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Science & technology | Ophthalmology

Short-sightedness was rare. In Asia, it is becoming ubiquitous

That is storing up problems for the future

2F70MT2 Path of light rays through the eye. Illustration of the 19th
century. Germany. White background.2F70MT2 Path of light rays through
the eye. Illustration of the 19th century. Germany. White background.
Jun 9th 2022
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In the early 1980s Taiwan's army realised it had a problem. More and
more of its conscripts seemed to be short-sighted, meaning they
needed glasses to focus on distant objects. "They were worried that
if the worst happened [ie, an attack by China] their troops would be
fighting at a disadvantage," says Ian Morgan, who studies myopia at
Australian National University, in Canberra. An island-wide study in
1983 confirmed that around 70% of Taiwanese school leavers needed
glasses or contact lenses to see properly.

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These days, that number is above 80%. But happily for Taiwan's
generals, the military disparity has disappeared. Over the past few
decades myopia rates have soared across East Asia (see chart 1). In
the 1960s around 20-30% of Chinese school-leavers were short-sighted.
These days they are just as myopic as their cousins across the
straits, with rates in some parts of China running at over 80%.

Elsewhere on the continent things are even worse. One study of male
high-school leavers in Seoul found 97% were short-sighted. Hong Kong
and Singapore are not far behind. And although the problem is worst
in East Asia, it is not unique to it. Reliable numbers for America
and Europe are harder to come by. But one review article, published
in 2015, claimed a European rate of between 20% and 40%--an order of
magnitude higher than that which people working in the field think is
the "natural", background rate.

Don't be short-sighted about this

For most of those affected, myopia is a lifelong, expensive nuisance.
But severe myopia can lead to untreatable vision loss, says Annegret
Dahlmann-Noor, a consultant ophthalmologist at Moorfields Eye
Hospital, in London. A paper published in 2019 concluded that each
one-dioptre worsening in myopia was associated with a 67% increase in
prevalence of myopic maculopathy, an untreatable condition that
causes blindness. (A dioptre is a measure of a lens's focusing
power.) In some parts of East Asia, 20% of young people have severe
myopia, defined as -6 dioptres or worse (see chart 2). "This is
storing up a big problem for the coming decades," says Kathryn Rose,
head of orthoptics at the University of Technology, Sydney.

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All that, in turn, is beginning to attract official attention. In
2018 Xi Jinping, China's president, made controlling childhood myopia
a national priority. Crackdowns on the country's private-tutoring and
video-games industries, which began in 2021, were partly motivated by
worries about children's eyesight, says Dr Morgan. The governments of
Taiwan and Singapore are likewise trying to do something about the
matter. "I think it's fair to say that public health is starting to
wake up to myopia as a problem," says Dr Dahlmann-Noor.

Most myopia is caused by misshapen eyeballs. A properly working eye
focuses incoming light precisely onto the retina, the light-sensitive
surface at the back of the eyeball (see picture above). In a myopic
eye, by contrast, the eyeball is distorted in a way that causes the
light to end up focused short of the retina. Sufferers can see
normally up close, but distant objects are blurred. And the condition
tends to be progressive, with vision worsening throughout childhood
and adolescence, before stabilising in adulthood.

For decades, researchers had thought myopia was mostly genetic. It
runs in families, and genomic studies have turned up several gene
variants which increase the risk of developing the condition. There
were early hints, though, that this could not be the whole story. A
study of Inuit in Alaska, published in 1969, found that myopia was
virtually unknown in those middle-aged or older, but that rates were
above 50% in older children and young adults. Such a change is much
too fast to be purely genetic, and it had happened just as the study
participants had begun to adopt a more settled, Westernised way of
life. But the results went against the dogma of the day, says Dr
Morgan, and were ignored.

The spike in East Asia, which occurred as places there
industrialised, was harder to dismiss. Short-sightedness is
stereotypically an affliction of the bookish, and a procession of
studies has confirmed a strong, reliable link with education. "The
more educated you are, and the higher your grades, and the more you
participate in after-school classes and tutorials--the more likely you
are [to be myopic]", says Dr Morgan. And an intriguing study on
orthodox Jewish children in Israel, in the 1990s, confirmed the link
with long school hours. It showed that boys--who receive intensive
religious education in addition to the normal curriculum--were more
myopic than their sisters, who do not.

