The diameter of the optic nerve is referred to as Optic Nerve Sheath Diameter (ONSD). It can be determined sonographically using a small ultrasound probe placed over the eye.
Normal Values
A measurement in 40 healthy adult test subjects found an average ONSD of 5.4 ± 0,6 mm, ranging from 4,3 mm to 7,6 mm1.
Clinical Relevance
The diameter of the optic nerve correlates with intracranial pressure2 and can be used for indirect assessment of intracranial pressure3. In contrast to intracranial pressure measurement using an intracranial pressure probe, sonographic determination of the ONSD is only an indirect parameter of intracranial pressure and varies depending on the examiner.
Figure
References
Bäuerle J, Lochner P, Kaps M, Nedelmann M. Intra- and Interobsever Reliability of Sonographic Assessment of the Optic Nerve Sheath Diameter in Healthy Adults. Journal of Neuroimaging. December 2010:42-45. ↩ ↩
Komut, Erdal, et al. "Bedside sonographic measurement of optic nerve sheath diameter as a predictor of intracranial pressure in ED." The American journal of emergency medicine 34.6 (2016): 963-967. ↩ ↩
Kimberly, Heidi Harbison, et al. "Correlation of optic nerve sheath diameter with direct measurement of intracranial pressure." Academic Emergency Medicine 15.2 (2008): 201-204. ↩ ↩