vision and ergonomics Protect your eyes

If you were Bifocals:
Bifocals are designed for reading at an approximate distance of 16 inches. The typical computer monitor is positioned 18 to 30 inches away from the user. Bifocals are angled downward for reading. Bifocal users must tilt their necks and heads in order to see the screen.
It is a good idea to lower the monitor so that the neck can remain in a neutral position while looking out of the glasses.
One other option would be to get a pair of glasses that are used solely for the computer.
Contact Lenses/dry eyes:
Individuals who wear contact lenses blink less than people who have normal vision or wear glasses. Contact wearers need to ensure they blink enough (average is 22 a minute, typically computer users and contact lens wearers about 6 to 10 times a minute)
Consider using use artificial tears to reduce eye irritation. NOTE: Do not use vasoconstrictors to reduce redness and irritation in the place of artificial tears.
Differences in Computer versus Printed Material:
Printed material is characterized by smooth, dense, black lines with edges that are well defined. Eyes focus to printed material differently than characters on the computer screen, because the characters on the computer screen fade out around the edges, or are fuzzier and irregular edges with pixels. The characters are the brightest in the middle and then fade out, so the eyes have difficulty focusing on them. Eyes can end up being fatigued and this can result in eyestrain.
VISION TIPS
Rest your eyes for at least 20 seconds every 20 minutes at a minimum. ( the 20/20 rule!)
Change the distance of your focusing during rest periods. Look out the window at something 20 feet away or more.
Keep your screen clean with proper contrast.
For CRT users : Reduce glare on your screen by eliminating or reducing overhead, direct lighting or direct glare for windows. If you can see your own image in the monitor screen before it is turned on, reflections and indirect glare from the screen it may cause glare problems.
For LCD screen users, keep light levels around the screen as even as possible.
Monitor/Screen distance
Use the one third rule for distance to the monitor, put something on the screen you typically read every day, Move back as far away as you can and still see the text clearly. One third of that distance is your best viewing distance. (if less than 24 inches, consider changing glasses or enlarging font.
Unless you wear bifocals, the top of the monitor should come to approximately your mid forehead ( or in other words, the top of the viewing screen should be at eye level)