How to use these guides
The articles in this series, which can be torn out for use in practice, are intended to support clinician development and to assist in the overall assessment of patient presentations. The information should be used to aid consideration of differential diagnoses in situations where life-threatening conditions have been ruled out.
The extent and explanation of each examination will not be to the depth of those provided in core literature texts, so further reading and consolidation are advised to support understanding, supplemental to these articles. Key questions will be included for reader consideration and to direct further study.
Most examinations are taught in a rigid format. However, in clinical practice, practitioners need to be able to be flexible and adapt their approach dependent on the presenting condition and circumstance. While there is no single set way for each of these examinations, a good structure will reduce omissions and errors, and support the gathering of information to inform patient care.
Contemporary texts will provide the underpinning reference sources throughout this series, as many of the examination processes and techniques are universally applied but differences will be highlighted. Readers will be signposted to these key texts for each clinical examination.
The series will cover the following systems:
Cranial nerves I–VI
There are 12 pairs of cranial nerves, which originate from the brain or brainstem. Most of their names refer to either their functions or the structures they innervate (Marieb and Hoehn, 2019). Cranial nerves are generally referred to in Roman numerals from I (1) to XII (12) (Bickley and Szilagyi, 2017). They are numbered from rostral (from the front) to caudal (towards the back), and all but the vagus nerve (X) innervate only the head and/or neck (Marieb and Hoehn, 2019).
This article describes the assessment of cranial nerves I–VI, with cranial nerves VII–XII covered next month.
The level and depth of the assessment will depend on your patient's presenting complaint and physiological status. The cranial nerve examination may form part of a wider neurological examination. Depending on the circumstances, you may decide to complete only specific parts of this examination; for example, a patient complaining of acute onset of blurred vision in the left eye may require only an examination of the eyes, which may include testing visual acuity, visual fields, pupillary responses and the eye muscles.
As explained in the series overview last month, it is important to introduce yourself to the patient, explain what you intend to do for each part of the assessment and gain consent before carrying the assessment out. This examination will form part of a detailed secondary survey following a primary survey and completion of the patient history. You should adhere to infection control principles before you start, as well as throughout the examination. Finally, always thank your patient on completion of your assessment.
Equipment required
The ideal position is for the patient to be sitting opposite you with their eyes at the same level as yours.
General observations
Before to completing a cranial nerve examination, note any general observations:
I: olfactory nerve
The olfactory nerve is a sensory nerve whose function supports the sense of smell.
This nerve is not routinely tested in the prehospital setting (Lindridge, 2016). However, simply asking the patient if they have noticed a change to or loss of their sense of smell is a useful form of assessment. Asking the patient to differentiate between different substances may be used in a more formal assessment (Swartz, 2014).
REFLECTION
Consider the causes of anosmia and parosmia
II: optic nerve
The optic nerve is a sensory nerve, whose function supports vision.
There are several tests for this nerve.
Visual acuity
REFLECTION
What does 20/20 (or 6/6) vision mean?
Visual fields
Fundoscopy
Assessment of the retina to check for papilloedema (swelling of the optic disc) with an ophthalmoscope usually forms part of the assessment of the optic nerve (Marieb and Hoehn, 2019).
However, it is not performed in prehospital environments. In urgent care settings, fundoscopy may be undertaken if the clinician is trained to do so (Lindridge, 2016).
III: oculomotor; IV: trochlear; and VI: abducens
These three nerves are routinely assessed together as they are all involved in the motor function of eyeball movement (Thomas and Monaghan, 2014). The oculomotor nerve is also involved in pupil constriction and eyelid movement (Bickley and Szilagyi, 2017).
Pupillary response: light reflex
To assess the pupil response, shine a pen torch upwards and inferior to the pupil, avoiding direct glare (Thomas and Monaghan, 2014). Look for constriction in the pupil (direct reflex) and bilateral constriction of the opposing pupil (consensual reflex). Repeat this process for the other eye. The pupils should react and constrict at the same time (Swartz, 2014).
Pupillary response: convergence/accommodation
Eyeball movement
REFLECTION
Consider the causes of cranial nerve III palsy, ptosis, nystagmus and strabismus
V: trigeminal
The trigeminal nerve has both motor and sensory functions. It has three sensory divisions across the face (in the ophthalmic, maxillary and mandibular regions). The motor portion of this nerve is responsible for movement of the masseter and temporalis muscles, which are involved in chewing and jaw clenching (Swartz, 2014).
Sensory
REFLECTION
What could cause an impairment in sensation?
Motor
The corneal reflex is also part of this cranial nerve assessment but is not performed in the prehospital setting. Routine testing is not required (Innes et al, 2018).
REFLECTION
What is trigeminal neuralgia?
For each of the assessments for cranial nerves I–VI discussed in this article, consider the causes of acute and chronic impairments and the clinical significance of these. Next month's article will continue with a discussion on the assessment of cranial nerves VII–XII.