Cranial nerve palsies, Bell palsy and diplopia

• A cranial nerve palsy is a clinical diagnosis: a nerve supplying a muscle or sense organ has failed. The pattern of weakness tells you which nerve, and usually whether the lesion is central or peripheral.
• The seventh nerve (facial) palsy of Bell palsy is a lower motor neuron palsy of the whole ipsilateral face; a stroke affecting upper motor neurons spares the forehead because the upper face has bilateral cortical supply.
• Third, fourth and sixth nerve palsies produce diplopia. The main patterns are: third nerve palsy gives "down and out" eye with ptosis and (often) a dilated pupil; fourth nerve palsy gives oblique double vision worst on looking down; sixth nerve palsy gives horizontal double vision with the eye turned in.
• Bell palsy is treated with oral steroids started within 72 hours of onset; antiviral drugs alone do not help and are an optional add-on only in severe disease or when a viral cause is strongly suspected.
• Diplopia is binocular unless covering one eye makes it disappear; monocular diplopia is usually optical and rarely dangerous, while acute binocular diplopia with pupil involvement or headache can be an aneurysm until proven otherwise.

By the end of this page you should be able to:

1. Separate an upper motor neuron facial weakness from a lower motor neuron facial weakness, and from Bell palsy.
2. Name the presentations of third, fourth and sixth nerve palsies and give the urgent cause that must be excluded for each.
3. Interpret binocular diplopia from the history and bedside eye-movement tests.
4. Plan investigation and management of Bell palsy, and say when Ramsay Hunt is more likely.
5. Recognise papilloedema and optic neuritis, and know the red flags that convert diplopia or facial weakness into emergencies.
6. Explain the evidence behind steroids in Bell palsy, including what the AAN Bell palsy guideline concluded about antivirals.

Cranial nerve palsies, Bell palsy and diplopia belong together because they are the common clinical language of the head and neck. A patient complains of a dropped eyelid, a crooked smile, or two images; the job of the clinician is to turn that symptom into a nerve, a site of lesion, and a cause. Most are benign and self-limiting, but a few are emergencies, and the serious ones can look identical at first glance. This page covers the lower motor neuron facial palsy of Bell palsy (including its distinction from stroke), the vesicular facial palsy of Ramsay Hunt syndrome, the third, fourth and sixth nerve palsies that produce diplopia, the bedside approach to diplopia, and the two neuro-ophthalmological masqueraders that any clinician meeting diplopia or a red eye must recognise: optic neuritis and papilloedema. It also summarises the guideline positions on Bell palsy treatment: the AAN Bell palsy guideline (Gronseth 2012), the AAO clinical practice guideline on Bell palsy (Baugh 2013), the Cochrane review conclusions reproduced in later analyses, and the position of NICE CKS. ^[5]

A cranial nerve palsy is weakness of a muscle, or loss of a sensation, caused by failure of its cranial nerve. For motor nerves the first question is whether the lesion is upper motor neuron (UMN) or lower motor neuron (LMN).

• UMN (central) lesions interrupt the pathway from cortex to brainstem. The facial nucleus that supplies the upper face receives input from both cerebral hemispheres, so a one-sided UMN lesion spares the forehead and often allows the patient to wrinkle it. The lower face is weak on the opposite side.
• LMN (peripheral) lesions interrupt the nerve itself after it has left the nucleus. Every muscle on that side is weak, including forehead wrinkling and eye closure; there is no central recovery until the nerve repairs.

Bell palsy is an acute, idiopathic, peripheral (LMN) facial nerve palsy; it is diagnosed only once other causes have been excluded. Ramsay Hunt syndrome is a peripheral facial palsy caused by reactivation of varicella-zoster virus in the geniculate ganglion, classically with vesicles in the ear. Diplopia is the perception of two images of one object; it is usually binocular, alternating on covering either eye, and arises from misalignment of the visual axes. Optic neuritis is inflammation of the optic nerve. Papilloedema is swelling of the optic disc produced by raised intracranial pressure.

Cranial nerve palsies are common but the numbers come from different kinds of study, so ranges rather than single figures are honest.

