  Purpose: To evaluate nerve fiber layer (NFL) reflectance for glaucoma
diagnosis. Methods: Participants were imaged with 4.5X4.5-mm volumetric disc
scans using spectral-domain optical coherence tomography (OCT). The normalized
NFL reflectance map was processed by an azimuthal filter to reduce directional
reflectance bias due to variation of beam incidence angle. The peripapillary
area of the map was divided into 160 superpixels. Average reflectance was the
mean of superpixel reflectance. Low-reflectance superpixels were identified as
those with NFL reflectance below the 5 percentile normative cutoff. Focal
reflectance loss was measure by summing loss in low-reflectance superpixels.
Results: Thirty-five normal, 30 pre-perimetric and 35 perimetric glaucoma
participants were enrolled. Azimuthal filtering improved the repeatability of
the normalized NFL reflectance, as measured by the pooled superpixel standard
deviation (SD), from 0.73 to 0.57 dB (p<0.001, paired t-test) and reduced the
population SD from 2.14 to 1.78 dB (p<0.001, t-test). Most glaucomatous
reflectance maps showed characteristic patterns of contiguous wedge or diffuse
defects. Focal NFL reflectance loss had significantly higher diagnostic
sensitivity than the best NFL thickness parameter (overall, inferior, or focal
loss volume): 53% v. 23% (p=0.027) in PPG eyes and 100% v. 80% (p=0.023) in PG
eyes, with the specificity fixed at 99%. Conclusions: Azimuthal filtering
reduces the variability of NFL reflectance measurements. Focal NFL reflectance
loss has excellent glaucoma diagnostic accuracy compared to the standard NFL
thickness parameters. The reflectance map may be useful for localizing NFL
defects.
