Optic nerve sheath diameter assessment by neurosonology: A review of methodologic discrepancies

Ultrasonographic Optic Nerve Sheath Diameter Technical Pitfalls and Imaging Artifacts

Ultrasonographic optic nerve sheath diameter (ONSD) is a non-invasive intracranial pressure (ICP) surrogate. This article discusses the effect of ultrasound settings and imaging artifacts on ONSD assessment. Ultrasound settings that may affect ONSD assessment include gain, dynamic range, frequency, harmonic imaging, and focal zones. Artifacts can be related to imaged structures (acoustic shadowing, enhancement, comet tail, and speckle artifacts) or to beam properties (partial volume and refraction artifacts). In addition, optic nerve sheath (ONS) properties such as echogenicity changes based on ICP or ONS kinking are discussed.

Optic nerve sheath diameter measurement in healthy South Iranian adults from a cross-sectional ultrasonographic study

The measurement of optic nerve sheath diameter (ONSD) is a rapid, safe, and non-invasive method for assessing increased intracranial pressure (ICP). This study aimed to determine the mean ONSD in a healthy Iranian adult population and its correlation with demographic and anthropometric factors. Given that normal ONSD values can vary based on sex, age, ethnicity, and ultrasound techniques, establishing a local reference can enhance clinical assessment. In this cross-sectional study, 100 healthy Iranian adults (mean age 38.7 ± 9.8 years; 60 females) underwent ultrasonographic examination of the left optic nerve sheath. ONSD was measured 3 mm behind the globe in two planes, and the average of these measurements was calculated. The mean axial length (AL) was 23.53 mm (SD ± 0.94), and the mean ONSD was noted at 6.3 mm (SD ± 0.42). Statistical analysis did not reveal significant correlations between ONSD and various demographic or anthropometric factors (P:0.236). This study contributes to the literature by providing local reference values for ONSD in a healthy Iranian adult population, establishing an upper limit of 6.3 mm, and highlighting the consistency of these values with international norms, thereby improving the assessment of ICP in diverse populations.

The association of early passive mobilization with intracranial pressure in the adult intensive care unit: A prospective, cohort study

BACKGROUND

Early mobilization are key components of the ABCDEF Care Bundle and critical treatments to reduce acquired muscle weakness, delirium and prolonged intensive care unit (ICU) stay.

AIM

This study aimed to determine whether routine early mobilization related to intracranial pressure in intensive care patients on mechanical ventilation, using optic nerve sheath diameter measurement (ONSD).

STUDY DESIGN

This study was planned as a prospective, cohort study in the third-step adult ICU of a faculty hospital. The study included only patients who were intubated and followed up on a mechanical ventilator and were clinically stable. Passive range of motion (PROM) exercises were performed daily by the physiotherapists as part of routine care from the day of hospitalization. ONSD was assessed before, during and 10 min after PROM exercises.

RESULTS

The study included 20 eligible patients out of the 142 who were evaluated upon admission to the ICU. The median age of the patients was 65 years, and nine (45%) of them were female. The analyses showed that there was no statistically significant change in ONSD during and at the end of the PROM (ONSD right eye p:.621, Partial η2: 0.025, ONSD left eye p:.935, Partial η2: 0.004). Similarly, there was no statistically significant change in haemodynamic parameters in during and at the end of the PROM (Heart beat p:.849, Partial η2: 0.009, Systolic Pressure p:.435, Partial η2: 0.043, Diastolic Pressure p:.128, Partial η2:0.103, Saturation p:.103, Partial η2: 0.113 and Respiratory rate p:.071, Partial η2:0.130).

CONCLUSION

This study suggests that daily extremity physiotherapy exercises can be safely applied without causing increased intracranial pressure or haemodynamic instability in intensive care patients followed up on mechanical ventilation, including patients with vasopressor therapy.

RELEVANCE TO CLINICAL PRACTICE

Early mobilization, including PROM, is considered safe in terms of intracranial pressure for intubated patients in the ICU.

Change in Optic Nerve Sheath Diameter and Cerebral Ventricular Shunt Failure in Children

Importance

Ocular point-of-care ultrasonography (POCUS) may be a clinically useful method to evaluate shunt dysfunction for children with hydrocephalus presenting to the emergency department (ED).

Objective

To evaluate whether a change in the optic nerve sheath diameter (ONSD) from prior asymptomatic baseline was associated with shunt failure.

Design, Setting, and Participants

Participants in this prospective single-center observational cohort study at a tertiary care children's hospital were enrolled from January 5, 2018, to March 2, 2022. Children 18 years or younger with cerebrospinal fluid (CSF) shunts were consecutively recruited during routine asymptomatic visits in the outpatient neurosurgery clinic. The institution sees approximately 1000 children with shunts. Children with comorbid eye pathologic conditions known to increase the ONSD were excluded, as were those with shunt interventions between baseline and symptomatic ocular POCUS. Data analysis was completed in May 2024.

Exposures

Baseline ocular POCUS was performed on asymptomatic children with CSF shunts recruited in the outpatient neurosurgery clinic; a second ocular POCUS was performed if the patient subsequently presented to the ED with symptoms of shunt failure. Change in ONSD from prior asymptomatic baseline to symptomatic presentation was the main study exposure.

Main Outcomes and Measures

Shunt failure was defined as intraoperative confirmation of inadequate CSF flow through the shunt system associated with identifiable shunt complications, including catheter or valve obstruction, shunt tubing fracture or disconnection, or proximal catheter migration out of the ventricle within 96 hours from presentation to the ED.

Results

Seventy-six pairs of baseline and symptomatic ultrasonograms from 58 patients (mean [SD] age, 6.6 [4.7] years; 36 of 58 boys [62%]) were included. Twenty patients (35%) had 2 or more prior shunt revisions, and 29 (50%) had communicating hydrocephalus. The primary outcome of intraoperatively confirmed shunt failure was observed in 14 of 76 ED patient presentations (18%). The mean (SD) change in ONSD among patients with shunt failure was 0.89 (0.66) mm vs 0.16 (0.40) mm among patients without shunt failure (mean difference, 0.73 mm [95% CI, 0.47-0.99 mm]; P < .001). The odds of full shunt failure were 1.4 times higher (95% CI, 1.21-1.78; P < .001) for every 0.1-mm increase in ONSD. The area under the receiver operating characteristic curve was 0.86, with an optimal cutoff of 0.4 mm or more, yielding a sensitivity of 0.93, specificity of 0.73, positive predictive value of 0.43, and negative predictive value of 0.98, for a disease prevalence of 15%, with a positive likelihood ratio of 3.39 and negative likelihood ratio of 0.10.

Conclusions and Relevance

In this single-center, prospective cohort study of symptomatic children with CSF shunts, a change in ONSD measured by ocular POCUS was associated with shunt failure. A change in ONSD from prior asymptomatic baseline to symptomatic presentation of less than 0.4 mm identified a population at low risk of true shunt failure. Further research is warranted to validate these findings, the presented change in ONSD threshold, and to risk stratify low-risk patients for cross-sectional neuroimaging.

Asymmetric stress distribution on lamina cribrosa in glaucoma patients with high myopia

PURPOSE

To investigate the impact of biomechanical changes in the optic nerve head on glaucoma progression during ocular rotation in highly myopic eyes with primary open-angle glaucoma.

METHODS

This study retrospectively enrolled 147 patients with primary open-angle glaucoma, including 57 with high myopia and 90 with non-high myopia. Personalized optic nerve head models were designed, and simulations were performed using finite element analysis to evaluate the effect of ocular rotation on the optic nerve head. Biomechanical changes in the optic nerve head were analyzed and compared between the groups.

RESULTS

The mean strain on the lamina cribrosa was significantly higher in the high myopia group compared to the non-high myopia group during ocular rotation. The stress ratio, indicating asymmetric stress distribution, was higher in the high myopia group than in the non-high myopia group. The stress ratio increased significantly as axial length increased. Both stress ratio and mean lamina cribrosa strain were correlated with rate of retinal nerve fiber layer thickness reduction (stress ratio: partial coefficient = -0.171, P = 0.040; mean lamina cribrosa strain: partial coefficient = -0.196, P = 0.018).

CONCLUSION

High myopia leads to increased lamina cribrosa strain and asymmetric stress distribution during ocular rotation. These findings underscore the importance of considering optic nerve head biomechanics in patients with high myopia. Additionally, the stress ratio may serve as a novel indicator for predicting glaucoma progression.

KEY MESSAGES

What is known Biomechanical changes in the optic nerve head differ between patients with high myopia and those with non-high myopia. What is new Asymmetric stress distribution on the lamina cribrosa during ocular movement was higher in the high myopia group and was associated with structural progression of glaucoma. A longer axial length increased the asymmetric stress on the lamina cribrosa during ocular movement.

