Interventions for intermittent exotropia (Review)

Author: Pang Y, Gnanaraj L, Gayleard J, Han G, Hatt SR.

Geographical coverage: India, The USA, and Turkey 

Sector: Biomedical

Sub-sector: Treatment

Equity focus: None

Study population: Patients diagnosed with intermittent exotropia.

Review type: Effectiveness review

Quantitative synthesis method: Meta-analysis

Qualitative synthesis method: Not applicable

Background: Ocular misalignment (strabismus) develops in approximately 5% of developmentally normal children. Of these, approximately 25% present with an outward turning ocular deviation or exotropia. The clinical management of intermittent exotropia has been discussed extensively in the literature, yet there remains a lack of clarity regarding indications for intervention, the most effective form of treatment and whether there is an optimal time in the evolution of the disease at which any treatment should be carried out.

Objectives: To analyse the effects of various surgical and non-surgical treatments in randomised trials of participants with intermittent exotropia, and to report intervention criteria and determine the significance of factors such as age with respect to outcome.

Main findings:

The authors included one randomised trial in their review, which demonstrated that unilateral surgery was more effective than bilateral surgery for correcting basic intermittent exotropia. In the study, 36 patients with basic intermittent exotropia were randomised to undergo either bilateral lateral rectus recession or unilateral lateral rectus recession with medial rectus resection. These groups were compared to each other and to a non-randomised group of 68 patients with simulated distance exotropia who underwent bilateral lateral recession surgery. Outcomes were assessed at least one year post-surgery and categorised as either satisfactory or unsatisfactory based on specific criteria. However, stereoacuity was not reported before or after the surgery. The surgical procedures were standardised using surgical formula tables.

The randomised trial included found unilateral surgery more effective than bilateral surgery for basic intermittent exotropia. However, across all identified studies, measures of severity and thus criteria for intervention are poorly validated, and there appears to be no reliable natural history data. This study also found unilateral recess or resect surgery to be more effective than bilateral recession surgery in correcting basic X(T). This provides some guidance for this subgroup of X(T), but generally there remains a significant lack of reliable evidence to help inform practice. In the absence of good evidence of treatment effectiveness, the potential to do harm by correcting the appearance of misalignment by disrupting the ability to maintain BSV should be seriously considered when managing this condition.

Authors note the need for further randomised studies to provide more reliable evidence for the management of this condition. In particular, to: establish the natural history of the condition; clarify appropriate intervention criteria for non-surgical and surgical treatments; improve methods to measure severity; identify the most effective surgical procedure for different types of X(T), for example, simulated and true distance X(T); establish realistic treatment aims and long-term outcomes; determine influence of age and duration of misalignment on outcome; establish the effectiveness of non-surgical treatments; identify whether or not initial overcorrection is advantageous in achieving optimal treatment outcomes; and measure effects of X(T) on quality of life.

Methodology:

The inclusion criteria were randomised controlled trials involving any surgical or non-surgical treatment for intermittent exotropia. Participants were individuals diagnosed with intermittent exotropia, as defined under ‘presentation and diagnosis’, and must have shown evidence of exodeviation on a cover test, prism cover test, or another recognised alignment measurement method. Studies were excluded if they did not clearly include basic or distance types of intermittent exotropia, if other types of exotropia were included and data on intermittent exotropia could not be extracted, or if participants had received prior treatment. The interventions included various types of surgical and non-surgical treatments, such as fusion or convergence exercises, occlusion for anti-suppression, optical treatments like minus lens therapy, tinted lenses, prisms, and Botulinum toxin A injection. Criteria were established for primary outcomes, secondary outcomes, adverse events, and quality of life measures.

The authors conducted a comprehensive search for trials in various databases, including the Cochrane Central Register of Controlled Trials, Medline, EMBASE, LILACS, mRCT, ClinicalTrials.gov, and the WHO ICTRP, with no date or language restrictions. The databases were last searched on 4 May 2012. The British Orthoptic Journal and the proceedings of the ESA, ISA, and AAPOS were manually searched up to specific years. Active researchers in the field were contacted for additional published or unpublished studies.

Each author of the review independently evaluated the study abstracts identified from both electronic and manual searches. Their analyses were then compared, and full papers for relevant studies were procured. Both authors independently screened the titles and abstracts obtained from the searches to determine if they met the criteria. The quality of the studies was assessed according to the methods outlined in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions. Although data synthesis and sensitivity analysis were planned, they were not carried out in practice as only one study was included.

Applicability/external validity:

The authors of the review do not explicitly discuss the applicability and external validity of their findings. However, they do acknowledge some of the limitations and challenges of the existing evidence which interfere with the applicability and external validity of findings.

Geographic focus:

The scarcity of studies from low- and middle-income countries, reduces the generalizability and relevance of the findings to different settings and populations.

Summary of quality assessment:

The approaches used to identify, include and critically appraise studies were generally highly robust, with all key tasks being undertaken by at least two authors and the use of a search that was unrestricted by language or publication status. Many of the criteria associated with the analysis of the data were not relevant to this particular study, as only one review was ultimately identified for inclusion. Nevertheless, we have high confidence in the findings of this study.