KEY POINTS:
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 involves a single injection into the retina at the back of the
eye.
Steven Howarth, 18, from Bolton, has a rare inherited eye disorder which left him with extremely poor vision and completely unable to see in the dark.
After the treatment, he could navigate a maze in conditions similar to street lighting at night.
The injection was put into the back of Mr Howarth's worse-affected right eye, which had almost no vision, especially in low light.
A video of him with his "good" left eye covered, taken before the treatment, shows him trying to find his way through a maze of three doorways and repeatedly bumping into walls.
Six months after the injection, a repeat video shows an astonishing improvement. He can be seen negotiating a similar maze in low light in seconds, without mishap.
Mr Howarth is one of the first three patients to be treated with the experimental therapy by specialists at University College London and Moorfields Eye Hospital.
The other two patients, aged 17 and 23, had no ill effects but did not report any improvement.
In a similar trial which started at the University of Pennsylvania in Philadelphia eight months after the British trial, three patients, one aged 19 and two aged 26, had improved vision after injections,
But one of the American patients developed a hole in the retina, thought to be because of the surgery, though this did not affect their sight.
Robin Ali, professor of human molecular genetics at the University College London Institute of mology, 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 was 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 expect further success," Professor Ali said.
Mr Howarth, a student and a guitarist, said he had been nervous and excited before the treatment. His eye "felt like sandpaper" after the injection, and took more than 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.
The operation, done 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, especially at the periphery of the eye involved in night vision, which is worst affected in Leber's.
"This is a very significant milestone," he said.
