Conversion of intermittent exotropia types subsequent to part-time occlusion therapy and its sustainability

Purpose: To evaluate the effects of part-time occlusion therapy on types of intermittent exotropia and sustainability of converted types. Methods: Forty-four and 26 children with basic-type and convergence-insufficiency-type intermittent exotropia, respectively, were evaluated in this study. Upon initial examination, we obtained both distant and near deviating angles using prism cover tests, after correcting for refractive errors. The intermittent exotropia types were classified on the basis of the reference values of distance-near differences, as follows. In patients with distance angles in excess of 30 prism diopters (PD) the reference value of the distance-near differences was 10 PD, and in patients with distance angles of less than 30 PD, the value was one-third of the distance angles. We conducted 3 h a day of occlusion of the non-deviating eye for 3 months, and assessed the changes in types of intermittent exotropia. Results: Deviating angles mean±SD) were determined to be 22.1± 7.46 PD on the distance measurements and 30.6±7.92 PD on the near measurements. After 3 months of occlusion, the deviating angles were 25.9±9.10 PD on distance measurements 21.4±11.00 PD on near measurements, corresponding to significant conductions (p=0.005 and p<0.001 respectively). Fourteen patients (32%) suffering from basic-type intermittent exotropia converted to the pseudodivergence excess type. In patients suffering from the basic type who exhibited no change in type, 9 patients (20%) exhibited reductions on both near and distance angle measurements. Among the convergence-insufficiency type patients, 18 (69%) converted to basic type and 2 patients (7%) to the pseudodivergence-excess type. Conclusion: Part-time occlusion therapy resulted in the conversion of the basic and convergence-insufficiency types of intermittent exotropia to pseudodivergence-excess and basic types in more than half of the intermittent exotropes.