Non-invasive glucose meter

1. A method of determining the concentration of a substance in an eye, the eye having a cornea, a pupil, an iris, a lens, a liquid, and a retina, 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 with the measurement light beam, thereby passing the measurement light beam through the cornea, the pupil, the lens, and the liquid;

irradiating the retina with the reference light beam, thereby passing the reference light beam through the cornea, the pupil, the lens, and the liquid;

reflecting at least a portion of the measurement light beam from the retina and through the liquid, the lens, the pupil, and the cornea, thereby producing a measurement retro-reflected 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, thereby producing a reference retro-reflected light beam having the second wavelength;

providing a detector adapted to generate a measurement signal in response to being irradiated by light having the first wavelength and to generate a reference signal in response to being irradiated by light having the second wavelength, the detector located at a distance of at least 100 mm from the eye;

irradiating the detector with the measurement retro-reflected light beam;

irradiating the detector with the reference retro-reflected light beam; and

determining the concentration of the substance in the eye in response to the measurement signal and the reference signal from the detector.

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

3. 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.

4. The method of claim 3 , wherein the first infrared light source comprises a laser diode or an infrared light emitting diode.

5. The method of claim 3 , wherein the second infrared light source comprises a laser diode or an infrared light emitting diode.

6. The method of claim 1 , wherein the measurement light beam is provided by a wideband light source and the reference light beam is provided by the wideband light source.

7. The method of claim 6 , wherein the measurement light beam is transmitted through a first band filter and the reference light beam is transmitted through a second band filter.

8. The method of claim 1 , wherein the measurement light beam and the measurement retro-reflected light beam are substantially parallel, and the reference light beam and the reference retro-reflected light beam are substantially parallel.

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

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

11. 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 positionable to receive the retro-reflected measurement light beam and the retro-reflected reference light beam while the detector is located at a distance of at least 100 mm from the eye, the 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 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.

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

13. The apparatus of claim 11 , wherein the optical combiner further comprises an optical glass layer, a holographic beam splitter layer, and a cover glass layer.

14. The apparatus of claim 11 , further comprising a motor coupled to the measurement light source and the reference light source.

15. The apparatus of claim 11 , wherein the measurement light source comprises a first infrared light source and the reference light beam comprises a second infrared light source.

16. The apparatus of claim 15 , wherein the first infrared light source comprises a laser diode or an infrared light emitting diode.

17. The apparatus of claim 15 , wherein the second infrared light source comprises a laser diode or an infrared light emitting diode.

18. The apparatus of claim 11 , wherein the measurement light source comprises a wideband light source and the reference light source comprises the wideband light source.

19. The apparatus of claim 18 , wherein the measurement light beam is transmitted through a first band filter and the reference light beam is transmitted through a second band filter.

20. The apparatus of claim 11 , wherein the measurement light beam is substantially parallel to the retro-reflected measurement light beam, and the reference light beam is substantially parallel to the retro-reflected reference light beam.

21. The apparatus of claim 11 , wherein the electrical circuit comprises a central processing unit (CPU), memory, and a display.

22. The apparatus of claim 11 , wherein the electrical circuit is further coupled to the measurement light source and the reference light source.

23. An apparatus for measuring a concentration of a substance in an eye, the eye having a cornea, a pupil, an iris, a lens, a liquid, and a retina, the apparatus comprising:

means for providing a nearly parallel measurement light beam having a first wavelength at which the substance has a non-zero first absorption coefficient;

means for 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;

means for irradiating the retina with the measurement light beam, thereby passing the measurement light beam through the cornea, the pupil, the lens, and the liquid, wherein at least a portion of the measurement light beam is reflected from the retina and through the liquid, the lens, the pupil, and the cornea, thereby producing a measurement retro-reflected light beam having the first wavelength;

means for irradiating the retina with the reference light beam, thereby passing the reference light beam through the cornea, the pupil, the lens, and the liquid, wherein at least a portion of the reference light beam is reflected from the retina and through the liquid, the lens, the pupil, and the cornea, thereby producing a reference retro-reflected light beam having the second wavelength;

means for generating a measurement signal in response to the measurement retro-reflected light beam and for generating a reference signal in response to the reference retro-reflected light beam while the generating means is located at a distance of at least 100 mm from the eye; and

means for determining the concentration of the substance in the eye in response to the measurement signal and the reference signal.