Of the studied [[ultrasound]] [[noninvasive intracranial pressure monitoring]], [[optic nerve sheath]] diameter (ONSD), is the best estimator of [[ICP]]. The novel combination of [[optic nerve sheath diameter ultrasonography]] and [[venous transcranial Doppler]] (vTCD) of the [[straight sinus]] is a promising and easily available technique for identifying critically ill patients with [[intracranial hypertension]] ((Robba C, Cardim D, Tajsic T, Pietersen J, Bulman M, Donnelly J, Lavinio A, Gupta A, Menon DK, Hutchinson PJA, Czosnyka M. Ultrasound non-invasive measurement of intracranial pressure in neurointensive care: A prospective observational study. PLoS Med. 2017 Jul 25;14(7):e1002356. doi: 10.1371/journal.pmed.1002356. eCollection 2017 Jul. PubMed PMID: 28742869. )). The [[optic nerve sheath]] diameter has been verified by various clinical studies as a non-invasive indicator of intracranial hypertension ((Choi SH, Min KT, Park EK, Kim MS, Jung JH, Kim H. Ultrasonography of the optic nerve sheath to assess intracranial pressure changes after ventriculo-peritoneal shunt surgery in children with hydrocephalus: a prospective observational study. Anaesthesia. 2015 Nov;70(11):1268-73. doi: 10.1111/anae.13180. Epub 2015 Aug 24. PubMed PMID: 26299256. )). Correlations between ICP and Optic nerve sheath diameter (ONSD) using CT and MRI have been observed in adult populations. Ultrasound methods has been proposed as an alternative safe technique for invasive ICP measuring methods ((Karami M, Shirazinejad S, Shaygannejad V, Shirazinejad Z. Transocular Doppler and optic nerve sheath diameter monitoring to detect intracranial hypertension. Adv Biomed Res. 2015 Oct 22;4:231. doi: 10.4103/2277-9175.167900. eCollection 2015. PubMed PMID: 26645016; PubMed Central PMCID: PMC4647120. )). Admission ONSD in decompressive craniectomy (DC) patients is high but does not predict mortality and unfavorable outcomes ((Waqas M, Bakhshi SK, Shamim MS, Anwar S. Radiological prognostication in patients with head trauma requiring decompressive craniectomy: Analysis of optic nerve sheath diameter and Rotterdam CT Scoring System. J Neuroradiol. 2016 Feb;43(1):25-30. doi: 10.1016/j.neurad.2015.07.003. Epub 2015 Oct 20. PubMed PMID: 26492980. )). Intracranial pressure (ICP) can be noninvasively estimated from the sonographic measurement of the optic nerve sheath diameter (ONSD) and from the transcranial Doppler analysis of the pulsatility (ICPPI) and the diastolic component (ICPFVd) of the velocity waveform ((Robba C, Bragazzi NL, Bertuccio A, Cardim D, Donnelly J, Sekhon M, Lavinio A, Duane D, Burnstein R, Matta B, Bacigaluppi S, Lattuada M, Czosnyka M. Effects of Prone Position and Positive End-Expiratory Pressure on Noninvasive Estimators of ICP: A Pilot Study. J Neurosurg Anesthesiol. 2016 Mar 18. [Epub ahead of print] PubMed PMID: 26998650. )). Where pediatric patients present with an ONSD of over 6.1mm following a TBI, ICP monitoring should be implemented ((Young AM, Guilfoyle MR, Donnelly J, Scoffings D, Fernandes H, Garnett MR, Agrawal S, Hutchinson PJ. Correlating optic nerve sheath diameter with opening intracranial pressure in pediatric traumatic brain injury. Pediatr Res. 2016 Aug 11. doi: 10.1038/pr.2016.165. [Epub ahead of print] PubMed PMID: 27513519. )). Padayachy et al present a method for assessment of ONS pulsatile dynamics using [[transorbital ultrasound imaging]]. A significant difference was noted between the patient groups, indicating that deformability of the ONS may be relevant as a noninvasive marker of raised ICP ((Padayachy L, Brekken R, Fieggen G, Selbekk T. Pulsatile Dynamics of the Optic Nerve Sheath and Intracranial Pressure: An Exploratory In Vivo Investigation. Neurosurgery. 2016 Jul;79(1):100-7. doi: 10.1227/NEU.0000000000001200. PubMed PMID: 26813857; PubMed Central PMCID: PMC4900421. )). While the ultrasonographic mean binocular ONSD (>4.53 mm) was completely accurate in detecting elevated ICP, color Doppler indices of the ophthalmic arteries were of limited value ((Tarzamni MK, Derakhshan B, Meshkini A, Merat H, Fouladi DF, Mostafazadeh S, Rezakhah A. The diagnostic performance of ultrasonographic optic nerve sheath diameter and color Doppler indices of the ophthalmic arteries in detecting elevated intracranial pressure. Clin Neurol Neurosurg. 