The association between asymmetric stress distribution on the lamina cribrosa and glaucoma progression

PURPOSE

The purpose of this study was to assess the effect of ocular movements on the progression of glaucoma.

METHODS

A total of 118 primary open-angle glaucoma patients were enrolled, comprising 71 patients in the progression group and 47 patients in the non-progression group. Utilizing three geometric parameters-axial length, optic disc radius, and optic cup deepening-a personalized virtual optic nerve head (ONH) model was designed. ONH biomechanical changes during ocular movement were simulated using a finite element analysis. Simulation results were analyzed and compared between the progression and non-progression groups.

RESULTS

In both progression and non-progression groups, ONH strains significantly increased with increasing rotation angle. When the eye rotated by 10°, the stress on the anterior surface of the lamina cribrosa on the temporal side was significantly higher in the progression group compared to the non-progression group (16.19 ± 0.90 kPa vs. 13.24 ± 3.00 kPa, P < 0.001). The stress ratio, indicating asymmetric stress distribution, was higher in the progression group than in the non-progression group (0.56 ± 0.13 vs. 0.49 ± 0.19, P = 0.018). Stress ratio significantly increased with increasing optic disc radius (standardized β = 0.303, P < 0.001) and optic cup deepening (standardized β = 0.538, P < 0.001).

CONCLUSIONS

Asymmetric stress distribution with ocular movement was higher in the progression group. This asymmetry was associated with optic disc radius and optic cup deepening. Therefore, ocular movement may contribute to the progression of glaucoma, with ONH geometry playing a role.

KEY MESSAGES

WHAT IS KNOWN : Ocular movement is considered one of the physical stress factors affecting the optic nerve head.

WHAT IS NEW

Ocular movement increased the strain on the optic nerve head and resulted in an asymmetric stress distribution on the lamina cribrosa surface. Asymmetric stress distribution on lamina cribrosa with ocular movement was higher in the glaucoma progression group and associated with optic disc radius and optic cup deepening.

Intracranial pressure estimated non-invasively and postoperative outcomes in surgery in the Trendelenburg position with pneumoperitoneum

BACKGROUND

Surgery in the Trendelenburg position (TP) with pneumoperitoneum (PP) is beneficial in several aspects but is associated with postoperative complications, such as postoperative nausea and vomiting (PONV). The mechanism behind this is unknown, but an increase in intracranial pressure (ICP) has been suggested. There are several studies of non-invasively estimated ICP during surgery in TP with PP. The association between perioperative estimated ICP and postoperative complications has not yet been reviewed.

METHODS

We performed a scoping review of peer-reviewed clinical studies reporting on both perioperative estimation of ICP and postoperative complications in patients undergoing surgery in TP with PP. The literature search was performed in February 2025 on PubMed, CINAHL, and Web of Science.

RESULTS AND CONCLUSIONS

Ten of 12 included studies suggested associations between perioperative elevation of estimated ICP and postoperative complications, most notably PONV. This may have clinical implications since elevated ICP can be treated. Future research should focus on the association between perioperative ICP estimation and postoperative complications and the effects of ICP-lowering strategies on postoperative outcomes.

The impact of demographics and positioning on the imaging features of the optic nerve sheath and ophthalmic vessels

BACKGROUND

There are significant discrepancies in the optic nerve sheath diameter (ONSD) reported in the literature. We aimed to determine the ultrasonographic imaging features of ONSD and ophthalmic vessels in a healthy population, using a standardized protocol, and to estimate the effect of demographics and positioning changes on imaging measurements.

METHODS

We measured the mean values of the ONSD in supine and sitting position and the Doppler imaging parameters of the ophthalmic, central retinal and short posterior ciliary arteries. Inter-observer reliability was assessed using intraclass correlation coefficient (ICC). Linear regression models were fitted to predict the effect of demographic and clinical determinants on the imaging features.

RESULTS

A total of 50 measurements were obtained for each observer. The mean ONSD was 5.9 mm and there was a mean reduction of 0.2 mm when assessed in sitting position (p < 0.001). Doppler analysis showed higher peak-systolic velocity and resistive index in the ophthalmic artery (35.6 cm/s vs. 12.0 cm/s; 0.78 vs. 0.70) compared to the central retinal artery (p < 0.001). Age, sex, heart rate and systolic blood pressure were significant determinants of the imaging features, with ONSD being larger in males (p < 0.001) and increasing with heart rate (p = 0.001). ICC estimates indicated 'good' inter-observer reliability of the ONSD and the ophthalmic and central retinal arteries velocities and resistance.

CONCLUSIONS

Our findings suggest a significant impact of patient demographics and positioning during ultrasonography on the normal imaging features of the ONSD and ophthalmic vessels. The heterogeneity in methodology and clinical cohorts may justify previous discrepancies in the literature. These findings can assist in the interpretation of imaging features in clinical settings and in the standardization of point of care ONSD ultrasonography.

Real-Time Automated Measurements of Optic Nerve Sheath Diameter for Noninvasive Assessment of Intracranial Pressure in Aneurysmal Subarachnoid Hemorrhage

BACKGROUND

Optic nerve sheath diameter (ONSD) is a promising noninvasive parameter for intracranial pressure (ICP) assessment. However, in the setting of aneurysmal subarachnoid hemorrhage (aSAH), several previous studies have reported no association between ultrasonically measured ONSD and ICP. In this study, we evaluate ONSD in patients with aSAH using a novel method of automated real-time ultrasonographic measurements and explore whether factors such as having undergone surgery affects its association to ICP.

METHODS

We prospectively included adult patients with aSAH undergoing invasive ICP monitoring. ONSD was obtained using a prototype ultrasound machine with software for real-time automated measurements at the bedside. Correlation between ONSD and ICP was explored, and the ability of ONSD to discriminate dichotomized ICP was evaluated. Abovementioned analyses were performed for the whole cohort and repeated for subgroups by whether the basal cisterns had been surgically entered before ultrasound examination.

RESULTS

Twenty-six ultrasound examinations were performed in 20 patients. There was a positive correlation between ONSD and ICP (R = 0.43; p = 0.03). In the subgroup where the basal cisterns had not been surgically entered before ultrasound examination, there was a stronger correlation (R = 0.55; p = 0.01), whereas no correlation was seen in the subgroup where the basal cisterns had been surgically entered (R = - 0.16; p = 0.70). ONSD displayed an ability to discriminate ICP dichotomized at ≥ 15 mm Hg (area under the curve [AUC] = 0.84, 95% confidence interval [CI] 0.65-0.96). Subgroup analysis revealed a perfect discriminatory ability (AUC = 1, 95% CI 0.81-1) where the basal cisterns had not been surgically entered and no discriminatory ability (AUC = 0.47, 95% CI 0.16-0.84) where the basal cisterns had been surgically entered before ultrasound examination.

CONCLUSIONS

Automatically measured ONSD correlated well with ICP and displayed a perfect discriminatory ability in patients with aSAH in whom the basal cisterns had not been entered surgically before ultrasound examination, and may be a clinically valuable noninvasive marker of ICP in these patients. Caution should be exercised in using ONSD in patients in whom the basal cisterns have been entered surgically before ONSD measurements, as no association was observed in this subgroup.

Automation of Ultrasonographic Optic Nerve Sheath Diameter Measurement: A Scoping Review

Intracranial pressure (ICP) monitoring is a cornerstone of neurocritical care in managing severe brain injury. However, current invasive ICP monitoring methods carry significant risks, including infection and intracranial hemorrhage, and are contraindicated in certain clinical situations. Additionally, these methods are not universally available. Optic nerve sheath diameter (ONSD) measurement presents a promising noninvasive alternative for ICP monitoring, though its clinical adoption has been limited due to its operator dependence and inconsistencies in imaging acquisition and measurement techniques. Automating both ONSD image acquisition and measurement could enhance accuracy and reliability, thereby improving its utility as a noninvasive ICP estimation tool. A range of image analysis and machine learning (ML) techniques have been applied to address these challenges. In this paper, we provide a narrative review of the current literature on ONSD automation, examining the strengths and limitations of classical image analysis and ML models in improving ONSD-based ICP assessment.

Effects of Stress and Strain on the Optic Nerve Head on the Progression of Glaucoma

PRCIS

In primary open angle glaucoma, the rate of retinal nerve fiber layer thickness decrease was negatively correlated with lamina cribrosa strain, which was associated with intraocular pressure and optic nerve head geometric factors.

PURPOSE

We hypothesized that the biomechanical deformation of the optic nerve head (ONH) contributes to the progression of primary open angle glaucoma (POAG). This study investigated the biomechanical stress and strain on the ONH in patients with POAG using computer simulations based on finite element analysis and analyzed its association with disease progression.

