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ENG question

Tom Boismier boismier at umich.edu
Mon Sep 30 07:37:04 EST 1996

In article <324B28C6.5140 at postoffice.worldnet.att.net>, 
Jenn.the.audiologist at POSTOFFICE.WORLDNET.ATT.NET says...
>To everyone who has replied to me here or in private: Thank you!
>Let me address the issues put to me. First, I reinstructed the patient 
>to make sure he understood the task. I also had him move closer and move 
>back further (it crossed my mind that he might be too close).

Calibration is determined by using a known distance from the target. Most 
commercial systems use 48" as the standard distance. If you move the patient 
around, your calibration is in error, even if you recalibrate at the new 
distance, because the algorythm assumes you're at a constant distance. See 
Barber and Stockwell for a good discussuin of calibration parameters.  The ICS 
system we use has a sonar rangefinder, but we find that it get's easily 
confused (sonar bounces off of beerbellies...;), so we ignore it and use a 
tape measure to confirm that the eyes are 48" from the target. .

>difference really to speak of. Calibration was okay (he wasn't perfect 
>but acceptable). He also showed abnormal tracking results and failure of 
>fixation suppression during calorics.

If these findings are repeatable, I'd believe them more than the OPK, 
indicating CNS involvement localizing to vestibulo-cerebellum. If you're using 
a computerized ENG system, they will frequently analyze saccades as nystagmus 
(just like they confuse eyeblinks), which could explain your OPK results. If 
the patient could only make saccadic attempts at pursuing the OPK stimuli, and 
the computer analyzes the saccades as nystagmus, you would get abnortmally 
high velocities.

> I would also love to know what other facilities' ENG 
>test batteries consist of. Unfortunately, we do not have rotary chair or 
>DP available to us. THANKS!

I will send a copy of the U of Michigan ENG battery to you by e-mail. For a 
discussion of low cost substitutes (like $10...) for DP and rotary chair, see 
Shepard and Telian  "Practical Management of the Balance Disorder Patient" 
Singular Publishing 1996, ISBN 1-879105-84-5

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