A blight of bad eyesight plagues urban centers in China and other East Asian countries. In Hong Kong and Singapore, the rate of myopia, or nearsightedness, is as high as 90 percent in young adults. Though things aren't as blurry in the United States — about a third of the population has trouble seeing distant objects — rates have doubled since the 1970s. If current trends continue, half of the world could be myopic by 2050.

China blames video games for the eyeglass epidemic and recently took the video game industry to task. The state-run Xinhua News Agency recently wrote that the “vision health of our country’s young people has always been of great concern” to Xi Jinping, the Communist Party general secretary and China's president. Chinese media distributors, the New York Times reported Friday, will limit the number of new games approved for sale.

By singling out video games, China has taken a somewhat “extreme stance,” said Aaron M. Miller, a pediatric ophthalmologist and a clinical spokesman for the American Academy of Ophthalmology. “There's not a direct correlation or a clear relationship between video games, screen time and nearsightedness development."

The scientific literature can offer only a fuzzy picture of myopia's causes. Diet and genes influence myopia; myopic parents are more likely to have myopic children. Behaviors can play a role, too. Some ophthalmologists look to activities lumped together under a term called “near-work” — any prolonged focus on a nearby object, as when reading, checking phones, studying and, yes, watching screens. Researchers have observed higher rates of myopia in college students, post-literate societies and, in one study, people who frequently use microscopes.

There appears to be “a loose association” with near-work activities and nearsightedness, Miller said, though doctors do not fully understand the mechanism.

A recent and “very good study,” Miller said, tracked myopia in nearly 2,000 children, between ages 7 and 12, for four years in Taiwan. Most myopia studies focus on children around ages 4 to 12, when eyes grow and change shape.

In 2009, a quarter of the children had myopia, according to the report, published this summer in the journal Ophthalmology. By 2013, an additional 28 percent of the students in the study developed it. Taiwanese children who attended “cram schools” — for-profit courses where students learn English or other topics — had above-average risk for myopia.

"We're not sure if it's the near-work that's driving” these increased rates, Miller said, “or what's not happening because those individuals are doing near-work."

Reductions in the amount of natural sunlight exposure seem to correlate with nearsightedness. Put another way, the nature of the near-work — whether children are doing homework or reading or playing Fortnite — might matter less than the fact that they are not outside. In another recent study of schoolchildren, this time involving 10,000 children in Delhi, India, those who spent more than 14 hours outdoors a week developed myopia at lower-than-average rates.

Legions of children needing glasses or vision correction add up: Myopia costs the United States $16 billion each year. And the ramifications of this myopia boom can be even more serious. As nearsightedness worsens, the risk of diseases such as glaucoma rise.

Nearsighted eyes can physically change, Miller said, elongating from orbs into olive shapes. When this happens, the retina, the eye's lining, becomes thinner. Little tears form in retinas stretched too thin. Miller likened the tears to “wallpaper starting to peel off a wall.” In the worse case, the result is retinal detachment and blindness.

The American Academy of Ophthalmologists recommends that people rest their eyes occasionally by gazing at something other than screens. The academy has a 20-20-20 rule: Every 20 minutes, look at a thing 20 feet away for 20 seconds. Gaze out a window after beating a video game level or finishing a few book chapters. Alternate between an e-reader and an old-fashioned book. Don't forget to blink.

Or, if you really want to give your eyes a treat — get off your phone, shut down your laptop, go outside and watch the birds.

Read more: