Quantification of Optic Nerve and Sheath Diameter by Transorbital Sonography: A Systematic Review and Metanalysis

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.

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.

Transorbital sonography in idiopathic intracranial hypertension: Single-center study, systematic review and meta-analysis

BACKGROUND AND PURPOSE

Transorbital sonography (TOS) provides a noninvasive tool to detect intracranial pressure by assessing optic nerve sheath diameter (ONSD) and optic disc elevation (ODE). The utility of TOS in the diagnosis of idiopathic intracranial hypertension (IIH) has been increasingly recognized.

METHODS

A single-center case-control study sought to compare TOS-acquired ONSD and ODE among IIH-cases versus patients with other neurological diseases (controls). Furthermore, a systematic review and meta-analysis was conducted to present pooled mean differences and diagnostic measures of ONSD and ODE between IIH-cases and controls.

RESULTS

In the single-center study, consisting of 31 IIH-cases and 34 sex- and age-matched controls, ONSD values were higher among IIH-cases than controls (p<.001), while ODE was more prevalent in cases (65% vs. 15%; p<.001). The receiver-operating characteristic (ROC)-curve analysis revealed that the optimal cutoff value of ONSD for predicting IIH was 5.15 mm, with an area under the curve (AUC) of 0.914 (95% confidence interval [CI]: 0.861-0.967) and sensitivity and specificity values of 85% and 90%, respectively. In a meta-analysis of 14 included studies with 415 IIH-cases, ONSD and ODE values were higher in IIH-cases than controls (mean difference in ONSD 1.20 mm; 95% CI: 0.96-1.44 mm and in ODE 0.3 mm; 95% CI: 0.33-0.67 mm). With regard to ONSD, pooled sensitivity, specificity, and diagnostic odds ratio were calculated at 85.5% (95% CI: 77.9-90.8%), 90.7% (95% CI: 84.6-94.5%), and 57.394 (95% CI: 24.597-133.924), respectively. The AUC in summary ROC-curve analysis was 0.878 (95% CI: 0.858-0.899) with an optimal cutoff point of 5.0 mm.

CONCLUSIONS

TOS has a high diagnostic utility for the noninvasive diagnosis of IIH and may deserve wider implementation in everyday clinical practice.

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.

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).

Ultrasound measurement of optic nerve sheath diameter in a healthy adult Colombian population

BACKGROUND

Measurement of the optic nerve sheath diameter (ONSD) provides a rapid, safe, and easy method for detecting increased intracranial pressure (ICP). However, the normal mean and upper limit values may vary according to sex, age, ethnicity, and ultrasound technique.

AIM

We aimed to obtain the mean ONSD in a healthy Colombian adult population and to correlate it with demographic and anthropometric measures.

METHODS

In a prospective study using a 10-13 MHz linear ultrasound probe, eye transverse diameter (ETD) and ONSD in the transverse (ONSD-TP) and sagittal planes (ONSD-SP) were measured in healthy adult volunteers in Bogota, Colombia.

RESULTS

A total of 100 healthy subjects were included, with a mean age of 26,7 ± 8,3 years and 62 women. The mean ETD, ONSD-TP and ONSD-SP was 23.11 mm (95% confidence interval (CI): 22.90 mm-23.32 mm), 3.96 mm (95% CI: 3.85 mm-4.07 mm) and 4.0 mm (95% CI: 3.90 mm-4.11 mm), respectively. The ONSD in both planes ranged from 2.35 mm to 5.20 mm. There was a significant correlation between ONSD-SP and ONSD-TP (p < 0.0001) but no correlation between the ocular measures and demographic or anthropometric variables (p > 0.05). The intraclass correlation between the eyes was statistically significant.

CONCLUSION

Our study shows that ultrasound-measured ONSD in healthy adults in Colombia is similar to that found worldwide. An ONSD of 5.5 mm may be considered the upper limit for healthy adults in Colombia. ONSD can be measured in either plane; there is a good correlation between the two eyes; and ONSD is not modified by demographic or anthropometric characteristics.

