The presentation begins with an overview of the extraocular muscles, highlighting their crucial role in controlling eye movements and maintaining proper vision. Emphasized the significance of these muscles in daily activities and visual perception.

1. ANUJA DHAKAL.
OPTOMETRIST
ANATOMYAND
PHYSIOLOGY OF
EXTRAOCULAR MUSCLES

2. EXTRAOCULAR MUSCLES
 The movements of each eye is controlled by a set of six
muscles: extraocular muscles.
 Consist of 4 rectus & 2 oblique muscles.
 Rectus muscles : Superior Rectus
Inferior Rectus
Medial Rectus
Lateral Rectus
 Oblique muscles:
Superior Oblique
Inferior Oblique

3. Functions :
 The extraocular muscles work within the surrounding orbital
tissue to provide smooth movements of the eyes and allow for
binocular vision.
 The extraocular muscles and their surrounding tissue determine
the alignment of the eye.
 The muscles, composed almost entirely of fast, twitch-generating,
singly innervated fibers, allow for large, rapid, precise
movements.

4. Embroyology :
 The extraocular muscles are of mesodermal origin, development
beginning at 3–4 weeks’ gestation.
 The muscles originate from three separate foci of primordial cells,
one for the muscles innervated by the oculomotor nerve, one for the
superior oblique muscle, and one for the lateral rectus muscle.
 All of the extraocular muscles develop in situ; they do not begin
development at their origins and sprout toward their respective
insertions.

5.  The extraocular muscles receive input from their respective
cranial nerves as early as 1 month of gestation.
 The tissues that surround the extraocular muscles also develop
early in gestation.
 Formation of the trochlea begins at 6 weeks’ gestation, and early
fascial coverings can be detected around the extraocular muscles
by 3 months’ gestation.

6.  Tissues destined to become intermuscular septa and orbital fat
differentiate in the fourth and fifth months of gestation, respectively.
 All of the extraocular muscle and their surrounding tissues are
present and in their final anatomical positions by 6 months’
gestation, merely enlarging throughout the remainder of gestation.

7. EOM differ from other skeletal muscles :
 Diameter of these fibers is small.
 Contain enormous amount of fibroelastic tissue.
 Contain both slow & fast fibers.
 Connective tissue surrounding EOM is more delicate than that
around other skeletal muscles.
 Richly supplied by nerves & vessels.
 Require & receive more O2 than other skeletal muscles.

8. Light microscopic structures of EOM :
 Long, cylindrical,
multinucleated
 Epimysium
 Perimysium
 Endomysium
 Muscle fibre
 Sarcolemma
 Myofibril
 Sarcomere
 Cross- striation
 A-band, I-band
 Z line
 H band

9. Electron microscopic structure of EOM :
 Sarcomere
 2 types of filaments
 Thick filament
 Thin filament
 Ms contract
 Cross-bridging
 Hydrolysis of ATP

10. Summary of the main anatomic features of the EOM

11. Superior rectus muscle
 It arises from the tendinous
ring above the optic foramen.
 Its origin is attached to the
dural sheath of the optic nerve.
 The muscles passes forward
and somewhat laterally and
pierces the fascial sheath of the
eyeball.

12.  Inserted into the sclera about 7.7 mm posterior to the
limbus.by means of tendon 5.8 mm long.
 The line of insertion is slightly curved and oblique.
 The fascial sheath of the SR and that of LPS are connected
by a band of connective tissue – this ensures that two
muscles work synergistically.
 A further slip of fascia is also connected to the superior
fornix - this band permits these muscles to raise the
superior fornix of the conjunctiva as they contract.

13.  Relations :
Superiorly – LPS muscles, frontal nv. ,
roof of the orbit.
Inferiorly – Optic nerve, ophthalmic
artery, nasociliary nv.
 Nerve supply – superior div. of
occulomotor nv.
 Actions – elevates the eye,
medially rotates the eye, rotates the
eyeball medially on its
anteroposterior axis (intorsion).

14. Inferior rectus muscle
 Arises from the tendinous ring below the
optic foramen.
 Passes forward and somewhat laterally
and pierces the fascial sheath of eyeball.
 Inserted into the sclera about 6.5 mm
from the limbus by means of a tendon
5.5 mm long.
 The line of insertion is slightly curved
and oblique.

