Location of computer screen – Most people find it more comfortable to view a computer when the eyes are looking downward. Optimally, the computer screen should be 15 to 20 degrees below eye level (about 4 or 5 inches) as measured from the center of the screen and 20 to 28 inches from the eyes.
Blinking – To minimize your chances of developing dry eye when using a computer, make an effort to blink frequently. Blinking keeps the front surface of your eye moist.
The computer screen should be no closer than 20 to 26 inches from the eyes. The further the computer screen is from the eyes the less eye strain that develops, and the longer you can use the computer without symptoms. [Source]