Retinal prostheses, which restore partial vision to patients blinded by outer
retinal degeneration, are currently in clinical trial. The Argus II
retinal prosthesis system was recently awarded CE approval for commercial use in Europe. While
retinal prosthesis users have achieved remarkable visual improvement to the point of reading letters and short sentences, the reading process is still fairly cumbersome. This study investigates the possibility of using an epiretinal
prosthesis to stimulate visual braille as a sensory substitution for reading written letters and words. The Argus II
retinal prosthesis system, used in this study, includes a 10 × 6
electrode array implanted epiretinally, a tiny video camera mounted on a pair of glasses, and a
wearable computer that processes the video and determines the stimulation current of each
electrode in real time. In the braille reading system, individual letters are created by a subset of dots from a 3 by 2 array of six dots. For the visual braille experiment, a grid of six
electrodes was chosen out of the 10 × 6 Argus II array. Groups of these
electrodes were then directly stimulated (bypassing the camera) to create visual percepts of individual braille letters. Experiments were performed in a single subject. Single letters were stimulated in an alternative forced choice (AFC) paradigm, and short 2-4-letter words were stimulated (one letter at a time) in an open-choice reading paradigm. The subject correctly identified 89% of single letters, 80% of 2-letter, 60% of 3-letter, and 70% of 4-letter words. This work suggests that text can successfully be stimulated and read as visual braille in
retinal prosthesis patients.