Ординатура / Офтальмология / Английские материалы / Pediatric Ophthalmology Current Thought and A Practical Guide_Wilson, Saunders, Trivedi_2008

zontal rectus surgery should be done for the primary position deviation.

Special caution should be exercised when bilateral superior oblique weakening surgery is considered for a patient with high-grade stereopsis, specifically bifixating patients with normal (40 s/arc or better) stereoacuity. These patients will likely be sensitive to excyclotorsion induced by the superior oblique weakening. This can result in debilitating torsional diplopia and a very unhappy patient. Fortunately, large A patterns and SOOA are rarely found in bifixating patients.

13.4.1.4A-pattern XT

may cause some eso shift in the primary position. This effect is small enough that it is ignored by many surgeons, though anticipating a small eso shift of

0−8 PD may help in determining amounts of concomitant horizontal rectus muscle surgery.

There is concensus that inferior oblique weakening will collapse a V pattern by decreasing the deviation in upgaze and increasing it in downgaze. Although the IO has some abducting function, the effect of IO weakening on primary position deviation is minimal; therefore, any horizontal primary position deviation should be addressed by appropriate horizontal rectus surgery.

A-pattern XT with evidence of SOOA will also respond to weakening of the SOs. This will usually be found with large amounts of vertical incomitance.

Appropriate horizontal rectus muscle surgery for the primary position deviation should be carried out. The same caution regarding SO weakening in bifixating patients applies here as described in Sect. 13.4.1.3.

13.4.1.5A-XT with SOOA and DVD

A special form of strabismus, A-XT with SOOA and DVD, is well known and can occur either secondarily (e.g., consecutive XT following BMR for esotropia) or as a primary strabismus triad. Treatment is similar as withAXT without DVD except that surgery aimed specifically at the DVD should be added.

Most commonly this would involve large recessions of the superior rectus in each eye. In patients where the A pattern and SOOA are small, large recessions of the SRs alone will help the DVD and decrease the A pattern.

13.4.3Grading of Oblique Muscle Surgery

Grading of oblique muscle overaction is an inexact science. Most surgeons use a grading scale of 1+ to 4+ overaction. For inferior oblique grading, 1+ overaction means only slight overaction or over elevation in adduction. Grade 4+ means the most overelevation possible. Grades 2+ and 3+ overaction are the two gradations between those extremes. Other authors suggest that 1+, 2+, 3+, and 4+ overaction roughly translates to 5, 10, 15, and 20 PD of hypertropia on far-side gaze, respectively. In terms of how often the various grades of IOOA require surgery, Parks professed that 1+ was operated rarely, 2+ sometimes, 3+ frequently, and 4+ almost always. This scheme referred to primary IO overaction in absence of other more compelling surgical indications such as diplopia, asthenopia, or torticollis.

13.4.2Effect of Oblique Muscle Weakening on Primary Position Alignment

The tertiary action of the superior obliques is abduction of the eyes; therefore, bilateral SO weakening

13.4.4Inferior Oblique Muscle Weakening Procedures

Inferior oblique weakening is most commonly performed via recession or myectomy. Recessions can be graded: Parks’ scheme included 10-mm recession for mild-to-moderate overaction and 1-4mm recession for what he termed 3+ overaction. Other prac-

titioners prefer myectomy for most degrees of IO overaction on the theory that myectomy tends to be self-adjusting, i.e., greater effects are produced when the IO overaction is greater and lesser effects when overaction is less. Inferior oblique weakening of any sort to decrease a V pattern is discouraged when IO overaction is not present.

Most procedures for weakening the inferior oblique can be performed unilaterally if indicated or different procedures can be chosen for each side in asymmetric cases. The exception is that anterior transposition of the IO should not normally be performed on only one side because of the relative restriction to elevation it produces. This will frequently result in a secondary hypertropia of the opposite eye. Occasionally, this feature can be used to advantage when the hyperdeviating eye has a DVD component and has poor vision such as from dense amblyopia. In such a case, the deviating eye is likely to never be preferred for fixation and the secondary deviation is less likely to be manifest.

