Cranial nerve examination

This is an examination of the functions of the twelve cranial nerves. The cranial nerves may be noted in square brackets. For example, [VII] refers to the facial nerve.

Introduction

Introduce yourself, confirm the patient's name and date of birth, obtain consent and proceed to wash hands.

General inspection

Begin the examination by inspecting the patient. It is important to briefly assess the general appearance of the whole body including both sets of limbs.

Ask the patient about pain and comfort. Pain can indicate acute injury or be secondary to pathology. However, we primarily ask about pain to avoid hurting the patient and maximise their comfort. Next, look for paraphernalia around the bed. It is important to look out for walking aids, blood glucose monitors and medication.

Closer inspection

Inspect the face for any scars, rashes, muscle wasting or fasciculation.

Look for any ptosis (drooping of the eyelid, [III] or sympathetic lesion), changes in pupil size ([II] or [III] lesion), changes in eye position ([III], [IV] or [VI] lesion) or hearing aids ([VIII] lesion).

Be sure to check behind the ears for any hearing aids or scars. Ask patients with long hair to hold it up behind their head so that you can do a complete inspection.

Muscle wasting may present in a particular distribution. For example, in Bell's palsy, there will be drooping and wasting of the muscles of facial expression, all supplied by the posterior auricular branch of the facial nerve.

Olfactory nerve [I]

The olfactory nerve is purely sensory.

Ask the patient if they have had a recent change in smell. A more accurate assessment would be to use flavoured vials such as vanilla and peppermint. Smell should be tested in each nostril individually. Anosmia, a loss of sense of smell, is commonly a result of mucous blockage, trauma or old age.

The cranial nerve exam is unique in the sense that it involves asking patients numerous questions. These can be used to build good rapport. For example, when asking about smell, you could follow up by asking "so this morning did your breakfast smell as good as it does always?" Or something else along those lines.

Optic nerve [II]

The optic nerve is purely sensory.

There are many functions to assess with the optic nerve, and a useful mnemonic to remember them by is Afro BC.

Acuity

Visual acuity is tested using a Snellen chart positioned 6m away from the patient and covering each eye in turn. Ask the patient to dictate the letters on the smallest line that they can read. A normal visual acuity of 1.0 is considered when the patient can read the 6/6 line from 6m away. If the patient is only able to read the 6/12 line, then they have 0.5 visual acuity and need a magnification of 2x to read the line.

If the patient wears corrective lenses then it is important to ensure that they wear them, as you wish to get an idea of their functional visual acuity, not that which is easily corrected.

The final part of acuity is colour vision; this is addressed further down the page.

Fields

Visual neglect.

Begin by testing for visual neglect. Sit opposite the patient 1m away from them and ask them to focus on your nose, keeping their chin still at all times. Raise both your hands such that you have one hand in their right visual field and the other in their left. Wiggle your index fingers in turn and ask the patient to point to which finger is moving. An inattention to one side is indicative of visual neglect and a contralateral parietal lobe lesion.

The parietal lobe is associated with processing spatial orientation and attention on the contralateral side. Therefore, if there is damage to the parietal lobe then the patient will be inattentive in their contralateral visual field, even if all of the corresponding afferent communication is intact.

Visual range.

If there is absence of neglect, then proceed to test the range of the visual fields. Ask the patient to cover one eye with their palm whilst you close your own eye on the same side (i.e. if they cover their left, you close your right eye). Ask the patient to once again focus on your nose without moving their chin. Hold the white visual fields pin in the periphery of the patient's vision, slowly bring it into the centre and ask them to report when they see the pin. Repeat to test all the corners of their vision and then repeat the entire process with the other eye.

When testing the sensory components of the cranial nerves of a patient, you are often comparing their sensory input with your own. It is assumed that your sensory capabilities are unimpaired. For example, when testing the range of the patient's visual fields, the patient should be able to see the white pin at the same moment that you see the pin, as you are comparing their visual field to your own.

To ensure that you are accurately comparing their visual fields to your own, it is very important that you keep the pin at a mid-distance between you and the patient.

Visual fields can be affected in several ways.

The final part of visual field assessment is determining the location of the blind spot. This is addressed further down the page.

Reflexes

Accommodation reflex: Ask the patient to focus on a distant object. Hold the white fields pin 50cm away from their face and ask them to switch their focus to the pin. The patient's eyes should converge to the centre and the pupils constrict.

