Neuro Exam: Cranial Nerves Flashcards
What equipment is needed for the clinical nerves examination
Gather the appropriate equipment to perform cranial nerve examination:
Pen torch Snellen chart Ishihara plates Ophthalmoscope and mydriatic eye drops (if necessary) Cotton wool Neuro-tip Tuning fork (512hz) Glass of wate
Describe the introduction to the exam
Wash your hands and don PPE if appropriate.
Introduce yourself to the patient including your name and role.
Confirm the patient’s name and date of birth.
Briefly explain what the examination will involve using patient-friendly language.
Gain consent to proceed with the examination.
Ask the patient to sit on a chair, approximately one arm’s length away.
Ask the patient if they have any pain before proceeding with the clinical examination
What should you look for upon general inspection
Speech abnormalities: may indicate glossopharyngeal or vagus nerve pathology.
Facial asymmetry: suggestive of facial nerve palsy.
Eyelid abnormalities: ptosis may indicate oculomotor nerve pathology.
Pupillary abnormalities: mydriasis occurs in oculomotor nerve palsy.
Strabismus: may indicate oculomotor, trochlear or abducens nerve palsy.
Limbs: pay attention to the patient’s arms and legs as they enter the room and take a seat noting any abnormalities (e.g. spasticity, weakness, wasting, tremor, fasciculation) which may suggest the presence of a neurological syndrome).
Look for objects or equipment on or around the patient that may provide useful insights into their medical history and current clinical status:
Walking aids: gait issues are associated with a wide range of neurological pathology including Parkinson’s disease, stroke, cerebellar disease and myasthenia gravis.
Hearing aids: often worn by patients with vestibulocochlear nerve issues (e.g. Ménière’s disease).
Visual aids: the use of visual prisms or occluders may indicate underlying strabismus.
Prescriptions: prescribing charts or personal prescriptions can provide useful information about the patient’s recent medications.
Describe how we examine olfactory nerve function
The olfactory nerve (CN I) transmits sensory information about odours to the central nervous system where they are perceived as smell (olfaction). There is no motor component to the olfactory nerve.
Ask the patient if they have noticed any recent changes to their sense of smell.
Olfaction can be tested more formally using different odours (e.g. lemon, peppermint), or most formally using the University of Pennsylvania smell identification test. However, this is unlikely to be required in an OSCE.
Describe some causes of anosmia
There are many potential causes of anosmia including:
Mucous blockage of the nose: preventing odours from reaching the olfactory nerve receptors.
Head trauma: can result in shearing of the olfactory nerve fibres leading to anosmia.
Genetics: some individuals have congenital anosmia.
Parkinson’s disease: anosmia is an early feature of Parkinson’s disease.
COVID-19: transient anosmia is a common feature of COVID-19.
Describe the role of the optic nerve
The optic nerve (CN II) transmits sensory visual information from the retina to the brain. There is no motor component to the optic nerve.
Describe the assessment of pupil size and pupil shape
Assess pupil size
Normal pupil size varies between individuals and depends on lighting conditions (i.e. smaller in bright light, larger in the dark).
Pupils are usually smaller in infancy and larger in adolescence.
Assess pupil shape
Pupils should be round, abnormal shapes can be congenital or due to pathology (e.g. posterior synechiae associated with uveitis).
Peaked pupils in the context of trauma are suggestive of globe injury.
Describe the assessment of pupil symmetry
Note any asymmetry in pupil size between the pupils (anisocoria). This may be longstanding and non-pathological or relate to actual pathology. If the pupil is more pronounced in bright light this would suggest that the larger pupil is the abnormal pupil, if more pronounced in dark this would suggest the smaller pupil is abnormal.
Examples of asymmetry include a large pupil in oculomotor nerve palsy and a small and reactive pupil in Horner’s syndrome
Describe the assessment of visual acuity
Assessment of visual acuity (distance)
Begin by assessing the patient’s visual acuity using a Snellen chart. If the patient normally uses distance glasses, ensure these are worn for the assessment.
- Stand the patient at 6 metres from the Snellen chart.
- Ask the patient to cover one eye and read the lowest line they are able to.
- Record the lowest line the patient was able to read (e.g. 6/6 (metric) which is equivalent to 20/20 (imperial)).
- You can have the patient read through a pinhole to see if this improves vision (if vision is improved with a pinhole, it suggests there is a refractive component to the patient’s poor vision).
- Repeat the above steps with the other eye.
Describe how visual acuity is recorded
Visual acuity is recorded as chart distance (numerator) over the number of the lowest line read (denominator).
