Because Birdshot is difficult to diagnose, and is not widely known about, it may be diagnosed through ‘default’ – that is, all other, more common conditions that cause similar symptoms will be tested for, before Birdshot is considered.
Usually, the definitive diagnosis for Birdshot will be made through a blood test to establish whether you test positive for the HLA-A29 antigen. You may also receive one or more of the following tests:
Fluorescein angiography (fluorescein the type of dye that is used; angiogram – a study of the blood vessels) is an extremely valuable test that provides information about the circulatory system and the condition of the back of the eye. The test is performed by injecting a special dye, called fluorescein, into a vein in the arm. In just seconds, the dye travels to the blood vessels inside the eye. A camera equipped with special filters that highlight the dye is used to photograph the fluorescein as it circulates though the blood vessels in the back of the eye. If there are any circulation problems, swelling, leaking or abnormal blood vessels, the dye and its patterns will reveal these in the photographs. Please note that you will have yellow skin and yellow eyes for a while and your urine will be bright yellow. This is normal.
Indocyanine green angiography (ICG). This is a similar procedure to fluorescein angiography. ICG angiography uses IndoCyanine Green dye which fluoresces in the infra-red (non-visible) light. The infra-red wavelengths have the ability to penetrate the retinal layers, making the circulation in deeper layers visible when photographed with an infra-red sensitive camera.
Optical Coherence Tomography (OCT). This is a non-invasive technology used for imaging the retina, the multi-layered sensory tissue lining the back of the eye. This can determine whether you have any optic nerve damage or macular swelling.
Electroretinogram (ERG). This is a series of non invasive tests where small wires are placed alongside your eyelids and receptors are placed on your forehead and the back of your head. You will then look at a range of flickering lights and patterns. This will assess how well you have maintained your eyesight – particularly in your retina and choroid and your rods and cones.
Visual Field Test. This is a method of measuring an individual’s entire scope of vision, (central and peripheral (side) vision). Visual field testing actually maps the visual fields of each eye individually.