Presence of a scotopic scotoma in individuals with fragmented foveal avascular zones

Abstract

Purpose : Individuals with macular-foveal capillaries (i.e., a fragmented foveal avascular zone, FAZ) have been proposed to have an anomalous distribution of macular photoreceptors, based on an absence of the typical foveal scotoma on scotopic microperimetry.¹ Here we sought to replicate these findings in individuals objectively classified as having a fragmented FAZ.

Methods : 14 individuals participated, 7 with fragmented FAZs and 7 with normal FAZ morphometry. Each subject had testing performed on their right eye. Five 3 × 3-mm (nominal area) angiograms were acquired with the AngioVue OCT-A system (Optovue, Inc., Fremont, CA). Two scans (1 horizontal, 1 vertical) each consisting of 304 B-scans with 304 A-scans/B-scan were acquired and co-registered to create an angiogram for analysis (AngioVue software version:2018.1.0.43). From each volume, a custom slab from inner limiting membrane to 9mm above the outer plexiform layer was extracted. Slabs from five volumes were registered and averaged using bUnwarpJ in FIJI. The presence of a fragmented FAZ was objectively determined using a previously described method.² Scotopic microperimetry testing was performed using a MP-1S microperimeter (Nidek Technologies, Gamagori, Japan). A customized microperimetry pattern of 45 points within the central 8 degrees centered near the fovea was used, and interpolated maps of foveal sensitivity were generated from scotopic microperimetry responses. Where possible, scotoma area in deg² was estimated using a 1db threshold.

Results : For all participants (10 female, 4 male; aged 12-55 years) there was a central area of reduced sensitivity, though the scotoma area could only be estimated in 12 participants. The mean scotoma area in those with fragmented FAZs was 1.86 deg² (range: 0.310-4.15 deg²), while the mean scotoma area in the normal FAZ group was 1.53 deg² (range: 0.293-3.62 deg²). These values are consistent with histological estimates of the rod-free zone. There was no significant difference in scotoma area between individuals with normal and fragmented FAZs (p=0.42, unpaired t-test).

Conclusions : In contrast to previous reports, we do not observe an absence of a foveal scotoma using scotopic microperimetry in individuals with a fragmented FAZ.

References:
1. PMID: 31274711
2. PMID: 31956075

This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.