An injection of genes straight into the eye's retina could reverse a hereditary form of blindness within days.
Three patients who were born with an inherited condition, which made them blind in their teens, had their sight significantly improved within a month of being treated, Sky News reported.
Two responded within a few days.
The three were suffering from Leber's congenital amaurosis, which until now has been untreatable.
LCA occurs when faulty genes, called RPE65, stop cells in the retina at the back of the eye working.
It affects approximately one in 80,000 people, causing progressively worsening vision, often starting in the first few years of life.
It is responsible for one in 10 severe sight disorders in children.
Scientists say that injections of healthy genes could be a major boost for sufferers from other genetic eye problems.
The researchers, from Pennsylvania University, the University of Florida and Cornell University, suggested that the function of "cones" in the retina, which are used in daytime and color vision, could be boosted up to 50-fold — a "dramatic" improvement in function.