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Scott H Greenwald, Steven Laurie, Karina Marshall-Goebel, PhD, Laura P Pardon, Stuart MC Lee, Claudia Stern, Haleh Sangi-Haghpeykar, Eric M Bershad, Brandon Macias; Optic disc edema and chorioretinal folds develop during strict head-down tilt bedrest with and without artificial gravity. Invest. Ophthalmol. Vis. Sci. 2021;62(8):2276.
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Spaceflight-associated neuro-ocular syndrome (SANS) is a condition that is hypothesized to develop as a consequence of the chronic headward fluid shift that occurs in sustained weightlessness. Here, we exposed healthy subjects to strict 6° head-down tilt bedrest (HDTBR) to generate a sustained headward fluid shift in the Artificial Gravity Bedrest with the European Space Agency (AGBRESA) study and assessed SANS-related ocular changes (e.g., optic disc edema, chorioretinal folds). A subset of these subjects were exposed to artificial gravity (AG) via centrifugation during HDTBR to investigate whether this intervention can attenuate fluid shift-induced ocular changes.
Data were collected in 24 healthy subjects during 60 days of strict 6° HDTBR, as well as during the pre- and post-HDTBR phases with the subjects in seated and supine postures. The cohort was divided into 3 groups (n=8/group), two of which received 30 minutes total per day of AG (0.3 g at the eyes) by either continuous (cAG) or intermittent (iAG) short-arm centrifugation. Optical coherence tomography images were acquired to quantify changes in peripapillary total retinal thickness (TRT), retinal nerve fiber layer thickness, and choroidal thickness, and to detect chorioretinal fold development. Intraocular pressure, standard automated perimetry, and optical biometry data were also collected.
TRT increased from seated baseline as a function of HDTBR duration for each group. By HDTBR day 58, TRT was increased by 35.9 µm (95% CI, 19.9-51.9 µm, P < 0.0001), 36.5 µm (95% CI, 4.7-68.2 µm, P = 0.01), and 27.6 µm (95% CI, 8.8-46.3 µm, P = 0.0005) for the control, cAG, and iAG group, respectively. The cAG and iAG groups were not different from the control group for this measure during HDTBR (P > 0.6). Although not apparent at HDTBR day 30, chorioretinal folds were observed by HDTBR day 58 in 6 subjects (n≥1 per group).
The headward fluid shift generated by strict 6° HDTBR leads to the development of early optic disc edema, as detected by increased TRT, and chorioretinal folds in some subjects. Therefore, this spaceflight analog is an appropriate model for investigating the etiology of SANS and refining countermeasure strategies. 30 minutes of either cAG or iAG daily does not counter the effects of the headward fluid shift on the eye, suggesting that longer duration exposures are required.
This is a 2021 ARVO Annual Meeting abstract.
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