Comparison of central corneal thickness measurements by Ultrasound,Orbscan II ,AS-OCT and Pentacam pachymetry

Objective To analyze the difference and the agreement in central corneal thickness(CCT) measurements between the gold standard method of ultrasound pachymetry and 3 noncontact systems(Orbscan Ⅱ, AS-OCT, Pentacam)in ametropia eyes before laser refractive surgery.Methods Ninety consecutive patients(180 eyes)who had preoperative examination in Laser Refractive Surgery Center had Orbscan Ⅱ, AS-OCT, Pentacam, and ultrasound pachymetry.Data were analyzed using the paired sample t test, linear regression, and Bland-Altman plots.Results The mean CCT measured by ultrasound,OrbscanⅡ,Pentacam,and AS-OCT pacbymetry were,respectively,(542.1 ±30.4)μ m、(541.1±37.1)μ m、(530.3±29.3)μ m and(544.9±8.7)μ m.There was no statistically significant difference between ultrasound and OrbscanⅡ measurements(P>0.05).Compared with the ultrasound measurement,AS-OCT and Pentacam measurements significantly misestimate corneal thickness by a mean of(11.7±8.9)μ m(P <0.01)and(-2.8±1.0)μ m(P <0.01),re-spectively.OrbscanⅡ, AS-OCT, Pentacam pachymetry showed a high correlation with ultrasound pachymetry. Tbe95%limitsofagreement(LoA)withultrasoundwere-37.4～+39.3 μ m for the OrbscanⅡdevice and-5.6～+29.1 μ m for the AS-OCT device and -24.4～+18.8 μ m for the Pentacam device.Conclusions OrbscanⅡ,AS-OCT and Pentacam pacbymetry can be used to measure central corneal thickness.Compared with the ultrasound pachymetry, OrbscanⅡ pachymetry was effectd by it's AF, AS-OCT pachymetry had the best agreement, Penta-cam pacbymetry had the nearest CCT.However it is cautious to use the 4 devices interchangeably. Key words: Ultrasound pachymeter; Orbscan Ⅱ ; AS-OCT;  Pentacam; Agreement