Visual prosthetic
From Wikipedia, the free encyclopedia
For the non-functional prosthetic or glass eye see Ocular prosthetic.
A visual prosthetic or bionic eye is a form of neural prostheses intended to 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 or optic nerve in order to augment or replace the real eye.
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[edit] History
Scientific research since at least the 1950s has investigated interfacing electronics at the level of the retina, optic nerve, thalamus, and cortex. Visual prosthetics do not yet offer the functionality of a real eye.
[edit] Biological considerations
The ability to give sight to a blind person via a bionic eye depends on the circumstances surrounding the loss of sight. Candidates for visual prosthetic implants find the procedure most successful if the optic nerve was developed prior to the onset of blindess. Persons born with blindness may lack a fully developed optical nerve, which typically develops prior to birth.[citation needed]
According to the Society for the Prevention of Blindness, between 10,000 and 12,000 people per year lose an eye. Though 50% or more of these eye losses are caused by an accident (in one survey more males lost their eyes to accidents compared to females), there are a number of inherited conditions that can cause eye loss or require a visual prosthetic. Microphthalmia is a birth defect where for some unknown reason the eye does not develop to its normal size. These eyes are totally blind, or at best might have some light perception.[1]
[edit] Technological considerations
Visual prosthetics are being developed as a potentially valuable aide for individuals with visual degradation. The visual prosthetic in humans remains experimental, while visual prosthetics have been implemented in other animals. Visual prosthetics providing a level of visual acuity comparable to that of a camera are currently undergoing research trials in rats. Bionic visual implants have demonstrated the ability to partially recover lost sight in rats during laboratory testing.[citation needed]
[edit] Ongoing projects
[edit] 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.[2]
[edit] Implantable Miniature Telescope
An Implantable Miniature Telescope is one type of visual prosthetic that has met with some success in the treatment of end-stage age-related macular degeneration.[3][4][5] 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.[4][5] Success has also been achieved with retinal implants which use an array of electrodes connected to an external camera.
[edit] Harvard/MIT Retinal Implant
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. [2]
[edit] Artificial Silicon Retina (ASR)
The brothers Alan Chow and Vincent Chow have developed a microchip containing 3500 solar cells, which detect light and convert it into electrical impulses, which stimulate healthy retinal ganglion cells. The ASR requires no externally-worn devices. [2]
[edit] The 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. One subject has had the system implanted in his brain since 1978 with no ill effects. [2]
[edit] The 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. [2]
[edit] Other projects
Other notable researchers include Richard Normann and David Bradley at University of Chicago, Ed Tehovnik at MIT, a California-based company named Second Sight and Mark Humayun at the University of Southern California. [6]
Clinical trials have recently been announced for a retinal implant developed in the US.[7]
[edit] References
- ^ How Products Are Made: Artificial Eye
- ^ a b c d e James Geary (2002). The Body Electric. Pheonix.
- ^ Chun DW, Heier JS, Raizman MB. (2005). "Visual prosthetic device for bilateral end-stage macular degeneration.". Expert Rev Med Devices. 2 (6): 657-65.
- ^ a b 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.
- ^ a b Lane SS, Kuppermann BD. (2006). "The Implantable Miniature Telescope for macular degeneration.". Curr Opin Ophthalmol. 17 (1): 94-8.
- ^ Mark Humayun
- ^ Jonathan Fildes. "Trials for bionic eye implants", BBC, 16 February 2007.
