Green or Red? Deuteranomaly

I suffer from a mild case of deuteranomaly, which is red-green colour blindness. Recently I read an interesting blog by “Jasmin Hartel” about the cultural perception of basic concepts like colour or smell. She included the famous colour blindness test “The Ishihara Test”, this reminded me of my condition and I decided to share my experience being mildly colour blind, and what does it mean to be deuteranomalic.


What makes the roses red?

Before I start with my story, let’s first learn what really is colour? Just imagine opening up a box of crayons, there is an entire spectrum of colours before you, do you wonder that why blue is blue and red is red? Well, basically it is because of the physical properties of the material that is used to manufacture each coloured crayon. The properties such as light absorption, reflection index, and emission spectrum dictate what coloured light is reflected off of them. The colour of the light is determined by its wavelength, red starts from around 650nm while blue is 450nm. Human eyes have millions of two special kinds of cells: rod and cones. Rod cells are very sensitive to light and are mostly responsible for low light perception. They do not sense any colour, which is the reason why we see very little colour in the dark. Cone cells on the other hand are responsible to perceive colour. Humans have trichromatic vision, means that we have three type of cone cells, each type is responsible to sense one of the three primary colours: red, green and blue. The signals from these three types are combined in our brain, which enables us to perceive the entire visible spectrum.


File:Linear visible spectrum.svg
The visible light spectrum. Source: Gringer, Wikimedia (public)

What makes me deuteranomalic?

Deuteranomaly is caused by malfunction of green perceiving cones in the eye, so brain receives a weak green signal resulting confusion between red and green hues. It is the most common type of colour blindness. Deuteranomaly affects nearly 5% of the male population and 0.5% of the females. Colour blindness has a strong genetic link, it is linked to the X chromosome. This is the reason why females are affected less as they have two X chromosomes, which decreases the chance of having only colour blind copies. Males only have one X chromosome and if it’s linked to colour blindness, then there is no way out.

1414 Rods and Cones.jpg
Light reception on the ratina. Source: OpenStax College, Wikipedia (CC)

Living with Deuteranomaly

I myself did not knew that I had colour blindness until I was about 16. I always suspected that there was something amiss, but previously I believed that I was kind of stupid and simply couldn’t remember the name of the colours (haha). It is amazing that even my parents or teachers did not suspect, maybe because I have a mild condition. At 16 I took the “Ishihara Test” and finally knew the name of my problem.

Although I have never been hindered by my colour blindness, but there are few stories which are quiet interesting. I would start with the traffic lights, back in my home city “Karachi”, traffic lights are red, yellow, and green. And there they use lighter shades which were nearly impossible for me to judge (I found all of them to be yellowish), so I mostly drove by judging the position of the light on the vertical signals. Once or twice I have caused chaos on the road just because lights were installed horizontally. It is a relief that signals here in Australia are quiet distinct, but still green light is more of a white light to me.

I own a dark green car, but I have never seen green in it, I perceive it as black. So there have been times when I have pointed my friends to my car in some parking lot “there the black one!” and they have looked at me bewildered. I confess when I first bought in 2 years back, first impression was good only because it was black to me :-p.

My Green Car! Photo: Author

I suppose I could also attribute my horrible artistic abilities to my colour blindness, but that would be a stretch as that has more to do with me laziness.

Human body is a wonder, each small part has had thousands of years to evolve to its perfect present form and I wonder what can be the logic behind the deuteranomalic mutation.