Pupillary reflex: Dim the lights in the room and ask the patient to hold their hand in the middle of their face, one eye on each side. Shine a pen torch into one eye and check for pupil constriction in the ipsilateral eye (direct reflex) and the contralateral eye (consensual reflex). It is important to repeat this in the other eye to check for any efferent defects in the reflex. Finally, swing the pen torch from eye to eye to check for a relative afferent pupillary defect.

To understand the impact of an afferent or efferent defect it is important to understand the reflex arc. When light is shone in an eye, afferent fibres in the optic nerve and tracts communicate this information to the pretectal and Edinger-Westphal nuclei on both sides of the brain. Then, efferent fibres from both Edinger-Westphal nuclei travel to the eyes by their respective oculomotor nerves to cause bilateral pupil constriction.

FundOscopy

Offer to perform fundoscopy to check the optic disc.

Blind spot

Sit 1m from the patient and ask them to focus on your nose whilst keeping their chin still and close one eye. You do the same. Hold the red pin mid-distance between you and the patient and slowly move it laterally towards the periphery. Ask the patient to say when the head of the pin disappears. This is their blind spot, and it should be at a similar position to your own.

You can assess the size of the blind spot by continuing to move the pin laterally and asking the patient to say when the pin reappears.

The blind spot is the place in the visual field that corresponds to the area of retina which is occupied by the optic disc. The brain "fills in" the blind spot with information from surrounding areas. An enlarged blind spot can be caused by papilloedema.

Colour vision

Test colour vision using ishihara plates. Ask the patient to read the numbers in the coloured circles. Poor colour vision can be a result of age related macular disease or colour blindness.

Colour vision and the blind spot should ideally be assessed with acuity and fields respectively. However, in keeping with the acronym Afro BC, Simple OSCE has explained these tests last.

Oculomotor [III], trochlear [IV] and abducens [VI] nerves

The oculomotor, trochlear and abducens nerves are purely motor, and are all tested together. The oculomotor nerve also has a parasympathetic component involved in pupil constriction and lens accommodation. Accommodation was tested previously with the optic nerve.

Begin with quick inspection for ptosis and strabismus (divergence or convergence of the eyes) and once again ask the patient if they are in any pain. Next ask the patient to focus on a white pin whilst keeping their chin still and to report any diplopia (double vision) or pain. Move the pin in an H pattern and focus on the eye movements. Finally, test for nystagmus (indicative of vestibular disease [VIII]) by moving the pin slowly laterally and then rapidly in the opposite direction.

The following movements are used to test each of the extrinsic ocular muscles:



The oculomotor nerve supplies motor innervation to the levator palpebrae superioris (elevates the eyelid), the inferior oblique, the superior, inferior, and medial rectus muscles. Its parasympathetic component is to the sphincter pupillae and ciliary muscle. As a result, an oculomotor nerve palsy will result in:



The trochlear nerve supplies the superior oblique muscle. Therefore, a trochlear nerve palsy will result in vertical diplopia, as the weakened muscle prevents the eyes from moving in the same direction together.



The abducens nerve supplies the lateral rectus muscle. Therefore an abducens nerve palsy will result in a convergent squint, as the eye is unable to abduct.

Trigeminal nerve [V]

The trigeminal nerve has three divisions, ophthalmic ([V1]), maxillary ([V2]) and mandibular ([V3]). [V1] and [V2] are both sensory only whilst [V3] has both a sensory and motor component.

Test the modalities of light touch, pain and temperature sense in the regions of the [V1], [V2] and [V3] dermatomes. Be sure to assess them in the same manner as described in upper and lower limb examination.

A trigeminal neuralgia results in chronic pain in the distribution of the trigeminal nerve. Demyelination is believed to contribute towards its cause.

Next test the muscles of mastication, all supplied by [V3]. Palpate the temporalis (place your fingers on the patient's temple) and the masseter muscle (place your thumb at the angle of the mandible) on each side and ask the patient to clench their teeth. You should be able to feel the contraction of the muscles. Next, test the medial pterygoids (ask the patient to move their jaw from side to side against lateral resistance) and the lateral pterygoids (ask the patient to open their jaw against resistance).

