In my personal experience, sitting in front of the computer too much can put a lot of strain on your eyes. When I was in Pensacola waiting to class up for API, I was spending maybe 3-4 hours a day in front of the computer. I noticed that I was having a harder time focusing on some things, and my eyes were hurting, almost like a strained muscle, believe it or not. I printed up a homemade eyechart of sorts, and taped it up on the wall. After about a week (maybe two) of limiting my time on the computer I found that I was able to read things on my little eyechart much more easily, and was able to read lines that I had been unable too when I was on the computer a lot. It's not a scientific test, but it convinced me.