Clinical features and frequency of microtropia identified in preschool screenings

PURPOSE: The purpose of this study was to determine the prevalence and clinical characteristics of microtropia (M) within a Turkish preschool screening cohort and to identify objective, data-driven diagnostic thresholds for the condition.
METHODS: This retrospective study reviewed the comprehensive refraction and orthoptic examination records of 2106 children (median age 61 months) who underwent preschool eye screenings at a single tertiary hospital between January 2023 and September 2025. Key variables included cycloplegic spherical equivalent (SE), visual acuity (VA), amount of deviation, near stereopsis (Frisby test), and accommodative response (dynamic retinoscopy). Statistical analysis, including receiver operating characteristic (ROC) curves, was used to compare strabismic and non-strabismic groups and define diagnostic cutoffs for M.
RESULTS: Strabismus was detected in 307 children (14.6% of the cohort). The prevalence of M was 1.6% (34 children) within the total sample, accounting for 11.0% of all strabismus cases. The strabismus group had significantly higher SE values (p<0.001), a greater prevalence of astigmatism (32.5% vs. 24.9%, p=0.048), and a significantly higher rate of weak accommodation (22.1% vs. 1.7%, p<0.001) compared to the non-strabismic group. The M group exhibited significantly lower VA and poorer stereopsis than the esophoria group (p=0.046 and p=0.012, respectively). ROC analysis identified an optimal deviation cutoff for diagnosing M at ≤8 prism diopters (PD) (100% sensitivity, 70.1% specificity) and a stereopsis cutoff of >75 seconds of arc (88.2% sensitivity).
CONCLUSION: In this tertiary clinic cohort, M was found in 1.6% of preschool children, suggesting it is a significant and potentially underestimated health burden. It is strongly associated with refractive errors (hyperopia and astigmatism), impaired accommodation, and reduced stereopsis. The ROC-defined threshold of ≤8 PD offers a robust, objective criterion for its diagnosis.

Keywords: Microtropia, Preschool, Screening, Stereopsis, Strabismus