title: The Argus II epiretinal prosthesis system allows letter and word reading and long-term function in patients with profound vision loss.
abstract: BACKGROUND
  Retinal prosthesis systems (RPS) are a novel treatment for profound vision loss in outer retinal dystrophies. Ideal prostheses would offer stable, long-term retinal stimulation and reproducible spatial resolution in a portable form appropriate for daily life.
  
  
  METHODS
  We report a prospective, internally controlled, multicentre trial of the Argus II system. Twenty-eight subjects with light perception vision received a retinal implant. Controlled, closed-group, forced-choice letter identification, and, open-choice two-, three- and four-letter word identification tests were carried out.
  
  
  RESULTS
  The mean±SD percentage correct letter identification for 21 subjects tested were: letters L, T, E, J, F, H, I, U, 72.3±24.6% system on and 17.7±12.9% system off; letters A, Z, Q, V, N, W, O, C, D, M, 55.0±27.4% system on and 11.8%±10.7% system off, and letters K, R, G, X, B, Y, S, P, 51.7±28.9% system on and 15.3±7.4% system off. (p<0.001 for all groups). A subgroup of six subjects was able to consistently read letters of reduced size, the smallest measuring 0.9 cm (1.7°) at 30 cm, and four subjects correctly identify unrehearsed two-, three- and four-letter words. Average implant duration was 19.9 months.
  
  
  CONCLUSIONS
  Multiple blind subjects fitted with the Argus II system consistently identified letters and words using the device, indicating reproducible spatial resolution. This, in combination with stable, long-term function, represents significant progress in the evolution of artificial sight.
authors: NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK. Lyndon.dacruz@moorfields.nhs.uk
authors: Lyndon
authors: L
authors: da Cruz
authors: Brian F
authors: BF
authors: Coley
authors: Jessy
authors: J
authors: Dorn
authors: Francesco
authors: F
authors: Merlini
authors: Eugene
authors: E
authors: Filley
authors: Punita
authors: P
authors: Christopher
authors: Fred K
authors: FK
authors: Chen
authors: Varalakshmi
authors: V
authors: Wuyyuru
authors: Jose
authors: J
authors: Sahel
authors: Paulo
authors: P
authors: Stanga
authors: Mark
authors: M
authors: Humayun
authors: Robert J
authors: RJ
authors: Greenberg
authors: Gislin
authors: G
authors: Dagnelie
mesh_terms: D000328:Adult; D000368:Aged; D015794:Choroideremia / Q000503:physiopathology* / Q000601:surgery; D004567:Electrodes, Implanted; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D019919:Prosthesis Implantation; D011932:Reading; D012174:Retinitis Pigmentosa / Q000503:physiopathology* / Q000601:surgery; D015354:Vision, Low / Q000503:physiopathology* / Q000601:surgery; D014792:Visual Acuity / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D057488:Visual Prosthesis