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Examination of the Cranial Nerves

Bare minimum screen: Check the fundi, visual fields, pupil size and reactivity, extraocular movements, and facial movements. CNs are best examined in numerical order, except grouping CN III, IV, and VI together due to shared function.

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CN I — Olfactory Nerve

• Testing is often omitted unless inferior frontal lobe disease (e.g., meningioma) is suspected.
• With eyes closed, ask the patient to sniff a mild, familiar odorant (toothpaste or coffee) and identify it.
• Test each nostril separately.

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CN II — Optic Nerve

• If a field defect is found on screening, test each eye individually and use focal perimetry or a tangent screen for full mapping.

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

• Describe size, shape, and equality at rest.
• Test direct and consensual light reflex.
• Test accommodation: ask patient to follow your finger moving toward the bridge of the nose — pupils should constrict (accommodation reflex).

• Ask patient to hold head still and track fingertip in the H-pattern (horizontal and vertical planes).
• Note any paresis, nystagmus, or saccadic pursuit.
• Horizontal nystagmus is best assessed at 45° lateral gaze (not extreme gaze) and held for several seconds.
• Ask about diplopia in any direction — true diplopia resolves with one eye closed.

• CN III palsy → ptosis + mydriasis (fixed, dilated pupil) ± "down and out" eye position.

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CN V — Trigeminal Nerve

• Test light touch and temperature (or pin-prick) in each territory bilaterally.
• Corneal reflex: touch cornea lightly with cotton wisp — afferent V1, efferent CN VII (blink). Test when suggested by history.
• Motor: ask patient to clench jaw — palpate the masseter muscles for bulk and symmetry. Pterygoids: jaw deviation on opening points to the weak side.

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CN VII — Facial Nerve

• UMN lesion (e.g., cortical stroke): weakness of the lower two-thirds only; forehead spared (bilateral cortical representation of forehead).
• LMN lesion (e.g., Bell's palsy): weakness of the entire ipsilateral half of the face, including forehead.

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CN VIII — Vestibulocochlear Nerve

• Screen: finger rub or whispered voice at each ear separately.
• Rinne test: vibrating 512 Hz tuning fork placed on mastoid (bone conduction), then at external meatus (air conduction). Normally air > bone (Rinne positive). Reversed in conductive hearing loss.
• Weber test: tuning fork on vertex of skull. Sound lateralizes to the affected ear in conductive loss; to the normal ear in sensorineural loss.

• Nystagmus assessment (see CN III/IV/VI section).
• If the patient is in coma or has altered consciousness: ice-water caloric testing (vestibulo-ocular reflex — see below).

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CN IX & X — Glossopharyngeal & Vagus Nerves

• Observe the palate and uvula at rest — look for asymmetry.
• Ask patient to say "aah" — the soft palate should rise symmetrically; the uvula deviates away from the side of CN X weakness.
• Gag reflex: stimulate the posterior pharyngeal wall with a tongue blade on each side. Note: the reflex may be absent in normal individuals.
• Check voice quality (hoarseness = vagal dysfunction) and swallowing.

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CN XI — Spinal Accessory Nerve

• Weakness of right SCM → difficulty turning head to the left.

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CN XII — Hypoglossal Nerve

• Inspect tongue at rest for atrophy or fasciculations (LMN lesion signs).
• Ask patient to protrude the tongue — it deviates toward the side of weakness.
• Test tongue strength: push tongue against inner cheek on each side against examiner's finger.

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Quick Reference Summary Table

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Clinical Pearls

• Pupillary response distinguishes structural from toxic-metabolic coma: pupils remain reactive in toxic-metabolic coma but are abnormal (often asymmetric) in structural lesions (e.g., transtentorial herniation).
• In CN III compression (e.g., herniation), pupil dilation precedes ophthalmoplegia because parasympathetic fibers run on the outside of the nerve.
• Pontine lesions cause pinpoint pupils (parasympathetic stimulation + sympathetic loss) — still reactive under magnification.
• Horizontal conjugate deviation: "look toward a stroke, look away from a seizure."
• Vertical dysconjugation (skew deviation) is almost always abnormal and signals a structural rostral brainstem lesion.

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Examination of Cranial Nerves — Full Clinical Detail

Source: Adams and Victor's Principles of Neurology 12th Ed; Harrison's Principles of Internal Medicine 22E (2025); Goldman-Cecil Medicine Standard: 4th Year MBBS / Clinical Neurology

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Overview

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CN I — Olfactory Nerve

Anatomy

• Bipolar olfactory receptor neurons → cribriform plate of ethmoid → olfactory bulb → olfactory tract → primary olfactory cortex (piriform/uncus)
• Only sensory CN with no thalamic relay

When to Test

Method

1. Ensure nasal passages are patent (no obstruction/rhinitis)
2. Ask patient to close eyes
3. Occlude one nostril at a time
4. Present a familiar, non-pungent odorant (toothpaste, coffee, vanilla, cloves) under the open nostril
5. Ask: "Can you smell something? What does it smell like?"
6. Repeat for other side

Abnormalities

Avoid ammonia — it stimulates trigeminal free nerve endings, not olfactory receptors, and can give false-positive results.

