Exploring the Maximum Detectable Percentage of Choriocapillaris Flow Deficits Within Geographic Atrophy Using SS-OCT Angiography.

Purpose: Swept-source optical coherence tomography angiography (SS-OCTA) was used to longitudinally image eyes with AMD to determine the maximum percentage of choriocapillaris flow deficits (CCFD%) within geographic atrophy (GA). Methods: A retrospective review was performed of prospectively collected SS-OCTA images of eyes with AMD and at least one large hypertransmission defect (hyperTD). Eyes were followed up for five years, by which time unambiguous GA had developed. A grid registration strategy was used to measure the change of CCFD% at the center of atrophy and in the surrounding regions. Results: Twenty eyes were analyzed over six visits separated by 12 ± 3 months. The mean hyperTD area across 20 eyes increased from 2.90 mm2 at visit 1 to 8.59 mm2 by visit 6 (P < 0.001), whereas the CCFD% at the target box placed at the center of atrophy showed no statistically significant change with a maximum recorded value of 43.8% by the final visit. Non-target boxes were subdivided into boxes affected by hyperTDs (hyperTD boxes) and boxes unaffected by hyperTDs at any timepoint (non-hyperTD boxes). A statistically significant CCFD% difference was noted between boxes, with the hyperTD boxes showing increases over time. Conclusions: CCFDs% measurements within atrophy never showed the complete loss of CC at the center of GA. This phenomenon is likely due to the displacement of choroidal vessels into the CC slab where their angiographic signal is detected.