Tears of Joy for Diabetes Sufferers

The concept of glucose detection from human tears is nothing new. As far back as the 1950s, scientists have looked to tear fluid for the possibility of less invasive glucose monitoring. However, until now this seemed an impossibility.

According to the CDC, diabetes affects over eight percent of Americans. Those who suffer from this disease must constantly monitor their blood glucose levels at least once and sometimes multiple times a day. Currently the most reliable way to do this is to measure the levels directly by drawing blood. Using a lancet, the patient must prick his finger and place a drop of blood on a test strip to be inserted into the monitor. Pricking the finger or other parts of the hand can be very painful and can discourage patients from taking care of themselves, and it is cumbersome to carry all the necessary supplies. A tear based system would provide a less painful and more convenient alternative for diabetes sufferers. 

Although other types of monitors have been developed, none have proved reliable when compared to the invasive blood testing systems. The levels of glucose in tears, however, correlate closely to those measured in blood directly. Unfortunately, this presents a host of new challenges in device development. Because tears contain 30-50 times lower glucose concentrations, a tear glucose sensor must be able to detect very small amounts of glucose even in the presence of higher concentrations of other substances. It also must be able to accomplish this with a very small sample size, only a few microliters. This is just what scientists at the University of Michigan are attempting to create.

Capillary Tear Glucose Monitor Yan et al. Analytical Chemistry

In a study published in the November issue of Analytical Chemistry, Mark Meyerhoff and team described and tested a glucose monitor that required only four or five microliters of tear fluid. Using 12 rabbits, they compared the tear samples to blood samples collected at precisely the same time. Their results indicate that the device is not only selective for glucose in the sample, but also shows strong correlation to glucose levels of individual rabbit blood samples. Their work shows progress in the field, but several questions about marketable monitors remain. Luckily, they are not alone in this endeavor.

Since March of 2010, Jeffrey La Belle and his team at Arizona State University have published sequential studies regarding the development of another tear glucose monitor they call the TOUCH system. Their work takes into account ease of use and affordability in addition to the other requirements previously mentioned. With this work, the team wishes to develop a quick use device you could touch to the white of your eye for only five seconds and then insert into a detector. In the future, they look to improve the reproducibility of device above FDA standards and create a more user friendly version of the device.

TOUCH Glucose Sensor Lan et al. Journal of Diabetes and Technology

Tear glucose monitors could benefit the lives of millions of people.  Although they may never replace blood glucose monitors completely, they could serve as useful tools for day to day monitoring of glucose levels in a normal range. Some hurdles still remain in the road ahead. Cost of device manufacturing is crucial to success. Also, the devices will have to be able to function for those who use eye drops or wear contact lenses. Thanks to these two teams of scientists, the answers to those problems might not be far away.

Ref:

1.  Measurement of Tear Glucose Levels with Amperometric Glucose Biosensor/Capillary Tube  Configuration Qinyi Yan, Bo Peng, Gang Su, Bruce E. Cohan, Terry C. Major, and Mark E. Meyerhoff Analytical Chemistry 2011 83 (21), 8341-8346

2. Kenneth Lan, Kenyon McAferty, Pankti Shah, Erica Lieberman, Dharmendra R. Patel, Curtiss B. Cook, Jeffrey T. La Belle. (2011). A Disposable Tear Glucose Sensor- Part 3: Assessment of Enzymatic Specificity. Journal of Diabetes Science and Technology. 5(5). 1108-1115.

3. Daniel K. Bishop, Jeffrey T. La Belle, Stephen R. Vossler, Dharmendra R. Patel, and Curtiss B. Cook. (2010). A disposable tear glucose biosensor – part 1: design and concept testing. Journal Diabetes Science and Technology. 2:6, 299-306.

4. Jeffrey T. La Belle, Daniel K. Bishop, Stephen R. Vossler, Dharmendra R. Patel, and Curtiss B. Cook. (2010). A disposable tear glucose biosensor – part 2: system integration and model validation. Journal Diabetes Science and Technology. 2:6, 307-11.