Abnormal biorbital angle in children with infantile exotropia

Purpose The causative factors of infantile exotropia are unknown. The purpose of this study was to investigate the relationships between the biorbital angle and the pathogenesis of infantile exotropia. Study design Retrospective. Methods Of all patients diagnosed as infantile exotropia with onset prior to 12 months of age between 2010 and 2017, 31 patients without any neurological disorders or developmental delay were identified. The angle between both lateral walls of the orbit, defined as the biorbital angle, was measured in the horizontal plane at the optic nerve and where the horizontal extraocular muscles appeared on axial magnetic resonance imaging (MRI) or computed tomography (CT) of the orbit. These patients' data were compared with those of 129 ophthalmologically normal children. All subjects of this study were Japanese. Results The mean biorbital angle was significantly larger in patients with infantile exotropia than in the normal children (106.6 +/- 5.7 degrees vs 94.2 +/- 5.1 degrees, p < 0.001). Of the patients with infantile exotropia, 21 (68%) had an angle outside the 95% confidence interval calculated in normal children. All cases were divided into a constant (15 cases) and intermittent (16 cases) group; there was no significant difference between them in the mean biorbital angles (107.9 +/- 5.6 degrees vs 105.4 +/- 5.8 degrees, p = 0.224). No correlations were identified between the biorbital angle and the angle of exodeviation, either distant or near. Conclusions Children with infantile exotropia have a larger biorbital angle. This anatomical abnormality may be an associate factor of infantile exotropia.