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Computer Vision Syndrome

CVS, or Computer Vision Syndrome, sounds like something out of a bad Ď60s sci-fi movie. But in reality, 75-90% of people that regularly work on a computer suffer from this disorder. In our modern world, it is difficult to find someone who does not use a computer at some point throughout the workday or at home. While we as eye care professionals cannot affect the general populationís computer use, we can offer suggestions and products to help our patients better deal with the problems caused by extended computer use.

The first thing we have to do is to identify the symptoms of computer vision syndrome. Symptoms of CVS include; tired, dry, burning or aching eyes, blurred or double vision, headaches, light sensitivity, and neck and shoulder pain. These symptoms can present themselves at different times and with changing intensity. They may also show up in nearly any combination. This makes communicating with your patients crucial to finding the best solution for each individual situation.

Now that we know the symptoms, letís discuss the causes of CVS. The human eye focuses very well on images with a well-defined edge, such as printed material with dark text on a light background. The eyes respond quite differently to electronically generated images shown on a screen. While printed letters and symbols have very distinct edges that are created by layering ink onto paper, images on a Video Display Terminal (VDT) are produced by grouping together small points on the screen known as pixels. This is true for standard CRT monitors as well as newer LCD screens. If you were to pass a light meter over a printed letter, you would notice very sharp contrast between the ink and paper known as a square wave. If you were to pass the same light meter over an electronically generated letter, you would see that each pixel has a higher intensity at the center and gradually fades away toward the edges in what is known as a Gaussian wave. Think of this as the bell curves you learned about in statistics class. This Ďbumpyí surface makes it very difficult for the eyes to maintain a comfortable focus on the screen for any extended amount of time.

The eyes will try to focus on the plane of the computer screen, but cannot maintain that focus for long and will eventually relax to a focal point somewhere behind the screen called the resting point of accommodation (RPA). The eyes constantly switch between focusing on the screen and the RPA, causing fatigue. To give you an idea of what this does to your eyes, imagine yourself holding your arm above your head and rapidly opening and closing your hand. This would be no problem at all for the first few minutes. Now imagine how your hand, arm, and shoulder would feel if you did this non-stop for 6-8 hours every day. You can understand the fatigue this would cause. Then, imagine trying to pick up a bottle of water with that same hand after doing this all day long. This is similar to how your eyes react when you try to focus on a distant object after a full day working on the computer. 

There are many techniques to ease the effects of CVS. Most experts agree that you should take a 10-minute break from the computer every hour. There is a technique called 20-20-20 that recommends looking away from your screen to an object 20 feet away for 20 seconds every 20 minutes of computer use. It is also helpful to dim the lights in the room to reduce reflected glare and to maintain proper posture and ergonomics while working. Some people may even need artificial tears or other drops to alleviate more severe dry-eye symptoms.

Luckily, there are lenses that are specifically designed to help focus on the computer or other mid-range tasks. Lenses such as the Shamir Office, HOYA Tact, and the Zeiss Gradal RD have been created for computer use. These specialty lenses are a type of progressive that allows for relaxed wide-angle viewing at an intermediate distance with the head held in a more normal posture. The principle behind the near variable focus lenses works on digression rather than progression. The lab starts with a known near vision power and adds more minus going up to the intermediate area of the lens. 

The HOYA Tact has two different options when it comes to power; you can choose either 40% or 60% of the add power available in the intermediate area of the lens depending on which is better suited to the patient. The Gradal RD is actually calculated more like a traditional progressive. The lab will take the patientís prescription and add +.50 to the distance power and reduce the add power by -.50. This gives full reading power at near and also gives better intermediate vision at the top of the lens. The Shamir Office offers the most choice of the lenses mentioned here. In the traditional Office lens, you can choose from four dynamic powers; .75, 1.25, 1.75, or 2.25. The dynamic power is based on the patients add power and is subtracted from the add to give a more controllable intermediate focus. Shamir also offers the Office lens in a free-form variety where the lab will choose the dynamic power based on the prescription as well as fitting information and the patientís preferred working distances. The free-form dynamic powers are available in .01 steps from .75-2.25 giving 150 different powers available for each prescription. Contact your lab for lens availability and necessary parameters.

By helping the eyes focus on the monitor in a more relaxed state, there is less fatigue on the eyes and computer work becomes much less taxing. These lenses will also allow your patients to read as they do with traditional bifocal or progressive lenses. Keep in mind that while these lenses were designed for computer use, they also work well for musicians or hobbyists that need to focus on things at armís length.

While this lens technology will help to prevent some aspects of computer vision syndrome, it is important that we as eye care professionals help to educate our patients on the other techniques listed above as well. Whether you love them or hate them, computers have become an integral part of our everyday lives. Our goal is to allow our patients to do what they need to do without having to constantly worry about their tired, aching eyes.

Bob Faktor, ABOC


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