants for patients requiring –8.00 to 12.00 diopters of correction shows that the two tech-
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niques yield similar levels of uncorrected visual acu- Section 7 ity. There is a slight statistically significant improvement in results seen with the Artisan lens over the Subjects Index LASIK patients, but the difference is not dramatic. On the other hand, there is a dramatic difference in the patients’ overall vision, measured by their postoperative BCVA. In this study, the Artisan implant patients had improved vision more often, and the LASIK patients had reduced vision more often. Help ? It is, therefore, my opinion that implanting an Artisan implant may be both safer and more beneficial than LASIK for myopia for –8.00 to –12.00 diopters. This conclusion, however, should be tempered because LASIK is a much simpler operation for patient and surgeon, and lens implantation is more intensive in terms of work effort and involves a greater risk of intraocular infection. Therefore, a rationale needs to be devised for selecting one procedure over the other.
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Recommendations We now select a procedure based upon a patient’s corneal curvature and thickness. We use an arbitrary postoperative flat threshold for corneal curvature at 37.0 diopters. If we are comfortable that we can perform the LASIK procedure and maintain a corneal curvature of at least 37.0 diopters, we tend to recommend LASIK rather than lens implantation. If, on the other hand, it appears that the postoperative corneal curvature will be less than 37.0 diopters, we are more likely to recommend lens implantation. The thickness of the corneal flap we typically make is 160m. We want, in all cases, to have a residual corneal bed after the ablation of at least 250m. If the patient’s preoperative corneal thickness would
allow us to do the LASIK under a 160m flap and still maintain at least 250m of corneal bed, we are apt to recommend LASIK. If, on the other hand, the flap would be thinner than 160m, or the residual bed would be thinner than 250m, we are more likely to recommend lens implantation. (Table 9) I do not think it is accurate to say that either technique is more suitable for all patients in the – 8.00 to –12.00 diopter range. If not for the intensity of the effort involved implanting the phakic implant, our results would probably suggest the phakic implant as the preferred technique in most patients. LASIK, however, retains several advantages, including ease of performance and the ability to perform bilateral procedures. Therefore, its use in this target population must not be discounted. Contents
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Paul S. Koch, MD Koch Eye Associates 566 Tollgate Road Warwick, RI 02886 USA Fax: 401-738-0174 E-mail:
[email protected]
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INTACS TM REFRACTIVE CORRECTION WITH AN INTRACORNEAL DEVICE
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Chapter 46 INTACS TM REFRACTIVE CORRECTION WITH AN INTRACORNEAL DEVICE Terry E. Burris, MD, Debby Holmes-Higgin, MS
Intracorneal Intracorneal ring technology has shown rapid development in the past twelve years, and clinical results are confirming outstanding results for the correction of low to moderate refractive myopias. Results to date indicate the surgical procedure is safe and easily performed, visual results are excellent, and the device provides stable and predictable correction postoperatively. Enhancements can be easily performed by device exchange, and Intacs can be removed, reversing the refractive effect
History The intrastromal ring concept was proposed by A. E. Reynolds in 1978. The device was to be placed in the corneal periphery through a single, peripheral radial incision. Central corneal curvature could be either flattened or steepened, respectively, by constricting or expanding the ring. As a refractive surgical device, the proposed benefits included surgical preservation of the central cornea, elimination of wound healing as a determinant of surgical outcome, rapid vision improvement, and capability to adjust or even reverse the procedure to expand patient options. Later theoretical and animal study work on this device continued with funding from KeraVision, Inc. (Fremont, CA) [1] to confirm its feasibility. Human eye bank eye studies by Burris and associates [2] showed that ring thickness produced corneal flattening, which eliminated the need to constrict or expand
the device. The current product, the intrastromal corneal ring segments (ICRS‚), or Intacs‘ corneal ring segments, is designed to correct low to moderate myopia by modulation of device thickness.
