Uveitis means inflammation of the part of the eye called the uvea. The uvea, also called the uveal tract, is a continuous layer of fibrous tissue that surrounds the eye. It is made up of three structures:
The iris — The donut-shaped part that gives the eye its color
The choroid — A membrane full of tiny blood vessels that lines the eye
The ciliary body — A thick ring of tissue that helps control the shape of the lens, and is attached to the iris and to the front portion of the choroid
Various terms are used for the condition, depending on the part of the uvea affected. They include:
Anterior uveitis (iritis) — Affects the front portion of the uvea, the iris
Iridocyclitis — Affects the iris and the ciliary body
Intermediate uveitis (also called pars planitis) — Affects the middle portion of the uvea, between the retina and the ciliary body
Posterior uveitis (choroiditis) — Affects the back part of the uvea, the choroids
Diffuse uveitis — Inflammation of all portions of the uvea
The most common types of uveitis are anterior uveitis and iridocyclitis. Posterior uveitis is rare.
Many cases of uveitis are related to an autoimmune disorder (such as ankylosing spondylitis, lupus, juvenile rheumatoid arthritis, multiple sclerosis or sarcoidosis) or an infection, such as tuberculosis, toxoplasmosis, herpes, syphilis or cytomegalovirus (especially in patients with AIDS).
A number of conditions, including pars planitis, birdshot choroidopathy and sympathetic ophthalmia, are diseases of the eye that may cause uveitis but usually do not affect other parts of the body.
Rarely, uveitis occurs as a side effect of a medication. In up to half of cases, the cause is not known, but recent research has linked certain genes to the development of the disease. One possibility is that some people are prone to uveitis because they have genes that program the immune system to attack the uvea, a process that may be triggered by an infection.