Notes

Sections

Here, we will learn the six cardinal positions of gaze and the extraocular muscle actions.

Draw a left eye.
Then draw the superior-inferior and medial-lateral axes of our diagram from the perspective of the left eye.
First, show that the lateral rectus directs the eye laterally (called abduction).
Then, that the medial rectus directs the eye medially (called adduction).
Next, show that when the eye is abducted, the superior rectus directs the eye superiorly and the inferior rectus directs the eye inferiorly.
Now, show that when the eye is adducted, the superior oblique directs the eye inferiorly and the inferior oblique directs the eye superiorly.

Across the top row, write: Cranial nerve, Extraocular muscle, Primary action, Secondary action, and Tertiary action.
Indicate that primary action is the eye muscle's chief action in primary position (ie, looking straight ahead).
Secondary and tertiary actions are the muscle's additional rotational effects on the eye.

Now, show that cranial nerve 3 innervates the medial rectus, superior rectus, inferior rectus, and inferior oblique muscles (which are the majority of the extraocular muscles).
Then show that cranial nerve 6 innervates the lateral rectus.
Finally, indicate that cranial nerve 4 innervates the superior oblique.

Next, indicate that the medial rectus muscle's primary action is adduction and that it does not have secondary or tertiary actions.
Then, show that the lateral rectus muscle's primary action is abduction, and also show that it does not have secondary or tertiary actions, either.
In the next row, write that the superior rectus muscle’s primary action is elevation, its secondary action is intorsion, and its tertiary action is adduction.
Then, write that the inferior rectus muscle's primary action is depression, its secondary action is extorsion, and its tertiary action is adduction.
Next, show that the superior oblique muscle's primary action is intorsion, its secondary action is depression, and its tertiary action is abduction.
Finally, show that the inferior oblique muscle's primary action is extorsion, its secondary action is elevation, and its tertiary action is abduction.

To simplify matters, include the following two mnemonics:
SUPERIOR people do NOT extort
- which means that the superior muscles are both intorters
OBLIQUE muscles rotate the eye OUT
- which means that the oblique muscles are abductors

ADVANCED

Now, in order to better understand the extraocular movements, draw an axial view of the eye within the orbit.
Show the optical axis of the eye.
Next, draw the eye muscle plane.
Now, draw the orbital apex, which lies anterior to the orbital opening of the optic canal.
The eye muscle plane originates from the orbital apex.
Indicate that all of the extraocular muscles except for the inferior oblique attach at the orbital apex in a common tendinous ring: the annulus of Zinn.
Denote that the inferior oblique attaches to the medial orbital floor, instead.
Now, show that the primary position of the eye (the position of the eye when it is looking straight ahead) is 23 degrees nasal to the eye muscle plane.
As a result, the vertical eye muscles (superior and inferior rectus and superior and inferior oblique) have three different actions on the eye in primary position: vertical, rotational, and horizontal.