ROVING EYE MOVEMENTS

ROVING EYE MOVEMENTS-These are slow, random deviations of eye position
that are similar to the eye movements
seen in normal individuals during light sleep.
As in sleeping individuals who typically have
some degree of exophoria, the eye positions
may not be quite conjugate, but the ocularexcursions should be conjugate. Most roving
eye movements are predominantly horizontal,
although some vertical movements may also
occur. Most patients with roving eye movements
have a metabolic encephalopathy, and
oculocephalic and caloric vestibulo-ocular responses
are typically preserved or even hyperactive.
The roving eye movements may disappear
as the coma deepens, although they may
persist in quite severe hepatic coma. Roving
eye movements cannot be duplicated by patients
who are awake, and hence their presence
indicates that unresponsiveness is not psychogenic.
A variant of roving eye movements is
periodic alternating or ‘‘ping-pong’’ gaze,126
in which repetitive, rhythmic, and conjugate
horizontal eye movements occur in a comatose
or stuporous patient. The eyes move conjugately
to the extremes of gaze, hold the position
for 2 to 3 seconds, and then rotate back
again. The episodic movements of the eyes
may continue uninterrupted for several hours
to days. Periodic alternating eye movements
have been reported in patients with a variety of
structural injuries to the brainstem or even
bilateral cerebral infarcts that leave the oculomotor
system largely intact, but are most
common during metabolic encephalopathies.