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.