Ever wondered what it's like to be colour blind ?
Colour deficiency is a very common problem, with 1 in 12 men being colour deficient. Of course, for those who aren’t colour deficient, it’s very hard to imagine what it’s like to be colour blind. For people with colour blindness, they perceive colours in a different way of what most of us see. People who do not have a severe type of colour blindness may not know they have a colour deficiency unless they are tested in a clinic. There are many different ways to test your colour vision when you go for an eye exam. The main test is the Ishihara colour test, which is a quick screening test to see if there are any defects. Another test is the Farnsworth-Munsell 100 hue test, which measures if you are able to discriminate subtle colour changes.
Noticing a difference in colour is due to our eyes and brain working together to see different properties in light. Natural and artificial lighting is normally seen as white, however it is actually a mixture of colours. If the mixtures of colours were seen individually, the visual spectrum would be seen from a deep blue to deep red. The colour of light is mainly determined by its wavelength, where a longer wavelength normally corresponds to red light and shorter wavelength normally corresponds to blue light.
Let’s take a red apple as an example. Most people would say this apple is red. The reason they are able to distinguish the apple as red, as the surface is only reflecting the longer wavelengths in the visual spectrum, while the other wavelengths are absorbed. An object tends to look white when it reflects all the wavelengths of the visual spectrum, and it looks black when it absorbs all the wavelengths of the visual spectrum.
Humans tend to have trichromatic vision, meaning we have three different cone photopigments. Most other mammals have only two photopigment types.
The most common type of colour vision defects tend to be inherited. These are due to defects in the genes that contain instructions for making the photopigments found in cones. There isn’t just one classification of colour deficiency, there are many different types; Protanopia, deuteranopia (red-green colour blindness), or tritanopia (blue-yellow colour blindness). Deuteranopia is the most common type. A complete absence of colour vision (total colour blindness) is rare. Colour blindness can be also caused by physical or chemical damage to the eye, the optic nerve, or parts of the brain that process colour information. Colour vision can also change with age, the most common reason being a cataract - a clouding and yellowing of the eye’s lens.
Red-green colour deficiency:
- Protanomly: this is where the red cone photopigment is abnormal. Red, orange and yellow look more green. This does not interfere with day to day life.
- Protanopia: this is where no red cone cell is working, so red appears black. Orange, yellow and green can appear yellow.
- Deuteranomaly: the green photopigment is abnormal here. Yellow and green can look more red, and it is hard to tell the difference between violet and blue. This again, doesn’t interfere with day to day life.
- Deuteranopia: this is where no green cone cell is working, reds are normally seen as brown-yellow, and greens are seen as beige.
Blue-yellow colour deficiency:
- Tritanomaly: people with this have limited blue cone cells, so blue appears greener and you may not be able to see a difference between yellow and red from pink. This is very rare.
- Tritanopia: this is where a person lacks blue cone cells. Blue looks green, while yellow looks violet/light grey.
If there is a total loss of colour vision, their vision may also be affected.
There is no cure for colour blindness, however if people are affected in their day to day living, there are options such as lenses/overlays to perceive colours more accurately. iPhones, and iPads, also have apps which can help people discriminate colours.
Most people with a colour deficiency are able to get on with day to day living, mainly it can affect children especially if the colour deficiency has not been detected yet so it is important for children to have an eye test. Other than this, even tasks like driving can be done.