Optic disc edema during strict 6° head-down tilt bed rest is related to one-carbon metabolism pathway genetics and optic cup volume.

Some astronauts on International Space Station missions experience neuroophthalmological pathologies as part of spaceflight associated neuro-ocular syndrome (SANS). Strict head-down tilt bed rest (HDTBR) is a spaceflight analog that replicates SANS findings and those who had 3-4 risk alleles (G and C alleles from the methionine synthase reductase [MTRR] A66G and serine hydroxymethyltransferase [SHMT1] C1420T, respectively) as compared to 1-2 risk alleles, had a greater increase in total retinal thickness (TRT). The objective of this study was to identify factors that contribute to the individual variability of the development of SANS in a 60 d HDTBR at the German Aerospace Center's:envihab facility, Cologne Germany.

Development of optic disc edema during 30 days of hypercapnic head-down tilt bed rest is associated with short sleep duration and blunted temperature amplitude.

Sleep and circadian temperature disturbances occur with spaceflight and may, in part, result from the chronically elevated carbon dioxide (CO) levels on the international space station. Impaired sleep may contribute to decreased glymphatic clearance and, when combined with the chronic headward fluid shift during actual spaceflight or the spaceflight analog head-down tilt bed rest (HDTBR), may contribute to the development of optic disc edema. We determined if strict HDTBR combined with mildly elevated CO levels influenced sleep and core temperature and was associated with the development of optic disc edema.

Eye-brain axis in microgravity and its implications for Spaceflight Associated Neuro-ocular Syndrome.

Long-duration human spaceflight can lead to changes in both the eye and the brain, which have been referred to as Spaceflight Associated Neuro-ocular Syndrome (SANS). These changes may manifest as a constellation of symptoms, which can include optic disc edema, optic nerve sheath distension, choroidal folds, globe flattening, hyperopic shift, and cotton wool spots. Although the underpinning mechanisms for SANS are not yet known, contributors may include intracranial interstitial fluid accumulation following microgravity induced headward fluid shift.

Evaluation of Optic Disc Edema in Long-Duration Spaceflight Crewmembers Using Retinal Photography.

Background: Long-duration spaceflight crewmembers are at risk for spaceflight-associated neuro-ocular syndrome (SANS). One of the earliest manifestations of SANS is optic disc edema (ODE), which could be missed using the subjective Frisén scale. The primary objective of this study is to determine the inter-rater and intrarater reliability of Frisén grade for SANS-induced ODE among a trained observer cohort.

Assessing the effects of artificial gravity in an analog of long-duration spaceflight: The protocol and implementation of the AGBRESA bed rest study.

A comprehensive strategy is required to mitigate risks to astronauts' health, well-being, and performance. This strategy includes developing countermeasures to prevent or reduce adverse responses to the stressors astronauts encounter during spaceflight, such as weightlessness. Because artificial gravity (AG) by centrifugation simultaneously affects all physiological systems, AG could mitigate the effects of weightlessness in multiple systems.

Future research directions to identify risks and mitigation strategies for neurostructural, ocular, and behavioral changes induced by human spaceflight: A NASA-ESA expert group consensus report.

A team of experts on the effects of the spaceflight environment on the brain and eye (SANS: Spaceflight-Associated Neuro-ocular Syndrome) was convened by NASA and ESA to (1) review spaceflight-associated structural and functional changes of the human brain and eye, and any interactions between the two; and (2) identify critical future research directions in this area to help characterize the risk and identify possible countermeasures and strategies to mitigate the spaceflight-induced brain and eye alterations. The experts identified 14 critical future research directions that would substantially advance our knowledge of the effects of spending prolonged periods of time in the spaceflight environment on SANS, as well as brain structure and function. They used a paired comparison approach to rank the relative importance of these 14 recommendations, which are discussed in detail in the main report and are summarized briefly below.

Optic disc edema and chorioretinal folds develop during strict 6° head-down tilt bed rest with or without artificial gravity.

Spaceflight associated neuro-ocular syndrome (SANS) is hypothesized to develop as a consequence of the chronic headward fluid shift that occurs in sustained weightlessness. We exposed healthy subjects (n = 24) to strict 6° head-down tilt bed rest (HDTBR), an analog of weightlessness that generates a sustained headward fluid shift, and we monitored for ocular changes similar to findings that develop in SANS. Two-thirds of the subjects received a daily 30-min exposure to artificial gravity (AG, 1 g at center of mass, ~0.

Potential Involvement of the Ocular Glymphatic System in Optic Disc Edema in Astronauts.

A significant proportion of the astronauts who spend extended periods in microgravity develop ophthalmic abnormalities, including optic disc edema, optic nerve sheath distention, globe flattening, chorioretinal folds, hyperopic refractive error shifts, and nerve fiber layer infarcts. A constellation of these neuro-ophthalmic findings has been termed spaceflight-associated neuro-ocular syndrome. An increased understanding of factors contributing to this syndrome is one of the top priorities for ESA and NASA because the length of missions is expected to increase substantially in the future.

Optic Disc Edema and Choroidal Engorgement in Astronauts During Spaceflight and Individuals Exposed to Bed Rest.

Importance: Optic disc edema develops in astronauts during long-duration spaceflight and is a risk for all future astronauts during spaceflight. Having a ground-based analogue of weightlessness that reproduces critical features of spaceflight-associated neuro-ocular syndrome will facilitate understanding, preventing, and/or treating this syndrome.

Objective: To determine whether the ocular changes in individuals exposed to an analogue of weightlessness are similar to the ocular changes in astronauts exposed to a duration of spaceflight comparable to this analogue of weightlessness.

Dilated Prelaminar Paravascular Spaces as a Possible Mechanism for Optic Disc Edema in Astronauts.

A number of ophthalmic abnormalities, including optic disc edema, have been reported in several astronauts involved in long-duration spaceflights. An increased understanding of factors contributing to this syndrome, initially designated visual impairment and intracranial pressure syndrome and recently renamed spaceflight-associated neuro-ocular syndrome, has become a high priority for ESA and NASA, especially in view of future long-duration missions, including trips to Mars. The underlying pathophysiological mechanisms of this syndrome are still not well understood.

Intracranial and Intraocular Pressure During Various Degrees of Head-Down Tilt.

Background: More than half of astronauts develop ophthalmic changes during long-duration spaceflight consistent with an abnormal intraocular and intracranial pressure (IOP, ICP) difference. The aim of our study was to assess IOP and ICP during head-down tilt (HDT) and the additive or attenuating effects of 1% CO2 and lower body negative pressure (LBNP).

Methods: In Experiment I, IOP and ICP were measured in nine healthy subjects after 3.

Optic disc edema, globe flattening, choroidal folds, and hyperopic shifts observed in astronauts after long-duration space flight.

Purpose: To describe the history, clinical findings, and possible etiologies of ophthalmic findings discovered in 7 astronauts after long-duration space flight, and document vision changes in approximately 300 additional astronauts.

Design: Retrospective, observational examination of ophthalmic findings in 7 astronauts and analysis of postflight questionnaires regarding in-flight vision changes in approximately 300 additional astronauts.

Participants: Seven astronauts with ophthalmic anomalies upon return from long-duration space missions to the International Space Station and 300 additional astronauts who completed postflight questionnaires regarding in-flight vision changes.