Visual prosthesis

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. Many devices have been developed, usually modeled on the cochlear implant or bionic ear devices, a type of neural prosthesis in use since the mid-1980s. The idea of using electrical current (e.g., electrically stimulating the retina or the visual cortex) to provide sight dates back to the 18th century, discussed by Benjamin Franklin, Tiberius Cavallo, and Charles LeRoy. The ability to give sight to a blind person via a bionic eye depends on the circumstances surrounding the loss of sight. For retinal prostheses, which are the most prevalent visual prosthetic under development (due to ease of access to the retina among other considerations), patients with vision loss due to degeneration of photoreceptors (retinitis pigmentosa, choroideremia, geographic atrophy macular degeneration) are the best candidate for treatment. Candidates for visual prosthetic implants find the procedure most successful if the optic nerve was developed prior to the onset of blindness. Persons born with blindness may lack a fully developed optical nerve, which typically develops prior to birth, though neuroplasticity makes it possible for the nerve, and sight, to develop after implantation. Visual prosthetics are being developed as a potentially valuable aid for individuals with visual degradation. Argus II, co-developed at the University of Southern California (USC) Eye Institute and manufactured by Second Sight Medical Products Inc., is now the only such device to have received marketing approval (CE Mark in Europe in 2011). Most other efforts remain investigational; the Retina Implant AG's Alpha IMS won a CE Mark July 2013 and is a significant improvement in resolution. It is not, however, FDA-approved in the US. Mark Humayun, who joined the faculty of the Keck School of Medicine of USC Department of Ophthalmology in 2001; Eugene Dejuan, now at the University of California San Francisco; engineer Howard D. Phillips; bio-electronics engineer Wentai Liu, now at University of California Los Angeles; and Robert Greenberg, now of Second Sight, were the original inventors of the active epi-retinal prosthesis and demonstrated proof of principle in acute patient investigations at Johns Hopkins University in the early 1990s. In the late 1990s the company Second Sight was formed by Greenberg along with medical device entrepreneur, Alfred E. Mann,:35 Their first-generation implant had 16 electrodes and was implanted in six subjects by Humayun at University of Southern California between 2002 and 2004.:35 In 2007, the company began a trial of its second-generation, 60-electrode implant, dubbed the Argus II, in the US and in Europe. In total 30 subjects participated in the studies spanning 10 sites in four countries. In the spring of 2011, based on the results of the clinical study which were published in 2012, Argus II was approved for commercial use in Europe, and Second Sight launched the product later that same year. The Argus II was approved by the United States FDA on 14 February 2013. Three US government funding agencies (National Eye Institute, Department of Energy, and National Science Foundation) have supported the work at Second Sight, USC, UCSC, Caltech, and other research labs. Designed by Claude Veraart at the University of Louvain, this is a spiral cuff electrode around the optic nerve at the back of the eye. It is connected to a stimulator implanted in a small depression in the skull. The stimulator receives signals from an externally worn camera, which are translated into electrical signals that stimulate the optic nerve directly. Although not truly an active prosthesis, an Implantable Miniature Telescope is one type of visual implant that has met with some success in the treatment of end-stage age-related macular degeneration. This type of device is implanted in the eye's posterior chamber and works by increasing (by about three times) the size of the image projected onto the retina in order to overcome a centrally located scotoma or blind spot. Created by VisionCare Ophthalmic Technologies in conjunction with the CentraSight Treatment Program, the telescope is about the size of a pea and is implanted behind the iris of one eye. Images are projected onto healthy areas of the central retina, outside the degenerated macula, and is enlarged to reduce the effect the blind spot has on central vision. 2.2x or 2.7x magnification strengths make it possible to see or discern the central vision object of interest while the other eye is used for peripheral vision because the eye that has the implant will have limited peripheral vision as a side effect. Unlike a telescope which would be hand-held, the implant moves with the eye which is the main advantage. Patients using the device may however still need glasses for optimal vision and for close work. Before surgery, patients should first try out a hand-held telescope to see if they would benefit from image enlargement. One of the main drawbacks is that it cannot be used for patients who have had cataract surgery as the intraocular lens would obstruct insertion of the telescope. It also requires a large incision in the cornea to insert. A Cochrane systematic review seeking to evaluate the effectiveness and safety of the implantable miniature telescope for patients with late or advanced age-related macular degeneration found only one ongoing study evaluating the OriLens intraocular telescope, with results expected in 2020.