The document discusses the anatomy and embryology of the extraocular muscles. It covers topics such as the origin of the muscles from mesoderm and neural crest, the development of pulleys and connective tissues, the internal structure of the muscles including fiber types, and the surgical anatomy of structures like the rectus muscles and Tenon's capsule. The physiology of muscle contraction and the characteristics that make extraocular muscles unique are also summarized.

1. The Anatomy of the
Extraocular Muscles
Tukezban Huseynova, MD
Specialist in Strabismus and Refractive Cornea,
Briz-L Eye Clinic, Baku, Azerbaijan
Tukezban@gmail.com

2. Embryology of Extraocular Muscles
• The fibers of the striated EOMs
originate from condensations of
cranial mesoderm, whereas their
associated connective tissues
and the orbital smooth muscles
(SMs) originate from the neural
crest.

3. Embryology of Extraocular Muscles
Myogenesis
Primary
11 weeks
Secondary
 the trochlea
 the soft
pulley
 The periocular
connective
tissues

4. Embryology of Extraocular Muscles
Adult skeletal muscles retain a quiescent stem cell
population that allows regeneration. After muscle
damage has occurred, the regenerative process
recapitulates development as the precursor cells in
the adult, now known as satellite cells, proliferate to
produce myoblasts, which fuse to form new muscles
fibers.

5. Embryology of Extraocular Muscles
1. The types of contractile proteins expressed in a given muscle
fiber
2. The apparatus that links activation of the muscle fiber from a
motor nerve to the production of a muscle contraction,
excitation-contraction coupling.
Contraction speed, in turn, is a function of
two factors

6. Embryology of Extraocular Muscles
• The central contractile unit of a skeletal muscle fiber is
the sarcomere.
• Each sarcomere is approximately 2 to 3 mm long.
• End-to-End arrangement of sarcomeres produces the
characteristic longitudinal banding pattern of striated
muscle.

7. İnternal Structure of the EOM
The oculorotary EOMs, although not the levator
palpebrae superioris (LPS), consist of two distinct
layers:
 Global layer
 Orbital layer ( SIMFs and MIMFs)

8. Origins and paths of the EOM
The rectus EOMs originate in
the orbital apex from a common
fibrous ring surrounding the optic
nerve called the annulus of Zinn
The SO muscle originates from
the periorbita of the superonasal
orbital wall
The IO muscle originates much
more anteriorly from the periorbita
of the inferonasal orbital rim
adjacent to the anterior lacrimal
crest

9. Pulleys of the EOM
Pulleys consist of discrete rings of dense collagen encircling
the EOM and are about 2 mm in length coaxial
Has less substantial collagenous sleeves around the EOM.
Anteriorly, these sleeves thin to form slings convex to the
orbital wall, and
More posteriorly the sleeves thin to form slings convex
toward the center of the orbit.
The anterior pulley slings are also known as the intermuscular
septa.
The collagenous pulley ring forms the fulcrum of the pulley
that inflects the EOM path.

10. Pulleys of the EOM

11. Pulleys of the EOM
The pulleys function as the mechanical origins of
the EOMs and play a vital role in ocular kinematics,
the rotational properties of the eye.
Normal pulleys form a natural mechanical
substrate for Listing's law and other aspects of ocular
kinematics, and they render ocular rotations
effectively commutative.

12. Pulleys of the EOM
 Donder's law, stating that there is only one torsional
eye position for each com-bination of horizontal and
vertical eye positions.
 Listing's law, a specific case of the more general
Don-der's law, states that any physiologic eye
orientation can be reached from any other by rotation
about a single axis, and that all such possible axes lie
in a single velocity plane, Listing's plane.

13. Pulleys of the EOM
 Listing's law is satisfied if the axis of
ocular rotation shifts by exactly one half of
the shift in ocular orientation for any eye
movement.This is the so-called Listing's half-
angle rule.

14. Pulleys of the EOM
Shifts in horizontal rectus
pulley position required to
maintain the Listing's half-angle
relation in tertiary positions of
adducted elevation and
adducted depression. Pulleys
are depicted as rings. Paths of
global layers of rectus
extraocular muscles are shown
in black; orbital layers inserting
in pulleys are shown in gray.
Pulley suspensions are also
shown in gray.

