Age-Related Macular Degeneration, 2nd Edition

Age-Related Macular Degeneration

Age-Related Macular Degeneration Second Edition

Edited by

Jennifer I. Lim, M.D. University of Illinois School of Medicine, Department of Ophthalmology Eye and Ear Infirmary, UIC Eye Center Chicago, Illinois, USA

Informa Healthcare USA, Inc. 52 Vanderbilt Avenue New York, NY 10017 q 2008 by Informa Healthcare USA, Inc. Informa Healthcare is an Informa business No claim to original U.S. Government works Printed in the United States of America on acid-free paper 10 9 8 7 6 5 4 3 2 1 International Standard Book Number-10: 0-8493-7214-3 (Hardcover) International Standard Book Number-13: 978-0-8493-7214-8 (Hardcover) This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. A wide variety of references are listed. Reasonable efforts have been made to publish reliable data and information, but the author and the publisher cannot assume responsibility for the validity of all materials or for the consequence of their use. No part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright.com (http://www. copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC) 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Age-related macular degeneration / edited by Jennifer I. Lim. – 2nd ed. p. ; cm. Includes bibliographical references and index. ISBN-13: 978-0-8493-7214-8 (hardcover : alk. paper) ISBN-10: 0-8493-7214-3 (hardcover : alk. paper) 1. Retinal degeneration–Age factors. I. Lim, Jennifer I., 1962[DNLM: 1. Macular Degeneration. WW 270 A26491 2007] RE661.D3A322 2007 617.7’35–dc22

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2007023317

I wish to dedicate this book to my students, my family, and especially my daughter, Bernadette.

Foreword to the Second Edition

Five years ago, Jennifer Lim, MD, and her expert colleagues published the first edition of Age-Related Macular Degeneration, a state-of-the-art summary of knowledge about this frequently blinding disease. In the Foreword to that edition, I noted that Dr. Lim had “fashioned this valuable compendium of the way things are—for now!” It is relevant to ask, therefore, if the state of the art and level of knowledge have progressed in the interval since then. Why indeed they have, and, in the vernacular of the day, they have evolved “big time!” The most important development, of course, has been the clinical proof that agents aimed at inhibiting vascular endothelial growth factor not only preserve visual acuity in the neovascular (wet) form of age-related macular degeneration, but also improve visual functioning in a substantial percentage of patients. This class of compounds is, therefore, truly revolutionary and of major benefit to patients with wet age-related macular degeneration. There have been numerous additional developments in both the understanding and treatment of agerelated macular degeneration since the first edition, and they are very well described in this new book. Some of them are briefly mentioned subsequently in this Foreword, but none compares with the monumental impact of the anti–vascular endothelial growth factor approach to therapy of wet macular degeneration. The discoverers of key knowledge related to vascular endothelial growth factor and its antagonism—Drs. Harold Dvorak, Judah Folkman, Napoleon Ferrara, and others—deserve enormous credit and gratitude for their ingenuity and scientific contributions. These achievements have directly lead, over a decades-long evolutionary process of basic and applied research, to the initial, successful pharmacologic treatment techniques of today. In the history of therapy for other blinding retinal diseases, have there been other clinical advances that compare favorably with the tremendous impact of the anti–vascular endothelial growth factor approach to age-related macular degeneration? In my personal experience, photocoagulation, and particularly laser photocoagulation, had analogous therapeutic effects when fully developed in the 1960s and 1970s. With the advent of photocoagulation, another irreversibly and commonly blinding disorder, diabetic retinopathy, suddenly and dramatically came

under control, as proved by appropriate clinical trials. The invention and development of automated pars plana vitrectomy in the 1970s and 1980s represented another quantum leap forward. This innovative surgery has restored vision to innumerable patients who were blind from a variety of retinal diseases, including proliferative diabetic retinopathy. Such exciting therapeutic advances come infrequently in modern medicine—often they are decades apart. At their outset, they require brilliant insights followed by painstaking, time-consuming, and expensive clinical trials for adequate proof of both efficacy and safety. When successful, such activity is clearly worthwhile, as measured by enormous improvement in both personal and public health. Have the beneficial results of age-related macular degeneration therapy yet reached their asymptote? Far from it! Although the frustrating state of therapeutic affairs at the time of the first edition has been substantially ameliorated in the interim, there is much about age-related macular degeneration that is yet to be understood and yet to be accomplished. Even the relatively “established” worlds of photocoagulation and vitrectomy are characterized by useful, ongoing refinements. Analogous events will undoubtedly characterize the evolution of the anti–vascular endothelial growth factor approach. We will certainly see a “dramatic flourishing of new hypotheses, experiments, and clinical procedures,” as predicted in the Foreword to the first edition. New delivery systems and schedules, for example, will undoubtedly enhance the inconvenient and invasive intravitreal treatment regimens that are now utilized. Moreover, new combinations of therapeutic agents (both pharmacologic and physical) will be proposed and evaluated. Many will inevitably flounder (as have some other forms of initially promising treatments for age-related macular degeneration, such as irradiation, submacular surgery, and photocoagulation of drusen), but some will indeed succeed. We have just embarked on a new era in the treatment of wet age-related macular degeneration. But what of dry age-related macular degeneration (and its major variants, including geographic atrophy), for which prophylaxis, such as that with antioxidants, is in its formative phases and for which restoration of lost vision does not yet exist?

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FOREWORD TO THE SECOND EDITION

And what of wet age-related macular degeneration and an understanding of its etiology, pathogenesis, and prophylaxis? We remain in the infancy of these subjects. Fortunately, numerous chapters in this second edition provide up-to-the-minute summaries of relevant knowledge. For example, allele associations, such as those related to complement factor H and others, and single gene mutations, such as those involving ABCR, ELOVl4, VMD2, TIMP3, peripherin/RDS, and Fibulin3/EFEMP1, represent discoveries that are largely new since the appearance of the first edition. They are well described herein, and clinicians must know about them. Clinicians must, of course, also know about advances in fundus imaging. Much of the valuable, pragmatic information on optical coherence tomography, for example, has appeared since the first edition and is well described in this book. Additional new information on avant-garde subjects, such as artificial vision, retinal prostheses, retinal pigment epithelial transplantation, and new surgical techniques, are also reported by Dr. Lim and her collaborators. Thus, this second edition plays a pivotal role in educating those individuals concerned with the diagnosis and treatment of age-related macular degeneration.

Finally, what of visual rehabilitation and its newer techniques? Clinicians must be well informed about developments that impact patients with low vision. The relevant chapter in this edition has practical, current information. Despite the extraordinary advances of the last five years, and despite the superlative therapeutic armamentarium that we now possess, too many patients still lose their vision to both dry and wet forms of age-related macular degeneration. Their well-being must remain at the forefront of our consciousness. If progress over the last five years can be used as a predictor for the future, we can assume that ongoing clinical care will continually evolve—until the passage of time (and hopefully another edition) permits identification of those ideas that can safely be discarded and those that herald better vision for our patients. Morton F. Goldberg The Joseph Green Professor of Ophthalmology Former Director, the Wilmer Eye Institute Johns Hopkins University School of Medicine Baltimore, Maryland, U.S.A.

Foreword from the First Edition

Age-related macular degeneration (AMD) has become a scourge of modern, developed societies. In such groups, where improved living conditions and medical care extend human longevity, degeneration of bodily tissues slowly but relentlessly occurs as the life span increases. Sooner or later, the ‘‘warranty’’ on such tissues expires, and so do critically important cells that, in the case of the macula, would have allowed normal visual function if they had survived. Those cells occupy a tiny area having a diameter of only about 2 to 3 mm in human eyes. When the cells lose their function or die and disappear, sharp central visual acuity fails, and lifestyle is compromised—often severely. The ability to read, drive, recognize faces, or watch television can be impaired or lost. This group of diseases—AMD—has become the leading cause of visual impairment in those countries where increasingly large numbers of individuals live to a so-called ‘‘ripe old age.’’ Most of these senior citizens had anticipated, with pleasure, the opportunity to enjoy their mature and less frenetic years, but too many of these individuals, ravaged physically and emotionally with AMD, frequently and understandably complain that the golden years are not quite so golden. This is the human and emotional side of AMD, a group of disorders now under intense scientific and clinical scrutiny, as ably summarized herein by Dr. Jennifer Lim and her expert group of coauthors. The chapters in this book are devoted to pathophysiology, clinical features, diagnostic tests, current and experimental therapies, rehabilitation, and research. They represent what we know today. They also tell us explicitly or by inference what we need to know tomorrow. In effect, they are cross-sectional analyses of the present state of knowledge, analogous to photos in an album, for example. Here, in this book, we have comprehensive, definitive, analytic reviews of the current state of macular affairs. Such albums and books are often informative and beautiful, but they best realize their inherent potential, as does this book, by whetting our appetite for more information, both for today as well as for tomorrow. For example, what are the precise etiology and pathophysiology of AMD? Will they change? What are the best diagnostic tests for different forms of AMD? (Parenthetically, it is historically noteworthy to realize that fluorescein angiography remains the definitive test for diagnosing

the presence of choroidal neovascularization and related phenomena in AMD, despite having been developed almost half a century ago.) What are the best therapies of today and how might we improve them in the future? At present, we think primarily of thermal laser photocoagulation and photodynamic therapy. How can they be enhanced? What roles, if any, will other techniques play? Will they include low-power transpupillary thermal or x-irradiation, antiangiogenic drugs, genetic manipulation, or surgery? Will combinations of these or even newer modalities be demonstrated to be both safe and effective? Will wide-scale population-based preventive measures, including antioxidants, for example, be more important than therapeutic intervention ex post facto? Clairvoyance is an imperfect attribute, but the largely palliative and incompletely successful treatments of today are quite frustrating. There is a compelling mandate for intense and sustained efforts to improve both treatment and prophylaxis. The crystal ball for AMD suggests that the immediate future will be characterized by refinements in today’s favored interventions, especially photodynamic therapy, but no one can really hope or believe that the therapeutic status quo will be preserved. Substantial change is a certainty. Physicians and patients appropriately demand more. The intermediate and long-range future will probably include a large number of definitive clinical trials devoted to fascinating new pharmacological agents, many of which are now in the evaluative pipeline, but many of which have not yet even been conceived. Classes of drugs will include antiangiogenic or angiostatic steroids with glucocorticoid and nonglucocorticoid qualities, as well as diverse agents to bind and inactivate cytokines and chemokines at different points in the angiogenic and vasculogenic cascades. Many will involve blockage of the actions of vascular endothelial growth factor (VEGF). Ingenious surgical approaches will also come, and some will then go, as more and more new approaches of this nature undergo clinical evaluation and gain either widespread acceptance or rejection. Today’s requirements for ‘‘evidence-based’’ medical decisions invoke Darwinian selection processes for numerous known, as well as currently unknown, diagnostic and therapeutic approaches to

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FOREWORD FROM THE FIRST EDITION

AMD. Outstandingly good techniques, such as fluorescein angiography, will persist—at least for the foreseeable future. Less desirable ones, such as subfoveal thermal photocoagulation, for example, will be supplanted by something better, such as photodynamic therapy—at least for the moment. The accretion of scientific and clinical knowledge is usually an extremely slow process, but that is not necessarily bad because new ideas and techniques are afforded ample opportunity for dispassionate evalution. Sudden breakthroughs, on the other hand, intellectual or technical epiphanies, are infrequent. When they do occur—such as angiography, photocoagulation, or intravitreal surgery—they abruptly create quantum leaps characterized by dramatic flourishing of new hypotheses, experiments, and clinical procedures. The world of AMD would benefit from such giant steps (such as a new class of drugs or a new physical modality or type of equipment), but, because they are unpredictable in their origin and timing, we are presently faced with the less spectacular, but important, responsibilities of initiating and sustaining more prosaic, but potentially useful research efforts. Hopefully, in the future more emphasis will be placed on preventive approaches. Modification of relevant risk factors for AMD may prove to be much more effective, from the perspective of the public health, than therapeutic attempts aimed at a disease that has already achieved a threshold for progressive degeneration and visual impairment. Thus far, epidemiological studies have largely been inconclusive and occasionally contradictory, and we now know of only one clear-cut modifiable risk factor, namely, cigarette smoking (and possibly systemic hypertension). The influences of race and heredity remain tantalizing, and it will be important to understand

why some races are protected from severe visual loss in AMD and why others are not. Moreover, the major influence of heredity is inescapable, but we now know only that this influence is complex, and it may be even more complex than anticipated because of a multiplicity of unknown contributory environmental and other genetic factors. We do know the genes responsible for a previously enigmatic group of juvenile forms of inherited macular degeneration, such as the eponymously interesting diseases named for Best, Stargardt, Doyne, and Sorsby, but there appears to be no universally accepted or substantive relationship between any of these single-gene, rare Mendelian traits and the far more common AMD, which has no clear-cut Mendelian transmission pattern, but currently affects millions of aging individuals. The march of time related to scientific progress is ceaseless, and this is certainly true of research related to AMD. Darwinian selection of the best new ideas will inevitably emerge, allowing an evolutionary approach to enhanced understanding and improved treatment or prophylaxis. Should we be fortunate enough to witness a bona fide revolution or breakthrough in ideas related to AMD, such an advance is likely to emanate from those scientists and clinicians meeting Louis Pasteur’s observation that ‘‘chance favors the prepared mind.’’ It is toward that goal— the creation of the prepared mind—that Dr. Lim has fashioned this valuable compendium of the way things are—for now!! Morton F. Goldberg Director and William Holland Wilmer Professor of Ophthalmology The Wilmer Eye Institute Baltimore, Maryland, U.S.A.

Preface

Research has yielded major discoveries about the etiology, pathophysiology, and treatment of agerelated macular degeneration over the last decade. Indeed, the desire to summarize and synthesize this new information for clinicians and scientists involved in age-related macular degeneration patient care and research resulted in the first edition of this book. Since then five years have flown by, and the pace of basic science and translational research in age-related macular degeneration has accelerated. The resultant novel discoveries have improved and will continue to improve the daily lives of our patients. These novel therapies offer not only sight saving, less destructive forms of treatment for exudative age-related macular degeneration, but also treatments that can improve visual acuity. In addition, preventive treatments are being developed for non-exudative age-related macular degeneration. The goal of this second edition is to inform the reader about the latest information available on the pathophysiology, diagnosis, management, and treatment of age-related macular degeneration. A significant amount of new information is presented throughout this second edition. I asked retinal experts to first summarize the established information and then to present the most novel developments in their field. The first section of this book includes the pathophysiology, epidemiology, and genetics of age-related macular degeneration. Updated light and electron microscopic findings of age-related macular degeneration are presented to facilitate the understanding of its ultrastructural pathophysiology. Such an understanding is useful in directing future areas of research towards a cure. At the time of the first edition, the genetics of age-related macular degeneration was largely unknown, and the role of the immune system was mostly a theoretical one. Since then, the key role of the immune system on the pathophysiology of age-related macular degeneration has been shown by such findings as complement factor H and HTRA1 gene associations with exudative agerelated macular degeneration. The second section focuses on the clinical diagnosis and treatment of age-related macular degeneration. The clinical findings seen in the nonexudative and exudative forms are discussed. Additional color photos have been added and are

shown within each chapter (instead of the color insert used in the first edition). The natural history data of untreated age-related macular degeneration is retained and contrasted with the outcomes from treatment trials. The third section on imaging includes newly added chapters on fundus autofluorescence and quantitative imaging techniques. The imaging modalities are discussed with attention to their usefulness in planning treatment and assessing treatment responses of age-related macular degeneration patients. The next sections present in-depth information on current and experimental forms of treatment for non-exudative and exudative forms of age-related macular degeneration. The presentation of the treatment options includes a discussion of the mechanism of action, the clinical treatment technique, the targeted patient population, the expected outcomes, and a balanced discussion of both positive and negative aspects of each treatment. The following section of this book focuses on visual rehabilitation and active areas of basic science research that may lead to other forms of treatment in the near future. It is a reality that despite the recent progress in treatments, some patients still lose visual acuity. For these patients, visual rehabilitation remains extremely important. An updated discussion of the available low vision devices and the psychosocial aspects of visual loss are included to help counsel patients with agerelated macular degeneration and visual loss. The progress in the areas of retinal prostheses and retinal pigment cell transplantation are presented. These areas of research may one day lead to future treatments that help to overcome visual loss and damage. Progress in these areas renews our hope for the future generations afflicted with age-related macular degeneration. Promising new therapies will need to undergo clinical trials to evaluate clinical efficacy. The last section of this book therefore presents the essentials of clinical trial design. As in the first edition, no single manageable volume can compile and analyze all of the existing knowledge concerning age-related macular degeneration. I have attempted to distill the most clinically salient and exciting research information from the vast body of knowledge for inclusion in this second edition. If this book can once again serve as a first-hand

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PREFACE

resource for researchers and clinicians in the area of age-related macular degeneration, then my goal has been achieved. It is my hope that the information presented herein continues to incite inquiry and ignite research that may unearth those enigmatic answers to questions about the etiology of and cure for age-related macular degeneration. I wish to thank my outstanding contributors without whom this book would not be possible. Their

eagerness to collaborate, their scholarship, and their expertise made my job as editor of this book extremely enjoyable, educational, and satisfying. I wish to thank my administrative assistants, Francine and Annel, for their invaluable secretarial assistance. I wish to thank my editors at Informa Healthcare for their assistance in compiling this book. Jennifer I. Lim

Contents

Foreword to the Second Edition Foreword from the First Edition Preface ix Contributors xiii PART I.

Morton F. Goldberg Morton F. Goldberg

v vii

PATHOPHYSIOLOGY AND EPIDEMIOLOGY OF AGE-RELATED MACULAR DEGENERATION

1. Histopathology of Age-Related Macular Degeneration 2. 3. 4. 5.

1 Shin J. Kang and Hans E. Grossniklaus Immunology of Age-Related Macular Degeneration 11 Karl G. Csaky and Scott W. Cousins Genetics of Age-Related Macular Degeneration 35 Jennifer R. Chao, Amani A. Fawzi, and Jennifer I. Lim Risk Factors for Age-Related Macular Degeneration and Choroidal Neovascularization 47 Kah-Guan Au Eong, Bakthavatsalu Maheshwar, Stephen Beatty, and Julia A. Haller Choroidal Neovascularization 87 Frances E. Kane and Peter A. Campochiaro

PART II. CLINICAL FEATURES OF AGE-RELATED MACULAR DEGENERATION 6. Non-exudative Age-related Macular Degeneration 97 Neelakshi Bhagat and Christina J. Flaxel 111 Sharon D. Solomon and Janet S. Sunness 8. Exudative (Neovascular) Age-Related Macular Degeneration Jennifer I. Lim and Jerry W. Tsong

7. Geographic Atrophy

PART III.

125

IMAGING TECHNIQUES FOR THE CLINICAL EVALUATION OF AGE-RELATED MACULAR DEGENERATION

9. Indocyanine Green Angiography in Age-Related Macular Degeneration

159 Scott C. N. Oliver, Antonio P. Ciardella, Daniela C. A. C. Ferrara, Jason S. Slakter, and Lawrence A. Yannuzzi 10. Optical Coherence Tomography in the Evaluation and Management of Age-Related Macular Degeneration 177 David Eichenbaum and Elias Reichel 11. Quantitative Retinal Imaging 185 Daniel D. Esmaili, Roya H. Ghafouri, Usha Chakravarthy, and Jennifer I. Lim 12. Fundus Autofluorescence in Age-Related Macular Degeneration 191 Rishi P. Singh, Jeffrey Y. Chung, and Peter K. Kaiser

PART IV.

MEDICAL TREATMENT FOR AGE-RELATED MACULAR DEGENERATION

13. Laser Photocoagulation for Choroidal Neovascularization

203 Catherine Cukras and Stuart L. Fine 14. Photocoagulation of AMD-Associated CNV Feeder Vessels: An Optimized Approach 207 Robert W. Flower 15. Photodynamic Therapy 223 ATul Jain, Darius M. Moshfeghi, and Mark S. Blumenkranz 16. Radiation Treatment in Age-Related Macular Degeneration 233 Christina J. Flaxel and Paul T. Finger

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CONTENTS

17. Anti-VEGF Drugs and Clinical Trials

247 Todd R. Klesert, Jennifer I. Lim, and Phillip J. Rosenfeld 18. Laser Prophylaxis for Age-Related Macular Degeneration Jason Hsu and Allen C. Ho

PART V.

257

SURGICAL TREATMENT FOR AGE-RELATED MACULAR DEGENERATION

19. Macular Translocation

273 Kah-Guan Au Eong, Dante J. Pieramici, Gildo Y. Fujii, Bakthavatsalu Maheshwar, and Eugene de Juan, Jr. 20. Age-Related Macular Degeneration: Use of Adjuncts in Surgery and Novel Surgical Approaches 295 Richard Scartozzi and Lawrence P. Chong

PART VI. VISUAL REHABILITATION 21. Clinical Considerations for Visual Rehabilitation

303 Susan A. Primo 22. Retinal Prostheses: A Possible Treatment for End-Stage Age-Related Macular Degeneration 319 Thomas M. O’Hearn, Michael Javaheri, Kah-Guan Au Eong, James D. Weiland, and Mark S. Humayun 23. Retinal Pigment Epithelial Cell Transplantation and Macular Reconstruction for Age-Related Macular Degeneration 329 Lucian V. Del Priore, Henry J. Kaplan, and Tongalp H. Tezel

PART VII. CLINICAL TRIAL DESIGN 24. Clinical Research Trials 349

A. Frances Walonker and Kenneth R. Diddie

Index

355

Contributors

Kah-Guan Au Eong Department of Ophthalmology and Visual Sciences, Alexandra Hospital, Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, The Eye Institute, National Healthcare Group, Jurong Medical Center, Singapore Eye Research Institute, and Department of Ophthalmology, Tan Tock Seng Hospital, Singapore Stephen Beatty Department of Ophthalmology, Waterford Regional Hospital and Department of Chemical and Life Sciences, Waterford Institute of Technology, Waterford, Ireland Neelakshi Bhagat The Institute of Ophthalmology and Visual Science, New Jersey Medical School, Newark, New Jersey, U.S.A. Mark S. Blumenkranz Vitreoretinal Surgery, Department of Ophthalmology, Stanford University Medical Center, Stanford, California, U.S.A. Peter A. Campochiaro Departments of Ophthalmology and Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, U.S.A. Usha Chakravarthy The Queen’s University of Belfast and Royal Hospitals, Belfast, Northern Ireland Jennifer R. Chao Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Lawrence P. Chong Doheny Retina Institute of the Doheny Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Jeffrey Y. Chung U.S.A.

Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, Ohio,

Antonio P. Ciardella Department of Ophthalmology, Denver Health Hospital Authority, Denver, Colorado, U.S.A. Scott W. Cousins Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina, U.S.A. Karl G. Csaky Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina, U.S.A. Catherine Cukras Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia, Pennsylvania, U.S.A. Eugene de Juan, Jr. Beckman Vision Center, Department of Ophthalmology, University of California, San Francisco, California, U.S.A. Lucian V. Del Priore Department of Ophthalmology, Columbia University, New York, New York, U.S.A. Kenneth R. Diddie California, U.S.A.

Retinal Consultants of Southern California, Westlake Village,

David Eichenbaum New England Eye Center, Tufts University School of Medicine, Boston, Massachusetts, U.S.A.

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CONTRIBUTORS

Daniel D. Esmaili Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Amani A. Fawzi Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Daniela C. A. C. Ferrara The LuEsther T. Mertz Retinal Research Department, Manhattan Eye, Ear, and Throat Hospital, New York, New York, U.S.A. Stuart L. Fine Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia, Pennsylvania, U.S.A. Paul T. Finger New York University School of Medicine, The New York Eye Cancer Center, New York, New York, U.S.A. Christina J. Flaxel Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, U.S.A. Robert W. Flower Department of Ophthalmology, University of Maryland School of Medicine, Baltimore, Maryland and Department of Ophthalmology, New York University School of Medicine and the Macula Foundation, Manhattan Eye, Ear, and Throat Hospital, New York, New York, U.S.A. Gildo Y. Fujii Parana, Brazil

Vitreous and Retina Department, State University of Londrina, Londrina,

Roya H. Ghafouri Department of Ophthalmology, Boston University Medical Center, Boston University School of Medicine, Boston, Massachusetts, U.S.A. Hans E. Grossniklaus Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, U.S.A. Julia A. Haller The Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Johns Hopkins Hospital, Baltimore, Maryland, U.S.A. Allen C. Ho Retina Service, Wills Eye Hospital, Philadelphia, Pennsylvania, U.S.A. Jason Hsu

Retina Service, Wills Eye Hospital, Philadelphia, Pennsylvania, U.S.A.

Mark S. Humayun Doheny Retina Institute, Doheny Eye Institute, Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. ATul Jain Department of Ophthalmology, Stanford University Medical Center, Stanford, California, U.S.A. Michael Javaheri Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Peter K. Kaiser Ohio, U.S.A.

Digital Optical Coherence Tomography Reading Center, Cleveland,

Frances E. Kane

Alimera Sciences, Inc., Alpharetta, Georgia, U.S.A.

Shin J. Kang L.F. Montgomery Ophthalmic Pathology Laboratory, Emory Eye Center, Emory University School of Medicine, Atlanta, Georgia, U.S.A. Henry J. Kaplan Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, U.S.A. Todd R. Klesert Doheny Eye Institute, University of Southern California, Los Angeles, California, U.S.A. Jennifer I. Lim University of Illinois School of Medicine, Department of Ophthalmology, Eye and Ear Infirmary, UIC Eye Center, Chicago, Illinois, U.S.A.

CONTRIBUTORS

Bakthavatsalu Maheshwar Department of Ophthalmology and Visual Sciences, Alexandra Hospital and Jurong Medical Center, Singapore Darius M. Moshfeghi Adult and Pediatric Vitreoretinal Surgery, Stanford University Medical Center, Stanford, California, U.S.A. Thomas M. O’Hearn Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Scott C. N. Oliver Department of Ophthalmology, Rocky Mountain Lions Eye Institute, University of Colorado School of Medicine, Aurora, Colorado, U.S.A. Dante J. Pieramici California Retina Research Foundation and California Retina Consultants, Santa Barbara, California, U.S.A., and Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Susan A. Primo Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, U.S.A. Elias Reichel New England Eye Center, Tufts University School of Medicine, Boston, Massachusetts, U.S.A. Phillip J. Rosenfeld

Bascom Palmer Eye Institute, Miami, Florida, U.S.A.

Richard Scartozzi Doheny Retina Institute of the Doheny Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Rishi P. Singh Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, Ohio, U.S.A. Jason S. Slakter The LuEsther T. Mertz Retinal Research Department, Manhattan Eye, Ear, and Throat Hospital, New York, New York, U.S.A. Sharon D. Solomon Retina Division, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, U.S.A. Janet S. Sunness The Richard E. Hoover Services for Low Vision and Blindness, Greater Baltimore Medical Center, Baltimore, Maryland, U.S.A. Tongalp H. Tezel Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, U.S.A. Jerry W. Tsong Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. A. Frances Walonker Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. James D. Weiland Doheny Retina Institute, Doheny Eye Institute, Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A. Lawrence A. Yannuzzi The LuEsther T. Mertz Retinal Research Department, Manhattan Eye, Ear, and Throat Hospital, New York, New York, U.S.A.

xv

Part I: Pathophysiology and Epidemiology of Age-Related Macular Degeneration

1 Histopathology of Age-Related Macular Degeneration Shin J. Kang

L.F. Montgomery Ophthalmic Pathology Laboratory, Emory Eye Center, Emory University School of Medicine, Atlanta, Georgia, U.S.A.

Hans E. Grossniklaus

Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, U.S.A.

INTRODUCTION Pathologic changes in age-related macular degeneration (AMD) occur in the various structures in the posterior pole, such as the outer retina, the retinal pigment epithelium (RPE), Bruch’s membrane and the choriocapillaries (1,2). Early lesions of AMD are located either between the RPE and its basement membrane [e.g., basal laminar deposits (BlamD)] or between the basement membrane of the RPE and the remainder of Bruch’s membrane [e.g., basal linear deposits (BlinD)] (2–5). Focal and diffuse deposition between the RPE and Bruch’s membrane is called drusen. Alterations of RPE such as hypopigmentation, depigmentation or atrophy as well as attenuation of photoreceptor cells are also observed. This form of macular degeneration is known as dry AMD (non-exudative AMD), whereas choroidal neovascularization (CNV) is the main feature of wet AMD (exudative AMD), which ultimately results in a disciform scar in end stage AMD.

HISTOPATHOLOGY OF NON-EXUDATIVE (DRY) AMD Changes of Bruch’s Membrane Bruch’s membrane increases in thickness with age (6,7). The pathologic changes with AMD first appear in the inner collagenous zone, and generally extend into the central elastic zone and outer collagenous zone, and the intercapillary connective tissue during later stages of the disease (8). Drusen and BlinD contribute to a diffuse thickening of the inner aspect of Bruch’s membrane (1,6,9–14). With change of pH of the collagenous fibers and the deposition of calcium salts in the elastic tissue, Bruch’s membrane shows increased basophilia. Accumulation of lipid substance from the RPE also results in Sudanophilia (Fig. 1A) (12,14–16). Thickening and hyalinization of Bruch’s membrane in the macular

area has also been found in the outer collagenous zone (5,17), presumably is due to the accumulation of cellular waste products (12,18). Ultrastructural examination of Bruch’s membrane in elderly humans typically shows focal areas of wide-spaced banded collagen, membrane-bounded bodies, tube-like structures of degenerated collagen fibers, electron dense granular material surrounded by a double membrane, and electron lucent droplets (3,6,14). These findings may be accompanied by an increase in native collagen within the central elastic layer (type IV collagen), the inner and outer collagenous zone (type I and III collagen), and in the intercapillary connective tissue (6,19). Focal thinning and disruption of Bruch’s membrane is also found associated with an increased cellular activity (e.g., macrophage-derived hematopoietic cells, leukocytes) on both sides of the membrane (Fig. 1A). The close relationship between inflammatory cell component and breaks in Bruch’s membrane suggests that these cells might be involved in the focal destruction of Bruch’s membrane (Fig. 1B) (5,18). Spraul and coworker showed that the degree of calcification as well as the number of fragmentations in Bruch’s membrane correlated with the presence of non-exudative and exudative AMD (Fig. 1C) (10). Eyes with exudative AMD demonstrated a higher degree of calcification and fragmentation of Bruch’s membrane in the macular area compared to the extramacular regions than eyes with non-exudative AMD. A correlation was also found between the degree of calcification, ranging from focal patches to long continuous areas, and the number of breaks in Bruch’s membrane (10).

Changes of Retinal Pigment Epithelium RPE cells with AMD have cytoplasmic “lipofuscin” granules, as the result of incompletely digested

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(A)

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Figure 1 (A) Macrophage derived inflammatory cells (arrows) are present at the outer aspect of Bruch’s membrane (arrowheads). (B) Transmission electron microscopy shows macrophages and multinucleated giant cells (asterisks) digesting basal laminar deposits overlying Bruch’s membrane. (C) Focal disruption of Bruch’s membrane (arrows) with ingrowth of new vessels (asterisks) in the space between the inner aspect (arrowheads) and the remainder of Bruch’s membrane in an eye with choroidal neovascularization.

photoreceptor outer segments. Accumulation of lipofuscin granules increases in the cytoplasm of RPE. Eyes with early AMD show a decreased number and density of RPE cells in the macula, resulting in RPE mottling (20). These changes include pleomorphism, enlargement, depigmentation, hypertrophy, hyperplasia, and atrophy of the RPE cells (1,9). Another clinical finding called non-geographic RPE atrophy is related to moderate RPE hypopigmentation and atrophy in areas overlying diffuse BlamD and BlinD (Fig. 2) (9). Hypopigmentation, attenuation or atrophy of the RPE may also be accompanied by soft drusen, RPE detachment and geographic atrophy (2,9,21,22). Lipoidal degeneration of individual RPE cells which are characterized by foamy cytoplasm may be found in eyes with nodular drusen. Figure 2 Histopathology of retinal pigment epithelium (RPE) and Bruch’s membrane in an eye with non-exudative age-related macular degeneration. The RPE cell monolayer (arrows) is diminished and exhibits hypopigmentation associated with areas of scattered prominent pigment granules. A thick layer of basal laminar deposit (asterisks) is located between the plasma membrane and basal lamina of the RPE. The remaining Bruch’s membrane is also thickened (arrowheads).

Changes of Choriocapillaris The choriocapillaris in eyes with AMD is usually thinned and sclerosed with a thickening of the intercapillary septae (23). Capillaries between hyalinized pillars of Bruch’s membrane are occasionally more widely spaced than in age-matched control eyes (14). The choroidal arteries are usually shrunken and show replacement of the muscular media by fibrillar fibrous

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tissue with retention of wide vascular lumens. Occasionally, remains of occluded vessels with collapsed fibrous walls may be present (2). However, it is unclear if these observed changes in the choriocapillaris in AMD are secondary to changes in the overlying RPE, or are primary changes directly from the disease (24,25).

Changes of Neurosensory Retina Aging changes of the neurosensory retina occur in Mu¨ller cells and axons of ganglion cells including hypertrophy, lipid accumulation or decrease and replacement by connective tissue (26). While rods gradually disappear with aging even without evidence of overt RPE disease, cones only begin to degenerate by advanced stages of non-exudative AMD (27,28). Red–green cones seem to be more resistant than blue cones to aging and may also increase in size in AMD (4,28,29). The greatest photoreceptor cell loss is located in the parafovea (1.58–108) and may finally result in disappearance of all photoreceptors in the presence of geographic atrophy or disciform degeneration (4,28). Basal Deposits Accumulation of waste material between the RPE and Bruch’s membrane (Fig. 3A) is termed “basal deposit”, one of the earliest pathologic features of AMD. Green and Enger have defined two distinct types of basal deposit(s); BlamD and BlinD (1–3,9,12,30).

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Basal Laminar Deposit BlamD is composed of granular material with much wide-spaced collagen located between the plasma and basement membranes of the RPE. BlamD stains light blue with Masson’s trichrome (Fig. 3A) and magenta with periodic acid-Schiff staining (Fig. 3A, inset). Electron microscopic examination shows that BlamD is composed of long-spacing collagen with a periodicity of 120 nm, membrane-bounded vacuoles and minor deposits of granular electron-dense material (Fig. 3B) (1). Studies have shown that BlamD is composed of collagen (type IV), laminin, glycoproteins, glycosaminoglycans (chondroitin-, heparinsulfate), carbohydrates (N-acetylgalactosamine), cholesterol (unesterified, esterified), and apolipoproteins B and E (31–33). Basal Linear Deposit BlinD is located external to the RPE basement membrane (e.g., in the inner collagenous zone of Bruch’s membrane; Fig. 3A, inset). Electron microscopy shows that BlinD is primarily composed of an electron dense, lipid-rich material with coated and non-coated vesicles and granules that result in diffuse thickening of the inner aspect of Bruch’s membrane (Fig. 3B, inset top left). BlinD may represent an extension or progression of BlamD and is found in association with soft drusen and small detachments of the RPE. BlinD appears to be a more specific marker than BlamD for AMD, particularly for progression to late stage disease, whereas the amount of BlamD seems to be a more reliable indicator

RPE

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Figure 3 (A) A prominent layer of basal laminar deposit (BlamD; asterisks) and basal linear deposits (BlinD; arrowheads) is located between the retinal pigment epithelium and Bruch’s membrane. Artifactual spaces are present between the inner collagenous zone and the remaining layers of Bruch’s membrane (arrows). (B) BlamD are composed of wide-spaced collagen (insets, arrows), electron dense material and membrane-bounded vacuoles. They are located between the plasma membrane and the basal lamina of the RPE. Ultrastructure of the BlinD shows abundant coated vesicles and electron dense granules. Abbreviations: BlamD, basal laminar deposits; BlinD, basal linear deposits; bm, basal lamina; pm, plasma membrane; RPE, retinal pigment epithelium.

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of the degree of RPE atrophy and photoreceptor degeneration (2,5,13).

Drusen Drusen are important features of AMD, which can be ophthalmoscopically observed as small yellowish white lesions located deep to the retina in the posterior pole. Nodular (Hard) Drusen Nodular (hard) drusen are smooth surfaced, domeshaped structures between the RPE and Bruch’s membrane (Fig. 4). They consist of hyaline material and stain positively with periodic acid-Schiff (1). Nodular drusen often contain multiple globular calcifications, mucopolysaccarides, and lipids (34). The latter supports the possibility of lipoidal degeneration of individual RPE cells (21,35,36). Ultrastructurally, nodular drusen are composed of finely granular or amorphous material, which is the same electron density as the basement membrane of the RPE. Variable numbers of pale and bristle-coated vesicles, tubular structures, curly membranes and occasionally abnormal collagen may also be found within these drusen (21,31,37). The RPE overlying the drusen is often attenuated and hypopigmented, while the cells located at the lateral border demonstrate a hyperpigmented and hypertrophic appearance (38). Drusen are primarily located in the inner collagenous zone of Bruch’s membrane, but may extend to the outer collagenous zone and to the intercapillary pillars if discontinuities of the central elastic layer occur (14,39). Immunohistochemical studies have shown that drusen are composed of acute phase proteins (e.g., vitronectin, a1-antichymotrypsin, C-reactive protein,

Figure 4 Photomicrograph shows a nodular druse with loss of the overlying retinal pigment epithelium.

amyloid P component, and fibrinogen), complement components (e.g., C3C5 and C5b-9 complex), complement inhibitors (e.g., clusterin), apolipoproteins (B, E), tissue metalloproteinase inhibitor 3, crystalline, serum albumin, fibronectin, mucopolysaccarides (e.g., sialomucin), lipids (e.g., cerebroside), mannose, sialic acid, N-acetylglucosamine, b-galactose and immunoreactive factors like immunoglobulin G, immunoglobulin light chains, Factor X and other components, termed drusen-associated molecules (DRAMS) (34,40–43).

Soft Drusen Cleavage in BlamD and BlinD may occur with the formation of a localized detachment (soft drusen). Soft drusen may become confluent with diameters larger than 63 mm, and are then termed “large drusen.” Soft drusen formation may result in a diffuse thickening of the inner aspect of Bruch’s membrane with separation of the overlying RPE basement membrane from the remaining Bruch’s membrane (Fig. 5) (9,21). At least three types of soft drusen can be differentiated by light microscopic examination: (i) a localized detachment of the RPE with BlamD in eyes with diffuse BlamD, (ii) a localized detachment of RPE by BlinD in eyes with diffuse BlamD and BlinD, or (iii) a localized detachment due to the localized accumulation of BlinD in eyes with diffuse BlamD but in absence of diffuse BlinD (9). All subtypes may appear as large drusen with sloping edges. The hydrophobic space between these types of soft drusen and Bruch’s membrane is a potential space for CNV (10). Soft drusen seem to be often empty or to

Figure 5 Photomicrograph shows soft drusen formation (asterisks) consisting of lightly staining proteinaceous material between the basement membrane of the retinal pigment epithelium and inner aspect of Bruch’s membrane (arrows). The overlying retinal pigment epithelium is partially lost or hypertrophic.

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contain pale staining amorphous membranous or fibrillar material (44). The overlying RPE may be attenuated, diminished or atrophic. In late stages, geographic atrophy may occur (1). Electron microscopy shows that soft drusen are composed of double-layered coiled membranes with amorphous material and calcification (18). BlamD overlying the soft drusen has been found in many eyes with AMD (21).

Diffuse Drusen Diffuse drusen is a diffuse thickening of the inner aspect of Bruch’s membrane (21,23). This term also includes basal laminar (cuticular) drusen, which are characterized by an internal nodularity (1,30). Electron microscopy shows that diffuse drusen have revealed the presence of vesicles, electron-dense particles, and fibrils between the thickened basement membrane of the RPE and the inner collagenous layer of Bruch’s membrane (21,23).

HISTOPATHOLOGY OF AGE-RELATED MACULAR DEGENERATION

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degeneration of the outer layers of the neurosensory retina (photoreceptors, outer nuclear layer, external limiting membrane), marked atrophy and sclerosis of the choriocapillaris, without breaks in Bruch’s membrane (Fig. 6) (2,21,22,45). Areas of geographic atrophy also are commonly characterized by residual pigmented material and a closely related monolayer of macrophages, which develop between the basement membrane of the RPE and the inner collagenous layer of Bruch’s membrane (22). Occasionally accompanying the macrophages are other cell types like melanocytes, fibroblasts and detached RPE cells in the subretinal space (22). The edges adjacent to areas of geographic atrophy, also termed junctional zones, are usually hyperpigmented and characterized by the presence of hypertrophic RPE cells and multinucleated giant cells which contain RPE-derived pigment in association with secondary lysosomes (22,31).

HISTOPATHOLOGY OF EXUDATIVE (WET) AMD Geographic Atrophy Geographic atrophy, which is characterized by the areas of well demarcated atrophy of RPE, represents the classic clinical picture of end-stage non-exudative AMD. Although drusen are apparently central direct factors for initiation of RPE cell loss, they may disappear over time, especially when geographic atrophy occurs (2). Histological studies have shown that the loss of RPE is usually accompanied by a gradual

Figure 6 Photomicrograph shows a section of an eye with geographic atrophy of the retinal pigment epithelium (RPE). The photoreceptor cell layer is atrophic and the RPE is largely absent (arrowheads). A thin fibrotic scar (asterisks) associated with mononuclear inflammatory cells is covering the inner aspect of Bruch’s membrane. Bruch’s membrane is focally disrupted (arrows).

Choroidal Neovascularization The hallmark of exudative (wet type) AMD is the development of CNV. CNV represents new blood vessel formation typically from the choroid (20). Such changes in Bruch’s membrane as calcification and focal breaks correlate with the presence of exudative AMD (10). Decreased thickness and disruption of the elastic lamina of Bruch’s membrane in the macula may also be a prerequisite for invasion of CNV into the space underneath the RPE (46). Vascular channels supplied by the choroid begin as a capillary-like structure and evolve into arterioles and venules (1,20,23,47,48). Most of the vessels arise from the choroid, although a retinal vessel contribution has been observed in about 6% of CNV in AMD (1). These choroidal vessels traverse the defects in the Bruch’s membrane and grow into the plane between the RPE and Bruch’s membrane (sub-RPE CNV: type 1 growth pattern), between the retina and RPE (subretinal CNV: type 2 growth pattern), or in the combination of both patterns (combined growth pattern) (48,49). The latter appears to arise from the type 1 growth pattern. Subretinal Pigment Epithelium CNV (Type 1 Growth Pattern) In type 1 pattern, CNV originates with multiple ingrowth sites, ranging from 1 to 12, from the choriocapillaris (Fig. 7). After breaking through Bruch’s membrane, CNV tufts extend laterally and merge in a horizontal fashion under the RPE. This is facilitated by a natural cleavage plane in the space between BlamD

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Figure 7 Photomicrographs of an eye with exudative agerelated macular degeneration. A choroidal neovascular membrane (asterisk) with prominent vessels (arrowheads) grows between Bruch’s membrane (arrows) and the overlying retinal pigment epithelium.

and Bruch’s membrane that has accumulated lipids with aging (Fig. 8) (1,2,44,48–53). The CNV growth recapitulates the embryologic development of the choriocapillaris, presumably in an attempt to provide nutrients and oxygen to ischemic RPE and photoreceptors. The relationship between the CNV and BlamD is similar to that between the choriocapillaries and Bruch’s membrane. Patients with type 1 CNV have relatively intact retina and few visual symptoms. This growth pattern likely corresponds to the “occult” type of angiographic appearance of CNV (49). Secondary changes can be noted in the surrounding retina such as serous or hemorrhagic detachment of the RPE and overlying

Figure 8 Separation of the basal laminar deposits (BlamD, arrowheads) and the remainder of Bruch’s membrane (arrows). The space between the BlamD and Bruch’s membrane acts as a natural cleavage plane facilitating vessel ingrowth (asterisk).

Figure 9 Choroidal neovascular membrane with a type 2 growth pattern (arrowheads) between the retinal pigment epithelium (RPE) and the outer segments of the photoreceptor cell layer. A reflected layer of RPE (asterisk) and atrophy of photoreceptors is present.

retina, RPE tears, and lipid exudation (20,54). In histopathologic studies of surgically excised CNV, type 1 membranes are firmly attached to the overlying native RPE as well as the underlying Bruch’s membrane. Therefore, it is difficult to surgically remove type 1 membrane without damaging the surrounding tissue (48).

Subretinal CNV (Type 2 Growth Pattern) The type 2 (subretinal) growth pattern demonstrates single or few ingrowth sites with a focal defect in Bruch’s membrane (Fig. 9). There is a reflected layer of RPE on the outer surface of the CNV and little or no RPE on its inner surface. Since there is no support from the RPE, the overlying outer layers of retina become atrophic. Angiographically, type II CNV membranes leak under the RPE and in the outer retina. This growth pattern correlates with the “classic” angiographic appearance (49,55). In the study of surgically excised CNV, there is a reflected layer of RPE lined on the outer surface of type 2 CNV by a monolayer of inverted proliferating RPE cells and the native RPE (Figs. 10 and 11) (48). The overlying photoreceptors are atrophic. Combined Growth Pattern CNV There are many theoretical variations leading to a combined pattern of CNV growth. A progression from the type 1 to the type 2 growth pattern as well as temporal development of the type 2 growth prior to the type 1 growth have been discussed (Fig. 10) (49). These growth patterns correspond to angiographic “minimally classic” and “predominantly classic” appearances.

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Figure 10 Photomicrographs demonstrates a combined growth pattern of a choroidal neovascularization with a reflected layer of retinal pigment epithelium (arrows). A new vessel (asterisk) extends through a break in the basal laminar deposits (inset, arrowheads).

Histopathology of CNV The cellular and extracellular components of CNV include RPE, vascular endothelium, fibrocytes, macrophages, photoreceptors, erythrocytes, lymphocytes, myofibroblasts, collagen, fibrin, and BlamD (48,56). These components are similar regardless of the underlying disease including AMD, ocular histoplasmosis syndrome, myopia, idiopathic, and pattern dystrophy. The only exception is BlamD, which is seen almost exclusively in AMD. These findings suggest that CNV represents a nonspecific wound repair response to a specific stimulus, similar to fibrovascular granulation tissue proliferation (48,54,56,57).

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Disciform Scar Disciform scar represents the end-stage of the exudative form of AMD. Disciform scars are usually vascularized, but predominantly composed of fibrotic scar tissue (Fig. 11). The vascular supply is provided from the choroid (96%), retina (2.5%) or both (0.6%) (1,54). A disciform scar is generally associated with the loss of neural tissue. Photoreceptor loss increases as the diameter and thickness of the disciform scar increases. In a morphometric analysis, eyes with disciform scars due to AMD showed severe reduction in the number of outer nuclear layer cells, but good preservation of cells in the inner nuclear layer and ganglion cell layer (58). Despite massive photoreceptor loss in exudative AMD, ganglion cell neurons are known to survive in relatively large numbers (59). SUMMARY POINTS &

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Figure 11 Late stage of age-related macular degeneration with the formation of a disciform scar between Bruch’s membrane (black arrows) and the photoreceptor outer segments. Prominent vessels (white arrows) and a reflected layer of the retinal pigment epithelium (arrowheads) are present in the scar.

HISTOPATHOLOGY OF AGE-RELATED MACULAR DEGENERATION

Early lesions of AMD are located either between the RPE and its basement membrane (e.g., BlamD) or between the basement membrane of the RPE and the remainder of Bruch’s membrane (e.g., BlinD). Focal and diffuse deposits between the RPE and Bruch’s membrane are called drusen. Pathologic changes with AMD first appear in the inner collagenous zone and generally extend into the central elastic zone and outer collagenous zone, and the intercapillary connective tissue during later stages of the disease. RPE cells with AMD have cytoplasmic “lipofuscin” granules due to incompletely digested photoreceptor outer segments. Although rods gradually disappear with age, cones begin to degenerate only with advanced stages of non-exudative AMD. Immunohistochemical studies have shown that drusen are composed of acute phase proteins, complement components, complement inhibitors, apolipoproteins, tissue metalloproteinase inhibitor 3, crystalline, serum albumin, fibronectin, mucopolysaccarides, lipids, mannose, sialic acid, N-acetylglucosamine, b-galactose and immunoreactive factors like IgG, immunoglobulin light chains, Factor X, and other components, termed DRAMS. CNV has two patterns: subretinal associated with “classic CNV” and sub-RPE associated with “occult” CNV.

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46. Chong NHV, Keonin J, Luthert PJ, et al. Decreased thickness and integrity of the macular elastic layer of Bruch’s membrane correspond to the distribution of lesions associated with age-related macular degeneration. Am J Pathol 2005; 16:241–51. 47. Schneider S, Greven CM, Green WR. Photocoagulation of well-defined choroidal neovascularization in age-related macular degeneration: clinicopathologic correlation. Retina 1998; 18:242–50. 48. Grossniklaus HE, Gass JDM. Clinicopathologic correlation of surgically excised type 1 and type 2 submacular choroidal neovascular membranes. Am J Ophthalmol 1998; 126:59–69. 49. Grossniklaus HE, Green WR. Choroidal neovascularization. Am J Ophthalmol 2004; 137:496–503. 50. Gass JDM. Biomicroscopic and histopathologic consideration regarding the feasibility of surgical excision of subfoveal neovascular memebranes. Am J Ophthalmol 1994; 118:285–98. 51. Gass JDM. Stereoscopic Atlas of Macular Diseases: Diagrams and Treatment. 4th ed., Vol. 1. Mosby: St. Louis, 1997:26–37. 52. Gass JDM. Pathogenesis of disciform detachment of the neuroepithelium: III. Senile disciform degeneration. Am J Ophthalmol 1967; 63:617–44.

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53. Sarks SH. New vessel formation beneath the retinal pigment epithelium in senile eyes. Br J Ophthalmol 1973; 57:951–65. 54. Ambati J, Ambati BK, Yoo SH, et al. Age-related macular degeneration: etiology, pathogenesis, and therapeutic strategies. Surv Ophthalmol 2003; 48:257–93. 55. LaFaut BA, Bartz-Schmidt KU, van den Broecke C, et al. Clinicopathologic correlation in exudative age-related macular degeneration: histological differentiation between classic and occult neovascularization. Br J Ophthalmol 2000; 84:239–43. 56. Grossniklaus HE, Martinez JA, Brown VB, et al. Immunohistochemical and histochemical properties of surgically excised subretinal neovascular membranes in age-related macular degeneration. Am J Ophthalmol 1992; 114:464–72. 57. Frank RN, Amin RH, Eliott D, et al. Basic fibroblast growth factor and vascular endothelial growth factor are present in epiretinal and choroidal neovascular membranes. Am J Ophthalmol 1996; 122:393–403. 58. Kim SY, Sadda S, Pearlman J, et al. Morphometric analysis of the macula in eyes with disciform age-related macular degeneration. Retina 2002; 22:471–7. 59. Medeiros NE, Curcio CA. Preservation of ganglion cell layer neurons in age-related macular degeneration. Invest Ophthalmol Vis Sci 2001; 42:795–803.

2 Immunology of Age-Related Macular Degeneration Karl G. Csaky and Scott W. Cousins

Department of Ophthalmology, Duke University Medical Center, Durham, North Carolina, U.S.A.

INTRODUCTION Traditionally, immune and inflammatory mechanisms of disease pathogenesis were applied only to disorders characterized by acute onset and progression associated with obvious clinical signs of inflammation. Recently, however, it has become clear that many chronic degenerative diseases associated with aging demonstrate important immune and inflammatory components. Indeed, over the last year an explosion of genetic findings have linked complement dysregulation and age-related macular degeneration (AMD). This chapter attempts to achieve three goals. First, a brief overview is provided of the biology of the low-grade inflammatory mechanisms relevant to chronic degenerative diseases of aging, excluding the mechanisms associated with acute severe inflammation. Innate immunity, antigen-specific immunity, and amplification systems are differentiated. Second, the immunology of AMD is discussed in the context of complement activation and in particular relationships to two other age-related degenerative diseases with immunologic features, including atherosclerosis and renal glomerular diseases. Since these disorders share epidemiologic, genetic, and physiological associations with AMD, the approach attempts to delineate the scope of the subject based on analysis of other agerelated degenerative diseases, and to highlight areas of potential importance to future AMD research. Finally, this chapter introduces the paradigm of “response to injury” as a model for AMD pathogenesis. This paradigm proposes that immune mechanisms, including the complement system, not only participate in the initiation of injury, but also significantly contribute to abnormal reparative responses resulting in disease pathogenesis and complications. The response to injury paradigm, emerging as a central hypothesis in the pathogenesis of atherosclerosis and glomerular diseases, provides a connection between immunologic mechanisms of disease and the biology of tissue injury and repair in chronic degenerative disorders.

OVERVIEW OF BIOLOGY OF IMMUNOLOGY RELEVANT TO AMD Innate vs. Antigen-Specific Immunity In general, an immune response is a sequence of cellular and molecular events designed to rid the host of an offending stimulus, which usually represents a pathogenic organism, toxic substance, cellular debris, neoplastic cell, or other similar signal. Two broad categories of immune responses have been recognized: innate and antigen-specific immunity (1–3). Innate Immunity Innate immunity (also called “natural” immunity) is a pattern recognition response by certain cells of the immune system, typically macrophages and neutrophils, to identify broad groups of offensive stimuli, especially infectious agents, toxins or cellular debris from injury (4–6). Additionally, many stimuli of innate immunity can directly interact with parenchymal cells of tissues [i.e., the retinal pigmented epithelium (RPE)] to initiate a response. Innate immunity is triggered by a preprogrammed, antigen-independent cellular response, determined by the preexistence of receptors for a category of stimuli, leading to generation of biochemical mediators which recruit additional inflammatory cells. These cells remove the offending stimulus in a nonspecific manner via phagocytosis or enzymatic degradation. The key concept is that the stimuli of innate immunity interact with receptors on monocytes, neutrophils, or parenchymal cells that have been genetically predetermined by evolution to recognize and respond to conserved molecular patterns or “motifs” on different triggering stimuli. These motifs often include specific amino acid sequences, certain lipoproteins, certain phospholipids, or other specific molecular patterns. Different stimuli often trigger the same stereotyped program. Thus, the receptors of innate immunity are identical among all individuals within a species in the same way that receptors for neurotransmitters or hormones are genetically identical within a species.

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The classic example of the innate immune response is the immune response to acute infection. For example, in endophthalmitis, bacterial-derived toxins or host cell debris stimulate the recruitment of neutrophils and monocytes, leading to the production of inflammatory mediators and phagocytosis of the bacteria. Bacterial toxins can also directly activate receptors on retinal neurons, leading to injury. The triggering mechanisms and subsequent effector responses to bacteria such as staphylococcus are nearly identical to those of other organisms, determined by nonspecific receptors recognizing families of related toxins or molecules in the environment.

Antigen-Specific Immunity Antigen-specific immunity (also called “adaptive” or “acquired” immunity) is an acquired host response, generated in reaction to exposure to a specific “antigenic” molecule and is not a genetically predetermined response to a broad category of stimuli (1–3). The response is initially triggered by the “recognition” of a unique foreign antigenic substance as distinguished from “self” by cells of the immune system (and not by nonimmune parenchymal cells). Recognition is followed by subsequent “processing” of the unique antigen by specialized cells of the immune system. The response results in unique antigen-specific immunologic effector cells (T and B lymphocytes) and unique antigen-specific soluble effector molecules (antibodies) whose aim is to remove the specific stimulating antigenic substance from the organism, and to ignore the presence of other irrelevant antigenic stimuli. The key concept is that an antigen (usually) represents an alien, completely foreign substance against which specific cells of immune system must generate, de novo, a specific receptor, which, in turn, must recognize a unique molecular structure in the antigen for which no preexisting gene was present. Thus, the antigen-specific immune system has evolved away for an individual’s B and T lymphocytes to continually generate new antigen receptor genes through recombination, rearrangement, and mutation of the germline genetic structure to create a “repertoire” of novel antigen receptor molecules that vary tremendously in spectrum of recognition among individuals within a species. The classic example of acquired immunity is the immune response to a mutated virus. Viruses (such as adenovirus found in epidemic keratoconjunctivitis) are continuously evolving or mutating new antigenic structures. The susceptible host could not have possibly evolved receptors for recognition to these new viral mutations. However, these new mutations do serve as “antigens” which stimulate an adaptive

antigen-specific immune response by the host to the virus. The antigen-specific response recognizes the virus in question and not other organisms (such as the polio virus).

Amplification Mechanisms for Both Forms of Immunity Although innate or antigen-specific immunity may directly induce injury or inflammation, in most cases, these effectors initiate a process that must be amplified in order to produce overt clinical manifestations. Molecules generated within tissues which amplify immunity are termed “mediators”, and several categories of molecules qualify including: (i) cytokines (growth factors, angiogenic factors, others), (ii) oxidants (free radicals, reactive nitrogen), (iii) plasma-derived enzyme systems (complement, kinins, and fibrin), (iv) vasoactive amines (histamine and serotonin), (v) lipid mediators [prostaglandins (PGs), leukotrienes, other eicosanoids, and platelet activating factors], and (vi) neutrophil-derived granule products. Since principally complement, cytokines, and oxidants seem to be relevant to many degenerative diseases of aging and AMD, these are discussed below. Complement Components and fragments of the complement cascade, accounting for approximately 5% of plasma protein concentration and over 30 different protein molecules, represent important endogenous amplifiers of innate and antigen-specific immunity as well as mediators of injury responses (7–9). All complement factors are synthesized by the liver and released into blood. However, some specific factors can also be synthesized locally within tissues, including within cornea, sclera, and retina. Upon activation, the various proteins of the complement system interact in a sequential cascade to produce different fragments and products capable of affecting a variety of functions. Three pathways have been identified to activate the complement cascade: classical pathway, alternative pathway, and the lectin pathway (Fig. 1). Antigen-specific immunity typically activates complement via the classical pathway with antigen/ antibody (immune) complexes, especially those formed by IgM, IgG1, and IgG3 (7–9). Innate immunity typically activates complement via the alternative pathway using certain chemical moieties on the cell wall of microorganisms [e.g., lipopolysaccharides (LPS)] or activated surfaces (e.g., implanted medical devices) (10). However, some innate stimuli, such as DNA, RNA, insoluble deposits of abnormal proteins (e.g., amyloid P), or apoptotic cells can also trigger the

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Classical Pathway (Immune Complexes (IgM, IgG), DNA, RNA, Apoptotic Cell, Memebrane Blebs, Amyloid P, etc) (+) C1q

Alternative Pathway (Activating Surfaces, Biomaterials, LPS) (+)

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Letin Pathway (Cell Surface Carbohydrates, Oxidative Stress) (+) Mannose Binding Lectin (MBL)

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Figure 1 Schematic of the components and fragments of the complement cascade indicating three primary sources of activation via the classical, alternative, or lectin pathway. Abbreviations: LPS, lippopolysacccharide; MBL, mannose-binding lectin; MAC, membrane attack complex.

classical pathway (10–13). Recently, a new innate activational pathway, the lectin pathway, has been identified (14). This pathway utilizes mannosebinding lectin (MBL) to recognize sugar moieties, such as mannose and N-acetylglucosamine, on cell surfaces. While MBL does not normally recognize the body’s own tissue, oxidant injury, as can occur in AMD, may alter surface protein expression and glycosylation causing MBL deposition and complement activation (15–18). Recently, photooxidative products of A2E, a bis-retinoid pigment that may accumulate in the RPE in AMD, have been shown to activate C3 into C3b and C3a (19). The activation of complement is also regulated by inhibitors, such as decay accelerating factor, factor H and others which serve to block, resist, or modulate the induction of various activation pathways (7–9). As will be discussed below, the role of complement factor H (CFH) in particular may have critical relevance for AMD. Each activation pathways results in the generation of the same complement byproducts which amplify injury or inflammation by at least three mechanisms: (i) a specific fragment of the third component, C3b, can coat antigenic or pathogenic surfaces in order to enhance phagocytosis by macrophages or neutrophils; (ii) activation of terminal complement components C5–C9, called the membrane attack complex (MAC), forms pores or leaky patches in cell membranes leading to activation of the cell, entrance of extracellular chemicals, loss of cytoplasm or lysis of the cell; and (iii) generation of small pro-inflammatory

polypeptides, called anaphylatoxins (C3a, C4a, and C5a), can induce many inflammatory mediators and lead to the recruitment of inflammatory cells. In addition, individual complement components (especially C3) can be produced locally by cells within tissue sites rather than derived from the blood (8). C3 and other complement proteins can be cleaved into biologically activated fragments by various enzyme systems, in the absence of the entire cascade, to activate certain specific cellular functions. Further, complement activation inhibitors can be produced by cells within tissues, including the RPE, serving as local protective mechanism against complement-mediated injury (20,21). Recently, several components of the complement system have been identified within Bruch’s membrane and drusen indicating a potential role for complement in AMD (22). Cytokines Cytokine is a generic term for any soluble polypeptide mediator (i.e., protein) synthesized and released by cells for the purposes of intercellular signaling and communication. Cytokines can be released to signal neighboring cells at the site (paracrine action), to stimulate a receptor on its own surface (autocrine action) or in some cases, released into the blood to act upon a distant site (hormonal action). Traditionally, investigators have used terms like “growth factors,” “angiogenic factors,” “interleukins,” “lymphokines,” “interferons,” “monokines,” “chemokines,” etc. to subdivide cytokines into families with related activities,

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sources and targets. Nevertheless, research has demonstrated that although some cytokines are cell-type specific, most cytokines have such multiplicity and redundancy of source, function and target that excessive focus on specific terminology is not particularly conceptually useful for the clinician. RPE as well as cells of the immune system can produce many different cytokines relevant to AMD such as monocyte chemoattractant protein-1 (MCP-1) and vascular endothelial growth factor (VEGF). Oxidants Under certain conditions, oxygen-containing molecules can accept an electron from various substrates to become highly reactive products with the potential to damage cellular molecules and inhibit functional properties in pathogens or host cells. Four of the most important oxidants are singlet oxygen, superoxide anion, hydrogen peroxide and the hydroxyl radical. In addition, various nitrogen oxides, certain metal ions and other molecules can become reactive oxidants or participate in oxidizing reactions. Oxidants are continuously generated as a consequence of normal noninflammatory cellular biochemical processes, including electron transport during mitochondrial respiration, autooxidation of catecholamines, cellular interactions with environmental light or radiation, or PG metabolism within cell membranes. During immune responses, however, oxidants are typically produced by neutrophils and macrophages by various enzyme-dependent oxidase systems (23). Some of these enzymes are bound to the inner cell membrane (e.g., NADPH oxidase) and catalyze the intracellular transfer of electrons from specific substrates (like NADPH) to oxygen or hydrogen peroxide to form highly chemically reactive compounds meant to destroy internalized, phagocytosed pathogens (24). Other oxidases, like myeloperoxidase, can be secreted extracellularly or released into phagocytic vesicles to catalyze oxidant reactions between hydrogen peroxide and chloride to form extremely toxic products that are highly damaging to bacteria, cell surfaces, and extracellular matrix molecules (25). Finally, several important oxidant reactions involve the formation of reactive nitrogen species (5). Oxidants can interact with several cellular targets to cause injury. Among the most important are damage to proteins (i.e., enzymes, receptors) by cross-linking of sulfhydryl groups or other chemical modifications, damage to the cell membrane by lipid peroxidation of fatty acids in the phospholipid bilayers, depletion of ATP by loss of integrity of the inner membrane of the mitochondria, and breaks or cross-links in DNA due to chemical alterations of

nucleotides (1,26). Not surprisingly, nature has developed many protective antioxidant systems including soluble intracellular antioxidants (i.e., glutathione or vitamin C), cell membrane-bound lipid soluble antioxidants (i.e., vitamin E) and extracellular antioxidants (1,26). In the retina, oxidation induced lipid peroxidation and protein damage in RPE and photoreceptors have been proposed as major injury stimuli (27–30). Relevant sources of oxidants in AMD might include both noninflammatory biochemical sources (e.g., light interactions between photoreceptors and RPE, lysosomal metabolism in RPE, PG biosynthesis, oxidants in cigarette smoke) and innate immunity (e.g., macrophage release of myeloperoxidase).

Cells of the Immune Response Both innate and antigen-specific immune system use leukocytes as cellular mediators to effect and amplify the response (i.e., immune effectors). In general, leukocyte subsets include lymphocytes (T cells, B cells), monocytes [macrophages, microglia, dendritic cells (DC)] and granulocytes (neutrophils, eosinophils and basophils). A complete overview is beyond the scope of this chapter, especially since no evidence exists that all of these cellular effectors participate in AMD. Thus, this section will focus only upon leukocyte subsets potentially relevant to AMD, including monocytes, basophils/mast cells and B lymphocytes/antibodies. Monocytes and Macrophages The monocyte (the circulating cell) and the macrophage (the tissue-infiltrating equivalent) are important effectors in all forms of immunity and inflammation (4). Monocytes are relatively large cells (12–20 mm in suspension, but up to 40 mm in tissues) and traffic through many normal sites. Most normal tissues have at least two identifiable macrophage populations: tissue resident macrophages and blood-derived macrophages. Although many exceptions exist, in general, tissue-resident macrophages represent monocytes that migrated into a tissue weeks or months previously, or even during embryologic development of the tissue, thereby acquiring tissue-specific properties and specific cellular markers. In many tissues, resident macrophages have been given tissue-specific names (e.g., microglia in the brain and retina, Kupffer cells in the liver, alveolar macrophages in the lung, etc.) (31–33). In contrast, blood-derived macrophages usually represent monocytes that have recently migrated from the blood into a fully developed tissue site, usually within a few days, still maintaining many generic properties of the circulating cell.

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Macrophages serve three primary functions: as scavengers to clear cell debris and pathogens without tissue damage, as antigen presenting cells (APCs) for T lymphocytes, and as inflammatory effector cells. Conceptually, macrophages exist in different levels or stages of metabolic and functional activity, each representing different “programs” of gene activation and synthesis of mediators. Three different stages are often described: (i) scavenging or immature macrophages, (ii) “primed” macrophages, and (iii) “activated” macrophages. Activated macrophages often undergo a morphologic change in size and histologic features into a cell called an epithelioid cell. Epithelioid cells can fuse into multinucleated giant cells. Only upon full activation are macrophages most efficient at synthesis and release of mediators to amplify inflammation and to kill pathogens. Typical activational stimuli include bacterial toxins (such as LPS), antibody-coated pathogens, complement-coated debris or certain cytokines (Fig. 2) (34–36). A fourth category of macrophage, often called “reparative” or “stimulated,” is used by some authorities to refer to macrophages with partial or intermediate level of activation (37–40). Reparative macrophages can mediate chronic injury in the absence of inflammatory cell infiltration or widespread tissue destruction. For example, reparative macrophages contribute to physiologic processes such as fibrosis, wound repair, extracellular matrix

Stimulated T Cells

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Figure 2 Overview of macrophage biology indicating process to “primed” macrophage (step 1) by interferon-g and subsequent activation through the exposure to lipopolysaccharide (step 2). Alternatively, via scavenging and phagocytosis (step 3), macrophages can become “reparative” resulting in local tissue rearrangement. Abbreviation: LPS, lipopolysacccharide.

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turnover and angiogenesis (41–49). Reparative macrophages play important roles in the pathogenesis of atherosclerosis, glomerulosclerosis, osteoarthritis, keloid formation, pulmonary fibrosis and other noninflammatory disorders, indicating that the “repair” process is not always beneficial to delicate tissues with precise structure-function requirements. In eyes with AMD, choroidal macrophages and occasionally choroidal epithelioid cells have been observed underlying areas of drusen, geographic atrophy and choroidal neovascularization (CNV) (50–54). Also, cell culture data suggest that blood monocytes from patients with AMD can become partially activated into reparative macrophages by growth factors and debris released by oxidant-injured RPE (55).

Dendritic Cells DC are terminally differentiated bone-marrow derived circulating mononuclear cells distinct from the macrophage–monocyte lineage and comprise approximately 0.1% to 1% of blood mononuclear cells (56). However, in tissue sites, DC become large (15–30 mm) with cytoplasmic veils which form extensions two to three times the diameter of the cell, resembling the dendritic structure of neurons. In many non-lymphoid and lymphoid organs, DC become a system of APCs. These sites recruit DC by defined migration pathways, and in each site, DC share features of structure and function. DC function as accessory cells which play an important role in processing and presentation of antigens to T cells, and their distinctive role is to initiate responses in naive lymphocytes. Thus, DC serve as the most potent leukocytes for activating T cell dependent immune responses. However, DC do not seem to serve as phagocytic scavengers nor effectors of repair or inflammation. Both the retina and the choroid contain high density of DC (57,58). Basophils and Mast Cells Basophils are the blood-borne equivalent of the tissue bound mast cell. Mast cells exist in two major subtypes, connective tissue versus mucosal types, both of which can release preformed granules and synthesize certain mediators de novo (59,60). Connective tissue mast cells contain abundant granules with histamine and heparin, and synthesize PGD2 upon stimulation. In contrast, mucosal mast cells require T cell cytokine help for granule formation, and therefore normally contain low levels of histamine. Also, mucosal mast cells synthesize mostly leukotrienes after stimulation. Importantly, the granule type and functional activity can be altered by the tissue location, but the regulation of these important differences is not well understood. Basophils and mast cells differ from other granulocytes in several important ways.

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The granule contents are different from those of polymorphonuclear neutrophils or eosinophils and mast cells express high-affinity Fc receptors for IgE. They act as the major effector cells in IgE-mediated immune-triggered inflammatory reactions, especially allergy or immediate hypersensitivity. Mast cells also participate in the induction of cell-mediated immunity, wound healing, and other functions not directly related to IgE-mediated degranulation (61,62). Other stimuli, such as complement or certain cytokines, may also trigger degranulation (63). Mast cells are also capable of inducing cell injury or death through their release of TNF-a. For example, mast cells have been associated with neuronal degeneration and death in thiamine deficiency and toxic metabolic diseases. Recent reports have demonstrated the presence of mast cells in atherosclerotic lesions and the co-localization of mast cells with the angiogenic protein, plateletderived endothelial growth factor (63–69). Mast cells are widely distributed in the connective tissue and are frequently found in close proximity to blood vessels and are in present in abundance in the choroid (57,70). Mast cells may play important roles in the pathogenesis of AMD since they have an ability to induce angiogenesis and are mediators of cell injury. Mast cells have also been shown to accumulate at sites of angiogenesis and have been demonstrated to be present around Bruch’s membrane during both the early and late stages of CNV in AMD (51). Mast cells can interact with endothelial cells and induce their proliferation through the release of heparin, metalloproteinases (MMPs) and VEGF (71–73). Interestingly, oral tranilast, an antiallergic drug which inhibits the release of chemical mediators from mast cells has been shown to suppress laser induced CNV in the rat (74).

T Lymphocytes Lymphocytes are small (10–20 mm) cells with large dense nuclei also derived from stem cell precursors within the bone marrow (3,75,76). However, unlike other leukocytes, lymphocytes require subsequent maturation in peripheral lymphoid organs. Originally characterized and differentiated based upon a series of ingenious but esoteric laboratory tests, lymphocytes can now be subdivided based upon detection of specific cell surface proteins (i.e., surface markers). These “markers” are in turn related to functional and molecular activity of individual subsets. Three broad categories of lymphocytes have been determined: B cells, T cells and non-T, non-B lymphocytes. Thymus-derived lymphocytes (or T cells) exist in several subsets (77,78). Helper T cells function to assist in antigen processing for antigen-specific immunity within lymph nodes, especially in helping B cells to produce antibody and effector T cells to become sensitized. Effector T lymphocyte subsets function as

effector cells to mediate antigen-specific inflammation and immune responses. Effector T cells can be distinguished into two main types. CD8 T cells (often called cytotoxic T lymphocytes) serve as effector cells for killing tumors or virally infected host cells via release of cytotoxic cytokines or specialized pore forming molecules. It is possible, but unlikely that these cells play a major role in AMD. CD4 T cells (often called delayed hypersensitivity T cells) effect responses by the release of specific cytokines such as interferon-g and TNF-b. They function by homing into a tissue, recognizing antigen and APC, becoming fully activated and releasing cytokines and mediators which then amplify the reaction. Occasionally, CD4 T cells can also become activated in an antigen-independent manner, called bystander activation (79–81), a process which may explain the presence of T lymphocytes identified in CNV specimens surgically excised from AMD eyes.

B Lymphocytes and Antibody B-lymphocytes mature in the bone marrow, and are responsible for the production of antibodies. Antibodies [or immunoglobulins (Igs)] are soluble antigen-specific effector molecules of antigen-specific immunity (3,75,76). After appropriate antigenic stimulation with T cell help, B cells secrete IgM antibodies, and later other isotypes, into the efferent lymph fluid draining into the venous circulation. Antibodies then mediate a variety of immune effector activities by binding to antigen in the blood or in tissues. Antibodies serve as effectors of tissue-specific immune responses by four main mechanisms. Intravascular circulating antibodies can bind antigen in the blood, thereby form circulating immune complexes (ICs). Then the entire complex of antigen plus antibody can deposit into tissues. Alternatively, circulating B cells can infiltrate into a tissue and secrete antibody locally to form an IC. Third, antibody can bind to an effector cell (especially mast cell, macrophage, or neutrophil) by the Fc portion of the molecule to produce a combined antibody and cellular effector mechanism. It is unlikely that any of these mechanisms play a major role in AMD. However, one possible antibody-dependent mechanism relevant to AMD is the capacity for circulating antibodies, usually of the IgG subclasses previously formed in lymph nodes or in other tissue sites, to passively leak into a tissue with fenestrated capillaries (like the choriocapillaris). Then, these antibodies form an IC with antigens trapped in the extracellular matrix, molecules expressed on the surface of cells or even antigens sequestered inside the cell to initiate one of several types of effector responses described below (Fig. 3) (3,75,76,82–85).

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Antibody Effectors in ARMD RPE BM CC IC Formation in Bruch's Membrane

IC on Cell Surface Intracellular IC with MAC Activation

Figure 3 Possible antibody effects in age-related macular degeneration (AMD) with subsequent immune complex (IC) formation at variation locations in the subretinal space, on or within the retinal pigment epithelium (RPE). Abbreviation: MAC, membrane attack complex.

Immune Complexes with Extracellular-Bound Antigens When free antibody passively leaks from the serum into a tissue, it can combine with tissue-bound antigens (i.e., antigen trapped in the extracellular matrix). These “in situ” or locally formed complexes sometimes activate the complement pathway to produce complement fragments called anaphylatoxins. This mechanism should be differentiated from deposition of circulating ICs which are preformed in the blood. Typically, the histology is dominated by neutrophils and monocytes, but at low level of activation minimal cellular infiltration may be observed. Many types of glomerulonephritis and vasculitis are thought to represent this mechanism. Immune Complexes with Cell-Surface Antigen If an antigen is associated with the external surface of the plasma membrane, antibody binding might activate the terminal complement cascade to induce cell injury via formation of specialized pore-like structures called the MAC. Hemolytic anemia of the newborn due to Rh incompatibility is the classic example of this process. Hashimoto’s thyroiditis, nephritis of Goodpasture’s syndrome, and autoimmune thrombocytopenia are other examples. Immune Complex with Intracellular Antigen: A Novel Mechanism Circulating antibodies can cause tissue injury by mechanisms different from complement activation, using pathogenic mechanisms not yet clearly elucidated (84,85). For example, some autoantibodies in systemic lupus erythematosus appear to be internalized by renal cells independent of antigen binding, but then combine with intracellular nuclear or

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ribosomal antigens to alter cellular metabolism and signaling pathways. This novel pathway of intracellular antibody/antigen complex formation may cause some cases of nephritis in the absence of complement activation. This pathway has also been implicated in paraneoplastic syndromes, especially cancer associated retinopathy (CAR), in which autoantibodies to intracellular photoreceptor-associated antigens may mediate rod or cone degeneration (86).

Mechanisms for the Activation of the Immune Responses in Degenerative Diseases Activation of Innate Immunity Cellular Injury as a Trigger of Innate Immunity Not only can immune responses cause cellular injury, but cellular responses to nonimmune injury are also common initiators of innate immunity (3,75,76,87–89). Injury can be defined as tissue exposure to any physical and/or biochemical stimulus that alters preexisting homeostasis to produce a physiological cellular response. In addition to injury stimuli produced by the immune effector and amplification systems described above, nonimmune injurious stimuli include physical injury (heat, light, mechanical) or biochemical stimulation (hypoxia, pH change, oxidants, chemical mediators, cytokines) (89). Typical cellular reactions to injury include a wide spectrum of responses, including changes in intracellular metabolism, plasma membrane alterations, cytokine production, and gene upregulation, morphological changes, cellular migration, proliferation, or even death. Some of these cellular responses, in turn, can result in the recruitment and activation of macrophages or activation of amplification systems, especially if they include upregulation of cell adhesion molecules, production of macrophage chemotactic factors or release of activational stimuli. Two important injury responses relevant to AMD that commonly activate innate immunity include vascular injury and extracellular deposit accumulation (89,90). Vascular injury induced by physical stimuli (i.e., mechanical stretch of capillaries or arterioles by hydrostatic expansion induced by hypertension or thermal injury from laser) or biochemical stimuli (i.e., hormones associated with hypertension and aging) can upregulate cell adhesion molecules and chemotactic factors that lead to macrophage recruitment into various vascularized tissues. Extracellular deposit accumulation can also contribute to activation of innate immunity by serving as a substrate for scavenging and phagocytosis, especially if the deposits are chemically modified by oxidation or other processes (see atherosclerosis below).

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Infection as a Trigger of Innate Immunity Infection can also activate innate immunity, usually by the release of toxic molecules (i.e., endotoxins, exotoxins, cell wall components) that directly interact with receptors on macrophages, on neutrophils or, in some cases, on parenchymal cells. Active infection is differentiated from harmless colonization by the presence of invasion and replication of the infectious agent (91). However, active infections do not always trigger innate immunity, illustrated by some retinal parasite infections in which inflammation occurs only when the parasite dies. Recently, the idea has emerged that certain kinds of chronic infections might cause (or at least contribute to) degenerative diseases that are not considered to be truly inflammatory (88–91). One of the most dramatic examples is peptic ulcer disease, recently recognized to be caused by infection of the gastric subepithelial mucosa with a gram-positive bacterium called Helicobacter pylori (92). Accordingly, ulcer disease is now treated by antibiotics and not with diet or surgery. Recently, chronic bacterial or viral infection of vascular endothelial cells has been suggested as an etiology for coronary artery atherosclerosis, and infection with an unusual agent called a prion has been shown as a cause of certain neurodegenerative diseases. The relevance to AMD is discussed below.

Activation of Normal and Aberrant Antigen-Specific Immunity Activation of Antigen-Specific Immunity It is often expressed as the idea of the “immune response arc.” This idea proposes that interaction between antigen and the antigen-specific immune system at a peripheral site (such as the skin) can Immune Response Arc APC

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Figure 4 The immune response arc indicating cross-talk between the tissue site, where antigen recognition and effector processes take place, and the lymph node, the site of antigen processing. Abbreviation: APC, antigen presenting cell.

conceptually be subdivided into three phases: afferent (at the site), processing (within the immune system), and effector (at the original site completing the arc) (Fig. 4) (3,75,76). Antigen within the skin or any other site is recognized by the afferent phase of the immune response, which conveys the antigenic information to the lymph node in one of two forms. APCs, typically DC, can take up antigen (almost always in the form of a protein) at a site, digest the antigen into fragments and carry the digested fragments to the lymph node to interact with T cells (77,78,93). Alternatively, the natural, intact antigen can directly flow into the node via lymphatics where it interacts with B cells (3,75,76). In the lymph node, processing of the antigenic signal occurs where antigen, APC, T cells and B cells interact to activate the immune response. For tissues without draining lymph nodes (such as the retina and choroid), the spleen is often a major site of processing. Immunologic processing has been the topic of extensive research and the details are too complex to discuss in this brief review. Processing results in release of immune effectors (antibodies, B cells and T cells) into efferent lymphatics and venous circulation which conveys the intent of the immune system back to the original site where an effector response occurs (i.e., IC formation or delayed hypersensitivity reaction). Compared to that of the skin, the immune response arc of the retina and choroid express many similarities as well as important differences (i.e., immune privilege, anatomy), which are discussed in recent reviews (94,95). Aberrant Activation of Antigen-Specific Immunity The inappropriate activation of antigen-specific immunity may play a role in the pathogenesis of chronic degenerative diseases. Autoimmunity is the activation of antigen-specific immunity to normal self antigens, and two different mechanisms of autoimmunity may be relevant to AMD: molecular mimicry and desequestration. Additionally, immune responses directed at “neo-antigens” or foreign antigens inappropriately trapped within normal tissues may also play a role in AMD. Molecular mimicry is the immunologic crossreaction between antigenic regions (epitopes) of an unrelated foreign molecule and self-antigens with similar structures (96). For example, immune system exposure to foreign antigens, such as those present within yeast, viruses, or bacteria, can induce an appropriate afferent, processing, and effector immune response to the organism. However, antimicrobial antibodies or effector lymphocytes generated to the organism can inappropriately cross-react with similar antigenic regions of a self-antigen. A dynamic

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process would then be initiated, causing tissue injury by an autoimmune response that would induce additional lymphocyte responses directed at other self-antigens. Thus, the process would not require the ongoing replication of a pathogen or the continuous presence of the inciting antigen. Molecular mimicry against antigens from a wide range of organisms, including Streptococcus, yeast, E. Coli and various viruses, has been shown to be a potential mechanism for anti-retinal autoimmunity (97). A second mechanism for aberrant autoimmunity is desequestration (98–100). For most selfantigens, the immune system is actively “tolerized” to the antigen by various mechanisms, preventing the activation of antigen-specific immune effector responses even when the self antigen is fully exposed to the immune system. For some other antigens, however, the immune system relies on sequestration of the antigen within cellular compartments that are isolated from APCs and effector mechanisms. If the sequestered molecules are allowed to escape their protective isolation, they can become recognized as foreign, thereby initiating an autoimmune reaction. For example, certain nuclear or ribosomal-associated enzymes are apparently sequestered, and if organelles become extruded into a location with exposure to DC or macrophages, an immune response can be triggered against these antigens (99). Accordingly, some RPE and retinaassociated peptides appear to be sequestered from the immune system and could potentially serve as antigens if RPE injury or death leads to their release into the choroid (94,100). Another mechanism for aberrant activation of antigen-specific immunity is the formation of neoantigens secondary to chemical modification of normal self proteins trapped or deposited within tissues (101). For example, oxidation or acetylation of peptides in apolipoproteins trapped within atherosclerotic plaques can induce new antigenic properties resulting in specific T cell and antibodies immunized to the modified protein. A final mechanism for aberrant antigen-specific immunity is antigen trapping (102). Antigen trapping is the immunologic reaction to circulating foreign antigens inappropriately trapped within the extracellular matrix of a normal tissue site containing fenestrated capillaries. Typically occurring after invasive infection or iatrogenically administered drugs, this mechanism may be very important in glomerular diseases (102) and has been postulated to induce ocular inflammation (103,104). Physical size and charge of the antigen are important. For example, antigen trapping within the choriocapillaris may contribute to ocular histoplasmosis syndrome (OHS) (104).

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EXAMPLES OF IMMUNE AND INFLAMMATORY MECHANISMS OF NONOCULAR DEGENERATIVE DISEASES Immune Mechanisms in Atherosclerosis Myocardial infarction due to thrombosis of atherosclerotic coronary arteries is the major cause of death in western countries, and epidemiologic studies suggest a possible association with AMD (105,106). The pathology of atherosclerosis suggests a spectrum of changes whose pathogenesis may be relevant to the understanding of AMD (107,108). The fatty streak, representing the earliest phase of atherosclerosis, is characterized by lipid deposition and macrophage infiltration within the vessel wall (101,108,109). Some investigators have suggested similarities in pathogenesis between fatty streak formation and early AMD (110). The fatty streak can progress into the fibrous plaque, characterized by the proliferation of smooth muscle cells, increasing inflammation, and formation of connective tissue with neovascularization within the vessel wall. The fibrous plaque predisposes to the complications of atherosclerosis such as thrombosis, dissection or plaque ulceration (101,108,109). The pathogenesis of the fibrous plaque may share similarity with mechanisms for the late complications of AMD, including formation of CNV and disciform scars (Fig. 5). Many mechanisms contribute to the pathogenesis of atherosclerosis, including genetic predisposition and physiologic risk factors like high blood cholesterol, smoking, diabetes, and hypertension. However, most authorities now believe that chronic low grade inflammation, induced by a wide variety of injury stimuli, followed by a fibroproliferative (wound healing) response within the vessel wall is central to the pathogenesis of atherosclerosis. Thus, various immune mechanisms implicated in atherosclerosis might be relevant to AMD. Innate Mechanisms Injury and Atherosclerosis The response to injury hypothesis for the initiation and progression of atherosclerosis has been supported by numerous investigators who cite many different participating injury stimuli (101,108,109). For example, hemodynamic injury by blood flow turbulence can directly injure endothelial cells at bifurcations of major vessels (113). Biochemical injury secondary to exposure to polypetide mediators associated with hypertension (i.e., angiotensin II or endothelin-1) can stimulate the endothelial and smooth muscle responses. Oxidized low density lipoprotein (LDL) cholesterol particles in the blood, advanced glycosylation end products in diabetes or toxic chemicals

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(B)

(A)

BLD

Plaque

AMD

Figure 5 Micrographs of an atheromatous plaque (left) and a choroidal neovascular membrane (right) indicating similar histologic components of intrastromal neovascularization (arrows) and macrophages (left—B) and (right—asterisk). Abbreviations: AMD, age-related macular degeneration; BLD, basal laminar deposits. Source: From Refs. 111, 112.

secondary to smoking are other potential sources of injury (114). Macrophages in Atherosclerosis Blood-derived macrophages are major contributors to the pathogenesis of atherosclerosis (101,108,115). In the fatty streak phase of atherosclerosis, lipids accumulate in the subendothelial vascular wall at sites of vascular injury. Injury results in the oxidation of lipids or endothelial production of specific macrophage chemotactic signals, like macrophage chemotactic protein-1, recruiting circulating monocytes to sites of endothelial injury. There, they migrate into the subendothelial extracellular matrix to scavenge the extracellular lipid-rich deposits (i.e., scavenging macrophages). Macrophages may also contribute to the solubilization of lipid deposits by the release of apolipoprotein E (ApoE), which may facilitate uptake and scavenging of lipids. Genetic polymorphisms of ApoE have been associated with variations in the severity of atherosclerosis and AMD (116). Foam cells and macrophages are very numerous in fibrous plaques, and probably play a major role in lesion progression. Although overly simplistic, experimental data suggest that scavenging macrophages can become activated into reparative “foam” cells by numerous stimuli, including phagocytosis of oxidized lipoproteins (115,116). Reparative macrophages secrete amplifying mediators, including platelet derived growth factor (PDGF), VEGF, matrix MMPs or others which contribute to fibrosis, smooth muscle proliferation, or vascularization of the plaque (117–120).

Infectious Etiology of Atherosclerosis Although numerous risk factors are associated with the initiation and progression of atherosclerosis, an infectious etiology has been suggested by recent data. Many patients with atherosclerosis exhibit signs of mild systemic inflammation, especially elevated serum C-reactive protein (CRP) and erythrocyte sedimentation rate (121). Statistical evidence has been generated to suggest that infection with various infectious agents, especially Chlamydia pneumoniae or cytomegalovirus (CMV), might initiate vascular injury and explain the systemic inflammatory signs (122–125). Numerous epidemiologic studies have revealed a statistical correlation between atherosclerosis and serologic evidence of infection with C. pneumoniae (122). Follow-up studies have demonstrated the presence of C. pneumoniae by histochemical methods within atherosclerotic plaques and organisms have been cultured from the lesions (125). Additionally, pilot studies using appropriate antibiotic therapy have demonstrated a beneficial effect in patients with severe atherosclerosis (123,124). Several proposed mechanisms for the role of C. pneumoniae in atherosclerosis may be relevant to AMD. Chronic infection of vascular endothelial cells may upregulate cell surface molecules that recruit macrophages or alter responses to injury. For instance, C. pneumoniae endothelial infection can enhance endotoxin binding to LDL particles which might induce various inflammatory cascades at the site of uptake (126). Additionally, chlamydial heat shock proteins (HSPs) can directly stimulate macrophages and other cellular

2: IMMUNOLOGY OF AGE-RELATED MACULAR DEGENERATION

amplification systems (127). Also, antigen-specific immune responses directed against chlamydial HSPs may cross-react with host cellular HSP including those expressed in the retina (128). Similar, but less extensive data have been generated to support a role of CMV infection in atherosclerosis (129–131). CMV infects 60% to 70% of adults in the U.S.A. Several studies have linked serologic evidence of prior CMV infection to atherosclerosis. Although the association is mild, studies have elucidated possible mechanisms for this association such as enhanced scavenging of LDL particles by virally infected endothelial cells.

Antigen-Specific Immunity The potential importance of antigen-specific immune mechanisms in atherosclerosis is illustrated by the observation of accelerated atherosclerosis in heart transplant patients who experience vascular injury associated with mild, chronic allograft rejection (93). In normal patients with atherosclerosis, T lymphocytes are numerous in fibrous plaques and a role for lymphocyte-mediated antigen specific immunity has been proposed for progression of atherosclerotic fibrous plaques (101). Experimental data suggest that oxidized lipoproteins can become neo-antigens to activate an immune response arc (132). Scavenging macrophages may become APCs at the site, serving to restimulate recruited T cells thereby activating the effector phase of the immune response. Immune responses to bacterial or viral antigens, especially chlamydial HSPs, trapped in tissues after occult infection may also stimulate antigen-specific immunity, or autoimmunity by cross-reactive molecular mimicry (133). Alternatively, T cells may be recruited by innate responses and become activated by antigenindependent bystander mechanisms. Interestingly, vaccination against oxidized LDL produces antibodies which seem to prevent or reduce formation of atherosclerotic plaques (19), similar to that observed in Alzheimer’s disease (AD) (see below). Nonspecific Amplification Cascades Complement Activation in Atherosclerosis In atherosclerotic lesions, several complement components and inhibitory proteins have been detected including MAC complexes (134–136). Cholesterol is also a potent activator of the complement system in vitro. Alternatively, MAC complex concentration has been shown to induce macrophage chemotactic factor production in smooth muscle cells and studies have shown MAC deposition in the arterial wall prior to monocyte infiltration and foam cell formation. Interestingly, in addition to its cytotoxic function, limited complement activation and deposition of the complement precursor protein C1q on apoptotic cells,

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cell debris and cell membrane blebs can enhance phagocytosis by C1q—receptor bearing macrophages and may play a role in tissue repair. Oxidants and Cytokines in Atherosclerosis Oxidation is considered to be a major injury stimulus in the initiation and progression of atherosclerosis. The role of oxidized lipoproteins in circulating LDL cholesterol as an initiating injury stimulus as well as oxidation of lipid deposits within vessel walls as an amplifier of foam cell activation has been discussed above (114,115,137). Numerous cytokines, especially PDGF and transforming growth factor-b have also been implicated as major mediators of atherosclerosis progression (117–120).

Immune Mechanisms in Glomerular Diseases Glomerular diseases account for 70% of chronic renal failure in the U.S.A. Many glomerular diseases are primarily mediated by inflammatory mechanisms, and are usually classified as glomerulonephritis. Other glomerular diseases are mediated by a mixture of degenerative and inflammatory mechanisms, and these are often classified as glomerulosclerosis (138,139). Genetic and systemic health factors contribute to the pathogenesis of both groups (138–141). The glomerulus shares some anatomic similarities with the outer retina and inner choroid, so that analysis of the mechanism of deposit formation and extracellular matrix changes of glomerular disorders might be informative in terms of AMD (138). For instance, both the glomerulus and inner choroid/outer retina can be described as containing capillary lobules with endothelium on one side of an extracellular matrix and epithelium on the other. In the glomerulus, endothelial cells (conceptually corresponding to the choriocapillaris) cover the internal surface of an extracellular matrix, whose external surface is covered by an epithelial layer (the podocyte). External to the podocyte is Bowman’s capsule (conceptually corresponding to the subretinal space). Smooth muscle cells located internally to the endothelium, called mesangial cells, are responsible for regulating contractility and maintaining the glomerular matrix. These cells may share analogies with choroidal pericytes underlying and surrounding the choriocapillaris. Innate Immunity in Glomerular Diseases Chronic Injury As is the case for atherosclerosis, a response to injury hypothesis has been substantiated for glomerulosclerosis due to aging, hypertension or diabetes (138–145). Glomerulosclerosis is characterized by progressive thickening of the glomerular extracellular matrix ultimately associated with loss of glomerular

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M ELM

M

RPE

RPE

BLD

GS

AMD

Figure 6 Electron micrographs from glomerulosclerosis and geographic atrophy from age-related macular degeneration (AMD) showing appearance of excessive extracellular material and cellular loss. In glomerulosclerosis (GS) there is accumulation of glomerular extracellular material (asterisks) and loss of cellular structure (M) while in AMD there is accumulation of basal laminar deposits (BLD) and loss of retinal pigment epithelium (RPE) cells under the external limiting membrane. Abbreviation: ELM, external limiting membrane. Source: From Refs. 146, 147.

capillaries and epithelial cells. If enough glomeruli are involved, renal impairment occurs. In some ways, glomerulosclerosis resembles geographic atrophy in AMD (Fig. 6). The response to injury hypothesis has been thoroughly evaluated for renal hypertension, a major cause of glomerulosclerosis (141–145,148). The hemodynamic injury hypothesis proposes that glomerular capillary hypertension causes excessive flow through the glomerulus or hydraulic stretching of the capillary wall to activate injury responses in glomerular cells. The humoral hypothesis proposes that hypertensionassociated hormones or cytokines associated with low grade systemic inflammation induced by hypertensive vascular injury, activate cellular injury responses. In either case, the injured endothelium, podocytes and mesangial cells demonstrate abnormal production and turnover of collagen and other matrix molecules, leading to collagenous thickening of the matrix with degeneration of the glomerulus (148–150). Genetic background and gender can influence the rate of progression. Since hypertension is a risk factor associated with AMD and glomerular disease, hypertension-associated inflammation may also injure the choriocapillaris endothelium or RPE in an analogous fashion. Macrophage-Mediated Injury Macrophages contribute significantly to glomerular damage in renal diseases (151–161). Not surprisingly, infiltration with activated inflammatory macrophages is a significant histologic feature in inflammatory glomerulonephritis caused by antigen-specific immune mechanisms (i.e., IC disease or allograft

rejection) (161), and blockade of macrophage infiltration or function ameliorates glomerular damage (155). Perhaps of more relevance to AMD is the contribution of reparative macrophages to glomerulosclerosis. Recruitment of blood-derived reparative macrophages develops early in the course of glomerulosclerosis in proportion to the severity of the injury (151,152). Various innate injury stimuli, including renal hypertension, hyperlipidemia, and glomerular capillary endothelial injury by oxidized LDL, can upregulate macrophage chemotactic factors and adhesion molecules in the capillaries to induce macrophage recruitment (156–158). Experimental data suggest that reparative macrophages release mediators that induce mesangial cell proliferation, amplify the accumulation of extracellular matrix and might induce killing of endothelial cells.

Antigen-Specific Immunity in Glomerular Diseases Antigen-specific immunity contributes significantly to inflammatory glomerular disorders. Lymphocytemediated immunity clearly contributes to glomerulonephritis, especially in renal allograft rejection (161). However, the relevance of this mechanism to AMD is probably minimal. Many forms of chronic glomerulonephritis are caused by antibody-dependent mechanisms, and some of these disorders are characterized by subendothelial or subepithelial deposit formation (102,162–164). Direct deposition of circulating antibodies targeted at antigens uniformly expressed within the glomerular matrix is a welldefined but rare form of glomerulonephritis, especially in Goodpasture’s syndrome. Deposition of preformed circulating antigen/antibody complexes in the blood has been proposed as another major mechanism in many types of glomerulonephritis associated with deposit formation. Nevertheless, it is unlikely that deposition of either anti-basement membrane antibodies or circulating ICs plays an important role in AMD. However, another interpretation of the clinical and experimental data is that some forms of glomerulonephritis may actually represent antigen trapped or “planted” within the glomerular matrix, followed by the subsequent formation of in situ ICs. This alternative explanation is probably especially relevant to glomerulonephritis associated with subepithelial deposits rather than subendothelial deposits (since it is unlikely that large ICs would be able to filter through the matrix). For example, glomerulonephritis that occurs 10 to 20 days after streptococcal pharyngitis or streptococcal skin infections is characterized by subepithelial deposits [similar to homogenous basal laminar deposits (BLD)]. These do not stain for ICs (165).

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EVIDENCE FOR IMMUNE AND INFLAMMATORY MECHANISMS IN AMD RPE

Choroid

Figure 7 Electron micrograph of dense deposit disease of the retina demonstrating subretinal deposit (box) located between the retinal pigment epithelium (RPE) and its basement membrane. Source: From Ref. 172.

Nonspecific Amplification Cascades in Glomerular Diseases Complement deposition plays a major primary role in many glomerular diseases associated with deposits, especially those mediated by antigen-specific ICs. In these disorders, various fragments of the complement cascade, including C3, C5, and others are usually identified within extracellular deposits in association with Ig and acute cellular inflammation (166–168). Complement seems to participate as a secondary amplification mechanism in some glomerular diseases. Type II membranoproliferative glomerulonephritis (or dense deposit disease), is especially relevant to AMD since these patients also develop drusen-like changes in the retina (168–171). Clinically, the retina demonstrates whitish drusen-like changes, and some eyes develop CNV. Histologically, the subretinal deposits appear to be localized between the RPE and its basement membrane (similar to BLD) (Fig. 7). The glomerular deposits are characterized as electron dense linear deposits within the glomerular extracellular matrix, occasionally demonstrating dome-shaped subepithelial “humps” under the podocyte. Complement 3 is present within the deposits, but the presence of other complement proteins, Igs, and fibronectin is highly variable. Systemic complement is usually normal. The source of complement (i.e., locally synthesis or blood-derived) as well as the mechanisms for activation (typical cascades vs. enzymatic cleavage) remain unknown. Finally, oxidants have been implicated as important mediators and amplifiers in progression of renal disease (173).

Direct Evidence for Innate or Antigen-Specific Immune Effectors Direct evidence for the role of immune mechanism in AMD is scant. The best data suggest an important role for macrophage-mediated innate immunity (22,50–58). Investigators have observed that choroidal macrophages appear to be important in the pathogenesis of both early and late AMD. However, macrophage involvement is clearly different than their participation in overt inflammatory disorders characterized by widespread cellular infiltration. In early AMD, macrophages have been detected along the choriocapillaris-side of Bruch’s membrane underlying areas of thick deposits. Processes from choroidal monocytes have been noted to insert into Bruch’s membrane deposits, presumably for the purpose of scavenging debris. The identity of these cells is uncertain, but they seem to lack typical phagocytic vacuoles and express human leukocyte antigen DR, suggesting that the cells may represent DC or nonactivated macrophages (22). In late AMD, macrophages and giant cells have been observed around choroidal neovascular membranes (CNVM) and are numerous in excised CNVM, suggesting a role in promoting choroidal angiogenesis (50,53,174). Also, macrophages are present underlying zones of geographic atrophy, suggesting a role in RPE or endothelial death (52). These observations imply a potential pathogenic role for cytokines, chemical mediators, MMPs, mitogens or angiogenic factors released by macrophages from the choroid. In support of this concept, numerous investigators have demonstrated that macrophage-derived cytokines (especially TNF-a) induce major functional and morphological changes in RPE cells (175–179). Further, macrophage involvement may be underestimated in AMD. Choroidal macrophages are often difficult to detect by routine histopathology in noninflammatory disorders because they typically acquire much flattened profiles. Finally, evidence from several recent clinical trials has shown a benefit from intravitreal corticosteroid therapy in the treatment of CNV in AMD patients (180,181). Corticosteroids are potent modulators of macrophage function and these studies suggest that more research should explore the therapeutic potential of nonspecific anti-inflammatory therapy in AMD. Evidence for antigen-specific immunity has not been described in AMD. The possible contribution of antibody-dependent mechanisms is suggested by recent understanding of the mechanism for CAR (see next section below). In AMD, one group has identified IgG and MAC association with RPE overlying drusen

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(182). However, another study has identified only antibody light chains within drusen, but not the presence of associated heavy chain to indicate an intact Ig molecule (22). Lymphocytes, especially T cells, have been identified within some CNV (53). It remains unknown if these cells are recruited as part of bystander activation or are responding to antigen-specific immunity. However, bystander recruitment of T cells occurs in many other forms of pathological neovascularization and wound healing. Nonspecific amplification mechanisms may also play a role in AMD. Recently, several groups have identified complement components in drusen (22,182). Fragments of C5 and the MAC were identified in most specimens, and C3 was present in some. The activation pathway remains unknown. The RPE express specific and nonspecific complement inhibitors such as decay accelerating factor and vitronectin to suggest intrinsic defense mechanisms to prevent against complementmediated injury (183).

Ocular Immune and Inflammatory Disorders Resulting in Atrophic Retinal Degeneration or CNV Ocular Histoplasmosis Syndrome OHS may represent a condition to suggest a role for infection-triggered immunity as a mechanism for RPE injury and CNV formation. The syndrome is presumed to be induced by the inhalation of live histoplasmosis capsulatum, which infects the lung and hilar lymph nodes (184). In some patients, systemic dissemination of the organism occurs, including into the choroid, but the organism is rapidly recognized and killed by the immune response. According to data from a primate model, the acute phase of immune response can induce clinically detectable, small multifocal creamy lesions in the deep retina and choroid caused by localized choriocapillaris inflammation mediated by CD4 T cells (presumably delayed hypersensitivity) (185,186). However, many other areas of active choroidal inflammation are clinically not apparent. Ultimately the overlying RPE become detectable as atrophic “histo spots.” Chronic persistent low grade inflammation apparently triggers CNV formation (187,188). Additionally, many other forms of chronic chorioretinitis are also associated with RPE atrophy and CNV formation, and some of these may represent occult infection of the choroid or RPE with virus or other infectious agents (189). The role of infection in AMD remains entirely speculative. Although it is unlikely that histoplasmosis contributes to AMD, trapping of antigens related to other common organisms conceivably could occur. Based on analogies to the role of infection

in fibrous plaque progression, investigation of possible contributions from choroidal endothelial infection with chlamydia or CMV might be informative. Finally, as new unusual infectious agents, such as prions, are being discovered, the potential role of retinal or RPE infection in AMD should at least be considered.

Complement Activation in AMD CFH is a single polypeptide chain plasma glycoprotein of 155 kDa size that is found in the plasma at a concentration of 110–615 mg/mL as well as in multiple tissues (190). The structure of CFH is composed of 20 repetitive units of 60 amino acids so-called short consensus repeats (SCRs) (Fig. 10). CFH binds principally to C3b and accelerates the decay of the alternative pathway D3-convertase and participates as a cofactor for the factor-I–mediated proteolytic inactivation of C3b (190). Interestingly, it is the binding of CFH to sialic residues on the cell surface which is critical to its ability to inhibit C3b. CFH also binds to other multiple residues within various bacteria. While the primary site of synthesis is the liver, multiple extrahepatic sites of synthesis have been demonstrated including within lymphocytes, fibroblasts, endothelial cells, neurons, and glial cells (192). Recently CFH has also been shown to be produced by the RPE/choroid complex (193) and abundant CFH is present in both choroid and outer retina of patients with AMD (193,194). The function of the protein is to prevent inadvertent complement activation in all tissues. Multiple studies have confirmed the association of mutations with the CFH gene and an increased risk of AMD (194–202). Of the many mutations, a tyrosine to histidine amino acid shift at residue 402 has been the most consistent finding. This amino acid shift occurs within SCR 7, a position which important because of binding both to heparin residues and CRP and also to various bacterial components specifically those from Streptococcus pyogenes, Borrelia burgdorferi, Borrelia afzellii, and Candida albincans (Fig. 8) (203,204). This is interesting because of the recent demonstration of C. pneumoniae remnants found in CNV pathology specimens suggesting a link between acquired infection, interaction with CFH and CNV formation (205). The idea that altered activity of CFH may allow unbridled activation of the complement thereby leading to various stages of AMD has been supported by laboratory experiments. Complement 3 deposition has been shown in a laser induced CNV model and its depletion in knockout animals prevents CNV from forming (206). In addition, MAC deposition was also demonstrated and its inhibition also prevented experimental CNV (206) while the absence of receptors for C3a and C5a also reduced CNV formation. The role of other inflammatory mediators which associate with

2: IMMUNOLOGY OF AGE-RELATED MACULAR DEGENERATION

C3b

CRP Heparin

Heparin C3b

Sialic acid Heparin C3b

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 S. Pyogenes C. Albincans B. Burgdorferi

Figure 8 Schematic of the structure of complement factor H demonstrating the 20 tandem repeats of short consensus repeats (SCR). The SCR 7 is highlighted because of the high prevalence of mutations at the tyrosine 402 residue within that domain which might affect binding to the various structures outlined. Abbreviations: CRP, C-reactive protein.

CFH is also now being explored. For example, recently, high levels of CRP have been demonstrated in the choroid of patients with a homozygous 402 CFH mutation (207). New information suggests that the alternative pathway for complement activation may be the most critical method for CNV formation (207). The possibility of inadvertent activation of complement in the study of an AMD microenvironment was shown in-culture with photoactivation of A2E, a portion of lipofuscin that accumulated in RPE cells, can activate C3 (19). Bioactive fragments of C3a and C3b have been demonstrated in drusen of patients with AMD (208).

IMMUNE MECHANISMS IN AMD: FINAL QUESTIONS AND FUTURE DIRECTIONS Is the Response to Injury Hypothesis Applicable to ARMD? As discussed above, the response to injury hypothesis has become one of the central paradigms for the pathogenesis of atherosclerosis, AD, and glomerulosclerosis. The response to injury paradigm proposes that pathological features of degenerative diseases can be explained by exaggerated or abnormal cellular reparative responses induced by exposure to chronic, recurrent injurious stimuli. Both genetic and physiologic factors can contribute to injury or repair. This chapter has focussed on the physiologic role of innate immunity, antigen-specific immunity and immune amplification systems as potential triggers of injury and as modulators of abnormal repair. In terms of AMD, response to injury is implicit in pathogenic models that propose a role for various injurious stimuli, such as oxidants, lipofuscin cytotoxicty and other factors. Injury stimuli relevant to other systemic diseases associated with AMD have not been carefully evaluated, including hyperlipidemia,

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oxidized lipoproteins, hormonal changes associated with aging or hypertension (209). Presumably, photoreceptors, RPE, choricapillaris endothelium and/or choroidal pericytes may all be relevant targets. However, to exploit the full power of the response to injury paradigm, AMD investigators must more precisely delineate the relevant cellular responses to injury in order to explain the specific pathological changes in AMD. Cellular repair responses are manifested by a wide spectrum, ranging from transient metabolic changes to cell death (210,211). The appropriate cellular response must be matched to a specific pathological change. For example, analysis of programmed cell death in response to lethal injury is relevant to the understanding of geographic atrophy of the RPE (212). However, it is unlikely that analysis of cell death will explain the formation of sub RPE deposits, recruitment of macrophages or CNV formation. RPE can react to nonlethal injury by many responses relevant to deposit formation, including by extruding patches of cell membranes and cytosol (i.e., blebs) (211), by altering the synthesis of collagen, matrix MMPs and other matrix molecules, by increasing production of chemotactic signals or angiogenic factors, and many other responses (213). These other specific responses need to be correlated with specific injury stimuli. Recent studies of RPE injury responses may serve as an example how immunity can induce deposits or promote abnormal repair. RPE can be injured by myeloperoxidase-mediated lipid peroxidation of the cell membrane, which represents a physiologically relevant macrophage-derived oxidative stimulus. Such oxidant-injured RPE undergo significant blebbing of cell membrane (Fig. 9), cytosol,

RPE

Blebs

RPE

Figure 9 Image of retinal pigment epithelial (RPE) cells in-culture exhibiting extensive cell membrane blebbing following sublethal oxidative injury.

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and organelles, but without activation of programmed cell death or nuclear fragmentation. However, oxidant injured cells downregulate another response, matrix MMPs production (Cousins and Csaky, personal communication). Irrespective of the stimulus, accumulation of blebs can lead to deposit formation which, in turn, can activate an immune response which interferes with healthy repair. For example, under certain conditions, blebs might serve as an innate stimulus for recruitment and activation of reparative macrophages (see below). In addition to innate immunity, blebbing might cause desequestration of intracellular antigens to provide a target for antigen-specific immunity or blebs might provide a substrate for nonspecific activation of complement or other amplification systems, as described for atherosclerosis, AD, and glomerular diseases. Response to injury may also be relevant to formation of CNV. All blood vessels, including the choriocapillaris, must continuously repair endothelial and vessel wall damage following injury. Increasing evidence suggests that aging is associated with dysregulated vascular repair after injury (113,214,215). For example, abnormal and exaggerated repair following acute vascular injury is a well-defined mechanism for accelerated restenosis after coronary artery angioplasty in older patients (196). A similar phenomenon may exist in the choroid in terms of CNV. Aging mice exposed to laser injury of the choroid develop much larger CNV than do younger animals. Investigation of differences between younger and aging individuals in terms of activation of immune and reparative responses after vascular injury may be an important topic for research in AMD (Cousins and Csaky, personal communication).

What Is the Role of Choroidal Monocytes? Although the presence of choroidal monocytes in AMD has been established, their identity and function remains uncertain. If analogies with atherosclerosis are correct, then these cells are probably scavenging macrophages recruited to remove lipids and deposits within Bruch’s membrane. As is the case for atherosclerosis or AD, the function of scavenging monocytes in AMD can be protective or pathogenic depending upon the activation status (Fig. 10). Scavenging macrophages probably can remove sub RPE deposits safely and assist in healthy repair of Bruch’s membrane. However, activation into reparative macrophages may result in the production of mediators that can damage Bruch’s membrane, injure choriocapillaris and promote CNV. Recently, it has been shown that blood monocytes from some patients with AMD can become stimulated into reparative macrophages after

BLD

M

MO

N AD

AMD

Figure 10 Electron micrographs from a patient with Alzheimer’s disease (AD) and age-related macular degeneration (AMD) indicating similar appearance of scavenging of cellular debris by immune cells. AD shows microglia (M) with cellular processes (asterisks) around extracellular debris (arrows) from a dying neuronal cell (N) while figure AMD indicates digestion of basal laminar deposits (BLD) by subretinal macrophage (MO). Abbreviation: MO, subretinal macrophage. Source: From Refs. 52, 191.

phagocytosis with RPE-derived cell debris and membrane blebs. Analysis of interaction between sub RPE deposits and scavenging macrophages may address this topic.

Does Antigen-Specific Immunity Participate in the Progression of AMD? If the identification of DC in association with drusen is confirmed, this observation implies an entirely different function for choroidal monocytes and suggests a role for T cell-mediated antigen-specific immunity. DC lack scavenging and inflammatory effector functions. However, they might sample antigens within drusen (perhaps inappropriately desequestered or chemically modified proteins), and then might initiate the afferent phase of the immune response by presenting these antigens to T lymphocytes within lymphoid tissues. The participation of antibody-dependent immune responses in AMD is intriguing but remains speculative. Typically, B cells require exposure to the natural, intact antigen within lymph nodes to become activated, not exposure to antigens that were processed and presented by DC. It is possible, but unlikely, that intact retina-specific antigens in AMD can diffuse into the choroid, gain access to lymphoid compartments and trigger a “de novo” retina-specific immune antibody response. Nevertheless, as in CAR, circulating antibodies, perhaps produced in response to immunity triggered elsewhere in the body by molecular mimicry, desequestration, or neoantigen formation, might cross-react with similar antigens trapped within subretinal deposits or expressed within ocular cells. A similar mechanism has been described in atherosclerosis. Finally, investigators should explore the idea that protective immunization may improve the clearance of extracellular deposits, as observed in AD and atherosclerosis.

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Do Inflammatory Amplification Cascades Contribute to Injury or Progression? Ongoing research indicates that various cytokines and growth factors are crucial in the development of AMD complications. However, the contribution of macrophages, mast cells or lymphocytes as potential sources for these factors in AMD remains unexplored. The identification of terminal complement components C5–C9 (i.e., MAC) within drusen and near RPE is intriguing and suggests that complement-mediated cell injury may play a role in AMD. However, investigators must demonstrate intact MAC in association with endothelial or RPE cell membranes as well as local activation of these complement fragments. Further, a clear mechanism must be established to link this injury stimulus to relevant cellular responses involved in deposit formation. The role of immune and nonimmune derived oxidants as potential injury stimuli and amplifiers of injury responses was briefly described above and reviewed elsewhere. Evidence to demonstrate an age-related loss of protective antioxidants in AMD patients is controversial, but is currently being evaluated by several groups (216). Can Anti-inflammatory Therapy Play a Role in the Treatment of AMD? Recently, intravitreal corticosteroids were found to be partially effective in improving vision and decreasing exudation due to CNV, suggesting the possibility that anti-inflammatory therapy might be effective in AMD treatment. Clinical medicine is on the verge of a revolution in anti-inflammatory therapy based on drugs and other therapeutics developed from knowledge of the molecular basis of effector mechanisms and amplification systems described above. Perhaps some of these new approaches may be relevant to the treatment of AMD. One anti-inflammatory approach might be to block the upregulation of amplification systems discussed above. For instance, various complement inhibitors are in development, especially inhibitors of C3 activation and the MAC formation (217). The potential role for vitronectin as an inhibitor of MAC was mentioned above (183). The role of specific antioxidant agents, rather than generic antioxidant cocktails, must also be better evaluated. Relatively high doses of the lipophilic antioxidant vitamin E, which inserts into the plasma membrane to quench cell membrane lipid peroxidation, has been shown to diminish complications of myocardial infarction and stoke, in part by diminishing secondary inflammation-mediated oxidant injury (218). However, recent research suggests that dosing and bioavailability will be important issues for the eye. For

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example, exogenous supplementation with soluble antioxidants, such as glutathione, may be inadequate because the compound is not taken up by RPE (218). Effective treatment may require the use of agents that upregulate intracellular synthesis. Biosynthesis of PGs by immune or parenchymal cells also results in the generation of oxidants. Accordingly, the use of nonsteroidal anti-inflammatory agents slow the progression of other chronic neurodegenerative disorders, although they have not been evaluated in AMD (219). Another anti-inflammatory approach is to block mast cell or macrophage recruitment to the choroid, or inhibit their local activation. In this regard, blockade of endothelial cell adhesion molecule expression to prevent the recruitment of macrophages or other leukocytes to injured sites, is an active area of research (220). Pentoxyphylline has been shown to diminish macrophage adhesiveness and cell activation in arthritis, suggesting a rationale for use in AMD (221). The mast cell inhibitor, tranilast, was observed to be effective in experimental CNV (74). These approaches might not only target macrophage-derived cytokines, like TNF-a, which can injure RPE or endothelium, but also to RPE-derived cytokines, like MCP-1 which serve to activate macrophages. Finally, should an infectious etiology be determined, specific anti-infective agents for chlamydia or CMV might be considered.

SUMMARY POINTS Biology of the Immune Response in AMD &

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&

&

Innate immunity & Activation by retinal or choroidal injury or infection Antigen specific immunity & Normal activation by foreign antigens & Aberrant activation in AMD by molecular mimicry, antigen desequestration, neoantigen formation, or antigen trapping Amplification mechanisms & Complement, cytokines, oxidants, others Immune cells & Monocytes/macrophages, DC, mast cells, lymphocytes Innate immunity, antigen-specific immunity, and amplification cascades contribute to pathogenesis of atherosclerosis, AD, and glomerular diseases Innate immunity, antigen-specific immunity, and amplification cascades may contribute to AMD

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197. Seddon JM, George S, Rosner B, Klein ML. CFH gene variant, Y402H, and smoking, body mass index, environmental associations with advanced age-related macular degeneration. Hum Hered 2006; 61(3):157–65. 198. Sepp T, Khan JC, Thurlby DA, et al. Complement factor H variant Y402H is a major risk determinant for geographic atrophy and choroidal neovascularization in smokers and nonsmokers. Invest Ophthalmol Vis Sci 2006; 47(2):536–40. 199. Klein RJ, Zeiss C, Chew EY, et al. Complement factor H polymorphism in age-related macular degeneration. Science 2005; 308(5720):385–9. 200. Haines JL, Hauser MA, Schmidt S, et al. Complement factor H variant increases the risk of age-related macular degeneration. Science 2005; 308(5720):419–21. 201. Edwards AO, Ritter R, III, Abel KJ, et al. Complement factor H polymorphism and age-related macular degeneration. Science 2005; 308(5720):421–4. 202. Shastry BS. Further support for the common variants in complement factor H (Y402H) and LOC387715 (A69S) genes as major risk factors for the exudative agerelated macular degeneration. Ophthalmologica 2006; 220(5):291–5. 203. Zipfel PF, Skerka C. Complement factor H and related proteins: an expanding family of complement-regulatory proteins? Immunol Today 1994; 15(3):121–6. 204. Zipfel PF, Skerka C, Hellwage J, et al. Factor H family proteins: on complement, microbes and human diseases. Biochem Soc Trans 2002; 30(Pt 6):971–8. 205. Kalayoglu MV, Bula D, Arroyo J, et al. Identification of Chlamydia pneumoniae within human choroidal neovascular membranes secondary to age-related macular degeneration. Graefes Arch Clin Exp Ophthalmol 2005; 243(11):1080–90. 206. Bora PS, Sohn JH, Cruz JM, et al. Role of complement and complement membrane attack complex in laserinduced choroidal neovascularization. J Immunol 2005; 174(1):491–7. 207. Johnson PT, Betts KE, Radeke MJ, et al. Individuals homozygous for the age-related macular degeneration risk-conferring variant of complement factor H have elevated levels of CRP in the choroid. Proc Natl Acad Sci USA 2006; 103(46):17456–61.

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208. Nozaki M, Raisler BJ, Sakurai E, et al. Drusen complement components C3a and C5a promote choroidal neovascularization. Proc Natl Acad Sci USA 2006; 103(7):2328–33. 209. Kain HL, Reuter U. Release of lysosomal protease from retinal pigment epithelium and fibroblasts during mechanical stresses. Graefes Arch Clin Exp Ophthalmol 1995; 233:236–43. 210. Malorni W, Donelli G. Cell death. General features and morphological aspects. Ann N Y Acad Sci 1992; 663:218–33. 211. Malorni W, Iosi F, Mirabelli F, Bellomo G. Cytoskeleton as a target in menadione-induced oxidative stress in cultured mammalian cells: alterations underlying surface bleb formation. Chem Biol Interact 1991; 80:217–36. 212. Adler R, Curcio C, Hicks D, Price D, Wong F. Cell death in age-related macular degeneration. Mol Vis 1999; 5:31. 213. Campochiaro PA, Soloway P, Ryan SJ, Miller JW. The pathogenesis of choroidal neovascularization in patients with age-related macular degeneration. Mol Vis 1999; 5:34. 214. Bilato C, Crow MT. Atherosclerosis and the vascular biology of aging. Aging (Milano) 1996; 8:221–34. 215. Spagnoli LG, Sambuy Y, Palmieri G, Mauriello A. Agerelated modulation of vascular smooth muscle cells proliferation following arterial wall damage. Artery 1985; 13:187–98. 216. Cai J, Nelson KC, Wu M, Sternberg P, Jr., Jones DP. Oxidative damage and protection of the RPE. Prog Retin Eye Res 2000; 19:205–21. 217. Makrides SC. Therapeutic inhibition of the complement system. Pharmacol Rev 1998; 50:59–87. 218. Rimm EB, Stampfer MJ. Antioxidants for vascular disease. Med Clin North Am 2000; 84:239–49. 219. Hull M, Lieb K, Fiebich BL. Anti-inflammatory drugs: a hope for Alzheimer’s disease? Expert Opin Investig Drugs 2000; 9:671–83. 220. Simon LS, Yocum D. New and future drug therapies for rheumatoid arthritis. Rheumatology (Oxford) 2000; 39(Suppl. 1):36–42. 221. Graninger W, Wenisch C. Pentoxifylline in severe inflammatory response syndrome. J Cardiovasc Pharmacol 1995; 25(Suppl. 2):S134–8.

3 Genetics of Age-Related Macular Degeneration Jennifer R. Chao and Amani A. Fawzi

Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A.

Jennifer I. Lim

University of Illinois School of Medicine, Department of Ophthalmology, Eye and Ear Infirmary, UIC Eye Center, Chicago, Illinois, U.S.A.

INTRODUCTION Age-related macular degeneration (AMD), like Alzheimer’s disease and atherosclerosis, is a lateonset degenerative disease. The multifactorial nature of these diseases has made the search for absolute genetic contributions challenging. However, recent advances in the study of genetic associations with AMD have provided evidence that there may be strong genetic contributions to this disease. The goal of recent genetic analysis in AMD is to identify mutations and polymorphic variants that affect the lifetime risk of developing the disease. The three main methods of finding genes contributing to AMD are candidate gene screening, linkage mapping, and case-association studies (1). Candidate gene screening involves evaluating genes responsible for phenotypically similar diseases and genes involved in pathways thought to contribute to the pathophysiology of AMD. Linkage analysis searches for chromosomal regions that cosegregate with the AMD disease trait by evaluating the segregation of chromosomal regions in families with AMD. Finally, case–control association studies find genetic variants of genes that are associated with AMD by evaluating differences in frequency between those variants in persons with AMD and their matched controls. All of the above methods have resulted in our current understanding of the genetics of AMD.

EARLY SUSPICIONS: TWIN AND FAMILIAL AGGREGATION STUDIES The search for a genetic etiology of AMD was initially sparked by twin studies that found familial clustering of AMD cases. The first report of genetically tested monozygotic twins affected by AMD showed high concordance in both degree of disease severity and onset of vision loss (2). The concordance among monozygotic twins may have been explained by similarities in environmental factors; however, the

twin studies provided a strong rationale to pursue further study of the potential genetic etiology of AMD. Klein and coworkers reported on nine twin pairs (seven confirmed monozygotic) examined between 1984 and 1993 (3). Of the nine twin pairs, whose environmental factors such as diet, geographic background, and medical history were similar, eight pairs demonstrated similar fundus appearances and incidence of visual impairment. In 1995, Meyers reported a statistically different concordance of AMD between monozygotic twin pairs (100%, 25 of 25) and dizygotic twin pairs (42%, 5 of 12), further emphasizing the importance of a genetic etiology (4). Two other studies confirmed this finding, demonstrating a significantly higher concordance of AMD in monozygotic versus dizygotic twin pairs (5,6). A Scandinaviau study demonstrated a significantly greater concordance of AMD (pZ0.0279) among monozygotic twin pairs (90%) as opposed to that of twin/spouse pairs (70.2%) (7). Most recently, Seddon and colleagues evaluated 840 elderly male twins (210 monozygotic and 181 dizygotic), out of which 509 were diagnosed with maculopathy and 106 had evidence of severe disease (8). They reported heritability estimates of 46% for the overall five-step grade assignment (based on the Clinical Age-Related Eye Disease Study), 0.67% for intermediate and advanced disease (grades 3–5), and 0.71% for advanced disease only (grades 4 and 5). It has been suggested from these data that advanced disease may have higher heritability. The heritability estimates of the Seddon report are similar to that described in an earlier twin study by Hammond and colleagues of 45% (5). The latter study found that the most heritable phenotypes were soft drusen R125 mm (57%) and hard drusen R20 mm (81%), although it should be noted that none of the study participants demonstrated lesions consistent with advanced AMD. Other groups have studied the concordance rates among persons with AMD and their non-twin

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siblings, offspring, and spouses (9–14). Klaver et al. examined the first-degree relatives (siblings and offspring) of 87 persons with late AMD and 135 control subjects (9). They reported that the lifetime risk estimate of late AMD for first-degree relatives of patients was 50% [95% confidence interval (CI)Z26– 73], while that of non-affected controls was 12% (95% CIZ2.6–6.8). The risk for first-degree relatives was significantly higher among relatives of affected individuals (p!0.001). These data confirmed the findings reported by Seddon et al., who also found that the prevalence of AMD was significantly higher among first-degree relatives (mostly siblings) of patients with exudative AMD when compared with those of unaffected controls (26.9% and 11.6% respectively). Together, these studies served to initiate and underscore the strong role of genetics and heritability in the etiology of AMD.

HEREDITARY RETINAL DYSTROPHIES: CANDIDATE GENES Genes examined for their role in AMD have included those associated with phenotypically similar diseases. The genes responsible for monogenic hereditary macular dystrophies such as Stargardt disease, Stargardt-like macular dystrophy (STGD3), autosomal dominant macular dystrophy (adMD), Sorsby fundus dystrophy, Best macular dystrophy, Butterfly dystrophy, and Doyne honeycomb retinal dystrophy (malattia leventinese) have been well characterized (15–20). Several of the genes implicated in these diseases have been considered candidate genes for AMD.

ABCR ABCR (also ABCA4 or STGD1) is a gene that encodes a photoreceptor-specific ATP-binding cassette transporter of retinaldehyde. ABCR is defective in autosomal recessive Stargardt disease, autosomal recessive cone–rod dystrophy, and autosomal recessive retinitis pigmentosa (16). Abnormal function of the transporter, caused by mutations in the ABCR gene, is characterized by accumulation of a major lipofuscin fluorophore (A2-E) in the retinal pigment epithelium (RPE), making this gene attractive as a candidate gene for AMD (21). An early study identified heterozygous mutations of ABCR in 16% of AMD patients (22). Subsequently, two specific sequence changes in the ABCR gene, G1961E and D2177N, were found to predict a three- and fivefold increased risk of AMD respectively (23). Further research indicated that in a cohort of families, the AMD-affected relatives of Stargardt disease patients were more likely to be carriers of the pathogenic Stargardt alleles (24). Sixteen specific

ABCR mutations were found to cause to functional abnormalities of the transporter protein, including ATP-binding and ATPase activities (24). Additionally, it is believed that ABCR gene variants may be associated with AMD in at least six families (25,26). One study of a group of unrelated multiplex cases of exudative AMD reported finding six heterozygous missense changes in the ABCR gene. Using familial segregation analysis, Souied et al. were able to associate two of the codon changes with familial AMD (25). In contrast, other studies did not find an association of specific ABCR allelic variants to AMD (27–30). The allelic variants, G1961E and D2177N, from the initial report by Allikmets et al. were later evaluated in individuals of Somali ancestry, and the allelic frequencies were not significantly different between those with AMD and controls (31). Studies evaluating other allelic variations of the ABCR gene in participants of Japanese, Chinese, and German origin have also reported no significant difference between allelic variants in participants (32–34). The disparate findings encountered in these studies can be difficult to reconcile. A possible consideration is the unique prevalence of ABCR polymorphisms in each study population. For example, the most common ABCR allele associated with Stargardt disease in patients of European origin was found to be quite common in normal controls of Somali origin (31,35). Moreover, there is a large spectrum in allelic variations of the ABCR gene in the populations as a whole, making the differentiation between diseasecausing mutations and nonpathogenic polymorphisms difficult.

ELOVL4 A five-base pair deletion in the gene located on chromosome 6q14, ELOVL4, has been reported to be closely associated with two forms of macular dystrophy, STGD3 and adMD, in two families (17). The clinical findings of STGD3 and adMD are similar to the atrophic form of AMD. The normal gene product, ELOVL4, is thought to be a retinal photoreceptor-specific protein that functions in the biosynthesis of very long-chain fatty acids. A study examining ELOVL4 polymorphisms in unrelated individuals with predominantly atrophic AMD revealed eight variants in the coding region; however, none of them were significantly associated with AMD susceptibility (36). Interestingly, a later case–control study of predominantly exudative AMD in familial cases observed that a variant of the ELOVL4 gene previously described by Ayyagari et al., Met299Val, was significantly associated with AMD (37). The discrepancy in these findings may be due to differences in the type of AMD examined (atrophic versus exudative) or in the

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sampling of study participants (sporadic versus familial).

Other Genes: VMD2, TIMP3, Peripherin/RDS, Fibulin 3/EFEMP1 A variety of genes responsible for phenotypically similar, monogenic macular dystrophies have had less promising associations with AMD (15,19,38–48). Mutations in VMD2 (Best macular dystrophy), TIMP3 (Sorsby fundus dystrophy), peripherin/RDS (butterfly dystrophy), and Fibulin 3/EFEMP1 (Doyne honeycomb retinal dystrophy or malattia leventinese) have been studied and were not been found to be significantly associated with AMD (38,39,42,43,45–48). PATHOGENESIS OF AMD: CANDIDATE GENES Multiple studies support the hypothesis that drusen are products of inflammatory responses to RPE injury and are composed of proteins similar to deposits seen in diseases where inflammatory and oxidative damage play a significant role (49,50). Analysis of the molecular components of drusen has revealed evidence of localized inflammation and oxidative injury (49–54). Protein components found in drusen include complement factors, apolipoproteins B and E, immunoglobulins, MHC class II antigens, human leukocyte antigen (HLA) DR, cholesterol esters, phospholipids, and carboxyethyl pyrrole protein adducts (53–56). Systemic inflammatory markers, such as C-reactive protein and interleukin-6, have been shown to be independent risk factors for AMD and progression of the disease (57,58). Drusen observed in the disease, membranoproliferative glomerulonephritis type II, believed to result from a complementmediated immune system dysfunction, are immunohistochemically similar to drusen found in AMD (59). Finally, there is a distinct similarity between proteins contained in drusen in AMD and extracellular deposits seen in atherosclerosis (49). Thus, multiple genes derived from inflammatory and oxidative pathways, RPE basement membrane proteins, and extracellular deposits of atherosclerotic disease, amyloidosis, and Alzheimer’s disease have been considered candidate genes in the pathogenesis of AMD.

Genes with Possible Association to AMD Extracellular Matrix: Fibulin, CST3, and MMP-9 Due to the association of a Fibulin 3 mutation to heritable drusen and the significant role played in basement membrane structure by the Fibulin family of proteins, Fibulins 1–6 were evaluated for their association with AMD (47,60,61). While allelic variations in the Fibulin 1–4 genes could not conclusively

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be associated with AMD (47), a missense mutation in Fibulin 5 was noted to be present in 1.7% of participants with AMD and absent in controls (47). Fibulin 5 is thought to connect cellular surface receptors and extracellular elastic fibers, and thus play a key role in the link between the RPE and Bruch’s membrane (60). An allelic variation in exon 104 of Fibulin 6 (or HEMICENTIN-1) results in a non-conserved amino acid substitution, Gln5345Arg in a large AMD family cohort, which segregates exclusively with the presumptive disease haplotype (61). However, multiple subsequent studies have not been able to confirm this finding (37,41,47,62–64). In a few studies, the allelic variant was not detected in any of the participants with AMD or in controls (41,62,64). The Gln5345Arg variant was found in 2 of 402 patients and in 1 of 263 controls in a study by Stone et al., and there was no significant association between the allelic variation and AMD (47). Additionally, in the study population where the Tyr402His variant of complement factor H (CFH) was found to be significantly associated with AMD, the Gln5345Arg variant of HEMICENTIN-1 did not demonstrate allelic association to AMD in the discovery sample (63). Nevertheless, it is possible that the association of this allelic variant of Fibulin 6 (HEMICENTIN-1) and AMD is unique to the family in which it was originally reported, but other allelic variations in HEMICENTIN-1 have to be explored for significant associations in a broader population of affected individuals (61). Two other genes thought to play a role in the functioning of the RPE and extracellular matrix components are CST3 and MMP-9 (65,66). The CST3 gene encodes for cystatin C, a cysteine protease inhibitor that regulates the activity of cathepsin S, a protease with regulatory functions in the RPE (67). One study of German AMD patients revealed an increased susceptibility to the disease in individuals homozygous for the recessive allele, CST B (66). The second gene, MMP-9, encodes the matrix metalloproteinase-9 protein, and was found to have a polymorphic allele in its promoter region that was significantly associated to exudative AMD in an Italian population (65).

Inflammation: CX3CR1, TLR4, and HLA Genes encoding inflammatory factors have been studied, including polymorphisms in the CX3CR1, tolllike receptor 4 (TLR4), and HLA genes (41,62,68–71) . Two single-nucleotide polymorphisms (SNPs), V249I and T280M, in the CX3CR1gene, which encodes a chemokine receptor expressed in the eye, were screened and found to have a significantly higher prevalence among persons with AMD when compared with controls (70). Additional analysis of ocular tissue with evidence of advanced AMD revealed an even higher

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prevalence of the T280M allele compared with those with a clinical AMD diagnosis. TLR4 was examined as a possible candidate gene since it is located in a chromosomal region with strong linkage to AMD, 9q32–33 (41,62,69). Additionally, the gene product is thought to function as a key mediator in pro-inflammatory signaling pathways, regulation of cholesterol efflux, and the phagocytosis of photoreceptor outer segments by the RPE (71). Two allelic variants were screened, D299G and T399I, in 667 unrelated AMD patients and 439 controls. The study demonstrated an increased risk of AMD in D299G allele carriers. Interestingly, the authors examined the effects of the TLR4 allelic variant in combination with the ABCA1 R219K and the APOE-34 alleles, and they reported a fourfold increased risk of AMD in carriers who exhibit the D299G TLR4 and R219K ABCA1 alleles but not the APOE-34 allele (71). This latter finding supports a polygenic etiology of AMD. Principal allele groups of HLA genes, including HLA class I-A, -B, -Cw and Class II DRB1 and DQB1, were examined for their relationship to AMD (68). HLA antigens are expressed in eyes, and HLA DR has been located immunohistochemically in both hard and soft drusen (49). The principal allele groups were first screened in a cohort of 100 AMD cases and 92 controls. Alleles with p!0.1 on initial typing were then screened in an additional 100 AMD cases and 100 controls. Logistic regression for all possible pairwise HLA combinations was performed, along with Bonferroni corrections. The results were a positive correlation of allele Cw*0701 with AMD, whereas the B*4001 and DRB1*1301 alleles were negatively associated (68).

Lipid Metabolism: APOE and PON1 APOE encodes apolipoprotein E, a protein that plays a central role in lipid transport and distribution in the peripheral and central nervous system (72). It has been found in soft drusen and basal laminar deposits, making it a good candidate gene for AMD (49,73). The gene has three alleles (32, 33, and 35), each coding different protein isoforms, with the 33 allele being most common. Several case–control studies conducted in The Netherlands, Italy, France, United States, Australia, and Iceland have reported that the 34 allele may confer a protective effect against AMD (74–79). However, there appeared to be no significant association of the 34 allele with AMD in other case– control studies conducted in Japan, Hong Kong, and the United States (37,80–83). Separately, the APOE allele, 32, has been suggested to confer an increased risk of developing AMD (74,76,78); however, other studies have found no significant association (37,80,82,83). The disparate results of these studies may be a result of the variable baseline distribution

of the 32, 33, and 35 alleles in different ethnic populations (84). Additionally, the studies differed greatly in the severity and type of AMD examined, which varied from early stages of the disease to advanced atrophic or exudative AMD. One recent study conducted in the United States examined the combined effect of APOE genotypes and smoking history (85). The study was based on the premise of the authors’ earlier work that the 34 allele reduces the risk of AMD while the 32 allele increases it (78). The more recent analysis suggested that among participants with exudative AMD (nZ260), smoking conferred the greatest risk in 32 allele carriers with odds ratio (OR) of 1.9 for 34 carriers (pZ0.11), 2.2 for 33 homozygotes (pZ0.007), and 4.6 for 32 carriers (pZ0.001) when compared with non-smoking 33 homozygote controls (85). They conclude that smoking likely poses a greater risk factor in 32 allele carriers compared with other APOE alleles’ carriers. PON1 encodes paraoxonase, a calcium-dependent glycoprotein that prevents low-density lipoprotein oxidation. It contains two polymorphic sites, Gly192Arg (A/B) and Leu54Met (L/M), which give rise to different protein products of varying enzymatic activities. Ikeda et al. reported a higher frequency of the BB and LL genotypes in participants with exudative AMD when compared with controls (52.8% vs. 35% with pZ0.0127 and 91.7% vs. 77.1% with pZ0.009 respectively) in unrelated Japanese participants (72 exudative AMD and 140 age- and gender-matched controls) (86). Later studies in the populations of Anglo-Celtic and Northern Irish descent did not find a significant association of allelic variation to either exudative or atrophic AMD (87,88). The association of the PON1 alleles and exudative AMD may therefore be population specific.

Other Genes: LPR6, VEGF, VLDLR, ACE, MnSOD, and EPHX1 Several candidate genes have been studied in both family-based and case–control cohorts. Low-density lipoprotein receptor-related protein 6 and vascular endothelial growth factor showed linkage and allelic association in both family-based and case–control data sets (89). In the same study, the gene encoding very lowdensity lipoprotein receptor (VLDLR) did not demonstrate significant linkage, but the family-based result was nominally significant and case–control results were significant (89). The ambiguous VLDLR association results echo those previously reported by Conley et al., where VLDLR was significant only for the allelebased test but not the linkage analysis (37). Angiotensin-converting enzyme (ACE) was thought to be a good candidate gene for neovascular AMD because an Alu polymorphism had been associated with proliferative diabetic retinopathy. Hamdi

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et al. examined the association of the Alu polymorphism in patients with neovascular/wet AMD (nZ86), atrophic AMD (nZ87), and age-matched controls (nZ 189). Individuals carrying the Alu element insertion (Alu C/C) in the gene were 4.5 times more frequent in the control population than in the dry/atrophic AMD patients (OR 5, pZ0.004), while the frequency did not differ significantly from the neovascular/wet AMD population (OR 1.4, pZ0.4). The Alu polymorphism in the ACE gene was therefore believed to confer protection against dry AMD (90). However, two later multiple candidate gene studies did not find a significant association between the Alu polymorphism in the ACE gene (DCP1) and either atrophic or neovascular AMD (37,89). Other studies have sought to evaluate the role of oxidative damage in AMD (88,91). The genetic polymorphisms of four genes, cytochrome P-450 (CYP) 1A1, glutathione-S-transferase (GPX1), microsomal epoxide hydrolase (EPHX1), and manganese superoxide dismutase (MnSOD), were evaluated in 102 Japanese participants with exudative AMD and in 200 controls (91). The results suggested a strong association between a valine/alanine polymorphism of the MnSOD gene and exudative AMD. A weaker association to an exon-3 polymorphism of the EPHX1 gene was also noted. In contrast, a subsequent candidate gene analysis of patients with exudative AMD in at least one eye found no significant association with any of the genes evaluated in the earlier study by Kimura et al., including MnSOD and multiple CYP genes (including CYP1A1, CYP1A2, CYP2E1, and CYP2D6), EPHX1, and GPX1 (88).

