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1
Summaty of Findings
INTRODUCTION
Background
Video display terminals (VDTs)~ are used in a broad range of
occupations (e.g., clerical work, printing, computer work, air
traffic control), and their use in offices is growing rapidly. The
number of VOT operators in the United States was estimated to be
approximately 7 million in 1980, with ~10 million VDTs in use
(Center for Disease Control, 1980~.
Workers and union representatives around the world have
expressed concern that harmful effects may result from working
with VDTs (see, e.g., Bergman, 1980; New York Committee for
Occupational Safety and Health, 1980; Working Women, National
Association of Office Workers, 1980; DeMatteo et al., 1981;
Canadian Labour Congress, 1982~. Much of this concern has
involved visual functions, human factors, 2 radiation, and
tVDTs are devices for visually displaying (with symbols, graphics,
or both) information that is stored and processed electronically.
Keyboards are commonly used to control the processing and
display of information. Most VDTs now commercially available
use cathode-ray tubes (CRTs) and are similar to television
receivers in their display characteristics; however, VDTs that use
solid-state display devices instead of CRTs are increasingly
coming into use.
2Human factors are characteristics of people—for example, size,
shape, ability to see and hear, strength, and mental capacities--
that should be considered in the design of equipment and socio-
technical systems. The effects of design variables on human
performance are studied in the field of human factors in order to
develop and apply principles to improve the effectiveness,
5
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6
psychosocial aspects of VDT-related work. A number of surveys
of VDT operators have reported a high incidence of complaints of
visual and musculoskeletal discomfort. In several studies in which
various visual functions have been measured, they have been
reported to be temporarily altered following work at VDTs. Many
workers and labor representatives have expressed concern that
VDTs may emit harmful levels of radiation that may cause
cataracts and other adverse health effects (Working Women,
National Association of Office Workers, 1980; DeMatteo et al.,
1981; Canadian Labour Congress, 1982~. There have been
anecdotal reports that clusters of VDT operators have had
spontaneous abortions and miscarriages and have given birth to
children with birth defects (microwave News, 1981~. Reports of
skin rashes among VDT operators have recently appeared (W. C.
Olsen, 1981; Nilsen, 1982~. Some types of clerical jobs in which
VDTs are used have been characterized by some labor represen-
tatives as being more stressful than clerical jobs performed using
traditional technologies (Working Women, National Association of
Office Workers, 1980; Canadian Labour Congress, 1982~.
Focus of the Study
This report primarily concerns issues involving vision and the
visual system. However, because factors that affect operator
comfort and performance cannot be elucidated by analyzing only
the optical characteristics of VDTs, relevant human factors and
psychosocial issues are also considered. Because much of the
concern about the possibility of radiation hazards has been based
on misinformation, we analyze the results of surveys in which the
levels of radiation have been measured and compare those levels
with ambient levels of radiation emitted by human-made and
natural sources and with current standards for occupational
exposure. We did not reopen the question of what is an acceptable
level of radiation exposure, a question that has been extensively
studied and was beyond our mandate. We discuss whether there is
evidence that ocular diseases or abnormalities, including cata-
racts, are associated with VDT-related work (see Chapters 3 and
7~. We discuss only briefly the possibility of disorders that do not
involve vision (i.e., effects on pregnancy and skin rashes; see
efficiency, safety, and comfort of people who use machines. In
Europe this field is referred to as ergonomics and somewhat
greater emphasis is given to biomechanics and physiological
aspects of work than in the United States. The two terms are used
interchangeably in this report.
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7
Chapter 3) because there are few published data and because we
lack the appropriate expertise.
Organization of the Report
This chapter is intended to provide a nontechnical review of issues
and a summary of the panel's findings. The following chapters
provide a more extensive analysis of technical issues and litera-
ture. Chapter 2 analyzes issues concerning the methodologies
encountered in field studies in which VDT workers were asked to
respond to questions about visual and other complaints. Short-
comings in the methodologies of these studies make it difficult to
draw firm conclusions about the factors underlying visual com-
plaints and symptoms of workers. The first section of Chapter 3
reviews studies of radiation emissions from VDTs and compares
the level of emissions with current occupational standards and
background radiation from natural and human-made sources. The
second section reviews concerns about cataracts and discusses
epidemiological issues. Chapter 4 evaluates what is known about
the relationship between specific characteristics of display
devices and observers' visual performance, subjective responses,
and physiological responses. Chapter 5 analyzes the problems VDT
workers sometimes experience with improper workstation lighting
and reflections, and Chapter 6 examines the ways in which the
comfort and performance of workers are affected by constraints
on posture and motion imposed by the physical layout of
workstations. Chapter 7 explores what is known about the causes
of ocular discomfort and difficulties sometimes reported with
vision and discusses the limited efforts that have been made to
compare visual tasks in jobs that involve VDTs and jobs that do
not. Chapter 8 discusses the influence of job design and organiza-
tional factors on the well-being of VDT workers. Chapter 9
presents principles of good design and practice that could alleviate
problems encountered in VDT work and discusses the feasibility of
standards for VDT design. Last, Chapter 10 discusses research
needs.
