Cranial Nerve 3 Palsy

Third Nerve Palsy

Eye movements are controlled by 6 muscles around the eye called extraocular muscles. These muscles receive their signals from the brain from a group of nerves called the cranial nerves. Three of these cranial nerves, cranial nerve III (3), cranial nerve IV (4) and cranial nerve VI (6) are responsible for all of the eye's movements.  Problems with these nerves can cause issues with eye position and movement including eyes turning in, turning out, or being vertically misaligned or causing double vision.


Cranial Nerve 3

Eye movement in 3rd Cranial Nerve Palsy.
Eye movement in 3rd Cranial Nerve Palsy.

Cranial nerve 3, also called the oculomotor nerve, has the biggest job of the nerves that control eye movement. It controls 4 of the 6 eye muscles in each eye:

  • Medial rectus muscle (moves the eye inward toward the nose)
  • Inferior rectus muscle (moves the eye down)
  • Superior rectus muscle (moves the eye up)
  • Inferior oblique muscle (moves the eye up and out)

This nerve also controls the main muscle that lifts the upper eyelid and the muscle that constricts, or shrinks, the pupil. When this nerve is damaged, it may not be able to do its job. This condition is called a palsy. It can be total or partial.


Effects of a Cranial Nerve 3 Palsy

Some or all of the following can occur:

  • The eye can be turned outward and/or downward
  • Inability to move the eye up, down, or in toward the nose
  • Double vision (because the two eyes are not pointed in the same direction). The double vision is usually horizontal and vertical.
  • A droopy or closed eyelid
  • A dilated (larger than normal) pupil
  • Difficulty focusing on close-up objects

What causes a Cranial Nerve 3 Palsy?

It can be caused by a tumor, an inflammatory disorder, trauma, stroke or sometimes it is idiopathic (unknown reason). Sometimes infants are born with a cranial nerve 3 palsy.


What is the treatment for a Cranial Nerve 3 Palsy

Often, no treatment is needed as many patients have spontaneous recovery (complete or nearly complete resolution) within 6-8 months. During that time, treatment is aimed at relieving symptoms.  Often, one eye can be covered with a patch to relieve double vision. Another option is use a Fresnel prism, a special type of overlay for glasses that can relieve double vision by bringing the two images together. If there is no improvement in symptoms after 6-8 months, surgery on the eye muscles can be done to bring the eye into a more normal position. It is very difficult to completely cure the muscle imbalance with a third nerve palsy since so many muscles can be involved. It is important to have appropriate expectations for after surgery as the goal is most importantly to restore single vision in the straight ahead position and when looking down.