Lecture 13 - Extraocular Muscle And Eye Movements Flashcards
Why do we have 2 eyes?
Can perceive depth (stereoscopic vision)
Wider FOV than 1 central eye
What is conjugate gaze?
When both the eyes move synonymously to ensure that the light/image focuses at the same point on each eye so that the image is perceived as one
What is the visual axes?
The central point at which the eye rotates
What is double vision called?
Diplopia
What does misalignment of the visual axis cause?
Why?
Diplopia
The visual axis misaligning means the images focused on different points in each eye so the brain cant fuse the images together
If a patient has Diplopia, what should happen when you cover either of the eyes?
Diplopia should disappear
What are the 2 main axes of the eye?
Visual axes
Orbital axes
Compare the visual axes and the orbital axes in relation to one another when the eye is in primary resting gaze:
Visual axis straight ahead
Orbital axis oblique laterally (follow the pyramid shape of the orbit)
Where do the extraoccular muscles originate from?
Apex of the orbit
Where do all of the extra-ocular muscles insert?
Sclera of the eye
How many extra-ocular muscles are there?
What axis do they run in line with?
6
In line with orbital axis
What are the 6 extra-occular muscles?
4 recti muscles:
Superior rectus
Inferior rectus
Lateral rectus
Medial rectus
2 oblique muscles:
Superior oblique
Inferior oblique
What is the mock chemical formula used to remember the innervation of all the extra-ocular muscles?
LR6SO4(R3)
What does the formulae LR6SO4(R3) tell us the innervation of the extraoccular muscles are?
Lateral Rectus = Abducens nerve (VI)
Superior Oblique = Trochlea nerve (IV)
Rest of muscles = Occulomotor nerve (III)
Go to the last slide and label image 1:
1 = trochlea
2 = superior oblique
3 = medial rectus
4 = superior rectus
5 = lateral rectus
6 = inferior rectus
7 = inferior oblique
8 = levator palpebrae superioris
What is the only extra ocular muscle that doesn’t arise form the common tendinous ring at the back of the orbit?
Superior oblique
What are the extra-ocular muscles doing during primary resting gaze?
Equal and opposite pull
(Agonists = antagonists)
Constant tone
What are the actions of the extra-ocular muscles when the eyes move?
Why is this important?
Agonists contract strongly and antagonists relax
Both eyes must ct simultaneously to ensure the visual axes remain aligned (conugate gaze) to prevent Diplopia
What are the actions of the extra-ocular muscles when the eyes move?
Why is this important?
Agonists contract strongly and antagonists relax
Both eyes must ct simultaneously to ensure the visual axes remain aligned (conugate gaze) to prevent Diplopia
What are the different types of movement the eye can do?
ABduction + ADduction
Elevation + Depression
Intorsion (Internal rotation) + Extorsion (external rotation)
Go to the last slide and label image 2:
1 = elevation
2 = depression
3 = adduction
4 = abduction
5 = INtorsion/internal rotation
6 = EXtorsion/external rotation
What muscles move the right eye laterally/right/abduction?
What muscles move the right eye medially/left/adduction?
Abduction/Lateral = lateral rectus
ADduction /medial = medial rectus
What is the function of superior rectus?
From resting gaze
What its main function?
Elevation
Intorsion
Slight adduction
Main function is elevation
How can you isolate the main elevation function of superior rectus?
Lateral gaze, then look up
What is the main function of the inferior rectus?
What are its functions from primary resting gaze?
Depresses eye
Depression
Extorsion
Adduction
How can you isolate the main depressor function of the inferior rectus?
Lateral gaze then look down
What is the trochlea?
Fascial belly/hook that redirects the superior oblique to insert on the upper lateral sclera
What is the function of superior oblique from primary resting gaze?
Intorsion
Abduction
Depression when medial
How can you isolate the functionality of the superior oblique?
When the eye is positioned medially its depressor action dominates
What 2 muscles depress the eye?
Which muscle dominates depression when the eye is positioned laterally and then medially?
Inferior rectus
Superior oblique
Lateral gaze = inferior rectus
Medial gaze = superior oblique
What is the function of inferior oblique from primary resting gaze?
Extorsion
Abduction
Elevation when eyes medial
How can you isolate the function of the inferior oblique?
When the eye is positioned medially the elevator action dominates
What 2 muscles elevate the eye?
Which muscle dominates elevation when the eye is positioned laterally and then medially?
Superior rectus
Inferior oblique
Lateral gaze = superior rectus
Medial gaze = inferior oblique
Go to last slide and fill out the table labelled 3:
1 = superior rectus
2 = superior rectus and inferior oblique
3 = inferior oblique
4 = inferior rectus
5 = inferior rectus and superior oblique
6 = superior oblique
What is a deviating eye/lazy eye called?
Strabismus
What is it called when a patients eye is abnormally adducted when in resting gaze?
Esotropic
If an eye is adducted in resting gaze (esotropic), what muscle is lost/weak?
What nerve innervates this muscle?
Lateral rectus
Abducens Nerve (VI)
LR6SO4(R3)
Look at last slide and look at the image of the girl and answer the questions:
Eye is adducted (esotropic) + elevated (hypertropic)
Abduction and depression gone
Superior oblique gone
Superior oblique = Trochlea nerve (IV)
LR6SO4(R3)
What muscles elevate?
SR
IO
What muscles depress?
IR
SO
How do you test Lateral Rectus and Medial Rectus?
LR = abduct eye
MR = ADuct eye
How do you test Superior Rectus and Inferior Rectus?
SR = abduct eye (laterally) then look up
IR = abduct eye (laterally) then look down
How do you test Superior oblique and inferior oblique?
SO = Adduct eye then look down
IO = adduct eye the look up
What is strabismus?
Ocular misalignment
What can cause strabismus/ocular misalignment?
Kids (congenital or develop in infancy)
Adults (acquired pathology of neuromuscular junction, extraocular muscles or nerves supplying muscles)
What are the cranial nerves supplying the extra-ocular nerves that can lead strabismus if they’re damaged?
III, IV and VI
What is an example of a neuromuscular junction condition that can cause strabismus?
Myasthenia gravis
What are the clinical features of damage to the trochlea nerve and why?
Eye adducted and elevated since VI innervates superior oblique
Vertically displaced images
Diplopia worsens when looking down
Patient may have head tilt
What can cause trochlea nerve damage?
Born with it
Head trauma
Tumour on trochlea nerve
Diabetic Macrovascular ischamia
Why may a patient Tilt their head with Trochlea nerve damage?
Supplies superior oblique
SO does Intorsion so eye becomes extorted so patient tilts head to counteract
What are the clinical presentations of Occulomotor nerve (III) damage?
Ptosis (severe since innervates skeletal portion of Levator Palpebrae superioris)
Blown pupil
Eyes down and out
What can cause Occulomotor nerve (III) damage?
Micro vascular ischaemia but the pupil is spared
Tumor
Posterior communicatin artery aneurysm
Uncal herniation to due increased Intracranial pressure
What are the clinical features of an Abducens nerve injury?
Affected eye adducted during resting gaze
Worsening Diplopia on affected eye side horizontal gaze
What can cause Abducens nerve injury?
Micro vascular ischaemia
Tumor
Raised intracranially pressure
Look at the last slide and identify what nerve is damaged on image 5:
Trochlea nerve (VI)
Look at the last slide and identify what nerve is damaged on image 6:
Occulomotor nerve (III)
Look at the last slide and identify what nerve is damaged on image 7:
Abducens nerve (VI)
