VI Nerve Palsy - Abducens

Question 1

Where will the patient notice an issue if they have a 6th nerve palsy?

Answer 1

• Only motor nerve – only supplies LR
• LR works in distance so deviation is bigger at distance
• LR keeps eye straight in distance, MR keeps eye straight at near
• Px with an eso deviation
• Px may not have issue in their house or in the garden etc but when they’re driving & look far away they see things become double – further away they look the worse it gets

Question 2

What is the pathway of CN6?

Answer 2

• Abducens nucleus in pons (sitting in midbrain)
• Exits brainstem at junction between pons & medulla
• Enters arachnoid space & runs along dorello’s canal
• Passes above tip of petrous temporal bone (point where nerve is at most risk from damage)
  o This bone also sits near inner ear – Gradenigo Syndrome (px would present w/ deafness on one side, with palsy)
• Enters cavernous sinus where it runs alongside the internal carotid artery (at risk if px has stroke or aneurysm – vascular problems)
• Enters lateral aspect of superior orbital fissure & passes anteriorly to innervate lateral rectus
• 6th nerve has longest route – high risk of being damaged
• 6th nerve palsy is most common nerve palsy
  The more nerves that become affected (total ophthalmoplegia – eye does not move) – the lesion must be v close to eye (around about cavernous sinus)

Question 3

What is the aetiology of VI Palsy in >50s?

Answer 3

• Most common aetiology in >50s is a microvascular incident due to:
  o Diabetes
  o Hypertension
  o High cholesterol
• Other aetiologies include:
  o Trauma – due to petrous temporal bone
   Can cause intracranial fluid to increase – nerve gets squashed onto petrous temporal bone
  o Giant cell arteritis – EMERGENCY!!!
   Extreme tenderness on temporal side of head & 6th nerve palsy on same side
  o Stroke

Question 4

What is the aetiology of VI Palsy in <50s?

Answer 4

• Most common cause in <50s:
  o Multiple sclerosis – demyelination
   Pons is a common place to have demyelination – INO is also common due to MS
  o Raised intracranial pressure due to space occupying lesions
   Look for papilloedema – if have this w/ 6th nerve palsy then almost certain px has a tumour  DO NOT WANT TO MISS A TUMOUR
  o Idiopathic increased intracranial pressure
   Too much intracranial pressure can lead to blindspots due to papilloedema  they get bigger & bigger (VFs often non reversible)
  o Trauma
  o Cavernous sinus mass
  o Viral infection
   Children especially – easily pick up viruses
   Could be due to COVID
  o Can be idiopathic
   These pxs should be scanned to check and make sure
• If under 50 then must phone the hospital

Question 5

What is the aetiology of VI Palsy in children (<16)?

Answer 5

• Most common cause in <16s:
  o Congenital VI Palsy
  o Space occupying lesions
  o Trauma
  o Idiopathic
  o Viral infection affecting ears, nose or throat
  o Hydrocephalus – spina bifida
• Tumour is main cause  children can suppress diplopia
  o Child will also have vomiting, papilloedema
• This can look similar to Duane’s Syndrome

Question 6

What are the clinical features of VI Palsy?

Answer 6

• Esotropia in PP greater on distance fixation
  o Worse as they look to affected side
• Esotropia increasing in size on attempted ABDUCTION of affected eye
• Limited abduction of affected eye
• Px complaining of uncrossed diplopia – more so on distance fixation
  o Uncrossed diplopia = esotropia
  o Crossed diplopia = exotropia
• Px may have face turn to affected side
• Field of Binocular Single Vision (BSV) moved towards unaffected eye
  AHP from 6th N palsy – looking to side that’s affected  Right 6th, face turned to R – moving eyes away from problem

Question 7

How do you refer 6th nerve palsy?

Answer 7

REFER 6th into hospital – not a same day emergency if it is a unilateral 6th
Bilateral 6th is an EMERGENCY EYE REFERRAL – be over-cautious

Question 8

What are the differential diagnoses of VI Palsy?

Answer 8

• Myasthenia Gravis
• Duane’s Retraction Syndrome – Type 1
  o Mechanical & congenital
• Infantile esotropia
  o Don’t have something that gets worse in distance
• Mobeius Syndrome – combined 6th & 7th nerve palsy
  o Aetiological problem – congenital
  o 7th – facial nerve –> no facial expression
  o 6th nerve bilateral –> eyes markedly in
• Medial Wall Fracture

Question 9

What are the investigations of VI Palsy in order to differentiate it?

Answer 9

• In order to differentiate VI Palsy:
  o Assess FAR distance (20m) – cover test & measurements
  o Lateral version measurements to compare varying size of esotropia
   Looking L & R – does eso get bigger??
  o Smooth pursuits will show limitation of abduction of affected eye
   Maintain foveal fixation – slowly follow torch
  o Saccades may show hypometria of affected eye
   Saccadic testing – horizontally & vertically
• 2 targets – ask px to look quickly between them
• Isolate an eye by bringing it closer to them and to one side
• If neurogenic palsy – no power to anything so saccades are not as quick
• Saccades require force to complete
  o Lees screen will support smooth pursuit findings & allow comparison of palsy at future visits

Question 10

What are further investigations into a VI Palsy?

Answer 10

• Unless px has high risks factors indicating microvascular incident then px most likely requires neuro-imaging (scan) to determine cause of palsy
  o Send straight to GP for testing – then pick up phone & refer immediately
• Important to establish aetiology of palsy to rule out anything sinister e.g. space occupying lesion or multiple sclerosis

Question 11

What is the management of VI Palsy?

Answer 11

• Orthoptic:
  o Prisms to join diplopia & restore binocular single vision (BSV)
   Prisms should not be given unless stable
  o If deviation too large to control w/ prims then occluding one eye will alleviate px’s symptoms of diplopia
  o Allow 6 month for recovery – most neurogenic palsies will recover within 6 months
   If they do not start to recover then they need further investigations
  o If only partial recovery then Botox or surgery can be used to regain BSV in PP
  Incomitant strabismus – deviation is always bigger when fixing with affected eye
  If px has had a stroke – they can still be at risk of having another