Aaron Michelle T, Applegate Raymond A, Porter Jason, Thibos Larry N, Schallhorn Steve C, Brunstetter Tyson J, Tanzer David J
United States Air Force, School of Aerospace Medicine, San Antonio, Texas, USA.
Optom Vis Sci. 2010 Nov;87(11):861-6. doi: 10.1097/OPX.0b013e3181f6fb49.
To critically evaluate the following clinical wisdom regarding custom (wavefront-guided) laser in situ keratomileusis (LASIK) that subjects with better-than-average best-corrected visual acuity (BCVA) before surgery have a greater risk of losing BCVA postoperatively than do subjects with worse-than-average BCVA before surgery.
High contrast BCVA was measured once before and 3 months after custom LASIK in one eye of 79 subjects. Preoperative spherical equivalent refractive error ranged between -1.00 and -10.38 D. The sample was divided into one of two subsamples: eyes that had better-than-average preoperative BCVA (<-0.11 logMAR) and eyes that had average or worse-than-average preoperative BCVA (≥-0.11 logMAR). Controls were implemented for retinal magnification and for the statistical phenomenon of regression to the mean of the preoperative acuity measurement.
On average, for the entire sample, moving the correction from the spectacle plane to the corneal plane increased letter acuity 4.7% (1 letter, 0.02 logMAR). For each subsample, the percentage regression to the mean was 57.24%. After correcting for magnification effects and regression to the mean, eyes with better-than-average preoperative acuity had a small but significant gain in acuity (∼1 letter, p = 0.040) that was nearly identical to the gain for eyes with worse-than-average preoperative acuity (∼1.5 letters, p = 0.002).
Custom LASIK produced a statistically significant gain in visual acuity after correction for magnification effects. Dividing the sample into two subsamples based on preoperative acuity confirmed the common clinical observation that eyes with better-than-average acuity tend to remain the same or lose acuity, whereas eyes with worse-than-average acuity tend to gain acuity. However, when only one acuity measurement is taken at a single time point and the sample is subsampled nonrandomly, this clinical observation is due to a statistical artifact (regression to the mean) and is not attributable to the surgery.
对以下关于定制（波前引导）准分子原位角膜磨镶术（LASIK）的临床观点进行批判性评估，即术前最佳矫正视力（BCVA）优于平均水平的患者术后丧失BCVA的风险高于术前BCVA低于平均水平的患者。
对79名受试者的一只眼睛在定制LASIK术前和术后3个月各测量一次高对比度BCVA。术前等效球镜屈光不正范围在-1.00至-10.38 D之间。样本被分为两个子样本之一：术前BCVA优于平均水平（<-0.11 logMAR）的眼睛和术前BCVA为平均水平或低于平均水平（≥-0.11 logMAR）的眼睛。对视网膜放大率和术前视力测量的均值回归统计现象进行了对照。
总体而言，对于整个样本，将矫正从眼镜平面移至角膜平面使字母视力提高了4.7%（1个字母，0.02 logMAR）。对于每个子样本，均值回归百分比为57.24%。在校正放大率效应和均值回归后，术前视力优于平均水平的眼睛视力有小幅但显著的提高（约1个字母，p = 0.040），这与术前视力低于平均水平的眼睛的提高幅度（约1.5个字母，p = 0.002）几乎相同。
校正放大率效应后，定制LASIK在视力方面产生了具有统计学意义的提高。根据术前视力将样本分为两个子样本，证实了常见的临床观察结果，即术前视力优于平均水平的眼睛往往保持不变或视力下降，而术前视力低于平均水平的眼睛往往视力提高。然而，当仅在单个时间点进行一次视力测量且样本非随机抽取子样本时，这种临床观察结果是由于统计假象（均值回归），而非手术所致。
