If you want your kids to have great eyesight, send them outside to play each day.
New UK research shows children who play outdoors halve their chance of needing glasses for short-sightedness.
Researchers at Bristol and Cardiff universities found children who spend a lot of time outdoors were almost 50 percent less likely to be short-sighted when they were 15 compared with those who remained inside as children.
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The researchers asked the parents of 14,000 eight- and nine-year-olds how much time their child spends outdoors.
Kids who spent more than three hours outdoors in summer and more than an hour outdoors in winter were classified as "high". Any less was classified as "low".
The results showed time spent outdoors was a more important preventer of myopia (short sightedness) than being physically active — but they are still unsure why this is the case.
The researchers hypothesised that daily exposure to bright light could stimulate the neurotransmitter dopamine in the retina.
Jeremy Guggenheim, a reader in optometry and vision science at Cardiff University, who contributed to the research, said this study shows that the long-held belief that bookworms have eye problems is probably not true.
"There doesn't seem to be much connection between the time spent on different indoor activities, such as reading, and myopia," he said.
"The more people have tried to nail down reading as the cause, the less convincing the evidence has looked."
Twenty-eight percent of Australians suffer from short-sightedness.
Dr Padmaja Sankari Durg, program leader for myopia at the Brien Holden Vision Institute at the University of NSW, told ninemsn that Australian researchers are looking to undertake more comprehensive studies.
"There need to be more studies where you use outdoor activity as intervention and find out if children who spend more time outdoors are less likely to be myopic compared to the ones who don't spend much time outdoors," she said.
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"We need to take the current research on board then go and run a proper clinical trial where you go and get children of the same age group and one group goes and gets three hours of outdoor activity and the other group doesn't get the outdoor activity and then see if there are any differences."
The study is published in the journal Investigative Opthalmology and Visual Science.