Week 1 - Review & Intro Flashcards
What are the three categories of testing included in the ENG/VNG battery?
- Oculomotor Testing
- Positional/Positioning Testing
- Caloric Testing
What is included in oculomotor testing?
Calibration
Gaze
Saccade
Smooth Pursuit
OPK/OKN
What is included in Positional/Positioning Testing?
Calibration
Positional Testing
Positioning Testing
What is included in Caloric Testing?
Calibration
Caloric stimulation
What are the two primary functions classes of eye movements?
- Holding images steady on the retina
- Directing the foveae to an object of interest
What tests are performed to assess the ability to hold an image steady on the retina?
Visual fixation
Vestibular
Optokinetic (OPK, OKN)
What tests are performed to assess the ability to direct the foveae to an object of interest?
Saccades
Nystagmus fast phases
Smooth pursuit
Vergence
What are the circuit levels of the oculomotor system?
- Lower Level (Output)
- Middle Level
- High Level
- Calibration and Repair
What are the lower level circuits?
Orbit and Globe
Extraocular Muscles
Cranial Nerve Nuclei
What are the middle level circuits?
Version circuits
Vergence circuits
Neural Integrator
What are the high level circuits?
Saccades
Pursuit and OKN
Fixation
Vestibular
What is the calibration and repair circuit?
Cerebellum
What are the appropriate conditions of oculomotor testing for gaze, saccade, smooth pursuit, and OPK/OKN?
Sitting upright
Following the light (without moving the head)
Voluntary, volitional eye movements
Must be alert
What would abnormal findings during oculomotor testing indicate?
Usually central findings if pharmacological effects and fatigue are ruled out
What is GAZE?
“stare” or “fixate” at a non-moving target; holds image steady on retina
Center
Right
Left
Up
Down
What assesses gaze?
Visual fixation
How should the graph look for typical gaze testing results?
Straight horizontal lines.
Top line, blue = Horizontal gaze
Bottom line, red = Vertical gaze
How does the graph look for abnormal gaze testing results?
Horizontal line
Rises up
Nystagmus
Drops down
Slower nystagmus
What is endpoint nystagmus?
Occurs with eccentric gaze (away from primary position)
Happens in normal subjects
What circuit level is visual fixation?
High Level
What are SACCADES?
Directs the foveae to an object of interest
What is the circuit level for saccades?
High Level
How do you analyze saccades?
Evaluate:
Accuracy
Latency
Peak Velocity
What causes abnormal saccade patterns?
Ocular dysmetria
Abnormal velocity
Abnormal latency
Disconjugate eye movements
What is ocular dysmetria? What are the two types?
Inability to control distance, speed, and range of motion for smooth coordinated eye movements
I. Hypermetric (overshoot)
II. Hypometric (undershoot)
What are two conditions that cause disconjugate eye movements?
Internuclear Ophthalmoplegia (INO)
One-and-Half Syndrome
What is INO?
Internuclear Ophthalmoplegia
What is One-and-Half Syndrome?
Syndrome characterized by horizontal movement disorders of the eyeballs
What does ocular dysmetria assess?
Accuracy
What is hypertremia?
Eyes overshoot the target
What causes hypermetria?
Cerebellar dorsal vermis
Must rule out:
Vision loss
Blinking
Improper calibration
What is hypotremia?
Eyes undershoot the target
What causes hypotremia?
Cerebellar impairments, INO, supranuclear palsy, basal ganglia disorders
Must rule out:
Vision loss (macular degeration)
Fatigue
Medication
Lack of alertness
Blinking
What is normal saccade velocity?
Greater than 88 deg/sec at 20 deg eye movement
~.15 at 20 deg refixation
Larger saccadic refixations: FASTER
Smaller saccadic refixations: SLOWER
What are two categories of abnormal saccade velocity?
Slow Saccades
Fast Saccades
What are the site of lesions that cause slow saccades?
PPRF
MLF
Superior Colliculus
Cortex
Must rule out:
Drowsiness
Intoxication
What are the possible causes for fast saccades?
Mass or trauma to eye
Cerebellar impairments
Brainstem impairments
Must rule out:
Technical problems (calibration, eye range of motion)
What are the two categories of abnormal latency?
Late Initiation
Early Initiation
What affects late initiation latency?
Age
Alertness
Inattention
Visual impairment
Degenerative disorders
T/F: Abnormal latency has limited clinical utility on its own
True - must support other test results to confirm disorder
How do you correct early initiation latency?
Reinstruction
What is SMOOTH PURSUIT?
Directs foveae to a object of interest
Allows us to follow a moving target
Stabilizes a moving target on the foveae
What circuit level is pursuit?
High level
How do saccades look on the graph?
