Extraocular muscles - function and testing Flashcards
what is the medial rectus innervated by and what is its function
cn iii- abbduction only
what is the inferior rectus innervated by and what is its function
inferior rectus is innervated by cranial nerve 3 and depresses the eye (extorsion and adduction)
what is the lateral rectus innervated by and what is its function
- lateral rectus is innervated by cranial nerve 6 and abbducts the eye
what does the superior rectus do and what is its function
- superior rectus - elevates the eye (intorsion and adduction)
what does the superior oblique do
the superior oblique is innervated by cranil nerve 3 and is responsible for intorsion (depression and abduction)
what is the inferior oblique responsible for
innervated by cranial nerve 3 and is responsible for extorsion (elevation and abduction)
what is the lps responsible for
levator palpabrae superioris innervated by cn iii and lid elevation
which nerves pass outside the common tendinous ring
lacrimal
frontal
trochlear nerve
what nerves pass inside the common tendinous ring
- superior divison of the third nerve
- nasocillary nerve - opthalmic division of trigeminal nerve
- inferior division of your third nerve
- abducens nerve - cn 6
which eom are innervated by your superior division of cn III
levator
superior rectus
which eom are innervated by the inferior divison of cn 111
- medial rectus
- inferior rectus
- inferior oblique
where does the cranial nerve 3 branch that goes to your inferior oblique go
- you have a branch coming off your inferior obique that goes to your cillary ganglion
- your cillary ganglion is a parasympathetic ganglion - from there you have short cillary nerves that go to your pupillary sphincter muscles and the cillary muscles
what does rad sin stand for
recti adduct , supeiror intort , obliques abduct
remmber this is only for superior and inferior recti not medial and lateral recti
what does duction mean in terms of eye movement
duction = monocular movement - abbduction and abduction
your only reffering to one eye
what are version eye movements
binocular , simultaneous , conjugate eye movements
dextroversion (right gaze) laevoversion (left gaze)
conjugate means that the eyes are looking in the same direction
if your looking to the right
your right eye will abbduct and your left eye will adduct- this is a conjugate movement because they are both working together to look in the same direction
what are vergence movements
- binocular, simultaneous, disjugate eye movements
related to both eyes working together, but the eyes are working in different directions
e.g. when you accomodate and both eyes move inwards
describe the difference between the axis of the orbit and the eyeball
the axis of the orbit and the eyeball are offset by 23 degrees
difference between the visual axis and the orbital axis
in the primary position the muscles arent fully relaxed they are in a position of tonic contraction - they need to keep the eye looking straight forward- there will be a balance between the different muscles to keep the eye looking straight forward
e.g. if you have a cranial 6 palsy the lateral rectus will be affected- in the primary position the eye will be turned in because the medial rectus is working unnoposed their is nothing that is balancing the function of the medial rectus- you have more adduction than abbudction- the lateral rectus is the main abbducter of the eye - therefore when you lose the medial rectus function the eye becomes turned in - because you have unnoposed medial rectus function and that is when the state of tonic contraction becomes apparent
it is not just that the patient is unable to look out in the - in the primary position the eye is turned inwards-
what are agonist antagonist pairs
- pairs of muscles in the same eye that move the eye in opposite directions
e. g. right lateral rectus and right medial rectus
right lateral rectus abbducts and the eye and the right medial rectus adducts the eye
name an agonist antagonist pair
- right inferior rectus and right inferior oblique
what are synergic muscles
muscles in the same eye that move the eye in a particular direction of gaze
e.g. right superior rectus and right inferior oblique both work in eye elevation
what muscle is a synergistic to the left medial rectus
- left superior and inferior rectus
(the medial rectus adducts the eye - moves the eye in towards the nose)
RAD SIN
(vertical recti - superior and inferior rectus are addducters of the eye)
what are yoke muscles
pairs of muscles in each eye that work together to allow for simultaneous, conjugate gaze (i.e. eyes looking in the same direction)
e.g. right lateral rectus and left medial rectus for the right gaze
what is the difference between synergisitc muscles and yoke muscles
- synergistic muscles = considering movement in one eye
- yoke muscles = considering movement in both eyes
what is the sherrington law of reciprocal innervation
increased innervation to an extraocular muscle is accompanied by a reciprocal decrease in innervation in its antagonist
e.g. when looking to the right the right lateral rectus recieves increased innervation to allow for abduction - as per sherringtons law the right medial rectus recieves decreased innervation so you have less resistance to the movement of the right lateral rectus
(sherringtons law - considers one eye - (agonist- antagonist pairs)
what is herrings law of ocular motility
during a conjugate eye movement - yoke pairs ( allow the eyes to work together to look in a particular direction of gaze) of muscles recieve equal and simultaneous innervation
e.g. during left gaze the left lateral rectus and right medial rectus recieve equal simultaneous innervation
what is the difference between herrings law and sherringtons law
herrings law - both eyes, yoke pairs of muscles
sherringtons law - single eye , one eye at a time
what are agonist antagonist pairs
