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Course: Health Assessment

Unit Title: Cranial nerves

Jackie Christianson, MSN, RN, FNP-C

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MODULE GOALS

Learner outcome:

At the completion of these modules the learner will demonstrate knowledge and skills to perform a complete health assessment of an individual

Module Objectives:

List the number, name, and function of each of the 12 cranial nerves
Describe how to assess the functioning of each of the 12 cranial nerves
Discuss the documentation of cranial nerve assessment
Interpret cranial nerve assessment findings

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NERVOUS FUNCTION REVIEW

Neurons

Action potentials
Synapses

Two parts based on anatomy

Central vs Peripheral

Afferent vs efferent
Glial cells

Myelin sheaths/Schwann cells
Ependymal cells
Astrocytes

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THE CRANIAL NERVES

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COMMON INDICATIONS FOR CRANIAL NERVE TESTING

Concern for neurologic functioning

Acute: Acute head injury, post-cranial surgery
Chronic: Known neurologic disease or problem
Any report of problems in body parts controlled by cranial nerves

Suspected emergency

CVA, myasthenia gravis crisis, acute MS attack, Guillain-Barre syndrome, head injury with severe mechanism or LOC changes

Known neurologic problem

Post-CVA, chronic MS, Bell’s palsy

Order per provider

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A brief review of the past few weeks:

The nervous system is made up of neurons and their support cells. Neurons are divided into three basic parts: cell body, dendrites, and axons. The cell body contains most of the neuron’s organelles. Dendrites and axons are extensions from the cell body. Axons are typically much longer and tail-like in appearance. The dendrites accept signals from other cells and transfer the nerve impulse to the cell body. The axons transmit signals to other cells. Action potentials, or an electrical change within the cell stimulated by flow of ions into and out of the cell, stimulate the release of neurotransmitters. Synapses are the gaps between axons and dendrites where the neurotransmitters are released.

The central nervous system refers to the brain and spinal cord. The peripheral nervous system refers to all other parts of the nervous system, such as the nerves that branch off of the spinal cord.

Afferent neurons are responsible for receiving messages from the peripheral nervous system. Efferent neurons are responsible for sending messages from the central nervous system.

Glial cells are neural cells that support the neurons. Some examples include Schwann cells which produce the myelin sheaths that insulate axons, astrocytes, and ependymal cells.

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CN I – OLFACTORY NERVE

Sense of smell
Testing procedure

Obtain a familiar strong scent
Plug one nare by holding shut with a finger
Place the scent near the open nare
Repeat with the other nare

Not routinely tested

Patient complaints of changes
Specific neurologic conditions

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CN II – OPTIC NERVE

Vision, visual field
Testing procedure

Visual acuity using Snellen chart
Visual field testing

Visual ability alone is not always adequate testing!

Some conditions can cause loss of part but not all of the field of vision

Routinely tested

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Cranial nerve testing is one component of a complete head-to-toe exam, but in your practice relatively few patients will require a comprehensive assessment. A cranial nerve exam is most commonly done in the setting of a concern for a patient’s neurologic functioning or a suspected emergency, a known neurologic deficit, a post-surgical patient for a cranial procedure, or when there is an order to have neurologic testing done from a provider. A cranial nerve exam is considered to be part of a complete neurologic assessment.

Note: Suspected emergency conditions do not always involve the cranial nerves themselves. Guillain-Barre syndrome, for example, is a peripheral nervous problem and does not affect the cranial nerves. A cranial nerve assessment is still an important part of assessing a patient with suspected or confirmed Guillain-Barre syndrome because a change in cranial nerve function can indicate missed diagnosis, additional neurologic problems, and help affirm or refute a suspected case that has not yet been confirmed.

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THE SNELLEN CHART – CLINICAL PEARLS

Always document: vision corrected or uncorrected

Corrected vision is preferred for CN function assessment

Do not apply any pressure on covered eye; can negatively impact that eye’s score
Test each eye individually then both
Test interpretation

First 20 in “20/X” score refers to the average vision at X feet away from the chart

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VISUAL FIELD TESTING – CLINICAL PEARLS

Do not apply pressure to covered eye
Test each eye individually; no need to test both together
Visual fields are tested in quadrants: left upper, left lower, right upper, and right lower

‘Left’ and ‘Right refer to the side of each eye, not the eye itself.