The Literature Base
The literature related to visual effects of VDTs is growing
rapidly. The number of articles published per year went from ' 1 in
1972 to 43 in 1980 (Matula, 1981~. This literature, however, has
done little to answer the questions that have been raised. Only a
dozen or so formal studies of visual complaints or changes in
visual function among VDT workers have been published, and most
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8
fail to meet major criteria for acceptable scientific research.
The remaining literature on visual effects consists mainly of
nontechnical reviews of the concerns of- workers, technical
discussions of standards for VDT and workstation design, and
handbooks for workstation design.
In contrast to the literature on visual effects of VDTs, there is
a substantial technical literature on the quality of visual displays,
the effective design of lighting, and human factors. We are not
aware of any formal studies of job design in VDT-related work.
The Nature of VDT Work
This study considers only VDTs used for the display of alpha-
numeric information; it does not consider graphic displays (e.g.,
air traffic control scopes, radar scopes). Nevertheless, the kinds
of jobs in which alphanumeric VDTs are used must be at least in
the hundreds and include both clerical and professional occu-
pations. These jobs, of course, differ greatly on many dimensions:
in the function of the VDT within the job as a whole, in the
amount of time the worker spends on tasks in which the VDT is
directly involved, in the visual tasks required, etc. It seems likely
that the nature and incidence of visual and other problems would
vary greatly among diverse VDT jobs; thus, generalizations should
be made with caution.
Unfortunately, there has been no formal analysis of task
characteristics in various VDT jobs, and there is no ready clas-
sification scheme for such jobs. To illustrate the diversity among
jobs in which VDTs are used, we can characterize some jobs by a
predominant mode of interaction with the VDT (see Table 1.1~.
In data entry work, information that is usually noncontextual
(numbers, letters, or symbols) is keyed into the computer, often in
a repetitive manner according to a set format. In many cases the
data have no intrinsic meaning, especially when specialized sym-
bols are used. The work pace in data entry is often quite high--
8,000-12,000 keystrokes/in is not unusual (Grandjean, 1980--and
VDT operators may be expected to meet production quotas.
Operators may read from printed or handwritten material or use
auditory sources. In many cases the task does not require that the
operator often look at the video screen. Operators in jobs that
primarily involve data entry work usually have little or no control
over the structure of their work.
Data acquisition involves calling up information from the
computer and reading it from the screen; it is thus more screen-
intensive (attention is directed primarily to the screen) than data
entry work. Telephone information operators often work pre-
dominantly in this mode.
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OCR for page 10
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Interactive communication (sometimes called conversational)
work involves both data entry and data acquisition. The data may
be more complicated than those involved in data entry jobs, and
the task is likely to be more screen-intensive. To some degree an
operator sustains a dialogue with the computer and has some
opportunity for decision making. Airline reservation clerks are an
example of workers who seem to work predominantly in this mode.
Word processing involves text entry, text recall, searching text
for errors, keying in corrections, and organizing format. The term
is often used to refer to secretarial tasks in document preparation,
but there are similar operations in such job tasks as layout,
formatting, proofreading, and editing. Some of the task elements
are source-document-intensive, some are screen-intensive, and
word processing jobs usually involve different combinations of
these elements at different times. There is wide variation among
these jobs in the degree of control an operator may have over the
structure and pace of work.
Programming, computer-assisted design (CAD), and computer-
assisted manufacturing (CAM) involve some aspect of program-
ming computers using VDTs. Many professional jobs for example,
data analysis, computer programming, scientific research--include
such use of VDTs. In these jobs the VDT may be only one of
several tools used, and the amount of time a worker spends at a
terminal often varies greatly from day to day. A worker's control
over the job task is considerable.
Obviously many jobs have elements of more than one of these
categories, and some jobs may not fit into any of them.
The comfort, satisfaction, and performance of VDT workers
are affected by interacting factors that range from optical to
psychosocial (see Figure 1.1~. Unfortunately, the existing
literature on the effects of VDTs has done little to distinguish the
relative contributions of these factors. And VDT jobs have not
been systematically analyzed and compared with non-VDT jobs.
Furthermore, many jobs have been substantially altered by the
introduction of VDTs; and it is difficult to determine from existing
data whether reported visual problems and other concerns of
workers result from the new technology itself or the way in which
it is being introduced.
FIELD STUDIES OF VDT WORKERS AND WORKSTATIONS
Studies of Radiation Emission from VDTs
Video display terminals are designed to emit visible radiation
(light), but in the process of producing visible light small amounts
of several other types of electromagnetic radiation are also
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11
Job Design
Working Environment
Physical
Characteristics
Physical Characteristics
Furniture and equipment design
Lighting (illumination, glare,
temperature, reflectance)
Humidity
Noise
Human Operator
Physiological status (age, pathology,
visual functions)
Performance capabilities
Needs and values
Job Design
Task demands (acuity, speed,
vigilance, workload)
Rewards
Control of job structure and
pace
Interpersonal interaction
1 · r Human
| Thor
VDT
Screen
Keyboard
VDT Screen
Regeneration
Luminance (symbols/
background )
Contrast
Image quality
Phosphor characteristics
Colors
Presence of filter
Symbol characteristics
(font, size)
Angle of screen with regard
to operator
Location
Screen separate or attached
to keyboard
FIGURE 1.1 Some interacting factors in VAT jobs.