Genes Not Associated with AMD IMPG2 IMPG2 is a gene encoding the retinal interphotoreceptor matrix proteoglycan IMP200, which is thought to be integral to the interaction of RPE and photoreceptors, specifically regulating the turnover of photoreceptor outer segments. Kuehn et al. screened 92 individuals with AMD and 92 controls and reported three coding and one intronic polymorphism in IMPG2. However, none of the allelic variants were present at a significantly different frequency in the AMD versus control participants (92). GPR75 Rhodopsin is a G-protein coupled receptor, and when it became known that the gene GPR75 encoded another G-protein coupled receptor expressed in the retina, it was thought to be a possible candidate gene for AMD. However, in a screening of 535 AMD and 252 control cases, only six allelic variants were found once in single AMD patients (93). These rare mutations were deemed unlikely to be significantly

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associated with AMD pathology in the majority of affected patients.

LAMC1, LAMC2, and LAMB3 The LAMC1, LAMC2, and LAMB3 genes were selected as positional and functional candidate genes. They are located in a region on chromosome 1q25–31 that has been strongly linked to AMD (41,62,69,82,94–98). The genes code for laminins, which are extracellular matrix proteins located in the basal lamina of the RPE, Bruch’s membrane, and choriocapillaris (64). A total of 69 sequence variants, 25 in coding regions, were detected in the three laminin genes. However, none were found to be at a significantly higher frequency in the AMD population when compared with the controls (64). In a separate study, polymorphisms in LAMC1 and LAMC2 were also not significantly different between the affected individuals and control cases (37). Multicandidate Gene Screening Several large candidate genetic screening studies have searched for genes with significant associations to AMD (37,88,89). Esfandiary and colleagues examined genes involved in the detoxification of reactive oxygen species, including CYP1A1, CYP1A2, CYP2E1, CYP2D6, EPHX1, MnSOD, AhR, NAT2, CAT, GPX1, PON1, and ADPRT1. Their study population was comprised of 94 persons with exudative AMD and 95 controls from Northern Ireland (88). The study screened a number of SNPs for 12 genes, but none of them revealed a significant association with AMD (88). Conley et al. examined a second category of genes involved in fatty acid biosynthesis and inflammatory pathways (37). They reported a significant association for allelic variants of CFH and ELOVL4 as described earlier; however, no association was noted for other genes, including GLRX2, OCLM, PRELP, RGS16, TGFb2, ApoH, and ITGB4. This study also did not find an association with ACE and APOE, and these genes are described elsewhere in detail. Finally, Haines and colleagues conducted a large screening study of family-based and case–control data sets, and evaluated several genes, of which a-2 macroglobulin (A2M), creatine kinase (CKB), ACE (DCP1), interleukin-1a (IL1A), and microsomal glutathione-S-transferase 1 (MGST1) were found to have no significant association with AMD (89). LINKAGE MAPPING Linkage mapping has provided a wealth of possible genetic associations to AMD. The multifactorial nature of the disease is reflected in the number and variety of chromosomal associations detected. Genetic markers covering several human chromosomes have been

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tested for segregation in multiple combined subsets of AMD families. Genetic loci purportedly linked to AMD include 1q25–31, 2q14.3, 2q31.2–2q32.3, 2p21, 3p13, 4q32, 4p16, 5p, 5q34, 6q25.3, 6q14, 8, 9p24, 9q31, 9q33, 10q26, 12q13, 12q23, 14q13, 15q21, 16p12, 17q25, 18p11, 19p, 20q13, 22q, and X (41,62,69,95–100). Once a chromosomal region has been identified, finer mapping narrows the search for possible candidate genes. Two chromosomal loci that are most consistently associated with AMD are discussed here. One of the first disease loci mapped by linkage analysis to AMD was a 9-cM region of chromosome 1q25–31 (gene symbol, ARMD1) (101). The association was demonstrated in a family who demonstrated a predominantly dry phenotype of AMD. While the disease segregated as an autosomal dominant trait in this family, two individuals were identified as having the disease allele but not the phenotype, i.e., the allele was non-penetrant. At this time, the Stargardt disease gene (ABCR) was known to be located near this new disease locus at chromosome 1p21, but linkage analysis excluded it as an AMD disease locus in this family. Since then, this region of chromosome 1 has been the most commonly found site to segregate with AMD, both dry and exudative types, in genome-wide scans involving large numbers (34–530) of families (41,62,69,82,94–98). Interestingly, one study of 70 families did not demonstrate linkage to chromosome 1q (102). Nevertheless, genes located in this region were viewed as possible candidate genes for AMD, including CFH, HEMICENTIN-1 (or Fibulin 6), LAMC1, LAMC2, and LAMB3 (37,61,64). These genes are discussed in detail elsewhere in this chapter. Another locus consistently associated with AMD was found during an early full genome-wide scan of 225 families with both wet and dry forms of AMD, revealing a strong linkage to chromosome 10 (99). Further evidence from independent studies of different family cohorts narrowed the region to chromosome 10q26 (69,96), and follow-up studies confirmed this finding, including a recent metaanalysis of genome scans (41,94,98,102). Three genes in this locus have since been implicated in AMD, including PLEKA1, LOC387715, and PRSS11 (103).

RECENT ALLELE ASSOCIATION STUDIES Complement Factor H Three research groups, each working from distinct cohorts, reported that a common allelic variant of the CFH gene was found at a significantly higher frequency in affected individuals when compared with controls (63,104,105). The AMD participants, all Americans of European origin, exhibited a range of clinical findings, including extensive drusen,

geographic atrophy, and neovascular complications (63,105). The studies utilized SNPs and haplotype blocks to test for associations among AMD cases, and they independently found a strong signal at a CFH SNP (rs1061170). Thus, they were able to map a specific chromosomal location to the disease manifested in their study populations (106). The CFH polymorphism is located in exon 9, and the allelic variant results in the replacement of tyrosine with histidine at amino acid 402 (Tyr402His). The tyrosine to histidine substitution is located within a region of the CFH protein (SCR7) that contains overlapping binding sites for C-reactive protein, heparin, and M protein (107). This substitution is thought to alter the level of inflammation in the outer retina. An in-depth discussion of the role of CFH can be found in Chapter 2. The initial studies report that persons heterozygous (carrying a single copy) for the histidine allele in the Tyr402His polymorphism have a 2.45- to 4.6-fold increased risk of AMD, while individuals homozygous for the histidine allele have a 5.57- to 7.4-fold increased likelihood compared with those who do not carry the allele. The attributable risk of AMD due to the histidine allele is estimated to be approximately 50% in their study populations (63,104,105). Further case–control association studies involving individuals of European descent (American, Icelandic, and French) manifesting a wide clinical range of AMD, including drusen only, geographic atrophy, and/or neovascular, were subsequently published. They independently confirmed the finding that the Tyr402His variant was significantly associated with AMD (37,103,108–111). An incidence study of the Rotterdam population in The Netherlands indicated that the presence of two histidine alleles (homozygous) increased the risk of developing AMD by 12.5 times, and that smoking, in combination with being homozygous for the allele, increased the risk 34-fold (smoking alone increased the risk by 3.3 times) (112). The particularly high risk for AMD in smokers who are homozygous for the Tyr402His allele was confirmed by another study involving participants from England (113). A prospective study confirmed the association between the Tyr402His variant and an increased risk of AMD, reporting an estimated population-attributable risk for CFH Tyr402His of 25% (114). In contrast to studies involving persons of European descent, reports of AMD in persons of other ethnicities describe a more tenuous association with the Tyr402His polymorphism. A case–control study of Japanese individuals with exudative AMD reported that affected patients were at no greater frequency of having the histidine allele in the

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Tyr402His polymorphism than unaffected individuals (115). Another recent study reported wide ethnic variations in the frequencies of the Tyr402His allele in control populations: African Americans 0.35G0.04, Caucasians 0.34G0.03, Somalis 0.34G0.03, Hispanics 0.17G0.03, and Japanese 0.07G0.02 (116). Because the frequency of the Tyr402His polymorphism is not proportionate to the frequency of AMD in their respective populations, it has been suggested that the Tyr402His polymorphism may not play as integral a role in AMD of some ethnic groups as in those of European descent (116). Finally, a study evaluating the Tyr402His polymorphism in Latinos suggests that the allele is not a major risk factor for AMD in this population (117). However, it is important to note that in contrast to the original CFH studies, the large majority of affected individuals in the latter study demonstrated only early AMD. There may be some association between the Tyr402His allele and the severity of AMD. Postel et al. recently reported that the polymorphism is associated with an increased risk of developing grades 3–5 AMD, but not grades 1 and 2 (118). Together, these studies indicate that the relative importance of the CFH polymorphism in AMD is in part dictated by both the particular ethnic population in question and the severity of AMD exhibited in the population.

Factor B and Complement Component 2 Given the significant association of the CFH polymorphism with AMD, Gold et al. screened for polymorphisms in two other regulatory genes in the same pathway, factor B (BF) and complement component 2 (C2) (119). They report a statistically significant common risk haplotype (H1) and two protective haplotypes, the L9H variant of BF and the E318D variant of C2, as well as a variant in intron 10 of C2 and the R32Q variant of BF. The latter two combination of haplotypes confer a significantly reduced risk of AMD, with an OR of 0.45 and 0.36 respectively (119). Chromosome 10q26: PLEKHA1, LOC387715, PRSS11, and HTRA1 Jakobsdottir and colleagues had previously identified a strong association of chromosome 10q26 and AMD, and they conducted a follow-up study in order to identify candidate genes in that region (103). Three overlying genes, PLEKHA1, LOC387715, and PRSS11, and their respective non-synonymous SNPs were identified. Genotyping yielded a highly significant association between PLEKHA1/LOC387715 and AMD, with the SNPs in PLEKHA1 being more highly associated to AMD than those of LOC387715.

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PLEKHA1 encodes the protein TAPP1, which is an activator of lymphocytes, and PLEKHA1 transcripts are expressed in the central macula. They report that the association of either a single or double copy of the high-risk allele in the PLEKHA1/LOC387715 locus accounts for an OR of 5.0 and an attributable risk of 57% in their study population (103). Additionally, the study notes a weaker association of the GRK5/RGS10 locus with AMD. All of these associations were independent of the association of AMD with the Tyr402His allele of CFH. Another study reported a significant association of the polymorphism Ala69Ser at LOC387715 in two case–control cohorts of German descent (120). This polymorphism was associated with AMD, independent of the Tyr402His CFH polymorphism. In fact, the contribution of the two genetic alleles were additive. A third study confirmed the role of the Ala69Ser polymorphism of the LOC287715 gene as another major AMD-susceptibility allele (121). The adjusted population-attributable risk percentage estimates reported in their study were 36% for LOC387715 and 43% for CFH, with a significantly higher risk of AMD when coupled with cigarette smoking. Most recently, Yang and associates found that a SNP in the promoter region of the HTRA1 gene, rs11200638, conferred a population-attributable risk of 49.3% in a Caucasian cohort of persons with AMD in Utah (122). They demonstrated HRTA1 expression in drusen from eyes of patients with AMD by labeling with HTRA1 antibody. Additionally, they report elevated expression of HRTA1 mRNA and protein in the RPE and lymphocytes of AMD patients. HRTA1 appears to regulate the degradation of extracellular matrix proteoglycans and facilitates the access of other degrading matrix enzymes, such as matrix metalloproteinases and collagenases. This study noted an allele dosage effect, where persons homozygous for the allele have an increased risk [OR 7.29 (3.18, 16.74)] over those who are heterozygous [OR 1.83 (1.25, 2.68)]. An estimated population-attributable risk from a joint model with the CFH Tyr402His allele (i.e., a risk allele at either locus) is 71.4%. DeWan and colleagues concurrently reported an association of the identical SNP from the HTRA1 promoter in a Chinese population with wet AMD, thus confirming the significant role of this allelic variation in AMD populations of various ethnicities (123).

CONCLUSION The recent discovery of specific allelic variants of major disease genes has come after many years of searching for the genetic etiology of AMD. The early twin and familial aggregation studies strongly suggested that the disease was heritable, and this

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was soon followed by linkage analyses implicating large regions of chromosomes and candidate gene screenings describing possible culprit disease genes. Only recently, case-association studies, in conjunction with the completion of the human genome project, have enabled the identification of SNPs in major disease genes, including CFH, BF/C2, PLEKHA1, LOC387715, and HTRA1. Despite the discovery of major disease loci, our understanding of the fundamental nature of AMD etiology is still lacking. Current evidence still suggests the disease to be multifactorial, shaped by multiple genes as well as environmental influences. For example, several studies have demonstrated an additive effect in the population risk of having more than one allelic variant from a major disease locus. Additionally, there appears to be an increased risk of developing AMD when both the disease allele and certain environmental factors, such as cigarette smoking, are present. Moreover, the varying effects of the major disease loci on AMD development across different ethnic groups underscore the multifactorial nature of the disease. Future progress in studying the etiology of AMD not only includes the discovery of other major disease loci throughout the genome, but also the protein products of identified allelic variants. SNPs that result in coding changes need to be studied for their effect on protein function. An understanding of this step downstream from genetic coding is fundamental to providing important confirmation of the significance of these genetic variations. The identification of genetic allelic variants has opened a window into the study of the pathophysiologic mechanisms of AMD disease development and also disease intervention.

SUMMARY POINTS &

&

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Twin studies and familial aggregation studies provided the earliest evidence for the role of heritability in AMD. Candidate genes were derived from phenotypically similar diseases and from genes involved in pathways thought to contribute to the pathophysiology of AMD. Linkage mapping, which searches for chromosomal regions that cosegregate with the AMD disease trait, and multicandidate gene screening have implicated multiple genetic loci in almost every chromosome, including 1q25–31, 2q14.3, 2q31.2–2q32.3, 2p21, 3p13, 4q32, 4p16, 5p, 5q34, 6q25.3, 6q14, 8, 9p24, 9q31, 9q33, 10q26, 12q13, 12q23, 14q13, 15q21, 16p12, 17q25, 18p11, 19p, 20q13, 22q, and X.

&

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Recent case-association studies have identified allelic variations of several genes thought to be major risk loci for AMD. These are CFH, BF/C2, PLEKHA1, LOC387715, and HTRA1. The etiology of AMD is multifactorial, involving the presence of multiple disease loci as well as environmental factors.

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69. Majewski J, Schultz DW, Weleber RG, et al. Age-related macular degeneration—a genome scan in extended families. Am J Hum Genet 2003; 73(3):540–50. 70. Tuo J, Smith BC, Bojanowski CM, et al. The involvement of sequence variation and expression of CX3CR1 in the pathogenesis of age-related macular degeneration. Faseb J 2004; 18(11):1297–9. 71. Zareparsi S, Buraczynska M, Branham KE, et al. Toll-like receptor 4 variant D299G is associated with susceptibility to age-related macular degeneration. Hum Mol Genet 2005; 14(11):1449–55. 72. Ignatius MJ, Gebicke-Harter PJ, Skene JH, et al. Expression of apolipoprotein E during nerve degeneration and regeneration. Proc Natl Acad Sci USA 1986; 83(4):1125–9. 73. Anderson DH, Ozaki S, Nealon M, et al. Local cellular sources of apolipoprotein E in the human retina and retinal pigmented epithelium: implications for the process of drusen formation. Am J Ophthalmol 2001; 131(6):767–81. 74. Baird PN, Guida E, Chu DT, Vu HT, Guymer RH. The epsilon2 and epsilon4 alleles of the apolipoprotein gene are associated with age-related macular degeneration. Invest Ophthalmol Vis Sci 2004; 45(5):1311–5. 75. Klaver CC, Kliffen M, van Duijn CM, et al. Genetic association of apolipoprotein E with age-related macular degeneration. Am J Hum Genet 1998; 63(1):200–6. 76. Simonelli F, Margaglione M, Testa F, et al. Apolipoprotein E polymorphisms in age-related macular degeneration in an Italian population. Ophthalmic Res 2001; 33(6):325–8. 77. Souied EH, Benlian P, Amouyel P, et al. The epsilon4 allele of the apolipoprotein E gene as a potential protective factor for exudative age-related macular degeneration. Am J Ophthalmol 1998; 125(3):353–9. 78. Schmidt S, Klaver C, Saunders A, et al. A pooled casecontrol study of the apolipoprotein E (APOE) gene in agerelated maculopathy. Ophthalmic Genet 2002; 23(4):209–23. 79. Zareparsi S, Reddick AC, Branham KE, et al. Association of apolipoprotein E alleles with susceptibility to agerelated macular degeneration in a large cohort from a single center. Invest Ophthalmol Vis Sci 2004; 45(5):1306–10. 80. Gotoh N, Kuroiwa S, Kikuchi T, et al. Apolipoprotein E polymorphisms in Japanese patients with polypoidal choroidal vasculopathy and exudative age-related macular degeneration. Am J Ophthalmol 2004; 138(4):567–73. 81. Pang CP, Baum L, Chan WM, Lau TC, Poon PM, Lam DS. The apolipoprotein E epsilon4 allele is unlikely to be a major risk factor of age-related macular degeneration in Chinese. Ophthalmologica 2000; 214(4):289–91. 82. Schultz DW, Klein ML, Humpert A, et al. Lack of an association of apolipoprotein E gene polymorphisms with familial age-related macular degeneration. Arch Ophthalmol 2003; 121(5):679–83. 83. Wong TY, Shankar A, Klein R, et al. Apolipoprotein E gene and early age-related maculopathy: the Atherosclerosis Risk in Communities Study. Ophthalmology 2006; 113(2):255–9. 84. Corbo RM, Scacchi R. Apolipoprotein E (APOE) allele distribution in the world. Is APOE*4 a ’thrifty’ allele? Ann Hum Genet 1999; 63(Pt 4):301–10. 85. Schmidt S, Haines JL, Postel EA, et al. Joint effects of smoking history and APOE genotypes in age-related macular degeneration. Mol Vis 2005; 11:941–9. 86. Ikeda T, Obayashi H, Hasegawa G, et al. Paraoxonase gene polymorphisms and plasma oxidized low-density

3:

87.

88.

89.

90.

91.

92.

93.

94. 95.

96.

97.

98.

99. 100.

101.

102.

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103. Jakobsdottir J, Conley YP, Weeks DE, Mah TS, Ferrell RE, Gorin MB. Susceptibility genes for age-related maculopathy on chromosome 10q26. Am J Hum Genet 2005; 77(3):389–407. 104. Haines JL, Hauser MA, Schmidt S, et al. Complement factor H variant increases the risk of age-related macular degeneration. Science 2005; 308(5720):419–21. 105. Klein RJ, Zeiss C, Chew EY, et al. Complement factor H polymorphism in age-related macular degeneration. Science 2005; 308(5720):385–9. 106. Clark AG. The role of haplotypes in candidate gene studies. Genet Epidemiol 2004; 27(4):321–33. 107. Giannakis E, Jokiranta TS, Male DA, et al. A common site within factor H SCR 7 responsible for binding heparin, C-reactive protein and streptococcal M protein. Eur J Immunol 2003; 33(4):962–9. 108. Hageman GS, Anderson DH, Johnson LV, et al. A common haplotype in the complement regulatory gene factor H (HF1/CFH) predisposes individuals to age-related macular degeneration. Proc Natl Acad Sci USA 2005; 102(20):7227–32. 109. Magnusson KP, Duan S, Sigurdsson H, et al. CFH Y402H confers similar risk of soft drusen and both forms of advanced AMD. PLoS Med 2006; 3(1):e5. 110. Souied EH, Leveziel N, Richard F, et al. Y402H complement factor H polymorphism associated with exudative agerelated macular degeneration in the French population. Mol Vis 2005; 11:1135–40. 111. Zareparsi S, Branham KE, Li M, et al. Strong association of the Y402H variant in complement factor H at 1q32 with susceptibility to age-related macular degeneration. Am J Hum Genet 2005; 77(1):149–53. 112. Despriet DD, Klaver CC, Witteman JC, et al. Complement factor H polymorphism, complement activators, and risk of age-related macular degeneration. JAMA 2006; 296(3):301–9. 113. Sepp T, Khan JC, Thurlby DA, et al. Complement factor H variant Y402H is a major risk determinant for geographic atrophy and choroidal neovascularization in smokers and nonsmokers. Invest Ophthalmol Vis Sci 2006; 47(2):536–40. 114. Schaumberg DA, Christen WG, Kozlowski P, Miller DT, Ridker PM, Zee RY. A prospective assessment of the Y402H variant in complement factor H, genetic variants in C-reactive protein, and risk of age-related macular degeneration. Invest Ophthalmol Vis Sci 2006; 47(6):2336–40. 115. Gotoh N, Yamada R, Hiratani H, et al. No association between complement factor H gene polymorphism and exudative age-related macular degeneration in Japanese. Hum Genet 2006; 120(1):139–43. 116. Grassi MA, Fingert JH, Scheetz TE, et al. Ethnic variation in AMD-associated complement factor H polymorphism p.Tyr402His. Hum Mutat 2006; 27(9):921–5. 117. Tedeschi-Blok N, Buckley J, Varma R, Triche TJ, Hinton DR. Population-based study of early age-related macular degeneration: role of the complement factor H Y402H polymorphism in bilateral, but not unilateral disease. Ophthalmology 2007; 114(1):99–103. 118. Postel EA, Agarwal A, Caldwell J, et al. Complement factor H increases risk for atrophic age-related macular degeneration. Ophthalmology 2006; 113(9):1504–7. 119. Gold B, Merriam JE, Zernant J, et al. Variation in factor B (BF) and complement component 2 (C2) genes is associated with age-related macular degeneration. Nat Genet 2006; 38(4):458–62. 120. Rivera A, Fisher SA, Fritsche LG, et al. Hypothetical LOC387715 is a second major susceptibility gene for age-

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related macular degeneration, contributing independently of complement factor H to disease risk. Hum Mol Genet 2005; 14(21):3227–36. 121. Schmidt S, Hauser MA, Scott WK, et al. Cigarette smoking strongly modifies the association of LOC387715 and agerelated macular degeneration. Am J Hum Genet 2006; 78(5):852–64.

122. Yang Z, Camp NJ, Sun H, et al. A variant of the HRTA1 gene increases susceptibility to age-related macular degeneration. Science 2006; 314(5801):992–3. 123. DeWan A, Liu M, Hartman S, et al. HTRA1 promoter polymorphism in wet age-related macular degeneration. Science 2006; 314(5801):989–92.

4 Risk Factors for Age-Related Macular Degeneration and Choroidal Neovascularization Kah-Guan Au Eong

Department of Ophthalmology and Visual Sciences, Alexandra Hospital, Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, The Eye Institute, National Healthcare Group, Jurong Medical Center, Singapore Eye Research Institute, and Department of Ophthalmology, Tan Tock Seng Hospital, Singapore

Bakthavatsalu Maheshwar

Department of Ophthalmology and Visual Sciences, Alexandra Hospital and Jurong Medical Center, Singapore

Stephen Beatty

Department of Ophthalmology, Waterford Regional Hospital and Department of Chemical and Life Sciences, Waterford Institute of Technology, Waterford, Ireland

Julia A. Haller

The Wilmer Ophthalmological Institute, Johns Hopkins University School of Medicine, Johns Hopkins Hospital, Baltimore, Maryland, U.S.A.

INTRODUCTION Age-related macular degeneration (AMD), the most frequent cause of blindness among individuals R55 years in developed countries, is a major public health problem (1–5). Using estimated rates from a metaanalysis of recent population-based studies in the United States, Australia, and Europe, and the 2000 U.S. census data, it has been estimated that the overall prevalence of late AMD (neovascular AMD and/or geographic atrophy) in the U.S. population R40 years is 1.47% [95% confidence interval (CI), 1.38–1.55] (1). This translates to 1.75 million citizens having the most severe forms of the disease. The prevalence of AMD increases dramatically with age such that in white women R80 years, more than 15% have neovascular AMD and/or geographic atrophy. More than 7 million individuals have drusen measuring 125 mm or larger and are, therefore, at substantial risk of developing late AMD. Owing to the progressive increase in the life expectancy and the proportion of elderly persons in the population, it is estimated that the number of persons having late AMD will increase by 50% to 2.95 million in 2020 (1). The increasing impact of AMD, coupled with the limited therapy available for its treatment, has led many investigators to search for factors that could be modified to prevent the onset or alter the natural course and prognosis of AMD. The identification and modification of risk factors has the potential for greater

public health impact on the morbidity from AMD than the few treatment modalities at hand.

EPIDEMIOLOGIC STUDIES ON RISK FACTORS FOR AMD Despite the high prevalence and public health importance of AMD, its pathogenesis remains unknown. The types of epidemiologic studies that have explored AMD risk factors are case–control, cross-sectional, and prospective cohort studies. Case–control studies [e.g., the Eye Disease Case–Control Study (6,7)] have compared the frequency of possible risk factors among individuals with AMD to a cohort of control patients without the disease. Cross-sectional studies [e.g., the Framingham Eye Study (3) and the National Health and Nutrition Examination Survey I (NHANES-I) (8)] have correlated eye examination data with sociodemographic, medical, and other variables collected as part of larger studies. Prospective cohort studies [e.g., the Physicians’ Health Study (9)] collect data in a group of subjects over time. Tables 1–3 show some case–control, cross-sectional, and prospective cohort studies that have explored risk factors for AMD.

PROBLEMS AND LIMITATIONS OF EPIDEMIOLOGIC STUDIES ON RISK FACTORS FOR AMD There may be different causative factors that damage the macula and result in common clinical (Text continues on page 51.)

Syracuse, New York Baltimore, Maryland Boston, Massachusetts and Fort Myers, Florida Miami, Florida Sydney, Australia Baltimore, Maryland; Boston, Massachusetts; Chicago, Illinois; Milwaukee, Wisconsin; and New York, New York/Eye Disease Case–Control Study London, England Beaver Dam, Wisconsin/Beaver Dam Eye Study Rotterdam, The Netherlands/ Rotterdam Study Newcastle, Australia Kanto district, Japan France/FRANCE-DMLA Study Valencia, Spain New York, New York/Age-related Macular Degeneration Risk Factors Study Palo Alto, California Boston, Massachusetts and Portland, Oregon Counties of Norfolk, Suffolk, Cambridgeshire, and Buckinghamshire, United Kingdom Four counties in North Carolina, California, Maryland, and Pennsylvania/Cardiovascular Health Study

Delaney and Oates (11)

Hyman et al. (1983) (12)

Weiter et al. (1985) (13)

Blumenkranz et al. (1986) (14)

Tsang et al. (1992) (15)

Eye Disease Case–Control Study Group (1992, 1993) (6,7), Seddon et al. (1994) (16)

Mares-Perlman et al. (1995) (18)

Tamakoshi et al. (1997) (21)

Chaine et al. (1998) (22)

Belda et al. (1998) (23)

Hyman et al. (2000) (24)

Kalayoglu et al. (2003) (25)

Seddon et al. (26)

Khan et al. (2006) (27)

Abbreviation: AMD, age-related macular degeneration.

McGwin et al. (2006) (28)

Darzins et al. (1997) (20)

Vingerling et al. (1995) (19)

Holz et al. (1994) (17)

Jersey City, New Jersey

Maltzman et al. (1979) (10)

Place/name of study

Nested case–control within a population-based cohort

Case–control

Case–control

Case–control

Case–control

Case–control

Case–control

Case–control

Case–control

Nested case–control within a population-based cohort Nested case–control within a population-based cohort

Case–control

Case–control

Case–control

Case–control

Case–control

Case–control

Case–control

Case–control

Design

Some Case–Control Studies that Have Investigated the Risk Factors of AMD

Author(s) (year)

Table 1

390 cases 2365 controls

409 cases 286 controls 52 male cases 82 male controls 1844 cases 1844 controls 25 cases 15 controls 182 neovascular AMD cases 227 nonneovascular AMD cases 235 controls 25 cases 18 controls 747 cases with varying degrees of AMD 183 controls 435 cases 280 controls

102 controls 167 cases 167 controls 59 female cases 295 female controls

101 cases

30 cases 30 controls 50 cases 50 controls 162 cases 175 controls 650 cases 363 controls 26 cases 23 controls 80 cases 86 controls 421 cases 615 controls

Study population Method of diagnosis

Fundus photography

Fundus photography

Fundus photography

Clinical examination

Fundus photography

Clinical examination

Fundus photography for cases Clinical examination for controls Fundus photography

Fundus photography

Fundus photography

Clinical examination and fundus photography for cases Clinical examination for controls Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Clinical examination and fundus photography Fundus photography

Clinical examination

Risk factors studied

Use of cholesterol-lowering medications

Smoking

Chlamydia pneumoniae infection C-reactive protein

Various personal and environmental factors Serum vitamin E and zinc, sunlight exposure Systemic hypertension, cardiovascular disease, and cholesterol intake

Cigarette smoking

Sunlight exposure

Reproductive and related factors

Antioxidants

Iris color

Various personal and environmental factors Various personal and environmental factors Various personal and environmental factors Iris color and fundus pigmentation Various personal and environmental factors Various personal and environmental factors Various personal and environmental factors

48 AU EONG ET AL.

Vingerling et al. (1995) (58,59), Ikram et al. (2005) (60)

Klein et al. (1992, 1993, 1994) (47–52), Cruickshanks et al. (1993, 2001) (53,54), Heiba et al. (1994) (55), MaresPerlman et al. (1995) (56) Schachat et al. (1995) (57)

West et al. (1994) (46)

Vinding (1989, 1990, 1992) (43–45)

West et al. (1989) (39), Bressler et al. (1989) (40), Taylor et al. (1990, 1992) (41,42)

Klein and Klein (1982) (35), Goldberg et al. (1988) (8), Liu et al. (1989) (36), Obisesan et al. (1998) (37) Gibson et al. (1986) (38)

Kahn et al. (1977) (29,30), Leibowitz et al. (1980) (3), Sperduto et al. (1980, 1981, 1986) (31–33) Martinez et al. (1982) (34)

Barbados, West Indies/ Barbados Eye Study Rotterdam, The Netherlands/Rotterdam Study

Baltimore, Maryland and Washington, DC/Baltimore Longitudinal Study of Aging Beaver Dam, Wisconsin/ Beaver Dam Eye Study

Melton Mowbray, England/Melton Mowbray Eye Study Somerset County, Maryland and lower Dorchester County, Maryland/ Chesapeake Bay Watermen Study Copenhagen, Denmark

Population-based crosssectional Population-based crosssectional

Population-based crosssectional

Cross-sectional

Population-based crosssectional

Occupational cross-sectional

Population-based crosssectional

Population-based crosssectional Population-based crosssectional

Gisborne, New Zealand United States/National Health and Nutritional Examination Survey I

Population-based crosssectional

Design

Framingham, Massachusetts/ Framingham Eye Study

Place/name of study

3444 participants aged 40–84 years 6251 participants aged 55–98 years

924 survivors from the Copenhagen City Heart Study aged 60–79 years 916 participants of the Baltimore Longitudinal Study of Aging aged R40 years 4926 participants aged 43–84 years

782 male watermen aged R30 years

529 participants aged R75 years

2631 survivors of the Framingham Heart Study cohort, mean ageZ65.3 years 481 participants aged R65 years 3082 participants aged R45 years

Study populationa

Some Cross-Sectional Studies that Have Investigated the Risk Factors of Age-Related Macular Degeneration

Author(s) (year)

Table 2

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Clinical examination

Clinical examination

Clinical examination

Method of diagnosis

(Continued)

Various personal and environmental factors Various personal and environmental factors

Various personal and environmental factors

Antioxidants

Various personal and environmental factors

Age and sunlight exposure

Various personal and environmental factors

Various personal and environmental factors

Age and sex

Various personal and environmental factors

Risk factors studied

4: RISK FACTORS FOR AMD AND CHOROIDAL NEOVASCULARIZATION

49

a

Victoria, Australia/Visual Impairment Project Fukuoka City, Kyushu, Japan/Hisayama Study Los Angeles, California/Los Angeles Latino Eye Study State of Andhra Pradesh, India/Andhra Pradesh Eye Disease Study

4744 participants aged R40 years 1482 participants aged R50 years 5875 participants aged R40 years 3723 participants aged 40– 102 years

8270 participants aged R40 years

5308 participants aged R40 years 11,532 participants aged 48–72 years

Population-based crosssectional Population-based crosssectional

Complex, multistage area probability sample design (certain groups, e.g., Americans R60 years, Mexican Americans, and non-Hispanic blacks were sampled at a higher probability than other persons) Population-based crosssectional Population-based crosssectional Population-based crosssectional Population-based crosssectional

500 participants aged R70 years 2196 participants aged R60 years

Population-based crosssectional Population-based crosssectional

Oulu County, Northern Finland Sete, France/Pathologies Oculaires Liees a l’Age Study East Baltimore, Maryland/ Baltimore Eye Study Forsyth County, North Carolina; city of Jackson, Mississippi; Minneapolis, Minnesota; and Washington County, Maryland/Atherosclerosis Risk in Communities Study United States/National Health and Nutritional Examination Survey III

3654 participants aged R49 years

Study populationa

Population-based crosssectional

Design

Blue Mountains region, Sydney, Australia/Blue Mountains Eye Study

The sample size may vary slightly among the different reports.

Fraser-Bell et al. (2005, 2006) (84,85) Krishnaiah et al. (2005) (86)

Miyazaki et al. (83)

McCarty et al. (2001) (82)

Klein et al. (1995, 1999) (80,81)

Klein et al. (1999) (79)

Delcourt et al. (1998, 1999) (74–76), Defay et al. (2004) (77) Friedman et al. (1999) (78)

Mitchell et al. (1995, 1996, 1998, 1999, 2002) (61–65), Attebo et al. (1996) (4), Smith et al. (1997, 1998, 1999, 2000) (66–70), Wang et al. (1998, 1999) (71,72) Hirvela et al. (1996) (73)

Place/name of study

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Fundus photography

Method of diagnosis

Some Cross-Sectional Studies that Have Investigated the Risk Factors of Age-Related Macular Degeneration (Continued )

Author(s) (year)

Table 2

Various personal and environmental factors Various personal and environmental factors Various personal and environmental factors Various personal and environmental factors

Various sociodemographic, ocular, medical, and environmental factors

Various personal and environmental factors

Age and race

Various personal and environmental factors Various personal and environmental factors

Various personal and environmental factors

Risk factors studied

50 AU EONG ET AL.

4:

Table 3

51

Some Prospective Cohort Studies that Have Investigated the Risk Factors of Age-Related Macular Degeneration

Author(s) (year)

Place/name of study

Moss et al. (1996) (87), Beaver Dam, Klein et al. (1997, Wisconsin/Beaver 1998) (88–90) Dam Eye Study Seddon et al. (91) 11 states in the United States/Nurses’ Health Study Christen et al. (1996, United States/ 1999) (9,92), Ajani Physicians’ Health et al. (1999) (93), Study Schaumberg et al. (2001) (94) Cho et al. (2000, 2001, United States/Nurses’ 2004) (95–97) Health Study and Health Professionals Follow-Up Study Klein et al. (2006) (98)

a

RISK FACTORS FOR AMD AND CHOROIDAL NEOVASCULARIZATION

Six communities in United States/MultiEthnic Study of Atherosclerosis

Design Population-based prospective cohort Prospective cohort Prospective cohort

Prospective cohort

Prospective cohort

Study populationa 3684 participants aged 43–86 years 31,843 female registered nurses aged R50 years 21,157 male physicians aged 40–84 years at baseline 32,764 female registered nurses and 29,488 male health professionals aged R50 years 6166 participants aged 45–85 years

Method of diagnosis

Risk factors studied

Fundus photography

Alcohol consumption, cardiovascular disease risk factors Diagnosis by treating Cigarette smoking ophthalmologists or optometrists Diagnosis by treating Cigarette smoking, ophthalmologists antioxidant vitamin or optometrists supplements, alcohol consumption Diagnosis by treating Intake of alcohol, zinc, ophthalmologists fruits, vegetables, or optometrists vitamins, and carotenoids Fundus photography

Race/ethnicity

The sample size may vary slightly among the different reports.

manifestations that we recognize as AMD. The analysis of risk factors for AMD is inherently difficult because many of them are closely interrelated, e.g., race, ocular pigmentation, and sunlight exposure, or socioeconomic status, smoking, and nutrition. Studying risk factors such as sunlight exposure include challenges in measurement of acute and chronic lifetime exposure and the effect of potential confounding factors such as sun sensitivity and sun-avoidance behavior. In addition, the difficulties in establishing a causal link between a chronic disease and a potential risk factor are magnified for a condition such as AMD because it manifests itself late in life. Additional problems in this circumstance include a long lead time, a possible recall bias, and survivor cohort effects. Despite the extensive past and ongoing research on AMD worldwide, there is currently no universally accepted definition of AMD. Different definitions of early and late signs of AMD have been used in various studies, making direct comparison of the results difficult or impossible (Table 4) (99). The problem is further compounded by differences in methodology used in the various studies. A wide range of different diagnostic tools has been used in different clinical and epidemiologic studies (99). For example, NHANES-I, a population-based study of a sample of the noninstitutionalized U.S. population, relied solely on clinical examinations by multiple independent examiners with varying levels of experience, and standardization of the diagnosis of AMD was uncertain (8,35). Fundus photographs of a subset of the study population were reviewed and discrepancies in the macular gradings

were disclosed (100). The Framingham Eye Study, which has provided the most frequently cited prevalence data on AMD to date, was based mainly on clinical examination and fundus photography was performed only on a small subset of the study population (29). More recent studies have used fundus photography to detect and grade AMD but the details were not always standardized among the studies (40,47,57,61,74). In an effort to standardize disease definition and study methodology, the International Age-related Maculopathy Epidemiological Study Group published in 1995 an international classification and grading system for AMD in the hope of producing a common detection and classification system for epidemiologic studies (99). It defined age-related maculopathy (ARM) to include two alternate late lesions (neovascular maculopathy and geographic atrophy), termed AMD or late ARM, and early lesions (soft or large drusen and retinal pigmentary abnormalities), termed early ARM (Table 5). In this definition, visual acuity is not a criterion for the presence or absence of ARM. This new terminology, however, has not been universally accepted. In this chapter, we will use the more conventional definition of AMD to include the entire spectrum of the disease (i.e., equivalent to ARM in the new terminology). Neovascular AMD and geographic atrophy will be collectively termed late AMD (equivalent to late ARM) and the early lesions of AMD will be termed early AMD (equivalent to early ARM). It is possible that the factors associated with early AMD may be different from those associated with

52 Table 4

AU EONG ET AL.

Definitions of and Age Limits in AMD (ARM) Used in Population-Based Studies

1. Framingham Eye Study (3) An eye was diagnosed as having senile macular degeneration if its visual acuity was 20/30 or worse and the ophthalmologist designated the etiology of changes in the macula or posterior pole as senile Age limits: 52–85 years 2. National Health and Nutrition Eye Study I (8) Age-related macular degeneration: Loss of macular reflex, pigment dispersion and clumping, and drusen associated with visual acuity of 20/25 or worse believed to be due to this disease Age-related disciform macular degeneration: Choroidal hemorrhage and connective-tissue proliferation between RPE and Bruch’s membrane causing an elevation of the foveal retina (this condition should be differentiated from disciform degenerations of other causes, e.g., Histoplasmosis, toxoplasmosis, angioid streaks, and high myopia) Age-related circinate macular degeneration: Perimacular accumulation of lipoid material within the retina Age limits: 1–74 years 3. Gisborne Study (34) Senile macular degeneration. When the visual acuity in the affected eye was 6/9 (20/30) or worse and senile macular degeneration was identified as the probable cause of this visual loss Age limits: R65 years 4. Copenhagen Study (43) AMD. Best-corrected visual (Snellen) acuity (including pinhole improvement) of 6/9 or less, explained by age-related morphologic changes of the macula Atrophic (dry) changes. Disarrangement of the pigment epithelium (atrophy/clustering) and/or a small cluster of small drusen and/or medium drusen and/or large drusen and/or pronounced senile macular choroidal atrophy/sclerosis without general fundus involvement Exudative (wet) changes. Elevation of the neurosensory retina and/or the pigment epithelium and/or hemorrhages, and/or hard exudates and/or fibrovascular tissue Age-related macular changes without visual impairment (AMCW) is defined as similar morphological lesions but without visual deterioration Age limits: 60–80 years 5. Chesapeake Bay Study (40) No specific overall definition Geographic atrophy. An area of well-demarcated atrophy of the RPE in which the overlying retina appeared thin Exudative changes. Choroidal neovascularization, detachments of the RPE, and disciform scarring Grading of AMD in four grades: Grade 4: Geographic atrophy of the RPE or exudative changes Grade 3: Grade 4 or eyes with large or confluent drusen or eyes with focal hyperpigmentation of the RPE Grade 2: Grade 4 or 3 or eyes with many small drusen (R20) within 1500 mm of the foveal center Grade 1: Grade 4, 3, or 2 or eyes with at least five small drusen within 1500 mm of the foveal center or at least 10 small drusen between 1500 and 3000 mm from the foveal center No visual acuity included Age limits: R30 years 6. Beaver Dam Eye Study (47) Early ARM was defined as the absence of signs of late ARM as defined below and as the presence of soft indistinct or reticular drusen or by the presence of any drusen type except hard indistinct, with RPE degeneration or increased retinal pigment in the macular area. Late ARM was defined as the presence of signs of exudative AMD or geographic atrophy The grade assigned for the participant was that of the more severely involved eye No visual acuity included Age limits: 43–86 years 7. Rotterdam Study (58) All ARM changes had to be within a radius of 3000 mm of the foveola. No definition of early ARM, but separate prevalence figures for drusen and RPE hyperpigmentations or hypopigmentations attributable to age-related causes Late ARM (is similar to AMD). The presence of atrophic AMD (well-demarcated area of RPE atrophy with visible choroidal vessels) and/or neovascular AMD (serous and/or hemorrhagic RPE detachment, and/or subretinal neovascular membrane and/or hemorrhage, and/or periretinal fibrous scar) attributable to age-related causes. In a participant, the most severely involved eye was taken for the analysis No visual acuity included Age limits: R55 years Abbreviations: AMD, age-related macular degeneration; ARM, age-related maculopathy; RPE, retinal pigment epithelial. Source: From Ref. 99.

progression to neovascular AMD or geographic atrophy. In addition, although neovascular AMD and geographic atrophy are termed collectively as late AMD (or late ARM), they may have different causes (99). For these

reasons, it may be important to pay attention to the different stages of AMD and to separate the two manifestations of late AMD in epidemiologic studies, as has been done in several recent studies (24,66).

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Table 5

RISK FACTORS FOR AMD AND CHOROIDAL NEOVASCULARIZATION

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Definitions of ARM

ARM is a disorder of the macular area of the retina, most often clinically apparent after 50 years of age, characterized by any of the following primary items, without indication that they are secondary to another disorder (e.g., ocular trauma, retinal detachment, high myopia, chorioretinal infective or inflammatory process, choroidal dystrophy, etc.): † Drusen that are discrete whitish-yellow spots external to the neuroretina or the RPE. They may be soft and confluent, often with indistinct borders Soft distinct drusen have uniform density with sharp edges Soft indistinct drusen have decreasing density from center outwards with fuzzy edges Hard drusen, usually present in eyes with as well as those without ARM, do not of themselves characterize the disorder † Areas of increased pigment or hyperpigmentation (in the outer retina or choroid) associated with drusen † Areas of depigmentation or hypopigmentation of the RPE, most often more sharply demarcated than drusen, without any visibility of choroidal vessels associated with drusen † Late stages of ARM, also called age-related macular degeneration AMD is a later stage of ARM and includes both “dry” and “wet” AMD Dry AMD is also called geographic atrophy and is characterized by: † Any sharply delineated roughly round or oval area of hypopigmentation or depigmentation or apparent absence of the RPE in which choroidal vessels are more visible than in surrounding areas that must be at least 175 mm in diameter on the color slide (using a 308 or 358 camera) Wet AMD is also called “neovascular” AMD, “disciform” AMD, or “exudative” AMD and is characterized by any of the following: † RPE detachment(s), which may be associated with neurosensory retinal detachment, associated with other forms of ARM † Neovascular membrane(s) that may be subretinal or sub-RPE † Scar/glial tissue or fibrin-like deposits that may be epiretinal (with exclusion of idiopathic macular puckers), intraretinal, subretinal, or subpigment epithelial † Subretinal hemorrhages that may be nearly black, bright red, or whitish-yellow and that are not related to other retinal vascular disease. Hemorrhages in the retina (retinal hemorrhages) or breaking through it into the vitreous (vitreous hemorrhages) may also be present Hard exudates (lipids) within the macular area related to any of the above and not to other retinal vascular disease Abbreviations: ARM, age-related maculopathy; RPE, retinal pigment epithelial. Source: From Ref. 99.

Some studies have evaluated huge numbers of variables for possible associations with ocular findings. For example, the Framingham Eye Study correlated its ophthalmic diagnoses with almost all of 667 variables from the Framingham Heart Study (29). Because of the very large number of variables evaluated, it is possible that some of the associations found may be due to chance alone (101). Similarly, while it is plausible that risk factors may be different for the various manifestations of AMD [e.g., drusen, increased retinal pigment, retinal pigment epithelial (RPE) depigmentation, geographic atrophy, and neovascular AMD], simultaneously conducting multiple comparisons within individual studies increases the likelihood of chance findings (102). In fact, one in 20 variables should have a positive association (for pZ0.05) by chance alone (103), and this probably contributes partly to the inconsistent results between studies. To provide compelling evidence of a real association between AMD and potential risk factors, repeated findings of the same risk factors in well-designed studies conducted in different populations are necessary. While results from epidemiologic studies may identify risk factors for AMD, proof that modifying a particular established risk factor can influence the course of the disease can emerge only from randomized prospective clinical trials.

RISK FACTORS OF AMD A number of risk factors for AMD have been incriminated from various epidemiologic studies, suggesting that the condition is multifactorial in etiology (Table 6). These risk factors may be broadly classified into personal or environmental factors, and the personal factors may be further subdivided into sociodemographic, ocular, and systemic factors.

SOCIODEMOGRAPHIC FACTORS Age Age is the strongest risk factor associated with AMD. The prevalence, incidence, and progression of all forms of AMD rise steeply with advancing age (47,88). There is a consistent finding across multiple population-based studies of an increase in prevalence of late AMD with age, from near absence at age 50 years to about 2% prevalence at age 70, and about 6% at age 80 (47,80,86,104). In the Framingham Eye Study, the prevalence of any AMD (defined as degenerative changes of the macula with visual acuity of 20/30 or worse) was 1.6% for persons 52 to 64 years, 11.0% for persons 65 to 74 years, and 27.9% for persons 75 to 85 years (30). Although closely linked to the aging process, AMD is not universal and is not inevitable with increasing age.

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Table 6

Risk Factors for Age-Related Macular Degeneration

Established risk factors Age Race/ethnicity Heredity Smoking Possible risk factors Sex Socioeconomic status Iris color Macular pigment optical density Cataract and its surgery Refractive error Cup/disc ratio Cardiovascular disease Hypertension and blood pressure Serum lipid levels and dietary fat intake Body mass index, waist circumference, and waist–hip ratio Hematologic factors Chlamydia pneumoniae infection Reproductive and related factors Dermal elastotic degeneration Antioxidant enzymes Sunlight exposure Micronutrients Dietary fish intake Alcohol consumption Factors probably not associated with AMD Diabetes and hyperglycemia Abbreviation: AMD, age-related macular degeneration.

Gender Gender has not been consistently found to be a risk factor for AMD. Sex was not associated with AMD in a study in Gisborne, New Zealand (34), the NHANES-I (8), the Copenhagen Study (43), the Rotterdam Study (58), a Finnish population-based study (73), and the Andhra Pradesh Eye Study in South India (86). Frequency estimates for drusen and the high-risk features of AMD among the black participants in the Barbados Eye Study were similar for men and women (57). In the Blue Mountains Eye Study, there was consistent, although not statistically significant, sex differences in prevalence for most lesions of AMD, with women having higher rates for late AMD and soft indistinct drusen than men, but not retinal pigmentary abnormalities, which were slightly more frequent in men (61). In addition, a significantly higher rate of bilateral involvement in women than men was found for neovascular AMD [odds ratio (OR), 7.7; 95% CI, 1.3–46.7] in the Blue Mountains Eye Study (71). For all other lesions of AMD, nonsignificant increased ORs were found for bilateral involvement in women (OR, 2.4; 95% CI, 0.6–10.0 for geographic atrophy and OR, 1.6; 95% CI, 0.7–3.5 for early AMD). In the Beaver Dam Eye Study, exudative AMD was more

frequent in women R75 years compared with men in the same age group (6.7% vs. 2.6%, pZ0.02) (47). In addition, in an incidence study, after adjusting for age, the incidence of early AMD was 2.2 times (95% CI, 1.6–3.2) as likely in women R75 years compared with men this age (88). Smith and associates pooled data from the Rotterdam Study (58), the Beaver Dam Eye Study (47), and the Blue Mountains Eye Study (61) to determine if females have a higher age-specific AMD prevalence than males (105). These three recent largescale population-based studies used almost identical diagnostic techniques and criteria for AMD, and the published data are presented in identical form for age groups 55 to 85 years. The overall pooled data show a significant but modest increase in AMD prevalence among females compared with males, with OR of 1.15 (95% CI, 1.10–1.21) adjusting for 10-year age categories. Age stratum-specific pooled ORs (95% CI) show an increase in risk, rising from 0.62 (0.35–1.10) for ages 55 to 64 years to 1.04 (0.87–1.26) for ages 65–74 years, and 1.29 (1.20–1.38) for ages 75 to 84 years. The Melton Mowbray Eye Study (38) and the Framingham Eye Study (3,106) also found a higher prevalence of AMD among women. In NHANES-III, after controlling for age, white women (OR, 1.32; 95% CI, 1.10–1.61) and black women (OR, 1.39; 95% CI, 1.00–1.92) had statistically significant higher odds of having soft drusen (defined as drusen O63 mm) than did men of the same race/ethnicity group, respectively (80). White women (OR, 1.24; 95% CI, 1.02–1.51) and black women (OR, 1.47; 95% CI, 1.06–2.03) were also more likely to have early AMD present than white and black men, respectively (80). The Los Angeles Latino Eye Study, a populationbased, cross-sectional study of Latinos (primarily Mexican American) aged 40 years and older, found that compared with Latino women, Latino men were at an approximately twofold increased risk of any (OR, 1.78; 95% CI, 1.47–2.16) or early (OR, 1.80; 95% CI, 1.47–2.19) AMD (84). Men were also more likely to have late AMD than women (OR, 1.6; 95% CI, 0.7–3.5), but this was not statistically significant. The reason for the increased risk of AMD in men is not known. Some studies have shown that several reported risk factors for AMD such as smoking, alcohol consumption, and cardiovascular disease tend to have a higher prevalence in men than women. Indeed, Latino men were more likely to smoke (21% vs. 9%, p!0.0001), drink alcohol regularly (22% vs. 3%, p!0.0001), and had elevated diastolic blood pressure (23% vs. 16%, p!0.0001) than Latino women. However, after adjusting for smoking, alcohol intake and elevated diastolic blood pressure, men were still more likely than women to have early AMD (OR, 1.91; 95% CI, 1.56–2.34).

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Race/Ethnicity Differences in genetic susceptibility probably explain part of the disparities in the prevalence of AMD in different races. The low numbers of black participants in the Macular Photocoagulation Study (MPS) trials for AMD suggested that the condition is less prevalent in black than in white populations (107). As of July 1, 1991, only 1 (0.08%) out of 1319 patients enrolled in the MPS trials for AMD was black while 1314 were white and 4 were listed as “other” (107). Several studies have suggested that AMD is more prevalent among whites than blacks (57,78,108, 109). Gregor and Joffe, comparing 377 white patients from London, England, with 864 age- and sex-matched black South Africans, found that drusen and pigment epithelial changes were twice as common in whites as in black Africans (18.3% vs. 9.3%, p!0.001 and 11.4% vs. 4.6%, p!0.001, respectively) (108). They also observed that disciform degeneration was present in 3.5% of white patients compared with 0.1% of South African patients (p!0.001). In the Baltimore Eye Survey, a cross-sectional population-based study of black and white residents of East Baltimore in Maryland, all AMD-related blindness were found in whites (78,109). Drusen (O63 mm) were identified in about 20% of individuals in both blacks and whites, but large drusen (O125 mm) were more common among older whites (15% for whites vs. 9% for blacks over 70 years old) (78). Retinal pigmentary abnormalities were also more common among older whites (7.9% for whites vs. 0.4% for blacks over 70 years old) (78). The prevalence ratio (white:black) was 10.7 for geographic atrophy, 8.8 for neovascular AMD, and 10.1 for all late AMD (geographic atrophy plus neovascular AMD) (78). In the Barbados Eye Study (57), a populationbased study in a large population of persons primarily of African descent, age-related macular changes occurred at a lower frequency than in the predominantly white populations of the Maryland Watermen Study (40) and the Beaver Dam Eye Study (47). The findings of at least one small (!63 mm) drusen was present in 66.2% of the Barbados Eye Study participants, which is lower than that of 86% of Maryland Watermen Study participants and 94% of the Beaver Dam Eye Study participants. The frequency of at least one large drusen of 1.1% in the Barbados Eye Study was also lower compared with these other studies, which had rates of 9% and 20% for the Maryland Watermen Study and Beaver Dam Eye Study, respectively. Neovascular AMD was found in 0.6% in the Barbados Eye Study. This was similar to the Maryland Watermen Study but lower than the 1.2% found in the Beaver Dam Eye Study. One caveat in the interpretation of the Barbados Eye Study, which is based on 308 stereoscopic fundus photographic grading, is that

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because the gradability of the fundus photographs decreased significantly with increasing age, predominantly as a result of an increasing incidence and severity of media opacities, and the participants excluded from the data analyses tended to the older, the frequencies presented in the Barbados Eye Study may underestimate the true frequency of AMD in this population (57). In NHANES-III, after adjusting for age, the frequency of early AMD was similar in non-Hispanic whites compared with that of non-Hispanic blacks and Mexican Americans (80). Although the frequencies of soft drusen appear similar among the racial/ethnic groups, retinal pigmentary abnormalities and signs of late AMD are more frequent in non-Hispanic whites than in non-Hispanic blacks and Mexican Americans. For increased retinal pigment and RPE depigmentation, the ORs (95% CI) comparing non-Hispanic blacks with non-Hispanic whites were 0.47 (0.31–0.72) and 0.59 (0.33–1.04), respectively, and for comparing Mexican Americans with non-Hispanic whites, they were 0.41 (0.21–0.81) and 0.72 (0.44–1.19), respectively. For late AMD, the OR (95% CI) for non-Hispanic blacks compared with non-Hispanic whites was 0.34 (0.10–1.18) and for Mexican Americans compared with non-Hispanic whites, it was 0.25 (0.07–0.90). Interestingly, before 60 years of age, Mexican Americans (OR, 1.53; 95% CI, 1.00–2.35) and non-Hispanic blacks (OR, 1.59; 95% CI, 0.86–2.95) had a greater chance of having any AMD than non-Hispanic whites; thereafter, Mexican Americans (OR, 0.63; 95% CI, 0.44–0.90) and non-Hispanic blacks (OR, 0.50; 95% CI, 0.37–0.68) had a lesser chance than non-Hispanic whites (81). Other Hispanics, Asians, and native Americans were included in NHANES-III but were not reported due to inadequate sample sizes. Klein et al. studied the prevalence of a large cohort of black and white participants in the Atherosclerosis Risk In Communities Study and found that the overall prevalence of any AMD was lower in blacks (3.7%) than whites (5.6%) (79). After controlling for age and sex, the OR for any AMD in blacks compared with whites was 0.73 (95% CI, 0.58–0.91). The prevalence of most of the component lesions that define early AMD was also lower in blacks than whites R60 years of age. Klein et al. recently reported the prevalence of AMD in four racial/ethnic groups (white, black, Hispanic, and Chinese) that participated in the Multi-Ethnic Study of Atherosclerosis (98). This prospective cohort study examined 6166 45- to 85-year-old subjects selected from six U.S. communities. The study found the prevalences of any AMD were 2.4%, 4.2%, 4.6% and 5.4% for blacks, Hispanics, Chinese, and whites, respectively (p!0.001 for any differences among groups). Estimated prevalences of late AMD were 0.3%, 0.2%, 1.0%, and 0.6% for blacks,

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Hispanics, Chinese, and whites, respectively. The frequency of neovascular AMD was highest in Chinese (age- and gender-adjusted OR, 4.30; 95% CI, 1.3–14.27) compared with whites. Differences in age, gender, pupil size, body mass index (BMI), smoking, alcohol drinking history, diabetes, and hypertension status did not explain the differences of AMD prevalences among the racial/ethnic groups. Klein and Klein, using data from NHANES-I, found no difference between whites and blacks in the percentage of patients with AMD (35). Another analysis of the same data came to the same conclusion (8). It is unclear whether the degree of fundus pigmentation affects the ability to detect lesions such as hyperpigmentation and hypopigmentation of the RPE, and soft drusen that characterize AMD. It is plausible that variations in normal fundus pigmentation may lead to errors in detecting subtle early AMD lesions, resulting in apparent differences among the ethnic groups. Overall, current evidence suggests that early AMD is common among blacks and Hispanics but less common than among non-Hispanic whites. However, late AMD is less frequent in these groups compared with non-Hispanic whites. Racial differences in AMD support a potential genetic component to this condition.

Heredity Analysis of heredity in the disease process of AMD is limited by the fact that the disorder is associated with aging, frequently causing its most significant phenotypic manifestations in the later years of life. As a result, usually only one generation in the appropriate age range is available for study. The parents of the proband are often deceased, and the children are often too young to manifest the disease. Because information from several generations of families of multiple affected individuals is often lacking, genetic analysis is limited. Clinical experience indicates that AMD demonstrates familial clustering, suggesting that heredity may be an important factor in the etiology of this condition although the exact role and relative contribution of genetics in the pathogenesis is unknown (55,110–113). It is believed that this genetic predisposition, in the presence of appropriate environmental influences, causes the aging macula to manifest AMD. Although Hutchinson and Tay observed a familial occurrence of AMD as early as 1875 (114), the association between heredity and AMD has not been well studied until recently. Bradley in 1966 commented on his patients with AMD that “nearly every patient I have seen has had other members of the family similarly afflicted” (115). In 1973, Gass reported

a positive family history of loss of central vision in 10% to 20% of his patients with AMD (116). Hyman et al. reported a statistically significant association between AMD and a family history of the disease either in the parents and siblings (OR, 2.9; 95% CI, 1.5–5.5) (12). A significantly higher correlation of number of drusen between siblings than between spouses was found by Piguet et al. (110). The lack of concordance between spouses who have shared a common environment for at least 20 years suggests that environmental factors may not play a key role in the etiology of AMD (110). Seddon et al. found the overall prevalence of AMD was higher among first-degree relatives of cases than among relatives of controls (OR, 2.4; 95% CI, 1.2–4.7) (117). They also found that familial aggregation of AMD was associated with the type of AMD in the proband, i.e., dry AMD (large or extensive macular drusen, RPE abnormalities, and geographic atrophy) versus exudative AMD [RPE detachment or choroidal neovascularization (CNV)]. Relatives of probands with exudative disease were significantly more likely to have AMD than were relatives of control probands after adjusting for age and sex (OR, 3.1; 95% CI, 1.5–6.7). On the other hand, relatives of probands with dry AMD were slightly more likely to have AMD than were relatives of control probands (OR, 1.5; 95% CI, 0.6–3.7), but this difference was not statistically significant. In another study, the OR of siblings for AMD of patients compared with siblings of controls was 25.2 (95% CI, 3.4–519.0) (118). In the Blue Mountains Eye Study, subjects with signs of AMD (4.5%) were more likely to report a firstdegree family history of AMD than among subjects without AMD (2.3%) (67). The highest rate was reported by subjects with late AMD (6.9%), particularly those with neovascular AMD (8.2%). After adjusting for age, sex, and current smoking, a clear increase in risk associated with family history, from no AMD [OR, 1.0 (index)] to early AMD (OR, 2.17; 95% CI, 1.04–4.55), late AMD (geographic atrophy or neovascular AMD) (OR, 3.92; 95% CI, 1.34–11.46), and neovascular AMD (OR, 4.30; 95% CI, 1.37–13.45) was observed (67). Klaver et al. examined the siblings and children of probands derived from the population-based Rotterdam Study (119). First-degree relatives of 87 patients with late AMD (geographic atrophy or neovascular AMD) were compared with those of 135 controls without AMD. For siblings, the prevalence of early AMD was 9.5% for siblings of patients versus 2.9% for siblings of controls (pZ0.04, age and sex adjusted), and for late AMD was 13.4% versus 2.2% (pZ0.001, age and sex adjusted). For offspring, the prevalence of early AMD was 6.3% for offspring of

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patients versus 1.9% for offspring of controls (pZ0.05, age and sex adjusted), and late AMD was present in only 1.4% of offspring of patients (pZ0.20, age and sex adjusted). The prevalence of early (OR, 4.8; 95% CI, 1.8–12.2) and late (OR, 19.8; 95% CI, 3.1–126.0) AMD was significantly higher in first-degree relatives of patients with late AMD than in relatives of controls. The lifetime absolute risk estimate of developing early AMD was 48% (95% CI, 31–65%) for relatives of patients versus 23% (95% CI, 10–37%) for relatives of controls (pZ0.001), yielding a risk ratio of 2.1 (95% CI, 1.4–3.1). The lifetime risk estimate of late AMD was 50% (95% CI, 26–73%) for relatives of patients versus 12% (95% CI, 2–16%) for relatives of controls (p!0.001), yielding a risk ratio of 4.2 (95% CI, 2.6–6.8). The authors calculated that the population-attributable risk related to genetic factors was 23% (119). No association, however, was found between family history and AMD in the small populationbased Melton Mowbray Eye Study (38). It should be pointed out that in studies in which the family history data were ascertained by interview alone, the data should be interpreted with caution since reported histories of ocular disease are unreliable (120). Three reports of single pairs of monozygotic twins (121–123) and two larger series, with 9 (112) and 50 pairs of identical twins (124), described a high concordance of early and late AMD in the twins. Gottfredsdottir et al. examined the concordance of AMD in 100 monozygotic twins (50 pairs) and 47 spouses (124). The average duration of marriage for the twin/spouse pair was 30 years (range, 26–50 years). The concordance of AMD was 90% in monozygotic twin pairs which significantly exceeded that of 70% for twin/spouse pairs (pZ0.0279). In the nine twin pairs that were concordant, fundus appearance and visual impairment were similar. Although the environmental influences are probably more similar for identical twins than for dizygotic twins, other siblings, or unrelated individuals, the strikingly similar incidence of age-related macular changes in these identical twins suggests that a substantial genetic component may exist in some patients with AMD. Although AMD runs in families, the phenotypic appearance of the macula within families with the disorder tends to be quite variable and representative of the wide range of findings typically associated with AMD, i.e., both neovascular AMD and geographic atrophy, and early signs of AMD may be present in different individuals within the families (125). Indeed, neovascular and nonneovascular AMD were observed among different individuals in four of eight families in the study, suggesting that geographic atrophy may be part of the same disease process as neovascular AMD. On the other hand, the distinctly different phenotypes of the two forms of late AMD may also indicate

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different origins. It is currently unknown why geographic atrophy develops in some instances and neovascular AMD in others, even within the same family.

Socioeconomic Status In NHANES-I, a significant negative trend (p!0.03) of decreased prevalence of AMD was found with increasing levels of education (8). Compared with the least educated group, persons who attended high school have a reduced prevalence of AMD (OR, 0.64; 95% CI, 0.44–0.92) as do persons who have some education beyond high school (OR, 0.71; 95% CI, 0.44–1.15). The Eye Disease Case–Control Study found that persons with higher levels of education had a slightly reduced risk of neovascular AMD, but the association did not remain statistically significant after multiple regression modeling (7). The Beaver Dam Eye Study found no relation of income, educational level, or marital status to AMD (48). No association between social class and AMD was found in the Melton Mowbray Eye Study (38). Two case–control studies found no association between AMD and occupations (10,12). OCULAR FACTORS Macular Pigment Optical Density Recently, there is heightened interest in the potential role of macular pigment in protecting against AMD (126). The yellow macular pigment, which characterizes the retinas of primates including man, was shown in 1985 to be composed of two chromatographically separable components, namely lutein and zeaxanthin (127). Of note, lutein and zeaxanthin are entirely of dietary origin. Although the exact role of the macular pigment remains uncertain, several functions have been hypothesized. These include limiting the effects of light scatter and chromatic aberration on visual performance (128,129), reducing the damaging photooxidative effects of blue light through its pre-receptorial absorption (130,131), and protecting against the adverse effects of reactive oxygen intermediates through its antioxidant properties (132). There is a growing body of evidence that oxidative damage plays a role in the pathogenesis of AMD (133–136). Consequently, some have suggested that the absorption characteristics and antioxidant properties of macular pigment confer protection against AMD (132,137). In brief, the evidence that macular pigment optical density confers protection against AMD rests on a biologically plausible rationale and the fact that several risk factors for this condition are themselves associated with a relative lack of the pigment. Any

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beneficial effect of macular pigment must reside in its ability to protect against chronic and cumulative damage. In other words, macular pigment levels in young and middle age are likely to determine the protection, if any, that this pigment confers against AMD. For example, some studies have found that macular pigment optical density declines with increasing age in normal eyes (138,139), although some have not (140,141). In addition, it has been found to be significantly different between males and females. In one study, macular pigment optical density for males was 38% higher than for females (142). Given the putative protective role of macular pigment (132), this finding may explain the higher prevalence of AMD in females found in some studies (see above). Likewise, a strong inverse relationship between smoking and macular pigment optical density has been shown by Hammond et al., and this may explain how smoking increases the risk of AMD (see below) (143). Interestingly, the average levels of macular pigment have been reported as 32% lower in eyes with AMD than in normal age-matched control eyes in subjects not consuming high-dose lutein supplements (pZ0.001) (138). Although discussed under the heading of ocular risk factors, macular pigment optical density is inherently related to nutrition since it can be altered by dietary modification or supplementation (144–147). Consumption of certain fruits and vegetables will increase the dietary intake of lutein and zeaxanthin (148). Hammond et al. reported that an average increase of approximately 20% in human macular pigment optical density was obtained after four weeks of a diet enriched in corn and spinach (145). The Eye Disease Case–Control Study reported that a high dietary intake of macular pigments from leafy green vegetables was associated with a reduced risk of neovascular AMD (see below) (16). In one report, two subjects who took a daily dose of 30 mg of lutein for 140 days had mean increases in the macular pigment optical density of 39% and 21% in their eyes, respectively (146). The authors estimated that this increase in macular pigment resulted in a 30% to 40% reduction in blue light reaching the photoreceptors, Bruch’s membrane, and the RPE. Because human macular pigment can be augmented with dietary modification and nutritional supplementation, the protective effect of macular pigment, if proven, has potential therapeutic implications. Nevertheless, evidence that dietary modifications or supplementation with lutein and/or zeaxanthin can prevent, delay, or modify the course of AMD is still lacking. Ultimately, a well-designed randomized controlled trial with a long follow-up such as the second phase of the National Eye

Institute’s Age-Related Eye Disease Study (AREDS) will be required to test such a hypothesis.

Cataract and Its Surgery Since cataract and AMD are the most frequent causes of visual impairment in older individuals and their prevalence is strongly age related (149), a possible association between the two conditions has long been debated. There are potential risk factors common to both conditions, such as antioxidant intake (150), cigarette smoking (151), and sunlight exposure (41,42,152–154). The association between cataract and AMD has not been found consistently. In the small population-based study in Melton Mowbray (38) and a case–control study by Tsang et al. (15), no statistically significant association was found between cataract and AMD. Sperduto and Siegel found no association between cataract and AMD when the various agerelated lens changes were pooled in the Framingham Eye Study and they concluded that cataract and AMD are unrelated and developed entirely independently (31). However, when they reexamined the same data to study specific types of cataracts, they found a positive association between AMD and cortical changes and a negative association between AMD and nuclear sclerosis (32). The Andhra Pradesh Eye Disease Study, a population-based study involving 3723 participants aged 40 to 102 years in southern India, also found cortical cataract, but not nuclear sclerotic or posterior subcapsular cataract, to be significantly associated with an increased prevalence of AMD (adjusted OR, 2.87; 95% CI, 1.57–5.27) (86). In contrast, Klein et al. found a positive association between early or any AMD and nuclear sclerosis but no relationship of cortical cataract or of posterior subcapsular cataract to early or late AMD in the Beaver Dam Eye Study (49). In addition, there was no relationship of nuclear or cortical cataract to the incidence and progression of AMD (89). An analysis of the data from NHANES-I by Liu et al. found that the ORs of having AMD in eyes with lens opacity without visual impairment and cataract when compared with eyes with no lens opacity were 1.80 (95% CI, 1.40–2.30) and 1.14 (95% CI, 0.84–1.55), respectively (36). The authors postulated that the weak association between cataract and AMD may reflect the difficulty of visualizing the ocular fundus in eyes with dense cataract. Other theories include the possibility that retardation of transmission of light to the retina by cataract decreases the extent of light damage, and that different kinds of cataracts may have differing pathogeneses and for some types, no common factors may be shared with AMD (36). The FRANCE-DMLA Study Group, comparing 1844 cases of AMD with a similar number of age- and

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sex-matched controls, found that persons with lens opacities had an increased risk of AMD (OR, 1.69; 95% CI, 1.45–1.97) (22). Several authors have noted deterioration of AMD following cataract surgery (155–159). In one study, Pollack et al. evaluated 47 patients with bilateral, symmetric, early AMD who underwent extracapsular cataract extraction with intraocular lens implantation in one eye (157). They found that progression to neovascular AMD occurred more often in the operated eyes (19.1%) compared with the fellow eyes (4.3%). This concurs with a histologic study that suggested a higher prevalence of disciform macular degeneration in pseudophakic eyes than in age-matched phakic eyes (160). Interestingly, Pollack et al. found that progression to neovascular AMD occurred significantly more often in men than in women (p!0.05) (157). In the Beaver Dam Eye Study, eyes that had undergone cataract surgery before baseline, compared with eyes that were phakic at baseline, were more likely to have progression of AMD (OR, 2.71; 95% CI, 1.69–4.35) and to develop signs of late AMD (OR, 2.80; 95% CI, 1.03–7.63) after controlling for age (89). These relationships remained after controlling for other risk factors in multivariate analyses. The FRANCE-DMLA Study Group found an increased risk of AMD in persons with a history of previous cataract surgery compared with those with no lens opacities or cataract surgery (OR, 1.68; 95% CI, 1.45–1.95) (22). Similarly, prior cataract surgery was significantly associated with an increased prevalence of AMD in the Andhra Pradesh Eye Disease Study (adjusted OR, 3.79; 95% CI, 2.1–6.78) (86). Liu et al. found that data from NHANES-I suggest the OR of having AMD in eyes with aphakia compared with eyes with no lens opacity was 2.00 (CI, 1.44–2.78) (36). They suggested that an increase in light transmittance following cataract surgery may reinitiate and dramatically accelerate progression to more advanced AMD. It is also possible that the association is a result of easier visualization and detection of AMD lesions after cataract surgery (89). It has also been hypothesized that inflammatory changes that may occur in eyes following cataract surgery may be related to the development of late AMD (160). In the Blue Mountains Eye Study, a higher prevalence of late AMD in eyes with past cataract surgery (6.3%) than in phakic eyes (1.3%) was observed. However, the association was primarily an effect of age because the OR for late AMD reduced to 1.3 (95% CI, 0.6–2.6) and became nonsignificant after adjusting for age and sex, and to 1.2 (95% CI, 0.5–2.9), after multivariate adjustment (72). Similarly, a higher prevalence of early AMD was found in eyes with a history of cataract surgery (7.1%) than in phakic eyes

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(4.4%), with a multivariate-adjusted OR of 0.7 (95% CI, 0.4–0.9), which suggests a protective effect for cataract surgery (72). The Rotterdam Study also did not find any association between cataract surgery and AMD prevalence (161). It is unclear why the results vary among the studies. It is possible that these variations in findings may have resulted from differences in the study population and/or from differences in methodology and case definitions.

Iris Color Iris color is a hereditary factor that may be associated with AMD (13). However, this association has not been consistently found in studies. A number of studies have reported an increased risk of AMD in people with blue or light iris color compared with those with darker iris pigmentation (12,13,17,22,62) and one study documented worse AMD in subjects with light iris color (162). Others, however, have found no association between iris color and AMD (7,14,15,38, 39,44,89). The Beaver Dam Eye Study did not find any relationship between iris color and the incidence and progression of AMD (89). One histologic study found no significant correlation between iris color and macular aging (160). Data from NHANES-III showed that blue iris color was negatively associated with soft drusen in non-Hispanic whites (OR, 0.69; 95% CI, 0.55–0.88) but not in Mexican Americans (OR, 0.35; 95% CI, 0.05–2.72) (80). The reasons for these disparities are not clear. Case–control studies by Hyman et al. (12) and Weiter et al. (13) demonstrated a positive association between light iris color and AMD. In Hyman et al.’s series, only 9.2% of 162 cases had brown irides compared with 26.4% of 174 controls (pZ0.0002) (12). Blue or lightly pigmented irides were associated with a higher risk of AMD, the degree of association being greater for men (OR, 8.3; 95% CI, 2.3–29.7) than for women (OR, 2.4; 95% CI, 1.1–5.0) (12). Weiter et al. found that 76% of 650 patients with AMD had light irides compared with 40% of 363 controls (pZ0.0001) (13). In addition, patients with AMD and light iris color were found to be significantly younger (mean age, 73.6G7.3 years) than those with dark iris color (mean age, 78.3G5.8 years; pZ0.0008) (13). The FRANCEDMLA Study Group found that persons with light iris color (blue, green, and gray) had increased risk of AMD compared with those with dark iris color (OR, 1.22; 95% CI, 1.05–1.42) (22). This concurs with the Blue Mountains Eye Study which found that blue iris color was significantly associated with an increased risk for both early AMD (OR, 1.5; 95% CI, 1.1–1.9) and late AMD (OR, 1.7; 95% CI, 1.0–2.9) (62). Holz et al. found that lighter present iris color, but not initial iris color during youth, was

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associated with an increased risk of AMD (17). They calculated that a history of decreasing iris color was associated with a 5.55-fold (95% CI, 2.03–15.91) increase in risk of AMD (pZ0.0001). Some studies have shown that declines in the melanin content of the iris and RPE occur with age (163,164). The Beaver Dam Eye Study showed higher prevalences of blue or gray iris color with increased age, but no relationship was found between iris color and the incidence or progression of AMD in the study (89). The mechanism by which iris pigmentation might influence AMD is uncertain, but a plausible explanation is that the lower risk for AMD among subjects with darker iris color may be due to the fact that these individuals have more tissue melanin, including the choroid. Indeed, fundus pigmentation was found to correspond closely to iris pigmentation both clinically and by objective histologic microdensitometric techniques (13). This increased pigmentation may provide some protection to the retina from exposure to sunlight, reducing direct photooxidative damage and thus reducing the risk of AMD (see below). This is consistent with the observation in some studies that AMD is more prevalent among whites than among the more pigmented races (57,78,109).

Refractive Error Several case–control studies have found an association between AMD and refractive error, with hyperopic eyes at greater risk of AMD (10–12,22). Hyman et al. found that statistically significant differences in mean refractive error were present between female cases and controls (pZ0.009), but not between male cases and controls (pZ0.16) (12). Female cases had a more positive refractive error (meanZ1.8 diopters) than female controls (meanZ1.1 diopters). The FRANCEDMLA Study Group found the ORs for AMD in hyperopes and myopes, compared with emmetropes, were 1.33 (95% CI, 1.11–1.59) and 0.99 (95% CI, 0.78–1.25) (22). The Eye Disease Case–Control Study found that persons with hyperopia had a slightly higher risk of neovascular AMD, but the association did not remain statistically significant after multivariate modeling (7). One caveat in the interpretation of findings in these case–control studies is that because the controls were recruited from ophthalmologic clinics, the control groups may be enriched in the proportion of myopes compared with the general population. In fact, in the case–control study by the FRANCE-DMLA Study Group, the authors stated that “the majority of the control group was seen for refractive problems” (22). Data from NHANES-I showed that the ORs (95% CI) of AMD in hyperopes and myopes,

compared with emmetropes, were 1.61 (1.15–2.25) and 1.33 (0.69–2.57), respectively (8). This differs from the Beaver Dam Eye Study, which showed a protective effect of borderline significance of hyperopia at baseline on the incidence of early AMD, but no relationship to the incidence of late AMD or to the progression of AMD (89).

Cup/Disc Ratio The Eye Disease Case–Control Study found that eyes with large horizontal and vertical cup/disc ratios were at reduced risk for neovascular AMD (7). The horizontal cup/disc ratio persisted as statistically significant after multivariate modeling, adjusting for known and potential confounding factors. This finding is consistent with the association between AMD and hyperopia. SYSTEMIC FACTORS Cardiovascular Disease and Its Risk Factors A number of documented risk factors for cardiovascular disease such as age, hypertension, hypercholesterolemia, diabetes, smoking, and dietary intake of fats, alcohol, and antioxidants have been associated with AMD in some studies (165). This raises the possibility that the causal pathways for cardiovascular disease and AMD may share similar risk factors. Results from studies, however, have not been consistent. Cardiovascular Disease A number of studies have suggested an association between AMD and various clinical manifestations of cardiovascular disease. In a case–control study, Hyman et al. found AMD to be positively associated with a history of three cardiovascular conditions (12). These conditions are arteriosclerosis, circulatory problems, and stroke and/or transient ischemic attacks, with ORs (95% CI) of 2.3 (1.9–2.7), 2.0 (1.1–3.5), and 2.9 (1.3–6.9), respectively (12). The FRANCE-DMLA Study Group found an increased risk of AMD in persons with a history of coronary artery disease (OR, 1.31; 95% CI, 1.02–1.68) (22). In NHANES-I, a positive association between AMD and cerebrovascular disease was found, but positive associations with other vascular diseases did not reach statistical significance (8). The Rotterdam Study found that atherosclerotic plaques in the carotid bifurcation, as assessed ultrasonographically, were associated with a 4.5 times increased prevalence OR (95% CI, 1.9–10.7) of either geographic atrophy or neovascular AMD (59). Those with plaques in the common carotid artery or with lower extremity arterial disease (as measured by the ratio of the systolic blood pressure level of the ankle

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to systolic blood pressure of the arm) had the same increased prevalence OR of 2.5 (95% CI, 1.4–4.5). From these observations, the authors suggested that atherosclerosis may be involved in the etiology of AMD. However, other cardiovascular disease risk factors such as hypertension, systolic blood pressure, total cholesterol, and high-density lipoprotein (HDL) cholesterol were not associated with AMD in the same study (59). Diastolic blood pressure was marginally higher in AMD cases than in those without AMD, but this did not reach statistical significance (59). In subjects participating in the Atherosclerosis Risk In Communities Study, presence of carotid artery plaque was significantly associated with RPE depigmentation (OR, 1.77; 95% CI, 1.18–2.65) (79). Focal retinal arteriolar narrowing was also associated with RPE depigmentation (OR, 1.79; 95% CI, 1.07–2.98) in the same study. In a Finnish population-based study, a significant correlation between the severity of retinal arteriolar sclerosis and AMD (pZ0.0034) was found (73). Several case–control studies, including the Eye Disease Case–Control Study, found that persons who report a history of cardiovascular disease did not have a significantly increased risk of AMD (7,10,15). The Beaver Dam Study (50), the Atherosclerosis Risk In Communities Study (79), and the Blue Mountains Eye Study also found no statistically significant relationship between a history of stroke or cardiovascular disease with early or late AMD.

Hypertension and Blood Pressure Two large population-based studies showed a small and consistent significant association between AMD and systemic hypertension (8,29,33). Kahn et al., using the Framingham Heart and Eye Studies data, found a positive association between the presence of AMD and higher levels of diastolic blood pressure measured many years before the eye examination (29). Diastolic blood pressure was also associated with AMD in a small Israeli study (166). Also using data from the Framingham Heart and Eye Studies, Sperduto and Hiller found the age- and sex-adjusted relative risk (RR) for any AMD was 1.18 (95% CI, 1.01–1.37) for persons diagnosed with hypertension 25 years before the eye examination and 1.04 (95% CI, 0.96–1.23) for persons with hypertension at the time of the eye examination, when compared with those without hypertension (33). In addition, an increase in the OR of AMD with longer duration of systemic hypertension was documented. The NHANES-I showed that systolic blood pressure and hypertension were associated with AMD (8). Persons with a history of hypertension were 1.36 times (95% CI, 1.00–1.85) more likely to have AMD compared with persons without such a history. In addition, the prevalence of AMD increased with increasing levels of systolic blood

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pressure although the test for trend was only marginally significant (p!0.08). However, elevated diastolic blood pressure was not associated with AMD. The Beaver Dam Eye Study found elevated systolic blood pressure to be significantly related to the presence of RPE depigmentation in females (OR, 1.07; 95% CI, 1.00–1.14) but not in males (50). Pulse pressure was also related to the presence of RPE depigmentation (OR, 1.10; 95% CI, 1.01–1.19), increased retinal pigment (OR, 1.07; 95% CI, 1.00–1.15), and pigmentary abnormalities (OR, 1.08; 95% CI, 1.01–1.15) in females but not in males (50). However, hypertension or diastolic blood pressure was not related to any sign of early or late AMD in either sex. In an incidence study, after controlling for age and sex, both higher systolic blood pressure (OR per 10 mmHg, 1.16; 95% CI, 1.05–1.27) and uncontrolled “treated” hypertension (OR, 1.98; 95% CI, 1.00–3.94) were related to the incidence of RPE depigmentation, but not development of neovascular AMD (90). Higher pulse pressure was significantly associated with increased incidence of RPE depigmentation (OR per 10 mmHg, 1.27; 95% CI, 1.14–1.42) and neovascular AMD (OR per 10 mmHg, 1.29; 95% CI, 1.02–1.65) after controlling for age and sex. Systemic hypertension was found to be a significant risk factor for AMD by the FRANCE-DMLA Study Group (22). Another recent case–control study by the Age-Related Macular Degeneration Risk Factors Study Group analyzed risk factors separately for neovascular and nonneovascular AMD to address the possibility that the two forms of AMD have different risk factors (24). The group showed that neovascular AMD, but not nonneovascular AMD, is associated with moderate to severe hypertension (24). Neovascular AMD was found to be positively associated with diastolic blood pressure greater than 95 mmHg (OR, 4.4; 95% CI, 1.4–14.2), self-reported use of antihypertensive medications more potent than diuretics (OR, 2.1; 95% CI, 1.2–3.0), physicianreported history of hypertension (OR, 1.8; 95% CI, 1.2–3.0), and physician-reported use of any antihypertensive medications (OR, 2.5; 95% CI, 1.5–4.2). The findings in this study suggest that neovascular AMD and hypertension may have a similar systemic process. In addition, it supports the hypothesis that neovascular and nonneovascular AMD may arise through different pathogenetic mechanisms. No association between hypertension and AMD was found in several population-based cross-sectional studies including the Rotterdam Study (59), Blue Mountains Eye Study (66), Atherosclerosis Risk In Communities Study (79), and Andhra Pradesh Eye Disease Study (86), or in several case–control studies (7,10,12,15). In the Eye Disease Case–Control Study, no significant association was found with hypertension

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and AMD, but a trend for an increased risk associated with higher systolic blood pressure was seen (7).

Serum Lipid Levels and Dietary Fat Intake Some evidence suggests that dietary fat intake, particularly intake of saturated fat and cholesterol, is associated with an increased risk for atherosclerosis (167). It is biologically plausible that higher dietary saturated fat intake increases the risk of AMD by promoting atherosclerosis. The Eye Disease Case–Control Study found that persons with midrange (4.889–6.748 mmol/L) and high (R6.749 mmol/L) total cholesterol levels compared with those with low levels (%4.888 mmol/L) had ORs for neovascular AMD of 2.2 (95% CI, 1.3–3.4) and 4.1 (95% CI, 2.3–7.3), respectively, after controlling for other factors (7). A slight but not statistically significant increased risk in neovascular AMD was seen with increasing levels of serum triglycerides in the same study (7). In the Beaver Dam Eye Study, after controlling for age, total serum cholesterol was inversely related to early AMD in women (OR, 0.89; 95% CI, 0.80–0.98), whereas the total cholesterol/HDL cholesterol ratio was inversely related (OR, 0.89; 95% CI, 0.84–0.96) and HDL cholesterol was positively related to early AMD in men (50). The Cardiovascular Health Study also showed a small but significant inverse association between total serum cholesterol and early AMD (168). Pooled data from three cross-sectional studies (Blue Mountains Eye Study, Beaver Dam Eye Study, and Rotterdam Study) found that total serum cholesterol was associated inversely with incident neovascular AMD (OR, 0.94 per 10 mg/dL; 95% CI, 0.88–0.99) (169). The reasons for these associations are not clear although some authors have suggested selective survival as a possible explanation. Because persons with higher cholesterol levels or lower HDL cholesterol levels are at higher risk of cardiovascular deaths than persons with normal levels of cholesterol, a positive relationship may have been obscured. Interestingly, the pooled data also showed that total serum cholesterol was associated directly with incident geographic atrophy (OR, 1.08 per 10 mg/dL; 95% CI, 1.00–1.15) (169), and this association cannot be explained by selective survival. The Age-Related Macular Degeneration Risk Factors Study Group found neovascular AMD, but not nonneovascular AMD, to be positively associated with HDL level (OR, 2.3; 95% CI, 1.1–4.7) and dietary cholesterol level (OR, 2.2; 95% CI, 1.0–4.8) (24). In the Beaver Dam Eye Study, persons with intake of saturated fat and cholesterol in the highest compared with the lowest quintile had ORs of 1.8 (95% CI, 1.2–2.7) and 1.6 (95% CI, 1.1–2.4) for early AMD, respectively, after adjusting for age and beer intake

(56). However, no significant association between these intakes was found with late AMD (56). The findings in this study concurs with the Blue Mountains Eye Study, which found that total and saturated fat intake were associated with a borderline significant increase in risk for early AMD [ORs (95% CI) for highest compared with lowest quintiles of intake, 1.60 (0.94–2.73) and 1.50 (0.91–2.48), respectively], but not for late AMD (68). A significant association (p for trend Z0.05) for increasing prevalence of early AMD with increasing monounsaturated fat intake was observed. Cholesterol intake was associated with a borderline significant increased risk for late AMD [OR (95% CI) for highest compared with lowest quintiles of intake, 2.71 (0.93–7.96); p for trend Z0.04]. The Rotterdam Study (59), Blue Mountains Eye Study (66), and Atherosclerosis Risk In Communities Study (79) did not find any association between serum cholesterol and HDL cholesterol with AMD. No significant association between AMD and serum cholesterol was also found in the Framingham Eye Study (29), NHANES-I (8), and several small studies (15,170,171). No difference in the levels of plasma cholesterol and fatty acids was found between 65 cases of neovascular AMD and control pairs in a study by Sanders et al. (172). Several studies have evaluated the relationship of lipid-lowering agents and AMD and found conflicting results. The Beaver Dam Eye Study (173), Blue Mountains Eye Study (174), Rotterdam Study (175), and a recent case–control study using data from the Cardiovascular Health Study (28) found no association between the use of a lipid-lowering agent and the risk of developing AMD. There was, however, a suggestion that use of 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors or statins might increase the risk of AMD (OR, 1.40; 95% CI, 0.99–1.98) after controlling for age, sex, and race (28). Conversely, two cross-sectional studies (176,177) and one nested case–control study (178) reported that individuals with AMD were less likely to have used statins.

Diabetes and Hyperglycemia The majority of studies that have investigated the relationship between diabetes and/or hyperglycemia and AMD have found no significant association (7,10,12,15,29,73,79,179). One small study by Vidaurri et al. observed an association between drusen and serum glucose in females but not in males (166). In the Beaver Dam Eye Study, diabetes was not associated with early AMD (51). In persons R75 years, those with diabetes had a higher frequency of neovascular AMD (9.4%) than those without (4.7%) but both groups had similar frequencies of geographic atrophy. The RR of neovascular AMD in diabetic men compared with nondiabetic

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men R75 years was 10.2 (95% CI, 2.4–43.7); for females, it was 1.1 (95% CI, 0.4–3.0). The authors suggested that the relationship of neovascular AMD in older men, but not women, might be the result of chance. In the same study, no relationship was found between glycosylated hemoglobin and any signs of AMD in nondiabetic persons (51). The Blue Mountains Eye Study found geographic atrophy to be significantly associated with diabetes (OR, 4.0; 95% CI, 1.6–10.3), but no association was found with either neovascular AMD (OR, 1.2; 95% CI, 0.4–3.5) or early AMD (OR, 1.0; 95% CI, 0.5–1.8) (63). There was also no association found between impaired fasting glucose and AMD (63). The Atherosclerosis Risk In Communities Study (79) did not find any association between AMD with diabetes. Overall, there is scant evidence in the literature to suggest a real relationship between diabetes and/or hyperglycemia and AMD.

BMI, Waist Conference, and Waist Hip Ratio In the Blue Mountains Eye Study, having a BMI [defined as body weight in kilograms divided by height in meters squared (kg/m2)] either lower or higher than the accepted normal range (20–25) was associated with a significantly increased risk of early AMD (66). Low BMI (OR, 1.92; 95% CI, 1.16–3.18) conferred an increased risk for early AMD almost equal to that of obesity (OR, 1.78; 95% CI, 1.19–2.68). Although the ORs were similar for association with late AMD, they did not reach statistical significance. This finding is similar to that of the Physicians’ Health Study, which also found a J- or U-shaped association between BMI and the incidence of visually significant AMD, with the highest incidence among obese men with a BMIR30 and a somewhat less elevated incidence among the leanest men with a BMI!22 (94). This association is difficult to explain in terms of cardiovascular risk. A Finnish population-based study found that a high BMI was associated with an increased risk of AMD in men but not in women (73). On the other hand, the Beaver Dam Eye Study found that BMI was associated with increased frequency of RPE degeneration, increased retinal pigment, and increased presence of pigmentary abnormalities in women but not in men (50). No association between BMI and AMD was found in the Atherosclerosis Risk In Communities Study (79) or the Andhra Pradesh Eye Disease Study (86). Seddon et al. found that persons with higher BMI had increased risk for progression to advanced AMD. The RR was 2.35 (95% CI, 1.27–4.34) for BMIR30, and 2.32 (95% CI, 1.32–4.07) for BMI 25 to 29 relative to the lowest category (BMI!25) after controlling for other factors (pZ0.007 for trend) (180). In addition, the authors also found that higher waist circumference was associated with a twofold

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increased risk for progression of AMD (RR for the highest tertile compared with the lowest, 2.04; 95% CI, 1.12–3.72), with a significant trend for increasing risk with a greater waist circumference (pZ0.02). Higher waist–hip ratio also increased the risk for progression of AMD (RR, 1.84; 95% CI, 1.07–3.15) for the highest tertile compared with lowest (pZ0.02).

Hematologic Factors and Other Cardiovascular Biomarkers The Beaver Dam Eye Study found that, after controlling for age, sex, diabetes, and smoking history, neovascular AMD was associated with higher hematocrit values (OR, 1.09; 95% CI, 1.00–1.19) and higher leukocyte count (OR, 1.10; 95% CI, 1.00–1.19) in people R65 years (50). Blumenkranz et al. also found a higher leukocyte count in cases with neovascular AMD compared with controls (14). No association between hematocrit and AMD was found in NHANES-I (8). The Blue Mountains Eye Study found that plasma fibrinogen level was associated with late but not early AMD (66). The Eye Disease Case–Control Study found a nonsignificant increased risk of neovascular AMD with increasing plasma fibrinogen levels (7). A number of inflammatory biomarkers which are known to be associated with cardiovascular disease have now been found to be independently associated with the progression of AMD (181). These include C-reactive protein (26,181) and interleukin 6 (181). Chlamydia pneumoniae Infection Chronic inflammatory events have recently been identified as plausible causes of atherosclerosis and much interest has been focused on infections by Chlamydia pneumoniae. C. pneumoniae can multiply in various host cells including macrophages and endothelial cells. Like a parasite, the obligate intracellular prokaryote consumes energy that is needed by the host cells, and in the end, destroys them and then infects nearby cells. Thus, the hallmark of chlamydial disease is persistent infection and chronic inflammation. There is strong evidence indicating a close interaction between C. pneumoniae and systemic vascular diseases, including the direct detection of C. pneumoniae (182,183) and the heat shock proteins of C. pneumoniae (184) in the plaques of coronary and carotid arteries. Recent sero-epidemiologic data suggest that C. pneumoniae infection is associated with AMD. Case–control studies have shown that patients with AMD were more likely to have higher levels of antiC. pneumoniae antibodies compared with patients with AMD (25,111). Although the significance of the increased titers of specific IgG and IgA antibodies against C. pneumoniae is not fully understood, higher IgG and IgA antibodies titers may indicate an

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exposure to greater amounts of C. pneumoniae and recurrent or chronic infections. Remarkably, C. pneumoniae has been detected in four out of nine AMD CNV by immunohistochemistry and two out of nine AMD CNV by polymerase chain reaction (185). In contrast, none of 22 non-AMD specimens including 5 non-AMD CNV showed evidence for C. pneumoniae. These data indicate that a pathogen capable of inducing chronic inflammation can be detected in some AMD CNV, and support the theory that infection may contribute to the pathogenesis of AMD. The Cardiovascular Health and Age-Related Maculopathy Study in Australia recently showed that the rate of progression of AMD over a sevenyear period was increased in those with higher titers of anti-C. pneumoniae antibodies, after controlling for age, smoking, family history of AMD, and history of cardiovascular diseases (186). Subjects in the two upper tertiles of antibody titer were at a significantly greater risk of AMD progression than those in the lowest tertile. A twofold increased risk of AMD progression for subjects in the middle tertile of antibody titers was consistent for three different definitions of AMD progression. In the upper tertile of antibody titers, the risk of progression was 2.07 (95% CI, 0.92–4.69), 2.58 (95% CI, 1.24–5.41), and 3.05 (95% CI, 1.46–6.37) using different definitions of AMD progression.

Cigarette Smoking This will be discussed under environmental factors (see below). Reproductive and Related Factors The relationship of cardiovascular disease to AMD has generated some interest in the effect of estrogenrelated variables on the risk of AMD in women. The Eye Disease Case–Control Study found that use of postmenopausal exogenous estrogen was negatively associated with neovascular AMD (7). Current and former users of estrogen had ORs of 0.3 (95% CI, 0.1–0.8) and 0.6 (95% CI, 0.3–0.98) for neovascular AMD, respectively, when compared with women who never used estrogen. This is compatible with findings from a nested case–control study within the Rotterdam Study which suggest that early artificial menopause increases the risk of late AMD (atrophic or neovascular AMD) (19). Women with early menopause after unilateral or bilateral oophorectomies had an increased risk of late AMD compared with women who had their menopause at 45 years or later. No significant excess risk was found for early spontaneous menopause and early hysterectomy. In the Blue Mountains Eye Study, a significant protective association for early AMD was found with increased

years from menarche to menopause (OR, 0.97; 95% CI, 0.95–0.99) (105). Other female-specific factors including late menarche, history of hormone replacement therapy, and early menopause were not significantly associated with early or late AMD (105). No significant relationship, however, was found in the Beaver Dam Eye Study between years of estrogen therapy and neovascular AMD, geographic atrophy, or early AMD (187). It should be noted that because the number of cases of late AMD in the Beaver Dam Eye Study was small, the power to detect a real association is limited. Similarly, the Pathologies Oculaires Liees a l’Age (POLA) Study did not find any association of hormone replacement therapy, hysterectomy, or oophorectomy with soft drusen, pigmentary abnormalities, or late AMD (77). Women who have ever been pregnant (parityR1) had increased OR of 2.2 (95% CI, 1.3–3.9) compared with women who have never been pregnant (parityZ0) in the Eye Disease Case–Control Study (7). On the other hand, the Beaver Dam Eye Study documented that the number of past pregnancies was significantly inversely related to soft drusen, with OR of 0.94 per pregnancy (95% CI, 0.90–0.98) (187). The relationship with the number of pregnancies to any AMD was of borderline significance, the OR being 0.96 per pregnancy (95% CI, 0.92–1.01). The number of pregnancies was not significantly related to neovascular AMD or geographic atrophy. Past use of birth control pills, age of menarche, or the number of years of menstruation had not significant effect on AMD in the Beaver Dam Eye Study (187).

Dermal Elastotic Degeneration In a small case–control study, Blumenkranz et al. found a correlation between the degree of dermal elastic degeneration in sun-protected skin with the development of neovascular AMD (14). However, there was no significant difference in outdoor sun exposure as estimated by patients. In fact, cases admitted to fewer average hour outdoors weekly than controls. The authors suggested that patients with neovascular AMD may have a generalized systemic disorder characterized by abnormal susceptibility of elastic fibers to photic or other as yet unrecognized degenerative stimuli. Antioxidant Enzymes Recently, the POLA Study, a large-scale populationbased cross-sectional study in Southern France, found that higher levels of plasma glutathione peroxidase were significantly associated with a ninefold increase in late AMD prevalence, but not with prevalence of early AMD (75). Plasma glutathione peroxidase therefore appears to be one of the strongest indicators of late AMD ever found, but the biologic meaning of

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this finding remains to be elucidated. The authors suggest that oxidative stress may lead to the induction of antioxidant enzymes, and therefore high concentrations of antioxidant enzymes may be indicators of oxidative stress. In the same study, levels of erythrocyte superoxide dismutase activity were not associated with either early or late AMD.

ENVIRONMENTAL FACTORS Cigarette Smoking Of the environmental influences, smoking has most consistently been associated with increased risks of AMD and is the strongest environmental risk factor for all forms of AMD (7,12,21,27,45,52,64,65,76,82,85, 91,92,104,188–190). A group of authors have estimated that 28,000 cases of AMD causing visual loss worse than 20/60 in people R75 years in the United Kingdom may be attributable to smoking (104). Another group estimated that 53,900 U.K. residents older than 69 years have visual impairment because of AMD attributable to smoking of whom 17,800 are blind (191). Paetkau et al. noted in their case series of 114 patients with at least one eye blind from AMD that the mean age at the onset of blindness in the first eye was 64 years in current smokers compared with 71 years in the group that had never smoked (189). However, because there was no control group, confounding factors such as increased mortality in the smoking group cannot be excluded. In a Japanese case–control study, compared with male nonsmokers, the age-adjusted OR of developing neovascular AMD was 2.97 (95% CI, 1.00–8.84) for male current smokers and 2.09 (95% CI, 0.71–6.13) for male former smokers (21). In addition, smoking habit-related variables such as use of extra filter, smoke inhalation level, age at starting smoking, duration of smoking, and the Brinkman index, defined as the numbers of cigarette smoked per day times smoking years, were found to be significantly related to an increased risk of neovascular AMD (21). The Beaver Dam Eye Study found that the relative OR for neovascular AMD in men and women who were current smokers compared with those who were former smokers or who never smoked were 3.29 (95% CI, 1.03–10.50) and 2.50 (95% CI, 1.01–6.20), respectively (52). However, there was no significant relation between smoking status and geographic atrophy. In addition, smoking status, pack-years smoked, and current exposure to passive smoking were not associated with signs of early AMD, except for a higher frequency of increased retinal pigment in men who were former smokers compared with those who had never smoked (52).

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The Blue Mountains Eye Study found current cigarette smoking to be significantly associated with both early and late AMD, after adjusting for the effects of age and sex (65). The OR of early and late AMD when comparing current smokers with those who never smoked was 1.89 (95% CI, 1.25–2.84) and 4.46 (95% CI, 2.20–9.03), respectively. A history of having ever smoked was significant for late AMD (OR, 1.83; 95% CI, 1.07–3.13) but not early AMD (65). In addition, passive smoking among subjects who never themselves smoked, but lived with a smoking spouse, incurred a moderate but not statistically significant increase in the risk of late AMD (OR, 1.42; 95% CI, 0.62–3.26). In the Genetic Factors in AMD Study, passive smoking exposure was associated with an increased risk of late AMD (OR, 1.87; 95% CI, 1.03–3.40) (27). The Blue Mountains Eye Study also disclosed age-standardized five-year incidence rates of early AMD at 10.6%, 8.2%, and 9.3%, respectively, among baseline current, past, or never smokers (64). The mean age for cases with incident late AMD was 67 years for baseline current smokers, 73 years for past smokers, and 77 years for those who had never smoked (pZ0.02). After adjusting for age, current smokers, compared with never smokers, had an increased risk of incident geographic atrophy (ageadjusted RR, 3.6; 95% CI, 1.1–11.3) and any late AMD lesions (RR, 2.5; 95% CI, 1.0–6.2). In the POLA Study, after adjustment for age and sex, current (OR, 3.6; 95% CI, 1.1–12.4) and former smokers (OR, 3.2; 95% CI, 1.3–7.7) had an increased prevalence of late AMD when compared with nonsmokers (76). The risk of late AMD increased with increasing number of pack-years, with up to a 5.2-fold increase in risk among participants (current and former smokers combined) who smoked 40 packyears or more (OR 1.9, 95% CI 0.6–6.4 for 1–19 packyears; OR 3.0, 95% CI 0.9–9.5 for 20–39 pack-years; and OR 5.2, 95% CI 2.0–13.6 for 40 pack-years and more). In addition, the risk of late AMD remained increased until 20 years after cessation of smoking. Another two studies from the United Kingdom also found that the risk in those who had stopped smoking for over 20 years was comparable to nonsmokers (27,104). The Los Angeles Latino Eye Study also disclosed that having ever smoked was associated with a higher risk of having late AMD (OR, 2.4; 95% CI, 1.03–5.4) (85). The strength of association is confirmed in a pooled analysis of data from three cross-sectional studies (Blue Mountains Eye Study, Beaver Dam Eye Study, Rotterdam Study), totaling 12,468 participants, in which current smokers had a significant three- to four-fold increased age-adjusted risk of AMD compared with never smokers (192). A latter analysis of pooled data from the same three studies also found current smoking to be associated with an increased

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incidence of late AMD (OR relative to nonsmokers, 2.35; 95% CI, 1.30–4.27) (169). Two large prospective cohort studies evaluated the relationship between smoking and AMD (91,92). In the Nurses’ Health Study with 12 years of followup, women who currently smoked R25 cigarettes per day had a RR of AMD of 2.4 (95% CI, 1.4–4.0) compared with women who never smoked (91). Risk of AMD also increased with an increasing number of pack-years smoked (p for trend !0.001). Past smokers of this amount also had a RR of 2.0 (95% CI, 1.2–3.4) compared with women who never smoked. Compared with current smokers, little reduction in risk was found even after quitting smoking for 15 or more years. In the Physicians’ Health Study, men who were current smokers of R20 cigarettes per day had a RR of AMD of 2.5 (95% CI, 1.6–3.8) compared with men who never smoked (92). Men who were past smokers had a modest elevation in RR of AMD of 1.3 (95% CI, 1.0–1.7). Some investigators have suggested that the effect of cigarette smoking on the development of AMD may be related to its effect on antioxidants in the body (21). Studies have shown that smokers have much lower plasma levels of b-carotene than do nonsmokers (172,193). Stryker et al. found that men and women who smoked one pack per day had 72% (95% CI, 58–89) and 79% (95% CI, 64–99) of the plasma b-carotene levels of nonsmokers, respectively, after accounting for dietary carotene and other variables (193). Another study also disclosed that smokers had lower plasma concentrations of total carotenoids, a-carotene, and b-carotene than nonsmokers (172). In addition, smokers have significantly lower macular pigment optical density compared with nonsmokingmatched controls (143). The macular pigment optical density and smoking frequency are inversely related in a dose–response relationship. In an experimental study using mice, exposure to cigarette smoke or the smoke-related potent oxidant hydroquinone results in the formation of sub-RPE deposits, thickening of Bruch’s membrane, and accumulation of deposits within Bruch’s membrane (194). In another study, nicotine has been found to increase the size and severity of experimental CNV in a mouse model, with older mice being more affected than younger mice (195). Interestingly, the effects of nicotine on the CNV lesions were reversed with concurrent subconjunctival administration of hexamethonium, a nonspecific nicotinic receptor antagonist which could counteract the effects of nicotine. Despite the strong association between smoking and AMD, the awareness of blindness as another smoking-related condition is low. In a recent crosssectional survey of 358 adult patients (both smokers and nonsmokers) attending a district general hospital

in the United Kingdom, only 9.5% of patients believed that smoking was definitely or probably a cause of blindness, compared with 92.2% for lung cancer, 87.6% for heart disease, and 70.6% for stroke (196). Although there was a disparity in the knowledge of these smoking-related conditions, about half of the smokers stated that they would definitely or probably quit smoking if they developed early signs of blindness and the other three conditions, with no significant differences in the proportions for these four conditions. Increasing the awareness of the link between smoking and blindness may therefore be an effective additional approach to encouraging smoking cessation. A small number of studies (10,14,15,22,73), including the Framingham Eye Study (29) and NHANES-III (80), did not find an association between smoking and AMD. In fact, one study by West et al. even showed smoking to be protective (39). However, when this decreased risk of AMD associated with smoking was further investigated, no clear dose– response relationship was demonstrated. In the large case–control study by the FRANCE-DMLA Study Group, a past history of smoking, but not current smoking status, was associated with an increased risk of AMD after univariate analysis (22). After multivariate adjustment, both factors were not significantly associated with AMD. In summary, data from several large populationbased studies (52,65,76,85,190), case–control studies (7,12,21), and two large prospective cohort studies (91,92) provide convincing evidence that cigarette smoking is a risk factor for AMD. The strongest risk is for current smokers, suggesting that there may be potential benefits of targeting antismoking patient education, especially for those who are current smokers and have signs of early AMD (65). The benefit of stopping smoking is seen after 10 years with reductions in risk although the risks do not return to that of never smokers until 20 years after stopping smoking (27,104).

Sunlight Exposure It is well established that ultraviolet (UV) and visible radiation has the potential to damage the retina and RPE (197,198). Fortunately, the human retina is protected from short-wavelength radiation, which is particular damaging, by the cornea which absorbs below 295 nm and the lens which absorbs strongly below 400 nm (199). The human retina is therefore only exposed to the “visible component” of the electromagnetic spectrum from 400 to 760 nm and some shorter wavelength infrared. This part of the electromagnetic spectrum may result in chronic or acute tissue damage when it is absorbed by any one of a number of photosensitisers or chromophores,

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e.g., the visual pigments, melanin, melanopsin, lipofuscin, flavins, and flavoproteins (199). There are some similarities between long-term changes seen in laboratory animals exposed to shorter wavelength visible light and changes seen in patients with AMD (133,200–205). It is theorized that light may lead to the generation of reactive oxygen species in the outer retina and/or choroid (133), perhaps by photoactivation of protoporhyrin (206). The activated forms of oxygen may, in turn, cause lipid peroxidation of the photoreceptor outer segment membranes, leading to the development of AMD. Tso and Woodford have shown that short exposure of intense visible light can produce atrophy at the photoreceptor level in nonhuman primates (207), but these animals did not develop histopathologic changes of drusen, diffuse thickening of Bruch’s membrane, or CNV seen in clinicopathologic studies of AMD (208). In addition, the short intense light exposure used in animal studies is different from the typical chronic exposure to light that occurs in people in their lifetime. The only animal model for lightinduced deposits in Bruch’s membrane is that of Gottsch et al. who have proposed that photosensitization of choriocapillary endothelium with blood-borne photosensitizers, such as photoporphyrin IX, is a mechanism for the histopathologic features seen in AMD (206,209). The epidemiologic evidence of an association between light exposure and AMD is lacking, with only a few clinical studies showing a positive association between sun exposure and late AMD. A small Spanish case–control study found a higher sun exposure index in AMD cases compared with controls (23). In the Chesapeake Bay Watermen Study, an association between late AMD (geographic atrophy or disciform scarring) and ocular exposure in the previous 20 years to blue or visible light (OR, 1.36; 95% CI, 1.00–1.85) was found in phakic men (41). However, no positive association was seen for early AMD (large drusen or RPE abnormalities) (41). In addition, there was no association between UV-A or UV-B exposure and any degree of AMD in the same population (39,41). The Beaver Dam Eye Study found that leisure time outdoors in summer was significantly associated with the presence of neovascular AMD when both men and women were analyzed together (OR, 2.26; 95% CI, 1.06–4.81) (53). Time spent outdoors in summer was significantly associated with the prevalence of increased retinal pigment in men (OR, 1.44; 95% CI, 1.01–2.04) but not in women (OR, 0.93; 95% CI, 0.63–1.38). Use of sunglasses and hats with brims was inversely associated with the prevalence of soft indistinct drusen in men (OR, 0.61; 95% CI, 0.38–0.98) but not in women (OR, 0.99; 95% CI, 0.69–1.45). The

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association between light exposure and AMD is not consistent across the study, since an association was found in men only and involves only a specific subset of light exposure (time spent outdoors in summer but not in winter) and a specific subset of early AMD (53). Another analysis from the Beaver Dam Eye Study to investigate the relation of sunlight exposure and indicators of sun sensitivity with the five-year incidence of early AMD showed that leisure time spent outdoors while person were teenagers (aged 13–19 years) and in their 30s (aged 30–39 years) was significantly associated with the risk of early AMD (OR, 2.09; 95% CI, 1.19–3.65) (54). However, there were no association between estimated ambient UV-B exposure or markers of sun sensitivity and the incidence of early AMD. A number of case–control studies, including the Eye Disease Case–Control Study (7), failed to show an association between sunlight exposure and AMD (12,20). An Australian case–control study in fact showed that control subjects had greater median annual ocular sun exposure (865 hours) than cases (723 hours) (pO0.0001) (20). Despite the analysis stratified by sun sensitivity, sun exposure was greater in control subjects than in cases with AMD (20). Margrain and colleagues have suggested that the equivocal findings reported in epidemiologic studies are quite unremarkable because firstly, the absence of a relationship of AMD with UV exposure simply confirms that the adult lens absorbs almost all radiation below 400 nm (199). Secondly, they suggested that the assumption that it is lifetime exposure to sunlight that is the relevant variable is probably incorrect. Instead, they suggested that the phototoxicity of blue light increases with age and is likely to be particularly great for those with lipofuscin “hot spots.” In summary, there is currently no convincing data to support strategies to reduce light exposure to the eye for the prevention of AMD. It would be premature to recommend the widespread use of blue-blocking intraocular lens during cataract surgery in the elderly because although there is considerable circumstantial evidence for such a measure, there is no direct evidence that environmental light causes retinal damage (199). However, there are now compelling reasons for undertaking a large-scale clinical trail to evaluate the prophylactic effects of blue light filtration in AMD. In addition, since there is little, if any, risk to a person wearing sunglasses, and UV light exposure has been associated with the presence of cataract (153), it is reasonable to suggest that individuals wear sunglasses for comfort and to reduce exposure of UV light to ocular structures. It must be emphasized, however, that there is no published data to indicate whether the wearing of sunglasses is of any benefit in preventing any eye disease, including AMD.

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Nutritional Factors Micronutrients The potential role of nutritional supplement to reduce the incidence or severity of AMD has received a great deal of attention (132,150). The lack of an effective treatment for the majority of cases of AMD, coupled with the public’s perception that over-the-counter nutritional supplements are relatively harmless, creates the potential for widespread use of these supplements in the absence of demonstrated effectiveness (210). Because of a possible, but as yet unproven, benefits of antioxidant vitamins in cancer, cardiovascular, and other chronic diseases, vitamin supplement usage in the United States has increased steadily in recent years. It is estimated that more than half of the adult population in the United States uses dietary supplements, including supplements of antioxidant vitamins, at a cost of approximately $12 billion annually (102). Although epidemiologic studies provide support for a protective role of nutritional antioxidants in the prevention of AMD, results of prospective randomized clinical trials are necessary before firm conclusions can be drawn about the balance of benefits and risks of nutritional supplements for the prevention of AMD. In fact, use of nutritional supplement has been shown to have deleterious effects in some nonophthalmic medical trials. The Alpha-Tocopherol, Beta-Carotene (ATBC) Cancer Prevention Study found a higher incidence of lung cancer among men who received b-carotene than among those who did not (change in incidence, 18%; 95% CI, 3–36%) (211). There were also more deaths due to lung cancer, ischemic heart disease, and ischemic and hemorrhagic stroke among recipients of b-carotene, with an increased overall mortality of 8% (95% CI, 1–16%). Those randomized to vitamin E supplementation had higher rates of hemorrhagic stroke, but there was no overall difference in mortality rates or cancer incidence (211). In the Carotene and Retinol Efficacy Trial, participants who were given b-carotene and vitamin A supplements had a 28% (95% CI, 4–57%) increased incidence of lung cancer and a 17% (95% CI, 3–33%) higher mortality compared with those who were not (212). Antioxidants Some have suggested that supplementation with antioxidants and a variety of trace minerals necessary for the proper functioning of some key enzyme systems may reduce the risk of AMD (133,213,214). Photochemical damage from light can induce the production of activated forms of oxygen, which in turn can cause lipid peroxidation of the photoreceptor outer segment membranes. Antioxidants, such as vitamin C, vitamin E, b-carotene, and

glutathione, and antioxidant enzymes, such as selenium-dependent glutathione peroxidase, in theory could act as singlet oxygen and free radical scavengers and thereby prevent cellular damage (215). There is considerable interest in determining if free radicals contribute to the pathogenesis of AMD and if high levels of these antioxidants may protect against AMD. This hypothesis is supported by findings of disruption of retinal photoreceptors in nonhuman primates with deficiencies of vitamins A and E (216) and a protective effect of vitamin C in reducing the loss of rhodopsin and photoreceptor cell nuclei in rats exposed to photic injury (217). Many studies have used serum levels of micronutrients to investigate the relationship of these micronutrients and AMD. Unfortunately, high and low levels are defined differently for most studies. Most have defined the high and low categories on the basis of percentile categories, i.e., those individuals with serum concentrations above a given percentile were categorized as high and those below a given percentile were categorized as low. Blumenkranz et al. reported in their small case– control study that the serum levels of vitamins A, C, and E were not different in cases of neovascular AMD and in controls (14). In another case–control study, serum levels of vitamin E in cases and controls were similar but serum selenium was significantly lower in cases compared with controls (pZ0.02) (15). The Eye Disease Case–Control Study found that persons with carotenoid scores in the medium and high percentile groups, compared with those in the low group, had markedly reduced levels of risk of neovascular AMD, with levels of risk reduced to one-half (OR, 0.5; 95% CI, 0.4–0.8) and one-third (OR, 0.3; 95% CI, 0.2–0.6), respectively (6). Similarly, except for lycopene, higher levels of individual carotenoids (lutein/zeaxanthin, b-carotene, a-carotene, or cryptoxanthin) were associated with statistically significant reductions in risk of neovascular AMD. In addition, there was a progressive decrease in risk of neovascular AMD with increasing levels of the carotenoids and increasing levels of the antioxidant index. However, no statistically significant overall association was seen with neovascular AMD and serum levels of vitamin C, Vitamin E, and selenium in the study (6). West et al. examined the relationship between plasma levels of retinol, ascorbic acid, a-tocopherol, and b-carotene in 630 participants of the Baltimore Longitudinal Study on Aging (46). They found a favorable association between plasma antioxidants and AMD. Their data suggest that only a-tocopherol was significantly associated with a protective effect (OR for middle vs. lowest quartiles 0.50, 95% CI 0.32–0.79; OR for highest vs. lowest quartiles 0.43, 95% CI 0.25–0.73). This is consistent with findings from

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a small Spanish case–control study (23). There was a suggestion of a protective effect with ascorbic acid and b-carotene in the Baltimore Longitudinal Study on Aging, but their effects were not statistically significant (46). No protective effect was noted for retinol. For late AMD (neovascular AMD or geographic atrophy), no significant protective effect was observed for any plasma micronutrient. An antioxidant index constructed of ascorbic acid, a-tocopherol, and b-carotene, controlled for age and sex, suggested that high values were protective for AMD compared with low values. It is now generally recognized that plasma a-tocopherol level should be expressed in terms of its concentration within lipids or lipoproteins (218–220). For this reason, the POLA Study correlated ocular findings with both plasma a-tocopherol and lipid-standardized a-tocopherol levels (74). The study found a weak negative association between late AMD and plasma a-tocopherol level which was not statistically significant (pZ0.07) but this relationship was strengthened when a-tocopherol–lipid ratio instead of plasma level was used (pZ0.003). After adjusting for confounding factors, the ORs (95% CI) for late AMD in persons with a-tocopherol–lipid ratio in the highest and middle quintiles, compared with those with ratio in the lowest quintile, were 0.18 (0.05–0.67) and 0.46 (0.22–0.95), respectively. The ORs (95% CI) for any sign of early AMD in persons with a-tocopherol– lipid ratio in the highest and middle quintiles, compared with those with ratio in the lowest quintile, were 0.72 (0.53–0.98) and 0.78 (0.61–1.00), respectively. No association was found with plasma retinol and ascorbic acid levels or with red blood cell glutathione values (74). Data from NHANES-I, collected between 1971 and 1972, suggest that the frequency of consumption of fruits and vegetables characterized as rich in vitamin A is inversely related to the prevalence of AMD, after adjustment for medical and demographic factors (8). This concurs with the Nurses’ Health Study and the Health Professionals Follow-Up Study which showed that fruit intake was inversely associated with the risk of neovascular AMD (95). Participants from the two studies who consumed three or more servings per day of fruits had a pooled multivariate RR of 0.64 (95% CI, 0.44–0.93) compared with those who consumed less than 1.5 servings per day. The Eye Disease Case–Control Study evaluated the relationship of dietary intake of carotenoids, and vitamins A, C, and E, with neovascular AMD (16). Those in the highest quintile of carotenoid intake, after adjusting for other risk factors of AMD, had an OR of 0.57 (95% CI, 0.35–0.92) for neovascular AMD compared with those in the lowest quintile. Among the specific carotenoids, the strongest association with a reduced risk for

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neovascular AMD was found with lutein and zeaxanthin, which are primarily obtained from dark green, leafy vegetables. Intake of vitamin C was associated with a small but nonsignificant reduction in risk of neovascular AMD. No reduction in risk was found with intake of vitamin A or E. The Rotterdam Study, using a 170-item semiquantitative food frequency questionnaire, found a significant inverse association for intake of vitamin E and incident AMD (221). After adjustment, a one standard deviation increase in intake of vitamin E was associated with a reduced risk of AMD of 8% (95% CI, 0–16%). The risk of AMD by quartile of nutrient intake also indicated a dose–response relationship between vitamin E and reduced risk of AMD (p value for trend Z0.04). The authors in the Rotterdam Study also estimated the impact of the combined dietary intake of the four nutrients (b-carotene, vitamins C and E, and zinc) that were studied in AREDS (see below) (222). It should, however, be pointed out that the intake of these nutrients in the Rotterdam Study was considerably lower than the high-dose supplements used in AREDS. An above-median intake of the four nutrients compared with a below-median intake of at least one of these nutrients, was associated with a reduced risk of AMD [hazard ratio (HR), 0.65; 95% CI, 0.46–0.92] adjusted for all potential confounders. In persons with a below-median intake of all four nutrients, the risk of AMD was increased but not significantly so (HR, 1.20; 95% CI, 0.92–1.56). The Blue Mountains Eye Study, using a validated 145-item semiquantitative food frequency questionnaire, found no significant associations between early or late AMD and dietary intakes of carotene, vitamin A, or vitamin C, from combined diet and supplement, after adjusting for age, sex, current smoking, and AMD family history (69). There were no statistically significant trends for decreasing AMD prevalence with increasing intake of any antioxidant. Consumption of supplements was also not significantly associated with either early (OR, 1.0; 95% CI, 0.7–1.4) or late (OR, 1.2; 95% CI, 0.6–2.3) AMD. In addition, a nested case–control study within the Blue Mountains Eye Study did not find any association between AMD or serum a-tocopherol or b-carotene (70). Similarly, no significant associations between the intake of vitamin C or E, or carotenoids from the diet or supplements and the prevalence of early or late AMD were observed in the Beaver Dam Eye Study (223). However, in a nested case–control study within the Beaver Dam Eye Study population-based cohort, low levels of serum lycopene, but not other carotenoids (a-carotene, b-carotene, b-cryptoxanthin, or lutein and zeaxanthin), was related to an increased likelihood of AMD (OR, 2.2; 95% CI, 1.1–4.5) (18).

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The association between self-selection for antioxidant vitamin supplement use and incidence of AMD was examined among 21,120 participants in the Physicians’ Health Study I who did not have a diagnosis of AMD at baseline (9). A total of 279 incident cases of AMD with vision loss to 20/30 or worse were confirmed during an average follow-up of 12.5 years. Compared to nonusers of vitamin supplements, persons who reported taking vitamin E supplements at baseline had a nonsignificant 13% reduced risk of AMD (RR, 0.87; 95% CI, 0.53–1.43), after adjusting for other risk factors. Users of multivitamins had a nonsignificant 10% reduced risk of AMD (RR, 0.90; 95% CI, 0.68–1.19). No reduced risk of AMD was observed for users of vitamin C supplements (RR, 1.03; 95% CI, 0.71–1.50).

2–17%). The risk of AMD by quartile of zinc intake also showed a dose–response relationship between zinc intake and reduced risk of AMD (p value for trend Z0.06). A lower serum level of zinc was found in AMD cases compared with controls in a small Spanish case–control study (23). However, zinc intake was unrelated to late AMD in the same study. The Eye Disease Case–Control Study did not find any significant relationships between serum zinc levels or zinc supplementation and risk of neovascular AMD (7). This concurs with findings from the Blue Mountains Eye Study (69). Two large prospective studies, the Nurses’ Health Survey, and the Health Professionals Follow-up Study, also concluded that moderate zinc intake, either in food or in supplements, was not associated with a reduced risk of AMD (96).

Zinc Zinc has received attention because of its high concentration in ocular tissues, particularly the sensory retina, RPE, and choroid (224) and its role as a cofactor for numerous metalloenzymes, including retinol dehydrogenase and catalase (225). In addition, there are some reports of zinc deficiency in the elderly, the population subgroup at greatest risk of AMD (226). Data from NHANES-III suggest that persons aged R71 years, together with young children aged 1 to 3 years and adolescent females aged 12 to 19 years, were at the greatest risk of inadequate zinc intakes (227). It has been hypothesized that zinc deficiency in elderly persons may cause the loss of zinc-dependent coenzymes in the RPE, resulting in the development or worsening of AMD (228). Newsome et al. conducted a prospective, randomized, double-blind, placebo-controlled trial that investigated the effects of oral zinc administration on the visual acuity outcome in 151 subjects with early to late AMD (229). They showed that eyes in zinc-treated group had significantly less visual loss than the placebo group after a follow-up of 12 to 24 months. In addition, there was less accumulation of drusen in the zinctreated group compared with the placebo group. However, in another double-masked, randomized, placebo-controlled trial, oral zinc supplementation did not have any short-term effect on the course of AMD in patients who have neovascular AMD in one eye (230). The Beaver Dam Eye Study found that people in the highest quintile, compared with those in the lowest quintile, for intake of zinc from foods had lower risk of early AMD (OR, 0.6; 95% CI, 0.4–1.0) (223). This is consistent with the Rotterdam Study which showed a significant inverse association between zinc intake and incident AMD (221). After adjustment, a one standard deviation increase in intake of zinc was associated with a reduced risk of incident AMD of 9% (95% CI,

Randomized Trials of Antioxidant Vitamins and AMD The most reliable, and only direct, method of testing the potential protective effects of nutritional supplements is to conduct randomized clinical trials. A small prospective randomized clinical trial showed that a specific 14-component antioxidant-mineral capsule (Ocuguard w, Twin Lab, Inc., Ronkonkoma, New York, U.S.A.) taken twice daily stabilized but did not improve dry AMD over one-and-a-half years (231,232). Several large-scale randomized clinical trials, including AREDS (210,222), the Physicians’ Health Study II (233), the Vitamin E, Cataract, and Age-related macular degeneration Trial (VECAT) (234,235), the Women’s Health Study (236), and the Women’s Antioxidant Cardiovascular Study (237), have been designed to address the issue of antioxidant vitamins and AMD (Table 7). Results of these major trials should provide the strongest evidence to support or to refute an association of antioxidant intake with AMD. Of these trials, AREDS (222), sponsored by the National Eye Institute (National Institutes of Health, Bethesda, Maryland, U.S.A.), and VECAT (235) have been completed. The AREDS is an 11-center double-masked clinical trial that randomly assigned participants to receive oral total daily supplementation of (i) antioxidants (vitamin C, 500 mg; vitamin E, 400 IU; and b-carotene, 15 mg); (ii) zinc (zinc, 80 mg as zinc oxide, and copper, 2 mg as cupric oxide to prevent potential anemia); (iii) antioxidants plus zinc; or (iv) placebo (222). Participants from aged 55 to 80 years were enrolled from November 1992 through January 1998 and followed-up until April 2001. Enrolled participants in the AREDS AMD trial had extensive [drusen area R125 mm diameter circle (about 1/150 disc area)] small (!63 mm) drusen, intermediate (63–124 mm) drusen, large (R125 mm) drusen, noncentral geographic atrophy, or pigment abnormalities in

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71

Table 7 Some Large-Scale Randomized Trials Addressing the Balance of Risks and Benefits of Antioxidant Vitamins for AgeRelated Macular Degeneration Name of randomized trial

Details of trial

Remarks

Age-Related Eye Disease Study (210,228)

A multicenter prospective, double-blind, randomized clinical trial evaluating the role of antioxidant micronutrients (b-carotene, vitamins E and C, and/or zinc) in AMD and cataract. Patients with early AMD to advanced unilateral AMD were randomized to receive antioxidant vitamins, zinc, combination therapy, or placebo. Four thousand, seven hundred and fifty-seven individuals aged 55–80 years at baseline were enrolled. Morbidity and mortality associated with the supplements were monitored. Endpoints include doubling of visual angle and morphologic progression of AMD A randomized, double-blind, placebo-controlled trial enrolling 15,000 willing and eligible physicians R55 years. It will test alternate day b-carotene, alternate day vitamin E, daily vitamin C, and a daily multivitamin, in the prevention of AMD as well as cataract, total and prostate cancer, and cardiovascular disease A four-year randomized, placebo-controlled, double-masked trial of vitamin E on the rate of progression of cataract and AMD in 1193 elderly Australian volunteers

Sponsored by the National Eye Institute of the National Institutes of Health. Trial was completed in 2001

A randomized, double-blind, placebo-controlled trial of vitamin E and low-dose aspirin in the prevention of cancer and cardiovascular disease among 39,876 apparently healthy, postmenopausal U.S. female health professionals A randomized, double-blind, placebo-controlled, secondary prevention trial to test antioxidant vitamins (b-carotene, vitamin C, vitamin E), and a combination of folate, vitamin B6, and vitamin B12, among 8171 female health professionals, aged 40 or older, who are at high risk for cardiovascular disease

Has been funded by the National Eye Institute to extend its investigation to include AMD and cataract

Physicians’ Health Study II (PHS II) (233)

Vitamin E, Cataract, and Age-Related Macular Degeneration Trial (234,235) Women’s Health Study (102,236) Women’s Antioxidant Cardiovascular Study (102,237)

PHS II is sponsored by BASF AG. Approximately half of the PHS II cohort comprises participants of the PHS I cohort which was sponsored by the National Institutes of Health Sponsored by the National Health and Medical Research Council of Australia and other sources

Has been funded by the National Eye Institute to extend its investigation to include AMD and cataract

Abbreviations: AMD, age-related macular degeneration; PHS, Physicians’ Health Study.

one or both eyes, or advanced AMD or vision loss due to AMD in one eye. At least one eye had a bestcorrected visual acuity of 20/32 or better [the study eye(s)]. The average follow-up of the 3640 enrolled study participants in the AREDS AMD trial was 6.3 years, with 2.4% lost to follow-up. Compared with patients receiving placebo, patients randomized to supplementation with antioxidants plus zinc had a statistically significant odds reduction for the development of advanced AMD (OR, 0.72; 99% CI, 0.52–0.98). Advanced AMD was defined as photocoagulation or other treatment for CNV, or photographic documentation of any of the following: geographic atrophy involving the center of the macula, nondrusenoid RPE detachment, serous or hemorrhagic retinal detachment, hemorrhage under the retina or RPE, and/or subretinal fibrosis. The ORs for zinc alone and antioxidants alone are 0.75 (99% CI, 0.55–1.03) and 0.80 (99% CI, 0.59–1.09), respectively. The study found that participants with extensive small drusen, nonextensive intermediate size drusen, or pigment abnormalities had only a 1.3% five-year probability of progression to advanced AMD. There was no evidence of any treatment benefit in delaying the progression of these patients to more severe drusen pathology. When

these 1063 participants were excluded and analysis performed for the rest of the participants who had more severe age-related macular features {extensive [drusen area R360 mm diameter circle (about 1/16 disc area) if soft indistinct drusen are present or drusen area R656 mm diameter circle (about 1/5 disc area) if soft indistinct drusen are absent] intermediate drusen, large drusen, or noncentral geographic atrophy in one or both eyes, or advanced AMD or vision loss [best-corrected visual acuity !20/32] due to AMD in one eye} and who are at the highest risk for progression to advanced AMD, the odds reduction estimates increased (antioxidants plus zinc: OR 0.66, 99% CI 0.47–0.91; zinc: OR 0.71; 99% CI 0.52–0.99; antioxidants: OR 0.76; 99% CI 0.55–1.05). Estimates of RRs derived from the ORs suggested risk reductions for those taking antioxidants plus zinc, zinc alone, and antioxidants alone of 25%, 21%, and 17%, respectively. Both antioxidants plus zinc and zinc significantly reduced the OR of developing advanced AMD in this higher risk group. However, the only statistically significant reduction in rates of at least moderate vision loss [defined as decrease in best-corrected visual acuity score from baseline of R15 letters in a study eye (equivalent to a doubling or more of the initial visual angle, e.g., 20/20 to 20/40 or worse, or 20/50 to 20/100

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or worse)] occurred in persons randomized to receive antioxidants plus zinc (OR, 0.73; 99% CI, 0.54–0.99) in this same group. The estimated 27% odds reduction of at least moderate vision loss for the combination arm (antioxidants plus zinc) may be the combined benefit of the zinc component (odds reduction of 17%) and the antioxidant component (odds reduction of 15%). There was no statistically significant serious adverse effect associated with any of the formulations. The study recommended that persons older than 55 years should have dilated eye examinations to determine their risk of developing advanced AMD. Those with extensive intermediate size drusen, at least one large druse, noncentral geographic atrophy in one or both eyes, or advanced AMD or vision loss due to AMD in one eye, and without contraindications such as smoking, should consider taking a supplement of antioxidants plus zinc to reduce their risk of progression to advanced AMD and vision loss. Because results from two other randomized clinical trials suggested increased risk of mortality among smokers supplementing with b-carotene (211,212), persons who smoke cigarettes should probably avoid taking b-carotene, and they might choose to supplement with only some of the study ingredients. It has been estimated that 8 million persons aged R55 years in the United States have monocular or binocular intermediate AMD, or monocular advanced AMD as defined in AREDS (238). They are considered to be at high risk for advanced AMD. Of these people, 1.3 million are expected to develop advanced AMD if left untreated. It is thought that if all of those at risk of advanced AMD received supplements such as those used in AREDS, more than 300,000 (95% CI, 158,000–487,000) of them would avoid advanced AMD and any associated vision loss during the next five years. The VECAT is a prospective randomized placebo-controlled clinical trial in Australia involving 1193 healthy volunteers aged 55 to 80 years (235). One of the major arms of the trial looked at vitamin E supplementation and incidence and progression of AMD. Participants were randomized to receive either 500 IU natural vitamin E (335 mg D-a tocopherol) in a soybean oil suspension encapsulated in gelatin or a matched placebo capsule and were followed-up for four years. No protective or deleterious effect of the daily dietary supplementation was found on the incidence or progression of AMD. Secondary analyses of visual acuity and visual function also failed to show an intervention effect. The lack of a protective effect of vitamin E supplementation in VECAT could mean that vitamin E does not have an important role in protecting against AMD (235). However, it is possible that the follow-up of four years in this study was too short and vitamin E

may need to be taken for a longtime to have an effect. The lowered risk of AMD linked with high intakes or blood levels of antioxidants in some observational studies could reflect a lifelong pattern of eating (239). There may be a longtime lag between the time of damage and appearance of clinical signs of AMD. Another possibility is that the baseline antioxidant status of the trial participants was too high for supplementation to be effective (239). The plasma vitamin E levels were near the top of the reference range and over 25% of participants had been taking supplementary vitamin E prior to the trial. Lastly, the trial was originally set up with statistical power to detect a 15% reduction in cataract. Although the authors stated that the sample size may have been adequate to detect a 50% reduction in the incidence of AMD, it may have been unrealistic to expect vitamin E to have such a huge effect. The ATBC Cancer Prevention Study, which took place in Finland between 1984 and 1993, was originally designed to investigate the efficacy of a-tocopherol and b-carotene in the prevention of lung cancer in over 29,000 smoking males aged 50 to 69 years (211). The participants were randomly assigned to a-tocopherol (50 mg/day), b-carotene (20 mg/day), both of these, or placebo. An end-of-trial ophthalmic examination on a random sample of 941 participants aged R65 years from 2 of the 14 study areas was performed to investigate if the five- to eight-year intervention was associated with a difference in the AMD prevalence (240). Although no ophthalmic examination was performed at baseline, an equal spread of AMD among the different treatment groups is assumed due to randomization. The study found more cases of AMD in the a-tocopherol group (32%; 75/237), b-carotene group (29%; 68/234), and combined antioxidant group (28%; 73/257) than in the placebo group (25%; 53/213). However, neither antioxidant was significantly associated with an increased risk of AMD in a logistic regression analysis controlling for possible risk factors.

Dietary Carotenoids Lutein and Zeaxanthin These have been discussed under the subheading macular pigment optical density as one of the ocular risk factors of AMD (see above). Dietary Fish Intake A high proportion of polyunsaturated u-3 fatty acids, particularly docosahexaenoic acid, is present in the human retina and macula (213,241). Docosahexaenoic acid appears to play an important role in the normal functioning of the retina and is found predominantly in oily fish and offal (172). Increased consumption of fish and fish oils containing u-3 fatty acids has been

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associated with a protective effect against atherosclerosis in several studies (242–244). The Blue Mountains Eye Study found that more frequent consumption of fish appeared to protect against late AMD but not early AMD, after adjusting for age, sex, and smoking (68). The protective effect of fish intake for late AMD commenced at a relatively low frequency of consumption (OR for intake 1–3 times/ month vs. intake !1 time/month, 0.23; 95% CI, 0.08– 0.63) and overall had an OR of 0.5. A borderline protective effect for consumption of polyunsaturated fat was also observed (OR for intake in highest vs. lowest quintile, 0.40; 95% CI, 0.14–1.18). This concurs with the finding in the Beaver Dam Eye Study that increased consumption of margarine, which contains higher ratios of polyunsaturated to saturated fatty acids, was associated with a reduction in risk for early AMD (OR for intakes in highest vs. lowest quintile, 0.5; 95% CI, 0.4–0.8) (56). However, intake of seafood, a marker of intake of u-3 fatty acids, was unrelated to early or late AMD (56). Sanders et al. also found no association between AMD and the proportion of polyunsaturated fatty acids in the plasma and erythrocyte phospholipids in a case– control study (172). The relation of other dietary fat intake and AMD has been dealt with under cardiovascular disease risk factors (see above).

Alcohol Consumption Obisesan et al. used data from NHANES-I to investigate the relationship of alcohol consumption and AMD and found that persons who consumed 12 or fewer drinks of alcohol per year appear to be less likely to develop AMD when compared with nondrinkers (4% vs. 7%, respectively), although this was not statistically significant (37). Beer consumption alone did not have a significant effect on the development of AMD (OR, 0.72; 95% CI, 0.45–1.12). After adjusting for the effect of age, gender, income, history of congestive heart failure, and hypertension, wine consumption showed a statistically significant negative association with AMD (OR, 0.81; 95% CI, 0.67–0.99). In the Eye Disease Case–Control Study, higher alcohol intake was also found to be related to a reduced risk of neovascular AMD (245). The Andhra Pradesh Eye Disease Study also found a lower prevalence of AMD in light alcohol drinkers compared with nondrinkers (adjusted OR, 0.38; 95% CI, 0.19–0.7) (86). Considering that AMD may share similar pathologic processes with cardiovascular diseases (73), the findings that moderate wine consumption is associated with decreased OR of developing AMD are consistent with reports of a protective effect of moderate alcohol intake for coronary artery disease and stroke (246).

RISK FACTORS FOR AMD AND CHOROIDAL NEOVASCULARIZATION

73

In the Beaver Dam Eye Study, beer consumption was found to be associated with increased prevalence of retinal pigment and neovascular AMD (247). In an incidence study, beer consumption was found to be positively associated with the incidence of soft indistinct drusen, increased drusen area, and confluence of soft drusen (87). People who reported being heavy drinkers at baseline were more likely to develop late AMD (RR, 6.94; 95% CI, 1.85–26.1) after 10 years than people who reported never having been heavy drinkers (248). The Blue Mountains Eye Study found no association between alcohol consumption and the prevalence of early or late AMD or large drusen, although there was a significant positive association between consumption of distilled spirits and early AMD (249). Prospective data from 111,238 women and men in the Nurses’ Health Study and the Health Professionals Follow-Up Study do not support a protective effect of moderate alcohol consumption on the risk of AMD (97). No substantial association between total alcohol intake and incidence of AMD was found from the 697,498 person-years of follow-up in women and 229,180 person-years of follow-up in men. After controlling for age, smoking, and other risk factors, the pooled RRs (95% CI) for AMD compared with nondrinkers were 1.0 (0.7–1.2) for drinkers who consumed 0.1–4.9 g/day of alcohol, 0.9 (0.6–1.4) for 5–14.9 g/day, 1.1 (0.7–1.7) for 15–29.9 g/day, and 1.3 (0.9–1.8) for 30 g/day or more. However, there was a modest increased risk of early AMD and geographic atrophy in women who consumed 30 g/day or more of alcohol (RR, 2.04; 95% CI, 1.22–3.42). There was no association between alcohol intake and neovascular AMD in either sex, but it should be pointed out that the number of neovascular AMD was small in the study. Prospective data of 21,041 male physicians with an average follow-up of 12.5 years in the Physicians’ Health Study also indicate that alcohol intake is not appreciably associated with the risk of AMD (93). The overall RR of any AMD among men who reported baseline alcohol consumption of R1 drink/week compared with those drinking !1 drink/week was 0.97 (95% CI, 0.78–1.21) after multivariate adjustment. Similarly, the RR of AMD with visual loss and neovascular AMD were 0.99 (95% CI, 0.75–1.31) and 0.87 (95% CI, 0.51–1.51), respectively, after multivariate adjustment. For AMD with vision loss, the RRs (95% CI) for those reporting !1 drink/week, 1 drink/week, 2 to 4 drinks/week, 5 to 6 drinks/week, and R1 drink/day at baseline were 1.0 (referent), 0.75 (0.47–1.21), 1.0 (0.69–1.45), 1.20 (0.81–1.78), and 1.19 (0.87–1.61), respectively. Several other smaller studies also found no association between the history of alcohol consumption and AMD (10,15,45).

