Colour blindness: Types and causes

Colourblindness is not a form of blindness at all, but a deficiency in the way you see colour.

If you are colourblind, you have difficulty distinguishing certain colours, such as blue and yellow or red and green.

Colourblindness (or, more accurately, colour vision deficiency) is an inherited condition that affects males more frequently than females. According to Prevent Blindness, an estimated 8% of males and less than 1% of females have colour vision problems.

Red-green colour deficiency is the most common form of colourblindness.

Much more rarely, a person may inherit a trait that reduces the ability to see blue and yellow hues. This blue-yellow colour deficiency usually affects men and women equally.

Colourblindness: Signs and symptoms

Do you have difficulty telling if colours are blue or yellow, or red or green? Do people sometimes inform you that the colour you think you're seeing is wrong?

If so, these are primary signs that you have a colour vision deficiency.

Contrary to popular belief, it is rare for a colourblind person to see only in shades of gray.

Most people who are considered "colourblind" can see colours, but certain colours appear washed out and are easily confused with other colours, depending on the type of colour vision deficiency they have.

If you develop colour vision problems when normally you have been able to see a full range of colour, then you definitely should visit your optician. Sudden or gradual loss of colour vision can indicate any number of underlying health problems, such as cataracts.

Colourblindness testing can help determine the kind of colour deficiency you have.

What causes colourblindness?

Colourblindness occurs when light-sensitive cells in the retina fail to respond appropriately to variations in wavelengths of light that enable people to see an array of colours.

Photoreceptors in the retina are called rods and cones. Rods are more plentiful (there are approximately 100 million rods in the human retina) and they are more sensitive to light than cones, but rods are incapable of perceiving colour.

The 6 million to 7 million cones in the human retina are responsible for colour vision, and these photoreceptors are concentrated in the central zone of the retina called the macula.

The center of the macula is called the fovea, and this tiny (0.3 mm diameter) area contains the highest concentration of cones in the retina and is responsible for our most acute colour vision.

Inherited forms of colourblindness often are related to deficiencies in certain types of cones or outright absence of these cones.

Besides differences in genetic makeup, other causes of colour vision defects or loss include:

Parkinson's disease (PD). Because Parkinson's disease is a neurological disorder, light-sensitive nerve cells in the retina where vision processing occurs may be damaged and cannot function properly.

Cataracts. Clouding of the eye's natural lens that occurs with cataracts can "wash out" colour vision, making it much less bright. Fortunately, cataract surgery can restore bright colour vision when the cloudy natural lens is removed and replaced with an artificial intraocular lens.

Certain medications. For example, an anti-seizure drug called tiagabine has been shown to reduce colour vision in about 41% of those taking the drug, although effects do not appear to be permanent.

Leber's hereditary optic neuropathy (LHON). This type of inherited optic neuropathy can affect even carriers who don't have other symptoms but do have a degree of colourblindness. Red-green colour vision defects primarily are noted with this condition.

Kallman's syndrome. This inherited condition involves failure of the pituitary gland, which can lead to incomplete or unusual gender-related development such as that of sexual organs. Colourblindness can be one symptom of this condition.

Colourblindness also can occur when ageing processes damage retinal cells. An injury or damage to areas of the brain where vision processing takes place also can cause colour vision deficiencies.

Colourblindness treatment

Gene therapy has cured colourblindness in monkeys, according to researchers at the University of Washington.

While these findings in animals look promising, gene therapy will not be considered for humans until treatments are proven to be safe.

Meanwhile, there is no cure for colourblindness. But some coping strategies may help you function better in a colour-oriented world.

Most people are able to adapt to colour vision deficiencies without too much trouble. But some professions, such as graphic design and occupations that require handling various colours of electrical wiring, depend on accurate colour perception.

If you become aware early in life that you are colourblind, you may want to choose a career that does not require accurate colour perception.

Diagnosing colour vision deficiency early also may prevent learning problems during school years, particularly because many learning materials rely heavily on colour perception.

If your child has a colour deficiency, be sure to speak with his or her teachers about it, so they can plan their lessons and presentations accordingly.

Lenses for the colourblind

Some people use special lenses to enhance colour perception, which are filters available in either contact lens or eyeglass lens form.

One example are colourblind glasses developed by EnChroma. The tinted lenses in EnChroma's colourblind glasses include patented light-filtering technology to give people with the common forms of colourblindness the ability to see the broad spectrum of bright colours most of us take for granted, according to the company.

If you have a colour vision deficiency, see an optician near you to discuss if colourblind glasses are a good choice for you.

You also can learn ways to work around your inability to pick out certain colours. For example, you might organise and label your clothing to avoid colour clashes. (Ask friends or family members who have normal colour vision to help with this project.)

Also, learn to recognise certain coloured items by their order rather than their colour. For example, recognise that the red light is at the top of the traffic signal, and green is at the bottom.

Also, a variety of downloadable apps to assist with colour detection have been developed for Android and iOS devices.

See an optician for additional help and guidance if you have difficulty distinguishing colours or if you suspect your child may be colourblind.

Is red-green colourblindness hereditary?

Red-green colourblindness is the most common inherited form of colour vision deficiency. It is caused by a fairly common X-linked recessive gene.

Mothers have an X-X pairing of chromosomes carrying genetic material, and fathers have an X-Y pairing of chromosomes. A mother and father each contribute chromosomes that determine the sex of their baby.

When an X chromosome from one parent pairs with an X chromosome from the other parent, the baby will be a girl. And when an X chromosome from the mother pairs with a Y chromosome from the father, the baby will be a boy.

If you have red-green colourblindness caused by an X-linked recessive gene, your mother will be a carrier of the gene or be colour-deficient herself.

Fathers with this inherited form of red-green colourblindness pass the X-linked gene to their daughters but not to their sons, because a son cannot receive X-linked genetic material from his father.

A daughter who inherits the colour-deficient gene from her father will be a carrier of the gene but she will not be colourblind — unless her mother carries the gene, and she receives a paired colour-deficient gene from her mother as well. If a daughter inherits the X-linked trait from both her father and her mother, then she will be colourblind.

When a mother passes along this X-linked trait to her son, he will inherit the colour vision deficiency and have trouble distinguishing reds and greens.

Again, a daughter can be a carrier but will have this form of colourblindness herself only when both her father and mother pass along the X-linked gene. This is why more men than women are colourblind.

WORRIED YOUR CHILD MIGHT BE COLOURBLIND? Find an optician near you an schedule a pediatric eye exam.

Page published on Monday, 27 July, 2020