Electronystagmography

Electronystagmography

Electronystagmography (ENG) serves as a diagnostic tool to record involuntary eye movements associated with nystagmus, aiding in the diagnosis of conditions related to vertigo, dizziness, or balance disturbances by assessing the vestibular system.

During the test, electrodes are affixed around the nose to monitor eye movements relative to the ground electrode. The vestibular system, responsible for monitoring head position and movements to stabilize retinal images, integrates this data with visual input and spinal afferents in the brain stem to generate the vestibulo-ocular reflex (VOR).

ENG offers an objective evaluation of the oculomotor and vestibular systems. A more advanced recording method involves infrared video systems, enabling enhanced observation and analysis of eye movements, known as Video Nystagmography. Another variant of the test assesses vertigo using the caloric reflex test, induced by air or water at specific temperatures, usually +/- 7 degrees Celsius from body temperature.

The standard ENG test battery comprises three components:

- Assessment of oculomotor function
- Positioning or positional testing
- Caloric stimulation of the vestibular system

Comparing results from different ENG subtests aids in distinguishing between central and peripheral disorders. Peripheral vestibular disorders can be localized based on caloric stimulation results and, to some extent, positional findings.

ENG or VNG can record nystagmus during various oculomotor tests, including saccades, pursuit and gaze testing, optokinetics, and calorics (bithermal or monothermal). Abnormal results in oculomotor tests may suggest systemic or central pathology rather than peripheral (vestibular) issues.

Optokinetics serve as a supplementary check for abnormal responses to oculomotor tests, involving a moving light (typically red) that the patient tracks with their eyes.

Caloric irrigation is the sole vestibular test allowing individual assessment of the vestibular organs, albeit it only evaluates the horizontal semicircular canal.

While ENG remains a widely utilized clinical test for vestibular function assessment, normal results do not necessarily indicate typical vestibular function. Abnormal ENG findings can aid in diagnosing and localizing the site of the lesion; however, many abnormalities lack specificity. Therefore, thorough clinical history and otologic examination are crucial for diagnosing and planning treatment for patients with dizziness or vertigo symptoms.