Ideally the curvature of the cornea is shaped regularly like the surface of a ball. Astigmatism occurs when the corneal surface is more irregularly shaped like that of an egg. Light is refracted differently through the different curvatures of the cornea resulting in a distorted image.

Optical correction of astigmatism redirects the light rays such that they once again meet in one point of focus onto the area of best vision on the retina.

The corrective lens is indicated as a cylinder. The power of a cylindrical lens is measured in diopters (D). A cylinder lens must be placed in a particular orientation in front of the eye. This position is indicated by the given axis of the lens e.g. -1.50D x 180º.

LASIK is a safe method of treating astigmatism. Over 95% of astigmatic patients treated can forgo the usage of spectacles and contact lenses after a LASIK procedure.