Oculomotor nerve (III) lesion
Arises anteriorly from the midbrain and passes between the posterior cerebral and superior cerebellar arteries, pierces the arachnoid dura and runs forward in the lateral wall of the cavernous sinus, then divides into:
· Superior ramus which enters orbit via the lower part of superior orbital fissure within a tendinous ring. It supplies superior rectus and levator palpebrae superioris muscles.
· Inferior ramus travels with superior ramus, but gives branches to inferior rectus and medial rectus muscles. It gives off a branch to the inferior oblique muscle, which carries parasympathetic nerve fibres to the ciliary ganglion, and thence to the pupillary sphincter and ciliary muscle.
Full retraction of the upper eyelid, looking medially, pupillary constriction.
Affecting III alone (not IV and VI) – trauma, diabetes mellitus, giant cell arteritis, aneurysm of posterior communicating artery, idiopathic, raised intracranial pressure causing temporal lobe herniation, basal meningitis.
Ptosis, dilated unreactive pupil, eye turned down and out (divergent strabismus).