Why Nearsightedness Has More Than Doubled in 50 Years (It’s Not What You Think)


By Melissa Breyer | treehugger.com

eye test

In the U.S. and Europe, myopia for kids and young adults has doubled; in China it’s up 80 percent. Scientists think they’ve found out why, and it’s probably not what you think.

Sixty years ago, 10 to 20 percent of the Chinese population was nearsighted, now up to 90 percent of teenagers and young adults have trouble seeing distance. In other parts of the world the story is similar: Half of the young adults in the United States and Europe now have myopia, double the number of half a century ago. And some are predicting that by 2020, one-third of the world’s population could be diagnosed with the condition.

While glasses, contact lenses and surgery can help to correct nearsightedness, they don’t actually cure the defect – a slightly elongated eyeball, which means that the lens focuses light from far objects slightly in front of the retina, rather than directly on it, reports Elie Dolgin in the science journal Nature. And when it’s severe, there exists the risk of retinal detachment, cataracts, glaucoma and blindness.

The condition usually develops in school-age kids because this is when the eyes are growing; around 20 percent of young adults in East Asia now have severe myopia, and half of them are expected to develop irreversible vision loss.

What in the world is going on?

For years the thinking was that myopia was largely genetic, but research began to show that it wasn’t purely a matter of genes. And indeed, the current increase in myopia reflects a similar increase in children reading and studying more – in fact, is there a caricature of a “bookworm” that doesn’t include glasses? Add to this a newfound addiction to computer and smartphone screens and the answer seems obvious, right? Our kids are so focused on these close-at-hand objects, of course they’re losing their ability to see distance.

“On a biological level, it seemed plausible that sustained close work could alter growth of the eyeball as it tries to accommodate the incoming light and focus close-up images squarely on the retina,” notes Dolgin.

But surprisingly, it’s not the reading and computers and smartphones that are to blame. Now researchers believe that it’s the very act of spending too much time inside that is causing the problem. After a great deal of research and eliminating other factors, scientists now think that it boils down to exposure to light. Regardless of what kids are doing – whether sports, or playing, and even those who continue to do “close work” (like reading) outside – what seems to be key is the eye's exposure to bright light.

So while our kids are losing their connection to nature – while they’re becoming increasingly unfamiliar with the feeling of grass underfoot, mud in the hands, the sound of birds, the smell of dirt – they’re also losing the ability to see.

While some researchers think more data is needed to confirm the theory, animal experiments further support the idea that being outdoors, and exposure to the light that comes with it, is protective. The leading hypothesis, explains Dolgin, is that light stimulates the release of dopamine in the retina, and this neurotransmitter in turn blocks the elongation of the eye during development.

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