Researchers have used gene therapy to restore vision in a small group of young adults with a form of retinal degeneration, two new studies report.

The studies' subjects had a form of retinal degeneration known as Leber congenital amaurosis (LCA). LCA causes blindness by damaging the retina so it can no longer process light.

Scientists injected a normal version of a gene known as RPE65, which is mutated in one form of LCA, into the eyes of patients with the disease. They injected one eye and left the other eye untreated.

In the American study, the patients, one aged 19 and two 26-year-olds, were treated at The Children's Hospital of Philadelphia. Within two weeks, they noticed that their vision improved in the treated eye.

Over a six-month period, researchers found continued improvement.

"After the injection, all of the individuals could read at least four lines on the eye chart," said one of the study's authors, Dr. Jean Bennett of the University of Pennsylvania.

None of the patients reported adverse side effects, except for one patient who developed a hole in the retina that did not affect eyesight and was probably caused by the surgery.

However, only one of three patients in a corresponding British study responded to the therapy. That patient found he could walk easily through a maze that he previously had difficulty with.

Both studies were published in the New England Journal of Medicine.

Symptoms of LCA begin in early childhood, and patients lose their sight completely by the time they are in their twenties or thirties. There is no treatment.

Speaking on CTV's Canada AM, Dr. Robert Koenekoop of Montreal Children's Hospital said that these findings are a major breakthrough.

"I believe that this is one of the most significant advances in human history in the field of medicine, to be able to treat a complicated retinal disease that we thought only ten years ago was untreatable," Koenekoop said.

Gordon Gund of the Foundation Fighting Blindness, who lost his sight when he was 31, said that he believes the findings will lead to future treatments.

"It's amazing because children who are born blind will soon be able to have normal vision," Gund said.

Maureen Hartnett of Oakville, Ont., is a mother of two children, Roisin, 18, and Niall, 15, with LCA. While Roisin has some light perception ability, Niall is completely blind.

"I think it is exciting and scary at the same time, being suddenly able to see," Hartnett said.

"It is scary because they have spent their entire lives without sight. It would change their lives."

Roisin, who studies education at Queen's University, uses a seeing eye dog named Mitsou. She said that she would willingly undergo the procedure.

"I would love to be able to see people's facial expressions," Roisin said.

"My boyfriend wishes that I had eye contact. And I would love to return to Italy to see the art galleries and the Sistine Chapel."

Niall was just as intrigued by the findings, but also a little wary.

"This is very new. I would like to wait 'till it is more secure and has been tested to be completely safe."

Researchers hope that this gene therapy could one day treat other debilitating eye diseases, such as macular degeneration.

Canadians looking for more information on LCA and other genetic retinal diseases can call the Foundation Fighting Blindness in Canada at 1-800-461-3331, ext. 25, or visit www.ffb.ca.

With a report from CTV's medical correspondent Avis Favaro and producer Elizabeth St. Philip.

Link to Studies