Inferior Oblique Procedures
Yasmin Poustchi Mali, MD
WEAKENING OF THE INFERIOR OBLIQUE: MYECTOMY, RECESSION, ANTERIORIZATION, AND EXTIRPATION
Preoperative Considerations
Unilateral superior oblique palsy:
Perform preoperative strabismus measurements and intraoperative forced duction testing, specifically the superior oblique traction test (see chapter 42), which may influence the surgical plan. Specifically, consider the following factors when determining the surgical plan:
Magnitude of the hypertropia.
Pattern of the hypertropia.
Presence of superior oblique laxity.
Weakening of the inferior oblique muscle is preferred if:
The hypertropia is worse on adduction and contralateral upgaze.
The tropia is <15-20 prism diopters in primary gaze.
There is no superior oblique laxity on forced duction testing.
Either inferior oblique recession or myectomy have been found to be successful to weaken the inferior oblique muscle function.
In cases of large hypertropia in primary position or in downgaze, operation on 2 or 3 muscles may be necessary and almost always includes inferior oblique weakening. The patient is at higher risk for overcorrection when simultaneous surgery is performed.
Always consider the possibility of bilateral superior oblique palsy prior to operation as unilateral inferior oblique weakening may unmask superior oblique palsy on the other side.1
“V”-pattern strabismus (see Chapter 51):
Perform careful and detailed preoperative strabismus measurements and assessment of extraocular muscles. When developing a surgical plan, consider the following factors:
The prism diopter difference between upgaze and downgaze.
The presence of inferior oblique overaction.
The presence of hypertropia in side gaze.
Weakening of the inferior oblique muscles is preferred if there is significant inferior oblique overaction, a V-pattern strabismus with a difference between upgaze and downgaze of at least 15 prism diopters, and hypertropia documented in side gaze.
Inferior oblique weakening procedures have little effect on horizontal strabismus correction. Therefore, surgery to correct the horizontal strabismus is performed concomitantly.
Dissociated vertical deviation (DVD):
Frequently seen in conjunction with inferior oblique overaction.
Inferior oblique recession and anteriorization (also called “inferior oblique anteriorization” or “inferior oblique anterior transposition”) weakens the inferior oblique and can be used for the same indications as other inferior oblique weakening procedures. This procedure has the added benefit of holding the eye down and can be particularly useful in the setting of dissociated vertical deviation (DVD) with inferior oblique overaction.
When the inferior oblique insertion is transposed from beneath the lateral rectus to the lateral border of the inferior rectus insertion, the inferior oblique will function to mechanically hold the eye down. The neurovascular bundle of the inferior oblique along the lateral border of the inferior rectus becomes the effective origin for the distal portion of the inferior oblique.
Inferior oblique anteriorization, especially if the inferior oblique is placed closer to the limbus than the inferior rectus insertion, may lead to postoperative hypotropia and limitation of elevation, especially in abduction (“antielevation syndrome”).2
The type of inferior oblique weakening procedure is typically based on surgeon preference as no difference in effectiveness has been found.1
Surgical Procedure: Inferior Oblique Exposure and Isolation (Video 46.1)
Place a traction suture or a Moody locking forceps at the limbus between the inferior and lateral rectus muscles. Expose the inferotemporal quadrant of the eye by pulling the eye superiorly and nasally.
Use two forceps to elevate the conjunctiva about 8 mm from the limbus.
Expose the bare sclera by opening the conjunctiva and Tenon capsule with one snip to create an incision parallel with the limbus.
Use two toothed forceps to grasp the posterior aspect of the opening and then elevate the Tenon capsule out of the incision.
The pinkish-appearing inferior oblique muscle is embedded in the whitish-appearing Tenon capsule. Use a low temperature cautery to maintain good hemostasis as blood staining in the Tenon capsule can make identifying the pink inferior oblique muscle belly difficult.
Use a hand over hand technique to lift the Tenon capsule until the inferior oblique muscle belly appears in the wound.
After identifying the inferior oblique, firmly grasp the anterior aspect and carefully elevate it out of the incision using two forceps about 5 mm apart.
Once you have direct visualization of the posterior aspect of the muscle, use a Stevens tenotomy hook to enter the Tenon capsule under the inferior oblique and elevate the muscle on the hook by aiming the hook superiorly.
Avoid damage to the vortex vein by carefully visualizing it along the temporal border of the inferior rectus muscle, about 10-12 mm posterior to insertion.
Use two forceps to apply gentle downward pressure to push the point of the hook through the Tenon tissue without splitting the inferior oblique.
Insert a second muscle hook into the same hole as the first taking care to minimally spread these hooks apart until you are sure that the muscle has not been split.
Avoid blindly passing muscle hooks in the fornix because defects in posterior Tenon can lead to fat prolapse, adhesions, and restriction. Any large defects should be closed with sutures.
Carefully inspect the inferior border of the inferior oblique to ensure that it has been completely isolated. A completely white triangular-shaped space should be visible when viewing the muscle anteriorly and posteriorly (use a Desmarres retractor for exposure, if necessary). If a pinkish material is seen in the Tenon space under the inferior oblique, remove one of the hooks, place it under the remaining tissue and hook it as described above until the entire inferior oblique is isolated. Forceps may also be used to help place remaining inferior oblique fibers onto the hook.
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