title: Stimulation of a Suprachoroidal Retinal Prosthesis Drives Cortical Responses in a Feline Model of Retinal Degeneration.
abstract: OBJECTIVE
  Retinal prostheses have emerged as a promising technology to restore vision in patients with severe photoreceptor degeneration. To better understand how neural degeneration affects the efficacy of electronic implants, we investigated the function of a suprachoroidal retinal implant in a feline model.
  
  
  METHODS
  Unilateral retinal degeneration was induced in four adult felines by intravitreal injection of adenosine triphosphate (ATP). Twelve weeks post injection, animals received suprachoroidal electrode array implants in each eye, and responses to electrical stimulation were obtained using multiunit recordings from the visual cortex. Histologic measurements of neural and glial changes in the retina at the implant site were correlated with cortical thresholds from individual stimulating electrodes.
  
  
  RESULTS
  Adenosine triphosphate-injected eyes displayed changes consistent with mid-to-late stage retinal degeneration and remodeling. A significant increase in electrical charge was required to induce a cortical response from stimulation of the degenerated retina compared to that in the fellow control eye. Spatial and temporal characteristics of the electrically evoked cortical responses were no different between eyes. Individual electrode thresholds varied in both the control and the ATP-injected eyes and were correlated with ganglion cell density. In ATP-injected eyes, cortical threshold was also independently correlated with an increase in the extent of retinal gliosis.
  
  
  CONCLUSIONS
  These data suggest that even when ganglion cell density remains unaffected, glial changes in the retina following degeneration can influence the efficacy of suprachoroidal electrical stimulation. A better understanding of how glial change impacts retinal prosthesis function may help to further the optimization of retinal implants.
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, East Melbourne, Victoria, Australia 2Department of Anatomy and Neuroscience, The University of Melbourne, Melbourne, Victoria, Australia 3The Bionics Institute, East Melbourne, Victoria, Australia.
authors.forename: Felix P
authors.initials: FP
authors.lastname: Aplin
authors.affiliation: Department of Anatomy and Neuroscience, The University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Erica L
authors.initials: EL
authors.lastname: Fletcher
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, East Melbourne, Victoria, Australia 4Department of Surgery (Ophthalmology), The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Chi D
authors.initials: CD
authors.lastname: Luu
authors.affiliation: Department of Anatomy and Neuroscience, The University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Kirstan A
authors.initials: KA
authors.lastname: Vessey
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, East Melbourne, Victoria, Australia.
authors.forename: Penelope J
authors.initials: PJ
authors.lastname: Allen
authors.affiliation: Centre for Eye Research Australia, Royal Victorian Eye and Ear Hospital, East Melbourne, Victoria, Australia 4Department of Surgery (Ophthalmology), The University of Melbourne, Parkville, Victoria, Australia.
authors.forename: Robyn H
authors.initials: RH
authors.lastname: Guymer
authors.affiliation: The Bionics Institute, East Melbourne, Victoria, Australia 5Medical Bionics Department, The University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Robert K
authors.initials: RK
authors.lastname: Shepherd
authors.affiliation: The Bionics Institute, East Melbourne, Victoria, Australia 5Medical Bionics Department, The University of Melbourne, Melbourne, Victoria, Australia.
authors.forename: Mohit N
authors.initials: MN
authors.lastname: Shivdasani
mesh_terms: D000818:Animals; D002415:Cats; D004195:Disease Models, Animal; D004558:Electric Stimulation / Q000379:methods; D004567:Electrodes, Implanted; D005074:Evoked Potentials, Visual / Q000502:physiology*; D008839:Microelectrodes; D012160:Retina / Q000503:physiopathology / Q000601:surgery*; D012162:Retinal Degeneration / Q000503:physiopathology / Q000601:surgery*; D014793:Visual Cortex / Q000503:physiopathology*; D057488:Visual Prosthesis