Uveitis is swelling and irritation of the uvea, the middle layer of the eye. The uvea provides most of the blood supply to the retina. Uveitis can be caused by autoimmune disorders, including rheumatoid arthritis or ankylosing spondylitis. It can also be caused by infection or exposure to toxins. In many cases, the cause is unknown. The most common form of uveitis is anterior uveitis. This involves inflammation in the front part of the eye. It is often called iritis because it usually only affects the iris, the colored part of the eye. The disorder may affect only one eye. The inflammation may be linked with autoimmune diseases, but most cases occur in healthy people. It is most common in young and middle-aged people. Symptoms may develop rapidly and can include: blurred vision, dark, floating spots in the vision, eye pain, redness of the eye, and sensitivity to light. With proper treatment, most attacks of anterior uveitis go away in a few days to weeks. However, the problem often returns. Inflammation related to posterior uveitis may last from months to years. It may cause permanent vision damage, even with treatment.