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Binocular vision YR 3 > 4th nerve palsy > Flashcards

4th nerve palsy Flashcards

1
Q

where does the trochlear nerve nucleus lie

A

in the midbrain caudal to the 3rd N.nucleus

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2
Q

list the route that the 4th nerve takes from it’s nucleus in the midbrain up till the where the muscle it attaches to is inserted

A
  • Its fibres pass dorsally and emerge decussating in the anterior medullary velum, caudal to the inferior colliculi
  • The nerve passes laterally around the midbrain tectum, crossing the superior cerebellar artery and enters the dura at the free edge of the tentorium
  • It then runs forward in the cavernous sinus and enters the orbit via the SOF, above the annulus formed by the rectus muscles
  • The superior oblique has its origin above and medial to the optic foramen
  • It runs forward to the TROCHLEA at the angle between the superior and medial wall
  • The tendon of the muscle passes through the trochlea and runs at angle of about 54 degrees
  • The SO tendon‘fans’ out making a curved insertion - functionally 2 insertions
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3
Q

what is the 4th nerve the only nerve with

A

a dorsal exit from the brain stem

i.e. only nerve that comes out from the back (the other exit from the front)

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4
Q

which 2 places in the brain can cause damage to the 4th nerve

A

the cavernous sinus and the superior orbital fissure

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5
Q

what type of insertion does the SO make when attaching to the globe

A

tendon‘fans’ out making a curved insertion

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6
Q

what is the 2 insertions that the superior oblique makes and what action of the muscle does each insertion give

A
  • The anterior portion (aligned transversely)
    giving the muscle a torsional action (to intort the globe)
  • The posterior portion (parallel to the anteroposterior axis)
    giving the muscle a depressing and abducting action
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7
Q

what is the primary, secondary and tertiary action of the SO and in which position each action is at it’s maximum

A

INTORSION
maximum in depression and when globe is abducted

DEPRESSION
maximum action when globe is adducted

ABDUCTION
minor role

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8
Q

which 2 types of 4th nerve palsies is there and why is it important to ddx between them

A

Congenital
Unilateral or bilateral

Acquired
Unilateral or bilateral

ddx between them is important for management for each one

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9
Q

what is seen with the position of the eye in a unilateral SO palsy
at which distance is this deviation seen more
what may be seen with it’s position in pp
at which gaze position does this deviation size increase

A
  • Hyperdeviation in affected eye (eso and extortion)
  • hyper > at 1/3m than 6m (greater at near than distance)
  • In primary position may be hyperphoric or hypertrophic
  • Hyperdeviation increases in gaze to the opposite side
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10
Q

what 4 symptoms will a px with a SO plays experience

A
  • diplopia

- AHP

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11
Q

in which type of 4th nerve palsy is the diplopia more prominent
which 2 types of diplopia is experienced
and where is each one seen at maximum

A
  • More prominent in acquired than congenital which may suppress or won’t notice until they start looking for it
  • Vertical diplopia maximum on contralateral depression
    e.g. is at the main action of the SO muscle = down and in,
    so for R eye is seen when it is down and looking to the left
  • Torsional diplopia (if recognised) maximum on ipsilateral depression
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12
Q

what is the AHP for a SO palsy

A
  • Head tilt to the opposite side
  • Head turn to the opposite side
  • Chin depression
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13
Q

who may control to an AHP

A

those with a long standing SO palsy

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14
Q

what is the muscle sequelae for a Right SO palsy

A

RIO + (usually the most prominent sign - not always present - significant for management)
= over actions of ipsilateral antagonist

LIR +
= over action of contralateral synergist

LSR –
= underaction of ipsilateral antagonist

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15
Q

what pattern on OM can be seen with a SO palsy

A

V pattern of

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16
Q

list the muscle sequelae for a bilateral SO palsy and what pattern is most likely to be seen in OM
what will be seen if the L and R SO palsy is symmetrical and if its asymmetrical

