Anatomy and phusiology of eom

1. Presenter : Dr. Reshma Peter
Anatomy and Physiology
of
Extra Ocular Muscles
and
Its Applied Aspects

2. Extraocular musles(EOM)
They are six in number
Four recti:
 Superior rectus
 Inferior rectus
 Medial rectus
 Lateral rectus
Two oblique muscles:
 Superior oblique
 Inferior oblique

3. SUPERIOR RECTUS MUSCLE
.
Origin
Superior part of common annular tendon of Zinn
Course
Passes anterolaterally beneath the levator
At 23 degrees with the globe ‘s AP axis
Pierces Tenon s capsule
Insertion
into sclera by flat tendinous 10 mm broad insertion
7.7 mm behind sclero-corneal junction.
42 mm long
9 mm wide

4. Nerve supply
Sup division of 3rd N
Blood Supply
Lateral Muscular br. of Ophthalmic A
APPLIED:
SR loosely bound to LPS muscle.
• During SR resection- eyelid may be pulled forward  narr
owing palpebral fissure
• In hypotropia pseudoptosis may be present
Origin of SR and MR are closely attached to the dural sheat
h of the optic nerve
pain during upward & inward movements of the globe in
RETROBULBAR NEURITIS

5. RELATIONS
• SUP:Frontal nerve
• INF:Nasociliary nerve
ophthalmic artery
tendon of SO muscle
• LAT:Lacrimal A and Nerve
• MED:Ophthalmic A
Nasociliary N

6. Action
• Primary action - Elevation (Superior Insertion )
• Secondary action – Adduction (Lateral Insertion )
• Tertiary action - Intorsion(Oblique Insertion)

7. • In primary position ,SR muscle plane forms an angle of
23 degrees with the y-axis (the median plane of the eye)
and therefore does not coincide.
• Thus, in primary position,
SR not only elevates the globe but also adducts it and r
otates it around AP Y-axis, causing incycloduction

8. If the globe is abducted
its axis of rotation approaches the y-axis more and more
when it is abducted 23 degrees
Axis of rotation and Y axis coincide.
SR becomes a pure elevator ,no longer has a cycloducting component
The elevating action of SR maximal in abducted positions of the eye.
APPLIED:
SR- Only elevator in full abduction becau
se IO is ineffective .Thus when SR is paral
ysed , abducted eye cant be elevated

9. The opposite effect applies to incycloduction
The more the globe is adducted
the greater the incycloduction effect.
If the globe could be adducted 67 degrees
SR would produce pure incycloduction.
Since the globe cannot adduct that far, there is some elevating
component to the action of the SR, even in adduction.

10. INFERIOR RECTUS
Origin
Inferior part of common tendon of Annulus of zinn below
the optic foramen
Course
Passes anterolaterally along the floor of the orbit
At an angle of 23 degrees
Insertion
obliquely in the sclera 6.5 mm behind sclero corneal junction
by a 5.5mm long tendon
40 mm long
9 mm wide

11. Attached to lower lid by fascial sheath
.
Nerve supply
Inf. division 3rd N
Blood Supply
Med. muscular br. of Ophthalmic A
APPLIED:In Thyroid orbitopathy, MR and IR thicken. especially
near the orbital apex - compression of the optic nerve as it
enters the optic canal adjacent to the body of the sphenoid b
one.
APPLIED:
Alteration of IR – ass with palpebral fissure changes
IR Recession –widens palpebral fissure
IR Resection –narrows palpebral fissure

12. RELATIONS
• SUP:Optic N
Inf. Div of 3rd N
• INF: Floor of the orbit roofing the maxillary sinus
Orbital Palatine process
Infraorbital vessels and nerves
IO
• LAT:Nerve to IO

13. • Fascial attachments below attached to inferior lid coordinate
depression and lid opening.
• Actions
Primary depressor.
Subsidiary actions are adduction and extorsion.
Depression increases in abduction,becomes nil in full adduction.
Subsidiary actions increase with adduction

14. MEDIAL RECTUS
Origin-
• Widely attached medial and inf to optic foramen by common
tendon of annulus of zinn
• from optic nerve sheath
Course :Passes along medial wall of the orbit
Insertion-
in sclera 5.5mm behind sclero-corneal junction by a tendon
3.7 mm in length
40 mm long
Largest ocular muscle
Thicker than the others

15. • APPLIED:
 In Thyroid orbitopathy, MR and IR thicken;Visibility
of Muscle insertion through conjunctiva allows
swelling to be detected in Endocrine Exophthalmos
 Pain in Retrobulbar neuritis- Origin close to dural
sheath of Optic Nerve
 Medial rectus inserts closest to the limbus and is
therefore susceptible to injury during ant. segment
surgery.
 Inadvertent removal of the MR is a well known
complication of Pterygium removal

