Learning Retina Implants with Epiretinal Contacts

Abstract

Retina implants are currently being developed by several interdisciplinary research consortia worldwide for blind humans with various retinal degenerative diseases. It is the aim of our retina implant project to develop a novel type of visual prosthesis to regain a moderate amount of vision such as perception of location and shape of large objects in the first stage and to approach reading quality in a subsequent stage. In our planned retina implant, a retina encoder (RE) outside the eye has to replace the information processing of the retina. A retina stimulator (RS), implanted adjacently to the retinal ganglion cell layer, has to contact a sufficient number of retinal ganglion cells/fibers for electrical elicitation of spikes. A wireless signal and energy transmission system has to provide the communication between the RE and RS. This paper outlines the retina implant project of our consortium of 14 expert groups and describes first results of the learning RE. The RE approximates the typical receptive field (RF) properties of primate retinal ganglion cells by means of individually tunable spatiotemporal RF filters. The RE as a cluster of RF filters maps visual patterns onto spike trains for a number of contacted ganglion cells. A concept is presented to train the individual RF filters in an unsupervised learning process, which employs neural networks in a dialog with the individual human subject. The desired aim of this dialog is an optimization of the visual perception by matching the various RF filter properties with those ‘expected’ by the central visual system for each contacted ganglion cell.

High-Resolution Electrical Stimulation of Primate Retina for Epiretinal Implant Design

“…These considerations raise a more general question: how can the ϳ20 different ganglion cell types in primate retina be differentially activated to produce a natural visual signal in the optic nerve? A possible approach may include tunable retinal encoders that are trained in a learning process involving feedback from the human subject (Eckmiller, 1997). In this perception-based iterative tuning procedure, each cell will be stimulated as required to produce the desired visual percept.…”

New Trends and Challenges in the Development of Microfabricated Probes for Recording and Stimulating of Excitable Cells

“…In the end of the 1980s, several North American, Australian and European teams (Eckmiller (1997)) started developing retinal prostheses. Notably, these are the groups of M. Humayun (John Hopkins University) (Schmidt et al (1996)) and that of J. Rizzo (Harvard University) (Rizzo et al (2003)) in association with the Massachusetts Institute of Technology, which develop epiretinal implants.…”

Status of the feline retina 5 years after subretinal implantation

“…Two main approaches exist: the epiretinal approach in which the implant is placed on the vitreal side of the retina [6] and the subretinal approach in which the implant replaces degenerated photoreceptors [7][8]. The epiretinal approach involves stimulation of the nerve fiber layer with electrodes that receive input from an external camera [6,[9][10][11]. Alternatively, the subretinal approach activates outer retinal layers with microphotodiodes that respond to incident light in a graded fashion [12][13] or microelectrodes that are externally powered [14][15].…”