An interesting article by Nathan Seppa in the February 9 Science News reports that rates of nearsightedness have been on the increase in recent decades in North America and Europe. For example, in the United States among people ages 12 to 54, the percentage with nearsightedness went from 25% to 42% from the early 1970s to the early 2000s.
But it's in East Asia that the trend is striking. "Recent studies of young men in Seoul and college students in Shanghai find that more than 95 percent are nearsighted." It's not known for certain what's causing the increase, but there's some evidence that children playing outside, especially in rural areas with distant horizons, are much less likely to become nearsighted in adulthood. So the heavy emphasis on study in many countries of East Asia may lead to student's spending less time outside.
Incidentally, the evidence suggests that while doing a lot of close work (reading, using a computer, etc.) might help contribute to nearsightedness, it's the lack of outdoor time that appears to be the main problem.