Swinging Flashlight Test

The swinging flashlight test helps identify an afferent pupillary defect (a lesion of CN 2, such as optic neuritis). To perform this test, alternately swing the light from one of the patient’s eyes to the other, holding it on each eye for 3-5 seconds. The patient’s pupil should remain constricted throughout this time. If an afferent pupillary defect is present, as the flashlight swings from the normal eye to the abnormal eye, both pupils will dilate. If a CN 3 lesion is present, the abnormal pupil will not constrict regardless of which eye in which you shine the light.