London, Apr 19 (IANS): British scientists have shown for the first time that transplanting special cells into the eyes of visually impaired mice can restore their night vision, an experiment that holds promise for human beings.

A paper published online by the journal Nature said that loss of photoreceptors is the cause of blindness in many humans. These include eye diseases like age-related macular denegation and diabetes-related blindness.

There are two types of photoreceptor cells in the eye -- rods and cones. The cells transplanted in this study were rod-photoreceptor cells. Rod cells are especially important for seeing in the dark as they are extremely sensitive to low levels of light.

Scientists based at University College London injected cells from young healthy mice directly into the retinas of adult mice that lacked functional rod-photoreceptors, which means they could not see in the dark, Xinhua reported.

After four to six weeks, the transplanted cells appeared to be functioning almost as well as normal rod-photoreceptor cells and had formed the connections needed to transmit visual information to the brain.

During tests, mice with newly transplanted rod cells were able to use a visual cue to quickly find a hidden platform in a dark maze, whereas untreated mice found the platform only by chance after extensive exploration of the maze.

"We've shown for the first time that transplanted photoreceptor cells can integrate successfully with the existing retinal circuitry and truly improve vision," said Robin Ali, the professor who led the research at University College London.

"We're hopeful that we will soon be able to replicate this success with photoreceptors derived from embryonic stem cells and eventually to develop human trials," he said.