The purpose of this study was to evaluate the efficacy and safety of artificial vision by using a direct optic nerve electrode (AV-DONE) in a blind patient with retinitis pigmentosa (RP). This device, comprising three wire electrodes (0.05 mm in diameter), was implanted into the optic disc of a patient with RP with no light perception vision and the device was left implanted. Six months later, visual sensations were elicited by electrical stimulation through each electrode and the thresholds for the phosphene perception elicited by pulses of 0.25-ms duration/phase and a pulse frequency of 320 Hz were 30, 5, and 70 microA for each electrode. The phosphenes, which ranged in size from that of a match head to an apple, were round, oval, or linear, primarily yellow, and focally distributed. The area of the phosphenes changed when the electrical stimulation was supplied from different electrodes. No complications arose during the follow-up period. Localized visual sensations were produced in a blind patient with advanced RP, suggesting that our system could lead to the development of a useful visual prosthesis system.

A visual prosthesis is an artificial sensory organ that transmits visual information to a blind person by electrically stimulating residual neurons in the visual nervous system. Such a system requires a large number of stimulating electrodes: It is technically difficult to connect a stimulator placed behind the ear to each of the stimulating electrodes over any significant distance with high reliability. We propose a visual prosthesis containing a multiplexer that is separately placed from the stimulator unit. The array of stimulating electrodes is connected to the stimulation unit through a multiplexer. The stimulating electrodes and multiplexer are placed onto the suprachoroidal space. The stimulation unit consists of a metal case and a coil and is implanted in the postauricular region of the cranium. The multiplexer and the stimulator unit are connected by a cable composed of six wires. Incorporating the multiplexer enables us to control of a large number of electrodes using a small number of conductors in the cable. We have developed a system with 100 electrodes which is powered and controlled wirelessly. Then we have confirmed that the proposed system functions successfully both in vitro and in vivo.