飞秒激光辅助的准分子激光原位角膜磨镶术和准分子激光上皮下角膜磨镶术矫正高度近视术后两年患者角膜后表面的变化

目的　探讨飞秒激光辅助的准分子激光原位角膜磨镶术（femtosecond-assisted laser in situ keratomileusis，fLASIK）和准分子激光上皮下角膜磨镶术（laser subepithelial keratomileusis，LASEK）矫正高度近视术后2 a角膜后表面的变化。方法　本研究为回顾性病例分析。收集2015年1月至12月来我院角膜屈光科行激光矫正手术的高度近视患者48例92眼。将患者依照术式分为两组，fLASIK组25例47眼，等效球镜度为-6.00~-11.00 D；LASEK组23例45眼，等效球镜度为-6.00~-9.50 D。利用Pentacam测量各组患者术前及术后1个月、6个月、1 a、2 a时角膜后表面高度及曲率和非球面因子Q值变化，角膜后表面高度取自中央角膜厚度最薄点、角膜顶点及距角膜顶点1 mm范围4个位点（0°、90°、180°和270°），同时记录视力、屈光度数、眼压、中央角膜厚度、切削深度等。采用独立样本t检验和重复测量方差分析进行统计处理。结果　两组患者术前年龄、裸眼视力、最佳矫正视力、等效球镜度、眼压、中央角膜厚度、切削深度之间差异均无统计学意义（均为P>0.05）。两组患者术前及术后各时间点角膜最薄点和角膜顶点后表面高度的差异均无统计学意义（均为P>0.05），其余4个位点差异亦无均统计学意义（均为P>0.05）。角膜最薄点和角膜顶点以及4个位点后表面高度不随时间变化而变化。两组患者术前及术后各时间点角膜曲率和Q值的差异均无统计学意义（均为P>0.05）；曲率和Q值不随时间的变化而变化。术后2 a时两组患者角膜最薄点后表面高度和术前的差值与切削深度/术前中央角膜厚度比值无相关性（fLASIK组:r=0.017，LASEK组:r=0.061，均为P>0.05）；角膜后表面Q值差值与切削深度/术前中央角膜厚度比值亦均无明显相关性（fLASIK组:r=0.062，LASEK组:r=0.103，均为P>0.05）。结论　经fLASIK或LASEK矫正的高度近视患者，术后角膜后表面保持稳定；这两种术式在保留足够的角膜基质床厚度前提下是长期安全的。

Changes of posterior corneal surface two years after correction of high myopia by femtosecond-assisted LASIK and LASEK

Objective To investigate changes of posterior corneal surface two years after correction of high myopia by femtosecond-assisted laser in situ keratomileusis(fLASIK)and laser subepithelial keratomileusis(LASEK).Methods A retrospective study was conducted on 92 eyes of 48 cases with high myopia who received refractive surgery in ourhospital from January 2015 to December 2015.The patients were divided into two groups according to methods of surgery:fLASIK group(47 eyes of 25 cases)with the range of equivalent spherical refraction from-6.00 D to-11.00 D,and LASEK group(45 eyes of 23 cases)with the range of equivalent spherical refraction from-6.00 D to-9.50 D.The changes in posterior corneal elevation,curvature and aspheric factor(Q value)were measured using Pentacam before surgery,1 month,6 months,1 year and 2 years after surgery.The posterior corneal elevation was determined by the thinnest point of corneal thickness,the cornea vertex and 4 points located in 1 mm range from corneal vertex(0°,90°,180°and 270°).Additionally,visual acuity,refraction,intraocular pressure(IOP),central corneal thickness(CCT)and ablation depth(AD)were measured.The results were analyzed with unpaired t test and repeated measurement ANOVA.Results There were no significant differences in age,uncorrected visual acuity,best corrected visual acuity,equivalent spherical refraction,IOP,CCT or AD before surgery between the two groups(all P>0.05).There were no significant differences in posterior corneal elevation at the thinnest point,the vertex and the other 4 points before and after surgery(all P>0.05)and these parameters did not change over time.For corneal surface curvature and Q value,there was also no difference between both two groups(all P>0.05)and did not change over time.The posterior corneal elevation difference in the thinnest point,Q value difference had no correlation with the ratio of AD/CCT(posterior corneal elevation:r=0.017 for femtosecond LASIK,r=0.061 for LASEK;Q value:r=0.062 for femtosecond LASIK,r=0.103 for LASEK,all P>0.05).Conclusion Corneal posterior surface is stable after correction of high myopia with femtosecond LASIK and LASEK.These two methods are safe in the long term if the residual bed thickness is enough after surgery.