bleb.
Surgical Techniques for the Extraocular Muscles and Tendons
Step-by-step descriptions of each surgical procedure are beyond the scope of this volume. The references that follow are among several in which this information can be found.
Coats DK, Olitsky SE, eds. Strabismus Surgery and Its Complications. Berlin: Springer; 2007.
Wright KW. Color Atlas of Strabismus Surgery. 3rd ed. Irvine, CA: Wright; 2007.
Approaches to the Extraocular Muscles
Fornix incision
The fornix incision is made in either the superior or, more frequently, the inferior quadrants. The incision is located on bulbar conjunctiva, not actually in the fornix, 1–2 mm to the limbal side of the cul-de-sac, so that bleeding is minimized. The incision is made parallel to the fornix and is approximately 8–10 mm in length.
Bare sclera is exposed by incising the Tenon capsule deep to the conjunctival incision. Using this exposed bare sclera, the surgeon engages the muscle with a succession of muscle hooks. The conjunctival incision is pulled over the hook that has passed under the muscle. All 4 rectus muscles and both oblique muscles can be explored, if necessary, through inferotemporal and superonasal conjunctival incisions.
When properly placed, the 2-plane incision can be self-closing at the end of the operation by gentle massage of the tissues into the fornix, with the edges of the incision splinted by the overlying eyelid. Some surgeons prefer to close the incision with conjunctival sutures.
Limbal incision
The fused layer of conjunctiva and Tenon capsule is cleanly severed from the limbus. Some surgeons make the limbal incision (peritomy) 1–2 mm posterior to the limbus to spare limbal stem cells. A short radial incision is made at each end of the peritomy so that the flap of conjunctiva and Tenon capsule can be retracted to expose the muscle for surgery. At the completion of the operation, the flap is reattached, without tension, close to its original position with a single suture at each corner. If the conjunctiva is scarred from prior surgery and is tight, closure should be accomplished with recession of the anterior edge.
Rectus Muscle Weakening Procedures
Table 14-3 defines various rectus muscle weakening procedures and describes when each is used. The most common of these is simple recession, for which typical amounts of surgery for esotropia and exotropia are given in Tables 14-1 and 14-2. Because the conventional technique for rectus muscle recession involves passing sutures through thin sclera with the attendant risk of perforation, some surgeons prefer a hang-back recession, in which the recessed tendon is suspended by sutures that pass through the thicker stump of the original insertion. Although it is not known where the tendon reattaches to the sclera, there is empirical experience indicating that this method is usually reliable.
Table 14-3
Rectus Muscle Strengthening Procedures
Strengthening procedures do not actually give the muscles more strength. Rather, they produce a tightening effect that tends to offset the opposite action of the antagonist muscle. Surgeons usually use the resection technique for this purpose, for which typical amounts of surgery for esotropia and exotropia are given in Tables 14-1 and 14-2. Plication of the tendon can be used as an alternative to produce a similar effect. A rectus muscle can also be tightened by advancing its insertion toward the limbus. This is an effective procedure when previous recession has resulted in an overcorrection.
Rectus Muscle Surgery for Hypotropia and Hypertropia
For reasonably comitant vertical deviations, recession and resection of vertical rectus muscles is appropriate. Recessions are generally preferred as a first procedure. A rough guideline is that approximately 3Δ of correction in primary position can be expected for every millimeter of vertical rectus muscle recession. For comitant vertical deviations of less than 10Δ that accompany horizontal deviations, displacement of the reinsertions of the horizontal rectus muscles in the same direction, by about one-half the tendon width (up for hypotropia, down for hypertropia), performed during a recession-resection procedure, is often sufficient. In order to use this option to correct a small vertical deviation, the surgeon may choose to do a recession-resection procedure in a situation where bilateral symmetric recessions would otherwise be preferred.
Adjustable Sutures
Some surgeons employ adjustable sutures to avoid an immediately obvious poor result or to increase the likelihood of success with 1 operation, but this modification does not ensure long-term satisfactory alignment. The surgeon completes the operation using externalized sutures and slipknots that allow the position of the surgical muscle to be altered during the early postoperative period. This technique can be used in children; however, a second general anesthesia is usually required.
