NM I: Vestibular/Ocular System Anatomy and Physiology

what is the orientation of the horizontal semicircular canal

the horizontal canal is not horizontal until you tilt the head down 30 degrees

what are the utricle and saccule?

they are two small fluid filled sacs that are located in your inner ear

what does the superior division of the vestibular nerve supply?

supplies the superior and horizontal semicircular canal

what does the inferior division of the vestibular nerve supply?

supplies the posterior semicircular canal

what does the stereocilia and kinocilium detect

they detect motion

what is an otoconia

crystals that are located in the inner ear which sit on a gel-like membrane and it tells our brain if we are moving or not

where are otoconia located

utricle

what does the saccule do specifically

detects vertical acceleration of head

what does the utricle do specifically

detects horizontal acceleration of head

there is a strong relationship between BPPV and diabetes, why?

diabetes causes decreased microcirculation --> poor blood flow --> otoconia are not healthy

if the otoconia move towards the cupula is it excitatory or inhibitory?

excitatory

if the otoconia moves awat from the cupula is it excitatory or inhibitory?

inhibitory

what does the otolithic membrane sense?

gravity

the cerebellum is often referred to as "the garage," why?

it is the place where things go to get fixed

damage to the cerebellum is very debilitating for individuals with vestibular issues bc there cerebellum can't help fix it

what is the gain of the VOR?

it is the ratio of eye velocity to head velocity

what is an ideal gain?

1

immediately following a unilateral labyrinthine lesions for head movements toward the affected side, what is the percentage of people that have a reduction in VOR gain?

25-50%

what is VOR adaptation

it is an attempt to change the amplitude or speed of the eye movement to bring the target on the fovea so that it is stabilized on the retina

what drives VOR adaptation?

a retinal slip associated with head movement is what is believed to drive VOR adaptation

what is a retinal slip

the difference between eye velocity and head velocity

for normal vision what must the retinal slip be

less than 2deg/sec

what is the vision if the retinal slip velocity is 3deg/sec?

20/60 vision

what is the vision if the retinal slip velocity is 11deg/sec?

20/200 vision

what is needed for VOR adaptation

movement and light are needed

when does VOR gain adaptation not occur?

when there's damage to the flocculus and paraflocculus of the vestibulocerebellum

VOR adapttion is context dependent, meaning that gain is dependent on ___

therefore we need to do exercises that ___

orientation of head, maybe velocity

put the head in different planes (yaw, pitch roll) , involve high frequency movements

what is the DHI

dizziness handicap inventory, outcome measure similar to the ODI

what is an observed brain mechanism for people with migraines and dizziness

asymmetric cerebellar hyperactivity

what does the slow phase of a nystagmus reflext?

the function of VOR

how is a nystagmus named?

after the fast phase

how is torsional nystagmus named

fast phase of upper pole of eye

with a unilateral peripheral vestibular injury, what happens with the sick right ear when the head is stationary?

- no discharge of the right horizontal SCC, but normal resting discharge of left horizontal SCC

- you would see a left beating nystagmus

what is spontaneous nystagmus? when does it often occur?

when you see nystagmus in a resting position

acutely, usually resolves w/in a few days

peripheral vestibular nystagmus characteristics

it will always beat in the same direction and away from the lesion regardless of the direction of head position

- jerk nystagmus has a clear fast and slow phase

- the slow component of the nystagmus reflects the underlying pathology and the fast component defines the direction of the nystagmus

T/F, it is easy to tell the fast and slow phases apart with spontaneous nystagmus

false

what is the cervico-ocular reflex (COR)? what is the gain? who is it adaptable in?

- interacts with the VOR to drive eye movement based on input from the cervical proprioceptors

- normally the gain of the COR is low

- can be adaptable in some people with vestibular hypofunction

T/F, not all patients can utilize the COR

T, called on only when needed

are smooth pursuits and saccadic eye movemets affected by vestibular loss?

no

what causes damage to the smooth pursuit system?

cerebellar lesions

how fast is the smooth pursuit movement? what do they allow us to do

<60 degrees/s

maintain gaze on moving targets

what does impaired function of the saccadic or smooth pursuit system indicate? what should you do next?

brain dysfunction

assess cranial nerves (lowk im referring out)

how fast do saccades move? what do they allow us to do

move at 350-600 degrees/sec

allow us to quickly shift gaze from one point of focus to another

how do you examine nystagmus

- observe the position of the eye in orbit

- check with fixation

- observe the direction of the nystagmus

- observe head position

what is physiologic nystagmus

- normal nystagmus

- vestibular induced (caloric, rotational)

- visually induced (optokinetic)

- extreme end point induced

what are pathlogic nystagmus

- spontaneous

- gaze evoked

- positional

someone tells you that their patient has a L beating spontaneous nystagmus

from this you know that their patient's nystagmus is occurring when? and you know that which ear is the problem?

at rest

R ear

what does it mean when a spontaneous nystagmus gets worse with fixation?

indicates a central problem

what is the alexander's law

- looking in the direction of the fast component of the nystagmus increases the amplitude and frequency of the nystagmus

- looking in the opposite direction of the fast component decreases the amplitude and frequency of the nystagmus

what is first degree nystagmus

nystagmus seen only looking in the direction of the fast phase of the nystagmus

what is the second degree of nystagmus?

