Abstract

Retinal vessel oximetry allows the measurement of blood oxygen saturation (O₂S) in individual retinal vessels.¹ O₂S measurement involves determining vessel and fundus background optical density at three wavelengths. Artifacts in O₂S values have been traced to the nonuniform fundus background. A novel approach that eliminates the need for background reflectance measurement is proposed. It requires measuring the intensity of laser light that has been singly backscattered by the blood. This intensity can be extracted from the Doppler shift power spectrum (DSPS) recorded from the moving red cells. Since this backscattered light obeys Lambert-Beer’s law, a vessel density D = α + c • d • E [Eq. (1)] can be defined. The constant α is assumed legitimately to be wavelength independent, d is the path length, c is the total hemoglobin concentration, and E is the specific extinction coefficient of blood, from which O₂S can be directly obtained. The three unknowns in Eq. (1): α, c • d, and E can be determined by recording DSPS at three wavelengths. The implementation of this approach is discussed using laser recordings of DSPS at 0.63 μm from blood flowing through capillary tubes (various c • dand O₂S).

© 1988 Optical Society of America