16. Nerve supply
lower division of 3rd N
the specific branch runs along the inside of the muscle cone on
the lateral surface.
Blood supply
Medial muscular branch of Ophthalmic A
Action
Primary adductor of the eye in Primary position
If axis elevated or depressed by other muscles , horizontal recti
no longer exert purely around vertical axis, also exerts
Slight elevator or depressor movements.
APPLIED :Such small movements
Significant when displacing insertions of
horizontal Recti for vertically incomitant
squint

17. RELATIONS
• SUP: Separated from SO by
Ophthalmic A
Ethmoidal N
Infratrochlear N
• INF: Floor of the orbit
• MED: Peripheral fat
Orbital plate of ethmoid
Ethmoidal sinuses
• LAT: Central orbital fat
Optic N

18. LATERAL RECTUS
Origin
Annular Tendon of zinn where it crosses Sup Orbital Fissure,cont
inuous with spina recti lateralis on greater wing of sphenoid
Course
At first adjoins lateral orbital wall separated by fat
More anteriorly , it passes medially and pierces tenon ‘s Capsule
Insertion
on the sclera 6.9mm behind sclerocorneal junction by a tendon
8.8 mm
Nerve supply
abducent nerve which enters the muscle on the medial surface.
Blood supply
Lateral muscular branch of Ophthalmic A
Lacrimal A
48 mm long
2/3rd CSA of MR

19. Relations
• SUP:
Lacrimal A and N
Anteriorly , lacrimal gland
• INF:
Floor of the orbit
IO Tendon
• MED:
6TH N
Ciliary Ganglion
Ophthalmic A
Nerve to IO
• LAT:
Post: periorbita
Ant:perimuscular fat
Lacrimal gland

20. Apex of Orbit
Oculomotor foramen

21. ACTION -
Primary abductor of eye.

22. INSERTION OF THE RECTI
Sclera is thinnest (0.3mm
) just posterior to 4 recti
muscle insertions
APPLIED:
Site for most procedures,
specially Recession Risk of Scleral perforation
Risk minimized by
• Spatulated needles
• Clean dry blood free field
• Loupe magnification
• Head mounted fibreoptic light

23. SPIRAL OF TILLAUX
5.5 mm
6.5 mm
6.9 mm
7.7 mm
Imaginary line joining the insertions of the 4 recti

24. SUPERIOR OBLIQUE
• Longest and thinnest EOM
Origin-
body of sphenoid above and medial to optic canal.
Attached superomedially to optic foramen by narrow te
ndon overlapping the levator
Course
Passes forwards b/w roof and medial wall of the orbit to
its trochlea or pulley

25. Relations
Becomes a rounded tendon 1 cm posterior to trochlea ,
turns posterolaterally at 55 degrees(Trochlear angle )
Pierces tenon‘s capsule, descends inf to SR
This is the only extraocular muscle with a rich vascular tunic.
Insertion-
Posterosuperior quadrant of sclera behind equator of eyeball.
Line of insertion :10.7 mm long
Nerve supply- trochlear nerve
Blood supply-
Sup. Muscular branch of Ophthalmic A

26. ACTIONS
 Primary action-intorsion.
 Subsidiary actions-abduction and depression.
 It is the only Adductor in depression.

27. • When the globe is adducted to 51 ͦ, the visual axis
• coincides with the line of pull of the muscle, the SO acts as
a depressor
• When the globe is abducted to 39 ͦ, the visual axis and the
SO make an angle of 90 ͦ, the SO causes only intorsion

28. INFERIOR OBLIQUE
Origin
Anteromedial part of orbital floor, from a small depression on
orbital plate of maxilla lateral to nasolacrimal groove.
Course
Inclined posterolaterally at an angle of 45 degrees with AP plane ,
almost parallel with tendon of SO
Insertion
posteroinferior surface of globe near the macula(2.2 mm from it)
oblique line of attachment 9.4mm long

29. Actions
• Primary action-extorsion
• Subsidiary actions-elevations and abduction.
• Only elevator in adducted position of eyeball
Nerve supply
inferior division of 3RD N
Blood Supply
Infraorbital and medial muscular br. of Ophthalmic A.
• .
APPLIED:
• Parasympathetic supply to Sphincter pupillae and ciliary
muscle accompanies N. to IO , pupillary abnormalities from
surgery in this area
• N. To IO enters lateral portion of muscle where the muscle
crosses IR- chance of damage in this area

