Assessment of an Afferent Pupillary Defect When Only One Iris is Functional

Assessment of an afferent pupillary defect when only one iris is functional. In this example, a right-sided parasellar tumor is compressing both the optic and oculomotor nerves, causing an optic neuropathy and a pupil-involving third crainial nerve palsy. The pupil on the affected side has both an afferent as well as an efferent defect. The room is darkened and the examiner uses a dim light to illuminate the unaffected left pupil from below. The right-sided afferent defect is detected by observing that the left pupil dilates when the right eye is stimulated (top), and then constricts when the left eye is stimulated (bottom), during the swinging flashlight test.