Maldonado Miguel J, Nieto Juan C, Díez-Cuenca Maite, Piñero David P
Department of Ophthalmology, University Clinic, University of Navarra, Pamplona, Spain.
Ophthalmology. 2006 Nov;113(11):1918-26. doi: 10.1016/j.ophtha.2006.05.053. Epub 2006 Aug 28.
To assess the repeatability and reproducibility of posterior corneal curvature (PCC) measurements made by combined scanning-slit/Placido-disc topography (Orbscan II) after LASIK.
Experimental instrument validation study.
We recruited 22 consecutive postmyopic LASIK patients for the repeatability study and another 50 consecutive postmyopic LASIK patients for the reproducibility study.
To analyze intrasession repeatability, 1 examiner measured 22 postmyopic LASIK eyes 10 times successively in the shortest time possible. To study intersession reproducibility, the same operator obtained measurements from another 50 eyes with stable refraction in 2 consecutive visits at the same time of the day between 6 and 9 months after myopic LASIK. We explored any association between residual stromal bed thickness and measurement variability.
Orbscan II scanning-slit PCC data, precision, within-subject coefficient of variation (CV(w)), limits of agreement (LoA), and intraclass correlation coefficient (ICC).
For intrasession repeatability, precision was 0.067 mm (best-fit sphere [BFS]), 0.110 diopters (D; power within 5 mm), 0.158 D (power within 3 mm), and 0.46 (eccentricity). Repeatability was high for PCC BFS and power measurements within 3-mm and 5-mm zones (CV(w) ranged from 0.5%-1.2%) but poor for eccentricity data (CV(w), 31.6%). Correspondingly, ICCs ranged from 0.89 to 0.98 for PCC BFS and power, and the ICC was 0.20 for PCC eccentricity values. For intersession reproducibility, on average, no difference in PCC measurements could be found, indicating that when there is variability, it is due to random factors. The width of the 95% LoA between sessions was clinically acceptable for BFS (0.25 mm) and power (0.4 D [within 5 mm] and 0.6 D [within 3 mm]). Similarly, ICCs indicated good intersession reliability for BFS and power (0.98, 0.96, and 0.85 for BFS, power within 5 mm, and power within 3 mm, respectively) but poor reliability for eccentricity (0.59). Repeatability and reproducibility were unrelated to stromal bed thickness.
Orbscan II provides reliable post-LASIK PCC data for symmetrical parameters (BFS and power), independent of the residual stromal bed thickness, but is unreliable for measurements that are radially asymmetrical (eccentricity). Orbscan II is useful for monitoring the PCC after LASIK once the early postoperative period is over.
评估准分子激光原位角膜磨镶术（LASIK）后采用联合扫描裂隙/普拉西多盘角膜地形图仪（Orbscan II）测量后表面角膜曲率（PCC）的可重复性和再现性。
实验仪器验证研究。
我们招募了22例连续的近视LASIK术后患者进行可重复性研究，另外招募了50例连续的近视LASIK术后患者进行再现性研究。
为分析测量过程中的可重复性，1名检查者在尽可能短的时间内对22只近视LASIK术后眼连续测量10次。为研究不同测量时段间的再现性，同一名操作人员在近视LASIK术后6至9个月的同一天同一时间对另外50只屈光稳定的眼睛进行连续2次测量。我们探究了剩余基质床厚度与测量变异性之间的任何关联。
Orbscan II扫描裂隙PCC数据、精密度、受试者内变异系数（CV(w)）、一致性界限（LoA）和组内相关系数（ICC）。
对于测量过程中的可重复性，精密度为0.067mm（最佳拟合球面[BFS]）、0.110屈光度（D；5mm范围内的屈光度）、0.158D（3mm范围内的屈光度）和0.46（偏心率）。PCC的BFS以及3mm和5mm区域内的屈光度测量的可重复性较高（CV(w)范围为0.5%-1.2%），但偏心率数据的可重复性较差（CV(w)为31.6%）。相应地，PCC的BFS和屈光度的ICC范围为0.89至0.98，PCC偏心率值的ICC为0.20。对于不同测量时段间的再现性，平均而言，PCC测量未发现差异，这表明若存在变异性，则是由随机因素导致的。不同测量时段间95%LoA的宽度对于BFS（0.25mm）和屈光度（5mm范围内为0.4D，3mm范围内为0.6D）在临床上是可接受的。同样，ICC表明BFS和屈光度在不同测量时段间具有良好的可靠性（BFS、5mm范围内的屈光度和3mm范围内的屈光度的ICC分别为0.98、0.96和0.85），但偏心率的可靠性较差（0.59）。可重复性和再现性与基质床厚度无关。
Orbscan II可为对称参数（BFS和屈光度）提供可靠的LASIK术后PCC数据，且与剩余基质床厚度无关，但对于径向不对称测量（偏心率）不可靠。一旦术后早期结束，Orbscan II可用于监测LASIK术后的PCC。