13.4.5Superior Oblique Muscle Weakening Procedures

There is more variety in methods proposed for superior oblique weakening, as shown below.

13.4.5.1Tenotomy or Tenectomy

The strongest weakening procedure of the SO tendon is a full-thickness tenotomy nasal to the superior rectus. Some practitioners like to excise a section of tendon (tenectomy) in addition to transecting it on the theory that this will decrease the likelihood of recurrent overaction; however, a properly performed tenotomy nasal to the SR, completeness of which is confirmed with traction testing immediately post-ten- otomy, is a very effective weakening procedure.

Modifications to the standard tenotomy/tenectomy procedure are designed to lessen the weakening effect on the SO. Potential modifications are given below.

13.4.5.2Spacer

A foreign element, e.g., silicone segment or a socalled chicken suture made of non-absorbable synthetic material can be used to provide a permanent connection between the two severed ends of the SO tendon. Although the weakening effect of these adjuncts should be complete, they can theoretically decrease the tendency toward long-term overcorrection which can turn the A pattern into a V pattern. In cases where the A pattern and SO overactions are large and the patient has sub-normal binocular vision, these modifications to standard tenotomy may not offer compelling benefit.

13.4.5.3Partial Tenotomy

If a lesser weakening effect is desired, this can be accomplished by a partial tenotomy, e.g., seven-eighths (or three-quarter) tenotomy. This is performed by identifying and disinserting the thin spread out fibers of the SO tendon at their scleral attachment on the temporal side under the superior rectus. Theoretically, lysis of these posterior-most fibers should decrease the vertical effect of the SO without decreasing much of the torsional effect of the anterior most fibers. This can be a useful procedure in cases where only mild SO overaction is present or when it is used unilaterally to balance a mild asymmetry in SO overaction, but it is not effective enough for most cases of significant A-pattern strabismus.

13.4.6 Horizontal Rectus Surgery

Patients with A or V pattern and no significant overelevation or depression in adduction are best treated with vertical shifts of the horizontal rectus muscles [16, 19]. Whether the primary position deviation is ET or XT, the direction of shift for the horizontal recti is the same. Specifically, medial recti are shifted toward the apex of the pattern (up forApattern, down for V pattern) and lateral recti are shifted toward the open or empty direction of the pattern (up for V pattern and down for A pattern). Some practitioners find the pneumonic MALE (medial-apex, laterals-empty) helpful to remember the proper direction of shift.

Typically surgery for pattern strabismus is done bilaterally, e.g., a V-pattern ET would be treated with bimedial rectus recession with downshift; however, the same deviation can be treated with unilateral surgery by recession with downshift of one MR and resection with upshift of the ipsilateral LR [4].

The amount of vertical shift is typically half to one full tendon width depending on the magnitude of the pattern. The recession effect of horizontal rectus surgery is not significantly impacted by upor downshifting the muscle.

In these secondary cases of consecutive XT, the pattern occurs because of deficiency of adduction fromeitherexcessivemedialrectusrecessionorinthe presence of slipped medial rectus muscles. Because the eyes do not adduct fully, they appear to overelevate and overdepress when the patient is called on to elevate or depress the eye while adducted.

Correction of the pattern does not require weakening of all four obliques; instead, addressing the adduction deficiency and straightening the eyes in primary position by advancing the medial recti, fixing slipped muscles, and/or recessing restricted lateral rectus muscles will diminish the pattern (Fig. 13.9).

13.4.7 Vertical Rectus Surgery

The A and V patterns can be diminished by horizontal offsets of the vertical rectus muscles. For instance, temporal transposition of the superior recti will expand the closed end of the A pattern. Similarly, temporaltranspositionoftheinferiorrectiwillexpandthe closed end of the V pattern by weakening the adductionvectoroftheinferiorrectiindowngaze.Transposing the SRs nasally will help close the open end of the

V pattern in an exotropic patient and transposing the IRs nasally will help close an A-pattern exotropia.

