The viability of using tears to measure glucose is still in relatively early stages of investigation.
Existing continuous glucose sensors embedded below the skin face similar questions about accuracy in measuring glucose levels. If a person's blood glucose level is rising, it might take 20 to 30 minutes for the subcutaneous glucose to reach the same level, according to Dr. Al Powers, director of the Vanderbilt Diabetes Center in Nashville
“The first thing you have to measure and determine is if the glucose level correlates and what's the lag time,” Powers said.
If the glucose measured in tears is indeed found to be a reliable metric for measuring glucose in the blood, Ratner cautions that there are still other practical concerns to be addressed, such as how often the lens would need to be replaced or if it could be worn overnight.
“We know routine contact lenses have some limitations about sleeping in them,” he said.
Despite all the unknowns, Ratner called Google's latest development “a highly innovative approach that could become very important,” particularly because 25.8 million people in the U.S., or 8.3% of the population, have diabetes. Worldwide, the International Diabetes Federation estimates that 1 in 10 will have diabetes by 2035.
Google announced Jan. 16 that it is testing a “smart” contact lens that isn't designed to improve vision, but to help people with diabetes monitor their glucose levels.
Google has completed multiple clinical studies, but is still testing prototypes and having discussions with the Food and Drug Administration. It is also looking into other features, including LED warning lights that would alert wearers when their glucose levels are too high or too low.
Using a tiny sensor and a wireless chip to transmit readings to an external device, the lens would capture tears and measure glucose in the optical fluid—possibly in a continuous fashion. The prototype that Google is testing is one that would generate a reading once per second, enabling people to better monitor and respond to changes in their glucose levels.
The technology has the potential, according to a blog posted by Google, to replace the need for diabetics to prick their fingers in order to test their blood glucose levels. For some, that could mean eliminating 15 tests a day, Ratner said.
Follow Rachel Landen on Twitter: @MHrlanden