The swinging flashlight test is used to show a relative afferent pupillary defect or a Marcus Gunn pupil of the left eye. The left eye has perceived less light stimulus (a defect in the sensory or afferent pathway) then the opposite eye so the pupil dilates with the same light stimulus that caused constriction when the normal eye was stimulated. NeuroLogic Exam has been supported by a grant from the Slice of Life Development Fund at the University of Utah, the Department of Pediatrics and the Office of Education at the University of Nebraska Medical Center. Viewing the video requires installation of the free QuickTime Plug-in.