Astigmatism

Astigmatism is usually caused by an abnormal corneal curvature that resembles the shape of a football rather than that of a basketball. Light rays focus at different places depending on their orientation, and objects at all distances appear blurred. Astigmatism may be accompanied by myopia or hyperopia.

For example, this picture demonstrates that the vertical light beams are focused in front of the retina, while light beams oriented 90 degrees away (horizontal) are focused at or near the retina. The result is two different focal planes 90 degrees apart, instead of a sharp focal point.

Spectacle Correction:

A special type of lens (called a "cylinder") is used to correct astigmatism. Soft contact lens are not able to correct astigmatism unless they are a special type known as toric lens. Large amounts of astigmatism often can only be treated by rigid contact lenses.

Surgical Correction:

Most commonly, moderate astigmatism (1 to 4 diopters) is corrected using a diamond scalpel by making accurate incisions across the steep meridan of the cornea. This technique can be used in conjunction with radial keratotomy or laser treatment. Arcuate keratotomy flattens the steep areas of the cornea, giving it a more spherical shape. Recently, one excimer laser was approved for the correction of astigmatism in the United States, and others are undergoing clinical trials..