Unilateral CNIV Palsy

Question 1

What does the superior oblique do?

Answer 1

Depresses, Intorts, Abducts

Question 2

What are the symptoms of a CNIV palsy?

Answer 2

The affected eye cannot intort and go down. As a result, people see double images, one above and slightly to the side of the other.

Question 3

What is difficult to do in CNIV palsy?

Answer 3

Going downstairs because this requires both intorsion and downgaze

Question 4

What AHP are we likely to see in unilateral CNIV palsy?

Answer 4

Tilting the head to the side opposite the affected eye muscle can compensate and eliminate the double images.

This position can eliminate the double images because people use eye muscles that are unaffected by the palsy to focus both eyes on an object.

Question 5

What diplopia do cases of unilateral CNIV palsy present with?

Answer 5

Patients can present with binocular, vertical or torsional diplopia.

The superior oblique causes eye depression in adducted gaze. This can explain the worsening of a patient’s diplopia when they attempt to visualize objects in primary position, especially in down-gaze.

Question 6

When is diplopia most prominent in CNIV nerve palsies?

Answer 6

More prominent diplopia in acquired opposed to congenital cases as they’re more likely to suppress or won’t notice until they start looking at it

Question 7

When is vertical diplopia at it’s maximum in unilateral CNIV palsy?

Answer 7

Vertical diplopia maximum on contralateral depression
e.g. is at the main action of the SO muscle = down and in,
so for R eye is seen when it is down and looking to the left

Question 8

When is torsional diplopia at it’s maximum in unilateral CNIV palsies?

Answer 8

Torsional diplopia (if recognised) maximum on ipsilateral depression

Question 9

When does a congenital CNIV palsy develop?

Answer 9

This occurs during development in the womb and is thought to be caused by either a dysfunction of the nerve or a weakness of the muscle tendon. The exact cause is unclear. Some congenital palsies may not be diagnosed until much later in life. This is due to the brain’s ability to adapt and patients may have no symptoms for many years. Sometimes also known as an SO underaction because they don’t actually have anything wrong with the nerve itself.

Question 10

What is a congenital CNIV palsy also known as?

Answer 10

SO underaction (because they don’t actually have anything wrong with the nerve itself)

Question 11

In a congenital unilateral CNIV palsy what is their BSV like?

Answer 11

• Typically controlled to BSV with AHP
• May decompensate in childhood (mother sees eye deviate) or adult life (get diplopia)
• Rare to find no evidence of BSV (as most control with a AHP)

Question 12

What might a congenital CNIV palsy experience when they decompensate?

Answer 12

In congenital 4th nerve palsy when they decompensate:

• asthenopia
• blurred vision
• possible diplopia but rather vague onset and duration
• in adulthood
• if this happens in childhood - mother will notice a big hyper deviation when child looks to the ipsilateral side

If IO+ marked may c/o cosmesis (i.e. parents of children) or may observe AHP

Question 13

What are some features of congenital CNIV palsies?

Answer 13

• AHP for unilateral palsy (often unaware of it) chin down; face turn & head tilt to opposite side
• Bilateral cases chin down may have slight FT/HT if asymmetric palsies
• BSV of varying quality depending on compensation; px will have stereopsis; fusion – vertical range may be increased ~20^ = a sign that somethings been there for a long time
• Concomitance develops = if can see a full muscle sequelae it is a sign its been there a long time
• Convergence may be reduced due to increasing hyperdeviation as eyes converge = asthenopic symptoms

Question 14

How might one acquire a CNIV palsy?

Answer 14

May be caused by conditions such as diabetes and hypertension or, in old age, small vessel disease or vascular changes. Damage may also occur as a result of trauma and is sometimes seen in patients who have had road traffic accidents or other “closed head trauma”. Fourth nerve palsy may be seen in patients who have had a stroke and in rare cases of patients with a brain or ocular (eye) tumour. Neurological conditions such as MS can also cause fourth nerve palsy.

Poor blood flow, concussions and whiplash, vascular disease, aneurysm, increased IOP, stroke and brain tumour

Question 15

What are the most common causes of acquired CNIV palsy?

Answer 15

• With closed head trauma and loss of consciousness
  e.g. car accidents or falling off a horse; something that causes you to suddenly stop and when the brain hits the front of the skull and then goes back and breaks the roots of the 4th nerve at the brainstem
• Point of trauma may be decussation of nerve fibres in anterior medullary velum or more likely due to avulsion (break off) of tiny nerve rootlets as they emerge form the dorsal brainstem = bilateral SO nerve palsy

Question 16

What is the possible AHP in unilateral CNIV palsy?

Answer 16

Chin-down and head tilt/turn contralateral to affected eye. There are paradoxical head tilts (towards higher eye) to make the deviation worse and separate the images further to eliminate discomfort associated with the effort to fuse images.

Question 17

What do we see on a cover test in unilateral CNIV palsy?

Answer 17

• Hypertropia in primary on horizontal gaze to the unaffected side (in adduction) or tilt to ipsilateral side
• Positive Bielschowsky head tilt test to ipsilateral shoulder
• Degree of excyclotorsion (usually around 5 degrees when unilateral)

Question 18

How to does a unilateral CNIV palsy present on Parks-Bielschowsky?

Answer 18

If the hypertropia is worse in ipsilateral tilt this implicates the ipsilateral superior oblique as the intorsional ability of the superior oblique is weakened. In this head position, the ipsilateral superior rectus will compensate for the weak intorsion of the ipsilateral superior oblique, but will elevate the eye and further worsen the hypertropia. Patients may develop a compensatory head tilt to the contralateral side to reduce their diplopia. In a patient with hypertropia that worsens in left gaze and right head tilt is most compatible with a right superior oblique palsy.

