Computer Vision Syndrome
Vision is our most precious sense. Our eyes are in constant use every waking minute of every day. The way we use our eyes can determine how well we work throughout our lifetime. Over eighty percent of our learning is mediated through our eyes, indicating the important role our vision plays in our daily activities. Vision disturbance is a silent enemy that only appears afte along period of continued stress.
Computers have 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 VDTs. 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 VDT 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 VDT users also have a higher incidence of complaints than non-VDT users in the same environment.
Lets review 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 VDT environment, eyestrain- in all of its manifestations- can be caused by a number of different environmental and visual conditions.
Headaches are 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.
Visual headaches 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 symptoms.
VDT workers 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.
Visual acuity 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.
Blurred vision 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 Eyes
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 eyelids.
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 VDT workers dropped very significantly during work at a VDT 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.
Neck and/or Back Ache
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 20-25" 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.
Discomfort 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 fixtures.
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.
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 symptom occurs.
Computer Vision Syndrome is a by-product of excessive viewing of VDT 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.