15. Pulleys of the EOM
Shift of pulley location can produce an "A" & "V"
pattern of strabismus
Pulleys cause "V" Pulleys cause "A"

16. Pulleys of the EOM
• The ‘pulley zone’ is roughly at the junction of the middle
and posterior third of the globe, similar to Listing’s plane

17. Pulleys of the EOM
• The pulleys which
‘inflect the paths of the
muscle.’
A. Medial rectus pulley
B. Lateral rectus pulley
• The functional origin of the
rectus muscles is at the
pulleys

18. Pulleys of the EOM
• The orbital fibers insert into the
pulleys of the horizontal recti and
the global fibers insert into
sclera.

19. Pulleys of the EOM
The muscle - tendon anterior to the pulley
A. Passes straight in primary position
B. Courses upward in upgaze
C. Courses downward in downgaze
D. The direction of the muscle posterior to the pulley does
not change during up and downgaze

20. Pulleys of the EOM
Some combination of:
Upward displacement of the
lateral recti
Downward displacement
leads to ‘A’ pattern

21. Pulleys of the EOM
Some combination of:
Downward displacement
of the lateral recti
Upward displacement of
the medial recti leads to
‘V’ pattern

22. Pulleys of the EOM
The reasons that the strabismus surgeon is not
likely to see the pulleys are several.
First, surgery of the extraocular muscles is carried out beneath anterior
Tenon's capsule and in the plane of posterior Tenon's capsule.
Second, dissection carried posterior to the origin of anterior Tenon's
capsule will expose extraconal fat, which both complicates surgery and
obscures the surrounding anatomy, including the pulleys.
Third, although the pulleys are located in the orbital fat just behind the
insertion of anterior Tenon's capsule, they are virtually impossible to
identify for what they are.

23. Scleral İnsertion of EOM
Anatomic relations of
rectus extraocular muscle
insertions to the corneal
limbus.

24. Smooth muscles of the orbit
SMs in four areas of the human orbit:
The inferior palpebral muscle,
The superior palpebral muscle,
The “orbital muscle” spanning the inferior orbital
fissure, and
The “peribulbar muscle” surrounding the anterior
aspect of the globe.

25. Physiology of EOM
Key traits of muscle function
1. Contraction speed
a. The types of contractile proteins expressed in a given muscle
fibers.
b. The apparatus that links activation of the muscle fiber from
a motor nerve to the productionof a muscle contraction,
excitation – contraction coupling.
2. Fatique resistance is a direct consequence of cellular
metabolism.

26. Physiology of EOM
• The contractile unit of a skeletal muscle – sarcomere
• End – to – end sarcomere forms striated muscle
Thick agregates of myosin
(Light and heavy chains)
Thin filaments
(polymers and α- actin)

27. Physiology of EOM
• 2 proteins modulate the contractile process
Tropomyosin Troponin
Attach to the α – actin backbone.

28. Physiology of EOM
Sarcomere
Dark
Anisotropic band
(A band)
contain actin and myosin
Light
Isotropic band
(I band)
contain actin
H zone (center)
presence only
myozin
M zone
containing protein,
bisect by H zone
Z line
longitudinary boundary of
each sarcomere.

29. Physiology of EOM

30. Physiology of EOM

31. Physiology of EOM
• Each end – to – end sarcomere is known as
myofibril, myofibril are separated from each
other by a membranous calcium storage system,
the sarcoplasmic reticulum.

32. Physiology of EOM
Fiber Types:
1. Slow twitch, fatigue resistant (red or Type I)
2. Fast twitch, fatigue resistant (intermediate or Type II A)
3. Fast twitch, fatigable (white or type II B)
4. Fast twitch, intermediate (Type II C or II X/D)

33. Physiology of EOM
Six distinct fiber types
1. Orbital singly innervated fiber (predominant)
2. Orbital multiply innervated fiber
3. Global red singly innervated fiber (1/3 of global fiber)
4. Global intermediate singly innervated fiber (1/4 of global fiber)
5. Global white singly innervated fiber (1/3 of global fiber)
6. Global multiply innervated fiber

34. Physiology of EOM
• The energy requirement for muscle contraction is
by adenosine triphosphate (ATP) cleavage via a
myofibrillar ATPase. Both anaerobic (glycolytic) or
aerobic (mitochondrial oxidative) mechanism.

