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X. Shan, J. Tian, H. S. Ying, M. Walker, R. Tamargo, D. S. Zee; Dynamic Changes of Vertical Saccades With Head Tilt in Unilateral IV Nerve Palsy Monkeys. Invest. Ophthalmol. Vis. Sci. 2008;49(13):1120. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To study changes in vertical saccades dynamics with 30° head tilt following induced IV nerve palsy in rhesus monkeys.
The IV nerve was sectioned intracranially in 2 rhesus monkeys (M1 and M2). With sclera search coils, 20° vertical saccades were recorded pre- and post-lesion with the head upright and tilted (±30º) with normal eye (NE) viewing. Saccade amplitude (pulse) was defined from saccade onset (vel>30°/s) to saccade end (vel<30°/s). Pulse-pulse ratios (PPr) was the ratio of paretic eye (PE)/NE (PPE/PNE). Post saccadic drift was quantified as a pulse-step ratio (P/S); the step was taken at 80ms after the pulse. Dynamic (‘blip’) torsion during vertical saccades was calculated from the amount of torsion above that expected from the change in static torsion during fixation before and after the saccade.
Pre-lesion with head tilt to the paretic side the PPr was ~1.06 for M1 and ~1.04 for M2, when tilted to the normal side ~1.0 for M1 and ~0.95 for M2. Post-lesion, vertical saccades by the PE were hypometric and the PPr of 20° up and down saccades (between -10° to 10°) decreased. The change was larger for M1 when tilt to the paretic side, but about the same for M2 on either side, although M2 had a relatively larger change in static vertical deviation with head tilt to the paretic side.Pre-lesion comparing with upright there was little change in vertical post-saccadic drift of the PE with the head tilt to either side for both monkeys except slightly increased backward drift following downward saccades of M1. Post-lesion, for both up and downward saccades, there were increased backward drift (P/S>1) and more so with the head tilt to the paretic side.Post-lesion, during both up and down vertical saccades, both monkeys developed an increased extorsional ‘blip’ in the PE. The change was larger for up saccades than down saccades, and larger when tilted to the paretic side than to the normal side except for up saccades in M2.
Rhesus monkeys with acquired IV nerve palsy show a specific effect of head tilt on the dynamic properties of vertical saccades. The most striking changes were an increase in postsaccadic vertical drift (backward drift) and an increase in dynamic (‘blip’) torsion (extorsion), especially with the head tilted to the paretic side. These findings can serve as a reference for studies in human patients with putative SOP.
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