What is the iris in relation to the eye?

The iris is correctly identified as the colored portion of the eye. It is a thin, circular structure that surrounds the pupil and is responsible for controlling the diameter and size of the pupil, which in turn regulates the amount of light that enters the eye. The color of the iris varies among individuals and can be influenced by genetic factors. It plays a significant role not only in aesthetics but also in vision, as its adjustments help in protecting the retina from excessively bright light and optimizing vision in varying lighting conditions. The other options refer to different parts of the eye or structures that are not related to the iris itself; thus, they do not accurately describe what the iris is.