Video on testing visual acuity:

http://kellogg.umich.edu/theeyeshaveit/screen/visual_fields.html
Click ‘What do you do?’ then click the link for ‘confrontation visual field testing’

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To test pupillary response, place the patient in a dimly lit but not completely dark area. Using a light source like a pen light, approach one eye laterally with the light and watch the response of both pupils. Both the pupil that is exposed to light and the pupil that is not exposed to light should constrict equally and at the same time. When no longer exposed to the light source, both pupils should dilate. Perform this exam on both eyes.

An acronym used to document normal pupillary response is PERRLA, which stands for “pupils equal round and reactive to light and accommodation.” This means that pupils are equal in size, found to be round (not jagged or oval-shaped), they constrict when exposed to light and dilate when exposed to dark, and that when one pupil constricts or dilates, the other constricts and dilates in equal proportions to the exposed eye. Pupils may be unequal in size but may be accommodating, meaning they are not the same size but they constrict and dilate in conjunction with the opposite eye. Likewise, pupils that are equal in size are not always accommodating.

Cardinal fields of gaze are tested by instructing the patient to look at your finger by moving only their eyes. The tester can then move the finger in each of the 6 directions marked on the eye diagram on the slide. Watch both eyes for any jerking of either or both eyes (nystagmus), crossing of the eyes (strabismus), or inability to move either or both eyes in any particular direction. A normal exam can be documented as “EOMs normal” (EOMs are extra-ocular movements).

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CN III IV & VI – OCULOMOTOR, TROCHLEAR, & ABDUCENS

Trochlear nerve

Muscle that moves eyes medially and inferiorly (superior oblique muscle)

Abducens nerve

Muscle that moves eyes laterally (lateral rectus)

Oculomotor nerve

All other eye movements and pupillary response

Pupillary response

PERRLA

Cardinal fields of gaze test

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The trigeminal and facial nerve are both routinely tested during a neuro exam. The trigeminal nerve is both a sensory and motor nerve, the facial nerve is only sensory with regards to the cornea.

Corneal reflex how sensation of the facial nerve is tested. It is not routinely tested in the clinical setting, especially in patients who wear contact lenses as this reflex is dulled in patients who routinely manipulate the cornea. It is a more invasive exam and not always a helpful in evaluating cranial nerve function. It is tested by gently touching a cotton swab to the cornea and examining for a reflexive blink.

To test the sensory aspect of the trigeminal nerve, use your fingertip and the sharp end of a cotton swab. Prior to testing, show them what sharp and dull feels like so they know how to answer. Ask the patient to close their eyes and touch their face on either side or both sides alternating randomly where you touch and if you use the dull touch (fingertip) or sharp touch (the stick of the cotton swab). Ask them to tell you which side of the face you are touching, and if it is sharp or dull. An abnormal test is either an area or an entire side of the face that has diminished or absent sensation as measured by inability to distinguish soft vs dull or feel the touch at all.

Motor function testing of the trigeminal and facial nerve is done concurrently during most neurologic and cranial nerve exams. Ask the patient to do each of the following tasks:

-Raise eyebrows up

-Shut eyes as tightly as they can

-Smile showing all of the teeth

-Puff out cheeks

An abnormal test is a test in which the patient is either unable to do any of these tasks OR in which you notice a difference between the sides of the face (ie: one side can do the task, the other side does not look approximately equal). Particularly during the smile test, examine the patient’s nasolabial fold; there can be subtle flattening of one side of the nasolabial fold that is not always intuitive to see, but does constitute an abnormal test finding particularly in suspected CVA patients.

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Testing CN III IV & VI

OCULOMOTOR, TROCHLEAR, & ABDUCENS

Pupillary response and Cardinal fields of gaze test

Pupillary response:

https://www.youtube.com/watch?v=_0oC1P4sqBQ

Cardinal fields of gaze test:

https://www.youtube.com/watch?v=HY8z52fwAzQ

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The trigeminal and facial nerve are both routinely tested during a neuro exam. The trigeminal nerve is both a sensory and motor nerve, the facial nerve is only sensory with regards to the cornea.

Corneal reflex how sensation of the facial nerve is tested. It is not routinely tested in the clinical setting, especially in patients who wear contact lenses as this reflex is dulled in patients who routinely manipulate the cornea. It is a more invasive exam and not always a helpful in evaluating cranial nerve function. It is tested by gently touching a cotton swab to the cornea and examining for a reflexive blink.

