Once upon a time, they said books would ruin your eyesight. Then TV. Then computers and video games. Then tablets. Now phones. They were totally wrong. And totally right.
If you haven’t seen the news, we’re in the midst of a global myopia epidemic. Also known as shortsightedness or nearsightedness, myopia is an elongation of the eyeballs that causes distant objects to look blurry. This blurriness can be compensated for by glasses or contact lenses, although they don’t correct the underlying physical deformation of the eyeball. Myopia takes root during childhood, when the eyeballs are still forming. In later life, depending on the severity of myopia, the problem can lead to increased risk of retinal detachment, cataracts, glaucoma, and irreversible vision loss.
In Europe, myopia now affects roughly 50% of young adults. In East Asia, the numbers are even more eye-watering. According to the science journal Nature, in China and Taiwan, around 90% of teens and young adults are shortsighted, while in the South Korean city of Seoul that number rises to nearly 95%. And it’s only getting worse.
We’ve long looked for the cause of myopia. Nearly four centuries ago, German scientist Johannes Kepler, whose own eyesight started failing him, blamed his books. It was no idle guess – in addition to being a noted astronomer, Kepler literally wrote the book on optics: his 1604 manuscript Astronomiae Pars Optica is considered the foundation for the modern science.
Kepler’s theory of myopia has remained influential because it seems that wherever book learning has spread, or intensified, myopia has too. In the 1960s, amidst dramatic changes away from their traditional lifestyles, Alaskan Inuits saw a sudden increase in myopia. In Israel, Yeshiva students, who spend years of intense study of religious texts, have much higher incidence of myopia. And throughout East Asia, where schooling and high-stakes examinations have been the engines driving postwar economies, myopia has simply exploded.
So like Kepler before her, your great grandmother may have seemed plenty justified in focusing on books. You’ll ruin your eyesight! she may have warned. More recent generations have blamed TV, computers, and mobile phones. They’re all wrong. But they’re not far off the mark.
Thanks to science, the picture is getting a lot clearer. It’s not books or screens that cause the problem, but lack of sunlight – everywhere science looks, there’s an inverse relationship between myopia incidence and time spent outdoors. The current thesis is that daylight – which even on an overcast day is 20X brighter than even a well-lit classroom – stimulates retinal dopamine production in children, and retinal dopamine essentially tells the eyeball to stay sphere-shaped, and stop growing longer. In Taiwan, when public awareness campaigns pushed for a minimum two hours outside every day for young children, they had success in temporarily reversing the trend – that is, until Covid struck and emergency regulations forced everybody back inside.
So while your great grandmother might not have seen the culprit clearly – the role of daylight in stopping myopia still just coming into focus for modern science – she would have known exactly what to prescribe to 21st century kids.
Get off the sofa. Get away from the screen. Go outside and play.
It’s a solution that couldn’t be any clearer.