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 Zrenner implanted 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.
Limited vision
But it is not simply a case of insert implant, switch on and hey presto sight is restored, says Humayun. “It’s like a broken arm that’s been in a cast,” he says. “You have to get them reoriented about how to use their eyes.” Their brains also need time to adjust. Blind people famously repurpose the visual centres of their brains towards other senses, like smell or hearing. But Humayun notes that those same areas could “drift back to serving vision again”.
It has taken years to overcome these challenges, and fewer than 100 patients – all with retinitis pigmentosa – have taken part in clinical trials. But their experiences have provided all the motivation needed to plough ahead. “We had patients telling us “I was sitting in my garden and I could see a sunflower”,” says Zrenner. “One patient said he could walk around at night, because he could see streetlamps and headlights. Another told us that he saw the face of his fiancée for the first time. He could make out the shadows between individual teeth when she laughed.”