To test the sensory aspect of the trigeminal nerve, use your fingertip and the sharp end of a cotton swab. Prior to testing, show them what sharp and dull feels like so they know how to answer. Ask the patient to close their eyes and touch their face on either side or both sides alternating randomly where you touch and if you use the dull touch (fingertip) or sharp touch (the stick of the cotton swab). Ask them to tell you which side of the face you are touching, and if it is sharp or dull. An abnormal test is either an area or an entire side of the face that has diminished or absent sensation as measured by inability to distinguish soft vs dull or feel the touch at all.

Motor function testing of the trigeminal and facial nerve is done concurrently during most neurologic and cranial nerve exams. Ask the patient to do each of the following tasks:

-Raise eyebrows up

-Shut eyes as tightly as they can

-Smile showing all of the teeth

-Puff out cheeks

An abnormal test is a test in which the patient is either unable to do any of these tasks OR in which you notice a difference between the sides of the face (ie: one side can do the task, the other side does not look approximately equal). Particularly during the smile test, examine the patient’s nasolabial fold; there can be subtle flattening of one side of the nasolabial fold that is not always intuitive to see, but does constitute an abnormal test finding particularly in suspected CVA patients.

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CN V & VII – TRIGEMINAL & FACIAL

Trigeminal

Sensory and motor nerve of the lower 2/3 of face

Facial

Sensory for cornea, motor for certain facial muscles

Sensation testing throughout both sides of face

Sharp vs dull sensation
Corneal reflex

Motor function

Equal masseter muscle tone
Smile to show teeth
Raise eyebrows
Puff out cheeks
Examine for nasolabial fold flaccidity

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CN VIII - VESTIBULOCOCHLEAR

Sensory

Hearing
Webber and Rinne tests
What if you don’t have a tuning fork?
Finger rub test

Motor

Sense of balance
Rhomberg test

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Webber test: Strike the tuning fork and place it on the patient’s midline forehead. The sound should be approximately equal on both sides. A positive test finding is a louder sound on one side compared to the other.

Rinne test: Strike the tuning fork and hold it approx. 6 cm away from the external ear. Strike the tuning fork again, but place the end (not the pronged part) on the mastoid bone (directly posterior to the external ear). The volume should be perceived as approximately equal. A positive test is a test in which the air conduction is louder than conduction over the mastoid bone. Do this exam bilaterally.

If no tuning fork is available, it is acceptable to use the finger rub test to evaluate for hearing. Standing behind the patient, ask the patient to close their eyes. Hold each of your hands outside the patient’s ears on each side approximately 10 cm from the external ear. Instruct the patient to tell you which side they hear your fingers rubbing on. Alternate each side and both sides and evaluate the patient’s hearing with strong finger rub (10 cm from the head). Then repeat the test with your hands positioned at an arms length away (faint finger rub). This test is also called the CALFRAST test.

Rhomberg test: Ask the patient to stand up with their feet together, hands extended, palms up. Have the patient close their eyes. A normal Rhomberg test is a test in which the patient maintains their balance without wavering or assistance. A positive Rhomberg test is one in which the patient cannot maintain balance, breaks out of their stance due to balance issues, or falls while attempting to close their eyes.

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CN IX - GLOSSOPHARYNGEAL

Motor control of pharynx, larynx
Sensory control of tongue
Motor: Gag reflex testing

Not routinely performed intentionally
Tongue depressor to back of throat
Should produce a visible gag

Sensory: Taste testing

Not routinely performed
Easily skewed or misinterpreted
Taste testing

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The glossopharyngeal nerve is not routinely tested, but may be useful in cases in which the patient is unable to or having difficulty swallowing. The motor aspect is more commonly tested than the sensory one.

Gag reflex testing is accomplished very simply; find a clean item, like a tongue depressor or a cotton swab, and touch it to the back of the throat. It should produce a visible and sometimes audible gag. An abnormal test finding is an absent gag reflex. There is great variety in what a normal gag reflex looks like; some people have very strong gag reflexes where others have a minimal gag reflex. A very strong or a very minimal gag reflex is not abnormal. Additionally, the gag reflex can be suppressed via training as with the knife swallower in the photo.

Sensory testing of CN IX is not routinely done even with testing of this cranial nerve, but can be accomplished by plugging the nose and having the patient, with their eyes closed, taste a strong and familiar taste, like an orange, garlic, or coffee.

