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Diagnostic
Information
For most of the population, balance
control occurs at an unconscious level. Signals from the inner ear
continuously drive the eye muscles to coordinate eye movement with head
movement. This coordination is necessary to have clear vision and
balance. The communication between the ear and the eye is called the
vestibulo-ocular reflex (VOR). When the VOR is functioning properly, eye
speed and timing are equal and opposite to those of the head. But, if
the speed or timing is off, even slightly, vision is distorted because
of apparent motion of the visual field.
The
VAT® is an 18 second test of the high frequency horizontal and vertical
VOR’s for diagnosis, treatment planning and monitoring of vestibular
disease. The frequency tested ( 2 - 6 Hz) closely approximates normal
head movements. For example, many patients complain of dizziness or loss
of balance when they are walking, bending over or turning their head
quickly. The VAT® quickly and comfortably monitors a patient’s head and
eye motions to record what is happening in the vestibular portion of the
inner ear.
Testing with the VAT® often identifies problems not found with other
vestibular tests, because the VAT® tests natural, faster motions and
unlike other conventional vestibular tests, evaluates both the
horizontal and vertical canals. Because the VAT® is sensitive to changes
of the VOR and is easy to perform, it is often the first screening test
a patient receives who complain of dizziness or balance problems.
Patients do not object to repeated testing which makes the VAT® the
ideal test to monitor ototoxic medication and vestibular rehabilitation.
The
data shown below illustrates the VAT® test results from a gentamicin
ototoxicity patient. The normative data is shown as the blue error bars
( ± 2 std.) Individual patient VAT® data are shown in various colors.
Notice that both the horizontal and vertical gains (top two graphs) are
well below the normal data. The horizontal and vertical phases ( bottom
two graphs) are above the normal data. This data pattern is typically
seen in gentamicin ototoxicity.
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