COLOUR VISION


HOW ARE WE ABLE TO SEE COLOUR?
Being able to see the world around us in all its vibrant shades of colour - is a real privilege!

The warm reds, oranges and yellows of autumn, the mesmerizing turquoise and aquamarines of a tropical sea and the lush greens and ochres of a rainforest; these are all rich examples of how the perception of colour can enhance the quality of our visual experience.

The system that enables us to see these life-enhancing colours, is a complex one.

Light from the outside world is translated into a myriad of signals by the retina (the layer at the back of the eye) and is rapidly transmitted to the brain. Ninety two percent of the world’s population has ‘normal’ colour vision.

Did you know that all the many colours that we see are “mixtures” of just three colours; red, blue and green?

The start of the colour vision journey begins in specialised retinal cells called cones. These are situated in an area of the retina called the macula. There are 3 types of cones, each detecting a different spectrum of light wavelength entering the eye. The 3 cone types are the red, green and blue. All the many colours that we see are made up of “mixtures” of just these three shades.

Once light passes into a cone, pigment within the cell converts it into an electrical impulse or signal. The pigment in each cone is specific to the cone type; red, green and blue. This signal passes through a complicated system of neural cells to the optic nerve.

This nerve transmits that signal to an area in the brain called the “hue centre”.

In this centre, all the information is combined to determine which colour the eye sees.


COLOUR BLINDNESS
Colour blindness occurs when:
  • One or two of the cones are defective or absent
  • The pigment inside each cone is at an abnormal concentration or the cone contains the incorrect pigment
  • The “wiring” of the neural cells that transmit the signal, is malfunctioning
There are a few terms used to describe the various forms of colour blindness depending on where in the system the “fault” occurs.

If a Blue cone (B) is absent, the person is said to have tritanopia.

Dichromats are people who have healthy cone cells, but the wrong pigmentoccurs in every third cone.

If a perfectly normal Green (G) cone cell contains red pigment, the condition is called deutranopia.


When a normal Red cone (R) contains green pigment, the person is said to have protanopia.

Dichromats have difficulty in distinguishing red from green. All red-green disorders are inherited in an X-linked recessive manner. This means that this condition occurs predominantly in men.

In anomalous trichromatism, the correct pigment occurs in each cone, but in every third one, the pigment functions suboptimally. This means that the sufferer struggles to tell the difference between pastel colours and or between dark colours.

As there are three types of pigment, there are three different conditions in which this occurs; protanopia, deuteranopia and tritanopia. These conditions are inherited as autosomal dominant traits which means that both men and women have an equal chance of presenting with the anomaly.

WHAT WOULD MAKE YOU CONCERNED THAT YOUR CHILD MIGHT BE COLOUR BLIND?
The first point to be aware of is your family’s health history. As most conditions related to the loss of colour vision are genetic, it is important to be aware of anyone in the family suffering from this problem, especially on the mother's side.

Did you know that a heightened sense of smell may indicate the presence of a colour vision disorder?

Next, be aware of any difficulties that your child may experience when identifying or using colour.
For example:
  • Using the wrong colours for an object, especially using dark colours inappropriately
  • He or she may have problems in identifying red or green colour pencils or any colour pencil with red or green in its composition, for example, purple or brown
  • They may resist colouring in or participating in games that involve sorting coloured objects like beads or blocks
  • Identification of colour may be made worse by low light, small areas of colour and colours of the same hue
  • They may struggle to read words printed on a coloured background, especially if the word is typed in a colour other than black
  • They may experience discomfort when looking at a red object on a green background or vice versa
  • Your child may have compensated for the loss of colour vision by hightenening other senses like their sense of smell. They may use this to differentiate one food item from another

IS THERE ANY SIMPLE ASSESSMENT THAT YOU AS A PARENT CAN PERFORM?
Is there a history of colour blindness in your family? If the answer is ‘yes’, you need to be aware that your child / children can inherit the condition

A simple test that you can perform with your child is to ask them to identify blocks of colour that you draw on a white piece of paper. Make sure that the process is as fun as possible and don't bring any judgement into your interaction. Do the test in a room filled with natural light and ensure that there are no other people around at the time.

Choose 12 colours - include red, green, brown, purple, grey and blue. Remember to include colours that a child with red/green colour blindness can identify with ease, such as pink and orange.

Draw 12 blocks of approximately 2 x 2cm in size and colour them in. Then play a game with your child, identifying colours as you go. Once the game is over, stop. Don't go on to identify colours in your environment as it can lead to distress and a negative perception being created around the condition.


What steps do you take if you suspect that your child may suffer from colour blindness?

Start by making an appointment with an ophthalmologist.

Book the appointment for a time of day that you know your child will be alert and ensure that they have had something to eat before going in.

The ophthalmologist will assess your child's eye health and will test for colour blindness. Reassure your child that this is a painless and positive experience.

WHAT TREATMENT IS AVAILABLE CURRENTLY FOR COLOUR BLINDNESS?
Unfortunately, at present, there is no treatment available. However, medical science is advancing so rapidly that there will inevitably be gene therapy in the future.

In the meantime, there are many things that can be done to assist your child. Start by gathering as much information about the condition that you can. There are excellent websites that have great ideas for helping your child at home, in school and on the sports field. An example of this is "Colour blindness awareness. Org"- especially this article on other colour blind kids

It is important to include anyone who will be teaching your child, on the journey, so that your child can have the best possible support.

An important consideration for the future is to think about career options. There are certain professions where colour blindness is an exclusion criterion, such as becoming a pilot, so you will need to guide your child accordingly.

References:
“Ophthalmology Secrets, Third Edition” by Dr. James F. Vander and Dr. A. Gault. Pages 33 - 40. Colour Blind Awareness .org

Download the article here:
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