A
  • Bilateral IO overactions
  • Bilateral SR underactions
  • Bilateral IR overactions
  • V pattern due to bilateral IO overactions seen in muscle sequelae
  • if symmetrical = don’t see hyper deviations as much in pp
  • if asymmetrical = can see hyper deviation in pp
    can also see an alternating hyper deviation e.g. when looking to LHS = R eye is higher and looking to RHS = L eye is higher, because of the IO overactions
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17
Q

list the 4 things you will see in OM in someone with a bilateral SO palsy

A
  • Hyperdeviation will reverse in contralateral field: R/L on left gaze, L/R on right gaze esp
  • V pattern (=/>15^)
  • Torsion significant if acquired
  • AHP
    Chin down only (no head turn or tilt as its bilateral)
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18
Q

what is the AHP for a bilateral SO palsy

A

chin down only

no head turn or tilt

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19
Q

what type of diplopia do patients with a bilateral SO palsy complain about in pp

A

only complain about torsion - 2 things being tilted

as theres no hyper deviation in pp if its symmetrical bilateral palsy

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20
Q

what is impossible to do for patients who have a bilateral acquired SO palsy

A

reading is impossible as they get torsional diplopia when they look down so these patients are very symptomatic
when investigating, can use a target such as a pen to see 2 that are tilted

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21
Q

what may a bilateral SO palsy be

therefore what principle do you have to work on

A
  • Bilaterality may be masked (may not often see, even if acquired)
  • Work on the principle that all SO – (congenital or acquired) are bilateral until proven otherwise
  • May be very asymmetrical
  • Bilaterality not always apparent until after surgery for unilateral SO
    (so may only see second palsy when the main one is corrected by surgery)
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22
Q

when may a bilateral SO palsy be more apparent

A

until after surgery for unilateral SO

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23
Q

what is a congenital SO palsy more appropriately referred to as and why

A

a SO underaction - because they don’t actually have anything wrong with the nerve

24
Q

which 3 structures of the SO can be affected in a 4th nerve congenital palsy and what is exactly affected within each structure
how can these abnormalities be observed

A
  • SO tendon
    absent
    ‘loose’
    abnormally inserted on the globe
  • SO muscle
    may be abnormally developed
  • Trochlea - for muscle to go through
    may be abnormally developed/absent

Abnormalities may be observed at surgery and nowadays an MRI scan

25
Q 
what problems can the: 
tendon 
muscle 
trochlea 
of the SO have in a congenital palsy
A
  • SO tendon
    absent
    ‘loose’
    abnormally inserted on the globe
  • SO muscle
    may be abnormally developed
  • Trochlea - for muscle to go through
    may be abnormally developed/absent
26
Q

what is the presentation of someone with a congenital 4th nerve palsy
what is it rare to find

A
  • Typically controlled to BSV with AHP
  • May decompensate in childhood (mother sees eye deviate) or adult life (get diplopia)
  • Rare to find no evidence of BSV (as most control with a AHP)
27
Q

what 3 symptoms if present typical of decompensation, will a px with congenital 4th nerve palsy have and when will they tend to decompensate
what may be seen in the IO+ is quite marked

A

Symptoms if present typical of decompensation

  • asthenopia
  • blurred vision
  • possible diplopia but rather vague onset and duration
  • in adulthood
  • if this happens in childhood - mother will notice a big hyper deviation when child looks to the ipsilateral side

If IO+ marked may c/o cosmesis (i.e. parents of children) or may observe AHP

28
Q

list 5 typical features seen in congenital 4th nerve palsies

A
  • AHP for unilateral palsy (often unaware of it) chin down; face turn & head tilt to opposite side
  • Bilateral cases chin down may have slight FT/HT if asymmetric palsies
  • BSV of varying quality depending on compensation; px will have stereopsis; fusion – vertical range may be increased ~20^ = a sign that somethings been there for a long time
  • Concommitance develops = if can see a full muscle sequelae it is a sign its been there a long time
  • Convergence may be reduced due to increasing hyperdeviation as eyes converge = asthenopic symptoms
29
Q

what will a px with a congenital bilateral 4th nerve palsy who has concomitant fields referral be like

A
  • no need to refer for brain scan
  • as doesn’t get any worse
  • so can refer slowly
30
Q

what is the most common cause of an acquired 4th nerve palsy and how does this cause the damage

