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oVEMP testing with Eclipse

What is oVEMP?
The Ocular Vestibular Evoked Myogenic Potential (oVEMP) is an evoked potential measured from the inferior oblique muscle and is used to assess the vestibular system. There is still some debate over the origin of the response (Piker et al., 2011), however, the oVEMP is largely dependent on the integrity of the superior vestibular nerve (Jacobson et al., 2011).

The oVEMP is recorded using surface electrodes at four sites on the face and an Amplitude Asymmetry Ratio is calculated to determine if the above-mentioned parts of the vestibular system are intact and working normally.

The figure shows oVEMP recordings from a normal young adult (Murnane & Aki, 2009).

Why oVEMP?
The oVEMP is a test used in addition to traditional vestibular testing (e.g., VNG) to assist in the assessment of vestibular function. oVEMP recordings provide value information to medical practitioners to assist them in the diagnosis of disorders such as Superior Semicircular Canal Dehiscence (SSCD) (Watters et al., 2006) and Meniere’s disease (Sandhu, 2012).

How to test?
Patient Preparation is very important. The electrode sites must be prepared and cleaned in order to obtain acceptably low skin impedances. It is recommended to have impedance values of 3kΩ or lower. The impedance value between each electrode should be balanced or similar in value.

The subject is either seated or in a reclined position and is instructed to maintain an upward gaze at 35 degrees for the duration of the recording (Kantner & Gürkov, 2014). Placing a static visual target on the wall or ceiling for the patient to look at during testing will ensure consistent activation of the inferior oblique muscle.

Electrode placement (example)

Use of this electrode montage does not require the active (white) electrode to be shifted during testing and is reported to provide the largest oVEMP amplitude (Piker et al., 2011).

The reference electrodes should be placed as close as possible underneath the eye in the orbital midline. Avoid placement close to the medial canthus (inner corner of the eye) as a null-point exists where there is no oVEMP response present (Sandhu, George & Rea, 2013).

The oVEMP response is recorded from the inferior oblique muscle underneath the contralateral eye. Therefore, the right (red) electrode is placed under the left eye while the right ear is stimulated. Correct positioning of the electrode on the inferior oblique muscle is essential in obtaining a response (Sandhu, George & Rea, 2013).

Alternative electrode placement (examples)

Electrode montage for testing the left ear. For testing of the right ear, move the active (white) electrode to the other side (underneath the red electrode).

Typically, the air-conduction stimulus used is a 500Hz tone burst at high intensity level (e.g., 90/95dBnHL). Ensure that the patient is relaxed prior to starting the test. After confirming impedances.

Setting up the Eclipse
The Eclipse comes with pre-programmed protocols so the system is ready to use immediately. Protocols can be created or modified easily to fit your clinical needs. Consult the Eclipse Additional Information manual to learn how to create or modify a protocol. The procedure described below is simply a suggested test process and to be used only as a guideline. 

oVEMP testing procedure
Choose an oVEMP protocol from the dropdown menu 
The oVEMP test should be run in the Manual Mode controlling/selecting stimuli manually. For more collection parameters details, please refer to instruction for use manual.

Manual mode

  1. To begin in manual mode, choose the intensity and select the ear to test on the Record sheet. Instruct the patient to look up and hold their gaze without moving their head.
  2. Next choose Start or press F2.
  3. 100-200 sweeps are typically collected per waveform.

Setting up L & R waveform partners
After collection, choose a left or right ear waveform by double clicking the waveform handle. Next, right click the waveform handle of the opposite ear and select Set as VEMP Partner. The selected waveforms are used in the Asymmetry Ratio Calculation.

EMG scaling
The EMG scaling is not to be used in the oVEMP testing, as there is no contracted muscle as in cVEMP. The reason for gazing up, is not to contract the oblique muscle, but instead to positioning the inferior oblique muscle closer to to the recording electrode.

Marking peaks
The oVEMP response is well documented and is said to be represented by two distinct peaks; N1 occurring at approximately 10 ms and P1 occurring at approximately 15 ms.

Waveforms can be marked from the Record sheet or the Edit sheet. To mark a waveform double click on the waveform handle you would like to mark. Right click and then choose the correct marker. Drag your mouse to the correct area and click. You can also choose 1-4 on the keyboard to bring up the appropriate marker and use Enter to place it.

Example of an oVEMP where N1 and P1 are marked for both ears.

Normative data
A large study investigating the normal characteristics of the oVEMP by Piker and colleagues (2011) defined an upper limit of oVEMP amplitude asymmetry to be 34% (mean + 2 SD).

Example of scaled oVEMP waveforms indicating an abnormal asymmetry ratio between left and right side, along with lowered oVEMP thresholds on the right.

Reporting
Choose the Report Icon 
When complete, choose Save and Exit.


References
Kantner, C., Gürkov, R. (2014). The effects of commonly used upward gaze angles on ocular vestibular evoked myogenic potentials. Otology & Neurotology, 35(2), 289-293.

Jacobson, G. P., McCaslin, D. L., Piker, E. G., Gruenwald, J., Grantham, S. L., & Tegel, L. (2011). Patterns of abnormality in cVEMP, oVEMP and caloric tests may provide topological information about vestibular impairment. J Am Acad Audiol, 22, 601-611.

Murnane, O. D., & Akin, F. W. (2009). Vestibular-evoked myogenic potentials. Seminars in Hearing, 30(4), 267-280. Piker, E.G., Jacobson, G.P., McCaslin, D.L., & Hood, L.J. (2011). Normal characteristics of the ocular vestibular evoked

myogenic potential. J Am Acad Audiol, 22, 222-230.
Sandhu, J. S., George, S. R., & Rea P. A. (2013). The effect of electrode positioning on the ocular vestibular evoked

myogenic potential to air-conducted sound. Clinical Neurophysiology, 124(6), 1232-1236.
Sandhu, J. S., Low, R., Rea, P. A., & Sauders, N. C. (2012). Altered frequency dynamics of cervical and ocular vestibular

evoked myogenic potentials in patients with Meniere’s disease. Otology & Neurotology, 33(3), 344-440.
Watters, K. F., Rosowski, J. J, Sauter, T., & Lee, D. J. (2006). Superior semicircular canal dehiscence presenting as postpartum vertigo. Otology & Neurotology, 27(6), 576-768.

September 2017
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