Extraocular Muscles for Eye Movement

Apex of the Orbit

Annulus of Zinn is located at the?

• Medial Rectus

• Lateral Rectus

• Superior Rectus

• Inferior Rectus

Muscles that originates from the Annulus of Zinn? (4)

Medial Rectus

Shortest tendon in the four rectus muscle.

5.5mm

Insertion of the MR?

• Medial Rectus

• Superior Rectus

• Inferior Rectus

• Inferior Oblique

Muscles that is innervated by the Oculomotor Nerve? (4)

Adduction

Primary movement of the Medial Rectus?

6.9mm

Insertion of the LR?

Lateral Rectus

Broadest arc of contact?

Lateral Rectus

Thinnest of the extraocular muscles?

Abduction

Primary action of LR?

Abducens Nerve

Lateral Rectus is innervated by the?

7.7mm

Insertion of SR?

Superior Rectus

Rectus muscle with the farthest insertion from the limbus.

1. Elevation

2. Intorsion

3. Adduction

Actions of the Superior Rectus?

6.5mm

Insertion of the IR?

1. Depression

2. Extorsion

3. Adduction

Actions of the Inferior Rectus?

Periosteum of the Sphenoid Bone

Superior Oblique originates from the?

Superior Oblique

It is the longest of the extraocular muscles.

1. Intorsion

2. Depression

3. Abduction

Actions of the Superior Oblique?

Trochlear Nerve

Superior Oblique is innervated by the?

Arises from the Orbital Floor

Inferior Oblique originates from the?

1. Extorsion

2. Elevation

3. Abduction

Actions of the Inferior Oblique?

Fascial sheath of the inferior oblique with that of the inferior rectus

Together they contribute to the formation of the suspensory ligament of the eyeball (Lockwood’s Ligament).

Listing Plane

It is an imaginary equatorial plane that passes through the center of rotation of the globe.

Fick’s Axes

The eye rotates around three mutually perpendicular axes known as the?

Elevation and Depression

Rotation around the X-axis results in vertical movements, including? (2)

Adduction and Abduction

Rotation around the Z-axis results in horizontal movements, including? (2)

Intorsion and Extorsion

Rotation around the Y-axis results in torsional movements, including? (2)

Understanding these axes provides a useful framework for describing the movements produced by each extraocular muscle.

Why is it important to learn about the axes of the eyes?

Arc of Contact

It refers to the portion of an extra ocular muscle that remains in direct contact with the surface of the globe before the muscle begins to leave the eye and continue toward its origin.

Ductions

Monocular movements is also known as?

Versions

Binocular movements is also known as?

Vergence

When the eyes move in opposite directions, the movement is called a?

Primary Position

It refers to the normal straight-ahead position of the eyes when the head is erected and the patient is looking directly at a distant target.

Secondary Position

Obtained when the eyes move from the primary position in a single direction without combining horizontal and vertical movements.

Tertiary Position

It result from combining a horizontal movement with a vertical movement.

Examination of the tertiary position is important because they isolate the actions of individual extra ocular muscles during ocular testing.

Why is important to examine the tertiary positions of the eye?

Understanding these principles provides the foundation for studying ocular motility and the relationship between the muscles of both eyes.

Why is it important to learn about the Laws of Ocular Motility?

Laws of Ocular Motility

The coordinated movement of the eyes is governed by several principles collectively known as the?

Agonist

Primary muscle responsible for producing a particular eye movement.

Antagonist

Muscle that produces opposite movement.

Synergists

Two or more muscles of the same eye that work together to produce a common movement.

Yoke Muscles

Pair of muscles, one from each eye, that work together to produce conjugate eye movements.

Donder’s Law

It states that when the head is upright and stationary, every eye movement from the primary position to any other position of gaze can be described as a rotation around a single axis that lies within Listing’s plane.

Hering’s Law of Equal Innervation

It states that equal and simultaneous neural impulses are sent to a pair of yoke muscles during binocular eye movements.

Sherrington’s Law of Reciprocal Innervation

It states that when an agonist muscle contracts, its antagonist in the same eye relaxes by an equivalent amount.