gms | German Medical Science

Objective: Over 8 million people suffer from retinitis pigmentosa and macular degeneration, leading to loss of photoreceptor function and blindness. Electronic retinal implants have been developed to restore visual function in these patients. The Alpha AMS implant developed in Tübingen has shown the best patient performance of any implant, however, patient performance still falls short of the widely accepted threshold for blindness of 20/200. One possibility for improvement is to selectively activate the ON and OFF information channels of the eye. Therefore, we are studying selective electrical activation of defined retinal ganglion cell (RGC) types.

Methods: We are testing both amplitude-modulated electrical pulse trains and varying pulse train frequencies (without amplitude modulation) for differential activation of the ON and OFF pathways. Such activation is examining in both blind and healthy mouse retina using a microelectrode array (MEA) to stimulate epi- and subretinally. While the MEA is used to record the action potentials of RGCs during epiretinal stimulation, sharp microwire, flexible MEA, and patch electrodes are used to record during subretinal stimulation. To explore signalling within network-mediated RGC responses, pharmacological inhibitors are applied. To characterize the stimulated ON and OFF RGCs, visual stimulation, presynaptic currents, and morphological classification are used.

Results: Although preliminary experiments have yet to yield differential activation, continued methods refinement holds promise.

Outlook: Recording from blind mouse retina mounted on the chip, it is our final goal to show selective activation of ON and OFF RGC types. Eventually, by proving that pathway-specific activation via the implant is possible, we hope to foster the development of new retinal implants that integrate the natural visual coding used in healthy eyes.

Acknowledgment: BMBF: 031 A 308; Tistou and Charlotte Kerstan Stiftung