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目的:探讨猪眼LASIK术后角膜的应力松弛特征方法:新鲜猪眼,经视神经灌注维持眼压恒定,行常规LASIK手术,基质床分别切削30%,50%,70%整体角膜厚度,用自制的模具尺,切取哑铃型试件,200mL/L人血白蛋白液浸泡,冰箱4℃过夜保存。将试样吸干蛋白液,置于自制夹具固定,于美国Tytron250力学实验机做应力松弛实验。应力松弛突加载荷的加载速率为385mm/min,伸长比为1.5,松弛时间1000s,计算机自动采集数据。结果:LASIK手术中,单纯切开角膜瓣即导致了角膜的应力松弛程度降低,P<0.05(P=0.49),但是程度不大,可能角膜依然保持其粘弹特性。当激光消融30%角膜整体厚度及大于此值时,角膜的应力松弛程度几乎下降了一倍,P<0.01。在LASIK手术中角膜的纵向应力松弛程度不如横向的变化明显,尤其是在70%切削深度条件下,角膜的横向应力松弛程度小于纵向应力松弛程度,有显著的统计学差异(P<0.001)。结论:猪眼角膜在横向上的应力松弛程度与纵轴方向的应力松弛程度相似,猪眼角膜LASIK手术后,角膜横轴方向的应力松弛程度小于纵轴方向应力松弛程度,在70%角膜厚度的切削深度时,差异有显著性意义。猪眼LASIK手术中,切削深度越深,角膜的应力松弛程度越差,也就越容易引起角膜的形变和蠕变。
Objective: To investigate the characteristics of corneal stress relaxation in pigs after LASIK. Methods: Fresh pig’s eyes were maintained with constant intraocular pressure (IOP) by perfusion of optic nerve. The total corneal thickness was cut by 30%, 50% and 70% Mold ruler, cut dumbbell specimens, 200mL / L human serum albumin soak, refrigerator overnight at 4 ℃ save. The samples were sucked dry protein solution, placed in a fixture made of self-made, in the United States Tytron250 mechanical testing machine to do the stress relaxation experiment. The stress relaxation sudden load loading rate of 385mm / min, elongation ratio of 1.5, relaxation time 1000s, the computer automatically collect data. Results: In LASIK surgery, simply incising the corneal flap resulted in the reduction of corneal stress relaxation, P <0.05 (P = 0.49), but to a lesser extent, the cornea may still maintain its viscoelastic properties. When laser ablation 30% of the total corneal thickness and greater than this value, the degree of stress relaxation of the cornea almost doubled, P <0.01. In LASIK, the stress relaxation of the cornea was not as significant as that of the transverse direction. Especially at 70% depth of cut, the horizontal stress relaxation of the cornea was less than that of the longitudinal stress relaxation with significant statistical difference (P <0.001). CONCLUSIONS: The degree of stress relaxation in porcine cornea in horizontal direction is similar to that in longitudinal axis. After LASIK surgery, stress relaxation in the horizontal axis of cornea is less than that in longitudinal axis. After 70% corneal thickness The depth of cut, the difference was significant. Pig LASIK surgery, the deeper the depth of cut, the worse the degree of stress relaxation of the cornea, the more likely to cause corneal deformation and creep.