OBJECTIVE: To develop a reference range for ultrasonographically measured optic nerve sheath diameter (ONSD-US) in dogs. We hypothesized that ONSD-US can be measured reliably and is associated with weight but not age, sex, or body condition score (BCS), and that the relationship between weight and ONSD-US in dogs is allometric due to canine size variations.
DESIGN: Prospective, observational study.
SETTING: University teaching hospital.
ANIMALS: Seventy-eight healthy adult dogs.
INTERVENTIONS: The ONSD was measured by a standardized transpalpebral approach.
MEASUREMENTS AND MAIN RESULTS: Regression analysis showed the relationship between weight and ONSD was better fit with a linear model (R = 0.8510) than an allometric model (R = 0.7917). Multiple regression analysis showed ONSD is associated with weight (P < 0.0001), age (P = 0.0021), and BCS (P = 0.0007), but not with sex. Dominance analysis showed 94.6% of the variance explained by the model was due to weight. Intraclass correlation coefficient (ICC) analysis showed excellent interobserver (ICC = 0.9338-0.9608) and intraobserver (ICC = 0.9893) reliability.
CONCLUSIONS: These results suggest that ONSD-US may be reliably measured in dogs using our described transpalpebral approach, and we have calculated prediction intervals based on body weight. Future studies are needed to determine if ONSD-US measurements are associated with intracranial hypertension as shown in human medicine.