A Comparative Study On Electrical Response Characteristics Of Ganglion Cells In Distinct Retinal Areas By Simulation Modeling

Retinal degenerative diseases such as retinitis pigmentosa and age-related macular degeneration are major cause of permanent vision loss,and there is still no effective cure at this stage.As an implantable micro-electronic device,visual prosthesis can be used to repair part of the visual function of the blind,and has made important progress.Among them,the epi-retinal prosthesis is the most rapidly developing type of visual prosthesis.However,because the electrode array of the prosthesis on the retina can only cover a limited field of vision and the number of electrodes is limited,the restoration effect is still far from the normal human vision.Electrode arrays with large coverage field of view and high density electrodes will be one of the major trends in the development of epi-retina prostheses.Moreover,the number of retinal ganglion cells(RGC)and retinal layer thickness change with the increase of retinal fovea eccentricity,different retinal regions may show different response characteristics to electrical stimulation,which presents a new challenge to the design of large-size and high-density electrode arrays.Therefore,based on the morphological parameters of human and primate retina,an electrical stimulation model of epi-retinal prosthesis with different RGC density distribution and different layer thickness was established in this study.The method of potential distribution and activation function(AF)generated by stimulation electrodes was introduced to analyze the response of rgc in two regions to various electrical stimulation.In the single electrode stimulation model,it was found that the difference of RGC population thresholds in different retinal regions was mainly determined by cell density.And change of the diameters of the electrode and the electrode retina distances,the number of responsed RGC in the central retinal area is large than the peripheral area at the same threshold times of current intensity stimulation.The short electrode retina distance electrical stimulation of the small electrode can easily cause the distal axonal response of peripheral area,thus making the patient 's visual perception deformation.Therefore,this study proposed a design idea to appropriately increase the size of the electrode in the peripheral region of the retina,which can not only ensure the tissue safety of the peripheral region of the retina and sufficient number of neuron activation,but also reduce the possibility of activation of the distal axons in the peripheral retina.In addition,the response characteristics of RGC population at different electrode sizes,electrode spacing and electrode retina distances in the central and peripheral areas of retina were studied under synchronous electrical stimulation with two electrodes,in order to provide a theoretical basis for current steering technology.It is found that for the central area of the retina,when the distance between electrodes is larger and the electrodes retina distance is close,the RGC response induced by simultaneous stimulation of two electrodes is more diffuse,while the peripheral retina does not induce the divergence of the RGC response.It is shown that in the design of the peripheral retinal electrode array,the appropriate increase in electrode spacing may still get a more concentrated population response.The results of this study will provide a theoretical reference for optimizing the electrode array and improving the spatial resolution of the epiretinal prosthesis.