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Initial Clinical Studies
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The ICR was placed in the first ten human sighted eyes in 1991 [5]. The most recently reported Section 3 results indicated that uncorrected visual acuity was Section 4 20/40 or better in nine eyes, eight eyes were within +1.00 D of their intended correction as determined Section 5 by manifest spherical equivalent refraction, and refractive effect was stable over time. One patient had Section 6 the ICR removed at postoperative Month 6. Section 7 Clinical trials in the U.S. were begun in 1993 under the direction of David Schanzlin, MD. (Note Subjects Index from the Editor in Chief: The other major study was conducted in Sao Paulo, Brazil, under the direction of Prof. Rubens Belfort Mattos Jr.). These studies, conducted with either a radial or circumferential incision, further confirmed that the ICR was well tolerated in the cornea with predictable, stable optical Help ? correction of myopic eyes. Recently reported results indicated that, of sixty-six patients who had reached postoperative Month 12 at the reporting period, 85% had uncorrected visual acuity of 20/40 or better [6]. The original 360º ICR was modified to consist of two 150º PMMA segments (ICRS) in order to facilitate the surgical procedure and avoid potential incision related complications. Each device segment is inserted into its respective semi-circular shaped intrastromal channel made through a single 1.8 mm
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radial incision located in the superior cornea near the limbus. An Intacs in situ is presented in Figure 46-1. Original thicknesses of the Intacs for clinical studies were 0.25, 0.30, 0.35, 0.40 and 0.45 mm; an additional thickness of 0.21 mm was added.
Surgical Procedure The surgical procedure is illustrated in stepwise fashion by Figure 46-2. [6] Patient preparation and Intacs placement are performed under topical anesthesia using techniques similar to LASIK. The corneal geometric center is marked and peripheral corneal thickness is measured by ultrasonic pachymetry over the planned incision site, typically at the 12:00 meridian. A diamond knife is set to 68% of the peripheral corneal thickness and is used to create a 1.8 mm incision allowing introduction of the lamellar dissecting instruments (KeraVision, Inc., Fremont, CA). A pocket spreader (modified Suarez spreader) is used to initiate the lamellar dissection in both a clockwise and counterclockwise direction. A vacuum centering guide is applied to the globe, and the clockwise or counterclockwise stromal separator is introduced through the incision and rotated 180º to 190º to create a midperipheral semi-circular channel. The separator is rotated out of the channel, and the other separator is used to fashion the opposing half channel. The vacuum centering guide is removed. One of two Intacs is irrigated with BSS, in-
serted and rotated into either the clockwise or counterclockwise channel, and finely placed with a Sinskey hook. Its mate is similarly rotated into its respective portion of the channel. A single 10-0 or 11-0 nylon suture (optional) is placed to ensure closure of the incision edges, drops of topical antibiotic/ corticosteroid combination are applied and an eye shield taped into place for the immediate postoperative period. Postoperative discomfort is managed with a topical non-steroidal anti-inflammatory agent such as Voltaren“. An antibiotic steroid combination drop, such Tobradex“, is used four times a day for one week, and can then be tapered rapidly over the following week. The nylon suture, if placed, is removed when loose, or by two weeks postoperatively. Any suture removal should be covered with antibiotic three to four times a day for four days after the removal. TheThe patients should be examined about one week after cessation of antibiotic to ensure no late infections have occurred.
CLINICAL OUTCOMES
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Visual Results
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Nominal predicted correction was –1.30 Section 6 diopters for the 0.25 mm Intacs, -2.00 diopters for Section 7 the 0.30 mm Intacs and –2.70 diopters for the 0.35 mm Intacs. Uncorrected visual acuity in 97% Subjects Index of patients (total n=410) was 20/40 or better
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Figure 46-1: The Intacs refractive device placed in situ.
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Surgical Procedure for Placement of the INTACS
2-A Incision and placement for Intacs marked
2-B Radial incision (~1.8 mm) made
2-C Pocket created as a requisite for stromal separation and Intacs placement
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Section 6 2-D Vacuum centering guide used to facilitate stromal separation
2-E Stromal separation in the clockwise direction
Section 7 2-F Intacs segment inserted
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2-G Incision closed
Figure 46-2
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(Figure 46-3). Ninety-nine percent of patients (409/410) had preserved best spectacle-corrected visual acuity at postoperative Month 12 (Figure 46-4). One eye lost eleven ETDRS letters (about two lines) at postoperative Month 12, but had visual acuity (both uncorrected and best spectacle-corrected) of 20/20.
Peri-Operative Observations and Complications Mild subconjunctival hemorrhages are seen at surgery from manipulating the conjunctiva with surgical instruments. Adverse intraoperative complications for this clinical study cohort included one posterior corneal perforation into the anterior chamber, due to a deviation in surgical procedure, three anterior corneal surface perforations, due to superficial dissection of the intrastromal channel, and one case of subconjunctival chemosis, resulting from an allergic response to the surgical scrub. In all five cases the Intacs were not placed at the time the event occurred, although two of these patients subsequently had Intacs successfully placed in contralateral eyes. Best spectacle-corrected visual acuity for patients experiencing intraoperative complications have re-
turned to baseline, or improved, compared to preoperative values.
