Transcript Anatomy of the Extraocular Muscles

IN THE NAME OF GOD
ANATOMY OF THE EXTRAOCULAR
MUSCLES

MOHAMMAD REZA AKHLAGHI
EXTRAOCULAR MUSCLES
There are 7 extraocular muscles:
 4 rectus muscles,
 2 oblique muscles
 levator palpebrae superioris muscle.
EXTRAOCULAR MUSCLES
INNERVATION
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.

EYE POSITION & MUSCLE ACTIONS
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

RANGE OF ACTION
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

ANNULUS OF ZINN

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
EXTRAOCULAR MUSCLES
MEDIAL RECTUS
Origin: annulus of zinn
 Insertion: medially, in hori meri, 5.5 mm from
limbus
 Length: 40mm L, 10mm W, 4mm T
 Direction: 90o
 Innervation: lower CN III
 Blood supply: Inf. Mus. Branch Of Oph. A.
 Action: addu

MEDIAL RECTUS
LATERAL RECTUS
Origin: annulus of zinn
 Insertion: laterally, in horizontal meridian, 6.9mm
from limbus
 Length: 40 mm L, 9 mm W, 8 mm T
 Direction: 90o
 Innervation: CN VI
 Blood supply: Inf. Mus. Branch Of Oph. A.
 Action: abd

LATERAL RECTUS
INFERIOR RECTUS
Origin: annulus of zinn
 Insertion: inferiorly, in ver. Mer. 6.5 mm from
limbus
 Length: 40 mm L, 10 mm W, 5.5 mm T
 Direction:23o
 Innervation: lower CN III
 Action: Dep. Ext, Add,

INFERIOR RECTUS
SUPERIOR RECTUS
Origin: annulus of zinn
 Insertion: superiorly, in ver. Mer. 7.7 mm from
limbus
 Length: 40 mm L, 10 mm W, 5.5 mm T
 Direction:23o
 Innervation: upper CN III
 Action: Dep. Ext, Add,

SUPERIOR RECTUS
SUPERIOR OBLIQUE
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:51o
 Innervation: CN IV
 Action: Int, Dep, Abd,

SUPERIOR OBLIQUE
INFERIOR OBLIQUE
Origin: behind of lacrimal fossa
 Insertion: post. to equator in macular area.
 Length: 37 mm L, 10 mm W, 1 mm T
 Direction:51o
 Innervation: lower CN III
 Action: Ext, Elev, Abd,

INFERIOR OBLIQUE
LEVATOR PALPEBRAE SUPERIORIS
Origin: above of annulus of zinn
 Insertion: above and anterior surface of tarsus.
 Innervation: upper CN III
 Action: eyelid elevation

ADDUCTOR MUSCLES
ABDUCTORS
ELEVATORS
DEPRESORS
INTERNAL ROTATORS
EXTERNAL ROTATORS
INSERTION RELATIONSHIPS OF THE RECTUS MUSCLES
 Spiral of Tillaux
MUSCLE CONE

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
TENON'S CAPSULE
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

INTERMUSCULAR SEPTUM
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.

ANATOMICAL CONSIDERATIONS DURING
SURGERY

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.

CONT.
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.