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

Abstract 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 subject’s 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 patient’s retinal neurophysiology. One Sentence Summary We 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 patient’s retinal ganglion axon pathways.