Birdshot chorioretinopathy, also called birdshot uveitis, is a rare condition that can damage eyesight. It causes inflammation in the retina (the light-sensitive layer lining the back of the eye) and the supportive layer of blood vessels underneath it (the choroid).
It is named after the light-coloured spots that appear on the retina in a pattern resembling birdshot from a shotgun barrel.
What causes birdshot chorioretinopathy?
Birdshot is thought to be an autoimmune disorder, where the immune system starts to attack parts of its own body. Most people with birdshot have the HLA-A29 antigen, indicating a possible inherited immune system defect. Some people who carry the antigen never get birdshot, and the exact trigger remains unknown.
It affects mostly people of white European origin. It is more common in women and in people aged 40 to 60.
What are the signs and symptoms of birdshot chorioretinopathy?
Early symptoms of birdshot chorioretinopathy are floaters (small specks) in the line of sight and blurred vision in one or both eyes. These can also be symptoms of other eye conditions, so it can be hard to diagnose, but early diagnosis and treatment is important in birdshot chorioretinopathy.
As the condition develops it can lead to other sight problems, including:
Night blindness (difficulty seeing at night)
Problems with colour vision (reduced colour or difficulty with contrast)
Sensitivity to bright lights
Trouble with glare
Seeing flashing lights
A loss of depth perception
A loss of peripheral (side) vision
Pain in the eyes
Some people may be mildly affected, while others may experience significant vision loss.
Is birdshot chorioretinopathy serious?
Yes, birdshot chorioretinopathy is a serious form of uveitis (inflammation of the uvea, the back of inner lining of the eye), causing damage and swelling to the retina and choroid. About 20% of people with the condition get better without needing treatment and don’t experience vision loss.
For others, it can lead to complications that may result in vision loss or blindness. These include cystoid macular oedema (a swelling in the part of the eye responsible for central vision) or glaucoma.
How is birdshot chorioretinopathy diagnosed?
Typically other eye conditions are ruled out first before conducting a blood test for the antigen HLA A29 (a specific protein found on the surface of cells, which the immune system responds to). Most people with birdshot carry the antigen, although not everyone who has the antigen will develop birdshot.
Other tests to diagnose birdshot chorioretinopathy can include:
Biopsy: A biopsy (taking a sample of a tiny amount of tissue) is sometimes needed to confirm a diagnosis of birdshot chorioretinopathy
Electroretinogram test (ERG): Assesses how well the retina’s electrical responses work
Fluorescein angiography (FA): The test uses fluorescein dye to show how well the blood vessels at the back of the eye are working. These tests may show defects in areas of birdshot lesions or evidence of macular oedema.
Indocyanine green angiography: Uses a dye visible in infrared light to take angiogram images of the retina, choroid, and optic disc blood vessels. This test acquires an angiogram of the choroid.
Optical coherence tomography: a non-invasive imaging method that uses reflected light to create pictures of the back of your eye. The test can show decreased reflectivity of the macular photoreceptor bands.
Visual field tests: to test your peripheral vision.
Birdshot chorioretinopathy is hard to diagnose. It is often misdiagnosed or missed, particularly during its early stages when the tell-tale yellow and white, or cream and orange, spots in the retina aren’t always visible.
What are the treatments for birdshot chorioretinopathy?
Treatments for birdshot chorioretinopathy focus on suppressing the immune system so it doesn’t produce the unhelpful response that attacks your body’s own tissues. Sometimes a combination of treatments for birdshot chorioretinopathy works better than one type of drug alone.
Steroids: These are taken orally to reduce inflammation and suppress the immune system. They can be linked to weakening of the bones (osteoporosis). They can also have side effects such as bruised skin and stomach irritation, and cataracts.
Immunosuppressants: These also suppress the immune system. Often these take time to become effective.
Vitamin D and calcium supplements: You may be prescribed these to help your bones with the side effects of taking high doses of steroids:
Biologics: Biologics are newer medicines, which are bioengineered molecules produced in living systems. Biologics are increasingly being used to treat birdshot that doesn’t respond to more conventional forms of immunosuppression. These may be given by injection or drip.
What can help birdshot chorioretinopathy?
There is no way to prevent birdshot chorioretinopathy. Early detection and treatment are essential, and regular eye tests can help to detect early symptoms.
It’s normal to have flare-ups and remissions when you have birdshot chorioretinopathy. Speak to your doctor if you have any concerns about side effects from your treatments.