Job performance
Job satisfaction
Strains (physiological and
psychological )
VDT Keyboard
Layout
Type and spacing of keys
Force/travel/size of keys
Angle and height of
keyboard
Color (e.g., to separate
function)
Grouping of keys
generated, particularly X radiation and radio frequency radiation
in the 15-125 kHz frequency range.
In response to concerns expressed by VDT operators and labor
representatives that radiation emitted by VDTs might be harmful,
field surveys and laboratory studies of radiation emissions from
VDTs have been conducted over the last several years by govern-
ment agencies in the United States and Europe and by private
organizations and independent groups (see references in Chapter
3~. Taken collectively, these studies have examined a wide variety
of models and hundreds of terminals. Measurements of emissions
from older and newer VDT models have not differed significantly.
Measurements have been made both under normal operating
conditions and under conditions designed to maximize
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potential emissions (by using maximum contrast and screen
brightness, filling the screen completely with characters, using
high line voltage, misadjusting service and user controls, causing
component failures, etc.~. These studies have concluded that the
levels of all types of electromagnetic radiation emitted are below
existing occupational and environmental health and safety stan-
dard limits of exposure. The levels of radiation measured in these
studies have generally been orders of magnitude below occupa-
tional exposure standards.3
In one study (Bureau of Radiological Health, 1981) VDT sets
were tested under conditions designed to maximize the emission of
X radiation by combining artificially induced worst~ase com-
ponent failures and misadjustment of user and service controls.
Under those conditions, 8 of the 125 sets tested exceeded the 0.5
mR/h standard for television receivers, although under normal
conditions no X-radiation emissions were detected from any of the
sets. Those eight sets represented three models that were
subsequently recalled by the manufacturers to be redesigned for
compliance with standards or were excluded from the U.S. market.
It is useful to compare the levels of radiation emitted by VDTs
to ambient levels of radiation emitted by natural and human-made
sources. A person is exposed to greater radiation levels in all
parts of the electromagnetic spectrum from ambient sources than
from a VDT. The level of ultraviolet (UV) radiation emitted by
VDTs has been found to be far lower than that emitted by ordi-
nary fluorescent lights and thousands of times lower than outdoor
(sunlight) UV levels. Emissions of visible and infrared radiation
from VDTs are less than 1 percent of outdoor levels. Radio fre-
quency radiation is emitted from VDTs at levels comparable to
ambient levels generated by radio transmitters in metropolitan
areas. The level of X radiation emitted by VDTs is far less than
the ambient background level of ionizing radiation from natural
sources (i.e., cosmic radiation, terrestrial radiation, and internal
radionuclides) to which the general population is exposed.
Standards for occupational exposure to radiation are based on
existing knowledge of both acute and long-term biological effects,
and they take into consideration the cumulative exposure of
workers to various human-made and natural sources of radiation.
There is an enormous literature on the biological effects of
radiation (reviews are cited in Chapter 3~; we found no evidence to
suggest that levels of radiation emitted from VDTs might produce
harmful effects. As noted above, we did not attempt in
3In some cases the instruments used to measure some forms of
radiation were not sensitive enough to measure emissions
substantially below the standard.
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13
this study to evaluate the appropriateness of these standards, an
issue with both technical and policy aspects. Neither did we
attempt to evaluate issues concerning thresholds for biological
effects of low levels of various forms of radiation to which
humans are commonly exposed.
Cataracts
Concern about the possibility of radiation hazards from VDTs has
been raised in part by anecdotal reports of cataracts (opacities of
the lens of the eye) occurring among some VDT workers. Exposure
to high levels of ionizing or microwave radiation is known to cause
cataracts, and there is some evidence that chronic exposure to
high levels of ultraviolet radiation may also cause cataracts. Both
laboratory studies of animals and surveys of humans indicate,
however, that the levels of radiation required to produce cataracts
are thousands to millions of times higher than the levels emitted
by VDTs (see Chapter 3~.
Some VDT workers will, of course, develop cataracts, since
cataracts occur throughout the general population. The causes of
most cataracts are not known. Small, inconsequential opacities of
the lens are common; as many as 25 percent of normal people may
have such congenital or developmental opacities that do not affect
vision. Opacities that substantially interfere with vision are much
less common but increase in prevalence with age. Some mild
opacities may be precursors of senile cataract.
There have been no well-designed studies suggesting an associ-
ation of VDT work with cataracts or other ocular abnormalities
(see Chapter 3~. We cannot adequately assess anecdotal claims of
cataracts resulting from VDT work because data sufficient to
document the claims have not been published. We found no scien-
tifically valid evidence to support the assertion that cataracts
with characteristics of those caused by radiation exposure result
from VDT work. The ten anecdotal reported cases of cataracts
among VDT workers do not suggest an unusual pattern attributable
to VDT work: six of the cases appear to be common, minor
opacities not interfering with vision, and each of the remaining
four cases had known, preexisting pathology or exposure to
cataractogenic agents.
Two pilot epidemiological studies that include analyses for
cataract were underway at the time this report was written. The
National Institute for Occupational Safety and Health (NIOSH) has
recently completed a study of VDT workers at the Baltimore Sun
(Smith et al., 1982~. Preliminary results of this study indicate that
the small size and self-selected nature of the study population
preclude any assessment of a relationship between VDT use and
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14
the development of cataracts (see Chapter 3 and Appendix B).
