Patent ID: 8364219

Claim:
A method of determining the concentration of a substance in an eye, the method comprising: providing a nearly parallel measurement light beam having a first wavelength at which the substance has a non-zero first absorption coefficient; providing a nearly parallel reference light beam having a second wavelength at which the substance has a second absorption coefficient which is substantially equal to zero; irradiating the retina of the eye with the measurement light beam; irradiating the retina of the eye with the reference light beam; reflecting at least a portion of the measurement light beam from the retina, thereby producing a retro-reflected measurement light beam having the first wavelength; reflecting at least a portion of the reference light beam from the retina, thereby producing a retro-reflected reference light beam having the second wavelength; generating a measurement signal in response to the retro-reflected measurement light beam; generating a reference signal in response to the retro-reflected reference light beam; and determining the concentration of the substance in the eye in response to the measurement signal and the reference signal.