Cell transplants that restored sight to blind mice have raised hopes that similar kinds of blindness in people could also be cured.

UK and American researchers cautioned that a lot more work needs to be done but said that, in time, it may be possible for doctors to treat conditions that cause irreversible blindness, such as age-related macular degeneration and diabetic eye damage.

In a breakthrough described as "stunning", the researchers implanted immature retinal cells into the eyes of the mice which then developed into fully functioning photoreceptors. Photoreceptors are the pixel-like light-sensitive cells in the retina that make it possible to see.

Previous attempts to achieve the same result using undifferentiated stem cells which have not yet acquired a specific function failed.

But in this research, published in the magazine Nature, the scientists used "precursor" cells, which are similar to stem cells but they had already been programmed to become photoreceptors.

They were extracted from newborn mice which were in the process of developing their eyesight.

Research suggests that human embryonic stem cells could be coaxed to become photoreceptor precursors. However the scientists believe a better approach might be to grow the precursors from adult stem cell-like cells found at the margins of the retina. These could then be transplanted into patients.

Dr Robert MacLaren, a member of the team from Moorfields Eye Hospital in London, said: "This research is the first to show that photoreceptor transplantation is feasible.

"We are now confident that this is the avenue to pursue to uncover ways of restoring vision to thousands who have lost their sight.

"We will be pursuing the idea of using the stem cell-like retinal cells particularly as these could be harvested from the affected patient, thus avoiding rejection."

The precursor retinal cells used in the study were implanted into three different strains of blind mice with retinal degeneration caused by genetic defects.

Tests confirmed that the photoreceptors were functioning and connected and that the animals could see.

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