圆锥角膜与激光角膜屈光手术后角膜生物力学参数的对比研究

目的　应用角膜生物力学眼压分析仪Corvis ST对圆锥角膜、角膜屈光手术后角膜和健康角膜的生物力学参数进行测量，探讨圆锥角膜与角膜屈光手术后角膜生物力学的变化及差异。方法　选取2011年4月至2016年11月在西安市第四医院眼科已确诊的临床期圆锥角膜患者63例（96眼）作为圆锥角膜组；另选取2016年11月至2017年3月在我院行飞秒激光制瓣的准分子激光角膜屈光手术后1个月的患者60例（120眼）作为术后角膜组；选取同期来我院检查的角膜健康者51人（102眼）作为健康角膜组。应用角膜生物力学眼压分析仪Corvis ST对三组入选者角膜的第一次压平长度、第二次压平长度、第一次压平速率、第二次压平速率、最大变形幅度、顶点距离和曲率半径等进行测量；数据之间总体差异采用单因素方差分析，两两比较采用SNK法进行对比分析，角膜形态学参数与生物力学参数之间进行Pearson或Spearman相关分析。结果　三组间第一次压平长度和第二次压平长度总体差异均无统计学意义（均为P>0.05）。圆锥角膜组第一次压平速率为（0.189±0.230）m·s^-1，大于健康角膜组的（0.151±0.017）m·s^-1，差异有统计学意义（P<0.05）；圆锥角膜组第二次压平速率明显大于健康角膜组和术后角膜组，而术后角膜组小于健康角膜组，差异均有统计学意义（均为P<0.05）；圆锥角膜组最大变形幅度大于健康角膜组和术后角膜组，术后角膜组小于健康角膜组，差异均有统计学意义（均为P<0.05）；术后角膜组顶点距离大于健康角膜组，差异有统计学意义（P<0.05）；圆锥角膜组、术后角膜组、健康角膜组曲率半径分别为（5.696±0.881）mm、（7.129±0.681）mm、（7.012±0.728）mm，圆锥角膜组曲率半径小于健康角膜组和术后角膜组，术后角膜组大于健康角膜组，差异均有统计学意义（均为P<0.05）。圆锥角膜组前表面平均角膜曲率与最大变形幅度和曲率半径之间具有明显的相关性（r=-0.205、0.184，P=0.023、0.041），后表面最大高度与第二次压平速率、最大变形幅度和曲率半径之间均具有明显的相关性（r=-0.579、-0.307、0.256，P=0.022、0.002、0.000）。术后角膜组前表面平均角膜曲率除了与第二次压平长度之间存在明显的相关性（r=-0.297，P=0.026）外，与其他参数均无明显相关性（均为P>0.05），后表面最大高度与各参数均无明显相关性（均为P>0.05）。结论　圆锥角膜及角膜屈光手术后角膜生物力学特性均有所下降，圆锥角膜下降更加明显，角膜生物力学眼压分析仪可作为角膜屈光手术后早期排除继发性圆锥角膜的辅助诊断工具。

Comparison of corneal biomechanical parameters between keratoconus and laser corneal refractive surgery

Objective　To measure biomechanical parameters of the cornea after keratoconus and laser corneal refractive surgery by Scheimpflug noncontact tonometry （Corvis ST），and analyze the changes and differences in these parameters.Methods　From April 2011 to November 2016，63 patients （96 eyes） with clinically diagnosed as keratoconus were selected as the keratoconus group，and 60 patients （120 eyes） underwent laser corneal refractive surgery between November 2016 to March 2017 were selected as postoperative cornea group，and totally 51 healthy person （102 eyes） who received physical examination during the same period were selected as healthy cornea group.Scheimpflug noncontact tonometry （Corvis ST） was performed to measure the length of appl 1，length of appl 2，velocity of appl 1，velocity of appl 2，maximum deformation amplitude，apex distance and radius of curvature in the three groups.Total comparison of biomechanical parameters was performed using ANOVA test among the three groups，while pairwise comparison was performed to analyze the difference of these parameters by SNK methods.Pearson or Spearman correlation analysis was applied to assess the differences in corneal morphological and biomechanical parameters.Results　There was no significant difference in length of appl 1，length of appl 2 of the three groups （all P>0.05）.And velocity of appl 1 in the keratoconus group was significantly higher than that of the healthy cornea group ［（0.189±0.230） m·s^-1 vs.（0.151±0.017）m·s^-1］ （P<0.05）.As for velocity of appl 2，the keratoconus group was larger than the healthy cornea group，both which were larger than the postoperative cornea group，and the differences were significant （all P<0.05）.And this was true of maximum deformation amplitude in the three groups，with the significant differences（all P<0.05）.The apex distance in the keratoconus group was significantly longer than that in the healthy cornea group（P<0.05）.The radius of curvature of the keratoconus group，postoperative cornea group and healthy cornea group were （5.696±0.881）mm，（7.129±0.681）mm and （7.012±0.728）mm，respectively，which approached significant differences（all P<0.05）.There was significant correlation between the anterior surface refractive power (Km) and apex distance and radius of curvature in the keratoconus group （r=-0.205，0.184；P=0.023，0.041），and maximum posterior surface elevation had a statistically significant correlation with velocity of appl 2，maximum deformation amplitude and radius of curvature（r=-0.579，-0.307，0.256，P=0.022，0.002，0.000）.For the eyes in the postoperative cornea group，there were no significance correlation between the anterior surface refractive power (Km) and biomechanical properties （P>0.05），but significant correlation with length of appl 2 （r=-0.297，P=0.026）.There were no significant correlation between maximum posterior surface elevation and biomechanical properties （P>0.05）.Conclusion　The corneal biomechanical parameters are decreased in eyes after keratoconus and laser corneal refractive surgery，and Corvis ST can become an auxiliary examination tool for earlier diagnosis of secondary keratoconus after corneal refractive surgery.