In my family (n=basically_none), it seems that myopia correlates strongly with habits. The most bookish, indoors-y kids ended up in glasses - and the more so, the thicker the glasses - while folks who spent their childhoods running around outside tend to have 20/20 vision.

Assuming such an effect really exists, I expect it would be very difficult to statistically distinguish from straight heredity. Kids' early childhood habits tend to reflect family culture.