In vivo depth-resolved birefringence measurements of the human retinal nerve fiber layer using polarization sensitive optical coherence tomography

摘要

Changes in retinal nerve fiber layer thickness and birefringence may both precede clinically detectable glaucomatous vision loss. Early detection of retinal nerve fiber layer changes may enable treatment to prevent permanent loss of vision. Polarization sensitive optical coherence tomography (PS-OCT) can provide objective information on retinal nerve fiber layer thickness and birefringence. PS-OCT scans around the optic nerve head (ONH) of two healthy young volunteers were made using 10 concentric circles of increasing radius. Both the mean retinal nerve fiber layer thickness and mean retinal nerve fiber birefringence for each of 48 sectors on a circle were determined with data analysis. Birefringence of healthy RNFL is constant as a function of scan radius but varies as a function of position around the ONH, with higher values occurring superior and inferior to the ONH. Measured double pass phase retardation per unit depth values around the ONH range between 0.10 and 0.35 °/μm, equivalent to birefringence values of 1.2?10-4 and 4.1·10-4 respectively, measured at a wavelength of 840 nm. Consequently, conversion of phase retardation measurements (as obtained with scanning laser polarimetry) to RNFL thickness measurements, assuming a constant birefringence value, will yield thickness values that are incorrect.