title: Electrical stimulation of anterior visual pathways in retinitis pigmentosa.
abstract: OBJECTIVE
  To explore electrically induced phosphenes in blind patients with retinitis pigmentosa (RP) in comparison with healthy subjects and to develop a screening test for candidates for an optic nerve visual prosthesis implantation.
  
  
  METHODS
  Phosphenes are obtained by charge balanced biphasic pulse stimulations through a surface cathode over the closed eyelids and an anode near the opposite ear. The resulting strength-duration relationship for somatosensory, phosphene, and pain threshold has been recorded in five RP patients as well as in 10 healthy volunteers.
  
  
  RESULTS
  In sighted subjects, the average rheobase and chronaxy for phosphene perception are 0.28 mA and 3.07 msec, respectively. For pulse durations longer than 2 msec, phosphenes are usually obtained at current strengths below the level giving rise to any other electrically generated sensation. In RP patients, however, phosphenes are not so easily obtained. One in five had no visual response at all. Another patient reported a flash perception for the longest pulse durations only. Spontaneous phosphenes interfered heavily with the stimulation in a third person. Finally, despite the higher threshold, two patients displayed normally shaped strength-duration curves.
  
  
  CONCLUSIONS
  The surface stimulation has proven harmless, adequate, and very helpful to ascertain that the optic nerve can be electrically activated in completely blind individuals. Long-duration stimulation pulses yield very low phosphene thresholds in healthy subjects. Anterior visual pathways activation requires higher currents in RP patients.
authors.affiliation: Neural Rehabilitation Engineering Laboratory, Université Catholique de Louvain, Brussels, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Delbeke
authors.forename: D
authors.initials: D
authors.lastname: Pins
authors.forename: G
authors.initials: G
authors.lastname: Michaux
authors.forename: M C
authors.initials: MC
authors.lastname: Wanet-Defalque
authors.forename: S
authors.initials: S
authors.lastname: Parrini
authors.forename: C
authors.initials: C
authors.lastname: Veraart
mesh_terms: D000328:Adult; D000368:Aged; D001766:Blindness / Q000503:physiopathology*; D004558:Electric Stimulation; D005260:Female; D006801:Humans; D008297:Male; D008433:Mathematics; D008875:Middle Aged; D009900:Optic Nerve / Q000502:physiology*; D010719:Phosphenes / Q000502:physiology*; D011601:Psychophysics; D012174:Retinitis Pigmentosa / Q000503:physiopathology*; D012677:Sensation / Q000502:physiology; D014795:Visual Pathways / Q000503:physiopathology*; D014796:Visual Perception