Comparison of epidemiologic factors and eye manifestations of twin children with controls.

Purpose: The present study was aimed to compare the epidemiological and ocular findings of twin children in comparison with non- twin age matched individuals as their control.

Methods: In this cross sectional study, a total of 90 twins (180 cases) were compared with 182 non- twin matched children. All the study participants were examined by a comprehensive ophthalmic examination including measurement of the best corrected visual acuity (BCVA), cycloplegic refraction, ocular deviation, strabismus as well as the anterior and posterior ophthalmic examinations. Demographic information of children were collected by using an organized questionnaire. Monozygotic twins were considered if there were similarity of their phenotypic characteristics and gender, otherwise the twins were considered as dizygotic.

Results: The mirror- image twins (MIT) was defined according to the laterality of symmetrical ocular characteristics of twins. In this study, the mean age of the study participants was 7.08±4.42 and 7.58±3.99 years in twins and non-twins groups, respectively (P=0.253). Among the twins, 27 (30%) were monozygotic. Refractive form of MIT was seen in 5 twins (2.8%). The spherical refractive error was more hyperopic in twins compared to non- twins (P=0.041). BCVA in the twin 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 (37.2% versus 10.4%, P=0.005). Twin and controls had strabismus in 17.2% and 1.6%, respectively (P < 0.001). Regarding the comparison between mono- and dizygotic twins, more significant percentage of monozygotic twins had amblyopia (P=0.004) and strabismus (P=0.047). 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, amblyopia and strabismus to prevent their further complications.