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GUIDE for the Evaluation of VISUAL Impairment

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GUIDE for the Evaluation of VISUAL Impairment International Society for Low vision Research and Rehabilitation GUIDE for the Evaluation of VISUAL Impairment Published through the Pacific Vision Foundation, San Francisco for presentation at the International Low Vision Conference VISION-99. TABLE of CONTENTS INTRODUCTION 1 PART 1 – OVERVIEW 3 Aspects of Vision Loss 3 Visual Functions 4 Functional Vision 4 Use of Scales 5 Ability Profiles 5 PART 2 – ASSESSMENT OF VISUAL FUNCTIONS 6 Visual Acuity Assessment 6 In the Normal and Near-normal range 6 In the Low Vision range 8 Reading Acuity vs. Letter Chart Acuity 10 Visual Field Assessment 11 Monocular vs. Binocular Fields 12 PART 3 – ESTIMATING FUNCTIONAL VISION 13 A General Ability Scale 13 Visual Acuity Scores, Visual Field Scores 15 Calculation Rules 18 Functional Vision Score, Adjustments 20 Examples 22 PART 4 – DIRECT ASSESSMENT OF FUNCTIONAL VISION 24 Vision-related Activities 24 Creating an Activity Profile 25 Participation 27 PART 5 – DISCUSSION AND BACKGROUND 28 Comparison to AMA scales 28 Statistical Use of the Visual Acuity Score 30 Comparison to ICIDH-2 31 Bibliography 31 © Copyright 1999 by August Colenbrander, M.D. All rights reserved. GUIDE for the Evaluation of VISUAL Impairment Summer 1999 INTRODUCTION OBJECTIVE Measurement Guidelines for Collaborative Studies of the National Eye Institute (NEI), This GUIDE presents a coordinated system for the Bethesda, MD evaluation of the functional aspects of vision. It has been prepared on behalf of the International WORK GROUP Society for Low Vision Research and Rehabilitation (ISLRR) for presentation at The GUIDE was approved by a Work Group VISION-99, the fifth International Low Vision including the following members: conference. The GUIDE is based on currently August Colenbrander, MD, Chair, available standards. This means that some parts, Director, Low Vision Services, California for which standardized measuring tools are still Pacific Medical Center, and Smith-Kettlewell lacking, are not yet developed in as much detail as Eye Research Institute, San Francisco would be desirable. It is hoped that input received over the next three years will allow presentation Aries Arditi, PhD, Vice-President for Vision of an updated version at the VISION-2002 Science, Lighthouse International, New York, conference and at future tri-annual conferences Co-chair, Scientific Committee for the thereafter. Vision-99 Conference The assessment of young children and multiply Ian Bailey, OD, Director of Low Vision, School handicapped individuals is another area where of Optometry, University of California - more extensive guidelines may be developed for Berkeley VISION-2002. Eleanor Faye, MD, Consultant, Lighthouse International Center for Vision and Aging, SOURCES New York The GUIDE is based on current concepts and Donald Fletcher, MD, Past-Chair, Low Vision insights and conforms to the Rehabilitation Committee, American Academy of Ophthalmology Classification of Vision Loss as found in ICD-9- CM (code 369) (1978), based on the Lea Hyvärinen, MD, Vision Rehabilitation recommendations of the World Health Specialist, Helsinki, Finland Organization (WHO) and the International Alan Johnston, PhD, Low Vision Researcher, Council of Ophthalmology (ICO) University of Melbourne International Classification of Impairments, Robert Massof, PhD, Director, Low Vision Disabilities and Handicaps (ICIDH), by the Center, Wilmer Eye Institute, Johns Hopkins World Health Organization (WHO) (1980) University, Baltimore, MD and its replacement (ICIDH-2) (in preparation) Anne L. Corn, Ed.D, Professor of Special Education, Vanderbilt University, Tennessee Visual Acuity Measurement Standard (1984) of the International Council of Mary Warren, OT, Low vision Rehabilitation Ophthalmology (ICO) Specialist, Kansas City, MO Standard # 8596 – Visual Acuity testing (1994) of the International Standards Organization RELATION to the AMA GUIDES (ISO) The purpose of PART 2 and PART 3 of this GUIDE is similar to that of the AMA Guides for the Evaluation of Permanent Impairment. Page 1 GUIDE for the Evaluation of VISUAL Impairment Summer 1999 However, the scales in this GUIDE differ from other than visual acuity and visual field. (See the those presented in the 4th edition (1993) of the list on page 4). Vision chapter of the AMA Guides. Neither have standardized scales been developed A new Guide was needed since the Vision section for the various activities that constitute functional in the 4th edition of the AMA Guides is still based vision (see Part 4). Such scales are needed for the on employability studies from 1925 and has proper assessment of rehabilitation needs. accumulated multiple internal inconsistencies over The GUIDE does not