Computer Vision Syndrome

Explained at Vox:

A significant number of heavy computer users experience a range of symptoms that researchers group under the umbrella phrase "computer vision syndrome."...
Studies have shown that when people read from computer screens, their blink rate plummets — but this also happens when people read words from a printed page. In either case, when you blink less frequently, your eyes are much more likely to become dried out....
Eye strain is the second-most common complaint of computer vision syndrome, and can be accompanied by headaches and pain in or around the eyes... It may also lead to a related problem: difficulty focusing...
Observational studies have found that, in general, a person's level of education — and thus the amount of reading they've done over their lifetime — is positively correlated with their risk of myopia. But the direction of causation could go either way: they could have read more growing up, becoming both more educated and myopic, or for various reasons people prone to myopia could be more likely to read more...
Every twenty minutes, a person should look away from their desk for twenty seconds, and focus on something at least twenty feet away," he says. This prevents your eyes from focusing at near distances for extremely long durations, forcing them to alter their focal distance. It's also a good idea to consciously do some blinking at this sort of regular interval, in order to prevent excessive dryness. Your desk should also be set up in a way to minimize eye stress. It's recommended that your monitor be positioned 20 to 40 inches in front of your eyes, and the top of the monitor should line up with your eye level, so you're looking down about 15 degrees when you stare at the screen.