Comprehensive evaluation of total corneal refractive power by ray tracing in predicting corneal power in eyes after small incision lenticule extraction

PurposeTo assess the prediction accuracy of four variations of total corneal refractive power (TCRP) by the ray tracing method in determining corneal power in eyes after myopic small incision lenticule extraction (SMILE).MethodsForty eyes of forty patients who had undergone myopic SMILE were enrolled in this prospective study. Manifest refraction and Pentacam HR were performed preoperatively and three months or more postoperatively. Mean keratometry (Km), true net power (TNP), equivalent keratometry readings (EKR) and 4 subtypes of TCRP (pupil centered or apex centered within a ring or a zone)—TCRPpupil,ring, TCRPpupil,zone, TCRPapex,ring and TCRPapex,zone—were recorded and compared to the theoretical postoperative keratometry value using the clinical history method (CHM).ResultsThe only keratometric values that showed no statistically significant differences from the CHM were 4.0 mm and 4.5 mm EKR, 6.0 mm TCRPpupil,zone and TCRPapex,zone. Pearson’s correlation test revealed that 4.0 mm TCRPpupil,zone exhibited the highest correlation coefficient (r = 0.974) followed by TCRPapex,zone 4.0 mm (0.972) and EKR 4.5 mm (0.970). The 95% limits of agreement (LOA) of the 4.0 mm EKR and CHM, the 4.5 mm EKR and CHM, the 6.0 mm TCRPpupil,zone and CHM, the 6.0 mm TCRPapex,zone and CHM were (-1.27 to 1.22 D), (-1.04 to 0.98 D), (-1.39 to 1.08 D) and (-1.38 to 0.96 D), respectively, while the modified 4.0 mm TCRPpupil,zone (TCRPpuil,zone + 0.70 D) and TCRPapex,zone (TCRPapex,zone+0.70 D) yielded the narrowest 95% LOA of (-0.96 to 0.95 D) and (-0.96D, 1.05 D).ConclusionsTotal corneal refractive power using the ray tracing method could predict corrected corneal power derived from the CHM in eyes following SMILE surgery after simple modification.研究目的：本研究旨在评估光线追踪法下四种全角膜屈光力（total corneal refractive power, TCRP）变体在近视小切口角膜基质透镜取出术（small incision lenticule extraction, SMILE）后眼球角膜屈光力测定中的预测准确性。研究方法：本前瞻性研究纳入40例接受近视SMILE手术患者的40只术眼，分别于术前及术后3个月及以上时段开展主觉验光与Pentacam HR检查，记录平均角膜曲率（mean keratometry, Km）、真实净屈光力（true net power, TNP）、等效角膜曲率读数（equivalent keratometry readings, EKR）以及4种亚型的全角膜屈光力（以瞳孔中心或角膜顶点为中心的环区或带区：TCRPpupil,ring、TCRPpupil,zone、TCRPapex,ring、TCRPapex,zone），并以临床病史法（clinical history method, CHM）得到的理论术后角膜曲率值作为对照进行比较。研究结果：仅4.0mm与4.5mm等效角膜曲率读数、6.0mm TCRPpupil,zone及6.0mm TCRPapex,zone这几项角膜曲率指标与CHM的结果无统计学显著性差异。皮尔逊相关性分析显示，4.0mm TCRPpupil,zone的相关系数最高（r=0.974），其次为4.0mm TCRPapex,zone（0.972）与4.5mm EKR（0.970）。4.0mm EKR与CHM、4.5mm EKR与CHM、6.0mm TCRPpupil,zone与CHM、6.0mm TCRPapex,zone与CHM的95%一致性界限（limits of agreement, LOA）分别为(-1.27~1.22 D)、(-1.04~0.98 D)、(-1.39~1.08 D)及(-1.38~0.96 D)；经修正后的4.0mm TCRPpupil,zone（TCRPpupil,zone + 0.70 D）与4.0mm TCRPapex,zone（TCRPapex,zone + 0.70 D）的95% LOA最窄，分别为(-0.96~0.95 D)与(-0.96 D~1.05 D)。研究结论：采用光线追踪法测得的全角膜屈光力经简单修正后，可准确预测SMILE术后眼球通过CHM得到的矫正后角膜屈光力。