Lecture: Action of Extraocular Muscles and Various Laws Involved

1. Action of Extraocular Muscles
and Various Laws Involved
Mohammad Arman Bin Aziz
Instructor Optometrist cum Faculty
Institute of Community Ophthalmology

2. Presentation layout
 Gross anatomy of EOM : Origin, Nerve and Blood
supply.
 Actions of EOM : Basic kinematics, Mechanics.
 Ocular movements.
 Fundamental Laws governing Ocular Motility
and Clinical Significances.

3. Extraocular Muscles (EOMs)
 Each eye – 6 (+1*) EOMs
 2 Horizontal Recti.
 2 Vertical Recti.
 2 Obliques.
 *1 Levator Palpebrae
Superioris (LPS).
 LPS lifts the upper eyelid.
 Rest of the muscles rotate
the eyeball.

4. Rectus Muscles
 4 in no.
 Vertical rectus
 Superior rectus
 Inferior rectus
 Horizontal rectus
 Medial rectus
 Lateral rectus
 Origin
 Common tendinous
ring: “annulus tendinous
communis”, the
annulus of Zinn
 SR and MR closely
attached to the dural
sheath of the optic
nerve at their origin

5. Oblique Muscles
 Superior Oblique Muscle
 Origin : from the bone, body of sphenoid
 But from physiological point, the origin is the trochlea
 Longest and thinnest of all EOM

6. Inferior ObliqueMuscle
 Origin
 From a shallow depression on the orbital plate of maxilla, lateral to
orifice of nasolacrimal duct
 Some fibres arise from lacrimal fascia
 Only muscle originating from front of the orbit
 Shortest EOM

7. Nerve supply to EOM
 EOMs supplied by: Cranial nerves III, IV and
VI
 Cranial nerve III (Oculomotor)
 Branches from the inferior division supplies medial, inferior
recti and inferior oblique muscles
 Branches from upper division supplies superior rectus

8. Nerve supply cont….
 Cranial nerve IV (Trochlear)
 Supplies Superior Oblique muscle
 Cranial Nerve VI ( Abducent)
 Innervates the Lateral Rectus Muscle

9. Nerve supply contd..

10. Blood supply
 Muscular artey, branch of
ophthalmic artery, branches
into lateral and medial
branches.
 Medial muscular branches
supply MR, IR, & IO muscles.
 Lateral muscular branches
supply the LR, SR, SO & LPS.
 MR also receives a branch
from the lacrimal artery.
 IR & IO muscles receive a
branch from the infraorbital
artery.

11.  Anterior ciliary arteries arises from muscular branches : a pair
from each recti except LR from which only a branch arises
 Veins from EOMs follow arterial pattern and
drain into the superior and inferior veins
respectively.

12. Physiology of ocular motility
basic EOMs’ kinematics
 Diagnostic position of
gazes
 A primary gaze
 4 secondary gazes
 4 tertiary gazes

13. Cardinal position of gaze
Allow the examination of each extra-ocular muscles separately.

14. Centre of rotation
 Hypothetical point around
which the eyeball performs
rotatory movements
 Does not have a zero
velocity
 Moves in semicircle plane
of rotation called Space
centroid
 In primary position lies
some 13.5 cm behind the
apex of cornea

15. Fick’s Axes and Listing’s Plane
 Fick’s axes: 3 axes to analyse the movements of
globe around the hypothetical centre of
rotation
 X Axis (Horizontal)
 When head is held upright, lies horizontal
 Rotation around this axis results in : Elevation and
Depression
 Y Axis (Anteroposterior)
 Rotation around this axis produces torsional
movements : Extortion and Intortion

16.  Z axis (Vertical)
 Rotation around this axis causes : Adduction and
Abduction
 Listng’s Plane
 The plane containing the X and Y axes and
passing through the centre of rotaion of the eye

18. Basic Concept of Action of
Extraocular Muscles
 The actions of extraocular muscles depend upon
the position of the globe at the time of muscle
contraction.
 The primary action of a muscle is at its major
effect when the eye is in primary position.
 The additional effects are subsidiary, secondary
or tertiary action.

19. Action of Horizontal Recti
 The horizontal recti muscles, lateral and medial
rectus, have a common muscle plane, horizontal in
primary position and their axis of rotaion coincides
with Z axis
 Thus, in primary position of eyes, contraction of a
horizontal rectus causes purely horizontal rotation
around Z axis
 They have only primary action
 Lateral rectus : Abduction
 Medial Rectus : Adduction

20. Muscle action of Horizontal Recti

21. Action of Vertical Recti
 The vertical recti have a common muscle plane
which is in the same line as the orbital axis and
thus form an angle of 23˚ with the Y-axis
 In primary position, action of Superior Rectus
 Primary action: Elevation
 Secondary action : Intortion
 Tertiary action : Adduction

22.  When globe is abducted 23˚, the only action : Elevation
 When adducted 67˚, only action : Incyclotortion

23. Muscle action of superior rectus

24. Inferior Rectus
 Analogous to Superior rectus
 In primary position,
 Primary action : Depression
 Secondary action: Extortion
 Tertiary action : Adduction
 When globe is abducted 23˚, action : Depression
 When globe adducted 67˚, action: Extortion

25. Action of Superior Oblique
 Forms an angle of 54˚ with the optical axis
 In primary position,
 Primary action : Intortion
 Secondary action: Depression
 Tertiary action: Abduction
 When globe is adducted 54˚,action : Depression
 When globe is abducted 36˚,action: Intortion

