Beause of my job nature, I often sitting in front of computer and stare at the monitor. WikiHow has a good how-to on ease the eyestrain and keep the eye healthy:
… It is even more important to do the exercises regularly than to do them for a long time. Even 30-60 seconds of eye movement every hour is very helpful. For example, when your computer takes its sweet time to do something, most people just swear at the poor thing and waste the time, but you can make a few circles with your eyes. Even the first day you do this, you should notice that, when you finish working, your eyes aren’t as tired as usual…
Consult your eye doctor before doing any of these exercises. The last thing you want to do is add further strain to your eyes, or damage them permanently.
How to Exercise Your Eyes – [WikiHow]