4th Cranial nerve – Trochlear nerve lesions


Trochlear (IV) nerve lesions are abnormal pathological processes which negatively affect the nerve’s function.


As with oculomotor nerve palsies, trochlear nerve palsies can be broadly divided into congenital and acquired.

Isolated acquired trochlear nerve palsies are difficult to diagnose, and are therefore often idiopathic. Below is a list of acquired cranial nerve IV palsies:

  • Head trauma
  • Aneurysms
  • Space occupying lesions
  • Raised intra-cranial pressure
  • Multiple sclerosis, meningitis
  • Myasthenia gravis


The patient will typically present with complaints of vertical diplopia, which is especially manifest as the patient tries to read. There may be an inability to look down and in, and horizontal diplopia.

The cranial nerves III, IV, and VI and usually tested together as the examiner instructs the patient to hold his/her head still and follow only with the eyes a finger that circumscribes a large “H” in front of the patient. The examiner is looking out for any signs of strabismus, and whether eye movement is smooth, synchronous and that both the patient’s eye are able to fix on the same point.