Extraocular muscle actions & motility

Extraocular muscle actions &
motility
Presenter: Ashim Chhusya
B.Optometry, Tilganga Institute of
Ophthalmology
12/25/2019 Ashim Chhusya

STRUCTURE OF THE EXTRAOCULAR MUSCLES
• The extraocular muscles have a
denser blood supply, and their
connective tissue sheaths are more
delicate and richer in elastic fibers
than is skeletal muscle.
• Fewer muscle fibers are included in
a motor unit in extraocular muscle
than are found in skeletal muscle
elsewhere i.e. each axon innervates
3 to 10 fibers.
LEE ANN REMINGTON; Clinical Anatomy and Physiology of the Visual System, 3rd ed. p183

• This dense innervation provides for precise fine motor control of the
extraocular muscles resulting in high velocity ocular movements,
necessary in saccades, (up to 1000 degrees per second) and very
accurate pursuits (velocities of 100 degrees per second) and fixations.
• The extraocular muscles have a range of fiber sizes, with the fibers
closer to the surface generally having smaller diameters (5 to 15 μm)
and those deeper within the muscle generally having larger
diameters (10 to 40 μm).

Origin & Insertion of EOMs

Origin of EOM

Insertion of EOM
Ref: Binocular Vision & Ocular Motility, GK Von Norden 6th Ed, p40
:Spiral of Tillaux

GK Von Norden; Binocular Vision & Ocular Motility, 6th Ed, p40

Origin & insertion of EOM
LPS:
Origin : Lesser wings of sphenoid bone
Insertion: Tarsus, pretarsal tissues & skin, lateral & medial palpebral
ligaments
LR:
origin on the common tendinous ring and the spina recti lateralis, a
prominence on the greater wing of the sphenoid bone
Insertion approximately 6.9 mm from the limbus (parallels that of the
medial rectus) and is, and the length of the tendon is approximately 8.8
mm.12/25/2019 Ashim Chhusya

SR:
• Origin on the superior part of the common tendinous ring and the sheath of
the optic nerve
• Insertion of the superior rectus is approximately 7.7 mm from the limbus
MR
• Origin: the upper and the lower parts of the common ring tendon and from
the sheath of the optic nerve
• Insertion of the medial rectus is about 5.5 mm from the limbus, and the
tendon is approximately 3.7 mm long

Clinical pearl: Retrobulbar Optic Neuritis
• An inflammation affecting the sheaths of the optic nerve.
• Pain with extreme eye movement can be one of the early presenting
signs.
• The optic nerve sheath is supplied with a dense sensory nerve
network and because of the close association of muscle sheath and
optic nerve sheath, eye movement can cause stretching of the optic
nerve sheath, resulting in a sensation of pain

INFERIOR RECTUS MUSCLE:
• Origin on the lower limb of the tendinous ring
• Insertion is about 6.5 mm from the limbus
SUPERIOR OBLIQUE MUSCLE
• Origin on the lesser wing of the sphenoid bone, supero-medial to the optic
canal near the fronto-ethmoid suture
• Courses forward and passes through the trochlea, a u-shaped piece of
cartilage attached to the orbital plate of the frontal bone
• Insertion of the superior oblique muscle attaches in the super-posterior
lateral aspect of the globe
INFERIOR OBLIQUE MUSCLE
• Origin on the maxillary bone just posterior to the inferior medial orbital rim
and lateral to the nasolacrimal canal.
• Insertion of the inferior oblique is on the posterior portion of the globe on
the lateral side, mostly inferior, lying just outer to the macular area

EOM blood supply
OD
OD

EOM innervation:
Reading site: https://www.youtube.com/watch?v=5OD-BnuOMHs
Transverse
section
View from above

View from right supero-
posterior

Terminologies in ocular movements
1. Center of Rotation
• A center point of globe around which the
eye performs rotary movements
• The approximate geometric center of the
eye
• In primary position the center of rotation is
located
• About 13.5 mm (in myopes, 14.5 mm)
behind the apex of the cornea on the
line of sight
• 1.3 mm behind the equatorial plane.
GK Von Norden; Binocular Vision & Ocular Motility, 6th Ed, p5212/25/2019 Ashim Chhusya

2. Fick’s axes
• All eye movement can be described as rotations
around one or more axes called FICK’S AXES.
• Comprises:
The x-axis The horizontal or transverse axis and runs from nasal to
temporal
The y-axis The sagittal axis running from the anterior pole to the
Posterior pole
The z-axis Is the vertical axis and runs from superior to inferior

3. The tangential point
• The point at which the center of
the muscle or of its tendon first
touches the globe
4. The arc of contact
The arc formed between the tangential point and
the center of the insertion of the muscle on the
sclera

5. The muscle plane
• Plane determined by the tangent
to the globe at the tangential point
and the center of rotation
6. An axis of rotation
• An axis, perpendicular to the
muscle plane erected in the
center of rotation

