33 © Springer Nature Switzerland AG 2021 C. Robba, G. Citerio (eds.), Echography and Doppler of the Brain, https://doi.org/10.1007/978-3-030-48202-2_4 Optic Nerve Sheath Diameter Thomas Geeraerts, Louis Delamarre, and Charles-Henri Houze-Cerfon Contents 4.1 Introduction 33 4.2 Anatomical Background 34 4.3 Technology and Methods 34 4.3.1 Technology 34 4.3.2 Methods 34 4.3.3 Normal Views 35 4.3.4 Feasibility and Reproducibility 36 4.4 Limits and Safety Issues 36 4.4.1 Limits 36 4.4.2 Safety 37 4.5 Recent Innovation and Future Perspectives 37 4.6 Conclusion 37 References 38 4.1 Introduction Ocular ultrasound has recently emerged as a prom- ising tool to assess noninvasive intracranial pres- sure (ICP). The optic nerve, as a part of the central nervous system, is surrounded by a subarachnoid T. Geeraerts (*) Anesthesiology and Critical Care Department, University Hospital of Toulouse, University Toulouse 3-Paul Sabatier, Toulouse, France Coordination d’Anesthésie, CHU Toulouse, Hôpital Pierre Paul Riquet, Toulouse, France e-mail: geeraerts.t@chu-toulouse.fr L. Delamarre Anesthesiology and Critical Care Department, University Hospital of Toulouse, University Toulouse 3-Paul Sabatier, Toulouse, France e-mail: delamarre.l@chu-toulouse.fr C.-H. Houze-Cerfon Emergency Medicine Department, SAMU 31, University Hospital of Toulouse, University Toulouse 3-Paul Sabatier, Toulouse, France e-mail: houze-cerfon.ch@chu-toulouse.fr 4 Electronic Supplementary Material The online version of this chapter (https://doi.org/10.1007/978-3-030-48202- 2_4) contains supplementary material, which is available to authorized users.