It is a common misconception that people with colour blindness cannot perceive colour at all and that they perceive the world in shades of grey. In fact, the scope of colour blindness is very large, including a very slight difference in colour perception to complete colour blindness. People who only struggle with a slight difference in colour perception, may not even be aware of their condition unless they are specifically tested for it.
The most common types of colour blindness are inherited. Depending on the affected retinal cones, problems can arise with red, green or blue colour vision. Inherited colour blindness can be present at birth, begin in early childhood, or not appear until the adult years. Colour blindness can also be caused by damage to the eye, the nerve or to the parts of the brain that process colour vision.
“How do we see colour” is a debate that eye care professionals frequently have. What colour is a strawberry? The answer is red, but do we all see the same red? Our colour perception depends on how the eyes absorbs the reflected light from an object and how the brain interprets the light.
Colour blindness can make it difficult to read colour-coded material such as graphs and maps. It might be difficult to buy clothes or selecting ripe fruit. Children with colour blindness can find it difficult to finish certain tasks or complete an art project. It is recommended that children are screened for colour blindness before starting Grade R.
Types of colour blindness
There are three types of colour blindness – red-green colour blindness, blue-yellow colour blindness and a complete absence of colour vision.
Red-green colour blindness
The most common type is red-green colour blindness. As many as 8 percent of men and 0.5 percent of women have red-green colour blindness.
If the red cones photopigment is abnormal, it is referred to as protanomaly. Red, orange and yellow appear greener and dull. Protanopia is where there are no working red cones. Red appears black. Certain shades of orange, yellow and green all appear as yellow.
If the green cones photopigment is abnormal it is referred to as deuteranomaly. Yellow and green will appear redder. This is the most common form of colour blindness, affecting up to 5% of males. Deuteranopia is where there are no working green cone cells. Reds will appear brownish and greens will appear beige.
Blue-yellow colour blindness
If the blue cone cells are affected, it is referred to as tritanomaly. Blue will appear greener and it is difficult to distinguish yellow and red from pink. It is very rare and affects males and females equally. Tritanopia is where there are no blue cone cells. Blue will appear green and yellow will appear light grey or violet.
Complete Colour blindness
This is also referred to as monochromacy. There are two types of monochromacy – cone monochromacy and rod monochromacy. Rod monochromacy is the most severe type of colour blindness and is present from birth. People with rod monochromacy see the world in black, white and grey.
Diagnosis and treatment of colour blindness
There is variety of diagnostic tests used by eye care professionals. At VDM Optometrists we use the Ishihara colour test. The test consists of a series of coloured circles, each of which contains a collection of dots in different colours and sizes. The collection of dots forms a shape that is clearly visible to people with normal colour vision and difficult for people with colour vision defects.
Follow the link for an online Ishihara test: https://www.colour-blindness.com/colour-blindness-tests/ishihara-colour-test-plates/
People with red-green colour blindness can use a special set of lenses to assist in perceiving colour more accurately. Various visual aids exist, such as cellphone or tablet apps. Unfortunately, there is no cure for colour blindness.