• Horizontal and vertical components of oblique saccadic eye movements are dynamically independent. That Is, they have independent dynamic trajectories determined by either the presence, or the absence, as well as the magnitudes of dynamic overshoot, glissades, overlapping saccades, and closely spaced saccades. Temporally, oblique movements manifest varying degrees of independence, for the two components can begin and end either together or separately. Purely horizontal saccades (ie, between two points on a horizontal line) usually show crosstalk demonstrated by extraneous, transient, vertical components. Therefore, saccades are very seldom linear or straight; the trajectories are usually curved.
(Arch Ophthalmol 95:1258-1261, 1977)
Bahill AT, Stark L. Oblique Saccadic Eye MovementsIndependence of Horizontal and Vertical Channels. Arch Ophthalmol. 1977;95(7):1258-1261. doi:10.1001/archopht.1977.04450070156016