7.2 Cranial Nerve IV (Trochlear) Palsy

Cranial nerve IV palsies are extremely common in examinations. Although it is the most common cause of a vertical strabismus, the examiner should remember other causes (e.g. TED, orbital fractures) and not rush into Parks 3 step test unless the clinical picture is suggestive of CNIV palsy. Care should be taken to identifying bilateral CNIV palsies and signs indicating a congenital (versus traumatic) aetiology.

Presentation

Children

Congenital: abnormal head position

Adults

Congenital: vague, intermittent vertical diplopia

Acquired

History of trauma, torsional diplopia

Bilateral

Often complain of difficulty reading (not diplopia)

Examination Structure

1. Visual Acuity (Best Corrected)

2. Spectacles

  • BD prism on affected side?

3. Inspection

  1. Abnormal head position- head turn / tilt to the opposite side and down
    1. This counters the loss of depression / intorsion. (cf. DVD where tilt is to the higher side)
  2. Hirschberg (Pupil margin = 15°, Iris margin = 30°)
  3. (Lids normal)
  4. (Pupils normal)
  5. ± Facial asymmetry (congenital CNIV) – hypoplasia on side of head turn suggests congenital
Figure 7.2.1 Right CNIV Palsy

Figure 7.2.1 Right CNIV Palsy
A: Primary. Slight right hypertropia
B: Right head turn (left gaze). Right hypertropia worse
C: Left head turn (right gaze). Right hypertropia less apparent

4. Cover-Testing

  • Hypertropia on affected side
Parks 3-Step Test
  • Does not apply if multiple muscles are involved or if there is a restrictive process i.e. do not start doing this on someone who clearly has thyroid eye disease even if there is height in primary
  • This test is less useful with time due to spread of comitance

(RRR: Right hypertropia worse on Right head turn and Right head tilt; LLL).

  1. Determine which eye is hypertropic in primary
  2. Determine if hypertropia is worse with R or L head turn (worse on ipsilateral head turn due to unopposed ipsilateral IO)
  3. Determine if hypertropia is worse with R or L (Bielschowsky) head tilt (worse on ipsilateral head tilt due to unopposed ipsilateral SR overaction- the only intorter left)
  4. ± 4th step: Hypertropia worse in downgaze (chin up)? (c.f. skew deviation where it is worse in upgaze)
Figure 7.2.2 Left CNIV Palsy

Figure 7.2.2 Left CNIV Palsy
Left hypertropia worse on left head tilt.

Figure 7.2.3 Parks-Bielschowsky Three-Step Test

Figure 7.2.3 Parks-Bielschowsky Three-Step Test
1. Right hypertropia can be due to weakness of the right depressors or left elevators
2. Right hypertropia that increases on right head turn isolates the pathology to the right superior oblique or left superior rectus
3. Right hypertropia that increases on right head turn and right head tilt isolates the pathology to the right superior oblique

5. Ocular Rotations

Look for a “falling eye”:

  • When the affected eye is fixating and adducts along horizontal, the other eye “falls”
  • “IO overaction”(IOOA) & SO underaction (try chin up if can’t hold lids for alternate cover)
  • Look for vertical movement on alternate cover testing
  • May not be seen due to spread of comitance
Figure 7.2.4 Typical Sequelae of a Left CNIV Palsy When Testing Versions

Figure 7.2.4
Typical Sequelae of a Left CNIV Palsy When Testing Versions

6. Other Cranial Nerves

  • CN III, V (corneal sensation), VII, VIII

7. Other Measurements

i. Vertical Fusional Amplitude
  • Congenital CNIV >3Δ vertical fusional amplitude
ii. Torsion
  • Double Maddox rod, Maddox wing, Torsion meter, Synoptophore
iii. Height
  • BD prism on affected side - hold prism parallel to axis of face if there is a head tilt- i.e. not vertical

8. Fundoscopy

  • Check fundus to see if fovea is (abnormally) above the optic disc (loss of SO intorsion)

Bilateral CNIV

Traumatic CNIV are often bilateral

  1. Chin down → diplopia worst in downgaze
  2. Alternating hypertropia (hypertropia of RE with R head turn, hypertropia of LE with L head turn)
  3. V pattern due to paralysis of SO abduction in depression
  4. Bilateral SO underaction, IOOA
  5. 10° of excyclotorsion on Double Maddox rod (NB: Skew deviation gives incyclotorsion)

Clinical Sign

Unilateral

Bilateral

SO Underaction (SO UA)

Unilateral

Ipsilateral SO UA

Bilateral

Bilateral SO UA

IO Overaction (IO OA)

Unilateral

Ipsilateral IO OA

Bilateral

Bilateral IO OA

V Pattern

Unilateral

<10 PD (eso)

Bilateral

>10 PD (eso)

Hypertropia

Unilateral

>5 PD

Bilateral

<5 PD (except asymmetric paresis)

Head Tilt Test

Unilateral

Increasing hypertropia on ipsilateral head tilt

Bilateral

Positive head tilt test to both sides (right hypertropia on right tilt and left hypertropia on left tilt)
Reversing hypertropia on R and L gaze

Objective Torsion on Fundus

Unilateral

Ipsilateral

Bilateral

Bilateral

Extorsion on Double Maddox Rod

Unilateral

<10 degrees (congenital usually do not have subjective extorsion)

Bilateral

>10 degrees (congenital usually do not have subjective extorsion)

Figure 7.2.4 Typical Sequelae of a Left CNIV Palsy When Testing Versions

Figure 7.2.5 Double Maddox Rod Test
Maddox rods are placed vertically in front of each eye. In a CNIV palsy the (horizontal) line image of one will not be parallel to the other because of excyclotorsion of the eye. The amount of excyclotorsion can be measured by rotating the lens until the images of the two lines are parallel. In a bilateral CNIV palsy the amount of excyclotorsion is typically >10°.

Congenital CNIV

Usually unilateral with decompensation.

Usually an abnormal tendon:

  1. Usually less symptomatic torsion / diplopia, despite objective torsion
  2. Old photos (head tilt)
  3. Facial asymmetry (“apex” to opposite side in majority)
  4. 3Δ vertical fusional amplitude (however, fusional amplitudes are also increased in long-standing acquired deviations e.g. TED)

Summary

  • Right or left (unilateral or bilateral)
  • Isolated or other associated CN palsies
  • Congenital

Aetiology

1. Congenital

2. Trauma (Often Bilateral)

Uncommonly

3. Vascular

4. Neoplastic

5. Inflammatory

6. Infective

Investigations

  1. ± MRI brain
    1. Other CN palsies
    2. Progressive
  2. BP, BSL / HbA1C, Lipids (for vascular risk factors)
  3. ± ESR / CRP (for GCA)
  4. ± Tests for Myasthenia
  5. Hess (right CNIV palsy)
    1. No difference in chart size
    2. R hypertropia especially on adduction
    3. R chart: Underaction of SO, Overaction of IO
    4. L chart: Overaction of IR, Underaction of SR
  6. Look at old photographs – driver licence

NB: Remember that a Hess chart does not measure torsion.

Figure 7.2.6 Hess Chart of Acquired Right CNIV Palsy

Figure 7.2.6
Hess Chart of Acquired Right CNIV Palsy

Management

Indications for Treatment:

  1. Abnormal head posture
  2. Diplopia
  3. (Cosmesis)

A) Non-Surgical

  1. Uniocular occlusion for diplopia
  2. (Fresnel) Prism (BD on affected side) if there is minimal torsional component
    1. Only have to prescribe enough for comfort (not necessarily the whole amount up to 10Δ is reasonable)

          

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