Humans receive 90% information about the world through eyes. They are responsible for vision that enables humans to receive and process visual information, distinguish colours and perceive depth. There are six types of eye colours: amber, hazel, blue, grey, brown and green. The structure of the eye is complex, and the most complex part of the eye is the iris. The accumulation of the pigment melanin in the iris results in a perception of the specific colour of the eye. Melanogenesis, the process of producing melanin, is mostly under the influence of two genes: OCA2 and HERC2, which are both located on chromosome 15. For a long time, it was thought that the colour of the eye is inherited as a monogenetic trait, but nowadays it's known that is a polygenetic trait. This phenotypic trait is controlled with 16 different genes, although the effect of OCA2 and HERC2 is the most pronounced. Any change in those genes may result in a change of the colour or can be associated with development of a disease. Despite the equal distribution of the number of melanocytes between different eye colourations, the distribution of melanocytes numbers between populations is more different. Lighter eye colours are more frequent in Europeans and their descendants which can be correlated with the appearance of blue eyes. Also, it seems that Asian irises have fewer melanocytes than Africans and Europeans because of the smaller surface of the iris or lower density of the melanocytes.