30. Actions of EOM
ACTION PRIMARY SECONDARY TERTIARY
MR ADDUCTION ------ ---------
LR ABDUCTION ------ ---------
SR ELEVATION INTORSION ADDUCTION
IR DEPRESSION EXTORSION ADDUCTION
SO INTORSION DEPRESSION ABDUCTION
IO EXTORSION ELEVATION ABDUCTION

31. Anomalous EOM
Gracilis orbitis or comes obliqui superioris
• originates from the proximal dorsal surface of the SO and
inserts on the trochlea or its surrounding connective tissue.
• It is supplied by the trochlear nerve
Accessory lateral rectus muscle
• is a single slip . sometimes found in the monkey
• homologous to the nictating membrane.
• It is supplied by the abducent nerve

32. Two anomalous muscles may occasionally be associated with the
LPS. Both muscles are supplied by the superior division of the ocul
omotor nerve
Tensor trochleae
• arises from the medial border of the levator muscle
• inserts into the trochlea or its environs.
Transversus orbitus
attaches between the medial and lateral walls of the orbit, connec
ting with the levator muscle en route.

33. OPHTHALMIC
ARTERY
Medial
Muscular Artery
MR,IR,IO
Lateral
Muscular Artery
LR,SR,SO,LPS
BLOOD SUPPLY

34. • The arteries to the four rectus muscles give rise to the
anterior ciliary arteries.
• IO and IR also receive a branch from the infraorbital artery,
and the medial rectus muscle receives a branch from the lacr
imal artery.
• The veins from the extraocular muscles correspond to the ar
teries and empty into the superior and inferior orbital veins,
respectively.
APPLIED :
• Accident risk of severing of Vortex veins during IR and SR Rece
ssion or Resection , IO muscle weakening and SO muscle tendo
n exposure
• Blood supply to EOM supplies most of anterior segment ,Part
of nasal half supplied by Long Posterior ciliary artery…thus sim
ultaneous surgery on 3 recti induce Anterior
segment ischaemia

35. • The anterior ciliary arteries pass to the episclera, give branches
to the sclera, limbus, and conjunctiva, and pierce the sclera
not far from the corneoscleral limbus.
• These perforating branches cross the suprachoroidal space to
terminate in the anterior part of the ciliary body.
• Here they anastomose with the lateral and medial long ciliary
arteries to form the major arterial circle of the iris.
APPLIED :Variations in the number of anterior ciliary arteries
supplied by each muscle become clinically relevant with regar
d to the anterior segment blood supply when disinserting mo
re than two rectus muscle tendons during muscle surgery

36. Muscle Sheaths and Their Extensions
• EOM pierce Tenon’s capsule, enter the subcapsular space, and
insert into the sclera.
• In their extracapsular portions, muscles are enveloped by a
muscle sheath- reflection of Tenon’s capsule and runs
backward for 10 to 12 mm.
APPLIED :During Strabismus sx, Buckling for RD , Periocular t
rauma ,care must be taken to avoid penetration of Tenon ‘s
Capsule.
If integrity lost 10 mm posterior to limbus,
Fatty tissue prolapse forms restrictive adhesion
 limit ocular motility

37. • The muscle sheaths of 4 recti are connected by intermuscu
lar membrane, which closely relates these muscles to each
other .
• Numerous extensions from all the sheaths of EOM, form an
intricate system of fibrous attachments interconnecting the
muscles, attaching them to the orbit,supporting the globe,
and checking the ocular movements.

38. The fascial sheath of the SR muscle
closely adheres in its anterior external surface to the undersurface of
the sheath of LPS of upper lid
In front of the equator it also sends a separate extension obliquely for
ward that widens and ends on the lower surface of the levator muscle.
The fascial sheath of the IR muscle
divides anteriorly into two layers:
an upper one, which becomes part of Tenon’s capsule
a lower one, which is about 12 mm long and ends in the fibrous tissue
between the tarsus of the lower lid and the orbicularis muscle
This lower portion forms part of Lockwood’s ligament.
APPLIED :The fusion of SR and LPS accounts for the coop
eration of upper lid and globe in elevation of the eye, a
fact that must be kept in mind during surgical procedure
s on the superior rectus muscle

39. The fascial sheath of the reflected tendon of SO muscle
consists of two layers of strong connective tissue .
The two layers are 2 to 3 mm thick, so the tendon and its sheath ha
ve a diameter of about 5 to 6 mm.
Many attachments extend from the sheath of SO
to the sheath of the levator muscle
to the sheath of the SR muscle
to the conjoined sheath of these two muscles
to Tenon’s capsule, behind,above, and laterally.
Numerous fine fibrils that connect the inner surface of the sheath t
o the tendon
APPLIED :Potential space between the sheath and the te
ndon is continuous with the episcleral space.
Material injected into Tenon’s space therefore may pen
etrate into this space

