Repeatability of Fractal Analysis in OCT Angiography of the Macula and Optic Nerve Head

Purpose

To evaluate the repeatability of OCT angiography (OCTA) vessel density measurements using fractal analysis in the macula and optic nerve head (ONH) regions.

Design

A prospective longitudinal observational cohort study.

Participants

One hundred sixteen eyes from 71 primary open-angle glaucoma patients with valid macula OCTA scans and 91 eyes from 59 primary open-angle glaucoma patients with valid ONH OCTA scans, with 53 patients contributing scans for both regions.

Methods

Participants underwent 5 OCTA imaging sessions at weekly intervals using the Spectralis spectral-domain OCT (Heidelberg Engineering). OCT angiography images were processed for fractal analysis focusing on small vessels (<25 μm in diameter) within en face slabs of the superficial vascular complex (SVC), deep vascular complex (DVC), full retina, and nerve fiber layer vascular plexus (NFLVP). Vessel density repeatability was assessed using the coefficient of variation (CoV) with bootstrapped 95% confidence intervals. Associations between fractal analysis parameters and peripapillary retinal nerve fiber layer (RNFL) thickness were analyzed.

Main Outcome Measures

Repeatability of OCTA vessel density quantified by fractal analysis and correlation with RNFL thickness.

Results

One thousand three hundred twenty-eight macula OCTA scans from 269 visits and 801 ONH scans from 164 visits were included. Fractal analysis demonstrated high repeatability for vessel density measurements, with CoVs ranging from 0.4% to 0.9% in the macula and 0.7% to 1.8% in the ONH region. Full retina slabs exhibited the best repeatability in both regions, while DVC measurements in the ONH showed the highest variability (CoV = 1.8%). Moderate correlations between fractal parameters and RNFL thickness were observed in the ONH (SVC: rho = 0.65; NFLVP: rho = 0.67; P < 0.001) and macula (SVC: rho = 0.33, P < 0.001).

Conclusions

High repeatability of OCTA vessel density measurements using fractal analysis was observed in the macula and ONH regions, supporting its potential utility in monitoring vascular changes in glaucoma. Future studies should investigate its diagnostic accuracy and ability to detect disease progression.

Financial Disclosure(s)

Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.