What is astigmatism?

Astigmatism is a condition of the eye, where vision is blurred by an irregularly shaped cornea. The cornea, instead of being shaped like a sphere (like a football), is ellipsoidal (like a rugby ball). This means that a different prescription is found in different meridians of the eye, (i.e. the eye has different focal points in different planes.) For example, the image may be clearly focused on the retina in the horizontal direction, but not in front of the retina in the vertical direction. Astigmatism causes difficulties in seeing fine detail, and in some cases vertical lines (e.g., walls). Astigmatism of the eye can be corrected by toric lenses (i.e. a lens that has different radii of curvature in different planes). Astigmatism can occur by itself or in conjunction with myopia and hyperopia.