Ocular Motility Testing (ENG/VNG)

Question 1

Are vestibular tests tests of function or structure?

Answer 1

Function
The purpose of vestibular testing is to determine if a symptom (e.g. dizziness, imbalance, oscillopsia) is caused by the inner ear (a peripheral etiology), by the brain (a central etiology), both (mixed etiology) or other
For central and peripheral conditions abnormalities of function can often serve for lesion localization

Question 2

What are the most common VNG systems?

Answer 2

Micromedical (most known company, recently merged with interacoustics)
Interacoustics micromedical (joint products)
ICS otometrics (GN)
Difra (big in Europe, not big here)
Vitalys
HouseEAR

Question 3

Why do we evaluate eye movements?

Answer 3

Because of the close anatomic and physiologic connections between the peripheral vestibular and central ocular motor systems

Question 4

Can ENG/VNG results be influenced by certain medications and subject arousal state?

Answer 4

Yes
Important to ask what medications they’re taking
When possible have patients refrain from taking these meds for at least 12 hours prior:
Sleeping pills, tranquilizers, Valium, Diazepam, Ativan, Lorzepam, Halcion, Xanax, Alprazolam, Klonopin and Clonazepam
Antivert, Meclizine, Dramamine or Bonine (vestibular suppressants)
Minimize pain medications which can cause drowsiness
Refrain from alcoholic beverages
*all other meds should be taken as directed

Question 5

What are some pre-test instructions for patients?

Answer 5

Don’t eat a big meal prior to testing to lessen chance nausea/emesis
Wear comfortable clothing
Remove eye makeup prior to testing (or minimize use; machine locks onto the darkest part of the eye)

Question 6

Why are patient questionnaires or case history very important for vestibular diagnostics?

Answer 6

Important in correctly identifying vestibular disorders because patient subjective symptoms are widely varied, ‘non-textbook’ and often difficult to quantify
Many don’t understand the difference between the words vertigo, dizziness & imbalance
Not all vestibular diagnoses are made in the face of readily visible test results so the patient report can be critical (Meniere’s disease, vestibular migraine, etc.)

Question 7

What are some key points to address during the case history?

Answer 7

Description of problem (have them describe it for you, what it feels like)
Timing (when did it start)
Frequency
Provoking factors (what triggers symptoms)
Associated symptoms (associated with central vs peripheral; anything that co-occurs with the symptoms)
Any other medical history
Medications

Question 8

What are some other potentially relevant questions for patients?

Answer 8

Family history (migraine, meniere’s disease, neurologic disorders, anxiety/depression, hearing loss)
Progression (improved, worsened, same)
Level of disability (1-10)

Question 9

Is nystagmography (ENG/VNG) the most common test for evaluation of dizziness, vertigo, or imbalance?

Answer 9

Yes, because it assesses both central and peripheral components

Question 10

What are the three components of nystagmography (ENG/VNG)?

Answer 10

Ocular motor evaluation
Positional/positioning evaluation (static and dynamic; move into certain positions)
Caloric irrigations (hyper-stimulate vestibular organ with air or water)

Question 11

What are the limitations of ENG/VNG?

Answer 11

Only tells us about horizontal semicircular canal function, superior vestibular nerve and central vestibular pathways
*Doesn’t tell us the whole story

Question 12

What are the 4 possible outcomes of vestibular testing?

Answer 12

Normal (non-vestibular origin or vestibular origin but not sensitive to VNG)
Central (generalized, non-specific, cerebellum, cerebral cortex, brainstem)
Non-localizing (consistent with lesions in central or peripheral vestibular system or both; may be able to softly localize)
Peripheral (BPPV, unilateral vestibular loss compensated or uncompensated, or bilateral vestibular loss suspected (confirmed with rotary chair))

Question 13

What is the typical ENG/VNG battery?

Answer 13

Oculomotor Exam: (centrally mediated)
Calibration (horizontal and vertical) (line eyes up to goggles)
Spontaneous
Gaze (leftward, rightward, upward, downward)
Saccades (fastest centrally moving eye movements without moving head)
Pursuit / Tracking (slow, continuous eye movement; following a target)
Optokinetic (OPK/OKN)
Vergence (not performed due to inability of systems to track torsional movement)
VOR
Positioning / Positional Exams:
Dix-Hallpike maneuver
Static positional testing (supine head right, head center, head left, lateral right, lateral left)
Caloric Irrigations:
Right Warm, Left Warm. Right Cool, Left Cool

Question 14

Is calibration very important?

