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 Cranial
Nerve 1 - Olfaction
This CN is tested one nostril at a time by using a nonirritating smell such
as tobacco, orange, vanilla, coffee, etc. Detection of the smell is more
important than the actual identification.
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Cranial
Nerve 2 - Visual acuity
The first step in assessing the optic nerve is testing visual acuity. This
can be done with a standard Snellen chart or with a pocket chart (Rosenbaum).
Have the patient use their glasses if needed to obtain best-corrected vision.
Have the patient hold the pocket chart at the focal length that is best
for them which is usually 14 inches. Have them recite the line with the
smallest letters that they can read and record the acuity.
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Cranial
Nerve 2 - Visual fields
There are several different screening tests that can be used to assess visual
fields at the bedside. First hold up both hands superiorly and inferiorly
and ask the patient if they can see both hands and do they look symmetric.
Then test each eye individually using your fingers in the four quadrants
of the visual field and ask the patient to count fingers held up or point
to the hand when a finger wiggles using yourself as a control. A second
screening test is to use a grid card. Have the patient focus on the dot
in the center of the grid then ask if any part of the grid is missing or
looks different. A third method is to use a cotton tip applicator. Testing
one eye at a time ask the patient to say "now" as soon as they see the applicator
come into their side vision as they focus on the examiner's nose. All of
these tests are screening tests. Formal perimetry is the most accurate way
of assessing visual fields.
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Cranial
Nerve 2 - Fundoscopy
Direct visualization of the optic nerve head is an important and valuable
part of assessing CN 2. Systematically look at the optic disc, vessels,
retinal background and fovea.
Images
are courtesy Dr. Kathleen Digre, The University of Utah.
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Cranial
Nerves 2 & 3 - Pupillary Light Reflex
The afferent or sensory limb of the pupillary light reflex is CN2
while the efferent or motor limb is the parasympathetics of CN3. Shine a
flashlight into each eye noting the direct as well as the consensual constriction
of the pupils.
The swinging flashlight test is used to test for a relative afferent
pupillary defect or a Marcus Gunn pupil. Swinging the flashlight
back and forth between the two eyes identifies if one pupil has less light
perception than the other. Shine the flashlight at one eye noting the size
of both pupils. Then swing the flashlight to the other eye. If both pupils
now dilate then that eye has perceived less light stimulus (a defect in
the sensory or afferent pathway) than the opposite eye.
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Cranial
Nerves 3, 4 & 6 - Inspection and Ocular Alignment
Before checking ocular movements it is important to inspect the eyes. Look
for ptosis. Note the appearance of the eyes and check for ocular alignment
(the reflection of your light source should fall on the same location of
each eyeball).
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Cranial
Nerves 3, 4 & 6 - Versions
Testing extraocular range of motion with both eyes open and following the
target (conjugate gaze) is called versions.
The patient is asked to follow a target through the six principle positions
of gaze. Note any misalignment of the eyes or complaint of diplopia (double
vision).
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Cranial
Nerves 3, 4 & 6 - Ductions
If there is any misalignment of the eyes or diplopia on versions it is important
to then examine each eye with the other covered (this is called ductions).
The patient should follow an object through the six principle positions
of gaze so each extraocular muscle's function is tested.
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Supranuclear
gaze systems - Introduction
The purpose of supranuclear control of gaze is to insure that the image
that is being looked at is centered or maintained on the fovea of the retina.
The following maneuvers test the major systems that control eye movements.
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Saccades
Saccades are tested by holding up your two hands about three feet
apart and instructing the patient to look at the finger that is wiggling
without moving their head. The patient's eyes should be able to quickly,
smoothly and accurately jump from target to target.
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Smooth
Pursuit
To test Smooth Pursuit ask the patient to keep watching the target
without moving their head. Then move the target slowly from side to side
and up and down. The eyes should be able to follow the target smoothly without
lagging behind or jerking to catch up with the target.
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Optokinetic
Nystagmus
Optokinetic Nystagmus is a test of smooth pursuit with quick resetting
saccades. Use a tape with repeating shapes on it and ask the patient to
look at each new object as it appears as you run the tape between your fingers
to the right, left, up, and down. The patient will have brief pursuit eye
movements in the direction of the tape movement with quick saccades or jerks
in the opposite direction. The resetting saccades are easier to observe
than the brief pursuit movement.
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Vestibulo-ocular
reflex
The vestibulo-ocular reflex is obtained by having the patient visually
fixate on an object straight ahead, then rapidly turning the patient's head
form side to side and up and down. The eyes should stay fixed on the object
and turn in the opposite direction of the head movement.
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Vergence
Vergence eye movements occur when the eyes move simultaneously inward
(convergence) or outward (divergence) in order to maintain
the image on the fovea that is close up or far away. Most often convergence
is tested as part of the near triad. When a patient is asked to follow
an object that is brought from a distance to the tip of their nose the eyes
should converge, the pupil will constrict and the lens will round up (accommodation).
