Ultrasound assessment of optic nerve sheath diameter in healthy volunteers.

BACKGROUND: Ultrasound assessment of optic nerve sheath diameter (ONSD) has been suggested as a non-invasive measure of intracranial pressure. Numerous small studies suggest its validity; however, discrepancy exists around normal values for ONSD. In this study we sought to define a normal value range for ONSD in a population of healthy adult volunteers. METHODS: ONSD was measured in healthy adult volunteers and a normal range was defined using descriptive statistics. A regression analysis was used to determine relationship between ONSD measurements and sex, age, height and weight. RESULTS: One hundred twenty adults were recruited (age 18-65 [mean 29.3]) with 55 male and 65 female subjects. Mean ONSD was 3.68 mm (95% confidence interval [CI], 2.85-4.40). Upon regression analysis, mean ONSD did not vary with age, weight, or height but did vary with sex. Mean ONSD measurements for men were 3.78 mm (95% CI, 3.23-4.48) compared with 3.60 mm (95% CI, 2.83-4.11) for women. CONCLUSION: This study has defined the range of ONSD in a healthy cohort of volunteers. The lack of relationship to age, weight and height is similar to other studies but this is the first study to find a difference depending on sex suggesting the possible need for separate reference ranges for men and women.