Extra-occular Eye Muscles, Actions And Diplopia Flashcards
Which muscle groups makes up the extrinsic and intrinsic muscles of the eye and orbit and what are their nerve innervations?
Extrinsic muscles somatic motor Ns
- muscles of the eyelid (also sympathetic innervation)
- extra ocular muscles that move the eyelid
Intrinsic muscles of the eye autonomic/ visceral Ns
- muscles of the iris dilate/ constrict pupil
- ciliary muscle controls thickness of lens
What are the 7 extra-ocular muscles, from superior to inferior?
4 recti (S, M, L, I) 2 Obliques (S, I) LPS
7 S-> I
Superior oblique (onto side eyeball turns 45d) Levator palpebrae superioris Superior rectus (onto front eyeball) Medial rectus (side eyeball) = Lateral rectus (side eyeball) Inferior oblique (side eyeball under M/LR & starts floor of orbit) Inferior rectus (onto bottom eyeball)
All origins from apex (bar IO)
Supplied by cranial nerves
What occurs at primary resting gaze?
Equal and opposite pull of all extraoccular muscles
Each muscle has antagonist
Allows for forward gaze, visual axis both aligned , 2 images reach cortex then fused to be seen as one
Binocular vision - depth perception enabling ‘3D’ vision
What occurs during changing position of gaze? What happens if this malfunctions?
Exert greater pull through action of certain extraoccular muscles while antagonists relax
Muscles moving both eyes must be highly co-ordinated & move simultaneously -> visual axis must remain aligned (conjugate gaze)
If visual axis maligned = diplopia
What directions can the eyeball move in?
Elevation Depression Internal rotation External rotation Adduction abduction
Some extraoccular muscles have one action some have several depending on starting position of eyeball
How do some extraoccular muscles have several actions on the eye?
Run in line with axis of orbit
Some attach to globe at an oblique angle (those attach superior and inferior)
Confers some muscles several actions of movement on globe
What are the anatomical actions of extraoccular eye muscles? Define
Action each individual muscle exerts on eyeball at resting gaze and when moving from primary resting gaze
Which muscle aDduct and aBduct the eye and what is their nerve innervation?
Medial rectus aDducts - oCCulomotor
Lateral rectus - aBducts - ABDUcens
What are the actions of superior rectus muscle?
SR (&IR) arise from apex of orbit
SR inserts into superior anterolateral surface of globe
If starting from primary resting gaze:
Elevate
Slightly aDducts
Slightly intorts/ internally rotates
What are the actions of inferior rectus?
Arises from apex of orbit
Inserts into anteroinferior surface of globe
If starting from primary resting gaze:
Depress
Slightly aDducts
Slightly extorts/ externally rotates
What are the actions of superior oblique?
Arises from apex of orbit passes through trochlea, turns 45d, and inserts superoposterior on globe
Action if starting from primary resting gaze:
Intort/ internal rotation
Depress
Slightly aBducts
Actions of inferior oblique
Arises from anteromedial surface of floor orbit
Inserts inferoposterior globe
Action from primary resting gaze:
Extort/ externally rotate
Elevate
Slightly aBduct
What can happen if an extraoccular eye muscle is weakened?
You can get abnormalities of gaze as one muscle action(s) is no longer antagonised e.g. resting position may deviate = strabismus (squint) or difficulties moving eye in certain directions
Can be congenital or acquired e.g. CN lesion
If a person in resting gaze has their right eye looking to the left and their left eye looking forwards what has occurred?
- The right eye is aDducted
- the action of aBduction is lost
- the muscle which mostly aBducts is lateral rectus
- innervated by CN 6 so could be a CN6 lesion
Diplopia would improve if they looked left and worsen if they looked right
If a person in resting gaze has their right eye elevated and looking left and their left eye looking forwards what has occurred?
- right eye is elevated and aDducted and (can’t see but) externally rotated
- muscular actions no longer acting are depression, aBduction and internal rotation
- superior oblique does all of the above
- Cn4 innervates so could be a lesion of this
May tilt head to correct rotation
Diplopia
When clinically examining actions of extraoccular muscles which movements of the eye do you make a patient do and why?
Make the patient follow your fingers as you draw a H
Lateral and medial rectus only have one action so could test by looking straight and aBducting and aDducting but some muscles >1 action
- superior rectus and inferior oblique both elevate the eye
- inferior rectus and superior oblique both depress the eye
So test by changing starting position; starting position of eye medial (aDducting first):
- IO will elevate alone
- superior oblique will depress alone
Starting position of eye lateral (aBducting first):
- superior rectus will elevate alone
- inferior rectus will depress alone
What can cause CN palsies of the eye? What signs might you find depending on what is causing the pathology?
CN 3/4/6 innervate muscles that move the eyeball
more concerning: Affected by raised intracranial pressure e.g. intracranial haemorrhage or tumour. Headache (+/- vomiting) suggests raised ICP, recent head injury, presence of pupil involvement = CN3 lesions
most likely cause for lesions is vascular disease (microvascular complications) from diabetes and hypertension - patients will otherwise by asymptomatic (apart from signs/ symptoms directly relating to CN lesion), usually self- resolves few months
Abnormalities of eye movements and diplopia, may be obvious from initial inspection
What lesions May affect CN 3, what affect will they have on the eye?
Most extraoccular muscles innervated by oculomotor N (3) (except LR and SO). Innervates majority of muscle of eyelid (LPS) and sphincter papillae muscle.
So eye will be in ‘down and out position’ from depression SO and aBduction LR
- Vasculopathic (microvascular lesions) e.g. diabetes/ hypertension PUPIL spared
- compressive lesions (raised ICP, tumour, posterior communicating artery aneurysm) parasympathetics run on periphery CN3 often involved first = Pupil involved
what effect will cranial nerve 4 palsies have on the eye? what are symptoms/ signs you should look for
Cranial nerve 4 = trochlear
innervates superior oblique muscle only
- acts to intort/ depress/ aBduct
Lose these actions so eye is extorted/ slightly elevated/ aDducted
Compensate for slight extortion by tilting head slightly
Abnormality in gaze v subtle and often missed
Worsening diplopia especially looking down and medially e.g. walking down stairs, reading bc SO main depressor when eye aDducted
what effect will cranial nerve 6 palsies have on the eye?
Cranial nerve 6 = abducens
Innervates lateral rectus
So get unopposed pull of medial rectus = Unable to aBduct affected eye
Diplopia made worse on horizontal gaze
