Motor physiology of extraocular muscles. 1) The document discusses the basic anatomy and physiology of the extraocular muscles, including definitions of eye movements, the actions of individual muscles, and laws governing ocular motility. 2) Key points covered include the center of rotation of the eye, cardinal movements like adduction and elevation, and terms like tangential point and muscle plane. 3) Laws of ocular motility such as Listing's law, Sherrington's law of reciprocal innervation, and Hering's law of equal innervation are explained in relation to eye muscle function. 4) Clinical testing for muscle weakness and restriction through passive duction is described.

1. Motor physiology of
extraocular
muscles.
Tukezban Huseynova, MD
Specialist in Strabismus and Refractive Cornea,
Briz-L Eye Clinic, Baku, Azerbaijan
Tukezban@gmail.com

2. Introduction
 A common coordinate system for translation and
rotation of the eye.

3. Basic Kinematics

4. Center of Rotation
In primary position the center of rotation is located about13.5 mm (in myopes,
14.5 mm) behind the apex of the cornea on the line of sight, which places it 1.3
mm behind the equatorial plane.

5. Definitions of Terms and Action of
Individual Muscles
Cardinal movements of the eye.
Duction movements - The rotations of the single eye are termed.
Adduction - Rotations around the vertical axis (horizontal excursions of
the globe), movement nasalward .
Abduction - Rotations around the vertical axis, movement templeward.
Elevation or sursumduction - Rotations around the horizontal axis
(vertical excursions of the globe), movement upward.
Depression or deorsumduction - Rotations around the horizontal
axis movement downward.

6. Definitions of Terms and Action of
Individual Muscles
 Ductions. Secondary positions, right eye. A, Adduction. B,
Abduction. C, Sursumduction (elevation). D, Deorsumduction
(depression).

7. Definitions of Terms and Action of
Individual Muscles
Cycloductions - Rotations around the anteroposterior
axis of the globe, known as, rotate the upper pole of the
cornea templeward (excycloduction) or nasalward
(incycloduction).
Ductions. Secondary positions, right eye. A, Adduction. B, Abduction.
C, Sursumduction (elevation). D, Deorsumduction (depression).

8. Definitions of Terms and Action of
Individual Muscles
Positions of the globe
Primary position is assumed by the eye when one is lookin straight ahead
with body and head erect.
Secondary positions is the adducted, abducted, elevated, or
depressed positions of the globe.
Tertiary positions is the oblique positions of the eye.

9. Definitions of Terms and Action of
Individual Muscles
 Some tertiary positions, right eye. A, Gaze up and right. B,
Gaze up and left. C, Gazedown and right. D, Gaze down and left.

10. Definitions of Terms and Action of
Individual Muscles
Terms related to the mechanism of muscles.
Tangential point is a point at which the center of the muscle or
of its tendon first touches the globe.
The arc of contact is the arc formed between the tangential
point and the center of the insertion of the muscle on the
sclera.
The muscle plane is determined by the tangent to the globe at
the tangential point and the center of rotation.

11. Definitions of Terms and Action of
Individual Muscles
 Schematic presentation of muscle plane, medial rectus, axis
of rotation, tangential point, and arc of contact.

12. Definitions of Terms and Action of
Individual Muscles
Muscle Primary Secondary Tertiary
Medial rectus Adduction — —
Lateral rectus Abduction — —
Inferior rectus Depression Excycloduction Adduction
Superior rectus Elevation Incycloduction Adduction
Inferior oblique Excycloduction Elevation Abduction
Superior oblique Incycloduction Depression Abduction
Action of the Extraocular Muscles from the Primary Position.

13. The Fundamental Laws
of
Ocular Motility.

14. Donder’s Law
Donders34 expressed this theory in 1848
by stating that to each position of the line
of sight belongs a definite orientation of
the horizontal and vertical retinal
meridians relative to the coordinates of
space.

15. Listing’s Law.
 Listing suggested that each movement of the
eye from the primary position to any other position
involves a rotation around a single axis lying in the
equatorial plane, also called Listing’s plane.
 Listing’s law implies that all eye movements from
the primary position are true to the meridians and
occur without ‘‘torsion’’ or cyclorotation with respect
to the primary position.

16.  Bowl with inscribed meridians and movable disk carrying a
cross to produce afterimage to show that eye movements from
primary position are true to
meridians.

17. Sherrington’s Law of Reciprocal
Innervation.
 Considered as the mover producing that movement,
the muscle is called an agonist.
 A movement in the direction opposite that produced
by the agonist is caused by its antagonist.
 Two muscles moving an eye in the same direction are
synergists.
 Synergistic muscles in the two eyes—muscles that
cause the two eyes to move in the same direction
—are known as yoke muscles.

18. Sherrington’s Law of Reciprocal
Innervation.
 Whenever an agonist receives an impulse to contract,
an equivalent inhibitory impulse is sent to its antagonist,
which relaxes and actually lengthens. This is
Sherrington’s law of reciprocal innervation.
 Sherrington’s law applies to all striated muscles of
the body and is not limited to the extraocular muscles.

19. Sherrington’s law of
reciprocal innervation.
A, On levoversion, increased
contraction (+) of the RMR and left
lateral rectus LLR is accompanied by
decreased tonus (0) of the antagonistic
RLR and LMR muscles
B, Increased activity of both medial
rectus muscles and decreased tonus
of both lateral rectus muscles during
convergence.
C, Contraction and relaxation of
opposing muscle groups on
dextrocycloversion when the head is
tilted to the left shoulder. RSO,; RSR,;
LSO,; LSR,; RIO,; RIR,; LLO,; LIR..

