Pioneering transplants to restore the sight of people affected by the leading cause of blindness in the Western world could start in three years, after successful human cell implants in pigs.

The animals look a little human, now that they have a lawn of human cells growing in an area about size of about half of a little fingernail at the back of their eyes, which are ideal for testing treatments before they are used on people.

More than 500,000 people in the UK have irreversible blindness caused by macular degeneration and it is estimated that one third of the population could be affected by 2070.

The disease is marked by a progressive loss of central vision due to degeneration of the macula - a pigmented spot at the back of the retina.

Now the first success has been recorded by a London-led team given £4 million by an anonymous American philanthropist, who saw his father go blind, towards the cost of developing a stem cell therapy, where cells taken from a surplus human IVF embryo are used to repair the eye.

Prof Pete Coffey and Lyndon da Cruz, an eye surgeon, of the UCL Institute of Ophthalmology, have teamed up with Prof Peter Andrews, of the University of Sheffield, to take the treatment into hospitals. The pig tests mark a milestone.

"The results are really encouraging," says Prof Coffey. "We plan to do the first patient within three years."

Using surgical instruments introduced through three one millimetre holes in the eye, the team goes under the retina, a translucent layer, then inflate it so it separates from the underlying cells.

The human eye cells derived from embryonic cells were then introduced on a rolled up patch and injected through a one millimetre hole, where the patch of human cells unfolded under the retina.

"I was over the moon when I got the results because it is a proof of concept," says Prof Coffey. "We really can do it."

Although the implanted human cells are black, the same as the surrounding pig cells, they can be distinguished when light of a given colour is shone into the eye. The human cells glowed when viewed this way under the gaze of an instrument called a scanning laser opthalmoscope. "That indicates good function," says Prof Coffey.

The operation on three sighted pigs took only 30 minutes, suggesting the stem cell implants could eventually become a routine outpatient operation, they told an event backed by the company Mostra at the Globe Theatre to promote the London Project to Cure Blindness - a scientific initiative between UCL, Moorfields and The University of Sheffield.

Although it has already raised £4 million for the work, the team has failed to raise matching funding from the troubled UK Stem Cell Foundation to fully develop the treatment. "The main issue is to raise more funding," says Prof Coffey. "If we do not get the money it will seriously slow down the project."

As a human trial run for the operations, the team has also repaired the vision of four out of 12 patients with the wet form of macular degeneration by moving around their own tissue within the eye.

They told the meeting that the method has now also been tested on in five with the dry form, with tissue from their own eyes, moving it from the region of the eye responsible for peripheral vision to repair the damaged macula.

The treatment is not initially aimed at the transparent skin of nerve cells that detect light but at an underlying carpet of cells called the retinal pigment epithelium, or RPE.

RPE was transplanted by surgeons, without the use of stem cells. in an experimental procedure using RPE taken from another site in their own retina. However, moving around RPE in what are long, complex operations is of limited benefit in treating common eye diseases such as macular degeneration.

Prof Coffey has now found a way to turn stem cells taken from early human embryos surplus to test tube baby clinicinto RPE cells by adding growth factors and it was these derived human RPE cells that were implanted into the eyes of the pigs.

"Now we have to get clinical grade cells produced, which is under way in Sheffield for phase one trials," says Prof Coffey.