Extraocular muscles, gaze, and eye movements

Abstract

There are six extraocular muscles attached to each eyeball: medial rectus, lateral rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique muscle. Contraction of the medial rectus and lateral rectus muscles rotates the eyeball medially and laterally, respectively. The exact action of other four muscles depends on the eye position. The superior and inferior rectus muscles are attached to the top and the bottom, respectively, of the anterior hemisphere of the eyeball, and act most efficiently when the eye is slightly abducted. Therefore, contraction of the superior rectus muscle rotates the eyeball upward diagonally in the lateral direction, and contraction of the inferior rectus muscle rotates the eyeball downward diagonally in the lateral direction. The superior and inferior oblique muscles are attached to the top and the bottom, respectively, of the posterior hemisphere of the eyeball, and act most efficiently when the eye is slightly adducted. Furthermore, the direction of muscle power for these two muscles is reversed by a hook (trochlea), which is attached to the upper and lower medial wall, respectively, of the orbit. Therefore, contraction of the superior and inferior oblique muscles rotates the eyeball downward and upward, respectively, diagonally in the medial direction.