The eye has two curved structures called the cornea and the lens that bend or refract light onto the retina, which makes the image that you see. In a perfectly shaped eye, each of these elements has a round curvature like a smooth ball. A cornea and lens with such curvature refract all incoming light equally to make a sharply focused image directly on the retina.
If either your cornea or lens is egg-shaped with two mismatched curves, light rays aren’t bent the same, which forms two different images. These images overlap or combine and result in blurred vision.
Astigmatism occurs when your cornea or lens is curved more steeply in one direction than in another.
It is not known what causes astigmatism, but genetics is a big factor. It may also occur as a result of an injury to the eye or after eye surgery.
It often occurs with nearsightedness or farsightedness.