At this point you should also offer to test the corneal reflex (lightly touch a cotton cool to the sclera of the eye) and the jaw jerk reflex (using a tendon hammer, lightly tap the mandible with a downwards motion just inferior to the lips, with the jaw slightly open).

Corneal reflex: The afferent pathway is communicated by [V1]. Signals are sent to the facial motor nucleus and fibres travel to the orbicularis oculi muscle via [VII]. The orbicularis oculi muscle closes the eye.

Jaw jerk reflex: Both the afferent and efferent pathways are communicated by [V3]. When stimulated, [V3] will cause elevation of the mandible. An exaggerated jaw jerk suggests an upper motor neurone lesion.

Facial nerve [VII]

The facial nerve has both a sensory and motor component.

Ask the patient if they have had any change in their taste sensation. This tests both [VII] and [IX]. The facial nerve supplies taste fibres to the anterior 2/3 of the tongue whilst the glossopharyngeal nerve supplies taste fibres to the posterior 1/3.

Next instruct the patient to perform a series of facial expressions. Ask them to shut their eyes and prevent you from opening them (tests orbicularis oculi), raise their eyebrows and prevent you from lowering them (tests frontalis), smile (tests zygomatic major), purse their lips (tests buccinator) and puff out their cheeks against resistance (tests orbicularis oris). Lesions to the facial nerve may result in a partial or complete droop.

Tip: Imagine that the patient is having a surprise birthday party. They first close their eyes, then open them wide in surprise and smile, then they purse their lips and blow out the candles.

You could also do Schirmer's test (insert a paper strip onto the lower eyelid) to test innervation to the lacrimal gland ([VII]) and ask the patient to produce saliva to test innervation to the salivary glands ([VII],[IX]). These tests are rarely performed however as they can be cumbersome and unsightly.

Complete droop: A lower motor neurone lesion to [VII] will result in a unilateral complete droop as there is weakness of all the muscles of facial expression on that side. This could be a result of Bell's palsy, a demyelinating disease or Ramsey-Hunt syndrome.

Forehead sparing droop: An lesion to an upper motor neurone supplying the facial nerves will result in an ipsilateral forehead sparing droop. There will be weakness in the muscles of facial expression on that side, but only those present the lower part of the face. This is because upper motor neurones corresponding to the forehead connect to both facial nuclei bilaterally. Such a presentation could be due to a stroke or motor neurone disease.

Vestibulocochlear nerve [VIII]

The vestibulocochlear nerve is purely sensory.

Ask the patient about hearing and balance, both supplied by [VIII]. [V3] and [VII] also contribute to hearing by stabilising the ossicles of the ear in response to loud noises. Therefore, a hearing defect may be due to a lesion in one of these nerves.

Next perform the whispered voice test. With the patient sat down in a chair, stand approximately 0.6m behind them and ask them to cover one ear. Quietly whisper a number and ask the patient to repeat it back to you. If they are unable to do this, this suggests a gross hearing loss in the tested ear. Repeat this process in the other ear.

The whispered voice test is just a screening test. If you suspect a problem with hearing, you could offer to perform pure tone audiometry, a test in which the patient listens to a number of machine generated frequencies at difference volumes, and indicates to the examiner when they can hear each of these.

Perform the Rinne and Weber tests using a 512Hz tuning fork.

Weber test
No lateralisation Lateralises left Lateralises right
Rinne test Both ears AC>BC Normal Sensorineural loss in the right ear Sensorineural loss in the left ear
Left ear BC>AC Not possible Conductive loss in the left ear Mixed loss in the left ear
Right ear BC>AC Not possible Mixed loss in the right ear Conductive loss in the right ear

AC: Air conduction. BC: Bone conduction.

Conductive loss: This is when there is impairment of sound conduction at any point up until the round window. Causes of conductive loss include ear wax and otitis media.
Sensorineural loss: This is when there is damage to the nerve fibres themselves and can be due to a brainstem stroke or Meniere's disease.

Glossopharyngeal [IX] and Vagus [X] nerves

The glossopharyngeal and vagus nerves are sensory and motor and are both tested together.

The gag reflex tests the sensory component of [XI]. This is performed by stimulation of the posterior tongue and back of the mouth. Do not attempt to perform this in an OSCE scenario. The efferent arc of the reflex involves both [IX] and [X].

