Development of retinal prosthesis module for fully implantable retinal prosthesis

To restore visual sensation of blind patients, we have proposed a fully implantable retinal prosthesis comprising an three dimensionally (3D) stacked retinal chip for transforming optical signal to electrical signal, a flexible cable with stimulus electrode array for stimulating retina cells, and coupling coils for power transmission. For realizing the fully implantable retinal prosthesis, we developed a key component of retinal prosthesis module comprising a retinal prosthesis chip and a flexible cable with stimulus electrode array. In this study, we used a 2D retinal chip as a prototype retinal prosthesis chip. We fabricated a polyimide-based flexible cable of 20μm thickness with 16 channels Pt stimulus electrode array. The retinal prosthesis chip was mounted on the flexible cable and encapsulated by a silicone to protect from corrosive environments in an eyeball. Then, the retinal prosthesis module was completely implanted into an eyeball of a rabbit. We successfully recorded the waveforms of electrically evoked potential (EEP) elicited from the rabbit brain by the current stimulation supplied from the implanted retinal prosthesis module for the first time. EEP amplitudes were proportionally increased according to illumination intensity and irradiation time of the incident light. It means that the rabbit would recognize the change of optical signal by changing the frequency of stimulus current pulse through the implanted retinal chip.