Non-invasive glucose meter

1. 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.

2. The method of claim 1 , wherein the detector primarily receives the retro-reflected measurement light beam and the retro-reflected reference light beam without receiving other reflections from the eye.

3. The method of claim 1 , wherein the measurement light beam and the reference light beam are focused at a point on the retina and the detector is located such that the retro-reflected measurement light beam and the retro-reflected reference light beam propagate along an optical path of at least 100 mm between the eye and the detector.

4. The method of claim 1 , wherein the substance comprises glucose.

5. The method of claim 1 , wherein the measurement light beam is provided by a first infrared light source and the reference light beam is provided by a second infrared light source.

6. The method of claim 1 , wherein the measurement light beam is focused at a point on the retina.

7. The method of claim 1 , wherein the reference light beam is focused at a point on the retina.

8. An apparatus for measuring a concentration of a substance in an eye having a retina, the apparatus comprising:

a measurement light source producing a nearly parallel measurement light beam having a first wavelength, the substance having a non-zero first absorption coefficient for light at the first wavelength;

a reference light source producing a nearly parallel reference light beam having a second wavelength, the substance having a second absorption coefficient which is substantially equal to zero for light at the second wavelength;

an optical combiner comprising a dichroic coating layer, the optical combiner positionable so that at least a portion of the measurement light beam retro-reflects from the retina and so that at least a portion of the reference light beam retro-reflects from the retina;

a detector responsive to light having the first wavelength by generating a measurement signal and responsive to light having the second wavelength by generating a reference signal; and

an electrical circuit operatively coupled to the detector, the electrical circuit responsive to the measurement signal and the reference signal to measure the concentration of the substance in the eye.

9. The apparatus of claim 8 , wherein the detector is positionable to primarily receive the retro-reflected measurement light beam and the retro-reflected reference light beam without receiving other reflections from the eye.

10. The apparatus of claim 8 , wherein the measurement light source and the reference light source are positionable such that the measurement light beam and the reference light beam are focused at a point on the retina, and the detector is positionable such that the retro-reflected measurement light beam and the retro-reflected reference light beam propagate along an optical path of at least 100 mm between the eye and the detector.

11. The apparatus of claim 8 , wherein the substance comprises glucose.

12. The apparatus of claim 8 , wherein the measurement light source comprises a first infrared light source and the reference light beam comprises a second infrared light source.

13. A substance-measuring meter comprising:

an optical system adapted to irradiate the retina of an eye with a nearly parallel measurement light beam having a first wavelength at which a substance has a non-zero first absorption coefficient and adapted to irradiate the retina of the eye with 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, such that at least a portion of the measurement light beam and at least a portion of the reference light beam are retro-reflected from the retina, thereby producing a retro-reflected measurement light beam having the first wavelength and a retro-reflected reference light beam having the second wavelength;

a detector adapted to generate a measurement signal in response to the retro-reflected measurement light beam and to generate a reference signal in response to the retro-reflected reference light beam; and

an electronic circuit responsive to the measurement signal and the reference signal to determine the concentration of the substance in the eye.

14. The meter of claim 13 , wherein the detector is positionable to primarily receive the retro-reflected measurement light beam and the retro-reflected reference light beam without receiving other reflections from the eye.

15. The meter of claim 13 , wherein the detector is positionable such that the retro-reflected measurement light beam and the retro-reflected reference light beam propagate along an optical path of at least 100 mm between the eye and the detector.

16. A method of using a meter adapted to measure a concentration of a substance in an eye, the method comprising:

irradiating the retina of the eye with a nearly parallel first light beam having a first wavelength;

irradiating the retina of the eye with a nearly parallel second light beam having a second wavelength;

receiving at least a portion of the first light beam retro-reflected from the retina;

receiving at least a portion of the second light beam retro-reflected from the retina;

providing a detector adapted to generate a first signal in response to light having the first wavelength and to generate a second signal in response to light having the second wavelength;

irradiating the detector with the received portion of the retro-reflected first light beam;

irradiating the detector with the received portion of the retro-reflected second light beam; and

determining the concentration of the substance in the eye in response to signals generated by the detector in response to the received portion of the retro-reflected first light beam and in response to the received portion of the retro-reflected second light beam.

17. The method of claim 16 , wherein the detector is primarily irradiated by the received portion of the retro-reflected first light beam and the received portion of the retro-reflected second light beam without being irradiated by other reflections from the eye.

18. The method of claim 16 , wherein the detector is located such that the received portion of the retro-reflected measurement light beam and the received portion of the retro-reflected reference light beam propagate along an optical path of at least 100 mm between the eye and the detector.

19. The method of claim 16 , wherein the substance comprises glucose.