15.  The IR is covered by a fascial sheath derived from the fascial
sheath of the eyeball.
 The fascial sheath of the IR and the inferior oblique are attached to
one another and to suspensory ligament of the eyeball.
 A band of connective tissue also connects the IR sheath to the lower
eyelid.

16.  Relations :
Superiorly – occulomotor nv., optic
nv. imbedded in orbital fat and the
eyeball.
Inferiorly – floor of the orbit,
infraorbital vessels and nerves in their
canal, and the underlying maxillary
sinus.
 Nerve supply – inferior div. of
occulomotor nerve.
 Actions – depresses the eye,
medially rotates the eye, rotates
the eyeball laterally on its
anteroposterior axis (extorsion).

17. Lateral rectus muscle
 Arises from the lateral portion of the
tendinous ring as it bridges the superior
orbital fissure.
 A second small head arises from the
orbital surface of greater wing of the
sphenoid bone, lateral to the fibrous ring.
 Muscle then passes forward close to the
lateral wall of the orbit and pierces the
fascial sheath of the eyeball.

18.  Inserted into the sclera about 6.9 mm from the limbus by means
of tendon 8.8 mm long.
 The line of insertion is nearly vertical.
 LR muscle is covered by sheath that derives from the eyeball.
 Sheath of LR sends off an expansion that attached to lateral wall
of orbit to form lateral check ligament.

19. Relations :
 Superiorly – lacrimal nv. and
lacrimal art.
 Inferiorly – floor of the orbit
 Medially – abducent nv. and
orbital fat.
Nerve supply – abducent nv.
Action –rotates the eye laterally
(abductor)

20. Medial rectus muscle
 Largest of the EOM.
 Arises from the medial portion of the tendinous ring and is
attached to dural sheath of the optic nerve.
 Passes forward close to the medial wall of the orbit and and
pierces the fascial sheath of the eyeball.
 Inserted into the sclera about 5.5 mm from the limbus by means
of a tendon 3.7 mm long.
 The line of insertion is vertical.

21.  MR is covered by a fascial sheath covered by a fascial sheath
of the eyeball.
 The sheath of the MR sends off an expansion that is attached to
the medial wall of the orbit to form the medial chek ligament.

22. Relations :
 Superiorly – superior oblique ms, ophthalmic artery and
its branches, the nasociliary nerve.
 Inferiorly – floor of the orbit.
Nerve supply – inferior division of occulomotor nerve.
Action – rotates the eyeball medially (adduction).

23. Superior oblique muscles
 Long, slender, fusiform muscle arises
from the body of sphenoid bone above
and medial to the optic canal just outside
the tendinous ring.
 The muscle belly runs forward between
the roof and medial wall of orbital cavity
and quickly gives rise to a rounded
tendon.
 The tendon then passes through a pulley
or trochlea of fibrocartilage that is
attached to the trochlear fossa of the
frontal bone.
 Longest & thinnest of all EOM

24.  As the tendon passes through the
pulley, it is surrounded by a
delicate synovial sheath.
 After emerging from the trochlea ,
the tendon bends downward,
backward, and laterally.
 It then pierces the fascial sheath of
eyeball and passes inferior to the
SR ms.

25.  The tendon now expands in a fan shaped
manner and inserts into the sclera posterior
to the equator of the eyeball.
 The line of insertion is convex posteriorly
and laterally.
 The tendon of the SO ms is covered by a
fascial sheath derived from the sheath of the
eyeball – it extend as far as trochlea.

26. Relations :
Superiorly – roof of the orbit
Inferiorly – ophthalmic art. and its branches , and the
nasociliary nv.
The supratrochlear nv. lies above and lateral to the
ms, and lateral to the trochlea.
Nerve supply – trochlear nv.
Action – depresses the eye, turns it laterally (abducts), also rotates
the eyeball medially on its anteroposterior axis (intorts).