Most patients requiring correction of A or V pattern will have a primary position deviation that would benefit from horizontal rectus recession or resection. Offsetting the horizontal recti vertically at the same time makes more sense, is technically easier, and obviates potential complications with eyelid position changes and anterior-segment ischemia compared with operating on all four rectus muscles concurrently. For these reasons, correction of A or V patterns with surgery on the vertical rectus muscles is of more theoretical interest than practical utility.

13.4.8 X-Pattern Strabismus

The strabismus pattern marked by increase in the deviation of the eye as the eyes move from primary gaze toward upgaze and also by increase from primary gaze toward downgaze is termed an X pattern. It occurs almost exclusively in exodeviations and can be primary or secondary, the latter usually following medial rectus recessions for esotropia.

13.4.9Complications of Surgery for A and V Patterns

13.4.9.1Consecutive Pattern

Conversion of an A pattern to a V pattern, and vice versa, can occur. This is more likely to occur when a strong oblique muscle weakening procedure is performed in a patient with mild oblique dysfunction pre-operatively. Trying to strengthen an iatrogenically weakened oblique is not a satisfying procedure to attempt; correction of a symptomatic consecutive pattern is more likely to respond to weakening of the newly overacting oblique muscles or shifts of the horizontal rectus muscles.

It would be unusual to convert a pattern with vertical shifts of the horizontal recti alone.

13.4.9.2Asymmetric Result

Inducing a hyperdeviation with perhaps diplopia and/ or a compensatory head posture in a patient when none was present pre-operatively can occur when asymmetric surgery is performed (whether intentionally or not). One source of this problem is incompletely performed weakening of the oblique on one side. In the case of SO tenotomy or IO myectomy, completeness of the weakening procedure can be most assured at the time of surgery by performing the procedure under direct observation followed by confirmation of completeness with oblique traction testing.

Take Home Pearls

•In general, if the A or V pattern is caused by SO or IO “overaction,” surgery should be directed at the obliques.

•If there is no significant oblique overaction, surgery should involve vertical shift of the horizontal rectus muscles in the appropriate direction.

•Bilateral inferior oblique weakening can collapse large V patterns when significant IO overaction is present.

•In patients with V pattern and IOOA in association with congenital esotropia complex, consideration should be given to performing IO anterior transposition, even if DVD is not obvious.

•Correction of X pattern with apparent overaction of all four oblique muscles in association with large-angle exotropia can be accomplished with correction of the horizontal deviation alone without surgery on the oblique muscles.

•Bilateral superior oblique weakening can collapse largeApatterns up 30−40 PD or more. Bilateral IO weakening is not expected to collapse as large a pattern.

•Bilateral SO weakening should not be done in patients with normal binocular vision, i.e., bifixators with high-grade stereopsis (40 s/arc stereo or better).

Correction of this asymmetric result usually involves return to the operating room where oblique traction testing should help pinpoint the problem

[11]. If there is no asymmetric residual oblique dysfunction, then standard vertical rectus recession may be needed.

13.4.9.3Surgical Misadventure

As with any strabismus surgery, careful attention to surgical planes, fat pads, and basic strabismus principles must be observed. This is particularly true when operating on the oblique muscles. The inferior oblique is encased in fat pads that must not be violated and the superior oblique has tenuous connections to the underside of the superior rectus that must be identified. Even the levator complex can be violated with indiscriminate dissection around the superior oblique tendon.

References

1.Breinin GM (1961) Vertically incomitant horizontal strabismus. The A-V syndromes. NY State J Med 61:2243

2.Breinin G (1964) The physiopathology of the A and V patterns. In: Symposium: the A and V patterns in strabismus. Trans Am Acad Ophthalmol Otolaryngol 68:363

3.Folk ER (1997) Costenbader Lecture. A and V syndrome: a historical perspective. J Pediatr Ophthalmol Strabismus 34:154

4.Goldstein JH (1967) Monocular vertical displacement of the horizontal rectus muscles in the A and V patterns. Am

J Ophthalmol 64:265

5.Jampolsky A (1965) Oblique muscle surgery of the A and V pattern. J Pediatr Ophthalmol 2:31

6.Knapp P (1959) Vertically incomitant horizontal strabismus: the so-called A and V syndrome. Trans Am Ophthalmol Soc57:666