The Mt. Sinai School of Medicine is conducting a larger study for
the Newspaper Guild; however, we were unable to obtain
sufficient detail about the study design to evaluate it adequately..
The sample size required for useful epidemiological studies of
VDT workers depends on the nature of the cataract in question. If
careful ocular examinations revealed a specific, unusual form of
cataract in a substantial proportion of workers, samples of the
size used in the Baltimore Sun or Mt. Sinai studies might be
adequate. But larger sample sizes would be required to detect a
small increase in prevalence of common cataracts among VDT
workers. Exposure to very high levels of some forms of radiation
(millions of times higher than levels emitted by VDTs) produces
cataracts of characteristic appearance. Similar cataracts
(specifically, posterior capsular and cortical cataracts) may,
however, occur idiopathically.
The weight of available evidence indicates that an association
between VDT work and the development of cataracts is highly
improbable. Thus, unless contrary evidence is produced by pilot
studies now under way, we believe that large-scale epidemio-
logical studies of cataracts among VDT workers are not now
justified.
Field Surveys Based on Self-Reports of VDT Operators
Several studies have been published in which surveys of VDT
operator complaints were reported. The findings and conclusions
of these surveys and of several experimental studies have been
widely cited, especially in nontechnical articles, as evidence that
VDT work causes visual problems. Our review of field surveys (see
Chapter 2) indicates that existing studies have not established
whether VDT work per se produces more visual complaints than
comparable non-VDT work. Neither have those studies established
the causal factors underlying the complaints of workers regarding
visual difficulties.
The methods used in field studies have been heterogeneous (see
Table 2.1 in Chapter 2~. The surveys have generally used both
health questionnaires, with questions on ocular, musculoskeletal,
and other physical complaints, and psychological questionnaires
with items on psychological states, job satisfaction, and job
characteristics. Some surveys have included measurements of
Results from the Mt. Sinai study were not available when our
report was completed.
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visual status, such as acuity and phoria, and some have recorded
information on workplace conditions, such as lighting levels and
postural constraints of workstations.
The prevalence of visual and musculoskeletal complaints
reported by VDT operators has varied greatly among surveys,
probably because of the diverse methods used and differences in
the populations studied. In some studies, more than one-half of
the VDT workers complained of some degree of visual discom-
fort. When comparison groups have been used, the percentages of
non-VDT workers reporting the same symptoms have generally``
been lower. In most surveys that have used comparison groups,
however, the VDT and non-VDT groups have not been matched to
control for differences (e.g., in demographic characteristics,
workstation design, job design) other than the use of VDTs.
Appropriate multivariate statistical procedures have seldom been
used in VDT studies. Several of the studies have other flaws in
method (such as low response rates or potential bias in selection of
respondents) that severely limit the possibility of interpreting
apparent differences. Thus it is not possible to determine from
existing studies to what extent complaints reported by VDT
operators have resulted from the VDT itself as opposed to such
factors as workstation or job design.
Video display image characteristics, workstation features such
as ambient lighting, and the design of VDT jobs may all affect the
visual comfort of workers as well as their performance, job
satisfaction, and levels of job-related stress. Extensive, well-
designed research would be required to determine the relative
contributions of these interacting factors. A careful analysis of
job and workstation characteristics (see Chapters 7 and 8) should
precede any attempt to design field surveys; in this way appro-
priate controls can be selected and appropriate questionnaire
items can be designed. We suggest that if future surveys are
conducted, they should be designed to compare explicitly the
relative influences on worker complaints of interacting variables
such as job and employee characteristics, workstation design, and
display image characteristics.
EQUIPMENT AND WORKSTATION DESIGN
VDT Design and Display Quality
Although well~esigned video displays are available, many displays
in commercial use employ components similar to those in home
television receivers, which can be inexpensively manufactured and
purchased. These displays are not specifically designed for pro-
longed work by operators performing close visual inspection of
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19
sive. Data entry operators, however, may experience more
difficulty with luminance differences among the source document,
screen, and background. No well-designed studies have examined
incidence of complaints as a function of differences in task
characteristics.
Filters can be placed over VDT screens to reduce glare and
reflections to some degree. Because their effectiveness is
limited, filters should be considered only as a supplement, never as
a replacement, for control of light and reflecting sources through
proper lighting design. Several types of filters are available, with
different levels of effectiveness, at prices ranging from a few
dollars to more than $100. Filters are often used without adequate
understanding of the trade-offs involved in their use. Some filters,
for example, only slightly reduce glare while substantially reducing
character image quality or luminance; the net effect of such
filters may be to reduce rather than enhance worker comfort and
performance.
Human Factors
Several field surveys have reported that many VDT operators
experience job-related muscular discomfort (see Chapter 6~. Most
surveys have been based on subjective reports, but some studies
have also included medical observations, measurements of work-
station dimensions, or both. Approximately one-half of the
surveys have compared the incidence of muscular discomfort in
VDT operators with that in workers in non-VDT jobs. Some studies
have also compared the incidence of discomfort in specific parts
of the body in VDT and non-VDT workers. The results of studies
have been conflicting; some have found that VDT operators report
more discomfort overall or more in specific parts of the body
than do non-VDT workers, and some have found the reverse.
