CNIII Palsy

Question 1

What is the normal function of CNIII?

Answer 1

Supplies all extraocular muscles except lateral rectus (CNVI) and superior oblique (CNIV)

Levator palpebrae superioris= lifting eyelid

Parasympathetic inn of papillae sphincter

Question 2

What are the classical 3 signs of CNIII palsy?

Answer 2

Ptosis= drooping eyelid due to loss of innervation to levator palpebrae superioris

Fixed/non-reactive dilated pupil= loss of innervation to papillary sphincter m

Down and out= due to loss of extraocular muscle innervation and SO and LR functioning w/o resistance

Question 3

What are the 2 broad types of CNIII palsy? What causes are associated with these types?

Answer 3

Pupil sparing= micro vascular

• diabetes
• hypertension
• ischaemia

Full CNIII palsy= “surgical third” i.e. physical compression

• idiopathic
• tumour
• trauma
• cavernous sinus thrombosis
• posterior communicating artery aneurysm
• RICP

Question 4

What structure does CNIII pass through and what pathology in this structure can lead to compression?

Answer 4

Cavernous sinus

• cavernous sinus thrombosis
• posterior communicating artery aneurysm

Question 5

What causes cavernous sinus thrombosis?

Answer 5

Due to spread of bacterial infection from another area of the skull
-sinusitis= staphylococcal infection