Electronic subretinal implants allow blind retinitis pigmentosa patients to read letters and recognize the direction of fine stripe patterns

Abstract

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.

Monopolar vs. bipolar subretinal stimulation—An in vitro study

“…The subretinal stimulation is based on an array of microelectrodes implanted in contact with the outer plexiform layer of a degenerated retina to replace the lost neural input of the photoreceptors by supplying electrical stimulation to the remaining retinal nerve cells. Due to the fact that electrical stimulation of retinal nerve cells causes a phosphene perception (Humayun et al, 2003), it is now proven (Zrenner et al, 2009(Zrenner et al, ,2010) that multiphosphene perceptions, generated by a subretinally implanted microelectrode array, can code for visual images and scenes, thus creating an artificial sense of vision.…”

Repeated transchoroidal implantation and explantation of compound subretinal prostheses: An exploratory study in rabbits

“…17,18 But several other scenarios where explantation and possibly reimplantation of implants is necessary can be anticipated, as in cases of implant failure, severe adverse events (e.g., endophthalmitis or retinal detachment), or following the patient's request, for example, when newer and better implants become available. Therefore, safe explantation and reimplantation techniques are needed.…”

Restoration of useful vision up to letter recognition capabilities using subretinal microphotodiodes

“…The three patients correctly recognized geometric forms, flatware, dishes, and were also able to reach out for them. Patient eleven (P11 in the pilot study) reached the best visual performance achieved so far in our study [14], [15]. This included passing a Landolt "C" test with a visual acuity of 20/1000.…”