Changes in the Optic Nerve Head and Choroid Over 1 Year of Spaceflight

Question  Are 6-month spaceflight missions sufficiently long to characterize the spaceflight-associated neuro-ocular syndrome risks of proposed longer-duration missions to the moon and Mars?

Findings  In a case series study of 2 crew members from a 1-year–long mission, 1 crew member developed mild optic disc edema after 270 days in spaceflight. In the other crew member, optic disc edema and choroid folds progressively worsened over the duration of the 1-year mission.

Meaning  Additional observations of crew members on missions longer than 6 months may be warranted to characterize spaceflight-associated neuro-ocular syndrome risks of extended duration spaceflight.

Importance  While 6-month data are available regarding spaceflight-associated neuro-ocular syndrome, manned missions for 1 year and beyond are planned, warranting evaluation for spaceflight-associated neuro-ocular syndrome beyond 6 months.

Objective  To determine if the manifestation of spaceflight-associated neuro-ocular syndrome worsens during International Space Station missions exceeding the present 4- to 6-month duration.

Design, Setting, and Participants  The One-Year Mission Study used quantitative imaging modalities to investigate changes in ocular structure in 2 crew members who completed a 1-year–long spaceflight mission. This study investigated the ocular structure of crew members before, during, and after their mission on the International Space Station. Two crew members participated in this study from March 2015 to September 2016. Analysis began in March 2015 and ended in May 2020.

Exposures  Crew members were tested before, during, and up to 1 year after spaceflight.

Main Outcomes and Measures  This study compares ocular changes (peripapillary retinal edema, axial length, anterior chamber depth, and refraction) in two 1-year spaceflight mission crew members with cohort crew members from a 6-month mission (n = 11). Minimum rim width (the shortest distance between Bruch membrane opening and the internal limiting membrane) and peripapillary total retinal thickness were measured using optical coherence tomography.

Results  Both crew members were men. Minimum rim width and total retinal thickness increased in both participants throughout the duration of spaceflight exposure to the maximal observed change from preflight (minimum rim width: participant 1, 561 [+149 from preflight] μm at flight day 270; participant 2, 539 [+56 from preflight] μm at flight day 270; total retinal thickness: participant 1, 547 [+135 from preflight] μm at flight day 90; participant 2, 528 [+45 from preflight] μm at flight day 210). Changes in peripapillary choroid engorgement, axial length, and anterior chamber depth appeared similar between the 1-year mission participants and a 6-month mission cohort.

Conclusions and Relevance  This report documents the late development of mild optic disc edema in 1 crew member and the progressive development of choroidal folds and optic disc edema in another crew member over the duration of 1 year in low Earth orbit aboard the International Space Station. Previous reports characterized the ocular risk associated with 4 to 6 months of spaceflight. As future spaceflight missions are planned to increase in duration and extend beyond low Earth orbit, further observation of astronaut ocular health on spaceflight missions longer than 6 months in duration may be warranted.