Nearsightedness is increasingly affecting young people in particular, and many even face partial blindness. But scientists now know what is causing this myopia epidemic - above all it’s a lack of daylight. Almost a quarter of the world's population suffers from myopia. No problem, you might think - because minor forms of myopia can be corrected. But the disease is now reaching alarming proportions: a fifth of those affected are severely short-sighted, and if nothing is done, up to a billion people could become virtually blind by 2050. How has this dramatic eyesight development come about? Nearsightedness is everywhere, especially in Asia - in the South Korean capital, Seoul, normal eyesight is even a rarity: 95 percent of people in their twenties can’t see properly unaided. Europe is still a long way from that, but here, too, the proportion of young people with myopia is already close to 50 percent. This worrying development is a global phenomenon: cases of myopia in Europe and the United States have almost doubled in the past 30 years and tripled in Asia. Although scientists have been searching for the cause of nearsightedness for years, there is still little public awareness of the problem of myopia. What triggers myopia? Genetic factors? Environmental influences? Too much staring at exercise books and computer screens? After years of guesswork, researchers now seem to have found the real cause of rampant myopia: daylight is a critical factor in the development of the sense of eyesight.