A pioneering gene therapy trial has helped a blind man to see in a breakthrough that brings hope to millions affected by eye diseases. British scientists have claimed a world first for the revolutionary treatment, which involved a single injection into the retina at the back of the eye.

Steven Howarth, 18, from Bolton, who has a rare inherited eye disorder which has left him with extremely poor vision and completely unable to see in the dark, improved sufficiently after the treatment to be able to navigate a "maze" in conditions similar to street lighting at night.

Experts hailed the research, supported by £1m from the Department of Health, as a major advance in the treatment of blindness and predicted it would lead to new developments in gene therapy for other conditions.

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Dawn Primarolo, the Public Health minister, said: "This is a major achievement for British science and the NHS and shows we truly are at the forefront of innovation."

Mr Howarth is one of the first three patients to be treated with the experimental therapy by specialists at University College London (UCL) and Moorfields Eye Hospital. The other two patients, aged 17 and 23, suffered no ill effects but did not report any improvement. The results are published today in the New England Journal of Medicine.

Results of a similar trial by a rival US group at the University of Pennsylvania, which began eight months after the British trial, are also reported in the journal today. Three patients, one aged 19 and two aged 26, were injected and are reported to have improved vision as measured by standard eye tests. One showed an improved ability to navigate an obstacle course. However, one of the American patients developed a hole in the retina, thought to be due to the surgery, though this did not affect their sight.

Robin Ali, professor of human molecular genetics at UCL Institute of Ophthalmology, who led the British study, said: "We are thrilled. We started with the most difficult cases – with late-stage disease, using a low dose and in the worst affected eye – because we were being cautious. As we move to younger patients with an increased dose we expect better results."

The technique has already been shown to work in animals where results were better in those with less-advanced disease, he said. It is now being tried in nine younger patients, aged eight to 16, and the researchers hope for improved results.

"It is too early to say anything but we anticipate further success," Professor Ali said.

Mr Howarth, a student and a guitarist, said he had been nervous and excited before the treatment. He said his eye "felt like sandpaper" after, and took over a week to return to normal.

"Now, when it's getting dark or it's badly lit, my sight is definitely better. It's a small change – but it makes a big difference to me. Before the operation, I used to rush home from college when it started to get dark because I was worried about getting around. Now I can take my time and stay later if I need to, for band rehearsals and things like that."

Mr Howarth and the two other patients were born with Leber's congenital amaurosis, an inherited degenerative disorder which leads to progressive loss of sight caused by a fault in a single gene, RPE65. The operation, carried out by James Bainbridge, a consultant ophthalmologist at Moorfields Eye Hospital, involved injecting normal versions of the defective gene into the back of the eye, beneath the retina.

Extreme surgical precision was required to inject the solution containing the normal genes, gently lifting the retina and causing a temporary detachment. One slip could have torn the retina and destroyed the patient's remaining sight.

Professor Ali said the treatment had not merely halted the degeneration but had improved vision. "This is a very significant milestone. This trial establishes proof of principle of gene therapy for inherited retinal disease and paves the way for development of gene therapy approaches in a broad range of eye disorders," he said.

It is only the second time gene therapy has been proved successful in humans, after trials showed it was effective in the rare inherited disorder called SCID (severe combined immune deficiency) which leaves babies without a functioning immune system so they have to live in a bubble to protect them from infection. This advance could open the way to treatment in other conditions, including blood and immune disorders, Professor Ali said.

Len Seymour, professor of gene therapies at Oxford University and president of the British Society for Gene Therapy, said: "Carefully designed studies such as this demonstrate the remarkable power of gene therapy to correct the basis of many diseases. The encouragement this study will bring to patients and scientists alike should give increased confidence in applying similar approaches for treatment of a host of debilitating disorders, unleashing the prospect of major advances through genetic medicine."