5. DUCTION MOVEMENTS:
• The rotations of the single eye are termed “duction” movements

6. VERGENCES AND VERSIONS
Vergence movements: both the eyes move in opposite
direction simultaneously so called disjunctive movements
Comprises:
• Convergence
• Divergence
• Incyclovergence
• Excyclovergence

Version movements are conjugate movements and occur when the eyes move
in the same direction
Comprises:

5. POSITIONS OF GAZE
• The primary position of gaze the position of eye with the head erect,
the eye located at the intersection of the sagittal plane of the head
and the horizontal plane passing through the centers of rotation of
both eyes, and the eye focused for infinity.
• Secondary positions of gaze are rotations around either the vertical
axis or the horizontal axis;
• Tertiary positions are rotations around both the vertical and the
horizontal axes.

Primary
Eye when looking straight ahead with body
and head erect
Secondary
Adducted, abducted, elevated, or depressed
positions
Tertiary Oblique positions of the eye

EOMS’ Actions In Primary Gaze Position

Muscles Primary action
Secondary
action
Tertiary
action
LPS Eyelid elevation - -
SR Eyeball elevation Incycloduction Adduction
IR Depression Excycloduction Adduction
LR Abduction of globe - -
MR Adduction - -
SO Incycloduction Depression Abduction
IO Excycloduction Elevation Abduction
EOMS’ Actions In Primary Gaze Position

The vertical gaze center: Rostral interstitial
Nucleus Of Medial Longitudinal Fasciculus
(riMLF) & INC
at midbrain (thalamo-mesencephalic junction)
The horizontal gaze center:-
PPRF in Pons adler’s physio.p235
Ipsilateral trochlear
nuclei adler’s physio.p235
B/L oculomotor
nuclei
The ipsilateral
abducens nucleus
adler’s physio.p235
Contralateral oculomotor nucleus
Ipsilateral LR Contralateral yoke muscle
Yoke muscle
What are the centers for making Eye Movements?
=2 centers

Parinaud's Syndrome
Parinaud's syndrome, is a group of abnormalities
of eye movement and pupil dysfunction caused
by lesions that compresses the vertical gaze
center at riMLF at thalamo-mesencephalic
junction resulting an inability to move the eyes
up (most commonly) and down.
It is named after Henri Parinaud, French
ophthalmologist and neurologist

How does eyes makes movements for gazing?
1. Saccadic movement
2. Smooth pursuit movement
3. Vergence movement
4. Vestibulocular movement

1. Saccadic movement

Saccadic system

Test for saccadic movement
a. To each side of the head for horizontal movement
b. Above & below the head for vertical movement
• The movement, speed & accuracy of either eye is compared & any
asymmetry between the eyes is noted
• The patient is asked to look from one
target to another, one held on the
primary position and the other:

Smooth Pursuit System
Dorsal lateral pontine premotor nuclei
(DLPN)
Ref: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3164106/

Test for smooth pursuit movement
• Smooth pursuit movements are tested monocularly & binocularly.
• Version SPM test is done using a spotlight to observe the movement from
the primary position into the eight cardinal positions of gaze with the
head erect & immobile.
• Ductions are tested to compare with versions & the following is noted:
• Symmetry of eyes’ movement
• Whether the movement is smooth or jerky
• If, presence of Nystagmus
• Effect of fatigue
• Torsional movement
• Abnormal head movements

Vergence system
Supraoculomotor area (SOA) in the midbrain
Cortical neural signals
Stimuli: disparity between images on the retina, retinal blur (an
unfocused image), proximity of objects, the change in size of an
image
Cortical processing: occipital lobe, the parietal lobe and frontal eye
fields
Evidence that an area located anteriorly to the saccade
and smooth pursuit zone in the frontal eye fields is linked
with depth perception suggests that this area could be
involved with the initiation of vergence eye movement
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5122972/
3rd & 6th CN nuclei12/25/2019 Ashim Chhusya

Vestibulo-ocular
reflex movement
Head rotation

Vestibulocular reflex test
1. Doll’s head maneuver
• Patients head is moved quickly by the examiner to the right & left for
horizontal movement & up-down for vertical movement.
• A normal response is of the eyes is moving in the opposite direction to the
head movement
2. Induced vestibular nystagmus
• Warm water: slow phase to opposite side & fast phase to same side
• Cold water: slow phase to the same side & fast phase to opposite side
• Vertical caloric nystagmus: by stimulating both ears

The Fundamental Laws of Ocular Motility
1. DONDERS’ LAW(1848):
States that:
• To each position of the line of sight belongs a definite orientation of
the horizontal & vertical retinal meridians relative to the coordinates
of space.
• In other words, “the orientation is always the same irrespective of
where the eye came from i.e. The orientation of the eye when looking
in a specific direction is always the same
• For example, the orientation of the eye when looking up and right is
the same when the eye reached this position by first rotating right and
then up or first up and then right.