Black line: target
Blue line: eye movements
Should match as close as possible; some latency is normal. Close match = high accuracy
How does normal smooth pursuit look on a graph?
Horizontal Eye Position: waveform, lines overlap/match well
Tracking Gain: evenly spaced, high velocity; above the abnormal grey range; mirror image
How does abnormal smooth pursuit look on a graph?
Horizontal Eye Position: cog-wheel pattern
Tracking Gain: uneven spacing of dots, low velocity; in abnormal range
T/F: Smooth pursuit system is involuntary
False - voluntary control
What is the most common causes of impaired pursuit?
Pharmacology
Fatigue
T/F: We cannot “track” smoothly unless there is a smoothly moving target
True
What does pursuit abnormality indicate?
Not clinically robust!
Affected by lots of things!
-inattention, fatigue, sedation, inability to follow direction, age
If all ruled out:
Cerebellar lesion likely
What is optokinetic tracking?
Assesses optokinetic nystagmus
What is optokinetic nystagmus?
Combination of saccadic (eyes jump to target) and pursuit eye movements (track target movement)
Provides minimal diagnostic information on ENG
Poor stimulus
T/F: Optokinetic nystagmus symmetry is not affected by spontaneous nystagmus
False, it does!
What tests optokinetic nystagmus?
OPK, OKN
Describe OPK/OKN testing.
Visually mediated sense of self motion (requires full visual field movement)
Responsible for detecting SLOW head/body motion
Assumes the world does not move
More robust than smooth pursuit
What neural structures are involved in OPK with a small stimulus?
MT
MST
Pontine nuclei
Essentially the same pathway as pursuit
What neural structures are involved in OPK with a full-field stimulus?
Nucleus of optic tract (NOT)
Pontine nucleus
Bypasses cortex
What is NOT?
Nucleus of optic tract
Responds only to ipsilateral stimuli
How does stimulus matter with OPK?
Why is symmetry important?
TBD -
Spontaneous nystagmus
What are the two categories of fixation suppression?
Saccadic eye movements
Slow eye movements
Saccadic Eye Movements
aka square wave jerks
Internally generated “noise” without specific localization (but in high level)
What mediates fixation suppression of saccadic eye movements?
Saccadic System
Superior Colliculus
Slow Eye Movements
E.g. Vestibular Mediated Nystagmus
What partially mediates fixation suppression of slow eye movements?
Pursuit System
What are Positional Tests?
Static
Effect of the head position on nystagmus (eye movements)
Eyes are closed/covered + task
What are Positioning Tests?
Dynamic
Effect of the head movement on nystagmus (eye movements)
Eyes are open and fixate
What is the single most important test for diagnosing BPPV?
Dix-Hallpike Maneuver (dynamic positioning test)
BPPV has what kind of nystagmus?
Transient, but severe nystagmus
What are the characteristics of BPPV?
Latency of onset: 2-10 sec but can be delayed as much as 40 sec
Duration of nystagmus: 5-30 sec
Nystagmus is transient; declines slowly and subsides within a minute
Accompanied by vertigo
Response habituation / fatiguable
Canalithiasis
otoconia (debris) float freely within the endolymph of the affected semicircular canal
Cupulolithiasis
otoconia (debris) settle on or adhere to the cupula of the affected semicircular canal
How do you perform a static positional test?
Sitting up right / Spontaneous
Supine
Head right
Head left
(Body right / right lateral)*
(Body left / left lateral )*
Head hanging center
30 deg incline (from horizontal plane)
*only if nystagmus is nystagmus is present with head right/left to rule out that nystagmus is caused by neck rotation
Spontaneous Nystagmus
Should be tested immediately after gaze testing
IF nystagmus is observed:
describe nystagmus by direction and horizontal/vertical components
Is nystagmus suppressed by fixation?
Positional Nystagmus
IF observed:
describe nystagmus by direction, amplitude, horizontal/vertical components, and duration of nystagmus (persistence)
Is it suppressed by fixation?
Does the direction change between positions or within a single position?
T/F: Positional nystagmus is non-localizing by itself
True
What are the patterns of nystagmus?
Right beating
Left beating
Geotropic
Apogeotropic
Ageotropic
Rotary/Torsional
Geotropic
Apogeotropic
Ageotropic
Right beating
Left beating
Rotary / Torsional
Clockwise
Counter clockwise
What is the goal of lateral (side-lying) position testing?
Differentiate head position effects from neck rotation effects
Follow-up test to head right and head left positions
Caloric Testing
Vision denied
Task
Dark room
250 cc
Fixation light (if nystagmus is observed)
5 mins between irrigations
total 4 irrigations
Bithermal vs Monothermal
What is the temperature for water irrigation?