A
  • with closed head trauma and loss of consciousness
    e.g. car accidents or falling off horse
    something that causes you to suddenly stop and when the brain hits the front of the skull and then goes back and breaks the roots of the 4th nerve at the brainstem
  • Point of trauma may be decussation of nerve fibres in anterior medullary velum or more likely due to avulsion (break off) of tiny nerve rootlets as they emerge form the dorsal brainstem = bilateral SO nerve palsy
31
Q

list all 3 aetiologies of a acquired 4th nerve palsy
which type of patients each are more common in
what else a 4th nerve palsy may also occur with

A
  • Closed head trauma
    horse riders, car accident
  • Vascular
    in older patients (>60-65) e.g. microvascular = DM or HTN
  • tumours and raised ICP
    children and young adults (so look at disc to see if elevated)
  • may also occur in combination with 3rd and 6th n.palsy
32
Q

if a px has a 3rd nerve palsy, how do yo check that the 4th nerve is still in tact and why do you have to do this

A
  • look for intorsion of the affected eye as depression is attempted as sign that 4th n. function is intact
  • because depression is severely affected in both cases
33
Q

what is the appearance of the eye in torsion and what will be the projected image in a SO palsy

A
  • eye will be extorted

- projected image will be intorted

34
Q

what is a key feature of differentiating an acquired 4th nerve palsy to a congenital nerve palsy
and why does this differentiation occur

A
  • A patient seeing torsion is a key feature for differentiating acquired 4th nerve palsy from congenital
  • In congenital palsy a sensory adaptation to torsion has occurred (presumably in the cortex)
35
Q

how can you see if a congenital patient has torsion objectively as these patients do not complain of symptoms
what value in this assessment will be indicative of torsion

A
  • assessment of the fundus with indirect ophthalmoscope may show macula is considerably lower than the OD – i.e. the fundus is extorted
  • Normal fovea approx. 0.3disc diameters below OD; more than this indicative of torsion
36
Q

what 2 tests can you use to measure torsion

A
  • synoptophore

- double maddox rods

37
Q

what 4 clues in a history will indicate a 4th nerve palsy is acquired

A
  • usually precise onset
  • may know cause
  • symptomatic++ cyclovertical diplopia
  • In bilateral cases torsion may prevent fusion in any position of gaze (c.10 degs)
38
Q

how can you use prisms to determine is someone has an acquired 4th nerve palsy

A
  • prisms cannot correct torsional deviations
  • so if when you put up prisms to fix a vertical deviation and the patient still complains of double vision = a suspect torsional deviation i.e. 4th nerve palsy
39
Q

why is a Bielschowsky Head Tilt Test (BHTT) done

why can this be a misleading test

A
  • As diagnostic test to confirm SO underaction
  • Often misleading results and a positive test result seems to depend on the degree of IO+ (which occurs in other conditions than SO-)

a +ve test = very positive
a -ve test = very negative

40
Q

explain the principle of the Bielschowsky Head Tilt Test (BHTT)

A

Based on righting reflexes head tilt causes intorsion of ipsilateral eye and extorsion of contralateral eye

In SO- hyperdeviation increases on head tilt to affected side; RSO and RSR intort the RE but RSO- so elevation caused by contraction RSR is not balanced by depression from RSO

  • So if theres a weak SO, then can’t intort the eye and so the SR has to do it, but the SR is a primary elevator and secondary intorter
  • So if you tilt the head to the RHS towards the weak SO, this will cause the SR to intort the eyes = causes a big amount of elevation
  • So if you see a big variation in deviation between tilting the head to the right and left = it is bound to be a SO weakness when tilting towards the affected side
41
Q

how is the Parks’ 3 step test for SO palsy carried out

which 2 types of SO palsy is it not great for

A
  • Rt or Lt hyper in pp?
    look at vertical deviation in pp
  • Hyperdeviation increases on adduction or abduction?
    look at vertical deviation in R and L stage
  • Hyperdeviation increases on head tilt to Rt or Lt? (BHTT)
    look at head tilt to R and L

Not great for acquired or bilateral 4th nerve palsy

42
Q

list 5 signs of evidence seen in a 4th nerve palsy that shows it is unilateral and not bilateral

