Transorbital Sonographic Evaluation of Optic Nerve Sheath Diameter in Normal Hong Kong Chinese Adults

Abstract

Objective To establish the range of normal values of optic nerve sheath diameter (ONSD) measured by bedside ocular ultrasonography (USG) in Hong Kong Chinese adults. Design and methods This was a prospective study conducted between May and June 2007 in the Accident and Emergency Department (AED) of Ruttonjee and Tang Shiu Kin Hospital. Subjects without neurological and ophthalmologic complaint were recruited by convenience sampling. The ONSD of both eyes were measured 3 mm behind the globe using a 7.5 MHz linear probe on the closed eyelids of supine subjects. Repeated measurements (n=4) were carried out for every optic nerve to control the variability of this scanning procedure. Range, mean values and standard deviations were calculated. Results One hundred subjects were recruited to the study. The range for ONSD was from 3.7 mm to 4.7 mm with a mean of 4.05 mm and standard deviation (SD) of 0.19 mm. There were no significant differences in ONSD measurement between males and females (p=0.44), between right and left eye (p=0.83) or between volunteer AED staff and recruited patients (p=0.10). The differences among different age groups (p=0.13) and the correlation between age and ONSD with r=0.19 (p=0.05) were not significant. Conclusion Our results suggest that the range of ONSD in normal Hong Kong Chinese adults is between 3.7 mm and 4.7 mm which is similar to the finding in previous literatures. This study also suggests that bedside ocular USG is a convenient and useful tool in measuring ONSD and the application of this technique is acceptable by patients in our locality.