Photoacoustic measurement of analyte concentration in the eye

Abstract

In one aspect, the invention features a method and device for measuring blood concentration of a substance such as glucose in the aqueous humor by illuminating the aqueous humor with a light source at a frequency that is absorbed by the substance to the measured, and then sensing photoacoustically generated sound waves originated within the aqueous humor as a consequence of illumination by the light source. The blood concentration can be estimated from the amplitude of the sound waves received. The method may be combined with other optical techniques for glucose measurement and / or with optical or ultrasonic techniques for topographic mapping of eye structures.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of U.S. application Ser. No. 60 / 727,078, filed Oct. 14, 2005, which is hereby incorporated by reference herein in its entirety.FIELD OF THE INVENTION [0002] The invention relates to a non-invasive, in-vivo method and a system for the determination of the concentration of a substance in different areas of the eye. BACKGROUND OF THE INVENTION [0003] Many medical diagnostic techniques project radiant energy into the body of an animal for testing for the existence of a biomedical disorder or condition. For example, the integrity of the skeletal structure may be examined by passing X-rays through the body. The dense bony material substantially blocks the passage of the X-rays, permitting a doctor or other medical care provider to visually inspect for fractures or other defects in the skeletal structure. [0004] To examine the soft tissue of the body, other techniques are available. These include, among other...

AI Technical Summary

Benefits of technology

[0018] This method has the advantage that the radiant energy used to stimulate the photoacoustic response need not pass through soft tissue, but rather passes through a relatively clear and optically transmissive media. Furthermore, this method has the advantage that light need not be reflected or otherwise directed to a detector for the measurement to be accomplished, as the measurement is accomplished from acoustic, rather than electromagnetic, response signals.

[0019] Although it has been known to use a photoacoustic method to measure blood glucose in opaque tissue such as through the skin, use of this method in the aqueous humor is believed to be new, and has distinct advantages over these known applications for the reason that the aqueous humor is relatively transparent, and thus permits focused illumination over a larger range of tissue structure than could be achieved in opaque areas. At the same time, the glucose concentration within the aqueous humor is reflective of the body as a whole and thus the quality of the measurement is not compromised

Problems solved by technology

Unfortunately, these approaches all suffer from a number of drawbacks.

Specifically, light is scattered by body tissue, and thus even in the '904 patent where light is focused to a region inside the body, the location and size of the absorbing tissue region are not accurately known.

Measurements of blood glucose levels can therefore be affected by unknown variables that substantially compromise the reliability of those measurements.

However, several problems are associated with these techniques.

However, this method suffers from poor sensitivity, in part because it relies on reflecting the radiant energy off the iris.

Although this test is able to achieve high accuracy, it is difficult to administer because of the shallow angle at which the radiant energy must be passed through the eye.

All of these methods, however, measure glucose in only one area of the eye at any one time, and each relies upon optical methods for transmission and return of information.

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