By Maddie Stone and Diane Kelly
A company called EnChroma has built a pair of glasses that claims to restore colour vision for the colourblind. Predictably, the internet has erupted with excitement. But it’s not the first instance in which a piece of technology has made this bold assertion, and the science behind colour perception isn’t straightforward. We decided it was time to figure out what’s really going on.
For some colourblind people, donning EnChroma lenses is nothing short of life-changing. For others, the experience is lacklustre. To understand why, let’s take a deep dive into the science of colour vision, some of the different forms of colourblindness, and what these glasses are actually doing.
How Does Colour Vision Work?
When people with normal colour vision look at a rainbow, they see the whole swath of colours – from red to violet – within the part of the spectrum we call ‘visible light.’ But although every shade represents a specific wavelength of light, our eyes don’t contain unique detectors to pick out each and every wavelength.
Electromagnetic spectrum. Image Credit: Wikimedia
Instead, our retinas make do with only three types of colour sensitive cells. We call them cone cells. They’re specialised neurons that fire off electrical signals in response to light, but they’re not actually very precise: a cone cell is sensitive to a wide range of coloured light. But when the brain collects and aggregates the information collected by all three types of cone cell in the eye, it’s able to make fine discriminations between different shades of the same colour. Here’s how that works.
Cone cells contain a light-sensitive pigment that reacts to wavelengths of light from one segment of the spectrum. The photopigment is slightly different in each type of cone cell, making them sensitive to light from different parts of the spectrum: we may call them red, green, and blue cones, but it’s actually more accurate to say that each type detects either long (L), medium (M), or short (S) wavelengths of light.
Typical light response curves for cones in a human eye. Image Credit: BenRG / Wikimedia
The graph above, which shows how strongly each kind of cone cell responds to different wavelengths of light, makes that idea easier to visualise. You can see that each type of cone cell has a strong response (shown by a peak) for only a narrow range of wavelengths. The ‘red’ L cones respond most strongly to yellow light, the ‘green’ M cones to green light, and the ‘blue’ S cones to blue-violet light. Cones are also triggered by a wide range of wavelengths on either side of their peaks, but they respond more weakly to those colours.
That means there’s a lot of overlap between cone cells: L, M, and S cones actually respond to many of the same wavelengths. The main difference between the cone types is how strongly they respond to each wavelength. These features are absolutely critical to the way our eye perceives colour.
Image Credit: EnChroma
Imagine you have a single cone cell. Make it an M cone if you like. If you shine a green light on the cell, it’s perfectly capable of sensing that light. It’ll even send an electrical signal to the brain. But it has no way to tell what colour the light is. That’s because it can send out the same electrical signal when it picks up a weak light at a wavelength that makes it react strongly as when it detects a strong light at a wavelength that makes it react more weakly.
To see a colour, your brain has to combine information from L, M, and S cone cells, and compare the strength of the signal coming from each type of cone. Find the colour of a beautiful cloudless blue sky on the graph, a wavelength around 475 nm. The S cones have the strongest reaction to that wavelength, but the red and green cones are weighing in with some signal action, too. It’s the relative strength of the signals from all three cone types that lets the brain say “it’s blue”! Each wavelength of light corresponds to a particular combination of signal-strengths from two or more cones: a three-bit code that lets the brain discriminate between millions of different shades.
What Makes Someone Colourblind?
The three-bit code is sensitive, but lots of things can mess it up. The gene for one of the three photopigments might go AWOL. A mutation could shift the sensitivity of a photopigment so it responds to a slightly different range of wavelengths. (Damage to the retina can cause problems, too.) In a colourblind person, the cone cells simply don’t work the way they’re supposed to; the term covers a huge range of possible perceptual differences.
The most common forms of inherited colour blindness are red-green perceptual defects. One version is an inability to make L photoreceptors, another stems from a lack of M photoreceptors. People with these genetic defects are dichromats: they have only two working photoreceptors instead of the normal three. Their problem is actually pretty straightforward. Remember that the brain compares how strongly each type of cone responds to a given wavelength of light? Now disappear either the L or M curve in that photoreceptor response graph in your mind, and you can see how the brain loses a ton of comparative information.
The problem is more subtle for people who have a version of the L or M photoreceptor that detect a slightly different range of wavelengths than normal. These people are anomalous trichromats: like someone with normal vision, their brains get information from three photoreceptors, but the responses of one type of photoreceptor are shifted out of true. Depending on how far that photoreceptor’s response curve has shifted, an anomalous trichromat may perceive reds and greens slightly differently than a person with normal vision, or be as bad at discriminating between the two as a dichromat.
Fall colours, seen six different ways. Top left: Normal colour vision. Bottom left: Deuteranomaly (Green weak). Top middle: Protanomaly (Red weak). Bottom middle: Tritanomaly (Blue weak). Top right: Deuteranopia (Green blind). Bottom Right: Tritanopia (Blue blind).
