Optic nerve sheath diameter
Dilatation of the optic nerve sheath has been shown to be a much earlier manifestation of ICP rise 1) 2).
ONSD is a simple noninvasive measurement on initial CT in patients with TBI that could be a surrogate for ICP monitoring. However, further studies are warranted 3).
Maissan et al. found that the optic nerve sheath diameter was distended during and after endotracheal intubation (ETI) in anesthetized patients, and intravenous lidocaine attenuated this effect 4).
For Liu et al. ONSD measured via head CT correlates with ICP and can predict the requirement for surgery in patients with TBI following admission to the emergency department 5).
In a study of Agrawal et al. optic nerve sheath diameter demonstrated a modest, statistically significant correlation with intracranial pressure, a predetermined level of diagnostic accuracy to justify routine clinical use as a screening test was not achieved. Measurement of optic disc elevation appears promising for the detection of elevated intracranial pressure, however, verification from larger studies is necessary 6).