• Bell palsy itself has an annual incidence of about 20 to 30 cases per 100,000 people, and it is the commonest form of peripheral facial palsy, accounting for roughly 51% of cases in hospital series. The seventh cranial nerve is also the most commonly paralysed cranial nerve overall. ^{[1] [5]}
• Facial palsy of any cause has an incidence of about 20 to 30 cases per 100,000 per year, and Bell palsy represents 38% to 66% of those cases in large series. ^[5]
• Varicella-zoster virus accounts for 4% to 12% of peripheral facial palsy cases; it is the main differential diagnosis of Bell palsy. ^[5]
• Bell palsy is 3.3 times more frequent during pregnancy than outside it. ^[1]
• Optic neuritis most often affects young adults (roughly 20 to 45 years), although it can occur at any age. ^[4]
• Diplopia is a common symptom: in the United States it is the chief complaint in about 850,000 medical consultations per year, and about 16% of those patients have a potentially life-threatening underlying cause. ^[3]
• In adults aged 60 years and over, vascular causes are the commonest explanation for a cranial nerve palsy. ^[3]
• Most patients with Bell palsy recover well: approximately 71% achieve complete recovery and about 84% near-normal recovery without treatment, but roughly 15% to 20% have incomplete recovery. ^[1]

Bell palsy. The cause is not proved but most authorities accept a viral and inflammatory mechanism: reactivation of herpes simplex virus type 1 in the geniculate ganglion, with inflammation, oedema and compression inside the facial canal. Risk factors include diabetes, hypertension, pregnancy (late pregnancy and the early postpartum period especially), upper respiratory infection, and cold exposure. A family history is uncommon.

Ramsay Hunt syndrome. Reactivation of varicella-zoster virus in the geniculate ganglion; an identical syndrome without the rash is called zoster sine herpete. ^[5] Vesicles may appear before, with, or after the paralysis, and can be hidden in the ear canal or mouth, so the diagnosis is easily missed.

Third, fourth and sixth nerve palsies. Causes are diverse: microvascular (diabetes, hypertension, older age), inflammatory and demyelinating disease, trauma, raised intracranial pressure (especially sixth nerve), infections (including meningitis), aneurysm and neoplasm at the skull base, and cavernous sinus or orbital disease. A sixth nerve palsy developing within a single day is usually vascular if trauma is excluded. ^[3]

Optic neuritis. Most cases are demyelinating and form part of the multiple sclerosis, neuromyelitis optica spectrum disorder (NMOSD) or MOG antibody-associated disease (MOGAD) spectrum. Less common causes are infection (syphilis, tuberculosis, borreliosis, Bartonella, toxoplasmosis, viruses such as varicella-zoster, HIV and West Nile virus), systemic autoimmune disease (sarcoidosis, systemic lupus, Sjogren), paraneoplastic disease, toxins and nutritional deficiency. ^[4]

Papilloedema. The cause is raised intracranial pressure, which can be due to a space-occupying lesion, hydrocephalus, cerebral venous sinus thrombosis, malignant hypertension, medications, or idiopathic intracranial hypertension.

Facial nerve paralysis follows damage inside the facial canal. Inflammation and oedema raise pressure around the nerve; ischaemia and axonal interruption follow, and Wallerian degeneration is largely complete within about 2 to 14 days. That time window is the reason treatment must be started early: steroids reduce oedema and protect the remaining fibres. The blood supply of the facial nerve is segmental, and the most vulnerable segment is the meatal portion in the internal auditory canal. ^[1]

The third cranial nerve is a mixed nerve. Its somatic motor fibres supply the levator palpebrae and all the extraocular muscles except the lateral rectus and superior oblique; its parasympathetic fibres run superficially and supply the sphincter pupillae and ciliary muscle. Compression on the outside of the nerve (as by an aneurysm or uncal herniation) therefore affects the pupil first, whereas microvascular ischaemia tends to spare it. The fourth nerve is the only cranial nerve to leave the brainstem dorsally and it supplies the superior oblique; it is the nerve most often damaged by minor head trauma, sometimes with a delay of days. The sixth nerve has the longest intracranial course of the three and so is the most vulnerable to stretch, traction and raised intracranial pressure (as a false localising sign).

Diplopia itself is simply the brain failing to fuse two images. Fusion requires symmetrical input from both eyes; any misalignment of the visual axes, at any level from cornea to cortex, produces it. The pattern of misalignment (horizontal, vertical, torsional) and its dependence on gaze direction are what allow bedside localisation.

