Pupil constriction, also known as miosis, is the process where the pupil of the eye becomes smaller. This reaction occurs in response to bright light or when focusing on nearby objects. The constriction helps protect the retina from excessive light and improves depth of field, allowing for clearer vision. The constriction is controlled by the iris, the colored part of the eye, which contains muscles that adjust the size of the pupil. Various factors, such as certain medications, emotional responses, or neurological conditions, can also influence pupil size and lead to constriction.