The iris is part of the eyeball’s middle layer. It has an annular shape and is situated behind the cornea. Considering that the iris is an annular muscle (sphincter), its main role is to change the form of the pupil with its contraction and thus to regulate the quantity of light that enters the eye. The colour of the iris itself is determined by the quantity of pigment in the eye, and thus brighter eyes have a small quantity of pigment, while the darker ones has a larger quantity of pigment. The iris is unique to every human being in the world and, like a fingerprint; it helps to identify a person.