Colour Vision Deficiency

The ability to perceive colour adds an extra dimension to the way we see the world. The process of colour perception starts with the absorbtion of light by small cells known as “Cones”   which form part of the retina at the back of the eye. The retina contains some cone cells that respond best to short (blue), medium (green) and long (red) wavelengths of light, and it’s the relative amount of activation of each of these three types that in turn relays that particular colour code to the brain.

Approximately 7-8% of males and 0.5% of females show some form of colour vision defect. Telling the difference between red and green is the most common defect and will always be exclusively in males since it is carried on their genetic chromosome.

Very occasionally people are born with only one (monochromats) or two (dichromats) types of cone but by far the most common type of defect is where the individual is born with all three cone types but one is partially defective (anomalous trichromat). This shows that most affected individuals are only “colour deficient” and not “colour blind” as the harsh term suggests.

Occasionally, colour vision deficiency may develop later in life as the result of:

• an underlying health condition – such as diabetes, glaucoma, age-related macular degeneration and multiple sclerosis
• a side effect of a medication – including digoxin, ethambutol, chloroquine, hydroxychloroqine, phenytoin and sildenafil
• exposure to harmful chemicals – such as carbon disulphide and styrene

Many people also find it more difficult to distinguish between colours as they get older. This is normally just a natural part of the ageing process.

Your optometrist can easily check for deficiencies using the ‘Ishihara’(for red-green), ‘City’(blue-yellow) or ‘D15’ tests. Colour vision deficiency isn’t usually anything to be concerned about. Most people get used to it over time, it won’t normally get any worse and it’s rarely a sign of anything serious.

However, it can sometimes cause issues such as:

• difficulty at school if colours are used to help with learning
• problems with food, such as identifying whether meat is fully cooked or whether fruit is ripe
• getting medications confused if they’re not clearly labelled
• trouble identifying safety warnings or signs
• slightly limited career choices – certain jobs, such as pilots, train drivers, electricians and air traffic controllers, may require accurate colour recognition

Overall, many people with a colour vision deficiency have few, if any, difficulties. They can do most normal activities, including driving.