NEW YORK (Reuters Health) - Children who regularly spend time outside may be less likely than their peers to develop nearsightedness, new research suggests.
In several studies reported in the journal Optometry and Vision Science, researchers found that kids who spent more time outside during the day tended to have better distance vision than those who favored indoor activities.
The reasons are not yet clear, but children's physical activity levels did not seem to be a factor.
Instead, the researchers speculate, exposure to sunlight may play a role, as may the fact that being outside often makes kids focus on objects at a distance. Animal studies suggest that this affects eye development in a way that helps prevent nearsightedness, or myopia.
On the other hand, there was no strong evidence that "near-work" -- like reading or using a computer -- raised children's risk of nearsightedness.
In one of the studies, Dr. Jane Gwiazda and Li Deng of the New England College of Optometry in Boston surveyed parents of 191 children who were 13 years old, on average, and tested the children's vision annually.
Overall, the researchers found, children who developed myopia spent an average of 8 hours outside per week, compared with nearly 13 hours among non-myopic children. Nearsighted children also tended to watch more TV, but there was no such correlation with time spent reading, studying or using a computer.
In two other studies -- one from Australia, one from Singapore -- researchers found similar connections between outdoor time and lower myopia risk. Lower rates of near-work did not explain the link, and the Singapore study found no evidence that children who read a lot were at greater risk of nearsightedness.
More work is needed, the investigators say, to find out why outdoor time might affect children's visual development.
SOURCE: Optometry and Vision Science, January 2009.