Cranial nerves are part of the peripheral nervous system and are directly in contact with the brain. There are 12 pairs of cranial nerves and they can be seen on the ventral surface of the brain. Each nerve has got a specific name that is either related to its appearance or function. They have got a number assigned to it which corresponds to its position along the longitudinal axis of the brain starting at the cerebrum. Each cranial nerve attaches to the brain near the associated sensory or motor nuclei. 1) Each cranial nerve is classified into a specific group such as; sensory, special sensory, motor or mixed which ill each perform a different function and carry different forms of information. The cranial nerve assessment has been undermined due to modern imaging modalities where in the past it was essential in order to find and diagnose specific lesions(2) although saying this, a Cranial nerve examination still forms part of a complete neurological assessment and needs to be performed.
The reason for the cranial nerve examination is to identify problems with the cranial nerves by means of a physical examination. In order for a full examination to take place all 12 pairs of cranial nerves need to be tested in their own pecific way that is related to their function. How to perform the cranial nerve examination: Before starting with the examination you as the practitioner needs to make sure that you are prepared by making sure that you have the appropriate PPE on or that your hands are clean and that you are competent and comfortable with the procedure that you are about to perform.
Ensure that the environment that you will be working in is comfortable for you as well as for the patient and that it has all the right lighting and ventilation to allow for a comfort and a thorough examination that yields accurate results. A mnemonic known as WIPE can be used to remember all the above. (3) • Wash hands Introduce yourself Permission from the patient to allow you to perform the exam. Position (patient should be sitting facing you and at the same eye level. • Exposure (Face exposed only) Once you are satisfied with the above you need to perform a general assessment of the patient by checking whether or not the patient is in pain or uncomfortable in any way. While you are talking to the patient you may notice other abnormal findings such as facial asymmetry or other signs that may indicate that there is a problem. When you are satisfied with everything so far you can move on to the actual examination of each pair of cranial nerves.
It is best to have a systemic approach and to do the assessment in the order of each cranial nerve as to not leave anything out. AND REMEMBER TO EXPLAIN EACH PROCEDURE TO THE PATIENT BEFORE IT IS DONE!! Olfactory Nerves (I) Since the Olfactory Nerve is responsible for smell it is important to ask the patient if they have noted any changes regarding their smell or their taste, as anosmic patients do not always complain about loss of smell but rather about altered taste. ) Once you start examining the patient you first need to look at the external appearance of the nose to for any obvious deformity. (2)(4) You will ask the patient to close his/her eyes and occlude one nostril and ask them to detect the odour that is placed before them, you will do this to both nostrils separately and compare the two.
It is important to use non-irritating substances and those that stimulate trigeminal nerve endings or taste buds. (5) • Optic Nerves (II) In order to test the optic nerves there are 3 main tests that need to be done namely: 1. Visual acuity 2. A Snellen chart can be used. Ask the patient to cover one eye (not close it) and read all the letters line by line starting from the top with the larger letters and working their way down to the smaller letters. 1. 2Each line that is read has got a corresponding number which indicates the distance that a normally sighted person would be able to see. 6/12 means that at 6m the patient can just read the line that should just be visible at 12m. (6) 2. Visual fields You as the examiner need to make sure that you and your patient are at the same level and about 1m apart.
You cover the patient’s one eye while you close the opposite eye to which the patient is closing and ask them to look at your open eye. A red pen should then be brought in from 4 directions (the upper temporal, lower temporal, upper nasal, lower nasal)(3) diagonally towards the centre of the visual fields. The patient needs to say “yes” when the red pen becomes clearly visible. (2) You then compare their visual fields to your own noting any defects. You then repeat this procedure for the other eye. (3) 3.
Fundoscopy In order to perform a Fundoscopy you require an phthalmoscope in order to assess the optic disk and retina. The room needs to be darkened and you need to be sitting at eye level with the patient. You then need to adjust the ophthalmoscope lens between 0 and -4 if both you and the patient don’t wear glasses but if you do then just dial in the approximate power of your lenses in order to get accurate results. Put the ophthalmoscope to your right eye and asses the patients right eye and then do the same with the left eye.
Start by looking about 1m from the patient and you should notice a bright pink reflection coming from the patient’s eye, this is nown as the red reflex which means that there is no cloudiness s no or denseness preventing the light reaching the fundus. The next step is asking the patient to focus on a distant object while you look for the optic disk.
Then you need to follow the superior and inferior temporal and nasal arteries and veins from the disk and examine the 4 quadrants of the fundus ensuring that all is normal. 6) Oculomotor Nerves (III), Trochlear Nerves (IV), Abducens Nerves (VI) Since cranial nerve III, IV and VI innervate the muscles of eye movement they are tested as a unit. (4) When testing these erves it is important to do a number of tests involving: • The appearance of the eyes: assess the shape and symmetry and look for ptosis and nystagmus. • ASsess the movement of the eyeball: You will ask the patient to not move their head or keep it as still as possible while they will be instructed to follow the practitioner’s finger.
You as the practitioner want to move your finger laterally and then up and down on the left hand side and then up and down on the right hand side. (finger movement is in the shape of an H) While doing this you need to look out for any tosis or a limitation in eye movement and ask the patient if they have double vision at any point. • Assess the pupils for symmetry and their size. • Test papillary light reaction: You will want to shine a light into the patient’s eye but bring the light in from the side to test their reactions more accurately.
