Anterior and posterior ocular structures change during long-duration spaceflight and one year after landing

Abstract

Purpose : Spaceflight-associated neuro-ocular syndrome (SANS) is reported to affect ~40% of astronauts on long-duration spaceflights (as of May 2017) as assessed by one or more findings: optic disc edema, hyperopic shifts, globe flattening, cotton-wool spots, or choroidal folds. The purpose of this study was to quantify morphologic change of the optic nerve head (ONH), peripapillary choroid thickness, axial length, and anterior chamber depth (ACD), which are variables hypothesized to be associated with SANS during long-duration International Space Station (ISS) missions.

Methods : Eleven long-duration (170 ± 19 d) ISS astronauts participated in testing before, during, and up to 1 year after spaceflight. Preflight (12 to 3 mos. before launch) and postflight (10, 30, 90, 180, and 365 d after landing) tests included assessments of eye structure (fundoscopy, optical coherence tomography [OCT], and optical biometry). Inflight (days 10 ± 7, 30 ± 7, 90 ± 7, and 150 ± 30) evaluations included fundoscopy and OCT imaging of the posterior eye. A mixed-effects linear regression model was used to compare preflight outcomes to multiple inflight and postflight observations. Data are presented as mean with 95% CI.

Results : Minimum rim width (ONH rim tissue) and peripapillary choroidal thickness significantly increased from preflight values as early as the first inflight time point, and maximally on flight day 150 (minimum rim width: 39 (32 – 46) µm, P < 0.001; choroidal thickness: 47 (34 – 60) µm, P < 0.001). Both variables recovered to preflight values 45 d after landing. Two of the 11 subjects demonstrated Frisen grade 1 edema during flight (OD: day 150, OD day 90). At the first postflight exam (day <10), axial length and ACD were significantly decreased by 0.10 (0.11 – 0.08) mm (P < 0.001) and by 0.11 (0.14 – 0.09) mm (P < 0.001), respectively. Both of these variables remained significantly lower than preflight values for up to 1 year.

Conclusions : The results suggest that ocular changes are not limited to a specific subset of individuals with disc edema. Future studies should determine the specific retinal components that are affected. These data provide further evidence that SANS is not limited to the posterior segment of the eye, and the anterior segment warrants further investigation. Quantitative OCT of the ONH during long-duration spaceflight may be an important tool for monitoring of optic disc edema.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.