Association between Optic Nerve Sheath Diameter and Lamina Cribrosa Morphology in Normal-Tension Glaucoma

(1) Background: To compare optic nerve sheath diameter (ONSD) in normal-tension glaucoma (NTG) and healthy eyes and to investigate the association between ONSD and lamina cribrosa (LC) morphology. (2) Methods: This cross-sectional study included 69 NTG eyes and 69 healthy eyes matched for age, axial length, and intraocular pressure. The LC curvature index (LCCI) was measured from horizontal Cirrus HD-OCT B-scan images from five uniformly divided positions vertically of the optic nerve. The average LCCI was defined as the mean of the measurements at these five locations. ONSD was measured as the width of the optic nerve sheath at the site perpendicular 3 mm behind the posterior globe. LCCI and ONSD were compared in eyes with NTG and healthy eyes. The clinical factors that could affect LCCI were analyzed. (3) Results: NTG eyes had significantly smaller mean ONSD (4.55 ± 0.69 mm vs. 4.97 ± 0.58 mm, p < 0.001) and larger average LCCI (11.61 ± 1.43 vs. 7.58 ± 0.90, p < 0.001) than matched healthy control eyes. LCCI was significantly correlated with smaller ONSD, higher intraocular pressure, thinner global retinal nerve fiber thickness, and worse visual field loss in all subjects (all Ps ≤ 0.022). (4) Conclusions: NTG eyes had smaller ONSD and greater LCCI than healthy control eyes. In addition, a negative correlation was observed between ONSD and LCCI. These findings suggest that cerebrospinal fluid pressure, which ONSD indirectly predicts, may affect LC configuration. Changes in the retrolaminar compartment may play a role in glaucoma pathogenesis.

POCUS, how can we include the brain? An overview

Point-of-care ultrasound (POCUS) is an essential tool to assess and manage different pathologies in the intensive care unit, and many protocols have been proposed for its application in critical care literature. However, the brain has been overlooked in these protocols.

Brain ultrasonography (BU) is easily available, and it allows a goal-directed approach thanks to its repeatability and immediate interpretation and provides a quick management and real time assessment of patients’ conditions. Based on recent studies, the increasing interest from intensivists, and the undeniable benefits of ultrasound, the main goal of this overview is to describe the main evidence and progresses in the incorporation of BU into the POCUS approach in the daily practice, and thus becoming POCUS-BU. This integration would allow a noninvasive global assessment to entail an integrated analysis of the critical care patients.

Echographic criteria for the assessment of the optic nerve condition in intracranial hypertension

Purpose: to develop objective acoustic criteria of the condition of the optic nerve and its sheaths for an early diagnosis of intracranial hypertension (IH). Material and methods. The research involved 24 patients (average age 35.8 ± 8.5 years) with suspected IH. The control group consisted of 48 healthy subjects (average age 28.5 ± 9.5 years). Ultrasound examination of the retrobulbar part of the optic nerve (ON) included the measurement of the ON thickness with sheaths (ONSD) and without sheaths (OND) and the calculation of the ratio K = ONSD/ OND. Echodensitometry was used to evaluate the echographic density of the parenchyma and the sheaths of the optic nerve. All patients were tested with magnetic resonance imaging (MRI) to analyse brain images. Results. The biometrical parameters of ON in healthy subjects were as follows: ONS 2.64 ± 0.21 mm and ONSD — 4.60 ± 0.34 mm. In patients with suspected IH the average parameters of the ON diameter were as follows: ONS — 2.57 ± 0.25 mm and ONSD — 5.81 ± 0.42 mm. A comparative assessment of the ON thickness with and without sheaths showed that in the control group the values of ONS did not exceed 3.5 mm and ONSD did not exceed 5.0 mm. In patients with IH, the values of ONSD were significantly higher than those in the control group (p < 0.05). The ratio coefficient (K)=ONSD/ONS in the group of healthy subjects ranged from 1.53 to 2.0 and averaged 1.75 ± 0.14. In patients with IH the values of K exceeded 2.0 (2,40 ± 0.18). The analysis of acoustic density data showed a significant variability in the parameters of the ON sheaths echodensitometry in IH patients as compared to the norm. Conclusion. The echography of the ON makes it possible to determine the acoustic and biometric parameters of the ON with high accuracy, to assess its structure and relationship with the surrounding tissues. The ratio coefficient (K) of ONSD/ONS makes it possible to determine IH in the early stages of the disease, even in the absence of objective clinical criteria.