agonist antagonist pairs refer to muscles in the same eye that work against each other
what are synergistic pairs
synergistic pairs refers to muscles in the same eye that work together
what are yoke pairs
- yoke pairs refers to muscles in both eyes that work together in a direction of gaze
what is sherringtons law
- sherringtons law of reciprocal innervation refers to the reciprocal decreased innervation of a muscles antagonist in the same eye e.g. right medial rectus and right lateral rectus
what is herrings law
- refers to the equal simultaneous innervation of yoke muscle pairs
how do you test the right gaze
- you test the right gaze in adduction and the left gaze in abbduction
how do you test the function of the medial rectus
the medial rectus rotates the eye medially - adduction
to test this you ask the patient to look towards their nose
how do you test the functioning of the lateral rectus
- the lateral rectus - rotates the eye laterally - abduction
so to test it you ask the patient to look away from the midline
how do you test the function of the superior rectus
the fundtion of the superior rectus is to move the eye up and in
- elevates the eye
- intorts the eye (rotates the eyeball medially on its anteroposterior axis)
- adducts the eye
there is an angle between the insertion of the superior rectus and the visual axis
( if you ask the patient to look straight up - because both the inferior oblique and superior rectus are involved in looking up you dont know which one is not working properly)- therefore you want to place the eye in a position where the superior rectus is the strongest elevator of the eye
if you ask the patient to look up and out the eye is aligned with the muscle ( if you ask the patient to look up and out you are more certain that the weakness is in the superior rectus) - so you are trying to find a positon where the superior rectus is the strongest elevator of the eye compared to the inferior oblique
why do you ask the patient to look up and out when testing the superior rectus
- because eye elevation involves both the superior rectus and the inferior oblique it is important to isolate the superior rectus function and asess it in a position where it can only elevate the eye
- this is achieved by aligning the visual axis with the line of insertion of the muscle i.e. by abucting the eye
sr testing = up and out
in 23 degrees abduction the superior rectus is only able to elevate the eye
it is not able to adduct or intort in this position
therefore the sr function is tested in abduction and elevation
how do you test the function of the inferior rectus
- the function of the inferior rectus - is moving the eye down and in
- depresses the eye
- extorts the eye (rotates the eyeball laterally on its anteroposterior axis)
- adducts the eye
- if you ask the patient to look straight down the superior oblique and inferior rectus will move the eye down - you want to ensure that the inferior rectus muscle is much stronger looking down compared to the inferior oblique - you do this by aligning the visual axis with the line of insertion from the muscle
why do you ask the patient to look down and out when testing the inferior rectus
- the inferior rectus muscle needs to be isolated
- eye depression is aided by the inferior rectus and superior oblique
- by ABducting the eye the inferior rectus can only depress the eye and is therefore best tested in abduction and depression
ir testing = down and out
how would you test the superior oblique
you ask the patient to look down and in (adduct the eye) - so that the visual axis is in line with the line of insertion of the muscle
by ADucting the eye 51 degrees the visual axis is aligned with the insertion of the superior oblique
in this position the superior oblique can only depress the eye and is therefore isolated in function and is thus tested
so testing = down and in
how do you test the inferior oblique
ask the patient to look up and in
- io is tested by ADucting the eye so that the visual axis and line of muscle insertion are aligned
in this positon the io can only elevate the eye
io testing = up and in
what is the parks - bielskchowksy three step test
used to diagnose cyclovertical muscle palsy (i.e. obliques or vertical recti)
three steps
- which eye is hypertropic - one eye being above another in the primary position
does hypertropia increase in right or left gaze
does hypertropia increase in right or left head tilt
if someone has a right hypertropia what could the possible muscle weaknesses be
possibilities - right depressors are weak
- right inferior rectus
- right superior oblique
left elevators are weak
left superior rectus
left inferior oblique
if the hypertropia increases in the left gaze what muscle weakness could it be
- left gaze
possibilities
weak right depressor muscle on left gaze (i.e. adduction)
right superior oblique
weak left eleavator muscle on left gaze (abduction)
- left superior rectus
- which muscle introrts the eye - superior rectus and superior oblique
-
during intorsion there should be a balance between the superior rectus and the superior oblique
- as the eye looks in the eye moves up - the superior rectus muscle is working fine - the superior oblique which is also trying to intort the eye and depresses the eye does not have as much power - therefore when the eye is trying to intort the hypertropia increases because the superior rectus is pulling the eye up more
- therefore the muscle weakness is in the right superior oblique muscle
does the hypertropia increase on right or left head tilt
- since the right hypertropia increases in right head tilt
it can be conculuded that there is an imbalnce in the vertical actions f the right superior rectus and the right superior oblique which the right superior oblique being unable to counterbalance the right superior rectus
therefroe the paretic muscle is the right superior obliqeue
