By the time Corey Haas was 7, the retinal disease he was born with had already stolen much of his vision.
 
Legally blind, Corey was expected eventually to lose all sight. Then, 13 months ago, after his eighth birthday, he underwent an experimental gene therapy procedure, receiving an injection in his left eye.
 
His vision in that eye improved quickly. Now 9, Corey plays Little League baseball, drives go-carts, navigates wooded trails near his home in Hadley, N.Y., and reads the blackboard in class. "It's gotten, like, really better," he said.
 
Experts in vision problems say that while it is unclear how many visually impaired people gene therapy could help, they consider the research promising for some types of blinding diseases, and an achievement for gene therapy, which has had many setbacks.
 
The study, reported in the journal Lancet, involved five children and seven adults, from Belgium, Italy and the United states, with a type of Leber's congenital amaurosis, rare but serious congenital retinal diseases.
 
The researchers injected into the eyes of the patients a virus with the normal version of the gene REP65 inserted into its genome. When the virus invaded the light-sensing cells in the eye and inserted its own DNA into the cells' DNA, the crucial human gene was included.
 
Starting at about two weeks, "all 12 had significant improvement," said Stephen Rose, chief research officer at the Foundation Fighting Blindness, which helped finance the study. That meant the inserted gene was functioning. "You're not returning 20-20 vision, let's be real," Rose said, "but you're returning a tremendous amount of vision."
 
Dr. Jean Bennett, an ophthalmology professor at University of Pennsylvania who was a leader of the study, said participants could "read signs or see numbers on their cell phones, stripes on their clothes, patterns on furniture, wood on a violin or marble on a table." Some read several more lines on eye charts.
 
Children improved the most, perhaps because fewer photoreceptors had decayed.
 
In a burst of new research on restoring sight, gene therapy is one of the methods closest to achieving results, but it will not help everyone because some eye diseases destroy photoreceptor cells, which are crucial for allowing gene therapy to work. Also, specific genes must be identified for different strains of diseases.
 
"Gene therapy is great, but it's going to work only when patients have viable photoreceptor cells," said Dr. Gerald Chader, chief scientific officer at Doheny Retina Institute in Los Angeles, who was not involved in the study.