title: 3D finite element modeling of epiretinal stimulation: Impact of prosthetic electrode size and distance from the retina.
abstract: OBJECTIVE
  A novel 3-dimensional (3D) finite element model was established to systematically investigate the impact of the diameter (Φ) of disc electrodes and the electrode-to-retina distance on the effectiveness of stimulation.
  
  
  METHODS
  The 3D finite element model was established based on a disc platinum stimulating electrode and a 6-layered retinal structure. The ground electrode was placed in the extraocular space in direct attachment with sclera and treated as a distant return electrode. An established criterion of electric-field strength of 1000 Vm-1 was adopted as the activation threshold for RGCs.
  
  
  RESULTS
  The threshold current (TC) increased linearly with increasing Φ and electrode-to-retina distance and remained almost unchanged with further increases in diameter. However, the threshold charge density (TCD) increased dramatically with decreasing electrode diameter. TCD exceeded the electrode safety limit for an electrode diameter of 50 µm at an electrode-to-retina distance of 50 to 200 μm. The electric field distributions illustrated that smaller electrode diameters and shorter electrode-to-retina distances were preferred due to more localized excitation of RGC area under stimulation of different threshold currents in terms of varied electrode size and electrode-to-retina distances. Under the condition of same-amplitude current stimulation, a large electrode exhibited an improved potential spatial selectivity at large electrode-to-retina distances.
  
  
  CONCLUSIONS
  Modeling results were consistent with those reported in animal electrophysiological experiments and clinical trials, validating the 3D finite element model of epiretinal stimulation. The computational model proved to be useful in optimizing the design of an epiretinal stimulating electrode for prosthesis.
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Sui
authors.forename: Yu
authors.initials: Y
authors.lastname: Huang
authors.forename: Fuchen
authors.initials: F
authors.lastname: Feng
authors.forename: Chenhui
authors.initials: C
authors.lastname: Huang
authors.forename: Leanne Lai Hang
authors.initials: LL
authors.lastname: Chan
authors.forename: Guoxing
authors.initials: G
authors.lastname: Wang
mesh_terms: D000818:Animals; D004599:Electric Stimulation Therapy; D020342:Finite Element Analysis; D008839:Microelectrodes; D008962:Models, Theoretical; D012160:Retina; D057488:Visual Prosthesis