Ординатура / Офтальмология / Английские материалы / Strabismus Surgery and Its Complications_Coats, Olitsky_2007

Surgery is performed more commonly on the inferior oblique muscle than on any other cyclovertical muscle. Surgical access to the inferior oblique muscle and procedures designed to alter the effect of contraction of the inferior oblique muscle on the globe are relatively straightforward and complications are infrequent in experienced hands. The most common indications for surgery on the inferior oblique muscle include superior oblique palsy, primary inferior oblique overaction, V-pattern horizontal strabismus with inferior oblique overaction, and dissociated vertical deviation associated with inferior oblique overaction. Accordingly, most operations on the inferior oblique muscle are designed to diminish its function. Weakening procedures on the inferior oblique muscle are numerous and include myotomy, myectomy, recession, marginal myotomy, disinsertion, anterior transposition, and denervation and extirpation. The most recently described weakening operations on the inferior oblique muscle are nasal myectomy and anterior and nasal transposition. The techniques required to perform each of these procedures are reviewed in this chapter.

Rarely, a procedure designed to enhance the function of the inferior oblique muscle is required. These unusual indications include persistent or large incyclotorsion and persistent inferior oblique underaction in a patient with an inferior oblique palsy, despite other more traditional surgical approaches. The function of the inferior oblique muscle can be enhanced through advancement of the muscle with or without concurrent resection and by tucking of the belly of the muscle. The techniques for performing these procedures are briefly reviewed.

der of the muscle can usually be identified approximately 10– 12 mm from the limbus. Its path can often be visualized as a deflection created by the muscle and an adjacent fat pad in the overlying intact conjunctiva in the inferotemporal quadrant (>Fig. 11.1). When making a conjunctival incision for surgery on the inferior oblique muscle, many surgeons prefer to place the incision more posterior than a standard fornix incision, feeling that access to the surgical space is enhanced. If this approach is used, the surgeon should avoid placing the incision over the fat pad located in the inferotemporal quadrant of the orbit (>Fig. 11.1), because violation of this fat pad can result in intrusion of orbital fat into the operative site, compromising visualization during surgery, producing bleeding, and resulting in postoperative fat adherence syndrome (Chap. 25). Many techniques are possible for visually identifying and surgically isolating the inferior oblique muscle once the conjunctival and Tenon’s capsule incisions have been created. Techniques that first identify and isolate the lateral rectus muscle help to both simplify the process of surgical isolation of the inferior oblique muscle and reduce the risk that the lateral rectus muscle will be inadvertently isolated rather than the inferior oblique muscle (Chap. 25).

11.1Identification and Isolation of the Inferior Oblique Muscle

All surgical procedures commonly performed on the inferior oblique muscles are conducted on the distal half of the muscle. Techniques for identification and isolation of the inferior oblique muscle along its proximal half are described later. Access to the distal portion of the inferior oblique muscle is gained through a standard fornix conjunctival incision, and incision through Tenon’s capsule in the inferotemporal conjunctival quadrant as described in Chap. 8. The inferior oblique muscle itself is located in Tenon’s capsule. The anterior bor-

Fig. 11.1. Inferior oblique muscle and surrounding fascia and inferotemporal orbital fat pad visualized through the intact conjunctiva

11.1.1 Technique

11.1.1.1 Exposure of the Surgical Site

Good exposure of the surgical site is important for all operations, but is particularly important for surgery on the inferior oblique muscle. The location of the insertion of the inferior oblique muscle in the posterior orbit, the presence of surrounding orbital fat, and proximity of the muscle belly to a vortex vein in the inferotemporal quadrant all present areas of significant surgical risk when exposure is suboptimal. Exposure of the surgical site and positioning of the eyes can be facilitated through several techniques.

