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Giovanni Taibbi, Ronita L. Cromwell, Susana B. Zanello, Patrice O. Yarbough, Gianmarco Vizzeri; Evaluation of Ocular Outcomes in two 14-day Bed Rest Studies. Invest. Ophthalmol. Vis. Sci. 2012;53(14):4903.
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To test the safety of 14-day bed rest (BR) on ocular structures and visual function, we evaluated ocular outcomes in two 14-day BR studies designed to simulate the effects of microgravity on the human body.
Two 14-day BR studies were conducted at the NASA Flight Analogs Research Unit. Subjects were selected using NASA standard screening procedures. Standardized conditions for all NASA BR studies were implemented, including a strict sleep-wake cycle, a standardized diet, remaining in bed for 24 hours a day, and continuous video monitoring. In the first study, subjects maintained a horizontal (0°) position and followed an integrated resistance and aerobic training program 6 days a week. In the second study, subjects remained in a 6° head-down tilt (HDT) position and did not engage in exercise. Ophthalmological examinations, including Spectralis and Cirrus scans centered on the macula and the optic disc, were performed pre- and two-day post-BR. Changes from baseline were evaluated for the following outcomes: best corrected visual acuity; spherical equivalent; intraocular pressure (IOP); Cirrus optic disc parameters, average retinal nerve fiber layer thickness (RNFLT), macular thickness and volume; Spectralis average RNFLT, macular and peripapillary retinal thickness and volume.
Nine healthy adults (8 males, 1 female; mean age 34 ± 8.5) completed the 0° BR study. Three of these subjects also completed the 6° HDT study (6 males, 4 females; mean age 40 ± 9.4), after a minimum 3-month interval from completion of the 0° BR study. Overall, for both studies, no significant changes compared to baseline were detected for the ocular parameters measured. For example, IOP were 14.0 and 13.0 mmHg pre- and post-BR (P = 0.96), respectively, for the 0° study, and 15.3 and 14.9 mmHg pre- and post-BR (P = 0.33), respectively, for the 6° HDT study. Cirrus average RNFLT were 93.6 and 91.7 µm pre- and post-BR (P = 1.00), respectively, for the 0° study, and 94.9 and 96.0 µm pre- and post-BR (P = 0.56), respectively, for the 6° HDT study. Spectralis average RNFLT were 97.4 and 96.4 µm pre- and post-BR (P = 1.00), respectively, for the 0° study, and 99.4 and 100.9 µm pre- and post-BR (P = 0.98), respectively, for the 6° HDT study.
The experimental conditions appeared to be safe for the integrity of the visual system. Further study is needed to evaluate ocular changes related to long-duration BR, and determine the validity of HDT BR as a ground-based analog to study microgravity-induced ocular changes.
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