SYDNEY - Just spending two to three hours outdoors daily is a great way of halting short sightedness or myopia, which is fast spreading among urban children worldwide.
Myopia affects over 1.6 billion people worldwide, is spreading rapidly among city populations and, in its most severe form, can cause blindness by middle-age.
Scientists from The Vision Centre said that increased exposure to daylight can prevent the permanent short-sightedness and eye damage which now afflicts up to 80-90 per cent of East Asian children.
The finding demolishes long-held beliefs that short sight is due mainly to reading, and overuse of TVs and computers by youngsters, or is primarily linked to genetic factors.
'The prevalence of myopia in the Australian population is dramatically lower than in other urban societies round the world - yet we do just as much reading and computer work,' said Ian Morgan of the ARC Centre of Excellence in Vision Science (The Vision Centre) and Australian National University.
Comparing myopia levels among people of Indian origin, the team noted five percent short-sightedness among rural Indians, 10 percent among city Indians - and 65 per cent among Indians living in Singapore.
'Our hypothesis is that the light intensity experienced outdoors - which can be hundreds of times brighter than indoor light - causes a release of dopamine, which is known to block the growth of the eyeball. This prevents it taking on the distorted shape found in myopic people. We are now testing this idea,' said Morgan.
The team's conclusions are borne out by new research in Singapore and the US, which has reached similar conclusions, said a Vision Centre release.
'Looking at children of Chinese origin, we found only three percent of those in Sydney suffered from myopia, compared with 30 per cent in Singapore, where there is an epidemic,' said Morgan.
Yet, if anything, the children of Chinese origin in Sydney read more than those in Singapore. This clearly suggests that myopia was triggered by something in the environment, rather than the genes. The critical factor seemed to be the fact that the children in Singapore spent much less time outdoors.'
'We're seeing large increases in myopia among children in urban societies all around the world - and the outstanding common factor may be less and less time spent outdoors,' said Morgan.
'The idea that 'reading makes you short-sighted' has been popular for a couple of hundred years. But recent data shows that the time spent indoors is a more important factor. Children who read a lot, but still go outdoors, have far less myopia.'
Morgan explained that myopia is essentially an eye that has grown too long, and once it is too long, you can't shorten it again: 'So you have to stop it happening in the first place.