Postoperative Observations Epithelial wound closure over the incision occurred for 96% of patients by Day 7 after receiving Intacs. All eyes had completely healed by Day 14. Small epithelial inclusion cysts were noted in 37.6% of patients at some point postoperatively, and appeared well embedded in the stroma with no fluorescein staining; these remained in only 7% of eyes at postoperative one year. At Month 3, other clinically insignificant findings included mild channel haze, as well as tiny refractile deposits in the lamellar channel, and hazy cloudy deposits in the segment positioning holes, and / or at the ends of the segments in most patients. The location of the haze correlates with the zone of blunt lamellar stromal dissection, which is slightly larger than the width of the Intacs. Small amorphous chalky deposits develop adjacent to the ICRS in many patients. These increase for several months in many patients and tend to disappear by two years postoperatively. Haze and deposits have never been ob-
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Figure 46-3: Uncorrected visual acuity at postoperative Month 12 with the Intacs.
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Figure 46-4: Best spectacle-corrected visual acuity at postoperative Month 12 with the Intacs.
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served to extend outside the channel either peripherally or toward the visual axis for any patient. Eight patients (8%) had corneal sensation losses of 20 mm or greater (Cochet-Bonnet aesthesiometry) at Month 3, and no patient had total loss of corneal sensation. This effect appears to be transient and principally limited to the central three millimeters of the cornea. No patient demonstrated signs of neurotrophic keratitis, such as punctate keratitis, filaments, epithelial breakdown or trophic ulceration. Subsequent study shows corneal sensation to be returning in all patients. Postoperative adverse included one incident of infectious keratitis, one incident of shallow segment placement, and two incidents of anterior chamber perforation during surgery. All adverse event patient eyes had a best spectacle-corrected visual acuity of 20/20 or better at their last reported exam and none of them has experienced a permanent loss. Twenty patients experienced induced astigmatism of greater than or equal to 1.0 D based on manifest refraction (Month 3). This is believed to be related to incisional healing effects and possibly due to suture tightness at surgery. Corneal topography in these cases confirm a typical with-the-rule induced cylinder effect originating from the area of the incision site at 12:00. In spite of the induced cylinder, nineteen of the twenty patients maintained uncorrected visual acuity of 20/40 or better. By Month 12, 15/410 patients (3.7%) had greater than one diopter of induced refractive astigmatism. Three patients (0.7%) experienced greater than one and a half diopters of induced astigmatism. All three of these patients had uncorrected visual acuity of 20/25 and best spectacle-corrected visual acuity of 20/16 or better.
Corneal Topography Corneal topography observations confirm that central corneal flattening increases incrementally with greater thickness Intacs [2]. In addition, postoperative corneal shape remains prolately aspheric, a potentially unique optical characteristic of the Intacs compared to other refractive correction procedures [2,9-12] . Color axial maps representing typical anterior corneal surface topography, preoperatively and with a 0.35 mm Intacs, are presented in Figure 46-5. These
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Section 6 Section 7 Figure 46-5: Color axial topography maps representing normal Subjects Index corneal topography before and after the Intacs refractive procedure.
maps qualitatively illustrate the topographic flattening which occurs with Intacts. Preoperative prolate asphericity is accentuated with Intacs, but does not appear to be related to standard clinical visual performance measures including best spectacle-corrected visual acuity and contrast sensitivity [10-12]. Radius of curvature flattening profiles, adapted from methodology reported for previous corneal topography investigation, [13] were used to quantify induced topographic corneal flattening with each Intacs thickness. Flattening across the zero to six millimeter diameter optical zones was determined by subtracting the average postoperative axial radius of curvature values
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for each zone from respective preoperative values. Profiles have been designed to visually simulate mean axisymmetrical corneal curvature change; the zero millimeter zone mean value is placed at the center of each profile and each successive mean zone value is shown redundantly to each side. These profiles graphically illustrate average central and pericentral corneal flattening, in addition to showing trends of topographic change between the corneal diameter millimeter zones. Radius of curvature difference profiles indicated that flattening with Intacs was prolately aspheric; relatively more flattening occurred pericentrally than centrally (Figure 46-6). Confidence intervals (95%) suggested that the average radius of curvature change was significantly different between Intacs thicknesses for most millimeter diameter optical zones. Anterior corneal surface topography with the Intacs has been typified. Color axial topography maps from eyes in the Phase III FDA clinical trial were classified by predominant qualitative pattern by two masked observers according to pre-specified topography classifications and guidelines [14]. The classification scheme was developed primarily from previously published works [15-21] and included the follow-
ing prolate patterns: spherical (SPH), non-toric prolate asphere (PAS), symmetrically toric (STO), asymmetrically toric (ATO), multizonal (MZA), or noncentral prolate asphere and unclassifiable (UNC). Preoperative and postoperative Month 6 corneas with the Intacs approximated patterns published for normal eyes, with a few exceptions [15].
