Published: 21 October, 2004

Squinting changes eye's shape

Why does squinting help people with vision problems see better?

Everyone knows that we see with our eyes, but not everyone knows how the eye works. If you look into a mirror you can see the black circle in the middle - it's called the pupil. The pupil is the eye's window on the world and it is how light enters the eye. Once light enters the eye, it passes through the lens, which focuses the light on an area in the back of the eye known as the retina. Here there are special cells that can detect the light and those cells send signals to the brain which then puts all those signals back together and, voila, we see!

As we get older, the lens of the eye becomes harder and cannot focus light as well as it used to. Also, some people have eyes that are slightly longer from front to back, which can make the light not focus correctly. By squinting people are actually changing the shape of their eye, just ever so little, so that the light focuses correctly on the retina.

Squinting also decreases the amount of light that enters the eye. Go ahead and squint right now - notice that you can start to see your bottom and top eyelid. When a lens is misshapen (due to age, damage or genetics) the light that passes through the lens is deflected incorrectly and misses the focal point; the farther the light rays are from the center of the lens, the more they are deviated from the focal point. By limiting the rays of light that come in through the bottom and top of the pupil, squinting allows rays to pass closer to the center of the lens, thereby creating a more focused image. So, that means that squinting works by two mechanisms - by both changing the shape of the eye and by letting in light that can be focused more precisely by the lens.

A new surgery you may have heard of, called lasik, can also help change the shape of the front of the eye so that the light will correctly focus at the back of the eye. You or I cannot look at a person a tell if he or she has had this type of surgery, but the person can see much better without ever having to squint again!