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Sangeeta Khanna, John D. Porter; Evidence for Rectus Extraocular Muscle Pulleys in Rodents. Invest. Ophthalmol. Vis. Sci. 2001;42(9):1986-1992.
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purpose. Extraocular rectus muscle (EOM) pulleys are important determinants of
orbital biomechanics in humans. In this study, the authors evaluated
orbital connective tissue morphology, specifically characterizing
rectus muscle pulleys, in the rat, a species with laterally placed
eyes, afoveate vision, and a less complex visuomotor repertoire than
methods. Adult rat orbits were paraffin processed and serially sectioned for
histochemical and immunohistochemical staining. Frozen sections of
enucleated globes with intact EOMs and associated connective tissue
were also studied with myosin immunohistochemistry and histochemistry
for the mitochondrial enzyme, nicotinamide adenine dinucleotide
(NADH)-tetrazolium reductase, to delineate the orbital layer
relationship with the pulley tissue.
results. Focal condensations of collagenous connective tissue were found in
relationship to the rectus muscles in the equatorial Tenon’s fascia,
similar to those described as human recti muscle pulleys. The
fibroelastic pulley rings were coupled to adjacent EOM pulleys by bands
containing collagen and elastin. The coupling of pulleys to the orbital
walls was significantly less than that previously described in humans.
As in humans, there was a dual insertion of rodent rectus muscles, with
the orbital layer inserting on the muscle pulley and the global layer
attaching to the sclera.
conclusions. The data support the presence of structures in the rat orbit that are
the morphologic equivalent of the human rectus pulley system. Although
rodent and human pulleys were similar in many respects, there were
species-specific properties that may relate to established differences
in orbital anatomy and/or visuomotor behavior. These data extend the
rectus muscle pulley concept to rodents and may provide insight into
pulley structure–function relationships.
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