Astigmatismus

Astigmatism, a common condition, occurs when the curvature of the cornea is asymmetric. A normal cornea is shaped spherically, similar to the lens of a camera. Horizontal as well as vertical lines are refracted to form a focused image. A dot-like source of light, such as a street light, will produce a dot-like image. But if the curvature of the cornea is elliptic instead of spherical light rays focus at different points causing image distortion. In our example, the street light will not produce the image of a bright dot but a small line.

Astigmatism occurs frequently in combination wiht nearsightedness or farsightedness.