Abstract
Purpose :
To determine the test-retest repeatability of capillary density quantified using fractal analysis from optical coherence tomography angiography (OCTA) scans of the optic nerve head (ONH).
Methods :
This prospective longitudinal study included subjects with glaucoma and healthy controls. OCTA scans of the ONH were obtained five times at approximately weekly intervals using the Spectralis SDOCT (Heidelberg Engineering, GmbH, Germany). Global peripapillary RNFL thickness was measured at each visit with spectral-domain OCT. A circular 2mm-radius mask centered at the Bruch’s membrane opening was applied and images with quality score worse than 70% were excluded. The repeatability was assessed by the coefficient of variation (CoV) with bootstrapped 95% confidence intervals (CI). The standard deviation (SD) of the residuals from linear mixed-effects regression models, nested at patient and eye levels for each cluster, were calculatedto evaluate the magnitude of the variability in fractal units. Fractal analysis results were also correlated with the peripapillary RNFL thickness.
Results :
We included 801 valid OCTA exams across 164 clustered visits from 91 eyes of 59 subjects. The mean RNFL thickness was 76.0±19.4µm (range: 35 to 121µm). Vascular density from fractal analysis demonstrated high repeatability in all layers, with a CoV [95% CI] for the Nerve Fiber Layer Vascular Plexus (NFLVP) of 0.95% [0.85-1.05%], 0.94% [0.86-1.05%] for the Superficial Vascular Complex (SVC), 1.80% [1.67-1.94%] for the Deep Vascular Complex (DVC), and 0.67% [0.61-0.75%] for the full retina. The SD of the residuals demonstrated low absolute variability for all layers, with the lowest variability at the full retina (0.012 [0.010-0.013] fractal units) and the highest for the DVC (0.030 [0.028-0.032] fractal units). Significant correlations with RNFL thickness were observed for SVC (rho = 0.65, P<0.001), NFLVP (rho = 0.67, P<0.001), and Retina (rho = 0.33, P<0.001), but not for the DVC (rho = 0.072, P=0.387).
Conclusions :
This is the first report of fractal analysis used to analyze vascular density in the ONH region. The results show its high repeatability and may prove valuable in diagnosing and detecting glaucoma progression.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.