What is colour-blindness and why does it occur?

Colour-blindness, also known as colour vision deficiency, is the inability of the human eye to see or differentiate between colours. This optical condition, which is mostly genetic, occurs due to a fault in the development of cone cells present in the eye. Cone cells and rod cells, present in the retinal section, ensure colour vision and night and low-light vision respectively. 

There are three types of cone cells present in the eye enabling it to distinguish between red, green and blue. The lack or malfunction of one or more of these cones gives rise to different types of colour-blindness.

Deuteranopia, a type of colour vision deficiency where red and green are perceived identically, is also called ‘Daltonism’. It is named after the English chemist John Dalton, who published the first scientific paper on colour-blindness after realizing he himself was colour blind. The test used to identify deuteranopia is called the Ishihara Test.