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Joseph L. Demer, Sei Yeul Oh, Vadims Poukens; Evidence for Active Control of Rectus Extraocular Muscle Pulleys. Invest. Ophthalmol. Vis. Sci. 2000;41(6):1280-1290. doi: https://doi.org/.
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purpose. Connective tissue structures constrain paths of the rectus extraocular
muscles (EOMs), acting as pulleys and serving as functional EOM
origins. This study was conducted to investigate the relationship of
orbital and global EOM layers to pulleys and kinematic implications of
methods. High-resolution magnetic resonance imaging (MRI) was used to define the
anterior paths of rectus EOMs, as influenced by gaze direction in
living subjects. Pulley tissues were examined at cadaveric dissections
and surgical exposures. Human and monkey orbits were step and serially
sectioned for histologic staining to distinguish EOM fiber layers in
relationship to pulleys.
results. MRI consistently demonstrated gaze-related shifts in the
anteroposterior locations of human EOM path inflections, as well as
shifts in components of the pulleys themselves. Histologic studies of
human and monkey orbits confirmed gross examinations and surgical
exposures to indicate that the orbital layer of each rectus EOM inserts
on its corresponding pulley, rather than on the globe. Only the global
layer of the EOM inserts on the sclera. This dual insertion was
visualized in vivo by MRI in human horizontal rectus EOMs.
conclusions. The authors propose the active-pulley hypothesis: By dual insertions
the global layer of each rectus EOM rotates the globe while the orbital
layer inserts on its pulley to position it linearly and thus influence
the EOM’s rotational axis. Pulley locations may also be altered in
convergence. This overall arrangement is parsimoniously suited to
account for numerous aspects of ocular dynamics and kinematics,
including Listing’s law.
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