Document file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=cover.html9/30/2006 2:34:05 PM Document Page i Clinical Optics file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_I.html9/30/2006 2:34:28 PM Document Page ii Other books of interest Clinical Orthoptics Fiona Rowe 0 632 04274 5 Diagnosis and Management of Ocular Mobility Disorders Second Edition A. Anson & H. Davis 0 632 04798 4 Ocular Anatomy and Physiology T. Saude 0 632 03599 4 Clinical Anatomy of the Eye R.S. Snell & M.A. Lemp 0 632 04344 X Orthoptic Assessment and Management Second Edition D. Stidwill 0 632 05012 8 file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_II.html9/30/2006 2:34:29 PM Document Page iii Clinical Optics Third Edition Andrew R. Elkington CBE, MA, FRCS, FRCOphth Consultant Ophthalmologist Southampton Eye Unit Southampton General Hospital. Professor of Ophthalmology University of Southampton. President, Royal College of Ophthalmologists (1994–1997). Helena J. Frank BMedSci, FRCS, FRCOphth Consultant Ophthalmologist Royal Victoria Hospital Bournemouth. Michael J. Greaney MD, FRCSEd, FRCOphth Specialist Registrar Southampton Eye Unit Southampton General Hospital. file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_III.html (1 of 2)9/30/2006 2:34:30 PM Document Page iv © 1984, 1991, 1999 by Blackwell Science Ltd Editorial Offices: Osney Mead, Oxford OX2 0EL 25 John Street, London WC1N 2BL 23 Ainslie Place, Edinburgh EH3 6AJ 350 Main Street, Malden MA 02148 5018, USA 54 University Street, Carlton Victoria 3053, Australia 10, rue Casimir Delavigne 75006 Paris, France Other Editorial Offices: Blackwell Wissenschafts-Verlag GmbH Kurfürstendamm 57 10707 Berlin, Germany Blackwell Science KK MG Kodenmacho Building 7–10 Kodenmacho Nihombashi Chuo-ku, Tokyo 104, Japan The right of the Author to be identified as the Author of this Work has been asserted in accordance with the Copyright, Designs and Patents Act 1988. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, except as permitted by the UK Copyright, Designs and Patents Act 1988, without the prior permission of the publisher. First edition published 1984 Reprinted 1988 Second Edition published 1991 Reprinted 1995, 1997 Third Edition published 1999 Set in 10/13pt Palatino by DP Photosetting, Aylesbury, Bucks Printed and bound in Great Britain by MPG Books Ltd., Bodmin, Cornwall The Blackwell Science logo is a trade mark of Blackwell Science Ltd, registered at the United Kingdom Trade Marks Registry file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_IV.html (1 of 3)9/30/2006 2:34:30 PM Document DISTRIBUTORS Marston Book Services Ltd PO Box 269 Abingdon Oxon OX14 4YN (Orders: Tel: 01235 465500 Fax: 01235 465555) USA Blackwell Science, Inc. Commerce Place 350 Main Street Malden, MA 02148 5018 (Orders: Tel: 800 759 6102, 781 388 8250 Fax: 781 388 8255) Canada Login Brothers Book Company 324 Saulteaux Crescent Winnipeg, Manitoba R3J 3T2 (Orders: Tel: 204 837-2987 Fax: 204 837-3116) Australia Blackwell Science Pty Ltd 54 University Street Carlton, Victoria 3053 (Orders: Tel: 03 9347 0300 Fax: 03 9347 5001) A catalogue record for this title is available from the British Library ISBN 0-632-04989-8 file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_IV.html (2 of 3)9/30/2006 2:34:30 PM Document Library of Congress Cataloging-in-Publication Data Elkington, A.R. Clinical optics/Andrew R. Elkington, Helena J.Frank, Michael J. Greaney. – 3rd ed. p. cm. Includes bibliographical references and index ISBN 0-632-04989-8 (pbk.) 1. Physiological optics. 2. Optics. I. Frank, Helena J. II. Greaney, Michael J. III. Title. [DNLM: 1. Eye Diseases–physiopathology. 2. Lenses. 3. Optics. 4. Refraction, Ocular. WW 300 E43c 1999] QP475.E48 1999 617.7'5–dc21 DNLM/DLC for Library of Congress 99-20296 CIP For further information on Blackwell Science, visit our website: www.blackwell-science.com file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_IV.html (3 of 3)9/30/2006 2:34:30 PM Document Page v Contents Preface to the Third Edition vii Acknowledgements viii 1 1 Properties of Light and Visual Function 2 25 Reflection of Light 3 33 Refraction of Light 4 43 Prisms 5 54 Spherical Lenses 6 66 Astigmatic Lenses 7 74 Optical Prescriptions, Spectacle Lenses 8 89 Aberrations of Optical Systems Including the Eye 9 99 Refraction by the Eye 10 113 Optics of Ametropia file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_V.html (1 of 2)9/30/2006 2:34:31 PM Document 11 141 Presbyopia 12 152 Contact Lenses 13 160 Optics of Low Vision Aids 14 165 Instruments 15 216 Lasers 16 230 Practical Clinical