To determine the clinical characteristics of strabismus and the clinical course after treatment, such as surgery or glasses, in siblings with strabismus.

Siblings diagnosed with strabismus were investigated according to sex, age and type of strabismus. The initial angle of deviation and the change of angle after treatments in the same type were evaluated and analyzed. The analysis showed that therapeutic results corresponded in cases of siblings at the last visit.

Fifteen out of 58 sibling couples (average age: 6.2 years old) were enrolled in this study on the same initial visit date. In the cases where sibling couples had their initial examination on different dates, siblings were on average 5.3 and 6.4 years old, irrespectively ( p <0.05). Fifty-one out of 58 sibling couples had the same type of strabismus. The deviated angles in 19 sibling couples before treatment were statistically different ( p <0.05). There was no statistical difference in the deviated angle in siblings between 3 months and 2 years of age ( p >0.05). The concordance of the final result after treatment was 68.4%, and was statistically significant.

There were many cases in which siblings demonstrated the same type of strabismus. In these cases, the clinical courses and final results were similar. Therefore, if one sibling was treated, the other sibling's course and result after treatment could be predicted accurately.