Patent ID: 7643859

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, thereby passing the measurement light beam through the cornea, the pupil, the lens, and the liquid of the eye; irradiating the retina of the eye with the reference light beam, thereby passing the reference light beam through the cornea, the pupil, the lens, and the liquid of the eye; reflecting at least a portion of the measurement light beam from the retina and through the liquid, the lens, the pupil, and the cornea of the eye, 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 and through the liquid, the lens, the pupil, and the cornea of the eye, thereby producing a retro-reflected reference light beam having the second wavelength; providing a detector responsive to light having the first wavelength and responsive to light having the second wavelength; irradiating the detector with the retro-reflected measurement light beam, the detector generating a measurement signal in response thereto; irradiating the detector with the retro-reflected reference light beam, the detector generating a reference signal in response thereto; and determining the concentration of the substance in the eye in response to the measurement signal and the reference signal.