40. The fascial sheath of the inferior oblique muscle
covers the entire muscle.
• It is rather thin at the origin but thickens as the muscle continues
laterally and develops into a rather dense membrane where it
passes under IR
• At this point, the sheath of the IO muscle fuses with the sheath of
IR muscle suspensory ligament of Lockwood .
• This fusion may be quite firm and complete or so loose that the tw
o muscles may be relatively independent of each other.
The extensions that go from there upward on each side to the sheaths
of the MR and LR muscles form a suspending hammock, which suppo
rts the eyeball
Includes extensions of fibrous bands to the tarsal plate of the lower lid
, the orbital septum, and the periosteum of the floor of the orbit.
Near the insertion of the muscle the sheath of the inferior oblique m
uscle also sends extensions to the sheath of LR muscle and to the shea
th of the optic nerve.

41. Fascial expansions of Extraocular muscles

42. Check Ligaments
• well-developed fibrous membranes
• extend from the outer aspect of the muscles to the correspon
ding orbital wall
The check ligament of LR
 appears in horizontal sections as a triangle
 apex is at the point where muscle sheath pierces Tenon’s ca
psule.
 goes forward and slightly laterally
 fans out to attach to the zygomatic tubercle, the posterior as
pect of the lateral palpebral ligament, and the lateral conjunc
tival fornix.

43. The check ligament of the MR
 extends from the sheath of the muscle
 attaches to the lacrimal bone behind the posterior la
crimal crest and to the orbital septum behind.
 triangular and unites at its superior border with
a strong extension from the sheath of LPS
a weaker extension from the sheath of SR
 Inf border is fused to extensions from the IO and IR
muscle sheaths.
The other EOM do not have clearly distinct check ligam
ents

44. Intracapsular Portion of the Muscle
• The muscles move freely through the openings in Tenon’s capsule
• In the intracapsular portion, they have no sheath but are covered
by episcleral tissue fused with the perimysium.
• This tissue expands laterally, going along the muscle on each side
, from the entry of the muscle into the subcapsular space to the
insertion.
• Posteriorly,this tissue attaches to the capsule and laterally to the
sclera.
• At the tendon this tissue becomes rather dense and appears to s
erve to fixate the tendon, forming the falciform folds of Gue´rin
or adminicula of Merkel.
• Merkel and Kallius remarked that these structures make it difficul
t to determine accurately the width of the insertions.

45. Thus, the position of the center of rotation of the eyeball remains f
airly constant in relation to the orbital pyramid
Due to the action of the check ligaments, the eye movements beco
me smooth and dampened.
As the muscles contract, their action is graduated by the elasticity
of their check systems, which limits the action of the contracting m
uscle and reduces the effect of relaxation of the opposing muscles
This ensures smooth rotations and lessens the shaking up of the co
ntents of the globe when the eyes suddenly stop or change the dire
ction of their movement.
Functional Role of the Fascial System
• Serve as a cavity within which the eyeball may move
• Connect the globe with the orbit
• Supporting and protecting the globe
• In the control of the eye movements.
• It prevents or reduces retractions of the globe, as well as movements in t
he direction of action of the muscle pull.

46. Developmental Anomalies of Extraocular Muscles and the Fascial
System
• Patients with congenital absence of a muscle present with th
e clinical picture of complete paralysis
There may be no preoperative clues to alert the surgeon that th
e apparently paralyzed muscle is absent. Consequently, the surg
eon must be prepared to use alternative surgical approaches if a
muscle cannot be located at the time of the operation.
Anomalies of the fascial system
• more common
• act as a check to active and passive movements of the globe i
n certain directions, although the muscles that should produc
e the active movement may be quite normal anatomically an
d functionally.
• various forms of strabismus fixus and the SO tendon sheath
Syndrome of Brown

47. • The primary position is assumed by the eye in binocular
vision
 when one is looking straight ahead
 with body and head erect
 object of regard is at infinity
 lies at intersection of sagittal plane of head and horizontal
plane passing through centres of rotation of 2 eyeballs
• The adducted, abducted, elevated, or depressed position
s of the globe are designated as secondary positions.
• The oblique positions of the eye are termed tertiary posi
tions

48. Diagnostic positions of gaze:-9
 1 Primary position of gaze:-assumed by eyes when fixating
a distant object with head erect.
 4 secondary
1. Up
2. Down
3. Right
4. Left
 4 tertiary positions
1. Dextroelevation
2. Dextrodepression
3. Levoelevation
4. Levodepression

