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Brief Report
May 20, 2021

Association of Structural Changes in the Brain and Retina After Long-Duration Spaceflight

Author Affiliations
  • 1KBR, Houston, Texas
  • 2NASA, Johnson Space Center, Houston, Texas
  • 3University of Texas Health Science Center at Houston, McGovern Medical School, Houston
  • 4MEI Technologies, Houston, Texas
  • 5University of Houston, Houston, Texas
  • 6University of Michigan, Ann Arbor
  • 7Henry Ford Hospital, Detroit, Michigan
  • 8University of California, San Diego, San Diego
JAMA Ophthalmol. 2021;139(7):781-784. doi:10.1001/jamaophthalmol.2021.1400
Key Points

Question  What is the association between spaceflight-induced structural changes in the brain and retina?

Findings  In this cohort study, a positive association between spaceflight-induced changes in total retinal thickness, a quantitative assessment of optic disc edema, and lateral ventricle volume, but not white matter or intracranial volume, is suggested although not definitive.

Meaning  A weak association between spaceflight-induced changes in lateral ventricle volume and total retinal thickness in this study suggests that cerebrospinal fluid redistribution that likely underlies brain structural changes does not play a substantial role in the development of optic disc edema; ocular changes are likely complex and multifactorial in nature.

Abstract

Importance  Long-duration spaceflight induces structural changes in the brain and eye. Identification of an association between cerebral and ocular changes could help determine if there are common or independent causes and inform targeted prevention strategies or treatments.

Objective  To determine if there is an association between quantitative changes in intracranial compartment volumes and peripapillary total retinal thickness after spaceflight.

Design, Setting, and Participants  This cohort study included healthy International Space Station crew members before and immediately after long-duration spaceflight. Data on race were not collected. Analysis was conducted from September to November 2020.

Exposures  Long-duration spaceflight (mean [SD], 191 [55] days).

Main Outcomes and Measures  Optical coherence tomography–derived peripapillary total retinal thickness as a quantitative assessment and early sign of optic disc edema and magnetic resonance imaging–derived measures of lateral ventricle volume, white matter volume, and whole brain plus cerebrospinal fluid volume.

Results  In 19 healthy crew members included in this study (5 women [26.3%], 14 men [73.7%]; mean [SD] age, 45.2 [6.4] years), analyses revealed a positive, although not definitive, association between spaceflight-induced changes in total retinal thickness and lateral ventricle volume (4.7-μm increase in postflight total retinal thickness [95% CI, −1.5 to 10.8 μm; P = .13] per 1-mL postflight increase in lateral ventricle volume). Adjustments for mission duration improved the strength of association (5.1 μm; 95% CI, −0.4 to 10.5 μm; P = .07). No associations were detected between spaceflight-induced changes in total retinal thickness and white matter volume (0.02 μm; 95% CI, −0.5 to 0.5 μm; P = .94) or brain tissue plus cerebrospinal fluid volume, an estimate of intracranial volume (0.02 μm; 95% CI, −0.6 to 0.6 μm; P = .95).

Conclusions and Relevance  These results help characterize spaceflight-associated neuro-ocular syndrome and the physiologic associations of headward fluid shifts with outcomes during spaceflight on the central nervous system. The possibly weak association between increased total retinal thickness and lateral ventricle volume suggest that while weightlessness-induced fluid redistribution during spaceflight may be a common stressor to the brain and retina, the development of optic disc edema appears to be uncoupled with changes occurring in the intracranial compartment.

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