Why We're Losing Sight
Although studies of eyesight in identical twins have suggested that there may be some genetic component to myopia, heredity seems to play less of a role than environment, says Richard A. Stone, MD, vice chair for research at the Scheie Eye Institute and professor of ophthalmology at the University of Pennsylvania in Philadelphia.
"There is a tremendous increase in myopia generally as societies change, moving from rural to urban industrialized societies," he tells WebMD. "That's what happened in Asia: There's very good data showing a tremendous increase in myopia prevalence from about 10% to 50%-80% over just a few decades, so obviously there's a tremendous environmental component."
What's more, the stereotype of the nearsighted intellectual who polishes his eyeglasses with the end of his tie may not be too far off the mark, Stone says.
Other studies show a very strong association between myopia and increased education and increased intelligence. "The theory is that [the myopia] is caused by near work, reading, using the eyes for stuff up close, but it's proved extraordinarily difficult to get convincing evidence that actually using the eyes up close is what's responsible," says Stone.
Stone and colleagues examined another possibility: That exposure to light, or, more accurately, less time spent in darkness, might have an effect on myopia progression. Stone tells WebMD that decades of animal studies have suggested that alterations in normal cycles of light and darkness can have an adverse effect on vision, and that this might account for at least some myopic changes.
To test this, they looked at myopia progression and various potential myopia risk factors in third-year law students at the University of Pennsylvania. They found that while having nearsighted parents didn't seem to make much difference, burning the midnight oil did. Of the 96 students who were nearsighted before law school, myopia progressed in 86% during law school, and among 75 students with normal vision at the beginning of law school, 19% became myopic. Students who were exposed to less than about 5.5 hours of darkness each day were more likely to experience worsening of myopia than those getting more darkness -- presumably in sleep.