Association Between Orbital Volume and Body Mass Index.

PURPOSE: Obesity is a major public health concern, and fat comprises a substantial portion of the orbital volume. We aimed to evaluate the relationship between body mass index (BMI) and orbital fat volume, and to assess whether BMI is associated with radiographic proptosis. METHODS: We conducted a cross-sectional study of 99 orbits from patients who underwent orbital CT imaging between January 1 and December 31, 2018. Patients with systemic diseases affecting the orbits were excluded. When applicable, only the healthy orbit was analyzed. Subjects were evenly stratified into normal-weight, overweight, and obese groups by BMI. Using Visage Imaging Software, orbital structure volumes were measured. Orbital fat volume was calculated by subtracting extraocular muscle, globe, and optic nerve volumes from the total orbital volume. Multivariable linear regression, adjusted for age, gender, and race, assessed associations between BMI and orbital measurements. RESULTS: Among individuals with BMI 17 to 25, total orbital volume increased by 1.20 cm3 and orbital fat volume by 1.05 cm3 per unit BMI. For BMI >25, both increased at a flatter slope. Obese patients had nearly double the orbital fat volume of normal-weight patients (10.7 vs. 5.4 cm3, p < 0.001). Radiographic proptosis trended higher in obese patients by 1.7 mm (p = 0.114). Males had larger orbital structures and greater mean proptosis than females. CONCLUSIONS: Total orbital and fat volumes increased with BMI, particularly in the normal-to-overweight range. These findings support the need to update normative proptosis data and suggest weight loss may aid in managing mild symptomatic proptosis.