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Robert A. Clark, Joel M. Miller, Joseph L. Demer; Three-dimensional Location of Human Rectus Pulleys by Path Inflections in Secondary Gaze Positions. Invest. Ophthalmol. Vis. Sci. 2000;41(12):3787-3797.
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purpose. Connective tissue pulleys serve as the functional mechanical origins of
the extraocular muscles (EOMs). Anterior to these pulleys, EOM paths
shift with gaze to follow the scleral insertions, whereas posterior EOM
paths are stable in the orbit. Inflections in EOM paths produced by
gaze shifts can be used to define the functional location of pulleys in
three dimensions (3-D).
methods. Contiguous magnetic resonance images in planes perpendicular to the
orbital axis spanned the anteroposterior extents of 22 orbits of 11
normal adults with the eyes in central gaze, elevation, depression,
abduction, and adduction. Mean EOM cross-sectional area centroids
represented in a normalized, oculocentric coordinate system were
plotted over the length of each EOM to determine paths. Path
inflections were identified to define pulley locations in 3-D.
results. All rectus EOM paths exhibited in secondary gaze positions distinct
inflections 3 to 9 mm posterior to globe center, which were consistent
across subjects. The globe center and the lateral rectus pulley
translated systematically in the orbit with lateral gaze, whereas other
pulleys remained stable relative to the orbit.
conclusions. Distinct inflections in rectus EOM paths in secondary gaze positions
confirm the existence of pulleys and define their locations in 3-D. The
globe and lateral rectus pulley translate systematically with gaze
position. The EOM pulleys may simplify neural control of eye movements
by implementing a commutative ocular motor plant in which commands for
3-D eye velocity are effectively independent of eye
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