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Binocular Vision > 4th Nerve - MEH > Flashcards

4th Nerve - MEH Flashcards

1
Q

What does the 4th nerve control?

A

Superior oblique muscle. From the back to the top and runs through the trochlea.

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2
Q

Reminder : What does the superior oblique muscle do?

A

The eye turns inwards and downwards

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3
Q

How is the 4th nerve different to other cranial nerves?

A

The only nerve start at the back of the brain (has a longer pathway compared to other nerves)

The only nerve to originate from a nucleus contralateral to the muscle it supplies

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4
Q

How does the nerve enter the eye?

A

Through an opening at the back of the eye and then to the superior oblique muscle.

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5
Q

Where does the nerve originate from?

A

Trochlear nucleus in the midbrain.

The nerve crosses when leaving brainstem

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6
Q

How does the this nerve enter the orbit?

A

Through the cavernous sinus then through the superior orbital fissure

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7
Q

What is a congenital 4th nerve palsy SO under action?

A

They have it from birth and it is related to other health problems

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8
Q

Three things that can cause a congenital 4th nerve?

A

Tendon : Loose, absent or inserted abnormally in the globe
Superior oblique muscle: Abnormal
Trochlea : This is abnormal or absent

You can see all of these abnormalities during surgery

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9
Q

What is acquired 4th nerve palsy and give examples of causes?

A

This happens later on in life.
1.Head injury.
2.Microvascular causes (poor blood supply) - more common in older px
3. Inflammation in the region
4. Trauma and raised ICP in children

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10
Q

Can acquired 4th nerve palsy be resolved?

A

Yes it can, 80% is resolved in 3-6 months.

However, it due to a tumour or a head injury it less likely to heal on its own

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11
Q

How is 3rd nerve palsy relevant to 4th nerve palsy?

A

3rd nerve palsy will affect depression

We should look for intorsion in the eye when the eye is depressing : this will show 4th nerve is intact

Remember you can have more than 1 palsy at once

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12
Q

What are actions of the superior oblique?

A
  1. Intorsion (max depression and adduction)
  2. Depression (max when abducted)
  3. Abduction (minor role)
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13
Q

How do we classify the 4th nerve? So we can refer relevantly

A

Congenital - uni or bi
Acquired - uni or bi

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14
Q

What do you see with a unilateral nerve palsy on cover test?

A
  1. Hyper deviation and maybe eso/extortion
  2. This may be higher in the near
  3. Latent or manifest

The hyper deviation will increase when looking at the opposite side

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15
Q

What type of 4th nerve palsy is diplopia more prominent in?

A

Acquired,
It will have a sudden onset and the second image will be twisted to one side

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16
Q

When will the px experiance dipolopia?

A

When they look in and downwards. Therfore they may face problems with eating and reading

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17
Q

With unilateral 4th nerve palsy what AHP will happen?

A

Their chin will be down and face turned and tilted to the opposite side

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18
Q

With bilateral 4th nerve palsy what AHP will happen?

A

Chin down, head turn / face turn if asymmetrical

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19
Q

What is the muscle sequelae for unilateral 4th nerve palsy?

A
  1. Superior Oblique underaction
  2. contralateral IR overaction
  3. IO o/a (MOST PROMINENT sign)
  4. Contralateral SR u/a

May have a V pattern too

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20
Q

Is the muscle sequelae the same of bilateral?

A

yes similar
- bilateral IR o/a
- bilateral IO o/a
- bilateral SR u/a
V pattern

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21
Q

Can bilateral 4th nerve palsy be masked?

A

Yes, it may look like a unilateral palsy.

This is why we assume they all are bilateral until proven otherwise.

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22
Q

when is it apparent it is bilateral?

A

After having a unilateral squint surgery

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23
Q

What are some signs of patients with congential palsies (there are 5)?

A

BSV
AHP
Well-controlled latent deviation
Full muscle sequelae
Reduced convergence

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24
Q

As the patient has BSV what will they also have?

A

Stereopsis, vertical fusion range increased

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25
Q

If the px begins to decompensated, what symptoms would they complain of with a congenital 4th nerve palsy?

A

Asthenopia, blurred vision, diplopia possibly, IO o/a reported from a parent

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26
Q

What is acquired 4th nerve palsy commonly associated with ?

A

Closed head trauma + loss of consciousness

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27
Q

What is a KEY feature from differentiating congential and acquired 4th nerve palsies?

A

The affected eye is extorted and projected image is intorted with an acquired palsy

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28
Q

What are three ways torsion can be investigated with?

A
  1. Double Maddox rod
  2. Using an ophthalmoscope to see if the optic disc and macula are aligned
  3. Synoptophore (this is repeatable )
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29
Q

If a px had a left 4th palsy, what head tilt are the likely to have ?

A

Tilt right

30
Q

In the history with an acquired 4th nerve palsy, what must you know?

