The cranial nerve examination is often considered one of the most difficult OSCE stations, but with plenty of practice, you’ll be fine. The important thing to remember is that in an OSCE you’ll not be required to complete an entire cranial nerve exam in one station. This guide provides a step by step approach to cranial nerve examination, with an included video demonstration.
Confirm patient details – name / DOB
Explain the examination – “I’m going to be testing the nerves that supply your face”
Position patient on a chair at eye level – approximately one arm’s length away
Ask if the patient currently has any pain.
- Pen torch
- Snellen chart
- Ishihara plates
- Cotton wool
- Tuning fork (512hz)
- Glass of water
- Mydriatic eye drops (if necessary)
General appearance – comfortable at rest?
Obvious facial asymmetries?
Position of eyes – normal alignment/strabismus
Ptosis – is this unilateral or bilateral?
Abnormality of speech or voice – dysarthria
Signs around the bed – e.g. hearing aid/glasses
I – Olfactory nerve
Any change in sense of smell? – “Have you noticed any recent change in your sense of smell?”
Olfaction can be tested more formally using different odours, e.g. lemon, or most formally, using the University of Pennsylvania smell identification test. However, this is unlikely to be required in an exam.
II – Optic nerve
Size – normal size varies between individuals and depends on lighting conditions (smaller in bright light, larger in the dark). Pupils are usually small in infancy, larger in adolescence, “normal” size in adulthood and become increasingly smaller in old age.
Shape – pupils should be round – abnormal shapes can be congenital or due to pathology
Symmetry – note any asymmetry between the pupils (anisocoria). This may be longstanding and non-pathological, but may relate to pathology. For example, large and fixed in a CN III palsy, small and reactive in Horner’s syndrome.
Decreased visual acuity has many potential causes:
- Refractive errors
- Ocular media opacities such as cataract or corneal scarring
- Retinal diseases such as age-related macular degeneration
- Optic nerve (CN II) pathology such as optic neuritis
- Lesions higher in the visual pathways
Optic nerve (CN II) pathology usually causes a decrease in acuity in that eye. In comparison, papilloedema (optic disc swelling from raised intracranial pressure), does not usually affect visual acuity until it is at a late stage.
Assessment of visual acuity
1. Stand the patient at 6 metres from the Snellen chart.
2. If the patient normally uses distance glasses, ensure these are worn for the assessment.
3. Ask the patient to cover one eye and read the lowest line they are able to.
4. Visual acuity is recorded as chart distance in meters (numerator) over the number of the lowest line read (denominator).
5. Record the lowest line the patient was able to read.
6. If the patient reads the 6/6 line, but gets 2 letters incorrect, you would record as 6/6 (-2).
7. If the patient gets more than 2 letters wrong, then the previous line should be recorded as their acuity.
8. You can have the patient read through a pinhole to see if this improves vision (if vision is improved with pinhole, it suggests there is a refractive element to their poor vision).
9. When recording the vision it should state whether this vision was unaided (UA), with glasses or with pinhole (PH).
10. Repeat above steps with the other eye.
If the patient is unable to read the top line at 6 metres (even with pinhole) move through the following steps as necessary:
1. Reduce the distance to 3 metres from the Snellen chart (the acuity would then be recorded as 3/denominator).
2. Reduce the distance to 1 metre from the Snellen chart (1/denominator).
3. Assess if they can count the number of fingers you’re holding up (recorded as “Counting Fingers” or “CF”).
4. Assess if they can see gross hand movements (recorded as “Hand Movements” or “HM”).
5. Assess if they can detect light from a pen torch shone into each eye (“Perception of Light”/”PL” or “No Perception of Light”/”NPL”).
To best see pupillary reflexes the room should be dimly lit.
Direct pupillary reflex (afferent CN II, efferent CN III)
Shine a light into the pupil and observe constriction of that pupil.
Sluggish reaction or lack of constriction may suggest pathology – optic nerve / brain stem / drugs
Consensual pupillary reflex
Again shine a light into the pupil, but this time observe the contralateral pupil.
A normal consensual response involves the contralateral pupil constricting.
Lack of a normal consensual response may suggest:
- Damage to one or both optic nerves
- Damage to the Edinger-Westphal nucleus
Swinging light test
1. Move the pen torch rapidly between the two pupils, shining the light for three seconds in each eye.
This test may detect a relative afferent pupillary defect (RAPD) – caused by damage to the tract between the optic nerve and optic chiasm (e.g. optic neuritis in multiple sclerosis). It’s also known as a “Marcus-Gunn” pupil.
