Image caption X-ray of skull showing position of chip with cable running to control unit

Two British men who have been totally blind for many years have had part of their vision restored after surgery to fit pioneering eye implants.

They are able to perceive light and even some shapes from the devices which were fitted behind the retina.

The men are part of a clinical trial carried out at the Oxford Eye Hospital and King's College Hospital in London.

Professor Robert MacLaren and Mr Tim Jackson are leading the trial.

The two patients, Chris James and Robin Millar, lost their vision due to a condition known as retinitis pigmentosa, where the photoreceptor cells at the back of the eye gradually cease to function.

The wafer-thin, 3mm square microelectronic chip has 1,500 light-sensitive pixels which take over the function of the photoreceptor rods and cones.

The surgery involves placing it behind the retina from where a fine cable runs to a control unit under the skin behind the ear.

I am able to make out a curve or a straight line close-up but I find things at distance more difficult. Chris James, Patient

'Magic moment'

When light enters the eye and reaches the chip it stimulates the pixels which sends electronic signals to the optic nerve and from there to the brain.

The chip can have its sensitivity altered via an external power unit which connects to the chip via a magnetic disc on the scalp.

Chris James from Wroughton in Wiltshire said there was a "magic moment" when the implant was switched on for the first time and he saw flashing lights - showing that the device was functional.

"I am able to make out a curve or a straight line close-up but I find things at distance more difficult. It is still early days as I have to learn to interpret the signals being sent to my brain from the chip."

Mr James, a motor-racing enthusiast, says his ambition is to be able to make out the silhouettes of different cars on the race-track.

Prof MacLaren, who fitted the first implant in the UK at the Oxford Eye Hospital, said:

"It's the first time that British patients who were completely blind have been able to see something.

"In previous studies of restorative vision involving stem cells and other treatments, patients always had some residual sight.

"Here the patients had no light perception at all but the implant reactivated their retina after more than a decade."

The chip results in the brain receiving flashes of light rather than conventional vision - and it is in black and white rather than colour.

Colour vision

But in an unexpected development, the other British man to have the implant says he is now able to dream in colour for the first time in 25 years. Robin Millar says he is also able to stand in a room and detect light coming through windows.

Prof MacLaren said the results might not seem extraordinary to the sighted, but for a totally blind person to be able to orientate themselves in a room, and perhaps know where the doors and windows are, would be "extremely useful" and of practical help.

In 2010 a Finnish man who received the experimental chip was able to identify letters, but his implant worked only in a laboratory setting, whereas the British men's devices are portable. The implant was developed by a German company, Retina Implant AG.

'Pioneering'

Mr Tim Jackson, eye surgeon at King's College Hospital who has also fitted one of the devices, said:

"This pioneering treatment is at an early stage of development, but it is an important and exciting step forward, and may ultimately lead to a much improved quality of life for people who have lost their sight from retinitis pigmentosa.

"Most of the people who receive this treatment have lost their vision for many years, if not decades. The impact of them seeing again, even if it is not normal vision, can be profound, and at times quite moving."

Both surgeons stress that the chip is not a treatment but part of a clinical trial. Up to a dozen British patients will be fitted with the implants.

Although it could ultimately benefit patients with the most common form of progressive blindness, age-related macular degeneration, they are not eligible for the study at present.

Nor are patients with glaucoma or optic nerve disease.

Nick Astbury, Chair of VISION 2020 UK, a global initiative for the elimination of avoidable blindness said: "This trial will bring hope to two million blind and partially-sighted people living in the UK. It is the first step on a long journey to help people with sight loss to see again and live independently".