Cogan syndrome is a rare autoimmune disease that affects the eyes and inner ears. Symptoms of the syndrome include irritation and pain in the eyes, decreased vision, hearing loss, and vertigo. Other symptoms may include joint or muscle pain or inflammation of the blood vessels. The exact cause of Cogan syndrome is not well-understood. It is thought that the syndrome is caused by an autoimmune response that causes the immune system to attack the tissues of the eyes and ears. Cogan syndrome is not known to run in families. Diagnosis of Cogan syndrome is based on observing symptoms associated with the syndrome and ruling out other possible causes of the symptoms.