Uveitis occurs when the eye becomes inflamed (red and swollen).
Inflammation is the body's response to illness or infection.
Most cases of uveitis are linked to a problem with the immune system (the body's defence against infection and illness).
Rarely, uveitis may occur without the eye becoming red or swollen.
Uveitis often occurs in people who have an underlying autoimmune condition (where the immune system mistakenly attacks healthy tissue).
Autoimmune conditions known to cause uveitis include:
Uveitis can also be caused by an infection, such as:
Uveitis can also be caused by:
Sometimes, a specific cause of uveitis can't be identified.
Although uveitis isn't passed down through families, a gene known as HLA-B27 has been linked to an increased risk of developing anterior uveitis (uveitis at the front of the eye).
About half of all people with anterior uveitis have the HLA-B27 gene. The gene has been found in people with certain autoimmune conditions, including ankylosing spondylitis, ulcerative colitis, psoriatic arthritis, Crohn's disease and reactive arthritis.