It is not about sunlight or UV. And it is not "just genetics".
replyThe natural rest position of the human eye is to focus at the infinite. Focusing on closer objects like books or screens requires a constant effort (we don't feel it).
The eye simply adapts and elongate to relieve some of the strain. Wearing corrective lenses further amplify the process.
If you want your kids to have perfect vision they should spend a lot of time playing outside, until early adulthood.
Yeah I'm not sure what currently "science" says, but from first principles something along these lines must be true, because "genetics" can't explain why some places like China went from low levels of myopia to extremely high levels in a couple of generations.
replyClearly there's some significant environmental factor, and constantly focusing at short distances and/or getting no bright light exposure are the two obvious candidates (in other words, being inside all the time)