But why staring at computer screen would subject you to less sunlight than reading a book?
(Well, you can read it outdoors, but who does this nowadays).
It is hard to believe that reading a lot does not contribute to myopia.
Everyone knows about watchmakers who work all their lives with very small things and very close to their eyes. They all have high myopia degree. Similar embroideress.
But other craftsmen who work indoors and not in the sunlight (for example, carpenter or plumber) do not develop myopia.
Look at professional ballet dancers or ping-pong players. They coach a lot of hours daily and all indoor. Are they myopic?
Myopia is directly related with two factors: (1) genetic factor (2) straining your eyes in short distance.
Perhaps sun light is also important, but reading, working on computer and especially smartphone may hours a day (as you hold smartphone very close to your eyes) - this what really increases myopia.
If sunlight were crucial factor, it would be obvious that in northern countries myopia would be much more wide spread, but it does not happen.
The sunlight theory sounds interesting, but why is myopia so much widespread in Asia, where there is plenty sunlight?
OK, it could be because of different genes in Europeans and Asian people, but in Europe myopia is not more common in Sweden than in Spain.
Have a look here (book about myopia) : http://www.myopia.org/ebook/12chapter7.htm