Variability of angle of deviation measurements in children with intermittent exotropia

BackgroundA change in the angle of deviation is often used to monitor the change in severity of intermittent exotropia over time; nevertheless, thresholds for a clinically significant change in angle have not been determined. We analyzed variability associated with test–retest differences and short-term variability in the condition, to provide thresholds for assessing clinically significant, long-term change in angle of intermittent exotropia.MethodsTwenty-six children with intermittent exotropia (median age, 7; range, 1-13 years) underwent repeat prism and alternate cover test measures during 3 or 4 examinations (2 hours apart) over the course of a day; 95% repeatability coefficients were derived to determine test–retest differences at distance and near fixation.ResultsDerived 95% repeatability coefficients at distance were 3.4Δ (95% CI, 0.7Δ-6.2Δ) for angles ≤20Δ and 7.2Δ (95% CI, 4.4Δ-9.9Δ) for angles >20Δ; at near, 6.6Δ (95% CI, 3.7Δ-9.6Δ) for angles ≤20Δ and 12.8Δ (95% CI, 5.3Δ-20.3Δ) for angles >20Δ.ConclusionsTest–retest reliability data in this study provide thresholds to help determine clinically significant change in angle of strabismus in children with intermittent exotropia. These data should facilitate evidence-based assessment of long-term change in intermittent exotropia over time.