Refraction 17 242 Refractive Surgery Appendix I 255 Appendix II 256 Index 257 file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_V.html (2 of 2)9/30/2006 2:34:31 PM Document Page vii Preface to the Third Edition In the preface to the second edition of this book we stressed that we had written the text in the hope of helping those trainee eye surgeons who were preparing to take their basic professional examinations. We assumed that the optics they had learned at school had long since been forgotten, and we therefore set out to explain the subject from first principles. Our aim was to keep the text logical and simple and we used diagrams liberally to complement the written word. These diagrams themselves were simplified so that they could be both easily memorised and reproduced – even under the stress of examination conditions. Throughout the book we emphasised the clinical relevance of each topic and we hoped that this approach would allow readers to understand better the optical problems experienced by many of their patients. During the eight years since that edition was published, many changes have taken place in the practice of ophthalmology. New methods of examination have become available, including sophisticated automated visual field analysers. There have been great advances in the design of intraocular lenses. Corneal refractive surgery has become more popular and also more complex. There are many new types of lasers in clinical use. All these advances depend upon the application of basic optical concepts in new settings. In writing this third edition we have taken the opportunity to identify these principles and to explain their application in the context of modern ophthalmic practice. In so doing our aim remains the same, namely to enhance the care of patients by helping ophthalmologists to master the optical principles that underpin so much of their everyday work. file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_VII.html9/30/2006 2:34:32 PM Document Page viii Acknowledgements It is a pleasure to pay a tribute to Dr. Jock Anderson OBE FRCS, who both commented on the typescript and prepared the index. We thank, too, our Publishers for inviting us to write the third edition and for their subsequent encouragement and support in the preparation of this book. A.R.E. H.J.F. M.J.G. APRIL 1999 file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_VIII.html9/30/2006 2:34:32 PM Document Page 1 1— Properties of Light and Visual Function Light may be defined as energy to which the human eye is sensitive. Scientists do not yet fully understand the true nature of light in the physical sense, but the behaviour and properties of light have been extensively studied and are well known. This book aims to describe with the aid of diagrams those aspects of optics which are relevant to the practising ophthalmologist. In this first chapter a simple account is given of the nature and properties of light. Electromagnetic Spectrum: Optical Radiation Optical radiation lies between X-rays and microwaves in the electromagnetic spectrum (Fig. 1.1), and is subdivided into seven wavebands. Each of these seven wavebands group together wavelengths which elicit similar biological reactions. These seven domains are ultraviolet C (UV-C), 200– Fig. 1.1 The electromagnetic spectrum. file:///C|/download/www.netlibrary.com/nlreader/nlreader.dll@bookid=51924&Filename=Page_1.html9/30/2006 2:34:32 PM Document Page 2 280 nm; ultraviolet B (UV-B), 280–315 nm; ultraviolet A (UV-A), 315–400 nm; visible radiation, 400– 780 nm; infrared A (IRA), 780–1400 nm; infrared B (IRB), 1400–3000 nm; and infrared C (IRC), 3000– 10000 nm. As with all electromagnetic radiation, the shorter the wavelength, the greater the energy of the individual quanta, or photons, of optical radiation. The cornea and sclera of the eye absorb essentially all the incident optical radiation at very short wavelengths in the ultraviolet (UV-B and UV-C) and long wavelengths in the infrared (IR-B and IR-C). The incident UV-A is strongly absorbed by the crystalline lens while wavelengths in the range 400– 1400 nm (visible light and near infrared), pass through the ocular media to fall on the retina. The visible wavelengths stimulate the retinal photoreceptors giving the sensation of light while the near infrared may give rise to thermal effects. Because the refractive surfaces of the eye focus the incident infrared radiation on the retina, it can cause retinal damage, e.g. eclipse burns. Colour Vision The visible wavelengths of the electromagnetic spectrum are between 400 nm and 780 nm.