Comparison Of Corneal Curvature Measured By Three Kinds Of Instruments Before And After FS-LASIK For Myopia

BackgroundCorneal curvature plays great importance in corneal contact lens fitting, calculating intraocular lens, selecting cataract operation incision and evaluating the safety, accuracy, and validity of refractive operation, etc. Now there are many instruments that can measure corneal curvature including Keratometer, IOL-master, Topographer, Pentacam and so on. And the comparison of corneal curvature obtained by different instruments are various. Sirius combines Scheimpflug with Placido topography, the study and comparison of anterior depth and corneal thickness measured by Sirius and other instruments are not rare to see, but the comparison of corneal curvature measured by Sirius, Auto-Keratometer KR-8900 and IOL-master is few, especially in myopia patients before and after FS-LASIK. So, in this article, we discuss the difference and evaluate the agreement of these instruments.ObjectiveThis study was to evaluate the differences and agreement of corneal curvature measured by Sirius, Auto-Keratometer and IOL-master in patients with myopia before and after FS-LASIK.Methods198 eyes of 101 patients were enrolled, male patients accounted for 77cases, females 24 cases. All patients are classified as the Low to moderate myopia group (SE is less than 6.00 diopter) and high myopia group(SE is more than6.00 diopter).Corneal curvature K1, K2, Km, of Which Km equals (K1+K2)/2, were taken by Sirius, Auto-Keratometer and IOL-master respectively. After FS-LASIK, 24 patients were picked up randomly, and followed up for 1 week. A paired t test and Pearson linear correlation were used for each two instruments to do the statistical analysis. The agreement of corneal curvature acquired by Sirius, IOL-master and Auto-Keratometer was analyzed using Bland-Altman.Independent-samples t test is used to analyze the difference between males and females, between two groups, and between Sirius and Auto-Keratometer measuring corneal curvature of patients after FS-LASIK.ResultsFor patients before FS-LASIK, K1 values were (42.52±1.35) D, (42.54±1.34) D and (42.70±1.37) D obtained by Sirius, Auto-Keratometer and IOL-master respectively. Values of K2 were (43.69±1.44) D, (43.62±1.47) D and (43.95±1.51) D, and the values of Km were (43.11±1.36) D, (43.08±1.37) D and (43.33±1.41) D. The corneal curvature examined by the three instruments showed significant difference (P<0.05), except for the comparison of K1 measured by Sirius and KR-8900 (P>0.05). All of the instruments revealed good linear correlation (r>0.900,P<0.05). The difference between Sirius and Auto-Keratometer measurements of corneal curvature for K1, K2 and Km were 0.01D,0.09D and 0.03D, respectively. 95% limits of agreement were (-0.35-0.32) D,(-0.41-0.59) D and (-0.31-0.38)D. The difference between Sirius and IOL-master measurements of corneal curvature for K1, K2 and Km were -0.17D,-0.25D and-0.21D, respectively. 95% limits of agreement were (-0.77-0.42) D,(-0.93-0.43) D and (-0.79-0.37) D. The difference between IOL-master and Auto-Keratometer measurements of corneal curvature for Kl, K2 and Km were 0.16D,0.33D and 0.25D, respectively. 95% limits of agreement were (-0.44-0.76) D,(-0.34-1.01) D and (-0.33-0.82) D. The Km values of males showed great significance with females, and the values of females is bigger the values of males, the two SE groups showed no significance (P>0.05). After FS-LASIK, K1 and Km values obtained by Sirius and Auto-Keratometer showed no significant differences (P>0.05), K2 showed differences (P<0.05). The difference between Sirius and Auto-Keratometer measurements of corneal curvature for K1, K2 and Km were 0.04D,-0.16D and -0.06D, respectively. 95% limits of agreement were (-0.50-0.58) D,(-0.88-0.55) D and (-0.63-0.51) D.ConclusionThe corneal curvature examined by the three instruments showed significant difference, except for the comparison of K1 measured by Sirius and KR-8900 (p>0.05). Good agreement is exhibited in corneal curvature between Sirius and KR-8900. They can be used interchangeably in clinical examination. But the two devices may not be interchangeable for corneal curvature in patients after FS-LASIK.All of the instruments revealed good linear correlation (r>0.900,p<0.05). The mean values of males showed great significance with females, and the values of females is bigger than the values of males, we should pay attention to it, when giving glasses or doing refractive operation.