Vision Impairment and Intracranial Pressure in Astronauts
Since 1989, as part of the postflight eye examination, astronauts were queried as to whether they perceived a subjective improvement or degradation in distant or near vision (none, mild, moderate, or severe) during their short- and long-duration missions. Prompted by persistent reports of vision changes, NASA began a stepwise operational process to determine the c ause(s). Several ophthalmic procedures were initiated on astronauts, including dilated fundus (the rear portion of the eye) examinations with binocular ophthalmoscopy, cycloplegic refraction, optical coherence tomography (OCT), magnetic resonance imaging (MRI) of orbits, and fundus photography for before and after space missions.
In a follow-on study, twenty-seven astronauts underwent thin-section, three-dimensional, eye orbital, and conventional MRI brain scans. Eight astronauts underwent repeat imaging after an additional mission in space. All astronauts had previous exposure to microgravity. Image analysis of the optic nerve sheath, optic disc, posterior globe, and pituitary gland was performed and compared for association with intracranial evidence of excessive fluid buildup inside the skull, cells, tissues, or body cavities, venous blood clotting in the brain and/or mass lesion.
Visual acuity degradation in astronauts exposed to microgravity is a newly recognized phenomenon. Although the exact mechanism is yet to be fully determined, many MRI findings suggest that intracranial hypertension is an important component. However, a large proportion of astronauts do not show these ocular effects, suggesting there could be variable biologic response to the spaceflight environment and warrants a search for existing risk factors. Standardization of qualitative and quantitative imaging criteria will further help in the identification of asymptomatic changes and allow for the use of countermeasures to mitigate potential long-term vision damage. Future studies involving advance tissue imaging techniques would improve our understanding of the cause-versus-effect relationship of intracranial pressure after exposure to microgravity (Kramer 2012).
Results Publications
Zwart SR, Gibson CR, Mader TH, Ericson K, Ploutz-Snyder RJ, Heer MA, Smith SM. Vision Changes After Spaceflight Are Related to Alterations in Folate- and Vitamin B-12-Dependent One-Carbon Metabolism. Journal of Nutrition. 2012 Mar 1; 142(3): 427-431. DOI: 10.3945/jn.111.154245. PMID: 22298570.
Mader TH, Gibson CR, Pass AF, Kramer LA, Lee AG, Fogarty J, Tarver WJ, Dervay JP, Hamilton DR, Sargsyan AE, Phillips JL, Tran D, Lipsky W, Choi J, Stern C, Kuyumjian R, Polk JD. Optic Disc Edema, Globe Flattening, Choroidal Folds, and Hyperopic Shifts Observed in Astronauts after Long-duration Space Flight. Opthalmology. 2011 October; 118(10): 2058-2069. DOI: 10.1016/j.ophtha.2011.06.021. PMID: 21849212.
Chylack Jr LT, Feiveson AH, Peterson LE, Tung WH, Wear , Marak LJ, Hardy DS, Chappell LJ, Cucinotta FA. NASCA Report 2: Longitudinal Study of Relationship of Exposure to Space Radiation and Risk of Lens Opacity. Radiation Research. 2012 July; 178(1): 25-32. DOI: 10.1667/RR2876.1.
Kramer LA, Sargsyan AE, Hasan KM, Polk JD, Hamilton DR. Orbital and Intracranial Effects of Microgravity: Findings at 3-T MR Imaging. Radiology. 2012 June; 263(3): 819-827. DOI: 10.1148/radiol.12111986. PMID: 22416248.
NASA News Release
Washington Post Story
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