what does it indicate

present in the primary position and when looking lateral towards the fast phase

acute unilateral loss

what is the third degree of nystagmus

nystagmus is seen in all directions, always beating in the same direction

central nystagmus

often changes direction of beating and persists despite visual fixation

if nystagmus improves with light, this may indicate what?

peripheral loss

what is a VNG

video nystagmography

what does the VNG record

horizontal eye movement well and vertical eye movement very poorly

what is one way to distinguish between cerebellar lesions and peripheral lesions

light will not reduce a vestibular nystagmus but it will reduce a peripheral nystagmus

T/F, posterior canal BPPV is easily detectable with positional testing during a VNG

F, VNG is bad at picking up vertical movement and posterior canal BPPV is characterized by upbeat torsional nystagmus

you need that dix hallpike bruh

what does the Dix-Hallpike maneuver pick up?

rotatory nystagmus that is classic of posterior canal BPPV

what is the VOR cancellation test

one can oscillate a swivel chair and have the pt attempt to fixate on their thumb in front of them

during the VOR cancellation test if the pt can't maintain fixation what does this indicate?

brain lesion

what does a down beating nystagmus almost always indicate?

central vestibular nystagmus

what is the etiology of downbeat nystagmus

- anticonvulsant meds

- alcohol

- lithium intoxication

- vitamin B12 deficiency

- congenital

- transient finding in normal infants

- cerebellar lesions

some reasons that people have slow saccades

- PD

- progressive supranuclear palsy

- intranuclear opthalmoplegia

- drug intoxication

- olivopontocerebellar atrophy

- huntington's chorea

sequential steps for treating pts with dizziness, vertigo, or instability

1. is nystagmus present?

2. nystagmus characteristics?

3. if HIT is indicated, what is the result

4. pt can stand/walk independently?

things that would indicate central cause of symptoms

spontaneous nystagmus that is direction changing/vertical/pure torsional

direction fixed spontaneous nystagmus with no corrective saccade during HIT

what is the HINTS exam used for

used to differentiate central and peripheral causes of continuous vertigo (diagnose vestibular neuritis and rule out stroke)

head impulse test

- sensitivity of the HIT for identifying vestibular hypofunction was 71% for UVH and 84% for BVH

- specificity was 82%

when will you see someone with a corrective saccades with the HIT?

a person with a unilateral vestibular loss will use a corrective saccade in order to re-stabilize gaze (positive HIT)

if someone has a vestibular loss bilaterally, what will you see with the HIT

positive ein both direction

what is gaze holding

ability to keep the eye steady in an eccentric (to the side) position

what structures are crtiical for gaze holding

- the cerebellum and brain stem

- nucleus prepositus hypoglossi and the medial vestibular nucleus

how does gaze holding work

elastic forces have a tendency within the extraocular eye mm to move the eye back to the primary position (straight ahead)

what happens if the gaze holding system doesn't work perfect

the eye will drift back to the primary position and then will have to use a corrective quick phase saccades will beat in the opposite direction of the slow drift which results in a gaze evoked nystagmus

what test is used to test VOR magnitude

dynamic visual acuity (illegible E test)

dynamic visual acuity (illegible E test)

you determine which line the person can read on a visual chart and then you rotate the persons head to the right and left and see how many lines they lose

what is a normal loss with the illegible E test?

what does abnormal loss indicate?

1-2 lines

low VOR magnitude (>2 lines)

head shaking nystagmus

- people with vestibular disorders may develop spontaneous nystagmus after 10 cycles of head shaking to the right and left

- positive findings have been related to the degree of caloric weakness

what position might someone with head shaking nystagmus tend to use

head in 30 degrees flexion

vibration induced nystagmus

- vibration applied over the mastoid process

- applied to persons with unilateral, central lesions and people with BPPV

- with unilateral loss, persons had horizontal nystagmus with slight torsion with the fast phase beating towards the strong ear

head shaking nystagmus typically occurs because of

VOR asymmetry

who usually has and doesn't have vibration induced nystagmus

- never seen in people without disease

- it is rare in general but seen sometimes with unilateral central lesions and with bppv

what does a positive VIN usually indicate? where is it most frequently evoked?

unilateral vestibular loss

over the mastoid

what is skew deviation? how is it usually named?

a vertical misalignment of the eye due to a supranuclear lesion

named for the side of the lower eye (ex. R eye low + L eye high would be a R skew deviation)

what can be used to detect more subtle skew deviations

cover test (have pt fixate on target and cover eye in alternating fashion to look for a vertical refixation when the cover moves)

strabismus

abnormal alignment of the eye

esotropia

both eyes deviate medially

estrophia

one eye deviates medially

exotrophia

one eye deviates laterally

hypertrophia

one eye deviates upward

hypotrophia

one eye deviates downward

heterophoria

intermittent tendency for misalignment

- eyes may deviate under stress, headaches, illness

- tropia

it'll always be deviated regardless if covered or uncovered

- phoria

it'll deviate when it's covered/uncovered

cover/uncover test

- normal alignment

- phoria: when deviating eye is covered, it tends to move, but when it becomes uncovered it resumes its former position

- tropia: when fixating eye is covered, the deviating (uncovered) eye moves