Comparison of ocular outcomes across two 14-day bed rest platforms

One possible mechanism for visual changes reported in astronauts may involve microgravity induced cephalad fluid shifts that lead to elevated retrobulbar cerebrospinal fluid pressure. Because head-down tilt (HDT) bed rest induces cephalad fluid shifts, vision monitoring was implemented for NASA bed rest campaigns. Subjects selected for these campaigns were healthy adults (14 males and 5 females). In one campaign, subjects maintained a horizontal (0°) position while in bed and were exercised six days per week. In the other campaign, subjects were placed at 6° HDT while in bed and did not engage in exercise. Measures common to both studies included intraocular pressure and retinal measures derived from optical coherence tomography. There were no significant differences between subject groups for pre- and post bed rest testing. These preliminary results suggest that exercise combined with horizontal bed rest as compared to 6° HDT bed rest did not produce differences in the ocular response of these subjects. Further investigation is needed to examine both the acute response and long term adaptation of structural and functional ocular parameters in the bed rest platform.