7.Knapp P (1971) A and V patterns. In: Symposium on strabismus. Trans New Orleans Acad Ophthalmol St. Louis, Mosby Year-Book, p 242

8.Kushner BJ (2006) Multiple mechanisms of extraocular muscle “overaction.” Arch Ophthalmol 124:680−688

9.Parks MM (1972) The weakening surgical procedures for eliminating overaction of the inferior oblique muscles. Am J Ophthalmol 73:107

10.Plager DA(1992) Tendon laxity in superior oblique palsy. Ophthalmology 99(7):1032−1038

11.Plager DA (2004) Reoperation strategies. In: Plager DA (ed) Strabismus surgery: basic and advanced strategies.

Oxford University Press, Oxford

12.Scott AB (1968) A and V patterns in exotropia. An electromyographic study of horizontal rectus muscles. Am J

Ophthalmol 65:12

13.Urist MJ (1951) Horizontal squint with secondary vertical deviations. Arch Ophthalmol 46:245

14.Urist MJ (1958) The etiology of the so-called A and V syndromes. Am J Ophthalmol 46:835

15.Urist MJ (1968) Recession and upward displacement of the medial rectus muscles in A-pattern esotropia. Am J Ophthalmol 65:769

16.Noorden GK von, Olson CL (1965) Diagnosis and surgical management of vertically incomitant horizontal strabismus. Am J Ophthalmol 60:434

17.Robb RM, Boger WP (1983) Vertical strabismus associated with plagiocephaly. J Pediatr Ophthalmol Strabismus 20:58

18.Clark RA, Miller JM, Rosenbaum AL, Demer JL (1998) Heterotopic muscle pulleys or oblique muscle dysfunction? J AAPOS 2:17

19.Scott WE, Drummond GT, Keech RV (1989) Vertical offsets of horizontal recti muscles in the management of A and V pattern strabismus. Aust NZ J Ophthalmol 17:281

Contents

14.2Surgical Planning  . . . . . . . . . .   180

14.3Good Muscle Function

14.3.3Partial Third-Nerve Palsy  . . . . . . .   182

14.4Moderate Decreased Duction  . . . . . .   182

14.4.1 Fourth-Nerve Palsy  . . . . . . . . .   183

14.4.2Sixth-Nerve Palsy  . . . . . . . . . .   184

14.5Absent Muscle function  . . . . . . . .   185

14.6Multiple Muscle Paresis  . . . . . . . .   186 References  . . . . . . . . . . . . . . . . .   190

Core Messages

•Improve ocular movement into the field of the paretic muscles either by increasing the action of the involved muscle through a resection or tucktype procedure, or by creating an alternate force vector (often necessary in complete paralysis) by an extraocular muscle transposition procedure.

•Create matching weaknesses of movement in the yoke muscles of the other eye. Since it is generally impossible to

restore normal function to the paralytic muscle, the “normal” eye needs to be matched to whatever resulting function can be achieved in the involved eye.

•Minimize the creation of new deviations by selecting appropriated surgical options.

•The direction of greatest deviation determines which muscles are operated and the quality of the remaining duction (good, fair, poor) helps

select what operation to perform.

14.1 Introduction

Paralytic strabismus is challenging to treat because the amount of ocular misalignment varies depending on the direction of gaze [1−3]. This incomitance makes it impossible to manage these situations successfully with prisms or standard strabismus techniques that work best when the size of the deviation is the same in the major gaze positions. The problem becomes more complicated if multiple muscles are affected. This is especially true with third cranial nerve palsies where both horizontal and vertical muscles are paretic. In such circumstances, both types of deviations need to be addressed to get a satisfactory result. In patients with fourth cranial nerve palsies there may also be a torsional issue that can be an extremely bothersome, and failure to eliminate the torsion can result in an unsatisfactory outcome. Finally, in patients who have had a long-standing paralysis, the ocular motility defect may have a restrictive component. The most common type of restriction is a contracture of the antagonist muscle. The more profound the muscle weakness, the more likely a restriction will result. Recognition of this phenomenon is paramount in designing a successful surgical procedure.

