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Focal Loss Analysis of Nerve Fiber Layer Reflectance for Glaucoma Diagnosis

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Document pages: 31 pages

Abstract: Purpose: To evaluate nerve fiber layer (NFL) reflectance for glaucomadiagnosis. Methods: Participants were imaged with 4.5X4.5-mm volumetric discscans using spectral-domain optical coherence tomography (OCT). The normalizedNFL reflectance map was processed by an azimuthal filter to reduce directionalreflectance bias due to variation of beam incidence angle. The peripapillaryarea of the map was divided into 160 superpixels. Average reflectance was themean of superpixel reflectance. Low-reflectance superpixels were identified asthose with NFL reflectance below the 5 percentile normative cutoff. Focalreflectance loss was measure by summing loss in low-reflectance superpixels.Results: Thirty-five normal, 30 pre-perimetric and 35 perimetric glaucomaparticipants were enrolled. Azimuthal filtering improved the repeatability ofthe normalized NFL reflectance, as measured by the pooled superpixel standarddeviation (SD), from 0.73 to 0.57 dB (p<0.001, paired t-test) and reduced thepopulation SD from 2.14 to 1.78 dB (p<0.001, t-test). Most glaucomatousreflectance maps showed characteristic patterns of contiguous wedge or diffusedefects. Focal NFL reflectance loss had significantly higher diagnosticsensitivity than the best NFL thickness parameter (overall, inferior, or focalloss volume): 53 v. 23 (p=0.027) in PPG eyes and 100 v. 80 (p=0.023) in PGeyes, with the specificity fixed at 99 . Conclusions: Azimuthal filteringreduces the variability of NFL reflectance measurements. Focal NFL reflectanceloss has excellent glaucoma diagnostic accuracy compared to the standard NFLthickness parameters. The reflectance map may be useful for localizing NFLdefects.

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