Extraocular movements
Nerves and muscles
- LR6 SO4, all the rest 3 - lateral rectus = VI, superior oblique = IV, everything else + levator + pupil = III
| Muscle | Nerve | Primary action | Tested by |
|---|---|---|---|
| Lateral rectus | VI | Abduction | Look laterally |
| Medial rectus | III | Adduction | Look medially |
| Superior rectus | III | Elevation in abduction | Up-and-out |
| Inferior rectus | III | Depression in abduction | Down-and-out |
| Superior oblique | IV | Depression in adduction, intorsion | Look down and in |
| Inferior oblique | III | Elevation in adduction, extorsion | Up-and-in |
- III also carries: levator palpebrae (ptosis), and parasympathetic pupillomotor fibres running on the outer surface of the nerve
- That superficial position is the whole clinical rule: compression hits the pupil first, ischaemia (vasa nervorum, central) spares it
Conjugate gaze - the wiring
- Frontal eye field initiates contralateral saccades; occipital/parietal drives smooth pursuit
- Both act via the PPRF (horizontal gaze centre, pons) -> ipsilateral VI nucleus
- VI nucleus interneurons cross and ascend in the MLF to the contralateral III nucleus (medial rectus)
- A lesion anywhere in this chain gives a conjugate defect, not diplopia from one muscle
- Frontal lesion -> eyes deviate towards the lesion (contralateral gaze palsy); overcome by doll's-eye - it is supranuclear
- Pontine lesion -> eyes deviate away from the lesion (ipsilateral gaze palsy); not overcome by doll's-eye
- Vertical gaze centre = rostral interstitial nucleus of the MLF, dorsal midbrain
Named syndromes
- INO - MLF lesion: impaired adduction on looking to the other side + nystagmus of the abducting eye; convergence preserved (does not use the MLF)
- One-and-a-half syndrome - PPRF/VI nucleus plus ipsilateral MLF
- "One" = conjugate gaze palsy to the side of the lesion; "half" = INO looking the other way
- Only surviving movement is abduction of the contralateral eye, which sits exotropic
- Parinaud (dorsal midbrain) - upgaze palsy + light-near dissociation + convergence-retraction nystagmus + lid retraction (Collier sign). Pinealoma, hydrocephalus
- Supranuclear gaze palsy (PSP) - bilateral, vertical (downgaze) first, no diplopia, slow vertical saccades, doll's-eye overcomes it
Epidemiology
- VI is the commonest isolated ocular motor palsy (longest intracranial course)
- IV is the commonest cause of isolated vertical diplopia; also the commonest congenital ocular motor palsy
- Over 50 with vascular risk factors: microvascular ischaemia accounts for the majority of isolated III, IV and VI palsies
- Pupil involvement in >90% of aneurysmal III palsies; pupil spared in ~70-80% of ischaemic III palsies
- Aneurysm accounts for a minority of III palsies overall but is the one that kills
CN III
- Central - midbrain infarct, tumour, demyelination
- Weber (III + contralateral hemiparesis), Benedikt (III + contralateral tremor/ataxia)
- Compressive - posterior communicating artery aneurysm, uncal herniation, tumour, basal meningitis, nasopharyngeal carcinoma, pituitary apoplexy, Tolosa-Hunt / superior orbital fissure syndrome
- Ischaemic - diabetes, hypertension, giant cell arteritis, migraine
- Cavernous sinus - with IV, VI and V1
CN IV
- Trauma - long, thin, dorsally exiting nerve; bilateral IV palsy after head injury is characteristic
- Congenital, decompensating in adult life (look for a long-standing head tilt in old photographs, and a large vertical fusional range)
- Microvascular ischaemia (diabetes)
- Dorsal midbrain lesion near the nucleus - may have accompanying cerebellar signs
CN VI
- Microvascular - diabetes, hypertension
- Raised intracranial pressure - a false localising sign, especially if bilateral (long course, tethered over the petrous ridge)
