Visual prosthesis - AbsoluteAstronomy.com

For the non-functional prosthesis or glass eye see Ocular prosthesis
Ocular prosthesis
An ocular prosthesis or artificial eye replaces an absent natural eye following an enucleation, evisceration, or orbital exenteration. The prosthetic fits over an orbital implant and under the eyelids. Often referred to as a glass eye, the ocular prosthesis roughly takes the shape of a convex...

and Craniofacial prosthesis
Craniofacial prosthesis
Craniofacial prostheses are prostheses made by individuals trained in anaplastology or maxillofacial prosthodontics who medically help rehabilitate those suffering from facial defects caused by disease , trauma or birth defects...

.

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

Blindness

Blindness is the condition of lacking visual perception due to physiological or neurological factors.Various scales have been developed to describe the extent of vision loss and define blindness...

. Many devices have been developed, usually modeled on the cochlear implant
Cochlear implant
A cochlear implant is a surgically implanted electronic device that provides a sense of sound to a person who is profoundly deaf or severely hard of hearing...

or bionic ear devices, a type of neural prosthesis

Neuroprosthetics

Neuroprosthetics is a discipline related to neuroscience and biomedical engineering concerned with developing neural prostheses....

in use since the mid 1980s.

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), 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.

Technological considerations

Visual prosthetics are being developed as a potentially valuable aid for individuals with visual degradation. The visual prosthetic in humans remains investigational.

Argus Retinal Prosthesis

Drs. Mark Humayun and Eugene DeJuan at the Doheny Eye Institute (USC

University of Southern California

The University of Southern California is a private, not-for-profit, nonsectarian, research university located in Los Angeles, California, United States. USC was founded in 1880, making it California's oldest private research university...

) along with 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

Johns Hopkins University

The Johns Hopkins University, commonly referred to as Johns Hopkins, JHU, or simply Hopkins, is a private research university based in Baltimore, Maryland, United States...

in the early 1990s along with Dr. Robert Greenberg. In the late 1990s the company Second Sight was formed by Dr. Greenberg along with medical device entrepreneur, Alfred E. Mann

Alfred E. Mann

Alfred E. Mann , who is also known as Al Mann, is an American entrepreneur and philanthropist. According to Forbes magazine, his estimated net worth exceeded $2.2 billion as of 2007, ranking him the 204th richest man in America and the 390th richest man in the world.Born and raised in Portland, his...

, 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

Food and Drug Administration

The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

approval to begin a trial of its second generation, 60 electrode implant, in the US. Additionally they have planned clinical trials worldwide, which all got underway in 2007. Second generation Argus II trials are currently ongoing in the U.S. and are still waiting on FDA approval for public sale. Only around ten people in the U.S. currently have this model. It was recently approved in Europe, yet it costs roughly $100,000. The Argus III model is currently in process of improved sight with 240 electrodes. 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)

Université catholique de Louvain

The Université catholique de Louvain, sometimes known, especially in Belgium, as UCL, is Belgium's largest French-speaking university. It is located in Louvain-la-Neuve and in Brussels...

, 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

Human eye

The human eye is an organ which reacts to light for several purposes. As a conscious sense organ, the eye allows vision. Rod and cone cells in the retina allow conscious light perception and vision including color differentiation and the perception of depth...

's posterior chamber

Posterior chamber

The posterior chamber should not be confused with vitreous chamber. The posterior chamber is a narrow chink behind the peripheral part of the iris of the lens, and in front of the suspensory ligament of the lens and the ciliary processes. The Posterior Chamber consists of small space directly...

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

Scotoma

A scotoma is an area of partial alteration in one's field of vision consisting of a partially diminished or entirely degenerated visual acuity which is surrounded by a field of normal - or relatively well-preserved - vision.Every normal mammalian eye has a scotoma in its field of vision, usually...

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. The implant doesn’t affect your natural eye movement; you’ll need to wear glasses and may need to sometimes use a hand-held magnifying glass to read or see fine details.

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

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

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

Retinitis pigmentosa

Retinitis pigmentosa is a group of genetic eye conditions that leads to incurable blindness. In the progression of symptoms for RP, night blindness generally precedes tunnel vision by years or even decades. Many people with RP do not become legally blind until their 40s or 50s and retain some...

. 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.

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.

Dobelle Eye

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

Cataract

A cataract is a clouding that develops in the crystalline lens of the eye or in its envelope, varying in degree from slight to complete opacity and obstructing the passage of light...

, or a damaged cornea

Cornea

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, with the cornea accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea is...

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 sightless 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.

Other projects

Other note-worthy researchers include Richard Normann (University of Utah) and David Bradley at University of Chicago

University of Chicago

The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...

, Eduardo Fernandez and the European Consortium CORTIVIS (http://cortivis.umh.es), Ed Tehovnik at MIT, Tohru Yagi in Japan Visual Prosthesis Project, and the Bionic Vision Australia multi-institute partnership.

External links

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