Abstract
Purpose :
To report a novel observation of a physiological extravascular motion (EVM) signal detected by optical coherence tomography angiography (OCTA) and test the hypothesis that the phenomenon is related to glaucoma.
Methods :
We used existing data from ongoing longitudinal studies of unilateral experimental glaucoma (EG) in nonhuman primates (NHP, rhesus macaque, N=47, 41F/6M, ages 6-18 y) induced by trabecular meshwork photocoagulation. OCT/A scans centered on the ONH (768x768x496 voxels over 15x15°) were done biweekly using Spectralis (Heidelberg Engineering, GmbH) to measure the thickness of the optic nerve head neuroretinal rim (minimum rim width, MRW), circumpapillary RNFL (RNFLT) and macular ganglion cell complex (GCCT). Scans were exported to custom software for all image segmentation and quantification. Here, we used the final eligible time point from the longitudinal series of each NHP prior to any experimental therapeutic intervention. Major blood vessels and EVM lines were manually segmented from en face angiographs (35 pixels summed voxel slab projection image). Two-way ANOVA with Šídák's multiple comparisons post-hoc tests and linear regression were applied for statistical analysis.
Results :
The range of structural damage in EG relative to fellow control eyes (FC) eyes was: -12 to -87% MRW, +4 to -81% RNFLT, +2 to -47% GCCT. EVM signals manifest as isolated line segments along the fast-scanning axis (i.e., along individual B-scan lines, Fig1). Their inter-B-scan spacing produced an estimate of heart rate that accurately predicts the actual heart rate. EVM lines were more common adjacent to arteries compared to veins, and uncommonly, non-vascular areas (P<0.0001, Fig2). They were more numerous (P=0.0008) and longer in EG than in FC eyes (P<0.0001). EVM count and average length were significantly correlated with IOP (P<0.0001), but not significantly correlated with MRW, RNFLT, GCCT, age or heart rate at the time of the scan. EVM average length was significantly higher in EG eyes compared to FC eyes after adjusting for IOP (P=0.029).
Conclusions :
We described a novel OCTA EVM signal representing pulsatile tissue displacement caused by the cardiac cycle, most commonly adjacent to arteries, more prominent in EG eyes and strongly influenced by IOP. Their enhancement in EG may be indicative of altered biomechanical properties of the vasculature and/or paravascular retinal parenchyma.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.