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Ultrasonography measurement of optic nerve sheath diameter. Vertical axial B-scan demonstrating good centration of the optic nerve and distinct optic nerve sheath boundaries. ONSD (yellow line) was quantified 3 mm (white dashed line) posterior to the globe.
Source publication
Purpose:
The purpose of this study was to determine changes in optic nerve head (ONH) morphology in seated and 6° head-down tilt (HDT) postures over a 12-hour period.
Methods:
Thirty eyes of 30 healthy human subjects (15 females) were included. Composite radial and circular optical coherence tomography (OCT) scans centered on the ONH, intraocula...
Context in source publication
Context 1
... the frame with the best quality was used for ONSD quantification. Quality B-scans demonstrated a well-centered optic nerve extending from the posterior globe and parallel and distinct optic nerve sheath boundaries and represented the widest diameter in the absence of artifact. ONSD was measured 3 mm behind the globe using the software's calipers (Fig. 2). ...
Similar publications
This study aimed to compare the optic nerve head (ONH) structure in acute angle-closure glaucoma (AACG) and open-angle glaucoma (OAG) to investigate the differences in glaucomatous damage. The AACG and OAG eyes were matched with regard to global retinal nerve fiber layer thickness (RNFLT). AACG eyes were divided into two subgroups based on the pres...
Citations
... 10,11 On the other hand, IOP varies much less with posture than ICP; only a 1to 4-mmHg increase in IOP was observed in HDT compared to a seated upright posture. [12][13][14] Taken together, the TLPD is higher in the upright posture than in the supine or HDT position. 12,13 We recently examined the role of posture in physiological fluctuations of ONH structure throughout the day (07:00-19:00 h) and observed a continuous reduction in the neuroretinal rim thickness, reaching a 9.6 μm change on average at 15:00 h in 30 healthy subjects positioned in a seated posture in which TLPD is relatively high. ...
... 12,13 We recently examined the role of posture in physiological fluctuations of ONH structure throughout the day (07:00-19:00 h) and observed a continuous reduction in the neuroretinal rim thickness, reaching a 9.6 μm change on average at 15:00 h in 30 healthy subjects positioned in a seated posture in which TLPD is relatively high. 14 However, such thickness reduction was 'blunted' in a subset of 10 subjects who maintained a 6° HDT posture over the same period of time on a different day, consistent with the decreased TLPD that occurs when ICP is elevated to a greater extent than IOP in HDT. 14 ICP is commonly estimated from the CSF opening pressure with lumbar puncture in the lateral decubitus position. This technique is not suitable for studying the normal population or for assessing ICP in a standing/seated position. ...
... 14 However, such thickness reduction was 'blunted' in a subset of 10 subjects who maintained a 6° HDT posture over the same period of time on a different day, consistent with the decreased TLPD that occurs when ICP is elevated to a greater extent than IOP in HDT. 14 ICP is commonly estimated from the CSF opening pressure with lumbar puncture in the lateral decubitus position. This technique is not suitable for studying the normal population or for assessing ICP in a standing/seated position. ...
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.
... Traditional obliquity observation methods include single-point observation, photographic observation, etc. In these two methods, the workload of a single measuring instrument is relatively large [1]. The monitoring effect of this method is not good, and the monitoring effect has a certain bias. ...
With the development of modern surveying and mapping technology, 3D laser scanners are increasingly used for building dip scanning. Building inclination characteristics are analyzed using three-dimensional point cloud data and binary linear regression. It can easily and intuitively obtain the inclination of the building. This method extracted the building inclination Angle from the point, line, plane, surface, and other angles. Then, a matching method based on two dimensions and surfaces is proposed, with a strong anti-noise ability. An optimal matching algorithm of structural plane and surface based on quadratic linear regression is proposed. Experiments prove the anti-interference ability and accuracy of this method. It is found that the binary linear regression fitting method can effectively identify the noise signal when there is a lot of noise interference in the point cloud data. It has good anti-interference ability.
... Analogously, Pardon et al. (38) studied the ONSD differences over 12 h in seated and 6 • head-down tilt postures in 30 healthy individuals, reporting no significant difference in sitting position, while ONSD increased during the head-down tilt posture. ...