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DEVELOPMENT OF CNV IN AMD AMD is a bilateral condition that tends to be fairly symmetric in its presentation and clinical course (250,251). A study of the symmetry of disciform scars found a significant correlation between eyes in terms of the final scar size, and large macular scars were more frequent in the second eye if the first eye had a large scar (250). In the Blue Mountains Eye Study, 40% of the neovascular AMD cases were bilateral (71). Once one eye is affected, there is a significant risk for involvement in the fellow eye. Although peripheral vision is almost always retained in late AMD, bilateral central scotomas result in decreased mobility and impaired reading ability, and dramatically impact on occupational and recreational activities. It has been demonstrated that choroidal neovascular lesions of AMD account for the vast majority of severe visual loss from this condition (252). The 79% and 90% of eyes legally blind due to AMD in the Framingham Eye Study (3) and a large case–control study (12), respectively, had CNV. Thus, patients at risk of bilateral CNV are at the greatest risk of severe visual loss. Because the treatment of CNV is most effective when it is new and has not caused irreversible scarring and photoreceptor damage, it is important to identify high-risk patients and educate them about the

importance of daily self-monitoring of the central visual field for each eye.

Risk of CNV in AMD A number of studies have reported the natural course of patients with bilateral drusen with good visual acuity (Table 8) (116,254–256) while others have assessed the risk of developing CNV in the fellow eye in patients with age-related CNV in one eye (Table 9) (116,257–266). Variation in the reported risk among the studies is probably due partly to variation in the clinical features of the macula (e.g., drusen size and confluence, presence of focal hyperpigmentation, and/or RPE depigmentation) (253). Lanchoney et al. (267), using the follow-up studies of Smiddy and Fine (254) and Holz et al. (255), predicted that the proportion of patients with bilateral soft drusen developing CNV in either one or both eyes would be 12.4% within 10 years, but this risk varied from 8.6% to 15.9%, depending on sex and age of the patient. In their model, the rate of development of CNV in the first eye was reduced after five years to 75% of the initial rate observed in follow-up studies and to 50% of the initial rate after 10 years (267). Gass reported that of 91 patients who were seen initially with loss of vision due to disciform macular detachment or degeneration in one eye, neovascular

Table 8 Risk of Developing Choroidal Neovascularization in Age-Related Macular Degeneration Patients with Bilateral Drusen and Good Bilateral Visual Acuity

Study Gass (1973) (116)

Number of eyes/patients 98/49

Mean age (range in years) 61 (29–81)

Initial visual acuity

Mean follow-up (range in years)

20/20 OU in 21 patients (43%) 20/25 to 20/40 OU in 18 patients (37%) 20/50 or better in 132 (93%) of eyes studied

4.9

9 (18%) of 49 patients developed central visual loss in one eye because of CNVs

4.3 (0.5–8.6)

8 eyes (9.9%) of 7 patients developed CNVs over 4.3 years (14.5% cumulative risk) 7 eyes (8.5%) of 6 patients developed severe visual loss (12.7% 5-year cumulative risk) 17 (13.5%) of 126 patients developed new lesionsa Cumulative incidence of new lesions among patients R 65 years old was: 8.55% @1 year 16.37% @ 2 years 23.52% @ 3 years 1 (0.2%) of 483 patients developed CNV 1 (0.2%) of 483 patients developed peripapillary CNVs None developed geographic atrophy

Smiddy and Fine 142/71 (1984) (254)

58 (16–78)

Holz et al. (1994) 126 patients (255)

68

“Good”

3

Bressler et al. (1995) (256)

NA

NA

5

483 patients

Results

a Classic or occult CNVs, RPE detachmentGCNVs, or geographic atrophy extending to the fovea. Abbreviations: NA, information not available; OU, both eyes; CNV, choroidal neovascularization.

42 patients

36 patients

104 patients

84 patients

127 patients with extrafoveal CNVs in one eye

670 patients with juxtafoveal or subfoveal CNVs in one eye

Teeters and Bird (1973) (257)

Gragoudas et al. (1976) (259)

Gregor et al. (1977) (260)

Strahlman et al. (1983) (261)

Bressler et al. (1990) (269)

Macular Photocoagulation Study Group (1997) (266)

NA

NA

68 (47–91)

NA

NA

NA

67 (49–82)

Mean age (range in years) Initial visual acuity

20/400 or better

NA

NA

NA

“Good”

20/20 in 30 patients (33%) 20/40 or better in all but 7 patients (92%) NA

b

Serous RPE detachment of RPE and retina without evidence of CNVs. Five or more drusen, large (O63 mm in diameter) focal hyperpigmentation, systemic hypertension. Abbreviations: NA, information not available; RPE, retinal pigment epithelial; CNV, choroidal neovascularization.

a

91 patients

Number of patients

NA

5 years

27 months (6–95 months)

Up to 5 years

22 months (12–48 months)

21 eyes (50%) followed-up for 12 months (7–19 months) 16 eyes (38%) followed-up for 10 months (4–19 months) 3 eyes (7%) followed-up for 9, 16, and 21 months 2 eyes (5%) followed-up for 19 and 24 months

4 years

Mean follow-up (range)

All three eyes developed avascular disciform appearancea Both eyes developed neovascular disciform appearance Overall, 5 (12%) of 42 eyes developed “avascular” and neovascular complications 13 (36%) of 36 patients developed disciform macular lesions 12–15%/year developed CNVs Results were: 9/104 (9.8%) @ 1 year 18/74 (19%) @ 2 years 17/53 (30%) @ 3 years 11/23 (48%) @ 4 years 5/11 (45%) @ 5 years Using Kaplan–Meier technique, the risk of developing exudative maculopathy in fellow eye was estimated to be 3–7% yearly 6/84 (7%) developed CNVs 2/84 (2%) developed pigment epithelial detachment 1/84 (1%) developed geographic atrophy over 18 months (range 5–36 months) 10% of eyes with no large drusen or RPE hyperpigmentation compared with 58% of eyes with both large drusen and hyperpigmentation developed CNVs in the fellow eye within 5 years Estimated 5-year incidence rates ranged from 7% for the subgroup with one risk factor to 87% for the subgroup with all four risk factorsb The presence of occult CNVs in the first eye affected had no influence on the type of CNVs in the fellow eye

Increased drusen and pigmentation

No change

31 eyes (34%) lost central vision because of CNVs during follow-up

Results

Risk of Developing Choroidal Neovascularization in the Fellow Eye of Age-Related Macular Degeneration Patients with Choroidal Neovascularization in One Eye

Gass (1973) (116)

Study

Table 9

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lesions developed in the second eye in 31 patients (34%) over an average follow-up of four years (116). Chandra et al. reported that among 36 patients with unilateral disciform lesions, bilateral involvement occurred in 13 (36%) after an average follow-up of 22 months (258). Gregor et al. followed 104 patients aged 60 to 69 years who initially had a disciform macular degeneration in one eye for between one and five years (260). From their data, they estimated that the annual incidence of developing a disciform lesion in the fellow eye to be 12% per year in the first five years. Strahlman et al. reported that among 84 patients with unilateral exudative AMD, 9 (11%) developed bilateral involvement after a mean follow-up of 27 months (261). Baun et al. studied 45 patients with unilateral neovascular AMD for four years and documented CNV in the fellow eye in 14 (31%) patients (262). Sandberg et al. found an average of 8.8% of patients with unilateral neovascular AMD develop CNV in the fellow eye each year in their prospective series of 127 patients with 4.5 years of follow-up (263). The MPS Group examined the data of fellow eyes of study participants in the MPS randomized trial for argon laser photocoagulation for extrafoveal CNV secondary to AMD (265) and the randomized trials of laser photocoagulation for new juxtafoveal CNV, new subfoveal CNV, or recurrent subfoveal CNV secondary to AMD (266). In the extrafoveal CNV trial, 128

100

participants had a fellow eye that was initially free of CNV at baseline (265). During five years of follow-up, choroidal neovascular lesions associated with AMD were observed in 33 (26%) of the 128 fellow eyes. In the other three MPS trials, among 670 patients with no classic or occult CNV in the fellow eye at the time of enrollment, CNV developed in 236 (35%) within five years (266). The cumulative incidence rates of CNV in the fellow eye for this group of patients were estimated to be 10%, 28%, and 42% at one, three, and five years, respectively (Fig. 1). The AREDS also evaluated the incidence of neovascular AMD among participants of the randomized trial (268). Neovascular AMD was defined in the study as photocoagulation for CNV, or photographic evidence of any of the following: nondrusenoid RPE detachment, serous or hemorrhagic retinal detachment, hemorrhage under the retina or the RPE, and subretinal fibrosis. Of individuals with early or intermediate AMD at baseline with a median follow-up of 6.3 years, 788 were at risk of developing advanced AMD in one eye (the fellow eye had advanced AMD) and 2506 were at risk in both eyes. Of the 2506 participants in the bilateral drusen group, 256 (10%) developed neovascular AMD in at least one eye during the course of the study. Of the 788 participants in the unilateral advanced AMD group, 278 (35%) developed neovascular AMD during the study.

0 (n=35) 1 (n=105) 2 (n=142) 3 (n=105) 4 (n=45)

90

87 81

Eyes with choroidal neovascularization, %

80

61

60 50

48

27

28 20

20 10

4 0 1.5 3

0 6

16 14

12

11 7 3 0

22

13

13

7

5 0 12

23 20

0 18

24

30

7

3 36

32 23

23

7

7

25

19

15

3

0

38

30

28

53 44

38

34 30

49

47

40

40

0

72

68

70

42

48

54

7 60

Follow-up period, mo

Figure 1 Incidence of choroidal neovascularization by number of risk factors present including hypertension, R5 drusen, R1 large drusen (greatest linear dimension O63 mm), and focal hyperpigmentation. Source: From Ref. 266.

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Risk Factors for Progression to CNV The MPS Group evaluated selected risk factors for development of CNV in the fellow eye of patients in the randomized trials of laser photocoagulation for new juxtafoveal CNV, new subfoveal CNV, or recurrent subfoveal CNV secondary to AMD (266). A trend for increased incidence with age (pZ0.06) was observed. No strong association was found between female sex, higher frequency of aspirin usage, cigarette smoking, and hyperopia with an increased risk of CNV. Certain drusen and RPE abnormalities within 1500 mm of the foveal center present in the fellow eye and patient characteristics at baseline were identified as risk factors for the development of CNV in these eyes (266,269). Specific risk factors include the presence of five or more drusen (RR, 2.1; 95% CI, 1.3–3.5), focal hyperpigmentation (RR, 2.0; 95% CI, 1.4–2.9), definite systemic hypertension (systolic pressure R140 mmHg, diastolic pressure R90 mmHg, or use of antihypertensive medications) (RR, 1.7; 95% CI, 1.2–2.4), and one or more large drusen (greater 63 mm in greatest linear dimension) (RR, 1.5; 95% CI, 1.0–2.2). The risk of CNV developing within five years after presenting with CNV in the first eye ranged from 7% if none of these risk factors was present to 87% if all four risk factors were present (Fig. 1). Multivariate analysis of the risk factors for progression to CNV in AREDS participants yielded two risk factors (268). In persons at risk of advanced AMD in both eyes, while controlling for age, gender, and AREDS treatment group, white race (OR, white vs. black, 6.77; 95% CI, 1.24–36.9) and smoking O10 pack-years (OR, O10 vs. %10 pack-years, 1.55; 95% CI, 1.15–2.09) were independently associated with incident neovascular AMD.

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major side effects, it may be reasonable to wear sunglasses to reduce UV and other light exposure to ocular structures. The challenge for researchers is to more firmly establish modifiable risk factors and to conduct large-scale prospective intervention trials on these factors so that preventive measures and better treatments can be developed.

SUMMARY POINTS &

&

&

CONCLUSION In summary, many risk factors for AMD have been identified from case–control, cross-sectional, and prospective cohort studies. Risk factors such as increasing age, gender, or family history of the disease cannot be modified. One important modifiable risk factor is cigarette smoking (91). Dietary habits are also modifiable, and findings from AREDS suggest that persons with extensive intermediate size drusen, at least one large druse, noncentral geographic atrophy in one or both eyes, or advanced AMD or vision loss due to AMD in one eye, and without contraindications such as cigarette smoking, should consider taking a supplement of antioxidants plus zinc to reduce their risk of progression to advanced AMD and vision loss. Since sunglasses may protect against cataract formation, are inexpensive, and are not associated with any

77

& &

& &

Importance of identifying risk factors for AMD. The identification and modification of risk factors for AMD has the potential for greater public health impact on the morbidity from the disease than the few treatment modalities currently available Studies on risk factors for AMD. Case–control, crosssectional, and prospective cohort studies can identify risk factors for AMD. Repeated findings of the same risk factors in well-designed studies conducted in different populations are necessary to provide compelling evidence of a real association between AMD and potential risk factors. However, only randomized prospective clinical trials can prove that modifying a particular established risk factor can influence the course of AMD Classification of risk factors. Risk factors for AMD may be broadly classified into personal or environmental factors (e.g., smoking, sunlight exposure, and nutritional factors including micronutrients, dietary fish intake, and alcohol consumption). Personal factors may be further subdivided into sociodemographic (e.g., age, sex, race/ethnicity, heredity, and socioeconomic status), ocular (e.g., iris color, macular pigment optical density, cataract and its surgery, refractive error, and cup/disc ratio), and systemic factors (e.g., cardiovascular disease and its risk factors, reproductive and related factors, dermal elastotic degeneration, and antioxidant enzymes) Established risk factors. Age, race/ethnicity, heredity, and smoking Possible risk factors. Sex, socioeconomic status, iris color, macular pigment optical density, cataract and its surgery, refractive error, cup/disc ratio, cardiovascular disease, hypertension and blood pressure, serum lipid levels and dietary fat intake, body mass index, hematologic factors, Chlamydia pneumoniae infection, reproductive and related factors, dermal elastotic degeneration, antioxidant enzymes, sunlight exposure, micronutrients, dietary fish intake, and alcohol consumption Factors probably not associated with AMD. Diabetes and hyperglycemia Risk factors for progression to choroidal neovascularization. Presence of five or more drusen, focal

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hyperpigmentation, systemic hypertension, one or more large drusen (O63 mm in greatest linear dimension), white race, and smoking Current opinion on modifying risk factors. A number of well-established factors such as increasing age and a family history of the disease unfortunately cannot be modified. One modifiable well-established risk factor is cigarette smoking. There may be potential benefits of antismoking patient education for primary and secondary prevention of AMD. The Age-Related Eye Disease Study suggested that persons older than 55 years with extensive intermediate size drusen, at least one large druse, noncentral geographic atrophy in one or both eyes, or advanced AMD or vision loss due to AMD in one eye, and without contraindications such as cigarette smoking, should consider taking a supplement of antioxidants plus zinc to reduce their risk of progression to advanced AMD and vision loss. Although sunlight exposure has not been established as a risk factor for AMD, it may be reasonable to wear sunglasses to reduce ultraviolet and other light exposure to ocular structures since sunglasses may protect against cataract formation, are inexpensive, and are not associated with any major side effects

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5 Choroidal Neovascularization Frances E. Kane

Alimera Sciences, Inc., Alpharetta, Georgia, U.S.A.

Peter A. Campochiaro

Departments of Ophthalmology and Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, U.S.A.

INTRODUCTION Despite substantial recent progress in treatment development, choroidal neovascularization (CNV) remains one of the most challenging problems faced by retina specialists. It is a common cause of severe visual loss in patients with age-related macular degeneration (AMD) and younger patients with one of many diseases that affect the choroid–Bruch’s membrane–retinal pigment epithelium (RPE) complex, including but not limited to ocular histoplasmosis, myopic degeneration, angioid streaks, and multifocal choroiditis. As our understanding of the molecular pathogenesis of CNV is increasing, new treatments are being developed which specifically target molecules that are involved. Therefore, it is critical to continue to elucidate the molecular mechanisms involved in CNV.

INFERENCES FROM NEOVASCULARIZATION ELSEWHERE IN THE BODY Neovascularization (NV) is a critical process during embryonic development and wound repair and occurs in almost all tissues of the body. It is well-tolerated in most tissues, but not in the eye where normal functioning depends upon maintenance of blood–ocular barriers. NV varies somewhat in different tissues because endothelial cells differ in different parts of the body and surrounding cells participate in the neovascular response resulting in tissue-specific aspects [see (1) for review]. One thing that is similar for several disease processes in many tissues is that vascular endothelial growth factor-A (VEGF-A) plays a central role as a stimulator of NV.

VASCULAR ENDOTHELIAL GROWTH FACTOR Increased expression of VEGF-A in the retina is sufficient to cause sprouting of new vessels from the deep capillary bed of the retina, but is not sufficient to induce

NV at the retinal surface typical of that seen in ischemic retinopathies (2,3). Likewise, increased expression of VEGF-A in RPE cells is not sufficient to cause sprouting of new vessels from the choroid (4). Thus, other factors are involved in the initiation of new vessel growth in the retina and choroid, but despite any contribution by other factors, VEGF antagonists strongly suppress ischemia-induced retinal NV or CNV in animal models (5–11). In order to determine the magnitude of the contribution of VEGF-A, complete blockade of VEGF would be needed, which is not possible by pharmacologic means since no drug treatment is 100% efficient. Also, many antagonists are not totally selective making it difficult to know how much inhibitory effect can be attributed to blockade of VEGF. Soluble VEGF receptors are very efficient when expressed by gene transfer or when given systemically so that sustained serum levels are achieved, and they are relatively specific, although they cannot distinguish effects of VEGF-A and placental growth factor (PlGF). In a mouse model of laser-induced CNV, systemic administration of VEGF-trap, a chimeric protein that has binding domains from VEGF receptors 1 and 2, resulted in 66% inhibition (11) and periocular gene transfer of soluble VEGF receptor 1 resulted in 86% inhibition (12). Intraocular gene transfer of soluble VEGF receptor 1 resulted in 53% inhibition of ischemia-induced retinal NV (13). These data suggest that VEGF family members account for a large portion of the driving force for these two types of ocular NVand are key targets for therapeutic intervention. These predictions have been largely substantiated in clinical trials. Intravitreous injection of pegaptanib, an aptamer that binds only the VEGF165 isoform, reduced the percentage of patients with classic CNV due to AMD who experienced moderate loss of vision (loss of 15 letters or more) over the course of a year from 45% in the sham injection group to 30% (14). Six percent of patients treated with pegaptanib compared to 2% in the sham injection group had a

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substantial improvement in vision (gain of 15 or more letters). Compared to sham treatment, increase in size of CNV lesions was slowed, but not stopped. Ranibizumab is an Fab fragment of an antibody that binds all isoforms of VEGF-A. Monthly intravitreous injections of ranibizumab in AMD patients with occult or minimally classic subfoveal CNV reduced the percentage of patients with moderate loss of vision over the course of a year from 38% in the sham injection group to 5%, and the percentage of patients who experienced substantial improvement in vision was increased from 4.6% to 34% (15). These data suggest that antagonism of VEGF-A in AMD patients with CNV can result in stabilization of vision in the majority of patients and substantial improvement in vision in about one-third of patients. These results confirm that VEGF-A is a very important target in the treatment of neovascular AMD, but suggest several questions. Are the superior results with intravitreous injection of ranibizumab compared to those with pegaptanib due to the inhibition of all VEGF-A isoforms compared to inhibition of only VEGF165, superior pharmacokinetics, a combination of both, or some other reason? Are there alternative modes of delivery of VEGF antagonists that provide superior pharmacokinetics compared to repeated intraocular injections? What is the anatomic basis for the visual improvement with ranibizumab treatment? Clinical observations have suggested that a substantial amount of the initial improvement due to VEGF antagonists is related to reduction in excessive vascular permeability resulting in reduction in retinal thickness and subretinal fluid as visualized by optical coherence tomography (OCT). A case series of AMD patients with subfoveal CNV treated with systemic infusions of bevacizumab, a full-length humanized monoclonal antibody that binds all isoforms of VEGF-A, showed rapid reduction in retinal thickening and subretinal fluid visualized by OCT and an average improvement in visual acuity of 12 letters over the course of 12 weeks (16). Can improvement be sustained long-term (over several years) if the CNV is not eliminated? Can additional improvement be achieved by inhibiting PlGF as well as all isoforms of VEGF-A? Clinical trials investigating the efficacy of VEGF-trap should answer this question. Can greater benefit be achieved by combining antagonism of VEGF with other antiangiogenic agents that work by other mechanisms? Is it possible to achieve drug-induced involution of CNV and would that result in greater benefits than simply suppressing leakage and growth of CNV? Clearly great progress has been made, but there is still a great deal of work to do. The studies described above have conclusively shown that VEGF-A is a critical stimulus for

development of CNV in patients with AMD. What about CNV that occurs in other disease processes, such as pathologic myopia, ocular histoplasmosis, angioid streaks, multifocal choroiditis, and others? Recently, two patients with subfoveal CNV due to pathologic myopia were treated with four or five infusions of bevacizumab, resulting in resolution of retinal thickening assessed by OCT, elimination of leakage and reduction in size of CNV lesions assessed by fluorescein angiography, and improvement in visual acuity (17). These patients have not had evidence of leakage or other signs of recurrent CNV for over nine months. This finding suggests that VEGF is an important stimulus for CNV growth and maintenance in pathologic myopia and it appears that in that disease process as opposed to AMD, blockage of VEGF can result in complete involution of CNV. Additional studies are needed to determine if this is in fact the case and whether antagonism of VEGF provides benefits in patients with CNV due to all causes.

Other Soluble Proangiogenic Factors Based upon in vitro assays and in vivo effects in some tissues in addition to VEGFs, some other proteins have been demonstrated to have proangiogenic acitivity, including fibroblast growth factors (FGFs) (18), tumor necrosis factor-a (19), insulin-like growth factor-1 (20,21), and hepatocyte growth factor (22). The FGFs do not participate in CNV (23), but it is possible that the other factors may; however, despite their possible participation, blockade of VEGF has a profound effect on CNV. It will be interesting to determine if inhibition of one or more of these factors combined with antagonism of VEGF provides added benefit. Soluble Antiangiogenic Factors In many tissues, including the eye, new vessel growth appears to be regulated by a balance between proangiogenic and antiangiogenic factors. Transforming growth factor-b and related family members inhibit endothelial cell migration and proliferation in vitro, but have been suggested to be proangiogenic or antiangiogenic in vivo, depending on the context (24–26). Several purported endogenous inhibitors of angiogenesis have been described, including angiostatin (27), endostatin (28), antithrombin III (29), platelet factor 4 (30), thrombospondin (31), and pigment epithelium-derived factor (PEDF) (32). Signals from the Extracellular Matrix Along with soluble proangiogenic and antiangiogenic factors, extracellular matrix (ECM) molecules also

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participate in several ways in the regulation of NV. Acting through integrins on the surface of endothelial cells, ECM molecules may directly stimulate or inhibit endothelial cell processes involved in angiogenesis (33). Soluble angiogenic factors exert some of their effects through ECM molecules by altering expression of integrins on endothelial cells. Endothelial cells of dermal vessels have increased expression of avb3 integrin when participating in angiogenesis and avb3 antagonists block angiogenesis (34). Integrin avb3 is upregulated in endothelial cells participating in retinal NV and avb3 antagonists suppress retinal NV (35). Integrin a5b1 is upregulated in CNV and a small molecule antagonist of a5b1 causes regression of established NV by inducing apoptosis of endothelial cells within the NV (36). Signals from the ECM are often unmasked or eliminated by proteolysis. Components of the ECM may bind and sequester soluble factors, preventing them from activating receptors on endothelial cells until they are released by proteolysis (37–39). Degradation of ECM also liberates fragments with antiangiogenic activity that provide negative feedback slowing vessel growth, making it more orderly, and eventually helping to turn it off and reestablish quiescence. Endostatin was the first collagen fragment demonstrated to inhibit angiogenesis (28), but subsequently several others have been identified (40–46). Interestingly, several of these antiangiogenic peptides are derived from noncollagenous (NC1) domains of the basement membrane collagens IV, XV, and XVIII. The NC1 domains are important for assembly of the supramolecular structures of the collagens and under normal circumstances do not interact with cells (47–49). However, after cleavage from native collagens several of the NC1 domains bind endothelial cells and inhibit angiogenesis. Endostatin is derived from the NC1 domain of collagen XVIII and restin is a somewhat similar antiangiogenic peptide derived from the NC1 domain of collagen XV (40). Collagen IV is unusual in that there are six distinct collagen IV chains that have different tissue distributions (50–54). The NC1 domains of several of the collagen IV chains, including 1, 2, 3, and 6 have antiangiogenic activity, but effects may vary in different organs (41–46). In the eye, the NC1 domain of a2(IV) causes regression of CNV (55). Two proteolytic systems that play a prominent role in angiogenesis are the urokinase type of plasminogen activator (56) and matrix metalloproteinases (57,58), and the relative importance of these systems could vary in different types of angiogenesis. Tissue inhibitor of metalloproteinases-1 (TIMP-1) has been touted as an inhibitor of NV (59), but it stimulates VEGF-induced NV in the retina (60).

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Transcription Factors that Participate in NV The clinical observation that retinal NV almost always occurs in association with retinal capillary nonperfusion led to the hypothesis that retinal ischemia is the driving force (61–63). This hypothesis is supported by experimental models in which damage to retinal vessels leads to retinal NV (64–68). Advances in the understanding of hypoxia-mediated gene regulation have suggested potential molecular signals such as hypoxia-inducible factor-1 (HIF-1), involvement of which has been confirmed by experimental studies (69). As a result, many of the molecular signals involved in retinal NV have been defined [for review see (70)]. Hypoxia has not been definitely implicated in the occurrence of CNV. While there is evidence that choroidal blood flow is decreased in patients with AMD, it is not clear whether the decrease is sufficient to cause hypoxia of photoreceptors and RPE (71,72). Furthermore, hypoxia cannot be invoked in patients with ocular histoplasmosis, myopic degeneration, angioid streaks, or many other diseases in which young people get CNV. However, whether or not hypoxia plays a role, it appears that HIF-1 is involved. Mice in which the hypoxia response element, through which HIF-1 acts, has been deleted from the VEGF promoter are protected from laser-induced CNV. This indicates that HIF-1-induced stimulation of VEGF is necessary for CNV (73). The JAK–STAT pathway has been implicated in angiogenesis in some tissues (74). In the retina, Leptin, an adipocyte-derived hormone, stimulates NV by STAT-3-mediated enhancement of VEGF expression (75). The proinflammatory cytokine IL-6 increases expression of VEGF by activating STAT-3 (76). STAT5 may work downstream of VEGF to enhance endothelial survival in the setting of hypoxia and thereby promote angiogenesis (77). The Pathogenesis of CNV One thing that patients with CNV share is that they all have abnormalities of Bruch’s membrane and the RPE. In patients with AMD, pathologic studies have demonstrated that diffuse thickening of Bruch’s membrane is highly associated with the occurrence of CNV (78). Large soft drusen and pigmentary abnormalities are clinical risk factors for CNV (79); soft drusen indicate the presence of diffuse subRPE deposits and pigmentary changes suggest compromise of the RPE. Therefore, there is disordered metabolism of ECM in patients with AMD that may compromise RPE cells leading to cell dropout and proliferation, and CNV. Breaks in Bruch’s membrane and/or other abnormalities of the ECM of RPE cells occur in other diseases in which CNV occurs. Patients with Sorsby’s fundus dystrophy have a mutation in

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the TIMP-3 gene that results in abnormal processing of the protein so that it is deposited along Bruch’s membrane (80). This collection of an ectopic protein along Bruch’s membrane is associated with RPE and photoreceptor degeneration and a high incidence of CNV (81,82). Why would abnormal ECM along the basal surface of RPE cells result in cell compromise and CNV? Like most epithelial cells, the phenotype and behavior of RPE cells is regulated in part by interaction with its ECM. Cultured RPE cells display alterations in morphology and gene expression when grown on different ECMs (83). Presentation of some ECM molecules such as vitronectin or thrombospondin to the apical or basal surface of RPE cells results in small increases in FGF-2 and large increases in VEGF in the media of the cells (84). Therefore, alterations in the ECM of RPE cells can cause them to increase production of proteins with angiogenic activity. Defects in Bruch’s membrane contribute to CNV. In wild-type mice, laser-induced rupture of Bruch’s membrane results in CNV (23). In rho/VEGF or rho/ FGF2 transgenic mice, rupture of Bruch’s membrane resulted in very large areas of CNV, much larger than those in wild-type mice (85). Low-intensity laser, which ruptured photoreceptor cells but did not rupture Bruch’s membrane, resulted in CNV in rho/ FGF2 mice, but not rho/VEGF or wild-type mice. These experiments demonstrate that choroidal vessels are capable of responding to excess VEGF or extracellular FGF2 when there is a concomitant rupture of Bruch’s membrane. This suggests that Bruch’s membrane constitutes a mechanical and biochemical barrier to CNV. Increased expression of VEGF or FGF2 is unable to cause a breech in the barrier. In the case of FGF2, sequestration is likely to be an important control mechanism, because lowintensity laser that ruptures photoreceptor cells and releases FGF2, but does not rupture Bruch’s membrane, results in CNV. This is not the case for VEGF, which stimulates CNV only when the Bruch’s membrane barrier has been disrupted by another means. The importance of the Bruch’s membrane barrier for prevention of CNV may help to explain difficulties in modeling CNV. Laser-induced rupture of Bruch’s membrane, first established in primates and later adapted to rodents, has been widely used (23,86,87). All other models of CNV, whether they involve implantation of sustain release polymers or gene transfer, have a component of surgical damage to Bruch’s membrane (88,89). Therefore, some sort of compromise of Bruch’s membrane must accompany increased levels of angiogenic factors in order to generate CNV.

Laser-induced rupture of CNV in mice (23) has provided a particularly valuable tool, because it can be used in genetically engineered mice to explore the role of individual gene products. Using this strategy, Ozaki et al. (90) demonstrated that mice with targeted deletion of FGF2 develop CNV similar to that in wild-type mice indicating that FGF2 is not necessary for the development of CNV after rupture of Bruch’s membrane. This approach was also used to demonstrate that nitric oxide (NO) is proangiogenic in both the retina and the choroid, but different isoforms of NO synthetase play a role (91). For retinal NV, eNOS plays an important role, while for CNV, nNOS is important. This suggests that nitric oxide synthase inhibitors may be useful in patients at risk for CNV.

Pharmacologic Treatments for CNV Ranibizumab, a potent antagonist of VEGF-A, is the first treatment to improve visual acuity in a substantial proportion of patients with neovascular AMD. It is likely that VEGF antagonists will remain the basis of treatment, but improvements may be made in mode of delivery. Orally active VEGF antagonists are being to be tested. New agents will be added if they can provide additional benefits to treatment with VEGF antagonists alone. An appealing approach is to reduce leakage and stop growth of CNV with intraocular injections of a VEGF antagonist and then maintain stability with a less invasive approach. Topically active drugs would be ideal. Amfenac, 2-amino-3-benzoylbenzeneacetic acid, is an inhibitor of cyclooxygenase-1 (COX-1) and COX-2 that strongly suppresses pain (92). Nepafenac, the amide analog of amfenac, has unusually high ocular penetration and acts as a prodrug that significantly inhibits prostaglandin synthesis in the retina/ choroid by 55% for four hours after topical administration and blocks ocular inflammation (93,94). Topically administered Nepafenac also reduces expression of VEGF and inhibits the development of ischemia-induced retinal NV and CNV due to rupture of Bruch’s membrane (95). This is consistent with recent studies that have demonstrated that increased COX activity enhances and COX inhibitors reduce VEGF expression in several other tissues (96–98). Agents that block NV by mechanisms distinct from those of VEGF antagonists are good candidates for combination therapy. Polyamine analogs block polyamine metabolism, which is required by all proliferating cells including endothelial cells participating in NV. Intravitreous or periocular injections of polyamine analogs induced regression of established CNV by inducing apoptosis in endothelial cells participating in CNV (99). Over a seven-day treatment period, the regression was not complete and could

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not be increased beyond 40% by increasing the dose of polyamine analogs or by combining them with DL-alpha-difluoromethylornithine, an inhibitor of polyamine biosynthesis. To provide perspective on this effect, intravitreous injection of adenoviral vectors expressing PEDF caused a similar amount of regression in the same model over a 10-day period (100) and over a seven-day period combretastatin-A-4phosphate, a vascular targeting agent, caused 66% regression of CNV (101). Intraocular injections of polyamine analogs cause apoptosis of some retinal neurons, but after periocular injections only endothelial cells participating in CNV are affected and retinal function assessed by electroretinograms (ERGs) remains normal. Therefore, periocular injection of polyamine analogs deserves further study. VEGF promotes the survival of endothelial cells in newly formed vessels (102). Over time endothelial cells in new vessels become less dependent upon VEGF for survival, because they obtain new sources of survival signals. The ECM is a major source of survival signals and blockade of those signals is likely to enhance the effects of VEGF antagonists. This is particularly true for CNV in which endothelial cells seem to achieve independence in terms of survival from VEGF more rapidly than in retinal NV, possibly because of the exuberant ECM associated with CNV. One of the receptors on endothelial cells that mediates survival signals from ECM is integrin a5b1, and a small molecule that binds a5b1 and prevents its interaction with ECM components causes regression of CNV (36). This and other agents that target a5b1 are good candidates for combination therapy. Some of the endogenous antiangiogenic proteins, such as endostatin or the NC1 domain of the a2 chain of collagen IV, block survival signals from the ECM. Intraocular or periocular injection of a recombinant fragment of the NC1 domain of the a2 chain of collagen IV causes regression of CNV (55) and is another good candidate for combination therapy. Increased expression of endostatin either systemically or in the eye by gene transfer not only inhibits several types of ocular NV, but also prevents VEGF-induced vascular leakage (103,104). A potential advantage of gene therapy is that intraocular injection of a vector containing an expression construct provides a potential means of sustained local delivery. Intravitreous injection of an adenoviral vector encoding PEDF (AdPEDF) resulted in high levels of PEDF in the eye and strongly suppressed several types of ocular NV (105) and caused regression of CNV (100). Gene transfer of PEDF using adeno-associated viral vectors was also a very effective way to inhibit CNV many weeks later (106). Several studies have suggested that PEDF has neuroprotective activity (107–112) and it might

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contribute to the tropic support of photoreceptors provided by RPE cells, because in an in vitro model of photoreceptor degeneration in which the RPE is removed from Xenopus eyecups, PEDF protected photoreceptors from degeneration and loss of opsin immunoreactivity (113). Therefore, intraocular PEDF gene transfer may provide a good approach in patients with AMD, because it could possibly benefit both neovascular and nonneovascular AMD. A phase I study investigating the effects of a single intraocular injection of AdPEDF.11 in patients with advanced neovascular AMD showed an excellent safety profile (114). There were no serious adverse events related to AdPEDF.11 and no dose-limiting toxicities. Signs of mild, transient intraocular inflammation occurred in 25% of patients, but there was no severe inflammation. Six patients experienced increased intraocular pressure that was easily controlled by topical medication. At three and six months after injection, 55% and 50%, respectively, of patients treated with 106 to 107.5 pu and 94% and 71% of patients treated with 108 to 109.5 pu had no change or improvement in lesion size from baseline. The median increase in lesion size at 6 and 12 months was 0.5 and 1.0 disc areas in the low-dose group compared to 0 and 0 disc areas in the high-dose group. These data suggest the possibility of antiangiogenic activity that may last for several months after a single intravitreous injection of doses greater than 108 pu of AdPEDF.11. This study provides evidence that adenoviral vector-mediated ocular gene transfer is a viable approach for treatment of ocular disorders and that further studies investigating the efficacy of AdPEDF.11 in patients with neovascular AMD should be performed.

SUMMARY POINTS & &

&

&

Over the past few years our understanding of the molecular pathogenesis of CNV has improved. It is clear that VEGF is a critical stimulus and antagonism of VEGF has led to the first treatment that improves vision in a substantial number of patients with neovascular AMD. As knowledge of the molecular signals that contribute to CNV continues to improve, additional treatments will be developed. VEGF antagonists will serve as baseline treatment to which other therapies are added, although their mode of delivery is likely to improve. Induction of regression followed by noninvasive treatments that suppress recurrences is an important strategy for prolonged treatment of patients with neovascular AMD.

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ACKNOWLEDGMENTS Supported by grants from the Macula Vision Research Foundation. PAC is the George S. and Dolores Dore Eccles Professor of Ophthalmology and Neuroscience.

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52. Miner JH, Sanes JR. Collagen IV. alpha 3, alpha 4, and alpha 5 chains in rodent basal laminae: sequence, distribution, association with laminins, and developmental switches. J Cell Biol 1994; 127:879–91. 53. Tanaka K, Iyama K, Kitaoka M, et al. Differential expression of alpha 1(IV), alpha 2 (IV), alpha 5(IV), and alpha 6 (IV) collagen chains in the basement membrane of basal cell carcinoma. Histochem J 1997; 29:563–70. 54. Fleischmajer R, Kuhn K, Sato Y, et al. There is temporal and spatial expression of alpha1(IV), alpha2(IV), alpha5(IV), and alpha6(IV) collagen chains and beta 1 integrins during the development of the basal lamina in an “in vitro” skin model. J Invest Dermatol 1997; 109:527–33. 55. Lima e Silva R, Kachi S, Akiyama H, et al. Recombinant non-collagenous domain of alpha2(IV) collagen causes involution of choroidal neovascularization by inducing apoptosis. J Cell Physiol 2006; 208(1):161–6 (epub ahead of print). 56. Pepper MS, Vassalli J-D, Montesano R, Orci L. Urokinasetype plasminogen activator is induced in migrating capillary endothelial cells. J Cell Biol 1987; 105:2535–41. 57. Moscatelli DA, Rifkin DB, Jaffe EA. Production of latent collagenase by human umbilical vein endothelial cells in response to angiogenic preparations. Exp Cell Res 1985; 156:379–90. 58. Cornelius LA, Nehring LC, Roby JD, Parks WC, Welgus HG. Human dermal microvascular endothelial cells produce matrix metalloproteinases in response to angiogenic factors and migration. J Invest Dermatol 1995; 105:170–6. 59. Johnson MD, Kim H-RC, Chesler L, Tsao-Wu G, Bouck N, Polverini PJ. Inhibition of angiogenesis by tissue inhibitor of metalloproteinase. J Cell Physiol 1994; 160:194–202. 60. Yamada E, Tobe T, Yamada H, et al. TIMP-1 promotes VEGF-induced neovascularization in the retina. Histol Histopath 2001; 16:87–97. 61. Michaelson I. The mode of development of the vascular system of the retina with some observations on its significance for certain retinal diseases. Trans Ophthalmol Soc UK 1948; 68:137–80. 62. Ashton N. Retinal vascularization in health and disease. Am J Ophthalmol 1957; 44(4):7–17. 63. Shimizu K, Kobayashi Y, Muraoka K. Midperipheral fundus involvement in diabetic retinopathy. Ophthalmology 1981; 88:601–12. 64. Miller JW, Stinson W, Folkman J. Regression of experimental iris neovascularization with systemic alphainterferon. Ophthalmology 1993; 100:9–14. 65. Virdi P, Hayreh S. Ocular neovascularization with retinal vascular occlusion. I. Association with retinal vein occlusion. Arch Ophthalmol 1980; 100:331–41. 66. Pournaras C, Tsacopoulos M, Strommer K, Gilodi N, Leuenberger PM. Experimental retinal branch vein occlusion in miniature pigs induces local tissue hypoxia and vasoproliferative microangiopathy. Ophthalmology 1990; 97:1321–8. 67. Penn JS, Tolman BL, Lowery LA. Variable oxygen exposure causes preretinal neovascularization in the newborn rat. Invest Ophthalmol Vis Sci 1993; 34:576–85. 68. Smith LEH, Wesolowski E, McLellan A, et al. Oxygeninduced retinopathy in the mouse. Invest Ophthalmol Vis Sci 1994; 35:101–11. 69. Ozaki H, Yu A, Della N, et al. Hypoxia inducible factor-1a is increased in ischemic retina: temporal and spatial correlation with VEGF expression. Invest Ophthalmol Vis Sci 1999; 40:182–9.

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70. Campochiaro PA. Retinal and choroidal neovascularization. J Cell Physiol 2000; 184:301–10. 71. Grunwald J, Hariprasad S, DuPont J, et al. Foveolar choroidal blood flow in age-related macular degeneration. Invest Ophthalmol Vis Sci 1998; 39:385–90. 72. Ross RD, Barofsky JM, et al. Presumed macular choroidal watershed vascular filling, choroidal neovascularization, and systemic vascular disease in patients with age-related macular degeneration. Am J Ophthalmol 1998; 125:71–80. 73. Vinores SA, Xiao WH, Aslam S, et al. Implication of the hypoxia response element of the VEGF promoter in mouse models of retinal and choroidal neovascularization, but not retinal vascular development. J Cell Physiol 2005; 206:749–58 (epub ahead of print, 21 Oct 2005). 74. Valdembri D, Serini G, Vacca A, Ribatti D, Bussolino F. In vivo activation of JAK/STAT-3 pathway during angiogenesis induced by GM-CSF. FASEB J 2002; 16:225–7. 75. Suganami E, Takagi H, Ohashi H, et al. Leptin stimulates ischemia-induced retinal neovascularization: possible role of vascular endothelial growth factor expressed in retinal endothelial cells. Diabetes 2004; 53:2443–8. 76. Huang SP, Wu MS, Shun CT, et al. Interleukin-6 increases vascular endothelial growth factor and angiogenesis in gastric carcinoma. J Biomed Sci 2004; 11:517–27. 77. Dudley AC, Thomas D, Best J, Jenkins A. A VEGF/JAK2/STAT5 axis may partially mediate endothelial cell tolerance to hypoxia. Biochem J 2005; 390:427–36. 78. Green WR, Enger C. Age-related macular degeneration histopathologic studies. Ophthalmology 1993; 100:1519–35. 79. Bressler SB, Maguire MG, Bressler NM, Fine SL, Group at MPS. Relationship of drusen and abnormalities of the retinal pigment epithelium to the prognosis of neovascular macular degeneration. Arch Ophthalmol 1990; 108:1442–7. 80. Weber BHF, Vogt G, Pruett RC, Stohr H, Felbor U. Mutations in the tissue inhibitor of metalloproteinases-3 (TIMP3) in patients with Sorsby’s fundus dystrophy. Nat Genet 1994; 8:352–6. 81. Sorsby A, Mason MEJ, Gardener N. A fundus dystrophy with unusual features. Br J Ophthalmol 1949; 33:67–97. 82. Hoskin A, Sehmi K, Bird AC. Sorsby’s pseudoinflammatory macular dystrophy. Br J Ophthalmol 1981; 65:859–65. 83. Campochiaro PA, Hackett SF. Corneal endothelial cell matrix promotes expression of differentiated features of retinal pigmented epithelial cells: implication of laminin and basic fibroblast growth factor as active components. Exp Eye Res 1993; 57:539–47. 84. Mousa SA, Lorelli W, Campochiaro PA. Extracellular matrix-integrin binding modulates secretion of angiogenic growth factors by retinal pigmented epithelial cells. J Cell Biochem 1999; 74:135–43. 85. Yamada H, Yamada E, Ando A, et al. FGF2 decreases hyperoxia-induced cell death in mice. J Am Pathlol 2001; 159:1113–20. 86. Miller H, Miller B, Ryan SJ. The role of the retinal pigmented epithelium in the involution of subretinal neovascularization. Invest Ophthalmol Vis Sci 1986; 27:1644–52. 87. Dobi ET, Puliafito CA, Destro M. A new model of choroidal neovascularization in the rat. Arch Ophthalmol 1989; 107:264–9. 88. Spilsbury K, Garrett KS, Shen WY, Constable IJ, Rakoczy PE. Overexpression of vascular endothelial growth factor (VEGF) in the retinal pigment epithelium leads to the development of choroidal neovascularization. Am J Pathol 2000; 157:135–44.

89. Baffi J, Byrnes G, Chan C-C, Csaky KG. Choroidal neovascularization in the rat induced by adenovirus mediated expression of vascular endothelial growth factor. Invest Ophthalmol Vis Sci 2000; 41:3582–9. 90. Ozaki H, Okamoto N, Ortega S, et al. Basic fibroblast growth factor is neither necessary nor sufficient for the development of retinal neovascularization. Am J Pathol 1998; 153:757–65. 91. Ando A, Mori K, Yamada H, et al. Nitric oxide is proangiogenic in retina and choroid. J Cell Physiol 2001; 191:116–24. 92. Jain AK, Hunley CC, Kuebel J, McMahon FG, Ryan JJ. Analgesic efficacy of amfenac, aspirin and placebo after extraction of impacted teeth. Pharmacotherapy 1986; 6:236–40. 93. Gamache DA, Graff G, Brady MT, Spellman JM, Yanni JM. Nepafenac, a unique nonsteroidal prodrug with potential utility in the treatment of trauma-induced ocular inflammation: I. Assessment of anti-inflammatory efficacy. Inflammation 2000; 24:357–70. 94. Ke T-L, Graff G, Spellman JM, Yanni JM. Nepafenac, a unique nonsteroidal prodrug with potential utility in the treatment of trauma-induced ocular inflammation: II. In vitro bioactivation and permeation of external ocular barriers. Inflammation 2000; 24:371–84. 95. Takahashi K, Saishin Y, Saishin Y, et al. Topical nepafenac inhibits ocular neovascularization. Invest Ophthalmol Vis Sci 2003; 44:409–15. 96. Ben-Av P, Crofford LJ, Wilder RL, Hla T. Induction of vascular endothelial growth factor expression in synovial fiboblasts by prostaglandin E and interleukin-1: a potential mechanism for inflammaroty angiogenesis. FEBS Lett 1995; 372:83–7. 97. Hoper MM, Voelkel NF, Bates TO, et al. Prostaglandins induce vascular endothelial growth factor in a human monocytic cell line and rat lungs via cAMP. Am J Respir Cell Mol Biol 1997; 17:748–56. 98. Majima M, Hayashi I, Muramatsu M, Katada J, Yamashina S, Katori M. Cyclo-oxygenase-2 enhances basic fibroblast growth factor-induced angiogensis through induction of vascular endothelial growth factor in rat sponge implants. Br J Pharmacol 2000; 130:641–9. 99. Lima e Silva R, Saishin Y, Saishin Y, et al. Suppression and regression of choroidal neovascularization by polyamine analogs. Invest Ophthalmol Vis Sci 2005; 46:3323–30. 100. Mori K, Gehlbach P, Ando A, McVey D, Wei L, Campochiaro PA. Regression of ocular neovascularization by increased expression of pigment epithelium-derived factor. Invest Ophthalmol Vis Sci 2001; 43:2428–34. 101. Nambu H, Nambu R, Melia M, Campochiaro PA. Combretastatin A-4 phosphate suppresses development and induces regression of choroidal neovascularization. Invest Ophthalmol Vis Sci 2003; 44:3650–5. 102. Alon T, Hemo I, Itin A, Pe’er J, Stone J, Keshet E. Vascular endothelial growth factor acts as a survival factor for newly formed retinal vessels and has implications for retinopathy of prematurity. Nature Med 1995; 1:1024–8. 103. Mori K, Ando A, Gehlbach P, et al. Inhibition of choroidal neovascularization by intravenous injection of adenoviral vectors expressing secretable endostatin. Am J Pathol 2001; 159:313–20. 104. Takahashi K, Saishin Y, Saishin Y, et al. Intraocular expression of endostatin reduces VEGF-induced retinal vascular permeability, neovascularization, and retinal detachment. FASEB J 2003; 17:896–8.

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105. Mori K, Duh E, Gehlbach P, et al. Pigment epitheliumderived factor inhibits retinal and choroidal neovascularization. J Cell Physiol 2001; 188:253–63. 106. Mori K, Gehlbach P, Yamamoto S, et al. AAV-mediated gene transfer of pigment epithelium-derived factor inhibits choroidal neovascularization. Invest Ophthalmol Vis Sci 2002; 43:1994–2000. 107. Taniwaki T, Becerra SP, Chader GJ, Schwartz JP. Pigment epithelium-derived factor is a survival factor for cerebellar granule cells in culture. J Neurochem 1995; 64:2509–17. 108. Araki T, Taniwaki T, Becerra SP, Chader GJ, Schwartz JP. Pigment epithelium-derived factor (PEDF) differentially protects immature but not mature cerebellar granule cells against apoptotic cell death. J Neurosci Res 1998; 53:7–15. 109. DeCoster MA, Schabelman E, Tombran-Tink J, Bazan NG. Neuroprotection by pigment epithelial-derived factor against glutamate toxicity in developing primary hippocampal neurons. J Neurosci Res 1999; 56:604–10. 110. Bilak MM, Corse AM, Bilak SR, Lehar M, Tombran-Tink J, Kuncl RW. Pigment epithelium-derived factor (PEDF)

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protects motor neurons from chronic glutamate-mediated neurodegeneration. J Neuropathol Exp Neurol 1999; 58:719–28. Cao W, Tombrin-Tink J, Chen W, Mrazek D, Elias R, McGinnis JF. Pigment epithelium-derived factor protects cultured retinal neurons against hydrogen peroxideinduced cell death. J Neurosci Res 1999; 57:789–800. Houenou LJ, D’Costa AP, Li L, et al. Pigment epithelium derived factor promotes the survival and differentiation of developing spinal motor neurons. J Comp Neurol 1999; 412:506–14. Jablonski MM, Tombran-Tink J, Mrazek DA, Iannoaccone A. Pigment epithelium-derived factor supports normal development of photoreceptor neurons and opsin expression after retinal pigment epithelium removal. J Neurosci 2000; 20:7149–57. Campochiaro PA, Nguyen QD, Shah SM, et al. Adenoviral vector-delivered pigment epithelium-derived factor for neovascular age-related macular degeneration: results of a phase I clinical trial. Hum Gene Ther 2006; 17:167–76.

Part II:

Clinical Features of Age-Related Macular Degeneration

6 Non-exudative Age-related Macular Degeneration Neelakshi Bhagat

The Institute of Ophthalmology and Visual Science, New Jersey Medical School, Newark, New Jersey, U.S.A.

Christina J. Flaxel

Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, U.S.A.

INTRODUCTION Age-related macular degeneration (AMD), also known as age-related maculopathy (ARM), is the leading cause of blindness in the Western world (1). It is also the leading cause of irreversible central vision loss in whites over 50 years of age in the United States (2). The disease affects approximately eight million people in the United States (3); its advanced form affects more than 1.75 million people (4). The prevalence and progression of AMD increases with age (Table 1), from a prevalence of 1.6% in the age group 52 to 64 years to 28% in the age group 74 to 85 years (5). In the Blue Mountain Study, the prevalence of early AMD was reported to increase from 1.3% in the age group 49 to 54 years to 28.0% for those over 80 years of age; the prevalence of late ARM, on the other hand, increased from 0.1% in the age-group 49 to 54 years to 7.1% in the age group 75 to 86 years. The population older than 65 years is the fastest growing segment of our society and the prevalence of AMD is predicted to increase dramatically in the next decade (6,7). There is a pressing need for new therapies to either prevent AMD or treat the exudative AMD.

CLINICAL FEATURES OF AMD The clinical hallmarks of non-exudative AMD are soft drusen, localized deposits noted between the basement membrane of the retinal pigment epithelium (RPE) and the Bruch’s membrane, associated RPE pigmentary changes, and mild loss in visual acuity (VA) (8). The advanced form of non-exudative AMD, termed geographic atrophy (GA), is characterized by outer retinal and RPE atrophy with loss of choriocapillaris. The presence of subretinal fluid, subretinal hemorrhage, RPE detachment, a subretinal greenish– greyish membrane, or hard exudates indicates choroidal neovascularization (CNV), which heralds the onset of exudative macular degeneration (9). Fluorescein angiography delineates the exact location

(subfoveal, juxtafoveal, or extrafoveal), the size, and the pattern of leakage (classic vs. occult). Loss of central vision is usually due to RPE atrophy or GA in non-exudative AMD and due to subretinal fluid or subretinal hemorrhage in exudative AMD. Early-stage AMD (or early ARM) is defined as the presence of soft drusen (R63 mm) alone, RPE depigmentation alone, or a combination of distinct/ indistinct drusen with pigment irregularities. Latestage AMD (or late ARM) is defined as pure GA (both central and noncentral), signs of exudative macular degeneration, or a combination of both.

ASSOCIATED FACTORS Many epidemiologic studies have provided insight into the various factors that may be associated with AMD (10–17). Hereditary influence, photic injury, nutritional deficiency, toxic insult, and systemic factors have been implicated in epidemiologic studies (18–20). These factors can be grouped into following categories: (i) demographic characteristics, which include age, sex, race, and eye color (21–23); (ii) systemic diseases, e.g., hypertension, cardiovascular disease, and hypercholesterolemia (1,14,18, 24–27); (iii) environmental influences such as smoking, sunlight, nutrition; and (iv) genetic predisposition (14,24,28–30).

Demographic Characteristics The prevalence and progression of all types of AMD increases with age (1,11,22,31–33). A statistically significant increased incidence of ARM lesions is also noted with age (P !0.05). Individuals 75 years of age or older at baseline have significantly (P !0.01) higher 10-year incidences of the following characteristics than people 43 to 54 years of age: larger sized drusen (125–249 mm), 26.3% versus 3.3%; R250 mm, 16.2% versus 1.0%; soft indistinct drusen, 22.2% versus 2.2%; retinal pigment abnormalities, 19.5% versus 0.8%; exudative macular degeneration,

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Table 1 Prevalence of Age-Related Macular Degeneration Epidemiologic studies 1.

2.

3. 4.

5. 6.

AMD prevalance (%) Age (years) Early Late Early or late

Chesapeake Bay (9) !50 50–59 60–69 70–79 80C Beaver Dam (9) 43–54 55–64 65–74 75C Klein and Klein (27) 45–64 65–74 Blue Mountains 49–54 Study group (36) 55–64 65–74 75–84 85C Copenhagen (47) 60–69 70–80 Framingham (18) 52–64 65–74 75–85

4.0 6.0 13.0 26.0 8.4 13.8 18.0 29.7

4.3 13.6 0.1 0.6 1.4 7.1

1.3

0.0

2.6 8.5 15.5 28.0

0.2 0.7 5.4 18.5

2.3 9.0

4.1 20.0 1.6 11.0 27.9

4.1% versus 0%; and pure GA, 3.1% versus 0%. Eyes with soft indistinct drusen or retinal pigmentary abnormalities at baseline are more likely to develop late ARM at follow-up than eyes without these lesions (15.1% vs. 0.4% and 20.0% vs. 0.8%, respectively) (3). AMD is commonly reported to be more prevalent in women (25,34), although conflicting results have been noted. The Beaver Dam Study, after adjusting for age, revealed that the incidence of early AMD was 2.2% higher in women 75 years of age and older than in men in this age group (25). On the other hand, the prevalence of early ARM was higher in men than in women in each age category in the Blue Mountains Eye Study (35). However, the pooled data from three different continents (the Beaver Dam Eye Study, the Blue Mountains Eye Study, and the Rotterdam Study) did not note such a difference in AMD prevalence between men and women (32). AMD is noted to be more common in whites than in pigmented races (36–38). The prevalence of any ARM in blacks is almost half of that noted in whites; 9.1% compared with 18.2% (38). It has been hypothesized that melanin may function as an antioxidant, and protect against lipofuscin accumulation in the RPE cells and development of CNV (39). The association between light-colored irides and AMD has been controversial (40,32). Most of the large case-control and population studies have found no association between iris color and AMD (9,41–44), but a few case-control studies have (45–47).

Systemic Diseases Hypertension and Cardiovascular Disease The Framingham Eye Study (1), the Age-Related Eye Disease Study (AREDS) (42), and the Macular Photocoagulation Study (26) reported a positive correlation between AMD and hypertension. This association was, however, was not seen in the Beaver Dam Eye Study (27), the Eye Disease Case-Control Study (EDCCS) (43), or in the Cardiovascular Health Study (38). A strong association has been noted between exudative AMD and moderate to severe hypertension, particularly in patients on antihypertensive therapy (24,26,34). In most studies, no justifiable association has been noted between AMD and atherosclerosis (24,25,42) though Hyman and coworkers (45) noted a positive correlation of AMD with stroke, arteriosclerosis, and ischemic attacks. Hypercholesterolemia There exist conflicting data regarding the effect of hypercholesterolemia on AMD. A positive correlation has been found between high intake of saturated fat and cholesterol, and AMD (29). A large prospective study of 70,000 individuals (Nurses’ Health Study and the Health Professionals Follow-up Study) clearly revealed that the total fat intake was positively associated with the risk of AMD (46). The EDCCS noted that patients with exudative ARM were more likely to have a higher serum total cholesterol. Some studies, however, have noted a protective effect of serum cholesterol on AMD—the total serum cholesterol has been reported to be inversely related to early AMD (25). A positive relationship has also been noted between high-density lipoprotein levels and AMD (25). Environmental Influences Environmental influences such as photic injury, smoking, and nutrition may have an effect on the development of AMD. Cumulative exposure to light may cause gradual loss of photoreceptor cells in the macula (48). Photooxidative damage by reactive oxygen intermediates induced by light may promote the development of AMD (28,30,49). The retina, particularly the macula, is highly susceptible to oxidative stress due to a high polysaturated fatty acid content that is prone to lipid peroxidation (28). There have been, however, conflicting reports regarding the association of ultraviolet or visible light with AMD (50,51). Antioxidants may prevent this damage (28). A low dietary intake or low plasma concentrations of antioxidants may be associated with AMD (52). High-dose antioxidants, as recommended by AREDS trial, are associated with the decreased risk of progression to the exudative form of AMD (53).

6:

In the randomized, placebo-controlled AREDS, supplements containing 5 to 13 times the recommended daily allowance of beta-carotene (15 mg), vitamins C (500 IU) and E (400 IU), and zinc (20 mg) taken by patients with early or monocular late AMD resulted in a 25% reduction in the five-year progression to late AMD (53). This benefit did not extend to patients without AMD or with few drusen. Much attention has been given to the dietary importance of carotenoids, lutein and zeaxanthin (54), and omega-3 fatty acids. A high intake of omega-3 fatty acids and fish is inversely associated with the risk of AMD when intake of linoleic acid is low (55), and high levels of docosahexaenoic acid (DHA) have been associated with a 30% reduced risk of AMD (46). Seddon and coworkers have reported the results of the EDCCS trial that revealed that a high dietary intake of carotenoids, particularly dark-green leafy vegetables, is associated with a 43% lower risk of AMD (53). AREDS II, a multicenter prospective National Institutes of Health-sponsored study, will evaluate the effects of DHA and omega-3 fatty acids on the progression of AMD. The effects of lutein and zeaxanthin will also be evaluated in AREDS II. The combined data from the Blue Mountain Eye Study, the Beaver Dam Eye Study, and the Rotterdam Study have clearly shown that current smokers have a significantly higher risk of incident GA and late AMD than both past smokers and those who never smoked. The mean age at diagnosis of AMD (GA, neovascular AMD, and late AMD) is lower for current smokers than for past smokers or those who never smoked (56). A statistically significant association has been noted between smoking and any one or more types of AMD, with increased risks for current smokers or past smokers compared with nonsmokers; the risk ratio or odds ratio has been described to be between 1.06 and 4.96 [reviewed in (57,58)]. The mechanism of injury with smoking is not well understood. It is plausible that smoking decreases choroidal flow potentiating macular hypoxia and ischemia promoting AMD (59). It has also been suggested that a possible small, independent association may exist between high homocysteine levels and AMD (60). Lycopene, a serum carotenoid, may be associated with AMD (61).

Genetic Influence A familial component of AMD has been suggested by twin concordance (62) and first-degree relative studies (63). A population-based study revealed an overall concordance of 37% in monozygotic twins versus 19% in dizygotic twins for early AMD (64). AMD is more likely in first-degree relatives than in agematched controls (65).

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The pathogenesis of AMD is not well understood. Recent published literature has demonstrated ties between inflammation and the pathogenesis of AMD (66–68). Complement factor H (CFH) gene located on chromosome 1 is in a region linked to AMD. Three different CFH gene variants have been identified that increase the risk of AMD from 2.45 to 7.4 times more likely to have AMD (66–68). CFH regulates the alternate complement pathway. The mutated variant gene may prevent inactivation of the alternate complement pathway, possibly leading to persistent inflammation in the retina and choroid.

DRUSEN Drusen were first described in 1854 by Donders (69). They are deposits of membranous debris, extracellular material (ECM) between the RPE and its basement membrane (basal laminar drusen) or between the RPE basement layer and the inner collagenous layer of Bruch’s membrane (basal linear drusen) (16,70–73). Drusen lead to secondary thickening of Bruch’s membrane and RPE degeneration. Visual loss in macular degeneration is the result of photoreceptor atrophy that follows RPE atrophy as a result of involution of choriocapillaris (74). Drusen form as deposition of membranous material between the plasma membrane and the basement membrane of the RPE, and can be found as early as the second decade of life. They represent a normal aging change (75,76). Experimental and postmortem human studies have shown that the drusen are RPEderived (77–79). Ishibashi and coworkers described the formation of drusen under electron microscopy as follows: (i) evagination or budding of the RPE cell in the subepithelial space; (ii) separation of the evaginated portion from the parent RPE cell; (iii) degeneration and disintegration of these evaginated cell components devoid of a nucleus; and (iv) accumulation of granular, vesicular, tubular, and linear material in the sub-RPE space (15). The etiology of the evagination is not known. AMD involves aging changes along with additional pathologic changes. In both aging and AMD, following changes occur: (i) oxidative stress resulting in RPE injury; (ii) inflammatory response in the Bruch’s membrane caused by the RPE injury; (iii) production of abnormal ECM by the injured RPE and choroid; and (iv) resultant disturbance in the RPE—Bruch’s membrane homeostasis ultimately leading to RPE and choriocapillaris atrophy or growth of choroidal neovascular membrane (80). Environment and genetics may have a superimposing effect that most likely alters a given patient’s susceptibility to the disease (80).

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Hard drusen are common in young people and do not lead to macular degeneration (70). Small, hard, distinct drusen were found in the macula of 94% of the Beaver Dam Eye Study population (9). These were not noted to increase in number with age. If present in excessive number, however, they may predispose to RPE atrophy (83). Hard drusen act as window defects on fluorescein angiogram with early hyperfluorecence and fading of fluorescence in late frames (Fig. 2).

Figure 1

Hard drusen.

Types of Drusen Different types of drusen are noted in the retina: (i) hard, (ii) soft, (iii) crystalline, and (iv) cuticular or basal laminar. Hard Drusen Hard drusen are discrete, small, yellow, nodular hyaline deposits in the sub-RPE space, between the basement membrane of RPE and the inner collagenous layer of Bruch’s membrane (81). These drusen are smaller than 50 mm in diameter (Fig. 1). Focal densifications of Bruch’s membrane, termed microdrusen, may precede the formation of hard drusen (82). Preclinical drusen appear ultrastructurally as “entrapment sites”, with coated membrane-bound bodies that form adjacent to the inner collagenous layer of Bruch’s membrane (82). These are structurally different from basal linear deposit.

(A)

Soft Drusen Soft drusen are clinically noted as pale yellow lesions with poorly defined edges (Fig. 3). They can also represent focal accentuations of basal linear deposits (71). They also represent localized accumulation of basal laminar deposits in an eye with diffuse basal laminar deposits (84). They gradually enlarge and may coalesce, termed confluent drusen, to form multiple irregular areas of localized RPE detachments. With time, soft drusen can become crystalline in nature. Crystalline drusen are discrete calcific refractile drusen (Fig. 4). These are dehydrated soft drusen that predispose to GA (Fig. 5) (83,85). Soft drusen are classified by size into small, medium, and large. A small soft druse is !63 mm wide, intermediate is between 63 and 128 mm and large is O128 mm. (The width of the retinal vein off the optic nerve is 128 mm.) The risk of progression from non-exudative to exudative AMD increases with the size and the total area of the drusen (86). Clinical and histological studies have shown that soft drusen precede macular degeneration (87,88). They lead to secondary Bruch’s membrane thickening and RPE atrophy with subsequent photoreceptor loss. This promotes the development of choroidal neovascular membrane (13,73,89).

(B)

Figure 2

Fluorescein angiogram: (A) early and (B) late frames of hard drusen in the macula.

6:

Figure 3

Soft drusen.

On fluorescein angiography, soft drusen show early hypofluorescence or hyperfluorescence with no late leakage.

Basal Laminar Drusen Basal laminar or cuticular drusen are tiny, white deposits found between the plasma membrane of RPE and its basement membrane (Fig. 6) (70). Such drusen are mainly composed of collagen, laminin, membrane-bound vesicles, and fibronectin. The deposits tend to accumulate over the thickened Bruch’s membrane, suggesting that they may be a local response to altered filtration at these sites (81). Basal laminar drusen are typically very numerous, distributed in a bilaterally symmetrical pattern, and are most prominent in the posterior poles. These unusual drusen are often seen in association with other typical hard, soft, or semisolid drusen. VA is typically minimally affected despite the large number

Figure 4

Calcific drusen.

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Figure 5

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Geographic atrophy.

of these drusen. They tend to occur in younger individuals and in normal eyes and do not predispose to macular degeneration. On fluorescein angiography, the basal laminar drusen hyperfluoresce early and give an appearance of “starry night” (Fig. 7) (85).

DISAPPEARANCE OF DRUSEN Various reports have described spontaneous disappearance of drusen (10,90). Bressler and colleagues noted in their Waterman study that the large drusen disappeared spontaneously in 35% of 47 individuals in five years of follow-up (87). They have also been reported to disappear after laser photocoagulation (Fig. 8) (94). RPE atrophy is noted as drusen disappear followed by photoreceptor and choriocapillaris loss (91). It has been hypothesized that disappearance of drusen may be linked to a lower risk of CNV. This was

Figure 6

Basal laminar drusen.

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Figure 7 Fluorescein angiographic late frame demonstrating “starry night” appearance.

the basis of undertaking three multicenter trials to evaluate the effect of light laser on drusen, the choroidal neovascularization prevention trial (CNVPT) (92), the Prophylactic Treatment of AMD (PTAMD) Study (93), and the Drusen Laser Study (DLS) (95). The CNVPT study, a multicenter, randomized prospective study of laser treatment versus observation evaluated the effect of low-intensity argon laser treatment in eyes with drusen secondary to AMD. The study included two groups: (i) unilateral group, 120 patients with CNVs in one eye and 10 or more drusen larger than 63 mm in diameter in the fellow eye, and (ii) bilateraldrusen group, 156 patients with non-exudative AMD and 10 or more drusen larger than 63 mm in diameter within 3000 mm of the foveola and good VA (92,96,97). The rate of CNV formation in the bilateral group

(A)

was not found to be statistically different, 4/152 in the laser-treated group versus 2/156 in the control group, PZ0.42 (92). However, a relatively high rate of CNV development was seen in the unilateral arm and the study was suspended in the treated cohort; 16.9% (10/59) versus 3.2% (2/61 eyes) in the laser treatment and control groups, respectively (PZ0.02) (92). The PTAMD trial, using subthreshold diode laser, has shown similar findings of increased risk of exudative maculopathy in fellow eyes of patients treated with laser (93). In the phase III PTAMD study, at one year, the rate of CNV formation was 15.8% for lasered versus 1.4% for observed eyes (PZ0.05). Most of the intergroup differences in CNV events occurred during the first two years of followup. Treated eyes showed a higher rate of VA loss (R3 lines) at three and six months follow-up relative to observed eyes (8.3% vs. 1% and 11.4% vs. 4%, respectively; PZ0.02, 0.07). After six months, no significant differences were observed in VA loss between groups. Prophylactic subthreshold 810-nm-diode laser treatment to an eye with multiple large drusen in a patient whose fellow eye has already suffered a neovascular event places the treated eye at higher risk of developing CNV (96). The bilateral-drusen arms of this trial are still in progress. The DLS trial has shown that the incidence of CNV in the unilateral arm was higher in the laser-treated arm than the control arm, though this was not found to be statistically significant. However, the onset of CNV was approximately six months earlier in the laser-treated group than in the control group, a statistically significant finding (95). The group recommends against prophylactic laser treatment when a neovascular process has already occurred in one eye. However, they were unable to determine the

(B)

Figure 8 This patient underwent diode laser photocoagulation in his left eye. (A) Fundus appearance shows multiple large soft drusen prior to laser. (B) Fundus appearance three years later shows a marked reduction in the number of drusen in this eye.

6:

(A)

(B)

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103

(C)

Figure 9 A 76-year-old woman who was enrolled and treated in the unilateral DLS pilot study. Visual acuity in the right eye was 20/30-2; confluent soft drusen were present. (A) By four months, drusen had resolved and at nine months, fleck hemorrhages were evident at the right fovea associated with a laser scar (arrow). (B,C) Fluorescein angiography showed leakage from this laser scar (arrow). Source: From Ref. 98.

role of prophylactic laser in patients with bilateral drusen and good vision as the event rate is very low in these eyes and a large number of eyes are needed, they were not able to achieve the necessary recruitment goals to answer this question (Fig. 9) (95). Another method of preventing the development of sight-threatening CNV is to deliver a medication to an at-risk eye to slow or stop angiogenesis. The anecortave acetate risk reduction trial completed enrollment in January 2006 of 2500 eligible patients to determine whether anecortave acetate, an angiostatic steroid given as a juxtascleral injection every six months, will reduce the risk of developing CNV and vision loss in eyes that are at high risk of this complication (Fig. 10A–J).

NON-EXUDATIVE AMD Soft drusen precede macular degeneration (74,87). The mere presence of drusen does not account for significant loss of vision (72). Soft drusen can lead to RPE atrophy, with resultant overlying photoreceptor atrophy and vision loss. When the vision falls below or equal to 20/30, the disease process is termed nonexudative or dry macular degeneration. Subretinal fluid, subretinal hemorrhage, RPE detachment, hard exudates, and subretinal fibrosis, all signs of exudative maculopathy, are absent in dry macular degeneration. GA is an advanced form of dry macular degeneration. This involves RPE atrophy with subjacent choriocapillaris and small choroidal vessel atrophy. This condition progresses slowly over years and often spares the center of the foveal avascular zone until late in the course of the disease (99). Non-exudative AMD is the most common form of AMD, accounting for 80% to 90% of cases overall (18). Bressler and coworkers reported a prevalence of 1.8% of AMD in men 50 years of age or older in the Chesapeake

Bay study. Of these, almost 75% had non-exudative maculopathy (100). It accounts for only 20% of all legal blindness associated with AMD and occurs with GA, an advanced form of dry AMD (101). Soft drusen and retinal pigmentary changes increase with age (31,10). In the five-year period of the Beaver Dam Eye Study, people 75 years or older were 3.3 to 8.4 times as likely to develop drusen between 63 and 250 mm in diameter when compared with person 43 to 54 years of age. Also, persons 75 years of age or over were 16 times more likely to develop confluent drusen when compared with people 43 to 54 years of age (31). The incidence of early AMD increases with advancing age (Table 2). These findings have been noted in all population-based studies: The Beaver Dam Eye Study (31), Blue Mountains–Australian (36), Rotterdam (102), and Colorado–Wisconsin (103) studies of AMD. Focal hyperpigmentation along with the presence of greater than five soft, large, and confluent drusen is associated with the increased risk of progression of RPE atrophy and choroidal atrophy. These eyes have a higher incidence of developing CNV (72,73). The mere presence of CNV in one eye increases the risk for CNV development in the remaining eye, compared with patients having bilateral drusen. The presence of large drusen in both eyes was a stronger risk factor for progression to advanced AMD than the presence in only one eye (53). The five-year risk of eyes with bilateral soft drusen and good VA to develop CNV is 0.2% to 18% (10,74,89,91). This risk increases to 7% to 87% if the fellow eye has CNV (34,73,87,104). Bressler and colleagues, in their age-adjusted analysis, showed that greater than 20 drusen, the presence of soft confluent type, and focal RPE hyperpigmentation were more often noted in the fellow eyes with unilateral exudative maculopathy than in eyes with

104

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(A)

(B)

(C)

(D)

(E)

(F)

Figure 10 An 81-year-old male who had undergone photodynamic therapy five times for subfoveal choroidal neovascularization in right eye, OD [3/28/05: (A) Color photo; (B) red-free photo; (E, G) - fluorescein angiogram, (FA)] was enrolled into the anacortave acetate risk reduction trial for high risk drusen for the left eye, OS [(C) Color photo; (D) red-free photo; (F, G) - FA]. He underwent anacortave acetate injections on 4/7/05 and 9/30/05. His visual acuity OS remained 20/20 even though a new pigment epithelial detachment was noted on 7/7/05 [(H) Color photo; (I & J) - FA]. (Continued )

6:

(G)

(H)

(I)

(J)

Figure 10 Continued

NON-EXUDATIVE AGE-RELATED MACULAR DEGENERATION

105

(Caption on facing page ).

bilateral drusen (88). Focal hyperpigmentation and confluence of drusen are associated with an increased risk of progression to exudative AMD (11). Focal hyperpigmentation may be associated with subclinical subretinal neovascularization that cannot be detected by fluorescein angiogram (91). It may also

Table 2 The Beaver Dam Eye Study; 5-Year Incidence of Non-exudative AMD Findings p-value 1. Large drusen (125–249 microns) 2. Large drusen (O250 microns) 3. Soft indistinct drusen 4. Retinal pigment abnormalities 5. Pure geographic atrophy Source: From Ref. 31.

O75 years 43–54 years of age of age

!0.05

17.6%

2.1%

!0.05

6.5%

0.2%

!0.05 !0.05

16.3% 12.9%

1.8% 0.9%

!0.05

1.7%

0%

Figure 11 High risk drusen showing large confluent drusen with RPE hyperpigmentation.

106

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reflect the changes that have already occurred in the RPE, Bruch’s membrane, and choriocapillaris, which facilitate future development of CNV and may simply suggest the chronicity of the disease process (Fig. 11) (91). The AREDS research study group has described a simplified clinical scale to define risk categories for a five-year risk of developing advanced AMD (86) in eyes without advanced AMD at baseline, or the risk in the unaffected fellow eye when advanced AMD is present in one eye at baseline. It is a five-step scale (0–4) that predicts an approximate five-year risk of developing advanced AMD in at least one eye as follows: 0 factor, 0.5%; 1 factor, 3%; 2 factors, 12%; 3 factors, 25%; and 4 factors, 50%. The scale sums retinal risk factors in both eyes. The risk factors are the presence of one or more large drusen (O125 mm— width of a retinal vein at the disk margin) and pigment stippling; each characteristic gets one point for each eye. Advanced AMD in one eye at baseline is given two scores. The presence of intermediate drusen (R63–128 mm) in both eyes is given one score. The AREDS trial also noted that the drusen area was stronger and a more consistent predictor of progression to advanced AMD than the drusen size. However, for practical clinical purposes, the drusen number and type was used for calculating the severity score.

MONITORING NON-EXUDATIVE AMD Patients with intermediate drusen (O63 mm) or those with exudative AMD in fellow eyes are recommended to take high-dose vitamins as per the AREDS study. Amsler grid testing is a sensitive indicator of progression of the disease process. Straight door and window frames may be the ways to check for any metamorphopsia. Patients are encouraged to seek medical help if visual distortion, metamorphopsia, loss of central vision, or any new symptoms occur. These herald the growth of choroidal neovascular membranes. The early detection of the choroidal neovascular membranes may facilitate treatment as discussed in other chapters.

SUMMARY POINTS & & &

Prevalence of AMD increases with age. Non-exudative AMD is the most common form of AMD. Factors associated with AMD include advancing age, genetic component, nutrition, photic injury, smoking, and systemic hypertension.

&

& & &

High-risk characteristics of drusen for development of CNV include: soft type, large size, greater than five in number, confluent, and presence of RPE stippling. Disappearance of drusen can occur spontaneously or may follow after laser. GA is the advanced form of non-exudative AMD. Monitoring VA and visual symptoms for the progression to the exudative AMD is of utmost importance in applying timely treatment (105).

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7 Geographic Atrophy Sharon D. Solomon

Retina Division, Wilmer Eye Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland, U.S.A.

Janet S. Sunness

The Richard E. Hoover Services for Low Vision and Blindness, Greater Baltimore Medical Center, Baltimore, Maryland, U.S.A.

INTRODUCTION Geographic atrophy (GA) of the retinal pigment epithelium (RPE) is the advanced form of nonneovascular age-related macular degeneration (AMD) and is associated with gradual, progressive loss of central vision. Dense scotomas have been shown to correspond to the retinal areas affected by GA (1). These scotomas involve the parafoveal and perifoveal retina early in the course of the disease, sparing the foveal center until late in the course of the disease (2–5). Consequently, GA is responsible for approximately 20% of the legal blindness secondary to AMD, compared to choroidal neovascularization (CNV), which tends to involve the foveal center much earlier in the course of the disease and accounts for nearly 80% of the legal blindness secondary to AMD (6). However, the parafoveal and perifoveal scotomas in the early stages of GA compromise the patient’s ability to read and to recognize faces, often despite the retention of good visual acuity, and account for a much larger percentage of moderate visual loss in those affected (7). In addition, GA is present binocularly in most patients. The prevalence of GA in the population 75 years of age or older is approximately 3.5%, half that of neovascular AMD (8,9), and increases to 22% in those 90 years of age or older (10). While there are treatments for CNV, there is presently no definitive treatment available for GA. As our understanding of GA grows, it is hoped that medical and surgical interventions will be developed to completely halt its progression rate and to prevent subsequent moderate and severe visual loss.

CLINICAL FEATURES OF GA GA is easily recognized clinically, as it appears as a well-demarcated area of decreased retinal thickness, compared to the surrounding retina, with a relative change in color that allows for increased visualization

of the underlying choroidal vessels. Both the location and pattern of the atrophy may vary in appearance. Forty percent of eyes with macular GA also have peripapillary GA, which may become confluent with the macular atrophy (7). There may be pigmentary alteration, either hypopigmentation or hyperpigmentation, surrounding the macular atrophy. Peripheral reticular degeneration of the pigment epithelium is present in about 41% of eyes (7). Drusen, usually a mixture of the soft and calcific types, are present in most eyes until the GA becomes so extensive as to resorb the macular drusen (2). The increased choroidal vessel detail in the area of GA is usually the most easily identified fundus change and further reflects the extent of RPE attenuation. On fluorescein angiography, this translates into an area of hyperfluorescence that corresponds to the ophthalmoscopic borders of the GA, secondary to transmission defect and staining. The intensity of hyperfluorescence from choroidal flush may vary depending on the presence or absence of the underlying choriocapillaris (4). Fluorescein angiography may also aid in distinguishing GA from occult CNV, which may otherwise appear clinically indistinguishable. Hemorrhage may occur in eyes with GA. Though this may be a reflection of the development of CNV and herald a more precipitous decline in visual function secondary to neovascular maculopathy, often the small areas of CNV that develop are transient and may become clinically inapparent a few months later (11). Hemorrhages have also been described in GA in the complete absence of any CNV (11,12). In general, however, the presence of hemorrhage, especially when associated with a sudden change in vision, warrants an angiographic evaluation for the presence of CNV (13). Though there are frequently small areas of retinal sparing within the GA, especially at the center of the macula, foveal localization may still prove challenging

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on clinical examination, on the color fundus photograph, and on the angiogram. Clinically, the location of xanthophyll, if visible, is helpful in determining the location of the foveal center. On fluorescein angiography, the intense hyperfluorescence associated with the GA may obscure the view of the entire foveal avascular zone, making foveal localization a less certain task. Under such circumstances, the redfree photographs can often be of significant help. The presence of xanthophyll may suggest that the fovea has visual function, even if the retina appears atrophic and nonfunctional (14). Testing with devices such as the scanning laser ophthalmoscope (SLO) may help to ascertain the central visual potential that remains (1,5).

HISTOPATHOLOGY AND PATHOGENESIS Histopathologic examination of eyes with GA demonstrates a loss of RPE cells in the area of atrophy with a secondary loss of overlying photoreceptor cells (15). The choriocapillaris may also be absent, and there is indeed some experimental evidence to suggest that when the RPE is removed or has atrophied, the choriocapillaris involutes secondarily (16,17). GA is associated with thickening of Bruch’s membrane secondary to the deposition of basal laminar and basal linear deposits in the surrounding retina (18). Therefore, histologically, GA has been thought of as the end stage of the AMD process if CNV does not develop (19). GA may also occur following the flattening of a retinal pigment epithelial detachment (20). There is controversy as to whether the loss of RPE cells, perhaps related to the deposits in and near Bruch’s membrane, is the primary event in the evolution of GA, or whether this RPE atrophy develops secondary to choroidal vascular insufficiency. Green and others have argued that the presence of choroidal vascular insuffiency should result in the subsequent degeneration of all the outer retinal layers (15). This is not seen in eyes with GA. Friedman suggests that choroidal vascular resistance may predispose to the development of AMD, specifically to the development of high-risk drusen and CNV (21). However, a causal association between choroidal vascular resistance and GA has not been established to date. Grunwald has found that foveal choroidal blood flow is reduced in eyes with early atrophic AMD and good visual acuity (22), and this work is continuing to better characterize the relationship between choroidal blood flow and the development of advanced AMD.

PREVALENCE AND EPIDEMIOLOGY OF GA Population-based studies, such as the Beaver Dam Eye Study and the Rotterdam Study, have examined the

prevalence of GA in the elderly and compared it to the prevalence of CNV in the same groups. The prevalence of GA is approximately 3.5% for people age 75 and above in the United States and other developed nations, half that of CNV (8,9). The prevalence of GA increases with age and is actually more common than CNV in older age groups. In the population over age 90, the prevalence of GA can reach levels of 20% to 35% (10,23). The studies indicate that there is a lower prevalence of GA in African-Americans (24). There does not appear to be a gender difference in prevalence across the populations studied. In the Beaver Dam Eye Study, 8% of eyes with drusen larger than 250 mm went on to develop GA over a five-year period. Eyes that developed GA all had pigmentary abnormalities and at least 0.2 Macular Photocoagulation Study (MPS) disc areas of drusen at baseline (25). Of the eyes with GA, 42% had a visual acuity of 20/200 or worse. This was similar to the 48% of eyes with neovascular AMD that had a comparable level of severe visual loss (25). GA is bilateral in 48% to 65% of cases (7,26). While the rate of bilateral severe vision loss is lower from GA than from CNV, GA is still responsible for a full 20% of the binocular legal blindness secondary to AMD (6). These statistics for severe visual loss measure only the incidence of legal blindness and significantly underestimate the disability associated with GA. A patient with GA and only moderately impaired visual acuity may not be able to read or to recognize faces because the object being visualized does not “fit” into the spared central island of vision (5).

Systemic Risk Factors A number of population-based studies have attempted to identify possible risk factors for the development of GA and neovascular AMD. The Beaver Dam Eye Study did not demonstrate a relationship between GA and cholesterol level or alcohol intake (8,27). While current or past smoking was a significant risk factor for the presence of GA for women in the Blue Mountains Eye Study, the same association did not reach statistical significance for men (28). In Sunness’ study, there was a trend for current smokers to have a more rapid progression of GA than nonsmokers (7). The same study suggested that patients who are pseudophakic or aphakic do not have more rapid progression of GA than their phakic counterparts (7). More recently, the Age-Related Eye Disease Study (AREDS), a multicenter study of the natural history of AMD and cataract, reported its findings on possible risk factors for the development of GA and neovascular AMD. The presence of GA was found to be associated with increasing age and smoking,

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confirming the findings of previous population-based studies (29). In addition, there appeared to be a positive association between the use of antacids and the use of thyroid hormones and the presence of GA (29). These two associations have not been previously reported and will certainly prompt further investigation. Level of education was found to be inversely proportional to the presence of GA in that persons with more years of formal schooling seemed to be at lower risk for GA (29).

Heredity Several studies have suggested that genetic factors may also be important in the pathogenesis of AMD. Hereditary retinal dystrophies, with clinical manifestations similar to AMD, may share potential candidate susceptibility genes. For example, a mutation of the RDS/peripherin gene has been shown to be associated with Zermatt macular dystrophy, which is a dominant, age-related, progressive macular dystrophy that resembles GA in its later stages (30). Particular interest has focused on the ABCR gene which is responsible for autosomal recessive Stargardt macular dystrophy. One study reported that 16% of patients with AMD had a mutation in this gene, compared with 13% of Stargardt’s patients and 0.5% of the general population (31). The mutation was identified primarily in eyes affected by atrophic AMD, on the continuum between early and advanced disease (32,33). There is some disagreement with these findings however. Pedigree studies have included families in which GA and CNV occur in different members as well as twin studies, where both twins are affected by GA or where one twin has GA and the other has an earlier atrophic form of AMD. In one large AMD family,

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linkage has been reported to markers in 1q25-q31 (34). Recent data also suggest that the apolipoprotein E epsilon 4 allele may be associated with a reduced risk for the development of AMD (34). Identification of those genetic factors that play a role in the pathogenesis of AMD may aid with the recognition of those at risk and permit possible lifestyle modifications to prevent or decrease the severity of disease. A recent exciting finding by several groups of investigators is the association of advanced AMD with specific complement factor H polymorphisms. This association is present for GA alone as well. The association suggests that there might be an inflammatory basis for advanced AMD (35).

NATURAL HISTORY OF GA Over the last three decades, several studies have described the progression of GA with respect to visual acuity loss and actual enlargement of the atrophy in populations of patients. Their observations form the foundation of our knowledge of the natural history of GA. GA typically develops in eyes that, at baseline, have drusen or pigmentary alteration. As drusen fade, focal areas of atrophy may develop in their place, enlarge, and evolve into GA (2,36,37). Alternatively, areas of mottled hypopigmentation may also predispose to the development of GA (2). The progression goes through a number of stages. Initially, single or multifocal areas of GA may be found in the region around the fovea. As these areas enlarge and coalesce over time, they can form a horseshoe of atrophy that spares the foveal center (Fig. 1). This horseshoe of atrophy may close off into a ring of

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Figure 1 Four-year progression in geographic atrophy (GA). (A) There are multifocal areas of GA, along with drusen and pigmentary alteration. (B) Four years later, the areas of GA have enlarged and coalesced, forming a horseshoe of atrophy surrounding the fovea.

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atrophy that still permits foveal preservation. In the late stages of GA, the fovea itself becomes atrophic and nonseeing, from further coalescence of the GA, requiring the patient to use eccentric retinal loci for fixation and seeing (2). GA may also occur secondary to an RPE detachment. Elman and others have reported RPE detachments flattening and going on to evolve into GA in about 20% of cases (20,38–40). Whether the GA was extrafoveal or foveal depended on the preceding location of the RPE detachment. Because visual loss tends to be gradual and subtle, and takes place over a period of years, patients may not seek medical attention until the solid central GA is present. Sunness demonstrated that the median visual acuity tended to be worse in eyes with larger total atrophic areas, with the most dramatic difference in median acuity occurring between eyes with less than three MPS disc areas of central atrophy (i.e., within four MPS disc areas of the foveal center) and those with greater than three MPS disc areas of central atrophy (7). GA continues to enlarge over time with a median rate of enlargement over a two-year period of 1.8 MPS disc areas (7). The amount of enlargement of total atrophic area has been shown to increase with increasing baseline size of atrophy up to approximately five MPS disc areas of baseline, above which the rate of enlargement stayed about the same. For eyes with more than 10 MPS disc areas, it is difficult to measure enlargement because the borders of the GA often extend past the photographic field. Baseline level of visual acuity did not appear to significantly affect the degree of enlargement of total atrophy (7). The only risk factor that has been linked to more rapid enlargement of the total atrophic area was a baseline total atrophy area greater than three MPS disc areas (7). Neither the phakic status of the study eye nor a history of hypertension in the patient was shown to be a risk factor for the enlargement of total atrophy (7). There was an apparent trend for smokers to have a more rapid enlargement of atrophy (7). GA is associated with a significant decline in visual acuity over time in many eyes. Overall, 31% of all study eyes lost three or more lines of visual acuity, doubling the visual angle, by two years of follow-up, and 53% lost three or more lines of visual acuity by four years of follow-up (7). Rates of severe vision loss, that is a quadrupling of the visual angle or at least six lines of visual acuity loss, were 13% for all study eyes by two years and 29% by four years (7). There was a significantly larger rate of moderate and severe vision loss for eyes with a baseline visual acuity of better than 20/50. At two years of follow-up, 41% of these eyes with good acuity at baseline lost three or more lines of visual acuity and 21% lost six or more lines of visual acuity (7). Those numbers grew to 70% at four years of follow-up for moderate vision loss and 45% at four

years for severe vision loss (7). Twenty-seven percent of the eyes with visual acuity of 20/50 or better at baseline had visual acuity of 20/200 or worse at four years of follow-up (7). The presence of CNV in the fellow eye did not appear to affect the rate of visual acuity loss in the GA study eye (7). Risk factors that have thus far been identified for moderate vision loss include baseline visual acuity of better than 20/50 and lightest iris color (7). Among eyes with visual acuity better than 20/50, the presence of GA within 250 mm of the foveal center was a strong risk factor for a three-line visual acuity loss (7). There was no apparent association between phakic status of the study eye, hypertension, or smoking with moderate vision loss demonstrated in the study by Sunness et al. (7). During the four-year follow-up period, GA appeared to progress through various stages, including the small, multifocal, horseshoe, ring, and solid stages described in previous studies (2,3,7). For eyes that did not have the solid pattern of atrophy at baseline and which did not develop CNV during the course of the study, 61% advanced to a different configuration over the two-year follow-up period (7). However, those eyes that had the same configuration at the two-year follow-up as at baseline still had visual acuity loss, most notably in the ring group where 50% of eyes lost three or more lines of visual acuity (7). The size and rate of progression of atrophy are highly correlated between the two eyes of patients with bilateral GA. This includes the baseline area of total atrophy, the baseline area of central atrophy, the presence of peripapillary atrophy, and the progression of total atrophy. However, the correlation between eyes for baseline acuity, for acuity at two years, and for two-year change in acuity is significantly smaller, reflecting the importance of the difference in foveal sparing between eyes (Fig. 2) (7). The two parameters used to describe the progression of GA in the Sunness’ study, namely the enlargement of the atrophic area and visual acuity loss, do not completely gauge the actual impact of GA on visual function and performance. Maximum reading rate can be significantly affected by encroachment of GA on the fovea, even while there may still be little change in visual acuity (5). Some patients may be able to read single letters on acuity charts but are unable to read words because of the size of the preserved foveal island (5). The median maximum reading rate decreased from 110 words per minute (wpm) to 51 wpm over a two-year period in patients with visual acuity better than 20/50, where the normal median rate for the reading test used in elderly people without advanced AMD is 130 wpm. Eighty-three percent of eyes that lost three or more lines of visual acuity had maximum reading rates less than 50 wpm at two-year follow-up. However, even in the group

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Figure 2 Bilateral geographic atrophy. (A) This eye had 20/30 visual acuity, and the patient was able to read 80 wpm, using the spared central area. (B) The fellow eye did not have a useable spared region and had 20/400 visual acuity.

that maintained good acuity at two years, one-third had maximum reading rates below 50 wpm (5). For eyes with visual acuity between 20/80 and 20/200, when the fovea is already involved at baseline, there is evidence to suggest that the maximum reading rate is inversely related to the size of the total atrophic area (41). This may mean that an intervention that could slow the rate of enlargement of atrophy could have a significant impact on preserving visual function, even in the presence of a central scotoma.

DEVELOPMENT OF NEW GA The relatively high prevalence of bilaterality of GA, reported to be anywhere from 48% to 65% (26) in the literature, would suggest that patients with GA in one eye and only drusen or pigmentary change in the fellow eye are at significant risk for developing GA in the fellow eye. In the Beaver Dam Eye Study, 12 patients had GA in one eye at baseline. After five years of follow-up, three of these patients (25%) had developed GA in the fellow eye (25). Patients with GA in only one eye were found to be 2.8 times more likely to develop advanced AMD in the fellow eye than were patients with only early changes from age-related maculopathy in either eye at baseline. This is in contrast to patients with neovascular AMD in only one eye where the relative risk of developing advanced AMD in the fellow eye, 1.1, was not significantly different from the rate at which advanced AMD developed in the fellow eye of those patients with only early changes from age-related maculopathy at baseline (25). In Sunness’ progression study of GA, two of nine patients (22%) with GA in one eye and

only drusen or pigmentary changes in the fellow eye developed new GA in the fellow eye during the twoyear follow-up period (7). There is limited information available on the rate of development of GA in the eyes of patients who have only drusen and pigmentary alteration bilaterally at baseline. In the Beaver Dam study population, there was a five-year incidence of new GA of 0.3% (25). Eyes with only drusen less than 125 mm in linear dimension at baseline were not observed to go on to develop GA. Of the eyes with drusen between 125 and 250 mm at baseline, 1% were described as developing GA. In comparison, 8% of eyes with drusen 250 mm or larger in linear dimension developed GA over a fiveyear period. Similarly, only those eyes with greater than 0.2 MPS disc areas of drusen had a tendency toward developing GA. All eyes that developed GA had pigmentary abnormalities at baseline as well (25). In addition to drusen size, there may be some correlation between the type of drusen present in eyes with early age-related maculopathy and the eventual development of GA. Both calcific drusen (42) and clusters of small, hard drusen have often been observed to be present in eyes with GA. Finally, other potential risk factors that have been identified in the development of GA include delayed choroidal filling on fluorescein angiography (43,44) and diminished foveal dark-adapted sensitivity (45).

DEVELOPMENT OF CNV IN EYES WITH GA Population-based studies have confirmed that the incidence of CNV in an eye with GA depends, in part,

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upon the status of the fellow eye. In patients with GA and no CNV in one eye, and CNV in the fellow eye, the eye affected with only GA follows a course that is essentially identical to that of patients with bilateral GA with respect to foveal preservation, rates of acuity loss, and rates of enlargement of atrophy, so long as it does not develop CNV (7). However, when the incidence of developing CNV in these eyes with baseline GA is assessed, it is found to be significantly higher if the fellow eye has CNV at baseline as opposed to GA. Of the patients enrolled in the extrafoveal MPS with CNV in the study eye, 11 were found to have only GA in the non-study eye at baseline. During the next five years of follow-up, 45% of these eyes went on to develop CNV (46). More recent findings from the MPS Group’s juxtafoveal and subfoveal CNV trials support this incidence. Forty-nine percent of patients with CNV in the study eye and only GA in the fellow eye at baseline went on to develop CNV over the fiveyear follow-up period (47). A prospective study by Sunness et al. in which 31 patients had GA and no CNV in the study eye and CNV in the fellow eye reported a two-year rate of 18% and a four-year rate of 34% for developing CNV in the GA study eye (11). This is in contrast to the results reported by Sunness et al. for patients with bilateral GA at baseline, who had a two-year rate of developing CNV in one eye of 2% and a four-year rate of 11%. Also, none of the patients with GA in one eye and drusen in the fellow eye developed CNV over the two-year period (11). These data all demonstrate that there is a higher incidence of CNV in eyes with GA at baseline that have fellow eyes with CNV. When CNV does develop in an eye with GA, it seems to have a propensity for areas of preserved retina surrounding the GA or in spared foveal regions. In a study by Schatz and McDonald, 8 of 10 patients who developed CNV in eyes that had only GA previously at baseline, developed the CNV at the edge of the atrophy. In the two cases, where the CNV developed over the atrophy, fluorescein angiography was able to demonstrate evidence of intact choriocapillaris in those areas (4). Sunness et al. observed the development of CNV over areas of GA only when there were areas of sparing within the atrophy. Otherwise, patients developed CNV in areas that were adjacent to atrophy (11). Some histologic work likewise suggests that CNV does not develop where the choriocapillaris is absent (15). CNV that is newly developing in eyes with baseline GA may be difficult to detect by both clinical examination and fluorescein angiography. In the absence of subretinal hemorrhage, it may be difficult to detect subretinal fluid that is shallow and overlying an area of atrophy. On fluorescein angiography, the hyperfluorescence already present from transmission

defects and staining due to the GA may obscure any new hyperfluorescence that is secondary to CNV. Because GA does not generally cause an abrupt loss in vision, a patient who presents with subjective and objective evidence of significant changes in baseline visual function should undergo evaluation for the presence of CNV (13). Although GA itself has been associated with subretinal hemorrhages without evidence of CNV (11,12), the presence of hemorrhage should certainly prompt further evaluation to detect newly developing CNV. In some patients, the CNV may spontaneously involute and have an appearance identical to that of GA or may leave small areas of fibrosis as remnants of earlier CNV (11).

IMPAIRMENT OF VISUAL FUNCTION IN EYES WITH GA Visual acuity alone is an inadequate marker of visual function in patients with GA. In addition to central and paracentral scotoma, eyes with GA have other visual function abnormalities that may be secondary to changes in the function of retina that is not yet atrophic (5). Eyes with GA have marked loss of function in dim environments and benefit greatly from increased lighting (5). Aside from delayed and decreased dark adaptation for both rods and cones (5,48–50), eyes with atrophic AMD may also be compromised by reduced contrast sensitivity (5,51,52). Therefore, despite good visual acuity, the patient’s ability to read may be significantly impaired by a combination of factors.

Central and Paracentral Scotomas Many patients with GA have difficulty in reading because of an inability to see a full enough central field. Even in the presence of good visual acuity, scotomas near the fovea and involving the foveal center compromise visual performance. Patients may complain that they can read small newsprint but not larger news headlines. On clinical examination, it may be apparent that the foveal center remains intact but with only a tiny preserved foveal island, which cannot accommodate the larger headline letters. For this reason, it is important to take into account that such patients may be able to read smaller letters on an eye chart even if they are unable to read the 20/400 letter (5). The impact that GA has on a patient’s lifestyle is not limited solely to the ability to read. Patients with GA may also describe having great difficulty in recognizing faces stemming from their inability to assimilate all the features simultaneously (53). Some find themselves assuming a more reclusive lifestyle after having repeatedly encountered friends and family that they fail to recognize and to greet. Moreover, the same small central islands of preserved retina

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that impair visual function in the first place also complicate low-vision treatment in these patients. By magnifying the object of interest, these low-vision devices can result in even fewer characters or features being seen by the patient within the spared area. Conventional visual field measurement is unreliable when an eye lacks steady, central fixation, and can result in plotting scotomas in the wrong location and of the wrong size (1). The SLO provides direct and real-time viewing of stimuli on the retina and permits the precise correlation of visual function with retinal location. SLO macular perimetry has demonstrated that areas of GA are indeed associated with dense scotomas with surrounding retinal sensitivity that may be near normal (1). The fixation behaviors adopted by patients and observed during SLO evaluation may explain the inherent variation in visual acuity in eyes with central scotomas from GA. In order for a patient with scotomas that involve the foveal center to realize his visual potential, he has to place the object of regard on functioning retina by adopting an extrafoveal location for fixation, referred to as a preferred retinal locus (PRL). Sunness et al. found that in a study of eyes with central GA and visual acuities ranging from 20/80 to 20/200, all patients who were able to adopt an extrafoveal location for fixation placed their PRL immediately adjacent to the area of atrophy. Most patients fixated with the scotomas to their right or above fixation in visual field space (41). In another study of GA patients by Sunness et al., patients reported improvement in the acuity of their worse-seeing eye when their betterseeing eye worsened somewhat. At baseline, it was noted that these patients had not developed eccentric PRLs in the worse-seeing eye so that they placed the object of regard into their scotoma where it could not be seen. Over three years of follow-up, these patients, with visual acuities ranging from 20/80 to 20/500, did demonstrate a spontaneous mean improvement of 3.2 lines in visual acuity in the worse-seeing eye. This improvement in the worse-seeing eye was concomitant with the deterioration of vision in the previously better-seeing eye. At follow-up with SLO macular perimetry, the patients were observed to have adopted eccentric PRLs, which appeared to account for the improvement in the vision of the previously worse-seeing eye (54). Awareness of the presence and location of scotomas can aid in the effective utilization of the remaining functional retina, lessening the searching eye movements some patients make when they have no strategy for moving the object of regard away from the scotomas. For example, having the patient fixate superior to the area of atrophy on the retina, that is, placing the scotoma above fixation, is a good strategy because it moves the blind spot out of the most

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important part of the visual field. Similarly, fixating with the scotoma to the right, that is to the left of the atrophy in a fundus photograph, allows the patient to anchor himself at the beginning of a line while reading (41,55). With the aid of a fundus photograph, a physician can help facilitate the patient’s development of a PRL. A fundus photograph has the same left-to-right orientation as visual field space since it has already been reversed by being viewed from the photographer’s perspective. Therefore, an area of atrophy to the left of the fovea, or of fixation, corresponds with a scotoma to the left of fixation. The fundus photograph is inverted in superior–inferior orientation relative to visual field space, such that a patient fixating above an area of atrophy in a fundus photograph has the scotoma above fixation in visual field space. If the fundus photograph indicates the likely location of fixation relative to the scotoma, the physician can then instruct the patient to look toward the scotoma in visual field space. This will have the effect of moving the scotoma farther out of the way. For example, if there is a scotoma to the right of fixation, as when a patient neglects the last letters on each line of an eye chart, having the patient look farther to the right should allow the object of regard to come into view.

Difficulties in Dimly Lit Environments Regardless of their level of visual acuity, most patients with GA have difficulties with reading and with performing other visually related tasks in dimly lit environments. A review of Sunness’ questionnaire response found that at least two-thirds of their patients with GA who still had good enough visual acuity to drive during the day had stopped driving at night (53). Visual function testing objectively confirms the presence of reduced function in dim illumination in eyes with GA, as demonstrated by Sunness et al. in a study of eyes with GA and visual acuity better than 20/50. When a control group of elderly patients with ocular findings limited to only drusen or pigmentary alteration, without advanced AMD, had a 1.5-log unit neutral density filter placed over the study eye, the median worsening in acuity was 2.2 lines on the Early Treatment Diabetic Retinopathy Study (ETDRS) acuity chart. No eye worsened more than five lines (5). For the study group, there was a median worsening in acuity of 4.6 lines on the ETDRS acuity chart when a 1.5-log unit neutral density filter was placed over the study eye (5). When foveal dark-adapted sensitivity was measured by gauging the patient’s ability to see a small red target light in the dark after dark adaptation, eyes with GA and good visual acuity had a median sensitivity that was 1.2 log units lower than the sensitivity of the control group of elderly eyes with only early changes from AMD (5).

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There is less worsening of visual acuity in dim illumination for eyes that have lost foveal fixation, suggesting that dark-adapted changes may be a sensitive marker for foveal changes even before clinically apparent atrophy of the fovea develops from encroachment of surrounding GA (5). These changes in dark-adapted function may also help to predict which patients with high-risk drusen and pigmentary alteration are more likely to eventually develop GA. In a small prospective study of eyes with drusen, Sunness et al. found that the eyes with the most reduced foveal dark-adapted sensitivity were those most likely to develop advanced AMD, including GA (45). Steinmetz et al. observed similar outcomes. Eyes with drusen that had associated delayed choroidal filling and dark-adaptation abnormalities were more likely to develop GA with time (43,44). In order to maximize the remaining retinal function in these patients, low-vision management of these patients should include an evaluation of lighting needs and appropriate recommendation for the necessary degree of lighting for reading and other tasks. For example, a GA patient may gain an increased sense of independence with the use of a small, handheld penlight to use in a dimly lit restaurant to read a menu. Sloan demonstrated, in a study of visual acuity as a function of chart luminance, that normal eyes reach a plateau and then do not improve further in visual acuity beyond a certain threshold luminance. Though GA was not specifically assessed, she found that eyes with AMD in general continued to improve in acuity with increased luminance for the values tested (56). Eyes with GA and some preservation of central vision likely follow a similar pattern.

Other Visual Function Abnormalities Several other abnormalities in visual function may occur in eyes affected with GA. Contrast sensitivity has been found to be reduced in eyes with GA and visual acuity better than 20/50 compared to eyes of elderly patients with only drusen and pigmentary alteration. Specifically, contrast sensitivity is reduced at low spatial frequencies, and is even more markedly reduced at higher spatial frequencies (5). Despite the presence of good acuity from preserved foveal islands in eyes affected with GA, the reading rate may be dramatically decreased secondary to paracentral scotomas. In Sunness et al.’s study of visual function in eyes with GA and visual acuity better than 20/50, 50% of eyes had maximum reading rates less than 100 wpm while 17% had maximum reading rates less than 50 wpm. In a comparison group of eyes with only the earliest manifestations of AMD, the median maximum reading rate was found to be 130 wpm, with no eye having a maximum reading rate less

than 100 wpm (5). For this reason, visual acuity alone is an inadequate measure of a patient’s ability to read. Patients with small, functional foveal islands may have to find an acceptable compromise between using their central fixation and their eccentric PRL to optimize their visual capacity. While the small foveal region has good acuity, it by definition has a limited visual field extent. Moreover, before the foveal center is frankly atrophic, it may still be affected by reduced retinal sensitivity, reduced contrast sensitivity, and a substantial worsening of function in dim illumination. An eccentric, preferred, retinal locus for fixation positioned outside the area of GA will inherently have a lower visual acuity but may be able to offer a larger area of functional retina less affected by dim illumination and reduced contrast sensitivity. Patients may therefore find themselves switching back and forth from foveal to eccentric fixation depending upon the visual tasks at hand, illumination conditions, and other factors (5,13,57,58). The combination of variables that can ultimately affect a GA patient’s ability to perform visually related tasks can make it difficult to prescribe low-vision magnification devices that can make the object of regard too large to be accommodated by the intact central region. Evaluation of low-vision requirements should always keep these variables in mind. Good illumination is essential in almost all visually related tasks. The Motor Vehicle Administration, along with a number of researchers, is currently attempting to develop better ways to evaluate the driving ability of patients with GA and compromised visual function. Patients with GA and good acuity are often able to pass the visual acuity test required for their driver’s license renewal and continue to drive. Those with more reduced acuity may still be able to secure restricted licenses. Most patients with GA tend to limit their driving only to areas that they are intimately familiar with and during daylight hours. One study of AMD patients that assessed their driving ability with a simulated video-type driving test found that performance was poor compared to age-matched controls without evidence of macular degeneration. However, it was observed that these patients had very few accidents as they tended to limit their driving (59). Specialized driver-training programs for low-vision patients are becoming increasingly available in an attempt to assess the ability of patients with GA to drive and to aid them in improving their driving ability.

CONDITIONS RESEMBLING GA There are other conditions of the eye that in one stage or other of their progression can resemble GA. Some of

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these are other manifestations of AMD and simply exist on a different part of the continuum from GA. Other conditions would be classified as retinal or macular degenerations that are not age related. CNV that has spontaneously involuted can leave an atrophic scar that resembles GA (60,61). Some scars may have small fibrotic areas that are remnants of previous CNV. Other scars appear identical to GA. In such cases, fluorescein angiography may aid in distinguishing CNV from GA. Old laser photocoagulation scars may also resemble GA. The history, however, should distinguish the two. Again, fluorescein angiography should demonstrate areas of hypofluorescence that correspond to the laser scars. Areas of GA generally show hyperfluorescence on angiography. An RPE tear may clinically resemble GA. On fluorescein angiography, however, the straight-line border of hyperfluorescence should be characteristic of a rip. It is unclear whether RPE tears develop atrophy in adjacent areas with time (62). Eyes with pattern dystrophy and vitelliform changes may develop atrophic changes that progress in a fashion similar to AMD-related GA. These patients may have areas of macular GA, and some may be accompanied by pigmentary alterations characteristic of these conditions and occasionally by reduced electrooculograms. However, other cases may be difficult to distinguish from age-related GA. The atrophy spreads in a parafoveal pattern with early foveal sparing, often resulting in a similar degree of visual compromise (63). Central areolar choroidal dystrophy is another degenerative, retinal condition that spares the fovea early in the course of disease. This hereditary condition is generally autosomal dominant and causes areas of atrophy in the macular region to develop since early adulthood. Unlike age-related GA, these lesions tend to have early atrophy of the choroidal circulation and choriocapillaris so that involved areas on fluorescein angiography appear as hypofluorescent (64). Disorders that cause central, atrophic lesions, and bull’s-eye maculopathies may also mimic age-related GA. Stargardt’s disease, cone dystrophy, North Carolina macular dystrophy, benign concentric annular macular dystrophy, and chloroquine, and other toxic maculopathies, may all have manifestations similar to GA from AMD. The history, including age of onset of symptoms and prior medication use, may be helpful in differentiating some of these disorders from GA. Associated clinical findings, such as sensitivity to light and significant electroretinographic or color vision abnormalities in cone dystrophy or pisciform flecks and an angiographically dark choroid in Stargardt’s disease may also facilitate differentiating

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the GA that results from these other entities from age-related GA.

AUTOFLUORESCENCE IMAGING AND GA Lipofuscin (LF) accumulates in the lysosomal compartments of postmitotic eukaryotic cells with age and may represent a biomarker for cellular ageing (65). It is assumed that in retinal pigment epithelial cells, LF is a byproduct of the phagocytosis of membranous discs shed from outer segments of photoreceptors and its accumulation may play a pathogenic role in retinal disease; thus, its detection in vivo may help to elucidate its pathophysiological significance (65). Cross-sectional studies on eyes with early and late AMD have shown that increased accumulations of autofluorescent material are present more frequently in eyes with GA than in eyes with drusen alone or with CNV. Furthermore, several findings suggest that this autofluorescence, which originates at the level of the RPE, is derived from LF accumulations (65). While the retina itself has a normal background level of autofluorescence, a number of groups have reported that there is a distinct loss of autofluorescence in areas of GA, which may be consistent with the absence of RPE cells (65). Autofluorescence imaging takes advantage of the fluorescent properties of LF within RPE cells. In fundus autofluorescence imaging, an argon blue laser (488 nm) is used for excitation, and a barrier filter prevents blue light from returning to the image detector, such that only light emitted by autofluorescence above 500 nm is detected. A confocal SLO can then be used to examine the fundus autofluorescence (66,67). Several studies have described the development of new and enlarging areas of preexisting atrophy associated with areas of abnormally high in vivo autofluorescence in eyes with GA secondary to AMD. Fundus autofluorescence was examined with a confocal SLO by Holz et al. in a study of 57 eyes in 38 patients with unifocal or multifocal GA secondary to AMD. The findings were compared to 43 eyes with atrophy secondary to non-AMD etiologies, such as juvenile macular dystrophy. The investigators found that increased autofluorescence outside GA was observed in 47 (82.5%) of 57 eyes with GA secondary to AMD compared to only 4 (9.3%) of 43 eyes with GA secondary to other causes (65). In addition, various patterns of autofluorescence in the presence of GA associated with AMD were noted. In 36 eyes, 76.6%, a continuous band at the margin of the GA with variable peripheral extension was observed. A diffusely increased autofluorescence that involved the entire posterior pole was noted in six eyes (12.8%) with GA secondary to AMD. Small focal spots of increased autofluorescence in the junctional zone of

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three eyes (6.4%) with GA associated with AMD were noted. The study also reported that of 19 patients with bilateral GA, 17 (89.5%) had an identical autofluorescent pattern in each eye (65). From their crosssectional examinations of fundus autofluorescence, the investigators also speculated that it is possible that one pattern of autofluorescence may evolve into another pattern over time, i.e., focal spots of increased autofluorescence could coalesce to become a continuous band of autofluorescence, thus representing a spectrum of the severity of functional compromise at the level of the RPE, which might serve as a useful prognostic indicator of disease progression (65). Holz and colleagues also performed a small pilot study in which the intensity of fundus autofluorescence as well as the occurrence of new GA and the spread of existing GA were recorded in three patients with AMD over a period of three years using a confocal SLO. Preliminary findings suggested that areas of increased autofluorescence preceded the development or enlargement of GA in eyes with AMD (67). GA did not develop in areas with normal background fluorescence. While autofluorescence imaging may have the potential to yield important clinical information regarding the pathogenesis and progression of disease, various limitations in its application have to be considered. Media opacity, such as a yellowing lens, may absorb the blue excitation light and prevent adequate imaging. In addition, it is important to be aware that absolute levels of autofluorescence cannot be assessed, only relative levels of autofluorescence. However, as more is learned about the correlation of autofluorescence pattern with progression of GA, autofluorescent imaging will become an important tool for assessing risk. Potential therapies may possibly be assessed as to whether they decrease the amount of increased autofluorescence, which may serve as an earlier marker of treatment benefit than gauging progression of GA clinically by ophthalmoscopy. Autofluorescence imaging is also an excellent way for imaging areas of GA themselves, which lack autofluorescence and appear black (68,69). This appearance allows for a simpler way of defining the borders of an area of GA, and is more amenable to automation. However, there must be clinical correlation, because drusen and other types of pigmentary change may also show a lack of autofluorescence (69).

POTENTIAL TREATMENT FOR GA Because GA can be clinically visualized in many patients before the development of moderate or severe vision loss, unlike CNV, there is greater potential for medical intervention to preserve visual function. While there is currently no definitive

treatment to reverse the progression of GA, there is therapy for retarding disease progression. The AREDS, a double-masked clinical trial, enrolled 3640 patients, ages 55 to 80 years, who had clinical evidence of extensive small drusen, intermediate drusen, large drusen, noncentral GA, or advanced AMD in one eye and randomly assigned them to receive daily oral supplements containing either antioxidants (vitamin C, 500 mg; vitamin E, 400 IU; and beta-carotene, 15 mg), zinc (80 mg, as zinc oxide and copper, 2 mg as cupric oxide), antioxidants plus zinc, or placebo. Average follow-up was 6.3 years. Investigators observed that treatment with zinc alone or in combination with antioxidants significantly reduced the risk of progression to advanced AMD in individuals with intermediate drusen, large drusen, noncentral GA, and advanced AMD (70). The risk reduction for those taking antioxidants plus zinc was most favorable at 25% (70). However, the data for GA alone were not statistically significant, perhaps because of inadequate numbers. In addition, the two measures related to GA that are reported had a trend toward showing opposite findings. The risk of developing central GA had a trend toward being lowered by antioxidants, zinc, or the combination. However, the development of any new GA (360 mm or greater in diameter) in an eye without GA at baseline showed a trend toward a reduced risk with antioxidants but an increased risk for zinc and the combination (70). These were small effects, and a larger clinical trial is necessary to be able to detect statistically and clinically significant effects on GA. Many retina specialists do recommend the AREDS supplements, because of the overall lessening of risk of advanced AMD. One approach that may hold promise for patients with GA in the future is to somehow supply trophic factors to delay or prevent RPE and photoreceptor cell death. A study is about to begin at National Institute of Health (NIH), using encapsulated cell technology, to determine if ciliary neurotrophic growth factor, made by encapsulated genetically engineered RPE cells placed intraocularly, can improve photoreceptor health. Studies have been performed to transplant fetal RPE to try to provide presumed humoral trophic factors, but attempts at transplantation, as reported for example in one case by Weisz et al., have been complicated by rejection of the transplanted cells (71). Currently, patients with GA and visual compromise can be offered rehabilitation in terms of lowvision intervention and new strategies for maximizing their utilization of remaining, healthy retina through the development of preferred retinal loci (PRLs). More cases of GA will continue to be seen in ensuing years as its prevalence grows in an ageing population. It is hoped that as more is learned about GA in the future, we can offer more to the patient with respect to the

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management and eventually prevention of this form of AMD.

SUMMARY POINTS &

&

&

&

&

& &

&

&

&

&

&

The prevalence of GA increases with age, being half as common as CNV at age 75, and more common than CNV in older age groups. GA continues to enlarge over time with a median rate of enlargement over a two-year period of 1.8 MPS disc areas. Scotomas from GA, the advanced form of nonneovascular AMD, involve the parafoveal and perifoveal retina early in the course of the disease, sparing the foveal center until late in the course of the disease. These parafoveal and perifoveal scotomas compromise the ability to read and to recognize faces, often despite the retention of good visual acuity, accounting for a large percentage of moderate visual loss in those affected. Hemorrhage may occur in eyes with GA in the absence of CNV. Small areas of CNV that can be associated with hemorrhage may be transient, becoming clinically inapparent, or appearing as increased atrophy, a few months later. There is a higher incidence of CNV in eyes with GA at baseline that have fellow eyes with CNV. GA is bilateral in more than half of the people with this condition. The size and rate of progression of atrophy are highly correlated between the two eyes of patients with bilateral GA, but the acuities may differ due to central sparing. Among eyes with GA with visual acuity better than 20/50, there is a 40% rate of three-line visual loss at two years. Maximum reading rate can be significantly affected by encroachment of GA on the fovea, even while there may still be little change in visual acuity. Eyes with GA have marked loss of vision in dim environments and benefit greatly from increased lighting. Oral supplementation with antioxidants and zinc, per the AREDS protocol, may slow the progression of GA and delay loss of vision, although the AREDS study did not have enough power to show a significant effect on GA itself. The development of a PRL can aid in the effective utilization of the remaining functional retina.

ACKNOWLEDGMENTS Supported in part by NIH R01 EY 08552 (JSS), NIH R03 EY14148 (JSS), the James S. Adams RPB Special Scholar Award (JSS), and the RPB Physician Scientist Award (JSS).

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8 Exudative (Neovascular) Age-Related Macular Degeneration Jennifer I. Lim

University of Illinois School of Medicine, Department of Ophthalmology, Eye and Ear Infirmary, UIC Eye Center, Chicago, Illinois, U.S.A.

Jerry W. Tsong

Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A.

INTRODUCTION Exudative age-related macular degeneration (AMD) was first described and illustrated in the literature in 1875 by Pagenstecher (1). Pagenstecher termed the condition chorioidioretinitis in regione maculae luteae. Then in 1905, Oeller first used the name disciform degeneration (degeneratio maculae luteae disciformis) (2). Later, Julius and Kuhnt in 1926 further elaborated on this condition and established it as a disease (3). Further study by clinicians and pathologists over the next several decades resulted in the understanding that choroidal neovascularization (CNV) was responsible for the manifestations of exudative AMD. The fact that disciform scars had associated CNV was revealed in 1928 by Holloway and Verhoeff who described eight eyes with disclike degeneration of the retina (4); histopathology showed CNV. In 1937, Verhoeff and Grossman similarly demonstrated CNV in their cases of macular degeneration and emphasized that blood vessels erupted through Bruch’s membrane (5). It was not until 1951 that clinicopathologic correlations by Ashton and Sorsby demonstrated that CNV with breaks in Bruchs membrane results in subretinal fluid (6). Finally, in 1967 Gass implicated CNV as having a primary role in what was then called “senile disciform macular degeneration” (7,8). In 1971, Blair and Aaberg showed the clinical and fluorescein angiographic characteristics of CNV in these eyes with “senile macular degeneration” (9). In 1976, Small published a clinicopathologic correlation of the evolution of a lesion, comprised of CNV with a serous pigment epithelial detachment (PED), to a disciform scar (10). In 1977, Green and Key (11) studied the histopathologic features of 176 eyes from 115 patients with AMD. Their results supported the view that drusen predispose to development of CNV. Since then, numerous studies have given us ample histopathologic data on CNV (see Grossniklaus chapter).

Since the earliest description of AMD, there have been numerous refinements in the categorization of the types of AMD. In fact, even the term, AMD, is a relatively recent development. Prior to 1990, the term “senile macular degeneration” was used to refer to what we now know as AMD. More recently, the two main types of AMD, non-exudative or non-neovascular AMD and exudative or neovascular AMD, have been referred to colloquially as dry AMD and wet AMD respectively. Although non-exudative AMD is typically associated with less severe degrees of visual disturbances than exudative AMD and may even have no associated visual disturbance, eyes with exudative AMD typically have some visual disturbance. Exudative or neovascular AMD has the most serious visual prognosis in terms of visual acuity outcomes. An overview of the epidemiology, risk factors associated with development of exudative AMD, fundus findings found in exudative AMD, diagnostic tools used in evaluating exudative AMD and treatment options for the various types of exudative AMD is presented.

EPIDEMIOLOGY Exudative (neovascular) AMD, although the less common form of AMD, is the leading cause of new blindness in the older age population in the United States, accounting for 16% of all new cases of blindness over the age of 65 years. Indeed, the majority of patients with severe visual loss have CNV (12). In fact, 79% of eyes legally blind in the Framingham Study and 90% of legally blind eyes in a large case control study had neovascular AMD (13,14). With the aging of the U.S. population, AMD is reaching epidemic proportions. In the United States alone, there are 50,000 new cases of CNV due to AMD each year. The number of persons aged 55 years or older is 38 million in the United States (U.S. census 2000 data) and is projected to increase to 88 million by 2030.

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The prevalence of AMD, in general, and that of the late forms of AMD increase with advancing age. In a study by Friedman and colleagues, the prevalence of advanced AMD (defined as presence of CNV or foveal geographic atrophy) is estimated to be 1.75 million in the United States. By 2020, the prevalence of advanced AMD is expected to reach 2.95 million. Currently, 1.22 million have neovascular AMD in at least one eye; 973,00 have geographic atrophy in at least one eye; 7.3 million individuals have large drusen in one or both eyes and are at high risk for progression to advanced AMD (15). There is indeed a strong need for the identification of risk factors for exudative AMD and for preventive therapies.

Risk Factors There are numerous risk factors associated with the development of CNV in AMD. These risk factors include ocular and non-ocular factors; they are discussed in great depth in the chapter by Au-Eong and Haller. Of the non-ocular risk factors, it appears that the strongest epidemiological associations are age, race, smoking and genetics. Of the ocular risk factors, soft large drusen, retinal pigment epithelium (RPE) pigmentary changes and presence of CNV in the fellow eye are strong associations for development of CNV. It is important to remember that these are associations and do not imply causation (cause and effect). Non-ocular Risk Factors Associated with Exudative (Neovascular) AMD Increased age is associated with increasing risk of neovascular AMD. Patients with exudative AMD have a mean age of 70.5 years versus 56.8 years for non-exudative AMD (16). Racial differences in the prevalence of exudative AMD (and also early AMD) exist. Gregor and Joffe (17) found that the prevalence of disciform AMD was 3.5% of the white South African patients compared to 0.1% of the black South African patients (p!0.001). The Baltimore Eye Survey revealed a prevalence ratio of 8.8 for white to black neovascular AMD (18). Over a nine-year period, the incidence of AMD in the Barbados Eye Study was 12.6% for early AMD but only 0.7% for late AMD (19). In National Health and Nutritional Examination Survey-III (NHANES-III), the odds ratio for late AMD was 0.34 for non-Hispanic blacks compared to non-Hispanic whites (20). The prevalence of neovascular AMD is higher in Caucasians than African Americans. The prevalence rates of neovascular AMD in other racial groups have recently been investigated. In the Latino Eye Study (6,357 Latino patients aged 40 years of age and older), the prevalence of early AMD increased from 6.2% in the 40 to 49 years old group to

29.7% in the 80 years or older group but that of advanced AMD increased from 0% in the 40 to 49 years old group to only 8.5% in the 80 years of age or older group (21). Similarly, in the Proyecto group, the prevalence of late AMD increased from 0.1% in 50 to 59 years old to 4.3% of those 80 years or older (22). These rates of advanced AMD are lower than those in Caucasians. In the Multi-ethnic Study of Atherosclerosis (MESA), the prevalence of AMD in four ethnic cohorts (whites, blacks, Hispanics, and Chinese) was determined. The prevalence of any AMD was 5.4% in whites, 2.4% in blacks, 4.2% in Hispanics, and 4.6% in Chinese aged 75 to 84 years of age. The prevalence of exudative AMD was highest for Chinese in which the odds ratio (OR) was 4.3 compared with Caucasians (23). Most of the Chinese in MESA were born outside of the United States. Further work on Asian AMD is needed to draw definitive conclusions about this group. Overall, several studies corroborate the racial differences in the prevalence of AMD in general and the neovascular or exudative form. Family history is a risk factor for the development of AMD, including neovascular AMD. The Blue Mountains Eye Study showed an odds ratio of 4.30 for neovascular AMD in patients with a family history (24). Klaver and colleagues found the lifetime risk estimate of late AMD to be 50% for relatives of patients versus 12% for relatives of controls (25). Cigarette smoking has been associated with exudative AMD in most studies, although it was not linked to AMD in the Framingham Study (13) and the NHANES-III Study (26). The Beaver Dam Eye Study (27) linked smoking to exudative AMD with a relative risk of 3.29 for current smokers and a relative risk of 2.50 for former smokers compared to those who had never smoked. In the Blue Mountain Eye Study (28), the odds ratio for exudative AMD was 4.46 for current smokers compared with those who never smoked and 1.83 for former smokers compared with those who never smoked. In the Pathologies Oculaires Liees a l’Age study, the odds ratio for exudative AMD increased with the number of pack-years smoked (29). This higher risk of exudative AMD persisted until 20 years after cessation of cigarette smoking. In a case control study by Khan et al. (30) smoking more than 40 pack years of cigarettes was associated with an odds ratio of 2.49 (95% CI 1.06 to 5.82) for CNV. Stopping smoking was associated with reduced odds and the risk in those who had not smoked for over 20 years was comparable to nonsmokers. Even passive smoking exposure was associated with an increased risk of AMD (OR 1.87; 95% CI 1.03–3.40) in the non-smokers. In an animal model of rats fed a high-fat diet, exposure to cigarette smoke or the smoke-related

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redox molecule, hydroquinone, resulted in the formation of sub RPE deposits, thickening of Bruch’s membrane, and accumulation of deposits within Bruch’s membrane. This animal model shows that cigarette smoking results in molecules that can cause oxidative injury to the choriocapillaris and RPE, and may explain the association between cigarette smoking and AMD (31). The association between sunlight exposure and late AMD is not clear. The Chesapeake Bay Watermen Study found an association between late AMD and sunlight (32) as did the Beaver Dam Eye Study (33). Yet, the Eye Disease Case-Control Study (34) and the Australian case-control study on sun exposure and AMD (35) did not show this same association. Since the use of sunglasses (ultraviolet blocking) is relatively inexpensive and also protective against cataract formation, it is reasonable to recommend sunglass protection for older patients. There have been reports of progression of early to late AMD following cataract surgery. The Beaver Dam Eye Study showed an odds ratio of 2.80 for progression of AMD to late AMD after cataract surgery (and after controlling for age) (36). Pollack and colleagues also noted progression to exudative AMD occurred in 19.1% of eyes operated on for cataracts versus 4.3% of the fellow eye (37,38). Further investigation is needed in this area.

Ocular Risk Factors Associated with Exudative (Neovascular) AMD The risk of CNV developing in a patient’s eye has been linked to the presence of soft drusen, pigmentary changes, status of the fellow eye and hypertension. Lanchoney and associates calculated the risk of CNV in patients with bilateral soft drusen to range from 8.6% to 15.9% within 10 years, depending upon the age and sex of the patient (39). These projections were based upon natural history studies of Smiddy and Fine (16) and Holz (40). The Macular Photocoagulation Study (MPS) group has determined the ocular risk factors for development of CNV in the fellow eye (when the opposite eye already has CNV) to include the presence of five or more drusen, focal hyperpigmentation, one or more large drusen (O63 mm) and systemic hypertension (41). The five year incidence rate for development of CNV ranged from 7% if none of these risk factors was present to 87% if all four risk factors were present. (This was based upon follow-up of patients with juxtafoveal CNV). The Age-Related Eye Disease Study (AREDS) has also yielded predicative rates of CNV for a patient based upon the ocular findings of both eyes. The AREDS group created a simplified scale for determining the risk of development of neovascular

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AMD. One risk factor is assigned for the presence of large soft drusen and one risk factor for any pigment abnormality in each eye. Intermediate drusen alone in both eyes is counted as one risk factor. Advanced AMD counts as two points for an affected eye. The values are then summed for both eyes. The five year risk of developing advanced AMD was 0.5% for zero risk factors, 3% for one risk factor, 12% for two risk factors, 25% for three risk factors and 50% for four risk factors (42). The AREDS group has recently determined the 10 years risk of developing advanced AMD is less than 1% for no risk factor, 10% for one risk factor, 30% for two risk factors, 50% for three risk factors and 70% for four risk factors. (oral communication, Retina Subspecialty Day presentation by Dr. Frederick Ferris, AAO Annual Meeting, Las Vegas, Nevada U.S.A., November 10, 2006).

Prevention of CNV and Genetics in AMD The protective role of antioxidants and vitamins in the prevention of AMD was shown in the AREDS Study (43). The AREDS study enrolled 3640 participants and randomized them to antioxidants alone, antioxidants plus zinc, zinc alone and placebo. The results showed that overall betacarotene (15 mg), vitamin C (500 mg), vitamin E (400 IU), zinc oxide (80 mg) and cupric oxide (2.2 mg) decreased the relative risk of progression of AMD by 28% (OR 0.72, 43% to 32% absolute risk) and the risk of moderate visual loss by 27% (OR 0.73). Patients with at least one large drusen in either eye, intermediate drusen in both eyes, noncentral geographic atrophy in one or both eyes and those with visual loss in one eye were considered at high risk for advanced AMD. Patients with these features are recommended to take the supplements. However, those who smoke cigarettes are at increased risk of lung cancer from the betacarotene component and it is therefore not recommended that they use the AREDS supplements. AREDS2 is a multicentered interventional trial that will investigate the protective effects of supplements on CNV development when no betacarotene is used in AMD patients who are cigarette smokers. AREDS2 will investigate the effect of oral supplementation with lutein, zeaxanthin and omega three fatty acids (in addition to the AREDS supplements) on the development of advanced AMD (CNV and geographic atrophy). The Physicians’ Health Study II is also evaluating the role of vitamin E, vitamin C, beta-carotene and a daily multivitamin. The Vitamin E, Cataract and Agerelated macular degeneration Trial (VECAT) and the Women’s Health Study (WHS) are two other randomized trials assessing the risk and benefits of antioxidant vitamins for AMD (44,45). The Carotenoids in Age-Related Eye Disease Study (CAREDS) was part of the WHS. In the CAREDS, the prevalence of

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intermediate AMD in 1787 participants was found to not statistically differ with respect to lutein and zeaxanthin intake (45). Recently, genetic markers for both the risks of AMD and CNV are being determined. (The genetics of AMD are discussed in detail in Chao et al.’s chapter.) One highly associated genetic finding is that of complement factor H (CFH). The inflammatory cascade has been found to play a role in the pathogenesis of AMD. (The chapter by Csaky and Cousins discusses the role of inflammation in AMD). Examination of the Submacular Surgery Trial (SST) specimens has revealed that inflammatory cells are found throughout the CNV specimens (46,47). The finding of CFH’s association with AMD and advanced AMD supports the role of the inflammatory cascade (48–51). (CFH is normally a regulator of the complement cascade and limits the immune reaction to spare host cells. When there is a CFH mutation, the CFH can no longer protect host cells and the host cell undergoes lysis through activation of complement.) In addition to CFH mutations, there are other complement factors being evaluated in the search for the inflammatory component of exudative AMD. It is also known that an imbalance in stimulators and inhibitors of AMD are involved in development of CNV. For example, pigment epithelial derived factor (PEDF) is a naturally found inhibitor of angiogenesis (52). It is manufactured by RPE cells in the eye. In AMD CNVMs, levels of PEDF are markedly lower and vascular endothelial growth factor (VEGF) levels markedly higher compared to normal controls. Further details on angiogenesis and rationale of antiangiogenesis treatments are found in the chapter by Campochiaro and Kane. Until all risk factors (and subsequent proof of causation) and the genetics of AMD are fully determined, prevention of exudative AMD remains an enigma. Further clinical trials proving benefit of intervention are necessary before recommendations can be made. However, at this time, modifiable risk factors (such as smoking, hypertension) should be addressed as they are also linked to systemic diseases. Future application of genetic therapy and targeted antiangiogenesis treatments are now beginningto play a role in the prevention of exudative AMD and attendant visual acuity loss. It is possible that future treatments of AMD will include targeted genetic therapy to replace defective genes.

SYMPTOMS AND MONITORING FOR EXUDATIVE (NEOVASCULAR) AMD Symptomatic patients with exudative AMD typically present complaining of sudden onset decreased visual acuity, metamorphopsia, and central or paracentral scotomas (53,54). Not infrequently, patients are

unaware that one of their eyes has already has already lost vision until he or she covers the unaffected eye. Other times, patients present with loss of vision in the previously “good eye” and may have been unaware of the visual symptoms in the fellow eye containing a macular scar (55). Yet other patients may be asymptomatic and routine ophthalmoscopy may reveal the CNV in the second eye (prior CNV in the fellow eye) (56). Thus, patients who are at risk for CNV should be periodically screened for development of CNV and should be encouraged to self monitor their vision daily. Monitoring options include using an Amsler grid or the preferential hyperacuity perimeter (PHP) (57,58). Patients with known cataracts may attribute blurred vision to their cataract and not suspect AMD as the cause. In some patients with dense cataracts, cataract extraction without pre-operative detection of the CNV may occur. After the cataract extraction, the ophthalmologist then detects the CNV. A careful preoperative examination for exudative AMD or advanced non-exudative AMD is therefore of utmost importance in patients with known AMD. Preoperative fluorescein angiography (FA) and optical coherence tomography (OCT) may help detect CNV. Alternatively, if the cataract density precludes ophthalmology, FA or OCT imaging, an ultrasound examination may be useful in screening for macular fluid or subretinal scar formation to rule out advanced AMD (59). The Amsler grid is a useful test for detecting the early visual symptoms of exudative AMD in patients with high risk AMD (60). Each box on the grid represents one degree of visual field. Thus, the Amsler grid tests the central 10 degrees of visual field beyond fixation. The patient is asked to fixate on the central black dot and to note whether surrounding lines are wavy, missing or obscured by scotomas (dark areas). If these findings are present, the patient should be instructed to seek attention urgently with his or her ophthalmologist as it is likely that the cause is neovascular AMD. There are limits to Amsler grid testing which includes the cortical completion phenomenon, crowding phenomenon and lack of forced fixation. A newly developed computer-automated, threedimensional, threshold, Amsler grid visual field test has been shown to be useful in earlier detection of AMD (61). The 3-D Amsler grid utilizes threshold testing. There appear to be different signatures based upon the type of AMD present. The PHP (PreView PHP, Carl Zeiss Meditec, Dublin, California) machine (Fig. 1) has shown promise in the early detection of exudative AMD (57,58). The PHP is based upon the concept of vernier (hyperacuity) acuity, the ability to detect a subtle misalignment of an object. The threshold of vernier acuity is three to six seconds of

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0.82 in detecting recent onset CNV. In comparison, PHP had a sensitivity of 83%, specificity of 87%, and overall accuracy of 0.85 in detecting the same lesions. The PHP may indeed be a useful diagnostic device for patient monitoring.

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Figure 1 Preferential hyperacuity perimeter (PHP) machine: PreView PHP, Carl Zeiss Meditec. Abbreviation: PHP, preferential hyperacuity perimeter.

arc in the fovea—10 fold smaller than to resolve an object clearly on the fovea. When photoreceptors are misaligned because of edema, CNV and or RPE elevation, the brain is able to detect the misalignment. The PHP is useful even in patients with media opacities due to its resistance to retinal image degradation. The central 14 degrees are tested in about five minutes. Patients are shown a series of linear dots with an area of artificial distortion (Fig. 2). The artificial distortion is progressively made smaller. If a patient has CNV, the CNV results in a true area of distortion of the dots. When their distortion is larger than the artificial distortion, the patient preferentially chooses that area. A computerized map of these areas is created. A study comparing retinal specialists’ gradings of stereoscopic color fundus photos to the PHP for the detection of CNV has been performed. The gold standard for the determination of CNV was FA. In 64 patients with recent onset CNV and 56 patients with intermediate AMD, retina specialists had a sensitivity of 70%, specificity of 95%, and an overall accuracy of

Figure 2 The preferential hyperacuity perimeter machine displays a series of dots with an area of artificial distortion on the screen. The patient is asked to select the area of distortion on the touch screen. The artificial distortion height is progressively decreased. The patient will preferentially select the area of distortion that is more severe.

The major clinical features of active exudative AMD include subretinal fluid, subretinal hemorrhage, sub-RPE fluid, sub-RPE hemorrhage, RPE pigment alterations and hard exudates. Chronic exudative AMD is characterized mainly by the presence of subretinal fibrosis with or without the other features of active exudation. These features may appear clinically as any one or any combination of the following: a serous or a hemorrhagic PED (Figs. 3 and 4), grayish subretinal membrane (Fig. 5), area of subretinal fluid, area of RPE alteration (Fig. 6), subretinal hemorrhage (Fig. 7), or hard exudates (Fig. 8). The late manifestation of exudative AMD is a disciform scar (Fig. 9) or geographic atrophy (Fig. 10), with or without subretinal fluid or subretinal blood. Spontaneous involution of CNV may manifest as any of the above findings with RPE alterations and or scar formation. Stereoscopic fundus examination is the best method for examining a patient with suspected CNV. A fundus contact or non-contact lens in conjunction with slit lamp biomicroscopy should be utilized for the exam. For those less comfortable with the non-contact fundus macular lenses, a fundus contact lens is easiest to use. The fundus contact lens or the 78 diopter lens

Figure 3 A patient with age-related macular degeneration and a serous pigment epithelial detachment (PED). Note the sharply demarcated borders of the PED.

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Figure 4 A patient with polypoidal choroidal vasculopathy with serous pigment epithelial detachments (PEDs). (A) Color fundus photo shows sharply outlines of the PEDs. (B) The corresponding fluorescein angiogram shows uniform filling of the PED. Note the sharp borders and absence of leakage.

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Figure 5 Grayish subretinal membrane fluorescein angiography choroidal neovascularization (CNV). (A) Color fundus photo shows subretinal blood and a subretinal pigmented lesion. (B) Fluorescein angiogram reveals the subfoveal classic CNV. Note the hyperfluorescent border and the central vessels within the membrane. (C) Later fluorescein angiogram phase showing leakage of the CNV.

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Figure 6 Retinal pigment epithelium mottling. Note the area of increased pigmentation in this eye with subfoveal choroidal neovascularization. There are numerous large drusen also present.

offers more magnification than the 90 diopter lens. During the exam, it is helpful to have the patient look directly at the thin slit lamp beam and to ask the patient whether the beam appears distorted. Elevation of the RPE or retina (due to underlying CNV) causes the patient to perceive distortion of the slit beam. Using biomicroscopy with a macular lens, the separation of the retina from the underlying RPE, due to underlying subretinal fluid, can be seen. The overlying retina may have cystic changes and may show cystoid macular edema. Sub RPE fluid appears as a

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Figure 8 Hard exudates in an eye with choroidal neovascularization. (A) Fundus photograph shows subretinal hemorrhage and the extensive hard exudates deposits. On the (B) vertical and (C) horizontal optical coherence tomography scans, the hard exudates appear as focal intraretinal areas of high backscattering (orange color). Beneath the hard exudates, there is a markedly decreased signal (black). The subretinal fluid appears as an elevation of the neurosensory retina above an optically clear space (black). Intraretinal cysts are also seen in the inner retinal layers.

