Implants for Epiretinal Stimulation of Retinitis Pigmentosa Patients

This work reports upon the development of a wireless epiretinal implant system (EPI-RET-3) to restore vision by stimulating the retinal ganglion cells of blind Retinitis Pigmentosa (RP) patients. This prosthesis is completely implanted into the eye of the patients. Data and energy are provided by inductive coupling at 13.56 MHz. As a flexible substrate for the electronic components a polyimide tape was used. The electronic parts of the implant include a planar integrated receiver coil, three-dimensional stimulation electrodes and CMOS based microchips for receiving and stimulation. The systems were implanted into 16 mini pigs to proof the safety. After the explantation a carefully analysis was performed on the explanted systems and eyes. No indication for complications was found. One system was left in a mini pig and is still working after more than two years. After these pre-studies the system was implanted into six legally blind patients for four weeks. All patients reported on visual sensations, evoked by electrical stimulation of their retina. The required stimulation thresholds were found to be very low. Implantation and explantation surgery were performed without complications. The implant was well tolerated for the duration of four weeks.