Prevalence and demographic characteristics of strabismus in adults

Background: Strabismus is a common ocular disorder and a major cause of visual impairment and amblyopia. Its prevalence varies widely across populations and may differ by age, ethnicity, and underlying risk factors. Despite its clinical and psychosocial impact, data on strabismus in Iranian adults remain limited. This study aimed to determine the prevalence of strabismus and its associated demographic factors in southeastern Iran. Methods: This cross-sectional analysis used baseline data from an adult eye cohort in Zahedan, southeastern Iran. A stratified cluster sampling design, based on socioeconomic status, was used to recruit residents aged 35–70 years between 2015 and 2019. Of 10 016 screened individuals, 9296 met inclusion criteria, which required Iranian nationality, ?9 months of local residency, and completion of baseline assessments; participants with prior ocular surgery or active ocular disease were excluded. All participants completed a standardized ocular history questionnaire and underwent comprehensive visual assessment, including Snellen visual acuity testing, objective and subjective non-cycloplegic refraction, automated lensometry for habitual correction, external examination, slit-lamp biomicroscopy, and Goldmann applanation tonometry. Ocular alignment was evaluated using cover–uncover and alternate cover tests at distance and near. Strabismus was classified based on manifest deviations detected under best correction. Results: Among 9296 adults, the overall prevalence of strabismus was 2.8% (262 cases; 95% CI: 2.5–3.2). The prevalence of exotropia, esotropia, hypertropia, intermittent exotropia, and intermittent esotropia was 1.3% (129 cases, 95% CI: 0.00–3.20), 0.2% (18 cases, 95% CI: 0.00–2.20), 0.3% (26 cases, 95% CI: 0.00–2.40), 0.8% (77 cases, 95% CI: 0.00–2.70), and 0.1% (12 cases, 95% CI: 0.00–1.80), respectively. Strabismus occurred most frequently in the 45–54-year age group (n = 92, 35.1%) and least often in those aged 65–75 years (n = 14, 8.3%). Women accounted for 61.8% (n = 162) of all cases, with all subtypes more common in women except esotropia, which was equally distributed. Strabismus was most frequent among individuals with high school education (n = 89, 34.0%) and least common in those with university degrees (n = 46, 17.6%). The Sistani ethnic group demonstrated the highest prevalence (n = 141, 53.8%) across all subtypes. Conclusions: Strabismus affected 2.8% of adults, with exotropia the most common subtype. Prevalence varied by age, sex, education, and ethnicity, with the highest burden in adults aged 45–54 years and among the Sistani group. Most cases were previously undiagnosed, underscoring the need for targeted screening and early detection. Ongoing longitudinal follow-up will clarify incidence, progression, and treatment outcomes, supporting improved clinical decision-making, resource allocation, and long-term visual outcomes.