Longitudinal Cohort Study of Patients With Birdshot Chorioretinopathy.

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.