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Fourth Nerve (Superior Oblique) Palsy

What is a fourth nerve palsy?

The fourth cranial nerve innervates the superior oblique muscle so weakness of the muscle is also known as superior oblique palsy. The superior oblique muscle produces downward, outward and inward rotation (intorsion) of the eye. Therefore weakness of the muscle causes a reduction in depression of the eye and a relatively elevated position compared to the other eye. The eye also often rotates outward (extorsion) and slightly inward. The upward movement of the eye is typically the most noticeable feature. Palsy refers to a complete weakness of a muscle while a paresis is a partial weakness.  This condition is usually unilateral (one eye) but can be bilateral (both eyes).

Does superior oblique palsy cause double vision (diplopia)?

Superior oblique palsy may cause diplopia because of misalignment of the eyes (the brain percieves an image from two different directions). The double vision is frequently vertical (one image on top of the other), diagonal (vertically and horizontally separated) and less often torsional (rotated or twisted). The torsional phenomenon is noted most frequently with bilateral superior oblique palsy. 

Why is the head tilted with superior oblique palsy?

Head tilt toward a shoulder (and/or turn) is common with superior oblique palsy. The abnormal head position allows the eyes to align better, sometimes actually aiding in relief of diplopia. A child with a head tilt should be evaluated for superior oblique palsy and other possible eye problems.

What causes superior oblique palsy?

There are two primary causes for superior oblique palsy. The first and most common cause is congenital (born with the problem for no apparent reason). Rarely congenital anomalies are associated (i.e. a misshaped skull – craniosynostosis). The second most common cause is head trauma including relatively minor trauma. A concussion or whip lash injury from a motor vehicle accident may be sufficient to cause the problem. Rare causes of superior oblique palsy include stroke, tumor and aneurysm.

How is superior oblique palsy?

Once the cause of an acquired superior oblique palsy has been treated, it is usual to wait 6 months for the palsy to resolve spontaneously. While awaiting spontaneous resolution, diplopia can be managed with prism glasses. Prisms merge two images into one but do not strengthen the eye muscles. If prism is not effective a patch or covering one eye can alleviate the double vision.

The treatment of choice for congenital superior oblique palsy and unresolved (after 6 months) acquired palsy is typically eye muscle surgery. Surgery often minimizes double vision, reduces the unsightly upward drift of an eye and corrects a compensatory head tilt. Surgery is performed on one or both eyes depending on the extent of the eye misalignment, the change of the misalignment in different directions of gaze, the amount of head tilt and the amount of torsion.