Conflicting results appear to be due, in part, to deficiencies in the
designs of most studies. The results of one study (Smith et al.,
1980; National Institute for Occupational Safety and Health, 1981
suggest that operators in VDT jobs that are characterized by high
pressure to perform and low control over the task report more
visual and muscular discomfort than do operators whose jobs allow
greater autonomy and flexibility. Because of the design of the
study, however, its results must be interpreted cautiously (see the
discussion of this study in Table 2.1 in Chapter 2 and in Chapter 6~.
Although we cannot draw firm conclusions about the com-
parative types and incidences of jo~related muscular discomfort
in VDT and non-VDT workers, the results of studies indicate that
many VDT operators do experience significant discomfort. It is
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likely that this discomfort is largely caused by inappropriate
workstation design. Video display terminals are often designed
and introduced into offices without the application of relevant
human factors design principles. In many instances poorly
designed VDTs are simply installed at desks formerly used for
traditional office work or placed on whatever furniture happens to
be available. Operators are often required to work in cramped
spaces that leave them little room to place document holders or
manuscripts in positions that allow comfortable working postures.
Operators in such situations are likely to experience visual dis-
comfort, muscular discomfort, and fatigue.
The physical design and arrangement of workstation com-
ponents have implications for both visual and postural task
requirements. Working at a VDT places a combination of
interacting demands on the human visual and musculoskeletal
systems that differs from that in traditional office work. The
design of many VDTs creates a number of relatively inflexible
fixation points for various parts of the body. For example, the
keyboard and the screen in many poorly designed VDTs are
permanently attached and the angle of the screen is fixed: this
configuration allows the operator to assume only a limited number
of working postures. If the operator places the VDT at a com-
fortable viewing distance that allows the display to be easily read,
the keyboard may then be at a distance that requires the operator
to hold his or her hands, wrists, and arms in uncomfortable
positions. This may be particularly difficult for operators with
presbyopia (the reduction of visual accommodative power with
age, causing the near point of focus to recede). The optical
correction for near work routinely provided presbyopic people is
likely to be inappropriate for the distances at which VDT screens
are usually viewed. Multifocal lenses may not be designed to
allow a person to view the screen through the segment for near
work without tilting the head at an uncomfortable angle. (The
problem is analogous to that of a presbyope with bifocals trying to
read labels on grocery store shelves that are above eye level.)
Unless multifocal lenses are designed specifically for VDT work,
there may be no strategy that a worker can adopt to obtain clear
vision without postural discomfort. Of course, this statement
applies to many non-VDT jobs and situations.
Static muscle load and consequent postural stress, discomfort,
and fatigue created by relatively fixed postures can often be
relieved simply by moving the body around. VDT workstations
should be designed so that operators can easily change work
postures. VDTs that have detachable keyboards, screens that can
be tilted to a comfortable viewing angle, and movable document
holders allow operators to change postures and aid in preventing
postural stress and discomfort. Appropriate supports, such as
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21
armrests and wristrests, can also help reduce static muscle load
and discomfort.
Although there has been little research on the effects of using
adjustable chairs and work tables, their use seems desirable, and
there is a great deal of anthropometric data that can be used to
design adjustable furniture for different populations. Several
manufacturers have recently begun offering adjustable furniture
for use with VDTs. Although some of this furniture is well
designed, the claims of some manufacturers that their equipment
is designed using principles of ergonomics or human factors do not
stand up to scientific scrutiny.
Older workers, because of visual changes such as presbyopia
and increased glare susceptibility' may be especially vulnerable to
problems of poor VDT workstation design. This issue is of special
concern in part because the workforce is expected to become
distributed toward older ages in the coming decades. Of course,
good workstation design facilitates the comfort and performance
of all workers.
THE CONCEPT AND STUDY OF "VISUAL FATIGUE"
Surveys of VDT operators have reported that complaints of ocular
discomfort and difficulties with vision are fairly common. The
complaints have included irritantlike effects (itching, dry, gritty,
stinging, or watery eyes), sensations of pain or fatigue involving
the eyes, and blurring or other difficulties with vision. Although
these surveys suggest that complaints of ocular discomfort are
more frequent among VDT workers than among non-VDT workers,
it cannot be determined from these studies whether the com-
plaints are related to the VDT itself or to other aspects of the job
situation, including workstation, lighting, and job design (see
Chapters 2 and 7~.
The ocular symptoms reported by VDT workers appear to us to
be similar to those reported to clinicians by many people of all
ages and many occupations. There has been little effort, how-
ever, to interview workers in depth to obtain a detailed charac-
terization of reported symptoms or comparisons of symptoms
among VDT and non-VDT workers. It would be useful to know
which aspects of visual tasks might contribute to the experience
of ocular discomfort sometimes reported by VDT workers and
non-VDT workers and how this experience might be affected by
the nonvisual features of a work situation. Unfortunately, neither
existing VDT studies nor the general scientific literature provides
answers to these questions, and the physiological and psychological
bases of ocular discomfort cannot be specified.
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Ocular complaints of workers have often been discussed in
terms of "eyestrain" and "visual fatigue." These terms, however,
are vaguely defined and do not correspond to known physiological
or clinical conditions.6 Confusion may result because different
discussions of visual fatigue may refer to quite different phenom-
ena: symptoms of ocular discomfort; changes in oculomotor
functions, such as accommodation and vergence;7 or changes in
performance of visual tasks, such as reading or visual search.
