6th Cranial Nerve – Abducens nerve lesions

Definition:

Abducens nerve (cranial nerve VI) lesions are pathological processes which negatively affect the nerve function.

Causes:

The exact aetiology of most of the cases of abducens nerve palsies is idiopathic. Research suggests that there may be a hereditary component to this condition.

Broadly speaking, this condition can be divided into acquired and inherited. Below is a list of the acquired forms of abducens nerve palsies:

  • Inflammation, and infections
  • Vascular disorders, including diabetes
  • Space occupying lesions
  • Multiple sclerosis
  • Autoimmune disorders, e.g: Myasthenia gravis

Examination:

The patient will typically present with complaints of diplopia, laziness in one eye, and difficulty or inability to look laterally on the side of the affected eye, as the abducens nerve supplies the lateral rectus muscle of the eye.

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.

In the case of abducens nerve palsy, the patient has a particular difficulty in looking laterally.