35. Surgical anatomy

36. Palpebral fissure size
• The average adult
palpebral opening is 28 mm
long and 10 mm high.
• An average 18-month-old
child has a palpebral
opening 20 mm long and 8.5
mm high.

37. Palpebral fissure size
• A newborn has a palpebral
opening measuring 18 mm
long and 8 mm high.
 The size and shape of the palpebral opening
should be considered at the outset of extraocular
muscle surgery.

38. Extraocular muscles size
• İn newborns, the posterior part of the globe is relatively
smaller than the anterior part, meaning that a recession of
3 mm could place the medial rectus at the equator. This is
important information but not for strabismus surgery,
which is not indicated anyway in the newborn because of
immaturity of the binocular system.
• The insertion of the medial rectus in an infant can be
closer than 5.5 mm from the limbus.

39. Extraocular muscles size

40. Palpebral fissue shape
• A patient with myelomeningocele and a straight lower lid margin
simulating a mongoloid slant. This is a common but unexplained
finding in such patients.

41. Palpebral fissue shape
• ‘V’ esotropia in a patient
with antimongoloid palpebral
fissures.

42. Palpebral fissue shape
• ‘A’ esotropia in a patient
with mongoloid palpebral
fissures.

43. Palpebral fissue shape
• The palpebral fissure may be level, mongoloid, or
antimongoloid, depending on the relative positions
of the medial and lateral canthi.
• If the outer canthus is higher than the inner canthus,
a mongoloid palpebral slant exists (Figure 15). If the
outer canthus is lower than the inner canthus, an
antimongoloid palpebral slant exists.

44. Epicanthal folds
A.This patient demonstrates
telecanthus with an interorbital
dimension clearly more than
one-half the interpupillary
distance and also an exotropia.
B. This patient with telecanthus
also has prominent epicanthal
folds.

45. Epicanthal folds
• A skin fold originating below and sweeping upward is called epicanthus
inversus. This deformity is frequently associated with blepharophimosis and
ptosis. These three deformities, which may be combined with telecanthus,
cause significant disfigurement and present a formidable therapeutic
challenge.

46. Epicanthal folds
A. Centered pupillary light
reflex
B. The ‘straightening’ effect
of exposing more ‘white’
nasally. (This is shown in an
older patient because it is
difficult to photograph the
younger child where the
test is more effective.)

47. Epicanthal folds
• Epicanthal folds obscure the
nasal conjunctiva in both
patients, giving the appearance of
esotropia. However, the light
reflex is centered in the pupil in
each case. This reflex indicates
the presence of parallel pupillary
axes and, therefore, straight eyes
or absence of manifest
strabismus. Cover testing must be
performed eventually to confirm
the presence of parallel visual
axes because a large angle
kappa* could hide a small
manifest esodeviation.

48. Epicanthal folds
• Epicanthal folds are present to some degree in
most infants and children during the first few years
of life.
• First, the examiner demonstrates the centered
pupillary reflexes with a muscle light. Second, the
examiner carefully pulls the skin forward over the bridge
of the nose to demonstrate the ‘straightening’ effect of
exposing the medial conjunctiva or ‘white of the eye’ .

49. Epicanthal folds
*Angle kappa is the angle formed by the pupillary axis
and the visual axis. A positive angle kappa is present
when the visual axis is nasal to the pupillary axis. This
simulates exotropia and is common. A negative angle
kappa is present when the visual axis is temporal to the
pupillary axis. This simulates esotropia and is much less
common than positive angle kappa.

50. Conjunctiva
• The plica semilunaris is a fold in the conjunctiva
located far medially in the palpebral fissure and is
mostly below the midline. The caruncle, located just
medial to the plica, is about 3 mm in diameter,
covered with squamous epithelium, and often
contains small hairs.

