REVISION CLINICAL OPTICS

REVISION CLINICAL OPTICS

REVISION CLINICAL OPTICS Montague Ruben and E. Geoffrey Woodward Drawings by Terry Tarrant M

Text Montague Ruben and E. Geoffrey Woodward 1982 Illustrations Terry Tarrant 1982 Softcover reprint of the hardcover 1st edition 1982 All rights reserved. No part of this publication may be reproduced or transmitted, in any form or by any means, without permission. First published 1982 by THE MACMILLAN PRESS LTD London and Basingstoke Companies and representatives throughout the world ISBN 978-0-333-30705-2 ISBN 978-1-349-16806-4 (ebook) DOI 10.1007/978-1-349-16806-4 The paperback edition of the book is sold subject to the condition that it shall not, by way of trade or otherwise, be lent, resold, hired out, or otherwise circulated without the publisher's prior consent in any form of binding or cover other than that in which it is published and without a similar condition including this condition being imposed on the subsequent purchaser.

Preface This text was first published almost twenty years ago by the Institute of Ophthalmology, London, for the use of postgraduate students taking the D.O. course. Prof. Montague Ruben selected and designed the drawings, which were drawn by Mr T. Tarrant. A second edition some years later included a short text for each drawing, but it has long since been out of print. The present text is designed as a revision text to supplement courses on ophthalmic optics and does not pretend to replace textbooks recommended by teachers. It may be of use to the student who is preparing for examinations in ophthalmology, optometry or orthoptics, and provides a quick method of revision; in particular it will enable the student to discover areas where further tutorials, or the reading of larger texts, are required. The new text has been coauthored by Dr Geoffrey Woodward, thus combining the attitudes of ophthalmologist and optometrist. The text has been enlarged and revised by including physiological optics and most instruments in current use. London, 1982 M.R. E.G.W.

Acknowledgeme11ts We have been fortunate in obtaining once again the services of Mr Terry Tarrant who has done all the drawings. The diagrams on pp. 149 to 151 were prepared with the help of Dr M. Guill on, PhD, FBOA. The authors wish to thank the Institute of Ophthalmology for permission to use the original drawings of Diagrammatic Outline of Clinical Optics, by M. Ruben and T. Tarrant, second edition, 1966.

Contents Preface Acknowledgements v vi SECTION I PHYSIOLOGICAL OPTICS Absolute Threshold Definition Transmittance of Cornea Lattice Theory Transmittance of the Human Lens at Various Ages Transmittance of Ocular Media The Stiles-Crawford Effect Adaptation Definition Cone (foveal) dark adaptation Rod (peripheral) dark adaptation Cone and rod combined to produce a typical dark adaptation curve Factors which slow adaptation Method of measurement (Goldman adaptometer) Rise in Dark Adaptation Threshold in Vitamin A Starvation Dark Adaptation of Different Parts of the Retina Purkinje Shift The Pulfrich Phenomenon The Critical Frequency of Flicker 3 3 5 6 7 8 9 10 11 11 11 12 12 12 13 14 15 16 17

After-Images Saccadic Suppression Field of Vision - Isopters Traquair's Island Field Analyser (Goldman Type) Colour Vision The CIE chromaticity diagram The anomaloscope (Nagel) Colour-vision tests Visual Acuity Resolution The Snellen system of recording visual acuity Visual acuity and level of illumination Variation of visual acuity across the retina Relationship between threshold visual angle and dioptres of spherical error of refraction Optokinetic drum 18 19 20 21 22 23 23 24 26 28 28 30 31 33 34 35 SECTION II BASIC OPTICS Sign Convention Diffraction of Light Interference and Wave Motion Diffraction from a Thin Film Polarisation Polariser Prism Reflection of Light The Law of Refraction (Snell's Law) Reduced vergence The critical angle Refraction by a prism Prism Dioptre Refraction at a Curved Surface Change of Vergence at a Curved Surface Principal rays, focal points and other conjugate points 39 40 41 42 43 44 45 48 51 52 53 55 56 57 58

