Trial of Overminus Spectacle Therapy for Intermittent Exotropia

The main objectives of this randomized trial comparing overminus lens treatment to non-overminus (spectacles without overminus or spectacles with plano lenses) are to determine: * The long-term on-treatment effect of overminus treatment on distance intermittent exotropia (IXT) control score. * The off-treatment effect of overminus treatment on distance IXT control score (following weaning and 3 months off treatment).

Inclusion Criteria: * Age 3 years to \< 11 years * Intermittent exotropia (manifest deviation) meeting all of the following criteria: * At distance: intermittent exotropia or constant exotropia o Mean distance control score of 2 points or more (mean of 3 assessments over the exam) * At near: intermittent exotropia, exophoria, or orthophoria o Subject cannot have a score of 5 points on all 3 near assessments of control * Exodeviation at least 15∆ at distance measured by PACT * Near deviation does not exceed distance deviation by more than 10∆ by PACT (convergence insufficiency type IXT excluded) * Distance visual acuity (any optotype method) in each eye of 0.4 logMAR (20/50) or better if age 3 years and 0.3 logMAR (20/40) or better if 4 years or older. * Interocular difference of distance visual acuity ≤0.2 logMAR (2 lines on a logMAR chart) * Refractive error between -6.00 diopters (D) standard error (SE) and +1.00D SE (inclusive) in the most myopic / least hyperopic eye based on a cycloplegic refraction performed within the past 2 months or at the end of the enrollment exam. * If refractive error (based on cycloplegic refraction performed within past 2 months or at the end of the enrollment exam) meets any of the following criteria, then pre-study spectacles are required and must have been worn for at least 1 week prior to enrollment: * SE anisometropia ≥1.00D * Astigmatism ≥1.50D in either eye * SE myopia ≥-1.00D in either eye Pre-study refractive correction, if worn, must meet the following criteria relative to the cycloplegic refraction performed within past 2 months or at the end of the enrollment exam: * SE anisometropia must be corrected within \