In astigmatism, both the cornea and the lens have an irregular curvature, causing light to focus on more than one point of the eye and distort vision.

In an astigmatic cornea, instead of having a spherical curve like the shape of a basketball, the curvature is more oval, like the shape of a football. Most corneas affected by astigmatism have two curves, a steeper curve and a flatter curve, which generate the multiple points of focus. Astigmatism often occurs in combination with myopia or hyperopia. The result is blurred, distorted vision at near or far distance.