[The dorso-mesencephalic syndrome. Electrooculographic study of 2 clinical cases].

Electro-oculographic recordings of horizontal eye movements in two patients with dorso-mesencephalic lesions are analysed. Tracings shows essentially: (A) dysconjugate glissadic dysmetria, with adduction overshoot and abduction undershoot, and (B) instability of ocular fixation. Fixation instability consists of bursts of 2 or 3 bilateral to-and-fro eye movements, of 4 degree or less amplitude. During a burst there is no evident latency between successive ocular movements. Bursts often appear following horizontal refixation saccades, and are then repeated once or twice with regular intervals. In one patient, fixation instability phases are more often elicited by saccades to the right than to the left. The typical occurrence of fixation instability after the fast phase of optokinetic nystagmus is described. The alteration of ocular fixation described in our patients belongs to the general group of "saccadic intrusions" as defined by Daroff et al. (1977). Resemblance with "lightning eye movements" (Atkin and Bender, 1964) and "opposed adducting saccades" in the Sylvian aqueduct syndrome (Ochs et al., 1979) is discussed.