For blind subjects with retina degenerative diseases (especially: retinitis pigmentosa and macular degeneration) to regain visual perception, a team of 14 expert groups develops a partially implantable, learning visual prosthesis (retina implant). This team with experts from several biological, medical, and technological areas is supported by the German research ministry (BMBF) and is coordinated by the author. Retina implants consist of a learning retina encoder (RE)-to be mounted on a frame of glasses or embedded in a contact lens-for the approximate simulation of parts of the retina by transforming light patterns into impulse trains similar to the receptive field properties of ganglion cells, a microcontact foil as retina stimulator (RS) to be implanted adjacent to the ganglion cell layer, and a wireless signal- and energy transmission between RE and RS. The function of the various spatiotemporal filters of the RE, which is being implemented by learning neural nets, will be tuned individually in a dialog with the implant-carrying subject for optimal visual perception. The development and successful test of retina implant prototypes in animals is expected at the end of the first 4-years research phase in 1999. In a subsequent research phase with participation from industry, the next step for adaptation of the retina implant system for application in humans and first trial tests with a small number of volunteers will follow It is expected that implant-carrying subjects will be able to recognize position and 'gestalt' of larger objects (e.g. window, door, chair, table) based on RE and RS with about 500 microcontacts in connexion with retinal ganglion cells, and that they will be able to walk and orient themselves without help in most unknown environments. This hope is partly based on recent findings that simple gestalt perceptions could already be elicited in several blind subjects by temporary microstimulation of retinal ganglion cells. Furthermore, anatomical studies have recently shown that a significant portion of the ganglion cells and the optic nerve in this group of blind subjects remain intact, even though the layer of photoreceptors is degenerated.
