13. Extra ocular eye muscles and movements Flashcards
why do we have binocular vision?
Binocular vision allows for wider field of vision and depth perception enabling ‘3D’ vision (stereoscopic vision)
What is needed so that binocular vision is effective?
- Visual axis of both eyes need to be aligned
- Eyes need to co-ordinate and move together- conjugate eye movement
- Two images that reach cortex are ‘fused’, so perceived as one
Describe how two eyes work together to look at an object?
if both eyes looking at the same object, they need to work together so that light from the object hits the same spot on the back of each eye
Describe how the two eyes work together to look at a moving object
If an object is moving, both eyes need to move together so that the light from the object hits the same spot on the back of the both eyes
what does misalignment of visual axis result in?
Diplopia - double vision
Why does misalignment cause diplopia?
Misalignment of two visual axes image focuses on different area of each retina
– Brain unable to ‘fuse’- thus see two separate images
Describe diplopia
two images seen, can be displaced horizontal, vertically and/or diagonally
What makes up the extrinsic muscles of the eyes?
- muscles of the eye lid
- extraocular muscles that move the eyeball
What are the intrinsic muscles of the eye?
- sphincter pupillae
- dilator pupillae
- ciliary muscle
What makes up the intrinsic muscles of the eyes?
- Muscles of the iris (dilator and constrictor of
the pupil) - Ciliary muscle controls thickness of the lens
What are the muscles of the eyelid and what innervates them?
- orbicularis oculi (palpebral part): facial nerve
- levator palpebrae superioris: oculomotor nerve
- superior tarsal smooth muscle: sympathetic innervation
What are the extraocular muscles of the eye and what is their innervation?
4 Recti:
- superior rectus
- inferior rectus
- medial rectus
- lateral rectus
2 obliques:
- superior oblique
- inferior oblique
What is the general function of the extra occular muscles
move the eyeball
where do the extra-ocular muscles insert?
sclera
where do the extra-ocular muscles originate?
Apex of orbit (exception of IO, arises floor of orbital cavity anteriorly)
Where exactly do the 4 recti extra-ocular muscles originate in the apex of the orbit?
from a common tendinous ring
What are the innervations of the extra- ocular muscles?
Oculomotor: - superior rectus, inferior rectus, medial rectus, inferior oblique Trochlear: - superior oblique Abducens: - lateral rectus
How can the innervation of extra-ocular muscles be remebered?
LR6SO4
lateral rectas = CN 6
superior oblique = CN 4
everything else = CN 3
What is the effect of the different extra-ocular muscles inserting at slightly diffferent positions of the sclera?
Each muscle will have a certain ‘pull’ and action on eye movement
What are the two axis of the eye?
- Axis of the orbit
- Visual axis (axis of the eyeball)
In what axis do the extraocular muscles run?
In line with axis of orbit
Which and why do some muscles have more than one action on the eyeball?
Run in line with orbit axis so attach to eyeball at an oblique angle
- superior/inferior rectus/oblique
• Confers several ‘actions’ of movement on globe (not just simply ‘up’ and ‘down’) for some of the extra ocular muscles
Contractions of which muscles is responsible for the primary resting gaze?
• Equal and opposite pull of all extraocular muscles
• During resting gaze their actions are balanced
allowing for forward gaze
• Each muscle has antagonist of its movement
What is required to change position of gaze?
Exert greater pull through action of certain extraocular muscles, while antagonists relax
What is a conjugate gaze?
Visual axis remain aligned
- eyes move together
• Muscles moving both eyes must be highly coordinated and move simultaneously
What are the terms used for direction of eye movement?
Up: elevation, Down: depression
Lateral: abduction, Medial: adduction
External and internal rotation
What is the action of the medial and lateral rectus muscles (if starting from primary resting gaze)?
Lateral rectus: abduction of eyeball
Medial rectus: adduction of eyeball
What are the actions of superior rectus (if starting from primary resting gaze)?
- elevation (main action)
- slightly adducts
- slightly intorts (internally rotates)
Where do the superior an inferior rectus originate from?
from apex of the orbit
Where does the superior rectus insert?
SR inserts into superior anterolateral surface of globe
When is the superior rectus a more powerful elevator?
when eye is positioned laterally
Where does the inferior rectus insert?
inserts obliquely into anteroinferior surface of globe
What are the actions of inferior rectus muscles (if starting from primary resting gaze)?
- depression (main action)
- slightly adducts
- slightly extorts (externally rotates)
When is the inferior rectus a more powerful depressor?
when eye is positioned laterally
Where does the superior oblique originate and insert?
Arises from apex of orbit, passes through trochlea, inserts into superior-posterior aspect of globe (posterior to equator)
What are the actions of superior oblique muscle (if starting from primary resting gaze)?
