Living Without Colour: Understanding Colour Deficiency
Did you know that colour blindness really isn’t blindness at all? It’s a deficiency. Did you know that about 8 percent of men are colour deficient, while less than 1 percent of women are? We’ve heard a lot about colour deficiency or “colour blindness” over the span of our lifetimes. But do we know how much is fact and how much is fiction?
We want to be compassionate and understanding, but to truly understand the struggles of colour deficiency, we must first understand what colour deficiency actually is and how it works.
How the Average Eye Perceives Colour
Your macula (the central area of the retina) is covered in light-sensitive cells called rods and cones. The average eye has roughly 100 million rods, and 7 million cones. Each of these cones is designed to detect a certain wavelength (or colour) of light. With 7 million cones, we can see a full range of colour and shades in sharp contrast.
How the Colour Deficient Eye Perceives Colour
In a colour deficient eye, the macula is still covered in rods and cones. However, in this case, there are fewer cones than what is considered average. Because each type of cone detects certain colours of light, a low number of specific cones means a lower sensitivity to that kind of light. In some cases, a patient is completely lacking one type of cone altogether, leaving them unable to perceive some colours, and struggling to differentiate others.
Types of Colour Deficiency
Because our perception of colour is based entirely on the types and number of cones we have, there are a variety of different colour deficiencies.
Red-Green Colour Deficiencies
Protanomaly- Too few red cones cause colours to appear duller, while reds, yellows, and oranges to appear greenish.
Protanopia- A total lack of red cones causes reds to appear black, while shades of orange and green appear yellow.
Deuteranomaly- Too few green cones cause yellow and green to appear more red, while blues and violets appear indistinguishable from each other.
Deuteranopia- A total lack of green cones causes reds and greens to appear brown or beige.
Blue-Yellow Colour Deficiencies
Tritanomaly- Too few blue cones cause blues to appear more green, while yellows, reds, and pinks all appear similar.
Tritanopia- A complete lack of blue cones causes blues to appear green and yellows to appear grey.
Complete Colour Deficiencies
Cone monochromacy– Two of the three types of colour-sensing cones do not work, leaving one colour indistinguishable from another.
Rod monochromacy- None of the colour-sensing cones function properly. In these cases, the patient can see only black, white, and greys. This condition usually leaves the patient very sensitive to light.