Myopia occurs when the eyeball stretches and grows too long, which makes far away objects look blurry.

Once a kid gets myopia, their eyeball will keep stretching and the condition will get progressively worse. If they develop high myopia, it can increase the risk of serious eye problems down the road, such as retinal detachments, glaucoma and cataracts. It can even lead to blindness.

There are treatments available to help slow the progression of myopia, including prescription atropine eye drops, special soft disposable contact lenses called MiSight, and hard contacts worn overnight known as orthokeratology, or ortho-K. But Ekdawi says the best approach is to protect children from developing myopia in the first place.

So how can spending time outside help?

That’s what Ian Morgan wanted to find out. Morgan is a myopia researcher at the Australian National University. A couple of decades ago, he noticed that the rates of myopia in East Asia were much higher than they were in Sydney.

He knew from animal studies that light stimulates the eye to release the neurotransmitter dopamine, which can slow the eyeball from stretching. “Australians are famous for their outdoor-oriented lifestyle,” he thought. “Maybe there’s a link between getting outside a lot and preventing the development of myopia.”

To test that theory, he and his colleagues designed a two-year study involving more than 4,000 6 and 12-year-olds in Sydney. Turns out, the researchers were right.

“The children who reported spending more time outdoors were less likely to be myopic and, we showed later on, less likely to become myopic,” Morgan says of the finding, which was published in 2008.

Morgan’s research caught the attention of Dr. Pei-Chang Wu, an ophthalmologist in Taiwan. As a retina specialist at Chang Gung Memorial Hospital in Kaohsiung, he’d seen the consequences of high myopia in patients as young as 10 with tears in their retina. Some even had retinal detachment – which can result in blindness if not treated quickly.

At the time, Wu’s young son was starting first grade, and he worried about Taiwan’s sky-high rates of myopia. Around 90% of teens there have it by the end of high school. Wu says the academic culture in Taiwan’s primary schools didn’t allow for much outdoor recess. “Many teachers want students to practice their homework during recess,” he says.

But Wu convinced his son’s elementary school to increase outdoor time. He also recruited a control school. A year later, his son’s school had half as many new myopia cases as the other school. “We saw the results – they were very successful,” Wu says.

He did more research, at more schools, and eventually convinced Taiwan’s Ministry of Education to encourage all primary schools to send students out doors for at least 2 hours a day, every day. The program launched in September 2010. And after decades of trending upward, the rate of myopia among Taiwan’s elementary school students began falling – from an all-time high of 50% in 2011 down to 45.1% by 2015. It’s a major achievement, says Ian Morgan.

“Certainly the people who have led the field are the people in Taiwan,” Morgan says.

Other studies have found that outdoor time can reduce the chances that kids will develop myopia even if they’re doing lots of near work, such as reading or looking at screens – something that has also risen dramatically in recent years. Outdoor time also helps even if kids have parents who have myopia.

To get that eyesight protection, research suggests kids should be spending at least two hours a day outdoors – every single day. And the younger you intervene, the better.

“To me, it’s like, eat your vegetables. You have to spend time outside,” Ekdawi says.

It doesn’t even matter if it’s sunny or cloudy – or what the kids are doing. “You can go to the park, you can ride your bike, you can sit and be a tree, walk your dog. All these things count,” she says.

And if you are worried about leaving time for homework, Ekdawi suggests having kids do that outside, too. As long as they are outdoors, that’s what matters.