IRIS, iris (lay. iris), a thin movable diaphragm of the eye in vertebrates with a hole (lat. pupil) in the center; located behind the cornea, between the anterior and posterior chambers of the eye, in front of the lens. Virtually opaque. Contains pigment cells (lat. melanocytes in mammals), circular muscles that constrict the pupil, and radial muscles that expand it .
Read next
From @thewritersblock