Characteristics Of Retinal Ganglion Cells Of Mice In Response To Current Steering Stimulation

Retinal degeneration diseases can lead to the disappearance of outer retina,making it difficult to help patients restore vision through medicine and surgery.Visual prostheses is a research hotspot to treat such diseases.It can convert the images acquired in external environment into certain pattern of electric signals,which are transmitted to the electrodes implanted in the visual pathway.By electrically stimulating the undamaged tissues in visual pathway with different functions,patients can obtain visual perception.Retinal prostheses are the most rapidly developing way for treating retinal degeneration diseases.Compared with the large number of neurons with different types that can form complex neural network in retina,the limited electrodes in visual prostheses,however,are difficult to provide a matching amount of information.Thus,the artificial vision is in low resolution.Current steering is a field-shaping technology.By simultaneously stimulating with two neighboring electrodes,an additional perception channel called virtual channel can be generated between the electrodes,which effectively improves the number of stimulating channels without increasing the number of physical electrodes.Although there have been preliminary studies on applying current steering strategy to visual prostheses,it is still unknown whether retinal ganglion cells can be regulated by current steering stimulation and its underlying mechanisms.In this paper,computational model and animal experiment were used to study the characteristics of retina in response to current steering stimulation.In modeling part,normal and degenerated retinal model were established in COMSOL.Electric field distribution of different retinal layers under current steering stimulation was studied in the mode of subretinal stimulation.Optimized configuration and parameters of electrodes for generating focal electric field in target region were also explored.Simulating results show that using current steering can successfully form focal electric filed.Setting proper return electrode,reducing diameter and shortening distance between electrodes can make the electric field more focused,which is beneficial to generate converged virtual channels.In animal experiment,we used the same stimulating mode as that in modeling research.According to modeling results the return electrode was placed in the lateral position of the retina.Subretinal stimulation was performed using a pair of electrodes and response of retinal ganglion cell was recorded by a multi-electrode array.Firstly,current threshold of cells stimulated by each electrode was measured.Then,response of retinal ganglion cells was studied by changing total current delivered equally to two electrodes in current steering mode.Finally the response characteristics of retinal ganglion cells were explored by changing current ratio between the electrodes.Results show that current threshold is influenced by relative position between cell and stimulating electrodes.Threshold increases with the relative distance rising.Changing total current and ratio can affect the activation and firing rate of retinal ganglion cells.Compared to monopolar stimulation,current steering can reduce the threshold.We also find electrical stimulation can significantly increase the light response and spontaneous activity of retinal ganglion cells.In this study,the same stimulation mode was used in computational model and animal experiment.The regulation of current steering on retina was studied theoretically and experimentally,which provided theoretical and experimental basis for the better application of current steering strategy in visual prostheses.