Oculomotor Nerve: What to Know

Medically Reviewed by Poonam Sachdev on October 07, 2022
5 min read

The human eye is a remarkably complex organ controlled by six cranial nerves. The third cranial nerve (CN III) is commonly called the oculomotor nerve. This nerve enables many vital eye movements and works with other cranial nerves to transmit sensations to your brain. 

Several serious diseases can cause oculomotor nerve damage and impair your vision. Understanding oculomotor nerve anatomy and symptoms of oculomotor nerve injury can help protect your vision.

The oculomotor nerve is the third of 12 cranial nerves. The cranial nerves transmit electrical impulses between your brain and your head, neck, and torso. 

The oculomotor nerve controls important muscles in your eye. It allows you to look up and down, fixate your gaze on a moving object, and perform other important eye movements. 

Interesting facts about the oculomotor nerve:

  • Each cranial nerve splits into two branches. One branch transmits messages to the right side of your body and the other to the left.  
  • Oculomotor nerve damage can be frightening, but 63% of people who acquire a third nerve palsy recover fully after receiving conservative treatment measures.

The oculomotor nerve is one of the 12 cranial nerves. These fibers play an important role in the nervous system, a collection of nerves that control essential bodily functions like breathing, your senses, and thought.  

The cranial nerves start near the back of the brain and travel to muscles and organs in your head, neck, and trunk. They're responsible for many essential muscle movements and sensory experiences. 

How does the oculomotor nerve function? This fiber controls five muscles in your eye, and it’s responsible for most voluntary and involuntary functions of this organ. 

Levator palpebrae superioris muscle. This muscle holds your upper eyelid open.

Superior rectus muscle. When you look straight forward, this muscle holds your eye up in its primary position. 

Medial rectus muscle. You use this muscle to move your eye from side to side. 

Inferior oblique muscle. This muscle gives you the ability to move your eye down. 

Inferior rectus muscle. You use this lowermost muscle to turn your eye in toward your nose. 

The oculomotor also plays a role in many other eye movements, like: 

  • Fixating your sight on a static object
  • Focusing your gaze on a moving object as it travels away or toward you 
  • Rapidly moving your eyes between multiple objects 
  • Returning your eyes to their previous location
  • Tracking a moving object with your gaze

Functions and sensations provided by the other 11 cranial nerves include: 

  • Olfactory nerve. This fiber allows you to smell. 
  • Optic nerve. This nerve transmits images from your eye to your brain, enabling you to see.
  • Trochlear nerve. You use this nerve to move your eye from side to side, down, and up. 
  • Trigeminal nerve. This fiber allows you to feel sensations in your face and controls jaw movements. 
  • Abducens nerve. This nerve also helps move your eyes. 
  • Facial nerve. This nerve is responsible for facial expressions and works with the glossopharyngeal nerve to give you your sense of taste. 
  • Auditory/vestibular nerve. This dual-functioning nerve allows you to hear and maintain your balance. 
  • Glossopharyngeal nerve. This nerve gives you the ability to taste and swallow. 
  • Vagus nerve. This fiber controls two essential bodily functions: digestion and heart rate. 
  • Accessory nerve. Also known as the spinal accessory nerve, this fiber controls muscles in your shoulder and neck. 
  • Hypoglossal nerve. This nerve controls the movement of your tongue.

The oculomotor nerve location spans from your brainstem to the back of your eye. The nerve follows this pathway:  

  • Begins in the midbrain 
  • Collects nerves from the cerebral hemispheres and the superior colliculus
  • Passes through the cavernous sinus behind your nose
  • Enters the eye through the superior orbital fissure
  • Divides into superior and inferior branches 
  • Travels to the ciliary muscle and pupillary sphincter muscle

Because the oculomotor nerve interacts with so many muscles and other cranial structures, damage to the nerve can cause serious problems with your vision.

If your eyes or vision feels off, it may indicate oculomotor nerve damage. Here are some other symptoms to watch out for:

  • Double vision 
  • The size of your pupil doesn’t change in response to light 
  • Strabismus, or the inability to properly align your eye 
  • Your eyelid droops uncontrollably 
  • Your pupil looks larger than normal

You should contact a doctor or ophthalmologist immediately if you experience these symptoms or other serious vision issues.

Several medical conditions can affect the function of your oculomotor nerve. 

Third nerve palsy. This disorder occurs when the oculomotor nerve can no longer perform its usual functions due to damage. If you suffer complete third nerve palsy, you will lose the ability to open your eyelid and look inward or up. A partial nerve palsy will reduce normal eye functions. Causes of third nerve palsy include:

  • Aneurysm 
  • Complications from neurosurgery
  • Compression from neoplasm caused by tumors or other diseases 
  • Microvascular diseases, including diabetes and high blood pressure
  • Trauma to the eye 

Congenital causes. Some infants may be born with third nerve palsy. This condition can be caused by birth trauma affecting the skull, developmental issues before birth, infections, and intrauterine trauma. 

Ophthalmoplegic migraine. This rare condition happens when a headache precedes oculomotor dysfunction. Symptoms may include double vision and pupil dilation. 

Tumor. Occasionally, the oculomotor nerve may be affected by cancer. For example, schwannomas, or cancers of the nervous system, have caused oculomotor palsy in some patients. 

Because brain aneurysms, cancer, and other serious disorders can cause oculomotor dysfunction, you should seek medical treatment immediately if you suddenly experience symptoms. 

If you suffer a third nerve palsy or other oculomotor nerve injury, your doctor may prescribe an eye patch or prism glasses to help correct double vision. You can also elect for eye muscle surgery to realign your eyes for proper vision, though this procedure doesn’t always completely resolve vision problems.

Many conditions that affect the oculomotor nerve are outside your control. For instance, you can’t prevent congenital developmental issues or a neurosurgery complication. 

However, there are a few steps that you can take to protect your oculomotor nerve, like:

  • Refraining from using tobacco products like cigarettes and vapes
  • Taking preventative measures to prevent head injury, like wearing a helmet 
  • Working with your doctor to treat chronic conditions like diabetes

Taking care of your oculomotor nerve can help preserve your vision and avoid serious problems.