Being?nearsighted is far more common than it once was. The prevalence of myopia, the condition’s medical name, in Americans has soared by 66 percent since the early 1970s, according to a 2009 study by the National Eye Institute; in China and other East Asian countries, as many as 90 percent of recent high school graduates are thought to be nearsighted.

Myopia results when eyeballs are longer than normal, changing the angle at which light enters the eye and therefore the ability to focus on distant objects.?

The disorder involves a complex?interplay?of genetics and environment and usually begins before adolescence, when the eye is growing, but it can worsen in early adulthood.

Some experts connect the elevated rates of myopia to the many hours young people stare at computers and other screens. But a recent study published in JAMA Ophthalmology suggests that a greater factor may be a side effect of all that screen-watching — it’s keeping children inside.?

This new study joins a growing body of research indicating that a lack of direct sunlight may reshape the human eye and impair vision.

Strong correlations were found between current eyesight and volunteers’ lifetime exposure to sunlight, above all UVB radiation (which is responsible for burning).?

Those who had gotten the most sun, particularly between the ages of 14 and 19, were about 25 percent less likely to have developed myopia by middle age.?

Exposure to sunlight up to the age of 30 also conferred a protective benefit.

This relationship held true even when the researchers controlled for education as a marker primarily of time spent reading and gazing at screens.

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