Several investigators have sought physiological correlates of
visual fatigue in VDT workers (see Chapter 7~. The hypothesis of
most of these studies apparently was that fatigue of oculomotor
muscles might underlie sensations of ocular discomfort. The
reported effects of several hours of VDT work include transient
changes in the near points of accommodation and convergence,
resting point of accommodation, so-called accuracy of accom-
modative response, time required to shift eye fixation and focus
between near and far targets, and visual acuity. All of the studies
suffer from flaws in method that make their results difficult to
interpret (see Chapter 7 and Appendix A). In particular, some
studies have not included non-VDT control groups, and others have
used non-VDT so called control groups that differed from the VDT
group not only in the use of VDTs but also in many other respects.
It is not possible to determine from these studies whether the
reported oculomotor changes were specifically related to VDT
visual tasks. A few studies have used appropriate controls but
suffer from other problems of method or interpretation and can at
best be considered preliminary investigations.
The oculomotor changes reported to follow VDT work are
consistent with a larger body of research in which such changes
are commonly found following periods of performing various
near-visual tasks. The relationship of these changes to the
subjective experience of ocular discomfort is poorly understood.
Many studies have reported recession of the near points of
accommodation and convergence following prolonged near-visual
work such as reading under difficult conditions or carrying out
inspection tasks. Shifts of accommodation toward the resting
6We suggest that these terms be avoided whenever possible in
scientific studies in favor of such terms as ocular discomfort,
changes in performance, and change in oculomotor functions that
specifically describe the phenomena discussed. When complaints
of "visual fatigue" or "eyestrain" are presented in clinical practice
or surveys of workers, it is important to attempt to determine
more precisely what phenomenon is being described.
7See Chapter 7 for discussion of technical terms having to do with
oculomotor functions.
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point have been found in subjects reading either hard copy or
microfiche. Several aspects of eye movements have been shown
to change during performance of various near-visual tasks. Some
of these changes in eye movements have been shown to be
reversed when subjects are aroused or highly motivated, which
suggests that either the changes arise in the central nervous
system or there is compensation for fatigue of oculomotor
muscles. No evidence has been presented to suggest that these
temporary oculomotor changes are harmful, although conceivably
they might have some effect on performance of VDT and other
visual tasks. None of the studies of VDT workers has provided
valid evidence of ocular diseases or abnormalities that can be
attributed to VDT work.
Several surveys of VDT operators have included tests of such
visual functions as acuity, astigmatism, stereopsis, phoria, and
color vision. Unfortunately, there has been only limited effort to
determine whether the status of these visual functions has any
correlation with ocular complaints of VDT workers. There are a
number of clinical conditions (especially those involving small
uncorrected refractive errors and oculomotor imbalances) that can
cause visual difficulties with prolonged near work or critical detail
work. It is possible that such conditions might underlie some of
the complaints of some VDT workers and non-VDT workers. If so,
careful clinical examination of those workers would be important,
and appropriate corrective lenses might relieve their symptoms.
The lack of objective measures of ocular discomfort has made
it difficult to determine possible causal factors. It is easier to
determine what factors influence the visual performance of VDT
workers, because performance is more readily measured than
discomfort (see Chapter 4~. It is often assumed that conditions
facilitating effective visual performance are less likely to pro-
duce ocular discomfort; however, the complex relationships among
visual performance, comfort, and psychological variables have not
been thoroughly explored.
It is important to ask whether there are factors in VDT visual
tasks that are inherently different from those in comparable
non-VDT visual tasks and if so, whether those factors might affect
worker comfort and performance. We cannot completely answer
this question because there has been only limited analysis of visual
and cognitive functions in VDT work tasks. Some unique features
of VDTs and VDT work are apparent. For example, the reflection
of images by the VDT screen (discussed above), can cause dif-
ficulties when no preventive measures are taken. Some other
features that are not inherent in VDTs or in VDT work are often
arranged in a potentially problematic way (e.g., the positioning of
VDT screens at angles or distances that are incompatible with
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conventional designs of bifocal spectacles, noted above). Many
features of VDT visual tasks are, of course, similar to those of
visual tasks in non-VDT jobs. It seems likely that with proper
design of VDT display characteristics, workplace lighting,
workstations, and jobs, VDT work would not cause any unique
visual problems (see Chapter 9~.
JOB DESIGN AND PSYCHOSOCIAL STRESS
There has been little formal study of psychosocial aspects of work
involving video display terminals (see Chapter 8~. A few studies
have attempted to identify psychosocial stressors in VDT work and
to relate them to self-reports of employee well-being and in some
cases to physiological changes such as increased blood pressure.
Although some studies have found that VDT operators report high
levels of job-related stress, no psychosocial stressors or
health-related outcomes have been shown to be unique to work
involving VDTs. However, the research literature is inconclusive
because of problems in the designs of most studies. The data that
exist suggest that where negative health effects do appear, they
may stem from factors in the job itself (including but not limited
to the VDT component) or from organizational relationships
involving the employees.
