Spaceflight is known to cause ophthalmic changes in a condition known as spaceflight-associated neuro-ocular syndrome (SANS). It is hypothesized that SANS is caused by cephalad fluid shifts and potentially mild elevation of intracranial pressure (ICP) in microgravity. Head-down tilt (HDT) studies are a ground-based spaceflight analogue to create cephalad fluid shifts. Here, we developed non-invasive magnetic resonance imaging (MRI)-based techniques to quantify ophthalmic structural changes under acute 15° HDT. We specifically quantified: (i) change in optic nerve sheath (ONS) and optic nerve (ON) cross-sectional area, (ii) change in ON deviation, an indicator of ON tortuosity, (iii) change in vitreous chamber depth, and (iv) an estimated ONS Young's modulus. Under acute HDT, ONS cross-sectional area increased by 4.04 mm² (95% CI 2.88–5.21 mm², p < 0. 000), while ON cross-sectional area remained nearly unchanged (95% CI −0.12 to 0.43 mm², p = 0.271). ON deviation increased under HDT by 0.20 mm (95% CI 0.08–0.33 mm, p = 0.002). Vitreous chamber depth decreased under HDT by −0.11 mm (95% CI −0.21 to −0.03 mm, p = 0.009). ONS Young's modulus was estimated to be 85.0 kPa. We observed a significant effect of sex and BMI on ONS parameters, of interest since they are known risk factors for idiopathic intracranial hypertension. The tools developed herein will be useful for future analyses of ON changes in various conditions.

众所周知，太空飞行会导致一种称为太空飞行相关神经眼综合征 (SANS) 的疾病的眼科变化。据推测，SANS 是由头侧流体转移和微重力下颅内压 (ICP) 可能轻度升高引起的。低头倾斜 (HDT) 研究是一种基于地面的太空飞行模拟，用于产生头侧流体变化。在这里，我们开发了基于非侵入性磁共振成像 (MRI) 的技术来量化急性 15° HDT 下的眼科结构变化。我们具体量化了：（i）视神经鞘（ONS）和视神经（ON）横截面积的变化，（ii）ON偏差的变化，ON曲折的指标，（iii）玻璃体腔深度的变化，和(iv) 估计的 ONS 杨氏模量。急性 HDT 下 ONS 截面积增加 4.04 mm ²（95% CI 2.88–5.21 mm ²，p < 0. 000），而 ON 横截面积几乎保持不变（95% CI -0.12 至 0.43 mm ²，p = 0.271）。HDT 下 ON 偏差增加了 0.20 毫米（95% CI 0.08–0.33 毫米，p = 0.002）。HDT 下玻璃体腔深度减少 -0.11 mm（95% CI -0.21 至 -0.03 mm，p = 0.009）。ONS 杨氏模量估计为 85.0 kPa。我们观察到性别和 BMI 对 ONS 参数的显着影响，因为它们是已知的特发性颅内高压的危险因素，因此我们很感兴趣。本文开发的工具将有助于未来分析各种条件下的 ON 变化。