Inter-eye Differences in Ocular Biometric Parameters of Concomitant Exotropia

Purpose: To evaluate the ocular biometric parameters in patients with constant and intermittent exotropia by the measurement of swept-source optical coherence tomography (SS-OCT) optical biometer OA-2000 and comparing it with the normal control subjects.Design: Cross-sectional case-control study.Participants: Fifty-five constant and 24 intermittent patients with exotropia with central fixation and 77 orthotropic normal control participants aged 4-18 years old.Methods: Non-contact and high-resolution optical biometric OA-2000 measurements were conducted under uniform ambient light conditions. The statistical analysis included intraclass correlation coefficient (ICC), Bland-Altman plot, and independent t-tests.Main Outcome Measures: Spherical equivalent (SE), ocular biological parameters such as pupil diameter (PD), anterior chamber depth (ACD), lens thickness (LT), and axial lengths (AL). The absolute values of inter-eye differences for SE, PD, ACD, LT, and AL were recorded as AnisoSE, AnisoPD, AnisoACD, AnisoLT, and AnisoAL, respectively.Results: AnisoSE (0.878 vs. 0.577, P = 0.019), AnisoAL (0.395 vs. 0.208, P = 0.001), AnisoACD (0.060 vs. 0.032, P < 0.001), AnisoLT (0.060 vs. 0.031, P = 0.002), and AnisoPD (0.557 vs. 0.340, P = 0.002) were significantly larger in concomitant patients with exotropia. The SE, AL, ACD, LT, and PD showed excellent binocular correlation with ICC values that ranged from 0.943 to 0.987 in control participants and from 0.767 to 0.955 in concomitant exotropia patients. Bland-Altman plots showed the wider range of agreement in patients with concomitant exotropia than the control participants (SE: 5.0288 vs. 3.3258; AL: 2.2146 vs. 1.3172; ACD:0.3243 vs. 0.1682; PD: 2.4691 vs. 1.9241; and LT:0.3723 vs 0.1858).Conclusion: Patients with concomitant exotropia showed larger inter-eye differences in SE, ACD, LT, PD, and AL. Advice should be given to suspicious children to avoid or delay the development of concomitant exotropia.