Color blindness

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- what is color blindness
- types of color blindness
- Symptoms of color blindness

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Color blindness

  1. 1. Color Blindness Color blindness, a color vision deficiency in animals, is the inability to perceive differences between some of the colors that others can distinguish. It is most often of genetic nature, but may also occur because of eye, nerve, or brain damage, or due to exposure to certain chemicals.Colour blindness occurs when one or more of the cone types are faulty or missing. This makes it difficult to see the cone colour that is missing or faulty. For example, if the red cone is missing you won't be able to see colours containing red as clearly. About eight in 100 men and one in 100 women are affected by colour blindness. Most people cannot distinguish certain shades of red and green. Very few people are not able to see any colour at all and are truly colour blind. The gene, which is responsible for the condition, which is carried on the X chromosome and this, is the reason why many more men are affected than women are. The inheritance process is explained in more detail in the section Inherited Color Vision Deficiency. Normal ProtanopiaTritanopiaDeuteranopia 8% of the male population and 4.5% of the population of the UK as a whole are colour blind and there are estimated to be over 250 million colour-blind people worldwide. Colour vision There are two types of light sensitive cells in your eyes, called rods and cones. They are both found in the retina, which is the layer at the back of your eye that processes images. Rods allow you to see in dim light or at night, whereas cones allow you to see in detail and distinguish colours. There are three types of cone cells – red, green, and blue. Each cone has a different level of sensitivity to light. When you look at an object, light enters your eyes and stimulates the cone cells. Other cells in your retina and brain then interpret the signals from the cone cells and allow you to see the colour of an object. The red, green and blue cones all work together to allow you to see
  2. 2. the whole spectrum of colours. For example, when the red and green cones are stimulated to a certain level you will see the colour yellow. Types There are many types of color blindness. The most common are red-green hereditary (genetic) photoreceptor disorders, but it is also possible to acquire color blindness through damage to the retina, optic nerve, or higher brain areas. Monochromatism This is the most severe form of colour blindness. Monochromatism (also called achromatopsia) is the least common type of colour blindness, where none of your cone cells function properly or where only one type works, as they should. This results in no colour vision – all you see is black, white, and shades of grey. Dichromatism Dichromatism is when one of the cones is missing. There are three types: protanopia – the red cones are missing deuteranopia – the green cones are missing tritanopia – the blue cones are missing
  3. 3. Anomalous trichromatism This is the mildest and most common form of colour blindness. Anomalous trichromatism is when you have all three cones but there is a fault in one of them, making you less sensitive to certain colours. Depending on which cone is faulty, this will cause: protanomalous trichromatism – the red cones are less sensitive deuteranomalous trichromatism – the green cones are less sensitive tritanomalous trichromatism – the blue cones are less sensitive Red and green cone defects are known as red-green colour blindness. People with anomalous trichromatism vary in their ability to distinguish between different colours – some are more affected than others are. Symptoms of colour blindness If you have colour blindness, the main symptom you will have is a difficulty in distinguishing certain colours or you may make mistakes when identifying them. You may see only a slight difference in the different shades of colour, or if you have severe colour blindness, all you see is black, white, and shades of grey. In particular, situations this may be made worse, for example: in low level lighting if the area of colour is small if you view a large area of colour at a distance if you try to distinguish pale colours or dark shades Causes of colour blindness Either colour blindness is usually inherited or you develop it at some stage of your life, for example, because of an illness, ageing, or exposure to chemicals.The effects of colour vision deficiency can be mild, moderate or severe so, for example, approximately 40% of colour blind pupils currently leaving secondary school are unaware that they are colour blind , whilst 60% of sufferers experience many problems in everyday life.
  4. 4. Diagnosed Colour blindness can be difficult to detect, particularly in children with inherited colour vision deficiency, as they may be unaware that they have any problems with their colour vision. A child with a severe condition such as deuteranopia may seemingly be able to accurately identify colours which they can’t see (e.g. red) because they have been taught the colour of objects from an early age and will know for example that grass is green and strawberries are red even if they have no concept of their true colours. Inherited colour Vision Deficiency Red/green colour blindness is a common hereditary condition which means it is usually passed down from your parents. Colour blindness is usually passed from mother to son on the 23rd chromosome, which is the sex chromosome. Chromosomes are structures which contain genes – these contain the instructions for the development of cells, tissues and organs. If you are colour blind it means the instructions for the development of your cone cells are wrong and the cone cells might be missing, or less sensitive to light or it may be that the pathway from your cone cells to your brain has not developed correctly. The X chromosome is the sex chromosome: males have an X chromosome and a Y chromosome and females have two X chromosomes. For a male to be colour blind the faulty colour blindness gene only has to appear on his X chromosome. For a female to be colour blind it must be present on both of her X chromosomes. This is why red/green colour blindness is far more common in men than women. Blue colour blindness affects both men and women equally, because it is carried on a non-sex chromosome.

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