When you were a kid, someone probably told you that if you crossed your eyes, they could get stuck that way. Maybe you’ve even said the same thing to your children. No matter what your role in perpetuating this medical myth, it’s just that—a myth. 

Control over the function of the eyes is incredibly complex, so it’s not surprising that people may be confused about eye crossing. In fact, when most people think about the eyes (if they do at all), they don’t consider the complicated set of muscles that allow the eyes to function— and to cross.

A basic lesson in eye anatomy: Light enters the front of the eye through the transparent cornea. It then travels through the pupil, a hole that increases in size when more light is needed and constricts in bright light. Then the light travels to the retina, which sends signals to the brain.

From the retina's perspective, the pupil acts as an automatic dimmer switch. This is all thanks to tiny muscles and ligaments that flex and relax automatically.

Other specialized muscles control the shape of the lens (for focusing) and eye movements (to keep the eyes moving together). If an object is close to the eye, the muscles controlling the lens automatically change its shape to bring the object into proper focus (a process called accommodation). Similarly, the muscles that keep the eyes moving in tandem normally contract and relax in a synchronized way.

You can upset this synchronicity by trying to see the tip of your nose: each inwardly turned eye sends signals to the brain that are so different than the normal signals that it causes vision to "double"—that is, the vision sees two disparate images that cannot be readily integrated into one. And this makes your eyes appear crossed.

Fortunately, these tiny muscles that control eye function are like other muscles in the body: they may fatigue, but they are resilient. Your body, including your eyes, evolved to handle a lot of daily wear and tear. So if you cross your eyes, you will tire your muscles out. But you won’t do any permanent harm—and you won’t get stuck like that.

Where did this medical myth come from? Maybe it’s due to excessive fear of harming such a complicated and valuable part of the body. Or, maybe some parents made it up to stop their kids from engaging in what they considered annoying behavior. Regardless of where it came from, my guess is that the myth about eye crossing is unlikely to go away any time soon.

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