DIAGNOSTICS
Videonystagmography
Test Made Simple
By Joe Saliba, MD | Neuro-otologist and Skull Base Surgeon
Discover what a Videonystagmography (VNG) test entails and how it can help diagnose balance and dizziness issues.
Introduction to the VNG
The Videonystagmography (VNG) test is a sophisticated diagnostic procedure that examines how well your inner ear and brain work together to control balance and eye movements. Using specialized goggles equipped with cameras, the VNG monitors eye movements in response to various stimuli. For people experiencing dizziness, vertigo, or balance problems, the VNG provides valuable information that can help identify the underlying cause.
What the VNG is Used For
Doctors often recommend a VNG if you have unexplained symptoms like persistent dizziness, vertigo, or frequent loss of balance. The VNG helps diagnose conditions that impact the vestibular (balance) system, such as benign paroxysmal positional vertigo (BPPV), vestibular neuritis, or Ménière’s disease. It’s particularly useful in differentiating between central causes (issues in the brain) and peripheral causes (issues in the inner ear) of balance disorders.
How to Prepare for Your VNG Test
Proper preparation is crucial for accurate VNG test results. It's important to follow these guidelines before your test, as they may affect your results:
- Avoid alcohol for 48 hours before the test
- Don't eat for 3 hours prior to testing, and avoid heavy meals on the day of the test (risk of nausea and sometimes vomiting with the caloric testing! See below)
- Avoid caffeine for 24 hours before the test
- Don't wear contact lenses; bring your glasses instead
- Skip the eye makeup on test day, it can interfere with the special infrared goggles.
Most importantly, consult with your doctor about your medications. You may need to temporarily (48 hours before the test) stop taking:
- Anti-vertigo medications (like meclizine)
- Sedatives or tranquilizers (Ativan for example)
- Certain antidepressants
- Anti-nausea drugs (like Gravol)
Never stop any medication without your doctor's approval.
Breaking Down the Components of the VNG Test
The VNG test comprises several parts, each designed to evaluate different aspects of your balance system:
1. Oculomotor Testing: This part assesses how well your eyes move in response to targets. You'll follow a moving dot on a screen or a light, allowing the doctor to observe how your eyes track moving objects. Problems with these movements can indicate central nervous system disorders.
2. Positional and Positioning Testing: Here, your head and body are moved into various positions (such as lying down or turning your head) to see if these movements trigger dizziness or abnormal eye movements (called nystagmus). This helps identify specific balance disorders such as BPPV.
3. Caloric Testing: This is often considered the most important (and sometimes uncomfortable) part of the test. This part evaluates how each ear responds to temperature changes. Warm and cool water is introduced into your ear canals to stimulate the inner ear. There are therefore 4 stimulations (hot and cold x right ear and left ear). It's not painful, but it will induce vertigo for about 30 seconds with each stimulation. Some centres will use air instead of water, but studies show that air stimulation is not as accurate as water stimulation. I would only recommend using air stimulation if you have an eardrum perforation. This WILL cause dizziness and a corresponding nystagmus (involuntary eye movements), which is then analyzed to see if both ears are responding equally. The strength and direction of this nystagmus can indicate how well each inner ear is functioning. If no dizziness is triggered, there is an abnormality of the vestibular system. Some people react strongly on this part of the test (typically patients with migraines or post-concussive syndromes), triggering nausea and sometimes vomiting. It is strongly recommended to avoid heavy meals before this VNG. The responses are recorded and some formulas are calculated to compare the function of each ear, showing if one ear is weaker or less responsive.
Interpreting VNG Test Results
Normal results in each part of the VNG indicate a well-functioning vestibular system.
Oculomotor Testing
- Normal: Eyes smoothly follow targets with minimal errors
- Abnormal: Jerky eye movements or inability to track targets may suggest neurological issues
Positional Testing
- Normal: No significant nystagmus in different positions
- Abnormal: Persistent nystagmus in certain positions could indicate inner ear problems or central nervous system disorders
Caloric Testing
- Normal: Similar responses from both ears (within 20-25% of each other)
- Abnormal: A difference greater than 20-25% between ears may indicate a weakness in one inner ear
For caloric testing, the speed of eye movements is measured in degrees per second. A total response (combining warm and cool stimulation) of less than 10-12 degrees per second in one ear is considered abnormally weak. When the combined responses of all four stimulations are less than 20 degrees per second, it may indicate a bilateral vestibular deficit.
Limitations of the VNG
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Limited frequency assessment: VNG primarily assesses vestibular function at very low frequencies (around 0.003 Hz) through caloric testing. This is equivalent to a very very slow head movement. It may not represent real-life head movements. The VNG doesn't evaluate the full range of frequencies at which the vestibular system operates in daily life, which are typically faster head movements (0.05 Hz to 5 Hz).
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Incomplete vestibular system evaluation: The caloric portion of VNG only assesses the horizontal semicircular canals. It therefore can only provide information about the superior vestibular nerve. It does not provide information about the rest of the inner ear nor about the inferior vestibular nerve. It can potentially miss issues in other parts of the vestibular system.
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Missed conditions: VNG may fail to detect certain vestibular disorders, especially in their early stages. Therefore, a normal VNG does not always exclude a vestibular disorder. For example:
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Early Meniere's disease
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Small vestibular schwannomas
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Third window syndromes (superior canal dehiscence)
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Some cases of Benign Paroxysmal Positional Vertigo (BPPV)
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Patient cooperation: The test requires active participation and understanding from the patient. Lack of cooperation or misunderstanding can lead to erroneous results.
- Medication interference: Certain medications like benzodiazepines, anti-depressants, and vestibular sedatives can suppress caloric responses.
- Physical limitations: Conditions like ankylosing spondylitis can contraindicate certain parts of the test, such as positional testing.
Conclusion
VNG is a helpful test for checking balance issues, but it shouldn't be used alone. It's important to combine VNG results with a proper clinical examination and potentially other vestibular and/or hearing tests for accurate diagnosis and treatment of vestibular disorders.
Joe Saliba, MD
Dr. Joe Saliba is an ENT surgeon specialized in neuro-otology and medical director at ODYO. He treats patients with various ear and skull base disorders, ranging from hearing loss and vertigo to vestibular schwannomas and cochlear implants.
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