Two monkeys have had their colour blindness corrected in gene therapy.
Research led by University of Washington ophthalmology professor Jay Neitz, which was published in the journal Nature, used a "Trojan horse" technique.
A harmless virus was placed into the monkeys" eyes to pass on a gene that would deliver a pigment that could detect red into the retina.
Weeks later, the monkeys were creating proteins that enabled them to identify the colours red and green.
The animals were squirrel monkeys named Dalton and Sam.
Colour blindness is more likely to affect men then women.
According to figures from Bupa, about eight per cent of men suffer from the condition, but just 0.4 per cent of women have it.
Red-green colour blindness is the most common type and is passed along the X chromosome.
Blue colour blindness, which is not passed on a sex chromosome, affects both genders equally.
People can be born colour blind or they may develop it later through such incidents as illness, injury or exposure to chemicals.
by Martin Burns