Assessing the Repeatability of Inner Choroid Flow Deficit Percentage in Intermediate AMD and Controls: A Comparative Study between Different Post-processing Approaches.

Abstract

Purpose: To assess repeatability of macular inner choroid flow deficit percentage (ICFD%) in intermediate age-related macular degeneration (iAMD) and controls employing various post-processing approaches.

Methods: Cross-sectional, observational study. We included (1) 22 iAMD and 24 control eyes, with (2) age >50 years, (3) visual acuity >20/32, and (4) no additional ocular and systemic confounders.

Participants: underwent four consecutive 6x6-mm OCTA scans (2 acquired at 100-kHz and 2 at 200-kHz speed; PLEX® Elite 9000) for intra-session analysis. Same protocol was repeated after 30 minutes for inter-session analysis. Three slabs of different thicknesses were generated underneath Bruch's membrane (4-14, 4-19, 4-24 µm). All slabs were processed with: (1) binarization-only using Phansalkar method (r=4-15 pixels); (2) compensation+binarization; (3) averaging+binarization; (4) averaging+compensation+binarization. ICFD% was measured within 3- and 5-mm circles, and measurements were repeated after excluding drusen areas.Repeatability was analyzed with generalized linear mixed-effects models, intraclass correlation coefficients (ICC) and Levene's variance test.

Results: Most post-processing approaches demonstrated high repeatability (ICC>0.75) with no significant test-retest differences (p>0.05). Compensation+binarization of 15-µm slabs at 200 kHz showed the highest repeatability (ICC: 0.96-0.98). Excluding drusen did not significantly impact ICFD% measurements (p>0.05), showing increased ICCs for 10 µm-thick and binarized-only slabs.

Conclusions: Strong repeatability can be achieved with various post-processing methods for assessing ICFD%, especially with compensation+binarization of 15-µm slabs acquired at 200 kHz. Drusen removal does not seem to impact repeatability in iAMD when using a swept-source device, except for specific settings.