address the assessment of the course of multiple revisions. These children and multi-handicapped individuals. differences are discussed in PART 5 of this GUIDE. Finally, this GUIDE shows some bias towards conditions in the United States, since detailed The next, 5th edition of the AMA Guides, which is comparisons of assessment methods in other presently in preparation and is expected to be counties were not readily available. published in 2000, is expected to conform to the scales in this GUIDE. In the mean time, the It is hoped that the publication of this GUIDE will scales presented in this GUIDE could be stimulate others to contribute their experiences combined with the evaluation guides for other and promote continued development in each of organ systems in the 4th edition of the AMA the mentioned areas. The next three years will Guides, when this is desirable. hopefully see continued development of standardized performance scales and assessment practices. When such scales have been ASSESSMENT of CHILDREN developed, a new, updated revision of this GUIDE This GUIDE is primarily directed at acquired may be possible for presentation at the next vision loss in adults. Special consideration needs International Low Vision conference: VISION- to be given to the assessment of vision in young 2002. Publication of further updates may thus children and in multi-handicapped individuals. become a standard feature of future tri-annual conferences Preferred-Looking tests and Grating acuity tests are detection tests and may significantly over- estimate the equivalent letter chart acuity, which is a recognition task related to reading. Vision loss in young children may also be a cause of Comments, suggestions and contributions secondary developmental delays, due to (including comparisons to various national insufficient visual input and communication. This standards) are requested and should be submitted can be even more pronounced when several to: problems interact in multi-handicapped August Colenbrander, MD individuals. California Pacific Medical Center P.O. Box 7999 ENDORSEMENTS San Francisco, CA 94120 In addition to incorporation in the upcoming Voice-mail: 415-923-3905 edition of the AMA Guides, endorsements for this E-mail: gus @ ski.org GUIDE are being sought from various national Fax: 415-923-3945 and international organizations. Such endorsements will be included in future printings. UPDATES This Guide reflects current standards. This means that it is deficient for aspects of visual impairment Page 2 GUIDE for the Evaluation of VISUAL Impairment Summer 1999 PART 1 – OVERVIEW ASPECTS OF VISION LOSS The first two aspects refer to the organ system. The first aspect is that of anatomical and structural The description of visual functions and functional changes. Defects are described as diseases, vision can be approached from various points of disorders or injuries. The second aspect is that of view. To understand the differences between functional changes at the organ level. Defects are these points of view, this GUIDE will use as a described as impairments. The next two aspects conceptual framework the four aspects of refer to the individual. One aspect describes the functional loss that were first introduced in the skills and abilities of the individual. Defects are WHO Classification of Impairments, Disabilities described as dis-abilities. The last aspect points to and Handicaps. The aspects are distinct, although the social and economic consequences of loss of different publications may use slightly different abilities. Defects are described as handicaps. terms. Some terms are summarized in Table 1. TABLE 1 – ASPECTS of VISION LOSS THE ORGAN THE PERSON ASPECTS: Structural change, Functional change at Skills, Abilities of the Social, Economic Anatomical change the Organ level individual Consequences Neutral terms: Health Condition Organ Function Skills, Abilities Social Participation Loss, Limitation Disorder, Injury Impairment Disability Handicap ICIDH-80: Disorder Impairment Disability Handicap ICIDH-2: Structural change Functional change, Activity + Participation + (see part 4) Impairment Performance code Performance code "visual functions" "functional vision" Application to measured described VISION: quantitatively qualitatively E.g.: Visual Acuity E.g.: Reading ability For this GUIDE, the impairment and (dis-)ability cannot. The term "functional vision" is often aspects are most important. The term “visual used to refer to visual abilities. functions” is used often to refer to the impairment A statement such as "the patient can read aspect. Most visual functions (visual acuity, newsprint (1M, J#6)" describes a level of visual field, etc.) can be assessed quantitatively functional vision. It tells us that the patient can and expressed in measurement units relative to a meet an important
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