Standardising reported outcomes of surgery for intermittent exotropia--a systematic literature review

Intermittent exotropia (IXT) is one of the most common strabismus entities worldwide, but it remains poorly understood. Investigators differ regarding which parameters should be used to characterize IXT and to evaluate interventions. Surgery is an established treatment option but problems can arise when comparing surgical effectiveness if there is a wide range of different outcome measures that can be used. This study aimed to assess the extent of standardization of reported outcomes in studies of surgery for IXT.

With institutional R&D committee approval, we conducted, according to a predefined protocol, a systematic literature review of outcomes of surgery for IXT published in the last 10 years. The databases used were Medline and EMBASE. Two analysts independently performed the searches. The separate lists were then compared and collated to maximize our return rate for included papers and allow evaluation of our strategies.

Fifty-six studies met our inclusion criteria. Thirty-two were retrospective and twenty-four prospective. Outcome measures varied widely between studies and variously included ocular alignment, stereopsis, visual acuity, re-operation rate, and postoperative drift. Even for ocular alignment, there was no agreed definition of postoperative success. Time frames for assessing outcomes ranged from two months to two years after surgery.

The lack of harmony in outcome reporting for studies of surgery for IXT is counterproductive. We suggest 4 core outcomes for all future studies, which have already been incorporated into two current randomized trials: alignment, near stereoacuity, control score, and quality of life score.