Visual prosthesis

The ability to give a blind person vision with a bionic eye depends on the circumstances that caused the loss of vision. The retinal prosthesis is the most common visual prosthesis. Patients with vision loss due to photoreceptor degeneration are best suited for this prosthesis. The chances of success increase if the patient’s optic nerve was developed before the appearance of blindness. People with congenital blindness may not have a fully developed optic nerve. Although neuroplasticity allows the nerve to develop after implant placement. ^[four]

Visual prosthetics is being developed as a potentially valuable aid for people with visual impairment. Argus II , developed in conjunction with the University of Southern California (USC) and manufactured by Second Sight Medical Products Inc., is currently the only such device to receive marketing approval (CE mark in 2011). ^[5] Most other projects are under development.

Argus II

Mark Humayun, Eugene Dejouan, Howard D. Phillips, Ventai Liu and Robert Greenber were the first inventors of an active visual prosthesis. ^[6] They proved the validity of their concept during research with patients at Johns Hopkins University . In the late 1990s, Greenberg, together with a medical equipment entrepreneur, founded Second Sight. ^[7] Their first-generation implant had 16 electrodes and was used at the University of Southern California from 2002 to 2004. ^[8] In 2007, the company began testing its second-generation 60-electrode implant called Argus II. ^[9] The test involved 30 people from 4 countries. In the spring of 2011, based on a clinical study published in 2012 ^[10] , Argus II was approved for commercial use in Europe, and Second Sight launched the product. In the USA, Argus II was certified on February 14, 2013. The National Eye Institute, the Department of Energy, and the National Science Foundation supported the development of Second Sight. ^[eleven]

Microsystem-based Visual Prosthesis (MIVP)

Claude Veraart of the University of Louvain has developed a prosthesis, which is an electrode with a spiral cuff around the optic nerve in the back of the eye. As planned, the stimulator should receive signals from an external camera, which are converted into electrical signals, and directly stimulate the optic nerve.

Implantable miniature telescope

The implantable miniature telescope, although it is not an active prosthesis, acts as one of the types of visual implants that can be used in the treatment of macular degeneration in its final stages. ^{[12] [13]} A device of this type is implanted in the eye, increasing (approximately three times) the size of the image projected onto the retina. ^[14]

An example is a telescope created by VisionCare Ophthalmic Technologies. It is the size of a pea and is implanted behind the iris of the eye. The image is projected onto healthy areas of the central retina, outside the degenerated macula and enlarged to reduce the effect of blind spots on vision. A magnification of 2.2 or 2.7 times allows you to see or distinguish an object of interest, while the other eye is used for peripheral vision. An implanted eye will have limited peripheral vision as a side effect. Patients using the device may still need glasses for optimal vision. Before surgery, patients should first test a hand-held telescope to see if it improves vision in their case. One of the main disadvantages is that it cannot be used for patients undergoing cataract surgery. And also, to install a telescope, you need to make a large incision in the cornea. ^[15]

MPDA Alpha IMS Project

In 1995, the development of subretinal retinal prostheses began at the University Eye Clinic Tübingen. A chip with microphotodiodes was placed under the retina, which received light and transformed it into electrical signals that stimulate ganglion cells, similar to the natural process in the photoreceptors of an intact retina. Natural photoreceptors are much more efficient than photodiodes and visible light is not powerful enough to stimulate MPDA. Therefore, to increase the level of stimulation, an external power source is used. The first experiments on micro-pigs and rabbits were started in 2000, and only in 2009 implants were implanted in 11 patients as part of a clinical pilot study. The first results were encouraging - most patients were able to distinguish day from night, some could even recognize objects - a cup, spoon, monitor the movement of large objects. ^[16] The first implantations in the UK took place in March 2012 and were performed by Robert McLaren at the University of Oxford and Tim Jackson at the Royal Hospital in London. ^{[17] [18]} For 2017, Alpha IMS, manufactured by Retina Implant AG Germany, had 1,500 electrodes, 3 × 3 mm in size, 70 microns thick. After installation under the retina, this allows almost all patients to get some degree of restoration of light perception. ^[nineteen]

