8. Extraocular Muscles Flashcards
Why do we have binocular vision?
Allows for wider field of vision and depth perception enabling 3D vision
Visual axis of both eyes need to be aligned
What is diplopia?
Misalignment of visual axes focuses on different area of each retina
Brain unable to fuse, thus see 2 separate images
Gives double vision
What are the 4 recti extra ocular muscles?
Superior
Inferior
Medial
Lateral
What are the 2 oblique extra-ocular muscles?
Superior
Inferior
Where do the extra-ocular muscles insert?
Sclera
What is the origin of the extra-ocular muscles?
Apex of orbit
Except from inferior oblique which arises from floor of orbital cavity anteriorly
4 recti arise from common tendinous ring
What are the extra-ocular muscles innervated by?
Most innervated by CNIII, lateral rectus by CNVI and superior oblique by CNIV
(LR6SO4)
What do the extra ocular muscles run in line with?
Axis of orbit
Therefore some muscles attach at an oblique angle
Confers several actions of movement on globe (not just up and down) for some of extra ocular muscles
Which muscle adducts the eye?
Medial rectus
Which muscle abducts the eye?
Lateral rectus
What is the role of superior rectus muscle?
Elevates eyeball
Slightly adducts
Slightly intorts (internally rotates)
What is the role of inferior rectus muscle?
Depresses eyeball
Slightly adducts
Slightly extorts (externally rotates)
What is the role of superior oblique muscle?
Intorts eyeball
Depress
Slightly abducts
What is the role of inferior oblique muscle?
Extort
Elevate
Slightly abduct
Which extra-ocular muscles have an action in elevating the eyeball?
Superior rectus
Inferior oblique
Which extra-ocular muscles have an action in depressing the eyeball?
Inferior rectus
Superior oblique
Which extra-ocular muscles are stronger elevators and depressors of the eyeball when the eye is in the adducted position?
Inferior oblique
Superior oblique
Which extra-ocular muscles are stronger elevators and depressors of the eyeball when the eye is in the abducted position?
Superior rectus
Inferior rectus
What happens if a muscle is weakened?
It’s influence (exerted by its anatomical action on the eyeball) is lost or reduced
Other muscle actions no longer antagonised - resting position of eyeball may deviate (strabismus) due to actions of remaining working muscles
Difficulties with moving eye in certain directions of gaze
What is a strabismus?
Squint
How do you test for lateral and medial rectus?
Straight forward as each only performs one action on the eye
Abduction (LR) and adduction (MR)
How do you test superior an inferior rectus muscles?
Start with eye abducted
Elevate and depress testing for superior and inferior rectus
How do you test for superior and inferior oblique muscles?
Start with eye adducted
Elevation and depression tests for superior and inferior oblique
Why can an adult present with strabismus?
Pathology or disease involving number of different structures:
- neuromuscular junctions e.g. myasthenia gravis
- nerves supplying muscles (CNIII, IV, VI)
How can cranial nerves be affected?
Vasculopathic - microvascular ischaemia, secondary to diabetes or hypertension
Physical compression - tumour or aneurysm
Raised ICP
What causes signs of CNIII palsy?
Innervates all extra-ocular muscles except LR and SO Innervates muscle of eyelid (LPS) Innervates sphincter pupillae muscle Pupil spared - vasculopathic lesions Pupil involved - compressive lesions
What position is the eye in and why in a CNIV palsy?
Innervates superior oblique muscle - intorts, depresses and abducts eye
Therefore those actions are lost and eye is extorted, slightly elevated and adducted
What are the signs and symptoms of CNIV palsy?
Worsening diplopia especially looking down and medially
Eye is extorted, slightly elevated, adducted
Head tilt to compensate extortion of eyeball
What are the signs of CNVI palsy?
Innervates lateral rectus, so unopposed pull of medial rectus muscle, unable to abduct eye on affected side
How can the history help give a clearer indication for more concerning underlying causes of eye problems?
Headache, vomiting could suggest raised ICP
Recent head injury
Presence of pupil involvement in CIII lesions and eye pain/headache