Optic neuritis is inflammation of the optic nerve; in the demyelinating forms immune-mediated attack strips myelin and can interrupt axonal conduction. Pain on eye movement reflects tension on the inflamed nerve sheath. Papilloedema is axoplasmic stasis: raised pressure in the subarachnoid space around the optic nerve impairs slow axonal transport at the lamina cribrosa, producing swelling of the disc and, if prolonged, pallor and visual field loss.

Bell palsy is acute and painless (or only slightly painful) in onset, reaching its maximum within 72 hours. The patient wakes with a lopsided face: the corner of the mouth droops, liquids spill, the eye will not close, and the forehead is smooth on that side. Taste may be lost over the anterior two-thirds of the tongue, sounds may seem louder (hyperacusis), and lacrimation may be reduced or paradoxically increased. Retroauricular ache is common. The palate and pharynx are spared, because the facial nerve has already exited the brainstem.

Ramsay Hunt is usually more painful. Look for vesicles on the pinna, in the external auditory canal or on the tongue and palate. Hearing loss, tinnitus and vertigo point to eighth-nerve involvement; dysphagia, dysarthria or sensory loss on the face suggest involvement of the trigeminal, glossopharyngeal or vagus nerve. This wider neurological picture is called polyneuropathy. Zoster sine herpete presents as Bell palsy with severe pain and no rash.

House-Brackmann grading is the standard bedside severity score, from grade I (normal) to grade VI (no movement). It is useful for follow-up and for research comparisons.

Third (oculomotor) nerve palsy. Complete external palsy gives ptosis of the upper lid, a "down and out" position of the eye (unopposed action of the lateral rectus and superior oblique), and an inability to elevate, depress or adduct the eye. An internal palsy gives mydriasis, anisocoria that is worse in bright light, and loss of accommodation. Combined (complete) palsy gives all of these.

Fourth (trochlear) nerve palsy. The only muscle affected is the superior oblique, so vertical misalignment is small and oblique. Diplopia is worst on looking down (reading, stairs) and is made better by tilting the head to the opposite shoulder; there is often a compensatory head tilt.

Sixth (abducens) nerve palsy. Abduction is impaired and the eye is esotropic; diplopia is horizontal and worse on looking towards the affected side. The patient turns the head towards the affected eye to avoid using abduction.

The single most important question is monocular or binocular. Monocular diplopia persists when the other eye is covered and is usually due to a problem of refraction or media in one eye (cornea, lens, tear film) or to a functional visual disturbance; it is not usually life-threatening. Binocular diplopia disappears on covering either eye and means the two eyes are not pointing at the same target.

In binocular diplopia the next questions are: horizontal or vertical; worse at distance or near; constant or varying; affected by direction of gaze; and accompanied by pain, headache, neurological symptoms, ptosis or nystagmus. Pain with eye movement suggests optic neuritis; a temporal course over minutes to hours suggests ischaemia; headache with a dilated pupil is an emergency. Compensatory head posture points to a fourth or sixth nerve palsy.

Acute or subacute visual loss, peaking over 7 to 10 days, in one or both eyes, with periocular pain that is worse on eye movement, impaired colour vision, a central or cecocentral scotoma, and (in unilateral disease) a relative afferent pupillary defect on the swinging flashlight test. The optic disc may be swollen (papillitis) or entirely normal (retrobulbar neuritis). Slit-lamp examination excludes anterior uveitis and vitritis. Onset in childhood or in patients over 70, painless or progressive loss, arcuate or altitudinal fields, or sectoral disc swelling are atypical and should prompt a search for another diagnosis. ^[4]

Bilateral swelling of the optic discs, usually fairly symmetric, with blurred margins, elevation and peripapillary haemorrhages or (in chronic cases) cotton-wool spots and exudates. Patients often have headache, transient visual obscurations (greying-out on bending or straining) and tinnitus. Enlargement of the blind spot is the characteristic field defect. Papilloedema is not, by itself, a cause of visual loss in its early stages, but acuity falls once secondary optic atrophy develops. Because it is caused by raised intracranial pressure, it must be investigated rather than treated as an isolated eye problem.

The first distinction is central versus peripheral, set out in the table above. Once a peripheral facial palsy is identified, the differential includes Bell palsy, Ramsay Hunt, otitis media or mastoiditis, Lyme disease in endemic areas, sarcoidosis, neoplasm involving the parotid or skull base, fracture of the temporal bone, and (in the neonate or young child) birth or congenital causes. A slowly progressive course of more than three weeks, complete absence of recovery by three months, weakness that is atypical or polyneuropathic, or recurrence all argue against simple Bell palsy and need imaging and specialist follow-up.

