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LONDON - British and American scientists have restored vision in blind mice by transplanting light-sensitive cells into their eyes in a breakthrough that could lead to new treatments of human eye diseases.

The mice suffered from eye damage called photoreceptor loss which occurs in macular degeneration, the leading cause of sight loss in the elderly, and other eye disorders.

A photograph released to Reuters on November 8, 2006 from Moorfields Eye Hospital in London. The image shows the back of the eye in a patient with age-related macular degeneration shows blood and degeneration in the central part of the retina. The circle to the right is the optic nerve, corresponding to the blind spot. The retina is lined with millions of light sensitive photoreceptor cells. [Reuters]

But instead of using stem cells, which could form into any cell type, the scientists transplanted cells that had reached a later stage of development toward becoming photoreceptor cells.

"We have shown for the first time that it is possible to transplant photoreceptors," said Dr Robert MacLaren, a scientist and eye surgeon at Moorfields Eye Hospital in London.

"These cells are lost in some of the more common causes of blindness" he added in an interview.

The scientists believe further research could lead to the first human retinal cell transplants for people with blinding diseases within a decade.

Photoreceptors are specialized light sensitive cells that line the back of the eye and are essential for sight. In eye diseases such as macular degeneration the cells are destroyed.

Previous studies that had used stem cells, master cells in the body that have the potential to become any type of cell in the body, had failed because the cells did not form into photoreceptors.

PROOF OF PRINCIPLE

Researchers had thought that the mature retina, the part of the eye that senses light and forms images, did not have the capacity for repair.

MacLaren and his collaborators showed using precursor cells that are already programmed to become photoreceptors but are not quite there yet was the key to successful transplantation.

"We have taken them out of the donor retina and transplanted them into a host retina extremely quickly at that precise point in time and with minimal trauma to the surrounding tissue," MacLaren explained.

The mice had eye diseases caused by genetic defects.

Scientists have recently found cells on the margin of the retina in humans which have stem-cell like properties and could potentially be grown in the lab to become photoreceptor precursor cells for treatment.

The findings by MacLaren and scientists from the Institute of Ophthalmology and the Institute of Child Health in London and the University of Michigan Medical School in the United States are published online by the journal Nature.

"Rather than focusing on stem cells we believed that if we could understand how cells develop and become photoreceptors ... our transplantation efforts would meet with greater success," said Professor Anand Swaroop, of the University of Michigan Medical School and a co-author of the study.

"This technique gives us new insights in repairing damage to the retina and possibly other parts of the central nervous system," he added in a statement.