Recently, I bellied up to a bar waiting for what seemed like an eternity to order my beer. It's not that the place was busy, in fact the bartender was waiting for me. But I'd forgotten my glasses, so reading the tap list—hung high on the back wall—was slow going, even though it was written in six-inch chalk letters. Just before I made my choice, I caught a glance of myself in the back mirror. I was squinting like a sea captain steering through a gale. With wide open eyes, the list would have been unreadable.

Why do people squint to see better? For the longest time, I thought squeezing my eyelids somehow reshaped my faulty eyeballs. And while squinting does slightly change the shape of your lenses, the real answer has to more to do with the back of your eye than the front.

Your eye is like a camera, and blurriness comes mostly from the way it captures and processes light. Photons pass through your lens, which focuses them onto a spot at the back of your retina. There, specialized photoreceptive structures called rods and cones convert these photons into electromagnetic impulses that your brain interprets as shapes, colors, and textures.

Your lens changes shape in order to focus on things both near and far. However, there are limits to its flexibility. When something is blurry, it usually means the light being focused by your lens is either under- or overshooting the focal point at the back of your retina (though blurriness can also be caused by physical damage to your eyeball).

The light from the thing you are trying to look at is also competing with light from everything else in your field of view. All this extra light is basically noise, and like static it obscures your desired signal. When you squint, you are reducing the amount of light coming from other sources—stripping some of the noise away.

A tight aperture the reason why the bee in this picture is so crisp compared to the immediate fore- and background. A Guy Taking Pictures/Flickr

This is like narrowing the aperture on your camera, which is what photographers do to give themselves super tight focus. Make a small hole with your forefinger and thumb, then hold it up to your eye and look at something far away. It's not exactly a telescope, but the thing you're looking at should be a bit less blurry. Or, if that's too low tech for you, you can always build yourself a piece of cybernetic auto-squinting headgear

Your eye lens reflexively changes shape when you squint (Your eyelid doesn't actually do any work). But, the shape change has little effect on the lens, and has little impact on vision compared to the light-reducing effect of a smaller aperture.

Of course, the best cure for blurry vision is a pair of glasses. I'm trying to remember to bring them with me when I go out more, so I can spend less time ordering my beer and more time enjoying it.