METHODS

We conducted a retrospective analysis that included patients diagnosed with early-to-moderate stage POAG. The strains and stresses on the retinal nerve fiber layer (RNFL) surface, prelaminar region, and lamina cribrosa (LC) were calculated using computer simulations based on finite element analysis. The correlations between the rate of RNFL thickness decrease and biomechanical stress and strain were investigated in both the progression and nonprogression groups.

RESULTS

The study included 71 and 47 patients in the progression and nonprogression groups, respectively. In the progression group, the factors exhibiting negative correlations with the RNFL thickness decrease rate included the maximum and mean strain on the LC. In multivariate analysis, the mean strain on the LC was associated with optic disc radius, optic cup deepening, axial length, and mean intraocular pressure (IOP), whereas the maximum strain was only associated with mean IOP.

CONCLUSIONS

In early-to-moderate stage POAG, the rate of RNFL thickness decrease was influenced by both the mean and maximum strain on the LC. Strains on the LC were associated with mean IOP, optic disc radius, axial length, and optic cup deepening. These results suggest that not only IOP but also ONH geometric factors are important in the progression of glaucoma.

The optic nerve sheath in hypertensive disorders of pregnancy and perinatal outcomes: a cohort study

BACKGROUND

Preeclampsia is implicated in 14% of maternal deaths worldwide, mostly due to complications such as intracranial hemorrhage and cerebral edema. Cerebral edema increases intracranial pressure, which can be predicted by ultrasonographic measurement of the optic nerve sheath diameter (ONSD). Greater diameters have been reported in women with preeclampsia and eclampsia; however, data are lacking on the possible association with maternal and neonatal adverse outcomes. This study aimed to determine whether there is an association between hypertensive disorders of pregnancy and the ONSD, and between this measurement and maternal and neonatal adverse outcomes.

METHODS

This was a cohort study involving 183 women in the third trimester of pregnancy or within 24 h following childbirth, distributed as follows: control group (n = 30), gestational hypertension (n = 14), chronic hypertension (n = 12), preeclampsia without severe features (n = 12), preeclampsia with severe features (n = 62), superimposed preeclampsia (n = 23) and eclampsia (n = 30). The participants underwent ocular ultrasonography, and data on maternal and neonatal outcomes were collected from the medical records. To compare the groups, analysis of variance was used for the normally distributed numerical variables and the Kruskal-Wallis test was used for variables with non-normal distribution. Two-tailed p-values ≤ 0.05 were considered statistically significant.

RESULTS

Overall comparison between the seven groups showed no statistically significant difference in the mean ONSD (p = 0.056). Nevertheless, diameters were significantly greater in the eclampsia group compared to the control group (p = 0.003). Greater diameters were associated with maternal admission to the intensive care unit (ICU) (p < 0.01) and maternal near miss (p = 0.01). There was no association between ONSD and admission to the neonatal ICU (p = 0.1), neonatal near miss (p = 0.34) or neonatal death (p = 0.26).

CONCLUSIONS

No association was found between ONSD and the hypertensive disorders of pregnancy in the overall analysis; however, ONSD was greater in women with eclampsia compared to controls. Greater diameters were associated with maternal admission to the ICU and maternal near miss. These findings suggest a potential use for bedside ultrasound as an additional tool for stratifying risk in patients with hypertensive disorders of pregnancy.

Which compartments of the optic nerve and its sheath are associated with intracranial pressure? An exploratory study

BACKGROUND AND PURPOSE

The optic nerve sheath diameter (ONSD) is a commonly used estimate of intracranial pressure (ICP). The rationale behind this is that pressure changes in the cerebrospinal fluid affect the optic nerve subarachnoid space (ONSAS) thickness. Still, possible effects on other compartments of the optic nerve sheath (ONS) have not been studied. This is the first study ever to analyze all measurable compartments of the ONS for associations with elevated ICP.

METHODS

We measured changes in ICP and changes in ONS compartments in 75 patients treated with invasive ICP monitoring at the Karolinska University Hospital. Associations between changes in ICP and changes in ONS compartments were estimated with generalized estimating equations. The potential to identify elevated ICP was assessed with the area under the receiver operating characteristic curve (AUROC) for ONS compartments associated with ICP changes.

RESULTS

Both ONSAS and perioptic dura mater thickness were significantly associated with changes in ICP in multivariable modeling. ONSAS was the only compartment that independently predicted changes in ICP, with an AUROC of 0.69 for predicting ICP increase. Still, both the perioptic dura mater thickness and the optic nerve diameter added value in predicting ICP changes in multivariable modeling.

CONCLUSIONS

The results from this study challenge the current understanding of the mechanism behind the association between ICP and ONSD. Contrary to the common opinion that ONSAS is the only affected compartment, this study shows a more complex picture. It suggests that all ONS compartments may add value in predicting changes in ICP.

Effect of systemic lidocaine infusion on optic nerve sheath diameter during laparoscopic hysterectomy: a randomized controlled study

BACKGROUND

During laparoscopic hysterectomy (LH), the elevation of intra-abdominal and intra-thoracic pressures due to pneumoperitoneum (PP) results in an increase in intracranial pressure (ICP). The Trendelenburg position (TP) is an accentuating factor. This trial aimed to assess the effect of intravenous (IV) lidocaine infusion on optic nerve sheath diameter (ONSD), a widely accepted surrogate measure for ICP, during PP and TP.

METHODS

A randomized, placebo-controlled study was conducted on 66 patients scheduled for LH, equally divided into a lidocaine group and a saline group. ONSD, the primary outcome, was recorded before induction (T1), before PP initiation in the supine position (T2), five minutes (T3), 30 minutes (T4), and 60 minutes (T5) after PP and TP, and five minutes after termination of PP in the supine position (T6). Secondary outcomes included numerical rating scale (NRS) scores at arrival to the post-anesthesia care unit (PACU), 6, 12, and 24 hours after surgery, and postoperative adverse effects.

RESULTS

ONSD at T4 and T5 was significantly lower in the lidocaine group than in the saline group (T4: 4.94±0.43 mm vs. 5.27±0.37 mm; P =0.003, T5: 5.08±0.46 vs. 5.41±0.38 mm; P =0.004). The lidocaine group had significantly lower NRS values than the saline group only at PACU arrival (median [Q1-Q3]: 5 [4-6] vs. 6 [5-6.25]; P =0.016). Fewer patients in the lidocaine group experienced postoperative headache (P =0.029).

CONCLUSIONS

IV lidocaine during LH can attenuate the ONSD distension, decrease pain scores at PACU arrival, and reduce the incidence of postoperative headache.

Dimensions of Arachnoid Bulk Ratio: A Superior Optic Nerve Sheath Index for Intracranial Pressure

Background Discrepancies in the literature regarding optimal optic nerve sheath diameter (ONSD) cutoffs for intracranial pressure (ICP) necessitate alternative neuroimaging parameters to improve clinical management. Purpose To evaluate the diagnostic accuracy of the dimensions of the perineural subarachnoid space to the optic nerve sheath ratio, measured using US, in predicting increased ICP. Materials and Methods In a prospective cohort study from April 2022 to December 2023, patients with suspected increased ICP underwent optic nerve US to determine the dimensions of arachnoid bulk (DAB) ratio and ONSD before invasive ICP measurement. Correlation between the parameters and ICP, as well as diagnostic accuracy, was assessed using area under the receiver operating characteristic curve (AUC) analysis. Results A total of 30 participants were included (mean age, 39 years ± 14 [SD]; 24 female). The DAB ratio and ONSD were significantly larger in participants with increased ICP (38% [0.16 of 0.42] and 14% [0.82 of 6.04 mm], respectively; P < .001). The DAB ratio showed a stronger correlation with ICP than ONSD (rs = 0.87 [P < .001] vs rs = 0.61 [P < .001]). The DAB ratio and ONSD optimal cutoffs for increased ICP were 0.5 and 6.5 mm, respectively, and the ratio had higher sensitivity (100% vs 92%) and specificity (94% vs 83%) compared with ONSD. Moreover, the DAB ratio better predicted increased ICP than ONSD, with a higher AUC (0.98 [95% CI: 0.95, 1.00] vs 0.86 [95% CI: 0.71, 0.95], P = .047). Conclusion An imaging ratio was proposed to predict ICP based on the relative anatomy of the cerebrospinal fluid space, demonstrating more accurate diagnosis of increased ICP and a strong correlation with ICP values, suggesting its potential utility as a neuroimaging marker in clinical settings. © RSNA, 2024 Supplemental material is available for this article. See also the editorial by Shepherd in this issue.

