Non-invasive measurement of blood analytes using photodynamics

Abstract

The determination of blood glucose in an individual is carried out by projecting illuminating light into an eye of the individual to illuminate the retina with the light having wavelengths that are absorbed by rhodopsin and with the intensity of the light varying in a prescribed temporal manner. The light reflected from the retina is detected to provide a signal corresponding to the intensity of the detected light, and the detected light signal is analyzed to determine the changes in form from that of the illuminating light. For a biased sinusoidal illumination, these changes can be expressed in terms of harmonic content of the detected light. The changes in form of the detected light are related to the ability of rhodopsin to absorb light and regenerate, which in turn is related to the concentration of blood glucose, allowing a determination of the relative concentration of blood glucose. Other photoreactive analytes can similarly be determined by projecting time varying illuminating light into the eye, detecting the light reflected from the retina, and analyzing the detected light signal to determine changes in form of the signal due to changes in absorptivity of a photoreactive analyte.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a continuation of prior application Ser. No. 10 / 012,902, filed Oct. 22, 2001, which claimed priority from provisional application No. 60 / 318,850, filed Sep. 13, 2001, which are incorporated herein by reference.FIELD OF THE INVENTION [0002] This invention pertains to the field of non-invasive in vivo measurement of blood analytes. BACKGROUND OF THE INVENTION [0003] The measurement of blood glucose by diabetic patients has traditionally required the drawing of a blood sample for in vitro analysis. The blood sampling is usually done by the patient himself as a finger puncture, or in the case of a child, by an adult. The need to draw blood for analysis is undesirable for a number of reasons, including discomfort to the patient, resulting in many patients not testing their blood as frequently as recommended, the high cost of glucose testing supplies, and the risk of infection with repeated skin punctures. [0004] Many of th...

AI Technical Summary

Benefits of technology

[0006] The present invention combines the accuracy of in vitro laboratory testing of analytes such as blood glucose with the advantages of a rapidly-repeatable non-invasive technology. The invention utilizes a hand-held instrument that allows non-invasive determination of glucose by measurement of the regeneration rate of rhodopsin, the retinal visual pigment, following a light stimulus. The rate of regeneration of rhodopsin is dependent upon the blood glucose concentration, and by measuring the regeneration rate of rhodopsin, blood glucose can be accurately determined. This invention exposes the retina to light of selected wavelengths in selected distributions and subsequently analyzes the reflection from the exposed region.

[0007] The rods and cones of the retina are arranged in specific locations in the back of the eye, an anatomical arrangement used in the present invention. The cones, which provide central and color vision, are located with their greatest density in the area of the fovea centralis in the retina. The fovea covers a circular area with a diameter of about 1.5 mm, with a subtended angle of about 3 degrees. The rods are found in the more peripheral portions of the retina and contribute to dim vision.

[0011] In accordance with the invention, a hand-held or stationary instrument that measures the resulting data in the reflected light from a periodically applied light stimulus (for example, a sinusoid) may be utilized for the determination of blood glucose values. There may be patient-to-patient variability and each device may be calibrated for each patient on a regular interval. This may be necessary as the changing state of each patient's diabetes affects the outer segment metabolism and thus influences the regeneration rates of rhodopsin. The intermittent calibration of the device is useful in patient care as it facilitates the diabetic patient returning to the health-care provider for follow-up of their disease. The device may be equipped with a method of limiting the number of tests, so that follow-up will be required to reactivate the device.

Problems solved by technology

The need to draw blood for analysis is undesirable for a number of reasons, including discomfort to the patient, resulting in many patients not testing their blood as frequently as recommended, the high cost of glucose testing supplies, and the risk of infection with repeated skin punctures.

As a result of the discomfort, many of these patients do not test as often as is recommended by their physician, with the consequence of poor blood glucose control.

This poor control has been shown to result in increased complications from this disease.

Prior efforts have been unsuccessful in the quest for a sufficiently accurate, non-invasive blood glucose measurement.

These efforts have been largely unsuccessful primarily due to the variability of absorption and scatter of the electromagnetic energy in the tissues.

To date, these efforts have not been successful for a variety of reasons.

Images