PMID: 9430565Jan 16, 1998Paper

Displacement of the medial rectus pulley in superior oblique palsy

Investigative Ophthalmology & Visual Science
Robert A ClarkJoseph L Demer

Abstract

The rectus extraocular muscles pass through fibromuscular connective tissue pulleys that stabilize muscle paths and control the direction of muscle pull. The authors investigated whether abnormal forces associated with superior oblique palsy can cause displacement of pulleys and muscle paths. Coronal magnetic resonance imaging (MRI) showing significantly reduced superior oblique cross-sectional areas and lack of contractile changes with vertical gaze confirms that seven subjects had superior oblique palsies. Binocular misalignment was quantified using the Hess test. In those seven subjects with palsies and in 18 normal orbits, coronal MRI scans corrected to standardized head position were analyzed digitally to determine muscle paths in primary gaze. Horizontal and vertical coordinates of the pulleys, known histologically to lie just posterior to the equator in primary gaze, were inferred from these muscle paths. Normal pulley coordinates were highly uniform. Compared with both normal orbits and fellow orbits, orbits with superior oblique palsies showed a statistically significant 1.1 mm superior displacement of the medial rectus pulley. No other pulley was displaced significantly from normal. Computer simulation using a biomech...Continue Reading

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