WHAT IS FOURTH NERVE PALSY (A.K.A. SUPERIOR OBLIQUE PALSY)?
There are 12 cranial nerves that begin in the stem of the brain and travel to different areas of the head and neck. Each of these nerves has a specific function. The fourth cranial nerve gives impulses to one of the muscles on the surface of the eye. This muscle is called the “superior oblique” muscle.
The main function of the superior oblique muscle is to move the eye downward. As this muscle’s function is weakened with a fourth nerve palsy, the eye tends to drift upwards. The resultant vertical strabismus is termed a “hypertropia”.
Fourth nerve palsy is often congenital and diagnosed in infancy. However, older children and adults can acquire this form of vertical strabismus. Often the signs and symptoms of congenital fourth nerve palsy may not appear until the later childhood or even adulthood years.
Most patients with isolated fourth nerve palsy have no known underlying cause.
What Are The Signs Of Fourth Nerve Palsy?
Adults who have a fourth nerve palsy will frequently observe double vision.
In children and adults, a noticeable vertical deviation of the eyes is not always the initial sign. Rather, an individual with a fourth nerve palsy will often have a habitual head tilt to the side opposite the palsied eye.
This abnormal head position (a.k.a. torticollis) is actually a natural compensation for the vertical strabismus. With the head tilted to the side opposite the palsy, the vertical misalignment of the eyes is least. The head tilt permits the affected child or adult to experience “binocular vision” thus enabling depth perception.