Why are we short-sighted?

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Myopia is among our most common complaints – but have we fundamentally misunderstood its origins and its treatment? David Robson squints at an answer.

When I was a teenager, my eyesight slowly began to fail and I had to wear spectacles.  What began as tiny slithers of glass soon started to approach double-glazing. “Why is this happening?” I would ask my ophthalmologist as I squinted at the blurry shapes on the eyechart and he upped my prescription. His response was always the same: I could blame my genes and a love of reading.

A common concern is that glasses are making things worse – the answer is no — Ian Flitcroft, eye surgeon

I had no reason to question him; it’s probably what your ophthalmologist told you, too, if you were diagnosed with short-sightedness. But recent research suggests those assumptions are quite wrong.
Many other things about the modern environment could be leading to poor eyesight. And, with just a few simple measures, our children may be prevented from the same blurry decline that has plagued our own generation.

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The idea that poor eyesight is primarily genetic had never really rung true for me, anyway. Without my glasses, I literally couldn’t tell a rock from a rhino. So shouldn’t my ancestors have been removed from the gene pool as they groped and squinted their way through the savannah? Yet short-sightedness is something of an epidemic; 30-40% of people in Europe and the US need glasses, and the figure has risen to as much as 90% in some Asian countries. If we had “short-sightedness” genes they have made it through the millennia regardless of their obvious disadvantages.
Ask an Eskimo

In fact, the experiences of the Inuit in Canada should have settled that question nearly 50 years ago. Whereas the older generation had next-to-no cases of short-sightedness, between 10-25% of their children all needed glasses. “That would never be possible with a genetic disease,” says Nina Jacobsen at Glostrup University Hospital in Copenhagen. Over that same period, the Inuit had started to leave their traditional lifestyles of hunting and fishing for a more Western way of life – a far more likely cause of their decline. “Short-sightedness is an industrial disease,” says Ian Flitcroft at Children’s University Hospital, Dublin. Our genes may still play a role in deciding who becomes short-sighted, but it was only through a change in environment that the problems began to emerge.

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Part of that change would have been education and literacy – one of the most common explanations for short-sightedness. At first the evidence seemed to be strong: just look at the sea of glinting specs in any university lecture theatre or academic conference, and you would seem to find proof of a link. Yet epidemiological studies suggest the effects are much smaller than once believed. “The more we studied it and measured the amount people read, the more the association seemed to vanish,” says Flitcroft. One large study following the progress of children in Ohio appeared to show no correlation at all with reading, though we should not yet rule out the effect completely, says Jacobsen.
Instead, many now argue that it is the time spent indoors, rather than reading per se, that matters most. Study after study, from Europe, Australia, and Asia, have all found that people who spend more time outside are far less likely to get short-sighted than people whose lives are mostly confined within four walls.

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Why would that be? One popular explanation is that sunlight somehow nourishes the eyes. Scott Read at Queensland University of Technology, for instance, recently equipped a group of schoolchildren with a special watch that recorded their overall movements, and the light intensity, every 30 seconds for two weeks.
The kids with good eyesight turned out to be no more active than those with specs – ruling out the possibility that exercise and general good health protect the eyes. Instead, glasses prescriptions seemed to hinge, almost exclusively, on the time spent in the sunshine. Bright sunlight can be thousands of times more intense than lighting inside (though your eyes may mask the difference) – and the more sunlight the children enjoyed, the less likely they were to need glasses.

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Perhaps it is because sunlight stimulates the production of Vitamin D, which is responsible for a healthy immune system and brain, and might also regulate eye health. A more widely accepted idea is that sunshine triggers the release of dopamine, directly in the eye itself. Short-sightedness is caused by excessive growth of the eyeball, making it more difficult for the lens to focus an image on the retina, but dopamine seems to put the brakes on this and keep it in a healthier shape.
Getting the blues

Alternatively, it could be a question of colour. Green and blue wavelengths tend to be focused at the front of the retina, while red light hits the back.  Since indoor lighting tends to be redder than the sun’s rays, the mismatch could confuse the eyeball’s control mechanisms. “It tells the eye that it’s not focusing on the optimal place, and so it has to grow and compensate for that,” says Chi Luu at the University of Melbourne. Sure enough, he has found that chicks raised in red light are more likely to be short-sighted than those growing up with blue or green surroundings.

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Flitcroft, meanwhile, thinks the problem lies in the clutter of objects clouding your visual field. Just take a look around you and you will see what he means. “If you look at a laptop screen, everything behind the screen is out of focus to quite a large degree,” he says. “And then if you look up from the laptop to a clock, you have a huge flip – the clock is in focus, but there are lots of things close to you in periphery, that are blurred.” Wherever you fix your gaze, there is always a blur that plays with the eye’s feedback mechanisms. Outdoors, however, things tend to lie at a greater distance, providing a clearer image that helps to regulate the eye’s development.
Such insights are hopefully not just of academic importance, since they could eventually direct us to new treatments. Luu, for instance, is hoping to put together a trial that offers blue lamps to short-sighted children. Not only does Luu hope it could slow further decline; it may actually reverse it; during his study of chicks, he found that a few hours a day under a blue lamp undid the damage of the red lights and returned the chick’s vision to normal.
Chance discovery

Flitcroft points out that there are promising trials of contact lenses that can reduce blur in the peripheral vision. He is also optimistic that an eye drop, called atropine, could be helpful. The drug has long been known to slow down the signalling that triggers eyeball growth and short-sightedness. Its unwelcome side-effects – such as causing pupil dilation and generating halos around sources of light – meant that it was once dismissed, but a chance finding recently showed that it is equally effective at a just one hundredth the original dose. At those levels, the side effects should be minimal – a discovery that has now sparked renewed interest in the eye drops.

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For the time being, Flitcroft stresses that we should be careful not to take any action in haste. One  misconception, for instance, is that glasses themselves make your eyes worse, but the evidence suggests this advice should be discarded. My own experience shows that this is sadly misguided; inspired by the controversial book “Better Eyesight Without Glasses”, I decided to go without my specs in the hope that it would reverse my prescription; instead, it doubled over the course of three years. “A common concern is that glasses are making things worse – but the answer to that question is no,” says Flitcroft. “If you are making sure your children can see properly – you’re doing things right.”
For those who would like to take action now, most of the researchers agree that encouraging children to play outside can do no harm, and a trial in Taiwanese schools has already shown moderate success. “Left to their natural, outdoors environment, humans don’t become myopic,” says Flitcroft. “Encouraging children to spend time outdoors can only be good.”
I wish that I’d known all of this during my youth. Today, I wear contact lenses that almost completely correct my vision, and the occasional dryness and irritation are small concerns in the grand scheme of things. But when I wake up and can’t even recognise my partner lying next to me, I can’t help hoping that future generations will be able to enjoy the crystal-clear vision that was once our ancestors’ birthright.


bbc.