© 2007, Elsevier Limited. All rights reserved. First published 2007

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, without the prior permission of the Publishers. Permissions may be sought directly from Elsevier’s Health Sciences Rights Department, 1600 John F. Kennedy Boulevard, Suite 1800, Philadelphia,

PA 19103-2899, USA: phone: (+1) 215 239 3804; fax: (+1) 215 239 3805; or, e-mail: healthpermissions@elsevier.com. You may also complete your request on-line via the Elsevier homepage (http://www.elsevier.com), by selecting ‘Support and contact’ and then ‘Copyright and Permission’.

ISBN-13: 978-07506-1815-1

ISBN-10: 0-7506-1815-9

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library.

Library of Congress Cataloging in Publication Data

A catalog record for this book is available from the Library of Congress.

Note

Neither the Publisher nor the Editors assume any responsibility for any loss or injury and/or damage to persons or property arising out of or related to any use of the material contained in this book. It is the responsibility of the treating practitioner, relying on independent expertise and knowledge of the patient, to determine the best treatment and method of application for the patient.

The Publisher

Working together to grow libraries in developing countries

www.elsevier.com | www.bookaid.org | www.sabre.org

The publisher’s policy is to use

paper manufactured from sustainable forests

Printed in China

Foreword

It may seem paradoxical, but visual impairment and the need for its rehabilitation are becoming more important because of improving health care. Worldwide, longevity is increasing. Having a larger proportion of the population in the older age groups means a higher prevalence of visual impairment because vision loss predominantly results from age-related diseases and disorders. As new or improved treatments are developed for various disabling eye diseases, there will inevitably be some shifts in the relative importance of different eye diseases, but for the foreseeable future, we can expect the incidence of age-related vision loss to continue to rise. Low vision care will continue to become increasingly important.

The goal of low vision rehabilitation is to minimise any functional impediments imposed by vision loss. In part, this is done by gaining as much use as possible from the patient’s remaining visual abilities. In this process, the ophthalmic clinician’s first task is to identify and understand the functional difficulties that the individual experiences as a direct or indirect result of their visual limitations. Tasks associated with reading, face recognition and mobility are likely to remain around the top of the list. Second, the clinician seeks a more detailed assessment of the individual’s vision through examining the eyes in order to better understand the causative pathology and the prognosis, evaluating the refractive characteristics of the eyes, and performing a range of tests of visual function. Visual acuity, visual fields, contrast sensitivity,

vii

Foreword

colour vision, light and dark adaptation, oculo-motor control and glare disability are all relevant and clinically-quantifiable visual functions. However, it is not enough to simply measure thresholds. Clinicians should also evaluate the ease, efficiency and accuracy of task performance, and dependencies on more subtle variation in the visual stimulus, such as lighting levels and visual clutter. As the third part of the process, the ophthalmic clinician’s job is to consider ways in which the performance of the patient’s visual tasks can be optimised or facilitated though optical manipulations by magnification, minification, prisms, filters, lighting control and through the use of electronic display systems or through training specific visual skills.

Taking care of the visual aspects of the patient’s tasks is only part of the overall rehabilitation process for the visually impaired patient. Accessing other rehabilitative services and support can be crucial. Rehabilitation specialists, mobility instructors, occupational and physical therapists, special educators and social workers are all important parts of the team of rehabilitation professionals that can provide strategies, techniques and training for improving task performance, or facilitating the use of devices that can make some tasks less dependent on vision. Often the psychological, social and recreational needs of visually impaired individuals warrant considerable attention and support from family, friends and, sometimes, professionals. For many, especially those who acquire their vision loss in adult life, there will be a need for vocational counselling and training, along with accommodations being made in the workplace environment.

Technological developments are presenting exciting new opportunities but also new challenges for low vision rehabilitation. In particular, display technologies are allowing a lot more scope for optimising the display of printed material to our visually impaired patients. Electronic display systems offer much more flexibility than the more traditional optical low vision aids. Most videomagnifiers allow easy variations in print size, contrast, luminance and colour of the printed or pictorial displays. The same set of visual parameters can be varied on computer-controlled display screens, but computerisation expands the range of modifications of the visual display through reformatting by changing font, style, columns, rows, spacing, highlighting, controlled scrolling, streaming, and other modes of visual presentation. Computers can also enable the information to be displayed as speech output or tactile output that may be used to supplement or replace the usual visual

viii

Foreword

screen images. In most societies, the information technology revolution is changing the visual demands of daily life. Mobile phones, automatic bank telling machines and similar displays for business transactions are becoming more commonly encountered by people from all walks of life. In Western societies at least, personal computers are becoming more important to individuals as the favoured means of communicating with friends, paying bills, checking bank and business records, as well as using the web-based technologies to access information for a wide variety of recreational, occupational, spiritual and intellectual purposes. Despite their difficulties in acquiring skills to use a keyboard or a mouse, the elderly are rapidly expanding their use of computers. In the least technologically-developed countries, there is currently an exponential increase in the use of mobile phones and the associated expansion of access to information technology through both visual and auditory displays.

With many of these electronically-controlled displays, there is scope for the user to experiment and make their own choices of display parameters. However, because ophthalmic clinicians understand eye diseases and their effects on vision, and they know how the visual system works and how visual images and displays may be manipulated, these practitioners should be able to provide well-informed advice and guidance on the selection of the display parameters, and on which methods and strategies are best for the individual. Whether the displayed image comes from an optical system or a display screen, the skills of ophthalmic clinicians are needed to provide the optical corrections so often required to ensure that the retinal image is in satisfactory focus.

Only a relatively small fraction of optometrists and ophthalmologists are specialising in low vision rehabilitation, maintaining a high level of expertise, and developing close working associations with other low vision rehabilitation specialists. Fewer still are active in research into relationships between functional performance, visual functions and quality of life, or in the development of improved methods for assessing visual functions or methods for training visual skills, or in creating new optical and electronic systems to assist visually impaired patients. But it is not just the experts who need to know about low vision rehabilitation. All optometrists and ophthalmologists engaged in clinical practice have a responsibility to be informed about low vision rehabilitation and what it can do. All eye-care practitioners need to be knowledgeable about today’s newly emerging pharmacological,

ix

Foreword

surgical and genetic treatments that hold promise for reducing the occurrence or severity of certain eye diseases. They need to be able to answer their patients’ questions on such matters, and to make appropriate referrals. As society’s experts in vision, all optometrists and ophthalmologists have a similar responsibility to be knowledgeable about methods for assessing functional vision, and the possibilities of patients benefiting from the use of the various optical and electronic low vision aids. As part of a healthcare delivery system, they all have a responsibility to be acquainted with the range of rehabilitation services and support systems that are available to visually impaired persons.

This Low Vision Manual presents a technically sound, comprehensive and up-to-date account of low vision rehabilitation that will serve as an excellent guide and resource for students and clinicians wishing to develop their knowledge and skills in low vision care. For those who simply wish to familiarise themselves with the state of the art in low vision care today, this Manual will be an accessible and valuable source of information. For clinicians who are already expert, this Low Vision Manual will provide new information and new insights from its knowledgeable team of authors.

Ian L. Bailey

x