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Video Displays, Work, and Vision Pane} on Impact of Video Viewing on Vision of Workers Committee on Vision Commission on Behavioral and Social Sciences and Education National Research Council NATIONAL ACADEMY PRESS Washington, D. C. 1983
NOTICE: The project that is the subject of this report was approved by the Goveming Board of the National Research Council, whose members are drawn from the councils of the Naffonal Academy of Sciences, the Naffonal Academy of Engineering, and the Insfftute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to proce- dures approved by a Report Review Committee consisting of members of the Naffonal Academy of Sciences, the Naffonal Academy of Engineering, and the Insfftute of Medi- cine. The Naffonal Research Council was established by the Naffonal Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and of advising the federal govemment. The Council operates in accordance with general policies determined by the Academy under the au- thority of its congressional charter of 1863, which establishes the Academy as a private, nonprofit, self-governing membership corporation. The Council has become the principal operating agency of both the Naffonal Academy of Sciences and the Naffonal Academy of Engineering in the conduct of their services to the govemment, the public, and the scien- fffic and engineering communities. It is administered jointly by both Academies and the Insfftute of Medicine. The Naffonal Academy of Engineering and the Institute of Medicine were established in 1964 and 1970, respectively, under the charter of the Naffonal Aca- demy of Sciences. This work relates to the Department of the Navy Contract N00014-81-C-0422 issued by the Office of Naval Research under Contract Authority NR 201-517. However, the con- tent does not necessarily reflect the position or the policy of the Department of the Navy or the govemment, and no official endorsement should be inferred. The United States government has at least a royalty-free, nonexclusive, and irrevocable license throughout the world for government purposes to publish, translate, reproduce, deliver, perform, dispose of, and to authorize others so to do, all or any portion of this work. Library of Congress Catalog Card Number 83-61880 Intemaffonal Standard Book Number 0-309-03388-8 NATIONAL ACADEMY PRESS 2101 Consfftuffon Avenue, NW Washington, DC 20418 Copyright ~)1983 by the Naffonal Academy of Sciences No part of this book may be reproduced by any mechanical, photographic, or electronic process, or in the form of a phonographic recording, nor may it be stored in a retrieval system, transmitted, or otherwise copied for public or private use, without written permis- sion from the publisher, except for the purposes of official use by the United States Gov- emment. Printed in the United States of America First Printing, July 1983 Second Printing, January 1984 Third Printing, October 1984
Pane! on Impact of Video Viewing on Vision of Workers EDWARD J. RINALDUCCI (Chair), School of Psychology, Georgia Institute of Technology JANET BERTINUSON, Alberta Federation of Labour ROBERT D. CAPLAN, Institute for Social Research, University of Michigan ROBERT M. GUION, Department of Psychology, Bowling Green State University VINCENT M. KING, College of Optometry, Ferris State College DAVID H. SLINKY, Laser Branch, U.S. Army Environmental Hygiene Agency STANLEY W. SMITH, Institute for Research in Vision, Ohio State University HARRY L. SNYDER, Department of Industrial Engineering and Operations Research, Virginia Polytechnic Institute and State University ALFRED SOMMER, International Center for Epidemiologic and Preventive Ophthalmology, Wilmer Ophthalmological Institute, Johns Hopkins University LAWRENCE W. STARK, Neurology Unit, University of California, Berkeley H. LEE TASK, Air Force Aerospace Medical Research Laboratory, Wright-Patterson Air Force Base HUGH R. TAYLOR, International Center for Epidemiologic and Preventive Ophthalmology, Wilmer Ophthalmological Institute, Johns Hopkins University Staff KEY DISMUKES, Study Director BARBARA S. BROWN, Staff Associate LLYN M. ELLISON, Administrative Secretary GRAY JACOBIK, Secretary · -
