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Astigmatism: A Simple Way to Understand it Completely

Everyone has astigmatism, but almost no one really understands what it means. There’s a very strong chance it was explained to you as having an eye shaped like a football. I’ve always found that description nearly useless — for two reasons.

By Joel Hunter, MD
 

Everyone has astigmatism, but almost no one really understands what it means. Let’s get the blame out of the way immediately by just agreeing that the explanations of it are terrible. There’s a very strong chance it was explained to you as having an eye shaped like a football. I’ve always found that description nearly useless — for two reasons.

The Confusing Explanation

First, it’s a perfect example of a description that requires a pre-existing understanding of what’s being described. It’d be like describing traffic lights to someone who has never seen a paved road by saying, “They are like Christmas lights that tell us what to do.” It only makes sense to you because you already know how they work. The second reason verifies that. Almost every patient I meet with astigmatism knows their eye is “shaped like a football” but they don’t know what that means. When your explanation needs explaining, it’s not working.

The Simple Explanation

Here’s the simple way to understand astigmatism completely. Imagine a camera. A real, wedding photographer, has-a-shutter-button and a big lens, type of camera. Your eye works almost exactly like that camera. We have a lens at the front (called the cornea), and it focuses an image inside onto a sensor (called the retina). If the image is focused perfectly with a camera, then you’ll have a clear photo. Similarly, if the image is focused perfectly with your eye, then you’ll have clear vision.

Photographers pay crazy amounts of money for the lenses that they put on the front of their camera. A lot of times the lens is more expensive than the camera itself. Why? Because the perfect contour and smoothness of that lens — on a level measured in thousandths of a millimeter — determines how perfectly that lens will focus an image. And it’s super expensive to produce camera lenses of that quality.

Now, imagine that during delivery of one of those perfect, super expensive camera lenses, the back of the delivery truck gets too hot. (Granted, it would have to be about 1400 degrees Celsius in this thought experiment, like Florida in August.) That beautiful glass lens gets a little bit soft. It squishes — just a little! — like a gel sphere would if you squeezed it between your fingers. The back of the truck opens, the glass cools and stays in that very slightly squished shape.

When the photographer uses that lens, every photo will be blurry. Why? That perfect lens lost its perfect contour. The shape it needed to focus an image perfectly has changed because of that slight “squish.” It can’t create the perfect focus it was designed for when it is deformed even in the very slightest. To say the exact same in different words, that lens now has astigmatism.

Most Eyes Aren't Perfect

It’s the exact same for our lens (the cornea) on the front of our eye. An otherwise perfectly contoured, high-quality lens has this slightly deformed shape — so subtle you can’t detect it without specialized cornea scanning equipment. That’s why it’s so common! It’s hard to find perfect shapes in nature. And to see perfectly, you need an absolutely perfect cornea with no squish, no deformation, no astigmatism at all.

A bonus paragraph on the weirdness of the “eye is shaped like a football” explanation:

Ophthalmologists aren’t typically what I’d call “sportsy,” myself very much included. We know that balls used in sports are spherically round with the exception of a football, which looks more squished around the middle. So, in the medical equivalent of showing up at a Super Bowl party and saying, “I hope we score touchdown points with no ball fumbles!” ophthalmologists tried to make astigmatism relatable by using the horrible analogy that eye is shaped like a football. Then we all high-fived over our ability use sports to explain science and asked how long till the Super Bowl commercials come on because that’s our favorite part.

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