Abstract
Abstract: :
Purpose: Polarization Sensitive Optical Coherence Tomography (PSOCT) is a new technique that can be used to measure the thickness and birefringence of the nerve fiber layer in vivo. Methods: Five healthy human subjects underwent multiple PSOCT scans. PSOCT scans around the optic nerve head (ONH) were made using concentric circles of increasing diameter. Each of the circular scans was divided into forty–eight 7.5° sectors for analysis of both retinal nerve fiber layer thickness and birefringence. Results: For all 5 subjects, both the retinal nerve fiber layer thickness and birefringence varied around the ONH. The retinal nerve fiber layer becomes thinner with increasing distance from the ONH. In contrast, the birefringence does not vary as a function of diameter. The birefringence of healthy RNFL does vary as a function of position around the ONH. Birefringence is higher in the thicker layers inferior and superior to the ONH but is lower in the thinner temporal and nasal areas. Measured double pass phase retardation per unit depth values around the ONH of five healthy subjects range between 0.1 and 0.4°/mm. These values are equivalent to birefringence values of 1.17 x10–4 and 3.5 x10–4 respectively, measured at a wavelength of 840 nm. Conclusions:PSOCT is a new instrument that can provide objective thickness and birefringence measurements of the RNFL, which is affected in glaucoma. Consequently, conversion of phase retardation measurements, as obtained with scanning laser polarimetry which assumes a constant birefringence value, to RNFL thickness measurements will yield thickness values that are incorrect.
Keywords: imaging methods (CT, FA, ICG, MRI, OCT, RTA, SLO, ultrasound) • nerve fiber layer • anatomy