Scientists say they are a step closer to curing colour blindness using gene therapy.
A US team were able to restore full colour vision to adult monkeys born without the ability to distinguish between the colours red and green.
Watch the squirrel monkey 'cured' of colour blindness. Previously, when untreated, he could only guess where to touch as the red colour looked no different to grey.
Although more studies are needed, the same treatment may work for humans who are colour blind, experts say in the journal Nature.
Footage courtesy of Neitz Laboratory