Optic Nerve Sheath Diameter (ONSD) Ultrasound

Another promising non-invasive method is optic nerve sheath diameter (ONSD) ultrasound. The optic nerve sheath is a continuation of the dura mater, and its diameter increases in response to elevated ICP due to the transmission of pressure from the intracranial compartment to the optic nerve. ONSD ultrasound measures the diameter of the optic nerve sheath approximately 3 mm posterior to the globe of the eye, and studies have shown a good correlation between increased ONSD and elevated ICP. In the anesthesia setting, ONSD ultrasound can be used both preoperatively and intraoperatively to assess the risk of elevated ICP. For example, in patients with known or suspected intracranial pathology, ONSD can be a useful screening tool to determine whether further invasive monitoring or interventions are required. Additionally, ONSD can provide a non-invasive, repeatable measure to track changes in ICP during surgery. A key advantage of ONSD ultrasound is its portability and ease of use. It can be performed at the bedside or in the operating room and does not require specialized equipment beyond a standard ultrasound machine. However, as with TCD, ONSD ultrasound is operator-dependent, and variations in technique can affect measurement accuracy. Moreover, while ONSD ultrasound is useful for detecting elevated ICP, it does not provide continuous monitoring, limiting its role in dynamic perioperative decision-making.