Model-based Stimulation Analysis On Epiretinal Electrical Stimulation Of Virtual Channels

A retinal prosthesis is a promising approach in the region of visual restoration.It assists subjects in obtaining prosthetic visual perceptions by using its implanted electrodes stimulating subjects’ remaining functional intact visual pathways.Nowadays,with the limited number of prosthesis electrodes,subjects can only perceive low-resolution visual perceptions,struggling to recognize complex objects.The virtual channel strategy is a promising approach to better prosthetic vision perception.In this thesis,a novel complex shape electrode array was designed,in which each electrode unit is comprised by a disk electrode and a ring electrode.Simulation results showed that the proposed electrode array could generate virtual channels by stimulating adjacent electrodes.On the basis of this,the number of phosphenes generated by electrode array increased,resulting in a better prosthetic vision acuity.The research process shows as follows: Firstly,the epiretinal stimulation model was built in COMSOL,simulating the spatial distribution of electric field under different stimulation conditions to investigate the conditions for the formation of virtual channels.After that,a complex shape electrode array was designed according to simulation results.Secondly,different types of retinal ganglion cell models were built in NEURON.After investigating responses of all types of ganglion cells,the multi-ganglion cells model in the macular region was established in NEURON.Thirdly,COMSOL and NEURON were linked by exporting electric field data to NEURON to investigate the response of ganglion cells under epiretinal stimulation.According to simulation results,electric fields with good electrical stimulation localization were formed by stimulating adjacent disk electrodes simultaneously,and virtual channels emerged between adjacent stimulating ring electrodes when they were stimulated at the same time.Additionally,the quasi-monopolar stimulation strategy was adopted in this thesis to further elevate electrodes’ stimulation localization.Finally,based on human’s visual staying phenomenon,to better prosthetic vision perception,a bold time sharing electrode array stimulation strategy was proposed,in which alternatively stimulating disk electrodes and ring electrodes to improve prosthetic vision perception.