To be able to see things clearly, your eyeballs need to be a certain shape. Today, though, around half of the world’s kids have eyeballs that are too long - and as a result, they have blurry vision. Welcome to MinuteEarth.
Most babies are born with short eyeballs. But as a baby grows, their eyeballs get longer - the lens and the retina get farther and farther apart. By the time the kid is about 6, their eyeballs are just the right length for the lens to be able to focus incoming light and form a crisp image right on the retina, rather than focusing well behind it; at that point, the brain sends a signal to the eyeballs, telling them to stop growing.
But, starting a few decades ago, many kids - like, more than 90% of kids in some countries… these kids’ eyeballs continued to lengthen well past that spot. As a result, instead of focusing light right onto the retina, the lenses in these kids’ longer eyeballs focus light on a point in front of the retina; from there, the light spreads back out, causing them to see a fuzzy image rather than a crisp one. For years, most scientists thought this was happening because of screens - or more specifically, because kids were spending most of their time looking at things only a short distance away.
You see, our eyes focus most easily on stuff in the middle distance. In order to clearly see stuff far away, the muscles have to work to stretch the lens to bring those images back to the sweet spot on the retina, and in order to clearly see things close up, the muscles have to work to smoosh the lens to bring those images forward to the sweet spot on the retina. Scientists wondered whether kids’ eyeballs were growing extra long to shift this entire range farther back, allowing them to see close up stuff in focus without having to use their muscles, but leaving their eyes unable to focus on things far away at all, no matter how much they strained.
But recently, we’ve found that kids who spend a lot of time parked in front of a screen don’t necessarily have longer eyeballs than those who don’t. Instead, it seems that the likely culprit is the hormone that carries the stop-growing signal from the brain to the eyeballs – or, really, a lack of this hormone. We still don’t totally understand how the entire signaling-process works, but we do know that our eyes need to be exposed to a certain level of light in order for the hormone to form in the first place.
Kids today - who only spend about half as much time outside as their parents did – simply aren’t getting the light their eyes need to create enough of that hormone and give the stop-growing signal. As a result, their eyeballs keep lengthening - past the sweet spot – creating an epidemic of blurry vision the likes of which the world has never . .
uhh . . seen.
Luckily, there’s an easy solution for future generations - go outside to watch your YouTube videos.
