What is astigmatism?!

What is astigmatism?

First a basic definition: Astigmatism, or an astigmatic focusing error, is a description of one of the ways the eye, or any optical system, can be out of focus. It's not a degeneration or disease.

Think of your eye as a camera. Light comes in the front, passes through a number of focusing elements, and an image is focused at the back of the eye onto the inner lining of the eyeball known as the retina. A camera does all of the same things except the image is focused onto a sheet of film or a flat screen.

For there to be a clear focus, all of the surfaces of the different focusing elements should be almost spherical, like the surface of a bowling ball. This includes the clear bubble that covers the colored part of your eye. The bubble is called the cornea.

Stay with me here. As you are seated, pretend you have an inner tube (not used much anymore) held between your legs, ready to roll away from you. If you look down at the surface of the inner tube, you will see that the top surface is NOT spherical. There is a flatter curve along the outside surface when measuring it in the direction that the tube will roll away. There is a very steep curve when you measure left-to-right along the top surface. Now picture the surface of a cornea having these two different curves - tight one way and steep in the other direction. Behind this non-spherical cornea an astigmatic focusing error would be created, which would require a compensating astigmatic spectacle or contact lens in order for a person to see clearly. All because of the difference in curvature.

I hope your imagination worked, and you have a little bit better understanding.