Association of Long-Duration Spaceflight With Anterior and Posterior Ocular Structure Changes in Astronauts and Their Recovery

Macias, Brandon R.; Patel, Nimesh B.; Gibson, Charles R.; Samuels, Brian C; Laurie, Steven S.; Otto, Christian; Ferguson, Connor R.; Lee, Stuart M. C.; Ploutz‐Snyder, Robert; Kramer, Larry A.; Mader, Thomas H.; Brunstetter, Tyson; Stenger, Michael B.

doi:10.1001/jamaophthalmol.2020.0673

Cited by 71 publications

(104 citation statements)

References 10 publications

(22 reference statements)

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“…Alternatively, our findings may indicate that the ONS area decreased immediately upon re-entry into Earth's gravitational environment, and that any ONS changes that occurred during spaceflight were no longer present by the first MRI scan. The average time to the first postflight MRI scan was 4 ± 2 days after return to Earth and retinal thickness has been shown to decrease at just 3 days post spaceflight compared to in-flight measures 2 .…”

Section: Discussionmentioning

confidence: 97%

“…In the present study, we did not observe an increase in ONS cross-sectional area after spaceflight in most individuals, which may indicate ICP is not pathologically elevated in space. Recent studies of a similar astronaut cohort found evidence of ICP elevation in some subjects post flight in the form of pituitary gland deformation and retinal thickening (i.e., optic disc edema) 2 . Alternatively, our findings may indicate that the ONS area decreased immediately upon re-entry into Earth's gravitational environment, and that any ONS changes that occurred during spaceflight were no longer present by the first MRI scan.…”

Section: Discussionmentioning

confidence: 99%

“…Here we report no change in ON deviation, ON area or ONS areas after immediately post flight, suggesting that on average, CSF pressure within the bulbar subarachnoid space is not pathologically elevated after spaceflight at this time point. While one subject was diagnosed with optic disc edema via ophthalmic imaging and showed an increase in ONS area post flight, most astronauts present with some degree of retinal thickening during and after spaceflight 2 . Further research is warranted to quantitatively assess ON parameters in a larger astronaut cohort.…”

Section: Discussionmentioning

confidence: 99%

“…As a result of extended spaceflight, some astronauts experience ophthalmic changes collectively referred to as spaceflight-associated neuro-ocular syndrome (SANS) 1 , 2 . The severity of SANS may increase with spaceflight duration and possibly result in permanent ocular structural and functional changes 2 . SANS is characterized by decreased near-visual acuity, globe flattening, optic disc edema, and choroidal folds 3 – 6 .…”

Section: Introductionmentioning

confidence: 99%

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Quantitative magnetic resonance image assessment of the optic nerve and surrounding sheath after spaceflight

et al. 2020

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A subset of long-duration spaceflight astronauts have experienced ophthalmic abnormalities, collectively termed spaceflight-associated neuro-ocular syndrome (SANS). Little is understood about the pathophysiology of SANS; however, microgravity-induced alterations in intracranial pressure (ICP) due to headward fluid shifts is the primary hypothesized contributor. In particular, potential changes in optic nerve (ON) tortuosity and ON sheath (ONS) distension may indicate altered cerebrospinal fluid dynamics during weightlessness. The present longitudinal study aims to provide a quantitative analysis of ON and ONS cross-sectional areas, and ON deviation, an indication of tortuosity, before and after spaceflight. Ten astronauts undergoing ~6-month missions on the International Space Station (ISS) underwent high-resolution magnetic resonance imaging (MRI) preflight and at five recovery time points extending to 1 year after return from the ISS. The mean changes in ON deviation, ON cross-sectional area, and ONS cross-sectional area immediately post flight were −0.14 mm (95% CI: −0.36 to 0.08, Bonferroni-adjusted P = 1.00), 0.13 mm2 (95% CI −0.66 to 0.91, Bonferroni-adjusted P = 1.00), and −0.22 mm2 (95% CI: −1.78 to 1.34, Bonferroni-adjusted P = 1.00), respectively, and remained consistent during the recovery period. Terrestrially, ONS distension is associated with increased ICP; therefore, these results suggest that, on average, ICP was not pathologically elevated immediately after spaceflight. However, a subject diagnosed with optic disc edema (Frisen Grade 1, right eye) displayed increased ONS area post flight, although this increase is relatively small compared to clinical populations with increased ICP. Advanced quantitative MRI-based assessment of the ON and ONS could help our understanding of SANS and the role of ICP.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Quantitative magnetic resonance image assessment of the optic nerve and surrounding sheath after spaceflight

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“…Long-duration stays in weightlessness also have resulted in changes in the function and structure of the eye in some astronauts that has been described as spaceflight-associated neuro-ocular syndrome (SANS; Lee et al, 2016;Macias et al, 2020). The leading hypothesis is that ocular changes result from chronic exposure to the weightlessness-induced fluid shift (Stenger et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

