Sustained ocular venous fluid shift during spaceflight may contribute to optic disc edema

Document Type

Conference Proceeding

Publication Date


Publication Title

Invest Ophthalmol Vis Sci


Purpose : The Spaceflight Associated Neuro-ocular Syndrome (SANS) is characterized by the development of optic disc edema, chorioretinal folds, globe flattening, and/or hyperopic shifts in astronauts during 6-month missions on the International Space Station (ISS). We hypothesize that a weightlessness-induced chronic headward fluid shift within the venous system contributes to these ocular changes. Methods : Astronauts (n=10) were studied before flight (seated and supine posture) and ∼150 days into a 6-month mission on the ISS. Ocular and vascular measures included optical coherence tomography (OCT; Spectralis, Heidelberg Engineering) assessments of sub-macular choroid thickness and peripapillary total retinal thickness (TRT; segmented from Bruch's membrane to the internal limiting membrane); ultrasound-derived internal jugular vein (IJV) cross-sectional area (GE VividQ) and non-invasive IJV pressure (Veinpress); and intraocular pressure (IOP; iCare pro pre-flight and TonoPen in-flight). Repeatedmeasures ANOVA with Tukey's post-test was used to determine the mean change between conditions; data are presented as group mean ± standard deviation. Results : The mean IJV area increased from 9 ± 6 mm2 in the seated position to 83 ± 27 mm2 in the supine position on Earth and to 64 ± 31 mm2 during spaceflight (P<.001). Similarly, mean IJV pressure increased from 4.3 ± 1.6 mmHg in the seated position to 16.6 ± 5.6 mmHg in the supine position on Earth and to 14.4 ± 5.3 mmHg in-flight (P<.001). No significant changes in sub-macular choroid thickness or TRT were detected during the acute preflight posture change, however after 150 days of weightlessness, choroid thickness increased by 50 ± 37 μm (P<.05) and TRT increased by 26 ± 32 μm (P=.05) relative to preflight seated values. IOP remained within a normal range in weightlessness, averaging 15.4 ± 2.1 mmHg after 150 days of spaceflight, compared to 14.8 ± 2.7 mmHg and 15 ± 1.1 mmHg pre-flight in the seated and supine positions, respectively. Conclusions : Although a transient posture-induced venous fluid shift has no effect on choroidal or retinal thickness, a sustained, unrelenting cephalad fluid shift during spaceflight results in increased choroidal and retinal thickness. These data suggest that altered venous hemodynamics during spaceflight may contribute to SANS.





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