探讨在空气脉冲作用下正常角膜、圆锥角膜及高度近视眼角膜表面压强的时间空间变化特征。

选取2022年1月至2022年12月于首都医科大学附属北京同仁医院北京同仁眼科中心就诊健康受试者2例(2只眼)、圆锥角膜患者2例(2只眼)及高度近视眼患者各2例(2只眼)。其中，健康受试者男性1例(1只眼)，女性1例(1只眼)；年龄30~32岁，平均年龄31岁。圆锥角膜患者男性1例(1只眼)，女性1例(1只眼)；年龄22~30岁，平均年龄26岁。高度近视眼患者男性1例(1只眼)，女性1例(1只眼)；年龄24~26岁，平均年龄25岁。使用计算流体力学与三维眼前节分析仪Scheimpflug摄像技术获取健康角膜、圆锥角膜及高度近视眼角膜受试者角膜前后表面的几何参数，构建个性化三维角膜模型。设定计算域和边界条件后，模拟可视化眼反应分析仪快速气流脉冲对角膜的影响，记录流场结构及表面压强分布。

5 ms流场时未形成较稳定的剪切层，靠近轴线处气流受阻减速增压，形成轴向逆压梯度，远离轴线的气流上卷，在约7 ms时到达壁面；10 ms流场时剪切层仍不稳定，压力波形成且仅在7 ms~13 ms射流加速过程中存在；15 ms流场时13 ms后形成较为稳定混合层，混合层内压力波动减弱和消失，对周围流动的引射作用增强，压强降低；20 ms流场时射流动压下降，驻点压强降低，剪切层外的负压绝对值降低，压力梯度趋向平缓；25 ms流场时出现不稳定剪切层压力波，角膜驻点和附近的压强迟滞。健康角膜射流速度达到峰值附近时的表面压强径向流动呈现典型的亚声速冲击射流流动特征，以角膜中心为驻点，全部动压转换为静压，速度滞止至0，压力达到峰值，驻点以外流体随后转向沿检测件表面向下游流动。角膜表面最大驻点压强发生在15 ms到16 ms之间。该特点可由Navier-Stokes方程组描述。圆锥角膜表面压强径向分布曲线在驻点附近比健康角膜的压强低，压强分布曲线下降比健康角膜缓，斜率绝对值更小，患病程度越重其径向压强离健康角膜压强越远，表面压强超过健康角膜表面压强的径向位置越靠外。近视眼患者角膜表面压强径向分布曲线在除角膜边缘都比健康角膜压强高，在径向无量纲距离0.4之前下降更缓。

空气脉冲约7 ms达到角膜顶点，正常角膜、圆锥角膜及高度近视眼患者角膜表面压强随时间与空间变化的规律一致，仅数值上有差异。压强以顶点为中心呈对称性变化，靠近驻点处流速降低而压强增大。射流加速和减速过程存在滞后现象，最大驻点压强与最大射流速度基本重合，二者时间曲线形态相似。

To investigate the spatiotemporal variation of pressure on the corneal surface under an air puff load among normal, keratoconic, and highly myopic corneas.

From January 2022 to December 2022, two healthy subjects (two eyes), two patients with keratoconus (two eyes), and two patients with high myopia (two eyes) were selected for the study at the Beijing Tongren Ophthalmic Center affiliated to Capital Medical University. Among them, the healthy subjects comprised one male (one eye) and one female (one eye) with an average age of 31 (ranging from 30 to 32 years). The keratoconus patients comprised one male (one eye) and one female (one eye) with an average age of 26 (ranging from 22 to 30 years). The high myopia patients comprised one male (one eye) and one female (one eye) with an average age of 25 years (ranging from 24 to 26 years). The geometric parameters of the anterior and posterior surfaces of the cornea from three groups of subjects: normal cornea, keratoconus, and high myopi using computational fluid dynamics coupled with three dimensional Scheimpflug imaging were performed. A personalized three-dimensional corneal model was constructed. After setting up the computational domain and boundary conditions, simulate and visualize the effects of the air puff from the ocular response analyzer on the cornea, recording the flow field structure and surface pressure distribution.

When the flow field was 5 ms, a relatively stable shear layer was not formed, and the airflow near the axis was obstructed, decelerated, and pressurized, forming an axial reverse pressure gradient. The airflow away from the axis rolled up and reached the wall at about 7 ms. When the flow field was 10 ms, the shear layer was still unstable, and the pressure waveform was formed and only existed for 7 ms~13 ms during the jet acceleration process. At a flow field of 15 ms, a relatively stable mixing layer was formed after 13 ms, and the pressure fluctuations within the mixing layer weaken and disappear. The jet′s injection effect on the surrounding flow was enhanced, and the pressure decreases. At a flow field of 20 ms, the jet dynamic pressure decreased, the stagnation pressure decreased, the absolute negative pressure outside the shear layer decreases, and the pressure gradient tended to flatten. Unstable shear layer pressure waves appeared in the 25 ms flow field, with pressure hysteresis near the corneal stagnation point. When the velocity of the healthy corneal jet reaches its peak, the radial flow of surface pressure exhibited typical subsonic shock jet flow characteristics. With the corneal center as the stationary point, all dynamic pressure was converted into static pressure, and the velocity stagnates to 0. When the pressure reacheed its peak, the fluid outside the stationary point then turned and flowed downstream along the surface of the detection piece. The maximum stationary pressure on the corneal surface occured between 15 ms and 16 ms. This characteristic was described by Navier-Stokes system of equations. The radial distribution curve of pressure on the surface of keratoconus was lower than that of healthy cornea near the stagnation point, and the pressure distribution curve decreased more slowly than that of healthy cornea. The absolute value of the slope was smaller. When more significant with the degree of disease, and the radial position where the surface pressure exceeded that of healthy cornea was further away. The radial distribution curve of corneal surface pressure in myopic eyes was higher than that of healthy cornea in a considerable ranged except for the corneal edge, and the decrease was slower before the radial dimensionless distance of 0.4.

The air puff reaches the apex of the cornea in approximately 7 ms. The changes in pressure over time and space for normal corneas, keratoconus corneas, and corneas with high myopia exhibit consistent patterns, differing only in numerical distribution. The pressure changes symmetrically around the apex, with a decrease in flow velocity and an increase in pressure near the stagnation point. There was a hysteresis phenomenon during the acceleration and deceleration processes of the jet, and the maximum pressure at the stagnation point closely coincides with the maximum jet velocity, with both time curves exhibiting similar shapes.