Ocular Motor Palsies - CN 3,4,6 (3)

Question 1

Third Nerve Palsy (Oculomotor):
What does it present with?

Why does it lead to a Down and Out pupil?

Why does it lead to Ptosis?
→ How is this differentiated from Horner’s?

Why does it lead to a Dilated, non-reactive pupil?

Answer 1

➊ Diplopia, Down and out pupil, Ptosis, Dilated non-reactive pupil, Squint

➋ Supplies all the extraocular muscles (except the lateral rectus and superior oblique), so when there’s a palsy, the eye is unopposedly affected by these other two muscles → Down and out pupil

➌ Supplies the levator palpebrae superioris, therefore a palsy → Ptosis
→ Horners = Partial ptosis. CN3 palsy = Complete ptosis.

➍ Supplies the sphincter muscle of the iris, therefore a palsy → Dilated, non-reactive pupil

Question 2

N.B. Some cases are idiopathic

What does an affected pupil suggest?
→ What can this be due to?

What does an un-affected pupil suggest?
→ What can this be due to?

Answer 2

➊ Compression of the nerve, affecting the parasympathetic fibres (Surgical lesion)
→ • Posterior communicating PCOM artery – Most common – Urgent MRI needed to exclude this
• Cavernous sinus thrombosis
• Tumour
• Trauma
• Raised ICP

➋ Parasympathetic fibres are spared (Medical lesion)
→ • MS
• DM
• HTN
• Ischaemia

Question 3

Fourth Nerve Palsy (Trochlear):
What does this nerve supply?

How does it present?

What are the causes?

Answer 3

➊ Superior oblique

➋ Diplopia
• At rest, the eye points upwards and inwards – Pt may tilt head to compensate (aka Ocular Torticollis)

➌ • In children, it’s commonly congenital
• In adults, it’s commonly due to trauma (Other causes include Stroke, DM, Idiopathic, Aneurysm, Raised ICP, MS)

Question 4

Sixth Nerve Palsy (Abducens):
How does it present?

What are the causes?

Answer 4

➊ Diplopia, Strabismus

➋ • In children, it’s commonly congenital
• In adults, it’s commonly due to trauma (Other causes include Stroke, DM, Idiopathic, Aneurysm, Raised ICP, MS)