Most people have some degree of astigmatism or ellipsoidal shape of the cornea, along with myopia. Astigmatism occurs when the cornea is shaped more like a cross section of a baseball, rather than a basketball. As a result, the images are not completely focused on the retina due to unequal refraction in different parts of the cornea, and both distant and near objects look blurry. Therefore, to people with high degrees of astigmatism, both distant (like myopic patients) and near objects appear blurry.

Astigmatism is measured in units of diopters. Astigmatism is classified as follows:

• Mild astigmatism: less than 1 diopter

• Moderate astigmatism: 1 to 2 diopters

• Severe astigmatism: 2 to 3 diopters

• Extreme astigmatism: more than 3 diopters

Astigmatism has different types and can occur alone, or with myopia or hyperopia.