4.1 Goals

In addition to the goals of strabismus surgery stated in Chapter 1.1 Goals, the goals of rectus muscle surgery include the following:

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  For intermittent exotropia, a small distance overcorrection of 8 to 10 prism diopters in the early postoperative period may improve the probability of long-term improved alignment, although the reported outcomes are variable and likely depend on the patient’s sensory status. ¹

  
  
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  Improvement of eye alignment in primary gaze and/or improvement of an anomalous head position in patients with incomitant strabismus due to Duane syndrome, other dysinnervation syndrome, or cranial nerve palsies.

  
  
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  With the Anderson-Kestenbaum procedure, ² improvement of an anomalous head turn in patients with nystagmus and a null point not in primary gaze.

  
  
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  With superior rectus recessions, improvement of manifest dissociated vertical deviations in patients without inferior oblique overaction or tightness of the inferior oblique muscles on forced duction testing.

4.2 Advantages

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  Refractive correction and amblyopia treatment may improve control of certain types of strabismus, including accommodative esotropia and intermittent exotropia. For those patients with constant or poorly controlled misalignment, strabismus surgery is offered as a treatment to improve the alignment. Strabismus surgery on the rectus muscles is likely to be more effective than botulinum toxin injection in patients with poor potential for fusion.

  
  
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  For rectus muscle recessions, the muscle can be reinserted with direct scleral passes at the new insertion site or at the original insertion using a hangback technique:

  
  
  
  
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    The hangback technique is useful for very large recessions, especially of the superior rectus muscle because far posterior scleral passes could interfere with the superior oblique tendon. ³

    
    
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    The hangback technique may also be preferred by inexperienced strabismus surgeons, including trainees, as the insertion is more easily accessible, possibly reducing the risk of scleral perforation.

    
    
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    However, the hangback technique may result in a larger recession than intended due to central sag and may increase the risk of stretch scar formation, which can lead to recurrent strabismus. ⁴

  
  
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  An alternative to a small resection is rectus muscle plication, which appears to preserve the anterior ciliary circulation, as the muscle is not disinserted. ⁵

4.3 Expectations

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  Diplopia, typically transient, may occur in the early postoperative period, usually due to anomalous retinal correspondence and sometimes due to early overcorrection and/or surgically induced incomitance.

4.4 Key Principles

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  A rectus muscle can be weakened by recessing the muscle and tightened by resecting or plicating the muscle to improve ocular alignment in patients with horizontal and vertical deviations.

  
  
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  Resections are tightening procedures, not strengthening procedures. Large resections can even result in restriction of ocular motility, which may be desired in some cases.

  
  
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  For bilateral procedures in children, bilateral recessions are typically performed before resections, depending on the deviation at distance and near, as well as versions and ductions. Unilateral procedures, such as recess-resect procedures, are indicated in some cases.

4.5 Indications

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  Various etiologies of strabismus may be treated with rectus muscle surgery, including:

  
  
  
  
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    Comitant esodeviations and exodeviations, including partially accommodative esotropia, nonaccommodative esotropia, infantile esotropia or exotropia, and intermittent exotropia.

    
    
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    Sensory esodeviations and exodeviations for which unilateral surgery is recommended.

    
    
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    Dissociated vertical deviations.

    
    
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    Congenital dysinnervation syndromes including Duane syndrome and monocular elevation deficiency.

    
    
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    Oculomotor nerve (3rd cranial nerve) palsies.

    
    
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    Abducens nerve (6th cranial nerve) palsies.

    
    
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    Restrictive strabismus.

  
  
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  Patients with nystagmus and a null point not in primary gaze, resulting in an anomalous head turn.

4.6 Contraindications

In patients who have a prior history of strabismus surgery on two to three rectus muscles in one eye, the increased risk of anterior segment ischemia is considered when planning the timing of and approach for subsequent strabismus surgery.

4.7 Preoperative Preparation

A complete sensorimotor examination is performed as discussed in Chapter 1.7 Preoperative Preparation. Surgical planning takes into consideration the amount of deviation, presence of amblyopia in determining the laterality of surgery, the presence of pattern strabismus, as well as forced duction testing under anesthesia before the start of surgery, especially if restriction is suspected.

