9.1.1 Transposition Procedures

Improve eye alignment in patients with poor function of a rectus muscle by tethering the eye in the direction of the weak muscle’s field of action.

9.1.2 Posterior Fixation Sutures

Weaken a rectus muscle in its field of action, by creating an ancillary insertion posterior to the insertion, without overcorrecting the alignment in other gaze positions. Innervation to the yoke muscle is, in turn, increased which may also serve as a mechanism to improve the alignment.

9.1.3 Y-split Procedure of the Lateral Rectus Muscle

Improve an isolated upshoot or downshoot in Duane syndrome caused by co-contraction (leash phenomenon) of the horizontal rectus muscles in adduction by broadening the lateral rectus insertion to stabilize the position of the lateral rectus muscle and prevent it from shifting superiorly or inferiorly over the globe. If significant globe retraction and associated enophthalmos are present, large recessions (approximately 10 mm) of both the medial and lateral rectus muscles can also correct an upshoot or downshoot, without the need for the Y-split procedure.

9.1.4 Partial Tendon Recession

Resolve diplopia secondary to small-angle vertical deviations, eliminating the need for prism glasses.

9.5.1 Transposition Procedures

Any condition in which a rectus muscle has poor function, usually due to abnormal innervation, which may be congenital or acquired.

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  Abducens nerve (6th cranial nerve) paresis with little to no function of the lateral rectus muscle, resulting in an esotropia.

  
  
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  Duane syndrome, particularly esotropic Duane syndrome with poor abduction.

  
  
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  Monocular elevation deficiency without restriction of the inferior rectus muscle.

  
  
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  Slipped rectus muscle that is iatrogenic or due to trauma, if it is unable to be recovered or with persistent underaction of the muscle.

  
  
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  Oculomotor nerve (3rd cranial nerve) paresis

  
  
  
  
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    Exotropia and hypotropia are usually present, but the deviation is dependent on the degree of involvement of the superior and inferior divisions of the oculomotor nerve which dictates the surgical management.

    
    
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    Medial transposition of the lateral rectus, ¹ passed between the sclera and both the vertical rectus and obliques muscles with the aid of a Gass hook to reach the medial rectus insertion, has been described.

    
    
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    Maximal but reversible weakening of the lateral rectus muscle by fixation with nonabsorbable suture to the periosteum of the orbital wall ² may also be considered.

  
  
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  Rare cases of congenitally absent rectus muscle(s).

9.5.2 Posterior Fixation Sutures

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  Esotropia with convergence excess (high AC/A).

  
  
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  Incomitant strabismus by operating on the yoke muscle on the unaffected fellow eye to balance it with the underacting muscle in the affected eye. For example, for a left abducens nerve paresis with a large secondary deviation of the right medial rectus muscle in left gaze but with a smaller esotropia in primary gaze, a posterior fixation suture may be placed on the right medial rectus muscle in addition to horizontal rectus muscle surgery in the left eye.

9.5.3 Y-split Procedure of the Lateral Rectus Muscle

The Y-split procedure of the lateral rectus muscle is performed specifically for Duane syndrome with an upshoot or downshoot.

9.5.4 Partial Tendon Recession

Symptomatic diplopia from small-angle vertical strabismus and desire for independence from prism glasses, such as a patient with diplopia who would like to play sports without the need for prism glasses.

9.8.1 Transposition Procedures

For a weak lateral rectus muscle, the superior rectus or both vertical rectus muscles are transposed and inserted adjacent to the lateral rectus insertion. For monocular elevation deficiency without significant tightness of the inferior rectus, a similar technique is used for superior transposition of the medial and lateral rectus muscles (Knapp procedure).

Several transposition techniques have been described:

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  Full tendon transposition is described below.

  
  
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  The Hummelsheim procedure, which is a partial tendon transposition of the vertical rectus muscles, spares the anterior ciliary vessels at the nondisinserted halves of the transposed rectus muscles.

  
  
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  The Jensen procedure also splits the transposed muscles but without disinsertion, joining the adjacent half of the transposed muscle to the weak muscle with a nonabsorbable polyester suture. While it is theoretically a vessel sparing procedure, anterior segment ischemia has been reported. ⁴ It is technically difficult and may result in greater scarring than the other techniques, making reoperations more challenging.

A fornix incision is created in the quadrant between the weak muscle and the muscle to be transposed. If two muscles are transposed, two fornix incisions are used. For example, superotemporal and inferotemporal fornix incisions are used for transpositions of the vertical rectus muscles to a weak lateral rectus muscle:

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   The rectus muscle to be transposed is isolated on a muscle hook and cleared of its overlying Tenon’s capsule and connective tissue with blunt dissection, which should be performed far posteriorly for transposition of vertical rectus muscles to avoid significant changes in the upper and lower eyelid positions. The fascial connection between the superior rectus and the superior oblique tendon should also be separated to decrease the risk of an unexpected vertical deviation.

   
   
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   The muscle is secured on a 6–0 double-armed polyglactin suture near its insertion and disinserted as described in Chapter 4.8.3 Rectus Muscle Recession.

   
   
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   The weak muscle is then isolated on a Jameson or Guyton muscle hook through the same fornix incision, clearing with blunt dissection the corresponding pole of the muscle to bare sclera where the transposed muscle will be reattached.

   
   
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   The disinserted muscle is then reattached adjacent to the weak muscle (Fig. 9.1). The pole of the transposed muscle proximal to the weak muscle can be reinserted just posterior to the corresponding pole of the weak muscle, while the distal pole of the transposed muscle is reinserted adjacent to the weak muscle, so that the center of the insertion of the transposed muscle is at the pole of the weak muscle.

Modifications of transposition to augment its effect include:

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  Scleral fixation using 6–0 nonabsorbable polyester suture of approximately one-fourth of the width of the transposed muscle belly to the sclera, adjacent to the weak muscle. This is performed far posteriorly at least 12 to 14 mm posterior to the insertion of the weak muscle and may be technically difficult.

  
  
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  Union of approximately one-fourth of the width of the transposed muscle belly to the adjacent one-fourth width of the weak muscle with a 6–0 nonabsorbable polyester suture, 5 to 6 mm posterior to the insertion of the weak muscle. ⁵