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This device -- a new type of retinal prosthesis -- involves aspecially designed pair of goggles, which are equipped with aminiature camera and a pocket PC that is designed to process thevisual data stream. The resulting images would be displayed on aliquid crystal microdisplay embedded in the goggles, similar towhat's used in video goggles for gaming. Unlike the regular videogoggles, though, the images would be beamed from the LCD usinglaser pulses of near-infrared light to a photovoltaic silicon chip-- one-third as thin as a strand of hair -- implanted beneath theretina. Electric currents from the photodiodes on the chip would thentrigger signals in the retina, which then flow to the brain,enabling a patient to regain vision. A study, to be published online May 13 in Nature Photonics , discusses how scientists tested the photovoltaic stimulationusing the prosthetic device's diode arrays in rat retinas in vitroand how they elicited electric responses, which are widely acceptedindicators of visual activity, from retinal cells. The scientistsare now testing the system in live rats, taking both physiologicaland behavioral measurements, and are hoping to find a sponsor tosupport tests in humans. "It works like the solar panels on your roof, converting lightinto electric current," said Daniel Palanker, PhD, associateprofessor of ophthalmology and one of the paper's senior authors."But instead of the current flowing to your refrigerator, itflows into your retina." Palanker is also a member of theHansen Experimental Physics Laboratory at Stanford and of theinterdisciplinary Stanford research program, Bio-X. The study'sother senior author is Alexander Sher, PhD, of the Santa CruzInstitute of Particle Physics at UC Santa Cruz; its co-firstauthors are Keith Mathieson, PhD, a visiting scholar in Palanker'slab, and James Loudin, PhD, a postdoctoral scholar. Palanker andLoudin jointly conceived and designed the prosthesis system and thephotovoltaic arrays. There are several other retinal prostheses being developed, and atleast two of them are in clinical trials. A device made by the LosAngeles-based company Second Sight was approved in April for use inEurope, and another prosthesis-maker, a German company calledRetina Implant AG, announced earlier this month results from itsclinical testing in Europe. Unlike these other devices -- which require coils, cables orantennas inside the eye to deliver power and information to theretinal implant -- the Stanford device uses near-infrared light totransmit images, thereby avoiding any need for wires and cables,and making the device thin and easily implantable. "The current implants are very bulky, and the surgery to placethe intraocular wiring for receiving, processing and power isdifficult," Palanker said. The device developed by his team,he noted, has virtually all of the hardware incorporated externallyinto the goggles. "The surgeon needs only to create a smallpocket beneath the retina and then slip the photovoltaic cellsinside it." What's more, one can tile these photovoltaic cellsin larger numbers inside the eye to provide a wider field of viewthan the other systems can offer, he added. Stanford University holds patents on two technologies used in thesystem, and Palanker and colleagues would receive royalties fromthe licensing of these patents. The proposed prosthesis is intended to help people suffering fromretinal degenerative diseases, such as age-related maculardegeneration and retinitis pigmentosa. The former is the foremostcause of vision loss in North America, and the latter causes anestimated 1.5 million people worldwide to lose sight, according tothe nonprofit group Foundation Fighting Blindness. In thesediseases, the retina's photoreceptor cells slowly degenerate,ultimately leading to blindness. But the inner retinal neurons thatnormally transmit signals from the photoreceptors to the brain arelargely unscathed. Retinal prostheses are based on the idea thatthere are other ways to stimulate those neurons. The Stanford device uses near-infrared light, which has longerwavelength than normal visible light. It's necessary to use such anapproach because people blinded by retinal degenerative diseasesstill have photoreceptor cells, which continue to be sensitive tovisible light. "To make this work, we have to deliver a lotmore light than normal vision would require," said Palanker."And if we used visible light, it would be painfullybright." Near-infrared light isn't visible to the naked eye,though it is "visible" to the diodes that are implantedas part of this prosthetic system, he said. Palanker explained what he's done by comparing the eye to camera,in which the retina is the film or the digital chip, and eachphotoreceptor is a pixel. "In our model we replace thosephotoreceptors with photosensitive diodes," he said."Every pixel is like a little solar cell; you send light, thenyou get current and that current stimulates neurons in the innernuclear layer of the retina." That, in turn, should have acascade effect, activating the ganglion cells on the outer layer ofthe retina, which send the visual information to the brain thatallows us to see. For this study, Palanker and his team fabricated a chip about thesize of a pencil point that contains hundreds of theselight-sensitive diodes. To test how these chips responded, theresearchers used retinas from both normal rats and blind rats thatserve as models of retinal degenerative disease. The scientistsplaced an array of photodiodes beneath the retinas and placed amulti-electrode array above the layer of ganglion cells to gaugetheir activity. The scientists then sent pulses of light, bothvisible and near-infrared, to produce electric current in thephotodiodes and measured the response in the outer layer of theretinas. In the normal rats, the ganglions were stimulated, as expected, bythe normal visible light, but they also presented a similarresponse to the near-infrared light: That's confirmation that thediodes were triggering neural activity. In the degenerative rat retinas, the normal light elicited littleresponse, but the near-infrared light prompted strong spikes inactivity roughly similar to what occurred in the normal ratretinas. "They didn't respond to normal light, but they did toinfrared," said Palanker. "This way the sight is restoredwith our system." He noted that the degenerated rat retinasrequired greater amounts of near-infrared light to achieve the samelevel of activity as the normal rat retinas. While there was concern that exposure to such doses ofnear-infrared light could cause the tissue to heat up, the studyfound that the irradiation was still one-hundredth of theestablished ocular safety limit. Since completing the study, Palanker and his colleagues haveimplanted the photodiodes in rats' eyes and been observing andmeasuring their effect for the last six months. He said preliminarydata indicates that the visual signals are reaching the brain innormal and in blind rats, though the study is still under way. While this and other devices could help people to regain somesight, the current technologies do not allow people to see color,and the resulting vision is far from normal, Palanker said. The e-commerce company in China offers quality products such as China IPL Beauty Machine , 808nm Diode Laser Hair Removal Manufacturer, and more. For more , please visit IPL Beauty Machine today!
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