The assignee for this patent, patent number 8626306, is
Reporters obtained the following quote from the background information supplied by the inventors: "As intraocular surgical techniques have advanced, it has become possible to apply stimulation on small groups and even on individual retinal cells to generate focused phosphenes through devices implanted within the eye itself. This has sparked renewed interest in developing methods and apparatuses to aid the visually impaired. Specifically, great effort has been expended in the area of intraocular retinal prosthesis devices in an effort to restore vision in cases where blindness is caused by photoreceptor degenerative retinal diseases such as retinitis pigmentosa and age related macular degeneration which affect millions of people worldwide.
"Neural tissue can be artificially stimulated and activated by prosthetic devices that pass pulses of electrical current through electrodes on such a device. The passage of current causes changes in electrical potentials across visual neuronal membranes, which can initiate visual neuron action potentials, which are the means of information transfer in the nervous system.
"Based on this mechanism, it is possible to input information into the nervous system by coding the information as a sequence of electrical pulses which are relayed to the nervous system via the prosthetic device. In this way, it is possible to provide artificial sensations including vision.
"One typical application of neural tissue stimulation is in the rehabilitation of the blind. Some forms of blindness involve selective loss of the light sensitive transducers of the retina. Other retinal neurons remain viable, however, and may be activated in the manner described above by placement of a prosthetic electrode device on the inner (toward the vitreous) retinal surface (epiretinal). This placement must be mechanically stable, minimize the distance between the device electrodes and the visual neurons, and avoid undue compression of the visual neurons.
"In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrode assembly for surgical implantation on a nerve. The matrix was silicone with embedded iridium electrodes. The assembly fit around a nerve to stimulate it.
"Dawson and Radtke stimulated cat's retina by direct electrical stimulation of the retinal ganglion cell layer. These experimenters placed nine and then fourteen electrodes upon the inner retinal layer (i.e., primarily the ganglion cell layer) of two cats. Their experiments suggested that electrical stimulation of the retina with 30 to 100 uA current resulted in visual cortical responses. These experiments were carried out with needle-shaped electrodes that penetrated the surface of the retina (see also U.S. Pat. No. 4,628,933 to Michelson).
"The Michelson '933 apparatus includes an array of photosensitive devices on its surface that are connected to a plurality of electrodes positioned on the opposite surface of the device to stimulate the retina. These electrodes are disposed to form an array similar to a 'bed of nails' having conductors which impinge directly on the retina to stimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describes spike electrodes for neural stimulation. Each spike electrode pierces neural tissue for better electrical contact. U.S. Pat. No. 5,215,088 to Norman describes an array of spike electrodes for cortical stimulation. Each spike pierces cortical tissue for better electrical contact.
"The art of implanting an intraocular prosthetic device to electrically stimulate the retina was advanced with the introduction of retinal tacks in retinal surgery.
In addition to obtaining background information on this patent, VerticalNews editors also obtained the inventors' summary information for this patent: "In a visual prosthesis or other neural stimulator it is advantageous to provide non-overlapping pulses in order to provide independent control of brightness from different electrodes. Non-overlapping pulses on geographically close electrodes avoids electric-field interaction which leads to brightness summation or changes in the shape and area of percepts. It is advantageous to apply pulses to nearby electrodes in a way that the currents do not overlap in time at all. The new finding is that even a small amount of separation results in a significant improvement as small as (ie. 0.225 msec). `Nearby` is defined as within a few millimeters of each other.
"Another new finding is that there is some additional benefit of separating the pulses in time even further. In particular, some experiments showed a benefit of separating them more than 1.8 msec. Another experiment showed a benefit of separating them greater than 3 msec. But, there is probably no benefit to separating them more than 5 msec. or 10 msec at the greatest.
"The same parameters that provide independent control of brightness also produce spatial patterns that the subjects' report as being similar to the sum of individual electrode phosphenes. For example, when neighboring electrodes are stimulated simultaneously, or closely in time, the spatial configuration of the resulting phosphene is not easily predicted by knowing the size and shape of the phosphenes produced by the individual electrodes when stimulated alone.
"Simultaneous stimulation of multiple electrodes can sometimes produce physical sensation or discomfort in the eye. Time-shifting the pulses can also be used to reduce the physical sensations felt by the patient. There is evidence that with a ground placed outside the sclera, stimulation of multiple electrodes simultaneously results in lower thresholds for these physical sensations than phase-shifted stimulation.
"Further embodiments are disclosed throughout the specification, drawings and claims of the present invention."
For more information, see this patent: Horsager, Alan M.; Greenberg, Robert J.; McMahon, Matthew J.. Visual Prosthesis for Control of Spatiotemporal Interactions. U.S. Patent Number 8626306, filed
Keywords for this news article include: Cells, Neurons,
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