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Objective
To analyze the repeatability of keratometry and astigmatism values measured by the OPD-Scan Ⅲ and the agreement of the parameters measured by OPD-Scan Ⅲ and Pentacam.
Methods
A diagnostic test study design was adopted.Fifty patients (100 eyes) with refractive errors, aged from 21 to 35 years old, were selected from Second Affiliated Hospital of Nantong University and Lixiang Eye Hospital of Soochow University during August 2018.Spherical equivalent, astigmatim degree and axis were measured by Autorefraction.Corneal biometric measurements were measured three times continuously with the above two instruments.Keratometry values at the flat axis (K1), keratometry values at the steep axis (K2), astigmatim degree, axis, vector parameters J0 (Jackson cross cylinder at 0°or 180°) and J45 (Jackson cross cylinder at 45°) were recorded.Intraclass correlation coefficient (ICC) was used for repeatability analysis.Wilcoxon signed rank test, Spearman correlation analysis and Bland-Altman graphs were employed to analyze the comparability.This study adhered to the Declaration of Helsinki and was approved by an Ethics Committee of Lixiang Eye Hospital of Soochow University (No.SLER2018112). Written informed consent was obtained from each patient prior to any examination.
Results
The ICC of K1, K2, astigmatism, astigmatic axis, J0 and J45 measured by OPD-Scan Ⅲ were all greater than 0.900; the ICC of the astigmatism measured by Pentacam was 0.896, and the ICC of the other parameters measured by Pentacam were greater than 0.900; The values of K2, astigmatism, J0 and J45 measured by OPD-Scan Ⅲ were greater than those measured by Pentacam, and the differences were statistically significant (all at P<0.05). The values of K1, K2, astigmatism degree, axis, J0 and J45 measured by OPD-Scan Ⅲ were positively correlated with those measured by Pentacam (rs=0.981, 0.982, 0.900, 0.737, 0.921, 0.703, all at P<0.01). The 95% agreement of limits (LOA) of K1, K2, astigmatism, axis, J0 and J45 measurement difference between OPD-Scan Ⅲ and Pentacam were -0.52-0.50 D, -0.39-0.59 D, -0.37-0.48 D, -17.29°-20.38°, -0.12-0.24 D and -0.22-0.28 D, respectively.
Conclusions
OPD-Scan Ⅲ has high credibility in measuring corneal refractive power and astigmatism degree, but its 95% LOA of astigmatism axis is too large to be accepted clinically.