Stanford’s Group of BioMedical Physics and Ophthalmic Technologies has developed a new type of retinal prosthesis:
We observed a fascinating effect of migration of retinal cells into the perforated sub-retinal implant. Within a few days after implantation neural retinal cells migrate into the pores where stimulating electrodes can be positioned, while preserving their axonal connections to the retina above the implant. In this way an intimate proximity between electrodes and target cells is achieved automatically along the whole surface of the implant.
The effect of cellular migration can also be utilized with an implant having an array of thin protruding electrodes insulated at their sides and exposed at the tops. When positioned under the retina, the cells migrate into the spaces between the pillars thus assuring penetration of the electrodes into the retina without high pressure and associated risk of mechanical injury. The depth of penetration is determined by the length of the electrodes. The approaches based on pores and on protruding electrodes are complimentary: in the first case the actively migrating cells penetrating into the pores will be stimulated. In the second case the actively migrating cells move towards the bottom of an implant, while the electrodes approach the target cells which did not migrate.
We are developing an optical system for a parallel delivery of information and energy to tens of thousands of pixels in the implant. This system permits normal eye scanning to observe a large field of view, as opposed to “hard wiring” of a video camera to the retinal stimulating array using a single emitter-receiver link. The image from a goggles-mounted video camera is processed in a portable microcomputer and then projected with a pulsed IR LED-LCD array onto the retina. The retinal implant has an array of powered photodiodes converting pulses of light into pulsed electrical current using power from an intraocular photovoltaic battery.