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Ocular sonography is a fast, simple, and non-invasive tool to detect elevated intracranial pressure (ICP) by measuring the optic nerve sheath diameter (ONSD). Several studies have shown a positive correlation between increased ONSD (>5.7mm) and elevated ICP (>20mmHg). Although ultrasound may not replace CT or MRI to diagnose the cause of the increased ICP, its use as a triage tool can expedite these tests.
The technique:
- Use linear probe on closed eyelid.
- Identify the optic nerve sheath.
- Measure the optic nerve sheath, 3mm behind globe.
- Rotate probe 90 degrees and measure again.
- Average both diameters.
Please see the references below for more information and, as with any new technique please consult local experts prior to making clinical decisions.
References
http://www.sonoguide.com/smparts_ocular.html
Soldatos, T. et al. Optic nerve sonography in the diagnostic evaluation of adult brain injury. Crit Care. 2008; 12(3): R67. Epub 2008 May 13.