Cranial Nerve 4 Palsy

Fourth 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 4

Cranial nerve 4, also called the trochlear nerve, controls the movement of the superior oblique muscle. This muscle moves the eye down and rotates the top of the toward the nose. It also helps pull the eye outward when the eye is looking downward. 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.

What causes a Cranial Nerve 4 Palsy?

It can be caused by a tumor, an inflammatory disorder, trauma or stroke. Sometimes the reason is unknown (idiopathic). Some infants are born with a cranial nerve 4 palsy.

Effects of a Cranial Nerve 4 Palsy

Some or all of the following can occur:

• The eye may turn up, causing it to sit higher than the other eye
• Inability to move the eye down and in toward the nose
• Double vision (because the two eyes are not pointed in the same direction). This double vision is vertical and torsional (tilted)
• Tilting of the head to compensate for the double vision

Treatment for a Cranial Nerve 4 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.