What does the iris control in the human eye?

The iris plays a crucial role in controlling the amount of light that enters the eye. It is the colored part of the eye, composed of muscle fibers that contract or relax to adjust the size of the pupil, which is the opening in the center of the iris. When light levels in the environment change, the iris responds by constricting (narrowing) the pupil in bright light to limit the amount of light reaching the retina, and dilating (widening) the pupil in low light conditions to allow more light in. This adjustment helps protect the inner structures of the eye from excessive light exposure while also optimizing vision across various lighting conditions. This function is essential for maintaining good visual acuity and overall eye health.