The first person to put on a pair of glasses probably lived in Italy in the late 13th century. Today, the industry they started is worth £100bn a year.
Demand is soaring for spectacles and contact lenses. And that’s partly because rates of short-sightedness, the most common problem with eyesight, is on the rise – especially among the young. The statistics are dizzying: 20 years ago experts estimate that about one in four people worldwide had myopia – the inability to see distant objects clearly. By next year it will be one in three. In 2050 it will be one in two. And given how the global population is expected to grow, that means within a generation or two there could be five billion short-sighted people on the planet.
In East Asia, myopia is a full-scale epidemic. Up to 90 per cent of teenagers and young adults in China are short-sighted. One study in South Korea found that more than 96 per cent of 19-year-old men in the country’s capital Seoul are affected.
“I would definitely go as far as to say it is an epidemic in places like Taiwan and Singapore,” says Dr Denize Atan, an expert in neuro-ophthalmology at Bristol Eye Hospital. “We’re talking about 80-90 per cent of school leavers and that’s worrying.”
What’s going on? Across the world, the eyeballs of young people are growing too large. Or, more specifically, too long – from front to back. It doesn’t have to be much, just a couple of millimetres. And then basic physics takes over. The retinas of all these people – the screens of super-sensitive light-spotting cells painted onto the backs of their eyes – are then slightly behind where they should be. And then their lenses and corneas – the bits of the eye at the front that bend and focus the light into shape – can’t reach to send the image quite that far back. At least not without losing definition and blurring the picture.
That’s where opticians come in: the extra help offered by the lenses in spectacles and contacts helps nudge the focused light that little bit further back, and so more accurately onto the retina. (That’s usually what laser eye surgery does, too, by reshaping the cornea.)
So far, so pretty typical: children and adults have managed with glasses for decades. Does it really matter if more join them? Yes it does. Because fixing vision with what companies now routinely call “eyewear” only addresses the symptoms of the problem: the skewed way the eyeball focuses the light. The underlying feature – the elongated eyeballs – remains. And in a significant number of cases this causes far more severe complications.
“As the eye continues to grow, the surface of the eyeball can become stretched far too thin. The neural layer can start to develop cracks and blood can leak into the eye and that can cause permanent damage to eyesight,” says Dr Hema Radhakrishnan, senior lecturer in optometry at the University of Manchester.
In other words, opticians can help manage myopia but they can’t fix it, or prevent it spreading or creating severe problems. To do so, the world must work out what is making the eyeballs of its young people grow too large, and then figure out a way to stop it. After years of research, scientists around the world think they have an answer – and it won’t be popular with everyone.
“There is a link between myopia and time spent in education,” Atan says. “The longer someone stays in school the worse it gets.”
The association is so strong that scientists have been able to gauge the deterioration in eyesight expected for every extra year that someone stays in education. Compared with if they had left school at 16 with relatively normal vision, those who graduate from university aged 21 will, on average, have seen their myopia increase to the point where they would need glasses to drive.
That’s quite a shift in thinking. For much of the 20th century many scientists assumed that short-sightedness was down to genetics (a perception that remains in the population at large). While it’s true that genes are important (they are for everything), and that myopia does run in families, the staggering rate of increase in the severity of the condition seen from generation to generation in some parts of the world is simply too fast to be blamed on DNA. Most strikingly, a famous 1969 study of Inuit people, who live on the northern tip of Alaska, showed that while just two of 131 adults in the community had myopia, almost half of their children and grandchildren did.
Education, per se, is not the culprit here. Instead it’s something to do with how we educate. For most kids today that means spending hours and hours indoors, looking at books, screens and work held quite close to their eyes. Close work has been associated with the onset of short-sightedness for more than a century, but most scientists who work on myopia now prefer to focus on the fact that it tends to happen indoors. The surge in short-sightedness, they say, is down to children spending much more time away from bright natural light.
Exactly how the lack of outside light could seed short-sightedness is still something of a mystery. It could change levels of the neurotransmitter dopamine in the eye, and so change the way it grows. Or it could be that certain frequencies of light, perhaps blue and violet, are especially important, and also the most likely to be blocked by glass. But, crucially, studies have shown that sending kids outside seems to protect against myopia: programmes are under way in places like Taiwan to see if encouraging (and sometimes compelling) them to leave the classrooms during break-times can help.
Pei-Chang Wu, director of ophthalmology at the Kaohsiung Chang Gung Memorial Hospital, helped to run one of these Taiwanese trials, which involved some 700 children across 16 schools. Published last year, the results showed that time outside could reduce both the number of children with myopia and the rate at which their eyeballs lengthened. “Children should be encouraged to spend a certain amount of time outdoors before the age of 18,” he says.
Time outside can’t reverse short-sightedness – an oversized eyeball can’t be squashed smaller again – but evidence is mounting that it can delay and reduce the severity of the symptoms. And that’s a vital step. The earlier the onset, the more likely that myopia can show itself as a severe health problem.
Instead of worrying about screen time, we should perhaps be thinking of outside time. Children are different, and it’s difficult to say exactly how much exposure to bright, natural light is needed to protect against the risk of severe eye problems.
Professor Seang-Mei Saw, head of the myopia unit at the Singapore Eye Research Institute, suggests: “Children should spend more than two hours a day, or 14 hours a week, outdoors to prevent the onset of myopia.” That especially applies to the under-tens, she says.
That might sound a lot of time to find. But it doesn’t have to be all done at once. A 15-minute walk to and from school? That’s two and a half hours a week right there.