- Chronic illnesses which can lead to colour blindness include Alzheimer’s disease, diabetes mellitus, glaucoma, leukaemia, liver disease, chronic alcoholism, macular degeneration, multiple sclerosis, Parkinson’s disease, sickle cell anaemia and retinitis pigmentosa.
- Accidents or strokes that damage the retina or affect particular areas of the brain/eye can lead to colour blindness.
- Medications such as antibiotics, barbiturates, anti-tuberculosis drugs, high blood pressure medications and several medications to treat nervous disorders may cause colour blindness.
- Industrial or environmental chemicals such as carbon monoxide, carbon disulphide and some containing lead can also cause colour blindness.
- Age – in people over 60 years of age physical changes can occur which might affect a person’s capacity to see colours.
- Most people who acquire colour vision deficiency retain some ability to perceive all colours and to them the world begins to appear similar to the way it appears to vision of someone with anomolous trichromacy (read below for more on this conditiuon)
- Unlike inherited colour blindness , acquired colour blindness can vary over time. Symptoms may be mild and remain stable or they can be severe and progress to more serious forms of colour blindness, such as monochromatism, very quickly. Often the cause of colour blindness determines how severe the symptoms will be.
Types of colour blindness:
- Anomalous Trichromacy
Normal colour vision uses all three types of light cones correctly and is known as trichromacy. People with normal colour vision are known as trichromats.
People with ‘faulty’ trichromatic vision will be colour blind to some extent and are known as anomalous trichromats. In people with this condition all of their three cone types are used to perceive light colours but one type of cone perceives light slightly out of alignment, so that there are three different types of effect produced depending upon which cone type is ‘faulty’.
The different anomalous conditions are protanomaly, which is a reduced sensitivity to red light, deuteranomaly which is a reduced sensitivity to green light and is the most common form of colour blindness and tritanomaly which is a reduced sensitivity to blue light and is extremely rare.
The effects of anomalous trichromatic vision can range from almost normal colour perception to almost total absence of perception of the ‘faulty’ colour.
People with deuteranomaly and protanomaly are collectively known as red-green colour blind and they generally have difficulty distinguishing between reds, greens, browns and oranges. They also commonly confuse different types of blue and purple hues.
People with reduced blue sensitivity have difficulty identifying differences between blue and yellow, violet and red and blue and green. To these people the world appears as generally red, pink, black, white, grey and turquoise.
See the dichromacy images below – about half of people with anomalous trichromacy will see the world in a similar way to those with dichromacy but their ability to perceive colours will improve in good light and deteriorate in poor light. Often their colour perception can be as poor as it is for those with dichromacy.
People with anomalous dichromacy can have either inherited colour blindness, in which case their ability to see colours will remain the same, or they can have acquired it, in which case their condition could get worse, or possibly improve over time
People with dichromatic colour vision have only two types of cones which are able to perceive colour i.e. they have a total absence of function of one cone type. Lack of ability to see colour is the easiest way to explain this condition but in actual fact it is a specific section of the light spectrum which can’t be perceived. For convenience we call these areas of the light spectrum ‘red’, ‘green’ or ‘blue’ . The sections of the light spectrum which the ‘red’ and ‘green’ cones perceive overlap and this is why red and green colour vision deficiencies are often known as red/green colour blindness and why people with red and green deficiencies see the world in a similar way.
People suffering from protanopia are unable to perceive any ‘red’ light, those with deuteranopia are unable to perceive ‘green’ light and those with tritanopia are unable to perceive ‘blue’ light.
People with both red and green deficiencies live in a world of murky greens where blues and yellows stand out. Browns, oranges, shades of red and green are easily confused. Both types will confuse some blues with some purples and both types will struggle to identify pale shades of most colours.
However, there are some specific differences between the 2 red/green deficiencies.
Protanopes are more likely to confuse:-
- Black with many shades of red
- Dark brown with dark green, dark orange and dark red
- Some blues with some reds, purples and dark pinks
- Mid-greens with some oranges
Deuteranopes are more likely to confuse:-
- Mid-reds with mid-greens
- Blue-greens with grey and mid-pinks
- Bright greens with yellows
- Pale pinks with light grey
- Mid-reds with mid-brown
- Light blues with lilac
The most common colour confusions for tritanopes are light blues with greys, dark purples with black, mid-greens with blues and oranges with reds.
The images show how the beautiful colours of the pigments are lost to people suffering with each type of dichromatic vision.
- Monochromacy (achromatopsia)
People with monochromatic vision can see no colour at all and their world consists of different shades of grey ranging from black to white, rather like only seeing the world on an old black and white television set. Achromatopsia is extremely rare, occuring only in approximately 1 person in 33,000 and its symptoms can make life very difficult. Usually someone with achromatopsia will need to wear dark glasses inside in normal light conditions.
We have had several very concerned people contact us via this website because they or their children have been diagnosed by their optician with ‘total colour blindness’. Although we are unable to advise on the diagnosis of specific cases we have undertaken further research to try and understand why so many people are being told they are totally colour blind when in reality they are much more likely to have a severe form of red-green colour blindness. Our research has revealed that in many cases opticians have only received basic training on colour vision deficiency and some may therefore be incorrectly interpreting the results of the Ishihara tests.
If you have been diagnosed as ‘totally’ colour blind please follow the links to these two specialist websites for further information. If you think you do have the symptoms of achromatopsia ask your optician to refer you to a specialist who can confirm your condition.
Take a free online test here:
For more information please call us or visit
McKenna & Scott Exclusive Optometrists in Pinelands.
Tel: 021 531 1953