Researcher use a micro-LED in a blood sugar level contact lens.

Researchers from Korea's Ulsan National Institute of Science and Technology (UNIST) and Sungkyunkwan University contact lenses that has an ultra-sensitive blood glucose sensor that analyze tears.

To the wearer, the contact lens appear like regular ones, but when the sensor detects fluctuations in the blood glucose level, it lights up the chipset and an embedded micro-LED that stays lit if the blood glucose level is normal, so the wearer understand his blood levels. The contact lens are powered by wirelessly transmitted electricity.

Source: Korea Biz Wire