Optic nerve sheath diameter at high altitude: standardized measures in healthy volunteers

Background

Increases in the diameter of the optic nerve sheath (ONSD) on ultrasound are associated with high intracranial pressure (hICP). The normal value varies with altitude and the population studied. The objective of this study is to describe the normal values of the ONSD in a healthy adult population of the city of Bogotá, Colombia, at 2640 meters above sea level (masl).

Patients and methods

A prospective observational study was conducted on a total of 247 healthy individuals recruited from May 2021 to May 2022 who were subjected to the color, low power, optic disk, safety, elevated frequency, dual (CLOSED) protocol for measuring the bilateral ONSD adjusted to the eyeball transverse diameter (ETD).

Results

A total of 230 individuals were analyzed; the average ONSD of the right eye (RE) was 0.449 cm (range 0.288–0.7) and that of the left eye (LE) was 0.454 cm (range 0.285–0.698); the correlation between RE and LE was 0.93 (p < 0.005), and the correlation of the ONSD/ETD ratios for the RE and LE was lower (r² = 0.79, p < 0.005). A total of 10.8% of the studied population had values greater than 0.55 cm.

Conclusions

The median ONSD and ONSD/ETD ratio in the city of Bogotá are similar to those described in other populations; however, approximately 10.8% of the healthy population may present higher values, which would limit the use of ONSD on its own for clinical decision-making, only repeated measurements with significant changes in the ONSD and ONSD/ETD or asymmetries between the measurements of both eyes linked to clinical findings would allow the diagnosis of hICP.

Optic nerve sheath diameter and spaceflight: defining shortcomings and future directions

Neuro-ocular changes during long-duration space flight are known as spaceflight-associated neuro-ocular syndrome (SANS). The ability to detect, monitor, and prevent SANS is a priority of current space medicine research efforts. Optic nerve sheath diameter (ONSD) measurement has been used both terrestrially and in microgravity as a proxy for measurements of elevated intracranial pressure. ONSD shows promise as a potential method of identifying and quantitating neuro-ocular changes during space flight. This review examines 13 studies measuring ONSD and its relationship to microgravity exposure or ground-based analogs, including head-down tilt, dry immersion, or animal models. The goal of this correspondence is to describe heterogeneity in the use of ONSD in the current SANS literature and make recommendations to reduce heterogeneity in future studies through standardization of imaging modalities, measurement techniques, and other aspects of study design.

Analysis of dynamic changes in optic nerve sheath diameter (ONSD) with ultrasound in post-craniotomy patients: Trends and correlation with computed tomography ONSD and Glasgow coma scale in post-operative period

Objectives

Intracranial pressure (ICP) monitoring in patients with intracranial tumors undergoing craniotomy is usually done in perioperative period in intensive care unit. Invasive measurement of ICP, though considered as the gold standard, has its own limitations such as availability of expertise, equipment, and associated complications. Period of raised ICP in post-operative period may impact patient outcomes. Post-craniotomy computed tomography (CT) assessment is done routinely and may need to be repeated if indicated during post-operative stay. Utility of sonographic serial optic nerve sheath diameter (ONSD) assessment in post-operative monitoring of patients who have undergone elective craniotomy was explored in this study. The primary objective of the study was to measure the dynamic change in ONSD as compared to baseline pre-operative measurement in the first 3 postoperative days after elective craniotomy. The secondary objective of the study was to evaluate correlation between ONSD value with Glasgow Coma Scale (GCS) and post-operative CT findings.

