Origin, Course, Insertion, and Innervation of the Extraocular Muscles
There are 7 extraocular muscles (EOMs) in the human eye: the 4 rectus muscles (lateral, medial, superior, and inferior), the 2 oblique muscles, and the levator palpebrae superioris muscle. Figure 3-1 shows an anterior view of the EOMs and their relationships to one another. Cranial nerve (CN) VI (abducens) innervates the lateral rectus muscle; CN IV (trochlear), the superior oblique muscle; and CN III (oculomotor), the levator palpebrae, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles. Cranial nerve III has an upper and a lower division: the upper division supplies the levator palpebrae and superior rectus muscles, and the lower division supplies the medial rectus, inferior rectus, and inferior oblique muscles. The parasympathetic innervation of the sphincter pupillae and ciliary muscle travels with the branch of the lower division of CN III that supplies the inferior oblique muscle. BCSC Section 5, Neuro-Ophthalmology, discusses the ocular motor nerves in more detail, and Section 2, Fundamentals and Principles of Ophthalmology, extensively illustrates the anatomical structures mentioned in this chapter.
Figure 3-1 Extraocular muscles, frontal composite view, left eye.
(Reproduced with permission from Dutton JJ. Atlas of Clinical and Surgical Orbital Anatomy. Philadelphia: Saunders; 1994:23.)
Table 3-1 summarizes the characteristics of the EOMs. The EOMs and their relationships to one another can be explored in ACTIVITY 3-1.
Activity developed by Mary A. O’Hara, MD.
Access the activity at www.aao.org/bcscactivity_section06.
Horizontal Rectus Muscles
The horizontal rectus muscles are the medial and lateral rectus muscles. Both arise from the annulus of Zinn. The medial rectus muscle courses along the medial orbital wall. The lateral rectus muscle courses along the lateral orbital wall.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.