Corneal Pachymetry using Ultrasound Vs Orbscan II in Normal and Post-LASIK Eyes

To compare orbscan II (O II) and ultrasound (US) pachymetry in normal and post-LASIK eyes. In a comparative prospective study, central corneal thickness (CCT) was measured in 168 eyes of 84 normal subjects and 42 eyes without corneal opacity of 21 post-LASIK patients by O II and US. Paired t test was used to identify significant differences between the two methods and Pearson test was used to identify the correlation of measurments between the two methods. Mean CCT measured by ultrasound (538.7  47.4 m) was less than that of O II (542.7  52.2 m) in the normal eyes (P<0.04), but mean CCT measured by ultrasound (477.8  38.2 m) was greater than that of O II (469.5  47.2 m) in the post-LASIK eyes. (p<0.02) There was significant linear correlation between US and O II in both groups. (r=0.87, P=0.000 and r=0.88, P=0.000, respectively). Mean difference of CCT measurements between O II and US in normal and post-LASIK clear cornea is not clinically significant and interchangeable use of data in planning or assessing corneal surgery is possible.