The main distinction is peripheral versus nuclear, fascicular or supranuclear. Nuclear and fascicular lesions in the brainstem carry other neurological signs. Supranuclear lesions (internuclear ophthalmoplegia, skew deviation, cerebellar disorders) produce patterns such as impaired adduction with preserved convergence, vertical misalignment with head tilt and torsion, or horizontal diplopia on distant gaze in later life. Examiners who are not ophthalmologists can distinguish vascular microangiopathic palsies from aneurysm largely by the pupil: a dilated, poorly reactive pupil with an acute third nerve palsy is an aneurysm of the posterior communicating artery until proved otherwise. Isolated trochlear palsy in an older adult is often microvascular; in a young person after even mild head injury it is traumatic; bilateral fourth nerve palsies suggest skull-base or cavernous sinus disease or trauma.

The systematic list, from eye to brain, is: monocular causes (refractive or media); myogenic and orbital causes (thyroid eye disease, myositis, myasthenia gravis, chronic progressive external ophthalmoplegia, orbital fracture or mass, sagging eye syndrome in older adults); heterophoria (latent strabismus unmasked by fatigue); childhood strabismus that has decompensated; cranial nerve palsies of the third, fourth and sixth nerves; nuclear and fascicular lesions; supranuclear lesions and internuclear ophthalmoplegia; and cerebellar disease. The relative frequencies given in a large review are approximately: decompensated latent strabismus about 40%, cranial nerve palsies about 30%, orbital disease (mainly thyroid eye disease) about 15%, and brainstem or cerebellar disease about 10%. ^[3]

The important mimics of optic neuritis are papilloedema, non-arteritic anterior ischaemic optic neuropathy (NAION), Leber hereditary optic neuropathy, compressive optic neuropathy, toxic or nutritional optic neuropathy, and functional visual loss. The table from the Indian consensus compares them directly; papilloedema is distinguished by bilateral disc swelling, generally symmetric, gradual and painless onset, an enlarged blind spot, signs of raised intracranial pressure, and imaging showing no optic nerve enhancement with lumbar puncture opening pressure that is high.

In a typical Bell palsy no investigation is needed; the diagnosis is clinical. Atypical or progressive features, bilateral disease, recurrent disease, failure to improve after 3 months, other cranial nerve involvement, or a parotid or temporal bone mass on examination all need gadolinium-enhanced MRI of the brain and skull base, and possibly cerebrospinal fluid examination. Serology for Lyme disease is added where it is endemic. Electrophysiological tests (electroneurography) are used in some centres to quantify degeneration and to guide decisions about surgical decompression, but their timing and thresholds are not standardised.

Every patient with an acute third nerve palsy needs brain imaging, because a pupil-involving palsy is an aneurysm until proved otherwise. Magnetic resonance imaging with MR angiography or CT angiography follows, urgently when headache is present; lumbar puncture is added if subarachnoid haemorrhage is suspected and imaging is negative. For fourth and sixth nerve palsies, MRI is indicated when there is no clear microvascular cause, when there is pain, when the palsy is multiple or progressive, or when the patient is young. An abducens palsy that is thought to be a false localising sign needs investigation for raised intracranial pressure. Vascular risk factors are screened for in microvascular palsies.

History leads; the examination narrows; imaging and lumbar puncture follow the working diagnosis rather than being requested as a blanket. All diplopic patients need directed eye and neurological examination, visual acuity, Hess or Lees charting where available, and dilated fundus examination. Brain and orbit MRI (usually with contrast), CT when fracture or bone is suspected, blood tests, and lumbar puncture for cerebrospinal fluid are used when the working diagnosis points to inflammatory, neoplastic or raised-pressure disease.

