In most Western nations, 20 to 40 percent of children have myopia, the technical term for nearsightedness. In the cities of East Asia, that number jumps as high as 90 percent, according to a new study in the British medical journal The Lancet. The culprit isn't genetics, as previously assumed, or even dietary factors like a dearth of carrots, says lead author Ian Morgan of the Australian National University. It's how kids in those education-obsessed nations spend their time: Reading, studying, watching TV, or staring at the computer rather than playing outside in the sun. Here's a look at Asia's eyesight problem, and what it might teach the rest of the world:

What are the study's key findings?
In the major cities in Japan, China, South Korea, Taiwan, Hong Kong, and Singapore, 80 to 90 percent of teens had myopia upon leaving high school. More worrisome, 10 to 20 percent of the high school grads were afflicted by high myopia, a more serious strain that can lead to blindness. The main problem, say the researchers, is lack of exposure to sunlight.

How does sunlight prevent myopia?
Bright light stimulates the release of dopamine, a neurotransmitter found in the brain, Morgan tells AFP. Dopamine, the theory goes, helps prevent the eyeball from growing into an elongated oval, which distorts the focus of light entering the eye. The average child in Singapore, for example, spends only half an hour outside each day, versus three hours for the typical kid in Australia, where the rate of myopia is about 10 percent. And in Africa, where much of life in conducted outside, myopia is barely a problem — "virtually none" exists, Morgan says.

Is this a new problem?
Yes. It's only recently that Asia saw an "extraordinary rise" in myopia, Morgan tells BBC News. Two generations ago, the rate was only 20 percent. "Children suffer from a double whammy in Southeast Asia," Morgan says. They face "massive educational pressures" and a culture that doesn't value time spent outside in bright light. That laser focus on learning isn't all bad, of course. "East Asian countries with high myopia now dominate international rankings of educational performance," the researchers note.

Are TV and computers part of the problem?
The amount of time in front of screens "can be a contributing factor," Morgan tells AFP. Though not harmful in itself, it becomes a problem when it's a substitute for getting outside. Attention, children, says Louis Peitzman at Gawker: "Keep this in mind when your parents advise you to stay inside and finish your work." 

How did researchers rule out genetics?
Morgan and his colleagues can't dismiss it entirely, but they don't think it's much of a factor and point to Singapore as evidence: All three major ethnic groups in the country — Chinese, Malay, and Indian — have seen sharp jumps in myopia. Also, Morgan tells BBC News, "simple genetic explanation just doesn't fit with that speed of change; gene pools just don't change in two generations." 

Can anything be done beyond making sure kids spend more time outside?
The damage is already done in Asia, says Morgan, and now we should focus on finding ways to treat myopia and, more crucially, prevent it from getting worse. "Even if successful prevention is possible, East Asia will still be faced, for close to the next 100 years, with an adult population at high risk of developing high myopia."

Sources: AFP, BBC News, Gawker, Medical Daily, Sky News, SmartPlanet