There is no question that the use of video display terminals is skyrocketing in the United States and around the world. As more tasks are computerized, the number of computer workers and the amount of time at work spent on computers is dramatically increasing. Approximately 75 percent of jobs in the year 2000 relied on computers, while 50 percent of homes contained a computer. Recreational use of VDTs for Internet surfing and video games is also rising; consequently, people are spending a larger part of the day in front of a computer.

Along with these increases has come an increase in ocular complaints. We all have patients who complain of dry eyes, fatigue and eyestrain at the computer. Others may experience glare, pain, redness, diplopia or headaches. In response, a considerable body of literature has grown around the problems of escalating VDT use.

The problem is significant, with VDT workers complaining of asthenopia one and a half times as often as patients who perform conventional office work. Computer-related headache and eyestrain are reported during as many as 10 to 15 percent of routine eye exams, and some state that nearly 50 percent of VDT workers experience some eye discomfort. The nature of eye symptoms among computer users (especially concerning glare, lighting and spectacle requirements) is different from those of other near-point workers, and the frequency and severity are worse. The yearly cost of diagnosing and treating these issues may approach $2 billion.

Studies show that ocular symptoms tend to occur independent of the type of computer work (i.e. word-processing vs. data entry). Duration of computer work is, however, directly correlated to symptoms. Longer duration tends to cause long-lasting complaints, well after VDT work is finished. Permanent changes in refraction or accommodation/phorias have not been supported in the literature. And concerns about dangers from emitted ionizing and non-ionizing radiation have not been verified. However, annoying, potentially reversible difficulties are extremely common. These can be addressed under the broad categories of dry eye/blink rate, refractive/vergence issues, and ergonomics.

Dry Eye/Blink Rate

Good experimental data has shown that people who use VDTs suffer from a higher incidence of dry-eye syndrome. The current belief is that a decreased spontaneous eye blink rate (SEBR) leads to increased evaporation of tears. The SEBR in healthy patients decreases to 32 to 42 percent of normal while using a VDT, compared to SEBR at rest. For patients who already have moderately dry eyes, the SEBR in one study dropped from 16.6 per minute (during conversation) to 5.9 (after 30 minutes of VDT use), with marked variability between individuals.

Current thinking is that decreased SEBR occurs during VDT use via a central neural mechanism, secondary to increased visual attention. The peripheral cues that normally increase blink rate (like dryness), appear to be over-ridden during VDT use. Decreased SEBR, combined with a larger exposed ocular surface area due to wide opening, causes the tear film to dry rapidly. The dry environment of many offices certainly may compound the problem. Studies show that dry eye is highly associated with ocular complaints of asthenopia and visual fatigue during VDT use.

In pilot studies, we have reported that patients with dry-eye complaints on the computer for three hours or greater have a higher association of significant meibomian gland dysfunction. Studies have suggested that ocular computer vision syndrome complaints may indeed be meibomian gland dysfunction. Patients with previously diagnosed dry eyes or who have had LASIK surgery may need extra warnings concerning computer use. We recommend that patients take frequent short breaks from computer use, such as five minutes per hour, in addition to infrequent longer breaks. Patients are encouraged to voluntarily blink frequently.

Artificial tears are another key treatment for patients with ocular complaints during VDT use. We recommend frequent use of artificial tears, if evidence of dry eye-symptoms is present. A nontoxic tear preparation should be used at least every 30 minutes during actual computer use. Punctal plugs may also be considered and are usually very helpful.

Refractive/Vergence Issues

Prolonged VDT use requires considerable visual attention and places great visual demands. Thus, patients with mild uncorrected refractive errors may need spectacles during computer use. Of course, presbyopic patients need proper correction, appropriate to VDT position. Middle- and near-distance refraction is important. Single-vision "computer glasses" for presbyopes are often more comfortable than bifocals or progressives, depending on the type of computer work. If multifocal spectacles are necessary, it has been shown that lenses that cover the area from near to 2 m tend to be more comfortable than those that cover greater distances. Given the nature of computer work, spectacle design and fit needs to be modified on a case-by-case basis.

