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H.S. Ying, X. Shan, J. Tian, R. Tamargo, D. Zee; Unilateral IV Nerve Palsy in Monkey: III. Saccades . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2490.
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To investigate changes in vertical saccades following induced IV nerve palsy in rhesus monkeys.
The IV nerve was sectioned intracranially in 2 rhesus monkeys (M1 and M2). Post–lesion the paretic eye (PE) was immediately patched for 6 (M1) and 9 (M2) days to prevent binocular viewing (BEV). With search coils, 20° vertical saccades were recorded along center, right and left (20°) pre– and post–lesion. Saccade amplitude (pulse) was defined from saccade onset (vel>30°/s) to saccade end (vel<30°/s). Pulse–pulse ratios (PPE/PNE) were determined with normal eye (NE) viewing. Postsaccadic drift was quantified as a pulse–step ratio (P/S); the step was taken at 80ms after the pulse.
Post–lesion, vertical saccades by the PE were hypometric (∼10%). Pre–lesion the PPE/PNE for 20° up and down saccades was ∼1.05 for M1 and ∼1.0 for M2. Immediately post–lesion the PPE/PNE decreased, being smallest for down saccades with the PE adducted (0.84, M1; 0.70, M2). For upward saccades with PE adducted, PPE/PNE was 0.92 for M1 and 0.89 for M2. After BEV, for down saccades, PPE/PNE for both monkeys decreased with the PE abducted and increased with the PE adducted. The main sequence was minimally affected. Pre–lesion there was little post–saccadic drift of the PE for M1 but there was a small upward drift (P/S, 0.98) after up saccades for M2. Post–lesion, with PEV but before BEV was allowed, for downward saccades both monkeys showed downward drift of the PE in adduction (P/S for M1, 0.97; M2, 0.96) and some upward drift in abduction (P/S for M1, 1.02; M2, 1.04). For up saccades there was downward drift in abduction and center gaze but upward drift in adduction. After BEV, the downward drift after down saccades by the PE in adduction decreased while upward drift of NE developed. Likewise the downward drift in PE following up saccades in abduction decreased while upward drift of NE developed.
Rhesus monkeys with induced IV nerve palsy showed changes in vertical saccade amplitude, conjugacy and postsaccadic drift. The changes were direction and orbital position dependent. After BEV was allowed there were further changes, both conjugate and disconjugate, even though neither animal could overcome its vertical phoria.
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