title: Approaches to a cortical vision prosthesis: implications of electrode size and placement.
abstract: OBJECTIVE
  In order to move forward with the development of a cortical vision prosthesis, the critical issues in the field must be identified.
  
  
  METHODS
  To begin this process, we performed a brief review of several different cortical and retinal stimulation techniques that can be used to restore vision.
  
  
  RESULTS
  Intracortical microelectrodes and epicortical macroelectrodes have been evaluated as the basis of a vision prosthesis. We concluded that an important knowledge gap necessitates an experimental in vivo performance evaluation of microelectrodes placed on the surface of the visual cortex. A comparison of the level of vision restored by intracortical versus epicortical microstimulation is necessary. Because foveal representation in the primary visual cortex involves more cortical columns per degree of visual field than does peripheral vision, restoration of foveal vision may require a large number of closely spaced microelectrodes. Based on previous studies of epicortical macrostimulation, it is possible that stimulation via surface microelectrodes could produce a lower spatial resolution, making them better suited for restoring peripheral vision.
  
  
  CONCLUSIONS
  The validation of epicortical microstimulation in addition to the comparison of epicortical and intracortical approaches for vision restoration will fill an important knowledge gap and may have important implications for surgical strategies and device longevity. It is possible that the best approach to vision restoration will utilize both epicortical and intracortical microstimulation approaches, applying them appropriately to different visual representations in the primary visual cortex.
authors.affiliation: School of Biological and Health Systems Engineering, Arizona State University, Tempe AZ, USA.
authors.forename: Breanne P
authors.initials: BP
authors.lastname: Christie
authors.forename: Kari R
authors.initials: KR
authors.lastname: Ashmont
authors.forename: Paul A
authors.initials: PA
authors.lastname: House
authors.forename: Bradley
authors.initials: B
authors.lastname: Greger
mesh_terms: D000818:Animals; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods; D004567:Electrodes, Implanted / Q000639:trends; D005074:Evoked Potentials, Visual / Q000502:physiology; D006801:Humans; D008839:Microelectrodes / Q000592:standards; D014786:Vision Disorders / Q000601:surgery / Q000628:therapy; D014793:Visual Cortex / Q000502:physiology*; D057488:Visual Prosthesis / Q000639:trends