Abstract

SO.09.09

Blind retinitis pigmentosa patients can read letters and combine them to words with subretinal electronic implants

Eberhart Zrenner1, Robert Wilke2, Karl Ulrich Bartz-Schmidt2, H. Benav2, Dorothea Besch2, Florian Gekeler2, Johannes Koch2, Katarina Stingl2, Helmut G. Sachs3, Barbara Wilhelm4
1Pathophysiologie des Sehens und Neuroophthalmologie, Universitäts-Augenklinik Tübingen, 2Universitäts-Augenklinik Tübingen, 3Augenklinik, Klinikum Dresden-Friedrichstadt, Dresden, 4Steinbeis Transfer Zentrum, Tübingen

Objective
Restoration of letter reading and pattern recognition via subretinal electronic implants in blind RP patients.
Methods
Subretinal implants were placed transchoroidally near the macula, consisting of two arrays: 4x 4 electrodes (100 x 100 μm), spaced 280 μm, controlled retroauricularly via a subdermal line for direct stimulation (“DS array”) and a "chip" (3 x 3 x 0,1 mm) with 1500 electrodes (50 x 50 μm) of the same kind, each electrode being activated by light falling onto a neighboring micro-photodiode that controls the output of its subretinal amplifier. Letters were presented to 3 patients either by stimulating retinal cells in 10ms steps via individual electrodes in a sequence or – via the light sensitive chip – by individualoptotypes or grids steadily presented at a screen.
Results
On the DS array patients reported uniformly for each electrode that the sensation evoked by each individual pulse consisted of a whitish round dot, clearly separated from ist neighbor. Patterns consisting of such 4 x 4 dots correspond to letters of approximately 5 cm diameter presented at 60 cm distance. Pat. 1 correctly (20/24) recognized the direction of the letter “U”, presented with the opening in four different directions in in a 4 alternative forced choice (4AFC) mode. Pat. 2 correctly (12/12) differentiated letters (e.g. C, O, I, L, Z, V) within few seconds, presented via DS electrodes. With the light sensitive subretinal chip, he also correctly (22/24) differentiated without head movements letters (e.g. L,I,T,Z; 8,5 cm high, 1.7 cm line width) steadily presented on a screen at 62 cm distance with a red light (630nm cutoff) of 3.4 cd/m2. Pat.3 recognized (15/20 correct, 4AFC) the direction of lines or stripe patterns with the chip, as did Pat.1 (11/14, 2AFC) and Pat.2 (11/12 4AFC) up to 0.35 cycles/deg.
Conclusions
Active subretinal multielectrode implants with currents close to recognition threshold (10 to 27nC/electrode) produce retinotopically correct patterns that allow for the first time recognition of individual letters (8cm high, viewed in appr. 62 cm distance) even at low luminance level, clearly supporting the feasibility of light sensitive subretinal multi-electrode devices for restoration of useful visual percepts in blind patients.

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