Researchers have tested the treatment in six patients ages 17 to 26 with the RPE65 (retinal pigment epithelium 65) defect. At Children's Hospital of Philadelphia, University of Pennsylvania (Penn) gene-therapy researcher Jean Bennett's team injected one eye of each patient with a harmless virus modified to carry the RPE65 gene. The gene therapy did not appear to cause side effects. (One patient's retina developed a small hole, but it didn't affect vision.) A few weeks later, a test based on pupil constriction showed that the patients could detect three times more light. Two patients who could see only hand motions before were able to read several lines of an eye chart. And one patient was able to navigate an obstacle course efficiently for the first time.

In a similar safety study at University College London, Robin Ali's team saw improvement in only one of three patients--the one with the most intact retinal tissue, an 18-year-old, Ali says. He was no better at reading an eye chart, but his light perception improved 100-fold. In a video before treatment, he stumbles through a simulated night street scene, bumping into walls several times in 77 seconds. Six months after the injection, he breezes through in 14 seconds. "It's more than we could have hoped for," Ali says. Both teams reported their findings online yesterday in the New England Journal of Medicine and presented them yesterday and today at the annual meeting of the Association for Research in Vision and Ophthalmology in Fort Lauderdale, Florida.

Interesting quote about the early hype around gene therapy:

"In the early days, says Dr Seymour, people wrongly thought that it would be easy to introduce genetic material into diseased cells. He likens attempts by researchers to introduce genes to “throwing a carburettor on to the passenger seat of a car and expecting the car to go”."

http://sciencenow.sciencemag.org/cgi/content/full/2008/428/2?rss=1

http://www.economist.com/science/PrinterFriendly.cfm?story_id=11288399

Dr. Ali points out that as this trial was just a safety phase trial, the patients being treated had very advanced sight loss. In the next trials, earlier stage patients will be enrolled and it would be expected that these treatments would deliver even more impressive improvements and more importantly, in a large majority of test subjects.

You are right.
The NEJM editorial says:
"One might also speculate that treatment of younger patients with less advanced retinal degeneration might allow greater improvement of visual function."
http://content.nejm.org/cgi/content/full/NEJMe0803081?resourcetype=HWCIT

Do you know of other interesting gene therapy trials, which have recently been reported or are in progress?