Ординатура / Офтальмология / Английские материалы / Handbook of Pediatric Strabismus and Amblyopia_Wright, Spiegel, Thompson_2006
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Faden and recession of the right medial rectus muscle is indicated. One may rightfully argue, however, that a large (5-mm) right medial rectus muscle recession would also work without the difficulty of performing the Faden. As you will see, there is often more than one way to approach a strabismus.
Rightgaze |
Primary position |
Leftgaze |
Orthotropia |
E 4 |
ET 10 |
ET, esotropia. Surgery: recess the right medial rectus muscle 3 mm with a Faden.
Sixth Nerve Paresis
An example where the Faden may be effective is a partial sixth nerve paresis and good lateral rectus function. The standard surgery has historically been a recession of the medial rectus muscle and resection of the lateral rectus muscle of the paretic eye, which helps correct the esodeviation in primary position but does not address the large esotropia that occurs with gaze to the side of the paretic lateral rectus muscle. Incomitance can be improved with a recession and a Faden operation of the contralateral medial rectus muscle. A Faden to the contralateral medial rectus muscle helps correct the esotropia that increases in the side of the paretic lateral rectus muscle by decreasing the rotational force of the yoke medial rectus, thus matching the paretic lateral rectus muscle. Matching yoke muscles only works if there is good lateral rectus function with no more than1 limitation of abduction.
High AC/A Ratio Esotropia
Theoretically, the Faden operation reduces convergence at near, thus lowering the AC/A ratio. Experience with this procedure indicates that most patients still require a bifocal add to obtain fusion at near. Augmented bilateral medial rectus recessions probably work just as well.7 The use of a Faden operation with a medial rectus recession in high AC/A ratio esotropia patients remains controversial.
MUSCLE TRANSPOSITION PROCEDURES
Transposition surgery is based on changing the location of the muscle insertion so the muscle pulls the eye in a different direction (i.e., changes the vector of force). Transposition surgeries
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can be used to treat A- and V-patterns, small vertical tropias, rectus muscle paresis, and torsion.
Horizontal Muscle Transposition for A- and V-Patterns
See Chapter 9: A- and V-Patterns and Oblique Dysfunction.
Transposition for Small Vertical Deviations
Transposition surgery can correct small vertical deviations by vertically offsetting the horizontal rectus muscles. A patient with an esotropia and a small right hypertropia, for example, can be corrected by a recession–resection procedure of the right eye with inferior infraplacement of the horizontal rectus muscles. By transposing the horizontal rectus muscles inferiorly, they act to pull the eye down, thus correcting the hypertropia. Each horizontal muscle is recessed or resected as specified by the magnitude of the horizontal deviation.
There is approximately 1 prism diopter of improvement in the vertical deviation per 1 mm of displacement; this is true when two muscles in the same eye are transposed in the same direction. Vertical muscle displacements as large as 6 to 7 mm may be readily performed with this technique. It is most useful when the surgeon is performing monocular recession–resection surgery in which both muscles are moved in the same direction (Fig. 11-10). This surgery, however, is not effective if restriction is present (e.g., thyroid orbitopathy).
FIGURE 11-10. Full-tendon-width inferior transposition of both horizontal rectus muscles. The muscle on the left has been resected and infraplaced; the muscle on the right has been recessed and infraplaced. This technique would be used with a recession/resection procedure to correct a hypertropia and horizontal strabismus.
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Transposition Procedures for Rectus Muscle Palsy
Three transposition procedures used to correct severe rectus muscle palsies are described here: Knapp, Jensen, and Hummelsheim. In a right lateral rectus palsy, there is limited abduction and a large esotropia that increases in rightgaze. If there is less than 50% lateral rectus function, the treatment should be a lateral transposition of all or part of the superior and inferior rectus muscles. Because the vertical muscles do not contract on attempted abduction, the amount of abduction would relate to the elasticity or tonic contraction of the transposed muscles, rather than the active contraction of the transposed muscles.