Materials and Methods

In this prospective, observational, and cohort study, we studied adult patients undergoing craniotomy for intracranial tumors. GCS assessment and sonographic measurement of ONSD were done preoperatively, immediate post-operative period, and 12, 24, and 48 h after surgery. CT scan to detect raised ICP was done at 24 h post-operative. Correlation of ONSD with GCS at respective period and correlation of CT scan finding with respective ONSD assessment were evaluated.

Results

A total of 57 patients underwent elective craniotomy for intracranial tumors. Significant difference was observed in ONSD value depending on time of measurement perioperatively (χ2 = 78.9, P = 0.00). There was initial increase in the first 12 h followed by decrease in ONSD in the next 48 h. Negative correlation was observed between baseline ONSD and 12 h GCS (ρ = -0.345, P = 0.013). There was significant change in GCS scores based on the status of ONSD (raised or normal) at 12 h after surgery (P = 0.014). Significant correlation between USG ONSD and CT ONSD was observed (ρ = 0.928, P = 0.000). Optimal cutoff value of ONSD to detect raised ICP with reference to CT signs was 4.8 mm with 80% sensitivity and 95% specificity.

Conclusion

ONSD undergoes dynamic changes, correlates with CT scan, and has good diagnostic accuracy to detect raised ICP post-craniotomy for intracranial tumors. It may serve as a useful tool in monitoring in resource-limited setup.

Observer Variability as a Determinant of Measurement Error of Ultrasonographic Measurements of the Optic Nerve Sheath Diameter: A Systematic Review

BACKGROUND

Ultrasonographic measurements of the diameter of the sheath of the optic nerve can be used to assess intracranial pressure indirectly. These measurements come with measurement error.

OBJECTIVE

Our aim was to estimate observer's measurement error as a determinant of ultrasonographic measurement variability of the optic nerve sheath diameter.

METHODS

A systematic search of the literature was conducted in Embase, Medline, Web of Science, the Cochrane Central Register of Trials, and the first 200 articles of Google Scholar up to April 19, 2021. Inclusion criteria were the following: healthy adults, B-mode ultrasonography, and measurements 3 mm behind the retina. Studies were excluded if standard error of measurement could not be calculated. Nine studies featuring 389 participants (median 40; range 15-100) and 22 observers (median 2; range 1-4) were included. Standard error of measurement and minimal detectable differences were calculated to quantify observer variability. Quality and risk of bias were assessed with the Guidelines for Reporting Reliability and Agreement Studies.

RESULTS

The standard error of measurement of the intra- and interobserver variability had a range of 0.10-0.41 mm and 0.14-0.42 mm, respectively. Minimal detectable difference of a single observer was 0.28-1.1 mm. Minimal detectable difference of multiple observers (range 2-4) was 0.40-1.1 mm. Quality assessment showed room for methodological improvement of included studies.

CONCLUSIONS

The standard errors of measurement and minimal detectable differences of ultrasonographic measurements of the optic nerve sheath diameter found in this review with healthy participants indicate caution should be urged when interpreting results acquired with this measurement method in clinical context.

Sonographic reference values of cranial nerve size: A Systematic Review and Meta-analysis

INTRODUCTION/AIMS

Ultrasonography of the cranial nerves has recently gained attention in assessing inflammatory, compressive or degenerative neuropathies. However, sonographic reference values of cranial nerves have received less attention than those of peripheral nerves. This systematic review and meta-analysis aimed to provide current evidence of sonographic reference values for cranial nerve size.