2016 Feb;141:82-8. doi: 10.1016/j.clineuro.2015.12.007. Epub 2015 Dec 15. PubMed PMID: 26771156. )). Bedside ultrasound may be useful in the diagnosis of midline intracranial shift by measurement of ONSD ((Kazdal H, Kanat A, Findik H, Sen A, Ozdemir B, Batcik OE, Yavasi O, Inecikli MF. Transorbital Ultrasonographic Measurement of Optic Nerve Sheath Diameter for Intracranial Midline Shift in Patients with Head Trauma. World Neurosurg. 2016 Jan;85:292-7. doi: 10.1016/j.wneu.2015.10.015. Epub 2015 Oct 17. PubMed PMID: 26485420. )). ---- In patients with SAH and acute hydrocephalus after aneurysm rupture, the ONSD remains expanded after normalization of ICP. This is most likely due to an impaired retraction capability of the optic nerve sheath. This finding should be considered when using transorbital sonography in the neuromonitoring of aneurysmal SAH ((Bäuerle J, Niesen WD, Egger K, Buttler KJ, Reinhard M. Enlarged Optic Nerve Sheath in Aneurysmal Subarachnoid Hemorrhage despite Normal Intracranial Pressure. J Neuroimaging. 2016 Mar-Apr;26(2):194-6. doi: 10.1111/jon.12287. Epub 2015 Aug 17. PubMed PMID: 26278326. )). ---- ONSD >5.5 mm yielded a sensitivity of 98.77% (95% CI: 93.3%-100%) and a specificity of 85.19% (95% CI: 66.3%-95.8%).In conclusion, the optimal cut-off point of ONSD for identifying IICP was 5.5 mm. ONSD seen on ocular US can be a feasible method for detection and serial monitoring of ICP in Korean adult patients ((Lee SU, Jeon JP, Lee H, Han JH, Seo M, Byoun HS, Cho WS, Ryu HG, Kang HS, Kim JE, Kim HC, Jang KS. Optic nerve sheath diameter threshold by ocular ultrasonography for detection of increased intracranial pressure in Korean adult patients with brain lesions. Medicine (Baltimore). 2016 Oct;95(41):e5061. PubMed PMID: 27741121; PubMed Central PMCID: PMC5072948. )). ===== Systematic review ====== The aim of a systematic review and meta-analysis will be to examine the accuracy of ONSD sonography for increased ICP diagnosis. Koziarz et al. will include published and unpublished randomised controlled trials, observational studies, and abstracts, with no publication type or language restrictions. Search strategies will be designed to peruse the MEDLINE, Embase, Web of Science, WHO Clinical Trials, ClinicalTrials.gov, CINAHL, and the Cochrane Library databases. We will also implement strategies to search grey literature. Two reviewers will independently complete data abstraction and conduct quality assessment. Included studies will be assessed using the Quality Assessment of Diagnostic Accuracy Studies-2 (QUADAS-2) tool. We will construct the hierarchical summary receiver operating characteristic curve for included studies and pool sensitivity and specificity using the bivariate model. We also plan to conduct prespecified subgroup analyses to explore heterogeneity. The overall quality of evidence will be rated using Grading of Recommendations, Assessment, Development and Evaluations (GRADE). Research ethics board approval is not required for this study as it draws from published data and raises no concerns related to patient privacy. This review will provide a comprehensive assessment of the evidence on ONSD sonography diagnostic accuracy and is directed to a wide audience. Results from the review will be disseminated extensively through conferences and submitted to a peer-reviewed journal for publication ((Koziarz A, Sne N, Kegel F, Alhazzani W, Nath S, Badhiwala JH, Rice T, Engels P, Samir F, Healey A, Kahnamoui K, Banfield L, Sharma S, Reddy K, Hawryluk GWJ, Kirkpatrick AW, Almenawer SA. Optic nerve sheath diameter sonography for the diagnosis of increased intracranial pressure: a systematic review and meta-analysis protocol. BMJ Open. 2017 Aug 11;7(8):e016194. doi: 10.1136/bmjopen-2017-016194. PubMed PMID: 28801417. )).