The iris is the coloured part of your eye, and it defines the amount of light that enters into the eye. Iris are considered to be the most visible part of the eyes due to their colour. Crystalline lenses lie in the back of the iris, separating the anterior and posterior chambers. The iris is located in the uveal tract, that also includes the ciliary body which lies behind the iris.
The colours of the iris depends on the melanin pigment amount inside the iris. Even though all eyes have the same melanin, these pigments differ and define the eye colour. Usually, the back of the iris is heavily pigmented to protect the eyes from light shining through the iris. The iris surrounds the pupil with muscle and a connective tissue made from a thin and circular structure.