Jobs in which VDTs are used are not purely "VDT jobs," even
when the VDT dominates everything else about the job. The total
job is defined less by the particular equipment used than by what
the equipment is used for: what the worker is expected to pro-
duce, the methods and procedures to be followed, the skills and
abilities required, and the interactions with other people on the
job. It is possible to design jobs carefully so that the work
experience is satisfying and productive, but in practice most jobs
develop with little real planning, and whatever planning occurs is
generally more concerned with the equipment than the person who
uses it.
At a public symposium organized by the panel, labor represen-
tatives described some VDT jobs that clearly are badly designed;
workers in these jobs must perform highly repetitive tasks at a
fast pace with no opportunity to vary the structure or pace of the
work or even to adjust uncomfortable equipment. Of course, not
all VDT jobs are badly designed, but unfortunately, we have no
data on what percentage of them are. Existing literature suggests
that most complaints are reported by workers in jobs in which a
single task (such as data entry) dominates the work day, pay is
relatively low, and the workers' responsibility is limited to main-
taining output and avoiding errors. Such jobs might be seen as
highly undesirable in that they stifle human initiative, creativity,
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and sense of achievement. The question that demands answering
is whether VDT workers who complain of problems are responding
to the equipment, the basic nature of the job, or their perceptions
of the job and its opportunitites and limitations.
Jobs in which VDTs are used- - s well as jobs in which VDTs are
not used vary greatly across factors that may act as sources of
psychosocial stress. These sources include the design of the job
itself, the social and psychological environment of the workplace,
and the broader organizational system of which the worker is a
part. One useful approach to analyzing the psychosocial stressors
in a work situation is to examine the degree of fit between the
characteristics of workers and the characteristics of work situa-
tions (see Chapter 8~. The assumption underlying this approach is
that a lack of fit between the characteristics of worker and work
environment leads to strain and poor performance. Two kinds of
person-environment fit, which may not always represent two
mutually exclusive classifications, can be examined: one is the fit
between a worker's needs (or preferences, desires, values, etc.)
and the related supplies for these needs in his or her job environ-
ment; the other is the fit between a worker's abilities and the
demands of his or her jObe This person-environment fit approach
has not yet been applied to work involving VDTs, but it has been
applied to the study of stressors in other work situations, and it
can provide a useful conceptual framework in which to study
possible psychosocial stressors in VDT work.
For example, VDT jobs, like other jobs, vary greatly on such
dimensions as the amount of control given an employee and the
employee's opportunity to participate in decisions that affect the
way in which his or her work is carried out. VDT jobs vary in the
extent to which an employee can control the introduction into the
workplace of VDT equipment, the amount of incoming work and
associated deadlines, the variety of the work content, the amount
and scheduling of time spent at the VDT, and the extent of inter-
actions with other people. Although research on VDT use does not
permit firm conclusions as to how variations in control influence
employee well-being, research on other types of work suggests
that lack of control has measurable, undesirable effects on
employee well-being. Because individuals vary in their need for
control, the person-environment fit approach would predict that
lack of (or too much) control can act as a psychosocial stressor for
workers in jobs in which there is a misfit between the worker and
the job on this dimension.
VDT jobs, like other jobs, also vary in a number of other pos-
sible sources of stress, including complexity of the work, quanti-
tative workload, predictability of events (such as computer system
breakdowns or processing delays), threat of job loss, and social
support. This list is not exhaustive, of course, but indicates
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the range of dimensions on which VDT jobs end other jobs very end
suggests potential stressors that might usefully be studied within
the framework of person~nvironment fit theory. Systematic
studies of the relative contribution of each psychosocial stressor
as a component of the context in which the VDT is used would
provide a much greater increase in knowledge about the psycho-
genic health effects of VDT use than studies that have simply
compared complaints of job-related stress in a "VDT group" and a
"non-VDT group" without attempting to match workers and jobs in
other respects. These kinds of evaluations would allow the
examination of the contributions of the worker and of the VDT and
its work environment to employee well-being, and could help
generate options for improving the fit between a person and a job.
Most, if not all, psychosocial stressors that may be associated
with VDT work under conditions in which the work is not organ-
ized with the well being of the worker in mind do not seem to be
inherent to VDT technology and software. VDTs, like any other
work technology, can be used properly or improperly, and VDT
work can be organized so that it reduces stress and increases
productivity or increases stress and reduces productivity.
In many, but not all, job settings, VDTs have been introduced
without consultation with the workers who are to use them. The
manner in which this new technology is introduced may influence
workers' perceptions of the VDT. The private use of VDTs (e.g.,
home computers and word processors) similar to those used occu-
pationally is growing rapidly. It might be interesting to compare
user attitudes in private and industrial settings; there have as yet
been no formal studies making such a comparison.
DESIGN, PRACTICE, AND STANDARDS
Principles of Good Design and Practice
VDTs have often been designed and introduced into workplaces
with little attention to well-established principles of, and existing
data about, good design and practice. There is a large base of
knowledge about image quality, workplace design, lighting and
reflections, and industrial and organizational psychology that has
often been disregarded or inappropriately applied. It is likely that
problems with and concerns about the use of VDTs would be
greatly alleviated by the appropriate application of this know 1-
edge to the design of VDT equipment and VDT jobs (see Chapter 9~.
