Extra-ocular Eye Muscles

Question 1

Identify the extra ocular muscles and other features of the image

Answer 1

Question 2

Where do the 4 rectus muscles meet?

Answer 2

Meet at the common tendinous ring at the apex of the orbit

Question 3

During primary resting gaze, what are the forces of all the extraocular muscles?

Answer 3

They are equal and opposite which balances the eyes and aligns the visual axis’ of both eyes

Question 4

What is conjugate gaze?

Answer 4

The alignment of the visual axis in both eyes

Question 5

What happens if the visual axes of the eye are maligned?

Answer 5

Diplopia (double vision)

Question 6

Why don’t the muscles of the eye just exert an ‘up’ and ‘down’ motion?

Answer 6

The extra ocular muscles run in the axis of the orbit at an oblique angle

The eye in resting gaze follows the visual axis which runs in a different angle

Question 7

What is the action of medial rectus and which nerve innervates this muscle?

Answer 7

Adducts the eye (towards the nose)

Innervated by occulomotor nerve

Question 8

What is the action of lateral rectus and which nerve innervates this muscle?

Answer 8

Abducts the eye (towards the ear)

Innervated by abducens (CN VI)

Question 9

What is the action of superior rectus and which nerve innervates this muscle?

Answer 9

Actions from primary resting gaze:

• Elevates
• Adducts (slightly)
• Internally rotates (slightly)

Innervated by occulomotor

Question 10

What is the action of inferior rectus and which nerve innervates this muscle?

Answer 10

Actions from primary resting gaze:

• depresses
• slighty adducts
• slight externally rotates

Innervated by occulomotor

Question 11

What is the action of superior oblique and which nerve innervates this muscle?

Answer 11

Action from primary resting gaze

• Depresses
• Intorts (main internal rotator)
• Slighty abducts

Innervated by trochlea

Question 12

What is the action of inferior oblique and which nerve innervates this muscle?

Answer 12

Action from primary resting gaze

• Extorts
• Elevates
• Slightly abducts

Question 13

Which muscle is weak in this person?

Which cranial nerve is affected?

Answer 13

Lateral rectus is weak due to Abducens nerve palsy

Causes unapposed adduction of the eye

Question 14

Which muscle is weak in this person?

Which cranial nerve is affected?

Answer 14

Superior Oblique is weak, due to trochlear nerve palsy

Question 15

Which muscles are tested in the H?

Answer 15

Question 16

Which cranial nerve is affected here?

Answer 16

Occulomotor nerve palsy CNIII

Innervates all the muscles except Lateral Rectus and Superior Oblique so the action of these muscles are unapposed giving the down and out appearrance

Question 17

How does the appearance of CNIII palsy differ whether the lesion is miscrovascular vs compressive?

Answer 17

Microvascular (diabetes/ hypertension): pupil spared as blood vessels run along the middle

Compressive lesions (Raised ICP, tumour): pupil involved as parasympathetics that innervate sphincter pupillae muscle run along the periphery of CNIII therefore vulnerable to damage in compression

Question 18

What is the most common cause for CN III, IV and VI lesions?

Answer 18

Vasculopathic

Patients otherwise asymptomatic, lesions will resolve within a few months