If you wear glasses, you may think that your glasses are gradually weakening your eyesight because the eye muscles that stretch the lens of your eye aren’t used as much as they should be, so they get weaker, and hence you keep needing stronger and stronger prescriptions to see clearly. Basically, what your glasses do is help you see clearly, so when you take them off, contrasting blurriness is obvious. But, is there any evidence to support that wearing glasses ruin eyesight?

No. In the latest video of SciShow’s “Do Glasses Ruin Your Eyesight?” Hank Green explains that the idea that glasses hurt your vision is a myth. There are two reasons people wear glasses – nearsightedness, or myopia, and farsightedness, or hypermetropia. Most people experience vision defects when their eyeball gets 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, leaving the vision blurry.

If distant objects appear blurred to you, you’re nearsighted, or myopic. Your eyeball is too long and light is focused in front of the retina. If you can’t focus on things close up, you’re farsighted, or hypermetropic. Your eyeball is too short, and light is focused behind the retina instead of on it.

Farsightedness is often age-related. Many people in their mid 40s would notice their difficultly in reading in low lighting. That’s because as you age, the lenses in your eyes get stiffer, making it harder for them to change focus or to adjust to different distances. The condition is called presbyopia. When people get to this stage, they usually opt for reading glasses. Hence they become more and more dependent on their glasses as their lenses become worse with age, leading them to conclude that wearing glasses have ruined their eyesight, which isn’t really true.

Does Wearing Glasses Ruin Eyesight?

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 clearly. And they also help reduce excessive strain on your eye muscles. Most believe weak eye muscles are the reasons you have bad eyesight, but that is not true. Because what your eye muscles actually do is bend the lens more or less to try and focus light onto the right place. And, these 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,” Hank explains. “If that were the case, we’d all be doing eye exercises to cure our poor vision.”

Decades ago, optometrists deliberately prescribed glasses for nearsighted children that didn’t fully correct their vision, because they thought giving them weaker glass than they really need, would slow down the elongation of the eyeball over time and thus prevent their eyesight from getting worse. This is because, in children, the eye is still growing, and usually gets longer as it grows in the skull. In kids who are nearsighted, doctors though this could make myopia worse 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 actually though under-prescribing the children would keep their eyes from elongation and hence slow down the progression of myopia. But a study conducted in Malaysia in 2002 found that children who were given undercorrected lenses showed a greater elongation of the eyeball, and hence they ended up with worse vision. So, there is no evidence that undercorrection helps, and optometrists have largely stopped the practice. A Cochrane review from 2011 suggests giving children the correct glasses, rather than trying to under-prescribe.

So glasses won’t ruin your vision. They actually prevent your vision from getting worse. But if you think otherwise, you are far from alone. A study conducted in Nigeria in 2013 found that 64 percent of students believed eyeglasses are harmful to the eyes. And even medical staff in Brazil believed glasses would gradually damage your eyes.