Correlation between Interpupillary and Inner-Outer Intercanthal Distances in Individuals Younger than 20

Purpose: To determine the correlation between interpupillary distance (IPD) and innerouterintercanthal distance (IOICD) and to find a regression equation for calculating IPDbased on IOICD measurements.Methods: The study subjects were randomly selected from individuals aged 3 monthsto 20 years who were referred to our ophthalmology clinic, health care centers and childrenattending kindergartens. Participants were divided into 4 age categories: .3, 3-5,5-12.5 and 12.5-20 years. IPD was measured by a PD meter (PD2, Oculus, Germany);other parameters including IOICD, nasal limbus to temporal limbus (NLTL), innerintercanthal distance (IICD) and outer intercanthal distance (OICD) were measuredusing a translucent plastic ruler.Results: The study included 254 female (60.6%) and 165 male (39.4%) subjects withmean age of 87.7 }73.2 (range 3-240) months. Significant correlation was observedbetween IOICD and IPD in the 3-5 yr and 12.5-20 yr age groups. In the .3 and 5-12.5year age groups, NLTL had the best correlation with IPD. The regression equationsfor calculating IPD according to IOICD were as follows. In male subjects, nearIPD= 0.941×IOICD (r2= 0.98, P 0.001) and for female subjects, near IPD= 0.948 ×IOICD(r^2= 0.98, P 0.001).Conclusion: IPD and IOICD measurements are strongly and positively correlated;IOICD measurements are simpler to obtain and may be used to calculate IPD readingswhich are more difficult to measure by usual methods in children.