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.

Figures

Figure 1

(A) Photograph of a subject with the Argus II system showing the video glasses (a), the Video processing unit (b) and the inductive coil (c). (B) Subject showing the format for the letter identification tasks with a letter displayed on a monitor in white on black, Century Gothic font. The monitor on the side shows the real time map of the electrodes being stimulated in the array (A) and the camera view (V); note that the actual test is carried out in the dark. (C) Fundus photograph of the retinal stimulating array in situ. The optic nerve is indicated and the retinal tack that secures the electrode array is clearly visible. (D) Diagram illustrating the difference between the electrode activation maps under the ‘home use’ (standard) and ‘scrambled’ mode when the camera is viewing the letter L. In the scrambled mode, the spatial correspondence between a point's real position and the stimulation position on the array has been randomised. In this way, the patient does not receive spatial information but does receive non-spatial light detection information.

Figure 2

Box and whisker graphs illustrating the median percentage correct and quartiles for Test I letter Groups A, B and C comparing the device on and off. For Groups A, B and C, n=21, 19 and 20, respectively. (**

Figure 3

A graph showing the mean and SEs of the total number of letters identified correctly in two test runs of letter size reduction using the Argus II retinal prosthesis system. (*p