Shabina Akhtar explains : Eye colour is an inherited trait influenced by more than one gene. It is determined by the amount and type of melanin present in the iris. There are basically three types of eye colours — brown, green and blue — but humans have many phenotypic (visible) variations.

“Colour variations among different irises are typically attributed to the melanin content within the iris stroma. The density of cells within the stroma affects how much light the underlying pigment absorbs,” says Dr Himadri Datta of the Regional Institute of ophthalmology, Calcutta.

Adds Dr Datta, “Different eye colours can provide information about an individual, and a classification of the various colours may be useful in documenting pathological changes or determining how a person may respond to various ocular pharmaceuticals.”

Brown eyes — the most common colour — contain large amounts of melanin in the iris which absorbs light, particularly at shorter wavelengths. Very dark brown irises may appear to be black.

Those with non-European ancestry usually have darker eyes and less variability in eye colour than those of European decent. Most of the original inhabitants of Africa, Asia and the Americas have brown eyes. Green eyes are the product of moderate amounts of melanin.

The question was sent by Anya Dey from Calcutta