Two monkeys were cured of colour blindness thanks to gene therapy that one day may open the way to treating eye disorders in humans, scientists said on Wednesday. The ground-breaking technique used a cold virus as a "Trojan horse" to infect cone-shaped cells in the retina, stealthily delivering a gene that provides a pigment which is sensitive to red.
About 20 weeks after the treatment, the two primates began to acquire full colour vision, according to the paper, published by the British journal Nature. "(...) We knew right away when it began to work," said Jay Neitz, a professor of ophthalmology at the University of Washington who led the work.
"It was as if they woke up and saw these new colours. The treated animals unquestionably responded to colours that had been invisible to them." Colour blindness is the inability to distinguish between different hues, particularly between red and green. Instead, these colours show up in shades of grey, causing problems for everyday tasks such as recognising traffic lights.
Red-green colour blindness is the commonest disease in humans that can be pinned to just a single mutation in the genetic code. It affects between five and eight percent of males and around one percent of women, according to various figures. The experiment was carried out on two adult squirrel monkeys (Saimiri sciureus).
One was called Dalton - named after the 18th-century British scientist, John Dalton, who discovered colour blindness - and the other Sam. Both had been colour-blind since birth. For more than a year, the monkeys were given an adapted form of a standard vision-testing technique to find out exactly which out of 16 hues they failed to see.