الفهرس 
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Abstract
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SUMMARY
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Electronyst8gllography is 8 technique for recording
nystagmu8 based on detection of the cameo-retinal potential.
The eye was found to function a8 a rotating dipole
with the cornea positively charged and the retina negatively
charged. When electrodes are placed at each outer canthu.,
horizontal eyeball move.nts are recorded, and when the
electrodes are placed above and below each eye. vertical
eyeball movements can be recorded. The changes in voltage
produced by eye displacell8nt are sll81l, only 20 III1crovolt8/
degree. The electronystagmograpb must detect minute voltage
change~. amplify them without distortion and display
the. in a usable form. Usually a differential aaplifier
ls used, thus only the potential difference between the
electrodes 1s amplified and any interfering 81gnale are
cancelled. It is more desirable to use DC, to couple the
electrodes to the amplifier, than AC coupling.
The ENG record of nystagmus is 8usceptible to variat-
10ns in conditions under which the patient i8 exaained·
Visual fixation supress8s vestibular nystagmus and enhances
nystagmus due to cerbellar or brain stem disturbances.
Mental alertness should be kept during ENG record 8S it
enhances nystagmus. Drugs which may alert ENG record should
be forbidden for 48 hours before the test.
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The following tests are al.ost always included in any
ENG examination:
1) Gaze test. Eye movements are recorded as the patient
looks straight ahead’, to the right and to the left.
The tracing is inspected for the presence of nystagmus
under any of these conditions.
2) Optokinetic test. Eye .ave.ents are recorded while the
patient watches vertical stripes moving at several
different speeds to the right and then to the left.
Normal individuals will experience an-optokinetic nystagmus
(OKN) which is equivalent for both directions of
target motion. Peripheral ocular diseases cause OKN
asymmetry. Peripheral vestibular diseases when In the
acute phase can impair OKN transiently, while In the
chronic phase they usually give normal OKN. Abnormalities
of OKN are of value in detection of eNS pathology.
They are also of help to localize the site of thiS
pathology.
3) Tracking test. Eye movements are recorded while the
patient follows a slowly moving Visual target. The
normal individual 1s able to follow the target with
negligible error, producing a.tracing that 1s sinusoidal
in shape. The abnormalities of the eye-tracking
test may be due to eye diseases, inner ear diseases or
more significantly neurological diseases. Peripheral
ocular diseases cause ataxic eye-tracking or fast
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movements superimposed on norlD8l tracking. Inner ear
diseases in the acute phase impair the normal eye-tracking
transiently, while in the chronic phase they give
normal results. Neurological diseases” particularly
1n the brain stem, can produce any of the three main
types of abnormal pendular eye-tracking curves.
4) Positional test and Hallpike aaneuver. In the positional
test, eye movements are recorded with the patient’s eyes
both open and close6, after the patient has been placed
in various positions (usually sitting, supine, right
lateral, left lateral and head hanging). The tracing
is inspected for the presence of nystagmus in any position.
In the Hallpike maneuver, the patient 1s moved
rapidly from sitting to the head-hanging right lateral
position, then returned to sitting. then moved rapidly
to the head-hanging left lateral position, and again
returned to sitting. The tracing 1s inspected for nystagmus
following each movement.
S) Caloric test~,using the technique of Fitzgerald and
Hallpike. Parameters of observation of caloric induced
nystagmus c~::msistof its latency, duration, frequency
and the velocity of the slow phase which 1s the most
accurate one. The recordings are evaluated according
to the following aspects: (A) the relative sensitivity
of each labyrinth which help to diagnose unilateral
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,
weakness’, (8) directional preponderance which represents
the difference in intensity between the two right-beating
nystagmus responses and the two left-beating nystagmus
responses and (C) effectiveness of visual fixation in
suppressing caloric nystag8Us which if fails is an indication
of a eNS disease.
6) Rotational tests. Eye move.ents are recorded with the
patient sitting on a revolving chair. There are three
methods of rotation. The Barany chair produces rapid
acceleration and deceleration. CupuloDetry employs a
slow subthreshold acceleration and a rapid deceleration.
The torsion swing generates 8 damped sinusoidal pattern
of deceleration. As both labyrinths are stiaulated
simultaneously rotational tests only provide an overall
picture of labyrinth:Lne function wh:Lch may be helpful
:Lndet.raining bilateral labyr:Lnth:Lnedamage.