Astronaut ophthalmic syndrome

Abstract

During and after missions on the International Space Station, some astronauts experience ophthalmic changes, including choroidal folds, optic disc edema, cotton-wool spots, globe flattening, and refraction changes. Astronauts with ophthalmic issues had significantly higher plasma concentrations of metabolites that are associated with the 1-carbon metabolic pathway than those without ophthalmic issues. We hypothesized that genetic differences might explain the metabolite differences. Indeed, genetics and B vitamin status were significant predictors of ophthalmic issues. We now have developed a hypothesis regarding the mechanisms that link 1-carbon pathway genetics and the condition that we suggest calling, "astronaut ophthalmic syndrome." We maintain that this condition is genetically predisposed and is associated with endothelial dysfunction that is induced by oxidative stress. Subsequent edema can hinder cerebrospinal fluid efflux and can lead to locally increased pressures in the subarachnoid space within the orbit, which impinges on the optic nerve and/or eye in affected individuals. Confirming this hypothesis will help characterize the genetics of 1-carbon pathway metabolism, homocysteine, oxidative stress, endothelial dysfunction, and cardiovascular and potentially other diseases.-Zwart, S. R., Gibson, C. R., Gregory, J. F., Mader, T. H., Stover, P. J., Zeisel, S. H., Smith, S. M. Astronaut ophthalmic syndrome.

Spaceflight associated neuro-ocular syndrome (SANS) and the neuro-ophthalmologic effects of microgravity: a review and an update

“…60,78 CONCLUSION In summary, novel and unique neuro-ophthalmic findings have been documented in astronauts during and after LDSF and have been termed SANS. Although a single unifying and overreaching mechanism has yet to be proven, 1,2,[4][5][6][7][8][9]19,40,41,44,[55][56][57] and a multifactorial pathogenesis may be involved, it is likely that SANS may be the end result of cephalad fluid shifts to the brain and orbit brought about by extended MG exposure. Mao et al reviewed the impact of spaceflight and artificial gravity in a mouse retinal model using biochemical and proteomic analysis.…”

“…The interested reader is directed to both our own prior review articles but also the animal and human work performed by the many intramural and extramural NASA related partners working on SANS. [6][7][8][9] Despite the recognition and research related to SANS for many years, several unanswered questions remain: (1) What, if any, is the significance of potential preferential laterality (i.e., right-sided bias) seen in the anatomical changes of SANS? (unpublished data, personal communication WT); (2) Are there changes in the eye's anterior segment (in addition to the posterior segment findings) associated with SANS?…”

“…In the terrestrial environment, CSF is largely produced in the choroid plexus and drains into the lower pressure cervical venous vasculature. [1][2][3][4][5][6][7][8][9] Although vascular autoregulation stabilizes the cerebral and ONH arterial diameter, 10,11 jugular venous distention has been well documented during both head down and microgravity (MG) studies 12 suggesting that cerebral and jugular venous congestion may be present in the MG environment. Jugular venous distention alone does not necessarily prove that venous pressure is increased during spaceflight and some studies have suggested that the venous pressure may in fact be decreased.…”

Red risks for a journey to the red planet: The highest priority human health risks for a mission to Mars

“…This multi-hit hypothesis posits that one-carbon pathway genetics is an indispensable factor, and that the combination with one or more other factors (e.g., fluid shifts, carbon dioxide, radiation, endocrine effects) lead to these pathologies. This has been detailed in a hypothesis paper 95 and in a recent review 96 . In brief, the hypothesis is that genetics and B-vitamin status contribute to endothelial dysfunction, as folate (and other B-vitamins) play critical roles in nitric oxide synthesis and endothelial function.…”

Effects of microgravity on bone

“…In the case of space man there are many problems related theirs conditions of the space environment. 1,2 Microgravity in the space is not appropriate to humans, and can affect the health of space man. [3][4][5] The bone is one of the affected organs.…”