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Monday, 12 November, 2001, 08:35 GMT
Hope of blindness cure
Scientists have developed a technique which they hope will restore sight to people left blinded by retinal damage.
A team in Japan has announced that they have successfully gown the light-sensitive receptors, or rods, that make up the eye's retina, from the iris of rats.
Although the research is at an early stage, it is already being suggested the technique may be transferred to human beings.
If that could be achieved, rods could be grown from a blind patient's own iris and then transplanted into the eye, ensuring the new tissue would not be rejected.
However, the new research, which is being conducted at Kyoto University, still has some way to go, as the scientists have yet to transplants the rods back into the eyes of blind rats.
At present, there is no treatment for retinal damage in humans, which can be caused by degenerative diseases or by looking directly at the sun.
This can result in permanent blindness because retina cells, once damaged do not grow back.
The Kyoto team extracted cells from the iris, the coloured muscular diaphragm at the front of the eye that controls the amount of light entering the eye. These cells are not sensitive to light.
Then, in the laboratory, they modified them so that they became light-sensitive, and thus potentially could be transplanted into the retina.
The retina is the light-sensitive membrane at the back of the eye made up of cells that when stimulated by light trigger messages along the optic nerve, which are then interpreted as visual images by the brain.
The cells were made light sensitive by adding a gene known as Crx that is normally found in the mature retina.
Once the gene was added to the cells, they began to produced a light-sensitive protein called rhodopsin, which is also found in the retina.
Although a cure for blindness is still a long way off, the scientists are encouraged by the fact that iris and retina cells share similar developmental characteristics.
The research is published in the journal Nature Neuroscience.