I vividly remember getting my first pair of glasses as a child. My mum is very near-sighted and dispatched me to the optician every year. My older sister was diagnosed at around the age of 8 and I prayed I wouldn’t follow suit for fear of being made fun of, but by the time I was the same age, the world was becoming a blur. That year’s visit to the optician confirmed it, and I have worn glasses or contact lenses ever since.
Back then, in the late 1970s, it was quite unusual to need glasses at such a young age. Not any more. Over the past 30 years, there has been a surge in near-sightedness, or myopia, especially among children. Today, around a third of 5 to 19-year-olds are myopic, up from a quarter in 1990. If that trend continues, the rate will be about – or 740 million myopic young people.
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That is more than an inconvenience. “Myopia is a disease,” says at the Johns Hopkins School of Medicine in Maryland, who co-chaired a recent . “It has wide-reaching ,” she says, not least the risk of going blind in severe cases. Increasingly, however, researchers think the epidemic can be slowed – or even reversed.
Most cases of myopia are axial, meaning the axis of the eyeball – the distance between the cornea at the front and the light-sensitive retina at the back – grows too long. This means that light entering the eye is focused in front of the retina, rather than on it, causing blurred vision. (Refractive myopia, which is less common, occurs when the eye’s cornea or lens is abnormally curved, causing blurriness.)
Babies are generally born long-sighted, but become less so as their eyeballs grow. When the sweet spot of perfect focus is reached, around their first birthday, the eyeball stops growing, a process called . Or, at least, it is meant to. In some children, the stop signal doesn’t arrive or is ignored, and the axis continues to elongate gradually. That growth speeds up and typically peaks between the ages of 8 and 16, according to at the University of Alabama at Birmingham.
Exactly why emmetropisation fails in some people is unclear. But once the retina is pushed beyond the perfect focal point, vision worsens progressively. Ophthalmologists refer to this as the “myopia cliff”, the point of no return – glasses, contact lenses and laser eye surgery, which permanently changes the shape of the cornea, can correct the blur but don’t cure the underlying problem.
The runs into thousands of pounds for each individual, but for around 10 per cent of people with axial myopia, there are added complications. Once their prescription goes beyond -5 dioptres – a measure of the strength of the lens needed to correct their vision – they are said to have high myopia.
That is potentially catastrophic, says Weise. “You don’t get a new retina – it has to stretch to accommodate the growth of the eye and that’s where you get some thinning at the edges.” This increases the risk of four conditions that can lead to irreversible blindness: detached retina, myopic macular degeneration, glaucoma and .
High myopia is more likely to develop if children fall off the cliff early. Myopia tends to progress by about half a dioptre a year in schoolchildren, according to Weise, so 10 years or more of abnormal and rapid eye lengthening can push them over the threshold. There is evidence that myopia is starting earlier, as soon as 3 years of age, according to at McMaster University in Hamilton, Canada. With estimates predicting that will be myopic by 2050, more people will spend more of their lives affected by this.
Causes of the great global blurring
What is causing the global blurring isn’t entirely clear, though there are clues. Although it is possible we are testing eyesight more regularly and therefore seeing more accurate rates of myopia, Weise says this would only explain a tiny percentage of the increase. And though there is a genetic component – a child with one myopic parent is about twice as likely to become myopic as a child with none, while – the increase is happening too quickly to be down to genetic change, says at Ohio State University. “So that makes us concentrate on environmental factors.”
Various culprits have been proposed – poor diets, urbanisation, increased screen time – but the evidence for all of these is weak. For many years, “near work”, any activity requiring close-up focus, was believed to be a cause of myopia. But “the evidence is just not there,” says Mutti, adding that smartphones, books and TV aren’t an important part of the problem.
The real villain seems to be too much time indoors. has long been known to be protective against developing myopia, for reasons that are still unknown, and “it is certainly the case that kids are outdoors less and indoors more than previous generations”, says Mutti.
Save your eyes, get outside
The power of increasing kids’ time outdoors was demonstrated by a nationwide experiment in Taiwan. In 2001, 34.8 per cent of children there aged 6 to 12 were myopic; by 2010, that figure had risen to 49.1 per cent. Alarmed by those numbers and motivated by the belief that too much near work was behind the precipitous rise, the government made changes to the school curriculum that year, encouraging 2 hours a day of outdoor activity.
Though near work probably wasn’t the cause of the children’s myopia, the experiment worked: within four years, the rate of new cases in Taiwan . It is still going down, although it hasn’t dropped back to where it was in the 1980s.
Another, more recent large-scale unintentional experiment also highlighted the importance of outdoor time: the covid-19 pandemic. Myopia rates rose dramatically in nations where children had to stay inside for long periods, according to .
Read more: How time outdoors could protect kids’ eyesight
The case for outdoor time as protective against developing the condition is supported by and reviews – the highest quality evidence. Based on multiple studies, the recommended level is at least 1 hour a day, preferably 2, and being exposed to a light intensity of at least , says Mutti, which is about the intensity you get in natural shade on a sunny day. Indoor light is typically a tenth of this or less.
The need for time outdoors may also explain the apparent link between myopia and near work. “I don’t think there’s strong evidence that what kids are doing indoors is a specific source of the myopia problem,” says Mutti. “It is the fact that they are indoors.”
