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Birdshot Retinochoroidopathy |
This is a rare form of uveitis and may be described as a form of posterior uveitis. Whilst its cause is unknown, it is thought to be of the autoimmune type of uveitis. The term ”birdshot” was used because of the pattern of the lesions at the back of the eye resembling that of shotgun pellets.
There are generally no other medical conditions associated with this type of uveitis, except for a very small minority who have a condition called vitiigo. This is a skin condition in which the pigment of the skin is missing and numerous milky white patches of skin occur.
HLA Typing
If BR is suspected then it is likely that an HLA type test will be carried out to find out if the patient is HLA A29 positive. HLA A29 is the term given to genes which are responsible for producing “markers” on the surface of cells, called antigens.(HLA’s). These are implicated in the way autoimmune diseases occur. It has been found that people who are positive for certain HLA types (there are numerous different ones) are more susceptible to particular autoimmune type diseases. Approx. 95% of people with BR are HLA A29 positive (as opposed to about 7% of the general population). Although genes are Involved the condition is not generally passed on from generation to generation.
Other investigations often made in the diagnosis of BR include Fluorescein angiography, where a dye injected into the arm shows the blood vessels at the back of the eye. This straightforward test is carried out at the eye out patient department.
The pale “birdshot” lesions at the back of the eye also lead to the diagnosis but are not always present at first. As with other forms of uveitis, the diagnosis is often not that simple and may involve a detailed investigation.