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Can playing outside keep kids from becoming nearsighted?

Whether you call it an epidemic or not (epidemic is a term that gets tossed around a bit too casually these days), there’s no denying the fact that the rates at which people are being diagnosed with nearsightedness (myopia) is truly astoundi

Whether you call it an epidemic or not (epidemic is a term that gets tossed around a bit too casually these days), there’s no denying the fact that the rates at which people are being diagnosed with nearsightedness (myopia) is truly astounding.

Particularly in Asia. In some Pacific-rim countries (Hong Kong, Taiwan, Singapore), about 80 percent of young adults are now myopic.

In Western countries, the rates of myopia seem to currently fall between 30 and 50 percent — and are rising, by some accounts.  The U.S. rate is at the lower end of that scale.

An article published recently in New Scientist explores the various theories about why myopia may be on the rise. Without a doubt, genetics plays some role. (Twin studies have confirmed this.) But, as reporter Nora Schultz points out, “genetics alone can’t explain the condition.”

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Reading out, exercise in?
Because nearsightedness seems to be more common among highly educated people, some scientists have proposed that it’s somehow linked to reading, computer use and other “near work.”

Here’s the theory: When young children are, say, reading “Green Eggs and Ham,” the lenses in their eyes develop a new elongated curvature that enables them to focus on the book’s small print. This helps the children with the visual task of reading, but the new curvature makes their eyes less able to see things at a distance.

Sounds reasonable. Research, however, has failed to support that theory.

Then, a couple of years ago, a study reported that 8-year-olds who spent more time engaged in outdoor sports and activities (12 versus 8 hours a week) were less likely to become nearsighted three years later, at age 11. Further research suggested that it was the time spent outside, not the physical activity per se, that offered the protection. (Kids who played indoors sports didn’t experience any benefits to their eyesight.)

A team of researchers decided to see if this theory could explain the incredibly high rate of myopia in Asia. Writes Schultz:

[The researchers] compared two groups of 6- to 7-year-old children, one in Singapore and one in Australia. The team looked only at children of Chinese ethnicity, to rule out genetic differences between races as an explanation for higher myopia rates in certain countries.
The result? On average the children in Sydney spent nearly 14 hours per week outside, and only 3 percent developed myopia. In contrast, the children in Singapore spent just 3 hours outside, and 30 percent developed myopia. Once again, close work had a minimal influence; the Australian children actually spent more time reading and in front of their computers than the Singaporeans.

Why would the outdoors have such an effect? Some research suggests, says Schultz, that sunlight slows down myopia-associated growth of the eyeball, perhaps by causing the retina to produce high levels of dopamine, a brain chemical known to inhibit eye growth.

(Of course, too much sun can also damage the eyes in ways that can lead to cataracts and other serious vision problems later in life. Schultz doesn’t address this issue in her article.)

Other possibilities
Researchers are also exploring the possibility, reports Schultz, that myopia may be more related to what’s going on in our peripheral vision than in our central vision (which may explain why cornea refractive therapy — the wearing of hard contact lenses overnight to temporarily reshape the cornea — has been found to slow the progression of myopia by about 50 percent).

And then there’s the highly controversial theory that the rising rates of myopia are linked to high blood-sugar levels caused by the world’s increasing consumption of refined carbohydrates.

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Whatever scientists eventually identify as the main cause behind the current skyrocketing incidence of myopia around the world, I’m thinking that, at least in the near future, investing in the stocks of a few eyeglass manufacturers might not be a bad way of tip-toeing back into the stock market.