Eyes / Vision

Colour Vision Deficiency


Colour vision deficiency is the decreased ability to distinguish different colours. People with the deficiency can usually distinguish most of the single colours (e.g. red and orange). However, if several colours are mixed together (e.g. purple and blue, red and green, etc.), people may fail to see the differences in colours and may perceive the colours as one single colour. In addition, the ability to distinguish different colours may be further weakened if the lighting is poor or the object is light-coloured. Therefore, as the signals of traffic light are bright and dark-coloured, people can easily identify the red and green traffic light signals, yet people may find difficulty in distinguishing light red and light green paints.


There are several types of colour vision deficiency. The most common one is the difficulty distinguishing between red and green (red-green deficiency). While another relatively common one is the difficulty distinguishing between blue and yellow (blue-yellow deficiency). If one cannot identify any colour and perceive brightness as the only variation of the colours, he/she is said to have colour blindness.


There are 3 types of cells that are responsible for colour vision in the retina. If any one type of these cells cannot function properly or completely, colour vision deficiency results. If any two types of these cells cannot function completely, colour blindness results.


Colour vision deficiency is typically an inherited genetic disorder, but there are also other causes (e.g. illnesses that affect the retina, choroid or optic nerve). However, colour blindness is a congenital medical condition.


More than 90% of inherited colour vision deficiency is red-green deficiency and the rest is blue-yellow deficiency. The risk of male inheriting the deficiency is much higher than that of female for about 8% of male but only 0.5% of female have the deficiency. While colour blindness is a rare condition for only 1 person suffers from the disorder in every 1 million of people.


People with colour vision deficiency usually fail to identify their symptoms as they presume that other people distinguish the same colours as they do. Although colour vision deficiency is incurable, it does not significantly affect one’s daily life. However, people with colour vision deficiency may find difficult to engage in certain occupations that require colour perception, for example, police officer, firefighter, Customs officer, Correctional Services officer, Immigration Service staff, pilot, pharmacist, laboratory technician, painter, etc.

(Revised in October 2019)

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Last Revision Date : 18 December 2019