Hemoglobin oxygen saturation (So2) in the human ocular fundus measured by reflectance oximetry: preliminary data in retinal veins

Abstract

Development of a reflectance oximeter to measure non-invasively the changes in oxygen saturation (SO 2 ) in the vessels of the human eye fundus, with the goal of obtaining a better understanding of the retinal circulation in health and disease. For retinal oximetry, an instrument must image the retina at multiple wavelengths (lambda) and measure the apparent optical density (OD lambda ) of retinal vessels. The new IRO oximeter acquires two-dimensional images of the retina at four different wavelengths simultaneously. The hemoglobin oxygen saturation is calculated using the spectral images at 569 nm (not sensitive to the oxygenation status of hemoglobin) and at 600 nm (sensitive to the oxygenation status). To test the method, two subjects were asked to breathe first room air and then pure oxygen. During hyperoxia (100 % O 2 breathing), the apparent optical density ratio (OD 600 /OD 569 ) decreases significantly, and consequently, the SO 2 in the veins increases. The optical density ratio method could be used for relative oxygen saturation measurements, for example, for determining the variation of the SO 2 under various physiological conditions, before and after an intervention or for monitoring retinal diseases such as diabetic retinopathy.