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  Horizontal deviations with V- or A-patterns without significant oblique muscle overaction can be addressed with vertical displacement of pairs of horizontal rectus muscles during reinsertion of the muscle. This is less commonly performed in unilateral recess-resect procedures, as patients with normal fusion may develop torsional diplopia, although it can be considered in those with limited fusion. ⁶ The mnemonic M-A-L-E is commonly used to recall the direction of displacement. For example, for a V-pattern, if the bilateral Medial rectus muscles are the operative muscles, they are infraplaced (toward the Apex of the “V”). If the bilateral Lateral rectus muscles are the operative muscles, they are supraplaced (toward the Empty space of the “V”). Understanding the rationale for this effect is advantageous for recalling how the muscles should be displaced for pattern horizontal strabismus (Fig. 4.1). ³ For example, when the lateral rectus muscles are recessed and supraplaced for a V-pattern exotropia, the muscles are effectively further recessed when the eye is in upgaze to treat the larger exodeviation in upgaze. Without changing the planned amount of recession or resection for the horizontal deviation in primary gaze, half-tendon-width to full-tendon-width displacements, depending on the difference in the deviation in upgaze and downgaze, may be used, or the amount of displacement may be measured in millimeters.

  
  
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  A small vertical deviation, such as one caused by a partial oculomotor nerve (3rd cranial nerve) paresis, can also be addressed with vertical displacements of the horizontal rectus muscles. For example, supraplacement of horizontal rectus muscles can effectively pull a hypotropic eye upward. Approximately 1 mm of displacement corrects 1 prism diopter of vertical deviation for up to 10 prism diopters.

  
  
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  In Duane syndrome, rectus muscle resections in the involved eye are usually avoided due to the risk of worsening restriction and globe retraction. In patients with severe globe retraction with or without an upshoot or downshoot, recessions of both the medial and lateral rectus muscles may be considered. In esotropic Duane syndrome, large recessions of the medial rectus muscles are usually needed for significant improvement of the deviation and head turn. Forced ductions prior to the start of surgery should be performed.

  
  
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  Dissociated vertical deviation (DVD) is a bilateral but often asymmetric form of strabismus. Thus, bilateral surgery is recommended in most cases, except in patients who are unable to alternate fixation due to a very strong fixation preference, usually due to significantly decreased visual acuity in one eye. Otherwise, unilateral surgery for an asymmetric DVD will unveil the DVD in the unoperated eye, requiring additional surgery.

4.8 Operative Technique

Guidelines for the amounts of surgery to perform for the horizontal rectus muscles based on preoperative measurements are given in Table 4.1. ⁷ Several tables are available for horizontal rectus muscle surgery which vary more for larger deviations and are less reliable for reoperations, restrictive and paretic strabismus, and dysinnervation syndromes. For the vertical rectus muscles, 1 mm of recession or resection corrects for approximately 3 prism diopters of deviation, usually with a recommended maximum of 5 mm of surgery. However, larger recessions of the superior rectus muscles are typically required to effectively treat dissociated vertical deviations (Table 4.2). ⁸ Table 4.3 ⁹ displays the amounts of surgery to perform for patients with a large right or left head turn due to nystagmus with a null point that is not in primary gaze, also known as the Anderson-Kestenbaum procedure. This procedure is typically performed in school-age children or older. When deliberating which muscles to recess and resect for this procedure, the adducted eye can be considered “esotropic” and the abducted eye “exotropic,” while allowing the preferred head turn. The large amounts of surgery used, particularly the resections, can result in limitations of postoperative ductions, which is part of the desired effect of this procedure. If strabismus is also present, the surgical numbers are modified. One method for surgical planning for a patient with strabismus and a head turn due to nystagmus is to place a loose prism over the fixating eye until the head turn resolves. While keeping the first prism in place, the strabismus is then measured with prisms over the nonfixating eye.

