What is the value of the pupillary reflex for diagnosing third nerve palsies?
Because the parasympathetic fibers travel along the outside of the third nerve, they are usually damaged by nerve compression, resulting in pupillary dilatation.
Third-nerve palsies that cause pupillary dilatation are usually masses (e.g., tumors, aneurysms), whereas palsies that do not involve the pupil are usually medical (e.g., ischemia, vasculitis).
