Bilateral Lateral Rectus Recession Versus Unilateral Recess-Resect for Intermittent Exotropia
Condition: Exotropia
MeSH terms: Exotropia
Study type: Interventional

Summary: 
      The purpose of this study is to evaluate the effectiveness of bilateral lateral rectus muscle
      recession versus unilateral lateral rectus recession with medial rectus resection procedures
      for the treatment of basic type and pseudo divergence excess type intermittent exotropia.
    

Detailed description: 
      Intermittent exotropia (IXT) is the most common form of childhood onset exotropia with an
      incidence of 32.1 per 100,000 in children under 19 years of age. Intermittent exotropia is
      characterized by an exotropia that is not constant and is mainly present when viewing at
      distance, but may also be present at near. Normal binocular single vision (BSV) is typically
      present at near when the exotropia is controlled, with evidence of normal (occasionally
      sub-normal) stereoacuity. Although the natural history of the condition is largely unknown,
      many children with IXT are treated using either surgical or non-surgical interventions. The
      rationale for intervention in childhood IXT is that extended periods of misalignment may lead
      to entrenched suppression, resulting in loss of BSV. Intervention may also aim to address the
      social effects caused by the appearance of misaligned eyes. Many children treated for IXT are
      currently treated surgically.

      There is poor agreement as to which type of surgery is most effective for the correction of
      IXT and the debate has long been related to differentiation between IXT sub-types. Based on
      distance-near angle disparity, IXT sub-types are classified as: 1) basic (similar magnitude
      of misalignment at distance and near); 2) true divergence excess (larger at distance); 3)
      pseudo divergence excess (initially larger at distance, but near angle increases following
      occlusion or with addition of plus lenses at near); 4) convergence insufficiency (larger at
      near). Basic and pseudo divergence excess appear to be the most common of the sub-types, and
      are also the types for which there is most disagreement regarding the optimum surgical
      approach. The two most common procedures are bilateral lateral rectus recession (BLRrec) and
      unilateral lateral rectus recession combined with a medial rectus resection in the same eye
      (R&R). Traditionally, BLRrec has been advocated where there is a larger distance angle, and
      R&R where there is a similar angle at distance and near. A survey of American strabismus
      surgeons published in 1990 found that the majority performed BLRrec for both basic and
      divergence excess types. Similarly, we found by polling our investigator group that the
      majority still perform a BLRrec for basic type IXT. Nevertheless, controversy still exists as
      to which of these surgical approaches is superior. Advocates of the BLRrec procedure tend to
      hold that surgery should be based purely on the distance angle of deviation. Proponents of
      R&R surgery suggest resection of the medial rectus best addresses the exodeviation at near.

      The proposed advantage of the R&R procedure is that resecting the medial rectus, with a
      possible longer term initial overcorrection, is necessary for a stable and superior long-term
      outcome. Nevertheless, those who favor the BLRrec procedure suggest that the more profound
      and prolonged initial overcorrection occurring with R&R is not only unnecessary, but may in
      fact be harmful. A persistent overcorrection may be associated with the development of
      diplopia, amblyopia, and loss of stereoacuity. On the other hand, critics of the BLRrec
      procedure suggest that long-term recurrence rates are higher. Poor motor outcomes are likely
      to require reoperation and therefore the long-term success rates of these surgeries have
      public health importance in terms of cost to society.

      Evaluating initial and long-term surgical outcomes in the proposed randomized clinical trial
      (RCT) will answer questions regarding the failure rates of these surgeries and also provide
      needed data on the potential harm of each procedure.

      Only one prospective randomized clinical trial addresses success rates of BLRrec versus R&R
      for IXT. After between 12-15 months of follow up, 82% of 17 patients undergoing an R&R had a
      satisfactory outcome compared to 52% of 19 patients undergoing a BLRrec. Nevertheless, there
      are some important limitations of this previous study. The sample size was very small. The
      study population was a sub-group of patients with basic type IXT, excluding patients with
      basic IXT whose angle of deviation increased at far distance or following occlusion, thus
      limiting the generalizability of the results. In addition, outcomes were assessed unmasked,
      potentially biasing the results. One observational study of 103 patients (90% of whom had
      basic type IXT) found 1-year success rates of 56% for BLRrec and 60% for R&R. A retrospective
      study of 115 patients with basic type IXT reported success rates of 69% for BLRrec and 77%
      for R&R after an average of 15 months of follow up. Other studies comparing surgery types are
      limited not only by retrospective study design but also by inclusion of other types of
      exotropia, making it difficult to interpret results. In addition, many different criteria for
      success are used, precluding meaningful comparison of success rates between studies. This
      lack of evidence makes it very difficult to counsel parents of children with IXT regarding
      the likely success and complication rate of either procedure, limiting our ability to make
      informed management decisions. Establishing the respective failure rates through the proposed
      study will allow physicians to offer patients the type of surgery with the highest chance of
      long-term success, minimizing suboptimal results and repeat surgeries.

      The present study is being conducted to compare the effectiveness of BLRrec with R&R for the
      surgical treatment of basic type and pseudo divergence excess type IXT.
    

Intervention name(s): Bilateral lateral rectus recession (BLRc); Unilateral lateral rectus recession with medial rectus resection (R&R)
Intervention type(s): Procedure; Procedure
Intervention description(s): Bilateral lateral rectus recession surgery; A unilateral lateral rectus recession combined with a medial rectus resection in the same eye. Choice of eye at investigator discretion based on any interocular difference, position under anesthesia, fixation preference, or forced duction testing. Reason for choice of eye will be recorded.
Other intervention name(s): BLR; BLRc; R&R
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: Single (Outcomes Assessor)
Primary purpose: Treatment
Keywords: IXT; Exotropia; Strabismus; Intermittent exotropia