Characterization of Blue-Green Lateral Scattering for Retinal Oximetry

Abstract

Retinal oximetry is the science of measuring hemoglobin oxygen saturation in retinal vessels. To date, instruments designed for retinal oximetry have nearly all been experimental. Retinal oximetry has never fully translated from research to clinical use due to the optical complexities involved with noninvasively controlling light paths at the retina. Tissue optics, biological processes, and natural variability between subjects present very real challenges to the development of reliable oxygen monitoring in retinal vessels. The research described herein investigates the potential of improved methods in retinal oximetry through the controlled collection of scattered light at the retina. We have developed the ROx-3, a specialized scanning-laser ophthalmoscope designed to measure blue-green spectral lateral scattering from focused illumination at the retina, and we performed experiments with our instrument on animal eye specimens. We found that the spectral influence of hemoglobin is strengthened through the targeted collection of laterally scattered light, but it was also determined that the unique spectral characteristics of this light prevented immediate measurements of calibrated oxygen saturation values from being made. We also found that high variability in the measured spectra was caused by the fine geometry of retinal vessels as well as the region at which laterally scattered light was collected. Further characterization of the spectral lateral scattering profile at the retina must be made in light of these influences if the improved measurement of oxygen saturation in retinal vessels is to be made using laterally scattered light.