- intortion (main action)
- depression
- slight abduction
What is the main action of the superior oblique muscle when eye is positioned medially?
more powerful depressor
What is the origin and insertion of inferior oblqiue?
IO arises from anteromedial surface of floor of orbit;
inserts into infero-posterior aspect of globe (posterior to equator)
What are the actions of inferior oblique muscle (if starting from primary resting gaze)?
- extortion (main action)
- elevation
- slight abduction
What is the main action of the inferior oblique muscle when eye is positioned medially?
more powerful elevator
Which extra-ocular muscles have an action in elevating the eye ball?
superior rectus, inferior oblique
Which extra-ocular muscles have an action in depressing the eye ball?
inferior rectus, superior oblique
Which extra-ocular muscles are stronger elevators and depressors of the eyeball when the eye is in the adducted position?
strongest elevator - inferior oblique
strongest depressor - superior oblique
Which extra-ocular muscles are stronger elevators and depressors of the eyeball when the eye is in the abducted position?
strongest elevator - superior rectus
strongest depressor - inferior rectus
What the term for deviation of resting position of eyeball?
Strabismus (condition of having a squint)
What is the effect of an extra-ocular muscle is weakened?
• If a muscle(s) weakened, its ‘influence’ (i.e. exerted by its anatomical action on the eyeball) is lost (or reduced)
• Other muscle actions no longer antagonised (“balanced” out)
– Resting position of eyeball may deviate = strabismus (squint) due to actions of remaining working muscles
• Difficulties with moving eye in certain directions of gaze
What is the action of lateral rectus?
abduction
what is the action of medial rectus?
adduction
What is important when testing movements of the eye?
Need to Isolate an Action of Each Muscle to Test Them
What shape is used to test the movements in each eye?
H (for each eye)
How are the lateral/medial rectus muscles tested?
Abduction (LR) and adduction (MR) of the eye
Why is elevation and depression of eye more complicated to test?
elevation and depression (in midline) involves two muscles each
How is are the superior/inferior rectus muscles testing?
Start with the eye in the abducted position:
- elevate to test superior rectus
- depress to test inferior rectus
(as Recti muscles are main elevator (SR) and depressor (IR) of the eye when the eyeball is starting from the lateral position)
How is are the superior/inferior oblique muscles testing?
Start with the eye in the adducted position:
- elevate to test the inferior oblique
- depress to test the superior oblique
(as Oblique muscles are main elevator (IO) and depressor (SO) of the eye when the eyeball is starting from the medial position)
who are ocular misalignment common in and what causes it?
Common in children (congenital or develops in infancy)
– exact cause not always known
if ocular misalignment is acquired in adults, what could be the cause?
• pathology or disease involving number of different structures…
– E.g. Neuromuscular junctions (e.g. myasthenia gravis)
– Nerves supplying the muscles (CN III, IV, VI)
What are the possible causes of cranial nerve palsies?
- Vasculopathic (microvascular ischaemia -secondary to diabetes, hypertension)
– Physical compression e.g. from tumour or aneurysm (III)
– raised intracranial pressure
what do the CNIII innervate?
- all extra -ocular muscles(except LR and SO)
- muscle of eyelid(LPS)
- sphincter pupillae muscle
How will the eye be positioned in a CN III palsy?
Down and out - abducted and depressed
What type of CNIII lesions typically affect the pupil?
Compressive lesions (parasympathetics in periphery of the nerve)
What type of CNIII lesions typically spare the pupil?
Vasculopathic lesions (microvascular ischaemia -secondary to diabetes, hypertension)
What type of commpressive lesions might affect cause a CNIII palsy?
raised ICP, tumour, posterior communicating artery aneurysm
How will the eye be positioned in a CN IV palsy and why?
EXTORTED, slightly elevated and adducted
- unopposed action of inferior oblique as loss of actions of superior oblique (only muscle innervated by CN IV)
How might a person with CN IV palsy compensate?
Compensate for the slight extortion of eyeball by tilting the head slightly
When is diplopia worse in CNIV palsy?
Worsening diplopia (on downward vertical gaze) especially looking down and medially e.g. walking down stairs, reading - Remember SO is main depressor of the eyeball when in adduction so this action affected when weak
What is the presentation of CNVI palsy, when is it worse?
- Unable to abduct the eye on affected side - eye thus adducted - unopposed pull of medial rectus
- CNVI innervates lateral rectus
- Report diplopia, made worse on horizontal gaze
What other symptoms may be associated with CN lesions and what might these indicate?
- Headache (+/-) vomiting could suggest raised ICP (secondary to tumour or haemorrhage)
- Recent head injury
- Presence of pupil involvement in CN III lesio
what is the most likely cause for CN III, IV, VI lesions?
vasculopathic
– Patients will be otherwise asymptomatic (apart from signs/symptoms directly relating to CN lesion)
– Lesions usually self-resolve within few months