2. LISTING’S LAW
• 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
occur without ‘‘torsion’’ or cyclo-
rotation with respect to the primary
position

Does Listing's Law hold for other types of eye
movements?
a) Vestibular ocular reflex (VOR):
Function: to keep the image of the world stationary on the retina
when the head rotates
It does this by rotating the eyes in the opposite direction of the head.
If the head tilts to the side (torsionally) the eye counter-rolls, i.e. it
moves out of Listing's plane.
Thus the VOR does not obey Listing's law.
http://schorlab.berkeley.edu/vilis/othereye.htm

b) Saccades & Pursuit
Function: to keep the fovea on a small moving target, e.g. tracking a
tennis ball.
As in saccades, pointing the fovea at this moving ball is a 2D problem
and Listing's law used to resolve which of many eye position to choose.
Thus listing law is obeyed.

c) Vergence
Function: to align a near target on the fovea of each eye.
Listing's law is violated during vergence between targets at different
distances.
Listing's law holds at a constant distance.

3. Herring's Law of Equal Innervation
• It states “whenever an impulse for the performance of an eye
movement is sent out, corresponding muscles of each eye receive
equal innervations to contract or relax.
• Also called the law of motor correspondence of the eyes
• Herring's law applies only to extraocular muscles
• For example: rt. LR & lt. MR in dextroversion.

4. 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”
• The finely graded interplay between opposing eye muscles makes
movements of the globe smooth and steady
• Sherrington’s law is not limited to the extraocular muscles and
applies to all striated muscles of the body

Test for extra-ocular motility (cardinal positions of
gazes)

RIR, LSO
RSR, LIO
RLR, LMR
ODO
S
Dextroelevation
Dextrodepression
Dextroversion

LIR, RSO
LSR, RIO
LLR, RMR
ODO
S
Laevoelevation
Laevodepression
Laevoversion
23⁰
67⁰
90⁰

RSR LIO
RLR LMR
RIR LSO
LSRRIO
LLR
RM
R
RSO LIR
LeftRight

How to test Extra-ocular Motility?
Have the patient look in the six cardinal positions of gaze.
• With monocularly to test ductions.
• with both eyes open to assess versions

Recording of ocular Motility
Ocular movements are graded on a 9-point scale of −4 through to +4.
-4 No movement of the eye(s) past midline (marked).
-3 75% deficit of movement (moderate).
-2 50% deficit of movement (small).
-1 25% deficit of movement (slight).
0 Full normal movement
# Limitations of movement
Fiona J. Rowe; Clinical Orthoptics 3rd ed, p42412/25/2019 Ashim Chhusya

-1
-1
-2
0
0
00
0
0
0
0
0
R L

Force Duction Test
• Also known as traction test
• Done in patients with impaired extraocular
motility / strabismic
• It helps to differentiate whether the deviation is due to paralysis of EOM or
due to mechanical restriction of the ocular movement.

Procedures
1. Eye is anesthetized topically (abnormal eye)
2. Then the patient is directed to look at a target that is held in the
direction of action of the possible paretic muscle
3. The eye is then grasped with toothless forceps near the limbus
at opposite site of paretic muscle insertion
4. An effort is then made to rotate the eye with the forceps in the
direction of action of the possible paretic muscle

Results:
• If the eye can be rotated freely with the forceps – FDT is recorded as
negative i.e. the impaired extraocular motility is not due to
restriction but the muscle paresis or palsy.
• FDT is positive in cases of squint (incomitant) due to mechanical
restriction

Fixation
• Fixation refers the seemingly steady maintenance of the image of the
object of attention on the fovea.
• Uniocular (monocular) fixation or binocular or bifoveal fixation
• Thus fixation is a well-integrated sensorimotor process that is
essentially immature at birth and is acquired in the first 6 months of
life.

EYE MOVEMENTS DURING FIXATION
• Eye movements during fixation of small magnitude are also referred to as
micro or miniature eye movements.
• Comprises:
1. Microsaccades:
• Range in amplitude from 1 to 23 seconds,
• They correct for slippage of the visual target off the fovea.
2. Tremor:
• When the amplitude of fixation tremor is on the order of the diameter of the
smallest cone 5 to 50 seconds
• Disjunctive between the two eyes.
3. Drift:
 Slower on the order from 2 to 5 minutes
 Apparently disjunctive GK Von Norden; Binocular Vision & Ocular Motility, 6th Ed, p8012/25/2019 Ashim Chhusya

The field of fixation
GK Von Norden; Binocular Vision & Ocular Motility, 6th Ed, p8012/25/2019 Ashim Chhusya

Any Query?
Thank YOU ^_^

Extraocular muscle actions & motility

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