Why has nearsightedness more than doubled in 50 years?

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.

Based on epidemiological studies, Ian Morgan, a myopia researcher at the Australian National University in Canberra, recommends that children spend three hours per day under light levels of at least 10,000 lux for protection against the condition. Ten thousand lux would be about the amount of light one would get from beneath a shady tree on a bright summer day (and wearing sunglasses). For comparison, a well-lit schoolroom or office is generally under 500 lux.

In Australia, where three hours of outdoor time is normal, only 30 percent of 17-year olds are nearsighted. In other parts of the world where myopia rates are higher – like the U.S. and Europe – many children don’t see more than an hour or two of outdoor time.

With all of this in mind, new programs and research are measuring the beneficial effect of adding outdoor class time to school schedules, and they are seeing a notable improvement in myopia rates as compared to control groups. Morgan is happy to see preliminary progress, but is eager to see more.

“We've got proof of principle that increasing the amount of time children spend outside actually works,” Morgan says. “The question then is how do we make this work in practice at a level that would have a significant impact?”

Since he understands that outdoor class time isn’t a practical option for many schools, he has started a pilot program to begin building glass classrooms to allow natural light in. And while it sounds like a lovely step in the right direction, it’s not as comprehensive an approach as just allowing kids more time to be outside and play; especially given the other benefits beyond those for the eyes. Along with instilling a deeper connection to nature, “It probably also increases physical activity, which decreases likelihood of obesity and enhances mood,” Kathryn Rose, head of orthoptics at the University of Technology, Sydney says. “I can only see it as a win – and it's free.”

So there you have it. Now kids, get outside and play ... it may very well allow you to see the forest for the trees.

Read more about the research in Nature.

Tags: Health | Kids | Nature

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