• Children under the care of a pediatric optometrist or pediatric ophthalmologist will be eligible for the study if they meet all the following criteria:

• Age 3 to \< 9 years

• IXT meeting all of the following criteria:

‣ Intermittent or constant XT at distance (mean distance control 2.0 or more) with at least 1 control measure of 3, 4 or 5 (i.e., indicating spontaneous tropia)

⁃ Either IXT, exophoria, or orthophoria at near (cannot have control score of 5 on all 3 near assessments)

⁃ Distance exodeviation between 15∆ and 50∆ by PACT

⁃ Near exodeviation between 0∆ and 50∆ by PACT

⁃ Near exodeviation does not exceed distance by more than 10∆ by PACT (convergence insufficiency-type IXT excluded)

• Age-normal visual acuity in both eyes:

‣ 3 years: 20/50 or better (\>=63 letters)

• Interocular difference in distance VA of 2 logMAR lines or less (10 letters or less on E-ETDRS for patients ≥7 years old). Testing by ATS HOTV for participants 3 to \< 7 years old and by E-ETDRS for participants ≥7 years old.

• Cycloplegic refraction within the last 7 months.

• Refractive error between -6.00 D SE and +2.00 D SE (inclusive) based on a cycloplegic refraction within 7 months

• Participants with refractive error meeting any of the following based on a cycloplegic refraction within 6 months must be wearing spectacles for at least 2 weeks:

‣ Myopia \> -0.50 D spherical equivalent (SE) in either eye

⁃ Anisometropia \> 1.00 D SE

⁃ Astigmatism in either eye \> 1.00 D

• Any refractive correction worn at enrollment (required or not) must meet the following guidelines based on a cycloplegic refraction within 7 months:

‣ Anisometropia SE must be within 0.50 D of the full anisometropic difference correction

⁃ Astigmatism must be corrected within 0.50 D

⁃ Axis must be within ±10 degrees if cylinder power is ≤1.00 D and within ±5 degrees if cylinder power is \>1.00 D.

⁃ For hyperopia, the spherical component can be reduced at investigator discretion provided the reduction is symmetrical and does not meet the definition of deliberate overminus (see below).

⁃ For myopia, the intent is to fully correct, but the spherical component can be undercorrected at investigator discretion provided the reduction is symmetrical and results in no more than -0.50 D SE residual (i.e., uncorrected) myopia. Deliberate overminus is not allowed.

⁃ Deliberate overminus is defined for this protocol as any refractive correction prescribed to yield lenses that are overminused by more than -0.50D SE than cycloplegic refraction SE

∙ Less than the full cycloplegic hyperopic correction (i.e., prescribing reduced plus) is not considered the same as overminusing for this protocol (because most patients without IXT but with hyperopic SE refractions up to +2.00 D SE would not typically be prescribed a refractive correction.)

⁃ For refractive errors with an emmetropic or myopic SE, the intent is to fully correct, but the spherical component can be undercorrected at investigator discretion provided the reduction is symmetrical and results in no more than -0.50 D SE residual (i.e., uncorrected) myopia. Prescribing a correction that yields more than 0.50 D more minus SE than the cycloplegic refraction SE is considered deliberate overminus and is not allowed.

⁃ Note that the refractive correction guidelines and the requirement to wear refractive correction for at least 2 weeks apply not only to participants who require refractive correction under the above criteria but also to any other participant who is wearing refractive correction.

• Gestational age \> 30 weeks

⁃ Birth weight \> 1500 grams

⁃ Patient and/or parent understands protocol, is willing to enroll, and is willing to accept that other (i.e., nonrandomized) treatment for IXT will not be offered by the investigator for 3 months

⁃ Parent has phone and is willing to be contacted by Jaeb Center staff

⁃ Relocation outside of area of an active PEDIG site within 3 months not anticipated