Intra- and interobserver reliability of transorbital sonographic assessment of the optic nerve sheath diameter and optic nerve diameter in healthy adults

Purpose: Transorbital optic nerve sonography (TOS) can measure the optic nerve inclusive the sheath diameter (ONSD) and the optic nerve diameter (OND), which are useful parameters in the diagnosis of several neurological disorders. Data on the reproducibility of TOS are, however, required to use B-mode sonography for clinical purposes. The aim of this study was to assess intra- and interobserver reliability of ultrasound-based evaluations of both OND and ONSD in healthy subjects. Methods: Using a 4-11-MHz linear array transducer, the OND and ONSD of 20 healthy subjects were independently measured by two expert investigators. Results: Depicting the optic nerve and its sheath was possible in all subjects. The intra- and interobserver reliability was high for both ONSD and OND measurements. Intraobserver agreement, analyzed with Cronbach´s Alpha, was higher for ONSD (range: 0.69–0.72) than for OND measurements (range: 0.55–0.65). No differences in interobserver reliability between ONSD and OND measurements were found (p = 0.83 for right and 0.47 for left eye). Conclusions: Transorbital B-mode sonography is a feasible method to assess both ONSD and OND with a high intra- and interobserver reliability. Technical difficulties in differentiating the optic nerve from its sheaths may explain the lower intraobserver agreement for OND than that for ONSD measurements.