Cranial nerve VI (abducens) innervates the lateral rectus muscle cranial nerve IV (trochlear) innervates the superior oblique muscle cranial nerve III has an upper and a lower division: innervates the levator palpebrae, superior rectus, medial rectus, inferior rectus, and inferior oblique muscles.
primary position The primary action is the major effect of a muscle, when the muscle contracts while the eye is in primary position. The secondary and tertiary actions: of a muscle are the additional effects on the position of the eye in primary position
The globe usually can be moved about 50° in each direction from primary position. Under normal viewing circumstances, the eyes move only about 15°-20° from primary position before head movement
A cone-shaped structure, behind the eyeball, composed of five extraocular muscles (medial rectus, lateral rectus, superior rectus, inferior rectus, and superior oblique), within which runs the optic nerve (cranial nerve II), the ophthalmic artery, and the ophthalmic vein
Origin: annulus of zinn Insertion: medially, in hori meri, 5.5 mm from limbus Length: 40 mm L, 10 mm W, 4 mm T Direction: 90 o Innervation: lower CN III Blood supply: Inf. Mus. Branch Of Oph. A. Action: addu
Origin: annulus of zinn Insertion: laterally, in horizontal meridian, 6.9 mm from limbus Length: 40 mm L, 9 mm W, 8 mm T Direction: 90 o Innervation: CN VI Blood supply: Inf. Mus. Branch Of Oph. A. Action: abd
Origin: superior of annulus of zinn (func. At trochlea Insertion: post. to equator in suprotemp. Length: 32 mm L, 6 mm W, 25 mm T Direction:51 o Innervation: CN IV Action: Int, Dep, Abd,
The muscle cone lies posterior to the equator. It consists of the extraocular muscles, the extraocular muscle sheaths, and the intermuscular membrane. The muscle cone extends posteriorly to the annulus of Zinn at the orbital apex
Is the bulk of the orbital fascial system Forms the envelope within which the eyeball moves Fuses posteriorly with the optic nerve sheath and anteriorly with the intermuscular septum Posterior portion is thin and flexible Posterior to the equator, it is thick and tough, suspending the globe to the periorbital tissues
a membrane that spans between rectus muscles and fuses with the conjunctiva 3 mm posterior to the limbus. Posterior to the globe, it separates the intraconal fat pads from the extraconal fat pads. Numerous extensions from all the extraocular muscle sheaths attach to the orbit and help support the globe.
Damaging of nerves during anterior surgery An instrument thrust more than 26 mm posterior to the rectus muscle's insertion may cause injury to the nerve. The nerve supplying the inferior oblique muscle enters the lateral portion of the muscle, where it crosses the inferior rectus muscle; the nerve can be damaged by surgery in this area. Cranial nerve IV would not be affected by a retrobulbar block.
The intermuscular septum connections, especially between rectus muscles and oblique muscles, can help locate a lost muscle during surgery. Extensive intermuscular septum dissections are not necessary for rectus recession surgery. During resection surgery, the intermuscular septum connections should be severed
The blood supply to the extraocular muscles provides almost all of the temporal half of the anterior segment circulation and the majority of the nasal half of the anterior segment circulation. Therefore, simultaneous surgery on 3 rectus muscles may induce anterior segment ischemia, particularly in older patients.
The inferior rectus muscle is distinctly bound to the lower eyelid by the fascial extension from its sheath
The sclera is thinnest just posterior to the 4 rectus muscle insertions. This area is the site for most muscle surgery, especially for recession procedures. Therefore, scleral perforation is always a risk during eye muscle surgery.