The document summarizes the anatomy and physiology of the extraocular muscles (EOMs). It describes the 7 EOMs, their origins, insertions, actions, and nerve supply. The EOMs allow for precise eye movements through arrangements of fibers and innervation that provide both rapid and fatigue-resistant function. Their coordinated actions follow laws of ocular motility to produce conjugate and vergent eye movements in the cardinal gazes.

1. EXTRAOCULAR MUSCLES
Dr.Lhacha Wangdi (Resident), Department of Ophthalmology
JDWNRH

2. Learning objectives
1. Physiology of ocular movement
2. Anatomy of extra ocular muscles (EOM)
3. Clinical correlates

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

5. Extraocular muscles
7 extraocular muscles
1. Lateral rectus
2. Medial rectus
3. Superior rectus
4. Inferior rectus
Levator Pelpebrae
Superioris
Two oblique musclesFour Rectus muscles
5.Superior oblique
6.Inferiro Oblique

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)

37. 37

38. References
 J.J Kanski clinical ophthalmology- 7th edition
 Yanof and Duker ophthalmology-4th edition
 AAO- section 4 & section 6
 Stallards surgical method
 Oxford textbook of ophthalmology
 Daun’s clinical ophthalmology
 Internet sources