Colour Vision Deficiency: Definition, Causes, Symptoms, Diagnosis, and Treatment

Colour vision deficiency, also known as colour blindness, refers to an eye condition in which the eyes have trouble seeing colour properly. There are three main types of colour blindness or colour vision deficiency: blue-yellow colour blindness known as tritanopia, red-green colour blindness known as protanopia and deuteranopia, and complete colour blindness known as monochromatism. Colour vision deficiency is often caused by a defect in the cones and rods of the eyes, passed on from parent to child. Colour vision deficiency can also be caused by certain medical conditions, the use of certain medications, a stroke, or certain head and eye injuries. Colour vision deficiency that is not inherited and develops later is called acquired colour vision deficiency. Colour vision deficiency is diagnosed by an optometrist or other eye care professional using tests such as a colour hue test or an Ishihara test. Colour vision deficiency does not have a cure. Treatment for colour vision deficiency usually involves colour blindness glasses or contact lenses, however, these will not always work for everyone.

What is Colour Vision Deficiency or Colour Blindness?

Colour vision deficiency, more colloquially known as colour blindness, is a condition in which the eyes have difficulty seeing colours in a normal way. Colour blindness may make people confuse colours, or make some colours appear less bright, according to Health Direct. There are three main types of colour vision deficiency according to Health Direct; blue-yellow colour blindness known as tritanopia, red-green colour blindness known as protanopia and deuteranopia, and complete colour blindness known as monochromatism.

How Does Colour Vision Deficiency (Colour Blindness) Work?

Colour vision deficiency or colour blindness is caused by an error in the genes that determine visual photopigments in the eyes. Colour blindness is often a genetic condition, meaning it works by being passed down from family members. When colour blindness is passed down, it means there is a defect in the genes that are involved in producing visual photopigments, which are what help the eye see and absorb light, according to Victoria’s Better Health Channel. Defects in visual photopigments can affect how the eyes see light and certain colours, causing colour blindness. Colour blindness or colour deficiency can also be caused later on in life by things like eye diseases, although this phenomenon is not as understood as congenital colour blindness, according to the American Academy of Ophthalmology.

An image showing normal vision, versus vision with colour blindness.

What Part of the Eye Is Affected by Colour Blindness?

The parts of the eye that are affected by colour blindness are cells called the cones and the rods, which are located in the retina. The cones and the rods are types of cells that help the eye detect light. Rods are photoreceptors that are sensitive to light and help people see in low light. Cones are active in higher levels of light and help people to see colour. According to the National Institute of Health, there are three different types of cone cells that detect colour; blue, green and red. According to the American Academy of Ophthalmology, if there is an issue or defect with the cones in the eye, this may affect how the eye sees colour. For example, if one of the three cones does not work correctly, then the eye may see a different colour than what is actually present.

What are the Causes of Colour Vision Deficiency?

The most common and well-understood cause of colour vision deficiency, or colour blindness is genetics. Most cases of colour blindness will be congenital, passed down from a parent. When colour blindness occurs later in life, known as acquired colour blindness, this can be caused by head or eye injuries, different eye conditions including glaucoma and macular degeneration, a stroke, other medical conditions such as liver diseases or diabetes, use of specific medications and exposure to certain chemicals. The possible causes of colour vision deficiency or colour blindness are listed below.

Genetics: Genetics is the most common cause of colour vision deficiency. Genetics refers to the genes that produce visual photopigments having defects or problems.
Head or Eye Injury: Head or eye injuries may lead to colour vision deficiency, if the injury has damaged parts of the eye like the retina, or impacted certain parts of the brain.
Different Eye Conditions Including Glaucoma and Macular Degeneration: Different eye conditions may cause colour vision deficiency if the eye conditions affect the photoreceptors in the eye.
Stroke: A stroke may lead to colour vision deficiency if the stroke has impacted the part of the brain that helps the eyes see colour.
Other Medical Conditions such as Liver Disease and Diabetes: Liver disease and diabetes are medical conditions that have a correlation with colour vision deficiency.
Use of Specific Medications: The use of specific medications may lead to colour blindness, which is known as acquired colour vision defects meaning the colour blindness is not inherited.
Exposure to Certain Chemicals: Exposure to certain chemicals such as carbon monoxide and carbon disulphide, may lead to colour vision deficiency.

