Trials on rats bring scientists a step closer to restoring sight to the blind

Geneticists they may be close to achieving one of the goals that has eluded medical science for centuries: restoring sight to the blind.

Researchers are developing techniques that extract cells from the muscular tissue of the eye and modify them in a laboratory so that they can be transplanted back into the retina, the light-sensitive membrane at the back of the eye.

A team led by Kyoto University's Masayo Takahashi has already turned cells from the eyes of laboratory rats that are not light-sensitive into the active photoreceptors needed in the retina. Although the research is in its early stages, Ms Takahashi might eventually cure people with retinal damage who are now considered "incurably" blind, she says in the journal Nature Neuroscience.

If the technique can be perfected in humans, it would also remove the possibility of transplanted cells being rejected after surgery, because the modified cells would originate from the patient's own eye.

Ms Takahashi reports that her team extracted cells from the iris, the coloured muscular diaphragm that controls and surrounds the pupil. The cells were then exposed to a "growth factor" – a chemical that promotes their reproduction – in the laboratory. As the cells proliferated, a gene was added that made them sensitive to light and, therefore, similar to cells in the retina.

The crucial gene, known as Crx, is normally found in the mature retina and is crucial to the creation of light-sensitive tissue. A harmless virus was used to carry the genetic material into the cells. After being infected, they began to produce rhodopsin, a light sensitive protein found in the retina.

Although Ms Takahashi believes a method of repairing the retina to restore sight is a long way off, she believes it may be possible. She said iris cells could be turned into retinal cells because both arise from the same part of the "optic cup'' in a foetus and, therefore, share characteristics.

Blindness caused by retinal damage does not repair itself. The eye's retina is made up of two types of cell, known as rods and cones, which send nerve messages to the brain when they are stimulated by light. When these cells are damaged – for instance by a neuro-degenerative disease – they do not grow back.