ONSD
Also written as: ONSD — Optic Nerve Sheath Diameter
Optic nerve sheath diameter measurement used as a non-invasive indicator of elevated intracranial pressure.
Full Definition
Optic nerve sheath diameter (ONSD) measurement via ultrasound or CT imaging provides a non-invasive method for assessing intracranial pressure in neurocritical care patients. The optic nerve is surrounded by cerebrospinal fluid within the subarachnoid space, and increases in intracranial pressure cause distension of this sheath, measurable as an increased diameter. Normal ONSD values are typically less than 5.0-5.7mm depending on the measurement technique and patient factors. This technique is particularly valuable in settings where invasive ICP monitoring is not available or contraindicated, though it provides less precise information than direct measurement. Serial ONSD measurements can help track trends and guide management decisions in patients with suspected elevated intracranial pressure.
Usage
Usage note: Increasingly used abbreviation in point-of-care ultrasound documentation.
In Context
- "Bedside ultrasound revealed an ONSD of 6.2mm, concerning for elevated ICP." — Emergency department note
- "Serial ONSD measurements showed improvement following osmotic therapy." — Monitoring report