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Purpose and principlesIndications, selection and cautionsMethod and interpretationClinical next stepsRisks, monitoring and follow-upSpecial situationsCommon pitfallsQuestionsSources
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Educational draft · awaiting clinical reviewThe full textbook explains uncertainty but does not replace live national or local guidance, specialist advice, or current prescribing information.

Cranial nerve examination

Neurology · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

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Time-critical presentation

Sudden visual loss, a painful pupil-involving third-nerve palsy, acute multiple cranial neuropathies, papilloedema with deteriorating neurology, new dysphagia or secretion failure, acute ophthalmoplegia with limb signs, or facial weakness within a possible stroke syndrome requires immediate senior neuro-ophthalmic, stroke, neurological, airway or imaging assessment.

Purpose and principles

Examine the afferent, efferent and brainstem functions of the cranial nerves systematically, then localise single and multiple deficits while recognising neuro-ophthalmic and bulbar emergencies.

Cranial-nerve examination samples sensory input, motor output and tightly packed brainstem pathways. It should be directed by symptoms: visual loss requires acuity, pupils, colour, fields and fundoscopy; diplopia requires alignment, movement and ptosis; facial symptoms require motor and sensory mapping; dysphonia and dysphagia require airway, voice, cough and swallow assessment. A rapid stroke screen does not replace this work when posterior-circulation or skull-base disease is possible.

Visual localisation begins by separating monocular from binocular dysfunction. Monocular loss generally lies anterior to the chiasm; bitemporal field loss suggests chiasmal disease; homonymous loss lies behind the chiasm on the contralateral side. A relative afferent pupillary defect reflects asymmetric retinal or optic-nerve input, not refractive error or a purely occipital lesion. Fundoscopy can reveal optic-disc swelling, pallor, retinal vascular disease or haemorrhage but competence and image quality must be stated.

Eye movement is controlled through supranuclear gaze systems, the third, fourth and sixth cranial nerves, neuromuscular junctions and extraocular muscles. Diplopia that disappears when either eye is covered is binocular and usually reflects misalignment; monocular diplopia often has an ocular optical cause. Internuclear ophthalmoplegia produces impaired adduction with abducting nystagmus and localises to the medial longitudinal fasciculus, whereas conjugate gaze deviation points to supranuclear or brainstem networks.

Lower cranial-nerve deficits can threaten airway and nutrition. A wet voice, weak voluntary cough, pooling secretions, recurrent choking or fatigable articulation deserves urgent swallow and respiratory review even if the palate appears symmetrical. Unilateral tongue wasting and deviation, palatal asymmetry or shoulder weakness should be integrated with long-tract signs, neck surgery, trauma, malignancy and multiple-nerve involvement rather than treated as isolated curiosities.

Key points

  • Start with observation of eyelid position, pupil size, eye alignment, facial symmetry, voice, articulation, secretion handling and spontaneous eye movements before following a numbered sequence.
  • Test visual acuity in each eye with habitual correction before interpreting colour, fields, pupils or fundi; a binocular result can hide severe unilateral impairment.
  • Confrontation fields localise pre-chiasmal, chiasmal and retrochiasmal dysfunction only as a screen. Repeat carefully and arrange formal perimetry or urgent imaging when the history and field defect require it.
  • Pupils are described by size, symmetry and direct and consensual responses in appropriate light. The swinging-flashlight test detects relative afferent dysfunction; it is not a test for unequal efferent pupils.
  • Assess ocular position, ptosis and movements in all cardinal directions, asking about diplopia and looking for nystagmus. Record the direction and separation of double images rather than labelling a nerve prematurely.
  • An isolated third-nerve palsy with a dilated or poorly reactive pupil, severe pain or incomplete pattern needs urgent aneurysm and compressive-lesion assessment through the local pathway.
  • For trigeminal function, compare facial sensation in the three divisions, assess muscles of mastication and use corneal reflexes only when clinically necessary and performed safely; corneal sensation is the afferent limb and facial closure the efferent limb.

Indications, selection and cautions

Optic-nerve dysfunctionRed flag

Monocular acuity or colour loss, a central field defect, relative afferent pupillary defect and disc swelling or later pallor suggests optic neuropathy. Pain on eye movement favours optic neuritis but is neither required nor specific.

Compressive third-nerve patternRed flag

Ptosis with the eye positioned down and out plus a dilated or poorly reactive pupil, particularly when painful or sudden, raises posterior communicating artery aneurysm or another compressive lesion and requires emergency imaging.

Internuclear ophthalmoplegia

Impaired adduction of one eye with nystagmus of the abducting fellow eye during horizontal gaze supports a medial longitudinal fasciculus lesion. Cause varies with age and context, including demyelination and brainstem ischaemia.

Peripheral facial palsy

Weak forehead elevation, eye closure and lower facial movement on one side supports a lower motor neurone facial pattern. Vesicles, ear disease, trauma, parotid mass, tick exposure and additional neurology argue against uncomplicated Bell's palsy.

