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It is possible that greater exposure to natural UV light outdoors makes a key difference, along with more time spent looking at the horizon and distant objects. Picture: Leon Lestrade

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London - Spending more time outdoors reduces a child’s risk of becoming short-sighted, academics suggest.

For every hour spent outside, the chances of needing glasses drops by two percent, a review of previous studies shows.

Overall, children who are short-sighted spend on average 3.7 fewer hours a week outdoors than those who had normal vision or were long-sighted.

It is possible that greater exposure to natural UV light outdoors makes a key difference, along with more time spent looking at the horizon and distant objects.

It is thought natural light, which is many times brighter than artificial, can trigger the release of the brain chemical dopamine, which then stops the eyeball growing out of shape.

The review cuts across the popular notion that it is too much time spent reading and on computers that causes short-sightedness, although experts say this may contribute to the problem.

Its alternative theory is that time spent outdoors helps protect the eyesight against other risk factors.

Short sightedness or myopia, which-makes distant objects seem blurred, often begins in childhood and the teens. An estimated 23 percent of British adults are short-sighted and need glasses, contact lenses or corrective laser surgery.

Dr Justin Sherwin, of Cambridge University, who led the analysis of eight studies involving 10,400 children and adolescents, said the protective effect seemed to come from being outdoors, rather than any specific activity.

The researcher in epidemiology said it was important to look at time spent outdoors rather than the reverse - time spent on computers and reading. Time spent outdoors in sporting activities appeared to be more protective than similar amounts of time spent doing sport indoors, he said.

In Singapore, 80 percent of adults suffer from myopia, which some have put down to the intensive education system there.

The review was presented at a meeting of the American Academy of Ophthalmology.

Dr Sherwin said there were many factors that might lower the risk of short-sightedness including more UV rays on the eyeball, preventing distortion that can lead to myopia.

Insufficient sunlight also lowers vitamin D levels, which might raise the risk of myopia, he said.

“But there has also been speculation that looking more often at the horizon when outdoors could be a protective factor. It’s likely to be an interaction of all these factors, with the risk of near-sightedness lowest in those who spend most time outdoors and least time doing close work.

Dr Sherwin said living in cities led to a higher risk of short-sightedness, with increasing population density linked to increasing risk. Different ethnic and racial groups also had different risk patterns, with children in Hong Kong, Singapore and some cities in China having the worst rates.

Studies are under way in Singapore to determine if children with a family history of myopia could be protected by spending more time outdoors, he added.

A study of 80 children with myopia in China found those who followed a regime of 30 hours or less on close work and more than 14 hours outdoors each week were less near-sighted than those who did not change their habits.

A study of Australian children found three hours of natural light a day could halve the risk of short-sightedness in children. - Daily Mail

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