Tony Quan, better known as TemptOne, was a fixture of the L.A. graffiti and politcal-activism scene before he was diagnosed with ALS in 2003. The disease quickly rendered him unable to move anything except his eyes. In the intervening years, the disease has ended his days of graffiti writing--but he's tagging again, thanks to a new invention, the Eyewriter.
The device was developed by Free Art and Technology, OpenFrameworks, and Graffiti Resarch Lab, which are all part of the burgeoning hactivist scene. It combines eye-tracking hardware and GRO's famed L.A.S.E.R. tagging system, which uses a laser pointer and an LED projector to create virtual graffiti as big as a building. (Check out this video of baffled cops encountering L.A.S.E.R. and trying unsuccessfully to get the writers to stop.)
As Infosthetics points out, if you check out side by side pictures of Quan's writing before and after the Eyewriter, it's amazing that basically nothing was lost in translation:
True to the hacktivist spirit of its creators, the Eyewriter is an open-source project, and the technical details are open to anyone who wants to get involved. Of course, the applications are broader than graffiti--Eyewriter is meant to provide a creative outlet to anyone who is disabled.