AstigmatismBook eye test »
Astigmatism is the optical term for more than one point of focus. It occurs when the surface of the cornea or crystalline lens is not spherical. Light from an object does not focus exactly on the retina but at two separate points. An astigmatic eye has curves that are steeper in one direction than the other. An example of this could be where the cornea is not spherical and shaped more like a Rugby ball than football - of course this is not noticeable by just looking at someone's eyes.
As a result, the eye is unable to focus a point or object into a sharp focused image on the retina. There are two types of astigmatism, regular and irregular. Irregular astigmatism is often caused by a corneal scar or scattering in the crystalline lens and cannot be corrected by standard prescription lenses, but may be corrected by contact lenses. Regular astigmatism arising from either the cornea or crystalline lens can be corrected by a toric lens.