Developmental change of the biorbital angle in normal Japanese infants.

Abstract

PurposeTo investigate postnatal changes in the biorbital angle in normal Japanese children.Subjects and methodsAxial imaging of the orbit in the transverse plane of the horizontal extraocular muscles was obtained in 129 ophthalmologically healthy infants (age ranging from a few months to 11 years). The opening angle between both lateral walls of the orbit was defined as the biorbital angle.ResultsThe mean biorbital angle in 11 infants less than a year of age was 105.0°±6.0°. The mean biorbital angles for each of the subsequent age groups were 97.7°±3.1°, 96.2°±4.0°, 96.3°±4.1°, 92.8°±3.8°, 92.3°±2.3°, 93.1°±2.8°, 91.5°±3.9°, 91.9°±2.3°, 91.4°±2.3°, and 90.9°±3.1°. The mean biorbital angle in infants less than a year old was significantly larger than those found in the groups of infants older than 1 year (P<0.01, Newman–Keuls test).ConclusionThe biorbital angle in infants less than a year old was larger than that found in infants older than 1 year, with this larger biorbital angle potentially the causative factor of the observed exotropia seen in 70%–80% of newborns gradually disappearing in most cases by 2–4 months of age.