Measurement of retinal nerve fiber layer retardation by polarization sensitive OCT at 840 and 1060 nm

Abstract

Purpose: To compare the retardation of the retinal nerve fiber layer (RNFL) in the optic nerve head (ONH) area of healthy volunteers measured by polarization sensitive OCT (PS-OCT) at imaging wavelengths of 840 and 1060 nm.

Methods: Two PS-OCT instruments operating at the wavelength ranges of 840 and 1060 nm were developed. The 840 nm instrument is a spectrometer based (SD) system operating at a speed of 70,000 A-scans/s. It covers scan fields of up to 40x40°. The 1060 nm instrument is based on swept source (SS) technology and operates at a speed of 100,000 A-scans/s. Scan fields of similar size as the 840 nm system can be covered. Both instruments are capable of recording intensity, retardation, optic axis orientation, and depolarization images simultaneously. 5 eyes of healthy subjects were imaged. Scan fields of 20x20°, centered at the ONH, were recorded. After software cornea compensation, a circumpapillary analysis of retardation distribution was carried out.

Results: Average circumpapillary single pass retardation ± SD was 42.7 ± 3.1 nm for 840 nm wavelength and 44.8 ± 4.8 nm for 1060 nm wavelength. The respective values in the superior (inferior) quadrants were 52.4 ± 7.9 nm (48.2 ± 4.1 nm) for 840 nm and 51.2 ± 7.9 nm (50.8 ± 4.2 nm) for 1060 nm. The Wilcoxon signed rank test was applied to test the average circumpapillary, superior quadrant and inferior quadrant data pairs at 840 and 1060 nm for statistically significant differences between wavelengths. The obtained p-values were 0.14, 0.50 and 0.23 respectively. This indicates that there is no significant difference in RNFL retardation values in the analyzed regions observed by OCT systems with a wavelength of 840 and 1060 nm.

Conclusions: PS-OCT at the new wavelength of 1060 nm provides similar results for RNFL retardation as PS-OCT at the established wavelength of 840 nm. Because of the better penetration of 1060 nm light through media opacities, PS-OCT at 1060 nm might be useful for glaucoma diagnostics based on RNFL retardation in patients with media opacities.

Keywords: 610 nerve fiber layer • 552 imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound)