Spectral reflectance technique for retinal blood oxygen evaluation in humans

Retinal diseases such as diabetic retinopathy, glaucoma, vein occlusion and optic nerve atrophy are associated with abnormal oxygen tension and bloodflow in surface vessels of the retina. Visible reflected light spectroscopy has in the past been applied to hemoglobin oxygen saturation measurements from the body surface, as with measurements from skin and wounds, from intact brain vessels during surgical intervention, and as well, from the retinal vessels and other ocular structures inside the body. All of these measurements are complicated by lack of visible light penetration, interference from secondary chromophores, specular return of light and wavelength-dependent penetration to different layers in different structures. We present spectral reflectance curves obtained with a prism-grating-prism (PGP) spectrographic camera from structures producing hemoglobin signatures, including the retinal artery and vein, the pigmented retina and the optic disk, as well as from the macular area which is free of this signature. Oxygen-dependent changes in the hemoglobin signature are determined from vessels and tissue surround.