Study On Virtual Channel Electrical Stimulation Strategy Based On Different Retinal Ganglion Cell Population Models

Degenerative diseases of the retina may cause progressive apoptosis of photoreceptor cells,leading to progressive loss of vision and eventually,total blindness.Retinal prosthesis,one of the therapies already in use to treat such diseases,uses electrical stimulation to activate parts of the visual pathway that remain intact,allowing the blind to produce optical illusions,thereby restoring partial vision.However,the retina is a very complex structure.Limited by the size and number of electrodes,the number of phosphenes generated by the visual prosthesis and the resolution of the prosthesis vision are very limited at present,so patients with implants are still legally blind.Therefore,high resolution and wide field electrode array will be the main research direction in the future.Virtual channels can be created between simultaneously stimulated of adjacent electrode pairs to make the peak the superimposed electric field appear in the region between the electrodes,which can increase the resolution by adding new activation sites without increasing the number of physical electrodes.The thickness and the distribution and types of neurons vary greatly in different retina areas.In order to increase the area of retinal prosthesis,it is necessary to determine the optimal stimulation mode according to the electrical stimulation response in different areas of the retina.In this paper,a stratified model of the pericentral and peripheral regions of the retina was established.By means of simulation,we studied the potential distribution of different regions of retina under the stimulation of virtual channels,and observed the influence of the changes in electrode parameters on the potential distribution,so as to explore the conditions needed to generate the superimposed focused electric field.The study found that the smaller electrode size and the distance between the electrodes,and the larger electrode distance from the retina were more likely to produce the virtual channel phenomenon.We also found that under the same type of stimulation,the potential value of the pericentral region was generally higher than that of the peripheral region.We also established the ganglion cells population model of the pericentral and peripheral regions of the retina to simulate the activation in the retina under the stimulation of virtual channels,and compared the similarities and differences of the two regions.The results showed that although the activation threshold of the pericentral ganglion cells was generally lower than that of the peripheral neurons,the peripheral neurons were more easily activated when the stimulation current intensity was the same.When a fixed suprathreshold current stimulation was adopted and only the current ratio of the two electrodes was changed,the shape and areas of the activated region of the two regions remain relatively stable,while the activation center presents an s-shaped movement,that was,a controllable virtual channel was generated.Finally,by comparing the difference of the response between the two regions under different electrode parameters,and considering the current safety,we came to the conclusion that the pericentral area of the retina requires the electrode array of small size,electrode spacing,and electrode to retina distance,while the peripheral area requires the large electrode array with small electrode spacing and large electrode to retina distance.This study confirmed the possibility of virtual channel technology to improve the stimulation resolution of the prosthesis from the perspective of modeling,and pointed out that the different electrode configurations were needed in different areas of the retina,providing theoretical basis for the use of virtual channel and the production of wide-field electrodes in the future.