Moving on to motor assessment, begin by asking the patient about swallowing ([IX], [X]) and if they have noticed any change in their voice ([X]). Ask the patient to open their mouth and observe the uvula. This is maintained by the vagus nerve, and if there is a lesion then the uvula will deviate away from the affected side. Ask the patient to cough ([X]), say aah ([X]) and the words "British constitution." Finally ask the patient to swallow. If there is a lesion to the vagus nerve, this will result in abnormalities in the above actions.

The words "British constitution" also assess the hypoglossal nerve, as the individual phonemes require the tongue to be accurately enunciated.

Accessory nerve [XI]

The accessory nerve is purely motor.

Inspect the sternocleidomastoid and trapezius muscles for wasting. These are both supplied by the accessory nerve. Ask the patient to raise their shoulders against resistance (tests trapezius) and turn their head from side to side against resistance (tests sternocleidomastoid). A [XI] palsy will result in weakness and wasting of these muscles.

Hypoglossal nerve [XII]

This nerve is purely motor.

Inspect the tongue for wasting and fasciculations. Ask the patient to protract their tongue, move it horizontally and against resistance by sticking it into their cheek. A lower motor neurone lesion such as a bulbar palsy will result in weakness and wasting of the tongue. There will also be tongue deviation towards the side of the lesion.

There are four extrinsic muscles which move the tongue. The genioglossus, styloglossus and hyoglossus are all innervated by the hypoglossal nerve. The palatoglossus however is innervated by the vagus nerve.

Completion

Complete the examination by offering to obtain a full history, an upper and lower limb examination and then, if appropriate, suggest further tests such as a lumbar puncture (if meningitis is suspected), CT scan (if a recent stroke or brain haematoma is suspected) or an MRI scan (if a space-occupying or demyelinating disorder is suspected).

Interactive markscheme


When assessing each other, please click on each list item as you go along. Doing so will turn the list item green. Make careful note of any steps missed at the end.
We recommend completing any examination or procedure in under 10 minutes, but you can adjust the timer to suit your needs.
:

  1. Introduction: “Hello, I’m SimpleOSCE and I am a medical student. I need to test the function of the nerves in your head today, this will just require me to ask a few questions and do some exercises, would that be okay? Can I confirm your name and DOB? Thank you.”
  2. Wash hands.
  3. Ensure adequate exposure and ask about pain or discomfort.
  4. General inspection of body, limbs and around the bed (walking aids, medication).
  5. Closer inspection of face for scarring, rashes, wasting or fasciculation.
  6. [I]: Ask if the patient has noticed a change in smell.
  7. [II]: Test visual acuity in both eyes using a Snellen chart.
  8. [II]: Test for neglect and assesses visual field in both eyes.
  9. [II]: Test for the accommodation reflex.
  10. [II]: Test for the pupillary reflex in both eyes and performs swinging torch test.
  11. [II]: (Optional) Tests the blind spot in both eyes.
  12. [II]: Test colour vision using ishihara plates in both eyes.
  13. [II]: Offer to perform fundocscopy.
  14. [III], [IV], [VI]: Test eye movements.
  15. [III], [IV], [VI]: Ask the patient to mention if they have pain or double vision.
  16. [V]: Test light touch sensation at all dermatomes. Offer to test other modalities.
  17. [V]: Test the masseter and temporalis with jaw clench and the pterygoids with lateral and downward jaw movement against resistance.
  18. [V], [VII]: Offer to test for the jaw jerk and corneal reflexes.
  19. [VII], [IX]: Ask if the patient has noticed a change in taste.
  20. [VII]: Test the muscles of facial expression.
  21. [VIII]: Ask if the patient has noticed a change in hearing and test crude hearing.
  22. [VIII]: Perform the Rinne and Weber tests using a 512Hz tuning fork.
  23. [IX], [X]: Offer to test for the gag reflex.
  24. [IX], [X]: Enquire about swallowing and check the uvula for deviation.
  25. [X]: Ask the patient to say aah, cough and say British constitution.
  26. [XI]: Test the trapezius and sternocleidomastoid muscles.
  27. [XII]: Test the muscles of the tongue.
  28. Thank the patient.
  29. "To complete my exam I would like to take a full history and perform an upper and lower limb neurological examination."
  30. Present findings.
Overall: 0/28