Look, up in the sky! Is it a bird? Is it a plane? Whatever it is, it’s incredibly small and blurry, and you’re probably squinting to get it in focus. Why is it that squinting helps you see? It all comes down to how your eye focuses light.
Before you think about how your eyeballs perceive the world, let’s think about how a camera perceives the world. At its simplest, a film camera takes in light through a hole, or aperture, and exposes it onto light-sensitive film to create an image. Of course, if you just exposed film to light, you wouldn’t actually get an image because every light particle (aka photon) would strike every area of the film willy-nilly. That’s why cameras also focus light by narrowing the aperture, which lets less random light in, and by adjusting the lens. A camera lens is a specially shaped piece of glass that bends the light waves that enter it so that they all converge on a single point, just like a magnifying glass in the sun.
But if light waves in a single point create an image, that means you don’t even need a lens to make a camera — all you really need is a very small hole that only lets in enough light to make a single point, right? In fact, such cameras exist. They’re called pinhole cameras, and they’re simple enough to make at home. A pinhole camera consists of an enclosed box with a small hole poked through one side, which shines light onto film placed on the opposite wall of the box. The hole lets in only a small quantity of light waves, which are mostly all going in the same direction. That helps the light form a focused image (albeit one that’s inverted and reversed) on the film. The smaller the hole, the less extra light there is bouncing all over the place, and the sharper the image.
Your eye works very similarly to a camera. It has an aperture (the pupil), a lens, and a light-sensitive surface (the layer of rod and cone cells in the back of your eye known as the retina). Like in a camera, most of the focusing happens in the lens. Your eyeballs actually contain a ring of muscle that helps to stretch and squish the lens into shape as you focus on things that are close up and far away. The lens helps to bend the light waves that enter your eye so they converge as a sharp image on the retina.
But just like narrowing a camera’s aperture or punching a tiny pinhole can create a sharper image, narrowing your eyelids — that is, squinting — reduces the amount of light coming in from all over and only lets in a small, unidirectional quantity of light waves that pass closer to the center of the lens. Basically, when you squint, you’re seeing the world through a pinhole camera, and the world is sharper as a result.
Don’t believe us? Try this: Ball up one fist so that you create a tiny hole with your fingers and thumb, then look through it at something blurry in the distance. The blurry object should come into focus, even if it’s just a little bit.
There’s one more thing that squinting may do for you: ever-so-slightly change the shape of your eyeball. Sometimes, poor vision is caused not by a problem with the lens, but by an irregularly shaped eye. By squinting, you’re not only letting in a smaller, more focused quantity of light, you may also be altering the shape of your eye to better focus that light.
Of course, squinting will only get you so far. If you find yourself squinting all the time, it might be a good idea to head to an optometrist and get fitted for glasses. After all, a pinhole camera is a great party trick, but a camera with a fully functional lens will capture the best images.
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