A bionic eye that can restore sight to the blind should be available commercially within two years, scientists behind the revolutionary technology announced yesterday.

The artificial retina has been cleared by US regulators to begin trials on between 50 and 75 people suffering from two of the most common causes of blindness, opening the way for millions more to benefit from similar implants in the future.

If the research progresses well, a device could be on the market early in 2009 at a likely cost of about £15,000, said Mark Humayun, Professor of Ophthalmology at the Doheny Eye Institute, part of the University of Southern California.

An early version of the prosthetic retina has already been fitted to six patients with retinitis pigmentosa, a degenerative and incurable eye condition that affects 1 in 3,500 people. All have recovered the ability to detect light and motion, and even to make out large letters and to distinguish between objects such as a cup, a knife and a plate.

The second-generation device that is now starting trials should provide even better vision, as it contains 60 light-sensitive electrodes, compared with 16 in the previous model.

More improvements are expected within five to seven years with a 1000-electrode implant that will enable previously blind people to recognise faces, Professor Humayun said.

“The ultimate aim is to allow people recognise faces, and to allow the completely blind to get around on their own,” he told the American Association for the Advancement of Science conference in San Francisco. “The first phase began in 2002, and the results were not what we expected: we thought they would only see light and dark, but they have done far better than that.

“They can differentiate between a cup, a plate and a knife. They can see motion. They can avoid stumbling around into large objects. That is just with 16 electrodes, and we’re now going up to 60. The models suggest 1,000 will be enough for face recognition, and we hope to get there in five to seven years.”

The bionic eye consists of three elements. First, a miniature camera worn in a pair of dark glasses, which transmits images to a radio receiver implanted near the patient’s eye.

This then sends a signal on to a tiny silicon and platinum chip, about 4mm square, that sits on the retina. The chip’s electrodes stimulate the ganglion cells that transmit visual information to the optic nerve and onwards to the brain, which can then construct a visual image.

“A plate is seen as a saucer of light, and a knife as a runway of light,” Professor Humayun said. “It works by building up images like a dot-matrix printer, or pixels on a computer screen.” The implant is suitable for people who are blind because they have lost the photoreceptor cells known as rods and cones that respond to light — the electrodes effectively provide artificial replacements. This includes those with macular degeneration — the most common cause of blindness, which affects up to 15 per cent of over-75s.

The technology cannot restore sight to patients who are blind because of severe optic nerve damage, such as that caused by glaucoma, or because of a stroke.

Professor Humayun said that it would also work better for people who have been able to see as older children or adults, than for those who have been blind since birth.

It generally takes patients a month or two to get used to the Argus device, before their brains learn to interpret the images. While the operation to install it took seven hours originally, it now takes 90 minutes.

In the first phase of the trials, patients were able to use the implant in the laboratory only. For the past year they have also been allowed to try it at home. “Perhaps what we’re most excited about in this next study is we will be able to test the new device with patients at their homes, churches, schools and similar locations,” Professor Humayun said.

The trials will be conducted at five centres in the US, on patients over 50. The US Food and Drug Administration has insisted on older subjects as they have less to lose if the experiments go wrong.

Thousands of people have already volunteered.

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