Visible light optical coherence tomography of peripapillary retinal nerve fiber layer reflectivity in glaucoma

Purpose: To evaluate the clinical utility of visible light optical coherence tomography (VIS-OCT) and to test whether VIS-OCT reflectivity and spectroscopy of peripapillary retinal nerve fiber layer (pRNFL) are correlated with severity of glaucoma, compared with standard-of-care OCT thickness measurements. Design: Cross-sectional study. Method: Fifty-four eyes from three groups of subjects (normal, glaucoma suspect, and glaucoma) were scanned by a custom-designed dual-channel device that simultaneously acquired visible (VIS-OCT) and near-infrared OCT (NIR-OCT) images. A 5x5 mm2 scan was taken of the peripapillary nerve fiber layer (pRNFL). The pRNFL reflectivity was calculated for both channels and the spectroscopic marker was quantified by pVN, defined by the ratio of VIS-OCT to NIR-OCT pRNFL reflectivity. The results were compared with ophthalmic exams and clinical Zeiss OCT measurements. Mixed linear model was used to evaluate the association of imaging markers with glaucoma severity. Results: VIS-OCT pRNFL reflectivity significantly, sequentially declined from normal to suspect to glaucoma (3.42 {+/-} 0.35, 2.58 {+/-} 0.37, 2.16 {+/-} 0.39, mean {+/-} SD), as did NIR-OCT pRNFL reflectivity (2.46 {+/-} 0.24, 2.27 {+/-} 0.24, 1.96 {+/-} 0.25). The pVN also had the same decreasing trend among three groups (1.39 {+/-} 0.08, 1.14 {+/-} 0.08, 1.08 {+/-} 0.10). Normal and suspect eyes were significantly different in VIS-OCT pRNFL reflectivity (p=0.002), pVN (p<0.001) but not in NIR-OCT pRNFL reflectivity (p=0.14), circumpapillary RNFL (cpRNFL) thickness (p=0.17), or macular ganglion cell layer and inner plexiform layer (GCL+IPL) thickness (p=0.07) in the mixed linear model. Conclusion: VIS-OCT pRNFL reflectivity and pVN was more sensitive in separating suspect eyes from normal ones than clinical OCT thickness measurements. VIS-OCT pRNFL reflectivity and pVN could be a useful metric in early detection of glaucoma upon further longitudinal validation.