The Iris and Pupil:

The most commonly known parts of the eye are the iris and the pupil. The iris is made of connective tissue and muscle that contains a hole in the midst of them. The iris is the part of the eye that is colored, either brown, green, blue, hazel, etc. The color is a result of the amount of pigment that is found in the eye, brown eyes have a lot of pigment, and light eyes, such as blue, have little pigment.

The pupil is the hole in the eye that allows light to reach the retina. The pupil widens in a darker room to allow more light in, and narrows when in the light to restrict the amount of light to reach the retina. The pupil is adjusted by the iris muscles.