A model of ganglion axon pathways accounts for percepts elicited by retinal implants

Retinal prostheses, now implanted in over 250 patients worldwide, electrically stimulate surviving cells in order to evoke neuronal responses that are interpreted by the brain as visual percepts ( phosphenes). However, instead of seeing focal spots of light, current implant users perceive highly distorted phosphenes that vary in shape both across subjects and electrodes. We characterized these distortions by asking users of the Argus retinal prosthesis system (Second Sight Medical Products) to draw elicited percepts on a touchscreen. We found that phosphene shape could be accurately predicted by simulating the topographic organization of nerve fiber bundles in each subjects retina. Our model shows that activation of ganglion axons contributes to a rich repertoire of phosphene shapes, successfully replicating percepts ranging from blobs to oriented streaks and wedges depending on electrode location. This work provides a first step towards future devices that incorporate stimulation strategies tailored to each individual patients retinal neurophysiology.\n\nOne Sentence SummaryWe show that the perceptual experience of retinal implant users can be accurately predicted using a computational model that simulates the topographic organization of each individual patients retinal ganglion axon pathways.