There's already a very similar thread on the first page:
Another reading thread.
One person gave a link to a website that said "nearwork" does not affect eyesight, but I disagree. I don't think your eyes are made to focus on the same thing for hours at a time. I'm fairly certain I've heard that cultures where reading was popular had high rates of myopia, but I'm not sure. This website suggests that reading does cause myopia, but it's also trying to push eye exercises which are proven ♥♥♥♥♥♥♥♥:
Myopia and Eye Exercises – American Vision Institute
Anyways, I also have a desk job sitting at a computer 9 hours a day. Then I go back home and work on my website or some programming and I talk to friends online. I surf message boards. I do most of my coursework on a computer. I pretty much live on a computer or I'm reading. I really do think it's likely that there's a link between nearwork and myopia. I had to get glasses in 8th grade and it was around that time when I started playing Asheron's Call, one of the first mmorpgs. Needless, to say it was addictive and I spent way too much time on it.
On the other hand, I have been using computers in a similar way for nearly a decade. I wear glasses, but my eyesight hasn't really gotten worse. I'm actually more worried about carpal tunnel syndrome.