KNAPP PROCEDURE
A full-tendon transfer, or Knapp procedure, was originally described for the management of double elevator palsy. This procedure, however, can also be used for a sixth nerve palsy. The key for successful surgery is symmetrical transposition to avoid induced vertical or horizontal deviations. A large posterior dissection to free the muscle of the intermuscular septum and check ligaments is necessary to mobilize the muscle for the tendon transfer (Fig. 11-11).
JENSEN PROCEDURE
The Jensen procedure is a split-tendon transfer with the adjacent muscle tied together but not disinserted (Fig. 11-12). This procedure has the advantage of leaving the anterior ciliary arteries intact, diminishing the risk of anterior segment ischemia. Even with the Jensen procedure, however, some vascular compromise occurs, and anterior segment ischemia has been associated with this procedure.
HUMMELSHEIM PROCEDURE
The Hummelsheim procedure is a split-tendon transposition technique designed to preserve anterior ciliary artery perfusion. Half of each of the two rectus muscles adjacent to the weak muscle is mobilized. The halves are then transposed and inserted at the insertion of the weak or lost muscle (Fig. 11-13). In contrast to the Jensen procedure, the Hummelsheim procedure can be used for a lost muscle, as it does not require the
FIGURE 11-11. Knapp procedure. The medial rectus (MR) and lateral rectus (LR) muscles are transposed superiorly to the insertion of the superior rectus (SR) muscle.
FIGURE 11-12. Jensen procedure. Nonabsorbable sutures tie muscle halves from adjacent muscles. The final result shows the tendon unions of superior rectus to lateral rectus and inferior rectus to lateral rectus muscles. The posterior location of the union is important, and sutures should be at least 12 mm posterior to the insertions. Anterior union sutures will reduce the effect of the transposition.
FIGURE 11-13. Hummelsheim procedure. Half of each of the superior and inferior rectus muscles is transposed to the lateral rectus insertion. Note that the transposed muscle halves touch the lateral rectus insertion, and the muscles are sutured together 3 mm posterior to the insertion (Foster modification).
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presence of the weak muscle. The Hummelsheim procedure is the author’s procedure of choice for a muscle palsy.
MODIFICATION OF THE HUMMELSHEIM
Two modifications of the Hummelsheim procedure, which increase the effect of the transposition, are described here.
Augmented Hummelsheim Brooks of Augusta, Georgia, has augmented the Hummelsheim by resecting 4 to 6 mm of the transposed rectus muscle halves. Resecting some of the transposed muscle halves tighten the transposition, increasing the leash effect.
Muscle Union Modification (Foster modification)
Increased effect of the Hummelsheim has been suggested if the transposed muscle is sutured to the paretic muscle. The transposed and paretic muscles are sutured together and then to sclera, 4 mm posterior the insertion.
Complications of Transposition Surgery
Transposition procedures for rectus muscle palsies can induce unwanted deviations if there is asymmetrical muscle placement. In split-tendon procedures, it is important to split and transpose the muscle equally to prevent inadvertent deviations.
Anterior segment ischemia is always an important consideration. Split-tendon procedures such as the Jensen and Hummelsheim lessen the risks, but even these procedures have been associated with anterior segment ischemia. The best strategy is to preserve as many anterior ciliary arteries as possible. A limbal conjunctival incision disrupts local vessels and may increase the risk of anterior segment ischemia, suggesting that a fornix incision may be preferable.
