SAN FRANCISCO - People who have been blind for most of their lives have been able to see everyday objects with the help of a "bionic" eye that may one day restore sight to patients with degenerative eye diseases.
Results of the first clinical trial of an artificial retina in six blind patients have been so successful that scientists have gained approval to go to a more advanced stage involving operations on up to 75 volunteers.
Scientists behind the project said they were astonished by the success of the artificial eye - a tiny video camera embedded in a pair of spectacles that sends images to electrodes implanted into the light-sensitive retina at the back of the eye.
"We expected that all they would be able to see is just light and dark," said Mark Humayun, professor of ophthalmology at the University of Southern California in Los Angeles. "But the subjects can differentiate in a test environment between a cup, a plate and a knife.
"They can detect motion around them, they can tell large objects without stumbling into them ... It's not what we expected. It really speaks to the brain's ability to fill in the missing information," Professor Humayun told the American Association for the Advancement of Science in San Francisco.
The first clinical trial, which began in 2002, involved a retinal implant with 16 tiny electrodes.
The US Food and Drug Administration (FDA) has approved the next stage, involving an implant with 60 electrodes, which should give better picture quality.
"It's amazing that even with 16 pixels, or 16 channels or electrodes, just how much our first six subjects have been able to do," he said.
"The FDA has just approved our next-generation device which is going to have 60 channels, and about four times the number of pixels we hope, and be about a quarter of the size," he added.
Millions of people in the world with macular degeneration, which causes tunnel vision and eventual blindness, or retinitis pigmentosa, which progressively destroys the light-sensitive cells of the retina, could benefit from the device if it could be refined still further and produced at a cheap enough price.
The tiny video camera embedded in a pair of spectacles sends information to a receiver implanted behind the ear and from there to an electrode-studded array implanted behind the retina.
It took 7 1/2 hours to implant the old, 16-electrode device but the new one should take just one hour because it would be a quarter of the size, Professor Humayun said.
"It works by collectively stimulating the nerve cells, which results in the perception of seeing a spot of light. When a subject was asked to differentiate between a plate and a knife, they say they saw a saucer of light for the plate and a sort of runway of light for the knife," he explained.
Patients have to practise with the artificial retina for a few weeks before they can begin to distinguish between different objects. The speed at which they learn depends on several factors.
"It has to do with how smart the patient is and for how long they have been blind. It takes in the order of a month or two months for them to really start to use the device, it's not overnight," Professor Humayun said.
One unexpected outcome of the experiment is that the patients often report being able to see objects in colour, even when they are in reality just black and white.
"They say they see colour, but the colours are not in the real world and we don't know why. They say, 'You changed the colour on me'. They see deep oranges, they see blue, they see yellow, they see different types of colours."
- INDEPENDENTBy Steve Connor