A
  • Unilateral hyperdeviation in pp
    unlikely to be in bilateral, but can be is asymmetrical
  • No reversal on OM/BHTT
    will have reversal if bilateral in R and L gaze
  • Excyclo if present 10 deg is definitely bilateral when looking in down in depression
  • V usually
43
Q

what 2 things may happen in time with a acquired 4th nerve palsy

A
  • May recover with time - esp microvascular cause
    or
  • SO palsy persists; relative concomitance spreads across the lower field and up and down on the affected side; rarely becomes totally concomitant (unlike congenital palsies)
44
Q

what 3 things will you carry out in the management of a SO palsy

A
  • History
    Signs and symptoms
  • Full Orthoptic examination
    Covert test
    Eye movements
    Measurements inc torsion
  • Funduscopy
    Papilloedema
    Cyclotorsion
45
Q

what will you do whilst managing your patient during history and why

A

Signs and symptoms
because it is very important to take a detailed history
as a px with a disease can easily decompensate their 4th nerve palsy etc
or you want to know if its well controlled
is the px on any drugs

46
Q

what 3 things will you look at when managing your px during a full orthoptic examination

A

Covert test
Eye movements
Measurements inc torsion

47
Q

what 2 things will you look for when managing your px during funduscopy

A

Papilloedema

Cyclotorsion

48
Q

list 3 treatment options you have for managing a congenital 4th nerve palsy

A
  • surgery
  • diagnostic fresnel prisms
  • small amounts of incorporated fresnel prisms
49
Q

who with a congenital 4th nerve palsy will need surgery
why will they need it
why is surgery 1st choice in adults
why is surgery also done for cosmetic aspects

A
  • To eliminate or reduce AHP in children and prevent decompensation
  • Because they will have sore necks and end up with changes in their neck bone
  • Surgery usually the 1st choice in adults to reduce symptoms/AHP
  • Surgery also for cosmetic aspects - updrifts on lateral gaze
50
Q

why may you try diagnostic fresnel prisms for managing congenital 4th nerve palsy in adults and which type of fresnel prism will you use
what is the drawback of incorporating small amounts of prisms and which type will you use
what must the patient be warned of when deciding to operate and why

A
  • May try diagnostic Fresnel prisms BD in adults to confirm resolution of symptoms
    if it doesn’t resolve = torsion is the problem
  • Small amounts of prism BD may be incorporated into specs - but tend to increase with time and require surgery
    But if they have torsion, then they need surgery as the prism wont correct
  • May need more than 1 operation – patient must be warned
    As this may unmask the other SO
51
Q

what 3 steps will you take when managing someone with an acquired 4th nerve palsy

A
  • Investigate cause
  • Allow time for recovery
    Prisms may join vertical diplopia
    Torsional diplopia will need occlusion
  • Surgery for residual deviation (whatever left)
52
Q

which 2 surgery options is there for a SO palsy and give reasons for why you will decide on one out the the two

A

IO weakening or SO strengthening

  • Usually target the overacting inferior oblique/a IO
    Weakening procedure
  • If not much IO+ or SO tendon obviously lax, may tuck SO which carries some risk of producing a Brown’s syndrome
53
Q

when will you decide to strengthen the SO as oppose to weaken the IO in surgery and what risk can this procedure carry

A
  • If not much IO+ or SO tendon obviously lax
  • may tuck SO
  • carries some risk of producing a Brown’s syndrome = can’t look up and in properly as prevents SO muscle going through trochlear
  • as the muscle doesn’t slip so easily through the trochlear and so can end up with elevation problems
54
Q

what can be a further surgery for a SO palsy
what does the surgeon need to be careful of when carrying this out and why
what is this procedure best for instead

A
  • Contralateral IR recession
  • Needs careful dissection of fibres from IR to lower lid to avoid lower lid retraction post-op
  • Best as an adjustable procedure to avoid overcorrection
55
Q

for the surgical management of acquired SO palsy:

  • what is used as a temporarily and under what circumstance
  • how long do you have to wait until doing surgery
  • what may you also need to do and why
  • what is the surgical decision based on
A
  • Fresnel prisms temporarily if torsion superable
    and
  • Wait 6-12 months post-onset to do surgery
  • May need to occlude for torsion or for loss of fusion
  • Surgical decision on presence of torsion
56
Q

what type of surgery is required to treat the torsion in an acquired 4th nerve palsy and what outcome does it give

A
  • Harada-Ito procedure on SO
    = operate on anterior portion of the SO
  • To enhance torsional action of SO

Binocular vision YR 3 (20 decks)

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