Most of the eye’s focusing power comes from the cornea, the clear saucer of tissue at the front of the eye. A normal cornea is round-shaped like half of a basketball-with the surface curving evenly in every direction. The even curve allows it to focus light sharply and produce clear vision.

Sometimes, however, the curve of the cornea is steeper in one direction than in another-more like half of a football. When the curve is not even, the cornea cannot focus light properly. This condition, known as astigmatism, can result in blurriness, distortion or ghost images around objects. It affects both close-up and distance vision.

In the United States, two-thirds of all people who suffer from nearsightedness (myopia) also have astigmatism. For most patients, astigmatism can be corrected with either glasses or contact lenses. Some people with astigmatism can improve their eyesight through refractive surgery.