Screw your eyes! What about the other problems!?
It's bad to stay with your computer too long. You'll develop certain traits most people would consider anti-social and hermit-like. Your personal hygiene will suffer and your sleep pattern will be thoroughly disrupted.
Staying with your computer too long might also make you start having certain 'feelings' for your hardware. Very dangerous since they become obsolete faster than Paris Hilton can spend her family's money.