Central facial weaknessRed flag

Predominantly contralateral lower facial weakness with relative forehead preservation, especially alongside arm weakness, aphasia or neglect, supports a supranuclear lesion and should trigger an acute stroke pathway when sudden.

Bulbar palsy patternRed flag

Dysarthria, dysphonia, nasal escape, impaired palate or tongue movement, weak cough and dysphagia suggest lower motor neurone, junctional or muscle dysfunction. Secretion difficulty or respiratory change makes it an airway emergency.

Method and interpretation

  1. 01
    Monocular acuity, colour and visual-field assessmentFirst step
    Why
    Quantify afferent visual dysfunction and determine whether the pattern is pre-chiasmal, chiasmal or retrochiasmal.
    Interpretation and limitations
    Record correction, chart and distance. Reduced red saturation is supportive but subjective; confrontation fields need formal confirmation unless an emergency pathway already mandates imaging.
  2. 02
    Pupillary examination and fundoscopy
    Why
    Assess afferent asymmetry, autonomic efferent function, optic discs and retina.
    Interpretation and limitations
    Anisocoria greater in light suggests impaired constriction, while greater difference in dark suggests impaired dilation. Drugs, ocular surgery and ambient light alter pupils; suspected papilloedema requires urgent expert confirmation in context.
  3. 03
    Cover testing and ocular-movement charting
    Why
    Separate tropia from phoria and document the gaze direction that provokes misalignment or nystagmus.
    Interpretation and limitations
    The pattern may localise a nerve, muscle, orbit, junction or brainstem. Variable ptosis and ophthalmoplegia suggest myasthenia, while pain, proptosis or optic loss points to orbital or compressive disease.
  4. 04
    CT and CT angiography of head or orbits
    Why
    Evaluate aneurysm, haemorrhage, fracture, orbital disease, cavernous-sinus pathology and time-critical stroke according to presentation.

Clinical next steps

01Painful ophthalmoplegiaExclude aneurysm and compressionFirst stepSudden diplopia or ptosis with ocular-motor deficit, pupillary abnormality, severe headache, orbital signs or additional neurology.+
  1. 1Perform ABCDE, glucose, acuity, pupils, fields, eye position and movements, face and limb examination; document onset, pain, trauma, anticoagulation, diabetes and vascular history.
  2. 2Discuss immediately with stroke, neurology, ophthalmology and neuroradiology according to local arrangements and obtain urgent vascular and structural imaging suited to aneurysm, stroke, cavernous sinus or orbital disease.
  3. 3DefinitiveDo not label the deficit microvascular solely because diabetes is present; monitor consciousness, pupils and emerging focal signs while definitive review proceeds.
02Acute visual deficitSeparate eye, optic nerve and retrochiasmal diseaseNew monocular loss, field defect, colour desaturation, afferent pupil defect or visual complaint within a neurological syndrome.

Risks, monitoring and follow-up

  • Repeat acuity, fields, pupils, ocular alignment and conscious level when visual or ocular-motor symptoms are acute or evolving.
  • In bulbar weakness, trend voice quality, secretion handling, cough, respiratory rate and locally approved respiratory-function measures rather than relying on gag reflex.
  • Photograph or diagram facial and ocular findings only with consent and secure clinical systems, recording time and treatment context.
  • Reassess eye protection in peripheral facial weakness because incomplete closure can injure the cornea even while motor recovery is awaited.
  • Track the emergence of additional cranial nerves or long-tract signs, which can relocate an apparently isolated lesion to brainstem, meninges or skull base.
  • Give explicit emergency advice for worsening vision, headache, anisocoria, dysphagia, breathlessness, new limb symptoms or reduced alertness.

Special situations

Afferent and efferent differ

An eye with severe optic-nerve dysfunction can still constrict consensually when light enters the healthy eye; the swinging-flashlight test compares input, not the mechanical ability of each pupil to constrict.

Forehead sparing is relative

Bilateral cortical innervation often preserves upper facial movement in supranuclear lesions, but bedside asymmetry and incomplete exceptions occur. Use accompanying limb and cortical signs rather than a rigid rule.

Fourth palsy is positional

Vertical diplopia that worsens on looking down and in, such as on stairs or reading, can suggest trochlear dysfunction; compensatory head tilt and old photographs may reveal chronicity.

Gag is an unreliable screen

Healthy people may lack a gag response, and an apparently present gag does not prove coordinated swallowing. Voice, cough, secretion handling and formal swallow assessment are more clinically useful.

Horner syndrome is a pathway

Miosis and mild ptosis can arise anywhere from hypothalamus to upper chest and carotid sympathetic fibres. New pain, trauma or focal neurology changes imaging urgency.

Diplopia must be classified

Binocular double vision resolves when either eye is covered and reflects misalignment; persistent monocular duplication usually points toward an ocular optical problem rather than an ocular-motor nerve palsy.

Common pitfalls

  1. 01

    Testing fields binocularly and missing a major monocular defect.

  2. 02

    Calling pupils normal without documenting anisocoria, light conditions or direct and consensual responses.

  3. 03

    Assuming every complete-looking third-nerve palsy in diabetes is benign microvascular disease.