27. Inferior oblique muscle
 Only voluntary muscle to take origin from the
front of the orbit.
 Arises from the floor of the orbit, just posterior
to orbital margin and just lateral to the
nasolacrimal canal.
 It may attached to the fascia covering the
lacrimal sac.
 The ms passes laterally, posteriorly, and
superiorly, following the curve of the lower
surface of the eyeball.

28.  It runs inferior to the IR muscle.
 Reaches the posterolateral aspect of the eyeball,where it
inserts into the sclera under cover of LR muscle.
 The line of insertion is convex above and laterally.
 The IO ms is surrounded with the fascial sheath derived
from the fascial sheath of the eyeball.
 The muscle sheath is attached to that of the IR ms.

29. Relations :
Superiorly – orbital fat, inferior rectus muscle, and the eyeball.
Inferiorly – floor of the orbit.
Nerve supply – inferior division of the occulomotor nv.
Action – elevates the eye, laterally rotates the eye (abducts), also
rotates the eye laterally on its anteroposterior axis (extorsion).

30. SPIRAL OF TILLAUX
 It is imaginary line joining the insertion of
4 recti & is important anatomical
landmark when performing surgery.
 The insertions get further away from
limbus & make a spiral pattern.

31. Blood supply of EOM
 Muscular arteries usually two in number –medial & lateral; branches
of Ophthalmic artery.
 Medial muscular branch supplies MR, IR & IO.
 Lateral muscular branch: LR, SR, Levator ms & SO
 A branch of Lacrimal artery also supply MR.
 A branch of Infraorbital artery also supply IR and IO.

32.  Anterior Ciliary arteries from muscular branches are 7
in number :
2 each from SR, IR & MR.
1 from LR.
 Veins from EOM correspond to arteries & empty into
:superior & inferior ophthalmic veins.

33. Motor innervation of the extraocular
muscles :
 The motor nv. reaches the EOM in the region of the muscles
middle and posterior thirds.
 It breaks up into numerous branches, which run both distally
and proximally between the muscle fiber.
 Two types of myoneural junctions are present.
 The common form of motor end plate that is found on skeletal
muscle elsewhere is present in the singly innervated muscle
fiber.

34.  The second type , shaped like a bunch of grapes, is found in
multiple innervated muscle fibers.
 The motor fibers entering the motor end-plate are always
myelinated.
 The grapelike endings have smaller nerves, which are
myelinated or nonmyelinated.

35. Myoneural junction in skeletal muscles.
 As each large myelinated fibers enters a skeletal muscle, it
branches many times.
 A single branch then terminates on a muscle fiber at a site
referred to as a neuromuscular junction or motor end plate.
 On reaching the muscle fiber , the nerve loses its myelin
sheath and breaks to number of subsidiary branches.
 Each branch ends as a naked axon and forms the neural
element of motor end plate.

36.  The axon is expanded slightly and contains numerous mitochondria
and vesicles (apprx. 45 nm in diameter).
 At the site of motor end plate the surface of the muscle fiber is
elevated to form muscular element of the plate (sole plate).
 The expanded naked axons lies in the groove on the surface of
muscle fiber.
 The floor of the groove contains sarcolemma , which is thrown into
numerous folds, called junctional folds.

37.  The plasma membrane of the axon
(axolemma or presynaptic membrane)
is separated by a space about 20 to 50
um wide from the plasma membrane
of the muscle fiber (sarcolemma or
post synaptic membrane).
 This space constitute the synaptic
cleft.

38.  On reaching the motor end plate, a nerve impulse causes the
release of acetylcholine from some of the axonal vesicles.
 The acetylcholine discharges into the synaptic cleft by a process
of exocytosis.
 It diffuses rapidly through the basement membrane to reach the
receptors on the postsynaptic membrane.
 This makes the post synaptic membrane more permeable to Na+
ions, creating a local potential called end-plate potential.

39.  If the end plate potential is large enough, an action potential will
be initiated to spread along the surface of sarcolemma.
 The wave of depolarization is carried into the muscle fiber to
contractile myofibrils.
 This leads to release of Ca+ ions from the sarcoplasmic reticulum
– which in turn causes the muscle to contract.