4.8.1 Forced Duction Testing

For forced duction testing of the horizontal rectus muscles, two pairs of 0.3- or 0.5-mm toothed forceps are used to grasp the eye at 12 and 6 o’clock near the limbus (Fig. 4.2). The eye is gently proptosed, as retropulsion of the globe places the rectus muscles on slack and can give a false negative result. The eye is adducted and abducted to evaluate for tightness of the medial and lateral rectus muscles. For the vertical rectus muscles, the eye is grasped at 3 and 9 o’clock. If a pattern strabismus is present, exaggerated traction testing of the oblique muscles is also performed, as described in Chapter 6.8.1 Exaggerated Traction Testing.

Following the creation of a fornix incision, as described in Chapter 3.8.1 Fornix Incision, the steps for rectus muscle surgery are described below.

4.8.2 Isolating the Operative Muscle

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   The eye continues to be grasped at the limbus, and the conjunctival incision is held open with forceps. A Stevens hook is used to isolate the operative rectus muscle with the handle nearly perpendicular to the insertion (Fig. 4.3a), keeping in mind the approximate location of the insertion from the limbus. Once the muscle is securely hooked, the assistant can release the forceps from the limbus, while keeping the conjunctival incision open with forceps.

   
   
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   A Jameson hook is then used to sweep along the muscle insertion just posterior to the Stevens hook, which is subsequently removed (Fig. 4.3b). A Guyton hook may subsequently be used to hook the muscle in a similar manner, after which the Jameson hook is removed.

   
   
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   The bulb of the Guyton or Jameson hook is swept to nearly reach the limbus subconjunctivally as an early test to confirm that the entire width of the muscle has been isolated. If not, toothed forceps can be used to gently grasp the muscle through the conjunctiva to bring the entire muscle onto the hook.

   
   
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   Point the bulb of the Guyton or Jameson hook slightly away from the globe to gather the width of the muscle in the elbow of the hook and use a Stevens hook to drape the overlying conjunctiva over the bulb of the Guyton or Jameson hook. Care should be taken during this part of the procedure to avoid either unhooking the muscle or tearing the conjunctiva. Also ensure that the conjunctiva is not folded over the bulb of the hook before snipping the intermuscular septum in the next step to avoid creation of a buttonhole in the conjunctiva.

   
   
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   Blunt Westcott scissors are used to snip the intermuscular septum just under the bulb of the Guyton or Jameson hook until an opening is created (Fig. 4.4a). The assistant should retract the conjunctiva away from the bulb of the Guyton or Jameson hook with a small hook to expose the intermuscular septum. The closed blades of the Westcott scissors, a small hook, or toothed forceps are then used to expose the bulb of the Guyton or Jameson hook through the opening of the intermuscular septum (Fig. 4.4b).

   
   
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   A pole test is now performed to confirm that the entire width of the muscle has been isolated. The assistant and the surgeon each place a Stevens hook in the opening of the intermuscular septum with both hooks oriented so that the tips are flushed on the sclera. One hook holds open the incision, and the second hook performs the pole test by sweeping the tip from posterior to the insertion, around the pole of the insertion, to anterior to the insertion (Fig. 4.5). If the hook does not easily slide anteriorly and comes to a stop at the plane of the insertion, the muscle has likely been split. The split portion of the muscle can be hooked with a small hook and brought onto the Guyton or Jameson hook to re-join the split muscle. Step 5 is repeated, followed by the pole test. The pole test can also be performed on the opposite pole of the muscle in the same manner.

   
   
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   The two Stevens hooks are then used by the assistant to tent the overlying conjunctiva to expose the muscle (Fig. 4.6), Tenon’s capsule, and check ligaments which are bluntly and sharply dissected using blunt Westcott scissors while taking care not to cut the muscle.

   
   
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   One Stevens hook is brought anteriorly to retract the conjunctiva away from the insertion to dissect Tenon’s capsule to bare sclera, while holding the muscle taut on the Guyton or Jameson hook to visualize the area anterior to the insertion. The Tenon’s capsule can be grasped and tented with forceps, and Westcott scissors used to bluntly clear the Tenon’s capsule from sclera (Fig. 4.7a). Once the Tenon’s capsule is separated from sclera, it can be sharply dissected off the muscle and sclera, if needed (Fig. 4.7b).

   
   
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   The center of the anterior insertion is dried and marked on sclera (Fig. 4.8), keeping in mind any planned vertical displacement for a pattern strabismus.

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