FAQs

What is Birdshot Chorioretinopathy (BSCR)?

BSCR (often shortened to Birdshot Uveitis) is a rare, chronic and potentially sight-threatening posterior uveitis. Although the cause is unknown it is thought to have an autoimmune basis and usually affects both eyes.

The term ‘uveitis’ means inflammation in the uvea, which comprises the iris, choroid layer and ciliary body. It provides the majority of the blood supply to the retina, the light sensitive inner eye surface.

BSCR is characterized by the appearance of small opaque yellowish-white lesions in a scattered ‘birdshot’ pattern in the retina. As it is a rare disease, it can often take many years to be diagnosed. Floaters and blurred vision may present in the early stages and initially, birdshot lesions are not always visible. Visual acuity on the Snellen chart is not a reliable marker of disease severity.

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image of retina highlighting various anatomy

What are the common symptoms with BSCR?

Patients may report a range of visual symptoms including:

• floaters

• blurred and distorted vision

• night blindness (nyctalopia)

• sensitivity to bright lights

• seeing flickering and flashing lights (photopsia)

• ‘ceiling fan’ effect

• altered depth perception

• decreased colour vision

The severity of symptoms can vary but most people will experience inflammatory flareups. If these are not controlled over time it can lead to macular edema (CME). It is the most common cause of vision loss as well glaucoma, epiretinal membrane, cataract, new blood vessel growth (neovascularization) between the choroid and retina.

What is HLA-A29?

Human leukocyte antigens (HLA) are molecules located on the surface of all cells, unique to each individual. Antigens are any substances that the immune system recognizes and initiates an immune response.

HLA-A29 is a genetic marker unique to Birdshot that is present in 80-98% of cases versus 7% in the general population.

Blood tests to determine the presence of HLA -A29 in patients can assist in the diagnosis, however not all Birdshot patients are HLA-A29 positive. There are also many people who may carry the gene and yet never develop the disease. The triggers that cause the disease have not yet been identified but may perhaps be related to infectious or environmental factors, which then affect the immune system.

What is the leading cause of visual loss with Birdshot Uveitis?

The most common cause of visual loss as mentioned above, is macular edema (ME), which can occur in up to 50% of cases. The macula is responsible for the detailed central vision. A breakdown of the inner and/or outer blood-retina barrier can occur, leading to a thickening of the macular region. There is resulting leakage from blood capillaries in the area of the fovea (the depression in the macula), leading to the accumulation of fluid. The swelling occurs, at least in part, because pro inflammatory cytokines alter the permeability of the tight junctions within the retinal layers.

How is Birdshot diagnosed?

Birdshot diagnosis is determined through clinical examination by a specialist using a
slit lamp to view dilated eyes and a series of tests. These can include the following:

Optical Coherence Tomography (OCT) is a non-invasive imaging test, using light waves to take cross sectional pictures of the retina. It can detect changes and problems early before they affect your vision, also checking for fluid build up which occurs with macular edema.

Fluorescein angiography (FA) is a medical procedure in which a fluorescent dye is injected into a vein. Fluorescein is made from an organic compound that has a wide use as a colouring agent. The dye highlights the retinal vessels at the back of the eye and a series of photographs are taken throughout the procedure. An FA can show evidence of macular edema, retinal vasculitis, optic nerve inflammation and new blood vessel growth in the choroid (choroidal neovascularization).

Indocyanine green angiography (ICG) is used to examine blood flow in the choroid, (the vascular layer of the eye between the retina and the sclera) and associated pathology. The green dye shows up under infra-red light after injection into a vein and photographs are taken at timed intervals.

Visual Field Test is a test taken in sitting and looking into a dome shaped instrument. It uses a computer program to test an individual’s visual field using a series of flashing lights on the dome. It measures how much you can see out of the corners of your eyes and determine if you have blind spots in your vision.

Electroretinogram (ERG) measures the electrical response of the light sensitive cells forming the retina. These cells are the rods and cones, comprising of around 120 million rods and six to seven million cones. An ERG can be a very useful tool in diagnosis to establish a baseline and in assessing response to treatment over time.

What is the treatment for Birdshot?

As Birdshot Uveitis is a very rare disease, there is no established protocol for treatment. The disease often requires early use of immunomodulatory therapies because if left untreated, a progressive decline in visual function can occur. Treatment may include a combination of steroids (oral, injections or implants) to reduce inflammation. Long term use of immunosuppressants is often added to help control inflammation and stop the immune system from attacking the eyes. Due to the long term effects of steroid use, which can include bone thinning and stomach issues, close monitoring is required.

Ongoing clinical research is highlighting the emerging use of biologics which are directed against particular cytokines (small proteins which help to regulate inflammation and can be pro-inflammatory or anti-inflammatory) or cell-surface receptors.