7 deg Celsius above and below body temperature (37 deg C)
Warm: 44 C
Cool: 30 C
What is the temperature for air irrigation?
13 degrees Celsius above and below body temperature (37 deg C)
Warm: 50 C
Cool: 24 C
Ice Water Calorics
Caloric Irrigation Options
Open-Loop Water
Closed Loop Water
Airx
Set up: Caloric Irrigation
Head inclined 30 deg from horizontal plane
Vision denied
Task
Caloric Irrigation - Irrigation Time
50 sec (ideal)
30 sec (ok with water if flow rate is increased)
Caloric Irrigation - Recording Time
At least 1 min following the end of irrigation
Why do we record a minute after the end of irrigation?
Peak velocity occurs at 30-40 sec post-irrigation
Caloric Irrigation - Patient Instructions
What you’ll be doing and what they’ll experience:
-water in each ear
-temperatures of water
-duration of irrigation
-duration of recording
What you want them to do:
-eyes open (VNG) or closed (ENG)
-talk (tasking)
-don’t jump when water starts!
Reasons
What do you avoid doing to minimize patient anxiety?
AVOID:
you will get dizzy
hot water
cold water
moving through steps without explaining
DO:
You may feel like you’re turning
Warm water
Cool water
How should you instruct to minimize patient anxiety?
Describe everything that you’re doing that the patient cannot see:
Now I’m looking in your ear
I’m placing the basin underneath your ear
This is the tip that will deliver water into your ear
I will start the water on the count of three
Unilateral Weakness (UV) /
Reduced Vestibular Response (RVR)
Ear difference (right EAR vs left EAR)
Define weaker ear
Directional Preponderance
right BEATING vs left BEATING
Define stronger beating direction
What do you look for in caloric irrigation response?
Unilateral Weakness (UV)
Reduced Vestibular Response (RVR)
Directional Preponderance
Gain Asymmetry
Gain Asymmetry
Directional preponderance (DP) change corrected for spontaneous nystagmus
What is the formula for unilateral weakness?
(RW+RC) - (LW+LC) divided by RW+RC+LW+LC x 100%
What is the formula for directional preponderance?
(RW+LC) - (LW+RC) divided by RW+RC+LW+LC x 100%
What is the norm for bilateral RVRs?
Total SPEV of all 4 irrigations less than or equal to 20 deg/sec
What is considered a hyperactive caloric response?
Total SPEV > 300 deg/sec
What do you do first when you notice an extremely rare abnormality?
Rule out technical errors!
(Extremely) Rare Abnormalities
Caloric Inversion
Caloric Perversion
Premature Caloric Reversal
Caloric Dysryhthmia
Caloric Inversion
[DEFINITION]
In all 4 irrigations
Caused by: posterior fossa lesions
Caloric Perversion
[DEFINTION]
Purely vertical nystagmus
Vestibular nuclei; horizontal canal w/ normal vertical canals; NORMAL
Premature Caloric Reversal
Reversal of nystagmus earlier than anticipated
Overadaptation in the vestibular nuclei?
Patients with Friedreich’s ataxia
Caloric Dysrhythmia
Inconsistent variability in SPV
Caused by: fatigue, inattention
Test Conditions: GAZE
Room Lighting: dark or light
Vision: Yes
Task: No
Test Conditions: Saccade
Room Lighting: dark or light
Vision: Yes
Task: No
Test Conditions: Tracking
Room Lighting: dark or light
Vision: Yes
Task: No
Test Conditions: OPK
Room Lighting: dark
Vision: Yes
Task: No
Test Conditions: Positional
Room Lighting: dark
Vision: denied
Task: yes
Test Conditions: Positioning
Room Lighting: dark or light
Vision: yes / denied
Task: no
Test Conditions: Calorics
Room Lighting: dark
Vision: denied
Task: yes
What is the purpose of ice water irrigation?
Ice Water Irrigation
4-5 cc saline in cup of ice water
Hold in ear canal for 30 sec
Caloric position
Prone position
What should happen during ice water irrigation?
Should reverse nystagmus direction in prone position
[UNK] Monothermal Testing
Which temperature?
Calculations for asymmetry
Effects of baseline on DP and monothermal calculations
How do you explain caloric pod/figures?
Calculate RVR, DP, and GA as applicable
Validity of irrigations?
Other issues? (how did you resolve, or would you?)
What other VNG findings (abnormalities) might you see during oculomotor and positional tests?
Can you make some diagnoses?
-peripheral, central
-laterality
-compensation status
Monothermal Screening
No abnormalities in an VNG subtests
Each warm irrigation is 11 deg/sec or greater
Monothermal difference is < 10%
Normal FI
