Ocular Motor Palsies - CN 3,4,6
Third Nerve Palsy (Oculomotor)
Presents with Diplopia, Down and out pupil, Ptosis, Dilated non-reactive pupil, and Squint. Reasons for this are:
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
Supplies the levator palpebrae superioris, therefore a palsy → Ptosis
This is differentiated from Horner's syndrome by the extent of ptosis. Horners = Partial ptosis. CN3 palsy = Complete ptosis.
Supplies the sphincter muscle of the iris, therefore a palsy → Dilated, non-reactive pupil
N.B. Some cases are idiopathic.
With the oculomotor nerve, the parasympathetics control the pupil size and its nerve fibres are along the periphery (outer part) of the nerve. A way to determine the cause of its palsy is by finding out if the pupil is affected.
An affected pupil suggests a Surgical lesion where there's compression of the nerve, therefore affecting the parasympathetic fibres. Causes of this include:
Posterior communicating PCOM artery – Most common – Urgent MRI needed to exclude this
Cavernous sinus thrombosis
Tumour
Trauma
Raised ICP
An un-affected pupil suggests a Medical lesion where the parasympathetic fibres are spared. Causes of this include:
MS
Diabetes
HTN
Ischaemia
Fourth Nerve Palsy (Trochlear)
This nerve supplies the superior oblique muscle. It presents with:
Diplopia
At rest, the eye points upwards and inwards – Patient may tilt head to compensate for this (aka Ocular Torticollis)
Causes:
In children, it’s commonly congenital
In adults, it’s commonly due to trauma
Other causes include stroke, diabetes, idiopathic, aneurysm, raised ICP, MS
Sixth Nerve Palsy (Abducens)
It presents with Diplopia and Strabismus.
Causes:
In children, it’s commonly congenital
In adults, it’s commonly due to trauma
Other causes include stroke, diabetes, idiopathic, aneurysm, raised ICP, MS
