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Binocular vision YR 3 > 6th nerve palsy > Flashcards

6th nerve palsy Flashcards

1
Q

what is the name of the 6th nerve

A

abducens

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2
Q

describe the anatomy of the abducens nerve and what it can be at risk of because of this

A
  • The nerve has a long tortuous course

- It is predisposed to lesions all along its course from brainstem to the orbit

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3
Q

list all 7 different aetiologies of a 6th nerve palsy in adults

A
  • Neoplasm : chordoma, meningioma, nasopharyngeal carcinoma, pituitary adenoma
  • Trauma : head injury, skull fracture
  • Systemic disorders : diabetes, hypertension – most commonly seen cause of acquired VIN palsy in A and E
  • Other vascular causes : aneurysm, cerebrovascular insults, bleed from an arteriovenous malformation in the midbrain
  • Associated neurological disorder : migraine, demyelinating disease (MS), raised intracranial pressure
  • Iatrogenic : post lumbar puncture, post spinal or epidural anaesthesia - rare
  • Other : idiopathic, inflammatory, infections e.g. post viral (rare)
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4
Q

what is the prognosis of a 6th nerve palsy caused by a vascular aetiology

A

gradual recovery between 6-12 months

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5
Q

list the 5 most common aetiologies of a 6th nerve palsy in children

A

most common:

  • congenital
  • intra cranial tumours
  • trauma
  • idiopathic
  • post viral
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6
Q

list the 3 main features of a 6th nerve palsy

A
  • Esodeviation greater in the distance – may be binocular at near fixation with an esophoria, but this depends on the severity of the paresis they have
  • AHP of face turn to affected side – greater when looking in the distance
  • Field of BSV displaced to the unaffected/opposite side
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7
Q

list the 4 stages of muscle sequelae of a 6th nerve palsy

A
  • Under action of affected lateral rectus
  • Over action/contracture of contralateral medial rectus
  • Over action/contracture of ipsilateral medial rectus
  • Secondary inhibitional palsy of contralateral lateral rectus
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8
Q

list 7 things you can do to investigate a 6th nerve palsy

A
  • History
  • Cover test
  • Ocular movements
  • Hess chart
  • Field of BSV
  • Assessment of binocular vision
  • Measurement of the deviation
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9
Q

what will the history of a recent onset 6th nerve palsy tell

A

Clear, concise time of onset of palsy as main presenting symptom is horizontal diplopia binocularly, greater in distance than near fixation

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10
Q

what may a patient with a partial 6th nerve palsy complain of

A

only of diplopia in the distance and worse to the affected side

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11
Q

what may a patient with a total 6th nerve palsy complain of

A

constant diplopia or a marked AHP

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12
Q

list 5 things you will want to ask/find out about an adult with a 6th nerve palsy

A
  • The diplopia may have changed since the onset - ? better/worse
  • Does the patient adopt an AHP to achieve BSV in pp?
  • Details of the general health and age of patient may indicate the cause e.g.diabetes, hypertension
  • May be a history of head injury
  • It is important to establish the presence of any pre-existing squint as this will affect the management
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13
Q

why should you ask about if the diplopia has changed and how long have they had it for

A
  • because if the diplopia is of recent onset, then you must refer the patient to A and E on the same day
  • but if the diplopia has been present for a few days later, then you do need to ask if the diplopia has progressed or gotten worse, or is it the same as when they first got/noticed it
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14
Q

list 3 characteristics of a 6th nerve palsy

A

The LR muscle abducts the eye and has increased function in the distance and on elevation, so a 6th nerve palsy causes:

  • An esotropia results - may be esophoric for near
  • Larger angle in the distance
  • Should be larger on elevation (A) but in practice often larger on depression (V)
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15
Q

what will you see in partial 6th nerve palsy and compare this to a total 6th nerve palsy