49.  6 cardinal positions :- to test 12 EOM in their main fiel
d of action
1. Dextroversion
2. Laevo version
3. Dextro elevation
4. Leavo elevation
5. Dextro depression
6. Laevo depression

50. Centre of Rotation
• The eye performs rotary movements around a center of
rotation within the globe
• Centre of rotation moves in a semicircle in the plane of
rotation- Space centroid
• In primary position the center of rotation is located 13.5
mm behind the apex on the cornea on the line of sight
1.3 mm behind the equatorial plane
(in myopes--- posterior -14.5 mm
In hyperopes --anterior )
• For practical purposes, one may assume that a line
connecting the middle of the lateral orbital margins
goes through the center of rotation of the two eyes if
they are emmetropic

51. Action of an individual muscle is controlled by the dire
ction of its pull to 3 axes around which the globe rota
tes.
• Ocular movements take place round a centre correspondin
g approximately to that of the eye, which is therefore not s
ignificantly displaced.
• The movements defined relative to 3 primary axes which p
ass through the centre of movement at right-angles to eac

52. Elevation & Depression – Around the transverse axis (X)
nasal -> temporal
Adduction & Abduction – Around the vertical axis (Z)
superior -> inferior
Intortion & Extortion – Around the AP axis (Y)
anterior -> posterior
FICK’S AXES
These axes intersect at the center of rotation - a fixed
point, defined as 13.5 mm behind cornea.

53. Basic Kinematics
Translatory movements
• The body can move sideways, up or down, and forward
or backward
• the center of the body moves with it
Rotary movements
• it can rotate around a vertical, horizontal, or anteropost
erior axis
• the center would not shift its position
• it would have zero velocity.

54. • The posterior pole of the eye moves in an opposite di
rection, except in torsional movements.
• Despite their formalized terms, all movements are rota
tions, and are not necessarily confined to the above ar
bitrary axes, the movements of which are sometimes c
alled cardinal.
• Because of the geometric relations between the orbita
l and global attachments of each muscle, each acts to g
reatest effect in one plane, and this is known as its pri
mary action.

55. The point at which the center of the muscle or of its tendon first
touches the globe is the tangential point.
indicates the direction of pull of that muscle.
The position of this point changes when the muscle contracts or
relaxes and the globe rotates
•

56. • The arc of contact is the arc formed between the tangenti
al point and the center of the insertion of the muscle on t
he sclera.
• Since the position of the tangential point is variable, the a
rc of contact changes in length as the muscle contracts.
• It is longest when the muscle is relaxed and its antagonist
contracted and shortest when the muscle is contracted an
d its antagonist relaxed.
•

57. • The muscle plane is determined by the tangent to the globe at the
tangential point and the center of rotation.
• It is the plane determined by the centers of origin and insertion an
d the center of rotation
• The muscle plane describes the direction of pull of the muscle an
d determines the axis around which the eye would rotate if the pa
rticular individual muscle were to make an isolated contraction
• Axis of rotation, which is perpendicular to the muscle plane erect
ed in the center of rotation, corresponds to each muscle plane.

58. Factors involved in mechanics of EOM action
1.Cross sectional area of the muscle
Muscles exert force in proportion to their crosssectional a
rea
2.Length of the muscle
For normal amplitude of rotation 45-50 degres  10mm ch
ange in muscle length is required in each direction
APPLIED :Antagonists such as medial and lateral recti are similar in siz
e –balancing opposing forces
APPLIED : Sacrifice of muscle length during resections reduces the am
plitude of eye rotations

59. 3. The arc of contact
Distance between the anatomic and physiologic insertion
The power of the muscle is proportionate to its length and arc
of contact,
APPLIED :Recession weakens muscle action by shortening its effective
length and its arc of contact in various positions of gaze
Advancement of EOM has strengthening effect because ef increase in
effective length as well as arc of contact

60. Types of Eye Movements
1. Uniocular Eye Movements
 Ductions
2.Binocular Eye Movements
 Version: (Binocular Conjugate Eye Movements)
 Vergence: (Binocular Disjugate eye movements)

61. Uniocular movements
 Ductions – only one eye is open, the other covered/closed te
sted by asking the patient to follow a target in each direction
of gaze.
 Types of ductions:-

62. Binocular movements
 Versions:-
 Binocular ,simultaneous, conjugate movements in same direct
ion.
 both eyes open, attempting to fixate a target &moving in sam
e direction.
 Abduction of one eye accompanied by adduction of other eye
is called conjugate movements.

