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K. Irsch, D. L. Guyton, M. Roggia, P. Phamonvaechavan, H. S. Ying; Can Patients with Superior Oblique Paresis Mimic the Neural Output of the Ocular Counter-Roll Mechanism to Fuse Vertically?. Invest. Ophthalmol. Vis. Sci. 2010;51(13):2534.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate cyclovertical eye movements during fusion in patients with unilateral superior oblique paresis (SOP).
Five patients diagnosed with congenital unilateral SOP without previous muscle surgery were examined with our tilting haploscope that allows assessment of simultaneous horizontal, vertical, and torsional eye movements, binocularly, through the use of video-oculography. Vertical vergence was stimulated using concentric circle targets without torsional cues, subtending >54 degrees. Eye movements were recorded during binocular and monocular viewing in straight ahead gaze with head straight and when tilted 45 degrees right and left. If the patient was unable to fuse the targets in any position, the targets were re-aligned so that the patient could barely fuse them in the head straight position, and eye movements were recorded again.
With the head remaining straight, four of the five patients showed torsion of both eyes (a cycloversion) toward the side of the hyperdeviation when overcoming their hyperdeviation with vertical fusional vergence. As expected, head tilt away from the side of the hyperdeviation also decreased the hyperdeviation, even under monocular conditions, accompanied by a cycloversion toward the side of the hyperdeviation, the familiar ocular counter-roll as mediated by the otoliths.
In SOP, the imbalance of vertical forces creates a hyperdeviation on the side of the paretic superior oblique muscle (SOM). Actively tilting the head away from the paretic SOM normally decreases its stimulation and thus its participation in the alignment of the eyes. Affected patients use such a head tilt to maintain fusion. Our four patients appeared to perform cyclovertical movements of their eyes during vertical fusional vergence as if they were tilting the head (but with the head remaining straight), thus avoiding stimulating the paretic SOM and thereby regaining fusion. These results suggest that some patients with SOP may have learned to mimic the neural output of the ocular counter-roll mechanism to fuse vertically.
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