Comparative study of central corneal thickness measurements with Sirius and ultrasound pachymetry

Abstract

Objective To assess the repeatability of central comeal thickness (CCT) performed by Sirius before and after SBK,and to compare the agreement and differentiation of the Sirius with ultrasound pachymetry in the measurements of CCT.Methods Retrospective case series.Sixty eight myopic eyes of 35 consecutive patients in Chongqing Medal Eye Institute from May to Novenber 2011 were enrolled in this study.Central corneal thicknesses were examined using Sirius and ultrasound pachymetry preoperatively and at two weeks,one month,three months postoperatively.The data were analyzed using intraclass correlation coefficient (ICC),paired t tests,the correlation coefficient,the Bland-Altman technique and repeated measures analysis of variance.Results The ICC of the Sirius were 0.988 (pre-op),0.993 (2 w),0.992 (1 mo),0.996 (3 mo),respectively.The 95％ limits of agreement in CCT were-14.04 to 11.20μm (pre-op),-21.10 to 5.16μm (2 w),-28.00 to 10.76μ m (1 mo),-27.18 to 12.30μm (3 mo),respectively.The CCT values of the Sirius and ultrasound pachymetry were positively related by linear correlation analysis,r =0.970 (pre-op),0.987 (2 w),0.980 (1 mo),0.978 (3 mo).The preoperative CCT measurements by Sirius and ultrasound pachymetry were (mean ± standard deviation) (541.45±25.78)μm,(542.87±23.41)μm,respectively.Preoperative Sirius was not significantly different compared to ultrasound pachymetry (P ＞0.05).Postoperative Sirius measurements were (428.29±43.30)μm (2 w),(430.02±45.71)μm (1 mo),(435.73±46.10)μm (3mo),respectively.Ultrasound pachymetry measurements were (436.26±41.61)μm (2 w),(438.65±41.14)μm (1 mo),(443.16±42.91)μm (3 mo),respectively.Postoperative measurements were significant difference between Sirius and ultrasound pachymetry (P ＜0.01).Conclusions The measurements of CCT with Sirius yield excellent repeatability.There is great agreement and positive correlation between Sirius and ultrasound pachymetry.But postoperative Sirius measurements are significantly thinner than ultrasound pachymetry measurements. Key words: Sirius; Ultrasound pachymetry; Central corneal thickness; SBK