Astigmatism is a refractive error not an eye disease. It is a problem with how the eye focuses light on the retina. The cornea is shaped like an egg instead of a ball. Large amounts of astigmatism can cause distorted vision, eye discomfort and headaches. It is a common eye condition easily diagnosed in an eye examination by your Optometrist. There are three types: Myopic, Hyperopic and mixed. Keratoconus is a rare condition where the cornea becomes thinner and cone shaped. It can be corrected by glasses or contact lenses. Sometimes a corneal transplant is required.