Measurement of Radial Peripapillary Capillary Density in the Normal Human Retina Using Optical Coherence Tomography Angiography

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Abstract
Aim: To image the radial peripapillary capillary (RPC) network with optical coherence tomography angiography (OCTA) and measure its capillary density (CD) in the normal human retina. Materials and Methods: Fifty-two normal participants underwent OCTA imaging with RTVue XR 100 Avanti OCT. The angioflow enface RPCs network was extracted from OCTA and 8 peripapillary sectors with a sector angle of 45 degrees were selected for quantitative analysis: superior nasal, superior temporal, temporal upper, temporal lower, nasal upper, nasal lower, inferior nasal, and inferior temporal. CD was measured within a 3.4-mm circle diameter around the optic nerve head (ONH) using the Bar-Selective Combination of Shifted Filter Responses method. Results: Using OCTA, the RPC network was visualized with excellent detail as a distinctive pattern of parallel, long, uniform-diameter vessels around ONH, oriented parallel to the retinal nerve fiber layer. The mean overall RPC density within the circle diameter of 3.4 mm around ONH was 0.21±0.053 (95% confidence interval: 0.204-0.216). The CD at the superior temporal (0.243±0.045) and inferior temporal (0.242±0.047) sectors was higher (PP=0.7), and disc size (P=0.3) did not have a significant effect on CD measurement. Conclusions: We imaged and describe a reproducible method to measure the RPC density, which would help us to understand the role of this vascular bed in the functioning of the retinal nerve fiber layer. Our study demonstrated that there was symmetry in superior and inferior corresponding pair sectors with respect to the horizontal meridian and symmetry between paired sectors at the nasal and temporal poles with respect to the vertical meridian.

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