Planet Earth

Retinal implant partially restores sight in blind people

Not Exactly Rocket ScienceBy Ed YongNov 3, 2010 5:00 AM


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Miikka is blind. He is one of over 15 million people across the world who suffers from genetic disorders that rob them of their sight as they grow older. At the age of 18, he became night blind, making it very difficult for him to see in low light although he could see well enough to pass his driving test. At 30, he started having problems recognising faces and reading. At 38, he could no longer read at all and by 44, he could only sense the direction of bright light, relying on a cane to get around. But Miikka’s world recently changed. He is one of three people whose sight has been partially restored by a small chip, implanted directly into his retina. The other two can locate bright objects on a dark table, while Miikka can read large letters, name objects like a fork or fruit, approach people in a room and discern different shades of grey. In people like Miikka with retinitis pigmentosa, the light-detecting cells of the retina break down with age. Eberhart Zrenner and a team of German scientists have designed a chip that does the same job as these defunct cells. Just a few millimetres across, it contains 1,500 light-detecting diodes that detect light and convert it into a current. The brighter the light that hits the chip, the stronger the current it puts out. The current is delivered directly to the bipolar cells, which would normally transmit the signals from the retina’s actual light detectors.

Zrenner’s team have been developing the implant for over a decade, painstakingly establishing that their method could work, checking its safety, finding the right materials, and testing the chip in cats. Finally, they moved on to a pilot study with real patients. They recruited 11 in total and at least five of them managed to recognise large bright objects. The last three patients to go through the operation are described in the group’s new paper. They include Miikka, another man, and a woman, who had all lost their previously excellent sight due to inherited disorders. Their vision had deteriorated for decades, and all of them had been fully blind for at least five years. The surgery wasn’t easy. The chip sits at the end of a long steel tube, which had to be threaded through a hole behind the ear. After that, the surgeons had to remove a lot of the vitreous jelly in the front of the eye to work on the deeper layers, and they had to detach a small part of the retina to guide the chip into place. Thankfully, all three operations were successful. Around 7 to 9 days later, Zrenner began the testing his patients. She found that they could detect differences in contrast between grids of dark and light stripes. In a more realistic test, they could discern bright objects on a dark table, including cutlery, plates and mugs. The patients got back a visual field of around 11 degrees in front of them; it’s narrow, but enough for the basic aspects of everyday life. Reading, for example, only requires a field of three to five degrees. One of the patients, a man named Miikka, did substantially better than the others. He was the last to be operated on and his chip was implanted directly within the fovea, the area responsible for our sharpest central vision. His performance was excellent. With no training, he could detect several subtly different shapes, a variety of common objects, clock faces, slightly different shades of gray and letters displayed on a screen. He could even read his own name, written in large white letters, and distinguish it from the incorrectly spelled Mika. Zrenner’s success comes in the midst of a fierce race to develop a working retinal prosthesis. Since the late 1990s, scientists have launched trials to electrically stimulate the retina with implanted electrodes. In 2005, a team from Rush University Medical Center became the first to try out an implant that’s similar to the one that Zrenner has created. But the device wasn’t powerful enough; the energy from light hitting the chip didn’t provide enough of a stimulus to the underlying neurons. To get around this, Zrenner added an amplifier to each of his 1,500 diodes. Many other trials and studies are underway and as Zrenner writes, “it is too early to compare the final long-term outcome of the various designs.” There’s still a long way to go in this field and Zrenner’s study, while promising, is just a pilot. It will need to be repeated in a larger group of people (and especially now that the team have become more confident in their surgical techniques). Zrenner is working on ways of improving the contrast, resolution and field of vision that the chip provides. But his main challenge now is endurance. The pilot was only meant as a short-term test to prove that the concept of a retinal implant could work. As such, the chip was connected to an external power source and set of controls, and which isn’t really tenable in the long-term. But Zrenner is already in the midst of a follow-up study. This time, the chip has been connected to a local power source that has also been implanted behind the patients’ ears. This new version has been implanted into 25 European patients and only time will tell how well it works. As a final twist to this tale, the patients’ sight actually improved beyond their original abilities in a fascinating way. The diodes in their chips aren’t exactly the same as our own natural light-detectors and they respond to light slightly different ways. The upshot of this is that they implant made the patients very sensitive to infrared light, something that we can’t actually see. Reference: Proc Roy Soc B disclosure note: Zrenner acts as Chairman of the Supervisory Board for Retina Implant AG, the company that produces the retinal chip. He and a few of the other authors are inventors on patents owned by the company, and minor stock-holders. Images by Retina Implant AG More on new medical advances:

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