Use of a bridle suture around the lateral rectus muscle is a very effective means of gaining superior surgical exposure. The lateral rectus muscle insertion is isolated on a Gass muscle

Chapter 11

hook (Chap. 7). There is a hole in the toe of the Gass muscle hook, making placement of a bridle suture simple and safe. After hooking the lateral rectus muscle, the toe of the Gass muscle hook is directed anteriorly, tenting the conjunctiva. A 4-0 silk suture is passed through the conjunctiva and the hole in the toe of the Gass muscle hook (>Fig. 11.2a). The suture is then withdrawn through the conjunctiva and behind the lateral rectus muscle insertion (>Fig. 11.2b). The globe is then retracted upward and nasally and fixed in this position by attaching the bridle suture to the surgical drapes with a hemostat. Retracting the globe to this position directs the belly of the inferior oblique muscle anteriorly and greatly facilitates identification and isolation of the muscle.

One or two large hooks are then placed deeply into the incision which is retracted inferiorly by the assistant surgeon (>Fig. 11.2c). The surgeon visually inspects Tenon’s capsule, which has been retracted inferiorly in an effort to identify the inferior oblique muscle (>Fig. 11.2c). Identification of the

Fig. 11.2a–c. Exposure of the surgical site for inferior oblique muscle surgery using a lateral rectus muscle bridle suture (surgeon’s view). a A Gass muscle hook is placed behind the lateral rectus muscle insertion and a 4-0 silk suture is passed through a hole in the toe of the hook. b The suture is withdrawn behind the lateral rectus muscle insertion, the globe retracted upward and nasally, and the bridle attached to the sur-

gical drapes using a hemostat to maintain this position of the globe. c One or two hooks are placed into the incision and retracted inferiorly. The inferior oblique muscle can be seen in Tenon’s capsule. Important landmarks that can aid in identification of the inferior oblique muscle include visualization of the border of the inferior oblique muscle, the sclera, and a vortex vein simultaneously

muscle can be facilitated by retraction of the globe slightly superiorly using a small muscle hook.. The posterior border of the inferior oblique muscle should be easily identified. Important landmarks that can aid the surgeon in confirming that the posterior border of the inferior oblique muscle has been identified include visualization of the posterior border of the inferior oblique muscle, the sclera, and the adjacent vortex vein simultaneously (>Fig. 11.2c).

Alternatively, some surgeons gain exposure to the surgical site by placement of a hook behind the insertion of the lateral and inferior rectus muscles. These two hooks are held in position by an assistant surgeon (>Fig. 11.3) while the surgeon identifies the inferior oblique muscle as described above. A disadvantage of this technique is that both hands of the assistant surgeon are occupied holding these muscle hooks, so that the assistant surgeon is not available to help with other tasks during isolation of the muscle.

11.1.1.2Isolating the Muscle on a Muscle Hook

A Scobee muscle hook or Steven’s muscle hook (we prefer a Scobee muscle hook) is passed beneath the border of the inferior oblique muscle, directed first toward the floor of the orbit and then drawn gently anteriorly (>Fig. 11.4). This maneuver should not be thought of as a “blind sweep.” Rather, the surgeon should clearly visualize the posterior border of the inferior oblique muscle followed by careful placement of the hook and methodical movements inferiorly and anteriorly to isolate the muscle. With experience, the surgeon develops a “feel” for the technique, allowing isolation of the entire muscle without associated orbital fat and other adjacent tissues. An optional step in the surgical isolation of the inferior oblique muscle is gentle blunt dissection of the border between the posterior margin of the inferior oblique muscle and Tenon’s capsule. This maneuver aids in the placement of a hook under the posterior border of the muscle.

Fig. 11.3. Exposure of the surgical site for inferior oblique muscle surgery using muscle hooks behind the lateral and inferior rectus muscles

11.1.1.3Dissection of the Capsule

of the Inferior Oblique Muscle

The surgical assistant should place the belly of the inferior oblique muscle under mild anterior traction with the Scobee hook and simultaneously retract the incision temporally. This combined maneuver places Tenon’s fascia and the capsule of the inferior oblique muscle under mild traction as well. The surgeon then sharply dissects the capsule to expose the inferior oblique muscle insertion on the sclera temporally (>Fig. 11.5). Care should be taken to avoid the inferotemporal vortex vein and to avoid violation of posterior Tenon’s capsule, which can result in intrusion of orbital fat into the operative site (Chap. 25).

