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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.