Page 138 - Edited - Webster HEAD AND NECK - part 2-Merge PDF

HN 326
NYSTAGMUS
Nystagmus is normal during and after a period of rotation. During the initial acceleration, it is a vestibulo-
ocular reflex; during constant rotation it is an opto-kinetic reflex: in both cases the slow component of the
nystagmus has the same angular velocity as the rotation and, because it is an attempt to stabilise the gaze
(Vol. I, p. 110 and A, below), its direction is opposite to that of the rotation. When rotation ceases, the
momentum of the endolymph in the semicircular canals signals a rotational deceleration in the opposite
direction: the directions of the post-rotational slow and fast components of the nystagmus are therefore
reversed, e.g. if the subject has been spinning about a vertical axis and to his/her LEFT, the slow
component of the postrotational horizontal/lateral nystagmus is to the left, the fast to the right (B, below).
Fixation of the eyes on an object suppresses such post-rotational nystagmus in 5 - 10 secs; ethanol and
vestibulo-cerebellar pathology prolong it.

A. Nystagmus when spinning at a constant
Direction of rotation velocity is an opto-kinetic reflex: the slow
to subject's left component represents a fixated gaze
maintained against the direction of rotation
until the fixated point (f) is out of view (f1).
fast
fast The fast (saccadic) phase is the shift to a
new fixation point which the rotation is
bringing into view. During the initial
slow slow acceleration the vestibulo-ocular reflex
f1 f
reinforces this.
B.
Direction of
previous rotation Deceleration or post-rotational nystagmus:
as above directions of slow and fast components
slow slow depend on direction of previous rotation,
and are due to momentum of endolymph.
The directions of the fast and slow
fast components reverse. Except in the tipsy
fast
and cerebello-vestibularly challenged, post-
rotational nystagmus can be suppressed in
a few seconds by fixating the gaze.

C. Lateral/horizontal nystagmus
slow can be set up by irrigating the
slow
external auditory meatus with
water at 37 ± 7°C. Cold
~ 30°C water "attracts" the slow
fast fast phase of the nystagmus. This
forms the basis of a test of
vestibular function - and is
one reason why water for
syringing wax from ears
should be at body
temperature.
(In clinical parlance, this is a right nystagmus)

slow slow
In labyrinthine pathology, the slow
component of the nystagmus is usually
fast fast towards the diseased side. Clinicians name
a nystagmus left or right according to the
direction of the fast phase.
D.
Pendulous nystagmus: rapid lateral
oscillations of both eyes with no fast or
slow components.

E.
Vertical nystagmus KEW.