silicon and Blindness

To determine the safety and efficacy of the artificial silicon retina (ASR) microchip implanted in the subretinal space to treat vision loss from retinitis pigmentosa.. The ASR microchip is a 2-mm-diameter silicon-based device that contains approximately 5000 microelectrode-tipped microphotodiodes and is powered by incident light. The right eyes of 6 patients with retinitis pigmentosa were implanted with the ASR microchip while the left eyes served as controls. Safety and visual function information was collected.. During follow-up that ranged from 6 to 18 months, all ASRs functioned electrically. No patient showed signs of implant rejection, infection, inflammation, erosion, neovascularization, retinal detachment, or migration. Visual function improvements occurred in all patients and included unexpected improvements in retinal areas distant from the implant.. Subjective improvements included improved perception of brightness, contrast, color, movement, shape, resolution, and visual field size.. No significant safety-related adverse effects were observed. The observation of retinal visual improvement in areas far from the implant site suggests a possible generalized neurotrophic-type rescue effect on the damaged retina caused by the presence of the ASR. A larger clinical trial is indicated to further evaluate the safety and efficacy of a subretinally implanted ASR.

Topics: Aged; Blindness; Electric Stimulation; Electrodes, Implanted; Electroretinography; Evoked Potentials, Visual; Fluorescein Angiography; Follow-Up Studies; Humans; Male; Middle Aged; Pilot Projects; Prosthesis Implantation; Retina; Retinitis Pigmentosa; Safety; Semiconductors; Silicon; Visual Acuity; Visual Fields; Visual Perception

There are currently no therapies to restore vision to patients blinded by photoreceptor degeneration. This project concerns an experimental approach toward a semiconductor-based subretinal prosthetic designed to electrically stimulate the retina. The present study describes surgical techniques for implanting a silicon microphotodiode array in the cat subretinal space and subsequent studies of implant biocompatibility and durability. Using a single-port vitreoretinal approach, implants were placed into the subretinal space of the right eye of normal cats. Implanted retinas were evaluated post-operatively over a 10 to 27 month period using indirect ophthalmoscopy, fundus photography, electroretinography, and histology. Infrared stimulation was used to isolate the electrical response of the implant from that of the normal retina. Although implants continued to generate electrical current in response to light, the amplitude of the implant response decreased gradually due to dissolution of the implant's gold electrode. Electroretinograms recorded from implanted eyes had normal waveforms but were typically 10-15% smaller in amplitude than those in unimplanted left eyes. The nonpermeable silicon disks blocked choroidal nourishment to the retina, producing degeneration of the photoreceptors. The laminar structure of the inner retinal layers was preserved. Retinal areas located away from the implantation site appeared normal in all respects. These results demonstrate that silicon-chip microphotodiode-based implants can be successfully placed into the subretinal space. Gold electrode-based subretinal implants, however, appear to be unsuitable for long-term use due to electrode dissolution and subsequent decreased electrical activity.

Topics: Animals; Blindness; Cats; Disease Models, Animal; Electric Stimulation; Electrodes, Implanted; Electrophysiology; Electroretinography; Ophthalmoscopy; Photoreceptor Cells, Vertebrate; Prosthesis Design; Prosthesis Implantation; Retina; Retinal Diseases; Silicon