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A myopia epidemic is sweeping the globe. Here's how to stop it
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  * NEWS FEATURE
  * 29 May 2024

A myopia epidemic is sweeping the globe. Here's how to stop it

Time spent outdoors is the best defence against rising rates of
short-sightedness, but scientists are searching for other ways to
reverse the troubling trend.

    By
  * Elie Dolgin^0

 1. Elie Dolgin
     1. Elie Dolgin is a science journalist in Somerville,
        Massachusetts.

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A Chinese doctor examines the eyesight of a young myopic kid at an
ophthalmologic hospital in Handan City, north China's Hebei Province.

A physician examines the eyesight of a child with myopia in Hebei
province, northern China. Credit: Sipa US/Alamy

You have full access to this article via your institution.

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The COVID-19 pandemic didn't just reshape how children learn and see
the world. It transformed the shape of their eyeballs.

As real-life classrooms and playgrounds gave way to virtual meetings
and digital devices, the time that children spent focusing on screens
and other nearby objects surged -- and the time they spent outdoors
dropped precipitously. This shift led to a notable change in
children's anatomy: their eyeballs lengthened to better accommodate
short-vision tasks.

Study after study, in regions ranging from Europe to Asia, documented
this change. One analysis from Hong Kong even reported a near
doubling in the incidence of pathologically stretched eyeballs among
six-year-olds compared with pre-pandemic levels^1.

This elongation improves the clarity of close-up images on the
retina, the light-sensitive layer at the back of the eye. But it also
makes far-away objects appear blurry, leading to a condition known as
myopia, or short-sightedness. And although corrective eyewear can
usually address the issue -- allowing children to, for example, see a
blackboard or read from a distance -- severe myopia can lead to
more-serious complications, such as retinal detachment, macular
degeneration, glaucoma and even permanent blindness.

Rates of myopia were booming well before the COVID-19 pandemic.
Widely cited projections in the mid-2010s suggested that myopia would
affect half of the world's population by mid-century (see 'Rising
prevalence'), which would effectively double the incidence rate in
less than four decades^2 (see 'Affecting every age'). Now, those
alarming predictions seem much too modest, says Neelam Pawar, a
paediatric ophthalmologist at the Aravind Eye Hospital in
Tirunelveli, India. "I don't think it will double," she says. "It
will triple."

Rising prevalence: chart that shows the expected rise in myopia in
the world's population up until 2050.

Source: Ref. 2

Research already points to a simple solution for curbing the tide:
more outdoor activities during childhood, a time when changes in eye
structure are most likely to occur.

Randomized trials from East Asia have shown that about one hour of
extra outdoor breaktime daily can markedly reduce the incidence of
short-sightedness^3^,^4. But it has proved difficult to implement
such changes consistently, particularly in societies with a strong
emphasis on academic achievement or in urban areas with limited
access to safe, green spaces.

"Getting kids to go outdoors is a tough sell," says Nathan Congdon,
an ophthalmologist at Queen's University Belfast, UK, who has worked
in China for nearly 20 years.

Affecting every age: bar chart that shows the expected rise in myopia
in every age group in 2050 compared to 2000.

Source: Ref. 2

So instead, researchers are working on ways to bring the outside in --
glass classrooms, special lighting rigs, nature-themed wallpapers and
light-emitting spectacles -- interventions that do not demand
overhauls in child behaviour, educational systems or parenting
techniques. They are also exploring other light-based and
pharmaceutical interventions.

Some of these approaches are showing promise. But there's a stumbling
block when it comes to testing them: researchers don't fully
comprehend what it is about outdoor exposure that helps to prevent
myopia. Clinical trials are still preliminary and many animal studies
remain inconclusive.

A firmer understanding would help scientists to develop better
treatments, says Christine Wildsoet, an optometrist at the University
of California, Berkeley. "Because once we know the key features," she
says, "then we can bring some of them indoors."

