The natural habitat of the squirrel monkey is the rainforest canopy. This is a young male in the Brazilian Amazon. All male squirrel monkeys are red-green color blind but the majority of females have trichromatic color vision.

WASHINGTON-SEATTLE (US)—Color blindness in adult monkeys has been cured using gene therapy, according to researchers at the University of Washington.

The scientists say the work dispels the theory that “critical periods” for the development of many capacities end prior to adolescence, implying that treatments involving the adult visual system would be impossible.

The results show that in the case of color vision, the nervous system is capable of responding to newly added sensory input, allowing adult monkeys to respond to colors that they could not see previously.

The researchers used a computerized test for human color blindness, similar to the well-known testing books in which colored numbers or symbols are concealed in a pattern of dots that look like jellybeans on a plate.  Because the monkey visual system is similar to that of humans, a human gene was used to replace the missing visual pigment of the monkeys.

Prior to treatment, the monkeys could not distinguish red or green, but following treatment that added the missing visual pigment gene, the monkeys passed the test easily for all colors.

Red-green color blindness, which results from loss of either the red- or green-sensitive visual pigment in the eye, is the most common genetic disorder. One in 12 men and 1 in 230 women are affected, while 1 in 6 women is a carrier of the inherited condition.

While the procedure is not yet available to humans, scientists say they are optimistic about that possibility in the future.

Researchers at the University of Florida and the Medical College of Wisconsin contributed to the study, which was published in the Sept. 17 issue of Nature.

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