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Optic Nerve Sheath Diameter: Which Axis Should Be Measured?
Jakob Pansell1,2, Tina Thomsson1,2, Emelie Eng1,2
1The Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden.
Summary
Transverse and sagittal optic nerve sheath diameter (ONSD) measurements are not interchangeable for estimating intracranial pressure (ICP). While diagnostic accuracy was similar, transverse ONSD remains the standard for point-of-care ultrasound (POCUS).
Area of Science:
- Neurocritical care
- Point-of-care ultrasound (POCUS)
- Intracranial pressure (ICP) monitoring
Background:
- Optic nerve sheath diameter (ONSD) measured by POCUS is a non-invasive ICP estimate.
- Methodological variations, including imaging axes, limit standardization.
- Transverse and sagittal ONSD measurements represent key variations.
Purpose of the Study:
- To evaluate agreement and diagnostic accuracy for elevated ICP between transverse and sagittal ONSD measurements.
- To determine if transverse and sagittal ONSD measurements are interchangeable.
- To inform standardization of ONSD POCUS techniques.
Main Methods:
- Post-hoc analysis of 213 intensive care patients from three prior studies.
- ONSD measured in transverse and sagittal planes (externally and internally of dura mater).
- Agreement assessed using Lin's concordance correlation coefficient (CCC); diagnostic accuracy evaluated using AUROC for ICP ≥20 mmHg in 139 patients.
Main Results:
- Sagittal ONSD was significantly larger than transverse ONSD (median difference 0.2 mm).
- Poor agreement was found between transverse and sagittal ONSD measurements (CCC range: 0.43–0.70).
- No significant differences in diagnostic accuracy (AUROC) were observed between methods.
Conclusions:
- Transverse and sagittal ONSD measurements are not interchangeable due to significant differences and poor agreement.
- Diagnostic accuracy for elevated ICP was similar across both measurement planes.
- Transverse ONSD measurement is supported as the standard clinical practice for ONSD POCUS.
