I guess staring at anything for too long wouldn't be a good idea. That is to say, unless that something is Megan Fox. . .
But seriously, I know personally I've gotten eye fatigue, where one eye twitches uncontrollably in my MMORPG days. That was like 15+ hours on the computer. Yeah, I know.
Maybe an occasional headache, etc. But I've been at this for so long I don't notice anything really.
Oh and I have bad eyes anyway (worn glasses since age 10), so yeah.