My favorite theory is that reading causes a lot of neural activity at and near the fovea (the center of the eye that we focus on) but not as much around the periphery (as say sports would). Some neurotransmitters double as growth factors, so over time all that localized neural activity makes the eyeball elongate along the visual axis into a prolate ellipsoid.
If true, I’m sure it’s not the only mechanism. Myopia runs in my family, and I was blessed with 16 diopters’ worth. As in Coke bottle bottoms. Choose your parents with care, folks!
The difference is only -1 dioptre for those who have a university degree vs those who don’t.
Anecdote ahoy! I got my first pair of glasses at 10.
The eye doctor told me that if I spent more time outdoors, playing sports rather than reading, I could put off having to wear glasses full time. I already loved baseball, so I joined little league softball and played for 4 years.
I began wearing glasses full time at 19, but its only now, at 45, that I wear them for reading.
Every adult in my family wears glasses, so I don’t think I could have avoided it, but I think it’s interesting how what you do with your eyes can affect their ability to focus at a specific range.
Presbyopia. Completely different from nearsightedness.