title: Outer retinal degeneration: an electronic retinal prosthesis as a treatment strategy.
abstract: OBJECTIVE
  To review progress toward an electronic retinal prosthesis for outer retinal degeneration.
  
  
  METHODS
  Literature review.
  
  
  RESULTS
  Retinal degenerations such as retinitis pigmentosa result in a loss of photoreceptors. There is a secondary loss of inner retinal cells, but significant numbers of bipolar and ganglion cells remain for many years. Electrical stimulation can produce phosphenes in the eyes of individuals who are blind as a result of retinitis pigmentosa. Several research groups are trying to exploit this phenomenon to produce artificial vision with electronic retinal prostheses. Two groups, with private company sponsorship, have recently implanted first-generation devices in subjects with advanced retinitis pigmentosa. They have reported limited preliminary results. This article seeks to put these results in a broader context and review potential obstacles to successful prosthesis development. These include inner retinal cell viability, high thresholds, signal encoding, power requirements, biocompatibility, and device encapsulation.
  
  
  CONCLUSIONS
  There has been substantial progress toward an electronic retinal prosthesis, but fully functional, long-lasting devices are not on the immediate horizon.
authors.affiliation: Retina Service, Massachusetts Eye and Ear Infirmary, 243 Charles Street, Boston, MA 02114, USA. john_loewenstein@meei.harvard.edu
authors.forename: John I
authors.initials: JI
authors.lastname: Loewenstein
authors.forename: Sandra R
authors.initials: SR
authors.lastname: Montezuma
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Rizzo
mesh_terms: D001672:Biocompatible Materials; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D005549:Foreign-Body Reaction / Q000209:etiology; D006801:Humans; D010775:Photic Stimulation / Q000295:instrumentation*; D019919:Prosthesis Implantation; D012160:Retina / Q000601:surgery*; D012162:Retinal Degeneration / Q000601:surgery*; D012666:Semiconductors; D014796:Visual Perception
chemical_list: D001672:Biocompatible Materials