We strongly urge designers of VDT jobs to draw upon well-
established principles for organizing work in ways that are
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conducive to the well-being of workers (see Chapter 9~. Our
analysis suggests two principles that should be given special con-
sideration: (1) stress can best be reduced by optimizing the fit
between a worker and his or her working environment, rather than
standardizing environments regardless of individual needs and
abilities; and (2) participation in decision making and some degree
of individual control over the nature and pace of work allows
workers to achieve maximum person-environment fit. Among the
implications of these principles is that flexibility is preferable to
fixed rest breaks. It should be noted, however, that rigidly de-
signed jobs with high quotas for productivity, in which the output
of workers is monitored moment by moment, allow little or no
flexibility; in these cases, fixed rest breaks may provide the only
opportunity to move around or to rest tired eyes.
Public Education
To a substantial degree, alleviation of problems associated with
the use of VDTs depends on educating users, both those who decide
to have others use such equipment and those who operate it.
Users of VDTs and of related equipment need to be aware that
many ergonomic problems can be overcome immediately by
applying what is already known about display quality and work-
place design; it is not necessary to wait for further research (see
Chapters 6 and 9)e Well-designed, high~uality displays and
related workplace equipment and furniture are commercially
available. Manufacturers should standardize definitions of
equipment characteristics and techniques used to measure them
and make this information available so that users will be in a
position to make informed choices. Users should also learn as
much as possible about the characteristics of well-designed
equipment so that they can effectively evaluate and compare
products. Users can also apply existing knowledge in reducing
glare and in adjusting angles of view, visual distances between
display and operator, display contrast and luminance, and so on.
Both managers and workers can support the use of good employee-
management practices in the introduction and use of VDTs.
Education about these matters involves more than just making
such information available. Consumers need to learn how to dis-
tinguish between reports that are based on scientific research and
those that argue from uncontrolled collections of cases. The
scientific community could help with this goal by taking a more
active stance in contributing information to media that are widely
available to the general public (while continuing to document
findings through scientific publication). The media could help by
reporting both the claims made by various parties regarding the
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health effects of VDTs and the basis for those claims; such report-
ing may require better knowledge of scientific methods on the
part of reporters and writers. Unfortunately, sensationalized
accounts often draw more attention, and sometimes more
credence, than do careful analyses of evidence.
Standards and Guidelines for VDT Uses
Standards have been proposed or enacted, primarily in Europe, for
VDT design characteristics and use. Various standards have been
specified in labor agreements, directives or guidelines from gov-
ernment agencies, or legislation. Some standards cover work-
station design features, image display characteristics, and lighting
and reflection conditions; some also specify provision of rest
breaks, operator training in VDT use, and eye examinations for
VDT operators. Most, though not all, standards specify numerical
values for such parameters as display character size, luminance
levels, key force, and viewing distance. Substantial differences
and conflicts in specifications are found among these standards,
which appear to be based on varying assumptions (see Chapter 9~.
Some specifications do not have a clear empirical basis, and some
do not reflect existing knowledge about visual performance.
Judicious use of guidelines and standards can be helpful, but we
feel that it would be premature to establish mandatory standards.
Careful research and discussion are needed to resolve conflicts in
the specifications given in existing and proposed standards. There
do not appear to have been any careful follow-up studies to
evaluate the efficacy of standards now in use. Because VDT
technology is rapidly evolving, standards that are premature may
impede improvements or become irrelevant. Standardized,
appropriate methods for measuring and evaluating image quality
are needed in order to develop appropriate guidelines for displays.
Without such standard techniques, compliance with mandatory
Tin this discussion we use standards to refer to specifications of
values for design parameters to which strict adherence is
expected. These include legally binding specifications, such as the
German Safety Standards; specifications written into contracts,
such as the U.S. Military Standard 1472C; and specifications
voluntarily adopted by industry, such as those promulgated by the
American National Standards Institute. In contrast we use
guidelines to refer to specifications that are suggested with the
understanding that implementation be flexible, depending on
circumstances and needs.
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standards (including those that specify equipment maintenance
procedures and schedules) would be difficult.
In addition to careful, systematic research, we suggest that
there should be a continuing dialogue among scientists, manufac
turers, and VDT users so that useful guidelines can evolve. It
seems likely that different sets of guidelines will be appropriate
for different kinds of VDT applications and operations.
RESEARCH NEEDS
-
A number of questions raised in our analysis of the research
literature on effects of VDT work remain unanswered. Many of
these questions could be answered by appropriately designed
research. Chapter 2 discusses criteria that should be considered in
the proper design of research. We suggest several avenues of
research that might be taken, but we urge that competing prior-
ities in the field of occupational health be carefully considered
(Chapter 10~.
Objective measures that can be used to relate visual discom-
fort to patterns of visual activity, VDT characteristics, and visual
performance are needed. Such research would be relevant to an
understanding of performance of a range of near-work tasks in
addition to VDT work. The implications of positive- versus nega-
tive-contrast displays should be investigated in greater depth.
Research on the efficacy of screen filters is needed to evaluate
the claims made by manufacturers. Research comparing cathode-
ray tube displays to geometrically stable displays (e.g., gas or
electroluminescent panels) would also be useful.
We suggest that research on factors such as workload, social
support, and task complexity that affect all job - -including but not
limited to VDT work -be given priority over research with a
narrow focus on what is stressful or not stressful about VDT work
per se.
Representative terms from entire chapter:
vdt workers
