Superior Oblique Palsy
Fourth Nerve (Superior Oblique) Palsy
What is a fourth nerve palsy?
The Superior Oblique muscle is one of 6 muscles of the each eye. These muscles are called extraocular muscles. The superior oblique is resopnsible for moving the eye downward, inward and causes an inward rotation of the eye also known as intorsion.
The fourth cranial nerve (Trochlear Nerve) innervates the superior oblique muscle, so weakness of the nerve is also known as superior oblique palsy. Weakness of the superior oblique muscle causes a combination of vertical, horizontal and torsional misalignment of the eyes. Naturally, because as mentioned this muscle is responsible for three types of eye movements. The vertical misalignment is typically the most noticeable feature. Palsy refers to a complete weakness of a muscle while a paresis is a partial weakness. It is said that Superior Oblique Palsy ( SOP) is bilateral unless proved otherwise.
Does superior oblique palsy cause double vision (diplopia)?
Superior oblique palsy may cause double vision because of misalignment of the eyes (the brain perceives an image from two different directions). The double vision may be vertical (one image on top of the other), diagonal (vertically and horizontally separated) and less often torsional (rotated or twisted). The torsional phenomenon occurs more frequently with acquired cases of superior oblique palsy.
Why is the head tilted with superior oblique palsy?
Head tilt and/or turn is common with superior oblique palsy. The abnormal head position allows better alignment of the eyes, sometimes aiding in relief of diplopia or double vision. A child with a head tilt should be evaluated by an ophthalmologist for superior oblique palsy and other possible eye problems.
If a child with SOP has a head tilt, it means that she is tilting her head so that she can use both eyes and is doing so by tilting her head. The head tilt in this situation is a good thing. It means the child can use both the eyes. It also means that most likely the child is not supressing one eye or not using one eye. Prolonged supression of vision in one eye can lead to what is known as Amblyopia.
What causes superior oblique palsy?
Superior oblique palsy can be congenital (present at birth) or acquired. Other congenital anomalies may be associated with superior oblique palsy (e.g. a misshaped skull – craniosynostosis). A common cause of acquired superior oblique palsy is head trauma, including relatively minor trauma. A concussion or whiplash injury from a motor vehicle accident may be sufficient enough to cause the problem. Rare causes of superior oblique palsy are stroke, tumor and aneurysm. SOP due to trauma is usually bilateral.
How is superior oblique palsy treated?
In cases of acquired superior oblique palsy it is important to identify and treat the underlying cause first. Once the cause of an acquired superior oblique palsy has been treated, the ophthalmologist will usually wait 6 months for possible spontaneous resolution of the palsy. During that period, diplopia can be managed with prism glasses. Prisms merge two images into one but do not strengthen the eye muscles. If prisms are not effective, patching or covering one eye can alleviate the double vision. If the palsy does not recover over this 6 month period and if prisms are not able to adequately control the diplopia, surgery may be indicated.
The treatment of choice for congenital superior oblique palsy and for an unresolved (after 6 months) acquired palsy is typically eye muscle surgery. Surgery usually 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.
Frequently Asked Questions
Surgically correcting a superior oblique palsy involves moving the position of the eye muscles. Depending on a few factors that surgeon may choose to operate on one or both eye and one or two or three muscles. The time of surgery would depend on the number of muscles needed to be operated upon but usually you can go with about 15 minutes per muscle.
After surgery your doctor would prescribe you certain eye drops to help with the healing. The eyes will also remain red for a few weeks after surgery and that is fine. Nothing to be alarmed about. Result wise we expect an almost immediate effect of the surgery however the muscles may need a few weeks to adjust to their new position but as mentioned a significant portion of the effect of the surgery would be the next day after surgery.
When we operate for this type of squint or rather when we operate for all kinds of squint we always inform patients that there is an 80% chance that the squint would be corrected with one surgery only.
Unfortunately nothing is 100% in medicine and one must know this fact. The chances of this particular squint needing another surgery are probably slightly lower than some other types of squint but yes there is always a chance that a second surgery may be needed.
If needed the second surgery may be needed 6 months to 10 years after the first surgery. So yes, it is diffucult for the doctor to predict when the second surgery would be needed.