Astigmatism is always difficult to explain to people. I end up waving my arms around a lot, since it has to do with curvatures. The front surface of the eye – the front surface of the cornea – is the primary light-bending surface of the eye, and the amount of light-bending is a function of the curvature of the front surface of the cornea.
In astigmatism two different curvatures are at work. The two curvatures are usually roughly 90 degrees away from each other and one curvature is more curved than the other curvature. So, if there are two different curvatures, there are two different powers. Does that make sense?
So, I’ve been getting my upper body workouts waving my arms around to draw curvatures in the air for a few decades now. It’s still hard for a lot of people to visualize. A colleague and friend of mine told me he had a chalkboard in his office to explain this.
Then I happened to be watching a car rebuilding television show. One of the participants in explaining one of the tools they use referred to a potato chip. Specifically a Pringles chip.
I need everyone to go out and buy a can of Pringles chips. You can choose whatever flavor you like. Take out one unbroken chip. Hold the chip by the edge with the “opening” pointing down. Look at it holding it lengthwise, so it’s long sideways. Imagine the chip surface is the front of your eye. You will see one curvature – actually, it’s pretty flat. Not turn the chip and look down the length of the chip with the open portion still down. You’ll see a second, much sharper curvature. If you make that chip the front of your eye, you now have astigmatism.
Play with your potato chips for awhile and see if you can make sense of that. Then, once you have the concept down, eat the chips.