Rectus Muscle Transposition for Torsion
Torsional strabismus can be improved by moving vertical rectus muscles nasally or temporally. Nasal placement of the superior rectus causes extorsion (corrects intorsion) whereas temporal placement causes intorsion (corrects extorsion). The opposite is true for the inferior rectus muscle, with nasal transposition induces intorsion (corrects extorsion) and temporal transposition induces extorsion (corrects intorsion). Transposition of a
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tendon width (approximately 7 mm) will induce about 4° to 5° of torsion. Most of the torsional effect is seen in the field of action of the transposed muscle. If the superior rectus muscle is nasally transposed 7 mm and the inferior rectus muscle temporally transposed 7 mm, a total of 8° to 10° of extorsion would be induced, thus correcting 8° to 10° of intorsion. Horizontal rectus muscle transposition will also produce some torsional changes, but less than vertical rectus muscle transpositions. Supraplacement of the medial rectus muscle induces intorsion; infraplacement induces extorsion. The opposite is true for the lateral rectus muscle. It is unusual for a vertical transposition of a horizontal muscle to induce significant torsion. Most cases of torsional strabismus are caused by oblique dysfunction and are best treated with oblique muscle surgery to correct the torsion. For example, extorsion associated with bilateral superior oblique paresis is usually best handled with a bilateral Harada–Ito procedure, not a rectus muscle transposition.
INFERIOR OBLIQUE MUSCLE
WEAKENING PROCEDURES
Surgical management of inferior oblique muscle overaction is based on weakening or changing the function of the inferior oblique muscle. Techniques include myectomy, recession, and anterior transposition. Inferior oblique myotomy is not effective because the cut ends of the muscle inevitably reunite or scar to sclera; this causes residual inferior oblique overaction and an unacceptably high reoperation rate. Myectomy weakens the inferior oblique, as removing a portion of muscle reduces the chance of local reattachment. A very large myectomy with surgical transection of the neurovascular bundle virtually eliminates inferior oblique overaction and is termed inferior oblique extirpation–denervation. Extirpation–denervation may be indicated for severe residual inferior oblique overaction after previous inferior oblique surgery. An inferior oblique recession places the insertion closer to the origin and induces muscle slack, thus reducing muscle tension (Fig. 11-14). Apt1 and Elliot4 were the first to describe the inferior oblique anterior transposition. It is similar to a recession, but the inferior oblique muscle insertion is moved anterior to its origin, thus changing the function of the inferior oblique muscle from an elevator to more of a depressor
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FIGURE 11-14. Inferior oblique recession. The muscle is reattached along the path of the inferior oblique, but closer to its origin, thus slackening the muscle.
(Fig. 11-15). The more anterior the placement of the inferior oblique muscle insertion, the more the muscle becomes a depressor. This procedure has been shown to be very effective for treating both primary inferior oblique overaction and inferior oblique overaction secondary to superior oblique palsy.6
One possible complication of the anteriorization procedure is postoperative limited elevation. Limited elevation usually occurs from three possible mechanisms: (1) the new insertion is too anterior (i.e., anterior to the inferior rectus insertion); (2) resection of too much muscle ( 3 mm) at the time of securing
FIGURE 11-15. Inferior oblique anterior transposition. The diagram shows placement of the inferior oblique (IO) muscle in relationship to the inferior rectus (IR) insertion. The inferior oblique muscle is placed 1 mm posterior to the inferior rectus insertion. Note that the posterior inferior oblique muscle fibers are placed posterior to the anterior fibers and parallel to the inferior rectus muscle (no J-deformity).
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and disinserting the inferior oblique muscle; and (3) anterior placement of the posterior fibers of the inferior oblique muscle. Stager described this last mechanism as a common cause for limited elevation after the anterior transposition procedure. The posterior fibers of the inferior oblique muscle are important, as the neurovascular bundle of the muscle inserts into these muscle fibers. Because the neurovascular bundle is inelastic, large anteriorizations of the posterior muscle fibers will create a J-deformity of the muscle, with the neurovascular bundle tethering the inferior oblique muscle and limiting elevation of the eye (Fig. 11-16).12a
To prevent postoperative limitation of elevation, the author (K.W.W.) recommends:
FIGURE 11-16. Full anteriorization of the inferior oblique muscle including the posterior fibers with J-deformity. Anteriorization of the posterior fibers creates the J-deformity, as the neurofibrovascular bundle tethers the posterior muscle fibers; this can limit elevation of the eye. Because of this complication, the author (K.W.W.) does not perform the “J” deformity anteriorization, except if performed bilaterally for severe dissociated vertical deviation (DVD) and inferior oblique overaction.
