Definition
An acute onset, idiopathic paralysis of seventh cranial nerve (CN VII). This is usually self limiting, and the exact aetiology is unclear but viral reactivation (particularly herpes simplex virus type 1) is a leading hypothesis. This is the most common cause of seventh cranial nerve palsy.
Anatomy/physiology
CN VII provides both motor and sensory function, including special sensory function.
Course of CN VII: originates from the ponto-medullary junction of the brainstem. CN VII runs intra- and extra-cranially. It travels through the internal acoustic meatus, through the temporal bone where it branches off to the greater petrosal nerve and travels through the stylomastoid foramen. At this point, CN VII becomes extracranial and travels though the parotid gland where it branches into five nerves, innervating the muscles of facial expression.
Pathophysiology:
The facial nerve innervates the muscles of facial expression and provides parasympathetic supply to the lacrimal glands. Inflammation of this nerve-typically within the facial canal-leads to compression, ischaemia, and subsequent dysfunction. The resultant facial muscle weakness impairs eyelid closure (lagophthalmos), tear film distribution, and blink reflex, predisposing the eye to desiccation and exposure-related complications.
Motor function – facial muscles (inc. orbicularis oculi), stapedius
Parasympathetic – lacrimal gland, submandibular + sublingual salivary glands.
Sensory function – anterior 2/3 of tongue
Who gets it?
- Males and females equally affected
- Peak age of incidence is 40 years old.
- Associated with pregnancy and diabetes
Differential Diagnoses:
Infections – Ramsay-Hunt syndrome, Guillian-Barre syndrome, Lyme disease, meningitis
Tumour – cerebellopontine angle lesions, parotid gland mass, acoustic neuroma
Trauma – iatrogenic following surgery
Signs/symptoms:
- Symptoms are worst at 48hrs and usually resolve by week 3.
- Brow ptosis
- Ectropion
- Lagophthalmos
- Epiphora
- Dry eyes
- Non-ophthalmic symptoms – Hyperacusis, difficulty speaking, decreased salivation, altered taste
Examination
History is key! A thorough history with a good systemic enquiry is required to isolate which part of CN VII has been affected.
Bell’s Palsy is a clinical diagnosis of exclusion. First, the other causes of a seventh nerve palsy must be investigated.
- Examine the face:
- Is it unilateral or bilateral palsy?
- Is the forehead affected? If not, stroke most be ruled out as upper motor neuron lesions are forehead sparing.
- Examine the eyelid position and check the motor function of orbicularis oculi – can it fully close?
- Check for lagophthalmos
- Corneal reflex
- Complete a full ophthalmic assessment – pupillary reflexes, ocular motility, visual acuity, fundoscopy.
- Test the other cranial nerves.
Investigations
Bell’s Palsy is a clinical diagnosis and when confirmed clinically no further investigations are required. However, if there is doubt regarding the diagnosis or upper motor neuron lesions, this warrants further investigation.
- CT/MRI – to assess for the presence of intracranial lesions or inflammatory changes
- Viral/bacterial serology + bloods
Management
- If presenting <48hrs, oral prednisolone (check your local guidelines).
- Early and proactive ocular care is essential to prevent sight-threatening complications. The approach should be individualised based on the severity of eyelid dysfunction.
- Corneal exposure management:
Conservative:
- Topical lubricants: Frequent instillation of preservative free lubricating eye drops with ointment at night time.
- Eyelid taping at night to prevent exposures.
Surgical if failed conservative management and no recovery:
- botulinum toxin injections to levator palpebrae superioris muscle to induce ptosis
- gold/platinum weights in the upper eyelid to assist with eye closure
- temporary tarsorrhaphy or permanent tarsoraphy. This involves partially sewing the upper and lower eyelids closed to protect the cornea.
Complications:
- Exposure keratopathy
- Hemifacial spasm
- Synkinesis – involuntary movements accompanied by voluntary facial movements.
References:
Curry L. The Facial Nerve (CN VII). TeachMeAnatomy [Internet]. Teachmeanatomy.info. 2024. Available from: https://teachmeanatomy.info/head/cranial-nerves/facial-nerve/ [Accessed 27 June 2025]
Clifford R, Yen MT, Lee BW, Thyparampil P, Burkat CN. Facial Nerve Palsy. EyeWiki [Internet]. 2025. Available from: https://eyewiki.org/Facial_Nerve_Palsy. [Accessed 27 June 2025]
Salmon JF. Eyelid: paralytic ectropion/facial nerve palsy. In: Kanski’s clinical ophthalmology: a systematic approach. 9th ed. Edinburgh: Elsevier; 2019. p82.
Denniston AKO, Murray PI. Neuro-ophthalmology: seventh nerve disorders. In: Oxford handbook of ophthalmology. 4th ed. Oxford: Oxford University Press; 2018. p790.792.
Written by Dr Aleena Thomas (FY1) and reviewed by Dr Bayan Shahin (ST7, Ophthalmology)
