Oculomotor Nerve - Pathology

Pathology

Paralysis of the oculomotor nerve, i.e., oculomotor nerve palsy, is a rare condition. It can arise due to:

• direct trauma,
• demyelinating diseases (e.g., multiple sclerosis),
• increased intracranial pressure (leading to uncal herniation)
  • due to a space-occupying lesion (e.g., brain cancer) or a
  • spontaneous subarachnoid haemorrhage (e.g., berry aneurysm), and
• microvascular disease, e.g., diabetes.

In people with diabetes and older than 50 years of age, an oculomotor nerve palsy, in the classical sense, occurs with sparing (or preservation) of the pupillary reflex. This is thought to arise due the anatomical arrangement of the nerve fibers in the oculomotor nerve; fibers controlling the pupillary function are superficial and spared from ischemic injuries typical of diabetes. On the converse, a subarachnoid haemorrhage, which leads to compression of the oculomotor nerve, usually affects the superficial fibers and manifests as a palsy with loss of the pupillary reflex.