Nearsightedness is reaching epidemic levels worldwide, but nowhere is its rise more prevalent than East Asia, where as many as 90% of teenagers and young adults now suffer from blurry distance vision. Why the sudden spike? Book work has long been blamed, but recent findings point to something else.

Photo Credit: Cathy via flickr | CC BY-NC 2.0

That so-called "close work," like reading and homework, is responsible for the rise in nearsightedness (aka "myopia") is an attractive idea. It's also an old idea. When German astronomer Johannes Kepler's eyes began to fail him more than four centuries ago, he blamed his crummy distance vision on all the time he spent engaged in careful study.

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But as Elie Dolgin reports in a feature published today at Nature, the close-work hypothesis, while tantalizing, has failed to endure scientific scrutiny:

In the early 2000s, when researchers started to look at specific behaviours, such as books read per week or hours spent reading or using a computer, none seemed to be a major contributor to myopia risk. But another factor did. In 2007, Donald Mutti and his colleagues at the Ohio State University College of Optometry in Columbus reported the results of a study that tracked more than 500 eight- and nine-year-olds in California who started out with healthy vision. The team examined how the children spent their days, and "sort of as an afterthought at the time, we asked about sports and outdoorsy stuff", says Mutti.

It was a good thing they did. After five years, one in five of the children had developed myopia, and the only environmental factor that was strongly associated with risk was time spent outdoors. "We thought it was an odd finding," recalls Mutti, "but it just kept coming up as we did the analyses." A year later, Rose and her colleagues arrived at much the same conclusion in Australia. After studying more than 4,000 children at Sydney primary and secondary schools for three years, they found that children who spent less time outside were at greater risk of developing myopia.

...Based on epidemiological studies, Ian Morgan, a myopia researcher at the Australian National University in Canberra, estimates that children need to spend around three hours per day under light levels of at least 10,000 lux to be protected against myopia. This is about the level experienced by someone under a shady tree, wearing sunglasses, on a bright summer day. (An overcast day can provide less than 10,000 lux and a well-lit office or classroom is usually no more than 500 lux.) Three or more hours of daily outdoor time is already the norm for children in Morgan's native Australia, where only around 30% of 17-year-olds are myopic. But in many parts of the world — including the United States, Europe and East Asia — children are often outside for only one or two hours.

These and other findings linking time spent in and out of doors to visual development have been made fairly recently, and are not without their critics. That hasn't prevented researchers like Morgan from wondering how they might be used to support impactful policy changes. One idea? Teach kids in classrooms made of glass.


Contact the author at rtgonzalez@io9.com.