Reversibility of Refractive Effect After Intacs Removal A unique characteristic of the Intacs refractive surgical procedure is its potential reversibility. Recently reported results for 449 eyes indicated that Intacs have been removed from 31 eyes (6.9%) with no apparent residual refractive effect [8,22]. Reasons for Intacs removal included dissatisfaction with correction achieved (12 eyes), dissatisfaction relating to glare and/or halos (16 eyes), bacterial infection (1 eye), and personal reasons (2 eyes). Manifest refraction spherical equivalent at Month 3 after Intacs removal returned to within one diopter of preoperative value for most eyes (Figure 46-7). Corneal topography analyses supported these refractive results [23].
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Figure 46-6: Mean (with 95% confidence intervals) radius of curvature flattening profiles for three different thickness Intacs.
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Figure 46-7. Manifest refraction spherical equivalent preoperatively and after removal (Month 3) of the Intacs for individual eyes.
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Contents Figure 46-8. Color axial corneal topography trend map for a case eye preoperatively and after removal of the Intacs.
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Color axial trend maps for a sample eye clearly demonstrate the return of corneal curvature to approximate baseline levels after removal of the Intacs (Figure 46-8).
Refinement of Refractive Effect with Intacs Exchange Several patients have undergone Intacs exchange to treat over-or undercorrection. These brief procedures were easy to perform and preliminary reports indicate a good response [8].
Safety Assurance and Further Indications Intracorneal ring technology demonstrates a promising new technique for rapid, predictable vision correction with no removal of corneal tissue or surgical violation of the central cornea. At postoperative Month 12, uncorrected visual acuity is stable and best spectacle-corrected visual acuity is maintained. Preliminary Intacs exchange data show enhancements to be easily performed and efficacious.
Finally, Intacs are removable and the optical effect is Section 4 reversible, making this technique uniquely appealing to patients who want to preserve future correc- Section 5 tive options. Section 6 The effective range of treatment with the current Intacs design will likely apply to myopias up Section 7 to five diopters, although newer permutations may have other refractive applications (i.e. astigmatism Subjects Index concurrent with myopia, hyperopia,). Complications of the U.S. Intacts procedure to date have been few and easily managed. Importantly, there have been no complications resulting in permanent loss of uncorrected or best spectacle-corrected visual acuity. Transient loss of corneal sensaHelp ? tion is consistent with that seen in cataract surgery, incisional keratotomy and ablation procedures [29-32]. In all cases where the Intacs were removed, the refractive effect has been shown to be reversible. The unique topography of the Intacs, showing maintenance of prolate corneal asphericity, has theoretical optical advantages that may be further exploited in the future [9]. One of our surgical refractive goals should be to minimize induced optical anomalies such as spherical aberration, which can degrade contrast sensitivity and image quality. Fur-
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ther studies of intracorneal implant technology and correlation with clinical outcomes will help refine our understanding of ocular optical principles as they apply to refractive surgery.
REFERENCES 1. Fleming JR, Reynolds AI, Kilmer L, Burris TE, Abbott RL and Schanzlin DJ. The intrastromal corneal ring: Two cases in rabbits. J Refract Surg 1987; 3:227-232. 2. Burris TE, Baker PC, Ayer CT, Loomas BE, Mathis ML, Silvestrini TA: Flattening of central corneal curvature with intrastromal corneal rings of increasing thickness: an eye-bank eye study. J Cataract Refract Surg 1993;19(suppl):182-187. 3. Nosé W, Neves RA, Schanzlin DJ, Belfort R: Intrastromal corneal ring — one-year results of first implants in humans: a preliminary nonfunctional eye study. Refract & Corneal Surg 1993;9:452-458.
