Colour blindness is a condition that is often misunderstood. The name implies that colour blind people are unable to see colour and can see only black and white, but this is not true. A more accurate term would be “colour vision deficiency” because people are able to see colour but they see a much narrower range of colour. It is estimated that with normal colour vision, people can see up to one million shades of colour, while people with colour vision deficiency may see only about ten thousand shades. To the normally sighted person, a rainbow features all seven colours. For many colour blind people, however, a rainbow only appears to have two or three colours.
HOW WE SEE COLOUR
The retina has two different types of cells, called photoreceptors, that detect and respond to light. These are the rods and cones. On average, we have about 110 million rods, which are activated in low or dim light, and 6 million cones, which are stimulated in brighter environments. Cones contain photo pigments, or colour-detecting molecules. Colour is not inherent in objects; rather, the surface of the object absorbs some colours and reflects others. The reflected colours enter the eye, are picked up by the photoreceptors on the retina, and sent via the optic nerve to the brain which processes them and interprets them as the sensation of colour. Cones are sensitive to red, green and blue light. If only the rods are activated, we see only shades of grey.
WHAT IS COLOUR DEFICIENCY?
Colour deficiency is an inherited condition that is thought to affect 300 million people throughout the world. It affects 1 in 12 males and 1 in 200 females. Usually, the condition is carried by the mother and passed down to her son. Babies are born colour blind. As they grow, their colour vision improves and is typically fully developed by the age of 6 months.
When the cones have all the various pigments, called photopigments, the eye sees all possible colours. Colour vision deficiency is caused by a change or reduction of sensitivity of one or more of the photopigments, resulting in colours not being perceived as they should be. Sometimes there is less sensitivity to some colours than to others, and sometimes certain colours cannot be perceived at all.
TYPES OF COLOUR VISION DEFICIENCY
Perception of colour is more subjective than objective. Because it is learned and based on each individual’s subjective perception and past experience, it is not possible to be completely sure how the world of colour is seen, whether by people who have colour deficiency or not. However, it is possible to differentiate the various degrees and types of colour deficiency.
Red-green colour deficiency is the most common form of colour deficiency. It is characterised by confusion between all colours that have some red or green in them. More rarely, sufferers have a reduced ability to see blue and yellow hues. Achromatopsia, also known as “complete colour blindness”, is the only type that fully lives up to the term “colour blind”. It is extremely rare, and those who have achromatopsia only see the world in shades of grey, black and white, and may be extremely sensitive to light.
LOOKING THROUGH COLOUR DEFICIENT EYES
Colour confusion can manifest in many everyday situations that people without the condition take for granted. The frustration of a mismatched outfit, questionable paint choices, difficulty interpreting colour coded information, and being unable to determine whether fruit is ripe or food is cooked are just a few examples. Drivers with colour deficiency often judge traffic lights by their position rather than their colour but may have trouble if the lights are oriented differently, for example side by side or high above an intersection. On the sports field, the difficulty assessing the distance or pace of a fast-moving ball on green grass may influence the response of a player with colour deficiency.
Being colour deficient can impact career choices, because it could be a handicap, for example, for an electrician, a pilot, a doctor, a painter, a chef, a web designer, a florist, and many others in which the accurate perception of colour plays a critical role.
“Blindness to one’s color blindness is common,” remarks one expert, as many people are unaware that they do not experience colour as other people do. There are tests that are performed by optometrists to determine what type of colour deficiency a person has. While certain promoters of glasses with specific colour filters claim that the glasses enhance the colour signal and help make colour vision deficiency less stressful for sufferers, further evidence is needed. Most people with colour vision deficiency have learnt to adapt to their condition.