According to the American Optometric Association, Computer Vision Syndrome is now considered the No. 1 occupational hazard of the 21st Century. If you are surprised, you shouldn't be.

Today, there are more than 264 million personal computers in the United States alone (Computer Almanac 2008) and more than 98 million American workers use a computer on a daily basis (2001 U.S. Census). This widespread computer use has fueled growing complaints of eye strain and fatigue. The AOA reports that 14 percent of all optometric patients report computer-related symptoms and more than 10 million eye examinations are given annually in response to these complaints. With the range and scope of computer use increasing annually, it is important to understand the causes of CVS and how it can be managed.

The AOA defines CVS as the complex of eye and vision problems related to near work that people experience during or related to computer use. CVS is characterized by a wide variety of visual symptoms that result from the user's interaction with the computer display and/or its environment.

Not surprisingly, studies have shown that 50 to 90 percent of computer users will experience visual symptoms while working on a computer. Users experience these visual symptoms because the visual demand of the task exceeds the abilities of the user.

Research has revealed that the visual demands of computer work are much more challenging for the eye than the visual demands required to read the printed page. This is mostly due to the differences in contrast between the letters and the backgrounds on which they are placed. Even though computer screens have improved drastically over the last decade, they are still unable to provide a contrast comparable to the printed page. Until this is possible computer users will experience CVS symptoms.

What are other visual symptoms and causes of CVS'

Reduced blink rates are another common cause of CVS symptoms. Computer users often experience red, irritated or dry eyes due to evaporation of the tear film. Studies have shown that blink rates under normal circumstances measure about 22 blinks per minute, while computer users' blink rates measure less than seven blinks per minute. These drastically reduced blink rates allow the tear film to degrade and evaporate-resulting in a dry eye.

Uncorrected refractive error can also contribute to CVS symptoms. When the eyes are not corrected with the proper prescription, it puts undue stress on the visual system. The eyes try to compensate for this deficiency by using the accommodative or focusing system. This often results in complaints of blur and headaches depending on the individual's age and focusing ability.

Lighting has been identified as the most significant environmental factor contributing to CVS symptoms. Light from windows, overhead and supplemental lighting can cause glare and reflection problems that result in complaints of eye strain and headaches. Today most offices and workstation lighting are designed for desktop use, not computer use. According to the Occupational Safety and Health Administration, lighting should only be as bright as necessary to complete the task. OSHA claims that most office lighting is at least twice as bright as it needs to be and recommends 20 to 50 foot-candles for CRT use and up to 73 foot-candles for LCD use.

CVS isn't just a vision-related syndrome, it also has musculoskeletal symptoms. According to the National Institute of Occupational Safety and Health, 22 percent of computer users experience disorders. These disorders range from neck, shoulder and backache to wrist and hand pain. Proper ergonomics plays a large role in alleviating these symptoms.

Working distances and monitor placement are keys to combating neck and back pain. It is generally agreed that acceptable working distances should be at least 16 inches, ideally 20 to 26 inches, and source documents should be placed at the same viewing distances. Monitors or LCD screens should be placed approximately 10 to 15 degrees below the line of sight or 4 to 5 inches down from the center of the screen.

Don't forget about adjusting your chair, keyboard and work material. Proper placement of these will result in less stress on the body, which means fewer CVS symptoms. For more information on ergonomic standards please refer to the DOD Ergonomics Working Group's guide "Creating the Ideal Computer Workstation: A Step by Step Guide" available at:

How do you combat CVS' Prevention plays a large role in treating CVS symptoms. First and foremost, a computer user experiencing symptoms should obtain a comprehensive eye examination. Be sure to mention how often you use a computer and what symptoms you are experiencing. A new or updated prescription will often reduce or even eliminate CVS symptoms.

Another step you can take to help alleviate CVS symptoms is taking breaks during computer work. NIOSH, among others, recommends taking a 10 to 15 minute break every hour. Another recommended practice is to follow the 20-20-20 rule. This entails looking away from the computer every 20 minutes to something that is at least 20 feet away for 20 seconds.

In addition to the items listed above computer users can also increase their blink rates, upgrade to an LCD flat screen monitor and adjust the brightness and contrast of their computer screen.

For more information on CVS:

All About Vision,

American Optometric Association,