LASIK术后继发圆锥角膜与原发圆锥角膜地形图特征比较

Comparative analysis of corneal topography characteristics in primary keratoconus and secondary keratoconus after LASIK

目的 分析LASIK术后继发圆锥角膜与原发圆锥角膜的角膜地形图形态学差异,为临床诊断及分析继发圆锥角膜的危险因素提供参考.方法 回顾性病例研究.选取1997年1月至2012年12月在山东省眼科研究所确诊的LASIK术后继发圆锥角膜完成期患者13例（20眼）为继发组,随机选取相同时期某一时间段内确诊的原发圆锥角膜完成期患者18例（25眼）为原发组.原发组与继发组患者的年龄分别为（18.9±2.8）岁（15～28岁）和（24.3±9.1）岁（19～48岁）;眼轴平均长度分别为（25.39±1.33）mm（23.3～27.8 mm）和（27.09±2.43）mm（25.3～30.1 mm）（t=3.942,P＜0.01）.对2组患者的OrbscanⅡ角膜地形图形态学特征进行分析,主要比较2组角膜最溥点位置,角膜前表面最大模拟曲率（Kmax）,角膜模拟散光度,角膜中央3 mm区平均曲率及3 mm区散光度,角膜前、后表面距最佳拟合球面距离（Diff值）,角膜后表面形态等.对数据进行独立样本t检验、单因素方差分析和Pearson相关分析.结果 原发组角膜最薄点在4个象限的分布为颞下18眼（72％）、颞上4眼（16％）、鼻下1眼（4％）和鼻上2眼（8％）,继发组为颞下8眼（40％）、颞上4眼（20％）、鼻下4眼（20％）、鼻上4眼（20％）.原发组和继发组角膜模拟散光度分别为（5.85±3.26）D和（3.95±2.51）D（t=-2.142,P＜0.05）;3 mm区散光度分别为（4.12±2.11）D和（2.82±1.50）D（t=-2.187,P＜0.05）;2组患者后表面形态差异无统计学意义（P＞0.05）.结论 继发圆锥角膜地形图形态较原发圆锥角膜相对规则,角膜散光度小.角膜最薄点分布均匀且靠近角膜中央,提示角膜中央过多切削可能是继发圆锥角膜发生的危险因素。

Objective To analyze the difference in corneal topography between primary keratoconus and secondary keratoconus after LASIK; to provide a reference for the clinical diagnosis and analysis of risk factors in secondary keratoconus.Methods In this retrospective case analysis,13 secondary keratoconus patients （20 eyes,secondary group） were diagnosed and accepted for treatment in Shandong Eye Institute between January 1997 and December 2012.Correspondingly,18 primary keratoconus patients （25 eyes,primary group） were randomly selected during the same period.The mean ages of the primary group and secondary group were 18.9±2.8 years （15-28 years） and 24.3±9.1 years （19-48 years）,respectively.The mean axial lengths were 25.39±1.33 mm （23.3-27.8 mm） and 27.09±2.43 mm （25.3-30.1 mm）,and the differences were statistically significant （t=3.942,P〈0.01）.The morphological features of the topography were observed with an Orbscan Ⅱ system,which primarily included the position of the thinnest point of the cornea,the maximum simulation curvature of the anterior corneal surface （Kmax）,astigmatism,the average power and astigmatism in the central 3 mm region of the cornea,the Diff-values of the anterior and posterior corneal surfaces,and the morphology of the elevation map pattern.The collected data were analyzed with a t-test,one-way ANOVA and Pearson correlation coefficient.Results The distribution of the thinnest points in the corneal quadrants for the primary group were 18 eyes （72%） infratemporal,4 eyes （16%） supertemporal,1 eyes （4%） intranasal,2 eyes （8%） supernasal,and the distributions for the secondarv group were 8 eyes （40%）,4 eyes （20%）,4 eyes （20%） and 4 eyes （20%）,respectively.Corneal astigmatisms in the primary and secondary groups were 5.85±3.26 D and 3.95-2.51 D,and the astigmatism values in the 3 mm region were 4.12±2.11 D and 2.82±1.50 D.The differences were statistically significant （t=-2.142,-2.187.P〈0.05）.There was no significant difference in posterior surface morphology between the 2 groups of patients （P〉0.05）.Conclusion Compared to primary keratoconus,the morphological features of the corneal topography follow the same rules,and the astigmatism value is smaller.In addition,the thinnest point of the cornea is uniformly distributed near the central corneal area,which points out that excessive cutting may be a risk factor for secondary keratoconus.