9. Burris TE, Holmes-Higgin DK, Silvestrini TA, Scholl JA, Proudfoot RA, Baker PC. Corneal asphericity in eye bank eye implanted with the intrastromal corneal ring. J Refract Surg 1997;13(6):556-567. 10. Holmes-Higgin, DK, Baker, PC, Burris, TE, Silvestrini, TA. Characterization of the aspheric corneal surface in ICRS“ (Intrastromal Corneal Ring Segments) Patients. IOVS 1998;39(4):S74. 11. Holmes-Higgin, DK, Baker, PC, Burris, TE, Silvestrini, TA. Characterization of the aspheric corneal surface with the ICRS“ (Intrastromal Corneal Ring Segments). Accepted for publication, J Refract Surg 1999. 12. Holmes-Higgin, DK, Burris, TE, Silvestrini, TA, Baker, PC, Torres, AR and the Phase III ICRS Study Group. Topographic corneal asphericity and visual outcome with the ICRS“ (Intrastromal Corneal Ring Segments). In PreAAO International Society of Refractive Surgery Meeting. New Orleans, LA, 1998.
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4. Assil KK, Barrett AM Fouraker BD, Schanzlin DJ for the Intrastromal Corneal Ring Study Group. One-year result of the intrastromal corneal ring in nonfunctional human eyes. Arch Ophthalmol 1995;113:159-167.
13. Waring GO, Hannush SB, Bogan SJ, Maloney RK. Classification of corneal topography with videokeratography. In: Schanzlin DS, Rubins B (eds.). Corneal Topography. New York, NY:Springer Verlag; 1992:47-73.
5. Nosé W, Neves RA, Burris TE, Schanzlin DJ, Belfort R, Jr. Intrastromal corneal ring: 12-month sighted myopic eyes. J Refract Surg 1996; 12(1):20-28.
Section 6 14. Burris, TE, Holmes-Higgin, DK, Asbell, PA, Durrie, Section 7 DS, Schanzlin, DJ. Month 3 corneal topography analysis of patients with the ICRS (Intrastromal Corneal Ring Subjects Index Segments). In American Academy of Ophthalmology Meeting, Atlanta, GE, 1996.
6. Schanzlin DJ, Asbell, PA, Burris TE and Durrie DS. The ICRS: Phase II results for the correction of myopia. Ophthalmology 1997; 104(7):1067-1078. 7. Waring, GO III, Abbott, RL, Asbell, PA, Assil, KK, Burris, TE, Durrie, DS, Fouraker, BD, Lindstrom, RL, McDonald, JE II, Verity, SM, Schanzlin, DJ. One-year outcomes of Intrastromal Corneal Ring Segments for the correction of -1.0 to -3.5 diopters of myopia. In American Academy of Ophthalmology Meeting, New Orleans, LA, 1998. 8. Waring, GO III, Abbott, RL, Asbell, PA, Assil, KK, Burris, TE, Durrie, DS, Fouraker, BD, Lindstrom, RL, McDonald, JE II, Verity, SM, Schanzlin, DJ. One-year outcomes of Intrastromal Corneal Ring Segments for the
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correction of -1.0 to -3.5 diopters of myopia. Submitted for publication, Ophthalmology, 1998.
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Section 5
15. Bogan, SJ, Waring, GO, Ibrahim, O, Drews, C, Curtis, L. Classification of normal corneal topography based on computer assisted videokeratography. Arch Ophthalmol 1990; 108:945-949. Help ?
16. Lin, DTC, Sutton, HF, Berman, M. Corneal topography following excimer photorefractive keratectomy for myopia. J Cataract Refract Surg 1993; 19(Suppl):149154. 17. Lin, DTC. Corneal topographic analysis after excimer photorefractive keratectomy. Ophthalmology 1994;101(8):1432-1439.
INTACS TM REFRACTIVE CORRECTION WITH AN INTRACORNEAL DEVICE
18. Young, JA and Siegel, IM. Three dimensional digital subtraction modeling of corneal topography. J Refract Surg 1995; 11:188-193. 19. Hersh, PS, Schwartz-Goldstein, BH, and the PRK study group. Corneal topography of Phase III excimer laser photorefractive keratectomy. Ophthalmology 1995; 102:963-978.