The diagnosis is clinical, but confirmation and subtyping need:

• Contrast-enhanced MRI of the brain and orbits (multiple sclerosis protocol, at least 1.5 Tesla), which is the gold standard. It confirms optic nerve enhancement and looks for brain lesions that classify the disease (periventricular ovoid lesions for MS; chiasmal or optic tract involvement for NMOSD; perineural sheath enhancement for MOGAD). ^[4]
• Cell-based antibody testing for aquaporin-4 and MOG antibodies in all patients.
• Autoimmune screening (antinuclear antibody, ANCA, ENA) when systemic disease is suspected.
• Infectious screening (syphilis, tuberculosis, Lyme, HIV) when the history or geography suggests it.
• Automated visual fields (24-2 or 30-2) and optical coherence tomography for documentation and follow-up.
• Lumbar puncture for oligoclonal bands in selected cases.

In settings where imaging is not available, the consensus is that empirical high-dose steroid treatment should not be given; the patient should be referred to a centre that can image.

Immediate MRI of the brain with gadolinium followed by MR venography to exclude a mass, hydrocephalus or venous sinus thrombosis. If imaging is normal, lumbar puncture measures the opening pressure and examines cerebrospinal fluid; a high opening pressure with normal fluid and normal imaging supports idiopathic intracranial hypertension. Visual fields (automated perimetry) track any loss, and optical coherence tomography of the peripapillary nerve fibre layer and macular ganglion cell complex are useful adjuncts.

There is no single diagnostic criterion for a cranial nerve palsy; the diagnosis is a pattern recognised from history and examination, sometimes confirmed by imaging. Severity is scored with the House-Brackmann scale for facial palsy (grade I normal to grade VI no movement). For optic neuritis, diagnostic classification rests on MRI and antibody status as above. Bell palsy is idiopathic by definition; if an aetiology is found, the palsy is re-labelled. Diplopia is diagnosed by the bedside tests summarised in the Lagrèze review, and papilloedema by its fundus appearance plus raised intracranial pressure on investigation.

Oral corticosteroids are the standard of care. The commonly used regimen is prednisolone 60 mg once daily for 5 days, then reducing by 10 mg each day for the remaining 5 days; alternatively prednisolone 50 mg once daily for 10 days. ^[1] The evidence base is the Cochrane review of corticosteroids for Bell palsy, and the AAN Bell palsy guideline (Gronseth 2012) concluded that oral steroids are the one medication a clinician should feel obliged to offer. ^[2] Treatment should start as soon as possible, ideally within 72 hours of onset; the AAO clinical practice guideline on Bell palsy (2013) makes a strong recommendation to prescribe oral steroids within 72 hours for patients aged 16 years and over. ^[1] NICE CKS also provides UK primary care guidance on Bell palsy; readers in the UK should follow the current CKS topic alongside the AAN and AAO recommendations summarised here. In the analysis summarised by Kim and Kwak, steroid treatment increases the rate of complete recovery from about 71% to about 88%. ^[1]

Antiviral drugs (acyclovir, valaciclovir or famciclovir) as monotherapy are not recommended; they are ineffective and should not be prescribed alone. Combination therapy is a different matter: AAO 2013 says clinicians may offer an oral antiviral in addition to oral steroids within 72 hours, and the AAN guideline and the Canadian 2014 guideline suggest addition in severe or complete paralysis. Valaciclovir is usually dosed at 1000 mg three times daily for 7 days, and aciclovir at 800 mg five times daily, with other regimens listed in published tables. ^[1] The benefit is small: the Gronseth 2012 analysis put the risk difference of antivirals added to steroids at zero, with a 95% confidence interval from minus 8% to plus 7%. ^[2] The decision should be made with the patient. Antivirals are more strongly indicated when the palsy is severe or painful, or when zoster sine herpete or Ramsay Hunt is suspected.

Steroids carry the usual cautions: diabetes, peptic ulcer disease, uncontrolled hypertension, renal or liver disease, glaucoma, pregnancy (especially the first trimester) and psychiatric illness. Short courses of 10 days are generally safe; gastric protection with an H2 blocker is commonly recommended. In pregnancy the recovery rate is lower (about 52% compared with 77% to 88% in non-pregnant patients), and prescribing should be discussed with the obstetric team. ^[1] In children a dose of about 1 mg/kg/day prednisolone for 7 to 10 days with tapering is commonly used, although the optimal dose is not established. ^[1]

Eye care is not optional: the cornea is exposed when the orbicularis is weak, and keratitis and ulceration can follow. Prescribe daytime lubricating drops, ointment at night, and a shield or taping if the eye will not close fully; tarsorrhaphy may be needed. Facial physiotherapy and neuromuscular retraining are used during recovery but high-quality evidence of benefit is mixed. Decompressive surgery of the facial nerve is not routine; it is reserved for selected cases in specialist centres.

