In astigmatism, vision is blurred a variable amount for all distances.

Astigmatism means that light is focused at several points in the eye instead of all at one point. For example, light that is horizontal may focus in back of the retina and, at the same time, light that is vertical in nature may focus in front of the retina. The eye cannot focus light ALL AT THE SAME TIME on one point. This creates an area of confused or variably focused light rays causing blurred vision. It is important to realize that astigmatism may be "regular" or "irregular". This discussion is limited to "regular" astigmatism as the cause of blurred vision which is usually correctable either with glasses or contact lenses.

Astigmatism occurs for one of two reasons. First, the curve on the clear cornea (clear window at the front of the eye) may be different in one direction than another. For example, if a round clear ball was cut in half and one of the halves used as the cornea, then the cornea would be spherical and have no astigmatism.

If, however, a clear football shaped ball was cut in half, and one half of the football used to make the cornea, the curves would have a different steepness or radius in different directions. Such an eye would have a cornea (clear window) with an "astigmatic" surface and would have "astigmatism".

The second reason that astigmatism can occur is because the lens in the eye, rather than the cornea, focuses light better in one direction than another. This is called "lenticular" astigmatism. In fact, the eye may have astigmatism because of either cornea astigmatism or lenticular (lens) astigmatism or even both types of astigmatism at the same time!

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