The Lens Image formation Rays from extra-axial points The cylindrical lens The sphero-cylinder Sturm's conoid Thick lens principal points 59 60 61 62 64 65 66 SECTION III CLINICAL OPTICS Back Vertex Power Thick Lens Shapes or Forms Toric Surfaces and Lenses Prism-Induced Effect Thin Lens Forms Positive lenses Negative lenses Refraction by a Lens Using the principles of tangents and prisms Refraction by two lenses Magnification of Objects Simple microscope Image Formation with a Negative Lens Reflection From a curved convex surface From a curved concave surface From the eye's curved surfaces Aberrations From curved surface refraction - spherical aberrations From lenses Oblique astigmatism Magnification distortion Prism aberration Effective Power Power in different planes Power of a lens 69 70 71 72 73 73 74 75 75 76 77 77 78 79 79 81 82 84 84 85 86 87 88 89 89 90

Near and Distance Fixation and Ocular Refraction Myopia Hyperopia Multivision Spectacle Lenses Bifocals Multifocals Fitting 91 91 92 93 95 100 102 SECTION IV VISUAL OPTICS The Schematic (Average) Eye The Emmetropic and Ametropic Eye Ametropia Correction of ametropia Correction of hyperopia Ocular Astigmatism Retinal Image Size (R.I.S.) (Spectacle Magnification) Axial Myopia and Magnification of Image Relative Magnification and Myopia Magnification of Images in Myopia Aphakia Temporary aphakia spectacles Magnification with correction Aphakia and Retinal Image Magnification Pseudo-lens plastic implant Pseudo-lens implant powers Fixation Axis Relationship to Optic Axis Accommodation Accommodation and Hyperopia Depth of Focus 105 106 107 109 111 112 113 114 115 116 117 118 118 120 121 122 123 124 125 126 SECTIONV INSTRUMENTS Focimeter to Measure Lens Power (The Lensometer) Woolaston Prism Used for Doubling the Image 131 134

The Ophthalmoscope (Direct) The Ophthalmoscopy of the Emmetropic Eye Direct Opthalmoscopy Use as visuscope and optometer Use for fixation location and slit beam Pleoptoscope Slit-beam projection Optical magnification in emmetropia Magnification in myopia Indirect Ophthalmoscopy The observation system and magnification Self-illuminated binocular instrument Fundus Camera Objective Refraction Retinoscopy Automated instrumentation Humphrey's Subjective Refractometer Astigmatism Jackson's cross-cylinder The pin-hole and the Scheiner disc Compound Microscope Slit-Lamp Microscope The Corneal Pachometer Zoom-Lens Principle Operation Microscope (Zoom) Telescopes Java1 Schiotz 'Keratometer' (Ophthalmometer) Placido Disc Keratoscope (Klein-Keeler) The Photokeratoscope (The Wesley-Jessen P.E.K.) Contact Lenses Measurement of back curves of contact lens The Radiuscope (Using Drysdale's Principle) Sagitta Sagitta system applied to radius measurement of contact lenses 134 135 136 136 137 138 138 138 139 140 140 142 143 144 144 149 152 153 153 154 155 156 157 158 159 160 162 164 164 165 169 170 171 172

Gonioscope Contact Lens Various Miniature Gonioscopes and Fundus-Viewing Contact Lenses Fundus-viewing contact lens Applanation Tonometer Specular Microscopy 172 174 174 176 176 SECTION VI BINOCULAR VISION Horopter Panum's Area Crossed and Uncrossed Diplopia Diplopia in Strabismus Change of Apparent Size of Objects with Convergence and Divergence Stereoscopes Mirror Stereoscopes Aniseikonia (Image Size Difference) Synoptophore (Haploscope) Maddox Rod Prism Effect of Spectacles Convergence 179 180 181 182 183 184 185 186 187 187 188 189 SECTION VII MISCELLANEOUS Exophthalmometer (Hertel) Magnifying Aids Coherent Light and Laser Fresnel's Principle 193 194 195 196