A RAPD can be detected by paradoxical dilatation of the affected pupil when a light is shining into it (it should normally constrict). This points to pathology in the optic nerve (afferent pathway) on this side. The test is essentially comparing the function of the two optic nerves, so when the light is shone into the eye in which the optic nerve is functioning less well, it dilates.
1. Ask the patient to focus on a distant object (clock on the wall / light switch).
2. Place your finger/object approximately 15cm in front of the eyes.
3. Ask the patient to switch from looking at the distant object to the nearby finger/object.
4. Observe the pupils, you should see constriction and convergence bilaterally.
Assess colour vision using Ishihara charts (unlikely to do this in an OSCE setting)
Visual fieldsSit directly facing the patient, approximately one metre away.
1. Ask the patient to cover their left eye with their left hand.
2. You should cover your right eye and be staring directly at the patient (mirroring the patient).
3. Ask the patient to look into your eye and not move their head or eyes during the assessment.
4. Ask the patient to tell you when they can see your fingertip wiggling.
5. Outstretch your arms, ensuring they are situated at an equal distance between yourself and the patient.
6. Position your fingertip at the outer border of one of the quadrants of your visual field.
7. Slowly bring your fingertip inwards, towards the centre of your visual field until the patient sees it.
8. Repeat this process for each quadrant – at 10 o’clock /2 o’clock / 4 o’clock / 8 o’clock.
9. If you are able to see your fingertip but the patient cannot, this would suggest a visual field defect.
10. Map out any visual field defects you detect.
11. Repeat the same assessment process on the other eye.
1. Darken the room.
2. The patient should ideally have their pupils dilated with short-acting mydriatic eye drops.
3. Ask the patient to fixate on a distant object.
Assess for red reflex
1. Position yourself at a distance of around 30cm from the patient’s eyes.
2. Looking through the ophthalmoscope and ensure the light is directed into the pupil. Observe for a reddish/orange reflection in the pupil.
An absent red reflex may indicate the presence of cataract, or in rare circumstances neuroblastoma.
Move in closer and examine the eye with the ophthalmoscope
1. Find a vessel on the fundus and focus on it using the dial on the ophthalmoscope.
2. Follow the vessel along to the optic disc. If you can’t find the optic disc, stay on the same vessel and follow it the other way.
3. Assess the optic disc – colour / margin / cupping
4. Assess the retinal vessels – cotton wool spots / AV nipping / neovascularization
5. Finally, assess the macula – ask the patient to look directly into the light – Drusen noted in macular degeneration
III, IV, VI – Oculomotor, Trochlear & Abducens nerves
Note any evidence of ptosis:
- Oculomotor nerve pathology
- Horner’s syndrome
- Neuromuscular pathology (e.g myasthenia)
1. Hold your finger about 30cm directly in front of the patient’s eyes and ask them to look at it. Look at the eyes in the primary position for any deviation or abnormal movements.
2. Ask the patient to keep their head still and follow your finger with their eyes.
3. Ask the patient to report any double vision.
4. Move your finger through the various axes of eye movement (“H” shape).
5. Observe for restriction of eye movement and note any nystagmus.
This tests for a manifest strabismus/squint.
1. Ask patient to focus on a target (e.g. your pen top).
2. Cover one of the patient’s eyes.
3. Observe the uncovered eye for movement:
- No movement = normal response
- Eye moves temporally = convergent squint (esotropia)
- Eye moves nasally = divergent squint (exotropia)
4. Repeat the cover test on the other eye.
V – Trigeminal nerve
Assess light touch and pinprick sensation:
- Forehead – ophthalmic branch (V1)
- Cheek – maxillary branch (V2)
- Jaw – mandibular branch (V3)
Compare left to right for each branch.
Demonstrate sensation on patient’s sternum first, to ensure they understand what it should feel like.
1. Ask the patient to clench their teeth whilst you feel the bulk of masseter and temporalis bilaterally.
2. Ask the patient to open their mouth whilst you apply resistance under the jaw – note any deviation (jaw will deviate to side of lesion).
