ABSTRACT
AIM:To evaluate the repeatability of axial length (AL) and anterior chamber depth (ACD) obtained by A scan ultrasonography, and to compare AL and ACD obtained by A scan with those obtained by IOL Master.METHODS:Two hundred and fifty-seven cataract eyes of 170 patients were included.IOL Master and A scan were performed for each eye.Five measurements of IOL Master and 3 measurements of A scan were obtained.All the tested eyes were divided into 5 groups according to AL obtained by A scan:Group A (2129mm, 21 eyes).Cronbach's Alpha coefficient and intraclass correlation coefficient (ICC) were applied to evaluate the repeatability of AL and ACD obtained by A scan.Paired t test and Pearson correlation coefficient were used to analyze the differences and correlations of AL and ACD obtained by the 2 devices, respectively.Bland-Altman plots were presented to analyze the agreements of AL and ACD obtained by the 2 devices.RESULTS:All the Cronbach's Alpha and ICCs of AL and ACD values were more than 0.98.The differences of AL values between A scan and IOL Master were-0.11±0.08mm in Group A,-0.15±0.10mm in Group B,-0.19±0.15 mm in Group C,-0.29±0.16mm in Group D and-0.45±0.29mm in Group E, respectively (all P0.89, all P<0.01).CONCLUSION:The AL and ACD values in cataract eyes obtained by A scan were repeatable.The AL and ACD values obtained by A scan were smaller than those obtained by IOL Master.With the increase of AL values, the differences of AL values between A scan and IOL Master increased.
ABSTRACT
Background Corneal parameters (such as curvature,thickness,etc) are essential to the diagnosis of corneal related diseases,contact lenses fitting and corneal refractive surgery.Objective The aim of this study was to assess the repeatability and accuracy of corneal parameters obtained by RTVue Fourier-domain optical coherence topography (FD-OCT).Methods In this prospective study,77 eyes of 43 subjects with the refraction from-1.25 D to-10.00 D and astigmatism ＜2 D were enrolled in keratorefractive surgery center,Eye Hospital of Wenzhou Medical College.The anterior and posterior corneal curvature in 3 mm central zone (Ranterior and Rposterior),the ratio of posterior and anterior curvature (Rposterior/Ranterior),corneal central thickness (CCT),total corneal power(Knet),the simulated corneal power (Sim K),the anterior and posterior corneal power (Kanterior,Kposterior)were measured by FD-OCT.Corneal power (Km) was obtained by Topolyzer topography based on Placido ring.Three consecutive scans were acquired in every tested eye.Repeatability of FD-OCT measurement was assessed using the coefficient of variation CV),Cronbach Alpha and intra-class correlation coefficient (ICC).Repeated measure ANOVA was used to analyze the differences among SimK,Knet and Km.Pearson correlation analysis was used to analysis the correlation between SimK and K Knet and Km,SimK and Km.The agreement between Sim K and K Knet and Km,SimK and Km was assessed by Bland-Altman plots analysis.All the subjects understood the purpose of this investigation and written informed consent was obtained prior to the medical examination.Results The Ranterior,Rposterior,Rposterior/Ranterior,Kanterior,Kposterior,Sim K,Knet and CCT were (7.691 ±0.302) mm,(6.532±0.276) mm,0.849±0.014,(48.97±1.92)D,(-6.13±0.26)D,(43.95±1.72) D,(42.95±1.68) D and (545.20± 35.04) μm,respectively.The CV of all parameters was less than 1％.The Cronbach Alpha and ICC were both more than 0.9 except 0.802(ICC)of the Rposterior/Ranterior.SimK was (0.27±0.34) D higher than Km,and Knet was (0.73±0.37) D lower than Km.SimK was (1.01 ±0.11) D higher than K and all the differences showed a statistical significance (P＜0.001).There were close positive correlations between SimK and Km,Knet and Km,SimK and Knet(all r ≥ 0.976,P＜0.001).The Bland-Altman analysis showed a poor agreement between SimK and Km,Knet and Km,SimK and Knet.Conclusions The RTVue FD-OCT measuring corneal curvature and CCT performes good repeatability.The Sim K obtained by RTVue FD-OCT is slightly greater than that obtained by corneal topography,and the Rposterior/Ranterior obtained by RTVue FD-OCT is slightly lower than that from Gullstrand model eye.These results offer a basis for establishing a more accurate standardized model eye.