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H. S. Ying, K. Irsch, N. A. Ramey, D. L. Guyton; Vertical Vergence Adaptation Produces an Incomitant Transient Cyclovertical Deviation Changing With Gaze Direction and Head Tilt. Invest. Ophthalmol. Vis. Sci. 2009;50(13):1990.
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With the aim of understanding the cyclovertical mechanisms involved in both binocular fusion and ocular misalignment, we asked normal volunteers to adapt to a steadily increasing vertical misalignment.
We designed and built a novel research haploscope capable of tilting with the subject 45 degrees to the right or the left about the naso-occipital axis and measuring binocular horizontal, vertical, and torsional eye movements with video oculography. Circular targets consisting of multicolored concentric circles without torsional cues and subtending >54 degrees were used to stimulate vertical vergence. Two subjects with normal orthoptic exams were instructed to fuse a gradually increasing right over left target disparity in straight head position for 30 minutes. Static eye positions were measured during monocular viewing in the nine diagnostic positions of gaze (10-degree excursions) with head straight and tilted 45 degrees right and left. Subjects re-fused right over left target disparity between measurements in different head tilts.
After adaptation, both subjects developed a transient cyclovertical ocular deviation with at least two degrees of vertical deviation in the straight ahead position. The right hyperdeviation decayed slowly over 60 to 90 seconds. This hyperdeviation increased in down gaze or with 45-degree left tilt and reduced with 45-degree right head tilt. Relative extorsion that was greatest in left gaze developed in all three head tilts. An esodeviation also developed in most positions of gaze which increased with tilt to either side.
Changes in a vertical deviation with head tilt are often taken as evidence for a cyclovertical muscle paresis. These results indicate that vergence adaptation may induce a transient cyclovertical deviation that can also show changes with head tilting. Therefore, changes in vertical deviation with head tilting are not pathognomonic of cyclovertical muscle paresis.
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