Comparison among 3 methods to measure central corneal thickness: Sirius, Orbscan-II and Ultrasound Pachymetry

Abstract

Objective To assess the difference and agreement of central corneal thickness measurements between Sirius,Orbscan Ⅱ,and ultrasound pachymetry (USP).Methods On 250 myopic patients (500 eyes),the central corneal thickness was measured using Sirius,Orbscan Ⅱ and ultrasound pachymetry in turn.Results The mean measurements of average central corneal thickness by Sirius,Orbscan Ⅱ,and USP were 525.7±36.7μm,515.5±44.1μm and 529.1±35.8μm respectively.There was high correlation between the three instruments:Sirius with USP (r =0.964,P ＜0.001),Orbscan Ⅱ with USP (r =0.932,P ＜0.001) and Sirius with Orbscan Ⅱ (r =0.940,P ＜0.001).The mean differences (and upper/lower LOA) for central corneal thickness measurements were 3.4±9.8μm (-15.7,22.6) between Sirius and USP, 13.6±16.9μm (-19.4,46.7) between Orbscan Ⅱ and USP,and 10.2±15.8μm (-20.8,41.2) between Sirius and Orbscan Ⅱ.Conclusions Sirius and Orbscan Ⅱ underestimate corneal thickness compared with that measured with USP.Sirius has better correlation and agreement with the gold standard USP,as compared with Orbscan Ⅱ.The three instruments can not be used interchangeably for measuring central corneal thickness.Sirius eventually may replace USP as the gold standard for corneal pachymetry. Key words: Central corneal thickness; Sirius; Orbscan Ⅱ; Ultrasound pachymetry