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
A physician examines the eyesight of a child with myopia in Hebei province, northern China. Credit: Sipa US/Alamy
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 levels1.
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 decades2 (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.”
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-sightedness3,4. 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.
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.
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 region5.
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.
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 year6.
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 teachers7. 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 studies8. 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.
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 mice9 and chicks10. 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 eyeballs11.
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.
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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 therapy12.
“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 one13. “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 therapy14.
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 myopia15. 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 kite16. “I just tried to make it as fun as possible,” says Lan.
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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