What is Fourth Nerve Palsy?
The fourth cranial nerve supplies innervation to the superior oblique muscle. The superior oblique muscle is one of the six muscles attached to the eye. The superior oblique muscle moves the eye downward when the eye is turned toward the nose. If the eye is turned outward, it causes the eye to rotate inward. A fourth nerve palsy is the loss or decrease in innervation to the superior oblique muscle. Fourth nerve palsy may also be known as Superior Oblique Palsy or Trochlear Nerve Palsy.
What Causes a Fourth Nerve Palsy?
There are many causes and one of the more common causes is idiopathic (unknown cause). Due to the long course in the brain, the fourth nerve is susceptible to head trauma.
CVA (cerebrovascular accident or stroke)
The fourth nerve palsy may be present for many years before it becomes evident. As we age our ability to fuse the eyes together can become diminished. The double vision may not occur until years after the trauma incident.
Symptoms of Fourth Nerve Palsy
Double Vision or Diploplia
The person will see two objects while having both eyes open. The double vision is mostly vertical but may be torsional as well.
When the person looks down the deviation of the two eyes becomes greater. The person may see double when looking down or complain of eye fatigue when reading.
The person will tilt their head away from the side of the fourth nerve palsy to decrease or eliminate their double vision.
Other Symptoms of Fourth Nerve Palsy
Treatment of Fourth Nerve Palsy
Treatment is based on the etiology of the fourth nerve palsy. Most cases are idiopathic and the treatment is conservative. Prisms may help and temporary Fresnel prisms can be applied to glasses. Once the fourth nerve palsy is stable which can be six to twelve months, permanent prisms can be ground into glasses.
If prisms cannot correct the double vision or the person’s head tilt becomes a problem, surgery may be necessary to correct the condition.