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Zia Chaudhuri, Robert A. Clark, Joseph L. Demer; Horizontal Rectus Pulley Heterotopy Correlates With Cyclovertical Strabismus in Sagging Eye Syndrome. Invest. Ophthalmol. Vis. Sci. 2012;53(14):6339.
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Sagging Eye Syndrome (SES), attributed to orbital connective tissue degeneration, is associated with inferior displacement of horizontal rectus extraocular muscle (EOM) pulleys and has been correlated with divergence paralysis esotropia. This study used functional magnetic resonance imaging (MRI) to quantitatively relate horizontal rectus EOM pulley positions to cyclovertical strabismus in SES.
Quasi-coronal plane surface coil MRI (2 mm slices, 312 μm resolution) was obtained using T2 fast spin echo in target controlled central gaze in 14 orbits of 2 men and 5 women of mean age 74 ± 10 (SD) years clinically diagnosed with sagging eye syndrome. All subjects had acquired, vertical, binocular diplopia with an average best-corrected visual acuity (BCVA) of 0.07 ± 0.13 (SD) logMAR and mean refractive error of +0.61± 1.63 D (SD) spherical equivalent. Horizontal rectus EOM cross-sections were analyzed in a normalized, oculocentric coordinate system throughout the length of each EOM to identify pulley locations comparable to published young adult norms. MRI was correlated with horizontal and vertical binocular alignment by prism-cover testing, and torsional eye position by the angle of a line connecting fovea and optic nerve center.
Significant (p < 0.0001) bilateral, asymmetrical sag of both medial (MR) and lateral rectus (LR) pulleys was ubiquitous in all eyes. Mean LR sag of 8.32 ± 4.49 mm significantly exceeded MR sag of 2.76 ± 0.79 mm (p=0.0001) and was associated with excyclotropia. Bilateral asymmetry of combined total LR and MR sag correlated with degree of hypotropia (R = 0.43), with the eye exhibiting greater total sag more hypotropic. However, horizontal pulley positions did not correlate quantitatively with torsional eye position. Most subjects exhibited sag of brow and lid tissues, or previous blepharoplasty.
Significant, asymmetrical horizontal rectus pulley sag occurs in non-myopic older subjects with cyclovertical strabismus and periocular tissue laxity. Significant correlation of horizontal pulley sag suggests that the hypotropia is due to mechanical redirection of "horizontal" rectus EOM force to infraduction, with hypotropia in the more severely affected eye when asymmetrical. Other mechanisms may compensate for the extorsion anticipated from greater LR than MR sag.
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