Jaw jerk (afferent CN V, efferent CN V):
- Ask patient to open mouth loosely
- Place your finger horizontally across the chin
- Tap your finger with a tendon hammer
- Normal = slight closure of the jaw
- Abnormal = brisk complete closure of the jaw – UMN lesion
Corneal reflex (afferent CN V, efferent CN VII):
- Explain procedure and gain consent
- Depress lower eyelid
- Ask patient to look upwards
- Touch edge of cornea using a wisp of cotton wool
- Normal response = Direct and consensual blinking
- Not usually required in an OSCE setting
VII – Facial nerve
Inspect the patient’s face at rest for asymmetry:
- Forehead wrinkles
- Nasolabial folds
- Angles of the mouth
Ask the patient to perform specific facial movements
Raised eyebrows – “raise your eyebrows as if you’re surprised” – note asymmetry
Closed eyes – “scrunch up your eyes and don’t let me open them” – assess power
Blown out cheeks – “blow out your cheeks and don’t let me deflate them” – assess power
Smiling – “can you do a big smile for me?” – note asymmetry
Pursed lips – “can you attempt to whistle for me?” – note asymmetry
Closed lips – “close your lips tight and don’t let me open them” – check each side, assess power
Other things to check…
Inspect external auditory meatus (EAM) – herpes zoster lesions – Ramsay Hunt syndrome
Any hearing changes? – facial nerve supplies stapedius – paralysis results in hyperacusis
Any taste changes? – supplies taste sensation to the anterior two-thirds of the tongue
VIII – Vestibulocochlear nerve
Gross hearing testing
Ask the patient if they have noticed a change in their hearing recently.
Assess each ear individually, standing behind the patient.
1. Explain to the patient that you’re going to say a word or number and you’d like them to repeat it back to you.
2. With your mouth approximately 15cm from the ear, whisper a number or word.
3. Mask the ear not being tested by rubbing the tragus.
4. Ask the patient to repeat the number or word back to you.
5. If the patient repeats the correct word or number, repeat the test at an arm’s length from the ear (normal hearing allows whispers to be perceived at 60cm).
6. Assess the other ear in the same way.
1. Tap a 512 Hz tuning fork and place its base on the mastoid process
2. Ask the patient if they are able to hear it (bone conduction)
3. If they are able to hear it, ask them to let you know when they can no longer hear it
4. Once the patient is unable to hear the sound via the mastoid process move the tuning fork to approximately 1 inch from the external auditory meatus
5. Ask the patient if they are able to hear the tuning fork (this is air conduction)
6. If the patient is able to hear the tuning fork via air conduction (after they were no longer able to hear via bone conduction) it suggests their air conduction is better than bone conduction (Rinne’s positive).
Summary of Rinne’s test results:
- Normal = Air conduction > Bone conduction (Confusingly termed “Rinne’s positive”, despite it being the normal result. It is probably best to avoid this term and just describe the result)
- Neural deafness = Air conduction > Bone conduction (both air and bone conduction reduced equally)
- Conductive deafness = Bone conduction > Air conduction (“Rinne’s negative” – again best to avoid this term and describe the result)
1. Tap a 512 Hz tuning fork and place in the midline of the forehead
2. Ask the patient where they can hear the sound:
- Normal – sound is heard equally in both ears
- Neural deafness – sound is heard louder on the side of the intact ear
- Conductive deafness – sound is heard louder on the side of the affected ear
Vestibular testing – “Unterberger” or “Turning test”
Ask patient to march on the spot with arms outstretched and eyes closed:
- Normal – patient remains in the same position
- Vestibular lesion – patient will turn towards the side of the lesion
Vestibular testing – “Head thrust test” or “Vestibular-Ocular Reflex (VOR)”
1. Sit facing the patient.
2. Ask if they have any neck pain and ask permission to turn their head very quickly.
3. Ask them to fixate on your nose at all times. Hold their head in your hands (one hand covering each ear) and rotate it very rapidly to the left, at a medium amplitude.
4. Repeat to the right.
The normal response is that fixation is maintained. In a patient with loss of vestibular function on one side, the eyes will first move in the direction of the head (losing fixation), before a corrective refixation saccade occurs towards your nose.
IX & X – Glossopharyngeal and Vagus nerves
Assess soft palate and uvula:
- Symmetry – note any obvious deviation of the uvula
- Ask patient to say “ahhhh” – observe uvula moving upwards – any deviation? (deviation away from side of lesion)
Gag reflex (afferent IX, efferent X) – you won’t be expected to do this in the OSCE, but make sure you mention it
Ask patient to cough– damage to nerves IX and X can result in a bovine cough
Swallow – ask patient to take a sip of water – note any coughing / delayed swallow
XI – Accessory nerve
Ask patient to shrug shoulders and resist you pushing down – trapezius
Ask patient to turn head to one side and resist you pushing it to the other – sternocleidomastoid
Note any weakness
XII – Hypoglossal nerve
1. Inspect tongue for wasting and fasciculations at rest (minor fasciculations can be normal)
2. Ask patient to protrude tongue – any deviation? (deviates towards side of lesion)
3. Place your finger on the patient’s cheek and ask to push their tongue against it – assess power
To complete the examination
Suggest further assessments and investigations
- Perform further testing of any nerves that had abnormal results (if appropriate)
- Carry out a full neurological examination of the upper and lower limbs
- Further imaging – e.g. CT Head/MRI head
Dr Gemma Maxwell
Neurology Registrar (ST6)