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Hank brings the answer into focus.

Hosted by: Hank Green
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Hank: If you’re a four-eyes like me, you may have heard that wearing glasses will ruin your eyesight. Over time, the thinking goes, the eye muscles that stretch the lens of your eye aren’t worked out as much, so they get weaker, and you keep needing stronger and stronger prescriptions to see clearly. But the idea that glasses hurt your vision is a myth. Because... that’s not really how glasses work.

Most vision problems occur because the eyeball is either too long or too short, causing the cornea and lens to bend, or refract, light either too far in front of or behind the retina, giving you blurry vision. If your eyeball is too long, and light is focused in front of the retina, you’re nearsighted, or myopic, and you can see things up close but struggle with things in the distance.

If it’s too short, and light is focused behind the retina, you’re farsighted, and you can read that sign halfway down the street, but have trouble reading what’s right in front of you. Your eye muscles can bend the lens more or less to try and focus light onto the right place. But those muscles can only contract or relax so much to accommodate squat or oblong eyes.

So, weak eye muscles aren’t why you have bad eyesight. If that were the case, we’d all be doing eye exercises to cure our poor vision. Glasses do what properly shaped eyeballs do, which is to make it possible to focus the light that’s coming into your eye directly onto the retina, allowing you to see crisp images. The only effect they may have on your eye muscles is reducing excessive strain on them.

There was a time, though, when doctors thought eyeglasses could do more. For decades, optometrists purposely prescribed glasses for nearsighted kids that didn’t fully correct their vision, because they thought it would keep their eyesight from getting worse.

That’s because, in children, the eye is still growing, and usually gets longer as it grows in the skull. In kids who are nearsighted, this could make myopia worse. And doctors thought that fully restoring distance vision would make kids’ eyes grow even longer, as they tried to compensate to see things up close through corrective lenses.

So doctors under-prescribed, thinking that would keep the eyes from elongating as much. But in 2002, a clinical trial called that into question. After two years, kids who were given weaker lenses actually ended up with worse vision. The results were so striking that the researchers had to stop the study early due to ethical concerns.

Subsequent studies haven’t always found such a strong negative effect of subpar glasses, but there’s no evidence that under-correction helps, and optometrists have largely stopped the practice.

So glasses won’t ruin your vision — if anything, they may prevent it from getting worse. And, of course, yes, you might need stronger prescriptions as time goes by. Because, as you age, the lenses of your eyes get stiffer, making it harder for them to change focus. But it’s not your glasses’ fault. So, keep wearing them. Because they help you see stuff. And also just look cool!

Thanks to all of our patrons on Patreon, who probably have a higher than average number of corrective lenses among them. You’re great for supporting this so that everybody in the world can get it for free. If you want to get more SciShow and just want to help us out without money, you can go to and subscribe. We appreciate that. And also... you get SciShow in your subscription box!