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Last Updated: Thursday, 6 April 2006, 09:46 GMT 10:46 UK
Algae protein may aid eye health
Conditions affecting cells in the retina could be aided by the treatment
Scientists have been able to make eye nerve cells respond to light by adding a protein from green algae.

The study in mice, published in Neuron, could one day treat degenerative sight problems such as retinitis pigmentosa.

People with RP lack light-sensitive cells - this research seeks to replace them.

A UK eye expert said the finding was interesting, but more work was needed to show if it could do more than allow people to tell light from dark.

[It] could potentially allow restoration of sight even to patients who's retinas have degenerated to a point far beyond any of the limited therapies now being developed
Professor Chris Inglehearn, University of Leeds

The researchers studied mice that had been genetically bred to lose rods and cones, the light-sensitive cells in their retinas.

It is usually these cells which respond to light and send signals through the retina and the optic nerve to the visual cortex of the brain, where visual images are formed.

But when degenerative eye diseases, such as RP, cause the rods and cones to die, it leads to people going progressively blind.

The mice in the study experienced the same deterioration in their sight.

Light generation

The researchers, from Wayne State University's School of Medicine used a harmless virus to introduce a green algae gene into cells in the mouse retinas.

The gene controls a light-absorbing protein called ChR2. These cells were not previously sensitive to light.

But they became so, and generated signals through the optic nerve to the visual cortex.

The light sensitivity persisted for at least six months.

The researchers said the mice probably did not regain usable vision, but said they were investigating ways of making that possible.

Dr Zhuo-Hua Pan, of Pennsylvania College of Optometry, said: "This study demonstrates the feasibility of restoring visual responses in mice after they lose the light-sensitive photoreceptor cells."

They add that the technique is easier to use than other potential methods.

The researchers now plan to carry out further work, including looking at whether expressing ChR2 in other types of retinal cells may aid sight.

Big question

Professor Chris Inglehearn, of the department of Ophthalmology and neurosciences at the University of Leeds, said: "What this study shows is that, even after all the light sensitive cells have been lost, other nerve cells in the eye can be reprogrammed to respond to light.

"That could potentially allow restoration of sight even to patients whose retinas have degenerated to a point far beyond any of the limited therapies now being developed.

"However, those light sensitive cells are the pixels with which our brains assemble the image.

"The big question begged by this research is, could the brain assemble a picture using such input.

"If it can't it, all this will achieve is to give patients the ability to distinguish between light and dark - useful, but not the big breakthrough one might hope for."

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