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Human Eye Can Repair Itself, Research Suggests Pauline Tam
From The Ottawa Citizen

Discovery promises revolutionary advances in treating injuries

Robert Cross, The Ottawa Citizen / Reasearchers hope some day to activate retinal stem cells to generate healthy new cells. Dormant in adults, stem cells have been found in the ciliary margin surrounding the lens.

A team of Toronto scientists has uncovered the first evidence suggesting damaged eyes can heal themselves.

The discovery could revolutionize the way doctors treat future eye injuries like those suffered by Bryan Berard, the Toronto Maple Leafs defenceman who was hit by a stick in the right eye last Saturday during a hockey game in Ottawa.

Mr. Berard's known injuries include a detached retina, meaning the light-sensitive part of his eye is severed from delicate nerve tissue connecting it to the brain. Retinal detachment is one of the most serious causes of lost vision.

At the moment, doctors can repair most cases by fusing the retina back in place using laser surgery or freezing techniques. In the future, it might also be possible to coax the retina -- the most important part of the eye -- to produce new and healthy cells, essentially allowing the eye to repair itself.

That would be particularly good news for millions of Canadians who suffer from hard-to-treat diseases such as glaucoma, macular degeneration and the inherited disorder known as retinitis pigmentosa.

"One of the things that our research suggests is that the alternative to trying to put broken things back together is to try and generate a new eye," says University of Toronto professor Derek van der Kooy.

Mr. van der Kooy's research team made the discovery in collaboration with Toronto's Hospital for Sick Children.

Their work, published today in the U.S. journal Science, marks the first time scientists have found that even adult mammals have master cells, known as retinal stem cells, whose descendants are responsible for making every type of tissue in the eye.

Until now, researchers believed only fish and amphibians had retinal stem cells capable of mending damaged eyes. It was also thought that these cells were found only in embryos or mammals in their early stages of development.

That theory effectively ruled out the possibility that as humans age, their fully developed eyes could repair themselves by generating new and normal nerve cells, or neurons.

But according to Mr. van der Kooy and his team, a smattering of retinal stem cells can be found hibernating under the fine brown ring that surrounds the irises of full-grown mice, cows and humans.

In normal adults, these cells are programmed to be inactive once the eye is fully developed. But researchers have found that retinal stem cells don't remain in their pristine state once they're extracted from the eye. Instead, when left in a dish of salts and proteins, the cells can be coaxed into making virtually all the essential types of neurons found in the eye.

"Making the new cells is just the first step," says Vince Tropepe, lead author of the study. "The next step will be to show how those new neurons get to the right spot and make the right connections to the brain so that the eye will function."

The challenges don't stop there. Scientists are years from being able to tame retinal stem cells so that they make select types of neurons found to be missing or deficient in damaged eyes.

What's more, the molecular switch that somehow prevents retinal stem cells from making new neurons in adult mammals remains a mystery.

Clearing those two hurdles would pave the way for cell transplants, in which doctors extract a few retinal stem cells from a patient, grow the right kind of neurons in a laboratory dish, then inject the healthy new cells into the damaged eye.

In the longer term, scientists even hope to bypass transplants altogether by programming retinal stem cells to repair themselves while in the eye.

The discovery is considered so profound that the United States has already granted the Toronto researchers a patent on the adult mammalian retinal stem cell. It has also attracted interest from a number of U.S. and Canadian companies eager to capitalize on the cell's therapeutic potential.

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Date last modified 3/26/2000