Obtaining spectral images of an eye includes taking an optical system that images eye tissue onto a digital sensor array and optically fitting a multi-spectral filter array and the digital sensor array, wherein the multi-spectral filter array is disposed between the digital sensor array and an optics portion of the optical system. The resulting system facilitates acquisition of a snap-shot image of the eye tissue with the digital sensor array. The snap shot images support estimation of blood oxygen saturation in a retinal tissue. The resulting system can be based on a non-mydriatic fundus camera designed to obtain the retinal images without administration of pupil dilation drops.