Bionic eye implant powered by infra-red

A tiny silicon chip placed in the back of the eye has the potential to restore sight to around a quarter of the world’s blind people. The crucial breakthrough that sets this development apart from so many other attempts is that it is remotely powered by an infra-red LED fitted to the patient’s spectacles. This shines invisible energy onto a photoreceptor connected via a polyimide foil strip PCB to the chip. The breakthrough comes from the University Eye Hospital in Tübingen in Germany, building on research and development which has been going on across the world, including in the UK, since at least the 1950s. Those who stand to benefit have become blind because of degeneration of or damage to either the retina or the macula, the normally transparent membrane in front of it. An obvious solution is to make a microchip array of photoreceptors which can be implanted in the crucial area of the eye responsible for detailed vision. Tiny electric currents generated by the array can then be used to stimulate the neural cells beneath via titanium nitride electrodes made porous on a nanoscale to increase surface area. The device being developed at Tübingen is 3mm square and has about 1,600 pixels. It includes light sensors, amplifier and stimulation electrodes, and results in a visual field of 12°. The individual pixel elements are 70µm apart, resulting in a resolution of 16 minutes of arc, which is nowhere near as good as an undamaged eye retina, but is a lot better than nothing and at least allows the recognition and avoidance of large objects. The overall implant size is 20mm long and 3mm wide. Sophisticated nano scale circuitry allows the implant to adapt to different illumination levels. Previous attempts have foundered on problems of biological incompatibility and infection, a problem greatly exacerbated by the need to provide power. Eureka knows of at least one attempt some years ago in the UK where a much less sophisticated device was implanted in the eye of a particularly brave and desperate patient. The device worked well enough to show the idea was valid but, sadly, had to be removed because of infection. Development has now reached the stage where the device is being experimentally implanted in rabbits and a miniature strain of pigs. Pig eyes are biologically very close to those of humans but since pigs are unable to explain what they can see, the effectiveness of the implants is established by monitoring brain activity in the animal’s visual cortex. While the development is still a very long way from that portrayed in the TV series, ‘The Six Million Dollar Man’, it is already evident that the brain responds more quickly to the electronic implants than to natural cells. Hence it is not inconceivable that, one day, electronic implants may be developed which outperform the natural organs. In the meantime, the technology works well enough for possible industrial applications, while providing hope for blind people. A company has already been spun off to exploit the commercial potential.University of Tuebingen Design Pointers: A retinal eye implant is being developed that will be powered by infra-red light shone into the eye from an LED on the patient’s spectacles The technology has also involved the development of new biocompatible encapsulation materials, nano porous titanium nitride electrodes and nanoscale electronics