title: Effects of different three-dimensional electrodes on epiretinal electrical stimulation by modeling analysis.
abstract: BACKGROUND
  Epiretinal prostheses have been greatly successful in helping restore the vision of patients blinded by retinal degenerative diseases. The design of stimulating electrodes plays a crucial role in the performance of epiretinal prostheses. The objective of this study was to investigate, through computational modeling analysis, the effects on the excitation of retinal ganglion cells (RGCs) when different three-dimensional (3-D) electrodes were placed in the epiretinal space.
  
  
  METHODS
  3-D finite element models of retinal electrical stimulation were created in COMSOL using a platinum microelectrode, a vitreous body, multi-layered retinal tissue, and retinal pigment epithelium (RPE). Disk and non-planar electrodes with different 3-D structures were used in the epiretinal electrical stimulation. In addition, a multi-RGC model including ionic mechanisms was constructed in NEURON to study the excitability of RGCs in response to epiretinal electrical stimulation by different types of electrodes. Threshold current, threshold charge density, and the activated RGC area were the three key factors used to evaluate the stimulating electrode's performance.
  
  
  RESULTS
  As the electrode-retina distance increased, both threshold current and threshold charge density showed an approximately linear relationship. Increasing the disk electrode's diameter resulted in an increase in threshold current and a decrease in threshold charge density. Non-planar electrodes evoked different activation responses in RGCs than the disk electrode. Concave electrodes produced superior stimulation localization and electrode safety while convex electrodes performed relatively poorly.
  
  
  CONCLUSIONS
  Investigation of epiretinal electrical stimulation using different 3-D electrodes would further the optimization of electrode design and help improve the performance of epiretinal prostheses. The combination of finite element analysis in COMSOL and NEURON software provides an efficient way to evaluate the influences of various 3-D electrodes on epiretinal electrical stimulation. Non-planar electrodes had larger threshold currents than disk electrodes. Of the five types of electrodes, concave hemispherical electrodes may be the ideal option, considering their superior stimulation localization and electrode safety.
authors: School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China. caoxun@sjtu.edu.cn.
authors: Xun
authors: X
authors: Cao
authors: School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China. suixhong@sjtu.edu.cn.
authors: Xiaohong
authors: X
authors: Sui
authors: School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China. lqai0828@sjtu.edu.cn.
authors: Qing
authors: Q
authors: Lyu
authors: School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China. lilm@sjtu.edu.cn.
authors: Liming
authors: L
authors: Li
authors: School of Biomedical Engineering, Shanghai Jiao Tong University, No.800 Dongchuan Road, Shanghai, People's Republic of China. xychai@sjtu.edu.cn.
authors: Xinyu
authors: X
authors: Chai
mesh_terms: D000465:Algorithms; D003198:Computer Simulation; D004599:Electric Stimulation Therapy / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods*; D004566:Electrodes / Q000009:adverse effects; D020342:Finite Element Analysis; D006801:Humans; D008564:Membrane Potentials; D008959:Models, Neurological; D008962:Models, Theoretical; D058117:Neural Prostheses; D011474:Prosthesis Design; D012160:Retina / Q000033:anatomy & histology; D012165:Retinal Ganglion Cells / Q000502:physiology