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H.J. Simonsz, S.P. van den Bedem, S. Schutte, F.C. van der Helm, F. van Keulen; Orbital Mechanics Studied in Fresh Exenteration Specimens . Invest. Ophthalmol. Vis. Sci. 2003;44(13):3126.
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Purpose: The rectus muscles do not displace at the level of the posterior pole in eye movements out of the plane of the muscle. Several anatomical structures, like the intermuscular membrane and the faisceaux tendineux (Tenon) or pulley bands (Demer) are purportedly keeping the muscle bellies into place, but no mechanical measurements support these inferences. Material properties of fat and muscle change within minutes after death, therefore such measurements were performed during orbital exenteration. Methods: Patients received subtotal exenteration of the orbit for sebaceous carcinoma of the eyelid, cutting the periorbit, the muscles and the optic nerve a few mm behind the posterior pole. All patients gave oral informed consent. The orbital specimens were examined mechanically within one minute after removal from the orbit. The white connective tissue encircling the medial or lateral rectus slightly behind the equator, forming a port in Tenon’s capsule, was grasped with a forceps introduced from posterior over the outside of the muscle. The periorbit behind the medial or lateral canthus, the point of attachment of the faiseaux tendineux, was hooked onto a spring force gauge. Force applied with the force gauge was increased over a few seconds, while the exerted force and resultant strain was recorded by video taping. Results: Observed was that the white connective tissue encircling the medial or lateral rectus was firmly attached to the outside of the muscle. The faiseaux tendineux could be stretched approximately 10mm in an anterior-posterior direction from approximate primary-position length with little resistance, but force increased steeply thereafter. Finally observed was that Tenon's capsule easily slides several mm over the sclera despite the fact that it is attached anterior to the limbus and posterior to the optic nerve. Conclusions: The faisceaux tendineux can be mechanically identified in fresh orbital specimens. When stretched to a length corresponding to extreme lateral gaze, force rises considerably. Their tension seems low, however, when the eye is in primary position, although smooth muscle cells could play an additional role. The contribution of faisceaux tendineux to either pulley-action or suspension of the eye in the orbit remains to be determined.
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