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Purpose Restoration of letter reading and stripe pattern recognition in blind RP patients by placing subretinal implants transchoroidally near the macula, consisting of two arrays: 4x4 electrodes controlled retroauricularly via a subdermal line for direct stimulation (“DS array”) and a "chip" (3x3x0,1 mm),1500 electrodes. Methods Letters and stripe pattern were presented to 3 patients via the light sensitive chip – by patterns steadily presented at a screen. On the DS array the sensation evoked by each individual pulse consists of whitish round dot, clearly separated from its neighbor. Patterns consisting of such 4 x 4 dots correspond to letters of approximately 5 cm diameter presented at 60 cm distance. Results Pat.1 correctly (20/24) recognized the direction of the letter “U”, presented with the opening in four different directions (DS array). Pat.2 correctly (12/12) differentiated letters via DS array (e.g. COIL). With the light sensitive chip, he correctly (22/24) differentiated letters (e.g. LITZ; 8,5 cm high, 1.7 cm line width) steadily presented on a screen at 62 cm distance 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. Conclusion Active subretinal multielectrode implants with currents close to produce retinotopically correct patterns that allow for the first time recognition of individual letters and stripe patterns up to 0.35 cycles/deg clearly supporting the feasibility of light sensitive subretinal multi-electrode devices for restoration of useful vision.

Eleven patients have received subretinal implants, powered and controlled via a subdermal cable that enters the body retroauricularly and ends in a thin intraocular foil, placed transsclerally between the retinal pigment epithelium and the neuroretina. The tip of this foil carries two distinct arrays, a Multiphotodiode Array (MPDA) with 1500 electrodes, each electrode being controlled by an adjacent photodiode and an amplifier within a 3x3x0.1 mm chip, as well as a second array (1.2x1.2 mm) with 16 electrodes, for direct stimulation (DS) controlled via wires from outside. Safety of the approach has been investigated by means of angiography, OCT and fundus photography. The implant was well tolerated in all patients. Efficacy has been investigated in terms of threshold voltages to elicit phosphenes and the ability to perceive visual information mediated by the MPDA. Patients were tested for 4 weeks and spatial as well as temporal characteristics of repetitive multielectrode-stimulation were investigated. Letters were presented to the 3 most recent patients either by stimulating retinal cells in 10 ms steps via individual electrodes in a sequence patients had learned to write such letters or - via the light sensitive chip - by individual bright letters or stripe patterns steadily presented at a screen in 62 cm distance.