11.2Weakening Procedures

on the Inferior Oblique Muscle

As noted earlier, the vast majority of procedures performed on the inferior oblique muscle are designed to limit its function on the globe. Many inferior-oblique-weakening procedures can be used to treat a wide range of deviations without the need to precisely titrate surgery to specific measurements obtained in the office. Some have characterized many surgical procedures on the inferior oblique muscle as “self adjusting.” For example, the same inferior oblique muscle recession

Fig. 11.5a,b. Dissection of the muscle capsule of the inferior oblique: a exposure of the hook, followed by b sharp dissection of the muscle capsule while the assistant surgeon places the capsule under mild traction

done to treat a superior oblique paresis may be just as effective if there is a hypertropia of 14 prism diopters as it is for a hypertropia of 5 prism diopters. Weakening procedures on the inferior oblique muscles are generally accomplished with few serious complications. Most of the complications that can occur during inferior oblique muscle surgery occur during the steps to isolate the muscle and dissect its capsule.

Much of the decision for choosing a particular procedure is dependant on the training and experience of the surgeon. Our usual procedure of choice for inferior oblique muscleweakening procedures is loosely outlined in Table 11.1. Many surgeons prefer inferior oblique recessions to disinsertion,

myectomy, and myotomy because these other procedures, unlike recessions, may be associated with reattachment of the oblique muscle insertion back to the sclera in an unpredictable location [1] (>Fig. 11.6). Not only can this result recurrence of inferior oblique overaction after surgery, but makes reoperations more difficult. Several techniques been described to prevent this complication as outlined

Chap. 25.

2.1Technique of Inferior Oblique Muscle Recession

exposure and isolation of the muscle and dissection muscle capsule as reviewed above, the inferior oblique is detached from the sclera at its insertion. Two techcan be utilized. A hemostat can be placed across the oblique muscle several millimeters proximal to its into the sclera (>Fig. 11.7a). Scissors are then used

transect the inferior oblique muscle between the hemostats muscle insertion. Cautery may be applied to the proximal edge to prevent bleeding following the removal of the although this often is not necessary. Absorbable susuch as 6-0 polyglactin suture is then placed in the muscle to the hemostat (>Fig. 11.7b). The muscle is then to the sclera along the normal course of the inferior muscle. We most commonly place the anterior muscle 2–4 mm posterior to the temporal border of the inferior

rectus muscle insertion, a position which places it just anterior to a vortex vein exit from the sclera in this area (>Fig. 11.7c). The muscle can be placed in other positions at the discretion of the surgeon. The conjunctiva is then closed with interrupted absorbable suture.

Alternatively, the inferior oblique muscle insertion can be dissected from the sclera directly by cutting the muscle flush with the sclera. Cautery is applied to the distal edge of the muscle and absorbable sutures are placed in the distal end of the muscle. The practice of placing sutures in the muscle prior to disinsertion of the muscle from the sclera is cumbersome, unnecessary, and generally requires resection of a substantial portion of the distal part of the muscle.

Fig. 11.6. Position of reattachment of the inferior oblique muscle to the globe after myectomy in monkey eyes. (Reprinted from [1] Ar­ chives of Ophthalmology, volume 95, Wertz RD, Romano PE, Wright P. Inferior oblique myectomy, disinsertion, and recession in rhesus monkeys, page 859, 1977, with permission from American Academy of Ophthalmology)

11.2.1.1 Graded Inferior Oblique Recession

In our experience, graded recession of the inferior oblique muscle is unnecessary in most cases, and the surgical results are similar regardless of where the new inferior oblique muscle insertion is placed (within excepted standards) except when the new insertion is significantly advanced anteriorly. Some surgeons, however, titrate recessions of the inferior oblique muscle depending on the severity of the inferior oblique overaction. Figure 11.8 demonstrates possible placement of the new muscle insertion if the surgeon believes that titration of surgical effect is warranted.

