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Astigmatism In astigmatism the cornea is shaped like a football rather than a tennis ball

In astigmatism the cornea is shaped like a football rather than a tennis ball

In order for the eye to work correctly, light coming into the eye must be properly focused on the retina (the back of the eye). When the image is not focused, an irregularity in the eye is to blame. The irregularity comprises either the overall shape of the eye or the curvature of the cornea (the clear outer covering of the eye), or both. The cornea should be curved equally in all directions. Astigmatism occurs when the cornea is curved more in one direction than another and has more of the shape and curvatures of a football, compared to the normal shape of a tennis ball.

Astigmatism is quite common and, in the vast majority of cases, it is due simply to genetic variation. Just as different people have different shaped feet or hands, people also have different shaped corneas. Occasionally, astigmatism is caused by lid swellings such as chalazia, corneal scars, or keratoconus (a rare condition in which the cornea becomes misshapen and pointed rather than smooth and rounded). Astigmatism may cause blurred vision, eye strain or even headaches. It can also cause images to appear doubled, particularly at night. Small amounts of astigmatism can be ignored. But if any of its symptoms are present, astigmatism can be corrected by glasses or contact lenses. In most patients hard contact lenses do a better job of correcting for astigmatism than soft contact lenses.

More Detailed Explanation of Astigmatism:

Because the cornea is shaped more like a football, the image is broken down into two focal lines separated in space and rotated 90⁰ from each other. To correct this condition, cylindrical lenses are made to bring the two focal lines together and make them a point (or stigma in Latin) focus on the retina rather than an "astigma" (meaning not or not a point in Latin).