Synopsis
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.
- 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.
- 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.
Key red flags
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.
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.
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.
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.
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.
Investigation priorities
Quantify afferent visual dysfunction and determine whether the pattern is pre-chiasmal, chiasmal or retrochiasmal.
Management branches
Sudden diplopia or ptosis with ocular-motor deficit, pupillary abnormality, severe headache, orbital signs or additional neurology.
- Perform ABCDE, glucose, acuity, pupils, fields, eye position and movements, face and limb examination; document onset, pain, trauma, anticoagulation, diabetes and vascular history.
- Discuss 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.
- Do not label the deficit microvascular solely because diabetes is present; monitor consciousness, pupils and emerging focal signs while definitive review proceeds.