26. Action of SO in adduction and abduction

27. Action of Inferior Oblique
 Forms an angle of 51˚ with the optical axis
 In primary position,
 Primary action : Extortion
 Secondary action: Elevation
 Tertiary action: Abduction
 When globe is adducted 51˚, action : Elevation
 When globe is abducted 39˚, action: Extortion

28. Muscle action of inferior oblique

29. Muscle Primary secondary tertiary
MR Adduction ----- -----
LR Abduction ----- -----
SR Elevation Intortion Adduction
IR Depression Extortion Adduction
SO Intortion Depression Abduction
IO Extortion Elevation Abduction
Muscle actions

30. EOM Action
Fig: Marquez diagram

31. Tips to remember
 All obliques - Abductor
 All recti - Adductor
(except lateral rectus)
 All superior muscles - Intortor
 All inferior muscles - Extortor

32. Few Terms
 AGONISTS
 Any particular extraocular muscle producing a
specific ocular movement
 Eg. Right lateral rectus : Abduction of Right Eye
 SYNERGISTS
 Two muscles of the same eye which move the eye in
same direction
 Eg. Right Superior Rectus and Right Inferior oblique :
Elevation of Right Eye

33.  ANTAGONISTS
 Muscles from the same eye which have opposite
action in that eye
 Eg. Right Medial rectus and Right Lateral Rectus
 Right Superior Rectus and Right Inferior oblique in
respect to torsional movement

34.  YOKE MUSCLES (CONTRALATERAL SYNERGISTS)
 A pair of muscle one from each eye, which contract
simultaneously during version movement
 Eg. Right Lateral Rectus and Left Medial Rectus :
Dextroversion
 CONTRALATERAL ANTAGONISTS
 A pair of muscle one from each eye having opposite
action
 Eg. Right Lateral Rectus and Left Lateral Rectus

35. Agonist Synergist Antagonist
Medial Rectus Superior Rectus
Inferior Rectus
Lateral Rectus
Superior Oblique
Inferior Oblique
Lateral Rectus Superior Oblique
Inferior Oblique
Medial Rectus
Superior Rectus
Inferior Rectus
Superior Rectus Inferior Oblique
Medial Rectus
Inferior Rectus
Superior Oblique
Inferior Rectus Superior Oblique
Medial Rectus
Superior Rectus
Superior Oblique
Superior Oblique Inferior Rectus
Lateral Rectus
Superior Rectus
Inferior Oblique
Inferior Oblique Superior Rectus
Lateral Rectus
Superior Oblique
Inferior Rectus

36. Cardinal Direction of Gaze Yoke muscle pair
Dextroversion Rt. LR
Lt.MR
Levoversion Lt. LR
Rt. MR
Dextroelevation Rt. SR
Lt. IO
Levoelevation Lt. SR
Rt. IO
Dextrodepression Rt. IR
Lt. SO
Levodepression Lt. IR
Rt. SO

37. Fundamental Laws governing Ocular Motility
 DONDER’S LAW
 To each positon of line of sight belongs a definite orientation
of the vertical and horizontal retinal meridians relative to the
coordinates of space.
 Orientation depends solely on amount of elevation or
depression and lateral rotation of the globe.
 The orientation of the retinal meridians pertaining to a
particular position of globe is achieved irrespective of the
path the eye has taken to reach that position.
 In short, it implies that there is one and only one orientation
of the retinal meridians with each position of the eyes.

38.  LISTING’S LAW
 Every eye movement from the primary into tertiary
position can be described as a rotation around one
axis, which would be perpendicular to the plane that
contains the line of sight in the primary position ad
the line of sight in the tertiary position into which
the eye has moved.
 The axis is known as Listing’s plane.
 This law implies that all eye movements from
primary position are true to meridians and can occur
without torsion or cyclotorsion with respect to
primary position.

39. Hering’s Law of Equal Innervation
 Also known as Hering’s law of motor
correspondence
 States ‘ equal and simultanous innervation flows
from the brain to a pair of muscles of both eyes
(yoke muscles) which contract simultaneously in
different binocular movements.’
 Eg:
 Right Lateral Rectus and Left Medial rectus:
Dextroversion
 Both Medial Rectus : Convergence
 Right Inferior Rectus and Left Superior Oblique:
Dextrodepression

40. Hering’s law

41. Contd..
 Major physiologic principle involved in the
binocular motor co-operation of the eyes
 Applicable to all normal ocular movements
including vergence and involuntar movemens
 Exception:
 Assymmetric convergence

42. Clinical Applications
 In Paralytic Strabismus
 Secondary Deviation >> Primary Deviation
 Deviation of the normal eye under cover when
patient fixates with the squinting eye is more than
deviation of the squint eye when patient fixates
with normal eye.
 Inhibitional Palsy of Contralateral antagonist
 When right lateral rectus is paralysed, then left
lateral rectus is also paralysed.

43. Sherrington’s Law of Reciprocal
Innervation
 ‘During ocular motility, an increased flow of
innervation to the contracting agonist muscle is
accompanied by a decreased flow of innervation to
the relaxing antagonist muscle’.
 Implies that the state of tension in the agonist
exerts a regulatory influence on the state of tension
in the antagonist and vice versa.
 Eg. During Dextroversion,
 Increased innervation – Right LR and Left MR
 Decreased innervation – Left LR and Right MR

44. Sherrington’s law

45. Clinical Significance
 Occurence of stabismus following paralysis of
an extraocular muscle
 Reciprocal innervation should be considered
while performing surgery of extraocular
muscle
 EXCEPTION TO SHERRINGTON’S LAW
 Duane’s Retraction Syndrome

46. References
 Anatomy and Physiology of Eye
 A. K. Khurana
 Binocular Vision and Ocular Motility
 Gunter K. von Noorden
 Adler’s physiology of eye
 Lecture notes