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- IELTS Reading Diagram completion
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IELTS Reading Passage – Colour Blindness
Colour Blindness
The absence or malfunction of colour-sensitive cells in the retina causes colour blindness. Behind the lens, the retina is a neuro-membrane lining the inner back of the eye. The retina contains both rod cells (active in low light or night vision but incapable of colour discrimination) and cone cells (active in colour vision but inactive in low light or night vision) (active in average daylight, sensitive to colour). Cone cells, also known as photoreceptors, are primarily located in the macula, a central region of the retina. Cone cells allow for sharp, clear colour vision. The cones contain pigments that are sensitive to the spectrum of wavelengths and are light-sensitive. One type of cone is sensitive to short wavelengths, or the colour blue, while another type is sensitive to medium wavelengths, or the colour green, and the third type is sensitive to longer wavelengths, or the colour red. All of these cells transmit colour information to the brain via the optic nerve, which connects to the retina near the macula. Normal individuals, known as trichromats, are able to match all colours of the spectrum by combining these three fundamental colour sensitivity characteristics. Consequently, the vast spectrum of colours we perceive results from the response of cone cells to different wavelengths of light.
There are numerous types of colour blindness. When there are deficiencies in the cones, either at birth or through other means, the cones are unable to distinguish between wavelengths, resulting in an altered perception of the colour spectrum. Those with impaired colour vision are deficient or lacking in one or more pigments. Anomalous trichromats are people with a deficiency in one of the pigments, the most common type of colour vision disorder. Dichromacy occurs when one of the cone pigments is absent and the colour is reduced to two dimensions. Typically, these individuals are aware of their colour vision impairment, which can have a significant impact on their daily lives. They cannot distinguish between red, orange, yellow, and green. All of these colours, which appear so dissimilar to the average observer, appear identical to them. The absence of the cones responsible for green and red hues can also impair the ability to perceive brightness.
Out of the vast majority of cases of colourblindness, approximately 99 per cent, are inherited, resulting from partial or total loss of function in one or more of the different cone systems, and affecting both eyes without worsening over time. Red-green inherited (genetic) photoreceptor disorders are the most prevalent and are collectively referred to as “red-green colour blindness.” It affects 8% of European males and 0.4% of European females. The X chromosome carries the gene for this. Due to the fact that males have an X-Y pairing and females have an X-X pairing, colour blindness is much more prevalent in males and is typically transmitted by their mothers. In other words, females may be carriers of colourblindness, but males are significantly more frequently affected. People with this disorder are unable to recognise red or green on their own but can do so when surrounded by other colours. Other forms of colour blindness are extremely uncommon. They include difficulties distinguishing blue from yellow. Both hues are regarded as white for conditions such as liver disease and diabetes.
Monochromacy is the rarest form of colorblindness, in which a person can only see shades of black, grey, and white, as in a black-and-white film or photograph. Monochromacy occurs when two or all three cone pigments are absent, reducing colour and brightness perception to a single dimension. Achromatopsia is another term for total colour blindness, which is the inability to perceive colour.
Problems with inherited colour vision cannot be treated or corrected. Depending on the cause, some acquired colour vision problems can be treated with surgery, such as the removal of a cataract. Certain tinted filters and contact lenses may also improve a person’s ability to differentiate between colours. In addition, computer software has been created to aid those with visual colour difficulties and those with mild colour deficiencies in learning to associate colours with particular objects, so that they can identify colour in the same manner as everyone else. A common issue is with traffic lights, and worst of all, warning lights: colour-blind individuals are always aware of the position of the colours on the traffic light; red on the top, yellow in middle, and green at bottom. However, warning lights pose an entirely different issue. In this situation, there is only one light; there is no top, no bottom, and no right or left, just a single red or yellow light.
Problems with colour vision can significantly affect a person’s life, learning abilities, and career options. On a daily basis, there are certain annoyances and frustrations, such as not being able to tell the difference between green and ripe tomatoes when preparing food, or purchasing matching clothes that appear positively garish to the ‘normal’ eye. However, individuals with colour vision deficiencies typically learn to compensate for their inability to perceive colours. Although there is little or no treatment for colour blindness, the majority of colour-blind individuals compensate well for their condition and may even discover instances in which they are able to perceive details and images that normal-sighted individuals would miss. The U.S. Army once discovered that colour-blind individuals can detect camouflage colours in situations where those with normal colour vision are typically fooled.
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Colour Blindness Reading Questions
Questions 1-3
Choose the correct letter A, B, C or D
1. Which group of people are least common?
- Anomalous trichromats
- People with dichromacy
- People with achromatopsia
- People who cannot detest blues from yellows
2. What would colour-blind people consider an everyday nuisance?
- Not being able to tell an apple from a tomato
- Not being able to identify the colour of warning lights
- Not being able to buy matching clothes
- Not being able to cook
3. What causes colour blindness?
- The malfunction of rod cells
- The absence of rod cells
- The malfunction of cone cells
- The retina’s inability to detect light
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Questions 4-10
Complete each sentence with the correct ending A-K from the box below. Write the correct letter A-K in the boxes 17-23 on your answer sheet.
4. Surprisingly, some people who are colour-blind ________ 5. People with hereditary colour blindness _______ 6. Because of our genetic make-up, colour blindness ________ 7. Red-Green genetic photoreceptor disorders mean that people ________ 8. People with monochromacy _______ 9. The inability to see certain lights _______ 10. Colour blindness can be caused by a birth defect, or ________
- cannot be treated by surgery.
- Can have very dangerous consequences for colour-blind people.
- Can be acquired or inherited.
- can affect men much more easily than women.
- can see better at night than during the day.
- can see no colour at all, other than shades of black, grey and white
- can affect their sensitivity to bright lights.
- can see things that people with normal vision cannot.
- cannot distinguish certain colours if they stand alone
- can mean having to wear contact lenses.
- can match all colours of the spectrum.
Questions 24–26
Complete the diagram below.
Choose NO MORE THAN TWO WORDS from the passage for each answer.
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Colour Blindness reading answers
1. C
2. C
3. C
4. H
5. A
6. D
7. I
8. F
9. B
10. C
11. OPTIC NERVE
12. RETINA
13. MACULA
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