Another alternative, used mainly in adults, is performance of surgery with the patient awake. Anesthetic agents that might affect ocular motility are avoided, and the patient’s dynamic ocular motility and ocular alignment are observed and adjusted at the time of surgery. This technique can be difficult in patients with significant scarring, persons with thyroid eye disease, and children.
Isenberg SJ, Abdarbashi P. Drift of ocular alignment following strabismus surgery. Part 1: using fixed scleral sutures. Br J Ophthalmol. 2009;93(4):439–442.
Isenberg SJ, Abdarbashi P. Drift of ocular alignment following strabismus surgery. Part 2: using adjustable sutures. Br J Ophthalmol. 2009;93(4):443–447.
Oblique Muscle Weakening Procedures
Weakening the inferior oblique muscle
Table 14-3 lists the various inferior oblique muscle weakening procedures. These procedures are most commonly used for treatment of overelevation in adduction when it is believed to be due to inferior oblique muscle overaction. In all of these procedures, the surgeon must be sure that the entire inferior oblique muscle is weakened, since the distal portion and the insertion can be anomalously duplicated.
In cases that show marked asymmetry of the overactions of the inferior oblique muscles and no superior oblique muscle paralysis, unilateral surgery only on the muscle with the more prominent overaction is often followed by a significant degree of overaction in the fellow eye. Therefore, some surgeons recommend bilateral inferior oblique muscle weakening for asymmetric cases. A symmetric result is the rule and overcorrections are rare; however, inferior oblique muscles that are not overacting at all—even when there is overaction in the fellow eye—should not be weakened.
Secondary overaction of the inferior oblique muscle occurs in many patients who have superior oblique muscle paralysis. A weakening of that inferior oblique muscle typically corrects up to 15Δ of vertical deviation in primary position. The amount of vertical correction is roughly proportional to the degree of preoperative overaction (see Chapter 11).
Frequently, a weakening procedure is performed on each inferior oblique muscle for V-pattern strabismus. This is discussed in Chapter 10.
Moving the insertion of the inferior oblique muscle anteriorly to a point adjacent to the lateral border of the inferior rectus muscle (inferior oblique anterior transposition, inferior oblique anteriorization) weakens the normal actions of the inferior oblique. Because the neurofibrovascular bundle along the lateral border of the inferior rectus muscle can then serve as the effective origin for the distal portion of the muscle, anteriorization also allows the inferior oblique muscle to actively oppose elevation of the eye; that is, this muscle becomes an anti-elevator (see Chapter 3). This procedure has been found to be effective for treatment of dissociated vertical deviation (DVD) and is especially useful when DVD and inferior oblique muscle overaction coexist. See also Chapter 11.
Awadein A, Gawdat G. Bilateral inferior oblique myectomy for asymmetric primary inferior oblique overaction. J AAPOS. 2008;12(6):560–564.
Weakening the superior oblique muscle
Procedures to weaken the superior oblique muscle include tenotomy; tenectomy; Z-lengthening; placement of a spacer of silicone, fascia lata, or nonabsorbable suture loops between the cut edges of the tendon to functionally lengthen it; and recession. The purpose of spacers is to prevent an excessive gap between the cut edges, but they have the disadvantage of possible adhesion formation, which can alter motility. Unilateral weakening of a superior oblique muscle is not commonly performed except as the treatment for Brown syndrome (see Chapter 12) or for an isolated inferior oblique muscle weakness, which is rare. Unilateral superior oblique muscle weakening can affect not only vertical alignment but also torsion, potentially creating undesired extorsion. Many ophthalmologists favor a tenotomy of just the posterior 75%–80% of the tendon to preserve the torsional action, which is controlled by the most anterior tendon fibers.
Bilateral weakening of the superior oblique muscle can be performed for A-pattern deviations (see Chapter 10) and can be expected to cause an eso-shift in downgaze and almost no change in upgaze. In surgery on patients with normal binocularity, the possibility of creating diplopia from vertical or torsional strabismus must be considered.