Color blindness in adult male squirrel monkeys is reversible, found researchers from the University of Washington and the University of Florida. Male squirrel monkeys are born with red-green color blindness. Researchers used a gene-transfer technique to add the third cone pigment to the dichromatic retinas of two monkeys. Over a period of five weeks, the monkeys acquired full color vision, which researchers confirmed through the use of Cambridge color tests. 

In the computerized test of color blindness, monkeys receive a drop of grape juice as a reward for getting the right answer.
Photo: Neitz Color Vision Lab
“We’ve added red sensitivity to cone cells in animals that are born with a condition that is exactly like human color blindness,” says William W. Hauswirth, Ph.D., professor of ophthalmic molecular genetics at the University of Florida College of Medicine. “We used human DNA, so we won’t have to switch to human gene as we move toward clinical treatment.”

The testing took more than a year and a half, and the researchers found that the monkeys were able to discern 11 intensities of 16 colors. “We’ve shown that we can cure a cone disease in a primate, and that it can be done very safely,” says Dr. Hauswirth. “That’s extremely encouraging for the development of therapies for human cone diseases that really are blinding.” 

Mancuso K, Hauswirth WW, Li Q, et al. Gene therapy for red-green color blindness in adult primates. Nature. 2009 Sep 16; [e-pub ahead of print]