Optic Nerve Ultrasound Evaluation in Animals and Normal Subjects

Abstract

In recent years, ultrasonographic measurement of the optic nerve sheath diameter (ONSD) has been widely used to identify the presence of increased intracranial pressure (ICP). Intracranial hypertension is a life-threatening condition that can be caused by various neurological and non-neurological disorders, and it is associated to poor clinical results. Ultrasonography could be used to qualitatively and efficiently detect ICP increases, but to reach this purpose, clear cut-off values are mandatory. The aim of this review is to provide a wide overview of the most important scientific publications on optic nerve ultrasound normal values assessment published in the last 30 years. A total of 42 articles selected from PubMed medical database was included in this review. Our analysis showed that ocular ultrasonography is considered to be a valuable diagnostic tool, especially when intracranial hypertension is suspected, but unfortunately this research provided conflicting results that could be due to the different ultrasound protocols. This is mainly caused by the use of B scan alone, which presents several limitations. The use of B-scan coupled with the standardized A-scan approach could give more accurate, and reliable ultrasound evaluation, assuring higher data objectivity.

Optic Nerve Ultrasound Evaluation in Idiopathic Intracranial Hypertension

“…B-scan offers the benefit of being quick and transportable and could be used by different specialists after a specific training ( 40 ). Unfortunately, B-scan has several limitations such as the blooming effect and artifacts that can make the measurements unreliable and poorly reproducible ( 41 ). For this reason, the use of standardized A-scan, which provides the best possible accuracy, is recommended for the diagnosis and during the follow-up, when the maximal care in measurements is needed ( 42 ).…”

Accuracy of Optic Nerve Sheath Diameter Measurements in Pocket-Sized Ultrasound Devices in a Simulation Model

“…Another limitation to our study is inherent to the popular B-scan ultrasound technique used to acquire images. Due to non-standardized gain settings used to acquire images, a “blooming effect” occurs, where larger gains cause the ONS to appear larger, and smaller gains cause it to appear smaller ( 40 ). This effect leads to artifacts ( 41 ) and decreased repeatability of measurements between ONSD studies ( 42 ).…”

A-Scan Ultrasonographic Evaluation of Patients with Idiopathic Intracranial Hypertension: Comparison of Optic Nerves

“…For this reason, the measurement of the optic nerve (ON) diameter has been suggested as a sensitive and reliable method for following these patients. ICP rise will lead to a subarachnoidal fluid increase in the ON sheaths that can be quite easily detected by measuring its diameter with ultrasound [ 9 , 10 , 11 , 12 , 13 ].…”