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Facial nerve and the eye (CN VII)
Anatomy & Optics
Key Points
- •CN VII provides motor supply to orbicularis oculi (temporal + zygomatic branches) = eye closure; is the efferent limb of the corneal reflex (afferent: CN V1); carries parasympathetic fibres to the lacrimal gland (greater petrosal nerve → pterygopalatine ganglion)
- •Bell's phenomenon (globe rolls upward on attempted closure) is protective; present in ~90% of population; absent Bell's phenomenon in CN VII palsy = very high risk of exposure keratopathy
- •UMN vs LMN: UMN spares the forehead (bilateral cortical supply); LMN affects the entire ipsilateral face including forehead - key distinction for localising the lesion
- •CN VII course: labyrinthine (shortest/narrowest, greater petrosal nerve) → tympanic → mastoid (nerve to stapedius, chorda tympani) → stylomastoid foramen → 5 terminal branches (temporal, zygomatic, buccal, marginal mandibular, cervical)
- •Aberrant regeneration → crocodile tears (gustatory lacrimation: salivary parasympathetics misdirect to lacrimal gland) and synkinesis; never occurs in UMN lesions; treat with botulinum toxin
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Keep reading Facial nerve and the eye (CN VII)
17 more sections are included with the Clinical plan.
- Definition
- Epidemiology
- Aetiology and causes
- Pathogenesis
- Classification
- Risk factors and associations