Figure 7 Subretinal hemorrhage. Extensive subretinal hemorrhage is present. Note that this myopic patient has large soft drusen as well as an adjacent area of retinal pigment epithelial detachment temporal to the hemorrhage.

PED and typically has more sharply demarcated borders as compared to subretinal (subneurosensory) fluid (Fig. 14). Often, there is a combination of sub-RPE and subretinal fluid associated with the CNV. The CNV itself may be visible as an area of discoloration (Fig. 5). Other times, overlying subretinal blood or lipid may be the only clinical clue to the presence of an acute CNV. The definitive test for the presence of CNV has been FA. This is further discussed below.

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OCT has been an extremely useful tool in the detection and management of CNV in AMD patients. The OCT resolution may be 3 to 5 mm for high resolution OCT and 10 mm for the third generation OCT machine (62). Microscopic areas of subretinal fluid and areas of elevation can be detected on OCT imaging of the macular area of AMD patients. Areas of CNV appear as RPE thickening with or without intraretinal cysts and subretinal fluid (Figs. 11–13). PEDs are clearly seen on the OCT (Fig. 12). OCT has been used in the recent anti-angiogenesis clinical trials as another measurement of treatment outcome. Successful treatment of PEDs and CNVMs has been shown to result in normalization of the OCT appearance (Fig. 13). Recurrence of the CNV can appear as slight areas of elevation of the RPE, neurosensory retina or presence of cystic retinal change. Details of the usefulness of OCT imaging in management of AMD patients is found in the chapter by Reichel and coworkers. Further refinements in OCT continue; volumetric evaluation of the CNV lesions is becoming a reality. Other instruments can image the lesions and provide

Figure 9 Disciform scar. There is extensive subretinal fibrosis (white areas) on the color fundus photograph of this end-stage age-related macular degeneration eye. Note the sharp margins of the fibrotic lesion. There are areas of pigmentary abnormality with some retinal pigment epithelial atrophy in addition to the whitish fibrotic scar tissue. Note the residual central hemorrhage.

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Figure 10 (A) Color fundus photo shows a well demarcated area of retinal pigment epithelial and choriocapillaris atrophy. Note the orange color of the atrophic lesion and the visibility of the deep choroidal blood vessels within the area. There are no drusen in the atrophic area but soft drusen in the area adjacent to the lesion. (B) The corresponding early fluorescein angiogram frame shows hyperfluorescence corresponding to the atrophic area. (C) The corresponding late fluorescein angiogram frame shows well-demarcated borders that match the area of atrophy seen clinically (staining). No fluorescein dye leakage is seen (no blurring of image). The borders remain sharply demarcated. Note that the area stained on the angiogram corresponds with the clinically visible lesion borders.

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Figure 11 Optical coherence tomography from an age-related macular degeneration patient with subfoveal choroidal neovascularization (CNV). The overlying retina shows multiple cysts. The CNV is seen as an area of thickening in the subfoveal zone at the retinal pigment epithelial level.

quantitative information. The retinal thickness analyzer can determine lesion dimensions of CNV (63). Quantitative measurements of the retina will undoubtedly prove useful in the management of patients with CNV. Further information on quantitative imaging can be found in the chapter by Esmaili and colleagues.

Pigment Epithelial Detachment The borders of a PED are usually sharply demarcated (Fig. 3). Clinically, hemorrhage or hard exudates may or may not be present depending upon the presence or absence of associated CNV. A fluorescein angiogram or indocyanine green (ICG) angiogram is clinically useful to detect the presence of associated CNV. A serous PED shows early hyperfluorescence and uniform fluorescence on the late frames of the angiogram (Fig. 4B). The dye pools in the PED on the late phase. The borders remain sharp and the area does not increase in size. On ICG angiography, the PED is hypofluorescent (see ICG chapter by Oliver and colleagues). Whereas a serous PED will show uniform filling of

Figure 12 Optical coherence tomography from an age-related macular degeneration patient with a subfoveal pigment epithelial detachment (PED) and adjacent choroidal neovascularization. There is a dome-shaped elevation of the retinal pigment epithelium (RPE) reflective border (orange). This represents the PED. The adjacent dark areas under the neurosensory retina and above the RPE represent subretinal fluid.

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Figure 13 Vertical optical coherence tomography scans before and after ranibizumab (Lucentis, Genentech, South San Francisco, California, U.S.A.) treatment of a subfoveal choroidal neovascularization. (A) Prior to ranibizumab injection, there is extensive intraretinal cystic edema and underlying subretinal fluid. The visual acuity is 20/400. (B) One month after the first ranibizumab intravitreal injection, the subretinal fluid is resolved. Visual acuity is 20/200. The intraretinal cystic edema is markedly decreased in severity. The patient continues with the intravitreal ranibizumab injection therapy.

the PED, a vascularized PED shows irregular filling, notching of the PED (Fig. 14) or irregular margins on the FA. On the OCT, the RPE elevation is readily seen. If there is CNV present with the PED, occult CNV will frequently show associated subretinal fluid, hard exudate, or subretinal blood. The fluorescein angiogram typically demonstrates irregular filling of the PED and the PED borders may be blurred in the area of the CNV. Leakage on the late frames of the FA is commonly noted (Fig. 14). ICG angiography has been shown to be helpful in this regard (64). As shown in the chapter by Oliver and colleagues, ICG can identify areas of CNV associated with the PED. Laser photocoagulation of the hot spots may result in resolution of the PED, subretinal fluid, blood and lipid (64–66). CNV has been associated with 28% to 58% of PEDs (65). A study by Elman and colleagues showed that 32% of serous PEDs develop CNV at a mean of 19.6 months (67). Risk factors associated with CNV in these eyes included patient age greater than 65 years, associated sensory retinal detachments and fluorescein findings of hot spots, notches, late or irregular filling. The association of CNV with PED increases the chance for visual acuity loss (67–69). In a natural history study by Poliner and associates, the risk of developing CNV was 26% at one year,

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Figure 14 Pigment epithelial detachment (PED) with associated choroidal neovascularization (CNV). (A) (Stereo photo pair.) The PED is elevated on the stereo images. There is subretinal fluid overlying the entire lesion in addition to the sub retinal pigment epithelium PED fluid. Note the grayish area on the superonasal edge of the PED. This grayish area corresponds to the CNV. (B) The corresponding fluorescein angiogram from the late transit phase shows a notch of the PED superonasally. (C) The corresponding fluorescein angiogram from the late phase shows fluorescein dye leakage in the area corresponding to the CNV. The adjacent PED shows sharp edges in the areas not involving the CNV.

42% at two years and 49% at three years in eyes with PEDs followed for 12 or more months (68). The risk of 20/200 or worse visual acuity increased from 17% at one year to 33% at two years and 39% at three years. The majority of eyes (78%) that developed CNV were 20/200 or worse, while only 3% of eyes that did not develop CNV lost vision to that level. Even with spontaneous flattening of PEDs, the visual acuity outcome is poor (67–70). Unfortunately, most clinical trials have excluded PEDs with CNV and there remains no good treatment for this group of eyes. Currently, off label treatments are being applied to

these CNV lesions with PEDs. Anti-VEGF therapies such as ranibizumab (Lucentis) and off-label bevacizumab (Avastin) have been used to treat CNV with PED with some success. The risk of an RPE tear/rip occurring in this setting is a real concern in these eyes (Fig. 15). An RPE tear is readily identifiable as a sharply-demarcated area of bare choroid with a straight, linear edge. This straight, linear edge corresponds to the location of the associated retracted, scrolled RPE. The fluorescein angiogram shows blocked fluorescence in the area of scrolled RPE and hyperfluorescence in the area without RPE.

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The natural history of PEDs includes RPE tears, but treatment of CNV with PEDs has also been temporarily associated with RPE tears (71).

Choroidal Neovascularization The MPS group has defined the various forms and components of CNV (72). The entire complex of components termed a “CNV lesion” includes the CNV itself, blood, elevated blocked fluorescence (due to a pigment or scar that obscures the neovascular borders), and any serous detachment of the RPE. The classic clinical description of a choroidal neovascular membrane is that of a dirty gray-colored membrane (Fig. 5). There is associated subretinal fluid and there may or may not be subretinal blood and lipid. Sometimes the outlines of the CNV are clearly visible with the subretinal vessels readily seen. Other times, the CNV is manifest only by a neurosensory detachment or even subretinal blood. The fluorescein angiogram is a key test in the evaluation of patients with CNV. On FA, a well-

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Figure 15 Retinal pigment epithelium (RPE) tear occurring after several anti-vascular endothelial growth factor (VEGF) treatments. (A) Color fundus photo shows the area of exposed choroid where the RPE tear is located. Note that this area has one linear edge. This linear edge is formed by the scrolled RPE. There are also choroidal folds in the macular area. (B) Early fluorescein angiography (FA) phase frame shows hyperfluorescence in the area of denuded RPE and blocked fluorescence in the area of the scrolled RPE tear. (C) Late FA phase frame shows hyperfluorescent staining in the area of the RPE rip. There is blocked fluorescence corresponding to the scrolled RPE. The adjacent choroidal neovascularization shows some mild leakage.

demarcated area of choroidal hyperfluorescence is seen early (Figs. 5 and 16). The MPS group characterized classic CNV as only occasionally showing a lacy pattern of hyperfluorescence in the early fluorescein phases. In the later frames of the angiogram, the boundaries of the CNV are obscured by progressive pooling of dye in the subneurosensory space. With the advent of photodynamic therapy (PDT), the term “predominantly classic” was coined. A predominantly classic lesion is one in which the lesion is more than 50% classic CNV in composition (Fig. 16). Occult CNV has been classified as either fibrovascular PED (FVPED) (Fig. 17) or late leakage of undetermined source (LLUS) (Fig. 18). These types of occult CNVs are differentiated on the basis of the fluorescein angiogram. A stereoscopic FA is very helpful in recognizing occult CNV. FVPEDs show early hyperfluorescence with irregular elevation of the RPE. These areas are not as bright or as discrete as the classic CNV seen on the transit phases. Within one to two minutes, an area of stippled

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Figure 16 Predominantly classic choroidal neovascularization (CNV). (A) Color fundus photo of a patient with subfoveal CNV. There is subretinal fluid overlying the subfoveal lesion. Areas of hemorrhage and hard exudates are seen in the macular lesion. (B) The corresponding early fluorescein angiographic frame shows an area with bright, well demarcated fluorescence (classic CNV). There is blocked fluorescence corresponding to the areas of hemorrhage. There are also areas of speckled fluorescence (occult CNV) beyond the area of classic CNV. Since the area of classic CNV occupies more than 50% of the entire lesion, the lesion is predominantly classic CNV in composition. (C) The corresponding late fluorescein angiographic frame shows intense leakage from the entire CNV component. The areas of blocked fluorescence corresponding to the hemorrhage remain unchanged.

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hyperfluorescence is present. By ten minutes there is persistent fluorescein staining or leakage within the subneurosensory detachment. The borders of the occult CNV may be either well-demarcated or poorly

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demarcated (72). Late leakage is present, although it is not as intense as that seen in classic CNV (72). LLUS in contrast does not show early hyperfluorescence. LLUS appears as speckled hyperfluorescence

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Figure 17 Fibrovascular pigment epithelial detachment. (A) The subfoveal area shows hyperfluorescence. The early fluorescein angiographic frame shows hyperfluorescence with some stippled fluorescence. On stereo viewing (not shown) irregular elevation of the retinal pigment epithelium is seen within the area of leakage. The leakage is not as bright as that seen by the same phase of classic choroidal neovascularization. (B) On the late fluorescein angiographic frame, at five minutes, more intense fluorescein leakage is seen in this area.

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Figure 18 Late leakage of undetermined source. (A, B) The earlier angiographic frame show no evidence of leakage. (C, D) On the late angiographic frames, areas of fluorescein dye leakage appear. This area shows no corresponding area of leakage on the early angiographic frames. The leakage is extrafoveal.

with pooling of dye in the overlying neurosensory space; choroidal leakage is apparent between two and five minutes after fluorescein injection. The boundaries of this type of occult CNV are never well-demarcated. In fact, the later frames show hyperfluorescent leakage in an area that showed no hyperfluorescence on the early frames (Fig. 18) (72). Lastly, there is a slow-filling form of classic CNV in which hyperfluorescence is not seen until two minutes. However, in this form of CNV, the late frames of leakage and pooling of the dye in the subneurosensory space correspond with the area seen at two minutes. Using ICG angiography, occult CNVs can be further classified into those with hot spots, plaques,

combination of these two types, retinal-choroidal anastomosis and polypoidal-type CNV. Using ICG angiography, about one third of eyes with occult CNV become eligible for treatment (73). ICG angiography is also useful for evaluating eyes with subretinal hemorrhage for the presence of CNV. Further details of the usefulness of ICG angiography and ICG-guided laser photocoagulation of CNV in AMD can be found in the chapter by Oliver and colleagues. With the recent finding that pegaptanib sodium (Macugen) and ranibizumab (Lucentis) work equally well for different types of CNV, the classification of the CNV may become less important in the future. The prognostic implication of CNV type on response to treatment remains to be determined.

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Figure 19 Juxtafoveal choroidal neovascularization (CNV). The fluorescein angiography (FA) shows that the closest edge to the foveal center is within the foveal avascular zone. Note however that the edge of the CNV does not involve the foveal center itself.

CNV lesions are further characterized by their location in relation to the foveal center. The location of the CNV is divided into extrafoveal, juxtafoveal and subfoveal. These definitions were created by the Macular Photocoagulation Study Group and are as follows: Location of CNV Extrafoveal Juxtafoveal Subfoveal

Distance from foveal avascular zone center 200–2500 mm 1–199 mm 0 mm

A lesion is juxtafoveal if the CNV border closest to the foveal center is within (but not involving the foveal center itself) the foveal avascular zone (FAZ) (Fig. 19). A lesion whose closest border to the foveal edge is beyond the FAZ is considered extrafoveal.

Disciform Scar A disciform scar shows an area of subretinal fibrosis or subRPE fibrosis. Dull, white fibrous tissue is seen and may accompany the CNV lesion or replace it over time (Fig. 9). Areas of retinal pigment epithelial atrophy may or may not be present. FA may show leakage associated with the scar if active CNV is present. The fibrotic scar may otherwise show only staining of the fibrotic tissue. Patients with CNV typically present with symptoms of metamorphopsia, decreased vision, uniocular diplopia, Amsler grid distortion, scotoma or macropsia. The severity of the symptoms varies

depending upon the location of the CNV. Obviously lesions closer to fixation will cause more noticeable symptoms in the patient’s visual field. Patients complaining of such symptoms require prompt clinical evaluation and FA to detect any CNV or PED and to characterize the CNV by type, location and size. Treatable lesions should undergo laser photocoagulation within 72 hours of the fluorescein angiogram for extrafoveal and juxtafoveal CNV. Subfoveal lesions can now be treated by PDT within one week if the lesion is eligible for PDT or by a variety of antiangiogenesis therapies. Anti-angiogenesis treatments should be preceded by a fluorescein angiogram for diagnosis and determination of the extent of the CNV. OCT prior to treatment and during follow-up is useful to gauge the clinical response. Central retinal thickness, presence of subretinal fluid and retinal cysts are all parameters that can be monitored using the OCT. Recently, the anti-angiogenesis therapies have shown visual improvement is possible even after weeks of untreated disease (74). Thus, because of this potential visual recovery, as long as subfoveal scarring is absent, it seems reasonable to treat active CNV even if it is not of recent onset. In the phase I/II ranibizumab trials, nine of the eleven eyes in the untreated group were switched to treatment at day 98. Even at that delayed time interval between onset of CNV and therapy, these eyes experienced a mean visual acuity improvement at six months (7.3G13.1 letters for those switched to 0.3 mg ranibizumab and 3.2G9 letters in the 0.5 mg group).

Feeder Vessels A feeder vessel is a choroidal vessel that connects the CNV to the underlying choroidal vasculature thus supplying blood to the CNV membrane. Green has suggested that there are two to three feeder vessels crossing Bruch’s membrane per CNV (75). Feeder vessels are sometimes ophthalmoscopically visible within the CNV lesion (see chapter by Flower). Recent work has focused on applying laser photocoagulation to feeder vessels in an attempt to close the CNV. Feeder vessels have been reported to be present in 15% of cases of CNV. Shiraga and coworkers first reported identification and photocoagulation of feeder vessels using ICG videoangiography via a scanning laser ophthalmoscope (76). In 70% of the patients, the exudative findings resolved; visual acuity improved or stabilized in 68% of patients. Later, Staurenghi and coworkers verified the superiority of dynamic ICG angiography with an scanning laser opthalmoscope system for identifying feeder vessels in subfoveal CNV (77). Dynamic ICG can detect smaller feeder vessels and enables more targeted treatment of these vessels with a 75% success rate (78).

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Most recently, using high speed high resolution digital angiography, it is possible to detect more feeder vessels in eyes with CNV. The combined ICG angiography/dye-enhanced photocoagulation system allows one to synchronize photocoagulation with the arrival of the dye bolus at a targeted vessel site.

PATHOGENESIS OF CNV The pathogenesis of CNV is not fully understood at this time. However it is well accepted that angiogenic factors, such as VEGF, has a primary role in the initiation and maintenance of CNV. The primary stimulus resulting in the increase in angiogenic factors remains unknown. The angiogenesis factors involved in the neovascular response are discussed in detail in the chapter by Campochiaro and Kane. Of the known isoforms of VEGF, the most important in the eye is VEGF A. VEGF A has five known isoforms. VEGF 165 and VEGF 121 are important in ocular neovascularization as well as the cleaved VEGF breakdown product, VEGF 110. Clues to the pathogenesis of CNV are available from surgically excised membranes (46,47). The most consistent pathological finding is accumulation of abnormal extracellular matrix (ECM) resulting in diffuse thickening of Bruch’s membrane (49). Focal areas of thickening form drusen and this diffuse thickening suggests an altered metabolism of the ECM. There is data to suggest that altered ECM of RPE cells causes increased secretion of angiogenic growth factors that could contribute to the growth of CNV (46,47). Iatrogenic breaks of Bruch’s membrane in animals have led to animal models of CNV (79). Laser-induced CNV in primates has been used to investigate the mechanisms of CNV production and the role of the RPE (80). The chapter by Kang and Grossniklaus discusses these changes in detail. It is known that RPE cells produce VEGF and fibroblast growth factor 2. Both are present in fibroblastic cells and in transdifferentiated RPE cells of surgically excised CNV (81–83). Healthy photoreceptors are needed to prevent the choriocapillaris from responding to excess VEGF (84). In addition, inflammatory cells are now felt to be key ingredients to CNV development. In a murine laser-induced model of CNV, CNV volume was significantly suppressed when inflammatory mechanisms were inhibited (85). Angiotensin II type I receptor (AT1-R) signaling blockade with telmisartan inhibited macrophage infiltration and upregulation of VEGF, intercellular adhesion molecule-1 (ICAM-1), monocyte chemoattractant protein-1, and Interleukin-6 in the retinal pigment epithelium-choroid complex. The

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research showed that AT1-R-mediated inflammation plays a pivotal role in the development of CNV. Perhaps, AT1-R blockade may serve as another therapeutic strategy to inhibit CNV. The fact that VEGF is present in CNV has led to the development of drugs that bind VEGF (antibodies or aptamer) or its receptor or drugs that block VEGF signaling. Blockage of VEGF signaling has been shown to inhibit the development of CNV in the laser-induced CNV mouse model (86,87). Initially it was thought that VEGF 165 was the most significant VEGF isoform for CNV. This led to the development of an aptamer to bind VEGF 165 and thus inhibit VEGF 165 as a treatment for CNV in AMD patients (88). Anti-VEGF antibodies were also developed as a treatment for CNV (89,90). The results of the clinical trials evaluating these treatments will be discussed later in this chapter. Further details are found in the chapter by Klesert and colleagues.

IDIOPATHIC POLYPOIDAL CHOROIDAL VASCULOPATHY OR POLYPOIDAL CHOROIDAL VASCULOPATHY Idiopathic polypoidal choroidal vasculopathy (PCV) has recently been classified as a form of CNV that may occur in elderly patients. A recent study by Yannuzzi and colleagues determined the frequency and nature of PCV in patients suspected of harboring exudative AMD (91). In their prospective study of 167 newly diagnosed patients with exudative AMD, CNV was diagnosed in 154 (92.2%) and PCV in 13 (7.8%). Nonwhite race (23.1%), absence of drusen (16.7% had drusen) and peripapillary location were felt to distinguish between PCV and AMD. Since then, it is now recognized that PCV occurs in all races (92). PEDs are commonly seen in PCV (Fig. 4). ICG angiography is useful in the diagnosis of this entity. Further information is found in the ICG chapter by Oliver and colleagues.

RETINAL ANGIOMATOUS PROLIFERATION One other distinct type of neovascular AMD is retinal angiomatous proliferation (RAP). This entity is characterized by an anomalous retinal vascular complex which is most commonly associated with retinal and subretinal neovascularization (93,94). It has been described predominantly in elderly Caucasians and is often seen bilaterally. While its natural history is not fully understood, it is thought to progress ultimately to a disciform scar. Prior to the

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recognition of this entity, it was often misdiagnosed as occult CNV. A three-stage classification system of RAP has been proposed by Yannuzzi and colleagues to describe the various clinical presentations and to theorize on the disease’s natural history (94). In stage I, a nodular mass of intraretinal neovascularization is seen and originates from the deep capillary plexus in the paramacular area. There is usually one or more associated retinal vessels which either perfuse or drain the vascular complex. Intraretinal hemorrhages and intraretinal edema are often present. FA typically shows a focal area of staining corresponding to the intraretinal neovascularization. Surrounding leakage is present and often misinterpreted as occult CNV. ICG angiography can aid in the diagnosis by identifying the neovascularization as a focal “hot spot” and intraretinal cystic spaces as focal hyperfluorescent areas. Stage II, subretinal neovascularization, involves both retinal and subretinal vascular proliferation. The neovascularization occurs in a tangential direction with minimal horizontal extension. Other common signs include increased intraretinal edema, neurosensory retinal detachment, serous PED, and preretinal and subretinal hemorrhages. In many cases, a clear retinal–retinal anastomosis can be seen. FA often shows a diffuse area of leakage which is, again, often misinterpreted as occult CNV. Stage III of RAP is defined by the Stage II findings plus the clear presence of CNV (Fig. 20). This is most often documented by the presence of a

(A)

FVPED or a predisciform scar. Occasionally, the presence of a retinal-choroidal anastomosis helps confirm the staging. OCT images representative of RAP are found in the chapter by Oliver and colleagues (Figs. 3 and 4 in the chapter 9).

PROGNOSTIC IMPLICATIONS OF EXUDATIVE AMD: NATURAL HISTORY OF UNTREATED CNV The natural history of untreated CNV in the setting of AMD is well established in both retrospective reviews and prospective randomized controlled clinical trials. Untreated, eyes with CNV often loose visual acuity. The location (extrafoveal, juxtafoveal, subfoveal) of the CNV is linked with the visual acuity prognosis. Obviously, subfoveal CNV causes more immediate visual symptoms than lesions further from the foveal center.

Natural History of Extrafoveal CNV The Macular Photocoagulation Study on extrafoveal CNV provides us with robust natural history outcome data for eyes with similar baseline characteristics and extrafoveal CNV. In the MPS untreated group, initial visual acuity was 20/100 or better in these symptomatic eyes. When untreated, 50% of patients with extrafoveal CNV had, by the time of the first follow-up visit (three months after enrollment for 98 eyes), already lost two or more lines of visual acuity; 10% had suffered a loss of six or more lines of visual acuity (95). Thus, eyes with classic extrafoveal CNV are at

(B)

Figure 20 Retinal angiomatous proliferation (RAP). (A) Early and late fluorescein angiography images of a patient with RAP. The early frame shows a focal area of staining around a retinal vessel off of the infero-temporal arcade. There are associated pinpoint areas of hypofluorescence from blockage from blood. (B) The late frame shows increasing fluorescence and leakage associated with the choroidal neovascularization in this RAP lesion. Patient’s visual acuity was 20/100.

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high risk for visual acuity loss without prompt treatment. Patients remain in this non-subfoveal phase for only a short time after the onset of symptoms (96). At the conclusion of the extrafoveal study, in the untreated (natural history) group, 80% of women and 67% of men lost two or more lines of visual acuity from baseline; 43% of women and 47% of men lost six or more lines of visual acuity from baseline (95). Thus, the natural course of extrafoveal CNV may be visually devastating. Although photocoagulation is not a cure for the majority of eyes, the MPS results as summarized below show that there is a statistically significant benefit to photocoagulation versus observation.

Natural History of Juxtafoveal CNV Thirteen percent of patients with juxtafoveal CNV in the natural history arm (249 eyes) of the MPS lost six or more lines of visual acuity by three months after enrollment and 58% lost six or more lines by 36 months. The juxtafoveal study included eyes with visual acuity 20/400 or better at entry (97). By five years 61% suffered six or more lines of visual acuity loss (98). Only 9.6% of eyes remained unchanged and 5.9% of eyes gained two or more lines of visual acuity by five years. Natural History of Subfoveal CNV The MPS Subfoveal Study is the largest study of the natural history of eyes with subfoveal CNV and initial visual acuity of 20/100 or better. This study found that a majority of eyes will loose significant amounts of visual acuity over time if untreated. In fact, 77% of patients lost four or more lines of visual acuity at 24 months and 64% lost six or more lines. The smaller the lesion at baseline, the better the initial visual acuity (99). In the MPS subfoveal trials, eyes with subfoveal CNV were enrolled if initial visual acuity was between 20/40 and 20/320. The visual acuity outcomes were dependent upon the baseline visual acuity and the lesion size. For all of the groups (A–D), visual acuity in the natural history group continued to drop during follow-up. For lesions one disc area or smaller in size with visual acuity 20/125 or worse and for lesions greater than one and up to two disc areas with visual acuity 20/200 or worse (Group A), 14% of untreated eyes lost six or more lines of visual acuity at three months after enrollment. By one year, 25% lost six or more lines of visual acuity. By four years, 35% lost six or more lines of visual acuity. These were eyes with small lesions and poor visual acuities. For lesions one disc area or smaller in size with visual acuity 20/100 or better and for lesions greater than one and up to two disc areas with visual acuity 20/160 or better (Group B), 11% of the natural history group lost six or more lines of visual acuity at three

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months, 19% at six months, 38% at one year, 52% at two years and three years and 55% at four years after enrollment. Thus these eyes with better initial acuity and smaller lesion size had more visual acuity to loose over time. For lesions two or more disc areas in size and initial visual acuity 20/200 or worse (Group C), 8% lost six or more lines of visual acuity at six months, 15% at one year, 13% at two years, 16% at three years and 25% at four years. Thus eyes with larger lesions and poorer initial acuity had less visual acuity to loose over time. For lesions more than two disc areas is size and initial visual acuity 20/160 or better (Group D), 13% lost six or more lines of visual acuity by three months, 26% at six months, 31% at one year, 54% at two years, 45% at three years and 55% at four years. Eyes with larger lesions and better visual acuity had more visual acuity to loose over time.

MACULAR PHOTOCOAGULATION STUDY The MPS studies represent the first randomized clinical trials for evaluation of treatments of neovascular AMD. The MPS studies gave us robust natural history data for eyes with classic CNV in various locations. Although laser is now rarely used for treatment of CNV, the results will be summarized here for historic purposes. (Further details are found in the chapter by Cukras and colleagues.) The MPS enrolled patients with classic CNV. However, analysis of the data revealed that eyes were enrolled that had classic CNV associated with occult CNV. The MPS treatment recommendations, however, should apply to eyes with classic CNV. Only about 13% of AMD patients with CNV are eligible for treatment by the MPS criteria (100). Patients should be informed that laser treatment results in a permanent scotoma (location, size, effect on central vision function such as reading) and that there is a high risk of persistent CNV (CNV seen within six weeks of treatment after closure) or recurrent CNV (CNV developing after six weeks of treatment and initial closure). In the current era, laser photocoagulation should be considered only for non-subfoveal lesions.

Extrafoveal CNV The original MPS report on the efficacy of laser photocoagulation for extrafoveal CNV in the setting of AMD was published in 1982 (95). That study showed an overwhelmingly positive effect of laser treatment for extrafoveal CNV (200–2500 mm from the foveal center). Eligibility criteria included patient age of 50 years or more, best corrected visual acuity at least 20/100, presence of drusen, symptoms due to the CNV, no prior laser treatment, and no other eye diseases that could affect visual acuity. Treatment

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was applied to the entire CNV and all surrounding blocked fluorescence (based on FA) or subretinal blood. The treatment, performed with 200 mm spots of 0.5 second duration argon blue-green laser, extended 100 to 125 mm on all sides of the CNV beyond blood, pigment or blocked fluorescence. The intention was to treat any occult CNV in those regions. After 18 months follow-up, 60% of untreated eyes versus 25% of treated eyes suffered severe visual loss (p!0.001) (severe visual loss was defined as a loss of six or more lines of visual acuity). The study recruitment was halted at 18 months because of this overwhelming treatment benefit and control group patients were offered laser treatment if there were eligible lesions. This report which was the first randomized controlled multicenter clinical trial for treatment of AMD lead to a firm treatment recommendation of laser photocoagulation for extrafoveal CNV due to AMD (95). Three years and five years data later confirmed the long term efficacy of laser photocoagulation in treated versus control, despite development of recurrent CNV in the treated eyes (101). Recurrent CNV occurred in 54% of the eyes; these eyes had worse visual acuity outcomes than eyes without recurrences. At the time of the study, no treatment was possible for the eyes that developed subfoveal recurrent CNV. Now, with our current armamentarium of subfoveal treatment, better visual results would be expected even in eyes with the subfoveal CNV (88–90,102).

Juxtafoveal CNV The MPS juxtafoveal AMD studies showed that krypton laser photocoagulation for juxtafoveal CNV was effective for prevention of moderate and severe visual acuity loss. This study incorporated krypton red laser because the red wavelength would not be absorbed by the xanthophyll as much as blue laser light and was thus felt to be safer. CNV lesions between one to 199 mm of the foveal center or CNV between 200 and 2500 mm of the center with associated blood or blocked fluorescence within 200 mm of the FAZ center were enrolled. Peripapillary CNV was eligible if the required laser photocoagulation would spare at least 1.5 clock hours along the temporal half of the disc. Treatment of the entire CNV with a 100 mm border was required on the non-foveal border and in areas of blood or blocked fluorescence. Eighty-six of 174 (49%) treated eyes versus 98 of 169 (58%) observed eyes lost six or more lines of visual acuity at three years (97). At the 36 month visit, 62% of untreated and 49% of treated eyes had visual acuity worse than 20/200 (pZ0.02). The treatment effect depended strongly on the presence or absence of hypertension. Untreated eyes without hypertension were twice as likely to lose six or more lines of visual acuity compared to treated eyes (64% vs. 31%). This

effect was only 1.5 times for the eyes with hypertension (70% vs. 46%). At five years, 71 (52%) of treated eyes versus 83 (61%) of untreated eyes lost six or more lines of visual acuity (95). The effect was greater for normotensive (RRZ1.82) than hypertensive (RRZ0.93) patients. The MPS study found 32% of treated eyes showed persistence and an additional 47% of treated eyes developed recurrent CNV within five years after krypton laser to juxtafoveal CNV (103). Eyes without persistent or recurrent CNV maintained 20/80 to 20/100 visual acuity. Persistent CNV was twice as high when there was 10% or more of the foveal side of the CNV not treated. Central leakage in the MPS studies was not linked to a worse outcome. Forty-one percent of the eyes in the juxtafoveal group did not have adequate coverage of the CNV on the foveal edge in contrast to 14% for the extrafoveal group. The MPS recommended that the visual loss may be reduced by covering the entire CNV lesion with laser treatment. More than 90% of recurrences are on the foveal side following laser treatment of extrafoveal and juxtafoveal CNV.

Subfoveal CNV Subfoveal CNV was investigated by the MPS group beginning in 1986. Investigators felt that the poor natural history of eyes with subfoveal CNV (99,104) and scattered reports of outcomes of subfoveal laser not resulting in uniformly poor visual acuity warranted trial of photocoagulation of subfoveal CNV lesions (105). In Jalkh et al.’s study of 94 eyes followed up for an average of 15 months, CNV was closed in 88 eyes and visual acuity was stabilized or improved in those eyes (105). Patients were eligible for inclusion into the MPS subfoveal study if there was some classic CNV, the lesion borders were well-defined, the lesion was 3.5 disc areas or less in size, or less than six disc areas (new area of treatment plus old scar) if recurrent CNV was present. Visual acuity had to be at least 20/320 but no better than 20/40. A total of 373 eyes (371 patients) with new onset CNV and a total of 206 eyes (206 patients) from 13 clinical centers were randomized to laser treatment (argon green or krypton red as assigned during randomization) versus observation. Treatment was performed to all areas of classic and occult CNV within the lesion. Treatment included a border 100 mm beyond the margins for initial treatments or 300 mm into the old treatment scar for recurrent CNV; treatment was based on a fluorescein angiogram not more than 96 hours old. Posttreatment photographs were taken to check adherence to the MPS standards (106). For treated eyes, visual acuity usually decreased three lines from baseline within three months after

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treatment and then was stable for 42 months after treatment. In contrast, untreated eyes had less decreased visual acuity initially but continued to decrease throughout the follow-up period. Treated eyes lost 3.3 lines at 12 months versus 3.7 lines for untreated eyes. At 24 months, treated eyes lost 3.0 lines versus 4.4 lines for untreated eyes. At three months, 20% of treated eyes lost six or more lines of visual acuity loss; this remained stable at 42 months. For untreated eyes, 11% at three months had lost six or more lines of vision, but increased to 48% at the 42 months follow-up with pZ0.006. At the 42 months follow-up, reading speed and contrast sensitivity were better for the treated than untreated eyes (106). The persistence rate was 24%; recurrence rate was 32% at three years. There was no difference between the argon and the krypton groups. However, persistence and recurrence did not affect visual acuity outcomes, unlike in the extrafoveal and juxtafoveal groups. The three year rate for subfoveal persistent or recurrent CNV was 56%. Subgroup analysis showed that treated eyes with smaller CNV lesions (one disc diameter or less) experienced an earlier treatment benefit. Eyes with 20/40 to 20/100 visual acuity lost on average more than four lines of vision posttreatment and did not experience any treatment benefit until 18 months later. For the recurrent CNV subfoveal group, the MPS found a similar treatment benefit. Ninety-seven eyes were treated (49 argon, 48 krypton) and 109 were observed. Treated eyes lost approximately 2.5 lines of visual acuity three months after treatment followed by stable vision for 30 months. Untreated eyes continued to lose visual acuity throughout follow-up such that the average loss was 1.1 lines more than the treated eyes at 24 months. Six or more lines of visual acuity were lost in 14% of treated versus 9% of untreated eyes at three months. This remained about 10% for the treated group but increased to 32% for the untreated group at 18 months of follow-up. Treated eyes retained contrast sensitivity whereas untreated eyes lost contrast sensitivity. After thermal laser photocoagulation, patients require close monitoring consisting of visual acuity, Amsler grid, biomicroscopy, and FA to help detect persistent or recurrent CNV. Usually patients are checked three weeks after laser for extrafoveal/subfoveal CNV and two to three weeks after laser for juxtafoveal CNV. The second visit is typically four to six weeks after laser, the third visit is six to twelve weeks after the laser and the fourth visit three to six months after laser. Any symptomatic patient should be examined immediately. Overall, we no longer recommend thermal laser photocoagulation to patients with subfoveal CNV. PDT and newer anti-angiogenesis treatments are

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more efficacious and safe. Instead of an immediate visual loss with laser photocoagulation, these newer treatments slow down the progression of visual loss in most patients and sometimes even result in improved visual acuity.

OCCULT CHOROIDAL NEOVASCULARIZATION Natural History The MPS group reviewed the results of the juxtafoveal study with respect to the presence or absence of occult CNV. In the subgroup, they noted that there were eyes with only occult CNV, occult and classic CNV and only classic CNV. For eyes with occult CNV that were untreated, 41% within 12 months lost significant visual acuity. Of the 26 symptomatic eyes with occult only lesions, classic CNV developed in 23% within three months and an additional 23% developed classic CNV by 12 months. For the eyes which developed classic CNV, 58% developed severe visual loss. In the group that did not develop classic CNV, only 18% developed severe visual loss. Overall, 23% of eyes which initially had occult-only CNV lesions remained stable or improved at the 36 months follow-up. Of these, 5% of the occult-only group had a two lines or more increase in visual acuity at 36 months follow-up (107). Bressler et al. performed a natural history study of 84 eyes in 74 patients with poorly-defined fluorescein angiographic CNV (108). The lesions were subfoveal in 89% of the eyes. Initial visual acuity averaged 20/80 and 93% had no classic CNV component. Over a follow-up ranging from six months to 53 months (mean 28 months), 14% remained stable or improved, 21% lost three to six lines of visual acuity and 42% lost more than six lines of visual acuity. Additional analysis, which included only those 46 eyes with two or more years of follow-up, similar results were found: 17% remained stable or improved, 22% lost three to six lines of visual acuity and 48% lost more than six lines of visual acuity. Eyes which developed disciform scars had worse visual acuities compared with eyes which had poorly-defined CNV and leakage. Soubrane et al. (109) analyzed visual and angiographic outcomes of 156 patients (82 untreated) with symptomatic occult CNV and initial visual acuity of 20/100 or better. This series excluded eyes with turbid fluid, subretinal blood, PED or visible CNV. Follow-up ranged from one to eight years. There was no difference between treated and untreated eyes with CNV. Sixty-five percent of eyes with presenting subfoveal CNV had initial visual acuity of 20/50 or better. In this natural history group, visual acuity fell from 20/40 to 20/70. Similar to Bressler et al.’s results (108), when visible new vessels developed, the visual acuity

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decreased. Treatment, when compared to the natural history group, did not result in better visual acuity outcomes over time (109). Bressler et al. also evaluated macular scatter (grid) laser treatment of symptomatic eyes with poorly demarcated subfoveal CNV. Visual acuity ranged form 20/25 to 20/320 visual acuity in the 51 treated eyes and the 52 observed eyes (110). For observed eyes, median visual acuity was 20/80 initially and decreased to 20/320 at 24 months. The difference in visual acuity loss was significant between the treated and observed groups only at six months (1.8 lines lost in the observed vs. 3.8 lines lost in the treated group). At six months follow-up, treated eyes lost two more lines of visual acuity compared with observed eyes. However, by 24 months, approximately 40% had severe visual acuity loss in both groups; mean change was a loss of 4.3 lines for observed eyes and 4.6 lines for treated eyes. At 12 months, 35% observed and 29% treated had improved or remained stable, with 37% observed and 30% treated losing two to five lines and 28% observed and 41% treated losing six or more lines of visual acuity. At 24 months, 31% observed and 31% treated had improved or remained stable, 31% observed and 28% treated lost two to five lines and 38% observed and 42% treated lost six or more lines of visual acuity. Thus, conventional laser photocoagulation (either confluent or scatter) is not beneficial for AMD patients with subfoveal occult CNV. However, we are now in an era with several effective alternatives to laser photocoagulation. These treatments are not unique to occult CNV and apply to other CNV lesion subtypes.

CURRENT THERAPEUTIC OPTIONS FOR CNV The last few years have witnessed an explosion in the available non-ablative therapies for subfoveal CNV. The first proven and effective alternative treatment to laser photocoagulation of subfoveal CNV was PDT. Large studies on the efficacy of antiangiogenesis agents have not been performed on non-subfoveal lesions. More recently, the anti-angiogenic agents have been shown to be effective treatments. These agents are capable not only of stabilizing visual acuity but also improving visual acuity. Gene therapy and combination treatments are investigational treatments.

Phototodynamic Therapy PDT utilizes a photosensitizer drug that is given intravenously. The drug preferentially localizes to the CNV. A diode laser is used to deliver the diode wavelength of light (689 nm) to the lesion. Details of the application of PDT is found in the chapter by Blumenkranz and colleagues. PDT was initially

demonstrated to be effective for treatment of subfoveal predominantly classic (classic CNV comprises greater than 50% of the CNV lesion) CNV. PDT treatment of subfoveal CNV offers an obvious advantage over laser photocoagulation, which causes an irreversible scotoma and hence visual acuity loss. The Treatment of AMD with Photodynamic Therapy (TAP) study showed PDT with verteporfin dye (Visudyne, Novartis, East Hanover, New Jersey, U.S.A.) for subfoveal CNV in AMD patients resulted in 61% of treated eyes versus 46% of placebo eyes losing less than 15 letters (approximately three lines of visual acuity) at one year. Subgroup analysis showed that eyes with predominantly classic CNV (defined as 50% or more of the lesion as classic CNV) had the best treatment benefit (67% treated vs. 39% placebo lost less than three lines of visual acuity) (111). Two-year results demonstrated continued efficacy with PDT treatment versus placebo (112). For eyes with 50% or less classic CNV, 66% of treated versus 32.5% placebo lost less than three lines of visual acuity at 24 months. Only a small percentage of patients (16% vs. 7%) gained one or more lines of visual acuity. Thus patients should be told that, although PDT can help prevent severe visual loss, improvement of visual acuity is indeed rare. Despite PDT treatment a significant proportion of patients will still lose visual acuity. PDT is also useful in situations where the treating ophthalmologist feels that conventional laser (113) could lead to visual loss (e.g., juxtafoveal lesions close to the foveal center). Eyes with occult lesions were studied as part of the Verteporfin in Photodynamic Therapy Study (VIP). The VIP study showed PDT for occult CNV lesions was beneficial at year 2; the one-year data showed no statistically significant difference between Visudyne and placebo, but did show a trend in favor of Visudyne therapy (114). At year 2, 45% of Visudyne eyes versus 31% of placebo eyes (pZ0.03) lost less than three lines of visual acuity and 71% of Visudyne versus 53% of placebo eyes (pZ0.004) lost less than six lines of visual acuity. The treatment effect was best for eyes with 20/50 or less visual acuity and lesion size smaller than four MPS disc areas. Further evaluation of smaller lesion sizes in the Visudyne in Occult CNV (VIO) showed no benefit at year 1 or year 2 (115). PDT treatment is not very beneficial for occult CNV lesions. The visudyne in minimally classic (VIM) study evaluated the use of Visudyne PDT using reduced fluence (RF) and standard fluence (SF). RF was investigated as a way to increase selectivity while limiting potential adverse effects to normal tissue. At 12 months, the VIM study showed 14% (5 of 36) of RF eyes and 28% (10 of 36 eyes) of SF eyes, compared with 47% (18 of 38) of placebo eyes (RF, pZ0.002; SF, pZ0.08; RFCSF, pZ0.004) lost three or more lines of visual acuity. At month 24, this loss occurred in 26% (nine of 34) of

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RF eyes and 53% (17 of 32) of SF eyes, compared with 62% (23 of 37) of placebo eyes (RF, pZ0.003; SF, pZ0.45; RFCSF, pZ0.03) (116). There were more eyes that progressed from minimally to predominantly classic CNV by 24 months in the placebo group than either treatment groups [11 (28%) of 39 patients compared with 2 (5%) of 38 in the RF group (pZ0.007) and 1 (3%) of 37 in the SF group (pZ0.002)]. No unexpected ocular or systemic adverse events were identified. It was concluded that PDT with Visudyne safely reduced the risks of moderate visual loss and progression to predominantly classic CNV for at least two years in individuals with subfoveal minimally classic lesions due to AMD measuring six MPS disc areas or less. More recently, combination therapy using PDT with triamcinolone or with anti-angiogenic agents has been tried. Limited case reports show a decreased number of required PDT treatments as well as improved visual acuity results from combined intravitreal steroid injections with PDT (117–119). One group however found no visual benefit but a decreased number of required PDT treatments to close the CNV (119). There are currently several multicenter studies investigating the benefit of intravitreal triamcinolone combinations with PDT. Further details of PDT are found in the chapter by Jain and colleagues in this book. Others are now combining PDT with antiangiogenesis treatments.

Anti-angiogenesis Treatments As mentioned previously, VEGF plays a major role in angiogenesis. Inhibition of VEGF is therefore a rational treatment approach for CNV therapy. The first anti-VEGF treatment study, the VEGF Inhibition Study in Ocular Neovascularization (V.I.S.I.O.N.) trial used a VEGF aptamer (pegaptanib sodium, Macugen) to treat subfoveal CNV. All lesion subtypes and lesions up to 12 disc areas were included. Patients were randomized to receive an intravitreal injection of Macugen (three does) or to a usual care group. The usual care group allowed the use of PDT for predominantly classic lesions. In this study of 1186 patients, the 0.3 mg pegaptanib dose was effective in the prevention of visual loss: 70% versus 55% (p!0.001) lost less than three lines of visual acuity. Overall, 6% of treated eyes gained three or more lines of visual acuity in the 0.3 mg dose versus 2% in the usual care group. Twenty-two percent of eyes gained one or more lines of vision in the 0.3 mg dose group versus 12% in the sham group. Angiographically, there was a slowing in the rate of the CNV lesion growth, CNV size and leakage by 30 and 54 weeks. No antibodies were detected against pegaptanib. Significant ocular adverse events in the Macugen treated eyes included endophthalmitis in 1.3% patients, vitreous floaters in

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33% and anterior chamber inflammation. The 0.3 mg dose of Macugen was approved for use for subfoveal CNV due to AMD in 2005. Exploratory subgroup analysis of the V.I.S.I.O.N. trial results showed Macugen was effective for all subgroups and that no single subgroup drove the efficacy results. The use of PDT could have enhanced the usual care group results and lessened the differences between treatment and usual care. This was the first time that a CNV treatment was independent of lesion subtype. The benefit was maintained at year 2 (120). Macugen has been shown to be quite safe, with low rates of endophthalmitis. The continuous treatment group of eyes did better than the group of eyes in which treatment was halted after one year (and then allowed to resume treatment if losing ten or more letters). A subgroup analysis of early lesions was subsequently performed (121). Two groups of early lesions were identified: group 1 included small lesions less than two disc areas in size, with O54 letters, without prior therapy and without scarring or atrophy. Group 2 included occult only lesions without lipid and with better visual acuity than the fellow eye. For these early lesions, there was a better response to Macugen therapy. For group 1, 76% of treated eyes versus 50% of usual care eyes lost !15 letters (pZ0.03). Twelve percent of treated and 4% of usual care eyes gained 15 or more letters. For group 2 eyes, 80% of treated versus 57% of usual care eyes lost !15 letters (pZ0.05). Twenty percent of treated eyes and 0% of usual care eyes gained 15 or more letters. Another anti-VEGF treatment approach is that of an antibody to VEGF. The VEGF antibody, rhuFAb (ranibizumab, Lucentis) is a humanized monoclonal antibody antigen-binding fragment (Fab) that binds to and neutralizes the biological activities of all known human VEGF-A isoforms including its proteolytic cleavage products. Lucentis blocks all VEGF isoforms, unlike Macugen which is an aptamer that specifically binds VEGF 165. Ranibizumab was given as an intravitreal injection monthly in the initial clinical trials. In these clinical trials, visual acuity was maintained within three lines of baseline in over 90% of eyes. Visual acuity improved three or more lines in 33% to 40% of patients (89,90). These one and two year studies showed the best visual acuity results to date for any randomized multicenter clinical trial on exudative AMD (89,90). The MARINA (Minimally Classic/Occult Trial of Anti-VEGF Ranibizumab In Antibody the Treatment of Neovascular AMD) study was a phase III, multicentered, randomized trial comparing the efficacy of monthly intravitreal injections of ranibizumab compared to sham injections in 716 patients with minimally classic or occult CNV. Eyes were

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randomized equally to one of three groups: the 0.3 mg ranibizumab, 0.5 mg of ranibizumab, or sham. Approximately 95% (0.3, 0.5 mg) of ranibizumab eyes versus 62% of control eyes maintained or lost less than 15 letters from baseline (p!0.0001) at one year. Twenty-five percent of 0.3 mg ranibizumab dose eyes and 34% of 0.5 mg dose ranibizumab eyes versus 5% of sham eyes gained three or more letters from baseline at month 12. The results were maintained at two years. Ninety percent of ranibizumab eyes compared with 53% of control eyes lost less than 15 letters (p!0.0001) at year 2 for the 0.5 mg dose. Thirty-three percent of ranibizumab eyes versus 3.8% of sham eyes gained three of more lines of visual acuity (p!0.0001) at year 2 for the 0.5 mg dose. Ranibizumab eyes gained an average of 7.2 letters at year 1 and 6.6 letters at year 2 versus control eyes which lost 10.4 letters at year 1 and 14.9 letters at year 2 (89). Anatomic findings (lesion size, area of leakage, OCT thickness) were in favor of ranibizumab over sham. The ANCHOR (ANti-VEGF Antibody for the Treatment of Predominantly Classic CHORoidal Neovascularization in AMD) study was a phase III, multicenter, randomized clinical trial comparing efficacy of monthly intravitreal injections of two doses of ranibizumab (0.3 mg, 0.5 mg) with PDT in 423 patients with predominantly classic CNV. Ninety-four percent (0.3 mg) and 96% (0.5 mg) of ranibizumab eyes versus 64% of PDT eyes lost less than 15 letters (p! 0.0001). Forty percent of ranibizumab eyes versus 5.6% of PDT eyes improved at least 15 letters (p!0.0001) from baseline at one year. The average change was a gain of 11 letters for ranibizumab eyes versus a loss of 9.5 letters for sham eyes at one year (90). The PIER (A Phase IIIb, Multicenter, Randomized, Double-Masked, Sham Injection-Controlled Study of the Efficacy and Safety of Ranibizumab in Subjects with Subfoveal Choroidal Neovascularization with or without classic CNV Secondary to AgeRelated Macular Degeneration) study was a phase III study that evaluated the safety and efficacy of intravitreal injections of two different doses (0.3 mg, 0.5 mg) of ranibizumab administered monthly for three doses and then every three months compared with sham for eyes with subfoveal CNV in 184 patients. The one year results showed no gain in visual acuity gain from baseline in the treated groups versus a loss of 16.3 letters in the sham group (p! 0.0001). Ninety percent of the ranibizumab 0.5 mg dose lost less than 15 letters versus 49% of the sham eyes (p!0.0001). There was no difference in the percentage of eyes with improvement of 15 or more letters: 15% of ranibizumab eyes versus 10% of sham eyes (pZ0.71) (122). Based on these positive results, the 0.5 mg dose of Lucentis was approved for treatment of subfoveal CNV by the FDA in 2006.

The FOCUS study was a phase I/II randomized, multicentered, single-masked, controlled study comparing the safety and efficacy of monthly intravitreal injections of ranibizumab (0.5 mg dose) in combination with verteporfin PDT to PDT alone in patients with predominantly classic CNV. PDT was given at baseline and then on an as needed basis every three months. Eyes receiving ranibizumab and PDT did better than the eyes receiving PDT alone. 90.5% of combination eyes lost less than 15 letters from baseline as compared with 68% of PDT eyes (pZ0.0003) (123). Approximately 24% of ranibizumab and PDT eyes gained 15 letters from baselines as compared with 5% of PDT eyes (pZ 0.0033). In all of the ranibizumab studies, the rates of serious adverse events were low. The incidence of hypertension and thromboembolic events did not differ significantly between the ranibizumab treated patients and the sham or PDT groups. The incidence of endophthalmitis was low between 1% and 2%. Ocular serious adverse events occurred in !0.1% of intravitreal injections. Bevacizumab (Avastinw) has recently been used off-label for treatment of CNV in AMD patients. Avastin is a full length anti-VEGF antibody, which contrasts with ranibizumab, which is a VEGF antibody fragment specifically developed for intraocular use. Bevacizumab is FDA approved for use in metastatic colorectal cancer and has significant systemic side effects, including hypertension and increased thromboembolic events, when given intravenously in cancer patients (124,125). In the open label Systemic Avastin for Neovascular AMD (SANA) trial, patients with progressive visual loss who were ineligible for PDT were given intravenous bevacizumab (126,127). Based on the risks of bevacizumab therapy, patients were excluded if they had uncontrolled hypertension, a history of thromboembolic events, current anticoagulation therapy, or proteinuria, or if elective surgery was planned within three months. Patients were followed weekly initially and then monthly. Significant improvements in visual acuity and decreased retinal thickness on OCT were seen. Ten of the 18 patients required medication or adjustment of existing medication for systemic hypertension. These systemic side effects led to the exploratory use of intravitreal injection of bevacizumab to treat CNV in AMD patients. Intravitreal use of bevacizumab involves both an off-label application of the drug and an alternative route of drug delivery. Rapid visual acuity improvement and decreased retinal thickness (126–129) have led to widespread use in the retinal community. The main force driving intravitreal bevacizumab usage is the high percentage of patients that

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Choroidal Neovascularization Secondary to AMD Lesion Location?

Juxtafoveal: Laser Photocoagulation Photodynamic Therapy Anti-VEGF Drug ?

Subfoveal

Extrafoveal: Laser Photocoagulation Photodynamic Therapy Anti-VEGF Drug ?

Type of Leakage? Predominantly Classic: Photodynamic Therapy Lucentis, Macugen Avastin

Occult with No Classic or Minimally Classic Recent Disease Progression?

Yes, Recent Disease Progression

No: Observation

Lesion Size < 4 MPS Disc Areas? No: Photodynamic Therapy Lucentis, Macugen Avastin

Yes, < 4 MPS Disc Areas

Visual Acuity < 20/50? Yes: Visual Acuity < 20/50 Photodynamic Therapy Lucentis, Macugen Avastin

No: Lucentis, Macugen Avastin

Figure 21 Flowchart illustrating treatment options for choroidal neovascular lesions in agerelated macular degeneration (AMD). BoldZefficacy proven in phase 3 clinical trials.

experience symptomatic relief from active subfoveal CNV. Currently, the National Eye Institute (NEI) is sponsoring the Comparison of Treatment Trial (CATT) study, which will directly compare the efficacy and safety of bevacizumab to ranibizumab in monthly and alternate dosing regimens in patients with subfoveal CNV in AMD eyes. The current treatment paradigm using these medical treatments is illustrated in Figure 21. Treatments with proven efficacy are shown in bold.

Thermotherapy Other treatments for subfoveal exudative AMD include thermotherapy, radiation therapy, other forms of antiangiogenesis therapy, submacular surgery, submacular surgery with RPE transplantation surgery and translocation surgery. Some of these alternative therapies have shown no benefit whereas others, such as antiangiogenesis treatments, have shown great visual acuity improvement in eyes with CNV.

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Thermotherapy (TTT) is the treatment by which a modified diode laser is used to deliver heat to the choroid and RPE through the pupil. Prior success has been demonstrated for treatment of small choroidal melanoma and retinoblastoma with this method (130,131). Reichel and colleagues (132) performed a pilot study in which 16 eyes of 15 patients with occult CNV were treated with TTT. Over a mean follow-up time of 12 months, 19% improved by two or more lines of visual acuity, 56% remained the same, and 25% lost two or more lines of visual acuity. Ninetyfour percent showed decreased exudation despite the visual acuity results. Reichel and coworkers have since performed a multicenter, double-masked, placebocontrolled trial, the TTT4CNV trial. The TTT4CNV trial enrolled 303 patients with small (%3 mm) occult subfoveal CNV with visual acuities ranging from 20/50 to 20/400. Patients randomized to treatment received 800 mW TTT over 60 seconds using a 3 mm spot size from the Iris OcuLight SLx 810 nm laser and the large spot size slit lamp adapter. Compared to placebo eyes, treated eyes did not show a beneficial effect on prevention of moderate visual loss at one year. However, for the subgroup of eyes (41% at baseline) with 20/100 or worse visual acuity at baseline, 23% of treated eyes gained one or more lines of visual acuity and 14% gained three of more lines of visual acuity at one year. No further studies are planned using TTT (133).

Radiation Radiation therapy has been advocated as a therapy for exudative AMD. Low dose radiation inhibits neovascularization (134–137). The key factor in the use of radiation therapy is achieving a balance between destruction of abnormal CNV tissue and preservation of normal retinal and choroidal blood vessels (138). Since proliferating tissues are more radiosensitive, this balance is theoretically achievable. Conflicting data about the efficacy and morbidity of radiation therapy has led to the Age-related Macular Degeneration Radiation Trial (AMDRT) an NEI-sponsored pilot study comparing observation to radiation. The AMDRT enrolled patients with lesions not amenable to laser treatment (classic, occult or mixed). The AMDRT found no clinically significant difference between eyes assigned to radiation and those to observation (138). At 6 months, 9 radiated eyes (26%) and 17 observed eyes (49%) lost R3 lines of visual acuity [pZ0.04; stratified chi-square test]. At 12 months, 13 radiated eyes (42%) and 9 observed eyes (49%) lost R3 visual acuity lines (pZ0.60). The radiated group demonstrated smaller lesions and less fibrosis than the nonradiated group (pZ0.05 and 0.004, respectively) at 12 months. Experimental work

continues in this area. More information on the use of radiation for treatment of CNV in AMD can be found in the chapter by Flaxel and Finger and in that of Chong and Scartozzi.

Surgical Treatments Pilot studies evaluating submacular surgery for CNV in AMD patients showed some promise and led to the definitive Submacular Surgery Trails (SSTs). The SST was comprised of four studies, which included a pilot trial. One of the arms of the SST study, the recurrent CNV arm, showed no difference between surgery or laser treatment and no further study was recommended (139). The other three arms included new subfoveal CNV associated with AMD (Group N), large subfoveal hemorrhage associated with AMD (Group B) and subfoveal histoplasmosis CNV and idiopathic CNV (Group H). Long-term visual outcomes and recurrence rates after submacular surgery compared similarly with the natural history of untreated CNV. Thus, the SSTs did not show a benefit for removal of CNV and a modest benefit for subretinal hemorrhage evacuation. Some groups are combining submacular surgery with RPE transplantation. Since the RPE is often removed during submacular surgery or since RPE atrophy often follows submacular surgical procedures, researchers are evaluating the efficacy of transplanting RPE cells to repopulate the RPE layer. Loss of the RPE leads to choriocapillaris loss. The details of this technique and the rationale for RPE transplantation is given in detail in Del Priore and colleagues’ chapter in this book. Retinal translocation and limited macular translocation surgery (140–146) have been described for treatment of subfoveal CNV. The rationale behind these surgical techniques is to move the macular area from the underlying CNV to a healthier RPE environment. The underlying CNV is thus moved relative to the foveal center and can be treated with conventional laser or surgically removed. Limited macular translocation surgery (141–142) and 360 degree translocation surgery (143–146) is discussed in detail in the chapter by Au Eong and colleagues. In the current era of antiVEGF therapy, translocation surgery is used less often than in the past. Emerging Treatments Newer mechanisms of antiangiogenesis treatments continue to be developed. Small interfering (short inhibitory) RNA technology (147–150) targeted against VEGF is being evaluated. VEGF trap has been evaluated in phase I and II studies (151). NonRNA inhibitors of VEGF receptor tyrosine kinase activity are in development (152,153). Tubulin-binding

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agents, such as combretastatin A-4 phosphate, are in early clinical trials (154). Some emerging drugs in development have recently been pulled from the developmental pipeline because the efficacy is much lower than that of anti-VEGF treatments. This has occurred with squalamine lactate (155–158). Exciting work with gene therapy using adenoviral vectors (159–164) is in progress.

Small Interfering RNA In 1998, Fire and Mello (147) discovered that injection of gene-specific double stranded RNA into cells results in potent silencing of that gene’s expression. This RNA interference is one of the fundamental mechanisms by which a cell regulates gene expression and protects itself against viral infection. (Fire and Mello were awarded the Nobel Prize in Physiology and Medicine for 2006.) Double-stranded RNA binds to a protein complex called a Dicer. The Dicer cleaves the doublestranded RNA into multiple smaller fragments. A second protein complex called RNA-induced silencing complex (RISC) then binds these RNA fragments and eliminates one of the strands. The remaining strand stays bound to RISC, and serves as a probe that recognizes the corresponding messenger RNA transcript in the cell. When the RISC complex finds a complementary messenger RNA transcript, the transcript is cleaved and degraded, thus silencing that gene’s expression. Reich and Tolentino (148,149) used a small interfering RNA (siRNA) inhibitor of VEGF designed for intravitreal injection for treatment of CNV. A phase I, open-label, dose escalation study of 15 patients revealed no serious ocular or systemic adverse effects at a dose up to 3.0 mg. The drug was later named bevasiranib/Cand5 (Acuity Pharmaceuticals, Philadelphia, Pennsylvania, U.S.A.) in the phase II trial, known as the CARE study (Cand5 Anti-VEGF RNAi Evaluation). In this multicenter, randomized, doublemasked, trial of bevasiranib/Cand5 in patients with CNV secondary to AMD (Brucker et al., Retina Society Meeting, Cape Town, October 2006. Thompson et al., AAO Meeting Las Vegas, November 2006), 127 patients with predominantly classic, minimally classic, or RAP lesions (occult no classic lesions excluded) were randomized to receive one of three doses of the drug (0.2, 1.5, and 3.0 mg) at baseline and at six weeks. The primary endpoint was the mean change in Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity from baseline at 12 weeks. The drug was found to be safe. At 12 weeks, mean change in ETDRS visual acuity was K4 letters (0.2 mg), K7 letters (1.5 mg), and K6 letters (3.0 mg) for the drug doses respectively. The authors theorized that the disappointing visual results resulted from the fact

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that bevasiranib/Cand5 only blocks the production of new VEGF and not existing VEGF. They postulated that a baseline combination treatment with a VEGF blocker may be required to “mop up” the preexisting VEGF load. However, the half-life of VEGF is short and it does not explain why the results were not seen by the 12 weeks time point. Further work remains to be done to determine efficacy for the proposed treatment combination. Other therapeutic targets for siRNA are being investigated. siRNA directed against the vascular endothelial growth factor receptor-1 (VEGFR-1) have shown promise in a mouse model of CNV (150), and are currently in clinical development (Sirna-027—Sirna Therapeutics, Boulder).

VEGF Trap VEGF Trap (Regeneron, Tarrytown, New York, U.S.A.) is an experimental new drug designed to inhibit all members of the VEGF family: VEGF-A, -B, -C, -D, and placental growth factor-1 and -2. VEGF Trap is a recombinant, chimeric, VEGF receptor fusion protein. The binding domains of VEGFR-1 and -2 are combined with the Fc portion of immunoglobulin G to create a stable, soluble, high-affinity inhibitor. VEGF trap binds VEGF-A with a higher affinity (Kd !1 pmol/L) than currently available anti-VEGF drugs (151). Whether the broader spectrum and higher affinity of VEGF Trap equates to improved efficacy in the treatment of CNV secondary to AMD is yet to be determined. The CLEAR-AMD 1 Study is a randomized, multicenter, placebo-controlled, dose-escalation study designed to assess the safety, tolerability and bioactivity of VEGF Trap (151). In this study, 25 AMD patients with subfoveal CNV with lesions less than 12 disc areas in size and more than 50% active leakage were enrolled. Patients were randomized to receive either placebo or one of three doses of VEGF Trap (0.3-, 1.0-, or 3.0-mg/kg) as a single IV dose, followed by a four week observation period. Three additional doses were given two weeks apart. Dose-limiting toxicity was observed in two of five patients treated with the 3.0 mg/kg dose: one patient developed grade 4 hypertension and the other developed grade 2 proteinuria. The maximum tolerated IV dose of VEGF Trap was 1.0 mg/kg. Reduced leakage on FA and reduced retinal thickening on OCT were observed in the treated patients. No corresponding reduction in CNV lesion size or improvement in visual acuity was observed in these patients over the short 71 day study period. The CLEAR-IT 1 Study is now underway and will assess the safety, tolerability and bioactivity of VEGF Trap through the intravitreal route of administration (Nguyen et al., abstract, Retina Society Meeting, Cape Town, October 2006). The study has enrolled

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21 patients using the same inclusion criteria as CLEAR-AMD 1, and randomized them to receive one of six doses of VEGF Trap as single intravitreal injection: 0.05, 0.15, 0.5, 1.0, 2.0, or 4.0 mg. After 43 days of follow-up, no adverse ocular or systemic events were observed. Mean decrease in excess foveal thickness for all patients was 72%. The mean increase in ETDRS visual acuity was 4.75 letters and visual acuity remained stable or improved in 95% of patients. Notably, three out of six patients treated with the higher doses (2.0 or 4.0 mg) gained R3 lines of visual acuity by day 43. VEGF Trap shows promise as a novel treatment for CNV in AMD patients.

Receptor Tyrosine Kinase Inhibitors Non-RNA inhibitors of VEGF receptor tyrosine kinase activity have been identified. The anti-angiogenic properties are being investigated for use in the treatment of systemic malignancy, as well as CNV. One advantage of this class of drugs is the possibility of an oral route of administration, thereby avoiding the ocular complications associated with intravitreal injections. One promising compound is PTK787, which is a non-selective inhibitor of all known VEGF receptors. PTK787 has been shown to inhibit retinal neovascularization in a hypoxic mouse model (152,153). Phase I/II clinical trials of PTK787 (Vatalanib, Novartis, East Hanover), have been done in patients with both solid and hematologic malignancies. A multicenter phase I trial of PTK787/Vatalanib in patients with macular degeneration—the ADVANCE study—is currently enrolling patients. Patients with all CNV lesion types will receive PDT with Visudyne at baseline, and randomized to receive concurrent treatment with either 500 or 1000 mg of oral PTK787/Vatalanib, or placebo, once daily for three months (Joondeph, abstract, Retina Society Meeting, Cape Town, October 2006). ADVANCE is designed to assess the safety and efficacy of the drug. AG-013958 (Pfizer, San Diego, California, U.S.A.) is a selective VEGFR and platelet-derived growth factor receptor inhibitor that is currently in Phase I and II clinical testing. The drug is administered as a subtenons injection. Preliminary results of 21 patients with subfoveal CNV indicated that adverse events were mild (165). Squalamine Lactate Squalamine lactate (Evizon, Genaera, Plymouth Meeting, Pennsylvania, U.S.A.) is another antiangiogenic compound which was investigated as a potential treatment of CNV. It is a chemically-synthesized aminosterol which was originally isolated from the liver of the dogfish shark Squalus acanthias (155). It is thought to inhibit angiogenesis by acting on the sodium-hydrogen antiporter sodium-proton

exchangers (specifically the NHE3 isoform) to inhibit endothelial cell proliferation. It works intracellularly and binds calmodulin. It inhibits VEGF signaling and integrin expression, and reverses cytoskeletal formation. These effects result in endothelial inactivation and apoptosis. It has the greatest effect on new vessel formation with no appreciable effect on unstimulated endothelial cells (156). In addition to its antiangiogenic properties, it also has direct antitumor effects and is currently being studied in human clinical trials as a treatment for advanced cancers. In rats with laser-induced trauma, systemic squalamine was shown to reduce histological evidence of CNV development (157). In a small, four-month study of forty humans with AMD-associated CNV, squalamine was found to improve mean visual acuity in ten (26%) of the subjects by R3 lines (approximately R15 letters). Vision was stable in 74% of subjects (%G2 lines) (158). A subsequent study is investigating the use of monthly infusions of squalamine lactate in combination with PDT. Three different doses of squalamine are being investigated. Preliminary safety data on the 46 subjects showed no drug-related serious adverse events during the first 29 weeks. However, of the ten “probably related” adverse events, there was one retinal detachment and one incidence of prolonged prothrombin time, and eight infusion site reactions. The interim results of this study have led to a decision to halt further investigation as the efficacy does not near that seen with the anti-VEGF drug Lucentis treatment for AMD-associated CNV. Anti-VEGF treatment has enabled a sizeable proportion of treated patients to attain significant visual improvement or to maintain vision. Future research will hopefully continue to build on these advances and make restoration of vision a reality for the majority of these patients.

Tubulin Binding Agents Vascular targeting agents are also being investigated as treatments for CNV. These agents have shown efficacy in causing tumor regression. Combretastatin A-4 is a naturally occurring agent that binds tubulin and causes necrosis and shrinkage of tumors by damaging their blood vessels. A CA-4 prodrug, combretastatin A-4-phosphate (CA-4-P), has been tested in two models of ocular neovascularization. CA-4-P is a novel agent that bind tubulin and causes endothelial cells which are normally flat to become round, resulting in narrowing of the lumen and cessation of blood flow in the vessels (160). It is only effective on newly formed blood vessels which have no actin and are therefore susceptible to tubulin structure disruption. CA-4-P increases endothelial cell permeability, while inhibiting endothelial cell

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migration and capillary tube formation predominantly through disruption of vascular endothelialcadherin/beta-catenin/Akt signaling pathway, thereby leading to rapid vascular collapse and tumor necrosis (161). Nambu and coworkers quantitatively assessed the effect of CA-4-P to suppress CNV in transgenicmice with overexpression of VEGF in the retina (rho/VEGF mice) and mice with CNV due to laser-induced rupture of Bruch’s membrane. CA-4-P suppressed the development of VEGF-induced neovascularization in the retina. CA-4-P blocked development and promoted regression of CNV. Therefore, CA-4-P shows potential for both prevention and treatment of ocular neovascularization (162).

Gene Therapy Gene therapy approaches include delivery of adenoviral vectors contained antiangiogenic proteins such as PEDF or RNA that can attenuate VEGF. Use of adenoviral vectors to continuously deliver the protein would eliminate the need for multiple injections. One approach is to use short hairpin RNA (shRNA) that could attenuate VEGF as a potential therapy for AMD (163). Cashman and colleagues developed several shRNAs from recombinant adenovirus. The investigators found potent shRNA sequences that were able to silence VEGF in human RPE cells by 94% at a 1:5 molar ratio (VEGF to shRNA) and 64% at a 1:0.05 molar ratio. Co-injection of VEGFexpressing viruses into mice with shRNA targeting VEGF led to a substantial (84%) reduction in CNV. shRNA may hold promise as a therapy for AMD. Campochiaro and colleagues have studied the use of human PEDF to treat CNV. PEDF is one of the most potent known antiangiogenic proteins found in humans. Campochiaro and colleagues use adenovirus adsorbed PEDF, Ad(GV)PEDF.11D. cDNA for PEDF is the transgene on E1-, partial E3-, E4- deleted replication-deficient, adenovirus serotype 5, the gene transfer vector. The natural blood retinal barrier limits the ability of Ad(GV)PEDF.11D to affect tissues other than in the eye. Intravitreal administration of Ad(GV)PEDF.11D is a convenient means of delivering PEDF “factories” to the relevant cells within the eye, thus resulting in local PEDF production. In three murine disease models (the laser-induced CNV model, the VEGF transgenic model, and the retinopathy of prematurity model) significant inhibition of neovascularization (up to 85%) was shown with doses of Ad(GV)PEDF vectors ranging from 1!108 to 1!109 particle units (PUs). Toxicology studies in Cynomolgus monkeys showed a dose-related inflammatory response to Ad(GV)PEDF. A dose of 1!108 PU caused no adverse effects, while the inflammatory

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response observed at 1!109 PU was minimal and fully reversible. Higher doses produced increasingly severe inflammatory responses (164). An open-label, dose-escalation, phase I study investigated the safety, tolerability and potential activity of intravitreal injection of Ad(GV)PEDF.11D in patients with advanced AMD and CNV with visual acuity 20/200 or worse (165). Twenty-eight patients received a single intravitreal injection of Adenovector pigment epithelium-derived factor 11(AdPEDF.11), at doses ranging from 106 to 109.5 PU. No serious adverse events related to AdPEDF.11 and no dose-limiting toxicities were found. Signs of mild, transient intraocular inflammation occurred in 25% of patients, but there was no severe inflammation. All adenoviral cultures were negative. Six patients had increased intraocular pressures, which were controlled with topical medications. At three and six months after injection, 55% and 50%, respectively, of patients treated with 106–107.5 PU and 94% and 71% of patients treated with 108–109.5 PU had no change or improvement in lesion size from baseline. The median increase in lesion size at 6 and 12 months was 0.5 and 1.0 disk areas in the low-dose group compared with 0 and 0 disk areas in the high-dose group. These data suggest the possibility of antiangiogenic activity that may last for several months after a single intravitreal injection of doses greater than 108 PU of AdPEDF.11. This study provided evidence that adenoviral vector-mediated ocular gene transfer is a viable approach for the treatment of ocular disorders. Further studies investigating the efficacy of AdPEDF.11 in AMD patients with CNV are planned.

Low Vision For patients in whom visual acuity is impaired and no treatment is possible or for whom no treatment possibilities remain, visual rehabilitation is of utmost importance. Low vision rehabilitation may help these patients best utilize their remaining visual acuity and teach them to utilize ancillary tools such as closed circuit television and magnifiers. These patients should also be reminded that AMD affects central and not peripheral vision. Expectations of the magnitude benefit of low vision rehabilitation should be realistically explained to the patient. Further details of the devices and the services available for the low vision patient are detailed in the chapters by Primo. SUMMARY The era of improvement of visual acuity as a goal in the treatment of AMD patients with CNV has arrived with the advent of the anti-angiogenesis agents. Ultimately, prevention of CNV must be our goal in

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order to prevent visual loss in patients with AMD. Some experimental approaches have included laser to drusen, which did not prove beneficial. At present, the anecortave acetate risk reduction trial (AART) is in progress. AART is a prospective study in which eyes at high risk for CNV are randomized either to anecortave acetate (delivered via a juxtascleral injection) or observation. The Age-Related Eye Disease Study 2 (AREDS 2) will explore nutritional supplementation for prevention of CNV in high risk AMD eyes. (Further details of these studies can be found in the non-exudative AMD chapter by Bhagat and Flaxel). Perhaps gene therapy will play an important role in the future as discussed further in the chapter by Chao and colleagues. The next decade will undoubtedly usher in even more exciting developments in our battle against exudative (neovascular) AMD. Basic science research into the pathophysiology of AMD and CNV has resulted in, and hopefully will continue to result in, translational discoveries for preventive and innovative targeted treatments against CNV in patients with AMD. Clinical trials investigating the efficacy and safety of these new treatments will continue to decipher useful from non-useful therapy. (The role of clinical studies is further elaborated in the chapter by Walonker and Diddie.) Perhaps, a combination approach using two or more of the following: antiangiogenesis agents, anti-inflammatory therapy, gene therapy and basement membrane stabilizers may one day be preferred treatments for CNV. It is even possible that such agents may some day be used as prophylactic treatment in high risk eyes. Although great progress has been achieved in the last decade, much remains to be done in the battle against visual acuity loss from exudative AMD.

SUMMARY OF MAIN POINTS & & &

&

&

&

Exudative form of AMD is the major cause of visual blindness in patients with AMD. Systemic risk factors associated with CNV include increased age, Caucasian race, smoking. Ocular risk factors associated with increased risk of CNV include large drusen (O5), confluent drusen, hyperpigmentation and hypertension. The simplified AREDS scale predicts the risk of CNV over the next 5 years and 10 based upon the presence of drusen and pigment abnormalities in each eye. Symptoms may be absent in the presence of CNV. Amsler grid testing and PHP may help to detect problems earlier. Prompt evaluation of symptomatic patients is essential for preventing visual loss due to CNV.

&

&

&

& & &

&

&

&

&

& &

FA is used to characterize the location (extrafoveal, juxtafoveal, subfoveal), type of CNV (classic, occultFVPED, LLUS) and to ascertain treatment effects. Signs of CNVinclude subretinal fluid, hard exudates, subretinal hemorrhage or intraretinal hemorrhage, pigmented subretinal lesions, and subRPE fluid. The MPS showed a beneficial effect of laser photocoagulation for extrafoveal or juxtafoveal CNV (classic or well-demarcated forms). Persistent and recurrent CNV risk is high for extrafoveal and juxtafoveal CNV treated with thermal laser. Subfoveal laser should not be used in the current era of effective non-ablative therapy. ICG is useful for evaluating eyes with occult CNV or PEDs, or subretinal hemorrhage. Occult CNV has a better natural history than that of classic CNV. OCTimaging is useful for the detection of intraretinal cystic changes, subretinal fluid, sub-RPE fluid and for monitoring CNV treatment responses. PDT is useful for: (i) eyes with subfoveal CNV that are at least 50% or more classic in composition and (ii) for eyes with subfoveal minimally classic CNV (less than six disc areas) and eyes with occult CNV with visual acuity less than 20/50 and lesion size less than four MPS disc areas. Antiangiogenesis treatments can now result in visual acuity improvements in eyes with subfoveal CNV. Ranibizumab (Lucentis) can results in visual acuity improvement in about one-third of patients with new onset subfoveal CNV. Avastin is being used off-label. The CATT will further investigate the efficacy and safety of Avastin and compare Avastin to Lucentis. Thermotherapy did not prevent moderate visual loss for treated eyes versus placebo in the TTT4CNV study. A subgroup of eyes with 20/100 or worse visual acuity, however, showed some visual benefit compared to placebo. Radiation therapy was not useful in the AMDRT. Other methods radiation therapy (plaque, beta particle) are still being investigated. Clinical trials investigating agents to prevent CNV in high risk eyes are in progress (AREDS 2, AART). Several new avenues of treatment for CNV include VEGF receptor inhibitors, tubulin binding agents, RNA interference and other gene therapy.

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associated with early treatment of neovascular agerelated macular degeneration with pegaptanib sodium: an exploratory analysis. Retina 2005; 25:815–27. Regillo CD, Brown DM, Abraham H, Kaiser PK, Mieler WF. Randomized, double-masked, sham-controlled trial of ranibizumab for neovascular age-related macular degeneration: PIER study year 1. Am J Ophthalmol 2007 (in press). Heier JS, Boyer DS, Ciulla TA, et al. Ranibizumab combined with verteporfin photodynamic therapy in neovascular age-related macular degeneration: year 1 results of the FOCUS Study. Arch Ophthalmol 2006; 124:1532–42. Ferrara N, Hillan KJ, Novotny W. Bevacizumab (Avastin), a humanized anti-VEGF monoclonal antibody for cancer therapy. Biochem Biophys Res Commun 2005; 333:328–35. Salesi N, Bossone G, Veltri E, et al. Clinical experience with bevacizumab in colorectal cancer. Anticancer Res 2005; 25:3619–23. Michels S, Rosenfeld PJ, Puliafito CA, Marcus EN, Venkatraman AS. Systemic bevacizumab (Avastin) therapy for neovascular age-related macular degeneration twelve-week results of an uncontrolled open-label clinical study. Ophthalmology 2005; 112:1035–47. Moshfeghi AA, Rosenfeld P J, Puliafito CA, et al. Systemic bevacizumab (Avastin) therapy for neovascular agerelated macular degeneration: twenty-four-week results of an uncontrolled open-label clinical study. Ophthalmology 2006; 113:2002–11. Rosenfeld PJ, Moshfeghi AA, Puliafito CA. Optical coherence tomography findings after an intravitreal injection of bevacizumab (Avastin) for neovascular age-related macular degeneration. Ophthalmic Surg Lasers Imaging 2005; 36:331–5. Rich RM, Rosenfeld PJ, Puliafito CA, et al. Short-term safety and efficacy of intravitreal bevacizumab (Avastin) for neovascular age-related macular degeneration. Retina 2006; 26:495–511. Godfrey DG, Waldron RG, Capone A, Jr. Transpupillary thermotherapy for small choroidal melanoma. Am J Ophthalmol 1999; 128:88–93. Shields CL, Santos MC, Diniz W, et al. Thermotherapy for retinoblastoma. Arch of Ophthalmol 1999; 117:885–93. Reichel E, Berrocal AM, Ip M, et al. Transpupillary thermotherapy of occult subfoveal choroidal neovascularization in patients with age-related macular degeneration. Ophthalmology 1999; 106:1908–14. Reichel E, Musch DC, Blodi BA, Mainster MA, TTT4CNV Study Group. Results from the TTT4CNV Clinical Trial. Invest Ophthalmol Vis Sci 2005; 46 (E-abstract 2311). Archambeau JO, Mao XW, Yonemoto LT, et al. What is the role of radiation in the treatment of subfoveal membranes: review of radiobiologic, pathologic, and other considerations to initiate a multimodality discussion. Int J Radiat Oncol Biol Phys 1998; 40:1125–36. Del Gowin RL, Lewis JW, Hoak JC, Mueller AL, Gibson DP. Radiosensitivity of human endothelial cells in culture. J Lab Clin Med 1974; 84:42–8. Hosoi Y, Yamamoto M, Ono T, Sakamoto K. Prostacyclin production in cultured endothelial cells is highly sensitive to low doses of ionizing radiation. Int J Radiat Biol 1993; 63:631–8. Sagerman RH, Chung CT, Alterti WE. Radiosensitivity of ocular and orbital structures. In: Alberti WE, Sagerman RH, eds. Radiotherapy of Intraocular and Orbital Tumors. Berlin: Springer, 1993:375–85.

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138. Marcus DM, Peskin E, Maguire M, et al. The age-related macular degeneration radiotherapy trial (AMDRT): one year results from a pilot study. Am J Ophthalmol 2004; 138:818–28. 139. Submacular Surgery Trials Pilot Study Investigators. Submacular surgery trials randomized pilot trial of laser photocoagulation versus surgery for recurrent choroidal neovascularization secondary to age-related macular degeneration: I. ophthalmic outcomes. Am J Ophthalmol 2000; 130(4):387–407. 140. de Juan E, Jr., Loewenstein A, Bressler NM, Alexander J. Translocation of the retina for management of subfovealchoroidal neovascularization II: a preliminary report in humans. Am J Ophthalmol 1998; 125:635–46. 141. Fujii GY, Pieramici D, Humayun MS, et al. Complications associated with limited macular translocation. Am J Ophthalmol 2000; 130:751–62. 142. Lewis H, Kaiser PK, Lewis S, Estafanous M. Macular translocation for subfoveal choroidal neovascularization in age-related macular degeneration: a prospective study. Am J Ophthalmol 1999; 128:135–46. 143. Pertile G, Claes C. Macular translocation with 360 degree retinotomy for management of age-related macular degeneration with subfoveal choroidal neovascularization. Am J Ophthalmol 2002; 134(4):560–5. 144. Mruthyunjaya P, Stinnett SS, Toth CA. Change in visual function after macular translocation with 360 retinectomy for neovascular age-related macular degeneration. Ophthalmology 2004; 111(9):1715–24. 145. Fujikado T, Asonuma S, Ohji M, et al. Reading ability after macular translocation surgery with 360-degree retinotomy. Am J Ophthalmol 2002; 134(6):849–56. 146. Toth CA, Lapolice DJ, Banks AD, Stinnett SS. Improvement in near visual function after macular translocation surgery with 360-degree peripheral retinectomy. Graefes Arch Clin Exp Ophthalmol 2004; 242(2):541–8. 147. Fire A, Xu S, Montgomery MK, Kostas SA, Driver SE, Mello CC. Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature 1998; 391:806–11. 148. Reich SJ, Fosnot J, Kuroki A, et al. Small interfering RNA (siRNA) targeting VEGF effectively inhibits ocular neovascularization in a mouse model. Mol Vis 2003; 9:210–6. 149. Tolentino MJ, Brucker AJ, Fosnot J, et al. Intravitreal injection of vascular endothelial growth factor small interfering RNA inhibits growth and leakage in a nonhuman primate, laser-induced model of choroidal neovascularization. Retina 2004; 24:132–8. 150. Shen J, Samul R, Silva RL, et al. Suppression of ocular neovascularization with siRNA targeting VEGF receptor 1. Gene Ther 2006; 13:225–34. 151. Nguyen QD, Shah SM, Hafiz G, et al. A phase I trial of an IV-administered vascular endothelial growth factor trap for treatment in patients with choroidal neovascularization due to age-related macular degeneration. Ophthalmology 2006; 113:1522–32, 33.

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152. Maier P, Unsoeld AS, Junker B, et al. Intravitreal injection of specific receptor tyrosine kinase inhibitor PTK787/ ZK222 584 improves ischemia-induced retinopathy in mice. Graefes Arch Clin Exp Ophthalmol 2005; 243:593–6. 153. Ozaki H, Seo MS, Ozaki K, et al. Blockade of vascular endothelial cell growth factor receptor signaling is sufficient to completely prevent retinal neovascularization. Am J Pathol 2000; 156:697–707. 154. Nambu H, Nambu R, Melia M, Campochiaro PA. Combretastatin A-4 phosphate suppresses development and induces regression of choroidal neovascularization. Invest Ophthalmol Vis Sci 2003; 44:3650–5. 155. Moore KS, Wehrli S, Roder H, et al. Squalamine: an aminosterol antibiotic from the shark. Proc Natl Acad Sci USA 1993; 90:1354–8. 156. Sills AK, Jr., Williams JI, Tyler BM, et al. Squalamine inhibits angiogenesis and solid tumor growth in vivo and perturbs embryonic vasculature. Cancer Res 1998; 58:2784–92. 157. Ciulla TA, Criswell MH, Danis RP, Williams JI, McLane MP, Holrovd KJ. Squalamine lactate reduces choroidal neovascularization in a laser-injury model in the rat. Retina 2003; 23:808–14. 158. Garcia CA, Connolly B, Thomas E, et al. A phase 2 multi-dose pharmacokinetic study of MSI-1256F (squalamine lactate) for the treatment of subfoveal choroidal neovascularization associated with age-related macular degeneration (AMD). Invest Ophthalmol Vis Sci 2005; 46:E-Abstract 206. 159. Cashman SM, Bowman L, Christofferson J, KumarSingh R. Inhibition of choroidal neovascularization by adenovirus-mediated delivery of short hairpin RNAs targeting VEGF as a potential therapy for AMD. Invest Ophthalmol Vis Sci 2006; 47:3496–504. 160. West CM, Price P. Combretastatin A4 phosphate. Anticancer Drugs 2004; 15:179–87. 161. Vincent L, Kermani P, Young LM, et al. Combretastatin A4 phosphate induces rapid regression of tumor neovessels and growth through interference with vascular endothelial-cadherin signaling. J Clin Invest 2005; 115: 2992–3006. 162. Mori K, Gelbach P, Ando A, McVey D, Wei L, Campochiaro PA. Regression of ocular neovascularization in response to increased expression of pigment epitheliumderived factor. Invest Ophthalmol Vis Sci 2002; 43:2428–34. 163. Rasmussen H, Chu KW, Campochiaro P, et al. Clinical protocol. An open-label, phase I, single administration, dose-escalation study of ADGVPEDF.11D (ADPEDF) in neovascular age-related macular degeneration (AMD). Hum Gene Ther 2001; 2:2029–32. 164. Campochiaro PA, Nguyen QD, Shah SM, et al. Adenoviral vector-delivered pigment epithelium-derived factor for neovascular age-related macular degeneration: results of a phase I clinical trial. Hum Gene Ther 2006; 17:177–9. 165. Kaiser PK. Antivascular endothelial growth factor agents and their development: therapeutic implications in ocular diseases. Am J Ophthalmol 2006; 142:660–8.

Part III: Imaging Techniques for the Clinical Evaluation of Age-Related Macular Degeneration

9 Indocyanine Green Angiography in Age-Related Macular Degeneration Scott C. N. Oliver

Department of Ophthalmology, Rocky Mountain Lions Eye Institute, University of Colorado School of Medicine, Aurora, Colorado, U.S.A.

Antonio P. Ciardella

Department of Ophthalmology, Denver Health Hospital Authority, Denver, Colorado, U.S.A.

Daniela C. A. C. Ferrara, Jason S. Slakter, and Lawrence A. Yannuzzi

The LuEsther T. Mertz Retinal Research Department, Manhattan Eye, Ear, and Throat Hospital, New York, New York, U.S.A.

INTRODUCTION Fluorescein angiography (FA) revolutionized the diagnosis of retinal disorders (1,2). However, there are certain limitations to this technique. Overlying hemorrhage, pigment, or serosanguineous fluid can block underlying pathologic changes and prevent adequate visualization by FA. Indocyanine green (ICG) is a Food and Drug Administration-approved tricarbocyanine dye that has several advantageous properties over sodium fluorescein as a dye for ophthalmic angiography. The clinical usefulness of indocyanine green angiography (ICGA) in the past has been limited by our inability to produce high-resolution images. However, enhanced high-resolution ICG angiograms can now be obtained owing to the technological advance of coupling digital imaging systems to ICG cameras (3,4). Thus, digital ICGA finally allows the theoretical advantages of ICG as an ophthalmic dye to be realized.

SPECIAL PROPERTIES OF ICG The ICG absorbs and fluoresces in the near-infrared range. Owing to the special characteristics of the dye, there is less blockage by the normal eye pigments, which allows enhanced imaging of the choroid and choroidal abnormalities. For example, Geeraets and Berry (5) have reported that the retinal pigment epithelium (RPE) and choroid absorbs 59% to 75% of blue–green (500 nm) light, but only 21% to 38% of near-infrared (800 nm) light. The activity of ICG in the near-infrared range also allows visualization of

pathologic conditions through overlying hemorrhage, serous fluid, lipid, and pigment that may block structures by FA. This property allows enhanced imaging of occult choroidal neovascularization (CNV) and pigment epithelial detachment (PED) in age-related macular degeneration (AMD) (4,6). A second special property of ICG is that it is highly protein-bound (98%). Therefore, less dye escapes from the choroidal vasculature, which allows enhanced imaging of choroidal abnormalities.

HISTORICAL PERSPECTIVES ICG dye was first used in medicine in the mid-1950s at the Mayo Clinic to obtain blood flow measurements (7). In 1956, ICG was used for determining cardiac output and characterizing cardiac valvular and septal defects. In 1964, studies of systemic arteriovenous fistulas and renal blood flow were reported. The finding that exclusively the liver excreted the dye soon led to development of its application for measuring hepatic function. Recently, the use of real-time intraoperative ICGA provided information about vessel patency during neurosurgical aneurysm repair (8,9). ICG first became attractive to ophthalmologists interested in better ways to image the choroidal circulation because of its safety and its particular optical and biophysical properties. Kogure and coworkers (10) in 1970 first performed choroidal absorption angiography in monkeys, using intraarterial ICG injection. The first ICG angiogram in a human was performed by David (11) during carotid angiography.

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In 1971, Hochheimer (12) described choroidal absorption angiography in cats using intravenous ICG injections and black-and-white infrared film instead of color film. One year later, Flower and Hochheimer performed intravenous absorption ICGA for the first time in a human (13,14). These same investigators then described the superior technique of ICG fluorescence angiography (15,16). Further technological improvements followed (17), and, in 1985, Bischoff and Flower (18) reported on their 10-year experience with ICGA, which included 500 angiograms of various disorders. However, the sensitivity of infrared film was too low to adequately capture the low-intensity ICG fluorescence, as the fluorescence efficacy of ICG is only 4% of that of sodium fluorescein. The resolution of ICGA was improved in the mid-1980s by Hayashi and coworkers, who developed improved filter combinations and described ICG videoangiography (19–21). However, their video system lacked freezeframe image recording and possessed cumulative light toxicity potential due to its 300-W continuous halogen lamp illumination. In 1985, Destro and Puliafito (22) described a similar video system. In 1989, Scheider and Schroedel (23) reported the use of the scanning laser ophthalmoscope for ICG videoangiography; refinements of their technique allowed for improved imaging of choroidal neovascular membranes (24,25). In 1992, Guyer and coworkers (3) and Yannuzzi and associates (4) introduced the use of a 1024-line digital imaging system to produce high-resolution enhanced ICG images. These systems have improved the resolution of ICGA such that this technique is now of practical clinical value.

PHARMACOLOGY ICG is a sterile, water-soluble tricarbocyanine dye, which is anhdyro-3,3,3 0 ,3 0 -tetramethyl-1-1 0 -di(4-sulfobutyl)-4,5,4 0 ,5-dibenzoindotricarbocyanine hydroxide sodium salt. Its empirical formula is C 43H 47N 2 NaO 6S 2 and its molecular weight is 775 Daltons (26). It is highly protein-bound (98%). Although it has been thought that ICG is primarily bound to albumin in the serum (27), 80% of ICG in the blood is actually bound to globulins, such as A1lipoproteins (28). ICGs spectral absorption is between 790 and 805 nm (28–30). The dye is excreted by the liver via bile. ICG is not reabsorbed from the liver, is not detected in cerebrospinal fluid (31,32) and does not cross the placenta (33).

TOXICITY ICG is a relatively safe dye, with only a few side effects reported in clinical use (7,27,34–36). In our experience,

it is safer than sodium fluorescein. In contrast to FA, nausea and vomiting are extremely uncommon during ICG angiography. We have observed two serious vasovagal-type reactions during ICGA. No complications were reported in one study using intravenous ICG doses of 150 to 200 mg. No side effects were noted in another series of 700 procedures (18). In a study 1226 consecutive patients undergoing ICGA, there were three (0.15%) mild adverse reactions, four (0.2%) moderate reactions, one (0.05%) severe reaction, and no deaths (36). ICGA should not be performed on patients allergic to iodide, since it contains approximately 5% iodide by weight. In addition, it should not be performed on patients who are uremic (18) or who have impaired hepatic clearance. Appropriate emergency equipment should be readily available, as with FA.

TECHNIQUE OF INJECTION ICGA can be performed immediately before or after FA. We inject intravenously 25 to 50 mg of ICG (Cardio-Green: Hynson, Westcott & Dunning Products, Cockeysville, Maryland, U.S.A.) which has been diluted in the aqueous solvent supplied by the manufacturer. Rapid injection is essential and should be followed by a 5-mL normal saline flush. For wide angle angiography, the dosage is increased to 75 mg. Bindewald and associates (37) recently tested the lower limits fluorescein and ICG dye doses for angiography. Using a confocal scanning laser ophthalmoscope (cSLO) (Heidelberg retina angiograph 2, Heidelberg Engineering, Dossenheim, Germany), they found that a fluorescein dose as low as 166 mg, and an ICG dose as low as 5 mg, allowed adequate resolution for diagnosis and management of neovascular AMD. Resolution was impaired, however, in late phase images, compared to standard doses.

DIGITAL IMAGING SYSTEMS The coupling of a digital imaging system with an ICG camera allows production of enhanced high-resolution (1024-line) images, which are necessary for ICGA. The instantaneous images from these systems produce images which decrease patient waiting time and expedite treatment. Digital imaging systems also allow image archiving, hard-copy generation, and direct qualitative comparison between fluorescein and ICGA findings. These systems are useful for planning preoperative treatment strategies and for monitoring the adequacy of treatment postoperatively. Imaging systems contain film, video, or digital cameras with special antireflective coatings and appropriate excitatory and barrier filters. Flash

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synchronization allows high-resolution image capture. The digitally charged coupling device camera captures the digitized images and transmits them to a digital imaging workstation. These images are captured at one frame per second, stored in buffer memory, and displayed on a high-contrast, high-resolution video monitor. The images can be printed to photographs or slides, transferred via a variety of storage media, or networked to other stations in treatment areas and in other offices.

INTERPRETATION OF ICGA FINDINGS IN AMD Definitions The terminology used to describe the angiographic manifestations of AMD corresponds, with certain exceptions described below, to definitions previously reported by the Macular Photocoagulation Study Group (38). Most relevant to the interpretation of ICGA in AMD are the definitions of serous pigment epithelium detachment (SPED), vascularized pigment epithelial detachment (VPED), classic CNV, and occult CNV (4,19,22,39). Serous Pigment Epithelial Detachment The SPED is an ovoid or circular detachment of the RPE. On FA study there is rapid filling with dye of the fluid in the subRPE space. This corresponds to early hyperfluorescence beneath the PED, which increases in intensity in the late phase of the study resulting in a bright and homogeneous well-demarcated pattern. ICGA reveals a variable, minimal blockage of normal choroidal vessels, more evident in the mid-phase of the angiogram. Thus, a SPED is bright (hyperfluorescent) on FA and dark (hypofluorescent) on ICG. This difference is caused by the fact that ICG molecules are larger and almost completely bound to plasma proteins, which prevents free passage of ICG dye throughout the fenestrated choriocapillaris in the subRPE space. Also, it is important to remember the difference of appearance on ICGA between a SPED in AMD and a SPED in central serous chorioretinopathy (CSC). In fact, in CSC there is increased permeability of the choriocapillaris that causes leakage of ICG molecules under the PED. As a result, a SPED in CSC appears bright (hyperfluorescent) with ICGA. Approximately 1.5% of newly diagnosed patients with exudative AMD present with a pure SPED. Choroidal Neovascularization CNV is defined as a choroidal capillary proliferation through a break in the outer aspect of Bruch’s membrane under the RPE and/or the neurosensory retina. CNV is divided into classic and occult based on the FA angiography appearance.

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Classic CNV Classic CNV is an area of bright, fairly uniform hyperfluorescence identified in the early phase of the FA. The fluorescence increases through the transit phase with leakage of dye obscuring the boundaries of this area by the late phase of the angiogram. With ICGA, a classic CNV has a similar appearance to that seen with FA angiography, but is usually less well delineated (Fig. 1) and exhibits little or no leakage in the late phases of the ICG study. Only 12% of newly diagnosed patients with exudative AMD present with classic CNV. Occult CNV Occult CNV is characterized as either fibrovascular pigment epithelial detachment (FVPED) or late leakage of undetermined source (LLUS). FVPED consists of irregular elevation of the RPE consisting of stippled hyperfluorescence not as bright or discrete as classic CNV within one to two minutes after fluorescein injection, with persistence of fluorescence 10 minutes after injection. LLUS consists of areas of leakage at the level of the RPE in the late phase of the angiogram not corresponding to an area of classic CNV or FVPED discernible in the early or middle phase of the angiogram to account for the leakage. Also any area of blocked fluorescence contiguous to the CNV is considered occult CNV. More than 85% of newly diagnosed patients with exudative AMD present with occult CNV (Fig. 2). Two main types of occult CNV are recognized on ICGA.

Figure 1 Classic choroidal neovascularization. Early phase indocyanine green angiogram shows a well-defined hyperfluorescent vascular network consistent with a classic choroidal neovascular membrane.

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Figure 2 Occult choroidal neovascularization. Midphase fluorescein angiogram (A) demonstrates hyperfluorescent drusen, while the late phase indocyanine green angiogram (B) reveals a hyperfluorescent occult choroidal neovascular membrane.

Without SPED. The first type of occult CNV is caused by subRPE CNV that is not associated with a PED. The early stages of FA study reveal minimal subretinal hyperfluorescence of undetermined source that slowly increases over a period of several minutes to produce an irregular staining of the subRPE tissue. The ICG angiogram reveals early vascular hyperfluorescence and late staining of the abnormal vessels. If the ICG angiographic image has distinct margins, it is considered to be a well-defined CNV on ICGA. Twothird of newly diagnosed patients with an occult CNV present without an associated SPED. With SPED. The second type of occult CNV is associated with a SPED of at least 1-disc diameter in size. Combined CNV and SPED are called a VPED. This lesion is the result of subRPE neovascularization associated with a serous detachment of the RPE. Onethird of newly diagnosed patients with AMD have an associated SPED. The determination of whether a SPED is present is best made on the basis of the FA study. FA may also demonstrate occult vessels as late, indistinct, subretinal hyperfluorescence beneath, or at the margin of the SPED. ICGA reveals early vascular hyperfluorescence and late staining of the CNV. The SPED, as noted previously, is comparatively hypofluorescent, because only minimal ICG leakage occurs beneath the serous detachment. ICG is more helpful than FA in differentiating between a SPED and a VPED. It also permits better identification of the vascularized and serous component of VPEDs. These differentiations between the vascularized and serous components are often not possible with FA alone

because the serous and vascularized portions of a PED demonstrate late hyperfluorescence and leakage respectively. Although fluorescein staining is more intense in the serous portion of the detachment than in the vascularized component, differences in intensity are often too minimal for accurate interpretation. However, the ICG angiographic findings are infinitely more reliable for this differentiation; the serous component of a PED is hypo-32#fluorescent and the vascularized component is hyperfluorescent. Occult CNV is also sub grouped in two types, one with a solitary area of well-defined focal neovascularization (hot spot) and the other with a larger and delineated area of neovascularization (plaque).

Hot Spot (Focal CNV) Focal CNV or a “hot spot” is an area of occult CNV that is both well-delineated and no more than 1-disc diameter in size on ICGA. Also a hot spot represents an area of actively proliferating and more highly permeable areas of neovascularization (active occult CNV). Chorioretnal anastomosis and polypoidaltype CNV may represent two subgroups of hot spots (see below). Plaque A plaque is an area of occult CNV larger than 1-disc diameter in size. A plaque often is formed by latestaining vessels, which are more likely to be quiescent areas of neovascularization that are not associated with appreciable leakage (inactive occult CNV).

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Plaques of occult CNV seems to slowly grow in dimension with time. Well-defined and ill-defined plaques are recognized on ICG study. A well-defined plaque has distinct borders throughout the study and the full extent of the lesion can be assessed. An illdefined plaque has indistinct margins or may be one in which any part of the neovascularization is blocked by blood. In a review of our first 1000 patients with occult CNV by FA, which were imaged by ICGA, we categorized occult CNV into three morphologic categories: focal CNV or hot spots, plaques (well-defined and ill-defined), and combination lesions in which both hot spots and plaques were noted (39). The results of that study are discussed later in this chapter under clinical applications. Two other forms of occult CNV are identified by ICGA: polypoidal choroidal vasculopathy (PCV) and retinal angiomatous proliferation (RAP).

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POLYPOIDAL CHOROIDAL VASCULOPATHY PCV is a primary abnormality of the choroidal circulation characterized by an inner choroidal vascular network of vessels ending in an aneurysmal bulge or outward projection, visible clinically as a reddish orange, spheroid, polyp-like structure. The disorder is associated with multiple, recurrent, serosanguineous detachments of the RPE and neurosensory retina, secondary to leakage and bleeding from the peculiar choroidal vascular abnormality (40,41). ICGA has been used to detect and characterize the PCV abnormality with enhanced sensitivity and specificity (Fig. 3) (42–55). In the initial phases of the ICG study, a distinct network of vessels within the choroid becomes visible. Optical coherence tomography (OCT) (Fig. 3C) delineates the polypoidal extensions of the choroidal vasculature. In patients with juxtapapillary involvement, the vascular channels extend in a radial, arching pattern and are interconnected with smaller spanning branches that become more evident and numerous at the edge of the PCV lesion (Fig. 4). Early in the course of the ICG study, the larger vessels of PCV network start to fill before the retinal vessels, but the area within and surrounding the network is relatively hypofluorescent compared with the uninvolved choroid. The vessels of the network appear to fill more slowly than the retinal vessels. Shortly after the network can be identified on the ICG angiogram, small hyperfluorescent “polyps” become visible within the choroid. These polypoidal structures correspond to the reddish, orange choroidal excrescence seen on clinical examination. They appear to leak slowly as the surrounding hypofluorescent area becomes increasingly

(B)

(C)

Figure 3 Polypoidal choroidal vasculopathy. Color photograph (A) demonstrates hemorrhagic detachment of the macula. Latephase indocyanine green study (B) reveals a peripapillary polyplike vascular network. Note central hypofluorescence indicative of a pigment epithelial detachment. Optical coherence tomography (C) delineates the polypoidal extensions of the choroidal vasculature.

hyperfluorescent. In the later phase of the angiogram there is a uniform disappearance of the dye (“washout”) from the bulging polypoidal lesions. The late ICG staining characteristic of occult CNV is not seen in the PCV vascular abnormality. While the first reports of PCV were in middleaged black females, it is now recognized that PCV may be a variant of CNV seen in white patients with AMD, it may be localized in the macular area without any

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Figure 4 Polypoidal choroidal vasculopathy. Peripapillary hyperfluorescent lesions are apparent in the midphase fluorescein angiogram (A); however, the indocyanine green (B) delineates a more extensive vascular network.

peripapillary component (Figs. 5 and 6), and it may be formed by a network of small branching vessels ending in polypoidal dilation difficult to image without ICGA (Fig. 6). Ahuja and colleagues sought to determine the prevalence of PCV among British patients in their

practice (50). Of 40 consecutive patients with hemorrhagic or exudative PEDs, 34 (85%) were attributed to PCV. Of those with PCV, 65% were female, the mean age was 65 years (range 44–88), 74% were white, 20% black, and 6% Asian. Eight had a history of hypertension. Sixty-eight percent of lesions were located in the macula.

RETINAL ANGIOMATOUS PROLIFERATION

Figure 5 Macular polypoidal choroidal vasculopathy. Midphase indocyanine green angiogram demonstrates a prominent lesion of polypoidal channels in the macula.

RAP is a distinct subgroup of neovascular AMD, manifested by intraretinal neovascularization (IRN) that extends into the deep retinal, subretinal, and subRPE spaces. Clinical evidence of pre-, intra-, or subretinal hemorrhage, sometimes with associated exudates or cystoid macular edema, in the setting of a PED suggests a RAP lesion. Often dilated compensatory vessels perfuse and drain the neovascularization, forming a retinal–retinal anastomosis. Extension of the neovascular complex to the subretinal space may result in a retino-choroidal anastomosis (RCA). On FA, indistinct RPE staining, often with associated PED, resembles occult CNV. Presence of active IRN extending into a PED is difficult to distinguish from a standard VPED. ICG allows better characterization of a VPED, revealing the neovascular hotspot contained within the hypofluorescent PED (Fig. 7A,B). The OCT (Fig. 7C) shows

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Figure 6 Macular polypoidal choroidal vasculopathy. Despite a fundus appearance (A) only of mild pigment epithelial change, the indocyanine green reveals progressive macular hyperfluorescence of polypoidal lesions in the early (B), mid (C) and late (D) phases of the angiogram.

intraretinal cystic changes overlying a PED along with a hyperreflective area suggestive of a RCA. Late intraretinal leakage may arise from the IRN. ICG permits visualization of the direct communication between the retinal and the choroidal components of the neovascularization as they form an RCA (Fig. 8) Lafaut and coworkers (56) documented the histopathology of an RCA, in which neovascularization grows out from the neuroretina into the subretinal space.

Kuhn et al. (57), in 1995, first identified RCA as a potential manifestation of this form of neovascular AMD in the setting of a VPED. With ICGA for enhanced choroidal imaging, this group found RCA in 50 of 186 (28%) patients with AMD and an associated VPED. Slakter et al. (58) detected RCA in 34 of 150 eyes (21%) with occult AMD and a focal hot spot in ICG. Fernandez and coworkers (59) reported a series of 190 patients with neovascular AMD in which ICGA revealed 34 eyes (16%) with RAP lesions.

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Figure 7 Retinal angiomatous proliferation. Fluorescein angiogram (A) indicates a pigment epithelial detachment, while the indocyanine green (B) reveals a focal area of hyperfluorescence adjacent to two retinal arterioles. The optical coherence tomography (C) shows intraretinal cystic changes overlying a pigment epithelial detachment along with a hyperreflective area suggestive of a retino-choroidal anastomosis.

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Yannuzzi and colleagues (60) classified RAP into three stages: stage I involves IRN, stage II results from extension to subretinal neovascularization, and stage III occurs once CNV is documented. Clinical knowledge and recognition of RAP is important because this form of neovascular AMD may have a natural course, visual prognosis, and response to treatment distinct from other forms of neovascular AMD. Different forms of treatment may be preferable

for each stage of the disorder. For example, we have found that an uncomplicated focal area of IRN may be amenable to conventional thermal laser treatment; whereas, a more advanced stage involving a VPED and an RCA is less likely to respond to any form of currently available treatment. Bottoni and colleagues (61) retrospectively reported results of 99 eyes of 81 patients with RAP treated with direct laser photocoagulation of the

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Figure 8 Retinal angiomatous proliferation (RAP) vasculature. Retino-choroidal anastomosis stands out in this indocyanine green angiogram (A) that reveals a larger underlying choroidal neovascularization. Optical coherence tomography (B) of this stage III RAP lesion demonstrates vessels from a low neurosensory detachment diving towards a subretinal choroidal neovascular membrane.

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vascular lesion, laser photocoagulation of the feeder retinal arteriole, scatter gridlike laser photocoagulation, photodynamic therapy (PDT), or transpupillary thermotherapy. Complete obliteration was achieved in 24 (57%) cases of stage I lesions (73% closure from direct laser and 45% closure from PDT, 11 (26%) of stage II lesions (38% closure from scatter gridlike photocoagulation and 17% closure from direct photocoagulation of the vascular lesion), and only 3 (15%) of stage III lesions. The uncontrolled use of therapeutic interventions in this study makes it difficult to draw definitive conclusions about a superior treatment modality, but the study makes clear the difficulty in effectively treating more advanced stages of RAP. More recent series using PDT alone or PDT with triamcinolone confirm the challenge in effectively treating RAP lesions. Boscia and colleagues (62) treated 21 eyes with stage II or III RAP using PDT alone and reported an overall decline in vision from 20 out of 80 to 20 out of 174, stabilization of vision in six eyes (29%), occlusion of RAP and PED flattening in three eyes (14%), and an RPE tear in four eyes (19%). Nicolo and colleagues (63) reported 10 eyes with stage II RAP treated with 20 mg of intravitreal triamcinolone acetonide (IVTA) followed one month later by PDT. All patients experienced flattening of the PED prior to PDT, six patients (60%) showed improved vision of at least three early treatment of diabetic retinopathy study (ETDRS) lines at three, six, and nine months, and four patients (40%) maintained visual improvement at 12 months. PDT with a photosensitizing dye such as verteporphin may have a different effect on RAP than on classic-CNV or occult-CNV lesions (64,65). Given the tendency for ICG dye to stain the retina in eyes with RAP, there is a possibility that similar staining may occur with the verteporphin molecule, theoretically predisposing the retina to photochemical damage when exposed to the excitatory light used in PDT. This possibility is speculative, since verteporphin has not yet been imaged successfully with good spatial and temporal definition in the human. Because eyes with RAP are generally classified as pure occult CNV based on FA, it is possible that patients with RAP were actually treated in the treatment of age-related macular degeneration with photodynamic therapy (TAP) trial (65). ICGA was not used in the TAP trial, so the frequency of RAP in the subset of patients classified as occult-CNV is unknown. Future studies of AMD that use ICG will be able to delineate between these two distinct forms of macular degeneration.

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CLINICAL APPLICATION OF ICGA TO THE STUDY OF AMD Patz and associates (26) were the first to study CNV by ICG videoangiography. They could resolve only 2 of 25 CNVs with their early model. Bischoff and Flower (18) studied 100 ICG angiograms of patients with AMD. They found “delayed and/or irregular choroidal filling” in some patients. The significance of this finding is unclear, however, because these authors did not include an age-matched control group. Tortuous vessels and marked dilation of macular choroidal arteries, often with loop formation, were also observed. Hayashi and associates (19,21) found that ICG videoangiography was useful in the detection of CNV. ICG videoangiography was able to confirm the fluorescein angiographic appearance of CNV in patients with well-defined CNV. It revealed a more welldefined neovascularization in 27 eyes with occult CNV by FA. In a subgroup of patients with poorly defined occult CNV, the ICG angiogram, but not the FA, imaged a well-defined CNV in 9 of 12 (75%) cases. ICG videoangiography of the other three eyes revealed suspicious areas of neovascularization. Hayashi and coworkers (19,21) were also the first to show that leakage from CNV with ICG was slow compared to the rapid leakage of sodium fluorescein. While the results of these investigators concerning ICG videoangiographic imaging of occult CNV were promising, the spatial resolution that they could obtain was limited by the 512-line video monitor and analog tape of their ICG system. Destro and Puliafito (22) reported that ICG videoangiography was particularly useful in studying occult CNV with overlying hemorrhage and recurrent CNV. Guyer and coworkers (3) used a 1024-line digital imaging system to study patients with occult CNV. These authors reported that ICG videoangiography was useful in imaging occult CNV and that this technique could allow photocoagulation of otherwise untreatable lesions. Scheider and coinvestigators (25) have reported enhanced imaging of CNV in a study of 80 patients using the scanning laser ophthalmoscope with ICG videoangiography. Yannuzzi and associates (4) have shown that ICGA is extremely useful in reclassifying occult CNV into “well-defined CNV.” In their study, 39% of 129 patients with occult CNV were reclassified as welldefined CNV based on information added by ICGA. Five of seven (72%) cases of occult CNV with SPED were reclassified as “well demarcated” CNV by ICG. In 17 of 38 (45%) VPED cases and in 11 of 19 (58%) combined VPED and SPED cases, ICGA allowed occult CNV to be reclassified as well defined CNV. These authors concluded that ICGA was especially

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useful in identifying occult CNV in patients with SPED or with recurrent CNV. Lim et al. found that ICG demonstrated welldemarcated hyperfluorescence in 50% of eyes thought to have occult CNV by FA and in 82% of eyes with PED (66). Baumal et al. found that ICG demonstrated underlying CNV in 19 of 23 eyes (83%) with an isolated PED and in 21 of 21 eyes (100%) with PED and occult CNV (67). Yannuzzi and coworkers (68) studied with ICGA 235 consecutive AMD patients with occult CNV and associated VPED. These eyes were divided into two groups, depending on the size and delineation of the CNV. Of the 235 eyes 89 (38%) had a solitary area of neovascularization that was well delineated, no more than 1-disc diameter in size, and defined as focal CNV. The other 146 (62%) eyes had a larger area of neovascularization, with variable delineation defined as a plaque CNV. In a further report, 657 consecutive eyes with occult CNV determined by FA were studied with ICGA. Of 413 eyes with occult CNV without pigment epithelium detachments, focal areas of neovascularization were noted in 89 (22%). Overall, 142 (34%) eyes had lesions that were potentially treatable by thermal laser photocoagulation based on additional information provided by ICGA. Of the 235 eyes with occult CNV and VPEDs, 98 (42%) were eligible for photocoagulation therapy based on ICGA findings. The authors calculated that ICGA enhances the treatment eligibility by approximately one-third (69). In a expanded series (39) the same authors reported their results on ICGA study of 1000 consecutive eyes with occult CNV by FA. They recognized three morphologic types of CNV, which included focal spots, plaques (well defined and poorly defined), and combination lesions (in which both focal spots and plaques are noted). Combination lesions were further subdivided into marginal spots (focal spots at the edge of plaque of neovascularization), overlying spots (hot spots overlying plaques of neovascularization), or remote spots (a focal spot remote from a plaque of neovascularization). The relative frequency of these lesions was as follows: focal spots 29%, plaques 61% consisting 27% of well-defined plaques and 34% of poorly defined plaques, and combination lesions 8%, consisting of 3% of marginal spots, 4% of overlying spots and 1% of remote spots (39). A follow-up study from the same authors of patients with newly diagnosed unilateral occult CNV secondary to AMD showed that the patients tended to develop the same morphologic type of CNV in the fellow eye (70). Chang et al. (71) reported on the clinicopathologic correlation of AMD with CNV detected by ICGA. Histopathologic examination of the lesion revealed a

thick subRPE CNV corresponding to the plaque-like lesion seen with ICGA. Watzke and colleagues analyzed 104 consecutive AMD patients to determine the sensitivity of ICG in detecting lesions originally identified by FA (72). ICG hyperfluorescence was present in 87% of eyes with classic CNV and in 93% of eyes with fibrovascular pigment epithelium detachments (FVPEDs). Of eyes diagnosed with LLUS by FA, 50% were hyperfluorescent and 50% were isofluorescent by ICG. Additionally, three fellow eyes with dry AMD had hyperfluorescent lesions by ICG, but it is unknown whether these eyes progressed to neovascular AMD. Finally, Lee et al. (73) reported on 15 eyes with surgically excised subfoveal CNV that underwent preoperative and postoperative ICGA. All excised membranes were examined by light microscopy, and all surgically excised ICG-imaged membranes corresponded to subRPE and subneurosensory CNV. The above studies demonstrate that ICGA is an important adjunctive study to FA in the detection of CNV. FA is more sensitive than ICGA in imaging fine capillaries that connect larger vessels and capillaries at the proliferating edge of well-defined CNV. While FA images well-defined CNV better than ICGA in some cases, ICGA allows reclassification of FA-defined occult CNV into well-demarcated CNV eligible for ICG-guided thermal laser treatment in about 30% of cases (74). The best imaging strategy to thoroughly classify CNV is the combination of FA and ICGA. Helbig et al. studied 502 patients using simultaneous FA and ICG to characterize AMD, and found that 3% of eyes had a hot spot within an occult lesion, 4% had plaques within an occult lesion, 9% had RAP, and 6% had PCV (75). Yanagi and colleagues (76) compared simultaneous fluorescein and ICG injection with FA-guided ICGA, in which FA was used to detect an area of leakage, allowing a lower dose ICG injection and focusing the ICG detector only on the lesion in question. Overall detection of feeder vessels (FVs) was similar between the simultaneous and FA-guided ICG groups, but the latter group required lower quantities of ICG and had shorter examination times. The benefits of simultaneous procedures, such as convenience and accurate diagnosis of treatable cases, must be weighed against the disadvantages of increased cost and adverse effects.

RECURRENT CNV IN AMD Recurrent CNV following photocoagulation treatment is a major cause of treatment failure. Although most recurrences can be detected and imaged with clinical biomicroscopic examination and FA, a significant number of patients demonstrate new exudative

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manifestations and visual symptoms without a clearly defined area of recurrent neovascularization identified by FA. These patients may exhibit diffuse staining and leakage at the site of previous treatment or may demonstrate no FA evidence of recurrence despite the new exudative manifestations identified clinically. ICGA has proven to be often useful in detecting the recurrence. Sorenson et al. (77) reported the use of ICGguided laser treatment in 66 cases of recurrent occult CNV secondary to AMD. Only 29 (44%) were eligible for laser retreatment, and of these 29 eyes 18 (62%) had anatomic success with an average follow-up of six months (54). Similar results were reported by Reichel et al., who reported 58 eyes with recurrent CNV from AMD (78). In 14 eyes (24%), a well-defined recurrent CNV could be identified by evaluating the fluorescein angiogram. In 6 (14%) of the remaining 44 eyes, a welldefined recurrent CNV was identifiable by ICGA. However, clinical evidence of recurrence must accompany a hot spot detected by ICG. Chen and colleagues (79) performed ICGA two weeks after krypton laser treatment on 230 consecutive eyes with exudative AMD. Forty patients (18%) developed ICG hot spots after treatment, and these hot spot spontaneously resolved without development of CNV in 31 patients. Recurrent CNV was present at the hot spot in four patients and away from the hot spot in five patients.

ICG-ASSOCIATED TREATMENT STRATEGIES FOR CNV IN AMD In the past, patients were considered potentially eligible for laser photocoagulation therapy by ICG guidance if they had clinical and FA evidence of occult CNV. Of the two types of occult CNV identifiable by ICG study, hot spots and plaques, direct laser photocoagulation was recommended only to hot spots. In fact as mentioned above, hot spots represent areas of actively leaking neovascularization that can be obliterated by laser photocoagulation in attempt to eliminate the associated serosanguineous complications, and stabilize or improve the vision. On the contrary, plaques seem to represent a thin layer of neovascularization, which is not actively leaking, and which may benefit from PDT (80) or intravitreal antiangiogenic agents (81–86). In the case of a lesion comprised of a hot spot and a plaque, and in which the hot spot is at the margin of the plaque (that may extend under the fovea), laser photocoagulation to the extrafoveal hot spot spares the fovea. This treatment approach was successful in obliterating the CNV and stabilizing the vision in 56% of a consecutive series of AMD patients (74). On the contrary we have had poor success with

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direct laser treatment of hot spots overlying plaques, or confluent treatment of the entire plaque. Slakter and associates (87) performed ICGguided laser photocoagulation in 79 eyes with occult CNV. The occult CNV was successfully eliminated with stabilized or improved visual acuity in 29 (66%) of 44 eyes with occult CNV associated with neurosensory retinal elevations, and in 15 (43%) of 35 eyes with occult CNV associated with PED. This study demonstrated that in some cases ICGA imaging can successfully guide laser photocoagulation of occult CNV. Another pilot study of ICG-guided laser treatment of occult CNV had similar results (88). Guyer and coworkers (74) reported a pilot study with ICG-guided laser photocoagulation of 23 eyes with occult CNV secondary to AMD with focal spots at the edge of a neovascular plaque of the ICG study. ICG-guided laser photocoagulation was applied solely to the focal spot at the edge of the plaque. At 24 months of follow-up anatomic success with resolution of the exudative findings was obtained in 6 (37.5%) of 16 eyes. Importantly, these studies set the foundation for future prospective studies of ICG-guided laser treatment. In addition, they proved that the presence of a PED is a poor prognostic factor in the treatment of exudative AMD. Lim et al. reported the visual acuity outcome after ICGA-guided laser photocoagulation of CNV associated with PED in 20 eyes with AMD (89). At three months after laser photocoagulation, visual acuity had improved two or more Snellen lines in two eyes (10%), worsened by two or more lines in 10 (50%), and remained unchanged in eight of 20 (40%). At nine months after laser photocoagulation, visual acuity had improved by two or more lines in one eye (9%), worsened by two or more lines in nine (82%), and remained unchanged in one of 11 (9%). They concluded that ICG-guided laser photocoagulation may temporarily stabilize visual acuity in some eyes with CNV associated with PED, but final visual acuity decreases with time. More recently, Da Pozzo and associates evaluated the efficacy of ICG-guided photocoagulation in 86 eyes with occult CNV and a hot spot on ICG (90). Of the 53 eyes without PED, 32 (60%) had stable or improved vision at one year, but 27 (51%) had recurrence of the CNV. Of the 33 eyes with PED, only five (15%) had stable or improved vision at one year, and 23 (70%) had CNV recurrence. Another potential therapeutic application using ICG is ICG dye-enhanced diode laser photocoagulation. The peak absorption of ICG (795 to 810 nm) is at a similar wavelength as the peak emission of the diode laser (805 nm). Thus, dye-enhanced laser photocoagulation may allow selective ablation of the ICG-containing CNV with relative sparing of the

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normal neighboring retina. However, leakage of ICG into the intraretinal space, which occurred in 11% of 149 eyes in a series reported by Ho and colleagues, may be a contraindication to ICG dye-enhanced diode photocoagulation (91). A pilot study by Reichel and associates of 10 patients with poorly defined CNV resulted in closure of the CNV in all cases, but a severe immediate vision loss occurred in one patient (92). A larger series by Obana et al. studied 38 eyes with classic or occult CNV, and found that CNV occlusion was achieved in 92% of eyes, with and 18% recurrence rate over an average follow-up of 26 months (93). Ten eyes (26%) showed improved visual acuity, 16 (42%) showed no change, and 12 eyes (32%) worsened. A pilot study by Arevalo et al. compared ICG dye-enhanced diode laser photocoagulation alone with dye-enhanced laser combined with IVTA (94). In their initial series of 19 eyes selected irrespective of lesion subtype, none of the 9 eyes receiving combination therapy required retreatment at seven months, while 4 of 10 eyes receiving ICG dyeenhanced laser alone needed retreatment. A follow up paper by the same group reported 31 eyes treated with dye-enhanced laser and 4 mg of IVTA followed for a mean of nine months (95). Nineteen eyes (61%) showed stable vision, seven eyes (23%) improved, and five eyes (16%) worsened. In the occult subgroup, however, the proportion of patients who worsened was greater (33%). No severe acute vision loss was reported. Topically treatable glaucoma occurred in five eyes.

NEW TECHNIQUES IN ICG ANGIOGRAPHY Recent advances in ICGA are real-time angiography, contrast enhancement ICGA, wide-angle angiography, digital subtraction-indocyanine green (DS-ICG) angiography, dynamic ICG-guided FV laser treatment of CNV, ICGA for dry AMD, and use of cSLO-ICG.

Contrast Enhanced ICG Angiography Contrast enhancement of ICG angiographic images using digital imaging software may enhance the diagnostic sensitivity and specificity of the study. Maberley and Cruess compared nonenhanced and contrastenhanced ICG angiographic images of 50 consecutive patients with occult CNV from AMD (96). Only 36% of the nonenhanced images demonstrated well-defined membranes, whereas 58% were well defined with the contrast-enhanced images. Real-Time ICGA Real-time ICGA (97) uses a modified Topcon 50IA camera with a diode laser illumination system that

has an output at 805 nm (Topcon 50IAL camera), can produce images at 30 frames per second, and allows continuous recording. The images can be acquired either as a videotape, or as single image at a frequency of 30 images per second. To make printed copies of these images single frames are digitized, but the resolution is limited to 640 by 480 pixels.

Wide-Angle ICGA Wide-angle images of the fundus can be obtained by performing ICG videoangiography with the aid of wide angle contact lenses. The contact lenses used are the Volk SuperQuad 160, the Volk Quadraspheric, or the Volk Transequator (Volk, Mentor OH). Because the image formed by these lenses lies about 1 cm in front of the lens, the fundus camera is set on A or C so that the camera is focused on the image plane of the contact lens. This technique allows instantaneous imaging of a large area of the fundus. The combined use of the contact lens and of the laser illumination system in a high-speed digital fundus camera allows realtime imaging of a 1608 of field of view. Staurenghi and colleagues recently developed a combined contact and noncontact system to achieve wide-field images up to 1508 with a cSLO ICG (98). Digital Subtraction-Indocyanine Green Angiography DS-ICGA uses DS of sequentially acquired ICG angiographic frames to image the progression of the dye front in the choroidal circulation (99,100). A method of pseudocolor imaging of the choroid allows differentiation and identification of choroidal arteries and veins. DS-ICGA allows imaging of occult CNV with greater detail and in a shorter period of time than with conventional ICGA. Matsumoto et al. performed DS-ICGA on 20 patients with CNV accompanied by subretinal hemorrhage (101). In six of the 20 eyes, DS-ICGA distinguished hyperfluorescence due to a slowly expanding, poorly defined, large lesion from simple leakage with a well-defined lesion. The DS-ICGA technique made clear the expanding wave of hyperfluorescence from a more slowly filling, illdefined lesion. FV Therapy Staurenghi et al. (102) considered a series of 15 patients with subfoveal CNVM in whom FVs could be clearly detected by means of dynamic ICGA but not necessarily with FA. Based on the pilot study, the authors simultaneously reported a second series of 16 patients with FVs smaller than 85 mm. FV were treated with argon green laser. The ICGA was repeated

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immediately after treatment, and at two, seven, and thirty, and then every three months, to assess FV closure. A FV that remained patent was immediately retreated, and ICGA follow-up started again. In the pilot study, 40% of FVs were successfully occluded; this result was affected by the width and number of FVs. The occlusion success rate in the second series, with FVs under 85 mm, was 75%. The authors concluded that dynamic ICGA may detect small FVs that are more successfully occluded by argon photocoagulation.

ICG FOR DRY AMD Hanutsaha et al. studied 432 patients by ICG with exudative AMD in one eye and drusen without exudation in the fellow eye (103). Eighty-nine percent of eyes with drusen had normal fluorescence on ICG, while 11% of eyes with drusen had focal hot spots or hyperintense plaques. Over an average follow-up of 22 months, 27% of eyes with drusen and an abnormal ICG developed CNV, while only 10% of drusen eyes and a normal ICG developed exudative AMD. The authors suggested that ICG may be a predictive indicator of future exudative changes in eyes with drusen. Patchy and slow choroidal filling on FA, in association with reduced choroidal fluorescence on ICGA, was associated by Pauleikoff and associates with early changes in AMD (104). One hundred eyes with early AMD were studied for the above characteristics, termed a prolonged choroidal filling phase (PCFP), which was associated with confluent drusen in the study eye, focal RPE atrophy in the study eye, and geographic atrophy in the fellow eye. The group postulated that PCFP was a clinical indicator of Bruch membrane deposits and a predictor for geographic atrophy from AMD. Ultra-late phase ICGA, performed 24 hours after dye injection, demonstrates hypofluorescent geographic lesions in patients with both exudative and dry AMD, as shown by Mori and associates. They demonstrated that 95% of AMD eyes with CNV had geographic hypofluorescent lesions, and that all CNV detectable by FA or ICG was contained within these lesions. In 73% of eyes without CNV, the same geographic areas were present, while agematched normal subjects did not have the lesions. Mean fluorescence intensity was higher in a normal group older than 62 years, compared to normal subjects less than 36 years. The authors postulated that these geographic hypofluorescent areas may represent areas predisposed to CNV development.

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CONFOCAL SCANNING LASER OPHTHALMOSCOPE ICG With the relatively recent availability of cSLO to perform ICG, many retinal physicians are choosing this modality over high-speed digital angiography because of the ability to use the cSLO for other functions, such as autofluorescence and FA. Gelisken and colleagues simultaneously compared cSLO ICG with high-resolution fundus camera ICG in 100 eyes with occult CNV (105). Confocal SLO was superior in delineating vessel architecture of the neovascular lesion; however fundus photography was much more sensitive than cSLO in detecting focal lesions (52% vs. 37%, respectively) and plaques (35% vs. 13%, respectively).

CONCLUSION The role ICGA in the treatment of AMD is in evolution. As photocoagulation of extrafoveal CNV gave way to treatment of all types of CNV with PDT, ICG angiography has proven very useful in adding information to FA about lesion subtype. The ability of ICG to identify subtypes of occult CNV, such as VPED, hot spots, plaques, and RCA, allows targeted and sometimes effective therapy for these refractory types of CNV. Given that approximately 87% of new CNV from AMD is minimally classic or occult (106), many patients have derived some benefit from the additional information obtainable by ICGA. The approval of pegaptanib sodium (Macugen) heralded a new era in AMD treatment (81). Shown to be equally efficacious for all lesion subtypes, pegaptanib was a departure from traditional laser-based, destructive procedures. Ranibizumab (Lucentis) has been shown to be even more efficacious and beavcizumab (Avastin) appears to show similar results to ranibizumab (82–85). Further research is necessary to determine whether lesion subtype remains an important predictor of treatment response with these new modalities. A systematic evidence based review of the PubMed indexed literature in English or with an English abstract yielded a strong recommendation for the use of ICGA for the following conditions: PCV, occult CNV, neovascularization associated with PED, and recurrent choroidal neovascular membranes (107). The same review reported only modest evidence supporting the use of ICGA for routine choroidal neovascular membranes and for identifying FVs in AMD. Future advances in ICGA, such as wide angle, real-time, and DS techniques may improve our diagnostic ability in AMD.

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SUMMARY POINTS &

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&

&

ICGA is a useful adjunctive technique to FA for the diagnosis of AMD. This is especially true in the presence of occult CNV. ICG allows better recognition of subtypes of occult CNV such as VPED, hot spots, plaques and retinal-choroidal anastomosis. ICGA is useful in the diagnosis of PCV, RAP, and recurrent choroidal neovascular membranes. Preliminary studies suggested that ICG-guided laser photocoagulation was beneficial in the treatment of CNV prior to the era of antivascular endothelial growth factor therapy. Further research is necessary to improve our understanding of all the information obtained by ICGA and its potential role in new therapeutic regimens. Real-time ICGA, wide-angle ICGA, and DS-ICGA may improve our diagnostic ability in AMD.

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34. Leevy CM, Smith F, Kiernan T. Liver function test. In: Bockus HL, ed. Gastroenterology. 3rd ed., Vol. 3. Philadelphia, PA: Saunders, 1976:68. 35. Shabetai R, Adolph RJ. Principles of cardiac catheterization. In: Fowler NO, ed. Cardiac Diagnosis and Treatment. 3rd ed. Hagerstown, MD: Harper & Row, 1980:117. 36. Hope-Ross M, Yannuzzi LA, Gragoudas ES, et al. Adverse reactions due to indocyanine green. Ophthalmology 1994; 101(3):529–33. 37. Bindewald A, Stuhrmann O, Roth F, et al. Lower limits of fluorescein and indocyanine green dye for digital cSLO fluorescence angiography. Br J Ophthalmol 2005; 89(12):1609–15. 38. Macular Photocoagulation Study Group. Occult choroidal neovascularization. Influence on visual outcome in patients with age-related macular degeneration. Arch Ophthalmol 1996; 114(4):400–12. 39. Guyer DR, Yannuzzi LA, Slakter JS, et al. Classification of choroidal neovascularization by digital indocyanine green videoangiography. Ophthalmology 1996; 103(12):2054–60. 40. Kleiner RC, Brucker AJ, Johnston RL. The posterior uveal bleeding syndrome. Retina 1990; 10(1):9–17. 41. Yannuzzi LA, Sorenson J, Spaide RF, Lipson B. Idiopathic polypoidal choroidal vasculopathy (IPCV). Retina 1990; 10(1):1–8. 42. Spaide RF, Yannuzzi LA, Slakter JS, Sorenson J, Orlach DA. Indocyanine green videoangiography of idiopathic polypoidal choroidal vasculopathy. Retina 1995; 15(2):100–10. 43. Phillips WB, II, Regillo CD, Maguire JI. Indocyanine green angiography of idiopathic polypoidal choroidal vasculopathy. Ophthalmic Surg Lasers 1996; 27(6):467–70. 44. Yannuzzi LA, Ciardella A, Spaide RF, Rabb M, Freund KB, Orlock DA. The expanding clinical spectrum of idiopathic polypoidal choroidal vasculopathy. Arch Ophthalmol 1997; 115(4):478–85. 45. Yannuzzi LA, Nogueira FB, Spaide RF, et al. Idiopathic polypoidal choroidal vasculopathy: a peripheral lesion. Arch Ophthalmol 1998; 116(3):382–3. 46. Moorthy RS, Lyon AT, Rabb MF, Spaide RF, Yannuzzi LA, Jampol LM. Idiopathic polypoidal choroidal vasculopathy of the macula. Ophthalmology 1998; 105(8):1380–5. 47. Schneider U, Gelisken F, Kreissig I. Indocyanine green angiography and idiopathic polypoidal choroidal vasculopathy. Br J Ophthalmol 1998; 82(1):98–9. 48. Yannuzzi LA, Wong DW, Sforzolini BS, et al. Polypoidal choroidal vasculopathy and neovascularized agerelated macular degeneration. Arch Ophthalmol 1999; 117(11):1503–10. 49. Yannuzzi LA, Freund KB, Goldbaum M, et al. Polypoidal choroidal vasculopathy masquerading as central serous chorioretinopathy. Ophthalmology 2000; 107(4):767–77. 50. Ahuja RM, Stanga PE, Vingerling JR, Reck AC, Bird AC. Polypoidal choroidal vasculopathy in exudative and haemorrhagic pigment epithelial detachments. Br J Ophthalmol 2000; 84(5):479–84. 51. Escano MF, Fujii S, Ishibashi K, Matsuo H, Yamamoto M. Indocyanine green videoangiography in macular variant of idiopathic polypoidal choroidal vasculopathy. Jpn J Ophthalmol 2000; 44(3):313–6. 52. Uyama M, Wada M, Nagai Y, et al. Polypoidal choroidal vasculopathy: natural history. Am J Ophthalmol 2002; 133(5):639–48. 53. Sho K, Takahashi K, Yamada H, et al. Polypoidal choroidal vasculopathy: incidence, demographic features, and clinical characteristics. Arch Ophthalmol 2003; 121(10): 1392–6.

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70. Chang B, Yannuzzi LA, Ladas ID, Guyer DR, Slakter JS, Sorenson JA. Choroidal neovascularization in second eyes of patients with unilateral exudative age-related macular degeneration. Ophthalmology 1995; 102(9):1380–6. 71. Chang TS, Freund KB, de la Cruz Z, Yannuzzi LA, Green WR. Clinicopathologic correlation of choroidal neovascularization demonstrated by indocyanine green angiography in a patient with retention of good vision for almost four years. Retina 1994; 14(2):114–24. 72. Watzke RC, Klein ML, Hiner CJ, Chan BK, Kraemer DF. A comparison of stereoscopic fluorescein angiography with indocyanine green videoangiography in age-related macular degeneration. Ophthalmology 2000; 107(8):1601–6. 73. Lee BL, Lim JI, Grossniklaus HE. Clinicopathologic features of indocyanine green angiography-imaged, surgically excised choroidal neovascular membranes. Retina 1996; 16(1):64–9. 74. Guyer DR, Yannuzzi LA, Ladas I, Slakter JS, Sorenson JA, Orlock D. Indocyanine green-guided laser photocoagulation of focal spots at the edge of plaques of choroidal neovascularization. Arch Ophthalmol 1996; 114(6):693–7. 75. Helbig H, Niederberger H, Valmaggia C, Bischoff P. Simultaneous fluorescein and indocyanine green angiography for exudative macular degeneration. Klin Monatsbl Augenheilkd 2005; 222(3):202–5. 76. Yanagi Y, Tamaki Y, Sekine H. Fluorescein angiographyguided indocyanine green angiography for the detection of feeder vessels in subfoveal choroidal neovascularization. Eye 2004; 18(5):474–7. 77. Sorenson JA, Yannuzzi LA, Slakter JS, Guyer DR, Ho AC, Orlock DA. A pilot study of digital indocyanine green videoangiography for recurrent occult choroidal neovascularization in age-related macular degeneration. Arch Ophthalmol 1994; 112(4):473–9. 78. Reichel E, Pollock DA, Duker JS, Puliafito CA. Indocyanine green angiography for recurrent choroidal neovascularization in age-related macular degeneration. Ophthalmic Surg Lasers 1995; 26(6):513–8. 79. Chen CJ, Chen LJ, Miller KR. Clinical significance of postlaser indocyanine green angiographic hot spots in age-related macular degeneration. Ophthalmology 1999; 106(5):925–9 (discussion 929–31). 80. Photodynamic Therapy Study Group. Verteporfin therapy of subfoveal choroidal neovascularization in age-related macular degeneration: two-year results of a randomized clinical trial including lesions with occult with no classic choroidal neovascularization-verteporfin in photodynamic therapy report 2. Am J Ophthalmol 2001; 131(5): 541–60. 81. Gragoudas ES, Adamis AP, Cunningham ET, Jr., Feinsod M, Guyer DR. Pegaptanib for neovascular agerelated macular degeneration. N Engl J Med 2004; 351(27):2805–16. 82. Avery RL, Pieramici DJ, Rabena MD, Castellarin AA, Nasir MA, Giust MJ. Intravitreal bevacizumab (Avastin) for neovascular age-related macular degeneration. Ophthalmology 2006; 113(3):363–72. e5. 83. Michels S, Rosenfeld PJ, Puliafito CA, Marcus EN, Venkatraman AS. Systemic bevacizumab (Avastin) therapy for neovascular age-related macular degeneration twelve-week results of an uncontrolled open-label clinical study. Ophthalmology 2005; 112(6):1035–47. 84. Spaide RF, Laud K, Fine HF, et al. Intravitreal bevacizumab treatment of choroidal neovascularization secondary to age-related macular degeneration. Retina 2006; 26(4):383–90.

