What is ENG & VNG Testing?

Electronystagmography (ENG) and Videonystagmography (VNG) are diagnostic tests used to evaluate the vestibular system—the part of the inner ear and brain responsible for balance and eye movements. These tests are critical for identifying the causes of dizziness, vertigo, and balance disorders. While ENG uses electrodes to record eye movements, VNG utilizes infrared video cameras for a more precise assessment. Both methods measure nystagmus (involuntary eye movements), which can reveal dysfunction in the inner ear or central nervous system. During testing, patients are asked to follow visual targets, change head positions, and undergo caloric stimulation (warm and cool air or water in the ear canal) to provoke a response.

Key Indications for ENG/VNG Testing

Healthcare providers recommend ENG or VNG testing for patients experiencing unexplained dizziness or vertigo. Common conditions that can be identified include Benign Paroxysmal Positional Vertigo (BPPV), Meniere's disease, vestibular neuritis, and labyrinthitis. Additionally, these tests help differentiate between peripheral vestibular disorders (inner ear issues) and central vestibular disorders (brainstem or cerebellar problems). Symptoms such as imbalance, oscillopsia (blurred vision with head movement), and nystagmus are strong indicators for testing. The results guide treatment plans, including vestibular rehabilitation therapy or surgical interventions.

The Testing Procedure

ENG and VNG testing typically takes 60 to 90 minutes and is performed in a quiet, dimly lit room. The test consists of three main components: ocular motor testing, positional testing, and caloric testing. During ocular motor testing, patients track moving targets to assess smooth pursuit, saccades, and optokinetic nystagmus. Positional testing involves moving the patient's head and body into various positions to trigger nystagmus related to BPPV. Finally, caloric testing irrigates the ear canal with warm and cool water or air to stimulate the horizontal semicircular canal. The resulting eye movements are recorded and analyzed for asymmetry, which indicates a unilateral weakness or directional preponderance.

Interpreting Results

Normal findings in ENG and VNG testing show symmetrical responses between both ears and appropriate eye movement patterns. Abnormal results may indicate a peripheral vestibular disorder such as reduced caloric response in one ear (suggesting vestibular neuritis or Meniere's disease) or positioning-induced nystagmus typical of BPPV. Central findings might include abnormal saccades or smooth pursuit, pointing to brainstem dysfunction or cerebellar disorders. The results are correlated with clinical history and other diagnostic tests like MRI or CT scans for a comprehensive diagnosis of dizziness and balance disorders.

Benefits and Limitations

ENG and VNG testing offer non-invasive, objective data on vestibular function. They are particularly valuable for patients with chronic vertigo and imbalance that remains unexplained. However, limitations include the inability to test all parts of the vestibular system (e.g., otolith organs) and the fact that some patients may experience discomfort during caloric testing. VNG is generally preferred over ENG due to its higher resolution and comfort, as it avoids skin electrodes. These tests are contraindicated in patients with certain cardiac conditions or labyrinthine fistulas. Overall, they remain gold standards for diagnosing vestibular disorders and guiding vestibular rehabilitation therapy.