Red–green colour blindness, which results from the absence of
either the long- (L) or the middle- (M) wavelength-sensitive visual
photopigments, is the most common single locus genetic disorder.
Here we explore the possibility of curing colour blindness using
gene therapy in experiments on adult monkeys that had been
colour blind since birth. A third type of cone pigment was added
to dichromatic retinas, providing the receptoral basis for trichromatic
colour vision.