Saturday, March 13, 2021

Oculomotor Nerve Palsy Case File

Posted By: Medical Group - 3/13/2021 Post Author : Medical Group Post Date : Saturday, March 13, 2021 Post Time : 3/13/2021
Oculomotor Nerve Palsy Case File
Eugene C. Toy, MD, Lawrence M. Ross, MD, PhD, Han Zhang, MD, Cristo Papasakelariou, MD, FACOG

CASE 42
A 38-year-old male presents to the emergency room with complaints of a persistent headache and problems with his left eye. He has no known medical problems, and his headache is slightly improved with ibuprofen. He denies having any previous vision problems. Examination reveals ptosis, dilated pupil, and displacement “down and out” in his left eye The remainder of the exam is normal. An MRI shows an aneurysm of the circle of Willis.

 Given the physical exam, what ocular muscles are likely to have been unaffected?
 Which nerve is likely to have been affected?


ANSWER TO CASE 42:

Oculomotor Nerve Palsy
Summary: A 38-year-old healthy male with recent-onset left eye findings of ptosis, dilated pupil, and displacement of eye “down and out.”

• Ocular muscles not involved: Superior oblique and lateral rectus

• Nerve affected: Oculomotor nerve (CN III)


CLINICAL CORRELATION
Findings of ptosis, dilated pupil, and down-and-out eye displacement are most consistent with oculomotor nerve palsy. The oculomotor nerve is the third of 12 paired cranial nerves and originates from the midbrain. It controls most eye movements, constriction of the pupil, and eyelid position. Down-and-out displacement of the eye occurs from the unopposed action of the lateral rectus and superior oblique. The superior oblique muscle is innervated by the trochlear nerve (CN IV), and the lateral rectus muscle is innervated by the abducens nerve (CN VI). An oculomotor nerve palsy may be caused by an aneurysm, compression, infection, infarction, or tumor.


APPROACH TO:
Extraocular Muscles of the Orbit

OBJECTIVES
1. Be able to name the seven extraocular eye muscles of each orbit, and also their attachments, actions, and innervation
2. Be able to describe how each of these muscles is optimally tested in a clinical setting
3. Be able to describe the presentation of a patient with injury to each nerve that innervates these muscles

DEFINITIONS
PTOSIS: Drooping or partial closure of the upper eyelid

NERVE PALSY: Partial or incomplete paralysis

ANEURYSM: Dilatation of the wall of an artery due to an acquired or congenital condition

Table 42-1 • EXTRAOCULAR MUSCLES OF THE ORBIT

Muscle

Origin

Insertion

Action

Innervation

Superior oblique

Posterior orbit

Posterosuperior

sclera

Depresses and

abducts the eye

CN IV

Inferior oblique

Anterior orbital

floor

Posteroinferior

sclera

Elevates and

abducts the eye

CN III

Superior rectus

The common

tendinous ring

The anterior

portion of sclera

Elevates and

adducts

CN III

Inferior rectus

The common

tendinous ring

The anterior

portion of sclera

Depresses and

adducts

CN III

Lateral rectus

The common

tendinous ring

The anterior

portion of sclera

Abducts

CN VI

Medial rectus

The common

tendinous ring

The anterior

portion of sclera

Abducts

CN III



DISCUSSION
The extraocular muscles of the orbit are the levator palpebrae superioris, four rectus (superior, inferior, lateral, and medial), and two oblique (superior and inferior) muscles. All of the extraocular muscles originate from the apex of the pyramidal shaped orbit near the optic canal, except for the inferior oblique muscle, which arises from the anterior orbital floor. The levator superioris attaches directly to the eyelid and controls its movements. Rarely do any of the six muscles attaching directly to the eyeball move the eyeball independently from the other muscles, although their individual actions are typically described. Their attachments, actions, and innervation are listed in Table 42-1 and illustrated in Figure 42-1.

Oculomotor Nerve Palsy anatomy

Figure 42-1. Diagram of eye muscles.

The levator palpebrae superioris muscle originates from the posterior orbit and attaches to the skin and tarsal plate of the upper eyelid, which it elevates. It is opposed by the superior portion of the orbicularis oculi muscle. It contains smooth muscle fibers forming the superior tarsal muscle that is innervated by sympathetic nerve fibers during fright or startle responses.

The superior oblique muscle originates anatomically from the posterior apex of the orbit and passes anteriorly to the trochlea, a pulley like fibrous ring at the superomedial margin on the orbit. The trochlea is the functional origin of this muscle. Its tendon passes through the trochlea to insert on posterosuperior portion of the sclera. On contraction, it pulls the posterior portion of the eyeball anteriorly and medially. Thus the pupil is turned down and out. The inferior oblique muscle originates from the anteromedial floor of the orbit, thus simulating the portion of the superior oblique between the trochlea and insertion. It inserts into the posteroinferior sclera and therefore opposes the action of the superior oblique. It will turn the pupil of the eye up and out. The two oblique muscles also produce extorsion or lateral rotation of the eyeball.