Question 19

What will be shown on a double maddox rod in unilateral CNIV palsy?

Answer 19

• In fourth nerve palsy the Double Maddox rod should demonstrate unilateral excyclotorsion.
• Skew deviation may demonstrate bilateral torsion or incyclotorsion, both of which are inconsistent with fourth nerve palsy.
• Bilateral CN IV palsy may have large degree of bilateral excylotorsion (e.g., > 10 degrees) on the Double Maddox rod test

Question 20

How can fundus photography show a unilateral CNIV palsy?

Answer 20

• Could demonstrate that the fundus of the affected eye is excyclotorted.
• Skew deviation may display incyclotorsion of the affected eye or bilateral torsion.
• Bilateral CN IV palsy might show bilateral excyclotorsion.

Question 21

How can the upright-supine test lead to a CNIV palsy diagnosis?

Answer 21

• In a fourth nerve palsy, ocular torsion and hypertropia should be unaffected by positional changes.
• Skew deviation may demonstrate decreasing vertical strabismus with position change from upright to supine. Greater than 50% change in vertical strabismus with position change from upright to supine is a positive test.

Question 22

How can a PAT or Diagnostic Occlsuion be used to determine the true angle of deviation in unilateral CNIV palsy?

Answer 22

• Aim:
  Determine the true angle of deviation
  Advocated for longstanding unilateral SO palsy
• Prism Adaptation Method:
  Fully correct angle of deviation with prisms for 1-2 weeks
  Perform PCT on return to determine if angle has increased
• Diagnostic Occlusion Method:
  Occlude the paretic eye (non-fixing eye) for 1 day - 2 weeks FT.
  Perform PCT before occlusion and on return without allowing binocular vision

Question 23

What is the RSO sequelae pattern?

Answer 23

u/a RSO, o/a LIR, o/a RIO, u/a LSR

Question 24

What is the LSO sequelae pattern

Answer 24

u/a LSO, o/a RIR, o/a LIO, u/a RSR

Question 25

What do we expect in primary position in a unilateral CNIV palsy?

Answer 25

In primary we would expect hypertropia, excyclo and ET (ET may be minimal)

Question 26

When will a patient with a unilateral CNIV palsy experience diplopia the most?

Answer 26

• Tilting their head to the affected eye (ipsilateral head tilt)
• Increase in vertical deviation towards contralateral horizontal gaze (i.e. RSO palsy = increased in left gaze). Increased vertical deviation at near.
• Increase in excyclotropia in abduction (where the secondary action is most effective) meaning with RSO palsy we’d see an excyclo increase in right gaze and in LSO palsy we’d see an excyclo increase in left gaze. Particularly more prominent in depression.
• Excyclo diplopia will be greatest in abduction
• Vertical diplopia will be greatest in direction of action of palsied muscle (contralateral depression)
• Uncrossed diplopia may be minimal or absent but will be greatest in abduction
• BSV will therefore be in the direct opposite position of the action of the palsied muscle so in a RSO BSV will be greatest in dextroelevation (as the SO is greatest in laevodepression) and LSO will have the most BSV in laevoelevation

Question 27

How does a congenital unilateral CNIV palsy present?

Answer 27

• Frequently present with appearance of deviation or AHP
• Diplopia not bothersome as suppression is often present. They often are absent of symptomatic excyclotorsion whilst objective torsion is noted.
• May be amblyopic
• Onset unknown
• AHP often seen in old photos
• CT large hyperphoria at times exceeding 20PD and presents as relatively concomitant. As a result of this the area of BSV is often larger than expected (as the fusion range is larger).
• OM’s muscle sequelae is fully developed which can be difficult to determine primary affected muscle so there’s little difference on size of field on Hess Chart.

Question 28

How does a congenital unilateral CNIV palsy present in terms of muscle sequelae?

Answer 28

OM’s muscle sequelae is fully developed which can be difficult to determine primary affected muscle so there’s little difference on size of field on Hess Chart.

Question 29

How big is a hyperphoria in unilateral CNIV palsy cases during CT?

Answer 29

CT large hyperphoria at times exceeding 20PD and presents as relatively concomitant. As a result of this the area of BSV is often larger than expected (as the fusion range is larger).

Question 30

How can facial asymmetry cause a CNIV palsy?

Answer 30

Facial asymmetry can cause congenital; distance between lateral canthus and corner of the mouth is reduced on side of head tilt due to chronic tilting of head

Question 31

What are the classes (accordingly to Von-Noorden & Helveston) of congenital CNIV palsy with “lax” tendons?

Answer 31

Congenital SO palsy can often have anomalous tendons meaning it is “lax” and thus redundant tendons (87% who 4th nerve palsies have this) which creates a weak SO. There are 4 classes: (Von-Noorden and Helveston)
o I – Redundant Tendon
o II – Misdirected Tendon
o III – Tendon in Tenons
o IV – Absent Tendon

Question 32

What can you see in decompensating CNIV palsies that show it is decompensating and not acquired?

Answer 32

In decompensating they have learned to control deviation, but with time might struggle to control the deviation and begin to decompensate and begin to be symptomatic but you will find the markers of a long-standing palsy like extended fusion ranges and complete muscle sequalae

Question 33

How can we look for a concomitant CNIV palsy?

Answer 33

Look for intorsion (by observing the movement of the vessels on the conjunctiva) during attempted depression in abduction

OR

Check fundus to see if fovea is still (normally) below the optic disc (SO / CNIV and SR / CNIII) intort the eye. Loss of intorters will cause fovea to be above the optic disc.