Programmers have a much greater tendency to go near-sighted. What I was told was that we spend so much time making our eyes focus on things up close that our eyes start to get inflexible.
Have you ever noticed how extreme bodybuilders have trouble making their arms hang straight down? Instead, they curl up a bit. That's what happens to your eyes after years of focusing up close so much; they get too pumped up and can't relax anymore.
What is suggested is that you take periodic breaks and try to focus your eyes on something far away. If you are in one end of a big building, you can praire-dog up and try to look at the far wall for a while. For most of us, a walk outside is probably the best option though. It's healthier, and you won't look quite so much like a loon.