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 macular degeneration and retinitis pigmentosa. The former is the foremost cause ofvision loss in North America, and the latter causes an estimated1.5 million people worldwide to lose sight, according to thenonprofit group Foundation Fighting Blindness. In these diseases,the retina's photoreceptor cells slowly degenerate, ultimatelyleading to blindness. But the inner retinal neurons that normallytransmit signals from the photoreceptors to the brain are largelyunscathed.
Retinal prostheses are based on the idea that there areother 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 lot morelight than normal vision would require," said Palanker. "And if weused visible light, it would be painfully bright." Near-infraredlight isn't visible to the naked eye, though it is "visible" to thediodes that are implanted as part of this prosthetic system, hesaid.
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 pixelis like a little solar cell; you send light, then you get currentand that current stimulates neurons in the inner nuclear layer ofthe retina." That, in turn, should have a cascade effect,activating the ganglion cells on the outer layer of the retina,which send the visual information to the brain that allows us tosee. 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 restored with oursystem." He noted that the degenerated rat retinas required greateramounts of near-infrared light to achieve the same level ofactivity 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. Additional References Citations. I am a professional writer from Plastics & Products, which contains a great deal of information about blank trucker hats , mont blanc gmt, welcome to visit!
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