Contact lenses may be useful for restoring vision to people who are short- or long-sighted, but they're less useful at correcting color blindness. Now researchers from the University of Birmingham have developed a contact lens that can help correct certain kinds of color blindness, thanks to a safe, low cost dye.

Color is perceived by light hitting clusters of cells called cones in the back of the eye. Different cones pick up different wavelengths of light, and working together they let us see the entire spectrum of colors. When these cones don't work properly, usually for genetic reasons, they affect a person's ability to sense certain colors, resulting in what we know as color blindness – or color vision deficiency (CVD), as it's technically known.

The most common form of CVD affects the red and green parts of the spectrum. When light of either of these colors enters the eye, red-sensitive cones and green-sensitive cones are triggered simultaneously, meaning sufferers can't readily identify the difference between these two colors. This "color confusion" means all they see is a kind of muddy yellow-brown, which can disrupt everyday situations like looking at traffic lights.

Past research has set out to correct the problem using gene therapy to grow new cones in the eyes of color-blind monkeys, while EnChroma has developed sunglasses that can help correct the problem. But these kinds of devices, according to the Birmingham team, are expensive and bulky, and can't be used with regular corrective lenses.

The new contact lenses work on the same principle as EnChroma's sunglasses. The lenses are colored with a dye derived from rhodamine, which absorbs certain wavelengths of light between red and green. By blocking those wavelengths out, light is more readily absorbed by either the red- or green-sensitive cones, and not both sets, allowing the patient to better distinguish between those colors.

"Contact lenses are of interest for color blindness correction because it is easier to correct the entire field of view," says Haider Butt, lead researcher on the study. "The dye processing we carried out does not need any complex preparation, it is not toxic to the human eye, and our method could be easily used in both glasses and contact lenses at low cost."

The Birmingham researchers tested out the idea on people with red-green CVD. The dye was applied to a glass slide, and participants looked through it at colored numbers on the other side. Sure enough, the patients reported being able to better identify the color and clarity of the numbers.

"We are now looking into using a similar process to correct purple-blue color blindness, and also to bring together a number of dyes to make lenses perform for both red-green and purple-blue colour blindness simultaneously," says Butt. "We are about to commence human clinical trials shortly."

The research was published in the journal Advanced Materials Healthcare.