METHODS

By searching Medline (via PubMed), Scopus, Embase, Cochrane Central Register of Controlled Trials (CENTRAL), and Web of Science, we conducted a systematic review and meta-analysis of studies that reported ultrasound measurements of the facial, spinal accessory, and hypoglossal nerves in healthy adults. We included studies that reported either the sonographic cross-sectional area (CSA) or the nerve diameter; the included nerves were sub-grouped according to the site of nerve measurement.

RESULTS

Fourteen studies with a total of 661 participants and 1437 ultrasound nerve measurements met the inclusion criteria. The anatomical sites for each nerve were combined to provide single nerve mean measurements. We found an overall mean nerve diameter of 0.80 mm for the facial nerve, 0.63 mm for the spinal accessory nerve, and 1.82 mm² for the hypoglossal nerve CSA.

DISCUSSION

This meta-analysis provides reference values for the diameter and cross-sectional area of the facial, spinal accessory, and hypoglossal nerves at different sites, which can be used as guidance in clinical practice to detect pathological changes in cranial nerve size in cranial neuropathies. We recommend further validation in large-scale studies as well as standardization of the scanning protocols.

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.

Sonografisches Neuromonitoring auf der Stroke Unit und in der neurologischen Intensivmedizin

Hintergrund Der Artikel gibt einen Überblick über die aktuellen diagnostischen Einsatzmöglichkeiten sonographischer Anwendung in der neurologischen Intensivmedizin.

Methoden Selektive Literaturrecherche mit kritischer Beurteilung ab dem Jahr 1984 sowie nationaler und internationaler Leitlinien sowie Expertenmeinung.

Ergebnisse Neben der raschen validen Abklärung akuter Schlaganfälle bieten verschiedene neurosonografische Monitoring-verfahren gerade in der Intensivmedizin spezifische Vorteile wie die beliebig häufige Wiederholbarkeit am Patientenbett selbst und die Darstellung in Echtzeit. Innovative Entwicklungen machen die Neurosonografie auch wissenschaftlich zu einem interessanten Gebiet.

Schlussfolgerung Die neurosonografische Diagnostik nimmt seit Jahren einen wichtigen Stellenwert in der neurologischen Intensivmedizin ein. Weitere Anstrengungen sind notwendig, um die Verbreitung der Methode zu fördern und durch wissenschaftliche Evidenz zu stärken.

Ultrasound measurement of the optic nerve sheath diameter in traumatic brain injury: a narrative review

Background : Raised intracranial pressure (ICP) needs to be investigated in various situations, especially in traumatic brain injury (TBI). Ultra-sonographic (US) measurement of the optic nerve sheath diameter (ONSD) is a promising noninvasive tool for assessing elevated ICP. Objectives : This narrative review aimed to explain the history of and indications forUS measurement of ONSD. We focused on the detection of elevated ICP after TBI and discussed the possible improvements in detection methods. Conclusions : US measurement of ONSD in TBI cases provides a qualitative but no quantitative assessment of ICP. Current studies usually calculate their own optimum cutoff value for detecting raised ICP based on the balance between sensitivity and specificity of the method when compared with invasive methods. There is no universally accepted threshold. We did not find any paper focusing on the prognosis of patients benefiting from it when compared with usual care. Another limitation is the lack of standardization. US measurement of ONSD cannot be used as the sole technique to detect elevated ICP and monitor its evolution, but it can be a useful tool in a multimodal protocol and it might help to determine the prognosis of patients in various situations.

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.

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

BACKGROUND AND PURPOSE

Reported cutoff values of the optic nerve sheath diameter (ONSD) for the diagnosis of elevated intracranial pressure (ICP) are inconsistent. This hampers ONSD as a possible noninvasive bedside monitoring tool for ICP. Because the influence of methodological differences on variations in cutoff values is unknown, we performed a narrative review to identify discrepancies in ONSD assessment methodologies and to investigate their effect on reported ONSD values.

