4th Nerve - MEH Flashcards
What does the 4th nerve control?
Superior oblique muscle. From the back to the top and runs through the trochlea.
Reminder : What does the superior oblique muscle do?
The eye turns inwards and downwards
How is the 4th nerve different to other cranial nerves?
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
How does the nerve enter the eye?
Through an opening at the back of the eye and then to the superior oblique muscle.
Where does the nerve originate from?
Trochlear nucleus in the midbrain.
The nerve crosses when leaving brainstem
How does the this nerve enter the orbit?
Through the cavernous sinus then through the superior orbital fissure
What is a congenital 4th nerve palsy SO under action?
They have it from birth and it is related to other health problems
Three things that can cause a congenital 4th nerve?
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
What is acquired 4th nerve palsy and give examples of causes?
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
Can acquired 4th nerve palsy be resolved?
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
How is 3rd nerve palsy relevant to 4th nerve palsy?
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
What are actions of the superior oblique?
- Intorsion (max depression and adduction)
- Depression (max when abducted)
- Abduction (minor role)
How do we classify the 4th nerve? So we can refer relevantly
Congenital - uni or bi
Acquired - uni or bi
What do you see with a unilateral nerve palsy on cover test?
- Hyper deviation and maybe eso/extortion
- This may be higher in the near
- Latent or manifest
The hyper deviation will increase when looking at the opposite side
What type of 4th nerve palsy is diplopia more prominent in?
Acquired,
It will have a sudden onset and the second image will be twisted to one side
When will the px experiance dipolopia?
When they look in and downwards. Therfore they may face problems with eating and reading
With unilateral 4th nerve palsy what AHP will happen?
Their chin will be down and face turned and tilted to the opposite side
With bilateral 4th nerve palsy what AHP will happen?
Chin down, head turn / face turn if asymmetrical
What is the muscle sequelae for unilateral 4th nerve palsy?
- Superior Oblique underaction
- contralateral IR overaction
- IO o/a (MOST PROMINENT sign)
- Contralateral SR u/a
May have a V pattern too
Is the muscle sequelae the same of bilateral?
yes similar
- bilateral IR o/a
- bilateral IO o/a
- bilateral SR u/a
V pattern
Can bilateral 4th nerve palsy be masked?
Yes, it may look like a unilateral palsy.
This is why we assume they all are bilateral until proven otherwise.
when is it apparent it is bilateral?
After having a unilateral squint surgery
What are some signs of patients with congential palsies (there are 5)?
BSV
AHP
Well-controlled latent deviation
Full muscle sequelae
Reduced convergence
As the patient has BSV what will they also have?
Stereopsis, vertical fusion range increased
If the px begins to decompensated, what symptoms would they complain of with a congenital 4th nerve palsy?
Asthenopia, blurred vision, diplopia possibly, IO o/a reported from a parent
What is acquired 4th nerve palsy commonly associated with ?
Closed head trauma + loss of consciousness
What is a KEY feature from differentiating congential and acquired 4th nerve palsies?
The affected eye is extorted and projected image is intorted with an acquired palsy
What are three ways torsion can be investigated with?
- Double Maddox rod
- Using an ophthalmoscope to see if the optic disc and macula are aligned
- Synoptophore (this is repeatable )
If a px had a left 4th palsy, what head tilt are the likely to have ?
Tilt right
In the history with an acquired 4th nerve palsy, what must you know?
Precise onset
Cause
If they are symptomatic ( cyclovertical dipl)
Does torsion that prevents fusion in any position of gaze happen in a bilateral or unilateral 4 NP?
Bilateral
Is this a unilateral or bilateral 4 NP?
Unilateral
Is this a unilateral or bilateral 4 NP?
Bilateral
What is a diagnostic test to confirm SO u/a?
Bielschowsky Head Tilt Test (BHTT)
What is an issue with the BHTT?
Can give misleading results, +ve result it dependent on IO o/a
What is a BHTT?
PCT at 3m which is carried out by tilting your head right then to the left
What principle does BHTT work on ?
Righting reflexes - head tilt causes intorsion of IPSILATERAL eye and extortion of contralateral eye
What will a BHTT show if there is a SO palsy ?
Hyperdeviation increase on head tilt to affected side
Why does hyperdeviation increase on head tilt to affected side with px with a SO palsy ?
SO and SR both intort but elevation caused by contraction SR is not balanced by the depression from SO
With a unilateral 4th nerve palsy what deviation will they have in PP?
Unilateral hyperdeviation
With a unilateral 4th nerve palsy, will reversal be detected on BHTT?
No
With a unilateral 4th nerve palsy, how many degrees of extorsion is likely to be present?
<10 degrees
How may ^ D of V pattern is liekly to be present in, with unilateral 4th nerve palsy?
<15 ^
What deviation is present in a bilateral 4th nerve palsy?
Alternating hyperdeviation
Will reversal be acheived with BHTT in a bilateral 4th nerve palsy?
Yes, reversal of heights R to L gaze
In a bilateral 4th nerve palsy, how many degrees of extorsion is there?
> 10 degrees
How may ^ D of V pattern is liekly to be present in, with bilateral 4th nerve palsy?
> = 15 ^ D
Is it likely for a masked bilateral 4th nerve palsy to be detected?
No
What are some features you should be looking for when doing fundoscopy?
Papilloedema and cyclo torsion
Will someone who has a congential 4th nerve palsy complain of torsion?
No- but can be seen on the fundus
Wha should be included in a full orhtopic examination in particular?
PCT
OM
Measurements including torsion
What is part if H&S will help you decided if it is congenital or acquired?
Signs and symptoms
What is some management objectives for someone with congential 4th nerve palsy?
Reduce AHP, prevent decompensation, reduce sx, cosmesis
—> all of which can be achieved b surgery
What is the management for congential 4th nerve palsy?
Surgery
Will the surgical procedure by completed in one surgery?
No- px should be warned it may take two stages
How is a fresnel prism used as a diagnostic tool for congenital 4 NP in adults?
Sx should be resolved with this which will confirm symptoms
How is an acquired 4th nerve palsy investigated?
CT or MRI scan
Should you allow time for recovery of an acquired 4th nerve palsy?
Yes
What can incorporated prisms help with patients who allowing time for recovery?
Join vertical dipl
Patients who are allowing time for recovery, how is torsional diplopia resolved?
Requires occlusion/ occlusive CL
Will someone with a congenital 4th nerve palsy who has small amounts of prism incorporated need surgery?
As the prisms strength will be required to increase, yes they may eventually require surgery
After you have given time for an acquired surgery to resolve, what should happen?
Surgery for residual deviation
How long may it take for an acquired 4th nerve palsy to resolve?
3-6 months
What surgery is normally performed with 4th nerve palsy?
IO weakening surgery for the o/a IO
If there is not an IO o/a, what surgery will be performed and what condition does it put them at risk of developing?
SO tuck (strengthening procedure) as SO lax , they may produce Brown’s
What is the surgical management of 4th nerve palsy with the presence of torsion too?
SO tuck
Harada-Ito on SO in acquired 4th nerve palsies for the torsion
Contralateral IR recession
What is risky about IR when carrying out SO tuck and Harada-Ito procedure?
They need to carefully dissect fibres from IR to lower lid to avoid lower lid restriction
What is the Harada-Ito procedure’s purpose?
treat torsional diplopia caused by excyclotorsion
What is the key deciding factor on further management of 4th nerve palsies?
Measurement of torsion
What is the longest muscle?
SO
