The Real Reason Why You’re Nearsighted

When I was growing up, I was always led to believe that needing glasses was just something that happened to people. You were simply born to be nearsighted or farsighted, and that was all there was to it. To some extent this idea is true. Scientists have found genes that can be linked to these visual ailments, which are widely known to be passed down in certain families; but does that tell the whole story?

When you really think about it, it doesn’t make a whole lot of sense. Conditions like myopia are incredibly common. Everybody knows somebody who needs glasses or corrective surgery. So you have to ask yourself, if vision problems are mostly genetic, and they’re so common in children all over the world, why didn’t natural selection weed this trait out of the gene pool?

You have to imagine that not being able to see properly would be so much more hazardous for our ancestors than it is for us. How could hundreds of millions of people be suffering from a genetic disease that just a few centuries ago, would have nearly been a death sentence? Honestly, this totally defies our notions of evolution.

Well it turns out that the scientific community is slowly changing its mind on the origins of childhood vision problems, specifically with myopia. Genetics still play a role, but the research that has been done over the past few years has revealed a new risk factor.

For starters, the vast numbers of people with myopia blows the whole genetics theory out of the water. But the countries that have it the worst, can give us a hint to its true causes.

East Asia has been gripped by an unprecedented rise in myopia, also known as short-sightedness. Sixty years ago, 10–20% of the Chinese population was short-sighted. Today, up to 90% of teenagers and young adults are. In Seoul, a whopping 96.5% of 19-year-old men are short-sighted.

Other parts of the world have also seen a dramatic increase in the condition, which now affects around half of young adults in the United States and Europe — double the prevalence of half a century ago. By some estimates, one-third of the world’s population — 2.5 billion people — could be affected by short-sightedness by the end of this decade. “We are going down the path of having a myopia epidemic,” says Padmaja Sankaridurg, head of the myopia programme at the Brien Holden Vision Institute in Sydney, Australia.

So what do all of these countries have in common? They’re all developed nations, or soon to be developed nations. But what do advanced nations have in common? Literacy and education of course. While all developed nations have a myopia problem, East Asians nations seem to have it at a much higher rate, and their children spend much more time studying and reading than ours do. The average teenager in Shanghai spends 14 hours a week doing homework, compared to 6 hours in the United States.

Studies across the planet have stumbled upon this phenomenon over and over again. Whenever a culture is exposed to the modern world, their myopia rates go through the roof, and it appears that the amount of time that a child spends reading and studying, has a strong effect on their vision. For a long time, it was believed that spending so much time focusing your eyes on nearby objects was hurting them, but after a while, it was realized that this also doesn’t fully explain the myopia epidemic. Though it does seem to be related.

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.

It was initially thought that exercise was playing a role, but that didn’t hold up either. Eventually the scientists in these studies realized that sunlight was the greatest contributing factor. For some reason, exposure to light reduces the chance of becoming nearsighted, which has been subsequently demonstrated in both humans and animals.

So far it isn’t 100 percent conclusive, but the evidence is mounting. The leading theory now is that when light reaches the eye, it stimulates the release of dopamine into the retinas, which apparently prevents the eyeball from elongating and causing myopia. They’ve tested this theory on chickens by injecting them with dopamine inhibitors, and have found that light no longer protects their vision.

Right now there doesn’t seem to be any evidence that sunlight can cure myopia, but it does appear to either prevent it in most people, or at least stop it from progressing. So if you don’t want your kids to become nearsighted, the best thing you can do for them is kick their butts outside and let them play for a few hours.