But a child born with one of these colour perception deficiencies has no way to tell the difference. Learning he sees the world differently from the people around him can be an enormous surprise. That was true for media consultant Carlos Barrionuevo, who first discovered he was colourblind when he was 17.
“I didn’t really notice it when I was a kid.” he told Gizmodo. “And my parents didn’t pick up on it. I honestly did not know until I applied for the Navy. I went in for my physical, and they start flipping through this book and say ‘Just tell us what number you see.’ And I said, ‘What number? There’s a number?’”
The book Barrionuevo mentions contained some version of the Ishihara test: circles made up of coloured dots in a variety of sizes and shades that serve as a quick-and-dirty way to screen for colourblindness. The circle can contain a symbol or a number that is difficult if not impossible for someone with one form of colour blindness to see. It can also be designed so the symbol is visible to the colourblind, but invisible to everyone else. The test below looks like a 74 to people with normal vision, but appears to be a 21 to people with red/green colourblindness.
Ishihara colour test plate. People with normal colour perception can see the number 74. People with red/green colourblindness see a 21. Image Credit: Wikimedia
Barrionuevo stresses that it’s really not a simple matter of not seeing red or green. “I can usually tell what’s green and what’s red, but different shades of red or green all look the same to me. I get very confused on certain colours. If I go in a paint store, a lot of those paint chips just look similar, and I can’t make distinctions between them.”
What Are EnChroma Lenses Doing?
If colour perception is basically an intensity game, that raises an obvious question: Could we restore normal colour vision, simply by tweaking the proportions of light a colourblind person’s eyes are exposed to?
Andy Schmeder, COO of EnChroma, believes that we can. A mathematician and computer scientist by training, Schmeder began exploring colour vision correction a decade ago, along with his colleague Don McPherson. In 2002, McPherson, a glass scientist, discovered that a lens he’d created for laser surgery eye protection caused the world to appear more vivid and saturated. For some colourblind people, it felt like a cure.
Image Credit: EnChroma
With a grant from the National Institutes of Health, McPherson and Schmeder set about to determine whether the unusual properties of this lens could be translated into an assistive device for the colourblind.
“I created a mathematical model that allows us to simulate the vision of a person with some kind of colourblindness,” Schmeder told Gizmodo. “Essentially, we were asking, if your eyes are exposed to this spectral information and your eye is constructed in this particular way, what does that do to your overall sense of colour?”
Using their model results, Schmeder and McPherson developed a lens that filters out certain slices of the electromagnetic spectrum; regions that correspond with high spectral sensitivity across the eye’s M, L, and S cones. “Essentially, we’re removing particular wavelengths of light that correspond to the region of most overlap,” Schmeder said. “By doing so, we’re effectively creating more separation between those two channels of information.”
Spectral response of red, green, and blue cones, with grey regions indicating regions of “notch filtering” by the EnChroma glasses. Image Credit: EnChroma
EnChroma doesn’t claim its lenses will help dichromats, those people who lack an M or L cone. It also isn’t claiming to have developed a cure. Rather, the company likes to call its product an “assistive device,” one that can help anomalous trichromats (those people with M or L cones that have shifted their wavelength sensitivities) discriminate colours in the red-green dimension.
Many users report dramatic changes to their colour vision while wearing EnChroma glasses. “Any colour with red or green appears more intense,” one anonymous user reported in a product validation study. “In fact, almost everything I see looks more intense. The world is simply more interesting looking.” Another user writes: “I never imagined I would be so incredibly affected by the ability to see distinct vivid colours, once confusing and hard to differentiate.” If you’re curious about the experience, you can check out any one of EnChroma’s many promotional videos, in which a colourblind person dons the glasses and is immediately overwhelmed by the vibrancy of the world.
But some wearers are underwhelmed. “It’s not like they were worse than regular sunglasses — there was a way in which certain things popped out — but not in the way that it felt like it was advertised,” journalist Oliver Morrison told Gizmodo. Morrison’s account of his experience with the glasses, which appeared in The Atlantic earlier this year, highlights the challenge of objectively evaluating whether a device of this nature works. Here’s an excerpt:
I met Tony Dykes, the CEO of EnChroma, in Times Square on a gray, rainy day, our eyes hidden behind his glasses’ 100 reflective coatings... I described to Dykes what I saw through the glasses: deeper oranges, crisper brake lights on cars, and fluorescent yellows that popped. I asked him if that is what a normal person sees.
Dykes, a former lawyer and an able salesman, answered quickly. “It’s not something where it’s immediate,” he said. “You’re just getting the information for the first time.”
Maybe the glasses were working. Maybe exchanging the colours I was accustomed to for real colours just wasn’t as great an experience as I’d been expecting. Dykes asked if I could tell the difference between the gray shoelaces and the pink “N” on the side of my sneakers. “The ‘N’ is shiny,” I said. “So I don’t know if I can tell they’re different by the colours or because of the iridescence.”
