Final answer:
The iris is a thin structure that adjusts the amount of light entering the eye by controlling the size of the pupil. The iris is a thin, circular structure that gives the eye its color (blue, brown, green, etc.) and regulates the amount of light entering the eye.
Step-by-step explanation:
The iris is a thin structure that constitutes the colored part of the eye and functions to adjust the amount of light entering the eye. The iris controls the size of the pupil, the opening through which light enters the eye. In response to the brightness of light, the iris causes the pupil to narrow in bright light and widen in dim light, thereby regulating the amount of light reaching the retina.
The structure you are referring to is the iris. The iris is a thin, circular structure that gives the eye its color (blue, brown, green, etc.) and regulates the amount of light entering the eye. It does so by controlling the size of the pupil, which is the opening at the center of the iris. In bright conditions, the iris constricts the pupil to reduce the amount of light entering the eye, and in dim conditions, it dilates the pupil to allow more light in. This adjustment helps maintain optimal visual clarity and sensitivity under varying lighting conditions.