ENG Versus VNG: Which Is Better?
Artifact
Artifact affects both ENG and VNG recordings, but not from the same source. With ENG (electronystagmography), the recording is subject to contamination from ambient muscle electrical activity and artifact associated with eye blinks. Eye blinks can occur with the eyes open or closed.
Many patients exhibit activity in the vertical channel whenever their eyes are closed. Because this can be mistaken for vertical nystagmus on the ENG recording, the patient’s eyes should be inspected visually for any type of eyelid flutter while the recording is taking place.
Some older single-channel ENG equipment does not allow recordings in the vertical channel. In this case, the examiner must also be careful to rule out eye blinks or eyelid flutter, which also can be mistaken for horizontal nystagmus. Again, visual observation of the eyes eliminates misinterpretation of the recording.
Here is an example of eyeblinks on an ENG recording (Click on the photo to enlarge it, then hit the “back” arrow to return to the text):
Even with VNG (Videonystagmography) eye blinks are visible on most recordings. The most common source of artifact in a VNG recording is the inevitable temporary loss of tracking. If there is something in the recording field that is as dark as the pupil (typically eye make up, but occasionally the side of the goggle holding the camera in place), then there will be a temporary loss of tracking until the camera is moved or the recording threshold is adjusted.
Here is an example of loss of tracking on a VNG recording:
Even when you lose tracking while performing VNG, you still have a clear view of the eye. If your tracing is unclear, most VNG units allow you to play back the video of the eye movement in question. Round 2 definitely goes to VNG.
Tracing examples courtesy of Dr Tim Hain’s website (www.dizzinessandbalance.com)
Title photo courtesy of: https://www.integratedmortgageplanners.com/blog