METHODS

We used a structured and quantitative approach in which each ONSD methodology found in the reviewed articles was categorized based on the characteristic appearance of the ultrasound images and ultrasound marker placement. Subsequently, we investigated the influence of the different methodologies on ONSD values by organizing the ONSDs with respect to these categories.

RESULTS

In a total of 63 eligible articles, we could determine the applied ONSD assessment methodology. Reported ultrasound images either showed the optic nerve and its sheath as a dark region with hyperechoic striped band at its edges or as a single dark region surrounded by lighter retrobulbar fat. Four different ultrasound marker positions were used to delineate the optic nerve sheath, which resulted in different ONSD values and more importantly, different sensitivities to changes in ICP.

CONCLUSIONS

Based on our observations, we recommend to place ultrasound markers at the outer edges of the hyperechoic striped bands or at the transitions from the single dark region to the hyperechoic retrobulbar fat because these locations yielded the highest sensitivity of ONSD measurements for increased ICP.

Study of the effect of anaesthesia on the canine ultrasonographic optic nerve sheath diameter

OBJECTIVES

To investigate the effects of anaesthetic duration and serial anaesthetic events on optic nerve sheath diameter in a population of dogs without intracranial disease using point-of-care ultrasonography.

MATERIALS AND METHODS

Client-owned dogs requiring advanced head imaging were prospectively enrolled. Exclusion criteria included signs of elevated intracranial pressure, glaucoma and optic nerve disease. Using a transpalpebral technique, two optic nerve sheath diameter measurements were recorded for each eye at three timepoints: following premedication, after induction within 7 minutes and before discontinuing isoflurane. Mixed model analysis was used to characterise optic nerve sheath diameter behaviour and investigate the effects of anaesthetic duration, bodyweight and anaesthetic protocol, age and sex.

RESULTS

Fourteen dogs of various ages, breeds and bodyweights were enrolled. A positive linear relationship was detected between body weight and optic nerve sheath diameter. In 12 of 14 dogs, the optic nerve sheath diameter increased from measurements taken after premedication when compared to measurements taken after induction within 7 minutes. In a subset of patients, measurements subsequently decreased when anaesthetic duration exceeded 120 minutes. Age, side, sex, final body temperature, blood pressure and anaesthetic protocol did not significantly affect optic nerve sheath diameter. No significant association was noted between optic nerve sheath diameter and end-tidal carbon dioxide after induction and before discontinuing isoflurane.

CLINICAL SIGNIFICANCE

When using point-of-care ultrasound, a transient increase in optic nerve sheath diameter occurs between premedication and within 7 minutes following induction, regardless of bodyweight. This should be taken into consideration when serial monitoring is performed.

Optic disc drusen mimicking Idiopathic Intracranial Hypertension (IIH): rely on ultrasound

Optic nerve ultrasound is an established routine supplementary diagnostic tool for idiopathic intracranial pressure but it can also be helpful in avoiding misdiagnoses. We describe a case of an obese 15- year-old girl with persistent headaches, fundoscopic findings suggesting papilledema, normal brain imaging who underwent two lumbar punctures with unremarkable cerebrospinal fluid findings before ultrasound revealed optic disc drusen as the cause of the optic disc elevation.

An Automated Algorithm for Optic Nerve Sheath Diameter Assessment from B-mode Ultrasound Images

BACKGROUND AND PURPOSE

The optic nerve sheath diameter (ONSD) is a promising surrogate marker for the detection of raised intracranial pressure (ICP). However, inconsistencies in manual ONSD assessment are thought to affect ONSD and the corresponding ONSD cutoff values for the diagnosis of elevated ICP, hereby hampering the full potential of ONSD. In this study, we developed an image intensity-invariant algorithm to automatically estimate ONSD from B-mode ultrasound images at multiple depths.

METHODS

The outcomes of the algorithm were validated against manual ONSD measurements by two human experts. Each expert analyzed the images twice (M1 and M2) in unknown order.

