Question #515
Features of a third nerve palsy include
A third nerve palsy is characterised by ptosis (due to loss of innervations to levator palpebrae superioris), dilated pupil (due to loss of parasympathetic innervation to sphincter pupillae, loss of accommodation and light reflex (due to loss of parasympathetic innervations to the ciliary muscle and sphincter pupillae respectively) on that side and an eyeball orientated down and out (due to unopposed action of superior oblique and lateral rectus muscles).
It is important to be able to distinguish this from Horner’s (ptosis, miosis and anhydrosis) which occurs following damage of the cervical sympathetic chain.
Papilloedema is swelling of the optic disc on fundoscopy and occurs when there is increased intracranial pressure. Although raised intracranial pressure may cause a third nerve palsy papilloedema is not a feature of a third nerve palsy.
Tear production is controlled by parasympathetic fibres from the facial nerve not the oculomotor nerve.