When English chemist John Dalton first wrote about color blindness in 1798, he must have wondered how science would improve the quality of life for people living with the condition. Today, spectacles, contact lenses and revolutionary corrective eye surgery combat the effects of a myriad of vision disorders, yet people with color blindness still live in quiet acceptance of this common genetic disorder. Now researchers have delivered promising results by successfully treating two squirrel moneys with defective color perception using a gene therapy that could also safely eradicate color blindness in humans.

Although not a particularly debilitating condition, millions of people around the world, including 3.5 million Americans, 13 million people in India and 16 million in China, are affected by color blindness. It is a congenital problem, largely experienced by men, that renders its sufferers incapable of discerning mainly red and green hues: seemingly trivial but, in reality, a necessity for everyday practicalities such as recognizing traffic lights.

The results have come to fruition after many years of collaboration between researchers from the University of Washington and the University of Florida. As explained by William W. Hauswirth, Ph.D., a professor of ophthalmic molecular genetics at the University of Florida’s College of Medicine, the gene therapy has involved adding "red sensitivity to cone cells in animals that are born with a condition that is exactly like human color blindness.”

Hauswirth’s team developed a gene-transfer technique to produce a desired protein. In this study, the monkeys Dalton and Sam, were treated with a substance called long-wavelength opsin, a colorless protein that works in the retina to produce pigments that are sensitive to red and green. Strengthening this study’s link to a human cure is the use of human DNA to avoid having to “switch to human genes as we move toward clinical treatments,” said Hauswirth.

The research team at the University of Washington, responsible for the long-term care and post-treatment assessment of Dalton and Sam’s color blindness, developed a variation of the Cambridge Color Test, the standard vision-testing technique given to school children whereby they must identify a specific pattern of colored dots among a field of dots varying in size, color and intensity. In this study, the test was modified to perfect the way the monkeys could communicate with the researchers and “tell” them which colors they were seeing.

According to Jay Neitz, professor of ophthalmology at the University of Washington, “Nothing happened for the first 20 weeks…but we knew right away when it began to work. It was as if they woke up and saw these new colors. The treated animals unquestionably responded to colors that had (previously) been invisible to them.” It has taken more than 18 months of testing the monkeys' ability to discern 16 hues, with some varying as much as 11-fold in intensity. The monkeys were able to trace color patterns on a computer touch screen and, when they chose correctly, they were rewarded with grape juice.

Even more rewarding are the wider implications of this study for other vision disorders. For example, approximately one in 30, 000 Americans has achromatopsia, an hereditary form of blindness, which causes nearly complete color blindness and extremely poor central vision. “Those patients would be targets for almost exactly the same treatment. Even in common types of blindness such as age-related macular degeneration or diabetic retinopathy, vision could potentially be rescued by targeting cone cells,” says Hauswirth. “We’ve shown that we can cure a cone disease in a primate, and that it can be done safely. That’s extremely encouraging.”

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