THE WORLD OF ENGLISH

A 46 year-old man called Miikka spotted a simple spelling mistake. A group of scientists had misspelled his name as Mika. He told them as much, and they responded with delight. Why? It was the clearest evidence yet that Miikka, who had been blind for many years, might be able to see again.

This miracle is thanks to a pioneering chip implanted in his retina. Just as cochlear implants have restored hearing to people once considered deaf, devices like this are being developed that can restore sight to the blind.

Miikka suffers from a particular form of blindness called retinitis pigmentosa, an inherited disease that gradually destroys the light-detecting cells of the retina. As the cells die, a person’s field of view begins to collapse from the edges. Miikka’s case was so advanced that he could only sense the direction of a bright light, and he needed a cane to get around.

That changed when German scientists led by Eberhart Zrennerimplanted the tiny chip in his retina. The chip consists of 1,500 light-detecting electrodes, which stand in for the retina’s own degenerated sensors by producing an electric current whenever light falls upon them. In early trials, this was enough to restore vision at a low resolution – enough to recognise objects and read large letters. Miikka has been one of their best success so far – he could not only see spelling errors, he was also able to recognise cutlery and a mug on a table, he could read a clock face and he could even distinguish seven different shades of grey.

Zrenner’s chip, produced by Retina Implant AG, is one of several “retinal prostheses” in development. So far, only one has been approved for use in Europe: the Argus II implant by California-based company, Second Sight. Unlike the device Miikka received, the Argus II detects light with an external camera mounted on a pair of glasses, and it uses just 16 electrodes rather than 1,500.

The two implants might look different, but the challenges in creating them are the same. Developing these implants meant years of animal experiments to understand how much current you need to produce the sensation of light. It meant creating surgical techniques for cutting a flap in the eye and attaching the devices in the space beneath the retina. It meant using “biocompatible” materials that will not send the immune system into intruder alert mode, and that can be sterilised without damaging the electronics.

And it meant protecting the delicate chip from any eye-related wear and tear. “The eye is a salty warm environment. It’s very corrosive for electronics,” says Mark Humayun from the University of Southern California, who worked on the Argus II.

http://www.bbc.com/future/story/20120308-will-we-ever-restore-sight