Cities light up in red and green every December as the streets come to life with Christmas festivities. Santa, dressed in his iconic red get-up and fluffy white beard, merrily greets you wherever you turn. Huge, green Christmas trees tower over busy shoppers, bedecked in brightly coloured baubles, tinsel and fairy lights.
To most people, Christmas is a colourful affair. However, to some people, Christmas looks entirely different.
What is Colour Vision Deficiency?
Colour Vision Deficiency (CVD) is the inability to distinguish certain shades of colour. It is often known as ‘colour blindness’, although this term can be misleading as very few people are completely colour blind. Those with mild colour deficiencies can see colours normally in good lighting but find it difficult in dim lighting. Others cannot distinguish certain colours in any light. ‘Colour blindness’, in which everything is seen in shades of grey, is rare. Colour blindness usually affects both eyes equally and remains stable throughout life.
Around the world, an estimated 1 in 12 men and 1 in 200 women have a colour vision defect.
What are the Common Types of Colour Vision Deficiency?
Specialized cells in the eye allow us to appreciate colour. They contain three pigments that are sensitive to light: red, green and blue. Those with defective colour vision have a deficiency or absence in one or more of these pigments.
1) Red-Green Deficiency
The most common type of deficiency, those affected have trouble distinguishing between some shades of red, yellow, and green. Their visual acuity, or clarity of vision, is not affected.
Normal Vision
Red-Deficient
Green-Deficient
2) Blue-Yellow Deficiency
The most common type of deficiency, those affected have trouble distinguishing between some shades of red, yellow, and green. Their visual acuity, or clarity of vision, is not affected.
Normal Vision
Blue-Deficient
3) Complete Achromatopsia
This condition means total colour blindness, where everything is seen in white, black and shades of grey.
Normal Vision
Complete Achromatopsia
What causes Colour Vision Deficiency?
CVD may be a hereditary condition or caused by disease of the eye (specifically the optic nerve or retina). Inherited CVD is most common, affects both eyes, and does not worsen over time. If you are interested in finding out more about how CVD is inherited and why men are more prone to having colour vision defects, you can find a detailed explanation in this article “Inherited Colour Vision Deficiency” published on Colour blind awareness website.
- Diabetes
- Glaucoma
- Alzheimer’s Disease
- Parkinson’s Disease
- Multiple Sclerosis
- Chronic Alcoholism
- Leukemia
- Sickle Cell Anemia
In particular, a study done by Singhealth Polyclinics and Singapore Polytechnic in 20181 has revealed that people with Type 2 Diabetes have a much higher chance of having CVD than those without. Everyone enrolled in the study had Type 2 Diabetes, and approximately 1 in 5 of them also had CVD, a much higher frequency than usual. The risk of having CVD also increased with each year they had Type 2 Diabetes.
How is Colour Vision Deficiency Diagnosed?
CVD is most commonly detected with specially coloured charts called the Ishihara Test Plates. On each plate is a number composed of coloured dots. This number is coloured in a ‘pseudoisochromatic’ way, meaning that the dots appear to be the same (-iso) colour (-chromatic) as the surrounding pattern. However, to a person with normal colour vision, they are not the same (-pseudo). While holding the chart under good lighting, the patient is asked to identify the number. Those with normal vision see a number where those with colour vision defects see none, or see a different number. Once the colour defect is identified, more detailed colour vision tests may be performed.
A person could very well have poor colour vision and not be aware of it, because they have learned to see the ‘right’ colour. For example, they know that tree leaves are ‘green’, so the colour they see becomes ‘green’ to them.
Here is an example of four different views of the same Ishihara Test Plate, which is testing for Red-Green Colour Vision Deficiency. Those with Normal and Blue-Deficient vision see the number 8, whilst people with Red-Green Deficiency see a different number, the number 3.
Normal Colour Vision: Number 8
Blue-Deficient Vision: Number 8
Red-Deficient Vision: Number 3
Green-Deficient Vision: Number 3
Can Colour Vision Deficiency Be Cured?
There is no treatment or cure for colour blindness. Those with mild colour deficiencies learn to associate colours with certain objects and are usually able to identify colour as everyone else. However, they are unable to appreciate colour in the same way as those with normal colour vision. If the cause is a disease or eye injury, treating these conditions may improve colour vision.
What Can You Do If You Have Colour Vision Deficiency?
- Using special tinted eyeglasses or contact lenses can increase some people’s ability to differentiate between colours, although it cannot help them to truly see the deficient colour.
- Organize and label furniture, clothing or other coloured objects for ease of recognition.
- Remember the order of things rather than the colour. For example, a traffic light has red on top, yellow in the middle and green on the bottom.
Reference:
- Tan NC, Yip WF, Kallakuri S, Sankari U, Koh YLE. Factors associated with impaired color vision without retinopathy amongst people with type 2 diabetes mellitus: a cross-sectional study. BMC Endocr Disord. 2017;17(1):29. Published 2017 Jun 2. doi:10.1186/s12902-017-0181-7