In recent years, ultrasonographic measurement of the optic nerve sheath diameter (ONSD) has been widely used to identify the presence of increased intracranial pressure (ICP). Intracranial hypertension is a life-threatening condition that can be caused by various neurological and non-neurological disorders, and it is associated to poor clinical results. Ultrasonography could be used to qualitatively and efficiently detect ICP increases, but to reach this purpose, clear cut-off values are mandatory. The aim of this review is to provide a wide overview of the most important scientific publications on optic nerve ultrasound normal values assessment published in the last 30 years. A total of 42 articles selected from PubMed medical database was included in this review. Our analysis showed that ocular ultrasonography is considered to be a valuable diagnostic tool, especially when intracranial hypertension is suspected, but unfortunately this research provided conflicting results that could be due to the different ultrasound protocols. This is mainly caused by the use of B scan alone, which presents several limitations. The use of B-scan coupled with the standardized A-scan approach could give more accurate, and reliable ultrasound evaluation, assuring higher data objectivity.
... In contrast, eyes with disc edema have axoplasmic stasis and fluid accumulation, both of which are more pronounced closer to the ONH rim margin. Hence, it is not surprising that, for most moderate to severe disc edema cases, measures of RNFL thickness and total retinal thickness (TRT) from circumpapillary scans are greater than for healthy eyes (Karam & Hedges, 2005;Kulkarni et al., 2014;Menke et al., 2005;Pardon et al., 2020;Savini et al., 2006;Scott et al., 2010). However, circumpapillary RNFL thickness does not effectively differentiate mild cases of disc edema from healthy or eyes with pseudopapilledema (Karam & Hedges, 2005;Kulkarni et al., 2014;Pardon et al., 2020). ...
... Hence, it is not surprising that, for most moderate to severe disc edema cases, measures of RNFL thickness and total retinal thickness (TRT) from circumpapillary scans are greater than for healthy eyes (Karam & Hedges, 2005;Kulkarni et al., 2014;Menke et al., 2005;Pardon et al., 2020;Savini et al., 2006;Scott et al., 2010). However, circumpapillary RNFL thickness does not effectively differentiate mild cases of disc edema from healthy or eyes with pseudopapilledema (Karam & Hedges, 2005;Kulkarni et al., 2014;Pardon et al., 2020). This is relevant for SANS, as most cases only have mild optic disc edema. ...
... The rim tissue is known to be sensitive to changes in the translaminar pressure difference (intraocular pressure À cerebrospinal fluid pressure) (Agoumi et al., 2010;Pardon et al., 2020;Patel et al., 2018a). As edema is typically greatest adjacent to the optic nerve head, the ideal scan for quantification would traverse the nerve itself. ...
The optic nerve and retinal abnormalities seen in Spaceflight Associated Neuro-Ocular Syndrome (SANS) are likely to involve imbalances of intraocular pressure (IOP) and intracranial pressure (ICP). In this chapter, we briefly summarize the changes in IOP and ICP, which occur during spaceflight. Next, we describe IOP–ICP relationships at the optic nerve head in health and disease, highlighting the importance of the translaminar pressure difference (TLPD), which is defined as the difference between IOP and ICP (IOP − ICP). Finally, we review the theoretical and experimental basis for SANS countermeasures that are based on the manipulation of IOP or ICP to correct an abnormal TLPD. In this last section, we discuss recent literature in both animals and humans to address the validity of this approach, as well as potential pitfalls.
... A recent study used OCT to show that the neuroretinal rim thins during the day in healthy individuals, consistent with our finding of increased global RNFL thickness in supine subjects in the ITU. However, in a different study, when subjects shifted from a seated to a head down tilt position, IOP increased but neuroretinal rim thinning did not occur, although head down tilt was only maintained for 3 h [42], while our cohort were supine for a prolonged period, nearing 48 h by the time of the first post-op assessment at scan 2. We suggest that the postural change to the supine position may have changed the effect of gravity on the retrobulbar cerebrospinal fluid dynamics, which may be comparable to the changes seen in space-associated neuro-ocular syndrome [43]. Unfortunately, as a result of time constraints with the patients in the ITU, it was not possible to assess optic nerve head blood flow, and we also did not assess optic nerve head volume on structural scans. ...