Stop signals

As the eye develops, it constantly fine-tunes its shape in response
to certain visual cues. If those cues indicate that the eye is too
short, it stretches to bring objects into focus. Conversely, if the
eye becomes too long, it will receive 'stop' signals, which are
crucial for preventing myopia.

The source of these stop signals has been a subject of much debate in
the myopia research community. Studies in monkeys, tree shrews and
chickens -- all common animal models for myopia research -- have
pointed to the release of the neurotransmitter dopamine in the back
of the eye as a likely trigger. The neurotransmitter is thought to
increase in response to high ambient-light levels found in sunlit
surroundings.

[d41586-024]

Nature Reviews Disease Primers: Myopia

But an alternative theory holds that the protective benefits of
outdoor exposure might be less related to light and more associated
with the patterns of blur experienced across the retina in different
visual environments.

The visual landscape outdoors is rich and textured, and elements of
it are typically viewed at such great distances that the vast array
of details merge into a more uniform image. This uniformity of focus
is what tells the eye to stop growing, contends Ian Flitcroft, a
paediatric ophthalmologist at the Centre for Eye Research Ireland in
Dublin. "An effective stop signal is where the whole retina is seeing
a clear image," he says.

By contrast, interior spaces are filled with jumbles of objects at
varying distances, surrounded by flat walls that typically lack
detail. Such conditions require constant adjustments of focus, which,
according to Flitcroft, deprives the retina of the necessary stop
signals for regulating healthy eye growth.

Going outside offers the benefit both of bright sunlight and the
enriched visual experience of wide-open spaces -- with the bonus of
physical activity and improved well-being to boot. But only a few
places have managed to encourage children to go outside more.

In 2010, public-health officials in Taiwan introduced a programme
called Tian-Tian 120, meaning everyday 120, which encourages a
minimum of two hours of outdoor activity daily. It is widely credited
with having curbed the rapidly increasing rates of myopia in the
region^5.

And although there was a minor increase in myopia cases in Taiwan
during the pandemic, this uptick was substantively smaller than those
observed in other parts of East Asia at the time, according to data
compiled by Pei-Chang Wu, a retinal surgeon and myopia specialist at
the Kaohsiung Chang Gung Memorial Hospital in Taiwan. What's more,
the outdoor programme does not seem to have hurt students' test
scores in mathematics, reading or science, which remain among the
highest in the world.

For some, the message is clear: when it comes to promoting more
outdoor time, "wide-scale implementation now seems feasible and
likely to succeed", says Ian Morgan, a myopia researcher at the
Australian National University in Canberra -- if only more governments
were willing to recalibrate their educational agendas to do so.

Until then, however, Taiwan stands as an exception. Other regions in
Asia, where myopia rates are among the highest in the world, have not
seen similar broad-scale successes, and most regions continue to
prioritize treating myopia over public-health measures to prevent it.
"There is certainly a lot of emphasis on clinical interventions at
the moment," says Morgan.

[d41586-024]

The myopia boom

This has led many eye specialists to search for workarounds that
mimic the benefits of the outdoors in indoor settings.

Many strategies centre on light. A 2015 study found that equipping
classrooms with brighter-than-usual ceiling light fixtures, along
with souped-up blackboard lamps, significantly reduced the incidence
of myopia among primary- and middle-school students in north-eastern
China -- from a 10% onset rate down to just 4% in a single year^6.

Other approaches focus on letting more natural light into learning
environments, using glass and steel to create 'bright classrooms'.
These earned high praise from students and teachers^7. But according
to Congdon, who led one such effort in southern China, the high costs
associated with construction, coupled with stringent building codes
enacted after a devastating 2008 earthquake that collapsed numerous
school buildings, rendered the concept impractical.

Lighting the way

An alternative method involves delivering light directly into the
eyeball -- although researchers disagree on what wavelength of light
is most beneficial, and why.

