A new bionic eye implant, which could help to partially restore the sight of millions of blind people, may be available for mass production within two years. American scientists have been given the all-clear to implant the Argus II prototype in up to 75 patients.

"What we are trying to do is take real-time images from a camera and convert them into tiny electrical pulses that would jump-start the otherwise blind eye and allow patients to see," said professor Mark Humayan at the University of California .

The first version of the Argus implant was trialled in 2005, when a man who had been blind for 50 years partially regained his sight. The implant the man was fitted with was capable of processing 16 pixels at a time, which was enough for the man to identify colours and shapes.

The Argus II is more advanced and packs nearly four times as many pixels, opening up the possibility that the sight of some blind people could be significantly improved.

It works by inserting a bionic eye implant which has a mass of electrodes that connect with the back of the retina. A small camera at the front of the implant sends the visual data into a processing unit worn on a belt, which converts the information into electrical signals which are then fed back through the implant and up the optical nerve into the brain.

Each implant would potentially cost around £15,000. The technology is expected to improve significantly in the coming years.