The term Pupil refers to the hole surrounded by the iris in the center of an eye which is actually essential to one's sight.  Light passes through this hole on its way toward the lens, through the vitreous humor, and onto the retina which enables actual sight. In the context of art, World famous artist and sculptor, Michelangelo (Italian, 1475-1564) depicted pupil in his art work, the left eye of David made in marble. In the sculpture, the pupil was carved to represent its values. The sculptor has preserved a bit of marble in the pupil of the figure in order to create a highlight.