Developmental Change of the Biorbital Angle in Normal Japanese Children
Yoshimi Yokoyama, MD; Teiji Yagasaki, MD; Makiko Tsukui, MD
Department of Ophthalmology, Japan Community Health Care Organization Chukyo Hospital
Introduction: To investigate changes in the biorbital angle with increasing age in normal Japanese children.
Methods: Axial magnetic resonance imaging or computed tomography of the orbit in the transverse plane of the horizontal extraocular muscles was obtained in 129 ophthalmologically healthy children (aged a few months to 11 years: mean age ± SD = 5.14 ± 2.65 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 children older than one year (p<0.01, Newman-Keuls test).
Discussion: The morphology of the orbit is known to gradually change from wider to narrower as gestation progresses. Current results suggest that the orbital change continues to be normal within a year after birth, with exotropia in 70-80% of newborns gradually disappearing in most cases by 2-4 months of age.
Conclusion: The biorbital angle in infants less than a year old was larger than that found in children older than one year, with this larger biorbital angle potentially the causative factor of exodeviation in newborns.
References: Tsukitome H, Hatsukawa Y, Morimitsu T, et al. Changes in angle of optic nerve and angle of ocular orbit with increasing age in Japanese children. Br J Ophthalmol. 2015 Feb;99(2):263-6.