A

some movement of that eye

If you try to test a patient with a 6th nerve palsy abduction monocularly i.e. by covering up their other eye to see if that eye does move any further, you will have a slightly improved abduction if you were to test monocularly.
But on the other hand, on a patient with a total 6th nerve palsy, where they got absolutely no abduction of that eye, whether you test them with both eyes open or monocularly, there will be no improvement to the movement of that eye at all= no further abduction of that eye

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16
Q

what will you see in a cover test when investigating a 6th nerve palsy and why

A

small ET at near, moderate ET at distance with diplopia

because the LR works better for distance and elevation, and because it tends to work better for elevation, you will expect these patients to have an A pattern as the degree of esot is greater in elevation compared to the depression for a 6th nerve palsy, but in clinic they are actually seen to have a V pattern instead

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17
Q

what type of AHP will you see with a 6th nerve palsy and what may you see with a bilateral 6th nerve palsy

A
  • May adopt an AHP of face turn to affected side to achieve BSV in pp
  • If the VIN palsy is bilateral – usually a very large esotropia and in order to fix with either eye in the pp the patient may have to adopt an AHP of face turn to either side so px can fix with each eye individually
18
Q

name 2 possible outcomes of ocular movements when investigating a 6th nerve palsy

A
  • In a palsy there is increased movement of the affected eye when tested monocularly i.e. on abduction
  • In a total VIN palsy the eye will not be able to abduct beyond the mid-line so abduction will not improve monocularly i.e. no further improvement, eye will still remain in the middle or slightly eso
19
Q

what 2 things does a Hess chart provide when investigating a 6th nerve palsy

A
  • Pictorial record

- Repeatable under the same conditions, of the degree of the palsy and the development of muscle sequelae

20
Q

what can’t you tell on a Hess chart that shows a full muscle sequelae

A

which eye was the effected eye

21
Q

what does a field of BSV do and when is it done

A
  • Plots the size and area of single vision

- Plotted at each visit and the results compared

22
Q

where will the field of BSV be plotted for a px with a unilateral 6th nerve palsy and how must the field of BSV be carried out to obtain valid results

A
  • the field of BSV will be deviated to the opposite side of the deviated eye
  • for the patients who adopt a AHP, you need to make sure the px is looking with their head straight
23
Q

explain what tests are done in assessment of binocular vision and why

A
  • CT: done for DV and NV, with and without AHP. It is done without the AHP to identify if they are straight and binocular at near fixation or if they are manifest and it is also done in the distance to prove that they have a manifest esotropia.
    It is done with the AHP to make sure that with the AHP, they are corrected and single and to prove any binocular functions in the presence of the AHP
  • In constant deviations the eso must be corrected first with prisms or on the Synoptophore to measure the angle of deviation and and to see if it gets rid of the double vision at the corrected angle
  • field of BSV
  • Hess chart
  • Full history: px will tell you when they see single and when they see double

are all done

24
Q

when may you find that during assessment of binocular function, there may be no demonstrable BV

A

due to:

  • pre-existing squint where px may not complain of double vision
  • significant head trauma as it is possible to lose BV/fusion ability following head injury = px will have complete total double vision, so even at the corrected angle of deviation

if you measure a 20 dioptre prism esotropia and put up a 20 dioptre prism base out, the patient will still have double vision as they lost their fusion as a result of the trauma

25
Q

how is the measurement of deviation carried out when investigating a 6th nerve palsy

A
  • the prism cover test is performed for near and distance and on side gaze
  • may also measure in elevation and depression to assess A and V patterns
  • done without their AHP so can get a complete picture of their deviation, because with their AHP, they can control to a esop
26
Q

why is a patient seen regularly when managing their 6th nerve palsy

A

in order to monitor the condition and to see if there is spontaneous recovery

27
Q

what is given to patients to relieve diplopia

A
  • Fresnel prisms

- may have to loan planos or fit to lightly tinted sunglasses if the patient does not wear distance glasses