Measurement of Optic Nerve Sheath Diameter by Bedside Ultrasound in Patients With Traumatic Brain Injury Presenting to Emergency Department: A Review

The aim of this review article is to outline the effectiveness of using bedside ultrasound to measure the optic nerve sheath diameter (ONSD) in order to identify variations in intracranial pressure (ICP) and subsequently avoid the complication of secondary brain injury in patients with traumatic brain injury (TBI), who are admitted to an emergency department (ED). Reputable publications and numerous studies demonstrate the problem's exponential rampancy and pervasiveness. In a TBI patient, the emergence of secondary brain damage has been recognized as a serious emergency. It is believed that secondary brain damage is caused by an abnormally high ICP. High levels of ICP can be measured using both invasive and non-invasive approaches. ONSD measurement via bedside ultrasound has been identified as a quick, useful technique to be used in the ED to avoid potential morbidity and mortality owing to secondary brain injury.

Sex differences in the diagnostic value of optic nerve sheath diameter for assessing intracranial pressure

The optic nerve sheath diameter (ONSD) can predict elevated intracranial pressure (ICP) but it is not known whether diagnostic characteristics differ between men and women. This observational study was performed at the Karolinska University Hospital in Sweden to assess sex differences in diagnostic accuracy for ONSD. We included 139 patients (65 women), unconscious and/or sedated, with invasive ICP monitoring. Commonly used ONSD derived measurements and associated ICP measurements were collected. Linear regression analyses were performed with ICP as dependent variable and ONSD as independent variable. Area under the receiver operator characteristics curve (AUROC) analyses were performed with a threshold for elevated ICP ≥ 20 mmHg. Analyses were stratified by sex. Optimal cut-offs and diagnostic characteristics were estimated. The ONSD was associated with ICP in women. The AUROCs in women ranged from 0.70 to 0.83. In men, the ONSD was not associated with ICP and none of the AUROCs were significantly larger than 0.5. This study suggests that ONSD is a useful predictor of ICP in women but may not be so in men. If this finding is verified in further studies, this would call for a re-evaluation of the usage and interpretation of ONSD to estimate ICP.

Chemical Insights into Topical Agents in Intraocular Pressure Management: From Glaucoma Etiopathology to Therapeutic Approaches

Glaucoma encompasses a group of optic neuropathies characterized by complex and often elusive etiopathology, involvihttng neurodegeneration of the optic nerve in conjunction with abnormal intraocular pressure (IOP). Currently, there is no cure for glaucoma, and treatment strategies primarily aim to halt disease progression by managing IOP. This review delves into the etiopathology, diagnostic methods, and treatment approaches for glaucoma, with a special focus on IOP management. We discuss a range of active pharmaceutical ingredients used in glaucoma therapy, emphasizing their chemical structure, pharmacological action, therapeutic effectiveness, and safety/tolerability profiles. Notably, most of these therapeutic agents are administered as topical formulations, a critical aspect considering patient compliance and drug delivery efficiency. The classes of glaucoma therapeutics covered in this review include prostaglandin analogs, beta blockers, alpha agonists, carbonic anhydrase inhibitors, Rho kinase inhibitors, and miotic (cholinergic) agents. This comprehensive overview highlights the importance of topical administration in glaucoma treatment, offering insights into the current state and future directions of pharmacological management in glaucoma.

Optic Nerve Sheath Diameter for Assessing Prognosis after Out-of-Hospital Cardiac Arrest

PURPOSE

Evaluate optic nerve sheath and pial diameters (ONSD, ONPD) via sonography and computed tomography (CT) after out-of-hospital cardiac arrest (CA) and to compare their prognostic significance with other imaging and laboratory biomarkers.

MATERIALS AND METHODS

A prospective observational study enrolling patients after successful resuscitation between December 2017 and August 2021. ONSD and ONPD were measured with sonography. Additionally, ONSD, and also grey-to-white ratio at basal ganglia (GWRBG) and cerebrum (GWRCBR), were assessed using CT. Lactate and neuron specific enolase (NSE) blood levels were measured.

RESULTS

Sonographically measured ONSD and ONPD yielded no significant difference between survival and non-survival (p values ≥0.4). Meanwhile, CT assessed ONSD, GWRBG, GWRCBR, and NSE levels significantly differed regarding both, survival (p values ≤0.005) and neurological outcome groups (p values ≤0.04). For survival prognosis, GWRBG, GWRCBR, and NSE levels appeared as excellent predictors; in predicting a good neurological outcome, NSE had the highest accuracy.

CONCLUSIONS

CT diagnostics, in particular GWRBG and GWRCBR, as well as NSE as laboratory biomarker, appear as excellent outcome predictors. Meanwhile, our data lead us to recommend caution in utilizing sonography assessed ONSD and ONPD for prognostic decision-making post-CA.

Quantitative ultrasound image assessment of the optic nerve subarachnoid space during 90-day head-down tilt bed rest

The elevation in the optic nerve sheath (ONS) pressure (ONSP) due to microgravity-induced headward fluid shift is the primary hypothesized contributor to SANS. This longitudinal study aims to quantify the axial plane of the optic nerve subarachnoid space area (ONSSA), which is filled with cerebrospinal fluid (CSF) and expands with elevated ONSP during and after head-down tilt (HDT) bed rest (BR). 36 healthy male volunteers (72 eyes) underwent a 90-day strict 6° HDT BR. Without obtaining the pre-HDT data, measurements were performed on days 30, 60, and 90 during HDT and at 6 recovery time points extended to 180-days (R + 180) in a supine position. Portable B-scan ultrasound was performed using the 12 MHz linear array probe binocularly. The measurements of the ONS and the calculation of the ONSSA were performed with ImageJ 1.51 analysis software by two experienced observers in a masked manner. Compared to R + 180, the ONSSA on HDT30, HDT60, and HDT90 exhibited a consistently significant distention of 0.44 mm2 (95% CI: 0.13 to 0.76 mm2, P = 0.001), 0.45 mm2 (95% CI: 0.15 to 0.75 mm2, P = 0.001), and 0.46 mm2 (95% CI: 0.15 to 0.76 mm2, P < 0.001), respectively, and recovered immediately after HDT on R + 2. Such small changes in the ONSSA were below the lateral resolution limit of ultrasound (0.4 mm) and may not be clinically relevant, possibly due to ONS hysteresis causing persistent ONS distension. Future research can explore advanced quantitative portable ultrasound-based techniques and establish comparisons containing the pre-HDT measurements to deepen our understanding of SANS.

Measurement of Optic Nerve Sheath Diameter by Computed Tomography in the Pediatric Population: Normal Values

PURPOSE

To determine the normal values of optic nerve sheath diameter (ONSD) by computed tomography (CT) in the pediatric population.

METHODS

The CT scans of pediatric patients aged 1 to 16 years who underwent brain CT for different reasons, who did not have intracranial pathology or increased intracranial pressure, and who had no pathology on CT were included in the study. Four age groups were defined with the following ranges: 1 to 2, 3 to 6, 7 to 10, and 11 to 16 years. ONSD was measured from axial CT images, 3 and 10 mm behind the optic globe.

RESULTS

The normative values of ONSD measured on CT imaging in children aged 1 to 16 years were reported. The change in ONSD according to age was investigated. ONSD was found to increase with age at both levels measured. The difference was statistically significant.

CONCLUSIONS

Normal values should be known to detect pathologies that may cause an increase in optic nerve diameter. The values reported in this study can serve as a reference for normal optic nerve sheath diameter in the pediatric age group. [J Pediatr Ophthalmol Strabismus. 2024;61(1):38-43.].

Additional predictive value of optic nerve sheath diameter for neurological prognosis after cardiac arrest: a prospective cohort study

BACKGROUND

The goal is to estimate the additional value of ultrasonographic optic nerve sheath diameter (ONSD) measurement on days 1-3, on top of electroencephalography (EEG), pupillary light reflexes (PLR), and somatosensory evoked potentials (SSEP), for neurological outcome prediction of comatose cardiac arrest patients. We performed a prospective longitudinal cohort study in adult comatose patients after cardiac arrest. ONSD was measured on days 1-3 using ultrasound. Continuous EEG, PLR, and SSEP were acquired as standard care. Poor outcome was defined as cerebral performance categories 3-5 at 3-6 months. Logistic regression models were created for outcome prediction based on the established predictors with and without ONSD. Additional predictive value was assessed by increase in sensitivity for poor (at 100% specificity) and good outcome (at 90% specificity).

RESULTS

We included 100 patients, 54 with poor outcome. Mean ONSD did not differ significantly between patients with good and poor outcome. Sensitivity for predicting poor outcome increased by adding ONSD to EEG and SSEP from 25% to 41% in all patients and from 27% to 50% after exclusion of patients with non-neurological death.

CONCLUSIONS

ONSD on days 1-3 after cardiac arrest holds potential to add to neurological outcome prediction.

TRIAL REGISTRATION

clinicaltrials.gov, NCT04084054. Registered 10 September 2019, https://www.

CLINICALTRIALS

gov/study/NCT04084054 .

