Cranial nerve palsies of the eye

Table of Contents

Bell’s palsy

Genu VII Bell’s palsy

Stroke masquerading as Bell’s palsy
Involves cranial nerve VI and ipsilateral CN VII as it genuflects around the VI nerve nucleus
Get CN VII palsy identical to Bell’s (affecting upper and lower portions of face) but with added inability to abduct the ipsilateral eye (CN VI palsy)
MUST TEST EOM in all Bell’s palsy patients

Acute diabetic CN III palsy
- Get pupil sparing as vascular compromise occurs of central nerve fibres rather than peripheral nerve fibres (efferent pupillomotor fibres run in periphery of the nerve)
- Will see inhibition of ipsilateral medial gaze, upward gaze and downward gaze
- Lateral gaze preserved and diplopia worsens when patient attempts to look to contralateral side (failed adduction)
Acute CN VI palsy
- Lateral gaze inhibited on ipsilateral side
Need neuroimaging to rule out intracranial lesion
Can discharge with ophthal and/or neurology follow-up if no intracranial cause found, BP and BSL under control

Acute CN III palsy with ipsilateral pupillary dilatation is a posterior communicating artery aneurysm until proven otherwise
Concomitant headache is common but not universal
Expansion causes compression of outer fibres of nerve (where efferent pupillary parasympathetic fibres run)
Need emergent BP reduction if hypertensive, neuroimaging and neurosurgical consult

Ipsilateral ptosis, miosis and anhydrosis
Interruption of sympthetic nerve fibres controlling Mueller muscle in upper eyelid and iris dilators
Can occur anywhere from brainstem to sympathetic plexus around carotid artery
Need CXR, CT of brain and cervical region, CT angiogram of head/neck vessels for carotid dissection
Differentials
- Adults: CVA, tumors, ICA dissection, herpes zoster and trauma
- Children: Neuroblastoma, lymphoma, metastases
Neck pain and acute Horner’s suggests acute carotid dissection and can occur spontaneously (usually >30) or be traumatic in origin

Idiopathic intracranial hypertension
Increased ICP, papilloedema, normal CSF fluid pressure and normal CT/MRI characterise this entity
Nausea, vomiting, headache and blurred vision
Can develop CN VI paresis leading to horizontal diplopia (failed LR)
Key part of exam is identifying any visual field defect

Myaesthenia gravis (MG) is an autoimmune condition causing weakness and fatiguability of skeletal muscle
Ocular MG refers to that which involves only levator palpebrae superioris, orbicularis oculi and the oculomotor muscles
50% of patients with MG present with initial isolated ptosis, diplopia or both
It is unknown why the ocular muscles are specifically targeted
Stays localised to the eyes in 15%
Generally fluctuating and worse at the end of day
Ptosis
- Often unilateral or asymmetric on presentation
- May alternate from side to side (pathognomic)
- Sustained upgaze for 1-2 minutes may reveal fatiguability
- Hering law suggests contralateral eyelid curtaining will occur if hold the ptosed eyelid up
Diplopia
- May include individual or multiple, bilateral ocular motor muscles
- If medial or lateral recti involvement -> binocular and horizontal diplopia
- If superior or inferior obliques involved -> Vertical or diagonal component
- Fluctuation in the degree or direction of maximal diplopia suggests fatiguability
- Pupillary involvement is generally not seen in MG

Impaired horizontal eye movements with weak and slow adduction of the affected eye and abduction nystagmus in the contralateral eye
Caused by lesion in medial longitudinal fasciculus
Diplopia is usually not present in primary gaze
- Some patients will have vertical skew deviation however
Patients with demyelinating conditions may show bilateral involvement
Most lesions will spare the vergence pathways, thus leaving convergence intact via CN III
- This ability to converge differentiates INO from a partial CN III palsy
- Impaired convergence does NOT rule out INO however
Often exhibit impaired vertical eye movements
- Vertical nystagmus
- Skew deviation
- Diminished vertical gaze holding
Causes
- Multiple sclerosis (30%) – Most common if under 45yo and bilateral in 75%
- Cerebrovascular disease – Most common in older patients. Usually small artery occlusion or lacunar disease from basilar artery perforators. May be isolated or 50% show other neurological signs e.g. ataxia.etc.
Differential diagnosis
- Partial third nerve palsy with prominent medial rectus weakness
  - Distinguished by pupillary involvement, weakness of elevation, ptosis, impaired convergence and absence of contralateral abduction nystagmus
- Progressive Supranuclear Palsy
- Myaesthenia gravis
- GBS

Gaze palsy in one direction (bottom row in picture) with an INO on horizontal gaze in the other direction (middle row in picture)
Convergence is spared

Long course of nerve makes it particularly prone to blunt head trauma or compression from raised ICP
Present with vertical diplopia and subjective tilting of objects (torsional diplopia)
May adopt a head tilt as torsional and vertical diplopia improve with head tilting towards the side of the lesion
May subconsciously close one eye to reduce diplopia
On examination have ipsilateral hypertropia (deviation upwards) and excyclotorsion (rotation outward)
Non-isolated syndromes
- Midbrain lesion – Hemisensory/hemiparesis/central Horner
- Subarachnoid space lesions e.g. meningitis/SAH
- Cavernous sinus – 3rd/5th/6th or Horners
- Orbital apex – 3rd/5th/6th/proptosis/chemosis
- Dorsum of brainstem lesions – Cerebellar signs
Differential
- Restrictive vertical strabismus – Graves, orbital pseudotumor, orbital tumors, orbital floor fracture
- CN III palsy affecting inferior rectus, superior rectus or inferior oblique
- MG
Causes of isolated CN IV palsy
- Microvascular disease (rare but does occur)
- Idiopathic
- Tumors of brainstem
- Aneurysm of superior cerebellar artery
- Schwannoma of CN IV
- Cavernous haemangioma
- Intracranial or meningeal infection
- Raised ICP of any cause

Last Updated on March 14, 2022 by Andrew Crofton