The four rectus muscles (superior, inferior, lateral, and medial) all originate from a common tendinous ring surrounding the optic canal and a portion of the superior orbital fissure in the posterior orbit. Each inserts on the anterior half of the sclera on that portion of the eyeball according to their name. Thus the lateral rectus inserts on the anterolateral sclera. Note that the superior and inferior rectus muscles will turn the eyeball in or adduct the pupil and will also produce intorsion or medial rotation of the eyeball.

For the sake of clarity, the following descriptions for muscle testing are for only the right eye. For optimal testing of the extraocular muscles, the axis of the muscle is placed parallel with the axis of muscle pull. With the eyeball (pupil) abducted, the superior and inferior recti are in line with their pull, and their action on the eyeball is almost purely elevation and depression, respectively. For the superior and inferior oblique muscles, adduction of the eyeball (pupil) places the axis of the muscle in line with its pull (remember that the functional origin of the superior oblique is the trochlea). Thus the eyeball (pupil) is depressed and elevated for these two muscles. The lateral and medial recti are tested by simply adducting or abducting the eyeball (pupil) (see Figure 42-2).

If the oculomotor nerve (CN III) is injured as in this case, the pupil of the affected eye will be turned down and out (because of the unopposed action of the superior oblique and lateral rectus muscle). The pupil will also be dilated because of loss of the parasympathetic innervation to the constrictor muscle of the pupil. Loss of the trochlear nerve, although rare, results in slight adduction of the affected eye, weakness of downward gaze due to paralysis of the superior oblique, and head tilting to eliminate diplopia (double vision). Loss of abducens nerve (CN VI) function results in paralysis of the lateral rectus muscle, and thus the patient’s affected eye will be turned in or adducted.

Diagram of eye muscle action

Figure 42-2. Diagram of eye muscle action.


COMPREHENSION QUESTIONS

42.1 While examining a patient, you notice ptosis of the patient’s left eye. This
would indicate to you there is paralysis of which muscle?
    A. Orbicularis muscle
    B. Superior oblique muscle
    C. Inferior oblique muscle
    D. Inferior rectus muscle
    E. Levator palpebrae muscle

42.2 While performing a physical examination, you test the function of the muscles attached to the eyeball and thereby the integrity of their innervation. You would test the function of the superior oblique muscle by having the patient do which of the following?
    A. Look in toward the nose
    B. Look laterally
    C. Look in toward the nose and then upward
    D. Look in toward the nose and then down
    E. Look laterally and then down

42.3 During this same physical exam, you ask the patient to look laterally with her right eye, and then upward. You have just tested the function of which muscle?
    A. Superior rectus muscle
    B. Superior oblique muscle
    C. Inferior oblique muscle
    D. Inferior rectus muscle
    E. Medial rectus muscle


ANSWERS
42.1 E. Ptosis or drooping of the eyelid is due to paralysis of the levator palpebrae muscle. The orbicularis muscle closes the eyelid.

42.2 D. Turning the eyeball inward places the portion of the superior oblique between the trochleae, and its insertion places the axis of the muscle in line with its axis of muscle pull. Because the muscle’s insertion is on the posterior portion of the sclera, it will then turn the eye (pupil) down (depress).

42.3 A. Turning the eyeball out places the axis of the superior rectus muscle parallel to its pull, and the muscle will then turn the eyeball upward (elevate).


ANATOMY PEARL
 LR6SO4AO3: lateral rectus, CN VI; superior oblique, CN IV; all others, CN III.
 The functional portion of the superior oblique muscle is between the trochlea and the insertion of the tendon.
 The oculomotor nerve (CN III) innervates the majority of the extraocular muscles, the sphincter muscle of the pupil, and the smooth muscle fibers of the superior tarsal muscle.

References

Gilroy AM, MacPherson BR, Ross LM. Atlas of Anatomy, 2nd ed. New York, NY: Thieme Medical Publishers; 2012:501, 538−539, 541−543. 

Moore KL, Dalley AF, Agur AMR. Clinically Oriented Anatomy, 7th ed. Baltimore, MD: Lippincott Williams & Wilkins; 2014:898−899, 903−905, 913. 

Netter FH. Atlas of Human Anatomy, 6th ed. Philadelphia, PA: Saunders; 2014: plates 86, 88, 122.

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