B-mode transorbital ultrasonography for the diagnosis of idiopathic intracranial hypertension: an updated systematic review and meta-analysis

OBJECTIVES

This systematic review and meta-analysis aimed to evaluate the role of B-mode transorbital ultrasonography (TOS) for the diagnosis of idiopathic intracranial hypertension (IIH) in adults.

METHODS

MEDLINE, EMBASE, and Cochrane Central Register of Controlled Trials (CENTRAL) (1966-May 2022) were searched to identify studies reporting ultrasonographic data about the optic nerve sheath diameter (ONSD) and optic disc elevation (ODE) in adults with IIH compared to subjects without IIH. The quality of the included studies was evaluated by the Newcastle-Ottawa Quality.

RESULTS

Fifteen studies were included (total of 439 patients). The values of ODE ranged from 0.6 to 1.3 mm in patients with IIH. The values of ONSD ranged from 4.7 to 6.8 mm in IIH patients and from 3.9 to 5.7 mm in controls. In IIH patients, the ONSD was significantly higher compared to controls (standardized mean difference: 2.5 mm, 95% confidence interval (CI): 1.6-3.4 mm). Nine studies provided data about the presence of papilledema and the pooled prevalence was 95% (95% CI, 92-97%).

CONCLUSIONS

In adults, the thickness of ONSD and the entity of ODE were significantly associated with IIH. B-mode TOS enables to noninvasively detect increased ICP and should be performed, potentially routinely, in any patient with suspected IIH.

The role of optic nerve sheath ultrasonography in increased intracranial pressure: A systematic review and meta analysis

OBJECTIVES

To review the optimal diagnostic cut-off of ultrasonographic optic nerve sheath diameter (ONSD) in the diagnosis of increased intracranial pressure (IICP).

METHODS

A systematic search was conducted of available studies assessing the use of ONSD ultrasonography in patients with suspected IICP. Meta-analysis of diagnostic accuracy of ultrasonographic ONSD was performed using a bivariate model of random effects to summarize pooled sensitivity and specificity. A summary receiver operating characteristics (SROC) curve was plotted. Accuracy measures associated with ONSD cut-off and predefined covariates were investigated with meta-regression.

RESULTS

We included 38 studies, comprising a total of 2824 patients. A total of 21 studies used invasive techniques as a reference standard estimation of IICP and meta-analysis revealed a pooled sensitivity of 0.90 (95% CI 0.85-0.93) and specificity of 0.87 (95% CI 0.80-0.91). Optimal ONSD cut-off values ranged between 4.1 mm and 7.2 mm. Meta-regression analysis showed that ONSD cut-off values of 5.6 to 6.3 mm were associated with higher pooled specificity compared to cut-off values of 4.9 to 5.5 mm (0.93, 95% CI 0.85-0.97 vs. 0.78, 95% CI 0.65-0.87; p = 0.036).

CONCLUSIONS

Ultrasonography of ONSD shows a high diagnostic accuracy for IICP, with high pooled sensitivity and specificity. Additionally, larger cut-off values seem to significantly increase specificity without compromising sensitivity, which support their use as optimal ONSD cut-off. The overall high sensitivity of ultrasonographic ONSD suggests its usefulness as a screening tool for IIC, which may provide an estimate of when invasive methods are warranted.

CLINICAL RELEVANCE

ONSD ultrasonography is a fast and cost-effective method with a high diagnostic accuracy to detect IICP. The optimum ONSD cut-off hasn't been established before, but we suggest the 5.6 to 6.3 mm range as the best for the diagnosis of IICP.

Automation of ultrasonographic optic nerve sheath diameter measurement using convolutional neural networks

BACKGROUND AND PURPOSE

Ultrasonographic optic nerve sheath (ONS) diameter is a noninvasive intracranial pressure (ICP) surrogate. ICP is monitored invasively in specialized intensive care units. Noninvasive ICP monitoring is important in less specialized settings. However, noninvasive ICP monitoring using ONS diameter (ONSD) is limited by the need for experts to obtain and perform measurements. We aim to automate ONSD measurements using a deep convolutional neural network (CNN) with a novel masking technique.

METHODS

We trained a CNN to reproduce masks that mark the ONS. The edges of the mask are defined by an expert. Eight models were trained with 1000 epochs per model. The Dice-similarity-coefficient-weighted averaged outputs of the eight models yielded the final predicted mask. Eight hundred and seventy-three images were obtained from 52 transorbital cine-ultrasonography sessions, performed on 46 patients with brain injuries. Eight hundred and fourteen images from 48 scanning sessions were used for training and validation and 59 images from four sessions for testing. Bland-Altman and Pearson linear correlation analyses were used to evaluate the agreement between CNN and expert measurements.

RESULTS

Expert ONSD measurements and CNN-derived ONSD estimates had strong agreement (r = 0.7, p < .0001). The expert mean ONSD (standard deviation) is 5.27 mm (0.43) compared to CNN mean estimate of 5.46 mm (0.37). Mean difference (95% confidence interval, p value) is 0.19 mm (0.10-0.27 mm, p = .0011), and root mean square error is 0.27 mm.

CONCLUSION

A CNN can learn ONSD measurement using masking without image segmentation or landmark detection.

Optic Nerve Diameter on Non-Contrast Computed Tomography and Intracranial Hypertension in Patients With Acute Brain Injury: A Validation Study

Intracranial hypertension is a feared complication of acute brain injury that can cause ischemic stroke, herniation, and death. Identifying those at risk is difficult, and the physical examination is often confounded. Given the widespread availability and use of computed tomography (CT) in patients with acute brain injury, prior work has attempted to use optic nerve diameter measurements to identify those at risk of intracranial hypertension. We aimed to validate the use of optic nerve diameter measurements on CT as a screening tool for intracranial hypertension in a large cohort of brain-injured patients. We performed a retrospective observational cohort study in a single tertiary referral Neuroscience Intensive Care Unit. We identified patients with documented intracranial pressure (ICP) measures as part of their routine clinical care who had non-contrast CT head scans collected within 24 h, and then measured the optic nerve diameters and explored the relationship and test characteristics of these measures to identify those at risk of intracranial hypertension. In a cohort of 314 patients, optic nerve diameter on CT was linearly but weakly associated with ICP. When used to identify those with intracranial hypertension (> 20 mm Hg), the area under the receiver operator curve (AUROC) was 0.68. Using a previously proposed threshold of 0.6 cm, the sensitivity was 81%, specificity 43%, positive likelihood ratio 1.4, and negative likelihood ratio 0.45. CT-derived optic nerve diameter using a threshold of 0.6 cm is sensitive but not specific for intracranial hypertension, and the overall correlation is weak.

Effects of head-down tilt on optic nerve sheath diameter in healthy subjects

PURPOSE

Intracranial pressure increases in head-down tilt (HDT) body posture. This study evaluated the effect of HDT on the optic nerve sheath diameter (ONSD) in normal subjects.

METHODS

Twenty six healthy adults (age 28 [4.7] years) participated in seated and 6° HDT visits. For each visit, subjects presented at 11:00 h for baseline seated scans and then maintained a seated or 6° HDT posture from 12:00 to 15:00 h. Three horizontal axial and three vertical axial scans were obtained at 11:00, 12:00 and 15:00 h with a 10 MHz ultrasonography probe on the same eye, randomly chosen per subject. At each time point, horizontal and vertical ONSD (mm) were quantified by averaging three measures taken 3 mm behind the globe.

RESULTS

In the seated visit, ONSDs were similar across time (p > 0.05), with an overall mean (standard deviation) of 4.71 (0.48) horizontally and 5.08 (0.44) vertically. ONSD was larger vertically than horizontally at each time point (p < 0.001). In the HDT visit, ONSD was significantly enlarged from baseline at 12:00 and 15:00 h (p < 0.001 horizontal and p < 0.05 vertical). Mean (standard error) horizontal ONSD change from baseline was 0.37 (0.07) HDT versus 0.10 (0.05) seated at 12:00 h (p = 0.002) and 0.41 (0.09) HDT versus 0.12 (0.06) seated at 15:00 h (p = 0.002); mean vertical ONSD change was 0.14 (0.07) HDT versus -0.07 (0.04) seated at 12:00 h (p = 0.02) and 0.19 (0.06) HDT versus -0.03 (0.04) seated at 15:00 h (p = 0.01). ONSD change in HDT was similar between 12:00 and 15:00 h (p ≥ 0.30). Changes at 12:00 h correlated with those at 15:00 h for horizontal (r = 0.78, p < 0.001) and vertical ONSD (r = 0.73, p < 0.001).

CONCLUSION

The ONSD increased when body posture transitioned from seated to HDT position without any further change at the end of the 3 h in HDT.