1. Genetics

Genetics is the most common cause of colour vision deficiency or colour blindness and refers to the genes that produce visual photopigments having defects or problems, leading to the eyes not seeing colour properly. Colour blindness or colour vision deficiency, is often a genetic condition, inherited or passed down from family members such as parent to child. The genes involved in helping the eyes see colour are called visual photopigments, according to Victoria’s Better Health Channel. If the visual photopigments have defects, it can affect how the eyes see light and specific colours, causing colour blindness.

2. Head or Eye Injury

A head or eye injury may lead to colour vision deficiency or colour blindness, if the injury has affected the retina, or has an impact on the part of the brain that detects colour. A head or an eye injury can be broadly defined as physical damage to the eye or the head areas. If an injury to the eye impacts the retina, this could lead to colour blindness, as the retina houses the rod and the cones that help the eye see colour properly. A head injury may also lead to colour blindness or colour vision deficiency if the injury has affected parts of the brain that help the eye see colour. Cerebral achromatopsia for example is a type of colour blindness that is caused by damage to the ventral medial region of the occipital lobe, which is the part of the brain that helps people see colour, according to Bartles and Zeki.

3. Different Eye Conditions Including Glaucoma and Macular Degeneration

Different eye conditions including glaucoma and age-related macular degeneration (AMD), may cause colour blindness or colour vision deficiency if the eye conditions affect the retina part of the eye. Eye conditions encompass a range of issues that affect the eye and its function, including glaucoma, age-related macular degeneration (AMD) and cataracts. Certain eye conditions may lead to issues seeing colour properly if the condition affects the retina part of the eye that houses the rods, cones and photoreceptors all needed to help a person see colours correctly. Glaucoma describes a group of eye conditions in which vision is affected due to damage to the optic nerve. Glaucoma may lead to colour blindness if the optic nerve is compressed, which can affect how colour is seen, according to Vision Science Academy. Age-related macular degeneration (AMD) is an eye disease that affects central vision due to damage in the macula, located in the retina part of the eye. Age-related Macular Degeneration may lead to colour blindness as the photoreceptors that help the eye see light are located in the macula, which is most affected by AMD. If the photoreceptors are damaged or not working properly due to AMD, this can lead to issues seeing colour, according to the Living Well with Low Vision Organisation.

4. Stroke

A stroke may lead to colour blindness or colour vision deficiency if the stroke has affected the part of the brain that helps process colours, according to the Brain Recovery Project. A stroke occurs when there is a sudden lack of blood in the brain, which leads to the brain not receiving the oxygen or nutrients it needs, according to Health Direct. The lack of oxygen and nutrients to the brain during a stroke can damage the brain, including the parts of the brain that process colour, such as the ventral occipital lobe.

5. Other Medical Conditions Such as Liver Disease and Diabetes

Other medical conditions including liver disease and diabetes may lead to colour vision deficiency. Cirrhosis of the liver, which is a type of liver disease that causes healthy cells to be replaced by scar tissue, has been found to be linked to colour blindness. According to a study consisting of a hospital population, published in the Oxford University Press, there is a genetic association between cirrhosis of the liver and colour blindness. In terms of diabetes, according to an article published in the National Library of Medicine titled, Color vision abnormalities in type II diabetes: Sankara Nethralaya Diabetic Retinopathy Epidemiology and Molecular Genetics, there is a correlation between people with type 2 diabetes and colour vision abnormalities. This study found that among people with type 2 diabetes, 43% of them also exhibited impaired colour vision.

