What is the black portion of an individual's eye known as?

The black portion of an individual's eye is known as the pupil. The pupil is the opening in the center of the iris that allows light to enter the eye. It appears black because the inside of the eye is dark, and the light that enters is absorbed rather than reflected back out. Its size can change in response to lighting conditions and the emotional state, as the muscles of the iris, the colored part around the pupil, control its size. This adaptation helps regulate the amount of light that reaches the retina, which is crucial for optimal vision.

In contrast, the iris is the colored part of the eye surrounding the pupil and does not appear black; the sclera is the white outer layer of the eyeball, and the cornea is the transparent front part of the eye that covers the iris and pupil. Each of these structures has distinct functions, but none represent the black opening through which light enters, which is specifically the pupil.