Third Nerve Palsy

The complete 3rd nerve palsy syndrome:
1) Complete ptosis
2) The eye looks down and out
3) Dilated pupils unreactive to direct light and to accommodation

The 3rd feature is important in differentiating surgical vs medical lesions.


a. SURGICAL lesions
Aneurysms, trauma, & uncal herniation involves the pupil by compression.

b. MEDICAL lesions
Hypertension, diabetes usually spare the pupil because the microangiopathy associated with these medical lesions involves the vasa nervorum, causing neural infarction of the trunk of the nerve, but sparing the superficial pupillary fibres.