Eye fatigue, or asthenopia, is a weakness of the eye that can cause pain, dimmed vision, double vision, nausea and several different types of headaches. The kind of asthenopia that is associated with computer use is accommodative asthenopia, which is due to a strain of the ciliary (eyelid) muscle. To understand what this means, the eye care professional must have a broad understanding of accommodation, the change that the eye goes through to enable a person to see an object at various distances. Accommodation is a multistep process that involves the crystalline lens, ciliary muscles, a cranial nerve and the Zonules of Zinn. The process works as following:

• The brain recognizes a blurred near or intermediate image;

• Cranial nerve III (oculomotor) is activated. This nerve controls accommodation, papillary constriction and ocular convergence;

• Eyes converge as the medial recti muscles contract and the pupils undergo miosis, or constriction;

• The ciliary muscles contract and move toward the crystalline lens, causing the crystalline lens to move forward;

• Zonule fibers relax and cause the crystalline lens to bulge, increasing its power;

• Light is refocused through the lens so that the image falls on the retina.

Now, when an individual concentrates on something at a close or intermediate distance, the ciliary muscles are in a constant state of contraction. As the contraction continues, fatigue sets in and the muscles are forced to begin to relax. When the muscles begin to loosen, the crystalline lens flattens and the image starts to blur slightly. This constant state of contraction can also lead to pain in and around the eye, squinting, headaches as well as a condition known as pseudo myopia.

Pseudo myopia is a spasm in the ciliary muscle caused by a constant state of ciliary contraction. When a spasm occurs, distance objects become blurry, because the crystalline lens remains in a constant state of accommodation. The eye would then be in a myopic state due to the fact that the eye is now over plus in power from the spasm. All of the images are focused before the retina, just like in traditional myopia. When the spasm releases, vision goes back to normal.

In the case of the computer, this situation is aggravated by the construction of the image that the patient is trying to view. Computer images are created by pixels or small dots that are aligned to create the image. However, a pixel does not have the same sharp definition that the printed counterpart contains. This causes the eyes to work harder trying to see the computer image. In addition, the computer screen has a refresh rate that re-draws the screen every so often. This causes further strain on our accommodative mechanism, as we try to follow this movement unconsciously. Finally, the glare from the screen and the overhead lighting can cause even further accommodative strain.
 

One of the easiest ways to treat computer eye fatigue syndrome is to provide the patient with computer lenses. By providing spectacle lenses formulated just for computer distance, accommodation relaxes and eyestrain and blurred vision are reduced. The hard part is trying to convince a patient that he or she needs a separate pair of glasses for the computer.

Computer glasses are needed for the unusual distance most computers are set in relation to the eye. They are usually positioned 20 to 26 inches from the eye, closer than distance or driving visual needs and farther away than near or reading visual needs. Glasses are not commonly prescribed for this distance. Most single vision glasses are prescribed to correct near or far vision. Bifocal lenses correct near and far but neglect the intermediate area, and other multifocals such as progressives and trifocals have only a small area dedicated to this zone and are inadequate for long time computer use. This inadequacy stems from the unusual head position required to view most computer screens through a progressive or trifocal.
 

• Intermediate single vision only lens

This computer lens is designed to have only the prescription for computer distance throughout the whole lens. If the patient is in a multifocal prescription, the eye care professional must take half of the add power and add it to the distance. This provides the intermediate power correction for most cases. The benefits to this lens are that it provides the widest intermediate area possible with no image jump or possibly distracting lines. The main drawback is the lack of a near area. This can be a serious problem, because many people who work on a computer usually have to look at a near distance also if only to see the keyboard.

• Flat top occupational lens

A modified flat top is a very successful way to ease computer eye fatigue syndrome. The portion of the lens that is usually prescribed to treat distance is modified for intermediate use and the segment remains for near use.

Essilor has developed a lens called the Anti Fatigue Lens. It is different from traditional computer lenses, because it is intended for fulltime wear and it does not follow a progressive type lens design. It has a power boost at the bottom of the lens of a little over half a diopter that helps to ease eyestrain and fatigue. The lens is intended for myopes experiencing fatigue and emerging presbyopes, making it an excellent lens for those with computer eye fatigue once it has been prescribed.
 

Computer eye fatigue syndrome is an increasing concern and problem today. It is estimated that as many as 90 percent of the United States workforce have this condition to a certain extent. It not only causes discomfort for the individual, but a decrease in productivity and enjoyment for the ever-increasing computer-using population.
 
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