[throwawayperson]

That's kind of a survivorship bias, and again uninformed.

People in China aren't allowed to move to cities freely especially back then, there are hukous to bind you to your birthplace, back then there were even police in Shenzhen dedicated to rounding up migrant workers (so called "blindly-moving migrants") and sending them back.

What I want to say is that you likely went to some major cities and observed people there, without realizing that those people are entitled to live there, meaning good chunk of them are well-educated and that education was a privilege you need to fight for, that means dedicated learning.

If myopia in China is genetic, then there is a big contradiction: in a generation of teens, those early drop-outs who went to factories and those who were putter around in schools rarely were myopic, yet those who are good academically and skinny had a high rate of myopia.

[seanmcdirmid]

Yes, people who study hard and perhaps watch too much TV will have more eye problems, but they also have to use their eyes more and will be diagnosed more often with eye problems. You don’t need great eye sight to pick rice, and it is very probable that many farmers have bad vision but just never care (or could even afford) glasses, especially back 20 years ago.