Prostheses Visual

A consortium of 13 technical and medical partners works on different tasks to develop a complete system for a visual prosthesis (Fig. 25). The neural pros-theses comprises a unit to record and process ambiance light, an encoder that transforms visual information into a sequence of stimulation pulses, a micro-electromechanical system that is implanted into the eye for interfacing the retina and for generating the appropriate stimuli. 

Both allergic and irritant mechanisms have been proposed as explanations for nasal symptoms. Measures that have successfully been used include nasal swabs (eosinophils), nasal lavage or biopsy, acoustic rhinometry (nasal volume), anterior and posterior rhinomanometry (plethysmography), and measures of nasal hyperreactivity (visual, using a dental prosthesis as a head fixative, and using an ear surgery microscope to measure distances and swelling). 

Computer-brain interfaces can work two ways. Cochlear implants have been developed to detect sound with an external microphone and relay the electrical signal to electrode arrays that directly stimulate inner ear nerve fibers. A visual prosthesis promises to similarly help the blind by applying electrical signals from a camera to an array of microelectrodes implanted into the visual cortex of the brain. Electrical signals from the brain can be used to control prosthetic limbs, computer software, or robots. Electrodes implanted into the pleasure centers of the brains of rats have been used to train rats to respond to investigators commands. 

The Neural Prosthesis Program, launched in 1972 and spearheaded by F. Terry Hambrecht, MD, brought funding, focus, and coordination to the multidisciplinary effort to develop technologies to restore motor function in paralyzed individuals. The initial efforts were in electrode-tissue interaction, biomaterials and neural interface development, cochlear and visual prosthesis development and control of motor function using implanted and nonimplanted electrodes. 

Auditory prostheses, which provide patterned stimulation of the eighth cranial nerve, were the first commerdaUy available sensory neural prosthesis. As of this writing, it is the only approved sensory prosthesis however, visual prostheses are already in cHnical trials and are Hkely to be available in the not too distant future. 

The restoration of vision has captivated the imagination of man since biblical times. Now, after 4 decades of modern research, beginning with the stimulation of the visual cortex by Giles Brindley in 1966 [75], visual prostheses are making the transition from basic science research to commercialization. William Dobelle, Ph.D. achieved similar results using cortical stimulation to evoke phospheses in 1974 [76,77], and he was a pioneer in the drive to commercialize the visual cortex prosthesis. In 1983, he acquired Avery Labs, a manufacturer of electrodes for brain stimulation. From this and other ventures he derived funds to advance his vision prosthesis research and developments efforts at the Dobelle Institute, located in Portugal. An excellent historical review is provided in this volume by Greenberg. 

On February 19, 2000, the inaugural symposium of the Alfred Mann Institute-University of Southern California (AMl-USC) titled, Can We Make the Blind See — Prospects for Restoring Vision to the Blind was held. The list of lecturers included Dean Baker Director of the AMI-USC Gerald Loeb, a FES researcher at the AMl-USC Dean Bok, a retinal physiologist from UCLA Retinal prosthesis researchers — Robert Greenberg, Mark Humayun, Joseph Rizzo, John Wyatt, and Alan Chow Cortical prosthesis researchers —Richard Normann and Philip Troyk and Dana Ballard, a visual psychophysicist from the University of Rochester. 

Many amputees who wear a body-powered prosthesis develop increased control due to a phenomenon called extended proprioception [ 90]. Extended proprioception gives the wearer feedback as to the position of the terminal device. The subject will know whether the hook is open or closed by the extent of pressure the harness is exerting on his or her shoulder area without having to visually inspect the operation. Many amputees do not like the cosmetic appearance of the hook and control cables and they request a natural-like part of the body replacement. 

For a first exploratory in vivo test only 5 prostheses were tried, each of which was coated under different conditions. Thus, no statistically conclusive statements are yet possible. So far, 1 prosthesis was still patent upon removal after 4 weeks. The others were occluded after 1 week. But among the prostheses which were still patent at explantation, interesting differences were noted between the coated prostheses and the uncoated prostheses, which, according to the opinion of the surgeons, possibly indicates good long-term properties. As demonstrated in Fig. 6, the uncoated prostheses had a thick, loosely constructed protein layer with numerous entrapped cells, whereas the carbon-coated prostheses exhibited a thin, dense protein layer with no cellular materials. Visually a shiny grayish-white layer over more than 90 % of the inner surface... 

Another emphasis has been given to the design of optimal and appropriate adaptive stimulation with respect to the interindividual retinal degeneration in retinitis pigmentosa and the implantation site. An adaptive retinal encoder has been under development [45]. Adaptive visual fields are employed which are adjusted to the function of retinal ganglion cells. The arrangement of electrodes allows sophisticated stimulation procedures. The described retinal prosthesis is considered to be one of the most challenging adaptronic systems of the future. The first patients have been implanted in Europe and the USA... 

Walter, R Kisvarday, Z.F. Gortz, M. Alteheld, N. Rossler, G. Stieglitz, T. Eysel, U.T. Cortical Activation with a Completely Implanted Wireless Retinal Prosthesis. Investigative Ophthalmology and Visual Science, vol. 46, no. 5... 

Stieghtz T, Haberer W, Lau C, Goertz M (2004) Development of an inductively coupled epiretinal visual prosthesis. Proc Ann Int Conf IEEE Eng Med Biol Soc, 26th, San... 

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