Optic Nerve Head Morphological Changes Over 12 Hours in Seated and Head-Down Tilt Postures

Pardon, Laura P; Cheng, Huang; Chettry, Pratik; Patel, Nimesh B.

doi:10.1167/iovs.61.13.21

Cited by 8 publications

(12 citation statements)

References 53 publications

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“…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].…”

Section: Discussionmentioning

confidence: 54%

Stability of OCT and OCTA in the Intensive Therapy Unit Setting

et al. 2021

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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.

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Section: Discussionmentioning

confidence: 54%

Stability of OCT and OCTA in the Intensive Therapy Unit Setting

et al. 2021

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“…Given that approximately 10 to 15 minutes of exposure to 15° HDT had no effect, the lack of a response to a similar duration of LBNP during spaceflight may be a result of insufficient exposure duration rather than the magnitude of the fluid shift. Evidence that changes in MRW and TRT occur over hours in response to pressure and posture changes suggests that it may be possible for longer-duration LBNP application to reverse spaceflight-induced ocular changes.…”

Section: Discussionmentioning

confidence: 99%

Changes in Optic Nerve Head and Retinal Morphology During Spaceflight and Acute Fluid Shift Reversal

et al. 2022

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IMPORTANCECountermeasures 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 PARTICIPANTSIn 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 EXPOSURESSpaceflight and lower-body negative pressure. MAIN OUTCOMES AND MEASURESChanges 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 mm 3 ; 95% CI, 0.030-0.046 mm 3 ; 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.

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“…Assessment of the abovementioned preflight anatomical characteristics provides an initial characterization of factors associated with spaceflight-induced ODE development; however, this study considered only static preflight measures of ocular morphology as factors. Investigating dynamic tissue responses (eg, to diurnal changes or intraocular pressure modulation) could provide additional insight into underlying biomechanical properties of ocular tissues that may contribute to individual variability.…”

Section: Discussionmentioning

confidence: 99%

Identification of Factors Associated With the Development of Optic Disc Edema During Spaceflight

et al. 2022

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ImportanceApproximately 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.ObjectiveTo 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 ParticipantsThis 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.ExposureApproximately 6 to 12 months of spaceflight.Main Outcomes and MeasuresIn-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.ResultsThis 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 &lt; .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 &lt; .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 RelevanceFindings 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.

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Optic Nerve Head Morphological Changes Over 12 Hours in Seated and Head-Down Tilt Postures

Cited by 8 publications

References 53 publications

Stability of OCT and OCTA in the Intensive Therapy Unit Setting

Stability of OCT and OCTA in the Intensive Therapy Unit Setting

Changes in Optic Nerve Head and Retinal Morphology During Spaceflight and Acute Fluid Shift Reversal

Identification of Factors Associated With the Development of Optic Disc Edema During Spaceflight

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