Diagnostic Value of the Combination of Ultrasonographic Optic Nerve Sheath Diameter and Width of Crural Cistern with Respect to the Intracranial Pressure in Patients Treated with Decompressive Craniotomy

BACKGROUND

The monitoring of intracranial pressure (ICP) and detection of increased ICP are crucial because such increases may cause secondary brain injury and a poor prognosis. Although numerous ultrasound parameters, including optic nerve sheath diameter (ONSD), width of the crural cistern (WCC), and the flow velocities of the central retinal artery and middle cerebral artery, can be measured in patients after hemicraniectomy, researchers have yet to determine which of these is better for evaluating ICP. This study aimed to analyze the correlation between ICP and ultrasound parameters and investigate the best noninvasive estimator of ICP.

METHODS

This observational study enrolled 50 patients with brain injury after hemicraniectomy from January 2021 to December 2021. All patients underwent invasive ICP monitoring with microsensor, transcranial, and ocular ultrasound postoperatively. We measured the ONSD including the dura mater (ONSDI), the ONSD excluding the dura mater, the optic nerve diameter (OND), the eyeball transverse diameter (ETD), the WCC, and the flow velocities in the central retinal artery and middle cerebral artery. Then, we calculated the ONSDI-OND (the difference between ONSDI and OND) and ONSDI/ETD (the ratio of ONSDI to ETD). Patients were divided into a normal ICP group (n = 35) and an increased ICP group (≥ 20 mm Hg, n = 15) according to the ICP measurements. Correlations were then assessed between the values of the ultrasound parameters and ICP.

RESULTS

The ONSDI, ONSDI-OND, and ONSDI/ETD were positively associated with ICP (r = 0.455, 0.482, 0.423 and p = 0.001, < 0.001, 0.002, respectively), whereas the WCC was negatively associated with ICP (r = - 0.586, p < 0.001). The WCC showed the highest predictive power for increased ICP (area under the receiver operating characteristic curve [AUC] = 0.904), whereas the ONSDI-OND and ONSDI also presented with acceptable predictive power among the ONSD-related parameters (AUC = 0.831, 0.803, respectively). The cutoff values for increased ICP prediction for ONSDI, ONSDI-OND, and WCC were 6.29, 3.03, and 3.68 mm, respectively. The AUC of the combination of ONSDI-OND and WCC was 0.952 (95% confidence interval 0.896-1.0, p < 0.001).

CONCLUSIONS

The ONSDI, ONSDI-OND, and WCC were correlated with ICP and had acceptable accuracy levels in estimating ICP in patients after hemicraniectomy. Furthermore, WCC showed a higher diagnostic value than ONSD-related parameters, and the combination of ONSDI-OND and WCC was a satisfactory predictor of increased ICP.

Optic Nerve Sheath Diameter: A Cross-Sectional Study of Ultrasonographic Measurement in Healthy Black South African Adults

Ultrasonographic optic nerve sheath diameter (ONSD) measurement is an accurate, portable, and non-invasive method of detecting raised intracranial pressure that can also reflect dynamic, real-time changes in intracranial pressure fluctuations. Various studies have shown the mean range of ONSD to vary greatly across different population groups. This study aimed to determine the mean ONSD in healthy Black South African adults. In this cross-sectional study, healthy black South African adult participants underwent optic nerve sheath ultrasound of the right eye, with the diameter being measured at 3 mm behind the retina in two different planes. The average of the two measurements was used to find the mean optic nerve sheath diameter. This measurement was compared to that found in a Canadian adult population, and the effect of age, gender, and co-morbidities on ONSD was assessed. A total of 99 participants were included in this study, of which 39 were male and 60 were female. The mean ONSD was found to be 5.1 mm (SD ± 0.33). This value was significantly higher than the mean ONSD observed in the Canadian population (p < 0.001). There was no significant difference found between the mean ONSD in males and females (p = 0.652), and both age and presence of co-morbidities were not found to significantly correlate with ONSD. (p = 0.693 and p = 0.974, respectively).

Effect of paediatric caudal injection volume on optic nerve sheath diameter and regional cerebral oximetry: A randomised trial

BACKGROUND

Caudal injections commonly used for neuraxial anaesthesia in children can displace cerebrospinal fluid cranially causing safety concerns in terms of raised intracranial pressure. Optic nerve sheath diameter (ONSD) is a noninvasive surrogate for the measurement of intracranial pressure. Regional cerebral oximetry (CrSO 2 ) can monitor brain oxygenation, which may decrease by a reduction in cerebral flow due to increased intracranial pressure.

OBJECTIVES

Comparing how caudal injection volumes of 0.8 and 1.25 ml kg -1 influence ONSD and CrSO 2 within the first 30 min after injection.

DESIGN

Prospective, randomised and parallel group trial.

SETTING

Operating room.

PATIENTS

Fifty-eight elective paediatric surgical patients between ages 1 and 7 years old, ASA class I or II, without previous intracranial or ocular pathology and surgery appropriate for single - shot caudal anaesthesia.

INTERVENTION

Single-shot caudal anaesthesia with 0.8 ml kg -1 (group L, n  = 29) and 1.25 ml kg -1 (group H, n  = 29) of 2 mg kg -1 bupivacaine solution.

MAIN OUTCOME MEASURES

Optic nerve sheath diameter measured with ultrasonography and regional cerebral oximetry measured by near - infrared spectroscopy before (NIRS), immediately after, 10, 20 and 30 min after the block.

RESULTS

Mean ONSD values increased from a baseline of 4.4 ± 0.2 mm to a maximum of 4.5 ± 0.2 mm 20 min after injection in group L and from a baseline of 4.5 ± 0.3 mm to a maximum of 4.8 ± 0.3 mm 10 min after injection in group H. Eight of 29 patients in group H and none in group L had an ONSD increase by more than 10%. Both groups had a reduction of less than 2.5% in CrSO 2 .

CONCLUSION

Caudal injection with 1.25 ml kg -1 increased ONSD, an indirect measurement of ICP, more than 0.8 ml kg -1 and neither volume caused a clinically important reduction in CrSO 2 .

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04491032.

Optic Nerve Sheath Diameter in Hyponatremia: A Closer Look

How to cite this article: Jose J, Suresh V, Magoon R. Optic Nerve Sheath Diameter in Hyponatremia: A Closer Look. Indian J Crit Care Med 2023;27(6):452.

Transorbital Ultrasonography Used to Detect Papilledema, in a Patient With Intracranial Hypertension

Intracranial hypertension (IH) is an important cause of secondary brain injury, and it is often associated with poor outcomes; due to that monitoring of intracranial pressure (ICP) is essential for the management of neurocritical patients. Although invasive methods have been the gold standard for ICP monitoring, recent non-invasive ultrasonography techniques have been used to estimate ICP. Among the most used methods are the measurement of the diameter of the optic nerve sheath and transorbital ultrasonography to evaluate papilledema. This presented case is of a patient with refractory IH due to subarachnoid hemorrhage, measured through an intraventricular catheter. A transorbital sonogram was performed and showed the presence of papilledema.

Optic Nerve Sheath Diameter and Sodium Levels: A Friend of a Friend is Still a Stranger

How to cite this article: Arunachala S. Optic Nerve Sheath Diameter and Sodium Levels: A Friend of a Friend is Still a Stranger. Indian J Crit Care Med 2023;27(4):235-236.

Management of traumatic brain injury in the non-neurosurgical intensive care unit: a narrative review of current evidence

Each year, approximately 70 million people suffer traumatic brain injury, which has a significant physical, psychosocial and economic impact for patients and their families. It is recommended in the UK that all patients with traumatic brain injury and a Glasgow coma scale ≤ 8 should be transferred to a neurosurgical centre. However, many patients, especially those in whom neurosurgery is not required, are not treated in, nor transferred to, a neurosurgical centre. This review aims to provide clinicians who work in non-neurosurgical centres with a summary of contemporary studies relevant to the critical care management of patients with traumatic brain injury. A targeted literature review was undertaken that included guidelines, systematic reviews, meta-analyses, clinical trials and randomised controlled trials (published in English between 1 January 2017 and 1 July 2022). Studies involving key clinical management strategies published before this time, but which have not been updated or repeated, were also eligible for inclusion. Analysis of the topics identified during the review was then summarised. These included: fundamental critical care management approaches (including ventilation strategies, fluid management, seizure control and osmotherapy); use of processed electroencephalogram monitoring; non-invasive assessment of intracranial pressure; prognostication; and rehabilitation techniques. Through this process, we have formulated practical recommendations to guide clinical practice in non-specialist centres.

