Myopia, or short-sightedness, has skyrocketed in recent years, reaching epidemic levels in parts of Asia. But short of buying glasses in bulk, is there anything that can be done?
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A new Chinese study pulished in the Journal of the American Medical Association this month says yes - put children outside for 40 minutes every day.
Researchers gave almost 1000 six-year-old children an additional 40-minute class of outdoor activities over three years, while a separate control group carried on as they had before.
The outcome was staggering: the extra outside time resulted in 25 percent less of the group developing short-sightedness compared to the control group.
Though it's tempting to associate short-sightedness with screens or too much close-up work, but Dr John Phillips of Auckland University's myopia laboratory said it was a little more complicated.
Listen to Dr John Phillips on Nine to Noon
To begin with, he said, it was a question of genes.
"I think the inheritance bit is an inheritance of susceptibility to myopia in the wrong environment, and I expect that susceptibility is greater in some ethnic groups than others.
"It's probably always been there, it's just that we've now introduced the wrong sort of environment in modern life, and the consequence is that many children are becoming short-sighted."
Dr Phillips said the environmental factors were complex: "It's really to do with intense educational processes, high urbanisation, very stressful and early education, and early near-work.
"Along with that of course goes reduction in outdoor activity, and living in apartments, and my take on it is that it's not simply one factor that's led to the dramatic increase in myopia, it's a combination of them."
"It's clearly the early environment that a child is exposed to that is having the effect, and that's the thing that has to be modified."
And the most important factor so far as screens are concerned is not their size or how much they are used, but the time of day.
"The role that screens play is complex, and is something to do with when these screens get used - if they get used during the day, it probably doesn't matter, but if they get used at night, because they emit light, potentially they are a culprit," said Dr Phillips.
Looking at screens in the evening upsets the eye's circadian rhythms, he said, as do electric lights.
But ultimately, it comes down to genetics - and if you're one of the lucky ones, you'll escape short-sightedness, regardless of how often you check your phone in the middle of the night.