By Sarah Zhang

MODERN LIFE TAKES a toll on bodies. It’s easy to tick off the uniquely 21st-century diseases that plague humans today: obesity, heart disease, diabetes. But those are the visible afflictions, the ones that show up on expanding bellies and skyrocketing death rates. Out of sight, another epidemic is silently raging: myopia, or nearsightedness. Between the 1970s and the early aughts, the incidence of myopia in the US nearly doubled, to 42 percent. Myopia’s rise has been the starkest in Asia; one survey in Korea found a rate as high as 96 percent among teenagers.

Clearly, something is going on. But scientists can’t agree on exactly what. Being constantly tethered to devices and books indoors might be part of it: Based on a handful of large epidemiological studies on myopia, spending time outdoors—especially in early childhood—reduces the onset of myopia. (So nerds and glasses? It’s true.) But what exactly about the outdoors helps? Is it the bright sunlight or how eyes focus on objects far away outside or something else entirely?

The exact answer matters, because just shooing kids outside has downsides, too. As Thomas Norton, a vision scientist at the University of Alabama at Birmingham, puts it, “You don’t want to trade myopia for skin cancer.”

The confusion around myopia is even more complicated because scientists can’t agree on how to study it. You can’t just take healthy children and deliberately make them nearsighted (obviously). So the best you can do is induce myopia in animals—usually chickens, tree shrews, or monkeys. “This is a controversial area as to what is the best model for human myopia,” says Ian Morgan, a retired vision researcher at Australian National University. What works to prevent myopia in one model doesn’t seem to work in another. In other words, to find a cure for myopia, scientists need to understand the nitty gritty of animal models.

This excellent article was originally published here – http://www.wired.com/2016/02/silent-epidemic-myopia/

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