Birdshot chorioretinopathy is a bilateral chronic posterior uveitis that has been named
in 1980. The "birdshot lesions" are the hallmark of the disease. In their most typical
aspect these lesions are ovoid shaped hypopigmented spots at the level of the choroid.
One of the main difficulties of the diagnosis lies in the spectrum of presentations of
the disease. The typical birdshot lesions are ovoid with their main axis oriented toward
the optic disc. However, some are round and the can be clearly seen on fundus examination
while others can be limited to subtle depigmentations. Typical lesions are one-quarter to
one-half disc diameters, but confluent lesions may yield larger areas of depigmentation
that are difficult to recognize. Although the typical lesions are depigmented, their
presentation may change over time and pigment or atrophy may replace the initial
cream-colored spots. The typical location, or the most easily seen location of the spots,
is nasal to the optic disc. However, involvement of the posterior pole inside the
temporal arcade is also possible. The spots usually predominate in the mid-periphery, but
may also extend to the equator. A standardized classification of the birdshot lesions
according to their size, their number, their pigmentation and their localization has been
suggested to help in the categorization of the various disease presentations and for the
longitudinal follow-up of affected patients. Spots clearly visible at the time of the
diagnosis may disappear later. Hence, if the diagnosis of the birdshot chorioretinopathy
is not made when spots are clearly visible, later presentations may not meet the
definition commonly used for the disease. The disappearance of birdshot spots after
treatment has been documented, but the effect of treatment on spots has not yet been
assessed in large cohorts of patients. Indocyanine green angiography has been suggested
as a reliable method to detect spots. However, it remains to be validated by a randomized
assessment comparing indocyanine green angiography to color photographs for the detection
of birdshot lesions.
Fluorescein angiography is useful in patients with birdshot chorioretinopathy to assess
disease activity. In active disease, angiographic findings include leakage of the retinal
veins, macular edema and optic disk hyperfluorescence. These findings are not disease
specific, but they require a careful examination of the fundus seeking subtle spots when
birdshot lesions are not obvious.
Given the above, the first goal of our prospective cohort study is to assess the
heterogeneity of the disease, its spectrum of presentation and its evolution over time.
One of the characteristics of birdshot chorioretinopathy is its association with the
HLA-A29 allele, which constitutes the strongest link between a disease and class I HLA
allele. The mechanism by which HLA-A29 confers a risk for birdshot chorioretinopathy is a
key question that remains unanswered. As with other associations between HLA class I
antigens and diseases (HLA-B27 with spondylarthropathies and HLA B51 with Behçet's
disease), the physiopathogeny of these links have not been elucidated.
Other factors playing a role in the physiopathogeny of the disease and not linked to the
major histocompatibility complex are researched. A few families of patients with birdshot
chorioretinopathy have been reported, which could point to additional genetic factors for
disease susceptibility but does not rule out an environmental effect.
Hence, the complex physiopathology of birdshot chorioretinopathy could involve the
HLA-A29 allele, other unknown genetic factors, as well as environmental factors.
Given the above, we are planning a GWAS (Genome Wide association Study) based on DNA of
the cohort patients, which will be performed with the aim to identify other
susceptibility genes associated with BCR.
