Ophthalmic Changes in Spaceflight: The evidence, etiological theories, and implications for the future of human space exploration
- Paper number
IAC-14,A1,3,2,x27273
- Author
Mr. Michael R. Greene, University of Calgary, Canada
- Coauthor
Dr. Douglas R. Hamilton, University of Calgary, Canada
- Year
2014
- Abstract
Visual acuity shifts have been described in reports dating back several decades of human spaceflight. These, often anecdotal accounts, were regularly minor, transient, and not accompanied by other significant clinical findings. As such they were previously thought to be associated with presbyopia, hyperopic shifts attributed to age or fatigue. No formal testing was previously implemented to evaluate potential pathophysiological mechanisms. Recent indications suggest that these vision changes are more common than previously anticipated, and are often accompanied by a myriad of findings. Evidence of spaceflight-induced ophthalmic changes has been documented. These changes include optic disc edema, globe flattening, choroidal folds, optic nerve sheath distension, and retinal changes such as cotton wool spots. Evidence also indicates an elevation in intracranial pressure (ICP) in some astronauts, measured postflight. These discoveries have stimulated research and ongoing efforts to determine the direct mechanism and contributing factors involved in spaceflight-induced ophthalmic changes. Although consensus is yet to be attained, microgravity-induced cephalad fluid shift - causing raised ICP - is commonly accepted as the primary precipitated factor. Proposed contributing factors include spacecraft cabin carbon dioxide levels, strenuous on-orbit exercise programs, and nutritional factors such high sodium diets. A recent study also suggests a potential relationship between radiation exposure and elevated ICP, exacerbating these effects. It is likely that the etiology is multifactorial, as opposed to being the result of one of the aforementioned; however alterations in cardiovascular, ocular and cerebrospinal fluid dynamics are suspected to be causative. The incidence of ophthalmic changes is estimated to be on the order of 40% for astronauts whose microgravity exposure approaches 6 months. Although vision changes have thus far been managed with corrective lenses, long-term sequelae may have significant implications for the safety and success of future long-duration space missions. The individual risk of permanent visual changes remains unknown. National space agencies have implemented expanded preflight, inflight, and postflight testing regiments and capabilities to determine the existence and severity of the ophthalmic changes. These studies increase the amount and quality of relevant data, providing essential steps towards fully characterizing this newly recognized syndrome. Once causative mechanisms are identified, appropriate mitigation strategies can be developed. This paper investigates spaceflight-induced ophthalmic changes, providing a review of the evidence, current level of understanding, ongoing areas of research, and a discussion of the implications to the future human spaceflight.
- Abstract document
- Manuscript document
IAC-14,A1,3,2,x27273.pdf (🔒 authorized access only).
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