Optic nerve sonography: a new window for the non-invasive evaluation of intracranial pressure in brain injury.

Enlargement of the optic nerve sheath has been described in patients with raised intracranial pressure (ICP), thereby serving as one of its indicators. Optic nerve sonography offers rapid bedside assessment of the optic nerve sheath diameter and has recently been introduced for the non-invasive detection of raised ICP, particularly in patients with severe brain injury. This review explains the pathophysiology of optic nerve sheath enlargement as a result of intracranial hypertension, describes the technique and clinical use of optic nerve sonography, and summarises the studies which have tested this modality in the non-invasive evaluation of ICP.