When the inability to distinguish colours and shades occur it can be that you are colour deficient. Worldwide, males are 16.7 times more likely than women to have this condition.
This is usually a genetic condition passed on from your mother’s DNA but can also be caused by trauma, disease, aging, certain medications and industrial or environmental chemicals.
Your retina has two types of light-sensitive cells. Cones and rods are found in the retina layer which processes images. In low light conditions rod cells work to help night vision, but during daylight, cone cells are responsible for colour discrimination.
A trichromat (normal colour vision) is where the three types of light cones work correctly and colour is perceived correctly.
Anomalous trichromacy is when one of the three cones is slightly out of alignment. Depending on what cone is ‘faulty’ a different type of effect is produced. There are three types:
- Deuteranomaly (most common form) – Reduced sensitivity to green light.
- Protanomaly – Reduced sensitivity to red light.
- Tritanomaly (extremely rare) – Reduced sensitivity to blue light.
Dichromacy is the total lack of one of the three cones which are able to perceive colour:
- Deuteranopia – Unable to perceive ‘green’ light.
- Protanopia – Unable to perceive ‘red’ light.
- Tritanopia – Unable to perceive ‘blue light’.
Monochromacy (achromatopsia) is the lack of colour and occurs in approximately 1 in 33,000 people. Their world consists of different shades of grey ranging from black to white. Usually someone with achromatopsia will need to wear dark glasses inside in normal light conditions.
The test for colour deficiency typically involves the viewing of a series of coloured plates (Ishihara Test) with numbers or designs. The plates have been created in such a way that a person with normal colour vision can see certain figures in the designs. A person with a colour deficiency will either see a different number of designs or will be unable to distinguish the figures. There is also other tests that can be performed e.g. Farnsworth Test.
Children should be checked for colour deficiency by at least age five. Detection of colour deficiency must be addressed early because colour coded learning materials are used extensively in the primary grades.
Colour deficiency may affect the career path of an individual, since the ability to distinguish colours is an important aspect of some jobs, such as pilots, electricians, some military personnel, police officers and others.