Comment by digikata

I don't know which it is or if multiple other factors are involved, but if you look at the structure of an eye, there are tissues which compose the iris which are connected to the adjacent tissue of where the lens is nestled. It's quite possible to me that increased use of the iris outdoors to close down and reduce light entering the eye could affect the "dynamic range" of the lens response to focal inputs - especially during the growth stages of kids.