Answer 14

Yes
Sets the stage for proper interpretation and treatment or recommendations

Question 15

How is gaze testing done?

Answer 15

Holding gaze
Center, left, right, up, down
Performed with and without fixation
Requires multiple systems

Question 16

What disorders perform abnormality on gaze holding? (will not be on test)

Answer 16

Gaze-evoked nystagmus
Rule out end-point spontaneous nystagmus (gaze angles <20-30 degrees)
Square wave jerk nystagmus
Abnormal when present with fixation

Question 17

How are saccades tested?

Answer 17

Primarily volitional, gets the fovea to target, fastest movements
Performed horizontally and vertically
Control begins in frontal cortex
Eyes look at target, even when it moves

Question 18

What are fixed saccades?

Answer 18

Only moving from one point to another
Different than random

Question 19

What are parameters for interpretation of saccades?

Answer 19

Velocity = speed of eye movement
Latency = how long after target moves does eye move
Accuracy = does the eye reach the target
Hypometria (undershoot)
Hypermetria (overshoot)

Question 20

What is dysmetria?

Answer 20

Sometimes overshooting
Sometimes undershooting

Question 21

How do you do pursuit testing?

Answer 21

Movement the eyes make while tracking an object
Keeps image on the fovea (need moving object otw saccadic)
Performed horizontally and vertically
Correlates with OPK/OKN
Involves ipsilateral cerebellar hemisphere, brain stem, or parieto-occipital region

Question 22

What are the parameters for interpretation of pursuit?

Answer 22

Gain = Eye movement relative to target movement
Phase = Rightward versus leftward
Some systems include # of saccades too

Question 23

What is optokinetic (OPK/OKN)?

Answer 23

Eye movement generated by the retina
Elicited by the tracking of a moving field
Different from smooth pursuit (eye movement elicited by tracking of a single target)
Combination response tracking/pursuit mechanism and saccadic retinal response (fast/slow phases)
Weakest subtest in ocular motility battery
Should involve movement in both central and peripheral visual fields (about 80% or more)

Question 24

What are the parameters for interpretation for OPK/OKN?

Answer 24

Symmetry = rightward versus leftward
Gain normative values exist but less sensitive due to numerous different stimuli and parameters
Often performed with increasing stimulus speeds whereby failure to increase eye speed would denote central abnormality

Question 25

What is vergence?

Answer 25

Directing vision from a far object to a near one
Based on image moving on/off fovea
Eyes rotate in opposite directions (as opposed to saccades)
Much slow than saccadic movement
Relies on occipital to cerebellar control
Can’t be tested by ENG/VNG
Disorders: cerebellum
*just can’t really measure how the eyes rotate in or out to a image

Question 26

What is the typical ENG/VNG test battery?

Answer 26

Calibration (horizontal, vertical - match to the eyes)
Tests of Ocular Motility - spontaneous (center gaze), eccentric gaze (horizontal, vertical), pursuit, aaccades, optokinetic (OPK/OKN)
Dynamic Positioning Test (dix-hallpike maneuver)
Static Positional Tests (supine head roll (Pagnini-McClure Maneuver), head center, head left, head right, body (lateral) left, body (lateral) right)
Caloric Tests

Question 27

Should calibration precede each subtest?

Answer 27

Yes
Calibration should stay pretty consistent unless they take the goggles off
Calibration is the process of relating eye position to the movement recording devices

Question 28

Is calibration different for all of the systems?

Answer 28

Yes
But they are all performed with the subject seated upright and the head kept still
May be asked to look in different directions at certain degrees
The system is calibrated when the waves match
The patient is instructed to look at each light as it comes on, without moving their head, move eyes only
The plane of the lights should be horizontal for one calibration and vertical for another calibration

Question 29

Can you override the calibration if necessary?

Answer 29

Yes
Might need to do if the patient has a glass eye, lazy eye, etc.

Question 30

What is saccadic testing?

Answer 30

Ability to track a fast moving target
Stimulus is a light that can be fixed in frequency or can be random
Useful in diagnosis of CNS disorders
Will give you a rectangular square wave

Question 31

What are the three parameters of saccadic eye movements?

Answer 31

Latency – time to acquire post stimulus
Velocity – peak velocity eye movement
Accuracy – overshoot / undershoot

Question 32

What does saccadic velocity typically refer to?

