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A visual prosthesis or bionic eye is a form of neural prosthesis intended to partially restore lost vision or amplify existing vision. It usually takes the form of an externally-worn camera that is attached to a stimulator on the retina, optic nerve, or in the visual cortex, in order to produce perceptions in the visual cortex.
These experimental visual devices are modeled on the cochlear implant or bionic ear devices, a type of neural prosthesis in use since the mid 1980s. These are an externally-worn microphone and processor that is attached to a stimulator in the cochlea, auditory nerve, in order to produce sound perception in the auditory cortex.
Scientific research since at least the 1950s has investigated interfacing electronics at the level of the retina, optic nerve, thalamus, and cortex. Visual prosthetics, which have been implanted in patients around the world both acutely and chronically, have demonstrated proof of principle, but do not yet offer the visual acuity of a normally sighted eye.
Biological considerations Edit
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), vision loss due to degeneration of photoreceptors (retinitis pigmentosa, choroideremia, geographic atrophy macular degeneration) is 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.[How to reference and link to summary or text]
Technological considerations Edit
Visual prosthetics are being developed as a potentially valuable aide for individuals with visual degradation. The visual prosthetic in humans remains investigational.
Argus Retinal ProsthesisEdit
Drs. Mark Humayun and Eugene DeJuan at the Doheny Eye Institute (USC) 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 to develop a chronically implantable retinal prosthesis. Their first generation implant had 16 electrodes and was implanted in 6 subjects between 2002 and 2004. Five of these subjects still use the device in their homes today. These subjects, who were all completely blind prior to implantation, can now perform a surprising array of tasks using the device. More recently, the company announced that it has received FDA approval to begin a trial of its second generation, 60 electrode implant, in the US.  Additionally they have planned clinical trials worldwide, all getting underway in 2007. Three major US government funding agencies (National Eye Institute, Department of Energy, and National Science Foundation) have supported the work at Second Sight and USC.
Microsystem-based Visual Prosthesis (MIVIP)Edit
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 TelescopeEdit
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.
Tübingen MPDA ProjectEdit
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 Yucatan 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 eight participants suffering from RP. The results were to be presented in detail on the ARVO 2007 congress in Fort Lauderdale.[How to reference and link to summary or text]
Harvard/MIT Retinal ImplantEdit
Joseph Rizzo and John Wyatt at MIT and the Massachusetts Eye and Ear Infirmary have developed a stimulator chip that sits on the retina and is in turn stimulated by 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. 
Artificial Silicon Retina (ASR)Edit
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. 
Optoelectronic Retinal ProsthesisEdit
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. Current can be further increased by approximately an order of magnitude using a common bias voltage provided by a radiofrequency-driven implantable power supply  Close proximity between electrodes and neural cells necessary for high resolution stimulation can be achieved utilizing effect of retinal migration.
The Dobelle EyeEdit
- Main article: William H. Dobelle
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.[How to reference and link to summary or text]
Intracortical Visual ProsthesisEdit
- Main article: 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. [How to reference and link to summary or text]
The Virtual Retinal Display (VRD)Edit
- Main article: Virtual retinal display
Other note-worthy researchers include Richard Normann (University of Utah) and David Bradley at University of Chicago, Eduardo Fernandez and the European Consortium CORTIVIS (http://cortivis.umh.es), Ed Tehovnik at MIT, Tohru Yagi in Japan Visual Prosthesis Project, and the Australian Vision Prosthesis Group at the University of New South Wales.
- ↑ U.S. Department of Energy Office of Science. How the Artificial Retina Works.
- ↑ Second Sight. Ending the Journey through Darkness: Innovative Technology Offers New Hope for Treating Blindness due to Retinitis Pigmentosa.
- ↑ includeonly>Jonathan Fildes. "Trials for bionic eye implants", BBC, 16 February 2007.
- ↑ 4.0 4.1 4.2 4.3 James Geary (2002). The Body Electric, Phoenix.
- ↑ Chun DW, Heier JS, Raizman MB. (2005). Visual prosthetic device for bilateral end-stage macular degeneration.. Expert Rev Med Devices. 2 (6): 657-65.
- ↑ 6.0 6.1 Lane SS, Kuppermann BD, Fine IH, Hamill MB, Gordon JF, Chuck RS, Hoffman RS, Packer M, Koch DD. (2004). A prospective multicenter clinical trial to evaluate the safety and effectiveness of the implantable miniature telescope.. Am J Ophthalmol. 137 (6): 993-1001.
- ↑ 7.0 7.1 Lane SS, Kuppermann BD. (2006). The Implantable Miniature Telescope for macular degeneration.. Curr Opin Ophthalmol. 17 (1): 94-8.
- ↑ Palanker Group. Artificial Sight: Optoelectronic Retinal Prosthesis.
- ↑ J.D. Loudin, D.M. Simanovskii, K. Vijayraghavan, C.K. Sramek, A.F. Butterwick, P. Huie, G.Y. McLean, and D.V. Palanker (2007). Optoelectronic retinal prosthesis: system design and performance. J Neural Engineering 4: S72–S84.
- ARMD, Retinal Electronic Prosthesis and RPE Transplantation - eMedicine.com
- 'Bionic' eye implants look ahead - BBC
- NewScientist.com: 'Bionic eye' may help reverse blindness
- BBC: 'Artificial eye'
- How does a "bionic eye" allow blind people to see? - HowStuffWorks.com
- Research opens way for bionic eye; BBC, 24 April 2007.
- Visual Prosthesis Links; Japan Visual Prosthesis Group