EOMs Flashcards
What is the action of a muscle due to
The direction of its pull around the axes
This is a muscles major effect on the postion of the eye when the muscle contracts while the head is in the primary postion
Primary action
These are the additional effect a muscle has on the position of the eye
Secondary and tertiary action
How far can the eyes move before the head moves
Move about 50 degrees, but at about 20, the head turns
Point at the center of the muscle or tendon that first touches the globe
Tangential point
This the arc formed between the tangential point and the center of insertion of the muscle on the sclera. It changes in length as a muscle contracts.
Arc of contact
When is arc of contact longer
When a muscle is relaxed
When is the arc of contact shorter
When a muscle interacts
Describes the direction of pull of the muscle and determines the axis the muscle will move around
Muscle plane
The visual axis passes from the ______ to the _______
Fovea to the point of fixation
The visual axis from both eyes in normal binocular single vision
Intersects at fixation
An imaginary coronal plane through the center of the globe
Listing plane
The globe rotates on the ______
Axes of fick
The eye rotates vertically (up and down) on this axis
X
The eye makes torsional rotations like a wheel around this axis. This axis is similar to the anatomical axis of the eye. The top of the eye rotates clockwise or counter clockwise
Y
The eye rotates horizontally (left and right) on this axis
Z
Zide to zide
How many EOMs
6
How many rectus muscles
4
How many oblique muscles
2
Rectus muscles
Superior
Inferior
Medial
Lateral
Oblique muscles
Superior
Inferior
The imaginary line joining the insertions of the 4 rectus muscles
Spiral of Tillaux
What is an important reference for surgery when it comes to EOMs
Spiral of tillaux
How is the spiral of Tillaux situated
Starting at the medial rectus, each rectus muscle is located further away from the limbus
What is the order of rectus muscles in order from being closest to farthest from the limbus
medial rectus
Inferior rectus
Lateral rectus
Superior rectus
In primary gaze, what axis do the horizontal rectus muscles muscles move around
Z
Where do the horizontal and the vertical rectus muscles insert
In front of the equator
What axis do the vertical rectus muscles move around
X
Where do all EOMs arris from
The annulus of zinn
Moves the eye to the nose (ADDuction)
Medial rectus
What nerve innervates medial rectus
CN3
Where does medial rectus insert from the nasal limbus
5.5mm
How does the medial rectus course
Along the medial orbital wall
Why is the medial rectus prone to injury during surgery or after trauma
Because it is close to the ethmoid sinus
Moves the eye away from the nose (ABducts)
Lateral rectus
What innverates lateral rectus
CN 6
Where does the lateral rectus insert from the temporal limbus
6.9MM
How does the lateral rectus course
Along the lateral orbital wall
The medial and lateral orbital walls are ______ of each other
45 degrees
How many degrees is the orbital axis from the two orbital walls
23 degrees
The ______ is from the apex of the orbit to the opening of the orbit
Orbital axis
In primary gaze, the orbital axis is at ____ of the visual axis
23 degrees
Angle of the vertical recti in the orbit
Vertical recti muscles run with the orbital axis, 23 degrees of visual axis
Primary action is to move the eye up (elevation)
Superior rectus
Secondary action of the superior rectus
intorsion
Tertiary action of the superior rectus
Adduction
What innervates the superior rectus
CN 3
Where does the superior rectus insert relative to the superior limbus
7.7mm
How does the superior rectus course
Anteriorly and upward over the eyeball and laterally forming a 23 degree angle with the visual axis
When do the visual and orbital axes coincide
When the globe is abducted 23 degrees
What’s the best postion to evaluate the function of the superior rectus
When the globe is abducted 23 degrees. At this point, the superior rectus acts ONLY as an elevator
What what point does the superior rectus act only as an elevator
When the globe is abducted 23 degrees
When does the superior rectus act only as an intortor?
When the globe is aDDucted 67 degrees, making the angle between the visual and orbital axes 90 degrees.
Not the best way to evaluate the superior rectus
Primary action is the move the eye down (depression)
Inferior rectus
Secondary action of inferior rectus
Extortion
Tertiary action of the inferior rectus
ADDuction
What is the inferior rectus innervated by
CN 3
Where does the inferior rectus insert relative to the inferior limbus
6.5mm
How does the inferior rectus course
Inferior and downward and laterally along the floor of the orbit forming a 23 degree angle with the visual axis
What position does the inferior rectus act only as a depressor?
When the globe is abducted 23 degrees
What is the best position to evaluate the function of the inferior rectus
When the globe is abducted 23 degrees
When does the inferior rectus act only as an intorter?
When the globe is aDDucted 67 degrees. Not the best way to test this
Those positions where there are yoked muscles/one muscle is responsible for movement
Cardinal positions
Primary action os superior oblique
Intortion
Secondary action of superior oblique
Depression
Tertiary action of superior oblique
Abduction
Superior oblique innervated by
CN 4
How does the superior oblique pass
Through the trochlea found between the superior and medial walls, reflects backwards and inserts in the posterior quadrant of the globe
Where does the superior oblique originate
From the orbital apex above the annulus of zinn, passes superiorly and upward along the superiomedial wall
Where doesthe superior oblique become tendinous
As it passes through the trochlea at the superior nasal aspect of the orbit
How does the superior oblique get redirected as it passes through the trochlea
Inferiorly, posteriorly, and laterally forming a 51 degree angle with the visual axis
Where does the superior oblique insert
Posteiror to the equator in the superotemporal quadrant of the eye
Primary action of the inferior oblique
Extortion
Secondary action of the inferior oblique
Elevation
Tertiary action of the inferior oblique
Abduction
What is the inferior oblique innervated by
CN 3
How does the inferior oblique originate
At a small depression at orbital floor
Where does the inferior oblique insert
In posterior lower temporal quadrant of the globe close to the macula
How does the inferior oblique course
Inferiorly under the inferior rectus muscle
What kind of angle does the inferior oblique form with the visual axis
51 degree angle
In terms of angles, what is the best way to test an EOM
Line it up on the angle it is relative to the visual axis
At what angle does the superior oblique act only as an intorter?
When the globe is abducted 39 degrees, making the visual axis and the superior oblique at 90 degrees from each other
At what angle does the superior oblique act as a total depressor
When aDDucted 51 degrees
At what angle does the inferior oblique act only as an extorter?
When the globe is abducted 39 degrees, making the angle between the visual axis and the inferior oblique 90 degrees from each other.
At what angle does the inferior oblique act only as an elevator?
When aDDucted 51 degrees
When you tell a patient to look up and to the nose (OD), and they cant, what muscle is not working?
IO