Commidee on vision DEREK H. FENDER (Chair), Jorgensen Laboratory of Information Science, California Institute of Technology ANTHONY ADAMS, School of Optometry, University of California, Berkeley ELIOT L. BERSON, Berman-Gund Laboratory for the Study of Retinal Degenerations, Department of Ophthalmology, Harvard Medical School NIGEL W. DAWN, Departments of Physiology and Biophysics, Washington University School of Medicine JOHN E. DOWLING,2 Department of Biology, Harvard University DONALD A. FOX, College of Optometry, University of Houston JULIAN HOCHBERG,2 Department of Psychology, Columbia University DOROTHEA JAMESON,2 Department of Psychology, University of Pennsylvania LLOYD KAUFMAN, Department of Psychology, New York University KEN NAKAYAMA, Smith-Kettlewell Institute of Visual Sciences, San ~ . tranclsco DONALD G. PITTS,1 College of Optometry, University of Houston LUIS M. PROENZA,2 Department of Zoology, University of Georgia ROBERT SEKULER, Departments of Psychology, Ophthalmology, and Neurobiology/Physiology, Northwestern University HARRY SNYDER, Department of Industrial Engineering and Operations Research, Virginia Polytechnic Institute anc] State University Staff KEY DISMUKES, Study Director BARBARA S. BROWN, Staff Associate RAYMOND P. BRIGGS, NRC Fellow LLYN M. ELLISON, Administrative Secretary GRAY JACOBIK, Secretary Member as of July 1982 2Term ended June 1982 iv
Preface In the spring of 1981 the National Institute for Occupational Safety and Health (NIOSH) requested the National Academy of Sciences to under- take a critical review of existing studies of visual issues encountered in occupational video viewing, analyze methodological problems, and sug- gest lines of research to resolve remaining questions. In response to this request, the National Research Council's Committee on Vision estab- lished the Panel on Impact of Video Viewing on Vision of Workers, which has prepared this report. The National Research Council appointed panel members with exper- tise in the diverse scientific and technical areas relevant to occupational video viewing, in particular, ophthalmology, optometry, oculomotor function, physiological optics, epidemiology, occupational health, raclia- tion biophysics, display technology, illuminating engineering, human fac- tors, and industrial anc! organizational psychology. The areas of expertise of individual panel members are described in Appendix D. This report focuses on the six issues that NIOSH asked the panel to address: 1. How well are the visual factors and underlying mechanisms that produce discomfort in video viewing understood? 2. What problems are encountered in attempting to define "eye- strain" and "visual fatigue" and to relate physiological, subjective, ergo- nomic, and performance measures of these concepts? 3. Is existing knowledge sufficient to establish adequate standards for display characteristics (contrast ratios, luminance levels, regeneration rate, etc.? Is there an adequate basis for standardizing viewing condi- tions, such as the portion of operators' time spent viewing video display terminals? 4. To what extent are the problems reported with video terminals due to substandard operating conditions (e.g., excessive glare from overhead v
Vl Prelace illumination), and to what extent would these problems remain even under ideal viewing conditions? 5. What can be said about the relative roles of visual, ergonomic, and psychosocial factors in visual problems encountered? What can be said about the relation of visual symptoms encountered and more general stress responses (e.g., general fatigue) to other aspects of the worker's job? 6. How do visual problems in video viewing compare with those en- countered in comparable tasks, such as prolonged editing or typing of print? Because many workers and labor union representatives have been con- cerned that radiation hazards may be associated with the use of video display terminals (VDTs), the panel also decided to consider radiation issues in its work. In the course of its study the pane] reviewed diverse literatures, includ- ing reports of field surveys of VDT workers and VDT workplaces, labo- ratory studies of visual functions in VDT work tasks, news articles, anc! pamphlets prepared by labor unions concerned with VDT issues. The panel also drew upon the substantial technical literatures on visual func- tion, image quality, lighting design, ergonomic design, and industrial and organizational psychology that are highly germane but often neglected in discussions of VDT issues. To further its discussions of technical issues and to promote the ex- change of information among scientists and representatives of labor, in- dustry, and federal agencies, the panel held a public symposium on video display terminals and vision of workers on August 20-21, 1981, in Washington, D.C. (summarized by Brown et al., 1982~. Investigators from around the world were invited to present their research on VDTs and to review field surveys of VDT workers. Discussion panels included scientists, who analyzed technical aspects of VDT studies, anti labor rep- resentatives, who described the concerns of workers. The panel has drawn on the symposium presentations and discussions in analyzing the issues discussed in this report. The panel recognized early in its deliberations that visual issues in VDT work must be considered within the larger context of the working environment, including the quality of VDT workstation equipment, job design, and workers' concerns and needs for information. This larger context was discussed extensively at the panel's meetings anc] is consid- ered explicitly in this report. Early drafts of material were prepared for the panel's review and dis- cussion by panel members, consultants, and staff. The panel's analyses
