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People who spend more than two hours on a computer each day will experience symptoms of CVS or Computer Vision Syndrome.

The most common symptoms include

• dry eyes
• tired eyes
• headaches
• aching eyes
• burning eyes
• double vision
• blurred vision
• light sensitivity
• general eyestrain
• focusing difficulties
• neck and shoulder pain

Suggestions That Can Help Reduce Some of the Effects of CVS

• Glare screen filters may be helpful for some people, but they will not solve your computer  problems because they only affect glare from the computer screen, not the problems caused by the constant refocusing the eyes must do when working on a computer. An anti-reflective coating (AR Coat) on the lenses of glasses will reduce the glare coming at you and from behind you that causes eyestrain.            

• Proper lighting can reduce eyestrain and glare. Glare is created by glare on walls and other surfaces, reflections from the computer screen, bright light coming in from outside, and bright light inside. To decrease light and reflections from external light, close drapes or blinds. When using computers, lighting should be about half of that used in most offices. Using fewer light bulbs or florescent bulbs or use lower intensity bulbs can reduce glare caused by overhead lighting.

• Take a 10-15 minute break every hour to reduce eyestrain. Look away from the computer screen every 10-15 minutes and focus for 5-10 seconds on a distant object outside or down the hallway or get up and take a short walk. Everyone tends to stare at the computer and blink less, about 5 times less than normal, according to studies. Staring and decreased blinking dry the eyes out. Taking frequent breaks allows normal blinking and better wetting of the eyes. Office buildings tend to be dry environments that also reduce tearing. If you are experiencing significant dryness, ask your eye doctor about artificial tears or eye drops that you can use during the day. By modifying your work area, you can reduce eyestrain and other effects of CVS. If you need to look back and forth between the printed or written page and the computer, eyestrain can occur. Place written pages on a copy stand next to the monitor. Properly light the copy stand. Adjust your workstation and chair to the correct height. Purchase ergonomic furniture to assure proper screen locations and posture. Poor ergonomic setup is a cause of head, neck, shoulder, and back pain.

• Place your monitor directly in front of you, not off to one side. It should be about 20 to 26 inches away from you. Make sure your monitor is just right for you, not too high and not too low. You may need to raise or lower your chair. If you reposition your chair, keep in mind that your arms should be parallel to the floor when you type, and your feet should be flat on the floor or on a footstool. Finally, maintain good posture at your desk: keep your back straight and your shoulders back. Adjust the contrast between the background and the characters on the screen by adjusting the brightness on your computer screen.[1]

Hitzeman recommends looking away from the computer screen for a minute or two several times per hour.

Additionally, he says there are many other risks associated with using a computer monitor for long periods of time, but each one can be helped with these tips:

1. Blink. It may sound strange, but remembering to blink is important. According to Hitzeman, when someone stares at one object for a long time, they don't blink. This can lead to dry eyes, which can in turn lead to corneal irritation and diseases. People who have dry eyes naturally are especially at risk of chronic dry eye, which weakens the corneal structure.
2. Position your monitor correctly. Besides making sure your monitor is about two feet away and four inches below eye level to minimize neck strain, Hitzeman recommends making sure your monitor is glare-free. Any glare on the screen makes it harder to focus, which causes additional stress on the eye.
3. Get computer glasses. Just like reading glasses, those extremists who look at a monitor eight hours a day should consider getting computer glasses. These are specially designed to make it as easy as possible for your eyes to focus on the computer screen. According to Hitzeman, the optometrists will test your eyes while you look at a monitor, giving the ideal computer screen prescription.
4. Get regular eye exams. According to the American Optometric Association, adults should get their vision checked once at least every two years. This is especially important to computer vision syndrome, because improperly corrected vision can lead to the syndrome more easily, and even can cause permanent ocular damage. "Other than the dry eye issues, the only other damage that can occur from working excessive hours with a computer monitor comes from improperly corrected vision," said Hitzeman. "Everything else is just fatigue and can be fixed with rest." [2]

There is a difference in visual demand when one is viewing the display on the computer screen compare to reading a printed text. An image which is produced on the screen is made up of thousands of tiny spots or pixels and rasters which collectively form the image. The margin of the image or a word is usually not sharp and this is worsening if the image or word is formed by minimal pixels, or what is known as low resolution. As the resolution goes down the image become poor in quality and the visual demand of a reader has to be increased in order to appreciate well the wording or image. The contrast (intensity of the light) of the word to the background, the glare of the computer screen and the reflection from the glass screen are all important factors determining the amount of visual demand one must put in order to perceive the image well.[3]

Reference:

1. mdsupport.org/library/cvs.html 
2. newsinfo.iu.edu/news/page/normal/10479.html
3. ncbi.nlm.nih.gov/pmc/articles/PMC4170366