Six blind patients have had their sight partially restored by a "bionic eye" surgically implanted on to their retina. Although it restores only very rudimentary vision, the device has proved so successful that its developers are about to begin a study of a more sophisticated version with between 50 and 75 patients.
If this trial goes to plan the device could be available to patients in two years, and one day it could be used to digitally enhance human sight. The bionic eye works by converting images from a tiny camera mounted on a pair of glasses into a grid of 16 electrical signals that transmit directly to the nerve endings in the retina.
"It's amazing that even with 16 pixels how much our subjects have been able to do," said Mark Humayun, of the Doheny Eye Institute at the University of Southern California, who has pioneered the device. "We were completely wrong," he said. "We thought from simulations that 16 would only give you distinction between light and dark and maybe some grey scale." In fact, subjects are able to tell the difference between objects such as a cup, a plate and a knife. They can also tell which direction objects are moving in front of them. "The brain is able to fill in a lot of the information," he added.
One of Prof Humayun's patients is Terry Byland, 58, from Corona, near Los Angeles. He used to sell power tools before going blind from a condition called retinitis pigmentosa in 1993. "At the beginning, it was like seeing assembled dots - now it's much more than that," he said. His field of view is about 30 centimetres wide, but it allows him to cross a busy street and see white lines on the road. "When I am walking along the street I can avoid low hanging branches - I can see the edges of the branches, so I can avoid them."
And it has had a profound impact on his life. "I was with my son, walking, the first time - it was the first time I had seen him since he was five years old. I don't mind saying, there were a few tears wept that day." The camera in the glasses sends a signal to a pocket device the size of a Blackberry which processes the images in real time into a grid of electrical signals. This is then beamed to the eye implant, which sends it directly to nerve endings in the retina.
In the current devices the receiver for the signal is implanted under the skin behind the ear with a wire connection to the eye implant, but the team have shrunk the electronics so much that the improved version fits under the skin around the eye. More significantly, it now has 60 pixels instead of 16 and because it is smaller the operation to implant it is much less traumatic, taking just an hour and a half instead of eight hours. Prof Humayun predicts that it will cost around $30,000 (£15,400).
All of the image processing happens instantaneously. "It has to be real time because if it isn't and you move your head and the screen is delayed, you start to feel sick and dizzy. I'm sure you've experienced that in movie theatres," he said. Developing the first device took 16 years of research, but the 60 pixel version has taken just four. The implant is not suitable for every form of blindness. Prof Humayun believes his implants will be most successful in patients who were once fully sighted rather than people who were blind from birth. However, he wants to try the device out in those people too. "I don't think it will be as effective as somebody who had vision into their 20s, 30s and 40s, but it is definitely a population we would like to try."
Stevie Wonder is one of his patients who has expressed an interest in the technology, but as someone who lost his sight very early in life, he will not be one of the initial trial patients. "He is very much for really raising awareness of the technology so that people can get to hear about it and really understand it." Prof Humayun predicts that future versions of the bionic eye would need at least 1,000 pixels for patients to recognise faces.