Anatomy of the Extraocular Muscles AAO SECTION 6 CHAPTER 3 I Gusti Agung Ratna Noviantari

Agenda 01 02 03 04 05 Origin, Course, Insertion, Innervation Blood Supply Agenda 03 Structure 04 Orbital and Fascial Relationships 05 Anatomical Consideration for Ophthalmic Procedure

Origin, Course, Insertion, and Innervation of the Extraocular Muscles There are 7 extraocular muscles (EOMs) 4 Rectus Muscles (Lateral, Medial, Superior, and Inferior) 2 Oblique Muscles (Superior and Inferior Oblique) Levator Palpebrae Superioris Muscle

Horizontal Rectus Muscles The horizontal rectus muscles are the medial and lateral rectus muscles. Both arise from the annulus of Zinn

Vertical Rectus Muscles The vertical rectus muscles are the superior and inferior rectus muscles. The superior rectus muscle originates from the annulus of Zinn and courses anteriorly, upward over the eyeball, and laterally, forming an angle of 23° with the visual axis or the midplane of the eye in primary position The inferior rectus muscle also arises from the annulus of Zinn, and it then courses anteriorly, downward, and laterally along the floor of the orbit, forming an angle of 23° with the visual axis or midplane of the eye in primary position

Bola mata berada di dalam cavum orbita Aksis dalam bola mata dan aksis dari orbita tidak sejajar, namun membentuk sudut sebesar 23 untuk otot rektus dan 51 untuk otot oblikus

Oblique Muscles 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 , with the tendon forming an angle of 51° with the visual axis or midplane of the eye in primary position

Oblique Muscles 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 courses 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 or midplane of the eye in primary position

Levator Palpebrae Superioris Muscle The levator palpebrae superioris muscle arises at the orbital apex from the lesser wing of the sphenoid bone, just superior to the annulus of Zinn. At its origin, the muscle blends with the superior rectus muscle inferiorly and with the superior oblique muscle medially. The levator palpebrae superioris passes anteriorly, lying just above the superior rectus muscle

BLOOD SUPPLY

ARTERIAL SYSTEM The muscular branches of the ophthalmic artery provide the most important blood supply to the EOMs. The lateral muscular branch supplies the lateral rectus, superior rectus, superior oblique,and levator palpebrae superioris muscles; The medial muscular branch, supplies the inferior rectus, medial rectus, and inferior oblique muscles. The lateral rectus muscle is partially supplied by the lacrimal artery; The infraorbital artery partially supplies the inferior oblique and inferior rectus muscles.

VENOUS SYSTEM The venous system parallels the arterial system, emptying into the superior and inferior orbital veins.

STRUCTURE

Structure of The Extraocular Muscle The important functional characteristics of muscle fibers are contraction speed and fatigue resistance. The eye muscles participate in motor acts that are among the fastest (saccadic eye movements) in the human body and among the most sustained (gaze fixation and vergence movements). The EOMs exhibit a distinct 2-layer organization: an outer orbital layer, which acts only on connective tissue pulleys an inner global layer, whose tendon inserts on the sclera to move the globe

Orbital and Facial Relationships

Orbital and Fascial Relationships Adipose tissue - The inferior part of the eye is supported and cushioned in the orbit by a large amount of fatty tissue. External to the muscle cone, the fatty tissue advances to the rectus muscle, stopping about 10 mm from the limbus. Fat tissue also exists within the muscle cone, pushed away from the sclera by the Tenon's capsule Muscle cone The muscle cone is located posterior to the equator. It consists of the EOM, sheath, and the intermuscular septum

Orbital and Fascial Relationships Muscle Capsules, Each rectus muscle has a fascial capsule around it that extends from the origin to the insertion. This capsule is thin and smooth posteriorly and anteriorly to the equator, between the lower surface of the muscles and the sclera, there is almost no fascia, only thin connective tissue that connects the muscles to the eyeball. The smooth, avascular surface of the muscle capsule allows muscles to contract easily. The Tenon capsule is attached posterior to the sheath of the optic nerve and anterior to the intermuscular septum at a position 3 mm from the limbus.

The Pulley System The 4 rectus muscles are surrounded by fibroelastic pulleys that maintain the position of the EOMs relative to the orbit. The pulleys consist of collagen, elastin, and smooth muscle, enabling them to contract and relax. The pulleys may also serve to stabilize the muscle path, preventing sideslipping or movement perpendicular to the muscle axis

Anatomical Considerations for Ophthalmic Procedures

Anatomical Considerations for Ophthalmic Procedures The nerves to the rectus muscles and the superior oblique muscle enter the muscles approximately one-third of the distance from the origin to the insertion (or trochlea, in the case of the superior oblique muscle). Damaging these nerves during anterior surgery is unlikely but not impossible. An instrument thrust more than 26 mm posterior to a rectus muscle’s insertion may injure the nerve. Cranial nerve IV is outside the muscle cone and is usually not affected by a retrobulbar block. However, any EOM could be reached by a retrobulbar needle and injured by injection of local anesthetic. The nerve supplying the inferior oblique muscle enters the lateral portion of the muscle, where it crosses the inferior rectus muscle; surgery performed in this area can damage the nerve. Because parasympathetic fibers to the sphincter pupillae (for pupil constriction) and the ciliary muscle (for accommodation) accompany the nerve to the inferior oblique muscle, with a synapse

Anatomical Considerations for Ophthalmic Procedures The blood supply to the EOMs provides almost all of the temporal half of the anterior segment circulation and most of the nasal half of the anterior segment circulation, which also receives some blood from the long posterior ciliary artery. Therefore, simultaneous surgery on 3 rectus muscles may induce anterior segment ischemia, particularly in older or vasculopathic patients. Whenever muscle surgery is performed, special care must be taken to avoid penetration of the Tenon capsule 10 mm or more posterior to the limbus. If the integrity of the Tenon capsule is violated posterior to this point, fatty tissue may prolapse through the capsule and form a restrictive adhesion to sclera, muscle, intermuscular septum, or conjunctiva, limiting ocular motility. When surgery is performed near the vortex veins, accidental severing of a vein is possible. The procedures that present the greatest risk of damaging a vortex vein are recession or resection of the inferior rectus or superior rectus muscle, weakening of the inferior oblique muscle, and exposure of the superior oblique muscle tendon. Hemostasis can be achieved with cautery or with an absorbable hemostatic sponge. The sclera is thinnest just posterior to the 4 rectus muscle insertions, an area that is the site of most eye muscle surgery, especially recession procedures. Thus, scleral perforation is always a risk during eye muscle surgery.

THANK YOU