Why We're Losing Sight
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.
"This study confirms high myopia prevalence and a high rate of myopia progression among law students. The strongest association, especially in those with myopia onset before college, was a relation of myopia progression during law school with less daily exposure to darkness, a potential risk factor previously identified in childhood myopia," the researchers write.
Other researchers, however, argue that it's not too much light exposure, but too much time spent hunched over textbooks that has studious students squinting.
Karla Zadnik, OD, PhD, and colleagues at the Ohio State University College of Optometry in Columbus found in a study of eighth graders that children who had at least one myopic parent, who did more near work and/or less sports, and who scored higher in reading on a standardized test were more likely to be myopic. Significantly, increasing the amount of near work doubled the risk of becoming myopic, but that was less significant an effect than having a myopic parent. The finding suggests both heredity and environment play a role, the researchers say.
A third study found that among 71 nearsighted schoolchildren, myopia progressed more during the school year, when the kids were more likely to be doing the three "R's" or working at a computer, than it did during the summer months, when they were more likely to use their eyes for tasks requiring distance vision.