Developmental change of the biorbital angle in normal Japanese infants

Abstract

Purpose

To investigate postnatal changes in the biorbital angle in normal Japanese children.

Subjects and methods

Axial 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.

Results

The 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).

Conclusion

The 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.

Keywords:

• orbit
• computed tomography
• magnetic resonance imaging
• exotropia
• infant

Acknowledgments

The authors would like to thank Dr Mariko Maeda for her useful discussions and advices. The abstract of this paper was presented at the 44th annual meeting of the American Association for Pediatric Ophthalmology and Strabismus held at Washington DC/USA; March 18–22; as a poster with interim findings. The abstract was published in e Journal of the American Association for Pediatric Ophthalmology and Strabismus in August 2018;22(4):e84.

Author contributions

All authors contributed toward data analysis, drafting and revising the paper and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.