To assess the stability of retinal structure and blood flow measures over time and in different clinical settings using portable optical coherence tomography angiography (OCTA) as a potential biomarker of central perfusion in critical illness, 18 oesophagectomy patients completed retinal structure and blood flow measurements by portable OCT and OCTA in the eye clinic and intensive therapy unit (ITU) across three timepoints: (1) pre-operation in a clinic setting; (2) 24–48 h post-operation during ITU admission; and (3) seven days post-operation, if the patient was still admitted. Blood flow and macular structural measures were stable between the examination settings, with no consistent variation between pre- and post-operation scans, while retinal nerve fibre layer thickness increased in the post-operative scans (+2.31 µm, p = 0.001). Foveal avascular zone (FAZ) measurements were the most stable, with an intraclass correlation coefficient of up to 0.92 for right eye FAZ area. Blood flow and structural measures were lower in left eyes than right eyes. Retinal blood flow assessed in patients before and during an ITU stay using portable OCTA showed no systematic differences between the clinical settings. The stability of retinal blood flow measures suggests the potential for portable OCTA to provide clinically useful measures in ITU patients.
... A 6 • , 12-h study HDTBR observed no significant global minimum rim width thinning compared to significant thinning seen in the seated position for 12 h, although it was noted that Bruch's membrane opening height moved anteriorly during HDTBR. The study suggested that this attenuation in neuroretinal rim thinning in postural differences from seated to HDTBR may be due to translaminar pressure difference, which has been proposed as a contributing factor in glaucoma (58). A postural study on ambulatory neurosurgical patients with continuous ICP monitoring observed an increase in ICP during postural change from standing or supine to 10 • & 20 • head-down tilt (4,59). ...
Astronauts who undergo prolonged periods of spaceflight may develop a unique constellation of neuro-ocular findings termed Spaceflight Associated Neuro-Ocular Syndrome (SANS). SANS is a disorder that is unique to spaceflight and has no terrestrial equivalent. The prevalence of SANS increases with increasing spaceflight duration and although there have been residual, structural, ocular changes noted, no irreversible or permanent visual loss has occurred after SANS, with the longest spaceflight to date being 14 months. These microgravity-induced findings are being actively investigated by the United States' National Aeronautics Space Administration (NASA) and SANS is a potential obstacle to future longer duration, manned, deep space flight missions. The pathophysiology of SANS remains incompletely understood but continues to be a subject of intense study by NASA and others. The study of SANS is of course partially limited by the small sample size of humans undergoing spaceflight. Therefore, identifying a terrestrial experimental model of SANS is imperative to facilitate its study and for testing of preventative measures and treatments. Head-down tilt bed rest (HDTBR) on Earth has emerged as one promising possibility. In this paper, we review the HDTBR as an analog for SANS pathogenesis; the clinical and imaging overlap between SANS and HDTBR studies; and potential SANS countermeasures that have been or could be tested with HDTBR.
Importance:
Approximately 70% of crew members who complete long-duration missions to the International Space Station develop signs of optic disc edema, a hallmark finding of spaceflight-associated neuro-ocular syndrome. The onset and magnitude of edema differ across individuals, and the reason for this variability remains unknown. Identifying risk factors for spaceflight-induced disc edema is important because this condition may become more severe during extended-duration missions to the moon and Mars and could be associated with irreversible vision loss.
Objective:
To assess whether preflight indicators of crowded optic nerve head morphology, other ocular measures (such as choroid thickness and axial length), body weight, body mass index, sex, age, and previous flight experience are associated with optic disc edema development.
Design, setting, and participants:
This cohort study analyzed ocular, body weight, and demographic data collected from 31 US and international crew members before, during, and after spaceflight at the NASA Johnson Space Center and International Space Station. Ocular factors assessed included preflight and in-flight peripapillary total retinal thickness, minimum rim width, optic cup volume, mean cup depth, mean cup width, cup-disc ratio, Bruch membrane opening area, retinal nerve fiber layer thickness, choroid thickness, axial length, and refractive error. In addition, body weight, body mass index, sex, age, and previous spaceflight experience were assessed for associations with optic disc edema development. The data were analyzed from August 2021 to June 2022.
