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.

SUMMARY This study focuses on the design of electrical stimulator for retinal prosthesis. The stimulator must be designed such that the occurrence of electrolysis or any irreversible process in the electrodes and flexible lead is prevented in order to achieve safe stimulation over long periods using the large number of electrodes. Some types of biphasic current pulse circuits, charge balance circuits, and AC power delivery circuits were developed to address this issue. Electronic circuitry must be introduced in the stimulator to achieve the large number of electrodes required to obtain high quality of vision. The concept of a smart electrode, in which a microchip is embedded inside an electrode, is presented for future retinal prostheses with over 1000 electrodes.

Implantable retinal prostheses are stimulation devices used to compensate for the light sensitivity loss of retinal cells. In this study, we propose and demonstrate a novel method to significantly reduce the setting time for the stimulation conditions of a retinal prosthesis chip capable of multi-electrode stimulation. The efficiency of the control method is increased while using only two wires, as in our previous work. The chip comprises an 8 bit ID and 7 electrodes, and the stimulation current value can be set from 50 to 1550 μA. The fabricated chip requires only 32 pulses to set the stimulation conditions, which is approximately 1/65 of that of our previous chip. Furthermore, it is equipped with a complementary metal–oxide–semiconductor rectifier to enable it to be driven by a rectangular AC power supply. The effectiveness of the chip is demonstrated by setting the stimulation conditions at approximately 18 μs per electrode at a clock frequency of 2.3 MHz.