63. Types of versions:-
Dextroversion & laevo version
Elevation & depression
Dextro elevation & dextro depression
Laevo elevation & laevo depression

64. • Vergences:
• binocular,simultaneous,disjugate/disjunctive movements (o
pp.direction)
 Convergence– simultaneous adduction
 Divergence– outward movement from convergent position

65. Agonist,Antagonist,synergists and yoke mu
scles
• Agonist :a muscle producing movement on contraction
• Antagonist muscles : A muscle producing a movement in the
direction opposite produced by agonist.
EG -sup.&inf. Recti ,sup.&inf.oblique
• Synergists muscles :Two muscles moving an eye in the same
direction are synergists.
 Ex:-sup.rectus & inf.oblique----elevators
inf.rectus&sup.oblique-----depressors
• Yoke muscles :Muscles that cause the two eyes move in sam
e direction

66. Yoke muscle(contralateral
synergists)
 Ref. to muscles which are
primary muscles (one from
each eye) that accomplish
(contract) a given version.

67. Laws of ocular motility
1.Hering’s law of equal innervation
During any conjugate movement equal & simultaneous inner
vation flows to yoke muscles to contract or relax
• For movements of both eyes in the same direction, the cor
responding agonist muscles receive equal innervation
 Isolated innervations to an extraocular muscle of the e
ye do not occur nor can the muscles from the one eye a
lone innervated ,
to perform an eye movement, impulses are always
integrated.

68. Clinical application of Herings’
law

69. APPLIED:
• In patient with paralytic squint,
Secondary Deviation > primary deviation
Primary dev- deviation of squinting eye, when patient fixates
with normal eye
Sec dev- deviation of normal eye under cover, when patient fix
ates with squinting eye
Excess innervation is required to the paralysed muscle to fixat
e, when patient fixates with squinting eye
Concomitant excess supply to yoke muscle causes excess contr
action leads to more secondary deviation

70. APPLIED:
Inhibitional palsy of contralateral antagonist muscle in pa
ralytic squint is also based on Hering’s law
Eg – In RSO paresis,
fixating with Right eye on an object located up and to the
left
Less innervation of its antagonist RIO is required less i
nnervation of LSR
Inhibitional Palsy of the
antagonist of the yoke muscle of paretic muscle
LSR LIR RSO

71. 2. Sherrington law of reciprocal
innervation
 Increased innervation to an EOM is accompanied by r
eciprocal decrease in innervation to its antagonist.
 The antagonist relaxes as the agonist contracts

72. Clinical application of Sherringto
n's law

73. APPLIED:
• Occurrence of strabismus following paralysis of EOM is e
xplained by the law
• Reciprocal innervation must be kept in mind while perfo
rming surgery of extraocular muscles
• Exceptions
• Duane’s retraction syndrome co-contraction of
antagonistic muscles instead of relaxation antagonist
muscle occurs. In duane s , it limits the amount of movem
ent achievable

74.  During fixation, saccades and smooth pursuit the eye rotates
freely in horizontal and vertical dimensions but torsion is cons
trained. This restriction on ocular torsion is described by dond
er’s law and listing’s law.
3.Donder’s law
 Donder stated that each position of line of sight belongs to t
he definite orientation of vertical and horizontal retinal meri
dian relative to the coordinate of the space.
 Orientation of retinal meridian is always same irrespective ir
respective of the path the eye has taken to reach that positio
n and depends upon the amount of elevation or depression
and lateral rotation of the globe, after returning to the initial
position the retinal meridian is oriented exactly as it was bef
ore the movement was initiated

75. 4.LISTING’S LAW
 Listing ‘s law states that each movement of the eye fro
m the primary position to any other position involves a
rotation around a single axis lying in the equatorial plan
e ,also called as listing’s plane.
 This plane was defined earlier as being fixed in the orb
it and passing center of rotation of the eye and its equa
tor, when the eye is primary position
 Any position of the eye can described by specifying the
orientation of the axis of rotation in listing’s plane and
magnitude of rotation from primary position

76. • Listing’s law implies that all eye movements from prima
ry position are true to the meridians and occurs withou
t torsion with respect to the primary position.
• This law is obviously true for movements around horizo
ntal and vertical axes in the equatorial plane.
• Listing’s law holds during fixation, saccades, smooth pur
suit but not during sleep .

77. Extraocular muscles structure
• EOM consists of cross striated fibres.
• They show a high degree of differentiation
• Perform functions of both white and red muscles.
• The motor units are small, with only from 5 to 18
muscle fibers contact by each motor nerve
Differ from other skeletal muscles in terms of
 Diameter of these fibres is small
 Richly supplied by nerves and vessels
 Contains enormous amount of fibroelastic tissue
 Contain both slow and fast fibres
 Require and receive more O2

78. Each muscle is made up of large no: of muscle fibres.
• Each muscle fibre is a long cylindrical multinucleated cell , s
urrounded by a cell membrane –Sarcolemma
Sarcotubular system –Sarcolemma+Sarcoplasm
Each fibre has a diameter of 5-40 um (c/f 10-100 um in sk
eletal muscles.
punctiform appearance in transverse section and a striate
d appearance in longitudinal section.

