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OCR for page R1
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
OCR for page R2
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
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emment.
Printed in the United States of America
First Printing, July 1983
Second Printing, January 1984
Third Printing, October 1984
OCR for page R3
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
· -—
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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
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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
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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
OCR for page R7
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
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· -—
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
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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
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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
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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
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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
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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
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