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CN X – VAGUS NERVE

More challenging to evaluate

Innervates the parasympathetic nervous system
Difficult to easily evaluate function of all branches

Uvula control

Ask the patient to open their mouth and say “Ahhhhhh”
Uvula should remain midline while making the sound
Abnormal exam is uvular deviation

to one side

Lesion is located on the opposite
side of the deviation

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CN XI – ACCESSORY

Controls some of the shoulder muscles

Upper trapezius
Sternocleidomastoid

Shoulder shrug test

Face patient
Place one hand on each shoulder
Ask the patient to shrug
Evaluate strength, equality between sides

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CN XII - HYPOGLOSSAL

Motor: muscles of the tongue

Ask the patient to read you a short passage
Stick tongue out
Wiggle tongue to both sides

Abnormal findings:

Slurred speech
Tongue deviation to either side
Difficulty moving tongue

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WHAT WOULD THE NURSE DO?

Combine aspects of the cranial nerve assessment

Focus on each body part to streamline your exam
Learn to distinguish each CN during your exam, but do not necessarily do the exam in order of CN

Example: Eyes

Test visual acuity

CN II

Test pupillary response

CN III

Test cardinal fields of gaze

CN III, IV, VI

Test visual field

CN II

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Generally speaking, the order in which you test each body part involved in a cranial nerve assessment is not important. It is just as acceptable to do hearing testing, if deemed necessary, before you do the eye portion of the exam as it is to start with the eye portion, then perform the facial movements, then evaluate the hearing. It is important to always perform your assessments using the same technique and it is helpful to always do your assessment in the same order every time. Be conscientious of exams that may affect later exams, for example testing pupil reactivity after visual acuity as mentioned in a previous slide.

Before you perform your assessment, evaluate what is known about the patient. Do they have any known neurologic deficits, cranial surgeries, or any other complicating factors? Will part of your assessment pose any risk to the patient? Adjustments may need to be made to help the patient complete the exam such as age-related changes and for patients with functional deficits. Always document any changes made as a result of a functional deficit, for example if the patient is blind in one eye document this when assessing for that eye’s field of vision and visual acuity.

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COMMON DISORDERS AFFECTING THE CRANIAL NERVES

Acute

Emergent: CVA, trauma
Subemergent: Dystonic reaction
Non-emergent: Bell’s palsy, migraine

Chronic

Multiple sclerosis, trigeminal neuralgia, HIV/AIDS, Parkinson’s, neurofibromatosis, underlying TBI

Some chronic problems may imitate cranial nerve deficits

Sturge-Weber, Myasthenia gravis, etc.

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Aspects of the cranial nerve assessment can be combined into a more fluid exam. Rather than testing each cranial nerve in order, you can test each body part and evaluate cranial nerves together. For example, it does not make sense to test the eye movement infero-medially to test cranial nerve IV, then test the sensory and motor skills of the lower 2/3 of the face (CN V), then test lateral eye movement (CN VI), then test corneal sensation and motor muscles of mouth (CN VII).

It is acceptable to do different aspects of the cranial nerve exam in different orders, but it is important to develop a routine method for testing them. For example, it is acceptable to test the olfactory nerve (if it is deemed necessary) at any point during the exam, but it does not make sense to interrupt the series of eye exams to do the olfactory testing in the middle of examining all of the cranial nerves that affect the eyes. When determining your practice for cranial nerve testing, you should also be conscientious of exam practices that may impact later exams. For example, do not test visual acuity immediately after testing pupillary response because the bright light in the eyes can negatively impact visual acuity and cause your test to be inaccurate.

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EVALUATING THE PATIENT WITH KNOWN CHRONIC CRANIAL NERVE DYSFUNCTION

Challenging, especially in non-communicative patients
Ask the patient, caregiver:

Baseline function
Noted changes (if any)

Consult previous medical records

Previous diagnoses and assessment findings

Report any new neurologic findings to the provider

If in doubt, err on the side of reporting findings

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When evaluating for cranial nerve function (versus evaluating for function of the eye itself), it is ideal to do a corrected visual acuity screening using the patient’s glasses or contact lenses whenever possible. A physical correctable problem with the eye may cause false positive tests if cranial nerve testing is done without vision correction.

When screening for vision, make sure pressure is not applied to the covered eye. Ideally, use a piece of paper to cover the eye like a window shade rather than the patient’s hand over the eye. Light pressure over one eye can negatively impact that eye’s score, so avoid this if at all possible to preserve accurate findings.

Start with each eye at the top-most row. Have the patient continue to read letters or name symbols down the chart until they are unable to continue to read the letters or symbols correctly. The last line they can read is the patient’s score; each line comes with a number “20/X” that tells you what to document as their score for each try.

