Hope for a cure has been extended to millions of blind people, thanks to a new surgical technique that has successfully returned sight to blind mice.

The blind mice had genetic defects that resulted in loss of photoreceptors, the light-sensitive cells in the retina that make it possible to see.

Photoreceptor loss is believed to be responsible for more blindness in the developed world than all other eye diseases combined.

The mice were implanted with immature retinal cells, similar to stem cells, which had been extracted from newborn mice whose eyesight was developing. The transplanted cells developed into fully functioning photoreceptors that successfully connected to nerves leading to the brain.

Using differentiated cells may be the key to the success of the procedure, according to the research team from University College London, Moorfields Eye Hospital, London, and the University of Michigan. Previous attempts to achieve the same result using undifferentiated stem cells have failed.

It may be possible to grow precursor photoreceptor cells using cells similar to stem cells that are found at the margins of the adult retina, researchers suggest.

Using the patient's own cells would also avoid the possibility of 'foreign' cells being rejected by the body.

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

Tests confirmed that the photoreceptors were functioning and that the animals' vision had been restored to about one fourth of the normal level.

Future attempts are expected to produce greater results by increasing the number and type of cells transplanted.

The initial tests involved 'rod' cell transplants -- those that control peripheral and night vision. Transplanting 'cone' cells -- those that control color and detail -- would greatly improve results.

The technique is still in its infancy, but there is reason to believe that human photoreceptor transplants will occur within ten years, researchers note.