RESULTS

The algorithm proved capable of segmenting the ONSD in 39 of 42 images, hereby showing mean differences of -.08 ± .45 and -.05 ± .41 mm compared to averaged ONSD values (M1 + M2/2) of Operator 1 and Operator 2, respectively, whereas the mean difference between the two experts was .03 ± .26 mm. Moreover, differences between algorithm-derived and expert-derived ONSD values were found to be much smaller than the 1 mm difference that is expected between patients with normal and elevated ICP, making it likely that our algorithm can distinguish between these patient groups.

CONCLUSIONS

Our algorithm has the potential to improve the accuracy of ONSD as a surrogate marker for elevated ICP because it has no intrinsic variability. However, future research should be performed to validate if the algorithm does indeed result in more accurate noninvasive ICP predictions.

Scleral Lens Use in Neurotrophic Keratopathy: A Review of Current Concepts and Practice

OBJECTIVE

Neurotrophic keratopathy (NK) is a rare corneal condition characterized by epitheliopathy, which is associated with reduced or absent corneal sensation. The main goal of treatment of this condition is the preservation of ocular surface integrity. Contact lenses provide a nonsurgical and reversible option to provide the necessary corneal protection. The purpose of this review was to summarize the available literature regarding the use of contact lenses in the management of NK, with particular emphasis on the use of scleral lenses.

METHODS

Literature related to both soft and scleral contact lens use as treatment options for NK was reviewed.

RESULTS

As of yet, randomized clinical trials have compared neither the efficacy of contact lens therapy for NK to other therapeutic alternatives nor outcomes of therapy with different contact lens modalities. However, clinical case reports and limited case series have suggested that scleral lenses may be a safe and effective treatment option for NK at any stage of the disease, preserving epithelial integrity and even improving visual function in patients with this condition.

CONCLUSIONS

Scleral lenses may be effective in reducing the need for surgical intervention and improving the quality of life in patients with NK.

Prognostic Role of Optic Nerve Sheath Diameter for Neurological Outcomes in Post-Cardiac Arrest Patients: A Systematic Review and Meta-Analysis

Objective

The present study investigated whether optic nerve sheath diameter (ONSD) could be used to predict neurological outcomes in post-cardiac arrest (CA) patients.

Methods

We performed a comprehensive literature search in the Cochrane Library, ScienceDirect, PubMed, and Web of Science from inception to June 2020 for eligible articles. Stata 14.0 software was used to calculate the pooled odds ratios (ORs) and 95% confidence intervals (95% CIs), sensitivity, specificity, summary receiver operating characteristic (SROC) curve, subgroup analysis, sensitivity analysis, and publication bias.

Results

Eight studies involving 473 patients were considered eligible for this meta-analysis. The pooled result using a random-effects model showed that broadened ONSD is associated with poor neurological outcomes in post-CA patients (OR = 15.62, 95% CI: 5.50-44.34, P < 0.001; I ² = 58.4%, P = 0.018), with a sensibility of 0.60 (95% CI: 0.45-0.73) and specificity of 0.94 (95% CI: 0.83-0.98). The area under the curve of the SROC curve for ONSD was 0.87 (95% CI: 0.84-0.90). Subgroup analysis revealed that sample size and time of ONSD measurement may be the source of heterogeneity. Sensitivity analysis demonstrated the stability of the results of this meta-analysis. No publication bias using Deeks' funnel plot was noted across the studies (P = 0.23).

Conclusion

This meta-analysis confirmed that ONSD can be used to predict neurological outcomes in post-CA patients.