Although I’d never confused my shoelace with my shoe before, I realised then that, until he had told me, I didn’t know the “N” was pink.
Jay Nietz, a colour vision expert at the University of Washington, believes EnChroma is capitalising on this lack of objectivity. “Since red-green colourblind people have never experienced the red and green colours a normal person sees, they are easily fooled,” Nietz told Gizmodo in an email. “If the glasses could add light, maybe it’d be different. But all they can do is block out light. It’s hard to give people colour vision by taking things away.”
Neitz, for his part, believes the only way to cure colourblindness is through gene therapy — by inserting and expressing the gene for normal M or L cones in the retinas of colourblind patients. He and his wife have spent the last decade using genetic manipulation to restore normal vision to colourblind monkeys, and they hope to move on to human trials soon.
A monkey named Dalton, post gene therapy, performing a colourblindness test. Dalton used to be red-green colourblind.
But if the glasses aren’t enabling people to see more colours, what could account for the positive testimonials? Nietz suspects the lenses are altering the brightness balance of reds and greens.
“If somebody was totally colourblind, all the wavelengths of light in a rainbow would look exactly the same,” Nietz said. “If they went out in the real world and saw a green and red tomato, they’d be completely indistinguishable because they’re the same brightness to our eyes. Then, if that person put on glasses with a filter that blocked out green light, all of a sudden, the green tomato looks darker. Two things that always looked identical now look totally different.”
“I wouldn’t claim that the EnChroma lens has no effect on brightness,” Schmeder said in response to Gizmodo’s queries. “Pretty much anything that’s strongly coloured will suddenly seem brighter. It’s a side effect of the way the lens works.”
But according to Schmeder, the lens’s neutral grey colour maintains the balance of brightness between reds and greens. That is, all red things aren’t going to suddenly become brighter than all green things, he says.
In the end, the best way to sort out whether the glasses are working as advertised is through objective testing. EnChroma has relied primarily qualitative user responses to evaluate the efficacy of its product. The company has also performed some clinical trials using the D15 colourblindness test, wherein subjects are asked to arrange 15 coloured circles chromatically (in the order of the rainbow).
In the 100 hue test, subjects arrange the colours within each row to represent a continuous spectrum of shade from one end to the other. colours at the end of each row serve as anchors. Image Credit: Jordanwesthoff / Wikimedia
In test results shared with Gizmodo, nine subjects all received higher D15 scores — that is, they placed fewer chips out of sequence — while wearing EnChroma glasses. “What is apparent from the study is that not everyone exhibits the same degree of improvement, nor does the extent of improvement correlate to the degree of [colourblindness] severity,” EnChroma writes. “However, everyone does improve, some to that of mild/normal from severe.”
But there’s still the concern that wearing a coloured filter while taking the D15 test will alter the relative brightness of the chips, providing a context cue that can help subjects score higher. For a more objective test, Nietz recommends the anomaloscope, in which an observer is asked to match one half of a circular field, illuminated with yellow light, to the other half of the field, which is a mixture of red and green. The brightness of the yellow portion can be varied, while the other half can vary continuously from fully red to fully green.
Screenshot from an online colour matching test that mimics the anomaloscope. Via color-blindness.com.
“This is considered to be the gold standard for testing red-green colour vision,” Nietz said. “The anomaloscope is designed in such a way that adjustments can be made so that colourblind people can’t use brightness as a cue so the brightness differences produced by the glasses would not help colourblind people cheat.”
Is it all About Perception?
Whether EnChroma’s glasses are expanding the red-green colour dimension, or simply creating a more saturated, contrast-filled world, there’s no doubt that the technology has had positive effects for some colourblind people.
“The biggest point for me wearing this glasses is that I’m more inspired,” guitarist and EnChroma user Lance Martin told Gizmodo.
Image Credit: Shutterstock
Martin, who has been “wearing these things nonstop” for the last several months, says that ordinary experiences, like looking at road signs or foliage while driving, now fill him with insight and awe. “I always interpreted interstate road signs as a really dark evergreen, but they’re actually a colour green i’d never been able to see before,” he said. “I’ve been walking more, just to see the flowers. Inspiration fuels my career, and for me to be inspired by the mundane, everyday — that is mind-blowing.”
The world of colour is inherently subjective. Even among those who see “normally,” there’s no telling whether our brains interpret coloured light the same way. We assume that colours are a shared experience, because we can distinguish different ones and agree on their names. If a pair of glasses can help the colourblind do the same — whether or not the technology causes them to see “normally” — that’s one less reason to treat this condition as a disadvantage.
“People are looking for access to jobs where they’re being excluded because of colourblindness,” Schmeder said. “My belief is that if we really analyse this problem closely, we can come up with a reasonable accommodation that works for some situations. Even if we can’t help everyone, if we can elevate the level of discussion around this and help some people, that’d be amazing.”
Top image: En Chroma (edited)