There are several types of inherited colour blindness. For information on acquired colour vision defects refer to our page Acquired Colour Vision Defects

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.



Anomalous Trichromacy

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’.

Normal Vision Deuteranomaly

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

Dichromacy





Normal Vision Deuteranopia Protanopia Tritanopia





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 with 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.

Protanopia

Protanopes are more likely to confuse:-

1. Black with many shades of red

2. Dark brown with dark green, dark orange and dark red

2. Some blues with some reds, purples and dark pinks

3. Mid-greens with some oranges

Deuteranopes

Deuteranopes are more likely to confuse:-

1. Mid-reds with mid-greens

2. Blue-greens with grey and mid-pinks

3. Bright greens with yellows

4. Pale pinks with light grey

5. Mid-reds with mid-brown

6. Light blues with lilac

Tritanopes

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 with each type of dichromatic vision.

Monochromacy (achromatopsia)

Normal Vision Monochromacy

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.

www.achromat.org

www.achromatopsia.org

Statistics

There is general agreement that worldwide 8% of men and 0.5% of women have a colour vision deficiency. These figures rise in areas where there is a greater number of white (Caucasian) people per head of population, so in Scandanavia the figures increase to approximately 10-11% of men. By contrast in sub-Saharan Africa there are few colour blind people. Countries such as India and Brazil have a relatively high incidence of colour vision deficients because of the large numbers of people with mixed race genes in their genetic history.

The 8% of colour blind men can be divided approximately into 1% deuteranopes, 1% protanopes, 1% protanomalous and 5% deuteranomalous. Approximately half of colour blind people will have a mild anomalous deficiency, the other 50% have moderate or severe anomalous conditions.

Numbers of tritanopes/tritanomalous people and achromats is very small, perhaps 1 in 30-50,000 people.

Reliable statistics for people with an acquired form of colour vision deficiency are difficult to find but as many as 3% of the population could be affected because age-related deficiency is relatively common in the over 65s and therefore on the increase in the UK due to the rising numbers of elderly people per capita.

To put these statistics in context, an all-boys school in the Home Counties of England with 1000 pupils would have approximately 100 colour deficient students. 12-13 would be deuteranopes, 12-13 would be protanopes, 12-13 would have a form of protanomaly and 62 would have a form of deuteranomaly. About half of those with an anomalous condition would have a moderate to severe form of deficiency.