A method and an apparatus for detecting change in retinal oxygen saturation over time are provided. The method includes the steps of capturing a first group of images of two or more wavelengths, calculating oxygen saturation of a vessel in the first group of images, storing the first group of images on a data storage device, capturing a second group of images of two or more wavelengths, calculating the oxygen saturation of a vessels in the second group of images, storing the second group of images on a data storage device, spatially registering the pair of the group of images, captured at different time and calculate the change in oxygen saturation. The method also includes means to validate whether an observed change in oxygen saturation is a real physiological change or artificial.