Fig. 11.7a–c. Inferior oblique recession. a The muscle is transected distal to a hemostat placed across the muscle near the insertion. b Cautery is applied to the proximal muscle edge and absorbable sutures placed in the muscle adjacent to the hemostat. c The muscle is sutured to the

sclera; the anterior suture is most commonly placed 2–4 mm posterior to the temporal border of the inferior rectus muscle. Note the vortex vein just behind this location

Some surgeons prefer simple disinsertion of the inferior oblique muscle without suturing the distal end of the muscle back to the sclera. One potential problem with such an approach is that the muscle may become reattached to the sclera in an unpredictable location, resulting in recurrence of unwanted inferior oblique muscle function [1].

After exposure, isolation and dissection of the muscle capsule, the inferior oblique muscle is disinserted from the sclera using the technique of choice. Cautery may be applied to the cut edge of the muscle, the muscle released, and the conjunctiva closed with absorbable suture (>Fig. 11.9).

11.2.3Technique of Inferior Oblique Myectomy

Myectomy of the inferior oblique muscle is an effective procedure for limiting the function of the inferior oblique muscle. The indications for this procedure are similar to the indications for an inferior oblique muscle recession, though we tend to reserve myectomy for patients with pronounced inferior oblique overaction. The advantages of an inferior oblique myectomy include limited time required for surgery, simplicity, and the fact that sutures are not placed in the sclera, essentially eliminating the risk of endophthalmitis that is present when sutures are placed in the sclera (Chap. 22). Potential disadvantages of an inferior oblique myectomy include reattachment of

Fig. 11.9. Disinsertion of the inferior oblique muscle. The inferior oblique muscle is disinserted from the sclera, cautery is applied to the cut edge of the muscle, and the conjunctiva closed with absorbable suture

the muscle to the sclera at an unpredictable location postoperatively [1] which can result in recurrence of unwanted inferior oblique function. Reoperations on the inferior oblique muscle may also be more difficult following myectomy procedures because of scarring and because the final location of the distal end of the muscle is not known.

After exposure, isolation, and dissection of the capsule of the inferior oblique muscle, two hemostats are placed across the inferior oblique muscle separated by approximately 5–10 mm (>Fig. 11.10a). Muscle between the hemostats is excised, discarded, and cautery is applied to the cut edges of the muscle (>Fig. 11.10b). The muscle is then released and the proximal segment of the muscle is allowed to retract into Tenon’s capsule. Some surgeons prefer to suture Tenon’s capsule closed after the muscle has retracted into Tenon’s capsule to reduce the chance that the muscle will reattach to the sclera. The conjunctiva is then closed with interrupted absorbable suture.

Chapter 11

11.2.4Technique of Inferior Oblique Myotomy

Marginal or complete myotomy of the inferior oblique muscle can be performed to weaken the function of the inferior oblique muscle. A complete myotomy is considered by some surgeons to be as effective as myectomy or recession of the inferior oblique muscle. Some surgeons perform marginal myotomy on the inferior oblique muscle for mild inferior oblique overaction.

To perform a complete myotomy, one or two hemostats are placed across the inferior oblique muscle. The muscle is then transected and cautery may be applied to the cut edges of the muscle. The hemostat(s) is removed, the surgical site inspected to ensure that no active bleeding is present, and the conjunctiva is closed with interrupted absorbable suture (>Fig. 11.11a).

A marginal myotomy requires the creation of overlapping partial myotomies of the inferior oblique muscles ranging from 60% to 75% of the muscle’s width. A hemostat is placed across the muscle at the site of the planned marginal myotomy and removed after 30–60 s. The marginal myotomy is then performed along the area crushed by the hemostat and cautery applied (>Fig. 11.11b). In order for a marginal myotomy to be effective, all fibers of the muscle must be cut in overlapping myotomies [2]. We have not found a satisfactory indication for marginal myotomy of the inferior oblique muscle, usually preferring observation alone for eyes with mild inferior oblique overaction that would be most appropriate for consideration of a marginal myotomy procedure.

