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S.M. Garbutt, L.F. Dell'Osso, J.B. Jacobs; "Staircase" Saccadic Intrusions and Transient Yoking and Neural Integrator Failures Associated with Cerebellar Hypoplasia . Invest. Ophthalmol. Vis. Sci. 2003;44(13):1968.
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Purpose. To investigate the eye movements and elucidate mechanisms of ocular motor control in a patient with general motor apraxia, plagiocephaly, developmental delays, and torticollis who exhibited "staircase" saccadic intrusions and transient failures of his yoking mechanism and neural integrators. Methods. Ocular motility recordings were made using infrared reflection during fixation of targets at gaze angles varying between ±30° and at convergence angles ranging from far to 20D and during smooth pursuit at velocities of 5-40°/sec. Results. T1-weighted MRI showed hypoplasia of the cerebellar vermis and inferior cerebellar peduncles. No abnormal enhancement was seen with gadolinium. During far and near fixation, the subject exhibited conjugate "staircase" saccadic intrusions (rightward more often than leftward), with intersaccadic intervals equivalent to the normal visual latency (250 msec). During smooth pursuit, rightward pursuit was markedly better than leftward, which was often absent. However, for short periods he occasionally generated good pursuit in both directions. Conclusions. Staircase intrusions may result from a failure of the saccadic system to properly use visual information to correct eye position (e.g., the sign of retinal feedback is suddenly reversed). The frequent presence of uniocular, convergent, and divergent saccades, including double saccades, provides further evidence in support of the hypothesis that the ocular motor system is wired in a uniocular manner and therefore, due to its inherent bilateral architecture, a unimuscular manner.
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