What is the definition or description of: iris?

Colored part of eye: The iris is a structure within the eye that helps reduce the amount of light that reaches the retina. The iris is known as the colored part of the eye, and can be blue, brown, or any color or combination of colors in between. The iris is the portion of the eye that responds to light stimulation.

The pupil opening : The iris is the muscular ring around the pupil which opens and closes in response to light. The name iris derives from the greek for rainbow due to the multiple colors of the iris. The iris determines the color of the front of the eye and is responsive to light, stress, many pharmaceuticals agents and can be altered with surgery or trauma.