Colour Blindness

By: Dr. Jenna Snow, OD – Family Vision Clinic

Some people have the misconception that people who are colour blind see the world in only black, white, and gray. While this condition does exist, called achromatopsia, it is a quite rare form of complete colour blindness with a prevalence of only 1 in 30 000 people1. There are actually many different kinds of colour vision deficiencies, depending on the range of colours one may see, or the perceived difference between colours. In most types of colour blindness, there is no actual loss of vision, so the term “colour blindness” is often more accurately described as a “colour vision deficiency”.

Our retinas are made up of millions of tiny photoreceptor cells called rods and cones. Rods are responsible for perceiving light, and function mostly in low lighting and cones are responsible for our vision in bright light conditions and perceiving colour. There are three types of cones: short wavelength cones “see” the colour blue, medium wavelength cones see the colour green, and long wavelength cones see the colour red. To determine what colour we are seeing, the visual processing system in our brain compares the intensity and wavelength of light that is absorbed by each type of our cones. The absorption of light rays by all of our cones produces the thousands of shades of colours people with normal colour vision can perceive. When one or more of the types of cones is missing or defective, this is what causes a colour vision deficiency. Often times, all 3 cones still exist, but one of the cones has decreased sensitivity to the light rays it is supposed to absorb.

People with a colour vision defect are not unable to see colour altogether, but they have difficulty distinguishing between groups of colours and may only see a few shades of colours instead of thousands. Some colours may appear faded or washed out, while others may be identical to the way people with normal colour vision see them.

The most common type of colour blindness is a “red-green” deficiency, meaning people will have difficulty differentiating reds, oranges, browns and pinks from each other, and also greens, blues, and purples from each other3. But, another more rare type of colour blindness known as “blue-yellow” also exists. In this type of colour deficiency, people will have trouble deciphering between shades of blues from greens and different shades of yellows3. Even rarer, is the condition called achromatopsia which means a complete lack of cones. With no cones at all, this person will see the world in gray-scale (monochromatic) and will also have very poor vision.

While some colour vision deficiencies can be a result of eye disease, most are usually inherited genetically; aka, it is something you are born with. The way in which these genes are inherited (X-linked recessive) means that males are more predisposed to have a colour vision problem than females. About 8% of males have some degree of colour deficiency, and only 0.5% of females. If the colour vision defect is from genetics and not disease, it will not get worse over time.

Depending on the severity of a colour deficiency, some people don’t even realize that they don’t see colours the way others do. Growing up as a child, everyone learns their colours the same way, and what you are told is a shade of “blue” is what you will identify with. It is not un-heard of that adults come in for an eye exam and find out that they have been colour blind their whole life and never knew the difference. For the most part, having a mild colour deficiency is something that doesn’t have a huge impact on one’s life.

It can however affect potential career options, for example: commercial pilots, police officers, and electricians (because of coloured wiring). Professions like these require near perfect colour vision to pass requirements. This is why it is important to know from an early age what kind of limitations your child may have when it comes to the impact on their future. It may also help explain why a child is having some difficulties with learning. It is important to inform your child’s teachers of all visual problems they have. Many teaching tools rely on colour recognition, so it is important for them to know if your child is struggling in that area.

Routine eye examinations are recommended for all children. The Canadian Association of Optometry recommends regular eye exams for children, beginning at age 6 months, and then annual after the age of 3 until 18 years old.


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