6. Use of Specific Medications

The use of specific medications may lead to colour blindness, which is known as acquired colour vision defects meaning the colour blindness is not inherited. According to the Colour Blind Awareness Organisation, the medications that may cause colour blindness include high blood pressure medications, antibiotics, anti-tuberculosis drugs, barbiturates and some medications used to treat nervous disorders. The drugs or medications that may affect a person’s colour vision belong to a wide range of pharmacological classes.

7. Exposure to Certain Chemicals

Exposure to certain chemicals may lead to colour vision deficiency. According to the Colour Blind Awareness Organisation, there are certain environmental and industrial chemicals that have been linked to colour vision deficiency, such as carbon monoxide and carbon disulphide. Changes to colour vision caused by chemicals are often found in the blue-yellow axis.

Does Damage to the Optic Nerve Cause Colour Vision Deficiency?

Damage to the optic nerve may cause a degree of colour vision deficiency, or colour blindness. According to the American Optometric Association, damage to the optic nerve may cause a loss of colour recognition. The optic nerve is responsible for transmitting visual information from the eyes to the brain. If the optic nerve is damaged, it may affect how colour is transmitted to the brain.

Who is at Risk for Colour Vision Deficiency?

Those at risk for having colour vision deficiency or colour blindness include men and those with eye conditions such as glaucoma and age-related macular degeneration (AMD). According to the National Eye Institute, men are more likely to have colour blindness than women due to the genetics involved in passing down the eye condition from parent to child. Colour blindness is passed down on the X chromosome, which men only have 1 of, whereas women have two, meaning it is more likely for men to have colour blindness than women. Those with eye conditions may also be at more risk of developing colour vision deficiency as certain eye conditions can affect the retina and photoreceptors within the eye that help the eye distinguish between colours. People with certain medical conditions such as Alzheimer’s disease and diabetes may also be at more risk of developing colour vision deficiency according to the Colour Blind Awareness Organisation.

How Does Being Colour Blind Affect the Individual?

The way being colour blind affects the individual will depend on how bad the colour blindness is and what type of colour blindnesses they have. For most people with colour blindness, they will not see the world in black and white, they will instead have trouble differentiating between colours. For example, if a person has red-green colour blindness, they will have trouble telling the difference between red and green. According to Health Direct, some of the ways colour blindness can affect the individual involve not knowing if meat is cooked, or being able to see the colour of traffic lights. Being colour blind may also impact career choices. For example, those who wish to become a pilot may be limited in how much they can do with colour vision impaired.

What is it Like to Live with Colour Blindness?

For most people, living with colour blindness may cause some troubles, but these can usually be overcome with the help of optometrists and treatment devices such as glasses.

Is There a Benefit to Being Colour Blind?

No, there do not appear to be many benefits to being colour blind, with the condition more often being a detriment to vision than a help. However, some studies have posited that people who are colour blind may have better pattern and texture recognition than those with full-colour vision. According to a 2005 article in Nature, those who are red-green colour blind may be able to differentiate between shades of camouflage and khaki that look the same for those who have full-colour vision.

What are the Symptoms of Colour Vision Deficiency (Colour Blindness)?

The main symptoms of colour vision deficiency or colour blindness include trouble seeing the difference between colours, trouble seeing the differences in shades of colours and trouble seeing the brightness of colours. For kids with colour blindness, these symptoms may become obvious in activities such as colouring or painting. For some, the symptoms of colour vision deficiency may be so mild that they don’t know they have it, according to the American Academy of Ophthalmology. The possible symptoms of colour vision deficiency are listed below.

Trouble seeing the differences between colours: Having trouble seeing the differences between colours, such as not being able to see a difference between the colour red and green, is one of the main symptoms of colour blindness.
Trouble seeing the differences in shades of colours: Trouble seeing the differences in shades of the same colour, such as not being able to determine the difference between shades of red, may also be a sign of colour vision deficiency.
Trouble seeing the brightness of colours: Having trouble seeing the brightness of colours, such as the colour red being very dull, may also be a symptom of colour vision deficiency or colour blindness.

