In the last few days I was practically unable to look at any monitor. So I went to two medics (that's because the first one gave me the impression that she decided the treatment the moment she heard that I'm a programmer; after that moment she was very opaque to anything I said -- so, don't go to Biomedica if you have eye problems; they have some good medics but not in this domain).
It turns out that I may need glasses: -0.25/m for the left eye and +0.25/m for the right one. But the second medic thought these values are too small to explain what I told her. So she kept investigating and found out that my left eye is not converging correctly: when I look at things that are close my left eye has a tendency to keep looking ahead, instead of going towards the center. This means extra stress for the brain because it has to do corrections.
Two possible reasons are: lack of calcium and something wrong inside with the muscles. I am already taking calcium as a result of blood tests I took one month ago. So she recommended that I try to have longer breaks and try to look somewhere in the distance during those breaks. If things aren't better in 2 months with those breaks and Ca then I should go back and she will probably prescribe some glasses that allow the eyes to stay in the "look in the distance" position and see things that are close.
So this morning I had a bit of fun (despite the title) thinking about things like what kind of lenses should one use to allow the muscles that focus the lens to stay more relaxed, and the relation between the shape of a lens end its focal point. I could have looked those up in some high-school textbook, but it's always fun to do it yourself :) However, I won't write my results here because I already looked for too long in the monitor :p I need a longer rest period (1 week?) I never had such problems before...