79. • Vessels and nerves enter each muscle belly at its hilum.
• The blood supply of the recti is greater than that of the
myocardium, primarily due to richness of the closed type
capillary network in the orbital layer.
• This blood supply is required by the larger numbers of fa
st twitch fibres in the orbital layer, which have a highly a
erobic metabolism.
• Blood flow is thought to be highest in the MR, although
that in SR may be higher

80. Each myofibril consists of linearly arranged thick and thin myofil
aments, which form the chief element of fibre's repeating unit,
the sarcomere
THICK- Myosin
THIN- Actin. Tropomyosin, Troponin T, I , C
• Between myofibrils are two membranous systems involved i
n excitation and contraction :
the transverse tubular system and the sarcoplasmic reticulum

81. Excitation Contraction Coupling

82. Rapid 'twitch' fibres
 Fibres of larger diameter
 With a 'fibrillenstruktur' having a regular distribution of myofi
brils and abundant sarcoplasm.
 Innervation is by single, 'en plaque' endings (i.e.motor end pla
tes) These fibres resemble somatic striated fibres elsewhere
 Two types of striated twitch fibres are described
Slow or 'tonic' fibres
 so-called 'felderstruktur‘ ill-defined and myofibrillar arrangem
ents and little sarcoplasm.
 Their respiratory metabolism is chiefly aerobic
 innervated by diffuse ('en grappe') myoneural endings.
• Mitochondria are in general fewer in skeletal than in extraocu
lar muscle fibres .Although fibres are smaller in the orbital zo
nes than in global zones, both contain mixtures in size of fibre
.

83. •
Type I muscle fibres
'slow twitch‘
'slow, oxidative and fatigue resistant'
stain weakly for myosin ATPase at pH 9.4 but strongly at acid pH
strongly for oxidative enzymes but weakly for glycolytic enzymes.
'
Type II muscle fibres
'fast twitch'
stain strongly for ATPasc at pH 9.4.
 IIA fibres
stain poorlv on preincubation at pH 4.6 and pH 4.3
oxidative and glycolytic features
resistant to fatigue on repeated stimulation
 IIB fibres
stain poorly at only pH 4.3.
glycolytic features
are fatiguable
 IIC fibres
found chiefly in infancy and differs from that shown in adult muscle.

84. The extraocular muscles possess a resident population of imm
unocompetent cells including numerous macrophages and a s
maller number of HLA-DR positive cells and T cells; B cells are a
bsent.
 The majority of the T cells are CD8 (suppressor/cytotoxic) p
ositive, whereas in skeletal muscle, CD4-positive (helper) ce
lls predominate
 The medial and inferior recti contain about twice as many
macrophages as the lateral rectus and superior oblique mus
cles.
APPLIED :Of importance in certain orbital immune disorders such
as endocrine ophthalmopathy.

85. ORBITAL AND GLOBAL ZONES
• at birth fibre size -generally uniform
• later an outer shell of smaller-diameter fibres is distinguished from a
core of larger fibres
• this pattern is retained into adult life
• These zones are referred to as
 orbital (outer; facing the orbit)
 global (inner; facing the globe and contents of the muscle cone)
• Orbital fibre diameter - 5 and 15 IJ.m,
global fibres diameter - 10 and 40 IJ.m.
• The global layer of SO is totally enclosed by the orbital layer,
• In the recti orbital zones are deficient on their internal surfaces, so th
at the global layer is exposed to adjacent adipose tissue around the o
ptic nerve at a 'hilum'.
• The recti are strap-like, with maximum width at their global insertion
• the global fibres are longer than the orbital and only the global tonic
fibres appear to run the full length of the muscle belly which maximi
zes the possible change in length of the muscle in contraction, and co

86. Types of eom
Spencer and Porter nomenclature
• Type 1: Orbital singly innervated
• Type 1 fibres small and make up 80% of the orbital layer
• accounts for most of the sustained force generated by the mu
scle.
• Mitochondria occur in abundant clusters
• Individual fibres are ringed by capillaries and motor endplates
• Abundant and well-delineated SR and T-system and a regular
myofibrillar arrangement.
• They correspond to skeletal type II differs from skeletal IIA by i
ts high fatigue resistance and unique myosin profile.
• coarse, fast twitch fibres
• rich in oxidative enzymes (e.g. SOH) but also capable of anaer
obic metabolism.
• singly innervated

87. Type 2: Orbital multiply innervated fibres
a slow fibre comprising 20% of the orbital zone.
• It stains strongly for myosin ATPase after acid preincuba
tion, but variably with alkaline ATPase
• associated with a structural variation along their length
• The staining properties not uniform along the length of
the muscle fibre; thus acid-stable myosin ATPase is foun
d only in the proximal and distal thirds of the fibre.
• moderate oxidative activity.
• has sparse membranous systems and an irregular myofi
brillar arrangement by electron microscopy.

