Feb 21st 2015 http://www.economist.com/news/science-and-technology/21644122-new-device-may-restore-vision-those-whose-sight-dwindling-bionic-eyes MACULAR degeneration is a form of sight loss caused by the death of photoreceptor cells in the macula--the central part of the retina. It afflicts 30m-50m people, most of them elderly. The result is a shadowlike void in the centre of a sufferer's visual field. Many solutions have been proposed, from injecting a patient's eyes with stem cells that will grow into new photoreceptors to building small telescopes into spectacles or contact lenses.
Another is to implant a light-sensitive chip in the affected part of the retina--a promising idea in principle, but one that has not worked well in practice. Daniel Palanker of Stanford University thinks he can do better. He has developed a chip-based system which, although it will not fully restore vision, may bring someone back to a point where he is no longer legally blind. Dr Palanker's apparatus, currently being tested on rats, but intended for clinical trials on people within a year, has two parts. One is a special pair of glasses. The other is not a single photosensitive chip, but a set of them. The spectacles let light into the eye as normal, so that unaffected bits of the retina can continue to do their job. But they also use a small camera to capture the scene the wearer is looking at. That image is then beamed through the pupil of the affected eye to the part of the retina where the chips are. The retransmitted image is 1,000 times brighter than the one created by natural light, but because it is sent in the infra-red part of the spectrum, the eye's photoreceptor cells cannot see it. The chips, however, can. Each of them is 1mm across, and is covered with elements 75 microns (millionths of a metre) wide that are made of three photosensitive diodes and two electrodes. When hit by infra-red light, the diodes generate an electric current and, via the electrodes, stimulate nerve cells in the retinal tissue in the way that a natural photoreceptor would. That signal gets sent to the brain. The result is a picture which fills in the blank part of the user's visual field. The chips themselves are easy to implant, using a special syringe-like applicator that is pushed through the eyeball (a routine procedure, gruesome though it sounds). With this tool members of Dr Palanker's team can "tile" the affected area with as many chips as is necessary. Unlike some existing chip systems, this one does not need an external power supply (though the glasses themselves need batteries). It also has better resolution than its competitors. Although 75 microns is still a bit coarse, Dr Palanker hopes to improve it soon, to 40 microns. The definition of legal blindness in America corresponds to the resolving power that elements 50 microns across or smaller would give, so in that sense the device really would restore sight to the blind. Experiments on rats, in which they are shown alternating black and white lines of different widths, suggest that the theoretical resolution is actually being achieved. If clinical trials show the same is true in people, Dr Palanker's invention may go on to bring visual relief to many whose eyesight is failing. -- Avinash Shahi Doctoral student at Centre for Law and Governance JNU Register at the dedicated AccessIndia list for discussing accessibility of mobile phones / Tabs on: http://mail.accessindia.org.in/mailman/listinfo/mobile.accessindia_accessindia.org.in Search for old postings at: http://www.mail-archive.com/[email protected]/ To unsubscribe send a message to [email protected] with the subject unsubscribe. To change your subscription to digest mode or make any other changes, please visit the list home page at http://accessindia.org.in/mailman/listinfo/accessindia_accessindia.org.in Disclaimer: 1. Contents of the mails, factual, or otherwise, reflect the thinking of the person sending the mail and AI in no way relates itself to its veracity; 2. AI cannot be held liable for any commission/omission based on the mails sent through this mailing list..
