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The Argus II epiretinal prosthesis system allows letter and word reading and long-term function in patients with profound vision loss
  1. Lyndon da Cruz1,
  2. Brian F Coley2,
  3. Jessy Dorn3,
  4. Francesco Merlini2,
  5. Eugene Filley4,
  6. Punita Christopher3,
  7. Fred K Chen1,5,
  8. Varalakshmi Wuyyuru3,
  9. Jose Sahel6,
  10. Paulo Stanga7,
  11. Mark Humayun3,8,
  12. Robert J Greenberg3,
  13. Gislin Dagnelie9,
  14. for the Argus II Study Group
  1. 1NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital, London, UK
  2. 2Second Sight Medical Products, Inc, Lausanne, Switzerland
  3. 3Second Sight Medical Products, Inc, Sylmar, California, USA
  4. 4Retina Foundation of the Southwest, Dallas, USA
  5. 5Centre for Ophthalmology and Vision Science, Lions Eye Institute, University of Western Australia, Nedlands, Western Australia
  6. 6Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts, Paris, France
  7. 7Manchester Biomedical Research Centre, Manchester Royal Eye Hospital, University of Manchester, Manchester, UK
  8. 8Doheny Eye Institute, Los Angeles, California, USA
  9. 9Johns Hopkins Hospital, Lions Vision Center, Baltimore, Maryland, USA
  1. Correspondence to Lyndon da Cruz, NIHR Biomedical Research Centre for Ophthalmology, Moorfields Eye Hospital, 162 City Road, London EC1V 2PD, UK; Lyndon.dacruz{at}


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.

This is an open-access article distributed under the terms of the Creative Commons Attribution Non-commercial License, which permits use, distribution, and reproduction in any medium, provided the original work is properly cited, the use is non commercial and is otherwise in compliance with the license. See: and

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