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1.Keep the new insertion at or behind the inferior rectus insertion.
2.Secure the muscle close to its insertion to avoid resecting too much muscle (this would shorten the muscle).
3.Avoid the “J” deformity by keeping the posterior muscle fibers posterior to the anterior muscle fibers and posterior to the inferior rectus muscle insertion by at least 3 mm.8,14 The full anteriorization with a “J” deformity has been used for the treatment of bilateral dissociated vertical deviation (DVD) with inferior oblique overaction. If performed, the full anteriorization with “J” deformity should be performed bilaterally to avoid asymmetrical elevation of the eyes.
Graded Recession–Anteriorization
The author (K.W.W.) has reported on a graded recession– anteriorization approach for the management of inferior oblique overaction.8,14 This procedure tailors the amount of anteriorization according to the amount of inferior oblique overaction. The basis of the graded anteriorization procedure is that the more anterior the inferior oblique insertion, the greater the weakening affect. Table 11-1 lists the inferior oblique placement for a specific amount of inferior oblique overaction and represents only a guideline for the management of inferior oblique overaction. The final surgical decision must be based on a combination of factors, including the amount of V-pattern and the presence of a vertical deviation in primary position. Asymmetrical graded anteriorization is indicated if a hypertropia is present in primary position; otherwise, consider symmetrical surgery. More anteriorization of the inferior oblique should be done on the side of the hyperdeviation. A full anteriorization (without J-deformity) on the side of the hypertropia and 4 mm anteriorization on the opposite side will correct approximately 6 prism diopters (PD) of hypertropia. In the case of a unilateral
TABLE 11-1. Graded Recession–Anteriorization of Inferior Oblique
Muscle.
Overaction |
Inferior oblique placement |
1 |
4 mm posterior and 2 mm lateral to inferior rectus (IR) insertion |
2 |
3 mm posterior to IR insertion |
3 |
1–2 mm posterior to IR insertion |
4 |
At the IR insertion |
|
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inferior oblique overaction (e.g., associated with congenital superior oblique paresis), a unilateral anteriorization of 1 mm will correct approximately 8 to 12 PD of hypertropia.
COMPLICATIONS
Limited elevation after inferior oblique anteriorization has been discussed previously, but another problem of inferior oblique surgery is persistence or recurrence of the overaction. A common cause of residual overaction is incomplete isolation of the inferior oblique muscle, leaving posterior fibers intact. It is important to explore posteriorly along the globe for bridging muscle fibers that would indicate missed inferior oblique fibers.
Weakening procedures of the inferior oblique muscle for primary overaction only rarely produce a postoperative torsional diplopia. Even so, an adult patient may complain of a transient excyclodiplopia after weakening of the inferior oblique muscle.
An important anatomic consideration is the proximity of the inferior oblique muscle insertion to the macula. A misadventure with a stray needle in this area can cause the loss of central vision. Another consideration is the course of the inferior temporal vortex vein, which lies underneath the inferior oblique and can be inadvertently traumatized during surgery. The proximity of extraconal fat to the inferior oblique muscle is also an important concern, and fat adherence syndrome should be kept in mind; this may occur when the inferior oblique muscle is approached blindly and posterior Tenon’s capsule is violated. Other possible complications of inferior oblique surgery include orbital hemorrhage, pupillary dilation, endophthalmitis, and inadvertent surgery or damage to the lateral rectus muscle.11 Paramount in avoiding these complications is the clear and direct visualization of the inferior oblique muscle during its isolation. Blind hooking procedures must be avoided. Meticulous surgical dissection and hemostasis are the key to proper exposure and visualization of the anatomy.
SUPERIOR OBLIQUE MUSCLE
TIGHTENING PROCEDURES
The superior oblique tendon can be functionally divided into the anterior third, responsible for intorsion, and posterior twothirds, responsible for depression and abduction (Fig. 11-17).