猪眼LASIK术后角膜的应力松弛和连续松弛谱

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1 000s,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.

Stress and continuous relaxation spectrum of porcine cornea after LASIK

AIM:To explore the characteristic of relaxation of porcine cornea after LASIK METHODS:Usual LASIK was performed on fresh porcine corneas with stable intraoculer pressure(IOP) maintained through optic nerve irrigation.The ablation depth on stroma is 30%,50% and 70% respectively.Then the dumbbell-shaped corneal strip specimens were cut and stored in 20% Human Albumin solution for use(4oC) .Sip up the Albumin solution on specimens,and fixed them on homemade jig.Stress relaxation tests were erformed on Tytron250 Dynamics Experiment System.the loading speed was 385mm/min,extending rate was 1.5,and relaxation time was 1 000s.The data were collected electronically and automatically.RESULTS:In LASIK procedure,though a single flap-cutting can cause a little reduction of corneal stress relaxation(P <0.05,P =0.49) ,the cornea may still remain its property of visco-elasticity.When ablation depth was 30% or more,corneal stress relaxation decreased to almost one half(P <0.01) .The change of corneal stress relaxation degree in vertical meridian specimen was lower than that in horizontal specimen,especially when ablation depth was 70%,and it's statistically significant(P <0.001) .In LASIK operation,the more depth the ablation,the more reduce the stress relaxation degree,and it's easy to cause deformation and creep deformation.CONCLUSION:The changes of the stress relaxation in vertical and longitudinal meridian specimens are similar,and slightly obvious in longitudinal specimen,especially in 70% ablation group.