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Uveitis happens when the eye becomes red and swollen (inflamed).
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 happen without the eye becoming red or swollen.
Immune system problems
Uveitis often happens in people who have an autoimmune condition. This is 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:
- toxoplasmosis – an infection caused by a parasite
- herpes simplex virus – the virus responsible for cold sores
- varicella-zoster virus – the virus that causes chickenpox and shingles
- cytomegalovirus – a common infection that does not usually cause any noticeable symptoms, but can cause sight-threatening uveitis in people with a lowered immune system
- HIV and syphilis are rare causes
Uveitis can also be caused by:
Sometimes, a specific cause of uveitis cannot be identified.
Although uveitis is not passed down through families, a gene known as HLA-B27 has been linked to an increased risk of developing uveitis at the front of the eye (anterior uveitis).
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 and ulcerative colitis.