What is Gaze testing in electronystagmography (ENG)?

Updated: Aug 06, 2019
  • Author: Angela G Shoup, PhD; Chief Editor: Arlen D Meyers, MD, MBA  more...
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Answer

Answer

Gaze testing is conducted to evaluate for the presence of nystagmus in the absence of vestibular stimulation. In the ENG test battery, essentially 3 types of information are obtained: presence or absence of spontaneous nystagmus (no task or center gaze); presence, absence, or exacerbation of nystagmus with addition of off-center gaze tasks to stress the system; and fixation suppression of spontaneous nystagmus.

For gaze testing, the patient is instructed to look straight ahead and then fixate on a target 30 degrees to the right, left, up, and down. Fixation is maintained for approximately 30 seconds in center gaze and 10 seconds in eccentric gaze. The test can be conducted with the same targets placed on the wall or ceiling for calibration or with computer-generated stimuli as mentioned above.

For evaluation of spontaneous nystagmus, eliminating any possibility of suppression is important. Fixation suppression can be eliminated by having the patient's eyes open in a dark room with Frenzel lenses or dark goggles used for infrared assessment. With electrode-based systems, spontaneous nystagmus may be evaluated with the patient’s eyes closed. In addition, the patient may be asked to participate in a number of mental tasks (eg, answering questions, counting by multiples of 2).

Square-wave jerks are the most common abnormality found with eyes closed (absence of visual fixation). Caution must be exercised in the interpretation of square-wave jerks. Many healthy patients exhibit this pattern with their eyes closed. Furthermore, the frequency of square-wave jerks increases with age. In young patients, square-wave jerks may be considered atypical if they occur more frequently than once per second or with visual fixation. In such cases, square-wave jerks are suggestive of a cerebellar disorder. [9]

Spontaneous nystagmus may indicate either central or peripheral pathology. The presence of nystagmus with visual fixation is always diagnostically significant.

Peripheral indicators include horizontal or horizontal rotary nystagmus, nystagmus suppressed by visual fixation, non–direction-changing nystagmus, and nystagmus exacerbated by gazing in the direction of the fast phase.

Central indicators include vertical nystagmus, nystagmus not suppressed by fixation, and direction-changing nystagmus.

By Alexander's law, nystagmus evident with visual fixation always beats in the same direction and increases when the patient gazes in the direction of the fast phase. Nystagmus decreases or disappears when the patient gazes in the direction opposite to the fast phase. This pattern is often seen in peripheral vestibular disorders and occasionally in central disorders.

Unilateral gaze-paretic nystagmus only occurs with eccentric gaze in one direction. Elicited nystagmus beats in the direction of the gaze. This is consistent with CNS pathology.

With bilateral gaze-paretic nystagmus, when the patient gazes to the right, nystagmus is elicited that beats to the right; when the patient gazes to the left, left-beating nystagmus occurs. This pattern suggests CNS pathology.

Bruns nystagmus is a combination of unilateral gaze-paretic nystagmus and vestibular nystagmus, which is evidenced as nystagmus in both directions of a gaze that is asymmetrical. Bruns nystagmus is associated with extra-axial mass lesions on the side of the gaze-paretic nystagmus.

Congenital nystagmus often has a spiky appearance and increases with lateral gaze. Congenital nystagmus may decrease in velocity or completely disappear in the absence of visual fixation.

Rebound nystagmus is characterized by a burst of nystagmus that lasts approximately 5 seconds and begins when the eyes return to center gaze. When this is present, the clinician may suspect brainstem or cerebellar lesions.

For peripheral lesions, nystagmus that is evident with eyes closed or in the dark should be suppressed by visual fixation. If visual fixation does not suppress nystagmus, CNS pathology is possible.


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