Some cases of uveitis are thought to be caused by inflammation.
When your body is under threat from infection, your immune system (the body’s natural defence against infection and illness) reacts by sending infection-fighting white blood cells to the site of the infection. This causes the affected area to become warm, red and swollen. This is what’s known as inflammation.
Sometimes, the inflammation associated with uveitis is in response to a real infection. This is known as infectious uveitis. However, uveitis often occurs for no apparent reason as the result of the immune system malfunctioning and triggering the process of inflammation even though no infection is present. This is known as non-infectious uveitis.
The differences between infectious and non-infectious uveitis are explained in more detail below.
Infectious uveitis
In England, the most common causes of infectious uveitis are:
- the herpes simplex virus – the virus that's responsible for cold sores and genital herpes (a sexually transmitted infection [STI] that causes painful blisters to appear on the genitals)
- the varicella-zoster virus – the virus that causes chickenpox
- cytomegalovirus – a common type of viral infection that usually only causes noticeable symptoms in people with weakened immune systems, such as those with HIV and unborn babies
- toxoplasmosis – an infection that's spread by parasites; it usually only causes noticeable symptoms in people with a weakened immune system and in unborn babies
Less common causes of infectious uveitis include:
- Lyme disease – a bacterial infection that's spread by insects
- syphilis – a type of STI that's now uncommon in England since the introduction of antibiotics
- tuberculosis – a bacterial infection that mainly affects the lungs
Non-infectious uveitis
Many cases of non-infectious uveitis develop in people who have an underlying autoimmune condition (where the immune system mistakenly attacks healthy tissue). Autoimmune conditions that are known to trigger the symptoms of uveitis in some people include:
Other causes of non-infectious uveitis include:
- trauma or injury to the eye(s)
- some types of cancers, such as lymphoma, although this is a very rare cause of uveitis
Idiopathic uveitis
Around 1 in 3 people with uveitis have no history of an underlying autoimmune condition. This is known as idiopathic uveitis. Most experts suspect that the immune system plays a role in cases of idiopathic uveitis, although the exact nature of the role remains unclear.
Now read about getting a diagnosis for uveitis.
