What is the name of the adjustable opening in the center of the eye through which light enters?

The adjustable opening in the center of the eye that allows light to enter is referred to as the pupil. The pupil is an essential structure in the visual system, as it changes size in response to light levels, helping to regulate the amount of light that reaches the retina. This adjustment is controlled by the iris, which is the colored part of the eye surrounding the pupil. When there is bright light, the iris contracts, making the pupil smaller to reduce light entry; conversely, in low light conditions, the iris dilates to enlarge the pupil and allow more light in. Understanding the role of the pupil is crucial in grasping how the eye adapts to different lighting conditions, which is a fundamental concept in both psychology and biology related to sensory processing.