How is Colour Vision Deficiency (Colour Blindness) Diagnosed?

Colour vision deficiency or colour blindness is most often diagnosed by an optometrist during an eye test. Colour vision deficiency can be diagnosed during a colour vision test using a colour arrangement test or an Ishihara test.

What are the Tests for Diagnosing Colour Vision Deficiency (Colour Blindness)?

The tests most commonly used for diagnosing colour vision deficiency or colour blindness are a colour hue test or an Ishihara test. The tests used to diagnose colour vision deficiency are listed below.

Colour Hue Test: A colour hue test is a way to see if a person has colour blindness through the process of ordering coloured blocks.
Ishihara Test: An Ishihara test, also known as a colour plate test, consists of circles or plates made up of dots of a certain colour in varying shades

An image showing the colour plate test for colour blindness.

1. Colour Hue Test

A colour hue test is a way to determine if a person has colour blindness using blocks that are varying colours. The aim of the test is for the patient to order the blocks, often in rainbow order. If the blocks are not in the specified order, it can indicate colour blindness according to the National Eye Institute.

2. Ishihara Test

An Ishihara test or a colour plate test is a way to determine if a person has colour blindness, using plates made up of different coloured dots. An Ishihara test consists of circles or plates made up of dots of a certain colour in varying shades, with a number in the middle made out of the same dots but in a different colour. If a person can not see the number in the middle of an Ishihara test, then they may have colour blindness as their eyes have not differentiated between the two colours on the plate.

What are the Different Types of Colour Vision Deficiency (Colour Blindness)?

There are several different types of colour vision deficiency or colour blindness, with the main three being blue-yellow colour blindness known as tritanopia, red-green colour blindness known as protanopia and deuteranopia, and complete colour blindness known as monochromatism, according to Health Direct. Red-green colour blindness refers to colour blindness in which a person has trouble differentiating between red and green colours. According to Britannica, red-green colour blindness is more prominent in males, often passed down from a parent. Blue-yellow colour blindness refers to colour blindness in which a person has trouble seeing the difference between yellow and blue and this occurs in both men and women. Complete colour blindness also known as monochromatism, is less common than other forms of colour blindness and refers to a person being unable to see any colour.

Image showing the different types of colour vision deficiency or colour blindness.

Is Colour Vision Deficiency a Disability?

Yes, colour vision deficiency can be classified as a disability, depending on the country you live in. In Australia, colour vision deficiency is considered a disability, according to the Australian Disability Clearinghouse on Education and Training.

How is Colour Vision Deficiency (Colour Blindness) Treated?

Colour vision deficiency or colour blindness can generally be treated through the use of glasses or contact lenses, however, the effectiveness of these devices will be different for everyone and are not a cure. There is not currently any cure for colour blindness that is inherited from a parent, as inherited colour blindness is concerned with a defect in the cones within the retina. Colour blind glasses or contact lenses may be used to help the eyes see colour better, but these are not guaranteed to always work and their effectiveness can be down to the individual. Colour blindness glasses work by using a filter across the lens of glasses to help the brain filter certain wavelengths of light and allow the brain clearer signals to try and see colours better, according to the American Academy of Ophthalmology.

Can Colour Vision Deficiency (Colour Blindness) be Prevented?

No, colour vision deficiency or colour blindness can not be prevented if it has been inherited from a parent, as this kind of colour vision deficiency is concerned with genes, and they can not be altered. A person may help reduce their risk of developing acquired colour vision deficiency if they book regular eye tests and have their overall health checked consistently by their doctor.

Do Colour Blind Glasses Help Fix Colour Blindness?

No, colour blind glasses will not fix or cure colour blindness or colour vision deficiency but may help improve the way you see colour slightly. Colour blind glasses work by putting a filter across the lens of glasses to help filter some of the wavelengths of light, confusing the brain less and allowing it to perceive colours slightly better according to the American Academy of Ophthalmology. However, colour blind glasses may not work for everyone and their level of effectiveness is down to the individual.