What Is an oVEMP?

The ocular vestibular evoked myogenic potential (oVEMP) is an electromyographic response recorded from the extraocular muscles, mainly the inferior oblique muscle, after vestibular stimulation. The test is used to evaluate the otolith organs and the superior vestibular nerve. The oVEMP waveform typically contains an initial negative peak near 10 ms, called n10, followed by a positive peak near 15 ms, called p15. The response is commonly recorded from electrodes placed beneath the eyes while the patient maintains upward gaze.

With air-conducted sound, the dominant oVEMP is recorded from the eye contralateral to the stimulated ear. With bone-conducted vibration at the forehead, oVEMPs are usually present bilaterally. The n10 component is considered the most clinically important part of the response.

Which Parameters Are Measured?

• n10 latency: time from stimulus onset to the first negative peak.
• p15 latency: time from stimulus onset to the following positive peak.
• n10-p15 amplitude: peak-to-peak voltage measured between the n10 and p15 peaks.
• Asymmetry ratio: a side-to-side comparison of amplitude, expressed as a percentage.
• Threshold: the lowest stimulus level that produces a reproducible response.

The asymmetry ratio is usually calculated as (larger amplitude − smaller amplitude) ÷ (larger amplitude + smaller amplitude) × 100. A ratio near 0% indicates symmetric responses; a ratio near 100% indicates that no response is present on one side.

Typical Normative Values

Normative values vary with equipment, stimulus type, stimulus intensity, and electrode placement. The values below are broad reference ranges used by many laboratories; they should not replace laboratory-specific norms.

Many laboratories regard an n10 latency above about 13 ms as delayed. A delayed or absent n10 may be interpreted with caution because latency also increases with age and lower stimulus intensity.

Factors That Influence oVEMP Results

• Age: Older healthy adults often show smaller amplitudes and slightly longer n10 latencies.
• Sex: Some studies report larger amplitudes in women; others do not. Sex differences are usually smaller than age differences.
• Stimulus parameters: Higher stimulus intensities produce larger amplitudes and shorter latencies.
• Electrode montage: Small changes in electrode position can alter waveform morphology and amplitude.
• Eye position: The magnitude of the oVEMP is highly dependent on the degree of upward gaze.
• Alertness and muscle activity: Low or variable muscle activation can reduce the recorded response.
• Hearing status: In patients with severe hearing loss, air-conducted oVEMPs may be difficult to elicit at high intensities.

Interpretation of Abnormal Results

A response is usually considered present only when a reproducible n10 peak is seen. A unilateral absent n10 is more clinically localizing than a bilateral absent response. In general, an absent or markedly asymmetric oVEMP on one side raises the possibility of reduced utricular and superior vestibular nerve function on the side of the lesion.

Bilateral absence of oVEMPs is less specific because it can occur in older adults, with certain anatomical differences, or with severe bilateral vestibular loss. The result should be interpreted alongside other vestibular tests, including the cervical vestibular evoked myogenic potential, video head impulse testing, audiometry, and clinical examination.

Normative Data Must Be Laboratory-Specific

Age, sex, stimulus frequency, stimulus type, and recording filters all influence the normal range. A value that is normal at one facility may be outside the reference range at another facility. For this reason, each laboratory should collect its own healthy control data using the same protocol that is used clinically. When laboratory-specific data are not available, published reference values should be applied only with clear understanding of their limitations.