20. Hering’s Law of Equal Innervation.
 Herington Law of equal innervation states that during
any conjugate eye movement, equal and simultaneous
innervation flows to the yoke muscles
 In the case of a paretic squint, the amount of innervation
to both eyes is symmetrical, and always determined by
the fixating eye, so that the angle of deviation will vary
according to which eye is used for fixation.

21. Hering’s law of equal innervation.
A, During levoversion the right medial
rectus and the left lateral rectus muscles
receive an equal and simultaneous flow of
innervation.
B, During convergence the right and left
medial
rectus muscles receive equal and
simultaneous innervation.
C, When the head is tilted to the left, the
musclegroups controlling excycloduction of
the right eye and incycloductionof the left
eye receive equal and simultaneous
innervation. However, inclination of the
head is only partially compensated for by
wheel rotations of the eyes.

22. Survey of Ocular
Movements
and Their
Characteristics.

23. Terminology of Ocular Movements
Uniocular movements.
- All uniocular rotations are termed ductions.
- Prism vergences should never be called ductions.
Binocular movements.
- Synchronous simultaneous movements of the two
eyes in the same direction are called versions.
- Synchronous simultaneous movements of the two eyes in
opposite directions are called vergences.
- Versions are fast and vergences are slow eye movements.

24. Monocular Movements Binocular Movements
(ductions)
Versions Vergences
Adduction Dextroversion Convergence
Abduction Levoversion Divergence
Sursumduction Sursumversion Right sursumvergence*
Deorsumduction Deorsumversion Right deorsumvergence†
Incycloduction Dextrocycloversion Incyclovergence
Excycloduction Levocycloversion Excyclovergence
Terminology of Ocular Movements

25. Versions
 To enlarge the field of view and to bring the object of
attention onto the fovea.
 Versions are either voluntary or involuntary.
 They are voluntary if the subject moves the eyes of his
or her own volition.
 They can be horizontal, vertical and oblique versions.

26. Versions
 Naturally occurring cycloversions are postural reflexes.
 They arise from stimuli in the neck muscles and the
inner ear.
 When the head is lifted, the eyes go down; when the
head is lowered, the eyes go up.
 This is the oculocephalic reflex - doll’s head
phenomenon, oculovestibular
reflex,Puppenkopfphanomen.

27. A, Levoversion with
the head turned to the
right.
B, Dextroversion with
the head turned to the
left.
C, Depression of the
eyes with the chin
elevated.
D, Elevation of the
eyes with the chin
depressed.

28. Vergences
 The vergences fulfill the second of the two tasks assigned to
the motor system of the eyes.
 They are movements of the two eyes in opposite
directions,they are also known as disjunctive movements.
 Vergence movements serve not only to bring the eyes into
proper alignment but also to maintain this alignment.
 These movements are performed also in the interest of
single binocular vision.
 Divergence movements are not an active function but
simply the return of the globes to a more parallel position by
elastic forces when convergence impulses were relaxed.

29. Coordination of Eye Movements
 Separate systems exist to control each different
subtyppe of eye movement: saccades, smooth pursuit,
and vergence.
 May be nuclear or supranuclear.
 May be reflexive or voluntary.
 Separate systems exist to govern vertical and
horizontal eye movements.

30. Targeting Eye Movements.
1. Saccades: Quick, darting conjugate movements
which direct the to eye to a new target.
2. Smooth pursuit: A slower conjugate movement
which allows for tracking of a moving object, or of a
stationary object while we are moving.
3. Convergence: A dysconjugate movement of both
eyes toward the midline to allow for focusing on a
near object by adjusting the angle between the eyes.

31. How the Extraocular Muscles
Work
 Underaction of the extraocular muscles can
be readily explained due to reduced rotation of
the globe.
 Observation of clinical strabismus
suggests that only cases of excess
innervation such as occurs in the yoke
muscle of a paretic muscle can legitimately
be called overaction.

32. Testing for Muscle
Weakness and
Restriction.

33. Clinical evaluation of strabismus with
restricted motility
Underaction.
A. Fixing with the sound eye (primary
deviation) - a right esotropia is
observed.
B. Levoversion is essentially normal.
C. Dextroversion shows limitation of
abduction in the right eye.
D. Fixing with the paretic eye and/or
mechanically restricted right eye
produces a larger secondary deviation.

34. Clinical evaluation of strabismus with
restricted motility
Overaction.
.

35. Passive duction testing of the oblique
muscles
A. The eye is grasped at the 2 o’clock
and 10 o’clock position (right eye from
above) in preparation.
B. The eye is pushed back into the
orbit and is guided from nasal to
temporal. As it goes over the normal
superior oblique tendon, the eye
‘pops’ up.
C. With a lax or loose tendon the
cornea disappears and remains
hidden behind the upper lid as the
eye is rotated.
D. The relative path of the globe as it
passes over a normal tendon.
E. A lax superior oblique tendon
allows the globe to be pushed
backward into the orbit.
The superior oblique traction test.

36. Passive duction testing of the oblique
muscles
A .The right eye is grasped at the limbus.
B. The eye is rotated nasally and ‘pushed
back’ in the orbit.
C1. The eye is brought temporally -- the
surgeon ‘feels’ for the ‘pop up’ of the
inferior oblique which is still present.
C2. If no ‘pop’ is felt, the inferior oblique
has been effectively weakened.
D. The eye normally recedes in abduction
regardless of the state of the inferior
oblique.
The inferior oblique traction test viewed from above
the patient’s head.

37. Thank You.