Key messages

• Unilateral recess/resection might achieve greater surgical success and probably decreases the rate of undercorrection/recurrence compared to bilateral lateral rectus recession.
• Unilateral recess/resection could be a better surgical option than bilateral lateral rectus recession in the management of basic intermittent exotropia. However, it is important to keep in mind the limitations of the existing evidence for decision-making.

What is the evidence.
See evidence matrix in Epistemonikos later

We found five systematic reviews [1],[2],[3],[4],[5] including seven primary studies [6],[7],[8],[9],[10],[11],[12], of which three were randomized trials [6],[7],[8].

One systematic review [4] did not find studies meeting its inclusion criteria and another systematic review [5] did not mention which studies were included (authors were contacted via e-mail, with no response).

This table and the summary in general are based on the three randomized trials identified [6],[7],[8], since the observational studies [9],[10],[11],[12] did not increase the certainty of the existing evidence, nor did they provide relevant additional information.

What types of patients were included*

All the trials included patients with a diagnosis of basic intermittent exotropia with an exodeviation angle ranging between 22 and 50 diopters **.
The age at the time of surgery was between 3 and 37 years.

What types of interventions were included*

All trials compared both types of surgeries, unilateral recess/resection versus bilateral lateral rectus recession.

The surgical correction formula used by the trials, or the equivalence between them, was not reported by the included reviews.

What types of outcomes
were measured

The trials measured multiple outcomes, but the identified systematic reviews pooled them as follows:

• Surgical success: defined as <5 diopters endophoria and <10 diopters exophoria or as <10 diopters endophoria and <10 diopters exophoria.
• Overcorrection
• Subcorrection/ recurrence.

The minimum follow-up of the studies was 12 months, with a range from 12 to 15 months. All the results reported here correspond to the last follow-up consultation.

To whom this evidence does and does not apply

• The evidence reported in this summary applies to patients diagnosed with basic intermittent exotropia. These data cannot be extrapolated to other types of intermittent exotropia, due to their different physiopathological mechanism.
• This information is applicable to both children and adults.

• The outcomes selected were those considered critical for decision-making according to the authors of this summary.
• The definition of surgical success in intermittent exotropia is not yet standardized, which may explain the differences found between the studies: one study reported what most experts currently accept as optimal correction (less than 10 diopters of exophoria) [8] and the other two applied a stricter criterion (less than 5 diopters of exophoria) [6],[7]. This could result in an increase in the rate of undercorrection/recurrence and overcorrection in the latter, since the definition of these outcomes is dependent on the definition of surgical success used.
• No evidence was found for the outcomes improvement in stereopsis, need for reoperation, development of incomitance, postoperative discomfort and quality of life, notwithstanding they were considered critical for the surgical indication and decision-making.

• Current evidence suggests unilateral recess/resection technique could lead to greater surgical success and probably decrease the rate of undercorrection/recurrence of basic intermittent exotropia compared to bilateral lateral rectus recession. However, its effect on overcorrection outcome is not clear, because the certainty of the evidence is very low.
• Furthermore, unilateral recess/resection could be the best surgical option in the management of basic intermittent exotropia, with greater benefit and lower risks than the bilateral lateral rectus recession. However, it is important to take into account the limitations of the existing evidence, especially considering the lack of information on critical outcomes.

• No systematic reviews or primary studies were found that considered economic analysis within their outcomes. However, both interventions have similar costs.

• The most used surgical technique is bilateral lateral rectus recession. It is believed unilateral recess/resection could lead to more overcorrection and development of incomitance, which could lead to major complications, such as suppression and subsequent amblyopia. These beliefs arise from the fear of generating an important asymmetry in the tone of the extraocular musculature when only one eye is operated and that would be avoided when operating both.
• Based on the evidence presented in this summary, most clinicians should lean in favor of the unilateral recess/resection surgical technique as it could achieve greater surgical success.
• However, because bilateral lateral rectus recession technique has been used preferentially in recent years, there is little knowledge and lack of expertise in the unilateral recess/resection technique, which could tip the balance towards bilateral surgery despite the existing evidence. The limitation of the evidence regarding some critical outcomes would also lead to variation in decision-making.
• Unilateral recess/resection may be a better surgical option for patients, since many are reluctant and do not understand why both eyes have to be operated, when they notice that the deviation mainly occurs in one eye.

Differences between this summary and other sources

• The systematic reviews identified, including the most complete and updated [1], reached to similar conclusions to those presented here, being cautious about the results due to the limitations of the primary studies and their risk of bias.
• The conclusions of this summary reveal new evidence that is currently not used by the American Academy of Ophthalmology in its main clinical guideline of strabismus [13], which indiscriminately recommends both surgeries as options to be performed in intermittent exotropia, mentioning that there are no established results of proven superiority of one over the other, leaving the decision to the doctor. In this sense, it only suggests to perform bilateral lateral rectus recession over unilateral recess/resection in cases in which intermittent exotropia is concomitant with anisotropies, a situation not evaluated in this summary.

• The probability that future research changes the conclusions of this summary is high, due to the uncertainty of the existing evidence.
• There is one randomized trial published in 2017 [14] that until the publication of this summary had not been included in any systematic review.
• We identified one ongoing trial [15] in the International Clinical Trials Registry Platform of the World Health Organization evaluating this question.
• We identified one systematic review in progress [16] in the International Prospective Register of Systematic Reviews (PROSPERO), which could provide new information on unreported outcomes and include the new randomized trial identified [14].