The first clinical trial of a gene therapy that could treat an inherited progressive form of blindness was more successful that researchers had expected it to be.

In order for the groundbreaking therapy to work a medical professional must insert genes into a patient's retina cells without causing damage, an Oxford University news release reported.

The patients were only treated in one eye for the trial in order to make a comparison between the two.  

Six months after the initial treatment the patients showed visual improvement when in dim light, and two of the six subjects could read more lines on an eye chart. Nine patients have been treated with the therapy so far, one of which has been followed for two years.

Choroideremia affects about one in every 50,000 people; the first signs usually show up in young boys, who eventually are left completely blind. The condition us currently incurable, and is caused by a "defects in the CHM gene on the X chromosome." A lack of protein from the CHM gene slowly starves off retina cells.

This new treatment uses a "small, safe virus" to deliver the missing CHM gene to light-sensing retina cells. In order to inject this carrier medical professionals detach the retina and inject the it underneat using a fine needle.

 "It is still too early to know if the gene therapy treatment will last indefinitely, but we can say that the vision improvements have been maintained for as long as we have been following up the patients, which is two years in one case," Professor Robert MacLaren of the Nuffield Laboratory of Ophthalmology at the University of Oxford, and a consultant surgeon at the Oxford Eye Hospital and honorary consultant at Moorfields Eye Hospital, said.

"In truth, we did not expect to see such dramatic improvements in visual acuity and so we contacted both patients' home opticians to get current and historical data on their vision in former years, long before the gene therapy trial started. These readings confirmed exactly what we had seen in our study and provided an independent verification," he said.

The patients' improvement shows the virus can successfully deliver its "DNA payload" without harming the sensitive retina, according to MacLaren.

So far, the patients seem to be excited by the results.

"My left eye, which had always been the weaker one, was that which was treated as part of this trial...Now when I watch a football match on the TV, if I look at the screen with my left eye alone, it is as if someone has switched on the floodlights. The green of the pitch is brighter, and the numbers on the shirts are much clearer," Wayne Thompson, 43, an IT project manager, who was treated with the new therapy, said.

The team plans to continue working on the treatment in hopes that it will be sustainable in the long term.

"We are now trying higher doses of the gene therapy in the next part of the clinical trial to find what level is needed to stop the degeneration," MacLaren said,  "I am incredibly excited to see what will happen. The difficult bits are done: we know the virus carrying the gene therapy gets into the cells and the retina recovers after the surgery. Now it's just waiting to see how the patients progress."