Normal Age- and Sex-Related Values of the Optic Nerve Sheath Diameter and Its Dependency on Position and Positive End-Expiratory Pressure

Optic nerve sheath diameter (ONSD) sonography is a reliable method for evaluation of intracranial pressure, yet there is a lack of reliable normal values. In the study described here, we established normal ONSD values in three different age groups and both sexes. One hundred eighty-seven volunteers without central nervous system disease were enrolled in this prospective study. ONSD measurements were taken in volunteers in the supine and upright positions and after application of positive end-expiratory pressure (PEEP). Normal ONSD values were 4.9-5.3 mm (patient age range: 20-85), with significant differences between men and women (p < 0.001). ONSD values increased with age (∆ = 0.34 mm, p < 0.001). There were no differences compared with the upright position but application of PEEP led to significantly increased ONSD values (∆ = 0.21 mm, p = 0.008). ONSD values increased with age, correlated well with the width of the third ventricle, were significantly lower in the female cohort and quickly responded to PEEP, especially in women.

Optic Nerve Sheath Diameter Measured by Point-of-Care Ultrasound and MRI

BACKGROUND AND PURPOSE

Ultrasound (US) measurement of the optic nerve sheath diameter (ONSD) and optic nerve diameter (OND) is a method frequently used to screen for an increased intracranial pressure. The aim of this study was to assess the accuracy of US measurements of ONSD and OND, when compared to magnetic resonance imaging (MRI) measurements as the criterion standard.

METHODS

In this prospective, single-institution study, orbital US was performed for those patients requiring an emergent brain MRI. ONSD and OND of both eyes were measured in the axial and coronal planes in straight gaze by US. ONSD and OND from brain and orbital MRI were measured by two neuroradiologists. Correlation and agreement between readings were assessed using Pearson's correlations.

RESULTS

Eighty-two patients met inclusion criteria. The mean axial and coronal ONSD in the MRI examinations was 5.6 and 5.7 mm at 3-5.9 mm behind the globe, respectively. The mean ONSD from the US measurements was 6.22 and 5.52 mm in the axial and coronal planes, respectively. The mean OND in US examinations was 4.31 mm (axial) and 3.68 mm (coronal). Axial versus coronal measurements of ONSD had a modest correlation in US assessment with an r² of .385 (P < .001) but there were no correlations between any of the US and MRI measurements.

CONCLUSIONS

In measuring ONSD and OND, US measurements showed a modest correlation between axial and coronal measurements, but no concordance was found between US and MRI in our setting.

Neuromonitoring Using Neurosonography and Pupillometry in A Weaning and Early Neurorehabilitation Unit

BACKGROUND AND PURPOSE

Long-term surveillance of intracranial pressure (ICP) in neurological/neurosurgical patients during ventilator weaning and early neurorehabilitation currently relies on clinical observation because neuroimaging is rarely readily available. In this prospective study, multimodal neurosonography and pupillometry are evaluated for follow-up monitoring.

METHODS

Sonographic neuromonitoring was used to noninvasively examine patients' ICP during weaning and early neurorehabilitation. It allowed assessments of third ventricle width, possible midline shift, middle cerebral artery flow velocities, and bilateral optic nerve sheath diameters. Quantitative pupillometry was used to determine pupil size and reactivity. Other neuroimaging findings, spinal tap ICP measurements, and clinical follow-up data served as controls.

RESULTS

Seventeen patients-11 suffering from intracranial hemorrhage, four from encephalopathies, and two from ischemic stroke-were examined for ICP changes by using neurosonography and pupillometry during a mean observation period of 21 days. In total, 354 of 980 analyses (36.1%) yielded pathological results. In 15 of 17 patients (88.2%), pathological values were found during follow-up without a clear clinical correlate. In two patients (11.8%), clinically relevant changes in ICP occurred and were identified using neurosonography. Abnormal pupillometry findings displayed a high predictive value for absent clinical improvement.

CONCLUSION

Multimodal neurosonography may be a noninvasive means for long-term ICP assessment, whereas pupillometry may only detect rapid ICP changes during acute neurointensive care. The study also illustrates common pitfalls in neuromonitoring in general, with large numbers of pathological albeit nonsignificant findings. Additional controlled studies should validate the influence of detected subtle changes in ICP on neurological outcome.