Point-of-care ultrasound (POCUS) measurement of the optic nerve sheath diameter (ONSD) has been shown to correlate with increases in intracranial pressure (ICP).
In adults, an ONSD measurement of less than 5 mm is considered normal, while a measurement greater than 6 mm suggests elevated ICP.
How to Measure the Optic Nerve Sheath Diameter:
A small cross-sectional study examined whether ONSD measurements varied when taken at different depths. The findings indicated that ONSD increased by 0.32 mm at a depth of 4 mm and decreased by 0.54 mm at a depth of 2 mm.
These variations highlight the importance of maintaining a consistent measurement depth. To ensure accuracy and avoid misinterpretation, the ONSD should always be measured 3 mm posterior to the retina.
Gottlieb M, Kayarian F, Johnson J, Peksa GD. Differences in mean optic nerve sheath diameter measurements based on depth. Am J Emerg Med. 2024 Aug;82:197-198. doi: 10.1016/j.ajem.2024.06.013.
