Abstract Objective To explore the normal value of inner canthal index in children and the diagnositic value of inner canthal index measurements in children with mental retardation. Methods Head circumference and width of the inner and external canthus were measured in 360 normal children aged 0～12, years and in 52 children with mental retadation aged from 6 months to 6 years. Two indices were studied: Index Ⅰ=the ratio of the inner canthus to the external canthus and Index Ⅱ=the ratio of the inner canthus to head circumference. Results In the normal children Index Ⅰ was 0.34 ± 0.03 and Index Ⅱ was 0.068 ± 0.008 . In children with Trisomy 21, Index Ⅰ was 0.51 ± 0.02 and Index Ⅱ was 0.091 ± 0.004 (P< 0.01 vs. control). In infants with cretinism, Index Ⅰ was 0.48 ± 0.04 (P< 0.01 vs. control) and Index Ⅱ was 0.096 ± 0.007 (P< 0.05 vs. control). Children with brain dysplasia had an Index Ⅰ of 0.51 ± 0.07 (P< 0.05 vs. control); and they had an index Ⅱ of 0.089 ± 0.008 . There was no significant difference vs control (P> 0.05 ). No significant differences in Index Ⅰ ( 0.38 ± 0.06 ) or Index Ⅱ ( 0.064 ± 0.004 ) were noted in infants with intracranial hemorrhage. (P> 0.05 ) Conclusions Index Ⅰ and Index Ⅱ can reflect the width of the inner canthus and they are not influenced by age. Index Ⅰ may have a more important value than Index Ⅱ in the clinical application.
