ENG Information

Jeff Sirianni sirianni at uts.cc.utexas.edu
Wed Aug 31 00:25:39 EST 1994

Sorry that I did not include the original message (I will learn this
editor in time).  But the question that was raised concerned ENG

ENG's are performed on patients complaining of balance problems,
usually associated with hearing loss.  When a tumor (ie acoustic
neuroma) pressed against the 8th CN, hearing problems including
sensitivity loss plus tinnitus, plus balance problems are often
reported.  An ABR and ENG are often ordered by the ENT (Ears, Nose
and Throat physician).  An MRI is also usually ordered.

Anyway, back to ENG's... ENG's provide information concerning the
function of the vestibular mechanism, both in the inner ear (semi-
circular canals), plus central balance function (ie in the brain).
Results can indicate whether the problem stems from a malfunctioning
inner ear mechanism or whether it is centrally misfunctioning.

ENG testing involves numerous tests including optical tracking,
positional testing, and caloric testing (water irrigation of the
ear canals).  What is measured is the eye's movements during these
procedures.  Nystagmus can be induced (by caloric stimulation) and 
during some positional testing.  There is limits to the speed of
eye movements and this is what is assessed.

ENG's have been classically monitored by measuring ocular muscle
potentials with surface electrodes placed around the eyes.  These
potentials give inference to what the eyes are actually doing during
testing.  A new wave of testing equipment uses video cameras and
lasers that lock in on the eye (I believe the iris) and track the
eye movements this way instead of via ocular muscle potentials.

For those interested in reading about vestibular testing, a good
source is a chapter in a recent audiology text : Handbook of
Auditory Evoked Potentials, James W. Hall (1992).

Jeff Sirianni
University of Texas at Austin
Communication Sciences and Disorders  

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