The iris is a thin, circular structure made of connective tissue and muscle that surrounds the pupil. The color of our eyes is determined by the amount of pigment in the iris. In addition to giving color to the eye, the iris acts like the aperture of a camera and controls the size of the pupil. One muscle inside the iris causes the pupil to shrink in bright light, and the other iris muscle enlarges the pupil in dim light and darkness. The iris is the colored part of the eye that can be seen from behind the cornea. There is a hole in the middle of the iris through which the light passes to the lens and then to the retina. This hole is called the pupil and its size varies according to the amount of light that is visible to the eye.
