An eye doctor I know volunteers down in Central America. He flies down a few times a year and donates his expertise to the locals.
He states that among these people, who do very little reading, there are very few cases of nearsightedness. They have other problems, of course, but this doctor believes that close work can contribute to nearsightedness.
When he comes back to the states then he deals with those of us who should be using reading glasses to protect our eyes from the strain of focusing. He said that a close focus for long periods of time is unnatural.
MS