Types Of Colour Blindness In Humans

Introduction

Definition of colour blindness

Colour blindness, also known as colour vision deficiency, is a condition in which a person is unable to distinguish certain colours or shades of colour. It is a genetic disorder that affects the colour-sensing cells in the retina of the eye, known as cones. Three types of cones are responsible for colour vision: red, green, and blue.^2,6 When one or more of these cones are missing or not functioning properly, colour blindness can occur.

Importance of understanding types of colour blindness

Understanding the types of colour blindness is important for several reasons.^4,5 Firstly, it helps individuals with colour blindness to identify their specific condition and understand how it affects their daily lives. Secondly, it helps educators, designers, and other professionals to create materials that are accessible to individuals with colour blindness. Thirdly, it raises awareness about colour blindness and promotes a more inclusive society.

Types of colour blindness

Colour vision is an important aspect of our visual perception that enables us to differentiate between different colours. However, some people have a colour vision deficiency or colour blindness, making it difficult or impossible to distinguish between certain colours. In this article, we will discuss the types of colour blindness in humans, their causes, symptoms, and management.

There are different types of colour blindness, and they can be broadly classified into three categories based on the affected cones: red-green colour blindness, blue-yellow colour blindness, and complete colour blindness.

Red-Green colour blindness

Red-green colour blindness is the most common type of colour blindness, and it affects the ability to distinguish between red and green colours. There are two subtypes of red-green colour blindness: protanopia and deuteranopia.

Protanopia

Protanopia is a type of red-green colour blindness that affects the ability to distinguish between red and green colours. In this condition, the red cone cells in the retina are missing or are not functioning properly. This results in reduced sensitivity to red light and a shift towards green on the colour spectrum.

• Causes: Protanopia is a genetic disorder caused by a gene mutation that codes for the red cone cells
• Symptoms: Individuals with protanopia may have difficulty distinguishing between red and green colours and may perceive these colours as shades of yellow or grey
• Prevalence: Protanopia affects approximately 1% of those assigned male at birth (AMABs) and 0.02% of those assigned female at birth (AFABs)

Deuteranopia

Deuteranopia is another type of red-green colour blindness that affects the ability to distinguish between red and green colours. In this condition, the green cone cells in the retina are missing or are not functioning properly. This results in reduced sensitivity to green light and a shift towards red on the colour spectrum.

• Causes: Deuteranopia is also a genetic disorder that is caused by a mutation in the gene that codes for the green cone cells
• Symptoms: Individuals with deuteranopia may have difficulty distinguishing between red and green colours and may perceive these colours as shades of grey or brown
• Prevalence: Deuteranopia affects approximately 1% of AMABs and 0.01% of AFABs

Blue-yellow colour blindness

Blue-yellow colour blindness is a type of colour blindness that affects the ability to distinguish between blue and yellow colours. There are two subtypes of blue-yellow colour blindness: tritanomaly and tritanopia.

Tritanomaly

Tritanomaly is rare, and the person usually finds it difficult to distinguish between the colours blue and green and red and yellow as the blue cone cells in the retina are less sensitive.

• Causes: It is caused by a genetic mutation in the blue cone cells
• Symptoms: Some of the symptoms of tritanopia include a reduced ability to differentiate between the colours blue and green, purple and red, and yellow and pink 
• Prevalence: Extremely rare in both AMABs and AFABs

Tritanopia

Tritanopia is a rare type of colour blindness that affects the ability to distinguish between blue and yellow colours. In this condition, the blue cone cells in the retina are missing or are not functioning properly so, you will not be able to perceive blue light. You would mostly see reds, blues, pinks and lavender. This results in reduced sensitivity to blue light.

• Causes: It is caused by a genetic mutation, usually because of the exposure of the eye to ultraviolet light
• Symptoms: Some of the symptoms of tritanopia include a reduced ability to distinguish between the colours blue and green, purple and red, and yellow and pink 
• Prevalence: Tritanopia is the rarest form of colour blindness, affecting only around 0.001% of the population

Blue cone monochromacy

Blue cone monochromacy is also a rare condition caused when the red and green cones are missing in the retina. This results in severe colour blindness and visual impairment.¹

• Causes: It is an inherited condition caused by genetic mutations in certain genes coding for the red and green cones
• Symptoms: Some of the symptoms of this condition include severe colour vision impairment, poor vision, light sensitivity, and nystagmus (abnormal movements of the eye)
• Prevalence: This is a very rare condition affecting 1 in 100,000 individuals

Diagnosing colour blindness

It is an essential step in providing appropriate management strategies for individuals with the condition. Diagnosing colour blindness is usually done through screening tests, which can determine the type and severity of the condition.

Screening tests

A common screening test is the Ishihara colour vision test, which involves looking at a series of plates with numbers or symbols made up of dots in various colours. A person with normal colour vision can easily distinguish numbers or symbols, but those with colour blindness may not be able to see them correctly.

Genetic testing

Genetic testing can also be used to diagnose inherited colour blindness.^2,3 Genetic testing is necessary to confirm the presence of inherited colour blindness and determine the specific type of colour blindness. Genetic testing involves analysing DNA samples to identify mutations in genes that are associated with colour vision.

Several genes can cause colour blindness, but the most common are the OPN1LW and OPN1MW genes located on the X chromosome. These genes encode for the long-wavelength-sensitive (L) and medium-wavelength-sensitive (M) cone photo-pigments in the retina, which are responsible for detecting red and green light. Mutations in these genes can result in red-green colour blindness, the most common form of colour blindness.

Genetic testing can also identify other types of colour blindness, such as blue-yellow colour blindness, which is caused by mutations in the OPN1SW gene that encodes for the short-wavelength-sensitive (S) cone photopigment, and complete colour blindness, which is caused by mutations in the CNGB3 or CNGA3 genes that are involved in the function of all three cone types.

Genetic testing for colour blindness can be performed using various methods, including:

• Polymerase chain reaction (PCR)
• Gene sequencing
• Microarray analysis 

These tests can identify specific genetic mutations associated with colour blindness and help diagnose the condition in individuals and families.

Management of colour blindness

Colour blindness can impact a person's daily life in various ways, from difficulties in reading colour-coded information to challenges in certain careers such as graphic design or electrical engineering. However, with proper management and support, people with colour blindness can lead fulfilling lives.

Colour-correcting lenses

While there is no cure for colour blindness, there are management strategies that can help people with the condition. Some people use colour-correcting lenses or glasses, such as Enchroma glasses, to help distinguish colours more accurately. These glasses work by selectively filtering out certain wavelengths of light to enhance colour discrimination.

It is important to note that the management strategies for colour blindness may vary depending on the type and severity of the condition. A medical professional or an eye specialist can guide you on the most appropriate management techniques for an individual's specific situation.

In addition, individuals with colour vision deficiencies need to receive regular eye exams to monitor their vision and catch any potential complications early on. This is especially important for individuals with inherited colour blindness, as they may be at a higher risk for other eye conditions.

Summary

Colour blindness, also known as colour vision deficiency, is a condition in which a person is unable to distinguish certain colours or shades of colour. It is a condition that affects many people worldwide, with different types and degrees of severity. Understanding the types of colour blindness is essential in recognising the symptoms and providing appropriate management strategies. While there is currently no cure for colour blindness, there are various options available to help those with the condition, from colour-correcting glasses to awareness and accommodations in different settings. By promoting the awareness of colour-blindness and providing support for colour-blind individuals, we can work towards a more inclusive and understanding society.