central corneal thickness measurements in normal and keratoconic eyes using three corneal pachymeters

purpose: to assess the agreement of ultrasonic pachymetry, the galilei dual scheimpflug analyzer and orbscan ii in measuring central corneal thickness (cct) in normal and keratoconic eyes. methods: in this prospective comparative study, cct was measured in 88 refractive surgery candidates and 76 (39 right) eyes of 45 keratoconic patients using ultrasonic pachymetry, galilei and orbscanii. readings by the three instruments were compared using one-way analysis of normal variance. agreement between the three devices was assessed using pearson (r) and intraclass correlation (icc) coefficients, mountain plots, and bland-altman plots. results: in the normal group, mean cct was 551.0±39.4, 566.9±33.5, and 565.5±40.9µm measured by ultrasonic pachymetry, galilei and orbscan ii, respectively (p<0.001). corresponding figures in the keratoconus group were 488.4±61.5, 504.1±42.0, and 473.8±58.5µm, respectively (p<0.001). cct measurements by the three instruments were significantly correlated in both groups. the association was strongest in the normal group and between the galilei and orbscanii (r=0.91, icc=0.90), where 95% limits of agreement (loa) were narrowest (-35 to 32 µm). the correlation was weakest in the keratoconus group and between ultrasonic pachymetry and galilei (r=0.67, icc=0.61). conclusion: to measure cct, galilei and orbscanǁ can be used interchangeably in normal eyes but not in keratoconic eyes. agreement between the two optical devices and ultrasonic pachymetry is low and therefore they cannot replace ultrasonic pachymetry in measuring cct in normal or keratoconic corneas.