Neurology Cranial Nerves

Afferent Pupillary Defect

This is the most common pupil defect, characterized by asymmetric pupillary constriction to light, but these pupils are equal (no anisocoria). Main etiology is optic neuritis, but other diseases of the optic nerve or retina may cause it. The swinging flashlight test is performed by shining a light for 1-2 seconds in one eye and then moving the light to the other. Have the patient look at a distant object to not cause confounding pupil constriction due to accommodation. Normally, the direct and consensual responses are equal but in diseases of the optic nerve or retina, the direct response is less than normal, so that when the light passes from the “good” eye, rather than constriction one will see a slight, paradoxical dilation of the pupil, as the perceived light is dimmer than in the good eye, and the consensual response will also be decreased symmetrically. The consensual response in the affected eye, however, is intact, so when light is shone in the good eye, even the bad eye constricts normally (since the consensual response is independent of the optic nerve and retina from the bad eye)

Patient 1

This patient is an old woman with a history of multiple strokes who was admitted with confusion.