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Binocular vision- my one > 6th nerve palsy > Flashcards

6th nerve palsy Flashcards

1
Q

What does the 6th nerve supply

A

The sixth nerve supplies only the lateral rectus; therefore, a lesion afecting this nerve will cause an inhibition of abduction only.

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2
Q

Why is the 6th nerve vulnerable to injury?

A

The sixth nerve originates from the back of the brain (from the pons) and, as it has a long way to reach the lateral rectus, hence making it is vulnerable to injury.

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3
Q

What is a 6th nerve palsy?

A

Failure of the eye to abduct causing esotropia (LR affected)

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4
Q

What is the main symptom of esotropia?

A

Horizontal diplopia- 2 images appear side to side

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5
Q

In which position is the diplopia worse and why?

A

On elevation and in the distance because the LR had a bigger function on elevation and in the distance

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6
Q

What is a partial 6th nerve palsy?

A

Patient getting intermittent diplopia meaning diplopia only sometimes, they would get dipl in the distance and worse on the affected side Also increased movement of abduction when tested monocularly

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7
Q

What is a total 6th nerve palsy?

A

Patient having constant diplopia/constant deviation Eye will not move beyond midline so abduction will not improve monocularly

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8
Q

How can you investigate 6th nerve palsy?

A
  1. History 2. Cover test 3. Occular motility 4. Prism cover test
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9
Q

What are the 2 main symptoms patient will present with if they have 6th nerve palsy

A
  1. Diplopia
  2. They may also present with a compensatory head posture consisting of a face turn to the affected side or report that the diplopia is relieved
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10
Q

What do you ask in history to establish 6th nerve palsy?

A

Px will be complaining of diplopia If recently acquired -need to ask px specific time of onset of horizontal diplopia-(recent onset will say I went to put my mascara on and there were two of me in the mirror Is dipl constant or intermittent? Constant diplopia suggests total CN6 palsy, intermittent suggests partial palsy (e.g. I’m okay when I’m reading but can’t watch TV) Did the diplopia change since onset? Got better/worse? Does the px adopt AHP to achieve BSV in pp? GH?- diabetes, hypertension, alcohol – vascular cause Age? Head injury?

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11
Q

How can cover test show 6th nerve palsy?

A

CT may show esotropia in distance with dipl and esophoric at near, (larger angle in distance)

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12
Q

How do you know if patient as BSV?

A

If on cover test they are latent at near, this can indicate BSV. There may be BSV on direction of gaze that’s not affected

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13
Q

Why may patient not have BSV?

A

Following head trauma or pre-existing squint-may be no BSV.

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14
Q

How can ocular motility show 6th nerve palsy?

A

LR underaction one or both eyes on horizontal version Overaction of contralateral MR, contraction of ipsilateral MR, secondary inhibitional palsy of contralater LR Recently acquired=won’t see full muscle sequel: will only see overaction of contralateral synergist. If u see muscle squele then its longstanding

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15
Q

Would you see A or V pattern?

A

LR works more on elevation so you should see A pattern but more likely see a V pattern (worse on down gaze) so trouble when looking down

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16
Q

Why should you do prism cover test to investigate a palsy?

A

Measure deviation and monitor for near and distance if it gets worse refer

17
Q

What is differential diagnosis with 6th nerve palsy and why is it important to differentiate between the two?

A

Duanes looks similar to 6th nerve palsy but Duane’s is not urgent referral whereas 6th is urgent

18
Q

What else can look similar to 6th nerve palsy?

A

Age related distance eso in 70+ pxs also looks similar- BO prims, some progress and need surgery

19
Q

What is a congenital 6th nerve palsy and how common is it?

A

Born with it, very rare but most common palsy in children

20
Q

Can congenital 6th nerve palsy recover?

A

Yes fully recover Benign and not associated with any other neurological or developmental condition.

21
Q

What are the causes of a congenital 6th nerve palsy?

A

Delivery by forceps, trauma like RTA, post viral illness, raised ICP, idiopathic

22
Q

If a child can not abduct, what other investigation should you do to rule out raised ICP?

A

Check optic discs for papilledema

23
Q

What is an acquired 6th nerve palsy?

A

Recently acquired

24
Q

What are the causes of a acquired 6th nerve palsy in childhood?

A

Neoplasm
Trauma
Raised intracranial pressure

Inlammatory conditions

Post viral infection

25
Q

What are the causes of a acquired 6th nerve palsy in yound adults?

A

Neoplasm
Multiple sclerosis

Diabetes
Post viral infections

Trauma

26
Q

What are the causes of a acquired 6th nerve palsy in older adults?

A

Hypertension

Diabetes

Neoplasm

27
Q

What is the most common cause of a aquired 6th nerve palsy in children?

A

Neoplasm-brain tumour

28
Q

What is the most common cause of a aquired 6th nerve palsy in adults?

A

Vacular- DM or HTN

29
Q

How do you manage a suspected 6th nerve palsy in a child?

A

Urgent referral within 1 week to orthoptics and opthalmologist to establish if acquired or congenital and determine underlying cause

30
Q

How is child managed at hospital?

A

Main goal is to regain BSV

If aquired=

Temporary use of prisms while a period of time is given for the condition to self-resolve

Occlusion therapy may be required to treat any amblyopia present

Strabismus surgery may be indicated where a compensatory head posture is uncomfortable or where the esotropia is cosmetically unacceptable.

31
Q

When does opthalmic management for a child not really matter?

A

Depending on the cause of the sixth nerve palsy- eg.
neoplasm; however, improving survival rates more important

32
Q

How do you manage a sudden onset 6th nerve palsy in an adult

A

Urgent referral to investigate the underlying cause to orthoptics and opthalmologist

33
Q

How do orthoptist manage 6 th nerve palsy

A

The condition will be monitored by orthoptics for a period of time to observe recovery of the nerve function.

Fresnel prism to relieve diplopia in the interim, or patients can opt for an occlusive lens/ patch. Similar to third nerve palsies

34
Q

For aquired 6th nerve palsy when is the chance of recovery better?

A

The prognosis for spontaneous recovery is better when the cause is vascular, compared with traumatic or compressive tumours

35
Q

When is prism considered and when is patch considered?

A

Frensel prims in distance glasses for diplopia in small palsy if elderly and unfit for surgery

Large deviation-blenderm occlusion, some prefer eye patch

36
Q

When is surgery considered?

A

Surgery is to reduce symptoms and give large bsv area. Surgery depends on unilat/bilat, degree of paresis and size of deviation

  • Small deviation & reasonable abduction= MR recession and LR resection
  • Complete abence of abduction= BTXA to ipsilateral MR to assess abduction

Binocular vision- my one (11 decks)

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