A new study has found that up to 90 per cent of school-leavers in Asia's major cities are suffering from myopia, or short-sightedness.

Of these affected, scientists said that 10 to 20 per cent had a condition called high myopia, which can lead to blindness.

The study, published in The Lancet medical journal, linked the eye damage with the long hours spent by Asian students studying as well as the lack of outdoor light.

Ian Morgan, a researcher in the Australian National University, said "most of what we've seen in East Asia is due to the environment, it is not genetic", contrary to the common belief 50 years ago.

Morgan said children who spent two to three hours outside every day were "probably reasonably safe".

The ones who are at major risk are the ones who study hard and don't get outside," he said.

"The amount of time they spend on computer games, watching television can be a contributing factor. As far as we can tell, it is not harmful in itself, but if it is a substitute for getting outside, then it is."

According to the study, the most myopic school-leavers in the world are to be found in cities in China, Taiwan, Hong Kong, Japan, Singapore and South Korea.

Researchers found that the average primary school pupil in Singapore, where up to nine in 10 young adults are myopic, spent only about 30 minutes outdoors every day - compared to three hours for children in Australia where the myopia prevalence among children of European origin is about 10 per cent.

The figure in Britain was about 30 to 40 per cent and in Africa "virtually none" - in the range of two to three per cent, according to Morgan.

More than other groups, children in East Asia "basically go to school, they don't go outside at school, they go home and they stay inside. They study and they watch television", Morgan said.

He said ways must be found to get children to spend more time in reasonably bright daylight without compromising their schooling.

"It is going to require some sort of structural change in the way a child's time is organised in East Asia because there is so much commitment to schooling and there is also a habit of taking a nap at lunchtime, which is, from our perspective, prime myopia prevention time," Morgan said.