共轴注视定位法测量SMILE术透镜偏心值及偏心对视觉质量的影响

Measurement of Lenticular Decentration with the Coaxial Subject-Fixation Alignment Method in SMILE and Its Impact on Visual Quality

目的:观察飞秒激光小切口角膜基质透镜取出术(SMILE)术中采用共轴注视定位法时,透镜中心偏离术前视轴角膜反光点的矢量距离(透镜偏心值)及其对术后客观视觉质量的影响。方法:前瞻性临床研究。选择2017年8-10月在河南省人民医院接受SMILE术且术中采用共轴注视定位法的近视及近视散光患者37例(74眼),检查术前、术后1d、术后1周和术后1个月的视力、屈光状态、角膜地形图和客观视觉质量。建立以瞳孔中心为原点的笛卡尔直角坐标系,根据角膜地形图的offset值和SMILE手术录像截图来测量并计算出透镜偏心值。根据透镜偏心值分为A组(<200μm)、B组(200~300μm)及C组(>300μm)。利用双通道视觉质量分析系统所检测的调制传递函数截止频率(MTFcutoff)来评价客观视觉质量。数据采用配对样本t检验、方差分析、Spearman相关性检验进行分析。结果:透镜的偏心值为9~464(223±108)μm,均<500μm,其中A组为32眼占43%,B组为26眼占35%,C组为16眼占22%。术前MTFcutoff为(39.6±5.2)周/度(c/d),其中A组为(39.7±5.8)c/d,B组为(39.0±5.2)c/d,C组为(40.2±3.9)c/d;术后1个月MTFcutoff为(38.6±5.8)c/d,其中A组为(37.8±5.9)c/d,B组为(38.8±6.6)c/d,C组为(40.6±3.8)c/d,C组手术前和术后1个月及各组间MTFcutoff值的差异均无统计学意义。术前与术后1个月的MTFcutoff值呈正相关(r=0.53,P<0.001)。术中透镜中心偏离瞳孔中心的矢量距离为(209±104)μm,透镜偏心值与术中透镜中心偏离瞳孔中心的矢量距离呈正相关(r=0.49,P<0.001)。结论:SMILE术共轴注视定位法虽可引起轻微的透镜偏心,但其对术后视觉质量无明显影响。

Objective:To measure lenticular decentration with the coaxial subject-fixation alignment method after femtosecond laser small incision lenticule extraction(SMILE),and to investigate its impact on visual quality.Methods:A total of 37 patients(74 eyes)with myopia and myopic astigmatism who underwent the SMILE procedure using the coaxial subject-fixation alignment method were included in the prospective study from August to October 2017 in Henan Provincial People's Hospital.Visual acuity,refraction,corneal topography and objective visual quality were measured.The Cartesian coordinate was established with the pupil center as the origin of the coordinate.Lenticular decentration was measured and calculated according to the offset value of the corneal topography and the video capture of the SMILE procedure.Patients were divided into groups based on lenticular decentration:group A(<200μm),group B(200-300μm)and group C(>300μm).The modulation transfer function cutoff(MTF cutoff)was used to evaluate objective visual quality.Pre-op and post-op indexes were compared with a paired t-test and ANOVA,and the correlation of factors affecting the correction of astigmatism was analyzed by Spearman correlation.Results:Lenticular decentration was 223±108μm and all treated eyes(100%)were within 500(9-464)μm:group A(<200μm)consisted of 32 eyes(43%),group B(200-300μm)consisted of 26 eyes(35%),and group C(>300μm)consisted of 16 eyes(22%).The mean value of the MTF cutoff preoperatively was 39.6±5.2 circle/degree(c/d),of which group A was 39.7±5.8 c/d,group B was 39.0±5.2 c/d,and group C was 40.2±3.9 c/d.The mean value of the MTF cutoff was 38.6±5.8 c/d one month after surgery:group A was 37.8±5.9 c/d,group B was 38.8±6.6 c/d,group C was 40.6±3.8 c/d,and there was no statistically significant difference among groups and between preoperation and 1 month postoperation in group C.There was a significant relationship between the MTF cutoff before and one month after the surgery(r=0.53,P<0.001).The vector distance that the lenticular center deviated from the pupil center was 209±104μm,which was found to be associated with lenticular decentration(r=0.49,P<0.001).Conclusions:Although the coaxial subject-fixation alignment method in SMILE can cause slight lenticular decentration,it has no significant impact on visual quality after surgery.