85. Heier JS, Antoszyk AN, Pavan PR, et al. Ranibizumab for treatment of neovascular age-related macular degeneration: a phase I/II multicenter, controlled, multidose study. Ophthalmology 2006; 113(4):642. e1–4. 86. Rosenfeld PJ, Heier JS, Hantsbarger G, Shams N. Tolerability and efficacy of multiple escalating doses of ranibizumab (Lucentis) for neovascular age-related macular degeneration. Ophthalmology 2006; 113(4):632.e1. 87. Slakter JS, Yannuzzi LA, Sorenson JA, Guyer DR, Ho AC, Orlock DA. A pilot study of indocyanine green videoangiography-guided laser photocoagulation of occult choroidal neovascularization in age-related macular degeneration. Arch Ophthalmol 1994; 112(4):465–72. 88. Regillo CD, Benson WE, Maguire JI, Annesley WH, Jr. Indocyanine green angiography and occult choroidal neovascularization. Ophthalmology 1994; 101(2):280–8. 89. Lim JI, Aaberg TM, Capone A, Jr., Sternberg P, Jr. Indocyanine green angiography-guided photocoagulation of choroidal neovascularization associated with retinal pigment epithelial detachment. Am J Ophthalmol 1997; 123(4):524–32. 90. Da Pozzo S, Parodi MB, Ravalico G. A pilot study of ICG-guided laser photocoagulation for occult choroidal neovascularization presenting as a focal spot in agerelated macular degeneration. Int Ophthalmol 2001; 24(4):187–94. 91. Ho AC, Yannuzzi LA, Guyer DR, Slakter JS, Sorenson JA, Orlock DA. Intraretinal leakage of indocyanine green dye. Ophthalmology 1994; 101(3):534–41. 92. Reichel E, Puliafito CA, Duker JS, Guyer DR. Indocyanine green dye-enhanced diode laser photocoagulation of poorly defined subfoveal choroidal neovascularization. Ophthalmic Surg 1994; 25(3):195–201. 93. Obana A, Gohto Y, Nishiguchi K, Miki T, Nishi S, Asada A. A retrospective pilot study of indocyanine green enhanced diode laser photocoagulation for subfoveal choroidal neovascularization associated with age-related macular degeneration. Jpn J Ophthalmol 2000; 44(6):668–76. 94. Arevalo JF, Mendoza AJ, Fernandez CF. Indocyanine green-mediated photothrombosis with and without intravitreal triamcinolone acetonide for subfoveal choroidal neovascularization in age-related macular degeneration: a pilot study. Retina 2005; 25(6):719–26. 95. Arevalo JF, Garcia RA, Mendoza AJ. Indocyanine greenmediated photothrombosis with intravitreal triamcinolone acetonide for subfoveal choroidal neovascularization in age-related macular degeneration. Graefes Arch Clin Exp Ophthalmol 2005; 243(11):1180–5. 96. Maberley DA, Cruess AF. Indocyanine green angiography: an evaluation of image enhancement for the identification of occult choroidal neovascular membranes. Retina 1999; 19(1):37–44. 97. Spaide RF, Orlock DA, Herrmann-Delemazure B, et al. Wide-angle indocyanine green angiography. Retina 1998; 18(1):44–9. 98. Staurenghi G, Viola F, Mainster MA, Graham RD, Harrington PG. Scanning laser ophthalmoscopy and angiography with a wide-field contact lens system. Arch Ophthalmol 2005; 123(2):244–52. 99. Miki T, Shiraki K, Kohno T, Moriwaki M, Obana A. Computer assisted image analysis using the subtraction method in indocyanine green angiography. Eur J Ophthalmol 1996; 6(1):30–8. 100. Spaide RF, Orlock D, Yannuzzi L, et al. Digital subtraction indocyanine green angiography of occult choroidal neovascularization. Ophthalmology 1998; 105(4):680–8.

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10 Optical Coherence Tomography in the Evaluation and Management of Age-Related Macular Degeneration David Eichenbaum and Elias Reichel

New England Eye Center, Tufts University School of Medicine, Boston, Massachusetts, U.S.A.

The widespread use of optical coherence tomography (OCT) has changed the way ophthalmologists evaluate and treat age-related macular degeneration (AMD). OCT has been added to the armamentarium of macular imaging that now includes color fundus photography, fluorescein angiography (FA), and indocyanine green angiography. Although each of these modalities is important in the management of macular degeneration, OCT provides useful information regarding retinal structure. Cross-sectional imaging with commercially available units gives an axial resolution of 10 to 15 mm, and ultrahigh resolution OCT (UHR-OCT) provides 2- to 3-mm resolution. This data can be used in the diagnosis and management of AMD; reliance on OCT as part of the decision making process in treatment with different antivascular endothelial growth factor (VEGF) agents is rapidly becoming standard of care.

OCT IMAGING PRINCIPLES AND THE NORMAL OCT IMAGE The different layers of the retina have a characteristic appearance on the OCT scan. The principle used in creating OCT images is Michelson interferometry, which uses the property of light passing through the eye and producing different reflections from different cell layers. A split beam of infrared light in commercially available OCT units reflects light from the layers of the retina and interacts with light reflected from a reference mirror (1). The interference pattern produced is digitally processed and the false-color map shown on the scan is a representation of the reflection characteristics of the cells in each layer, with hyperreflective areas being bright and hyporeflective areas being dark. When compared to in vivo specimens, layers of relative high reflectivity correspond to horizontally aligned retinal components (2). The innermost layers of the retina, the nerve fiber layer, and ganglion cells, are bright on the false-color map. As the scan progresses to the outer retina, the

more densely packed nuclear layers are hyporeflective and dark, and the horizontally oriented plexiform layers are hyperreflective and bright. In the outermost retina, the photoreceptors are hyporeflective, although the junction between the inner segment (IS) and outer segment (OS), as best visualized with UHR-OCT, is bright. The outermost layers, those further distal than the OS of the photoreceptors, are hyperreflective and bright, and pathologic studies have shown the tissues responsible for this signal are the basement membrane of the retinal pigment epithelium (RPE) and the inner choroid (3). The OCT image also reflects the topographical shape of the normal retina, and the OCT software can combine the topographical radial scans to create a volumetric measurement of retinal tissue. The retinal thickness is displayed on a separate false color map, with cool colors (greens and blues) representing areas of less retinal volume, and warm colors (yellows and reds) representing areas of greater retinal volume. The normal foveal depression of the umbo is visible on topographic and volumetric OCT, and the quantitative thickness of a normal fovea can be compared with known approximate normal central field (central 1-mm diameter) thickness, which is about 175 mm (4,5).

OCT in Assessment of Choroidal Neovascularization in AMD OCT can help characterize retinal pathology, even when this information is difficult to discern on clinical examination or angiography. It is possible to define the location of choroidal neovascular membranes above or below the RPE. Solid fibrous tissue can be differentiated from subretinal fluid when these findings may be angiographically equivocal. Other features of AMD, including cystoid macular edema (CME), drusenoid RPE detachments and RPE tears can be imaged by OCT (6). Optical coherence is useful for quantitative assessment of retinal thickness and subretinal fluid when associated with choroidal neovascularization (CNV). A characteristic appearance of CNV has also

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Figure 3 Cross-sectional optical coherence tomography appearance of eye in Figures 1 and 2 revealing hyporeflective subretinal fluid and thickening of adjacent layer just anterior to the intensely hyperreflective retinal pigment epithelium. There is essentially preservation of the normal foveal anatomy and only a minimal increase in retinal thickness.

been described, consisting of thickening and fragmentation of the reflective layer corresponding to the RPE and choriocapillaris (Figs. 1–3) (7). The extent and location of subretinal fluid associated with CNV can be used to assess whether the pathology is subfoveal, as long as there is preservation of some foveal architecture (8). As noted on clinical examination and FA, CME is frequently associated with CNV in wet AMD (9). However, the presence of CME may be difficult to definitively diagnose through those modalities alone. In addition to imaging subretinal fluid, OCT is effective in identifying intraretinal edema, compared to

both clinical stereoscopic images (10) and FA (3,11). The appearance of CME on OCT images is seen as hyporeflective, dark spaces within retinal tissue. Its presence is important clinically, since CME as seen on OCT scan in wet AMD correlates with decreased visual acuity (Figs. 4–7) (9). RPE detachments and sub-RPE neovascularization has been associated with occult CNV in AMD as defined histopathologically. This finding has been corroborated in studies using OCT imaging. In one series, new neovascular AMD lesions were characterized as occult or classic according to their angiographic findings (12). OCT scans of those same lesions revealed subretinal opacities separate from the RPE present in over 87% of lesions characterized as classic and only 13% of lesions characterized as occult. OCT findings consistent with RPE detachment were present in none of the lesions characterized as classic and in one-third of those characterized as

Figure 2 Fluorescein angiography of the eye in Figure 1 exhibiting classic choroidal neovascularization.

Figure 4 Transit phase fluorescein angiography of a right eye exhibiting a large neovascular membrane.

Figure 1 Color picture of choroidal neovascularization in a patient’s left eye.

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Figure 7 Topographical optical coherence tomography map of the lesion shown in Figures 4–6, showing marked thickening of retinal tissue.

Figure 5 Recirculation phase fluorescein angiography of the same eye as Figure 4 revealing late leakage and cystoid macular edema from the membrane.

occult (13). The relationship of CNV and RPE detachments has been further elucidated in another OCT series, and a pattern of double RPE detachments separated by a notch, as well as highly reflective tissue beneath the dome of the RPE detachment have been correlated with CNV that was observed on angiography (Figs. 8–11) (14).

OCT in Assessment of Non-exudative Macular Degeneration Although the utility of commercially available OCT scanning in the clinical diagnostic setting has been examined mostly for neovascular AMD, there are characteristic OCT findings in nonneovascular forms of AMD. “Drusenoid” RPE detachments, which appear angiographically as staining of drusen,

Figure 6 Cross-sectional optical coherence tomography (OCT) of the lesion in Figures 4 and 5, revealing large hyporeflective spaces typical of cystoid edema. It is present with thickening and fragmentation of the hyperreflective layer corresponding to the retinal pigment epithelium, which is the characteristic OCT appearance of choroidal neovascularization.

are documented by OCT as elevations of the pigment epithelium itself (Figs. 12–14) (15). The UHR-OCT is an experimental imaging modality which builds upon the interferometry principles of commercially available OCT imaging devices. The standard OCT axial resolution of 10 to 15 mm is improved to 3 mm using a femtosecond titanium-sapphire laser with a broader bandwidth. This improvement in resolution allows for better delineation and characterization of changes within the intraretinal layers, especially the IS and OS photoreceptors and the IS–OS junction (also known as the external limiting membrane) (16,17), which are the site of many early changes in AMD. In UHR-OCT, the outermost retina is seen as the hyperreflective RPE underlying hyporeflective OS photoreceptors, which

Figure 8 Color picture of a left eye showing a complex neovascular membrane. Lesion components include a large retinal pigment epithelium detachment, subretinal blood, and subretinal exudate.

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Figure 11 Cross-sectional optical coherence tomography of the lesion in Figures 12–14. There is diffuse retinal thickening and numerous hyporeflective spaces consistent with severe cystoid macular edema. There is a small amount of subretinal fluid. The retinal pigment epithelium (RPE) detachment is very apparent, underlying the retina and the hyperreflective band corresponding to the RPE. Figure 9 Transit phase of the eye shown in Figure 12. There is some early filling of a superotemporal retinal pigment epithelium detachment with relative hypofluorescence of the central, neovascular component of the lesion.

are in turn distinguished from hyporeflective IS photoreceptors by the intensely hyperreflective IS–OS junction. UHR-OCT has been used to evaluate eyes with dry AMD and subtle patterns associated with drusen have been observed. One pattern shows changes similar to those seen with drusen in commercially available OCT, with the RPE excrescences overlying reflective material consistent with drusen. A second patter seen on UHR-OCT in dry AMD is a saw-toothed

Figure 10 Late recirculation phase of the eye shown in Figures 12 and 13. There has been filling of the retinal pigment epithelium detachment, as well as filling of cystoid spaces in the center of the macula. There is leakage from the central and inferior occult choroidal neovascularization and blockage from the subretinal blood.

configuration or bunching of the RPE. This pattern is seen associated with atrophy of the inner and outer photoreceptors and the outer nuclear layer, although there is no change in retinal tissue further inward (Fig. 15A–C). The third UHR-OCT pattern in dry AMD shows discrete nodular drusen which actually disrupt as opposed to distort the RPE and are associated with collections of reflective material. This third pattern corresponds to large hard drusen that are observed on clinical examination. Patients with dry AMD can have all three patterns present, or a variety of combinations. A very small percentage of patients in the series of dry AMD eyes studied with UHR-OCT were noted to have findings consistent with early CNV, despite no clinical or angiographic evidence

Figure 12 Color picture of a right eye showing moderate pigment atrophy centrally and confluent soft drusen.

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Figure 13 Recirculation phase fluorescein angiography of the eye shown in Figure 12. There is staining of the soft drusen and transmission of dye fluorescence through the retinal pigment epithelium atrophy.

of CNV. This finding is particularly interesting, as very early diagnosis of neovascular AMD may be facilitated by UHR imaging (18). Geographic atrophy has also been examined, both with conventional OCT and UHR-OCT. A typical pattern of geographic atrophy consisting of enhanced reflectivity of the choroid and significant thinning of overlying retinal tissue has been described using conventional OCT. The bright, well demarcated signal of the choroid is felt to be due to loss of the RPE, a common feature of geographic atrophy that has been well described in histopathologic studies (19). These findings are similar to those seen on UHR-OCT, with associated generalized retinal thinning and increased reflectivity from tissue below the absent RPE, which is likely choriocapillaris (19).

Figure 14 Cross-sectional optical coherence tomography of the eye shown in Figures 13 and 14. There are sub-RPE hyporeflective spaces typical of “drusenoid” RPE detachments. There is preservation of the retinal architecture. Of note, there is a mild epiretinal membrane.

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OCT in the Treatment of AMD The ability of OCT to accurately map and quantitate retinal findings has added an entirely new dimension for monitoring the response of neovascular AMD to treatment. Prior to OCT, qualitative clinical examination and FA were the only means by which one could assess disease progression, stability, or regression. In addition to the quantitative accuracy of OCT, its noninvasive nature, and absent risk of allergic response, OCT appears to be surpassing the use of angiographic techniques as the test of choice for visitto-visit monitoring of neovascular AMD. (See also Chapter 11 on quantitative imaging). Visudyne photodynamic therapy (PDT), which has been a Food and Drug Administration (FDA) approved treatment for neovascular AMD since 2000, was the first new AMD treatment introduced in the era of OCT, and the first pharmacologic treatment for CNV secondary to AMD. OCT findings 6- and 12-month following the initiation of CNV treatment with PDT show macular thickness declining after treatment, but did not show a decrease in the thickness of the CNV following treatment. However, that same study also found that OCT has an excellent sensitivity but only a fair specificity for monitoring CNV activity, though it served as a useful adjunct for verifying intraretinal or subretinal fluid, especially when angiography was inconclusive (20). Many of PDT effects have been shown by OCT, including a transient increase in intraretinal and subretinal fluid in the first week after treatment (21), which has also been described as an early response stage in an OCT grading system developed to monitor treatment by PDT and help clarify angiographic changes seen after treatment (22). Pegaptanib (Macugenw) is a new class of drug for neovascular AMD, a molecular agent known as an aptamer, which targets VEGF isoform 165. OCT has been used to evaluate patients’ response to this therapy. Since the introduction of pegaptanib treatment, OCT has been used to document complications of therapy, and RPE rips have been documented with OCT after a single pegaptanib treatment of CNV with turbid pigment epithelial detachments (23,24). (It is important to note that RPE rips have also been documented with thermal laser treatment (25) and PDT treatment (26) of CNV, as well as other anti-VEGF agents including bevacizumab and ranibizumab.) Evaluation of eyes treated with a single intravitreal injection of pegaptanib showed that there was no difference in OCT anatomy compared to baseline (27). OCT has played a pivotal role in the introduction of VEGF inhibitors in the treatment of neovascular AMD. Following the initial treatment of neovascular AMD with systemic bevacizumab (28), a full-length antibody approved by the FDA for the treatment of

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Figure 15 (A) Color photo of a left eye with retinal pigment epithelium (RPE) changes and pigment clumping. (B) Ultrahigh resolution optical coherence tomography (UHR-OCT) showing thickening and bunching of the RPE. There is a loss of both the outer segment (OS) and inner segment (IS) of the photoreceptors, with a fragmenting of the IS–OS junction. Intraretinal pigment migration is noted by the arrow. (C) Stratus OCT showing less distinction of intraretinal pigment migration. The photoreceptors cannot be distinguished, although the thickening of the RPE remains apparent. Abbreviations: IS, inner segment; OS, outer segment Source: From Ref. 18.

colon cancer, studies of intravitreal bevacizumab emerged in the ophthalmic literature supporting this off-label treatment. The results of intravitreal bevacizumab were also striking, with initially a single case report (29) followed by small prospective studies showing OCT evidence of improvement or resolution of intraretinal, subretinal, and sub-RPE fluid in a large percentage of patients as early as four weeks

after treatment that was also associated with improvement in visual acuity. Treatment effects persisted up to 12 weeks after treatment (30–32). In all of these studies, OCT results supported anatomical efficacy of treatment. The PrONTO study, a small, single center, prospective, nonrandomized efficacy study, showed that patients given a “loading dose” of ranibizumab

Figure 16 Optical coherence tomography of the baseline lesion, showing hyperreflective retinal pigment epithelium (RPE) detachments, thickening of the tissue adjacent to the RPE, and intraretinal hyporeflective fluid with thickening of retinal tissue. The first treatment with intravitreal ranibizumab is administered.

Figure 17 Optical coherence tomography one month after the fourth ranibizumab treatment. There is complete resolution of the intraretinal and sub-retinal pigment epithelium (RPE) fluid, no subretinal scarring, and a normal contour to the retinal tissue. Note that the RPE band has a normal thickness to it.

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monthly for three months and then given a customized dosing scheme based upon visual acuity and OCT findings had equivalent efficacy compared to monthly dosing with ranibizumab after one year of follow-up (33). This study is remarkable because it allowed a variable dosing regimen for all types of lesions at the discretion of the treating physician that was primarily guided by OCT. The following sequence (Figs. 16 and 17) is an example of a ranibizumab treatment of CNV with OCT used as guidance to retreat.

CONCLUSIONS OCT has the ability to verify the presence of neovascular disease and quantitatively evaluate treatment response. The utility of OCT as a guide for treatment is suggested by early clinical experience from many centers and results from the PrONTO study. Further studies using UHR-OCT may determine the role of screening high risk eyes for the early detection of neovascular AMD. OCT has been utilized as supportive data in some trials for the treatment of macular degeneration, though its incorporation as a key endpoint in the evaluation of treatments for neovascular AMD has yet to be conclusively established. OCT will continue to be a key component in the evaluation, treatment and development of new therapeutic modalities in patients with AMD.

SUMMARY POINTS &

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Cross-sectional imaging with commercially available units give an axial resolution of 10 to 15 mm, and UHR-OCT provides 2- to 3-mm resolution. OCT is useful to verify the presence of neovascular disease and quantitatively evaluate treatment response as suggested by clinical trials experience. Further studies using UHR-OCT may determine the role of screening high risk eyes for the early detection of neovascular AMD. OCT will continue to be a key component in the evaluation, treatment and development of new therapeutic modalities in patients with AMD.

REFERENCES 1. Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science 1991; 254:1178–81. 2. Toth CA, Narayan DG, Boppart SA, et al. A comparison of retinal morphology viewed by optical coherence tomography and by light microscopy. Arch Ophthalmol 1997; 115:1425–8.

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3. Ghazi N, Dibernardo C, Ying HS, Mori K, Gehlbach PL. Optical coherence tomography of enucleated human eye specimens with histological correlation: origin of the outer “red line”. Am J Ophthalmol 2006; 141:719–26. 4. Hee MR, Puliafito CA, Duker JS, et al. Topography of diabetic macular edema with optical coherence tomography. Ophthalmology 1998; 105:360–70. 5. Massin P, Erginay A, Haouchine B, Mehidi AB, Paques M, Gaudric A. Retinal thickness in healthy and diabetic subjects measured using optical coherence tomography mapping software. Eur J Ophthalmol 2002; 12:102–8. 6. Voo I, Mavrofrides EC, Puliafito CA. Clinical applications of optical coherence tomography for the diagnosis and management of macular diseases. Ophthalmol Clin North Am 2004; 17:21–31. 7. Hee MR, Baumal CR, Puliafito CA, et al. Optical coherence tomography of age-related macular degeneration and choroidal neovascularization. Ophthalmology 1996; 103:1260–70. 8. Jaffe GJ, Caprioli J. Optical coherence tomography to detect and manage retinal disease and glaucoma. Am J Opthalmol 2004; 137:156–69. 9. Ting TD, Oh M, Cox TA, Meyer CH, Toth CA. Decreased visual acuity associated with cystoid macular edema in neovascular age-related macular degeneration. Arch Ophthalmol 2002; 120:731–7. 10. Strom C, Sander B, Larsen N, Larsen M, Lund-Andersen H. Diabetic macular edema assessed with optical coherence tomography and stereo fundus photography. Invest Ophthalmol Vis Sci 2002; 43:241–5. 11. Antcliff RJ, Stanford MR, Chauhan DS, et al. Comparison between optical coherence tomography and fundus fluorescein angiography for the detection of cystoid macular edema in patients with uveitis. Ophthalmology 2000; 107:593–9. 12. Treatment of Age-Related Macular Degeneration with Photodynamic Therapy (TAP) Study Group. Photodynamic therapy of subfoveal choroidal neovascularization in agerelated macular degeneration with verteporfinone-year results of 2 randomized clinical trials-TAP report. Arch Ophthalmol 1999; 117:1329–45. 13. Hughes EH, Khan J, Patel N, Kashani S, Chong NV. In vivo demonstration of the differences between classic and occult neovascularization using optical coherence tomography. Am J Ophtalmol 2005; 139:344–6. 14. Sato T, Iida T, Hagimura N, Kishi S. Correlation of optical coherence tomography with angiography in retinal pigment epithelial detachments associated with age-related macular degeneration. Retina 2004; 24:910–4. 15. Emfietzoglou I, Grigoropoulos V, Kipioti A, Alimisi S, Theodossiadis PG, Theodossiadis GP. Optical coherence tomography appearance of “drusenoid” pigment epithelial detachments. Ophthalmic Surg Lasers Imaging 2005; 36:147–50. 16. Drexler W, Morgner U, Ghanta RK, Ka¨rtner FX, Schuman JS, Fujimoto JG. Ultrahigh-resolution optical coherence tomography. Nat Med 2001; 7:502–7. 17. Drexler W, Sattmann H, Hermann B, et al. Enhanced visualization of macular pathology with the use of ultrahigh-resolution optical coherence tomography. Arch Ophthalmol 2003; 121:695–706. 18. Pieroni CG, Witkin AJ, Ko TH, et al. Ultrahigh resolution optical coherence tomography in non-exudative age related macular degeneration. Br J Ophthalmol 2006; 90:191–7. 19. Hassenstein A, Ru¨hl R, Richard G. Optical coherence tomography in geographic atrophy—a clinicopathological study. Klin Monatsbl Augenheilkd 2001; 218:503–9.

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20. Salinas-Alama´n A, Garcı´a-Layana A, Maldonado MJ, SainzGo´mez C, Alva´rez-Vidal A. Using optical coherence tomography to monitor photodynamic therapy in age related macular degeneration. Am J Ophthalmol 2005; 140:23–8. 21. Ozdemir H, Karacorlu SA, Karacorlu M. Early optical coherence tomography changes after photodynamic therapy in patients with age related macular degeneration. Am J Ophthalmol 2006; 141:574–6. 22. Rogers AH, Martidis A, Greenberg PB, Puliafito CA. Optical coherence tomography findings following photodynamic therapy of choroidal neovascularization. Am J Ophthalmol 2002; 134:566–76. 23. Dhalla MS, Blinder KJ, Tewari A, Hariprasad SM, Apte RS. Retinal pigment epithelial tears following intravitreal pegaptanib sodium. Am J Ophthalmol 2006; 141:752–4. 24. Singh RP, Sears JE. Retinal pigment epithelial tears after pegaptanib injection for exudative age-related macular degeneration. Am J Ophthalmol 2006; 142:160–2. 25. Gass JDM. Retinal pigment epithelial rip during krypton red laser photocoagulation. Am J Ophthalmol 1984; 98:700–6. 26. Gelisken F, Inhoffen W, Partsch M, Schneider U, Kreissig I. Retinal pigment epithelial tear after photodynamic therapy for choroidal neovascularization. Am J Ophthalmol 2001; 131:518–20. 27. Schuman S, Rogers AH, Duker JS, Reichel E, Baumal CR. Six-week outcomes after pegaptanib. Ophthalmology 2006; 113:501.

28. Michels S, Rosenfeld PJ, Puliafito CA, Marcus EN, Venkatraman AS. Systemic bevacizumab (Avastin) therapy for neovascular age-related macular degeneration: twelveweek results of an uncontrolled open-label clinical study. Ophthalmology 2005; 112:1035–47. 29. Rosenfeld PJ, Moshfeghi AA, Puliafito CA. Optical coherence tomography findings after an intravitreal injection of bevacizumab (Avastin) for neovascular age-related macular degeneration. Ophthalmic Surg Lasers Imaging 2005; 36:331–5. 30. Avery RL, Pieramici DJ, Rabena MD, Castellarin AA, Nasir MA, Giust MJ. Intravitreal bevacizumab (Avastin) for neovascular age-related macular degeneration. Ophthalmology 2006; 113:363–72. 31. Spaide RF, Laud K, Fine HF, et al. Intravitreal bevacizumab treatment of choroidal neovascularization secondary to age-related macular degeneration. Retina 2006; 26:383–90. 32. Rich RM, Rosenfeld PJ, Puliafito CA, et al. Short-term safety and efficacy of intravitreal bevacizumab (Avastin) for neovascular age-related macular degeneration. Retina 2006; 26:495–511. 33. Rosenfeld PJ. An OCT-guided variable-dosing regimen with Lucentis(TM) (ranibizumab) in neovascular AMD: one year results from the PrONTO study. In: Program and abstracts of the 24th Annual American Society of Retina Specialists and 6th Annual European Vitreoretinal Society Meeting. Cannes, France, September 9–13, 2006.

11 Quantitative Retinal Imaging Daniel D. Esmaili

Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A.

Roya H. Ghafouri

Department of Ophthalmology, Boston University Medical Center, Boston University School of Medicine, Boston, Massachusetts, U.S.A.

Usha Chakravarthy

The Queen’s University of Belfast and Royal Hospitals, Belfast, Northern Ireland

Jennifer I. Lim

University of Illinois School of Medicine, Department of Ophthalmology, Eye and Ear Infirmary, UIC Eye Center, Chicago, Illinois, U.S.A.

INTRODUCTION Historically, clinical ophthalmology developed rapidly as the transparency of the ocular media permitted direct examination of the intraocular structures. The development of methods to examine the fundus of the eye considerably improved the understanding of retinal anatomy, structure, and circulation. Consequently, great advantages were gained in the diagnosis of retinal disease and comprehension of systemic disorders. The development of innovative imaging techniques such as fluorescein and indocyanine green angiography followed by tomographic image capture has further improved the examination of the retina and its vasculature. These advances have allowed ophthalmologists to better describe retinal diseases and to develop classification systems in areas such as diabetic retinal disease and age-related macular degeneration (AMD). Investigators, for example, have developed systematic grading systems based on stereoscopic examination of color fundus and angiographic images to characterize disease progression and response to therapy (1,2). However, these classification systems are descriptive and categorical. By contrast, other medical specialties have made enormous strides in the development of quantitative methods to both describe and categorize diseases and to assess the efficacy of intervention. For example, an internist can use quantifiable markers such as blood pressure, cholesterol, and cardiac ejection fraction to predict patients at highest risk for a cardiovascular event and then offer preventive

treatments. Likewise, neurologists can image the brain with precision and accuracy to identify volumetric changes in tumor size and contour. Similar advances in retinal imaging are clearly possible and a number of quantitative methods are currently being developed. To understand the complexities of the tissue layers and vasculature that can be imaged, it is necessary to review the various imaging modalities and techniques for interpretation that are currently available.

FUNDUS PHOTOGRAPHY Color fundus photography has been a significant tool in the documentation of macular disease for many years (1,2). Clinical trials have used photographic documentation to ensure quality assurance and adherence to standards. Advances in image capture, allowing the transition from film-based photography to high-resolution digital acquisition, have resulted in many advantages. First, retrieval of information is easier. Second, computer-assisted image analysis can be easily applied. Third, parametric descriptors can be developed. All these contribute toward providing greater accuracy, objectivity, and reproducibility. Application of quantitative techniques to evaluate eyes with AMD is becoming a reality. Quantitative techniques are useful for evaluating the type and number of drusen and retinal pigment epithelium pigmentary changes, both of which are key features of early AMD (3,4). The careful analysis of drusen number, size, area, and morphology allows clinicians to assess

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disease severity and may aid in predicting conversion from non-neovascular to neovascular forms (5). The goals of quantifying macular pathology such as drusen are multifactorial. Quantified data provide objective information that can be compared over time, giving an index of progression. Such data can be used to evaluate the response to treatment as well as to grade disease progression. Quantification of drusen would also allow for better designed epidemiological and clinical studies of the natural history of AMD. Manual grading is the oldest form of photographic quantitation and is accurate, although labor and resource intensive (1,2). Currently, several semiautomated and automated modalities have been developed to address the shortcomings of manual grading (6–9). Shin and coworkers describe a supervised method of automated drusen grading with good correlation to manual grading, with interclass correlation coefficients of 0.92 and 0.93 (10). Semiquantitative methods have also been shown to have good interobserver reproducibility by graders at different institutions (11). Several limitations have prevented the widespread adoption of such technology. To date, no automated system free of observer supervision exists that can accurately and reproducibly assess drusen burden. Obstacles that have limited progress in this field include difficulties in distinguishing features such as soft drusen with indistinct borders from other pale retinal lesions. The presence of branching and crossing points in retinal blood vessels also detract from detection of drusen as the former produce dark haloes around the lighter retinal background. This phenomenon causes lesion thresholds to be calculated below retinal backgrounds, thus creating a propensity for the false detection of drusen (8). A major technical obstacle has been accounting for differences in macular reflectivity (6). As one moves toward the central macula, normal background reflectivity decreases in intensity. Thus, if there existed identical soft drusen, with one located in the central macula and the other parafoveally, the difference in normal background reflectance would affect the threshold at which the drusen could be detected. Semi-automated methods based on the geometry of fundus reflectance as well as newer, more automated technology utilizing mathematical modeling to reconstruct and then level the background reflectance are being explored to overcome such limitations (6,12). The lack of true automation may limit the utility of drusen quantification in clinical practice. However, an automated method that is precise and reproducible would allow large-scale population-based studies to be performed with fewer resource implications. Furthermore, the technology could also be applied in trials assessing therapeutic interventions.

OPTICAL COHERENCE TOMOGRAPHY Optical coherence tomography (OCT) was first described by Huang and colleagues as a method of utilizing near infrared light to provide a noninvasive means of evaluating ocular structures including the retina (13). In many ways, OCT is an ideal modality for obtaining quantifiable data for the evaluation of retinal pathology (14). The current generation of OCT scanners is able to provide topographic numerical determinations of retinal thickness, which in recent years has become an increasingly popular means of evaluating disease and, particularly, the localization of fluid within the different tissue layers of the fundus (15,16). The role of OCT in quantifying changes due to AMD has yet to be established. This may partly be due to the fact that OCT is a relatively new modality, and that until recent years, the drive to create a numerical index of disease was perceived as irrelevant since treatment options were less than satisfactory. Currently, new therapeutic modalities leading to impressive improvements in visual acuity have been introduced in the management of neovascular AMD. OCT is now recognized as having an important role in the measurement of retinal thickness and subretinal pathology in monitoring choroidal neovascularization (CNV) activity after appropriate therapy (17). With an increasing number of treatment options available including combination therapies, a quantifiable understanding of the therapeutic response will be needed to allow meaningful comparisons of the morphological and functional outcomes. The potential role of quantitative OCT in neovascular AMD is substantial. Automated image analysis algorithms are being developed to better define retinal layers (18). Software like the OCTOR system developed at the Doheny Eye Institute allows for delineation of retinal layers as well as pathologic entities such as subretinal fluid, area occupied by choroidal neovascular membranes, and the size of serous retinal pigment epithelial detachments. This software is currently employed as a research tool to evaluate the efficacy of various treatment modalities in neovascular AMD.

FLUORESCEIN ANGIOGRAPHY Fluorescein angiography (FA) is a well-established modality for assessment of neovascular AMD. Quantitative FA can also provide similar benefits as OCT in the management and treatment of AMD. Current software allows for the measurement of neovascular membrane size, which is a parameter that can influence the therapeutic outcome. One such example is the use of photodynamic therapy (PDT) in the treatment

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of occult CNV. Optimal outcomes were detected in eyes with lesions smaller than four disc diameters, while larger lesions were associated with a worse outcome than natural history (19). Semi-automated detection and quantification of hyperfluorescent leakage has been described by Phillips et al., who manipulated digitized fluorescein angiograms via gradient threshold and regiongrowing techniques to detect leakage (20). This method superimposes paired images (early and late angiograms) to produce a composite with the area of leakage mapped onto a frame. A numerical value can then be determined to describe a total edema value. Chakravarthy et al. (21) have described quantitative FA to assess the multiple pathological components of CNV using a unique algorithm that subtracts the background and adds a term for the positive change in fluorescence corrected to background [positive fluorescence quotient (PFQ)]. This work has shown that the PFQ for CNV and leakage are important determinants of visual function, and are better correlated with functional measures such as visual acuity and reading ability. Shah and coworkers used quantitative methods to demonstrate the utility of quantitating the amount of hyperfluorescence intensity and area seen on FA images of AMD patients before and after treatment for CNV (22). The investigators used image processing to measure the area of hyperfluorescence and fluorescence intensity above background fluorescence. Values for each image were plotted against time after dye injection to generate curves. Each area under the curve (AUC) was calculated. The investigators found an 11% decrease in AUC for fluorescence area and a 32% decrease in AUC for fluorescence intensity in the patients who clinically improved with treatment, but increases of 131% and 292% in the patients who worsened after PDT. Similarly, a 38% decrease in AUC for fluorescence intensity and a 19% decrease in AUC for fluorescence area were observed in patients who received vascular endothelial growth factor trap compared with increases of 66% (pZ 0.004, Mann–Whitney U-test) and 21% (pZ0.07) for patients who received placebo. FA quantification is still being developed and will undoubtedly serve as a means to furnish important clinical information regarding the progression of AMD. Like quantified fundus photography and OCT, developments in computer technology hold the promise of creating truly automated methods to better understand retinal pathology.

MICROPERIMETRY Microperimetry, also known as fundus perimetry, is a noninvasive method by which focal areas of retinal

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sensitivity loss can be measured in those with macular disease. Several systems are currently in practice, including the scanning laser ophthalmoscope (Rodenstock, Germany) and the Micro Perimeter 1 (Nidek Technologies, Italy) (23). By integrating real-time fundus imaging and computerized threshold perimetry, these systems can provide fixation control by accounting for eye movement disturbances that can be common in patients with central visual loss. As a result, this technology can provide point-to-point correlation of the area and magnitude of retinal sensitivity loss at a precise location in the macula. In other words, this technology serves to delineate absolute and relative scotomas while allowing for elucidation of preferential fixation location and fixation stability. Traditionally, distance visual acuity has been the gold standard for assessment of macular function in those with AMD. Although visual acuity is a useful and easily assessed parameter, it does not provide a complete description of visual function, and correlations with self-reported visual functioning are generally poor. Performance in daily activities such as reading are better correlated to the integrity of the central visual field (24). Microperimetry has shown itself to be a useful tool in assessing the functional deficits due to AMD beyond that of visual acuity as it generates information on the location and depth of relative and absolute scotomas. For example, this technology has revealed changes in retinal sensitivity over drusen (25). Sunness and coworkers have also described changes in fixation patterns and quantified the area of scotomas in those with geographic atrophy (26,27). Microperimetry has proved useful in the evaluation of neovascular AMD. Absolute scotomas have been measured over CNV, subretinal hemorrhage, and chorioretinal scars (28). Fujii and colleagues evaluated the characteristics of visual loss in subfoveal CNV and suggest that functional deterioration may begin with a mild decrease in retinal sensitivity that later evolves into fixation instability and eventual absolute central scotoma with subsequent eccentric fixation (29). This technology has also been used to assess macular function following treatment. Schmidt-Erfurth et al. quantified the size of absolute and relative scotomas in patients with CNV at baseline and following treatment with PDT (30). Microperimetry has also been applied to assess functional changes with other treatment modalities for CNV including laser photocoagulation, submacular surgery, and macular translocation (31–34). In contrast to the other imaging modalities that assess structural integrity, microperimetry provides a functional measure of macular function. Much like the Humphrey visual field is used to assess visual loss

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in glaucoma, microperimetry can functionally assess macular deterioration in AMD. As newer treatments emerge for AMD, this modality may supplement the anatomic evaluation of drug efficacy by providing a functional measure of the area and degree of retinal recovery or deterioration. Furthermore, microperimetric analysis to evaluate progression of macular deterioration may aid in clinical decision making.

CONCLUSION The value of quantitative retinal imaging will undoubtedly increase as the image processing software and the quantification methods improve over time. These advances are already assisting ophthalmologist through improved education of the patient on the nature and progression of AMD disease with important implications for better physician–patient relationships and compliance with treatment. It now seems likely that quantitative retinal imaging will also provide robust endpoints for assessing the effectiveness of interventions in clinical trials and epidemiological studies.

SUMMARY POINTS &

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Quantitative techniques are useful for objectively evaluating the type and number of drusen, retinal pigment epithelium pigmentary changes, and components of CNV lesions. OCT based software, such as the OCTOR system developed at the Doheny Eye Institute, allows for delineation of retinal layers as well as pathologic entities such as subretinal fluid, area occupied by choroidal neovascular membranes, and the size of serous retinal pigment epithelial detachments. Quantification of fluorescein angiographic information is being developed and will provide important clinical information regarding the progression of AMD and response to therapy. Microperimetry is a useful tool in assessing functional deficits due to AMD beyond that of visual acuity since it provides information on the location and depth of relative and absolute scotomas.

REFERENCES 1. Klein R, Davis MD, Magli YL, et al. The Wisconsin agerelated maculopathy grading system. Ophthalmology 1991; 98:1128–34. 2. Bird AC, Bressler NM, Bressler SB, et al. An international classification and grading system for age-related maculopathy and age-related macular degeneration. Surv Ophthalmol 1995; 39:367–74.

3. Bressler NM, Bressler SB, Seddon LM, et al. Drusen characteristics in patients with exudative versus non-exudative age-related macular degeneration. Retina 1988; 8:109–14. 4. Bressler NM, Maguire MG, Bressler SB, et al. Relationship of drusen and abnormalities of the retinal pigment epithelium to the prognosis of neovascular macular degeneration. The Macular Photocoagulation Study Group. Arch Ophthalmol 1990; 108:1442–7. 5. Ferris FL, Davis MD, Clemons TE, et al. A simplified severity scale for AMD: AREDS Report No. 18. Arch Ophthalmol 2005; 123:1570–4. 6. Smith RT, Nagasaki T, Sparrow JR, et al. A method of drusen measurement based on the geometry of fundus reflectance. Biomed Eng Online 2003; 2:10. 7. Peli E, Lahav M. Drusen measurement from fundus photographs using computer image analysis. Ophthalmology 1986; 93:1575–80. 8. Morgan WH, Cooper RL, Constable IJ, et al. Automated extraction and quantification of macular drusen from fundal photographs. Aust NZ J Ophthalmol 1994; 22:7–12. 9. Kirkpatrick JN, Spencer T, Manivannan A, et al. Quantitative image analysis of macular drusen from fundus photographs and scanning laser ophthalmoscope images. Eye 1995; 9:48–55. 10. Shin DS, Javornik NB, Berger JW. Computer-assisted, interactive fundus image processing for macular drusen quantification. Ophthalmology 1999; 106:1119–25. 11. Sivagnanavel V, Smith RT, Lau GB, et al. An interinstitutional comparative study and validation of computer aided drusen quantification. Br J Ophthalmol 2005; 89:554–7. 12. Smith RT, Chan JK, Nagasaki T, et al. A method of drusen measurement based on reconstruction of fundus background reflectance. Br J Ophthalmol 2005; 89:87–91. 13. Huang D, Swanson EA, Lin CP, et al. Optical coherence tomography. Science 1991; 254:1178–81. 14. Puliafito CA, Hee MR, Lin CP, et al. Imaging of macular diseases with optical coherence tomography. Ophthalmology 1995; 102:217–29. 15. Hee MR, Puliafito CA, Wong C, et al. Quantitative assessment of macular edema with optical coherence tomography. Arch Ophthalmol 1995; 113:1019–29. 16. Hee MR, Puliafito CA, Duker JS, et al. Topography of diabetic macular edema with optical coherence tomography. Ophthalmology 1998; 105:360–70. 17. Salinas-Alamon A, Garcia-Layana A, Maldonado MJ, et al. Using optical coherence tomography to monitor photodynamic therapy in age related macular degeneration. Am J Ophthalmol 2005; 140:23.e1–23.7. 18. Shahidi M, Wang Z, Zelkha R. Quantitative thickness measurement of retinal layers imaged by optical coherence tomography. Am J Ophthalmol 2005; 139:1056–61. 19. Verteporfin Photodynamic Therapy (VIP) Study Group. Verteporfin therapy of subfoveal choroidal neovascularization in age related macular degeneration: two-year results of a randomized clinical trial including lesions with occult with no classic choroidal neovascularization—Verteporfin in Photodynamic Therapy Report 2. Am J Ophthalmol 2001; 131:541–60. 20. Phillips RP, Ross PG, Tyska M, Sharp PF, Forrester JV. Detection and quantification of hyperfluorescent leakage by computer analysis of fundus fluorescein angiograms. Graefes Arch Clin Exp Ophthalmol 1991; 229:329–35. 21. Chakravarthy U, Walsh AC, Muldrew A, Updike PG, Barbour T, Sadda SR. Quantitative fluorescein angiographic analysis of choroidal neovascular membranes: validation and correlation with visual function. Invest Ophthalmol Vis Sci 2007; 48:349–54.

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22. Shah SM, Tatlipinar S, Quinlan E, et al. Dynamic and quantitative analysis of choroidal neovascularization by fluorescein angiography. Invest Ophthalmol Vis Sci 2006; 47:5460–8. 23. Rohrschneider K, Springer C, Bultmann S, et al. Microperimetry—comparison between the micro perimeter 1 and scanning laser ophthalmoscope—fundus perimetry. Am J Ophthalmol 2005; 139:125–34. 24. Sunness JS, Applegate CA, Haselwood D, et al. Fixation patterns and reading rates in eyes with central scotomas from advanced atrophic age-related macular degeneration and Stargardt disease. Ophthalmology 1996; 103:1458–66. 25. Takamine Y, Shiraki K, Moriwaki M, et al. Retinal sensitivity measurement over drusen using scanning laser ophthalmoscope microperimetry. Graefes Arch Clin Exp Ophthalmol 1998; 236:285–90. 26. Sunness JS, Bressler NM, Maguire MG. Scanning laser ophthalmoscopic analysis of the pattern of visual loss in age-related geographic atrophy of the macula. Am J Ophthalmol 1995; 119:143–51. 27. Sunness JS, Bressler NM, Tian Y, et al. Measuring geographic atrophy in advanced age-related macular degeneration. Invest Ophthalmol Vis Sci 1999; 40:1761–9. 28. Tezel TH, Del Priore LV, Flowers BE, et al. Correlation between scanning laser ophthalmoscope microperimetry

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30. 31.

32. 33.

34.

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and anatomic abnormalities in patients with subfoveal neovascularization. Ophthalmology 1996; 103:1829–36. Fujii GY, De Juan E, Jr., Humayun MS, et al. Characteristics of visual loss by scanning laser ophthalmoscope microperimetry in eyes with subfoveal choroidal neovascularization secondary to age-related macular degeneration. Am J Ophthalmol 2004; 136:1067–78. Schmidt-Erfurth UM, Elsner H, Terai N, et al. Effects of verteporfin therapy on central visual field function. Ophthalmology 2004; 111:931–9. Rohrschneider K, Gluck R, Becker M, et al. Scanning laser fundus perimetry before laser photocoagulation of well defined choroidal neovascularization. Br J Ophthalmol 1997; 81:568–73. Fujii GY, de Juan E, Jr., Sunness J, et al. Patient selection for macular translocation surgery using the scanning laser ophthalmoscope. Ophthalmology 2002; 109:1737–44. Hudson HL, Frambach DA, Lopez PF. Relation of the functional and structural fundus changes after submacular surgery for neovascular age-related macular degeneration. Br J Ophthalmol 1995; 79:417–23. Loewenstein A, Sunness JS, Bressler NM, et al. Scanning laser ophthalmoscope fundus perimetry after surgery for choroidal neovascularization. Am J Ophthalmol 1998; 125:657–65.

12 Fundus Autofluorescence in Age-Related Macular Degeneration Rishi P. Singh and Jeffrey Y. Chung

Cole Eye Institute, Cleveland Clinic Foundation, Cleveland, Ohio, U.S.A.

Peter K. Kaiser

Digital Optical Coherence Tomography Reading Center, Cleveland, Ohio, U.S.A.

INTRODUCTION Autofluorescence (AF) is the intrinsic fluorescence emitted by a substance after being stimulated by excitation energy. Ocular structures that autofluoresce include the corneal epithelium and endothelium, lens, macular and retinal pigment epithelium (RPE) pigments, optic nerve drusen and RPE deposits in Best’s disease. The AF emitted by macular pigments is in the 520 to 800 nm range with peak emission at 590 to 630 nm. Clinically, AF of macular pigments can be produced in vivo by an exciting light source with a wavelength between 400 and 590 nm with peak excitation occurring between 490 and 510 nm (1). This can be achieved with a modified fundus camera or scanning laser ophthalmoscope (SLO). The SLO uses blue laser light at 488 nm for illumination and a 500 nm barrier filter to isolate light from other ocular autofluorescent structures (2,3). The use of confocal scanning laser ophthalmoscope (cSLO) is considered superior to modified fundus camera images because cSLO helps eliminate the competing AF of the lens. As the plane of the cSLO detection system is conjugate to the plane of fundus, competing light signals from other planes are reduced (4). In addition, cSLO images have a higher reliability in comparing images in one patient from one visit to the next than modified fundus camera imaging (5). However, a cSLO requires the purchase of a new imaging device whereas most offices already have a fundus camera. Spaide has described an easy and inexpensive modification to preexisting fundus camera by adding 580 nm excitation and 695 nm barrier filters. With the proper barrier filter signals, wavelengths shorter than 695 nm including fluorescence emitted by the lens from 510 to 670 nm, would be blocked (4). The predominant source of AF in the macula is lipofuscin, a complex mixture of fluorophores. When the RPE phagocytize photoreceptor outer segments, consisting of retinoids, fatty acids, and proteins,

lipofuscin accumulates as an oxidative byproduct within the RPE cells (1,6,7). Lipofuscin has an affinity for acidic organelles and thus accumulates in RPE lysosomes and it can account for as much as 20% of the free cytoplasmic space of a RPE cell (8,9). A loss of RPE cells has been shown to be accompanied by substantial loss of AF content (10). The pigment within lipofuscin that causes this fluorescence was isolated and characterized by Eldred to be A2E, named for its derivation from two molecules of vitamin A aldehyde and one molecule of ethanolamine (Fig. 1) (12,13). A2E has been shown to inhibit human RPE cell growth and induce apoptosis in vitro. It exhibits detergent-like activity, disrupting membrane bound ATPase that maintain lysosomal pH (13–15). In mitochondria, A2E inhibits oxygen consumption synergistically with light by inhibiting cytochrome c oxidase (16). By mobilizing cytochrome c and apoptosis-inducing factor from mitochondria into the cytoplasm and nucleus, apoptosis is induced in RPE cells (17). A2E has also been shown to confer a dose related sensitivity to blue light damage in RPE cells via oxidative mechanisms (18). AF is a rapid noncontact, noninvasive way to evaluate RPE function. AF can evaluate the amount of lipofuscin that is accumulated in RPE. By evaluating fundus autofluorescence images and thus lipofuscin accumulation, disturbances within the RPE can be readily detected. In a normal retina, lipofuscin is most concentrated in the macula with the exception of the fovea and decreases towards the periphery (1). The highest lipofuscin AF level in the eye is found 78 to 138 away from the fovea, correlating with the area with the highest distribution of rod photoreceptors (19). Even though high inter-subject variability is seen in the distribution of macular AF, Delori found similarity of AF level within the same retina, as well as that of the fellow eye (20,21). Lipofuscin fluorescence

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iso-A2E

Structure of A2E and isomer iso-A2E from human retinal pigment epithelium. Source: From Ref. 11.

levels increases linearly with age. In humans, intracellular lipofuscin levels occupy 1% of cell volume during the first decade, increasing to 12% to 13% in the 50- to 80-year-olds and reaching 19% of the cell volume in the 81- to 90-year-olds (9).

AF AND AMD Several studies have found that the accumulation of lipofuscin over time may promote the development of AMD (Figs. 2 and 3). The age, spatial, and racial distribution of lipofuscin correlates well with the AF patterns seen with AMD. Dorey and colleagues found significant correlation between photoreceptor loss and

elevated lipofuscin levels in RPE within donor eyes of Caucasians over 50 years old. They hypothesized that lipofuscin accumulation may be indicative of increased phagocytic and metabolic stress on the RPE cells leading to photoreceptor death (22,23). Excessive lipofuscin accumulation may precede the development of GA and the enlargement of preexisting GA (24). Thus, AF imaging may be useful in evaluating the risk of AMD progression by mapping retinal AF and lipofuscin accumulation over extended periods. Previous work has shown a significant correlation in the amount of large, foveal, soft drusen and patterns of increased AF (5). Spaide reported greater levels of AF in fellow eyes of patients with exudative

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Figure 2 Lipofuscin accumulation in a 68-year-old patient over three years. Source: Photos courtesy of L. Yanuzzi, R. Spaide, and P. Bhatnagar.

AMD than in patients without a history of AMD (4). Delori and colleagues identified that RPE overlying drusen have a central area of decreased AF with surrounding ring of increased AF, suggesting damage to RPE health (7).

Abnormal AF

An International Fundus Autofluorescence Classification Group (IFAG) was organized by the Fundus autofluorescence in Age-Related Macular Degeneration (FAM) group to establish an international classification system to describe the abnormal fundus

GA formation

Figure 3 Progression to geographic atrophy over three years with abnormal autofluorescence. Abbreviations: AF, autofluorescence; GA, geographic atrophy. Source: Photos courtesy of L. Yanuzzi, R. Spaide, and P. Bhatnagar.

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(A)

(B)

Figure 4 (Continued ) Patterns of fundus autofluorescence (AF) as established by IFAG. (A–H) (A) Normal pattern; (B) minimal change pattern—very limited irregular increases or decreases of AF due to multiple small hard drusen.

AF patterns seen in AMD (25). The multinational group of clinicians established eight distinct patterns of AF in AMD: normal AF, minimal change pattern AF, focal increased pattern, patchy pattern AF, linear pattern AF, lacelike pattern AF, reticular pattern AF, and speckled pattern AF. Standardized photos of these AF patterns were established (Fig. 4). 1. Normal pattern. The normal AF pattern is characterized by a homogeneous background AF with a gradual decrease from the inner macula toward the

fovea due to the masking effect of yellow luteal macular pigment. 2. Minimal change pattern. The minimal change pattern is characterized by very small irregular increases or decreases of background AF without an obvious topographic pattern. 3. Focal increased pattern. Focal increased AF is described as the presence of at least one spot (less than 200 mm diameter) of markedly increased AF brighter than the surrounding fluorescence. The borders are well defined and some areas of focal

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(C)

(D)

Figure 4 (Continued ) (C) focal increased pattern—several well-defined spots with markedly increased AF; (D) patchy pattern—multiple large areas of increased AF corresponding to multiple large soft drusen and/or hyperpigmentation in the fundus photograph.

increased AF may be surrounded by a darkerappearing halo. Visible alterations (focal hyperpigmentation or drusen) seen on color fundus photos may or may not correspond to areas of AF. 4. Patchy pattern. Patchy AF is defined as at least one larger area (greater than 200 mm diameter) of markedly increased AF where the borders of the areas are typically less well-defined than the previous pattern. There is a gradual increase in AF from the back-

ground to the patchy area. This pattern may also correspond to large drusen, soft drusen and areas of hyperpigmentation seen on color photographs. 5. Linear pattern. The linear pattern describes the presence of at least one linear area of markedly increased AF with well-demarcated borders and no gradual decrease in AF. These AF areas usually correspond to hyperpigmented lines on the color fundus photograph.

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(E)

(F)

Figure 4 (Continued) (E) linear pattern—at least one linear area with marked increased AF; (F) lacelike pattern—multiple branching linear structures of increased AF.

6. Lacelike pattern. The lacelike pattern typically exhibits numerous branching linear structures of increased AF that form a lace pattern. The borders are poorly defined and a decline in AF is observed from the center of the AF areas to the surrounding areas. These lacelike areas can correspond to hyperpigmentation on the color image, but it may correspond to normal fundus areas as well. 7. Reticular pattern. The reticular pattern is exemplified by the presence of multiple small areas (less than

200 mm diameter) of decreased AF with poorly defined borders. Fundoscopically, there are usually visible small soft drusen, hard drusen, or areas with pigmentary changes overlying these areas, but the fundus can be normal as well. 8. Speckled pattern. The speckled AF pattern has the simultaneous presence of a variety of AF abnormalities that extend beyond the macular area. There can be multiple, small areas of irregularly increased and decreased AF which appear punctuate or

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(G)

(H)

Figure 4 (Continued ) (G) reticular pattern—multiple small areas of decreased AF with bright lines in between; (H) speckled pattern—presence of a variety of AF abnormalities, which extend beyond the macular area to the posterior pole.

resemble linear structures. Color fundus photographs may include corresponding hyper- and hypopigmentation and multiple subconfluent and confluent drusen. Of 149 eyes studied within the IFAG group’s initial study of 107 patients (44 male, 63 female patients) with unilateral or bilateral GA, the diffuse pattern was the most common (57%), followed by the banded, focal and normal patterns at about 12% per group. The other patterns were less commonly seen (25).

AF with Drusen There have been numerous reports examining AF in drusen associated with dry AMD. Delori and associates identified a specific pattern of AF spatially associated with hard and soft drusen ranging between 60 and 175 mm in size. The pattern is characterized by a central area of decreased AF surrounded, in most cases, by an annulus of increased AF around the drusen (7). It was hypothesized by Delori that this AF pattern is due to RPE impairment with secondary accumulation of lipofuscin around drusen, with RPE

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atrophy overlying drusen. Spade interprets the appearance of this pattern as secondary to thinner RPE cells on top of the drusen, and thicker RPE cells around the base (26). These areas of increased AF around drusen showed normal or near-normal photopic sensitivity, but moderately reduced scotopic sensitivity (27). Soft drusen larger than 175 mm and confluent soft drusen show either a heterogenous distribution of AF or multifocal areas of decreased AF (7). But, both normal, hyper- and hypofluorescence of the RPE cells overlying soft drusen has been reported with no proven biochemical explanation and thus future larger studies are needed to refine this classification (3,5,28,29).

AF in Geographic Atrophy With loss of RPE containing lipofuscin, areas of GA appear dark under AF. Holz and colleagues found 83% of the geographic atrophic from AMD has increased AF pattern at the border (30). This ring of elevated AF from lipofuscin bordering the GA supports the concept that excessive lipofuscin may be associated with RPE damage (21). In fact, the increased AF in the junctional zone around GA is thought to be characteristic for AMD since only 9% of geography atrophy from other causes exhibit similar findings (3,30). When tested with fundus perimetry, a significant degree of retinal sensitivity loss is found in the junctional area between the inner dark zone and ring of increased AF (31). Photopic and scotopic fine matrix mapping of these areas has shown a scotopic sensitivity loss demonstrating a preferential loss of rods (27). This correlation of AF abnormality to a loss of function may further suggest a relationship between GA and its increased AF border. Holz found that 90% of the AMD patients with bilateral GA exhibited the same AF pattern in both eyes (30). Longitudinal studies have demonstrated that AF is useful for the precise mapping and measuring of GA areas (Fig. 5) (24). Moreover, progression of increased AF from GA has been described in several studies (3,30). It has been noted that the rate of GA spread accelerates with expansion of GA area, then levels off at five disc areas (32,33). However, the natural progression of GA is poorly understood. Manual measurement of GA is time consuming and results in significant inter-observer variability (31). Previous studies have found that automated quantification and delineation of AF images is superior to fundus photography or fluorescein angiography in the delineation of GA (31). When combined with cSLO, the measurement of GA area improves significantly (34). The quantification of these lesions adds to the understanding of the natural history of GA formation and allows for the monitoring of future therapeutics to slowdown its progression.

In a three year prospective study of three patients, Holz and colleagues found the development and enlargement of GA within areas of increased AF (24). In another study by Holz, eyes with only diffuse patterns of AF were examined and found to have higher levels of AF on the transitional area between GA and healthy RPE. The study determined that the greater the area of increased AF adjacent to the GA, the faster the expansion of GA. They concluded a positive correlation between increased AF and GA expansion in this population (35). With evidence linking lipofuscin to cell death in a dose-dependent manner, it is plausible to propose the zone of increased AF around GA may be the advancing border of GA. As GA advances, RPE cells absorb lipofuscin materials from adjacent dead RPE cells, thus increasing its susceptibility for destruction. This effect spread like dominos, and accelerates as the area of GA containing lipofuscin grows exponentially. Expansion of GA slows only when the spread reaches less vulnerable and healthier RPE cells. However, in a retrospective study of AF photographs with differing baseline patterns of AF, Hwang and colleagues found that only 34% to 50% of the new areas of GA fell into an area of increased AF. The positive predictive value for increased AF to form new GA was no better than chance (36). Given these two conflicting reports, it difficult to form a consensus on whether increased AF at the border of GA truly predicts future progression of GA to this area.

AF in Choroidal Neovascularization While the majority of studies with AF in AMD have concentrated on the dry form, there has been limited work on determining a correlation between AF and choroidal neovascularization (CNV). Eyes with early CNV lesions show various patterns of increased AF (Fig. 6). Einbock and colleagues studied eyes with exudative changes and found that 17% of eyes exhibited “patchy” AF pattern, as well as some with “focal increased” plaque and “reticular” patterns. Other less intense patterns were not associated with progression to late AMD during 18-month follow-up (37). Dandekar and colleagues studied AF in 65 consecutive eyes with CNV secondary to AMD (38). Patients were stratified by age of lesion. Eyes with recent onset lesions (one to six months) showed no AF abnormalities indicating relatively healthy RPE initially. Older CNV lesions (greater than six months) exhibited decreased AF levels indicating RPE damage and photoreceptor loss. Similar to pattern seen in GA, increased AF in the junctional zone is also seen in some eyes with CNV. Eyes with better visual acuity are those with intact AF in early onset lesions and others

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Figure 5 Precise mapping of geographic atrophy over time with autofluoresence. Source: Photos courtesy of L. Yanuzzi, R. Spaide, and P. Bhatnagar.

with intact AF in the foveal area. This study highlighted the possible use of AF to determine visual prognosis for AMD lesions. In an observational case series examining pigment epithelial detachments (PEDs) associated with AMD, increased AF was seen in all serous PEDs regardless of whether there was an underlying CNV in the area of detachment (Fig. 7). The authors concluded that the increased AF seen with serous PEDs may be due to AF of sub-retinal pigment epithelial fluid. In the case of a drusenoid PED, AF levels were dependent on pigment clumping with increased pigment correlating with lower AF levels. Larger numbers of patients are needed to verify this morphological features (39). A few studies have attempted to classify CNV lesion type based on the AF pattern seen.

In a study examining AF of 68 eyes undergoing photodynamic therapy (PDT) treatment, Framme found 79% of the untreated classic lesions were associated with decreased AF and a junctional zone of increased or normal AF. In untreated occult membranes, a normal or mottled AF pattern with foci of hyper- and hypofluorescence were seen. After PDT treatment, 90% of the classic CNV lesions showed decreased AF signal. There appeared to be no AF change in occult parts of CNV lesions after PDT (40). These baseline AF patterns were also described by McBain and collegues in patients with exudative AMD. Low AF signal at the site of classic CNV was detected in 90% of exudative AMD lesions. While multiple foci of low AF was seen in half of occult CNV lesions, focally increased AF was rarely seen with CNV lesions (41).

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Figure 6 Fundus autofluorescence corresponding to subretinal fluid with choroidal neovascularization. Abbreviation: AF, autoflourescence. Source: Photos courtesy of L. Yanuzzi, R. Spaide, and P. Bhatnagar.

Red Free

FA

ICG

Autoflurescence

Figure 7 Serous pigment epithelial detachment imaged with various modalities. Abbreviations: FA, fluorescein angiography; ICG, indocyanine green. Source: Photos courtesy of L. Yanuzzi, R. Spaide, and P. Bhatnagar.

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AF after Laser Treatment AF has shown to be useful tools in localizing laser lesions after treatment. In a pilot study, Framme attempted Nd:YAG RPE selective laser treatment for diabetic maculopathy and central serous chorioretinopathy. Changes to AF levels around laser lesions 10 minutes after treatment were seen in 22 out of 26 patients. These laser lesions later exhibit a lower AF level in comparison to surrounding tissues at three to six months (5,42). In a study of subthreshold infrared diode laser for the reduction of drusen in dry AMD, visualization of laser lesions using AF was shown to be more sensitive than fluorescein angiogram in 75% of the eyes immediately post laser treatment, and 55% of the eyes three months after treatment (43).

&

&

&

&

&

LIMITATIONS There are several limitations in the use of AF in the evaluation of patients for AMD. AF detection is limited in patients with significant media opacities such as cataract and vitreous hemorrhage. Furthermore, the comparative quantification of AF images cannot occur amongst patients. Rather, only images from the same patient can be compared to determine changes in intensities of AF seen over time. Thus, the use of AF is still in its infancy and further studies need to be performed to evaluate its role in the diagnosis and management of AMD. Reports on the use of AF in the diagnosis and management of AMD are preliminary at best and sometimes conflicting. There remains a need for further data to clarify the relationship of AF patterns in formation and expansion of GA. More information is needed to substantiate the relationship between AF patterns and risk of CNV. There is a lack of studies identifying AF criteria useful in the classification of CNV subtype. The current literature thus far consists mostly of non-randomized small case series limiting its applicability to the general population. To address these limitations, the FAM study group, a multi-center study is currently under way, with some results already in press. The goal of the group is to investigate the correlation between fundus AF and the natural history of AMD. The group also intends to identify high-risk AF characteristics that can predict patients who will progress to late AMD (37).

SUMMARY POINTS & &

The predominant source of AF in the macula is lipofuscin, a complex mixture of fluorophores. The pigment within lipofuscin that causes this fluorescence is A2E (named for its derivation from two molecules of vitamin A aldehyde and one molecule of ethanolamine).

&

201

Fundus autofluorescence is a useful modality to image lipofuscin in RPE cells and is a unique way to assess RPE function in AMD. In GA, automated imaging analysis by AF has been shown superior to fundus photo or FA in assessing the extent of the atrophy. Increased AF, especially at the edge of GA area, may predict GA formation and expansion. AF has been helpful in assessing RPE health in exudative AMD, and can consistently visualize serous PED. AF can also be helpful in the early localization of previous retinal laser treatments where it may be up to three times more sensitive than fluorescein angiogram. AF is shown to be helpful in indicating graft visualization in RPE-choroidal grafts for AMD patients. Larger randomized controlled studies using AF are needed to further assess its potential in the detection and management of AMD.

REFERENCES 1. Delori FC, Dorey CK, Staurenghi G, Arend O, Goger DG, Weiter JJ. In vivo fluorescence of the ocular fundus exhibits retinal pigment epithelium lipofuscin characteristics. Invest Ophthalmol Vis Sci 1995; 36:718–29. 2. von Ruckmann A, Fitzke FW, Bird AC. Distribution of fundus autofluorescence with a scanning laser ophthalmoscope. Br J Ophthalmol 1995; 79:407–12. 3. von Ruckmann A, Fitzke FW, Bird AC. Fundus autofluorescence in age-related macular disease imaged with a laser scanning ophthalmoscope. Invest Ophthalmol Vis Sci 1997; 38:478–86. 4. Spaide RF. Fundus autofluorescence and age-related macular degeneration. Ophthalmology 2003; 110:392–9. 5. Lois N, Owens SL, Coco R, Hopkins J, Fitzke FW, Bird AC. Fundus autofluorescence in patients with age-related macular degeneration and high risk of visual loss. Am J Ophthalmol 2002; 133:341–9. 6. Gaillard ER, Atherton SJ, Eldred G, Dillon J. Photophysical studies on human retinal lipofuscin. Photochem Photobiol 1995; 61:448–53. 7. Delori FC, Fleckner MR, Goger DG, Weiter JJ, Dorey CK. Autofluorescence distribution associated with drusen in age-related macular degeneration. Invest Ophthalmol Vis Sci 2000; 41:496–504. 8. Kennedy CJ, Rakoczy PE, Constable IJ. Lipofuscin of the retinal pigment epithelium: a review. 1995; 9(Pt 6): 763–71. 9. Feeney-Burns L, Hilderbrand ES, Eldridge S. Aging human RPE: morphometric analysis of macular, equatorial, and peripheral cells. Invest Ophthalmol Vis Sci 1984; 25:195–200. 10. Katz ML, Eldred GE. Retinal light damage reduces autofluorescent pigment deposition in the retinal pigment epithelium. Invest Ophthalmol Vis Sci 1989; 30:37–43. 11. Parish CA, Hashimoto M, Nakanishi K, Dillon J, Sparrow J. Isolation and one-step preparation of A2E and iso-A2E, fluorophores from human retinal pigment epithelium. Proc Natl Acad Sci USA 1998; 95:14609–13.

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12. Sakai N, Decatur J, Nakanishi K, Eldred GE. Ocular age pigment “A2E”: an unprecedented pyridinium bisretinoid. J Am Chem Soc 1996; 118:1559–60. 13. Eldred GE. Age pigment structure. Nature 1993; 364:396. 14. Mellman I, Fuchs R, Helenius A. Acidification of the endocytic and exocytic pathways. Annu Rev Biochem 1986; 55:663–700. 15. Sparrow JR, Parish CA, Hashimoto M, Nakanishi K. A2E, a lipofuscin fluorophore, in human retinal pigmented epithelial cells in culture. Invest Ophthalmol Vis Sci 1999; 40:2988–95. 16. Shaban H, Gazzotti P, Richter C. Cytochrome c oxidase inhibition by N-retinyl-N-retinylidene ethanolamine, a compound suspected to cause age-related macula degeneration. Arch Biochem Biophys 2001; 394:111–6. 17. Suter M, Reme C, Grimm C, et al. Age-related macular degeneration. The lipofusion component N-retinyl-Nretinylidene ethanolamine detaches proapoptotic proteins from mitochondria and induces apoptosis in mammalian retinal pigment epithelial cells. J Biol Chem 2000; 275:39625–30. 18. Nilsson SE, Sundelin SP, Wihlmark U, Brunk UT. Aging of cultured retinal pigment epithelial cells: oxidative reactions, lipofuscin formation and blue light damage. Doct Ophthalmol 2003; 106:13–6. 19. Delori FC, Goger DG, Dorey CK. Age-related accumulation and spatial distribution of lipofuscin in RPE of normal subjects. Invest Ophthalmol Vis Sci 2001; 42:1855–66. 20. Bellmann C, Jorzik J, Spital G, Unnebrink K, Pauleikhoff D, Holz FG. Symmetry of bilateral lesions in geographic atrophy in patients with age-related macular degeneration. Arch Ophthalmol 2002; 120:579–84. 21. Robson AG, Moreland JD, Pauleikhoff D, et al. Macular pigment density and distribution: comparison of fundus autofluorescence with minimum motion photometry. Vision Res 2003; 43:1765–75. 22. Dorey CK, Wu G, Ebenstein D, Garsd A, Weiter JJ. Cell loss in the aging retina relationship to lipofuscin accumulation and macular degeneration. Invest Ophthalmol Vis Sci 1989; 30:1691–9. 23. Dorey K, Staurenghi G, Delori FC. Lipofuscin in age and ARMD eyes. In: Hollyfield JG, ed. Retinal Degeneration. New York: Plenum Pub Corp., 1993:3–14. 24. Holz FG, Bellman C, Staudt S, Schutt F, Volcker HE. Fundus autofluorescence and development of geographic atrophy in age-related macular degeneration. Invest Ophthalmol Vis Sci 2001; 42:1051–6. 25. Bindewald A, Schmitz-Valckenberg S, Jorzik JJ, et al. Classification of abnormal fundus autofluorescence patterns in the junctional zone of geographic atrophy in patients with age related macular degeneration. Br J Ophthalmol 2005; 89:874–8. 26. Spaide RF. Macular autofluorescence. AAO Retina Subspecialty Day 2005; 1:192–7. 27. Scholl HP, Bellmann C, Dandekar SS, Bird AC, Fitzke FW. Photopic and scotopic fine matrix mapping of retinal areas of increased fundus autofluorescence in patients with agerelated maculopathy. Invest Ophthalmol Vis Sci 2004; 45:574–83. 28. Solbach U, Keilhauer C, Knabben H, Wolf S. Imaging of retinal autofluorescence in patients with age-related macular degeneration. Retina 1997; 17:385–9.

29. Sunness JS, Ziegler MD, Applegate CA. Issues in quantifying atrophic macular disease using retinal autofluorescence. Retina 2006; 26:666–72. 30. Holz FG, Bellmann C, Margaritidis M, Schutt F, Otto TP, Volcker HE. Patterns of increased in vivo fundus autofluorescence in the junctional zone of geographic atrophy of the retinal pigment epithelium associated with age-related macular degeneration. Graefes Arch Clin Exp Ophthalmol 1999; 237:145–52. 31. Schmitz-Valckenberg S, Jorzik J, Unnebrink K, Holz FG, FAM Study Group. Analysis of digital scanning laser ophthalmoscopy fundus autofluorescence images of geographic atrophy in advanced age-related macular degene 132#ration. Graefes Arch Clin Exp Ophthalmol 2002; 240:73–8. 32. Schatz H, McDonald HR. Atrophic macular degeneration rate of spread of geographic atrophy and visual loss. Ophthalmology 1989; 96:1541–51. 33. Sarks SH. Drusen patterns predisposing to geographic atrophy of the retinal pigment epithelium. Aust J Ophthalmol 1982; 10:91–7. 34. Deckert A, Schmitz-Valckenberg S, Jorzik J, Bindewald A, Holz FG, Mansmann U. Automated analysis of digital fundus autofluorescence images of geographic atrophy in advanced age-related macular degeneration using confocal scanning laser ophthalmoscopy (cSLO). BMC Ophthalmol 2005; 5:8. 35. Schmitz-Valckenberg S, Bindewald-Wittich A, DolarSzczasny J, et al. Correlation between the area of increased autofluorescence surrounding geographic atrophy and disease progression in patients with AMD. Invest Ophthalmol Vis Sci 2006; 47:2648–54. 36. Hwang JC, Chan JW, Chang S, Smith RT. Predictive value of fundus autofluorescence for development of geographic atrophy in age-related macular degeneration. Invest Ophthalmol Vis Sci 2006; 47:2655–61. 37. Einbock W, Moessner A, Schnurrbusch UE, Holz FG, Wolf S, FAM Study Group. Changes in fundus autofluorescence in patients with age-related maculopathy. Correlation to visual function: a prospective study. Graefe’s Arch Clin Exp Ophthalmol 2005; 243:300–5. 38. Dandekar SS, Jenkins SA, Peto T, et al. Autofluorescence imaging of choroidal neovascularization due to age-related macular degeneration. Arch Ophthalmol 2005; 123:1507–13. 39. Karadimas P, Bouzas EA. Fundus autofluorescence imaging in serous and drusenoid pigment epithelial detachments associated with age-related macular degeneration. Am J Ophthalmol 2005; 140:1163–5. 40. Framme C, Bunse A, Sofroni R, et al. Fundus autofluorescence before and after photodynamic therapy for choroidal neovascularization secondary to age-related macular degeneration. Ophthalmic Surg Lasers Imaging 2006; 37:406–14. 41. McBain VA, Townend J, Lois N. Fundus autofluorescence in exudative age-related macular degeneration. Br J Ophthalmol 2006; 91(4):491–6. 42. Framme C, Brinkmann R, Birngruber R, Roider J. Autofluorescence imaging after selective RPE laser treatment in macular diseases and clinical outcome: a pilot study. Br J Ophthalmol 2002; 86:1099–106. 43. Bessho K, Rodanant N, Bartsch DU, Cheng L, Koh HJ, Freeman WR. Effect of subthreshold infrared laser treatment for drusen regression on macular autofluorescence in patients with age-related macular degeneration. Retina 2005; 25:981–8.

Part IV: Medical Treatment for Age-Related Macular Degeneration

13 Laser Photocoagulation for Choroidal Neovascularization Catherine Cukras and Stuart L. Fine

Department of Ophthalmology, Scheie Eye Institute, University of Pennsylvania, Philadelphia, Pennsylvania, U.S.A.

INTRODUCTION Until the initial Macular Photocoagulation Study (MPS) outcome data were published in June 1982, there were no reported treatments of proven benefit for patients with choroidal neovascularization (CNV) secondary to age-related macular degeneration (AMD). The MPS trials conducted from 1979 to 1994 showed that laser photocoagulation was preferable to observation for several categories of well-defined CNV based on the fluorescein angiographic location of the CNV with respect to the geometric center of the fovea, i.e., extrafoveal, juxtafoveal, and subfoveal (1–5). The MPS publications also described the factors which limited the utility of laser photocoagulation treatment. 1. Only a small proportion of symptomatic AMD eyes met MPS eligibility criteria as being appropriate for laser treatment (6,7); 2. There was a high rate of persistent and recurrent leakage even after initially successful closure of the CNV (8,9); 3. Laser photocoagulation caused immediate and permanent damage to the retina in the area treated and this damage typically resulted in an immediate decrease in visual acuity (VA) (2); 4. Treated as well as untreated eyes continued to lose central vision over time, despite initial closure of the CNV in laser-treated eyes. In addition, because laser photocoagulation is a focal treatment, there is no expected beneficial effect beyond the area of laser application. Specifically, laser photocoagulation does not inhibit the development of new areas of CNV. With the advent of safe and effective antiangiogenic therapies which treat not only the existing neovascularization but also reduce the risk of developing CNV, it would appear that laser photocoagulation will have an extremely limited role in the

management of CNV secondary to AMD. Thus, the following narrative is presented primarily for an historical perspective on how treatment for CNV secondary to AMD developed over the last quarter century.

EPIDEMIOLOGY AND NATURAL HISTORY AMD is a leading cause of severe and irreversible central vision loss in the developed world among people over the age of 55 (10–13). Up to 90% of the severe vision loss in AMD is caused by CNV (14–16). Before the MPS was initiated in 1979, there were several natural history studies which documented the unfavorable visual prognosis of eyes with untreated CNV secondary to both AMD and ocular histoplasmosis (17,18). These natural history data were substantiated by the visual outcomes of untreated eyes among participants in the MPS. In the MPS trial of juxtafoveal CNV, 65% of untreated eyes lost six or more lines of acuity after five years follow up, and 93% progressed from juxtafoveal to subfoveal CNV (4,19). The initial component of the MPS evaluated argon laser photocoagulation in patients with extrafoveal CNV secondary to AMD. At the time, this trial was known as the Senile Macular Degeneration Study (SMDS). Eyes with extrafoveal CNV were assigned randomly to immediate argon laser treatment or to observation. By 18 months after enrollment, 60% of untreated eyes had lost six or more lines of VA. By one year after enrollment, fluorescein angiography showed that 73% of untreated eyes had progressed from extrafoveal to subfoveal CNV (20). In 1985, Guyer et al. reported that among 92 AMD patients with subfoveal neovascular lesions, 64% lost six or more lines of vision within two years (18). In the MPS trial of subfoveal lesions, 30% of untreated eyes lost six or more lines of VA at 12 months follow up, and 39% lost six or more lines of vision by two years (2).

Size

!3.5 MPS standard disc area (1 MPS standard areaZ1.77 mm2); some area within 2 disc diameters of retina must be able to be left untreated New vessels under FAZ Area of treatment plus scar center or CNV within %6 MPS disc areas 150 mm of FAZ scar under (10.6 mm2) and some portion of retina within FAZ center 1-disc diameter (1.5 mm) of FAZ must remain untreated

1–199 mm from center of FAZ or O200 mm from FAZ if adjacent blood or pigment extended to within 200 mm New vessels under FAZ center

200–2500 mm from center of FAZ

Location

R20/100

20/40–20/320 inclusive

R50 yr

R20/100

VA

R50 yr

R50 yr

Age

Previous treatment directly to the center of the FAZ, other ocular disease, systemic steroids

Prior laser, other ocular disease, systemic steroids

VA!20/400, prior laser, other ocular disease, systemic steroids VA!20/400, prior laser, other ocular disease

Exclusion

Abbreviations: AMDS-K, age-related macular degeneration study-krypton laser; CNV, choroidal neovascularization; FA, fluorescein angiography; FAZ, foveal avascular zone; MPS, Macular Photocoagulation Study; VA, visual acuity. Source: From Ref. 26. Copyright 2007 from Thermal laser treatment in AMD: therapeutic and prophylactic. International Ophthalmology Clinics. Reproduced by permission of Lippincott Williams and Wilkins.

FA within 96 hr of randomization; leaking CNV with “welldemarcated borders”; most of lesion either classic or occult Recurrent subfoveal CNV (1,3) FA within 96 hr of randomization; leaking CNV with “well-demarcated borders”; contiguous to the scar from earlier treatment

Angiographic evidence of leaking CNV with “welldemarcated borders”

Juxtafoveal—AMDS-K (4)

New subfoveal CNV (1,2)

Angiographic evidence of leaking CNV with “welldemarcated borders”

Extrafoveal (5)

CNV description

Summary of the Major Results of the Macular Photocoagulation Study

MPS study lesion type

Table 1

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13:

The MPS Trials The MPS documented that the visual outcome of laser treatment for eyes with extrafoveal CNV was better than the natural history (21–23). In fact, recruitment into the argon laser trial of extrafoveal CNV (SMDS) was halted early because 18 months after enrollment, only 25% of laser treated eyes compared to 60% of observed eyes had lost six or more lines of VA (21). Although laser treatment did not reverse or stop progression of vision loss, laser treated eyes continued to have better vision than untreated eyes even after five years of follow up (5). Trials of similar design conducted at Moorfields Eye Hospital in London, England and by Coscas and Soubrane in Creteil, France also demonstrated a benefit of laser treatment versus observation in AMD patients with selected CNV lesions (24,25). Several MPS trials reported that the difference in vision loss between laser-treated and untreated eyes was maintained over a four to five years course of follow up. The patient eligibility criteria defining the study population as well as the results from the key trials are summarized in Tables 1 and 2 (1–5,27).

vision in laser-treated versus untreated eyes within the first three months after laser treatment (3). This observation documents the immediate harmful effects of laser treatment to the fovea. However, when patients with subfoveal CNV were followed for longer periods, it became evident that laser treated eyes had less vision loss than observed eyes, indicating some long-term benefit of laser treatment even when applied to subfoveal CNV (3). This benefit was maintained over the three years course of follow up. As indicated in the opening paragraphs, this review and the accompanying tables are provided for historical perspective. At present, anti vascular endothelial growth factor (AntiVEGF) therapy appears to be the preferred management strategy for all forms of CNV secondary to AMD irrespective of the geographic location of the CNV with respect to the foveal center. The reasons are listed below (20,29–33). 1. AntiVEGF therapy is not associated with immediate loss of vision due to destruction of visual elements in the retina. 2. AntiVEGF therapy is more effective than laser photocoagulation or photodynamic therapy. 3. AntiVEGF therapy discourages the formation of new vessels as well as treating the new vessels.

Decreased Vision after Laser Treatment The studies which showed a benefit of laser treatment compared to observation for eyes with study eligible CNV lesions also documented that laser treatment did not prevent the progressive vision loss associated with CNV. Significant vision loss occurred over time in most treated eyes. Follow up also showed that persistent and recurrent CNV were responsible for the progressive loss of vision. For example, 24 months after laser treatment of extrafoveal CNV lesions, 52% of eyes showed evidence of recurrence (28). Even for subfoveal lesions, after three years of follow up, nearly half the treated eyes had persistent or recurrent CNV (9). One MPS trial reported that eyes with recurrent CNV had less vision loss with laser treatment than with observation (Table 2) (3). It must be noted that in eyes with subfoveal lesions and relatively good VA, there is greater loss of Table 2

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LASER PHOTOCOAGULATION FOR CHOROIDAL NEOVASCULARIZATION

SUMMARY POINTS &

&

&

The MPS trials were conducted from 1979 to 1994 and showed that laser photocoagulation was preferable to observation for several categories of well-defined CNV based on the fluorescein angiographic location of the CNV with respect to the geometric center of the fovea, i.e., extrafoveal, juxtafoveal, and subfoveal. The MPS studies also documented that laser treatment did not prevent the progressive vision loss associated with CNV. Significant vision loss occurred over time in most treated eyes.

Percentage Progressing to Severe Vision Loss Defined as Loss of More than Six Lines of Visual Acuity One year

MPS AMD study Treated (%) Extrafoveal CNV (5) Juxtafoveal CNV (4) Subfoveal CNV (new) (1) Subfoveal CNV (recurrent) (1)

Control (%)

Three years for all (except four years “subfoveal new”)

Two years

Five years

Treated (%)

Control (%)

Treated (%)

Control (%)

Treated (%)

Control (%)

24

41

33#

51#

45

63

46

64

31

45

45

54

51

61

55

65

23

39

23

45

9

28

17

39

24 (20)C 11

30 (11)C 29

C, 3 months; #, 18 months. Abbreviations: AMD, age-related macular degeneration; CNV, choroidal neovascularization; MPS, Macular Photocoagulation Study. Source: From Ref. 27. Copyright 2002 from Age-Related Macular Degeneration by J Lim editor. Reproduced by permission of Routledge/Taylor & Francis Group, LLC.

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CUKRAS AND FINE

REFERENCES 1. Macular Photocoagulation Study Group. Laser photocoagulation of subfoveal neovascular lesions of age-related macular degeneration. Updated findings from two clinical trials. Arch Ophthalmol 1993; 111(9):1200–9. 2. Macular Photocoagulation Study Group. Laser photocoagulation of subfoveal neovascular lesions in age-related macular degeneration. Results of a randomized clinical trial. Arch Ophthalmol 1991; 109(9):1220–31. 3. Macular Photocoagulation Study Group. Laser photocoagulation of subfoveal recurrent neovascular lesions in agerelated macular degeneration. Results of a randomized clinical trial. Arch Ophthalmol 1991; 109(9):1232–41. 4. Macular Photocoagulation Study Group. Laser photocoagulation for juxtafoveal choroidal neovascularization. Five-year results from randomized clinical trials. Arch Ophthalmol 1994; 112(4):500–9. 5. Macular Photocoagulation Study Group. Argon laser photocoagulation for neovascular maculopathy. Five-year results from randomized clinical trials. Arch Ophthalmol 1991; 109(8):1109–14. 6. Ciulla TA, Danis RP, Harris A. Age-related macular degeneration: a review of experimental treatments. Surv Ophthalmol 1998; 43(2):134–46. 7. Freund KB, Yannuzzi LA, Sorenson JA. Age-related macular degeneration and choroidal neovascularization. Am J Ophthalmol 1993; 115(6):786–91. 8. Macular Photocoagulation Study Group. Persistent and recurrent neovascularization after krypton laser photocoagulation for neovascular lesions of age-related macular degeneration. Arch Ophthalmol 1990; 108(6):825–31. 9. Macular Photocoagulation Study Group. Persistent and recurrent neovascularization after laser photocoagulation for subfoveal choroidal neovascularization of agerelated macular degeneration. Arch Ophthalmol 1994; 112(4): 489–99. 10. Fine SL, Berger JW, Maguire MG, Ho AC. Age-related macular degeneration. N Engl J Med 2000; 342(7):483–92. 11. Evans J, Wormald R. Is the incidence of registrable agerelated macular degeneration increasing? Br J Ophthalmol 1996; 80(1):9–14. 12. Vingerling JR, Dielemans I, Hofman A, et al. The prevalence of age-related maculopathy in the Rotterdam Study. Ophthalmology 1995; 102(2):205–10. 13. Klein R, Klein BE, Jensen SC, Meuer SM. The five-year incidence and progression of age-related maculopathy: the Beaver Dam Eye Study. Ophthalmology 1997; 104(1):7–21. 14. Leibowitz HM, Krueger DE, Maunder LR, et al. The Framingham Eye Study monograph: an ophthalmological and epidemiological study of cataract, glaucoma, diabetic retinopathy, macular degeneration, and visual acuity in a general population of 2631 adults, 1973–1975. Surv Ophthalmol 1980; 24:335–610. 15. Ferris FL, III, Fine SL, Hyman L. Age-related macular degeneration and blindness due to neovascular maculopathy. Arch Ophthalmol 1984; 102(11):1640–2. 16. Hyman LG, Lilienfeld AM, Ferris FL, III, Fine SL. Senile macular degeneration: a case-control study. Am J Epidemiol 1983; 118(2):213–27. 17. Bressler SB, Bressler NM, Fine SL, et al. Natural course of choroidal neovascular membranes within the foveal

18.

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avascular zone in senile macular degeneration. Am J Ophthalmol 1982; 93(2):157–63. Guyer DR, Fine SL, Maguire MG, et al. Subfoveal choroidal neovascular membranes in age-related macular degeneration. Visual prognosis in eyes with relatively good initial visual acuity. Arch Ophthalmol 1986; 104(5):702–5. Macular Photocoagulation Study Group. Krypton laser photocoagulation for idiopathic neovascular lesions. Results of a randomized clinical trial. Arch Ophthalmol 1990; 108(6):832–7. Barbazetto I, Burdan A, Bressler NM, et al. Photodynamic therapy of subfoveal choroidal neovascularization with verteporfin: fluorescein angiographic guidelines for evaluation and treatment—TAP and VIP Report No. 2. Arch Ophthalmol 2003; 121(9):1253–68. Macular Photocoagulation Study Group. Argon laser photocoagulation for senile macular degeneration. Results of a randomized clinical trial. Arch Ophthalmol 1982; 100(6):912–8. Macular Photocoagulation Study Group. Argon laser photocoagulation for ocular histoplasmosis. Results of a randomized clinical trial. Arch Ophthalmol 1983; 101(9): 1347–57. Macular Photocoagulation Study Group. Argon laser photocoagulation for idiopathic neovascularization. Results of a randomized clinical trial. Arch Ophthalmol 1983; 101(9): 1358–61. The Moorfields Macular Study Group. Treatment of senile disciform macular degeneration: a single-blind randomised trial by argon laser photocoagulation. Br J Ophthalmol 1982; 66(12):745–53. Coscas G, Soubrane G. Argon laser photocoagulation of subretinal neovascularization in senile macular degeneration. Results of a randomized study of 60 cases. Bull Mem Soc Fr Ophtalmol 1982; 94:149–54. Cukras C, Fine SL. Thermal laser treatment in AMD: therapeutic and prophylactic. Int Ophthalmol Clin 2007 Winter; 47(1):75–93. Review. Yoken J, Duncan JL, Berger JW, et al. Laser photocoagulation for choroidal neovascularization in age-related macular degeneration. In: Lim JI, ed. Age-Related Macular Degeneration. New York: Marcel Dekker, 2002:181–201. Macular Photocoagulation Study Group. Recurrent choroidal neovascularization after argon laser photocoagulation for neovascular maculopathy. Arch Ophthalmol 1986; 104(4):503–12. Brown DM, Kaiser PK, Michels M, et al. Ranibizumab versus verteporfin for neovascular age-related macular degeneration. N Engl J Med 2006; 355(14):1432–44. Rosenfeld PJ, Brown DM, Heier JS, et al. Ranibizumab for neovascular age-related macular degeneration. N Engl J Med 2006; 355(14):1419–31. Rosenfeld PJ, Rich RM, Lalwani GA. Ranibizumab: phase III clinical trial results. Ophthalmol Clin North Am 2006; 19(3):361–72. Ferrara N, Damico L, Shams N, et al. Development of ranibizumab, an anti-vascular endothelial growth factor antigen binding fragment, as therapy for neovascular agerelated macular degeneration. Retina 2006; 26(8): 859–70. Ferrara N. Role of vascular endothelial growth factor in physiologic and pathologic angiogenesis: therapeutic implications. Semin Oncol 2002; 29(6 Suppl. 16):10–4.

14 Photocoagulation of AMD-Associated CNV Feeder Vessels: An Optimized Approach Robert W. Flower

Department of Ophthalmology, University of Maryland School of Medicine, Baltimore, Maryland and Department of Ophthalmology, New York University School of Medicine and the Macula Foundation, Manhattan Eye, Ear, and Throat Hospital, New York, New York, U.S.A.

INTRODUCTION Feeder vessel treatment (FVT) of age-related macular degeneration (AMD)-related choroidal neovascularization (CNV); that is, occlusion of just the vessels delivering blood to CNV membranes has long been viewed as an attractive clinical approach, particularly when the neovascular membrane is very near or underlies the fovea. Available clinical evidence clearly indicates that this treatment approach is a successful one that, beyond lesion stabilization, often results in visual improvement. While in recent years the focus of an aggressive quest for an efficacious treatment for AMD-related CNV has been dominated by drug-based approaches, refinement of FVT has continued and reached the point that results from its application appear to rival and in some cases exceed those of other currently available methodologies. Moreover, as reaction to the unmet expectations of single-drugbased approaches has led to investigation of combining extant therapies, FVT—its attributes as a stand-alone treatment notwithstanding—is an attractive combination candidate, because it is not drug based, and it acts directly on the source of blood flow that must be present in every viable CNV membrane. Although elegantly simple as a concept, successfully implementing a routine FVT method has been a protracted process. The history of its development spans a period of nearly 30 years, and the case can be made that its development has been coupled to the evolution of fundus angiography technology, especially choroidal angiography. Today FVT has been refined to take advantage of improvements not only in the devices used for angiogram acquisition and application of laser photocoagulation energy, but also in diagnostic angiogram analysis. In one method of FVT described here, even the method of applying laser energy to feeder vessels (FVs) has been optimized by introduction of dye-enhanced photocoagulation (DEP), wherein indocyanine green (ICG) dye transiting targeted FVs at the instant of photocoagulation acts

to selectively enhance absorption of the laser energy, thereby focusing the thermal tissue damage onto the targeted FV and sparing the surrounding tissues.

ORIGINS OF THE CONCEPT Perhaps the earliest description of FVT in ophthalmology was in 1972 by Behrendt, who discussed argon laser photocoagulation of intraretinal and vitreous FVs of neovascular membranes associated with diabetic retinopathy (1). The then recent availability of visible light wavelength lasers led to numerous such novel approaches aimed at controlling ocular neovascularization. Understandably, all of those were related to retinal and anterior segment neovascularization, since they could be directly visualized by means of readily available optical devices. The choroidal vasculature, on the other hand, was not a popular target of interest, since direct visualization of it was obscured by retinal and choroidal pigments, and in sodium fluorescein angiography images it appeared mostly only as a diffuse “choriocapillaris (CC) flush.” The deeper-lying vascular layers remained obscured so far as routine clinical observations were concerned. At about that same time, in the early 1970s, the concept of routine clinical angiography of the choroidal circulation using ICG dye was being developed. ICG fluorescence angiography initially had been explored as an investigative tool for studying choroidal blood flow in animal experiments. However, since ICG dye already had a long documented history of biocompatibility, exploring its use in human subjects as well was compelling. Since up to that time, relatively little attention had been paid to the choroidal circulation compared to the retina, there was no well-defined clinical goal at first in visualizing human choroidal blood flow beyond academic curiosity, so a rudimentary survey of both normal and diseased eyes was undertaken (2). One of the first groups of patients considered in the survey was those with macular degeneration.

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Figure 1 Simultaneously-acquired fluorescein (left frame) and indocyanine green (1CG) (right frame) angiogram images of the first patient with choroidal neovascularization studied by use of ICG fluorescence angiography.

Figure 1 shows simultaneously acquired fluorescein and ICG angiogram images of the first patient successfully studied by that methodology. The greatly improved ability to visualize the angioarchitecture of AMD-associated CNV lesions afforded by ICG angiography, coupled with the concept of FV photocoagulation, led to the first attempts at ICG-guided photocoagulation of CNV-FVs. Unfortunately, the results of those first attempts were not encouraging: clear differentiation between CNV afferent and efferent vessels was not easy—or in most cases not possible— since both spatial and temporal resolution of the early ICG fluorescence angiogram images was limited, the spot size and aiming precision of the first visible light laser photocoagulation delivery systems also was limited, and perhaps most importantly, the laser light wavelengths available were not ideally suited to the task. For some time thereafter, the concept of FV photocoagulation was not seriously pursued as a clinical tool. Instead, the dominant treatment approach for AMD-associated CNV came to be based on Macular Photocoagulation Study (MPS) recommendations (3). These included destruction of the entire CNV membrane—as delineated by fluorescein angiography—along with an additional margin around the CNV, even when the procedure resulted in an immediate, non-recoverable additional loss of visual acuity (VA). The results of the MPS suggested

that despite an immediate vision loss, three years later a patient so treated statistically would have better VA than if untreated. Those results notwithstanding, few ophthalmologists remained comfortable with the notion of having to destroy the retina in order to save it, preferring for the most part to avoid photocoagulation near the fovea.

REVISITING THE CONCEPT The first notable clinical application of ICG fluorescence angiography was its use in guiding laser photocoagulation of CNV. This method was applied to patients whose clinical and fluorescein angiographic features did not meet the eligibility criteria for laser therapy defined by the MPS recommendations; generally it was applied to cases of poorly defined, or occult, CNV. In this application, use of ICG angiography resulted in improved localization of abnormal choroidal vessels, thereby making treatment by photocoagulation possible (4,5). Whereas this clinical use of ICG undoubtedly contributed to sustaining interest in ICG angiography, arguably it was the commercial availability of the scanning laser ophthalmoscope (SLO) that contributed to increasing interest in ICG angiography. Compared to the predominantly available commercial ICG angiography systems based on fundus camera optics capable of acquiring images at a rate of about one per second,

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the SLO afforded the ability to perform high-speed imaging. Ready access to high-speed ICG image acquisition systems was an important component of renewed interest in FV photocoagulation treatment. The concept of FV photocoagulation was revisited as a treatment for AMD-associated CNV in February, 1998 by Shiraga and coworkers; they reported the results of a pilot trial to assess the feasibility of extrafoveal photocoagulation of subfoveal CNV secondary to AMD (6). Their use of SLO ICG angiography resulted in the identification of FVs in 37 of 170 consecutive patients (22%). In 70% of those 37 cases (26 cases) extrafoveal photocoagulation of the FVs, using 575- to 630-nm wavelength light, resulted in resolution of the exudative manifestations and improved or stabilized VA. The following December, Straurenghi and coworkers (7), also using SLO ICG angiography, reported finding treatable FVs in 15 of 22 patients having subfoveal CNV not amenable to the treatment suggested by the MPS (3). They successfully obliterated the FVs in 40% of the cases, resulting in improved or stabilized VA after more than two years. In a second group of 16 patients they reported a much higher success rate of 75%, attributed to the smaller FV diameters (less than 85 mm) found in this group. In December 1997, yet another series of FV treatments was begun using a high-speed, pulsed-laser (HSPL) fundus camera system for FV identification. (Flower RW, Glaser BM, Murphy RP, Macula Soc. Presentation, 1999.) The HSPL used in this study consisted of a Zeiss fundus camera modified to include a pulsed 805-nm-wavelength diode laser for excitation of ICG dye fluorescence in the choroidal circulation; images were acquired at a rate of 30 per second (8). In this latter study, a higher incidence (about 66%) of FV identification was achieved, apparently due to use of the HSPL system and different angiogram analysis techniques. Nevertheless, treatment success of the latter study appears to be equivalent to that of the other groups, even though the follow-up period was shorter and it focused on occult CNV, whereas the other studies appear to have focused on classic CNV. The common experience of all these studies was that FV photocoagulation appeared to be a viable treatment approach and worthy of continued pursuit, even though the exact nature of the vessels being treated and the most efficacious application of laser energy remain to be determined. Clearly, there is a catch-22 associated with this methodology. There are no histological data on treated CNV-FVs, per se, and the only proof currently available of the accuracy of angiographic CNV-FV identification is improvement or stabilization of the patient’s VA following treatment. But this standard of proof is biased toward failure, since conventional laser photocoagulation of CNV-FVs already has proven to be difficult or

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incomplete in some cases. Therefore, if the full potential of FV treatment is to be accurately assessed and eventually realized, a more consistently successful approach to laser photocoagulation must be devised. And at the same time, a much better understanding of the hemodynamic consequences of FV photocoagulation must be developed in order to facilitate rational analysis of treatment successes and failures.

WHAT IS A FV? Properly characterizing CNV-FVs in terms of their locations within the choroid, their vessel wall structure and the blood flow, is a necessary step in developing the most efficacious photocoagulation method. In that regard, however, histological data about CNV angioarchitecture appear to be at odds with the angiographic appearance of the so-called FVs being treated.

Histological Appearance of CNV-FVs The vessels passing through breaks in Bruch’s membrane and connecting a CNV to the choroidal blood supply can be capillaries, arteries, or veins, as determined by the vessel wall structure. In general, CNV complexes up to 300 mm diameter have only one break containing a capillary-like vessel (9,10). Complexes on the order of 500 mm have two to four breaks, and at least one or two contain a capillary-like vessel; the others transmit only cells. CNV complexes of these dimensions consist of a single layer of capillary vessels on the inner surface of Bruch’s membrane, and they arise from a layer of vessels which lies just beneath, instead of between, the intercapillary tissue pillars; so it is assumed these are new vessels replacing the choroidal capillaries. Because many tissue sections must be cut to find and track these vessels, there are only a few examples in which the vessels can actually be tracked in the choroid, and even then it is not always clear whether they lead to an artery or a vein. (Sarks JP and Sarks SH, written communication, March 14, 1999). Complexes on the order of 2000 mm have more than four breaks, and the vessels passing through are of medium size. These complexes usually are two layers thick, but still lie beneath the retinal pigment epithelium (RPE), and they can be served by wellformed arterial and venous vessels. Complexes from patients with disciform scars have breaks containing larger arteries and veins; these disrupt the RPE and invaded the retina. (Sarks SP and Sarks SH, written communication, March 14, 1999). It has been suggested that on average, there are 2.3 vessels passing through Bruch’s membrane and connecting each CNV to the underlying choroidal vasculature (11). The frequency with which these vessels are capillaries, arteries, or veins has not yet

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Figure 2 Examples of choroidal neovascularization feeder vessels, identified using the high-speed, pulsed-laser fundus camera system, that were successfully photocoagulated, resulting in improved or stabilized vision. In each case, arrows indicate the course of the feeder vessel. Source: From Ref. 12.

been reported, but it is clear that the majority of penetrating vessels encountered are relatively short capillary-like vessels. It is clear also that such small vessels are not likely to be recognized in ICG angiogram images.

Angiographic Appearance of CNV-FVs The most frequently identified and treated FVs reported in studies to date appear to be on the order of one to several millimeters long, a dimension quite large with respect to the penetrating vessels most frequently found in histological preparations. Figure 2 shows examples of FVs, identified using the HSPL fundus camera system, which have been successfully photocoagulated, resulting in improved or stabilized vision. In using that system, identification of FVs is made by first carefully examining the area surrounding the location of a known or suspected CNV complex in high-speed ICG angiogram images,

since the most obvious characteristic of a FV is proximity to CNV. Some FVs are easily identified, as in Figure 2 (top left and right), when they are prominent and easily distinguishable from adjacent choroidal vessels. Often, however, FVs are less prominent, as in Figure 2 (bottom left and right), and identification requires use of an analytical technique such as phi-motion a angiography, which helps a

Phi-motion is a phenomenon first identified by Wertheimer in 1912 (13); it refers to visual perception of motion where none exists. In a situation where there is a gap in visual information, the brain fills in what is missing. An example of the case in point is the appearance of two spatially separated points of light wherein first one is illuminated and, a finite time later, the second one is illuminated. The perception is that of a single point moving from the location of the first point to that of the second. By repeatedly viewing an appropriate segment of a high-speed angiogram image sequence in continuous loop fashion and at an appropriate speed, the phi-motion phenomenon accentuates perception of the movement of dye through vessels.

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Figure 3 A scanning electron micrograph of a corrosion cast of the posterior (Sattler’s) layer of small diameter choroidal arteries and veins that feed and drain the choriocapillaris, which can be seen in the background. For the most part, the veins are oriented from the upper left-hand corner of the image toward the lower right-hand corner; they overlie the arteries. Source: From Ref. 12. Courtesy of Dr. Andrzej W. Fryczkowski.

differentiate a FV from its surroundings by enhancing visualization of blood flow through it, toward the CNV. Determining direction of flow is essential to correctly identifying CNV-FVs—as opposed to their draining vessels—even when their angioarchitecture seems obvious.

Reconciling Histological and Angiographic Data Clearly, the vessels identified in histological specimens as the conduits of blood from the CC to CNVs appear to be different from the so-called FVs identified in

(A)

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angiograms. Typically “FV” refers to an afferent vessel supplying blood to a particular vascular complex, one directly connected to the complex. To be precise, in the case of CNV that definition should apply to the short capillary-like vessels that penetrate Bruch’s membrane and form a CNV/CC connection. The vessels in ICG angiograms dubbed FVs in the recently reported studies of CNV-FV photocoagulation—especially in the case of occult CNV—meet the criterion of being afferent, but they appear to be much larger than the capillary-like vessels seen in the histological specimens. Strictly speaking, therefore, the term “CNVFV,” as applied in angiographic descriptions, appears to be a misnomer for some other choroidal vessel; most likely Sattler’s layer arterioles. The so-called FVs seen in angiograms very much resemble vessels of the choroidal middle layer, or Sattler’s layer, which lies just beneath the CC. Comparison of the ICG angiogram images of the FVs in Figure 2 to the scanning electron micrographs of corrosion casts of the anterior aspect of the CC in Figure 3 demonstrates this similarity. Therefore, it seems a reasonable assumption that the FVs identified in ICG angiograms and reported to have been successfully treated by photocoagulation are Sattler’s layer arteriolar vessels. There is additional evidence to support the notion that the angiographically-defined CNV-FVs are Sattler ’s layer vessels: a commonly observed characteristic of successfully treated FVs is their “beaded” appearance in ICG angiograms (RP Murphy, symposium presentation, Chicago, June

(B)

Figure 4 (A) Indocyanine green (ICG) angiogram demonstrating the commonly observed “beaded” appearance of choroidal neovascularization feeder vessels. (B) The same beaded appearance seen more prominently in the high-speed ICG angiograms of rhesus monkey eye following carotid arterial dye injection. When crossed by small non-dye-filled vessels, the intersections appear as dark segments along the feeder vessel (vessel indicated by the lower arrow); when crossed by small dye-filled vessels, the intersections appear hyperfluorescence due to additivity of fluorescence from the overlapping vessels (vessel indicated by the upper arrow). Source: From Ref. 14.

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3, 2000); an example of that appearance is shown in Figure 4A. The most likely explanation for the beaded appearance is that the dye-filled FV is crossed throughout its length by smaller non-dye-filled choroidal vessels. This same phenomenon is more pronounced in high-speed ICG angiograms of rhesus monkey eyes following carotid arterial dye injection, as demonstrated in Figure 4B, wherein carotid dye injection improves dye wave front definition, enhancing observation of the temporal filling differences between various layers of choroidal vessels. When crossed by small non-dye-filled vessels, the crossings result in dark segments along the FV; when crossed by small dye-filled vessels, the crossings result in hyperfluorescence, due to additivity of fluorescence from the overlapping vessels. The presence of small vessels between the FV and the CC fixes the FV location well below the CC, consistent with the notion that CNV-FVs are Sattler’s layer vessels. Additionally, Arnold and coworkers (15) have shown the choroids of AMD eyes to be as little as half the thickness of those in age-matched normal eyes (e.g., 90 mm compared to 180 g), primarily due to a significant decrease in the number of vessels that normally occupy the middle choroidal layers (Sattler’s layer). So it is possible that the relatively high contrast of some FVs (Fig. 2) is a result of there being fewer than normal adjacent vessels in the same layer, and in the absence of the normal number of adjacent vessels, the FVs may have become preferential channels for blood flow through a diminished Sattler’s layer. Therefore, the assumption that many of the FVs investigators have identified and photocoagulated are Sattler ’s layer arteriolar vessels is at least consistent with the evidence at hand.

THE RELATIONSHIP BETWEEN SATTLER’S LAYER VESSELS (FVs) and CNVs The explanation for apparently successful photocoagulation treatment of so-called CNV-FVs (i.e., Sattler’s layer vessels) lies in the hemodynamic relationship between the Sattler’s layer vessels and the capillarylike vessels that form the CC/CNV communication.

An Anthropomorphic Model of the CC/CNV Connection The relationship proposed to exist between these two types of vessels is modeled in Figure 5, wherein there is no anatomical continuity between them, although functionally they behave as if there were. The figure also demonstrates how blood could move in a functionally contiguous manner from a Sattler’s layer FV, into the CC, and then through a nearby capillary vessel

leading to the CNV during the systolic phase of the intraocular pressure pulse. By comparison to the sinusoid-like structure of the CC vascular plexus, it is likely that resistance to blood flow would be higher through a parallel CNV complex, connected to the CC by the capillary-like vessels that penetrate Bruch’s membrane. In this model, blood flow through the CNV would occur, but it would not be as great as through the underlying CC. In keeping with the pulsatile nature of CC blood flow shown to exist as the result of the perpendicular interface of arterioles and the wide, flat choriocapillaries (8,16), a high hydrostatic pressure head must exist at the interface early during systole, relative to the surrounding CC (as indicated by the collapsed state of the choriocapillaries and the CNV vessels in Fig. 5A,B). In addition to pushing blood into the choriocapillaries, the pressure head would be partially dissipated in forcing some blood into the adjacent penetrating vessel. Thus, a small, pulsatile pressure gradient would be established through the CNV, even though the majority of flow would be through the CC. In this model, closure of the FV or even significant partial closure would have the effect of reducing the pressure head available at the penetrating vessel to a level so low that resistance to flow through the CNV could not be overcome, thereby effectively closing the CNV as well. Thus, there is considerable evidence to support the hypothesis that ultimately the source of blood supplying a CNV is a Sattler’s layer arteriole whose entry into the CC is situated near one of the capillarylike vessels that penetrate Bruch’s membrane, forming a CC/CNV communication. That is, the FVs identified for focal photocoagulation treatment of CNV appear to be Sattler’s layer arterioles that are functionally— but not directly physically—connected to the CNV. Throughout the rest of this discussion, the term CNVFV is intended to imply a Sattler’s layer vessel that is functionally contiguous with a CNV. This leads to the possibility that in some case a direct, anatomically contiguous connection between a Sattler ’s layer vessel and a CNV eventually could evolve, obviating any CC involvement at all; indeed, such an evolution might be the path leading from occult to classic CNV.

A Model of the FV/CC/CNV Hemodynamic Relationship The simple anthropomorphic model of FV/CNV blood flow described above was conceived to account for the clinically observed resolution of retinal edema following FV photocoagulation, even when only partial FV vessel closure is achieved (12). However, since the submacular CC is a true vascular plexus—fed and drained by multiple interspersed arteries and veins—a much more sophisticated

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(D)

Figure 5 A schematic representation of the presumed relationship between a vessel penetrating Bruch’s membrane (penetrating vessel) and connecting a choroidal neovascularization (CNV) membrane to the choriocapillaris (CC). The posterior margin of Bruch’s membrane is represented by the dark horizontal line. A Sattler’s layer choroidal arteriole (presumably a feeder vessel) is shown entering the CC from beneath. The four frames of the figure indicate how blood would move in a functionally contiguous manner from a Sattler’s layer feeder vessel, into the CC, and then though a nearby penetrating vessel during the systolic phase of the intraocular pressure pulse even though the penetrating and feeder vessels are not anatomically contiguous: (A) At the onset of the blood pressure pulse, a high hydrostatic pressure head of blood (represented by the black dots) would develop at the perpendicular interface of arteriole and the wide, flat CC (as indicated by the collapsed state of the choriocapillaries and the CNV membrane). (B) Slightly later during the pulse, In addition to pushing blood into the choriocapillaries, part of the pressure head would be dissipated in forcing some blood into the adjacent penetrating vessel. Thus, a small pressure gradient would be established through the CNV. (C) Still later, blood flow through the CNV would occur, but it would not be as great as through the underlying CC, because by comparison to the sinusoid-like structure of the CC vascular plexus, it is likely that resistance to blood flow through a parallel CNV complex, connected to the CC by capillary-like penetrating vessels, would be higher. (D) Eventually, flow through the CNV would be complete. Source: From Ref. 12.

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Figure 6 Schematic representation of the computer simulated model of the choriocapillaris (CC) and an overlying choroidal neovascular (CNV) membrane. The CC segment is represented by the thin green rectangular box; the red disks within the volume of the box represent the interstitial spaces surrounded by the network of choriocapillaries. One Sattler’s layer arteriolar (red cylinder) and one venous (blue cylinder) vessel are shown connected to the posterior CC. A CNV membrane is represented by the very thin purple rectangular box. Two capillary-like vessels (green cylinders) penetrate Bruch’s membrane (not depicted) and form the CC/CNV connection (penetrating vessels) is shown; in the text, these are referred to as penetrating vessels. In the simulation, the position of the penetrating vessels with respect the Sattler’s layer vessels was varied. Source: From Ref. 14.

model is needed to describe the changes in CC blood flow beneath the CNV following FV photocoagulation. Therefore, a theoretical model for the human CC, based on available histologic and hemodynamic data, was developed to simulate the CC blood flow field before and after FV photocoagulation.b Known angioarchitectural and hemodynamic parameters for the CC and CNV from the literature were used to construct the theoretical model of a section of submacular CC and a small overlying CNV membrane shown in Figure 6. The CC plexus consists of two parallel sheets separated by 7.5 mm, between which 10 in. diameter columns are placed at regular intervals, leaving 15 mm wide channels in between to simulate the CC plexus. Isolated, but well b

This model was developed in collaboration with C. von Kerczek. L. Zhu, A. Ernest, C. Eggleton, and L.D.T. Topoleski from the Department of Mechanical Engineering University of Maryland, Baltimore, Maryland, U.S.A.

separated, precapillary arterioles and venules communicate with the CC plexus and perfuse it with blood. The cross-sectional dimensions of the arterioles and venules are of the same order as the CC thickness, h. The center-to-center spacing between adjacent arterioles and venules is much larger than h. Therefore, the CC was modeled as a planar porous medium containing a widely dispersed set of fluid inflows and outflows, simulating the feeding and draining vessels of Sattler ’s layer. Feeding arteriolar and draining venous vessels consist, respectively, of 7.5 and 15 mm diameter tubes entering the CC from beneath. An overlying CNV membrane was modeled as a parallel miniature version of the CC, but with smaller dimensions that will result in a significantly higher resistance to fluid flow. The communication between the CNV and the CC is by way of two capillary-dimensioned vessels that penetrate Bruch’s membrane. In the model, the position of the CNV

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A1

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Figure 7 The anterior aspect of the computer simulated segment of a human submacular choriocapillaris, marked with the actual locations of arteriolar and venous vessels Sattler’s layer vessels connected to its posterior aspect; the figure also shows the simulated choroidal neovascularization in two different locations. Abbreviation: CNV, choroidal neovascularization. Source: From Ref. 14.

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Normal Condition 0.9621.28 0.325 0.643 0.643 1.917 0.962 1.28 1.599 2 0.962 2.554 0.643 0.962 2.236 1.28 2.873 1.917 1.5993.511.28 0.6431 0.962 0.325 0.3252.236 1.917 0.6431.599

could be changed in order to achieve various spatial relationships between the penetrating vessels and the Sattler’s layer vessels that feed and drain the CC. This theoretical model became the basis for computer simulation of blood flow distribution in a segment of human sub-foveal CC approximately 1300!1000 mm in area. The actual placement of the multiple Sattler’s layer vessels to feed and drain blood from the simulated CC plexus segment was made according to the histologically determined locations of those vessels in one normal human eye (17). Figure 7 shows the anterior aspect of the computer simulated segment of that human submacular CC, marked with the actual locations of arteriolar and venous vessels, Sattler’s layer vessels connected to its posterior aspect; the figure also shows the simulated CNV in two different locations. Blood flow rates in the feeding arterioles and venules were then estimated by matching the predicted precapillary arteriole and venule pressure difference to experimentally measured data; the experimentally measured maximum pressure difference between a feeding arteriole and venule was found to be 4.5 mmHg (18).

0.956

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Figure 8 Isogramic maps of the blood pressure and blood speed fields of the choriocapillaris (CC) segment shown in Figure 7 under normal and simulated vascular photocoagulation conditions. The isogramic lines in the left-hand two frames identify locations of constant pressure (upper frame) and flow (lower frame) throughout the CC segment under normal conditions. The pattern of these lines change, as shown in the other pairs of frames, when either the underlying Sattler’s layer arteries (middle frames) or veins (right-hand frames) are occluded. The particular vessels occluded in these examples are aretriole A1 and venule V1 identified in Figure 7. Source: From Ref. 14.

1.064 2.126 2.3923.845 1.861.372 1.595 1.064 1.33 0.799

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Experimentally measured pressures and pressure differences were applied across the feeding and draining vessels in order to generate maps of blood flow through the computer-simulated model CC segment. Figure 8 shows the normal isobar and isoblood-speed distributions in the computer simulated segment of CC from Figure 7; it also shows how those distributions are altered when one of the Sattler’s layer feeding arterioles is completely occluded. A significant reduction in the local CC pressure probably results in significant changes in the blood flow through an overlying CNV network, since the driving force for CNV blood flow is the pressure difference between the capillary-like vessels that penetrate Bruch’s membrane, forming the CC/CNV communication. Clinical observations indicate that partial—as well as complete—photocoagulation of the (presumed Sattler ’s layer) FV adjacent to a CNV’s penetrating vessel(s) is an effective means of decreasing the blood flow in the CNV (BM Glaser, RP Murphy, G Staurenghi, personal communications, 1999). Therefore, the model also was used to simulate blood flow through a CNV before and after FV laser photocoagulation; the simulation was performed for the CNV membrane situated in two different locations, as indicated in Figure 7. The first location, CNV #1, was between arteriole #2 and venule #1, while the second, CNV #2, was between arteriole #3 and a point equidistant from venules #1 and #2. Photocoagulation of arteriole #2 and of venule #1 resulted in significant reduction of CNV #1 blood flow (71% and 79%, respectively), with similar results in CNV #2 when arteriole #3 was photocoagulated (84% reduction). On the other hand, even the complete closure of venules #1 or #2 produced less than 30% decrease in blood velocity through CNV #2.

Implications of the FV/CC/CNV Hemodynamic Relationship This model predicts that even 50% closure of a blood vessel entering the posterior aspect of the CC in the vicinity of a capillary-like vessel leading to a CNV can be effective in reducing or possibly stopping CNV blood flow, regardless of whether that vessel is a feeding arteriole or a draining venule. In other words, the important hemodynamic event with respect to reducing or stopping CNV blood flow is significant reduction of the blood pressure—hence, blood flow as well—in the local underlying CC. Thus, the predictions of the present computer simulated model support the novel approach to CNV management made previously, namely that (i) rather than total obliteration of a CNV (which frequently results in recurrence), the end point of laser photocoagulation treatment can be reduction of CNV blood flow to the extent that undesirable

manifestations of the CNV—most notably retinal edema—are halted or reversed and (ii) that CNV blood flow reduction can be mediated by reduction of blood flow through the underlying CC (12). There are two important implications to that novel approach, one related to FV treatment and the other related to the mechanics of successful CNV treatments in general. Regarding FV photocoagulation treatment of CNV, the selection criterion for targeted FVs might be extended to include venous as well as arteriolar vessels entering the posterior CC in the vicinity of a CNV membrane. If, indeed, reduction of the underlying CC blood flow is the important treatment goal, then depending upon the orientation of the CNV’s penetrating vessels with respect to the field of vessels feeding and draining the CC, targeting veins or veins in conjunction with arteries may yield the best results. After all, the ramifications of occluding a venous drainage channel to a true vascular plexus, like the posterior pole CC, is not the same as occlusion of the drainage vein of a true end-arteriolar vascular complex. In the former case, blood is diverted to adjacent venous channels, without excessive increase in capillary transmural pressure; whereas in the latter case, venous occlusion likely results in blood flow stasis and elevation of capillary transmural pressure to a level near that across the feeding arterial vessel wall. Since the predicted relationship between CC and CNV blood flows actually is independent of the specific means by which CC blood flow is reduced, the second implication of the results is that reduction of CC blood flow underlying a CNV membrane may be a component mechanism common to successful CNV photocoagulation treatments, including photodynamic therapy (PDT), transpupillaty thermal therapy (TTT), and drusen photocoagulation. It is well established that post-PDT angiograms routinely evidence reduced CC fluorescence (19), and that appears also to be the case following TTT (20). In the case of TTT, reduced CC blood flow may be due to increased resistance to plexus blood flow resulting from heat-induced interstitial tissue swelling and concomitant reduction of CC lulninal space. Angiographic data specifically related to submacular blood flow following photocoagulation destruction of macular drusen have not been presented anywhere; however, it has been demonstrated that CC obliteration occurs with application of moderate to heavy laser burns and that loss of choriocapillaries can add significant resistance to blood flow through the CC plexus (8). If reduced CC blood flow is a component mechanism of successful CNV treatment, regardless of the photocoagulation modality used, then FV photocoagulation arguably might be viewed as the

14: PHOTOCOAGULATION OF CNV FEEDER VESSELS

most effective method. The difference between FV photocoagulation and the other methods is analogous to removing a weed from a lawn by pulling out its roots (FV) versus just cutting off the weed’s leaves. It can be argued that FV photocoagulation is the most precise of the various methods in terms of manipulating CC blood flow, and it minimizes the area of tissue–laser interaction. Moreover, since blood flow through a particular CC area apparently can be manipulated by modulation of adjacent venous or as arteriolar vessels connected to the plexus’ anterior side, it may be that the most precise manipulation of CC blood flow—and hence, treatment of CNV—will be by controlled, partial photocoagulation of carefully selected combinations of arterioles and venules in Sattler’s layer vessels.

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targeted choroidal vasculature. The main premise of DEP is that application of laser light energy with a wavelength matched to the primary wavelength absorbed by a bolus of dye passing through the target blood vessel produces the most efficient

∗

DEVELOPMENT OF A MORE EFFICACIOUS METHOD OF FV TREATMENT The models of CNV-FVs are consistent with the clinical observation that often, even incomplete closure of a FV produces reduction of CNV dye filling, resolution of associated edema, and improved VA. Of course, partial closure of targeted FVs at present is an unintended end-point of Argon and Krypton laser photocoagulation application. In such cases, failure to completely close the relatively deep-lying targeted vessels may be attributable to generation of an insufficiently high temperature gradient, emanating from the RPE where laser light-to-heat transduction occurs. The temperature gradient that is produced does extend into the sensory retina and can produce significant damage there, so the location for FV photocoagulation must be chosen so as not to involve the fovea. It would be desirable, therefore, to avoid the concomitant retinal damage and to make FV photocoagulation more efficient and predictable. This would have the additional potential benefit of allowing such treatment to be applied much closer to the fovea than is presently possible, thereby increasing the number of patients who might benefit from CNV-FV treatment.

The Concept of ICG-DEP An example of a successfully treated FV is shown in Figure 9, and it also shows an undesirable side effect as well: damage to the nerve fiber layer overlying the site of FV photocoagulation. Since CNV-FVs apparently lie below the plane of the CC, a method of photocoagulation that moves the epicenter of the lasergenerated heat closer to those vessels and away from the sensory retina would be an improvement over the presently available method. The concept of ICG-DEP has that potential and, therefore, should be revisited for this application, bearing in mind that its use must be optimized to accommodate characteristics of the

(A)

∗

(B)

∗

(C)

Figure 9 Post-treatment indocyanine green angiogram images of a successfully treated feeder vessel. (A) Pre-treatment: the FV is indicated by asterisk. (B) Post-treatment: note lack of CNV filling. (C) Image shows an undesirable side effect as well: damage to the nerve fiber layer overlying the site of FV photocoagulation. Source: From Ref. 12.

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photocoagulation burn in terms of vessel closure with minimum damage to surrounding tissue. Figure 10 demonstrates the main aspects of ICG-DEP and compares it to FV photocoagulation by conventional laser light photocoagulation. The concept of improving the efficiency of the photocoagulation process by ICG-dye enhancement is not new to

Conventional Visible Light Photocoagulation

treatment of AMD-related CNV, as Reichel and coworkers utilized it for treating poorly defined subfoveal CNV. Eventually they reported their initial clinical investigation in 10 patients (21), but in terms of visual outcome, their results were equivocal, and the technique did not achieve widespread use. The particular dye-enhancement technique they used relied on absorption of infrared laser light energy by dye-stained choroidal blood vessel walls minutes following dye injection. That apparently is a very inefficient process, compared to the one in which the same laser energy is absorbed by dye molecules within the target vessels during transit of a highconcentration dye bolus (12).

Retina RPE

(A) ICG Dye Enhanced Photocoagulation

Retina RPE

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Figure 10 Schematic comparison of choroidal vessel photocoagulation by (A) conventional laser and (B) ICG dye-enhanced laser and (C) ICG angiogram image made immediately posttreatment with ICG-DEP demonstrating incarceration of ICG dye in the treated feeder vessel (arrow) and choroidal neovascularization membrane (circle). Abbreviations: ICG, indocyanine green; RPE, retinal pigment epithelium. Source: From Ref. 12. Courtesy of Dr. B. Eric Jones, Baltimore, Maryland, U.S.A..

A Combined ICG Angiography/DEP System Performance of ICG-DEP requires use of a laser delivery system that permits visualization of intervenously-injected ICG dye as it traverses the vasculature. Such a system was constructed from a Zeiss fundus camera (Carl Zeiss, Oberkochen, Germany) modified to include a pulsed diode laser light source and a synchronized, gated CCD camera for performing high-speed ICG angiography, as previously described (8,22). The fundus camera was further modified so that the output tip of the fiber optic of an 810 nm diode laser photocoagulator (Oculight SLx, Iris Medical Instruments, Mountain View, California, U.S.A.) can be positioned in the plane of the fundus illumination optics pathway normally occupied by the internal fixation pointer; that plane is conjugate to the fundus of the subject’s eye. The He–Ne aiming beam emitted by the photocoagulator appears as a sharply focused spot when viewed through the fundus camera’s video system, and the position of the fiber optic with respect to the subject’s fundus can be controlled by the micromanipulator ’s X- and Y-adjustments. With this configuration, it is possible to deliver 810 nm photocoagulation light pulses to precisely located areas of the fundus while observing the fundus with visible light through the fundus camera eyepiece, making it possible to synchronize photocoagulation laser pulse delivery with arrival of a dye bolus at a targeted vessel site. The fundus camera/laser photocoagulation system is shown in Figure 11. Clinical Application of ICG-DEP Use of the ICG dye-enhanced camera system is demonstrated in the three frames of Figure 12, which show ICG angiogram images from a patient treated with ICG-DEP. Incarceration of ICG dye immediately following laser photocoagulation (center frame) not only provides immediate feedback as to the success of the procedure, but the

14: PHOTOCOAGULATION OF CNV FEEDER VESSELS

(B)

(A)

Figure 11 The fundus camera/photocoagulation system. (A) On the left side of the fundus camera body is a joystick control for positioning the 810 nm wavelength photocoagulation laser beam on the patient’s fundus. (B) The photocoagulation laser aiming beam (red spot) is visualized on the patient’s live indocyanine green (ICG) angiogram, which is seen in the left pane of the monitor located above the patient’s head. Reference ICG angiogram image from a previously made diagnostic study to determine the location of a treatable feeder vessel (FV); the targeted FV is indicated on the reference image by a white cross.

Figure 12 Demonstration of use of the indocyanine green (ICG) dye-enhanced camera system. Left : The site of application of laser energy during subsequent transit of a high concentration dye bolus (arrow). Middle: Incarceration of ICG dye in the choroidal neovascularization (CNV) (circle) distal to the burn site. Right: Validation of vessel closure by follow-up ICG angiography a week later (the circle indicates the location of the now non-perfused CNV).

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(B)

Figure 13 Demonstration of the reduction in retinal tissue damage concomitant to feeder vessel laser photocoagulation using indocyanine green (ICG) dye-enhancement, using identical choroidal arteries arising from a common origin in a pigmented rabbit eye as a model. (A) Arrows indicate locations of laser burns of identical energy on the two identical choroidal arterioles. The left-hand burn was applied without use of ICG dye-enhancement, and the right-hand burn was placed during transit of a highconcentration bolus of ICG dye. (B) Comparison of the extent of retinal pigment epithelium damage resulting from application of the identical laser burns inferior to the medullary rays.

incarcerated dye constitutes as a strongly absorbing target for further laser application without the need to inject additional dye boluses. The reduction in retinal tissue damage concomitant to FV laser photocoagulation using ICG dye-enhancement is demonstrated in Figure 13, which compares the extent of RPE damage resulting from application of identical laser burns to identical choroidal arteries of a rabbit eye, one with and one without presence of a transiting high-concentration dye bolus. Recently, a single center, prospective, randomized study of FVT using ICG-DEP was conducted by Dr. G. Staurenghi (University of Brescia, Italy) under the auspices of Novadaq Technologies, Inc. (Toronto, Canada). The objective of the study was to evaluate the safety and effectiveness of choroidal FV closure in the presence of ICG using the above described fundus camera/laser photocoagulation system. In the study, forty patients were evaluated for presence of visible FVs associated with CNV. Upon identification of the FVs, the patients were randomized into one of two treatment arms: one group of 20 patients was treated by choroidal FV photocoagulation during ICG dye transit (ICG-DEP arm), the other group of 20 patients (Control arm) was identically using the same device system, but FV photocoagulation was done without ICG-DEP, using the laser energy alone. All patients were followed and/or treated at 2, 4, 8, 12 weeks, and 6 months; with 1 additional follow-up at 12 months post-first treatment.

The study demonstrated that the fundus camera/laser photocoagulation system was easy to use, and that treatment session times decreased with experience with the system. The entire diagnostic, treatment and post-treatment confirmation ICG angiography took 21 to 23 minutes; this was similar for both treatment arms. On average, four to five treatment sessions were required for complete treatment in both arms over the course of the study. And on average, the ICG-DEP arm used approximately seven times less energy/treatment session than the Control arm (5.7 J per treatment session versus 38.9 J per treatment session) to close targeted choroidal FVs. Importantly, treatment was more effective and more durable in the ICG-DEP arm, as 90% of the patients were able to have their choroidal FVs closed or partially closed, with 70% of those vessels remaining closed at the last treatment assessment, compared to 77% and 44%, respectively, in the Control arm. During the course of the study, 45% fewer patients in the ICG-DEP arm went on to require alternative treatments for their wet AMD than patients in the Control arm. VA at the end of the treatment phase of this trial, as measured by the Early Treatment Diabetic Retinopathy Scale, showed that, for the whole treated population, on average the VA was stable, and 29% of all patients seen at this study milestone had an improvement in VA. Of those patients who completed the study as per the study prescribed treatment regimen, at the last scheduled treatment visit, 67% had stable or improved

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VA, with 42% having one to four line improvement in VA, while 33% had a decrease of more than three lines of VA: none experienced severe vision loss (more than six lines of VA). Of the nine patients who followed the study prescribed treatment regimen and had a VA equal or better than 20/100 at entry, seven (78%) had stable or improved VA at the last treatment visit, with four (44%) having a one to four line improvement in VA and two (22%) had more than three line decrease in VA. Overall, the study added to the body of data demonstrating the efficacy of the concept of FVT of wet AMD. In addition, it demonstrated that the fundus camera/laser photocoagulation system simplifies FV treatment by allowing for real-time visualization of choroidal FVs during treatment. Moreover, FV photocoagulation with ICG-DEP produced a more effective and more durable treatment outcome than FV photocoagulation using laser only.

THE FUTURE OF CNV-FV TREATMENT The current anti-vascular endothelial growth factor (anti-VEGF) drugs, Avastin or Lucentis, have experienced significant clinical success to date. It appears that these anti-VEGF drugs have such strong anti-permeability effects on CNV membrane vessels that fluid outflow into surrounding tissues is reduced or stopped, resulting in stabilized or even improved VA. This can occur early, before the CNV angioarchitecture is substantially changed in the process, leaving some CNV blood flow intact; but repeated injections are needed. Interestingly, this is analogous to what happens in FVT, where only partial FV closure occurs or where reperfusion recurs following complete closure. Apparently, even partial FV closure results in reduced transmural pressure across CNV membrane vessels, which in turn reduces fluid outflow. In these cases, CNV angioarchitecture also appears substantially unchanged, and there is no concomitant recurrent edema, resulting in stabilized or improved VA. It has been postulated that during the period of reduced transmural pressure, neovascular membrane maturation progresses to a level of vessel structural integrity such that fluid outflow no longer occurs once the higher pre-FVT transmural pressures are reestablished. If the foregoing understanding of the methods of action of the anti-VEGF and FVTs continues to hold true, then their use in combination might prove to be symbiotic in a way that leads to a very effective treatment approach, since both act to reduce edema resulting from CNV membrane fluid outflow, but by different pathways. However, as a stand-alone treatment, FVT ultimately still may prove to be the most desirable approach, since even when repeated treatments are applied, those treatments are totally non-

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invasive with respect to the peripheral retina and wall of the eye itself, and they are inexpensive. Moreover, consideration should be given to the long-term ramifications of successfully achieving the currently sought clinical treatment endpoint, namely CNV obliteration. To the extent that CNV (especially “occult” CNV) serves to augment or replace functionally compromised choriocapillaries, successful destruction of the CNV ultimately would leave the adjacent sensory retina and RPE without adequate metabolic support from the choroidal circulation. In that situation, the RPE and retina likely would atrophy. It is for this reason that CNV blood flow obliteration as the treatment endpoint should be reconsidered in favor of modulating CNV blood flow just to the point that retinal edema is ameliorated, since that leaves a level of choroidal metabolic support for the RPE and retina in place. Owing to FVT’s highly localized application and the ability it affords for immediate CNV blood flow assessment, DEP-FVT allows for a level of individual patient treatment titration that drug-based treatment cannot provide. Aggressive CNV behavior—rapid membrane growth, edema formation, etc.—has been viewed as a destructive event, and conventional treatment aims to remedy such behavior by complete CNV obliteration. But the frequent recurrence of CNV following such treatment could be nature’s continuing effort to compensate for the original—and perhaps now exacerbated—defect. Instead, such aggressive CNV behavior could be viewed as an over compensation for some metabolic or other blood flow related defect. And if laser treatment were to be applied in such a way as to just reduce the blood flow to aggressive CNV by an appropriate amount—perhaps until the CNV vasculature matures—then further aggressive behavior might be avoided; those cases of inadvertent incomplete FV closure resulting in improved vision would be examples. Photocoagulating the FVs supplying CNV associated with AMD not only can be a successful treatment method (6,7) especially for occult CNV. Indeed, there may be an important difference between the response of CNV evoked by direct application of laser energy, as in conventional treatment, and that evoked by reducing blood flow through the otherwise undisturbed membrane. If ultimately FV photocoagulation treatment were to be refined along these lines, the laser would become more a precision instrument to modulate blood flow than a weapon for destruction of the very retinal tissue whose function we are trying to conserve. Additionally, because of the pre- and posttreatment high-speed ICG angiograms the method requires, information about choroidal hemodynamics is being accrued that otherwise probably would never be available.

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Identification of FVs is made by first carefully examining the area surrounding the location of a known or suspected CNV complex in high-speed ICG angiogram images. It is a reasonable assumption that the FVs identified in ICG angiograms and reported to have been successfully treated by photocoagulation are Sattler’s layer arteriolar vessels. Clinical observations indicate that partial—as well as complete—photocoagulation of the (presumed Sattler’s layer) FV adjacent to a CNV’s penetrating vessel(s) is an effective means of decreasing the blood flow in the CNV. FV photocoagulation may be the most precise method of manipulating CC blood flow and minimizes the area of tissue/laser interaction. CNV blood flow eradication as the treatment endpoint should be reconsidered and replaced with modulation of the CNV blood flow just to the point that retinal edema is ameliorated, since that leaves a level of choroidal metabolic support for the RPE and retina in place.

REFERENCES 1. Behrendt T. Therapeutic vascular occlusions in diabetic retinopathy. Arch Ophthalmol 1972; 87:629–33. 2. Patz A, Flower RW, Klein ML, et al. Clinical application of indocyanine green angiography. In: DeLaey JJ, ed. International Symposium on Fluorescein Angiography. Documenta Ophthalmologica Proceedings Series. Vol. 9. The Hague: Dr. W. Junk b.v., 1976:245. 3. Macular Photocoagulation Study Group. Subfoveal neovascular lesions in age-related macular degeneration: guidelines for evaluation and treatment in the macular photocoagulation study. Arch Ophthalmol 1991; 109:1242–57. 4. Slakter JS, Yannuzzi LA, Sorensen JS, et al. A pilot study of indocyanine green videoangiography-guided laser treatment of primary occult choroidal neovascularizaton. Arch Opthtalmol 1994; 112:465–72. 5. Schwartz S, Guyer DR, Yannuzzi LA, et al. Indocyanine green videoangiography guided laser photocoagulation of primary occult choroidal neovascularizaton in age-related macular degeneration. Invest Ophthalmol Vis Sci 1995; 36:S244.

6. Shiraga F, Ojima Y, Matsuo T, et al. Feeder vessel photocoagulation of subfoveal choroidal neovascularization secondary to age-related macular degeneration. Ophthalmology 1998; 105:662–9. 7. Staurenghi G, Orzalesi N, La Capria A, et al. Laser treatment of feeder vessels in subfoveal choroidal neovascular membranes: a revisitation using dynamic indocyanine green angiography. Ophthalmology 1998; 105:2297–305. 8. Flower RW. Extraction of choriocapillaris hemodynamic data from ICG fluorescence angiograms. Invest Ophthalmol Vis Sci 1993; 34:2720–9. 9. Sarks SH. Aging and degeneration in the macular region: a clinicopathological study. Br J Ophthalmol 1976; 60:324–41. 10. Schneider S, Greven CM, Green WR. Photocoagulation of well-defined choroidal neovascularization in age-related macular degeneration. Retina 1998; 18:242–50. 11. Green WR, Enger C. Age-related macular degeneration: histopathologic studies. The 1992 Lorenz E Zimmerman lecture. Ophthalmology 1993; 100:1519–35. 12. Flower RW. Experimental studies of indocyanine green dye-enhanced photocoagulation of choroidal neovascularization feeder vessels. Am J Ophthalmol 2000; 129:501–12. 13. Wertheimer M. Experimentelle Studien ueber das Sehen von Bewegung. Z Psychol 1912; 61:161–265. 14. Flower RW, von Kerczek C, Zhu L, Ernest A, Eggleton C, Topoleski LDT. A theoretical investigation of the role of choriocapillaris blood flow in treatment of sub-foveal choroidal neovascularization associated with age-related macular degeneration, copyright 2001 (in press). 15. Arnold JJ, Sarks SH, Killingsworth MC, et al. Reticular pseudodrusen: a risk factor in age-related maculopathy. Retina 1995; 15:183–91. 16. Flower RW. High-speed ICG angiography. In: Yannuzzi LA, Flower RW, Slakter JS, eds. Indocyanine Green Angiography. Mosby: St. Louis, 1997:86–94. 17. Fryczkowski AW, Sherman MD. Scanning electron microscopy of human ocular vascular casts: the submacular choriocapillaris. Acta Anat 1988; 132:265–9. 18. Maepea O. Pressures in the anterior ciliary arteries, choroidal veins and choriocapillaris. Exp Eye Res 1992; 54:731–6. 19. Flower RW, Snyder WA. Expanded hypothesis on the mechanism of photodynamic therapy action on choroidal neovascularization. Retina 1999; 19:365–9. 20. Reichel E, Berrocal AM, Ip M, et al. Transpupillary thermotherapy (TTT) of occult subfoveal choroidal neovascularization in patients with age-related macular degeneration. Ophthalmology 1999; 106:1908–14. 21. Reichel E, Puliafito CA, Duker JS, et al. Indocyanine green dye-enhanced diode laser photocoagulation of poorly defined subfoveal choroidal neovascularization. Ophthalmic Surg 1994; 25:195–201. 22. Flower RW. Variability in choriocapillaris blood flow distribution. Invest Ophthalmol Vis Sci 1995; 36:1247–58.

15 Photodynamic Therapy ATul Jain

Department of Ophthalmology, Stanford University Medical Center, Stanford, California, U.S.A.

Darius M. Moshfeghi

Adult and Pediatric Vitreoretinal Surgery, Stanford University Medical Center, Stanford, California, U.S.A.

Mark S. Blumenkranz

Vitreoretinal Surgery, Department of Ophthalmology, Stanford University Medical Center, Stanford, California, U.S.A.

INTRODUCTION Photodynamic therapy (PDT) is a therapeutic modality that entails the administration of a photosensitizer with its subsequent accumulation in the target tissue and then its activation by non-thermal monochromatic light corresponding to the sensitizer’s absorption profile (1). Powerful oxidizing agents such as cytotoxic singlet oxygen and free radicals are produced causing irreversible cellular damage. PDT has traditionally focused on the treatment of cancer (2), but the potential for selective destruction of diseased vessels, while sparing normal overlying tissues, coupled with promising clinical efficacy, resulted in its use for the treatment of age-related macular degeneration (AMD), particularly subfoveal choroidal neovascularization (CNV). PDT selectivity for the CNV is achieved both through photosensitizer retention in CNV new vessels and through targeted light application. Illumination is restricted to the diseased area and the limited depth of light penetration restricts damage to underlying tissues.

