Colour blindness

Colour blindness or colour deficiency refers to an inability to see or distinguish between certain colours.

Human eyes have specialised light-sensitive cells called cones that help them see colours and tell them apart. The cells are present in the centre of the central part of the retina (called the macula).

Each cone can perceive one of the three primary colours of light: red, blue and green. Once the cones recognise colours, they send the information to the brain, which then tells us what we are looking at.

Colour blindness occurs when a person either has an absence or deficiency of any of these cones (one or more) or when cone cells detect a different colour than they should.

Most people have red-green colour blindness, though blue-green colour deficiency does occur in rare cases. Complete colour blindness is even rarer.

Those with milder forms of colour blindness can see better in bright light than dim light. However, some have problems distinguishing colours in bright light too.

Depending on what range of colours a person can’t see, colour blindness is of three types:

• Red-green colour blindness: Red-green colour blindness is the most common type of colour blindness. It causes difficulty in differentiating between the colours red and green. The gene for red-green colour blindness is present on the X chromosome, so it is mostly seen in men (as they usually have one copy of this chromosome compared with two in most women).
  Red-green colour blindness can be further divided into the following types:
  • Deuteranomaly: In this type of colour blindness, the person has normal blue cones along with some normal red cones and some abnormal red-like cones. As a result, greens start to look a bit more red to the person. Deuteranomaly is a mild type of colour blindness and does not cause much interference with everyday life. 
  • Protanopia: A person with this type of colour blindness has blue and green cone cells functional. As a result, they have difficulty perceiving shades of red or differentiating them from greens.
  • Protanomaly: A person with protanomaly has normal blue cones along with some normal green cones and some abnormal green-like cones. As a result, reds appear more green and less bright to the person.
  • Deuteranopia: In this type of colour blindness, only the red and blue cones are functional. As a result, the person is not able to differentiate between red and green colours.
• Blue-yellow colour blindness: This type of colour blindness is rare but occurs equally in both men and women as the gene for blue-green colour blindness is located on an autosome (chromosome other than the sex chromosome). Blue-yellow colour blindness is further divided into two types:
  • Tritanopia: A person with tritanopia does not have the blue-detecting cones that help them see shorter wavelengths of light. As a result, colours appear a bit less bright than normal to the person, and he/she is unable to differentiate between purple and red, blue and green and pink and yellow.
  • Tritanomaly: A person with tritanomaly does not have properly functioning blue cones. So, they find it difficult to differentiate between blue and green and red and yellow.
• Complete colour blindness: Also known as monochromacy, complete colour blindness is extremely rare. A person with complete colour blindness is unable to see any colour, as they don’t have any of the three types of cones or the cones they have are non-functioning. Those with complete colour blindness also have vision problems and are sensitive to light.

The main symptom of colour blindness is the inability to see some colours clearly. In children, the condition is not apparent until they start to learn colours. Some other symptoms of colour blindness include:

• Difficulty or inability to differentiate between certain shades or colours
• Problem assessing the brightness of colours

Some people with colour blindness have mild symptoms—the person may not even realise they have a problem. While some people have a severe form of colour blindness that affects their vision. 

Total colour blindness is also associated with symptoms like lazy eye, light sensitivity and nystagmus (involuntary eye movement).

Colour blindness is usually hereditary (runs in families and you are born with it), though it can be acquired. The genes for hereditary red-green colour blindness are present on the X chromosome (a sex chromosome). 

Men have one X and one Y chromosome while women have two X chromosomes. A child gets half of its chromosomes from each parent. Male children get one X from the mother and a Y from the father, while female children get one X from both the parents. Since men only have one X chromosome, they have a higher chance of developing the disease. In women, the gene has to be on both X chromosomes for the disease to manifest.

Acquired colour blindness occurs later in life due to various causes including: 

• Eye diseases such as glaucoma, macular degeneration
• Trauma or injury to the eye
• Brain injury
• Neurological diseases such as Alzheimer’s
• Side effects of certain medications
• Alcoholism
• Sickle cell anaemia
• Leukaemia
• Diabetes

Colour blindness is diagnosed through an eye exam. Your doctor will ask you to read from cards with dots of various colours arranged in specific patterns. If you don’t have colour blindness, you would be able to recognise the patterns.

The cards also help the doctor to determine the kind of colour blindness you have, if any.

There is no treatment for colour blindness. Some mild forms of colour blindness do not hinder daily activities. However, often people with the condition are not allowed on certain kinds of jobs like a driver or a pilot.

Those with acquired colour blindness due to a health condition are given treatment for the underlying condition. If the colour blindness is due to the side effect of a medication, the doctor will either change the medication or change the dosage. 

Special glasses and contact lenses are suggested to those with severe colour blindness. The glasses don’t correct the condition completely but help the person better differentiate between colours.  

Living with colour blindness can be difficult at times, even when you are not doing things like driving or doing graphics. Here are some things that can help you improve your every day life if you have colour blindness: 

• Ask a friend or family member to help you label clothes and things with colours, if you want to. You can also ask them to check if a particular food is safe to eat. 
• Most electronics come with special settings that you can use instead of having to look for a red or green light.
• If you or people in your family have red-green colour blindness, it is best to tell all the boys in the family about it as there is a chance they may have it.
• If you have a child with colour blindness, talk to their teacher. Explain your child's condition to the teacher (for example, talk about which colours your child has trouble seeing). Ask the teacher to use marked crayons so the child does not feel lacking in any aspect. 
• Also, it is best if the child sits in a place where they have a clear view of the board. 
• The teacher may use black and white ink on sheets rather than coloured.