What are Electronystagmography (ENG) and Videonystagmography (VNG)?

Electronystagmography (ENG) and Videonystagmography (VNG): Diagnostic Tools for Vestibular Assessment

Electronystagmography (ENG) and Videonystagmography (VNG) are specialized diagnostic tests that record eye movements to evaluate vestibular function, with VNG being the more advanced technology that offers superior visualization and recording capabilities compared to the older ENG technology.

What are ENG and VNG?

• ENG is a vestibular function test that uses electrodes placed around the eyes to record eye movements in response to various stimuli by measuring changes in corneoretinal potential 1.

• VNG is the newer technology that uses infrared cameras to directly record and visualize eye movements, providing more detailed information about nystagmus and other eye movements 2.

• Both tests are designed to assess the integrity of the vestibular system by evaluating the vestibular-ocular reflex, which is the neurological relationship between eye movements and the balance organs 3.

Key Components of ENG/VNG Testing

• Both tests typically include a battery of specialized assessments that record nystagmus (involuntary rhythmic eye movements) in response to:

  • Labyrinthine stimulation (caloric testing using warm and cool water or air in the ear canals) 3
  • Voluntary eye movements 3
  • Positional changes 3

• Caloric testing is a critical component that evaluates each ear separately by stimulating the semicircular canals with warm and cool temperatures, allowing assessment of:

  • Canal paresis (reduced response in one ear) 4
  • Directional preponderance (stronger response in one direction) 4
  • Vestibular excitability 4

Differences Between ENG and VNG

VNG Advantages:

• Superior visualization: VNG permits direct visualization of eye movements in real-time, both in darkness and with open eyes 5.

• Better detection capability: VNG can record horizontal, vertical, and torsional eye movements, while ENG primarily detects horizontal movements 6.

• Higher accuracy: VNG provides more detailed tracings that can capture subtle clinical findings that might be missed by ENG 2.

• Better discrimination: VNG shows superior ability to differentiate between peripheral and central vestibular lesions 4.

ENG Limitations:

• Cannot directly visualize eye movements, only records electrical potential changes 5.

• More susceptible to electrical artifacts and interference 6.

• Less accurate for vertical and torsional eye movements 6.

Clinical Applications

• These tests are valuable for:
  • Identifying the site of vestibular lesion (peripheral vs. central) 4
  • Quantifying vestibular dysfunction 3
  • Providing information for treatment planning 3
  • Documenting objective evidence of vestibular disorders 1

When to Use ENG/VNG Testing

• Not recommended as routine tests for conditions with clear clinical diagnoses such as:

  • Benign Paroxysmal Positional Vertigo (BPPV) when diagnostic criteria are met 3
  • Ménière's disease with typical history and symptoms 3

• Appropriate uses include:

  • When diagnosis of vertigo/dizziness is unclear 3
  • When clinical presentation is atypical 3
  • When positional testing elicits equivocal or unusual nystagmus 3
  • When additional symptoms suggest accompanying CNS or otologic disorders 3
  • When multiple concurrent peripheral vestibular disorders are suspected 3
  • When patients remain symptomatic following treatment 3

Common Pitfalls and Caveats

• Unnecessary vestibular testing can lead to:

  • Delays in diagnosis and treatment 3
  • Increased direct and indirect costs to patients and providers 3
  • Patient discomfort including nausea and vertigo during testing 3

• Results of vestibular testing often fluctuate throughout the course of vestibular disorders like Ménière's disease, and the degree of damage detected correlates poorly with patient-perceived disability 3.

• Normal vestibular test results do not necessarily rule out vestibular disorders like Ménière's disease 3.

• The caloric test remains the gold standard component as it provides invaluable site-of-lesion information that objectively documents peripheral vestibular lesions 1.

Current Status and Future Directions

• While VNG represents newer technology with clear advantages, ENG is still considered a valuable test in clinical settings where VNG is not available 6.

• Portable and low-cost alternatives like the Nintendo Wii Balance Board are being explored for posturography assessment with promising preliminary findings 2.