Impact of slab selection on the relationship between choriocapillaris flow deficits and enlargement rate of geographic atrophy

Objective To evaluate the effect of changing slab position on the correlation between choriocapillaris (CC) flow deficits (FD) in eyes with geographic atrophy (GA) and yearly enlargement rate (yER) of GA. Methods OCT and OCTA images obtained on Cirrus HD-OCT device were collected from patients with GA. Each patient underwent OCTA scan at baseline and two OCT scans, one at baseline and one after at least 12 months. GA was delineated on en-face fundus image to calculate yER. OCTA images were generated from three 10 µm thick slabs 11, 21 and 31 µm posterior to RPE-fit line. 100 µm-wide concentric rings were generated around GA to calculate FD% in each ring which was correlated with yER. Results For the 11–21 µm slab, FD% was not significantly correlated with yER for any of the rings ( p > 0.05). For the 21–31 and 31–41 µm slab, FD% of rings located in the 600 µm region around GA was significantly correlated with yER ( p < 0.05). However, in all slab locations, there was no significant correlation between yER and CC FD% of rings located beyond the 600 µm region ( p > 0.05). Conclusions Slab selection for quantification of CC FD% may have a significant impact on quantitative results in eyes with GA.