Real-time evaluation of optic nerve sheath diameter (ONSD) in awake neurosurgical patients

Ultrasound measurement of the optic nerve sheath diameter (ONSD) has been utilized as an indirect assessment of intracranial pressure (ICP). Currently, the normal ONSD is believed to be < 5 mm, whereas diameters above 6 mm are considered to reflect a clinically significant increase in ICP. Despite these standard values, the ONSD has never been compared with simultaneously measured ICP values in awake, spontaneously breathing patients.