28
Q

how can you manage a patient with large deviations in practice when fresnel prisms don’t work

A
  • occlude one lens (blenderm) may need to use planos etc

- some patients prefer an eye patch

29
Q

how can you manage a patient with no recovery or patients who are elderly or unfit/reluctant to have surgery

A
  • may incorporate prisms in slight palsies and patient wears distance glasses
  • for patients who have a small angled deviation and a constant long standing partial 6th nerve palsy = can manage with fresnel prisms
  • if have been for minimum of 6 months time and no further improvement, for these patients you can incorporate a prism into their glasses
30
Q

how will you manage a patient who has a secondary 6th nerve palsy due to a vascular problem

A

do not need to do any active management such as surgery or botox as the px will usually have full recovery within 6 months

31
Q

what is the aim of surgery for managing a 6th nerve palsy

A

to overcome symptoms and give as large an area as possible of BSV especially in the pp and depression

32
Q

what is the surgical management for a unilateral 6th nerve palsy for someone with small deviations and reasonable abduction

A

MR recession and LR resection of affected eye

33
Q

what is the surgical management for a unilateral 6th nerve palsy for someone with complete absence of abduction

A
  • BTXA to ipsilateral MR to assess abduction as limitation might in part be due MR contracture not allowing the LR to abduct the eye at all
  • then review px after 2 weeks later to see for any abduction after the MR has been injected with BTXA for improvement
  • if there is no improvement of abduction with BTXA after 2 weeks, then the px needs surgery: MR recession and LR resection of affected eye
34
Q

what is the surgical management for a 6th nerve palsy for someone with no LR function i.e. a px who does not have increased abduction of affected eye and instead has a complete abduction deficit, and what are the outcomes of this procedure

A
  • transpose the SR and IR and suture them to the upper and lower borders of the LR of the affected eye and BTXA to ipsilateral MR either at the same time as the surgery or a week or so before
  • Successful procedure as gives a fairly good central area of BSV at pp, px still may have a slight AHP but to a smaller degree
  • Abduction still limited and also some deficit of adduction - so must tell px that surgery is to improve their eyes in pp, but will still limit some of the eye movements in affected eye
  • sometimes post operatively, the px may still have a small angled esotropia which can easily be corrected with a small amount of fresnel prism on their glasses
35
Q

what is the surgical management for a 6th nerve palsy for someone with a bilateral 6th nerve palsy

A
  • Factors similar to those for unilateral palsies and whether symmetrical or not
  • Tend to be total (severe head injury) and therefore necessitate transpositioning procedure combined with BTXA to MR
36
Q

when will you operate on the other eye for surgical management for someone with a bilateral 6th nerve palsy

A

one eye at a time with a 3 month gap

37
Q

what is vital in the management of a 6th nerve palsy in children and what must be done

A

to establish cause - MRI scan and other investigations so essential to refer to neurologist

38
Q

when may a child have a spontaneous recovery with a 6th nerve palsy

A

post viral VIN palsies

39
Q

what is important to avoid happening when managing a child with a 6th nerve palsy and list 4 ways you will carry out your management for this

A
  • Important BSV is not lost and amblyopia prevented in the esotropic eye:
  • Encourage adoption of head posture
  • Fresnel prisms if indicated
  • BTXA to ipsilateral MR muscle done in the onset of first developing the 6th nerve palsy, to straighten the eye and regain BSV in PP
  • Occlusion treatment
40
Q

how will you manage a child’s unrecovered 6th nerve palsy and describe the 2 types that there can be of unrecovery

A
  • If nearly full abduction with normal abducting saccade but a persistent esotropia thats greater in the distance than near, may use BTXA initially to try to restore BSV. If this fails – surgery MR recession and LR resection
  • In unrecovered total VIN palsy – transpose SR and IR to provide some abduction and BTXA to ipsilateral MR

Binocular vision YR 3 (20 decks)

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