title: Transretinal electrical stimulation by an intrascleral multichannel electrode array in rabbit eyes.
abstract: BACKGROUND
  A new method of stimulating the retina electrically, called suprachoroidal transretinal stimulation (STS), was shown to be effective in eliciting electrically evoked cortical potentials (EEPs) in Royal College of Surgeons (RCS) rats. Before extending this technique to patients, it is important to determine its safety and feasibility in eliciting EEPs from medium-size animal (rabbits). The purpose of this study was to determine the safety and efficacy of the surgical procedures used to implant an multichannel electrode array into a scleral pocket, and to determine whether the implanted electrodes can stimulate the retina effectively.
  
  
  METHODS
  These acute experiments were conducted on six rabbits. An array of eight gold microelectrodes, embedded in polyimide, was implanted into a scleral pocket over the visual streak area. The size of the microarray was 2 x 4 x 0.180 mm. The reference electrode was implanted into the vitreous. The electrode array and reference electrodes were connected to a stimulator to deliver monophasic current pulses. Cortical responses were recorded with a stainless steel electrode implanted into each rabbit's skull over the visual cortex. After the experiment, the eyes and electrodes were examined histologically.
  
  
  RESULTS
  The surgical procedures for electrode implantation were accomplished without serious complications. EEPs were recorded after monophasic electrical pulse stimulation from each electrode. The mean threshold for EEPs was 55.0+/-10.0 microA with a 0.5-ms duration inward current pulse. The charge delivered at threshold was about 27.5 nC, and the charge density was about 56.0 microC/cm2. Histopathological examination of the retinal tissue around the area of stimulation did not show damage at the light microscope level with the electrical parameters used.
  
  
  CONCLUSIONS
  Our technique for STS with an intrascleral microelectrode array is safe in rabbit eyes, and EEPs were elicited by current densities that did not induce tissue damage. These results suggest that STS via intrascleral multichannel electrodes is a feasible method for stimulating the retina.
authors.affiliation: Department of Visual Science, Osaka University Graduate School of Medicine, Room G4, 2-2 Yamadaoka, Suita-shi, Osaka, 565-0871, Japan.
authors.forename: Kazuaki
authors.initials: K
authors.lastname: Nakauchi
authors.forename: Takashi
authors.initials: T
authors.lastname: Fujikado
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kanda
authors.forename: Takeshi
authors.initials: T
authors.lastname: Morimoto
authors.forename: Jun S
authors.initials: JS
authors.lastname: Choi
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Ikuno
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Sakaguchi
authors.forename: Motohiro
authors.initials: M
authors.lastname: Kamei
authors.forename: Masahito
authors.initials: M
authors.lastname: Ohji
authors.forename: Tohru
authors.initials: T
authors.lastname: Yagi
authors.forename: Shigeru
authors.initials: S
authors.lastname: Nishimura
authors.forename: Hajime
authors.initials: H
authors.lastname: Sawai
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Fukuda
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Tano
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D008839:Microelectrodes; D011817:Rabbits; D012160:Retina / Q000166:cytology / Q000502:physiology*; D012449:Safety; D012590:Sclera / Q000166:cytology / Q000601:surgery*