Oculomotor Nerve Palsy

What is the Oculomotor Nerve?

The oculomotor nerve is one of 12 sets of cranial nerves. Many of these nerves are part of the autonomic nervous system. The autonomic nervous system supplies (innervates) organs, like your eyes.

The oculomotor nerve is the third cranial nerve. It allows movement of the eye muscles, constriction of the pupil, focusing the eyes and the position of the upper eyelid.

Cranial nerve III works with other cranial nerves to control eye movements and support sensory functioning.

It controls four of the six muscles that enable eye movement. 3rd Cranial nerve makes it possible to:

  • Elevate the upper eyelid.
  • Focus the eyes.
  • Respond to light by making the black centre of the eye (pupil) smaller.
  • Move your eyes inward, outward, up and down and control torsion.

It coordinates eye movement with motions that include:

  • Accommodation, focusing on an object that’s moving closer to or further away from you.
  • Optokinetic reflex, changing eyes back to their previous position after focusing on an object.
  • Saccades, quick motions that shift your gaze from one object to another.
  • Smooth pursuit (visual tracking), which enables you to hold your gaze on a moving object.
  • Vestibule-ocular reflex, which adjusts eye positioning when your head is moving.
  • Visual fixation, gazing at an object that is not moving.

Oculomotor dysfunction is a group of disorders affecting 3rd Cranial nerve. These disorders are also known as third nerve palsy. They occur when 3rdcranial nerve becomes paralyzed.

Third nerve palsy can be present at birth. It may also occur later in life due to:

  • Inadequate blood flow: Causes lack of oxygen that nerves need to function properly.
  • Nerve compression: Abnormal pressure on a nerve.

Conditions that may cause oculomotor dysfunction include:

  • Brain aneurysm.
  • Brain tumour.
  • Head injuries.
  • Demyelinating disease (multiple sclerosis)
  • Microvascular disease (diabetes and high blood pressure).
  • Infections, including HIV and Lyme disease. 
  • Migraine.
Oculomotor Nerve Palsy - eye clinic

Treatment for third nerve palsy depends on what caused it. There is no treatment to re-establish function of a congenital third nerve palsy. An acquired third nerve palsy may resolve on its own, depending on the cause. If a brain tumour or aneurysm is causing the third nerve palsy, surgery to relieve pressure on the third nerve may help it function. 

A Neuro-ophthalmologist will wait at least 6 months after onset of third nerve palsy to see if it gets better on its own. During this time, an eye patch or prism glasses may help you with double vision. Eye muscle surgery (strabismus surgery) may help to realign the eyes so that the eyes are straight when looking straight ahead. But it can sometimes take numerous procedures. People typically still experience double vision when looking to the sides after strabismus surgery.

Contact your Neuro-ophthalmologist if you experience symptoms of third nerve palsy. These include:

  • An abnormally large pupil. 
  • A pupil that doesn’t shrink in response to light.
  • Double vision (diplopia).
  • One or both eyes drifting off to the side (strabismus).
  • Drooping eyelid (ptosis) that may cause it to cover the pupil.
A note from Athens EyeCare Clinic

The oculomotor nerve is the third cranial nerve. It controls four of the six muscles that enable eye movement. Conditions affecting cranial nerve III include third nerve palsy. It is often a complication of medical issues such as uncontrolled diabetes or a brain aneurysm. Third nerve palsy might impact your vision and the appearance of one or both of your eyes. Many people make a full recovery, although it can take around six months.

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