The boston retinal prosthesis: A 15-channel hermetic wireless neural stimulator

A miniaturized, hermetically-encased, wirelessly-operated retinal prosthesis has been developed for pre-clinical studies in Yucatan minipig animal models. The prosthesis attaches conformally to the outside of the eye and drives a microfabricated thin-film polyimide stimulating electrode array with sputtered iridium oxide electrodes. This array is implanted in the subretinal space using a specially-designed ab externo surgical technique that uses the retina to hold the array in place while leaving the bulk of the prosthesis outside the eye. The implanted device includes a hermetic titanium case containing a 15-channel stimulator chip and discrete circuit components. Feedthroughs from the case connect to secondary power- and data-receiving coils. In addition, long-term in vitro pulse testing was performed on the electrodes to ensure that their lifetime would match that of the hermetic case. The final assembly was tested in vitro to verify wireless operation of the system in biological saline using a custom RF transmitter circuit and primary coils. Stimulation pulse strength, duration and frequency were programmed wirelessly using a custom graphical user interface. Operation of the retinal implant has been verified in vivo in two pigs for up to five and a half months by measuring stimulus artifact on the eye surface using a contact lens electrode.