Patent ID: 8219169

Claim:
A method of determining the concentration of a substance in a subject's blood, the method comprising: noninvasively irradiating an eye of the subject with a measurement light beam having a first wavelength and a first power, wherein at least a portion of the measurement light beam is retro-reflected from the retina of the eye, thereby producing a measurement retro-reflected light beam having the first wavelength; noninvasively irradiating the eye of the subject with a reference light beam having a second wavelength and a second power, the second wavelength different from the first wavelength, wherein at least a portion of the reference light beam is retro-reflected from the retina of the eye, thereby producing a reference retro-reflected light beam having the second wavelength; measuring at least one of a body temperature of the subject and an ambient temperature of the subject; detecting a power of the measurement retro-reflected light beam; detecting a power of the reference retro-reflected light beam; calculating a measurement ratio of the detected power of the measurement retro-reflected light beam and the first power; calculating a reference ratio of the detected power of the reference retro-reflected light beam and the second power; calculating a parameter dependent on the measurement ratio and the reference ratio, wherein the parameter comprises a difference between the measurement ratio and the reference ratio; and determining a concentration of the substance in the subject's blood in response to the calculated parameter and to the at least one of the body temperature and the ambient temperature.