Colour blindness also called as colour vision deficiency or CVD, is a genetic disorder where a person will not be able to see colours in a normal way or differentiate between certain colours, i.e., between green and red and occasionally blue. It affects both the eyes and one has to live with it throughout his/her life.
The eye consists of the light-sensitive tissue at the back of the eye called the ‘retina’. There are two types of cells to detect light known as rods and cones. Rods detect light and vision in darkness, while cones detect the colour. Cones are of three kinds which determine red, green and blue colours. When you see a colour, the message is sent to the brain. The brain uses these inputs given by the cone cells to perceive the colour. It depends on the number of cone cells that one will be able to see the colour. In case, any of these cones are absent/abnormal; one may fail to detect the particular colour. Colour blindness may be mild (one can see the colours in good light but not in dim light) or severe (one will see everything as grey).
Causes and risk factors
The causes and risk factors include:
⦁ Age – People above 60 years old.
⦁ Gender – Men are at increased risk compared to women.
⦁ Genetic – Inherited from parents.
⦁ Chronic diseases – Glaucoma, macular degeneration, Alzheimer’s disease, multiple sclerosis, Parkinson’s disease, chronic alcoholism, leukaemia, liver disease, sickle cell anaemia, diabetes, macular degeneration and retinitis pigmentosa.
⦁ Medications – Drug hydroxychloroquine (Plaquenil) used to treat rheumatoid arthritis.
⦁ Chemicals – Carbon monoxide, carbon disulphide and lead.
⦁ Accidents – Injuries which might damage the retina or any areas of the brain/eye.
Forms of colour blindness
Forms of colour blindness include:
a) Red-green colour blindness
This condition is due to the loss or decreased function of the red cone (protan) or green cone (deutran) photopigments which are found predominantly in males. Here, it does not mean that people will mix red and green, but they mix up all the colours which have some red or green as a part of the full colour. For example, if a pen is purple in colour, the person with colour blindness will see it as blue as they can’t see the red coloured component in it. Similarly, black may be seen as dark green or dark blue, etc.
Based on the presence of red or green cones, it is divided into:
i. Protanomaly (red cone pigment is abnormal): Here, colours such as red, orange, and yellow appear to be green.
ii. Protanopia (red cone pigment is absent): Here, the red colour appears as black. The shades of yellow, orange, and green appear as yellow.
iii. Deuteranomaly (green cone photopigment is abnormal): Here, yellow and green appear red and one finds it difficult to detect the violet colour from blue.
iv. Deuteranopia (green cone cells are not working): Here, people tend to see red as brownish-yellow and green as a beige colour.
b) Blue-Yellow Color Blindness
This is rare than red-green colour blindness, affecting both males and females. It is divided into:
i. Tritanomaly (blue cone cells are not working): Here, the blue appears green colour and one finds it difficult to tell yellow and red from pink colour.
ii. Tritanopia (blue cone cells are absent): Here, the blue colour appears as green and yellow seems to be violet or light grey in colour.
c) Partial or complete blindness
People with colour blindness will have normal vision. However, they will not be able to fully ‘see’ red, green or blue light. Few people may not be able to see any colour at all (monochromacy). Depending on the absence of cones (cone monochromacy) it can be red/green/blue monochromacy. Similarly, in case one lacks all cones and rods (cones/rod monochromacy), they tend to see the world in black, white, and grey colours.
Colour blindness does not harm one’s vision. It is often the parents who notice that their children have a problem in learning the colours, i.e., the child will not be able to differentiate between red and green, or blue and yellow. If the disease is severe, one may not be able to see any colour or see everything grey called as ‘achromatopsia;. This condition can be associated with nystagmus (involuntary, rapid eye movement), amblyopia and poor vision.
Types of colour blindness include:
1) Congenital colour blindness: This condition is caused where the disease is passed from the mother to son.
2) Acquired Colour Vision Defects: This condition is caused as a result of health-related issues.
Diagnosis and treatment
Colour blindness is diagnosed by:
- An ophthalmologist, who will examine and diagnose the condition through the test called ‘Ishihara Plate test’. A plate is made with a pattern of multi-coloured dots. A person without a colour deficiency will be able to see the numbers and shapes which are amongst the dots. But, an individual who is diagnosed with colour blindness will find it difficult to identify or may not see any pattern at all.
- Congenital colour blindness is hard to be treated. With the use of special contact lenses and glasses, one will be able to differentiate similar colours. Similarly, acquired form of colour blindness may be treated by addressing the underlying condition.
One may find it difficult to choose the vegetables, fruits, preparation of food, select a dress, identify the signals (green/red) while driving, sports, etc.
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- Color blind awareness. http://www.colourblindawareness.org/colour-blindness/living-with-colour-vision-deficiency/ . Accessed on July 25, 2016.
Color blind awareness. http://www.colourblindawareness.org/colour-blindness/types-of-colour-blindness/ . Accessed on July 25, 2016.