Each day, millions of diabetics across the world prick their fingers several times to check their blood glucose levels. Measuring glucose concentrations in tears may provide a noninvasive option for accomplishing the same objective, although it would likely need to be supplemented with some degree of blood measurement. “We are not suggesting that it is a replacement for blood glucose measurements. It could help in the monitoring of blood glucose by decreasing the number of blood finger pricks that a person with type 1 diabetes has to do,” says Mark Meyerhoff, PhD, a professor of chemistry at the University of Michigan (Ann Arbor, MI) who coauthored a paper titled “Measurement of Tear Glucose Levels with Amperometric Glucose Biosensor/Capillary Tube Configuration” published in November in 2011 in Analytical Chemistry. “Instead of measuring your blood glucose, say, seven or eight a day, you might do three a day of blood and four of tear.” More research, however, needs to be done to determine the feasibility of using of the technology, he says.
Many factors affect the blood glucose levels in tears and the level of glucose found in tears is likely to be individual and variable. Meyerhoff and a number of other researchers reported a correlation of blood and tear glucose in anesthetized rabbits in their research. “The ratio was different from animal to animal, and probably the same is true in humans,” he says. Also complicating matters is that the ratio may change as a result of environment conditions or scratches to the eye’s surface. “You have to be trained to [obtain tear samples] in a way where you don’t scratch the eye. If you have any blood, then the levels are, of course, very different,” Meyerhoff says.
Although tear measurement might not replace blood glucose measurement, even substantially reducing the number of finger sticks required to monitor glucose levels would be a significant breakthrough. Meyerhoff and fellow researchers are working to develop a simple electrochemical sensor that can accurately detect glucose in small tear volumes. Such a system also has to be capable of detecting minute concentrations of glucose, as the concentrations of tear glucose are much lower than they are in the blood. “Whereas blood glucose on normal is 5 millimolar, tear glucose might be only 50 micromolar or maybe even less in some cases,” Meyerhoff says. In research on rabbits, he and his colleagues used volumes of tear fluid measuring several microliters. “Since that time, we have improved things and we are now down to measuring in a half a microliter or a [single] microliter of volume,” he says. “Those are closer to the volumes that we need for humans and we have done some studies on rabbits that way and we see a correlation and we are getting geared up to potentially do some human testing,” he says.
Meyerhoff’s research group is partnering with EyeLab Group LLC (Ann Arbor, MI) to advance the research. “They are moving forward and excited about at least seeing what the correlations are once we get to humans.”
Meyerhoff was named on a patent titled “Methods and Systems for Measurement of Tear Glucose Levels” that was approved by the U.S. Patent Office awarded on January 10, 2013.