The superior oblique muscle originates from the orbital apex above the annulus of Zinn and passes anteriorly and upward along the superomedial wall of the orbit. The muscle becomes tendinous before passing through the trochlea, a cartilaginous saddle attached to the frontal bone in the superior nasal orbit. A bursa-like cleft separates the trochlea from the loose fibrovascular sheath surrounding the tendon. The discrete fibers of the tendon telescope as they move through the trochlea, the central fibers moving farther than the peripheral ones (Fig 2-2). The function of the trochlea is to redirect the tendon inferiorly, posteriorly, and laterally, forming an angle of 51° with the visual axis of the eye in primary position (see Chapter 3, Fig 3-6). The tendon penetrates the Tenon capsule 2 mm nasally and 5 mm posteriorly to the nasal insertion of the superior rectus muscle. Passing under the superior rectus muscle, the tendon inserts in the posterosuperior quadrant of the eyeball, almost or entirely laterally to the midvertical plane or center of rotation. In primary position, the primary action of the superior oblique muscle is intorsion (incycloduction), secondary action is depression, and tertiary action is abduction.
The inferior oblique muscle originates from the periosteum of the maxillary bone, just posterior to the orbital rim and lateral to the orifice of the lacrimal fossa. It passes laterally, superiorly, and posteriorly, going inferior to the inferior rectus muscle and inserting under the lateral rectus muscle in the posterolateral portion of the globe, in the area of the macula. The inferior oblique muscle forms an angle of 51° with the visual axis of the eye in primary position (see Chapter 3, Fig 3-7). In primary position, the muscle’s primary action is extorsion (excycloduction), secondary action is elevation, and tertiary action is abduction.
. The influence of superior oblique anatomy on function and treatment. The 1998 Bielschowsky Lecture.1999;14(1):16–26.