VNG: Oculomotor + Positional Flashcards
What is the purpose of VNG?
- Provides objective data to characterize hypo-vestibular function
- Helps diagnoise vestibular disorders
- Can provide useful, pathway-specific info to ENT/PCP/PT for vestibular rehabilitation purposes
Before starting VNG testing, what’t the first thing you should do and why?
Exam the eyes
* Helps to differentiate between nystagmus and noise during test
* Reveal if eye movements are conjugate so you can determine if you need to do mono vs binocular recording
What makes up the VNG Test Battery?
- Ocuolomoter Testing: Spontaneous Gaze, Saccade, Smooth pursuit, OPK/OKN
- Positional & Positioning Testing: Static & Dynamic
- Caloric Stimulation: Warm and Cool air or Water Irrigations
What are the three kinds of Nystagmus & how are they named?
- Horizontal
- Vertical
- Rotary
They are describes by the fast phase, strength (d/s), and duration
What is consider normal results for the Gaze test? What is being tested?
One’s ability to fixate on one spot
Normal results is when no nystagmus is present
State the deficiencies for moderate deviations for gaze evoked nystagmus
- Persistent gaze evoked nystagmus is associated with deficiency in the neural integrator
- Hortizontal Gaze = Nucleus Prepositus Hypoglossi
- Vertical Gaze = Interdtitial Nucleus of Cajal
What is the role of the neural integrator?
Generates the constant firing rate needed to hold the eye in an eccentric posture
For Gaze, what happens if there’s lesions of the Cerebellum?
It can produce gaze-evoked nystagmus in any direction
What would you expect if there’s a peripheral problem?
Spontaneous Nystagmus
What is Alexander’s Law
The amplitude of nystagmus is the strongest when the gaze moves in the direction of the fast phase
What is Peripheral Vestibular Nystagmus?
Is occurs from dysfunction of one or more of the SCCs or the peripheral nervous system
What are characteristics of Peripheral Vestibular Nystagmus?
- Shows mixture of horizontal and torsional but never vertical
- Suppressed by fixation
- Shows normal or low VOR gain but not high VOR gain
- There is no associated abnormality in pursuits and saccades
What is Central Vestibular Nystagmus?
Occurs from dysfunction in the brainstem or cerebellar regions serving the VOR
What are characteristics of Central Vestibular Nystagmus?
- Could display vertical, horizontal, or torsional components
- Not well suppressed by fixation and gets stronger when covered
- Show abnormally high VOR gain or low or normal VOR
- Has associated smooth pursuit abnormality
What is the purpose of saccades? Where are the targets presented? And what are being quantified?
Looks at quick eye movement to find or refocus a target on the fovea of the eye
- Target could be found n the left and right lateral positions
- Quantifies eye peak velocity, accuracy, and latency
For Saccades, describe latency, accuracy, and velocity
- Latency: How long it takes the patient’s eyes to find the target
- Accuracy: Can the pt move their eyes directly to the target without overshooting or undershooting the target
- Velocity: How fast can the eyes move from one point to next point
Saccades are from the horizontal canals; describe the process.
- When looking L/R a command from the frontal eye field is sent to the contralateral PPRF via the superior colliculus
- That caused a burst of neurons to send a excitatory signals to the LR (if eyes looks R) motor neurons in the abducens nucelar complex and to the MR motor neuron in the 3rd nerve nuclear complex via contralateral medial longitudinal fasciculus (MLF)
- *if we are looking right *Which could allow simultaneous abduction of the RT eye and adduction of the left eye
What are the impaired types of saccades?
Overall, there will be abnormal patterns
- Ocular dysmetria
* Hypermetric
* Hyometric - Disconjugate eye movement
- Delayed Latency
T/F: Are abnormalities in saccades expected in peripheral vestibular impairments?
False: They are not expected
What is Internuclear Ophthalmoplegia (INO)?
Happens only when one eye adducts
- It is indicated by disconjugate eye movements
- Adducting eye movemnts are slower than abducting eye movements
What is considered as “reduced velocity”
- Normal >188 d/s at 20 d/s
- Faster for larger saccadic refixations
- Slower for smaller refixations
What does slow saccades mean?
- A central lesion in the basal ganglia, brainstem, cerebellum, or peripheral oculomotor nerves or muscles
- Drug intoxication, spinocerebellar degeneration, Huntington’s dx, Progressive Supranuclear palsy, & Parkinson’s Dx
What is Smooth Pursuit Tracking?
It is a test of the central vestibular system that assess the pt’s ability to accurately track a visual target in a smooth and controlled manner
What are the causes of impaired pursuit?
- Age
- Pharmacology
- Fatigue
What do you have to dule out before considering cerebellar lesion for an impaired smooth pursuit?
- Inattention
- Fatigue
- Sedation
- Inability to follow direction
- Age
What to do if an abnormal pursuit it present?
Do OPK, fixation suppression. If all abnormal, that is meaningful info because three test all come from similar pathways
What is positional testing?
- It is a static test that is effected by gravity
- Looks at nystagmus based on head positions
- Eyes are closed/covered and pt is tasked
What is positioning testing?
It is a dynamic test that looks at the effect of plane-specific head movement
What are the positions for static positional testing?
- Supine
- Head right
- Head left
If present with head L/R do body L/R
T/F: Both peripheral and central vestibular disorders may produce static positional nystagmus?
T
What can you conclude if nystagmus disappears in the body R or L position?
It should be attributed to the neck rotation
For VNG what is considered abnormal for static positional testing?
If mean of 5 consecutive beats is >5 d/s in the horizontal plan or 6.5 d/s in the vertical plane
T/F
Horizontal nystagmus without fixation does always indicated an abnormality
False
T/F
Abnormal horizontal nystamus without fixtion does not provide localizing info?
T ; we need to include fixation
When is static positional nystagmus considered abnormal?
If for the horizontal or vertical static positional nystagmus occurs with fixation
What is horizontal nystagmus that changes direction in a single head position considered?
Abnormal and consistent with central lesion
What are the criterias for BPPV?
- Nystagmus has a delyed onset of 2-20secs
- The nystagmus is torsional
- Nystamus fatigues after a few seconds
- Nystagmus reverse directions when pt returns to sitting up
- Less intense upon retest