- Pontine lesion - the VII nucleus loops around the VI nucleus, so a VI palsy with an ipsilateral LMN facial palsy localises to the pons
- Cavernous sinus (with III, IV, V1), petrous apex (Gradenigo: VI palsy + facial pain + otitis media), nasopharyngeal carcinoma, low CSF pressure post-LP
Gaze palsies and INO
- INO - MLF: MS (young, bilateral), brainstem infarct (older, unilateral), brainstem glioma, Chiari malformation, Wernicke encephalopathy, SLE, paraneoplastic
- One-and-a-half - pontine stroke, MS plaque, dorsal pontine tumour
- Parinaud - pinealoma, hydrocephalus, midbrain infarct, Niemann-Pick C
Non-neurogenic mimics
- Myasthenia gravis - can imitate any pattern including a "III palsy" or INO; never affects the pupil; fatigable and variable
- Thyroid eye disease - restrictive; inferior rectus then medial rectus ("IM SLow"); positive forced duction test, proptosis, lid lag
- Orbital myositis, orbital cellulitis, blowout fracture with inferior rectus entrapment
- CPEO / Kearns-Sayre - bilateral, symmetric, slowly progressive, often no diplopia
- Miller Fisher (ophthalmoplegia + ataxia + areflexia, anti-GQ1b), Wernicke, botulism
Recognising each palsy
| Eye position | Diplopia worst | Extra | |
|---|---|---|---|
| III | Down and out, complete ptosis | All directions except abduction | Dilated unreactive pupil if compressive; impaired adduction, elevation, depression |
| IV | Hypertropia (affected eye higher) | Downgaze and adduction - reading, stairs | Head tilt away from the lesion; long-standing lesions overact the ipsilateral inferior oblique |
| VI | Convergent squint, esotropia | Gaze towards the lesion | Face turn towards the lesion |
- Cover test rule: the outer (more peripheral) image belongs to the affected eye
- III + IV together: with a complete III palsy, test IV by asking the patient to look down with the head tilted to the lesion side - if IV is intact the eye intorts (watch a conjunctival vessel)
- Parks-Bielschowsky three-step confirms a IV palsy: which eye is higher -> worse on which gaze -> worse on which head tilt (worse on tilt towards the affected side)
Discriminators that change the whole work-up
- Pupil involved in a III palsy = compressive (aneurysm) until CTA/MRA excludes it - do not accept "he's diabetic"
- Beware the partial/evolving palsy: a pupil can become involved over hours. Re-examine, and image anyway if young, painful, or incomplete
- Isolated VI palsy: always fundoscope - papilloedema turns it from microvascular into raised ICP
- INO vs mimic - INO preserves adduction on convergence; thyroid eye disease and orbital myositis do not
- Supranuclear vs nuclear/infranuclear - supranuclear is bilateral, produces no diplopia, spares reflex movements (doll's-eye, Bell's phenomenon)
- Any ophthalmoplegia + normal pupil + fatigability = myasthenia until proven otherwise
- Proptosis, lid retraction, chemosis, resistance to passive movement -> orbital/restrictive, not neurogenic
Investigation
- Pupil-involving III palsy: CTA or MRA today (+/- digital subtraction angiography); neurosurgical referral
- MRI brain (+ orbits, + MRA) for: any III palsy under 50, painful palsy, incomplete/atypical pattern, multiple nerves, no improvement by 3 months, or associated neurological signs
- ESR + CRP in anyone over 50 - GCA causes ocular motor palsies as well as visual loss
- Glucose/HbA1c, BP, lipids - the microvascular work-up
- AChR + MuSK antibodies, ice-pack test, repetitive nerve stimulation/single-fibre EMG; CT chest for thymoma
- TSH, fT4, TSH-receptor antibodies; orbital CT/MRI if restrictive
- LP with opening pressure (after imaging) if papilloedema or suspected raised ICP
- Anti-GQ1b if Miller Fisher pattern; thiamine and treat empirically if Wernicke possible
Exclude the emergencies first
A. Exclude the emergencies first
