A STUDY has taken a major step towards treating blindness by replacing lost light-sensitive cells in the eye.
Scientists injected immature photoreceptors into the retinas of genetically engineered mice that could not see in the dark.
The cells grew nerve connections and generated visual signals that were sent to the brain.
Treated mice were better able to perform a maze task in low light conditions.
Photoreceptors take two forms, rods and cones. Rods can function in less intense light, and it was these the scientists used to restore night vision to the mice.
The scientists, led by Professor Robin Ali from University College London (UCL), say much more work is needed before the technique can be attempted on human patients. The first clinical trials might be five or 10 years away.
But he said: "We've shown for the first time that transplanted photoreceptor cells can integrate successfully with the existing retinal circuitry and truly improve vision.
"Although there are many more steps before this approach will be available to patients, it could lead to treatments for thousands of people who have lost their sight through degenerative eye disorders."
The undeveloped precursor cells used in the study were taken from week-old mice. Tests showed visual responses in the brains of the mice were enhanced.
To see how the transplants affected behaviour, mice were placed in a dimly lit Y-shaped water maze in which one of two routes led to escape. This required swimming towards a visual cue, a grating pattern.
After treatment, four of nine night-blind mice completed the task in 70% of trials. Untreated mice, and those given "sham" treatments, performed no better than by chance.
Cell integration in animals that performed best tended to be clustered, rather than spread widely across the retina. This suggested that the closeness of the cells might be important.
Professor Phil Luthert, director of the UCL Institute of Ophthalmology, said: "This is a landmark paper and the techniques used here are part of a pretty big push in regenerative medicine."
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