Exposure:
Approximately 6 to 12 months of spaceflight.
Main outcomes and measures:
In-flight increases in peripapillary total retinal thickness. Linear mixed models were used to assess for associations between a wide range of risk factors and in-flight increases in peripapillary total retinal thickness, which is a sensitive objective measure for detecting optic disc edema.
Results:
This study included 31 International Space Station crew members with a mean (SD) age of 46.9 (6.0) years (25 men [80.6%]). During spaceflight, mean (SE) peripapillary total retinal thickness increased from 392.0 (5.8) μm to 430.2 (9.6) μm (P < .001), and greater individual changes were associated with smaller preflight cup volume (slope [SE], -62.8 [18.9]; P = .002), shallower preflight cup depth (slope [SE], -0.11 [0.03]; P < .001), and narrower preflight cup width (slope [SE], -0.03 [0.01]; P = .03). No associations were observed between changes in peripapillary total retinal thickness and any other variable evaluated.
Conclusions and relevance:
Findings of this cohort study suggest that smaller optic cup morphology may be associated with optic disc edema development during spaceflight. Crew members with this cup profile may benefit from enhanced ophthalmic monitoring during spaceflight and use of countermeasures against spaceflight-associated neuro-ocular syndrome.
Some of the ocular changes associated with Spaceflight Associated Neuro-Ocular Syndrome (SANS) include optic nerve head edema, globe flattening, increased choroidal thickness, and both retinal and choroidal folds. In this chapter, we describe how optical coherence tomography (OCT), a noninvasive imaging technique, has been instrumental in documenting and quantifying these findings. Reviewed are how the OCT metrics for SANS were established, and how these change with spaceflight.
Importance:
Countermeasures that reverse the headward fluid shift experienced in weightlessness have the potential to mitigate spaceflight-associated neuro-ocular syndrome. This study investigated whether use of the countermeasure lower-body negative pressure during spaceflight was associated with changes in ocular structure.
Objective:
To determine whether changes to the optic nerve head and retina during spaceflight can be mitigated by brief in-flight application of 25-mm Hg lower-body negative pressure.
Design, setting, and participants:
In the National Aeronautics and Space Administration's "Fluid Shifts Study," a prospective cohort study, optical coherence tomography scans of the optic nerve head and macula were obtained from US and international crew members before flight, in-flight, and up to 180 days after return to Earth. In-flight scans were obtained both under normal weightless conditions and 10 to 20 minutes into lower-body negative pressure exposure. Preflight and postflight data were collected in the seated, supine, and head-down tilt postures. Crew members completed 6- to 12-month missions that took place on the International Space Station. Data were analyzed from 2016 to 2021.
Interventions or exposures:
Spaceflight and lower-body negative pressure.
Main outcomes and measures:
Changes in minimum rim width, optic cup volume, Bruch membrane opening height, peripapillary total retinal thickness, and macular thickness.
Results:
Mean (SD) flight duration for the 14 crew members (mean [SD] age, 45 [6] years; 11 male crew members [79%]) was 214 (72) days. Ocular changes on flight day 150, as compared with preflight seated, included an increase in minimum rim width (33.8 μm; 95% CI, 27.9-39.7 μm; P < .001), decrease in cup volume (0.038 mm3; 95% CI, 0.030-0.046 mm3; P < .001), posterior displacement of Bruch membrane opening (-9.0 μm; 95% CI, -15.7 to -2.2 μm; P = .009), and decrease in macular thickness (fovea to 500 μm, 5.1 μm; 95% CI, 3.5-6.8 μm; P < .001). Brief exposure to lower-body negative pressure did not affect these parameters.
Conclusions and relevance:
Results of this cohort study suggest that peripapillary tissue thickening, decreased cup volume, and mild central macular thinning were associated with long-duration spaceflight. Acute exposure to 25-mm Hg lower-body negative pressure did not alter optic nerve head or retinal morphology, suggesting that longer durations of a fluid shift reversal may be needed to mitigate spaceflight-induced changes and/or other factors are involved.
