Application and repeatability of ocular biometric measures for gaze position calibration in children

The purpose of this study was to investigate the utility of two ocular biometric measurements to obtain Hirschberg ratios (HRs) in a binocularly normal paediatric population, and to assess the repeatability of this approach.

Ocular biometry data from 80 participants (aged 5 to 14 years) was obtained using the KM-1 LED manual keratometer and the Tomey Biometer AL-100 A-scan. HRs were calculated from corneal curvature and anterior chamber depth measurements in the horizontal and vertical meridians of each eye using a regression equation based on a geometric optics model. To assess intrasubject variability in the HRs obtained from biometry, measurements were repeated approximately 1 h later.

At the initial measurement, mean (SD, range) HRs were 10.77 (0.79, 9.14-12.73) and 11.02 (0.82, 9.48-13.32) °/mm for the horizontal and vertical meridians, respectively. There was a significant difference between the horizontal and vertical HRs (p < 0.0001). Mean intrasubject variability of HR was 0.06 °/mm (95% Limit of Agreement [LOA]: -0.82 to 0.94 °/mm), and 0.05 °/mm (95% LOA: -1.05 to 1.15 °/mm) for the horizontal and vertical meridians, respectively.

The results indicated that HRs obtained through ocular biometry in a binocularly normal paediatric population are consistent with previous studies in both strabismic children and adult cohorts. The HRs obtained with this technique were highly repeatable in this study population. This approach to gaze position calibration could be used in lieu of other empirical techniques in children.