Combine an antiviral with a systemic corticosteroid and start as soon as possible, ideally within 72 hours of onset. Intratympanic steroid as an adjunct has been reviewed but evidence is limited. Because of involvement of multiple cranial nerves and brainstem nuclei in some patients, consider admission for IV therapy where feasible. The prognosis is worse than Bell palsy: even with treatment complete recovery is less likely, and hearing loss present with the palsy can persist.

Management addresses both the palsy and its cause:

• Microvascular palsies improve spontaneously over 3 to 6 months; control blood pressure, glucose and lipids.
• Prism glasses, temporary occlusion or Bangerter foils control diplopia in the acute phase.
• Strabismus surgery is considered only when the angle has been stable for at least 6 months, because spontaneous recovery is common.
• Fourth nerve palsy after even minor trauma often recovers; surgery is reserved for persistent diplopia.
• Sixth nerve palsy from a compressive or inflammatory cause is treated at its source.
• Any palsy with pupil involvement, pain, or multiple cranial nerves needs urgent investigation and, for aneurysm, transfer to a centre that can clip or coil.

Intravenous methylprednisolone 1 g daily for 5 days, given as a single dose or in divided doses and infused slowly over 30 to 45 minutes, is the standard acute treatment of adult optic neuritis. ^[4] In children the dose is 30 mg/kg/day. ^[4] Intravenous steroids hasten recovery; they do not, in the typical MS-related case, alter the final visual outcome. Oral corticosteroids alone at standard doses are strongly discouraged because of an increased risk of relapse. In NMOSD and MOGAD a prolonged oral steroid taper after intravenous therapy reduces relapse. In seropositive disease which does not respond, plasma exchange or intravenous immunoglobulin should be considered early. Infectious causes are treated with the relevant antimicrobial, and systemic autoimmune causes require disease-specific long-term treatment. Follow-up is at 1 week, 1 month, 3 months, 6 months and 1 year, with visual fields, colour vision, contrast sensitivity and (optionally) optical coherence tomography at 3 months.

Treat the underlying cause. Where imaging is normal and pressure is high (idiopathic intracranial hypertension), measures include weight reduction, diuretics and (where a focal venous sinus stenosis is found) venous sinus stenting; therapeutic lumbar puncture gives temporary relief. In all cases ophthalmology and, where needed, neurosurgery share care. Optic nerve sheath fenestration or shunting is reserved for patients with progressive visual loss despite medical treatment.

• Bell palsy: lagophthalmos, exposure keratopathy, corneal ulcer, incomplete recovery, synkinesis (crocodile tears, hemifacial spasm), contracture of the facial muscles, taste disturbance.
• Ramsay Hunt: persistent facial weakness, permanent sensorineural hearing loss, chronic tinnitus and vertigo, persistent pain, post-herpetic neuralgia.
• Third, fourth and sixth nerve palsy: amblyopia in children if not corrected, diplopia, abnormal head posture, and (for third nerve) dry eye and ptosis.
• Diplopia of central cause: stroke, intracranial mass, cavernous sinus thrombosis.
• Optic neuritis: optic atrophy with irreversible visual field loss, relapse, and an early manifestation of multiple sclerosis, NMOSD or MOGAD.
• Papilloedema: optic atrophy, permanent visual field constriction, visual loss.

Bell palsy: roughly 71% complete recovery and 84% near-normal recovery without treatment, and better with steroid. Recovery of severe paresis is less predictable. Ramsay Hunt: prognosis is worse than Bell palsy and worse still when treatment is delayed beyond 72 hours; only about 20% of untreated patients achieve complete recovery, and over 80% of those treated within 72 hours reach House-Brackmann grades I or II. ^[5]

Microvascular palsies often improve spontaneously, and surgery on the eye muscles is considered only after at least 6 months because spontaneous recovery is common. ^[3] Fourth and sixth palsies after trauma may take longer. Optic neuritis associated with multiple sclerosis generally has a favourable visual prognosis, with about 72% of patients retaining visual acuity of 20/40 or better at 15 years. ^[4] NMOSD carries the poorest visual prognosis because of severe axonal injury, and MOGAD commonly relapses despite good initial response to steroids. Papilloedema carries a good visual prognosis if treated early; years of untreated raised pressure end in optic atrophy.