You only want to assess one eye at a time therefore it is imperative to block the other non -tested eye from the light. (Don’t completely cover it but place the patients hand vertically between the eyes which will stop the light reaching the other eye. ) • Pupillary reaction to convergence and ccommodation reflex: ask the patient to look at your finger once again, bring your finger in from an approximate distance of 1m and bring it within a few centimetres of the patient’s nose. The reaction that you want is for the eyes to converge and for the pupils to constrict.
Trigeminal Nerves (V) In order to test the Trigeminal nerve 3 aspects need to be assessed, (4)(5)(7) namely: facial sensation, muscles of mastication and the Corneal Reflex. (3) • Facial Sensation: Use a sterile sharp object and run it across the forehead, cheek and the jaw and determine if the patient is able to pick up the sensation. If any of these come back as abnormal then test temperature by using a water-heated/cooled tuning fork or light touch. •Muscles of mastication: The patient is required to clench their teeth. Palpate the temporal masseter muscles for any signs of abnormality.
The patient is then required to open their mouth while the practitioner assesses the symmetry of the mouth. A jaw jerk may also be tested by the practitioner, by placing fingers on the tip of the patients jaw then uses a hammer to tap their fingers lightly. • Corneal Reflex: use a piece of sterile cotton wool and touch the cornea of the patient’s eye gently. (Perform on both eyes. The blinking of both eyes is a normal response but if there is a blink in the contralateral eye this may indicate ipsilateral seventh nerve palsy. 2) • Facial Nerves (VII) The facial nerves need to be tested in 2 parts seeing that it controls most facial expressions, secretions of tears,saliva and taste. (4)
1. Testing the muscles of facial expression: 1. 1 Inspection of the face for any facial droop or signs of asymmetry. 1. 2Ask the patient to look up and to wrinkle their forehead and look for any wrinkling loss. 1. 3 Ask the patient to shut their eyes and test the strength by trying to open each one and compare. 1. 4 Ask the patient to puff out their cheeks and feel that both sides are similar on palpation. 1. 5Ask the patient to grin and assess naso-labial grooves. 2. Assess the sense of taste In order to adequately assess taste, four groups of receptors found on the tongue need to be tested namely the salty (sodium chloride), sweet (sugar), bitter (quinine) and sour (vinegar) receptors. (4) The patient is asked to extrude their tongue and one of the four ingredients is placed onto it, the patient may not stick their tongue back into their mouth until they have identified if it is either sweet, sour, salty or bitter.
Vestibulocochlear Nerves (VIII) Auditory acuity can be tested generally by rubbing the thumb and index finger together starting peripherally and moving towards the ear and ask the patient to say when they are able to hear the sound. There are 2 main tests that are performed namely the Rinne test and the Weber’s test. Vestibular function may also be tested if there are complaints of dizziness or vertigo or evidence of nystagmus. (4)
1. The Rinne test: In order for this test to make sense you need to know that air conduction is normally better than bone conduction. ) A vibrating fork is placed on the mastoid process and once this is done the patient is asked to confirm that they can hear the sound and when the sound stops. The fork is then removed and placed close to the ear and asked whether or not they can hear it again. If the sound is heard this will indicate a negative Rinne test which indicates that the patient is healthy. 2. The Weber’s test: a vibrating tuning fork is held in the middle of the patient’s forehead and asked on which side the sound is the loudest.
In the normal patient it should be equal in both ears but if the sound is louder on the one side than the other then conductive deafness exists on that particular side or the opposite side ear has sensorineural deafness. (6) • Glossopharyngeal Nerves (IX)Vagus Nerves (X) When assessing these nerves a number of tests need to be performed by assessing the motor function of the palate, pharynx, and larynx. Sensory function needs to be assessed if one suspects cranial neuropathy or a brain stem lesion. (4) 1. Testing the palatal elevation: Ask the patient to say “ah”, you are then able to assess for a full and symmetrical elevation of the palate.
One side may be weaker than the other and it may not elevate and will be pulled towards the strong side indicating an abnormality. 2. Assess the gag reflex(this is testing the afferent portion of cranial nerve IX and the efferent portion of cranial nerve X)(4): (ensure to explain this test to the patient and explain to them that this will be a bit uncomfortable) Using a cotton swab, tongue blade or q tip gently touch the back of the pharynx and the normal response is for the patient to gag. 3. Test the sensory function by lightly touching the soft palate with the tip of a cotton swab and ask if the patient felt it.
4. During the examination and while talking to the patient ensure to listen carefully to your patients quality of voice by listening for hoarseness which may suggest laryngeal weakness. • Accessory Nerves (XI) This nerve innervates the motor to the muscles of the neck and upper back (1) and is also involved in swallowing. When performing this assessment ensure to test both the sternocleidomastoid muscle and the trapezius muscle. 1. In order to test the sternocleidomastoid muscle place your hand on the patients jaw and ask them to rotate their head towards your hand as this will test the strength of the muscle while under resistance. Remember to compare both sides.
• To test the trapezius muscle place your hands on the patient’s trapezius muscle and ask them to shrug their shoulders while they are under resistance and compare the strength of both sides. • Hypoglossal Nerves (XII) 1. Ask the patient to open their mouth and note the resting position of the tongue. 2. Proceed to ask the patient to stick out their tongue and if the tongue deviates to either side then there is a lesion on that particular side. 3. Ask the patient to stick their tongue into their cheek while you push on the cheek from the outside to test the strength of the tongue.