If the patient reads the 6/6 line but gets 2 letters incorrect, you would record as 6/6 (-2).
If the patient gets more than 2 letters wrong, then the previous line should be recorded as their acuity.
When recording the vision it should state whether this vision was unaided (UA), with glasses or with pinhole (PH).
What further steps should be done for patients who have poor visual acuity
If the patient is unable to read the top line of the Snellen chart at 6 metres (even with pinhole) move through the following steps as necessary:
- Reduce the distance to 3 metres from the Snellen chart (the acuity would then be recorded as 3/denominator).
- Reduce the distance to 1 metre from the Snellen chart (1/denominator).
- Assess if they can count the number of fingers you’re holding up (recorded as “Counting Fingers” or “CF”).
- Assess if they can see gross hand movements (recorded as “Hand Movements” or “HM”).
- Assess if they can detect light from a pen torch shone into each eye (“Perception of Light”/”PL” or “No Perception of Light”/”NPL”).
What are the causes of decreased visual acuity
Decreased visual acuity has many potential causes including:
Refractive errors
Amblyopia
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 the affected eye. In comparison, papilloedema (optic disc swelling from raised intracranial pressure), does not usually affect visual acuity until it is at a late stage.
What should be done when assessing pupillary reflexes
With the patient seated, dim the lights in the assessment room to allow you to assess pupillary reflexes effectively.
Describe assessment of the direct pupillary reflex
Assess the direct pupillary reflex:
Shine the light from your pen torch into the patient’s pupil and observe for pupillary restriction in the ipsilateral eye.
A normal direct pupillary reflex involves constriction of the pupil that the light is being shone into
Describe assessment of the consensual pupillary reflex
Assess the consensual pupillary reflex:
Once again shine the light from your pen torch into the same pupil, but this time observe for pupillary restriction in the contralateral eye.
A normal consensual pupillary reflex involves the contralateral pupil constricting as a response to light entering the eye being tested.
Describe the swinging light test
Move the pen torch rapidly between the two pupils to check for a relative afferent pupillary defect (see more details below).
Describe assessment of the accommodation reflex
- Ask the patient to focus on a distant object (clock on the wall/light switch).
- Place your finger approximately 20-30cm in front of their eyes (alternatively, use the patient’s own thumb).
- Ask the patient to switch from looking at the distant object to the nearby finger/thumb.
- Observe the pupils, you should see constriction and convergence bilaterally.
Describe the afferent and efferent limbs of the pupillary light reflex
Each afferent limb of the pupillary reflex has two efferent limbs, one ipsilateral and one contralateral.
The afferent limb functions as follows:
Sensory input (e.g. light being shone into the eye) is transmitted from the retina, along the optic nerve to the ipsilateral pretectal nucleus in the midbrain. The two efferent limbs function as follows:
Motor output is transmitted from the pretectal nucleus to the Edinger-Westphal nuclei on both sides of the brain (ipsilateral and contralateral).
Each Edinger-Westphal nucleus gives rise to efferent nerve fibres which travel in the oculomotor nerve to innervate the ciliary sphincter and enable pupillary constriction.
What does each pupil reflex test assess
Normal pupillary light reflexes rely on the afferent and efferent pathways of the reflex arc being intact and therefore provide an indirect way of assessing their function:
The direct pupillary reflex assesses the ipsilateral afferent limb and the ipsilateral efferent limb of the pathway.
The consensual pupillary reflex assesses the contralateral efferent limb of the pathway.
The swinging light test is used to detect relative afferent limb defects.
Describe the RAPD
Relative afferent pupillary defect (Marcus-Gunn pupil): normally light shone into either eye should constrict both pupils equally (due to the dual efferent pathways described above). When the afferent limb in one of the optic nerves is damaged, partially or completely, both pupils will constrict less when light is shone into the affected eye compared to the healthy eye. The pupils, therefore, appear to relatively dilate when swinging the torch from the healthy to the affected eye. This is termed a relative…. afferent… pupillary defect. This can be due to significant retinal damage in the affected eye secondary to central retinal artery or vein occlusion and large retinal detachment; or due to significant optic neuropathy such as optic neuritis, unilateral advanced glaucoma and compression secondary to tumour or abscess.
Describe unilateral efferent deficits
Unilateral efferent defect: commonly caused by extrinsic compression of the oculomotor nerve, resulting in the loss of the efferent limb of the ipsilateral pupillary reflexes. As a result, the ipsilateral pupil is dilated and non-responsive to light entering either eye (due to loss of ciliary sphincter function). The consensual light reflex in the unaffected eye would still be present as the afferent pathway (i.e. optic nerve) of the affected eye and the efferent pathway (i.e. oculomotor nerve) of the unaffected eye remain intact.
