Being indoors more and more is only part of the problem. It’s what one does while indoors that makes a bigger impact on vision (i.e. being in front of computer monitors for hours on end, watching television constantly, etc.). Or, at least, that’s what I think.
Nope. Sounds resonable — computers.
You're close, except for the television. Television is viewed at a distance that is comfortable for most people. A study of the Inuit peoples of Alaska in the 60's revealed that the eyes are adaptable. If you do a lot of close up work, your eyes will adapt and you'll develop myopia to make up close work more comfortable.
The Inuit had no written language prior to contact with Westerners. When we introduced reading to them, the incidences of myopia increased several magnitudes overnight.