Fourth Nerve Palsies

Common cause of vertical strabismus

Anatomy nuggets

  • Nucleus lies just beneath the IIIn nucleus in the midbrain at the level of the inferior colliculus
  • Decussates and exits the midbrain posteriorly then curves around to travel anteriorly
  • Travels in the lateral wall of the cavernous sinus inferolateral to the IIIn
  • Enters the orbit through the SOF but outside of the annulus


  • 1/3rd are congenital but may manifest in adulthood
  • Acquired:
    • Traumatic (especially bilateral): fourth nerve palsy is the most common nerve palsy following closed head injury
    • Microvascular
    • Idiopathic
    • Iatrogenic (eg ENT or neurosurgery)
    • Tumour eg pinealoma
    • Demyelination
    • Vasculitis
    • Meningitis
    • Cavernous sinus lesion
    • Tolosa-Hunt syndrome
    • HZO

Features of congenital fourth

  • Large vertical fusion range (10-15 PD)
  • High concomitance (may also be present in longstanding acquired lesions)
  • Head tilt on old photos
  • Facial asymmetry

Clinical features

  • Vertical and torsional diplopia

  • Head tilt away from the side of the lesion

  • Aesthenopia (eye strain)

  • Ipsilateral hypertropia/phoria exacerbated on downgaze or head tilttowardsthe side of the lesion

  • Reduced depression especially on adduction

  • Extorsion: can be seen on fundoscopy compared to fellow eye (eg. consider fundus photos)

  • Parks-Bielschowsky 3-step test

    • 1. Cover test: identify higher eye
    • 2. Cover test with gaze to the right, then left: identify where deviation/diplopia is greatest
      • Ie. if greatest in adduction, then obliques involved; if greatest in abduction, then vertical recti involved
      • Step 2: tells you whether superior or inferior muscles
    • 3. Cover test with head tilt to the right, then left: identify where deviation is greatest
      • Superior muscles cause intorsion, while inferior muscles extort
      • Step 3: tells you which eye

Hot Topic

Bilateral fourth nerve palsies (eg. traumatic or congenital): reversing hypertropia

  • R/L on left gaze and L/R on right gaze

  • V patternesotropia

  • Chin down head posture

  • >10 degrees of excyclotorsion

  • Failure of adduction on depression bilaterally


  • Check old photos for abnormal head posture
  • Vascular risk factors (including arteritis)
  • Consider neuroimaging if unclear cause or no recovery after 3 months
  • Orthoptists monitoring including Hess charts
  • Double maddox rod: measure cyclotorsion

Hot Topic

Vertical fusion amplitudes: in congenital fourth, the misalignment from birth means patients are often able to fuse vertical deviations much larger than the normal 2-3 dioptres. Measuring these can be helpful in identifying a longstanding congenital fourth that may have recently decompensated.


  • Conservative: management of symptomatic diplopia with prisms, occlusion, CL
  • Botox
  • Muscle surgery:
    • Harada-Ito for excyclotorsion
    • Inferior oblique weakening (eg. myectomy, recession) for IOOA

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Third Nerve Palsies