VASCULAR TARGETING PDT has been used successfully in the treatment of certain cancers due to the remarkable selectivity of many photosensitizers for tumor tissue. PDT causes direct cellular injury in addition to microvascular damage or “shutdown” within the illuminated tumor. Uptake is considered to be due to the increased expression of low-density lipoprotein receptors on tumor cells and neovascular endothelial cells. Porphyrin photosensitization in mammals was studied as early as 1910 when Hausmann investigated the effects of hematoporphyrin and light on mice (3). The results established the phototoxic propensity of

porphyrins, and Hausmann concluded that the peripheral vasculature was one of the primary PDT targets. In 1963, Castellani and coworkers demonstrated the microvasculature to be a crucial target (4). PDT-mediated neovascular damage became a mainstay in the treatment of wet AMD and has only recently began to be replaced by newer anti-vascular endothelial growth factor (VEGF) therapies. Endothelial cells accumulate certain photosensitizers and are susceptible to PDT-induced destruction. The subcellular localization of motexafin lutetium (Lu-Tex) was determined in human umbilical vein endothelial cells using fluorescence microscopy. Lu-Tex exhibits a fluorescence emission profile at 750 nm and this signature fluorescence marker is used to characterize and quantify sensitizer concentrations within the tissues. Lu-Tex was found to localize within the lysosomes and endoplasmic reticulum as evidenced by co-staining with organelle-specific fluoroprobes. Following illumination, some relocalization of the sensitizer occurred with partitioning being observed in the mitochondria, suggesting that the primary subcellular localization site could not possibly fully account for all of the PDT-induced damages. Sensitizer-alone and light administrationalone treatment groups did not induce any changes in the cell viability. Significant cell death due to Lu-Tex-mediated PDT was observed in endothelial cells producing a steep dose response. Vascular occlusion following PDT is marked by the release of vasoactive molecules, vasoconstriction, blood cell aggregation, endothelial cell damage, blood flow stasis, and hemorrhage. The response is dependent on sensitizer type, concentration, and the time interval between administration and treatment. Benzoporphyrin derivative monoacid ring A (BPD-MA)-induced

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PDT resulted in selective destruction of tumor microvasculature in a chrondosarcoma rodent model when compared with the surrounding normal microvasculature; illumination was applied within 30 minutes following sensitizer administration (5). However, no acute change in vascular status was observed when illumination occurred at three hours. The vascular shutdown results correlated with the anti-tumor effect since tumor-bearing animals treated at five minutes responded more positively than those treated at three hours.

LIGHT APPLICATION The light used for ophthalmic applications is nonthermal monochromatic laser light matched to the sensitizer’s far-red (infrared) absorbance profile. Infrared light possesses greater transmission through both blood and tissue than light at lower wavelengths thereby enabling the treatment of pigmented or hemorrhagic lesions. The energy at which light is delivered is a product of the radiant power (expressed in milliwatts per square centimeter, mW/cm2) and the time of illumination. The radiant energy, often termed fluence, is expressed as joules per square centimeter (J/cm2). Therefore, to deliver a fluence of 50 J/cm2 light at a power density of 600 mW/cm2, an illumination time of 83 seconds is required. Upon illumination, photons (hy) interact with the ground singlet state sensitizer (1Sensitizer) causing it to undergo an electronic transition to an activated short-lived excited singlet state (1Sensitizer*). The singlet state can then either convert back to the ground state causing fluorescence or undergo intersystem crossing to generate the longer-lived excited triplet state sensitizer (3Sensitizer*). From the triplet state, a photon can be emitted causing phosphorescence with conversion to the ground state or the triplet state can interact with oxygen or biological substrates leading to microvascular damage (6,7). Two photooxidation processes can occur between the triplet state and molecular oxygen (3O2) causing irreversible damage to vascular components. The direct interaction of the excited triplet state with biomolecular substrates is termed the type-I mode and is favored in areas with low oxygen concentrations. Biomolecular radicals are generated and react with oxygen-forming cytotoxic oxidizing products. The type-II mechanism entails interaction from the excited triplet state sensitizer to ground state oxygen-producing singlet oxygen ð1 OÞ with theoretical regeneration of the ground state sensitizer. However, photobleaching and photoproduct formation can deplete the ground state sensitizer concentration. Singlet oxygen is highly electrophilic, oxidizing biological substrates and initiating a cascade of radical

chain reactions that damage cellular components. Singlet oxygen production is thought to be responsible for most of the damage induced by PDT. Singlet oxygen possesses a reactive path length of less than 0.02 mm so that any effect has a limited potency (2). The photochemical processes involved are complex and are different for each sensitizer and are also subject to the microenvironment. Intersystem crossing is kinetically important for the formation of the excited triplet state and for PDT potency. Molecules with high fluorescence quantum yields will generate lower triplet quantum yields and are more likely to be used as diagnostic agents. Conversely, molecules with low fluorescence quantum yields will generate high triplet quantum yields and therefore should produce a high yield of cytotoxic species.

PDT AGENTS The ideal photosensitizer should be chemically pure and possess the appropriate physical and biologic properties that make it inherently non-toxic until activated by light. The agent should possess strong absorption properties in the far-red spectral region (660–780 nm) where light has greatest penetration into blood and tissue and possess efficient photophysical properties for destroying neovascular endothelial cells. The sensitizer should also localize selectively in the neovasculature while being rapidly cleared from the blood and overlying photoreceptors. In addition, rapid cutaneous clearance would limit cutaneous photosensitivity. Several photosensitizers were explored and underwent different stages of preclinical and clinical development. Photosensitizing candidate molecules are generally related to porphyrins. Porphyrins are fused tetrapyrrolic macrocycles that are omnipresent in nature as major biological pigments. Protoporphyrin IX, a typical porphyrin molecule, forms the nonprotein portion of hemoglobin. Reduction, oxidation, or expansion of the macrocyclic ring leads to different molecular subclasses. A reduction at one of the four pyrrole rings in the porphyrin macrocycle yields a chlorin molecule. The electronic conjugation system is altered causing further absorption into the far-red wavelength region, from 630 to approximately 660 to 690 nm. Increasing the macrocycle conjugation system further, by the formation of a pentadentate, metallophotosensitizer yields a texaphyrin molecule and results in even further absorption in the far-red spectral region (700–760 nm). Phthalocyanines are tetrapyrrolic structures fused together by nitrogen atoms instead of carbon bridges; absorption is exhibited in the 650- to 700-nm wavelength region. Purpurins possess a reduced pyrrole ring and also

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an extended ring conjugation system; the absorption maxima is between 650 and 690 nm.

BENZOPORPHYRIN DERIVATIVE MONOACID (VERTEPORFIN, VISUDYNEe, BPD-MA) BPD-MA consists of equal amounts of two regioisomers that differ in the location of the carboxylic acid and methyl ester on the lower pyrrole rings of the chlorin macrocycle. BPD-MA, due to its hydrophobicity, is formulated with liposomes. The monoacid analogues were developed because they produced greater PDT responses compared with the diacids (8). The monoacid regioisomers are converted, in the liver, to the diacids. The regioisomers responded similarly in experimental efficacy settings; however, the pharmacokinetic properties were different in the rat, dog, and monkey but not in humans, where the plasma half-life was five to six hours (9,10). It is thought the latter may be due to differences in plasma esterases or lipoprotein profiles. PDT studies undertaken using experimentally induced CNV in primates resulted in closure of the neovasculature and choriocapillaris, but not the retinal vasculature. Liposomal BPD-MA was infused at a dose of 0.375 mg/kg for 10 to 32 minutes. Illumination with infrared light at a fluence of 150 J/cm2 (689–692 nm laser light at 600 mW/cm2) occurred 30 to 55 minutes following the start of the infusion (7). When the same treatment parameters were performed on normal primate eyes, some retinal pigment epithelium (RPE) damage and choriocapillaris closure occurred locally with little damage in contiguous tissues. When light was delivered within 30 to 45 minutes following sensitizer delivery, sensitizer administration rates had little effect on vascular occlusion rates. BPD-MA localization in the choroid and RPE was confirmed using fluorescence microscopy in rabbits. Retention occurred within five minutes with progression to the outer segments within 20 minutes. No BPD-MA was detected within the choroid or photoreceptors at two hours; however, a small trace was detected in the RPE at 24 hours (11). A similar pharmacokinetic pattern was observed in monkeys using in vivo fluorescence imaging (12). The long-term effects on the retina and choroid were evaluated in cynomolgus monkeys with experimental CNV (13). Fundus photography and angiography analyses were performed at 24 hours and then weekly for four to seven weeks following a treatment with 0.375 mg BPD-MA/kg and a fluence of 150 J/cm2. Eyes were examined histologically at the end of the follow-up period. CNV closure also resulted in the closure of the choriocapillaris with damage occurring to RPE cells. However, these areas appeared

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to regenerate somewhat in the four to seven weeks study period. Of 28 CNV lesions followed for four weeks, 72% remained closed. However, lesion retreatment was necessary to sustain vascular closure. The effect of three different dosing treatments was evaluated in disease-free primate eyes (14). Treatments, using sensitizer doses of 6, 12, or 18 mg/m2, 20 minutes after drug infusion and a fluence of 100 J/cm2 were performed every two weeks. A cumulative dose response was observed. Damage to the retina, choroid, and optic nerve was limited in the 6 mg/m2 sensitizer subgroup. The higher dose groups exhibited severe choriocapillaris and photoreceptor damage at six weeks. Many other photosensitizer agents [i.e., tin ethyl etiopurpurin (Purlytine, SnET2), (Optrine, lutetium texaphyrin, Lu-Tex), mono-L-aspartyl chlorin e6 (NPe6 or MACE), chloroaluminum sulfonated phthalocyanine (AlPcS4), and ATX-S10] have been explored for the treatment of exudative AMD and other retinal conditions; however, they have not been used in clinical practice (15–27). Verteporfin PDT has emerged as the dominant therapeutic option for exudative AMD since the publication of the previous edition of this book, and we will focus most of our discussion to the clinical results with this photosensitizer.

LIGHT CONSIDERATIONS Generally any light source that is matched to the photosensitizer’s absorption profile can be used for PDT. For ophthalmology, fiberoptic delivery of a laser source is required to permit focusing on the retina with a slit lamp system. Lasers are needed because highenergy monochromatic collimated light can be coupled efficiently to fiber optics allowing delivery within an acceptable time frame. Diode lasers that are stable, compact, and relatively inexpensive in the 630- to 730nm wavelength range are readily available.

CLINICAL OUTCOMES PDT is a superior alternative to laser photocoagulation for subfoveal CNV. Using preclinical CNV models, the neovascularization and normal choriocapillaris can be closed while preserving the outer and inner retina. In contrast, during the process of destroying neovascularization lying beneath the RPE and sensory retina with laser photocoagulation, thermal conductance to the retina results in acute necrosis of all layers of the retina. This later results in atrophy leading to loss of vision. However, with PDT treatment, visual acuity generally remains stable immediately after treatment and has been shown, in a minority of patients, to improve immediately.

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This suggests that the photoreceptors and inner retinal elements are generally preserved (28).

Verteporfin Human Trials The safety and efficacy of verteporfin (BPD-MA, Visudynee) have been confirmed (Table 1) in phase I, II, and III clinical trials (28,34,35). The phase I and phase II studies proved that a single treatment of verteporfin PDT could occlude CNV vessels for one to four weeks following administration, as measured by fluorescein angiography (34). The maximal tolerated light dose, defined by retinal closure, was 150 J/cm 2. The minimal light dose required to achieve closure of the vessels was 25 J/cm2. Treatment of Age-Related Macular Degeneration with Photodynamic Therapy Trial The one-year results of the Treatment of Age-Related Macular Degeneration with Photodynamic Therapy

(TAP) Study were published in 1999 (28). The study consisted of two multicenter, double-masked, placebocontrolled randomized trials with identical protocols. Eligible AMD patients had subfoveal CNV whose greatest linear dimension was up to 5400 mm and best-corrected visual acuity ranged from 20/40 to 20/200. Verteporfin at 6 mg/m2 was infused intravenously for 10 minutes. Then, a diode laser was used to activate the dye (689-nm diode laser, 50 J/cm 2, 600 mW/cm2, 83-second duration, spot size 1000 mm larger than greatest linear diameter of the CNV lesion) 15 minutes after the start of infusion. Patients were evaluated by clinical examination and fluorescein angiography approximately every three months, and retreated at the discretion of the treating ophthalmologist. Of the 609 eyes enrolled in the study (402 treatment and 207 placebo), 94% completed the 12 months follow-up. In the treatment group, 246 (61%) of 402 eyes lost fewer than 15 letters of visual acuity

Table 1 Summary of Treatment of Age-Related Macular Degeneration with Photodynamic Therapy Reports 1–6 TAP Report #

Follow-up (months)

Main outcomes

1 (28)

Two multicenter, double-masked, placebocontrolled randomized clinical trials

Study design

12

2 (29)

Two multicenter, double-masked, placebocontrolled randomized clinical trials

24

3 (30)

Subgroup analysis of TAP

24

4 (31)

Subgroup analysis of TAP

24

5 (32)

Open-label extension of TAP

36

6 (33)

Natural history data from TAP

61% PDT versus 47% placebo had less than 15 ETDRS letters loss (p!0.001) Predominantly classic SFCNV subgroup: 67% PDT versus 39% placebo had less than 15 ETDRS letters loss (p!0.001) 53% PDT versus 38% placebo had less than 15 ETDRS letters loss (p!0.001) Predominantly classic SFCNV subgroup: 59% PDT versus 31% placebo had less than 15 ETDRS letters loss (p!0.001) Predominantly classic SFCNV subgroup at 12 mo: 33% PDT versus 61% placebo had at least 15 ETDRS letters loss (p!0.001) Predominantly classic SFCNV subgroup at 24 mo: 41% PDT versus 69% placebo had at least 15 ETDRS letters loss (p!0.001) Predominantly classic SFCNV subgroup at 24 mo: 55% PDT versus 32% placebo greater than 20/200 visual acuity (p!0.001) Predominantly classic SFCNV subgroup at 24 mo: loss of six or more letters of contrast sensitivity was 21% PDT versus 45% placebo (p!0.05) Predominantly classic SFCNV subgroup at 24 mo: loss of 15 or more letters of contrast sensitivity was 7% PDT versus 12% placebo (p!0.05) Predominantly classic SFCNV subgroup treated with PDT: 37.5% at 24 mo versus 41.9% at 36 mo lost at least 15 ETDRS letters Predominantly classic SFCNV subgroup treated with PDT: visual acuity change of K1.9 lines at 24 mo versus K2.0 lines at 36 mo 40% of patients in the placebo arm with minimally classic disease converted to predominantly classic SFCNV

Abbreviations: ETDRS, Early Treatment Diabetic Retinopathy Study; PDT, photodynamic therapy; SFCNV, subfoveal choroidal neovascularization; TAP, treatment of age-related macular degeneration with photodynamic therapy.

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Verteporfin in Photodynamic Therapy Trial In the Verteporfin in Photodynamic Therapy (VIP) Study, patients with pathologic myopia, occult CNV, and classic CNV (with visual acuity better than 20/40)

Summary of Verteporfin in Photodynamic Therapy Reports 1–4

VIP Report # 1 (36)

2 (37)

3 (38)

4 (39)

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were evaluated (Table 2) (36–39). For pathologic myopia with subfoveal CNV, patients treated with verteporfin PDT were less likely than placebo to lose 8 and 12 Early Treatment Diabetic Retinopathy Study (ETDRS) letters at the 12-month follow-up (36). Additionally, at the 24-month follow-up, the distribution of change in visual acuity favored the PDT group over placebo (38). One arm of the VIP trial evaluated verteporfin for treatment of occult-only CNV with at least 50 letters on the ETDRS scale or some classic component with at least 70 letters (better than 20/40) on the ETDRS scale (37). For the subgroup of occult-only CNV, the PDT group was less likely than placebo to lose 15 and 30 ETDRS letters at the 24-month follow-up. For the subgroup of patients with a visual acuity score of less than 65 ETDRS letters or lesion size less than or equal to four disc areas, verteporfin PDT-treated patients were less likely than placebo to lose 15 and 30 ETDRS letters at the 24-month follow-up. While the overall safety profile was favorable, 4.4% of PDT-treated patients lost at least 20 ETDRS letters within seven days of treatment (37). This loss of at

from baseline, compared with 96 (47%) of 207 placebo eyes, a difference that was statistically significant (p!0.001) (28). Subgroup analysis demonstrated the greatest benefit (67% vs. 39% losing less than 15 letters of visual acuity, p!0.001) for those eyes with predominantly classic CNV (greater than 50% of the entire lesion being classic CNV at baseline before treatment). No significant lasting adverse effects were reported (28). The results at various time points following enrollment are summarized in Table 1 (28–33). The average number of verteporfin PDT treatments was 3.4 by 12 months and 5.6 by 24 months (28,29). The treatment effect for verteporfin PDT of predominantly classic subfoveal CNV persisted at 24 months (29). Additionally, for the subgroup of predominantly classic CNV patients, those treated with PDT were more likely to have visual acuity greater than 20/200 at the 24-month follow-up (30).

Table 2

PHOTODYNAMIC THERAPY

Study design Multicenter, double-masked, placebocontrolled randomized clinical trial for treatment of patients with SFCNV due to pathologic myopia Multicenter, double-masked, placebocontrolled randomized clinical trial for treatment of patients with occult SFCNV (at least 50 ETDRS letters) or some classic CNV (at least 70 EDTRS letters)

Multicenter, double-masked, placebocontrolled randomized clinical trial for treatment of patients with SFCNV due to pathologic myopia Prospective non-comparative case series looking at patients from control group in VIP trial

Follow-up (months) 12

24

24

24

Main outcomes 72% PDT versus 44% placebo lost fewer than eight ETDRS letters (p!0.01) 86% PDT versus 67% placebo lost fewer than 15 ETDRS letters (pZ0.01) 54% PDT versus 67% placebo lost at least 15 ETDRS letters (pZ0.023) 30% PDT versus 47% placebo lost at least 30 ETDRS letters (pZ0.001) Occult-only subgroup: 55% PDT versus 68% placebo lost at least 15 ETDRS letters (pZ0.032) Occult-only subgroup: 29% PDT versus 47% placebo lost at least 30 ETDRS letters (pZ0.004) Subgroup visual acuity score less than 65 ETDRS letters or lesion size less than or equal to four disc areas at baseline: 49% PDT versus 75% placebo lost at least 15 ETDRS letters (p!0.001) Subgroup visual acuity score less than 65 ETDRS letters or lesion size less than or equal to four disc areas at baseline: 21% PDT versus 48% placebo lost at least 30 ETDRS letters (p!0.001) 4.4% of PDT versus 0% of placebo lost at least 20 ETDRS letters within 7 days of treatment 36% PDT versus 51% placebo lost at least eight ETDRS letters (pZ0.11) Distribution of change in vision favored PDT (pZ0.05) Continued monitoring for patients with occult with no classic lesions If acuity decreases or predominantly classic features develop, PDT should be considered

Abbreviations: CNV, choroidal neovascularization; ETDRS, Early Treatment Diabetic Retinopathy Study; PDT, photodynamic therapy; SFCNV, subfoveal choroidal neovascularization; VIP, verteporfin in photodynamic therapy.

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least 20 ETDRS letters from baseline visual acuity within seven days was termed acute severe visual decrease (40).

TAP and VIP Trials The TAP and VIP trial data were combined and analyzed in a series of reports (Table 3) (40–43). The most significant data to be gleaned from these reports was that baseline lesion size was the most important predictor of visual acuity following verteporfin PDT, regardless of lesion composition (41). Size was a significant factor for patients with predominantly classic lesions greater than one disc area, minimally classic lesions less than four disc areas, and occult-only lesions less than five disc areas (42). Verteporfin PDT was also evaluated for the treatment of subfoveal CNV secondary to pathologic myopia, ocular histoplasmosis, angioid streaks, and idiopathic causes (44,45). The main findings of these

papers were that verteporfin was well tolerated, effective in decreasing fluorescein leakage, and broadly applicable to subfoveal CNV, regardless of etiology. Unfortunately, both studies are limited by their small numbers and lack of controls. The Photodynamic Therapy of Ocular Histoplasmosis Study trial has yielded two reports to date (46,47). In a non-comparative, prospective study, 56% and 45% of patients gained at least seven ETDRS letters following verteporfin for subfoveal CNV secondary to ocular histoplasmosis at the 12- and 24-month follow-up periods, respectively.

Evolution of PDT Treatment Spaide and colleagues popularized the use of concomitant intravitreal triamcinolone acetonide and PDT (48). They demonstrated that combination therapy resulted in improved visual acuity and lack of fluorescein leakage following therapy, with the greatest

Table 3 Summary of Treatment of Age-Related Macular Degeneration with Photodynamic Therapy and Verteporfin in Photodynamic Therapy Reports 1–4 TAP and VIP Report #

Purpose

Follow-up (months)

Outcomes Baseline: mean predominantly classic lesion (3.4 DA) smaller than occult-only (4.3 DA) and minimally classic (4.7 DA) Visual acuity change from baseline to 24 mo: significant treatment effect for lesion size effect (smallerOlarger), but not for composition or baseline visual acuity (pZ0.01) For the entire TAP and VIP population, only lesion size was a significant predictor following treatment (pZ0.032 and 0.043 with and without last observation carried forward respectively) Lesion size was significant at p!0.05 for the following lesion compositions: predominantly classic greater than 1 DA, minimally classic less than 4 DA, and occult-only less than 5 DA Lesion size was a significant predictor of at least 15 ETDRS letters loss at 24 mo (pZ0.009) Guidelines presented and examples given for interpretation of angiograms following PDT 15 occurrences in 14 eyes of 14 patients (0.7% in TAP and 4.4% in VIP trial) 11 events occurred following first treatment Ocular and non-ocular adverse events: 92.3% PDT and 89.1% placebo (pZ0.114) Higher “visual disturbances” following verteporfin: 22.1% PDT versus 15.5% placebo (pZ0.054) in TAP trial and 41.7% PDT versus 22.8% placebo (p!0.001) in VIP trial Injection site reactions: 13.1% PDT versus 5.6% placebo (p!0.001) Photosensitivity reactions: 2.4% PDT versus 0.3% placebo (pZ0.016) Infusion-related back pain: 2.4% PDT versus 0.0% placebo (pZ0.004)

1 (41)

To determine the effect of lesion size and visual acuity in patients with SFCNV treated with verteporfin PDT

24

2 (42)

To describe angiographic guidelines for PDT

24

3 (40)

To describe acute severe visual acuity loss (20 or more ETDRS letters) within 2– 4 days of PDT To determine safety data in the TAP and VIP trials

24

4 (43)

24

Abbreviations: DA, disk areas; PDT, photodynamic therapy; SFCNV, subfoveal choroidal neovascularization; TAP, treatment of age-related macular degeneration with photodynamic therapy; VIP, verteporfin in photodynamic therapy.

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effect seen in treatment-naı¨ve patients (48). These results were durable, lasting out to 12 months, and the most frequent side effect was increased intraocular pressure in 38.5%. These results have been supported by similar work, which suggests that the results are broadly applicable to all sub-types of AMD (49–55). Other combination therapies include other steroids and anti-VEGF drugs. Recently, retinal specialists have been utilizing dexamethasone in combination with PDT. The data from this and other steroid combination studies should be published in the near future. The FOCUS Study studied the combination of ranibizumab (Lucentis, Genentech, South San Francisco, California, U.S.A.) and PDT versus PDT alone as a treatment for AMD patients with predominantly classic CNV. The FOCUS Study showed that the combined use of PDT with ranibizumab (Lucentis) was better than PDT alone (56). Further details on the FOCUS Study are found in Chapter 8 of this book.

SUMMARY POINTS & &

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Verteporfin PDT has proven itself useful in the treatment of subfoveal CNV of several etiologies. There are many exciting reports indicating that the efficacy of verteporfin PDT can be enhanced with the concomitant intravitreal triamcinolone acetonide for all types of subfoveal and non-subfoveal CNV (46,48,50,53,57–60). While recent anti-VEGF therapies hold much promise for the treatment of CNV, there are initial reports that verteporfin PDT might play a significant role as an adjunctive treatment used in conjunction with these new therapies (56,61–65). There is a need for long-term prospective studies to quantify and validate these initial reports. Verteporfin PDT has been shown to be useful in the treatment of subfoveal CNV for AMD as well as other etiologies. Use of verteporfin PDT can be enhanced with the concomitant use of intravitreal triamcinolone acetonide. Many studies are currently underway evaluating the use of verteporfin PDT with other steroids and anti-VEGF agents with initially promising initial results. It may be that, in the future, the role of verteporfin PDT will be as an adjunct in combination with antiVEGF or other intravitreal therapies.

REFERENCES 1. Henderson BW, Dougherty TJ. How does photodynamic therapy work? Photochem Photobiol 1992; 55(1):145–57. 2. Dougherty TJ, Gomer CJ, Hender BW, et al. Photodynamic therapy. J Natl Cancer Inst 1998; 90(12):889–905.

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16 Radiation Treatment in Age-Related Macular Degeneration Christina J. Flaxel

Casey Eye Institute, Oregon Health & Science University, Portland, Oregon, U.S.A.

Paul T. Finger

New York University School of Medicine, The New York Eye Cancer Center, New York, New York, U.S.A.

INTRODUCTION Age-related macular degeneration (AMD) is a leading cause of rapid and severe visual loss and legal blindness in developed countries (1,2). Ten million Americans are visually disabled due to AMD and 10% of patients aged 66 to 74 show signs of AMD (3,4). Estimated prevalence is from 7% to 30% in persons aged 75 to 85 years (4–6). The “wet” form of AMD is responsible for the most severe and rapid vision loss. In North America, 200,000 to 400,000 people will develop this form of AMD each year. Wet AMD accounts for 12% of cases overall but 90% of cases of legal blindness (see chap 8 on Wet AMD) (4). Vision loss due to neovascular (wet) AMD involves the growth of abnormal “new” vessels through breaks in Bruch’s membrane from the choroid and under the retinal pigment epithelium (RPE). Unfortunately these new vessels, called choroidal neovascular membranes (CNV), leak serum, blood, and other exudates, resulting in many of the problems related to the wet form of the disease (refer to the chap 1 on pathology of AMD). It is these new vessels that have been the primary target of most current therapies (see Chapters 13–18). Of these therapies, laser treatment, photodynamic therapy (PDT), intravitreal injections with pegaptanib sodium and ranibizumab have been proven by prospective randomized clinical trials to be effective in treating CNV (7–35). Other anti-angiogenic agents that are targeting these new vessels are undergoing clinical trials (36–40) (Chapter 17).

RATIONALE FOR RADIATION THERAPY FOR AMD When compared with proven and experimental treatment methods, theoretical advantages of radiation therapy include absence of iatrogenic mechanical or thermal laser damage and systemic side effects (41).

An additional advantage is that eyes with primarily occult CNV are eligible for treatment (41) as are eyes with extensive subretinal hemorrhage. In addition, unlike PDT, pegaptanib or ranibizumab sodium treatment, radiation is known to exert a longer-term effect on tissues. Thus repeated treatments may not be necessary. Radiation therapy for AMD has been studied for the past 10 years. Eight randomized, controlled trials have evaluated the use of various radiation types and methods of delivery for treating AMD. Thus far, studies have shown varying degrees of benefit from radiation therapy, with a trend toward better results with higher radiation doses and fewer (larger) treatment fractions. The scientific rationale for using radiation therapy for a benign disease characterized by neovascular growth is based on experimental and clinical evidence. Radiation is known to potentially destroy vascular tissue (42–45). Specifically, low-dose radiation has been shown to inhibit neovascularization (46–49). For example, in plaque-irradiated choroidal melanomas, a ring of chorioretinal atrophy is commonly found around the tumor ’s base and decreased or absent blood flow are demonstrated by fluorescein angiography (Fig. 1). These findings demonstrate the ability of radiation to destroy normal and neovascular blood vessels, but the resultant chorioretinal atrophy is an unacceptable endpoint when treating macular degeneration (49,50). If relatively low-dose radiotherapy could inhibit CNV and secondary disciform scars, this would lead to better visual outcomes (Fig. 2A,B). The main question persists: is there a therapeutic window in which the dose of radiation used is high enough to induce regression of CNV but low enough to spare the normal retina and choroid? Radiation specialists believe this is possible. Proliferating endothelium is more susceptible to radiation damage than nonproliferating capillary endothelial cells and larger vessels, and thus neovascular endothelial cells and

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Figure 1 Example of chorioretinal atrophy at the edge of a melanoma treated with radioactive plaque.

inflammatory cells are particularly radiosensitive (51). There is also the potential for radiotherapy to inhibit further neovascular growth and induce neovascular regression by inducing programmed cell death and modifying the growth factor profiles of the neovascular complexes (44,52). This has been shown by the regression of both benign intracerebral arteriovenous malformations and choroidal hemangiomas after radiation therapy (53–55). Finally, it is thought that inflammation may play a role in neovascularization and, as noted, radiation inhibits the inflammatory response (44,56).

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Radiation Toxicity Doses of ionizing radiation absorbed by the body are reported in conventional units called grays (Gy) or Systeme Internationale (SI) units called rads, representing a given quantity of energy delivered per gram of tissue. A rad is 100 ergs of energy per gram of tissue, while a gray (Gy) equals 100 rads [as does a Gray Equivalent, used when the type of radiation is not standard (i.e., the charged particles of proton beam irradiation)]. The potential toxicity of radiation is well known (45,47,49,57–61). However, studies have shown that the normal neural retina and choroid are relatively radiation resistant (60,47). It is also known that factors influencing the development of radiation retinopathy include total dose delivered, daily fraction size, preexisting microangiopathy, and diabetes or prior chemotherapy (50,51). Fractionation of the radiation involves dividing the total amount of radiation into smaller doses and delivering these doses over an extended period of time. These small, frequent doses allow healthy cells time to grow back, repairing damage inflicted by the radiation. However, fraction size affects dose; for example, 400 cGy delivered in one over a five minutes period does not equal to 200 cGy per day for two days. The 400 cGy delivered over a short period of time will deliver a higher overall amount of radiation than the second dosage method. While radiation-induced retinopathy has been reported at doses of 30 to 35 Gy, it is more commonly associated with doses of 45 to 60 Gy (Fig. 3). Radiation optic neuropathy is rare at doses below 50 Gy (Fig. 4A–C) (50,51,57–59). Fraction sizes greater than 2.5 Gy may predispose to toxicity, especially with total doses greater than 45 Gy (58,59). However, there is increasing evidence that fractionated doses

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Figure 2 (A) Late phase fluorescein angiogram showing subfoveal choroidal neovascular membrane prior to treatment. (B) Late phase fluorescein angiogram of same lesion six months post-14 gray equivalent (GE) proton beam irradiation without leakage.

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Figure 3 Radiation retinopathy one year following proton beam radiation using 14 gray equivalent (GE).

with larger daily fraction sizes are lower than standard overall doses can be delivered safely and effectively to small regions. Lens doses of 15 Gy or more will induce cataract and transient dry eye; keratitis and epiphora are expected complications (57–59,62). Other concerns with external beam therapy are radiation exposure of the brain and contralateral eye (Fig. 5) (56–59).

PRIOR STUDIES AND ALTERNATE DELIVERY METHODS FOR RADIATION TREATMENT Initial reports regarding radiation for AMD began to appear in the literature in 1993 (63). Chakravarthy’s preliminary results described 19 patients who were treated with radiation therapy for subfoveal CNV due to AMD. The study also included seven matched control subjects. At one year, 63% of treated patients showed stabilization of vision, while there was deterioration of acuity in all control eyes over the same time period. By image analysis, this study also showed significant neovascular membrane regression in 77% of treated patients at one year, with concurrent progressive enlargement of the neovascular membranes in all control subjects (63). These results and those from other centers led to a prospective, randomized British trial of radiation therapy which reported results in 2002 and is discussed below in more detail (64). Multiple additional reports on external beam radiotherapy (EBRT) and plaque radiotherapy have showed promising but variable results. In 1996, Finger and colleagues reported the results of low-dose EBRT of 12 to 15 Gy and plaque

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Figure 4 (A) Post-radiation optic neuropathy after 14 gray equivalent (GE) proton beam treatment, one year after treatment. (B,C) Note in these early and late fluorescein angiography’s that the choroidal neovascular membrane (CNVM) appears dry.

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Figure 5 External beam radiotherapy (EBRT) dose overlay showing radiation delivered to other structures during EBRT. Source: From Ref. 65.

radiotherapy with equivalent dosage in 137 patients. They found decreased subretinal hemorrhages, exudates, and leakage of neovascular membranes with maintenance of visual acuity (65). Subsequently, Stalmans et al. reported failure to control CNV with radiation dosage of 20 Gy in 2 Gy fractions in 111 patients (66). Spaide and colleagues reported similar findings in 1997, when 10 Gy delivered in 5 Gy fractions that failed to control neovascular growth in AMD. This study never disclosed what percentage of treated patients had recurrent CNV (previously treated by laser photocoagulation) (67). Several further reports in 1998 and 1999 reported possible beneficial effects of radiation. Conducted in France, the Radiotherapy Study, conducted in France, reported potential benefit to 16 Gy delivered in foursessions of 4 Gy each with mean follow-up of 6.4 months (68). In 1999, a second French group from France also reported stabilization of visual acuity and anatomical outcome in eyes with AMD (69). However, this group also reported a significant rate of complications, including radiation retinopathy, optic neuropathy, choroidal vasculopathy, and branch retinal vein occlusion when patients received doses of either 20 Gy in five fractions via lateral beam (effectively, a 30 Gy dose) or 16 to 20 Gy in four to five fractions delivered via lateral arc (69). This study did not include a control group. Follow-up time ranged from 12 to 24 months (69). Chakravarthy undertook a meta-analysis of Phase I clinical trials utilizing low-dose external beam radiotherapy. Results were published in 2000 (70). This report suggested that low-dose EBRT inhibited exudative AMD, but that higher doses were more effective in preventing severe vision loss

(O6 lines on the Snellen visual acuity chart) (70). In support of this conclusion, Berginks and colleagues reported good results with relatively high-radiation doses of 24 Gy and concluded that there was a dose– response effect, with more favorable effects at higher dosages (71,72). The only published study to evaluate treatment of recurrent CNV with radiation was by Marcus and colleagues who reported the safety and visual outcome of radiation treatment (73). They treated 18 eyes consecutively with seven fractions of 2 Gy for a total dose of 14 Gy, then treated the next 16 eyes with five fractions of 3 Gy for a total dose of 15 Gy. They found no radiation toxicity, but also no significant differences in contrast sensitivity or fluorescein angiography stabilization rates, though they noted a trend for palliative benefit with higher fraction sizes of 4 Gy or higher (73).

Implant Radiation Therapy (Brachytherapy) Several groups have used brachytherapy to deliver a relatively high dose of radiation to the involved macula with less irradiation of surrounding structures, using methods developed for localized treatment of ocular tumors (Fig. 6A,B) (74–76). Finger and his group employed plaque radiotherapy in eyes with neovascular AMD with no adverse effects (65,74). They found no sight-limiting complications in this Phase I clinical trial, in which they treated 23 eyes with palladium-103 plaques (Figs. 7 and 9) (74). Encouraged by these early results, they enrolled an additional eight eyes and treated all eyes with a mean dose of 17.62 Gy by palladium-103 plaque (76). Their seven year results were reported in 2003, with the conclusion that most patients experienced decreased exudation or stabilization with the dosage employed. They recommended a randomized clinical trial to evaluate brachytherapy for AMD treatment (Fig. 8A,B) (76). Since this report, the group has increased their dose (35 Gy–2 mm from the inner sclera) utilizing 10 mm eye plaques and pallidium-103 seeds. They have noted no adverse effects and everyone had promising results (personal communication). Charged Particle Radiation Therapy In June 2000, Friedrichsen and Flaxel published on the use of proton beam irradiation for subfoveal CNV in AMD along with their data from the Phase I/II planned dose-escalation clinical trial (77). This method of irradiation allows a higher dose (and dose rate) to be delivered to a specific volume of tissue. Like most forms of external beam radiation therapy, proton beam therapy requires an entry site and irradiates all the tissue in its path. However, proton H dose volumes are limited to a section of the eye, decreasing irradiation of normal tissues outside the

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Figure 7 A palladium-103 plaque assembly with seeds prior to implantation.

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Figure 6 (A) Dose overlay of plaque radiation delivery. (B) Typical plaque used for brachytherapy treatment for AMD (10 mm). Source: From Ref. 65.

beam, and in the contralateral eye. Proton beam irradiation was delivered as a single dose, utilizing light field patient orientation with temporal beam entry, initially with 8 GE (Grey equivalent) beginning in March 1994 and increasing to 14 GE in March 1995. No acute radiation-related adverse effects were noted. Twenty-one eyes were treated with 8 GE followed by an initial stabilization of subretinal leakage on fluorescein angiography (FA) in 50% of eyes at 12-month follow-up but with regrowth in all but three eyes at 15-month follow-up. However, in the 14 GE-treated eyes, 83% showed no leakage after 12 months of follow-up and 78% of eyes had unchanged or improved vision. For those eyes followed for longer than nine months (in the 14 GE-treated group), 83% with 20 out of 100 or better vision prior to proton beam treatment showed improvement in vision. Also, severe visual loss

increased up to 37% at two years with 8 GE-treated eyes, while with 14 GE, the incidence of severe visual loss was 3.7% throughout the follow-up period. There were no cases of cataract, dry eye, lash loss, or optic neuropathy in any of the study eyes and no radiation retinopathy in the 8-GE group; however, radiation retinopathy was found in 48% of eyes treated with 14 GE at a mean of 14 months. There was one case outside the study of severe proliferative radiation retinopathy and optic neuropathy within one year of treatment, with severe visual loss. The authors concluded that their preliminary data suggest that proton beam irradiation correlates with CNV regression, maintains visual function, is more effective at 14 GE, is less beneficial in larger lesions and that radiation complications are more common with longer follow-up but only in the 14-GE group (77). Because of the significant risk of complications, proton beam treatment is not recommended until further studies can be done regarding dose delivery and with consideration of fractionization of the dosage.

REVIEW OF CONTROLLED RADIATION STUDIES FOR AMD There are now several completed studies in the use of radiation in AMD (Table 1). Reports on randomized trials of radiation treatment include those from Holz’s RAD Study Group in Germany (78), Kobayashi and colleagues in Japan (79), the United Kingdom group

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Figure 8 (A) Fluorescein angiography of an eye with CNV before implantation of palladium-103 plaque. (B) Fluorescein angiography of the same eye following treatment with palladium-103 plaque. Abbreviation: CNV, choroidal neovascular membranes.

(64), Valmaggia and colleagues from Switzerland (80), Marcus et al. from the Medical College of Georgia (81,82), and the Age-related Macular Degeneration Radiation Trial (AMDRT) study group report from the United States (84,85). The RAD study is a randomized, prospective, double-blind, placebo-controlled trial performed at nine centers throughout Germany (78). This study enrolled 205 patients who were treated with either eight fractions of 2 Gy (101 eyes), or eight fractions of 0 Gy (104 eyes). At one-year follow-up, no benefit was seen in either classic or occult subfoveal CNV due to AMD (approximately 50% of treated eyes had only

occult CNV, while the other half had a combination of classic and occult disease). There have been no serious complications relating to the radiation treatment to date (78). A randomized, prospective, placebo-controlled trial was also carried out at a center in Japan (79). This study enrolled 101 patients and followed them for two years. They also reported no significant treatment-related side effects from a total dose of 20 Gy delivered in 10 divided doses over a period of 14 days, with irradiation through a single lateral port. The investigators concluded that radiotherapy showed a beneficial effect compared with no treatment, with favorable factors being smaller area of CNV, higher degree of occult CNV, and better initial visual acuity (79). Both groups are continuing follow-up on all patients. Hart et al. reported the results of a large, multicenter randomized trial in the United Kingdom in 2002. This trial included 203 patients randomly assigned either to radiotherapy using 12 Gy of 6 mV photons (delivered in six fractions) or observation (64). They did not find a statistically significant benefit to radiation treatment and felt their results did not support the routine use of radiation treatment for AMD (64). A Swiss group reported the results of 18-month follow-up in 161 patients with subfoveal CNV who were enrolled in a prospective study (80). The examiners treated the posterior pole of the affected eye with 1 Gy (4!0.25 Gy) in the control group and 8 Gy (4!2 Gy) or 16 Gy (4!4 Gy) in the treatment groups. They found that patients with classic CNV, or with initial distance visual acuity R20/100, benefited more from treatment. However, no significant difference was found between control and treatment groups in reading ability and size of CNV (80). They also reported no radiation treatment side effects in any group (80). At Association for Research in Vision and Ophthalmology (ARVO) in 2003, Marcus and colleagues from the Medical College of Georgia reported the four-year results of a small, doublemasked clinical trial that included 42 observed and 41 treated eyes (81,82). They used low-dose external beam irradiation at 14 Gy in seven fractions of 2 Gy, and reported no benefit and possible detriment to vision in long-term (2–4 years) follow-up (81,82). Another Japanese study published in 2004 with two-year follow-up utilized external-beam radiation therapy in 21 eyes of 18 patients, with a group of 15 non-treated controls (83). This group reported improved or maintained visual acuity rates of 81% in the treated group versus 40% in the control group (83). This study, however, was non-randomized. Another non-randomized trial from Japan also reported shortterm benefit to low-dose radiation in 68 eyes (86).

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Figure 9 TheraSightw Ocular Brachytherapy System. (A) Assembled TheraSight System. (B) Representation of device behind the macula. (C) Closeup of applicator with lever engaged retract the shield.

(C)

The problem of conflicting data from multiple studies led the National Eye Institute to sponsor a prospective randomized pilot study in the United States (84,85). This non-funded, multi-center pilot study included two groups of patients randomized Table 1

RADIATION TREATMENT IN AMD

to either treatment or observation, and was called the AMDRT (84,85). Eligibility criteria for the new subfoveal CNV study included lesions not amenable to Macular Photocoagulation Study (MPS) laser treatment, classic, mixed or occult CNV by FA, blood

Comparison of Published Clinical Trial Results Utilizing Radiation in AMD No. of patients

Radiation dosage (total)

Holz (78) Kobayashi (79) Hart (64) Valmaggia (80)

Author

205 101 203 161

Marcus (81,82)

83

8 fractions 2 Gy (16 Gy) 10 fractions 2 Gy (20 Gy) 6 fractions 6 mV photons (12 Gy) 4 fractions of 2 Gy (8 Gy) or 4 fractions of 4 Gy (16 Gy) 7 fractions of 2 Gy (14 Gy)

Churei (83) Marcus (73)

36 34

AMDRT (84,85)

88

10 fractions of 6 mV X rays (20 Gy) 7 fractions of 2 Gy (14 Gy) or 5 fractions of 3 Gy (15 Gy) 5 fractions of 4 Gy (20 Gy)

Conclusion (follow-up) No benefit (1 yr) C benefit (2 yr) stable vision and stable lesion size No benefit (2 yr) C benefit (18 mo) less lines of vision lost in both treated groups No benefit (2 yr), possible detriment to vision in long term (4 yr) C benefit (2 yr) improved or maintained vision No benefit (1 yr) No benefit (1 yr) (modest short-lived benefit at 6 mo)

Abbreviations: AMD, age-related macular degeneration; AMDRT, age-related macular degeneration radiotherapy trial.

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(A)

(B)

Figure 10 (A) Immonen’s round strontium-90 plaque applicator. (B) Freire’s strontium-90 plaque applicator. Source: From Ref. 92.

obscuring !50% of the lesion, visual acuity (VA)O20/ 320, and no contraindication to EBRT (i.e., prior chemotherapy, diabetes, or history of periorbital or ocular radiation). Randomization was to either EBRT (five daily sessions of 4 Gy for a total dose of 20 Gy) or observation. The primary outcome measure was a three-line or greater loss of visual acuity over the five-year follow-up period. There was also a recurrent CNV study arm with similar criteria (84,85). Eighty-

eight patients were enrolled through 10 sites and were randomized to either radiotherapy [20 Gy delivered in five daily fractions of 4 Gy each; 6 mV (NZ41)] or no radiotherapy (sham NZ22 or observation NZ25). The results were reported in 2004 and concluded that external beam radiation at 5!4 Gy may have a modest and short-lived (six-month) benefit in preserving visual acuity. There were no safety concerns (84,85).

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Multimodality Treatment and Novel Methods for Radiation Delivery Marcus and colleagues from the Medical College of Georgia submitted an ARVO abstract in 2002, updated in 2004, on the use of transpupillary thermotherapy (TTT) and radiotherapy of CNV in AMD (87,88). The initial report was a safety evaluation in which four eyes of four patients were treated with TTT at 810 nm for 60 seconds at a power of 360 to 1000 mW, followed within eight hours by administration of 6 mV photon beam to deliver 20 Gy in five fractions at 4 Gy per fraction over five days (87). They found no safety risk and proceeded with a prospective non-randomized case series including eight patients following the same protocol (88). They found mixed results with the treatment of occult subfoveal CNV, but again, there were no safety concerns (88). This study has, however, been halted due to little subject interest in undergoing a combination of two experimental therapies (personal communication). In 2002, Tong and colleagues from the University of California at Davis reported on the use of stereotactic external beam radiation to treat eyes with AMD (89,90). This method allows radiation to be delivered to a smaller, better-defined area than standard EBRT. Patients treated with varying doses of radiation were followed for 24 months (89). They concluded that the method was safe at all studied dosages with stable visual acuity until 12 to 18 months posttreatment, at which time the effect of the radiation appeared to cease (89). At doses of 28–32 Gy, vision tended to stabilize for a longer period (at least 24 months) (89). The oneyear data from this pilot study werepublished in 2005 (90). The investigators found no significant acute side effects and no benefit in either VA or membrane size from increasing the radiation dosage. They concluded that their results were consistent with trends in palliative benefit and that there was no evidence that therapeutic effectiveness is dose-dependent. Therefore, they found no justification for potentially dangerous escalations in radiation dosage for treatment of neovascular AMD (90). Other novel methods of delivering radiation are being studied, including a spoon-shaped device made by Theragenics. This is inserted through a conjunctival incision and traverses to an episcleral submacular position, where the radiation source is uncovered for a short (minutes) period of time (75,91). Hubbard reported results of preliminary work with the Theragenics device (Therasight Ocular Brachytherapy System) at ARVO 2005 and found the device to be well tolerated by patients and readily positioned and inserted by clinicians. No adverse events were reported after short post-operative follow-up (75). In a personal communication, the company has supplied the following device description and Figure 9: “The

RADIATION TREATMENT IN AMD

241

TheraSightw Ocular Brachytherapy System (TheraSight System) is a radiation device that primarily consists of a sealed palladium–103 source on the distal end of an insertion applicator. The device delivers high dose rate, low energy X rays of 21–23 keV in a minimally invasive procedure where the source is inserted in the retrobulbar space behind the eye. The energy is deposited locally to the target tissue, consisting of new choroidal blood vessels intruding into the subretinal space. The radiation therapy is intended to reduce neovascularization.” This device delivers about 14 Gy to the inner retina. Other applicators include Immonen’s applicator and Freire’s applicator, both for strontium-90 (92). Immonen’s applicator was calculated to deliver 15 Gy to the inner retina (Fig. 10A) and Freire’s applicator allows a dose at 1.5 mm depth of 6 cGy/second, thus allowing the total dose delivered to be altered based on exposure time (Fig. 10B). Finger has pointed out that low-energy photo-emitting palladium-103 will deposit less radiation to the subjacent sclera, choroids, and retina than the beta-particle emitting 90Sr, possibly explaining why Immonen et al. noted increased and earlier chorioretinal atrophy within the targeted zone (Fig. 11A,B) (92).

(A)

(B)

Figure 11 (A) Immonen pre-treatment fluorescein angiography (FA) utilizing strontium-90. (B) Immonen posttreatment FA.

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Baseline 20/250 28 let.

3 Months 20/200 36 let.

6 Months 20/200 35 let.

(A)

15 Gy Dose

7-002

Baseline 20/250

3 Months 20/200

6 Months 20/200 (B)

(C)

15 Gy Dose

7-002

Figure 12 (A) Subretinal radiation dose of 15 Gy, FA at baseline, three and six months demonstrating development of inactivity and subretinal fibrosis without signs of radiation toxicity, respectively. (B) Same eye as (A) OCT at same time periods showing subretinal fibrosis and inactivity of lesion. Abbreviations: OCT, optical coherence tomography; FA, fluorescein angiography.

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Fujii et al. evaluated the feasibility and initial safety of retinal-sparing subretinal delivery of strontium beta-radiation using a novel-selective subretinal brachytherapy system (Neovista, Atlanta, Georgia) on 90 rabbit and 4 dog eyes (92). The surgery involved vitrectomy, creation of a subretinal bleb, and introduction of the probe, which was calculated to deliver a radiation dose of 0–246 Gy into the subretinal space (92). Lim and co-workers from Los Angeles presented further work with the Neovista device in 10 patients at the 2005 ARVO meeting (91). This was a tolerability and safety study that compared two probe designs delivering 26 Gy to the CNV over a period of two to three minutes, reportedly sparing the overlying retina. They found no retinal detachments or endophthalmitis complications; however, there were three adverse events that led to further device modifications (91). Figure 12 was supplied by the Neovista company demonstrating the results in one of their initial trial eyes. The group has since switched to an epiretinal radiation delivery device.

Several well-organized, multi-center clinical trials conducted in the United States and Europe have shown no benefit to EBRT (64,78–84). Most of these studied doses or dose rates less than those used in brachytherapy or proton irradiation studies. Three of these studies did show evidence of some benefit in limiting lesion size and vision loss, mainly with radiation dosages of 20 Gy and higher (Table 1) (79,80,83). In addition, it is possible that radiation treatment might be of benefit when combined with PDT or antiangiogenic drugs, or with TTT as described by Marcus and colleagues (87,88). Combined treatment would potentially allow complete closure of the neovascular complex, with PDT or injection of an anti-angiogenic agent followed by radiation to extend the effects of treatment. Similarly, groups studying low-dose proton beam radiation combined with PDT hope that this will limit CNV recurrence. This approach might avoid the complications seen with higher doses of radiation using the proton beam, or of multiple laser or pharmacologic treatments. Finally, other groups are evaluating different ways to deliver radiation in order to limit toxicity and allow higher radiation doses (75,91). This review has found significant evidence that radiation can halt the growth of choroidal neovascularization. However, the prospective randomized evidence-based studies reported to date do not support the widespread treatment of patients. Further prospective randomized studies are needed

243

to actually determine whether a different method of delivering the radiation will offer longer-term benefit with less chance of toxicity, or whether a more efficacious method might involve combining radiation with another treatment modality.

SUMMARY POINTS &

&

&

&

CONCLUSIONS

RADIATION TREATMENT IN AMD

Proliferating endothelium is more susceptible to radiation damage than are non-proliferating capillary endothelial cells and larger vessels, and thus neovascular endothelial cells and inflammatory cells are particularly radiosensitive. Radiation may induce programmed cell death and modify the growth factor profiles of the neovascular complexes as well as limit the inflammatory response. Factors influencing the development of radiation retinopathy include total dose delivered, daily fraction size, preexisting microangiopathy, and diabetes or prior chemotherapy. While radiation-induced retinopathy has been reported at doses of 30–35 Gy, it is more commonly associated with doses of 45–60 Gy (Fig. 5). Radiation optic neuropathy is rare at doses below 50 Gy.

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87. Lee S, Sheils W, Redd J, Samy C, Marcus D. Multimodality transpupillary thermotherapy and radiotherapy of choroidal neovascular membranes in age-related macular degeneration: a phase I safety study. Invest Ophthalmol Vis Sci 2002; 43 (E-abstract 4411). 88. Ying M, Fuller J, Alexander J, Sheils W, Lee Y, Marcus D. Multimodality transpupillary thermotherapy and radiotherapy of occult subfoveal choroidal neovascular membranes in AMD. Invest Ophthalmol Vis Sci 2004; 45 (E-abstract 5136). 89. Tong A, Hauser D, Barak A, et al. Stereotactic external beam radiation treatment in eyes with AMD CNV—a 2-year follow-up. Invest Ophthalmol Vis Sci 2002; 43 (E-abstract 1221). 90. Barak A, Hauser D, Yipp P, et al. A phase I trial of stereotactic external beam radiation for subfoveal choroidal neovascular membranes in age-related macular degeneration. Br J Radiol 2005; 78:827–31. 91. Lim JI, DeJuan E, Sadda V, et al. Subretinal radiation treatment of occult CNV due to AMD. Invest Ophthalmol Vis Sci 2005; 46 (E-abstract 1384). 92. Finger PT, Immonen I, Freire J, Brown G. Implant radiotherapy for exudative macular degeneration associated with subretinal neovascularization. In: Peyman G, Meffert S, Conway MD, Chou F, eds. Vitreoretinal Surgical Techniques. London: Martin Dunitz, 2001:555–60.

17 Anti-VEGF Drugs and Clinical Trials Todd R. Klesert

Doheny Eye Institute, University of Southern California, Los Angeles, California, U.S.A.

Jennifer I. Lim

University of Illinois School of Medicine, Department of Ophthalmology, Eye and Ear Infirmary, UIC Eye Center, Chicago, Illinois, U.S.A.

Phillip J. Rosenfeld

Bascom Palmer Eye Institute, Miami, Florida, U.S.A.

INTRODUCTION In 1989, Ferrara and Henzel (1) isolated a diffusible protein from bovine pituitary follicular cells that showed cell-specific mitogenic activity for vascular endothelium. They named this protein vascular endothelial growth factor (VEGF). Further research showed that VEGF was in fact Michelson’s factor X, which was the postulated diffusible angiogenesis factor (2). As discussed in Chapter 5, VEGF was then shown to have a major role in choroidal neovascularization (CNV) (3,4). The human VEGF-A gene, located on chromosome 6p21.3, consists of eight exons and seven introns. Alternative splicing produces mRNA transcripts that code for at least six different protein isoforms: 121, 145, 165, 183, 189, and 206 amino acids in length (5). These different isoforms vary in their affinity for heparin binding, and as such, in their affinity for the extracellular matrix. The larger isoforms, such as VEGF189 and VEGF206, bind heparin with high affinity, and are therefore almost completely sequestered in the extracellular matrix. The smaller isoform, VEGF121, does not bind heparin and is freely diffusible. All VEGF isoforms contain a plasmin cleavage site. Cleavage at this site creates a freely diffusible, 110 kD, bioactive form of VEGF (VEGF110). Plasmin-mediated extracellular proteolysis may therefore be an important regulator of VEGF bioavailablility (6).

CURRENT ANTI-VEGF THERAPIES Aptamers: Pegaptanib Sodium (Macugen, New York) The first anti-VEGF therapy to undergo clinical testing was a VEGF aptamer. Approved by the Food and Drug Administration (FDA) in 2004, Pegaptanib (Macugen—OSI/Eyetech Pharmaceuticals, New York) was the first anti-VEGF agent with proven efficacy for the treatment of CNV secondary to

age-related macular degeneration (AMD). Pegaptanib is an aptamer—a short single-stranded oligonucleotide sequence that functions as a high affinity inhibitor of a specific protein target. Aptamers are created by a form of in vitro evolution called systematic evolution of ligands by exponential enrichment (SELEX) (7). Pegaptanib is a 28-base RNA oligonucleotide that is covalently linked to two 20 kD polyethylene glycol moieties to extend the half-life. Pegaptanib selectively binds to the heparin-binding domain of VEGF165 and larger isoforms, preventing ligand-receptor binding. The smaller VEGF isoforms and proteolytic fragments are therefore not inhibited by pegaptanib (7). Safety and efficacy of pegaptanib for the treatment of neovascular AMD was established through the VEGF Inhibition Study in Ocular Neovascularization (VISION) study (8). VISION consisted of two phase III prospective, multicenter, randomized, controlled, double-masked trials comparing intravitreal injections of pegaptanib with sham injections. Patients (1186 total) were randomized to receive pegaptanib (at a dose of 0.3, 1.0, or 3.0 mg) or sham injection (usual care), every six weeks for a total of 54 weeks. The primary end point of the study was the number of patients losing less than 15 letters of Early Treatment Diabetic Retinopathy Study (ETDRS) visual acuity at 54 weeks. Patients with all CNV lesion subtypes with sizes up to and including 12 disc areas in size were included. Concomitant photodynamic therapy (PDT) with verteporfin (Visudynew, Novartis, East Hanover, New Jersey, U.S.A.) was allowed at the physician’s discretion. Twenty-five percent of the VISION patients received PDT during the study period. In the pooled analysis, efficacy was demonstrated for all three doses, without a dose–response relationship. Seventy percent of pegaptanib-treated patients lost less than 15 letters, compared with 55% of usual care patients. More pegaptanib-treated patients maintained or gained visual acuity (33%) at 54 weeks than usual care patients (23%). In addition, the usual

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care group was twice as likely to experience severe vision loss (R30 letters) during the study period than pegaptanib-treated patients. However, only 6% of pegaptanib-treated patients in the study gained R15 letters at 54 weeks (compared with 2% of usual care controls), and as a group, the pegaptanib-treated patients lost an average of eight letters over the study period (compared with 15 letters in the usual care group). Adverse ocular events in the VISION trial resulted in severe vision loss in 0.1% of patients. These adverse events included endophthalmitis (1.3%), traumatic lens injury (0.6%), and retinal detachment (0.6%). For year 2 of the VISION study, patients were re-randomized to the treatment and usual care arms (9). The results indicated that those patients continuing with pegaptanib treatment for a second year did better than those reassigned to the usual care control arm at 54 weeks, and better than those assigned to the usual care arm for the entire two years. The percentage of pegaptanib-treated patients who progressed to moderate visual loss (from baseline) during the second year of treatment was half (7%) that of those reassigned to the control group at 54 weeks (14%), and those who continued in the control group for the second year (14%). Of note, however, patients who had benefited from their year 1 treatment assignment (defined as %0 letters of vision loss from baseline), and who subsequently lost R10 letters of vision after re-randomization at 54 weeks, were allowed to receive “salvage therapy” (a reassignment back to their original year 1 treatment arm). Year 2 safety data continue to show that pegaptanib is a relatively safe drug. Non-ocular hemorrhagic events were not significantly different from the usual care group (10). Studies with pegaptanib continue. The Verteporfin Intravitreal Triamcinolone Acetonide Study (VERITAS) is a phase III prospective, multicenter, randomized, double-masked trial comparing PDT combined with one of two doses of intravitreal triamcinolone (1 mg, 4 mg) versus PDT combined with 0.3 mg of intravitreal pegaptanib. Approximately 100 patients have been enrolled, including all CNV lesion subtypes (11). Studies are also ongoing at OSI/Eyetech to create a sustained-release form of pegaptanib, with the goal of reducing the frequency of intravitreal injections required for treatment, and thereby reducing the risk of serious adverse events associated with intravitreal injections, such as endophthalmitis and retinal detachment. Preliminary animal work with poly(lactic-co-glycolic) acid (PLGA)-based microsphere encapsulation suggests that sustained-release of pegaptanib for greater than six months is possible with a single intravitreal injection (12).

Monoclonal Antibodies: Ranibizumab (Lucentis) In June 2006, ranibizumab (Lucentis—Genentech, South San Francisco, California, U.S.A.) became the second VEGF inhibitor approved by the FDA for use in the treatment of CNV secondary to AMD. Ranibizumab is a humanized, affinity-maturated Fab fragment of a murine monoclonal antibody directed against human VEGF-A. Ranibizumab is a potent, non-selective inhibitor of all VEGF-A isoforms and bioactive proteolytic products. Ranibizumab was specifically designed as a molecule smaller than its parent full-size precursor anti-VEGF antibody, because it was felt that the full-sized antibody was unable to cross the inner retina and choroid, as suggested by a histologic study of the Herceptin antibody (13). More recent histologic analysis of bevacizumab in rabbits by Sharar et al. (14) however, suggests that the full-length antibody actually does penetrate all layers of the retina quite effectively. Because ranibizumab is missing the Fc region, it is also felt that the molecule will be less likely to incite an immune response, as it can no longer bind to complement C1q or Fc gamma receptors (15). Efficacy and safety of ranibizumab has thus far been established through two large prospective, multicenter, randomized, double-masked, controlled clinical trials: Minimally Classic/Occult Trial of AntiVEGF Antibody Ranibizumab in the Treatment of Neovascular Age-Related Macular Degeneration (MARINA) (16) and Anti-VEGF Antibody for the Treatment of Predominantly Classic CNV in AMD (ANCHOR) (17). The MARINA trial was limited to patients with subfoveal occult or minimally classic CNV, either primary or recurrent, with evidence of recent disease progression. In MARINA, 716 patients were randomized 1:1:1 to receive monthly intravitreal injections of ranibizumab (either 0.3 or 0.5 mg) or sham injections. The primary outcome measure was the proportion of patients losing less than 15 ETDRS letters at 12 months. 94.5% of patients assigned to the 0.3 mg group and 94.6% of patients assigned to the 0.5 mg ranibizumab treatment arms, compared with 62.2% in the sham-treatment arm, met this endpoint. More eyes gained 15 or more letters of visual acuity by month 12 in the ranibizumab treatment arms than the control arms: 24.8% in the 0.3 mg group, 33.8% in the 0.5 mg group, 5.0% in the sham-treated group. Mean visual acuity increased by 6.5 letters in the 0.3 mg group and 7.2 letters in the 0.5 mg group at 12 months. In contrast, mean visual acuity dropped by 10.4 letters in the sham-treated group. In general, vision gains were maintained throughout year two of the MARINA trial in ranibizumab-treated patients, whereas vision continued to decline in the shamtreated patients; mean loss was 14.9 letters in the sham group.

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There was also a difference in the lesion size outcomes between the ranibizumab and control groups. While lesion size on average remained stable in the ranibizumab-treated patients, lesion size increased by about 50% in the sham-treated patients at 12 months. The area of leakage in the ranibizumab-treated lesions decreased on average by approximately 50%. Adverse ocular events in ranibizumab-treated patients in the MARINA trial over 24 months included presumed endophthalmitis in 1.0% of patients and serious uveitis in 1.3% of patients. No retinal detachments were observed in the ranibizumabtreated patients, although retinal tears were identified in two patients (0.4%). Lens damage as a result of intravitreal injection was seen in one patient (0.2%). No statistically significant difference in serious systemic adverse events was observed between the treatment and control arms of the study, although there was a trend toward the increased rate of serious (1.3% in 0.3 mg group; 2.1% in 0.5 mg group; 0.8% in sham group) and non-serious (9.2% in 0.3 mg group; 8.8% in 0.5 mg group; 5.5% in sham group) non-ocular hemorrhages. The ANCHOR trial—has likewise demonstrated efficacy of ranibizumab for the treatment of predominantly classic CNV lesions secondary to AMD. ANCHOR was designed as a head-to-head comparison between ranibizumab and PDT with verteporfin (Visudyne), which was then the standard of care for subfoveal CNV. 423 patients were randomized 1:1:1 to receive monthly intravitreal injections with ranibizumab 0.3 mg and sham PDT, ranibizumab 0.5 mg with sham PDT or monthly sham injections plus active verteporfin PDT. The primary end point was the number of patients losing fewer than 15 letters of baseline visual acuity at 12 months. This end point was achieved in 94.3% of the patients receiving 0.3 mg ranibizumab and 96.4% of patients receiving 0.5 mg ranibizumab versus 64.3% of the verteporfin group. The percentage of patients experiencing an improvement over baseline visual acuity of at least 15 letters was 35.7% and 40.3% respectively, in the ranibizumabtreated patients, versus only 5.6% in the verteporfintreated patients. Mean visual acuity increased by 8.5 letters in the 0.3 mg ranibizumab group and 11.3 letters in the 0.5 mg ranibizumab group at 12 months. In contrast, mean visual acuity dropped by 9.5 letters in the verteporfin PDT group at 12 months. Measurement of CNV lesion size throughout the ANCHOR study revealed positive morphologic effects similar to those observed in the MARINA study. In general, average total lesion size remained relatively stable in the ranibizumab-treated patients over one year, while increasing significantly in the verteporfintreated patients. Moreover, average total area of

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leakage and average total area of classic CNV leakage both decreased significantly at one year in the ranibizumab-treated patients, while they increased in the verteporfin-treated group. No statistically significant difference in serious systemic adverse events was observed between the ranibizumab and verteporfin arms of the study, but as in the MARINA trial, there was a trend toward an increased rate of serious (1.5% in 0.3 mg group; 2.1% in 0.5 mg group; 0% in PDT group) and non-serious (5.1% in 0.3 mg group; 6.4% in 0.5 mg group; 2.1% in PDT group) non-ocular hemorrhages. Serious adverse ocular events in the ranibizumab-treated ANCHOR trial patients over 12 months included presumed endophthalmitis in 0.7% of patients and significant uveitis in 0.4% of patients. One patient each developed a retinal detachment (0.4%) or vitreous hemorrhage (0.4%). There were no cases of lens damage as a result of the intravitreal injection. The most common adverse event (12% patients) was mild post-injection inflammation. The PIER study is a phase IIIb, prospective, multicenter, randomized, double-masked, controlled study of 184 patients with predominantly classic or occult CNV randomized to receive ranibizumab or sham injections monthly for the first three months, followed by once every three months for a total of 24 months. The purpose of PIER is to help determine the optimal dosing schedule for ranibizumab. The oneyear results of the PIER study showed that 83% (0.3 mg) and 90% (0.5 mg) of ranibizumab-treated eyes lost less than 15 letters of visual acuity, compared to 49% of sham eyes. However, the percentage of eyes improving 15 or more letters was only 12% (0.3 mg) and 13% (0.5 mg) in ranibizumab-treated eyes, compared with 10% of sham eyes (18). Prospective optical coherence tomography (PRONTO) imaging of patients with neovascular AMD treated with intraocular ranibizumab is a two-year, single site, open-label, uncontrolled study of 40 patients designed to evaluate the durability of response of ranibizumab and whether optical coherence tomography (OCT) can be used to guide treatment of neovascular AMD (19). As in the PIER study, patients receive monthly injections of ranibizumab for the first three months. Thereafter, re-treatment with ranibizumab is performed if one of the following changes were observed between visits: a loss of 5 letters in vision in conjunction with fluid on OCT, increase in OCT central retinal thickness of at least 100 mm, new onset classic CNV, new macular hemorrhage, or persistent macular fluid detected by OCT at least 1 month after the previous injection of ranibizumab. At 12 months, mean visual acuity improved by 9.3 letters (p!0.001) and the mean OCT central retinal thickness decreased by 178 mm

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(p!0.001). Visual acuity improved 15 or more letters in 35% of patients. These visual acuity and OCT outcomes were achieved with an average of 5.6 injections over 12 months. Once a fluid-free macula was achieved, the mean injection-free interval was 4.5 months before another reinjection was necessary. Unlike the PIER study, visual acuity gains did occur despite the less frequent dosing scheme. PRONTO outcomes suggest that OCT can be useful for guiding re-treatment with intravitreal ranibizumab in neovascular AMD, and that use of an OCT-guided variable-dosing regimen could decrease the injection burden without sacrificing improvements in visual acuity.

Monoclonal Antibodies: Bevacizumab (Avastin) Bevacizumab (Avastinw, Genentech, South San Francisco, California, U.S.A.) is a full-length humanized murine monoclonal antibody directed against human VEGF-A. It was FDA approved in 2004 for the intravenous treatment of metastatic colorectal cancer. Its potential for use in the treatment of CNV was first tested by Michels et al. (20) via intravenous infusion in a 12-week open-label uncontrolled study. Striking effects were observed on both visual acuity, and the OCT and angiographic characteristics of the neovascular lesions. However, patients experienced a mean increase of 12 mmHg in systolic blood pressure, which was felt to be a deterrent to its common use. This systemic side effect, combined with the promising visual and anatomic results from the intravenous infusion of bevacizumab, led investigators to consider intravitreal injection of bevacizumab (21). Since then, several retrospective, uncontrolled, openlabel case series have been published regarding the use of intravitreal bevacizumab for the treatment of CNV secondary to AMD (22–25). As with ranibizumab, the effect of bevacizumab has been impressive. Avery and colleagues (22) treated 79 patients with 1.25 mg of intravitreal bevacizumab monthly and reported the early results at three months follow-up. Many of these patients had prior failed treatment with verteporfin or pegaptanib. At three months, median Snellen visual acuity improved from 20/200 at baseline to 20/80. Mean central retinal thickness by OCT decreased by 67 mm at 3 months. No ocular or systemic adverse events were observed. Spaide and colleagues treated (23) 266 patients with monthly 1.25 mg of intravitreal bevacizumab. By three months, Snellen visual acuity improved from a mean of 20/184 at baseline to 20/109, with 38.3% of patients experiencing some improvement in visual acuity. Mean central retinal thickness by OCT improved from 340 mm at baseline to 213 mm at 3 months. Again, no adverse ocular or systemic adverse events were observed.

In contrast to the intravenous administration of bevacizumab, intravitreal injection of bevacizumab did not result in the systemic side effect of hypertension in any of these studies. The systemic concentration of bevacizumab when given intravenously is obviously several times larger than the systemic concentrations seen after intravitreal injections, and no elevation in blood pressure has yet been reported in patients treated with intravitreal bevacizumab. Animal and in vitro studies published thus far have failed to identify any specific toxicity associated with bevacizumab use. Luthra et al. (26) demonstrated that viability of human RPE cells, rat neurosensory cells and human microvascular endothelial cells in culture was normal after exposure to bevacizumab at concentrations of up to 1 mg/mL. Rabbit studies by Manzano et al. (27) found no changes in the electroretinogram (ERG) patterns of eyes injected with intravitreal bevacizumab at doses up to 5.0 mg. Mild vitreous inflammation was seen at 5.0-mg dose, but not at lower doses. Bakri et al. (28) looked at retinal histology of rabbit eyes injected with bevacizumab, and again found no histologic changes compared with control eyes. One important aspect in which ranibizumab and bevacizumab may differ is their pharmacokinetics. Because of its larger molecular weight, it is assumed that bevacizumab has a significantly longer half-life in the vitreous, and possibly systemically as well. A longer half-life may allow for less frequent injections to achieve the same biologic effect. Recent unpublished data, however, indicate that the half-lives of the two drugs may actually be quite similar. Per the package insert for Lucentis, the half-life of ranibizumab in the vitreous is approximately 3 days based on animal studies. Pharmacokinetic studies in rabbits reveal that the half-life of bevacizumab in the vitreous is only marginally longer at 4.3 days (29). Although the limited data thus far suggest that bevacizumab is highly effective and safe for the treatment of CNV secondary to AMD, without a head-to-head prospective clinical trial, the relative efficacy and safety of bevacizumab compared with ranibizumab will remain unknown. Fortunately, The National Eye Institute has agreed to sponsor a trial comparing bevacizumab with ranibizumab in AMD patients with subfoveal CNV. This study, the Comparison of Treatment Trial (CATT) study, will randomize patients into one of four treatment arms: monthly intravitreal injection of ranibizumab, monthly injection of bevacizumab, monthly injection of ranibizumab followed by as-needed treatment, and monthly injection of bevacizumab followed by as-needed treatment. Until the results of the CATT study are available, bevacizumab is nonetheless

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an attractive treatment option due to its cost advantage over ranibizumab, especially for those patients without drug insurance coverage or with large drug co-payment requirements. Because bevacizumab has been FDA approved only for the intravenous treatment of metastatic colon cancer, intravitreal injection of bevacizumab is an off-label use of drug by an altered route of administration. This makes documentation of the informed consent process especially important when using bevacizumab. During informed consent, the physician should explain to patients that the safety and efficacy of bevacizumab have not been established with certainty, and that there may be unknown risks with its use. A bevacizumab-specific consent form is recommended, and can be found on the website of the Ophthalmic Mutual Insurance Company (OMIC) (30,31). Bevacizumab comes in preservative-free 100 mg vials, containing 4 cc of a 25 mg/cc solution, intended for one-time use only for treatment of a single cancer patient. A single vial can theoretically be aliquoted out to provide up to eighty individual 0.05 cc intravitreal doses in 1 cc tuberculin syringes. The pharmacy should confirm the dose and sterility, provide proper storage instructions, and mark all aliquots with an expiration date. Although bevacizumab is a very stable drug with a shelf-life of many months, compounded aliquots will usually have an expiration date due to sterility concerns.

Combination Therapy with PDT The RhuFab V2 Ocular Treatment Combining the Use of VISUDYNEw to Evaluate Safety (FOCUS) study (32) is a two-year, phase I/II, multicenter, randomized, single-masked, controlled study of 162 patients with predominantly classic CNV. FOCUS compared the safety and efficacy of intravitreal ranibizumab (0.5 mg) combined with verteporfin PDT versus verteporfin PDT alone (combined with sham injection). Patients received monthly ranibizumab (0.5 mg) (nZ106) or sham (nZ56) injections. The PDT was performed seven days before initial ranibizumab or sham treatment and then quarterly as needed. The primary outcome measure was the proportion of patients who lost fewer than 15 letters from baseline at 12 months. At 12 months, 90.5% of the ranibizumabtreated patients and 67.9% of the control patients lost fewer than 15 letters (p!0.001). The most frequent ranibizumab-associated serious ocular adverse events were intraocular inflammation (11.4%) and endophthalmitis (1.9%; 4.8% if including presumed cases). On average, patients with serious inflammation had better visual acuity outcomes at 12 months than did controls. Key serious non-ocular adverse events included myocardial infarctions in the PDT-alone group (3.6%) and

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cerebrovascular accidents in the ranibizumab-treated group (3.8%). Notably, ranibizumab-treated patients experiencing intraocular inflammation still had better visual acuity outcomes at 12 months than the control patients. Thus, ranibizumab combined with PDT was more efficacious than PDT alone for treating neovascular AMD. In addition, the FOCUS study showed that despite a history of prior PDT therapy, a significant proportion of these patients were able to gain visual acuity when treated with ranibizumab and PDT. The need for additional PDT was 27.6% for the combined group but 91.1% for the PDT group. A difference in the rate of PDT re-treatment was seen by the 3-month follow-up period and maintained for the study. The FOCUS study however did not compare the ranibizumab plus PDT combination to ranibizumab alone. The DENALI study is a randomized, controlled, multicenter clinical trial that will perform the comparison study. The study will gauge the safety, efficacy and impact on re-treatment rates of Visudyne (verteporfin, Novartis) and Lucentis (ranibizumab, Genentech, South San Francisco, California, U.S.A.) as a combination therapy against wet AMD. DENALI is expected to enroll 300 wet AMD patients at 45 centers in the United States and five centers in Canada. The two-year study will investigate whether patients receiving the combination therapy require fewer re-treatments than control patients treated with Lucentis monotherapy.

Intravitreal Injection Technique It appears that the greatest risks associated with the use of current anti-VEGF therapies for the treatment of AMD (endophthalmitis, retinal detachment, lens trauma) come from the intravitreal injection itself. Therefore, proper injection technique and careful antiseptic practices are important. Supplies that are recommended for prepping the eye include 5% povidine-iodine solution, povidineiodine sticks, and a sterile lid speculum. At our center, we use sterile gloves, a sterile drape, and an empty sterile 1 cc tuberculin syringe to mark the sclera. Alternatively, one can use a caliper to mark the location for the injection procedure. The drug is drawn from the drug vial using a filtered needle attached to a tuberculin syringe. The needle is then changed to a sterile 30-gauge needle prior to the injection. Preinjection prophylactic antibiotic drops may also be used, although no benefit of antibiotic prophylaxis has been established. The eye should first be anesthetized. In our hands, topical anesthesia appears to work just as well as subconjunctival injection of lidocaine, but either method can be used. For topical anesthesia, a cotton tip applicator is soaked with tetracaine and

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placed under the upper or lower eyelid in the conjuntival fornix, so that it rests against the superotemporal or inferotemporal bulbar conjuctiva at the site where the injection is planned. The patient should be instructed to look in the opposite direction and remain that way, so as not to scratch the cornea on the cotton tip applicator. After three to five minutes, the applicator can be removed and the eye prepped with 5% povidine-iodine solution placed directly on the eye, and povidine sticks used to clean the eyelids, lashes and periocular skin. Gloves are worn and a sterile lid speculum is inserted between the eyelids. A sterile drape may be used over the eye if desired, but is not necessary. The patient is then asked to fix his or her gaze in the direction opposite to where the injection is planned, so as to provide the best possible exposure. Providing the patients with an object to fixate upon, such as their own raised thumb, can improve stability of the eye during the injection. A sterile 1 cc syringe hub or a sterile caliper can be used to mark the site of injection. The safest point of injection in phakic patients is 4 mm posterior to the limbus, and the round tip of the tuberculin 1 cc syringe happens to be 4 mm in diameter. The drug is then injected into the vitreous cavity through the pars plana using a 30-gauge needle (0.05 cc total volume in the case of ranibizumab or bevacizumab, 0.1 cc total volume in the case of pegaptanib). The needle is withdrawn and a dry cotton tip applicator is immediately applied over the injection site for a few seconds to help prevent prolapse and incarceration of vitreous in the wound, which can serve as a possible wick for the introduction of bacteria into the eye. Antibiotic drops are then placed in the eye and the lid speculum is removed. The eye pressure is monitored following the injection to confirm that it returns to normal. Finally, the patient is sent home with prophylactic antibiotic drops to be used for three days. Most compliant patients do not need to be rechecked in the clinic until they are due for their next injection four to six weeks later, presuming you give them clear instructions on the signs and symptoms of infection or retinal detachment and are confident that they will call you immediately if they were to develop these symptoms. Povidine-iodine can be quite irritating to the corneal epithelium. It is therefore normal for patients to have some degree of irritation, burning and tearing following their injection, in addition to varying amounts of subconjuctival hemorrhage. The wise physician will warn their patients of these possibilities at the time of injection in order to prevent the inevitable after-hours telephone call. However, any antiseptic-associated discomfort should resolve by the following day.

Therefore, any pain or decreased vision reported by the patient on post-injection day one or later should be taken very seriously.

Safety Considerations The observation that injection of intravitreal bevacizumab (33) or pegaptanib (34) for the treatment of proliferative diabetic retinopathy results in regression of neovascularization in the fellow eye provides compelling evidence that these molecules are indeed absorbed systemically to levels that are clinically relevant. Although no serious systemic concerns were raised by the MARINA, ANCHOR or VISION studies, it should be remembered that studies of this size are powered to detect only relatively large differences in rare events between the study groups. A modest increase in the risk of heart attack or stroke, for example, might not be detected by these studies. In this regard, both the MARINA (16) and ANCHOR (17) trials revealed a non-statistically significant trend toward an increased risk of serious systemic hemorrhage. In MARINA, the incidence of such events was 1.3% in 0.3 mg group, 2.1% in 0.5 mg group, versus 0.8% in sham group at 24 months. In ANCHOR, the incidence of such events was 1.5% in 0.3 mg group, 2.1% in 0.5 mg group, versus 0% in sham group at 12 months. A similar trend was observed for non-serious systemic hemorrhages. No such trend was observed in the VISION trial (10) of pegaptanib, in which the incidence of serious systemic hemorrhage was 0.5% in the treatment arm, versus 1.9% in the sham arm. These data simply underscore the fact that antiVEGF agents are potent drugs, and they should always be used with due caution and consideration. FUTURE ANTI-VEGF THERAPIES VEGF Trap Pegaptanib, ranibizumab and bevacizumab all act through inhibition of VEGF-A; they do not bind other members of the VEGF family. VEGF Trap (Regeneron, Tarrytown, New York, U.S.A.) is an experimental new drug designed to inhibit all members of the VEGF family: VEGF-A, -B, -C, -D, and Placental growth factors (PlGF-1 and PlGF -2). VEGF Trap is a recombinant chimeric VEGF receptor fusion protein in which the binding domains of VEGF receptors 1 and 2 are combined with the Fc portion of immunoglobulin G to create a stable, soluble, highaffinity inhibitor. VEGF Trap also binds VEGF-A with higher affinity (kD!1 pmol/L) than any of the currently available anti-VEGF drugs (35). Whether the broader spectrum and higher affinity of VEGF Trap equates to improved efficacy in the treatment of CNV secondary to AMD remains to be determined.

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The CLEAR-AMD 1 study is a randomized, multicenter, placebo-controlled, dose-escalation study designed to assess the safety, tolerability and bioactivity of VEGF Trap (35). The study enrolled 25 patients with CNV secondary to AMD with lesions %12 disc areas is size and with R50% active leakage, and with ETDRS visual acuity of 20/40 or worse. Patients were randomized to receive either placebo or one of three doses of VEGF Trap (0.3, 1.0, or 3.0 mg/kg). The VEGF trap was given as a single intravenous dose, followed by a four-week observation period, followed by three additional doses two weeks apart. Dose-limiting toxicity was observed for two of the five patients treated with the 3.0 mg/kg dose: one patient developed grade 4 hypertension and the other developed grade 2 proteinuria. Although reduced leakage on fluorescein angiography and reduced retinal thickening on OCT was observed in the treated patients, there was no corresponding reduction in CNV lesion size or improvement in visual acuity observed in these patients over the short 71-day study period. It was concluded that the maximum tolerated IV dose of VEGF Trap was 1.0 mg/kg. The CLEAR-IT 1 study is similarly designed to assess the safety, tolerability and bioactivity of VEGF Trap through the intravitreal route of administration (36). The study enrolled 21 patients using the same inclusion criteria as CLEAR-AMD 1, and randomized them to receive one of six doses of VEGF Trap as single intravitreal injection: 0.05, 0.15, 0.5, 1.0, 2.0 or 4.0 mg. After 43 days of follow-up, no adverse ocular or systemic events were observed. Mean decrease in excess foveal thickness for all patients was 72%. The mean increase in ETDRS visual acuity was 4.75 letters and visual acuity remained stable or improved in 95% of patients. Notably, 3 out of 6 patients treated with the higher doses (2.0 or 4.0 mg) gained R3 lines of visual acuity by day 43. Clearly, VEGF Trap given intravitreally shows promise as a novel treatment for CNV in AMD patients.

Small Interfering RNAs (siRNAs) The therapeutic potential of RNA interference was born in 1998, when Fire and Mello (37) discovered that injection of gene-specific double stranded RNA into cells resulted in potent silencing of that gene’s expression. They had discovered one of fundamental mechanisms by which the cell regulates gene expression and protects itself against viral infection: RNA interference. Fire and Mello were awarded the Nobel Prize in Physiology and Medicine for 2006. The components of the RNA interference machinery have since been identified. Doublestranded RNA binds to a protein complex called Dicer, which cleaves it into multiple smaller fragments. A second protein complex called RNA induced

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silencing complex (RISC) then binds these RNA fragments and eliminates one of the strands. The remaining strand stays bound to RISC, and serves as a probe that recognizes the corresponding messenger RNA transcript in the cell. When the RISC complex finds a complementary messenger RNA transcript, the transcript is cleaved and degraded, thus silencing that gene’s expression (38). Small interfering RNAs (siRNAs) have quickly become important tools in genetic research, and their potential as therapeutic agents is being explored in many areas of medicine. Reich and Tolentino (38,39) were the first to apply siRNA technology toward the treatment of CNV. Bevasiranib/Cand5 (Acuity Pharmaceuticals, Philadelphia, Pennsylvania, U.S.A.) is a siRNA inhibitor of VEGF, which is given as an intravitreal injection. A phase I, open-label, dose escalation study of 15 patients revealed no serious ocular or systemic adverse effects at a dose up to 3.0 mg. The CARE study (Cand5 Anti-VEGF RNA: Evaluation) is a phase II multicenter, randomized, double-masked, trial of bevasiranib/Cand5 in patients with CNV secondary to AMD (40). 127 Patients with predominantly classic, minimally classic, or retinal angiomatous proliferation lesions (occult no classic lesions excluded) were randomized to receive one of three doses of the drug (0.2, 1.5, and 3.0 mg) at baseline and at 6 weeks. The primary endpoint was the mean change in ETDRS visual acuity from baseline at 12 weeks, which was 4 letters (0.2 mg), 7 letters (1.5 mg), and 6 letters (3.0 mg). The authors have theorized that these disappointing results stem from the fact that bevaciranib/Cand5 only blocks the production of new VEGF–VEGF already present at the time of injection was not inhibited. The investigators postulated that a baseline combination treatment with a VEGF protein blocker may be required to “mop up” the preexisting VEGF load. However, the half-life of VEGF is short and it does not explain why the results were not seen by 12 weeks time point with siRNA treatment. Efficacy for the proposed treatment combination remains to be shown. The investigators envision a role of bevasiranib/Cand5 as a long-term “maintenance” drug. The CARE trial raised no safety concerns, with only one patient developing uveitis. Other therapeutic targets for siRNAs are being investigated. siRNAs directed against the VEGFR-1 receptor have shown promise in a mouse model of CNV (41), and are currently in clinical development (Sirna-027, Sirna Therapeutics, Boulder, Colorado, U.S.A.).

Receptor Tyrosine Kinase Inhibitors Non-RNA inhibitors of VEGF receptor tyrosine kinase activity have been identified, and their anti-angiogenic

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properties are being investigated for use in the treatment of systemic malignancy, as well as CNV. One advantage of this class of drugs over those discussed thus far in this chapter is the possibility of an oral route of administration, thereby avoiding the ocular complications associated with frequent intravitreal injections. One promising compound is PTK787, which is a non-selective inhibitor of all known VEGF receptors (42). PTK787 has been shown to inhibit retinal neovascularization in a hypoxic mouse model (43,44). Phase I/II clinical trials of PTK787 (Vatalanib, Novartis, East Hanover, New Jersey, U.S.A.), have been done in patients with both solid and hematologic malignancies, such as the randomized, doublemasked, multicenter, phase I/II study of the safety of vatalanib administered in conjunction with photodynamic therapy with verteporfin to patients with predominantly classic, minimally classic or occult with no classic subfoveal CNV secondary to AMD. A multicenter phase I trial of PTK787/Vatalanib in patients with AMD is the ADVANCE study. Patients with all CNV lesion types will receive PDT with Visudyne at baseline, and will be randomized to receive concurrent treatment with either 500 or 1000 mg of oral PTK787/Vatalanib or placebo, once daily for three months (45). ADVANCE is designed to assess the safety and efficacy of the drug. AG-013958 (Pfizer, San Diego, California, U.S.A.) is a selective VEGFR and PDGFR inhibitor that is currently in phase I/II testing. The route of administration being examined is subtenon injection. Preliminary results of 21 patients with subfoveal CNV indicated that adverse events were mild (15). Anti-VEGF treatment has enabled a sizeable proportion of treated patients to attain significant visual improvement or to maintain vision. Future research will hopefully continue to build on these advances and make restoration of vision a reality for the majority of these patients.

SUMMARY POINTS &

&

&

The only two anti-VEGF agents currently approved by the FDA for treatment of CNV are pegaptanib (Macugen, New York, U.S.A.) and ranibizumab (Lucentis). Pegaptanib, an aptamer (short oligonucleotide) that specifically binds and inhibits VEGF isoforms containing at least 165 amino acids, was shown to slow the rate of vision loss in a large, prospective, randomized clinical trial. Ranibizumab, an antigen binding fragment of a humanized monoclonal antibody directed against all the biologically active forms of VEGF, including the known active proteolytic breakdown products,

&

&

&

was shown to slow the rate of vision loss in two large, prospective, randomized clinical trials. Bevacizumab is a full-sized humanized monoclonal antibody with VEGF binding characteristics similar to ranibizumab, is approved by the FDA for systemic treatment of metststic colorectal cancer and lung cancer, but is used off-label for the treatment of neovascular AMD. Efficacy and safety of bevacizumab for the treatment of neovascular AMD have been reported in several retrospective case series and two small prospective studies, but a large, prospective, randomized, controlled clinical trial has not yet been performed. Additional anti-VEGF drugs are in different stages of development but none have yet entered phase III trials as of January 2007.

REFERENCES 1. Ferrara N, Henzel WJ. Pituitary follicular cells secrete a novel heparin-binding growth factor specific for vascular endothelial cells. Biochem Biophys Res Commun 1989; 161:851–8. 2. Michaelson IC. The mode of development of the vascular system of the retina with some observations on its significance for certain retinal disorders. Trans Ophthalmol Soc UK 1948; 68:137–80. 3. Kvanta A, Algvere PV, Berglin L, et al. Subfoveal fibrovascular membranes in age-related macular degeneration express vascular endothelial growth factor. Invest Ophthalmol Vis Sci 1996; 37:1929–34. 4. Wells JA, Murthy R, Chibber R, et al. Levels of vascular endothelial growth factor are elevated in the vitreous of patients with subretinal neovascularisation. Br J Ophthalmol 1996; 80:363–6. 5. Robinson C, Stinger S. The splice variants of vascular endothelial growth factor (VEGF) and their receptors. J Cell Sci 1991; 114:853–65. 6. Keyt BA, Berleau LT, Nguyen HV, et al. The carboxylterminal domain (111–165) of vascular endothelial growth factor is critical for its mitogenic potency. J Biol Chem 1996; 271:7788–95. 7. Ng EW, Shima DT, Calias P, et al. Pegaptanib, a targeted anti-VEGF aptamer for ocular vascular disease. Nat Rev Drug Discov 2006; 5:123–32. 8. Gragoudas ES, Adamis AP, Cunningham ET, Jr., et al. Pegaptanib for neovascular age-related macular degeneration. N Engl J Med 2004; 351:2805–16. 9. Chakravarthy U, Adamis AP, Cunningham ET, Jr., et al. Year 2 efficacy results of 2 randomized controlled clinical trials of pegaptanib for neovascular age-related macular degeneration. Ophthalmology 2006; 113:1508–21. 10. D’Amico DJ, Masonson HN, Patel M, et al. Pegaptanib sodium for neovascular age related macular degeneration: two-year safety results of the two prospective, multicenter, controlled clinical trials. Ophthalmology 2006; 113: 992–1001. 11. Kaiser PK, VERITAS Study Group. Abstract of Papers, Combined Meeting of Club Jules Gonin and The Retina Society, Cape Town, South Africa, October 15–20, 2006.

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12. Adamis AP, Cook G, Shima D, et al. Abstract of Papers, Combined Meeting of Club Jules Gonin and The Retina Society, Cape Town, South Africa, October 15–20, 2006. 13. Mordenti J, Cuthbertson RA, Ferrara N, et al. Comparisons of the intraocular tissue distribution, pharmacokinetics, and safety of 125I-labeled full-length and fab antibodies in rhesus monkeys following intravitreal administration. Toxicol Pathol 1999; 27:536–44. 14. Shahar J, Avery RL, Heilweil G, et al. Electrophysiologic and retinal penetration studies following intravitreal injection of bevacizumab (Avastin). Retina 2006; 26:262–9. 15. Kaiser PK. Antivascular endothelial growth factor agents and their development: therapeutic implications in ocular diseases. Am J Ophthalmol 2006; 142:660e1–10. 16. Rosenfeld PJ, Brown DM, Heier JS, et al. Ranibizumab for neovascular age-related macular degeneration. N Engl J Med 2006; 355:1419–31. 17. Brown DM, Kaiser PK, Michels M, et al. Ranibizumab versus verteporfin for neovascular age-related macular degeneration. N Engl J Med 2006; 355:1432–44. 18. Regillo CD, Brown DM, Abraham H, Kaiser PK, Mieler WF. Randomized, double-masked, sham-controlled trial of ranibizumab for neovascular age-related macular degeneration: PIER study year 1. Am J Ophthalmol 2007 (in press). 19. Fung AE, Lalwani GA, Rosenfeld PJ, et al. An OCT guided, variable dosing regimen with intravitreal ranibizumab (Lucentis) for Neovascular age-related macular degeneration. Am J Ophthalmol (in press). 20. Michels S, Rosenfeld JR, Puliafito CA, et al. Systemic bevacizumab (Avastin) therapy for neovascular agerelated macular degeneration: twelve-week results of an uncontrolled open-label clinical study. Ophthalmology 2005; 112:1035–47. 21. Rosenfeld PJ, Moshfeghi AA, Puliafito CA. Optical coherence tomography findings after an intravitreal injection of bevacizumab (Avastin) for neovascular age-related macular degeneration. Ophthalmic Surg Lasers Imaging 2005; 36:331–5. 22. Avery RL, Pieramici DJ, Rabena MD, et al. Intravitreal bevacizumab (Avastin) for neovascular age-related macular degeneration. Ophthalmology 2006; 113:363–72. 23. Spaide RF, Laud K, Fine HF, et al. Intravitreal bevacizumab treatment of choroidal neovascularization secondary to age-related macular degeneration. Retina 2006; 26:383–90. 24. Rich RM, Rosenfeld PJ, Puliafito CA, et al. Short-term safety and efficacy of intravitreal bevacizumab (Avastin) for neovascular age-related macular degeneration. Retina 2006; 26:495–511. 25. Bashshur ZF, Bazarbachi A, Schakal A, et al. Intravitreal bevacizumab for the management of choroidal neovascularization in age-related macular degeneration. Am J Ophthalmol 2006; 142:1–9. 26. Luthra S, Narayanan R, Marques LE, et al. Evaluation of in vitro effects of bevacizumab (Avastin) on retinal pigment epithelial, neurosensory retinal, and microvascular endothelial cells. Retina 2006; 26:512–8. 27. Manzano RP, Peyman GA, Khan P, et al. Testing intravitreal toxicity of bevacizumab (Avastin). Retina 2006; 26:257–61. 28. Bakri SJ, Cameron JD, McCannel CA, et al. Absence of histologic retinal toxicity of intravitreal bevacizumab in a rabbit model. Am J Ophthalmol 2006; 142:162–4.

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29. Bakri SJ, Snyder MR, Pulido JS, et al. Abstract of Papers, Combined Meeting of Club Jules Gonin and The Retina Society, Cape Town, South Africa, October 15–20, 2006. 30. www.omic.com (Accessed on July 15, 2007). 31. Klesert TR. So you want to try intravitreal Avastin. Retina Times 2006; 14:18–21. 32. Heier JS, Boyer DS, Ciulla TA, et al. Ranibizumab combined with verteporfin photodynamic therapy in neovascular age-related macular degeneration: year 1 results of the FOCUS study. Arch Ophthalmol 2006; 124:1532–42. 33. Avery RL, Pearlman J, Pieramici DJ, et al. Intravitreal bevacizumab (Avastin) in the treatment of proliferative diabetic retinopathy. Ophthalmology 2006; 113:1695e1–15. 34. Adamis AP, Altaweel M, Bressler NM, et al. Changes in retinal neovascularization after pegaptanib (Macugen) therapy in diabetic individuals. Ophthalmology 2006; 113:23–8. 35. Nguyen QD, Shah SM, Hafiz G, et al. A phase I trial of an IV-administered vascular endothelial growth factor trap for treatment in patients with choroidal neovascularization due to age-related macular degeneration. Ophthalmology 2006; 113:1522–38. 36. Nguyen QD, Hariprasad S, Shar SM, et al. Abstract of Papers, Combined Meeting of Club Jules Gonin and The Retina Society, Cape Town, South Africa, October 15–20, 2006. 37. Fire A, Xu S, Montgomery MK, et al. Potent and specific genetic interference by double-stranded RNA in Caenorhabditis elegans. Nature 1998; 391:806–11. 38. Reich SJ, Fosnot J, Kuroki A, et al. Small interfering RNA (siRNA) targeting VEGF effectively inhibits ocular neovascularization in a mouse model. Mol Vis 2003; 9:210–6. 39. Tolentino MJ, Brucker AJ, Fosnot J, et al. Intravitreal injection of vascular endothelial growth factor small interfering RNA inhibits growth and leakage in a nonhuman primate, laser-induced model of choroidal neovascularization. Retina 2004; 24:132–8. 40. Brucker AJ, The Cand5 Study Group. Abstract of Papers, Combined Meeting of Club Jules Gonin and The Retina Society, Cape Town, South Africa, October 15–20, 2006. 41. Shen J, Samul R, Silva RL, et al. Suppression of ocular neovascularization with siRNA targeting VEGF receptor 1. Gene Ther 2006; 13:225–34. 42. Wood JM, Bold G, Buchdunger E, et al. PTK787/ZK 222584, a novel and potent inhibitor of vascular endothelial growth factor receptor tyrosine kinases, impairs vascular endothelial growth factor-induced responses and tumor growth after oral administration. Cancer Res 2000; 60: 2178–89. 43. Maier P, Unsoeld AS, Junker B, et al. Intravitreal injection of specific receptor tyrosine kinase inhibitor PTK787/ ZK222 584 improves ischemia-induced retinopathy in mice. Graefes Arch Clin Exp Ophthalmol 2005; 243:593–6. 44. Ozaki H, Seo MS, Ozaki K, et al. Blockade of vascular endothelial cell growth factor receptor signaling is sufficient to completely prevent retinal neovascularization. Am J Pathol 2000; 156:697–707. 45. Joondeph BC, Szczesny P, Sforzolini B. Abstract of Papers, Combined Meeting of Club Jules Gonin and The Retina Society, Cape Town, South Africa, October 15–20, 2006.

18 Laser Prophylaxis for Age-Related Macular Degeneration Jason Hsu and Allen C. Ho

Retina Service, Wills Eye Hospital, Philadelphia, Pennsylvania, U.S.A.

INTRODUCTION Age-related macular degeneration (AMD) is the leading cause of visual loss in people older than 65 years in the United States (1–6). Approximately 200,000 Americans per year lose central vision due to AMD and 50,000 will lose vision in both eyes. Currently, there are an estimated 38 million American seniors with a projected 88 million by 2030, which will lead to a proportional increase in the population at risk from vision loss due to AMD. Ninety percent of the severe visual loss from AMD results from choroidal neovascularization (CNV) (2,7,8). Although thermal laser photocoagulation, photodynamic therapy, and various drug therapies to treat neovascular AMD are available or on the horizon, they have only proven to be moderately effective and applicable to a subset of patients (9–18). As a result, the development of preventive strategies for patients at high risk of developing CNV is very desirable. Even a modestly effective bilateral preventive treatment can have a substantial impact on the development of late AMD (geographic atrophy and/or CNV) and the rate of legal blindness caused by CNV. According to one estimate, an intervention that reduced the risk of developing CNV by just 30% in eyes of patients with bilateral large drusen could eventually halve the rate of bilateral blindness from AMD (19). Several natural history studies have identified the presence of large, soft drusen as a significant risk factor for the development of late complications of AMD (20–22). In 1973, Gass first described the disappearance of drusen after laser photocoagulation (23). Subsequently, laser photocoagulation to promote drusen resorption has been examined in numerous studies as a potential prophylaxis against late complications of AMD.

ANATOMY AND PATHOPHYSIOLOGY In order to rationalize the potential therapeutic role of prophylactic laser photocoagulation for drusen resorption, it is necessary to define drusen and

understand the anatomy and pathophysiology of the outer retina, retinal pigment epithelium (RPE), Bruch’s membrane and choriocapillaris. The RPE, a monolayer of hexagonal-shaped cells external to the neurosensory retina and internal to Bruch’s membrane, is intrinsically involved in the outer retina’s metabolism. Its functions include phagocytosis of photoreceptor outer segments, maintenance of the blood–retinal barrier and the transportation of nutrients and waste products (24–26). Bruch’s membrane is not a true membrane but a five-layered connective tissue sheet (27). The basal lamina of the RPE is the most internal layer. The inner collagenous layer, elastic lamina and outer collagenous layer comprise the middle elements. The basal lamina of the choriocapillaris is the final structure. The choriocapillaris is the innermost layer of the choroid and is comprised of an anastomosing sheet of large, fenestrated capillaries. The blood flow in the choroid is one of the highest in the body, largely to meet the high metabolic needs of the outer retina and RPE. Nutrients and waste products pass through the fenestrations of the choriocapillaris. Typically, Bruch’s membrane is not a barrier to these molecules and the RPE transports them to and from the outer retina via active and passive mechanisms (28). Druse (plural drusen) is a German-derived word that means “nodule.” Literally, drusen are crystalline nodules found in stones. In the ophthalmic literature, there have been numerous clinical and histopathologic definitions of drusen (27). The lack of standard terminology for drusen makes interpretation of the literature difficult. Recently, a clinical classification and grading for AMD was developed. In this system, drusen are whitish-yellow spots external to the retina or RPE (29). Hard drusen are less than 63 mm, well defined and yellow–white. Soft drusen are greater than 63 mm and are often also referred to as large drusen. They can have indistinct and distinct borders, may coalesce to form larger, confluent drusen and typically are white–yellow in color. Pathologically, three types of soft drusen have been described: (i) localized detachments of RPE and basal linear deposit in eyes with

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diffuse basal linear deposits; (ii) localized detachments of the RPE and basal laminar deposit in eyes with diffuse basal laminar deposits; and (iii) localized RPE detachments due to focal accumulation of basal linear deposit in eyes without diffuse basal linear deposits (30,31). Ultrastructurally, basal laminar deposits consist of membrane-bound vesicles, wide-spaced collagen and amorphous, granular material located between the plasma membrane and basal lamina of the RPE. Basal linear deposits are located external to the RPE’s basal lamina in the inner collagenous zone. They consist of vesicular and granular electron-dense material and small foci of wide-spaced collagen (30–35). Histochemically, drusen have been shown to consist of lipids, mucopolysaccharides, and glycoconjugates (36–38). The RPE is a metabolically active tissue layer and, most likely, drusen are derived from RPE (39–41). Studies have demonstrated that RPE cells over time accumulate intracellular lipofuscin and other byproducts of the catabolism of photoreceptor outer segments (42). It has been shown that the RPE deposits cellular material into the sub-RPE space via evagination of its plasma membrane. This probably represents the deposition of the intracellular accumulation of its phagocytic by-products. These plasma membranebound vesicles break down into drusenoid material (41). With normal aging, Bruch’s membrane also undergoes ultrastructural and histochemical changes (43–46). Bruch’s membrane increases in thickness, accumulates lipids and develops protein crosslinking. The hydraulic conductivity (flow per unit pressure) of Bruch’s membrane in normal eyes decreases with age (45). Similar to drusen, these alterations in Bruch’s membrane may also represent the accumulation of waste products from the RPE. The basal linear and laminar deposits and the alterations in Bruch’s membrane may impair the flow of fluid to and from the choriocapillaris. The reduced flow of nutrients and oxygen and the impaired removal of waste products may impose a metabolic strain on the outer retina and RPE. The relative hypoxia of the RPE and outer retina from an enlarged, hydrophobic (lipidladen) Bruch’s membrane and drusen may induce the formation of angiogenic factors and may promote the formation of CNV (47).

patients with bilateral macular drusen for an average of 4.3 years (20). Eight eyes of seven patients (9.9%) developed exudative maculopathy. Severe visual loss (more than six lines) occurred in seven eyes and the five-year cumulative risk of developing severe visual loss was 12.7%. Holz prospectively followed 126 patients with bilateral drusen and “good visual acuity” (48). The three-year cumulative incidence of developing CNV or pigment epithelial detachment was 13.3%. The risk for CNV is higher in patients with drusen in one eye and CNV in the other eye. In Gass’ study, 31 of 91 patients lost central vision from CNV in their fellow eye over an average of four years (23). The Macular Photocoagulation Study Group followed 127 patients who had extrafoveal CNV in one eye (21). In the fellow eye, the risk of developing CNV was 58% over five years if large drusen and RPE hyperpigmentation were present. The risk dropped to 10% if no drusen or hyperpigmentation was present. In another study, the Macular Photocoagulation Study Group verified that large drusen are a significant independent risk factor for CNV (49). In this same study, the risk for CNV jumped to 87% in eyes with five or more drusen, focal hyperpigmentation, one or more large drusen and systemic hypertension. In Sandberg’s study, 127 patients with unilateral CNV were followed for an average of 4.5 years (50). CNV developed in the fellow eyes at a rate of 8.8% per year. Macular appearance, which included large drusen, was significantly associated with CNV. One prospective study followed 101 patients with unilateral CNV and drusen in the fellow eye for up to nine years (51). The yearly incidence of CNV varied between 5% and 11%. Significant risk factors were the number, size and confluence of drusen. Numerous pathologic studies have shown a correlation between drusen and AMD. Spraul and Grossniklaus examined 51 eyes with AMD and 40 age-matched control eyes (34). Soft, confluent and large drusen as well as basal (linear) deposits correlated with AMD. Curcio demonstrated that basal linear deposits and large drusen are 24 times more likely to be found in eyes with AMD than age-matched control eyes (32).

DRUSEN AS A RISK FACTOR FOR CNV

IMPACT OF LASER PHOTOCOAGULATION ON PRESENCE OF DRUSEN

Laser-induced drusen regression has generated investigation because soft drusen have been identified as risk factors for CNV and subsequent visual loss. In 1973, Gass noted that 9 of 49 patients (18%) with bilateral macular drusen developed visual loss in one eye due to “disciform detachment or degeneration” over an average of 4.5 years (23). Smiddy followed 71

In order to understand how laser results in drusen resorption, it is necessary to examine the cellular effects of laser on the outer retina, RPE, Bruch’s membrane and choriocapillaris. Laser energy is largely absorbed by the melanin of the RPE and choroid with shorter wavelengths (e.g., 514 nm argon green laser) having better absorption compared to

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longer wavelengths (e.g., 810 nm diode laser). Absorption of the laser light elevates the tissue temperature and causes denaturation of proteins. This thermal effect is called photocoagulation (52,53). The histopathologic characteristics of a laser burn depend on the power, spot size and duration. Smiddy examined the light microscopic changes to a human retina 24 hours after argon laser application (54). The juxtafoveal region was treated with laser spots 200 mm in size and 0.5 seconds in duration. The power ranged between 200 and 400 milliwatts (mW). Histopathologically, there was a choroidal infiltrate of mononuclear and polymorphonuclear cells. The choriocapillaris was acellular at the center of the burn. The RPE was disrupted and the outer and inner retinal nuclear layers were pyknotic. The ganglion and nerve fiber layers were also affected. Thomas conducted a similar study examining a human eye 24 hours after argon laser (55). One laser spot with a power of 310 mW, spot size of 100 mm and duration of 0.5 seconds was applied in the superonasal quadrant. Variable RPE necrosis and advanced choriocapillaris necrosis was seen. A second argon laser burn with a power of 210 mW, spot size of 500 mm and duration of 0.5 seconds in the peripapillary region demonstrated significant RPE disruption, choriocapillaris necrosis and Bruch’s membrane disruption. A number of studies have been performed with laser on cynomologus monkeys whose fovea is similar to the human fovea. Smiddy placed a 13-spot burn in the juxtafoveal region of a cynomologus monkey with argon green laser and examined the histopathologic effects at one and seven days (56). He used a 200 mm spot size, 0.2 second duration and power between 100 and 200 mW. The desired reaction was a laser burn that turned the retina light gray. At day one, the ganglion cell layer was partially preserved but all deeper layers were necrotic with RPE hyperplasia. At day seven, there was disruption of the retina to the level of the ganglion cell layer. In a second study, Smiddy demonstrated that the RPE undergoes cellular proliferation after argon laser (57). Peyman examined the histopathologic effects of argon blue–green laser to the parafoveal area of cynomologus monkeys (58). He used a 100 mm spot size, 0.1 second duration and power of 100 mW. At day one, there was coagulative necrosis of the RPE, outer nuclear layer and outer plexiform layer. The choroid was minimally affected. At days 12 and 21, glial tissue had replaced the outer retina. There was an inflammatory infiltrate and the RPE was hyperplastic. If the power was increased to 320 mW, the basement membrane was ruptured and choroidal hemorrhages developed. Coscas treated the parafoveal region of adult baboons with argon green laser and examined the light and electron microscopic changes at one hour, three weeks and six weeks (59).

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As in the above studies, they showed disruption of the outer retina, necrosis of the RPE and a macrophage response. Depending on the laser settings, there was variable involvement of the choriocapillaris. In a review of macular photocoagulation, Swartz found that the histologic characteristics of a moderate argon-green burn showed a typical cone-shaped lesion sparing the inner retina (60). The laser intensities of these studies exceed those in most human laser to drusen trials. No histopathologic studies have been performed on human eyes examining the effects of laser on drusen. However, a limited number of experimental animal studies have been reported. Duvall and Tso applied argon green laser directly to drusen in two eyes of a rhesus monkey and noted the light microscopic and ultrastructural characteristics of drusen resorption (61). At zero to two days, outer segment retinal disruption, RPE necrosis and fibrin deposition were noted. The drusen were still present. At three to eight days, two types of macrophages were present. One type was in the outer retina and subretinal space and had an appearance that was consistent with blood-borne monocytes. The second type of macrophage contained cell processes that surrounded the drusen material. These cell processes were traced by serial sectioning to the pericytes of the choriocapillaris. At nine days and beyond, there was resorption of the drusen. Blood-borne monocytes were densely packed in the subretinal space. The cell processes of the choroidal pericytes contained drusenoid material. The authors postulated that the fibrin deposition from the laser photocoagulation initiated a phagocytic response, which resulted in clearance of the drusen by choroidal pericytes. Perry examined the choroidal microvascular response to argon laser in cats (62). He demonstrated activation of the endothelial cells in the choriocapillaris after laser photocoagulation. Della treated a rhesus monkey with soft large drusen (63). He used an argon laser to apply a grid pattern in the macula. Six weeks after laser, the directly treated drusen had disappeared.

THEORIES ON DRUSEN REDUCTION AND CNV PREVENTION Drusen disappearance after laser photocoagulation is clearly documented in the literature (64–76). However, the mechanism of drusen disappearance is not well understood. Several theories have been proposed: (i) phagocytosis of drusen; (ii) decreased deposits by removal of RPE; (iii) release of soluble mediators; (iv) thinning of Bruch’s membrane; and (v) mechanical alteration of the structure of Bruch’s membrane. It is clear from the above studies that laser induces an inflammatory response and the intensity

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of the reaction depends on the laser settings as well as the laser subjects. The differences in these factors between various studies make interpretation difficult (25,54–57,59–62). Furthermore, in most of the clinical studies of laser to drusen, the calibrated intensity is minimal whitening. This is different from the above studies where stronger intensities were evaluated. However, despite these limitations, we can postulate that laser-induced phagocytosis of drusen occurs. Blood-borne inflammatory cells may ingest the drusen material. Studies certainly indicate their presence after laser. Duvall and Tso noted drusenoid material in cell processes after laser photocoagulation and attributed the origin of these cell processes to choroidal pericytes (61). Dysfunctional RPE, destroyed by laser, is replaced by proliferating RPE (57). The RPE has phagocytic ability and the proliferating RPE may be involved in drusen resorption (69). Also, the removal of dysfunctional RPE cells may halt further drusen development and allow removal of accumulated material. After laser-induced tissue damage, the RPE and other cells may produce soluble mediators. For instance, Glaser showed that RPE cells release an inhibitor of neovascularization (77). These soluble mediators may enhance the natural processes that result in spontaneous drusen resorption (23,70,78). They might also account for the observation that drusen distant from laser burns disappear after photocoagulation. Bruch’s membrane in AMD eyes is diffusely thickened and hydrophobic. The structural effect on Bruch’s membrane by laser is variable. Thomas showed the integrity of Bruch’s membrane depended on the energy density of the laser (55). Photocoagulation may thin the abnormally thick Bruch’s membrane and, in theory, improve its hydraulic conductivity. The increased metabolic transport could improve drusen clearance and decrease drusen formation. The laser could also exert a mechanical effect on Bruch’s membrane, causing contraction of collagen and elastin (similar to laser trabeculoplasty) and improving egress of material through a more permeable Bruch’s membrane. Peyman showed that photocoagulation may improve perioxidase diffusion from the vitreous to the choroid (79). However, it is important to note that drusen reduction seems to occur during the natural course of AMD. Soft drusen often progress to confluence, drusenoid PED, and fading which leads to RPE disturbances or atrophy in some cases. Over the course of five years, large drusen have been seen to disappear in 34% of eyes with very early changes consisting of one or a few large drusen (78). Also, among fellow eyes of patients enrolled in the Macular Photocoagulation Study with CNV in one eye, areas of large drusen disappeared from one or more areas and

new large drusen appeared in an additional 13% of eyes (80). Nevertheless, large spontaneous reductions of greater than 50% in drusen area are uncommon in patients with 10 or more large drusen (81). Similar to drusen reduction, it is unclear how laser to drusen might prevent CNV. Some of the same theories on the mechanism of drusen reduction apply to CNV prevention. Improved transport of nutrients across Bruch’s membrane might reduce the metabolic strain on the RPE/outer retina and stop the production of angiogenic factors from the RPE. Indeed, laser might even induce the production of vasoinhibitory growth factors from the RPE. Gass postulated that laser “tacks” down the RPE to Bruch’s membrane, eliminating a potential cleavage plane for CNV (23). Proliferating RPE, induced by the laser, may envelop early CNV and prevent further growth.

UNCONTROLLED STUDIES AND CASE REPORTS Since Gass first described the disappearance of drusen after laser photocoagulation, there have been a number of case reports and uncontrolled clinical studies that have examined the prophylactic treatment of drusen. Sigelman published a case report of a 58-year old woman with a disciform scar secondary to AMD in the right eye and confluent soft drusen in the left eye (82). The patient’s vision dropped to 20/40 with metamorphopsia in the left eye. There was no CNV but an increased density and size of foveal drusen. Using a wavelength of 576 nm (yellow), power of 180 mW, duration of 0.3 seconds, and spot size of 200 mm, he directly treated drusen and also applied a parafoveal grid for a total of 56 spots. Treated and untreated drusen disappeared and the vision returned to 20/20 one year after treatment. Hyver reported laser photocoagulation in a patient with CNV in one eye and large, confluent soft drusen in the fellow eye (83). Using a wavelength of 630 nm, spot size of 200 mm, duration of 0.05 seconds and power of 200 mW, 24 burns were placed in the temporal macula with no direct drusen treatment. Burn intensity was calibrated to create barely visible whitening. Ten months after treatment the visual acuity had dropped from 20/25 to 20/60, which was felt to be due to the development of a granular subfoveal material. No CNV was noted on fluorescein angiography. Cleasby treated 29 eyes in patients with “exudative senile maculopathy (ESM)” in the fellow eye (65). In addition, one eye of 25 patients with “nonexudative senile maculopathy (NSM)” in both eyes was treated. The criteria for NSM included the presence of drusen, retinal pigment epithelial atrophy and clumping and/or cholesterol deposits in the macula in individuals older than 50. Argon laser was used to

18:

directly treat drusen “within a broad ring around the fovea.” The desired intensity was a minimally visible reaction in the retina. The laser parameters were a spot size of 50 to 100 mm, power between 100 and 150 mW and duration of 0.05 to 0.1 seconds. The number of applications was approximately 200 to 300 shots. In the group of 29 patients with ESM in one eye, three developed ESM in the treated eye over an average follow-up of 28.4 months. This represented a 4.4% yearly rate of ESM formation, which is less than the natural history of AMD. In the NSM group, neither the control eyes nor the treated eyes developed ESM over an average followup of 27.3 months. All 25 treated eyes and five control eyes showed a reduction in drusen. There were no reported complications from the laser. Despite a small number of patients, no control group for the ESM eyes and no randomization for NSM eyes, this study suggested prophylactic laser to drusen might be beneficial. Wetzig treated 42 eyes of 27 patients with prophylactic laser in a retrospective, nonrandomized study (75). All patients had macular soft drusen and recent visual changes (visual loss or metamorphopsia). The vision ranged from 20/20 to 20/400. Only 25% of eyes had a best-corrected pre-laser visual acuity of 20/40 or better. The mean age at treatment was 69 years. Eyes with CNV or hemorrhagic exudative changes were excluded. Thirty-one eyes were treated with krypton red laser, one eye with a combination of xenon and krypton, eight eyes with argon laser and two eyes with a combination of argon and krypton laser. Both eyes were treated in some patients and several eyes were retreated. The desired intensity of the laser reaction was a faint, white gray spot. Approximately 50 to 75 spots were applied in a scatter pattern around the fovea. The vision improved, remained stable or worsened by only one line in 22 eyes (52%) over an average follow-up of 3.7 years. CNV developed in 12%. Drusen disappeared in these treated eyes, usually beginning at three months. Wetzig published a follow-up of these patients six years after the original publication (76). The average follow-up time was 120 months. Of the treated eyes, 33% remained stable or lost one line of visual acuity, 21% lost two to three lines and 46% lost three or more lines. CNV developed in 21% of treated eyes during the follow-up and several patients had progressive enlargement of the treatment scars. While no control group was designated, seven eyes with drusen had gone untreated. In this untreated group, three eyes retained 20/40 or better visual acuity, two eyes lost two or more lines and two eyes worsened to 20/400 or less. Overall, no clear beneficial effect of prophylactic laser was demonstrated. However, the retrospective, nonrandomized design with a small number of eyes

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261

limits the conclusions that can be drawn from this study. Also, it included many patients with poor vision and selected patients with visual symptoms. These patients may have harbored subtle occult CNV. Figueroa treated 20 patients with argon laser (66). Group 1 consisted of 14 patients with bilateral drusen with one eye randomly assigned to receive laser treatment. Group 2 consisted of six patients with CNV in one eye and drusen in the fellow eye. The patients ranged in age from 55 to 80 years and the average follow-up was 18 months. Drusen temporal to the fovea were directly treated with the argon green laser with a spot size of 100 mm, duration of 0.1 seconds, power of 100 mW, and mean number of laser spots of 30. The desired laser intensity was calibrated to achieve a light gray–white lesion. Treated drusen disappeared by approximately two months while surrounding, untreated drusen disappeared at a mean of 10 months. Visual acuity improved in 30% of eyes by one line or more. This was secondary to the resorption of untreated subfoveal drusen. The visual acuity remained unchanged in 65% of eyes and decreased in 5% (one eye). The one eye that worsened developed a choroidal neovascular membrane away from the laser scars. Figueroa updated these results and presented new data in a second publication with 30 patients in Group 1 and 16 patients in Group 2 (67). The laser settings were the same as described above. All treated drusen disappeared at an average of 3.5 months. In all but three patients, the untreated drusen resolved by an average of 8.6 months. The drusen disappearance progressed in a temporal to nasal direction. Superonasal drusen persisted for the longest amount of time. Two of the 30 control eyes in Group 1 (bilateral drusen) demonstrated spontaneous drusen resolution. After an average of three years, one control eye but no treated eyes developed CNV. Three fellow eyes (18%) in Group 2 developed CNV. In one eye, the CNV developed adjacent to the laser scars. Again, due to the small number of patients, interpretation of these results should be approached with caution. Sarks treated 18 eyes of 16 patients with bilateral drusen and one eye of 10 patients with exudative changes in the other eye (74). Patients were 55 years or older and followed for a mean of 16.8 months. Inclusion criteria included visual acuity 20/40 or better and no evidence of atrophy or CNV. A ring of 40 to 50 non-confluent laser burns was applied approximately 1500 mm from the foveal center. Drusen were not directly targeted. Argon green laser was used with a spot size of 100 mm, duration of 0.05 to 0.1 seconds and power calibrated to produce “a barely discernable whitening of the RPE.” In 14 of the 16 patients with bilateral drusen, only one eye was treated. In these

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treated eyes, the vision remained stable in 10 eyes and improved in four eyes. Vision decreased in four eyes and remained stable in 10 eyes in the untreated group. Overall, in the two treated groups, visual acuity improved in 12 eyes (40%), remained unchanged in 16 eyes (53%) and worsened in 2 eyes (7%). Visual improvement was related to foveal drusen resorption, which occurred in all treated eyes but none of the untreated eyes. Two treated patients developed CNV at seven and eight months post-treatment in retina adjacent to laser burns. Expansion of laser-induced atrophy was minimal in this study. Guymer treated one eye of 12 patients at high risk for visual loss secondary to AMD (71). All 12 treated eyes demonstrated macular drusen and visual acuity of 20/40 or better. Ten patients had end-stage lesions in one eye and two patients had bilateral soft confluent drusen. Twelve laser spots were placed in a ring 750 to 1000 mm from the fovea. Argon green laser was used with a spot size of 200 mm, duration of 0.2 seconds and power calibrated to achieve faint blanching of the RPE (80–300 mW). The average follow-up was 16 months. Visual acuity remained the same or improved in 11 patients. Nine of the 11 patients had a reduction in drusen size, number and confluence. One patient lost four lines due to development of CNV that did not originate from a laser site. Two patients developed profound atrophy at the laser site and four others developed RPE pigmentary changes at the laser sites. This study showed that a small number of laser applications could promote drusen disappearance. It also showed no correlation between drusen resolution and improvement or deterioration of dark-adapted retinal thresholds. Ruiz Moreno performed a prospective, nonrandomized clinical study of laser photocoagulation and looked at the development of macular atrophy in a consecutive series of patients with soft drusen who underwent argon green laser photocoagulation (84). Eyes had to have documented recent loss of visual acuity preceding treatment in order to be included in

the study. Fifty-two consecutive eyes of 52 patients received direct photocoagulation to drusen. Laser parameters included a spot size of 200 mm, duration of 0.2 seconds and power titrated to a light gray–white retinal reaction. Treatment was performed greater than 500 mm from the foveal center with a mean of 117 spots and was completed over two sessions. Macular atrophy occurred in nine eyes (17.7%) about 37.2 months after photocoagulation (range 7–75 months) and was associated with a significant decrease in visual acuity. There was no significant correlation between the areas of atrophy and the number of treatment spots (pZ0.97) or the intensity of treatment spots (pZ0.09). Due to the uncontrolled nature of this study, it is unclear if the macular atrophy is attributable to the laser treatment or related to the natural course of AMD.

CONTROLLED STUDIES Information from the above studies confirmed that laser promoted drusen reduction. However, the visual benefit of this prophylactic laser was still unclear. These studies provided the impetus for more controlled studies and larger clinical trials. Tables 1 and 2 summarize the findings from these studies. Frennesson conducted a randomized, prospective study of prophylactic laser treatment (68). One eye of 13 patients with bilateral soft drusen was treated. In a second group, the fellow eye of six patients with a disciform lesion in the other eye was treated. The control group consisted of 19 patients who had been randomized to observation. The groups were matched for age and visual acuity but there were more men in the treatment group. The visual acuity in all treated eyes was 20/25 or better. Patients with macular pigment clumping, atrophy, pigment epithelial detachments or exudative AMD were excluded. A horseshoe-shaped grid pattern with direct drusen treatment as well as scatter treatment was applied with argon green laser. Laser parameters included

Table 1 Controlled Bilateral Drusen Studies Study Cleasby (65) Figueroa (66) Frennesson (68) Little (73) Olk (85) Scorolli (86) Choroidal neovascularization prevention trial (64) Drusen laser study (87)

Laser type

N (pts)

Mean follow-up (mos)

Argon—threshold Argon—threshold Argon—threshold Dye—threshold Diode—threshold and subthreshold Argon—threshold/ Diode—subthreshold Argon—threshold

25 30 13 27 77

27 36 96 38 24

78/66

18

156

30

105

36

Argon/dye—threshold

Drusen regression

CNV development

Treated

Control

Treated

Control

25 30

5 2

71

7

0 0 2 2 3

0 1 4 4 3

3/1

4

4

2

12

7

77

12

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Table 2

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LASER PROPHYLAXIS FOR AGE-RELATED MACULAR DEGENERATION

Controlled Fellow Eye Studies CNV development

Study Frennesson (68) Olk (85) Choroidal neovascularization prevention trial (64) Drusen laser study (87)

Laser type Argon—threshold Diode—threshold and subthreshold Argon—threshold Argon/dye—threshold

N (pts)

Mean follow-up (mos)

Treated

Control

6 75

96 24

0 8

5 7

120

30

10

2

177

36

27

15

a spot size of 200 mm, duration of 0.05 seconds and power of 100 to 200 mW. The number of laser spots varied from 51 to 154 spots with intensity calibrated to achieve a “grayish reaction.” Drusen area on color fundus photographs and fluorescein angiograms were calculated at baseline and follow-up for both groups. Follow-up results were published at 6 months, 12 months, 3 years, and 8 years (68–70,88). The mean drusen area significantly decreased in the treated eyes and significantly increased in the control eyes. Over three years, five eyes (33%) in the control group but none in the treatment group developed CNV. By eight years of follow-up, 29 patients including 13 treated and 16 controls remained in the study. Nine of the 16 controls (56%) developed CNV (five fellow eyes and four bilateral drusen eyes) and only 2 of 13 treated eyes (15%) developed CNV (two bilateral drusen eyes). While vision decreased significantly in both groups, the magnitude was greater in the control group with quadrupling of minimum angle of resolution in controls versus doubling of minimum angle of resolution in treated patients. This study demonstrated that laser treatment promotes drusen resorption, which had also been shown in the above studies. Importantly, it suggested that laser prophylaxis might prevent the exudative complications of AMD. However, as with the above studies, the sample size was small and the confidence interval large, making it difficult to draw valid conclusions. Little randomized one eye of 27 patients with bilateral confluent soft drusen to prophylactic treatment (73). Mean age of patients was 69.7 years. The minimum visual acuity was 20/60 with a mean followup of 3.2 years. Foveal atrophy, pigment epithelial detachments and exudative changes were exclusionary criteria. Drusen were directly treated. Laser settings for the dye laser (577–620 nm) were a spot size of 100–200 mm, duration of 0.05 to 0.1 seconds and power of 100–200 mW calibrated to induce a slight lightening of the RPE/outer retina. No laser spots were applied within 300 mm of the foveal center and rarely within 500 mm. A total of 23 to 526 laser spots were applied, and 37% of eyes were treated over more than one session. Six treated eyes and no control eyes improved two or more lines, 16 treated and 17 control

eyes remained stable, and five treated and 10 control eyes lost two or more lines. Drusen resorption within 1500 mm of the fovea occurred more completely in the treated eyes than control eyes. In five eyes of both groups, there was equal drusen disappearance. Four control patients and two treated patients developed CNV. Laser scar enlargement occurred in three eyes. It is again difficult to draw conclusions from this study due to the small sample size but visual acuity and drusen resorption were significantly better in the treated eyes. Olk studied the use of diode laser photocoagulation for 152 patients with macular drusen (bilateral drusen, 77 patients; fellow eye, 75 patients) (85). These investigators also compared the ability of subthreshold (invisible) diode laser photocoagulation with threshold (visible) laser photocoagulation to reduce the number of large drusen. Visual acuity was 20/63 or better at baseline. During the first 12 months of follow-up, threshold laser photocoagulation appeared to induce a more rapid disappearance of drusen compared with subthreshold laser. By 18 months, no difference was noted between the two groups. During the 24 months of follow-up, laser treated eyes had significant drusen reduction and improvement in visual acuity compared with observed eyes. CNV occurred at similar rates in both treated and observed eyes. Scorolli compared using argon laser with subthreshold 810 nm diode-laser in 144 patients with bilateral macular drusen (78 eyes received argon, 66 eyes received diode laser) (86). One eye of each patient was treated with the second eye serving as control. During a mean of 18 months follow-up, best-corrected visual acuity was statistically significantly improved in both treatment groups compared with controls, with no significant difference between the argon and diode groups. Drusen reduction occurred in both treated groups as well compared with controls. CNV developed in three eyes receiving argon laser, one eye receiving diode laser, and four eyes in the untreated group. Visual field testing revealed minor but statistically significant reductions in the argon group but not in the diode group. A slight reduction in contrast sensitivity was also noted in the argon group but not seen in the diode group. However, it should be noted

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that the treatment protocol in the argon group (green laser with power titrated to graying effect, 0.2 second duration, 100 mm spot size, and 200 spots placed 500 mm outside the foveal avascular zone) differed from the diode group (150 mW power, 0.1 second duration, 125 mm spot size, 48 spots placed 750 to 2250 mm outside the foveal avascular zone). In 1994, the largest randomized pilot trial to date, the Choroidal Neovascularization Prevention Trial (CNVPT) was begun (64,72,81,89,90). A total of 312 eyes of 156 patients without exudative AMD and more than 10 large (more than 63 mm) drusen in each eye were enrolled in the Bilateral Drusen Study and 120 eyes of 120 patients with exudative AMD in one eye and more than 10 large drusen in the other eye were enrolled in the Fellow Eye Study. Study eyes were required to have visual acuity of 20/40 or better with no evidence of current or past CNV and progressive ocular disease. Fluorescein angiography was used to exclude CNV in the study eye at baseline. Patients in the bilateral drusen arm had one eye randomized to laser treatment with the second eye serving as the control. Patients in the fellow eye arm had the nonexudative AMD eye randomized to laser treatment or control. Laser parameters included a spot size of 100 mm, duration of 0.1 seconds, and power titrated to a light gray–white lesion. Figure 1 shows the treatment protocol for 85% of the patients, which consisted of 20 laser spots placed in three rows temporal to the fovea and greater than 750 mm from the center. Figure 2 shows the treatment protocol for the remaining patients, who received 24 laser spots of the same intensity placed in two rows temporal to the fovea and greater than 750 mm from the center. The CNVPT protocol specified that eyes assigned to treatment be retreated at 6 months nasal to the fovea 100

00

300

3

0

30

750–1000 Microns Fovea

Figure 1 Configuration of burns in the Laser 20 treatment protocol of the choroidal neovascularization prevention trial. Source: From Ref. 64.

Figure 2 Configuration of burns in the Laser 24 treatment protocol of the choroidal neovascularization prevention trial. Source: From Ref. 64.

in a mirror image of the first treatment if the area of drusen had not decreased by 50% from baseline. At six months, 28% of 78 eyes in the Bilateral Drusen Study and 41% of 37 eyes in the Fellow Eye Study had a 50% reduction in drusen and were exempt from retreatment. By 12 months, 54% of 35 eyes in the Bilateral Drusen Study and 27% of 11 eyes in the Fellow Eye Study had a 50% reduction. One eye in the observed group had a 50% reduction in drusen area. Less than 10% of treated eyes and more than 90% of observed eyes showed no reduction in the area of drusen at 12 months (64). Laser-treated eyes with a 50% or more reduction in drusen at this follow-up were more likely to have improved contrast sensitivity as well as oneand two-line increases in visual acuity compared with laser-treated eyes with less drusen reduction or observed eyes (pZ0.001) (72). Enrollment was suspended early due to the apparent increase in CNV development within the first 12 months of follow-up in the Fellow Eye Study. CNV was seen in 10 of 59 treated eyes versus only 2 of 61 control eyes (pZ0.02). In the Bilateral Drusen Study, CNV developed in 4 of 156 treated eyes and 2 of 156 control eyes (pZ0.62). With additional follow-up, the significant increase in CNV incidence in treated fellow eyes compared with control eyes was maintained through 18 months but by 30 months the incidence of CNV was the same in both groups (91). Moreover, there were no statistically significant differences in these fellow eyes compared with controls in terms of change in visual acuity, contrast threshold, critical print size, or incidence of geographic atrophy. Owens who reported the results of a randomized, controlled clinical trial, the Drusen Laser Study, saw similar findings (87,92,93). A total of 177 eyes of 177 patients with exudative AMD in one eye and drusen with or without pigment clumping were enrolled in the fellow eye group and 210 eyes of 105 patients with soft

18:

drusen with or without pigment clumping were enrolled in the bilateral group. Baseline visual acuities of the study eyes were 20/40 or better, and fluorescein angiography was performed at baseline to exclude CNV. Argon green or yellow dye laser was used with a 200 mm spot size, 0.2 second duration, and 65 to 120 mW power. Twelve spots at a distance of 1000 mm from the center of the foveola were applied in a circular protocol pattern. Over three years of follow-up in the bilateral drusen group, CNV developed in 12 of 103 treated eyes (11.6%) and 7 of 103 observed eyes (6.8%, pZ0.23). Visual acuity decreased by 15 or more letters in 6 of 72 treated eyes (8.3%) and 10 of 72 observed eyes (13.9%, pZ0.39). During three years of follow-up in the fellow eye group, CNV developed in 27 of 91 treated eyes (29.7%) and only 15 of 85 observed eyes (17.7%, pZ0.06). Visual acuity decreased in 21 of 73 treated eyes (28.8%) and 13 of 66 observed eyes (19.7%, pZ0.21). Neither of these results was statistically significant, but the investigators felt compelled to halt recruitment into the trial due to concern for laser-induced CNV in the fellow eye group. In the final analysis, one of the most significant findings from the fellow eye group was that the incidence of CNV occurred six months earlier in the laser treated eyes compared with the no laser eyes (pZ0.05). This finding was maintained throughout the three years of follow-up. The increased incidence of CNV in laser-treated fellow eyes has been somewhat unexpected. It is known that fellow eyes are at higher risk for CNV development than bilateral drusen eyes. One possibility is that some of the fellow eyes had undetected CNV at baseline that was stimulated by the laser treatment. These eyes may simply harbor more advanced AMD that is less amenable to prophylaxis. Differences in laser treatment strategy may also play a role. While some groups have specifically targeted macular drusen, the CNVPT and Drusen Laser Study Group followed a pattern that resulted in laser being directed either between or directly on drusen. The intensity of laser photocoagulation may also play a role. Using a computerized method of laser burn quantitation, Kaiser demonstrated that patients in the CNVPT who received more intense burns were more likely to have greater drusen resolution (90). However, a higher laser burn intensity seemed to correlate with increased risk of CNV development. Ultimately, one major challenge may be to deliver a sufficient amount of energy to promote a protective effect while limiting the risk of CNV stimulation.

FUTURE DIRECTIONS: MULTICENTERED CLINICAL TRIALS Based on the favorable data from Olk using diode laser, a larger multicenter, randomized, prospective

LASER PROPHYLAXIS FOR AGE-RELATED MACULAR DEGENERATION

265

Figure 3 Artist’s illustration of 48 diode-laser lesions in a grid pattern of four concentric circles 750 to 2250 mm from the center of the foveal avascular zone. Source: From Ref. 86.

clinical trial known as the Prophylactic Treatment of AMD (PTAMD) Trial is currently in progress to compare subthreshold infrared (810 nm) diode laser photocoagulation with observation. Enrolled patients had visual acuities of 20/63 or better. Figure 3 demonstrates the laser protocol, which consisted of a grid of 48 sub-threshold 810-nm diode laser spots with a spot size of 125 mm applied in four concentric circles outside the foveal avascular zone. Only one laser treatment was applied throughout the study duration. Patients with at least five large drusen (more than 63 mm) within 2250 mm of the foveal avascular zone in both eyes were placed in the bilateral arm of the study with one eye being randomized to treatment and the other serving as control. Approximately 600 patients were enrolled into this arm by November 2001. A substudy of 100 eyes (50 patients) enrolled in this bilateral arm of the PTAMD revealed that the number of laser-induced lesions and the surface area of the laser-induced RPE changes on fluorescein angiography at three months post-treatment were strong predictors of major drusen reduction by 18 months post-treatment (94). This finding may explain the higher rate of drusen reduction in patients who were treated with threshold diode laser in the pilot study and echoes the findings of Kaiser from the CNVPT. The PTAMD also enrolled patients with neovascular AMD in one eye and at least five large drusen in the fellow eye. These patients were placed in the unilateral arm with the eligible fellow eye being randomized to treatment or observation. Enrollment in the unilateral arm was suspended in April 2000 after 242 patients were enrolled due to an increased incidence of CNV and higher rates of worsening visual acuity in treated eyes (95). Follow-up of these patients is on-going.

266

HSU AND HO

2000 μm

2500 μm

Fovea Fovea

1000 μm

1500 μm

(A)

(B)

Based on the findings of the CNVPT, the multi-center randomized clinical trial known as the Complications of Age-Related Macular Degeneration Prevention Trial (CAPT) was proposed and is being conducted with support from the National Eye Institute. The goal of CAPT is to determine whether prophylactic low-intensity laser treatment to the retina can prevent vision loss associated with the complications of advanced AMD (96,97). While fellow eyes in the CNVPT that were treated showed a higher rate of CNV development, in patients with bilateral drusen, the risk was found to be relatively low and similar between treated eyes and control eyes. As a result, only patients with bilateral high-risk drusen (10 or more drusen larger than 125 mm within 3000 mm of fovea) were incorporated into the CAPT design. Baseline visual acuity was 20/40 or better. The

(A)

= Drusen

Figure 4 (A) Initial laser treatment protocol in the complications of age-related macular degeneration prevention trial. (B) Repeat (12-month) protocol. Source: From Ref. 96.

laser treatment protocol also was modified based on the CNVPT findings. Given an apparent increased incidence of CNV in eyes that received more intense laser burns, the burn intensity was reduced to a barely visible lesion (90). The initial treatment consisted of 60 burns (100 mm spot size, 0.1 seconds duration) in a grid pattern within an annulus between 1500 and 2500 mm from the fovea. Retreatment could be performed at 12 months if 10 or more drusen 125 mm or larger remained within 1500 mm of the fovea. Figure 4 shows the follow-up treatment protocol, which consisted of 30 burns in the 1000 to 2000 mm annulus centered on the fovea with drusen being treated directly. A total of 1052 patients were recruited by March 2001 with one eye being randomized to receive laser treatment and the other eye to observation. Patients

(B)

Figure 5 (A) Extensive, confluent drusen in a 51-year-old woman at the time of enrollment in complications of age-related macular degeneration prevention trial; visual acuity was 20/40. (B) Marked regression of drusen in the same eye one year after laser treatment according to trial protocol; visual acuity had improved to 20/25. Note that the reddish discoloration in the central macula is not representative of hemorrhage.

18:

(A)

LASER PROPHYLAXIS FOR AGE-RELATED MACULAR DEGENERATION

267

(B)

Figure 6 (A) Extensive drusen in the macula in a 64-year-old man at the time of enrollment in complications of age-related macular degeneration prevention trial; visual acuity was 20/20. (B) Large, fibrous, disciform scar in the macula of the same eye one year after laser treatment according to trial protocol; visual acuity had decreased to 20/400.

will be followed for a minimum of five years with the primary outcome measure being change in visual acuity. Secondary outcome measures include the incidence of advanced stage AMD changes (CNV, pigment epithelial detachments, geographic atrophy), contrast threshold, and critical print size. Sample fundus photographs at baseline and 12

(A)

months follow-up from two patients in the lasertreatment group are depicted in Figures 5 and 6. Drusen regression is demonstrated in Figure 5, and CNV development with subsequent disciform scarring is shown in Figure 6. While studies have demonstrated regression of drusen in laser-treated eyes, it is important to remember that drusen

(B)

Figure 7 (A) Extensive macular drusen in a 75-year-old woman at the time of enrollment in complications of age-related macular degeneration prevention trial; visual acuity was 20/25. (B) Substantial regression of drusen in the same eye one year after enrollment; visual acuity was 20/25C. The eye had been assigned to the control group.

268

HSU AND HO

regression can also occur spontaneously though typically at a lower rate compared to laser-treated eyes. Fundus photographs from one patient in the observation group demonstrating spontaneous drusen regression are shown in Figure 7. Currently, many questions remain unanswered with regard to the use of laser photocoagulation in patients with high-risk drusen. Most of the studies reviewed support the fact that drusen number is reduced in patients who receive laser treatments. Furthermore, it seems that the greater the intensity of treatment, the faster the resolution. However, this increased intensity may also correlate with a higher risk of CNV (90). The clinical significance of drusen reduction is also unclear at this time. While several smaller studies have demonstrated a correlation between drusen reduction and improvement in visual acuity, this finding has yet to be confirmed by a large, randomized, controlled study. Another important finding from the CNVPT, PTAMD, and Drusen Laser Study has been the increased risk of CNV in patients with neovascular AMD in one eye who underwent laser treatment in the fellow eye with high-risk drusen. Moreover, the Drusen Laser Study demonstrated a six-month earlier onset of CNV in the laser-treated eyes compared with controls. As a result, these fellow eyes should not be considered for laser prophylaxis using these protocols. At this point, clinical studies on laser prophylaxis seem best reserved for patients with bilateral high-risk drusen in the absence of neovascular complications. Based on the multitude of laser treatment regimens, no single method has proven superior. Drusen reduction has been found with varying wavelengths, burn intensities, and treatment area of laser. Also in question is whether laser should be applied to drusen directly, indirectly, or both. As results become available from the CAPT and PTAMD trials as well as other ongoing studies, the effect of laser prophylaxis and drusen reduction on the natural course of AMD should become clarified.

