For the development of a retinal implant

A partial vision is expected to be restored in patients with retinal degeneration diseases using a retinal implant which is designed to stimulate electrically the survived neurons. A silicon retina emulating a function of the retinal circuit was developed for an image processing unit of retinal implant. In order to design an electrode of the retinal implant, physiological experiments were conducted to elucidate spatio-temporal properties of ganglion cell responses to transretinal current stimuli in the frog retina, Two typical classes of response were induced by the stimuli. One showed relatively constant latency of 1.5 to 4.5 msec with respect to the current amplitude and another showed a variable latency. The threshold of charge of the induced responses ranged 10 to 50nC. In most cases the current stimuli used in this study excited ganglion cells in a local I area. The ganglion cells at about 300 mum from the stimulation site were initiated by a probability of 50% when the retina was stimulated by a charge of 10nC.