LASIK手术偏心切削病例的分析

摘要

目的 分析因传统准分子激光原位角膜磨镶术(LASIK)和波前像差引导的LASIK(波前引导LASIK)偏心切削引发视觉质量下降的病例中,其高阶像差分布特征和偏心切削程度的评价.方法 回顾性病例对照研究.初次LASIK术后(包括传统LASIK和波前引导LASIK)出现重影和星芒等视觉症状的患者40例(48眼),术后复诊3个月以上[复诊期限:波前引导组平均为9个月(4至26个月),传统组平均为24个月(5个月至6年)],屈光度稳定在±1.00 D以内者,除外过矫、欠矫和眼表及眼内疾患导致的视力下降,行WaveScan(3.62版)波前像差仪检查.本研究选取了这部分患者中初次LASIK术后主导像差为彗差(垂直彗差或水平彗差)的26例(28眼),分析检测所得高阶像差结果,并测定术中偏心的切削中心相对瞳孔中心在水平方向(X轴)、垂直方向(Y轴)和矢量的偏移.将波前像差引导LASIK组的术前与术后结果采用配对t检验或者配对秩和检验进行比较;波前像差引导LASIK组术后与传统LASIK组术后结果采用独立样本t检验或者独立样本秩和检验进行比较.结果 波前引导组的总高阶像差均方根值(RMS)由(0.425±0.192)μm增加至术后的(1.262±0.590)μm,增加了1.96倍.总彗差RMS值由(0.190±0.114)μm增加至术后的(0.686±0.315)μm,增加了 2.61倍.水平彗差RMS值由(0.118±0.061)μm增加至术后的(0.257±0.237)μm,增加了1.17倍;垂直彗差RMS值由(0.130±0.122)μm增加至术后的(0.587±0.329)μm,增加了3.51倍.初次LASIK术后的水平彗差明显小于垂直彗差(Z=-2.803,P=0.004).传统组的总高阶像差、总慧差与波前引导组比较,差异无统计学意义,但总慧差占总高阶像差的比例,两组差异有统计学意义(t=-1.548,P=0.007).偏心切削量水平方向(X轴)位移右眼为(0.65±0.38)mm,左眼为(0.90±0.35)mm;垂直方向(Y轴)位移右眼为(0.80±0.30)mm,左眼为(0.53±0.34)mm;矢量位移右眼为(1.11±0.25)mm,左眼为(1.13±0.22)mm.全部28眼矢量位移均＞0.5 mm,71%的患眼切削中心偏移瞳孔中心的距离＞1.0 mm,矢量位移程度是LASIK术后无视觉症状人群的2.02倍.右眼在垂直方向(Y轴)的位移大于左眼(t=2.157,P=0.040)结论由于偏心切削引发的LASIK术后视觉质量下降病例中,高阶像差和总彗差明显增加,垂直彗差增加大于水平彗差;其偏心切削的程度属于中度和重度偏移.因此,偏心切削是LASIK术后视觉质量下降的主要原因之一.%Objective To study cases with visual complaints caused by ablation induced decentration after traditional laser in situ keratomileusis (LASIK) and wavefront-guided LASIK. To evalulate the distribution of higher-order aberrations and the degree of decentered ablation. Methods This was a retrospective case control study. Forty-eight eyes of 40 patients with double vision,starburst and other visual symptoms were checked with WaveScan (3.62 version) after LASIK. All postoperative cases were followed for more than 3 months. Their refractive errors were within ±1.0 D and stable except for overcorrection, under correction, and other eye diseases. The period of observation was (9.3±5.7)months (range: 4-26 months) for the wavefront-guided LASIK group, and (24.1±22.7)months (range: 5-72 months) for the traditional LASIK group. For this study, 28 eyes of 26 patients were selected whose dominant aberrations were vertical or horizontal comas due to decentered ablation after LASIK surgery. Higher-order aberrations in post-LASIK eyes were analyzed.The variations between the ablation center with the pupil center were measured and plotted on the horizontal (X-axis) and vertical (Y-axis) and the vector shift was drawn. The preoperative and postoperative results of the wavefront-guided LASIK group were compared (using a paired samples t test or Wilcoxon signed rank test). The postoperative results for the wavefront-guided LASIK group and tranditional LASIK group were also compared (using an independent samples t test or a Mann-Whitney test). Results The higher-order aberration root mean squares (RMS) value for the postoperative wavefront-guided eyes was (1.262±0.590)μm, which was 1.96 times greater than the average for preoperative eyes. The total coma RMS value of the postoperative wavefront-guided eyes was (0.686±0.315)μm, which was 2.61 times greater than the average for preoperative eyes. There was a 3.51 time increase in vertical coma and a 1.17 time increase in horizontal coma after LASIK.The horizontal coma after LASIK was significantly less than the vertical coma (Z=-2.803, P=0.004).The difference of total higher order aberrations and total coma between traditional LASIK and wavefront-guided LASIK was without any significance, however, the proportion of total coma in total higher order aberrations between the two groups was statistically significant (t=-1.548, P=0.007).Decentered ablation measurement: the mean ablation induced decentration was (0.65±0.38)mm for the right eye and (0.90±0.35)mm for the left eye horizontally (X-axis). The mean for the right eye was (0.80±0.30) and (0.53±0.34)mm for the left eye vertically (Y-axis). The mean ablation induced decentration vector was (1.11±0.25)mm for the right eye and (1.13±0.22)mm for the left eye. For all 28 eyes, the vector shift was ＞0.5 mm, and for 71% of the eyes, ablation centers differed from pupil centers ＞1.0 mm. The vector decentration for LASIK ablated eyes was 2.02 times higher than the population but with no visual symptoms. Right eyes had a more significant pupil shift than left eyes in the vertical direction (t=2.157, P=0.040). Conclusion Total higher-order aberrations and coma aberrations increased significantly in cases with visual symptoms caused by ablation induced decentration after LASIK surgery, with vertical coma increasing more than horizontal coma. The degree of decentration was moderate to severe in these patients. Therefore, decentration is one of the main factors that lead to distorted images after LASIK.