Optic Nerve Sheath Diameter: Which Axis Should Be Measured?

Background and purpose

Optic nerve sheath diameter (ONSD) measured by point-of-care ultrasound (POCUS) is a commonly used non-invasive estimate of intracranial pressure (ICP). However, methodological variations limit standardization of this promising technique. Different imaging axes are identified as one such source of ONSD POCUS methodological variation. This study aimed to evaluate the agreement and diagnostic accuracy for elevated ICP between transverse and sagittal ONSD measurements.

Methods

We conducted a post-hoc analysis of 213 intensive care patients from three prior studies. ONSD was measured in both transverse and sagittal planes, externally (ONSDext) and internally (ONSDint) of the dura mater. Agreement was assessed using Lin's concordance correlation coefficient (CCC). Diagnostic accuracy for detecting ICP ≥20 mmHg was evaluated using area under the receiver operator characteristics curve (AUROC) analyses in a subset of 139 patients.

Results

Sagittal ONSD was significantly larger than transverse ONSD (median difference 0.2 mm, p<0.001). Agreement between transverse and sagittal ONSD was poor (CCC: 0.65 and 0.70 for right and left side ONSDext, and 0.43 and 0.51 for right and left side ONSDint). No significant differences in AUROC were found between transverse, sagittal, or averaged measurements.

Conclusions

Transverse and sagittal ONSD measurements are not interchangeable due to significant differences and poor agreement. Diagnostic accuracy was similar across methods. These findings support continued use of transverse measurement as the standard approach for ONSD POCUS in clinical practice.