Comparison of central corneal thickness as measured by non-contact specular microscopy and ultrasound pachymetry before and post LASIK


Professor Jun Zou, Department of Ophthalmology, Shanghai Jiaotong University Affiliated Sixth People's Hospital, Shanghai, 200233, China. E-mail:


Purpose:  To compare central corneal thickness (CCT) measurements made by ultrasound pachymetry and non-contact specular microscopy in eyes before and post laser in situ keratomileusis (LASIK).

Methods:  Forty eyes of 20 consecutive refractive surgery candidates were included in this study. The CCT in both eyes was measured before and 3 months after LASIK with a non-contact specular microscope and a ultrasound pachymeter.

Result:  Both before and after LASIK, the difference of the mean CCT between non-contact specular microscopy and ultrasound pachymetry was statistically significant (P < 0.001 before surgery, and P = 0.02 after surgery). The difference between them was −14.41 μm and −3.69 μm, respectively. In both situations, non-contact specular microscopy and ultrasound pachymetry measurements were highly correlated (r = 0.959, before surgery, and r = 0.979 after LASIK). Bland–Altman analysis showed that either before or post LASIK, the 95% limits of agreement have a span of approximately 30 μm. Preoperatively, the mean standard deviation of repeated measurements was 4.26 μm by ultrasound pachymetry, and 4.02 μm by non-contact specular microscopy, whereas it was 3.83 μm by ultrasound pachymetry, and 3.89 μm by non-contact specular microscopy, postoperatively. No statistically significant differences were found between the mean standard deviations by these two devices in both situations (P = 0.561 before surgery, and P = 0.849 after LASIK).

Conclusions:  Both before and after LASIK, non-contact specular microscopy is not in complete agreement with ultrasound pachymetry in measuring CCT. Both devices provided comparable repeatability of measurements.