People with diabetes often have to check their blood sugar using a drop of blood squeezed from a finger, thigh or some other part of the body. It's an unpleasant part of managing the disease, but when diabetes patients' insulin levels falter, their sugar levels don't just rise in the bloodstream. They rise in urine and tears, too.

Now, one researcher is working on creating contact lenses that are able to detect unusual blood sugar levels in the eyes, then change color in response.

Chemist Jun Hu at the University of Akron in Ohio is working on a contact lens coated with a chemical that reacts to glucose in the tears that naturally surround the eye. That chemical reaction makes the lens change color. "It works just like pH paper in your high school chemistry lab," Hu told his university

Patients are able to record their blood sugar by aiming a smartphone at their eyes and snapping a photo. Hu is also working on an app that can calculate and record a person's blood sugar using that cellphone picture.

Only one of the two contact lenses would contain the glucose-sensing chemical. The other lens would be a normal contact, so that the app can calculate the color difference between the two eyes to make its blood-sugar calculation. 

The lenses will only need small amounts of the color-changing chemical, so they should feel as comfortable as normal contact lenses in use today, Hu said. The low amounts of color shouldn't interfere with people's vision, he added. 

Hu has held a patent for his idea since 2011. He hopes contact lens eye-monitoring can replace blood-monitoring for some patients and help uncover others' prediabetes conditions.  

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