A

Precise onset
Cause
If they are symptomatic ( cyclovertical dipl)

31
Q

Does torsion that prevents fusion in any position of gaze happen in a bilateral or unilateral 4 NP?

A

Bilateral

32
Q

Is this a unilateral or bilateral 4 NP?

A

Unilateral

33
Q

Is this a unilateral or bilateral 4 NP?

A

Bilateral

34
Q

What is a diagnostic test to confirm SO u/a?

A

Bielschowsky Head Tilt Test (BHTT)

35
Q

What is an issue with the BHTT?

A

Can give misleading results, +ve result it dependent on IO o/a

36
Q

What is a BHTT?

A

PCT at 3m which is carried out by tilting your head right then to the left

37
Q

What principle does BHTT work on ?

A

Righting reflexes - head tilt causes intorsion of IPSILATERAL eye and extortion of contralateral eye

38
Q

What will a BHTT show if there is a SO palsy ?

A

Hyperdeviation increase on head tilt to affected side

39
Q

Why does hyperdeviation increase on head tilt to affected side with px with a SO palsy ?

A

SO and SR both intort but elevation caused by contraction SR is not balanced by the depression from SO

40
Q

With a unilateral 4th nerve palsy what deviation will they have in PP?

A

Unilateral hyperdeviation

41
Q

With a unilateral 4th nerve palsy, will reversal be detected on BHTT?

A

No

42
Q

With a unilateral 4th nerve palsy, how many degrees of extorsion is likely to be present?

A

<10 degrees

43
Q

How may ^ D of V pattern is liekly to be present in, with unilateral 4th nerve palsy?

A

<15 ^

44
Q

What deviation is present in a bilateral 4th nerve palsy?

A

Alternating hyperdeviation

45
Q

Will reversal be acheived with BHTT in a bilateral 4th nerve palsy?

A

Yes, reversal of heights R to L gaze

46
Q

In a bilateral 4th nerve palsy, how many degrees of extorsion is there?

A

> 10 degrees

47
Q

How may ^ D of V pattern is liekly to be present in, with bilateral 4th nerve palsy?

A

> = 15 ^ D

48
Q

Is it likely for a masked bilateral 4th nerve palsy to be detected?

A

No

49
Q

What are some features you should be looking for when doing fundoscopy?

A

Papilloedema and cyclo torsion

50
Q

Will someone who has a congential 4th nerve palsy complain of torsion?

A

No- but can be seen on the fundus

51
Q

Wha should be included in a full orhtopic examination in particular?

A

PCT
OM
Measurements including torsion

52
Q

What is part if H&S will help you decided if it is congenital or acquired?

A

Signs and symptoms

53
Q

What is some management objectives for someone with congential 4th nerve palsy?

A

Reduce AHP, prevent decompensation, reduce sx, cosmesis
—> all of which can be achieved b surgery

54
Q

What is the management for congential 4th nerve palsy?

A

Surgery

55
Q

Will the surgical procedure by completed in one surgery?

A

No- px should be warned it may take two stages

56
Q

How is a fresnel prism used as a diagnostic tool for congenital 4 NP in adults?

A

Sx should be resolved with this which will confirm symptoms

57
Q

How is an acquired 4th nerve palsy investigated?

A

CT or MRI scan

58
Q

Should you allow time for recovery of an acquired 4th nerve palsy?

A

Yes

59
Q

What can incorporated prisms help with patients who allowing time for recovery?

A

Join vertical dipl

60
Q

Patients who are allowing time for recovery, how is torsional diplopia resolved?

A

Requires occlusion/ occlusive CL

61
Q

Will someone with a congenital 4th nerve palsy who has small amounts of prism incorporated need surgery?

A

As the prisms strength will be required to increase, yes they may eventually require surgery

62
Q

After you have given time for an acquired surgery to resolve, what should happen?

A

Surgery for residual deviation

63
Q

How long may it take for an acquired 4th nerve palsy to resolve?

A

3-6 months

64
Q

What surgery is normally performed with 4th nerve palsy?

A

IO weakening surgery for the o/a IO

65
Q

If there is not an IO o/a, what surgery will be performed and what condition does it put them at risk of developing?

A

SO tuck (strengthening procedure) as SO lax , they may produce Brown’s

66
Q

What is the surgical management of 4th nerve palsy with the presence of torsion too?

A

SO tuck
Harada-Ito on SO in acquired 4th nerve palsies for the torsion
Contralateral IR recession

67
Q

What is risky about IR when carrying out SO tuck and Harada-Ito procedure?

A

They need to carefully dissect fibres from IR to lower lid to avoid lower lid restriction

68
Q

What is the Harada-Ito procedure’s purpose?

A

treat torsional diplopia caused by excyclotorsion

69
Q

What is the key deciding factor on further management of 4th nerve palsies?

A

Measurement of torsion

70
Q

What is the longest muscle?

A

SO

Binocular Vision (30 decks)

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