25. Burris TE, Holmes-Higgin DK, Silvestrini TA, Scholl JA, Proudfoot, RA. Preliminary eye bank eye topography studies with toric ICR prototypes developed to reduce astigmatism. IOVS 1996;37(3):S66. 28. Belfort, R Jr, Nose, W, Neves, R, Burris, TE, Silvestrini, TA, Schanzlin, DJ. Intra Corneal Implants. In
21. Levin, S, Carson, CA, Garrett, SK, Taylor, HR. Prevalence of central islands after excimer laser refractive surgery. J Cataract Refract Surg 1995; 21:21-26. 22. Burris, TE, Holmes-Higgin, DK, Abbot, RL, Asbell, PA, Durrie, DS, Verity, SM and Schanzlin, DJ. Corneal topography after removal of the ICRS. IOVS 39(4):S74. 23. Burris, TE, Abbott, RL, Asbell, PA, Assil, KK, Durrie, DS, Fouraker, BD, Lindstrom, RL, McDonald, JE II, Schanzlin, DJ, Verity, SM, Waring, GO III. Reversibility of refractive effect after removal of the ICRS. In PreAAO International Society of Refractive Surgery Meeting. New Orleans, LA, 1998. 24. Holmes-Higgin DK, Burris TE, Silvestrini TA, Scholl JA, Proudfoot RA. Evaluation of topographic corneal astigmatism change in eye bank eyes with variable thickness ICR“ prototypes. IOVS 1996;37(3):S66.
Contents
Section 1 Section 2
Section 3
Section 4
Terry E. Burris, MD Debby Holmes-Higgin, MS Northwest Corneal Services 6950 SW Hampton, Suite 150 Portland, OR 97223 Phone: (503) 624-4814 Fax: (503) 624-4904
Section 5
Section 6 Section 7 Subjects Index
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• Part of the text and some of the figures of Chapters 43 and 46 are presented with permission from Agarwal et al textbook on REFRACTIVE SURGERY published by Jaypee, India , 1999.
LASIK AND BEYOND LASIK
521
SUBJECT INDEX
SUBJECT INDEX
CATARACT / CLEAR LENS EXTRACTION NO ANESTHESIA IN Advantages of Blurlex (Trypan Blue) use in Disadvantages of Nucleus removal techniques in Karate chop in Further chopping in Two halves in Phacodynamics of COMPLICATIONS IN Classications of Intraoperative Chemosis Corneal perforation Descentered flap Free cap Incomplete flap Irregular flap Limbal neovascularization Small palpebral fissure Subconjunctival hemorrhages Postoperative Early Diffuse lamellar keratitis (Sands of Sahara) Displaced flap Epithelial defects Flap striae Infectious keratitis Interface debris
Late Corneal ectasia Decreased contrast sensitivity Epithelial ingrowth Glare Halos Irregular astigmatism Overcorrection Regression Undercorrection Vitreoretinal
451-462 458 459 459 451 452 455 454 458
COMPUTED CORNEAL TOPOGRAPHY IN Fundamentals of Corneal Curvature in Keratometry Keratoscopy Photokeratoscopy Topographic maps Videokeratoscopy Human optics in Topographers in
247-266 247 247 248 250 249 249 249 250 248 248 247 250 250 252
LASIK IN CONFOCAL MICROSCOPY AND Contributions of Flap evaluation by Results of Sands of Sahara and Technical procedure of
251 251 252 252 251
xv
252 256 254 255 254 254 255 253 253 253 256
09-59 09 10 10 10 10 20 11 09 43 061 064 061 062 063 062
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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SUBJECT INDEX CORNEAL TOPOGRAPHY AND WAVEFRONT ANALYSIS Current status of Map variability in Useful information of
333-335 334 334 333
CUSTOM ABLATION THROUGH WAVEFRONT MAPPING Promising new technology in
337-338 337
CUSTOMIZED ABLATION Present role of Topolink in Examples of Results of Technique of
401-412 401 402 402 409 402
DISC FOLDS AND STRIAE IN Definition of Folds treatment Striae treatment
277-282 277 278 280
DOWN UP TECHNIQUE OF Hansatome microqueratome for Advantages of the Care and maintenance of the Disadvantages of the Power supply unit of Sterilization of the Suction ring of Surgical technique with the
109-118 109 117 112 117 109 113 109 114
FLAP COMPLICATIONS IN Division of Intraoperative Postoperative Early Late Management of Complete free flap Descentered flap Dislocated Dry eye syndrome Epithelial ingrowth Foreign bodies Half cut Incomplete flap Infection Keratitis Microstriae Perforated flap Sands of Sahara Thin flap
267-276 267 267 267 267 267 267 267 268 272 273 273 272 271 271 273 272 273 270 272 268
FLAP STRIAE IN Treatment of Hydrating the flap in the Massaging the flap in the
283-286 284 284 284