Answer 32

Peak velocity obtained during the eye movement, unless otherwise stated
Doesn’t mean mean velocity
Saccades typically have peak velocities ranging from 50o to 700o/sec

Question 33

What are the three types of disorders of saccadic velocity?

Answer 33

Saccades may be too slow,
too fast, or
have substantially different values in one eye or direction than the other

Question 34

When are prolonged saccades diagnosed?

Answer 34

When the mean saccadic velocity for a particular amplitude is less than the lower 5th percentile of normal
Drug ingestion should be the first consideration (anticonvulsants, sedatives, and antidepressants)
Can be slowed as much as 50% when subjects become drowsy

Question 35

What syndromes or disorders could be occurring if the patient is wide awake and not taking any centrally acting medication?

Answer 35

Basal ganglia syndromes (Huntington’s chorea, Progressive supranuclear palsy, Wilson’s disease)
Cerebellar syndrome (Olivopontocerebellar atrophy, Ataxia telangietasia, Joseph’s disease)
Peripheral oculomotor nerve or muscle weakness (VIth Cranial Nerve palsy and IIIrd Cranial Nerve palsy, Fisher syndrome, Myasthenia gravis, Progressive external ophthalmoplegia, Mitochondrial myopathy, Thyroid disorders)
White matter diseases (Adrenoleukodystrophy, Internuclear ophthalmoplegia)
Miscellaneous disorders (Niemann-Pick disease, Wernicke’s ophthalmoplegia)

Question 36

Can abnormally fast saccades usually be traced to an error in calibration or a noisy eye movement recording?

Answer 36

Yes
In rare instances, abnormally fast saccades may be real, and not due to a technical artifact

Question 37

What is one cause for abnormally fast saccades?

Answer 37

opsoclonus syndrome or its relative, ocular flutter
In these conditions, patients make unintended saccades without intersaccadic interval, which may be abnormally fast for their size
Can also happen in people after scorpion stings

Question 38

What is asymmetrical saccadic velocity?

Answer 38

Significant inequality between eyes or direction

Question 39

What are the two possible findings in disorders of saccadic latency?

Answer 39

Prolonged saccadic latencies and reduced (shortened) saccadic latencies
*in most instances this finding has no diagnostic significance because saccadic latencies are sensitive to the mental state of the subject

Question 40

Are asymmetrical saccade latencies clinically useful?

Answer 40

Yes
It may indicate the presence of a lesion involving the parietal or occipital cortex

Question 41

What is smooth pursuit?

Answer 41

Performed with a light that oscillates back and forth or up and down
CNS localization

Question 42

What are the two parameters for smooth pursuit?

Answer 42

Gain (ratio of eye velocity to velocity target)
Phase (the delay between the target and the tracking waveforms)

Question 43

Is pursuit the first to degrade with age?

Answer 43

Yes
Requires the most continuous attention
Symmetrical reduction of smooth pursuit is encountered frequently
For this reason, one should be conservative when diagnosing abnormalities of pursuit

Question 44

Who are the most important patients with abnormal pursuits to identify?

Answer 44

Those with no pursuit at all
Operationally defined as pursuit gain of less than 0.2, are the most important patients to be identified, because they will nearly always have a CNS disturbance

Question 45

What is asymmetrical pursuit?

Answer 45

Pursuit which is significantly worse in one direction is termed asymmetrical
While rare, asymmetrical pursuit is more often of clinical utility than is symmetrically reduced pursuit gain, because it is a specific indicator for a CNS disorder

Question 46

What does a vestibular tone imbalance result from?

Answer 46

The imposition of asymmetric vestibular input on an inherently normal horizontal gaze generator
This asymmetric input occurs if one vestibular apparatus (labyrinths, nerve, or brain stem nuclei) functions abnormally or if both sides are asymmetrically defective

Question 47

What is an integrator leak nystagmus?

Answer 47

Occurs only in an eccentric gaze position
The eyes are unable to maintain the eccentric position and drift back to the primary position with a decreasing velocity, reflecting a passive movement resisted by the viscous forces of orbital soft tissues

Question 48

Does Alexanders phenomenon last long?

Answer 48

No
They start to compensate
When you see it, it suggests a recent occurrence/injury

Question 49

Does no center gaze nystagmus typically suggest central?

Answer 49

Yes