Iris

Iris, colored circular part of the eye made of muscle and fiber and surrounding the black pupil. Responsible for regulating the amount of light entering the eye, it separates the front and back chambers of the eyeballs and rests against the front of the crystalline lens. Its color is determined by the location of pigment bodies known as melanophores: if these are at the back of the iris, it appears blue or gray; if in the middle, it appears brown.