Transorbital ultrasound measurement of optic nerve sheath diameter in normal rabbits

Objective: This study aimed to investigate the feasibility and reliability of transorbital ultrasound (TOUS) measurement of optic nerve sheath diameter (ONSD) in healthy rabbits and evaluate the influence of body weight and head circumference on the ONSD biometry. Methods: TOUS was performed to measure the ONSD 3 mm behind the optic disk in 31 adult male New Zealand White rabbits independently by two investigators. The values of the same animal measured by two investigators were compared with paired t test. Relationships between paired samples and the correlations of ONSD with body weight and head circumference were evaluated by Pearson correlation coefficient (r). The intra-observer reliability and agreement between two investigators were evaluated with Cronbach’s Alpha and Bland-Altman analysis, respectively. Results: Sixty-two optic nerves from 31 rabbits were well imaged by two observers. The mean ONSD was 1.17±0.01 mm (95% confidence interval (CI), 1.15-1.19 mm). No significant difference in ONSD was observed between left and right eyes and between two observers. The Pearson’s correlation coefficient between two observers was 0.81 and 0.84 for the right and left eye, respectively. Cronbach’s alpha was high (0.92~0.97). The difference between the values obtained by two investigators was 0.02. ONSD had no relationship with body weight (r=0.01, P=0.98) and head circumstance (r=0.02, P=0.56). Conclusion: ONSD measurement with TOUS is feasible and reliable in rabbits, which provides evidence on diagnosis of disorders affecting ONSD.