Human Anatomy - Kotsan I. Y. 2009

Sense Organs
Organ of Vision (Eye)
Muscles of the Eyeball

The motor apparatus of the Eyeball consists of six striated Muscles: 4 straight muscles—the superior, inferior, lateral, and medial (mm. recti superior, inferior, lateralis et medialis)—and 2 oblique muscles—the superior and inferior (mm. obliquus superior et inferior). In addition to these muscles, the Orbit also contains the levator palpebrae superioris Muscle (m. levator palpebrae superioris) and the orbital muscle (m. orbitalis) (Fig. 265).

All straight muscles and the superior oblique muscle originate deep within the orbit along the circumference of the optic canal and the adjacent part of the superior orbital fissure from the common tendinous ring (anulus tendineus communis), which funnel-wise encloses the optic, oculomotor, nasociliary, and abducens nerves, as well as the ophthalmic artery. The straight muscles run along the corresponding wall of the orbit and attach via tendons to the sclera anterior to the equator of the eyeball on four sides of the latter. The superior oblique muscle deviates medially and transitions into a thin tendon near the trochlear fossa of the Frontal bone. Here, looping over the fibrocartilaginous pulley (trochlea), it turns backward and laterally at an acute angle and attaches to the eyeball on its upper-lateral side posterior to the equator. The inferior oblique muscle, unlike the other eye muscles, originates from the orbital surface of the Maxilla below the opening of the nasolacrimal canal, runs along the floor of the orbit beneath the inferior rectus muscle of the eyeball, and, heading laterally and posteriorly, attaches to the sclera of the lateral surface of the eyeball posterior to the equator.

The straight muscles rotate the eyeball around two axes: vertical and frontal. The lateral and medial straight muscles rotate the eyeball outward and inward around the vertical axis, each in its own direction, to which the pupil likewise turns accordingly. The superior and inferior straight muscles rotate the eyeball around the frontal axis. Upon the action of the superior rectus muscle, the pupil turns upward and slightly outward, while upon the action of the inferior rectus muscle, it turns downward and inward.

The oblique muscles rotate the eyeball around the sagittal axis. The superior oblique muscle, when rotating the eyeball, directs the pupil downward and outward, whereas the inferior oblique muscle, upon its contraction, directs it upward and outward. It should be noted that all movements of both eyeballs are conjugate, since when one eye moves in any direction, the other eye moves simultaneously in the same direction. When all muscles are evenly toned, the pupil looks straight ahead and the visual axes of both eyes are parallel to each other. This occurs when looking into the distance. When viewing close objects, the visual axes converge anteriorly (eye convergence).

The levator palpebrae superioris muscle is located above the superior rectus muscle of the eyeball. It originates from the common tendinous ring, the periosteum of the orbit above the optic canal, and the adjacent part of the outer Sheath of the intra-canalicular portion of the Optic nerve. Heading forward, the muscle continues into a broad aponeurosis that divides into two laminae—superficial and deep.

A small number of smooth muscle fibers span across the inferior orbital fissure, together forming a thin orbital muscle (m. orbitalis), which covers the anterior segment of the inferior orbital fissure from above.