Extra-ocular Eye Muscles Flashcards
Identify the extra ocular muscles and other features of the image
Where do the 4 rectus muscles meet?
Meet at the common tendinous ring at the apex of the orbit
During primary resting gaze, what are the forces of all the extraocular muscles?
They are equal and opposite which balances the eyes and aligns the visual axis’ of both eyes
What is conjugate gaze?
The alignment of the visual axis in both eyes
What happens if the visual axes of the eye are maligned?
Diplopia (double vision)
Why don’t the muscles of the eye just exert an ‘up’ and ‘down’ motion?
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
What is the action of medial rectus and which nerve innervates this muscle?
Adducts the eye (towards the nose)
Innervated by occulomotor nerve
What is the action of lateral rectus and which nerve innervates this muscle?
Abducts the eye (towards the ear)
Innervated by abducens (CN VI)
What is the action of superior rectus and which nerve innervates this muscle?
Actions from primary resting gaze:
- Elevates
- Adducts (slightly)
- Internally rotates (slightly)
Innervated by occulomotor
What is the action of inferior rectus and which nerve innervates this muscle?
Actions from primary resting gaze:
- depresses
- slighty adducts
- slight externally rotates
Innervated by occulomotor
What is the action of superior oblique and which nerve innervates this muscle?
Action from primary resting gaze
- Depresses
- Intorts (main internal rotator)
- Slighty abducts
Innervated by trochlea
What is the action of inferior oblique and which nerve innervates this muscle?
Action from primary resting gaze
- Extorts
- Elevates
- Slightly abducts
Which muscle is weak in this person?
Which cranial nerve is affected?
Lateral rectus is weak due to Abducens nerve palsy
Causes unapposed adduction of the eye
Which muscle is weak in this person?
Which cranial nerve is affected?
Superior Oblique is weak, due to trochlear nerve palsy
Which muscles are tested in the H?
Which cranial nerve is affected here?
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
How does the appearance of CNIII palsy differ whether the lesion is miscrovascular vs compressive?
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
What is the most common cause for CN III, IV and VI lesions?
Vasculopathic
Patients otherwise asymptomatic, lesions will resolve within a few months
