3. Outline
1. Gross anatomy of EOM
2. Physiology of extra ocular movement
3. Perimuscular connective tissue
4. Microscopic anatomy of EOM
5. Law of ocular movements
4. Introduction
Extraocular muscle (EOM) plays vital role in visual
system
1. Provides static adjustment of binucular alignment
necessary to enable BSV and steropsis
2. Precise dynamic movements to acquire and maintain
visual targets
Fibers of EOMs are mesodermal in origin and
Perimuscular Connective tissues are neural crest in
origin
6. Muscle cone
The rectus muscle forms the muscle cone
within the orbit with apex at their origin
and base at their penetration of tenon’s
capsule.
Each muscle is surrounded by fibrous
capsule which are attached by thin
continuous membrane called
intermuscular septum
Intermuscular septum divides orbital fat
pad into extraconal fat and intraconal fat
which help to maintain cushioning
effects.
Intermuscular septum fuses with tenon
3mm from the limbus
Fibrous capsule
Intermuscular
septum
Intraconal fat
Extraconal fat
Muscle cone
7. The fascia bulbi
The tenon capsule/fascia bulbi is an envelope of
elastic fibrous connective tissue
Form protective covering and the site of attachment
of EOM
Tenon capsule fuses with optic nerve sheath
posteriorly and anteriorly with intermascular
septum, 3 mm posterior to the limbus.
EOM penetrates the tenon capsule 10 mm posterior
to their insertion
Tenons are divided into anterior and posterior parts
Tenon capsule
10mm
8. Muscle pulley
As the EOM penetrates the tenon
capsule the connective tissue forms
the sleeves around the muscles
creating muscle pulleys.
Discrete rings of dense collagen tissue
encircling EOM & are about 2mm
length
Pulley redirects the muscle and acts as
functional origin it also prevents
displacement of muscle during
movement
Because of pulley mechanism muscle
are inflect at the insertion forming
angle with the orbital axis. muscle
pulley
Pulley
Angle
9. Rectus origin- Annulus of zinn
Annulus of Zinn is a fibrous ring
in the orbital apex
It is attached to the lesser and
greater wing of spenoid bone
and spans over superior orbital
fissue
It gives attachment to all rectus
muscle
Annulus of zinn is also an
important landwark through
which many important
structure passes
Optic nerve
Ophthalmc
artery
Ocular
motor nerve
Nasociliary
branch of CN VI
Abducent
nerve
Trochlear
nerve
Lacrimal
nerve
Frontal
branches of
CN VI
Superiror
ophthalmic vein
10. Principle of ocular movement
Because of pear shape Medial
and lateral wall of an orbit
are at the angle of 45 ̊ each
other
Orbital axis therefore forms
23˚ with both medial and
lateral wall
When the eye in in primary
position the visual axis forms
23˚ of angle with the orbital
axis
Action of muscle depends on
muscle plane in relation to
optical axis
45̊
23̊
23̊
11. Fick model of EOM
Eye movement occurs through the central of
rotation
Listing plane is an imaginary coronal plane
passing through the centre of rotation of globe
Globe rotates on X and Y axis of Fick which
intersect with in the listing plane
Globe rotates right and
left(adduction/abduction)on the vertical axis
of Z
Moves up and down(elevation/depression)on
horizontal X axis
Torsional
movement(intorsion/extorsion)occurs on Y
axis
12. Medial Rectus
Originates from the medial part of annulus of zinn
It is 10.3 mm wide, 40.8 mm long with 3.7 mm tendon
extension at insertion
Inserts in horizontal meridian 5.5mm from the limbus
5.5 mm
Medial rectus
13. Lateral rectus
Originates from the lateral part of annulus of zinn
spanning the superior orbital fissure
It is 40.6 mm in length, 9.2 mm wide with 8 mm long
tendon at insertion
It inserts to the eye globe laterally in horizontal
meridian 6.9mm from the limbus.
6.9mmLateral rectus
14. Horizontal muscle- MR action
Insertion point of horizontal
muscle are straight and
vertical.
In primary position the
muscle plane of horizontal
recti (line from origin to
insertion) coincides with
visual axis
Horizontal recti are therefore are
purely horizontal movers on
vertical Z axis and have only
primary actions.
