ETS3

The study is being conducted to compare whether an optical correction of bifocal spectacle lenses (BFL) or single-vision spectacle lenses (SVL) is more effective for the treatment of children with esotropia greater at near. Children will be randomized to be treated with BFLs or SVLs for 3 years and be evaluated at regular intervals throughout the study to determine whether their condition has worsened. Children whose condition worsens during the study will either start BFL treatment (if randomized to SVL group) or continue BFL treatment (if randomized to BFL group) for 2 months to allow assessment of outcome in BFLs, and then be released to treatment at investigator discretion while continuing in study follow-up. Children whose condition has not worsened during the study will start or continue BFL (depending on treatment group) for 2 months at 3 years. All children return at 38 months to assess binocular function. The effectiveness and safety of both treatments will be compared.

Inclusion Criteria

1) Age 3 to <9 years 2) Visual acuity in better-seeing eye must be age-appropriate/normal 3) Esodeviation meeting all the following criteria is present in refractive correction (if required or worn): - Constant or intermittent esotropia ≥10∆ PD measurable by SPCT at near - Distance esotropia (constant, intermittent), esophoria, or orthophoria, with near esodeviation 10 PD∆ larger than distance deviation by PACT  - If constant ET at distance, then must be ≤6∆ PD by SPCT  - If intermittent ET or esophoric at distance, can be any magnitude at distance (as long as near esodeviation is 10∆ PD larger than distance deviation by PACT) 

Exclusion Criteria

1) Myopic refractive error of more than -6.00 D SE 2) Previous strabismus surgery (including Botox injection), intraocular surgery (e.g., laser, anti-VEGF injection, or cataract), extraocular surgery (e.g., scleral buckle), or refractive surgery 3) Amblyopia treatment other than refractive correction within prior 3 months 

Study Requirements

Patients will be randomly assigned to treatment with a bifocal (BFL) or single vision lens (SVL) spectacle correction for 3 years. Generally, participants will be followed at 3-month intervals for the first year and every 6 months thereafter until the primary outcome visit at 36 months. At each follow-up visit between 3 months and 36 months, ocular alignment and stereoacuity will be assessed to determine if any of the three study-specified failure criteria have been met (worsening of distance ET, reduction in near stereoacuity, or frequent diplopia (“more than 2 times per day” over the last week). The primary outcome is failure at or before 36 months. If a failure criterion is met between 3 to 30 months, participants randomized to SVLs will be prescribed BFLs and those in BFLs will be prescribed continued BFLs. All participants (i.e., regardless of failure status) will return for a 38-month Secondary Outcome Visit to assess binocular function.