In people with normal vision, the cornea of the eye is similar to a semi-sphere. In people with astigmatism its shape is elliptical. The irregular curvature of the cornea refracts the rays of light unevenly. This causes any dot to appear like a line or a rod.
With this form of defective vision, the rays of light do not meet at one focal point on the retina but at several points. Since only a single focal point can appear as a sharp image, the image as a whole appears blurry.
This can be corrected with what is known as cylinder lenses. They equalize the curvatures in the cornea so that all the rays of light meet at a single focal point. Lens and laser surgery can also correct astigmatism.