- Pupil-involving III palsy -> CTA and neurosurgery the same day (clip or coil)
- GCA -> high-dose corticosteroid before the biopsy
- Raised ICP -> imaging incl. venography, then LP; treat the cause
- Pituitary apoplexy -> hydrocortisone, urgent endocrine and neurosurgical review
- Cavernous sinus thrombosis -> antibiotics + anticoagulation, ENT/neurosurgery
Treat the underlying disease
B. Treat the underlying disease
- Microvascular palsy: optimise glucose, BP and lipids; no specific treatment - review at 3 months and image if not resolving
- MS/demyelinating INO: acute steroid if disabling; the important step is starting or escalating disease-modifying therapy
- Myasthenia: pyridostigmine, then immunotherapy (prednisolone + steroid-sparing agent); ocular myasthenia often needs treatment to prevent generalisation
- Thyroid eye disease: control the thyroid, stop smoking (the single biggest modifiable factor), selenium in mild disease
- Moderate-to-severe active disease: IV methylprednisolone (+/- mycophenolate) is first-line in the EUGOGO guideline; teprotumumab is first-line in the ATA/ETA consensus, particularly where proptosis dominates
- Teprotumumab is not routinely available in Australia - IV methylprednisolone remains the practical first-line here; tocilizumab and rituximab are second-line; orbital decompression for sight-threatening disease
- Wernicke: IV thiamine before glucose; botulism: antitoxin
Symptomatic relief of diplopia
C. Symptomatic relief of diplopia - while waiting for recovery
- Monocular occlusion or a patch (alternate eyes to avoid amblyopia in children)
- Fresnel prisms for small stable deviations
- Botulinum toxin to the antagonist (e.g. medial rectus in VI palsy) - prevents contracture and relieves diplopia during recovery
- Ptosis crutch or lid taping
Surgery - only once stable
D. Surgery - only once stable
- Wait >=6-12 months of stability before strabismus surgery (recession/resection, transposition)
- Ptosis surgery last, and only after ensuring corneal protection is adequate
- Ongoing: driving restriction while diplopia persists, falls prevention, occupational advice
Associations
- Diabetes and hypertension - microvascular III/IV/VI palsy
- Giant cell arteritis - ocular motor palsy as well as AION
- Multiple sclerosis - INO, especially bilateral, one-and-a-half syndrome
- Myasthenia gravis - thymoma, thyroid disease, other autoimmunity
- Graves disease - thyroid eye disease
- NF2 - bilateral vestibular schwannomas, multiple cranial neuropathies
- Nasopharyngeal carcinoma, skull-base metastasis, lymphoma, myeloma - multiple cranial nerves
- Pinealoma, hydrocephalus - Parinaud
- Mitochondrial disease - CPEO, Kearns-Sayre (+ retinitis pigmentosa + heart block)
- GBS/Miller Fisher, Wernicke, botulism, tetanus
- Cavernous sinus thrombosis - facial/sinus infection, hypercoagulability
Recovery
- Microvascular III, IV and VI palsies recover spontaneously - most begin improving within 4-6 weeks and resolve by 3 months
- No recovery by 3 months = image, whatever the risk factors
- Aberrant regeneration after a compressive or traumatic III palsy - lid elevates on adduction or downgaze, pupil constricts on adduction
- *Never occurs after a microvascular palsy* - its presence means a structural lesion
- Traumatic IV palsies often recover partially over 6-12 months; a proportion need surgery
- INO from MS often resolves; from infarct, less reliably
- Persistent diplopia -> loss of stereopsis, falls, inability to drive or work
- Untreated corneal exposure from ptosis or proptosis -> ulceration
- Untreated PCoM aneurysm -> subarachnoid haemorrhage; a painful III palsy is a warning event
- Ocular myasthenia: ~50% generalise, usually within 2 years - immunotherapy reduces this
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