A Narrative Review of Point of Care Ultrasound Assessment of the Optic Nerve in Emergency Medicine

Point of care ultrasound (POCUS) of the optic nerve is easy to learn and has great diagnostic potential. Within emergency medicine, research has primarily focused on its use for the assessment of increased intracranial pressure, but many other applications exist, though the literature is heterogeneous and largely observational. This narrative review describes the principles of POCUS of the optic nerve including anatomy and scanning technique, as well as a summary of its best studied clinical applications of relevance in emergency medicine: increased intracranial pressure, idiopathic intracranial hypertension, optic neuritis, acute mountain sickness, and pediatric intracranial pressure assessment. In many of these applications, sonographic optic nerve sheath diameter (ONSD) has moderately high sensitivity and specificity, but the supporting studies are heterogeneous. Further studies should focus on standardization of the measurement of ONSD, establishment of consistent diagnostic thresholds for elevated intracranial pressure, and automation of ONSD measurement.

Ultrasonographic measurement of the optic nerve sheath diameter to detect intracranial hypertension: an observational study

OBJECTIVES

To evaluate the ultrasonographic measurement of optic nerve sheath diameter (ONSD) as a predictor of intracranial hypertension as compared to the invasive measurement of intracranial pressure (ICP).

DESIGN

Cross-sectional observational study.

SETTING

Intensive Care Unit (ICU) of two tertiary university hospitals in Montevideo, Uruguay.

PATIENTS

We included 56 adult patients, over 18 years of age, who required sedation, mechanical ventilation, and invasive ICP monitoring as a result of a severe acute neurologic injury (traumatic or non-traumatic) and had a Glascow Coma Score (GCS) equal to or less than 8 on admission to the ICU.

INTERVENTIONS

Ultrasonographic measurement of ONSD to detect intracranial hypertension.

MEASUREMENTS AND MAIN RESULTS

In our study, a logistic regression model was performed in which it was observed that the variable ONSD is statistically significant with a p value of 0.00803 (< 0.05). This model estimates and predicts the probability that a patient will have an ICP greater than 20 mmHg. From the analysis of the cut-off points, it is observed that a value of 5.7 mm of ONSD maximizes the sensitivity (92.9%) of the method (a greater number of individuals with ICP > 20 mmHg are correctly identified).

CONCLUSIONS

In sedated neurocritical patients, with structural Acute Brain Injury, the ONSD measurement correlates with the invasive measurement of ICP. It was observed that with ONSD values less than 5.7 mm, the probability of being in the presence of ICP above 20 mmHg is very low, while for ONSD values greater than 5.7 mm, said probability clearly increases.

Diagnostic Ultrasonography in Neurology

OBJECTIVE

Ultrasonography allows neurologists to complement clinical information with additional useful, easily acquired, real-time data. This article highlights its clinical applications in neurology.

LATEST DEVELOPMENTS

Diagnostic ultrasonography is expanding its applications with smaller and better devices. Most indications in neurology relate to cerebrovascular evaluations. Ultrasonography contributes to the etiologic evaluation and is helpful for hemodynamic diagnosis of brain or eye ischemia. It can accurately characterize cervical vascular atherosclerosis, dissection, vasculitis, or other rarer disorders. Ultrasonography can aid in the diagnosis of intracranial large vessel stenosis or occlusion and evaluation of collateral pathways and indirect hemodynamic signs of more proximal and distal pathology. Transcranial Doppler (TCD) is the most sensitive method for detecting paradoxical emboli from a systemic right-left shunt such as a patent foramen ovale. TCD is mandatory for sickle cell disease surveillance, guiding the timing for preventive transfusion. In subarachnoid hemorrhage, TCD is useful in monitoring vasospasm and adapting treatment. Some arteriovenous shunts can be detected by ultrasonography. Cerebral vasoregulation studies are another developing field of interest. TCD enables monitoring of hemodynamic changes related to intracranial hypertension and can diagnose cerebral circulatory arrest. Optic nerve sheath measurement and brain midline deviation are ultrasonography-detectable signs of intracranial hypertension. Most importantly, ultrasonography allows for easily repeated monitoring of evolving clinical conditions or during and after interventions.

ESSENTIAL POINTS

Diagnostic ultrasonography is an invaluable tool in neurology, used as an extension of the clinical examination. It helps diagnose and monitor many conditions, allowing for more data-driven and rapid treatment interventions.

Optic nerve sheath diameter in intracranial hypertension: Measurement external or internal of the dura mater?

BACKGROUND AND PURPOSE

Optic nerve sheath diameter (ONSD) is a promising metric to estimate intracranial pressure (ICP). There is no consensus whether ONSD should be measured external (ONSDext) or internal (ONSDint) of the dura mater. Expert opinion favors ONSDint, though without clear evidence to support this. Adjustments of ONSD for eye diameter (ED) and optic nerve diameter (OND) have been suggested to improve precision. We examined the diagnostic accuracy of ONSDext and ONSDint for estimating ICP, unadjusted as well as adjusted for ED and OND.

METHODS

We performed an observational cohort study, measuring ONSDext and ONSDint in patients with invasive ICP monitoring at Karolinska University Hospital in Stockholm, Sweden. We used ONSDext and ONSDint unadjusted as well as adjusted for ED and for OND. We compared the area under the receiver operator characteristics curve (AUROC) for these methods. Thresholds for elevated ICP were set at ≥20 and ≥22 mmHg, respectively.

RESULTS

We included 220 measurements from 100 patients. Median ONSDext and ONSDint were significantly different at 6.7 and 5.2 mm (p = .00). There was no significant difference in AUROC for predicting elevated ICP between ONSDext and ONSDint (.67 vs. .64, p = .31). Adjustment for ED yielded better diagnostic accuracy (AUROC, cutoff, sensitivity, specificity) for ONSDext/ED (.76, .29, .81, .62) and ONSDint/ED (.71, .24, .5, .89).

CONCLUSIONS

ONSDext and ONSDint differ significantly and are not interchangeable. However, there were no significant differences in diagnostic accuracy between ONSDext and ONSDint. Adjustment for ED may improve diagnostic accuracy of ONSD.

The CLOSED protocol to assess optic nerve sheath diameter using color-Doppler: a comparison study in a cohort of idiopathic normal pressure hydrocephalus patients

BACKGROUND

Sonographic assessment of the optic nerve sheath diameter represents a promising non-invasive technique for estimation of the intracranial pressure. A wide inter-observer variability, along with a lack of a standardized protocol for the optic nerve sheath diameter measurements, could lead to over- or under-estimation. The present study was aimed at evaluating feasibility of color-Doppler for better delineating optic nerve sheath borders, comparing it to B-mode imaging, using the magnetic resonance measurements as a comparison.

METHODS

Optic nerve sheath diameters were evaluated using magnetic resonance by an expert radiologist in a cohort of patients with suspected idiopathic normal pressure hydrocephalus. Magnetic resonance findings were evaluated twice. In the first half of this cohort, optic nerve sheath diameters were measured using B-mode only, in the second half applying color-Doppler. Measurements obtained using these two techniques were compared to magnetic resonance imaging measurements. The Bland-Altman analysis and concordance correlation coefficient were computed to quantify the strength of agreement between the two magnetic resonance assessments. Box plots and average (± SD) were used to compare assessments by sonographic and magnetic resonance methods.

RESULTS

Fifty patients were included. MRI assessment showed a moderate concordance correlation coefficient. Optic nerve sheath diameters measured applying color-Doppler were lower (p < 0.001) and less scattered compared to B-mode assessment, which approached more to magnetic resonance measurements.

CONCLUSIONS

In this cohort of patients, magnetic resonance showed high intra-rater variability in optic nerve sheath diameter assessments. Optic nerve sheath diameter assessments using color-Doppler yielded lower and less scattered diameters compared to B-mode only.

Quality assessment of optic nerve sheath diameter ultrasonography: Scoping literature review and Delphi protocol

BACKGROUND AND PURPOSE

The optic nerve is surrounded by the extension of meningeal coverings of the brain. When the pressure in the cerebrospinal fluid increases, it causes a distention of the optic nerve sheath diameter (ONSD), which allows the use of this measurement by ultrasonography (US) as a noninvasive surrogate of elevated intracranial pressure. However, ONSD measurements in the literature have exhibited significant heterogeneity, suggesting a need for consensus on ONSD image acquisition and measurement. We aim to establish a consensus for an ONSD US Quality Criteria Checklist (ONSD US QCC).

METHODS

A scoping systematic review of published ultrasound ONSD imaging and measurement criteria was performed to guide the development of a preliminary ONSD US QCC that will undergo a modified Delphi study to reach expert consensus on ONSD quality criteria. The protocol of this modified Delphi study is presented in this manuscript.

RESULTS

A total of 357 ultrasound studies were included in the review. Quality criteria were evaluated under five categories: probe selection, safety, positioning, image acquisition, and measurement.

CONCLUSIONS

This review and Delphi protocol aim to establish ONSD US QCC. A broad consensus from this process may reduce the variability of ONSD measurements in future studies, which would ultimately translate into improved ONSD clinical applications. This protocol was reviewed and endorsed by the German Society of Ultrasound in Medicine.

