enchroma lenses and color vision deficiency

You may have seen the videos floating around the internet of colorblind people trying on EnChroma sunglasses for the first time. This month’s blog post is about how it all works!

Ishihara cupcakes

How do we see color?

The retina (the tissue that lines the back of the eye) contains specialized cells called photoreceptors that respond to light. There are two types of photoreceptors: rods and cones.  Rods are responsible for vision in dim light, and cones are responsible for vision in bright light as well as color vision. There are three types of coneseach type is sensitive to different wavelengths of light, and thus different colors. “S” cones are most sensitive to short wavelengths (blues), “L” cones are most sensitive to long wavelengths (reds), and “M” cones are most sensitive to medium wavelengths (greens). The information gathered from these cones is used by the brain to create our perception of color.  Normal trichromatic color vision involves the presence and proper functioning of all three cones.  Color vision defects arise when one of these cones is missing or altered.

In English? Objects reflect light. That light acts as a wave as it enters the eye, activating the cones. The wavelength of that reflected light determines which cones are most activated. This cone response is translated to a neural signal and sent to the brain. Color perception is based on the relative levels of activity in the different cones.

A graph showing the spectral sensitivity of each of the 3 cones in someone with normal color vision
Image source: Eye, Brain, and Vision

What is a color vision deficiency?

The term “color blind” is misleading, as most people use the term to describe someone with a color vision deficiency. They can see colors, but have trouble distinguishing between certain colors and shades.  Color vision defects can be inherited or acquired. The most common are inherited, meaning they are present at birth, affect both eyes equally, and are stable over a person’s lifetime. They occur in about 8% of males and 0.5% of females.  It is more common in males because the genes causing this type of color vision deficiency are located on the X chromosome.

My previous post on color vision deficiency outlines all of the color vision disorders. For this post, we will only look into anomalous trichromats, meaning people who have all 3 cones, but the sensitivity spectrum of one is shifted. This shift causes a greater overlap in the sensitivities of two cones. There are various degrees of severity, based on on how much the spectrums are shifted.

The bottom 2 visuals show red-green color vision deficiency (CVD).
Protanomaly occurs when the L cone is shifted closer to the M cone, reducing sensitivity to reds. 
Deuteranomaly, the most common type of CVD, occurs when the M cone is shifted closer to the L cone, 
reducing sensitivity to greens.
Note the separation in the peaks of the L and M cone sensitivities is much smaller in red-green CVD compared to normal.

The ratio of light entering the eye tells the brain what color to perceive. The greater overlap of red and green in color deficient individuals skews the ratio. For example, when you see a red apple, the cones that should have the greatest response are the red, or long, cones. When there is excessive overlap between the red and green cones, more green cones are responding than normal, which essentially dilutes the red cone response and causes confusion and color muddling. So the apple may be perceived as more brown than red.

What are EnChroma lenses and how do they work?

EnChroma is a company that makes glasses designed to enhance the vibrancy and saturation of colors for those with color deficiencies. They are available in indoor and outdoor lenses, and can be made with or without a prescription.

The lenses actually began as protective eyewear for doctors to use during laser surgery, and their application for color vision deficiencies was discovered somewhat serendipitously. Check out the full story here.

As we noted in the graphs above, the overlapping responses to light by the red and green cones are the issue in those with red-green color vision deficiency. Rather than each cone responding separately, their responses are similar, causing colors to be muddled. EnChroma lenses are designed with “multi-notch filters” that cut out the wavelengths of light that cause the overlapping responses to light. This allows the ratio of cone responses to more closely resemble that of a person with normal color vision. As a result, the EnChroma lenses enhance colors and may make reds and greens more vivid and distinguishable.

Donald McPherson, PhD, a glass scientist and EnChroma’s cofounder, explains it this way:

“EnChroma’s glasses work by reestablishing the correct balance between signals from the three photopigments in the eye of the color deficient. The eyewear does this by removing small slices of light from the visible spectra. At the cortical level, the neural machinery is intact and perfectly functioning in the color blind, so once the correct ratios entering the eye are reestablished, the neural mechanisms excite and the correct color can be seen and perceived.” via Forbes

Images taken from the Enchroma website

Will it work for me?

It depends! There are certainly no guarantees, but EnChroma suggests that their glasses can address the issue for 4 out of 5 individuals with anomalous trichromacy (which is what we described above- all 3 types of cones are present, but the sensitivity of one is shifted). These glasses would NOT work if you have a color deficiency where you are missing one of the three types of cones (dichromacy). The company offers a test that will give you an idea of how likely the glasses are to work for your type of color deficiency.

You can also visit an office that carries EnChroma lenses to try them out and ask an eye care professional for more information. Find an office near you via the website.

*EnChroma lenses do not cure color vision deficiencies, and they are not recommended for the color vision tests required for certain jobs.*

CliffsNotes: The most common color vision deficiencies occur as a result of a shift in the sensitivity of one of the cones, which causes a larger area of overlap between the red and green cones. EnChroma lenses use filters to remove the wavelengths of light in this overlap, which helps restore the proper ratio of cone responses, enhancing color vibrance and saturation. 


Additional recommended resources:

3 comments

  1. Color Vision problem is not comes under blindness but it is kind of deficiency in the eye. The most common color vision in men are red-green color deficiency around 2 to 6 percent men is affected by this problem. If you have any kind of such problem you can visit Rana eye Care Centre in Ludhiana.

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