The cause of astigmatism is almost always unknown and not associated with an external or genetic cause.
A rare cause of higher levels of astigmatism is keratoconus (KEHR-a-toh-kohn-nus), in which the cornea progressively becomes cone-shaped and thin. Keratoconus usually appears around puberty or early adulthood. The cornea is made of transparent collagen, and eyes with keratoconus have abnormal collagen synthesis. Keratoconus may progress to the point where corneal rigid contact lenses no longer solve the vision problems and transplantation of the cornea is necessary. Corneal transplantation for keratoconus has a very high success rate -- rejection is uncommon.
Another form of astigmatism is lenticular astigmatism. It is caused by abnormalities in another curved structure inside the eye -- the natural internal crystalline lens that also focuses incoming rays. Blurred vision from lenticular astigmatism can be treated with eyeglasses and contact lenses.
Important: The opinions expressed in WebMD User-generated content areas like communities, reviews, ratings, blogs, or WebMD Answers are solely those of the User, who may or may not have medical or scientific training. These opinions do not represent the opinions of WebMD. User-generated content areas are not reviewed by a WebMD physician or any member of the WebMD editorial staff for accuracy, balance, objectivity, or any other reason except for compliance with our Terms and Conditions. Some of these opinions may contain information about treatments or uses of drug products that have not been approved by the U.S. Food and Drug Administration. WebMD does not endorse any specific product, service, or treatment. Do not consider WebMD User-generated content as medical advice. Never delay or disregard seeking professional medical advice from your doctor or other qualified healthcare provider because of something you have read on WebMD. You should always speak with your doctor before you start, stop, or change any prescribed part of your care plan or treatment. WebMD understands that reading individual, real-life experiences can be a helpful resource, but it is never a substitute for professional medical advice, diagnosis, or treatment from a qualified health care provider. If you think you may have a medical emergency, call your doctor or dial 911 immediately.