The prototype, which Google says will take at least five years to reach consumers, is one of several medical devices being designed by companies to make glucose monitoring for diabetic patients more convenient and less invasive than the traditional finger pricks.
The lenses use a minuscule glucose sensor and a wireless transmitter to help those among the world's 382 million diabetics who need insulin keep a close watch on their blood sugar and adjust their dose.
The contact lenses were developed during the past 18 months in the clandestine Google X lab that also came up with a driverless car, Google's Web-surfing eyeglasses and Project Loon, a network of large balloons designed to beam the Internet to unwired places.
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