Intra-session and inter-session repeatability of inner choroidal flow deficit percentage in intermediate age-related macular degeneration and healthy controls.

Abstract

Purpose : Inner choroidal flow deficit percentage (ICFD%) is a quantitative metric to assess choriocapillaris alterations on optical coherence tomography angiography (OCTA). This study aims to evaluate the intra-session and inter-session repeatability of macular ICFD% in intermediate age-related macular degeneration (iAMD) and healthy controls using various post-processing approaches.

Methods : Cross-sectional, observational study including 22 iAMD and 24 control eyes. Participants underwent 4 consecutive 6x6-mm macular OCTA scans (2 acquired at 100-kHz and 2 at 200-kHz speed) with PLEX® Elite 9000 for intra-session analysis. Same protocol was repeated 30 minutes later for inter-session analysis (Figure 1A). Eye-tracking was activated for co-registration.
After applying Max Projection algorithm, 3 slabs with different thicknesses were generated underneath Bruch’s membrane (offsets: 4-14, 4-19, 4-24 µm). All slabs underwent the following post-processing in FIJI: (1) binarization-only with Phansalkar method (r=4 and 15 pixels); (2) compensation + binarization; (3) averaging + binarization; (4) averaging + compensation + binarization. ICFD% was measured in the central 3- and 5-mm circles (1B). Measurements were repeated after excluding areas occupied by drusen.
Repeatability was assessed with generalized linear mixed-effects models, intraclass correlation coefficients (ICC) and Levene’s variance test.

Results : Several post-processing approaches did not exhibit significant differences between test-retest measurements (all p>0.05) and showed good agreement between sessions (ICC>0.75; 1C). Notably, 15-µm slabs of scans acquired at 200-kHz and undergoing compensation+binarization had the highest intra-session (ICC: 0.97-0.98) and inter-session (ICC: 0.96-0.97) repeatability (1C).
After drusen removal, ICCs of ICFD% increased only for 10 µm-thick and binarized-only slabs.

Conclusions : Strong repeatability can be achieved for various post-processing methods used to assess ICFD%, particularly when performing compensation and binarization of 15-µm slabs acquired at 200 kHz. Our results suggest that removing drusen areas in iAMD eyes does not affect repeatability when using a swept-source device, except for specific settings. These findings contribute to refining choriocapillaris assessment, paving the way for future clinical and research applications.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.