Myopia, also known as nearsightedness, has become a lot more common in recent decades. Some even consider myopia an epidemic (流行病). But what causes myopia and what reduces it?
While having two myopic parents does mean you're more likely to be nearsighted, there's no single myopia gene. That means the causes of myopia are more behavioral than genetic.
Scientists have learned a great deal about the progression of myopia by studying visual development in baby chickens. They do so by putting little hats on baby chickens. Lenses (镜片) on the face of the hats cover the chicks' eyes and are adjusted to affect how much they see.
Just like in humans, if visual input is wrong, a chick's eyes grow too large, resulting in myopia. And it's progressive. Blur (模糊) leads to eye growth, which causes more blur, which makes the eye grow even larger, and so on.
Two recent studies featuring extensive surveys of children and their parents provide strong support for the idea that an important driver of the increase in myopia is that people are spending more time focusing on objects immediately in front of our eyes, whether a screen, a book or a drawing pad.
Other research has shown that this unnatural eye growth can be interrupted by sunlight. A 2022 study, for example, found that myopia rates were more than four times greater for children who didn't spend much time outdoors—say, once or twice a week—compared with those who were outside daily. At the same time, kids who spent more than three hours a day while not at school reading or looking at a screen close-up were four times more likely to have myopia than those who spent an hour or less doing so.
Fortunately, just a few minutes a day with glasses that correct blur stops the progression of myopia, which is why early vision testing and vision correction are important to limit the development of myopia.