40. The sequence of events that take
place at a motor end plate on
stimulation of motor nv can be
summarised as follows:
i. ACh +receptor→ Na + influx → End-
plate potential
ii. End-plate potential →actn potential
→ Ca2+ →Ms contract
iii. Hydrolysis of ACh by AChEsterase
→ repolarizatn of Ms

41. Physiology of ocular motility
 Visual Axis: Line of vision passes from fovea through
nodal point of the eye to point of fixation (object of
regard).
 Anatomical axis: a line passing from post pole through
center of cornea.
 Angle kappa: angle substened by visual & anatomical
axis. Angle is +ve, when fovea is temporal to post pole, is
–ve when converse applies.

42.  Primary action of muscle is its major effect when eye is
on primary position.
 Subsidiary actions are additional effect on the position of
eye.
 Listing plane is an imaginary coronal plane passing
through center of rotation of globe. Globe rotates on axes
of Fick which intersect in listing plane.

43. Axes of Fick
3 axes to analyse all movements of globe around the hypothetical
center of rotation.
 Globe rotates Lt & Rt on vertical Z-axis
 Globe moves upward & downward on horizontal X-axis
 Globe moves Torsional movement (front to back) on Y-axis

44. Positions of gaze :
Primary position of gaze :
-that position from which all other ocular movements
are initiated.
- Scobee defined it as in binocular vision when, with the
head erect, the object of regard is at infinity and lies at
the intersection of the sagittal plane of the head and a
horizontal plane passing through the centres of rotation
of the two eyeballs.

45.  Secondary position of gaze :
- these are the position assumed by the eyes while looking straight
up (supraversion) , straight down (infraversion), to the right
(dextroversion), and to the left (levoversion).
 Tertiary position of gaze :
- the position assumed by the eyes when combination of vertical
and horizontal movements occur. These include position of eyes
in dextroelevation, levoelevation and levodepression.

46. Cardinal position of gaze :
- these are the position which allow examination of each of the
12 extrocular muscles, of the two eyes, in their main field of
action.
-there are six cardinal position of gaze viz., dextroversion,
levoversion, dextroelevation, levoelevation, dextrodepression
and levodepression.

47. Ocular movement :
Monocular eye movement (duction):
1. Adduction: an inward movement (medial)rotation along
vertical axis
2. Abduction: outward movement (lateral)
3. Supraduction (sursumduction): upward movement
(elevation) along horizontal axis
4. Infraduction (deosursumduction): downward movement
(depression)

48. 6. Incycloduction (intorsion): rotatory movement along
anteroposterior axis in which superior pole of cornea
moves medially.
7. Excycloduction (extorsion): rotatory movement along
anteroposterior axis in which superior pole of cornea
moves laterally.
Binocular eye movement:
1. Versions: simultaneous movemt of BE in same direction.
2. Vergences: simultaneous movemt of BE in opposite
direction.

49. Classical concept of actions of EOM :
Horizontal rectus muscle
 The horizontal recti have a common muscle plane which is
horizontal in primary position and their axis of rotation
coincides with the z-axis of the globe.
 When the eye is in primary position , the horizontal recti are
purely horizontal movers around the vertical z-axis and
have only a primary action.
 Thus , LR causes abduction and MR causes adduction.

50. Vertical rectus muscles
 The superior and inferior
rectus muscles have a
common muscle plane,
which is in the same line as
the orbital axis and thus
form an angle of 23 degree
with optical axis.

51.  Actions of superior rectus :
 In the primary position, the primary action of SR is
elevation.
 This movement occurs about horizontal x-axis.
 The secondary action is intorsion around y-axis.
 The tertiary axis is adduction around z-axis.

52.  When the globe is abducted
23degree , the axis of rotation of SR
ms and optical axis coincide so that
the ms has no subsidiary action and
can only act as elevator.
 This is therefore , the best position
of the globe for testing the function
of SR ms.

53.  If the globe could be adducted 67
degree , the SR ms would produce pure
incycloduction.
 Since the globe cannot adduct ,
therefore there is some elevating
component to the action of SR even in
adduction.

