Department of Corneal and External Eye Diseases, St. Paul's Eye Unit, Royal Liverpool University Hospital, Liverpool, United Kingdom.
Department of Eye and Vision Science, University of Liverpool, Liverpool, United Kingdom.
Sci Rep. 2018 Aug 17;8(1):12345. doi: 10.1038/s41598-018-30173-7.
To investigate a method for precision analysis to discriminate true corneal change from measurement imprecision in keratoconus (KC). Thirty patients with KC and 30 healthy controls were included. Coefficients of repeatability and limits of agreement (LOA) were compared using multiple measurements for inter-observer and inter-device agreement with the Pentacam HR, Orbscan IIz, and Tomey Casia SS-1000. Correlation of repeated measurements was evaluated using a linear mixed effect model (also called random effect model). A formula was derived for the theoretical expected change in precision and compared with measured change. Correlation between measurements from the same eye was small (R = 0.13). The 99.73% LOA (3 SD) of the mean of three measurements, provided better precision than 95% LOA (2 SD) of single cut-off values as expected from statistical theory for uncorrelated measurements for evidence of a significant change in corneal shape in patients with keratoconus. This enabled the determination of cut-off values for the detection of true change in corneal shape. The mean of three repeated measurements will provide better precision when there is minimal correlation. Three (rather than two) standard deviations provides a precise estimate of the LOA within or between observers and can be used as a reliable measure for identifying stage-independent corneal shape changes (progression) in keratoconus.
为了研究一种用于角膜膨隆（KC）中准确区分真实角膜变化与测量不精确的方法。纳入 30 例 KC 患者和 30 例健康对照者。使用 Pentacam HR、Orbscan IIz 和 Tomey Casia SS-1000 对观察者间和仪器间的重复性和一致性界限（LOA）进行了比较。使用线性混合效应模型（也称为随机效应模型）评估重复测量的相关性。还推导了一个用于理论预期精度变化的公式，并与实测变化进行了比较。同一只眼的测量值之间相关性较小（R=0.13）。三个测量值的平均值的 99.73% LOA（3SD）提供了比单一切割值的 95% LOA（2SD）更好的精度，这与统计学理论对无相关性测量的证据一致，表明角膜形状有明显变化在角膜膨隆患者中。这使得能够确定角膜形状真实变化的检测的截止值。在相关性最小的情况下，三个重复测量的平均值将提供更好的精度。三个（而不是两个）标准差可以精确估计观察者内和观察者间的 LOA，可用于作为可靠的措施，以识别角膜膨隆中与阶段无关的角膜形状变化（进展）。
