title: Post-implantation impedance spectroscopy of subretinal micro-electrode arrays, OCT imaging and numerical simulation: towards a more precise neuroprosthesis monitoring tool.
abstract: OBJECTIVE
  Previous studies have shown that single-frequency impedance measurements could provide useful information about the distance between the neuroprosthesis and the retina. This work investigates the use of impedance spectroscopy in monitoring subretinal implantations of flexible micro-electrode arrays and focuses on determining what is governing impedance profiles.
  
  
  METHODS
  In this study, we use impedance spectroscopy together with optical coherence tomography imaging and numerical simulation to quantitatively evaluate the constituent elements of measured impedance.
  
  
  RESULTS
  We show the existence of specific impedance spectrum profiles for retinal detection and retinal detachment that are in good agreement with numerical simulations. These simulations suggest that monopolar impedance is mainly influenced by the subretinal space. Numerical simulations also provide a quantitative prediction of the lateral spread of current density in the vicinity of the measuring contact as a function of retina-electrode distance.
  
  
  CONCLUSIONS
  In general, our results point to the need for scanning a large frequency range for impedance measurements since capacitive and resistive regimes are strongly dependent on retina-electrode proximity. We believe that these results will contribute to a better understanding of electrical stimulation in neuroprostheses and ultimately improve their efficiency.
authors.affiliation: CEA/LETI-Minatec, 17 rue des Martyrs, F-38054 Grenoble, France. pascale.pham@cea.fr
authors.forename: Pascale
authors.initials: P
authors.lastname: Pham
authors.forename: Sébastien
authors.initials: S
authors.lastname: Roux
authors.forename: Frédéric
authors.initials: F
authors.lastname: Matonti
authors.forename: Florent
authors.initials: F
authors.lastname: Dupont
authors.forename: Vincent
authors.initials: V
authors.lastname: Agache
authors.forename: Frédéric
authors.initials: F
authors.lastname: Chavane
mesh_terms: D000818:Animals; D058266:Dielectric Spectroscopy / Q000379:methods*; D004599:Electric Stimulation Therapy / Q000295:instrumentation; D004567:Electrodes, Implanted; D019544:Equipment Failure Analysis; D008839:Microelectrodes; D010786:Photoreceptor Cells / Q000166:cytology* / Q000502:physiology*; D011182:Postoperative Care; D011474:Prosthesis Design; D019919:Prosthesis Implantation / Q000379:methods; D051381:Rats; D017208:Rats, Wistar; D041623:Tomography, Optical Coherence / Q000379:methods*; D057488:Visual Prosthesis