Optic nerve sheath diameter

Technique
Aspide et al. have proposed a particular protocol for optic nerve sheath diameter evaluation, which is as follows:

Device setting

 * Frequency: 10 MHz probe
 * Power output: reduce to 20-25%
 * Mechanical index: keep ≤0.23
 * Thermal index: keep ≤1°C
 * Depth: 40-45 mm
 * Focus: 25-30 mm
 * Gain: 55-60%

Patient positioning
Measurements
 * Supine, chest elevation of 15°-25°
 * Examiner behind the patient's head
 * Probe positioning
 * Horizontal: probe in center of closed upper eyelid, oriented horizontally, back of probe angled 15°-20° towards the forehead
 * Vertical: probe in center of closed eye, oriented vertically, angled slightly toward the nose
 * Identify sheath and measure 3 mm behind the merging point of the nerve from the papilla
 * Use color doppler to identify the central retinal artery and use it as a landmark to identify the correct anatomical plain
 * Capture a short video clip for measurements
 * Measure horizontal and vertical for each eye, using the best captured frame