LASIK手术对角膜前后表面非球面性的早期影响

目的探讨准分子激光原位角膜磨镶术（LASIK）对近视患者角膜前后表面不同范围内非球面性的早期影响。方法对54例（107眼）近视及近视散光患者行常规LASIK，使用Pentacam眼前节分析系统对患者角膜前后表面6、7、8、9mm等不同直径的平均Q值进行测量，研究术前术后Q值的变化规律及各相应范围内Q值的变化特点，并分析其与其他变量之间的相关性。结果术前角膜前后表面形态随着角膜直径取值范围的增大，Q值负向增大，呈椭球形的特点，前后表面Q值有一定的相关性，且越近周边越显著，Q值与屈光度间无相关性，角膜后表面7、8、9mm直径下的Q值与角膜厚度呈负相关。术后1个月，4个直径范围内角膜前后表面的Q值均往正向变化，除后表面9mm区域Q值变化与术前比较差异无统计学意义外（t=-1．495，P=0．138），其余前后表面各范同Q值与术前比较差异均有统计学意义（P〈0．05），切削区内增加最显著。术后角膜前表面△Q与切削深度及剩余基质床厚度均呈正相关（P〈o．05），而后表面△Q则与两参数无明显相关（P〉0．05）。结论角膜前后表面越靠近周边区域Q值越负，呈椭球形特点；LASIK不仅改变了角膜前表面的非球面特性，对角膜后表面的形态也产生了一定影响，使后表面发生了扁球形改变。

Short-term influence of LASIK on anterior and posterior corneal asphericity

Background Laser in situ keratomileusis (LASIK) is frequently performed to reduce or eliminate myopic refractive error.Some patients complain of a loss of visual function after surgery even when they have 20/20 visual acuity.One of the reasons is the change of asphericity of the cornea.Objective This study attempts to investigate the short-term changes of the anterior and posterior corneal asphericity after LASIK.Methods One hundred and seven myopic eyes of 54 subjects with the equivalent spherical diopter of -1.30 to -7.50 D who have received LASIK were enrolled in this prospective study.The Q-values of the posterior corneal surface for different corneal diameters (6mm,7mm,8mm and 9mm) were measured with Pentacam preoperatively and 1 month postoperatively.The correlations between Q-value,Q change (△Q),and the mean preoperative spherical equivalent refraction (SE),central corneal thickness (CCT),central ablation depth (AD) and residual bed thickness were investigated.Written informed consents were obtained from all the subjects prior to the clinical trial.Results The Q-values of the anterior and posterior corneal surfaces gradually decreased to negative values with the increase of corneal diameter in myopic eyes.Weak correlations were found between the asphericity of the anterior and posterior corneal surfaces from diameters of 6mm,7mm,8mm and 9mm (r=0.227,0.288,0.303,0.389;P=0.019,0.003,0.002 and 0.000,respectively).No statistically significant correlation was found between Q-value and the diopter of refractive error (P＞0.05).Both the anterior and posterior corneal Q-values varied toward the positive direction except that in the 9mm area of the posterior corneal surface at postoperative 1 month(t=-1.495,P=0.138).The increase of the anterior corneal asphericity (△Q) was more obvious than that of the posterior corneal surface and showed a positive correlation with ablation depth and a negative correlation with residual bed thickness.However,no statistically significant correlation was seen between △Q and these two parameters in the posterior corneal surface (P＞0.05).Conclusion The shape of the anterior and posterior corneal surface shows more prolateness as the increase of corneal diameter in myopic eyes.Both the anterior and the posterior corneal surfaces have an oblate shift within the ablation zone 1 month after LASIK.