Each eye should be tested individually, then both together. It is typical to have some differences between each eye and to have a difference between the individual eyes and both eyes together. Usually both eyes together produces the best visual acuity.

When interpreting the test, it is important to know what the numbers on the test mean. The first 20 in the “20/X” score refers to what an average person can X feet away from the chart. A score of 20/100, for example, means the patient can see at 20 feet from the chart what a normal person can see 100 feet away from the chart. A score of 20/40 means that the patient can see at 20 feet away what a normal person can see at 40 feet away. 20/20 is considered to be “perfect” vision, or vision that is exactly what is expected. Numbers in which the second number is greater than the first indicate nearsightedness, or patients who can see near well but have a harder time with long-distance viewing (examples: 20/100, 20/40…). Numbers in which the second number is less than the first indicate farsightedness, or patients who can see far away better than they can see near (examples: 20/10, 20/15).

When interpreting results, it is important to keep in mind the patient’s baseline functioning. Many patients have one eye that is stronger than the other, and there is wide variance in visual acuity. If the patient’s baseline visual acuity is not known, it is acceptable to ask them if they know, or if they think their vision is changed compared to their baseline and how it compares to their normal.

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PUTTING IT ALL TOGETHER

Order of CN exam generally unimportant

Few exceptions, usually functional in nature
Example: Test visual acuity before pupils

Assess every patient the same way every time

Do your assessments in the same order
Perform your assessments using the same techniques
Document your assessments in the same manner

Assess: Acute vs Chronic changes

Known neurologic deficit or condition
Complicating and possible risk factors

Adjust as needed for special circumstances

Age, functional deficits
Document changes in assessment technique

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‘Left’ and ‘Right refer to the side of each eye, not the eye itself. The right upper quadrant, for example, must be documented on both right and left eyes.

Visual field testing tests both how wide the visual field is and for deficits within each eye’s field of vision. Each eye is tested separately and do not need to be tested together. The visual field in each eye is divided into 4 quadrants. Stand face-to-face with the patient and have them look at your nose during this exam; encourage them to avoid moving their eyes to see the tests. There are a variety of ways to test the visual field; one method is to flash fingers in each of the 4 eye quadrants and ask the patient how many fingers you are holding up. The video linked is an example of this method.

A normal visual field test is intact vision in all 4 quadrants of both eyes. An abnormal test is either a loss of visual field in one of the 4 quadrants or a change in one of the halves of the field of vision in either or both eyes. Loss of half of the visual field is referred to as hemanopia and is a commonly assessed feature of CVA. Some patients with optic nerve damage or with certain conditions of the eye can also have loss of peripheral or central vision, but retain the other aspect. This is a common finding in patients with optic atrophy resulting from MS and other degenerative nervous diseases.

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Glossary

anterior- front of body

the stomach is anterior to the back

posterior- back of body
medial- closer to the midline of the body

the nose is medial to the ears

lateral-farther from midline of body

the ears are lateral the nose

superior- closer to the head
inferior- closer to the feet
superficial-close to the surface of the body
deep- farther from surface of the body
proximal- closer to main body

the bicep is proximal to the fingers

distal- further from main body

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REFERENCES

Damodaran, O., Rizk, E., Rodriguez, J., & Lee, G. (2014). Cranial nerve assessment: A concise guide to clinical examination. Clinical Anatomy, 27(1), 25-30.

Goldberg, C. (n.d.). Detailed review of cranial nerves. University of California School of Medicine. Retrieved from https://meded.ucsd.edu/clinicalmed/pe_cranialexam.pdf

Jarvis, C. (2015). Physical examination & health assessment (7th ed.). Philadelphia, PA: Elsevier Health Sciences.

Contact info: info@nursesinternational.org

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REFERENCES

Maher, A. (2016). Neurological assessment. International Journal of Orthopaedic and Trauma Nursing, 22(8), 44-53.

Marieb, E., & Hoehn, K. (2007). Human anatomy and physiology (7^th ed.). Benjamin Cummings Publishing,.

Ontaneda, D., & Rae-Grant, A. (2009). Management of acute exacerbations in multiple sclerosis. Annals of Indian Academy of Neurology, 12(4), 264-272.

Torres-Russotto, D., Landau, W., Harding, G., Bohne, B., Sun, K., & Sinatra, P. (2009). Calibrated finger rub auditory screening test (CALFRAST). Neurology, 72(18), 1595-1600.

Contact info: info@nursesinternational.org

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