Correcting chemistry’s colors

Driving while color-blind is dangerous: Green stoplights look white and are often hard to distinguish from streetlights. So you guess or get help. A company called EnChroma now makes lenses that it claims “enhance the vibrancy and saturation of colors and help the color-blind discriminate between colors that can be hard to see.” But EnChroma is careful to say its glasses are “not a cure, a fix, or a correction for color blindness,” says Kent Streeb, director of marketing at EnChroma.

[+]Enlarge Credit: Shutterstock/Matthew Wickline/Human-Computer Interaction Resource Network

Newscripts wanted to delve into the science of the special spectacles and see how the technology might help color-blind scientists in the lab.

Human color vision is based on three types of light-sensitive cells in the eye. Called cones, the cells respond to blue, green, and red light. The brain calculates perceived color by measuring how strongly the different types of cells are stimulated by the light coming from a given object.

Lab Tour EnChroma says its glasses can help some colorblind people distinguish colors better. C&EN took the special spectacles to the Department of Materials Science & Engineering at the University of Maryland, College Park, to see how helpful the technology could be in a working scientific laboratory. Credit: C&EN

All three kinds of cones use the same light-absorbing small molecule, or chromophore: 11-cis-retinal. In isolation, it has an absorption peak in the ultraviolet region of the spectrum. The biochemical trick to color vision is that this chromophore is placed inside a barrel-shaped protein, explains ophthalmology professor Jay Neitz of the University of Washington, Seattle. Amino acids point in from the walls of the barrel, altering the distribution of electrons on the chromophore. The more electron density is pushed onto a ring at one end, the further the absorbance of the light is shifted toward the red region.

The three varieties of cone cells each express a different version of the protein that shifts the chromophore’s absorbance so it peaks at 420 nm for blue, 530 nm for green, and 560 nm for red. But in 8.0% of men and 0.5% of women, a mutation in the genes coding for one or more of those proteins results in a cone that absorbs in the wrong place—or not at all.

Red-green color blindness, the most common type, is a result of the absorption band of the green cones being shifted to the red, or vice versa. The closer the two peaks are, the worse the color resolution gets.

EnChroma says its glasses work by blocking select bands of wavelengths of light—in optics lingo, the glasses contain a notch filter. The idea is that the notches create greater separation between the red and green signals entering the eye, allowing the brain to better calculate the colors.

Patrick Stanley is a graduate student in materials science at the University of Maryland, College Park. Stanley has a moderate case of deuteranomaly, meaning his green cones are red shifted. Newscripts went to UMD to let him try EnChroma’s glasses; the company provided two pairs free of charge for this experiment.

“Primary colors seemed more their color,” Stanley reports of his time wearing the glasses. “Labels and boxes caught my attention more—and I guess the point of a hazardous label is to catch my attention.” He also could tell the difference between red and green LEDs and felt more adept at color-matching tasks such as tracing gas lines and reading graphs. “I found myself being quicker in making color assertions,” he says.

Neitz, the color vision researcher, is skeptical of the technology. Until the absorbance peak difference drops from 30 nm to 3 nm, he says, most people don’t notice a problem. But that’s too close to fit a meaningful notch between the peaks. So the glasses wouldn’t work for people with impairment severe enough that they consider themselves color-blind, whereas the people the glasses can help don’t need it, he argues.

Neitz’s skepticism is bolstered by a UV-visible absorption spectrum Newscripts took of the glasses. The major notch we observed was centered at 595 nm, off to the red side of the red cones’ absorbance, not between it and the green. When asked, EnChroma asserted that the 595 nm band is properly placed to adjust the light signals that reach the cones.