Automated quantification of choriocapillaris anatomical features in ultrahigh-speed optical coherence tomography angiograms

In vivo visualization and quantification of choriocapillaris vascular anatomy is a fundamental step in understanding the relation between choriocapillaris degradation and atrophic retinopathies, including geographic atrophy. We describe a process utilizing ultrahigh-speed swept-source optical coherence tomography and a custom-designed "local min-max normalized masking" algorithm to extract in vivo anatomical metrics of the choriocapillaris. We used a swept-source optical coherence tomography system with a 1.6 MHz A-scan rate to image healthy retinas. With the postprocessing algorithm, we reduced noise, optimized visibility of vasculature, and skeletonized the vasculature within the images. These skeletonizations were in 89 % agreement with those made by skilled technicians and were, on average, completed in 18.6 s as compared to the 5.6 h technicians required. Anatomy within the processed images and skeletonizations was analyzed to identify average values ( mean ± SD ) of flow void radius ( 9.8 ± 0.7µm ), flow void area ( 749 ± 110µm 2 ), vessel radius ( 5.0 ± 0.3µm ), branch-point to branch-point vessel length ( 26.8 ± 1.1µm ), and branches per branch-point ( 3.1 ± 0.1 ) . To exemplify the uses of this tool a retina with geographic atrophy was imaged and processed to reveal statistically significant ( p < 0.05 ) increases in flow void radii and decreases in vessel radii under atrophic lesions as compared to atrophy-free regions on the same retina. Our results demonstrate a new avenue for quantifying choriocapillaris anatomy and studying vasculature changes in atrophic retinopathies.