ABSTRACT
Objective To analyze the reproducibility of keratometry and astigmatism measured by the VERION Digital Guidance System and the comparability of VERION with iTrace,Lenstar LS900 and manual keratometer.Methods The keratometry of 62 cataract patients were measured using four different devices.The steep keratometry (Ks),flat keratometry (Kf),astigmatic magnitude,astigmatic axis,cylinder at 0-degree meridian (vector component,J0) and cylinder at 45-degree meridian (vector component,J45) from each machine were recorded and analyzed.The three repeated measurements and the results of VERION system with other three devices were compared to analyze the reproducibility and comparability of VERION system.Results Reproducibility:Intraclass correlation coefficients and Cronbach's alpha values were higher than 0.9 for Ks,Kf,astigmatic magnitude,astigmatic axis,J0 and J45 measured by the VERION system (all P ＜ 0.001).Comparability:The results of Ks and magnitude of astigmatism of VERION were larger than the iTrace (all P ＜ 0.05) in the paired-samples t test.There was no statistical difference for the rest of parameters (all P ＞ 0.05).The Bland-Altman graphs revealed the 95％ limits of agreement (LOA) of J0,J45 and the astigmatic axis between VERION and iTrace were (-0.31-0.35) D,(-0.25-0.31) D and-13.5 °-12.3 °,respectively;There was no statistical differences for all parameters except for J45 in the paired-samples t test between the VERION and Lenstar LS900 (all P ＞ 0.05).The Bland-Altman graphs revealed the 95％ LOA of J0,J45 and the astigmatic axis were (-0.25-0.31)D,(-0.27-0.36) D and-13.5°-11.0°,respectively;There were statistical differences for the results of Kf and magnitude of astigmatism between the VERION and manual keratometer (all P ＜ 0.05).The Bland-Altman graphs revealed the 95％ LOA of J0,J45 and the astigmatic axis between VERION and manual keratometer were (-0.38-0.35) D,(-0.41-0.42) D,-12.6°-16.4°,respectively.Conclusion The VERION system is a reliable system for the measurement of keratometry and astigmatism.The keratometry and astigmatic magnitude of the VERION system have a good agreement with the iTrace,Lenstar LS900 and manual keratometer.However,the astigmatic axis measurements are significantly different among the four devices.
ABSTRACT
PURPOSE: To compare the keratometry measurements by the handheld Nikon Retinomax K-plus2, the on-table Canon RK-5 autokeratometer, and the manual Topcon OM-4 keratometer and to evaluate the degree of agreement among the three instruments. METHODS: Adults (n=30) and children (n=40) presenting toa tertiary eye hospital clinic were examined by an optometrist. Topcon OM-4 keratometer, Nikon Retinomax and the on-table Canon RK-5 autokeratometer analyses were performed in order. The horizontal and vertical keratometry data were measured. The vector components of astigmatism, mean bias and agreement among the three types of measurements were evaluated. RESULTS: There were no significant differences among the three keratometers in horizontal or vertical keratometry or in central corneal astigmatism in both the adult and child groups (p-value>0.05). The keratometers which were estimated with Retinomax K-plus2 were highly correlated with those by on-table RK-5 autokeratometer (min. 0.89, max. 0.97) and Topcon OM-4 keratometer (min. 0.67, max. 0.94) in the adult group, while in the child group, the three instruments showed slightly decreased correlation (min. 0.45, max. 0.97 on RK-5, min. 0.36, max. 0.92 on OM-4), especially in the left eyes. CONCLUSIONS: The handheld Retinomax K-plus2 provided comparable data to that of the conventional on-table Topcon and manual keratometers. This instrument will beuseful in the clinic to measure keratometry in children or immobilized patients who have difficulty sitting during the examination.