Birefringent Properties of the Peripapillary Retinal Nerve Fiber Layer in Healthy and Glaucoma Subjects Analyzed by Polarization-Sensitive OCT

PURPOSE. To study the circumpapillary retinal nerve fiber layer (RNFL) birefringence (BIR) of early glaucoma and age-matched healthy eyes using polarization-sensitive optical coherence tomography (PS-OCT). METHODS. In this prospective cross-sectional study, we compared virtual circular PS-OCT B-scans with a diameter of 3.5 mm centered on the optic disc (OD) acquired with a PS-OCT prototype (860 nm center wavelength). Early glaucoma was defined by the glaucomatous appearance of the OD and a pathologic visual field test with a mean deviation (MD) better than -6 dB. The main outcome parameters were BIR, RNFL-thickness (RNFL-T), and phase retardation (RET). The BIR value at each virtual A-scan position was the quotient of the RET measured at the inner segment/outer segment junction divided by the RNFL-T. RESULTS. The dataset comprised 49 early glaucoma patients (mean +/- standard deviation [SD]: 64 +/- 10 years) and 49 healthy control subjects (61 +/- 9 years). Glaucomatous eyes showed a statistically significant lower BIR globally (mean +/- SD: 0.108 +/- 0.008 degrees/mu m vs. 0.112 +/- 0.009 degrees/mu m, P = 0.033), superiorly (0.116 +/- 0.017 degrees/mu m vs. 0.126 +/- 0.013 degrees/mu m, P = 0.0001), and inferiorly (0.112 +/- 0.011 degrees/mu m vs. 0.121 +/- 0.011 degrees/mu m, P < 0.0001), and increased BIR in the temporal quadrant (0.088 +/- 0.015 degrees/mu m vs. 0.078 +/- 0.014 degrees/mu m, P = 0.0001) compared to healthy eyes. CONCLUSIONS. We report a reduced BIR of the RNFL in early perimetric glaucoma, which can be interpreted as a sign of loss or change of intracellular microtubules and may contribute to a better understanding of early disease development. Prospective longitudinal studies are needed to determine whether BIR is altered in pre-perimetric human glaucoma before RNFL-T decline.

Automated summary

This study used polarization-sensitive optical coherence tomography to investigate the birefringence of the circumpapillary retinal nerve fiber layer in early glaucoma. The results showed a reduction in birefringence in glaucomatous eyes, which may be indicative of changes in intracellular microtubules. Further longitudinal studies are needed to determine if birefringence changes occur before a decline in retinal nerve fiber layer thickness.