The incomitance of paralytic strabismus must be treated with surgical procedures which produce an incomitant result [4−19]. What is necessary to restore useable binocular function is an operation which has a greater effect in one field of gaze than in another.

Developing the appropriate “incomitant” strabismus surgery can be achieved by taking three fundamental principles into consideration:

1.Improve ocular movement of the involved eye.

2.Balance yoke muscles (create matching weaknesses in the other eye).

3.Minimize the creation of new incomitant deviations.

While the first two principles may seem obvious, avoiding or anticipating the “creation” of a new incomitant deviation is not always appreciated until it unexpectedly occurs. The “unexpected” part is relative because almost always it was predictable. It is important to consider the gaze positions where this new deviation may be created by the proposed surgical intervention and to use another approach or use the creation of a new deviation to assist in the overall surgical plan.

In most cases the one gaze position where the eyes are aligned prior to any surgical intervention is located in the opposite direction to the field of action of the paralytic muscle. (A patient with right sixth cranial nerve palsy often sees singly in left gaze.)

Strengthening or tightening the paralytic muscle will limit ocular rotation in the opposite direction creating a deviation where none existed before the surgery. The choice of surgical options should take into account what new deviations may be created. A recession may result in a new deviation since the muscle is now weaker or a resection may restrict the ocular movement in the opposite direction. Planning for, and dealing with, these predictable outcomes will help in obtaining the widest field of useable vision. This is an extremely important point. Often patients are extremely distressed when the previous area of single binocular vision is eliminated in an attempt to improve the diplopia in other fields of gaze. This becomes especially disconcerting if the resultant field of single binocular vision is extremely narrow, or if the diplopia changes direction with small gaze changes (i.e., esotropia in one field and exotropia in another).

14.2 Surgical Planning

In addition to the foregoing principles, when planning the actual surgical procedure it is important to take into consideration two additional factors: (a) the amount of residual muscle function that is present in the paretic muscle(s); and (b) the direction of gaze where the deviation is the greatest.

The amount of residual muscle function helps in determining how the muscle should be modified.

Good to moderate function responds best to simple strengthening procedures such as resection, weakening the antagonist muscle, or the opposite yoke muscle. Poor or absent function requires some alternative force or very large resections. The direction of gaze where the deviation is the greatest helps in selecting which muscles should be modified. If the deviation is greatest in the field of the antagonist, then this muscle needs to be weakened as opposed to the opposite yoke. By combining these factors with the three general principles listed above, a surgical approach can be proposed to achieve the optimum result (Table 14.1).

14.3Good Muscle Function (Mild Duction Limitation)

The most important factor to consider when designing a surgical procedure to correct paralytic strabismus is the amount of residual muscle function present in the paretic muscle(s). In patients with a mild duction limitation (slightly decreased movement in the muscle’s field of greatest action), the deviation can be improved equally by either strengthening the function of the paralytic muscle (resection), weakening the overacting yoke muscle (recession), or weakening the antagonist muscle (recession). Mild duction defects can be associated with fairly large deviations in the primary position; therefore, it is not the size of the deviation in primary position, but the ocular rotation that the muscle can achieve, that is important to assess. The actual choice of procedure depends on the second factor, the gaze position where the deviation is the greatest (Fig. 14.1). If the deviation is greatest in the field of the paralytic muscle, then strengthen the muscle and/or weaken the yoke. If it is greatest in the direction of the paretic muscle’s antagonist (i.e., the antagonist is overacting such as an overacting inferior oblique in superior oblique muscle palsy), weaken the antagonist.

Fig. 14.1  Strategy for designing a surgical procedure for patients with a paralytic muscle taking into account the muscle’s residual function and the field of greatest misalignment

14.3.1 Fourth-Nerve Palsy

A patient with a right fourth cranial nerve palsy has a right hypertropia worse on left gaze. If the deviation is worse up and left, then a right inferior oblique recession is performed (weaken the antagonist). If the deviation is worse down and left, then either strengthen the right superior oblique muscle (tuck)