Colour blindness

Definition

According to Wikipedia, colour blindness or a colour vision deficiency, is the inability to perceive differences between some of the colours that others can distinguish. It is most often of genetic nature.

The English chemist John Dalton published the first scientific paper on the subject in 1798, “Extraordinary facts relating to the vision of colours”, after the realisation of his own colour blindness.

Colour blindness is sometimes classed as a disability, however, in certain situations colour blind individuals have an advantage over those with normal colour vision. There are some studies that conclude that colour blind individuals are better at penetrating certain colour camouflages and it has been suggested that this may be the evolutionary explanation for the surprisingly high frequency of people born with red-green colour blindness.

Causes

The area at the back of the eye, called the retina, is sensitive to light and colour. It contains specialised cells, called cones, that respond to colour. There are three types of cone cells. One responds best to red light, one to green light, and one to blue light. When a specific type of cone cell doesn’t work properly, a person will have trouble seeing the colour that particular cone cell responds to. For example, a person with red colour blindness has a defect in red cone cells.

Most colour blindness is inherited, although some cases are caused by an injury or disease of the retina or optic nerve, the nerve that takes information from the eye to the brain. Brain damage or exposure to certain chemicals may also cause colour blindness.

People inherit colour blindness as a result of a defect on the gene for colour located on the X chromosome. Men inherit colour blindness ten times as often as women do. Colour blindness “shows up” in men because they have only one X chromosome. Since women have two X chromosomes, a healthy gene on one X chromosome can override the unhealthy gene on the other. A woman can still have the unhealthy gene; it just doesn’t always show up. She can, however, pass the gene on to her children.

Genetic factors

The following are some facts concerning colour blindness:

• • Male children of a carrier mother and non-colour blind father have a 50% probability of being colour blind and female children have a 50% probability of being carriers, that is, having one defective gene.

• • Male children of a father with colour blindness and a carrier mother have a 50% likelihood of being colour blind, and their female children are either carriers or colour blind.

• • Male children of a father with colour blindness and a non-colour blind mother will not inherit colour blindness, but all of the female children will be carriers.

• • Male children of a non-colour blind father and a colour blind mother will be colour blind and all the female children will be carriers.

• • All the children of two red-green colour blind parents will be red-green colour blind.

Symptoms

Seeing things in shades of grey rather than colour is actually what colour blind people experience. Also, people who are partially colour blind see similar shades as the same colour, for example purple and blue as the same colour or red and maroon as the same.

Our Employee Wellbeing Programme (EAP) is available 24 hours a day if you want to know more about colour blindness.