[The function of Tenon's capsule revisited]

Tenon's capsule is at the forefront of today's strabismus news. Its function as a muscle pulley was recognized by Tenon himself in 1806. Neiger, then Koornneef, and more recently Demer gave a more modern description of Tenon's capsule. The anterior or muscular part is made up of collagen, elastic, and smooth muscle fibers. It forms a sleeve around extraocular muscles from the Tenon foramen to their scleral insertion. Directly in front of the foramen, it includes a zone of strong capsular-muscular adherence, which is also solidly suspended by ocular suspension system to the periosteum of the orbit; the intermuscular membrane consolidates the adherence zones of the rectus muscles. The posterior part is simply a condensation of collagenous fibers. The function of Tenon's capsule is essential. At the place where it adheres to the muscles, the sleeve that it forms around the muscles plays the role of a pulley diverting the muscle's path, with the pulley representing the proximal functional insertion of the muscle. The position of a rectus muscle's pulley is stable during ocular movements perpendicular to the axis of this muscle because of the transversal and radial fastening of the capsular-muscular adherence zone. During movements along the muscle axis, the pulley moves with the ocular globe. In fact, it is positioned actively to accompany the ocular globe's movements. The anomalies of these pulleys can contribute to or be responsible for an extraocular muscle imbalance: a position anomaly, an instability, a displacement, or a pathological adherence of one pulley can be the cause. Surgery of Tenon's pulley has always been an integral part of extraocular muscle surgery. Any intervention on the muscular level involves, to a lesser or greater extent, the operated muscle's pulley. Different examples demonstrate this.