Besides reading lines on an eye chart, they could see better in dim lit, Bennett said.
"We were not expecting to restore their vision to 20/20," she said.
In the British group, the treatment only worked in 18-year-old Steven Howarth, whose disease was less advanced than the other two - a girl, 17; and a man, 23, who was followed for a year.
Howarth said he used to rush home from school because he was worried about getting around in the dark, according to remarks issued by the university.
"Now, my sight when it's getting dark or it's badly lit is definitely better. It's a small change - but it makes a big difference to me," said Howarth, who lives in Bolton, near Manchester.
After the injection last July, Howarth said his eye felt like sandpaper. It was better after a week, and his eyesight gradually improved. He was able to negotiate a dimly lit maze in 14 seconds without bumping into any obstacles; before it took him 77 seconds with eight errors.
There were no serious side effects reported in either group. One of the patients in Philadelphia developed a hole in his retina which didn't affect his eyesight. The researchers think the hole was related to the surgery and not the injected gene.
The researchers said there was no evidence that the altered virus used to ferry the gene into the retina's cells had traveled outside the eye to other areas of the body.
The groups have each treated a fourth patient, including a preteen in England. The researchers hope to see better results with higher doses and in younger patients with less eye damage.
The National Eye Institute is funding a third similar study at the University of Florida.
The research in Philadelphia and London was paid for by a variety of government agencies and private foundations. An employee of Targeted Genetics Corp., which made the altered virus used in London, is a co-author of their report. Four of the Philadelphia researchers, including Bennett, have either applied for or have patents related to gene therapy. Ali and another British researcher have also applied for a patent for the procedure.
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AP Science Writer Malcolm Ritter contributed to this report.
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On the Net:
New England Journal of Medicine: http://www.nejm.org
National Eye Institute: http://www.nei.nih.gov
