Monitor Your Computer Use

Long hours looking at screen root cause of CVS

By A.Paul Chous, MA, OD, FAAO

Computer Vision Syndrome (CVS) refers to a cluster of eye and vision symptoms often experienced by people who spend long hours looking at a computer monitor, whether it be for work, play, or a combination of the two. Symptoms include fatigue, blurred vision, eye strain, redness, watering, burning, dryness, headache, eye ache, double vision, and sore neck and shoulders resulting from poor posture adopted to improve these visual problems. In most cases, symptoms occur because the visual demands of the task exceed the visual abilities of the individual to comfortably perform the task. Various studies show that 50 to 90% of computer users experience some symptoms of CVS, with as many as 115 million American workers and 30 million school-aged children having at least some eye and vision complaints related to computer usage on a regular basis. It is likely that the rise in both CVS and the epidemic of type 2 diabetes is no mere coincidence, as both are linked to a more sedentary lifestyle.

CVS occurs because the eyes and brain react differently to characters on a video display terminal (VDT) screen than they do to printed characters on a page. Human eyes have little trouble accurately focusing on most printed materials, which typically consist of ‘high contrast,' dense, black characters with well-defined edges. Characters on a VDT screen have lower contrast and poorly defined edges because they are composed of individual pixels that are brightest in the center and diminish in intensity at the edges (see figure 1).

                   Paul C July Col

Figure 1 – Pixelated and Printed Letter "A"

Even perfectly functioning eyes have difficulty maintaining accurate focus on such optically imperfect characters, leading to fatiguing oscillation of the eyes' focusing muscles that ultimately lead to symptoms; if the eyes' natural ability to focus is further compromised by optical problems like nearsightedness, farsightedness, astigmatism (non-spherical curvature of the cornea or lens) and presbyopia (loss of normal focusing ability with age), or eye muscle coordination problems that prevent the two eyes from working together as a team, symptoms will not only develop sooner but will be more severe. In addition, it has been shown that the number of times per minute people blink is significantly decreased when looking at a computer screen, a factor which can lead to dry eye. Blinking re-moisturizes the front surface of the eyes, and anything that decreases the frequency of blinking can cause or exacerbate symptoms of dry eye like burning, stinging, redness, and blurry vision. Squinting to see the computer monitor more clearly, or to reduce discomfort from the glare of a monitor, cuts the blink rate in half and is now believed to be a major contributor to computer vision syndrome, causing symptoms of dry eye plus headache, eye strain, and fatigue.

The best defense against CVS is to consult your eye doctor about specific ways to optimize your visual efficiency when using a computer. In general, maintaining an 18-25 inch distance between your eyes and the monitor, positioning the monitor about twenty degrees below eye level (the eyes focus better in down gaze), eliminating glare from overhead lighting and windows (keep the monitor perpendicular to any open windows), use of (glass, not mesh) glare filters, and using a higher screen refresh rate (> 70 Hz) will help. Taking frequent, short breaks, one minute every 20 minutes, will also greatly improve overall efficiency and comfort, as will specially designed computer glasses that are customized for your workstation and unique prescription. Remember that computer use burns very few calories whether you are an adult or child, and that prolonged computer use is undoubtedly contributing to the epidemic of overweight and obesity that contributes to growing rates of diabetes in kids and grown-ups alike.

For more information on diabetic eye disease, consult Dr. Chous' book Diabetic Eye Disease: Lessons From a Diabetic Eye Doctor, Fairwood Press, Seattle, 2003.

Read more about Dr. Chous here.

Visit Dr. Chous' website here.




Last Modified Date: June 28, 2013


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