Summarise colour vision assessment
Colour vision can be assessed using Ishihara plates, each of which contains a coloured circle of dots. Within the pattern of each circle are dots which form a number or shape that is clearly visible to those with normal colour vision and difficult or impossible to see for those with a red-green colour vision defect.
Describe how to use the isihara plates
If the patient normally wears glasses for reading, ensure these are worn for the assessment.
- Ask the patient to cover one of their eyes.
- Then ask the patient to read the numbers on the Ishihara plates. The first page is usually the ‘test plate’ which does not test colour vision and instead assesses contrast sensitivity. If the patient is unable to read the test plate, you should document this.
- If the patient is able to read the test plate, you should move through all of the Ishihara plates, asking the patient to identify the number on each. Once the test is complete, you should document the number of plates the patient identified correctly, including the test plate (e.g. 13/13).
- Repeat the assessment on the other eye.
Describe some colour vision deficiencies
Colour vision deficiencies can be congenital or acquired. Some causes of acquired colour vision deficiency include:
Optic neuritis: results in a reduction of colour vision (typically red).
Vitamin A deficiency
Chronic solvent exposure
Describe visual neglect/inattention
Visual neglect (also known as visual inattention) is a condition in which an individual develops a deficit in their awareness of one side of their visual field. This typically occurs in the context of parietal lobe injury after stroke, which results in an inability to perceive or process stimuli on one side of the body. The side of the visual field that is affected is contralateral to the location of the parietal lesion. It should be noted that visual neglect is not caused by optic nerve pathology and therefore this test is often not included in a cranial nerve exam.
Describe the assessment of visual neglect
- Position yourself sitting opposite the patient approximately 1 metre away.
- Ask the patient to remain focused on a fixed point on your face (e.g. nose) and to state if they see your left, right or both hands moving.
- Hold your hands out laterally with each occupying one side of the patient’s visual field (i.e. left and right).
- Take turns wiggling a finger on each hand to see if the patient is able to correctly identify which hand has moved.
- Finally wiggle both fingers simultaneously to see if the patient is able to correctly identify this (often patients with visual neglect will only report the hand moving in the unaffected visual field – i.e. ipsilateral to the primary brain lesion).
What is important to remember about testing visual fields
This method of assessment relies on comparing the patient’s visual field with your own and therefore for it to work:
you need to position yourself, the patient and the target correctly (see details below).
you need to have normal visual fields and a normal-sized blindspot.
Describe the visual field assessment
- Sit directly opposite the patient, at a distance of around 1 metre.
- Ask the patient to cover one eye with their hand.
- If the patient covers their right eye, you should cover your left eye (mirroring the patient).
- Ask the patient to focus on part of your face (e.g. nose) and not move their head or eyes during the assessment. You should do the same and focus your gaze on the patient’s face.
- As a screen for central visual field loss or distortion, ask the patient if any part of your face is missing or distorted. A formal assessment can be completed with an Amsler chart.
- Position the hatpin (or another visual target such as your finger) at an equal distance between you and the patient (this is essential for the assessment to work).
- Assess the patient’s peripheral visual field by comparing to your own and using the target. Start from the periphery and slowly move the target towards the centre, asking the patient to report when they first see it. If you are able to see the target but the patient cannot, this would suggest the patient has a reduced visual field.
- Repeat this process for each visual field quadrant, then repeat the entire process for the other eye.
- Document your findings.
Describe the types of visual field defects
Bitemporal hemianopia: loss of the temporal visual field in both eyes resulting in central tunnel vision. Bitemporal hemianopia typically occurs as a result of optic chiasm compression by a tumour (e.g. pituitary adenoma, craniopharyngioma).
Homonymous field defects: affect the same side of the visual field in each eye and are commonly attributed to stroke, tumour, abscess (i.e. pathology affecting visual pathways posterior to the optic chiasm). These are deemed hemianopias if half the vision is affected and quadrantanopias if a quarter of the vision is affected.
Scotoma: an area of absent or reduced vision surrounded by areas of normal vision. There is a wide range of possible aetiologies including demyelinating disease (e.g. multiple sclerosis) and diabetic maculopathy.
Monocular vision loss: total loss of vision in one eye secondary to optic nerve pathology (e.g. anterior ischaemic optic neuropathy) or ocular diseases (e.g. central retinal artery occlusion, total retinal detachment).
