A visual prosthesis, often referred to as a bionic eye, is an experimental visual device intended to restore functional vision in those suffering from partial or total blindness. In 1983 Joao Lobo Antunes, a Portuguese doctor, implanted a bionic eye in a person born blind. Many devices have been developed, usually modeled on the cochlear implant or bionic ear devices, a type of neural prosthesis.
Harvard/MIT Retinal Implant
Joseph Rizzo and John Wyatt at the Massachusetts Eye and Ear Infirmary and MIT began researching the feasibility of a retinal prosthesis in 1989, and performed a number of proof-of-concept epiretinal stimulation trials on blind volunteers between 1998 and 2000. They have since developed a subretinal stimulator, an array of electrodes, that is placed beneath the retina in the subretinal space and receives image signals beamed from a camera mounted on a pair of glasses. The stimulator chip decodes the picture information beamed from the camera and stimulates retinal ganglion cells accordingly. Their second generation prosthesis collects data and sends it to the implant through RF fields from transmitter coils that are mounted on the glasses. A secondary receiver coil is sutured around the iris.
Artificial Silicon Retina (ASR)
The brothers Alan Chow and Vincent Chow have developed a microchip containing 3500 photo diodes, which detect light and convert it into electrical impulses, which stimulate healthy retinal ganglion cells. The ASR requires no externally worn devices. The original Optobionics Corp. stopped operations, but Dr. Chow acquired the Optobionics name, the ASR implants and will be reorganizing a new company under the same name. The ASR microchip is a 2mm in diameter silicon chip (same concept as computer chips) containing ~5,000 microscopic solar cells called "microphotodiodes" that each have their own stimulating electrode.
Photovoltaic Retinal Prosthesis
Daniel Palanker and his group at Stanford University have developed a photovoltaic system for visual prosthesis that includes a subretinal photodiode array and an infrared image projection system mounted on video goggles. Information from the video camera is processed in a pocket PC and displayed on pulsed near-infrared (IR, 850–915 nm) video goggles. IR image is projected onto the retina via natural eye optics, and activates photodiodes in the subretinal implant that convert light into pulsed bi-phasic electric current in each pixel. Charge injection can be further increased using a common bias voltage provided by a radiofrequency-driven implantable power supply[26] Proximity between electrodes and neural cells necessary for high resolution stimulation can be achieved utilizing the effect of retinal migration.
The procedure involved injecting rod precursors which formed an 'anatomically distinct and appropriately polarized outer nuclear layer' - two weeks later a retina had formed with restored connections and sight, proving that it was possible to reconstruct the entire light-sensitive layer. Researchers at Moorfields Eye Hospital had already been using human embryonic stem cells to replace the pigmented lining of the retina in patients with Stargardt's disease. The team is also restoring vision to blind patients with an electronic retinal implant which works on a similar principle of replacing the function of the light-sensing photoreceptor cells.