Abstract
We are developing a chronically implantable wireless subretinal prosthesis in hopes of restoring a useful level of vision to patients who are blind with outer retinal degenerations such as retinitis pigmentosa or macular degeneration. The receiver is attached to the outer wall of the sclera, with only a 10 um thick electrode array penetrating the sclera and lying in the subretinal space. The physical bulk of the implant lies in the ocular orbit, and the majority of the heat is released there, away from the delicate retina. Power and data are transmitted to the device by RF: power at 125 KHz and data at 13.56 MHz. The microchip for communication and stimulation has been fabricated and works as expected: the initial version can drive 15 electrodes. The design, testing and some construction steps for the implant were carried out in-house, including fabrication of the microelectrode arrays and an early version of the flexible substrate, test system development, design and testing of the chip, transmitter design and construction, paralyene encapsulation and soak testing. Processes sourced out to vendors include coil winding, flip-chip and wire bonding to the substrate, fabrication of the chip and later versions of the polyimide flexible substrate, teflon encapsulation and iridium oxide deposition on the electrodes. The prototype has the functionality, dimensions and mechanical properties required for a human subretinal prosthesis. We plan to implant chronically in Yucatan mini-pig and record the cortical response to wireless stimulation in the Fall of 2005.