PARIS, Oct 24 Exhilarated scientists on Saturday announced they had used gene therapy to restore eyesight to children blighted by a rare, inherited form of creeping blindness.

Youngsters were able to walk unaided around dimly-lit obstacles, take part in lessons at school without extra help — and one child saw the colour of his father's eyes for the very first time.

The revolutionary treatment targets a disease of light-catching retinal cells called Leber's congenital amaurosis, or LCA.

Caused by flaws in any one of around 13 key genes, LCA triggers severe loss of vision and abnormal eye movements in early infancy, usually leading to total blindness in the twenties or thirties.

Doctors led by Jean Bennett of the University of Pennsylvania School of Medicine tested a way of tackling this tragedy by inserting a corrective gene in a disabled cold virus.

Their study was published online by The Lancet on Saturday, coinciding with a presentation at a conference of American ophthalmologists in San Francisco.

The modified virus was injected into the eyeball, and infected the diseased cells — in effect, acting like a Trojan horse to deliver the right DNA to the retina.

Twelve patients aged eight to 44 years were recruited in the small, experimental study, and were given the treatment in the eye that had the worst vision.

None of the patients recovered normal sight, but all of them had an at-least 100-fold increase in so-called pupillary light response, meaning the constriction of the pupil when exposed to light.

Six of the 12 recovered sufficient sight that meant they may no longer be classified as legally blind. The best results were among four children aged eight, nine, 10 and 11. All four gained vision that enabled them to walk unaided along a dimly-lit simulated street route.—AFP