What are the different types of colour vision deficiency?
There are several types of CVD, depending on how many of the cone cells are working:
Anomalous trichromacy is where all three cone cells are working but one of them is not able to detect colour as sensitively. A person with anomalous trichromacy will see fewer colours compared to someone with normal colour vision.
Dichromacy is where only two cone cell types are working. A person with dichromacy will be unable to see certain colours and confuse more colours compared to a person with anomalous trichromacy.
Cone monochromatism is where there is only one cone cell which is working.
Achromatopsia or rod monochromatism is where none of the cone cells are working or they are all reduced in function. This means you are unable to see any colours at all.
Dichromacy and anomalous trichromacy are the most common types of CVD and the most commonly affected cone cells are the red and green cells.
Please also see What is colour vision deficiency (CVD)?
A factsheet with image examples of how each condition impacts the colour spectrum can be found on RNIBs colour deficiency webpage.
