Regan Ashby, assistant professor at the University of Canberra, said scientists once commonly thought too much time spent reading and working on a computer, combined with a genetic predisposition for the condition, led young people to become myopic, or shortsighted.

But then the Sydney Myopia Study, published in 2008, found children who spent a lot of time outside were less likely to develop myopia than their peers who stayed indoors.

Dr Ashby had shown exposure to bright light increased levels of neurotransmitter dopamine in the eyes of animals, which protected them against developing shortsightedness.

His results from the last few weeks suggested when animals were made myopic, then exposed regularly to bright light, it immediately stopped their condition from getting worse.

''If kid was already found to be myopic and you put them outside under high light, it would theoretically stop them going any further,'' he said.

Ian Morgan, a visiting professor at the ANU's college of medicine, biology and environment, was one of the authors of the Sydney Myopia Study. He said the study by his team in China, where the majority of young people needed glasses by the time they finished school, showed that when students sat through one class a day outside, the likelihood of developing myopia decreased.

He was working towards guidelines for school systems on how long children needed to spend outside to prevent myopia, currently thought to be about three hours a day.

Professor Morgan said he was also seeking funding to study sight in students at selective schools in NSW, who were more likely to develop shortsightedness than their peers. because they spend less time outdoors