Sustained ocular venous fluid shift during spaceflight may contribute to optic disc edema
Marshall-Goebel K, MacIas B, Laurie S, Lee S, Martin D, Dulchavsky S, Hargens A, and Stenger MB. Sustained ocular venous fluid shift during spaceflight may contribute to optic disc edema. Invest Ophthalmol Vis Sci 2019; 60(9).
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.