Birdshot chorioretinopathy

Last updated February 2023
Approved by Dr Graham Wallace, University of Birmingham

What is birdshot chorioretinopathy?

Birdshot is a rare condition that is hard to treat and may lead to blindness. It affects the choroid and retina. The retina is the light-sensitive layer of the eye. The choroid is a layer of blood vessels that supply the retina.

Birdshot chorioretinopathy is named after the painless, light-coloured spots that develop on the retina due to the condition. These spots are scattered in a birdshot pattern (the pattern from a shotgun barrel).

Some people will be mildly affected, whereas others will experience a significant decline in vision due to floaters (small specks) appearing in their line of sight.

What is birdshot chorioretinopathy also known as?

Birdshot chorioretinopathy is a rare chronic (long-term) inflammatory eye disease that can lead to vision loss or blindness. Birdshot is also known as ‘Birdshot uveitis’.

Uveitis means inflammation in the uvea (the back part of the inner lining of the eye.

Birdshot chorioretinopathy is a severe form of uveitis, a group of diseases that damage the eye tissue and cause swelling of the retina and choroid. Over time, damage can cause cystoid macular oedema or glaucoma.

While there's no cure, birdshot chorioretinopathy is a treatable disease. Early detection is essential.

How common is birdshot chorioretinopathy?

Birdshot chorioretinopathy is a rare eye condition.

It has yet to be discovered exactly how many people have birdshot. However, it is more common in Caucasian people and in those who are aged 45 to 50 years old.

However, it can also affect people who are much younger.

It is officially classified as a rare condition.

It is unknown what causes birdshot. However, it is believed to be an autoimmune disease (an illness that happens when the immune system, which normally keeps your body healthy, attacks the body’s tissues).

What causes birdshot chorioretinopathy?

Birdshot is thought to be what's known as an auto-immune disorder.

This means that the body's defence system for fighting infection (the immune system) starts to attack parts of its own body.

Most people diagnosed with birdshot have an inherited antigen called HLA-A29, a model involved in signalling between immune cells. It isn’t known what this means in relation to the functioning of the immune system.

However, people carrying the HLA-A29 gene may have an inherited immune system defect, making them susceptible to birdshot development. Some people who carry the antigen never get birdshot, so it isn’t known what triggers the disease.

Who is likely to get birdshot chorioretinopathy?

Most people with birdshot test positive for HLA-A29. But not everyone who tests positive will develop birdshot, so there must be other factors that put people at risk.

Almost everyone with birdshot is white; most are female and aged 40-60.

• Fight for Sight is funding research to discover better treatment options for Birdshot Chorioretinopathy.

What are the symptoms of birdshot chorioretinopathy?

Early symptoms of birdshot chorioretinopathy are floaters and blurred vision. These can also be symptoms of other eye conditions, which means birdshot chorioretinopathy may be challenging to diagnose in its early stages. In the early stages, people experience painless difficulty seeing in one or both eyes.

People who have birdshot chorioretinopathy may also go on to experience the following:

• Night blindness (difficulty seeing at night)
• Problems with colour vision (reduced colour or difficulty with contrast sensitivity)
• Sensitivity to bright lights (photophobia)
• Trouble with glare
• Seeing flashing lights
• A loss of depth perception
• A loss of peripheral (side) vision
• Pain in the eyes

People in the early stages of developing birdshot chorioretinopathy may have normal eye tests. However, an ophthalmologist may see cream or orange oval-shaped spots in the retina over time.

The severity of birdshot symptoms varies by individual. However, most people will experience flare-ups of inflammation in the eyes. These can lead to cystoid macular oedema, a swelling in the region of the eye responsible for central vision.

This can lead to potentially blinding damage to the eye.

How is birdshot chorioretinopathy diagnosed?

Birdshot chorioretinopathy is a rare disease and is hard to diagnose. It is often misdiagnosed or missed, particularly during its early stages. The tell-tale yellow and white lesions aren’t always visible in the early stages.

There is no single diagnostic test, and so, typically, other eye conditions are ruled out first before conducting a blood test for the antigen HLA A29. The majority of people who develop birdshot carry this antigen, although not everyone who has the antigen will develop birdshot.

Other tests to diagnose birdshot chorioretinopathy can include:

• Biopsy: A biopsy 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 images of the retina, choroid, and optic disc blood vessels. This test acquires an angiogram of the choroid. The choroid is the layer of blood vessels and connective tissue between the sclera (white of the eye) and retina. It supplies nutrients to the inner parts of the eye.
• 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.

Treatments for birdshot chorioretinopathy

Around 20% of people with birdshot uveitis get better without needing treatment and don't experience vision loss.

However, the condition may flare up again repeatedly. There are various treatment options available. Everyone will respond differently, and what works for one person may not work for someone else.

Types of treatment for birdshot chorioretinopathy

Some of the treatments for birdshot chorioretinopathy include the following:

• Steroids: One of the earlier interventions for birdshot is steroids. These are taken orally to reduce inflammation and suppress the immune system.
• Immunosuppressants: You may receive immunosuppressants for treating birdshot. Often these take time to become effective.
• Vitamin D and calcium supplements: You may be prescribed these to help with the side effects of taking high doses of steroids, including weakening of the bones (osteoporosis). Other side effects may include:
  • Bruised skin and stomach irritation
  • Cataract (when the lens in the eye turns from clear to cloudy). Cataracts can be treated with surgery to replace the cloudy lens with an artificial one.

Longer-term treatments for birdshot chorioretinopathy

In the longer term, treatments for birdshot chorioretinopathy may involve biologics. Biologics are newer medicines, which are bioengineered molecules produced in living systems.

Biologics are increasingly being used to treat birdshot that is unresponsive to more conventional forms of immunosuppression. These may be given by injection or drip.

Sometimes a combination of treatments works better than one type of drug alone.

Is it possible to reduce the risk of developing birdshot chorioretinopathy?

There's no known way to prevent birdshot chorioretinopathy. Regular eye exams can help detect early symptoms, so you can receive timely treatment if needed.

Living with birdshot chorioretinopathy

Most people living with birdshot chorioretinopathy need long-term steroids and immunosuppressant medicines.

People commonly experience flare ups and periods of remission.

Managing birdshot chorioretinopathy with medications

The best treatments can vary by individual. People taking immunosuppressants and steroids long-term may experience side effects. Speak to your healthcare team about any concerns, as they might be able to adjust the dosage.