Cranial Nerves 2 & 3: Swinging flashlight test is done by:

Swinging the flashlight back and forth between the two eyes identifies if one pupil has less light perception than the other. Shine the flashlight at one eye noting the size of both pupils. Then swing the flashlight to the other eye. If both pupils now dilate then that eye has perceived less light stimulus ( a defect in the sensory or afferent pathway) than the opposite eye.