  4. 04

    Using absence of gag to diagnose vagal palsy or presence of gag to clear oral intake.

  5. 05

    Diagnosing Bell's palsy without checking vesicles, ear and parotid findings or the rest of the neurological examination.

  6. 06

    Testing shoulder elevation without stabilising posture and accounting for pain.

  7. 07

    Treating several cranial neuropathies as unrelated instead of considering one skull-base, meningeal or brainstem lesion.

Practice

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NeurologyOriginal SBA

Painful third-nerve palsy

An adult develops sudden severe retro-orbital headache, complete left ptosis and a left eye positioned down and out. The left pupil is larger and reacts poorly to light. What is the most appropriate action?

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Sources and review status4 sources · checked 27 Aug 2026 · clinical review pending+
Sources

Sources and review status

National guidance is shown before implementation-dependent detail. Apply principles in context and verify current guidance when a decision affects care. Source check completed 27 Aug 2026; clinical approval remains outstanding.

  • NICE NG127 cranial neurological symptomsRecognition and referral guidance for facial weakness, diplopia, dizziness and other adult cranial presentations.
  • NICE NG128 stroke and TIA careAcute pathway for sudden visual, ocular-motor and brainstem deficits of possible vascular origin.
  • NICE NG232 head injury guidancePupillary, conscious-level and focal neurological assessment following trauma.
  • National Clinical Guideline for StrokeDetailed UK and Ireland standards for cranial and posterior-circulation stroke assessment.

Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

Authoring stateComplete draftClinical stateAwaiting reviewJurisdictionUnited Kingdom
  • Distinguish central facial weakness, often sparing forehead movement, from a peripheral pattern affecting upper and lower face, but recognise that symmetry, effort and occasional central exceptions limit a one-sign rule.
  • Hearing screens require occlusion and masking technique; sudden sensorineural hearing loss is an otological emergency and should not await a routine neurological clinic appointment.
  • Palatal movement, voice, cough, swallow and tongue assess bulbar function more safely than repeatedly provoking gag. Gag absence can be normal and does not establish swallowing safety.
  • Accessory-nerve testing must stabilise and observe the shoulder girdle because pain, rotator-cuff disease and poor positioning can mimic trapezius or sternocleidomastoid weakness.
  • Several ipsilateral cranial nerves together suggest a skull base, cavernous sinus, orbital apex, cerebellopontine angle or meningeal process; cranial-nerve plus contralateral body findings suggest brainstem localisation.
    • Cavernous sinus or orbital-apex pattern
    Red flag

    Painful ophthalmoplegia involving several ocular motor nerves with trigeminal V1 or V2 sensory change, proptosis, chemosis or optic dysfunction suggests a compact orbital-apex or cavernous-sinus process, including thrombosis, inflammation, aneurysm and tumour.

    Interpretation and limitations
    Imaging choice is syndrome-specific. A painful pupil-involving third palsy needs urgent arterial assessment; a non-contrast CT alone is not an adequate exclusion of every compressive or vascular lesion.
  • 05
    MRI brain, skull base and orbits
    Why
    Characterise optic pathways, brainstem, internal auditory canals, meninges, cavernous sinus and small structural lesions.
    Interpretation and limitations
    Coverage, contrast and thin-section sequences should be agreed with neuroradiology. Multiple neuropathies often need a broader anatomical protocol than an isolated nerve label implies.
  • 06
    Audiology and formal swallow assessment
    Why
    Quantify hearing loss and evaluate aspiration risk when bedside cranial findings are insufficient.
    Interpretation and limitations
    Bedside tuning-fork and cough tests are screens. Sudden sensorineural loss needs urgent ENT care, while instrumental swallowing studies are selected by speech and language therapy and the specialist team.
    • +
    1. 1Establish exact onset and monocular versus binocular perception, measure acuity in each eye, assess fields, pupils and fundi and look for headache, jaw symptoms, ocular pain and other focal deficits.
    2. 2Route sudden homonymous loss through stroke care, suspected giant-cell arteritis through same-day inflammatory and ophthalmic assessment, and retinal or optic emergencies to urgent eye services without waiting for routine review.
    3. 3Arrange formal fields, optical imaging, MRI or vascular tests under the receiving pathway and document driving and safety advice appropriate to the confirmed deficit.
    03Bulbar or multiple-nerve diseaseProtect airway and seek a unifying lesionDysphagia, weak voice or cough, secretion difficulty, tongue or palate weakness, or more than one cranial neuropathy.+
    1. 1Assess breathing, cough, voice, secretion control and ability to swallow, keep oral intake appropriate to risk and obtain urgent speech-and-language, neurological and critical-care input when physiology is threatened.
    2. 2Map every involved cranial nerve plus long-tract, cerebellar and limb signs; review fatigability, infection, malignancy, skull-base symptoms, surgery, trauma and toxins.
    3. 3Use targeted MRI, vascular imaging, CSF, antibody or neurophysiological testing under specialist direction while repeating airway and respiratory assessment during evolution.