This is a disease with wide-reaching quality of life and economic implications
Problem solved? Not entirely. Ideally, children aged 3 and above should be getting 2 hours of daily outdoor exposure, says Mutti, but this isn’t always possible. Moreover, being outdoors doesn’t stop kids who have already gone over the myopia cliff from falling further. “It would be nice to have a better understanding of what exactly is good about time outdoors so we can enhance its effect,” says Mutti, or replicate it indoors – prolonged exposure to the sun increases the risk of skin cancer, and outdoor light intensity can’t be relied on to hit 5000 lux every day.
Improving your ‘visual diet’
Even though light intensity seems to matter, this is only part of what is known as the “visual diet”. The spectrum of light is also different indoors than it is outdoors, as is the range of near and far objects, requiring the eye to focus on different points, the light-dark contrast and the level of fine detail the eye needs to resolve. Any or all could be involved in developing myopia, according to many researchers.
“Luminance, this 5000 lux figure, seems to be somewhat key,” says at Harvard Medical School. “But there’s a lot more research to be done in terms of dissecting what it is about the outdoors that’s better. As we identify these features, we can start to bring the benefits of the outdoors into the indoors.” That might mean changing indoor illumination in schools, for example, to better mimic natural light.
In the meantime, there are interventions that can slow down the elongation of the eyeball. One is eye drops containing a drug called atropine, which partially paralyses the muscles that change the aperture of the iris and reshape the lens while it is focusing on near objects. Atropine was first tested in the 1960s, on the basis that near work caused myopia, so limiting the eye’s ability to focus might solve the problem. , though researchers now know that the original rationale was wrong and they haven’t settled on a convincing alternative. “We don’t have a full understanding of why atropine works,” says Weise. The same goes for a similar drug called pirenzepine. Both, notably, come with unpleasant and common side effects, including blurred vision and light sensitivity.
The other treatment options include special glasses and contact lenses designed to blur peripheral vision. Researchers hypothesised that lenses fooling the peripheral vision into thinking it is myopic – called myopic defocus – would produce a stronger stop signal for growth of the eye and slow its elongation. “If you supply myopic defocus to more of the retina, you put the brakes on eye growth,” says Mutti. Another option is orthokeratology, rigid contact lenses that are worn at night and change the shape of the cornea in a way that helps improve vision.
Ways to tackle the global problem of myopia are finally coming into focus
According to a recent studies on controlling myopia, orthokeratology and atropine are the best available treatments, while others also work to some extent. But even the best therapies only reduce myopia by, at most, three-quarters of a dioptre before grinding to a halt.
“None of them work as much as we’d like them to. None of them prevent myopia,” says Weise, nor do they treat the underlying elongation. “Treatment effects are best in the first year – why would that be?” says Mutti. “We need solid evidence of exactly why they’re working.”
There are also signs that the therapies may ultimately do no good, or even lead to harm, says Weise: once the treatment is stopped, the eyeball can enter a period of rapid, haphazard “rebound” elongation, which may produce worse vision in the long run than slow and steady growth. For example, in research published in 2023, a team led by at the National University of Singapore 10 or 20 years previously. The researchers found no difference between these groups and those with untreated myopia. “Are we just delaying the inevitable?” asks Weise.
Finding the eye’s ‘stop’ signal
All of which points to a great need for better treatments. To get those, we need to clearly understand the mechanisms behind myopia, including what the eye growth “stop” signal is. “If we could understand this process, how biochemical signals create that growth… any part of that would help us to have much more effective treatments,” says at Emory University in Atlanta, Georgia.
One promising avenue is understanding the visual system’s method of detecting contrasts between light and dark. Known as the ON-OFF pathway, it is mediated by specialised cells in the retina connected to the brain’s visual cortex: bright light stimulates the ON pathway and darkness the OFF pathway.
“There’s evidence that defects in the ON pathway lead to myopia,” says Pardue. For example, people with a condition called complete congenital stationary night blindness, which is caused by genetic mutations in the ON pathway, tend to develop high myopia. So do mice in which .
Further evidence suggests that being indoors means getting insufficient bright light to stimulate the ON pathway and that firing up this pathway prompts the , which has been proposed as a possible stop signal for eye elongation. At the moment, research suggests that the ON-OFF pathway could offer a unifying theory of myopia and even a route to a permanent solution. “This is a theory at this point, but it deserves additional research,” says Pardue.
New treatments for nearsightedness in focus
In the meantime, new treatments are being rolled out, including what’s known as . In this, laser light with a wavelength of 650 nanometres and a luminance of 1600 lux is shone onto the retina for around 3 minutes, twice a day. It was developed to treat amblyopia, or lazy eye, but was inadvertently discovered to slow the progression of myopia – and in some cases send it into reverse.
In 2022, a team led by at Sun Yat-sen University in Guangzhou, China, published the , finding that it significantly slowed the progression of myopia. They also found, unexpectedly, that in around 40 per cent of the participants, the length of the eyeball shortened and vision improved. This sometimes happens spontaneously, but was much more common in the people who were treated – “a novel and important finding”, according to the researchers. Other studies using this therapy have since had .
“It looks like it works really well,” says Weise, though there are signs of strong rebound growth when the treatment is stopped. But it hints that the spectral composition of light hitting the retina matters, she says. “I do think there is something to the chromaticity of light and how we might use it to fool the retina into not growing.”
It may be too late for my eyes, but ways to tackle the global epidemic of myopia are finally coming into focus. “We are no longer fixing just the blur associated with near-sightedness,” says Weise. “This is a treatable condition, and we’d like to figure out how to treat it.”
