US scientists have successfully restored a woman's vision using eye cells taken from aborted foetuses.
Stem cell use is controversial
But while hailing their results as a triumph, the University of Louisville researchers are worried critics will say they are promoting abortion.
The UK has clear guidelines to ensure people cannot conceive and terminate a foetus to treat another person, but similar rules do not exist in the US.
The findings appear in New Scientist magazine.
Elisabeth Bryant's sight was restored by a transplant of retinal cells taken from the eyes of aborted foetuses.
The transformation appears not to have been a short-term effect, as the team who carried out the operation had feared.
Before the experimental surgery on her left eye, Elisabeth, who was 63 at the time, could barely see anything with it.
"Now I can see people's eyes, noses and mouths when they're sitting across the room from me," she told New Scientist.
So far, six patients with degenerative diseases of the eye - either advanced retinitis pigmentosa or another
disease called macular degeneration - have received similar transplants in the US.
Dr Robert Aramant, who developed the technique at the University of Louisville, said: "We have shown the way. It is possible to reverse these incurable diseases."
But his colleague Mr Norman Radtke, the surgeon who carried out the transplants, said: "People are going to claim that we are promoting abortion."
The team has been given the go-ahead by the US Food and Drug Administration to carry out more transplants on people with less advanced disease.
Earlier this week, Canadian researchers from the University of Toronto announced that they had shown that retinal stem cells taken from adults were capable of forming the cells needed to repair damaged eyes.
Although this method has only been tested in animals, the scientists are hopeful that it could be used to treat humans.
David Wong, chairman of the scientific committee of the Royal College of Ophthalmologists, said: "As ophthalmologists, we welcome research into stem cells as indeed it offers hope for patients suffering from degenerative conditions such as retinitis pigmentosa and macular degeneration.
"Particularly exciting is the fact that the Toronto group could harvest stem cells from adult human eyes," he said, which would overcome some of the ethical concerns.
A spokesman from Comment on Reproductive Ethics said using tissues from aborted foetuses was totally unnecessary.
"Why bother doing something that's ethically difficult or unacceptable when you can take stem cells from adults?" he said.