But it was obvious that genes could not be the whole story. One of the clearest signs came from a 1969 study of Inuit people on the northern tip of Alaska whose lifestyle was changing. Of adults who had grown up in isolated communities, only 2 of 131 had myopic eyes. But more than half of their children and grandchildren had the condition.After a long series of theories and retractions over the years, scientists think they have isolated the causative factor:
After five years, one in five of the children had developed myopia, and the only environmental factor that was strongly associated with risk was time spent outdoors. “We thought it was an odd finding,” recalls Mutti, “but it just kept coming up as we did the analyses.” A year later, Rose and her colleagues arrived at much the same conclusion in Australia. After studying more than 4,000 children at Sydney primary and secondary schools for three years, they found that children who spent less time outside were at greater risk of developing myopia.Two things about being outside might be involved: bright sunlight, and regularly focusing on distant objects. The scientific attention now is on light, and the best guess is that children need to spend at least three hours a day outside in the daylight to be protected from myopia.