A WORLD OUT OF FOCUS
Fifty years ago, about one American teenager in four was nearsighted1. Nearsighted people can usually read a book with no difficulty, but they cannot see faraway things clearly. Today the figure is more than four in ten, and in some cities in East Asia almost nine out of ten students finish high school needing glasses. Scientists long blamed this mainly on genes2 passed down from parents. Yet genes change very slowly, so they cannot explain such a fast rise.(lines 1–5)
For a child, poor distance vision3 is more than a small problem. Without glasses, a nearsighted pupil may struggle to read what the teacher writes on the board and may fall behind in class. "Glasses solve that problem quickly," says eye researcher Dr. Laura Hayes. "But they do not stop the eye itself from growing too long, and that is what makes a child nearsighted. So a seven-year-old with weak glasses often needs far stronger ones by eighteen."(lines 6–10)
Why do eyes grow too long? Most scientists now point to a lack of natural daylight. Bright outdoor light makes the retina4 send a chemical signal that slows the eye's growth. Children who stay indoors all day miss this signal, so their eyes may be unable to stop growing in time. "Even a classroom with big windows is far darker than a cloudy day outside," Hayes explains. "That is why the hours children spend outdoors matter more than what they do there."(lines 11–15)
Scientists in many countries are worried about what lies ahead. Researchers predict that by 2050, about half of the world's population will be nearsighted, and nearly a billion people will be very nearsighted. That matters because a very long eye has thin, stretched5 walls, and this makes serious eye diseases far more likely in later life. Some of these diseases can lead to blindness6, and many of them cannot be cured once they appear.(lines 16–20)
The good news, Hayes says, is that the trend can be slowed. In parts of Asia, schools have added an extra 40-minute outdoor break to every school day, and in one large study, fewer pupils became nearsighted over the next three years. "Parents can help too, by sending children out to play after school instead of letting them sit in front of a screen," she says. "About two hours of daylight a day seems to make a real difference."(lines 21–25)