Colourblindness: not just a black and white issue

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As a ten year old, I found myself waiting impatiently outside the nurse’s office. Like most of my time in school I was unsure of why I was there. No answers were provided as I was sat down, and I was instead shown a series of odd dot patterns similar to the one you see above. Some patterns contained numbers, some didn’t. I left the room even more confused than when I’d went in. The next day my parents got a note from the school explaining that I was red-green colourblind, and that’s when my life changed forever…

Except it didn’t really.

For people already aspiring towards certain careers, such as pilot, electrician or military work, this news could be devastating. However, due to a long list of reasons (including tremors, asthma, and a potent dislike of high stress situations) running around firing a gun or cutting potentially fatal electric wires never particularly appealed to me. I decided instead to pursue science, laboratories of course famous for being happy, stress-free environments that require no intense periods of perfect hand-eye coordination.

The only difference I really noticed, fairly instantly after my diagnosis, was the reaction of other people. Anyone else with a hue-viewing deficiency will be familiar with the classic ‘What colour is this object I’m holding?’ question, and equally familiar with the resulting shock from the asker as you correctly identify it (Most kids know Coke cans are red, even if they see red differently). I’m not just talking about when I was ten years old here either.

My personal favourite question was one asked of me as I had just begun learning to drive. I remember my friend’s frown clearly, “But Joe”, they had said, concern for fellow road users filling their voice, “Aren’t you colourblind? How will you know whether the traffic lights are red and green?”

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The same goes for the walking man on pedestrian crossings.

But I cannot blame people for being confused. Colourblindness, in my life at least, has seemed to occupy an odd sort of limbo between personality quirk and a genuinely limiting condition. Indeed, the UK does not classify colourblindness as a disability. However, as colourblindawareness.org states, it can be seen as more serious in other countries. In Japan the condition can get you excluded from many potential job roles, and some countries such as Romania and Turkey even ban people from driving due to their inability to see different coloured lights.

On the flipside, people with colourblindess have occasionally found themselves sought after. In World War Two it was thought men with colourblindness were more adept at seeing through camouflage, and researchers at both Cambridge and Newcastle universities recently discovered that red-green colorblind individuals have an ability to spot differences in shades of khaki indiscernible to the average person. It makes me worry I’ve actually been wearing nothing but differing shades of beige my whole life and no-one has had the heart to tell me.

So what causes this odd biological quirk? I believe the best way to explain would be to work our way forward from the very start, which would be colour itself.

Light is a wave, and whether you can perceive the light or not is defined by the frequency at which it waves. The visible light spectrum is found sandwiched between infra-red (Which powers your remote control) and ultraviolet (Which you probably don’t want to shine on your remote control) light.

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Waves not pictured: New, Mexican, Awkward

These different ‘wavelengths’ of light all enter through the retina of your eye, where they hit a layer of cells known as ‘photoreceptors’. There are two types of these photoreceptor cells, imaginatively referred to as ‘rods’ and ‘cones’

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Scientists’ imagination is often found lacking when it comes to naming things.

Rod cells, while interesting in their own right, are not colour processors, and thus our focus today will be on cones.

There are enough processes going on in each of the six to seven million cone cells in your eye to fill a year’s worth of blogs, but the key component in these cells is inarguably a protein known as ‘Opsin’. This protein has the handy function of changing shape when being hit by light, starting off a series of events which in essence causes the cone cell to send a signal to the brain saying ‘I can see light’.

What’s more interesting is that there are multiple types of opsins, and each one only changes shape when hit by a specific range of ‘wavelengths’. This makes the cone cells sensitive to different light shades depending on which opsin they have, and together the brain can use them to determine all colour in the environment.

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S,M,L =’Short’, ‘Medium’ and ‘Long’ opsins, corresponding to what range of wavelengths they change shape in. The height of the graph shows which colour they absorb the most.

You may now see where this is going, colourblind people such as me lack one of these opsins (The ‘Medium’ one in my case), and as a result cannot absorb a specific range of light wavelengths. As you can see, M and L overlap quite alot, meaning a deficiency in one of these opsins is not as serious as a deficiency in S. Thankfully S deficiency is alot rarer, as will soon be explained…

So what is the deeper mechanism here? What causes colourblind people to have lost the ability to perceive these different frequencies from birth? Well, as it so often does, it comes down to genes…

The instructions on how to build these three opsin proteins are found in three separate genes, for simplicity (a word that produces gasps from many geneticists) let us call them opsinL, opsinM and opsinS. Genes are long sections of DNA that in most cases contain the information on how to make a single protein, the rudimentary building block for all life. These genes are packed together into 23 pairs of chromosomes, which are in turn found within every cell of our bodies. These chromosomes contain all the instructions your body needs to function, with thousands of genes for thousands of proteins, but today we’re focusing on three.

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S is on the 7th pair, and M/L are both found on pair 23, which has two variations.

While most people will know very little about chromosomes 1 through 22, the 23rd pair are much more readily recognised. The ‘X’ and ‘Y’ chromosomes, the genetic definers of sex. The presence of both long and medium wave opsins here explains one key issue with colourblindness. Why it is so much more common in men.

When our genes are passed on, things can go wrong. The machinery makes mistakes in the instructions when trying to copy them, and that means they cannot be read. This means a specific protein cannot be produced. Thankfully, as the diagram above shows, almost all our genes come with a spare set of instructions, all that is, expect the X and Y in men. If a male inherits a damaged X, he has no insurance chromosome, and his body has to work with the damaged copy. S, due to being on a non-sex chromomsome, has an insurance copy in both men and women, explaining why a deficiency is much rarer.

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The leftmost female offspring is described as a ‘carrier’ as they have the ability to pass the disease on but non of the symptoms.

And so, depending upon whether you are missing the red (long wave) or green (medium wave) opsin gene, you never experience an entire part of the visual spectrum, and have to spend an inordinate amount of time trying to work out which type of Thai curry you’ve just made. Is there anyway back from this terrible fate?

Perhaps there is, extremely sophisticated gene therapy has potentially paved the way for cures at the gene level, fixing the mistakes in the instructions so your body can produce the correct opsin protein again. Although one of the main reasons it is easier is that you can push a needle containing the fixed DNA straight into your eye for direct treatment, which some may view as a sticking point, well I guess in a way needles are always sticking points, that’s how they work. However, at the minute it’s only being used to try and regenerate damaged rods and cones in fully blind individuals, this obviously bein the more medically pressing condition.

For colourblindness, a less gruesome solution seems to have unveiled itself in recent years, and it’s admittedly fairly stylish. The company ‘Enchroma’ have begun offering glasses that users claim increase the vividness of colour in the world around them. I haven’t had a chance to get my hands on some yet, partially in the fear that I won’t ever want to take them off, mostly because of the price tag. They claim to filter out wavelengths of light, simulating a greater distinction between colours that colourblind people have not experienced before.

So while colourblindness can be a hindrance to many, I can say I’m at least partially glad I have it, as it has opened up a whole new area of biology that may not otherwise have caught my eyes.

 

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Thanks for reading my second blog, Colourblindness is a more nuanced and interesting area than many think, and is actually a good entry point into learning a lot of things about genetics, evolution and inheritance. (Did you know that the M and L opsins were originally the same gene?) If you’re interested in learning more, let me know and I may expand on it in the future.

 

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