Colour vision deficiency

Red-green colour vision deficiency

Colour vision deficiency means you are unable to see certain colours. There are different types of colour vision deficiency. For example, you may be unable to tell red from green or blue from yellow. Red-green colour blindness is by far the most common form.

How do we see colour?

Different colours are seen by special cells in the retina at the back of your eye. There are two types of cells, called rods and cones. Cones are concerned with colour vision. There are three types of cones: red cones, blue cones and green cones.

Side view of the structure of the eye

Each type of cone senses a different range of light. Therefore the combination of light sensed by the different cones allows you to know the colour you are looking at. For example, stimulation of green and red cones makes you see green. If all three types of cone are stimulated then you see white.

If you don't have any of the three types of cone then you will only be able to see black, white and shades of grey. But this severe form of colour blindness is very rare.

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What are the causes of colour vision deficiency?

For most people with colour vision deficiency the cause is inherited (genetic) and the special code inside each cell in your body (the gene) is passed on from your parents. The most common type - red-green colour blindness - is caused by an abnormal gene on the X chromosome and is much more common in males.

Much more rarely colour vision deficiency can develop later in life as a result of conditions such as:

• Thyroid eye disease.

• Diabetes mellitus.

• Cataratas.

• Glaucoma.

• Macular degeneration.

• Alzheimer's disease.

• Enfermedad de Parkinson.

• Leucemia.

• Anemia falciforme.

DNA, genes and chromosomes

In most cells of your body you have 46 chromosomes arranged in 23 pairs. 22 of the pairs are matching pairs. The 23rd pair of chromosomes are the sex chromosomes, which match exactly in women (who have two X chromosomes) but not in men - who have one X and one Y. One chromosome from each pair comes from your mother and one from your father. Chromosomes are made of DNA, which stands for 'deoxyribonucleic acid'. This is your genetic material. It is found in the nucleus of every cell in your body.

Cada uno de sus 46 cromosomas contiene cientos de genes. Un gen es la unidad básica de su material genético. Está formado por un fragmento (una secuencia) de ADN y se sitúa en un lugar concreto de un cromosoma. Por tanto, un gen es una pequeña sección de un cromosoma. Un gen es un conjunto de instrucciones codificadas para las células. Cada gen tiene una función concreta en el organismo. Por ejemplo, un gen puede determinar el color de sus ojos o su estatura. A cada gen le corresponde un gen "emparejado" en el cromosoma correspondiente. Por tanto, en cuanto a los cromosomas, un gen de cada par se hereda de la madre y el otro del padre. El ser humano tiene entre 20.000 y 25.000 genes.

How is colour vision deficiency diagnosed?

Colour vision deficiency is usually first diagnosed using special coloured pictures called Ishihara plates. The Ishihara plate has 16 different diagrams made up of dots to show a number. The Ishihara plate below is used to assess red-green colour vision. People with red-green colour vision deficiency will not be able to see the number clearly.

Ishahara plate

Sakurambo, CC BY-SA 3.0, via Wikimedia Commons

(For more information see the link to 'Online colour vision tests' in Further reading below).

Can colour vision deficiency be treated?

There is no treatment that can correct or prevent inherited (genetic) colour vision deficiencies.

Colour blindness may be caused by an underlying condition such as thyroid disease or diabetes. The colour vision deficiency may improve with treatment for the underlying condition.

How common is colour vision deficiency?

Colour blindness affects about 1 in 12 men and 1 in 200 women. It is much more common in men because the most common form (red-green colour vision deficiency) is passed on in a gene on the X chromosome (see below for further explanation).

What problems can colour vision deficiency cause?

Nearly all people with colour blindness can see things as clearly as other people but they cannot see certain colours clearly. If you have red-green colour vision deficiency you will not be able to clearly see any colour which has some red or green as part of the whole colour. For example, you will confuse blue and purple (because red and blue make purple).

The effects of colour blindness can be variable, ranging from mild to severe. Some people with colour vision deficiency are unaware that they've got it.

Colour vision deficiency need not prevent someone from driving. Traffic lights can be distinguished by the position of the light.

Colour vision deficiency may cause difficulty at school. Colour vision deficiency can also affect the choice of certain jobs and careers. The list of careers that may not be possible for a person with colour vision deficiency includes:

• Determinados grados de las fuerzas armadas.

• Aviación civil: pilotos, ingenieros, personal técnico y de mantenimiento, controladores aéreos.

• Funcionarios de aduanas e impuestos especiales.

• Ferrocarriles: conductores, maquinistas y personal de mantenimiento.

• Oficiales del servicio de bomberos.

• Técnicos de laboratorio hospitalario y farmacéuticos.

• Trabajadores de la pintura, el papel y la fabricación textil, la fotografía y la reproducción de bellas artes.

However, the restrictions vary. For example, Australian airlines do now allow people with colour vision deficiency to be pilots.