From the BBC:

Researchers at Stanford University have invented a retinal implant that is powered by light.  The previous implant I wrote about had to have a battery on the outside of the head.  This version requires the patient to wear a pair of special video-glasses, which concentrate the light and send it into the eye, because natural light is 1000 times too weak to power the implant.

The precursor to Geordi’s visor from Star Trek perhaps?

(Yes, I know it doesn’t work quite the same, but we have to get there in small steps!)