Characterization of Retinal Microvascular Abnormalities in Birdshot Chorioretinopathy Using OCT Angiography

ObjectiveTo characterize changes in the retinal microvasculature in eyes with birdshot chorioretinopathy (BCR) using optical coherence tomography angiography (OCTA).DesignRetrospective, observational, single center.SubjectsTwenty-eight patients (53 eyes) with BCR and 59 age-matched controls (110 eyes).MethodsEn-face OCTA images of the superficial capillary plexus (SCP) and deep capillary plexus (DCP) of each eye were assessed for the presence of microvascular abnormalities and used to measure the vessel and foveal avascular zone (FAZ) areas. A longitudinal analysis was performed with a representative cohort of 23 BCR eyes (16 patients) at baseline and at a two-year timepoint.Main Outcome MeasuresWhole-image vessel density (VD, %), extra-foveal avascular zone (extra-FAZ) VD (%), and FAZ area (%) were calculated and compared between control and BCR eyes. The frequency of microvascular abnormalities in BCR eyes was recorded.ResultsIn the SCP, increased intercapillary space and capillary loops were common features present on OCTA images. Whole-image and extra-FAZ VD were lower in the BCR group compared with controls (P < 0.0001 [SCP and DCP]). FAZ area was enlarged in BCR eyes (P = 0.0008 [DCP]). Worsening best-corrected visual acuity was associated with a decrease in whole-image and extra-FAZ VD in the SCP (P < 0.0001 for both) and the DCP (P < 0.005 for both). Multivariable analysis, with vessel analysis parameters as outcomes, demonstrated that increasing age, increasing disease duration, lower central subfield thickness, and treatment-naïve eyes (compared to those on only biologics) were associated with a significant decrease in both DCP whole-image and extra-FAZ VD. Increasing disease duration was associated with a significant decrease in both SCP whole-image and extra-FAZ VD. Longitudinal analysis demonstrated no significant difference in any vessel analysis parameters except for an increase in DCP FAZ area.ConclusionOur results demonstrate a significant a decrease in VD in BCR eyes and an association on multivariable analysis with disease duration. Quantifying VD in the retinal microvasculature may be a useful biomarker for monitoring disease severity and progression in BCR patients. Further studies with extended longitudinal follow-up are needed to characterize its utility in monitoring disease progression and treatment response.