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CN II — Optic Nerve

Anatomy

Tests

1. Visual Acuity

• Use Snellen chart at 6 metres (20 feet), with glasses/contact lenses corrected
• Test each eye separately (cover the other)
• Record as 6/6 (normal), 6/9, 6/12, etc.
• If chart unavailable: count fingers (CF), hand movement (HM), perception of light (PL), or no perception of light (NPL)

2. Visual Fields by Confrontation

1. Sit facing the patient at ~0.6–1.0 m (2–3 feet)
2. Patient covers their right eye; examiner closes their own left eye (mirror image comparison)
3. Patient fixes gaze on the examiner's nose/opposite eye
4. Examiner places hands at periphery of their own visual field (equidistant plane)
5. Move one or two fingers in each quadrant (inferior temporal, inferior nasal, superior temporal, superior nasal)
6. Patient reports "now" when movement is seen
7. Test each eye separately; then both together (to detect visual inattention/neglect)

3. Colour Vision

• Use Ishihara plates (test for red-green colour defects — optic neuritis classically impairs colour early)
• Bedside: compare redness of a red hat pin in each eye

4. Pupillary Reflexes (see CN III for full detail)

• Swinging flashlight test (RAPD): Swing light between eyes every 2–3 seconds. If the pupil of one eye dilates when light swings to it (instead of maintaining constriction), there is a Relative Afferent Pupillary Defect (RAPD/Marcus Gunn pupil) → ipsilateral optic nerve or retinal disease

5. Fundoscopy (Ophthalmoscopy)

• Optic disc: colour (pale = optic atrophy), margins (blurred = papilloedema), cup-to-disc ratio
• Retinal vessels: calibre, AV nicking, silver/copper wiring, haemorrhages, exudates
• Macula: drusen, haemorrhage, degeneration
• Retina: pigmentary changes, detachment

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

Anatomy

Tests

1. Inspect for Ptosis

• Ptosis = drooping of upper lid (>2 mm)
• Partial ptosis + miosis (Horner syndrome): sympathetic chain lesion
• Complete ptosis + fixed dilated pupil: CN III palsy (compressive — posterior communicating artery aneurysm)
• Bilateral ptosis: myasthenia gravis, bilateral CN III, myopathy

2. Pupil Examination

3. Extraocular Movements (EOMs)

1. Ask patient to hold head still
2. Hold your finger ~0.5 m from the patient's face
3. Ask patient to track the finger with eyes only, following an "H" pattern:
   • Lateral → up → down (tests SR, IR, LR)
   • Medial → up → down (tests IO, SO, MR)
4. Pause at each position for 2–3 seconds and observe for:
   • Nystagmus (especially at lateral gaze — hold for 30 seconds)
   • Failure to move (palsy)
   • Conjugate vs. disconjugate movement

• Test at 45° lateral gaze (not at extreme gaze — physiological endpoint nystagmus occurs)
• Hold position for at least 30 seconds
• Note: direction, fast vs slow phase, horizontal/vertical/rotatory

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CN V — Trigeminal Nerve

Anatomy

• Three sensory divisions: Ophthalmic (V1), Maxillary (V2), Mandibular (V3)
• One motor division: muscles of mastication (masseter, temporalis, pterygoids) — via mandibular branch
• Sensory nucleus extends from pons to C3 spinal cord

Tests

1. Facial Sensation

• Test each division bilaterally with:
  • Light touch (cotton wisp) — dorsal column pathway via main sensory nucleus
  • Pain/pin-prick (broken orange stick, NOT a needle) — spinothalamic pathway via spinal nucleus
  • Temperature (cold tuning fork or tubes with hot/cold water) — optional but sensitive

Note: The angle of the jaw is supplied by C2/C3, NOT the trigeminal nerve — an important clinical discriminator for functional/psychogenic sensory loss.

2. Corneal Reflex

• Afferent: V1 (nasociliary branch → trigeminal ganglion → pontine sensory nucleus)
• Efferent: CN VII (facial nerve → orbicularis oculi)

1. Approach the cornea from the side (not from above — to avoid blinking to visual threat)
2. Touch the cornea (not conjunctiva) lightly with a fine wisp of cotton
3. Normal: bilateral blink (direct blink = efferent CN VII; consensual blink = opposite CN VII)

• Absent direct + absent consensual blink → CN V1 lesion (afferent arc)
• Absent direct + present consensual (other side) → CN VII lesion (efferent arc)

3. Motor (Muscles of Mastication)

• Finger on chin; tap with tendon hammer
• Absent or normal in healthy adults
• Brisk jaw jerk = bilateral UMN lesion above the pons (e.g., pseudobulbar palsy)

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CN VII — Facial Nerve

Anatomy

• Motor: muscles of facial expression (via stylomastoid foramen)
• Sensory: taste to anterior 2/3 tongue (via chorda tympani → lingual nerve → geniculate ganglion)
• Parasympathetic: lacrimal gland (via greater petrosal nerve), submandibular and sublingual glands (via chorda tympani)

