Cranial nerve testing is an important part in the neurology evaluation. Recently, I did a thorough article on how to perform an efficient neurology evaluation in physical therapy. In this article, I want to discuss cranial nerve testing in little depth.
Cranial Nerve 1 (Olfactory Nerve):
To test cranial nerve one, is to test the ability of a person to smell. You can provide a person a cup of coffee, orange (any citrus smell), etc. Have a person close the eyes and one nostril and ask him/ her to tell you the object based on the smell.
Honestly, I don’t do the cranial nerve 1 (olfactory) testing on day 1 of my neuro eval. Yes, I am aware that having a loss of sense of smell can be a huge safety issue, especially if a person is looking into going home independently. But, I don’t have to make that judgment call on day 1. Plus, loss of function of cranial nerve 1 is not clinically significant of anything.
Cranial Nerve 2 (Optic Nerve) :
Function of the optic nerve is tested by checking visual acuity and visual fields.
For Visual acuity, have the patient cover one eye, and ask them to read a Snellen chart from a 14 inches distance.
To assess visual fields, have the patient look into your both eyes. Hold your hands midway between you and your patient. Move your finger far enough laterally that you can barely see them out of the ocean of your eyes, without moving your head. Ask the patient to indicate on which side the finger is moving. Repeat it in upper and lower quadrants.
This reflex tests the pupillary reaction to the light. The Pupillary reflex has sensory innervation from CN 2 and motor innervation from CN 3. This is more for your knowledge, you are not going to need this info clinically, unless you have a patient who has one of these two nerves (CN 2 & 3) affected.
Cranial Nerve 3 (Oculomotor), 4 (Trochlear), & 6 (Abducens) :
As you know CN 3,4 & 6 are tested together as they supply ocular muscles. These nerves are tested by testing the gaze in all six (up, down, left, right & oblique) directions.
Here is a picture I like to follow for this movement. I like it as it also identifies the different muscles that are involved with the movement.
Hare, you also have to observe for Saccade, convergence, smooth pursuits and Nystagmus. These are cardinal central signs that differentiates from a peripheral injury.
This is a rapid eye movement from one object to another.
Hold two fingers 3 cm from midline, around 6 inches away from the patient. Ask the patient to quickly look from one to the other finger without moving their head.
You can test the saccadic movement by holding the finger 3 cm up and 3 cm down from the midline.
While the patient is rapidly moving their eyes, observe for the eye movement, for any under shooting or over shooting.
This is a slow movement of the eye.
You can hold one finger either vertically or horizontally and ask the patient to slowly follow the fingers from one to the other. Observe the smoothness of the movement.
It is misalignment of the eyes while focusing on the nearby object.
Hold a finger in front of the patient’s nose and gradually bring it close to the nose. Ask the patient when s/he starts seeing the double. You measure the distance from the tip of the nose to the point where your patient sees the double.
The distance is convergence insufficiency for your patient. Around 3 cm of distance for the double vision is considered normal.
Nystagmus is rapid rhythmic oscillatory movements of the eye.
It has two phases : fast phase and a slow phase. It is directional specific and sometimes changes direction. The direction of the fast phase determines the direction of the Nystagmus.
Nystagmus can be of many types and due to many reasons. This is one of the very important differential diagnostic signs for a therapist in neuro settings. One can observe Nystagmus in upward, downward, left, right, torsional, as well as direction changing. Usually, downward Nystagmus, and directional changing Nystagmus are of a central origin, while others can have a peripheral cause to it.
Vestibular disorders, MS, stroke, TBI, vascular insufficiency are a few examples where a therapist expects to see Nystagmus in the patients.
Knowing a little bit about Nystagmus helps to determine whether to treat or not to treat the patient. As always, if there is a new medical finding that we are observing, we should reach out to either PCP or a neurologist.
Cranial Nerve 5 (Trigeminal Nerve):
Trigeminal nerve is a mixed nerve. It has a sensory, motor and mixed component to it.
The cranial nerve is responsible for the facial sensation from forehead to chin. It has three divisions. V 1 (Ophthalmic), V 2 (maxillary) and V 3 ( mandibular). You can check patient;’s facial sensation by using a cotton swab on different parts of the face and asking the patient whether they feel the swab or not.
In addition to the sensation, it is also responsible for the strength of the temporalis muscle and masseter muscle. To check the muscle strength, ask the patient to clench the teeth, open the mouth etc.
Trigeminal Neuralgia is a clinical condition that occurs with an inflammation of the CN 5.
This reflex has sensory supply by CN 5 and motor by CN 7. To test this, lightly touch the peripheral part of the cornea with a swab of a cotton and look for a blinking response.
Cranial Nerve 7 (Facial Nerve) :
This nerve is responsible for all facial movement. It supplies all the facial muscles. So to test this, you ask your patient to perform various facial movements like smile, puff their cheeks, close their eyes, raise eyebrows etc..
Facial palsy and a Bell’s palsy are conditions that occur due to a damage to a facial nerve. The main differentiation of the conditions mentioned above, are based on a site of a lesion. Facial palsy is a UMN while bell’s palsy is a LMN.
Cranial Nerve 8 (Vestibulocochlear Nerve):
This nerve is responsible for mainly hearing. You may have heard terms like sensorineural hearing and conductive hearing, or bone conduction loss and air conduction loss. Those are fancy terminology to describe hearing conduction.
The easiest and fastest way to text the CN 8, is to rub your finger closer to the patient’s ear and ask the patient if they hear your finger.
To test the function of this nerve, use a tuning fork and put it on the mastoid process (behind the ear) of a patient’s ear and ask the patient if they can hear the vibration of the fork. You can also put the tuning fork on the head and ask the patient if s/he hears it on both ears the same. I honestly do not perform these tests on my stroke patient, unless I see a vestibular involvement. Or my patient shows other significant signs like Nystagmus, vertigo, loss of balance.
Vestibular Neuritis is one of the common conditions that can occur with damage to CN 8.
Cranial Nerve 9 (Glossopharyngeal Nerve) & CN 10 ( Vagus Nerve):
The best and easy way to test the function of these two nerves is by assessing, and testing swallowing, gag reflex, voicing, coughing as well as palate elevation. You can ask the patient to open their mouth wide, ask them to say “AH” and check for palate movement, any deviation, check uvula etc..
Vagus nerve is also responsible for visceral organ function and an important part of a parasympathetic nervous system.
Clinical Significance: Glossopharyngeal neuralgia is a clinical condition that can occur with irritation or inflammation of cranial nerve 9, or cranial nerve 10.
Cranial Nerve 11 (Spinal Accessory nerve):
A therapist needs to check the muscle strength of Trapezius (shrug the shoulder) and sternocleidomastoid (Head rotation) to assess this CN.
Cranial Nerve 12(hypoglossal Nerve):
Check the position, sensation, movement of the tongue to check this CN.
So, here is how we can test all cranial nerves. I hope this article helps you to assess cranial nerves and differentiate the clinical presentations during your neuro evaluation.