Xu Xin, Li Li, Cao Ruidan, Tao Ye, Guo Qun, Geng Jia, Li Yongzhi, Zhang Zuoming
Department of Clinical Aerospace Medicine, Key Laboratory of Aerospace Medicine of the National Education Ministry, Fourth Military Medical University, Xi'an, Shaanxi, China.
Aviat Space Environ Med. 2010 Apr;81(4):418-22. doi: 10.3357/asem.2629.2010.
Myopic eyes show structural differences from normal eyes and may respond differently to microgravity, increasing the risk for possible development of ocular hypertension and glaucoma on orbit. In this experiment we used head-down rest (HDR) at an angle of 15 degrees to produce hydrostatic changes similar to acute exposure to microgravity.
There were 65 subjects (129 eyes) who were divided into groups characterized by refraction: emmetropes (N = 46; refraction error between -0.99 D and +0.10 D), low myopes (N = 39; > or = -1.0 D to < -3.0 D), and moderate myopes (N = 44; > or = -3.0 D to < -6.0 D). Each subject was studied resting in a horizontal position and after 1, 6, 11, 16, and 21 min of HDR. Measured variables included systolic and diastolic blood pressure (SBP and DBP, respectively), intraocular pressure (IOP), and ocular perfusion pressure (OPP).
The mean values of IOP increased significantly in all eyes during HDR, with IOP peaking at 6 min. Compared to emmetropes and low myopes, moderate myopes showed a significantly greater increase in IOP and higher peak values for IOP (18.6, 18.7, and 19.8 mmHg for emmetropes, low, and moderate myopes, respectively). Mean values of OPP in moderate myopes were significantly lower than in emmetropes and low myopes during HDR. Compared with baseline, mean SBP and DBP decreased obviously in emmetropes during HDR, while changes were minimal in the other groups.
Abnormal auto-regulation of ocular blood pressure in myopes of moderate and greater severity may pose a risk factor for developing ocular hypertension and possibly glaucoma when exposed to microgravity. HDR may offer a method of screening candidates for spaceflight for this risk prior to microgravity exposure.
近视眼睛与正常眼睛在结构上存在差异，对微重力的反应可能也不同，这增加了在太空中发生高眼压和青光眼的风险。在本实验中，我们采用15度头低位休息（HDR）来产生类似于急性暴露于微重力的流体静力变化。
65名受试者（129只眼睛）按屈光状态分为正视组（N = 46；屈光不正度数在-0.99 D至+0.10 D之间）、低度近视组（N = 39；≥ -1.0 D至< -3.0 D）和中度近视组（N = 44；≥ -3.0 D至< -6.0 D）。每位受试者在水平位休息时以及在HDR 1、6、11、16和21分钟后接受研究。测量的变量包括收缩压和舒张压（分别为SBP和DBP）、眼压（IOP）和眼灌注压（OPP）。
在HDR期间，所有眼睛的眼压平均值均显著升高，眼压在6分钟时达到峰值。与正视眼和低度近视眼相比，中度近视眼的眼压升高更为显著，眼压峰值更高（正视眼、低度和中度近视眼的眼压峰值分别为18.6、18.7和19.8 mmHg）。在HDR期间，中度近视眼的眼灌注压平均值显著低于正视眼和低度近视眼。与基线相比，正视眼在HDR期间收缩压和舒张压平均值明显下降，而其他组的变化最小。
中高度近视患者眼血压的异常自动调节可能是在暴露于微重力时发生高眼压甚至青光眼的危险因素。HDR可能为在微重力暴露前筛选有此风险的太空飞行候选者提供一种方法。
