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Cranial Nerve Examination — Step-by-Step

Bare minimum to always perform: Check fundi, visual fields, pupil size and reactivity, extraocular movements, and facial movements.

Examine CNs in numerical order, but group CN III, IV, VI together because of their shared function.

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CN I — Olfactory Nerve

• Often omitted unless inferior frontal lobe pathology is suspected (e.g., meningioma, anosmia post-head injury)
• Ask the patient to close their eyes
• Present a mild, familiar odorant (toothpaste, coffee) to each nostril separately
• Ask them to identify the smell
• Abnormal: Anosmia or hyposmia — unilateral suggests local pathology; bilateral suggests cribriform plate involvement or central cause

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CN II — Optic Nerve

• Use a Snellen chart with the patient's glasses/contacts in place
• Test each eye separately
• Abnormal: Reduced acuity → optic neuritis, compressive lesion, glaucoma

• Face the patient at ~0.6–1.0 m (2–3 ft)
• Place your hands at the periphery of your visual fields in the plane midway between you and the patient
• Instruct the patient to look at the centre of your face and indicate when they see finger movement
• Test all four quadrants (inferior then superior), bilaterally and simultaneously
• Abnormal patterns:
  • Monocular loss → ipsilateral optic nerve
  • Bitemporal hemianopia → optic chiasm (e.g., pituitary adenoma)
  • Homonymous hemianopia → contralateral optic tract/radiation

• Examine the optic disc: colour, size, margins, swelling/elevation (papilloedema)
• Examine the retinal vessels: calibre, AV nicking, haemorrhages, exudates

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CN III, IV, VI — Oculomotor, Trochlear, Abducens

• Note size, shape, and symmetry at rest (in room light and dim light)
• Test direct and consensual pupillary light reflex with a bright light
• Test accommodation: ask the patient to follow your finger as it approaches the bridge of the nose — look for miosis and convergence
• Abnormal findings:
  • Fixed dilated pupil → CN III compression (parasympathetic fibres on the outside are compressed first)
  • Pinpoint reactive pupils → pontine lesion (sympathetic tracts interrupted)
  • Afferent pupillary defect (RAPD/Marcus Gunn) → optic nerve lesion
  • Horner's syndrome (miosis + ptosis + anhidrosis) → sympathetic chain interruption

• Ask the patient to keep their head still and follow your fingertip
• Move the target in an H pattern covering all six cardinal directions of gaze
• Observe for: paresis, diplopia, nystagmus, or abnormal smooth pursuit (saccadic intrusions)
• Test horizontal nystagmus at 45° (not at extreme lateral gaze) — hold the target for ≥ a few seconds to detect latent nystagmus
• Ask whether the patient sees double in any direction — true diplopia resolves when one eye is covered
• Lesion patterns:
  • CN III palsy: "down and out" eye, ptosis, dilated unreactive pupil
  • CN IV palsy: failure of intorsion; vertical diplopia worse on down-gaze; head tilt to opposite side
  • CN VI palsy: failure of abduction; horizontal diplopia on ipsilateral gaze

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CN V — Trigeminal Nerve

• Test light touch and temperature (two modalities from different pathways) over the forehead (V1 — ophthalmic), cheek (V2 — maxillary), and jaw (V3 — mandibular) bilaterally
• A cotton wisp for light touch and a cool tuning fork for temperature are sufficient for screening
• Abnormal: Unilateral or divisional loss → cavernous sinus, skull base, trigeminal neuralgia, MS plaque

• Lightly touch the cornea with a wisp of cotton from the side (avoid the conjunctiva and air current)
• Normal response: bilateral blink (afferent = CN V, efferent = CN VII)
• Absent direct reflex: ipsilateral CN V or CN VII lesion

• Ask the patient to clench their teeth — palpate the masseters bilaterally
• Ask the patient to open their mouth against resistance
• Abnormal: Jaw deviates toward the weak side on opening (pterygoids); unilateral wasting of masseter

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CN VII — Facial Nerve

1. Observe for facial asymmetry at rest and with spontaneous expression
2. Ask the patient to:
   • Raise their eyebrows / wrinkle the forehead
   • Close their eyes tightly (try to open them) — Bell's phenomenon (upward eye roll) is normal
   • Show their teeth / smile
   • Puff out their cheeks (hold air in against resistance)
3. UMN vs. LMN:
   • UMN lesion (contralateral cerebral hemisphere): lower face weakness (nasolabial fold flattening, corner of mouth drooping), forehead spared (bilateral cortical representation)
   • LMN lesion (peripheral — e.g., Bell's palsy, parotid): entire ipsilateral face affected including forehead wrinkling and eye closure

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CN VIII — Vestibulocochlear Nerve

• Screen with a finger rub or whispered voice beside each ear while occluding the other
• Rinne test (512 Hz tuning fork): compare air conduction (fork beside ear) vs. bone conduction (fork on mastoid)
  • Air > Bone = Normal OR sensorineural loss
  • Bone > Air = Conductive loss (e.g., otosclerosis, effusion)
• Weber test (512 Hz fork on vertex): lateralises to the worse ear in conductive loss, better ear in sensorineural loss

• Observe for spontaneous nystagmus (direction, fixation suppression)
• Head impulse test (HIT/Halmagyi): rapidly turn the head 10–20° to one side — corrective saccade indicates peripheral hypofunction
• Dix-Hallpike manoeuvre: for BPPV

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CN IX & X — Glossopharyngeal & Vagus Nerves

1. Listen to the patient's voice — hoarseness or nasal quality suggests CN X palsy
2. Ask the patient to open their mouth and say "Aah"
   • Observe the soft palate: it should rise symmetrically in the midline
   • Uvular deviation: deviates away from the weak side (pulled toward the normal side)
3. Gag reflex (use only when clinically necessary — uncomfortable):
   • Touch the posterior pharyngeal wall with a spatula
   • Afferent = CN IX; Efferent = CN X
   • An absent gag has low clinical significance in isolation; compare both sides
4. Swallowing: ask about or observe for dysphagia/aspiration

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CN XI — Spinal Accessory Nerve

1. Trapezius: ask the patient to shrug their shoulders against your downward resistance — look and feel for asymmetry
2. SCM: ask the patient to turn their head to one side against resistance — the contralateral SCM contracts (CN XI innervates ipsilateral SCM but turns head contralaterally)
3. Abnormal: Ipsilateral shoulder drop, winging of scapula, weakness turning head away from lesion side

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CN XII — Hypoglossal Nerve

1. Ask the patient to open their mouth — inspect the tongue at rest for wasting or fasciculations (LMN lesion)
2. Ask the patient to protrude the tongue
   • Deviation = toward the weak/lesion side (the unopposed contralateral genioglossus pushes it that way)
3. Ask the patient to push the tongue into each cheek against your resistance

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Summary Table

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