54.  Actions of inferior rectus :
 Analogous to SR.
 In primary position, its primary action is depression,
secondary action is extorsion, and tertiary action is
adduction.
 When the globe is abducted 23 degree, its only action is
depression.
 If the globe could be abducted 67 degree, IR would
produce only extorsion.

55. Oblique muscles
 The obliques are inserted beind the equator and form an
angle of 51 degree with the optical axis, and thus have the
following actions :
 Actions of superior oblique :
 In primary position, the primary action of SO is intorsion,
which occurs about anteroposterior y-axis.
 The secondary action is depression and the tertiary action
is abduction.

56.  When the globe is adducted 51
degree, the axis of muscle rotation
coincide with optical axis so that it
can only act as depressor.
 This is the best position of the globe
for clinically testing the action of SO
ms.

57.  When the eyeball is abducted by
39 degree, the optical axis and the
line of pull of SO on angle of 90
degree with each other.
 In this position, the SO can only
cause intorsion.

58. Actions of inferior oblique :
Analogous to superior oblique.
 In primary position, main action is extorsion,
secondary action is elevation and tertiary action is
abduction.
 When the globe is adducted 51 degree, its only action
is elevation.
 When the globe is abducted 39 degree, its only action
is extorsion.

59. Action of EOM

60. Agonists, Synergists, Antagonists and
Yoke muscles :
Agonists :
- it refers to any particular extraocular muscle
producing specific ocular movement: eg. For
producing abduction in right eye, the right LR ms is
agonist.
Synergists :
- two muscles moving an eye in the same direction are
called synergists.
-for eg, SR and IO of the same eye act as synergists for
elevation movement.

61. Antagonists :
- these are muscles having opposite actions in the same
eye.
- for eg, medial and lateral recti.
Each EOM has 2 synergist & 2 antagonist except medial &
lateral rectus which has 2 synergist & 3 antagonist.

63. Yoke muscles (contralateral synergists):
a pair of ms(1 from each eye) e.g. RLR
& LMR act as yoke ms for
dextroversion movement
Contralateral antagonist (antagonist of
yoke ms):
a pair of ms (1 from each eye) having
opposite action e.g. RLR & LLR.

64. Applied anatomy :
Infected surgical spaces associated with EOM:
 Space between cone of 4 rectus ms & periorbital lining the
orbital walls.
 Space within cone of 4 rectus ms.
 Space between sclera & fascial sheath of eyeball.
 In these space pus may accumulate within 1 of them,
forming an abscess.

65. Strabismus (squint): condition in
which visual axes of both eyes are not straight in primary
position.
Nystagmus: regular & rhythmic to & fro involuntary
oscillatory movement of eyes.
It is due to irregular motor impulses reaching the extraocular
muscles.
Retrobulbar neuritis: origin of SRM & IRM are
attached to dural sheath of optic nerve.
This attachment explainspain of retrobulbar neuritis
experiencedwhen moving eyeball.

66. Myasthenia Gravis: characterized by
ptosis+ 3D(diplopia, dysphasia,dysarthia)+ general ms
weakness.
An autoimmune disorder in which antibodies produced
against Ach-receptors.
Dysfunction of ocular movement
following a Blow –out fracture of
orbit: A blow-out fracture of orbit caused by a
frontal blow to eyeball may result in entrapment of
IRM & IOM and orbital connective tissue in the
fracture line in the orbital floor → serious limitation of
ocular mobility.

67.  Drugs & diseases affecting the motor end-
plate of EOM:
 Neuromuscular blocking agent: Tubocuranine,
Succinylcholine, Decamethonium → paralyze
skeletal ms
 Anticholesterases: Physostigmine, Neostigmine →
inactivate ACh.
 Bacterial toxins: Clostridium botulinum → inhibit
release of ACh.

68.  Exophthalmos associated with thyrotoxicosis :
-form of autoimmune diseases.
-abnormal production of T-lymphocytes against the thyroid
gland and retrobulbar muscle tissues.
-increase in the mucopolysachharides and oedema of the
muscles.
-exerts pressure on the back of eyeball and produces
exophthalmos.
- later fibrosis of EOM occurs, leading to immobility of
eyeball.
- extensive contraction of IR is common, causing vertical
diplopia and limitation in elevating the eye.