Patients with subclinical difficulties in accommodation or binocular vision during most tasks may have these problems surface during computer use. As duration of VDT use increases, transient changes in accommodation and vergence may follow. Breakdown of previously insignificant phorias may occur as fatigue increases. Reported results include diminished accommodative power, removal of the near point of convergence, and deviation of phoria for near vision. Careful examination of eye muscle balance is therefore important. Frequent breaks from VDT work and other near work may decrease the incidence of accommodative spasm and visual fatigue. In rare cases, prism glasses may be necessary. Changes in accommodative and vergence functions from computer use have, fortunately, been reported to be transient, with no cumulative effect.

Ergonomics

A host of factors in the work environment or home office can contribute to eyestrain during VDT use. Numerous studies have shown that placing the monitor below the horizontal plane of the eye increases visual comfort. One explanation is that less ocular surface area is exposed during downgaze; and measured tear-film volume is greater during downgaze. High monitor placement is associated with greater ocular discomfort and visual strain. There is some debate as to the ideal angle below horizontal. Individual adjustment of the angle based on comfort should be considered. Ten to 20 degrees below horizontal is often appropriate. Similarly, the viewing distance should be individually adjusted. However, placing the VDT 50-70 cm away allows for physiologic resting levels of vergence and accommodation. Recent studies demonstrate that even further placement of the monitor (90-100 cm) may produce even fewer symptoms. To maximize visual comfort, the top of the screen should not be tilted forward, as this can cause eyestrain.

We must not forget that overall ergonomics (i.e. seating, arm position, neck position, etc.) at the workstation should be adjusted to decrease body fatigue and musculoskeletal pain.

From a standpoint of ocular comfort, we recommend antiglare filters over VDT screens. These have been associated with shorter, less frequent, and less intense eye complaints during VDT use in some studies (though the results are controversial). The type of monitor is important as well, with high-resolution monitors (90 dpi or greater) being better-tolerated. Screens with dark characters against a light background are recommended. It may also help to regularly clean dust particles from the VDT surface.

We recommend VDTs with high refresh rates. Higher refresh rates (i.e. 300 Hz) correlate with lower perceived screen flicker and have been shown to improve accommodative amplitude and blink rate, compared with lower rates (i.e. 50-90 Hz). Liquid crystal displays (LCDs) have extremely high refresh rates and are well-tolerated.

Symptom Category	Symptoms	Diagnosis
Asthenopic	Eyestrain	Binocular Vision
	Tired Eyes Sore Eyes	Accomodation
Ocular-Surface Related	Dry Eyes Watery Eyes Irritated Eyes Contact Lens problems
Visual	Blurred Vision Slowness of focus change Double Vision	Refractive Error Accomodation Binocular Vision
Extra-Ocular	Neck Pain Back Pain Shoulder Pain	Presbyopic Correction Computer Screen Location

As may be expected, decreasing glare and illumination from bright overhead lights or windows is important to improve comfort and accommodative amplitude. Constant brightness, as opposed to bright and dim spots, is preferable. One source recommends sodium lamps over other types of illumination. Another recommends that screen background brightness should be three times greater than ambient lighting. VDT settings may need to be modified to increase text contrast as well.

VDT use is a remarkable risk factor for ocular discomfort. Ocular complaints from VDT use promise to become ever more important as computer use rises. These complaints can be related to dry eye, refractive issues or ergonomic issues. For each individual, we must remember to address all of these issues to achieve a successful treatment. Fortunately, these problems are relatively easy to treat, and treatment often has excellent success. Studies demonstrate that treatment of ocular issues combined with ergonomic workstation redesign cause a significant and lasting reduction in visual discomfort. By properly addressing ocular complaints from computer use, we can alleviate daily irritation for a huge number of patients.

Dr. Carlson is chief of the Corneal and Refractive Surgery Service at Duke University Eye Center, where Dr. Kanitkar is a clinical associate. Dr. Yee is a clinical professor in the Department of Ophthalmology and Visual Science at the University of Texas Health Science Center.

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