title: Electrophysiological and histological studies of chronically implanted intrapapillary microelectrodes in rabbit eyes.
abstract: OBJECTIVE
  To determine the safety and efficacy of transsclerally placed intrapapillary wire microelectrodes implanted chronically into the optic nerve head of rabbit eyes.
  
  
  METHODS
  Four platinum wire microelectrodes were passed through the sclera and implanted into the optic nerve head of five rabbit eyes for 4-6 months. Color fundus photography, fluorescein angiography, electroretinograms (ERGs), and visually evoked potentials (VEPs) were used to monitor the retina. Electrically evoked potentials (EEPs) were elicited by bipolar electrical stimulation of the optic nerve axons by different combinations of the four electrodes immediately after the implantation and at 1-month intervals thereafter. The effects of the chronic implantation of the electrodes on the morphology of the optic nerve were evaluated by histological and immunohistochemical examinations at 4 and 6 months after the implantation.
  
  
  RESULTS
  All of the electrodes remained stable in the implanted sites throughout the post-implantation period, except for one electrode that had pulled out of the optic nerve head at 1 month after implantation. No intraocular infection, inflammation, or vitreoretinal proliferation was observed in any eye. EEPs could be elicited from each pair of electrodes at all testing times. The mean threshold currents (charge densities) to evoke EEPs increased from 19.3 +/- 9.2 microA (6.0 +/- 2.9 microC/cm2) on the implantation day to 78.8 +/- 31.9 microA (24.6 +/- 10.0 microC/cm2) at 1 month after implantation, but did not change significantly thereafter. The implicit time and amplitude of the a- and b-waves of the ERGs and of P1 of the VEPs did not change significantly throughout the post-implantation period. Histological evaluation of the optic nerve head revealed slight tissue encapsulations surrounding the electrode and increased expression of glial fibrillary acidic protein near the surface of the optic nerve.
  
  
  CONCLUSIONS
  Implantation of transscleral intrapapillary microelectrodes appears to be safe and effective. These findings indicate that the implantation of microelectrodes in the optic nerve head should be considered for an optic nerve-based prosthesis.
authors.affiliation: Department of Ophthalmology E-7, Graduate School of Medicine, Osaka University, 2-2 Yamadaoka, Suita, Osaka, 565-0871, Japan. fangxyp@hotmail.com
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Fang
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Sakaguchi
authors.forename: Takashi
authors.initials: T
authors.lastname: Fujikado
authors.forename: Makoto
authors.initials: M
authors.lastname: Osanai
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ikuno
authors.forename: Motohiro
authors.initials: M
authors.lastname: Kamei
authors.forename: Masahito
authors.initials: M
authors.lastname: Ohji
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Yagi
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Tano
mesh_terms: D000818:Animals; D001369:Axons / Q000502:physiology*; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004596:Electroretinography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005074:Evoked Potentials, Visual / Q000502:physiology; D005451:Fluorescein Angiography; D008839:Microelectrodes; D008855:Microscopy, Electron, Scanning; D009887:Ophthalmoscopy; D009898:Optic Disk / Q000601:surgery* / Q000648:ultrastructure; D009900:Optic Nerve / Q000502:physiology*; D011817:Rabbits; D012160:Retina / Q000502:physiology