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CAUSES AND CURES
equaled the telephone is becoming the most indispensable piece of office equipment.
Because computer use is such a high visually demanding task, vision problems
and symptoms have become very common in todays workplace. Most studies
indicate that computer operators, who view their Video Display Terminals (VDTs),
report more eye-related problems than non-VDT office workers. A number of investigators
have indicated that visual symptoms occur in 75-90% of VDT workers. In contrast
to the popular conception regarding carpal tunnel syndrome, a study released
by NIOSH showed that only 22% of VDT workers have musculoskeletal disorders.
A survey of optometrists
indicated that 10 million eye examinations are annually given in this country
primarily because of visual problems at computers. This study delineated the
series of symptoms which eventually became known as Computer Vision Syndrome
(CVS). This condition most often occurs when the viewing demand of the task
exceeds the visual abilities of the computer user. The American Optometric Association
defines CVS as that complex of eye and vision problems related to near
work which are experience during or related to computer use. The symptoms
can vary but mostly include eyestrain, headaches, blurred vision (distance and/or
near), dry and irritated eyes, slow refocusing, neck and/or backache, light
sensitivity, and double vision.
The causes for
these visual symptoms are a combination of individual visual problems, poor
workplace conditions and improper work habits. The above mentioned survey also
concluded that two-thirds of the complaints were related to vision problems
while one-third was due to environmental factors. Many people have marginal
vision disorders which do not cause symptoms when performing less demanding
visual tasks. However, it has also been shown that computer users also have
a higher incidence of complaints than non-computer users in the same environment.
these symptoms and see why they arise.
Eyestrain is one
of those vague terms that has different meanings to different people. The term
eye care professionals use for eyestrain is asthenopia (AS-then-OH-pee-ah),
which itself is a rather vague term. The visual science dictionary defines asthenopia
as the subjective complaint of uncomfortable, painful and irritable vision.
It then gives twenty-four (24) different types of asthenopia based on various
causes. Asthenopia can be caused from such problems as focusing spasm, different
vision in each eye, astigmatism, hyperopia (far-sighted), myopia (near-sighted),
excess light, voluntary focusing, eye coordination difficulties, and more. In
the computer environment, eyestrain- in all of its manifestations- can be caused
by a number of different environmental and visual conditions.
another of those discomfort symptoms and are the primary reason
most people seek an eye examination. They are also one of the most difficult
maladies to diagnose and treat effectively.
most often occur toward the front of the head (there are a few exceptions to
this), occur most often toward the middle or end of the day, do not appear upon
awakening, often occur in a different pattern on weekends than during the week,
can occur on one side of the head more than the other, and other more general
most likely get tension-type headaches. These can be precipitated by many forms
of stress, including anxiety and depression; numerous eye conditions, including
astigmatism and hyperopia; improper workplace conditions, including glare, poor
lighting, and improper workstation setup. If all obvious factors have been considered,
medical management is in order, often starting with a complete eye examination.
is the ability to distinguish between two distinctive points at a particular
distance. Whenever we direct our gaze to some point within twenty feet, we must
activate our focusing mechanism to increase the focal power of the eye and regain
the clear image on the retina. The ability of the eye to change its focal power
is called accommodation and varies with age. An image that is not focused accurately
will appear blurred.
symptoms can result from refractive error (e.g., hyperopia, myopia, astigmatism),
improper prescription lenses, presbyopia (age-related focusing problem) or other
focusing disorders.. Considering the working environment, blurred images can
also arise from a dirty screen, poor viewing angle, reflected glare or a poor
quality or defective monitor. All of these factors should be considered when
this symptom occurs.
Dry and Irritated
The front surface
of the eye is covered with a tissue that consists of glands which secrete the
tears. These tears cover the eye surface and maintain moisture for normal eye
function. The tears also help to maintain the proper oxygen balance of the external
eye structures and to keep the optical properties of the visual system maintained.
The normal tear layer is cleaned off and refreshed by the blinking action of
The blink reflex
is one of the fastest reflexes in the body and is present at birth. However,
our blink rate varies with different activities- faster when we are very active,
slower when we are sedate or concentrating. Research has shown that the blink
rate of computer workers dropped very significantly during work at a computer
compared to before and after work. Possible explanations for the decreased blink
rate include concentration on the task or a relatively limited range of eye
movements. The size of the eye opening is related to the direction of gaze-
as we gaze higher, the eyes open wider. The amount of evaporation roughly relates
to eye opening, the higher gaze angle when viewing a VDT screen results in faster
tear loss. It is also likely that the higher gaze angle results in a greater
percentage of blinks that are incomplete.
It is often heard
in medical circles that the eyes lead the body. Nature has designed
our visual system to be so dominant that we will alter our body posture to accommodate
any deficiency in the way we see.
In many office
situations the vision of a worker is compromised and they must adapt their posture
to ease the strain on the visual system. For example, if an older worker is
using glasses (single vision) which are designed for a 16" viewing distance,
they must lean in toward a screen which may be 20 to 25" or more away in
order to clear the image. If the same worker is using traditional bifocals,
which are designed to see the near object in the lower visual field, they must
tilt their head backward and lean forward to put the viewing section of the
lens into proper position to see the screen. These situations will cause obvious
physical problems which can be easily remedied with the proper glasses.
The eyes are designed
to be stimulated by light and to control the amount of light entering the eyeball.
There are, however, conditions which exist today that are foreign to the natural
lighting environment and can cause an adverse reaction to light. The largest
single factor in the workplace is glare.
is largely caused by large disparities in brightness in the field of view. It
is much more desirable to eliminate bright sources of light from the field of
view and strive to obtain a relatively even distribution of luminances. A person
is at greater risk to experience discomfort glare when the source is brighter
and when it is closer to the point of attention.
One of the primary
reasons discomfort glare is a problem for computer users is that light often
leaves the overhead fluorescent fixture in a wide angle, resulting in light
directly entering the workers eyes. This is a particular problem of computer
workers because they are looking horizontally in the room (assuming the screen
is at eye level). Bright open windows pose the same risks as overhead light
Workers are also
at risk for discomfort glare is they use a dark background display screen- resulting
in a greater brightness disparity between the task and other object in the room.
Other sources of large brightness differences at the computer workstation include
white paper on the desk, light colored desk surfaces, desk lamps directed toward
the eyes, or which illuminate the desk area too highly.
When viewing a
near point object, the eye muscles converge the eyes inward toward
the nose. Convergence allows the eyes to maintain the alignment of the image
on the same place on both retinas. When we lose our ability to maintain the
lock between the eyes, they mis-align and aim at different points
in space. If both eyes continue to transmit the image back to the brain, we
will experience double vision.
is a very uncomfortable and unacceptable condition for our visual system. We
will most likely suppress or turn off the image of one eye rather
than experience the double images. Double vision is a serious symptom and can
be caused by several factors. A complete eye examination is indicated if this
Syndrome is a by-product of excessive viewing of computer screens without regard
to practical visual hygiene. By just using some common sense and education about
the visual system, the symptoms of CVS can be diminished or eliminated.