Preface of survey methodology and of psychosocial issues were prepared by Robert Caplan and Robert Guion. Janet Bertinuson provided guidance on characteristics of various types of working situations in which VDTs are used and on the concerns of the labor community. Davic! Sliney re- viewed surveys of radiation emissions, and AlfrecI Sommer and Hugh R. Taylor analyzed issues involving epidemiology and cataracts. Vincent King, Edward Rinalducci, Stanley Smith, Harry Snyder, anc! Lee Task prepared material on lighting and reflections and display technology. Pane! consultants Martin Helander and K. H. E. Kroemer cirafted mate- rial on human factors for the panel's discussion. Key Dismukes prepared material on visual tasks and symptoms in VDT work, drawing in part upon ideas and material contributed by NRC fellow Raymond Briggs, Committee on Vision member Julian Hochberg, and consultant John Merritt. Lawrence Stark reviewed the literature on oculomotor factors affecting visual performance. Phyllis ~Johnston, at the University of Cali- fornia, Berkeley, assisted in reviewing the literature on oculomotor func- tions. Harry Snyder and Martin Helander provicled information on current guidelines and standards for VDT use. Consultant R. Van Harri- son provided a review and critique of the NIOSH Baltimore Sun study, which appears as Appendix B. Barbara S. Brown and Key Dismukes prepared the summary chapter. All members of the panel were asked to critically review drafts of the report chapters, all of which were then discussed at panel meetings. The chapters were then revised accordingly, and at its final meeting in Feb- ruary 1982 the panel summarized its conclusions. Thus the study and the report are a collaborative effort of all members of the pane} and the staff. The pane] also benefited from thoughtful reviews of early drafts of this report by members of the Committee on Vision and the Commission on Behavioral and Social Sciences~and Education and other experts, whose comments the pane! cirew upon in preparing the final version. Julian Hochberg provided valuable insights on conceptual issues throughout the course of the study and contributed to the development of the en- tire report; Derek Fender made helpful comments and suggestions on the entire report and contributed to the panel's discussion of several key issues; and several other members of the committee, in particular An- thony Adams, Eliot L. Berson, Dorothea ~Jameson, and Luis Proenza, provided helpful comments and suggestions. The committee was as- sisted in its review by comments solicited from David Cogan, at the Na- tional Eye Institute; Arthur~Jampolsky, at the Smith-Kettlewell Institute of Visual Sciences; and Donald Pitts, at the University of Houston. Barbara S. Brown played a substantial and invaluable role, collaborat- ·e V11
· - V111 Preface ing with us to coordinate anci manage the study. In addition, she orga- nized and edited drafts of technical material, wrote supplementary material, and helped integrate the discussion of issues in the report. She also helped organize the panel's symposium and meetings. Llyn M. Ellison provided expert administrative and secretarial assis- tance throughout the study. She took care of many administrative de- tails, helped arrange meetings, and was centrally involved in preparing the manuscript for production. In the process of efficiently and expertly producing manuscript drafts on a VDT, she gained firsthand experience in some of the concerns of VDT workers. Gray Jacobik assisted with secretarial tasks and word processing. We are grateful for their skillful assistance. Eugenia Grohman, on the staff of the Commission on Be- havioral and Social Sciences and Education, gave helpful advice on or- ganizing the material in the report and expertly editec! the final version. EDWARD J. RINALDUCCI, Chair KEY DISMUKES, Study Director Panel on Video Viewing
Contents EXECUTIVE SUMMARY 1 SUMIA1\RY OF FINDINGS 5 Introduction / 5 Background / 5 Focus of the Study / 6 Organization of the Report / 7 The Literature Base / 7 The Nature of VDT Work / ~ Field Studies of VDT Workers and Workstations / 10 Studies of Radiation Emission from VDTs / 10 Cataracts / 13 Field Surveys Based on Self-Reports of VDT Operators / 14 Equipment and Workstation Design /15 VDT Design and Display Quality / 15 Lighting anc! Reflections / 17 Human Factors / 19 The Concept and Study of "Visual Fatigue" / 21 Job Design and Psychosocial Stress / 24 Design, Practice, and Standards / 26 Principles of Good Design and Practice / 26 Public Education / 27 Standards and Guidelines for VDT Use / 2~3 Research Needs / 29 ix
