LASIK手术剩余基质床厚度安全保留值的数值模拟

Numerical Simulation for the Safe Retention Value of Residual Stromal Bed Thickness in Laser-Assisted in situ Keratomileusis

目的分析准分子激光原位角膜磨镶术(laser-assisted in situ keratomileusis,LASIK)手术不同剩余基质床厚度(residual stromal bed thickness,RSBT)在不同眼压(intraocular pressure,IOP)下对角膜几何变形和应力变化的影响,并评估3种RSBT保留值(250、280、300μm)的安全性。方法利用ABAQUS有限元软件建立正常角膜与术后不同RSBT角膜的有限元模型,设置合适的加载与边界条件,计算得出相应的位移与应力。结果RSBT=250μm的术后角膜在IOP=2.66 k Pa作用下和正常角膜在IOP=5.32 k Pa作用下产生的顶点位移基本相等。RSBT=280μm处于圆锥角膜发病低危区,而RSBT=250μm已经进入高危区;RSBT为280~300μm之间某值时,应力分布规律与正常角膜基本一致。RSBT=300μm时,角膜基质层的张应力强度丧失约40%。结论RSBT=300μm为LASIK手术比较合理的最低保留值,RSBT=250μm是高风险值,在RSBT=330~340μm时,对大部分患者来说,LASIK手术足够安全。

Objective To study the effects of different residual stromal bed thickness(RSBT)in laser-assisted in situ keratomileusis(LASIK)surgery on geometric deformation and stress changes of the cornea under different intraocular pressures(IOP),and evaluate safety of the three retention values(250,280,300μm).Methods The models of normal cornea and corneas with different RSBT after surgery were established by the finite element software ABAQUS.Appropriate loading and boundary conditions were set and then the corresponding displacement and stress were calculated.Results The apical displacement of the postoperative cornea(RSBT=250μm)under IOP=2.66 kPa was basically the same as that of the normal cornea(RSBT=550μm)under IOP=5.32 kPa.RSBT=280μm was in the low risk area of keratoconus,while RSBT=250μm was in the high-risk area.At a value between 280μm and 300μm of RSBT,the stress distribution was nearly consistent with that of the normal cornea.With RSBT=300μm,the stromal layer of the cornea lost 40%of the strongest strength against tissue tension.Conclusions RSBT=250μm is the minimum retention value for LASIK surgery.RSBT=250μm is the high risk value.With RSBT=330-340μm,LASIK surgery is safe enough for most patients.