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

To evaluate the effects of part-time occlusion therapy on types of intermittent exotropia and sustainability of converted types.

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. We conducted occlusion of the nondeviating eye for 3 months at 3 h/day and assessed the changes in types of intermittent exotropia. We also observed the changes of deviating angles and sustainability of types after 3 months of cessation of part-time occlusion in patients who did not undergo surgery.

Preocclusion deviating angles (mean +/- SD) were determined to be 27.1+/-7.46 prism diopters (PD) on distant measurements and 30.6+/-7.92 PD on near measurements. After 3 months of occlusion, the deviating angles were 25.9+/-9.10 PD on distant measurements and 21.4+/-11.00 PD on near measurements, corresponding to a significant reduction (p=0.005 and p<0.001, respectively). Fourteen patients (32%) suffering from basic type of intermittent exotropia converted to the pseudodivergence excess type. In patients suffering from the basic type who exhibited no changes in type, 9 patients (20%) exhibited reductions on both near and distant angle measurements. Among the convergence insufficiency type of patients, 18 (69%) converted to basic type and 2 patients (7%) converted to the pseudodivergence excess type. In the 15 patients who did not undergo surgery, the converted types were maintained in 6 patients, though the other 9 patients showed regression to the prepatching types after cessation of patching for 3 months.

Part-time occlusion therapy resulted in the conversion of the basic and convergence insufficiency types to pseudodivergence excess and basic types in more than half of the intermittent exotropes. Future studies on correlation between type conversion and surgical outcome would be necessary.