USMLE Step 1 Review/Neurology

Localization Small, irregular pupil that does not react to light but does react to accommodation. Localization is to the midbrain and the cause is neurosyphilis. The pupil's better response to a near than to a light stimulus is because the lesion involves the more dorsally-located fibers that subserve the pupil response to light and spares the more ventrally-located fibers that subserve the pupil response to accommodation. Care should be taken to not confuse Argyll-Robertson pupil with an Adie's tonic pupil, Horner's syndrome or third nerve lesions. Regarding what to do in case of syncope: If the face is red, raise the head. If the face is pale, raise the tail!