Uveitis is a general term that refers to inflammation or swelling of the eye's structures responsible for its blood supply. These structures are collectively known as the uveal tract, and include the iris, ciliary body, and choroid. Uveitis is classified by the structures it affects, the underlying cause, and whether it is chronic (lasting more than 6 weeks), or acute in nature. There are four main categories of uveitis. Anterior uveitis (also known as iritis) involves the iris and ciliary body and is the most common type; intermediate uveitis affects the ciliary body, vitreous and retina; posterior uveitis involves the retina, choroid and optic nerve; and diffuse uveitis affects structures both in the front and back of the eye.
Common causes of uveitis include infection or underlying disease, but in some cases the cause is unknown. Uveitis usually affects people between 20-50 years of age.
Descriptive courtesy of St. Luke's Cataract and Laser Institute