The Retina Implant AG is a sub-retinal chip placed in the central macular area behind the retina. Their chip works by converting light that enters the eye into electrical impulses which get fed into the optic nerve behind the eye. It requires an external battery which was connected to a cable that protruded from the skin behind the ear.
It's not ready for prime-time just yet and they're not the only ones working on a solution. The BBC notes that a rival chip by US-based Second Sight sits on top of the retina and has already been implanted in patients, but the Second Sight version requires the patient to be fitted with a camera fixed to a pair of glasses.
Citation: Eberhart Zrenner, Karl Ulrich Bartz-Schmidt, Heval Benav, Dorothea Besch, Anna Bruckmann, Veit-Peter Gabel, Florian Gekeler, Udo Greppmaier, Alex Harscher, Steffen Kibbel, Johannes Koch, Akos Kusnyerik, Tobias Peters, Katarina Stingl, Helmut Sachs, Alfred Stett, Peter Szurman, Barbara Wilhelm, and Robert Wilke, 'Subretinal electronic chips allow blind patients to read letters and combine them to words', Proc. R. Soc. B published online before print November 3, 2010, doi:10.1098/rspb.2010.1747 (free to read)