Scientists have designed a smart contact lens to measure the wearer’s blood sugar without using a needle. So far, the needle-less prototype has only been tested in rabbits—and it’s not clear if it’s even possible to accurately monitor blood sugar using tears. But if it works, it would be a massive upgrade for people with diabetes.
The lens is made out of the same transparent, flexible material that’s in some soft contacts on the market. Inside, the researchers embedded electronics including a little LED light and a glucose sensor. If glucose levels rise above a certain level, the continuously lit LED light flickers off to alert the wearer, the researchers report today in the journal Science Advances.
The scientists, led by Jang-Ung Park at the Ulsan National Institute of Science and Technology in the Republic of Korea, tested the contact lens using artificial tears spiked with sugar to mimic the low glucose levels measured in tears by earlier studies. They also gave it a trial run in rabbits: The LED stayed on until the researchers squirted a glucose solution into the rabbit’s eye—and then the LED turned off, just like it’s supposed to. So far, it hasn’t been tested in humans or with human tears, however.
The device is the latest attempt to develop a needle-less blood sugar monitor for diabetics. Building the circuitry on a flexible contact lens is impressive, says John L. Smith, former chief scientific officer of Johnson & Johnson’s glucose monitoring division and author of The Pursuit of Noninvasive Glucose: Hunting the Deceitful Turkey. But the glucose readings from tears just don’t reflect the levels in blood reliably enough to guide treatment decisions for people with diabetes, he says. “It’s an unreliable measure of blood glucose,” Smith says. “And that’s something you have to measure with great reliability or you will expose people to harm.”
More than 30 million Americans have some form of diabetes, a group of diseases that result in too much sugar, or glucose, in the blood. To keep their blood sugar from spiking or dropping to dangerous levels, people with diabetes have to watch what they eat and sometimes inject themselves with insulin. That’s why accurate blood sugar readings are key. “People with diabetes are betting their life on that measurement,” Smith says.
Currently, the two main methods involve drawing blood by pricking a finger or inserting a needle under the skin to measure the glucose in the fluid between cells. Both can be unpleasant, which is why companies have been chasing a needle-less blood sugar monitor for decades. Many have tried—including Google. But its attempt to develop a glucose-sensing contact lens so far hasn’t seen the light of day.
Smith says that the levels of glucose in tears just don’t track closely enough with levels of glucose in the blood to be used for monitoring. A paper from the 1980s backs that up: after testing 100 patients, “no significant correlation was found between the glucose level of blood and tears,” the study reports. “This is a very, very difficult problem,” Smith says. The team behind today’s study is working with a hospital to start clinical trials, according to an emailed statement. But until we know more about how well this new contact lens works in humans, the quest for a needle-less glucose monitor continues.