HYPEROPIC Astigmatism and Correction Patient selection in Preoperative considerations in Scanning mechanism for Secondary Surgical technique of
161-167 165 162 163 163 162 165 164
INFECTION AND INFLAMMATION 293-306 AFTER Diffuse lamellar keratitis (sands of Sahara) 293 Causative agents of 293 Clinical findings of 294 Diagnosis of 295 Prevention of 296 Stages of 296 Treatment of 296 General considerations 293 Keratitis in 297 Causative organisms 299 Clinical findings of 297 Diagnosis of 300 Laboratory diagnosis 299 Treatment of 301 INTRACORNEAL SEGMENT RINGS (INTACS) Clinical outcomes of Clinical studies in Complications in Corneal topography in Reversibility of Surgical procedures in
513-521 514 513 516 517 518 514
IRREGULAR ASTIGMATISM IN 169-183 Classification of 170 Diagnosis of 170 Etiology of 169 Primary 169 Secondary 169 Evaluation of 171 Topography patterns of 170 Treatments of 173 Other procedures in the 181 Automated anterior lamellar keratoplasty 181 Contact lens management 182 Intracorneal ring segments (INTACS) 182 Surgical techniques in the 173
xvi
Contents
Section 1 Section 2
Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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SUBJECT INDEX Topographic Linked Excimer Laser Results of
179 179
KERATECTASIA IN Corneal stromal changes in Introduction Orbscan topography evaluation in Risk cases of
287-292 287 287 288 291
LASIK AND PHAKIC LENS IN Advantages of High myopia correction with Results of Surgical technique of
499-511 499 499 508 499
PRK RK Thermokeratoplasty (LTK) Corneal stromal bed thickness in Munnerlyn formula for IOL implantation after LASIK as Optical zone in the Presbyopia in the RK as
LASIK COMPLICATIONS PREVENTION AND MANAGEMENT OF 307-316 Intraoperative 307 Ablation 309 Central islands 309 Descentration 310 Flap 307 Anterior segment perforation 308 Bleeding 308 Buttonholes 307 Epithelial defects 308 Free cap 307 Incomplete flap 308 Thin flap 307 Postoperative 311 Diffuse lamellar keratitis (Sands of Sahara) 312 Ectasia 315 Epithelial ingrowth 313 Flap displacement 311 Flap striae 314 Haze 314 Infectious keratitis 312 Interface debris 311 Overcorrection 313 Punctate epithelial keratopathy 312 Undercorrection 313 Visual aberrations 315 LASIK - PALM Developments of General considerations of Introduction of Procedure of
395-400 399 395 395 398
LIMITATIONS OF Alternatives Lensectomy Phakic IOL
127-138 135 135 136
xvii
MICROKERATOMES IN Applanation lenses Automatic Corneal Shaper Power pack Presurgical set-up Sterilization of the Surgical technique with the Troubleshooting with the Corneal shaper head/blade Corneal shaper motor Suction ring Automatic disposable Barraquer Cables of the Carriazo-Barraquer Chiron Hansatome Corneal flaps and Detachments of the Displacements of the Folds of the Irregular cuts of the Perforation of the Disposable Automatic Flapmaker Draeger Free cap Generalities of Head of Hinge ablation Innovatome Moria Motor of Nidek Others Pendular Phoenix Universal Schwind SCMD Suction loss Suction ring Summit Krumeich-Barraquer Tonometers MIXED ASTIGMATISM IN
135 134 136 130 130 134 132 134 134 077-108 080 088,101 101 101 107 104 105 105 106 106 Contents 097 Section 1 087 080 Section 2 088 091 Section 3 085 085 Section 4 085 Section 5 085 083 Section 6 083 096 Section 7 097 096 Subjects Index 087 087 078 078 086 097 090 Help ? 079 094 098 096 093 092 093 083 080 094 080 185-191
SUBJECT INDEX Classification Treatment of Bitoric ablation in the Negative cylinder ablation in the Positive cylinder ablation in the Results of
185 187 188 187 188 190
PEARLS IN Adequate exposure Adequate suction Appropiate ablation Complete flap Flap adhesion Flap alignment Hydration Patient counseling
151-158 151 152 154 153 157 156 153 151
PEDIATRIC Patient selection in Surgical technique of Ablation parameters in the
233-240 234 234 234
PHAKIC IOL´s IN HIGH MYOPIA Advantages of Contributions of Limitations of Types of Anterior Chamber Artisan IOL Advantages of Disadvantages of Post-Operative complications of Surgical technique of Nu-Vita IOL Surgical technique of Posterior Chamber Barraquer Pre-Crystalline IOL in Advantages of Complications with Description of Disadvantages of Surgical technique of Foldable Plate Phakic IOL (ICL) in Complications of Disadvantages of Indications of LASIK and Surgical technique in
