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Fourth Nerve Palsy

In this video, we see the eye movements of a patient with a fourth cranial nerve palsy.

The fourth cranial nerve innovates the Superior Oblique (SO) Extraocular Muscle.

The SO muscle depresses, intorts (incyclotorsion) and abducts.

Therefore:

  • The eyes would sit straight or with a vertical misalignment.
  • When taken into laevodepression, an underaction of the SO muscle would be seen.
  • Other muscles will compensate for this imbalance and over/underact according to Herring’s and Sherrington’s Laws. This is called a muscle sequelae.

Causes of a 4th Nerve Palsy:

  • Congenital
  • Trauma (whiplash)
  • Vascular disease
  • Aneurysm or tumour (less common)
  • Stroke

‘See also’ below the eye movements recorded by an Orthoptist in a right fourth nerve palsy. Note the sequelae.

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Orthoptics: How to be a Brilliant Allied Health Professional

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