Pursuit and saccadic eye movements in response to unpredictable constant velocity targets

A clinically oriented approach to smooth pursuit eye movement quantitative evaluation

The electrooculographic technique was used to record smooth pursuit eye movements in 71 healthy subjects homogeneously distributed within an age range between the 2nd and the 6th decades. The target moved at constant velocity (triangular ramps) and 9 different target velocities (V), from 10 deg/s to 50 deg/s were considered and presented according to pseudorandom sequence. Ad hoc software suppressed catch-up saccades so that a pursuit index (PI) value was computed for each ramp taking into account only the smooth pursuit tracking modality. It was demonstrated that the relationship between V and PI could be described by the linear model PI = a + b * V. Pursuit index was proved to be influenced by the age of subject (decade factor in the analysis of variance), since an almost linear increase in b values yields a reduction of pursuit index values. The method was tested in 22 multiple sclerosis patients and an association was found between the occurrence of cerebellar signs and the reduction of a value.

The effect of alcohol on the vestibulo-ocular reflex and gaze regulation

To clarify the effect of the temporary decline in cerebellar function on the vestibulo-ocular reflex (VOR) and gaze functions, we examined 12 normal adults under passive rotations before and after they drank alcohol at dosages of 0.43 and 0.65 g/kg. Whereas spatial gaze fixation was maintained accurately with 0.65 g/kg administration (0.06% blood alcohol level), gaze fixation on a head-fixed target and smooth pursuit were impaired by the higher dosage of 0.43 g/kg (0.03% blood alcohol). The magnitude of the alteration in the VOR gain after drinking was correlated significantly with the VOR gain before drinking: while small values were enhanced by drinking, large values were suppressed. The present study indicates that the VOR in the dark is regulated by the balance between the amplifying and suppressing forces controlled by the cerebellum.