469-498 470 469 470 471 472 472 473 474 480 475 481 481 485 485 486 491 486 488 488 492 497 493 492 493 495
PHAKONIT Clear lens extraction in Introduction to Laser and
463-468 467 463 468
Principles of Refractive errors correction with Technique of PREDICTIVE FORMULAS Ablation nomograms in CHIRON technolas 116 Correction limits in the Healing of the cornea in Individualized Kritzinger nomogram in Main components VISX Star VISX S2
463 463 464 65-73 66 69 67 65 65 70 65 67 68
PRESBYOPIA Accomodation theories in Age-related changes of accomodation Contact lenses in Definition Glasses in Introduction Signs and Symptoms of Surgical methods in Intracorneal techniques Intraocular techniques Laser techniques Scleral techniques Treatments of
435-447 436 436 438 435 438 435 437 438 441 441 444 439 437
PRESBYOPIA - SURGICAL CORRECTION Anterior ciliary sclerotomy in Hyperopia combined with Ladarvision laser in Modifying the crystalline lens in Monovision in Scleral expansion in Scleral surgical methods in Schachar procedure in
427-433
PREVIOUS CORNEAL SURGERY AND Anterior lamellar keratoplasty (ALK) in Astigmatic Keratotomy in Corneal trauma in Lamellar thermalkeratoplasty (LTK) in Penetrating keratoplasty (PKP) in Complications of Eligible patients for Surgical technique of Time of surgery for Photorefractive keratectomy (PRK) in
215-232 227 217 228 223 207,223 210 208 209 209 201,221
xviii
433 427 427 433 427 429 428 433
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Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index
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SUBJECT INDEX Radial keratotomy (RK) in Hyperopia after Myopia after
201,215 216 215
PULSION FS LASER USE IN Ablation with the Patient selection for Preoperative preparation for Surgical technique with the
119-126 123 119 119 121
REFINING CUSTOM ABLATION WAVEFRONT MAPPING AND Wavefront analysis in Benefits of Corneal topography and Developments of Available methods Linking laser treatment with Mechanism of Personalized LASIK nomograms in
325-332
REFRACTIVE SURGERY LASERS Principles of Technology of Eye tracking systems in the Scanning ablation in the RELASIK Patient selection for Procedure for ROLE OF ABERRATIONS IN WAVEFRONT ANALYSIS Aberrations of the optical system in General considerations in Meaning of wavefront sensing analysis in Principles of
325 329 331 325 328 329 328 331 1-8 1 2 6 2 195-200 195 195
341-345 341 341 341 344
SUBLAMELLAR EPITHELIAL INGROWTH AFTER LASIK Non-invasive treatment of Technique of Present management techniques of Sequence of events in
243-246 243 244 243 243
SURGICAL TECHNIQUE OF Patient selection for Postoperative care Preoperative preparation Instruments Keratome Laser Patient
139-150 139 150 140 140 141 140 140
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Surgeon Procedure of Intraoperative bleeding during the Laser ablation during the Surgical preparation for the
142 143 148 145 142
VITREORETINAL COMPLICATIONS IN Dislocated IOL as Endophthalmitis Macular hemorrhage in Nerve fiber layer damage in Preoperative examination Prophylaxis for Retinal breaks Retinal detachment in PRK and
317-322 321 321 320 321 317 317 318 318 319
WAVEFRONT ANALYSIS IN Clinical examples of Definitions in General information of Hartmann method in Interpretation of
347-372 357 348 347 355 348
WAVEFRONT ANALYSIS AND CUSTOM ABLATION 339-340 Custom IOL in 340 Principles of 339 Promising achievements in 339
Contents
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Section 3
Section 4
Section 5 WAVEFRONT MEASUREMENTS OF THE EYE Hartmann-Shack senser and the Effectiveness of the Principles of aberrations with the Introduction
Section 6 413-419 413 Section 7 413 413 Subjects Index 413
ZYOPTIX Advantages of Disadvantages of Preoperative procedure of Preparing the laser in Zywave aberrometer in Optical aberrations Procedure of
379-394 391 391 379 389 380 380 384
ZYOPTIX - PERSONALIZED CORRECTION 373-378 Orbscan use in 374 Patient case in 377 Performing 373 Zywave aberrometer in 374
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Contents
Section 1 Section 2 Section 3
Section 4
Section 5
Section 6 Section 7 Subjects Index Help ?
