Lenses developed to help doctors spot veins more easily have a useful side effect - they enhance the ability to see reds and greens. The glasses, made by 2AI Labs in Boise, Idaho, use filters to enhance perception of blood-oxygen levels in vessels under the skin. The filters concentrate their effects around the wavelengths where people with red-green colour blindness have deficiencies. "We didn't design them for colourblind people," says Mark Changizi, of 2AI Labs, "but we weren't too surprised to find they help."
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