The uveal tract, which is the middle layer of the eye, is that part of the eye that becomes inflamed in uveitis. As shown in the figure the uveal tract extends from the very back of the eye to the very front, ending as the iris (the colored part of the eye surrounding the pupil).  In uveitis associated with juvenile arthritis the inflammation of the uveal tract is usually restricted to just the front part of the eye (involving the iris and ciliary body, as shown on the figure).  When the entire uveal tract is involved, from the very back of the eye to the very front, it is referred to as pan uveitis. \

While pan uveitis can occur in children with arthritis it is much less common that the uveitis that is restricted just to the front part of the eye (the iris and ciliary body involvement only, which is referred to as anterior uveitis). In addition to occurring in association with juvenile arthritis and other autoimmune diseases, pan uveitis can occur in association with certain infections, and eye injury or surgery, as examples. The inflammatory process involved with pan uveitis and anterior uveitis seems to be similar but further research is required to better explain why some children have anterior uveitis and others pan uveitis.