Medial rectus- adduction
Lateral rectus- abduction
visual axis
Muscle plane
of MR
Insertion
point
MR with
pulley
15. Inferior rectus
Originates from the inferior part of annulus of zinn
It is 40 mm in length, 9.8mm wide and has 5.5 mm
tendon extension at insertion
In is inserted inferiorly to eye globe in vertical
meridian 6.5 mm from the limbus
6.5mm
Inferior rectus
16. Inferior rectus- action
IR is inserted in laterally oblique
position 6.5mm behind the inferior
limbus
In primary position, muscle plane
forms 23˚ angle with visual axis
Primary action is depression
Due to its laterally oblique insertion
with angle of 23˚acting inferiorly 2nd
actions are adduction and extrosion
Clinical correlates-When globe is
abducted 23˚ it is purely depressor-
optimal position for testing the
function of IR
23˚
Visual
axis
Muscle
plane
17. Superior rectus
Originates from the superior part of annulus of zinn
It is 41.8mm long, 10.6mm wide with 5.8mm tendon
extension at insertion
Inserts to the eye lobe superiorly in vertical meridian
7.7mm from the limbus
7.7 mm
Superior
rectus
18. Superior rectus- action
SR is inserted in medially oblique
position 7.7mm above the superior
limbus
In primary position muscle plane
form 23˚ angle with visual axis
Primary action is elevation
Due to its medially oblique insertion
with 23˚angle, 2nd action are
adduction and intorsion
Clinical correlates-When eye is
abducted 23˚ it act only as elevator-
optimal position for testing the
function of SR
23˚
19. Superior oblique
Originates from the body of sphenoid bone, above and
medial to the optic foramen
It is 40mm long, 10.8 wide and has 20mm tendonous
extension(longest)
It passes through the trochlea (cartilaginous pulley ) at the
superonasal orbital rim, hook back from trochlea under the
superior rectus inserting posterior to the center of rotation.
trochlea Superior
oblique
20. Superior oblique- actions
Due to pulley effect of trochlea SO is
inserted in medial oblique position in
superior posterior temporal quadrant of
globe
In primary position the muscle plane of
SO forms 51˚ angle with the visual axis.
The primary action is intorsion
2nd actions are- depression and abduction
When the globe is adducted 51˚visual axis
coincides with the line of pull of muscle-
acts as pure depressor therefore optimal
position for testing SO function
Visual axis
Muscle
plane of SO
51˚
21. Inferior oblique
Originates from a shallow depression of orbital plate of maxillary bone
at the anteromedial cornerof orbital floor near the lacrimal fossa
It is 37mm long, 9.6mm long and has no tendon
It extends posterior to the inferior rectus, laterally and superiorly to
insert at posterior inferior temporal quadrant of eye globe behind the
medial rectus
Inferior
oblique
22. Inferior oblique
IO passes backward and laterally to insert
in lateral oblique position in temporal
lower quadrant of globe
In primary position muscle plane of IO
forms 51˚ angle with visual axis
primary action is extorsion (out and up)
2nd actions are- elevation and abduction
When the eye is adducted 51˚- it acts
purely as elevator therefore this position is
optimal for testing the function of IO
muscle. Visual axis
Muscle
plane of IO
51˚
Inferior
oblique
23. SPIRAL OF TILLAUX
Insertion of rectus muscle forms an imaginary spiral
ring around the limbus .
MR nearest and SR furthest from the limbus
5.5 mm
6.5mm
6.9mm
7.7mm
MR
SR
LR
IR
Clinical correlates;
1. Important landmark
during strabimus
surgery
2. Sclera is thinnest at the
insertion of rectus
(0.3mm)-common site for
perforation during severe
blunt trauma to the globe
24. Blood supply
EOM are supplied by the branches
of ophthalmic artery.
1. Muscular branches
2. Lacrimal braches
As the ophthalmic artery enter the
muscle cone through the optic
canal it braches to Lateral and
Medial muscular branches
Medial muscular
branch
Lateral muscular
branch
25. Muscular artery course along with
CN111 to enter rectus muscle at the
junction of posterior and middle
one third.
Lateral muscular branches-
a. lateral rectus
b. sup rectus
c. LPS
d. SO
Medial muscular branches-
a. medial rectus
b. inferior rectus
c. IO
Lacrimal branch-LR and SR
26. Anterior ciliary artery (ACA)
7 in no.
Branches of muscular arteries
Along tendons of muscles and pierce
sclera 4 mm from the limbus and
enter eyeball
Join the LPCA to form the major
arterial circle of iris.
