Most commonly encountered are those who cannot confidently distinguish the colours red and green. This is called colour blindness. Fortunately, complete colour blindness is rare. Those affected are only able to distinguish various shades of grey. The condition is hereditary. Spectacles and contact lenses don't help, but trickshere is some useful info.
Most people take the ability to see life in bright colours for granted. They make sure the colours of their clothing match, get hungry at the sight of a delicious red strawberry and enjoy all the colours of nature. But for some 180 million people around the world this colour experience remains partially or completely hidden – they either have red-green colour deficiency or blindness, have greatly reduced colour vision, or in very rare cases cannot distinguish any colours at all. This is colloquially known as colour blindness.
People with normal colour vision mix the three spectral colours red, green and blue to create all other colours. The cones, sensory cells on the retina, are responsible for this. They work only during the day: at night we actually see everything grey. However, not all colour blindness is all the same. Even though everyone thinks it's the same thing, the term covers many different defects. Experts distinguish the following conditions:
Those affected have only a limited ability to recognise certain shades. All the sensory cells – the red, green and blue cones – are present in the retina, but some of them work incorrectly, usually the cones responsible for seeing green. The technical term is deuteranomaly. People with a red deficiency are said by doctors to have protanomaly.
In this type of colour blindness some of the sensory cells are missing. People affected have only two functioning cone types. The result is that colour vision is significantly reduced. This can sometimes be dangerous especially for red-weak and red-blind car drivers. In fog, for example, they see only black instead of the red rear light of a vehicle in front of them.
The disorder known as achromatopsia is very rare. People with this condition cannot perceive shades of colour at all. They are also very sensitive to light. They are always in "night mode" and can only perceive rough outlines in the dark.
Both congenital colour blindness and innate colour visual deficiency are caused by a genetic defect. Men are affected significantly more often than women. The most commonly acquired colour vision defect is limited blue-yellow vision. It often occurs, as a result of macular degeneration. People who have been unable to see certain colours since birth, or who see colours only poorly, are often unaware of it. The problem is detected only when their environment brings it to their attention.
Colour blindness can be diagnosed with different colour tests, which is important because problems can occur both in professional life and in traffic. The following tests are possible:
This test shows numbers on a coloured background (often resolved into dots). It can be used to detect red-green colour blindness, for example.
Farnsworth coloured dot procedure
Here, patients sort stones of different hues. The test is somewhat more complicated. It can be used to detect a blue deficiency.
Here, the patient uses a circular colour testing device to mix and specify the shades of varying colours. Information concerning the degree of colour blindness is able to be ascertained with it. Red blindness can be diagnosed best with this method. It can be an exclusion criterion for some professions, such as painter, bus driver or pilot.
So far, it is not possible to correct colour blindness with spectacles or contact lenses. Special spectacles make it possible to change only the colour contrast, not the vision. Nevertheless, there is a valuable tip for everyone who is totally colour-blind: for them, there are special spectacles with red lenses. They deflect the glare of daylight better than normal spectacles or sunglasses.