Weakening Rectus Muscles



Weakening Rectus Muscles


Megan X. Law, MD



PREOPERATIVE CONSIDERATIONS

Recessions move the muscle insertion to a new location closer to its origin to weaken the effect of the muscle. There is an exponential increase in effect with large recessions as reflected in standard strabismus surgical charts (see Chapter 42).1,2 Recessing a single rectus muscle will induce incomitance, with a greater effect in the muscle’s field of action. Asymmetric bilateral recessions will also induce incomitance, with greater effect in the field of action of the more recessed muscle. Great caution should be taken in recessing a rectus muscle posterior to the equator as this can significantly impair the muscle’s function.3 A guideline for the maximal recession of the four rectus muscles without inducing duction limitation is listed in Table 44.1.1,2,3,4








TABLE 44.1. Maximal recession (approximate) from the limbus

Maximal recession (mm)


Medial rectus

7


Lateral rectus

10


Superior rectus

10


Inferior rectus

6



SURGICAL PLANNING

In most cases, a traditional recession is performed. Alternative weakening procedures include the hang-back recession and marginal myotomy1,2,3,4,5,6 (Table 44.2).



  • Traditional recession: muscle tendon is disinserted from the sclera and fixated at a new location posterior to the original insertion.


  • Hang-back recession: muscle tendon is disinserted from the sclera and suspended by sutures through the original insertion.


  • Marginal myotomy (Z-plasty): muscle tendon is partially cut at two parallel locations in opposite directions leading to elongation and lengthening.









TABLE 44.2. Pros and cons of three rectus muscle weakening techniques

Traditional recession

Hang-back recession

Marginal myotomy


Pros

Most predictable effect (standard surgical tables)

Safety: small deep-set eye, high myopia, staphyloma, scleral buckle, or glaucoma drainage device

Safety: small deep-set eye, high myopia, staphyloma, scleral buckle or glaucoma drainage device, previous recession


Easy access to knots for adjustable sutures

Can combine with recession for a “double” weakening effect


Standard surgical tables are available

Can further weaken a “maximally recessed” rectus muscle


Useful in large superior rectus recessions, “bypassing” the superior oblique insertion

Avoids scleral passes


Cons

Posterior scleral passes can be challenging

Risk of muscle slip posteriorly with small recessions (greater than intended effect)

Less predictable effect (no standard surgical tables)


Risk of muscle slip anteriorly with large recessions (smaller than intended effect)

Risk of severing the muscle


Risk of muscle slip perpendicular to the recession (eg, induced vertical deviation with a horizontal recession)

Cannot be easily reversed


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May 10, 2021 | Posted by in OPHTHALMOLOGY | Comments Off on Weakening Rectus Muscles

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