Method and Apparatus for Non-Invasive Monitoring of Blood Substances Using Self-Sampled Tears

Abstract

A method and apparatus for non-invasively determining the concentration of a substance in blood, such as glucose, include a sample portion arranged for contacting an eye region of a user to obtain a tear fluid sample, a sensor in communication with the sample portion for generating a signal related to the tear substance concentration, and a processor in communication with the sensor for determining a blood substance concentration corresponding to the tear substance concentration.

1 . An apparatus for determining the concentration of a substance in blood, the apparatus comprising: 
 a housing;    a test probe arranged to be received within the housing, the test probe arranged to engage an eye region of a user to obtain a tear fluid sample while the test probe is received within the housing;    a sensor disposed within the housing in communication with the test probe for generating a signal related to the tear substance concentration; and    a processor disposed within the housing in communication with the sensor for determining a blood substance concentration corresponding to the tear substance concentration.    
     
     
         2 . The apparatus according to  claim 1 , wherein the substance includes glucose.  
     
     
         3 . The apparatus according to  claim 2 , wherein the sensor is operable to detect glucose concentrations less than about 20 mg/dL with a resolution of at least 5 mg/dL.  
     
     
         4 . The apparatus according to  claim 1 , wherein the test probe is arranged to allow self-sampling of the tear fluid sample by a user.  
     
     
         5 . The apparatus according to  claim 1 , wherein the test probe includes an inlet extending outwardly therefrom.  
     
     
         6 . The apparatus according to  claim 5 , wherein the inlet includes a capillary member or a wicking membrane.  
     
     
         7 . The apparatus according to  claim 1 , wherein a volume of the tear fluid sample held by the test probe is less than about 0.5 μL.  
     
     
         8 . The apparatus according to  claim 1 , wherein the test probe is removable from the housing.  
     
     
         9 . The apparatus according to  claim 1 , further comprising a display screen in communication with the processor for displaying the blood substance concentration.  
     
     
         10 . The apparatus according to  claim 1 , further comprising memory in communication with the processor for storing the blood substance concentration.  
     
     
         11 . The apparatus according to  claim 1 , wherein the housing is generally pen-shaped.  
     
     
         12 . The apparatus according to  claim 1 , wherein the test probe includes an enzyme for reacting with the substance in the tear fluid sample.  
     
     
         13 . The apparatus according to  claim 12 , wherein the enzyme includes glucose dehydrogenase.  
     
     
         14 . The apparatus according to  claim 12 , wherein the test probe includes an electrode system provided therein, the apparatus further comprising a power source for applying a voltage to the electrode system to induce an electrochemical reaction of the enzyme and the substance, and wherein the sensor detects a current resulting from the electrochemical reaction and the processor determines a tear substance concentration from the detected current.  
     
     
         15 . The apparatus according to  claim 1 , wherein the apparatus is configured to allow the electronic transfer of substance concentration data.  
     
     
         16 . An apparatus for determining glucose concentration in a tear fluid sample, the apparatus comprising: 
 a housing;    a test probe arranged to be received within the housing, the test probe arranged to engage an eye region of a user to obtain a tear fluid sample while the test probe is received within the housing;    a sensor disposed within the housing in communication with the test probe for generating a signal related to the glucose concentration in the tear fluid sample; and    a processor in communication with the sensor for processing the signal to determine the tear glucose concentration.    
     
     
         17 . An apparatus for determining glucose concentration in blood, the apparatus comprising: 
 a housing;    a test probe arranged to be received within the housing, the test probe having an inlet arranged to engage an eye region of a user to obtain a tear fluid sample while the test probe is received within the housing, the test probe having an enzyme provided therein for initiating a reaction with the tear fluid sample, wherein a volume of the tear fluid sample held by the test probe is less than about 0.5 μL;    a sensor disposed within the housing in communication with the test probe for detecting a signal generated by the reaction;    a processor in communication with the sensor for determining a tear glucose concentration from the detected signal and correlating the determined tear glucose concentration with a blood glucose concentration; and    means for providing an output indicative of the blood glucose concentration.    
     
     
         18 . The apparatus according to  claim 17 , wherein the test probe is arranged to allow self-sampling of the tear fluid sample by a user.  
     
     
         19 . The apparatus according to  claim 17 , wherein the housing is generally pen-shaped.  
     
     
         20 . The apparatus according to  claim 17 , wherein the sensor is operable to detect glucose concentrations less than about 20 mg/dL with a resolution of at least 5 mg/dL.  
     
     
         21 . The apparatus according to  claim 17 , wherein the enzyme includes glucose dehydrogenase.  
     
     
         22 . The apparatus according to  claim 17 , wherein the test probe includes pyrrolo-quinoline-quinone as a coenzyme.  
     
     
         23 . The apparatus according to  claim 17 , wherein the test probe includes an electron transfer mediator.  
     
     
         24 . The apparatus according to  claim 23 , wherein the electron transfer mediator includes a ruthenium complex.  
     
     
         25 . The apparatus according to  claim 23 , wherein the test probe includes a base plate, a cover plate, and a spacer disposed between and joining the base and cover plates, the base and cover plates including a converse-type electrode system, the apparatus further comprising a power source for applying a voltage to the electrode system to induce an electrochemical reaction of the enzyme and the electron transfer mediator with glucose in the tear fluid sample and generate a current related to tear glucose concentration.  
     
     
         26 . The apparatus according to  claim 25 , wherein the processor determines a tear glucose concentration from the generated current and multiplies the tear glucose concentration by a calibration factor to determine the corresponding blood glucose concentration.  
     
     
         27 . The apparatus according to  claim 17 , further comprising a speaker in communication with the processor.  
     
     
         28 . The apparatus according to  claim 17 , wherein the apparatus is configured to allow the electronic transfer of glucose concentration data.