Take Eye Breaks!
Throughout the day, give your eyes a break by forcing them to focus on something other than on your computer screen. Repetitive stress injury (RSI) and eye strain are common ailments among computer users, and there's no silver bullet for avoiding them beyond taking regular breaks to relax.
To help you deal with this problem, the 20-20-20 rule suggest that after every 20 minutes, you (the computer user) should take a break for at least 20 seconds and look at objects that are 20 feet away from you.
Adjust Your Monitor!
Position your computer screen at a comfortable distance, usually 18" to 24" away, and adjust it to just below eye level. Your eyes will close slightly when you're staring at the computer, minimizing fluid evaporation and the risk of dry eye syndrome.
Sources and more information about relieving eyestrain: http://www.mayoclinic.com/health/eyestrain/DS01084/DSECTION=prevention, http://www.apple.com/about/ergonomics/vision.html, http://lifehacker.com/361899/improve-your-vision-and-reduce-eye-strain-at-your-computer, http://www.labnol.org/software/computer-eye-exercise/14069/