51. Conjunctiva
• The topographic landmarks of
the conjunctiva important to the
strabismus surgeon are the
following:
A The fusion of the conjunctiva
and anterior Tenon’s capsule with
the sclera at the limbus

52. Conjunctiva
A. The limbus
B. The plica semilunaris
C. The caruncle

53. Tennon’s capsule
• Tenon's capsule is a structure with definite body
and substance in childhood which gradually atrophies
in old age but not to the same degree as conjunctiva.
• Tenon's capsule has an anterior and posterior part.
• Anterior Tenon's capsule is the vestigial
capsulopalpebral head of the rectus muscles.
• This covers the anterior half to two-thirds of the
rectus muscles in their sheaths as well as the
intermuscular membrane.

54. Tennon’s capsule

55. Tennon’s capsule
• The muscle hook is placed in a
‘hole’ created in intermuscular
membrane adjacent to the muscle
insertion and glides along bare
sclera behind the rectus muscle
insertion and is exposed at the
opposite muscle border with a
snip incision.With a limbal
incision, the multiple layers and
surfaces associated with the
rectus muscles can be readily
seen. Conjunctiva and anterior
Tenon’s capsule shown here
separated are actually fused and
separated only with difficulty.

56. Tennon’s capsule
• Anterior Tenon's capsule is fused with the
undersurface of conjunctiva and attaches to sclera
at the limbus.
• Posterior Tenon's capsule is made up of the fibrous
sheath of the rectus muscles together with the
intermuscular membrane.

57. Surgical anatomy of the rectus muscles
• The spiral of Tillaux and
the relationship of the
rectus muscle insertions.
• Width of the rectus
muscle insertions.

58. Characteristics of EOM
• The extraocular muscles are similar to skeletal muscles though there are
differences undoubtedly related to the very specialized function of the
extraocular muscles.
• Both skeletal and extraocular muscles have several types of twitch fibers,
but the extraocular muscles are unique, having tonically contracting fibers
not found in skeletal muscle.
• The twitch fibers of extraocular muscles are called Fibrillenstruktur, and
the unique slow tonic fibers are called Felderstruktur.
• There are two muscle fiber layers in the medial and lateral recti. The
shorter orbital layer inserts in the muscle pulley, and the longer global
fibers insert into sclera at the muscle’s insertion.

59. Characteristics of EOM
• The shorter orbital layer inserts in the muscle pulley, and
the longer global fibers insert into sclera at the muscle’s
insertion.
• The muscle fibers are long, traversing the entire length of
the muscle, or in some cases, nearly so.
• The blood supply of the extraocular muscles is rich, coming
from the muscular branches of the ophthalmic artery.
• The extraocular muscles have the lowest innervation ratio
of any of the muscles of the body; that is, they have the most
nerve fibers per muscle fiber.

60. Surgical anatomy of Inferior oblique
• The inferior oblique
A. from in front and
B. from behind.

61. Surgical anatomy of Inferior oblique
• The inferior oblique behaves as if it had two potential origins and two
potential insertions because of its union with Lockwood's ligament as it
passes beneath the inferior rectus. In addition, at the mid-section of the
inferior oblique is a stout neurovascular bundle, described in detail by
Stager and associates, which acts both as a restraining anchor and a source
of innervation.

62. Lockwood ligament
A. The ligament of Lockwood could
be compared to a hammock
supporting the globe.
B. The inferior oblique passes
beneath the inferior rectus,
through Lockwood’s ligament and
orbital fat approximately 12 - 14
mm from the limbus.

63. Lockwood ligament
• The inferior fat pad is
prominent and should not be
disturbed during surgery of
the inferior rectus

64. Superior oblique
• The superior oblique tendon
is redirected to 54 from the
frontal plane and passes
posteriorly and temporally
beneath the superior rectus.

65. Superior oblique
• The superior oblique
remains attached to
the superior rectus
when the rectus is
detached and pulled
up.

66. Superior oblique
A. When the eye is rotated
downward, the superior rectus is
the intended distance in a very
large ‘hang loose’ recession even if
the superior oblique tendon -
superior rectus union is intact.
B. When the eye returns to the
primary position, the superior
rectus could be pulled forward,
reducing the
amount of recession.

