It is no wonder that when spending most of the day staring at the computer, ones eyes get progressively worse at seeing distant objects: after all, you are increasingly training your eyes to read up close, and losing the need to see something far away. Recently, this fact hit me hard when I went to the grocery store and realized I could no longer make out the aisle banners. Those banners are made for average people, with average eyesight, and I am not used to being below average!
It turns out that exercising your eyes regularly can help prevent some deterioration (or at least the type that is caused by spending most of the time in close focus, without training a farther focus). For some ideas, check out this page: http://www.wikihow.com/Exercise-Your-Eyes
In an effort to train my own eyes, I covered my office with those eye charts you would see at the eye doctor's. I put these on multiple walls, at different distances and different heights, all around my office, and in the corridor across from my office. I now force myself to take regular break from my computer, to look up and read out some of the letters on the various walls.
When there is no horizon outside your window (but the wall of the nearest building), you have to improvise and create your own horizons to train your eyes on.
It is ok that I eventually learn which letters are on which walls - because the point is not to to read them out from memory, but to force one's eyes to follow the letter contours. Even if I know there's an "E" there, it's hard to find all its pieces.
Ever since starting this, I've started noticing my eyes getting tired at staring at the screen (something I haven't noticed, or probably ignored previously) - a sign that my eyes know they should be doing something else as well. Moreover, I can track my progress by noticing which letters my eyes can make out. Similarly, I can see how my eyesight degrades throughout the day (as my eyes get more tired), if I don't do the exercises.
In any case, even if this type of eye training will not save me from the expected deterioration due to excessive computer usage, at least the regular breaks of looking away from the monitor will help my sanity.