LONDON: The ability of zebrafish to regenerate damaged retinas has given scientists a clue about restoring human vision and could lead to an experimental treatment for blindness within five years.

British researchers said on Wednesday they had successfully grown in the laboratory a type of adult stem cell found in the eyes of both fish and mammals that develops into neurons in the retina. In future, these cells could be injected into the eye as a treatment for diseases such as macular degeneration, glaucoma and diabetes-related blindness, according to Astrid Limb of University College London's Institute of Ophthalmology.

Damage to the retina - the part of the eye that sends messages to the brain - is responsible for most cases of sight loss.

"Our findings have enormous potential," Limb said. "It could help in all diseases where the neurons are damaged, which is basically nearly every disease of the eye."

Limb and her colleagues studied so-called Mueller glial cells in the eyes of people aged from 18 months to 91 years and found they were able to develop them into all types of neurons found in the retina. They were also able to grow them easily in the lab, they reported in the journal Stem Cells.

The cells have already been tested in rats with diseased retinas, where they successfully migrated into the retina and took on the characteristics of the surrounding neurons. Now the team is working on the same approach in humans. "We very much hope that we could do autologous transplants within five years," Limb said.

Autologous transplants, initially on a trial basis, will involve manipulating cells and injecting them back into an individual's own eye. Eventually, Limb hopes it will also be possible to transfer the cells between different people.

"Because they are so easy to grow, we could make stem cell banks and have cell lines available to the general population, subject to typing as with blood transfusions," she said.