Posterior Globe Depth for Optic Nerve Sheath Diameter Measurement in Ocular Ultrasound in Healthy Volunteers

Background Point-of-care ultrasound (POCUS) is a readily available imaging modality in many emergency departments and health care facilities globally. Optic nerve sheath diameter (ONSD) measurement via ocular ultrasound has been shown to accurately predict increased intracranial pressure. Classically, the preferred technique for sonographic measurement of ONSD has specified measurement at an optimal position of 3 mm posterior to the globe. This study aims to validate an alternative approach of depth measurement (between 3 and 8 mm), with the hypothesis that ONSD should not change in size as the distance posterior to the globe increases. Methods Healthy volunteers aged > 18 years were studied. A point 3 mm posterior to the optic disc was located. This was repeated at a point 5 mm as well as 8 mm posterior to the globe. Results We enrolled 10 healthy participants. When evaluating variability in ONSD measurements at each of the three distances, we found that the difference in the measurements at each distance was statistically significant. In investigating pairwise comparisons, there was no difference between 3 and 5 mm, but there were differences in ONSD measurements at 3 and 8 mm, as well as at 5 and 8 mm. Conclusion POCUS is readily available in many emergency departments and health care facilities across the world. The classically preferred technique for sonographic measurement of ONSD has specified measurement at an optimal position of 3 mm posterior to the globe. Our results identified that ONSD can be measured between 3 and 5 mm with no significant changes.