Contents 2 CRITIQUE OF SURVEY METHODOLOGY Introduction / 30 Surveys of VDT Users / 31 Adequacy of Theory / 32 Adequacy of Research Design / 33 Adequacy of Measurement / 33 Adequacy of Sampling / 40 Unanswered Questions / 41 Research Design Considerations / 42 Control and Choice in Studies of VDT Physical Parameters / 42 Practical Considerations / 43 3 RADIATION EMISSIONS AND THEIR EFFECTS Types and Levels of Radiation Emitted by VDTs / 44 Studies of Emission Levels / 45 Radiation Safety Standards / 51 VDT Emissions and Ambient Radiation / 52 Biological Effects of Radiation /53 Ionizing Radiation / 53 Nonionizing Radiation / 55 Skin Rashes / 56 VDT Use and Cataracts / 57 Prevalence and Causes of Cataracts / 57 The Evidence Regarding DOT Use and Cataracts / 58 Methods of Studying Whether There is a Relationship Between VDT Use and Cataracts / 60 Conclusions About Radiation Hazards / 64 4 DISPLAY CHARACTERISTICS ........... Effects of CRT Display Variables / 66 Luminance / 66 Contrast and Contrast Polarity / 73 Raster Structure / 74 Resolution / 79 Jitter and Temporal Instability / 79 Refresh Rate and Persistence / 80 Color / S! Reflection Characteristics / {32 ................ 30 44 .......... .................... 66
Contents A Summary Measure: Modulation Transfer Function / {33 Display Measurement: Techniques and Problems / 35 Measurement Techniques / 86 Measurement of Various Parameters / SS Standardization / 94 Flat-Panel Displays / 94 Dot-Matrix Display Variables / 95 Dot-Matrix Display Quality Measures / 101 Advantages and Disadvantages of Flat-Panel Displays Compared With CRTs / 103 Filters for VDTs / 104 Kinds of Filters / 104 Evaluation of Filters / 106 5 LIGHTING AND REFLECTIONS Illumination / 112 Transient Adaptation / 113 Reflections / 115 Glare / 116 Review of VDT Studies / 122 Field Surveys of VDT Workers / 122 Field Surveys Comparing VDT and Non-VDT Work / 125 Laboratory Studies / 127 Xl ............................ 1 1 1 6 ANTHROPOMETRY AND BIOMECHANICS IN VDT APPLICATIONS .............................................. Postural Strain / 130 Overview of Biomechanical Factors / 131 Work Posture / 131 Muscular Load / 133 Joint Angles / 133 Anthropometry / 135 Workstation Design /1353 Effects of Chair Design Features on the Spine / 138 Effects of Working Height on Postural Strain / 140 Effects of Display Position on Postural Strain / 141 ..129
xii 7 VISUAL TASKS, FUNCTIONS, AND SYMPTOMS Visual Issues in VDT Studies / 143 Field Surveys / 143 Contents ....... 143 Experimental Field and Laboratory Stuclies of Visual Functions in VDT Work / 145 The Need for Job and Task Analysis / 147 Are There Unique Features of VDT Tasks? / 148 The Special Task of Reacting / 150 The Problematic Concepts of "Visual Fatigue" anc! "Eyestrain" / 152 Refractive Errors and Visual Difficulties / 153 Myopia / 154 Oculomotor Factors Affecting Visual Performance / 154 Eye Movements / 155 Blinking / 160 Triadic Near Reflex: Combined Focusing, Convergence, and Aperture Mechanisms / 161 Summary and Conclusions / 171 8 JOB DESIGN AND ORGANIZATIONAL VARIABLES ... 173 Introduction / 173 Workers' Complaints and Job Structures / 173 Defining Psychosocial Stress anti Strain / 175 A Framework for Studying Psychosocial Stressors in VDT Work / 176 Person-Environment Fit / 176 Objective and Subjective Fit / 177 Stressors for Study in VDT Work / 178 Control / 17~3 Participation / 180 Predictability and Controllability / 180 Complexity / 1~32 Role Ambiguity / 184 Threat of Unemployment / 185 Quantitative Workload / 185 Prescription for Overload Deadline Plus Delay / 187 Responsibility for Persons / 18~3 Role Conflict / 189 Social Support / 1~39 Discussion and Conclusions /192
Contents 9 DESIGN, PRACTICE, AND STANDARDS FOR VDT EQUIPMENT AND WORK ............................... Principles of Good Design anc] Practice / 194 Image Quality and Display Design / 194 Lighting and Reflections / 195 Systematic Design of VDT Workstations / 197 dote Design and Organizational Variables / 199 Standards and Guidelines for VDT Design / 204 10 RESEARCH NEEDS Effects of Displays on Visual Activity / 214 Objective Correlates of Visual Complaints / 214 Relating Display Charactenshcs to Workplace Conditions / 215 Effects of Image Instability / 216 Distinguishing Specific Effects of VDTs / 216 Psychosocial Stressors / 216 xiii ...194 .............. 214 APPENDIXES ..... A A Review of Methodology in Studies of Visual Functions During VDT Tasks John 0. Merritt ....219 .219 B Review of a Preliminary Report on a Cross-Sectional Survey of VDT Users at the Baltimore Sun 227 R. Van Harrison C Dissent Lawrence W. Stark ............ 2 3 5 D Biographical Sketches of Pane! Members and Staff 2 3 7 REFERENCES ................. 2 4 3