SUMMARY POINTS &

& &

&

A prophylactic treatment for AMD is highly desirable and would have a significant public health impact. Laser photocoagulation can induce drusen regression. The long-term effect of laser-induced drusen reduction on the natural history of AMD and visual function remains unclear. In patients with neovascular AMD in one eye, prophylactic laser appears to increase both the risk of CNV development as well as promote

&

earlier CNV development when performed in the fellow eye and should be avoided. Results from randomized clinical trials are necessary before laser prophylaxis for eyes with drusen should be recommended outside this context.

REFERENCES 1. Kini MM, Leibowitz HM, Colton T, et al. Prevalance of senile cataract, diabetic retinopathy, senile macular degeneration and open-angle glaucoma in the Framingham Eye Study. Am J Ophthalmol 1978; 85:28–34. 2. Leibowitz HM, Krueger DE, Maunder LR, et al. The Framingham Eye Study monograph. Surv Ophthalmol 1980; 24:335–610. 3. The Eye Diseases Prevalence Research Group. Causes and prevalence of visual impairment among adults in the United States. Arch Ophthalmol 2004; 122:477–85. 4. Sommer A, Tielsch JM, Katz J, et al. Racial differences in the cause-specific prevalence of blindness in East Baltimore. N Engl J Med 1991; 14:1412–7. 5. Klein R, Klein BE, Linton KLP. Prevalence of age-related maculopathy: the Beaver Dam Eye Study. Ophthalmology 1992; 99:933–45. 6. National Eye Institute. Age-related Macular Degeneration: Status of Research. Bethesda, MD: National Eye Institute/ National Institutes of Health/U.S. Department of Health and Human Services, 1997. 7. Ferris FL. Senile macular degeneration: review of epidemiologic features. Am J Ophthalmol 1983; 118:132–51. 8. Ferris FL, Fine SL, Hyman L. Age-related macular degeneration and blindness due to neovascular maculopathy. Arch Ophthalmol 1984; 102:1640–2. 9. Macular Photocoagulation Study Group. Argon laser photocoagulation for neovascular maculopathy after five years. Results from randomized clinical trials. Arch Ophthalmol 1991; 109:1109–14. 10. Macular Photocoagulation Study Group. Subfoveal neovascular lesions in age-related macular degeneration: guidelines for evaluation and treatment in the Macular Photocoagulation Study. Arch Ophthalmol 1991; 109: 1242–57. 11. Macular Photocoagulation Study Group. Laser photocoagulation for subfoveal neovascular lesions of age-related macular degeneration: updated findings from two clinical trials. Arch Ophthalmol 1993; 111:1200–9. 12. Macular Photocoagulation Study Group. Laser photocoagulation for juxtafoveal choroidal neovascularization: five year results from randomized clinical trials. Arch Ophthalmol 1994; 112:500–9. 13. Treatment of Age-related Macular Degeneration with Photodynamic Therapy (TAP) Study Group. Photodynamic therapy of subfoveal choroidal neovascularization in agerelated macular degeneration with verteporfin: one-year results of 2 randomized clinical trials—TAP report 1. Arch Ophthalmol 1999; 117:1329–45. 14. Treatment of Age-related Macular Degeneration with Photodynamic Therapy (TAP) Study Group. Photodynamic therapy of subfoveal choroidal neovascularization in agerelated macular degeneration with verteporfin: two-year results of 2 randomized clinical trials—TAP report 2. Arch Ophthalmol 2001; 119:198–207. 15. Verteporfin in Photodynamic Therapy Study Group. Verteporfin therapy of subfoveal choroidal neovascularization in age-related macular degeneration: two-year results of a

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58. Peyman GA, Li M, Yoneya S, et al. Fundus photocoagulation with the argon and krypton lasers: a comparative study. Ophthalmic Surg 1981; 12:481–90. 59. Coscas G, Soubrane G. The effects of red krypton and green argon laser on the foveal region. Ophthalmology 1983; 90:1013–22. 60. Swartz M. Histology of macular photocoagulation. Ophthalmology 1986; 93:959–63. 61. Duvall J, Tso MO. Cellular mechanisms of resolution of drusen after laser coagulation. An experimental study. Arch Ophthalmol 1985; 103:694–703. 62. Perry D, Reddick R, Risco J. Choroidal microvascular repair after argon laser photocoagulation. Invest Ophthalmol Vis Sci 1984; 25:1019–26. 63. Della NG, Wilson DJ, Klein ML. Clinical and pathologic effects of grid macular laser in aged primate eyes containing drusen. Invest Ophthalmol Vis Sci 1997; 38(Suppl.):S18. 64. Choroidal Neovascularization Prevention Trial Research Group. Laser treatment in eyes with large drusen. Shortterm effects seen in a pilot randomized clinical trial. Ophthalmology 1998; 105:11–23. 65. Cleasby G, Nakanishi A, Norris J. Prophylactic photocoagulation of the fellow eye in exudative senile maculopathy. Mod Probl Ophthalmol 1979; 20:141–7. 66. Figueroa MS, Regueras A, Bertrand J. Laser photocoagulation to treat macular soft drusen in age-related macular degeneration. Retina 1994; 14:391–6. 67. Figueroa MS, Regueras A, Bertrand J. Laser photocoagulation for macular soft drusen. Updated results. Retina 1997; 17:378–84. 68. Frennesson CI, Nilsson SE. Effects of argon (green) laser treatment of soft drusen in early age-related maculopathy: a 6 month prospective study. Br J Ophthalmol 1995; 79:905–9. 69. Frennesson CI, Nilsson SE. Laser photocoagulation of soft drusen in early age-related maculopathy (ARM). The oneyear results of a prospective, randomised trial. Eur J Ophthalmol 1996; 6:307–14. 70. Frennesson CI, Nilsson SE. Prophylactic laser treatment in early age related maculopathy reduced the incidence of exudative complications. Br J Ophthalmol 1998; 82:1169–74. 71. Guymer RH, Gross-Jendroska M, Owens SL, et al. Laser treatment in subjects with high-risk clinical features of agerelated macular degeneration. Posterior pole appearance and retinal function. Arch Ophthalmol 1997; 115:595–603. 72. Ho AC, Maguire MG, Yoken J, et al. Laser-induced drusen reduction improves visual function at 1 year. Choroidal Neovascularization Prevention Trial Research Group. Ophthalmology 1999; 106:1367–74. 73. Little HL, Showman JM, Brown BW. A pilot randomized controlled study on the effect of laser photocoagulation of confluent soft macular drusen. Ophthalmology 1997; 104:623–31. 74. Sarks SH, Arnold JJ, Sarks JP, Gilles MC, Walter CJ. Prophylactic perifoveal laser treatment of soft drusen. Aust N Z J Ophthalmol 1996; 24:15–26. 75. Wetzig PC. Treatment of drusen-related aging macular degeneration by photocoagulation. Trans Am Ophthalmol Soc 1988; 86:276–90. 76. Wetzig PC. Photocoagulation of drusen-related macular degeneration: a long-term outcome. Trans Am Ophthalmol Soc 1994; 92:299–303. 77. Glaser BM, Campochiaro PA, Davis JL, Jr., et al. Retinal pigment epithelial cells release an inhibitor of neovascularization. Arch Ophthalmol 1985; 103:1870–5.

78. Bressler N, Munoz B, Maguire MG. Five-year incidence and disappearance of drusen and retinal pigment epithelial abnormalities: Waterman study. Arch Ophthalmol 1995; 113:301–8. 79. Peyman G, Spitznas M, Straatsma B. Chorioretinal diffusion of perioxidase before and after photocogulation. Invest Ophthalmol Vis Sci 1971; 10:489. 80. Javornik N, Hiner CJ, Marsh MJ, et al. Changes in drusen and RPE abnormalities in age-related macular degeneration. Invest Ophthalmol Vis Sci 1992; 33(Suppl.):1230. 81. Ho AC, Javornik N, Maguire MG, et al. The Choroidal Neovascularization Prevention Trial (CNVPT): assessment of macular risk factors for CNV at 1 year. Invest Ophthalmol Vis Sci 1997; 38(Suppl.):517. 82. Sigelman J. Foveal drusen resorption one year after perifoveal laser photocoagulation. Ophthalmology 1991; 98: 1379–83. 83. Hyver SW, Schatz H, McDonald HR, et al. A case of visual acuity loss following laser photocoagulation for macular drusen. Arch Ophthalmol 1997; 115:554–5. 84. Ruiz-Moreno JM, De La Vega C, Zarbin MA. Macular atrophy after photocoagulation of soft drusen. Retina 2003; 23:315–21. 85. Olk JR, Friberg TR, Stickney KL, et al. Therapeutic benefits of infrared (810-nm) diode laser macular grid photocoagulation in prophylactic treatment of nonexudative agerelated macular degeneration. Ophthalmology 1999; 106:2082–90. 86. Scorolli L, Corazza D, Morara M, et al. Argon laser vs. subthreshold infrared (810-nm) diode laser macular grid photocoagulation in nonexudative age-related macular degeneration. Can J Ophthalmol 2003; 38:489–95. 87. Owens SL, Guymer RH, Gross-Jendroska M, et al. Fluorescein angiographic abnormalities after prophylactic macular photocoagulation for high-risk age-related maculopathy. Am J Ophthalmol 1999; 127:681–7. 88. Frennesson CI. Prophylactic laser treatment in early agerelated maculopathy: an 8-year follow-up in a randomized pilot study shows a reduced incidence of exudative complications. Acta Ophthalmol Scand 2003; 81:449–54. 89. The Choroidal Neovascularization Prevention Trial Research Group. Choroidal neovascularization in the choroidal neovascularization prevention trial. Ophthalmology 1998; 105:1364–72. 90. Kaiser RS, Berger JW, Maguire MG, et al. Laser burn intensity and the risk for choroidal neovascularization in the CNVPT Fellow Eye Study. Arch Ophthalmol 2001; 119:826–32. 91. The Choroidal Neovascularization Prevention Trial Research Group. Laser treatment in fellow eyes with large drusen: updated findings from a pilot randomized clinical trial. Ophthalmology 2003; 110:971–8. 92. Owens SL, Bunce C, Brannon AJ, et al. Prophylactic laser treatment appears to promote choroidal neovascularization in high-risk ARM: results of an interim analysis. Eye 2003; 17:623–7. 93. Owens SL, Bunce C, Brannon AJ, et al. Prophylactic laser treatment hastens choroidal neovascularization in unilateral age-related maculopathy: final results of the Drusen Laser Study. Am J Ophthalmol 2006; 141:276–81. 94. Rodanant N, Friberg TR, Cheng L, et al. Predictors of drusen reduction after subthreshold infrared (810 nm) diode laser macular grid photocoagulation for nonexudative age-related macular degeneration. Am J Ophthalmol 2002; 134:577–85.

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95. Friberg TR, Musch D. Prophylactic treatment of age-related macular degeneration (PTAMD): update on the clinical trial. Invest Ophthalmol Vis Sci 2002; 43 (E-abstract 2904). 96. Complications of Age-Related Macular Degeneration Prevention Trial study group. The complications of age-related macular degeneration prevention trial (CAPT): rationale, design and methodology. Clin Trials 2004; 1:91–107.

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97. Complications of Age-Related Macular Degeneration Prevention Trial study group. Baseline characteristics, the 25-item National Eye Institute visual functioning questionnaire, and their associations in the Complications of AgeRelated Macular Degeneration Prevention Trial (CAPT). Ophthalmology 2004; 111:1307–16.

Part V: Surgical Treatment for Age-Related Macular Degeneration

19 Macular Translocation Kah-Guan Au Eong

Department of Ophthalmology and Visual Sciences, Alexandra Hospital, Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, The Eye Institute, National Healthcare Group, Jurong Medical Center, Singapore Eye Research Institute, and Department of Ophthalmology, Tan Tock Seng Hospital, Singapore

Dante J. Pieramici

California Retina Research Foundation and California Retina Consultants, Santa Barbara, California, U.S.A., and Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A.

Gildo Y. Fujii

Vitreous and Retina Department, State University of Londrina, Londrina, Parana, Brazil

Bakthavatsalu Maheshwar

Department of Ophthalmology and Visual Sciences, Alexandra Hospital and Jurong Medical Center, Singapore

Eugene de Juan, Jr.

Beckman Vision Center, Department of Ophthalmology, University of California, San Francisco, California, U.S.A.

INTRODUCTION In recent years, new treatment modalities such as photodynamic therapy and intravitreal anti-vascular endothelial growth factor (anti-VEGF) injections have been added to the armamentarium of physicians treating age-related macular degeneration (AMD). Prior to the introduction of these therapies, the treatment options for AMD were more limited. At that time, only laser photocoagulation had been shown in a large randomized controlled trial to be effective for the treatment of subfoveal choroidal neovascularization (CNV) secondary to AMD. This trial, the Macular Photocoagulation Study, documented that laser photocoagulation of subfoveal CNV confers a statistically significant benefit with regard to long-term visual acuity (VA) when compared to the natural history of the condition (1–3). Unfortunately, the Macular Photocoagulation Study also showed that the treatment of subfoveal CNV with laser photocoagulation was associated with an immediate average reduction of three Bailey– Lovie lines and the benefits of treatment over no treatment only became apparent six months after the treatment. In addition, retention or recovery of good

vision rarely occurred in patients treated with laser photocoagulation. For these reasons, many physicians worldwide did not use laser photocoagulation to treat subfoveal CNV, even at a time when it was the only treatment that had been proven effective by a large, well-designed, randomized clinical trial. This is nicely illustrated by a survey in 1999 of all consultant ophthalmologists in the United Kingdom and the Republic of Ireland by Beatty et al., which showed that only 13.6% of 339 ophthalmologists whose practice included laser photocoagulation of CNV secondary to AMD stated that they ablated subfoveal CNV with laser photocoagulation (4). The main reason (73.6%) the ophthalmologists gave for withholding treatment was that they were not prepared to accept the likelihood of an immediate drop in VA following laser ablation. Investigators who pursued alternative therapy such as interferon alpha-2a (5–8), radiation (9,10), subretinal endophotocoagulation (11), and submacular surgery (12–17) also had no or limited success. As a result of the limited treatment options in the pre-photodynamic therapy era, a number of investigators approached the management of subfoveal CNV with a totally new treatment paradigm. This

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treatment is known by several names including retinal relocation (18), retinal translocation (19,20), macular relocation (21–23), macular translocation (24–29), macular rotation (30), and foveal translocation (31–35). The term macular translocation is currently the most widely used (36). The popularity of macular translocation was highest in the few years prior to the introduction of photodynamic therapy in 2000 but has waned in recent years due to the wider availability of photodynamic therapy and the introduction of intravitreal anti-VEGF agents such as pegaptanib sodium, bevacizumab, and ranibizumab. However, it remains a potentially useful treatment option, and is still in use in some countries including the United States, Japan, and Germany. This chapter reviews the current status of macular translocation, with an emphasis on the two more widely used techniques, limited macular translocation and macular translocation with 3608 retinotomy.

CLASSIFICATION AND TERMINOLOGY There are several different macular translocation techniques currently in use (36). These techniques produce different degrees of postoperative foveal displacement. The various forms of macular translocation may be broadly classified into three categories depending on the size of the retinotomy/retinotomies used: (i) macular translocation with 3608 peripheral circumferential retinotomy (21,22,24,37), (ii) macular trans-location with large (but less than 3608) circumferential retinotomy (31–35), and (iii) macular translocation with either small (self-sealing) or no

retinotomy/retinotomies, with or without chorioscleral infolding or outfolding (Fig. 1) (19,20,23,28,38,39). Macular translocation with 3608 retinotomy is also known as full macular translocation while another name for macular translocation with either small or no retinotomy/retinotomies is limited macular translocation.

RATIONALE Although the exact pathogenesis of CNV secondary to AMD is not known, the natural history of this condition is progressive loss of central vision over time. The initial retinal dysfunction responsible for impaired vision in eyes with subfoveal CNV may be attributable to factors such as subretinal fluid, subretinal hemorrhage, and retinal edema. Accordingly, visual function may recover, at least partially, if these factors were removed. This improvement in macular function has been substantiated by focal electroretinography performed before and after macular translocation (40). When fibrous proliferation and degeneration of the overlying photoreceptors occur during the later stages of the disease, the visual loss becomes irreversible. The rationale of macular translocation is that moving the neurosensory retina of the fovea in an eye with recent-onset subfoveal CNV to a new location before permanent retinal damage occurs may allow it to recover or maintain its visual function over a healthier bed of retinal pigment epithelium (RPE)– Bruch’s membrane–choriocapillaris complex. In effect, macular translocation attempts to achieve

Macular Translocation (MT)

MT with Large Curvilinear “Incisions” of the Retina

MT with 360-degree Retinotomy (Full MT)

MT with Large Retinotomy

MT with Punctate or no Retinotomy (Limited MT)

With Chorioscleral Shortening

Chorioscleral Infolding (Imbrication or Inpouching)

Figure 1

Without Chorioscleral Shortening

Chorioscleral Outfolding (Outpouching)

Classification of macular translocation.

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a more normal subretinal space beneath the fovea. In addition, relocating the fovea to an area outside the border of the CNV allows ablation of the CNV by laser photocoagulation without destroying the fovea, thereby arresting the progression of the CNV and preserving central vision. Some surgeons have combined macular translocation with submacular surgery. Thomas et al. have shown that removal of subfoveal CNV secondary to AMD is frequently accompanied by removal of native RPE, accounting for the relatively poorer visual outcome of submacular surgery for AMD when compared with that for other etiologies such as ocular histoplasmosis syndrome (15). This is because the CNV in AMD typically lies in the sub-RPE space between the RPE and Bruch’s membrane (type 1 CNV), as opposed to that found anterior to the native RPE in the sub-neurosensory retinal space (type 2 CNV) in eyes with ocular histoplasmosis, multifocal choroiditis, and idiopathic neovascular membranes (41). When combined with removal of CNV, macular translocation allows the fovea to be relocated to an area outside the RPE defect created.

HISTORICAL BACKGROUND Lindsey et al. were the first to report their experiment with retinal relocation in 1983, but their aim was to study the anatomic dependency of the foveal retina on foveal RPE and choroid (18). Their techniques included creation of a retinal detachment and relaxing retinal incisions, shifting of the neurosensory retina and retinal reattachment. These techniques were expanded in 1985 by Tiedeman et al. who conceived the idea of rotating the macula of eyes with subfoveal CNV to a new area of underlying RPE–Bruch’s membrane–choriocapillaris complex as a treatment for the condition (42). They showed it was feasible to rotate the macula approximately 458 around the optic disc with reattachment of the fovea in animal eyes. After developing their surgical techniques in rabbit eyes (21), Machemer and Steinhorst in 1993 became the first surgeons to demonstrate the feasibility of macular translocation in humans (22). Their technique involves lensectomy, complete vitrectomy, planned total retinal detachment by transscleral infusion of fluid under the retina, 3608 peripheral circumferential retinotomy, rotation of the retina around the optic disc, and reattachment of the retina with silicone oil tamponade. Besides allowing retinal rotation to occur, the retinotomy also provided access to the subretinal space to remove blood and choroidal neovascular membranes. A number of investigators subsequently modified this technique, but many of them still require large or 3608 retinotomy to allow rotation of the retina (26,30,31,37).

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The early reports of proliferative vitreoretinopathy (PVR) complicating macular translocation with large retinotomy and 3608 retinotomy prompted Imai and de Juan to develop a new technique without the need for any retinotomy in 1996 (23). Their technique involves transscleral subretinal hydrodissection, anterior–posterior scleral shortening near the equator and retinal reattachment. Using this technique, they were able to achieve a predictable macular relocation of greater than 500 mm in rabbit eyes. As no retinal break was created, the likelihood of developing PVR was thought to be lower than that with earlier techniques. As they gained more experience with the surgery, de Juan et al. made additional modifications to their original technique (19,20,28,38). A 41-gauge retinal hydrodissection cannula is now used to make several tiny selfsealing retinotomies for subretinal hydrodissection to create a controlled, reproducible subtotal retinal detachment, and scleral resection during the scleral shortening procedure has been abandoned. They called this technique limited macular translocation since the operation achieves a smaller degree of postoperative foveal displacement and is less extensive compared with other techniques requiring large or 3608 retinotomy (43). To increase the redundancy of the detached retina relative to the shortened eyewall, some investigators have modified the technique of scleral shortening from chorioscleral infolding to outfolding. Kamei et al. work in an animal model (44) and a clinical trial (39,45) demonstrated that radial outfolding with clips was a predictable and effective method of limited macular translocation. Since radial outfolding technique carries the risk of the choroidal fold affecting the macula, and because it is technically difficult to create a sufficiently long radial fold, the surgeons have changed their technique from radial to diagonal outfolding. Other investigators have used nonabsorbable sutures instead of clips to effect the outfolding (46).

INDICATIONS Most surgeons use macular translocation to treat recent-onset exudative macular degeneration. However, some have also utilized it to treat nonexudative AMD and subfoveal RPE loss following submacular surgery.

Exudative Macular Degeneration The most common application of macular translocation is in the management of recent-onset subfoveal CNV from a variety of etiologies. AMD is the most common indication given the high prevalence of this condition, but subfoveal CNV due to other causes

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such as pathologic myopia, ocular histoplasmosis syndrome, angioid streaks, and multifocal choroiditis, as well as idiopathic neovascular membranes, have also been treated with this procedure (20). Some authors have reported better visual improvement after limited macular translocation for CNV secondary to pathologic myopia than for those due to AMD (47). It is possible to perform macular translocation for recurrent subfoveal CNV that develops after laser photocoagulation for initial nonsubfoveal CNV, although in such cases, the planned detachment of the macula is more difficult to achieve because the laser scar causes the retina to be more adherent to the underlying RPE (48).

Non-exudative Macular Degeneration A small number of surgeons have used macular translocation to treat atrophic AMD (49–51). In a series of seven patients who had non-exudative AMD treated with macular translocation with 3608 retinotomy, five of the patients had improved distance and near vision (49). One of these patients developed a new area of geographic atrophy in the translocated fovea 12 months after surgery. This was similar to another patient who had apparent continued progression of geographic atrophy in the newly translocated macular region after effective macular translocation with 3608 retinotomy (51). Subfoveal RPE Defect Macular translocation is a potentially useful remedy for eyes with subfoveal RPE defect caused by submacular surgery. A case of a patient who underwent successful limited macular translocation for subfoveal RPE defect following submacular surgery for CNV secondary to ocular histoplasmosis syndrome has been described (52). PREOPERATIVE CONSIDERATIONS Proper case selection is crucial to good anatomic and functional outcome following macular translocation. A careful and detailed preoperative evaluation is therefore very important, and attention should be paid to the characteristics of the lesion in the macula as well as to concurrent pathology elsewhere in the retina. A recent good quality fluorescein angiogram, preferably obtained within one week of the surgery, is necessary to evaluate the characteristics of the CNV and its precise relationship to the geometric center of the foveal avascular zone. If limited macular translocation is planned, special care should be paid to the retinal periphery during indirect ophthalmoscopy with scleral depression to look for concurrent peripheral retinal pathology that may lead to operative complications.

Several preoperative pathophysiologic and anatomic factors are important in determining the postoperative functional and anatomic outcome of patients undergoing the procedure.

Pathophysiologic Considerations Several pathophysiologic mechanisms responsible for visual loss in eyes with subfoveal CNV may have some bearing on the functional outcome following limited macular translocation. These factors may be broadly divided into “reversible” and “irreversible” components. "Reversible" Components of Visual Loss “Reversible” components of visual loss from subfoveal CNV secondary to AMD include (i) impaired photoreceptor function secondary to abnormal RPE function and impaired nutrient/waste exchange across the RPE and Bruch’s membrane, (ii) relative retinal ischemia/ hypoxia secondary to abnormal RPE–Bruch’s membrane–choriocapillaris complex, (iii) retinal edema and subretinal fluid, and (iv) retinal and subretinal hemorrhages. These problems may be evident early in the course of the disease, resulting in metamorphopsia and central blurring. Their effects are often not immediately devastating, and therefore affected eyes do not usually lose foveal fixation. Theoretically, effective macular translocation may, by reestablishing a relatively more normal subretinal space and underlying RPE–Bruch’s membrane–choriocapillaris complex, cause one or more of these factors to be reduced or reversed, thereby allowing visual recovery. The best candidates for surgery are therefore those with recentonset metamorphopsia or disturbance in central vision due to new or recurrent CNV, before massive subretinal fibrosis and degeneration of the photoreceptors permanently destroy the fovea. "Irreversible" Components of Visual Loss Untreated long-standing subfoveal CNV often results in permanent photoreceptor cell loss, an “irreversible” mechanism responsible for visual loss. This usually occurs in the late stages of the disease when there is fibrovascular scarring. Histopathologic studies have documented that the size and thickness of the disciform scar are directly related to the loss of photoreceptors (53). The visual loss associated with photoreceptor cell loss is often severe, but metamorphopsia becomes less prominent. Loss of foveal fixation may result from the severe visual impairment. Such a severely and irreversibly damaged foveal neurosensory retina is unlikely to achieve good functional recovery even after successful relocation to a healthier bed of RPE–Bruch’s membrane–choriocapillaris complex, and therefore is a poor candidate for limited macular translocation.

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Proper case selection, by identifying patients with good photoreceptor function for surgery and excluding others with irreversible photoreceptor damage, is critically important to achieving good visual outcomes. The foveal function can be assessed preoperatively by a number of means including measurement of VA, scanning laser ophthalmoscope (SLO) microperimetry, and focal electroretinography (54). An analysis of a large series has shown that preoperative VA is a significant predictor of postoperative visual outcome, with good preoperative VA being associated with better postoperative visual results (55). However, eyes presenting with poorer vision have a greater chance of visual improvement but less likelihood of achieving excellent vision of 20/40 or better. SLO microperimetry appears to be a useful way of identifying eyes that have viable foveal photoreceptors (54,56). It is particularly helpful in identifying patients who have maintained central fixation and may be a better indicator than VA in predicting good visual outcome following macular translocation.

Anatomic Considerations Effective macular translocation may be defined as successful postoperative relocation of the fovea to an area outside the boundary of the lesion to be treated, i.e., when a more “normal” subfoveal space has been established. In the case of CNV, effective macular translocation is the successful postoperative relocation of the fovea to an area outside the border of the CNV i.e., a previously subfoveal CNV becomes either juxtafoveal (1 to 199 mm from the foveal center) or extrafoveal (R200 mm from the foveal center) following the surgery. If submacular surgery were combined with macular translocation, then effective macular translocation is the successful postoperative relocation of the fovea to an area outside the border of the RPE defect associated with CNV removal during the surgery. Barring any complication, the anatomic success of macular translocation is dependent on two major factors: (i) the minimum desired translocation and (ii) the postoperative foveal displacement achieved. The minimum desired translocation can be measured prior to surgery and, when taken into consideration with the median postoperative foveal displacement normally achieved by the surgeon, can give some idea of the likelihood of achieving effective macular translocation following the surgery. Minimum Desired Translocation The minimum amount of foveal displacement required to achieve effective macular translocation is the distance between the foveal center and a point either on the inferior or superior border of the

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Figure 2 Schematic diagram showing fundus of the left eye. F is the foveal center, D is a point on the temporal edge of the optic disc, and I is a point on the inferior border of the subfoveal lesion (circle) such that DFZDI. The distance FI is the minimum desired translocation for an inferior translocation.

subfoveal lesion depending on whether the translocation is inferior or superior, all of these points being equidistant from the temporal edge of the optic disc. This distance is the minimum desired translocation (Fig. 2). The temporal edge of the optic disc rather than the center of the disc is taken as the pivoting point of the fovea because the papillomacular bundle enters the optic disc from temporally close to this point. This is therefore the point in which the papillomacular bundle would pivot when the fovea is relocated during macular translocation. Although the size of a subfoveal lesion is intuitively a factor in determining the minimum desired translocation, other factors such as eccentricity and shape of the lesion are important too. For example, in inferior macular translocation, a lesion that is eccentrically centered superiorly relative to the fovea has a smaller minimum desired translocation and is more likely to become juxtafoveal or extrafoveal following surgery compared with another lesion of the same size which is eccentrically centered downwards relative to the fovea, assuming that the net postoperative foveal displacement achieved is identical in both cases (Fig. 3). Lesions of the same size but of different shapes may also have different minimum desired translocations. On the other hand, lesions of different sizes and eccentricities may have the same minimum desired translocation (Fig. 4).

Median Postoperative Foveal Displacement The median postoperative foveal displacement normally achieved by a surgeon can be derived by

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Figure 3 Schematic diagram showing the fundi of three eyes with subfoveal lesions (circles a, b, and c) of equal size but different eccentricities relative to the foveal center (F). Lesion a is centered eccentrically upwards relative to the foveal center (F), lesion b is centered on the foveal center (F), and lesion c is centered eccentrically downwards relative to the foveal center (F). D is a point on the temporal edge of the optic disc and I is a point on the inferior border of the subfoveal lesions such that DFZDI. The minimum desired translocation (FI) for inferior translocation is smallest for lesion a and greatest for lesion c. Lesion a is therefore more likely to achieve effective macular translocation compared with lesions b and c following inferior macular translocation.

Figure 4 Schematic diagram showing ocular fundus with three possible subfoveal lesions (circles a, b, and c) of different sizes and eccentricities. F is the foveal center, D is a point on the temporal edge of the optic disc, and I is a point on the inferior border of the subfoveal lesions such that DFZDI. The minimum desired translocations (FI) for inferior translocation for lesions A, B, and C are identical. Lesions A, B, and C therefore have the same likelihood of achieving effective macular translocation following inferior macular translocation. Note, however, that the minimum desired translocations for superior translocation for lesions A, B, and C are different.

analyzing data collected either retrospectively or prospectively in a series of consecutive cases operated by the surgeon. To estimate the amount of translocation achieved, we first measure on the preoperative fluorescein angiogram the distance from a predetermined retinal landmark (such as a retinal vascular bifurcation) located superior to the CNV to a specific point along the inferior edge of the CNV. We then use the same points to obtain a similar measurement on the postoperative angiogram. The difference between these two measurements estimates the postoperative foveal displacement achieved (Fig. 5). If the time difference between the preoperative and postoperative angiograms is within two weeks, the size and characteristics of the CNV on the postoperative angiogram tend not to change significantly. Although this method of determining the postoperative foveal displacement is not very precise, especially for greater amounts of translocation, it does give useful estimates without the need to resort to sophisticated imaging equipment. Ideally, a surgeon should have some idea of the median postoperative foveal displacement he or she has achieved in his or her previous cases when evaluating potential patients for macular translocation. This is particularly relevant for limited macular translocation. This information, when considered

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Figure 5 Schematic diagram showing the fundus of an eye (A) before and (B) after inferior macular translocation. R is a point on a retinal vascular bifurcation (“retinal” landmark) situated superior to the subfoveal lesion (circle). C is a point on the inferior border of the subfoveal lesion (“choroidal” landmark) such that the line RC is close to and roughly parallel to the “path” of the foveal displacement. F and F 0 are the foveal centers before and after macular translocation, respectively. R 0 and C 0 are the same “retinal” and “choroidal” landmarks, respectively following macular translocation. The absolute difference between the distances RC and R 0 C 0 estimates the postoperative foveal displacement achieved.

together with the minimum desired translocation of a particular eye, gives some useful idea of the likelihood of achieving effective macular translocation. If the minimum desired translocation in an eye is equal to the median postoperative foveal displacement normally achieved by the surgeon, the eye has an approximately 50:50 chance of achieving effective macular translocation after the surgery, regardless of the other dimensions of the subfoveal lesion. If the minimum desired translocation is less than the median postoperative foveal displacement, the eye has a greater than 50% chance of achieving effective macular translocation. The chance of effective macular translocation is less than 50% if the minimum desired translocation is greater than the median postoperative foveal displacement for the surgeon. For example, if a surgeon has a postoperative foveal displacement greater than the patient’s minimum desired translocation in 75% of his previous cases, he could then tell his patient that he has an approximately 75% chance of effective macular translocation following surgery in his hands. If the macular translocation is combined with CNV removal, this rule may not apply if the area of the RPE defect accompanying the CNV removal differs greatly from the area of the original

CNV. This rule is more useful for limited macular translocation than for macular translocation with 3608 retinotomy since large amounts of postoperative foveal displacement are more readily achieved intraoperatively during the latter surgery. It is important to remember that the median postoperative foveal displacement for a particular surgeon is not static and may change with modifications or refinements in techniques.

OPERATIVE TECHNIQUE AND EARLY POSTOPERATIVE MANAGEMENT Limited Macular Translocation Since the initial publications of the procedure (19,20,23), the technique has seen a number of modifications to improve the amount of translocation and to reduce the incidence of complications (28,38,55). Unlike other techniques that require the creation of large retinotomies to allow foveal displacement (22,31), limited macular translocation relies on scleral infolding or outfolding to shorten the outer eyewall (sclera, choroid, and RPE), creating redundancy of the neurosensory retina relative to the eyewall. Instead of large retinotomies, several small self-sealing posterior retinotomies are used.

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Limited macular translocation may be either inferior or superior. Inferior limited macular translocation causes inferior movement of the neurosensory macula relative to the underlying tissues and vice versa. Our experience with this surgery is that inferior limited macular translocation achieves a greater median postoperative foveal displacement than superior translocation for the same amount of scleral imbrication used. When the patient’s head is upright postoperatively, the buoyancy of the intravitreal air bubble supports the superior retina while the weight of the subretinal fluid stretches the retina inferiorly. These forces probably contribute to the greater downward displacement of the fovea during inferior macular translocation and reduce the upward displacement of the fovea during superior translocation. For this reason, inferior limited macular translocation is more commonly performed than superior limited macular translocation, which may be done for the occasional case in which the CNV is markedly eccentrically centered inferiorly relative to the fovea. The technique described below is for inferior limited macular translocation with chorioscleral infolding.

Overview/Equipment Inferior limited macular translocation is essentially a five-step procedure (Table 1). The first step is placement of scleral imbricating sutures. The second step is a 3-port pars plana vitrectomy with separation of the posterior hyaloid face from the retina. The third step is creation of a neurosensory retinal detachment, with or without subretinal manipulation. The fourth step is tightening of the scleral imbricating sutures. The final step in the procedure is a subtotal fluid–air exchange. The equipment necessary to perform this procedure includes a standard 3-port pars plana vitrectomy equipment. Additional devices that are unique to this procedure include (i) a 41-gauge retinal hydrodissection cannula (MADLAB retinal hydrodissection cannula, Bausch & Lomb Surgical, St. Louis, Missouri, U.S.A.) for subretinal hydrodissection to create a detachment of the neurosensory retina (Fig. 6), (ii) a specially designed retinal manipulator (Bausch & Lomb Surgical) for gently grasping the detached retina, aiding in the separation of the macular neurosensory retina from the RPE and also

Table 1

Figure 6 Forty-one gauge retinal hydrodissection cannula (MADLAB retinal hydrodissection cannula, Bausch & Lomb Surgical, St. Louis, Missouri, U.S.A.).

permitting fluid–air exchange (Fig. 7), and (iii) a subretinal pick for subretinal dissection to break firm subretinal adhesions. In addition, we use an air humidifier (MoistAire humidifying chamber, RetinaLabs.com, Atlanta, Georgia, U.S.A.) that minimizes posterior capsular opacification in phakic patients (57) and potentially reduces excessive nerve fiber layer dehydration during the fluid–air exchanges (Fig. 8).

Operative Technique Placement of Imbricating Sutures We place three imbricating sutures in the superotemporal quadrant between the superior and lateral recti,

Key Surgical Steps of Limited Macular Translocation

Placement of imbricating sutures Pars plana vitrectomy Planned subtotal neurosensory retinal detachment Tightening of imbricating sutures Subtotal fluid–air exchange

Figure 7 Retinal manipulator (Bausch & Lomb Surgical, St. Louis, Missouri, U.S.A.). The tip of the instrument is enlarged to show the three small openings of the retinal manipulator.

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sutures have been selected empirically and are not based on precise data. The purpose of the imbricating sutures is to cause anterior–posterior shortening of the eyewall (sclera, choroid, and RPE) relative to the neurosensory retina. The sutures are placed in a mattress fashion and we use the same nonabsorbable sutures used for scleral buckling, i.e., either 4-0 silk or 5-0 dexon. The sutures are placed 6 mm apart from the anterior to posterior extent with the sutures straddling the equator. These sutures are not tightened until later on in the procedure.

Figure 8 Air humidifier (MoistAire humidifying chamber, RetinaLabs Inc, Atlanta, Georgia, U.S.A.).

one suture just nasal to the superior rectus in the superonasal quadrant and one suture just inferior to the lateral rectus in the inferotemporal quadrant (Fig. 9). The number and actual location of the

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Figure 9 Nonabsorbable imbricating sutures are placed straddling the equator of the globe prior to pars plana vitrectomy. The anterior scleral bites are placed 3 mm posterior to the recti insertion and the posterior scleral bites are placed 6 mm posterior to the anterior bites. Three imbricating sutures are placed between the SR and LR. The fourth imbricating suture is placed medial to the SR and the final one is placed inferior to the LR (not shown). Abbreviations: LR, lateral rectus; SR, superior rectus.

Pars Plana Vitrectomy Following preplacement of the imbricating sutures, vitrectomy is initiated. We prefer to fit the sclerostomies with metal cannulas for limited macular translocation because a “leaky” system is desirable during the creation of retinal detachment when balanced salt solution is injected into the subretinal space and during tightening of the imbricating sutures when the eye is deliberately kept soft. The metal cannula also facilitates the insertion of the delicate 41-gauge retinal hydrodissection cannula. Otherwise, the delicate cannula may be easily damaged during insertion through a sclerostomy. A subtotal vitrectomy is then performed. It is critical in these cases to be certain that the posterior hyaloid face is separated from the posterior pole, preferably up to the retinal periphery but at least past the intended positions of the posterior retinotomies. It appears that when the posterior hyaloid face has not been separated from the neurosensory retina, it tethers the neurosensory retina and reduces the amount of macular translocation. It is not necessary to trim the vitreous gel down to the vitreous base but the vitreous cavity needs to be debulked sufficiently to achieve a good air or gas fill. Planned Neurosensory Retinal Detachment To detach the retina, three to eight retinotomies are usually necessary. The preferred locations of initial retinotomy placement, which are just superior to the superotemporal vascular arcade and just inferior to the inferotemporal vascular arcade (Fig. 10). A third retinotomy is often necessary and is placed temporal to the macula (Fig. 11). The retinal detachments should be relatively large and need to extend in the superotemporal quadrant past the zone of intended imbrication. The 41-gauge retinal hydrodissection cannula is connected to an infusion pump to actively infuse balanced salt solution under the retina (Fig. 12). Prior to entering the vitreous cavity, the rate of infusion is set so that there is a steady drip of approximately two or three drops of balanced salt solution per second from the cannula. To initiate the subretinal blister, the 41-gauge retinal hydrodissection cannula is placed through the retina with the infusion

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Figure 12 The retina is detached by injecting BSS between the neurosensory retina and the RPE with a 41-gauge retinal hydrodissection cannula through a tiny retinotomy. Abbreviations: RPE, retinal pigment epithelium; CNV, choroidal neovascularization; BSS, balanced salt solution.

Figure 10 The first retinotomy for subretinal hydrodissection is placed near the superotemporal vascular arcade to detach the superior retina.

Figure 11 The third retinotomy for subretinal hydrodissection is placed a few disc diameters temporal to the fovea to detach the temporal retina. The inferior retina had earlier been detached with a retinotomy placed near the inferotemporal vascular arcade. Note that the retinal detachment from the first retinotomy extends anteriorly beyond the zone of intended scleral imbrication.

running. The neurosensory retinal detachment will initially progress rapidly and tends to expand towards the retinal periphery. As the blister becomes larger, the expansion of the blister is slower although the infusion rate remains constant. If the cannula inadvertently becomes dislodged from the retinotomy during the procedure, one can usually reenter the same retinotomy and continue with the detachment. If this is not possible, a new retinotomy can be made in another site nearby. It is uncommon for the macula to become completely detached during this maneuver since the detachments have a tendency to progress anteriorly, presumably because the macula is relatively more adherent to the RPE than the retinal periphery. The key to successful macular translocation is to completely detach the macula up to the temporal edge of the optic disc. At the same time, limit the detachment of the superonasal aspect of the retina because detachment of this area is associated with a higher risk of macular fold formation. The first step in completely detaching the macula is to perform a complete fluid–air exchange. The subretinal fluid will gravitate posteriorly and will usually dissect the macula off the underlying RPE (Fig. 13). When the macula is detached, the retinal bullae should extend to the optic nerve. However, this does not assure that all subretinal adhesions have been released. At this point, the air is exchanged for fluid, and inspection of the posterior retina with the aid of the retinal manipulator will confirm whether or not the macula is completely detached. If adhesions are present, the retinal manipulator can be activated with low suction to grasp a part of the detached retina. Gentle traction is then exerted with the retinal manipulator to release any persistent subretinal adhesion (Fig. 14). Care should be taken when using the retinal manipulator as it may result in iatrogenic retinal breaks, hemorrhage, macular hole,

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Figure 15 Subretinal blunt dissection (white arrows) with a pick through a small eccentric retinotomy may be necessary to break abnormal chorioretinal adhesions in the macula.

Figure 13 A complete fluid–air exchange allows the subretinal fluid to gravitate posteriorly (white arrow) and dissect the macula off the underlying retinal pigment epithelium.

and nerve fiber layer injury (48). If despite these maneuvers, the retina is still not completely detached, a repeat fluid–air exchange can be performed. If repeated attempts fail to free a localized area of subretinal adhesion, such a laser scar, a small retinotomy is created eccentrically in the macula through which a retinal pick can be used to break the adhesions (Fig. 15).

cavity, the imbricating sutures are tightened (Fig. 17). We tighten the sutures while the eye is filled with fluid rather than air to imbricate the eyewall under the bullous retina. Tightening the sutures while the eye is filled with air may cause the retina lying on the eyewall to be “caught” in the crevices of the imbrication and thus reduce the amount of retinal movement relative to the eyewall. To achieve adequate imbrication, the globe should be softened

Tightening of the Imbricating Sutures Following the neurosensory retinal detachment (Fig. 16), when there is still fluid in the vitreous

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Figure 14 Gentle traction on the retina (white arrows) with a retinal manipulator helps to break abnormal chorioretinal adhesions and fully detach the macula from the retinal pigment epithelium.

Figure 16 A large retinal detachment temporal to an imaginary vertical line bisecting the optic disc is obtained following coalescence of the multiple smaller localized retinal detachments. It is important to ensure that the macula is completely detached and that the retinal detachment extends anteriorly beyond the zone of intended scleral imbrication.

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Figure 17 Tightening the imbricating sutures (white arrow) causes the sclera to be imbricated under the detached retina and creates redundancy of the retina relative to the eyewall (sclera, choroid, and retinal pigment epithelium). Abbreviations: LR, lateral rectus; SR, superior rectus.

either by clamping the fluid infusion or leaving a sclerostomy open or both. There is a theoretical risk that this state of hypotony may increase the risk of intraocular hemorrhage such as suprachoroidal hemorrhage. Although we perform anterior–posterior shortening of the eyewall with scleral imbrication in the majority of our cases of inferior limited macular translocation, it is interesting to note that this is not always necessary, and effective macular translocation may still be achieved without employing scleral imbrication for very small subfoveal lesions (28). Subtotal Fluid–Air Exchange The sclerostomy sites and peripheral retina are inspected for inadvertent retinal breaks prior to the final fluid–air exchange. If present, they should be treated with laser retinopexy or cryoretinopexy and a longer-acting gas such as sulfur hexafluoride is then used instead of air for internal tamponade. The final fluid–air exchange is performed following tightening of the imbricating sutures (Fig. 18). An estimated 75% to 90% air–fluid exchange is carried out. The subretinal fluid is not completely drained as this tends to result in a smaller amount of macular translocation. After the sclerostomies and conjunctival incisions have been closed, a combination of corticosteroid–antibiotic subconjunctival injection is given. Intravenous corticosteroids may be given during the procedure to reduce the incidence of PVR.

Figure 18 Following scleral imbrication, a final subtotal fluid–air exchange is performed without draining the subretinal fluid.

Patient Positioning After the eye is patched, the patient is turned on the operative side for about five minutes. This allows the subretinal fluid to gravitate temporally to detach the temporal peripheral retina. From this position (without turning the patient on his or her back), the patient sat upright and instructed to keep his or her head upright overnight. Besides allowing the temporal peripheral retina to be completely detached, this maneuver also causes all the subretinal fluid to accumulate in the inferior retina, reducing the incidence of a postoperative macular or foveal fold (Fig. 19). If the superonasal retina has been inadvertently detached during the surgery, sitting the patient upright from the supine position may cause some subretinal fluid to become trapped under the superonasal retina, causing a retinal bulla or retinal fold to overhang from the superonasal retina. This bulla or fold will often cause a retinal fold to stretch from the superior margin of the optic disc into the macula. When such a macular or foveal fold persists postoperatively, undesirable visual consequences occur and remedial surgery is usually necessary to unfold the macula. The buoyancy of the intravitreal air bubble when the patient’s head is upright, coupled with the weight of the subretinal fluid inferiorly, stretches the retina in a downward fashion (Fig. 20). The superior retina is the first to become reattached, and this is quickly followed by the macula and the rest of the retina over the next several days.

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Figure 19 The immediate postoperative head-positioning maneuver (see text) causes all the subretinal fluid to accumulate under the inferior retina. The inferior retina is detached. Note the scleral imbrication (white arrows) and the fluid–air interface in the vitreous cavity (black arrows).

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Clinical Example A 63-year-old man with a five-month history of decreased vision in his left eye due to neovascular AMD presented for consideration of macular translocation surgery. His best-corrected VA at presentation was 20/200K1. Clinical examination and fluorescein angiography confirmed a subfoveal CNV approximately one Macular Photocoagulation Study disc area in size (Fig. 21). After written informed consent was obtained, inferior limited macular translocation was performed without complication. Clinical examination and fluorescein angiography on the third postoperative day disclosed effective inferior translocation of the fovea relative to the CNV (Fig. 22). The postoperative foveal displacement achieved was approximately 700 mm. Laser photocoagulation was applied to the area of the CNV. The best-corrected VA improved to 20/60C 2 and 20/40 at four and eight months, respectively after the surgery. He had no postoperative complication or recurrence of the CNV during the follow-up period (Fig. 23).

Combined Removal of CNV and Limited Macular Translocation Some surgeons have advocated surgically removing the CNV at the time of limited macular translocation (27). We tend not to favor this approach, particularly in patients with AMD, because of the uncertainty in the size of the RPE defect that may occur. Thus, even though the preoperative CNV may be of a size and location that effective macular translocation would have a good chance of being achieved, the RPE defect created during submacular surgical excision may be significantly larger and therefore jeopardize the chances of anatomic success. We feel that laser ablation is a much more precise method of treating the CNV.

Figure 20 With the head in an upright position following the surgery, the buoyancy of the air bubble supports the superior retina (white arrows) while the weight of the subretinal fluid stretches the retina downwards (black arrow), causing the fovea to be displaced downwards relative to the underlying eyewall (sclera, choroid and retinal pigment epithelium).

Postoperative Review, Fluorescein Angiography, and Laser Photocoagulation On the first postoperative day, the macula is typically attached, although there is often subretinal fluid in the inferior retina. At this time, the presence of the intravitreal air bubble usually makes the fundus view too poor for fluorescein angiography. The patient continues to position his head upright until the retina becomes completely attached. Complete retinal reattachment generally occurs within two to three days. By three to seven days following the procedure, the reduced air bubble no longer covers

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Figure 21 (A) Fundus photograph and (B) fluorescein angiogram at presentation demonstrates a subfoveal choroidal neovascular membrane approximately one Macular Photocoagulation Study disc area in size under the geometric center of the foveal avascular zone in the left eye. Visual acuity is 20/200K1.

the macula when the patient is upright. At this point, it is appropriate to consider fluorescein angiography so as to identify the postoperative location of the CNV. Interpretation of the postoperative fluorescein angiograms can be difficult in some cases given the additional retinal pigment epithelial changes induced by the surgical procedure. It is particularly important to obtain good quality angiograms and compare them with the preoperative angiograms to determine the actual location and extent of the CNV.

Figure 22 Three days following inferior limited macular translocation, fluorescein angiogram demonstrates effective macular translocation with displacement of the geometric center of the foveal avascular zone (arrow) to an area inferior to the choroidal neovascular membrane. The postoperative foveal displacement is approximately 700 mm.

Laser photocoagulation of the entire CNV lesion is considered following effective macular translocation when the CNV no longer lies under the geometric center of the foveal avascular zone. We follow the guidelines for laser treatment outlined in the Macular Photocoagulation Study (58). Following laser photocoagulation, the patient will be followed up in about three to four weeks with repeat fluorescein angiography to detect persistent or recurrent CNV.

Management of Persistent or Recurrent Subfoveal CNV When some parts of the CNV remains under the center of the fovea due to insufficient macular translocation or when CNV recurs subfoveally after effective macular translocation and laser photocoagulation, the patient and physician must choose between a number of options including photodynamic therapy, intravitreal anti-VEGF injections, laser ablation of the fovea, or observation. Successful treatment of CNV with photodynamic therapy following insufficient macular translocation has been reported (59). The use of intravitreal anti-VEGF injections following macular translocation has not been reported but it could potentially be helpful. We do not advocate partial laser treatment of the CNV because it has been shown to be ineffective by the Macular Photocoagulation Study Group (60). Repeated attempts of macular translocation are also not recommended because initial efforts of this resulted in retinal detachment with significant PVR in some patients. One must consider that even when a CNV has not completely moved out of the foveal center, the partial movement may still benefit the patient as less of the perifoveal retina will need laser ablation.

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Figure 23 (A) Postoperative fundus photograph and (B) fluorescein angiogram shows successful laser ablation of the choroidal neovascular membrane with no evidence of recurrence. The geometric center of the foveal avascular zone (arrow) is preserved. Visual acuity is 20/40.

Macular Translocation with 3608 Retinotomy Macular translocation with 3608 retinotomy requires more manipulation than limited macular translocation, and is often combined with phacoemulsification or lensectomy with preservation of the anterior lens capsule (Table 2) (43,61,62). After a near-complete vitrectomy, the retina is detached totally with subretinal infusion of balanced salt solution and a 3608 peripheral circumferential retinotomy is performed with a vitreous cutter or vertical scissors near the ora serrata. Removal of the CNV or drainage of subretinal hemorrhage, if desired, is then performed under direct visualization. Some perfluorocarbon liquid is then injected onto the posterior retina after unfolding the retina. The retina is then rotated around its optic disk, usually with the fovea displaced superiorly. Additional perfluorocarbon liquid is then injected to fill the vitreous cavity, followed by endolaser photocoagulation to the retinal edges. Finally, the perfluorocarbon liquid is directly exchanged with silicone oil before the sclerostomies and conjunctiva are closed. The silicone oil is removed several months later, with or without an intraocular lens implantation. Corrective surgery for globe counter-rotation may be done during the primary surgery (43) or at a later date. Table 2 Key Surgical Steps of Macular Translocation with 3608 Retinotomy Phacoemulsification or pars plana lensectomy Pars plana vitrectomy Planned total neurosensory retinal detachment 3608 circumferential peripheral retinotomy Retinal rotation and reattachment with perfluorocarbon liquid and endolaser photocoagulation Silicone oil exchange

MANAGEMENT OF POSTOPERATIVE CYCLOVERTICAL DIPLOPIA When the macula is moved sufficiently postoperatively, cyclovertical diplopia or awareness of a tilted image may occur in some patients. This is because the displacement of the fovea is around the optic disk and not directly upwards or downwards. This rotation of the retina can be measured using the Maddox rod test or the disk–fovea angle (63). This retinal torsion, coupled with the small range of fusional amplitude in the vertical direction, causes some patients to experience cyclovertical diplopia after successful macular translocation. As the degree of foveal displacement is relatively smaller following limited macular translocation compared with macular translocation with 3608 retinotomy, the incidence of postoperative cyclovertical diplopia is lower after limited macular translocation, and the symptoms may disappear spontaneously within a few months in many of these patients (27,43). For small degrees of cyclovertical diplopia, correcting the vertical component of deviation with vertical prism in glasses may allow the cyclodeviation to be compensated by the sensory fusion ability, which is driven by the central nervous system. Three out of 10 patients who had limited macular translocation by Lewis et al. experienced either distortion or tilting of image postoperatively and these symptoms persisted for six months postoperatively in only one patient (27). Ohtsuki et al. evaluated 20 patients who underwent limited macular translocation and found seven of them (35%) experienced cyclovertical diplopia postoperatively (64). They treated these patients with transposition of the anterior superior oblique insertion with or without additional vertical

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muscle surgery. Six of the seven patients (85.7%) became unaware of tilted image while three of them (42.9%) had successful restoration of single binocular vision at distance and near. Unlike limited macular translocation, macular translocation with 3608 retinotomy creates largeangle ocular torsion (30). This large magnitude and sudden onset of torsion causes disorientation and hinders use of the eye. Extraocular muscle surgery is usually required to decrease or eliminate torsion and improves the patient’s ability to function with the translocated retina. Several types of torsional muscle surgery for counter-rotation of the globe, sometimes with additional muscle surgery on the fellow eye, have been developed to reduce this complication (30,65–67). Following extraocular muscle surgery in a series of 63 patients who had undergone macular translocation with 3608 retinotomy, Freedman et al. were able to make 41% (23/63) of them free of both diplopia and tilt, while 5% (3/63) of patients had both symptoms constantly (66).

OUTCOME Although histopathologic analyses of a single human case and three animal models have shown some minimal changes including a decreased photoreceptor density in the retina after macular translocation (19,68–70). One advantage of macular translocation over many other experimental or established treatment is that it offers the potential for improvement in VA (20,27,38,55). While some surgeons have found the results of macular translocation encouraging in some cases (20,55,71), others have found the surgery unpredictable (27,61). The largest series of limited macular translocation by Pieramici et al. analyzed the outcomes of 102 consecutive eyes of 101 patients aged 41 to 89 years (median, 76 years) that underwent inferior translocation by one surgeon for new or recurrent AMD-related subfoveal CNV (55). The median postoperative foveal displacement achieved in the series was 1200 mm (range, 200–2800 mm). Seventy-five percent of the cases experienced at least 900 mm of postoperative foveal displacement and 25% achieved 1500 mm or more of foveal displacement. Sixty-two percent of the cases achieved effective macular translocation. At three and six months postoperatively, 31% and 49% of the eyes, respectively, achieved a VA better than 20/100 while 37% and 48% of the eyes, respectively, experienced R2 Snellen lines of visual improvement. Sixteen percent of the eyes experienced six or more Snellen lines of visual improvement. In a follow-up report on the same cohort of patients, 39.5% of 86 eyes with one-year follow-up experienced R2

Snellen lines of visual improvement, 29.0% remained unchanged, and 31.4% lost R2 lines of VA (72). Pieramici et al. found that good preoperative VA, achieving the desired amount of postoperative foveal displacement, a greater amount of postoperative foveal displacement and recurrent CNV at baseline were associated with better VA at three and six months postoperatively (55). The reason patients with recurrent CNV achieved better outcome was thought to be that this select group of patients, having undergone previous laser photocoagulation for a juxtafoveal or extrafoveal lesion, were better educated about the necessity to see their ophthalmologist for any new visual change and were already on close follow-up by their ophthalmologist treating them. The subfoveal disease in this group of patients may therefore be of a shorter duration and less severe than those seen in patients who never had prior laser photocoagulation. Poor preoperative VA and the development of a complication either during or after surgery were associated with worse VA at three and six months postoperatively. Ng et al. analyzed a consecutive series of 31 eyes of 29 patients who underwent limited macular translocation for recurrent subfoveal CNV after laser photocoagulation for initial nonsubfoveal CNV secondary to AMD (77.4%) and a variety of other pathologies (22.6%) (48). They achieved effective macular translocation in 77.4% of eyes. The postoperative foveal displacement ranged from 0 to 2230 mm (median, 1100 mm). Preoperatively, the VA ranged from 20/40 to counting fingers (median, 20/160), and 19% of eyes had VA better than 20/100. At six months, 54% of eyes achieved a VA better than 20/100, and 46% gained the equivalent of R2 Early Treatment Diabetic Retinopathy Study (ETDRS) lines. Subretinal dissection during the surgery to detach the macula was required in 25.8% of eyes and was associated with a significantly higher incidence of peripheral retinal breaks. Retinal detachment occurred in 19.4% of eyes, but the retinal detachment rate observed between the groups with and without subretinal dissection was not statistically significant (pZ0.30). By selecting only patients with subfoveal CNV that did not extend more than half a disk diameter inferior to the fovea for inferior limited macular translocation, Morizane et al. was able to achieve effective macular translocation in all 12 eyes that underwent the surgery (73). This is not unexpected since the small minimum desired translocation is more likely to be associated with effective macular translocation (36). In this group of five patients with AMD and seven with polypoidal choroidal vasculopathy, the VA improved by R2 lines in 92% and remained within 1 line in 8%. In 58% of the eyes, the postoperative VA was 20/40 or better.

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In a small series of 10 eyes of 10 patients with subfoveal CNV secondary to AMD treated by one surgeon, the median postoperative foveal displacement achieved was 1286 mm (range, 114–1919 mm) (27). The best-corrected VA, as measured with the ETDRS chart, improved in four eyes (median, 10.5 letters) and decreased in six eyes (median, 14.5 letters). The median change in VA for the entire series was a decrease of five letters. The final VA at six months postoperatively was 20/80 in two eyes, 20/126 in one eye, 20/160 in four eyes, 20/200 in one eye, 20/250 in one eye, and 20/640 in one eye. Pawlak et al. compared the visual outcome of limited macular translocation with photodynamic therapy for subfoveal predominantly classic CNV in AMD in a nonrandomized retrospective review of 65 consecutive patients with follow-up of at least six months (74). A total of 29 eyes were treated with photodynamic therapy with verteporfin and 36 eyes underwent limited macular translocation. Both groups were similar for age, refraction, and lesion size, but the initial VA was lower in the macular translocation group (20/200) than in the photodynamic therapy group (20/100). At one year, both groups had the same final VA (20/200), but the improvement was more favorable in the macular translocation group (gain of 0.7 line in the macular translocation group versus loss of 3.4 lines in the photodynamic therapy group, pZ0.007). In the photodynamic therapy group, 4.3% of eyes had a gain of 3 lines or more versus 38% in the macular translocation group. Using chorioscleral outfolding with titanium clips for macular translocation, Kamei et al. achieved larger postoperative foveal displacement with their modification of limited macular translocation than has been reported using chorioscleral infolding (39). They reported a median postoperative foveal displacement of 1576 mm (range, 349–3391 mm) in their series of 27 eyes followed up for more than two years compared with the 1200 mm reported by Pieramici et al. (55). In addition, because their outfolding technique required shortening of only 2 to 2.5 mm compared with 4 to 9 mm shortening for the infolding technique, there is less globe deformity and less induced corneal astigmatism (39). It has been postulated that the scleral shortening with chorioscleral outfolding ought to be more than 12 times larger than with infolding (75). However, clinical studies have found the difference in techniques to result in a less profound difference in postoperative foveal displacement (39,45). Histopathologic analysis of the scleral imbrication site in one patient has revealed pleating of the sclera rather than distinct infolding (68). It is thought that this pleating of the sclera would reduce the scleral surface area at the imbrication site more than true infolding, thereby

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explaining why the amount of postoperative foveal displacement is greater than expected with scleral infolding relative to outfolding. In a series of 50 consecutive eyes with subfoveal CNV from AMD that underwent macular translocation with 3608 retinotomy and followed up for a median period of 21 months (range, 12–36 months), Pertile and Claes reported that the postoperative bestcorrected VA improved by R2 Snellen lines in 66%, remained stable (G1 line) in 28%, and decreased by R2 lines in 6% of eyes (76). The final best-corrected VA was 20/50 or better in 32% of eyes while 16% had a final best-corrected VA worse than 20/200. In another large series by Mruthyunjaya et al. of 61 AMD patients who underwent the same operation and followed up for 12 months, all eyes had successful translocation, and the median VA improved from approximately 20/125 before surgery to approximate 20/80 after surgery (77). The median reading speed also improved from 71 words per minute before surgery to 105 words per minute at 12 months after surgery. At 12 months, the VA improved R1 line in 52% of patients. A Japanese study of 23 AMD patients also showed a significant improvement in reading ability after macular translocation with 3608 retinotomy despite an absence of improvement in the distance and near VA (78). Another report by Toth et al. also showed improvements in distance VA, near-VA, contrast sensitivity, and reading speed in a series of 25 consecutive AMD patients who underwent the procedure (79). Cahill et al. studied 50 patients’ quality of life (QOL) after macular translocation with 3608 retinotomy for AMD (80). They found that visionrelated QOL, as measured by the 25-item National Eye Institute Visual Function Questionnaire, improved after the surgery. Not surprising, the largest improvements in QOL were seen in patients with the greatest improvement in visual function, and the best postoperative QOL was seen in patients with the best postoperative visual patients. Park and Toth evaluated the outcome of eight patients who underwent macular translocation with 3608 retinotomy for CNV secondary to AMD following at least one episode of photodynamic therapy with verteporfin (81). All of these patients had demonstrated continued visual loss following their most recent photodynamic therapy treatment. They found the final (mean follow-upZ10 months) mean VA change for patients who had only one prior photodynamic therapy session (five eyes) was C10 ETDRS letters and those who had multiple photodynamic therapy sessions (three eyes) was K1 ETDRS letter. They concluded that macular translocation with 3608 retinotomy may be a viable option to stabilize

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vision for patients who continue to lose vision in their better eye following photodynamic therapy. In our experience, the most important aspects of macular translocation are patient selection, achieving the desired amount of macular translocation and avoiding complications. If this procedure is performed on a patient without viable foveal photoreceptors, there is no chance for visual improvement. If the minimum desired translocation is not achieved, we are left with a persistent subfoveal CNV lesion that will likely result in continued photoreceptor cell damage and visual deterioration. Development of a complication is associated with a poorer prognosis, particularly when retinal detachment occurs (55). To improve on the outcome of this surgery, care should be taken to select the appropriate patients and to reduce the incidence of complications.

COMPLICATIONS The usual risks inherent to pars plana vitrectomy exist for all patients undergoing macular translocation since posterior vitrectomy is an integral part of the procedure. In addition, for patients who undergo limited macular translocation with chorioscleral infolding, additional risks similar to those associated with scleral buckling surgery are presented (Table 3). Table 4 shows the intraoperative and postoperative complications documented in Pieramici et al.’ series (55).

Intraoperative Placement of sutures on the sclera for scleral imbrication may cause inadvertent scleral perforation. This may be associated with suprachoroidal hemorrhage, Table 3 Complications Associated with Macular Translocation Complications Intraoperative

Postoperative

Scleral perforation Unplanned retinal break Suprachoroidal hemorrhage Subretinal hemorrhage Vitreous hemorrhage Macular hole Unplanned translocation of retinal pigment epithelium Rhegmatogenous retinal detachment Proliferative vitreoretinopathy Endophthalmitis Cataract Vitreous hemorrhage Macular or foveal fold New choroidal neovascularization at site of retinotomy Transient formed visual hallucinations (Charles Bonnet syndrome)

vitreous hemorrhage, and retinal break. Retinal break can also occur during the later stages of the operation. The retina may be inadvertently cut or traumatized during vitrectomy. Vitreous traction near the sclerostomies, retinal incarceration at the sclerostomies and retinal manipulation during planned retinal detachment (27) may also tear the retina. Unintended retinal breaks occurred in 10 out of 102 consecutive eyes in Pieramici et al.’ series (55). Unintended nonselfsealing break(s) should receive laser retinopexy or cryoretinopexy during the surgery or in the early postoperative period. Longer-acting gas such as sulfur hexafluoride may also be necessary for internal tamponade. Macular hole formation is another complication that may also require longer-term internal tamponade. During planned detachment of the retina, subretinal hemorrhage may occur if the retinal hydrodissection cannula used for subretinal hydrodissection or the subretinal pick used for blunt dissection traumatizes the vascular choroid. Unplanned translocation of the RPE can occur when a patch of RPE adherent to the underlying surface of the neurosensory retina detaches with the retina (38). While the eye is deliberately kept soft momentarily to allow the imbricating sutures to be tightened, the eye is at risk of retinal incarceration at the sclerostomies and severe intraocular hemorrhage including suprachoroidal hemorrhage.

Postoperative Rhegmatogenous retinal detachment is the most common serious complication of macular translocation. Nine out of 102 eyes in Pieramici et al.’ series developed persistent postoperative retinal detachment (55). Additional surgery is usually necessary to reattach the retina should this complication occur. Pneumoretinopexy may be effective in treating some cases with retinal breaks in the superior two-thirds of the retinal periphery. The retinal detachment may be associated with PVR, especially if a repeat limited macular translocation has been performed for persistent subfoveal CNV. Postoperative endophthalmitis is another potentially devastating complication. The incidence of cataract formation appears to be similar to that following other vitrectomy procedures. Should cataract formation occur soon after limited macular translocation such as following intraoperative lens touch, it can impair visualization of the fundus postoperatively and interfere with clinical examination, fluorescein angiography, and laser photocoagulation. Early cataract surgery is indicated in such cases. Postoperative vitreous hemorrhage can also impair visualization and close follow-up with ultrasonography is warranted to look for associated retinal detachment.

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Table 4 Intra and Postoperative Complications Associated with Inferior Limited Macular Translocation in Pieramici and Associates’ Series (NZ102) Type of complication Macular hole Scleral perforation Choroidal hemorrhage Subretinal hemorrhage Unintended retinal break Vitreous hemorrhage Unplanned retinal detachment Macular fold New choroidal neovascularization at site of retinotomy

Intraoperative (no. of eyes)

Postoperative (no. of eyes)

Total (no. of eyes)

9 2 1 1 6 2 0 0 0

0 0 0 0 4 2 9 3 2

9 2 1 1 10 4 9 3 2

Source: From Ref. 55.

Folds running across the fovea are associated with poor vision, and reoperation to remove the fold may be necessary. A foveal fold formed postoperatively in 3 of 10 eyes reported by Lewis et al. (27). A single case of a macular fold that developed after limited macular translocation was successfully treated with release of the scleral imbrication and intravitreal gas injection four days after the initial surgery (82). Interestingly, effective macular translocation was maintained despite the release of the scleral shortening. Presumably, the mechanism by which the translocated fovea did not return to its original position after scleral shortening released is the redundancy achieved by stretching of the neurosensory retina (82). Induced corneal astigmatism is another complication of macular translocation. Not surprisingly, induced corneal astigmatism is more common after limited macular translocation than after macular translocation with 3608 retinotomy because chorioscleral infolding or outfolding deforms the globe (43). Between 1.75 and 7.37 diopters (mean, 4.6 diopters) of corneal astigmatism was found in a small series of eight eyes after macular translocation with chorioscleral infolding, with steepening along the axis of scleral shortening in the superotemporal quadrant of each eye (83). Rarely, new CNV can occur at the site of the retinotomy used for retinal detachment, presumably as a result of iatrogenic focal defect in Bruch’s membrane caused by the retinal hydrodissection cannula. A case of severe hypotony has been reported after macular translocation with 3608 retinotomy (84). Two cases of transient formed visual hallucinations (Charles Bonnet syndrome) developing within 24 hours following limited macular translocation have been reported (85). The visual hallucinations ceased completely three to seven days postoperatively following retinal reattachment and associated visual improvement.

CONCLUSION In this current era of photodynamic therapy and newer anti-VEGF injections, it is likely that the popularity of macular translocation for the treatment of CNV secondary to AMD will continue to wane. However, macular translocation does provide patients with a realistic hope of a shorter and more definitive treatment end-point when compared with photodynamic therapy and anti-VEGF injections where multiple retreatments are often necessary and the end-point of treatment sometimes uncertain. In eyes that continue to lose vision following photodynamic therapy, macular translocation may be a viable option to stabilize vision. In some countries where photodynamic therapy and anti-VEGF injections are either unavailable or yet to be approved, macular translocation remains a useful option for the treatment of certain subsets of patients with CNV.

SUMMARY POINTS &

&

&

Rationale. To displace the foveal neurosensory retina in an eye with recent-onset subfoveal CNV to a presumably healthier bed of RPE–Bruch’s membrane–choriocapillaris complex devoid of CNV before permanent retinal damage occurs; the foveal displacement allows the destruction of the CNV by laser photocoagulation without damaging the foveal center. Indications. Subfoveal CNV secondary to a variety of etiologies including exudative AMD. Some surgeons have also performed the operation on nonexudative AMD. Classification of macular translocation. The various forms of macular translocation may be broadly classified into three categories depending on the size of the retinotomy/retinotomies used: (i) macular translocation with 3608 peripheral circumferential retinotomy, (ii) macular translocation

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with large (but less than 3608) circumferential retinotomy, and (iii) macular translocation with either small or no retinotomy/retinotomies. Complications. Intraoperative complications include scleral perforation, unplanned retinal break, intraocular hemorrhage, macular hole, unplanned translocation of RPE and postoperative include rhegmatogenous retinal detachment, PVR, endophthalmitis, cataract, intraocular hemorrhage, foveal fold, new CNV at site of retinotomy, acute angle-closure glaucoma, and transient formed visual hallucinations. Role of macular translocation in current era of photodynamic therapy and anti-VEGF therapy. Macular translocation offers a realistic hope of a shorter and more definitive treatment end-point compared with photodynamic therapy and anti-VEGF therapy where multiple retreatments are often necessary and the end-point of treatment sometimes uncertain. However, because of its higher risk of complications, its popularity has waned since the advent of photodynamic therapy. It remains a useful option when these newer therapies are unavailable.

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46. Lin SB, Glaser BM, Gould D, Baudo TA, Lakhanpal RR, Murphy RP. Scleral outfolding for macular translocation. Am J Ophthalmol 2000; 130(1):76–81. 47. Glacet-Bernard A, Simon P, Hemelin N, Coscas G, Soubrane G. Translocation of the macula for management of subfoveal choroidal neovascularization: comparison of results in age-related macular degeneration and degenerative myopia. Am J Ophthalmol 2001; 131(1):78–89. 48. Ng EWM, Fujii GY, Au Eong KG, et al. Macular translocation in patients with recurrent subfoveal choroidal neovascularisation after laser photocoagulation for nonsubfoveal choroidal neovascularization. Ophthalmology 2004; 111(10):1889–93. 49. Eckardt C, Eckardt U. Macular translocation in nonexudative age-related macular degeneration. Retina 2002; 22(6):786–94. 50. Cahill MT, Freedman SF, Toth CA. Macular translocation with 360 degrees peripheral retinectomy for geographic atrophy. Arch Ophthalmol 2003; 121(1):132–3. 51. Khurana RN, Fujii GY, Walsh AC, Humayun MS, de Juan E, Sadda SR. Rapid recurrence of geographic atrophy after full macular translocation for nonexudative age-related macular degeneration. Ophthalmology 2005; 112(9):1586–91. 52. Fujii GY, de Juan E, Thomas MA, Pieramici DJ, Humayun MS, Au Eong KG. Limited macular translocation for the management of subfoveal retinal pigment epithelial loss after submacular surgery. Am J Ophthalmol 2001; 131(2):272–5. 53. Green WR, Enger C. Age-related macular degeneration histopathologic studies. The 1992 Lorenz E Zimmerman lecture. Ophthalmology 1993; 100(10):1519–35. 54. Fujii GY, de Juan E, Sunness J, Humayun MS, Pieramici DJ, Chang TS. Patient selection for macular translocation surgery using the scanning laser ophthalmoscope. Ophthalmology 2002; 109(9):1737–44. 55. Pieramici DJ, de Juan E, Fujii GY, et al. Limited inferior macular translocation for the treatment of subfoveal choroidal neovascularization secondary to age-related macular degeneration. Am J Ophthalmol 2000; 130(4):419–28. 56. Loewenstein A, Sunness JS, Bressler NM, Marsh MJ, de Juan E. Scanning laser ophthalmoscope fundus perimetry after surgery for choroidal neovascularization. Am J Ophthalmol 1998; 125(5):657–65. 57. Harlan JB, Lee ET, Jensen PS, de Juan E. Effect of humidity on posterior lens opacification during fluid–air exchange. Arch Ophthalmol 1999; 117(6):802–4. 58. Macular Photocoagulation Study Group. Krypton laser photocoagulation for neovascular lesions of age-related macular degeneration: results of a randomized clinical trial. Arch Ophthalmol 1990; 108(6):816–24. 59. Sawa M, Chan W-M, Ohji M, et al. Successful photodynamic therapy with verteporfin for recurrent choroidal neovascularization beneath the new fovea after macular translocation with 360-degree retinotomy. Am J Ophthalmol 2003; 136(3):560–3. 60. Macular Photocoagulation Study Group. Occult choroidal neovascularization: influence on visual outcome in patients with age-related macular degeneration. Arch Ophthalmol 1996; 114(4):400–12. 61. American Academy of Ophthalmology. Macular translocation. Ophthalmology 2000; 107(5):1015–8. 62. Terasaki H, Ishikawa K, Suzuki T, Nakamura M, Miyake K, Miyake Y. Morphologic and angiographic assessment of the macula after macular translocation with 360-degree retinotomy. Ophthalmology 2003; 110:2403–8.

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63. Freedman SF, Gearinger MD, Enyedi LB, Holgado S, Toth CA. Measurement of ocular torsion after macular translocation: disc fovea angle and Maddox rod. J AAPOS 2003; 7(2):103–7. 64. Ohtsuki H, Shiraga F, Morizane Y, Furuse T, Takasu I, Hasebe S. Transposition of the anterior superior oblique insertion as a treatment for excyclotorsion induced from limited macular translocation. Am J Ophthalmol 2004; 137(1):125–34. 65. Freedman SF, Rojas M, Toth CA. Strabismus surgery for large-angle cyclotorsion after macular translocation surgery. J AAPOS 2002; 6(3):154–62. 66. Freedman SF, Holgado S, Enyedi LB, Toth CA. Management of ocular torsion and diplopia after macular translocation for age-related macular degeneration: prospective clinical study. Am J Ophthalmol 2003; 136(4):640–8. 67. Holgado S, Enyedi LB, Toth CA, Freedman SF. Extraocular muscle surgery for extorsion after macular translocation surgery: new surgical technique and clinical management. Ophthalmology 2006; 113(1):63–9. 68. Albini TA, Rao NA, Li A, Craft CM, Fujii GY, de Juan E. Limited macular translocation: a clinicopathologic case report. Ophthalmology 2004; 111(6):1209–14. 69. Roig-Melo EA, Alfaro DVI, Heredia-Elizondo ML, et al. Macular translocation: histopathologic findings in swine eyes. Eur J Ophthalmol 2000; 10(4):297–303. 70. Fang X, Hayashi A, Morimoto T, et al. Retinal changes after macular translocation with 360-degree retinotomy in monkey eyes. Am J Ophthalmol 2004; 137(6):1034–41. 71. Au Eong KG. Initial experience of macular translocation in Singapore—one-year results. Ann Acad Med Singapore 2004; 33(5):641–8. 72. Fujii GY, de Juan E, Pieramici DJ, et al. Inferior limited macular translocation for subfoveal choroidal neovascularization secondary to age-related macular degeneration: 1-year visual outcome and recurrence report. Am J Ophthalmol 2002; 134(1):69–74. 73. Morizane Y, Shiraga F, Takasu I, Yumiyama S, Okanouchi T, Ohtsuki H. Selection for inferior limited macular translocation on the basis of distance from the fovea to the inferior edge of the subfoveal choroidal neovascularization. Am J Ophthalmol 2002; 133(6):848–50. 74. Pawlak D, Glacet-Bernard A, Papp M, Roquet W, Coscas G, Soubrane G. Limited macular translocation compared with

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photodynamic therapy in the management of subfoveal choroidal neovascularization in age-related macular degeneration. Am J Ophthalmol 2004; 137(5): 880–7. Sullivan P, Filsecker L, Sears J. Limited macular translocation with scleral retraction suture. Br J Ophthalmol 2002; 86(4):434–9. Pertile G, Claes C. Macular translocation with 360 degree retinotomy for management of age-related macular degeneration with subfoveal choroidal neovascularization. Am J Ophthalmol 2002; 134(4):560–5. Mruthyunjaya P, Stinnett SS, Toth CA. Change in visual function after macular translocation with 360 retinectomy for neovascular age-related macular degeneration. Ophthalmology 2004; 111(9):1715–24. Fujikado T, Asonuma S, Ohji M, et al. Reading ability after macular translocation surgery with 360-degree retinotomy. Am J Ophthalmol 2002; 134(6):849–56. Toth CA, Lapolice DJ, Banks AD, Stinnett SS. Improvement in near visual function after macular translocation surgery with 360-degree peripheral retinectomy. Graefe’s Arch Clin Exp Ophthalmol 2004; 242(2):541–8. Cahill MT, Stinnett SS, Banks AD, Freedman SF, Toth CA. Quality of life after macular translocation with 360 peripheral retinectomy for age-related macular degeneration. Ophthalmology 2005; 112(1):144–51. Park CH, Toth CA. Macular translocation surgery with 360-degree peripheral retinectomy following ocular photodynamic therapy of choroidal neovascularization. Am J Ophthalmol 2003; 136(5):830–5. Kadonosono K, Takeuchi S, Iwata S, Uchio E, Itoh N, Akura J. Macular fold after limited macular translocation treated with scleral shortening release and intravitreal gas. Am J Ophthalmol 2001; 132(5):790–2. Kim T, Krishnasamy S, Meyer CH, Toth CA. Induced corneal astigmatism after macular translocation surgery with scleral infolding. Ophthalmology 2001; 108(7):1203–8. Ichibe M, Yoshizawa T, Funaki S, et al. Severe hypotony after macular translocation surgery with 360-degree retinotomy. Am J Ophthalmol 2002; 134(1):139–41. Au Eong KG, Fujii GY, Ng EWM, Humayun MS, Pieramici DJ, de Juan E. Transient formed visual hallucinations following macular translocation for subfoveal choroidal neovascularization secondary to age-related macular degeneration. Am J Ophthalmol 2001; 131(5):664–6.

20 Age-Related Macular Degeneration: Use of Adjuncts in Surgery and Novel Surgical Approaches Richard Scartozzi and Lawrence P. Chong

Doheny Retina Institute of the Doheny Eye Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A.

INTRODUCTION Adjuncts that have been used in surgery for age-related macular degeneration (AMD) include tissue plasminogen activator (tPA), balance salt solution (BSS), and calcium- and magnesium-free retinal detachment-enhancing solutions. The surgeries in which these solution have been used include submacular surgery to excise choroidal neovascular membranes, large-scale macular translocation surgery, limited macular translocation surgery, evacuation, or displacement of submacular hemorrhages. In addition to these adjuncts, triamcinolone acetonide (TA) has been injected into the subretinal space for the treatment of choroidal neovascular membranes. Novel surgical approaches include the surgical implantation of sustained release drug devices, the surgical implantation of cell-based delivery systems, and the pre-retinal or subretinal delivery of radiation therapy through a pars plana approach.

TISSUE PLASMINOGEN ACTIVATOR tPA is a polypeptide of 527 amino acids that cleaves the Arg560-Val561 bond of plasminogen. Because of its high affinity for fibrin, its enhancement of binding of plasminogen to fibrin clots, and potentiation of its activity in the presence of fibrin, fibrinolysis occurs almost exclusively in fibrin clots. Commercial tPA (Activase, Genentech, Inc.; Actilyse, Boehringer Ingelheim International, GmbH) is a 70,000 mW, single-chain protein produced from a cloned human tPA gene using Chinese hamster ovary cells (1). Endogenous tPA is secreted in its single-chain form to be enzymatically converted by plasmin to its two chain form. Both forms of tPA are equally active. The vehicle consists of L-arginine phosphate, phosphoric acid, and polysorbate 80. tPA has been used both intracamerally and subretinally. The utility of intracameral tPA was demonstrated in animal models of fibrin (2–4), hyphema (5), vitreous

hemorrhage (6–8), and subretinal hemorrhage (9,10). The utility of subretinal injection of tPA was demonstrated in animal models of subretinal hemorrhage (11–13). In the anterior chamber, 0.05 mL containing up to 200 mg and 0.10 mL containing up to 360 mg have been injected without unusual inflammation or toxicity to the cornea or lens. In the vitreous cavity, 0.10 mL containing up to 25 mg has been injected without corneal or retinal toxicity. Repetitive injections (three times, separated by seven-day intervals) of 3 mg tPA also did not show retinal toxicity (8). A single report suggested probable retinal toxicity of 0.1 mL containing 25 mg (14). Dose-dependent retinal toxicity was seen with 0.10 mL injections of 50, 75, and 100 mg into the vitreous cavity (15). Tractional retinal detachments were seen following 100 mg (6) and 200 mg (7) tPA injections. In the subretinal space, no retinal toxicity was seen after subretinal injection of 25 and 50 mg of tPA in 0.1 mL of volume (11,12). Lewis and colleagues demonstrated in rabbits that subretinal clots, 30-minutes old, cleared faster after a 0.1 mL subretinal injection of 25 mg tPA as compared to an equivalent volume of BSS (11). However, the subretinal tPA could not completely prevent retinal damage. Both BSS and tPA decreased the toxic effect of blood partly on the basis of dilution of the subretinal blood. Johnson and colleagues showed a similar effect for lower doses of tPA (2.5 mg in 0.05 mL) on clots that were 24-hours old, but severe progressive retinal degeneration was still seen (12). An ultramicrosurgical approach using a microinfusion of 0.5 to 5 mg of tPA facilitated lysis of one- and twoday-old clots and their removal through micropipettes under stereotactic control. Good preservation of the retinal architecture was seen compared to untreated controls (13). The ability of intravitreal injections of tPA to lyse subretinal clots has been explored. Coll and colleagues found that 0.1 mL containing 50 mg of tPA facilitated

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the lysis and absorption of one-day-old subretinal clots compared to equivalent volume injections of saline (9). Unfortunately, retinal damage was not prevented. Boone and colleagues injected 25 mg of tPA into the vitreous space and found only partial clot lysis that was not enough to allow removal by aspiration alone (10). The inability of labeled tPA injected into the vitreous to penetrate the intact neural retina or a subretinal clot in rabbits was demonstrated by Kamei and colleagues (16). Some labeled tPA was able to penetrate into eyes with vitreous hemorrhage presumably from the microdefects through which blood escaped from the subretinal space into the vitreous. The previous studies spurred simultaneous interest in the clinical use of tPA to assist in the removal of subretinal hemorrhage. These techniques involved the injection of 6.25 to 12.5 mg of tPA in a volume of 0.05 mL into the subretinal space and then waiting 10 to 45 minutes before aspiration of the liquefied blood. Injections into the subretinal space were accomplished with a glass pipette (17), 33-gauge cannula (18), or bent-tipped 30-gauge needle (19,20). Aspiration was performed with double-barrel subretinal-injector aspirator (18), soft-tipped cannula (17,21), tapered 20-gauge Charles flute needle (20), or 30-gauge subretinal cannula (22). Liquefied subretinal blood was also manipulated with a small perfluorocarbon liquid bubble (19,23,24). In addition to intravitreal injection of tPA during the pars plana vitrectomy procedure, the injection of 0.1 mL of 25 mg of tPA into the subretinal clot by passing a 30-gauge needle through the pars plana under indirect ophthalmoscopy the day before pars plana vitrectomy has also been described (25). An intravitreal injection consisting of 6 mg of tPA in 0.1 mL was injected into the midvitreous cavity to liquefy subretinal clots 12 to 36 hours prior to vitrectomy and removal of blood through a retinotomy using perfluorocarbon liquid manipulation (26). Intravitreal injections of 0.1 to 0.2 mL containing 25 to 100 mg of tPA into the vitreous cavity have been given either the day before (27) or immediately before (28,29) injection of intravitreal gas to displace submacular hemorrhage. Exudative retinal detachments seen after 100 mg injections were attributed to tPA toxicity (28). A number of investigators have injected 25 to 50 mg tPA into the subretinal space following pars plana vitrectomy (30–32).An air fluid exchange was performed and the patient was kept erect to pneumatically displace the liquefied blood from the fovea. Lewis injected tPA into the subretinal space before excision of the choroidal neovascular membrane but found no improvement compared with injection of BSS into the subretinal space in a randomized trial (33).

CALCIUM- AND MAGNESIUM-FREE RETINAL DETACHMENT-ENHANCING SOLUTIONS Marmor had discovered that removing calcium and magnesium from a solution that bathed eye wall sections in vitro weakened retinal adhesive force (34). Wiedemann described a “detachment infusion” for macular translocation surgery that was calcium and magnesium free (35). Substituted for conventional vitrectomy infusion fluid, this solution enabled the immediate detachment of the retina from its peripheral, diathermy-induced perforation site to the center of the macula or macular area. He described its use in retinal organ culture and creation of experimental retinal detachment in rabbits and in human surgery. We hypothesized that BSS Part A might be an ideal retinal detachment-enhancing solution and studied its safety and efficacy in rabbits before using it clinically in humans. BSS was developed as an improvement over normal saline, lactated Ringer’s, and Plasma-lyte 148 as a physiologically compatible solution to be used in the eye during surgery (36,37). To further improve the physiological compatibility of BSS, glutathione, glucose, and bicarbonate buffer systems were added (38–40) resulting in BSS Plus. BSS Plus consists of two parts, which are reconstituted just prior to use in surgery. These two parts consist of Part B, a sterile 480-mL solution in a 500-mL singledose bottle to which Part A, a sterile concentrate in a 20-mL single-dose vial, is added. Compared to BSS, BSS Part A lacks magnesium and calcium, and the citrate and acetate buffers of BSS have been replaced with bicarbonate buffer. BSS Part B contains calcium and magnesium as well as the dextrose and the glutathione, which are unique to BSS Plus. We hypothesized that BSS Part A alone could be used safely in the human eye since it contained almost all the ingredients of BSS except for the calcium and magnesium with a different buffering system and a pH of 7.4. A tremendous advantage to the vitreous surgeons is the commercial availability of BSS. We felt that all these qualities plus the historical use of the solution in the operating room (albeit reconstituted with Part B) could make it an ideal solution to enhance retinal detachment during macular translocation surgery. We showed the safety and efficacy of a calcium- and magnesium-free macular translocation solution by comparing the results of injecting BSS Part A or BSS solution into the subretinal space of rabbit eyes using a 39-gauge cannula (40). No difference was seen in fundus appearance, fluorescein angiography, electroretinography, or light or electron microscopy in rabbit retinas that had been detached using retinal detachment solution compared to commercially available solution. Using a manual infusion system, no more than 100 mg of BSS compared to a much larger

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volume of retinal detachment solution could be infused into the subretinal space. The diameter of BSS retinal detachments was always less than that of BSS Part A retinal detachments after injection of 100 mg of subretinal fluid. Aaberg et al. have similarly shown the safety of subretinal BSS Part A in the sub-retinal space of the rabbit using transscleral infusion (41). We have used a 39-gauge cannula to atraumatically infuse BSS Part A underneath the retina in macular translocation surgery and to displace submacular hemorrhage. Clinically, we have found that macular translocation surgery requires only one or two penetrations through the retina with a 39-gauge cannula to detach the posterior retina sufficiently. We have used BSS Part A to displace submacular hemorrhages by performing pars plana vitrectomy, injecting the solution to detach the posterior pole of the retina, performing partial gas– fluid exchange, and then positioning the patient in an erect position for 24 hours to displace blood away from the fovea.

TRIAMCINOLONE ACETONIDE A discussion of the pharmacology and the mechanism of action of TA is presented in Chapters 8 and 15. The intravitreal injection of TA for the treatment of choroidal neovascular membranes is also discussed in those chapters. The subretinal injection of TA will be discussed here.

Figure 1 position.

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Forty-one gauge subretinal cannula in the extended

a 41-gauge cannula (Figs. 1 and 2) and the retinal openings that are created self-seal and do not need to receive retinopexy. In our institution, we have performed these injections after removal of the vitreous by pars plana vitrectomy and through formed vitreous without vitrectomy. These injections have been performed both in the operating room and in the clinic setting. In a pilot study, two eyes of two patients underwent pars plana vitrectomy, subretinal injection of 4 mg of TA (0.1 mL), and gas–fluid exchange for subfoveal neovascular AMD (42). The first patient sustained a limited subretinal hemorrhage intraoperatively that cleared spontaneously over approximately three months, as well as a rise in intraocular pressure that required the use of two topical medications to control. The second patient demonstrated progression of his nuclear sclerosis and posterior subcapsular lens

SUBRETINAL INJECTION OF TA Some current methods for treating retinal diseases involve the introduction of drugs directly into the vitreous chamber of the eye by intraocular injection or intravitreal implant. Solutions injected directly into the vitreous chamber, however, are often rapidly removed by the eye’s normal circulatory processes, requiring frequent injections or sustained release of the drug. These large-dose injections lead to the distribution of the drug throughout the whole eye and can be associated with complications, such as cataract formation and glaucoma. Additionally, these therapies do not address the issue of large molecular weight molecules (more than 70 kDa) that are virtually incapable of diffusing through retinal tissues. The delivery of TA into the subretinal space has been investigated for the treatment of subfoveal choroidal neovascularization (CNV) due to AMD. The subretinal delivery of a therapeutic agent could allow for the local, low-dose treatment of retinal pathology with fewer complications to other intraocular structures such as the lens and optic nerve. These subretinal injections can be delivered through

Figure 2 The body of the 41-gauge subretinal cannula has a sliding button which can be used to extend and retract the cannula itself.

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change over the 35 months of follow-up. Best corrected visual acuity improved from 20/400 to 20/200 in the first patient, and from counting fingers to 20/320 in the second patient. The size of the neovascular complexes increased modestly in both patients. The authors conclude that their complications were not prohibitive, and that their results may be likened to the course seen with PDT. A pilot study of 14 eyes of 14 patients with subfoveal CNV from AMD was performed where 0.5 to 5 mg of TA was injected subretinally, overlying the CNV (43). Three patients developed a subretinal hemorrhage in the immediate postoperative period, where two of these three patients’ final visual acuities improved (Fig. 3). Also, in the immediate postoperative period, one patient had an elevated intraocular pressure and one patient had a retinal detachment. There were no late postoperative complications. Although subretinal delivery of triamcinolone seems to be safe, maximizing durability of drug and minimizing injections is desirable. Therefore, a biocompatible, sustained-release subretinal drugdelivery platform has been developed which is capable of delivering either TA or sirolimus (44). The prototype implants were fabricated by coating nitinol, poly(methyl methacrylate) or chromic gut core filaments, with a drug-eluting polymer matrix, and tested in rabbits (Fig. 4). Initial observations of the implantation and elution characteristics revealed that the implants are well tolerated by the retinal tissue and that the implant can elute TA for a period of at least four weeks without eliciting an inflammatory response or complications.

Figure 3 After subretinal injection, the triamcinolone is located inferior and temporal to the fovea. There is hypopigmentation at the site of the injection which is located between the white mass and the fovea.

Figure 4 rabbit.

The drug-releasing filament lies under the retina in this

ENCAPSULATED CELL TECHNOLOGY Encapsulated cell technology (ECT) employs mammalian cells that are genetically engineered to secrete a therapeutic factor. These engineered cells are then encapsulated in a semi-permeable polymer membrane device which allows for the free exchange of nutrients and metabolites to sustain the cells, while allowing for the exit of a therapeutic factor (Figs. 5 and 6). At the same time, these membranes protect the engineered cells from host antibodies and immune cells. The devices are then surgically implanted into the vitreous cavity of the eye (Fig. 7). ECT allows for the continuous and long-term site-specific administration of drugs in the eye without subjecting the host to systemic exposure. Furthermore, these implants can be retrieved, providing an added level of control and safety. ECT-CNTF (human ciliary neurotrophic factor) devices were implanted in a dog model of retinitis pigmentosa (RP) (45). One eye was implanted at seven weeks of age, leaving the contralateral eye untreated. These devices were explanted at 7 or 14 weeks postimplantation. There was significant protection of the photoreceptors from degeneration in a dose-dependent and safe manner, as revealed by examining the number of cells in the outer nuclear layer histologically. Furthermore, the data from this study confirmed that sustained delivery of protein therapeutics is more effective than bolus injection, while avoiding the additive risks of frequent intraocular injections. The authors also concluded that this technology was superior to the use of viruses in gene therapy, as gene therapy tended to be effective only for a few weeks, induced an immune response, and produced unpredictable amounts of therapeutic agent. These data from animal studies enabled a prospective phase I clinical trial which safely delivered CNTF to the eyes of 10 subjects suffering from advanced RP (46). Though this nonrandomized trial

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299

Encapsulated Cell Protein Delivery Immunoisolatory Membrane Immune System Components

Oxygen and Nutrients

Therapeutic Factors

Figure 5 Cells that release therapeutic molecules are protected from the host immune system by a semipermeable membrane. The semipermeable membrane allows these cells to receive oxygen and nutrients.

had only a small number of participants and was not placebo-controlled, several of the implanted eyes showed a trend of better acuity on a letter recognition task compared with contralateral control eyes. At the end of the six-month implantation duration, all explanted capsules contained viable cells that secreted CNTF at expected levels that were therapeutic in the rcd1 (cGMP-PDE6b mutation) dog study (45). Smaller ECT devices that can be implanted through a 25-gauge opening are currently being developed (47). The application of this technology to other ocular diseases such as AMD is currently an active area of investigation.

SELECTIVE INTRAOCULAR RADIATION BRACHYTHERAPY Although the results of radiation treatment for neovascular AMD are mixed and generally unfavorable (48,49), there is data to suggest that higher dosages may produce better results (50–53). Flaxel and colleagues showed promising results with proton beam radiation at 8 to 14 Gray (Gy), but radiation

Encapsulated Cell Technology Membrane

Suture clip

Seal

Scaffold Cells

Figure 6 Living cells that release therapeutic molecules are encased in a proprietary scaffold, which serves as the semipermeable membrane to create the cell-based drug delivery device.

Figure 7 The cell-based drug delivery device is anchored by suturing an attached titanium ring to the pars plana.

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retinopathy was a serious complication and seen in 50% of the 14 Gy-treated eyes (54). To overcome this limitation in radiation delivery dosage caused by radiation retinopathy, a method of delivering focal radiation to the choroidal neovascular membrane by passing an intraocular radiation delivery device underneath the retina was developed. Retina exposure to radiation is minimized by directional shielding of the subretinal radiation source and by the focal nature of the radiation delivery. Creation of a subretinal bleb using a 41-gauge needle and a retinotomy allowed for the brachytherapy probe to be in direct contact with the retinal pigment epithelium (RPE) for a set amount of time. The brachytherapy device contains shielding which prevent radiation exposure on the retinal side. In a phase I clinical study, 10 eyes of 10 patients received 26 Gy of subretinal radiation via an angled or non-angled probe to active subfoveal CNV, with follow-up ranging from two to nine months (55). By fluorescein angiography, greatest linear dimension (GLD) leakage decreased by 46% in one month, 64% in three months, and 82% in six months. By optical coherence tomography, total macular volume decreased by 13% in one month, 19% in three months, and 30% in six months. Visual acuity was stable or improved in 44% by two and three months. Adverse events included RPE tears, RPE atrophy, RPE hyperpigmentation, subretinal hemorrhage, cataract, pre-retinal hemorrhage and vitreous hemorrhage. Because of these complications, efforts are now directed towards pre-retinal delivery of radiation. Preclinical study showed that the minimum threshold for acute damage using a pre-retinal focal radiation delivery device was above 103 Gy, nearly four times the dosage expected to cause beneficial effect described in the literature. As a result, a phase I clinical trial is in the planning stage to evaluate the safety and feasibility of focal delivery of radiation from a preretinal position using a sealed radiation source placed temporarily over the fovea in the vitreous cavity by means of a proprietary intraocular probe. The delivery device is a shielded canister containing a strontium90 beta-radiation source with an angled-tip that has a 1.0 mm outer diameter. In the storage (retracted) position, the radiation source is surrounded by a stainless steel and lead lining that effectively protects the surgeon and patient during the handling and initial positioning. This tip will allow for the directional delivery of approximately 24 Gy of betaradiation via a light touch approach on the retinal surface for a three to five minute period. In the treatment position, the source is located within a specially designed stainless steel tip that provides directional administration of the beta radiation while

Radiation Source In Storage Position

Radiation Source In Treatment Position

Figure 8 In a retracted position, the radiation source lies in the body of the delivery instrument and is shielded from the environment. The sliding button is used to extend the radiation source into the curved tip for radiation of the choroidal neovascular membrane.

shielding and protecting surrounding non-target, unaffected (i.e., disease free) tissues (Figs. 8 and 9).

SUMMARY POINTS & & &

& & &

Adjuncts are used primarily in the subretinal space during surgery for AMD. tPA can be infused into the subretinal space to liquefy subretinal blood. tPA may penetrate human retina after injection into the vitreous cavity through microperforations to liquefy subretinal blood. Calcium- and magnesium-free solutions enhance retinal detachment. BSS Plus Part A is a safe and readily available retinal detachment solution. Calcium- and magnesium-free solutions can aid macular translocation surgery and the displacement of submacular hemorrhage.

Figure 9 therapy.

Delivery device for intraocular radiation brachy-

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Novel surgical approaches seek a long term enhancement of existing therapies for AMD. These approaches include the surgical implantation of sustained release drug devices, the surgical implantation of cell-based delivery systems, and the pre-retinal or subretinal delivery of radiation therapy through a pars plana approach.

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17. Peyman GA, Nelson NC, Alturki W, et al. Tissue plasminogen activating factor assisted removal of subretinal hemorrhage. Ophthalmic Surg 1991; 22:575–82. 18. Lewis H. Intraoperative fibrinolysis of submacular hemorrhage with tissue plasminogen activator and surgical drainage. Am J Ophthalmol 1994; 118:559–68. 19. Vander JF. Tissue plasminogen activator irrigation to facilitate removal of subretinal hemorrhage during vitrectomy. Ophthalmic Surg 1992; 23:361–3. 20. Moriarty AP, McAllister IL, Constable U. Initial clinical experience with tissue plasminogen activator (tPA) assisted removal of submacular haemorrhage. Eye 1995; 9:582–8. 21. Manning LM, Contrad DK. Tissue plasminogen activator in the surgical management of subretinal haemorrhage. Aust NZ J Ophthalmol 1994; 22:59–63. 22. Ibanez HE, Williams DF, Thomas MA, et al. Surgical management of submacular hemorrhage: a series of 47 consecutive cases. Arch Ophthalmol 1995; 113:62–9. 23. Lim JI, Drews-Botsch C, Sternberg P, Jr., Capone A, Jr., Aaberg TM, Sr. Submacular hemorrhage removal. Ophthalmology 1995; 102:1393–9. 24. Kamei M, Tano Y, Maeno T, Ikuno Y, Mitsuda H, Yuasa T. Surgical removal of submacular hemorrhage using tissue plasminogen activator and perfluorocarbon liquid. Am J Ophthalmol 1996; 121:267–75. 25. Chaudhry NA, Mieler WF, Han DP, Alfaro VD, III, Liggett PE. Preoperative use of tissue plasminogen activator for large submacular hemorrhage. Ophthalmic Surg Lasers 1999; 30:176–80. 26. Kimura AE, Reddy CV, Folk JC, Farmer SG. Removal of subretinal hemorrhage facilitated by preoperative intravitreal tissue plasminogen activator. Retina 1994; 14:83–4. 27. Heriot W. Intravitreal gas and tPA: an outpatient procedure for subretinal hemorrhage. In: Vail Vitrectomy Meeting, Vail, Colorado, March 10–15, 1996. 28. Hesse L, Schmidt J, Kroll P. Management of acute submacular hemorrhage using recombinant tissue plasminogen activator and gas. Graefes Arch Clin Exp Ophthalmol 1999; 202:273–7. 29. Hassan AS, Johnson MW, Schneiderman TE, et al. Management of submacular hemorrhage with intravitreous tissue plasminogen activator injection and pneumatic displacement. Ophthalmology 1999; 106:1900–7. 30. Connor TB. Surgical displacement of submacular hemorrhage. In: Vail Vitrectomy Meeting, Vail, Colorado, March 15, 2000. 31. Federman IL. Variation in surgical management of submacular hemorrhage. In: Vail Vitrectomy Meeting, Vail, Colorado, March 15, 2000. 32. McCuen BW. A new concept in the treatment of submacular hemorrhage in AMD. In: Vail Vitrectomy Meeting, Vail, Colorado, March 14, 2000. 33. Lewis H, VanderBrug MS. Tissue plasminogen activatorassisted surgical excision of subfoveal choroidal neovascularization in age-related macular degeneration: a randomized, double-masked trial. Ophthalmology 1997; 104(11):1847–51 (discussion 1852). 34. Yao XY, Endo EG, Marmor MF. Reversibility of retinal adhesion in the rabbit. Invest Ophthalmol Vis Sci 1989; 30:220–4. 35. Faude F, Reichenbach A, Wiedemann P. A detachment infusion for macular translocation surgery. Retina 1999; 19(2):173–4. 36. Edelhauser HF, Van Horn DL, Hyndiuk RA, Schultz RO. Intraocular irrigating solutions: their effect on the corneal endothelium. Arch Ophthalmol 1975; 93:648–57.

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37. Waltman SR, Carroll D, Schinimelpfenning W, Okun E. Intraocular irrigating solutions for clinical vitrectomy. Ophthalmic Surg 1975; 6(4):90–4. 38. Benson WE, Diamond JG, Tasman W. Intraocular irrigating solutions for pars plana vitrectomy: a prospective, randomized, double-blind study. Arch Ophthalmol 1981; 99:1013–5. 39. Glasser DB, Matsuda M, Ellis JG, Edelhauser HF. Effect of intraocular irrigating solutions on the corneal endothelium after in vivo anterior chamber irrigation. Am J Ophthalmol 1985; 99:321–8. 40. Araie M. Barrier function of corneal endothelium and the intraocular irrigating solutions. Arch Ophthalmol 1986; 104:435–8. 41. Aaberg TM, Sharara NA, Edelhauser HF, Grossniklaus HE. Hydroseparation of the neurosensory retina with calcium free BSS Plus. In: XXIInd Meeting of the Club Jules Gonin, Taormina, Italy, September 2–6, 2000. 42. Kertes PJ, Coupland SG. The use of subretinal triamcinolone acetonide in the management of neovascular age-related macular degeneration: a pilot study. Can J Ophthalmol 2005; 40(5):573–84. 43. Equi RA, de Juan E, Jr., Sadda SR, Varner S, Lim JI. Subretinal triamcinolone for the treatment of neovascular age-related macular degeneration: a pilot study. In: 21st Annual Meeting of the American Society of Retina Specialists, New York, August 16–20, 2003. 44. Beeley NR, Stewart JM, Tano R, et al. Development, implantation, in vivo elution, and retrieval of a biocompatible, sustained release subretinal drug delivery system. J Biomed Mater Res A 2006; 76(4):690–8. 45. Tao W, Wen R, Goddard MB, Sherman SD, O’Rourke PJ, Stabila PF, Bell WJ, Dean BJ, Kauper KA, Budz VA, et al. Encapsulated cell-based delivery of ciliary neurotrophic factor reduces photoreceptor degeneration in animal models of retinitis pigmentosa. Invest Ophthalmol Vis Sci 2002; 43(10):3292–8.

46. Sieving PA, Caruso RC, Tao W, et al. Ciliary neurotrophic factor (CNTF) for human retinal degeneration: phase I trial of CNTF delivered by encapsulated cell intraocular implants. Proc Natl Acad Sci USA 2006; 103(10):3896–901. 47. Kauper KA, Stabila P, Mills J, et al. Delivery of encapsulated cell technology (ECT) device implants using a small gauge needle. Invest Ophthalmol Vis Sci 2006; 47:E-Abstract 5118. 48. The Radiation Therapy for Age-related Macular Degeneration (RAD) Study Group. A prospective, randomized, double-masked, trial on radiation therapy for neovascular age-related macular degeneration (RAD Study). Ophthalmology 1999; 106:2239–47. 49. Kobayashi H, Kobayashi K. Age-related macular degeneration: long-term results of radiotherapy for subfoveal neovascular membranes. Am J Ophthalmol 2000; 130:617–35. 50. Jaakkola A, Heikkonen J, Tommila P, Laatikainen L, Immomen I. Strontium plaque brachytherapy for exudative age-related macular degeneration: three-year results of a randomized study. Ophthalmology 2005; 112:567–73. 51. Jaakkola A, Heikkonen J, Tommila P, Laatikainen L, Immomen I. Strontium plaque irradiation of subfoveal neovascular membranes in age-related macular degeneration. Graefes Arch Clin Exp Ophthalmol 1998; 236:24–30. 52. Finger PT, Berson A, Ng T, Szechter A. Ophthalmic plaque radiotherapy for age-related macular degeneration associated with subretinal neovascularization. Am J Ophthalmol 1999; 127:170–7. 53. Rossi JV, Fujii GY, Humayun MS, et al. Submacular surgery for selective subretinal delivery of beta-radiation. Invest Ophthalmol Vis Sci 2004; 45:E-Abstract 5140. 54. Flaxel CJ, Friedrichsen EJ, Smith JO, et al. Proton beam irradiation of subfoveal choroidal neovascularisation in age-related macular degeneration. Eye 2000; 14(Pt 2):155–64. 55. Lim JI, deJuan E, Jr., Sadda S, et al. Subretinal radiation treatment of occult choroidal neovascularization due to age-related macular degeneration. Invest Ophthalmol Vis Sci 2005; 46:E-Abstract 1384.

Part VI: Visual Rehabilitation

21 Clinical Considerations for Visual Rehabilitation Susan A. Primo

Department of Ophthalmology, Emory University School of Medicine, Atlanta, Georgia, U.S.A.

INTRODUCTION While the trauma of macular degeneration is difficult enough for some patients to cope with, the visual impairment left afterwards is even tougher. Patients must not only learn to accept the fate of retinal disease, but must also summon the strength to accept the fact that they will surrender a certain degree of independence as visual acuity declines. The visual rehabilitative process helps the visually impaired patient to regain a satisfactory level of independence and can be achieved by assisting the patient in learning to cope with the psychological, emotional, and economic aspects of vision loss, as well as through the use of optical, nonoptical, and electronic devices, where there are some exciting new technologies available. Typically, this type of integrated rehabilitative process is necessary for patients with severe and profound visual impairment, i.e., legal blindness.

THE LOW VISION EVALUATION The term legal blindness as defined is a visual acuity of 20/200 or worse in the best-corrected better eye or a visual field of 208 or less in the widest diameter of vision. A patient cannot have poor vision in one eye only and be considered legally blind. This classification becomes a part of the patient’s permanent record and has implications for eligibility for state financial assistance, tax benefits, reduced public transportation fares, and other circumstances. In addition, in many states that have “commissions” for the blind, reporting of legal blindness may cause a driver’s license to be revoked. For many people, having a driver’s license, whether actually driving or not, has significant meaning and serves as a form of identification. The practitioner should be aware of these issues when designating this classification. The low vision examiner begins the evaluation with a complete understanding of the patient’s ocular history. Detailed documentation of surgical history and stage of pathology are important components.

Typically, a low vision evaluation should not commence until a patient has undergone all surgical and nonsurgical attempts at restoring visual function. The reasons for this are twofold. First, the low vision examiner is concerned with performing an extensive evaluation often using the state-of-the art devices, which can be quite expensive. If the patient’s final visual acuity is in question, these devices may not be suitable once the visual acuity has reached its final level and has stabilized. Secondly, the patient needs to have gone through the “mourning process” of losing sight with the understanding that the next step must be taken to begin the visual rehabilitative process. This is not to say that if miracle breakthroughs become available, then a patient should not have access to any possibility of restoring sight. However, success with low vision devices is completely dependent upon: (i) patients’ full acceptance of their visual impairment and (ii) the ability and desire to move on. During the history, the patient is asked about aspects of vision loss. These aspects include duration, symmetry, fluctuations, stability, loss of ability to discriminate color, effects of various illuminations or lighting conditions, and mobility concerns. These questions assist patients in learning to talk about the effects of the visual impairment on their lifestyle, an important step in beginning the rehabilitative process. While ascertaining this information, the low vision examiner also documents any current devices including glasses, which may already be in the patient’s possession. Frequently, a well-meaning spouse or relative has already offered the patient a magnifier of some sort. It is important to categorize all such devices for type, style, and power. It is also important to determine the usefulness of these devices. For example, can the patient read large print or headlines of a newspaper with glasses and/or a magnifier? Oftentimes, patients will say that all devices are useless, but in reality, they may be able to see large print and not regular print. While this may be considered useless to them, it is important to the examiner.

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Perhaps, the last and most important part of the history is an expression by patients of their goals and expectations. During this portion, the examiner determines whether the patient has realistic goals and expectations or whether the desire is to “just see again.” A detailed list of desired activities is recorded in order of importance to the patient. Sometimes it takes a little prodding, but virtually all patients’ primary desire is to be able to read again. It is important to determine if patients simply want to read mail or bills in order to handle their own finances and/or patients want to continue leisurely reading of printed materials such as newspaper, novels, etc. Second to a desire to read is usually improvement of distance vision. Again, specific distant activities (watching television, bird-watching, or driving) need to be discussed. The driving issue is an extremely sensitive area and the examiner uses compassion and sensitivity in discussing this topic. A more detailed discussion of driving will follow later in this chapter. Using a checklist approach is a quick and easy method for determining the patient’s current level of vision and, subsequently, any special material the patient wishes to read or certain activities the patient wishes to engage in, i.e., playing cards, sewing, drawing or painting, golf, etc. (Fig. 1). Finally, maximizing an education environment is critical for young children or adults, as is attention to patients’ workplace if they are employed or seeking gainful employment. Although there is a standard format to the low vision evaluation, the examiner always bears in mind

Checklist for Current Level of Vision/Goals Yes

No

Desires

Headlines Magazines Regular Newsprint Labels, Price Tags Money Recognize Faces Watch TV Cooking Sew, Knit, etc. Housekeeping Hygiene Handiwork Garden/Yard Work Sports (Golf, etc.) Play Cards Driving Other

____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____

____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____

____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ ____

____

____

____

Glare

____

____

Figure 1

Checklist of vision/goals.

a goal-orientated approach. For example, if a patient expresses the desire to read only, the focus will be on achieving this goal. The examiner might explain possibilities for improvement in distance vision, but if a patient is still uninterested, the telescopic evaluation is probably unnecessary. Likewise, if a patient’s only desire is to drive, a short near evaluation may be performed to demonstrate possibilities, but clearly the emphasis in this case would be on the telescopic evaluation. As the examiner notices head and body movements as the patient initially walks into the examination room, these seemingly minor observations provide information not only about visual status, but also about a patient’s level of adaptation to the vision loss. In addition, before visual acuity testing begins, any auxiliary testing is performed, which may include contrast sensitivity, Amsler grid, visual fields, etc. These tests can shed light on the size and extent of the central scotoma as well as on other subjective aspects of the acuity loss. As clear-cut as it may seem, visual acuity testing is an extremely important (and often long) part of the rehabilitative examination. Evaluating a patient with reduced visual acuity requires that basic examination techniques be modified. It is generally recommended that vision testing be done at 10 ft with a self-illuminated, portable eye chart. The Early Treatment Diabetic Retinopathy Study (ETDRS) chart is the most widely used. A projector chart is the least favorable means of measuring acuity in a patient with reduced vision. Not only is contrast not constant with a projector chart depending on the level of room illumination, but a patient would also have to be moved closer to the chart if vision was worse than 20/400. Moving a visually impaired patient only reinforces awareness of the vision loss and causes stress and negative feelings during the exam. The ETDRS chart has several advantages. It is self-illuminated with high contrast and is on wheels in order that it could be moved closer than 10 ft if necessary. Also, the chart has a wide spectrum of visual acuity values, ranging from a “Snellen 200 ft” equivalent to a 10-ft equivalent. Since the testing distance is always recorded as the numerator of the Snellen fraction, this chart gives an acuity range (at 10 ft) from 10/200 (20/400) to 10/10 (20/20). If the chart is moved closer, the test distance is again recorded as the numerator. It is best not to convert the acuity to the 20-ft equivalent when recording vision so that the examiner may always know the test distance for subsequent evaluations. “Counting fingers” vision for measurement is generally not used during a low vision evaluation. The fingers subtend approximately the same visual angle as a 200-ft Snellen figure. Therefore, a patient should be able to read the top line of the ETDRS chart at a closer distance. Recording visual

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acuity as “3/200” instead of counting fingers at 3 ft is much more accurate, which is important in determining which optical devices may be appropriate. Determination of eccentric view, if suspected, is done during acuity testing. The easiest method is called the clock-face method. Patients are asked to keep their head still and to face straight ahead. The examiner then asks the patient to imagine that the eye chart is at the center of a clock. Patients are asked to move their eye in various positions of the clock until the top line becomes the clearest and most complete. Typically, but not always, a patient with acquired macular disease will attempt to place the image on the temporal retina where the most room is, i.e., the right eye will eccentrically view towards the right (3 o’clock) and the left eye will view towards the left (9 o’clock). This position should be demonstrated to the patient several times and recorded next to visual acuity. The knowledge of the exact location of the eccentric view will become useful for the remainder of the evaluation with devices. Manifest refraction in a trial frame is generally the rule. In this case, the examiner can observe the patient’s eyes, particularly to reinforce the eccentric view. A phoropter does not allow a patient’s eyes to be observed and the use of an eccentric view by the patient becomes quite difficult. In addition, the lens increments may be too small for a patient to determine any subjective difference, i.e., a patient with 20/200 vision will not appreciate a difference of G0.25 D. The examiner cannot easily make large increments of change in the phoropter for patients with poorer vision. Generally, a patient whose vision is less than 20/100 will appreciate 0.50 D lens changes. For vision between 20/100 and 20/200, the examiner should use 0.75 to 1.50 D changes. If a patient’s vision is 20/200 to 20/400, 1.50 to 2.00 D lens increments should be used. This technique is called lens bracketing and is the most time efficient and effective. Likewise, when measuring astigmatic corrections, a higher powered Jackson Cross Cylinder (0.75–2.00 D) is employed to ensure that the patient appreciates the lens changes for power and axis refinements. To ensure that large refractive errors are not missed, keratometry, retinoscopy, and/or autorefraction offer a starting point. A scrupulous refraction is crucial before low vision devices are demonstrated. Spectacles should always be prescribed using polycarbonate lenses even if there seems to be a minimal increase in visual acuity; they serve as a important source of protection, particularly when the patient is engaged in activities where there may be hanging branches, flying objects, chemicals, etc., or simply unfamiliar terrain. Depending on the patient’s expression of initial goals, either a brief or extensive telescopic evaluation

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is performed next. Improvement of distance vision may have not initially been an expressed goal since a patient may be mostly tuned in to reading concerns. In any event, a brief introduction of a 3 or 4! powered telescope in the trial frame will demonstrate not only the device to the patient, but also the possibility of enhancing distance vision. Vision should generally improve proportionately with the power of the scope. For example, if a patient has best-corrected vision of 20/200, vision should improve to 20/50 with a 4! telescope. Exceptions to this rule may be a large or irregular central scotoma or the co-existence of other media opacities. Generally speaking, most distance activities usually require visual acuity of 20/30 to 20/50. It is rare that an individual would need to be corrected to 20/20 or better with a telescope. The aim should be to prescribe the lowestpowered telescope to achieve the required vision. The reasons for this are that as a telescope power becomes greater, the smaller the field of view and the more difficult it becomes to use effectively. If visual acuity is near equal between the two eyes, the examiner may choose to prescribe a binocular system which will give a much larger field of view for activities such as watching television, going to shows, etc. Another alternative for increased visual field may be a contact lens telescope (CLT). In this case, a contact lens (high minus power) is used as the ocular in conjunction with a high plus lens as the objective in a spectacle (1). As vision approaches 20/400 and worse, standard telescopic devices may not be useful; a CTL as well as more advanced technological electronic devices should be considered. The driving issue is one that remains controversial and requires special mention. Driving is an important component of everyday life for most patients. The inability to drive has psychological implications in terms of limited independence. The subject must be treated with extreme care and sensitivity. Driving remains an instrumental activity of daily living and should be routinely addressed during the case history and discussion of goals and expectations. Individuals with age-related macular degeneration do drive although their driving exposure is low by tending to avoid challenging and hazardous situations such as driving at night and in inclement weather (2). Visually impaired people are permitted to use bioptic telescopes for driving in 37 states when visual acuity falls below the state’s legal limit. The term bioptic simply implies two (bi-) optical centers. This form of a telescope is mounted several millimeters above the distance optical center. Therefore, a patient looks through his/her natural prescription through the carrier lens housing the telescope. When sharper acuity is needed for viewing street signs, etc., the patient lowers the chin and spots through the scope.

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This manner of use is similar to the fashion in which a driver would use the rearview mirror; the telescope is used only approximately 10% to 15% of the time while driving. This point is an extremely important one and often confused because it is thought that since there is a reduced field through the telescope, one could not possibly drive safely. Again, the driver is primarily looking through the carrier lens, not the telescopic device. Bioptic telescopes do meet the self-reported driving needs of the majority of visually impaired drivers and were found to be a useful device for resolving details such as road signs, etc. (3). Although visual acuity is a fundamental part of safe driving, several studies have demonstrated that peripheral field (or vision) appears to play a more critical role in driving than visual acuity (4–6). All states allowing bioptic telescopes have a minimum visual field requirement without the telescope (usually between 1208 and 1408). Other requirements include maximum acuity without the telescope (usually 20/200) and minimum visual acuity with the telescope (20/40–20/60). Certainly, there are issues that go beyond visual acuity and peripheral field in determining whether any given driver will drive safely, particularly one with a visual impairment. Factors such as age, experience, visual attention and processing, reaction times, and cognitive deficits all inarguably affect an individual’s ability to drive safely. Recent research has led to the development of a software called the Useful Field of View test (Visual Awareness, Inc., Birmingham, Alabama). This test requires higher-order processing skills, and not only determines a conventional visual field, but also allows for the assessment of the visual field area over which rapid stimuli are flashed, i.e., a car or other object moved into a cluttered background. Simulating the “real” driving experience with this test, an association has been shown between elderly drivers who have reductions in their useful field of view and crash involvement (7–9). This test is invariably more important in determining driving safety than traditional assessments of visual acuity and peripheral field. Most driver’s with visual impairment do limit driving exposure and tend to avoid challenging driving situations, i.e., driving at night, on interstates, during inclement weather, etc. There has been no association found between drivers with macular degeneration and increased accident rates/fatalities; however, driving exposure is taken into account (10). One study has demonstrated that, although patients with macular degeneration performed more poorly on driver simulator and on-the-road tests compared with a control group, this did not translate into an increased risk of real-world accidents (11). Hence, it still remains unclear whether reduced exposure decreases a driver ’s risk or whether any association exists

between increased injurious accidents and visual impairment secondary to macular degeneration. The decision to prescribe a telescopic device for a patient to legally maintain a driver’s license is a joint decision best left to doctors, patient, and family; the decision should be made on an individual basis. Following refraction and distance evaluation is the near evaluation. Near visual acuity is most appropriately measured and evaluated with continuous-text reading cards. These cards will test a patient’s functional ability to read versus the ability to read a line of numbers or letters. MNReade and Sloan make continuous-text near cards. “M” notation is generally used for recording near acuity. This notation uses the metric system, is standardized, and does not require a fixed testing distance. To begin the near evaluation, a reading lens addition should always be in place when testing patients above 50 years of age and test distance must be appropriate for the power of the add. For example, the test distance for a C2.50 D add should be 40 cm or 16 in. (100/2.50Z40 cm; 40/2.50Z16 in.), and the test distance for a C4.00 D add should be 25 cm or 10 in. (100/4.00Z25; 40/4.00Z10 in). Distance and near visual acuities (with standard C2.50 D add) should be approximately the same so that if a patient’s best-corrected vision is 20/200 in the distance, the near vision with standard add should also be 20/200. Pupil size, asymmetry, significant media opacities, and large central scotomas may create disparities; however, large differences between distance and near acuities should alert the examiner to an inaccurate manifest refraction. Once initial near acuity has been determined, the examiner increases the power of the add until the appropriate acuity is obtained. The approximate add it will take for any given patient to read newspaper size print (1 M or 20/50) can be predicted by calculating the reciprocal of the distance or near acuity. For example, if a patient’s vision is 20/200, it would take at least a C10.00 D add (200/20Z10) for the patient to read newspaper size print. This value may be modified depending upon the patient’s initial expression of goals for reading. If a patient wishes to read the stock pages, then more plus may be needed, and if a patient only wishes to read large-print text, then less plus is needed. Binocular adds are typically prescribed when the acuity is equal or near equal between the two eyes. Base-in prism is always required in binocular adds greater than C6.00 D because fusional vergence is exhausted and the eyes drift towards an exophoric posture. The amount of prescribed prism is two prism diopters more than the amount of plus. For example, if the examiner wishes to prescribe a C8.00 D add both eyes (OU), the prescribed prism should be 10 prism diopters base-in total split equally between the two

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eyes. Glasses should be prescribed in a half-eye frame size due to the thickness and heaviness of the lenses. Since the nasal edge of the standard lens becomes quite thick with increased prism, adds greater than C12.00 D should be prescribed monocularly with the eye not being used either occluded or the lens frosted to avoid diplopia. Recent advances using diffractive optics have greatly reduced the unsightly appearance of these half-eyes (Fig. 18). If a patient has one eye that is considerably better, the high add is prescribed monocularly. However, there may still be a “ghost” image or halo around letters or words coming from the poorer eye. In this instance, the lens of the poorer can be frosted (or occluded). For higher adds, most patients continually need reinforcement regarding the appropriate and close working distance. Most people are able to conceptualize inches rather than centimeters. Conversion of reading distance into inches requires the power of the add to be divided into 40. For example, if a C7.50 D add has been prescribed, the patient must hold all reading material at 51⁄3 in. (40/7.5Z5.33). The patient should begin with larger text initially to become adjusted to the closer than usual reading distance and probably increased fatigue. If a patient has not yet accepted his/her visual loss, success with high adds and close reading distances is virtually impossible. For those patients rejecting the close reading distance of high adds, other alternatives exist. Telemicroscopes (surgical loupes/telephoto lens) can be made with a specified reading distance. However, the patient must weigh the benefit of the increased distance versus the reduction in the field of view experienced. Although every attempt is made to prescribe a spectacle-borne reading device, electronic devices such as the closed-circuit television (CCTV) are good alternatives to spectacles. A patient can sit back at a comfortable distance and magnify the print large enough to read easily. A CCTV has not traditionally been a portable device and can cost several thousand dollars, but clearly can have a tremendous impact in allowing a patient to read (or work) again. There have been major recent advances here as well in portable versions of the reading machines (Figs. 7, 8, 13–16) allowing the devices to be carried to and from home, school, or work. Handheld or stand magnifiers can also increase working distances and are typically prescribed in conjunction with spectacles. These devices are most useful for spot reading rather than extended reading. However, for those patients rejecting spectacles, these devices are quite effective although the reading field of view is reduced. Contrast enhancement and glare reduction provide the final steps to the low vision evaluation. Patients with macular degeneration often experience a loss of contrast. Contrast enhancement lenses shield

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the eyes from very short wavelengths of light. These shorter wavelengths consist of high-energy visible blue light and can cause loss of contrast as well as glare, which reduces the eye’s overall function. The Corningw GlareControle family of lenses consists of seven filters which selectively block specific wavelengths of blue light while transmitting light at other wavelengths. There are six graduated filter levels, each numbered to block below the corresponding wavelength (CPFw 450, 511, 527, 527!, 550, and 550! D). The filters range in color from yellow (450) to deep red (550). The seventh filter is called the GlareCuttere lens and is for patients with initial to moderate light sensitivity. The lens color is more cosmetically appealing because it has more of a brownish hue rather than orange/red. All of the filters are photochromatic easing the transition between different light levels. These lenses are incredibly helpful to patients with macular degeneration. In addition to providing benefits of protection from ultraviolet (UV) light, they also provide contrast enhancement as well as glare reduction. Although the full range of filters are suitable for many ocular pathologies, usually the CPF 511 and 527 lenses work best in patients with moderate to advanced macular degeneration. Since the lenses are glass (and not high-impact polycarbonate plastic), they are best prescribed in the clip-on variety. These filters are now available in plastic also, yet are still photochromatic (Chadwick Optical, White River Jct., Vermont, U.S.A.) providing a nice alternative for prescription sunwear. Other nonoptical devices which might be considered are large-print books, check register, clock, watch, playing cards, etc., to name a few. There are talking books, watches, and clocks as well as specialized appliances for diabetics. Catalogues of such devices can be given to the patient and family. Occupational rehabilitation to assist in training of optical devices as well as activities of daily life is often quite useful for most patients with varying levels of visual impairment.

FUTURE IMPLICATIONS AND IMPROVEMENTS New Applications The Useful Field of View test as mentioned is an extremely important tool in determining driving safety of older patients, particularly those with visual impairment. Many times, the patient has expressed an interest to continue driving, but the examiner feels that the patient may not be a good candidate even with a bioptic telescope. This test gives objective results informing both patient and family whether the patient will be at risk for injurious accidents. Many

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state department of motor vehicles are beginning to use this software. Scanning laser ophthalmoscope (SLO) macular perimetry allows for the characterization of central field defects, i.e., macular scotomata. The presence or absence of macular scotomata and their characteristics are extremely important indicators of reading success and speed with low vision devices as well as performance with activities of daily living (12). The confocal SLO has graphic capabilities which allow a retinal map of the scotomata to be drawn by determining the retinal location of visual stimuli directly on the retina. The instrument obtains retinal images continuously using near-infrared (780 nm) laser while scanning graphics onto the retina with a modulated vision HeNe (633 nm) laser at the same time (13). Thus, the patient can see the stimuli and the investigator can view the stimuli on the retina. From these capabilities, a preferred retinal locus (PRL) can be identified and both relative and dense scotomata can be mapped. Patients with macular scotomata do not often perceive black spots. Rather they say that letters or words are missing in their central vision while reading or they simply have difficulties in functioning. The presence of these scotomata can decrease many areas of visual performance although the specific relationships between macular scotoma characteristics and visual performance have not been identified (14). Therefore, it becomes useful to be able to map out the scotomata and to know the exact location of preferred retinal loci in order to begin the rehabilitative process. Traditional approaches attempt to determine a direction of the eccentric view and then to basically repeat this direction to the patient during training, etc. Many times this technique is effective, but often patients do not respond as well as predicted to the devices, training, visual performance task, and/or during activities of daily living. The SLO can essentially determine the characteristics of the scotomata and their relationship to the PRL. Once the PRL is identified, the rehabilitative team can instruct and train the patient on better use of the PRL. Nilsson et al. (15) have also shown that using the eccentric view demonstrated in the SLO, patients with macular degeneration and large absolute central scotomata can be successfully trained and reading speeds increased by them using a new and more favorable retinal locus. Studies with the SLO have shown that there are different shapes and patterns of scotomata from round centered on a nonfunctioning fovea to ring scotoma surrounding a functioning fovea to highly complex amoeboid shapes (12). While the majority of patients do have dense scotomata, it was found that if the scotomata are complex and surround the PRL by more than two of its borders, these patients have the most difficulties in performing visual tasks when

compared with those with less encumbered PRL (12). This knowledge will aid in the prediction of patient success. A recent technique for developing low vision devices is called vision multiplexing (16). This technique attempts to avoid or reduce some of the limitations of traditional low vision devices such as reduced field of view from telescopes and magnifiers as well as loss of resolution from minifying devices that help increase field of view for mobility, etc. Vision multiplexing combines the wide field of view and high-resolution capabilities in ways that allow function to be both separate and useful for the user (16). This technique already lends itself to many electronic devices which are almost always more costly. The idea here would be to utilize vision multiplexing for use in lighter weight, less expensive, and more cosmetically appearing spectacles. An example would be a telescope built into the spectacle (not drilled in like a bioptic telescope) consisting of two curved lens mirrors for the ocular and objective and two additional curved mirrors for field enhancement (17).

New Technologies Enhanced Vision, Inc. (Huntington Beach, California, U.S.A.) has perhaps made some of the greatest breakthroughs for enhancing the quality of life of visually impaired patients. They have developed some incredible devices utilizing the latest advances in optical technology and continue to be at the forefront in this arena. The JORDY 2e is an amazing “virtual reality” system that immerses the patient in a video image. A tiny, color television camera is mounted in a headborne device weighing less than 10 oz (Fig. 2). Designed for patients whose vision is worse than 20/ 200, this device ranges in power from as little as 1! to as much as 24! for distance and up to 50 times for reading. It is considered the all-in-one system because it enhances distance, can attach to a television or computer, and has CCTV capabilities for reading or writing. For distance viewing, there is a wide (44 in.) field of view. The autofocus magnification has preset settings as well as zoom switches which are operated from an easy-to-use handheld control unit. Both contrast and brightness controls make the color image quite clear. For near viewing, the CCTV feature allows the device to be placed in a portable docking stand. The image is magnified depending on the size of the television screen or computer monitor. The light requirements are low with the system requiring no additional light thereby resulting in minimum glare. The device is not designed to be word while walking, driving, or during any mobility. The MaxPorte is a device that allows the visually impaired patient to read with the ease of a CCTV, but is

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Figure 2

CLINICAL CONSIDERATIONS FOR VISUAL REHABILITATION

The JORDY 2e with docking stand (left) and head-borne (right).

portable. The system consists of two components: a digital magnifier that captures the information and a pair of lightweight (4 oz) glasses that display the magnified image (Fig. 3). A patient would simply place the magnifier on any surface, either curved or straight, and view the magnified image on the glasses. The image can be magnified up to 28 times and is available in black and white or color and is most suitable for patients whose vision is 20/100 or worse. It is a great solution for professional, students, and seniors. Concise brightness control makes the image clear and crisp. There is also a special tracking guide (MaxTrake) which makes the magnifier move straight across the page. The device is incredibly easy to use as there are no connections or assembly required. It operates on a rechargeable battery and comes in a sleek carrying case. The Maxe is another innovative but lower priced magnifying system. It is a portable, handheld magnifier that easily connects to any television or computer monitor to magnify words, pictures, and more (Fig. 4). Using a 20 in. television, the device will magnify in both black and white and color from 16 to 28!. It is quite easy to use with either the right or left hand and the image is virtually distortion free;

Figure 3

The MaxPorte.

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Figure 4

it can also be used on any surface, curved or straight. The three viewing options (low contrast/photo, high contrast/positive, high contrast/negative) make it suitable for most patients whose vision is 20/100 or worse. The device can also now be connected to a completely portable liquid crystal display (LCD) 7 or 10 in. panel (MaxPanele). The Flippere products are a new family of devices that magnify distance, intermediate and near viewing. It is an innovative rotating camera that can be connected to a standard television or monitor, to a lightweight pair of electronic glasses (FlipperPorte), to a portable LCD panel (FlipperPanele), or placed in a desktop docking stand (Fig. 5). Magnification ranges from 6 to 50! and is in full-color or black/white options. The Flipper is great for students and professionals. The Acrobate is the newest product from Enhanced Vision and is a unique one of a kind of technology that will customize and memorize favorite settings for each of the three viewing modes: selfviewing which is a camera that gives a true mirror

The Maxe.

Figure 5

FlipperPanele.

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Figure 6

image for applying makeup, etc.; distance viewing; and near viewing. The camera is attached to a portable arm which can clamp on to any table or desk. Once attached, it can provide up to 72! magnification. The Acrobat is completely battery operated, making it truly a portable device (Fig. 6). The Amigoe is a revolutionary new portable mini CCTV. It is incredibly slim at less than 2 in. and weighs a mere 1.3 pounds (Fig. 7). The viewing screen is large at 6.5 in. with a tilting function to give the user more flexibility to view images at a comfortable angle. Magnification ranges from 3.5 to 14! and connects to any TV for increased magnification and viewing area. The device includes a writing stand and carrying case. Ocutech, Inc. (Chapel Hill, North Carolina, U.S.A.) continues to have innovative designs with several telescopic devices. The Vision Enhancing System-AutoFocus (VESwAF) is the first autofocus telescope available. It has extremely high optical quality and consists of 4! telescope focusing from as close as 12 in. to optical infinity (Fig. 8). The autofocus component works through computer-controlled infrared electrooptics which measure the focusing distance and another

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The Acrobate.

computer which moves the focusing lens to the proper position. The 4! telescope has an amazing 12.58 field and is lightweight (2.5 oz). The device is worn on the top of a frame and is. The VES-AF comes with rechargeable battery pack which can be worn around the waist or in a pocket or purse. This device is useful for distance, intermediate, and limited near vision including activities such as driving, card/ music playing, bird-watching, golf, etc., and works best for patients who have vision between 20/80 and 20/200.

Figure 7

The Amigoe.

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Figure 10 VESw-MINI expanded field telescope.

Figure 8

VESw-autofocus telescope.

Currently under development is a binocular autofocus telescope. This device has the same quick automatic focusing at distance and near, but has the added capability of binocular viewing for an enhanced field of view through the telescopes. While still under development, the device would be most beneficial for patients who have equal or near equal acuity in both eyes and wish to use the device for both distance and reading. The VESw-Sport is a bioptic telescope that was designed to address some of the major drawbacks of conventional bioptic telescope systems, namely poor acceptance by patients and fitting problems by the prescriber (Fig. 9). It offers significant improvements in the field of view, image brightness, and contrast when compared with conventional bioptics of similar powers. Probably, the nicest feature is the fully adjustable mounting design which gives the prescriber full control over the positioning of the telescope. Available in 4! and 6!, this innovative telescope is best prescribed for patients with visual acuity between 20/80 and 20/400. Though needs to be manually focused, it offers a less expensive alternative to the autofocus telescope.

Figure 9

VESw-sport telescope.

The VESw-MINI, also an innovative design, is a miniature 3! expanded field telescope (Fig. 10). It has a wide 158 field of view combined with a very compact physical design. The telescope is equivalent in size to small focusing galilean telescopes, but half the size of most expanded field telescopes. The optics are quite crisp and bright and can be prescribed for monocular or binocular use. Other special features include its unique design that minimized the ring scotoma which can be characteristic of many telescopic systems. Also, its field of view has been expanded horizontally to provide extra added vision in the most important lateral fields. The manual focus is quite fast with capabilities of focusing from optical infinity down to 12 in. covered in less than one complete turn. In addition to being extremely lightweight, it has internal refractive corrections from C12 to K12 D; eye piece corrections are available for other refractive errors. This telescope is a nice option for patients whose vision is better than 20/200. Optelec (Chelmsford, Massachusetts, U.S.A.), a leader in CCTVs, has developed a new line of these most popular electronic devices. Their new ClearView line has an ergonomic design and is user-friendly. The best features are the easy-to-use fingertip controls on the easy-glide X–Y table that deliver autofocus, dial-in zoom, normal text and reverse contrast modes, and choice of monitor types. The ClearView 517 series has all the bells and whistles with exceptional brightness/contrast, vibrant colors, and magnification from 2 to 50! (Fig. 11). The device delivers a full-color performance on an integrated 17 in. LCD thin film transister (TFT) monitor with an adjustable arm or on a color or black and white cathode ray tube (CRT) monitor. The CCTV has an open platform for future product enhancements as well as the ability to add optional features such as alternate colors, position locator,

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Figure 11 ClearView 517 with integrated tiltable monitor.

CLINICAL CONSIDERATIONS FOR VISUAL REHABILITATION

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windows/line markers, and an external personal computer (PC) switch. The ClearNotee is a lightweight, flexible solution for those who use a laptop (Fig. 12). The system offers 3 to 46! magnification and full-screen reading and writing capability. It also features full autofocus and can quickly and easily adjust to near and distance viewing—ideal for environments like classrooms or offices where taking notes and reading distance boards is often necessary. The TravellerCe is the newest addition to the Optelec family of devices. It is a completely portable CCTV with a bright 6.4 in. screen magnifying text and pictures up to 16 times (Fig. 13). The device also “stands up” to allow the user to write letters or take notes. Additionally, it can be connected to a television for even greater magnification. Vision Technology, Inc. (St. Louis, Missouri, U.S.A.) has its own new line of close-circuit televisions, but its greatest mark on the electronic industry thus far is a device called the VIEWe. This collapsible CCTV features a pop-up design and weighs only 15 lbs. The autofocus camera easily moves 3608 on a horizontal plane and 2408 on a vertical plane for the most flexible positioning system. The monitor and controls can be

Figure 12 The ClearNotee.

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Figure 13 The TravellerCe.

positioned directly in front of the user regardless of height. The VIEW is battery powered and is ideal for students, home, office, and travel (Fig. 14). Pulse Data Humanware (Concord, California, U.S.A.), a leader in technologies for blind and visually impaired patients, has developed two exciting new technologies. The Pocketviewere is a portable 7! electronic handheld magnifier that offers a full-color and high contrast black/white display. It has a retractable writing stand, built-in rechargeable battery in a compact 4 in.!3 in. compact viewing area (Fig. 15). It truly is pocket size and great for looking at details and price labels, signing checks and credit card payments, writing up brief meeting notes, reading menus, maps, instructions on packets or bottles and viewing photographs. It does all this by giving a larger field of view than a traditional magnifier of the same power. Truly, one of the most innovative and unique reading devices of late is the myReadere. It is a revolutionary reading system which is the only low vision auto-reader. Having easy push-button controls, the camera basically takes a snapshot of the reading material and displays it within three seconds and reads the text back out loud. It automates the reading process by allowing the user to set the speed and amount of the page that appears on the monitor. myReader is completely transportable and compact by

Figure 14

The Viewe.

folding down, and is a great device for home, school, and office (Fig. 16). It is expensive, but well worth the money for those patients needing this type of advanced technology.

Figure 15 The Pocketviewere.

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Figure 16 myReadere in use (above) and folded (right).

Eschenbach (Ridgefield, Connecticut, U.S.A.) remains at the forefront of superior optical quality and design of magnifiers, telescopes, reading glasses, and more. Some of the newest products include the Novese diffractive technology reading lens which greatly decreases the weight and optical aberrations of high plus reading glasses also enhancing the cosmetic appearance of these spectacles. These new ultrathin lenses are available in both monocular and binocular designs. Monocular systems come in 3 to 6! ; binocular range from 4 to 10 D (Fig. 17). Another great addition to their line is an light emitting diode (LED) barlight attachable via a clip to glasses, magnifiers, etc. It is of the size of a pencil with a wireless power source

Figure 17 Novese prismatic half-eyes (top) compared to standard thickness (bottom).

containing six white LEDs (Fig. 18). This added illumination often reduces the amount of magnification needed by the user. Designs for Vision, Inc. (Ronkonkoma, New York, U.S.A.) has always been at the forefront for producing high optical quality devices for visually impaired patients. In addition to their traditional line of bioptics (Figs. 19 and 20), they have also become quite innovative with reading devices. The ClearImage II Telephoto Microscope and HighPower Microscopes (Fig. 21) are high-powered reading microscopes available in powers 8! (C32 D) to 20! (C80 D). These lenses allow low vision patients to read

Figure 18 Eschenbach barlight clipped to spectacles.

