Older people can develop macular degeneration. Stem cells taken from the back of the eye could eventually be used to restore normal vision in people with sight problems, researchers have said.
Human retinal stem cells regenerated when they were transplanted into the eyes of mice and chicks, scientists at the University of Toronto found.

They now plan to see if the same happens in diseased eyes in the hope of eventually treating humans.

The findings appear in Proceedings of the National Academy of Sciences.

Clear vision

The retina sits at the back of the eye and is where light rays are turned into images.

It acts like the film in a camera to capture images, transform them into electrical signals, and send these signals to the brain.

The retina contains millions of cells called photoreceptors (divided into rods and cones), which contain visual pigments.

As a first step, I think this paper is superb.

Dr Stephen Minger, director of the stem cell biology laboratory at King's College, London 

When light strikes these pigments, they briefly lose their colour. This bleaching process triggers nerve impulses, which are transmitted to your brain.

The researchers took retinal stem cells from human cadavers and transplanted them into the eyes of one-day-old mice and chicks.

The transplanted cells developed into photoreceptor cells.

Lead researcher Brenda Coles said: "When their eyes fully developed, the human cells survived, migrated into the sensory part of the eye and formed the correct cells."

The are now exploring whether the retinal stem cells from these healthy mice will continue to develop when transplanted to mice with diseased eyes.

Blindness treatment

This will help them find out whether retinal stem cells can be used to treat degenerative diseases of the retina such as retinitis pigmentosa and macular degeneration, which are among the most common forms of blindness in developed countries.

These diseases affect rods and cones, the photoreceptor cells at the back of the retina, but the nerve cells in front of them usually remain intact.

Ms Coles said: "We're starting with mice to see if they can overcome the genetics involved in disease.

"The eye itself is telling the stem cells what to do, so when we go to a disease model, it is important to know what those signals from the eye are so we can inhibit them or protect the cells."

Dr Stephen Minger, director of the stem cell biology laboratory at King's College, London, said: "As a first step, I think this paper is superb.

"Being able to show that they can take a small number of cells from the human eye and expand them to relatively large numbers to implant them and get what appears to be site-specific differentiation into a wide variety of retinal cells is very encouraging."

He said it would be important to prove that the implanted cells functioned normally and that they also worked in disease states.

Also, it has yet to be determined whether enough of the required number of cells could be generated to repair damage in humans, he said.