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Bionic eyes bringing sight back to the blind

Since 1996, the National Science Foundation has been funding research into the development of artificial retina technology. A milestone on the road to true bionic sight came in February 2013, when the U.S. Food and Drug Administration (FDA) approved the mass manufacture and sale of the Argus II®, a retinal prosthesis that can restore partial eyesight to people who suffer from certain types of complete blindness. Prior to this people who had vision impairments might work with occupational therapists to help them learn how to manage living with their disability, as there was little doctors and nurses could do to help them recover their vision.

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The device, made by California company Second Sight Medical Products, detects light with an eyeglass-mounted camera that transmits images of contrasting light and dark to an array of electrodes implanted in the retina. That electrical information is then sent down the optic nerve and into the brain.

Argus II is designed to correct blindness caused by a specific congenital condition known as retinitis pigmentosa, in which the photoreceptor cells of the retina -- known more commonly as rods and cones -- begin to die off. Night vision and peripheral vision are usually the first to go, followed by color and sharp central vision, but the degeneration can take place differently in different patients. Bionic eye technology helps those who suffer from this condition by physically replacing those lost photoreceptive cells with digital receptor sites, allowing the visual cortex to once again access the light information that comes in through the eye. Researchers hope that this technology can also work for individuals suffering from age-related macular degeneration.

What a bionic eye sees

Although retinal implants can restore vision, the vision that results from a prosthetic retinal device has limited sensory ability compared to a fully functioning human eye. Users of the Argus II can recognize simple objects, locate doors and windows, find crosswalks, sense high-contrast shapes and, in some cases, read very large printed type.

For reasons that Second Sight has yet been unable to determine, certain patients seem to be more receptive to the device than others. Some can see flashes of color, for instance, while others may experience little to no benefit from the device. Researchers note that the person-to-person differences can derive from the exact placement of the tiny part of the eye that transmits light information from the retina to the associated neurons or the health of the biological optics that remain after the retinal cells degenerate.

To put the power of bionic vision in perspective, the U.S. threshold of legal blindness is a good benchmark for comparison. A person with a visual score of 20/200 -- which indicates that they can see an object from 20 feet away as clearly as normal-sighted people would see it from a distance of 200 feet -- is considered legally blind. The Argus II allows people with no vision at all to see at a level of detail equivalent to 20/1260. They may still be considered "blind" by the clinical definition, but patients who experience the low-resolution vision report a vast improvement over complete blindness.

Worldwide interest

Even though the first artificial retina was only recently approved for sale in the U.S., it's not the first entry on the world market. Europeans have the option to choose between the Argus, which has been available in Europe since 2011, and another device produced by a German company called Retina Implant AG.

The German device, known as Alpha IMS, differs from the Argus II in a multitude of ways. For starters, while patients with the Argus wear an externally-mounted camera that feeds light information to an array of electrodes, the Alpha IMS has a very small external presence. An implanted three-millimeter chip with 1,500 diode-equipped pixels makes use of the eye's natural ability to collect light, and an implanted signal amplifier boosts each diode's output before transmitting the input. The only piece of externally wearable equipment is the device's battery pack, which can be held inconspicuously behind the ear with magnets.

As one might expect for a device with more internal parts, the surgery to implant the Alpha IMS takes about three times as long as the procedure to install the Argus II. Its low-profile appearance and slightly higher resolution of 20/1000 might make the extra time on the operating table into a minor inconvenience for some patients. Both devices cost about the same as of September 2013 -- the MIT Technology Review reports a list price of around $135,000 for the Alpha IMS and $115,000 for the Argus II.

An ear to the future

Although artificial retina devices seem to be a ways away from reproducing natural vision, scientists working on the devices point to the cochlear implant as an example of sensory replacement technology that's come into its own. Anthony Burkitt, director of an Australian consortium of bionic vision researchers, put it this way: "[in 30 years,] that technology went from being an aid for lip reading to the point where now children with a cochlear implant can go through normal school and even use mobile phones."

Burkitt expects retinal implant technology to develop very rapidly in the next 10 years, and Second Sight seems to be intent on proving him right. Experts agree that adding more receptor sites is the surest way to enhance visual output, and the company has plans for a future release of the Argus to bear 240 electrodes, compared to the array of just 60 used by the current model.

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