Since there is no obvious way in which learning sums, spelling or
even the Talmud could cause short-sightedness directly, the
assumption was that education was a proxy for something else. One
possibility is the popular notion (raised by Johannes Kepler, a
German astronomer who himself needed glasses, more than 400 years
ago) that myopia is linked to too much close-in work, such as reading
and writing.

That theory remains popular, says Dr Rose, but evidence for it is
mixed at best. Instead, the dominant hypothesis now is that exposure
to daylight is the main variable. A study of Californian children,
published in 2007, found that time spent outdoors was strongly
associated with a lower risk of myopia. Another paper, published the
following year by Drs Rose and Morgan and their colleagues, followed
more than 4,000 children in Sydney for three years and came to a
similar conclusion. The type of activity--sports, walking, picnics--did
not seem to matter. Simply being outdoors was the crucial point. The
researchers cross-checked the close-work hypothesis and found that
being outside drastically reduced the risk of short-sightedness, even
for children that did a lot of it.

This theory fits the data neatly. It explains why myopia seems, like
diabetes and heart disease, to be what doctors call a "disease of
affluence"--more common in rich countries than poor ones--since
economic growth brings with it more education, and therefore, for
children, more time inside. It explains why rates are high in East
Asia in particular, says Dr Morgan, since the ubiquity of private
tutoring and after-school classes mean schoolchildren there routinely
work longer days than their Western counterparts. Most South Korean
students, for instance, attend private tutoring schools called
hagwons in which lessons often stretch well into the evening.

Seeing the light

The daylight-exposure theory is also bolstered by animal studies, in
which that exposure can be carefully controlled, and in which dimness
reliably produces short sight. Researchers have a putative mechanism,
too. Exposure to bright light appears to stimulate the production of
dopamine, a neurotransmitter, in the retina. Dopamine, in turn, seems
to help regulate the rate at which the eye grows. Too little, and the
eye grows too long to focus properly.

Human trials, too, confirm the theory. One of the biggest, led by
Pei-Chang Wu of the Chang Gung University College of Medicine, in
Taiwan, was published in 2020. It reported results from millions of
Taiwanese primary-school pupils who had gone through the school
system between 2001 and 2015. In 2010 the government instituted a
programme called "Tian-Tian Outdoor 120", which encouraged schools to
take pupils outside for two hours a day. After it was implemented,
rates of myopia fell, slowly but steadily, from 49.4% in 2012 to
46.1% in 2015--reversing a decades-long trend of rising rates.

Exactly how much light is needed is unclear, though Dr Morgan reckons
10,000 lux is in the right ballpark. That is about as much as you
might get in the shade on a reasonably sunny day. (Direct sunlight in
the tropics can exceed 100,000 lux.) Levels indoors, by contrast,
rarely exceed 1,000 lux. It is technically possible to light
classrooms to 10,000 lux, notes Dr Rose. But even with led lighting,
she says, the amount of heat produced would require specialist air
conditioning, and the glare might be enough to make reading tricky.

Researchers have also been working on ways to slow myopia's
progression once it has started. One is to use low doses of atropine,
a poisonous chemical found in deadly nightshade--the juice of which
was once used by women to dilate their pupils, in order to make
themselves look more attractive. Another is specially designed
"ortho-k" contact lenses, which are intended to reshape the cornea
while worn. (The cornea is the front, transparent part of the eye,
which does most of the work of focusing light on the retina; the
eye's so-called lens is mainly for fine tuning.) These also seem
effective, though Dr Rose worries about the side-effects from giving
contact lenses to children, since if misused they can cause
irreversible corneal scarring.

Sophisticated pairs of spectacles may help, too. In 2020 the bmj
published a Chinese trial of "defocus incorporated multiple segments"
(dims) glasses. The lenses of these have a central zone designed to
correct the wearer's sight, which is surrounded by hundreds of other
small zones of different optical power. The idea is to provide both
clear vision through the central part of the lens and deliberately
distorted vision through the smaller zones, since poorly focused
vision is thought to signal to the eye to slow its rate of growth.
Wearing dims glasses appeared to cut the rate of myopic progression
roughly in half.

Eyedrops, more sunlight and clever glasses might be able to prevent
or slow myopia in future generations of schoolchildren. But by the
time sufferers reach adulthood, the condition is permanent. This
means that in some countries, a public-health problem is already
baked in. For those with really serious myopia, says Dr Rose, and who
are at the highest risk of bad complications, unhealthy changes in
the eye can start to occur when patients are in their 40s. "And some
of those are not in any way treatable." #

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This article appeared in the Science & technology section of the
print edition under the headline "The eyes have it"

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