Optimizing the Repeatability of Choriocapillaris Flow Deficit Measurement From Optical Coherence Tomography Angiography

PURPOSE: To evaluate the impact of processing technique and slab selection on the repeatability of choriocapillaris (CC) flow deficit (FD) measurements as assessed using optical coherence tomography angiography (OCTA) DESIGN: Prospective, cross-sectional study. METHODS: Healthy subjects were imaged with 4 consecutive 3 3 3-mm OCTA using a swept-source OCT (PLEX elite 9000; Carl Zeiss Meditec). OCTA images were generated using the Max projection, and three 10-mu m-thick slabs starting 11, 21, and 31 mu m posterior to the automatically segmented retinal pigment epithelial band. The resultant images were binarized using the Phansalkar method with a 43.94-mu m radius and then the CCFD% was computed. The intraclass correlation coefficient (ICC) and coefficient of variation (CV) were computed for the 4 acquisitions to assess the repeatability of the CCFD%. This entire analysis was repeated after separately modulating several parameters: (1) Sum instead of the Max projection, (2) retinal pigment epithelial fit instead of the retinal pigment epithelial band as the offset reference, (3) 14.65 and 87.88 mu m radius values instead of 43.94 mu m. RESULTS: Twenty-four healthy eyes (mean age; 36.4 years) were enrolled. The CCFD% in the 11-21-, 2131-, and 31-41-mu m slabs generated by the Max algorithm and the retinal pigment epithelial band showed high repeatability values (ICCs = 0.963, 0.975, and 911; CVs = 0.05, 0.05, and 0.05, respectively). As most of the cases were confounded with the hypointense region when the 11-21-mu m slab was used, however, this slab could not be included in the subsequent analyses. Those values in the 21-31- and 31-41-mu m slabs were higher than those of the corresponding slabs by the Sum algorithm (ICC = 0.916 and 0.776; CV = 0.15 and 0.19, respectively) or by the retinal pigment epithelial fit (ICC = 0.907 and 0.802; CV = 0.06 and 0.06, respectively). The Phansalkar radius of 43.94 mu m had the highest ICC numerically, but this was not statistically significantly greater than for a radius of 14.65 mu m (ICC = 0.960 and 0.911, respectively) or a radius of 87.88 mu m (ICC = 0.958 and 0.897, respectively). Regardless of which parameter was modulated, the 21-31-mu m slab was the most repeatable. CONCLUSIONS: In normal eyes, en face CC OCTA images generated using the Max projection and a 10-mu m-thick slab offset of 21 mu m below the instrumentgenerated retinal pigment epithelial band yielded the most repeatable CCFD%. These findings have implications for the design of standardized processing algorithms for quantitative CC assessment. (C) 2020 Elsevier Inc. All rights reserved.