Prognostic factors for over-correction and under-correction in basic intermittent exotropia surgery

Purpose This study was designed to evaluate the prognostic factors for over-correction and under-correction following surgery for basic intermittent exotropia. Patients and methods This is a prospective nonrandomized study that included 86 patients with basic intermittent exotropia who were candidates for surgery. Patients were subjected to full ophthalmic and orthoptic examination and A scan measurement. The surgical plan was binocular surgery, with a goal of five prism diopters of over-correction. With at least 12 months of follow-up, postoperative correction within 10 prism diopters was considered orthophoric. Results The mean age of the patients was 7.83±4.67 years, and 51% of the patients were females. The range of preoperative angle of deviation was 30–80 prism diopters (mean=50.12±12.99). Myopia ranged from −0.5 to −5.0 diopters (D), and hypermetropia ranged from +0.5 to +4.0 D. The axial length ranged from 18.37 to 25.49 mm (mean=22.42±0.95 mm). The success rate was 74.4% after 1 year of follow-up, whereas 11.6 and 14% were over-corrected and under-corrected, respectively. In the under-correction group, a preoperative large angle of deviation was the only statistically significant factor ( P =0.02). In the over-correction group, the statistically significant factors were female sex ( P =0.0001), myopia ( P =0.001), longer axial length ( P =0.04), large preoperative angle of deviation ( P =0.005), and surgery involving greater than or equal to two muscles ( P =0.003). Conclusion Large preoperative angle of deviation was the only risk factor for under-correction, whereas in over-correction, the risk factors were female sex, myopic refraction, longer ocular axial length, large preoperative angle of deviation, and surgery involving more than two muscles.