Tests

1. Inspect at Rest and During Speech

• Look for facial asymmetry, flattening of nasolabial fold, drooping of one corner of mouth

2. Upper Face Tests

3. Lower Face Tests

4. UMN vs LMN Distinction — Critical Examination Point

5. Taste (Anterior 2/3 Tongue)

• Place salt, sugar, vinegar, or quinine solution on tongue with cotton bud
• Test anterior tongue quadrants on each side
• Patient identifies taste without retracting tongue
• Taste loss = chorda tympani lesion (proximal to its junction with lingual nerve)

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CN VIII — Vestibulocochlear Nerve

Anatomy

• Cochlear (auditory): spiral ganglion → cochlear nerve → cochlear nuclei in pons → bilateral ascending pathway → auditory cortex
• Vestibular: hair cells of semicircular canals/otolith organs → vestibular nerve → vestibular nuclei in pons/medulla → connections to cerebellum, spinal cord, and CN III/IV/VI (VOR)

Tests

COCHLEAR (Hearing)

• Rub thumb and finger together near each ear
• Whisper numbers at 60 cm in each ear (occlude opposite ear with finger)
• Watch tests: tick heard at ≥15 cm = normal

• Strike fork, hold base on mastoid process (bone conduction) until sound disappears
• Immediately hold vibrating tines next to ear canal (air conduction)
• Ask: "Where is it louder — before or now?"

• Place base of vibrating fork on vertex of skull (midline)
• Ask: "Does the sound feel louder in one ear, or is it the same?"

VESTIBULAR (Balance)

• Peripheral vestibular nystagmus: horizontal ± torsional, fatigable, inhibited by fixation
• Central vestibular nystagmus: pure vertical or direction-changing, non-fatigable, not inhibited by fixation

• Patient stands feet together, arms at sides, eyes open then closed
• Sways or falls with eyes closed (positive Romberg) = proprioceptive or vestibular problem (not cerebellar per se)

• Move patient rapidly from sitting to supine with head turned 45° and extended 30° below horizontal
• Positive: delayed onset (latency 5–10 sec), brief, fatigable nystagmus = posterior canal BPPV

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CN IX — Glossopharyngeal Nerve

Anatomy

• Sensory: posterior 1/3 tongue (taste + general sensation), oropharynx, tonsils, middle ear (tympanic branch = Jacobson's nerve), carotid body/sinus
• Motor: stylopharyngeus muscle
• Parasympathetic: parotid gland (via lesser petrosal nerve → otic ganglion)
• Reflex arcs: afferent limb of gag reflex; carotid sinus reflex

Tests

• CN IX and CN X are usually tested together as they share the nucleus ambiguus

• Stimulate posterior pharyngeal wall on each side with tongue blade
• Afferent: CN IX | Efferent: CN X
• Normal: bilateral elevation of palate ± retching
• Absent bilaterally is often normal in adults — clinically meaningful only if unilateral or if correlated with other deficits

• Tested as above (bitter substances) — rarely done routinely

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CN X — Vagus Nerve

Anatomy

• Motor: soft palate, pharynx, larynx (via recurrent laryngeal nerve — left loops around aortic arch, right loops around subclavian)
• Sensory: ear (auricular branch), viscera
• Parasympathetic: heart, lungs, GI tract to splenic flexure

Tests

1. Palate and Uvula

• Ask patient to open mouth and say "Aah"
• Observe: soft palate rises symmetrically
• Unilateral CN X palsy: palate fails to rise on affected side; uvula deviates away from the lesion (pulled by intact side)
• Unilateral CN IX/X palsy: uvula deviates to the normal side

2. Voice Quality

• Hoarseness = laryngeal muscle weakness (recurrent laryngeal nerve)
• Bovine cough = inability to build up expiratory pressure (vocal cord palsy)
• Nasal voice = palatal weakness (air escapes through nose)

3. Swallowing

• Ask patient to swallow water; note drooling, nasal regurgitation, coughing

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CN XI — Spinal Accessory Nerve

Anatomy

• Arises from upper cervical cord (C1–C5) + lower medulla
• Ascends through foramen magnum, exits via jugular foramen
• Two muscles: sternocleidomastoid (SCM) + trapezius

Tests

Mnemonic: Left SCM turns head to the RIGHT. Weak left SCM = difficulty turning head right.

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CN XII — Hypoglossal Nerve

Anatomy

• Nucleus in dorsal medulla
• Exits through hypoglossal canal
• Innervates all intrinsic and extrinsic muscles of the tongue (except palatoglossus = CN X)

Tests

• Look for fasciculations (fine flickering movements) = LMN lesion
• Look for atrophy (wasting, scalloped edges, thinning)

• "Stick out your tongue"
• Normal: midline protrusion
• Deviation toward the weak side (the intact genioglossus pushes the tongue toward the paralyzed side)

• "Push your tongue into your cheek" — examiner pushes from outside
• Test both sides

• "Say la-la-la quickly" (tests tongue tip) — dysarthria if CN XII paresis

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Bulbar vs. Pseudobulbar Palsy

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Quick Summary Table

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Important Clinical Syndromes

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