Polling 2009.

Study characteristics
Methods	Study design: parallel‐group randomized controlled trial Number randomized (total and per group): 124 participants in total (3 participants refused, 1 failed randomization process, and 1 withdrawn by surgeon), resulting in 60 randomized to bilateral group and 59 randomized to unilateral group  Unit of randomization (individual or eye): individual  Number analyzed (total and per group): 118 participants in total; 60 in bilateral group and 58 randomized to unilateral group  Unit of analysis (individual or eye): individual Exclusions and losses to follow‐up (total and per group): 3 participants refused after randomization, 1 failed randomization process, 1 withdrawn by surgeon, 1 participant in unilateral group lost to follow‐up How were missing data handled?: excluded from analysis Length of follow‐up: 3 months Reported power calculation (Y/N), if yes, sample size and power: assuming normal distributions of postoperative angles, a clinically relevant reduction in reoperation of 30% would correspond with a reduction in standard deviation (SD) of 1.8 degrees. The resulting F statistic would be 1.93 (assuming an SD of 5 degree in both groups on average). Inclusion of 120 participants would give the study 80% power at alpha = 0.05 to detect such an F ratio.
Participants	Country: Germany and the Netherlands Setting: university hospital (23 sites) Baseline characteristics: 1. Bilateral recession N = 62 Age (mean ± SD, range): 5.9 ± 1.3 years Gender: 32 boys and 30 girls 2. Unilateral recession N = 59 Age (mean ± SD, range): 5.6 ± 1.1 years Gender: 28 boys and 31 girls Overall N = 121 Age (mean): 5.8 years Gender: 60 boys and 61 girls Inclusion criteria: children aged 3 to 8 years with a normal psychophysical development and onset of esotropia before age 1 year Exclusion criteria: previous strabismus surgery, an angle of strabismus larger than 24 degrees or smaller than 10 degrees, any binocular vision, more than one line logMAR acuity difference between the two eyes, hypermetropia ≥ 6 diopters or myopia ≥ 3 diopters, up‐ or downshoot in (25 degree) adduction > 8 degree, V‐pattern (esotropia measured in 25 degree up‐ and downgaze) > 8 degree, A‐pattern > 5 degree and manifest vertical strabismus > 4 degree; cases with significant convergence excess with an angle of strabismus at near fixation more than 1.5 times as large as the angle at distance fixation Baseline equivalence: comparable
Interventions	Intervention: bilateral recession (BR) Comparator: unilateral recession‐resection (RR) The total relocation of the two muscles in millimeters for both was calculated as follows: the preoperative latent angle of strabismus at distance (in degrees) divided by 1.6. The preoperative latent angle of strabismus measured the day before surgery at distance fixation was the basis for the distance of relocation of the operated muscles. The study committee, consisting of the participating pediatric ophthalmologists, determined this procedure, including the fixed ratio of 1.6 mm per degree of angle of strabismus and the use of the angle measured the day before surgery. The relocation of the muscles by recession or resection was divided equally over the two muscles in either BR or RR. All ophthalmologists had a minimum of 5 years’ experience with both recessions and resections. To evaluate the inter‐operator differences and its accuracy, photos were taken in approximately every tenth participant during two stages of the operation in either recession or resection: (1) after fitting the sutures through the muscle, and (2) before closing the conjunctiva. A millimeter ruler next to the muscle was photographed with the eye.
Outcomes	Outcomes reported: whether the reduction in the latent angle of strabismus at distance fixation was more predictable with either technique, was the variation of the latent angle at distance fixation, 3 months postoperatively; the variation of the mean reduction in the angle of strabismus, divided by the distance of muscle relocation; the presence of binocular vision after surgery Adverse outcomes: "Dissociated vertical deviation (DVD) was reported in 10 cases. Latent nystagmus (LN) was reported in 26 cases. A combination of DVD and LN was reported in 19 cases." Measurement time points: 3 months Other issues with outcome assessment (e.g. quality control for outcomes, if any): none
Notes	Study period: not reported Publication language: English Trial registration: not found Conflicts of interest: "none" declared  Funding source: The Netherlands Society for Prevention of Blindness, Haags Oogheelkundig Fonds, Stichting Blindenhulp and the Rotterdamse Vereniging Blindenbelangen supported this study

BR: bilateral recession
DVD: dissociated vertical deviation
IE: infantile esotropia
LN: Latent nystagmus
PD: prism diopters
RR: unilateral recession‐resection