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Figure 21 Designs for Vision ClearImage II telephoto microscope. Figure 19 Designs for Vision Standard 2.2! BIO II bioptic telescope.

at a greater distance from the eye than any other comparable systems. The fields of view are quite large and lenses are virtually distortion free from edge to edge, which is what makes them innovative. Because of the higher powers, they are most suitable for patients whose vision is worse than 20/400. Corning Medical Optics (Corning, New York, U.S.A.) has a full range of filters in its line of GlareControl lenses (Fig. 22). The CPF 527! (extra) is slightly darker than the standard CPF 527. This filter works extremely well for increased contrast enhancement and adds additional glare reduction in patients with moderate to advanced macular degeneration. The second newest filter is called the CPF GlareCutter lens. This lens is fantastic for patients with early macular degeneration who do not need quite as much contrast enhancement, but who definitely need glare reduction. The lens also has less color distortion and a more attractive color for patients who reject the cosmetic appearance of the CPF 511 and 527 series. Blocking 99% UVA and 100% UVB rays, the lens transmits 18% of light in its lightened state and 6% in its darkened state. Chadwick Optical now has the full range of contrast enhancement filters available in photochromatic plastic providing an excellent option for either clip-ons or prescription sunwear.

Figure 20

Designs for Vision 3! bioptic telescope.

SUMMARY POINTS &

&

&

&

&

&

Patient success with low vision devices is dependent upon a number of factors including age, physical and mental status, level and stability of visual acuity, patient’s dependency on others, and the interval since visual loss. Resistance to low vision devices and thus limited success tend to be seen in those patients who have not yet accepted or mourned their visual loss. Generally speaking, the more profound the visual loss, the more difficult finding means of enhancing vision becomes. Nonoptical devices may be the only mechanism acceptable by the patient to regain a small degree of independence. The role of vocational rehabilitation and occupational therapy for orientation/mobility training, activities of daily living, etc., should always be considered for patients with advanced macular degeneration. Support groups may also provide comfort and new friendships in helping to cope with the visual impairment. Sometimes it is best to wait for a low vision consultation to when the patient seeks this care voluntarily after it has been suggested.

Figure 22

Corning family of filters.

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&

&

Success with visual rehabilitation is always based on identification and satisfaction of the visual requirements and goals of the patient. There are exciting new applications and devices happening in the field of low vision/visual rehabilitation. Much of the novelty utilizes the latest technology and will no doubt be of great benefit to many visually impaired patients suffering from macular degeneration.

WEB SITES OF COMPANIES FOR FURTHER INFORMATION & & & & & & & &

Enhanced Vision Systems—www.enhancedvision. com Optelec—www.optelec.com Ocutech, Inc.—www.ocutech.com Designs for Vision—www.designsforvision.com Corning Medical Optics—www.corning.com Vision Technology, Inc.—www.visiontechnology. com Chadwick Optical—www.chadwickoptical.com Eschenbach—www.eschenbach.com

REFERENCES 1. Lavinsky J, Tomasetto G, Soares E. Use of a contact lens telescopic system in low vision patients. Int J Rehabil Res 2001; 24:337–40. 2. DeCarlo DK, Scilley K, Wells J, et al. Driving habits and health-related quality of life in patients with age-related maculopathy. Optom Vis Sci 2003; 80(3):207–13. 3. Bowers AR, Apfelbaum DH, Peli E. Bioptic telescopes meet the needs of drivers with moderate visual acuity loss. Invest Ophthalmol Vis Sci 2005; 46(1):66–74. 4. Kelleher DK. Driving with low vision. J Vis Impair Blind 1968; 11:345–50.

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5. Lovsund P, Hedin A. Effect on driving performance of visual field defect. In: Gale A, Freeman MH, Haslegrave CM et al, eds. Vision in Vehicles. Amsterdam: Elsevier, 1989:323–9. 6. Wood JM, Dique T, Troutbeck R. The effect of artificial visual impairment on functional visual fields and driving performance. Clin Vis Sci 1993; 8:563–75. 7. Owsley C, Ball K, Sloane ME, et al. Visual/cognitive correlates of vehicle accidents in older drivers. Psychol Aging 1991; 6:403–15. 8. Owsley C, McGwin G, Jr., Ball K. Vision impairment, eye disease, and injurious motor vehicle crashes in the elderly. Ophthalmic Epidemiol 1998; 5(2):101–13. 9. Owsley C, Ball K, McGwin G, Jr., et al. Visual processing impairment and risk of motor vehicle crash among older adults. JAMA 1998; 279(14):1083–8. 10. McCloskey LW, Koepsell TD, Wolf ME, Buchner DM. Motor vehicle collision injuries and sensory impairments of older drivers. Age Aging 1994; 23:267–72. 11. Szkyk JP, Pizzimenti CE, Fishman GA, et al. A comparison of driving in older subjects with an without age-related macular degeneration. Arch Ophthalmol 1995; 113:1033–40. 12. Fletcher DC, Schuchard RA, Livingston CL, et al. Scanning laser ophthalmoscope macular perimetry and applications for low vision rehabilitation clinicians. Ophthalmol Clin North Am 1994; 7(2):257–65. 13. Schuchard RA, Fletcher DC, Maino J. A scanning laser ophthalmoscope (SLO) low-vision rehabilitation system. Clin Eye Vis Care 1994; 6(3):101–7. 14. Fletcher DC, Schuchard RA. Preferred retinal loci relationship to macular scotomas in a low-vision population. Ophthalmology 1997; 104:632–8. 15. Nilsson UL, Frennesson C, Nilsson SEG. Patients with AMD and a large absolute central scotoma can be trained successfully to use eccentric viewing, as demonstrated in a scanning laser opthalmoscope. Vis Res 2003; 43:1777–87. 16. Peli E. Vision multiplexing: an engineering approach to vision rehabilitation device development. Optom Vis Sci 2001; 78:304–15. 17. Peli E, Vargas-Martin F. In the spectacle-lens telescope for low vision. Ophthalmic Technologies XII 4611. In: Proceedings of SPIE, 2002:129–35.

22 Retinal Prostheses: A Possible Treatment for End-Stage Age-Related Macular Degeneration Thomas M. O’Hearn and Michael Javaheri

Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A.

Kah-Guan Au Eong

Department of Ophthalmology and Visual Sciences, Alexandra Hospital, Department of Ophthalmology, Yong Loo Lin School of Medicine, National University of Singapore, The Eye Institute, National Healthcare Group, Jurong Medical Center, Singapore Eye Research Institute, and Department of Ophthalmology, Tan Tock Seng Hospital, Singapore

James D. Weiland and Mark S. Humayun

Doheny Retina Institute, Doheny Eye Institute, Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A.

INTRODUCTION

EXTRAOCULAR APPROACHES

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness among people older than age 65 years in Western countries, with 700,000 patients newly diagnosed annually in the United States, 10% of whom become legally blind each year. AMD is estimated to affect more than 8 million people in the U.S., with the prevalence expected to increase by the year 2020, when the population over age 85 is expected to increase by 107% (1,2). Once photoreceptors are severely damaged, such as in end-stage AMD, no treatments have been shown to restore useful vision. An emerging modality of treatment has been visual restoration through the use of implantable retinal prostheses (3–9). Devices are currently under evaluation for use in patients with light perception or no light perception vision from retinitis pigmentosa (RP). The challenge for these prostheses is even greater in AMD patients where central visual acuity is often reduced only to the 20/400 level and peripheral vision spared, thus the prosthesis must be capable of improving this vision to justify the risk of implantation. A variety of modalities are currently under investigation, including electrical, neurotransmitter, and nanoparticle-based prostheses (10). These methods can be further subdivided by location of action within the visual system and eye: extraocular locations include the visual cortex, optic radiations, and optic nerve, and the exterior of the globe itself (4,6,8), while intraocular sites include the epiretinal and subretinal surfaces (3,5,7).

Cortical Prosthesis Brindley and Dobelle were early pioneers in the field of artificial vision, being the first to demonstrate the ability to evoke phosphenes and patterned perceptions by electrical stimulation of the occipital cortex via chronically implanted electrodes (4,11–13). Multielectrode arrays were placed in the subdural space over the occipital cortex, in individuals blind from damage to visual pathways anterior to the visual cortex (11–13). Dobelle’s 64-channel platinum electrode surface stimulation prosthesis was shown to allow blind patients to recognize 6-in. characters at 5 ft (approximately 20/1200 visual acuity) (4). Despite achieving early successes, these experiments did possess some significant difficulties in implanted patients. Important shortcomings included controlling the number of phosphenes induced by each electrode, interactions occurring between phosphenes, as well as the need for very high currents and large stimulating electrodes in order to achieve phosphene perception. In some patients, this lead to pain from meningeal stimulation and occasional focal epileptic activity following electrical stimulation. Importantly, subjects also reported the perception of halos surrounding each phosphene and not focal distinct percepts (11–13). Subsequent attempts at developing a cortical prosthesis used an intracortical approach in hopes of overcoming the shortcomings of surface cortical stimulation via a lower current, higher fidelity system. By employing smaller electrodes in closer apposition to

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the target neurons of stimulation, it was hoped that less current could be used and that resulting stimulation could be more localized. Initial human trials, during which the intracortical prosthesis was implanted for four months, demonstrated the ability to produce phosphenes which exhibited color (14,15). The Illinois Intracortical Visual Prosthesis project and the Utah Electrode Array are the two types of intracortical prosthesis currently under development (6,14,15). The Illinois device, consisting of 152 intracortical microelectrodes, has been chronically implanted in an animal model. Experiments have shown that receptive field mapping could be combined with eye-tracking to develop a reward-based training procedure. Furthermore, the experimental animal was able to be trained to use electrically-induced point-flash percepts in performing memory saccade tasks (14,15). The Utah device consists of multiple silicon spikes with a platinum electrode tip at each end organized in a square grid measuring 4.2 mm by 4.2 mm (6). The chief advantage of a cortical visual prosthesis lies in the ability to bypass all diseased visual pathway neurons rostral to the primary visual cortex with the potential to restore vision to the largest number of patients.

Optic Nerve Prosthesis The optic nerve is another site with the potential for the development of a visual prosthesis, as information from the entire visual field is represented in this small area. Although well established surgical techniques allow this region to be accessed readily, there remain significant hurdles to overcome regarding this approach. First, the optic nerve is an exceedingly dense neural structure with approximately 1.2 million axons confined within a 2-mm diameter nerve trunk. As a result of this density, as well as the difficulty in translating the exact retinotopic distribution of retinal ganglion cell axons within the optic nerve, achieving focal stimulation of neurons within the optic nerve will be extremely difficult. Furthermore, implantation within this area requires dissection of the dura, creating possible central nervous system (CNS) complications including infection and the possibility of compromising the vascular supply of the optic nerve itself (16). Lastly, intervention at this point within the visual pathway requires intact retinal ganglion cells and therefore is limited to the treatment of outer retinal (photoreceptor) degenerations (RDs). Veraart et al. reported a study in which a volunteer, with RP and no residual vision, was chronically implanted with an optic nerve electrode connected to an implanted neural stimulator and antenna. By using an external power source and controller, the subject was able to perceive phosphenes when the optic nerve

was stimulated. The volunteer used a head-worn video camera to explore a projection screen and underwent performance evaluations during the course of a specifically designed training program with multiple simple patterns. Throughout the course of the stimulation the patient was able to demonstrate pattern recognition a well as a learning effect for processing time and orientation discrimination (16). Recent work has also been directed at exploring intrapapillary placement of electrode microwires as an alternative means of creating an optic nerve-based prosthesis. Four platinum wire microelectrodes were placed transclerally in the optic nerve head of rabbits. Stimulation via the electrodes was able to produce recordable electrically evoked potentials (EEP’), however, thresholds increased significantly at one month of implantation, and histopathology revealed encapsulation of the electrodes (17).

Scleral Based Extraocular Stimulation A group form the University of New South Wales has proposed and carried out early feasibility studies in cats using both single electrodes and an electrode array mounted external to the globe and fixed to the sclera. Thresholds were determined by production of a cortical evoked response and at best were 100 mA with a duration of 400 mS, yielding a charge density of 1.27 mC/cm2, which is within safe limits. Although potentially avoiding some of the issues of chronic intraocular implantation facing other approaches, the ability of an implant mounted at the sclera to provide focal, high resolution stimulation remains a significant question (18). A second scleral based approach for a prosthesis is being pursued by Yasuo Tano’s group at Osaka University. Their prosthesis relies on suprachoroidaltranscleral stimulation (STS), and in its envisioned form the electrode array is implanted in a scleral pocket with a reference electrode in the vitreous cavity. Short-term stimulation studies using a nine channel array in two retinitis pigmentosa patients with light perception vision demonstrated the ability to produce distinct phosphenes with a current of 0.3 to 0.5mA. Charge densities were between 0.48 and 1.27 mC/cm2 (53). INTRAOCULAR APPROACHES Epiretinal Prosthesis The epiretinal approach to the retinal prosthesis involves the capture and digitization of images from the external world with a device such as a digital camera. In electrically based prostheses, captured images are transformed into patterns of focal electrical stimulation which are used to excite remaining,

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viable inner retinal neurons. Morphometric studies have been promising, documenting the survival of as much as 90% of inner retinal neurons in nonneovascular and neovascular AMD, however it is likely that changes in neural architectures occur as well which could complicate creating an effective prosthesis (19). As a means of sensory rehabilitation the epiretinal prosthesis is analogous to commercially available cochlear implants, where degenerated sensory hair cells are bypassed through the electrical stimulation of more distal neural elements. Several groups have developed various designs of epiretinal implants that differ in terms of the intraocular and external components and their method of enabling vision in patients. Each prototype is guided by similar requirements: preserving as much of the normal anatomy and physiology of the eye as possible, while minimizing the amount of implanted electronics required to power the device (20). The research team at the Doheny Eye Institute of the University of Southern California, in conjunction with Second Sight Medical Products, Inc. (Sylmar, CA) and engineers from other universities as well as the Department of Energy National Laboratories, have

developed a prototype intraocular retinal prosthesis (IRP). This device, named the Second Sight Argus 1, consists of two main components: first, an extraocular unit for image capture and an implanted unit for retinal stimulation. The external unit is comprised of a small, lightweight camera that is built into a pair of glasses, and a wearable, battery-powered visual processing unit (Fig. 1). The camera captures video, which is then translated into a pixilated image by software algorithms located in the visual processing unit. A transmitter coil sends image data to the implanted unit. The electronics of the implanted unit are in a ceramic case implanted in the temporal bone similar to a cochlear implant. The electrical stimulation pattern is delivered, via a transscleral cable, from the ceramic case to the intraocular portion of the prosthesis (20,21). The intraocular portion consists of a specially designed array of 16 microelectrodes, ranging in size from 250 to 500 mm, and made of platinum. Viable inner retinal neurons are stimulated by pulses from microelectrodes located on the array. The array is positioned over the posterior pole and attached to the inner retinal surface using a single tack, which is

Laser or RF Implant

Retina

Video Camera

Area of Photoreceptors Destroyed by Disease

Epiretinal Implant

Subretinal Implant

Figure 1 Illustration of functioning prostheses with representation of epiretinal and subretinal implants. Source: From Ref. 20.

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Figure 3 Photograph of the Second Sight Argus 1 epiretinal microelectrode array prior to insertion into the vitreous cavity in a patient with long-standing retinitis pigmentosa. Figure 2 Schematic representation of the Second Sight TM, Argus 1 intraocular retinal prosthesis apparatus, including camera, connector cable and microelectrode array.

inserted through the electrode array into the sclera during the surgical procedure (Fig. 2) (20,21). Preliminary tests of acute (!3 hours) epiretinal stimulation were performed on humans in the operating room using hand held electrodes as well as multielectrode arrays not affixed to the patients’ retina, only after studies in several different animal models demonstrated that epiretinal stimulation could safely elicit reproducible neural responses in the retina (22). These patients perceived phosphenes in response to the electrical stimulation to the retina and were able to detect motion as well as identify shapes, amounting to a crude form vision (23,24). In 2002, at the Doheny Retina Institute of the University of Southern California, clinical trials testing chronic, long-term implantation of the IRP began as part of a Food and Drug Administration Investigational Device Exemption study. To date, six patients have safely received the 16-electrode, Second Sight Argus 1 implants array (Figs. 3 and 4). Chronically implanted patients described visual perceptions of phosphenes that were seen and shown to be retinotopically consistent when local current was applied to the surface of the retina with the implanted electrodes. Patients ability to distinguish the direction of motion of objects (24) and to discriminate between percepts created by different electrodes based on their locations, implies that retinotopic organization is not lost when a patient loses sight due to chronic disease. In addition, varying the stimulation level correspondingly enhanced the brightness or dimness of percepts (25).

During the postoperative follow-up periods, electrically evoked responses (EERs) from the visual cortex and psychophysical tests eliciting visual perceptions in patients were subsequently recorded and added both quantitative and qualitative measures of visual perception in implanted patients. These EERs and other psychophysical testing have also been utilized preoperatively in potential patients not only for screening purposes, but also for improved evaluation of critical parameters such as stimulation thresholds and current levels necessary for visual perception after the implant has been activated postoperatively (26). Histological examination after chronic retinal stimulation showed no evidence of rejection,

Figure 4 Color fundus photograph of the Second Sight Argus 1 epiretinal microelectrode array in a patient with long-standing retinitis pigmentosa. Note placement of array in the macula.

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inflammatory reaction, neovascularization, or encapsulation in both normal and retinal rod-cone degenerate dog subjects implanted with an epiretinal prosthesis. There still exists a possibility that the affixed tack, in conjunction with the foreign material of the array as well as electrical impulses delivered to the implant, could result in fibrous encapsulation. However, histological analysis of the mechanical effects of the tack two to three months after implantation showed minimal effects on the retinal layers with epiretinal implantation (22). The second generation Second Sight implant, the Argus 2, which contains a 60 electrode epiretinal array, has received an investigational device exemption from the FDA to begin testing in patients in 2007. The Argus 2 contains four times as many electrodes as the Argus 1, yet they are packaged into an area one fourth the size of the previous implant. Future iterations of the implant will have even greater electrode numbers and densities and engineering towards this goal is already well underway with the goal of a 1000 electrode implant. Psychophysical studies in sighted volunteers simulating a 1000 electrode area in a 32x32 pattern has shown the ability for facial recognition (54). Since 1995, Rolf Eckmiller of Germany has led and developed the Learning Retina Implant. Similar to the epiretinal approaches discussed so far, their implant consists of both intraocular and extraocular components. The retina encoder (RE) attempts to simulate the typical receptive field properties and filtering characteristics of retinal ganglion cells and replaces the visual processing capabilities of the retina with 100 to 1000 individually tunable spatiotemporal filters. The RE output is then encoded and transmitted wirelessly to the implanted retina stimulator RS. The RS consists of a ring-shaped, soft microcontact foil centered at the fovea and affixed to the epiretinal surface. The REs are then used to map visual patterns onto spike trains which are transmitted to the contacted ganglion cells. The REs not only simulate the complex mapping operation of parts of the neural retina, but also provide an iterative, perception-based dialog between the RE and human subject. Via this dialog the implant is able to tune the various receptive field filter properties with information “expected” by the central visual system to generate optimal ganglion cell codes for epiretinal stimulation (29). The RE/stimulator has been successfully tested in animal models and normally sighted subjects (30). While Eckmiller and his consortium have made significant advances in the manufacturing and testing of the microcontact foils, as well as wireless signaling and energy transfer mechanisms, they have followed a cautious approach towards implanting the device in blind patients (31). Their group has chosen to tackle first

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the issues surrounding the information processing requirements of the implant, retina and brain. In the future, it will be necessary to define the proper stimulation coding of electrically induced neural signals for the retinal ganglion cells that are in contact with the RS if the dialog between the RS and the retina is to be optimal (29). As the thrust of the German effort thus far has been on the retinal encoder, clinical trials, primarily focusing on testing of the learning implant and dialogbased RE tuning, are just being initiated. Dr. Hornig at the University of Hamburg-Eppendorf and Intelligent Medical Implants have also pursued another version of an epiretinal prosthesis. Their prosthesis is implanted entirely within the orbit and has a 49 electrode epiretinal array affixed to the retina with a tack. Data presented to date in four chronically implanted retinitis pigmentosa patients indicate that the array can be well tolerated for up to nine months. Patients were able to distinguish points both vertically and horizontally. The current iteration of the implant, however, does not contain a camera as a part of the implant (55).

Subretinal Prosthesis In the subretinal approach to a prosthetic design, the array is implanted between the bipolar cell layer and the retinal pigment epithelium. Surgical access to the subretinal space is through either an ab externo (scleral incision) or ab interno (through the vitreous cavity and retina) approach. Alan and Vincent Chow of Optobionics Corp., were among the first to implant a subretinal prosthetic. In their original concept the subretinal implant would function as a simple solar cell without the need for an external power source or signal processing (3,32,33). Their artificial silicon retina (ASR) Microchip, which measures two millimeters in diameter, and contains approximately 5000 microelectrode-tipped microphotodiodes, is powered solely by incident light. The microphotodiodes convert incident light into electrical signals which are used to stimulate the remaining retinal neurons. To date the ASR Microchip has been implanted in six patients in a subretinal location outside of the macula, with a follow up of 6 to 18 months. Chow et al. reported gains in visual function in all patients as well as unexpected improvements in retinal areas distal to the implantation site. The study was potentially biased by the lack of randomization of which eye received the implant surgery, thus making both examiner and patient aware of which eye possessed the implant, as well as the confounder of the rescue effect of vitrectomy and subretinal surgery in RD (35). They noted that a larger clinical trial would be necessary to further demonstrate safety of the ASR Microchip as well as to further validate their results (34).

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Later experiments have shown that the concept behind this simple approach was actually not viable since ambient light levels do not cause the microphotodiodes to produce current sufficient enough to directly stimulate retinal neurons (36). In fact, Chow et al. have abandoned the notion that the ASR Microchip is efficacious as a prosthetic device and currently hypothesize that the small amount of current delivered from the implant, may be therapeutic through a neuroprotective effect to the deteriorating retinal photoreceptors. Studies by Pardue et al. are ongoing to determine whether these effects are indeed neuroprotective and whether the effects are durable and reproducible. Preliminary work in Royal College of Surgeons (RCS) rats showed similar amounts of photoreceptor sparing in sham operated and inactive device implanted eyes as compared to eyes implanted with the active ASR (37). Therefore, the effects documented with this type of an implant likely occur indirectly through a “growth factor” that then rescues the remaining photoreceptors. Thus, this device is not a true retinal prosthesis but is best classified as a therapeutic device. Given these results Optiobionics is reevaluating its efforts with the ASR. Recently, Schuchard et al. presented data evaluating contrast sensitivity in 20 patients with RP implanted with the subretinal ASR device. Luminance and color were evaluated separately through modified criteria. Although patients reported subjective improvements in color vision and luminance after implantation, contingency analysis found that the controlled testing and self-reported rating responses did not generally agree. They concluded that selfreported improvements in color and contrast vision may not correspond to controlled testing (38). Eberhart Zrenner and a consortium of research universities in Germany have been developing another subretinal implant since the mid-1990s. Their implant measures 3 mm across and consists of approximately 7000 microphotodiodes in a checker-board pattern configuration. Each microphotodiode has an area of 400 mm2, and is made of biocompatible silicon and silicon oxide, and designed to be both insulating and permeable to light (36,39). Zrenner et al. have demonstrated in several RD animal models that subretinal stimulation with their implant is capable of inducing neuronal activity in retinal ganglion cells. Their effort has been helped by first defining the parameters necessary for successful electric stimulation and then incorporating this data into the development of their photodiode arrays. Implanting their prosthesis in rabbits, cats, and pigs, they attempted to detect electrically stimulated activity in the visual cortex as a result of retinal stimulation as well as investigate the long-term biocompatibility and stability of these implants in the subretinal space (41–43). In chronic

implantation studies recording from epidural electrodes, they were able to record cortical evoked potentials during stimulation with light flashes as well as during electrical stimulation in the subretinal space. However, it should be noted that in roughly one half of the animals tested, no cortical activation was detected subsequent to implantation. The presence of subretinal fluid around the array was observed during examination after implantation. This could potentially have interfered with communication between the electrodes and the neuronal architecture, as well as raised stimulus thresholds by increasing the distance between them. After 14 months, angiography and histological findings of the retina adjacent to and in the vicinity of the implant site revealed no significant foreign tissue rejection reactions or occurrence of inflammation (44,45). More recent studies have attempted to further refine the surgical implantation using a combined ab interno/transcleral approach in pig eyes. By minimizing the intraocular component of the implantation to the creation of a small retinotomy necessary only to inject viscoelestic into the subretinal space, trauma to the retina is potentially reduced. However, in the study perfluorocarbon liquids were used to maintain retinal-implant apposition, thus limiting conclusions as to the potential success of this new technique (46). With evidence that the subretinal approach to a retinal prosthesis is not practical without an external source of energy to power the implant, the feasibility of polyimide film electrodes in a cat model was demonstrated and further exploration of film-bound electrical stimulation was planned (47). Prototypes of their subretinal device have attempted to address this issue using an external power source connected to the subretinal implant by fine wires that are run extraocularly until piercing the sclera. Future methods of powering the implant include transpupillary infrared (IR) illumination of receivers close to the chip and electromagnetic transfer. Currently Zrenner and colleagues are planning to conduct a clinical pilot study limited to 30 days and to 8 completely blind RP patients. Recently, Wilke et al. presented data related to perception of dots and patterns in two implanted patients with long standing RP on behalf of the Zrenner group. The influence of stimulation parameters on perception with respect to dot shape, size, color, duration, and pattern recognition were investigated. They demonstrated for the first time that electrical stimulation with subretinal implanted electrodes is capable of eliciting reproducible phosphenes of well defined shape, enabling clear pattern recognition. Changes in stimulation amplitude or frequency led to modulation of perceived brightness and to lesser extent in dot size while shape or

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color remained unchanged. In addition, stimulation of adjacent electrodes elicited dots of comparable size shape and color (48). Zrenner ’s group recently presented more data on the successful implantation of their 16 electrode subretinal array. The arrays were implanted in six patients legally blind from retinitis pigmentosa. Five of the six patients had the arrays removed at one month post-implantation as planned due to their lack of hermetic packaging. No complications related to the array implantation or explantation were encountered. One patient refused explantation. Of note with the surgical technique was the need for silicone oil tamponade for successful implantation (56). A third type of subretinal prosthesis has recently been developed by Rizzo and Wyatt. Named the Boston Retinal Implant, the prosthesis is in an early stage of development. Their studies so far have focused on biocompatibility issues surrounding the effects of a foreign material in the subretinal space, as well as the development of surgical techniques for implantation. Minimally invasive surgical techniques utilizing a posterior, ab externo approach to implant the prosthesis within the subretinal space have been tested. Results have been encouraging to date, however long-term biocompatibility studies in animals as well as further refinement of the implantation technique will need to carried out prior to conducting a clinical trial in human patients (47). As with other methods, the subretinal prosthesis approach has its distinct advantages and disadvantages. One advantage is that the microphotodiodes of a subretinal prosthesis directly replace the functions of the damaged photoreceptor cells while the retina’s remaining intact neural network is still capable of processing electrical signals. Placement of the subretinal prosthesis in closer proximity to remaining viable inner retinal neurons may be advantageous in possibly decreasing currents required for effective stimulation. Experiments conducted in RCS rats with subretinal arrays have shown significant migration of retinal cells into perforations within an array, as well as around protruding electrodes, conceivably reducing the distance between stimulating electrode and target cell, and therefore stimulus thresholds. However, whether migrating cells will remain viable, and with an intact neural circuitry remains a major concern (49). Furthermore, in studies of electrical stimulation in normal and rd1 degenerate mice lower thresholds with photoreceptor side stimulation, corresponding to a subretinally positioned implant, were only observed in normal mice. Measured thresholds for epiretinal versus subretinal electrode placement were not significantly different in rd1 retinas, questioning the potential advantage of subretinal implants in terms of lowering thresholds (50).

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Advantages of a subretinal approach include less surgically induced trauma upon implantation due to a lack of mechanical fixation and the relative ease in positioning and affixing of the microphotodiodes in the subretinal space. However, potential thermal injury is a significant factor due to the fact that there is a limited area within the subretinal space which will contain the microelectronics. Additionally, the lack of an external source of energy for the microphotodiodes has been the greatest deficiency of currently tested subretinal prostheses. Ambient light is not sufficient for the current generated by a single microphotodiode, to stimulate adjacent retinal neurons. An additional source of energy is needed to allow for adequate current to be available to modulate the prosthesis for sufficient stimulation of neurons in a retinotopic distribution. A group at Standford University has proposed an optoelectronic retinal prosthesis which attempts to address the shortcomings already discussed for subretinal microphotodiode based arrays. The implant consists of a subretinally placed microphotodiode array connected to a projection system, although it could be compatible with an epiretinal system as well. After the image is captured by video camera it is processed and then sent to a liquid crystal display microdisplay emitting in the near IR. The image is then bounced off a pair of transparent goggles worn by the patient and scanned onto, thus stimulating, the photodiode array. The external power source thus overcomes the fact that ambient light energy is insufficient to power the photodiodes. Theoretically, the array also has the advantage of allowing the patient to scan the visual field provided by the external camera with eye movements, as the projection array could be designed to track the implanted array, rather than by moving the externally mounted video camera with head movements. The use of IR light for projection, a wavelength not detected by human photoreceptors, allows the remaining peripheral vision in AMD patients to be utilized to its fullest without interference from the implant (49).

Neurotransmitter-Based Prostheses In an attempt to mimic physiologic chemical signaling in the retina, the microfluidic retinal prosthesis has been developed at the Kresge Eye Institute of Wayne State University. This team, headed by Dr. Raymond Iezzi, formulated a hypothesis that digital images can be converted into neurochemical signals through a microchip that provides chronic input to the CNS using naturally occurring signaling molecules. An important aspect of this device lies in the fact that the neurotransmitter release can be used to stimulate the retina with or without electrical stimulation. By functioning with a concurrent electrical device, the

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neurochemical transmission may help to decrease stimulatory thresholds, therefore decreasing the amounts of generated heat and tissue breakdown. In addition, this type of prosthesis offers the potential to deliver therapeutic drugs. Potential therapeutics can be stored as prodrugs, which can be photo-activated into their biologically active component, once a certain electrical stimulation is received (52). Future research by all groups will need to address the long-term biocompatibility of the prostheses within the saline environment of the eye in terms of hermetic packaging of the microfabricated arrays as well as maintaining the stability of the retina-array interface by avoiding any robust fibrotic or glial response from the retina. Issues specific to electrically based arrays also include minimization of heat production by the arrays, Neurotransmitter arrays meanwhile need to address issues of potential excitotoxic injury. Also included in these biocompatibility issues is the unknown effect of chronic electrical stimulation on the retina. In addition to this, significant attention needs to be given to the manner in which visual images will be encoded and delivered in patterns of electrical stimulation to the retina. Plasticity of the visual system in response to electrical stimulation as well as how the brain interprets a pattern of stimulation resulting from sixteen, or in the future thousands of electrodes is still not understood but will be crucial in the evolution of prosthetic design. Although significant advances have been made, the field of artificial vision is still relatively young. With ongoing advances in the technology of microelectronics, hermetic packaging, surgical techniques, and in the understanding of the visual nervous systems response to chronic stimulation, there remains hope that advancement to restoring some vision to patients suffering from end stage AMD will be possible in the future.

SUMMARY POINTS &

&

&

Once photoreceptors are damaged severely, such as in end-stage AMD, no treatments have been shown to restore useful vision to these patients. Despite early success, cortical prosthetics have shown limitations in their ability to precisely stimulate certain areas using large electrodes and high currents to achieve adequate perception. The Illinois Intracortical Visual Prosthesis project and the Utah Electrode Array are the two types of intracortical prosthesis currently under development. Optic nerve prostheses have shown limited promise in restoring visual perception. Some significant hurdles remain in perfecting this approach, including: translating the exact retinotopic

&

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distribution, the most minimally invasive surgical approach, and vascular and dural compromise. The Second Sight Argus 1 epiretinal IRP (Doheny Eye Institute) consists of and extraocular unit for image capture, which converts video to a pixilated image which is then delivered to an intraocular portion consisting of a platinum 16 microelectrode array. To date, six patients have safely received the Model 1and have described visual perceptions of phosphenes that were seen and shown to be retinotopically consistent when local current was applied to the surface of the retina with the implanted electrodes. Other epiretinal models include the Harvard group and Germany’s Learning Retinal Implant. Alan and Vincent Chow of Optobionics Corp., were among the first to implant a subretinal prosthetic. Their ASR Microchip, which measures 2 mm in diameter, and contains approximately 5000 microelectrode tipped microphotodiodes, is powered solely by incident light. To date the ASR Microchip has been implanted in six patients in a subretinal location outside of the macula, with a follow up of 6 to 18 months. For multiple reasons, they have abandoned the notion that the ASR Microchip is efficacious as a prosthetic device and currently hypothesize that the small amount of current delivered from the implant, may be therapeutic through a neuroprotective effect to the otherwise dying retinal photoreceptors. Zrenner and colleagues in Germany have been developing another subretinal implant since the mid-1990s and have demonstrated in several RD animal models that subretinal stimulation with their implant is capable of inducing neuronal activity in retinal ganglion cells. Future plans include further refining the surgical approach to create a better communication between the electrode and retina.

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23 Retinal Pigment Epithelial Cell Transplantation and Macular Reconstruction for Age-Related Macular Degeneration Lucian V. Del Priore

Department of Ophthalmology, Columbia University, New York, New York, U.S.A.

Henry J. Kaplan and Tongalp H. Tezel

Department of Ophthalmology and Visual Sciences, University of Louisville, Louisville, Kentucky, U.S.A.

INTRODUCTION Age-related macular degeneration (AMD) is the leading cause of blindness in the elderly population in the Western world (1). Ninety percent of AMD patients who experience severe vision loss do so as a result of choroidal neovascularization (2), which represents growth of neovascular tissue from the choriocapillaris, within Bruch’s membrane, and eventually in the sub-retinal pigment epithelium (RPE) and/or subretinal space. Developing new treatments that prevent or reverse vision loss in AMD is of paramount importance due to the severe visual loss that occurs with this condition and the knowledge that disease prevalence will increase with a shift demographics of western populations to older ages. The last decade has witnessed significant advances in the management of exudative AMD. Several drugs have become available for treatment of this condition; the first approved therapy in the United States was photodynamic therapy with verteporfin. The most important recent advances in the management of exudative AMD have come from the development of anti-vascular endothelial growth factor (VEGF) drugs, such an the anti-VEGF aptamer pegaptanib (3–16), which was the first anti-VEGF compound approved for use for exudative AMD, the anti-VEGF antibody fragment ranibizumab (17–22), and the widespread off-label use of intravitreal bevacizumab (23–30). Despite these significant advances in the management of exudative AMD, there is a large unmet need for many patients with this condition. More than 50% of patients do not respond to therapy with anti-VEGF drugs, and many patients with advanced disease have loss of vision due to scar formation and altered subretinal architecture. These limitations have led to the investigation of alternative

treatment modalities for subfoveal exudative AMD, including subfoveal membranectomy with and without RPE transplantation or translocation (31–35) and macular translocation (36). Initial efforts to improve vision with cell transplantation alone have not met with success; reconstitution of the normal subretinal architecture is necessary for visual improvement in these individuals. Ultimately this will require maculoplasty, which is defined as reconstruction of macular anatomy in patients with advanced vision loss in exudative AMD (37). In our view successful maculoplasty will require replacing or repairing damaged cells (using transplantation, translocation, or stimulation of autologous cell proliferation); immune suppression (if allografts are used to replace damaged cells); and reconstruction or replacement of Bruch’s membrane (to restore the integrity of the substrate for proper cell attachment). Successful maculoplasty will build on prior development of surgical techniques for managing severe vision loss in AMD patients with advanced subfoveal exudation. These techniques include surgical excision of choroidal neovascularization (31–35,38–40); surgical excision combined with allograft transplantation of adult or fetal RPE (41–52) or iris pigment epithelium (53–64) or macular translocation with or without choroidal membrane excision (65–83). Simple excision of the subfoveal neovascular membrane in AMD leaves a large RPE defect under the fovea due to the removal of native RPE along with the surgically excised neovascular complex (84). Resulting persistent RPE defects lead to the development of progressive choriocapillaris and photoreceptor atrophy (85). Histopathology after subfoveal membranectomy alone shows absence of large swatches of native RPE, combined with damage to the outer retina, choriocapillaris atrophy and absence or damage to the inner aspects of native Bruch’s

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membrane (86,87). We have previously shown that the status of host Bruch’s membrane has a profound effect on the behavior of RPE transplanted after subfoveal membranectomy (37,88–95). Thus reconstruction of Bruch’s membrane is a necessary component for successful maculoplasty (96). Herein, we review the current status of efforts directed at macular reconstruction in exudative AMD.

RATIONALE FOR RPE TRANSPLANTATION IN AMD In 1991, Thomas and Kaplan reported two patients who experienced significant visual improvement after surgical excision of subfoveal choroidal neovascularization from presumed ocular histoplasmosis syndrome (POHS) (32). One patient improved from 20/200 preoperatively to 20/40, whereas the other patient improved from 20/200 to 20/25. de Juan and Machemer (38) had previously performed disciform scar excision in four patients with end-stage AMD, but the manuscript by Thomas and Kaplan was the first to demonstrate that excellent visual acuity was possible after submacular surgery. Since these initial publications, several authors have reported small, uncontrolled series of patients undergoing submacular surgery for AMD (32–34,97,98). The recent Subfoveal Surgery Trial demonstrated that subfoveal membranectomy alone was better than observation for patients with POHS and an initial visual acuity better than 20/100, but was not better than observation for AMD patients with subfoveal neovascularization (39). Examination of the results of prior nonrandomized studies of submacular surgery suggests that significant visual improvement is limited after submacular surgery for AMD, and that RPE removal may be an important factor limiting postoperative visual recovery. There appear to be significant differences in the postoperative visual recovery after submacular surgery for patients with AMD versus POHS. There could be many factors responsible for this observed difference, including advanced patient age in AMD, disease within Bruch’s membrane in AMD, the size of the choroidal neovascular complex (larger in AMD eyes compared to POHS), the location of the ingrowth site and the relationship of the choroidal neovascular membrane to the native RPE (99). Patients with POHS and other disorders may have a better prognosis because the choroidal neovascular membrane lies anterior to the RPE and can thus be removed while leaving the native RPE intact (99). However in AMD eyes the choroidal neovascular complex is frequently deep to the native RPE, so that surgical membrane excision denudes Bruch’s membrane of native RPE.

The consequences of RPE removal during submacular surgery are significant because removal of the native RPE leads to progressive choriocapillaris atrophy and limits visual recovery after submacular surgery (100–103). The subfoveal choriocapillaris can be perfused one to two weeks after submacular surgery in AMD eyes but become non-perfused without further surgery or laser photocoagulation (100). Thach et al. examined the choroidal perfusion after surgical removal of subfoveal membranes in 12 eyes of 11 AMD patients (104). Stereoscopic fluorescein and indocyanine green angiograms of the excision bed revealed hypofluorescence with visible perfusion in the underlying medium and large choroidal vessels in all eyes. On the basis of these observations the authors concluded that the choriocapillaris and small choroidal vessels were frequently abnormal or absent in the bed of the removed neovascular membrane. We cannot exclude the possibility that some non-perfusion of the subfoveal choriocapillaris is present in patients before submacular surgery. However, patients who develop subfoveal choroidal neovascularization experience sudden and severe visual loss, demonstrating that the perfusion of the choriocapillaris is sufficient to support good visual function, even if it is not normal. Experimental evidence suggests that the native RPE is removed with the choroidal neovascularization in AMD. Grossniklaus et al. (105) examined specimens removed from the subretinal space as part of the Submacular Surgery Trial. Most of these patients (61 out of 78) had AMD and the balance had POHS or idiopathic neovascularization. The specimens contained fibrovascular tissue, fibrocellular tissue, and hemorrhage. Vascular endothelium and RPE were the most common cellular constituents. As expected, the membranes from AMD patients were more likely to be beneath the RPE and the size of the RPE defect was larger in AMD eyes. Histopathologic examination of an eye from a patient who had undergone surgical excision of a choroidal neovascular membrane in AMD revealed an RPE defect in the center of the dissection bed with incomplete resurfacing of the RPE defect after surgery (87). Thus, AMD patients are more likely to have a bare area of Bruch’s membrane after surgery and the RPE defect is more likely to persist after surgery in these eyes. There is extensive experimental evidence suggesting that RPE removal at the time of submacular surgery would lead to progressive atrophy of the subfoveal choriocapillaris. Destruction of the RPE with sodium iodate leads to changes in the RPE and choriocapillaris within one week and marked choriocapillaris atrophy within one month (106). In contrast, the choriocapillaris has a normal appearance in areas where the RPE still appeared healthy. Similar changes

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are seen after intravitreal ornithine injection and in an experimental model of thioridazine retinopathy (107–110). Repopulation of Bruch’s membrane occurs after RPE removal in the cat with choriocapillaris preservation under the areas of healed RPE and choriocapillaris atrophy in non-healed areas (111). RPE removal in the non-tapetal porcine eye yields similar results (85,112,113). Bruch’s membrane becomes repopulated with a monolayer or multilayer of variably pigmented cells one month after surgical debridement of the RPE. In these regions, the outer nuclear layer and outer limiting membrane remained intact and the choriocapillaris appeared patent. In regions of poor RPE healing the lumen of the choriocapillaris was collapsed and the choriocapillaris endothelium was separated from its basement membrane (85,112,113).

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Thus, a combination of experimental and clinical studies suggests that the following sequence of events occurs after choroidal neovascular membrane excision (Fig. 1). Subfoveal surgery can be performed without disturbing the native RPE in some eyes, but choroidal neovascular membrane excision results in a focal RPE defect in AMD eyes and in some younger eyes with other diseases. If the native RPE is not disturbed, the underlying choriocapillaris will not undergo secondary atrophy. If the native RPE is removed, the defect will heal by migration and proliferation of new RPE from the edge of the epithelial defect if the native basal lamina is intact. The proliferating RPE are hypopigmented, making it difficult to visualize these cells in vivo. There are no changes in the choriocapillaris if the area of the RPE defect is completely and rapidly repopulated by hypopigmented RPE.

Figure 1 (Top): Schematic of sub-retinal pigment epithelium (RPE) choroidal neovascular membrane typical in age-related macular degeneration. (Middle): Membrane removal denudes the native RPE from Bruch’s membrane and excises fragment of the inner aspects of Bruch’s membrane. Native RPE cannot heal the epithelial defect completely in the absence of native basal lamina. (Bottom): Non-pigmented RPE may heal the defect partially in the presence of residual basal lamina, but will not heal a large epithelial defect completely in the absence of basal lamina. A persistent RPE defect leads to atrophy of the subfoveal choriocapillaris.

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Incomplete or delayed healing of the RPE defect will lead rapidly to atrophy of the choriocapillaris although the medium and large vessels of the choroid can remain patent. The functional consequences of subfoveal choriocapillaris atrophy are significant because atrophy of the subfoveal choriocapillaris is correlated with poor visual recovery after surgery. Over 90% of AMD eyes and 37% of POHS eyes have atrophy of the subfoveal choriocapillaris after submacular surgery, and the rate of visual improvement to better than 20/50 was worse for AMD eyes than for POHS (103,100). Within the POHS subgroup, the subfoveal choriocapillaris was perfused in 24 out of 38 (63%) eyes and non-perfused in 14 out of 38 (37%) eyes. Best-corrected visual acuity improved by at least two lines in 17 out of 24 (71%) perfused eyes and 2 out of 14 (14%) non-perfused eyes (pZ0.0089). Additionally, a best-corrected vision of 20/100 or better was achieved in 18 (75%) of the perfused eyes and only 4 (29%) non-perfused eyes (p!0.05). Thus, both the final visual acuity and improvement in visual acuity were correlated with postoperative perfusion of the subfoveal choriocapillaris (103,100).

RPE HARVESTING TECHNIQUE We have previously described a method for harvesting and storage of intact adult human RPE sheets prior to transplantation (95). Briefly, human cadaver eyes are cleaned of extraocular tissue and the suprachoroidal space is sealed with cyanoacrylate glue (114). A small scleral incision is made 3-mm posterior to the limbus until the choroidal vessels are exposed. Tenotomy scissors are introduced through this incision into the suprachoroidal space and the incision is extended circumferentially. Four radial relaxing incisions are made in the sclera and the sclera is peeled away from the periphery to the optic nerve with care not to tear the choroid. The eye cup is then incubated with 25 U/mL of Dispase (Gibco) for 30 minutes, rinsed with carbon dioxide free medium, and a circumferential incision is made into the subretinal space along the ora serrata. The loosened RPE sheets are separated from the rest of the ocular tissue and placed on a slice of 50% gelatin on a 25!75!1 mm glass slide (Fisher Scientific, Pittsburgh, Pennsylvania) with the apical RPE surface facing upwards. Contamination with choroidal cells is avoided by directly visualizing the RPE sheets under a dissecting microscope while they are being harvested. The glass slide containing the gelatin film with the RPE sheet is then placed in a 100!15 mm polystyrene dish and incubated in a humidified atmosphere of 5% CO2 and 95% air at 378C for five minutes to allow the gelatin to melt and encase the RPE sheet. The specimen is kept at 48C for

five minutes to solidify the liquid gelatin and then stored in carbon dioxide free medium (pHZ7.4) at 48C. Harvested sheets are stained with cytokeratin to ensure purity of the cell population. Transmission electron microscopy shows intact RPE cells with well-developed microvilli, basal infoldings and intercellular connections (95). The initial viability of intact RPE sheets is 86% with a progressive decline in viability with increased storage time. Cells harvested within 24 hours after death maintain greater viability than those harvested after 24 hours (p!0.05) and maintain 82% viability for as long as 48 hours if stored at 48C.

BRUCH’S MEMBRANE CHANGES IN AMD At the light microscope level Bruch’s membrane appears to be a continuous structure that extends from the peripapillary area to the peripheral ora serrata. This anatomic structure was recognized by light microscopists in the 19th century on the basis of the staining pattern on light microscopy. The development of transmission and scanning electron microscopy revealed that human Bruch’s membrane is a pentilaminar structure composed of a central elastin membrane, surrounded by collagen layers bordered externally by the basement membrane of the RPE and choriocapillaris (Fig. 2). From internal to external, Bruch’s membrane has five anatomic layers with known structure and function. The innermost (i.e., closest to the RPE and furthest from the external sclera) layer of Bruch’s membrane is the RPE basal lamina, which serves as the anchoring surface for the RPE. Throughout the human body, basal lamina are thin acellular membranes, approximately 50 nm in thickness, that line one side of epithelia (115). The inner aspect of the RPE basal lamina is bordered by RPE-BL

ICL EL

OCL CC-BM

Figure 2 Anatomic layers of human basement membrane. Abbreviations: CC-BM, choriocapillaris basement membrane; EL, elastin layer; ICL, inner collagen layer; OCL, outer collagen layer; RPE-BL, basal lamina of the retinal pigment epithelium.

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the RPE plasma membrane; the outer surface borders the inner collagen layer and fibers from the inner collagen layer extend into the basal laminar layer of Bruch’s membrane. Next comes the inner collagen layer, which is a dense collagen matrix that interconnects the basal lamina and elastin layers of Bruch’s membrane. Most of the dysfunction within AMD starts in the inner collagen layer. For example, drusen-like material can accumulate either on the inner or outer aspect of the basal lamina layer; soft drusen, which represent accumulation of abnormal material within the inner collagen layer, will split the inner collagen layer from the basal lamina layer. Choroidal neovascularization often invades this tissue plane, essentially splitting the inner collagen layer from the basal lamina as it grows and progresses (116). Proceeding externally, the elastin layer is not continuous in humans from the optic nerve to the ora. In advanced AMD the elastin layer becomes fragmented (84). The outer collagen layer is similar to the inner collagen layer at the ultrastructural level. Structural changes occur within the outer collagen layer as a function of advancing patient age, including collagen cross-linking. However extracellular deposits, including drusen and lipid deposits, appear to spare this layer and accumulate mainly within the inner collagen layer as described above. Lastly, the basal lamina of the choriocapillaris separates the choriocapillaris from the outer collagen layer. Unlike the basal lamina of the RPE, there is no evidence of deposit formation on either side of the choriocapillaris basal lamina as a function of advancing patient age (117,118). Basal lamina are typically thin acellular membranes, approximately 50 nm in thickness, composed of collagen IV and XVIII, laminin, nidogen, agrin, and perlecan (115). Collagen I, collagen III and fibronectin are present within the inner and outer collagen layer; the RPE and choriocapillaris basal lamina are composed largely of laminin and collagen IV (119), but also contain collagen V and heparan sulfate proteoglycan (120). The elastin layer contains elastin and collagen VI (120). Fibronectin is associated with basement membranes, collagen fibers and elastic fibers throughout Bruch’s membrane, although precise immunolocalization of fibronectin is hampered by the fact that this is a soluble serum protein. There is differential distribution of different collagen IV a-chain isoforms within human Bruch’s membrane; a1 (IV) and a2 (IV) chains were identified in 55% of RPE basement membranes and 100% of choriocapillaris basement membranes, respectively (121). RPE basement membranes also contained a3 (IV), a4 (IV), and a5 (IV) chains, but these chains are not present within choriocapillaris basal lamina. The a6 (IV) chain was not identified in any sections (121).

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Collagen XVIII is also present within the inner aspects of human Bruch’s membrane; interestingly, endostatin, which is the C-terminal fragment of collagen XVIII, is typically released from collagen XVIII via proteolysis (122). Administration of intravitreal endostatin can inhibit experimental choroidal neovascularization (123) and gene therapy to increase levels of endostatin prevent the development of choroidal neovascularization in AMD (124). Mice lacking basement membrane collagen XVIII/endostatin have massive accumulation of sub-RPE deposits with striking similarities to basal laminar deposits, abnormal RPE, and age-dependent loss of vision (125).

CLINICAL RESULTS OF RPE TRANSPLANTATION, RPE, AND MACULAR TRANSLOCATION The goal of RPE transplantation is to repopulate Bruch’s membrane with donor RPE prior to the development of widespread atrophy of the choriocapillaris. There is some preliminary experimental evidence suggesting that RPE transplanted into a debrided bed will support the native choriocapillaris and healthy RPE may reverse choriocapillaris atrophy after it develops (126). To date all human studies of RPE transplantation for exudative AMD have been performed at the same time as submacular surgery, rather than after subfoveal choriocapillaris atrophy has progressed. Much can be learned from clinical trials of macular translocation as well, since this surgery tests the hypothesis that rotation of the fovea over areas of healthy RPE and choriocapillaris can lead to significant visual recovery. The following studies have been reported to date: &

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Peyman et al. performed submacular scar excision with translocation of an autologous RPE pedicle flap or transplantation of an allogeneic RPEBruch’s membrane explant in two patients (51). The final visual acuity was 20/400 in the first patient and count fingers at 2 ft in the second patient. Neither of these patients was immune suppressed. Algvere et al. initially reported subretinal membrane removal with transplantation of fetal human RPE patches in five AMD patients and subsequently reported on a larger series of 17 eyes (41,127,128). Cystoid macular edema developed and the grafts became encapsulated by white fibrous tissue within several months after surgery but none of these patients received systemic immune suppression. Scanning laser ophthalmoscopic microperimetry demonstrated that patients were able to fixate over the area of the RPE graft immediately after surgery, but an absolute scotoma developed in this region several months after

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surgery. These results are not surprising because the patients were not immune suppressed, and RPE transplanted into the subretinal space will be rejected (46,129–131). The authors observed better integrity of the graft margins in geographic atrophy patients, suggesting that rejection may be more common in exudative AMD. Long term, there is continued deterioration of function and graft integrity in all cases of exudative AMD and five out of nine eyes with nonexudative AMD (41,127,128). Subfoveal membranectomy with transplantation of adult human RPE sheets has been performed in 11 AMD patients who were immune suppressed postoperatively with prednisone, cyclosporine and immuran (49). Eligibility criteria included the presence of drusen, patient age O60, a best-correct acuity of %20 out of 63 (Bailey-Lovie chart) and subfoveal neovascularization %9 disc areas on preoperative fluorescein angiography. The mean visual acuity, contrast sensitivity and reading speed did not change significantly for six months postoperatively. Transplants showed no signs of rejection in patients able to continue immune suppression for the first six months after surgery but patients who discontinued immune suppression developed signs of graft rejection two weeks later. Histopathology is available on an 85-year-old female who died four months after RPE sheet transplantation (45). A complete autopsy demonstrated the cause of death to be congestive heart failure. A patch of hyperpigmentation was visible at the transplant site under the foveola after surgery. Mound-like clusters of individual round, large densely pigmented cells were present in the subretinal space and outer retina in this area, and the transplant site did not contain a uniform monolayer in most areas. There was loss of the photoreceptor outer segments and native RPE in the center of the transplant bed, with disruption of the outer nuclear layer predominantly over regions of multilayered pigmented cells. Cystic spaces were present in the inner and outer retina. A residual intra-Bruch’s membrane component of the original choroidal neovascular complex was present under the transplant site. The poor morphology at the transplant site was consistent with the lack of visual improvement seen after surgery in this patient. Weisz et al. delivered a patch of fetal RPE under the retina in one patient with geographic atrophy (132). Visual acuity remained stable at 20/80 one month surgery but deteriorated to 20/500 by five months postoperatively. Mild subretinal fibrosis developed after surgery. The patient demonstrated a systemic immune response to phosducin and rhodopsin postoperatively in the absence of systemic immune suppression.

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Binder and coworkers have reported on 53 eyes undergoing subfoveal surgery for choroidal neovascularization in AMD (14 undergoing subfoveal membranectomy alone and 39 undergoing membranectomy with transplantation of autologous RPE suspensions) (43,133). There was no difference in visual acuity postop between the groups, but postop reading vision was better in the transplant eyes and the recurrence rate of choroidal neovascularization was low (43,133). Van Meurs reported short-term results with patch transplantation techniques in which a free pedicle graft was harvested from the mid periphery and placed under the fovea immediately after subfoveal membranectomy. Their initial report concluded that surgery was technically feasible but was associated with a high surgical complication rate, with retinal detachment due to proliferative vitreoretinopathy in three out of eight eyes (134,135). Wolf et al. reported temporary improvement in vision in only one out of seven patients (136). In a larger series, Joussen et al. reported on autologous translocation of RPE and choroid in 45 eyes of 43 patients with subfoveal AMD. Surgical complications were significant, with half the eyes requiring addition procedures due to retinal detachment, proliferative vitreoretinopathy, macular pucker, or vitreous hemorrhage. Only four eyes achieved a 15 letters increase in best corrected visual acuity. The authors claimed that the graft was revascularized on indocyanine green angiography in most eyes, although definitive proof of revascularization awaits animal studies with histopathology (137). Stanga et al. reported on nine eyes with exudative AMD undergoing subfoveal surgery combined with patch RPE transplantation (82,83). Their initial paper reported transient fixation over the graft by scanning laser ophthalmoloscopy. However, long-term follow-up of four of these patients demonstrated that recovery of fixation is temporary, with a decline in fixation ability longterm, despite the fact that areas of hyper pigmentation, interpreted by the authors as representing a healthy graft, could still be seen ophthalmoscopically. Prior workers have emphasized the fact that much can be learned about the potential of RPE transplantation from studying macular translocation results. For exudative AMD, the macular translocation series suggests that approximately 20% of patients can achieve a final vision of 20/50 or better (65–68,78,136,138–155). However, several facts should be recalled before inferring the results of RPE transplantation on the basis of

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macular translocation studies alone. First, the surgical complication rate of macular translocation surgery is initially quite high, with a steep learning curve that may be surgeon-dependent. Second, in macular translocation surgery the fovea is shifted to a new location over healthy RPE and choriocapillaris; the native RPE is already attached to host Bruch’s membrane, thus avoiding issues that arise when RPE is translocated or transplanted to a new location. Third, macular translocation surgery causes a significant decline in the global electroretinogram (ERG) that may reflect the significant effects of this surgery on overall retinal function (81,156,157). The situation is further complicated by the observation that subfoveal atrophy recurred in three of four patients with geographic atrophy in AMD, thus implying that changes in the outer retina may be responsible for the development of geographic atrophy (140,158). This finding has significant implications for RPE transplantation in geographic atrophy, since one would expect similar rapid loss of RPE in AMD with geographic atrophy after transplantation. Rapid recurrence of geographic atrophy was also observed by Khurana et al. after macular translocation (159).

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MECHANISM OF RPE ATTACHMENT TO HUMAN BRUCH’S MEMBRANE

ECM was 66.0G6.0%. Coating the surface with albumin or an irrelevant anti-IgG antibody did not change the attachment rates significantly (64.5G3.0% and 63.5G3.4%, respectively; pO0.05 for each compared to ECM alone). The addition of fibronectin, laminin, type IV collagen or vitronectin increased the attachment rates to 79.0G7.0%, 76.0G6.0%, 80.3G 9.0%, or 81.3G6.3%, respectively (p!0.05 for each compared to ECM alone). The addition of anti-fibronectin, anti-laminin, anti-collagen IV, or antivitronectin (1:100 dilution) decreased the attachment rates to 56.2G3.0%, 49.4G5.0%, 55.2G4.1%, or 51.0G7.3%, respectively (p!0.05 for each compared to ECM alone). Increasing the concentration of antibodies to a ratio of 1:10 dilution did not inhibit RPE reattachment further (data not shown). Simultaneous addition of anti-fibronectin, anti-laminin, anti-collagen IV and anti-vitronectin antibodies (1:100 dilution) markedly decreased the attachment rates further to 25.3G9.0% (p!0.05). Treatment with RGDS, a tetrapeptide known to block the interaction between the b1-subunit of integrin and ECM proteins, markedly decreased the RPE reattachment rate to 21.0G6.3% (p!0.05). Treatment of RPE cells with anti-b1 integrin antibodies before plating the cells decreased the attachment rate to 15.0G7.0% (p!0.05). The reattachment rate of RPE to uncoated tissue culture plastic was 24.6G3.2%. The mechanism of attachment of RPE to human Bruch’s membrane explants is similar (163).

RPE Attachment in Tissue Culture Several investigators have characterized the ligands available for surface attachment of human RPE. The basal surface of RPE cells contains a b1-subunit of integrin (160,161) and the inner aspect of Bruch’s membrane contains laminin, fibronectin, heparan sulfate and collagen (120). Attachment of RPE to coated artificial surfaces can be mediated by an interaction between the b1-subunit of integrin and known extracellular matrix (ECM) molecules. For example, RPE cells bind to Petri dishes coated with laminin or fibronectin but do not attach to untreated, uncoated Petri dishes (161). The synthetic tetrapeptide arginine-glycine-aspartate-serine (RGDS), which is derived from the cell binding domain of fibronectin, decreases RPE binding to laminin-coated or fibronectin-coated dishes (162). Thus, in vitro binding studies suggest that RPE can attach to laminin or fibronectin coating a plastic surface via an interaction between the b 1-integrin subunit and laminin and fibronectin. Molecular binding studies demonstrate a role for integrins and ECM ligands in mediating RPE attachment to RPE-derived ECM and human Bruch’s membrane in a more direct fashion (Fig. 3) (163). The attachment rates of human RPE cells to RPE-derived

Importance of RPE Attachment for Cell Survival We have previously demonstrated that RPE harvested for transplantation must be allowed to reattach to a substrate to prevent RPE apoptosis (93). Second passage human RPE were plated onto tissue culture plastic precoated with ECM, fibronectin, laminin, uncoated tissue culture plastic, untreated plastic and untreated plastic coated with 4% agarose. Reattachment rates were determined for each substrate 24 hours after plating. The TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) technique was used to determine apoptosis rates in attached cells, unattached cells and the entire cell population. Attachment rates were as follows: ECM-coated tissue culture plastic O fibronectincoated tissue culture plastic O laminin-coated tissue culture plastic O uncoated tissue culture plastic O untreated plastic O agarose-coated untreated plastic. Apoptosis rates for the entire cell population were increased as the RPE cell attachment rate decreased, and the proportion of apoptotic cells in the entire population was inversely related to the percent attached cells (rZK0.95). These results imply that RPE cells removed from their substrate prior to transplantation must reattach rapidly to a substrate to prevent apoptosis.

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100 90 80

% Attachment

70 60 50 40 30 20 10

Anti- 1

RGDS

Anti-FN,LN,C IV,VN

Anti-VN

Anti-C IV

Anti-LN

Anti-FN

VN

C IV

LN

FN

Anti-IgG

Albumin

BM Only

0

Figure 3 Human retinal pigment epithelium (RPE) cell attachment rate to Bruch’s membrane in tissue culture was determined. Data are divided into four groups: (i) group 1, open bars: the attachment rate on extracellular matrix alone (64.0C9.5%) was not altered by the addition of albumin (63.4C5.7%) or an irrelevant anti-IgG antibody (62.8C5.3%), (ii) group 2, shaded diagonal stripes: the addition of extracellular matrix components increased the attachment rate over baseline. The attachment rate after the addition of fibronectin (72.4C6.8%), laminin (68.2C4.6%), collagen type IV (74.6C5.7%), or vitronectin (75.6C4.9%) was always higher than the attachment rate to Bruch’s membrane alone (64.0C9.5%; p!0.05 for all comparisons), (iii) group 3, solid grey: the addition of antibodies against Bruch’s membrane components decreased the attachment rate over baseline. The attachment rate after the addition of anti-fibronectin (47.0C10.0%), anti-laminin (52.6C9.6%), anti-collagen type IV (51.5C 3.0%), or anti-vitronectin (42.2C3.3%) was always lower than the attachment rate to Bruch’s membrane alone. Simultaneous addition of anti-fibronectin, anti-laminin, anti-collagen IV, and anti-vitronectin markedly decreased RPE reattachment to extracellular matrix (35.6C4.1%; pZ0.05), and (iv) group 4, black: striking inhibition of cell reattachment was produced by addition of the synthetic peptide RGDS or by preincubating the cells with anti-b1-integrin (33.3C3.0% and 37.4C5.9%, respectively). In addition, cell attachment to uncoated tissue culture plastic was 25.8C4.5%. Data presented as meanGstandard deviation, nZ9. Abbreviations: anti-b1, antibody to b1-subunit of integrin; anti-IgG, an irrelevant IgG antibody; C IV, type IV collagen; FN, fibronectin; LM, laminin; RGDS, arginine-glycine-aspartate-serine; VN, vitronectin. Source: From Ref. 163.

Effects of Prior Handling In Vitro on RPE Integrin Expression Prior to successful cellular transplantation it is necessary to harvest donor RPE and passage these cells in tissue culture to obtain the number of cells required for tissue transplantation. It is known that culturing conditions including the composition of the substrate can have a significant impact on cell behavior. Since integrins on the RPE surface are involved in attachment of RPE to native basal lamina, we have determined the effects of passaging in tissue culture and exposure to different ECM ligands on the

expression of integrin receptors in human RPE (88). First passage confluent human RPE were harvested and plated into 96-well plates coated with different ECM components, including laminin (4 mg/cm 2), fibronectin (10 mg/cm 2), vitronectin (4 mg/cm 2), collagen type IV (10 mg/cm2), or a mixture of all four ligands after nonspecific binding was blocked by adding 1% normal goat serum. Mouse antibodies against specific human integrin subunits were used as a primary antibody and alkaline-conjugated goat anti-mouse IgG was used as a second antibody. The absorbance at 405 nm was used to determine the

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relative expression of RPE integrin receptor subunits under each condition compared to primary RPE. Significant amounts of b1, b3, b4, and a5b1 integrin molecules were detected on the surface of primary RPE. Passaging RPE in tissue culture markedly increased the detection of b2 integrin subunits on the RPE surface, with a smaller increase in the detection of a2, a3, and aVb6 integrin subunits and decrease in b1 and a4. Coating with a mixture of all four ECM ligands increased the amount of b1, b2, b3, b4, a5, a2b1, and a5b1 detected on the RPE surface compared to RPE seeded onto tissue culture plastic. Coating with vitronectin alone increased the amount of b1, b3, and b4. Coating with collagen IV alone increased the expression of b2. b4 was increased by exposure to either fibronectin, collagen IV, vitronectin or to a mixture of all four ligands. These results demonstrate that at least two factors can control the expression of integrin subunits on the surface of human RPE; namely, passaging in tissue culture and seeding of passaged cells onto different ECM substrates. Since the attachment of human RPE to Bruch’s membrane is mediated partially by an interaction between integrin subunits and the underlying surface, surface-induced changes in integrin distribution may have a profound effect on the initial attachment and subsequent behavior of RPE seeded onto Bruch’s membrane. Pretreatment of RPE may alter the attachment and subsequent behavior of RPE transplanted onto human Bruch’s membrane.

EFFECTS OF AGE-RELATED CHANGES WITHIN BRUCH’S MEMBRANE ON RPE ATTACHMENT AND BEHAVIOR Importance of Bruch’s Membrane Layer and Age In RPE Attachment The inner layers of Bruch’s membrane are not intact after submacular membranectomy in AMD eyes (164,165). Histopathologic evidence suggests that the RPE basal lamina is excised with the choroidal neovascular membrane O90% of the time, thus exposing the inner collagen layer of Bruch’s membrane, and the dissection plane is not uniform throughout the excision bed (84,105). In addition aging of human Bruch’s membrane causes numerous changes within this structure such as collagen cross-linking, elastin fragmentation, and deposition of abnormal material with Bruch’s membrane as outlined above (166); survival of transplanted cells is substrate-and the dependent, and thus the age presence of disease within Bruch’s membrane plus surgical removal of the inner aspects of human Bruch’s membrane will have a profound and detrimental impact on transplant survival. In view

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of these considerations, we have examined the effects of Bruch’s membrane age and the layer available for cell attachment on RPE behavior (47,91,94). We have determined the effects of Bruch’s membrane layer on RPE attachment by isolating individual layers of human Bruch’s membrane in the lab as described previously (Fig. 4) (91). Human Bruch’s membrane explants were prepared from 10 human cadaver eyes by removing native RPE with 0.02N ammonium hydroxide. Six millimeters punch of peripheral Bruch’s membrane were stabilized on 4% agarose and placed in 96-well plates with Bruch’s membrane facing upwards. The RPE basal lamina, inner collagen layer, elastin layer and outer collagen layer were exposed by removing each apical layer sequentially by mechanical or enzymatic means. First passage human RPE harvested from a single donor were plated onto the surface (15,000 viable cells/ explant) and the RPE reattachment rate to each layer of Bruch’s membrane was determined. The RPE reattachment rate was highest to the inner aspects of Bruch’s membrane and decreased as deeper layers of Bruch’s membrane were exposed (i.e., basal lamina O inner collagen layer O elastin layer O outer collagen layer). The reattachment rate to the inner collagen layer, elastin layer and outer collagen layer harvested from elderly donors (age O60) was less than to the corresponding layers harvested from younger (age !50) donors (Fig. 5). These results demonstrate that the ability of harvested RPE to reattachment to human Bruch’s membrane depends on the anatomic layer of Bruch’s membrane present in the host tissue. The layer of Bruch’s membrane available also affects the morphology of the grafted RPE (Fig. 6) and their subsequent behavior. The apoptosis rate of attached cells increased as deeper layers of Bruch’s membrane were exposed (94). Both the proliferation rate and mitotic index (94) of the grafted cells were higher on basal lamina than on deeper layers. RPE cells plated onto basal lamina repopulated the explant surface within 14G3 days, whereas cells plated onto inner collagen layer and elastin layer eventually died and never reached confluence. These findings suggest that the ability of transplanted RPE cells to repopulate bare Bruch’s membrane will depend on the layer of Bruch’s membrane available for RPE cell reattachment (167).

ANATOMIC RECONSTRUCTION OF HUMAN BRUCH’S MEMBRANE As mentioned above there are two major factors related to Bruch’s membrane status that influence the ability of grafted RPE to survive after subretinal transplantation, namely, the layer of Bruch’s membrane available after subretinal membranectomy, and the presence of age-related changes within

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Figure 4 Preparation of basement membrane explants. Native retinal pigment epithelium (RPE) are removed by treatment with ammonium hydroxide. (A) Yielding a preparation with the RPE basal lamina on the uppermost surface. (B) RPE basal lamina is removed mechanically, exposing the inner collagen layer. (C) Addition of collagenase exposes the elastin layer; (D) Treatment with elastase exposes the outer collagen layer. Abbreviations: CC-BM, choriocapillaris basement membrane; EL, elastin layer; ICL, inner collagen layer; OCL, outer collagen layer; RPE-BL, basal lamina of the retinal pigment epithelium.

Bruch’s membrane. Several authors have suggested simply replacing Bruch’s membrane with another basement membrane substrate, such as thin silicone rubber, lens capsule, amniotic membrane, or a more complex bioengineered artificial structure (168,169). Although there is some appeal to this notion, it should be remembered that cells are exquisitely sensitive to all aspects of their substrate including chemical composition as well as mechanical substrate properties. Finding a substrate that mimics Bruch’s membrane chemically and mechanically presents a significant challenge; in addition, it will be difficult

to secure the artificial substrate to Bruch’s membrane itself and to establish a stable, long-term interface between biologic and synthetic tissue. We have taken a different approach to this problem by reconstructing Bruch’s membrane to make it a more hospitable substrate for RPE attachment (37). These efforts have involved deposition of exogenous attachment ligands on the inner aspects of Bruch’s membrane; cleaning deposits from aged Bruch’s membrane by treatment with sodium citrate and detergents; and a combined approach in which debris is removed from Bruch’s membrane, followed

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Figure 5 Ability of human retinal pigment epithelium (RPE) cells to reattach to different layers of human Bruch’s membrane explants (four donors age O50, three donors age !50) 24 hours after plating. (A) RPE reattachment rates on younger and older basal lamina were comparable (pZ0.13). However, the reattachment to older inner collagen layer (ICL) was significantly lower than to younger ICL (pZ0.02). The RPE reattachment rate to ICL was lower than to basal lamina in older donors (p!0.01) but was similar in younger donors (pO0.05). The reattachment to elastin was significantly lower than to basal lamina and ICL in both younger and older donors (p!0.05). (B) Addition of laminin and collagen IV to young basal lamina has no effect, but addition to older basal lamina increases the attachment rate on older Bruch’s membrane to same level seen on younger Bruch’s membrane. Similarly, addition of laminin, collagen IV and fibronectin has no effect on young ICL, but increases attachment onto older ICL to same level as young ICL. Addition of ligands to young or older elastin layer has no effect. Abbreviations: C IV, collagen IV; FN, fibronectin; ICL, inner collagen layer; LAM, laminin. Source: From Ref. 47.

by resurfacing with ECM ligands (37). Specifically we determined the effects of cleaning and/or ECM protein coating on the reattachment, apoptosis, proliferation, and final surface coverage of the transplanted RPE. Explants of aged Bruch’s membrane with inner collagen layer exposed were prepared from five human cadaver eyes (donor ageZ69–84 years) and treated with Triton-X and/or coated with a mixture of laminin (330 mg/mL), fibronectin (250 mg/mL), and vitronectin (33 mg/mL). 15,000 viable human fetal and (ARPE-19) a spontaneously immortalized human RPE cell line, cells were plated onto the surface and the RPE reattachment, apoptosis and proliferation ratios

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were determined on the modified surfaces. Cells were cultured up to 17 days to determine the surface coverage. Ultrastructure of the modified Bruch’s membrane and RPE morphology were studied with transmission and scanning electron microscopy. The reattachment ratios of fetal human RPE and ARPE-19 cells were similar on aged inner collagen layer (41.5G 1.7% and 42.9G2.7%, pO0.05). The reattachment ratio increased with ECM-protein coating and decreased with detergent treatment. Combined cleaning and coating restored the reattachment ratio of fetal RPE cells, but failed to increase the reattachment ratio of ARPE-19 cells. The highest apoptosis was observed on untreated inner collagen layer. Cleaning and the combined procedure of cleaning and ECM-protein coating decreased the fetal RPE apoptosis. Only RPE cells plated on cleaned or cleaned and ECM-coated inner collagen layer demonstrated proliferation that led to substantial surface coverage at day 17. Thus, these results demonstrate that age-related changes that impair RPE repopulation of Bruch’s membrane can be significantly reversed by combined cleaning and ECM protein coating of the inner collagen layer. Development of biologically-tolerant techniques for modifying the inner collagen layer in vivo may enhance the ability of the RPE to reattach and repopulate aged inner collagen layer. Figure 7 shows the effect of different treatments on the ultrastructural features of the inner collagen layer (37).

IRIS PIGMENT EPITHELIAL TRANSPLANTATION FOR AMD Within the last decade several investigators have pioneered the use of iris pigment epithelium as a replacement for RPE in retinal degenerations, including AMD (170). This use of iris pigment epithelium is based upon the common embryological origin of these two cell lines, the ready availability of autologous iris pigment epithelium via iris biopsy, and the need to replace RPE in various disease states. Application of iris pigment epithelium transplantation for treatment of tapetoretinal degenerations due to a known gene defect, such as Leber ’s congenital amaurosis and RPE-dependent forms of retinitis pigmentosa, are not likely to be fruitful since autologous iris pigment epithelium and RPE would have the same genetic defect. The largest clinical application for autologous iris pigment epithelium transplantation may be in repair of age-related cell and tissue loss in AMD; here transplanted iris pigment epithelium could replace native RPE removed during submacular surgery for exudative AMD or lost during the development of geographic atrophy in nonexudative AMD.

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(A)

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Figure 6 Morphology of human retinal pigment epithelium (RPE) cells (donor ageZ80) after seeding onto different layers of human basement membrane explants (six donors). (A,B) RPE plated onto basal lamina reached confluence within 14G3 days in over 90% of the wells. (C,D) Cells plated onto inner collagen layer detached from the surface, and only a few rare cells (arrow) could be seen on the surface 21 days after plating. Cells plated onto elastin exhibited similar behavior (not shown). Source: From Ref. 94.

To date a handful of laboratory and clinical studies have been performed to determine the ability of iris pigment epithelium to survive after subretinal transplantation and perform RPE functions, including outer segment phagocytosis, recycling of visual pigment, and release of cytokines and other growth factors (59). Prior authors have concluded that iris pigment epithelium can survive at least six months after subretinal transplantation but proper interpretation of these results is confounded by difficulty in identifying transplanted cells unequivocally (53,56, 57,63,171). Initial studies suggest that subretinal or choroidal iris pigment epithelium transplants may slow the rate of photoreceptor degeneration in the Royal College of Surgeons (RCS) rat for several months compared to untreated controls (59,60). However, iris pigment epithelium is not as good at rescue as RPE and no better than sham surgery (172). Iris pigment epithelium function in vitro and after subretinal transplantation in vivo has also been investigated by previous workers. Iris pigment epithelium is capable of retinol metabolism (173) and transplanted

iris pigment epithelium can ingest outer segments (172). The ability of cultured iris pigment epithelium to phagocytose latex beads is 76% of the activity of RPE (59). Cultured iris pigment epithelium maintains melanogenesis for up to five passages in tissue culture (54). Iris pigment epithelium and RPE form monolayers on Descemet’s membrane (174,175) and exhibit similar growth on native and micropatterned human lens capsule (176). Iris pigment epithelium can form tight junctions thus raising the possibility that transplanted iris pigment epithelium may reestablish the bloodretinal barrier normally formed by RPE (59). To date a handful of clinical studies have been performed on subretinal transplantation of iris pigment epithelium to replace surgically-excised RPE in patients with exudative AMD. Autologous iris pigment epithelium transplantation has been performed in 35 patients after removal of subfoveal choroidal neovascular membranes with no significant difference in vision between transplanted patients versus those who underwent choroidal neovascularization removal alone (170). Autologous iris

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Figure 7 Scanning electron microscopy of inner collagen layer modification with cleaning and resurfacing; 84-year-old donor. (A) Untreated inner collagen layer revealed replacement of fine interdigitating structure of the collagen framework by unidirectionally running cross-linked bundles of collagen (white arrows). Small globular structures on the collagen fibers probably represent aggregates of extracellular matrix (ECM)-proteins (white arrowheads). Macro deposits of lipoprotein debris filled interfibrillar spaces (asterisk). (B) ECM-protein coating without cleaning yielded an increased amount of ECM-protein aggregates on the collagen matrix. Cross-linking of collagen fibers was not effected by the coating (white arrows). (C) Cleaning with Triton-X and sodium citrate removed the debris and resulted in gaps between collagen fibers (white asterisk). Along with debris most of the globular ECM-proteins disappeared. Note that cross-links between collagen fibers were broken yielding individual fibers (white arrowheads) and rare incompletely separated macrofibers (white arrows). (D) Cleaning and subsequent ECM-protein coating not only broke the cross-links between collagen fibers but also allowed ECM-proteins to diffusely attach on the regenerated collagen framework. Note that ECM-proteins were smaller in size and did not form multimeric aggregates as on the native matrix. Removal of macroaggregates also created spaces between collagen fibers that may help to restore the hydraulic conductivity across Bruch’s membrane. (BarsZ0.5 mm). Source: From Ref. 37.

pigment epithelium translocation after submacular membranectomy can preserve foveal function at a low level but does not improve visual acuity (177). These poor functional results are consistent with the poor attachment and survival of iris pigment epithelium and RPE on aged Bruch’s membrane (178). Despite the lack of visual improvement, subretinal iris pigment epithelium transplants in AMD patients may prevent recurrence of subretinal neovascularization (60,170). We have demonstrated that there are major differences in the gene expression profile of primary RPE versus iris pigment epithelium harvested from the same donor eye, including the lack of expression in iris pigment epithelium of genes known to be critical for RPE function (49). For example, iris pigment epithelium does not express the gene for retinol

dehydrogenase, whose gene product is necessary for recycling visual pigments. Recoverin is a visual cycle protein expressed in abundance in the RPE but not iris pigment epithelium although its role in the RPE function is not known. Iris pigment epithelium do not express other major functional RPE genes, including angiopoietin 1, S-antigen and a transcriptional regulator of the c-fos promoter. Numerous cell adhesion genes and additional genes related to RPE phagocytosis, tight junction formation and Vitamin A metabolism are missing in iris pigment epithelium cells, including thrombospondin 1 and ras-related C3 botulinum toxin substrate. In order for iris pigment epithelium to replace surgically-excised or dysfunctional RPE, the transplanted iris pigment epithelium should develop an expression profile that closely resembles native RPE.

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Our results suggest that the native iris pigment epithelium expression profile may be a potential obstacle to successful subretinal transplantation. Since the microenvironment of cells influences their behavior and gene expression, we cannot exclude the possibility that the expression profile of iris pigment epithelium may change after subretinal transplantation to more closely resemble native RPE. However, our data suggest that the expression level of many genes must change for iris pigment epithelium to resemble RPE. Some authors have suggested that transplanted iris pigment epithelium can serve as a potential reservoir for a single growth factor or cytokine and thereby rescue adjacent cells from the effects of progressive tapetoretinal degeneration (179). For example, iris pigment epithelium induced to transcribe the brainderived neurotrophic factor (BDNF) gene protect against retinal damage due to N-methyl-D-aspartateinduced neuronal death and light toxicity (58,180). Iris pigment epithelium genetically modified to express pigment epithelial derived factor inhibit choroidal neovascularization in a rat model of laser-induced choroidal neovascularization, and increase the survival and preserve rhodopsin expression of photoreceptor cells in the RCS rat (181). For such applications, the striking difference in the gene expression profile between RPE and iris pigment epithelium may be less of an obstacle to successful cell-based therapy. Additional studies, including determining the gene expression profile of iris pigment epithelium and RPE after subretinal transplantation, are needed to determine if the microenvironment of the subretinal space will have a marked effect on the iris pigment epithelium gene profile.

FUTURE DIRECTIONS At the current time there are many unresolved issues that may influence the ability of transplanted cells to repopulate Bruch’s membrane and numerous questions need to be addressed before successful cell transplantation can occur. In the absence of an animal model for AMD the approach to this problem must rely on a mixture of in vivo studies of cell transplantation in healthy animals, in vitro studies of cell reattachment to human Bruch’s membrane diseased with AMD, and a small number of clinical trials on AMD patients. There are several important variables that need to be investigated.

Source of Cells The ideal source of cells for human transplantation studies is not known. Adult human RPE are readily available from donor Eye Bank eyes but it is not known if these cells are the best source or whether the age of the donor RPE makes any difference. Fetal

human RPE may be able to repopulate Bruch’s membrane better than adult RPE but there are ethical and legal issues involved with the use of human fetal cells, and fetal cells cannot be autologous. Use of immortalized human RPE cells lines has been proposed, but the effects of immortalization or passaging in tissue culture on the distribution of cell surface receptors necessary for cell attachment to Bruch’s membrane have not been considered in prior studies. We have shown that there are significant differences in the gene expression profile of native and immortalized human RPE, thus raising the important question of whether the immortalized cells can replace all aspects of cell function (in press) There is some concern about tumorogenic potential if immortalized cells are used. Several authors have already used iris pigment epithelial cells because these cells are related embryological to the RPE, are readily available, and will not be rejected immunologically (63,182). However, iris pigment epithelial transplantation combined with subfoveal surgery has not led to a dramatic improvement in vision to better than 20 out of 200 (62,63,183), and there are significant differences in the gene expression profile of these cells compared to RPE. Several other cell sources that may be useful for RPE transplantation have not been investigated fully. First, the recent isolation of retinal progenitor cells (stem cells) raises the interesting possibility of using these cells to repopulate denuded areas of Bruch’s membrane (182). This is an attractive possibility because a small population of such retinal progenitor cells could yield a large population of cells for transplantation, and isolation of progenitors from the recipient eye could avoid problems of immune rejection. Second, xenotransplantation of porcine cells has already been performed in the management of central nervous system disease including stroke, Parkinson’s disease, and Alzheimer’s disease. These cells have been well-tolerated after transplantation into the central nervous system in patients and the possibility of using xenografts could provide an attractive alternative to the use of human tissue (184).

Immune Suppression A second issue that needs to be resolved is related to the immune suppression necessary to ensure graft survival. In the original paper by Algvere et al. (41), the fundus photograph strongly suggests that immune rejection developed in these non-suppressed individuals since the grafts became encapsulated and cystoid macular edema developed within three months. Systemic immune suppression appears to be sufficient to prevent ophthalmic signs of graft rejection but local suppression with slow release devices

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(intravitreal cyclosporin implants, for example) may be preferable (41).

Status of Bruch’s Membrane after Submacular Surgery As mentioned above the status of Bruch’s membrane after submacular surgery is important for the ultimate success of cell transplantation. Disease within Bruch’s membrane and iatrogenic removal of the inner layers of Bruch’s membrane during submacular surgery affects the ability of transplanted RPE to repopulate this structure. There are several approaches that could be used to rectify this problem including cleaning of Bruch’s membrane surface deposits, deposition of soluble ECM ligands, or placement of an artificial substrate such as lens capsule, ECM or healthy Bruch’s membrane, into the subretinal space. Successful application of these techniques in humans in vivo has yet to be demonstrated. Timing of Surgery/Identification of Surgical Candidates The issue regarding the timing of surgery is still to be resolved. Patients with disciform scars have evidence of significant atrophy of the outer retina over the neovascular tissue. Thus, prompt intervention may be necessary to improve the visual prognosis. Also choriocapillaris atrophy may develop under the fovea in patients with chronic subfoveal neovascularization, so that prompt surgery may improve preservation of this vascular supply as well.

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Persistent bare areas of Bruch’s membrane will be present in patients who have large defects in the RPE monolayer, or in whom advanced patient age or disease to the inner aspects of Bruch’s membrane prevents complete RPE resurfacing by migration and proliferation of adjacent RPE. Initial studies on RPE cell transplantation have not lead to dramatic visual improvements, but the presence of disease within Bruch’s membrane, iatrogenic removal of the inner layers of Bruch’s membrane, and immune rejection of the transplant have limited visual recovery after surgery. The next challenges in submacular surgery is to deliver RPE into the subretinal space as an organized monolayer, ensure the rapid attachment of these cells to Bruch’s membrane and prevent immunologic rejection of these cells. Cell survival immediately after transplantation is important to prevent atrophy of the subfoveal choriocapillaris. Development of an elusive animal model would facilitate progress in this field, because in the absence of an animal model, conclusions must be drawn from a combination of in vitro studies studying cell attachment to normal and diseased Bruch’s membrane, in vivo studies of cell transplantation in normal animals, and a limited number of in vivo studies of RPE transplantation in individuals with AMD. At the dawn of the new millennium, the challenge is great but the potential benefit of success is even greater because of the sheer number of patients who are affected by this devastating disease.

SUMMARY POINTS &

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The development of techniques to surgically excise choroidal neovascular membranes has introduced the possibility of surgically reconstructing the subretinal space in patients who have subfoveal choroidal neovascularization in AMD, POHS, and other disorders. Early attempts at reconstructing the anatomy of the subretinal space were focused on simple surgical excision of choroidal neovascularization. Subfoveal membrane excision can lead to good visual results if the subfoveal RPE is not removed at the time of surgery, or if the RPE is removed and adjacent RPE then repopulates the subfoveal area of Bruch’s membrane within one week after surgery. The presence of native or regenerated RPE is required to prevent postoperative atrophy of the subfoveal choriocapillaris, because the subfoveal choriocapillaris will undergo atrophy if Bruch’s membrane remains devoid of RPE for R1 week after subfoveal surgery.

ACKNOWLEDGMENTS Supported in part by an unrestricted grant from Research to Prevent Blindness, Inc., New York.

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26. Manzano RP, Peyman GA, et al. Testing intravitreal toxicity of bevacizumab (Avastin). Retina 2006; 26(3):257–61. 27. Maturi RK, Bleau LA, Wilson DL. Electrophysiologic findings after intravitreal bevacizumab (Avastin) treatment. Retina 2006; 26(3):270–4. 28. Michels S, Rosenfeld PJ, et al. Systemic bevacizumab (Avastin) therapy for neovascular age-related macular degeneration twelve-week results of an uncontrolled openlabel clinical study. Ophthalmology 2005; 112(6):1035–47. 29. Rosenfeld PJ, Fung AE, Puliafito CA. Optical coherence tomography findings after an intravitreal injection of bevacizumab (Avastin) for macular edema from central retinal vein occlusion. Ophthalmic Surg Lasers Imaging 2005; 36(4):336–9. 30. Shahar J, Avery RL, et al. Electrophysiologic and retinal penetration studies following intravitreal injection of bevacizumab (Avastin). Retina 2006; 26(3):262–9. 31. Berger AS, Kaplan HJ. Clinical experience with the surgical removal of subfoveal neovascular membranes. Short-term postoperative results. Ophthalmology 1992; 99(6):969–75 (discussion 975–6). 32. Thomas MA, Kaplan HJ. Surgical removal of subfoveal neovascularization in the presumed ocular histoplasmosis syndrome. Am J Ophthalmol 1991; 111(1):1–7. 33. Thomas MA, Grand MG, et al. Surgical management of subfoveal choroidal neovascularization. Ophthalmology 1992; 99(6):952–68 (discussion 975–6). 34. Lambert HM, Capone A, Jr., et al. Surgical excision of subfoveal neovascular membranes in age-related macular degeneration. Am J Ophthalmol 1992; 113(3):257–62. 35. Coscas G, Meunier I. Surgery of macular neovascular subretinal membranes. J Fr Ophtalmol 1993; 16(11):633–41. 36. Hsiue GH, Lai JY, Lin PK. Absorbable sandwich-like membrane for retinal-sheet transplantation. J Biomed Mater Res 2002; 61(1):19–25. 37. Tezel TH, Del Priore LV, Kaplan HJ. Reengineering of aged Bruch’s membrane to enhance retinal pigment epithelium repopulation. Invest Ophthalmol Vis Sci 2004; 45(9):3337–48. 38. de Juan E, Jr., Machemer R. Vitreous surgery for hemorrhagic and fibrous complications of age-related macular degeneration. Am J Ophthalmol 1988; 105(1):25–9. 39. Submacular Surgery Trials Pilot Study Investigators. Submacular surgery trials randomized pilot trial of laser photocoagulation versus surgery for recurrent choroidal neovascularization secondary to age-related macular degeneration: II. Quality of life outcomes submacular surgery trials pilot study report number 2. Am J Ophthalmol 2000; 130(4):408–18. 40. Bressler NM, Bressler SB, et al. Submacular surgery trials randomized pilot trial of laser photocoagulation versus surgery for recurrent choroidal neovascularization secondary to age-related macular degeneration: I. Ophthalmic outcomes submacular surgery trials pilot study report number 1. Am J Ophthalmol 2000; 130(4):387–407. 41. Algvere PV, Berglin L, et al. Transplantation of fetal retinal pigment epithelium in age-related macular degeneration with subfoveal neovascularization. Graefes Arch Clin Exp Ophthalmol 1994; 232(12):707–16. 42. Berger AS, Tezel TH, et al. Photoreceptor transplantation in retinitis pigmentosa: short-term follow-up. Ophthalmology 2003; 110(2):383–91. 43. Binder S, Stolba U, et al. Transplantation of autologous retinal pigment epithelium in eyes with foveal neovascularization resulting from age-related macular degeneration: a pilot study. Am J Ophthalmol 2002; 133(2):215–25.

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Part VII: Clinical Trial Design

24 Clinical Research Trials A. Frances Walonker

Doheny Eye Institute and Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, California, U.S.A.

Kenneth R. Diddie

Retinal Consultants of Southern California, Westlake Village, California, U.S.A.

INTRODUCTION Historical Review Age-related macular degeneration (AMD) is an important public health problem. Of the estimated 34.8 million people in the United States who were 65 years of age or older in 2002, approximately 1.6 million had some form of visual impairment. Approximately 600,000 of these will have experienced a rapid, devastating loss of vision due to choroidal neovascularization (CNV), “wet AMD,” whereas the remaining 1.0 million may experience a slow, progressive retinal atrophy and possibly a severe visual handicap “dry AMD” (1). Most may have difficulty performing routine visual tasks, such as driving, reading printed material, or recognizing the faces of their friends. As the U.S. population continues to age, more and more persons will become visually impaired from AMD; more, in fact, than from any other eye disease. In AMD with CNV, some of the worst losses of vision can occur. Because a large number of individuals have AMD complicated by CNV, effective treatment of even a fraction of all cases (2) can lead to significant savings to society and can decrease the number of people requiring social security and other disability payments (not to mention the effects on patients’ dignity and independence), with savings far outweighing the costs of clinical research, management, and treatment. Treatments studied have included photodynamic therapy, submacular surgery, external beam radiation, medications such as interferon, thalidomide, corticosteroids, and anti-vascular endothelial growth factor drugs as well as various oral supplements that are believed to be preventative. At the present time a number of randomized clinical research trials are looking at these various therapies for macular degeneration. Basic scientists are working hand in hand with clinicians to find a cure for this blinding disease.

Clinical Relevance Prior to the Macular Photocoagulation Study (MPS), there was no proven treatment for AMD with CNV. The use of low vision aids and mobility training were recommended but little could be done other than observe the natural history of AMD with CNV. The MPS, a randomized, multicenter trial, showed that laser photocoagulation of AMD with CNV prevented the most severe types of vision loss, compared to no treatment. The study was also important as a natural history study of macular degeneration (2). Since the 1980s this randomized controlled clinical trial has served as a benchmark for AMD research, with other treatments evaluated in the same way. CLINICAL RESEARCH METHODOLOGY The path a new idea takes from the patient’s problem to the basic research laboratory to the clinical research center and ultimately back to the treatment of the patient in the clinical setting is extensive and expensive. The final research question can be answered and practice guidelines established, but the cost in time, commitment, and dollars is great. The pathway from the patient and back again to the patient starts when the ophthalmologist sees a patient with a disease that either has no cure or would benefit from an improved treatment. Caseseries studies, in which an investigator has noted some interesting or intriguing observation, frequently lead to the generation of a hypothesis that will subsequently be investigated. The ophthalmologist then teams up with the basic scientist to address the hypothesis. Together, they design appropriate laboratory experiments to address the hypothesis. Results from these basic science studies lead to preliminary clinical investigations of a possible new diagnostic technique, a treatment, a drug or even a drug delivery device. A small group of carefully selected patients participate in a pilot study to study the safety of these

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new treatments. In addition, for drug therapies, the dose levels that may be most effective are also studied. If successful, such a pilot study generates a single center clinical trial to further evaluate the tolerability, safety, and efficacy of the treatments. Subsequently a full-scale, multicenter, randomized clinical research trial is initiated to recruit enough patients to test the safety and the efficacy of the new procedure, operation, test or drug or device. These new approaches are also tested for their effects on the quality of life of patients with the initial disease. The order of the research steps are outlined in Table 1. The randomized clinical research trial is the gold standard, or reference, in medicine, as it provides the greatest justification for concluding causality and is subject to the least number of problems or biases. Clinical trials are the best type of study to use when the objective is to establish efficacy of a treatment or a procedure. Clinical trials in which patients are randomly assigned to different treatment arms are the strongest design of all. These innovative approaches to clinical practice are then presented and taught to other ophthalmologists through continuing medical education courses, publications in peer review journals, and presentations at national and international scientific meetings. Finally, the new techniques, medications, or test materials are available to all patients under standard practice guidelines for diagnosis and treatment for disease.

Design of a Clinical Research Trial The initial step in determining whether a research proposal would fulfill all the ethical and investigational guidelines necessary to protect human subjects involved in a clinical research trial, is to go through a formal decision making process. After all the data from previous observational, basic laboratory Table 1 Development Phases of a Clinical Trial Phase I

Phase II

Phase III

Phase VI

Actions of drugs etc. in humans: looking at side effects of dose levels/safety issues: early evidence of efficacy: may include normal subjects as well as patients: all subjects get study product: 5–15 patients (pilot study): can be multi or single center Evaluate efficacy/tolerability of drug etc. for a particular indication in patients with the disease under consideration looking at side effects and short-term risks: all study subjects get study product: can be multi or single center Expanded trials after preliminary evidence suggests efficacy: additional evidence of overall risk/benefit: may be randomized against standard of care for this disease, observation or a placebo: results submitted for approval pre-marketing Post-marketing to delineate additional information about the risks and benefits and the optimal use of the product

(in vitro and animal studies) case report studies, Phase I, and Phase II studies have been analyzed, and a protocol is established under which the trial will be conducted. This protocol is developed outlining every detail of the research study so that all personnel—investigator, coordinator, photographer, vision specialist—every participant in the study, is aware of the protocol detail and is able to follow this protocol for the length of the trial, maintaining standardization of evaluation, testing, surgery, and all other procedures. The steps that are involved in the development of a protocol are as follows.

The Rationale The ophthalmologist will team up with a basic science researcher or will work in his/her own laboratory to design a series of experiments that may address a specific disease entity for which there may be no adequate treatment. The results of these experiments, done again and again and replicated in other laboratories, may suggest an intervention or therapy that would be tested on some laboratory animal under the strict guidelines of a research laboratory. The results serve as the basis for a limited trial on a small group of carefully selected patients. If these patients react well to the therapy or tolerated the therapy with minimal side effects, clinical research proceeds to the next phase: a single or two to three center clinical study of the therapy in patients with a specific disease. This is the initial stage of the clinical research trial. All the data from prior studies are then analyzed along with any new information, and the rationale for conducting this particular study is outlined. The objectives of the study, the safety and efficacy of the treatment, the design of the experimental plan, the number of enrolled subject required to prove the hypothesis and most importantly, whether the research study will benefit the population at large. The Protocol The protocol for the study will include: Background &

&

& &

The background of the disease to be studied and the results of all previous related research, both basic science and clinical. All information to support the justification of this research project and the impact it will have on the population in general and the population with this specific disease entity. The expected benefits to be obtained from the study. All the information about the study product, be it drug, device, surgery, delivery system, with all the

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risks and adverse events noted during the prior uses of the product. Objectives & &

The primary objectives of the study could be: halt the progression of the disease. The secondary objectives could be: improve visual acuity by O than three lines.

Study Design &

Description of the study which will include: & Type of study: randomized/open label/multidose & Rationale answers why: Why that treatment? Why that dose? Why that duration? & Outcome measures: primary measures; safety and tolerability, secondary measures; for example: the change in visual acuity/leakage & Safety plan: unmasking/laboratory values/ detailed adverse event evaluations & Compliance: good clinical practice/Food and Drug Administration (FDA) guidelines/ IRB guidelines.

& & & & & & & &

Subject selection criteria with the inclusion and exclusion criteria with justification for both Justification for or against inclusion/exclusion of vulnerable subjects Treatment assignment: randomized/stratified Study treatment details: formulation/dose/storage Excluded therapies Study assessments: visual acuity/photography/ quality of life instruments/early exit criteria Discontinuation: subject/study Statistical methods: sample size/safety analysis/efficacy analysis Data quality assurance: DSMC/monitoring

&

&

&

&

&

Safety Assessment &

& & & &

Adverse event reporting. Serious adverse events that require hospital/surgical intervention or result in death are immediately reported to the IRB and the sponsor All adverse events are followed until resolution or stability All subjects are contacted after study completion if adverse events have occurred Medical condition confounders Laboratory assessments

The Informed Consent Before any research trial that includes human subjects can be instituted, an Institutional Review Board (IRB)

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must approve all the components of the trial. The responsibility of an IRB is to establish the requirements and procedures for requests for the performance of human research, development, demonstration, or other activities involving patients or patient products, in addition to the usual scope of established and accepted methods. The IRB monitors approved research in accordance with the requirements the Office of Protection from Research Risks, the regulations of the FDA, National Institutes of Health and the Department of Health and Human Services. The IRB uses a group process to review research protocols and related material, e.g., informed consent documents and investigator brochures, to ensure the following:

Material and Methods &

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&

&

Risks to human subjects are minimized by using procedures that are consistent with sound research design and that do not unnecessarily expose subjects to risk. Whenever appropriate, such procedures already will have been performed on subjects for diagnostic or therapeutic purposes. Risks to subjects are reasonable in relation to the anticipated benefits (if any) to the subjects and the importance of the knowledge that may be expected from the result. The selection of the subjects is equitable, i.e., the study subjects are of both genders and from different racial/ethnic groups, and no age limitations exist other than those associated with a disease entity. This will decrease the risk of bias in patient selection. Informed consent will be sought from each prospective subject or the subject’s legally authorized representative and will be documented in accordance with and to the extent required by informed consent regulations. Provisions to prevent the suggestion of coercion are documented. Where appropriate, the research plan makes adequate provision for monitoring the data collected to ensure the safety of subjects either by using a Data Safety Monitoring Board that looks at the data to note any untoward adverse events or even unexpected improvement that may determine the study should end. Adequate provisions are in place to protect the privacy of the subjects and to maintain confidentiality of the data. Appropriate additional safeguards have been included in the study to protect the rights and the welfare of subjects who are members of a vulnerable group (e.g., children etc.).

The IRB has the authority to disapprove, modify, or approve studies based on consideration of human

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subject protection aspects. It also has the authority to suspend or terminate a study, to place restrictions on a study, and to require progress reports and oversee the conduct of the study and the study investigators. The informed consent should be signed by the patient before entering into a clinical research trial. The informed consent will include the length of patient’s participation, the alternatives to this treatment modality, the risks involved in this trial, and a statement allowing the patients to withdraw from the trial at any time without consequence.

Data Collection It is imperative that the collection of the research data, based on the design of the study, is accurate and complete. All research trials have case report forms on which data is recorded. These forms do not contain any patient identifying information other than a unique identifying code number and/or a combination of the patient’s initials. These forms are sent to the sponsor and, therefore, can only contain this unique identifying information. The types of data collected include: & & & & & & & & &

Results of laboratory testing Quality of life questionnaires Clinical evaluations Eligibility criteria Medications, medical history, surgical history Detailed ophthalmic history including prior treatment details of the disease entity Adverse events both serious and non-serious The study product Investigator signatures

All data have to be checked and corrected before they are sent to the sponsor and this is done by representatives of the sponsor. These monitors’ responsibilities include: to make sure the data are correct and legible; that the patients have met the enrollment criteria and received the correct treatment to which they were assigned. The clinical chart where the investigator notes the clinical examinations is known as the source document. The data on the case report forms are matched to the source documents. This cross check of data verifies accuracy. All data and investigational study products are stored in a secured area with access to the area only by the study staff, investigator, and coordinator. The principal investigator of the clinical research study is responsible for the conduct of the study, the accuracy of the data collection and the conduct of the study staff and the safety of the study subjects at all times.

Settings for Research Trials Advancing medical knowledge—through screening, treatment, surgical, and pharmaceutical intervention—has prolonged the life of many people with disabling chronic disease conditions and increased the number of survivors of traumatic injury. At the present time, 13% of the population is over the age of 65; by the year 2040, this number will have grown to 23% of the population (3). By 2040, 70 million people will have some form of activity limitation, whether mental, physical, or visual, that will require intervention from the healthcare systems in some form. Research into the most effective care for persons with chronic disease, including eye disorders in particular, and efforts in prevention will be at the forefront of future clinical research. The projected cost of healthcare in the year 2040 is $906 billion, a huge percentage of the gross national product of the United States and the highest of the entire world’s developed countries (4). With such huge expenditures anticipated for health care, and in response to continued pressure by government regulatory agencies to drive down costs, evaluation of cost in conducting research is suggested. Researchers must include cost research objectives, such as costs associated with screening programs, alternative treatments and procedures, use of new technology and implementation of new regulatory measures associated with programs and trials. The results obtained from including cost analysis in research help health care decision makers weigh the costs and consequences of competing treatment alternatives. Cost information provides additional data that can supplement clinical judgment when making therapeutic choices. Therefore, clinicians and researchers at major academic institutions need to focus on advancing the care and prevention of eye disease. Efforts should be based on rigorous clinical methods, i.e., randomized controlled clinical trials and analysis of economic and humanistic outcomes. With research of this nature, the results can be applied directly to the patient, where they will accomplish the greatest good. This is especially true when these outcomes may mean the difference between sight and blindness, and when they impact on the outcome measures of quality of life and ultimately, life expectancy. Limitations of Randomized Clinical Trials The cost of developing the necessary infrastructure to support the scientific and clinical activities involved in conducting major national and international clinical research makes it prohibitive except for large academic ophthalmology centers unless under the sponsorship of industry. There are obvious downsides to this type of sponsorship that is somewhat obviated by the

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inclusion in the project of an independent clinical research organization. Most major academic ophthalmology centers involved in clinical and basic science research are referral centers for patients with complicated disease who have not responded to standard therapy or who have a disease with no known cure. However, because of the nature of this population, i.e., those with severe disease as well as those with rare and complicated disease, the numbers of patients who would be eligible to enter a clinical research trial would be limited, making recruitment difficult. This places a potential for selection bias on these clinical research studies, such that when the studies are completed, they may not translate to the population in general. On the other hand, a more common disease entity, such as macular degeneration, with its potential for marked vision loss if untreated, offers access to more subjects for inclusion in a clinical trial. These patients are seen routinely in the private practice ophthalmologist’s office that is now involved in clinical research. The disadvantage to academic institutions that have invested in the development of an infrastructure to rigorously support all basic and clinical research is that they no longer have access to this large patient population. The disadvantage to the patient may be that the strict protocol that is the hallmark of academic institutional research may not be adhered to so rigorously in a community where that infrastructure is not present. Another limitation is access to the underserved— those people who have no access to health care providers, either because of lack of insurance or distance from those same providers. These patients are likely to postpone needed care until their conditions have escalated in severity. This group would have no representation in the clinical research arena, the subsequent lack of diversity in the research population may result in possible bias. The tremendous increases in new technology have not been accompanied by changes in the clinical evaluation of new approaches. As a result, new approaches become established that may harm many patients, and researchers may have difficulty obtaining approval to perform properly designed clinical trials from the human subjects committees that oversee the ethics of research because of the presumed standard of practice that is present in the field.

RESEARCH STAFF AND DOCUMENTATION The goal of all clinical research is to provide information that will help the practitioner treat his or her

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patients more effectively. The clinical trial provides the best means to objectively quantify and compare the benefits and risks of new or alternative treatments to establish treatments for disease, especially when the difference between a new or old treatment is not clear or when a large number of factors may influence the course of the disease or the outcomes of the treatment (3). To ensure that the treatment groups are compared objectively, standardized methods of gathering data, training and certifying the personnel who collect the data, and treating patients either surgically or pharmaceutically, are imperative. Continuous monitoring of adherence to the protocol, uniform data accumulation and routine re-certification of personnel will eliminate any concerns of bias or ambiguity when the data is presented. All data accumulated on a case report form, the form that is submitted to a central data collection agency, must be documented in the patient file and these two documents must be reconciled at all times. All clinical research studies are monitored at regular intervals to ensure that all information is recorded on all the legal documents and that no data are missing or unsubstantiated. The success of all clinical research is totally dependent on this accurate and standardized collection of data, and strict adherence to the protocols.

SUMMARY POINTS & & &

&

MPS was the first clinical study to look at macular degeneration The aging population is 34.8 million with 1.2 million having some form of visual impairment. Clinical research is the best means to quantify and objectively compare the benefits and risks of new or alternative treatments for disease or injury especially when: & the difference between a new or old treatment is not clear; & the disease naturally follows a chronic, variable and erratic course; & a large number of factors, known or unknown, may influence both the course of the disease and the outcome of the treatment. A well-designed and conducted randomized clinical trial incorporates the following: & High ethical standards—of paramount importance are patient welfare, informed consent, adherence to protocol, and careful data monitoring. & Control groups that are matched to the treatment groups for the baseline characteristics. & Random assignment of patients to both study and control groups when comparability of results among groups is essential.

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& & &

Masking to minimize bias of both the examiner and the patient, if possible. Enrollment of an adequate number of patients enrolled in the trial for the results to be statistically significant. Completeness of patient follow-up. Use of statistical methods for study design and data analysis. Continuous monitoring of adherence to protocol and accumulation of data by the Data Safety Monitoring Committee (DSMC), the study Advisory Committee, the Executive Committee and the Steering Committee to ensure the safety of the subjects involved in the trial (5).

REFERENCES 1. Administration on Aging (AoA). A Profile of Older Americans. U.S. Department of Health and Human Services, 2000. 2. Macular Photocoagulation Study Group. Argon laser photocoagulation for senile macular degeneration. Results of a randomized clinical trial. Arch Ophthalmol 1982; 100:912–8. 3. Walonker AF, Sturrock D. The Ryan Leopold Beckman Center for Clinical Research. Masters Thesis School of Public Health, UCLA, 1999. 4. Chronic Care in America. A 21st Century Challenge. Princeton, NJ: Prepared by the Institute for Health and Aging University of California, San Francisco for the Robert Wood Johnson Foundation, August 1996. 5. Clinical Trials Supported by The National Eye Institute. U.S. Department of Health and Human Services, 1987.

Index

ABCR genes, 36 Aberrant antigen-specific immunity, 18–19 ACE. See angiotensin-converting enzyme. Acquired immunity, 12 Adaptive immunity, 12 Adjunct usage, age-related macular degeneration and, 295–301 AF. See autofluorescence. Age, as risk-factor in macular-degeneration, 53, 54 Age-related eye disease study (AREDS), 58, 69–72, 76–77, 98–99, 106, 127 Age-related macular degeneration (AMD) adjunct usage, 295–301 calcium and magnesium free retinal detachment enhancing solutions, 296–297 encapsulated cell technology (ECT), 298–299 selective intraocular radiation brachytherapy, 299–300 tissue plasminogen activator, 295–296 triamcinolone acetonide, 297–298 associated factors, 97 cardiovascular disease, 98 demographic characteristics, 97–98 environmental influences, 98–99 genetic influence, 99 hypercholesterolemia, 98 hypertension, 98 systemic diseases, 98 Bruch’s membrane, 1, 332–333 choroidal monoctyes, 26 neovascular membranes (CNVM), 23 neovascularization (CNV), 1 clinical features, 97 controlled radiation studies, 237–243 definitions of, 51–52, 53 Drusen, 99–101, 257–258 feeder vessel treatment (FVT), 207–222 fundus autofluorescence, 191–205 gene pathogenesis, 37–39 angiotensin-converting enzyme (ACE), 38–39 extracellular matrix, 37 inflammation, 37–38 lipid metabolism, 38 not associated with, 39 GPR75, 39 LAMC1, 39 multi-candidate gene screening, 39 oxidative damage, 39 genetics of, 35–42 allele association studies, 40–41 familial aggregation studies, 35–36 hereditary retinal dystrophies, 36–37

[Age-related macular degeneration (AMD)] [genetics of] linkage mapping, 39–40 twin aggregation studies, 35–36 histopathology of, 1–9 exudative AMD, 5–7 non-exudative, 1–5 immune mechanism, 23–27 evidence, 23–25 immunology, 11–27 biology of, 11–18 nonocular degenerative diseases, 19–23 indocyanine green angiography (ICGA), 159–172 inflammatory mechanisms, 23–25 injury hypothese response, 25–26 laser prophylaxis, 257–268 lesions, basal laminar deposits (BlamD), 1 linear deposits, (BlinD), 1 ocular immune disorder, 24–25 optical coherence tomography, 177–183 treatment of, 181–183 photodynamic therapy (PDT) clinical results and, 226–227 progression of antigen-specific immunity and, 26–27 inflammatory amplification cascades, 27 radiation treatment, 233–243 delivery methods, 235–237 implant therapy, 236 charged particle, 236–237 other types, 241–243 rationale for, 233–235 toxicity issues, 234–235 retinal pigment epithelial (RPE), 1 cell transplantation, 329–343 risk factors, 47–85 antioxidant enzymes, 64–65 case-control studies, 48 choroidal neovascularization, 74–77 cohort studies, 51 cross-sectional studies, 49–50 dermal elastotic degeneration, 64 environmental factors, 65–73 alcohol consumption, 73 carotenoids, 72 cigarette smoking, 65–66 dietary fish intake, 72–73 nutritional factors, 68–73 sunlight exposure, 66–67 epidemiologic studies of, 47 problems and limitations of, 47, 51–53

356

INDEX

[Age-related macular degeneration (AMD)] [risk factors] ocular, 57–60 cataract surgery, 58–59 cup/disc ratio, 60 iris color, 59–60 macular pigment optical density, 57–58 refractive error, 60 reproductive, 64 sociodemographic factors, 53–57 age, 53, 54 gender, 54 race/ethnicity, 55–56 heredity, 56–57 socioeconomic status, 57 systemic, BMI ratio, 63 cardiovascular biomarkers, 63 disease, 60–65 Chlamydia pneumoniae infection, 63–64 cigarettes, 64 diabetes, 62–63 dietary fat intake, 62 hematologic factors, 63 hyperglycemia, 62–63 hypertension and blood pressure, 61–62 serum lipid levels, 62 waist conference, 63 waist-hip ratio, 63 treatment, anti-inflammatory therapy, 27 Age-related maculopathy (ARM), 51–52, 53 Alcohol consumption, as risk factor in macular degeneration, 73 Allele association studies, 40–41 chromosome 10q26, 41 complement component 2, 41 complement factor H, 40–41 factor B, 41 Amplification cascades, 21 Amplification immunity mechanisms, 12–14 complement cascade, 12–13 cytokines, 13–14 oxidants, 14 Angiographic appearance, choroidal neovascularization feeder vessel, 210–212 Angiotensin-converting enzyme (ACE), 38–39 Anthropomorphic model, choriocapillaris/choroidal neovascularization, 212 Antiangiogenesis treatment, 145–147 Antiangiogenic factors, 88 Antibody, 16–17 cell-surface, 17 extracellular-bound antigens, 17 Antigen presenting cells (APC), 15 Antigen specific immunity, 21, 22 activation, 18 adaptive or acquired, 12 age-related macular degeneration progression and, 26–27 amplification mechanism, 12–14

[Antigen specific immunity] effectors, 23–24 innate vs., 11–14 Antigens extracellular-bound, 17 intracellular, 17 Anti-inflammatory therapy, 27 Antioxidant enzymes, age-related macular degeneration risk factors and, 64–65 Antioxidant vitamins, randomized trials, 70–72 Antioxidants, 68–70 age-related eye disease study (AREDS), 69 Anti-vascular endothelial growth factor current therapies, 247–252 aptamer, 247–248 intravitreal injections, 251–252 monoclonal antibodies, 248–251 photodynamic combination, 251 future therapies, 252–254 receptor tyrosine kinase inhibitors, 253–254 small interfering RNAs, 253 VEGF trap, 252–253 APC. See antigen presenting cells. ApoE. See apolipoprotein. Apolipoprotein E (ApoE), 20 Aptamer, 247–248 macugen, 247–248 pegaptanib sodium, 247–248 ARM. See age-related maculopathy. Atherosclerosis antigen-specific immunity, 21 complement activation, 21 cytokines and oxidants, 21 heat shock proteins (HSPs), 20 infectious etiology, 20–21 innate mechanisms, 19–21 injury, 19–20 macrophages, 20 apolipoprotein E (ApoE), 20 nonspecific amplification cascades, 21 Atrophic retinal degeneration, 24–25 Autofluorescence (AF), 191–205 age-related macular degeneration, 192–197 choroidal neovascularization, 198–199 drusen, 197–198 geographic atrophy, 198 imaging, 119–120 Avastinw, 250–251 B lymphocytes, 16–17 Basal deposits, 3–4 Basal laminar deposits (BlamD), 1 Drusen, 101 Basal linear deposits (BlinD), 1 Basophils, 15–16 Benzoporphyrin derivative monoacid, 225 BPD-MA, 225 verteporfin, 225 Visudyne e, 225 Bevacizumab, 250–251 Avastinw, 250–251

INDEX

Biomarkers, as risk factor in macular-degeneration, 63 BlamD. See basal laminar deposits. BlinD. See basal linear deposits. Blood pressure, as risk factor in macular-degeneration, 61–62 BMI ratio, as risk factor in macular-degeneration, 63 BPD-MA, 225 Brachytherapy. See implant radiation therapy. Bruch’s membrane, 1, 332–333 anatomic reconstruction, 337–339 changes in, 1 retinal pigment epithelial cell attachment and, 335–337 Calcium and magnesium free retinal detachment enhancing solutions, 296–297 Candidate genes, 36–37 ABCR, 36 ELOVL4, 36–37 Fibulin 3/EFEMP1, 37 peripherin/RDS, 37 TIMP3, 37 VMD2, 37 Cardiovascular disease, 98 age-related eye disease study (AREDS), 98 biomarkers, 63 as risk factor in macular-degeneration, 60–65 Carotenoids, lutein, 72 as risk factors in macular degeneration, 72 zeaxanthin, 72 Case-control studies, age-related macular degeneration risk factors, 48 Cataract surgery, as risk factors in maculardegeneration, 58–59 CC. See choriocapillaris. Cell-surface antigens, 17 Cellular injury, immunity activation trigger, 17 Central scotomas, 116–117 Charged particle radiation therapy, 236–237 Chlamydia pneumoniae infection, as risk factor in maculardegeneration, 63–64 Choriocapillaris (CC), 207 changes in, 2–3 choridal neovascularization anthropomorphic model of, 212 feeder vessel model, hemodynamic relationship of, 212–217 Choroidal monoctyes, 26 Choroidal neovascular membranes, (CNVM), 23 Choroidal neovascularization (CNV), 1, 2, 87–91, 198–199 atrophic retinal degeneration, 24–25 choriocapillaris, anthropomorphic model of, 212 combined growth pattern, 6 drusen as risk factor for, 258 feeder vessel, 138–139 angiographic appearance of, 210–212 vs. histological appearance, 211–212 choriocapillaris model, hemodynamic relationship of, 212–217 histological appearance, 209–212

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Choroidal neovascularization (CNV) [feeder vessel] relationship between, 212–217 treatment, 207–222 future of, 221 geographic atrophy and, 115–116 histopathology of, 7 indocyanine green angiography (ICGA) findings and, 161 laser photocoagulation, 203–205 neovascularization (NV) inferences, 87 occult, 143–144 ocular immune disorder, 24–25 optical coherence tomography and assessment of, 177–179 pathogenesis of, 89–90 pharmacologic treatment of, 90–91 prevention, exudative (neovascular) age-related macular degeneration and, 127–128 progression of, 77 as risk factor in macular degeneration, 74–77 subretinal, 6 pigment epithelium, 5–6 therapeutic options, 144–151 anti-angiogenesis treatments, 145–147 gene therapy, 151 low vision rehabilitation, 151 new types, 148–149 photodynamic, 144–145 radiation, 148 receptor tyrosine kinase inhibitors, 150 small interfering RNA, 149 squalamine lactate, 150 surgery, 148 thermotherapy, 147–148 tubulin binding agents, 150–151 VEGF trap, 149–150 vascular endothelial growth factor, 87–91 Chromosome 10q26, 41 Chronic injury, glomerular diseases and, 21–22 Cigarettes, as risk factor in macular-degeneration, 64 Classic CNV, 161 Classic subretinal choroidal neovascularization, 6, 7 Clinical research trials, 349–354 design of, 350 limitations of randomized, 352–353 methodology, 349–353 settings for, 352 staff and documentation, 353 CNV. See choroidal neovascularization. CNVM. See choroidal neovascular membranes. Cohort studies, age-related macular degeneration risk factors, cohort studies, 51 Combined growth pattern, 6 Combretastatin A-4 phosphate, 150 Complement activation atherosclerosis and, 21 ocular immune disorder and, 24–25 Complement cascade, 12–13 Complement component 2, 41 Factor B and, 41 Complement factor H, 40–41

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INDEX

Confocal scanning laser opthalmoscope indocyanine green angiography, 171 Contrast enhanced indocyanine green angiography (ICGA), 170 Controlled radiation studies, review of, 237–243 Cortical prostheses, 319–320 Cross-sectional studies, age-related macular degeneration risk factors, 49–50 CST3, 37 Cup/disc ratio, as risk factors in macular-degeneration, 60 Cytokines, 13–14, 21 Degenerative disease, immune responses to, 17–19 aberrant antigen-specific activation, 18–19 antigen-specific activation, 18 innate immunity activation, 17–18 Demographic characteristics, age-related macular degeneration and, 97–98 Dendritic cells, 15 Dermal elastotic degeneration, age-related macular degeneration risk factors and, 64 Diabetes, as risk factor in macular-degeneration, 62–63 Dietary fat intake, as risk factor in macular-degeneration, 62 Dietary fish intake, as risk factors in macular degeneration, 72–73 Diffuse drusen, 5 Digital imaging, indocyanine green angiography (ICGA) and, 160–161 Digital subtraction- indocyanine green angiography (ICGA), 170 Dimly lit environments, geographic atrophy and, 117–118 Disciform scar, 7 Drusen, 4–5, 99–101, 257–258 autofluorescence (AF) and, 197–198 as choridal neovascularization risk factor, 258 diffuse, 5 disappearance of, 101–103 laser prophylaxis on, 258–259 studies on, 262–265 nodular, 4 reduction, laser prophylaxis and, 259–262 soft, 4–5 types, 100–101 basil laminar, 101 hard, 100 soft, 100–101 Dry age related macular degeneration. See non-exudative age related macular degeneration. Dye enhanced photocoagulation (DEP), indocyanine green angiography (ICG), 217–221 clinical application of, 218–221 Dye-enhanced photocoagulation (DEP), 207 Dystrophies, retinal, 36–37 Early Treatment Diabetic Retinopathy Study (ETDRS), 117 ECT. See encapsulated cell technology. ELOVL4 genes, 36–37 Encapsulated cell technology (ECT), 298–299 End-stage age-related macular degeneration, retinal prostheses, 319–326

Environmental factors, age-related macular degeneration risk factors and, 65–73 alcohol consumption, 73 carotenoids, 72 cigarette smoking, 65–66 dietary fish intake, 72–73 nutritional factors, 68–73 sunlight exposure, 66–67 Environmental influences, age-related macular degeneration and, 98–99 age-related eye disease study (AREDS), 98 Epidemiologic studies, age-related macular degeneration risk factors and, 47 Epidemiology exudative (neovascular) age-related macular degeneration and, 125–128 geographic atrophy and, 112–113 Epiretinal prosthesis, 320–323 Estrogen-related factors, as risk factor in macular degeneration, 64 ETDRS. See Early Treatment Diabetic Retinopathy Study. Ethnicity, as risk-factor in macular-degeneration, 55–56 Extracellular-bound antigens, 17 Extracellular matrix (ECM), 37, 88–89 CST3, 37 fibulin, 37 MMP-9, 37 Extrafoveal CNV, 141–142 Extraocular approaches, retinal prostheses and, 319–320 Exudative (neovascular) age-related macular degeneration, 125–152 clinical features of, 129–139 pigment epithelial detachment (PED), 133–135 choroidal neovascularization, 135–139 epidemiology, 125–128 choroidal neovascularization prevention, 127–128 risk factors, 126–128 non-ocular, 126–127 ocular, 127 genetics, 127–128 idiopathic polypoidal choridal vasculopathy, 139 macular photocoagulation study, 141–143 natural history of, 140–141 natural history of untreated, 140–141 juxtafoveal CNV, 141 subfoveal CNV, 141 occult choroidal neovascularization, 143–144 retinal angiomatous proliferation, 139–140 symptoms of, 128–129 Exudative (wet) age related macular degeneration (AMD) choroidal neovascularization, 5–7 disciform scar, 7 Exudative macular degeneration, macular translocation and, 275–276 FA. See fluorescein angiography. Factor B, 41 complement component 2, 41 Familial aggregation studies, 35–36 Fat intake, as risk factor in macular-degeneration, 62

INDEX

Feeder vessel (FV) choriocapillaris, choridal neovascularization model, hemodynamic relationship of, 212–217 choroidal neovascularization and, 138–139 relationship between, 212–217 definition of, 209–212 Feeder vessel therapy, 170–171 Feeder vessel treatment (FVT), 207–222 choriocapillaris (CC), 207 choroidal neovascularization and, future of, 221 concept of, 207–209 development of, 217–221 feeder vessels (FV), 209–212 Fibulin, 37 3/EFEMP1 gene, 37 Fish diet, as risk factor in macular degeneration, 72–73 Fluid-air exchange, 284 Fluorescein angiography (FA), 159, 186, 285 Focal CNV, 162 Fundus autofluorescence, 191–205 Fundus photography, 185–186 FVT. See feeder vessel treatment. GA. See geographic atrophy. Gender, as risk-factor in macular-degeneration, 54 Gene screening, multi-candidate, 39 Gene therapy, 151 Genes age-related macular degeneration and, pathogenesis of, 37–39 candidate, 36–37 extracellular matrix, 37 Genetics age-related macular degeneration and, 35–42 allele association studies, 40–41 familial aggregation studies, 35–36 hereditary retinal dystrophies, 36–37 influences, age-related macular degeneration and, 999 linkage mapping, 39–40 risk factors, exudative (neovascular) age-related macular degeneration and, 127–128 twin aggregation studies, 35–36 Geographic atrophy (GA), 5, 111–121, 198 autofluorescence imaging, 119–120 bilateral development of, 115 choroidal neovascularization and, 115–116 clinical features, 111–112 conditions similar to, 118–119 epidemiology, 112–113 heredity factors, 113 histopathology and pathogenesis, 112 natural history, 113–115 prevalence, 112–113 systemic risk factors, 112–113 treatments, 120–121 visual function impairment, 116–118 central scotomas, 116–117 dimly lit environments, 117–118 other visual abnormalities, 118 paracentral scotomas, 116–117

Glomerular diseases, 21–23 antigen-specific immunity, 22 innate immunity, 21–22 chronic injury, 21–22 macrophage-mediated injury, 22 nonspecific amplification mechanism, 23 GPR75 type-gene, 39 Hard drusen, 100 Heat shock proteins (HSPs), 20 Hematologic factors, as risk factor in maculardegeneration, 63 Hemodynamic relationship, choriocapillaris, choridal neovascularization, feeder vessel model, 212–217 Hereditary retinal dystrophies, 36–37 candidate genes, 36–37 ABCR, 36 ELOVL4, 36–37 fibulin 3/EFEMP1, 37 peripherin/RDS, 37 TIMP3, 37 VMD2, 37 Heredity factors, geographic atrophy and, 113 Heredity, as risk-factor in macular-degeneration, 56–57 Histological appearance, choroidal neovascularization feeder vessel, 209–212 Histopathology age related macular degeneration and, 1–9 exudative (wet) age related macular degeneration (AMD), 5 Histopathy, geographic atrophy, 112 Hot spot occult CNV, 162 HSP. See heat shock protein. Hypercholesterolemia, 98 Hyperglycemia, as risk factor in macular-degeneration, 62–63 Hypertension, 98 age-related eye disease study (AREDS), 98 as risk factor in macular-degeneration, 61–62 ICGA. See indocyanine green angiography. Idiopathic polypoidal choridal vasculopathy, 139 Imaging, optical coherence tomography (OCT), 177–183 Imbricating sutures, 280–281, 283–284 tightening of, 283–284 Immune cells antibody, 16–17 B lymphocytes, 16–17 T lymphocytes, 16 Immune mechanisms antigen-specific immune effectors, 23–24 atherosclerosis, 19–21 antigen-specific immunity, 21 nonspecific amplification cascades, 21 direct evidence for innate immune effectors, 23–24 glomerular diseases, 21–23 nonocular degenerative diseases and, 19–23 Immune response, antigen-specific activation, 18 Immune response cells, 14–17 basophils, 15–16 dendritic, 15

359

360

INDEX

[Immune response cells] macrophages, 14–15 mast cells, 15–16 monocytes, 14–15 Immune system, degenerative disease responses, 17–19 Immunology age-related macular degeneration and, 11–27 biology of, 11–18 degenerative disease response, 17–19 immune response cells, 14–17 innate, antigen-specific vs., 11–14 Implant radiation therapy (brachytherapy), 236 Indocyanine green history of, 159–160 injection technique, 160 pharmacology, 160 properties of, 159 toxicity of, 160 Indocyanine green angiography (ICGA), 159–172 associated treatment strategies, 169–170 clinical application of, 167–168 confocal scanning laser opthalmoscope, 171 digital imaging systems, 160–161 dry age-related macular degeneration, 171 dye enhanced photocoagulation (DEP), 217–221 clinical application of, 218–221 findings, 161–163 choroidal neovascularization, 161 classic CNV, 161 focal occult CNV, 162 hot spot occult CNV, 162 occult CNV, 161–162 plaque, 162–163 serous pigment epithelial detachment, 161 new techniques, 170–171 contrast enhanced, 170 digital subtraction, 170 FV therapy, 170–171 real-time, 170 wide-angle, 170 polypoidal choroidal vasculopathy, 163–64 recurrent CNV, 168–169 retinal angiomatous proliferation, 164–167 Infection, immunity activation trigger, 18 as risk factor in macular-degeneration, 63–64 Infectious etiology, atherosclerosis and, 20–21 Inflammation factors, 37–38 Inflammatory amplification cascades, age-related macular degeneration progression, 27 Inflammatory mechanisms, nonocular degenerative diseases and, 19–23 Injury, atherosclerosis and, 19–21 low density lipoprotein (LDL), 19 Injury hypothese response, 25–26 Innate immunity activation trigger cellular injury, 17 infection, 18 amplification mechanisms, 12–14 effectors, 23–24

[Innate immunity] glomerular diseases and, 21–22 natural, 11 Innate immunology, antigen-specific vs., 11–14 Innate mechanisms, atherosclerosis and, 19–21 Intracellular antigens, 17 Intraocular radiation brachytherapy, 299–300 Intraoperative complications, macular translocation and, 290 Intravitreal injections, 251–252 Iris color, as risk factors in macular-degeneration, 59–60 Iris pigment epithelial transplantation, 339–342 Juxtafoveal CNV, 141, 142 LAMC-type genes, 39 Laminar basal deposits, 3 Laser light application, photodynamic therapy and, 224 Laser photocoagulation, 203–205, 285–286 Macular Photocoagulation Study (MPS), 203–205 results of, 205 Laser prophylaxis, 257–268 drusen and, 258–259 reduction, 259–262 studies on, 262–265 multicentered clinical trials, 265–268 LDL. See low density lipoprotein. Limited macular translocation, 279–280 equipment and overview, 280 fluorescein angiography, 285 key surgical steps, 280–284 fluid-air exchange, 284 imbricating sutures, 280–281, 283–284 pars plana vitrectomy, 281 planned neurosensory retinal detachment, 281–283 laser photocoagulation, 285–286 operative techniques, 280–284 patient positioning, 284 persistent subfoveal CNV, 286 postoperative review, 285–286 recurrent subfoveal CNV, 286 Linear basal deposits, 3–4 Linkage mapping, 39–40 Lipid levels, as risk factor in macular-degeneration, 62 Lipid metabolism, 38 Low density lipoprotein (LDL), 19 Low vision evaluation, 303–307 Low vision rehabilitation, 151 Lucentis, 248–250 Lutein, 72 Macrophage-mediated injury, glomerular diseases and, 22 Macrophages, 14–15, 20 antigen presenting cells (APC), 15 apolipoprotein E (ApoE), 20 Macugen, 247–248 Macular degeneration, non-exudative, 103–106 Macular Photocoagulation Study, 203–205 decreased vision, 205 extrafoveal CNV, 141–142 juxtafoveal CNV, 142

INDEX

[Macular Photocoagulation Study] subfoveal CNV, 142–143 trials, 205 (MPS) Macular pigment optical density, as risk factors in macular-degeneration, 57–58 age-related eye disease study (AREDS), 58 Macular translocation, 273–292 anatomic considerations, 277–279 classification and terminology of, 274 complications from, 290–291 intraoperative, 290 postoperative, 290–291 historical background of, 275 indications, 275–276 exudative macular degeneration, 275–276 non-exudative macular degeneration, 276 subfoveal RPE defect, 276 limited, 279–280 outcome, 288–290 pathophysiologic considerations re visual loss, 276–277 postoperative cyclovertical diplopia, 287–288 preoperative considerations, 276–279 rationale, 274–275 3608 retinotomy, 287 Macular transplantation, clinical results, 333–335 Mast cells, 15–16 Micronutrients, 68 Microperimetry, 187–188 MMP-9, 37 Monoclonal antibodies, 248–251 bevacizumab, 250–251 ranibizumab, 248–250 Monocytes, 14–15 MPS. See macular photocoagulation study. Multi-candidate gene screening, 39 Natural history, exudative (neovascular) age-related macular degeneration and, 140–141 Natural immunity. See innate immunity. Neovascularization (NV) inferences, 87 transcription factors, 89 Neurosensory retina changes in, 3 detachment, 281–283 Neurotransmitter-based prothesis, 325–326 Nodular drusen, 4 Non-exudative age related macular degeneration (AMD), 1–5, 103–106, 171 age-related eye disease study (AREDS), 106 basal deposits, 3–4 Bruch’s membrane, changes in, 1 choriocapillaris, changes in, 2–3 choroidal neovascularization, 1–2 drusen, 4–5 geographic atrophy, 5 macular translocation and, 276 monitoring of, 103–106 neurosensory retina, changes in, 3 optical coherence tomography and assessment of, 179–181 retinal pigment epithelium, changes in, 1–2

361

Nonocular degenerative diseases immune mechanisms, 19–23 atherosclerosis, 19–21 inflammatory mechanisms, 19–23 Nonocular risk factors, exudative (neovascular) age-related macular degeneration and, 126–127 Nonspecific amplification mechanism, glomerular diseases and, 23 Nutrition antioxidants, 68–70 micronutrients, 68 as risk factors in macular degeneration, 68–73 zinc, 70 NV. See neovascularization. Occult choroidal neovascularization, 143–144 Occult CNV, 161 focal, 162 hot spot, 162 Occult subretinal pigment epithelium, 6 OCT. See optical coherence tomography. Ocular factors, age-related macular degeneration risk factors and, 57–60 cataract surgery, 58–59 cup/disc ratio, 60 iris color, 59–60 macular pigment optical density, 57–58 refractive error, 60 Ocular histoplasmosis syndrome, 24 Ocular immune disorder, 24–25 atrophic retinal degeneration, 24–25 choroidal neovascularization (CNV), 24–25 complement activation, 24–25 histoplasmosis syndrome, 24 Ocular risk factors, exudative (neovascular) age-related macular degeneration and, 127 age-related eye disease study (AREDS), 127 Optic nerve prostheses, 320 Optical coherence tomography (OCT), 177–183 age-related macular degeneration treatment, 181–183 assessment of choroidal neovascularization, 177–179 non-exudative macular degeneration, 179–181 imaging principles, 177–183 normal imaging, 177–183 quantitative retinal imaging and, 186 Oxidants, 14, 21 Oxidative damage, age-related macular degeneration gene pathogenesis and, 39 Paracentral scotomas, 116–117 Pars plana vitrectomy, 281 Pathogenesis choroidal neovascularization and, 89–90 geographic atrophy, 112 Patient positioning, limited macular translocation and, 284 PDT. See photodynamic therapy. PED. See pigment epithelial detachment.

362

INDEX

Pegaptanib sodium, 247–248 Peripherin/RDS gene, 37 Pharmacologic treatment, choroidal neovascularization and, 90–91 Photodynamic therapy (PDT), 144–145, 223–229 agents of, 224–225 benzoporphyrin derivative monoacid, 225 anti-vascular endothelial growth factor and, 251 clinical results, 225–229 age-related macular degeneration, 226–227 verteporfin trials, 226 laser light application, 224 light types, 225 treatment evolution of, 228–229 vascular targeting, 223–224 Pigment epithelial detachment (PED), 133–135 Planned neurosensory retinal detachment, 281–283 Plaque, 162–163 Polypoidal choridal vasculopathy, 139, 163–164 Postoperative complications, macular translocation and, 290–291 Postoperative cyclovertical diplopia, management of, 287–288 Proangiogenic factors, 88 Prostheses, retinal, 319–326 Quantitative retinal imaging, 185–189 fluorescein angiography (FA), 186 fundus photography, 185–186 microperimetry, 187–188 optical coherence tomography (OCT), 186 Race, as risk-factor in macular-degeneration, 55–56 Radiation studies, review of, 237–243 Radiation therapy, 148 Radiation treatment, age-related macular degeneration and, 233–243 Radiation treatment delivery methods, 235–237 charged particle, 236–237 implant therapy, 236 Radiation treatment toxicity issues, 234–235 Ranibizumab, 248–250 Lucentis, 248–250 Real-time indocyanine green angiography (ICGA), 170 Receptor tyrosine kinase inhibitors, 150, 253–254 Recurrent CNV, 168–169 Refractive error, as risk factors in maculardegeneration, 60 Reproduction system, age-related macular degeneration risk factors and, 64 estrogen-related, 64 Retinal angiomatous proliferation, 139–140, 164–167 Retinal dystrophies, 36–37 Retinal pigment epithelial cell attachment age-related changes and effects of, 337 Bruch’s membrane, 335–337 cell survival, 335 prior and handling and effects of, 336–337 tissue culture, 335

Retinal pigment epithelial cell transplantation clinical results, 333–335 harvesting technique, 332 rationale for, 330–332 Retinal pigment epithelium (RPE), 1 changes in, 1–2 Retinal prostheses, 319–326 extraocular approaches, 319–320 cortical, 319–320 optic nerve, 320 scleral based, 320 intraocular approaches, 320–326 epiretinal prosthesis, 320–323 neurotransmitter-based, 325–326 subretinal, 323–325 Risk factors, age-related macular degeneration and, epidemiologic studies, 47 RNAs, small interfering, 253 RPE. See retinal pigment epithelium. Sattler’s layer vessels, 212–217 Scleral based extraocular stimulation, 320 Scotomas, 116–117 Serous pigment epithelial detachment, 161 Serum lipid levels, as risk factors in maculardegeneration, 62 siRNA. See small interfering RNAs. Small interfering RNAs (siRNAs), 253 type therapy, 149 Smoking cigarettes, as risk factor in maculardegeneration, 64–66 Sociodemographic factors, age-related macular degeneration risk factors and, 53–57 age, 53, 54 heredity, 56–57 race/ethnicity, 55–56 socioeconomic status, 57 Socioeconomic status, as risk-factor in maculardegeneration, 57 Soft drusen, 4–5, 100–101 Soluble antiangiogenic factors, 88 Soluble proangiogenic factors, 88 Squalamine lactate, 150 Subfoveal CNV, 141, 142–143 management of, 286 Subfoveal RPE defect, macular translocation and, 276 Subretinal choroidal neovascularization classic type, 6, 7 type 2 growth pattern, 5–6 Subretinal injection, triamcinolone acetonide (TA), 297–298 Subretinal pigment epithelium choroidal neovascularization occult type, 6 type 1 growth pattern, 5–6 Subretinal prosthesis, 323–325 Sunlight exposure, as risk factors in macular degeneration, 66–67 Surgical therapy for choroidal neovascularization, 148

INDEX

Systemic diseases, age-related macular degeneration and, 98 cardiovascular diseases, 98 hypercholesterolemia, 98 hypertension, 98 Systemic factors, age-related macular degeneration risk factors and BMI ratio, 63 cardiovascular biomarkers, 63 disease, 60–65 Chlamydia pneumoniae infection, 63–64 cigarettes, 64 diabetes, 62–63 dietary fat intake, 62 hematologic factors, 63 hyperglycemia, 62–63 hypertension and blood pressure, 61–62 serum lipid levels, 62 waist conference, 63 waist-hip ratio, 63 Systemic risk factors, geographic atrophy and, 112–113 T lymphocytes, 16 TA. See triamcinolone acetonide. Thermotherapy, 147–148 3608 retinotomy, 287 TIMP3 gene, 37 Tissue culture, retinal pigment epithelial cell attachment and, 335 Tissue plasminogen activator, 295–396 Transcription factors, neovascularization and, 89 Triamcinolone acetonide (TA), 297–298 subretinal injection, 297–298 Tubulin binding agents, 150–151 combretastatin A-4 phosphate, 150 Twin aggregation studies, 35–36 Type 1 growth pattern, 5–6 Type 2 growth pattern, 5–6

363

Vascular endothelial growth factor (VEGF), 87–91 drugs and clinical trials, 247–254 extracellular matrix (ECM), 88–89 soluble antiangiogenic factors, 88 proangiogenic factors, 88 trap therapy, 149–150 Vascular endothelial growth trap, 252–253 Vascular targeting, 223–224 VEGF. See vascular endothelial growth factor. Verteporfin, 225 trials, 226, 227–228 Visual function impairment central scotomas, 116–117 dimly lit environments, 117–118 geographic atrophy and, 116–118 other abnormalities, 118 paracentral scotomas, 116–117 Visual loss, considerations re, 276–277 Visual rehabilitation clinical considerations, 303–317 low vision evaluation, 303–307 new applications, 307–308 new technologies, 308–316 Visudyne e, 225 VMD2 gene, 37 Waist conference, as risk factor in maculardegeneration, 63 Waist-hip ratio, as risk factor in maculardegeneration, 63 Wet age related macular degeneration (AMD). See exudative age related macular degeneration (AMD). Wide angle indocyanine green angiography (ICGA), 170 Zeaxanthin, 72 Zinc, 70