A visual prosthesis, often referred to as a bionic eye, is an experimental visual device intended to restore functional vision in those with 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,[1] Tiberius Cavallo,[2] and Charles LeRoy.[3]
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Biological considerations
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,[4] though neuroplasticity makes it possible for the nerve, and sight, to develop after implantation[citation needed].
Technological considerations
Visual prosthetics are being developed as a potentially valuable aid for individuals with visual degradation. Only three visual prosthetic devices have received marketing approval in the EU.[5] Argus II, co-developed at the University of Southern California (USC) Eye Institute[6] and manufactured by Second Sight Medical Products Inc., was the first 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.[7]
Ongoing projects
Argus retinal prosthesis
Mark Humayun, who joined the faculty of the Keck School of Medicine of USC Department of Ophthalmology in 2001;[8] 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[9] 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[10] was formed by Greenberg along with medical device entrepreneur, Alfred E. Mann,[11]: 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.[11]: 35 [12] In 2007, the company began a trial of its second-generation, 60-electrode implant, dubbed the Argus II, in the US and in Europe.[13][14] 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,[15] 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.[16]
Microsystem-based visual prosthesis (MIVP)
Designed by Claude Veraart at the University of Louvain in 2002, 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.[17]
Implantable miniature telescope
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.[18][19][20] 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.[19][20]
Created by VisionCare Ophthalmic Technologies in conjunction with the CentraSight Treatment Program in 2011, 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.[21]
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.[22]
Tübingen MPDA Project Alpha IMS
A Southern German team led by the University Eye Hospital in Tübingen, was formed in 1995 by Eberhart Zrenner to develop a subretinal prosthesis. The chip is located behind the retina and utilizes microphotodiode arrays (MPDA) which collect incident light and transform it into electrical current stimulating the retinal ganglion cells. As natural photoreceptors are far more efficient than photodiodes, visible light is not powerful enough to stimulate the MPDA. Therefore, an external power supply is used to enhance the stimulation current. The German team commenced in vivo experiments in 2000, when evoked cortical potentials were measured from Yucatán micropigs and rabbits. At 14 months post implantation, the implant and retina surrounding it were examined and there were no noticeable changes to anatomical integrity. The implants were successful in producing evoked cortical potentials in half of the animals tested. The thresholds identified in this study were similar to those required in epiretinal stimulation. Later reports from this group concern the results of a clinical pilot study on 11 participants with retinitis pigmentosa. Some blind patients were able to read letters, recognize unknown objects, localize a plate, a cup and cutlery.[23] Two of the patients were found to make microsaccades similar to those of healthy control participants, and the properties of the eye movements depended on the stimuli that the patients were viewing—suggesting that eye movements might be useful measures for evaluating vision restored by implants.[24][25] Multicenter study started in 2010, using a fully implantable device with 1500 Electrodes Alpha IMS (produced by Retina Implant AG, Reutlingen, Germany), with 10 patients included; preliminary results were presented at ARVO 2011.[citation needed] The first UK implantations took place in March 2012 and were led by Robert MacLaren at the University of Oxford and Tim Jackson at King's College Hospital in London.[26][27] David Wong also implanted the Tübingen device in a patient in Hong Kong.[28]
On 19 March 2019 Retina Implant AG discontinued business activities quoting innovation-hostile climate of Europe's rigid regulatory and unsatisfactory results in patients.[29]
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 radio frequency fields from transmitter coils that are mounted on the glasses. A secondary receiver coil is sutured around the iris.[30]