Vestibular Diagnosis and Treatment
Utilizing Videonystagmography (VNG)
Purpose of Test:
To assess the patient’s ability to maintain a steady gaze on an object at various angles without the eye generating extraneous movements (i.e. square wave jerks or nystagmus). The inability to maintain a steady gaze is an indication of either a central or peripheral vestibular system lesion. Gaze positions tested are: center (straight ahead), gaze left, gaze right, gaze up and gaze down.
“You will see a green dot on the screen. Simply look at the dot. If the dot moves, follow it with your eyes only. Try not to move your head.”
What to Expect:
A patient with normal gaze ability will produce a tracing that is virtually a straight line once the eyes are fixated on the target. The right eye is represented by the red line and the left eye by the blue line. If nystagmus is present it will be identified by triangles on the eye position graph to represent each detected nystagmus beat. The average slow phase velocity value(s) will be plotted in the bar graphs to the right of the tracings. When the average slow phase velocity exceeds the threshold value of 6⁰/sec, the bar graph will be shaded grey and a red diamond will appear near the bar graph to indicate an out of threshold response.
Gaze test showing normal response for all gaze angles (center, left, right, up and down)
Abnormal Test Results:
An “abnormal” gaze tracing might present itself in several ways. A patient may present with square wave jerks, nystagmus, or gaze decay. Below are examples of abnormal tracings:
Gaze test showing bilateral gaze-evoked nystagmus
Gaze test showing down-beating nystagmus on gaze down 20⁰
Gaze testing is the ONLY test of the four ocular tests in which an “abnormal” result could be generated either from the peripheral vestibular system or from the central vestibular system.
For a complete discussion of differential diagnosis using the gaze stability test, refer to:
Jacobson, GP, and Shepard, NT. Balance Functional Assessment and Management, 2nd Ed. San Diego; Plural Publishing, 2015
Note: This is intended only as a guide, official diagnosis should be deferred to the patient’s physician.