There is no primary prevention of Bell palsy. Control of vascular risk factors (blood pressure, diabetes, lipids) lowers the risk of microvascular cranial nerve palsies and stroke, which is the commonest masquerade. Varicella vaccination reduces zoster and hence Ramsay Hunt in the long term. In Carney complex and similar syndromes (relevant mainly to other cardiac tumours, not here) screening is by family history. For optic neuritis, there is no screening; for papilloedema, patients with headaches plus obesity or visual symptoms need examination of the fundi.

Children. Bell palsy occurs in children and they tend to recover better than adults. The evidence for steroids in children is mixed because of high spontaneous recovery rates; some authors still recommend prednisolone 1 mg/kg/day for 7 to 10 days with tapering. Ramsay Hunt is uncommon but should be considered with vesicles. Optic neuritis in a child is more often bilateral and post-infectious; NMOSD and MOGAD are relatively more common in paediatric cases.

Pregnancy. Bell palsy is more common (3.3 times) in late pregnancy and the puerperium. Oral steroids should be used cautiously, especially in the first trimester, and recovery rates are lower. Decisions should be shared with the obstetric team. Optic neuritis in pregnancy: intravenous methylprednisolone remains the standard acute treatment; contrast imaging is often avoided.

Older adults. Microvascular third, fourth and sixth nerve palsies are common. The threshold for brain imaging is lower when there is atypia. Cerebrovascular and neoplastic causes must be excluded.

Immunocompromised patients. Ramsay Hunt is more severe, and antiviral doses and duration are longer; infectious and neoplastic causes of palsy are more frequent.

• A fundus examination with a direct ophthalmoscope and a visual acuity check distinguish papilloedema from optic neuritis and prove raised intracranial pressure on the spot.
• Facial palsy is mostly clinical. Bedside tests for diplopia (cover test in nine positions, pupil, head posture) cost nothing.
• Prednisolone tablets, aciclovir and artificial tears are cheap and widely available; start steroids early, protect the eye, and refer for imaging only when red flags exist.
• If MRI and CT are unavailable, a structured clinical approach, including fundoscopy and simple charting of diplopia, separates most urgent cases; ultrasound of the orbit can sometimes image a third nerve aneurysm if formal vascular imaging is absent.
• Optic neuritis should be referred when imaging or antibody testing is not locally available; do not give empirical high-dose steroids without imaging where at all possible.
• In many hospitals the eye-care component of facial palsy (taping the lid at night, lubricants) is the single most important intervention for preventing permanent corneal damage.

• Classify facial weakness first: forehead spared means upper motor neuron and therefore stroke until proved otherwise.
• Bell palsy is a peripheral, idiopathic facial palsy; recoveries are good, and oral steroids within 72 hours improve them.
• Antiviral monotherapy for Bell palsy does not work; combination with steroids is an option for severe disease or when a viral cause is likely.
• Ramsay Hunt (varicella-zoster) is the main masquerade; treat it with combined antiviral plus steroid within 72 hours.
• Third nerve palsy with a dilated pupil is an aneurysm until excluded; an acute third nerve palsy plus severe headache is an emergency.
• Fourth nerve palsy causes oblique diplopia worst on downgaze; sixth nerve palsy causes horizontal diplopia.
• Diplopia: monocular if it survives covering one eye, binocular if not. Binocular diplopia is peripheral cranial nerve, orbital or central in origin.
• About 30% of diplopia is due to cranial nerve palsy, about 40% to decompensated latent strabismus, and about 16% of diplopia presentations are potentially life-threatening.
• Optic neuritis: pain on eye movement, colour desaturation, central scotoma, relative afferent pupillary defect; treat with intravenous methylprednisolone 1 g daily for 5 days; do not use oral steroids alone.
• Papilloedema is disc swelling from raised intracranial pressure; investigate, never treat as an isolated eye problem.
• Common mimics of optic neuritis include papilloedema, ischaemic optic neuropathy and compressive neuropathy; atypical features must prompt re-investigation.

Acute stroke and transient ischaemic attack; multiple sclerosis; idiopathic intracranial hypertension; orbital disease and thyroid eye disease; myasthenia gravis; optic neuritis and visual pathway disease; headache; temporal bone and parotid tumours. (Links to other MedGrasp topics are listed in plain text only.)