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H. S. Ying, X. Shan, J. Tian, D. L. Guyton, R. Tamargo, M. Walker, D. S. Zee; Effect of Corrective Strabismus Surgery after Unilateral IV Nerve Palsy in Monkey: II. Torsion. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4870.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate the effect of corrective strabismus surgery on static and dynamic torsion misalignment following induced IV nerve palsy (SOP) in rhesus monkeys.
The IV nerve was sectioned intracranially in 2 rhesus monkeys (M1 and M2). More than 4 months after lesion, the ipsilateral IO muscle was denervated and extirpated for both M1 and M2. After an additional 4 months, M2 received contralateral IR recession (2.0 mm). Eye movements were recorded pre and post-correction during straight ahead or eccentric fixation (±20°, horizontal and/or vertical) with the head upright or tilted (±30º). The torsion reference position was zeroed for the immediate pre-lesion recording but not changed afterwards. Dynamic torsion was defined as the intrasaccadic torsion above Δ static torsion predicted from Δ vertical position.
With the initial SOP, monkeys developed extorsion of the paretic eye (PE) that increased with down gaze and abduction. Post-lesion, the PE was extorted by 5.8° in straight and 15.7° in abduction/down gaze for M1, and 5.5° and 15.3° for M2. Following IO weakening surgery, intorsion of the PE developed in up gaze for M1 and M2, increasing the torsion gradient across vertical positions. Dynamic torsion alignment during vertical saccades and post-saccadic torsional drift were also more intorting with all vertical saccades for M1 and with upward saccades for M2. In contrast to IO surgery, IR recession in M2 little affected torsional deviation, peak dynamic torsion or post-saccadic torsional drift. Listing’s horizontal primary position (PP) after SOP showed a large temporal rotation (27.1° for M1 and 26.7° for M2) that rotated more temporally after IO weakening surgery (13.6° for M1 and 9.82° for M2) but did not change after IR recession (-1.85° for M2).
Corrective strabismus surgery in monkeys with SOP produced characteristic patterns of change in both dynamic and static torsion which were quite different depending upon whether a rectus or an oblique muscle is operated upon. These effects of surgery on torsion are also reflected in changes in Listing’s Law behavior.
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