MIT Retinal Implan

Joseph Rizzo and John Wyatt of Massachusetts began exploring the possibility of creating a retinal prosthesis in 1989, and conducted stimulation tests on blind volunteers between 1998 and 2000. Since then, they have developed a subretinal stimulator, a set of electrodes that is placed under the retina and receives image signals from a camera mounted on a pair of glasses. The stimulator chip decodes the image information transmitted by the camera, and accordingly stimulates the retinal ganglion cells. The second-generation prosthesis collects data and transmits it to the implant through radio-frequency fields from a transmitter coil mounted on glasses. A secondary receiver coil is sewn around the iris. ^[20]

Artificial Silicon Retina (ASR)

The brothers Alan Chow and Vincent Chow developed a microchip containing 3,500 photodiodes that detect light and convert it into electrical pulses. They stimulate healthy retinal ganglion cells. ASR does not require external devices. The ASR microchip is a silicon chip with a diameter of 2 mm (the same concept as in computer chips), 25 microns thick, containing 5,000 microscopic solar cells called "microphotodiodes", each of which has its own stimulating electrode. ^[21]

Retina Photoelectric Prostheses (PRIMA)

Daniel Palanker and his team at Stanford University have developed a photovoltaic system, which is also the "bionic eye." The system includes a subretinal photodiode and an infrared projection image system mounted on video glasses. ^[22] Information from the video camera is processed in a handheld computer and displayed in a pulsed infrared (850-915 nm) video image. The IR image is projected onto the retina through the natural optics of the eye and activates the photodiodes in the subretinal implant, which convert the light into a pulsed biphasic electric current in each pixel. ^[23] An electric current flowing through the tissue between the active and reverse electrodes at each pixel stimulates nearby internal retinal neurons, primarily bipolar cells, which transmit exciting responses to the retinal ganglion cells. This technology is commercialized by Pixium Vision and, as of 2018, is undergoing clinical trials.

Bionic Vision

An Australian team led by Professor Anthony Burkitt is developing two retinal prostheses. The Wide-View device combines new technologies with materials that have been successfully used in other clinical implants. This approach includes a microchip with 98 stimulating electrodes and aims to increase patient mobility to help them move safely in their environment. This implant will be placed in the suprachoroidal space. The first patient tests with this device started in 2013.

The Bionic Vision Australia consortium is developing a High-Acuity device, which includes a number of new technologies for combining a microchip and an implant with 1024 electrodes. The device is designed to improve vision to help with tasks such as face recognition and reading in large print. The bionic visual system includes a camera that transmits radio signals to a microchip located in the back of the eye. These signals are converted into electrical impulses that stimulate cells in the retina and optic nerve. Then they are transmitted to the visual zones of the cerebral cortex and are converted into the image that the patient sees.

The Australian Research Council awarded Bionic Vision Australia a grant of $ 42 million in December 2009, and the consortium was formally launched in March 2010. ^[24]

Dobelle Eye

Dobelle Eye is similar in function to the MIT Retinal Implan device, except that the stimulator chip is located in the visual cortex , and not on the retina. The first impressions of the implant were not bad. Even in the developmental stage, after the death of Dobel, it was decided to turn this project from a commercial into a project funded by the state. ^[25]

Intracortical optic prosthesis

A neural prosthesis lab at the Illinois Institute of Technology in Chicago is developing a visual prosthesis using intracortical electrodes. Similar to the Dobel system, the use of intracortical electrodes can significantly increase the spatial resolution in stimulation signals. In addition, a wireless telemetry system is being developed to eliminate the need for transcranial (intracranial) wires. Electrodes coated with a layer of activated iridium oxide film (AIROF) will be implanted in the visual cortex located in the occipital lobe of the brain. ^[26] The outdoor unit will capture the image, process it and generate instructions, which will then be transmitted to the implanted modules via a telemetric link. The circuit decodes the instructions and stimulates the electrodes, in turn stimulating the visual cortex. The group is developing sensors for an external image capture and processing system to accompany specialized implantable modules built into the system. Animal studies and human psychophysical studies are currently underway to test the feasibility of implantation to volunteers. ^[27]

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