Normative interpupillary and canthal measurements in the Nepalese population: a hospital-based study

BACKGROUND: Interpupillary distance (IPD), inner canthal distance (ICD), outer canthal distance (OCD), and canthal index (CI) are essential craniofacial anthropometric parameters influenced by age, gender, ethnicity, genetics, and environmental factors. These measurements are important in various clinical disciplines, including optometry, ophthalmology, genetics, and reconstructive surgery. This study aimed to establish normative values for these parameters in the Nepalese population and to explore their interrelationships. METHODS: A cross-sectional study was conducted among 1,000 Nepalese aged 18–64, enrolled using consecutive purposive sampling. IPD was measured using a corneal reflex pupillometer, while ICD and OCD were measured using a digital Vernier calliper. CI was calculated as (ICD/OCD) × 100. Analyses included independent t-tests, one-way ANOVA, Pearson correlation, and multiple linear regression. RESULTS: The mean IPD was 62.7 ± 4.3 mm at distance and 58.5 ± 4.3 mm at near, while the mean ICD, OCD, and CI were 32.2 ± 2.7 mm, 87.8 ± 4.4 mm, and 36.66 ± 2.4%, respectively. IPD, ICD, and OCD varied significantly by gender (p < 0.05, d = 0.37–0.74), while CI showed no significant gender difference (p = 0.185, d = -0.09). Ethnic variations were significant for all parameters (p < 0.05, η² = 0.02–0.06), except for OCD (p = 0.315, η² = 0.01). IPD was strongly correlated with canthal distances (r = 0.64–0.76, p < 0.001). Regression equations for IPD were generated based on canthal distances across gender. CONCLUSIONS: This study provides normative values for IPD, ICD, OCD, and CI in the Nepalese population, highlighting significant variations by gender and ethnicity. Canthal distances were strongly correlated with IPD, suggesting their potential utility as alternative predictors for IPD estimation in clinical practice. However, the hospital-based, single-centre design may limit the population representativeness of the findings. Nevertheless, these values can still guide in planning for reconstructive surgery, general ophthalmic dispensing, and the fabrication of custom-made ocular prostheses.