67. Superior oblique
S.O. tendon excursion 8 mm either side of primary

69. Superior oblique

72. Whitnall’s ligament
A. The relationship of Whitnall’s ligament and
the superior oblique tendon. ‘Blind hooking’
the superior oblique tendon can damage
Whitnall’s, producing ptosis.
B. Whitnall’s ligament acts like a clothesline
with orbital structures suspended.
C. Nasal ptosis right eye from disruption of
Whitnall’s ligament after hooking of the
superior oblique tendon in a ‘blind sweep’
nasal to the superior rectus.

73. Trochlea
A. The trochlea attached to the medial orbital wall with the tendon
entering and exiting.
B. With fascial tissues removed the superior oblique tendon seen exiting
the trochlea through a cuff attached to the trochlea.

74. Trochlea
Dimensions of the trochlea
A. Saggital
B. Coronal

75. Trochlea
• Composite

76. Trochlea
A. CT scan showing trochlea on the left and no
trochlea on the right.
B. Same patient demonstrating the superior
oblique muscle on the right and no muscle on the
left.

77. Trochlea

78. Trochlea
A. Gaze positions showing
‘overaction’ of the right
inferior oblique and
underaction of the right
superior oblique.
B. At surgery, absence of the
right superior oblique tendon
was confirmed.

79. Anterior segment blood supply
Schematic of the blood supply of the
anterior segment from Saunders, et. al.
ACA = anterior ciliary artery
IMC = intramuscular circle
LPCA = long posterior ciliary artery
RCA = recurrent choroidal artery
From Saunders RA, et al. Anterior
segment ischemia after strabismus
surgery. Survey of Ophthalmology, 1994,
38(5):456-466. Used with permission.

80. Anterior segment blood supply
• The anterior ciliary arteries
are dissected from the
superficial capsular muscle
tissue allowing repositioning of
the muscle while leaving blood
flow undisturbed.

81. Vortex vein
The four vortex veins are
viewed from the posterior
aspect of the globe.
A. Lateral
B. Medial

82. Vortex vein
A.The superior temporal vortex
vein is seen at the posterior
insertion of the superior oblique.
Vortex veins are not seen routinely
during surgery on the superior
rectus.
B. A vortex vein may be seen but
rarely at either (or both) borders of
the medial rectus.

83. Vortex vein
C. A vortex vein is seen
routinely under the mid-belly
of the distal inferior oblique.
D. Vortex veins are seen at
one or both borders of the
inferior rectus.

84. Growth of the eye from the birth
through childhood

85. Sclera
• At the limbus, the sclera is 0.8 mm thick.
• Anterior to the rectus muscle insertions,
it is0.6 mm thick.
• Posterior to the rectus muscle insertions,
it is0.3 mm thick.
• At the equator, it is 0.5 to 0.8 mm thick.
• At the posterior pole, it is greater than 1
mm thick. The area of greatest surgical
activity for the extraocular muscle
surgeon coincides with the thinnest area
of the sclera.

86. Sclera
• The sclera is thinnest, 0.3
mm, posterior to the rectus
muscle insertion

87. Sclera
A. Keystone spatula, cutting tip down
B. Keystone spatula, cutting tip up
C. Hexagonal spatula, neutral cutting tip
D. Reverse cutting - tends to cut in - can be placed
sideways
E. Curved cutting - tends to be cut out

88. Blood supply of the EOMs
Ophthalmic
artery
Infraorbital artery supplies the rest of the inferior oblique
muscle.
Lacrimal artery supplies the rest of the lateral rectus
muscle.
Muscular artery
Lateral
Superior rectus & a
portion of the lateral
rectus muscle.
Medial
Inferior and medial rectus muscle
and a portion of the inferior oblique
Muscle.
Superior
Supplies superior oblique muscle.

89. Blood supply of the EOMs
The blood supply to the orbital layer is much more
extensive than that of the global layer.

90. Left Ocular Muscles and Innervation

91. Right Ocular Muscles and Innervation

94. Thank you