- Ultrasound (6- to 13-MHz linear array ultrasonic probe from Edge (Sonosite Corporation, USA)
- patient supine, head in middle, eyelids closed
- place probe horizontally above transverse axis of eyeball
- slowly and vertically move to the eyeball from forehead to nose, until clearest and artifact-free optimal plane echoed on the frozen images
- optic nerve image = low-echo strip structure located in the front and rear of the eyeball
- simultaneous appearance of lens and optic nerve means ultrasound probe is on the best place
- Measure the following:
- maximum external diameter of ONSD at 3mm behind the ball
- maximum diameter of ETD (parallel lens)
- measure both eyes 3x and average values as final ONSD and ETD
- US-ONSD / ETD ratio:
- AUC of ROC curve 0.920
- threshold value 0.25 (Sn90%, Sp82.3%)
- AUC of ROC curve 0.870
- threshold value 5.53 mm (Sn80%, Sp79.3%)
- CT-ONSD / ETD ratio:
- AUC of ROC curve 0.896
- threshold value 0.25 (Sn85.7%, Sp83.3%)
Figure. Optic nerve ultrasound examination.
Figure. Gray-scale image of eyeball, the ONSD is a linear hypoechoic structure posterior to the eyeball. Caliper ONSD identifies the measured point 3 mm posterior to the eyeball.
Axial CT scans showing a postoperation CT image with normal ICP.
The ONSD at 4.5 mm of the same patient. The CT-ONSD/ETD ratio is 0.19
My question – In patients at risk for delayed HCP, can this ratio predict need for VPS?
Du, J., Deng, Y., Li, H., Qiao, S., Yu, M., Xu, Q. and Wang, C. (2019). Ratio of Optic Nerve Sheath Diameter to Eyeball Transverse Diameter by Ultrasound Can Predict Intracranial Hypertension in Traumatic Brain Injury Patients: A Prospective Study. Neurocritical Care.