Parasympathetic & Sympathetic Actions on Pupil
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Pupillary Light Reflex Pathologies
Afferent Pupillary Defect
- If you shine a light in the patient’s eye and neither pupil constricts, the initial presumed abnormality is an ipsilateral CN 2 lesion.
- This lesion localization is confirmed, if the pupils constrict when light is shone into the opposite eye.
- However, if when light is shone into the opposite eye, both of the patient’s pupils still fail to constrict, the abnormality either localizes to bilateral CN 2 or bilateral CN 3 abnormalities.
Efferent Pupillary Defect
- If you shine a light in the patient’s eye and one pupil constricts but the other does not, the lesion localizes to the CN 3 that fails to constrict. - To confirm, this same pupil should fail to constrict when you shine a light in the patient’s other eye.