Astigmatism is an imperfection in the curvature of the cornea-the transparent convex membrane that forms the anterior portion of the eyeball’s fibrous tonaca-or in the shape of the lens.
Normally, the cornea the lens are smooth and have the same curvature in all directions, thus helping to focus at the back of the eye the light rays that strike the retina. However, if the cornea or lens is not smooth and evenly curved, light rays are not refracted properly. This is called refractive error. When the cornea is irregularly shaped, it is called corneal astigmatism; when there are lens changes, it is called lenticular astigmatism.
As a result of both types of astigmatism, vision appears blurred or distorted.