In Australia, researchers have run pilot studies with specialized
'light therapy' glasses that emit blue-green light, a portion of the
natural sunlight spectrum. Although marketed to alleviate jet lag and
enhance sleep quality, these devices -- reminiscent of the visor-like
eyewear from Star Trek -- have shown early promise in addressing
short-sightedness as well, inducing transient changes in certain eye
measurements linked to reduced myopia risk. The long-term benefits
aren't clear yet, notes Scott Read, an optometrist at Queensland
University of Technology in Brisbane, Australia, who led one of the
studies^8. But, he says, "there's certainly potential there".

Elsewhere, the medical-device company Dopavision, based in Berlin, is
trialling a virtual-reality headset that delivers short-wavelength
blue light to the 'blind spot' -- the point in the retina where the
optic nerve connects. In rabbit eyes, this therapy prompts a
significant increase in dopamine levels -- a molecular effect that
could explain why, in pilot clinical testing, the treatment has shown
promise at constraining eyeball elongation in people. A larger
clinical trial of the platform is ongoing in Europe, in which
children wear the headsets while playing video games.

Six school children doing nature studies with their teacher, hold
pictures of animals they have drawn.

Spending time outdoors can help to reduce rates of myopia.Credit:
Getty

Some research points to even shorter wavelengths of light as being
the key mediator of myopia development. Laboratory studies have found
that exposure to violet light could slow or prevent myopia
progression in mice^9 and chicks^10. Ophthalmologists at the Keio
University School of Medicine in Tokyo tested this idea in a pair of
randomized trials in which children with myopia aged 6-12 years wore
specialized eyeglasses equipped with frames that emitted violet light
for several hours every day. But even after months to years of
wearing the kitted-out spectacles, the treatment had little effect on
the growth trajectory of children's eyeballs^11.

Richard Lang, a biologist at the Cincinnati Children's Hospital
Medical Center in Ohio who studies the visual system, and who has
previously collaborated with the Keio team, thinks that he knows why
the glasses failed to make a difference.

The Keio researchers' wavelength of choice -- between 360 and 400
nanometres -- was based on studies in mice, but the human eye might
not respond to that part of the spectrum at all. Lang and his
collaborator Rafael Grytz, a bioengineer at the University of Alabama
at Birmingham, studied the tree shrew (Tupaia belangeri), which has
more human-like vision than the mouse does, and found that it filters
out most violet light with a wavelength shorter than 400 nanometres.

If the human eye filters light in the same way, that could explain
why the Keio team's violet-light glasses had little impact. At just
slightly longer wavelengths -- around 420 nanometres -- Lang and Grytz
could replicate the protective benefits of violet light in their tree
shrews, and they anticipate observing similar effects in people.

"There's this exquisite wavelength sensitivity," says Grytz, of the
unpublished tree shrew data. "I think violet light might be the key
for this problem and might change myopia treatment and prevention
forever," he adds. Grytz is so convinced of this potential that he
built a lamp that emits violet light to help safeguard his
eight-year-old daughter against myopia development. Lang and his
colleagues at Cincinnati Children's Hospital are testing a similar
lighting system in an ongoing randomized trial.

Seeing red

Yet, the light-based intervention that is gaining the most traction
around the world centres on wavelengths at the opposite end of the
visible-light spectrum. Known as repeated low-level red-light
therapy, the treatment involves use of a tabletop device that looks
similar to a microscope, and which emits a low-intensity,
long-wavelength laser directly into the user's eyes.

Originally developed for a different eye condition, it is thought to
work by enhancing blood flow in the eyeball -- a mechanism that would
be completely distinct from dopamine-inducing natural sunlight
exposure.

[d41586-024]

The surprising link between gut bacteria and devastating eye diseases

Trial data from China have demonstrated the therapy's promise for
controlling and preventing myopia as well. In a year-long study
conducted at ten primary schools in Shanghai, researchers found that
children at high risk of developing myopia who received red-light
therapy for three minutes twice per day, five days per week were half
as likely to develop it as were those who didn't receive the therapy^
12.

"If we do this red-light intervention, the prevalence of myopia will
reduce substantially over time," says Mingguang He, an
ophthalmologist at the Hong Kong Polytechnic University, who co-led
the study. He is also the co-founder and chief medical officer of
Eyerising International, a leading manufacturer of red-light therapy
machines based in South Yarra, Australia.

