Eye Health | Colour blindness
What is colour blindness?
“Colour blindness” is a misleading term, as it commonly refers to a condition where people are unable to distinguish between different shades of colour, not where they are unable to see colour at all. A more accurate term for this condition is colour vision deficiency. True colour blindness is a rare condition where the person who suffers from it is only able to see white, black and certain shades of grey. Colour blindness actually describes a condition where one is unable to distinguish between different shades of colours.
Types of colour blindness…
Defective colour vision may occur as a result of a genetic variation (often inherited) and is present from birth. 8% of men are affected by this and only a small 1% of women are affected. Other eye conditions which develop during the course of one’s life may cause acquired defective colour vision and are usually associated with poor vision. The most common type of colour blindness is genetic red-green colour blindness. Most people who have this type of colour blindness are unable to distinguish between red and green in dim light, and a small percentage have difficulty doing this even in brighter light.
How humans see colour
Once light enters through the lens of your eyeball and passes through the transparent main body of your eye, light-sensitive cells called cones in the retina enable you to see colour. There are chemicals in the cones of the retina which help you to distinguish between the different colours. These chemical send this information to your brain via the optic nerve. There exist three types of cones, each are sensitive to a different range of colours (red, green and blue).
Genetic colour blindness
This is the most common cause of colour blindness. Men are more likely to be born with this deficiency than women, due to biological and genetic reasons.
The type of genetic colour blindness someone experiences, depends on which one of the three types of cones are defective. The intensity of colour blindness that one experiences can be mild, moderate or severe, depending on the severity of the defect. The condition cannot improve over time.
Types of genetic colour blindness are:
- Protanopia : Red-purple appears grey.
- Protanomalia: A milder form Protanopia, where red-purple appears as a red-purplish type of grey.
- Deuteranopia: Green appears grey.
- Deuteranomalia: A milder form Deuteranopia, where green appears as a greenish type of grey.
- Tritanopia: Blue appears grey.
- Total colour blindness (Monochromatism): Inability to distinguish any colour variations, sufferers are only able to distinguish black, white and different shades of grey.
Acquired colour blindness:
The causes of acquired colour blindness are:
- Medication. This is fairly rare, but certain medications, such as tamoxifen (which is prescribed to inhibit breast cancer) and viagra can alter colour vision.
- Eye diseases. There are several diseases which can cause colour blindness. Certain degenerative diseases can affect the retina of the eye and limit your ability to see yellow and blue. Optic nerve disorders may also reduce your ability to distinguish between different colours.
Who is at risk for colour blindness?
Mostly European men, of which 8% suffer some form of genetic or acquired colour blindness. Men whose mothers have one defective X-chromosome have a higher chance of inheriting colour blindness. Approximately 1% of women suffer from the inherited (genetic) disorder. Others who are at risk include people with degenerative eye disease, such as cataracts, or inflammation of the optic nerve and those who suffer from a nutritional deficiency of Vitamin A. As these diseases worsen, so does the colour blindness.
Symptoms and signs of colour blindness
People who are colour blind from birth, are in most cases unaware of their disorder. It is usually picked up by people around them, who notice their inability to distinguish between different colours or between different shades of the same colour. Most people who are colour blind are only experience the condition mildly, therefore it can take years before it is actually noticed. It is not a serious condition and would only really have an impact on people’s lives who want to become train drivers, pilots and interior decorators.
Diagnosis and treatment of colour blindness
If you or your ophthalmologist suspects that you might be colour blind, an easy dot-pattern test can be used to determine in a short space of time whether you are indeed colour blind, and if so, which type of colour blindness you have. These tests mostly consist of seeing whether you are able to recognise numbers concealed in a dot pattern. If you are unable to distinguish between red and green, you will not be able to see the green number or shape amongst the red dots. An instrument called an anomaloscope is also used by some ophthalmologists in determining the type and the severity of the colour blindness. This tests colour blindness by requiring the patient to mix and match changing colours.
Colour blindness cannot be cured or prevented. The most a doctor can do is to check if there may be eye diseases causing the colour blindness, and to treat those. But this is very rarely the case.
When to see a doctor
Colour blindness is not really a condition that requires ongoing medical attention. If colour blindness is suspected in a child, it is always a good idea to have the child tested for colour vision and for visual sharpness. The child can then be guided with respect to career choices later in life. It is also a good idea to make sure that there may not be eye diseases causing the colour blindness.