British scientists have made a major leap forward in efforts to treat blindness.
They have grown part of an eye in the laboratory and raided it for theÂ light-sensitive cells which are the key to vision.
These cells were injected into mice, where they seemed to grow normally and formed the crucial connections between the eye and brain.
It is hoped the first human patients could be treated in as little as five years â€“ paving the way for a treatment which could eventually give millions back their sight.
Researcher Professor Robin Ali said that even transplanting a small number of cells could have a big impact on quality of life.
Those who could benefit include men and women with age-related macular degeneration â€“ the most common cause of blindness in the elderly.
It affects more than 600,000 Britons and the number is expected to triple in the next 25 years as the population ages.
There are few treatments for the condition â€“ and no cure.
The University College London researchers are trying to replace damaged cells in the retina, the light-sensitive â€˜filmâ€™ at the back of the eye.
Last year they used healthy cells from young mice to restore vision in adult animals.
The results were dramatic, with the treated animals able quickly to find their way out of a miniature swimming pool in dim light, while untreated ones swam around in circles.
The scientists took embryonic stem cells â€“ â€˜master cellsâ€™ capable of turning into other cell types and widely touted as a repair kit for the body â€“ and used a cocktail of nutrients to coax them into turning into a retina.
They then raided the lab-grown retina for rods â€“ key cells which pick up light and send it to the brain for conversion into images.
Finally, they transplanted the rods into the eyes of mice.
A retina has been grown in a dish before but the professorâ€™s team are the first to transplant cells from one successfully.
The journal Nature Biotechnology reports that the lab-grown cells integrated into the existing eye and formed the nerve connections needed to send information to the brain. Professor Ali said: â€˜It is a major advance.
â€˜We are getting closer and closer to carrying out a trial.â€™
The need to be highly confident that the treatment is safe and effective means that widespread use is at least ten years away.
Dr Rob Buckle, of the Medical Research Council, which funded the teamâ€™s work, said: â€˜This study is an important milestone on the road to developing a widely available cell therapy for blindness.â€™