11.2.5Technique of Denervation and Extirpation

Denervation and extirpation of the inferior oblique muscle is an infrequently used procedure. It is reserved for the most pronounced overaction of the inferior oblique muscle and many surgeons reserve the procedure for significant recurrent inferior oblique overaction despite previous weakening procedures on the inferior oblique muscle. The procedure involves identification and transection of the neurovascular bundle combined with removal of a large distal segment of inferior oblique muscle. An experienced surgical assistant is helpful in performing this procedure because exposure of the surgical site is difficult.

The inferior oblique muscle is isolated and detached from the globe through a standard incision in the inferotemporal conjunctival quadrant. Mild anterior traction is placed on the muscle and sharp dissection of the muscle capsule done in a nasal direction (>Fig. 11.12a). A fusiform expansion on the posterior side of the inferior oblique muscle near the lateral border of the inferior rectus muscle represents the neurovascular bundle, where a branch of the third cranial nerve and the vascular supply for the inferior oblique muscle enter the muscle [3]. A small hook, such as a Steven’s hook, is used to grasp the neurovascular bundle and place it under mild traction (>Fig. 11.12b). A hemostat is placed across the neurovascular bundle and cautery applied to cut and coagulate the neurovascular bundle anterior to the clamp (>Fig. 11.12c). If the neurovascular bundle has been completely severed, the muscle insertion can be advanced anteriorly (>Fig. 11.12d). A hemostat is then placed on the inferior oblique muscle as close to the muscle’s origin as possible, and the large distal portion of the muscle (representing most of the inferior oblique muscle) distal to the hemostat is excised, and cautery is applied to the proximal edge of the muscle for hemostasis (>Fig. 11.12e). The muscle stump is then allowed to retract into the posterior Tenon’s capsule. The capsule can be optionally closed with absorbable suture.

11.2.6Technique of Inferior Oblique Anterior Transposition

Anterior transposition of the inferior oblique muscle is performed in exactly the same manner as an inferior oblique recession procedure, with the exception that the new muscle insertion is located well anterior to the equator rather than along the normal course of the inferior oblique muscle. Anterior transposition of the inferior oblique muscle is an excellent procedure when needed and has several specific indications. The most common indication for the inferior oblique anterior transposition procedure is the treatment of dissociated vertical deviation and significant inferior oblique overaction in the same eye. Though the procedure is most commonly performed bilaterally, it can be performed unilaterally with caution [4–6]. Unilateral inferior oblique overaction can result in asymmetry of the lower eyelid that can be bothersome to patients (Chap. 26),

Fig. 11.12a–e. Denervation and extirpation. a After detachment of the inferior oblique muscle from the globe at its insertion, mild anterior traction is placed on the muscle. b A small hook is used to grasp the neurovascular bundle and place it under mild traction

Other less common indications have included treatment of unilateral superior oblique palsy [7], lost [8], ruptured [9, 10] or absent [11] inferior rectus muscles, V-pattern horizontal strabismus [12, 13], and hypertropia with marked inferior oblique overaction [6]. Parvataneni and Olitsky [4] reported use of inferior oblique muscle anterior transposition and resection to treat a hypertropia in patients at significant risk for anterior segment ischemia.

Fig. 11.12a–e. (continued) Denervation and extirpation. c Cautery is used to cut and coagulate the neurovascular bundle. d The muscle can be advanced significantly further anteriorly if the neurovascular bundle has been completely transected. e A hemostat is then placed on the inferior oblique muscle as close to the muscle origin as possible, and a large distal portion of the muscle is removed. Cautery is applied for hemostasis and the muscle stump allowed to retract into posterior Tenon’s capsule

After exposure, isolation, dissection of the muscle capsule, and disinsertion of the inferior oblique muscle at its insertion, the inferior oblique muscle insertion is reattached to the sclera near the temporal border of the inferior rectus muscle insertion. It is generally placed no more than 1 mm anterior or posterior to the insertion, and is most commonly placed at the level of the insertion (>Fig. 11.13a). Unlike inferior oblique recession, in which the new insertion is spread out to the nor-