The determination of blood glucose in an individual is carried out by projecting illuminating light into an eye of the individual to illuminate the
retina with the light having wavelengths that are absorbed by
rhodopsin and with the intensity of the light varying in a prescribed temporal manner. The light reflected from the
retina is detected to provide a
signal corresponding to the intensity of the detected light, and the detected
light signal is analyzed to determine the changes in form from that of the illuminating light. For a biased sinusoidal illumination, these changes can be expressed in terms of
harmonic content of the detected light. The changes in form of the detected light are related to the ability of
rhodopsin to absorb light and regenerate, which in turn is related to the concentration of blood glucose, allowing a determination of the relative concentration of blood glucose. Other photoreactive analytes can similarly be determined by projecting time varying illuminating light into the eye, detecting the light reflected from the
retina, and analyzing the detected
light signal to determine changes in form of the
signal due to changes in absorptivity of a photoreactive
analyte.