Astronauts have presented with a constellation of visual changes referred to as spaceflight-associated neuro-ocular syndrome (SANS). However, early markers of microgravity-induced optic remodeling have not been fully identified nor have countermeasures been developed. In order to identify early markers of SANS, we studied 10 subjects with optical coherence tomography and ultrasound when upright and supine, and again after 24 hours of 6-degree head down tilt (HDT) bedrest. Upon acute transition from upright to supine, choroid area (2.24±0.53 to 2.28±0.52 mm², p=0.001) and volume (9.51±2.08 to 9.73±2.08 mm³, p=0.002) increased. After 24 hours of HDT bedrest, subfoveal choroidal thickness (372±93 to 381±95 µm, p=0.02) , choroid area (2.25±0.52 to 2.33±0.54 mm², p=0.08) and volume (9.64±2.03 to 9.82±2.08 mm³, p=0.08) increased relative to the supine position. Subsequently, 7 subjects spent 3 days in -6 deg HDT bedrest to assess whether low-level lower body negative pressure (LBNP) could prevent the observed choroidal engorgement during bedrest. Maintaining the -6 deg HDT position for 3 days caused choroid area (Δ0.11 mm², p=0.05) and volume (Δ0.45 mm³, p=0.003) to increase. When participants also spent 8 hours daily under -20mmHg LBNP, choroid volume still increased, but substantially (40%) less than in the control trial (Δ0.27 mm³, p=0.05). Moreover, the increase in choroid area was diminished (Δ0.03 mm², p=0.13), indicating that low-level LBNP attenuates the choroid expansion associated with 3 days of -6 deg HDT bedrest. These data suggest that low-level LBNP may be an effective countermeasure for SANS.

中文翻译：

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每日产生的足部液体移位减轻了与头朝下倾斜的床架有关的眼部变化。

宇航员已经呈现出一系列视觉变化，这些变化被称为航天相关神经视觉综合征（SANS）。但是，微重力诱发的视神经重塑的早期标记物尚未完全确定，也未开发出对策。为了识别SANS的早期标记，我们对10名受试者进行了光学相干断层扫描和超声检查，这些受试者在直立和仰卧时进行了研究，并在24小时6度向下俯仰（HDT）卧床休息后再次进行了研究。在从直立向仰卧的急性过渡时，脉络膜面积（2.24±0.53至2.28±0.52mm ²，p ＝ 0.001）和体积（9.51±2.08至9.73±2.08mm ³，p ＝ 0.002）增加。HDT卧床24小时后，小凹脉络膜厚度（372±93至381±95 µm，p = 0.02），脉络膜面积（2.25±0.52至2.33±0.54 mm ²，p ＝ 0.08）和体积（9.64±2.03至9.82±2.08mm ³，p ＝ 0.08）相对于仰卧位置增加。随后，有7位受试者在-6度HDT卧床休息了3天，以评估低水平的下身负压（LBNP）是否可以防止在卧床休息期间观察到的脉络膜充血。保持-6度HDT位置3天会导致脉络膜面积（Δ0.11mm ²，p = 0.05）和体积（Δ0.45mm ³，p = 0.003）增大。当参与者还每天在-20mmHg LBNP下度过8小时时，脉络膜体积仍增加，但比对照试验（Δ0.27mm ³，p = 0.05）少得多（40％）。此外，脉络膜面积的增加减少了（Δ0.03mm ²，p = 0.13），表明低水平的LBNP会减弱与-6度HDT卧床休息3天相关的脉络膜扩张。这些数据表明，低水平的LBNP可能是SANS的有效对策。