Tens, if not hundreds of thousands of children in China -- and smaller
numbers elsewhere -- regularly look into red-light-emitting
instruments for three minutes each morning and evening to alleviate
their short-sightedness. "It's just like brushing your teeth twice
daily," says Kaikai Qiu, an ophthalmologist at the Fuzhou South East
Eye Hospital in China.

Families typically rent the device for a couple of dollars per day
and administer the therapy at home. But for red-light therapy to
truly become a viable public-health option for widespread myopia
prevention, the technology must become more accessible, says Congdon.
"We need a school-based solution," he says. "If it can't be
implemented in schools, it's not going to address the social
problem."

Myopia specialists have raised concerns about the safety of red-light
therapy devices, after a 12-year-old girl experienced retinal damage
after using one^13. "The technical specifications are worrying," says
Lisa Ostrin, a vision scientist at the University of Houston College
of Optometry in Texas, who co-authored a report earlier this year
highlighting the potential for thermal injuries to the eye caused by
the therapy^14.

But proponents that Nature spoke to argue that it is safe -- and
Congdon and his collaborators plan to pilot the intervention in
classrooms. Trials are due to commence for preschoolers in Singapore
and for primary-school students in Hong Kong.

There is one other preventive measure gaining momentum: a drug called
atropine. Similar to some light-based therapies, the treatment also
targets dopamine. Last year, researchers in Hong Kong reported that
eye drops containing atropine can reduce the incidence of myopia^15.
The drug is already widely used to help control the progression of
myopia, and generally has minimal side effects. Still, for a
preventive treatment, even mild tolerability issues could be greater
than some are willing to accept.

Eyes on the horizon

Meanwhile, research with primary-school students in Yunnan province,
in the south-western corner of China, points to a wholly different
way of emulating the outdoors. The approach doesn't rely on light but
instead recreates naturalistic visual environments that promote
retinal focus.

In nine classrooms in the city of Lijiang, a team led by
ophthalmologist Weizhong Lan at the Aier Eye Hospital in Changsha,
China, introduced into classrooms custom-made wallpaper that
replicated the visual complexity and spatial properties of a natural
parkland, complete with trees, jumping dogs, flapping sparrows and
the occasional butterfly. The ceiling was painted to resemble a blue
sky, featuring white clouds, flocks of gulls, floating balloons and a
kite^16. "I just tried to make it as fun as possible," says Lan.

Grade-3 students sit in an outdoor scene classroom in China, Lijiang
Shiyan School, Yunnan province in China.

An outdoor-scene classroom in Lijiang Shiyan School in China, which
aims to prevent myopia development.Credit: Weizhong Lan/AIER Academy
of Ophthalmology, Central South University

In unpublished research that Lan plans to present at the
International Myopia Conference later this year in Sanya, China, he
and his colleagues found that children who spent a year inside these
'outdoor scene classrooms' had much less eye elongation than did
those who were taught in standard white-walled classrooms. It also
has the bonus of being easy to implement, he says, and shows that
"light is not the only reason" that outdoor exposures are beneficial.

As evidence for numerous interventions mounts, researchers are left
with a choice of which approach to prioritize. Or they could opt for
the one non-clinical option already known to be cheap and effective:
encourage more outdoor time.

Researchers and public-health officials will need to decide whether
to spend resources on simulating the outdoors, says Kevin Frick, a
health economist at Johns Hopkins University in Baltimore, Maryland,
who is co-chairing a consensus study committee on myopia for the US
National Academies of Science, Engineering, and Medicine. "Or do we
want to take a much simpler route," he asks, "and find ways that are
useful to engage children to go outside?"

"Society has a fundamental choice to make," Frick says -- and the
health of children's eyesight hangs in the balance.

Nature 629, 989-991 (2024)

doi: https://doi.org/10.1038/d41586-024-01518-2

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