Venous and Arterial Responses to Partial Gravity

et al. 2020

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Introduction: Chronic exposure to the weightlessness-induced cephalad fluid shift is hypothesized to be a primary contributor to the development of spaceflight-associated neuro-ocular syndrome (SANS) and may be associated with an increased risk of venous thrombosis in the jugular vein. This study characterized the relationship between gravitational level (G z-level) and acute vascular changes. Methods: Internal jugular vein (IJV) cross-sectional area, inferior vena cava (IVC) diameter, and common carotid artery (CCA) flow were measured using ultrasound in nine subjects (5F, 4M) while seated when exposed to 1.00-G z , 0.75-G z , 0.50-G z , and 0.25-G z during parabolic flight and while supine before flight (0-G analog). Additionally, IJV flow patterns were characterized. Results: IJV cross-sectional area progressively increased from 12 (95% CI: 9-16) mm 2 during 1.00-G z seated to 24 (13-35), 34 (21-46), 68 (40-97), and 103 (75-131) mm 2 during 0.75-G z , 0.50-G z , and 0.25-G z seated and 1.00-G z supine, respectively. Also, IJV flow pattern shifted from the continuous forward flow observed during 1.00-G z and 0.75-G z seated to pulsatile flow during 0.50-G z seated, 0.25-G z seated, and 1.00-G z supine. In contrast, we were unable to detect differences in IVC diameter measured during 1.00-G seated and any level of partial gravity or during 1.00-G z supine. CCA blood flow during 1.00-G seated was significantly less than 0.75-G z and 1.00-G z supine but differences were not detected at partial gravity levels 0.50-G z and 0.25-G z. Conclusions: Acute exposure to decreasing G z-levels is associated with an expansion of the IJV and flow patterns that become similar to those observed in supine subjects and in astronauts during spaceflight. These data suggest that G z-levels greater than 0.50-G z may be required to reduce the weightlessness-induced headward fluid shift that may contribute to the risks of SANS and venous thrombosis during spaceflight.

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Changes in the Optic Nerve Head and Choroid Over 1 Year of Spaceflight

et al. 2021

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IMPORTANCE While 6-month data are available regarding spaceflight-associated neuro-ocular syndrome, manned missions for 1 year and beyond are planned, warranting evaluation for spaceflight-associated neuro-ocular syndrome beyond 6 months.OBJECTIVE To determine if the manifestation of spaceflight-associated neuro-ocular syndrome worsens during International Space Station missions exceeding the present 4-to 6-month duration. DESIGN, SETTING, AND PARTICIPANTSThe One-Year Mission Study used quantitative imaging modalities to investigate changes in ocular structure in 2 crew members who completed a 1-year-long spaceflight mission. This study investigated the ocular structure of crew members before, during, and after their mission on the International Space Station. Two crew members participated in this study from March 2015 to September 2016. Analysis began in March 2015 and ended in May 2020.EXPOSURES Crew members were tested before, during, and up to 1 year after spaceflight. MAIN OUTCOMES AND MEASURESThis study compares ocular changes (peripapillary retinal edema, axial length, anterior chamber depth, and refraction) in two 1-year spaceflight mission crew members with cohort crew members from a 6-month mission (n = 11). Minimum rim width (the shortest distance between Bruch membrane opening and the internal limiting membrane) and peripapillary total retinal thickness were measured using optical coherence tomography.RESULTS Both crew members were men. Minimum rim width and total retinal thickness increased in both participants throughout the duration of spaceflight exposure to the maximal observed change from preflight (minimum rim width: participant 1, 561 [+149 from preflight] μm at flight day 270; participant 2, 539 [+56 from preflight] μm at flight day 270; total retinal thickness: participant 1, 547 [+135 from preflight] μm at flight day 90; participant 2, 528 [+45 from preflight] μm at flight day 210). Changes in peripapillary choroid engorgement, axial length, and anterior chamber depth appeared similar between the 1-year mission participants and a 6-month mission cohort.CONCLUSIONS AND RELEVANCE This report documents the late development of mild optic disc edema in 1 crew member and the progressive development of choroidal folds and optic disc edema in another crew member over the duration of 1 year in low Earth orbit aboard the International Space Station. Previous reports characterized the ocular risk associated with 4 to 6 months of spaceflight. As future spaceflight missions are planned to increase in duration and extend beyond low Earth orbit, further observation of astronaut ocular health on spaceflight missions longer than 6 months in duration may be warranted.

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Association of Long-Duration Spaceflight With Anterior and Posterior Ocular Structure Changes in Astronauts and Their Recovery

Cited by 71 publications

References 10 publications

Quantitative magnetic resonance image assessment of the optic nerve and surrounding sheath after spaceflight

Quantitative magnetic resonance image assessment of the optic nerve and surrounding sheath after spaceflight

Venous and Arterial Responses to Partial Gravity

Changes in the Optic Nerve Head and Choroid Over 1 Year of Spaceflight

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