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.