Epidemiologic Factors and Ocular Manifestations of Twin Children Compared with Controls

Abstract Purpose: To compare the epidemiological and ocular findings of twin children with non- twin age matched individuals as their control.Methods: In this cross sectional study, a total of 92 twins (184 cases) were compared with 182 non- twin matched children. The comprehensive ophthalmic examinations including measurement of the best corrected visual acuity (BCVA), cycloplegic refraction, ocular deviation, strabismus as well as the anterior and posterior ophthalmic examinations were conducted. An organized questionnaire was also filled out for both groups to record their demographic information. Monozygotic twins were considered if there were similarity of their phenotypic characteristics and gender, otherwise the twins were considered as dizygotic. The mirror- image twins (MIT) was defined based on the laterality of symmetrical ocular characteristics of twins.Results: In this study, the mean age of the study subjects was 7.08±4.68 and 7.56±4.02 years in the twins and non-twins groups, respectively. Among the twins 27 (30%) were monozygotic. Refractive form of MIT was seen in 5 twins (5%). BCVA in the twins group (0.07±0.16LogMAR) was significantly worse than non-twins (0.03±0.08LogMAR, P<0.001) and higher percentage of them were amblyopic (21.8% versus 10.5%, P=0.005). Twin and controls had history of strabismus surgery in 7.8% and 3.3%, respectively (P=0.009). Multivariate analysis showed significant correlation among low gestational age and female gender, low birth weight and seizure. Conclusion: Female sex, less gestational age, low birth weight, amblyopia and strabismus were significantly higher in twins. Therefore, it is important to check their refractive error, anisometropia, MIT phenomenon and amblyopia to prevent their further complications.