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 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.
Visual prosthetics are being developed as a potentially valuable aid for individuals with visual degradation. Argus II, manufactured by Second Sight Medical Products Inc. is the only such device to have received marketing approval (CE Mark in Europe in 2011), all other efforts remain investigational, and most have not yet made it to any clinical use in patients.
Argus Retinal Prosthesis
Drs. Mark Humayun,and Eugene DeJuan at the Doheny Eye Institute (USC), Dr. Robert Greenberg of Second Sight, and Bio-electronics Engineer Dr Wentai Liu at University of California, Santa Cruz 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 Dr. Greenberg along with medical device entrepreneur, Alfred E. Mann, to develop a chronically implantable retinal prosthesis. Their first generation implant had 16 electrodes and was implanted in 6 subjects between 2002 and 2004. These subjects, who were all completely blind prior to implantation, could perform a surprising array of tasks using the device. 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 4 countries. In the spring of 2011, based on the seminal results of the clinical study which were recently published in Ophthalmology, 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 major 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.
Microsystem-based Visual Prosthesis (MIVIP)
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.
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.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.
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. The latest reports from this group concern the results of a clinical pilot study on 11 participants suffering from RP. Some blind patients were able to read letters, recognize unknown objects, localize a plate, a cup and cutlery. The results were to be presented in detail in 2011 in the Proceeedings of the Royal Society B doi:10.1098/rspb.2010.1747. In 2010 a new multicenter Study has been started using a fully implantable device with 1500 Electrodes Alpha IMS (produced by Retina Implant AG, Reutlingen, Germany), 10 patients included so far; first results have been presented at ARVO 2011. The first UK implantations took place in March 2012 and were led by Professor Robert MacLaren at the University of Oxford and Mr Tim Jackson[disambiguation needed] at King’s College Hospital in London. Professor David Wong[disambiguation needed] also implanted the Tübingen device in a patient in Hong-Kong. In all cases previously blind patients had some degree of sight restored, confirming that despite the complexity of surgery, the device can be implanted successfully at other specialist centers around the World.
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.
Optoelectronic Retinal Prosthesis
Daniel Palanker and his group at Stanford University have developed an optoelectronic 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, 850–900 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 Proximity between electrodes and neural cells necessary for high resolution stimulation can be achieved utilizing the effect of retinal migration.
Bionic Vision Australia
An Australian team led by Professor Anthony Burkitt is developing two retinal prostheses. The Wide-View device, combines novel technologies with materials that have been successfully used in other clinical implants. This approach incorporates a microchip with 98 stimulating electrodes and aims to provide increased mobility for patients to help them move safely in their environment. This implant will be placed in the suprachoroidal space. Researchers expect the first patient tests to begin with this device in 2013.
The Bionic Vision Australia consortium is concurrently developing the High-Acuity Device, which incorporates a number of new technologies to bring together a microchip and an implant with 1024 electrodes. The device aims to provide functional central vision to assist with tasks such as face recognition and reading large print. This high-acuity implant will be inserted epiretinally. Patient tests are planned for this device in 2014 once preclinical testing has been completed.
Patients with retinitis pigmentosa will be the first to participate in the studies, followed by age-related macular degeneration. Each prototype consists of a camera, attached to a pair of glasses which sends the signal to the implanted microchip, where it is converted into electrical impulses to stimulate the remaining healthy neurons in the retina. This information is then passed on to the optic nerve and the vision processing centres of the brain.
The Australian Research Council awarded Bionic Vision Australia a $42 million grant in December 2009 and the consortium was officially launched in March 2010. Bionic Vision Australia brings together a multidisciplinary team, many of whom have extensive experience developing medical devices such as the cochlear implant (or ‘bionic ear’).
Similar in function to the Harvard/MIT device, except the stimulator chip sits in the primary visual cortex, rather than on the retina. Many subjects have been implanted with a high success rate and limited negative effects. Still in the developmental phase, upon the death of Dr. Dobelle, selling the eye for profit was ruled against in favor of donating it to a publicly funded research team.
Intracortical Visual Prosthesis
The Laboratory of Neural Prosthesis at Illinois Institute Of Technology (IIT), Chicago, is developing a visual prosthetic using Intracortical Iridium Oxide (AIROF) electrodes arrays. These arrays will be implanted on the occipital lobe. External hardware will capture images, process them and generate instructions which will then be transmitted to implanted circuitry via a telemetry link. The circuitry will decode the instructions and stimulate the electrodes, in turn stimulating the visual cortex. The group is developing a wearable external image capture and processing system. Studies on animals and psyphophysical studies on humans are being conducted to test the feasibility of a human volunteer implant.
Virtual Retinal Display (VRD)
Laser-based system for projecting an image directly onto the retina. This could be useful for enhancing normal vision or bypassing an occlusion such as a cataract, or a damaged cornea.
Visual Cortical Implant
Dr. Mohamad Sawan, Professor and Researcher at Polystim neurotechnologies Laboratory at the Ecole Polytechnique de Montreal, has been working on a visual prosthesis to be implanted into the visual cortex. The basic principle of Dr. Sawan’s technology consists of stimulating the visual cortex by implanting a silicon microchip on a network of electrodes, made of biocompatible materials, wherein each electrode injects a stimulating electrical current in order to provoke a series of luminous points to appear (an array of pixels) in the field of vision of the blind person. This system is composed of two distinct parts: the implant and an external controller. The implant is lodged in the visual cortex and wirelessly receives data and energy from the external controller. It contains all the circuits necessary to generate the electrical stimuli and to monitor the changing microelectrode/biological tissue interface. The battery-operated outer controller consists of a micro-camera, which captures images, as well as a processor and a command generator, which process the imaging data to translate the captured images and generate and manage the electrical stimulation process. The external controller and the implant exchange data in both directions by a transcutaneous radio frequency (RF) link, which also powers the implant.
Nirenberg Lab Information Processing Prosthesis
Sheila Nirenberg as director of her laboratory team at Weill Cornell Medical College has found a method of treating retinal degeneration by using a deciphering of the retinal code combined with optogenetics. Work on the genetic engineering therapy for human trials is underway (now in the stage of working with mice and monkeys), but meanwhile Nirenberg is working with retinal-prosthesis maker Second Sight in Sylmar, California to upgrade their software currently on the market.