Focal Loss Analysis of Peripapillary Nerve Fiber Layer Reflectance for Glaucoma Diagnosis

TL;DR

This study demonstrates that focal nerve fiber layer reflectance loss, measured via spectral-domain OCT, provides superior diagnostic accuracy for glaucoma compared to traditional thickness measurements, especially in early stages.

Contribution

The paper introduces a novel focal reflectance loss metric that outperforms standard NFL thickness parameters in glaucoma diagnosis using OCT imaging.

Findings

Focal NFL reflectance loss has higher diagnostic accuracy than thickness measures.

Reflectance loss shows characteristic wedge or diffuse defects in glaucomatous eyes.

Diagnostic sensitivity improves at high specificity levels with reflectance analysis.

Abstract

Purpose: To evaluate nerve fiber layer (NFL) reflectance for glaucoma diagnosis using a large dataset. Methods: Participants were imaged with 4.9mm ONH scans using spectral-domain optical coherence tomography (OCT). The NFL reflectance map was reconstructed from 13 concentric rings of optic nerve head(ONH) scan, then processed by an azimuthal filter to reduce directional reflectance bias due to variation of beam incidence angle. The peripapillary thickness and reflectance maps were both divided into 96 superpixels. Low-reflectance and low-thickness superpixels were defined as values below the 5th percentile normative reference for that location. Focal reflectance loss was measured by summing loss, relative to the normal reference average, in low-reflectance superpixels. Focal thickness loss was calculated in a similar fashion. The area under receiving characteristic curve (AROC) was used to assess diagnostic accuracy. Results: Fifty-three normal, 196 pre-perimetric, 132 early perimetric, and 59 moderate and advanced perimetric glaucoma participants were included from the Advanced Imaging for Glaucoma Study. Sixty-seven percent of glaucomatous reflectance maps showed characteristic contiguous wedge or diffuse defects. Focal NFL reflectance loss had significantly higher diagnostic accuracy than the best NFL thickness parameters (both map-based and profile-based): AROC 0.80 v. 0.75 (p<0.004) for distinguishing glaucoma eyes from healthy control eyes. The diagnostic sensitivity was also significantly higher at both 99% and 95% specificity operating points. Conclusions: Focal NFL reflectance loss improved glaucoma diagnostic accuracy compared to the standard NFL thickness parameters.