Transorbital sonography: A non-invasive bedside screening tool for detection of pseudotumor cerebri syndrome

BACKGROUND

Our objective was to assess optic nerve sheath diameter (a marker of elevated intracranial pressure) and optic disc elevation (a marker of papilledema) in pseudotumor cerebri syndrome using transorbital sonography.

METHODS

The study was a prospective case-control study. We included patients with new-onset pseudotumor cerebri syndrome and matched healthy controls. All had fundoscopy, lumbar puncture with opening pressure and transorbital sonography. Sonography was assessed by a blinded observer.

RESULTS

We evaluated 45 patients and included 23 cases. We recruited 35 controls. Optic nerve sheath diameter was larger in pseudotumor cerebri syndrome compared to controls (6.3 ± 0.9 mm versus 5.0 ± 0.5 mm, p < 0.001) and so was optic disc elevation (0.9 ± 0.4 mm versus 0.4 ± 0.1 mm, p < 0.001). The optimal cut-off point for optic nerve sheath diameter was 6 mm with a sensitivity of 74% for prediction of pseudotumor cerebri syndrome and 68% for prediction of elevated opening pressure. Specificity was 94%. The optimal cut-off point for optic disc elevation was 0.6 mm. Sensitivity was 100% and specificity 83% for prediction of pseudotumor cerebri syndrome.

CONCLUSION

Optic disc elevation and optic nerve sheath diameter are increased in new-onset pseudotumor cerebri syndrome. Optic disc elevation achieved high specificity and excellent sensitivity for diagnosis of pseudotumor cerebri syndrome. Transorbital sonography (TOS) is a potential, non-invasive screening tool for pseudotumor cerebri syndrome in headache clinics.

Accuracy of Optic Nerve Sheath Diameter Measurements in Pocket-Sized Ultrasound Devices in a Simulation Model

Introduction

Transorbital sonographic measurement of optic nerve sheath diameter (ONSD) is an emerging non-invasive technique for the identification and monitoring of intracranial hypertension. In recent years, new pocket ultrasound devices have become available, and it is uncertain if they have the resolution to measure such small structures appropriately as compared to their predecessors. In this study, we measure the performance of three ultrasound units on a simulation model to establish their precision and accuracy.

Methods

ONSD was measured by three expert point-of-care sonographers using ultrasound machines three times on each of seven discrete ONS model sizes ranging from 3.5 to 7.9 mm. Two pocket ultrasounds (IVIZ, Sonosite, and Lumify, Philips) and one standard-sized portable ultrasound (M-Turbo, Sonosite) were used. Measurements were analyzed for mean error and variance and tested for significance using blocked covariance matrix regression analyses.

Results

The devices differed in their variances (Lumify: 0.19 mm², M-Turbo: 0.26 mm², IVIZ: 0.34 mm²) and their mean error (Lumify: -0.05 mm, M-Turbo: 0.10 mm, IVIZ: -0.10 mm). The difference in mean error between users is not significant (p = 0.45), but there is a significant difference in mean error between devices (p = 0.02).

Conclusions

Accurate ONSD measurement is possible utilizing pocket-sized ultrasound, and in some cases, may be more accurate than larger portable ultrasound units. While the differences in these devices were statistically significant, all three were highly accurate, with one pocket device (Lumify) outperforming the rest. Further study in human subjects should be conducted prior to using pocket ultrasound devices for in vivo diagnosis of intracranial hypertension.

Comparing ultrasonographic optic nerve sheath diameter to head computed tomography scan to predict intracranial pressure elevation

Introduction:

Intracranial hypertension is an emergency condition that needs to be recognized as soon as possible. Lumbar puncture, the gold standard diagnostic procedure for intracranial hypertension, is contraindicated in some conditions while brain imaging procedures may be too difficult to be performed on critically ill patients. To solve this problem, this study aims to assess an alternative method to detect intracranial hypertension by measuring optic nerve sheath diameter using ocular ultrasound and optic nerve sheath diameter difference in each etiology.

Methods:

This cross-sectional study was conducted at the Emergency Department of Dr Iskak Tulungagung General Hospital. Sixty-nine patients who visited the emergency room for the first onset of intracranial pathology were included for optic nerve sheath diameter measurement by ultrasound. Subjects were divided into elevated and non-elevated intracranial pressure groups based on head computed tomography scan findings. The optic nerve sheath diameter results were compared and analyzed.

Result:

There were 29 subjects in the elevated intracranial pressure group and 40 subjects in the non-elevated intracranial pressure group. The mean of optic nerve sheath diameter in the elevated and non-elevated intracranial pressure groups was 0.63 ± 0.06 and 0.57 ± 0.06 cm, respectively (p = 0.000). Based on receiver operating characteristics analysis, 0.58 cm was the most optimal cut-off value.

Conclusion:

Ultrasonographic optic nerve sheath diameter can be used to predict elevated intracranial pressure in suspected patients who are contraindicated to invasive intracranial pressure measurement or critically ill. There were significant differences between elevated and non-elevated intracranial pressure groups in stroke and trauma subjects.

Predictive Value of Optic Nerve Sheath Diameter for Diagnosis of Intracranial Hypertension in Children With Severe Brain Injury

BACKGROUND AND AIMS

Intracranial Hypertension (ICH) is a life-threatening complication of brain injury. The invasive measurement of intracranial pressure (ICP) remains the gold standard to diagnose ICH. Measurement of Optic Nerve Sheath Diameter (ONSD) using ultrasonography is a non-invasive method for detecting ICH. However, data on paediatric brain injury are scarce. The aim of the study was to determine the performance of the initial ONSD measurement to predict ICH occurring in children with severe brain injury and to describe the ONSD values in a control group.

METHODS

In this cross-sectional study, ONSD was measured in children aged 2 months-17 years old with invasive ICP monitoring: before placement of ICP probe and within the 60 min after, and then daily during 3 days. ONSD was also measured in a control group.

RESULTS

Ninety-nine patients were included, of whom 97 were analysed, with a median (IQR) age of 8.7 [2.3-13.6] years. The median (IQR) PIM 2 score was 6.6 [4.4-9.7] and the median (IQR) PELOD score was 21 [12-22]. Aetiologies of brain injury were trauma (n = 72), infection (n = 17) and stroke (n = 8). ICH occurred in 65 children. The median (IQR) ONSD was 5.58 mm [5.05-5.85]. ONSD performed poorly when it came to predicting ICH occurrence within the first 24 h (area under the curve, 0.58). There was no significant difference between the ONSD of children who presented with ICH within the first 24 h and the other children, with a median (IQR) of 5.6 mm [5.1-5.9] and 5.4 mm [4.9-5.8], respectively. Infants aged less than 2 years had a median (IQR) ONSD of 4.9 mm [4.5-5.2], significantly different from children aged more than 2 years, whose median ONSD was 5.6 mm [5.2-5.9]. Age, aetiology or ICP levels did not change the results. Thirty-one controls were included, with a median age of 3.7 (1.2-8.8) years. The median (IQR) of their ONSD measurement was 4.5 mm [4.1-4.8], significantly lower than the patient group.

CONCLUSION

In a paediatric severe brain injury population, ONSD measurement could not predict the 24 h occurrence of ICH. Severity of patients, timing and conditions of measurements may possibly explain these results.

Optic nerve sheath diameter measurement by ultrasound: Evaluation of a standardized protocol

BACKGROUND AND PURPOSE

Treatment of elevated intracranial pressure (ICP) is central to neurocritical care, but not all patients are eligible for invasive ICP-monitoring. A promising noninvasive option is ultrasound measurement of the optic nerve sheath diameter (ONSD). However, meta-analyses of ONSD for elevated ICP show wide confidence intervals. This might be due to baseline variations, inter-rater variability, and varying measurement methods. No standardized protocol has been validated. Corrections for eyeball diameter (ED) and optic nerve diameter (OND) may compensate for baseline variations. We evaluated a protocol and compared two different measurement methods for ONSD ultrasound.

METHODS

Two operators, blinded to each other's measurements, measured ONSD, ED, and OND twice in 20 patients. ONSD was measured with two different methods in use: internal (ONSDint) or external (ONSDext) of the dura mater. Intra-class correlation (ICC) was calculated for inter-rater and intra-rater reliability.

RESULTS

ICCs for inter-rater reliability of ONSDext and ONSDint (95% confidence interval) were 0.96 (0.93, 0.98) and 0.88 (0.79, 0.94), respectively. ICCs for intra-rater reliability of ONSDext and ONSDint were 0.97 (0.94, 0.99) and 0.93 (0.87, 0.96), respectively. There was no significant bias or difference in intra-rater reliability between operators.

CONCLUSIONS

ONSD can be measured with an excellent inter- and intra-rater reliability and low risk of inter-rater bias, when using this protocol. ONSDext yields a higher inter- and intra-rater reliability than ONSDint. Corrections for ED and OND can be performed reliably.