Supplies -- Cilliary body and iris.
ACA runs in pair in each rectus
muscle except LR which has only one
ACA
Muscular
branch
LR with single
ACA
Clinical correlates:
interruption of ACA during surgery
involving more than two rectus
muscle can result in anterior
segment ischemia!
27. Venous drainage of EOM
The venous drainage of the extraocular muscles is via
the superior and inferior orbital veins to ophthalmic
veins
Anterior ciliary
vein
Cavernous
sinus
Inferior
ophthalmic
vein
Superior
ophthalmic
vein
Superior
orbital vein
inferior
orbital vein
Clinical correlates:
Secondary
Perimuscular infection
following EOM trauma
can spread infection to
cavernous sinus .
Cavernous vascular
disease can present as
opthalmoplegia and
proptosis
28. Nerve supply of EOM
Three cranial nerves
3. Trochlear nerve2. Abducent nerve1. Oculomotor nerve
Superior obliqueLateral rectus
1. Superior rectus
2. Medial rectus
3. Inferior rectos
4. Inferior oblique
5. Levator pelpebrae
29. Innervation… ctn
Rectus muscle are
innervated from the
intraconal surface of
muscle belly at
junction of middle
and posterior third
of muscle.
SO is innervated by
trochlear nerve via
the extracornal
route above the
annulus of zinn
30. Structure of EOM
Each EOM consist of 2 layers –
1. Orbital layer which located
superficially near the orbital wall
2. Globar layer which is located more
deeper
Fibers of Global layer become
contiguous with tendon to insert on the
globe ; orbital layer is inserted on
muscle pulley
31. Microanatomy of EOM
EOM are striated muscles with
bundles of muscle fibers(functional
units) which is made up of actin and
myocin filaments
Compared to skeletal
muscle(SM)EOM fibers are small
and numerous with abundant
nucleus which are highly
innervated- ratio of nerve to muscle
fiber of 1:3-1:5 compared 1: 50-1:125 of
SM
EOM has more contractile units
This accounts for very precise and
rapid movement of eye by EOM
32. EOM Fibers Two type
2.Multiply innervated fibers (MIFs)1.Singly innervated fibers(SIFs)
• Large diameter
• Arranged irregularly
• Abundant mitochondria
Multiply innervated
Many branches 1 nerve as en
grappe
Mostly found in orbital layer of
EOM
Allows fatigue resistant
smooth ocular movement
• Small diameter
• Regularly arranged
• Fewer mitochondria
Singly innervated
1 nerve, 1 branch as en plaque
Mostly found in globular layer
of EOM
Allows rapid, saccadic and
precise movements
33. Law of ocular motility
Agonist-antogonist- pair of muscle of same eye that
move in opposite direction e.g- LR and MR
Synergist- pair of same eye muscle that move in same
direction e.g- SR and IO- elevation
Yoke muscle- contralateral pair of muscle that move in
same direction- e.g left SO and right IR-levoelevation
Sherrington law-reciprocal innervation- increased
innervation to one EOM is accompanied by reciprocal
decreased innervation to antagonist- agonist/antagonist
action eg. LR & MR
Hering law- equal innervation to EOM during
conjugate eye movement- yoke muscles.
34. Ocular movements
Ocular movement occurs around the axis of Fick
3 basic ocular movements
1.Ductions –
2.Version-
monocular movement
around the axis of Fick
Binocular,
simultaneous,
conjugate movements-
(in same direction)
Binocular,
simultaneous,
disjugate /disjunctive
movement-in opposite
direction
3.Vergences-
1.Convergence
2.divergence
35. Ductions
Are tested by occluding one eye and asking the patient
to follow target in each direction of gaze
Ductions consist of following-
1.adduction-MR
4.depression-
2.abduction-LR
6.Extorsion
(IO)
3.Elevation
(SR) 5.Intorsion
(SO)
OD
36. version
Tested with both eye open and asking patient to follow a
target in each direction of gaze.
Following are the various gaze of versions-9 cardinal gaze
3.Dextroelevation
(ODSR+OSIO)
2.Destroversion
ODLR+OSMR)
5.Laevoversion
(OSLR+ODMR)
6.Laevoelevation
(OSSR+ODIO)
7.Laevodrepression
(OSIR+ODSO)9.drepression
8.elevation
1.Primary position
4.Dextrodrepression
(ODIR+OSSO)