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Cranial
Nerve 5 - Sensory
Test for both light touch (cotton tip applicator) and pain (sharp object)
in the 3 sensory divisions (forehead, cheek, and jaw) of CN 5.
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Cranial
Nerves 5 & 7 - Corneal reflex
The ophthalmic division (V1) of the 5th nerve is the sensory or afferent
limb and a branch of the 7th nerve to the orbicularis oculi muscle is the
motor or efferent limb of the corneal reflex. The limbal junction
of the cornea is lightly touched with a strand of cotton. The patient is
asked if they feel the touch as well as the examiner observing the reflex
blink.
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Cranial
Nerve 5 - Motor
The motor division of CN 5 supplies the muscles of mastication (temporalis,
masseters, and pterygoids). Palpate the temporalis and masseter muscles
as the patient bites down hard. Then have the patient open their mouth and
resist the examiner's attempt to close the mouth. If there is weakness of
the pterygoids the jaw will deviate towards the side of the weakness. The
last test for this nerve is testing for a jaw jerk, which is a stretch
reflex. Have the patient slightly open their mouth then place your finger
on their chin and strike your finger with a reflex hammer. Normally there
is no movement. If there is a jaw jerk it is said to be positive and this
indicates an upper motor neuron lesion.
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Cranial
Nerve 7 - Motor
The motor division of CN 7 supplies the muscles of facial expression. Start
from the top and work down. Have the patient wrinkle forehead (frontalis
muscle), close eyes tight (orbicularis oculi) show their teeth (buccinator),
and purse lips or blow a kiss (orbicularis oris). If there is weakness especially
in a bilateral upper motor neuron distribution, get the patient to smile
by telling a joke or funny story. With a pseudobulbar palsy automatic or
emotional facial expression will be more complete than movements to command.
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Cranial
Nerve 7 - Sensory, Taste
Taste is the sensory modality tested for the sensory division of CN 7. The
examiner can use a cotton tip applicator dipped in a solution that is sweet,
salty, sour, or bitter. Apply to one side then the other side of the extended
tongue and have the patient decide on the taste before they pull their tongue
back in to tell you their answer.
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Cranial
Nerve 8 - Auditory Acuity, Weber & Rinne Tests
The cochlear division of CN 8 is tested by screening
for auditory acuity. This can be done by the examiner lightly rubbing their
fingers by each ear or by using a ticking watch. Compare right versus left.
Further screening for conduction versus neurosensory hearing loss can be
accomplished by using the Weber and Rinne tests. The Weber
test consists of placing a vibrating tuning fork on the middle of the head
and asking if the patient feels or hears it best on one side or the other.
The normal patient will say it is the same in both ears. The patient with
unilateral neurosensory hearing loss will hear it best in the normal ear
while the patient with a unilateral conductive hearing loss will hear it
best in the abnormal ear. The Rinne test consists of comparing bone conduction
(placing the tuning fork on the mastoid process) versus air conduction (placing
the tuning fork in front of the pinna). Normally, air conduction is greater
than bone conduction. For neurosensory hearing loss air conduction is still
greater than bone conduction but for conduction hearing loss bone conduction
will be greater than air conduction.
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Cranial
Nerve 8 - Vestibular
The vestibular division of CN 8 can be tested for by using the vestibulo-ocular
reflex as already demonstrated or by using ice water calorics to test vestibular
function. The later test is usually reserved for patients who have vertigo
or balance problems or in the comatose patient when one is testing brainstem
function.
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Cranial
Nerves 9 & 10 - Motor
The motor division of CN 9 & 10 is tested by having the patient say "ah"
or "kah". The palate should rise symmetrically and there should be little
nasal air escape. With unilateral weakness the uvula will deviate toward
the normal side because that side of the palate is pulled up higher. With
bilateral weakness neither side of the palate will elevate and there will
be marked nasal air escape.
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Cranial
Nerves 9 & 10 - Sensory and Motor: Gag Reflex
The gag reflex tests both the sensory and motor components of CN
9 & 10. This involuntary reflex is obtained by touching the back of the
pharynx with the tongue depressor and watching the elevation of the palate.
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Cranial
Nerve 11 - Motor
CN 11 is tested by asking the patient to shrug their shoulders (trapezius
muscles) and turn their head (sternocleidomastoid muscles) against resistance.
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Cranial
Nerve 12 - Motor
The 12th CN is tested by having the patient stick out their tongue and move
it side to side. Further strength testing can be done by having the patient
push the tongue against a tongue blade. Inspect the tongue for atrophy and
fasciculations. If there is unilateral weakness, the protruded tongue will
deviate towards the weak side.
By having the patient say lah-pah-kah, the examiner is testing the motor
components of CN 12, 7, and 9&10.
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