Department of Radiation Sciences, Umeå University, Umeå, Sweden.
Center for Biomedical Engineering and Physics, Umeå University, Umeå, Sweden.
Ann Neurol. 2016 Aug;80(2):269-76. doi: 10.1002/ana.24713. Epub 2016 Jul 15.
The discovery of a posture-dependent effect on the difference between intraocular pressure (IOP) and intracranial pressure (ICP) at the level of lamina cribrosa could have important implications for understanding glaucoma and idiopathic intracranial hypertension and could help explain visual impairments in astronauts exposed to microgravity. The aim of this study was to determine the postural influence on the difference between simultaneously measured ICP and IOP.
Eleven healthy adult volunteers (age = 46 ± 10 years) were investigated with simultaneous ICP, assessed through lumbar puncture, and IOP measurements when supine, sitting, and in 9° head-down tilt (HDT). The trans-lamina cribrosa pressure difference (TLCPD) was calculated as the difference between the IOP and ICP. To estimate the pressures at the lamina cribrosa, geometrical distances were estimated from magnetic resonance imaging and used to adjust for hydrostatic effects.
The TLCPD (in millimeters of mercury) between IOP and ICP was 12.3 ± 2.2 for supine, 19.8 ± 4.6 for sitting, and 6.6 ± 2.5 for HDT. The expected 24-hour average TLCPD on earth-assuming 8 hours supine and 16 hours upright-was estimated to be 17.3mmHg. By removing the hydrostatic effects on pressure, a corresponding 24-hour average TLCPD in microgravity environment was simulated to be 6.7mmHg.
We provide a possible physiological explanation for how microgravity can cause symptoms similar to those seen in patients with elevated ICP. The observed posture dependency of TLCPD also implies that assessment of the difference between IOP and ICP in upright position may offer new understanding of the pathophysiology of idiopathic intracranial hypertension and glaucoma. Ann Neurol 2016;80:269-276.
在视交叉层水平发现眼压（IOP）和颅内压（ICP）之间的姿势依赖性差异可能对理解青光眼和特发性颅内高压具有重要意义，并有助于解释暴露于微重力环境下的宇航员的视力障碍。本研究旨在确定体位对同时测量的 ICP 和 IOP 差值的影响。
研究纳入 11 名健康成年志愿者（年龄=46±10 岁），通过腰椎穿刺评估同时测量的 ICP 和 IOP，志愿者分别处于仰卧位、坐位和 9°头低位（HDT）。计算 IOP 与 ICP 之间的跨视交叉层压力差（TLCPD）。为了估计视交叉层的压力，从磁共振成像中估计几何距离，并用于校正静压效应。
仰卧位时 IOP 与 ICP 之间的 TLCPD（以毫米汞柱计）为 12.3±2.2，坐位时为 19.8±4.6，HDT 时为 6.6±2.5。假设地球上 8 小时仰卧位和 16 小时直立位，预计 24 小时平均 TLCPD 为 17.3mmHg。通过消除压力的静压效应，模拟微重力环境下相应的 24 小时平均 TLCPD 为 6.7mmHg。
我们提供了一种可能的生理解释，说明微重力如何引起类似于颅内压升高患者的症状。TLCPD 的观察到的体位依赖性也暗示，在直立位评估 IOP 和 ICP 之间的差异可能为特发性颅内高压和青光眼的病理生理学提供新的认识。Ann Neurol 2016;80:269-276.
