Colour deficiency and blindness

To understand this topic, one will need a preliminary knowledge on the structure of the eye.  Basically, the eye has photoreceptors in the form of rods and cones that are situated on the back of the eye (retina.) These are light sensitive cells that signal to the brain the perception of light and colour.   The rods aid in night vision, and help perceive light levels.  They are sensitive to black and white.  The cones in the eye are responsible for colour perception, and there three different kinds,  red, blue and green.  They are sensitive to different wavelengths of light,  which allows the eye to see multiple colours.

Colour blindness, or colour deficiency affects approximately 350 million people worldwide.  That works out to roughly 1 in 12 men, and 1 in 200 women.  Men are more likely to be colour blind due to the gene that causes colour blindness being passed on through the X chromosome.  In order for a woman to be colour blind, she would have to have the gene on both of her X chromosomes.
This particular gene causes the cones of the eye to be non-functional, damaged or missing, which causes a different perception of colour.  

Types of colour deficiency
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Very rarely is a person completely colour blind.  There are a few different types of colour blindness which have different effects on vision.   They can be divided into two different categories, red-green deficiency, and blue-yellow deficiency. 
Red-Green Deficiency Types
​Deuteranomaly
This is the most common form of colour deficiency.  People who have deuteranomaly have a reduced sensitivity to green light.  It's generally considered a very mild colour deficiency.
Protanomaly
This condition makes certain shades of red look more like green and less bright.  This type doesn't usually get in the way of every day activities.
Protanopia and deuteranopia 
Both of these conditions make someone unable to tell the difference between red and green at all.

Blue-Yellow Deficiency Types
This is a much less common type of colour vision deficiency, and it makes it difficult to tell the difference between several different colour combinations.
Tritanomaly 
This deficiency makes it hard to tell the difference between blue and green, and between yellow and red.
Tritanopia 
This condition makes someone unable to tell the difference between blue and green, purple and red, and yellow and pink. It also makes colors look less bright.

Complete Colour Blindness
Monochromacy or Acromatopsia
This is an incredibly rare form of colour deficiency in which a person sees the world in greyscale.  Often, people with this condtion have light sensitivity and need to wear dark glasses in normal light conditions.  The cones in the eyes are non-functional, causing the vision to be interpreted in shades of grey.  This colour blindness makes every day tasks very difficult.

There is a test one can take to determine if they are colour deficient or blind.  This test is known as the Ishihara test.  You can take an Ishihara test here:
https://www.colorblindnesstest.org/ishihara-test/

​Are you colour deficient or blind?