The use of an ultrasound-based evaluation of the optic nerve sheath diameter (ONSD) has previously been demonstrated for detecting raised intracranial pressure. In order to be feasible in clinical workup, the test qualities of transorbital ultrasonography need to be determined. The aim of this study was therefore to establish normal values and to assess the intra- and interobserver reliability of this method.
Using a 9-3 MHz linear array transducer, the ONSD of 40 healthy subjects was independently measured by 2 investigators.
Depicting the optic nerve and its sheath was possible in all individuals. The mean ONSD was 5.4 ± .6 mm with a range of 4.3-7.6 mm. The intraobserver reliability analyzed with Cronbach's Alpha was found to be high with values between .92 and .97. Pearson's correlation coefficient between the 2 investigators was .81 on the right side and .84 on the left. There was no correlation between ONSD and age, body mass index, or gender.
Transorbital B-mode sonography is a feasible method to assess the ONSD with a high intra- and interobsever reliability. Normal values on ONSD are presented in this study that will be useful in future studies on pathological conditions.