88. • Although they are multiply innervated, they show a twitch ca
pability near their centre and a slow contractility proximally a
nd distally
• Centrally the fibres resemble skeletal fast twitch fibres (IIC) (
but with a lower oxidative capacity),
• At either end they show the ultrastructural features and slow
ATPase of slow contracting fibres and contain embryonidneo
natal myosin.

89. Type 3: Global red singly innervated
• This makes up 30% of the global layer.
• It stains coarsely
• resembles the orbital singly innervated fibre.
• It is highly oxidative and glycolytic
• regarded as fast-twitch and fatigue-resistant fibre.
• does not show longitudinal structural variation
• Contains no coexpressed fast or embryonidneonatal
myosins
• fibre does express myosin IIA isoform along its length,
but differs from skeletal IIA by its high mitochondrial c
ontent.

90. Type 4: Global intermediate singly innervated
• This fibre makes up 25% of the global layer.
• Ultrastructure and ATPase content suggest that it is a fa
st-twitch fibre and myosin reactivity suggests a resembl
ance to skeletal type IIB
• fibre is granular and there are moderate levels of oxidat
ive and aerobic enzymes.
• There are numerous small mitochondria, singly or in clu
sters.
• Myofibril size and sarcoplasmic reticulum content are in
termediate between that of the other 2 singly innervat
ed fibres.

91. • Type 5: Global pale singly innervated
• This fibre comprises 30% of the global layer.
• a fast twitch fibre used infrequently because of low fatigu
e resistance.
• It resembles type lIB skeletal
• Mitochondria are small and few and arranged singly betw
een myofibrils.
• Fibre diameter increases from types 3 to 5.
• All show a regular myofibrillar arrangement on electron
microscopy with well-developed sarcoplasmic reticulum a
nd T systems in types 3 and 4 and slightly less so in type 5
• They are singly innervated.

92. Type 6: Global multiply innervated fibres
• makes up 10% of the global layer
• a slow fibre with strong acid-stable ATPase features
and weak oxidative properties.
• Ultrastructurally, it shows a felderstruktur with very
large myofibrils, sparse membranous systems and
occasional mitochondria in single file.
• multiply innervated, with numerous en-grappe endi
ngs along its length.

93. Embryological development
• All EOM develop from 3 distinct masses of Primordial c
ranial mesoderm
• 3 masses correspond to Rhombomeres and 3 cranial ne
rves innervate them accordingly
• Premandibular condensation gives rise to eye musces
innervated by 3rd N ( SR, MR, IR, IO)
• LR and SO arises from its own adjacent tissue mass in
Maxillomandibular mesoderm

94. • LR and SO lie as B/l masses close to stalk at 13.5 mm s
tage(6 weeks )
• 4 Recti differentiate at 20 mm stage ( 7 weeks )
• LPS differentiates from SR in its medial part at 8 weeks
• Later it grows laterally on a higher plane than SR at 3
months.
• Critical development occurs at 6-8 weeks ( maybe upt
o 12 weeks
APPLIED :Close proximity of analgens may facilitate development of ano
malous innervation of eye muscles
DUANES RETRACTION SYNDROME
Congenital absence of 6th N
Abnormal innervation of Lateral Rectus by 3rd N

95. • Eom develop in at least 2 waves of Myogenesis, formin
g primary and secondary generation fibres.
• Global multiply innervated fibres are phylogenetically ol
d and formed first while orbital layers mature last.
• EOM Pulleys –
 sleeves of Collagen, elastin , smooth muscle
 encircle EOM and are attached to orbital wall and adjacent c
onnective tissues
 Muscle with sheath passes through these pulleys
 Located near the equator of globe
 Seem to deflect anterior part of the muscle in gazes other th
an primary gaze
 Act as functional origin
APPLIED:
APPLIED :in abnormal situations, pulleys may be heterotropic , may cause
ocular motility problems

96. References
• Wolff’s anatomy of eye -8th e
• Clinical Anatomy of the eye –SNELL
• Von Noorden, A. Edward
• A.k.Khurana Anatomy and physiolog
y of the eye- 5th e
• Strabismus by Pradeep Sharma

97. THANK YOU