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Cranial Nerve Examination: CN I–XII

Minimum screen: Check fundi, visual fields, pupil size and reactivity, extraocular movements, and facial movements. For a full exam, test all CNs in numerical order (grouping III, IV, VI together).

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CN I — Olfactory Nerve

• Ask the patient to close their eyes
• Occlude one nostril at a time
• Present a mild, non-irritating odorant — toothpaste, coffee, vanilla, or cloves
• Ask the patient to identify the smell (identification) and confirm they can detect it (detection)

• Anosmia — absent smell; unilateral anosmia suggests a focal lesion (frontal meningioma, trauma); bilateral anosmia suggests neurodegenerative disease or post-viral etiology
• Note: Ammonia tests CN V (trigeminal), not CN I — do not use it

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CN II — Optic Nerve

1. Visual Acuity

• Test each eye separately with best correction (glasses/contacts)
• Use a Snellen chart at 6 m (20 ft) or a near card at 35 cm
• Record as fraction (20/20, 20/200, etc.)

2. Visual Fields by Confrontation

• Sit ~0.6–1.0 m (2–3 ft) from the patient
• Patient fixes gaze on your nose
• Hold hands at the periphery of your visual field, equidistant between you and the patient
• Wiggle a finger in each quadrant (inferior then superior) — monocularly and simultaneously
• Binocular simultaneous testing screens for visual neglect; individual eye testing detects monocular defects
• Formal perimetry (Humphrey/Goldmann) if an abnormality is found

3. Fundoscopy

• Optic disc: color (pale = atrophy), margins (blurred = papilledema), cup-to-disc ratio
• Retinal vessels: arteriovenous nicking, caliber changes, hemorrhages, exudates
• Retina: pigmentary changes, emboli, macular appearance

4. Pupillary Light Reflex (afferent limb = CN II)

• Shine a bright light in each eye; assess for briskness of constriction
• Relative Afferent Pupillary Defect (RAPD / Marcus Gunn pupil): in the swinging flashlight test, the affected eye dilates when light swings to it, indicating optic nerve dysfunction on that side

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

Pupils

• Describe size, shape, symmetry (document in mm if possible)
• Direct reflex: light → same eye constricts (efferent = CN III)
• Consensual reflex: light → opposite eye constricts
• Accommodation reflex: ask patient to follow your finger as it moves toward their nose → convergence + miosis + lens thickening
• Anisocoria: if >1 mm difference and one pupil is larger with ptosis → CN III palsy (parasympathetic compression — compressive lesions affect outer fibers first); if smaller pupil with ptosis and anhidrosis → Horner syndrome

Extraocular Movements (EOM)

• Ask patient to keep head still and track your finger tip
• Move target in an H-pattern (horizontal, then diagonals)
• Test each direction: lateral (CN VI), medial (CN III), up-and-out (CN III superior rectus), down-and-out (CN III inferior rectus), up-and-in (CN III inferior oblique), down-and-in (CN IV superior oblique)
• Observe for: paresis (limitation), nystagmus, saccadic pursuit, diplopia (ask patient)
• True diplopia resolves on covering one eye
• Test for horizontal nystagmus at 45° lateral gaze (not extreme gaze); hold position for several seconds

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CN V — Trigeminal Nerve

Sensory Testing

• Test light touch (cotton wisp) and pinprick or temperature (cold tuning fork)
• Compare left vs. right and between divisions

Corneal Reflex

• Touch cornea (not conjunctiva) with a fine wisp of cotton or sterile saline
• Normal: bilateral brisk eye closure
• Afferent limb = CN V1; efferent limb = CN VII
• Absent reflex on stimulus side → CN V lesion; absent closure only on stimulus side → CN VII lesion

Motor

• Ask patient to clench jaw → palpate masseter and temporalis muscles for bulk and symmetry
• Ask patient to open mouth against resistance
• With a unilateral lesion, jaw deviates toward the weak (ipsilateral) side on opening

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CN VII — Facial Nerve

Motor Testing (Upper and Lower Face)

• Forehead wrinkling — raise eyebrows
• Eye closure — close eyes tightly (Bell's phenomenon: upward eye deviation is normal)
• Cheek puff — puff out both cheeks; press to check for air escape
• Smile / show teeth — assess symmetry
• Platysma — grimace, pull mouth corners downward

Taste

• Test anterior 2/3 of tongue on each side separately
• Apply sweet (sugar) or bitter (quinine) solution with cotton applicator
• Patient identifies while tongue is extended (to avoid spreading solution)

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CN VIII — Vestibulocochlear Nerve

Hearing (Cochlear Division)

• Screening: Rub fingers next to each ear, or whisper a number at 60 cm; test one ear at a time while the other is masked
• Rinne Test (512 Hz tuning fork):
  • Place vibrating fork on mastoid process (bone conduction) → when no longer heard, place beside the ear canal (air conduction)
  • Normal (Rinne positive): air conduction > bone conduction
  • Conductive hearing loss (Rinne negative): bone conduction > air conduction
  • Sensorineural loss: both diminished but air > bone maintained
• Weber Test:
  • Place vibrating fork on forehead midline
  • Normal: equal sound in both ears
  • Sound lateralizes to the worse ear → conductive loss on that side
  • Sound lateralizes to the better ear → sensorineural loss on the opposite side
• Formal audiometry if any abnormality detected

Vestibular Division

• Not routinely tested in standard exams
• In dizziness or coma: ice-water caloric stimulation (oculocephalic reflex), Dix-Hallpike maneuver

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CN IX — Glossopharyngeal Nerve

• Elicit the gag reflex by touching the posterior pharyngeal wall on each side separately with a tongue depressor or blunt probe
• Observe for symmetric response; may be absent in some normal individuals
• Taste on posterior 1/3 of tongue is rarely formally tested clinically

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CN X — Vagus Nerve

• Ask patient to say "aah" — observe soft palate and uvula
• Normal: both sides of palate elevate symmetrically; uvula remains midline
• Unilateral vagus lesion: palate drops on the affected side; uvula deviates away from the lesion (toward the normal side)
• Hoarseness or dysphonia → suggests recurrent laryngeal nerve damage (branch of CN X)
• Gag reflex efferent arc — brisk bilateral contraction of pharyngeal muscles

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CN XI — Spinal Accessory Nerve

• Trapezius (shoulder shrug): Ask patient to shrug both shoulders against downward resistance from your hands; compare sides for strength and bulk
• Sternocleidomastoid (head rotation): Ask patient to turn head to each side against your resisting hand placed on the cheek; the active muscle is contralateral to the direction of rotation (turning left = left SCM contracts on the side you resist)
• Inspect for muscle atrophy or asymmetry

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CN XII — Hypoglossal Nerve

• Inspect tongue at rest in the floor of the mouth: look for atrophy (hemiatrophy) and fasciculations (LMN lesion)
• Ask patient to protrude the tongue: midline is normal
• Tongue deviates toward the side of the lesion (LMN — the weak side cannot push)
• UMN lesion: tongue deviates away from the lesion (contralateral), no atrophy or fasciculations
• Test tongue strength: ask patient to press tongue against each inner cheek while you press from outside

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Summary Table

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• Harrison's Principles of Internal Medicine 22E (McGraw Hill, 2025) — CN Examination chapter
• Textbook of Family Medicine 9e — Cranial Nerve Examination
• Goldman-Cecil Medicine International Edition — Cranial Nerve & Coma Examination