Hospital-Based Reference Values for Hertel Exophthalmometry in Nepal

Population-specific reference values for Hertel exophthalmometry are limited in South Asian populations, including Nepal. This limits clinical interpretation of ocular protrusion in routine practice. This study aimed to establish hospital-based reference values for exophthalmometry, evaluate intra-session measurement repeatability, and examine demographic and anthropometric associations.

Participants aged 6-85 years attending the outpatient department were enrolled using systematic sampling, with every fifth eligible attendee selected. Because recruitment was conducted within a tertiary eye hospital rather than through population-based sampling, the study was designed to provide hospital-based reference data rather than nationally representative estimates. Hertel exophthalmometry was performed by a single examiner with three repeated measurements per eye. Intra-session repeatability was assessed using intraclass correlation coefficient (ICC) and coefficient of variation. Group comparisons were performed using non-parametric tests, and multivariable linear regression identified independent correlates of right eye exophthalmometry value (EV).

This study provides the first hospital-based reference data for exophthalmometry in a Nepali clinical population with excellent intra-session repeatability. Provisional upper reference limits are 17.42 mm (95^th percentile) and 18.31 mm (mean plus 2SD). Inter-eye difference (IED) values exceeding 1.50 mm were uncommon in this sample (one participant, 0.2%). These findings are descriptive only; diagnostic thresholds for clinically significant asymmetry cannot be established from this study and require population-based investigations. Hertel base value (BV), age, ethnolinguistic ancestry, and geographical region were the independent associated with EV.

This study provides hospital-based reference values for Hertel exophthalmometry in a Nepali population. Mean EV was approximately 13.5 mm, with a 95^th percentile upper limit of 17.42 mm. Measurement repeatability was excellent. EV was independently associated with age, Hertel base value, and demographic grouping variables, although clinical interpretation should consider the methodological limitations of hospital-based sampling. These findings may assist clinicians in interpreting exophthalmometry in Nepal; however, population-based studies are needed to establish definitive normative ranges.