Method and apparatus for the non-invasive measurement of blood glucose levels in humans

• US 6,704,588 B2
• Filed: 06/14/2002
• Issued: 03/09/2004
• Est. Priority Date: 06/16/2001
• Status: Expired due to Fees

• Current Assignee: Oculose, LLC
• Original Assignee: Luigi Rovati, Rafat R. Ansari
• Inventors: Rovati, Luigi, Ansari, Rafat R.
• Primary Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US10/172,258
• Publication Number:
  US 20030233036A1
• Time in Patent Office: 634 Days
• Field of Search: 600/310, 600/316, 600/318, 600/319, 600/321
• US Class Current: 600/319
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14558 by polarisation

Abstract

An apparatus (10) for determining a diagnostic glucose level in a human subject includes a light source (30) that produces collimated light at a selected wavelength. The collimated light is arranged such that it passes through a portion of an eye (12) of the subject and reflects off an eye lens (16) at a selected angle (θ_B) as reflected light. A polarization analyzer (70) measures a polarization of the reflected light that exits the eye (12). A path length processor (68) determines an optical path length (L_λ) of the reflected light within an aqueous humor (22) of the eye (12). A glucose level processor (90) computes a glucose concentration based on the measured polarization and the determined optical path length (L_λ).

Claims

1. A method for determining a diagnostic glucose level for a person, the method comprising:

reflecting light off an ocular lens at a Brewster'"'"'s angle to produce an initial linear polarization of reflected light;

measuring a polarization rotation of the reflected light after exiting the eye, the polarization rotation being measured with respect to the initial linear polarization; and

determining a glucose concentration based on the measured polarization rotation.

2. The method as set forth in claim 1, wherein the reflecting step includes:

adjusting a light source incident angle to maximize a signal-to-noise ratio.

3. The method as set forth in claim 1, wherein the reflecting step includes:

reflecting circularly polarized light off the ocular lens at the Brewster'"'"'s angle of an aqueous humor/lens interface.

4. The method as set forth in claim 1, wherein the measuring step includes:

interferometrically measuring an optical path length through an ocular aqueous humor, the measured optical path length being used in the determining of a glucose concentration.

5. The method as set forth in claim 1, wherein the measuring step includes:

determining a major axis of an elliptical polarization of the reflected light after exiting the eye, the polarization rotation corresponding to a rotation of major axis.

6. The method as set forth in claim 1, wherein the steps of reflecting light and measuring a polarization rotation are repeated for a plurality of wavelengths, and the step of determining the glucose level based on the measured polarization rotation includes:

determining levels for a plurality of optically active substances including glucose in the aqueous humor based on the measured polarization rotations at the plurality of wavelengths.

7. A method for determining a diagnostic glucose level, the method comprising:

reflecting light from an internal ocular interface at an incident angle that has a selected reflection polarization characteristic;

measuring an elliptical polarization of the reflected light; and

computing a glucose concentration based on a polarimetric rotation parameter derived from the measured elliptical polarization of the reflected light and the selected reflection polarization characteristic.

8. The method as set forth in claim 7, wherein the incident angle is a Brewster'"'"'s angle.

9. The method as set forth in claim 7, wherein the internal ocular interface includes an ocular lens surface.

10. The method as set forth in claim 9, wherein the incident angle is within about an eight angular degree range centered about a Brewster'"'"'s angle of an aqueous humor/lens interface.

11. The method as set forth in claim 7, wherein the measuring step includes:

measuring a polarization of the reflected light;

correcting the measured polarization for refractive polarization changes occurring at selected ocular interfaces; and

determining a polarization rotation computed based on the corrected measured polarization and the selected reflection polarization characteristic.

12. The method as set forth in claim 7, further including:

adjusting a plane of incidence of the reflecting from the internal ocular interface to minimize an ellipticity produced by an ocular birefringence.

13. A method for determining a diagnostic glucose level, the method comprising:

reflecting light from a lens/vitreous humor interface at a critical angle for total reflection at the lens/vitreous humor interface;

measuring a polarimetric parameter of the reflected light; and

computing a glucose concentration based on the polarimetric parameter.

14. A method for determining at least a diagnostic glucose level, the method comprising:

reflecting light from an internal ocular interface at an incident angle that has a selected reflection polarization characteristic;

measuring a polarimetric parameter of the reflected light;

repeating the reflecting and measuring steps for light at a plurality of wavelengths to obtain a plurality of polarimetric parameters;

computing polarization rotation values at each of the plurality of wavelengths; and

determining compositions of a plurality of optically active substances including glucose based on the plurality of polarization rotation values.

15. An apparatus for determining a diagnostic glucose level in a human subject, the apparatus comprising:

a light source that produces collimated light at a selected wavelength, the collimated light arranged such that the collimated light passes through a portion of an eye of the subject and reflects off an eye lens at a selected angle as reflected light;

a polarization analyzer that measures a polarization of the reflected light that exits the eye;

a path length processor that determines an optical path length of the reflected light within an aqueous humor of the eye; and

a glucose level processor that computes a glucose concentration based on the measured polarization and the determined optical path length.

16. The apparatus as set forth in claim 15, wherein the selected angle is a Brewster'"'"'s angle, and the glucose level processor computes the glucose concentration based on polarization characteristics of the Brewster'"'"'s angle reflection.

17. The apparatus as set forth in claim 15, wherein the light source is selected from a group consisting of:

a white light source with one or more filter elements that spectrally filter light produced by the white light source,

an arc discharge lamp,

one or more light emitting diodes, and

a multiple-wavelength laser.

18. The apparatus as set forth in claim 15, further including:

a polarizer that polarizes light produced by the light source prior to entering the eye.

19. The apparatus as set forth in claim 15, wherein the path length processor includes:

an interferometric detector that measures a difference in optical path length between the collimated light after reflection from the eye lens and a reference beam derived from the light source.

20. The apparatus as set forth in claim 15, further including:

a head mount that fastens to a head of the subject and supports at least the polarization analyzer and the path length detector.

21. The apparatus as set forth in claim 15, further including:

a substrate on which the collimated light, the polarization analyzer, and the path length detector are arranged;

an actuator that operates on the substrate to adjust a substrate orientation with respect to the eye; and

a feedback circuit incorporating an output of the polarization analyzer, the feedback circuit driving the actuator to arrange the substrate at a selected substrate orientation that minimizes an ocular birefringence.